Apolipoprotein C-I reduces cholesteryl esters selective uptake from LDL and HDL by binding to HepG2 cells and lipoproteins

Plasma cholesterol from low- and high-density lipoproteins (LDL and HDL) are cleared from the circulation by specific receptors that either totally degrade lipoproteins as the LDL receptor or selectively take up their cholesteryl esters (CE) like the scavenger receptor class B type I (SR-BI). The aim of the present study was to define the effect of apoC-I on the uptake of LDL and HDL3 by HepG2 cells. In experiments conducted with exogenously added purified apoC-I, no significant effect was observed on lipoprotein–protein association and degradation; however, LDL- and HDL3-CE selective uptake was significantly reduced in a dose-dependent manner. This study also shows that apoC-I has the ability to associate with HepG2 cells and with LDL and HDL3. Moreover, pre-incubation of HepG2 cells with apoC-I reduces HDL3-CE selective uptake and pre-incubation of LDL and HDL3 with apoC-I decreases their CE selective uptake by HepG2 cells. Thus, apoC-I can accomplish its inhibitory effect on SR-BI activity by either binding to SR-BI or lipoproteins. We conclude that by reducing hepatic lipoprotein-CE selective uptake, apoC-I has an atherogenic character.