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PubMed1997

Electrospray analysis of biological samples for trace amounts of trichloroacetic acid, dichloroacetic acid, and monochloroacetic acid.

Trichloroethylene (TCE) has been identified as a widespread groundwater contaminant. Trichloroacetic acid (TCA) and dichloroacetic acid (DCA) are toxicologically relevant metabolites of TCE that produce tumors in B6C3F1 mice. A sensitive method for measuring these metabolites in plasma has been developed to obtain pharmacokinetic data from TCE exposure. This is particularly important because DCA is more potent at producing hepatoproliferative lesions than TCA. At present, it is unclear whether DCA is produced by humans. Existing gas chromatographic methods cannot detect DCA at low nanogram-per-milliliter levels. A Finnigan TSQ 700 mass spectrometer (MS) with electrospray ionization was used to measure TCA, DCA, and monochloroacetic acid (MCA) in plasma. The MS was operated in negative ion tandem MS mode. The limit of detection for TCA and DCA was 4 ng/ml, and the limit of detection for MCA was 25 ng/mL. Plasma samples from human subjects exposed to 100 ppm TCE for 4 h contained TCA at concentrations as high as 10 micrograms/mL. DCA concentrations were less than 5 ng/mL, and MCA was not detected (less than 25 ng/mL).

Acetates↗
PubMed1998

Biotransformation of perchloroethene: dose-dependent excretion of trichloroacetic acid, dichloroacetic acid, and N-acetyl-S-(trichlorovinyl)-L-cysteine in rats and humans after inhalation.

Chronic exposure of rodents to perchloroethene (PER) increased the incidence of liver tumors in male mice and resulted in a small but significant increase in the incidence of renal tumors in male rats. The tumorigenicity of PER is mediated by metabolic activation reactions. PER is metabolized by cytochrome P450 and by conjugation with glutathione. Cytochrome P450 oxidation of PER results in trichloroacetyl chloride which reacts with water to trichloroacetic acid (TCA) which is excreted. The formation of S-(trichlorovinyl)glutathione (TCVG) from PER results in nephrotoxic metabolites. TCVG is cleaved to S-(trichlorovinyl)-L-cysteine (TCVC) and acetylated to N-acetyl-S-(trichlorovinyl)-L-cysteine (N-ac-TCVC), which is excreted with urine. TCVC is also cleaved in the kidney by cysteine conjugate beta-lyase to dichlorothioketene which may react with water to dichloroacetic acid (DCA) or with cellular macromolecules. The object of this study was to comparatively quantify the dose-dependent excretion of PER metabolites in urine of humans and rats after inhalation exposure. Three female and three male human volunteers and three female and three male rats were exposed to 10, 20, and 40 ppm PER for 6 h, and three female and three male rats to 400 ppm. A dose-dependent increase in the excretion of TCA and N-ac-TCVC after exposure to PER was found both in humans and in rats. A total of 20.4 +/- 7.77 mumol of TCA and 0.21 +/- 0.05 mumol of N-ac-TCVC were excreted in urine of human over 78 h after the start of exposure to 40 ppm PER; only traces of DCA were present. After identical exposure conditions, rats excreted 1.64 +/- 0.42 mumol of TCA, 0.006 +/- 0.002 mumol of N-ac-TCVC and 0.18 +/- 0.04 mumol of DCA. Excretion of N-ac-TCVC in male rats exposed to 400 ppm PER (103.7 nmol) was significantly higher, compared to female rats (31.5 nmol) exposed under identical conditions. N-ac-TCVC was rapidly eliminated with urine both in humans (t1/2 = 14.1 h) and in rats (t1/2 = 7.5 h). When comparing the urinary excretion of N-ac-TCVC, a potential marker for the formation of reactive intermediates in the kidney, humans received a significantly lower dose (3 nmol/kg at 40 ppm) compared to rats (23.0 nmol/kg) after identical exposure conditions. In addition, rats excreted large amounts of DCA which likely is a product of the beta-lyase-dependent metabolism of TCVC in the kidney. The obtained data suggest that glutathione conjugate formation and beta-lyase-dependent bioactivation of TCVC in PER metabolism is significantly higher in rats than in humans. Thus, using rat tumorigenicity data for human risk assessment of PER exposure may overestimate human tumor risks.

