Triglyceride enrichment of HDL does not alter HDL-selective cholesteryl ester clearance in rabbits

Triglyceride (TG) enrichment of high density lipoprotein (HDL), which occur s in hypertriglyceridemic states, significantly enhances the rate at which HDL apolipoprotein (apo)A-I is cleared from the circulation of healthy huma ns. In the New Zealand White (NZW) rabbit, a species naturally deficient in hepatic lipase (HL), TG enrichment of HDL requires prior lipolytic modific ation to enhance apoA-I clearance, However, the effect of TG enrichment of HDL on the subsequent clearance of HDL cholesteryl ester (CE) has not previ ously been examined in vivo. Therefore, we investigated, in the NZW rabbit, the effect of ex vivo TG enrichment of rabbit HDL (by incubation with huma n very low density lipoprotein) on the clearance of HDL CE and apoA-I radio labeled with H-3-cholesteryl oleyl ether and with I-131, respectively. In n ine experiments, TG enrichment of rabbit HDL resulted in an 87% average inc rease in HDL TG and a corresponding 31% reduction in HDL CE content. The ca lculated apoA-I and CE fractional catabolic rates associated with TG-rich v ersus fasting: HDL tracers were not significantly different (apoA-I: 0.119 +/- 0.017 vs. 0.107 +/- 0.024 pools per h, P = 0.68; CE: 0.147 +/- 0.014 vs , 0.114 +/- 0.019 pools per h, P = 0.20). In an animal model deficient in H L, TG enrichment of HDL did not alter the rates of HDL apoA-I or selective CE clearance. Further studies are needed to determine whether, in the prese nce of HL, TG enrichment of HDL alters selective HDL CE clearance.