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We present an ab initio theoretical approach to accurately describe phonon thermal transport in semiconductors and insulators free of adjustable parameters. This technique combines a Boltzmann formalism with density functional calculations of harmonic and anharmonic interatomic force constants. Without any fitting parameters, we obtain excellent agreement (<5% difference at room temperature) between the calculated and measured intrinsic lattice thermal conductivities of silicon and germanium. As such, this method may provide predictive theoretical guidance to experimental thermal transport studies of bulk and nanomaterials as well as facilitating the design of new materials. [ABSTRACT FROM AUTHOR]

To investigate possible persistent nephrotoxic effects of trichloroethylene (TRI), a retrospective study was carried out on 39 workers exposed to high levels of TRI from 1956 to 1975. Total protein levels in urine, as well as serum and urine creatinine and serum urea were unchanged in comparison with the control. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was applied to differentiate between tubular and/or glomerular dysfunction. Urinary excretion of alpha-1-microglobulin and glutathione transferase (GST) alpha, as markers of proximal tubular damage, were correlated with the SDS-PAGE patterns of urinary proteins both in the TRI exposed and the control group. GST alpha was found in elevated concentrations in the urine of the TRI-exposed workers. No increase of urinary GST alpha was observed in the control group, even when alpha-1-microglobulin was elevated as a result of non-toxic damage. Both in the control and exposed groups, GST pi, a marker of distal tubular damage, was in the normal range. The results show that chronic exposure to high doses of TRI causes persistent changes to the proximal tubular system of the kidney and that GST alpha excretion into the urine is a marker well suited for quantitation of the extent of renal damage.

1. Musk xylene (1-tert-butyl-3,5-dimethyl-2,4,6-trinitrobenzene) is used as a fragrance component in toiletries, detergents and skin care products. Musk xylene is widely distributed in the environment and has been identified as a persistent contaminant in fish and in mothers' milk. Experimental data in man indicate a slow elimination of musk xylene and a potential for accumulation. Nitroarenes may be biotransformed to the respective amines. Some aromatic amines are known to be tumorigenic in animals and in man. Quantitation of the binding of those aromatic amines to haemoglobin has been proposed as a biomarker of internal exposure. 2. To determine bioavailability, metabolic reduction and haemoglobin binding of musk xylene in man, we investigated the presence of musk xylene metabolites bound to haemoglobin in blood samples from rat and from 10 human volunteers not knowingly exposed to musk xylene. 3. Haemoglobin from the blood samples was isolated, and bound metabolites were liberated as amines by alkaline hydrolysis. In haemoglobin samples from all individuals, 1-tert-butyl-3,5-dimethyl-4-amino-2,6-dinitrobenzene and, after chemical derivatization, the corresponding N-perfluoropropyl amide were identified by GC/MS using electron-impact and electron-capture mass spectrometry. 4. The amounts of 1-tert-butyl-3,5-dimethyl-4-amino-2,6-dinitrobenzene bound to haemoglobin in the human blood samples ranged from 13 to 46 fmol/mg haemoglobin. 5. These data demonstrate that musk xylene is bioavailable in man. The use of haemoglobin binding as a biomarker for nitromusk exposure in the general population warrants further studies.

