A link between periodontal disease (PD) and cardiovascular events has been proposed, but confounding by shared risk factors such as smoking and diabetes remains a concern. We examined the prevalence of PD and its contribution to C-reactive protein (CRP) levels in acute myocardial infarction (AMI) patients and in subjects without AMI and with angiographically nonobstructive coronary disease in the absence of these confounding risk factors.
Periodontal status and admission CRP levels were evaluated in 87 non-diabetic and non-smoking subjects undergoing cardiac catheterization. The study group comprised of 47 patients with documented AMI, and 40 subjects without AMI and with angiographically nonobstructive coronary disease (ANCD group).
Both the prevalence of PD and CRP levels were significantly higher in AMI patients compared with ANCD subjects (38.3% vs. 17.5%, p = 0.03 and 44.3 vs. 8.5 mg/L, p < 0.001 respectively). PD was associated with higher CRP levels in AMI patients (52.5 vs. 36.1 mg/L, p = 0.04) as well as in ANCD subjects, however, in this group this was not significant (12.6 vs. 7.6 mg/L, p = 0.5). Multivariable regression analysis confirmed two separate measures of PD as strong and independent contributors to elevated CRP levels in AMI patients ( R 2 = 0.28, R 2 = 0.30, p = 0.001).
PD contributes to elevated CRP levels in non-diabetic, non-smoking AMI patients, independently of other confounding factors. These findings imply that periodontitis may emerge as a novel target for reducing future risk in AMI survivors.
Periodontal disease (PD) is a common, bacterially induced chronic inflammatory oral disease associated with a systemic inflammatory response, evident by elevated systemic CRP levels. In terms of public health implications, the milder form (gingivitis), affects 30%–50% of adults, whilst the severe, generalized and destructive form that is considered PD affects 5%–15% of the adult population. The public health burden associated with cardiovascular disease (CVD) has been well documented since it consistently represents the leading cause of death in the developed world. An association between PD and CVD has been proposed by several studies, prompting stimulating discussions regarding the possible pathobiologic mechanisms underlying this link but potential confounding introduced by risk factors shared by both conditions, specifically smoking and diabetes remains a concern.
When reviewing the available studies it appears that a systemic inflammatory response rather than a direct bacterial vascular insult maybe underlying the link between PD and CVD. Several studies have demonstrated elevated CRP levels in patients with PD, a well established marker for increased cardiovascular risk. Specifically, for AMI patients, elevated admission levels of CRP are independently predictive of future events. In our study we sought to determine the prevalence of PD and its potential contribution to systemic CRP levels in non-diabetic, non-smoking patients suffering an AMI, as well as in non-diabetic, non-smoking subjects without AMI and with angiographically nonobstructive coronary disease.
Materials and methods
204 consecutive patients diagnosed with AMI and 102 consecutive subjects without AMI and with angiographically nonobstructive coronary disease (<30% luminal stenosis) underwent cardiac catheterization at the First Cardiology Clinic of the Hippokration Hospital, University of Athens. Exclusion criteria included diabetes mellitus, hepatitis or HIV infection, immunosuppressive therapy, current pregnancy or lactation, periodontal therapy in the preceding 6 months, and antibiotic therapy for 3 months prior to study entry. After excluding patients with history of ever smoking, the study group consisted of 47 patients with confirmed AMI, and 40 subjects with angiographically nonobstructive coronary disease (ANCD group). All study subjects completed medical and dental history questionnaires, and signed an informed consent form. The study was approved by the Institutional Review and Ethics Committee of the University of Athens.
Definition of AMI
Acute myocardial infarction was defined based on clinical presentation, admission electrocardiogram and serial myocardial enzyme determinations (troponin I, total creatinine phosphokinase (CPK) and myocardial band subfraction (CPK-MB). Creatinine phosphokinase-MB (CPK-MB) test is a sensitive cardiac marker used for the diagnosis of an AMI. The degree and the duration of CPK-MB elevation in serum approximate the extent of an AMI. CPK-MB levels rise 3–6 h after a heart attack, peak at 12–24 h and return to normal 12–48 h after tissue death.
All subjects underwent an oral examination performed by the same periodontist. Mean pocket probing depth (PPD) and clinical attachment loss (CAL) were used to measure periodontal status. PPD was measured as the distance from the gingival margin to the bottom of the probed pocket. CAL was measured as the distance from the cementoenamel junction to the bottom of the probed pocket. All measurements of PPD and CAL were recorded at six sites per tooth. Bleeding on probing (BOP %) was the presence of bleeding following pocket probing and the percentage of the total number of sites that bled was recorded. Plaque index (PI%) was recorded as the presence of visible plaque at the gingival margin of each tooth, recorded as per cent of the total number of sites. Periodontal disease was considered to be a systemic exposure when ≥30% of the sites examined had both CAL ≥ 3 mm and PPD ≥ 4 mm.
CRP measurements—biochemical measurements
AMI cases : CRP levels and the other markers of myocardial damage were measured from samples that were collected from subjects at the time of admission. CRP levels were measured with a high-sensitivity enzyme-linked immunosorbent assay (R&D Systems, Minneapolis, MN), with values expressed in milligrams per litre (mg/L). Blood samples for biochemical evaluation were collected from the antecubital vein between 8 and 9 a.m., after 12 h of fasting.
