Effect of exposure to four organic solvents on hepatic cytochrome P450 isozymes in rat

Changes of cytochrome P450 isozymes in livers of rats after exposure to four solvents at 4000 ppm for 6 h, were studied by enzyme assays and immunochemical detection using antibodies to cytochrome P450 isozymes. Toluene, benzene and trichloroethylene (TRI) exposure resulted in a significant increase in the activities of nitrosodimethylamine demethylase (152%, 134% and 118%) and 7-pentoxyresorufin O-depentylase (14-, 5- and 2.5-fold), respectively. 1,1,1-Trichloroethane (TCE) showed little effect on the activities of the enzymes. Anti-CYP2E1 and anti-CYP2B1/2 inhibitable activity of toluene side-chain oxidase was significantly enhanced in toluene-, benzene- and TRI-treated rats. Anti-CYP2C11 inhibitable activity was greatly reduced as compared with control. The change in CYP2E1 and CYP2C11 was confirmed by the increase and decrease in the activities inhibited by 4-methylpyrazole and cimetidine, respectively. Western blot analysis revealed that the increase in peak area of bands recognized by anti-CYP2E1 was consistent with toluene inhibition results. CYP2B1/2 was not detectable in control rats, but it was strongly induced by toluene, followed by benzene and TRI. Some increases in the peak areas of bands recognized by anti-CYP2A1 and CYP-4A1 were also observed in the three solvents exposed rat microsomes. Little immunoreactivity was found with anti-CYP1A1 in all microsomes, and no obvious change in peak area of bands recognized by anti-CYP3A and anti-CYP2C13 was observed. TCE exposure showed little effect on these bands. The formation of phenol and hydroquinone from benzene was enhanced to different degree by toluene, benzene and TRI. The hydroxylation of testosterone at 6 beta and 7 alpha was increased by benzene, and benzene and TRI, respectively. However, the metabolism at 16 alpha and 2 alpha was profoundly suppressed by the solvents except TCE. These results showed that the four solvents have different effects on specific cytochrome P450 isozymes and on the metabolism of both endogenous and exogenous substances.

Induction of toluene oxidation activity in Pseudomonas mendocina KR1 and Pseudomonas sp. strain ENVPC5 by chlorinated solvents and alkanes

Toluene oxidation activity in Pseudomonas mendocina KR1 and Pseudomonas sp. strain ENVPC5 was induced by trichloroethylene (TCE), and induction was followed by the degradation of TCE. Higher levels of toluene oxidation activity were achieved in the presence of a supplemental growth substrate such as glutamate, with levels of activity of up to 86% of that observed with toluene-induced cells. Activity in P. mendocina KR1 was also induced by cis-1,2-dichloroethylene, perchloroethylene, chloroethane, hexane, pentane, and octane, but not by trans-1,2-dichloroethylene. Toluene oxidation was not induced by TCE in Burkholderia (Pseudomonas) cepacia G4, P. putida F1, Pseudomonas sp. strain ENV110, or Pseudomonas sp. strain ENV113.

Trichloroethene-induced autoimmune response in female MRL +/+ mice

Trichloroethene (TCE) has been implicated in the pathogenesis of autoimmune diseases such as systemic lupus erythematosus (SLE) and scleroderma in humans. However, experimental studies have not been conducted to establish the role of TCE in causing autoimmunity and/or SLE. To clarify the role of TCE in autoimmune responses, subchronic studies were carried out in female autoimmune prone mice (MRL +/+). Three groups of mice (5 weeks old) received intraperitoneal injections of 10 mmol/kg of TCE, 0.2 mmol/kg of dichloroacetyl chloride (DCAC) (one of the metabolites of TCE with strong acylating property), or an equal volume (100 microliters) of corn oil alone (controls). Animals were dosed every 4th day for 6 weeks and euthanized 24 hr following the last dose. Sera and major tissues were collected and analyzed. Spleen weights in the TCE and DCAC groups increased 36% with a similar pattern of change in the spleen-to-body weight ratios. Serum IgG in the TCE and DCAC groups increased 45 and 322%, respectively. Using specific ELISA assays for mice, autoimmune antibodies were detected in the sera of TCE- and DCAC-treated mice in the following patterns: for anti-nuclear antibodies; controls, 0/4; TCE, 4/4; DCAC, 3/5; for anti-ssDNA antibodies; controls, 0/4; TCE, 2/4; DCAC, 5/5; for anti-cardiolipin antibodies; controls, 0/4; TCE, 0/4; DCAC, 3/5. An ELISA developed for the measurement of DCAC-specific antibodies using conjugated DCAC-albumin as an antigen showed the following pattern: for controls, 0/4; TCE, 0/4; DCAC, 5/5. These results suggest that TCE and its metabolite, DCAC, induce and/or accelerate autoimmune responses in female MRL +/+ mice. The greater responses induced by DCAC at a dose 50 times lower than TCE suggests that this metabolite may be important in the mechanisms leading to TCE-induced autoimmunity.

