Enzyme-catalysed conjugations of glutathione with unsaturated compounds

Factors involved in depletion of glutathione from A549 human lung carcinoma cells: implications for radiotherapy

We have measured the rate of GSH resynthesis in plateau phase cultures of A549 human lung carcinoma cells subjected to a fresh medium change. Buthionine sulfoximine (BSO) blocks this resynthesis. Diethyl maleate (DEM) causes a decrease in accumulation of GSH. If DEM is added concurrently with BSO there is a rapid decline in GSH that is maximal in the presence of 0.5 mM DEM. GSH depletion rapidly occurs when BSO is added to log phase cultures which initially are higher in GSH content. Twenty-four hr treatment of A549 cells with BSO results in cells that are more radiosensitive in air and show a slight hypoxic radiation response. A 2 hr treatment with either 0.25 mM or 0.5 mM DEM results in some hypoxic sensitization and little increase in the aerobic radiation response. The 24 hr BSO + 2 hr DEM treatment sensitizes hypoxic cells to a greater degree than either agent alone but does not increase the aerobic response more than is seen with BSO alone. Cells treated simultaneously with BSO + DEM show little increase in the hypoxic radiation response, compared to DEM alone, but are more sensitive under aerobic conditions. Decreased cell survival for aerobically irradiated log phase A549 cells occurs within minutes after addition of a mixture of BSO + DEM. The decreased cell survival following aerobic irradiation, after prolonged treatment with BSO or acute exposure to BSO + DEM, may be in part due to inhibition of glutathione peroxidases. For example, glutathione-S-transferase, known to have glutathione peroxidase activity (non-selenium), is nearly completely inhibited by the BSO treatments. In addition, cellular capacity to react with peroxide (glutathione peroxidase, selenium containing) was also inhibited. We suggest that the enhanced aerobic radiation response is related to an inability of GSH depleted cells to inactivate either peroxy radicals or hydroperoxides that may be produced during irradiation of BSO treated cells. Furthermore, enhancement of the aerobic radiation response may be useful in vivo if normal tissue responses are not also increased.

Depletion of the reduced glutathione level in the liver and production of the mutagens in the intestine in the mice inducing hepatoma by feeding on a high level dose of sorbic acid

Mutagenicity was detected using Salmonella typhimurium TA98 in the acidic components of the intestinal contents of mice, in which a high incidence of hepatoma had been reported due to feeding on a diet containing 15% sorbic acid (Ishizawa et al., 1980). Furthermore, the glutathione level in the liver of the 15% sorbic acid group was decreased to 40% of the amount found in controls after a 3-month feeding period, and this low level was maintained for long periods (12 months) until the end of the experiments. There was also a close correlation between the extent of depletion of the hepato-glutathione level and the concentration of sorbic acid added to the diet. Consequently, the hepatoma which developed in mice fed a 15% sorbic acid diet was considered to be induced both by the depletion of the hepato-glutathione level over the long periods, and by the gradual production of various mutagens in the intestine which were absorbed and transferred to liver to be metabolically activated.

Non-mutagenicity of 27 aliphatic acrylate esters in the Salmonella-microsome test

The mutagenicity of 27 acrylate esters was assessed in the Salmonella-microsome assay. Methyl, ethyl, butyl, t-butyl, pentyl, neopentyl, hexyl acrylate and methacrylate and 2-hydroxyethyl methacrylate were tested; furthermore ethanediol, butanediol, pentanediol, neopentanediol, hexanediol and diethyleneglycol diacrylate and dimethacrylate. None of these 27 acrylate esters appeared to be mutagenic in the standard Ames assay with TA1535, TA1537, TA1538, TA98 and TA100, both with and without Aroclor 1254 or phenobarbital-induced S9 mix. A liquid incubation assay of methyl methacrylate, methyl, butyl and hexyl acrylate with TA100 neither gave any indication of a mutagenic activity of these compounds.

Glutathione depletion and resynthesis in laboratory animals

The availability of tissue glutathione (GSH) appears to depend upon a balance between tissue concentrations, the rate of reactive metabolite formation and the re-synthesis of GSH. To test this hypothesis, diethyl maleate (DEM, 5.8 mmol/kg bw) was administered intraperitoneally to male and female mice, hamsters, rats and guinea pigs. The regeneration of hepatic and renal GSH was examined at 0.5, 1, 2, 4, 8 and 24 hr post-treatment. DEM caused a rapid and marked depletion of tissue GSH but re-synthesis began to occur by 4 hr post-treatment in all species with the exception of the guinea pig. By 24 hr after treatment, the mouse, hamster and rat had tissue levels of GSH in excess of usual values but, in the guinea pig, recovery of hepatic GSH was still significantly reduced. Considering the reported species differences in S-alkenetransferases which detoxify DEM, the present results revealed that the conjugation of DEM proceeded rapidly in all four species but that the toxicity elicited in the guinea pig may have arisen from the unavailability of GSH during the slow re-synthesis stage following maximal depletion of this agent.

