Keywords interleukin-1
β
- interleukin-6 - periodontitis - coronary heart disease
Introduction
Coronary artery disease arises as an outcome of hardening and lumen reduction of the
arteries that supply the heart due to atherosclerotic plaque buildup.[1 ] It is characterized by local and systemic host responses, in which cells such as
B and T lymphocytes and macrophages have an important role in the pathogenesis of
this disease by releasing of cytokines and other inflammatory mediators.[2 ] For many years, the coronary heart disease (CHD) is recognized as one of the most
common causes of mortality and morbidity.[3 ]
Chronic periodontitis (CP) is a destructive inflammatory disease affecting the supporting
tissues of the tooth including the periodontal ligament and alveolar bone.[4 ] A large body of work has been focused to the relationship between CHD and CP. These
diseases not only share several common risk factors such as smoking, but also share
potential mechanistic links through the presence of chronic inflammation.[5 ]
A large number of studies have indicated the presence of a positive correlation of
clinical signs and inflammatory changes in CP with atherosclerosis and CHD. CP may
amplify systemic inflammatory mediator levels as a consequence of persistent infection
which may affect other organs and systems, including the vascular endothelium, thus
potentially contributing to inflammation-associated atherosclerotic disease.[6 ] In serologic studies, high titers of antibodies to periodontal bacteria are found
in patients with atherosclerosis and CHD disease, and some viable bacteria can be
isolated from atherosclerotic plaques.[7 ]
Through their effects on inflammation and the immune system, interleukin-1β (IL-1β)
and interleukin-6 (IL-6) are considered important mediators of inflammation in both
periodontitis and atherosclerosis.[8 ] In periodontal tissues, IL-1β can stimulate bone resorption,[9 ] neutrophil and monocyte migration from the vasculature into the periodontal tissue,[10 ] and expression of proatherogenic members of the tumor necrosis factor super family.[11 ] IL-6 may also contribute to the relationship between CP and CHD through stimulation
of monocyte differentiation into osteoclasts resulting in bone destruction[12 ] and exacerbation atherosclerotic plaque development and destabilization through
a variety of mechanisms such as the release of other proinflammatory cytokines, activation
of metalloproteinases (MMPs), and increased acute phase protein secretion.[13 ]
The aim of this study was to investigate the relationship between serum levels of
IL-1β and IL-6 with periodontitis and CHD. We have shown that clinical disease parameters
are further raised in periodontitis patients with CHD and that serum IL-1β and IL-6
levels represent potential markers of this process. The presence of these interrelated
diseases must be taken into consideration as guidelines suggest patients with moderate
to severe periodontitis are notified of the increased risk of cardiovascular disease,
which may necessitate further evaluation.[14 ]
Materials and Methods
Eighty male subjects aged between 40 and 60 years were recruited to this study from
the Cardiology Clinic of the Baghdad Teaching Hospital and Periodontics Department
of the College of Dentistry, University of Baghdad, Baghdad, Iraq. This study was
conducted after the approval was granted by the relevant scientific committee (Ref.
122 at 08/11/2015). All the individuals were informed about the purpose of this study
and consented to participate in this study. The subjects were divided into study and
control groups. Thirty patients were examined and shown to possess CP and CHD (CP
+ CHD) diagnosed using the catheterization technique and were receiving clopidogrel
medication (Plavix/75 mg). A further 30 patients were examined and shown to have CP
as they had equal or less than 30% sites with pocket depths ≥ 4 mm with clinical attachment
loss of 1 to 2 mm or greater in accordance to the worldwide classification system
for periodontal disease (PD).[15 ]
The control group consisted of 20 patients with no CHD and clinically healthy periodontium
with gingival index (GI) scores < 0.5, no pockets, or clinical attachment loss. However,
certain exclusion criteria were applied including the presence of any chronic systemic
diseases such as diabetes mellitus, smoking, those using medication such as antimicrobial
and anti-inflammatory drugs, or having any periodontal treatment within the last 3
months.
Clinical periodontal examination was performed using a Michigan O periodontal probe
on four surfaces (mesial, buccal/labial, distal, and lingual/palatal) of all teeth
except third molars. All subjects had at least 20 teeth. The collected clinical data
consisted of plaque index (PLI) system,[16 ] GI system,[17 ] bleeding on probing (BOP),[18 ] probing pocket depth (PPD), and clinical attachment level (CAL).[19 ]
Following examination of the clinical periodontal parameters, 5 mL venous blood was
collected from study and control groups. After centrifugation, serum samples were
kept frozen at –40°C and analyzed for IL-1β and IL-6 using enzyme-linked immunosorbent
assay (Bioassay Technology Laboratory, Shanghai Korain Biotech Co.).
