Induction of mono-oxygenase activity in prostaglandin H synthase-competent ovine seminal vesicle cell cultures by 2,3,7,8-Tetrachlorodibenzo-p-dioxin.

Abstract Cell cultures derived from ovine seminal vesicles (OSV cells) express high levels of prostaglandin H synthase (PHS) and have been found to be a suitable in vitro model for studies on PHS-mediated bioactivation of certain xenobiotics The extrahepatic tissue of origin apparently lacks constitutively expressed mono-oxygenase (MFO) activity such as cytochrome P -450 (CYP1A1)-dependent ethoxyresorufin- O -deethylase (EROD). However, treatment of OSV cell cultures with 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD; 0.001–10 n m ) resulted in a dose-dependent induction of CYP1A1-associated EROD activity. Subconfluent OSV cells exposed to 100 p m TCDD for various lengths of time express the highest EROD activity after 48 hr of treatment. Benz[ a ]anthracene also induced EROD activity in OSV cells, but, in accordance with its low affinity for the Ah receptor at much higher concentrations (1–10 μ m ) than TCDD. In line with the observed functional response (EROD induction) the presence of Ah receptor was confirmed by biochemical analysis: on incubation with [ 3 H]TCDD 5 fmol ligand/mg nuclear protein were specifically bound to Ah receptor after incubation (2 hr) of OSV cells with [ 3 H] TCDD. TCDD was not cytotoxic for OSV cells up to 10 n m as judged by growth curves; rather, their growth was moderately stimulated by TCDD, significantly at 1 n m (a concentration which also induced EROD activity). Despite a clear dose-related response of OSV cells to known inducers of CYP1A1, the induced EROD activity levels (0.4−0.7pmol/min× 10 6 cells) are very low compared with values reported for hepatic cells in culture and lower than EROD activity induced in colon tumour cells. Thus, and since OSV cells do not constitutively express appreciable MFO activity, it is suggested that only PHS-mediated oxidation reactions contribute to the bioactivation of xenobiotics in this model. In conclusion, although OSV cells clearly respond to Ah receptor ligands by EROD induction, they are of limited value for bioassay of TCDD and related compounds in environmental samples. However, PHS-competent OSV cells are an interesting model for further studies of TCDD-related effects on PHS activity/expression, because of the functional Ah receptor.