Amount Of GSH Research Articles

Accumulation and handling of inorganic mercury in the kidney after coadministration with glutathione

The accumulation and handling of mercury in the blood, kidneys, and liver were evaluated and compared in rats 5 min, 1 h, and 24 h after the intravenous administration of either a 0.25 mumol/kg dose of inorganic mercury or a 0.25 mumol/kg dose of inorganic mercury plus a 0.5 mumol/kg dose of glutathione (GSH) to determine the possible role of extracellular GSH and complexes of GSH and inorganic mercury in the renal uptake and transport of inorganic mercury. Significantly more of the injected dose of inorganic mercury was present in the blood of the rats injected with inorganic mercury alone than in the blood of the rats injected simultaneously with both inorganic mercury and GSH at all times evaluated after injection. Of the mercury remaining in the blood, however, significantly more mercury was in plasma fraction of blood in the rats injected with both inorganic mercury and GSH than in the plasma fraction of blood in the rats injected with inorganic mercury alone. The blood and plasma findings indicate that much of the mercury injected with GSH was in some complex that allowed the mercury to be cleared from the blood more readily and prevented the mercury from entering readily into red blood cells. The renal concentration of mercury was significantly greater in the rats injected with both inorganic mercury and GSH than in the rats injected with inorganic mercury alone at 5 min and 1 h, but not 24 h, after injection. This increased renal accumulation of mercury during the initial hours after injection was due mainly to enhanced uptake and/or retention of mercury in the renal cortex. Urinary excretion of mercury, over 24 h, was also slightly, but significantly, greater in the rats injected with both inorganic mercury and GSH simultaneously. These data indicate that coadministration of a nontoxic dose of inorganic mercury with a twofold higher amount (in moles) of GSH increases significantly the clearance of mercury from the blood and increases the renal cortical accumulation of inorganic mercury during the initial 1 h after injection. Moreover, the data in this study are consistent with the hypothesis that extracellular GSH is an important ligand to which mercuric ions bind, and that complexes of inorganic mercury and GSH in the blood and/or ultrafiltrate probably play a role in the renal uptake of some of the mercury in blood after exposure to mercuric compounds.

Effects of N-acetyl- l-cysteine on T-cell apoptosis are not mediated by increased cellular glutathione

Thiol-containing antioxidants such as N-acetyl- l-cysteine (NAC) are known to inhibit apoptosis, although it is unclear whether this effect is direct or mediated through modulation of intracellular glutathione (GSH). In the present study, NAC treatment of the murine T-cell hybridoma DO-11.10 was found to inhibit apoptosis triggered by anti-CD3 antibody but enhance the process when induced by 6-α-methylprednisolone. HPLC measurements showed that these effects were not correlated with the levels of GSH or glutathione disulfide (GSSG) in the cells. Similar effects on DNA fragmentation were obtained when the experiments were repeated in the presence either of a specific inhibitor of GSH biosynthesis (buthionine sulfoximine) or the isomer N-acetyl- d-cysteine which cannot be enzymatically converted into GSH. We conclude that NAC can have divergent effects on apoptosis independent of changes in either the amount or redox state of intracellular GSH.

Glucocorticoid-Induced Cataract of Developing Chick Embryo as a Screening Model for Anticataract Agents

In order to develop an effective screening model for anticataract agents, we examined the age dependence of cataract induction by glucocorticoid in developing chick embryos. Hydrocortisone sodium succinate (0.25 mumol) was administered to chick embryos on day 15 (15-day-old) and cataract formation was examined 48 hr later. Administration earlier than on day 13 or later than on day 15 was a little or ineffective. These results indicate that the formation of glucocorticoid-induced cataract in developing chick embryos depends on developing stages. The embryos treated with hydrocortisone sodium succinate on day 15 decreased GSH amount in the lens, approximately 50% of the control in 48hr. However, the embryos treated at other ages, in which cataract was not induced, showed little or no decrease of GSH. The cataract formation in chick embryos appeared to depend on structure of steroid and was due to biological activities of glucocorticoids. Since cataract is easily produced in a reproducible manner with high incidence by glucocorticoid, our chick embryo model will be a valuable model system for screening anticataract agents.

