Effect of albumin binding on bilirubin conjugation and toxicity in cell culture of a clonal strain of rat hepatoma cells.

A clonal strain of rat hepatoma cells (MH₁C₁) known to take up and conjugate bilirubin was incubated in media containing bilirubin and albumin in different molar ratios at a constant bilirubin concentration. The highest rate of bilirubin conjugation was found at a molar ratio of 1/1. Excess bilirubin markedly reduced both the conjugation of bilirubin and the incorporation of [14C]alanine, indicating a toxic effect on the cells. Excess albumin also depressed the formation of bilirubin conjugates, but incorporation of [14C]alanine proceeded at a normal rate, indicating that the reduced conjugation is probably due to stronger binding of bilirubin to albumin and reduced cellular uptake of bilirubin. Bilirubin bound to albumin at a molar ratio of 1/1 had no toxic effects on the cells as judged by cell morphology and conjugation capacity, even at a total bilirubin concentration as high as 680 μmol/l.