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W Dekant

Publications and source records attributed to W Dekant.

At least 55 records · Page 3Linked to original sources
PubMed1998

Generation of antibodies to Di- and trichloroacetylated proteins and immunochemical detection of protein adducts in rats treated with perchloroethene.

Antibodies directed against chemical specific protein modifications are valuable tools to detect and comparatively quantify protein modifications. Both Nepsilon-(dichloroacetyl)-L-lysine and Nepsilon-(trichloroacety)l-L-lysine have been detected as modified amino acids in liver and kidneys of rats treated with perchloroethene (PER) after proteolysis. These protein modifications are formed by the interaction of reactive metabolites formed from PER with proteins. In this study we developed monospecific antibodies to dichloroacetylated and to trichloroacetylated amino acids to detect modified proteins in the target organs of PER toxicity. These antibodies were prepared by immunization of rabbits with modified keyhole limpet hemocyanin (KLH) coupled with either the dichloroacetyl or trichloroacetyl moiety. Enzyme-linked immunosorbent assays (ELISA) indicated that the polyclonal rabbit sera recognized dichloroacetylated or trichloroacetylated rabbit serum albumin (RSA), but not unmodified protein. Therefore, we further purified rabbit antisera on either Nepsilon-(dichloroacetyl)-L-lysine or Nepsilon-(trichloroacetyl)-L-lysine immobilized to immunoaffinity columns to obtain monospecific antibodies. The potential of these antibodies in the detection of di- and trichloroacetylated proteins and their selectivity for the desired dichloroacetyl or trichloroacetyl group was demonstrated in competitive enzme-linked immunosorbent assays with several structurally related compounds. Anti-dichloroacetyl (anti-DCA) antibody binding to dichloroacetylated RSA was inhibited by Nepsilon-(dichloroacetyl)-L-lysine with an IC50 value of 150 microM whereas inhibition by Nepsilon-(monochloroacetyl)-L-lysine and Nepsilon-(trichloroacetyl)-L-lysine showed an IC50 value of 100 mM. The binding of the anti-trichloroacetyl (anti-TCA) antibody to trichloroacetylated RSA was inhibited by Nepsilon-(dichloroacetyl)-L-lysine with an IC50 value of 80 mM. The inhibition by Nepsilon-(trichloroacetyl)-L-lysine was again 3 orders of magnitude stronger resulting in an IC50 value of 90 microM. Nepsilon-(acetyl)-L-lysine and unmodified RSA did not effect antibody binding to the chemically modified antigen. The antibodies were also successfully applied to detect modified proteins in subcellular fractions of liver and kidney from PER treated rats demonstrated in immunoblot. Protein adduct formation from different PER metabolism pathways was confirmed by the observation that the majority of dichloroacetylated proteins were located in kidney mitochondria and trichloroacetylated proteins were located in liver microsomes.

Animals↗
PubMed1998

Chlorothioketene, the ultimate reactive intermediate formed by cysteine conjugate beta-lyase-mediated cleavage of the trichloroethene metabolite S-(1,2-Dichlorovinyl)-L-cysteine, forms cytosine adducts in organic solvents, but not in aqueous solution.

Chlorothioketene has been suggested as a reactive intermediate formed by the cysteine conjugate beta-lyase-mediated cleavage of S-(1,2-dichlorovinyl)-L-cysteine, a minor metabolite of trichloroethene. Halothioketenes are highly reactive, and their intermediate formation may be confirmed by reactions such as cycloadditions and thioacylations of nucleophiles. A precursor of chlorothioketene, S-(1,2-dichlorovinyl)thioacetate, is readly accessible by the reaction of dichloroethyne with thioacetic acid. In presence of base, S-(1,2-dichlorovinyl)thioacetate is cleaved to chlorothioketene. Chlorothioketene is not stable at room temperature and was characterized after transformation to stable products by reaction with compounds such as cyclopentadiene, N,N-diethylamine, and ethanol. In organic solvents, the cleavage of S-(1, 2-dichlorovinyl)thioacetate in the presence of cytosine results in N4-acetylcytosine, N4-(chlorothioacetyl)cytosine, and small amounts of 3-(N4-thioacetyl)cytosine. No reaction products were seen with guanosine, adenosine, and thymidine under identical conditions. When cytosine was reacted with S-(1,2-dichlorovinyl)thioacetate in aqueous solutions, only N4-acetylcytosine was formed. N4-(Chlorothioacetyl)cytosine and 3-(N4-thioacetyl)cytosine were not detected even when using a very sensitive method, derivatization with pentafluorobenzyl bromide and electron capture mass spectrometry with a detection limit of 50 fmol/microliter of injection volume. Aqueous solutions of DNA cleave S-(1, 2-dichlorovinyl)thioacetate to give N4-acetyldeoxycytidine in DNA, but chlorothioketene adducts of deoxynucleosides were also not detected in these experiments. These results confirm the electrophilic reactivity of chlorothioketene toward nucleophilic groups of DNA constituents in inert solvents but also demonstrate that the formation of DNA adducts under physiological conditions likely is not efficient. Therefore, DNA adducts may not represent useful biomarkers of exposure and biochemical effects for trichloroethene.

