Phytogenic Compounds for Enhancing Intestinal Barrier Function in Poultry–A Review

Abstract

After the European Union ban of antibiotic growth promoters, works on different methods of improving gut health have intensified. The poultry industry is struggling with problems that were previously controlled by antibiotic growth promoters, therefore the search for optimal solutions continues. Simultaneously, there is also increasing social pressure to minimize the use of antibiotics and replace them with alternative feed additives. A variety of available alternatives is considered safe by consumers, among which phytogenics play a significant role. However, there are still some limitations that need to be considered. The most questionable are the issues related to bioavailability, metabolism of plant derivatives in birds, and the difficulty of standardizing commercial products. There is still a need for more evidence-based recommendations for the use of phytogenics in livestock. On the other hand, a positive influence of phytogenic compounds on the health of poultry has been previously described by many researchers and practical application of these compounds has auspicious perspectives in poultry production. Supplementation with phytogenic feed additives has been shown to protect birds from various environmental threats leading to impaired intestinal barrier function. Phytogenic feed additives have the potential to improve the overall structure of intestinal mucosa as well as gut barrier function on a molecular level. Recognition of the phytogenicsʼ effect on the components of the intestinal barrier may enable the selection of the most suitable ones to alleviate negative effects of different agents. This review aims to summarize current knowledge of the influence of various phytogenic constituents on the intestinal barrier and health of poultry.

Key words

intestinal permeability - gut health - alternative feed additives - poultry - plant derivatives

Abbreviations

AGPs: antibiotic growth promoters

AH: Allium hookeri

C10: sodium caprate

CD: crypt depth

CLDN: claudin

cOCM: coated cinnamon oil

CUR: curcumin

DON: deoxynivalenol

EO: essential oil

FD-4: fluorescein isothiocyanate-dextran 4000

HS: heat stress

JAMs: junctional adhesion molecules

LPS: lipopolysaccharide

MUC-2: mucin 2

NE: necrotic enteritis

OCLN: occludin

OTA: ochratoxin A

PFAs: phytogenic feed additives

PO: per o. s.

RT: total resistance

TEER: transepithelial electrical resistance

TJs: tight junctions

V : C: villus height to crypt depth

VH: villus height

VS: villus surface area

VW: villus width

ZO: zonula occludens protein
 

Introduction

The poultry industry accounts for a huge part of the worldʼs livestock production. According to the Food and Agriculture Organization, global poultry meat production increased from 9 to 122 million tons between 1961 and 2017, reaching about 37% of world meat production in 2017, and continues to grow. Optimizing the production process to be both consumer and environmentally friendly, as well as efficient, is now an enormous challenge for researchers, veterinarians, nutritionists, and breeders.

In recent years, the concept of “gut health” has received a lot of attention as it has been recognized as one of the key elements in determining animal performance. After the European Union ban of AGPs [1], works on different methods of improving gut health intensified. The debate on the use of anti-coccidial drugs has also begun due to the fear of increasing resistance among parasites and environmental residues [2]. In 2016, the Federation of Veterinarians of Europe published a position paper on coccidiostats or anticoccidials, recommending strict veterinary supervision of their use in the European Union [3]. Also noteworthy is that social pressure to use alternative feed additives is increasing, and the rise in awareness among customers results in a higher demand for antibiotic-free or “organic” poultry products as well [4], [5], [6].

According to EU legislation, feed additives mean substances, micro-organisms, or preparations that are intentionally added to feed or water for the purpose of satisfying the nutritional needs of animals, or to favorably affect animal production, performance, or welfare (particularly by affecting the gastrointestinal biota or digestibility of feeding stuffs), or to favorably affect the characteristics of feed or animal products or the environmental consequences of animal production. Feed additives also have a coccidiostatic or histomonostatic effect [1].

There is a variety of available alternative feed additives (pro-, pre- and synbiotics, phytogenics, and organic acids [7], [8], [9], [10]) that are considered safe and are welcomed by consumers. Most of the studies on their efficacy have concentrated mainly on their influence on growth performance [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], antimicrobial and antiparasitic activity [46], [47], [48], [49], [50], [51], [52], [53], [54], [55], or digestibility [13], [17], [19], [21], [28], [33], [34], [40], [41]. Despite the fact that much research has already been carried out in this field, the search for the most effective feed additives continues.

Although there are many factors that influence gut health, an integral and intact gut barrier is a vital component for its maintenance. The knowledge of mechanisms behind proper functioning of the intestinal barrier is rapidly changing. Enhanced understanding of the issue has determined that a lot of matters have been previously oversimplified [8], [56], [57]. Although numerous studies have investigated the effect of feed additives on the morphology of the digestive tract [12], [15], [17], [18], [23], [24], [27], [29], [31], [32], [33], [39], [41], [58], [59], their direct influence on individual elements of the intestinal barrier is still poorly described. An interesting review of the influence of plant bioactive compounds on the intestinal barrier of poultry, also in terms of immunology, was published by Patra [60]. Phytogenics are a promising group of feed additives that has the potential to directly improve gut barrier function in addition to exhibiting other positive effects on gut health [61]. Gut health is a complex issue, the improvement of which requires multitarget action. Plant extracts, thanks to their rich composition and variety of active components, have a chance to act multidirectionally and represent a promising alternative to AGPs [62]. The use of molecular technologies might be helpful for better understanding the mode of action of feed additives and what would justify their implementation into animal feeding. Although feed additives of natural origin are gaining popularity among veterinarians and poultry producers, there is still a need for more evidence-based scientific data to justify their use, prove their effectiveness, and gain general acceptance. This review aims to summarize current knowledge of the influence of various phytogenic components, plant extracts, their mixtures, and isolated ingredients on the intestinal barrier in poultry.

The search strategy for this topic included a screening of the electronic publication libraries PubMed and Google Scholar. The search was narrowed down to years 2000 – 2020. It was based on key words and combinations of them, such as “intestinal barrier”, “gut health”, “tight junctions”, “permeability”, “leaky gut”, “intestinal”, “gastrointestinal”, “poultry”, “chicken”, “broiler”, “phytogenics”, “essential oil”, “polyphenol”, “plant extracts”, “alternative feed additives”, “phytochemical feed additives”, and “flavonoid”. The available literature has also been studied for specific phytogenic components, such as “carvacrol”, “cinnamaldehyde”, “curcumin”, and “resveratrol”, and references of the selected papers were checked. In addition, several studies with other animal species or cell culture models were cited to present the perspectives for future research in poultry.

Gut Health and the Intestinal Barrier

The digestive system is a complicated, complex machinery. Its proper functioning is necessary for the effective absorption of nutrients and the right rate of animalsʼ development and growth, and therefore, the economic profit. The integrity of the intestinal barrier provides protection against pathogens and xenobiotics entering the body by the alimentary route and the gut immune system is crucial for overall immunity of an animal.

The intestinal barrier is a complicated structure formed by different components: a layer of mucus, gut microbiota, elements of immunological system, and, most importantly, adjacent intestinal epithelial cells [63]. All of these parts remain in dynamic interaction with each other and with the environment. The integrity and permeability of the intestinal barrier is largely maintained by the unimpaired epithelial cells monolayer and the functional junctions between them. Enterocytes are connected by different kinds of junctions, including desmosomes, adherent junctions, gap junctions, and TJs [61], [63], [64], [65], [66], [67], [68]. TJs play a crucial role in the regulation of paracellular permeability and maintenance of barrier function [61], [63], [66], [67], [69], [70], [71].

TJs are located on the basolateral side of the apical end of epithelial cells. They are multiprotein complexes formed by the transmembrane proteins, creating the extracellular and intracellular domains and plaque proteins connecting the transmembrane proteins to the perijunctional actomyosin ring [64], [66], [67], [69]. Over 50 TJ proteins have been identified so far [67], [69]. Transmembrane proteins include CLDNs, OCLN, JAMs, the Coxsackie and adenovirus-associated receptor, and tricellulin [66], [69]. They are linked with the cytoplasmic plaque, formed mainly by the ZO [64], [66], [67], [69].

TJ proteins are dynamic structures that can be modified depending on environmental conditions. For example, ZO proteins can shift cyclically between membrane and cytosolic pools, and can also be redistributed into the intracellular compartment as a response to various stressors [72], [73], [74], [75]. OCLN can undergo internalization in cytoplasmic vesicles, which results in changes in permeability of the epithelium [63], [66], [69], [74], [75]. On the contrary, the localization of CLDNs in TJs is relatively stable [74], [75], but their distribution and properties can significantly differ, which is reflected in the variable tightness of the epithelia [66], [69], [76]. It is well known that TJs presence and proper functioning is necessary for maintaining mucosal homeostasis. Apart from connecting the epithelial cells and regulating paracellular permeability, TJ proteins also play an important role in the signaling pathways [69], [75], [76].

Impairment of intestinal barrier function

A number of agents that can jeopardize intestinal health and, as a result, animal health has been described [69], [77], [78], [79], [80], [81], [82], [83], [84], [85], [86], [87], [88]. Changes in expression, phosphorylation, and distribution of different TJ proteins have been associated with many gastrointestinal and systemic diseases in humans and animals [66], [69], [89], [90], [91], [92], [93]. Significant changes in the structure of the intestinal barrier on the molecular level have been observed in cases of exposure to different agents, such as mycotoxins [79], [81], [85], [94], [95], [96], [97], [98], pathogens [69], [84], [86], [99], [100], and HS [78], [101], [102], [103], [104], [105], [106].

Pathogens

The role of TJs in the regulation of intestinal barrier function and its disruption by pathogens in chickens was widely described by Awad et al. [69], so it is not discussed further here. In brief, some of enteric pathogens, such as enteropathogenic Escherichia coli or Salmonella, can disrupt mucosal barrier function in chickens by modifying TJs. Disruption of specific TJ elements can result from degradation by pathogen-derived proteases, changes in the phosphorylation state of the proteins, and altered protein synthesis [107].

Withdrawal of antibiotic growth promoters

The AGPs withdrawal also, undoubtedly, brought some hardships for the poultry industry that are associated with gut health impairment, such as an increase in the feed conversion ratio, the reemergence of previously controlled diseases like NE, wet litter, or leaky gut syndrome, and the occurrence of illnesses caused by commensal microbiota capable of crossing the intestinal barrier due to its reduced integrity [69], [108], [109], [110], [111].

In an experimental drug-free program described by Gaucher et al., a number of negative effects had been noted [112]. The observations demonstrated serious challenges that must be addressed while considering drug-free poultry production on a mass scale. This program was associated with a higher prevalence of NE (clinical and subclinical) and increased litter moisture content. Animals reared without any medications also had a significantly lower live weight at slaughter and daily body weight gain, and there was an increase in the feed conversion ratio. Moreover, the poultry industry has to deal with the emerging problems of climate change, such as HS and increasing feed contamination by mycotoxins.

Heat stress

It has been reported that broiler chickens exposed to HS resulted in higher permeability of the intestinal barrier, manifested by increased serum endotoxin, inflammatory cytokines concentration, and translocation of intestinal pathogens (Salmonella spp.) [77]. Similarly, in another study, it was noted that broiler heat exposure lead to negative changes in jejunal morphology and increased paracellular permeability and the downregulation in the expression of TJ proteins OCLN and ZO-1 [102].

Mycotoxins

Although chickens are known to be relatively insensitive to toxic effects of DON, it has been proven that even subclinical exposure to this mycotoxin can lead to significant changes on a molecular level [96] and be an NE predisposing factor [113]. In cases of both in vivo and in vitro exposure to DON in broiler chickens, a decrease in TEER has been noted, which is indicative of increased gut barrier permeability [113], [114]. DON exposure has also been associated with poorer nutrient absorption in chicken intestines [114], [115], [116]. In vivo exposure to OTA in Pekin ducks resulted in growth impairment, reduced villous length, and downregulation of TJ proteins ZO-1 and OCLD expression [97]. Similarly, exposure to aflatoxin B1 in chickens led to changes on a molecular level, increased gut permeability, reduced amino acid digestibility, and impaired growth performance [85]. All the mentioned factors overlap and are known to play a role in the vicious cycle of disease, which negatively impacts gut health and overall bird performance ([Fig. 1]).

Fig. 1 PFAs potential to break the vicious cycle of disease.

