Metabolism of 1,1,2,2-tetrachloroethane- 14 C in the mouse

Metabolism of 14C-dichloroethyne in rats

1. The metabolism of 14C-dichloroethyne was studied in rats by inhalation in a dynamic nose-only exposure system. 14C-Dichloroethyne was generated in 95-99% yield from 14C-trichloroethene by alkaline dehydrochlorination. 2. After inhalation of 20 ppm and 40 ppm dichloroethyne for 1 h, the retention rates were 17.6% and 15.6% of the radioactivity introduced into the exposure system, respectively. During the period of observation (96 h), almost quantitative elimination of the dose was observed. Elimination with urine accounted for 60.0% (40 ppm) and 67.8% (20 ppm) of absorbed radioactivity and elimination with faeces for 27% (40 ppm) and 27.7% (20 ppm), 3.4-3.5% remained in the carcasses. 3. Metabolites of dichloroethyne identified are: N-acetyl-S-(1,2-dichlorovinyl)-L-cysteine, dichloroethanol, dichloroacetic acid, oxalic acid and chloroacetic acid in urine; N-acetyl-S-(1,2-dichlorovinyl-L-cysteine in faeces. 4. In bile of rats exposed to 40 ppm of dichloroethyne, S-(1,2-dichlorovinyl)glutathione was the only metabolite identified. Biliary cannulation did not influence the renal excretion of N-acetyl-S-(1,2-dichlorovinyl)-L-cysteine, indicating that glutathione conjugate formation occurs in the kidney. 5. The results suggest that two metabolic pathways are operative in dichloroethyne metabolism in vivo. Cytochrome P450-dependent oxidation represents a minor pathway accounting for the formation of 1,1-dichloro compounds after chlorine migration. The major pathway is the biosynthesis of toxic glutathione conjugates. Organ-specific toxicity and carcinogenicity of dichloroethyne is due most likely to the topographical distribution of gamma-glutamyl transpeptidase which is concentrated mainly in the kidney in rats.

Inter- and intramolecular deuterium isotope effects on the cytochrome P-450-catalyzed oxidative dehalogenation of 1,1,2,2-tetrachloroethane

The oxidation of 1,1,2,2-tetrachloroethane to dichloroacetic acid was investigated with rat liver microsomes and purified cytochrome P-450. Deuterium substitution had no effect on Km values, but both the inter- and intramolecular isotope effects (kH/kD) on Vmax were in the range 5.7-6.1. The equivalence of the inter- and intramolecular values indicates that 6.0 may be a good estimate of the intrinsic isotope effect. The intermolecular kH/kD value for the conversion of 1,1,2,2-trichloroethane and its 1-2H analog to chloroacetic acid was 5.5. These data, and the finding that 1 atom of 18O was incorporated into the product when TCEA was oxidized in an 18O2 atmosphere, support an oxidative dechlorination mechanism that involves hydrogen atom abstraction by the P-450 intermediate oxo complex.

Absorption, elimination and metabolism of trichloroethylene: a quantitative comparison between rats and mice

The absorption, elimination and metabolism of 14C-trichloroethylene (Tri) was studied in adult female Wistar rats and NMRI mice after administration of 200, 20 and 2 mg/kg Tri. Dose-dependent biotransformation of Tri to metabolites was observed in both species. Induction of hepatic mono-oxygenases by phenobarbital or polychlorinated biphenyls resulted in a higher rate of biotransformation after a single oral dose of 200 mg/kg 14C-Tri to rats. An increase in radioactivity covalently bound to liver and kidney macromolecules of induced rats as compared to control rats parallels the toxic effects of Tri on these organs after induction of cytochrome P-450. The urinary metabolites were analysed by h.p.l.c. In both species, 1,1,1-trichlorocompounds (trichloroacetic acid, trichloroethanol and its glucuronide, comprising 88.9-93.5% of the radioactivity excreted in the urine) constituted the main metabolites; in addition, N-(hydroxyacetyl)-aminoethanol (4.1-7.2%), dichloroacetic acid (0.1-2.0%) and oxalic acid (0.7-1.8%) were identified. The pattern of metabolites in the 72 h urine remained constant for each species in the dose range studied and no change was induced by pretreatment. The percentage of radioactivity exhaled as 14CO2 increased with dose in mice, which may indicate dose-dependent formation of dichloroacetic acid and saturation of deactivating mechanisms for reactive intermediates in mice.

