Effects of Nicotinic Acid Therapy on Plasma High Density Lipoprotein Subfraction Distribution and Composition and on Apolipoprotein A Metabolism

This report describes the effects of pharmacologic doses (3 g/d) of nicotinic acid on the plasma distribution and chemical composition of the high density lipoprotein (HDL) subfractions HDL(2) and HDL(3) and examines the influence of the drug on the metabolism of the major HDL apoproteins, apolipoproteins A-I (ApoA-I) and A-II (Apo-II). The drug lowered plasma cholesterol (15%, P < 0.05) and triglyceride (27%, P < 0.01); the former effect a result of a fall in the amount of cholesterol associated with very low density lipoproteins (31%, P < 0.02) and low density lipoproteins (36%, P < 0.02). Conversely, it raised plasma HDL cholesterol (23%, P < 0.05) and increased (by 345%) the plasma HDL(2):HDL(3) ratio. The latter derived from an absolute increment (646%) in circulating HDL(2), coupled with a fall (47%) in HDL(3). This change was not associated with major alterations in the overall cholesterol (free and esterified), triglyceride, phospholipid, or protein content of the subfractions; however, it was accompanied by substantial changes in their protein composition. In particular, the molar ratio of ApoA-I:ApoA-II in HDL(3) declined from 2.7:1 to 2.1:1 during nicotinic acid treatment.Significant perturbations of ApoA-I and ApoA-II metabolism accompanied the drug-induced HDL subfraction redistribution. Specifically, the plasma concentration of ApoA-I rose by 7% (P < 0.05) because of a decrease in its fractional catabolic rate. Moreover, whereas before treatment 6 and 94% of the plasma ApoA-I circulated with HDL(2) and HDL(3), after commencement of nicotinic acid therapy this distribution became 49 and 51% in HDL(2) and HDL(3), respectively. ApoA-II was found mainly in HDL(3), both before and during nicotinic acid treatment. Administration of the drug caused a 14% reduction in its plasma concentration (P < 0.05), which derived principally from a fall (22%, P < 0.01) in its synthetic rate. These data suggest that the effects of nicotinic acid on the HDL subfraction distribution may be mediated via (a) net transfer of ApoA-I from HDL(3) to HDL(2) and (b) a reduction in ApoA-II synthesis. Our present understanding of the association between HDL and atherosclerosis indicates that such changes may have prophylactic value in the prevention of coronary artery disease.