Acetylcysteine↗
PubMed1998

Glutathione transferase zeta catalyses the oxygenation of the carcinogen dichloroacetic acid to glyoxylic acid.

Dichloroacetic acid (DCA), a common drinking-water contaminant, is hepatocarcinogenic in rats and mice, and is a therapeutic agent used clinically in the management of lactic acidosis. DCA is biotransformed to glyoxylic acid by glutathione-dependent cytosolic enzymes in vitro and is metabolized to glyoxylic acid in vivo. The enzymes that catalyse the oxygenation of DCA to glyoxylic acid have not, however, been identified or characterized. In the present investigation, an enzyme that catalyses the glutathione-dependent oxygenation of DCA was purified to homogeneity (587-fold) from rat liver cytosol. SDS/PAGE and HPLC gel-filtration chromatography showed that the purified enzyme had a molecular mass of 27-28 kDa. Sequence analysis showed that the N-terminus of the purified protein was blocked. An internal sequence of 30 amino acid residues was obtained that matched the recently discovered human glutathione transferase Zeta well [Board, Baker, Chelvanayagam and Jermiin (1997) Biochem. J. 328, 929-935]. Western-blot analysis showed that the purified rat-liver enzyme cross-reacted with rabbit antiserum raised against recombinant human glutathione transferase Zeta. The apparent Km and Vmax values of the purified enzyme with DCA as the variable substrate were 71.4 microM and 1334 nmol/min per mg of protein, respectively; the Km for glutathione was 59 microM. Both the purified rat-liver enzyme and the recombinant human enzyme showed high activity with DCA as the substrate. These results demonstrate that the glutathione-dependent oxygenation of DCA to glyoxylic acid is catalysed by a Zeta-class glutathione transferase.

Amino Acid Sequence↗
PubMed1999

Inactivation of glutathione transferase zeta by dichloroacetic acid and other fluorine-lacking alpha-haloalkanoic acids.

Dichloroacetic acid (DCA) is a contaminant of chlorinated drinking water supplies, is carcinogenic in rats and mice, and is a therapeutic agent used for the treatment of congenital lactic acidosis. The biotransformation of DCA to glyoxylic acid is catalyzed by glutathione transferase zeta (GSTZ). Treatment of rats and human subjects with DCA increases its plasma elimination half-life and reduces the extent of DCA biotransformation in rat hepatic cytosol. In the investigation presented here, the kinetics of the DCA-induced inactivation of GSTZ, the turnover of GSTZ, and the susceptibility of GSTZ to inactivation by a panel of alpha-haloacids were studied. DCA rapidly inactivated GSTZ in both rat hepatic cytosol and intact Fischer 344 rats. The time course of inactivation in vivo was mirrored by a concomitant loss of immunoreactive GSTZ protein. The turnover of GSTZ in rat liver was 0.21 day(-1), which corresponded to a half-life of 3.3 days. The degree of GSTZ inactivation after daily administration of DCA could be predicted from the amount of inactivation after a single treatment. Other fluorine-lacking dihaloacetic acids also inactivated GSTZ, whereas alpha-monohaloacids and fluorine-containing dihaloacetic acids failed to inactivate GSTZ. These data show that the observed DCA-induced decrease in the level of DCA metabolism is caused by the inactivation of GSTZ.

Animals↗
PubMed2001

Detection of early gene expression changes by differential display in the livers of mice exposed to dichloroacetic acid.

Dichloroacetic acid (DCA) is a major by-product of water disinfection by chlorination. Several studies have demonstrated the hepatocarcinogenicity of DCA in mice when administered in drinking water. The mechanism of DCA carcinogenicity is not clear and we speculate that changes in gene expression may be important. In order to analyze early changes in gene expression induced by DCA treatment we used the differential display method. Mice were treated with 2 g/l DCA in drinking water for 4 weeks. Total RNAs were obtained from livers of both control and treated mice for analysis. Of approximately 48 000 bands on the differential display gels representing an estimated 96% of RNA species, 381 showed differences in intensity. After cloning and confirmation by both reverse-northern and northern analyses, six differentially expressed genes were found. The expression of five of these genes was suppressed in the DCA-treated mice while one was induced. After sequencing, four genes were identified and two were matched to expressed sequence tags through the BLAST program. These genes are alpha-1 protease inhibitor, cytochrome b5, stearoyl-CoA desaturase and carboxylesterase. Stearoyl-CoA desaturase was induced approximately 3-fold in the livers of DCA-treated mice and the other three genes were suppressed approximately 3-fold. Stearoyl-CoA desaturase, cytochrome b5 and carboxylesterase are endoplasmic reticulum membrane-bound enzymes involved in fatty acid metabolism. The expression pattern of four of these genes was similar in DCA-induced hepatocellular carcinomas and the 4 week DCA-treated mouse livers. The expression of stearoyl-CoA desaturase and one of the unidentified genes returned to control levels in the carcinomas. Understanding the roles and interactions between these genes may shed light on the mechanism of DCA carcinogenesis.

