DNA STRAND BREAKS IN TESTICULAR CELLS FROM HUMANS AND RATS FOLLOWING IN-VITRO EXPOSURE TO 1,2-DIBROMO-3-CHLOROPROPANE (DBCP)

Preparations of testicular cells from human organ transplant donors an d from Wistar rats were compared with respect to their composition of the different testicular cell types, their ability to metabolize 1,2-d ibromo-3-chloropropane (DBCP), and their relative sensitivity to induc tion of DNA single strand breaks and alkali labile sites (ssDNA breaks ) after treatment with DBCP, 4-nitroquinoline N-oxide (4-NQO), and x r ays. Flow cytometric and microscopic analysis demonstrated that the in terindividual variation in the composition of testicular cell types wa s considerably greater in the human tissue than in that from rats. The in vitro metabolic activation of DBCP (50 to 250 mu M), measured as r adiolabel covalently bound to macromolecules, was three-fold faster in rat testicular cells compared to human testicular cells. X rays (1 to 10 Gy) and 4-NQO (0.5 to 2.5 mu M) induced ssDNA breaks to a similar extent in both human and rat testicular cells as measured by single ce ll gel electrophoresis (SCGE) and alkaline filter elution. In contrast , 1,2-dibromo-3-chloropropane (DBCP) (3 to 300 I-IM) caused no signifi cant DNA damage in human testicular cells, whereas in rats there was a clear concentration-dependent increase in ssDNA breaks. The data show that, compared to rats, testicular cells from humans are less efficie nt in activating DBCP to metabolites binding covalently to macromolecu les. However, from the rate of covalent binding observed one would exp ect a significant degree of DBCP-induced ssDNA breaks in the human tes ticular cells. The low level of DBCP-induced ssDNA breaks in human tes ticular cells could indicate that different reactive DBCP metabolites are involved in binding to cellular macromolecules compared to DNA dam age, or that different rates of DNA repair exist in human and rat test icular cells.