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

The inhibitory effect of fumonisin B-1 (FB1) on epidermal growth facto r (EGF)-induced DNA synthesis in primary rat hepatocytes was investiga ted by monitoring the incorporation of [H-3]thymidine in the DNA. A pu lse-labelling technique was adapted to determine the incorporation of the radioactivity in the DNA (S-phase) quantitatively, FB1 inhibits th e EGF-induced DNA synthesis up to 90% when incorporated at concentrati ons of 150 to 300 mu M for a period of 44 h. A continued presence of F B1 is required to exhibit this inhibition as (i) the subsequent remova l of FB1 resulted in a reversal of the effect, (ii) a higher stimulato ry response in EGF-treated hepatocytes was found when the exposure per iod of hepatocytes to FB1 was reduced, and (iii) pretreatment of hepat ocytes with FB1 only slightly reduced (not significantly) DNA synthesi s induced by EGF. Whilst the growth inhibitory effect of FB1 was not a ssociated with a cytotoxic effect, binding studies using [I-125]EGF in dicated that the growth factor-receptor interaction was not altered. N o relationship was found between the disruption of the sphingolipid bi osynthesis by FB1 and (i) the mitoinhibitory effect on the EGF respons e and (ii) the cytotoxicity of FB1 in primary hepatocytes.