Effects of ochratoxin A on DNA repair in cultures of rat hepatocytes and porcine urinary bladder epithelial cells.

In cultured rat hepatocytes the mycotoxin ochratoxin A (OTA) induced unscheduled DNA synthesis (UDS) only in a narrow concentration range. Using a culture medium supplemented with 1% fetal calf serum, at 750 nM OTA a weak induction and at 1 microM OTA a marked induction of DNA repair was observed (15 +/- 11 and 38 +/- 24% cells in repair, respectively). Concentrations > 1 microM OTA were cytotoxic, and <750 nM no induction occurred. In cultures of cells from the urinary bladder (porcine urinary bladder epithelial cells; PUBEC), a target organ of the mycotoxin, OTA induced UDS in a concentration-dependent manner. To inhibit the proliferation of the cultured epithelial cells, which would counteract the detection of DNA repair, epidermal growth factor was omitted and an arginine-deficient medium (ADM) was used. Under these serum-free culture conditions the amount of cells undergoing DNA repair in PUBEC control cultures was approximately 7 +/- 4%, a value also comparable to those of control cultures of rat hepatocytes. At concentrations between 250 nM and 1 microM OTA a concentration-dependent increase of cells in repair was observed. Above 1 microM OTA was cytotoxic. At this concentration a maximum of approximately 61 +/- 9% of the cells undergo DNA repair. This amount is comparable to control cultures incubated with 5 or 10 mM ethylmethane-sulphonate (EMS) (49 +/- 9 and 69 +/- 10% cells in repair, respectively), used as a positive control. These results show that in cultured rat hepatocytes induction of UDS is relatively weak whereas in urothelial cells this effect was significant. Whether this effect is due to OTA metabolites formed locally in the urothelium cannot be excluded since PUBEC have been shown to be able to metabolize xenobiotics independently from the liver.