Redox reaction system conjugating electrochemical reduction of NADP + and enzymatic reaction across the electron transfer membrane

The conjugated redox reaction was driven across the electron transfer membrane prepared from a urethane prepolymer to carry positive charge, where NADP + as electron transfer carrier was adsorbed in the prepared polyurethane membrane. Glutathione reductase [NAD (P)H: oxidized-glutathione oxidoreductase (EC 1.6.4.1)] was used as the catalyst for production of the reduced form of glutathione (GSH) from the oxidized form (GSSG) in the objective reaction, and methyl viologen (MV) was used for the electrochemical regeneration of NADPH in the subreaction. The conjugated redox reaction in the separated reactions system, using the three-compartment cell with two membranes, was successful without MV contamination. Under the given conditions, the conversion ratio of GSH from GSSG reached 50% after 4 h of incubation at 30°C and the amount of GSH accumulated was 0.5 μmol ml −1 of reaction mixture.

Possible role of metallothionein in the cellular defense mechanism against UVB irradiation in neonatal human skin fibroblasts.

The role of metallothionein (MT) in protecting skin cells against UVB irradiation was investigated. Fibroblast strains from normal adult (HS-K) and neonatal (NB1RGB) human skins as well as keratinocyte strains from human skin (SV40-HSK) and newborn Balb/c mouse skin (Pam 212) were exposed to UVB irradiation. The sensitivity of HS-K and NB1RGB cells to UVB irradiation was similar; those of SV40-HSK and Pam 212 cells were two- and six-fold as sensitive to UVB irradiation as HS-K cells, respectively. The HS-K cells contained the greatest cellular reduced form of glutathione (GSH) levels compared to the three other skin cells: the levels were 13-, 7- and 6-fold of those in NB1RGB, SV40-HSK and Pam 212 cells, respectively. These results indicated that the sensitivity of skin cells to UVB irradiation was not always associated with their endogenous GSH levels. In particular, despite the fact that NB1RGB cells contained a relatively small amount of GSH, they were less sensitive to UVB irradiation. NB1RGB cells contained 4-30 times more MT than those in other skin cells examined. The sulfhydryl residues of MT molecules in the NB1RGB cells were estimated to be mostly unoccupied by metals, suggesting they act in a similar way to those of GSH. Moreover, NB1RGB cells in which the MT content was elevated by dexamethasone (1 microM) or Zn2+ (7 micrograms/mL) treatment were more resistant to UVB irradiation than nontreated ones. These results suggest that, at least in neonatal human skin fibroblasts, MT may play a role in protection against UVB irradiation.

POSSIBLE ROLE OF METALLOTHIONEIN IN THE CELLULARDEFENSE MECHANISM AGAINST UVB IRRADIATION IN NEONATAL HUMAN SKIN FIBROBLASTS

Abstract –The role of metallothionein (MT) in protecting skin cells against UVB irradiation was investigated. Fibroblast strains from normal adult (HS‐K) and neonatal (NB1RGB) human skins as well as keratinocyte strains from human skin (SV40‐HSK) and newborn Balb/c mouse skin (Pam 212) were exposed to UVB irradiation.The sensitivity of HS‐K and NB1RGB cells to UVB irradiation was similar; those of SV40‐HSK and Pam 212 cells were two‐ and six‐fold as sensitive to UVB irradiation as HS‐K cells, respectively. The HS‐K cells contained the greatest cellular reduced form of glutathione (GSH) levels compared to the three other skin cells: the levels were 13‐, 7‐ and 6‐fold of those in NB1RGB, SV40‐HSK and Pam 212 cells, respectively. These results indicated that the sensitivity of skin cells to UVB irradiation was not always associated with their endogenous GSH levels. In particular, despite the fact that NB1 RGB cells contained a relatively small amount of GSH, they were less sensitive to UVB irradiation.NB1RGB cells contained 4–30 times more MT than those in other skin cells examined. The sulfhydryl residues of MT molecules in the NB1RGB cells were estimated to be mostly unoccupied by metals, suggesting they act in a similar way to those of GSH. Moreover, NB1RGB cells in which the MT content was elevated by dexamethasone (1 μg/mL) or Zn2+ (7 μg/mL) treatment were more resistant to UVB irradiation than nontreated ones.These results suggest that, at least in neonatal human skin fibroblasts, MT may play a role in protection against UVB irradiation.