Investigations into the mechanism of coumarin-induced hepatotoxicity in the rat

The administration of single doses of coumarin to the rat was found to produce hepatic centrilobular necrosis and also to depress a number of hepatic enzyme activities within 24 h. Coumarin-induced liver damage was diminished by pretreatment with cobaltous chloride but potentiated by the administration of diethyl maleate. Hepatic reduced non-protein sulphydryl levels were rapidly depleted following coumarin treatment whereas urinary mercapturic acid excretion was enhanced suggesting the formation of a coumarin metabolite or metabolites hitherto undetected in this species. In in vitro studies [3-14C]coumarin was converted by rat hepatic microsomes to reactive intermediates which became bound covalently to microsomal proteins. Additional studies established that the formation of reactive metabolites was a cytochrome P-450 dependent process and that macromolecular binding could be inhibited by sulphydryl compounds (including reduced glutathione) and hepatic cytosol fractions. These results demonstrate that coumarin-induced hepatotoxicity in the rat is likely to be mediated via one or more reactive metabolites generated by cytochrome P-450 dependent enzymes and that reduced glutathione and other thiol agents constitute a detoxification pathway.

Computer-assisted structure-activity correlations

Several types of Michael acceptors, including alpha,beta-unsaturated ketones, lactones, and lactams, have been extensively studied as potential anticancer agents. A concerted effort was made to explore the relationship between the structures of these compounds and their antitumor activity against P388 and L1210 leukemias. This article describes the computer-assisted structure-activity evaluation of more than 14,000 compounds, representing different classes of Michael acceptors, in the NCI file. In this study, advantage has been taken of the computer's ability to search substructures according to precise definitions and to manipulate these substructures utilizing Boolean logic. Olefinic conjugated Michael-type acceptors, e.g., styrenes with different activating groups, cinnamic acid derivatives, and alpha,beta-unsaturated nitro, cyano, sulfone, sulfoxide, and acetylenic compounds, have shown appreciable activity against P388 lymphocytic leukemia. The analysis of lactones and lactams includes substructures representing a wide variety of exocyclic and endocyclic alpha,beta-unsaturated compounds. The analysis describes the effect of certain groups, such as an --OH, --OR, alpha,beta-unsaturated ester, or epoxide, adjacent to the alpha,beta-unsaturated center, on the antitumor activity of these compounds. A combination of one or more of these activating groups with an alpha-methylene-gamma-lactone moiety significantly enhanced the activity against P388. In general, many of the classes of compounds studied have shown poor activity against the more stringent L1210 lymphoid leukemia.

Acetaminophen overdose

Acetaminophen is a remarkably safe agent when used in therapeutic doses. Most reported overdoses of acetaminophen are the result of suicide attempts. The clinical course of patients with toxic blood levels follows four distinct stages. Symptoms of nausea, vomiting, diaphoresis, and anorexia usually begin within seven to 14 hours after ingestion. After 24 to 48 hours, these symptoms may diminish, but SGOT, SGPT, bilirubin, and prothrombin time begin to rise. Peak hepatotoxicity occurs at 72 to 96 hours, and SGOT levels of 20,000 I.U. are not unusual. Oral N-acetylcysteine is the drug of choice for acetaminophen overdose. Intravenous use of N-acetylcysteine is advocated in England, Europe, and elsewhere, but it is not available in the United States. Clinical studies of oral and intravenous N-acetylcysteine clearly demonstrate that the drug has a profound effect on reducing morbidity and mortality if it is administered during the first 16 hours after the overdose. In addition, data from these studies have shown that alcohol taken simultaneously with an overdose of acetaminophen is actually hepatoprotective. Therefore, patients who have consumed alcohol at the time of overdose, or those who are chronic alcoholics, should be managed in the same way as patients with no exposure to alcohol. However, study results also reveal that overdose in children under 10 to 12 years of age follows a distinctly different pattern. These children demonstrate a lesser degree of hepatotoxicity and have only minor increases in transaminase levels.

2-Chlorobenzylmercapturic acid, a metabolite of the riot control agent 2-chlorobenzylidene malononitrile (CS) in the rat

Adult male Wistar rats administered i.p. with 2-chlorobenzylidene malononitrile (CS) excreted one mercapturic acid in urine. The amount of mercapturic acid determined gaschromatographically was about 4% of the dose (0.07 mmol/kg, n = 12). The structure of the mercapturic acid methylester was identified by t.l.c. and confirmed by synthesis and mass-spectrography. The acid appeared to be 2-chlorobenzylmercapturic acid [N-acetyl-S-(2-chlorobenzyl)-L-cysteine]. CS and some of its metabolites were also tested in the Ames Salmonella/microsome assay. Both mutagenic and toxic effects were measured with strain TA 100 as the indicator organism. No mutagenic effects were found with any of the tested substances. At dosages of CS, higher than 1,000 micrograms/plate a bacteriotoxicity was revealed.

