Elevated levels of oxidized low-density lipoprotein and impaired nocturnal synthesis of melatonin in patients with myocardial infarction

This study was designed to investigate the relationship between nocturnal serum melatonin (MEL) levels and oxidized low-density lipoprotein (OxLDL) in patients with acute coronary syndrome (ACS). OxLDL plays a pivotal role in the development of atherosclerosis. Patients with coronary heart disease have an impaired nocturnal secretion of MEL. To date, there are no clinical human studies concerning the relationship of MEL to low-density lipoprotein (LDL) oxidation in patients with acute myocardial infarction (AMI). The study population contained 60 patients with AMI and 60 control subjects. Levels of circulating OxLDL were measured by a monoclonal antibody 4E6-based competition ELISA. Levels of circulating MEL were measured by an enzyme-immunoassay kit after chloroform extraction. Comparison of levels between AMI and controls, adjusted for age, revealed significantly higher nocturnal serum OxLDL levels (95.47 ± 6.81 versus 68.35 ± 4.07 U/l; p = 0.004) in the AMI subjects. Nocturnal serum levels of MEL were lower in AMI than the control group (20.97 ± 3.90 versus 53.19 ± 7.80 pg/ml; p = 0.009). Serum levels of total, high-density lipoprotein (HDL), and LDL cholesterol did not differ between the groups. Multiple regression analysis was performed on cases to study the association between AMI and serum levels of OxLDL and MEL (OR: 2.93; 95% CI, 2.89-2.98, p = 0.01 and OR: 0.94; 95% CI, 0.89-0.97, p = 0.02, respectively). This study demonstrates for the first time an independent association between nocturnal levels of OxLDL and MEL in patients with AMI. Additional population studies are necessary to further document these.