Niacin Therapy Increases High-Density Lipoprotein Particles and Total Cholesterol Efflux Capacity But Not ABCA1-Specific Cholesterol Efflux in Statin-Treated SubjectsSignificance

Objective We investigated relationships between statin and niacin/statin combination therapy and the concentration of high-density lipoprotein particles (HDL-P) and cholesterol efflux capacity, 2 HDL metrics that might better assess cardiovascular disease risk than HDL-cholesterol (HDL-C) levels. Approach In the Carotid Plaque Composition Study, 126 subjects with a history of cardiovascular disease were randomized to atorvastatin or combination therapy (atorvastatin/niacin). At baseline and after 1 year of treatment, the concentration of HDL and its 3 subclasses (small, medium, and large) were quantified by calibrated ion mobility analysis (HDL-P-IMA). We also measured total cholesterol efflux from macrophages and ATP-binding cassette transporter A1 (ABCA1)-specific cholesterol efflux capacity. Results Atorvastatin decreased low-density lipoprotein cholesterol by 39% and raised HDL-C by 11% (P=0.0001) but did not increase HDL-P-IMA or macrophage cholesterol efflux. Combination therapy raised HDL-C by 39% (P<0.0001) but increased HDL-P-IMA by only 14%. Triglyceride levels did not correlate with HDL-P-IMA (P=0.39), in contrast to their strongly negative correlation with HDL-C (P<0.0001). Combination therapy increased macrophage cholesterol efflux capacity (16%, P<0.0001) but not ABCA1-specific efflux. ABCA1-specific cholesterol efflux capacity decreased significantly (P=0.013) in statin-treated subjects, with or without niacin therapy. Conclusions Statin therapy increased HDL-C levels but failed to increase HDL-P-IMA. It also reduced ABCA1-specific cholesterol efflux capacity. Adding niacin to statin therapy increased HDL-C and macrophage efflux, but had much less effect on HDL-P-IMA. It also failed to improve ABCA1-specific efflux, a key cholesterol exporter in macrophages. Our observations raise the possibility that niacin might not target the relevant atheroprotective population of HDL.