Enhancement of BALB/c 3T3 cells transformation by 1,2-dibromoethane promoting effect

Two of the most representative halogenated aliphatic hydrocarbons, 1,2-dibromoethane and 1,1,2,2-tetrachloroethane, were tested in the two-stage cell transformation model for analysing the promoting ability. Both of these compounds had previously been found to exert genotoxic effects, probably acting as moderate initiators. BALB/c 3T3 cells were initiated with subtransforming doses of N-methyl-N-nitro-N-nitrosoguanidine or 3-methylcholanthrene and then exposed to a chronic treatment with different non-transforming dosages of the two haloalkanes. 1,1,2,2-Tetrachloroethane did not exert any promoting activity in that system. By contrast, significant promoting effects by 1,2-dibromoethane were observed both in cells treated with N-methyl-N-nitro-N-nitrosoguanidine and in cells treated with 3-methylcholanthrene. Promotion of the transformation process initiated with 3-methylcholanthrene was detectable when confluent cells in the chemical-treated plates were replated in the level-II amplification test. This experimental procedure allowed cells to perform further rounds of replications and transformed foci to became detectable. Results gave evidence for a promoting role of 1,2-dibromoethane in multistep carcinogenesis, probably responsible for the higher oncogenic ability of this compound with respect to 1,1,2,2-tetrachloroethane.

A new Salmonella typhimurium NM5004 strain expressing rat glutathione S-transferase 5-5: use in detection of genotoxicity of dihaloalkanes using an SOS/umu test system

The Escherichia coli mu operon was subcloned into a pKK233-2 vector containing rat glutathione S-transferase (GST) 5-5 cDNA and the plasmid thus obtained was introduced into Salmonella typhimurium TA1535. The newly developed strain S.typhimurium NM5004, was found to have 52-fold greater GST activity than the original umu strain S.typhimurium TA1535/pSK1002. We compared sensitivities of these two tester strains, NM5004 and TA1535/pSK1002, for induction of umuC gene expression with several dihaloalkanes which are activated or inactivated by GST 5-5 activity. The induction of umuC gene expression by these chemicals was monitored by measuring the cellular beta-galactosidase activity produced by umuC"lacZ fusion gene in these two tester strains. Ethylene dibromide, 1-bromo-2-chloroethane, 1,2-dichloroethane, and methylene dichloride induced umuC gene expression more strongly in the NM5004 strain than the original strain. 4-Nitroquinoline 1-oxide and N-methyl-N'-nitro-N-nitrosoguanidine were found to induce umuC gene expression to similar extents in both strains. In the case of 1-nitropyrene and 2-nitrofluorene, however, NM5004 strain showed weaker umuC gene expression responses than the original TA1535/pSK1002 strain. 1,2-Epoxy-3-(4'-nitrophenoxy)propane, a known substrate for GST 5-5, was found to inhibit umuC induction caused by 1-bromo-2-chloroethane. These results indicate that this new tester NM5004 strain expressing a mammalian GST theta class enzyme may be useful for studies of environmental chemicals proposed to be activated or inactivated by GST activity.

An in vitro and an in vivo unscheduled DNA synthesis assay with a zinc oxide/hexachloroethane (Zn/HCE) smoke

1. Since Zn/HCE smoke has been shown previously to be weakly positive in the Ames test, and negative in the bone marrow micronucleus assay, other assays including a second in vivo assay examining unscheduled DNA synthesis (UDS) in rat hepatocytes has been carried out, as recommended by the UK Department of Health guidelines. 2. Zn/HCE smoke was assessed for its ability to induce DNA repair in an UDS assay both in vitro in cultured rat hepatocytes and in rat hepatocytes after in vivo treatment by inhalation. 3. For the in vitro investigation, two studies were carried out assessing media exposed to Zn/HCE smoke using at least seven concentrations up to a toxic level. At the highest concentration of Zn/HCE smoke, where some viable cells were seen, an increase in UDS was observed in both experiments. However this was not statistically significant, was only seen at a level where toxicity was observed and was therefore considered not to be biologically significant. 4. In the in vivo investigation, one study was carried out in three separate parts, assessing two doses of Zn/HCE smoke characterised by their zinc content as approximately 20 and 56 micrograms l-1 air. A dose-related increase in UDS was observed which was not statistically significant. The positive control behaved as anticipated, showing a highly statistically significant response. 5. It was concluded that Zn/HCE smoke did not induce unscheduled DNA repair in the in vitro or in vivo UDS assays under the conditions used in the studies. The overall lack of genotoxic effect of this smoke in this and previous studies in this laboratory would not suggest a major health hazard.

