Glutathione protects against hypoxic/hypoglycemic decreases in 2-deoxyglucose uptake and presynaptic spikes in hippocampal slices

Glutaredoxin 2 Protein (Grx2) as an Independent Prognostic Factor Associated with the Survival of Colon Adenocarcinoma Patients

Glutaredoxin 2 (Grx2; Glrx2) is a glutathione-dependent oxidoreductase located in mitochondria, which is central to the regulation of glutathione homeostasis and mitochondrial redox, and plays a crucial role in highly metabolic tissues. In response to mitochondrial redox signals and oxidative stress, Grx2 can catalyze the oxidation and S-glutathionylation of membrane-bound thiol proteins in mitochondria. Therefore, it can have a significant impact on cancer development. To investigate this further, we performed an immunohistochemical analysis of Grx2 protein expression in colon adenocarcinoma samples collected from patients with primary colon adenocarcinoma (stage I and II) and patients with metastasis to regional lymph nodes (stage III). The results of our study revealed a significant relationship between the immunohistochemical expression of Grx2 and tumor histological grade, depth of invasion, regional lymph node involvement, angioinvasion, staging, and PCNA immunohistochemical expression. It was found that 87% of patients with stage I had high levels of Grx2 expression. In contrast, only 33% of patients with stage II and 1% of patients with stage III had high levels of Grx2 expression. Moreover, the multivariate analysis revealed that the immunohistochemical expression of Grx2 protein apart from the grade of tumor differentiation was an independent prognostic factors for the survival of patients with colon adenocarcinoma. Studies analyzing Grx2 levels in patients' blood confirmed that the highest levels of serum Grx2 protein was also found in stage I patients, which was reflected in the survival curves. A higher level of Grx2 in the serum has been associated with a more favorable outcome. These results were supported by in vitro analysis conducted on colorectal cancer cell lines that corresponded to stages I, II, and III of colorectal cancer, using qRT-PCR and Western Blot.

N-acetylcysteine ethyl ester as GSH enhancer in human primary endothelial cells: A comparative study with other drugs

Several drugs are currently in use as glutathione (GSH) enhancers in clinical, pre-clinical and experimental research. Here we compare the ability of N-acetylcysteine (NAC), 2-oxothiazolidine-4-carboxylic acid (OTC), glutathione ethyl ester (GSH-EE) and N-acetylcysteine ethyl ester (NACET) to increase the intracellular concentration of GSH using primary human umbilical vein endothelial cells (HUVEC) as in vitro model. Our experiments highlighted that NACET is largely the most efficient molecule in increasing the intracellular levels of GSH, cysteine, and γ-glutamylcysteine. This is because NACET is lipophilic and can freely cross plasma membrane but, inside the cell, it is de-esterified to the more hydrophilic NAC, which, in turn, is trapped into the cell and slowly transformed into cysteine. The higher availability of cysteine is matched by an increase in GSH synthesis, cysteine availability being the rate limiting step for this reaction. Surprisingly, the increase in GSH concentration was not linear but peaked at 0.5 mM NACET and gradually decreased when cells were treated with higher concentrations of NACET. We demonstrated that this puzzling ceiling effect was due to the fact that NAC released from NACET turned out to be a competitive inhibitor of the enzyme glutamate-cysteine ligase, with a Ki value of 3.2 mM. By using a cell culture medium lacking of cysteine and methionine, we could demonstrate that the slight increase in intracellular levels of cysteine and GSH induced by NAC in HUVEC grown in standard medium was due to the reduction of the cystine present in the medium itself there rather than to the action of NAC as Cys pro-drug. This fact may explain why NAC works well as GSH enhancer at very high concentrations in pre-clinical and in vitro studies, whereas it failed in most clinical trials.

Role of glutathione in cancer progression and chemoresistance

Glutathione (GSH) plays an important role in a multitude of cellular processes, including cell differentiation, proliferation, and apoptosis, and disturbances in GSH homeostasis are involved in the etiology and progression of many human diseases including cancer. While GSH deficiency, or a decrease in the GSH/glutathione disulphide (GSSG) ratio, leads to an increased susceptibility to oxidative stress implicated in the progression of cancer, elevated GSH levels increase the antioxidant capacity and the resistance to oxidative stress as observed in many cancer cells. The present review highlights the role of GSH and related cytoprotective effects in the susceptibility to carcinogenesis and in the sensitivity of tumors to the cytotoxic effects of anticancer agents.