Phytogenic additives for intestinal barrier enhancement

PFAs are plant derivatives that can be incorporated into livestock diets to improve their productivity and performance [117] ([Fig. 2]). This group of compounds includes herbs, spices, EOs, and oleoresins [117]. Positive influences of phytogenic compounds on the health of poultry have been previously observed by many researchers [11], [16], [17], [20], [21], [22], [24], [26], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [42], [49], [52], [53], [55], [59], [60], [86], [97], [118], [119], [120], [121], [122], [123] and practical application of these compounds is known to have auspicious perspectives in animal production [11], [17], [62], [124], [125], [126]. The growing interest in the use of PFAs is reflected in the latest survey on PFAs conducted in 2020 by Biomin [127]. The survey was completed by almost 700 respondents from 79 countries and revealed that over half of them currently use PFAs as part of their feeding program. What is even more promising is the fact that almost 70% of respondents declared that their PFA use will increase in the next 12 months.

Fig. 2 Target sites for PFAs to improve gut health and enhance bird performance.

Currently, there are several products on the market that contain either one phytogenic compound or, more often, a mixture of phytogenics, sometimes combined with other additives, such as pre-and probiotics or organic acids.

The unique, complex composition of many phytogenics is responsible for several positive properties related to plant-driven products, such as antioxidant, anti-inflammatory, immunomodulative, antimicrobial, and antiparasitic effects, that contribute to better animal health. Benefits of PFAs in poultry also include improved palpability, a stimulating effect on digestive activity, overall improvement of gastrointestinal morphology, and higher meat quality. These aspects of phytogenic implementation in animal nutrition have been reviewed extensively [6], [7], [9], [10], [117], [128], [129], [130], [131], [132], [133], [134], [135], [136], [137], [138], [139], [140], [141], [142] and will not be discussed in detail here. The main purpose of this paper was to collect and analyze the effects of phytogenic additives on the epithelial part of the intestinal barrier in poultry.

The vital part of the intestinal barrier is the physical barrier formed mainly by tightly connected enterocytes, goblet cells, and undifferentiated cells [123]. An important indicator of intestinal barrier quality and integrity might be the morphology of the mucosa [33], [143]. The phytogenic supplementation-induced changes in the structure of intestinal mucosa are presented in [Table 1]. Features most commonly used for evaluation of the physical barrier condition are VH, CD, V : C, and number of goblet cells. The V : C ratio is directly correlated with the balance between VH and CD [143]. The anti-inflammatory effect of PFAs is recognized as one of the mechanisms involved in their positive effects on gut morphology, and regulation of cell growth and apoptosis may also play a role, but the exact mechanisms behind this are not yet known [61]. Another possible protective feature of phytogenics is their antioxidant properties [117].

Table 1 PFAs: effects on intestinal morphology.

Feed additive	Dosea	Animal model	Challenge	Effect	Reference
a Dose in feed, unless stated otherwise
Plants and plant extracts
Berberis vulgaris extract	2 and 4% of total water consumption	mixed- sex broiler chicks (Cobb 500)	none	4%: Significantly increased duodenal VH and VS; 2 and 4%: significantly increased jejunal VH; a tendency to increase ileal VS	[59]
Allium sativum extract	75 and 150 mg/kg	male broiler chicks (Ross)	none	75 mg/kg: Increased jejunal VH	[33]
Lavandula angustifolia powder	0.3, 1, or 1.7%	male broiler chicks (Ross 308)	none	Significantly decreased jejunal CD and increased the V : C ratio	[35]
Mixtures of plant derivatives – complex products
Blend of three active ingredients (20% curcuminoids, 30% cinnamaldehyde, and 30% glycerol monolaurate)	1 kg/t	male broiler chicks (Cobb)	none	Greater VH and CD in the blend and control groups than in the antimicrobial-treated group; lower V : C ratio in the blend group compared to control group	[181]
Commercial product Anta Phyt (containing hops, licorice, and arabic gum derivatives)	400 mg/kg diet (starter), 300 mg/kg diet (grower), 200/kg diet (grower II and finisher)	male broiler chicks (Ross 308)	none	Significantly greater jejunal wall thickness at day 35; significantly increased jejunal CD and decreased VW at day 42	[180]
Commercial product Digestarom (containing cinnamon 20 g/kg, cumin 20 g/kg, peppermint oil 170 g/kg, garlic oil 150 g/kg, 50 g/kg anise oil g/kg, 40 g/kg fennel oil, and SiO2 and NaCl)	100, 125, and 150 mg/kg	male broiler chicks (Ross 308)	none	100 mg/kg: increased muscularis thickness and goblet cell number at day 21 and day 42; 125 mg/kg: decreased muscularis thickness and increased goblet cell number at day 21, increased VH and muscularis thickness at day 42; 150 mg/kg: significantly higher VH, muscularis at day 21	[12]
Commercial product Enterosan (containing 21.55 mg carvacrol/g, 18.76 mg thymol/g, and 27.62 mg cinnamaldehyde/g)	100 mg/kg	male broiler chicks (Cobb 500)	none	Increased jejunal VH and decreased CD	[49]
Commercial product Enterosan + CUR	100 mg/kg + 50 mg/kg	male broiler chicks (Cobb 500	none	Significantly higher jejunal V : C ratio	[49]
Commercial product Next Enhance150 (containing 54.13% carvacrol and 45.87% thymol)	100 and 200 mg/kg	male broiler chicks (Ross 308)	none	Improved VH, VS, V : C, and mucosal layer of jejunum at 21 and 42 days of age Increased ileal VH, V : C, mucosal layer and goblet cells number at day 21 and mucosal layer and goblet cells number at 42 days of age	[58]
Commercial product Sangrovit	20 – 50 g/t	male broiler chicks (Cobb 500)	C. jejuni	Increased VH and V : C ratios in the ileum and jejunum	[32]
Commercial product Tecnaroma Herbal Mix PL	100, 200, 300, 400, and 500 g/t	male broiler chicks (Ross 308)	none	300 g/t: Significantly increased VW and VS	[27]
Commercial product Xtract (containing 5% carvacrol, 3% cinnamaldehyde, and 2% Capsicum oleoresin)	100 mg/kg	male broiler chicks (Arbor Acres Plus)	cold stress	Intestinal diameter enlargement; increased VH and V : C ratio	[20]
Commercial product Xtract (5 carvacrol, 3% cinnamaldehyde, and 2% Capsicum oleoresin)	100 mg/kg	male broiler chicks (Hubbard HI-Ye hybrids)	none	Higher mucus secretion intensity and accumulation inside cells of the gastrointestinal mucosa; decreased jejunal VH and CD in chickens fed maize + XT at day 21	[145]
Herbal medicine complex (5 ppm carvacrol, 3 ppm cinnamaldehyde, 2 ppm capsaicin)	100 mg/kg	male broiler chicks (Ross)	none	Increased jejunal VH	[33]
Specific combination microencapsulated active plant extracts (containing 5.04% carvacrol, 2.9% cinnamaldehyde, 2.18% Capsicum oleoresin)	100 g/t	male broiler chickens (Arbor Acres Plus)	none	Increase in VH and V : C ratio in the ileum; decrease in ileal CD	[42]
Single phytoconstituents and essential oils
Blend of protected organic acids and EOs (containing organic acids fumaric, sorbic, malic, and citric and EOs thymol, vanillin, and eugenol)	300 g/t of feed	male broiler chicks (Cobb × Cobb 500)	Eimeria spp. at 1 day and with C. perfringens at 11, 12, and 13 days	Lower blood FITC-d concentration and histologic lesions score; increased MUC-2 mRNA expression compared to the challenged control group	[179]
Commercial carvacrol EO (containing 63.5% carvacrol, 3.4% thymol, and 13.1% paracymene)	200, 300, and 400 µL directly PO every day	mixed-sex broiler chicks (Ross 308)	none	Significantly higher goblet cell content in the small intestine epithelium (the highest in the 300 µL treatment group)	[123]
Commercial cOCM (containing 37.5% cinnamaldehyde)	50, 100, 200, and 300 mg/kg	mixed-sex broiler chicks (Cobb 500)	none	50, 100, 200, and 300 mg/kg: decreased jejunal CD; 100, 200, and 300 mg/kg: higher jejunal V : C ratio; 50 and 300 mg/kg: elevated duodenal CD; 300 mg/kg: significantly increased duodenal VH and the jejunal V : C ratio at day 21; 50 mg/kg increased the duodenal V : C ratio at 42 days and reduced jejunal VH	[144]
Commercial EO product (containing 25% thymol and 25% carvacrol)	60, 120, or 240 mg/kg	male broiler chicks (Cobb 500)	C. perfringens	Challenged birds: linear alleviation of the gut lesions and improved V : C ratio	[86]
Commercial product Orego-Stim (containing 5% EO of Origanum vulgare subsp. Hirtum plants and 95% natural feed grade inert carrier)	300 and 500 mg/kg	broiler chicks (Ross 308)	none	3 mg/kg: Significantly increased VH and decreased muscularis thickness in the jejunum and ileum; increased V : C ratio and VS in the jejunum and decreased CD in the jejunum; 5 mg/kg: significantly decreased muscularis thickness and CD in the jejunum and ileum	[31]
CUR	50 mg/kg	male broiler chicks (Cobb 500)	none	Decreased jejunal VH and CD	[49]
400 mg/kg	mixed-sex White Pekin duckling	OTA (2 mg/kg)	Partly restored villus length in the jejunum of OTA challenged birds	[97]
Genistein Hesperidin mixture of genistein and hesperidin (1 : 4)	5 mg/kg 20 mg/kg 5, 10, and 20 mg/kg	broiler chicks (Arbor Acres)	LPS challenge	Increase in gut VH and VW (21 and 42 days) and reduction in CD (in the duodenum and ileum at 21 days and duodenum at 42 days); alleviation of LPS-induced changes; decrease of VH and increase of CD	[24]
Piperine	60, 120, and 180 mg/kg	male broiler chicks (Cobb)	none	60 mg/kg: Increased VS in the duodenum and ileum; 120 and 180 mg/kg: reduced absorption surface of the jejunum; decrease in CD in the duodenum and jejunum	[15]
S. officinalis L. EO (0.1 g/kg diet containing α-thujone 0.04 g/kg, limonene 0.02 g/kg, camphor 0.02 g/kg, and α-humulene 0.01 g/kg)	0.1, 0.25, 0.5, and 1 g/kg	non-sexed laying strain chicks (Isa Brown)	none	Duodenum in Ussing chambers ex vivo: 0.1 and 0.25 g/kg: significantly higher TEER	[120]
S. officinalis L. EO (containing camphor 14.9%, α-thujone 14.8%, eucalyptol 8.5%, β-thujone 7.2%, borneol 3.7%)	0.01, 0.025, 0.05, and 0.1% EO + sodium selenite (0.4 ppm)	female laying chickens (Isa Brown)	none	0.05%: Increased thickness of the mucus layer in the duodenum; decreased the number of goblet cells containing acidic and neutral mucins in the duodenum and jejunum and increased in the ileum	[4]
Thyme EO and oregano EO mixture (encapsulated or non-capsulated)	200 mg/kg	mixed-sex broiler chicks (Ross 308)	none	Encapsulated EOs: significantly higher VH, VW, and CD; significantly lower V : C ratio	[182]
Thymus zigis L. EO (containing 0.1 mg/kg p-cymen and 0.08 mg/kg thymol)	0.5 g/kg	mixed-sex broiler chicks (hybrid Ross 308)	none	Duodenum in Ussing chambers ex vivo: significantly higher TEER	[119]

Intestinal villi are the most important part responsible for nutrients absorption, thus, changes in their length may directly affect a birdʼs performance. The greater the height of the villi, the greater its surface area, which equates to a larger area for effective absorption [33], [143]. It was observed that supplementation of various PFAs has the ability to increase the villous height in poultry [12], [20], [24], [31], [33], [42], [49], [58], [59], [144]. However, in some cases, although several positive effects of phytogenic supplementation were noted, it did not result in a significant change in growth performance. Moreover, apart from a positive influence on intestinal morphology in some aspects, PFA supplementation was sometimes associated with a decrease in villous height in the supplemented groups [49], [144], [145]. Dietary supplementation of chicken broilers with cOCM was associated with improved intestinal integrity manifested by villus development and modulation of the gene expression of TJ proteins and MUC-2, but no improvement in the birdsʼ growth performance was observed [144]. This is consistent with the results of PFA supplementation (commercial phytogenic product Digestarom) obtained by Ahsan et al., where there was no difference among the dietary treatments for growth performance and cecal microbe populations at any phase [12]. However, in the supplemented group, increased VH and VW were observed in comparison to birds fed control diets. Similarly, in a study conducted by Khattak et al., inclusion of EO (blend of EOs from basil, caraway, laurel, lemon, oregano, sage, tea, and thyme – Tecnaroma Herbal Mix PL) in poultry feed did not improve growth performance during the starter phase [27]. The authors associated it with relatively low digestive enzyme secretion capacity in young chicks, especially since an improvement in growth efficiency was later noted during the grower and finisher phases.