Data were processed and analyzed for both descriptive and inferential analyses using
SPSS (version 23, IBM, United States) and Microsoft Excel (version 2010, Microsoft
Corporation, United States). The statistical analysis for the determination of serum
IL-1β and IL-6 was assessed using t -test, analysis of variance test followed by Tukey’s post hoc test, and Pearson’s
coefficient of correlation.
Results
The results revealed that mean values of PLI, GI, PPD, and CAL were significantly
higher in the CP + CHD group compared with the CP and control groups. The percentage
of score 1 BOP sites was significantly higher in the CP + CHD group than the CP group.
The statistical analyses of clinical periodontal parameters for all groups are summarized
in [Figs. 1 ] and [2 ] and [Table 1 ].
Table 1
Mean plaque (PLI) and gingival index (GI) scores are significantly higher in association
with chronic periodontitis (CP) and coronary heart disease patients affected by periodontitis
(CP-CHD) when compared with the control group (Con)
Indices
Groups
Mean ± SD
Comparisons
p -Value*
Abbreviation: CP, chronic periodontitis; CHD, coronary heart disease; PLI, plaque
index; GI, Gingival index; SD, standard deviation.
*ANOVA test and post hoc.
PLI
Control
0.50 ± 0.112
Con vs. CP
< 0.001
CP
1.69 ± 0.125
Con vs. CHD
< 0.001
CP + CHD
1.78 ± 0.136
CP vs. CP + CHD
< 0.05
GI
Control
0.57 ± 0.119
Con vs. CP
< 0.001
CP
1.74 ± 0.121
Con vs. CP + CHD
< 0.001
CP + CHD
1.83 ± 0.131
CP vs. CP + CHD
< 0.05
Fig. 1 Percentage of bleeding on probing (BOP) in patients with chronic periodontitis (CP)
and coronary heart disease patients affected by periodontitis (CP-CHD).
Fig. 2 Mean probing pocket depth (PPD) and clinical attachment level (CAL) in patients with
chronic periodontitis (CP) and coronary heart disease patients affected by periodontitis
(CP-CHD). ***Indicates statistically significant differences at p ≤ 0.001.
The mean serum levels of IL-1β and IL-6 were significantly higher in the CP + CHD
group followed by the CP group then the control group (p < 0.001) ([Fig. 3A ] and [B ] ). The correlation analysis shows that there was a weak positive correlation between
BOP with serum IL-1β levels in the CP group, while there were moderately significant
positive correlations with both PLI and GI (p < 0.05), and a significant positive correlation with PPD and CAL (p < 0.01). For the CP + CHD group, there were weak positive correlations between serum
IL-1β levels with PLI and PPD, while highly significant positive correlations were
observed with GI, BOP, and CAL (p < 0.05). In the CP group there was moderate positive correlation between serum IL-6
levels and PLI, BOP, and PPD (p < 0.05) as well as strong positive correlations with GI and CAL (p > 0.01). In the CP + CHD group significant positive correlations were revealed between
serum IL-6 levels with GI and PPD (p < 0.01), while the correlation was weak with PLI and BOP and moderate with CAL (p < 0.05), as shown in [Table 2 ].
Table 2
Serum levels of IL-1β and IL-6 and clinical periodontal parameters in CP + CHD and
CP group
Cytokine
Groups
Statistics
PLI
GI
BOP
PPD
CAL
Abbreviations: BOP, bleeding on probing; CAL, clinical attachment level; CHD, coronary
heart disease; CP, chronic periodontitis; GI, gingival index; IL, interleukin; NS,
not significant; PLI, plaque index; PPD, probing pocket depth.
§Chi-square test; *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; ****P ≤ 0.0001.
IL-1β
CP
Pearson’s r
0.44
0.409
0.29
0.638
0.701
p -value§
0.01
0.02
0.01
< 0.001
< 0.001
Significance
*
*
NS
****
****
CP + CHD
Pearson’s r
0.36
0.49
0.433
0.378
0.457
p -value§
0.05
0.005
0.01
0.039
0.011
Significance
NS
**
*
*
*
IL-6
CP
Pearson’s r
0.41
0.63
0.42
0.454
0.619
p -value§
0.02
< 0.001
0.01
0.01
< 0.001
Significance
*
****
*
*
****
CP + CHD
Pearson’s r
0.34
0.62
0.365
0.645
0.453
p -value§
0.06
< 0.001
0.04
< 0.001
0.016
Significance
NS
****
*
****
*
Fig. 3 Mean serum concentration values of interleukin (IL)-1β (A ) and IL-6 (B ) in patients with chronic periodontitis (CP) and coronary heart disease patients
affected by periodontitis (CP-CHD) compared with the control group. *p < 0.05; ***p < 0.001.
