OP-20 - Generation of biliverdin reductase-a gene knockout mice to study the in vivo activities of bilirubin

Abstract

Bilirubin, a product of heme catabolism, inhibits free radical chain reactions and protects against oxidant-induced damage in vitro and ex vivo. However, direct evidence for bilirubin’s antioxidant effect in vivo remains limited. As bilirubin is formed from biliverdin by biliverdin reductase, we generated biliverdin reductase-a gene knockout (Bvra–/–) mice to assess bilirubin as an endogenous antioxidant. Bvra–/– mice are born in expected Mendelian ratios and appear normal. Compared to littermate Bvra+/+ and Bvra+/– mice, bile of Bvra–/– mice is green and their plasma concentration of bilirubin is ~100-fold lower, while plasma biliverdin is increased ~25-fold. Bvra–/– and Bvra+/+ mice have comparable plasma lipid profiles and low-molecular weight antioxidant, i.e., ascorbic acid, -tocopherol and ubiquinol-9. However, Bvra–/– mice have higher concentrations of plasma cholesteryl ester hydroperoxides, and their erythrocyte peroxiredoxin 2 is more oxidized compared to controls. This implies that the absence of bilirubin increases endogenous oxidative stress in the blood. Since plasma concentrations of the antioxidant bilirubin inversely correlate with cardiovascular and metabolic diseases, we are currently using Bvra–/– mice to assess the direct link of bilirubin to these diseases.