Crypts of Lieberkühn are the center of enterocyte production, so their depth is equivalent to the intensity of the epithelial cell synthesis process [33]. In order to maintain the integrity of the epithelium, damaged cells require intensive replacement with new ones, which results in rapid cell turnover. The more the epithelium is exposed to various harmful factors, the greater the depth of the crypts. The positive effect of PFAs (a combination of carvacrol, cinnamaldehyde, and Capsicum oleoresin, piperine, genistein and hesperidin, oregano EO, lavender powder, a combination of CUR, carvacrol, thymol and cinnamaldehyde, cOCM) on gut morphology includes reduced CD [15], [24], [31], [35], [42], [49], [144], [145], which can be interpreted as limited exposure to various stressors, lesser inflammatory response, and sloughing. The cell turnover is also an energy consuming process and shallow crypts suggest that the bird can spare nutrients for growth [12]. An increase in VH and a decrease in CD leads to an increased V : C ratio, which indicates the presence of mature enterocytes, balanced enterocyte migration and sloughing, and efficient nutrient absorption for growth [86], [143]. Increased villi length without increased CD demonstrates a longer survival of villi, without the need for intensive production of new cells [24]. It is consistent with the results of observations carried out in challenged animals. In the study conducted by Du et al. [86] Clostriudium perfringens challenge was associated with remarkably deeper crypts in the ileum and the presence of intestinal lesions. The dietary EO supplementation (commercial product containing 25% thymol and 25% carvacrol) linearly alleviated the intestinal lesions, and 60 – 240 mg/kg EO increased VH and decreased CD, which resulted in a significantly elevated V : C ratio. Similarly, Campylobacter jejuni challenge resulted in a decrease in villous length and an increase in CD, which were successfully alleviated by supplementation of PFAs (commercial product Sangrovit manufactured from extracts of Macleaya cordata) [32]. In the study conducted by Kamboh and Zhu, a significant increase in gut villus length and VW (on day 21 and day 42) and a reduction in CD (in the duodenum on day 42 and ileum on day 21) was observed in birds supplemented with dietary genistein and hesperidin regardless of LPS challenge [24]. However, LPS injection itself caused a deterioration in intestinal morphology as manifested by a shortening of the villi and an increase in CD, which was not observed in the supplemented groups.

The epithelial cells are covered by a layer of mucus that is produced and secreted by goblet cells distributed along the villi [4], [146], [147]. The main components of the mucus layer are glycoproteins called mucins, which have polymeric, viscoelastic, and protective properties [146]. The most important tasks of the mucus layer is protection against pathogens and other harmful factors present in the lumen of the intestine [146], and transport between the lumen and the brush border membrane [147]. Apart from creating a physical barrier, mucins contain mannosyl receptors, which competitively bind to the type 1 fimbriae of gram-negative bacteria [148]. Dietary PFA (Salvia officinalis EO, Digestarom, a commercial blend of cinnamon, cumin, and the EOs peppermint, garlic, anise, and fennel oil, a mixture of thymol and carvacrol, carvacrol EO, a blend of carvacrol, cinnamaldehyde, and Capsicum oleoresin) supplementation was associated with an increase in the number of goblet cells [4], [12], [58], [123], [145] and a higher expression of MUC-2, the major mucin gene in the small intestine [118], [122], [144], [149]. This could indicate the protective properties of PFAs related to villi [145] and a reduction of pathogen adhesion to the epithelium [148]. However, Guo et al. obtained two opposite modulatory effects of cOCM on intestinal MUC-2 expression at two sampling time points – days 21 and 42 [144]. In this study, supplementation of 50 and 300 mg/kg of cOCM increased MUC-2 expression in the jejunum on day 21 but decreased it in the duodenum on day 42. The authors associated this opposite effect with the fact that the results could have been influenced by hygienic conditions or the microbial environment of the intestinal sections. Downregulation of the MUC-2 gene was associated with LPS challenge in chicken broilers, and supplementation with 1% (but not 5%) AH fermented root resulted in significantly higher MUC-2 expression [122]. Contrary, Du et al. did not observe any significant changes in MUC-2 expression either from C. perfringens infection or from EO supplementation (commercial EO product containing 25% thymol and 25% carvacrol) [86].

The use of molecular technologies might broaden the knowledge of phytogenicsʼ mechanism of action, and it may enable the selection of the most suitable ones to alleviate negative effects of different factors. Unfortunately, there are not many papers that describe the direct influence of phytogenic substances on the presence and distribution of TJ proteins in poultry. The key results on this matter are presented in [Table 2].

Table 2 PFAs: effects on TJs.

Feed additive	Dosea	Animal model	Challenge	Effect	Reference
a Dose in feed, unless stated otherwise
Plants and plant extracts
AH (root or fermented root)	1 or 5%	male broiler chicks (Ross 708)	LPS	LPS challenged groups, all AH treatments: significantly higher OCLN expression level; 5% fermented root: OCLN level same as the control group; 1% fermented root: increased JAM-2 and MUC-2 expression	[122]
AH root	1 or 3%	male broiler chicks (Ross)	NE (Eimeria maxima followed by C. perfringens)	NE challenged groups with 1 or 3% AH: significantly higher JAM-2, ZO-1, OCLN, and MUC-2 expression level compared to birds fed a basal diet	[149]
Enzymatically treated A. annua	1 g/kg	male broiler chicks (Arbor Acres)	HS	Increased ileal OCLN, jejunal ZO-1, and OCLN mRNA expression in the HS group	[103]
Mixtures of plant derivatives – complex products
Commertial product Digestarom	100 and 150 mg/kg	male broiler chicks (Cobb 500)	none	100 mg/kg: Increased ileal mucosa CLDN-5 and MUC-2 mRNA expression	[183]
Single phytoconstituents and essential oils
Blend of protected organic acids and EOs (containing organic acids fumaric, sorbic, malic, and citric and EOs thymol, vanillin, and eugenol)	300 g/t	male broiler chicks (Cobb × Cobb 500)	Eimeria spp. followed by C. perfringens	Increased CLDN-1 and OCLN mRNA expression compared to challenged and non-challenged control groups	[179]
Commercial carvacrol EO (containing 63.5% carvacrol, 3.4% thymol, and 13.1% paracymene)	200, 300, and 400 µL directly PO every day	mixed-sex broiler chicks (Ross 308)	none	Significantly increased OCLN, CLDN-1, CLDN-5, ZO-1, and ZO-2 mRNA expression; 300 or 400 µL: increased CLDN-3 mRNA expression	[123]
Commercial cOCM (containing 37.5% cinnamaldehyde)	50, 100, 200, and 300 mg/kg	mixed-sex broiler chicks (Cobb 500)	none	Dose-, age-, and intestinal segment-dependent changes in mRNA expression of CLDN-1, OCLN, ZO-1, and MUC-2; 300 mg/kg: increased CLDN-1 mRNA expression at both day 21 and day 42	[144]
Commercial EO product (containing 25% thymol and 25% carvacrol)	60, 120, or 240 mg/kg	male broiler chicks (Cobb 500)	C. perfringens	Linear dose-dependent tendency to upregulate OCLN mRNA expression	[86]
CUR	400 mg/kg	mixed-sex White Pekin duckling	OTA (2 mg/kg)	Significantly higher OCLN and ZO-1 mRNA and protein expression in CUR + OTA group	[97]

In a study by Liu et al. [123], administering carvacrol EO at various doses to standard-reared birds increased the expression of important TJ proteins ZO-1 and -2, OCLN, and CLDN-1, -3 and -5. The positive modulatory influence of PFAs (cOCM) on TJ protein expression was also observed by Guo, although the effect was strongly dose-, segment-, and age-related [144]. cOCM supplementation commonly increased mRNA expression of CLDN-1, but it did not have a significant effect on ZO-1 mRNA expression. Moreover, cinnamon oil supplementation caused the upregulation of OCLN mRNA in the jejunum and downregulation in the duodenum. Similarly, Paraskeuas and Mountzouris reported that PFA (Digestarom, a commercial blend of cinnamon, cumin, and the EOs peppermint, garlic, anise, and fennel oil) administration significantly affected ileal mucosa gene expression of CLDN-5 and it was higher in broilers fed a diet supplemented with 100 mg PFAs/kg compared with the unsupplemented group [118]. However, the gene expression levels of ZO-1, CLDN-5, and OCLN in cecal mucosa were not affected by PFA inclusion.

The results obtained in challenged birds are extremely valuable as they clearly demonstrate the beneficial potential of PFAs. The LPS challenge affects the molecular structure of TJs and is a good model of inflammation [122]. In a study by Lee et al. [122], different doses of dietary AH root or fermented root were effective in alleviating the negative effects of LPS challenge by increasing the expression of TJs. A similar effect was observed by this research group in the case of AH root treatment and NE challenge [149]. Du et al. [86] also noted the beneficial influence of a mixture of phytogenic additives (containing mainly thymol and carvacrol as active compounds) on intestinal barrier of broilers exposed to C. perfringens challenge.

In the study conducted by Song et al. [103], administration of enzymatically treated Artemisia annua improved intestinal barrier function in heat-stressed broilers by upregulating the mRNA expression of jejunal and ileal OCLN and jejunal ZO-1. In this way, the treatment mitigated the negative effects of HS. However, no differences were found for jejunal and ileal CLDN-2 and -3 and ileal ZO-1 mRNA expression levels among treatments.

The dietary supplementation of CUR was reported by Ruan at el. to be effective in alleviating the toxic influence of OTA on Pekin ducks intestinal barrier [97]. Feeding the birds an ochratoxin-contaminated diet resulted in the significantly decreased expression of OCLN and ZO-1 proteins and mRNA. However, in ducks fed CUR in addition to OTA, the expression levels of both proteins and mRNA were significantly higher than with the toxic diet alone. The structure of enterocytes and TJs was also examined by transmission electron microscopy (TEM), which showed that enterocytes from ducks exposed to OTA had damaged microvilli and widened intercellular spaces. These adverse effects were alleviated in ducks receiving CUR supplementation in addition to the OTA-contaminated diet.

Perspectives

The collected results indicate that PFAs have the potential to improve the overall structure of intestinal mucosa as well as the gut barrier function on a molecular level. Moreover, supplementation with PFAs has been shown to protect birds from various environmental threats leading to impaired intestinal barrier function. This presents great prospects for including PFAs in the poultry diets. Promising results from phytogenic supplementation have also been obtained in other animal models, for example, berberine has been shown to ameliorate TJ damage in a mouse model of endotoxemia [150]. The inclusion of PFAs in the pigʼs diet has also been widely discussed [61], [140], [151], [152], [153]. Jang et al. proved that flavanol-enriched cocoa powder contributes to gut health improvement by a positive influence on gut microbiota and modulation of markers of localized intestinal immunity [154]. In the study conducted by Gessner et al., the addition of grape seed and grape marc extract in the pig diet showed the potential to suppress the inflammation process in the small intestine and improved the gain : feed ratio in growing pigs [155]. Similarly, Han et al. demonstrated that dietary grape seed proanthocyanidins improved intestinal microbiota and the mucosal barrier of weaned pigs [156]. Obtained results showed that the efficacy of this feed additive was comparable to antibiotics. It has been also demonstrated that oregano EO and thymol promote intestinal integrity in pigs and weaned piglets [157], [158].

The idea of using PFAs in human medicine is also gaining popularity, for example, as a possible treatment of inflammatory bowel disease [159], [160], [161]. Interest in the implementation of phytogenics in human treatment protocols has resulted in numerous studies in this field, mainly based on the use of human cell line models. The influence and modulation of TJs by phytogenics have been previously reviewed [67], [159], [162], [163]. Although, the results obtained in cell cultures cannot be directly extrapolated to the in vivo situation of poultry, especially when human cell lines are used. However, they can be an inspiration for further research in poultry species. Numerous studies indicated the potential of phytogenic compounds for preventing or mitigating epithelial barrier disruption by various factors, such as inflammatory cytokines [160], [164], [165], [166], [167] or mycotoxins [95], [98], which can also be of interest in poultry production. The results of studies on phytogenic compounds in various in vitro models are presented in [Table 3]. However, more research is needed to select the most beneficial phytogenics, as well as their formulation and dosage for application in poultry diets.

Table 3 PFAs: effect on in vitro models.

