Ws. Baldwin et Ga. Leblanc, IDENTIFICATION OF MULTIPLE STEROID HYDROXYLASES IN DAPHNIA-MAGNA AND THEIR MODULATION BY XENOBIOTICS, Environmental toxicology and chemistry, 13(7), 1994, pp. 1013-1021
Steroid hydroxylase activities were characterized in Daphnia magna and
evaluated for potential use as biomarkers of xenobiotic exposure. Mic
rosomes prepared from Daphnia magna generated a single NADPH-dependent
metabolite of [C-14]testosterone. However, intact daphnids excreted a
t least 10 polar metabolites of [ C]testosterone into the test medium.
Six of these metabolites were identified as 2alpha-, 16beta-, 6beta-,
6alpha-, 7alpha-, and 15alpha-[C-14]hydroxytestosterone. The unidenti
fied metabolites are also presumed to be hydroxylated products of test
osterone, based on their relative migrations during TLC. The inefficie
nt metabolism of [C-14]testosterone during the in vitro microsomal inc
ubations may have been due to the release of P450 inhibitors during mi
crosome preparation. Exposure of daphnids to the P450 modulators pheno
barbital, beta-naphthoflavone, piperonyl butoxide, and malathion diffe
rentially inhibited the steroid hydroxylase activities. Results from t
his study indicate that Daphnia magna expresses several P450 enzymes a
nd that these enzymes are differentially modulated by xenobiotic expos
ure. Steroid hydroxylase activities may serve not only as a biomarker
of toxicant exposure, but also as a predictor of toxicant effects invo
lving perturbations of steroid hormone homeostasis.