In vitro and in vivo genetic toxicology studies with diethylene glycol monohexyl ether.

Diethylene glycol monohexyl ether (DEGHE; CAS no. 112-59-4), an industrial chemical, was investigated for the potential to produce genotoxic effects using three in vitro and two in vivo tests. No mutagenic activity occurred in either the absence or presence of metabolic activation with a Salmonella typhimurium reverse assay using strains TA98, TA100, TA1535, TA1537 and TA1538. In a Chinese hamster ovary (CHO) forward gene mutation test (HGPRT locus) there was an increase in the mutation frequencies, which were relatively small compared with the solvent control values, somewhat inconsistent between duplicate cultures and occurred particularly in the presence of metabolic activation. Linear regression analysis indicated a marginally significant trend for dosage versus mutation frequency, suggesting that DEGHE was weakly positive in this test. A sister chromatid exchange test in CHO cells showed no significant dosage-related effects in the presence or absence of metabolic activation. A peripheral blood micronucleus test in mice by dosing with an intraperitoneal injection of DEGHE did not show any potential for DEGHE to increase the incidence of micronucleated polychromatophilic erythrocytes. In a first femoral bone marrow chromosome aberration test in the rat by peroral dosing, DEGHE did not cause any increase in aberrations for 12-h and 24-h samples with males and females or with females at 48-h sampling. However, with males at 48 h the two lowest doses showed an increased number of aberrations, but not at the high doses. A repeat study in males with a larger number of doses and 24-h and 48-h samples did not replicate this finding. It is concluded that DEGHE may have limited weak mutagenic activity in vitro but is devoid of clastogenic potential.

Biomarkers of exposure and effect as indicators of potential carcinogenic risk arising from in vivo metabolism of ethylene to ethylene oxide.

The purposes of the present study were: (i) to investigate the potential use of several biomarkers as quantitative indicators of the in vivo conversion of ethylene (ET) to ethylene oxide (EO); (ii) to produce molecular dosimetry data that might improve assessment of human risk from exogenous ET exposures. Groups (n = 7/group) of male F344 rats and B6C3F1 mice were exposed by inhalation to 0 and 3000 p. p.m. ET for 1, 2 or 4 weeks (6 h/day, 5 days/week) or to 0, 40, 1000 and 3000 p.p.m. ET for 4 weeks. N:-(2-hydroxyethyl)valine (HEV), N:7-(2-hydroxyethyl) guanine (N7-HEG) and HPRT: mutant frequencies were assessed as potential biomarkers for determining the molecular dose of EO resulting from exogenous ET exposures of rats and mice, compared with background biomarker values. N7-HEG was quantified by gas chromatography coupled with high resolution mass spectrometry (GC-HRMS), HEV was determined by Edman degradation and GC-HRMS and HPRT: mutant frequencies were measured by the T cell cloning assay. N7-HEG accumulated in DNA with repeated exposure of rodents to 3000 p.p.m. ET, reaching steady-state concentrations around 1 week of exposure in most tissues evaluated (brain, liver, lung and spleen). The dose-response curves for N7-HEG and HEV were supralinear in exposed rats and mice, indicating that metabolic activation of ET was saturated at exposures >/=1000 p.p.m. ET. Exposures of mice and rats to 200 p.p.m. EO for 4 weeks (as positive treatment controls) led to significant increases in HPRT: mutant frequencies over background in splenic T cells from exposed rats and mice, however, no significant mutagenic response was observed in the HPRT: gene of ET-exposed animals. Comparisons between the biomarker data for both unexposed and ET-exposed animals, the dose-response curves for the same biomarkers in EO-exposed rats and mice and the results of the rodent carcinogenicity studies of ET and EO suggest that too little EO arises from exogenous ET exposure to produce a significant mutagenic response or a carcinogenic response under standard bioassay conditions.

Genetic toxicity evaluation of octamethylcyclotetrasiloxane.