Active compound	Dose	In vitro model	Challenge	Effects	References
6-Gingerol	1, 5, 10, 50, and 100 µM	Caco-2 cell line	dextran sodium sulfate exposure	Restoration of the integrity of Caco-2 monolayer with a dose-dependent increase in TEER	[184]
Berberine	50 µM	HT-29/B6 cells	TNF-α 500 U/mL	Significant increase in TEER; prevention of TNF-α-induced TEER decrease and paracellular permeability increase; increase in CLDN-1 protein expression with or without TNF-α challenge; decrease in CLDN-2 protein expression with or without TNF-α challenge	[164]
	100 µM	Caco-2 cell line	simultaneous IFN-γ (10 ng/mL) and TNF-α (10 ng/mL) exposure	Small increase in TEER in control monolayers; significant attenuation of TEER decrease and paracellular permeability increase in IFN-γ- and TNF-α-treated monolayers; Attenuation of IFN-γ and TNF-α caused reorganization of ZO-1, OCLN, and CLDN-1	[166]
	50, 100, and 200 µM	Caco-2 cell line	none	Increase in TEER; 50 and 100 µM: decrease in mannitol flux; 100 µM: significant decrease in CLDN-2 expression, tendency to upregulate CLDN-3, -7, and OCLN expression	[185]
Biochanin A	50 µmol/L	Caco-2 cell line	none	TEER increase; reduced tyrosine phosphorylation of ZO-1 protein	[167]
	50 µmol/L	Caco-2 cell line	TNF-α (100 ng/mL) exposure	Prevention of TNF-α- dependent TEER decrease	[167]
Chrysin	100 µmol/L	Caco-2 cell line	none	TEER decrease; increased FD-4 flux; decrease in OCLN, JAM-1 and CLDN-1, -3, and -4 expression	[159]
Cinnamicaldehyde	12.5 or 25 µmol/L	IPEC-1 cell line	none	Dose-dependent reduction of FD-4 flux; increase in ZO-2 expression; 25 µmol/L: TEER increase, increase in CLDN-4, ZO-1, -2, and -3 expression; promotion of the localization of CLDN-1 and -3 to the plasma membrane	[186]
CUR	10 µmol/L	Caco-2 cell line	none	TEER increase	[167]
Daidzein	100 µmol/L	Caco-2 cell line	none	TEER increase	[159]
Epigallocatechin gallate	218 µM (100 µg/mL)	Caco-2 cell line	indomethacin (250 µM) exposure	Total protection against the induced decrease of TEER; dose-dependent protection against the induced increase of the FD-4 flux	[187]
Ferulate	5 or 15 µM	Caco-2 cell line	tertbutyl hydroperoxide (100 µM) exposure	Attenuation of t-BHP-induced barrier disruption; prevention of t-BHP-induced decrease in ZO-1 and OCLN expression; 15 µM: increase in ZO-1 expression	[188]
Ferulic acid	20, 50, 100, 500, and 1000 µM	T84 cell line	short-term apical C10 exposure	20 µM: Increased ZO-1 and CLDN-4 mRNA expression, decreased OCLN mRNA expression, TEER increase in C10-treated and C10-untreated T84 monolayers; 20 – 500 µM: dose-dependent TEER increase	[189]
Genistein	100 µmol/L	Caco-2 cell line	none	TEER normalization after transient decrease	[159]
50 µmol/L	Caco-2 cell line	none	TEER increase; reduced tyrosine phosphorylation of ZO-1 protein	[167]
50 µmol/L	Caco-2 cell line	TNF-α (100 ng/mL) exposure	Prevention of TNF-α-dependent TEER decrease	[167]
Hesperetin	100 µmol/L	Caco-2 cell line	None	TEER increase, slightly lower FD-4 flux; increase in OCLN and CLDN-4 expression	[159]
Hydroxytyrosol	10 µmol/L	Caco-2 cell line	none	TEER increase	[167]
Isoferulic acid	20 µM	T84 cell line	short-term apical C10 exposure	Increased ZO-1 and CLDN-4 mRNA expression; decreased OCLN mRNA expression; TEER increase in C10-treated and C10-untreated T84 monolayers	[189]
Kaempferol	10, 30, and 100 µmol/L	Caco-2 cell line	none	Dose-dependent TEER increase; promotion of the actin cytoskeletal association of ZO-1, ZO-2, OCLN, CLDN-1, -3, and -4	[190]
Luteolin	100 µmol/L	Caco-2 cell line	none	TEER increase after transient decrease; decrease in CLDN-1, -3, and -4 expression and increase in ZO-2 expression	[159]
Morin	100 µmol/L	Caco-2 cell line	none	TEER increase	[159]
Myricetin	10, 30, and 100 µmol/L	Caco-2 cell line	none	dose-dependent reduction of LY flux (no difference between 10 – 30 µmol/L)	[191]
Naringenin	100 µmol/L	Caco-2 cell line	none	TEER increase, slightly lower FD-4 flux; increase in OCLN and CLDN-4 expression	[159]
	10, 30, and 100 µM	Caco-2 cell line	none	At the levels of 30 and 100 µM: dose-dependent TEER increase and decrease in FD-4 flux; 100 µM: increase in the cytoskeletal association of TJ proteins; ZO-2, OCLN, CLDN-1, and -4 increased OCLN phosphorylation; increase in the total expression of CLDN-4	[192]
Oxyresveratrol	25 µM	IPEC-J2 cell line	DON (4 µM) exposure	Increase in TEER and reduction of FD-4 diffusion; significantly reduced DON-induced bacterial translocation; enhanced expression of CLDN-4 in untreated cells and reduced DON-induced decreased expression of CLDN-4	[98]
Polyphenolic extract obtained from red wine	200, 400, and 600 µg/mL	HT-29 cell line	mixture of proinflammatory cytokines (20 ng/mL TNF-α; 10 ng/mL IL-1; 50 ng/mL INF-γ) exposure	600 µg: Decrease in the paracellular permeability of FD-4; increase in OCLN, CLDN-5, and ZO-1 mRNA expression; dose-dependent increase in OCLN, CLDN-5, and ZO-1 expression; protection from cytokine-induced OCLN, CLDN-5, and ZO-1 expression decrease; inhibition of cytokine-induced CLDN-2 mRNA expression increase	[160]
Prunetin	50 µmol/L	Caco-2 cell line	none	TEER increase; reduced tyrosine phosphorylation of ZO-1 protein	[167]
	50 µmol/L	Caco-2 cell line	TNF-α (100 ng/mL) exposure	Prevention of TNF-α- dependent TEER decrease	[167]
Quercetin	200 µM	HT-29/B6 cell line	TNF-α (1000 U/mL) exposure	Decrease of CLDN-2 and -3 expression; partial inhibition of TNF-α-dependent decrease of RT	[165]
50, 100, and 200 µM	rat (male Wistar rats) small and large intestine in vitro in Ussing-type chambers	TNF-α 104 U/mL, IFN-γ 100 or 1000 U/mL exposure	Tendency toward CLDN-2 and -4 downregulation; RT increase; 200 µM: partial inhibition of the cytokine-induced RT decrease	[165]
50, 100, 150, and 200 µmol/L	Caco-2 cell line	none	Dose-dependent TEER increase; 200 µmol/L: increase in CLDN-4 expression; increase of CLDN-4 mRNA expression;	[193]
100, 200, or 400 µM	LLC-PK1 cell line		Dose-dependent increases in TEER; 400 µM: reduction in transepithelial mannitol leak; increase in CLDN-5 and -7 concentration, decrease in CLDN-2 concentration	[163]
33 µM (10 µg/mL)	Caco-2 cell line	indomethacin (250 µM) exposure	Total protection against the induced decrease of TEER; total protection against the induced increase of the FD-4 flux	[187]
66 µM (20 µg/mL)	Caco-2 cell line	indomethacin (500 µM) or rotenone (40 µM) exposure	Inhibition of induced ZO-1 immunofluorescence decrease; total protection against the ZO-1 and OCLN expression decrease caused by indomethacin	[187]
10, 30, and 100 µmol/L)	Caco-2 cell line	none	Dose-dependent reduction of LY flux and TEER increase; Enhancement of ZO-2, OCLN, CLDN-1, and -4 binding to the actin cytoskeleton, dose-dependent increase in CLDN-4 expression; 100 µmol/L: assembly of CLDN-1 and -4 at the TJ in the confocal images	[191]
100, 200, and 400 µM	Caco-2 cell line	none	Dose-dependent tendency in TEER increase; 400 µM: increase in CLDN-2, -4, and -5 expression, decreased tricellulin expression	[185]
Resveratrol	50 µM	IPEC-J2 cell line	DON (4 µM) exposure	Partial reduction of DON-induced bacterial translocation; reduction of FD-4 diffusion and TEER drop; Protection from DON-induced disassembly of CLDN-4, complete restoration of the level of CLDN-4 assembly	[95]
	438 µM (100 µg/mL)	Caco-2 cell line	indomethacin (250 µM) exposure	Total protection against the induced decrease of TEER; total protection against the induced increase of the FD-4 flux	[187]
	25 µM	IPEC-J2 cell line	DON (4 µM) exposure	Increase in TEER and reduction of FD-4 diffusion; enhanced expression of CLDN-4 in untreated cells and reduced DON-induced decreased expression of CLDN-4	[98]
Theaflavins (TF-3′-O-gallate)	5, 10, and 20 µM	Caco-2 cell line	none	Reduction in the apparent permeability of fluorescein; at the level of 10 µM: increase in mRNA levels for OCLN, CLDN-1, and ZO-1; enhancement of OCLN, CLDN-1, and ZO-1 protein expression	[194]

Limitations

Despite the promising results of in vitro and in vivo studies, there are still some issues that need to be addressed. First of all, the bioavailability of phytogenic compounds still remains a controversial topic [168]. Especially when the positive effects of their use are observed in vitro, the question arises about their in vivo effectiveness. In birds, the metabolism of phytogenics also remains an under-explored problem. There are extensive reviews of the bioavailability of various phytogenics in humans [169], [170], [171], some including animals, but mainly rodents [172]. The fate of phytogenic pigments in animal nutrition has been reviewed by Faehnrich et al. [173]. In relation to poultry studies on absorption and metabolism of phytogenics, they mainly concentrate on their content in eggs and tissues intended for consumption [174], [175], [176], [177], [178].

Moreover, the metabolism of phytogenics results in the formation of a large number of compounds with various chemical structures, which makes it difficult to assess their individual effects and modes of action [168]. On the other hand, it is clear that dietary PFAs reach the gastrointestinal tract, where they can affect its structural components. CUR, despite its poor bioavailability, has been shown to alleviate the negative effects of OTA exposure [97]. However, for EOs, the use of a delivery method, for example, microencapsulation, may be needed [19], [144].

Another possible complication is the fact that most of the products available on the market are multi-ingredient, which makes it difficult to assess the effects of using individual components and differentiating between them. It is also a serious obstacle in evaluating the published results. Sometimes evaluating and comparing published results can also be problematic as botanical species may be unclear, especially if only the common name is used or only the name of commercial product is stated, without its detailed composition [27], [179], [180]. Moreover, PFAs are usually characterized by variable chemical composition, depending on their ingredients and environmental conditions like climate, location, harvest stage, or storage conditions [7]. To maintain the constant properties of commercial products, standardization of their active components is needed, which is not always easy [7].

All this causes problems with determining optimal doses for poultry, especially since most of the additives are included in feed or in water, which makes it difficult to control the intake of individual birds. The doses are crucial for obtaining the desired result, because a low dose may not be effective, while a high dose may already be toxic and, inversely, impair barrier function [61]. Other factors influencing the efficacy of PFA application in poultry diets are the differences in bird genetics and overall diet composition [135]. Moreover, the possible interactions between phytogenic and other feed additives is another fact that needs to be considered [117]. The stability of phytogenic compounds during feed processing is also often questionable [62].

Another issue that is worth mentioning is the fact that although there are numerous examples of effective supplementation with phytogenic preparations, there are also a few that do not report any effect of this type of dietary treatment. For example, in a study conducted by Akbarian et al., lemon peel or orange peel extract did not have any effect on ileal histomorphology of birds exposed to HS [23]. In a drug-free experimental program led by Gaucher et al., alternative treatment of a diagnosed clinical NE with commercial EO-based products was ineffective in controlling disease outbreaks under field conditions as efficiently, economically, and quickly as antibiotics [112].

Moreover, while most phytogenics are generally considered as safe feed additives, there is hardly any information available regarding the safety and residual toxicity of these ingredients [62], [178]. Yu et al. tested five phytogenic compounds, among others, berberine, in this regard and concluded that their use in starter, grower, and finisher feeds for broiler chickens is safe [178]. However, more studies of this kind are needed to evaluate the use of various phytogenic compounds as feed additives for poultry.