Mutation spectra of 1,2-dibromoethane, 1,2-dichloroethane and 1-bromo-2-chloroethane in excision repair proficient and repair deficient strains of Drosophila melanogaster

DNA sequence changes produced by 1,2-dibromoethane (DBE), 1,2-dichloroethane (DCE) and 1-bromo-2-chloroethane (BCE) were analyzed using the vermilion locus of Drosophila melanogaster. Under excision repair proficient (exr+) conditions (mutagenized exr+ males mated with exr+ females) all mutants isolated from the first generation (F1) after DBE and DCE exposure represented DNA rearrangements (multi-locus deletions, small deletions with tandem repeats, duplicate insertions). By contrast, mutants expressing a vermilion phenotype only in the F2 (F1 mosaics) all carried single bp changes. When exr+ males, after exposure to DBE, were mated to excision repair deficient (exr-) mus 201 females 11 of 14 mutational events isolated from either F1 or F2 progeny were single bp changes. In general the mutation spectra for the three dihaloalkanes were similar to the spectrum obtained at the same locus for the direct-acting monofunctional agent methylmethanesulfonate (MMS). The data lend support to the conclusions that these 1,2-dihaloalkanes are genotoxic through modification at ring nitrogens in DNA, primarily at the N7 of guanine and, to a lesser extent, at the N1 of adenine. These N-adducts could be directly miscoding. However, more important for the mutagenic action of the chemicals seems to be the formation of non-coding lesions and/or misrepair.

Characterization of the genotoxic action of three structurally related 1,2-dihaloalkanes in Drosophila melanogaster

The genetic activity profiles of three structurally related dihaloalkanes, 1,2-dibromoethane (DBE), 1,2-dichloroethane (DCE) and 1-bromo-2-chloroethane (BCE), were compared in germ cells and somatic tissue of Drosophila melanogaster. The two genotoxicity indices estimated after mutagen exposure of male germ cells were (i) the hypermutability index fexr-/fexr+, measured by the increased frequency of induced recessive lethals (RL) in a strain defective in DNA excision repair (exr-), as compared to the wild type (exr+); (ii) the relative clastogenicity index CL/RL, expressed by the ratio of chromosomal aberrations (CL; ring-X loss) to RL determined in exr+ strains. The fexr-/fexr+ index for DBE was 4-5 times higher than those for DCE and BCE, suggesting a difference in the types of premutagenic lesions produced by DBE in comparison to DCE and BCE. The relative clastogenicity indices for BCE (CL/RL = 0.29) and DCE (0.41) are similar to the value of 0.37 estimated for DBE in an earlier study, all indicating that the three compounds or their metabolites are incapable of forming DNA crosslinks. In somatic cells, after inhalation treatment of female larvae, the effectiveness for the induction of interchromosomal recombination decreased in the order BCE > or = DBE > DCE. It is concluded that in accordance with other studies also in Drosophila the glutathione-mediated pathway is the major cause of genotoxicity caused by DBE, DCE and BCE.

Initiating activity of 1,1,2,2-tetrachloroethane in two-stage BALB/c 3T3 cell transformation

By using in vitro two-stage BALB/c 3T3 cell transformation assay, we have tested the effect of promoting treatment with tetradecanoylphorbol acetate (TPA) on transformation induced by 1,1,2,2-tetrachloroethane (1,1,2,2-TTCE). Cells were treated with subeffective or transforming concentrations of 1,1,2,2-TTCE in the presence of an S9-mix activating system, followed by TPA promoting treatment. The transforming activity of 1,1,2,2-TTCE is evident only by reseeding confluent cells and allowing additional rounds of cell replications in the amplification test. Treatment with TPA leads to a marked transformation yield in all plates scored even at the lowest assayed dosage of 1,1,2,2-TTCE, without performing amplification of transformation.

