Keywords HIF-1α - VEGF - hypoxia - radicular cyst - periapical granuloma
Introduction
Among the most common oral pathological lesions in humans are radicular cysts and
periapical granulomas. These lesions result in the loss of alveolar bone and the development
of granulation tissue in the area surrounding the root's apex.[1 ] When a root canal infection is persistent, pathogenic bacteria and bioproducts are
released into the periradicular tissues. Consequently, periapical granulomas and radicular
cysts were developed. Infected root canals, primarily caused by dental caries, lead
to continuous antigenic stimulation, which initiates cytokine release and triggers
inflammation. Periapical lesions are characterized by inflammation and the infiltration
of lymphocytes, macrophages, and plasma cells, representing the body's defense response
against microbial invasion.[2 ] Periapical granulomas are granulation tissue that is sometimes epithelized and infiltrated
by lymphocytes, plasma cells, and macrophages.[1 ] In radicular cysts, however, odontogenic epithelial remnants proliferate forming
the epithelial lining.[3 ] A key predictor of the presence of a periapical cyst, as identified on a dental
radiograph, was the involvement of multiple teeth in the periapical lesion.[4 ]
In recent years, scientists have been increasingly interested in understanding the
biology and prognosis of periapical lesions. Under a biological scope, cytokines have
been associated with characteristics of odontogenic lesions.
As a heterodimer, hypoxia-inducible factor (HIF-1) consists of α and β subunits. HIF-1β
is found in the nucleus and is constitutively expressed.[5 ] On the other hand, HIF-1α is found in the cytoplasm and is a transcription factor
that regulates the cellular response to hypoxia. In normal oxygen conditions, it is
posttranslationally hydroxylated by enzymes containing the prolyl hydroxylase domain,
and then degraded by proteasomes. However, hypoxia interferes with this enzymatic
degradation of HIF-1α, causing it to stabilize, translocate to the nucleus, and heterodimerize
with HIF-1β. Once the heterodimer binds to specific DNA sequences, the HIF-1 pathway
is activated.[6 ]
[7 ] Thus, cellular adaptation and resistance to hypoxia are increased by upregulating
multiple target genes. It has been found that HIF-1α plays a key role in the regulation
of more than 40 genes in response to hypoxia. Several previous studies have investigated
the expression of HIF-1α in radicular cysts and periapical granulomas,[2 ]
[8 ]
[9 ] and demonstrate their hypoxic nature.[2 ]
[9 ]
One of the major well-studied targets of HIF-1 is the vascular endothelial growth
factor (VEGF) pathway. VEGF is involved in a variety of processes, including angiogenic,
mitogenic, and permeability-modulating properties. Both endothelial and nonendothelial
cells possess VEGF receptors, which act via autocrine pathways to regulate cell survival
and function.[10 ] In addition, VEGF plays an important role in osteoblast differentiation as well
as osteoclast function, thereby maintaining bone homeostasis.[11 ] Furthermore, VEGF induces an increase in microvascular permeability, which is accompanied
by plasma protein extravasation and predictable changes in the stroma that promote
angiogenesis.[12 ] There is evidence that VEGF levels are higher in radicular cysts and granulomas
than in healthy tissues.[13 ]
[14 ]
A clear correlation exists between HIF-1α and VEGF in several physiological[15 ] and pathological conditions.[16 ]
[17 ] However, periapical lesions did not devote much attention to the significance of
this correlation. This study aimed to evaluate the expression levels of HIF-1α and
VEGF in radicular cysts and periapical granulomas, thereby contributing to the understanding
of their potential significance in the differential diagnosis and treatment of these
lesions.
Materials and Methods
Study Design, Sample Size, Tissue Samples, and Ethical Approval
The present cross-sectional study included 51 prediagnosed periapical lesion samples,
of which 24 were radicular cysts and 27 were periapical granulomas. Samples were collected
from the Oral Surgery Clinic at the University of Science and Technology of Fujairah.
