Effect of low-density lipoprotein on the incorporation of benzo(a)pyrene by cultured cells.

Benzo(a)pyrene added to human plasma in vitro associated with the plasma lipoproteins, especially the low-density fraction. The influence of plasma low-density lipoprotein on cellular uptake of benzo(a)pyrene was studied using WI-38, a human embryonic lung fibroblast line, and GM 1915, a skin fibroblast line derived from a patient with homozygous familial hypercholesterolemia. The WI-38 cells were low-density-lipoprotein receptor positive, and the familial hypercholesterolemia cells were receptor negative by standard binding studies with 125I-labeled low-density lipoprotein. Following 2 hr of incubation at 37 or 4 degrees, cell association of benzo(a)pyrene was determined with benzo(a)pyrene bound to lipoprotein or added at the same concentration to serum-free medium or medium containing delipidated serum. Uptake from delipidated or serum-free medium by both cell lines was linear with concentration, while incorporation of benzo(a)pyrene bound to low-density lipoprotein was much less and nonlinear at higher concentrations of lipoprotein. While low-density lipoprotein apparently influenced the availability of benzo(a)pyrene to the cell, no differences were noted in the incorporation of benzo(a)pyrene by WI-38 and familial hypercholesterolemia cells. Thus, benzo(a)pyrene entered the cells from low-density lipoproteins despite the absence of specific receptors, apparently by a rapid redistribution between the lipoprotein and cell membrane.