Nicotinic Acid Accelerates HDL Cholesteryl Ester Turnover in Obese Insulin-Resistant Dogs

Aim

Nicotinic acid (NA) treatment decreases plasma triglycerides and increases HDL cholesterol, but the mechanisms involved in these change are not fully understood. A reduction in cholesteryl ester transfer protein (CETP) activity has been advanced to explain most lipid-modulating effects of NA. However, due to the central role of CETP in reverse cholesterol transport in humans, other effects of NA may have been hidden. As dogs have no CETP activity, we conducted this study to examine the specific effects of extended-release niacin (NA) on lipids and high-density lipoprotein (HDL) cholesteryl ester (CE) turnover in obese Insulin-Resistant dogs with increase plasma triglycerides.

Methods

HDL kinetics were assessed in fasting dogs before and four weeks after NA treatment through endogenous labeling of cholesterol and apolipoprotein AI by simultaneous infusion of [1,2 ¹³C₂] acetate and [5,5,5 ²H₃] leucine for 8 h. Kinetic data were analyzed by compartmental modeling. In vitro cell cholesterol efflux of serum from NA-treated dogs was also measured.

Results

NA reduced plasma total cholesterol, low-density lipoprotein cholesterol, HDL cholesterol, triglycerides (TG), and very-low-density lipoprotein TG concentrations (p < 0.05). The kinetic study also showed a higher cholesterol esterification rate (p < 0.05). HDL-CE turnover was accelerated (p < 0.05) via HDL removal through endocytosis and selective CE uptake (p < 0.05). We measured an elevated in vitro cell cholesterol efflux (p < 0.05) with NA treatment in accordance with a higher cholesterol esterification.

Conclusion

NA decreased HDL cholesterol but promoted cholesterol efflux and esterification, leading to improved reverse cholesterol transport. These results highlight the CETP-independent effects of NA in changes of plasma lipid profile.