Baseline data were collected from patients' medical records, including age, gender,
lesion location, and the affected tooth or teeth. Lesion size was determined by measuring
the maximum craniocaudal and mesiodistal diameters on standard panoramic images, and
the arithmetic mean of these measurements was calculated to determine the final cyst
size. Diagnoses of inflamed periapical lesions followed the World Health Organization's
criteria, incorporating histopathology, clinical history, and radiographic features.
Radicular cysts were identified by their location in the periapical area of a tooth
with necrotic pulp, without periodontal communication, and a cystic cavity surrounded
by nonkeratinizing epithelium with inflammatory cells in the connective tissue. Periapical
granulomas were similarly located in the periapical region of a tooth with necrotic
pulp, but lacked epithelial lining, instead showing an infiltration of inflammatory
cells such as macrophages, lymphocytes, and plasma cells.
In accordance with the Declaration of Helsinki, this study was approved by the ethical
approval committee of Ajman University (reference number: H-17-05-08). Consent was
obtained from all subjects, with parental consent provided for the 15-year-old patient.
This sample size was calculated through the use of the statistical software G*Power
(version 3.1.9.7 software; University of Düsseldorf, Germany). Based on the information
provided by da Costa et al,[8 ] which determined that 15 patients were needed for each group, we opted for a more
convenient approach by using an effect size of 0.4, with 80% power and a 5% error
rate. Consequently, a total of 51 patients were selected as a convenience sample for
this study, with 24 samples from radicular cysts and 27 from periapical granulomas.
Inclusion and Exclusion Criteria
Patients over the age of 15 years with necrotic pulp and periapical radiolucency of
at least 2 mm in either jaw, as well as histopathological confirmation of radicular
cysts and periapical granulomas, were included in this study. Pregnant or lactating
women, individuals with systemic medical conditions, and those taking medications
were excluded from the study. Furthermore, samples were not included if there was
a history of acute local infection or if the diagnosis was not confirmed by histopathological
analysis.
Sampling Procedure
All patients were informed of the procedures to be performed prior to the operation
and signed informed consent forms. Samples were obtained either through surgical enucleation
or following nonrestorable tooth extraction, depending on the clinical circumstances.
Smaller, early-stage lesions were typically collected during tooth extraction. Lesions
harvested from extracted teeth were carefully isolated using a sterile no. 15 surgical
scalpel blade and rinsed in sterile normal saline. In cases where samples were collected
via enucleation, the wound site was sutured after bleeding was controlled.
Immunohistochemistry: Anti-HIF-1α and Anti-VEGFA Antibody Staining
Tissues were fixed in 10% neutral buffered formalin for 8 hours at room temperature
and embedded in paraffin. Formalin-fixed paraffin-embedded sections were cut into
4-µm sections and were adhered to positively charged slides (MIC3040, Thermo-Fisher
Scientific) by incubation at 37°C overnight. Following deparaffinization, the sections
were stained immunohistochemically for HIF-1α and anti-VEGFA antibody expression.
The immunohistochemical (IHC) detection of the protein targets was performed using
primary antibodies: anti-VEGFA antibody (Abcam cat#AB185238, rabbit monoclonal, clone
EP1176Y, 1:200) and anti-HIF-1α antibody (Abcam AB51608, rabbit monoclonal, clone
EP1215Y, 1:100). Antigen retrieval was done in pH 9.0 Tris-EDTA solution in a microwave
oven at 95°C for 30 minutes. The primed proteins were chromogenically detected with
AB64264, Abcam's HRP/DAB (ABC) IHC detection kit. Specimens with known positive antigenicity
were used as positive control specimens. For the negative controls, sections of periapical
lesions were incubated in normal rabbit serum without the addition of the primary
antibody.
