title: Interaction of bilirubin and biliverdin with reactive nitrogen species.
abstract: Bilirubin (BR) and biliverdin (BV), two metabolites produced during haem degradation by haem oxygenase, possess strong antioxidant activities toward peroxyl radical, hydroxyl radical and hydrogen peroxide. Considering the importance attributed to nitric oxide (NO) and its congeners in the control of physiological and pathophysiological processes, we examined the interaction of BR and BV with NO and NO-related species in vitro. Exposure of BR and BV to agents that release NO or nitroxyl resulted in a concentration- and time-dependent loss of BR and BV, as assessed by high performance liquid chromatography. Peroxynitrite, a strong oxidant derived from the reaction of NO with superoxide anion, also showed high reactivity toward BR and BV. The extent of BR and BV consumption largely depended on the NO species being analysed and on the half-lives of the pharmacological compounds considered. Of major importance, BR and BV decomposition occurred also in the presence of pure NO under anaerobic conditions, confirming the ability of bile pigments to scavenge the gaseous free radical. Increasing concentrations of thiols prevented BR consumption by nitroxyl, indicating that bile pigments and thiol groups can compete and/or synergise the cellular defence against NO-related species. In view of the high inducibility of haem oxygenase-1 by NO-releasing agents in different cell types, the present findings highlight novel anti-nitrosative characteristics of BR and BV suggesting a potential function for bile pigments against the damaging effects of uncontrolled NO production.
authors.affiliation: Vascular Biology Unit, Department of Surgical Research, Northwick Park Institute for Medical Research, Watford Road, Y Block, Middlesex HA1 3UJ, Harrow, UK.
authors.forename: Harparkash
authors.initials: H
authors.lastname: Kaur
authors.forename: Martin N
authors.initials: MN
authors.lastname: Hughes
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Green
authors.forename: Patrick
authors.initials: P
authors.lastname: Naughton
authors.forename: Roberta
authors.initials: R
authors.lastname: Foresti
authors.forename: Roberto
authors.initials: R
authors.lastname: Motterlini
mesh_terms: D000693:Anaerobiosis; D001663:Bilirubin / Q000378:metabolism*; D001664:Biliverdine / Q000378:metabolism*; D016166:Free Radical Scavengers / Q000378:metabolism*; D007700:Kinetics; D009569:Nitric Oxide / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D009589:Nitrogen Oxides / Q000378:metabolism; D030421:Peroxynitrous Acid / Q000378:metabolism; D026361:Reactive Nitrogen Species / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000494:pharmacology
chemical_list: D016166:Free Radical Scavengers; D009573:Nitrites; D009589:Nitrogen Oxides; D026361:Reactive Nitrogen Species; D013438:Sulfhydryl Compounds; D030421:Peroxynitrous Acid; C021229:oxyhyponitrite; D009569:Nitric Oxide; C039900:nitroxyl; D001664:Biliverdine; D001663:Bilirubin