Diane J. Abernethy

Exposure of hematopoietic stem cells to benzene or 1,4-benzoquinone induces gender-specific gene expression.

Chronic exposure to benzene results in progressive decline of hematopoietic function and may lead to the onset of various disorders, including aplastic anemia, myelodysplastic syndrome, and leukemia. Damage to macromolecules resulting from benzene metabolites and misrepair of DNA lesions may lead to changes in hematopoietic stem cells (HSCs) that give rise to leukemic clones. We have shown previously that male mice exposed to benzene by inhalation were significantly more susceptible to benzene‐induced toxicities than females. Because HSCs are targets for benzene‐induced cytotoxicity and genotoxicity, we investigated DNA damage responses in HSC from both genders of 129/SvJ mice after exposure to 1,4‐benzoquinone (BQ) in vitro or benzene in vivo. 1,4‐BQ is a highly reactive metabolite of benzene that can cause cellular damage by forming protein and DNA adducts and producing reactive oxygen species. HSCs cultured in the presence of 1,4‐BQ for 24 hours showed a gender‐independent, dose‐dependent cytotoxic response. RNA isolated from 1,4‐BQ–treated HSCs and HSCs from mice exposed to 100 ppm benzene by inhalation showed altered expression of apoptosis, DNA repair, cell cycle, and growth control genes compared with unexposed HSCs. Rad51, xpc, and mdm‐2 transcript levels were increased in male but not female HSCs exposed to 1,4‐BQ. Males exposed to benzene exhibited higher mRNA levels for xpc, ku80, ccng, and wig1. These gene expression differences may partially explain the gender disparity in benzene susceptibility. HSC culture systems such as the one used here will be useful for testing the hematotoxicity of various substances, including other benzene metabolites.

Cytotoxicity and mutagenicity of dinitrotoluenes in Chinese hamster ovary cells

Technical grade dinitrotoluene (DNT), a mixture composed predominantly of 2,4- and 2,6-DNT but containing lesser amounts of 2,3-, 2,5-, 3,4- and 3,5-DNT, has been shown to be a hepatocarcinogen in rats, The mutagenicity of these compounds has been evaluated using the CHO/HGPRT system, a quantitative mammalian somatic cell mutational assay. Dinitrotoluenes were tested for their ability to induce mutation to 6-thioguanine (TG) resistance in the presence and absence of microsomal preparations (PMS) from rats pretreated with the mixed function oxidase inducer Aroclor 1254. A marked difference in cytotoxicity of the isomers was observed. However, neither technical grade DNT nor any of the purified isomers resulted in a significant increase in the TG-resistant fraction of surviving cells, with or without added PMS.

Lack of di-(2-ethylhexyl) phthalate activity in the C3H10T12 cell transformation system

The widely used plasticizer and rodent carcinogen di-(2-ethylhexyl) phthalate (DEHP) was examined for activity in the C3H 10T 1 2 murine fibroblast cell transformation system. Treatment with DEHP or its metabolite, mono-(2-ethylhexyl) phthalate, did not produce oncogenic transformation, initiate the process of transformation in cultures treated with a tumour promoter or promote the process of transformation in cultures pretreated with a chemical carcinogen. These findings are consistent with the suggestion that the carcinogenicity of DEHP is mediated by an indirect mechanism and not by covalent interaction of DEHP with DNA.