Polyunsaturated fatty acids inhibit fatty acid synthase and spot-14-protein gene expression in cultured rat hepatocytes by a peroxidative mechanism

In vivo, polyunsaturated fatty acids (PUFA) inhibit the expression of hepat ic genes related to the lipogenic process such as fatty acid synthase and s pot-14-protein (S14) genes. In vitro studies have suggested that this was a direct transcriptional effect of PUFA. In hepatocytes, the inhibition of t he lipogenic rate by PUFA is not specific, but is linked to a cytotoxic eff ect due to peroxidative mechanisms. We have investigated whether peroxidati on could also explain the inhibitory effect of PUFA on gene expression. Rat hepatocytes were cultured for 24 h with mono-unsaturated or PUFA. PUFA inh ibited the expression of fatty acid synthase and S14 genes, and this inhibi tion was directly related to the number of unsaturations. However, the beta -actin and albumin mRNA concentrations were also affected by the most unsat urated fatty acids, suggesting a non-specific effect of PUFA on gene expres sion. Measurement of lactate dehydrogenase released into the medium indicat ed a cytotoxicity of PUFA. This was associated with their peroxidation as e valuated by the presence of thiobarbituric acid-reactive substances in the culture medium. The addition of high concentrations of antioxidants abolish ed lipid peroxidation and lactate dehydrogenase leakage and completely reve rsed the inhibitory effect of PUFA on gene expression. This suggests (i) th at the results obtained previously in cultured hepatocytes in the presence of low concentrations of antioxidants must be interpretated cautiously and (ii) that in vivo, the inhibitory effect of PUFA on lipogenesis-related gen es could be indirect through hormonal or metabolic changes or that their ef fect on gene expression is somehow linked to peroxidative mechanisms.