Infection With Helicobacter pylori Is Not a Major Independent Risk Factor for Stable Coronary Heart Disease
Lack of a Role of Cytotoxin-Associated Protein A–Positive Strains and Absence of a Systemic Inflammatory Response
Background—There is controversy about the association between Helicobacter pylori infection and manifestations of coronary heart disease (CHD), the potential role of the more virulent H pylori strains, and whether or not a positive serostatus is related to increased levels of markers of systemic inflammation.
Methods and Results—We assessed the prevalence of an infection with H pylori and in particular the anti–cytotoxin-associated protein A (CagA) antibody response of the more virulent strains expressing CagA in 312 patients with stable CHD and in 479 control subjects. Serological prevalence of H pylori infection (IgG titer) was significantly higher in patients than in control subjects after adjustment for age and sex (44.2% versus 31.3%, P<0.001). After adjustment for various covariates in multiple logistic regression, the odds ratio (OR) for CHD was 1.3 (95% CI, 0.9 to 1.9) given a positive IgG serostatus. The prevalence of CagA-positive strains was 27.9% in patients and 21.7% in control subjects (P=0.076 adjusted for age and sex). The OR for CHD in the fully adjusted model was 1.1 (95% CI, 0.7 to 1.7). None of the inflammatory markers (C-reactive protein, fibrinogen, plasma viscosity, or leukocytes) was significantly different according to serostatus.
Conclusions—In this large case-control study, the association of H pylori infection with stable CHD was strongly reduced and was no longer statistically significant after controlling for potential confounders. We also found no independent association between the more virulent strains and CHD. In addition, a positive serostatus was not associated with a systemic inflammatory response. Thus, these data do not support the hypothesis that infection with H pylori might be a major risk factor for stable CHD.
More than 20 epidemiological studies published during recent years have reported on the association between chronic infection with Helicobacter pylori and manifestations of coronary heart disease (CHD), and a recent meta-analysis has suggested a weak positive association.1
Most of the accumulated evidence has come from small case-control studies, most with no or little adjustment for potential confounders, whereas prospective studies showed no independent association.2 3 4 5 6 In a meta-analysis, classic cardiovascular risk factors found to be associated with both H pylori infection and CHD were low socioeconomic status,1 high body mass index (BMI), and low HDL concentrations.7 In addition, several studies have reported strong correlations between chronic H pylori infection and various markers of systemic inflammation (for an overview, see Reference 77 ), presenting a potential pathophysiological link with CHD.8 These correlations, however, have not been confirmed by other studies and were not significant in a meta-analysis.7
Most recently, evidence from a small case-control study9 has suggested that the association between H pylori and CHD might depend on the presence of the more virulent H pylori strains bearing the cytotoxin-associated gene A and producing the cytotoxin-associated protein (CagA).10 However, so far it has not been possible to detect H pylori DNA directly in atherosclerotic plaques, which would demonstrate a direct link with the pathoanatomic substrate.11
We therefore conducted a large case-control study to assess the association between various markers of previous infection with H pylori (IgG, IgA, and 13C-urea breath test) and angiographically confirmed stable CHD, controlling simultaneously for a variety of potential confounders. Specifically, we wanted to assess whether chronic infection with H pylori was associated with a systemic inflammatory response and whether this association was related to the presence of the more virulent H pylori CagA-positive strain.
Patients and Control Subjects
Patients and control subjects were recruited between October 1996 and November 1997. Participation was voluntary, and written, informed consent was obtained from each subject. The study was approved by the ethics committee of the University of Ulm. Participation rate was 78% in eligible patients and 84% in eligible control subjects.
The case group was admitted to the Department of Cardiology at the University of Ulm Medical Center for elective coronary angiography. A total of 312 patients of German nationality who were 40 to 68 years of age and had clinically stable, angiographically confirmed CHD (>50% diameter stenosis of ≥1 major coronary artery) diagnosed within the previous 2 years were included. Patients with acute ischemic syndromes within the previous 4 weeks, acute infectious diseases, or evidence of malignant diseases possibly associated with an acute-phase reaction were excluded.