Acetates↗
PubMed1998

Glutathione-dependent bioactivation of haloalkenes.

Several halogenated alkenes are nephrotoxic in rodents. A mechanism for the organ-specific toxicity of these compounds to the kidney has been elucidated. The mechanism involves hepatic glutathione conjugation to dihaloalkenyl or 1,1-difluoroalkyl glutathione S-conjugates, which are cleaved by gamma-glutamyltransferase and dipeptidases to cysteine S-conjugates. Haloalkene-derived cysteine S-conjugates may have four fates in the organism: (a) They may be substrates for renal cysteine conjugate beta-lyases, which cleave them to form reactive intermediates identified as thioketenes (chloroalkene-derived S-conjugates), thionoacyl halides (fluoroalkene-derived S-conjugates not containing bromide), thiiranes, and thiolactones (fluoroalkene-derived S-conjugates containing bromine); (b) cysteine S-conjugates may be N-acetylated to excretable mercapturic acids; (c) they may undergo transamination or oxidation to the corresponding 3-mercaptopyruvic acid S-conjugate; (d) finally, oxidation of the sulfur atom in halovinyl cysteine S-conjugates and corresponding mercapturic acids forms Michael acceptors and may also represent a bioactivation reaction. The formation of reactive intermediates by cysteine conjugate beta-lyase may play a role in the target-organ toxicity and in the possible renal tumorigenicity of several chlorinated olefins widely used in many chemical processes.

Alkenes↗
PubMed1998

Biotransformation of the anthraquinones emodin and chrysophanol by cytochrome P450 enzymes. Bioactivation to genotoxic metabolites.

The studies presented here were designed to elucidate the enzymes involved in the biotransformation of naturally occurring 1, 8-dihydroxyanthraquinones and to investigate whether biotransformation of 1,8-dihydroxyanthraquinones may represent a bioactivation pathway. We first studied the metabolism of emodin (1, 3,8-trihydroxy-6-methylanthraquinone), a compound present in pharmaceutical preparations. With rat liver microsomes, the formation of two emodin metabolites, omega-hydroxyemodin and 2-hydroxyemodin, was observed. The rates of formation of omega-hydroxyemodin were not different with microsomes from rats that had been pretreated with inducers for different cytochrome P450 enzymes. Thus, the formation of omega-hydroxyemodin seems to be catalyzed by several cytochrome P450 enzymes at low rates. The formation of 2-hydroxyemodin was increased in liver microsomes from 3-methylcholanthrene-pretreated rats and was inhibited by alpha-naphthoflavone, by an anti-rat cytochrome P450 1A1/2 antibody, and, to a lesser degree, by an anti-rat cytochrome P450 1A1 antibody. These data suggest the involvement of cytochrome P450 1A2 in the formation of this metabolite. However, other cytochrome P450 enzymes also seem to catalyze this reaction. The anthraquinone chrysophanol (1,8-dihydroxy-3-methylanthraquinone) is transformed, in a cytochrome P450-dependent oxidation, to aloe-emodin (1, 8-dihydroxy-3-hydroxymethylanthraquinone) as the major product formed. The mutagenicity of the parent dihydroxyanthraquinones and their metabolites was compared in the in vitro micronucleus test in mouse lymphoma L5178Y cells. 2-Hydroxyemodin induced much higher micronucleus frequencies, compared with emodin. omega-Hydroxyemodin induced lower micronucleus frequencies, compared with emodin. Aloe-emodin induced significantly higher micronucleus frequencies than did chrysophanol. These data indicate that the cytochrome P450-dependent biotransformation of emodin and chrysophanol may represent bioactivation pathways for these compounds.