Metabolic disposition study of chlorinated hydrocarbons in rats and mice

Chlorinated hydrocarbons found in a bioassay to be carcinogenic to both B6C3F1 mice and Osborne-Mendel rats (1,2-dichloroethane), carcinogenic only to mice (1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane, hexachloroethane, trichloroethylene, and tetrachloroethylene), and noncarcinogenic to either species (1,1-dichloroethane and 1,1,1-trichloroethane) were used to investigate the biochemical bases for tumorigenesis. Studies were conducted after chronic oral dosing of adult mice and rats with the MTD and 1/4 MTD of each compound. The extent to which the compounds were metabolized in 48 hr, hepatic protein binding, and urinary metabolite patterns were examined. Metabolism of the compounds (mmoles per kg body weight) was 1.7 to 10 times greater in mice than in rats. Hepatic protein binding (nanomole equivalents bound to 1 mg of liver protein) was 1.2 to 8.3 times higher in mice than in rats except for 1,2-dichloroethane and 1,1,1-trichloroethane. The noncarcinogens 1,1-dichloroethane and 1,1,1-trichloroethane exhibited 2 to 18 times more binding in mice than did the carcinogens 1,2-dichloroethane and 1,1,2-trichloroethane. Urinary metabolite patterns of the compounds were similar in both species. The biochemical parameters measured provided no clue to differentiate the carcinogens from the noncarcinogens.

Metabolism of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane in the mouse

The metabolites of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD) found in the urine of female Swiss mice are reported. The metabolites of DDT are DDD, 1-chloro-2,2-bis(p-chlorophenyl)ethene (DDMU), 1,1-dichloro-2-bis(p-chlorophenyl)ethene (DDE), 2,2-bis(p-chlorophenyl)acetic acid (DDA), 2-hydroxy-2,2-bis(p-chlorophenyl)acetic acid (alpha OH-DDA) and 2,2-bis(p-chlorophenyl)ethanol (DDOH), while DDD afforded DDMU, DDE, DDA, alpha OH-DDA and DDOH. The relative excreted levels of DDA and DDOH and the absence of 2,2-bis(p-chlorophenyl)acetaldehyde (DDCHO) are not consistent with the generally accepted pathway for DDA formation, which involves sequential metabolism of DDT and DDD via DDOH to afford DDA. The quantitative results are interpreted to mean that DDA is formed by hydroxylation at the chlorinated sp3-side chain carbon of DDD to give 2,2-bis(p-chlorophenyl)acetyl chloride (DDA-Cl), which in turn is hydrolyzed to DDA. The excretion of alpha OH-DDA from both DDT- and DDD-treated mice has never been previously observed. It is suggested that this metabolite arises from the initial epoxidation of DDMU, a metabolite of DDT and DDD, to yield 1,2-epoxy-1-chloro-2,2-bis(p-chlorophenyl)ethane (DDMU-epoxide). This chloroepoxide is then hydrolyzed and oxidized to produce the alpha OH-DDA.

Toxicity studies on trans-1,2-dichloroethylene

Trans-1,2-dichloroethylene (t-DCE), an industrial solvent, proved to be moderately toxic when studied in small laboratory animals. In adult female rats brief (8 h) and prolonged (8 h daily, on 5 consecutive days a week, for more than 16 weeks) inhalation of 200 ppm--the current TLV/MAC in various countries--produced histological evidence of slight to severe fatty degeneration of the liver lobules and Kupffer cells. In addition marked pulmonary hyperaemia and alveolar septal distention were noted. Fibrous swelling of the cardiac muscle (with striation) just barely maintained) and hyperaemia remained detectable for as long as 14 h post-exposure, but only occurred at 3000 ppm/8 h. A concentration of 1000 ppm/8 h was required to produce a fall in blood albumin, urea nitrogen, alkaline phosphatase activities and erythrocyte count. The cited concentrations failed to produce prenarcotic symptoms of narcosis (central nervous system (CNS) depression). The LD50 was found to be 6.0 ml/kg i.p. and 1.0 ml/kg p.o. for female rats, and 3.2 ml/kg i;p. for female mice. In some of the rats killed in these experiments the organ changes were found to be identical to those observed after inhalation.