Mutations that affect ion channels change the sensitivity of Drosophila melanogaster to volatile anesthetics

We have quantitated the response of D. melanogaster to general anesthetics with a device, the inebriometer, that assays the fly's geotactic and postural behavior. When alleles of several loci that encode or regulate subunits of ion channels were compared with control stocks, several ion channel mutants clearly increased the anesthetic sensitivity of Drosophila. The effects were specific in that: a) for several alleles, genetic tests indicated that the anesthesia phenotype was due to the ion channel mutation and not to extraneous genetic differences between the stocks; b) a given ion channel mutation often affected the response to one anesthetic but not another; and c) the behavior of decapitated flies in the inebriometer indicated that the anesthetic phenotype of several mutants did not merely reflect a global change in the fly's physiology. These results provide support for the idea that ion channels are on the pathway(s) influenced by anesthetics and that different anesthetics use different pathways. They also provide perspective on the behavior of previously isolated mutations (har) that decrease the sensitivity of Drosophila to anesthetics in the inebriometer.

[Shivering and rigor during the awakening period]

Muscular hyperactivity presenting as shivering and rigor during the awakening period after 116 surgeries with the use of microsurgical technique under balanced NLA-based anesthesia was studied. In some cases ketamine (0.5 to 0.75 mg/kg) and trilene (0.3 to 0.5 vol.%) were used at the stage of tissue revascularization under conditions of controlled and uncontrolled thermal loss. The efficacy of special drug (ketamine, trilene) and nondrug (warming measures) components of anesthesia preventing shivering and rigor was demonstrated. A correlation between the intensity of muscular hyperactivity and the degree of recovery of pain sensitivity (r from -0.73 to -0.98) and the level of consciousness recovery (r from 0.69 to 0.92) was revealed. The policy of treatment of shivering and chill was selected with due consideration for these data. Efficacies of tramal (96%) and ketamine (80%) were demonstrated. Nubain was found absolutely unfit for the purpose.

Dichloroacetic acid and related compounds: induction of prophage in E. coli and mutagenicity and mutation spectra in Salmonella TA100

We performed three types of studies to evaluate the genotoxicity of the chlorinated organic solvent perchloroethylene (PERC or tetrachloroethylene) and its volatile metabolites, trichloroacetyl chloride (TCAC) and trichloroacetic acid (TCA), as well as the volatile metabolites of trichloroethylene, i.e. dichloroacetyl chloride (DCAC), dichloroacetic acid (DCA), and 2,2,2-trichloroethanol (TCE). In the first set of studies, which involved the evaluation of these chemicals in the Microscreen prophage-induction assay, only DCA (+S9) was genotoxic, producing 6.6-7.2 plaque-forming units/mM. This places DCA among the weakest of the > 100 chemicals that have been identified previously as inducers of prophage in this assay. In the second set of studies, which involved the evaluation of these chemicals in the vapor state in Salmonella TA100 using a Tedlar bag vaporization technique, DCA (+/-S9), DCAC (-S9), and TCAC (+/-S9) were mutagenic, producing 3-5x increases in revertants/plate relative to the background. S9 enhanced the mutagenic potency of DCA but had no effect on the mutagenic potency of TCAC. The potencies ranged from 0.7 to 3.9 rev/p.p.m., resulting in a potency ranking of DCA > DCAC approximately TCAC. The lowest effective concentrations were 50-300 p.p.m., which are similar to those for ethylene oxide and epichlorohydrin in this assay. In the third set of studies, the mutation spectra of DCA, DCAC, and TCAC were determined at the base-substitution allele hisG46 of Salmonella TA100. DCA and DCAC induced primarily G.C-->A.T transitions, whereas TCAC induced primarily G.C-->T.A transversions, which was also the predominant mutation among the background revertants.(ABSTRACT TRUNCATED AT 250 WORDS)

