Differential effects of L-buthionine sulfoximine and ethacrynic acid on glutathione levels and mitochondrial function in PC12 cells

Oxidative stress in glial cultures: detection by DAF-2 fluorescence used as a tool to measure peroxynitrite rather than nitric oxide

4,5-diaminofluorescein diacetate (DAF-2DA) is widely used as a fluorescent probe to detect endogenously produced nitric oxide (NO). Recent reports that refer to the high sensitivity of DAF-2 toward NO prompted us to test its efficiency and specificity in a mixed murine primary glial culture model, in which the NO-synthesizing enzyme inducible nitric oxide synthase (iNOS) is expressed by stimulation with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma). Cultures were loaded with DAF-2DA and the fluorescence was measured using confocal microscopy. NO production in the cultures was determined using the ozone/chemiluminescence technique. Due to the extremely high photosensitivity of DAF-2, low laser intensities were used to avoid artifacts. No difference in DAF-2 fluorescence was observed in NO-producing cultures compared to control cultures, whereas the NO/peroxynitrite-sensitive dye 2,7-dihydrodichlorofluorescein (DCF) showed a significant fluorescence increase specifically in microglia cells. A detectable gain in fluorescence was seen when NO-containing buffer was added to the DAF-2DA-loaded cells with a minimum NO concentration at 7.7 microM. An additional gain of DAF-2 fluorescence was obtained when the cells were depleted of glutathione (GSH) with L-buthionine S,R-sulfoximine (BSO). Hence, we monitored the change in DAF-2 fluorescence intensity in the presence of NO and O(-*)(2) in a cell-free solution. The fluorescence due to NO was indeed larger when O(-*)(2) was added, implying a higher sensitivity of DAF-2 for peroxynitrite. Nevertheless, our results also indicate that measurement of DCF fluorescence is a better tool for monitoring intracellular changes in the levels of NO and/or peroxynitrite than DAF-2.

Glutathione might exert an important function in caerulein-stimulated amylase release in isolated rat pancreatic acini

AIMS

The effect of different modes of thiol depletion on pancreatic exocrine secretory function and potential mechanisms of interference with the secretory process in pancreatic acinar cells were investigated.

METHODOLOGY

After incubation with three thiol-modulating agents (L-buthionine sulfoximine, ethacrynic acid, and diamide) for 30 minutes, caerulein-stimulated amylase release and cholecystokinin (CCK) receptor binding characteristics were assessed in isolated rat pancreatic acini. The level of thiol groups (glutathione and protein thiols) and cytosolic-free calcium were measured in pancreatic acinar cells.

RESULTS

All three thiol-modulating agents decreased caerulein (10(-10)M)-stimulated amylase release and the level of pancreatic acinar glutathione in a dose-dependent fashion without a marked increase in cell damage. Diamide also diminished the level of protein thiols. Ethacrynic acid and diamide, but not L-buthionine sulfoximine, inhibited the caerulein (10(-9)M)-induced Ca(2+) mobilization in pancreatic acinar cells. None of the three thiol-modulating agents altered the CCK receptor binding characteristics.

CONCLUSION

The present findings strongly suggest an important role of glutathione in the secretory process in pancreatic acinar cells and in the secretory blockade observed in acute pancreatitis. A decrease in caerulein-induced Ca(2+) mobilization might participate in the inhibition of amylase release by some oxidative agents, but it is not the prominent cause in general.

Metabolism and functions of glutathione in brain

The tripeptide glutathione is the thiol compound present in the highest concentration in cells of all organs. Glutathione has many physiological functions including its involvement in the defense against reactive oxygen species. The cells of the human brain consume about 20% of the oxygen utilized by the body but constitute only 2% of the body weight. Consequently, reactive oxygen species which are continuously generated during oxidative metabolism will be generated in high rates within the brain. Therefore, the detoxification of reactive oxygen species is an essential task within the brain and the involvement of the antioxidant glutathione in such processes is very important. The main focus of this review article will be recent results on glutathione metabolism of different brain cell types in culture. The glutathione content of brain cells depends strongly on the availability of precursors for glutathione. Different types of brain cells prefer different extracellular glutathione precursors. Glutathione is involved in the disposal of peroxides by brain cells and in the protection against reactive oxygen species. In coculture astroglial cells protect other neural cell types against the toxicity of various compounds. One mechanism for this interaction is the supply by astroglial cells of glutathione precursors to neighboring cells. Recent results confirm the prominent role of astrocytes in glutathione metabolism and the defense against reactive oxygen species in brain. These results also suggest an involvement of a compromised astroglial glutathione system in the oxidative stress reported for neurological disorders.