Hexachlorobuta-1,3-diene (HCBD) is nephrotoxic in rodents. Its toxicity is based upon a multistep bioactivation pathway. Conjugation with glutathione by glutathione S-transferases to form (E)-S-(1,2,3,4,4-pentachlorobutadienyl)-L-glutathione (PCBG), further processing to the corresponding cysteine S-conjugate, and finally processing to a reactive thioketene are thought to be responsible for the observed nephrotoxic effects. A novel metabolite, identified as (E)-N-acetyl-S-(1,2,3,4, 4-pentachlorobutadienyl)-L-cysteine sulfoxide (N-AcPCBC-SO), was described after administration of [14C]HCBD to male Wistar rats. This metabolite is formed by sulfoxidation of N-acetyl-S-(1,2,3,4, 4-pentachlorobutadienyl)-L-cysteine (N-AcPCBC) mediated by cytochrome P450 3A and has been found to be cytotoxic to proximal tubular cells in vitro without activation by beta-lyase. In rats, given HCBD in vivo, only one diastereomer of the sulfoxide is excreted; however, in rat hepatic microsomes two diastereomers, (R)- and (S)-N-AcPCBC-SO, are formed. This study focuses on the mechanisms responsible for this discrepancy and on a possible contribution of N-AcPCBC-SO to the nephrotoxicity of HCBD in vivo. (R,S)-N-AcPCBC-SO (1:1 mixture of both diastereomers) and N-acetyl-alpha-methyl-S-(1,2,3,4,4-pentachlorobutadienyl)-d, L-cysteine sulfoxide (alpha-Me-N-AcPCBC-SO) were administered iv to male and female Wistar rats (20, 40, and 80 micromol/kg of body weight). alpha-Me-N-AcPCBC-SO cannot be cleaved by cysteine conjugate beta-lyase even if alpha-Me-N-AcPCBC-SO is deacetylated by acylases. Excretion of gamma-glutamyltranspeptidase, protein, and glucose in the urine, indicative for kidney damage, and histopathological examination of the kidneys showed marked differences in the renal damage in male and female rats after application of N-AcPCBC-SO and alpha-Me-N-AcPCBC-SO. Necroses of the kidney tubules were only found in male, but not female, rats. Major sex-specific differences were observed in the elimination of sulfoxides; the (R)-isomer was excreted in a 5-10-fold excess to the (S)-isomer after application of (R,S)-N-AcPCBC-SO. After purification, both isomers were administered to male rats resulting in the urinary excretion of (R)-N-AcPCBC-SO after giving the (R)-isomer; treatment with (S)-N-AcPCBC-SO, however, revealed the formation of (S)-N-acetyl-S-(2-glycinylcystein-S-yl-1,3,4, 4-tetrachlorobutadienyl)-L-cysteine. The results show major sex-specific differences in the nephrotoxic potency of N-AcPCBC-SO and alpha-Me-N-AcPCBC-SO. However, both N-AcPCBC-SO and alpha-Me-N-AcPCBC-SO are nephrotoxic in males, suggesting the formation of a vinyl sulfoxide as an additional, beta-lyase-independent mechanism in HCBD-caused nephrotoxicity.

The present study reports on a 17-year-old male who ingested approximately 70 ml trichloroethene (TRI) in a suicide attempt. The patient developed fever, tremor, general motor restlessness, and sinus tachycardia and lost consciousness 5 h after poisoning. After 5 days of intubation under narcosis with forced hyperventilation and diuresis he regained consciousness. During this period blood and urine were collected and TRI and its metabolites were quantified. The highest concentration of TRI in blood was detected 13 h after ingestion. Trichloroethanol and trichloroacetic acid, metabolites of the cytochrome P450-mediated pathway, and N-acetyl-S-(1, 2-dichlorovinyl)-l-cysteine and N-acetyl-S-(2, 2-dichlorovinyl)-l-cysteine from the glutathione-dependent pathway of TRI were quantified in urine samples. Besides these known metabolites in humans, chloroacetic acid and dichloroacetic acid were identified for the first time in urine of a human exposed to TRI. Although the patient exhibited normal levels of glucose and total protein in urine, excretion of alpha1- and beta2-microglobulin as well as beta-NAG was significantly increased. In addition to these typical markers of selective tubule damage, analysis of the urinary protein pattern by SDS-PAGE revealed increased excretion of several low-molecular-mass proteins between 10,000 and 50,000 Da, clearly indicating tubular damage. Based on the elucidated glutathione-dependent mechanism for the nephrotoxicity of TRI, activation of the formed S-conjugates by beta-lyases to reactive intermediates may account for the observed renal effects after a single, high dose of TRI., (Copyright 1998 Academic Press.)

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.

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.

Highly chlorinated beta-carbolines have a potential in vivo relevance to Parkinson's disease. In this paper, a gas chromatographic method for the determination of the neurotoxic 1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo), the condensation product of tryptamine and chloral hydrate, is described. The specific and sensitive assay involves purification of the biological samples by solid-phase extraction with C18 cartridges, derivatization with heptafluorobutyric anhydride, and chromatography on a non-polar fused-silica capillary column. Detection of TaClo was achieved by the registration of characteristic mass fragments of the TaClo heptafluorobutyric amide derivative using selected ion monitoring. The method was utilized to detect and quantify TaClo in blood, urine, bile, faeces, and brain tissue of rats treated with this alkaloid-type heterocycle. Four-fold deuterium-labelled TaClo was used as an internal standard.

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.