Animals↗
PubMed1997

Binding of hexachlorobutadiene to alpha 2u-globulin and its role in nephrotoxicity in rats.

Hexachlorobutadiene (HCBD) is nephrotoxic in rats causing damage to the proximal tubules. Renal toxicity is presumed to be due to bioactivation by glutathione S-conjugate formation and further processing by the enzymes of the mercapturic acid pathway to reactive intermediates. Recent studies revealed major sex-dependent differences in the pattern of urinary metabolites and gave evidence for the excretion of unmetabolized HCBD in the urine of male, but not female, rats. The objective of this study was to investigate the basis for the excretion of unchanged HCBD in the urine. We administered [14C]-HCBD (200 mg/kg bw, po) to male and female Sprague-Dawley (SD) and NCI Black-Reiter rats (NBR), an alpha 2u-globulin-deficient strain. No major differences in the disposition and in the rates of excretion of [14C]-derived radioactivity were observed between animals of both strains. Previously observed sex-specific differences in the formation of urinary metabolites in Wistar rats were now confirmed in SD rats and were also found in NBR rats. In contrast to male SD rats, however, NBR rats did not excrete unmetabolized HCBD with urine. [14C]-HCBD (10% of total urinary metabolites) was only present in the urine of male SD rats. Anion-exchange HPLC showed radioactivity associated with the alpha 2u-globulin fraction in urine and renal cytosol of male SD rats; the radioactive compound was identified as HCBD bound to the protein. The results indicate that the male-specific urinary excretion of HCBD is associated with its binding to alpha 2u-globulin. Light microscopic examination revealed the formation of hyaline droplets indicative of the accumulation of alpha 2u-globulin in the kidney of male SD rats after staining with Lee's methylene blue basic fuchsin. H&E staining additionally confirmed the finding of more pronounced necrotic changes in renal tubules of male SD rats than in females as previously described for Wistar rats. Binding of HCBD to alpha 2u-globulin may contribute to the pronounced nephrotoxicity in male rats.

Alpha-Globulins↗
PubMed1997

Biotransformation, excretion and nephrotoxicity of haloalkene-derived cysteine S-conjugates.

The formation of cysteine S-conjugates is thought to play an important role in the nephrotoxicity of haloalkenes such as trichloroethene, tetrachloroethene and hexachlorobutadiene. Glutathione S-conjugates formed from these haloalkenes in the liver are processed to the corresponding cysteine S-conjugates, which may be N-acetylated to mercapturic acids and may be accumulated in the kidney. Haloalkene-derived cysteine S-conjugates are also substrates for cysteine conjugate beta-lyases and reactive intermediates are formed in this reaction. The equilibrium between cysteine S-conjugate and mercapturic acid thus influences the extent of beta-lyase dependent bioactivation and subsequently the nephrotoxicity of S-conjugates. In this study, we compared the rates of N-acetylation in vitro and the biotransformation, excretion and nephrotoxicity of S-(1,2-dichlorovinyl)-L-cysteine (1,2-DCVC), S-(2,2-dichlorovinyl)-L-cysteine (2,2-DCVC), S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC) and S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine (PCBC) in rats after i.v. injection (40 micromoles/kg). Marked differences in the extent of enzymatic N-acetylation were observed; N-acetylation was most efficient with 2,2-DCVC and least efficient with 1,2-DCVC. In urine, within 48 h, most of the given 2,2-DCVC (77% of the recovered dose) and 1,2-DCVC (92%) were recovered as the corresponding mercapturic acids. In contrast, a higher percentage of cysteine S-conjugate and less of the mercapturic acid were recovered in urine after administration of PCBC and TCVC (50 and 23% of dose as mercapturic acid), respectively. Histopathological examination of the kidneys and urine clinical chemistry showed marked differences in the extent of renal damage. Necroses of the proximal tubules were found after TCVC, PCBC and 1,2-DCVC administration in male, but not in female rats. These differences in nephrotoxicity do not correlate with the balance of acetylation/deacetylation. The higher toxicity observed in male rats may indicate the involvement of other parameters such as uptake mechanisms.

Acetylation↗
PubMed1996

Biotransformation of the fungicide chlorthalonil by glutathione conjugation.

