title: Bilirubin and S-nitrosothiols interaction: evidence for a possible role of bilirubin as a scavenger of nitric oxide.
abstract: Bilirubin (BR), the final product of heme catabolism, plays a crucial role in the defense against reactive oxygen species in various cell types. In this study, we addressed the hypothesis that BR can act as a physiological scavenger of nitric oxide (NO), a gaseous mediator involved in many cellular functions and able to trigger the formation of reactive nitrogen species with pro-oxidant activity. We found that S-nitrosocysteine (SNOC) and S-nitrosoglutathione (GSNO), which have a half-life of 0.52+/-0.07 hr and 38+/-5 hr and release NO at a constant rate of 1.42+/-0.2 hr(-1) and 0.018+/-0.002 hr(-1), respectively, were able to decrease BR half-life in a concentration-dependent manner under physiological conditions. This effect appears to be dependent on NO formation as L-cysteine and GSH did not affect BR consumption and nitrite was four to five times less efficient than SNOC in reducing BR half-life. Oxyhemoglobin, a well-known scavenger of NO, protected BR from SNOC-mediated degradation. In addition, the reaction between SNOC/GSNO and BR modified the absorption spectrum of the bile pigment showing a gradual increase in the absorbance at 316 nm. This change in the BR spectrum indicates that the bile pigment could be a target for N-nitrosation reactions, since it resembles the modifications occurred when other molecules such as di-peptides and uric acid are nitrosated. Taken together, these data suggest that BR should not be considered only as an endogenous antioxidant but also as a molecule with the potential ability to counteract intracellular nitrosative stress reactions.
authors.affiliation: Institute of Pharmacology, Catholic University School of Medicine, Largo Francesco Vito 1, 00168 Rome, Italy. cmancuso@rm.unicatt.it
authors.forename: Cesare
authors.initials: C
authors.lastname: Mancuso
authors.forename: Alessia
authors.initials: A
authors.lastname: Bonsignore
authors.forename: Enrico
authors.initials: E
authors.lastname: Di Stasio
authors.forename: Alvaro
authors.initials: A
authors.lastname: Mordente
authors.forename: Roberto
authors.initials: R
authors.lastname: Motterlini
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001663:Bilirubin / Q000378:metabolism*; D004347:Drug Interactions; D009569:Nitric Oxide / Q000378:metabolism*; D015538:Nitrosation; D026361:Reactive Nitrogen Species / Q000378:metabolism*; D026403:S-Nitrosothiols / Q000378:metabolism*
chemical_list: D026361:Reactive Nitrogen Species; D026403:S-Nitrosothiols; D009569:Nitric Oxide; D001663:Bilirubin