DRUG-METABOLIZING ENZYME-ACTIVITIES IN PORCINE URINARY-BLADDER EPITHELIAL-CELL CULTURES (PUBEC)

Drug metabolizing enzyme activities have been determined in cultured p orcine urinary bladder epithelial cells (PUBEC) in order to evaluate t his system as an in vitro model for studies of urinary bladder carcino gens. Activities of several phase I and II enzymes were measured in ce lls cultured for various periods and compared with the activities dete rmined in freshly isolated PUBEC. Prostaglandin H synthase mediated pr oduction of prostaglandin E(2) was found both in freshly isolated and in cultured PUBEC, whereas cytochrome P450 1A1-associated EROD activit y was only detectable in freshly isolated bladder cells. The latter ac tivity was not inducible by benz(a)anthracene or 3-methylcholanthrene in PUBEC cultures. N-acetyltransferase (NAT) activity measured with p- aminobenzoic acid, a diagnostic substrate for human NAT-1, was stable and even higher during the culture period compared to freshly isolated cells. In contrast, isoniazid (a substrate for NAT-2) was not acetyla ted either in fresh or cultured PUBEC. Glutathione S-transferases acti vity determined with 1-chloro-2,4-dinitrobenzene decreased gradually t o 50% after 1 week and to 20% after 4 weeks in culture compared to fre sh cells. A similar decline was also observed for UDP-glucuronyltransf erase activities measured with l-naphthol. In accordance with the repo rted lack of sulfotransferases in pigs, no sulfation of l-naphthol or 2-naphthylamine was detected in PUBEC. Our results show that cultured porcine urinary bladder epithelial cells maintain several enzyme activ ities required for the biotransformation of xenobiotics. In future inv estigations on the mechanism of action of bladder carcinogens PUBEC cu ltures may thus provide a useful in vitro model for this target tissue .