The biotransformation of the nephrotoxic fungicide chlorthalonil (2,4,5,6-tetrachloroisophthalonitril) has been studied in the rat and in rat liver subcellular fractions. In rat liver cytosol, chlorthalonil was rapidly transformed to 4,6-bis(glutathion-S-yl)-2,5-dichloroisophthalonitril in the presence of glutathione in a reaction catalysed by glutathione S-transferases. 4-(Glutathion-S-yl)-2,5,6-trichloroisiphthalonitril was observed as an intermedite in the glutathione-dependent biotransformation of chlorthalonil. In the bile of rats dosed with chlorthalonil (0.18 mmol/kg, orally) 4,6-bis (glutathion-S-yl)-2,5-dichloroisophthalonitril was recovered as a minor metabolite. In rats, chlorthalonil was transformed to 4,6-bis (N-acetyl-cystein-S-yl)-2,5-dichloroisophthalonitril. This metabolite was excreted in small amounts in the urine of rats dosed orally with chlorthalonil (0.66 and 2.64 mmol/kg). In all experiments, a major part of the dose was recovered as unchanged chlorthalonil in feces. Oral administration of chlorthalonil (0.66 and 2.64 mmol/kg) resulted in a slight increase in the urinary excretion of gamma-glutamyltranspeptidase, indicative of nephrotoxicity. Other parameters indicative for renal proximal tubular damage (urinary glucose and protein excretion) were not changed by acute chlorthalonil administration. Very minor renal lesions were observed in chlorthalonil-dosed animals by histopathological examination.

Animals↗
PubMed1996

Biotransformation and renal processing of nephrotoxic agents.

Nephrotoxicity is often observed as an endpoint in animal toxicity studies. In recent years, the mechanisms of biotransformation, which often provide the basis for renal toxicity, have been elucidated for a variety of compounds. These studies showed that nephrotoxicity of chemicals is either due to accumulation of certain metabolites in the kidney and further bioactivation or due to intrarenal bioactivation of the parent xenobiotic. Both types of mechanisms will be discussed using two relevant samples. The polychlorinated olefin hexachlorobutadiene and other haloolefins cause necrosis of the S-3 segment of the proximal tubules; their nephrotoxicity is dependent on bioactivation reactions. In the liver, hexachlorobutadiene is transformed by conjugation with glutathione to (S-pentachlorobutadienyl)glutathione. This S-conjugate is processed by the enzymes of mercapturic acid formation to give N-acetyl-(S-pentachlorobutadienyl)-L-cysteine, which is accumulated in the proximal tubule cells and deacetylated there to give (S-pentachlorobutadienyl)-L-cysteine. Further bioactivation is catalyzed by renal cysteine conjugate beta-lyase. Both the renal accumulation by the organic anion transporter and the topographical distribution of cysteine conjugate beta-lyase along the nephron are major determinants of organ and cell selectivity. Vinylidene chloride (VDC) is nephrotoxic in mice after inhalation, but not after oral or intraperitoneal administration. The nephrotoxicity of VDC is due to the selective expression of an androgen-dependent cytochrome P450 in the proximal tubules of male mice. This enzyme oxidizes VDC to an electrophile and is not present in female mice, but can be induced be androgen treatment. The observation of nephrotoxicity of VDC after inhalation only is due to the high blood flow to the kidney and thus high concentrations of VDC delivered to the kidney after inhalation. After oral or intraperitoneal application, hepatic first-pass metabolism efficiently reduces the amount of VDC delivered to the kidney. The results demonstrated here demonstrate that prior to in vitro nephrotoxicity screening, toxicokinetics and biotransformation pathways for a chemical have to be elucidated and metabolites have to be included into the testing regimen.

Administration, Inhalation↗
PubMed1996

Biotransformation of trichloroethene: dose-dependent excretion of 2,2,2-trichloro-metabolites and mercapturic acids in rats and humans after inhalation.