On the hepatotoxicity of 1,1,2,2-tetrachloroethane

Intoxication of male and female mice with a single dose (300 or 600 mg/kg) of 1,1,2,2-tetrachloroethane (TTCE) resulted in significant decreases in cytochrome P-450 (to 58-73% of the control) and NADPH-cytochrome (P-450) c-reductase (to 29-35% of the control) in hepatic microsomes. This was accompanied by an alteration of mixed function monooxygenases stemming from the marked reduction (to 20-64% of the control) of several oxidative activities to selected substrates towards different P-450 isozymes (classes IA1, IA2, IIB1, IIE1 and IIIA). As phase II markers, epoxide hydrolase (approximately 35% loss), UDP-glucuronosyl transferase (approximately 42% loss) and to a lesser extent glutathione S-transferase (approximately 17% loss) were all affected. Also, the activity of delta-aminolevulinic (ALA) synthetase was decreased (approximately 57% of the control). On the contrary, heme oxygenase activity was increased (up to 35%) at the maximal dose tested. The decrease of P-450-function may be explained in terms of an alteration in the rate of heme biosynthesis and degradation, provoking a loss of heme content (approximately 33%) as well as of the direct inactivation of both P-450 and reductase. Because of increasing evidence on the involvement of free radical intermediates in the case of toxicity of haloalkanes, electron spin resonance spectroscopy (ESR) spin-trapping in vivo techniques were used to characterize the possible free radical species involved in the observed liver damage. The results obtained with the spin-trap N-benzylidene-2-methylpropylamine N-oxide (phenyl t-butylnitrone, PBN) provide evidence for the formation and trapping of the CHCl2CHCl free radicals. The detection of conjugated diene signals by means of second-derivative spectrophotometry, have enabled us to show that in vivo lipid peroxidation may be one of the main mechanisms responsible for TTCE hepatotoxicity.

Mutagenicity testing of condensates of smoke from titanium dioxide/hexachloroethane and zinc/hexachloroethane pyrotechnic mixtures

Condensates of smoke from titanium dioxide/hexachloroethane and zinc/hexachloroethane pyrotechnic mixtures were investigated for their potential to produce genetic damage in the tester strains TA98, TA100, TA1535 and TA1537 of Salmonella typhimurium and in the mouse bone marrow micronucleus assay. Both smoke condensates contained several chlorinated hydrocarbons among which tetrachloroethylene, hexachloroethane, hexachlorobutadiene and hexachlorobenzene were identified by GC/MS. Condensate of smoke from titanium dioxide/hexachloroethane showed a dose-related positive response in the Salmonella assay with strains TA98 and TA100 in the absence of metabolic activation from rat liver S9 fraction. Both smoke condensates were negative in the micronucleus assay but produced a small but significant depression of erythropoietic activity. The results indicate that smoke condensate from titanium dioxide/hexachloroethane mixtures contains unidentified compound(s) that may be considered mutagenic in the Salmonella assay.

Studies on the mutagenicity of a zinc oxide-hexachloroethane smoke

1. A suitable method has been developed for generating atmospheres of zinc oxide/hexachloroethane smoke (ZnHCE). 2. The smoke was investigated using the Ames test and the micronucleus assay. 3. It was weakly mutagenic to the bacteria, but in the bone marrow no increases in micronuclei were detected up to toxic levels of the smoke. 4. The method used here could be applied to other pyrotechnic mixtures which give rise to complex mixtures of products.

A physiologically based toxicokinetic model for the uptake and disposition of waterborne organic chemicals in fish

A physiologically based toxicokinetic model was developed to predict the uptake and disposition of waterborne organic chemicals in fish. The model consists of a set of mass-balance differential equations which describe the time course of chemical concentration within each of five tissue compartments: liver, kidney, fat, and richly perfused and poorly perfused tissue. Model compartmentalization and blood perfusion relationships were designed to reflect the physiology of fishes. Chemical uptake and elimination at the gills were modeled as countercurrent exchange processes, limited by the chemical capacity of blood and water flows. The model was evaluated by exposing rainbow trout (Oncorhynchus mykiss) to pentachloroethane (PCE) in water in fish respirometer-metabolism chambers. Exposure to 1500, 150, or 15 micrograms PCE/liter for 48 hr resulted in corresponding changes in the magnitude of blood concentrations without any change in uptake kinetics. The extraction efficiency for the chemical from water decreased throughout each exposure, declining from 65 to 20% in 48 hr. Extraction efficiency was close to 0% in fish exposed to PCE to near steady state (264 hr), suggesting that very little PCE was eliminated by metabolism or other extrabranchial routes. Parameterized for trout with physiological information from the literature and chemical partitioning estimates obtained in vitro, the model accurately predicted the accumulation of PCE in blood and tissues, and its extraction from inspired water. These results demonstrate the potential utility of this model for use in aquatic toxicology and environmental risk assessment.

