Cellular antioxidant activity of bilirubin in the human endothelial cell line EA.hy 926 is mediated by bilitranslocase

Background Oxidative stress plays an important role in the pathogenesis of cardiovascular degenerative diseases. Bilirubin is known to be a potent endogenous antioxidant, both in in vitro and in vivo. The latter can be ascribed to an efficient amplification cycle whereby bilirubin, acting as antioxidant, is itself oxidized to biliverdin and then recycled back to bilirubin by NADPH-dependent biliverdin reductase. Bilitranslocase, a bilirubin-specific membrane carrier that mediates cellular uptake of bilirubin, has recently been found in the vascular endothelium. However, the levels of albumin-free bilirubin in plasma and tissues are only 10 to 50 nM. Therefore, the objective of this study was to elucidate the antioxidant activity of low concentrations of bilirubin and the involvement of bilitranslocase-mediated plasma membrane transport in human endothelial cells.