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

Abstract

17β-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 E 2 and its fatty acyl esters (E 2-FAE) after uptake. [ 3H]E 2 or [ 3H] cholesterol was incubated with human serum for 24 h to allow for fatty acyl esterification. Total-HDL containing [ 3H]E 2-FAE or [ 3H]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-[ 3H]cholesterol, cellular uptake of HDL-[ 3H]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-E 2 uptake. HDL-E 2-FAE was hydrolyzed into free E 2 with the maximum at 24 h. Fu5AH cells facilitate HDL-E 2 uptake by at least SR-BI and LDL receptor pathways and intracellular hydrolysis of E 2-FAE into free E 2 ensues.