Depression of calcium dynamics in cardiac myocytes--a common mechanism of halogenated hydrocarbon anesthetics and solvents

Individual halogenated hydrocarbons (HC) have recently been demonstrated to depress Ca2+ dynamics in cardiomyocytes during excitation-contraction coupling. In the present study, eight widely used HC were systematically compared for their effects on Ca2+ dynamics in neonatal rat cardiomyocytes by means of spectrofluorometric analysis of fura-2-Ca(2+)-binding. Cells were exposed to dichloromethane (DCM), dichloroethane (DCE), 1,1,2-trichloroethane (112-TCE), trichloroethylene (TRI), halothane (HAL), 1,1,1-trichloroethane (111-TCE), perchloroethylene (PER), or pentachlorethane (PCE) in an environmentally controlled chamber. All HC tested decreased the height of electrically induced cytosolic free Ca2+ ([Ca2+]i) transients in a concentration-dependent and reversible manner (IC50 0.15-18.06 mM) without significant effects on diastolic [Ca2+]i. The increase in [Ca2+]i induced by depolarization with 90 mM KCl was inhibited to a lesser degree. Investigations with thapsigargin (100 nM) and ryanodine (1 microM)-inhibitors of Ca2+ release from the sarcoplasmic reticulum-provided evidence that the tonic Ca2+ response after KCl depolarization depends mainly on sarcolemmal Ca2+ influx. The potency of the eight HC to inhibit Ca2+ dynamics in cardiomyocytes correlated with their octanol/water partition coefficients. Results support the hypothesis that alteration of Ca2+ dynamics in cardiomyocytes is a common mechanism of cardiotoxic HC actions.

[Interaction of trichloroethylene and isopropyl alcohol in the perfused rat liver]

The interaction of trichloroethylene (TCEL) and isopropyl alcohol (IPA) was studied in the perfused rat liver. Experiments consisted of four parts; TCEL administration with or without IPA, chloral hydrate (CH) administration with or without IPA, IPA administration with or without CH, IPA administration with or without trichloroethanol (TCE). The chemicals were administered into the perfusate of Krebs-Henseleit buffer saturated with 95%O2/5%CO2 in a non-recirculating circuit. Concentrations of the following three metabolites in the effluent were continuously measured by gas chromatograph and chemical methods: TCE and trichloroacetate (TCA) (metabolites of TCEL and CH), and acetone (a metabolite of IPA). Fluorescence from intracellular reduced pyridine nucleotides (NADH, NADPH) was monitored by surface fluorometry. The results showed that IPA changed the TCA/TCE ratio in the TCEL metabolism because of an increase in NADH production, and IPA oxidation was suppressed by CH because of an inhibitory effect of TCE on alcohol dehydrogenase. It was concluded that IPA and TCEL, both ubiquitous agents, interacted with each other in their metabolic pathways in the perfused rat liver, suggesting a new feature of a combined effect of these chemicals when they coexist.

Increased oxidative stress in the liver of mice treated with trichloroethylene

In this study the trichloroethylene treatment-associated production of oxidative stress in mouse liver by measurements of changes in oxygen consumption, the disappearance of beta-nicotinamide adenine dinucleotide reduced form (NADPH), and the rate of malondialdehyde formation have been investigated. The treatment of mice with trichloroethylene (TCE), trichloroacetic acid (TCA), a metabolite of TCE, or clofibrate, a peroxisome proliferator, resulted in an increase in the oxygen consumption of liver microsomes compared to the values of the untreated controls. A maximum increase in the level of oxygen consumption in liver microsomes was observed in the mice treated with TCE, followed by clofibrate and TCA treatments. All three agents also increased the rate of NADPH oxidation in mice liver microsomes compared with untreated controls. NADPH oxidation was increased four fold by TCE or clofibrate (38 or 37 nmol/min) and two fold by TCA treatment (17 nmol/min) over that of the control animals (9 nmol/min). The concentration of malondialdehyde was higher in all three treated groups in comparison with control values. Malondialdehyde levels were elevated by 227%, 191%, and 118% by treatment with TCE, clofibrate, and TCA, respectively. Increases in the levels of oxygen consumption, NADPH disappearance, and malondialdehyde production in microsomes from liver of mice treated chronically with TCE or TCA are all indicative of elevated levels of oxidative stress. Increased oxidative stress may be involved in the induction of TCE-associated hepatotoxicity.

