MITOINHIBITORY EFFECT OF FUMONISIN B-1 ON RAT HEPATOCYTES IN PRIMARY CULTURE

The inhibitory effect of fumonisin B-1 (FB1) on epidermal growth factor (EGF)-induced DNA synthesis in primary rat hepatocytes was investigated by monitoring the incorporation of [H-3]thymidine in the DNA. A pulse-labelling technique was adapted to determine the incorporation of the radioactivity in the DNA (S-phase) quantitatively, FB1 inhibits the EGF-induced DNA synthesis up to 90% when incorporated at concentrations of 150 to 300 mu M for a period of 44 h. A continued presence of FB1 is required to exhibit this inhibition as (i) the subsequent removal of FB1 resulted in a reversal of the effect, (ii) a higher stimulatory response in EGF-treated hepatocytes was found when the exposure period of hepatocytes to FB1 was reduced, and (iii) pretreatment of hepatocytes with FB1 only slightly reduced (not significantly) DNA synthesis induced by EGF. Whilst the growth inhibitory effect of FB1 was not associated with a cytotoxic effect, binding studies using [I-125]EGF indicated that the growth factor-receptor interaction was not altered. No relationship was found between the disruption of the sphingolipid biosynthesis by FB1 and (i) the mitoinhibitory effect on the EGF response and (ii) the cytotoxicity of FB1 in primary hepatocytes.