Induction of cystine transport and other stress proteins by disulfiram: effects on glutathione levels in cultured cells

Hydrogen sulfide and its donors: Novel antitumor and antimetastatic agents for liver cancer

Hepatocellular carcinoma (HCC) is the sixth most frequent human cancer and the world's third most significant cause of cancer mortality. HCC treatment has recently improved, but its mortality continues to increase worldwide due to its extremely complicated and heterogeneous genetic abnormalities. After nitric oxide (NO) and carbon monoxide (CO), the third gas signaling molecule discovered is hydrogen sulfide (H₂S), which has long been thought to be a toxic gas. However, numerous studies have proven that H₂S plays many pathophysiological roles in mammals. Endogenous or exogenous H₂S can decrease cell proliferation, promote apoptosis, block cell cycle, invasion and migration through various cellular signaling pathways. This review analyzes and discusses the recent literature on the function and molecular mechanism of H₂S and H₂S donors in HCC, so as to provide convenience for the scientific research and clinical application of H₂S in the treatment of liver cancer.

The interaction of disulfiram and H2S metabolism in inhibition of aldehyde dehydrogenase activity and liver cancer cell growth

Disulfiram (DSF), a sulfur-containing compound, has been used to treat chronic alcoholism and cancer for decades by inactivating aldehyde dehydrogenase (ALDH). Hydrogen sulfide (H₂S) is a new gasotransmitter and regulates various cellular functions by S-sulfhydrating cysteine in the target proteins. H₂S exhibits similar properties to DSF in the sensitization of cancer cells. The interaction of DSF and H₂S on ALDH activity and liver cancer cell survival are not clear. Here it was demonstrated that DSF facilitated H₂S release from thiol-containing compounds, and DSF and H₂S were both capable of regulating ALDH through inhibition of gene expression and enzymatic activity. The supplement of H₂S sensitized human liver cancer cells (HepG2) to DSF-inhibited cell viability. The expression of cystathionine gamma-lyase (a major H₂S-generating enzyme) was lower but ALDH was higher in mouse liver cancer stem cells (Dt81Hepa1-6) in comparison with their parental cells (Hepa1-6), and H₂S was able to inhibit liver cancer stem cell adhesion. In conclusion, these data point to the potential of combining DSF and H₂S for inhibition of cancer cell growth and tumor development by targeting ALDH.

The effects of sodium diethyldithiocarbamate in fibroblasts V79 cells in relation to cytotoxicity, antioxidative enzymes, glutathione, and apoptosis

Sodium diethyldithiocarbamate (DETC) is the main metabolite of disulfiram. Recently, we reported that mechanism of disulfiram cytotoxicity in V79 cells might be partially connected with thiol redox-state imbalance. Here, we examined the effect of DETC on the level of intracellular glutathione (GSH), protein oxidation (measured as PC—protein carbonyl content), lipid peroxidation (measured as TBARS—thiobarbituric acid reactive substances), antioxidant enzymatic defense, as well as on apoptosis. We used V79 Chinese hamster fibroblasts cells with and without modulated glutathione (GSH) level by N-acetyl-l-cysteine (NAC). We showed that treatment with DETC at concentrations that cause a moderate increase in thiol-state imbalance but not cell death stimulates oxidative stress measured as increased level of PC and TBARS, adaptive response of GSH-related enzymes and apoptosis. Our results show that cellular effects of DETC are partially attributable to the initial redox cellular state, since the increase of GSH level by NAC pre-treatment prevented the observed changes.

Protective effect of N-acetyl-L-cysteine against disulfiram-induced oxidative stress and apoptosis in V79 cells

This work investigated the effect of N-acetyl-L-cysteine (NAC) on disulfiram (DSF) induced oxidative stress in Chinese hamster fibroblast cells (V79). An increase in oxidative stress induced by DSF was observed up to a 200 μM concentration. It was evidenced by a statistically significant increase of both GSH(t) and GSSG levels, as well as elevated protein carbonyl (PC) content. There was no increase in lipid peroxidation (measured as TBARS). DSF increased CAT activity, but did not change SOD1 and SOD2 activities. Analysis of GSH related enzymes showed that DSF significantly increased GR activity, did not change Se-dependent GPx, but statistically significantly decreased non-Se-dependent GPx activity. DSF showed also pro-apoptotic activity. NAC alone did not produce any significant changes, besides an increase of GSH(t) level, in any of the variables measured. However, pre-treatment of cells with NAC ameliorated DSF-induced changes. NAC pre-treatment restored the viability of DSF-treated cells evaluated by Trypan blue exclusion assay and MTT test, GSSG level, and protein carbonyl content to the control values as well as it reduced pro-apoptotic activity of DSF. The increase of CAT and GR activity was not reversed. Activity of both GPx was significantly increased compared to their values after DSF treatment. In conclusion, oxidative properties are at least partially attributable to the cellular effects of disulfiram and mechanisms induced by NAC pre-treatment may lower or even abolish the observed effects. These observations illustrate the importance of the initial cellular redox state in terms of cell response to disulfiram exposure.