Control subjects : CRP levels and the biochemical evaluation were measured from blood samples that were collected from the subjects, at a scheduled appointment, between 8 and 9 a.m., after 12 h of fasting.
Quantitive data are reported as mean ± SD. The normality of the data distributions was assessed using the Kolmogorov–Smirnov test. Comparisons between AMI cases and control subjects and within each group on the basis of the presence or absence of PD were performed with standard unpaired t -tests. CPK-MB values were not normally distributed and were log transformed and presented as means ± SD. Comparisons regarding the percentage of males and females and the presence/absence of hypertension across groups were carried out with chi-square-test. Relationships between CRP level elevations and various variables were investigated by performing simple linear regression analysis for each variable separately. Multivariable linear regression analysis was used to test associations between PD and CRP levels. No adjustment was made for multiple testing. A p value < 0.05 was deemed to be significant.
Baseline characteristics for the two groups are shown in Table 1 . AMI subjects tended to be older than ANCD subjects (69.6 ± 11.9 years versus 67.9 ± 10.9 years respectively, p = 0.5), but there were no differences in gender, lipid profile (with the exception of HDL), fasting glucose levels, or body mass index in the two groups. AMI cases and ANCD subjects differed significantly in all periodontal parameters examined, including both cumulative measures of past periodontal disease (CAL), as well as measures of ongoing inflammatory activity (PPD, BOP) ( Table 1 ). Accordingly, PD was significantly more frequent in the AMI group compared with ANCD subjects (38.3% versus 17.5%, p = 0.03, Fig. 1 ). Table 2 depicts the baseline characteristics for AMI cases, according to the presence of PD, with hypertension being more frequent in AMI patients with PD.
|ANCD ( N = 40)||AMI ( N = 47)||p|
|Mean age (years)||67.9 ± 10.9||69.6 ± 11.9||0.5|
|Men||20 (50%)||25 (53.2%)||0.76|
|Hypertension||5 (12.5%)||21 (44.7%)||0.001 *|
|Total cholesterol (mg/dL)||188.2 ± 42.9||177.1 ± 33.5||0.18|
|Fasting Glucose (mg/dL)||90.4 ± 5.6||92.9 ± 7.1||0.09|
|Triglycerides (mg/dL)||100.4 ± 46.1||113.6 ± 48.7||0.19|
|HDL (mg/dL)||46.8 ± 11.4||40.5 ± 10.7||0.01 *|
|LDL (mg/dL)||120.0 ± 35.8||114.6 ± 29.5||0.45|
|VLDL (mg/dL)||20.1 ± 8.1||22.9 ± 9.3||0.17|
|BMI||27.4 ± 3.6||27.1 ± 4.3||0.7|
|CRP (mg/L)||8.5 ± 19.1||47.9 ± 53.0||0.001 *|
|Mean probing depth (mm)||2.7 ± 0.36||3.0 ± 0.59||0.04 *|
|Mean clinical attachment loss (mm)||2.2 ± 0. 6||3.2 ± 0.7||0.001 *|
|Missing teeth||9.0 ± 10.6||16.9 ± 10.2||0.001 *|
|BOP (%)||27.2 ± 8.7||81.1 ± 17.7||0.001 *|
|PI (%)||35.7 ± 9.6||89.4 ± 12.9||0.001 *|
|AMI||No periodontal disease ( N = 29)||Periodontal disease ( N = 18)||p|
|Mean age (years)||70.1 ± 12.4||68.9 ± 11.3||0.7|
|Men||12 (41.3%)||13 (72.2%)||0.07|
|Hypertension||10 (34.4%)||12 (66.6%)||0.03 *|
|Mean total cholesterol (mg/dL)||173.8 ± 32.6||182.3 ± 35.1||0.4|
|Fasting glucose (mg/dL)||93.4 ± 6.8||92.1 ± 10.2||0.6|
|HDL (mg/dL)||41.3 ± 9.0||39.3 ± 13.3||0.5|
|LDL (mg/dL)||112.1 ± 29.1||118.8 ± 30.4||0.4|
|VLDL (mg/dL)||23.9 ± 10.4||21.4 ± 7.6||0.4|
|BMI||26.7 ± 3.7||27.7 ± 5.1||0.4|
|Log CPK-MB (IU/L)||1.35 ± 0.4||1.48 ± 0.6||0.4|
As expected, AMI patients had significantly higher mean CRP levels compared with ANCD subjects (44.3 mg/L vs. 8.5 mg/L, p < 0.001), whilst the presence of PD was associated with higher mean CRP levels in both groups ( Fig. 2 ). Specifically in both groups there was an about 1.5-fold increase in CRP levels associated with PD that in the AMI group achieved statistical significance (ANCD: 7.6 mg/L vs. 12.6 mg/L, p = 0.5, AMI: 36.1 mg/L vs. 52.5 mg/L, p = 0.04).