Mechanism of trichloroethylene-induced elevation of individual serum bile acids. I. Correlation of trichloroethylene concentrations to bile acids in rat serum

The temporal relationship between trichloroethylene (TRI) and individual serum bile acids (SBA) has been investigated to gain insight into the mechanism of solvent-induced increases in SBA. Male Sprague-Dawley rats were treated with 1 mmol/kg TRI in corn oil, while control rats received only corn oil. Blood samples were collected from the abdominal aorta at 2, 4, 8, and 16 hr after dosing. Individual SBA were determined by high-performance liquid chromatography (HPLC). Liver and blood concentrations of TRI and one of its metabolites, trichloroethanol (TCEOH), were determined by gas chromatography. SBA levels reached their peak at 4 hr and returned to control levels by 16 hr. There was a relationship between SBA levels and TRI concentrations, which were also at their peak 4 hr after dosing. By 16 hr the levels were undetectable. However, peak blood concentrations of TCEOH were reached 8 hr after dosing, and remained high at 16 hr. Cholic acid and taurocholic acid showed the highest levels of bile acids. Some other bile acids were also elevated, including deoxycholic acid, taurodeoxycholic acid, ursodeoxycholic acid, chenodeoxycholic acid, and taurochenodeoxycholic acid. Determination of total bile acids in serum using an enzymatic/colorimetric method showed a similar pattern of response to that obtained with the HPLC analysis. The data are consistent with TRI having a rapid and specific effect on SBA levels by a mechanism other than liver cell damage.

Mechanism of trichloroethylene-induced elevation of individual serum bile acids. II. In vitro and in vivo interference by trichloroethylene with bile acid transport in isolated rat hepatocytes

The effects of trichloroethylene (TRI) on bile acid transport in isolated rat hepatocytes have been studied using doses ranging from 0.5 to 4.0 microliters/flask and a 20-min equilibration period. It was found that TRI caused a dose-related suppression of initial rates of uptake of cholic acid (CA) and taurocholic acid (TC) with no significant effect on enzyme leakage and intracellular potassium ion contents. Accumulation over 30 min for each of those two bile acids was also inhibited. A noncompetitive inhibition of bile acid uptake was shown as indicated by a decrease in maximum velocity (Vmax) and unchanged Michaelis constant (Km). Thirty minutes after cessation of TRI exposure in vitro the uptake of bile acids had gradually returned to normal levels. No significant interference of efflux was found in cells preloaded with either CA or TC. After dosing rats with 1 mmol/kg TRI in vivo the inhibition of uptake of CA and TC by subsequently isolated hepatocytes was not detected until 4 hr. By 16 hr uptake had returned to normal. The accumulation of bile acids was also suppressed at 4 and 8 hr. The inhibition of uptake after in vivo treatment was also noncompetitive. The data are consistent with the reversible increase of serum bile acids (SBA) in experimental animals after exposure to TRI. Furthermore, they support the contention that it is an interference with bile acid uptake, rather than actual cell damage, that is responsible for TRI-induced increases in SBA. Thus, the changes in SBA seem to be the result of interference with a physiological process rather than an event associated with significant pathological consequences.

Acute effects of trichloroethylene on blood concentrations and performance decrements in rats and their relevance to humans

This study was designed to clarify the nature of effects of trichloroethylene (TCE) on the central nervous system, and to determine the critical concentrations in blood associated with specific behavioural changes. This was achieved by a follow up of the whole time course of TCE intoxication during and after exposure. The effects of a single four hour exposure to TCE on signalled bar press shock avoidance in rats were tested by methods previously applied to investigate the acute neurobehavioural effects of exposure to toluene. Even low exposure to TCE induced shock avoidance performance decrements in rats. Rats exposed to 250 ppm TCE showed a significant decrease both in the total number of lever presses and in avoidance responses at 140 minutes of exposure compared with controls. The rats did not recover their pre-exposure performance until 140 minutes after the exhaustion of TCE vapour. Exposures in the range 250 ppm to 2000 ppm TCE for four hours produced concentration related decreases in the avoidance response rate. No apparent acceleration of the reaction time was seen during exposure to 1000 or 2000 ppm TCE. The latency to a light signal was somewhat prolonged during the exposure to 2000 to 4000 ppm TCE. It is estimated that there was depression of the central nervous system with slight performance decrements and the corresponding blood concentration was 40 micrograms/ml during exposure. Depression of the central nervous system with anaesthetic performance decrements was produced by a blood TCE concentration of about 100 micrograms/ml. These results showed effects of TCE on the central nervous system that were considered to be a function of both the exposure concentration and the duration of exposure, which are closely related to the TCE concentration in blood.