In vitro transformation of BALB/c 3T3 cells by 1,1,2,2-tetrachloroethane

1,1,2,2-Tetrachloroethane (1,1,2,2-TTCE) was shown to be capable of inducing in vitro transformation of BALB/c 3T3 cells (clone A-31) either in the presence or in the absence of S9 activating system using an amplification-transformation (level-II) assay by reseeding confluent cells from each treatment and allowing additional rounds of cell replication. In the absence of metabolic activation, the highest assayed dose (1000 micrograms/ml), exerting the highest toxicity, was the only transforming dose. Lower doses of 1,1,2,2-TTCE were capable of transforming BALB/c cells in the presence of S9 activating system, the dose of 500 micrograms/ml exerting the highest transforming activity. The number and size of transformed foci recognized in the level-II plates were a function of the number of cells reseeded in the amplification assay. Foci obtained in the presence of S9 activating systems were larger in size, more deeply basophilic, and exhibited denser multilayering of constituent cells than foci recognized in the absence of exogenous metabolic activation.

Strategies for optimization of short-term genotoxicity tests: the synergistic effect of NADPH and NADH on P450 function in processing pre-mutagens

The synergistic effect of NADPH and NADH on P450 functions upon pre-mutagens requiring metabolism during the incubation conditions used in the liver microsomal assay (LMA) was studied. The mean specific activity (Asp) during 1 h of pre-incubation (LMA) of some microsomal mono-oxygenases (i.e. ethylmorphine N-demethylase, p-nitroanisole O-demethylase and aminopyrine N-demethylase) examined with S9 fractions from sodium phenobarbital and beta-naphthoflavone pre-treated mice, was doubled when both NADPH and NADH were present. In contrast, when lipid peroxidation was used as the main enzymatic inactivation index, there was no appreciable change. In agreement with biochemical data, in vitro DNA binding of the pre-mutagenic agent [14C]-1,1,1,2-tetrachloroethane ([14C]TTCE), mediated by mouse hepatic enzymes, showed a significant enhancement (4.4-fold) of specific activity in the presence of both pyridine nucleotides. Mutagenesis experiments using TTCE in the diploid D7 strain of Saccharomyces cerevisiae (from stationary growth phase) as a biological test system, showed a significant enhancement of mitotic gene conversion and reverse point mutation frequencies when using NADPH plus NADH in the medium. Conversely, no positive results without NADH were seen. These findings lead us to suggest the routine use of both NADPH and NADH in order to increase the 'sensitivity' of in vitro mutagenicity screens.

Comparison of the hepatotoxicity in mice and the mutagenicity of three nitroalkanes

The hepatotoxic and mutagenic potentials of 2-nitropropane, nitromethane, and nitroethane were compared. Hepatotoxicity was assessed biochemically and histopathologically in BALB/c mice. In male mice, plasma activities of the hepatic enzymes sorbitol dehydrogenase, alanine aminotransferase, and aspartate aminotransferase were significantly elevated 48, 72, and 96 hr after ip administration of 9 mmol/kg 2-nitropropane, but not at 24 hr and not after administration of smaller doses of 2-nitropropane nor after nitromethane or nitroethane (9 mmol/kg). In female mice a dose of 6.7 mmol/kg of 2-nitropropane was sufficient to cause hepatotoxicity. The histopathological evaluation supported the biochemical results, and livers of mice that had received 2-nitropropane (9 mmol/kg) showed damage, particularly in the periportal region. Mutagenicity was tested in Salmonella typhimurium tester strains TA98, TA100, and TA102. Both 2-nitropropane and its anionic form, propane-2-nitronate, were mutagenic but the nitronate was the more powerful mutagen. Nitromethane, nitroethane, nor their nitronates caused an increase in the number of revertant colonies over those seen in control plates. The results suggest that the primary nitroalkanes are much less hepatotoxic and mutagenic than 2-nitropropane.

Covalent binding of 1,1,1,2-tetrachloroethane to nucleic acids as evidence of genotoxic activity

Twenty-two hours after ip administration to male Wistar rats and BALB/c mice, 1,1,1,2-tetrachloroethane (1,1,1,2-TTCE) is bound covalently to DNA, RNA, and proteins of liver, lung, kidney, and stomach. The in vivo reactivity leads to binding values to DNA generally higher in mouse organs than in rat organs. The covalent binding index (CBI) values (82 in mouse liver DNA and 40 in rat liver DNA) classify 1,1,1,2-TTCE as a weak to moderate initiator. Both microsomal and cytosolic enzymatic systems from rat and mouse organs are capable of bioactivating 1,1,1,2-TTCE in vitro. Liver fractions are the most effective. When the activating systems are simultaneously present in the incubation mixture a synergistic effect is observed. Unlike the related chemical 1,1,2,2-tetrachloroethane (1,1,2,2-TTCE), which is bioactivated only through an oxidative route, 1,1,1,2-TTCE metabolism is carried on by oxidative and reductive pathways, both dependent on cytochrome P-450. 1,1,1,2-TTCE is also bioactivated by microsomal GSH-transferases from liver and lung. These data further confirm that correlations exist between structure and genotoxic activity of halocompounds.