Chronic bioassays with trichloroethene (TRI) demonstrated carcinogenicity in mice (hepatocellular carcinomas) and rats (renal tubular cell adenomas and carcinomas). The chronic toxicity and carcinogenicity is due to bioactivation reactions. TRI is metabolized by cytochrome P450 and by conjugation with glutathione. Glutathione conjugation results in S-(dichlorovinyl) glutathione (DCVG) and is presumed to be the initial biotransformation step resulting in the formation of nephrotoxic metabolites. Enzymes of the mercapturic acid pathway cleave DCVG to the corresponding cysteine S-conjugate, which is, after translocation to the kidney, cleaved by renal cysteine S-conjugate beta -lyase to the electrophile chlorothioketene. After N-acetylation, cysteine S-conjugates are also excreted as mercapturic acids in urine. The object of this study was the dose-dependent quantification of the two isomers of N-acetyl-S-(dichlorovinyl)-L-cysteine, trichloroethanol and trichloroacetic acid, as markers for the glutathione- and cytochrome P450-mediated metabolism, respectively, in the urine of humans and rats after exposure to TRI. Three male volunteers and four rats were exposed to 40, 80 and 160 ppm TRI for 6 h. A dose-dependent increase in the excretion of trichloroacetic acid, trichloroethanol and N-acetyl-S-(dichlorovinyl)-L-cysteine after exposure to TRI was found both in humans and rats. Amounts of 3100 mumol trichloroacetic acid + trichloroethanol and 0.45 mumol mercapturic acids were excreted in urine of humans over 48 h after exposure to 160 ppm TRI. The ratio of trichloroacetic acid + trichloroethanol/mercapturic acid excretion was comparable in rats and humans. A slow rate of elimination with urine of N-acetyl-S-(dichlorovinyl)-L-cysteine was observed both in humans and in rats. However, the ratio of the two isomers of N-acetyl-S-(dichlorovinyl)-L-cysteine was different in man and rat. The results confirm the finding of the urinary excretion of mercapturic acids in humans after TRI exposure and suggest the formation of reactive intermediates in the metabolism of TRI after bioactivation by glutathione also in humans.

Acetylcysteine↗
PubMed1996

Toxicology of chlorofluorocarbon replacements.

Chlorofluorocarbons (CFCs) are stable in the atmosphere and may reach the stratosphere. They are cleaved by UV-radiation in the stratosphere to yield chlorine radicals, which are thought to interfere with the catalytic cycle of ozone formation and destruction and deplete stratospheric ozone concentrations. Due to potential adverse health effects of ozone depletion, chlorofluorocarbon replacements with much lower or absent ozone depleting potential are developed. The toxicology of these compounds that represent chlorofluorohydrocarbons (HCFCs) or fluorohydrocarbons (HFCs) has been intensively studied. All compounds investigated (1, 1-dichloro-1-fluoroethane [HCFC-141b], 1,1,1,2-tetrafluoroethane [HFC-134a], pentafluoroethane [HFC-125], 1-chloro- 1,2,2,2-tetrafluoroethane [HCFC-124], and 1,1-dichloro-2,2,2-trifluoroethane [HCFC-123]) show only a low potential for skin and eye irritation. Chronic adverse effects on the liver (HCFC-123) and the testes (HCFC-141b and HCFC-134a), including tumor formation, were observed in long-term inhalation studies in rodents using very high concentrations of these CFC replacements. All CFC replacements are, to varying extents, biotransformed in the organism, mainly by cytochrome P450-catalyzed oxidation of C-H bonds. The formed acyl halides are hydrolyzed to give excretable carboxylic acids; halogenated aldehydes that are formed may be further oxidized to halogenated carboxylic acids or reduced to halogenated alcohols, which are excretory metabolites in urine from rodents exposed experimentally to CFC replacements. The chronic toxicity of the CFC replacements studied is unlikely to be of relevance for humans exposed during production and application of CFC replacements.

Animals↗
PubMed1996

Biotransformation and membrane transport in nephrotoxicity.

The kidney is a frequent target organ for toxic effects of xenobiotics. In recent years, the molecular mechanisms responsible for the selective renal toxicity of many nephrotoxic xenobiotics have been elucidated. Accumulation by renal transport mechanisms, and thus aspects of renal physiology, plays an important role in the renal toxicity of some antibiotics, metals, and agents binding to low molecular weight proteins such as alpha(2u)-globulin. The accumulation by active transport of metabolites formed in other organs is involved in the kidney-specific toxicity of certain polyhaloalkanes, polyhaloalkenes, hydroquinones, and aminophenols. Other xenobiotics are selectively metabolized to reactive electrophiles by enzymes expressed in the kidney. This review summarizes the present knowledge on the mechanistic basis of target organ selectivity of these compounds.

