Gisela H. Degen

The major metabolite of aflatoxin B1 in the rat is a glutathione conjugate

[14C]aflatoxin B1 (AFB1) was injected i.p. into female Wistar rats. Half of the dose was eliminated into the bile mostly as polar non-extractable metabolites. Among these a glutathione conjugate was the main component. The same conjugate was formed when rat liver postmitochondrial supernatant was incubated with AFB1 and [3H]glutathione. The conjugate was purified by ion exchange chromatography, gel-filtration and thin layer chromatography (TLC). It was tentatively identified as 2,3-dihydro-2-(S-glutathionyl)-3-hydroxy aflatoxin B1 (AFB1-GSH-conjugate). This structure was derived mainly from amino acid analysis, ultraviolet spectra and the enzymatic requirements for its formation in in vitro experiments. In the rat this detoxification product of the potentially ultimate reactive AFB1-epoxide constitutes about 10% of the administered dose and thus underlines the quantitative importance of this activating pathway.

Cooxidation of steroidal and non-steroidal estrogens by purified prostaglandin synthase results in a stimulation of prostaglandin formation

Estrone (E1), estradiol (E2), the catechol estrogens 2-OHE1 and 2-OHE2, and diethylstilbestrol (DES) were incubated with purified prostaglandin synthase (PHS) in vitro in the presence of arachidonic acid and their PHS-catalyzed cooxidation was determined. 2-OHE1, 2-OHE2, and DES were extensively metabolized by PHS peroxidase activity, E1 and E2 to a lesser extent. The cooxidation of the estrogens is accompanied by an increased prostaglandin formation and an increase in cyclooxygenase activity in vitro; progesterone and nylestriol are without effect. Prostaglandins have been proposed to play a role in events related to early estrogen action in tissues such as the uterus. The cooxidation of estrogens and their metabolites by prostaglandin hydroperoxidase might represent one type of interaction between the hormones and the arachidonic acid cascade that could lead to changes in prostaglandins.

Non-estrogenic metabolites of diethylstilbestrol produced by prostaglandin synthase mediated metabolism

Incubation of trans-diethylstilbestrol (E-DES) with prostaglandin synthase (PGS) in vitro leads to the formation of the metabolites cis, cis-dienestrol (Z,Z-DIES) and cis-diethylstilbestrol (Z-DES) which have considerably decreased estrogenic activity compared to their parent compound. Incubations of (14C)-E-DES with PGS in the presence of arachidonic acid (AA) predominantly catalyze formation of the oxidative metabolite Z,Z-DIES, accompanied by the formation of protein bound radioactivity. Inhibition of peroxidative metabolism through addition of indomethacin or absence of AA favors isomerization of E-DES to Z-DES without concomitant formation of protein bound radioactivity. Isomerization is inhibited by phenidone (1-phenyl-3-pyrazolidone). Since PGS activity is present in uterine tissue, these pathways may play a role in the metabolism of DES in its target tissue.