PHASE-I AND PHASE-II BIOTRANSFORMATIONS IN LIVING CACO 2 CELLS CULTIVATED UNDER SERUM-FREE CONDITIONS - SELECTIVE APICAL EXCRETION OF REACTION-PRODUCTS

CaCo 2 cells, cultivated in a synthetic, serum-free nutritive medium o n poly (ethylene terephthalate) membranes, form a confluent monolayer of differentiated cells, with the apical and basolateral poles exposed to the upper and lower compartments, respectively, of bicameral cultu re inserts (Halleux and Schneider, In Vitro Cell Dev Biol, 27A: 293-30 2, 1991). This cell culture system allows the passage of intact mannit ol by the paracellular route and the transcellular diffusion of testos terone which appears mainly as a biotransformed unconjugated metabolit e. When ethoxyresorufin is added to either the apical or basolateral p oles of living CaCo 2 cells, resorufin is formed, and more than 80% is excreted at the apical pole. Under our experimental conditions, no de tectable amounts of glucurono- or sulfoconjugates are found. Methylcho lanthrene and phenobarbital increase the biotransformation of ethoxyre sorufin 50 and 3 times, respectively, and induce that of benzoxyresoru fin, but not of pentoxyresorufin which remains absent under all condit ions. These substances do not affect the proportion of resorufin recov ered at the apical role. Verapamil inhibits by 25% the release of reso rufin but does not affect its distribution. Chlorodinitrobenzene is co njugated with glutathione and at least two-thirds of the product is ex creted at the apical pole; methylcholanthrene and phenobarbital do not increase this activity. These results demonstrate that differentiated CaCo 2 cells, under serum-free conditions, perform phase I and II rea ctions and that the biotransformation products are selectively excrete d at the apical pole.