Aminoglycosides↗
PubMed1996

N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine and 2,2,2-trichloroethanol: two novel metabolites of tetrachloroethene in humans after occupational exposure.

The excretion of tetrachloroethene metabolites in urine was studied in occupationally exposed workers to identify and quantify metabolites formed by glutathione conjugation and by cytochrome P450 oxidation of tetrachloroethene in humans. The glutathione conjugation pathway has been implicated in the chronic toxicity and possible tumorigenicity of tetrachloroethene to the kidney in rats. The biosynthesis of S-(1,2,2-trichlorovinyl)glutathione and N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine in humans had not been demonstrated. In this study, we investigated the biotransformation of tetrachloroethene in humans occupationally exposed during dry cleaning. Tetrachloroethene concentrations in the air of the dry cleaning shop were 50 +/- 4 ppm; two individuals were exposed for 8 hr daily and two individuals were exposed for 4 hr daily. In urine samples collected from the individuals at the beginning and at the end of the work week, N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine and 2,2,2-trichloroethanol as tetrachloroethene metabolites in humans were identified by GC/MS. The concentrations of N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine in the urine of the individuals were not significantly different at the start and at the end of the work week; however, concentrations of both N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine and 2,2,2-trichloro compounds (trichloroacetic acid and 2,2,2-trichloroethanol) as a marker for cytochrome P450-mediated metabolism were proportional to the length of daily tetrachloroethene exposure. A remarkable difference in the excretion pattern of 2,2,2-trichloro compounds, the major tetrachloroethene metabolites, was observed. Trichloroacetic acid and 2,2,2-trichloroethanol were present in the urine of two of the exposed individuals. Only 2,2,2-trichloroethanol was identified as a major urinary tetrachloroethene metabolite in two other individuals who did not excrete detectable amounts of trichloroacetic acid. The obtained results indicate that humans also have the ability to biosynthesize nephrotoxic glutathione S-conjugates from tetrachloroethene; however, when compared with rats, the human capacity for the biosynthesis of N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine seems to be lower.

Acetylcysteine↗
PubMed1995

Renal tumorigenicity of 1,1-dichloroethene in mice: the role of male-specific expression of cytochrome P450 2E1 in the renal bioactivation of 1,1-dichloroethene.

1,1-Dichloroethene is used as intermediate in the manufacture of polymers. In male mice, 1,1-dichloroethene caused renal tumors after inhalation. Renal tumors were not observed in female mice or in both sexes of rats. We investigated the metabolic basis for the species- and sex-specific nephrotoxicity and tumorigenicity of 1,1-dichloroethene. Kidney microsomes from male mice biotransformed 1,1-dichloroethene to chloroacetic acid; the amounts of chloroacetic acid formed were dependent on the hormonal status of the animals and correlated well with the ability of kidney microsomes to oxidize p-nitrophenol and chlorozoxazone, specific substrates for cytochrome P450 2E1. In kidney microsomes from naive females, significantly lower rates of oxidation of 1,1-dichloroethene, p-nitrophenol, and chlorozoxazone were observed; oxidation could be induced by testosterone. With a rabbit anti-rat liver cytochrome P450 2E1 antibody, a cross-reactive protein was detected in male mouse kidney microsomes with a molecular weight very similar to that of rat liver cytochrome P450 2E1; the expression of this protein was regulated by testosterone and correlated well with the ability of the microsomes to oxidize p-nitrophenol, chlorozoxazone, and 1,1-dichloroethene. When the relative cytochrome P450 2E1 contents of renal microsomes of male mice from different strains were compared, differences in the expression of cytochrome P450 2E1 were observed. Moreover, nephrotoxicity in Swiss-Webster mice after inhalation of 1,1-dichloroethene was observed only in males and testosterone-treated females, but not in naive females. In kidney microsomes obtained from both sexes of rats and in six samples of human kidney (male donors), no p-nitrophenol oxidase activity was detected. These data suggest that cytochrome P450 2E1 or a P450 enzyme with very similar molecular weight, substrate specificities, and immunological properties is expressed only in male mouse kidney and bioactivates 1,1-dichloroethene.

Acetates↗
PubMed1995

Sex differences in hexachlorobutadiene biotransformation and nephrotoxicity.