Status of reduced glutathione in primary cultures of rat hepatocytes and the effect on conjugation of benzo[a]pyrene-7,8-dihydrodiol-9,10-oxide

The intracellular level of reduced glutathione (GSH) and GSH conjugation have been investigated in primary cell cultures of hepatocytes isolated from control rats, phenobarbitone (PB) and 3-methylcholanthrene (MC) treated rats. The data demonstrate that in all cell cultures the GSH concentrations show a triphasic pattern: (i) within 1 h of culture an initial marked decrease to 50% of the levels found in fresh hepatocytes; (ii) recovery of GSH concentrations to above the levels observed in fresh cells. This occurs after 6 h in culture with control cells and after 10-24 h with cells from either PB or MC treated rats and was most prominent in cells from PB-treated rats. (iii) A slow decline to between 30 and 40 nmol GSH/mg protein from 24 to 96 h in culture. Synthesis of GSH was slower in cultured cells from PB treated rats and this was confirmed by the resynthesis rates when diethylmaleate (DEM) was used to deplete GSH. The formation of GSH conjugates with racemic 7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) was measured in control cells in suspension and after 3 and 24 h in culture. Despite the decrease in GSH concentrations observed between 1 and 4 h after culture, the conjugation rates were not decreased.

Uptake of elemental mercury by brain in relation to concentration of glutathione and activity of glutathione peroxidase

Uptake of mercury by brain after i.v. injection of elemental mercury was investigated in the rat, after depletion of glutathione or inhibition of glutathione peroxidase in brain tissue. When glutathione in brain was depleted 76% by an intraventricular injection of diethylmaleate, a 13% increase in mercury uptake by brain was observed. After an intraventricular injection of iodoacetate, activity of glutathione peroxidase in brain was inhibited 19% and the content of reduced glutathione was decreased 20%. In these animals mercury uptake by brain increased 66% relative to controls.

Comparative toxicokinetics of 2,3-14C-and 1-14C-acrylonitrile in the rat

The tissue distribution, elimination and covalent binding of 2,3-14C-and 1-14C-acrylonitrile (VCN) were studies in male Sprague-Dawley rats given an oral dose of 46.5 mg kg-1. Exhalation of unchanged VCN, 14CO2 and H14CN was monitored at selected intervals. Only 5% of the total dose administered was recovered was unchanged VCN. Rate given 2,3-14C-VCN exhaled only 2% of 14C activity was 14CO2 and none was recovered as H14CN, whereas rats given 1-14C-VCN exhaled about 12% of 14C activity as 14CO2 and 0.5% as H14CN. In the initial 24 h, 40% of radioactivity from 1-14C-VCN appeared in urine, while 60% was recovered in the urine of rats given 2,3-14C-VCN. The red blood cells retained significant amounts of radioactivity from both the compounds for more than 10 days after administration, whereas the 14C activity in plasma declined sharply. The highest level of radioactivity from both compounds was recovered in the gastrointestinal tract. In liver, kidney, brain, spleen, adrenal, lung and heart tissues the unbound percent radioactivity decreased, while irreversible percent covalent binding to macromolecules in relation to total increased concomitantly. Subcellular fractionation of the tissues showed that most of the covalently bound radioactivity was distributed in non-cytosolic fractions. As compared to 1-14C-VCN administered animals, the percentage of covalent binding of 2,3-14C-VCN was significantly higher even 72 h after dosing. The relationship between covalent binding and acrylonitrile toxicity is discussed.

Effects of methyl methacrylate on non-protein thiols and drug metabolizing enzymes in rat liver and kidneys

Male Wistar rats received methyl methacrylate monomer (MMA) i.p. in olive oil 1.0 g/kg body weight on 3 successive days. The weight of the livers and kidneys, and the body weights did not differ from their controls. On the fifth day after treatment, hepatic NADPH-cytochrome c reductase, 7-ethoxycoumarin 0-deethylase and the 2,5-diphenyloxazole hydroxylase exhibited maximal decreases in activity (25%, 58%, 36%, respectively) without any coincident effect on the total amount of cytochrome P-450 hemoprotein itself. One week later these activities had returned to control levels. The enzymatic changes in the kidneys were smaller in magnitude, and they were also reversed sooner. A single i.p. dose of MMA (2 g/kg body weight) caused elevation of serum alanine aminotransferase activity. A tenfold increase of the excretion rate of urinary thioethers was also discovered. The hepatic reduced glutathione (GSH) was depleted in 3 h to 20% and the GSSG to half of the value in controls. In kidneys, the GSH was decreased to 48% in 3 h before an apparent phase of overrecovery. At the end of the 24 h observation period, cytochrome P-450 concentrations were somewhat decreased in the liver. The GSH contents showed dose and time-dependent reversible decreases in isolated hepatocytes when incubated for 2 h in a medium containing MMA at the nominal concentrations of 0, 2, 5, or 10 mM. None of the treatments affected either the content of cytochrome P-450 or the viability of the liver cells.

