Loss of suppression of GSH synthesis at low cell density in primary cultures of rat hepatocytes

Targeting USP8 Inhibits O-GlcNAcylation of SLC7A11 to Promote Ferroptosis of Hepatocellular Carcinoma via Stabilization of OGT

Hepatocellular carcinoma (HCC) is a lethal and aggressive human malignancy. The present study examins the anti-tumor effects of deubiquitylating enzymes (DUB) inhibitors in HCC. It is found that the inhibitor of ubiquitin specific peptidase 8 (USP8) and DUB-IN-3 shows the most effective anti-cancer responses. Targeting USP8 inhibits the proliferation of HCC and induces cell ferroptosis. In vivo xenograft and metastasis experiments indicate that inhibition of USP8 suppresses tumor growth and lung metastasis. DUB-IN-3 treatment or USP8 depletion decrease intracellular cystine levels and glutathione biosynthesis while increasing the accumulation of reactive oxygen species (ROS). Mechanistical studies reveal that USP8 stabilizes O-GlcNAc transferase (OGT) via inhibiting K48-specific poly-ubiquitination process on OGT protein at K117 site, and STE20-like kinase (SLK)-mediated S716 phosphorylation of USP8 is required for the interaction with OGT. Most importantly, OGT O-GlcNAcylates solute carrier family 7, member 11 (SLC7A11) at Ser26 in HCC cells, which is essential for SLC7A11 to import the cystine from the extracellular environment. Collectively, this study demonstrates that pharmacological inhibition or knockout of USP8 can inhibit the progression of HCC and induce ferroptosis via decreasing the stability of OGT, which imposes a great challenge that targeting of USP8 is a potential approach for HCC treatment.

Glutathione: Lights and Shadows in Cancer Patients

In cases of cellular injury, there is an observed increase in the production of reactive oxygen species (ROS). When this production becomes excessive, it can result in various conditions, including cancerogenesis. Glutathione (GSH), the most abundant thiol-containing antioxidant, is fundamental to re-establishing redox homeostasis. In order to evaluate the role of GSH and its antioxi-dant effects in patients affected by cancer, we performed a thorough search on Medline and EMBASE databases for relevant clinical and/or preclinical studies, with particular regard to diet, toxicities, and pharmacological processes. The conjugation of GSH with xenobiotics, including anti-cancer drugs, can result in either of two effects: xenobiotics may lose their harmful effects, or GSH conjugation may enhance their toxicity by inducing bioactivation. While being an interesting weapon against chemotherapy-induced toxicities, GSH may also have a potential protective role for cancer cells. New studies are necessary to better explain the relationship between GSH and cancer. Although self-prescribed glutathione (GSH) implementation is prevalent among cancer patients with the intention of reducing the toxic effects of anticancer treatments and potentially preventing damage to normal tissues, this belief lacks substantial scientific evidence for its efficacy in reducing toxicity, except in the case of cisplatin-related neurotoxicity. Therefore, the use of GSH should only be considered under medical supervision, taking into account the appropriate timing and setting.

Taurine treatment prevents derangement of the hepatic γ-glutamyl cycle and methylglyoxal metabolism in a mouse model of classical homocystinuria: regulatory crosstalk between thiol and sulfinic acid metabolism

Cystathionine β-synthase-deficient homocystinuria (HCU) is a poorly understood, life-threatening inborn error of sulfur metabolism. Analysis of hepatic glutathione (GSH) metabolism in a mouse model of HCU demonstrated significant depletion of cysteine, GSH, and GSH disulfide independent of the block in trans-sulfuration compared with wild-type controls. HCU induced the expression of the catalytic and regulatory subunits of γ-glutamyl ligase, GSH synthase (GS), γ-glutamyl transpeptidase 1, 5-oxoprolinase (OPLAH), and the GSH-dependent methylglyoxal detoxification enzyme, glyoxalase-1. Multiple components of the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated antioxidant-response regulatory axis were induced without any detectable activation of Nrf2. Metabolomic analysis revealed the accumulation of multiple γ-glutamyl amino acids and that plasma ophthalmate levels could serve as a noninvasive marker for hepatic redox stress. Neither cysteine, nor betaine treatment was able to reverse the observed enzyme inductions. Taurine treatment normalized the expression levels of γ-glutamyl ligase C/M, GS, OPLAH, and glyoxalase-1, and reversed HCU-induced deficits in protein glutathionylation by acting to double GSH levels relative to controls. Collectively, our data indicate that the perturbation of the γ-glutamyl cycle could contribute to multiple sequelae in HCU and that taurine has significant therapeutic potential for both HCU and other diseases for which GSH depletion is a critical pathogenic factor.-Maclean, K. N., Jiang, H., Aivazidis, S., Kim, E., Shearn, C. T., Harris, P. S., Petersen, D. R., Allen, R. H., Stabler, S. P., Roede, J. R. Taurine treatment prevents derangement of the hepatic γ-glutamyl cycle and methylglyoxal metabolism in a mouse model of classical homocystinuria: regulatory crosstalk between thiol and sulfinic acid metabolism.

Sustained blockade of ascorbic acid transport associated with marked SVCT1 loss in rat hepatocytes containing increased ascorbic acid levels after partial hepatectomy

The liver has an extraordinary regenerative capacity in response to partial hepatectomy (PHx), which develops with neither tissue inflammation response nor alterations in the whole organism. This process is highly coordinated and it has been associated with changes in glutathione (GSH) metabolism. However, there are no reports indicating ascorbic acid (AA) levels after partial hepatectomy. AA and GSH act integrally as an antioxidant system that protects cells and tissues from oxidative damage and imbalance observed in a variety of diseases that affect the liver. Although rat hepatocytes are able to synthesize AA and GSH, which are the providers of AA for the whole organism, they also acquire AA from extracellular sources through the sodium-coupled ascorbic acid transporter-1 (SVCT1). Here, we show that hepatocytes from rat livers subjected to PHx increase their GSH and AA levels from 1 to 7 days post hepatectomy, whose peaks precede the peak in cell proliferation observed at 3 days post-hepatectomy. The increase in both antioxidants was associated with higher expression of the enzymes involved in their synthesis, such as the modifier subunit of enzyme glutamine cysteine ligase (GCLM), glutathione synthetase (GS), gulonolactonase (GLN) and gulonolactone oxidase (GULO). Importantly, rat hepatocytes, that normally exhibit kinetic evidence indicating only SVCT1-mediated transport of AA, lost more than 90% of their capacity to transport it at day 1 after PHx without evidence of recovery at day 7. This observation was in agreement with loss of SVCT1 protein expression, which was undetectable in hepatocytes as early as 2h after PHx, with partial recovery at day 7, when the regenerated liver weight returns to normal. We conclude that after PHx, rat hepatocytes enhance their antioxidant capacity by increasing GSH and AA levels prior to the proliferative peak. GSH and AA are increased by de novo synthesis, however paradoxically hepatocytes from rat subjected to PHx also suppress their capacity to acquire AA from extracellular sources through SVCT1.

Imaging thiol redox status in murine tumors in vivo with rapid-scan electron paramagnetic resonance

Thiol redox status is an important physiologic parameter that affects the success or failure of cancer treatment. