Clearance of cationized LDL cholesterol from a muscle depot is not enhanced in human apolipoprotein A-IV transgenic mice.

Abstract

Human apolipoprotein A-IV (apoA-IV) transgenic mice fed an atherogenic diet were shown previously to develop less atherosclerosis than control mice. The question arose whether the antiatherogenic effect of human apoA-IV is due to enhancement of reverse cholesterol transport despite no increase in plasma high-density lipoprotein (HDL) cholesterol. We studied male and female mice overexpressing human apoA-IV and their wild-type (WT) controls, all of which were fed a chow diet. Plasma total and HDL cholesterol and total phospholipids were not increased in the transgenic mice, and regression analysis showed no correlation between plasma levels of cholesterol or phospholipids and plasma human apoA-IV. To study reverse cholesterol transport in vivo, the disappearance of cholesterol from a depot of [(3)H]cholesterol-labeled cationized low-density lipoprotein injected into the rectus femoris muscle was compared in high expressers of human apoA-IV and WT controls. The loss of radioactivity and the diminution of the exogenous cholesterol mass were determined on days 8 and 12 after injection. No enhanced loss of radioactivity or cholesterol mass was seen in the transgenic mice even at levels of 2500 mg/dL of human apoA-IV. In some instances, there was even slower loss of exogenous cholesterol (radioactivity and mass) in the transgenic mice. Although [(3)H]cholesterol efflux from cultured human skin fibroblasts and mouse peritoneal macrophages was only approximately 30% higher in the presence of sera from high expressers of human apoA-IV, addition of phosphatidylcholine liposomes enhanced the efflux in both groups to the same extent. Another paradoxical finding was that the cholesterol esterification rate in plasma was 34% to 36% lower in human apoA-IV mice than in WT controls. In conclusion, even though apoA-IV was found previously to be atheroprotective under hypercholesterolemic conditions, high plasma levels of human apoA-IV did not enhance cholesterol mobilization in vivo in normocholesterolemic mice.