The control group consisted of 479 subjects who were occasional blood donors at the local Red Cross center serving the university hospitals of Ulm. All control subjects had no history of definite or suspected CHD and did not report infections or surgery within the previous 4 weeks.
Frequency matching for age and sex was performed, and a case-to-control ratio of 1:1.5 was intended. The sample size was sufficient to detect an odds ratio (OR) of ≥1.5-fold for an association of H pylori infection with CHD with 80% power at the 5% level of significance.
All subjects underwent standardized interviews conducted by trained interviewers. Participants were asked about medical history, including specific questions related to physician-diagnosed hypertension, diabetes, and gastroduodenal disease. Furthermore, current medication, sociodemographic data, and lifestyle habits, including smoking and alcohol consumption, were recorded.
Venous blood was drawn in the morning under standardized conditions, and a complete blood cell count was done (STKS chamber, Coulter Co). Within 30 minutes, the remaining blood was centrifuged at 3000g for 10 minutes, immediately divided into aliquots, and frozen at −70°C until analysis. Specific anti–H pylori IgGs were measured by use of a commercial ELISA (H pylori IgG ELISA, Medac Co) according to manufacturer’s instructions. Titers were defined as positive or negative according to a cutoff value of 8 U/mL. Humoral response to CagA protein was assessed by Western blot (H pylori Western Blot, AID Co) in ELISA IgG-positive samples. Current H pylori infection was further determined by means of a modified 13C-urea breath test.12 An initial breath sample and, after administration of 75 mg non–radioactive-labeled 13C-urea (Mass Trace) in 200 mL apple juice (pH, 2.2 to 2.4), a 30-minute breath sample was collected. Breath samples were analyzed with an isotope-selective, nondispersive infrared spectrometer (NDIRS, Wagner Analytical Systems). A change of the 13CO2/12CO2 ratio over baseline of >4‰ was considered positive. Lipoprotein concentrations were determined by routine enzymatic methods. In addition, C-reactive protein (CRP) determinations were done by an immunoradiometric assay (range, 0.05 to 10 mg/L) calibrated with the World Health Organization reference standard 85/506. Fibrinogen was measured by immunonephelometry (Behring Co) and according to the Clauss method. Finally, plasma viscosity was determined in a Harkness Coulter viscometer (Coulter Electronics Co). Intra-assay coefficients of variation were 4% for CRP, 3.7% for fibrinogen, and 0.7% for plasma viscosity. All laboratory analyses were done in a blinded fashion.
Demographic and clinical characteristics in patients and control subjects were compared in a descriptive way. The association of serum antibody levels or a positive 13C-urea breath test with the presence of CHD was calculated by χ2 statistics. Unconditional logistic regression was used to assess the independent association of a positive antibody titer against H pylori or a positive breath test with CHD, while simultaneously controlling for age (years), sex, BMI (kg/m2), smoking (pack-years), history of hypertension and diabetes, alcohol consumption (g/d), formal education (years), and plasma HDL cholesterol (mmol/L). Blood, plasma, and serum parameters are reported as mean±SD and were compared by use of the Wilcoxon rank-sum test. Because the distribution of CRP values was skewed, median values and geometric means were calculated. Categorical variables are reported as percentages. A 2-tailed value of P<0.05 was considered statistically significant. In addition, mean values of markers of inflammation were compared between H pylori–negative, CagA-negative, and CagA-positive subjects in cases and control subjects separately with a general linear model. Differences were tested for statistical significance after adjustment for age and sex. All computations were done with SAS software.13
The main characteristics of patients and control subjects are summarized in Table 1⇓. Control subjects were slightly younger; spent more years in school; more often had never smoked; showed a somewhat lower mean BMI; and less frequently reported a history of hypertension, diabetes, or gastroduodenal disease. Mean HDL cholesterol was considerably higher in control subjects than in patients. Levels of all markers of systemic inflammation were lower in control subjects compared with cases.
