Is Helicobacter pylori a Factor in Coronary Atherosclerosis?

A number of epidemiological studies have suggested associations between Helicobacter pylori seropositivity and coronary heart disease (2). High concentrations of immunoglobulin G antibody to H. pylori are fairly reliable indicators of chronic gastric infection, but the presence of antibodies in serum does not necessarily indicate persistent exposure of the coronary arteries to any type of insult. Although a number of pathological studies have reported the presence of Chlamydia pneumoniae DNA, antigens, or elementary bodies in diseased arterial specimens (3), there is little direct evidence available on the possible presence of H. pylori in the bloodstream or in vascular tissue. Hence, we investigated the presence of the H. pylori genome in buffy coat samples and in diseased arterial segments. We used a PCR that involved nested primers specific for the 16S rRNA gene of H. pylori, optimized to detect as little as 0.01 pg of genomic DNA (or about a dozen organisms) (6). DNA had been extracted from the buffy coat samples of 77 healthy individuals for a genetic study of myocardial infarction; 52 of these individuals were known to be strongly seropositive for immunoglobulin G antibodies to H. pylori, and 25 were chosen as seronegative controls. Samples of carotid atheroma were taken from another 39 individuals at carotid endarterectomy. DNA was extracted from the tissue by using a commercial kit (Puregene; Flowgen Ltd.) and analyzed by operators unaware of the tissue source. PCR products of samples appearing positive on gel electrophoresis were probed by Southern hybridization and autoradiographed for 1 week. Only 1 of the 77 buffy coat samples tested positive, and it belonged to a seropositive individual. Only 1 of the 39 atheromatous specimens collected at carotid surgery tested positive. A number of standard precautions were taken in the present study to protect against spurious results due to contamination, including the use of dedicated laboratory space, reagents, and instruments for pre- and post-PCR work and the testing of positive controls and negative controls in parallel with the test samples. Despite these precautions, the possibility of contamination in the two samples that tested positive for H. pylori DNA cannot be definitely excluded, nor can we exclude the possibility that a low-copy-number infection was actually present but undetected by our highly sensitive assay. Still, the present study adds to the sparse data that exists on H. pylori DNA in the bloodstream and in vascular tissue, being the first reported detection of H. pylori markers in human vascular tissue. It, however, does not support the likelihood of a high prevalence of the organism in buffy coat samples or in carotid atheroma. The only available report of H. pylori bacteremia involved positive blood cultures in a patient with gastric perforation due to malignancy (7), but in vitro studies suggest that any organisms penetrating beyond the gastric mucosa should be killed rapidly by complement proteins (5). Whereas a large number of studies have reported on the presence of markers of C. pneumoniae and cytomegalovirus in vascular lesions (2), there is only one previously reported study of H. pylori and atheroma (1). That study did not detect H. pylori DNA in any of the atherosclerotic plaques of 50 patients with abdominal aortic aneurysms, although about one-half of these samples tested positive for C. pneumoniae DNA (1). If H. pylori is relevant to the causation of vascular disease, it remains unclear how its effects are mediated. This suggests the need for further studies of coronary atheroma and comparisons of concentrations in plasma of vascular risk factors in seropositive and in seronegative individuals (4), as well as before and after H. pylori eradication treatment.