The effects of cadmium (Cd) on the fatty acid composition and Delta 9
desaturation activity were studied in hepatocytes which had been cultu
red in serum-free medium. The aim of this study was to determine wheth
er 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, increase
s 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 ind
uced. By contrast, essential fatty acids such as linoleic acid (18:2)
and arachidonic acid (20:4) decreased. These changes were similar to t
hose seen in the livers of essential fatty acid (EFA)-deficient rats.
When hepatocytes were cultured in the presence of CdCl2, the changes i
n the fatty acid composition were suppressed. The effect of CdCl2 was
concentration-dependent. The rate of the conversion of 18:0 to 18:1, w
hich 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 catalyze
d by Delta 6 desaturase, was slightly increased. Cd did not inhibit li
ver microsomal Delta 9 desaturase activity in vitro. We concluded that
Cd suppressed the induction of Delta 9 desaturase in cultured hepatoc
ytes. These phenomena can explain the selective inhibition of Delta 9
desaturase in the livers of Cd-treated rats.