Approximately two thirds of the patients (62%) had a history of myocardial infarction within the previous 2 years. By coronary angiography, 48% had single-vessel disease, 34% had double-vessel disease, and 18% had triple-vessel disease.
H pylori Infection
The prevalence of seropositivity to H pylori (IgG titer) was higher in patients than in control subjects, in men and in women (overall 44.2% versus 31.3%, P<0.001 after adjustment for age and sex; Table 2⇓). In both sexes, in patients and control subjects, a strong positive relation with age was seen. Anti-H pylori IgAs were detected in 55.8% of patients and 47.2% of control subjects (P=0.048 after adjustment for age and sex). When we looked for current infection by means of the 13C-urea breath test, 40.4% of patients were positive compared with 33.3% of control subjects (P=0.084 adjusted for age and sex).
Table 3⇓ presents the results of multivariable logistic regression analyses in which the association between H pylori infection and CHD was adjusted for age and sex and for age, sex, and a variety of other potential confounders. The OR for CHD given IgG seropositivity to H pylori decreases from 1.7 (95% CI, 1.3 to 2.3) to 1.3 (95% CI, 0.9 to 1.9) in the fully adjusted model and becomes statistically nonsignificant. Similar results are seen with IgA seropositivity, with a decrease in the OR from 1.4 (95% CI, 1.1 to 1.9) to 1.0 (95% CI, 0.7 to 1.5) in the fully adjusted model, and 13C-urea breath test, with a decrease in the OR for CHD from 1.3 (95% CI, 1.0 to 1.8) to 1.0 (95% CI, 0.7 to 1.5) in the fully adjusted model.
Prevalence of CagA-Positive H pylori Strains
The prevalence of CagA-positive H pylori strains was not significantly different between patients and control subjects (27.9% versus 21.7%, P=0.076 after adjustment for age and sex; Table 4⇓). There was also no clear positive relation with age as has been observed for the prevalence of IgG, IgA, and a positive 13C-urea breath test. The prevalence of CagA-positive H pylori strains was somewhat lower in patients with a history of myocardial infarction compared with patients without (24.7% versus 33.3%, P=0.11 after adjustment for age). Table 5⇓ shows an OR for CHD given a positive H pylori CagA status of 1.5 (95% CI, 1.0 to 2.1) after controlling for age and sex, which decreased to 1.1 (95% CI, 0.7 to 1.7) and became statistically nonsignificant after adjustment for known cardiovascular risk factors.
Markers of Systemic Inflammation and Serostatus
Table 6⇓ shows measures of central tendency for various markers of systemic inflammation in patients and control subjects according to H pylori IgG serostatus and CagA status. CRP, fibrinogen, plasma viscosity, and leukocyte count were not different between IgG seronegatives and seropositives, nor was there any appreciable difference between those carrying the CagA-positive strains and those not. In general, patients showed consistently higher levels of markers of systemic inflammation than did control subjects (eg, the geometric mean for CRP was 1.63 mg/L in patients compared with 1.13 mg/L in control subjects, P<0.001).
In this large case-control study, we found moderate associations between IgG or IgA seropositivity to H pylori and the presence of angiographically confirmed stable CHD, which, however were strongly reduced and were no longer statistically significant after controlling for a variety of potential confounders. It is not clear whether HDL cholesterol should be considered a potential confounder or a potential intermediate step in the suggested causal pathway between H pylori and CHD. In the latter case, it should not be included in the fully adjusted model. We therefore repeated the analyses without inclusion of HDL cholesterol and found no appreciable change in the OR. We also found no significant association between a positive 13C-urea breath test, indicating active infection with H pylori, and chronic, stable CHD. To the best of our knowledge, this is the first study to relate this test to the presence of CHD.