Versatile cytoprotective activity of lipoic acid may reflect its ability to activate signalling intermediates that trigger the heat-shock and phase II responses

Although lipoic acid (LA) and its reduced derivative (DHLA) have broad antioxidant activity, it seems unlikely that this can adequately explain the remarkable neuroprotective effects of LA observed in rodents and in diabetic patients. It is proposed that this protection is mediated, in large measure, by induction of various protective proteins. More specifically, there is some reason to suspect that LA can trigger both heat-shock and phase II responses, and that LA may achieve this by catalyzing the formation of intramolecular disulfides in certain signalling proteins that function as detectors of oxidants and/or electrophiles. This hypothesis is readily testable, and, if true, would suggest that LA may have general utility for preventing or treating neurodegenerative disorders, and possibly also may retard the adverse impact of aging on brain function. This model also predicts that LA should have anticarcinogenic activity.

Methamphetamine neurotoxicity: necrotic and apoptotic mechanisms and relevance to human abuse and treatment

Research into methamphetamine-induced neurotoxicity has experienced a resurgence in recent years. This is due to (1) greater understanding of the mechanisms underlying methamphetamine neurotoxicity, (2) its usefulness as a model for Parkinson's disease and (3) an increased abuse of the substance, especially in the American Mid-West and Japan. It is suggested that the commonly used experimental one-day methamphetamine dosing regimen better models the acute overdose pathologies seen in humans, whereas chronic models are needed to accurately model human long-term abuse. Further, we suggest that these two dosing regimens will result in quite different neurochemical, neuropathological and behavioral outcomes. The relative importance of the dopamine transporter and vesicular monoamine transporter knockout is discussed and insights into oxidative mechanisms are described from observations of nNOS knockout and SOD overexpression. This review not only describes the neuropathologies associated with methamphetamine in rodents, non-human primates and human abusers, but also focuses on the more recent literature associated with reactive oxygen and nitrogen species and their contribution to neuronal death via necrosis and/or apoptosis. The effect of methamphetamine on the mitochondrial membrane potential and electron transport chain and subsequent apoptotic cascades are also emphasized. Finally, we describe potential treatments for methamphetamine abusers with reference to the time after withdrawal. We suggest that potential treatments can be divided into three categories; (1) the prevention of neurotoxicity if recidivism occurs, (2) amelioration of apoptotic cascades that may occur even in the withdrawal period and (3) treatment of the atypical depression associated with withdrawal.

Adaptive responses to peroxynitrite: increased glutathione levels and cystine uptake in vascular cells

We and others recently demonstrated increased glutathione levels, stimulated cystine uptake, and induced gamma-glutamylcysteinyl synthase (gamma-GCS) in vascular cells exposed to nitric oxide donors. Here we report the effects of peroxynitrite on glutathione levels and cystine uptake. Treatment of bovine aortic endothelial and smooth muscle cells with 3-morpholinosydnonimine (SIN-1), a peroxynitrite donor, resulted in transient depletion of glutathione followed by a prolonged increase beginning at 8-9 h. Concentration-dependent increases in glutathione of up to sixfold occurred 16-18 h after 0.05-2.5 mM SIN-1. Responses to SIN-1 were inhibited by copper-zinc superoxide dismutases and manganese(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride, providing evidence for peroxynitrite involvement. Because glutathione synthesis is regulated by amino acid availability, we also studied cystine uptake. SIN-1 treatment resulted in a prolonged increase in cystine uptake beginning at 6-9 h. Increases in cystine uptake after SIN-1 were blocked by inhibitors of protein and RNA synthesis, by extracellular glutamate but not by extracellular sodium. These studies suggest induction of the x(c)(-) pathway of amino acid uptake. A close correlation over time was observed for increases in cystine uptake and glutathione levels. In summary, vascular cells respond to chronic peroxynitrite exposure with adaptive increases in cellular glutathione and cystine transport.

Metallothionein, glutathione, and cystine transport in pulmonary artery endothelial cells and NIH/3T3 cells

Both glutathione (gamma-glutamylcysteinylglycine; GSH) and the metalloprotein metallothionein (MT) are composed of approximately one-third cysteine. Both have antioxidant activity and are induced by oxidant stresses and heavy metals. Intracellular cysteine levels may depend on uptake and reduction of extracellular cystine. GSH synthesis can be limited by the activity of the xc- cystine transport system, which is induced by oxidants and other stresses. MT is induced by treatments that also increase GSH levels and may compete with GSH for intracellular cysteine. We investigated the induction of MT and GSH and cystine transport in NIH/3T3 cells and bovine pulmonary artery endothelial cells exposed to cadmium (Cd) or arsenite. Cd and arsenite increased MT and GSH in both cells. Increases in MT and GSH were accompanied by increases in cystine uptake. Inhibition of cystine transport by glutamate decreased GSH levels and blocked Cd-induced GSH increases in both cell types. MT levels were not significantly affected, suggesting that MT synthesis is less sensitive to intracellular cysteine levels than GSH synthesis.