Hyperinsulinemia, lipoprotein (a), and Chlamydia pneumoniae antibodies--are they risk factors or serologic predictors for progression of coronary artery disease?

Chronic infection and coronary artery disease

On a variety of fronts, chronic infection has been found to be significantly associated with the development of atherosclerosis and the clinical complications of unstable angina, myocardial infarction, and stroke. For the most part, these relationships are still just associations. Failure to confirm initial reports of serologic associations also has been common. Specific causative relationships on par with that determined between H pylori and peptic ulcer disease have not yet been established. Potential mechanisms whereby chronic infections may play a role in atherogenesis are myriad. In the case of C pneumoniae, the effect may result from direct vessel wall colonization that may damage the vessel either directly or indirectly by initiating immunologic responses. In other cases the effect may simply be that of enhancing the pre-existing chronic inflammatory response of the body to standard risk factors such as hyperlipidemia. Even though the infectious agent may not directly infect the vessel wall, it may perform its critical role from afar. Chronic infection might also influence pre-existing plaque by enhancing T-cell activation or other inflammatory responses that may participate in the destabilization of the intimal cap. Hence chronic infection may play a role either in the initiation, progression, or the destabilization of atherosclerotic plaques. The infectious agents with the most evidence to support an etiologic role in atherosclerosis include C pneumoniae and cytomegalovirus. Evidence is mounting for a variety of other potential agents including other herpes viruses, influenza, other specific bacteria (such as M pneumoniae), and chronic infections with common bacterial agents (periodontal disease, chronic bronchitis, and chronic urinary tract infection, among others) [191]. Future studies are expected to elucidate further the pathophysiologic relationship between chronic infection and atherosclerosis and to evaluate further the potential of a variety of treatment approaches, including antibiotics.

Secondary prevention of coronary artery disease with antimicrobials: current status and future directions

Over the past several decades, coronary artery disease (CAD) has become the major health problem in the Western world with more than 50% of deaths attributed to its complications. The exact causes of atherosclerosis are not clearly known, although multiple risk factors (e.g. hypertension, hyperlipidemia, diabetes mellitus, family history, and smoking) have been well described. However, these risk factors account for only about 50% of the total risk of CAD. Consequently, an ongoing search is under way to discover new risk factors for atherosclerosis as well as the basic underlying causes of progression. Although the evidence is not yet definitive, recent studies have shown that chronic infection by such bacterial organisms as Chlamydia pneumoniae, Helicobacter pylori, and a variety of dental pathogens may play a causative role in atherosclerosis. If this is true, then antimicrobial therapy may be helpful in the secondary prevention of CAD. Indeed, several small studies have already been completed testing this hypothesis. This article reviews the evidence associating these bacterial pathogens to CAD and presently available information regarding the use of antibiotics in the setting. At present, most studies evaluating the potential efficacy antimicrobials in the secondary prevention of CAD have tested the use of macrolide antibodies. Although several small preliminary studies have reported promising results favoring a clinical benefit from even short (<3 months) courses of antimicrobial therapy, the first large clinical trial, the Weekly Intervention with Zithromax for Atherosclerosis and its Related Disorders (WIZARD) study, did not show a statistically significant beneficial effect of a 3 month course of azithromycin over placebo by the end of up to 4 years follow-up. However, a statistically significant (p = 0.03) 33% reduction in death and myocardial infarction was found at 6 months, 3 months after the discontinuation of antibiotics. This robust clinical benefit, however, was not sustained over the ensuing 3.5 years of follow-up. These disappointing long-term outcomes of short-term therapy with antimicrobials may be explained by the recently discovered difficulty found in eradicating chronic vascular infections such as C. pneumoniae. It remains possible that longer term antimicrobial therapy or short-term use of more potent single agents or combinations, capable of effectively eradicating the offending organisms might provide added clinical benefit in the fight against CAD. Further studies are ongoing or planned to evaluate this potential. In the meantime, it is not presently recommended that antimicrobials be routinely prescribed for the secondary prevention of CAD.

Biochemical risk factors for cardiovascular disease in an aged male population: emerging vascular pathogens

The progressive increase of deaths and morbidity from cardiovascular disease (CVD) in most developed societies has led to the formulation of preventive strategies and application of several diagnostic guidelines. However, there is emerging evidence that most panels and algorithms are inadequate and require urgent revision and updating. Therefore, the aim of this study was the evaluation of a wide cardiovascular risk profile in elderly male patients with acute myocardial infarction (AMI) or peripheral occlusive disease (POD). The risk profile was assessed by measuring conventional serum lipid and lipoprotein levels and emerging parameters: lipoprotein(a) (Lp[a]), homocysteine (Hcy), and C-reactive protein (CRP). The concentration of triglycerides, Lp(a), Hcy and the total cholesterol/high-density lipoprotein (TC/HDL) ratio were significantly higher in both classes of patients than in a population of matched healthy controls and, similarly, patients with CVD displayed lower plasma values of HDL. No significant differences were observed for TC, low-density lipoprotein (LDL), and CRP. Patients with POD exhibited a marked atherogenic profile, as attested by substantially increased values of Hcy, Lp(a), triglycerides, and TC/HDL ratio. The frequency distributions of Lp(a) and Hcy concentrations were markedly shifted toward upper values in both classes of patients than in controls. In multivariate regression analysis, Lp(a) and Hcy were the best predictors for AMI, whereas Lp(a), Hcy, and the TC/HDL ratio were the best predictors for POD. Taken together, these data suggest that Lp(a) and Hcy excesses might exert a central role in the development of atherosclerotic disease in elderly male patients. Thereby, the inclusion of those tests, along with the TC/HDL ratio and other more conventional analyses in panels for the evaluation of the cardiovascular risk might be profitable in terms of effectual prevention.