In contrast to earlier studies, which had reported a positive association between H pylori infection and CHD, we carefully selected cases with a recent diagnosis of CHD, excluded patients with acute ischemic syndromes, and carefully controlled for potential confounders. The control group was not selected opportunistically but recruited from the same geographic area, and frequency matching with patients according to age and sex was done. Although voluntary blood donors may be somewhat healthier and thereby not fully representative of the patients’ population base, this could not explain the absence of a positive association between H pylori infection and CHD. Also, this study was larger than most of the studies reported1 so far and therefore had greater power to detect a potential independent association. The inconsistency of an association between H pylori infection and CHD found in previous studies may therefore be explained by a variety of methodological shortcomings already discussed in detail in a meta-analysis.1
Recently, an alternative explanation has been put forward suggesting that variations in the strength of H pylori strains to provoke an inflammatory response might play a crucial role in the relation with CHD.9 In particular, the CagA-positive H pylori strains have been found to be associated with enhanced virulence and cytotoxin production14 and were more frequently associated with peptic ulceration and higher grades of gastric inflammation compared with CagA-negative strains.10 Those with more severe forms of gastroduodenal disease expressed cytokines like interleukin-1 in the mucosa and showed elevated antral interleukin-8 protein levels significantly more often.10 Systemic increases in these inflammatory markers have not been reported in this context so far.
Although the relation of CagA-positive H pylori strains with gastroduodenal disease has been widely studied, only 1 small case-control study has assessed the possible role of the more virulent CagA-positive H pylori strains in prevalent CHD.9 In that study, prevalence of CagA-positive strains was considerably higher in patients (38 of 88; 43%) than in control subjects (15 of 88; 17%; difference, P=0.0002), and a strong association was found between angiographically confirmed CHD (>70% diameter stenosis) and infection with CagA-positive H pylori strains (OR, 3.8; 95% CI, 1.6 to 9.1; P<0.001), whereas no association was seen with CagA-negative strains. In the present, much larger study, prevalence of CagA-positive strains was only slightly higher in patients (87 of 312; 27.9%) than in control subjects (103 of 479; 21.7%).This difference was statistically nonsignificant (P=0.076) and was further reduced by control for known risk factors of CHD (adjusted OR, 1.1; 95% CI, 0.7 to 1.7). Although the design of the 2 studies and the definition of angiographically assessed CHD appear to be comparable and both studies have used voluntary blood donors as control subjects, the clinical presentation of patients was clearly different. In contrast to Pasceri et al,9 who studied mainly patients with acute ischemic syndromes (unstable angina and acute myocardial infarction, n=61 of a total of 88 patients), we used a carefully selected group of patients in clinically stable conditions with a history of CHD of ≤2 years. Therefore, the different clinical presentation of the patient groups might be an explanation of the contradictory results of these 2 studies.
Inflammation represents an important feature of CHD,15 16 and several authors have discussed the role of an increased inflammatory response to various infectious stimuli that might represent the pathophysiological link between infection and CHD.1 17 18 19 In this large case-control study, we found no consistent increase in CRP, fibrinogen, plasma viscosity, or leukocyte count related to seropositivity to H pylori as assessed by IgG antibody or, more specifically, to infection by the more virulent CagA-positive strains. This held true in patients and control subjects.
In conclusion, our results do not support the hypothesis of a clinically important role of a H pylori infection in CHD by means of increased systemic inflammation or another independent causal pathway.
This study was funded in part by grants from the medical faculty of the University of Ulm, ASTRA (Wedel, Germany), and MEDAC (Hamburg, Germany) and by MRC program grant G-790051 to Dr Pepys. We greatly appreciate the willingness of patients and blood donors to participate in this study. We are indebted to the staff of the blood bank for their help and to Gerlinde Trischler and Susanne Kuhn for excellent technical assistance.
- Received February 8, 1999.
- Revision received July 20, 1999.
- Accepted July 20, 1999.
- Copyright © 1999 by American Heart Association
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