Electroencephalographic and autonomic responses to trichloroethylene inhalation in freely moving rats

Effects of trichloroethylene (TRI) on the central nervous system (CNS) and autonomic functions were examined by means of continuous polygraphic measurements of electroencephalogram (EEG), electromyogram (EMG) and electrocardiogram (ECG) in electrode-implanted and freely moving rats, while they were exposed via inhalation to TRI vapor of 300, 1000 or 3000 ppm for 8 h/day or 6000 ppm for 4 h/day on 3 consecutive days. The exposures to 3000 and 6000 ppm produced abnormal EEG activity and incapacitation of postural maintenance during the exposure period, while the post-exposure period was characterized by decreased waking (W) time, lowered heart rate (HR) and increased numbers of bradyarrhythmic episodes after recovery from anesthesia. The exposure to 1000 ppm decreased W time without the appearance of anesthesia. The exposure to 300 ppm did not produce any observable effects except the lowered HR, which occurred during the post-exposure period. The relationships between internal doses of TRI and its metabolites and these TRI-induced pathophysiological responses were determined by blood and brain analyses of TRI, trichloroethanol and trichloroacetic acid in the TRI-exposed rats. Recordings of respiratory chest wall movement revealed that the number of TRI-induced bradyarrythmias accompanying apnea during paradoxical sleep (PS) increased significantly after cessation of exposure to 6000 ppm TRI. This suggests that TRI-induced hypoxemia due to apnea during PS triggers bradyarrhythmogenesis through increased cardiac vagal efferent tone.

Subclinical and reversible hepatic effects of occupational exposure to trichloroethylene

To detect early hepatic effects of chronic exposure to low-level trichloroethylene (TCE), serum total cholesterol (T-C), high-density-lipoprotein cholesterol (HDL-C) and activities of three serum enzymes [aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyl transpeptidase (GGT)] were determined in 148 workers (a cross-sectional study) and in 13 workers (a 2-year follow-up study) occupationally exposed to TCE in air. In the cross-sectional study, three exposure groups were defined by urinary total trichloro-compounds (U-TTC) levels of the workers [low-exposure group (n = 49): U-TTC < 10 mg/g creatinine; moderate-exposure group (n = 56): U-TTC 10- < 100; high-exposure group (n = 43): U-TTC > or = 100]. With increasing exposure levels, T-C (P = 0.143 by ANOVA) and HDL-C (P = 0.080 by ANOVA) slightly increased. The exposure, however, had no effect on the activities of the three serum enzymes. In the follow-up study, the fluctuations in U-TTC were well reflected in subclinical changes in HDL-C, AST, and GGT, but not in T-C or ALT. These results suggest that exposure to low-level TCE influences hepatic functions, affecting cholesterol metabolism rather than causing hepatic cell damage, and that these influences are subclinical and reversible. The increases in HDL-C caused by exposure to low-level TCE may be an example of "chemical hormesis" in humans.

In vivo and in vitro interaction of trichloroethylene with macromolecules from various organs of rat and mouse

Trichloroethylene was covalently bound in vivo to DNA, RNA and proteins of rat and mouse organs 22 hr after ip injection. The covalent binding index values of rat and mouse liver DNA classify trichloroethylene as a weak initiator. Labeling of RNA and proteins from various organs of both species was higher than that of DNA. In vitro, trichloroethylene was bioactivated by microsomal fractions dependent on cytochrome P450, mainly from liver of both species, to intermediate(s) capable of binding to exogenous DNA. No particular species-specific difference was evident except for mouse lung microsomes which were more efficient than rat lung microsomes. GSH-transferases capable of bioactivating P450-dependent were present in mouse lung microsomes and in liver microsomes of both species. These data, along those previously reported, provide sufficient evidence for a weak ability of TCY to interact covalently with DNA.

