INDUCTION OF MONOOXYGENASE ACTIVITY IN PROSTAGLANDIN-H SYNTHASE-COMPETENT OVINE SEMINAL-VESICLE CELL-CULTURES BY 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN

Cell cultures derived from ovine seminal vesicles (OSV cells) express high levels of prostaglandin H synthase (PHS) and have been found to b e a suitable in vitro model for studies on PHS-mediated bioactivation of certain xenobiotics The extrahepatic tissue of origin apparently la cks constitutively expressed mono-oxygenase (MFO) activity such as cyt ochrome P-450 (CYP1A1)-dependent ethoxyresorufin-O-deethylase (EROD). However, treatment of OSV cell cultures with 2,3,7,8-tetrachlorodibenz o-p-dioxin (TCDD; 0.001-10 nM) resulted in a dose-dependent induction of CYP1A1-associated EROD activity. Subconfluent OSV cells exposed to 100 pM TCDD for various lengths of time express the highest EROD activ ity after 48 hr of treatment. Benz[a]anthracene also induced EROD acti vity in OSV cells, but, in accordance with its low affinity for the Ah receptor at much higher concentrations (1-10 mu M) than TCDD. In line with the observed functional response (EROD induction) the presence o f Ah receptor was confirmed by biochemical analysis: on incubation wit h [H-3]TCDD 5 fmol ligand/mg nuclear protein were specifically bound t o Ah receptor after incubation (2 hr) of OSV cells with [H-3]TCDD. TCD D was not cytotoxic for OSV cells up to 10 nM as judged by growth curv es; rather, their growth was moderately stimulated by TCDD, significan tly at 1 nM (a concentration which also induced EROD activity). Despit e a clear dose-related response of OSV cells to known inducers of CYP1 A1, the induced EROD activity levels (0.4-0.7 pmol/min x 10(6) cells) are very low compared with values reported for hepatic cells in cultur e and lower than EROD activity induced in colon tumour cells. Thus, an d since OSV cells do not constitutively express appreciable MFO activi ty, it is suggested that only PHS-mediated oxidation reactions contrib ute to the bioactivation of xenobiotics in this model. In conclusion, although OSV cells clearly respond to Ah receptor ligands by EROD indu ction, they are of limited value for bioassay of TCDD and related comp ounds in environmental samples. However, PHS-competent OSV cells are a n interesting model for further studies of TCDD-related effects on PHS activity/expression, because of the functional Ah receptor. Copyright (C) 1996 Elsevier Science Ltd.