Hexachlorobutadiene is nephrotoxic in rats, causing damage to the proximale tubules. Renal toxicity is presumed to be due to bioactivation by glutathione S-conjugate formation. Hexachlorobutadiene is conjugated with glutathione to S-(1,2,3,4,4-pentachlorobutadienyl)glutathione and further transformed to S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine (PCBC), which is N-acetylated in the liver to form N-acetyl-S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine (N-ac-PCBC). N-ac-PCBC is accumulated in the kidney. Renal acylases cleave N-ac-PCBC to PCBC, which is a substrate for renal cysteine conjugate beta-lyase and transformed to a reactive thioketene. Binding of this intermediate to renal macromolecules is most likely responsible for the nephrotoxicity of hexachlorobutadiene. In this study, we administered [14C]HCBD (200 mg/kg, per gavage) to male and female Wistar rats and compared the distribution and biotransformation. No significant differences in the disposition and rates of excretion of [14C]hexachlorobutadiene-derived radioactivity were observed between male and female rats. A portion of the dose (15.6 +/- 4.2) was excreted in the feces and 3.1% ( +/- 0.7) in the urine of male rats, and 11.1% ( +/- 3.8) of the dose was excreted in the feces and 4.5% ( +/- 1.5) in the urine of female rats. The major metabolite excreted by female rats was N-ac-PCBC, while small amounts of PCBC were also detected. In the urine of male rats, in addition to small amounts of PCBC and N-ac-PCBC, N-acetyl-S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine sulfoxide and [14C]hexachlorobutadiene were identified. Formation of the electrophile N-ac-PCBC sulfoxide must be considered as an alternative, beta-lyase-independent, bioactivation pathway for hexachlorobutadiene-derived S-conjugates. In isolated rat renal tubular cells, N-ac-PCBC sulfoxide induced a significantly more marked loss in cell viability than N-ac-PCBC. After identical doses of hexachlorobutadiene, the extent of necrosis to the pars recta of the proximal tubules was increased in male rats compared to the necrotic changes in female rats. While female animals showed a normal liver histology, male rats revealed slight toxic centrilobular liver changes in addition to the renal necroses. In vitro, only liver microsomes from male rats catalyzed the formation of N-ac-PCBC sulfoxide from N-ac-PCBC. Our results describe a new pathway of hexachlorobutadiene biotransformation in male rats, the formation of a mercapturic acid sulfoxide. The formation of this Michael acceptor may contribute to sex differences in hexachlorobutadiene nephrotoxicity.

Animals↗
PubMed1995

The role of cytochrome P450 2E1 in the species-dependent biotransformation of 1,2-dichloro-1,1,2-trifluoroethane in rats and mice.

1,2-Dichloro-1,1,2-trifluoroethane (HCFC-123a) is a potential alternative to replace ozone-depleting chlorofluorocarbons. The metabolism of HCFC-123a was studied in microsomes of rats, mice, and humans as well as in rats and mice in vivo. Rat, mouse, and human liver microsomes metabolized HCFC-123a to inorganic fluoride and chlorodifluoroacetic acid. Fluoride formation was dependent on time and NADPH, HCFC-123a, and protein concentration. Microsomes from untreated rats oxidized HCFC-123a at low rates (0.49 nmol fluoride/20 min x mg protein). Pretreatment of rats with pyridine and ethanol, inducers of P450 2E1, increased the rates of fluoride release. In mouse liver microsomes, the rates of HCFC-123a oxidation to release fluoride were significantly higher (1.68 nmol fluoride/20 min x mg) than in rat liver microsomes. Incubation of HCFC-123a with microsomes and diethyldithiocarbamate (100 microM), an inhibitor of P450 2E1, reduced fluoride formation by more than 60%. In different samples of human liver microsomes, rates of fluoride formation were between two- and fourfold higher than those observed in liver microsomes from untreated rats. In rats and mice exposed to concentrations of HCFC-123a up to 5000 ppm in a closed recirculating exposure system, chlorodifluoroacetic acid, and inorganic fluoride were identified as urinary metabolites. The biotransformation of HCFC-123a in rats was saturated after exposure to more than 2000 ppm HCFC-123a for 6 hr, whereas no saturation was evident in mice exposed to concentrations of up to 5000 ppm. The obtained results suggest a major role of P450 2E1 in the oxidation of HCFC-123a and in the different capacities for oxidative biotransformation of HCFC-123a in rodents. Mice may thus be more sensitive to toxic effects of HCFC-123a depending on biotransformation after administration of high doses.

Animals↗