Cytotoxicity of bilirubin for human fibroblasts and rat astrocytes in culture. Effect of the ratio of bilirubin to serum albumin.

The sensitivity of rat brain astrocytes and human fibroblasts in culture to unconjugated bilirubin was investigated. Medium containing 6 mumol/1 bilirubin and increasing concentrations of human serum albumin giving ratios of 0.5-1.5 that resulted in an increase of the free bilirubin concentrations. The LDH activity in the culture medium was an index of cytolysis and the MTT assay was used as an index of mitochondrial impairment. The ratios producing half-maximum cell lysis after 24, 48, and 72 h, were 1.1, 0.9 and 0.85, for astrocytes, and 1.2, 0.75 and 0.75, for fibroblasts. Mitochondrial activity decreased after 24 h for ratio = 0.7 and partly recovered at 48 h. Mitochondrial activity was more impaired in fibroblasts than in astrocytes above ratio = 0.7. The cytotoxic effects were linked to the free bilirubin concentration. We conclude that astrocytes are less sensitive to bilirubin cytotoxic effects than are fibroblasts.