Fig 1.

Bilirubin is a suprastoichiometric cytoprotectant against oxidative stress (a) and BVRA can redox cycle the tetrapyrrole in vitro (b–d). (a) Viability of cultured HeLa cells was measured by MTT assay 8 h after the indicated treatment. (b) Bilirubin (Porphyrin Products) is oxidized to biliverdin by peroxyl radicals. The reaction was monitored by A₄₅₃ for bilirubin (□) or A₆₅₀ for biliverdin (•). (c) Bilirubin IXα is oxidized specifically to biliverdin IXα. An aliquot of the reaction shown in b was taken at 10 min and analyzed by HPLC as described (14). (d) BVRA regenerates bilirubin, slowing the consumption of bilirubin by ROS. The reaction was monitored at A₄₅₃ with (□) or without (•) 1 μg/ml recombinant BVRA. *, P < 0.005, using an unpaired Student's t test.