High-density lipoprotein-associated 17β-estradiol fatty acyl ester uptake by Fu5AH hepatoma cells:: Implications of the roles of scavenger receptor class B, type I and the low-density lipoprotein receptor

17 beta-Estradiol (E-2) fatty acyl esters naturally incorporate into high-density lipoprotein (HDL). The objective was to elucidate mechanisms involved in HDL-associated E-2 cellular uptake and to determine the intracellular distribution of E2 and its fatty acyl esters (E-2-FAE) after uptake. [3 H]E2 or [3 H] cholesterol was incubated with human serum for 24 h to allow for fatty acyl esterification. Total-HDL containing [3 H]E2-FAE or [3 H]cholesterol esters was isolated by sequential density ultracentrifugation and then incubated with Fu5AH rat hepatoma cells for various time points. Cellular uptake was determined by intracellular radioactivity as a percentage of total radioactivity. Chemical inhibition of scavenger receptor class B, type I and low-density lipoprotein (LDL) receptor competition assays were performed to determine cellular uptake mechanisms. Compared to HDL- [H-3]cholesterol, cellular uptake of HDL-[H-3]E-2 occurred at an initially rapid rate. SR-BI inhibition resulted in a decrease in HDL-E-2 uptake and LDL impaired this uptake in a concentration-dependent manner. Accordingly, pretreatment of cells with BLT-1 combined with LDL addition significantly attenuated HDL-E2 uptake. HDL-E-2-FAE was hydrolyzed into free E2 With the maximum at 24 h. Fu5AH cells facilitate HDL-E2 uptake by at least SR-B1 and LDL receptor pathways and intracellular hydrolysis of E2-FAE into free E2 ensues. (c) 2007 Elsevier B.V. All rights reserved.