Conclusions

The presented data on the use of PFAs in poultry indicate their significant influence on intestinal morphology and gut barrier physiology, especially in challenged animals. The development of molecular biology techniques and deepening the knowledge about the functions and regulation of the intestinal barrier offer great opportunities to improve compositions of alternative feed additives. EOs are a particularly promising group of PFAs because they include the major part of active substances in the plant [17]. The studies presented in this review confirm EOs potential to ameliorate mucosal morphology and modulate TJ proteins in both challenged and unchallenged animals. Moreover, many studies have focused on this group, so there is a greater chance that evidence-based data will form the basis of EOs use in animal diets. However, there is still a need for more research into phytogenic ingredients in poultry nutrition. In particular, determining the exact mechanism of action of various PFAs at the molecular level is necessary to assess their potential for use in poultry production. Furthermore, as most of the problems that threaten animal health are multifactorial, there is no single solution to all the issues. This results in the need for a holistic approach to poultry production and possibly for the implementation of a combination of different types of feed additives to break the vicious cycle of disease and improve the overall performance of animals.

Contributorsʼ Statement

Drafting the manuscript: U. Latek, M. Mendel; design of the review: U. Latek, W. Karlik; critical revision of the manuscript: U. Latek, M. Chłopecka, W. Karlik, M. Mendel. All authors read and approved the final version of the manuscript.

Conflict of Interest

The authors declare that they have no conflict of interest.

