Antioxidant properties of blirubin in the model organism, Caenorhabditis elegans.

We evaluated the effects of bilirubin on the nematode, C. elegans, specifically addressing the ability of bilirubin to induce oxidative stress and alter glutathione (GSH) content as measures of injury. Bilirubin exposure caused a doubling of the spectrophotometric absorption at 440 nm in wild-type C. elegans irrespective of the bilirubin concentration used, suggesting that bilirubin is readily taken up by the worms. No changes were noted in growth, phenotype or reproductive cycle at any bilirubin concentration at 24, 48, and 72 hrs. The oxidative stress inducible green fluorescent protein (GFP) expression in the gst-4::GFP strain was decreased upon exposure to bilirubin at a concentration of 0.5 mM at 24, 48 and 72 hrs. This trend was not statistically significant at 24 or 72 hrs, but did reach statistical significance at 48 hours (p < 0.05). Glutathione (GSH) content in the gst-4::GFP strain showed a significant increase as early as 20 hours post treatment with 0.5 mM bilirubin (p < 0.05). Microarray analysis showed that in bilirubin-exposed worms, 27 genes were up-regulated, and 90 genes were down-regulated (by >1.3 fold vs. controls). The transcription factor asc-1 was induced, whereas genes involved in transcription, trafficking and mitochondrial function were down-regulated. Our findings corroborate earlier findings of bilirubin's ability to act as an antioxidant, most likely by reducing the metabolic requirement in C. elegans.