Images of the stained sections were acquired with Olympus BX63 microscope equipped
with Olympus DP75 camera (resolution of 5,760 × 3,600 pixels and pixel size of 5.86 × 5.86 µm)
with Cell Sens Entry software (version 1.17). Images were acquired with ×20 (numerical
aperture 0.45; 1,920 × 1,200 pixels; 465.079 nm/pixel resolution in both x - and y -axes) and ×40 (numerical aperture 0.6; 1,920 × 1,200 pixels; 232.54 nm/pixel resolution
in both x - and y -axes) objective lenses. The IHC staining of HIF-1α and VEGF was yellowish to brown.
The IHC presence of HIF-1α and VEGF was assessed within the connective tissue of radicular
cysts and periapical granulomas, as well as in the epithelial lining of radicular
cysts and, where applicable, in the epithelium of periapical granulomas. Under a light
microscope, semiquantitative scoring was conducted. HIF-1α and VEGF immunostaining
was assessed by calculating the percentage of positive cells out of the total cells
in 10 representative high-power fields. There were four criteria for use: 0 when there
was no staining or if it was questionable; weak for results with a positivity of ≥25%,
mild for results with a positivity of 26 to 50%, and strong for results with a positivity
of more than 50%.
Statistical Analysis
The Statistical Package for the Social Sciences (SPSS) 28.0 software (IBM SPSS, Armonk,
New York, United States) was used to analyze the data. The chi-square test was used
to determine whether significant differences existed. The correlation of expressed
markers was further analyzed through Spearman's rank correlation coefficient. Results
were considered significant if the p -value was less than 0.05.
Results
A total of 51 samples were included in the study. There were 24 samples of radicular
cysts and 27 samples of periapical granulomas. Thirty-seven (72.5%) of these samples
were found in males and 14 (27.5%) in females. There were 28 cases located in the
maxilla (54.9%), while 23 cases (45.1%) were in the mandible. The mean age was 33.67
years ([Table 1 ]).
Table 1
Clinical features of the studied cases
Variables
Total
Periapical granulomas
Radicular cysts
Patients (
n
)
51
27 (52.9%)
24 (47.1%)
Age (y)
Mean = 33.67 ± 9.873
Range = 15–60
Mean = 33.26 ± 10.044
Range = 15–60
Mean = 34.13 ± 9.870
Range = 20–58
Gender,
n
(%)
Male
37 (72.5%)
17 (63.0%)
20 (83.3%)
Female
14 (27.5%)
10 (37.0%)
4 (16.7%)
Location,
n
(%)
Maxilla
28 (54.9%)
19 (70.4%)
9 (37.5%)
Mandible
23 (45.1%)
8 (29.6%)
15 (62.5%)
The most offending tooth
14 = 3 (11.1%)
15 = 2 (7.4%)
16 = 6 (22.2%)
17 = 2 (7.4%)
18 = 2 (7.4%)
22 = 1 (3.7%)
25 = 1 (3.7%)
26 = 1 (3.7%)
27 = 1 (3.7%)
36 = 3 (11.1%)
37 = 1 (3.7%)
44 = 1 (3.7%)
46 = 1 (3.7%)
47 = 2 (7.4%)
11 = 1 (4.2%)
12 = 1 (4.2%)
15 = 1 (4.2%)
17 = 1 (4.2%)
26 = 1 (4.2%)
2 = 2 (8.4%)
28 = 2 (8.4%)
31 = 1 (4.2%)
34 = 1 (4.2%)
35 = 3 (12.5%)
36 = 1 (4.2%)
37 = 1 (4.2%)
44 = 1 (4.2%)
45 = 1 (4.2%)
46 = 6 (25%)
Presence of pain
No = 9 (33.3%)
No = 11 (45.8%)
Yes = 18 (66.7%)
Yes = 13 (54.2%)
Size
Mean = 4.26 mm ± 1.457
Range = 2–7 mm
Mean = 8.83 mm ± 6.638
Range = 2–23 mm
In the studied radicular cyst samples, fibrous connective tissue walls were lined
with stratified squamous epithelium or with epithelial hyperplasia. A common finding
in the studied radicular cyst samples was the presence of inflammatory cells such
as neutrophils, plasma cells, and lymphocytes. In several samples of the periapical
granulomas, epithelial strands could be seen throughout sections. All periapical granulomas
showed significant infiltration of inflammatory cells.