Effect of glutathione status on covalent binding and pneumotoxicity of 3-methylindole in goats

A study was conducted to investigate the relationship between glutathione (GSH) status, in-vivo metabolite covalent binding and 3-methylindole (3MI)-induced lung injury in goats. Cysteine or diethylmaleate pretreatments were given to sustain or deplete GSH, respectively, prior to intravenous 14C-3MI administration. Cysteine pretreatment prolonged survival times, decreased (P less than .05) covalent lung injury. Diethylmaleate pretreatment shortened survival times, increased (P less than .05) covalent binding and enhanced lung injury. Covalent binding was higher (P less than .05) in lung compared to liver and kidney. 3-Methylindole alone depleted GSH in 4 hours to 36, 66, and 75% of controls in these tissues, respectively. The relationship between tissue GSH, covalent binding and toxicity supports the hypothesis that 3MI-induced pneumotoxicity results from the formation of activated intermediates and that GSH plays a role in detoxication of these 3MI metabolites.

Effects of diethyl maleate on protein synthesis in isolated hepatocytes

Diethyl maleate is commonly used in toxicological and drug metabolism research using isolated adult rat hepatocytes. At the highest concentrations used the effect of diethyl maleate is, however, not limited to glutathione depletion. In these conditions it inhibits protein synthesis and it impairs the "L" system for amino acid transport. It has, however, no effect on the cytochrome P-450 content or its dependent aldrin monooxygenase. The present report shows that a concentration of diethyl maleate as low as 0.2 mM is sufficient to deplete glutathione without affecting glycogen and protein synthesis, transport of amino acid or monooxygenase activity in isolated adult rat hepatocytes.

Lipid peroxidation: a possible mechanism of cephaloridine-induced nephrotoxicity

Cephaloridine produces renal cortical injury, but the precise mechanism responsible for this nephrotoxicity remains unclear. Recently cephaloridine has been shown to deplete reduced glutathione (GSH) concentration selectively in renal cortex. Cephaloridine nephrotoxicity can be potentiated by diethyl maleate (a GSH depletor), but no glutathione conjugate can be detected. Thus, it was of interest to investigate further the mechanism of depletion of renal cortical GSH by cephaloridine. In the present study, cephaloridine markedly decreased GSH in rat and rabbit renal cortex while concomitantly increasing oxidized glutathione (GSSG). Furthermore, cephaloridine increased lipid peroxidation specifically in renal cortical cells. Conjugated diene formation (an index of lipid peroxidation) was increased in renal cortex but not in the liver shortly following administration of cephaloridine. Removal of selenium and/or vitamin E from the diet, which should enhance lipid peroxidation, potentiated cephaloridine nephrotoxicity and enhanced cephaloridine-induced morphological damage in the kidney. These findings are consistent with a major role of lipid peroxidation in the etiology of cephaloridine nephrotoxicity.

Hepatic content of free sulfhydryl compounds in animals exposed to vinyl acetate

The content of free non-protein thiols (-SH) was investigated in the livers of guinea pigs, rats and mice after intraperitoneal injection of vinyl acetate (VA). A rapid change of the hepatic -SH level was found in guinea pigs after injection of 500 mg/kg VA. This resulted in a 50% decrease in -SH content. In mice the decrease was slower and amounted to only 23% four hours after injection of 300 mg/kg VA. Rats responded to a single dose of 450 mg/kg VA with only a 10% reduction of the -SH content of the liver. An approximately 20% decrease was observed after chronic intermittent exposure (5 h d-1 for 6 months) to 10, 100 or 500 mg/m3 VA.

Disulfiram-like effect of diethyl maleate on barbiturate-induced hypnosis and 5-hydroxytryptamine metabolism

Diethyl maleate (DEM, 600 mg kg-1 i.p.) significantly potentiated hexobarbitone hypnosis and lowered plasma hexobarbitone level on awakening. Sleeping time following intracerebroventricular (i.c.v.) injection of phenobarbitone was also prolonged by DEM treatment. When administered to DEM-treated rats, L-tryptophan (50 mg kg-1 i.p.) significantly potentiated hexobarbitone hypnosis, although alone it had no effect in control rats. DEM markedly diminished the activity of brain low-Km aldehyde dehydrogenase (A1DH) and the formation of 5-hydroxyindoleacetic acid from 5-hydroxytryptamine (5-HT) without affecting MAO activity in various areas of the brain. Conversely, the protein-bound radioactivity derived from i.c.v. [14C]-5-HT was increased by DEM treatment. These results showed that DEM is comparable with disulfiram, a brain A1DH inhibitor, in terms of its effect on 5-HT metabolism and barbiturate hypnosis.

