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D Henschler

Publications and source records attributed to D Henschler.

170 records · Page 10Linked to original sources
PubMedDate not supplied

Metabolism of the nephrotoxin dichloroacetylene by glutathione conjugation.

Dichloroacetylene (DCA) is a potent nephrotoxin and nephrocarcinogen in rodents. The activation reactions responsible for this organ-specific toxicity are not known. We now report the identification of S-(1,2-dichlorovinyl)glutathione (DCVG) as a product of the glutathione (GSH) dependent metabolism of DCA in vitro and the identification of N-acetyl-S-(1,2-dichlorovinyl)-L-cysteine (N-Ac-DCVC) as a urinary metabolite of DCA in rats. Formation of DCVG from DCA, used as 1:1 complex with diethyl ether, in male rat liver and kidney subcellular fractions was dependent on time, native protein, and the presence of GSH. Initial reaction rates at 23 degrees C were determined as 2923 nmol/(min.mg) for liver and 2838 nmol/(min.mg) for kidney microsomes. With cytosol, DCVG formation rates were 705 nmol/(min.mg) (liver cytosol) and 129 nmol/(min.mg) (kidney cytosol). With liver microsomes, a KM of 7.5 mM and a Vmax of 5464 nmol/(min.mg) for GSH were obtained. The product, DCVG, was definitively identified by 1H NMR spectrometry (400 MHz), mass spectrometry, and UV spectroscopy. N-Ac-DCVC was identified as a urinary metabolite from rats by GC/MS after esterification. Urine (collected for 24 h) from male rats exposed to 36 +/- 5 ppm DCA (100 mumol of DCA introduced into the exposure system) for 1 h contained 10.7 mumol of N-Ac-DCVC as determined by HPLC analysis. Formation of DCVG, renal processing to S-(1,2-dichlorovinyl)-L-cysteine, and cleavage of this cysteine S-conjugate by cysteine S-conjugate beta-lyase in the kidney with formation of reactive and mutagenic intermediates may account for DCA nephrotoxicity and nephrocarcinogenicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcysteine↗
PubMedDate not supplied

Genotoxicity of neurotoxic triaryl phosphates: identification of DNA adducts of the ultimate metabolites, saligenin phosphates.

2-Phenoxy-4H-1,3,2-benzodioxaphosphorin 2-oxide is an electrophilic and neurotoxic metabolite of o-tolyl phosphates. We have investigated the genotoxicity of this saligenin phosphate and the structure of adducts formed by incubation of 2-phenoxy-4H-1,3,2-benzodioxaphosphorin 2-oxide with nucleosides and DNA. o-Tolyl phosphate was mutagenic in the Ames test (695 revertants/mumol, Salmonella typhimurium TA 100) only with metabolic activation. 2-Phenoxy-4H-1,3,2-benzodioxaphosphorin 2-oxide, which is a cyclization product similar to those expected from o-tolyl phosphate, was a potent mutagen in bacteria (1452 revertants/mumol, S. typhimurium TA 100) which did not require metabolic activation. Incubation of 2-phenoxy-4H-1,3,2-benzodioxaphosphorin 2-oxide with guanosine, deoxycytidine, and deoxyadenosine resulted in formation of guanosine, deoxyuridine, and adenine adducts. These were identified as N-2-(o-hydroxybenzyl)guanosine, N-3-(o-hydroxybenzyl)deoxyuridine, N-1-(o-hydroxybenzyl)adenine, and N-3-(o-hydroxybenzyl)adenine by 1H-NMR spectroscopy, thermospray mass spectrometry, and pH-dependent electronic spectrometry. The deoxyuridine adduct is formed by an alkylation at N-3 of deoxycytidine followed by conversion of the adjacent exocyclic imino group to carbonyl (hydrolytic deamination). The formation of N-2-(o-hydroxybenzyl)-deoxyguanosine, N-3-(o-hydroxybenzyl)deoxyuridine, and N-1-(o-hydroxybenzyl)deoxyadenosine was also demonstrated when 2-phenoxy-4H-1,3,2-benzodioxaphosphorin 2-oxide was incubated with calf thymus DNA. Adducts formed with nucleosides in calf thymus DNA reacted with 2-phenoxy-4H-1,3,2-benzodioxaphosphorin 2-oxide in vitro were detected by the 32P-postlabeling technique and identified by comparison with synthetic references. DNA adducts are formed by an o-hydroxybenzylation from cyclic phosphoranes derived from o-alkyl-substituted triaryl phosphates.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Metabolism of tetrachloroethene in rats: identification of N epsilon-(dichloroacetyl)-L-lysine and N epsilon-(trichloroacetyl)-L-lysine as protein adducts.