Potential role of alpha-2 mu-globulin, protein droplet accumulation, and cell replication in the renal carcinogenicity of rats exposed to trichloroethylene, perchloroethylene, and pentachloroethane

Trichloroethylene (TCE), perchloroethylene (PER), and pentachloroethane (PENT) are used extensively as industrial solvents. These agents cause an increased incidence of renal tumors in male, but not female, rats. Male and female F-344 rats were gavaged for 10 days with TCE (1000 mg/kg), PER (1000 mg/kg), and PENT (150 mg/kg) to determine if chlorinated hydrocarbon-induced changes in levels of renal alpha-2 mu-globulin (alpha 2 mu), protein droplet accumulation (PDA), and cell replication were male rat specific. The animal strain, dose, and route of administration were the same as previous chronic bioassays in order to better understand the relationship between alpha 2 mu, PDA, and cell replication to the sex-specific renal carcinogenicity. In male rats, increases in protein droplet and crystalloid accumulation in the cytoplasm of the P2 segment of the proximal tubule were evident after PER and more notably PENT administration. Cell replication rates in male rats increased specifically in the histologically damaged P2 segments after PER or PENT exposure. Protein droplets and cell replication did not differ from controls in TCE-treated male rats or in female rats treated with TCE, PER, or PENT. Immunohistochemical staining for alpha 2 mu revealed a marked correlation between the presence of alpha 2 mu and the protein droplets. Renal alpha 2 mu concentrations in male rats increased after PER or PENT but not TCE administration. The protein droplet nephropathy induced in male rats after PER and PENT treatment appears identical to that observed with other male-rat-specific renal carcinogens such as unleaded gasoline. The differences observed in male and female rats after chlorinated hydrocarbon exposure suggest that increases in cell replication may be directly linked to the male-rat-specific protein alpha 2 mu. Since compensatory cell division is postulated to affect all stages of the carcinogenic process, the increased incidence of renal tumors in male rats after PER or PENT treatment may be related to nephrotoxicity and resulting enhanced cell replication. Mechanisms involved in TCE-induced renal carcinogenicity appear to be different from PER- and PENT-induced renal carcinogenicity.

Rat liver foci and in vitro assays to detect initiating and promoting effects of chlorinated ethanes and ethylenes

Nine chlorinated aliphatics (CAs) were examined in a rat liver foci assay for tumor initiating and promoting activities. In this model, young adult male Osborne Mendel rats were first subjected to a partial hepatectomy, the test chemical was then administered at the maximum tolerated dose in the initiation or promotion phase in conjunction with diethylnitrosamine (DEN; 30 mg/kg b.w.) or phenobarbital (PB; 0.05 percent, w/w, in the diet), and gamma glutamyltranspeptidase (GGT) was used as a putative preneoplastic indicator. When administered in the promotion protocol after initiation with DEN, 1,1-dichloroethane, 1,1,2-trichloroethane (1,1,2-TCE), 1,1,2,2-tetrachloroethane (1,1,2,2-TTCE), tetrachloroethylene (TTCY), and hexachloroethane induced significant increases in GGT+-foci above control levels. 1,1,2,2-TTCE, TTCY, and 1,1,2-TCE also induced significant increases in GGT+-foci when administered in the promotion protocol without DEN initiation. Two variants of GGT+-foci were observed: the classical type associated with PB promotion, and the other, which was more diffuse, less intensely stained, resembling foci undergoing redifferentiation and associated with CAs. A number of CAs were also genotoxic in short-term in vitro tests. Taken together, the studies suggest that CAs may be complete carcinogens in vivo with weak initiating activity and stronger promoting activity.