Octamethylcyclotetrasiloxane (OMCTS; CAS No. 556-67-2) was evaluated in a genetic toxicity battery. In preincubation tests with Salmonella typhimurium strains TA98, TA100, TA1535, TA1537, and TA1538, no mutagenicity was detected (maximum dose = 5 mg/plate) with or without S9 in two independent trials. Treatment of cultured Chinese hamster ovary (CHO) cells was limited by cytotoxicity at OMCTS concentrations greater than 0.003 mg/mL without S9 and 0.03 mg/mL with S9. CHO cells treated with up to 0.003 mg/mL without S9 and 0.03 mg/mL with S9 showed no significant dose-related increases in chromosomal aberration frequencies. No significant dose-related increases in sister chromatid exchanges (SCEs) occurred in OMCTS-treated CHO cells (maximum OMCTS concentration = 0.003 mg/mL without S9; 0.03 mg/mL with S9). Therefore, OMCTS was concluded to be negative in the SCE assay. In a screen for in vivo clastogenic potential, Sprague-Dawley rats received 700 ppm OMCTS by whole-body vapor inhalation 6 hr daily for 5 days. A negative control group received filtered air on the same schedule. A positive control group was exposed to filtered air on the same schedule and received cyclophosphamide 24 hr before termination. The OMCTS-treated animals were terminated 6 and 24 hr after the final exposure. Positive and negative control animals were terminated 24 hr after the last exposure. No significant, treatment-related increases in chromosomal aberrations were detected. The results of these studies indicate that OMCTS does not possess significant in vitro genotoxic potential. No adverse genetic findings were seen in the in vivo screen for chromosome aberrations.

Investigations on the in vitro and in vivo genotoxic potential of 5-vinyl-2-norbornene.

5-Vinyl-2-norbornene (VNB: CAS no. 3048-64-4), an industrial chemical that produces hyaline droplet nephropathy in the male rat with associated alpha2u-globulin increases, was investigated in vitro and in vivo for its genotoxic potential. A Salmonella typhimurium reverse mutation assay (strains TA98, 100, 1535, 1537, 1538) was negative both without (dose range 0.003-0.3 mg per plate) and with (0.003-0.3 mg per plate) metabolic activation. A forward gene mutation test in Chinese Hamster Ovary (CHO) cells (HGPRT locus) did not show any significant concentration-related increases in mutation frequencies in the absence (0.01-0.1 mg ml[-1]) or presence (0.005-0.1 mg ml[-1]) of metabolic activation. In a sister chromatid exchange (SCE) test, VNB did not produce statistically significant or dose-related increases in the incidence of SCEs in the absence (0.02-0.06 mg ml[-1]) or presence (0.005-0.03 mg ml[-1]) of metabolic activation. A bone marrow chromosome aberration test was conducted in groups of 10 male and 10 female Sprague-Dawley rats exposed for 6 hr/day for 5 consecutive days to mean (+/- SD) VNB vapor concentrations of 0 (air control), 48.1 +/- 1.29, 146 +/- 9.2, or 336 +/- 8.5 ppm. Marrow was collected 6 and 24 hr after the final exposure. No statistically significant or dose-related increases in chromosomal aberrations occurred in the VNB-exposed animals. 5-Vinyl-2-norbornene did not show any potential for genotoxic activity with this in vitro-in vivo battery of tests.

Assessment of the in vivo mutagenic potential of methyl tertiary-butyl ether.

Methyl tertiary-butyl ether (MTBE) is one of the highest production volume chemicals in the USA. Previous results from in vitro genetic toxicity studies suggested that it was not mutagenic. However, chronic exposure at high levels resulted in liver tumors in female mice and kidney tumors in male rats. The current program assessed in vivo genotoxicity and also explored the possibility that a mutagenic mechanism was involved in the carcinogenic process. The specific tests used included the Drosophila sex-linked-recessive-lethal test, the rat bone marrow cytogenetics test, the mouse bone marrow micronucleus test and the in vivo-in vitro hepatocyte unscheduled DNA synthesis test in the mouse. All tests produced negative results, indicating that the potential for in vivo mutagenic activity was low. These data also suggest that the tumorigenic activity was probably the result of a non-genotoxic process.

Effects of ethylene on micronucleus formation in the bone marrow of rats and mice following four weeks of inhalation exposure.

Male Fischer 344 rats and male B6C3F1 mice (10/species/group) were exposed to ethylene 6 h/day, 5 days/week, for 4 weeks. The ethylene target concentrations were 0, 40, 1000, and 3000 ppm. An ethylene oxide (EO) control group for each species was exposed under the same conditions at a target concentration of 200 ppm. Bone marrow was collected approximately 24 h after the final exposure. Polychromatic erythrocyte (PCE) to normochromatic erythrocyte (NCE) ratios were determined and 2000 PCE/animal were scored for the presence of micronuclei. Ethylene did not produce statistically significant, exposure-related increases in the frequency of micronucleated PCE (MNPCE) in the bone marrow of either rats or mice when compared to air-exposed control animals. As expected, EO exposure resulted in significant increases in the frequencies of MNPCE in both species.