Careful consideration of the effects induced by glutathione depletion in rat liver and heart. The involvement of cytosolic and mitochondrial glutathione pools

The effect of in vitro phorone exposure on glutathione content and T cell antigen receptor (CD3)-stimulated calcium mobilization in murine splenic T lymphocytes

An increase in cytosolic free calcium ([Ca(2+)](i)) is one of the earliest events to occur in T lymphocytes following stimulation of the transmembrane T cell receptor/CD3 complex (TCR/CD3). This [Ca(2+)](i) mobilization has been found to be sensitive to intracellular thiol redox status, which in turn is modulated by cellular glutathione (GSH) content. We have previously reported that GSH depletion, by treatment with either the alpha, beta-carbonyl diethyl maleate or the aromatic halo-compound 1-chloro-2,4-dinitrobenzene, correlates with decreased [Ca(2+)](i) mobilization in anti-CD3 monoclonal antibody (mAb)-stimulated human peripheral blood lymphocytes (HPBL). This prompted us to determine whether this correlation between GSH content and TCR/CD3 signal transduction capability was also present in murine lymphocytes, since the mouse model is often used as a surrogate for the human immune system. The results presented here demonstrate that in vitro treatment with the alpha, beta-carbonyl phorone dose-dependently depletes intracellular GSH in murine splenic T lymphocytes. Both CD4(+) and CD8(+) T lymphocytes depleted of GSH by greater than 40% were found to have a decreased [Ca(2+)](i) mobilization following anti-CD3 mAb stimulation. Similar to what has been described for HPBL, these results indicate that the cellular GSH status influences the initial response of murine T lymphocytes to TCR/CD3 stimulation.

Involvement of bioantioxidants in thrombosis in mice

An involvement of free radicals in thrombosis has been suggested previously. In order to further explore the role of free radicals and antioxidants in thrombosis, we have measured preventive (enzymes of the glutathione redox cycle) and chain-breaking antioxidants (vitamin E and C) in whole blood, platelets, neutrophils (PMNLs), heart and lung following collagen and adrenaline induced thrombosis in mice. A significant decrease in platelet glutathione (GSH) level (54%) and glutathione reductase activity was observed after thrombosis. In addition, GSH content in whole blood was also found to be reduced. In PMNLs, an increase in glutathione peroxidase activity and a four-fold elevation in vitamin C content was observed following thrombosis. However, levels of vitamin E and total thiol groups remained unchanged in both the cells and tissues. The results further suggest involvement of free radicals and PMNLs in thrombosis.

Studies on Hg(II)-induced H2O2 formation and oxidative stress in vivo and in vitro in rat kidney mitochondria

Studies were undertaken to investigate the principal actions underlying mercury-induced oxidative stress in the kidney. Mitochondria from kidneys of rats treated with HgCl2 (1.5 mg/kg i.p.) demonstrated a 2-fold increase in hydrogen peroxide (H2O2) formation for up to 6 hr following Hg(II) treatment using succinate as the electron transport chain substrate. No increase in H2O2 formation was observed when NAD-linked substrates (malate/glutamate) were used, suggesting that Hg(II) affects H2O2 formation principally at the ubiquinone-cytochrome b region of the mitochondrial respiratory chain in vivo. Together with increased H2O2 formation, mitochondrial glutathione (GSH) content was depleted by more than 50% following Hg(II) treatment, whereas formation of thiobarbiturate reactive substances (TBARS), indicative of mitochondrial lipid peroxidation, was increased by 68%. Studies in vivo revealed a significant concentration-related depolarization of the inner mitochondrial membrane following the addition of Hg(II) to mitochondria isolated from kidneys of untreated rats. This effect was accompanied by significantly increased H2O2 formation, GSH depletion and TBARS formation linked to both NADH dehydrogenase (rotenone-inhibited) and ubiquinone-cytochrome b (antimycin-inhibited) regions of the electron transport chain. Oxidation of pyridine nucleotides (NAD[P]H) was also observed in mitochondria incubated with Hg(II) in vitro. In further studies in vitro, the potential role of Ca2+ in Hg(II)-induced mitochondrial oxidative stress was investigated. Ca2+ alone (30-400 nmol/mg protein) produced no increase in H2O2 and only a slight increase in TBARS formation when incubated with kidney mitochondria isolated from untreated rats. However, Ca2+ significantly increased H2O2 and TBARS formation elicited by Hg(II) at the ubiquinone-cytochrome b region of the mitochondrial electron transport chain, whereas TBARS formation was decreased significantly when the Ca2+ uptake inhibitors, ruthenium red or [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA), were included with Hg(II) in the reaction mixtures. These findings support the view that Hg(II) causes depolarization of the mitochondrial inner membrane with consequent increased H2O2 formation. These events, coupled with Hg(II)-mediated GSH depletion and pyridine nucleotide oxidation, create an oxidant stress condition characterized by increased susceptibility of mitochondrial membranes to iron-dependent lipid peroxidation (TBARS formation). Since increased H2O2 formation, GSH depletion and lipid peroxidation were also observed in vivo following Hg(II) treatment, these events may underlie oxidative tissue damage caused by mercury compounds. Moreover, Hg(II)-induced alterations in mitochondrial Ca2+ homeostasis may exacerbate Hg(II)-induced oxidative stress in kidney cells.

