Human serum albumin and its structural variants mediate cholesterol efflux from cultured endothelial cells

Abstract

In the present study, we used the human EA.hy926 endothelial cell line as the model system to investigate the effect of human serum albumin (HSA) and its structural variants on cholesterol efflux. Initial studies showed that HSA promoted cholesterol efflux in a dose- and time-dependent manner, reaching a plateau at 10 mg/ml at 90 min. As a control, gelatin displayed no significant effect on efflux, while HSA was significantly more efficient than ovalbumin and bovine serum albumin (BSA) in promoting cholesterol efflux. Equal molar concentrations of HSA and apolipoprotein A-I (apoA-I) showed that apoA-I had considerably higher efficiency in efflux. However, the prevailing high plasma concentrations of HSA may compensate for its lower efflux rate compared to apoA-I. To characterize the mechanism of HSA-mediated cholesterol efflux, we studied the effects of cAMP and temperature on efflux using both EA.hy926 endothelial cells and murine RAW 264.7 macrophages. We found that HSA-mediated efflux occurred via a cAMP-independent and relatively temperature-insensitive pathway. We next examined the nature of HSA-cholesterol interaction by comparing the effects of various HSA mutants to wild-type HSA on cholesterol efflux. We found specific interactions between subdomains 2A and 3A and cholesterol, as indicated by the changes in the efflux rate of various HSA mutants. In conclusion, our study provides evidence for the role of HSA in cholesterol efflux, and shows that the substitution of specific amino acid residues in subdomains of 2A and 3A may be important structural determinants in its ability to bind to cholesterol and participate in cholesterol efflux.

Paradoxical Association of Enhanced Cholesterol Efflux With Increased Incident Cardiovascular Risks

“…It is also interesting to note that other investigators recently noted recombi-nant human albumin can serve as cholesterol acceptor and showed that several site-specific mutations can significantly reduce the cholesterol acceptor activity of the protein. 14 It is important to note that we observed different sources of human serum albumin had significantly different cholesterol acceptor activity, suggesting that a conformationally intact albumin is needed for full cholesterol acceptor activity.…”

Albumin and mammalian cell culture: implications for biotechnology applications

“…The function of serum albumin in cholesterol transfer between fibroblast cells and lipoproteins is well studied, as it is for endothelial cells, due to its central role in coronary vascular disease and atherosclerosis (Zhao and Marcel 1996; Ha et al 2003). This is an important function for albumin in many cell types and particularly for cholesterol dependent cell lines such as NS0 myeloma and derivative hybridoma cells.…”

Preferential incorporation of shorter and less unsaturated acyl phospholipids into high density lipoprotein-like particles in the ABCA1- and ABCA7-mediated biogenesis with apoA-I

“…HDL-like particle is assembled as a disk particle composed of phospholipid and unesterified cholesterol by ABCA1-helical apolipoprotein interaction Jayaraman et al, 2011). However, cholesterol by itself does not form lipid-protein complex particles with apolipoprotein, though it may directly bind to some proteins such as serum albumin (Ha et al, 2003;Peng et al, 2008). To the contrary, physicochemical assembly of the HDL-like particles, similarly to those produced by the ABCA1-mediated cell-apolipoprotein interaction may not essentially require cholesterol (Fukuda et al, 2010;Jayaraman et al, 2010).…”