Genes regulating glutathione concentrations in X-ray-transformed rat embryo fibroblasts: changes in gamma-glutamylcysteine synthetase and gamma-glutamyltranspeptidase expression.

The concentration of glutathione (GSH) and the expressions of gamma-glutamylcysteine synthetase and gamma-glutamyltranspeptidase (GGT) were assessed in rat embryo fibroblasts (REF) displaying various stages of X-ray-induced transformation. A secondary culture of REF cells was irradiated, and a normal-immortalized cell line (X-REF-23) was isolated. Chronic exposure of X-REF-23 cells to 12-O-tetradecanoyl-phorbol-13-acetate (TPA) yielded cells (X-REF-23-TP) capable of benign tumor formation in nude mice. These cells exhibited GSH concentrations and gamma-glutamylcysteine synthetase heavy subunit mRNA levels that were approximately 50% less than those measured in X-REF-23 cells. Neither X-REF-23 nor X-REF-23-TP cells exhibited detectable GGT mRNA or activity. Administration of 3 Gy of X-rays followed by chronic TPA treatment yielded cells (X-REF-23-TPX) capable of malignant tumor formation in nude mice. These cells expressed GGT mRNA and Concanavalin-A minus GGT activity. One TPX clone (X-REF-23-TPX.1) was chosen for further characterization. Northern blotting of X-REF-23-TPX.1 cells indicated that gamma-glutamylcysteine synthetase heavy subunit mRNA levels were similar to those of X-REF-TP cells. X-REF-23-TPX.1 cells contained nearly the same amount of GSH as X-REF-23 cells. However, the ability of diethylmaleate (DEM) to deplete GSH was diminished in X-REF-23-TPX.1 cells compared with X-REF-23 cells. Furthermore, exposure of X-REF-23-TPX.1 cells to DEM stimulated GSH resynthesis such that the GSH concentration exceeded control values during exposure. The resynthesis of GSH during a DEM exposure was found to be dependent upon the expression of GGT, as demonstrated by inhibition with AT-125. These experiments indicate that ionizing radiation can lead to elevated constitutive expression of GGT in transformed REF cells and that expression of GGT activity was responsible for the increased rate of GSH repletion observed in X-REF-23-TPX.1 cells.

ENHANCING EFFECT OF ETHANOL ON AFLATOXIN B1-INDUCED DNA-DAMAGE IN GLUTATHIONE-DEPLETED RAT HEPATOCYTES

The effect of reduced glutathione (GSH) and ethanol on aflatoxin B1 (AFB1)-induced DNA single strand breaks was studied in primary cultured hepatocytes. Buthionine sulfoximine (BSO) which decreased intracellular GSH to 13% of those of the control levels increased DNA fragmentation of AFB1-treated hepatocytes by over 17% of those without BSO. Thus, a decrease in hepatocyte GSH levels increased AFB1-induced DNA damage. Although ethanol in itself did not induce DNA damage, a combination of BSO and ethanol increased the percentage by over 23% of that with BSO only. Ethanol did not affect the amount of GSH, total cytochrome P-450 (P450), glutathione S-transferase (GST) and epoxide hydrolase (EHase) in cultured hepatocytes. However, GSH-depleted rat hepatocytes exposed to ethanol significantly increased the level of P450IIIA, which activates AFB1. The enhancing effects of ethanol in the presence of BSO are probably due to the induction of this isozyme in rat hepatocytes. The GSH-depleted hepatocytes are more susceptible to chemical carcinogens in the presence of ethanol.