In the present study we investigated the formation of sulfoxides from N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine (N-Ac-TCVC), N-acetyl-S-(1,2-dichlorovinyl)-L-cysteine (N-Ac-1,2-DCVC), and N-acetyl-S-(2,2-dichlorovinyl)-L-cysteine (N-Ac-2,2-DCVC), which are formed in the glutathione dependent bioactivation of tri- and tetrachloroethene. The first aim was to elucidate the enzymes involved in these oxidation reactions. N-Ac-TCVC, N-Ac-1,2-DCVC, and N-Ac-2,2-DCVC are oxidized to the corresponding sulfoxides mainly, if not exclusively, by cytochrome P450 enzymes in liver microsomes of untreated male rats, since no role for the flavin-containing monooxygenase (FMO) could be demonstrated by heat inactivation experiments and by the use of n-octylamine. The sulfoxidation rates were increased when using liver microsomes of phenobarbital and dexamethasone pretreated male rats as well as liver microsomes of dexamethasone pretreated female rats, while no sulfoxide formation was observed in liver microsomes of untreated female rats, suggesting an involvement of cytochrome P450 3A. Also, troleandomycin, a specific chemical inhibitor for cytochrome P450 3A, drastically reduced sulfoxidation rates. The observed rates of sulfoxidation also correlated well with the rates of oxidation of testosterone at the 6-beta-position, a specific marker for P450 3A activity. The second aim of this study was to compare the cytotoxicity of the sulfoxides with the cytotoxicity of the corresponding mercapturic acids in isolated rat renal epithelial cells. Both mercapturic acids and the corresponding sulfoxides were cytotoxic. Cytotoxicity of the mercapturic acids could be blocked by (aminooxy)acetic acid (AOAA), an inhibitor of cysteine conjugate beta-lyase, while the cytotoxicity of the sulfoxides was not influenced by this treatment. Moreover, the sulfoxides were significantly more cytotoxic than the corresponding mercapturic acids at equimolar doses. The results show that mercapturic acids derived from TRI and PER are oxidized to sulfoxides by microsomal monooxygenases from rat liver. The cytotoxicity of the produced sulfoxides could not be reduced by AOAA, consistent with a role of the sulfoxides as direct acting electrophiles (i.e., Michael acceptor substrates).

The sulfoxidation of the mercapturic acid N-acetyl-S-(1,2,3,4,4-pentachlorobuta-1,3-dienyl)-L-cysteine (N-Ac-PCBC), a urinary metabolite of the renal toxin hexachlorobutadiene (HCBD), was studied in human liver microsomes and with purified cDNA expressed human liver cytochrome P450 (P450) enzymes. N-Acetyl-S-(1,2,3,4,4-pentachlorobuta-1,3-dienyl)-L-cysteine sulfoxide (N-Ac-PCBC SO) is a major urinary metabolite of HCBD in male rats; only liver microsomes from male rats catalyze the sulfoxidation of N-Ac-PCBC. Our results presented here show that human liver microsomes from both male and female donors are capable of oxidizing N-Ac-PCBC to the corresponding sulfoxide diastereomers. The correlation of N-Ac-PCBC sulfoxidation with the rates of oxidation of P450 enzyme specific substrates suggests that only P450 3A enzymes oxidize N-Ac-PCBC. Moreover, only gestodene and troleandomycin, two selective inhibitors for P450 of the 3A family, significantly reduced the rates of N-Ac-PCBC sulfoxidation. No reduction in sulfoxidation rates was observed with inhibitors for other P450 enzymes, i.e., diethyldithiocarbamate, 4-methylpyrazole, 7,8-benzoflavone, or sulfaphenazole. Incubations of N-Ac-PCBC with purified and reconstituted recombinant P450s 1A2, 2E1, 3A4, and 3A5 resulted in sulfoxide formation only with P450s 3A4 and 3A5. In summary, these results indicate that P450 from the 3A family may sulfoxidize N-Ac-PCBC. Since these P450 enzymes account for a major fraction of the P450 in human liver and are also present in human kidney, the sulfoxidation reaction may also be expected to occur in humans exposed to HCBD.

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)

Dichloroacetylene is neurotoxic, nephrotoxic, and nephrocarcinogenic. The present experiments were designed to test further the hypothesis that the glutathione conjugate of dichloroacetylene, S-(1,2-dichlorovinyl)glutathione (DCVG), may be involved in dichloroacetylene-induced neurotoxicity. Hence, the biosynthesis of DCVG from dichloroacetylene and glutathione was studied in cytosolic, microsomal, and mitochondrial fractions of liver, lung, brain, and kidney. Enzymatic formation of DCVG was observed in liver microsomes and mitochondria, but only nonenzymatic formation of DCVG was seen in lung, brain, and kidney. The KM and Vmax for DCVG biosynthesis with glutathione as the variable substrate were 0.40 +/- 0.28 mM and 487 +/- 90.3 nmol/mg protein/min, respectively. No region-specific differences in the rates of DCVG biosynthesis in the brain were observed. In whole brain homogenates, DCVG was hydrolyzed to DCVC, which was biotransformed to pyruvate and S-(1,2-dichlorovinyl)-3- mercaptopyruvate, indicating cysteine conjugate beta-lyase-catalyzed beta-elimination and transamination reactions in cerebellar tissues. These findings indicate that the glutathione-dependent bioactivation of dichloroacetylene may be involved in the dichloroacetylene-induced neurotoxicity.