Glutathione and glutathione analogues; therapeutic potentials

BACKGROUND

Glutathione (GSH) and related enzymes are critical to cell protection from toxins, both endogenous and environmental, including a number of anti-cancer cytotoxic agents.

SCOPE OF REVIEW

Enhancing GSH and associated enzymes represents a longtime and persistent aim in the search for cytoprotective strategies against cancer, neurologic degeneration, pulmonary and inflammatory conditions, as well as cardiovascular ailments. The challenge is to identify effective GSH analogues or precursors that generate mimic molecules with glutathione's cellular protective effects. This review will provide an update on these efforts. Much effort has also been directed at depleting cellular GSH and related cytoprotective effects, in order to sensitize established tumors to the cytotoxic effects of anti-cancer agents. Efforts to deplete GSH have been limited by the challenge of selectivity doing so in tumor and not in normal tissue so as to avoid enhancing the toxicity of anti-cancer drugs. This review will also provide an update of efforts at overcoming the challenge of targeting the desired GSH depletion to tumor cells.

MAJOR CONCLUSIONS

This chapter provides a brief background and update of progress in the development and use of GSH analogues in the therapeutic setting, including the pharmacological aspects of these compounds.

GENERAL SIGNIFICANCE

This is an area of enormous research activity, and major advances promise the advent of novel therapeutic opportunities in the near future. This article is part of a Special Issue entitled Cellular functions of glutathione.

Prodrug approach for increasing cellular glutathione levels

Reduced glutathione (GSH) is the most abundant non-protein thiol in mammalian cells and the preferred substrate for several enzymes in xenobiotic metabolism and antioxidant defense. It plays an important role in many cellular processes, such as cell differentiation, proliferation and apoptosis. GSH deficiency has been observed in aging and in a wide range of pathologies, including neurodegenerative disorders and cystic fibrosis (CF), as well as in several viral infections. Use of GSH as a therapeutic agent is limited because of its unfavorable biochemical and pharmacokinetic properties. Several reports have provided evidence for the use of GSH prodrugs able to replenish intracellular GSH levels. This review discusses different strategies for increasing GSH levels by supplying reversible bioconjugates able to cross the cellular membrane more easily than GSH and to provide a source of thiols for GSH synthesis.

Glutathione monoethyl ester provides neuroprotection in a rat model of stroke

Oxidative stress plays an important role in the development of tissue damage following transient focal cerebral ischaemia. Glutathione is a central component in the antioxidant defence of cells. We have previously shown a close association between mitochondrial glutathione loss and cell death following middle cerebral artery (MCA) occlusion. Glutathione monoethyl ester increases cellular glutathione and is particularly effective in increasing the mitochondrial pool. In the present investigation, we infused glutathione monoethyl ester into the third ventricle during 2 h of MCA occlusion and 48 h of reperfusion. Infarct size was reduced from 46% of the total ischaemic hemisphere in saline-treated animals to 16% following ester treatment. Thus, glutathione monoethyl ester provides neuroprotection following transient focal cerebral ischaemia.

Enhanced neuronal protection from oxidative stress by coculture with glutamic acid decarboxylase-expressing astrocytes

Astrocytes expressing glutamic acid decarboxylase GAD67 directed by the glial fibrillary acidic protein promoter were shown to provide enhanced protection of PC12 cells from H(2)O(2) treatment and serum deprivation in the presence of glutamate. In addition, they protected non-differentiated, but not differentiated, embryonic rat cortical neurons from glutamate toxicity. Glutamic acid decarboxylase (GAD)-expressing astrocytes showed increased glutathione synthesis and release compared to control astrocytes. These changes were due to GAD transgene expression, as transient expression of a GAD antisense plasmid resulted in partial suppression of the increase in glutathione release. In addition to the previously demonstrated increases in NADH and ATP levels and lactate release, GAD-expressing astrocytes show increased antioxidant activity, explaining their ability to protect neurons from various injuries.