Inhibition of glycolysis of mammalian cells by misonidazole and other radiosensitizing drugs. prevention by thiols

Prolonged anaerobic incubation of Ehrlich ascites tumor cells and Chinese hamster V79-379A cells with misonidazole, desmethylmisonidazole, or niridazole led to inhibition of both glucose consumption and lactate formation. This effect was measured in cells washed free of the nitro compounds and resuspended in fresh buffer or medium. The degree of inhibition of glucose utilization was related to drug concentration, and to the rate of metabolic reduction, as measured under aerobic conditions by KCN-insensitive oxygen consumption. Misonidazole-induced inhibition of glycolysis developed concurrently with depletion of intracellular non-protein thiol (NPSH) and was protected against by the presence of cysteamine, cysteine and, to some extent, GSH in the cell incubate. These findings suggest diethyl maleate was used to deplete 90% of the endogenous NPSH, but this depletion did not alter the effects of misonidazole on glycolysis.

In vivo biotransformation and biliary excretion of 1-14C-acrylonitrile in rats

1-14C-Acrylonitrile (VCN) was give orally to rats, 27% of the given dose was excreted in bile in 6 h. When 1-14C-VCN was given to overnight fasted or cobaltous chloride treated rats, a significant increase in the biliary excretion occurred. Pretreatment of rats with phenobarbital produced no change, while diethyl maleate pretreatment significantly decreased the portion of the dose excreted in bile in 6 h. Four metabolites of 1-14C-VCN have been isolated from the collected bile, and characterized. The two major biliary metabolites were found to be glutathione (GSH) conjugates of VCN, indicating the importance of GSH in VCN biotransformation.

Role of glutathione in liver-mediated mutagenicity of acrylonitrile

The mutagenic activity of acrylonitrile (ACN) towards the Salmonella typhimurium strain TA1530 was evaluated after a short preincubation time in liquid medium in the presence of microsomes, cytosolic fractions and post-mitochondrial fractions of liver from untreated and phenobarbitone (PB)-pretreated rats and mice. The effect of the presence of glutathione (GSH) was also examined. GSH enhanced the microsomal-mediated mutagenicity of ACN; that effect was abolished in the presence of CO. The effect of GSH was usually greater after pretreatment by phenobarbitone. Other sulfhydryl compounds induce a weaker mutagenic activity than GSH. These observations support the hypothesis of a mediated formation of a mutagen involving GSH, but the adduct between ACN an GSH was not mutagenic.

Protective effect of sulfhydryl compounds on acute toxicity of morphinone

The ability of sulfhydryl compounds to provide protection against the acute toxicity of morphinone was investigated in mice. Subcutaneous administration of morphinone produced a reduction of hepatic non-protein sulfhydryl concentration. Pretreatments of mice with glutathione or cysteine significantly increased the survival rate of mice given a lethal dose of morphinone, whereas morphinone lethality was markedly potentiated by diethyl maleate. On the other hand, the administration of morphine produce a dose dependent reduction of hepatic non-protein sulfhydryl contents. However, neither glutathione nor cysteine protected mice from the acute toxicity of morphine. A possible explanation for these observations was proposed as follows: morphine is oxidized by morphine 6-dehydrogenase to morphinone, and the morphinone thus produced decreases the sulfhydryl contents in the liver. This mechanism is supported by the fact that morphinone reacts easily with glutathione and cysteine in vitro.

Isolation and identification of mercapturic acid metabolites of phenyl substituted acrylate esters from urine of female rats

The urinary mercapturic acid excretion by female rats of methyl atropate (alpha-phenyl methyl acrylate) and methyl cinnamate (beta-phenyl methyl acrylate) has been studied. On the basis of the structures of these mercapturic acids the conclusion can be drawn that these compounds arise from a conjugation of glutathione with the acrylic esters in a Michael fashion. Previous administration of (tri-orthotolyl) phosphate (TOTP), a carboxy esterase inhibitor, enhances the capacity of the acrylate esters to alkylate glutathione in vivo. The amount increased from 1.5 to 22.8% of dose (1.0 mmol/kg) for methyl cinnamate and from 10.4 to 14.8% of dose (0.2 mmol/kg) for methyl atropate. Upon inhibition of the esterase activity the major actual mercapturic acid is a conjugate of the acrylate in which the ester function is retained. In the absence of an esterase inhibition the excreted mercapturic acid is a formal conjugate of the free acrylic acid (Fig. 1). No mercapturic acids could be detected which might arise from glutathione conjugation of a, beta-epoxyesters. Such epoxides are potential primary metabolites of unsaturated esters. They were not detected by in vitro experiments. Therefore, the intermediacy of glycidic esters in the biotransformation of these acrylic esters may be considered as highly unlikely.

