The long range goal of this project is to study the oxidation of chemicals to toxic metabolites by prostaglandin synthetase (PHS) and to demonstrate the significance of this system in chemically induced toxicity or carcinogenesis. We have shown that PHS converts both polycyclic hydrocarbons and aromatic amines to mutagens as measured by bacterial tester systems. Other in vitro studies have demonstrated the formation of electrophilic metabolites that react with macromolecules. Benzo(a)pyrene-7,8-diol is metabolized to an anti-diol epoxide by PHS. We have compared PHS and NADPH-dependent metabolism in mouse skin epidermal cells. The aromatic amine carcinogen 2-aminofluorene (2-AF) is metabolized to free radical intermediates by PHS. The stable end products are azo-, nitro-fluorene and 2-aminodiffluorenylamine. We have studied the formation of phenolic 2-AF adducts and obtained evidence that 2-AF is oxidized to several free radicals or free radical derived products (nitrenium ion). These radicals may not only be responsible for covalent binding to DNA but also may indeed be the proximate carcinogenic and mutagenic agents. We have also studied the formation of 2-AF DNA adducts catalyzed by PHS. Several unique 2-AF-DNA adducts were detected. We have also shown that 2-napthylamine is oxidized to unique metabolites by PHS and demonstrated a free radical mechanism for the formation of styrene-GSH adducts. Our studies indicate that PHS activates chemicals to ultimate carcinogenic metabolites which may be of importance in the initiation of tumors in extrahepatic tissue. Thus PHS is an enzyme system that, like cytochrome P-450, is important in the metabolism of xenobiotics.
