Evaluation of hyperdiploidy in the bladder epithelial cells of male F344 rats treated with ortho-phenylphenol

Ortho-phenylphenol (OPP) is a broad-spectrum fungicide and anti-bacterial agent that has been shown to cause bladder cancer in male F344 rats. An earlier study to investigate the potential role of aneuploidy in OPP-induced bladder carcinogenicity, failed to detect increases in frequencies of hyperdiploidy/polyploidy in treated animals, presumably due to the presence of polyploid cells in the bladder. To overcome this problem, we utilized a novel approach to determine increases in numerical alterations in the slowly dividing replicating cells of the rat bladder following treatment with OPP. Collagenase digestion of the bladder was used to enrich for actively-dividing cells and FISH in conjunction with BrdU was employed to detect hyperdiploidy in the replicating interphase cells. Initial studies were performed using FISH with a chromosome 4 probe. Follow-up studies were conducted with OPP and a positive control, vinblastine sulfate using probes for chromosomes 4 and 19. No significant increases in hyperdiploidy/polyploidy were seen in the replicating bladder cells of the OPP-treated rats using FISH with either the chromosome 4 or 19 probes. As expected, no significant increases in hyperdiploidy were seen in the non-replicating cells. In contrast, highly significant increases in hyperdiploidy/polyploidy, as detected using FISH with probes for either chromosome 4 or 19, were seen in the replicating cells from rats treated with a combination of OPP and vinblastine. The inability to detect increases in hyperdiploidy/polyploidy in the bladder of OPP-treated rats indicates that chromosome gain is unlikely to play a major role in the early genotoxic effects of OPP. However, the increase in hyperdiploidy/polyploidy induced by vinblastine sulfate in OPP-treated rats, clearly demonstrates that this approach using FISH in combination with BrdU is capable of detecting changes in chromosome number even in slowly-dividing tissues, such as the urinary bladder. [Copyright &y& Elsevier]