Trichloroethylene toxicity in mice: a biochemical, hematological and pathological assessment

Oral administration of trichloroethylene (TCE; 0, 500, 1000 and 2000 mg/kg/day) to male mice once daily, 5 days a week for a period of 28 days, caused a significant increase in liver weight, degeneration/necrosis of hepatocytes and characteristics proliferation of endothelial cells of hepatic sinusoids. Increase in kidney weight, glomerular nephrosis, degeneration/desquamation of tubular epithelium and characteristic amyloid deposition in glomeruli were observed only in the group of mice treated with 2000 mg/kg TCE. These changes occurred concurrently with a significant increase in total protein and free sulphydryl contents, elevated activities of acid phosphatase and catalase and decreased activity of delta-aminolevulinic acid dehydratase (delta-ALAD) indicating the sensitivity of liver and kidney as target tissues in TCE-toxicity. Hematological studies showed a significant increase in RBC counts and a reduction in WBC counts without any statistically significant change in the hemoglobin, urea nitrogen, creatinine and uric acid levels in the blood of TCE-exposed mice. A dose-related increase in cell density and acid phosphatase activity with a parallel significant decrease in the activity of delta-ALAD were observed in the bone marrow, which appear to be responsible for hematological alterations in TCE-exposed mice. The results suggest that early metabolic, pathological and hematological perturbations following a short-term exposure of TCE in mice, can provide the basis for its documented potential for chronic effects like blood dyscrasia and cancer.

Trichloroethylene interactions with muscle cells

The toxic effect of trichlorethylene (TCE) was investigated on isolated muscles prepared from frog and rats. Twitch and tetanic contractions as well as caffeine-induced contractures, were recorded. Trichloroethylene at a concentration of 0.25-4.0 mM depressed the force development of both twitch and tetanic tension in a dose-dependent manner. This effect was not influenced by the type of muscle. As TCE shortened the time to peak of twitch contractions, it may alter the Ca2+ binding kinetics. Subthreshold caffeine concentrations applied after pre-exposure to TCE (1 or 2mM) induced contractures. The same TCE exposure enhanced regular caffeine contractures through increasing the speed of tension development and the absolute force. Exposure to 5 or 10 mM TCE did not affect the first caffeine-induced contracture but enhanced the potency of the second caffeine dose given 15 min after the first. The results suggest that the interaction of TCE with membrane sites is responsible for Ca2+ release for contractile processes.

An overview of peroxisome proliferator-induced hepatocarcinogenesis

Peroxisome proliferators are hepatocarcinogens in rats and mice. Chronic administration of these compounds results in the development of altered areas and neoplastic nodules followed by hepatocellular carcinomas. All three types of hepatic lesions do not express gamma-glutamyltranspeptidase, glutathione 8-transferase-P, and alpha-fetoprotein and are resistant to iron accumulation after overload. The mechanism by which nongenotoxic peroxisome proliferators induce hepatic tumors is not well understood. It has been proposed that with continuous administration of peroxisome proliferators, liver cells are subjected to persistent oxidative stress resulting from marked proliferation of peroxisomes and a differential increase in the levels of H2O2 producing (20- to 30-fold) and degrading (2-fold) enzymes. Free oxygen radicals lead to DNA damage (both directly and through lipid peroxidation) and thus may cause initiation and promotion of the carcinogenic process.

Damage and repair of mouse bronchial epithelium following acute inhalation of trichloroethylene

The time-course of damage and repair in the bronchial epithelium of the mouse was studied morphometrically after a single inhalation of trichloroethylene (TCE). Mice were exposed for 30 min to 500, 1000, 2000, 3500, or 7000 ppm of TCE under controlled conditions and sacrificed after 2 and 24 h, and 2, 5, and 7 days. At all TCE concentrations, the damage consisted of dilation of endoplasmic reticulum and was selective for nonciliated cells throughout the bronchial tree. Damage was quantitatively evaluated by counting the percentage of vacuolated cells. Injury was maximal 24 h after exposure and was significantly (p less than 0.05) higher in bronchi with a diameter smaller than 0.4 mm (67.0% +/- 8.5%) in comparison with larger bronchi (34.0% +/- 13.2%). Cell turnover was studied by autoradiography after [3H]thymidine injection. Following TCE inhalation, the percentage of [3H]thymidine labeled cells, which in the controls was virtually zero, increased to a maximum of 13.5% +/- 6.8% (average at all doses) 48 h after treatment and then rapidly decreased to baseline values at 7 days (0.2% +/- 0.1%). Repair of some cells occurred after 24 h, and at 48 h the percentage of vacuolated cells decreased and became significantly related (p less than 0.01) to the administered TCE dose (2.4% +/- 1.4% and 21.2% +/- 6.0% average in the 500 and 7000 ppm groups, respectively). Repair of bronchial epithelium took place by both recovery of less damaged cells and proliferation of residual nonciliated cells, leading to restoration of the normal ratio between ciliated and nonciliated cells.