Tetrachloroethene causes renal tumors in male rats after inhalation exposure. Tetrachloroethene is metabolized by cytochrome P-450 and by glutathione conjugation. Cytochrome P-450-dependent oxidation results in the formation of trichloroacetyl chloride, which may acylate cellular nucleophiles; glutathione conjugation results in the formation of S-(1,2,2-trichlorovinyl)glutathione, which is metabolized to the corresponding cysteine S-conjugate. S-(1,2,2-Trichlorovinyl)-L-cysteine is activated by renal cysteine conjugate beta-lyase to give dichlorothioketene. Covalent binding of this electrophile is presumably responsible for the renal toxicity of tetrachloroethene. In this report, we demonstrate the formation of protein adducts formed from tetrachloroethene using SDS-PAGE and immunochemical detection with rabbit anti-trifluoroacetyl serum. This serum recognizes dichloroacetylated rabbit serum albumin prepared by chemical modification of rabbit serum albumin with S-ethyl dichlorothioacetate and exhibited a high specificity for N epsilon-(dichloroacetyl)-L-lysine residues in proteins as shown by competitive ELISA. In the liver of [14C]tetrachloroethene-treated rats, the antibody recognized several modified proteins in microsomes. A protein adduct in rat liver identified by GC/MS after hydrolysis was N epsilon-(trichloroacetyl)-L-lysine. Western blots of renal fractions from rats treated with [14C]tetrachloroethene (200 mg/kg) or S-(1,2,2-trichlorovinyl)-L-cysteine (40 mumol/kg, iv) suggested the presence of modified mitochondrial and cytosolic proteins; no modified proteins were detected in microsomes. Proteins of identical molecular weight were modified by tetrachloroethene and by S-(1,2,2-trichlorovinyl)-L-cysteine in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMedDate not supplied

Bioactivation of tetrachloroethylene. Role of glutathione S-transferase-catalyzed conjugation versus cytochrome P-450-dependent phospholipid alkylation.

The metabolism of [14C]tetrachloroethylene (Tetra) and its metabolite S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC) was investigated with in vitro systems to substantiate metabolic pathways of Tetra deduced from in vivo experiments. In the presence of NADPH, rat hepatic microsomal fractions metabolized Tetra to soluble metabolites, which were identified as trichloroacetic acid and oxalic acid by gas chromatography/mass spectroscopy and a metabolite largely bound to microsomal macromolecules. The majority of the alkylated macromolecules were identified as N-trichloroacetylated phospholipids by high performance liquid chromatography and GC/MS. When Tetra was incubated with hepatic microsomes and cytosol in the presence of 10 mM glutathione, but in the absence of NADPH, the formation of a polar metabolite other than trichloroacetic acid and oxalic acid was observed. This metabolite was identified, after hydrolysis to the corresponding cysteine conjugate, as S-(1,2,2-trichlorovinyl)-glutathione (TCVG). Microsomal GSH S-transferases catalyzed TCVG formation more efficiently than cytosolic GSH S-transferases; the competitive substrate 1-chloro-2,4-dinitrobenzene inhibited TCVG formation. In the presence of both NADPH and GSH, TCVG formation in microsomes was decreased, indicating that oxidative metabolism and GSH conjugation of Tetra are competitive reactions. The Tetra metabolite TCVC was cleaved by bacterial cysteine conjugate b-lyase to dichloroacetic acid and pyruvate. The obtained results substantiate the postulated pathways of Tetra biotransformation and demonstrate that both oxidative and conjugative reactions occur in hepatic Tetra metabolism. Phospholipid alkylation, which occurs during oxidative metabolism, may be a deactivation reaction, whereas TCVG formation, renal metabolism to TCVC, and cleavage of TCVC by b-lyase under formation of mutagenic intermediates may contribute to the nephrocarcinogenic effect of Tetra.

