High-density lipoprotein-associated alpha-tocopherol uptake by human retinal pigment epithelial cells (ARPE-19 Cells): the irrelevance of scavenger receptor class B, type I.

The purpose of this study was to determine the high-density lipoprotein (HDL)-associated alpha-tocopherol (alpha-tocopherol-HDL) transport and clarify the contribution of scavenger receptor class B, type I (SR-BI) to the uptake in the human retinal pigment epithelial cell line (ARPE-19 cells). [(3)H]alpha-Tocopherol-HDL uptake into ARPE-19 cells seeded onto a transwell from both the apical (apical-to-cell) and basal compartment (basal-to-cell) exhibited a time-dependent increase for 90 min and there was a reduction at 4 degrees C. These results indicate the involvement of carrier-mediated process in alpha-tocopherol-HDL uptake in ARPE-19 cells. Immunoblot analysis revealed that SR-BI protein was expressed in ARPE-19 cells. However, the uptake of [(3)H]alpha-tocopherol from the apical or basal compartment was hardly inhibited by block lipid transport-1 (BLT-1), a specific inhibitor of the SR-BI-mediated lipid transfer. In conclusion, ARPE-19 cells have a carrier-mediated transport mechanism of [(3)H]alpha-tocopherol-HDL regardless of any SR-BI-mediated process.