Radioprotective effect of N-acetylcysteine in vitro using the induction of DNA breaks as end-point.

Cultures of Chinese hamster cells were treated with N-acetylcysteine (NAC) and irradiated under hypoxic or aerobic conditions. Protection factors (PFs) were calculated using the yield of DNA breaks as a measure of the radiation response. With NAC up to 50 mmol dm-3, the PF values were smaller for aerobically- than for hypoxically-irradiated cells. In contrast with NAC concentrations > 100 mmol dm-3, the PF values for aerobically-irradiated cells were larger than those for hypoxic cells. This reversal is in agreement with the predictions of a modified competition model, the 'X-model'. The value of X (the ratio of reparable to non-reparable damage) was calculated to be close to 5 for the NAC-treated cells, i.e. about 18% of the radiation damage was not reparable. The increase of the total non-protein bound thiols (NPSH) and GSH content after NAC treatment was measured both in whole cells and isolated nuclei. Measurement of the cellular NPSH content showed a continuous increase with increasing NAC concentrations in the medium, independent of treatment time. In contrast, the amount of intracellular and intranuclear GSH increased with prolonged incubation time with NAC. No quantitative relationship was found between PF values and cellular NPSH or GSH content.

Glutathione release by pulmonary alveolar macrophages in response to particles in vitro

We studied whether cultured rat pulmonary alveolar macrophages (PAM) could release glutathione (GSH) in response to latex beads, quartz, and crocidolite asbestos. PAM were exposed for 2 h to 0–100 μg of particles per l × 10 6 cells. Both quartz and asbestos produced concentration-dependent increases (up to 8–10-fold) in the amount of GSH recovered in the medium and decreases in the cellular GSH levels. In contrast, latex beads did not produce any changes in GSH levels. We also measured lactate dehydrogenase (LDH) levels as an index of toxicity. Only quartz and asbestos were able to produce increases in LDH levels in the medium. The release of GSH occurred at particle concentrations that did not cause release of LDH. Our results indicated that, in vitro, PAM release GSH in response to toxic particles.

Fate of dietary glutathione: disposition in the gastrointestinal tract

Studies were performed in rats that had been fasted 24 h, fed a glutathione (GSH)-free semisynthetic diet (AIN-76), and fed the same diet supplemented with GSH. The results from the fasted rats and those fed GSH-free diet showed that the duodenum and jejunum contained 0.2-0.5 mumol of GSH/gram wet wt of luminal contents. The GSH contents of biliary juice was sufficient to maintain this amount of GSH in the intestinal lumen. Other analyses showed that cell sloughing, bacterial GSH content, and GSH secretion by epithelial cells of the jejunum were not sufficient to account for this content. GSH concentrations following consumption of a GSH-supplemented diet (5-50 mg/g AIN-76) showed a rapid increase in all regions of the small intestine and indicated that removal occurred primarily in the jejunum. However, the combined activities of brush-border gamma-glutamyltransferase and GSH uptake systems were not sufficient to remove all of the ingested GSH. Results from in situ vascular perfusions of small intestine showed that the upper jejunum is a principal site of GSH absorption. Measurements of the GSH-to-glutathione disulfide (GSSG) ratio in the lumen after ingestion of GSSG (5 mg/g diet) indicated that the upper small intestine also has a mechanism for reducing GSSG to GSH. The results therefore indicate that GSH is present in the lumen of the small intestine of rat under most if not all conditions. Although the physiological importance of luminal GSH remains unclear, it could potentially be used to detoxify reactive electrophiles in the diet or be absorbed for intracellular detoxication reactions.