Animals↗
PubMed1995

Biochemical, pathologic and morphometric alterations induced in male B6C3F1 mouse liver by short-term exposure to dichloroacetic acid.

Dichloroacetic acid (DCA) is a complete hepatocarcinogen and tumor promoter in the male B6C3F1 mouse. Published reports indicate that the compound is non-genotoxic. This study examines possible non-genotoxic (epigenetic) mechanisms by which DCA elicits its carcinogenic response. Correlative biochemical, pathologic and morphometric techniques are used to characterize and quantify the acute, short-term response of hepatocytes in the male B6C3F1 mouse to drinking water containing DCA. Cellularity, [3H]thymidine incorporation, DNA concentration, nuclear size, and binuclearity are evaluated in terms of level of exposure (0, 0.5 and 5 g/l) and length of exposure to DCA. The dose-related alterations in hepatocytes of animals exposed to DCA for 30 days or less indicate that short-term exposure to DCA results in inhibition of mitoses, alterations in cellular metabolism and a shift in ploidy class. Thus, DCA carcinogenesis may involve cellular adaptations, development of drug resistance and selection of phenotypically altered cells with a growth advantage.

Analysis of Variance↗
PubMed2003

A 2-year dose-response study of lesion sequences during hepatocellular carcinogenesis in the male B6C3F(1) mouse given the drinking water chemical dichloroacetic acid.

Dichloroacetic acid (DCA) is carcinogenic to the B6C3F(1) mouse and the F344 rat. Given the carcinogenic potential of DCA in rodent liver and the known concentrations of this compound in drinking water, reliable biologically based models to reduce the uncertainty of risk assessment for human exposure to DCA are needed. Development of such models requires identification and quantification of premalignant hepatic lesions, identification of the doses at which these lesions occur, and determination of the likelihood that these lesions will progress to cancer. In this study we determined the dose response of histopathologic changes occurring in the livers of mice exposed to DCA (0.05-3.5 g/L) for 26-100 weeks. Lesions were classified as foci of cellular alteration smaller than one liver lobule (altered hepatic foci; AHF), foci of cellular alteration larger than one liver lobule (large foci of cellular alteration; LFCA), adenomas (ADs), or carcinomas (CAs). Histopathologic analysis of 598 premalignant lesions revealed that (a)) each lesion class had a predominant phenotype; (b)) AHF, LFCA, and AD demonstrated neoplastic progression with time; and (c)) independent of DCA dose and length of exposure effects, some toxic/adaptive changes in non-involved liver were related to this neoplastic progression. A lesion sequence for carcinogenesis in male B6C3F(1) mouse liver has been proposed that will enable development of a biologically based mathematical model for DCA. Because all classes of premalignant lesions and CAs were found at both lower and higher doses, these data are consistent with the conclusion that nongenotoxic mechanisms, such as negative selection, are relevant to DCA carcinogenesis at lower doses where DCA genotoxicity has not been observed.

Adenoma, Acidophil↗
PubMedDate not supplied

Conversion of trichloroacetic acid to dichloroacetic acid in biological samples.

Trichloroethylene (TCE) has been identified as an environmental contaminant in groundwater. Trichloroacetic acid (TCA), dichloroacetic acid (DCA), chloral hydrate (CH), trichloroethanol (TCOH), and trichloroethanol glucuronide (TCOG) have been identified as metabolites of TCE. Studies have shown that TCA and DCA are toxicologically significant metabolites that can induce liver tumors in B6C3F1 mice. Methods for the analysis of these metabolites are important for conducting pharmacokinetic studies. In this study, TCA and DCA were derivatized to their methyl esters by dimethyl sulfate under acidic conditions and analyzed by gas chromatography with electron capture detection. In developing a method for esterifying TCA and DCA, the conversion of TCA to DCA was observed in freshly drawn blood upon the addition of acid. After blood was drawn from the animals, the amount of TCA converted to DCA by the addition of acid decreased with time. This conversion could be prevented by freezing blood samples overnight prior to the addition of acid. Further experiments demonstrated that this activity could be restored by the addition of dithionite to inactivate blood samples or the addition of dithionite to methemoglobin prior to the addition of acid. The results reported here show that reduced hemoglobin may be involved in the acid-catalyzed conversion of TCA to DCA.

