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.     

Mutagenic activity in rat urine after feeding with the azo dye tartrazine

The azo dye tartrazine, after dosing by gavage, is transformed by rats into urinary metabolites which exert dose-dependent mutagenic activities in the Ames test with Salmonella typhimurium TA 98 after addition of rat liver metabolizing enzymes (S9 mix). The strain TA 100 showed no mutagenic response. Abbreviation: FD & C Yellow No. 5 (5-oxo-1-(p-sulphophenyl)-4-(sulphophenylazo)-2-pyrazoline-3-carboxylic acid, trisodium salt)     

Enzymatic transformation of mercapturic acids derived from halogenated alkenes to reactive and mutagenic intermediates

The metabolism of the mercapturic acids S-pentachlorobutadienyl-N-acetylcysteine (N-Ac-PCBC), S-trichlorovinyl-N-acetylcysteine (N-Ac-TCVC) and S-dichlorovinyl-N-acetylcysteine (N-Ac-DCVC) by subcellular fractions from male rat liver and kidney homogenates was studied. As a model compound, N-Ac-PCBC, 14C labelled, was synthesised. It was intensively metabolised by cytosolic but not by microsomal enzymes from rat liver and kidney. The major metabolite identified by GC/MS was pentachlorobutadienylcysteine, the amount produced being highest in kidney cytosol. Metabolic conversion of 14C-N-Ac-PCBC by kidney and liver cytosol resulted in covalent binding of radioactivity to protein, binding was strongly inhibited by the beta-lyase inhibitor aminooxyacetic acid (AOAA). N-Ac-TCVC and N-Ac-DCVC were also transformed by cytosolic enzymes to the corresponding cysteine conjugates (trichlorovinylcysteine and dichlorovinylcysteine). The three mercapturic acids tested were strong mutagens in the Ames-test after addition of rat kidney cytosol. In the absence of cytosol, N-Ac-TCVC and N-Ac-DCVC were weakly but definitely mutagenic, whereas N-Ac-PCBC was not. In contrast to N-Ac-PCBC, the "direct" mutagens N-Ac-TCVC and N-Ac-DCVC were both transformed to pyruvate by bacterial (S. typhimurium TA100) homogenate 100,000 g supernatants. It is concluded that mercapturic acids are deacetylated to the corresponding cysteine conjugates by cytosolic (N-Ac-PCBC, N-Ac-TCVC and N-Ac-DCVC) and bacterial enzymes (N-Ac-TCVC and N-Ac-DCVC) and further cleaved to reactive and mutagenic intermediates by mammalian and/or bacterial beta-lyase. The observed activation mechanisms for the mercapturic acids, whose formation from hexachlorobutadiene, tetrachloroethylene and trichloroethylene has been proven, might contribute to the nephrotoxicity and nephrocarcinogenicity of the parent alkenes.     

Identification of potential carcinogens in technical grade 1,1,1- trichloroethane

Summary Gas chromatography and gas chromatography-mass spectrometry were employed to analyze 22 samples of technical grade 1,1,1-trichloroethane for impurities. Eighteen contained vinylidene chloride (1,1-dichloroethylene) (30–900 g/ml) and further contaminants were identified as 1,1-dichloroethane (11), trichloroethylene (12), and 1,1,2-trichloroethane (9). Nitromethane (18), 1,2-epoxybutane (19), tert. butanol (7), and dioxane (10) were detected as stabilizers. It is recommended that the manufacturers should eliminate vinylidene chloride and stabilizers which carry a carcinogenic and/or mutagenic risk, from technical samples of 1,1,1-trichloroethane.     

Aktivierung von Tri(p-äthylphenyl-)phosphat in Darm und Leber zu neurotoxischen Metaboliten

Ohne Zusammenfassung     

Thioacylating intermediates as metabolites of S-(1,2-dichlorovinyl)-L-cysteine and S-(1,2,2-trichlorovinyl)-L-cysteine formed by cysteine conjugate beta-lyase

The bioactivation mechanism of S-(1,2-dichlorovinyl)-L-cysteine (DCVC) and S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC) was studied with cysteine conjugate beta-lyase (beta-lyase) from Salmonella typhimurium and with the pyridoxal phosphate model N-dodecylpyridoxal bromide (PL-Br) as catalysts and with GC/MS to identify the metabolites formed. PL-Br converted S-2-benzothiazolyl-L-cysteine to 2-mercaptobenzothiazole and S-benzyl-L-cysteine to benzyl mercaptan, demonstrating the ability of PL-Br to serve as a model for beta-lyase. PL-Br and bacterial beta-lyase converted DCVC to chloroacetic acid and chlorothionoacetic acid and TCVC to dichloroacetic acid. Incubations of PL-Br with the S-conjugates in the presence of diethylamine resulted in the formation of N,N-diethylchlorothioacetamide from DCVC and of N,N-diethyldichlorothioacetamide from TCVC. Attempts to trap the enethiols, which are the expected initial products formed by beta-elimination, by reaction with methyl iodide in incubations with the beta-lyase model were not successful. The formation of thioacylating agents from the enethiols may contribute to the cytotoxic and mutagenic effects of DCVC and TCVC.     

Mutagenicity of chlorinated cyclopentadienes due to metabolic activation.

Chlorinated cyclopentadienes of which hexachlorocyclopentadiene is used for pesticide synthesis is suggested to undergo metabolic conversion forming acylating and possibly mutagenic tetrachlorocyclopentadienone. Tetra-, penta-, and hexachlorocyclopentadiene differ in the chlorine substitution at C-1. Oxygen insertion into C-1, which results in the formation of the dienone should depend on the degree of chlorine substitution at this position. The dienone is not stable and can only be isolated as the dimer. To detect its formation an in vitro-test system, comprising mouse liver microsomes for metabolic activation and E. coll K 12 ($\text{343}\text{113}$) to detect mutagenicity, has been used.According to the previous suggestions tetrachlorocyclopentadiene and pentachlorocyclopentadiene were highly mutagenic after metabolic activation, whereas hexachlorocyclopentadiene was not.