Glutathione, oxidative stress and neurodegeneration

There is significant evidence that the pathogenesis of several neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, Friedreich's ataxia and amyotrophic lateral sclerosis, may involve the generation of reactive oxygen species and mitochondrial dysfunction. Here, we review the evidence for a disturbance of glutathione homeostasis that may either lead to or result from oxidative stress in neurodegenerative disorders. Glutathione is an important intracellular antioxidant that protects against a variety of different antioxidant species. An important role for glutathione was proposed for the pathogenesis of Parkinson's disease, because a decrease in total glutathione concentrations in the substantia nigra has been observed in preclinical stages, at a time at which other biochemical changes are not yet detectable. Because glutathione does not cross the blood-brain barrier other treatment options to increase brain concentrations of glutathione including glutathione analogs, mimetics or precursors are discussed.

Flupirtine and retigabine prevent L-glutamate toxicity in rat pheochromocytoma PC 12 cells

Flupirtine is an analgesic drug thought to have NMDA receptor antagonistic and antiapoptotic effects. We investigated the effects of Ethyl-2-amino-6-(4-(4-fluorbenzyl)amino)-pyridine-3-carbamamic+ ++ acid, maleate (flupirtine) and the related compound N-(2-amino-4-(4-fluorobenzylamino)-phenyl)-carbamic acid, ethyl ester) (retigabine) (Desaza-flupirtine) on the toxicity of L-glutamate and L-3,4-dihydroxyphenylalanine (L-DOPA) in rat pheochromocytoma PC 12 cells in vitro. Both drugs (10 microM) markedly decreased nonreceptor-mediated necrotic cell death in PC 12 cultures treated with L-glutamate (10 mM) for 72 h. In contrast, apoptosis induced by L-DOPA (250 microM) after 48 h was not affected by either substance. While L-DOPA elicited massive generation of reactive oxygen intermediates, L-glutamate-induced cell death was accompanied by only slightly increased levels of reactive oxygen intermediates. Flupirtine and retigabine exerted anti-oxidative effects in PC 12 cultures independent of their ability to prevent cell death. Further examination of the protective action of flupirtine and retigabine against L-glutamate toxicity showed that it had no influence on monoamine oxidase (monoamine: oxygen oxidoreductase (deaminating), EC 1.4.3.4., MAO) activity. Thus, flupirtine and retigabine provided protection against cystine deprivation and L-glutamate toxicity but did not protect against L-glutamate under cystine-free conditions indicating that both compounds are sufficiently effective to compensate the oxidative stress elicited by cystine deprivation but not excessive activity of monoamine oxidase after L-glutamate treatment.

Effect of 1-methyl-4-phenylpyridinium on glutathione in rat pheochromocytoma PC 12 cells

We investigated the effect of the selective dopaminergic neurotoxin 1-methyl-4-phenylpyridinium (MPP+) on glutathione redox status and the generation of reactive oxygen intermediates (ROI) in rat pheochromocytoma PC 12 cells in vitro. Treatment with MPP+ (250 microM) led to a 63% increase of reduced glutathione (GSH) after 24 h, while a 10-fold higher concentration of MPP+ (2.5 mM) depleted cellular GSH to 12.5% of control levels within that time. Similarly, the complex I-inhibitor rotenone induced a time-dependent loss of GSH at 1 and 10 microM, whereas treatment with lower concentrations of rotenone (0.1, 0.01 microM) increased cellular GSH. Both MPP+ and rotenone increased cellular levels of oxidised glutathione (GSSG) and the higher concentrations of both compounds led to an elevated ratio of oxidised glutathione (GSSG) vs total glutathione (GSH + GSSG) indicating a shift in cellular redox balance. MPP+ or rotenone did not induce the generation of ROI or significant elevation of intracellular levels of thiobabituric acid reactive substances (TBARS) for up to 48 h. Our data suggest that MPP+ has differential effects on glutathione homeostasis depending on the degree of complex I-inhibition and that inhibition of complex I is not sufficient to generate ROI in this paradigm.