Elimination of thioethers following administration of naphthalene and diethylmaleate to the rhesus monkey

As a measure of glutathione (GSH) conjugation, urinary, fecal and biliary excretion of thioethers and hepatic GSH content were measured in rhesus monkeys following administration of single doses of naphthalene and diethylmaleate (DEM). Naphthalene had little or no effect on hepatic GSH content and the excretion of thioethers into urine, feces or bile of rhesus monkeys which is similar to that observed in chimpanzees and humans and is in contrast to results obtained from rats. Apparently, conjugation of naphthalene and/or its metabolites with GSH does not play a major role in the metabolism of naphthalene in primates, whereas it is one of the major pathways in rodents. Rhesus monkeys, like chimpanzees, excreted about 13% of the various doses of DEM (30, 75 and 200 mg/kg) as thioethers into urine which is half of that excreted by rats. Six hrs after administration of 200 mg/kg DEM, the hepatic GSH content was decreased by 90% in the rhesus monkey. During the first day after this dose (200 mg/kg), the increase in the excretion of thioethers into bile corresponded to about 15% of the dose of DEM administered. Since fecal excretion of thioethers corresponded to only 1% of the dose and urinary excretion represented 12% of the dose, it appears that biliary thioethers of DEM are reabsorbed from the intestine and then excreted into urine. It appears that the rhesus monkey as well as the chimpanzee is, whereas the rat is not, a good animal model to study GSH-related conjugation reactions with predictive value for man.

Distribution and covalent interactions of [1-14C]acrylonitrile in the rat

The tissue distribution, elimination and covalent binding of [1-14C]-acrylonitrile (VCN) have been investigated in the rat. Rats, given an oral dose of 46.5 mg/kg (0.5 LD50) VCN, excreted 40% of the 14C in urine, 2% in feces, 9% in expired air as 14CO2, 0.5% as H14CN and 4.8% as unchanged VCN in 24 h. Bile flow increased 3 times after the administration of VCN and over a period of 6 h, 27% of the 14C was recovered in bile. The red blood cells retained significant amounts of radioactivity for more than 10 days after treatment, whereas the 14C activity declined sharply in plasma. Initially, the highest levels of radioactivity were found in the stomach and stomach content followed by the intestine. In liver, kidney, brain, spleen, adrenal, lung and heart tissues the radioactivity of the acid soluble fractions declined while covalent binding to macromolecules remained unchanged. In subcellular fractions of liver, kidney, spleen, brain, lung, and heart, 20-40% of the total radioactivity was bound to nuclear, mitochondrial and microsomal fractions whereas in cytosol only 6-14% was bound over a period of 6 h.

Excretion of zinc in rat bile - a role of glutathione

Fractionation of the bile from rats injected with 65ZnCl2 (5 mumol/kg) showed that zinc was mainly bound to low molecular weight compounds eluted corresponding to the zinc-glutathione complexes. Diethylmaleate (3.9 mmol/kg), cyclohexene oxide (4.9 mmol/kg) and acrylamide (3.5 mmol/kg) administered intraperitoneally to rats caused a rapid decrease in the endogenous excretion of both zinc and reduced glutathione into bile. This depression probably reflects the conjugation of the aforementioned substances to glutathione in the liver cells. These results indicate that zinc is transferred from liver to bile by glutathione dependent process and most likely as zinc-glutathione complexes.

Studies on in vitro metabolism of acrylamide and related compounds

The in vitro biotransformations of acrylamide and ten related compounds in the hepatic enzyme system of the mouse were studied in order to learn more about their toxic actions in vivo. Of nine analogues, which could be analyzed quantitatively by gas chromatography, seven compounds--N-tert-butylacrylamide, diacetone acrylamide, N,N-dimethylacrylamide, N-isobutoxymethylacrylamide,--were metabolized in microsomal enzymes with NADPH generating system. One or two metabolites from each of the seven compounds, except for N-isobutoxymethylacrylamide were detected by gas chromatography. The metabolite of N-isopropylacrylamide was identified as acrylamide by gas chromatography-mass spectrometry. The metabolite of N,N-dimethylacrylamide showed a RT value identical with and a mass spectrum similar to N-methylacrylamide. No metabolites from the other four compounds have yet been identified. Acrylamide and crotonamide did not seem to be metabolized in the same system. Phenobarbital pretreatment of mice enhanced the metabolic reactions of the seven compounds, but did not elevate those of acrylamide and crotonamide. The Km value of N-isopropylacrylamide was 0.35 mM, which was the smallest of all the test analogues. All of the eleven analogues studied were found to be metabolized by hepatic glutathione S-transferases as well. This reaction was also elevated by the phenobarbital treatment of mice. The relationships between the in vitro metabolisms and the in vivo toxicities of acrylamide analogues are discussed.