Animals↗
PubMed1998

Kinetics of trichloroacetic acid and dichloroacetic acid in the isolated perfused rat liver.

Trichloroacetic acid (TCA) and dichloroacetic acid (DCA) are environmental contaminants that are suspected human carcinogens. To obtain more detail on the role of the liver in the kinetics of TCA and DCA, experimental studies in the isolated perfused rat liver (IPRL) system were conducted. The IPRL system was dosed with either 5 or 50 micromol of either TCA or DCA (25 or 250 microM initial concentration, respectively). TCA and DCA concentrations were followed in perfusion medium and bile for 2 h. The chemical concentration in liver was determined at the end of exposure. Liver viability was monitored by measuring leakage of lactate dehydrogenase (LDH) into perfusion medium and the rate of bile production. Studies performed with TCA showed that the total TCA concentration in perfusion medium decreased slightly during the first 30 min of exposure and remained constant thereafter. Most TCA, greater than 90% of total, was bound to albumin in the perfusion medium. A low, linear excretion rate of TCA in bile was obtained. The calculated free TCA concentration in the liver intracellular water space was higher than the unbound TCA concentration in the perfusion medium. Parallel studies with DCA showed that the DCA concentration in perfusion medium decreased rapidly. Of the total DCA in the perfusion medium, 60% was bound to albumin. The concentration of DCA in bile decreased over time. There was no DCA detectable in the liver after 2 h of exposure at both DCA concentrations. Enzyme leakage and bile production did not change in the presence of TCA or DCA, indicating that these concentrations were not acutely cytotoxic to the liver.

Animals↗
PubMedDate not supplied

Trichloroethylene, trichloroacetic acid, and dichloroacetic acid: do they affect eye development in the Sprague-Dawley rat?

Maternal exposure to high doses of trichloroethylene (TCE) and its oxidative metabolites, trichloroacetic acid (TCA) and dichloroacetic acid (DCA), has been implicated in eye malformations in fetal rats, primarily micro-/anophthalmia. Subsequent to a cardiac teratology study of these compounds (Fisher et al. 2001, Int. J. Toxicol. 20:257-267), their potential to induce ocular malformations was examined in a subset of the same experimental animals. Pregnant, Sprague-Dawley Crl:CDR BR rats were orally treated on gestation days (GDs) 6 to 15 with bolus doses of either TCE (500 mg/kg/day), TCA (300 mg/kg/day), DCA (300 mg/kg/day), or all-trans retinoic acid (RA; 15 mg/kg/day). The heads of GD 21 fetuses were not only examined grossly for external malformations, but were sectioned using a modified Wilson's technique and subjected to computerized morphometry that allowed for the quantification of lens area, globe area, medial canthus distance, and interocular distance. Gross ocular malformations were essentially absent in all treatment groups except for the RA group in which 26% of fetuses exhibited micro-/anophthalmia. Using the litter as the experimental unit of analysis, lens area, globe area, and interocular distance were statistically significantly reduced in the DCA treatment group. Statistically significant reductions in lens and globe areas also occurred in the RA treatment group, all four ocular measures were reduced in the TCA treatment group but none significantly so, and TCE was without effect. Because DCA, TCA, and RA treatments were associated with significant reductions in fetal body weight (bw), data were also statistically analyzed after bw adjustment. Doing so dramatically altered the results of treatment group comparisons, but the severity of bw reduction and the degree of change in ocular measures did not always correlate. This suggests that bw reduction may not be an adequate explanation for all the changes observed in ocular measures. Thus, it is unclear whether DCA specifically disrupted ocular development even under these provocative exposure conditions. Clearly, however, if TCE is capable of disrupting ocular development in the Sprague-Dawley rat, a higher dose than that employed in the present study is required.