• References

• 1 European Parliament and the Council of the European Union. Regulation (EC) No 1831/2003. Off J Eur Union 2003; 4: 29-43
• 2 Kadykalo S, Roberts T, Thompson M, Wilson J, Lang M, Espeiße O. The value of anticoccidials for sustainable global poultry production. Int J Antimicrob Agents 2018; 51: 304-310
• 3 Federation of Veterinarians of Europe. Federation of Veterinarians of Europe Position Paper on Coccidiostats or Anticoccidials, 2016. Accessed January 20, 2021 at: https://www.fve.org/cms/wp-content/uploads/FVE-position-paper-on-coccidiostats-or-anticoccidials.pdf
• 4 Čapkovičová A, Maková Z, Piešová E, Alves A, Faix Š, Faixová Z. Evaluation of the effects of Salvia officinalis essential oil on plasma biochemistry, gut mucus and quantity of acidic and neutral mucins in the chicken gut. Acta Vet Brno 2014; 64: 138-148
• 5 Cervantes HM. Antibiotic-free poultry production: Is it sustainable?. J Appl Poult Res 2015; 24: 91-97
• 6 Huyghebaert G, Ducatelle R, Van Immerseel F. An update on alternatives to antimicrobial growth promoters for broilers. Vet J 2011; 187: 182-188
• 7 Applegate TJ, Klose V, Steiner T, Ganner A, Schatzmayr G. Probiotics and phytogenics for poultry: Myth or reality?. J Appl Poult Res 2010; 19: 194-210
• 8 Roberts T, Wilson J, Guthrie A, Cookson K, Vancraeynest D, Schaeffer J, Moody R, Clark S. New issues and science in broiler chicken intestinal health: Intestinal microbial composition, shifts, and impacts. Worlds Poult Sci J 2015; 71: 259-270
• 9 Sugiharto S. Role of nutraceuticals in gut health and growth performance of poultry. J Saudi Soc Agric Sci 2016; 15: 99-111
• 10 Yadav AS, Kolluri G, Gopi M, Karthik K, Malik Y, Dhama K. Exploring alternatives to antibiotics as health promoting agents in poultry – a review. J Exp Biol Agric Sci 2016; 4: 368-383
• 11 Abudabos AM, Alyemni AH, Dafalla YM, Khan RU. The effect of phytogenic feed additives to substitute in-feed antibiotics on growth traits and blood biochemical parameters in broiler chicks challenged with Salmonella typhimurium . Environ Sci Pollut Res 2016; 23: 24151-24157
• 12 Ahsan U, Kuter E, Raza I, Köksal BH, Cengiz Ö, Yıldız M, Kızanlık PK, Kaya M, Tatlı O, Sevim Ö. Dietary supplementation of different levels of phytogenic feed additive in broiler diets: The dynamics of growth performance, caecal microbiota, and intestinal morphometry. Rev Bras Cienc Avic 2018; 20: 737-746
• 13 Cross DE, McDevitt RM, Hillman K, Acamovic T. The effect of herbs and their associated essential oils on performance, dietary digestibility and gut microflora in chickens from 7 to 28 days of age. Br Poult Sci 2007; 48: 496-506
• 14 Ding X, Yang CW, Yang ZB. Effects of star anise (Illicium verum Hook.f.), essential oil, and leavings on growth performance, serum, and liver antioxidant status of broiler chickens. J Appl Poult Res 2017; 26: 459-466
• 15 da Silva Cardoso V, de Lima CAR, de Lima MEF, Gomes Dorneles LE, Danelli MGM. Piperine as a phytogenic additive in broiler diets. Pesqui Agropecu Bras 2012; 47: 489-496
• 16 Eler G, Gomes AVC, Trindade BS, Almeida LSL, Dilelis F, Cardoso VS, Lima CAR. Oregano essential oil in the diet of broilers: Performance, carcass characteristics, and blood parameters. South African J Anim Sci 2019; 49: 753-762
• 17 Murugesan GR, Syed B, Haldar S, Pender C. Phytogenic feed additives as an alternative to antibiotic growth promoters in broiler chickens. Front Vet Sci 2015; 2: 1-6
• 18 Giannenas I, Papaneophytou CP, Tsalie E, Pappas I, Triantafillou E, Tontis D, Kontopidis GA. Dietary supplementation of benzoic acid and essential oil compounds affects buffering capacity of the feeds, performance of turkey poults and their antioxidant status, pH in the digestive tract, intestinal microbiota and morphology. Asian-Australasian J Anim Sci 2014; 27: 225-236
• 19 Mohammadi Gheisar M, Hosseindoust A, Kim IH. Evaluating the effect of microencapsulated blends of organic acids and essential oils in broiler chickens diet. J Appl Poult Res 2015; 24: 511-519
• 20 Gharib HB. Evaluation of using dietary phytogenics, as growth promoters, on broiler performance, under normal and subnormal temperature conditions. Egypt J Anim Prod 2014; 51: 49-59
• 21 Hafeez A, Männer K, Schieder C, Zentek J. Effect of supplementation of phytogenic feed additives (powdered vs. encapsulated) on performance and nutrient digestibility in broiler chickens. Poult Sci 2016; 95: 622-629
• 22 Jang I, Ko Y, Yang H, Ha J, Kim J, Kim J, Kang S, Yoo D, Nam D, Kim D, Lee C. Influence of essential oil components on growth performance and the functional activity of the pancreas and small intestine in broiler chickens. Anim Biosci 2004; 17: 394-400
• 23 Akbarian A, Golian A, Kermanshahi H, Farhoosh R, Raji AR, De Smet S, Michiels J. Growth performance and gut health parameters of finishing broilers supplemented with plant extracts and exposed to daily increased temperature. Spanish J Agric Res 2013; 11: 109-119
• 24 Kamboh AA, Zhu WY. Individual and combined effects of genistein and hesperidin on immunity and intestinal morphometry in lipopolysacharide-challenged broiler chickens. Poult Sci 2014; 93: 2175-2183
• 25 Khalaji S, Zaghari M, Hatami KH, Hedari-Dastjerdi S, Lotfi L, Nazarian H. Black cumin seeds, Artemisia leaves (Artemisia sieberi), and Camellia L. plant extract as phytogenic products in broiler diets and their effects on performance, blood constituents, immunity, and cecal microbial population. Poult Sci 2011; 90: 2500-2510
• 26 Khaligh F, Sadeghi G, Karimi A, Vaziry A. Evaluation of different medicinal plants blends in diets for broiler chickens. J Med Plants Res 2011; 5: 1971-1977
• 27 Khattak F, Ronchi A, Castelli P, Sparks N. Effects of natural blend of essential oil on growth performance, blood biochemistry, cecal morphology, and carcass quality of broiler chickens. Poult Sci 2014; 93: 132-137
• 28 Lee KW, Everts H, Kappert HJ, Frehner M, Losa R, Beynen AC. Effects of dietary essential oil components on growth performance, digestive enzymes and lipid metabolism in female broiler chickens. Br Poult Sci 2003; 44: 450-457
• 29 Leusink G, Rempel H, Skura B, Berkyto M, White W, Yang Y, Rhee JY, Xuan SY, Chiu S, Silversides F, Fitzpatrick S, Diarra MS. Growth performance, meat quality, and gut microflora of broiler chickens fed with cranberry extract. Poult Sci 2010; 89: 1514-1523
• 30 Mohiti-Asli M, Ghanaatparast-Rashti M. Comparison of the effect of two phytogenic compounds on growth performance and immune response of broilers. J Appl Anim Res 2017; 45: 603-608
• 31 Mohiti-Asli M, Ghanaatparast-Rashti M. Comparing the effects of a combined phytogenic feed additive with an individual essential oil of oregano on intestinal morphology and microflora in broilers. J Appl Anim Res 2018; 46: 184-189
• 32 Gharib Naseri K, Rahimi S, Khaki P. Comparison of the effects of probiotic, organic acid and medicinal plant on Campylobacter jejuni challenged broiler chickens. J Agric Sci Technol 2012; 14: 1485-1496
• 33 Petrolli TG, Albino LFT, Rostagno HS, Gomes PC, de Castro Tavernari F, Balbino EM. Herbal extracts in diets for broilers. Rev Bras Zootec 2012; 41: 1683-1690
• 34 Amad AA, Männer K, Wendler KR, Neumann K, Zentek J. Effects of a phytogenic feed additive on growth performance and ileal nutrient digestibility in broiler chickens. Poult Sci 2011; 90: 2811-2816
• 35 Salajegheh A, Salarmoini M, Afsharmanesh M, Salajegheh M. Growth performance, intestinal microflora, and meat quality of broiler chickens fed lavender (Lavandula angustifolia) powder. J Livest Sci Technol 2018; 6: 3-38
• 36 Tiihonen K, Kettunen H, Bento MHL, Saarinen M, Lahtinen S, Ouwehand AC, Schulze H, Rautonen N. The effect of feeding essential oils on broiler performance and gut microbiota. Br Poult Sci 2010; 51: 381-392
• 37 Tanzim H, Das GB, Ahmad M, Barua M, Islam K. Influence of phytogenic feed additives and prebiotic in vegetable protein based diet on broiler performance. Progress Agric 2018; 28: 323-330
• 38 Wan XL, Song ZH, Niu Y, Cheng K, Zhang JF, Ahmad H, Zhang LL, Wang T. Evaluation of enzymatically treated Artemisia annua L. on growth performance, meat quality, and oxidative stability of breast and thigh muscles in broilers. Poult Sci 2017; 96: 844-850
• 39 Vieira SL, Oyarzabal OA, Freitas DM, Berres J, Peña JEM, Torres CA, Coneglian JLB. Performance of broilers fed diets supplemented with sanguinarine-like alkaloids and organic acids. J Appl Poult Res 2008; 17: 128-133
• 40 Aroche R, Martínez Y, Ruan Z, Guan G, Waititu S, Nyachoti CM, Más D, Lan S. Dietary inclusion of a mixed powder of medicinal plant leaves enhances the feed efficiency and immune function in broiler chickens. J Chem 2018; 2018: 4073068
• 41 Attia G, El-Eraky W, Hassanein E, El-Gamal M, Farahat M, Hernandez-Santan A. Effect of dietary inclusion of a plant extract blend on broiler growth performance, nutrient digestibility, caecal microflora and intestinal histomorphology. Int J Poult Sci 2017; 16: 344-353
• 42 Awaad MHH, Elmenawey M, Ahmed KA. Effect of a specific combination of carvacrol, cinnamaldehyde, and Capsicum oleoresin on the growth performance, carcass quality and gut integrity of broiler chickens. Vet World 2014; 7: 284-290
• 43 Bravo D, Utterback P, Parsons CM. Evaluation of a mixture of carvacrol, cinnamaldehyde, and capsicum oleoresin for improving growth performance and metabolizable energy in broiler chicks fed corn and soybean meal. J Appl Poult Res 2011; 20: 115-120
• 44 Cázares-Gallegos R, Silva-Vázquez R, Hernández-Martínez CA, Gutiérrez-Soto JG, Kawas-Garza JR, Hume ME, Méndez-Zamora GM. Performance, carcass variables, and meat quality of broilers supplemented with dietary Mexican oregano oil. Braz J Poult Sci 2019; 21: 1-10
• 45 Charal JW, Bidner TD, Southern LL, Janes ME, Gutierrez ME, Lavergne TA. Anise oil dosage and its effect on growth performance and jejunal lesions during a Clostridium perfringens challenge in battery trials, and growth performance in a floor pen trial. J Appl Poult Res 2017; 26: 240-252
• 46 Abdelqader A, Qarallah B, Al-Ramamneh D, Daş G. Anthelmintic effects of citrus peels ethanolic extracts against Ascaridia galli . Vet Parasitol 2012; 188: 78-84
• 47 Diaz Carrasco JM, Redondo LM, Redondo EA, Dominguez JE, Chacana AP, Fernandez Miyakawa ME. Use of plant extracts as an effective manner to control Clostridium perfringens induced necrotic enteritis in poultry. Biomed Res Int 2016; 2016: 3278359
• 48 Díaz Carrasco JM, Redondo EA, Pin Viso ND, Redondo LM, Farber MD, Fernández Miyakawa ME. Tannins and bacitracin differentially modulate gut microbiota of broiler chickens. Biomed Res Int 2018; 2018: 1879168
• 49 Galli GM, Gerbet RR, Griss LG, Fortuoso BF, Petrolli TG, Boiago MM, Souza CF, Baldissera MD, Mesadri J, Wagner R, da Rosa G, Mendes RE, Gris A, Da Silva AS. Combination of herbal components (curcumin, carvacrol, thymol, cinnamaldehyde) in broiler chicken feed: Impacts on response parameters, performance, fatty acid profiles, meat quality and control of coccidia and bacteria. Microb Pathog 2020; 139: 103916
• 50 Granstad S, Kristoffersen AB, Benestad SL, Sjurseth SK, David B, Sørensen L, Fjermedal A, Edvardsen DH, Sanson G, Løvland A, Kaldhusdal M. Effect of feed additives as alternatives to in-feed antimicrobials on production performance and intestinal clostridium perfringens counts in broiler chickens. Animals (Basel) 2020; 10: 240
• 51 Lee JH, Kim YG, Lee J. Carvacrol-rich oregano oil and thymol-rich thyme red oil inhibit biofilm formation and the virulence of uropathogenic Escherichia coli . J Appl Microbiol 2017; 123: 1420-1428
• 52 Lee SH, Lillehoj HS, Jang SI, Lee KW, Park MS, Bravo D, Lillehoj EP. Cinnamaldehyde enhances in vitro parameters of immunity and reduces in vivo infection against avian coccidiosis. Br J Nutr 2011; 106: 862-869
• 53 MacHado jr. PC, Beiraõ BCB, Fernandes Filho T, Lourenço MC, Joineau ML, Santin E, Caron LF. Use of blends of organic acids and oregano extracts in feed and water of broiler chickens to control Salmonella Enteritidis persistence in the crop and ceca of experimentally infected birds. J Appl Poult Res 2014; 23: 671-682
• 54 Miladi H, Zmantar T, Kouidhi B, Chaabouni Y, Mahdouani K, Bakhrouf A, Chaieb K. Use of carvacrol, thymol, and eugenol for biofilm eradication and resistance modifying susceptibility of Salmonella enterica serovar Typhimurium strains to nalidixic acid. Microb Pathog 2017; 104: 56-63
• 55 Reis JH, Gebert RR, Barreta M, Baldissera MD, Dos Santos ID, Wagner R, Campigotto G, Jaguezeski AM, Gris A, de Lima JLF, Mendes RE, Fracasso M, Boiago MM, Stefani LM, Dos Santos DS, Robazza WS, Da Silva AS. Effects of phytogenic feed additive based on thymol, carvacrol and cinnamic aldehyde on body weight, blood parameters and environmental bacteria in broilers chickens. Microb Pathog 2018; 125: 168-176
• 56 Choct M. Managing gut health through nutrition. Br Poult Sci 2009; 50: 9-15
• 57 Kogut MH, Arsenault RJ. Editorial: Gut health: The new paradigm in food animal production. Front Vet Sci 2016; 3: 10-13
• 58 Hashemipour H, Kermanshahi H, Golian A, Raji A, Krimpen MV. Effect of thymol+ carvacrol by next enhance 150 on intestinal development of broiler chickens fed CMC containing diet. Iran J Appl Anim Sci 2013; 3: 567-576
• 59 Yazdani A, Poorbaghi SL, Habibi H, Nazifi S, Rahmani Far F, Sepehrimanesh M. Dietary Berberis vulgaris extract enhances intestinal mucosa morphology in the broiler chicken (Gallus gallus). Comp Clin Path 2013; 22: 611-615
• 60 Patra AK. Influence of plant bioactive compounds on intestinal epithelial barrier in poultry. Mini Rev Med Chem 2019; 20: 566-577
• 61 Patra AK, Amasheh S, Aschenbach JR. Modulation of gastrointestinal barrier and nutrient transport function in farm animals by natural plant bioactive compounds – A comprehensive review. Crit Rev Food Sci Nutr 2019; 59: 3237-3266
• 62 Yang C, Chowdhury MAK, Hou Y, Gong J. Phytogenic compounds as alternatives to in-feed antibiotics: Potentials and challenges in application. Pathogens 2015; 4: 137-156
