Interaction of high and low density lipoproteins on glycosaminoglycan secretion by human vascular smooth muscle cells and fibroblasts.

Low density lipoprotein (LDL) increased secretion of glycosaminoglycans (GAG) and the cell cholesterol content of proliferating fibroblasts and smooth muscle cells in culture; with increasing cell density the GAG effect decreased, but the cholesterol effect did not. High density lipoprotein (HDL, d greater than 1.063) decreased GAG secretion by slowly proliferating cells; when cells were actively proliferating, HDL alone did not affect GAG secretion, but it inhibited the increase caused by LDL. Thus HDL appeared to influence GAG secretion by two separate mechanisms, an inhibition which was overcome by rapid proliferation and an anti-LDL effect. HDL2 (d = 1.063-1.100) partially reproduced the latter effect. In addition, HDL, HDL2, and HDL3 increased cell cholesterol; the ability of LDL to increase cholesterol was correspondingly reduced in the presence of HDL and its subfractions, suggesting that they act by common mechanisms.