Effect of in vitro ischemic or hypoxic treatment on mitochondrial electron transfer activity in rat brain slices assessed by gas-tissue autoradiography using

We have investigated the effect of in vitro ischemic or hypoxic treatment on mitochondrial electron transport function in brain slices using gas-tissue autoradiography technique with [15O]O2. Brain slices were preincubated in Krebs-Ringer phosphate medium bubbled with 100% O2 for 30 min at 37 degrees C. (1) Control culture was incubated in the same medium bubbled with 100% O2 for 5-40 min at 37 degrees C, then for another 30 min under the same conditions. (2) In vitro ischemia was induced by placing the culture in the medium deprived of glucose and bubbled with 100% N2 for 5-40 min, then returning it to control conditions and culturing for another 30 min. (3) In vitro hypoxia was induced by placing the culture in the medium with glucose and bubbled with 100% N2 for 5-40 min, then returning it to the control conditions for 30 min. After the three different treatments, the [15O]O2 fixation by brain slices reflect to mitochondrial electron transport function was determined using gas-tissue autoradiography technique with [15O]O2. The fixation of [15O]O2 by striatum, cerebral cortex and hippocampus was reduced dependent upon the period of in vitro ischemic treatment. In contrast, the [15O]O2 fixation by those brain regions was only slightly reduced by hypoxia treatment. The reduction in [15O]O2 fixation induced by ischemic treatment was prevented by an antioxidant: glutathione, glutathione monoethyl ester or acetylsalicylic acid. The preventive effect of antioxidants on the mitochondrial damage induced by ischemia was more remarkable in the striatum than in the cerebral cortex and hippocampus. In the comparison of [15O]O2 fixation between ischemia-treated young and senescent brain slices, reduction of 15O fixation by every brain region examined was more prominent in senescence than in the young. These results suggest that gas-tissue autoradiography using [15O]O2 is useful to assess mitochondrial electron transport dysfunction induced by ischemia treatment in brain slices and that the oxidative stress participates in the mechanism of ischemia-induced dysfunction in mitochondria.

Modulation of endogenous glutathione availability

Glutathione is quantitatively the most important antioxidant and scavenger. In addition it has a number of important functions in amino acid transport across membranes, in protein synthesis and degradation, in gene regulation and in cellular redox regulation. It becomes more and more evident that depletion of glutathione is associated with states of severe diseases. From this perspective, the possibility of manipulating the availability of glutathione becomes a very attractive form of treatment. In this review, new insights into pathophysiology and the regulation of glutathione metabolism, in addition to effects of precursors to and stimulants of glutathione synthesis, are covered. It is very likely that glutathione precursors will soon be an important pharmacological tool for treatment in a number of diseased states.

Glutathione and glutathione delivery compounds

Deficiency of GSH (BSO model) demonstrates the need for cellular protection from endogenous ROS. The pathology of various diseases is often associated with ROS and oxidative stress. The several methods for modulating cellular GSH levels presented in this chapter offer selective tools to study mechanisms and offer potential therapy of human diseases associated with GSH deficiency and oxidative stress.

Methylcobalamin attenuates the hypoxia/hypoglycemia- or glutamate-induced reduction in hippocampal fiber spikes in vitro

The effects of methylcobalamin, a vitamin B12 analogue, on the hypoxia/hypoglycemia- or glutamate-induced reduction in hippocampal CA1 presynaptic fiber spikes elicited by Schaffer collateral stimulation in rat brain slices were evaluated. Hippocampal slices were exposed to 15 min of hypoxia/hypoglycemia, and then these slices were returned to oxygenated and glucose-containing buffer for 3 h. Hypoxia/hypoglycemia reduced CA1 presynaptic potentials in vitro. Treatment with 10 microM methylcobalamin attenuated the impairment of CA1 presynaptic potentials induced by hypoxia/hypoglycemia or glutamate application (10 mM). Daily injection of methylcobalamin (0.5 mg/kg i.p./day) for 3 days in vivo also attenuated the hypoxia/hypoglycemia- or glutamate-induced reduction in presynaptic potentials in hippocampal slices. Pretreatment with cyanocobalamin at 10 microM failed to attenuate the impairment of CA1 presynaptic potentials. However, daily injection of cyanocobalamin (0.5 mg/kg i.p./day) for 3 days caused a protective action against the hypoxia/hypoglycemia- or glutamate-induced functional deficit. Furthermore, co-treatment of L-arginine (100 microM), a substrate for nitric oxide synthase, with methylcobalamin in vitro reversed the methylcobalamin-induced functional recovery. The present results demonstrate that methylcobalamin application in vivo or in vitro leads to functional recovery from hypoxia/hypoglycemia- or glutamate-induced impairment of CA1 presynaptic potentials. Neuroprotection was obtained by in vivo application of cyanocobalamin, but not by its in vitro application. It is reported that in vivo injected cyanocobalamin converted to methylcobalamin in the hepatic cells. Therefore, the results suggest that a transmethylation reaction in the hippocampal regions may be involved in the methylcobalamin-induced functional recovery from ischemic impairment.