MX, a by‐product of water chlorination, lacks in vivo genotoxicity in gpt delta mice but inhibits gap junctional intercellular communication in rat WB cells

Abstract

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a by-product of water chlorination, is a potent bacterial mutagen and rat carcinogen. In the present study, the in vivo mutagenicity, cell proliferative activity, and carcinogenicity of MX were investigated in gpt delta mice. Groups of 5 male and female 7-week-old gpt delta C57BL/6J transgenic mice were given MX at doses of 0, 10, 30, or 100 ppm in their drinking water for 12 weeks, and then killed to assess in vivo mutagenicity using 6-thioguanine and Spi- selection, and cell proliferative activity using immunohistochemistry for proliferating cell nuclear antigen (PCNA). Further groups of 10 male and female gpt delta mice were given 0 or 100 ppm MX for 78 weeks, and a full necropsy with histopathological examination of all organs was conducted to detect neoplastic lesions. The 12-week MX treatment did not result in mutagenicity in the livers or lungs or cell proliferative activity in several organs of the mice, and the 78-week treatment did not cause carcinogenicity. Additional investigations were conducted to evaluate the potential of MX to inhibit gap junctional intercellular communication (GJIC) in rat liver epithelial cells (WB cells) by the scrape loading/dye transfer method. Inhibition of GJIC was detected within 2 hr with a noncytotoxic dose of MX (4 microg/ml), followed by partial restoration after 5 hr. A second phase of inhibition occurred after 10 hr and then the lowered level persisted for the 24 hr-incubation period. Dose-dependent inhibition was evident at both 2 hr and 24 hr, with much stronger effects at the former time. These findings indicate that MX is not mutagenic, mitogenic or carcinogenic in mice, and suggest that the compound exerts epigenetic actions leading to GJIC inhibition.

Possible involvement of sulfotransferase 1A1 in estragole-induced DNA modification and carcinogenesis in the livers of female mice

“…6-Thioguanine (TG) and Spi − selections were performed as previously described [14,[17][18][19][20][21]. Briefly, genomic DNA was extracted from the livers, and lambda EG10 DNA (48 kb) was rescued as the lambda phage by in vitro packaging.…”

In vivo Approaches to Study Mechanism of Action of Genotoxic Carcinogens

“…We also conˆrmed that such reporter gene-carrying rodents are not susceptible or resistant to carcinogenicity (10,14,20) as compared with intact counterparts. Taken together, we propose a combined subchronic toxicity/in vivo genoxicity study using such transgenic rodents (Fig.…”

“…The 12-week MX treatment did not result in genotoxicity in the livers or lungs or cell proliferative activity in several organs of the mice, and the 78-week treatment did not cause carcinogenicity. Theseˆndings indicate that MX is not genotoxic, mitogenic or carcinogenic in mice, and suggest that the compound might exert epigenetic actions for carcinogenicity in rats although its in vivo genotoxicity remains unknown in rats (20).…”

“…In contrast to dicyclanil, MX exerted neither in vivo genotoxicity nor carcinogenicity in mice (20). Groups of male and female gpt delta transgenic mice were given MX at doses of 0-100 ppm in their drinking water for 12 weeks, and then killed to assess in vivo genotoxicity, and cell proliferative activity using immunohistochemistry for proliferating cell nuclear antigen (20).…”

Carcinogenicity Assessment for Risk Factors in Food:

“…Some genotoxic carcinogens showed significantly increased genotoxicity in the liver of gpt delta rats, the target organ for carcinogenicity 75) . In contrast, a genotoxic chlorinated water by-product, MX, failed to exert the in vivo genotoxicity and carcinogenicity in gpt delta mice 74) . On the other hand, a known non-genotoxic carcinogen dicyclanil increased the in vivo genotoxicity as well as oxidative DNA damage in female mice, in manners consistent with the sex specificity of its carcinogenicity, and thus albeit without clear evidence of direct DNA reactivity 72) .…”