[The behavior of substance P concentration in rat plasma in the acute single- and combined-actions of trichloroethylene and ethanol]

In experimental studies in male Wistar-rats exerted for determination of trichloroethylene, ethanol and combined action influences on the substance P plasma concentrations. These concentrations were determined by a radioimmunological method. The acute exposure of trichloroethylene and ethanol lead to a significant rise of substance P. We found high substance P concentration peaks, in principle, 4 h after acute exposure and the combined action shows the greatest effect.

The effect of haloalkene cysteine conjugates on rat renal glutathione reductase and lipoyl dehydrogenase activities

An early event in the nephrotoxicity of haloalkene cysteine conjugates is their metabolism by cysteine conjugate beta-lyase to generate a reactive "thiol moiety" which binds to protein. This reactive metabolite(s) has been reported to cause mitochondrial dysfunction. We have examined the effect of three haloalkene cysteine conjugates on the activity of rat renal cortical cytosolic glutathione reductase and mitochondrial lipoyl dehydrogenase, two enzymes which have been reported to be inhibited by S-(1,2-dichlorovinyl)-L-cysteine (DCVC) in the liver. N-Acetyl-S-(1,2,3,4,4-pentachloro-1,3-butadienyl)-L- cysteine (N-acetyl PCBC) produced a time- and concentration-dependent inhibition of glutathione reductase and kinetic studies showed that the inhibition was noncompetitive with a Ki of 215 microM. The enzyme activity from male rat kidney was more sensitive to N-acetyl PCBC than that from female rat kidney. Aminooxyacetic acid, an inhibitor of cysteine conjugate beta-lyase, and bis-p-nitrophenyl phosphate, an amidase inhibitor, blocked the effect of N-acetyl PCBC on glutathione reductase, indicating that metabolism by the cytosol is required to produce enzyme inhibition. S-(1,1,2,2-Tetrafluoroethyl)-L-cysteine (TFEC) and DCVC are also noncompetitive inhibitors of glutathione reductase but are less active than N-acetyl PCBC with Ki's of 2.6 and 6.2 mM for DCVC and TFEC, respectively, DCVC produced a time- and concentration-dependent inhibition of lipoyl dehydrogenase and kinetic studies showed that the inhibition was noncompetitive with a Ki of 762 microM. TFEC and PCBC also inhibit lipoyl dehydrogenase. Aminooxyacetic acid blocked the effect of DCVC, TFEC, and PCBC on lipoyl dehydrogenase, indicating that metabolism by the mitochondrial fraction is required to produce enzyme inhibition. Glutathione reductase activity in the renal cortex of male rats treated with 200 mg/kg hexachloro-1,3-butadiene (HCBD) was inhibited as early as 1 hour after dosing, before signs of marked morphological damage. The activity of lipoyl dehydrogenase was also reduced but was only statistically significant 8 hr after dosing when there was marked renal dysfunction. These findings indicate that the reactive thiol moiety formed by cysteine conjugate beta-lyase cleavage of PCBC can inhibit both glutathione reductase and lipoyl dehydrogenase activities in vivo following HCBD administration. We suggest that such inhibition is a general phenomenon, occurring with diverse and as yet unidentified renal proteins. The critical nature of mitochondrial function and the generation of reactive metabolites within this compartment make this organelle a prime target.

Praziquantel did not exhibit hepatotoxicity in a study with isolated hepatocytes

The effect of praziquantel in different concentrations on isolated rat hepatocytes as a cellular target was studied to detect any possible toxicity. Leakage of cytosolic enzymes, aspartate aminotransferase, alanine aminotransferase and lactate dehydrogenase (LDH) was monitored after one hour of incubation of all the cells with the drug. Levels of reduced glutathione (GSH) and cytochrome P450 were also assayed. The drug, in concentrations of 5, 25, 50 and 100 micrograms/ml, had no effect on any of these parameters. In contrast, the hepatotoxic compound trichloroethylene showed dose-dependent toxicity, as measured by trypan blue (TB) exclusion, LDH leakage, and reduction in GSH content in the present cellular model. These results suggest that praziquantel is a relatively safe drug with respect to liver function.