• 63 Turner JR. Intestinal mucosal barrier function in health and disease. Nat Rev Immunol 2009; 9: 799-809
• 64 Dubreuil JD. Enterotoxigenic Escherichia coli targeting intestinal epithelial tight junctions: An effective way to alter the barrier integrity. Microb Pathog 2017; 113: 129-134
• 65 Hu CAA, Hou Y, Yi D, Qiu Y, Wu G, Kong X, Yin Y. Autophagy and tight junction proteins in the intestine and intestinal diseases. Anim Nutr 2015; 1: 123-127
• 66 Suzuki T. Regulation of intestinal epithelial permeability by tight junctions. Cell Mol Life Sci 2013; 70: 631-659
• 67 Ulluwishewa D, Anderson RC, McNabb WC, Moughan PJ, Wells JM, Roy NC. Regulation of tight junction permeability by intestinal bacteria and dietary components. J Nutr 2011; 141: 769-776
• 68 Yu QH, Yang Q. Diversity of tight junctions (TJs) between gastrointestinal epithelial cells and their function in maintaining the mucosal barrier. Cell Biol Int 2009; 33: 78-82
• 69 Awad WA, Hess C, Hess M. Enteric pathogens and their toxin-induced disruption of the intestinal barrier through alteration of tight junctions in chickens. Toxins (Basel) 2017; 9: 60
• 70 Lee B, Moon KM, Kim CY. Tight junction in the intestinal epithelium: Its association with diseases and regulation by phytochemicals. J Immunol Res 2018; 2018: 2645465
• 71 Turner JR. Molecular basis of epithelial barrier regulation: From basic mechanisms to clinical application. Am J Pathol 2006; 169: 1901-1909
• 72 John LJ, Fromm M, Schulzke JD. Epithelial barriers in intestinal inflammation. Antioxid Redox Signal 2011; 15: 1255-1270
• 73 Rao RK, Basuroy S, Rao VU, Karnaky jr. KJ, Gupta A. Tyrosine phosphorylation and dissociation of occludin-ZO-1 and E-cadherin-β-catenin complexes from the cytoskeleton by oxidative stress. Biochem J 2002; 368: 471-481
• 74 Shen L, Weber CR, Turner JR. The tight junction protein complex undergoes rapid and continuous molecular remodeling at steady state. J Cell Biol 2008; 181: 683-695
• 75 Steed E, Balda MS, Matter K. Dynamics and functions of tight junctions. Trends Cell Biol 2010; 20: 142-149
• 76 Van Itallie CM, Anderson JM. Claudins and epithelial paracellular transport. Annu Rev Physiol 2006; 68: 403-429
• 77 Alhenaky A, Abdelqader A, Abuajamieh M, Al-Fataftah AR. The effect of heat stress on intestinal integrity and Salmonella invasion in broiler birds. J Therm Biol 2017; 70: 9-14
• 78 Pearce SC, Mani V, Boddicker RL, Johnson JS, Weber TE, Ross JW, Rhoads RP, Baumgard LH, Gabler NK. Heat stress reduces intestinal barrier integrity and favors intestinal glucose transport in growing pigs. PLoS One 2013; 8: 1-9
• 79 Pinton P, Tsybulskyy D, Lucioli J, Laffitte J, Callu P, Lyazhri F, Grosjean F, Bracarense AP, Kolf-Clauw M, Oswald IP. Toxicity of deoxynivalenol and its acetylated derivatives on the intestine: Differential effects on morphology, barrier function, tight junction proteins, and mitogen-activated protein kinases. Toxicol Sci 2012; 130: 180-190
• 80 Yegani M, Korver DR. Factors affecting intestinal health in poultry. Poult Sci 2008; 87: 2052-2063
• 81 Akbari P, Braber S, Varasteh S, Alizadeh A, Garssen J, Fink-Gremmels J. The intestinal barrier as an emerging target in the toxicological assessment of mycotoxins. Arch Toxicol 2017; 91: 1007-1029
• 82 Awad WA, Molnár A, Aschenbach JR, Ghareeb K, Khayal B, Hess C, Liebhart D, Dublecz K, Hess M. Campylobacter infection in chickens modulates the intestinal epithelial barrier function. Innate Immun 2015; 21: 151-160
• 83 Berkes J, Viswanathan VK, Savkovic SD, Hecht G. Intestinal epithelial responses to enteric pathogens: Effects on the tight junction barrier, ion transport, and inflammation. Gut 2003; 52: 439-451
• 84 Chen ML, Ge Z, Fox JG, Schauer DB. Disruption of tight junctions and induction of proinflammatory cytokine responses in colonic epithelial cells by Campylobacter jejuni . Infect Immun 2006; 74: 6581-6589
• 85 Chen X, Naehrer K, Applegate TJ. Interactive effects of dietary protein concentration and aflatoxin B1 on performance, nutrient digestibility, and gut health in broiler chicks. Poult Sci 2016; 95: 1312-1325
• 86 Du E, Wang W, Gan L, Li Z, Guo S, Guo Y. Effects of thymol and carvacrol supplementation on intestinal integrity and immune responses of broiler chickens challenged with Clostridium perfringens . J Anim Sci Biotechnol 2016; 7: 1-10
• 87 Fasano A, Nataro JP. Intestinal epithelial tight junctions as targets for enteric bacteria-derived toxins. Adv Drug Deliv Rev 2004; 56: 795-807
• 88 Ghareeb K, Awad WA, Böhm J, Zebeli Q. Impacts of the feed contaminant deoxynivalenol on the intestine of monogastric animals: poultry and swine. J Appl Toxicol 2015; 35: 327-337
• 89 Benard A, Desreumeaux P, Huglo D, Hoorelbeke A, Tonnel AB, Wallaert B. Increased intestinal permeability in bronchial asthma. J Allergy Clin Immunol 1996; 97: 1173-1178
• 90 Bosi E, Molteni L, Radaelli MG, Folini L, Fermo I, Bazzigaluppi E, Piemonti L, Pastore MR, Paroni R. Increased intestinal permeability precedes clinical onset of type 1 diabetes. Diabetologia 2006; 49: 2824-2827
• 91 Odenwald MA, Turner JR. Intestinal permeability defects: Is it time to treat?. Clin Gastroenterol Hepatol 2013; 11: 1075-1083
• 92 Wang Q, Zhou H, Lin H, Ma Z, Fan H. Porcine circovirus type 2 exploits JNK-mediated disruption of tight junctions to facilitate Streptococcus suis translocation across the tracheal epithelium. Vet Res 2020; 51: 1-12
• 93 Zeissig S, Bürgel N, Günzel D, Richter J, Mankertz J, Wahnschaffe U, Kroesen AJ, Zeitz M, Fromm M, Schulzke JD. Changes in expression and distribution of claudin 2, 5 and 8 lead to discontinuous tight junctions and barrier dysfunction in active Crohnʼs disease. Gut 2007; 56: 61-72
• 94 Antonissen G, Van Immerseel F, Pasmans F, Ducatelle R, Janssens GP, De Baere S, Mountzouris KC, Su S, Wong EA, De Meulenaer B, Verlinden M, Devreese M, Haesebrouck F, Novak B, Dohnal I, Martel A, Croubels S. Mycotoxins deoxynivalenol and fumonisins alter the extrinsic component of intestinal barrier in broiler chickens. J Agric Food Chem 2015; 63: 10846-10855
• 95 Ling KH, Wan MLY, El-Nezami H, Wang M. Protective capacity of resveratrol, a natural polyphenolic compound, against deoxynivalenol-induced intestinal barrier dysfunction and bacterial translocation. Chem Res Toxicol 2016; 29: 823-833
• 96 Osselaere A, Santos R, Hautekiet V, De Backer P, Chiers K, Ducatelle R, Croubels S. Deoxynivalenol impairs Hepatic and intestinal gene expression of selected oxidative stress, tight junction and inflammation proteins in broiler chickens, but addition of an adsorbing agent shifts the effects to the distal parts of the small intestine. PLoS One 2013; 8: e69014
• 97 Ruan D, Wang WC, Lin CX, Fouad AM, Chen W, Xia WG, Wang S, Luo X, Zhang WH, Yan SJ, Zheng CT, Yang L. Effects of curcumin on performance, antioxidation, intestinal barrier and mitochondrial function in ducks fed corn contaminated with ochratoxin A. Animal 2019; 13: 42-52
• 98 Wan MLY, Ling KH, El-Nezami H, Wang M. Oxyresveratrol protective effects against deoxynivalenol-induced intestinal barrier dysfunction and bacterial translocation on porcine intestinal epithelial IPEC-J2 cells. J Food Bioact 2018; 1: 116-123
• 99 Muza-Moons MM, Schneeberger EE, Hecht GA. Enteropathogenic Escherichia coli infection leads to appearance of aberrant tight junctions strands in the lateral membrane of intestinal epithelial cells. Cell Microbiol 2004; 6: 783-793
• 100 Zhang B, Shao Y, Liu D, Yin P, Guo Y, Yuan J. Zinc prevents Salmonella enterica serovar Typhimurium-induced loss of intestinal mucosal barrier function in broiler chickens. Avian Pathol 2012; 41: 361-367
• 101 Santos RR, Awati A, Roubos-van den Hil PJ, van Kempen TATG, Tersteeg-Zijderveld MHG, Koolmees PA, Smits C, Fink-Gremmels J. Effects of a feed additive blend on broilers challenged with heat stress. Avian Pathol 2019; 48: 582-601
• 102 Song J, Xiao K, Ke YL, Jiao LF, Hu CH, Diao QY, Shi B, Zou XT. Effect of a probiotic mixture on intestinal microflora, morphology, and barrier integrity of broilers subjected to heat stress. Poult Sci 2014; 93: 581-588
• 103 Song Z, Cheng K, Zhang L, Wang T. Dietary supplementation of enzymatically treated Artemisia annua could alleviate the intestinal inflammatory response in heat-stressed broilers. J Therm Biol 2017; 69: 184-190
• 104 Uerlings J, Song ZG, Hu XY, Wang SK, Lin H, Buyse J, Everaert N. Heat exposure affects jejunal tight junction remodeling independently of adenosine monophosphate-activated protein kinase in 9-day-old broiler chicks. Poult Sci 2018; 97: 3681-3690
• 105 Varasteh S, Braber S, Akbari P, Garssen J, Fink-Gremmels J. Differences in susceptibility to heat stress along the chicken intestine and the protective effects of galacto-oligosaccharides. PLoS One 2015; 10: 1-18
• 106 Zhang C, Zhao XH, Yang L, Chen XY, Jiang RS, Jin SH, Geng ZY. Resveratrol alleviates heat stress-induced impairment of intestinal morphology, microflora, and barrier integrity in broilers. Poult Sci 2017; 96: 4325-4332
• 107 Hara JRO, Buret AG. Mechanisms of intestinal tight junctional disruption during infection. Front Biosci 2008; 13: 7008-7021
• 108 Dahiya JP, Wilkie DC, Van Kessel AG, Drew MD. Potential strategies for controlling necrotic enteritis in broiler chickens in post-antibiotic era. Anim Feed Sci Technol 2006; 129: 60-88
• 109 Stalker MJ, Brash ML, Weisz A, Ouckama RM, Slavic D. Arthritis and osteomyelitis associated with Enterococcus cecorum infection in broiler and broiler breeder chickens in Ontario, Canada. J Vet Diagn Invest 2010; 22: 643-645
• 110 Tsiouris V. Poultry management: A useful tool for the control of necrotic enteritis in poultry. Avian Pathol 2016; 45: 323-325
• 111 Van Waeyenberghe L, De Gussem M, Verbeke J, Dewaele I, De Gussem J. Timing of predisposing factors is important in necrotic enteritis models. Avian Pathol 2016; 45: 370-375
• 112 Gaucher ML, Quessy S, Letellier A, Arsenault J, Boulianne M. Impact of a drug-free program on broiler chicken growth performances, gut health, Clostridium perfringens and Campylobacter jejuni occurrences at the farm level. Poult Sci 2015; 94: 1791-1801
• 113 Antonissen G, Van Immerseel F, Pasmans F, Ducatelle R, Haesebrouck F, Timbermont L, Verlinden M, Janssens GP, Eeckhaut V, Eeckhout M, De Saeger S, Hessenberger S, Martel A, Croubels S. The mycotoxin deoxynivalenol predisposes for the development of Clostridium perfringens-induced necrotic enteritis in broiler chickens. PLoS One 2014; 9: 1-8
• 114 Awad WA, Zentek J. The feed contaminant deoxynivalenol affects the intestinal barrier permeability through inhibition of protein synthesis. Arch Toxicol 2015; 89: 961-965
• 115 Awad WA, Razzazi-Fazeli E, Böhm J, Zentek J. Influence of deoxynivalenol on the D-glucose transport across the isolated epithelium of different intestinal segments of laying hens. J Anim Physiol Anim Nutr (Berl) 2007; 91: 175-180
• 116 Awad WA, Razzazi-Fazeli E, Böhm J, Zentek J. Effects of B-trichothecenes on luminal glucose transport across the isolated jejunal epithelium of broiler chickens. J Anim Physiol Anim Nutr (Berl) 2008; 92: 225-230
• 117 Windisch W, Schedle K, Plitzner C, Kroismayr A. Use of phytogenic products as feed additives for swine and poultry. J Anim Sci 2008; 86: E140-E148
• 118 Paraskeuas V, Mountzouris KC. Broiler gut microbiota and expressions of gut barrier genes affected by cereal type and phytogenic inclusion. Anim Nutr 2019; 5: 22-31
• 119 Placha I, Takacova J, Ryzner M, Cobanova K, Laukova A, Strompfova V, Venglovska K, Faix S. Effect of thyme essential oil and selenium on intestine integrity and antioxidant status of broilers. Br Poult Sci 2014; 55: 105-114
• 120 Placha I, Ryzner M, Cobanova K, Faixova Z, Faix S. Effects of dietary supplementation with sage (Salvia officinalis L.) essential oil on antioxidant status and duodenal wall integrity of laying strain growers. Pol J Vet Sci 2015; 18: 741-749
• 121 Varmuzova K, Matulova ME, Gerzova L, Cejkova D, Gardan-Salmon D, Panhéleux M, Robert F, Sisak F, Havlickova H, Rychlik I. Curcuma and Scutellaria plant extracts protect chickens against inflammation and Salmonella Enteritidis infection. Poult Sci 2015; 94: 2049-2058
• 122 Lee Y, Lee SH, Gadde UD, Oh ST, Lee SJ, Lillehoj HS. Dietary Allium hookeri reduces inflammatory response and increases expression of intestinal tight junction proteins in LPS-induced young broiler chicken. Res Vet Sci 2017; 112: 149-155
• 123 Liu SD, Song MH, Yun W, Lee J, Lee C, Kwak W, Han N, Kim H, Cho J. Effects of oral administration of different dosages of carvacrol essential oils on intestinal barrier function in broilers. J Anim Physiol Anim Nutr (Berl) 2018; 102: 1257-1265
• 124 Alloui MN, Agabou A, Alloui N. Application of herbs and phytogenic feed additives in poultry production. Glob J Anim Sci Res 2014; 2: 234-243
• 125 Hashemi SR, Davoodi H. Phytogenics as new class of feed additive in poultry industry. J Anim Vet Adv 2010; 9: 2295-2304
• 126 Pliego AB, Tavakoli M, Khusro A, Seidavi A, Elghandour MMMY, Salem AZM, Márquez-Molina O, Rene Rivas-Caceres R. Beneficial and adverse effects of medicinal plants as feed supplements in poultry nutrition: A review. Anim Biotechnol 2020; 0: 1-23
• 127 Biomin. 2020 Biomin Phytogenic Feed Additive Survey Results. Accessed January 26, 2021 at: https://www.biomin.net/science-hub/2020-biominr-phytogenic-feed-additive-survey-results/
• 128 Brenes A, Roura E. Essential oils in poultry nutrition: Main effects and modes of action. Anim Feed Sci Technol 2010; 158: 1-14
• 129 Lee KW, Everts H, Beynen AC. Essential oils in broiler nutrition. Int J Poult Sci 2004; 3: 738-752
• 130 Gadde U, Kim WH, Oh ST, Lillehoj HS. Alternatives to antibiotics for maximizing growth performance and feed efficiency in poultry: A review. Anim Heal Res Rev 2017; 18: 26-45
• 131 Sethiya NK. Review on natural growth promoters available for improving gut health of poultry: An alternative to antibiotic growth promoters. Asian J Poult Sci 2016; 10: 1-29
