Absence of the biliverdin reductase-a gene is associated with increased endogenous oxidative stress

Abstract Bilirubin, a byproduct of heme catabolism, has been shown to be an effective lipid-soluble antioxidant in vitro . Bilirubin is able to inhibit free radical chain reactions and protects against oxidant-induced damage in vitro and ex vivo . However, direct evidence for bilirubin's antioxidant effects in vivo remains limited. As bilirubin is formed from biliverdin by biliverdin reductase, we generated global biliverdin reductase-a gene knockout ( Bvra –/– ) mice to assess the contribution of bilirubin as an endogenous antioxidant. Bvra –/– mice appear normal and are born at the expected Mendelian ratio from Bvra +/– x Bvra +/– matings. Compared with corresponding littermate Bvra +/+ and Bvra +/– animals, Bvra –/– mice have green gall bladders and their plasma concentrations of biliverdin and bilirubin are approximately 25-fold higher and 100-fold lower, respectively. Naive Bvra –/– and Bvra +/+ mice have comparable plasma lipid profiles and low-molecular weight antioxidants, i.e. , ascorbic acid, α-tocopherol and ubiquinol-9. Compared with wild-type littermates, however, plasma from Bvra –/– mice contains higher concentrations of cholesteryl ester hydroperoxides (CE-OOH), and their peroxiredoxin 2 (Prx2) in erythrocytes is more oxidized as assessed by the extent of Prx2 dimerization. These data show that Bvra –/– mice experience higher oxidative stress in blood, implying that plasma bilirubin attenuates endogenous oxidative stress.