In radicular cysts, HIF-1α was present both in the cytoplasm and nucleus, with greater
positivity noted in the nucleus than in the cytoplasm ([Fig. 1 ]). Nevertheless, VEGF was found primarily in the cytoplasm ([Fig. 2 ]). Expression of both HIF-1α and VEGF was observed in both cystic epithelium and
cystic stroma including inflammatory cells. Many of the periapical granulomas examined
were positively immunolabeled for HIF-1α both in the cytoplasm and nucleus of the
cells, with a higher level of positivity noted in the cytoplasm than in the nucleus
([Fig. 1 ]). Meanwhile, VEGF immunopositivity was cytoplasmic in periapical granulomas. Fibroblasts,
epithelial, endothelial, and inflammatory cells showed reaction products, although
the intensity of immunostaining by the anti-VEGF antibody varied ([Fig. 2 ]). The periapical granulomas, however, displayed the highest number of VEGF-positive
inflammatory cells compared with the radicular cysts.
Fig. 1 Immunohistochemical staining of HIF-1α in radicular cysts and periapical granulomas
(magnification ×400). (A ) Intense HIF-1α nuclear and cytoplasmic staining throughout the whole layers of the
odontogenic epithelium of radicular cysts, (B ) less intense HIF-1α cytoplasmic and nuclear staining of epithelium with several
immunostained inflammatory infiltrates in the radicular cysts, (C ) intense nuclear and cytoplasmic HIF-1α staining of the positive cells throughout
the periapical granulomas, and (D ) less intense HIF-1α staining of the positive cells throughout the periapical granulomas.
HIF-1α, hypoxia-inducible factor 1-α.
Fig. 2 Immunohistochemical staining of VEGF in radicular cysts and periapical granulomas
(magnification ×400). (A ) Intense cytoplasmic VEGF staining throughout the layers of the odontogenic epithelium
of radicular cysts with few positive inflammatory infiltrates in the connective tissue,
(B ) less intense VEGF staining throughout the layers of the odontogenic epithelium of
radicular cysts with few positive inflammatory infiltrates in the connective tissue,
(C ) intense VEGF staining of the positive cells throughout the periapical granulomas,
and (D ) less intense VEGF staining of the positive cells throughout the periapical granulomas.
VEGF, vascular endothelial growth factor.
In radicular cysts, HIF-1α expression was absent in 1 (4.2%), weak in 5 (20.8%), mild
in 7 (29.2%), and strong in 11 (45.8%) cases ([Table 2 ]). VEGF expression was absent in 1 (4.2%), weak in 6 (25.0%), mild in 9 (37.5%),
and strong in 8 (33.3%) cases ([Table 2 ]); nevertheless, in periapical granulomas, HIF-1α expression was absent in 8 (29.6%),
weak in 6 (22.2%), mild in 9 (33.3%), and strong in 4 (14.8%) of the cases ([Table 2 ]). The expression of VEGF was absent in 4 (14.8%), weak in 16 (59.3%), mild in 4
(14.8%), and strong in 3 (11.1%) cases ([Table 2 ]).
Table 2
Expression of HIF-1α and VEGF in radicular cysts and periapical granulomas
Radicular cysts
(n = 24)
Periapical granulomas
(n = 27)
Absent
Weak
Mild
Strong
Absent
Weak
Mild
Strong
HIF-1α
1 (4.2%)
5 (20.8%)
7 (29.2%)
11 (45.8%)
8 (29.6%)
6 (22.2%)
9 (33.3%)
4 (14.8%)
VEGF
1 (4.2%)
6 (25.0%)
9 (37.5%)
8 (33.3%)
4 (14.8%)
16 (59.3%)
4 (14.8%)
3 (11.1%)
Abbreviations: HIF-1α, hypoxia-inducible factor 1-α; VEGF, vascular endothelial growth
factor.