Administration, Oral↗
PubMedDate not supplied

Trichloroethylene, trichloroacetic acid, and dichloroacetic acid: do they affect fetal rat heart development?

Trichloroethylene (TCE), trichloroacetic acid (TCA), and dichloroacetic acid (DCA) are commonly found as groundwater contaminants in many regions of the United States. Cardiac birth defects in children have been associated with TCE, and laboratory studies with rodents report an increased incidence of fetal cardiac malformations resulting from maternal exposures to TCE, TCA, and DCA. The objective of this study was to orally treat pregnant CDR(CD) Sprague-Dawley rats with large bolus doses of either TCE (500 mg/kg), TCA (300 mg/kg), or DCA (300 mg/kg) once per day on days 6 through 15 of gestation to determine the effectiveness of these materials to induce cardiac defects in the fetus. All-trans retinoic acid (RA) dissolved in soybean oil was used as a positive control. Soybean oil is commonly used as a dosing vehicle for RA teratology studies and was also used in this study as a dosing vehicle for TCE. Water was used as the dosing vehicle for TCA and DCA. Fetal hearts were examined on gestation day (GD) 21 by an initial in situ, cardiovascular stereomicroscope examination, and then followed by a microscopic dissection and examination of the formalin-fixed heart. The doses selected for TCA and DCA resulted in a modest decrease in maternal weight gain during gestation (3% to 8%). The fetal weights on GD 21 in the TCA and DCA treatment groups were decreased 8% and 9%, respectively, compared to the water control group and 21% in the RA treatment group compared to soybean oil control group. The heart malformation incidence for fetuses from the TCE-, TCA-, and DCA-treated dams did not differ from control values on a per fetus or per litter basis. The rate of heart malformations, on a per fetus basis, ranged from 3% to 5% for TCE, TCA, and DCA treatment groups compared to 6.5% and 2.9% for soybean oil and water control groups. The RA treatment group was significantly higher with 33% of the fetuses displaying heart defects. For TCE, TCA, and DCA treatment groups 42% to 60% of the litters contained at least one fetus with a heart malformation, compared to 52% and 37% of the litters in the soybean oil and water control groups. For the RA treatment group, 11 of 12 litters contained at least one fetus with a heart malformation. Further research is needed to quantify the spontaneous rates of heart defects for vehicle control rats and to explain the disparity between findings in the present study and other reported findings on the fetal cardiac teratogenicity of TCE, TCA, and DCA.

Animals↗
PubMed2006

Different net effect of TiO2 sintering temperature on the photocatalytic removal rates of 4-chlorophenol, 4-chlorobenzoic acid and dichloroacetic acid in water.

Our purpose was to show that the sintering temperature of TiO(2) can have a different net effect (thought to arise from a decrease in surface area against a decrease in recombination rate of charge carriers) on the photocatalytic removal rate of various organic pollutants in water. For that, we have chosen four chlorinated pollutants, viz. 4-chlorophenol (4-CP), 2,5-dichlorophenol (2,5-DCP), 4-chlorobenzoic acid (4-CBA) and dichloroacetic acid (DCAA). Their photocatalytic removal was studied over four TiO(2) samples (from Millennium Chemicals or affiliate) all obtained identically by TiOSO4 thermohydrolysis with subsequent calcination at various temperatures, TiO(2) Degussa P25 was used for comparison. At equal TiO(2) mass in the slurry photoreactor, the pseudo-first-order removal rate constant k increased with the calcination temperatures for the three aromatic pollutants, whereas it was the opposite for the aliphatic acid. Results obtained with P25 were consistent with the reasoning based on the combined effects of surface area and charge recombination rate. Similar k values for 4-CP and 2,5-DCP, irrespective of the TiO(2), further illustrate the importance of the molecular structure. For 4-CBA, the possibility of decarboxylation in addition to an attack on the ring, as well as a much higher extent of adsorption, can explain a higher k with respect to the chlorophenols. The implication of these results is that the hole attack mechanism for carboxylic acids is much more sensitive to surface area variation than would be the (diffusible) OH radical mechanism for aromatics which could react in the near-surface solution-phase.

Catalysis↗
PubMed1987

The carcinogenicity of trichloroethylene and its metabolites, trichloroacetic acid and dichloroacetic acid, in mouse liver.