Induction of cytochrome P-450, cytochrome b-5, NADPH-cytochrome c reductase and change of cytochrome P-450 isozymes with long-term trichloroethylene treatment

Several reports have described the effects of trichloroethylene (TCE) on the microsomal mixed function oxidase system (MFOS). These studies suggest that repeated TCE administration induces MFOS, especially cytochrome P-450 and NADPH-cytochrome c reductase. However, it is uncertain what isozymes are induced by TCE treatment, and it is not clear how microsomal enzymes or cytochrome P-450 isozymes are altered when TCE is administered for a duration longer than 28 days. We investigated the changes of MFOS by long-term TCE treatment. Male Wistar rats were injected with TCE, 1.0 g/kg body weight once a day for 5 continuous days or 2.0 g/kg body weight twice a week for 15 days. The mean body weight of the rats treated with TCE for 15 weeks was slightly, but not significantly, less than that of the control rats. Relative liver weights (liver wt/body wt) of the TCE-treated group were however significantly larger (21%) than those of the control group. The weights of the other organs were not changed by long-term TCE treatment. Trichloroethylene treatments for 5 days and 15 weeks caused significant increases in microsomal protein, cytochrome P-450, cytochrome b-5 and NADPH-cytochrome c reductase. TCE treatments produced an increase in a polypeptide band at 52,000 molecular weight range observed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). This increase in similar to, but less pronounced than that induced by phenobarbital (PB) treatment. There were no remarkable changes at 56,000 molecular weight range where a band appeared after the treatment with 3-methylcholanthrene (MC). It is likely that the induction of cytochrome P-450 by TCE is relatively similar to that by PB.

Metabolic activity of antipyrine in workers occupationally exposed to trichloroethylene

In order to investigate possible effects of occupational exposure to trichloroethylene (TRI) on the liver cytochrome P-450 dependent monooxygenases, the metabolic activity of salivary antipyrine was determined in workers (I; N = 32) employed in dry-cleaning shops (I-1; N = 17) and in an industrial metal degreasing process (I-2; N = 15). The studies were performed twice: (a) during the working period, (b) and after at least three weeks free of exposure. The control group (II) consisted of 29 subjects with no known exposure to chemicals. Analyses of the solvents used (TRI) showed them to be mixtures. Statistically significant differences were found (P less than 0.01) in antipyrine t1/2 and clearance within the exposed group (Ia:Ib), but not between the exposed (I) and control (II) group. A breakdown of antipyrine pharmacokinetic data by I-1 and I-2 subgroups demonstrated a statistically significant difference in t1/2 (P less than 0.02) and clearance (P less than 0.05) within I-1 subgroup (a:b), in contrast to the I-2 subgroup (a:b). The difference in antipyrine t1/2 between I-1,a and the control group (II) was also statistically significant (P less than 0.05). Although there was no difference in TRI exposure between I-1 and I-2 based on the biological parameters of TRI absorption, the TRI used in I-2 was of higher grade of purity. It can therefore be concluded that TRI itself is not an inducer of liver monooxygenases and that the monooxygenase induction in subgroup I-1 of TRI exposed workers could be due to TRI impurities.

Genetic effects of chlorinated ethylenes in the yeast Saccharomyces cerevisiae

The chlorinated ethylenes 1,1-dichloroethylene (vinylidene chloride), trans-1,2-dichloroethylene, trichloroethylene, and tetrachloroethylene (perchloroethylene) were assayed for their ability to induce mitotic gene conversion and point mutation as well as mitotic aneuploidy in diploid strains of the yeast Saccharomyces cerevisiae. From strain D7 late logarithmic-phase cells grown in 20% glucose liquid medium, containing a high level of cytochrome P-450, as well as stationary-phase cells combined with an exogenous metabolic activating system (S9) were used, in order to activate the chlorinated compounds and to produce electrophilic mutagenic intermediates. Only 1,1-dichloroethylene exhibited a dose-dependent genetic activity, while the other ethylenes did not. The 2 ways of metabolic activation were compared and were found to cause approximately the same effect. In contrast to the findings with strain D7, vinylidene chloride, trans-1,2-dichloroethylene, and trichloroethylene induced, without metabolic activation, mitotic chromosomal malsegregation in strain D61.M. The presence of liver homogenate as an activating system did not enhance the respective frequencies of chromosome loss. In the case of tetrachloroethylene, sufficient data have not become available, since this compound showed a highly toxic effect towards yeast cells, decreasing the rate of surviving cells to less than 30% at a concentration of 9.8 mM.