Unconjugated bilirubin modulates nitric oxide production via iNOS regulation.

To induce the in vitro endothelial dysfunction model, H5V cells were treated with tumor necrosis factor alpha (TNF alpha) and with unconjugated bilirubin (UCB) at two different physiological concentrations. The TNF alpha-induced reduction of nitric oxide (NO) concentration was reversed by UCB. Endothelial NO synthase (eNOS) gene expression was not influenced by treatments while inducible NO synthase (iNOS) expression was increased at 24 h. Co-treatment of H5V cells with pyrrolidine dithiocarbamate, TNF alpha (20 ng/mL) and UCB (Bf 15 or 30 nM) for 2 h caused a significant reduction of iNOS gene expression. We conclude that at physiological concentrations UCB prevents endothelial dysfunction by modulating NO concentration probably through inhibition of NF-kappa B.