Gamma-glutamylcysteine synthetase deficiency and hemolytic anemia

gamma-Glutamylcysteine synthetase is one of the enzymes of glutathione (GSH) synthesis. A deficiency of this enzyme has been found only once previously in humans: it was associated with spinocerebellar degeneration and hemolytic anemia. We report the case of a woman, daughter of fifth cousins, who was gamma-glutamylcysteine-synthetase- deficient. Modest decreases in the amount of GSH in cultured lymphoblasts and fibroblasts could be documented. The amount of residual enzyme was insufficient to permit detailed studies of the characteristics of the mutant enzymes, but no major abnormality in its Km for cysteine and glutamic acid or in its heat stability were found. In contrast to the earlier report, the only manifestation of the enzyme deficiency was hemolytic anemia. This leads us to conclude that either the occurrence of neurologic symptoms in the other reported family was a chance association or that the clinical expression of this rare defect is pleomorphic.

Gamma-Glutamylcysteine Synthetase Deficiency and Hemolytic Anemia

gamma-Glutamylcysteine synthetase is one of the enzymes of glutathione (GSH) synthesis. A deficiency of this enzyme has been found only once previously in humans: it was associated with spinocerebellar degeneration and hemolytic anemia. We report the case of a woman, daughter of fifth cousins, who was gamma-glutamylcysteine-synthetase-deficient. Modest decreases in the amount of GSH in cultured lymphoblasts and fibroblasts could be documented. The amount of residual enzyme was insufficient to permit detailed studies of the characteristics of the mutant enzymes, but no major abnormality in its Km for cysteine and glutamic acid or in its heat stability were found. In contrast to the earlier report, the only manifestation of the enzyme deficiency was hemolytic anemia. This leads us to conclude that either the occurrence of neurologic symptoms in the other reported family was a chance association or that the clinical expression of this rare defect is pleomorphic.

The significance of ascorbic acid and glutathione for chromate metabolism in man∗

Apart from the size of the inhaled chromate particles the ascorbic acid content (AS) as well as the glutathione (GSH) content of bronchioles, alveoli, plasma and of erythrocytes (RBC) as redox partners largely determine the extent of individually different cellular chromate binding. In the case of Cr(VI)‐exposure lower AS activities will lead to higher, lower GSH activities will lead to lower chromium binding in the RBC as a model of cellular fixation. Because of these findings the individually different rates of distribution of chromium concentrations in serum or RBC need a new interpretation. These observations explain the so far only descriptive differentiation between “strong and weak Cr(VI)‐reducers” as a consequence of differing availability of AS and/or GSH amounts. Since the amount of renal elimination of chromium only correlates directly with the amount of Cr(III)‐ and reduced Cr(VI)‐compounds in the plasma, determination of the loading of RBC by chromium is essential for the occupational medical...

Modulation of endothelial GSH concentrations: effect of exogenous GSH and GSH monoethyl ester.

We studied the effects of exogenous glutathione (GSH) and GSH monoethyl ester (GSH-MEE) on the enhancement of endothelial GSH concentrations. The preparation of GSH-MEE used contained 91% GSH-MEE, approximately 9% GSH diethyl ester (GSH-DEE) and a trace amount of GSH. Both GSH and GSH-MEE markedly stimulated the intracellular concentrations of GSH in endothelial cells. GSH-MEE was more potent than GSH. The enhancement of endothelial GSH concentration by exogenous GSH was completely inhibited by buthionine sulfoximine (BSO), a potent inhibitor of gamma-glutamylcysteine synthase, or acivicin (AT-125), an inhibitor of gamma-glutamyl transpeptidase, suggesting that it was due to the extracellular breakdown and subsequent intracellular resynthesis of GSH. In contrast, the effect of GSH-MEE was largely resistant to BSO and acivicin, suggesting that it was primarily due to transport of GSH-MEE followed by intracellular hydrolysis. The GSH-MEE preparation, which contained 9% GSH-DEE, at concentrations of 2 mM or higher caused vacuolization of endothelial cells. The enhancement of GSH concentrations by exogenous GSH, but not by GSH-MEE, protected endothelial cells against H2O2-induced injury.