Trichloroethylene (TCE) has previously been shown to be carcinogenic in mouse liver when administered by daily gavage in corn oil. The metabolism of TCE results, in part, in the formation of trichloroacetic acid (TCA) as a major metabolite and dichloroacetic acid (DCA) as a minor metabolite. These chlorinated acetic acids have not been shown to be genotoxic, although they have been shown to induce peroxisome proliferation. Therefore, we determined the ability they have been shown to induce peroxisome proliferation. Therefore, we determined the ability of TCE, TCA, or DCA to act as tumor promoters in mouse liver. Male B6C3F1 mice were administered intraperitoneally 0, 2.5, or 10 micrograms/g body wt ethylnitrosourea (ENU) on Day 15 of age. At 28 days of age, the mice were placed on drinking water containing either TCE (3 or 40 mg/liter), TCA (2 or 5 g/liter), or DCA (2 or 5 g/liter). All drinking waters were neutralized with NaOH to a final pH of 6.5-7.5. The animals were killed after 61 weeks of exposure to the treated drinking water (65 weeks of age). Both DCA and TCA at a concentration of 5 g/liter were carcinogenic without prior initiation with ENU, resulting in hepatocellular carcinomas in 81 and 32% of the animals, respectively. DCA and TCA also increased the incidence of animals with adenomas and the number of adenomas/animal in those animals that were not initiated with ENU. While 2.5 micrograms/g body wt ENU followed by NaCl in the drinking water resulted in only 5% of the animals with hepatocellular carcinomas, 2.5 micrograms/g body wt ENU followed with 2 or 5 g/liter DCA resulted in a 66 or 78% incidence of carcinoma, respectively, or, followed with 2 or 5 g/liter TCA, resulted in a 48% incidence at either concentration. None of the untreated animals had hepatocellular carcinomas. Therefore our results demonstrate that DCA and TCA are complete hepatocarcinogens in B6C3F1 mice.

Acetates↗
PubMed2005

A review of analytical methods for the determination of trichloroethylene and its major metabolites chloral hydrate, trichloroacetic acid and dichloroacetic acid.

Trichloroethylene (TCE) and some of its metabolites are potentially carcinogenic compounds that the general population is commonly exposed to in drinking water. Concentrations of TCE, dichloroacetic acid (DCA) and trichloroacetic acid (TCA) given to laboratory animals in cancer bioassays are high, whereas drinking water levels of the compounds are very low. It is not clear whether the trace amounts of TCE, DCA and TCA in drinking water pose a cancer risk to humans. The accuracy of pharmacokinetic studies relies on the analytical method from which blood and tissue concentration data are obtained. Models that extrapolate cancer risks of TCE and its metabolites from laboratory animals to humans, in turn, rely on the results of pharmacokinetic studies. Therefore, it is essential to have reliable analytical methods for the analysis of TCE and its metabolites. This paper reviews the methods currently in the literature for the analysis of TCE, DCA, TCA and, to a lesser extent, chloral hydrate (CH). Additional aspects of analytical methods such as method validation, species preservation and future directions in the analysis of TCE and its metabolites are also discussed.

Animals↗
PubMed2004

Glutathione transferase zeta-catalyzed bioactivation of dichloroacetic acid: reaction of glyoxylate with amino acid nucleophiles.

Dichloroacetic acid (DCA) is a drinking water contaminant, a therapeutic agent, and a rodent carcinogen. Glutathione transferase zeta (GSTZ1-1) catalyzes the biotransformation of a range of alpha-haloalkanoates and the cis-trans isomerization of maleylacetoacetate. GSTZ1-1 catalyzes the bioactivation of fluorine-lacking dihaloacetates to S-(alpha-halocarboxymethyl)glutathione, a reactive intermediate that covalently modifies and inactivates the enzyme or is hydrolyzed to glyoxylate. The purpose of this study was to examine the GSTZ1-1-catalyzed bioactivation of DCA, including the reaction of DCA-derived glyoxylate with amino acid nucleophiles and the characterization of the structures and kinetics of adduct formation by LC/MS. The binding of [1-(14)C]DCA-derived label to bovine serum albumin required both GSTZ1-1 and GSH, whereas the binding to dialyzed rat liver cytosolic protein was increased in the presence of GSH. Studies with model peptides (antiflammin-2 and IL-8 inhibitor) indicated that glyoxylate, rather than S-(alpha-chlorocarboxymethyl)glutathione, was the reactive species that modified amino acid nucleophiles. Both addition (+74 Da) and addition-elimination (+56 Da) adducts of glyoxylic acid were observed. Addition adducts (+74 Da) could not be characterized completely by mass spectrometry, whereas addition-elimination adducts (+56 Da) were characterized as 2-carboxy-4-imidazolidinones. 2-Carboxy-4-imidazolidinones were formed by the rapid equilibrium reaction of glyoxylate with the N-terminal amino group of antiflammin-2 to give an intermediate carbinolamine (K(eq) = 0.63 mM(-1)), which slowly eliminated water to give an intermediate imine (k(2) = 0.067 hour(-1)), which rapidly cyclized to give the 2-carboxy-4-imidazolidinone. Glucose 6-phosphate dehydrogenase was inactivated partially by glyoxylate when reactants were reduced with sodium borodeuteride, which may indicate that glyoxylate reacts with selective lysine epsilon-amino groups. The results of the present study demonstrate that GSTZ1-1 catalyzes the bioactivation of DCA to the reactive metabolite glyoxylate. The reaction of glyoxylate with cellular macromolecules may be associated with the multiorgan toxicity of DCA.

