Cadmium suppresses delta 9 desaturase activity in rat hepatocytes.

The effects of cadmium (Cd) on the fatty acid composition and delta 9 desaturation activity were studied in hepatocytes which had been cultured in serum-free medium. The aim of this study was to determine whether the inhibition of delta 9 desaturase seen in Cd-treated rat liver (Kudo et al. (1991) Toxicology, 68, 133-142) is the direct effect of Cd or not. When hepatocytes were cultured in serum-free medium, increases in the proportions of monounsaturated fatty acids such as oleic acid (18:1) were observed in the phospholipid (PL) and triacylglycerol (TG) fractions of hepatocytes, suggesting that delta 9 desaturase was induced. By contrast, essential fatty acids such as linoleic acid (18:2) and arachidonic acid (20:4) decreased. These changes were similar to those seen in the livers of essential fatty acid (EFA)-deficient rats. When hepatocytes were cultured in the presence of CdCl2, the changes in the fatty acid composition were suppressed. The effect of CdCl2 was concentration-dependent. The rate of the conversion of 18:0 to 18:1, which is catalyzed by delta 9 desaturase, was reduced by treatment with Cd, whereas the rate of conversion of 18:2 to 20:4, which is catalyzed by delta 6 desaturase, was slightly increased. Cd did not inhibit liver microsomal delta 9 desaturase activity in vitro. We concluded that Cd suppressed the induction of delta 9 desaturase in cultured hepatocytes. These phenomena can explain the selective inhibition of delta 9 desaturase in the livers of Cd-treated rats.