Changes in peroxisomes and mitochondria in liver of ethionine exposed rats: a biochemical and morphological investigation

Administration of ethionine resulted in a dose- and time-dependent enhancement of the activities of peroxisomal beta-oxidation, carnitine palmitoyltransferase and omega-oxidation, especially the 12-hydroxylation of lauric acid. The mitochondrial and, especially, the microsomal palmitoyl-CoA hydrolase activities were increased, whereas the peroxisomal and cytosolic activities were decreased. Ethionine administration decreased the catalase and urate oxidase activities in both a dose- and time-related manner. The liver cells and the volume fraction of cytoplasma decreased 40% in ethionine-exposed animals, whereas the average nuclei volume fraction increased approximately 50%. The volume fraction and the total number of mitochondria increased 1.5-fold after ethionine exposure and an accumulation of lipid in large droplets of the hepatocytes was observed. No proliferation of peroxisomes was observed after treatment; the volume fraction and the number of peroxisomes decreased. However, the size of peroxisomes in livers of ethionine-exposed rats tended to be greater than controls; a 1.5-fold increase in average size was observed. As there was no induction of the protein content of the bifunctional enoyl-CoA hydratase, an enzyme involved in peroxisomal beta-oxidation, it is considered that ethionine selectively stimulates the peroxisomal beta-oxidation due to increased peroxisome surface area rather than evoked a peroxisome proliferation capacity. Increased peroxisomal beta-oxidation was also observed in the kidney of ethionine-exposed rats at a dose of 750 mg/day/kg body weight. At that dose the amount of reduced glutathione (GSH) was significantly increased in kidney. The amount of GSH and the level of peroxisomal beta-oxidation were significantly increased in liver at an ethionine dose of 100 mg/day/kg body weight. These responses in liver were evident within 2 days of ethionine exposure and then leveled off whereas a significant increase in GSH and peroxisomal beta-oxidation in kidney was observed within 12 days. Whether the acute H2O2-generating peroxisomal oxidation of long-chain fatty acids in the liver may also make this organ susceptible to the long-term effects of low-dose ethionine and be an important step in the chain of events which eventually results in tumour development should be considered.

In vitro oxidation of ascorbic acid and its prevention by GSH

The interaction of glutathione (GSH) with ascorbic acid and dehydroascorbic acid was examined in in-vitro experiments in order to examine the role of GSH in protecting against the autoxidation of ascorbic acid and in regenerating ascorbic acid by reaction with dehydroascorbic acid. If a buffered solution (pH 7.4) containing 1.0 mM ascorbic acid was incubated at 37°C, there was a rapid loss of ascorbic acid in the presence of oxygen. When GSH was added to this solution, ascorbic acid did not disappear. Maximum protection against ascorbic acid autoxidation was achieved with as little as 0.1 mM GSH. Cupric ions (0.01 mM) greatly accelerated the rate of autoxidation of ascorbic acid, an effect that was inhibited by 0.1 mM GSH. Other experiments showed that GSH complexes with cupric ions, resulting in a lowering of the amount of GSH in solution as measured in GSH standard curves. These results suggest that the inhibition of ascorbic acid autoxidation by GSH involves complexation with cupric ions that catalyze the reaction. When ascorbic acid was allowed to autoxidize at 37°C the subsequent addition of GSH (up to 10 mM) did not lead to the regeneration of ascorbic acid. This failure to detect a direct reaction between GSH and the dehydroascorbic acid formed by oxidation of ascorbic acid under this condition was presumably due to the rapid hydrolysis of dehydroascorbic acid. When conditions were chosen, i.e., low temperature, that promote stability of dehydroascorbic acid, the direct reaction between GSH and dehydroascorbic acid to form ascorbic acid was readily detected. The marked instability of dehydroascorbic acid at 37°C raises questions regarding the efficiency of the redox couple between GSH and dehydroascorbic acid in maintaining the concentration of ascorbic acid in mammalian cells exposed to an oxidative challenge.