Alkylation↗
PubMedDate not supplied

Enzymatic conjugation of hexachloro-1,3-butadiene with glutathione. Formation of 1-(glutathion-S-yl)-1,2,3,4,4-pentachlorobuta-1,3-diene and 1,4-bis(glutathion-S-yl)-1,2,3,4-tetrachlorobuta-1,3-diene.

The glutathione-dependent metabolism of the nephrotoxin and nephrocarcinogen hexachloro-1,3-butadiene (HCBD) was investigated in subcellular fractions from rat liver and kidney. HCBD was metabolized by hepatic glutathione S-transferases to (E)- and (Z)-1-(glutathion-S-yl)-pentachlorobuta-1,3-diene (GPCB) in a ratio of 20:1, which were identified by secondary ion MS and by GC-MS after acid hydrolysis. The formation of GPCB was dependent on time and on protein and glutathione concentrations. Microsomal glutathione S-transferases from rat liver catalyzed GPCB formation more efficiently than did cytosolic glutathione S-transferases; very low rates of GPCB formation were observed in kidney subcellular fractions. GPCB is also a substrate for glutathione S-transferases and is metabolized to a diglutathione conjugate, which was identified by secondary ion MS and 13C NMR spectrometry as 1,4-bis(glutathion-S-yl)-1,2,3,4-tetrachlorobuta-1,3-diene (BTCB). BTCB formation from GPCB was dependent on time and on protein, glutathione, and GPCB concentrations. Hepatic cytosol catalyzed BTCB formation more efficiently than did hepatic microsomes; significant amounts of BTCB were also formed in kidney cytosol. Hepatic formation of glutathione S-conjugates, translocation of the S-conjugates to the kidney, and renal processing to form reactive intermediates may be the cause of HCBD-induced nephrotoxicity and, perhaps, nephrocarcinogenicity.

Animals↗
PubMedDate not supplied

Metabolism of chlorinated alkenes and alkanes as related to toxicity.

The chlorine substitution in aliphatic compounds results, by its electron attracting effect, in a destabilization in alkanes and a stabilization in alkenes. Thus, with alkanes the main pathways of metabolic transformation to reactive intermediates are radical formation by C-C break or dechlorination, or dehydrochlorination. In alkenes, the stability of the molecule increases with the number of chlorine substitutions. In the series of chlorinated ethylenes, the first step of metabolic transformation is the oxidation to electrophilic oxiranes which may be hydrolized enzymatically or non-enzymatically, react with cellular nucleophiles, or rearrange to either chlorinated aldehydes or acyl chlorides. With tetra-, 1,2-cis- and trans-di-, 1,1-di-, and monochloroethylene, the metabolites identified in in vivo experiments are identical with the thermal rearrangement products of the respective oxiranes. An important exception is found with trichloroethylene, where the thermal rearrangement product is dichloroacetyl chloride; the metabolites in vivo, however, are entirely derived from trichloroacetaldehyde (chloral). The reason for this peculiar behavior is most probably a Lewis acid catalysis by the oxidizing enzyme system. Mutagenic and carcinogenic activities in the series of chlorinated ethylenes are determined by the stability of their oxiranes, which is higher in symmetrical than in unsymmetrical chlorine substitution: the relatively unstable and unsymmetric oxiranes of trichloroethylene, 1, 1,-dichloro-, and monochloroethylene are mutagenic in the Ames test; the more stable symmetric oxiranes of tetra-, 1,2-cis- and trans-dichloroethylenes are inactive.

Animals↗