Detection of micronuclei, cell proliferation and hyperdiploidy in bladder epithelial cells of rats treated with o-phenylphenol

Abstract

o-Phenylphenol (OPP), a widely used fungicide and antibacterial agent, has been considered to be among the top 10 home and garden pesticides used in the USA. Earlier studies have consistently shown that the sodium salt of OPP (SOPP) causes bladder cancer in male Fischer 344 (F344) rats, whereas OPP has produced variable results. This difference has been attributed to the presence of the sodium salt. To determine cellular and genetic alterations in the rat bladder and the influence of the sodium salt, F344 rats were administered 2% OPP, 2% NaCl and 2% NaCl + 2% OPP in their diet for 14 days. Twenty-four hours before being killed the animals were administered 5-bromo-2'-deoxyuridine (BrdU) by i.p. injection. Bladder cells were isolated, stained with DAPI and scored for the presence of micronuclei and incorporation of BrdU into replicating cells. To determine changes in chromosome number, we used fluorescence in situ hybridization (FISH) with a DNA probe for rat chromosome 4. Significant increases in the frequency of micronuclei and BrdU incorporation were seen in bladder cells of rats from all treatment groups. In contrast, the frequency of hyperdiploidy/polyploidy in treated animals was not increased over that seen in controls. A high control frequency of cells with three or more hybridization signals was seen, probably due to the presence of polyploid cells in the bladder. The presence of polyploid cells combined with cytotoxicity and compensatory cell proliferation makes it difficult to determine whether OPP is capable of inducing aneuploidy in the rat urothelium. In summary, these studies show that OPP can cause cellular and chromosomal alterations in rat bladder cells in the absence of the sodium salt. These results also indicate that at high concentrations the sodium salt can enhance chromosomal damage in the rat urothelium.

Induction of mitosis delay, apoptosis and aneuploidy in human cells by phenyl hydroquinone, an Ames test-negative carcinogen

“…OPP and PHQ, however, may cause chromosomal damage, i.e. chromosome aberrations, micronuclei, sister-chromatid exchange and aneuploidy (Tayama-Nawai et al, 1984;Tayama et al, 1989;Balakrishnan et al, 2002).…”

Analysis of genotoxicity and the carcinogenic mode of action forortho-phenylphenol

“…Induction of micronuclei in rat urinary bladder cells by OPP, as reported by Balakrishnan et al [2002], provides evidence for an association between the formation of bladder tumors and simple chromosome breakage. Addi-tional support for this association was also found in an earlier study reported by Tadi-Uppala et al [1996], in which OPP, SOPP, NaCl, or OPP plus NaCl were administered to rats in their diet.…”

“…PHQ tested in the absence of PHS did not induce micronuclei in their studies. These results were initially encouraging, but in follow-up in vivo clastogenicity studies designed to detect aneuploidy [Balakrishnan et al, 2002;Balakrishnan and Eastmond, 2003], micronuclei were found, but there were no hyperdiploid (potential aneuploid) cells in male rat bladder epithelial cells exposed to carcinogenic dose levels of OPP. Although the studies do not rule out the induction of aneuploidy by chromosome loss, the induction of neoplasia through specific chromosome aneuploidy does not appear likely.…”

“…The observation that NaCl was capable of inducing micronuclei and cell proliferation in urinary bladder tissue raises the possibility that nongenotoxic processes contribute to chromosome damage and bladder tumors [Shibata et al, 1989]. The failure to find evidence for OPP-induced aneuploidy in rat urinary bladder cells [Balakrishnan et al, 2002] tentatively reduces the probability that aneuploidy is a primary mechanism for tumor induction. The in vivo results are consistent with a mode of action in which OPP/SOPPassociated clastogenic events might play a contributing role in tumor development at super-threshold doses associated with the induction of other preneoplastic lesions.…”

“…The first two are the reports by Balakrishnan et al [2002] and Tadi-Uppala et al [1996] showing that OPP and SOPP produce micronuclei in rat bladder tissue at dose levels associated with target organ toxicity and the presence of preneoplastic events. The only complication associated with the interpretation of these findings is the observation in the studies reported by Tadi-Uppala et al [1996] that NaCl at high concentrations produces micronuclei in the same tissue.…”