The chi-square test revealed a highly significant difference in the expression of
HIF-1α and VEGF between radicular cysts and periapical granulomas (chi-square test = 8.906,
p = 0.031; chi-square test = 10.401, p = 0.015, respectively). Spearman's correlation test showed a significant correlation
between HIF-1α and VEGF in total samples of radicular cysts and periapical granulomas
(rho = 0.385, p = 0.005).
Discussion
Proliferation and cellular aggregates in periapical lesion may limit oxygen diffusion
to the center of the island, resulting in hypoxia. This hypoxia affects many cellular
processes, including proliferation, angiogenesis, apoptosis, necrosis, and cell survival.[9 ] VEGF has been identified as a key downstream target of HIF-1α.[7 ] A complex interaction between cells, cytokines, and other inflammatory factors may
contribute to the development of radicular cysts and periapical granulomas.
We observed a high expression of HIF-1α protein in both radicular cysts and periapical
granulomas, with significantly greater expression in radicular cysts compared with
periapical granulomas. Conversely, a previous study reported comparable expressions
of HIF-1α in radicular cysts and periapical granulomas.[2 ] Meanwhile, previous research has shown that HIF-1α is overexpressed in radicular
cysts compared with dental follicles,[8 ] healthy dental pulp,[2 ] and healthy gingival tissue.[9 ] Interestingly, ameloblastomas and odontogenic keratocysts also exhibit higher levels
of HIF-1α than dental follicles and gingival tissues.[8 ]
[9 ]
[18 ] Moreover, the highest level of expression of HIF-1α was found in radicular cysts
compared with ameloblastomas and odontogenic keratocysts.[8 ] This variation in findings from previous studies suggests inconsistency in HIF-1α
expression across different research and highlights the need for further investigation.
It also supports the involvement of hypoxia in the pathogenesis of various odontogenic
lesions and implies that radicular cysts may experience a more pronounced hypoxic
environment, potentially playing a key role in their development and persistence.
According to previous studies, the expression of HIF-1α in odontogenic cysts and periapical
granulomas could be viewed as a cause of the pathology or a response to it. In fact,
increased hypoxia occurring in odontogenic lesions was attributed to ischemia during
the development of radicular cysts and periapical granulomas.[2 ]
[9 ] Interestingly, HIF-1α and caspase-3 immunoexpression and immunolocalization patterns
suggest a strong association between hypoxia, apoptosis, and cyst formation.[8 ] Additionally, phosphatidylinositol 3-kinase/protein kinase B signaling may be stimulated
by increased phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit α and
decreased phosphatase and tensin homolog expression, which promote cell survival and
support the mechanism of cyst formation under hypoxia conditions.[9 ] On the other hand, apoptosis is an adaptive cellular response to cellular stress,
such as hypoxia, that permits organisms to eliminate unwanted or dysfunctional cells.[19 ] Similarly, hypoxia-related proteins may induce autophagy in periapical lesions,
which may have a direct role in the development and maintenance of periapical lesions.[2 ] It is noteworthy that Szaraz et al proposed that odontogenic cysts may be influenced
by molecular mechanisms associated with primary cilia and hypoxia in similar ways
to autosomal dominant polycystic kidney disease.[20 ]
HIF-1α activation is thought to contribute to host defense against periapical lesions
by downregulating bone resorption cytokines, M1 macrophages, and nuclear factor-κB,
which is associated with osteoclastogenesis.[1 ] Furthermore, the HIF-1 pathway plays an essential role in neoangiogenesis and bone
healing.[21 ] Meanwhile, it has been proposed that hypoxia does not initiate cellular proliferation,
but rather involves an adaptive pathway, which is necessary for future proliferation.[19 ]
The present study found that HIF-1α is expressed in both the cytoplasm and nucleus
of immunopositive radicular cyst cells, with the nucleus being the most abundant.
