The role of bilirubin and its protective function against coronary heart disease

Abstract

Atherosclerotic cardiovascular disease is the leading cause of morbidity and mortality both in industrialized and developing countries. Atherosclerosis is a chronic inflammatory disease of the arterial wall, which also involves deposition and peroxidation of lipids. Bilirubin, an important endogenous antioxidant, may limit lipid peroxidation and retard the progression of atherosclerosis. Previous studies have reported an inverse relationship between serum bilirubin levels and the risk of coronary artery disease (CAD). Taking into account that atherosclerosis is a complex process that is initiated and accelerated by diverse risk factors, we aimed to test the antiatherosclerotic effects of bilirubin in a population with multiple risk factors for CAD. The study included 221 patients who underwent coronary angiography owing to symptoms suggestive of ischemia and/or positive noninvasive stress test results. Of the patients, 76 had normal coronary angiograms and served as the control group. The remaining 145 patients with documented CAD and two or more cardiovascular risk factors constituted the study group. The study group (n=145) was further classified according to the Gensini score as follows: group 1 if Gensini score was 1-19 (minimal CAD, n=82), and group 2 if Gensini score was 20 or higher (significant CAD, n=63). Biochemical assessments including total and direct serum bilirubin levels were carried out using standard methods in automated systems. All of the cardiovascular risk factors were found significantly more frequently in the study group (groups 1 and 2) than in the control group. Total and direct serum bilirubin levels did not differ significantly between the control group, group 1, and group 2. There was a moderate and significant positive correlation between direct bilirubin levels and the Gensini score (r = 0.158, p = 0.019). There was no significant correlation between total bilirubin levels and the Gensini score. In conclusion, our findings suggest that in the presence of multiple risk factors, similar concentrations of serum bilirubin may not confer the same level of protection against CAD as in an individual with a more favorable risk profile. The relationship between direct bilirubin levels and the Gensini score is unlikely to be causative, given the established antiatherosclerotic effects of bilirubin.