Discussion
CP is a multifactorial inflammatory disease characterized by irreversible progressive
loss of the tooth supporting tissues. The progression of this disease is influenced
by an imbalance between the microbial dental biofilm and the host immune response
including enhanced levels of cytokines such as IL-1β and IL-6, which can exacerbate
periodontal destruction.[2 ] The increase in the dental biofilm microbiota may increase the susceptibility to
various systemic diseases such as cardiovascular disease, mainly through bacteremia
and systemic inflammation. The presence of periodontal pathogens in vascular tissue
may directly stimulate atheroma formation and maturation.[19 ]
The mean values of PLI, GI, PPD, and CAL were higher in the CP + CHD group than the
CP group, which could be explained as hospitalized patients may neglect oral hygiene
measures, thus more gingival inflammation could be seen. Plaque biofilm bacteria secrete
a variety of byproducts (toxins, enzymes, and H2 S) that provoke an inflammatory response which can promote periodontal loss, pocket
formation, bone resorption, mobility, and tooth loss.[5 ]
[20 ]
[21 ]
The serum levels of IL-1β and IL-6 in this study were higher in the study group with
CP and atherosclerotic heart disease than other groups with highly significant differences
(p ≤ 0.01). Similar studies are lacking in the literature, while some have demonstrated
similar findings[22 ] others have shown no baseline differences in IL-6 levels in patients with periodontitis
and CHD.[23 ] In a study of cardiovascular disease patients, IL-6 levels were higher in those
with increased CAL but did not appear to specifically distinguish those with CP.[24 ]
The positive correlation of serum IL-1β levels with clinical periodontal parameters,
in both study groups, suggests that IL-1β levels are a potentially sensitive and reliable
marker of chronic inflammation activity and resultant tissue destruction. IL-1β is
thought to be important in the pathogenesis of PD[25 ] possibly due to its ability to cause atheromatous plaque instability through the
upregulation of MMPs at the site of plaque formation. It also mediates vascular smooth
muscle cell proliferation and migration during inflammation, which represents a key
step in the development of atherosclerosis.[26 ] In periodontal tissues, IL-1β is known to stimulate proliferation of keratinocytes,
fibroblasts, and endothelial cells and augments fibroblast synthesis of collagenase,
hyaluronate, fibronectin, and prostaglandin E2. In addition, it upregulates MMP and
downregulates tissue inhibitor of MMP production leading to bone resorption, an increase
in PPD, and loss of attachment.[27 ]
Serum IL-6 may be upregulated due to systemic exposure to oral bacteria and lipopolysaccharide
that enter the circulation from periodontal pocket, which in turn stimulates the liver
to release acute phase proteins including C-reactive protein.[28 ] In atherosclerosis, IL-6 has proinflammatory and procoagulant effects, thus may
contribute to the progression of atherosclerosis. Also, the retention of low-density
lipoprotein in the intima of a vessel may undergo oxidative changes and consequently
may increase secretion of chemokines and proinflammatory cytokines, such as IL-6.[29 ]
The positive correlation between IL-6 levels and different periodontal parameters
may be due to the dental plaque bacteria and bacterial byproducts inducing release
of proinflammatory cytokines which in turn gives rise to increased systemic IL-6 levels.
IL-6 is also secreted by osteoblasts which may have an effect on differentiation of
monocyte into osteoclasts that have key role in alveolar bone resorption which is
the hallmark of periodontitis progression.[8 ] It has also been revealed that in clinically healthy gingiva, inflammatory mediators
such as IL-1β and IL-6 are present at low levels[30 ] and that nonsurgical treatment of periodontal disease can result in reduced IL-6
levels.[23 ]
Conclusion
Patients with both CP and CHD have higher levels of the inflammatory markers IL-1β
and IL-6 than those with just periodontitis or control subjects. Cytokine levels also
correlated with several clinical periodontal parameters. These results may be used
to predict patients with periodontitis that are at increased risk of developing atherosclerotic
heart disease, and such correlation may be used as a marker for disease activity.
Increase awareness to obtain an optimum standard of periodontal health is necessary
to minimize the resultant bacteremia, which may influence the health of susceptible
organs including those of the cardiovascular system.