In contrast, periapical granulomas also express HIF-1α in the cytoplasm and nucleus,
although its expression is more pronounced in the cytoplasm. Consistent with our results,
a prior investigation revealed the presence of HIF-1α in both the cell nucleus and
cytoplasm of immunopositive cells within radicular cysts.[8 ] Indeed, under normoxic conditions, HIF-1α is primarily expressed within the cytoplasm
and undergoes rapid degradation. However, when hypoxia occurs, it is translocated
to the nucleus where it is activated. Hence, HIF-1α is theoretically inactive in the
cytoplasm.[19 ] Remarkably, research has revealed the presence of HIF-1α in the cystic regions of
ameloblastomas, located in both the nuclei and cytoplasm. Conversely, within solid
regions of ameloblastomas, HIF-1α expression was solely localized to the nuclei. This
observation indicates that the retention of HIF-1α in the cytoplasm may impede adaptation
to hypoxic conditions, potentially triggering apoptosis and the subsequent formation
of cystic cavities.[18 ]
The present study findings showed expression of HIF-1α protein in the epithelial cells,
inflammatory cells, and fibroblasts of the periapical lesions. Similar findings have
been reported in previous studies.[2 ]
[8 ] The increased nuclear localization of HIF-1α expression in radicular cysts may suggest
increased HIF-1α activity within these cysts. This potential activity could be reflected
in the present study by the elevated expression of VEGF in radicular cysts compared
with periapical granulomas.
Previous studies found that the expression of VEGF and its implication in odontogenic
cysts was controversial. The expression of VEGF in radicular cysts and dentigerous
cysts was comparable.[12 ] A previous study, however, found that VEGF expression was higher in radicular cysts
than dentigerous cysts, possibly because of the inflammatory process involved in radicular
cysts.[22 ] On the other hand, odontogenic keratocysts expressed more VEGF than radicular cysts[12 ] and dentigerous cysts,[12 ]
[23 ] indicating that angiogenesis may have a significant effect on clinical outcomes
of odontogenic keratocysts.[23 ] Again, contrary results were found in another report that showed greater expression
of VEGF in radicular cysts than in odontogenic keratocysts.[24 ] According to a previous study, radicular cysts and periapical granulomas expressed
comparable levels of VEGF.[14 ] In addition, radicular cysts contained higher levels of VEGF than periapical granulomas,
despite the lack of statistical significance.[25 ]
The contradictory findings of VEGF expression in odontogenic cysts and periapical
granulomas could be attributed to differences in the study design and methodology
used in previous studies, while the testing methodology has been temporarily improved
in terms of sensitivity. Additionally, heterogeneity of lesions depending on the type
and stage of the lesion, as well as patient characteristics and interpretation biases
are also nonneglectable factors. A rigorous research design, standardization of methodology,
larger sample sizes, and a comprehensive analysis of patient and lesion characteristics
will be necessary to resolve these discrepancies and improve understanding of VEGF
expression in odontogenic lesions. Furthermore, meta-analyses and systematic reviews
can be used to synthesize existing research and identify potential sources of variation
between studies.
The present results indicating a significant correlation between HIF-1α and VEGF in
the radicular cysts and periapical granulomas provide novel insights into the pathogenesis
of these odontogenic lesions and support the hypothesis that HIF-1α, a marker of hypoxia,
may trigger or enhance the production of VEGF.[10 ] The findings suggest that these lesions may expand and persist under hypoxic conditions,
where the activation of HIF-1α leads to the upregulation of VEGF, causing new blood
vessels to form to meet the metabolic demands of cystic or granulomatous tissue. The
angiogenic response may contribute to the maintenance of the lesion's structure and
survival.
