Enhancement by bilirubin of DNA damage induced in human cells exposed to phototherapy light

Normal human fibroblasts were exposed to light from three types of lamps commonly used for phototherapy treatment of neonatal hyperbilirubinemia. These irradiations were performed in either the presence or absence of exogenously added bilirubin. Using the alkaline elution assay, we found that each phototherapy lamp induced strand breaks in the DNA of exposed cells. However, the cross sections for DNA strand breakage were increased 30-40-fold when cells were irradiated in the presence of 100 μg/ml bilirubin. Hence, bilirubin acts as a photosensitizing agent enhancing the level of DNA damage in cells exposed to phototherapy light.