On interactions of cytostatic benzylidine hydrazines with SH-groups

The cytostatic and mutagenic compound N'-methyl-N'-cyano-(p-chloro)-benzaldehyde hydrazone (CyB4) has been found to be a strong SH-blocking agent since it reacts with the thiol groups of glutathione and of the cell membrane of Ehrlich ascites carcinoma cells (EAC). Furthermore, it decreases the intracellular, non-proteinogenic SH(NPSH)-level of tumor cells. CyB4 is not able to alkylate 4-(p-nitrobenzyl)-pyridine (NBP) by a nucleophilic substitution reaction, but it could be shown that the reactivity of CyB4 with thiol groups is due to a Michael-addition-type reaction of SH-groups with the cyano-group of CyB4. On the other hand, cytostatic beta-chloroethyl hydrazones showed a negligible reactivity against glutathione and led even to an increase of thiol groups, detectable by the 5,5'-dithiobis-2-nitrobenzoic acid (DTNB)-method, at the cell membrane of EAC when incubated in the presence of beta-chloroethyl hydrazones N-benzylidene-N'-methyl-N'-(2-chloroethyl) hydrazine (B1) and N-(4-dimethylaminobenzylidene)-N'-methyl-N'-(2-chloroethyl) hydrazine (B2). Therefore, it is concluded that the cytostatic efficiency of CyB4 is due to its SH-blocking while that of the beta-chloroethyl hydrazones is due to a rearrangement of the tumor cell membrane, as indicated by the increased level of reactive SH-groups.

Identification or urinary mercapturic acids formed from acrylate, methacrylate and crotonate in the rat

1. After administration to rats of methyl acrylate (I), methyl methacrylate (II) and methyl crotonate (III), urinary mercapturic acids were isolated and identified as the dicarboxylic acids N-acetyl-S-(2-carboxyethyl)cysteine (IV, R = H), N-acetyl-S-(2-carboxypropyl)cysteine (V, R = H) and N-acetyl-S-(1-methyl-2-carboxyethyl)cysteine (VI, R = H) and for a minor part as their monomethyl esters IV (R = CH3) and VI (R = CH3). 2. After a single dose of the acrylates (I), (II) and (III) (0.14 mmol/kg), the excretion of the thioethers amounted to 6.6 +/- 0.6, 0.0, and 2.0 +/- 0.6% dose respectively. 3. After 18 h previous administration of the carboxylesterase inhibitor tri-o-tolyl phosphate (0.34 mmol/kg) the excretion of the thioethers amounted to 40.6 +/- 2.1, 11.0 +/- 3.3, and 16.0 +/- 2.0% dose. 4. For methyl acrylate (I) the ratio of the excreted dicarboxylic acid and monomethyl ester was 20:1. After previous administration of tri-o-tolyl phosphate this ratio was 1:2.

Relationship between liver and kidney levels of glutathione and metallothionein in rats

The purpose of this study was to test if the tissue levels of glutathione and metallothioneins were inter-related. In rats, intraperitoneal administration of diethyl maleate or bromobenzene decreased glutathione levels in both the liver and kidney before doubling the metallothionein concentration in the liver and increasing that in kidneys by 40% starting from 6 h after intraperitoneal administration. Both Zn and Cd produced an increase in hepatic and renal metallothionein levels. However, unlike the responses to diethyl maleate and bromobenzene, the increase in metallothionein caused by the metals was not preceded by any significant changes in glutathione levels. Cd decreased the concentration of glutathione in the liver (at 36 h) and kidneys (at 24 h). In contrast, Zn produced an increase and no change in hepatic and renal glutathione concentrations, respectively. The conclusion is that tissue levels of metallothionein and glutathione are not always interrelated.

Interrelationship between cationic and anionic forms of glutathione S-transferases of bovine ocular lens

Since the eye is constantly exposed to potentially damaging chemical compounds present in the atmosphere and vascular system, we investigated the physiological role of glutathione S-transferase (GSH S-transferase) in detoxification mechanisms operative in the ocular lens. We have purified an anionic and a cationic GSH S-transferase from the bovine lens to homogeneity through a combination of gel filtration, ion-exchange and affinity chromatography. The anionic (pI 5.6) and cationic (pI 7.4) S-transferases were found to have distinct kinetic parameters (apparent Km and Vmax. pH optimum and energy of activation). However, both species were demonstrated to have similar molecular weights and amino acid compositions. Double-immunodiffusion and immunotitration studies showed that both lens S-transferases were immunologically similar. The very close similarity in amino acid compositions and immunological properties strongly indicates that these two transferases either originate from the same gene or at least share common antigenic determinants and originate from similar genes. The bovine lens GSH S-transferases had no glutathione peroxidase activity with either t-butyl hydroperoxide or cumene hydroperoxide as substrate. However, the antibody raised against the homogeneous anionic glutathione S-transferase from the bovine lens was found to precipitate both glutathione S-transferase and glutathione peroxidase activities out of solution in the supernatant of a crude bovine liver homogenate.

