Lack of effect of phenobarbitone administered in vivo on glutathione synthesis by rat liver supernatants

A spectrophotometric assay of gamma-glutamylcysteine synthetase and glutathione synthetase in crude extracts from tissues and cultured mammalian cells

An assay of gamma-glutamylcysteine synthetase (gamma-GCS) and glutathione synthetase (GS) in crude extracts of cultured cells and tissues is described. It represents a novel combination of known methods, and is based on the formation of glutathione (GSH) from cysteine, glutamate and glycine in the presence of rat kidney GS for the assay of gamma-GCS, or from gamma-glutamylcysteine and glycine for the assay of GS. GSH is then quantified by the Tietze recycling method. Assay mixtures contain the gamma-glutamyl transpeptidase (GGT) inhibitor acivicin in order to prevent the degradation of gamma-glutamylcysteine and of the accumulating GSH, and dithiothreitol in order to prevent the oxidation of cysteine and gamma-glutamylcysteine. gamma-GCS and GS levels determined by this method are comparable to those determined by others. The method is suitable for the rapid determination of gamma-GCS GS in GGT-containing tissues and for the studies of induction of gamma-GCS and GS in tissue cultures.

Effect of isoniazid on glutathione biosynthesis and degradation in Mycobacterium smegmatis

The mechanism of glutathione (GSH) depletion by isoniazid (INH) was studied in M. smegmatis. INH increased the activity of gamma-glutamyl transferase (GGT) whether added before medium inoculation or to actively growing cells. The activity of GGT in cells grown from the beginning in INH-containing medium increased significantly on growth days 2-6. Three-day old M. smegmatis cells treated with INH exhibited a 30-65% increase in the activity of GGT. The activities of gamma-glutamyl-cysteine synthase (GGCS) and GSH synthase (GS) were lowered by 50 and 56% respectively on the second day of growth when M. smegmatis was grown in a medium supplemented with 1.5 mg INH per L. In 3-day old M. smegmatis, INH significantly inhibited the activities of GSH biosynthetic enzymes. The results demonstrate that the increased activity of GGT and decreased activities of GSH biosynthetic enzymes are responsible for GSH depletion by INH in M. smegmatis.

Protective antioxidant mechanisms in rat and guinea pig tissues challenged by acute exposure to cigarette smoke

Cellular damage from reactive intermediates formed during xenobiotic biotransformation is prevented by the presence of adequate levels of antioxidant chemicals in the tissues. Equally important for cell protection is the rate at which these chemicals are replaced if tissue stores are depleted. The present experiments, using adult male Sprague-Dawley rats and Hartley guinea pigs, were conducted to ascertain what effects mainstream (MS) and sidestream (SS) tobacco smoke would have on the water-soluble, cytoplasmic antioxidants, ascorbic acid (AA) and reduced glutathione (GSH). The animals were exposed by nose-only inhalation to varying doses (40, 120, 240 puffs) of a 1:5 dilution of a 35-ml volume of freshly generated MS from cigarettes made from different types of tobacco and delivered by a B.-A.T-Mason inhalation apparatus. The animals were euthanized either immediately following exposure or at 3 and 6 h. The blood, lungs, liver, kidneys, heart and bladder were removed for the quantitation of AA and GSH following homogenization and deproteinization. Immediately following exposure to MS, dose-dependent decreases in pulmonary and renal GSH were observed in rats whereas, in guinea pigs, reductions in pulmonary, hepatic and renal GSH were observed only at the highest level of exposure. No reductions in tissue AA were observed in either species at any exposure level. In both species, blood levels of GSH and AA remained unchanged following exposure. Mainstream smoke (240 puffs) from flue-cured or dark, air-cured tobaccos elicited a significant, immediate reduction in pulmonary and renal GSH, but MS from low tar, filter cigarettes was without effect. Within 3 h of exposure, GSH in all tissues has returned to pre-exposure levels. Whole-body, chamber exposure to concentrated SS, generated from smouldering cigarettes, caused a dose-dependent reduction in rat pulmonary, hepatic, renal, cardiac and bladder muscle GSH but only affected pulmonary GSH in the guinea pig. Lesser effects were observed in tissues of rats exposed to diluted SS. In the rat, a comparison of the results of diethylmaleate- and smoke-induced depletion of tissue GSH suggested that, even at exceptionally high levels of exposure, there was a significant store of GSH in tissues that did not interact with tobacco smoke.

Effects of 1,2-dibromoethane on glutathione metabolism in rat liver and kidney

There are few reports of the effects of glutathione-depleting agents administered for periods longer than 24 hr on the turnover of glutathione (GSH) in mammalian tissues. Studies of such effects are important in relation to the protection of tissues from damage from, for example, reactive metabolites derived from xenobiotics. In the investigation described here, 1,2-dibromoethane dibromide)-a widely used insecticide, nematocide, fungicide and petrol additive, which is hepato- and nephrotoxic-was administered to rats and the effects on non-protein thiol contents and GSH-related enzyme activities were determined in liver and kidney. The classical GSH-depleter diethylmaleate was used in parallel studies for comparative purposes.

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.