Low concentrations of phospholipids and plasma HDL cholesterol subclasses in asymptomatic subjects with high coronary calcium scores

Objective: To determine whether HDL size distribution and HDL subclasses are associated with coronary calcium scores.

Methods: We screened 677 apparently healthy individuals by coronary tomography. One hundred twenty subjects were then recruited for the study and grouped by coronary artery calcification scores (CAC). Forty asymptomatic patients with atherosclerosis with CAC scores ≥75th percentile for gender and age were placed in the first group. Forty patients with CAC scores ≤25th percentile and 40 matched controls (CAC = 0) made up the two remaining groups. HDL samples were separated via sequential ultracentrifugation, followed by electrophoresis: they were then enzymatically stained and densitometrically analyzed to determine the triglycerides (Tg), phospholipids (Ph), and plasma cholesterol (C) concentrations corresponding to each HDL subclass.

Results: HDL size distribution, lipid and non-lipid risk factors for atherosclerosis were similar among the three groups: HDL-cholesterol and HDL-phospholipids were significantly lower in the CAC ≥75th percentile group, whereas HDL-lipids in the CAC ≤25th group were comparable to the controls. HDL2b- and HDL2a-cholesterol were decreased, whereas phospholipids were lower in patients constituting 4 of the 5 HDL subclasses. The Ph-to-Tg ratios of small HDL were higher in both experimental groups compared with the controls, suggesting that these lipoproteins had abnormal structures. In spite of the significant differences between the high-CAC score subjects and the controls, statistical analyses demonstrated no substantial relationship between CAC scores and HDL parameters: other lipid and non-lipid risk factors for atherosclerosis were not statistically linked to CAC scores. Only male gender and age contributed to CAC scores in our study population.

Conclusions: Our results suggest that CAC scores and traditional lipid profiles are independent aspects of atherosclerosis and that only lipids may be biomarkers of coronary calcification during the asymptomatic stages of the disease; however, HDL subclasses do not contribute to CAC scores.