Acetoacetates↗
PubMed2003

Altered gene expression in mouse livers after dichloroacetic acid exposure.

Dichloroacetic acid (DCA) is a major by-product of water disinfection by chlorination. Several studies have demonstrated that DCA exhibits hepatocarcinogenic effects in rodents when administered in drinking water. This chemical does not appear to be highly mutagenic, and the mechanism(s) involved in DCA induction of cancer are not clear. The present work was aimed at identifying changes in gene expression which may indicate critical alterations/pathways involved in this chemical's carcinogenic activities. We used cDNA microarray methods for analyses of gene expression in livers of mice treated with the tumorigenic dose of 2 g/l DCA in drinking water for 4 weeks. Total RNA samples obtained from livers of the control and DCA-treated mice were evaluated for gene expression patterns with Clontech Atlas Mouse 1.2 cDNA and Atlas mouse stress/toxicology arrays, and the data analyzed with AtlasImage 2.01 and one-way ANOVA in JMP4 software. From replicate experiments, we identified 24 genes with altered expression, of which 15 were confirmed by Northern blot analysis. Of the 15 genes, 14 revealed expression suppressed two- to five-fold; they included the following: MHR 23A, cytochrome P450 (CYP) 2C29, CYP 3A11, serum paraoxonase/arylesterase 1 (PON 1), liver carboxylesterase, alpha-1 antitrypsin, ER p72, glutathione S-transferase (GST) Pi 1, angiogenin, vitronectin precursor, cathepsin D (CTSD), plasminogen precursor (contains angiostatin), prothrombin precursor and integrin alpha 3 precursor (ITGA 3). An additional gene, CYP 2A4/5, had a two-fold elevation in expression. Further, in ancillary Northern analyses of total RNA isolated from DCA-induced hepatocellular carcinomas (from earlier reported studies of mice treated with 3.5 g/l DCA for 93 weeks), many of the same genes (11 of 15) noted above showed a similar alteration in expression. In summary, we have identified specific genes involved in the functional categories of cell growth, tissue remodeling, apoptosis, cancer progression and xenobiotic metabolism that have altered levels of expression following exposures to DCA. These findings serve to highlight new pathways in which to further probe DCA effects that may be critical to its tumorigenic activity.

Animals↗
PubMed2003

Improvement of thermal hydrolysis rate of dichloroacetic acid using alcohol.

Dichloroacetic acid (DCAA) is produced during the oxidation of trichloroethylene. It is also produced in drinking water treatment as a disinfection by-product. DCAA is a problem material, because of its toxicity. The objective of this research is to find the final products and the reaction pathway of the DCAA decomposition by hydrolysis, and to increase the hydrolysis rate. The removal of both chlorine atoms in DCAA structure was achieved with hydrolysis at around 75 degrees C, and the final products were oxalic acid and glycolic acid. The reaction pathway was the production of oxalic acid and glycolic acid from two glyoxylic acid molecules by Cannizzaro reaction after the glyoxylic acid production from dechlorination of DCAA with hydrolysis. The hydrolysis rate of DCAA was increased with the use of 90% ethanol solution as solvent. The activation energy of DCAA was about 80 kJ/mol in it, while it was around 105 kJ/mol in water.

Chromatography↗