The pathogenesis and enlargement of periapical granulomas and radicular cysts are
significantly affected by VEGF through several mechanisms. This role of VEGF has been
emphasized in several previous studies, including those regarding radicular cysts[14 ]
[25 ]
[26 ]
[27 ]
[28 ] and periapical granulomas.[14 ]
[25 ]
[29 ] VEGF in cystic lesions may increase angiogenesis and vascular hyperpermeability,
resulting in the accumulation of inflammatory cells and cystic fluid.[24 ]
[25 ]
[26 ]
[30 ] Eventually, this will lead to increased cystic pressure and the expansion of the
cyst.[12 ] In addition, upregulation of VEGF receptors in endothelial cells occurred during
the expanding phase of experimentally induced periapical lesions, suggesting that
VEGF is one of the modulators of angiogenesis that plays a role in the development
of periapical lesions.[13 ] It has been little studied how angiogenesis interacts with the skeletal system in
cysts.[25 ] It is possible that the variation in VEGF observed in the fibrous capsules of radicular
cysts and dentigerous cysts is a result of different osteolytic activities in these
lesions.[22 ]
A majority of the studied radicular cysts and periapical granulomas displayed immunopositive
cytoplasmic reactions to VEGF in the present study. Additionally, we found expression
of VEGF in both epithelium and connective tissue capsules of radicular cysts and periapical
granulomas. Similarly, previous studies have found expression of VEGF in both epithelium
and connective tissue of periapical granulomas[14 ]
[26 ] and radicular cysts.[14 ]
[25 ]
[26 ]
[27 ]
[28 ]
[31 ] Moreover, stromal cells expressed higher levels of VEGF than epithelial cells.[27 ]
In the present study, there was significant variation in the intensity of immunostaining
for VEGF in fibroblasts, epithelial cells, endothelial cells, and inflammatory cells.
More inflammatory cells were immunopositive for VEGF in periapical granulomas than
in radicular cysts. A previous study found that almost no inflammatory cells were
immunolabeled for VEGF in radicular cysts. Additionally, VEGF-positive inflammatory
cells were observed in periapical granulomas, but their number decreased with the
increase in epithelial components of the lesions.[26 ] Moreover, the lowest level of VEGF immunoexpression was observed in lesions with
few inflammatory infiltrates.[25 ] In contrast to these findings, a previous study found that inflammation and VEGF
expression are negatively correlated in periapical granulomas.[29 ] In addition, radicular cysts and residual cysts showed strong epithelial expression
of VEGF, regardless of the level of inflammatory infiltrate.[28 ]
A limitation of the present study is that it is a cross-sectional observational study.
A cause-and-effect model would be more predictably useful in investigating the pathways
of HIF-1α in periapical lesions. It would be beneficial to explore additional pathways
of hypoxia and HIF-1α in periapical lesions in future studies. The present study focuses
exclusively on the histopathological and immunobiological characteristics of the samples.
However, it would be ideal if clinical findings and follow-up results were included
in the report. Finally, periapical lesions include reactive tissues and inflammatory
cysts that replace healthy bone, so there is no true tissue equivalent to serve as
a control.[32 ]
In the light of high expression of HIF-1α and VEGF in radicular cysts and periapical
granulomas, one could suggest evaluating the nonsurgical treatment of these lesions
using anti-HIF-1α and anti-VEGF therapy. Further, intralesional injection of these
medications into radicular cysts and periapical granulomas may reduce bone resorption
and enhance bone formation in periapical lesions. Edaravone has previously been reported
to reduce bone resorption along with decreasing angiogenesis in arthritis. This is
believed to be related to the HIF-1α–VEGF–ANG-1 axis.[33 ] There is also evidence that VEGF might be regarded as a therapeutic target candidate
to inhibit bone resorption, angiogenesis, as well as immune responses in periodontitis,
periimplantitis, and apical periodontitis.[10 ] Intriguingly, a previous study found that combining anti-VEGF bevacizumab with moxifloxacin
on weekly basis along with standard care resulted in rapid regression of highly expressed
VEGF-tubercular granulomas.[34 ]
Conclusion
There is high expression of both HIF-1α and VEGF throughout the odontogenic epithelium
and connective tissue of the radicular cyst and periapical granuloma. Both HIF-1α
and VEGF are more highly expressed in radicular cysts than in periapical granulomas.
These findings may aid in the diagnosis and management of suspected periapical lesions,
suggesting that radicular cysts exhibit more advanced hypoxic conditions and associated
pathways compared with periapical granulomas.