Significant relationships were found between CRP concentrations and mean PPD and mean CAL measurements amongst AMI cases ( Table 3 ). In multivariable linear regression analysis mean CRP levels were significantly and positively associated with greater mean PPD and mean CAL ( R 2 = 0.30, R 2 = 0.28, p = 0.001). When PD exposure was examined as the percent of sites with CAL ≥ 3 mm and pocket depth ≥ 4 mm, multivariable linear regression analysis again indicated that PD in patients with AMI was associated with significantly higher mean CRP levels ( R 2 = 0.27, p = 0.001). In all models PD emerged as the single strongest contributor to CRP level elevation ( Table 4 ).
|log CPK-MB||14. 2||14.9||0.02||0.33|
|Mean clinical attachment level (CAL)||30.23||8.5||0.22||0.01 *|
|Mean pocket probing depth (PPD)||43.9||10.7||0.26||0.01 *|
|Model a ( R 2 = 0.28)||Model b ( R 2 = 0.30)||Model c ( R 2 = 0.27)|
|Total cholesterol||0.22||0.01||0.01||0.9||Total cholesterol||0.21||0.06||0.04||0.8||Total cholesterol||0.22||0.01||0.01||0.9|
|Mean CAL||27.4||9.1||0.43||.001*||Mean PPD||43.1||11.8||0.48||.001*||Periodontitis||44.9||15.4||0.43||.001*|
There are three main conclusions to our study. First, consistent with previous reports, we found PD to be more frequent in the AMI population compared to the ANCD group. Second, again consistent with existing literature, we found that the presence of PD is associated with higher CRP levels both in the AMI patients and ANCD subjects. Third, the contribution of PD to CRP elevations was strong, independent of other risk factors and consistent amongst a spectrum of PD measures evaluated. Most importantly, these observations were made in a study sample comprising of patients who have never smoked and are not diabetic, thereby eliminating the most commonly cited confounders.
The prevalence of PD in AMI patients in our study (38%) is almost double than the ANCD group and in accordance with the prevalence reported in previously published studies. One added strength of the present study is the inclusion of the ANCD group where significant coronary artery disease was excluded by coronary angiography (<30% stenosis), rather than simply implied by a negative history of clinical events. The prevalence of PD in the ANCD group (17.5%) is within the range of moderate to severe PD in the general population (10%–20%).
The association of PD with elevated systemic CRP levels has been well documented. Similarly, in our study, the presence of PD was associated with higher CRP levels both in the AMI group (52.5 vs. 36.1 mg/L, p = 0.04), as well as in the ANCD group (12.6 vs. 7.6 mg/L, p = 0.5). These findings are in accordance with the study by Deliargyris et al., which also showed significantly higher CRP levels in AMI patients with PD. In multivariable analysis, continuous measures of PD proved to be strongly and independently associated with CRP. Specifically, both mean CAL, a measure of past periodontal disease experience, and mean PPD, a measure of present inflammatory burden, were significantly and positively correlated with serum CRP levels.
Myocardial necrosis is also known to contribute to systemic CRP elevations and the size of infarction may have an impact on CRP levels. Thus, to rule out the possibility that the higher CRP levels present in AMI patients with PD were not the result of larger infarctions we compared peak log CPK-MB values in the two groups. Peak log CPK-MB values were similar in AMI patients with or without PD (1.48 ± 0.6 IU/L vs. 1.35 ± 0.4 IU/L, p = 0.4), suggesting that the higher CRP levels amongst AMI patients with PD was independent of infarction size.
The main criticism that casts doubt on the link between PD and CVD relates to the potential confounding introduced by the two major risk factors common to both conditions, namely diabetes and smoking. In fact Hujoel et al. have stated that only studies with inappropriate adjustment for tobacco smoking have found significant associations between PD and CVD since the effect of smoking is not adequately accounted for by the traditional categorization to current, former and never smokers. To address this issue and minimize the risk for residual confounding, we performed our study in patients who had never smoked and did not have diabetes.
Another condition that has been associated with increased levels of CRP is hypertension. In our study, hypertension was significantly positively associated with CRP levels and was more prevalent in the AMI group compared to ANCD group. Moreover, hypertension was more prevalent in the AMI patients with periodontal disease, which is in agreement with epidemiologic studies which showed an increased prevalence of hypertension in patients with periodontitis and that the severity of periodontal disease was related to the prevalence of myocardial infarction and hypertension. An important finding of our study was that periodontal disease significantly contributed to increased CRP levels, independently of other contributing factors, including hypertension.
In conclusion, in the last decade, there has been an extraordinary growth of interest in the bidirectional relation between systemic and periodontal disease. We demonstrated that amongst nondiabetic, nonsmoking patients suffering an AMI, PD is highly prevalent and when present it strongly and independently contributes to elevated systemic CRP levels. Systemic CRP levels in AMI patients carry an incremental and independent prognostic significance, therefore identifying modulators of CRP levels may represent novel therapeutic opportunities. Periodontal disease can be effectively treated and after successful therapy a reduction in systemic CRP levels has been shown. Secondary intervention studies should be designed to investigate the potential benefit of PD therapy in AMI survivors.
Conflict of interest
The authors declare that they have no conflict of interest.
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