The effect of serum on low density lipoprotein metabolism of human monocyte-derived macrophages.

Macrophages oxidatively modify low density lipoprotein (LDL). These cells then recognize and take up oxidized LDL (OxLDL) via the scavenger receptor. In the present study, we examined the effect of lipoprotein depleted serum (LPDS) on the oxidative modification of LDL and its uptake and degradation by human monocyte-derived macrophages. LPDS inhibited LDL oxidation in a concentration-dependent manner and the complete inhibition was observed in the concentration from 2.5 to 10.0%. In the presence of 5% of LPDS, cell-associated 125I-LDL was reduced by 70%, compared with that in the absence of LPDS. In contrast, 125I-LDL degradation increased in the presence of LPDS. The ratio of degradation products to cell-associated radioactivity in the presence of LPDS was five-fold greater than that in the absence of LPDS. In the presence of LPDS, unlabeled LDL competed for about 50% of cellular uptake and degradation of 125I-LDL. In the absence of LPDS, however, unlabeled LDL competed for only 20% of uptake and only 30% of degradation of 125I-LDL. Unlabeled OxLDL competed for about 80% of uptake and degradation in the absence of LPDS. These results suggest that LPDS inhibited the production of OxLDL which was taken up by macrophages via the pathway for the OxLDL.