Cytotoxicity of bilirubin photoproducts

Human cells in culture were exposed to light in the presence of bilirubin (BR). The cells were killed and at lower doses showed a decreased multiplication rate. No release of lactate dehydrogenase was observed after irradiation of the cells. Solutions containing BR become toxic upon irradiation with light, and this is probably responsible for a large part of the cytotoxicity induced by exposure of cells to BR and light. The cytotoxic products are peroxides and are sufficiently long-lived to cause toxicity for several hours after irradiation.