• 132 Karásková K, Suchý P, Straková E. Current use of phytogenic feed additives in animal nutrition: A review. Czech J Anim Sci 2015; 60: 521-530
• 133 Bozkurt M, Tüzün AE. Application of aromatic Plants and their Extracts in Diets of Turkeys. In: Florou-Paneri P, Christaki E, Giannenas I. eds. Feed Additives: Aromatic Plants and Herbs in Animal Nutrition and Health. Cambridge, MA: Academic Press; 2020: 205-226
• 134 Jin LZ, Dersjant-Li Y, Giannenas I. Application of aromatic Plants and their Extracts in Diets of Broiler Chickens. In: Florou-Paneri P, Christaki E, Giannenas I. eds. Feed Additives: Aromatic Plants and Herbs in Animal Nutrition and Health. Cambridge, MA: Academic Press; 2020: 159-185
• 135 Puvača N, Stanaćev V, Glamočić D, Lević J, Perić L, Stanaćev V, Milić D. Beneficial effects of phytoadditives in broiler nutrition. Worlds Poult Sci J 2013; 69: 27-34
• 136 Simitzis PE. Enrichment of animal diets with essential oils–A great perspective on improving animal performance and quality characteristics of the derived products. Medicines 2017; 4: 35
• 137 Yang Y, Iji PA, Choct M. Dietary modulation of gut microflora in broiler chickens: a review of the role of six kinds of alternatives to in-feed antibiotics. Worlds Poult Sci J 2009; 65: 97
• 138 Fallah R, Kiani A, Azarfar A. A review of the role of five kinds of alternatives to in-feed antibiotics in broiler production. Journal of Veterinary Medicine and Animal Health 2013; 5: 317-321
• 139 Madhupriya V, Shamsudeen P, Manohar GR, Senthilkumar S, Soundarapandiyan V, Moorthy M. Phyto feed additives in poultry nutrition–A review. Int J Sci Environ Technol 2018; 7: 815-822
• 140 Zeng Z, Zhang S, Wang H, Piao X. Essential oil and aromatic plants as feed additives in non-ruminant nutrition: A review. J Anim Sci Biotechnol 2015; 6: 7
• 141 Wallace RJ, Oleszek W, Franz C, Hahn I, Baser KH, Mathe A, Teichmann K. Dietary plant bioactives for poultry health and productivity. Br Poult Sci 2010; 51: 461-487
• 142 Shao Y, Guo Y, Wang Z. β-1,3/1,6-Glucan alleviated intestinal mucosal barrier impairment of broiler chickens challenged with Salmonella enterica serovar Typhimurium . Poult Sci 2013; 92: 1764-1773
• 143 Paiva D, Walk C, Mcelroy A. Dietary calcium, phosphorus, and phytase effects on bird performance, intestinal morphology, mineral digestibility, and bone ash during a natural necrotic enteritis episode. Poult Sci 2014; 93: 2752-2762
• 144 Guo S, Cheng Q, Li Y, Duan R, Hou Y, Yi D, Ding B. Effects of dietary coated-oleum cinnamomi supplementation on the immunity and intestinal integrity of broiler chickens. Anim Sci J 2018; 89: 1581-1590
• 145 Jamroz D, Wertelecki T, Houszka M, Kamel C. Influence of diet type on the inclusion of plant origin active substances on morphological and histochemical characteristics of the stomach and jejunum walls in chicken. J Anim Physiol Anim Nutr (Berl) 2006; 90: 255-268
• 146 Dharmani P, Srivastava V, Kissoon-Singh V, Chadee K. Role of intestinal mucins in innate host defense mechanisms against pathogens. J Innate Immun 2009; 1: 123-135
• 147 Uni Z, Smirnov A, Sklan D. Pre- and posthatch development of goblet cells in the broiler small intestine: Effect of delayed access to feed. Poult Sci 2003; 82: 320-327
• 148 Chacher MFA, Kamran Z, Ahsan U, Ahmad S, Koutoulis K, Qutab ud din HG, Cengiz Ö. Use of mannan oligosaccharide in broiler diets: An overview of underlying mechanisms. Worlds Poult Sci J 2017; 73: 831-844
• 149 Lee YS, Lee SH, Gadde UD, Oh ST, Lee SJ, Lillehoj HS. Allium hookeri supplementation improves intestinal immune response against necrotic enteritis in young broiler chickens. Poult Sci 2018; 97: 1899-1908
• 150 Gu L, Li N, Gong J, Li Q, Zhu W, Li J. Berberine ameliorates intestinal epithelial tight-junction damage and down-regulates myosin light chain kinase pathways in a mouse model of endotoxinemia. J Infect Dis 2011; 203: 1602-1612
• 151 Chaudhary SK, Rokade JJ, Aderao GA, Singh A, Gopi M, Mishra A, Raje K. Saponin in poultry and monogastric animals: A review. Int J Curr Microbiol Appl Sci 2018; 7: 3218-3225
• 152 Liu Y, Espinosa CD, Abelilla JJ, Casas GA, Lagos LV, Lee SA, Kwon WB, Mathai JK, Navarro DMDL, Jaworski NW, Stein HH. Non-antibiotic feed additives in diets for pigs: A review. Anim Nutr 2018; 4: 113-125
• 153 Patra AK. Interactions of plant bioactives with nutrient transport systems in gut of livestock. Indian J Anim Hlth 2018; 57: 125-136
• 154 Jang S, Sun J, Chen P, Lakshman S, Molokin A, Harnly JM, Vinyard BT, Urban jr. JF, Davis CD, Solano-Aguilar G. Flavanol-enriched cocoa powder alters the intestinal microbiota, tissue and fluid metabolite profiles, and intestinal gene expression in pigs. J Nutr 2016; 146: 673-680
• 155 Gessner DK, Fiesel A, Most E, Dinges J, Wen G, Ringseis R, Eder K. Supplementation of a grape seed and grape marc meal extract decreases activities of the oxidative stress-responsive transcription factors NF-κB and Nrf2 in the duodenal mucosa of pigs. Acta Vet Scand 2013; 55: 18
• 156 Han M, Song P, Huang C, Rezaei A, Farrar S, Brown MA, Ma X. Dietary grape seed proanthocyanidins (GSPs) improve weaned intestinal microbiota and mucosal barrier using a piglet model. Oncotarget 2016; 7: 80313-80326
• 157 Zou Y, Xiang Q, Wang J, Peng J, Wei H. Oregano essential oil improves intestinal morphology and expression of tight junction proteins associated with modulation of selected intestinal bacteria and immune status in a pig model. Biomed Res Int 2016; 2016: 5436738
• 158 Van Noten N, Degroote J, Van Liefferinge E, Taminiau B, De Smet S, Desmet T, Michiels J. Effects of thymol and thymol α-D-glucopyranoside on intestinal function and microbiota of weaned pigs. Animals (Basel) 2020; 10: 1-21
• 159 Noda S, Tanabe S, Suzuki T. Differential effects of flavonoids on barrier integrity in human intestinal Caco-2 cells. J Agric Food Chem 2012; 60: 4628-4633
• 160 Nunes C, Freitas V, Almeida L, Laranjinha J. Red wine extract preserves tight junctions in intestinal epithelial cells under inflammatory conditions: implications for intestinal inflammation. Food Funct 2019; 10: 1364-1374
• 161 Salaritabar A, Darvishi B, Hadjiakhoondi F, Manayi A, Sureda A, Nabavi SF, Fitzpatrick LR, Nabavi SM, Bishayee A. Therapeutic potential of flavonoids in inflammatory bowel disease: A comprehensive review. World J Gastroenterol 2017; 23: 5097-5114
• 162 Shigeshiro M, Tanabe S, Suzuki T. Dietary polyphenols modulate intestinal barrier defects and inflammation in a murine model of colitis. J Funct Foods 2013; 5: 949-955
• 163 Mercado J, Valenzano MC, Jeffers C, Sedlak J, Cugliari MK, Papanikolaou E, Clouse J, Miao J, Wertan NE, Mullin JM. Enhancement of tight junctional barrier function by micronutrients: compound-specific effects on permeability and claudin composition. PLoS One 2013; 8: 1-8
• 164 Amasheh M, Fromm A, Krug SM, Amasheh S, Andres S, Zeitz M, Fromm M, Schulzke JD. TNFα-induced and berberine-antagonized tight junction barrier impairment via tyrosine kinase, Akt and NFκB signaling. J Cell Sci 2010; 123: 4145-4155
• 165 Amasheh M, Luettig J, Amasheh S, Zeitz M, Fromm M, Schulzke JD. Effects of quercetin studied in colonic HT-29/B6 cells and rat intestine in vitro . Ann N Y Acad Sci 2012; 1258: 100-107
• 166 Cao M, Wang P, Sun C, He W, Wang F. Amelioration of IFN-γ and TNF-α-induced intestinal epithelial barrier dysfunction by berberine via suppression of MLCK-MLC phosphorylation signaling pathway. PLoS One 2013; 8: e61944
• 167 Piegholdt S, Pallauf K, Esatbeyoglu T, Speck N, Reiss K, Ruddigkeit L, Stocker A, Huebbe P, Rimbach G. Biochanin A and prunetin improve epithelial barrier function in intestinal CaCo-2 cells via downregulation of ERK, NF-κB, and tyrosine phosphorylation. Free Radic Biol Med 2014; 70: 255-264
• 168 Gil-Cardoso K, Ginés I, Pinent M, Ardévol A, Blay M, Terra X. Effects of flavonoids on intestinal inflammation, barrier integrity and changes in gut microbiota during diet-induced obesity. Nutr Res Rev 2016; 29: 234-248
• 169 Crozier A, Jaganath IB, Clifford MN. Dietary phenolics: Chemistry, bioavailability and effects on health. Nat Prod Rep 2009; 26: 1001-1043 DOI: 10.1039/b802662a.
• 170 Manach C, Williamson G, Morand C, Scalbert A, Rémésy C. Bioavailability and bioefficacy of polyphenols in humans. I · Review of 97 bioavailability studies. Am J Clin Nutr 2005; 81: 230S-242S
• 171 Marín L, Miguélez EM, Villar CJ, Lombó F. Bioavailability of dietary polyphenols and gut microbiota metabolism: Antimicrobial properties. Biomed Res Int 2015; 2015: 905215
• 172 Kohlert C, van Rensen I, März R, Schindler G, Graefe EU, Veit M. Bioavailability and pharmacokinetics of natural volatile terpenes in animals and humans. Planta Med 2000; 66: 495-505
• 173 Faehnrich B, Lukas B, Humer E, Zebeli Q. Phytogenic pigments in animal nutrition: Potentials and risks. J Sci Food Agric 2016; 96: 1420-1430
• 174 Fernandez ME, Palacio MA, Labaque MC. Thymol detection and quantitation by solid-phase microextraction in faeces and egg yolk of Japanese quail. J Chromatogr B Anal Technol Biomed Life Sci 2017; 1044 – 1045: 39-46
• 175 Fernandez ME, Kembro JM, Ballesteros ML, Caliva JM, Marin RH, Labaque MC. Dynamics of thymol dietary supplementation in quail (Coturnix japonica): Linking bioavailability, effects on egg yolk total fatty acids and performance traits. PLoS One 2019; 14: e0216623
• 176 Haselmeyer A, Zentek J, Chizzola R. Effects of thyme as a feed additive in broiler chickens on thymol in gut contents, blood plasma, liver and muscle. J Sci Food Agric 2015; 95: 504-508
• 177 Oceľová V, Chizzola R, Pisarčíková J, Novak J, Ivanišinoviá O, Faix Š. Effect of thyme essential oil supplementation on thymol content in blood plasma, liver, kidney and muscle in broiler chickens. Nat Prod Commun 2016; 11: 1545-1550
• 178 Yu DX, He Z, Pouton C, Hoerr FJ, Xiao ZC. Target animal safety and residual study for berberine and other phytogenic compounds in broiler chickens. Arch Clin Microbiol 2017; 8: 1-8
• 179 Stefanello C, Rosa DP, Dalmoro YK, Segatto AL, Vieira MS, Moraes ML, Santin E. Protected blend of organic acids and essential oils improves growth performance, nutrient digestibility, and intestinal health of broiler chickens undergoing an intestinal challenge. Front Vet Sci 2020; 6: 1-10
• 180 Ząbek K, Szkopek D, Michalczuk M, Konieczka P. Dietary phytogenic combination with hops and a mixture of a free butyrate acidifier and gluconic acid maintaining the health status of the gut and performance in chickens. Animals (Basel) 2020; 10: 1-12
• 181 Galli GM, Petrolli TG, Aniecevski E, Santo AD, Leite F, Griss LG, Dazuk V, Boiago MM, Dos Santos HV, Simões CADP, Wagner R, Bissacotti BF, Schentiger MR, Da Silva AS. Phytogenic blend protective effects against microbes but affects health and production in broilers. Microb Pathog 2021; 152: 104590
• 182 Heydarian M, Ebrahimnezhad Y, Meimandipour A, Hosseini SA, Banabazi MH. Effects of dietary inclusion of the encapsulated thyme and oregano essential oils mixture and probiotic on growth performance, immune response and intestinal morphology of broiler chickens. Poult Sci J 2020; 8: 17-25
• 183 Paraskeuas V, Mountzouris KC. Broiler gut microbiota and expressions of gut barrier genes affected by cereal type and phytogenic inclusion. Anim Nutr 2019; 5: 22-31
• 184 Chang KW, Kuo CY. 6-Gingerol modulates proinflammatory responses in dextran sodium sulfate (DSS)-treated Caco-2 cells and experimental colitis in mice through adenosine monophosphate-activated protein kinase (AMPK) activation. Food Funct 2015; 6: 3334-3341
• 185 Valenzano MC, DiGuilio K, Mercado J, Teter M, To J, Ferraro B, Mixson B, Manley I, Baker V, Moore BA, Wertheimer J, Mullin JM. Remodeling of tight junctions and enhancement of barrier integrity of the CACO-2 intestinal epithelial cell layer by micronutrients. PLoS One 2015; 10: e0133926
• 186 Sun K, Lei Y, Wang R, Wu Z, Wu G. Cinnamicaldehyde regulates the expression of tight junction proteins and amino acid transporters in intestinal porcine epithelial cells. J Anim Sci Biotechnol 2017; 8: 1-8
• 187 Carrasco-Pozo C, Morales P, Gotteland M. Polyphenols protect the epithelial barrier function of Caco-2 cells exposed to indomethacin through the modulation of occludin and zonula occludens-1 expression. J Agric Food Chem 2013; 61: 5291-5297
• 188 Kim HJ, Lee EK, Park MH, Ha YM, Jung KJ, Kim MS, Kim MK, Yu BP, Chung HY. Ferulate protects the epithelial barrier by maintaining tight junction protein expression and preventing apoptosis in tert-butyl hydroperoxide-induced Caco-2 cells. Phyther Res 2013; 27: 362-367
• 189 Bergmann H, Rogoll D, Scheppach W, Melcher R, Richling E. The Ussing type chamber model to study the intestinal transport and modulation of specific tight-junction genes using a colonic cell line. Mol Nutr Food Res 2009; 53: 1211-1225
• 190 Suzuki T, Tanabe S, Hara H. Kaempferol enhances intestinal barrier function through the cytoskeletal association and expression of tight junction proteins in Caco-2 cells. J Nutr 2011; 141: 87-94
• 191 Suzuki T, Hara H. Quercetin enhances intestinal barrier function through the assembly of zonnula occludens-2, occludin, and claudin-1 and the expression of claudin-4 in caco-2 cells. J Nutr 2009; 139: 965-974
• 192 Noda S, Tanabe S, Suzuki T. Naringenin enhances intestinal barrier function through the expression and cytoskeletal association of tight junction proteins in Caco-2 cells. Mol Nutr Food Res 2013; 57: 2019-2028
• 193 Amasheh M, Schlichter S, Amasheh S, Mankertz J, Zeitz M, Fromm M, Schulzke JD. Quercetin enhances epithelial barrier function and increases claudin-4 expression in Caco-2 cells. J Nutr 2008; 138: 1067-1073
• 194 Park HY, Kunitake Y, Hirasaki N, Tanaka M, Matsui T. Theaflavins enhance intestinal barrier of Caco-2 Cell monolayers through the expression of AMP-activated protein kinase-mediated Occludin, Claudin-1, and ZO-1. Biosci Biotechnol Biochem 2015; 79: 130-137

Publication History

Received: 17 February 2021

Accepted after revision: 04 June 2021

Article published online:
30 July 2021