Increased 4-hydroxynonenal levels in experimental alcoholic liver disease: association of lipid peroxidation with liver fibrogenesis

The precise role of lipid peroxidation in the pathogenesis of alcoholic liver disease is still being debated. To explore the issue, this study was undertaken to investigate the status of lipid peroxidation, antioxidants and prooxidants at two discrete stages of experimental alcoholic liver disease. Male Wistar rats were intragastrically fed a high-fat diet plus ethanol for 5 or 16 wk (the duration that resulted in initiation of centrilobular liver necrosis or liver fibrosis, respectively). Lipid peroxidation was assessed in isolated microsomes and mitochondria with three parameters: malondialdehyde equivalents as determined by thiobarbituric acid assay, conjugated diene formation and 4-hydroxynonenal as a 2,4-dinitrophenylhydrazone derivative. To assess antioxidant systems, hepatic concentrations of glutathione, methionine and alpha-tocopherol were determined. The concentration of nonheme iron, a known prooxidant, was also measured. At wk 5, centrilobular liver necrosis was already evident in the ethanol-fed animals, with two- or threefold increases in plasma AST and ALT levels. At this stage, neither malondialdehyde equivalents nor conjugated diene values were elevated, and the 4-hydroxynonemal level was below 0.2 nmol/mg protein. Hepatic concentrations of methionine and alpha-tocopherol in these animals were increased two- and threefold, respectively, whereas the reduced glutathione level remained unchanged. When alcoholic liver disease had progressed to perivenular or bridging fibrosis at wk 16, all three parameters of lipid peroxidation showed consistent increases that were accompanied by significant reductions in the hepatic glutathione and methionine levels. Interestingly, the control animals pair-fed with the high-fat diet also had significantly elevated 4-hydroxynonenal levels at wk 16 compared to the wk 5 level.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutathione and cysteine depletion in rats and mice following acute intoxication with diethylmaleate

We examined the dose-dependent glutathione (GSH) depletion in liver, kidney, heart and brain of rats and mice, and cysteine depletion in rat kidney, following i.p. administration of diethylmaleate (DEM). In either rodent, the fall in total GSH concentration in liver and heart reached an upper value of 90 and 80% with 3 and 4 mmol DEM/kg respectively, which did not increase with higher doses. This study suggests that the residual level of GSH corresponds to the mitochondrial pool, in which case DEM might serve as a tool for the measurement of mitochondrial GSH ex vivo. In further experiments, we studied the time course of GSH and cysteine after administration of 3 mmol DEM/kg in rat tissues. Maximal depletion was reached approximately 1 hr after the i.p. injection. Subsequent GSH repletion was fast in liver and kidney, whereas it was slow in heart and brain, with a return to control values by 8-12 and by 48 hr after intoxication, respectively. This study provides new data for cardiac GSH and renal cysteine decrease after intoxication with DEM and should help to optimize GSH depletion models for further pharmacological investigations, especially when the use of inhibitors of glutathione metabolic turnover is undesirable and when side-effects other than GSH depletion must be avoided.

Glutathione and ischemia-reperfusion injury in the perfused rat liver

Using the isolated perfused rat liver, we investigated the relationship of glutathione (GSH) with reactive oxygen species (ROS) generation and liver cell damage during ischemia/reperfusion in normal and GSH-depleted conditions. Lucigenin-enhanced chemiluminescence was used as a sensitive index of tissue ROS generation. After 30 minutes of equilibration, livers were subjected to global ischemia for various times (60 or 90 minutes) and then reperfused for another 120 minutes. Intracellular ROS levels increased sharply at the onset of reperfusion and then declined slowly. After 30 to 60 minutes of reperfusion, ROS levels started to increase progressively in a linear fashion. However, sinusoidal glutathione disulfide release did not increase during reperfusion in the same livers, suggesting that intracellular ROS generation is too low to cause a significant increase in GSH oxidation. Pretreatment with phorone (300 mg/kg intrapentoneally [ip]), which reduced hepatic GSH by 90%, did not cause any difference in intracellular ROS generation compared with the control livers. There were also no significant differences in lactate dehydrogenase and thiobarbituric acid reactive substances (TBARS) release between the control and phorone-treated livers during reperfusion after various times of ischemia. These data indicate that ROS generation in the normal isolated perfused liver during ischemia/reperfusion is extremely low and intracellular GSH does not serve as a major intracellular defense system against such a low oxidative stress.

Oxygen toxicity in the nervous tissue: comparison of the antioxidant defense of rat brain and sciatic nerve

Nervous tissue, central and peripheral, is, as any other, subject to variations in oxygen tension, and to the attack of different xenobiotics; these situations may promote the generation of activated oxygen species of free radical character. Results are presented showing that the content of total glutathione (GSH) in brain is 10-fold that found in the sciatic nerve of the rat (2620 vs. 261 nmol/g wet weight, respectively). The existence of a relatively high superoxide dismutase activity in peripheral nervous tissue, when compared with brain or liver, in combination with the DT-diaphorase activity detected in the sciatic nerve might represent an effective defense mechanism against quinone toxicity, as is also discussed. Nervous tissue, both central and peripheral lack Se-independent GSH peroxidase activity. Finally, the activities of other glutathione-related enzymes studied in the sciatic nerve are very low, when compared with the central nervous tissue, thus suggesting a higher susceptibility of peripheral tissue to oxidative stress damage, since GSH concentration and/or any GSH-related enzymatic activities, e.g. GSH peroxidase or glutathione disulfide reductase, might become limiting.