Aspects of the metabolism of the peripheral vasodilator mecinarone (14C-6809 MD) in rat, dog and man

The major proportion of oral doses of 14C-mecinarone was excreted in the faeces by rat, dog and man, and in all species the faecal metabolites were more polar than mecinarone and the O-desmethyl reference compounds. Rat faecal extracts contained two major components each accounting for about 30-40% of the radioactivity. Dog and human faecal extracts contained some mecinarone but also three major, more polar components, two of which corresponded to the rat metabolites. Rat bile contained three major components and dog bile two components. One of the components in both bile samples was shown to be a conjugate of O-desmethyl-mecinarone. Besides mecinarone human urine contained a component corresponding to the phenol resulting from 0-demethylation in the p-methoxycinnamoyl group. The same two compounds were also detected in human plasma. The two major components in rat and dog faecal extracts gave mass spectra identical to mecinarone and the p-hydroxycinnamoyl derivative (O-desmethyl-mecinarone). It is postulated that these thermally-labile metabolites were formed by nucleophilic addition of a substituent to the alpha, beta-unsaturated ketone. It has been demonstrated in vitro that mecinarone forms a glutathione conjugate. The metabolites may be compounds of this type where the glutathione moiety has been degraded in the gastrointestinal tract.

Decrease of reduced glutathione in isolated rat hepatocytes caused by acrolein, acrylonitrile, and the thermal degradation products of styrene copolymers

Decrease of reduced glutathione (GSH) was induced in isolated rat hepatocytes by incubation with acrolein or acrylonitrile for 120 min or exposure to the products of oxidative thermal degradation of acrylonitrile-butadiene-styrene copolymer (ABS), styrene-acrylonitrile copolymer (SAN), and high impact polystyrene (SB). The decrease of GSH by acrolein was rapid but the cells soon recovered at acrolein concentrations of 0.025--0.25 mM. 0.5 mM acrolein depleted the cells of GSH and they were uncapable of further GSH synthesis. At concentrations of 0.25--0.5 mM concomitant lipid peroxidation impaired the integrity of the cell membranes. Also acrylonitrile induced a dose dependent GSH decrease at concentrations of 0.05--1 mM. Neither membrane damage nor lipid peroxidation was detected during 120-min incubations at these acrylonitrile concentrations. The thermal degradation products of ABS, SAN and SB caused a decrease of GSH in hepatocytes. The extent of the decrease depended on the degradation temperature and the type of the plastic. The membrane integrity was impaired in the cases where GSH was depleted almost completely; ABS degraded at 350 degrees C and SB at 250 degrees C. The measurements of lipid peroxidation by the thiobarbituric acid and the diene conjugation methods were impossible because the degradation products contained compounds which interfered with these tests.

Soluble and microsomal glutatione S-transferase activities in pea seedlings (Pisum sativum L.)

Epicotyl and primary leaves of pea seedlings (Pisum sativum L., var. Alaska) were found to contain soluble and microsomal enzymes catalyzing the addition of glutathione to the olefinic double bond of cinnamic acid. Glutathione S-cinnamoyl transfer was also obtained with enzyme preparations from potato slices and cell suspension cultures of parsley and soybean.The pea transferases had pH-optima between pH 7.4 and 7.8 Km-values were 0.1-0.4 mM and 1-4 mM for cinnamic acid and glutathione, respectively. V-values were between 2-15 nmol mg(-1) protein x min.Chromatography on Sephacryl S-200 indicated that the soluble pea glutathione S-cinnamoyl transferase activity existed in molecular weight forms of 37,000, 75,000, and 150,000. The glutathione-dependent cleavage of the herbicide fluorodifen was catalyzed by a different soluble enzyme activity which eluted in molecular weight positions of 47,000 and/or 82,000.The microsomal fraction from pea primary leaves also catalyzed the conjugation of the carcinogen benzo[α]pyrene with glutathione.

Mutagenic activation of tris(2,3-dibromopropyl)phosphate: the role of microsomal oxidative metabolism

The flame retardant tris(2,3-dibromopropyl)phosphate (Tris-BP) is converted to products which are mutagenic for Salmonella typhimurium TA 100 in the presence of rat liver microsomes, NADPH and oxygen. Other bromopropyl-compounds were also mutagenic; 2,3-dibromopropene and 2,3-dibromopropionic acid were directly mutagenic, whereas 2,3-dibromopropanol and tris(2-bromopropyl)phosphate were weakly mutagenic after addition of liver microsomes and cofactors. Typical in vivo and in vitro inhibitors of cytochrome P-450 inhibited Tris-BP mutagenicity. The effects of inducers of cytochrome P-450 on Tris-BP mutagenicity was dependent on the concentration of mutagen and microsomal protein in the assay, indicating complexity in the kinetics involved when dealing with possible multiple pathways that lead to mutagenicity. Addition of glutathione strongly inhibited Tris-BP mutagenicity. It is suggested that Tris-BP is oxidized to a reactive electrophile, possibly the 2-keto derivative, which could react with nucleophilic groups in DNA and thus lead to mutagenic events.