Physiologically Relevant Levels of Biliverdin Do Not Significantly Oppose Oxidative Damage in Plasma In Vitro

AbstractAntioxidants have important physiological roles in limiting the amount of oxidative damage that an organism experiences. One putative antioxidant is biliverdin, a pigment that is most commonly associated with the blue or green colors of avian eggshells. However, despite claims that biliverdin functions as an antioxidant, neither the typical physiological concentrations of biliverdin in most species nor the ability of biliverdin to oppose oxidative damage at these concentrations has been examined. Therefore, we quantified biliverdin in the plasma of six bird species and found that they circulated levels of biliverdin between 0.02 and 0.5 μM. We then used a pool of plasma from northern bobwhite quail (Colinus virginianus) and spiked it with one of seven different concentrations of biliverdin, creating plasma-based solutions ranging from 0.09 to 231 μM biliverdin. We then compared each solution's ability to oppose oxidative damage in response to hydrogen peroxide relative to a control addition of water. We found that hydrogen peroxide consistently induced moderate amounts of oxidative damage (quantified as reactive oxygen metabolites) but that no concentration of biliverdin ameliorated this damage. However, biliverdin and hydrogen peroxide interacted, as the amount of biliverdin in hydrogen peroxide-treated samples was reduced to approximately zero, unless the initial concentration was over 100 μM biliverdin. These preliminary findings based on in vitro work indicate that while biliverdin may have important links to metabolism and immune function, at physiologically relevant concentrations it does not detectably oppose hydrogen peroxide-induced oxidative damage in plasma.