Differences in rat liver enzyme-altered foci produced by chlorinated aliphatics and phenobarbital

Nine chlorinated aliphatics (CAs)--1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene, tetrachloroethylene, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, and hexachloroethane--were examined in a rat liver foci assay for evidence of initiating and promoting potential. Young adult male Osborne-Mendel rats (ten/group) were given partial hepatectomies, followed 24 hr later by a single i.p. dose of either diethylnitrosamine (30 mg/kg body weight) or CA, 1 wk later either a diet containing 0.05% (w/w) phenobarbital or daily oral gavage (5 X/wk) of CA in corn oil for 7 weeks, and sacrificed 1 wk later. Putative preneoplastic markers monitored were foci with increased gamma-glutamyltranspeptidase activity [GGT(+)]. CAs were without significant effect in the initiation protocol at the maximum tolerated dose. In the promotion protocol, 1,1-dichloroethane, 1,1,2-trichloroethane, tetrachloroethylene, 1,1,2,2-tetrachloroethane, and hexachloroethane induced significant increases in GGT(+) foci above control levels. Two variants of GGT(+) foci were distinguishable, one associated predominantly with phenobarbital promotion, resembling preneoplastic foci in other models, and the other associated with CA promotion, which was less intensely stained and exhibited branching, resembling foci undergoing redifferentiation. The marked differences in response may relate to differences in cytotoxic potential or mechanism of action of the two types of agents.

In vitro transformation of BALB/c-3T3 cells by chlorinated ethanes and ethylenes

Eight chlorinated ethanes and 3 chlorinated ethylenes were tested in the BALB/c-3T3 cell transformation assay. Under the conditions of the assay, vinyl chloride and 1,1,1-trichloroethane induced a clear positive transformation response while 1,1,2-trichloroethane and trichloroethylene were weakly positive. Chloroethane, 1,1- and 1,2-dichloroethane, 1,1,1,2- and 1,1,2,2-tetrachloroethane, hexachloroethane and tetrachloroethylene were all negative in the assay conducted in the absence of an exogenous metabolic activation system. These results suggest that the BALB/c-3T3 cells possess capability to activate some, but not all, of the chlorinated hydrocarbons which exhibit species specificity in producing carcinogenicity in mice but not in rats.

Intermittent exposure to toxic compounds in the working-zone atmosphere viewed from the aspect of hygienic standardization

Four highly cumulative substances (carbon tetrachloride, 1,1,2,2-tetrachloroethane, benzene and dimethylformamide) were studied at two exposure levels under a monotonous and an intermittent exposure regimen in subacute experiments on rats. The biological effect produced by the intermittent concentrations as compared with the stable concentrations under time-weighted average concentrations depended both on the physiochemical properties and biological action of the poisons as well as on the exposure level. The intermittent concentration rises within certain limits (threefold as a rule) were injurious with some of the substances at a relatively high exposure level, but were not detrimental as compared with stable concentrations at a low exposure level. The other substances showed no difference between the effect of the monotonous and the intermittent regimens at either low or high exposure levels. The results of these studies form an experimental basis for a dual hygienic standardization: the establishment of maximum and average-shift admissible concentrations for the compounds studied as well as other highly cumulative substances.

Comparative in vivo genotoxicity and acute hepatotoxicity of three 1,2-dihaloethanes

Hepatic DNA damage was demonstrated by alkaline DNA unwinding/hydroxylapatite batch chromatography in male B6C3F1 mice treated with non-necrogenic doses of 1,2-dichloroethane, 1-bromo-2-chloroethane, and 1,2-dibromoethane. Intraperitoneal administration of 0.5 mmol/kg of 1-bromo-2-chloroethane and 1,2-dibromoethane produced similar levels of DNA damage. A 4-fold higher dose of 1,2-dichloroethane (2.0 mmol/kg) was required to produce a comparable effect.

Comparison of acute toxic effects of intraperitoneally injected nitromethane and nitroethane in rats

Male 3-month-old Wistar rats dosed i.p. with 200 mg/kg of nitromethane or -ethane showed increased acid proteinase activity in the brain 4 h after the injection. The change was accompanied by a marginal increase in the cerebral glutathione concentration. Nitroethane caused enhanced epoxide hydrolase and UDP-glucuronosyltransferase activity in the hepatic microsomal fraction up to 48 h while 7-ethoxycoumarin o-deethylase decreased. These biochemical changes were accompanied by proliferation of smooth endoplasmic reticulum and degranulation and disorganization of the rough endoplasmic reticulum of the nitroethane-exposed liver cells. The hepatic effects of nitromethane were restricted to decreased cytochrome c reductase activity with proliferation of smooth endoplasmic reticulum. The results point at limited peroxidative damage possibly involving reduction of the nitrogroup.