Glutathione localisation in benign and malignant human breast lesions.

Reduced glutathione (GSH) has been demonstrated in benign and malignant human breast lesions using a newly developed histofluorescence technique. GSH was present in every lesion and in each case was localised to the epithelium. A semi-quantitative assessment revealed a moderate amount of GSH in normal epithelium and fibroadenoma and a high level in apocrine metaplasia, epitheliosis and intraduct carcinoma. Invasive ductal carcinoma contained a variable amount of GSH. Correlation between fluorescence intensity and histological grade of ductal carcinomas was almost statistically significant but a relationship to oestrogen receptor status was not detected. The rapid assessment of GSH in breast cancer may aid in the selection of optimum chemotherapeutic regimens.

Inhibition of the low-Km mitochondrial aldehyde dehydrogenase by diethyl maleate and phorone in vivo and in vitro. Implications for formaldehyde metabolism.

Formaldehyde can be oxidized primarily by two different enzymes, the low-Km mitochondrial aldehyde dehydrogenase and the cytosolic GSH-dependent formaldehyde dehydrogenase. Experiments were carried out to evaluate the effects of diethyl maleate or phorone, agents that deplete GSH from the liver, on the oxidation of formaldehyde. The addition of diethyl maleate or phorone to intact mitochondria or to disrupted mitochondrial fractions produced inhibition of formaldehyde oxidation. The kinetics of inhibition of the low-Km mitochondrial aldehyde dehydrogenase were mixed. Mitochondria isolated from rats treated in vivo with diethyl maleate or phorone had a decreased capacity to oxidize either formaldehyde or acetaldehyde. The activity of the low-Km, but not the high-Km, mitochondrial aldehyde dehydrogenase was also inhibited. The production of CO2 plus formate from 0.2 mM-[14C]formaldehyde by isolated hepatocytes was only slightly inhibited (15-30%) by incubation with diethyl maleate or addition of cyanamide, suggesting oxidation primarily via formaldehyde dehydrogenase. However, the production of CO2 plus formate was increased 2.5-fold when the concentration of [14C]formaldehyde was raised to 1 mM. This increase in product formation at higher formaldehyde concentrations was much more sensitive to inhibition by diethyl maleate or cyanamide, suggesting an important contribution by mitochondrial aldehyde dehydrogenase. Thus diethyl maleate and phorone, besides depleting GSH, can also serve as effective inhibitors in vivo or in vitro of the low-Km mitochondrial aldehyde dehydrogenase. Inhibition of formaldehyde oxidation by these agents could be due to impairment of both enzyme systems known to be capable of oxidizing formaldehyde. It would appear that a critical amount of GSH, e.g. 90%, must be depleted before the activity of formaldehyde dehydrogenase becomes impaired.

Effect of sodium selenite upon bromobenzene toxicity in rats: I. Hepatotoxicity

The effects of sodium selenite on bromobenzene hepatotoxicity were examined in male rats. Rats pretreated with sodium selenite (12.5 or 30 μmol/kg, ip) 72 hr prior to injection of bromobenzene (7.5 mmol/kg, ip) showed a marked reduction in bromobenzene-induced liver injury as evidenced by decreased plasma alanine and aspartate transaminase values, sorbitol dehydrogenase activity, and reduced histologic damage. Administration of bromobenzene did not affect the selenium content of blood or liver. At 72 hr after treatment with selenite, hepatic reduced (GSH) and oxidized (GSSG) glutathione values or GSH synthetic and degradation enzyme activities were not altered. However, from 3 to 12 hr following bromobenzene administration, hepatic GSH and cysteine amounts declined less rapidly in selenite-treated rats compared to control. Thus, acute selenite treatment ameliorated bromobenzene hepatotoxicity in a manner suggesting facilitation of hepatic GSH production by selenite for use in bromobenzene detoxication.