1510 BILIRUBIN TOXICITY OF NEURAL CELLS IN CULTURE

Abstract

Bilirubin (B) toxicity was investigated in 2 neural cell lines NBR10A and N115 using a quantitative dye assay (MTT) as a measure of cell viability and ³H-Thymidine incorporation as a measure of DNA synthesis. The cells are adapted to grow in a protein free medium. Bilirubin concentration varying between 0.3 and 0.003 mM at bilirubin/albumin molar ratio (B/A) of 0.5 to 1.5 are introduced to the media and incubated for 2 and 24 hours. MTT (0.5 mg/ml) and/or ³H-Thymidine (1 μCi/dish) are added and incubated for a further 2 hours. Short exposures to B even up to a B/A of 1.5 showed no evidence of toxicity using both assays. After a 24 hour exposure to B, a decrease in cell viability and ³H-Thymidine incorporation was detected at B/A of 0.8 when B was 0.1 mM or higher, whereas at lower B at this molar ratio showed no deleterous effect. At B/A of 1.5 and B of 0.3 mM the decrease in viability was 90% and only 20% when B was 0.025 mM for NBR10A. N115 followed a similar but less dramatic response. The concentration effect is more evident in the ³H-Thymidine studies. At B/A of 2.5 and B of 0.075 mM or higher, there were both cell kill (decrease in DNA levels) and inhibition of ³H incorporation (decrease in specific activity). When B is reduced to 0.03 mM, even at B/A of 1.5 there was little or no cell death (no change in DNA levels), but decrease in DNA synthesis (42% decrease in specific activity) still existed. Results showed viability and function of these neural cell lines is dependent not only on B/A but also on absolute concentrations of B, and time of exposure.

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