No abstract

Forty-two chemicals were tested for their ability to induce cytogenetic change in Chinese hamster ovary cells using assays for chromosome aberrations (ABS) and sister chromatid exchanges (SCE). These chemicals were included in the National Toxicology Program's evaluation of the ability of four in vitro short-term genetic toxicity assays to distinguish between rodent carcinogens and noncarcinogens. The conclusions of this comparison are presented in Zeiger et al. [Zeiger E, Haseman JK, Shelby MD, Margolin BH, Tennant RW (1990): [Environ Molec Mutagen 16(Suppl 18): 1-14]. The in vitro cytogenetic testing was conducted at four laboratories, each using a standard protocol to evaluate coded chemicals with and without exogenous metabolic activation. Most chemicals were tested in a single laboratory; however, two chemicals, tribromomethane and p-chloroaniline, were tested at two laboratories as part of an interlaboratory comparison. Four chemicals (C.I. basic red 9 HCl, 2-mercaptobenzothiazole, oxytetracycline HCl, and rotenone) were tested for SCE in one laboratory and in a different laboratory for ABS. Tetrakis(hydroxymethyl)phosphonium sulfate was tested at one laboratory and the chloride form was tested at a different laboratory. Twenty-five of the 42 chemicals tested induced SCE. Sixteen of these also induced ABS; all chemicals that induced ABS also induced SCE. There was approximately 79% reproducibility of results in repeat tests, thus, we conclude that this protocol is effective and reproducible in detecting ABS and SCE.

The National Toxicology Program has undertaken a study to assess the ability of four genetic toxicology assays to predict the carcinogenicity of chemicals in 2-year rodent studies [Tennant et al.: Science 236:933-941, 1987]. Two of the assays, used for evaluating in vitro cytogenetic damage, were the SCE and chromosome aberration assays in Chinese hamster ovary cells. The results and data for 15 of the chemicals tested in these two assays are presented here. Each chemical was tested with and without exogenous metabolic activation. The chemicals tested were bisphenol A, 2-chloroethanol, C.I. acid orange 10, C.I. disperse yellow 3, C.I. solvent yellow 14, cytembena, D&C red 9, 1,2-dibromoethane, FD&C yellow 6, malaoxon, D,L-menthol, phenol, sulfisoxazole, titanium dioxide, and tris(2-ethylhexyl)phosphate. In vitro cytogenetic results from the other chemicals presented by Tennant et al. (Science 236:933-941, 1987) have been published by Galloway et al. (Environmental and Molecular Mutagenesis 10(Suppl 10): 1-175, 1987), Gulati et al. (Environmental and Molecular Mutagenesis 13:133-193, 1989), and Love-day et al. (Environmental Mutagenesis 13:60-94).

Forty-six coded chemicals were tested for their ability to induce sister chromatid exchanges (SCEs) and chromosomal aberrations (ABs) in cultured Chinese hamster ovary (CHO) cells using a standard protocol with and without exogenous metabolic activation. Sixteen chemicals were negative and 15 were positive in both assays; 15 were positive for SCEs only (one chemical that was positive for SCEs was equivocal for ABs), and no chemicals induced ABs only. The effect of cell harvest time on the ability to detect the induction of ABs was examined for 18 chemicals. Seven chemicals produced a positive response using both standard and extended harvest times, five were positive only using an extended harvest time, and six were negative using both harvest times. The relationship between cell cycle delay and SCE induction was also examined, and the two appear to be unrelated.

The in vitro genotoxic activity of mainstream cigarette smoke condensate (CSC) from cigarettes which heat but do not burn tobacco was compared to that of CSC from cigarettes which burn tobacco. CSCs from five cigarettes were compared. Three of the cigarettes [the Kentucky reference research cigarette (1R4F), a commercially available ultra-low tar brand (ULT) and a commercially available ultra-low tar menthol brand (ULT-menthol]) burn tobacco while two of the cigarettes [a regular (TEST) and a menthol (TEST-menthol]) heat tobacco. CSC from all cigarettes were collected by identical standard techniques, which involved collecting mainstream smoke particulate matter on Cambridge filter pads under FTC smoking conditions. The pads were extracted with DMSO, and the CSCs obtained [10 mg total particulate matter (TPM)/ml DMSO] were evaluated at identical concentrations in an in vitro genetic toxicology test battery. CSCs from 1R4F, ULT, and ULT-menthol cigarettes were mutagenic in Ames bacterial strains TA98, TA100, TA1537, and TA1538 in the presence of metabolic activation (S9 from Aroclor-induced rat liver) but negative in strain TA1535. In the absence of metabolic activation, 1R4F, ULT, and ULT-menthol CSCs were not mutagenic except for a weak response in strain TA1537 for the 1R4F and ULT CSCs. TEST and TEST-menthol CSCs were nonmutagenic in all five bacterial strains, both with and without metabolic activation. CSCs from 1R4F, ULT, and ULT-menthol cigarettes were positive in the CHO-chromosomal aberration assay and in the CHO--sister chromatid exchange assay both with and without metabolic activation while TEST and TEST-menthol CSCs were negative in both assays, either with or without metabolic activation. CSCs from 1R4F, ULT, and ULT-menthol cigarettes were weakly positive in inducing DNA repair in cultured rat hepatocytes while TEST and TEST-menthol CSCs were negative in this assay. All five CSCs were nonmutagenic in the CHO-HGPRT assay both with and without metabolic activation. CSCs from the 1R4F, ULT, and ULT-menthol cigarettes were cytotoxic in the CHO-HGPRT assay, both with and without metabolic activation, while TEST and TEST-menthol CSCs were not cytotoxic under either condition. These results demonstrate that mainstream CSCs from the TEST and TEST-menthol cigarettes are neither genotoxic nor cytotoxic under conditions where CSCs from 1R4F, ULT, and ULT-menthol cigarettes are genotoxic and/or cytotoxic in a concentration-dependent manner.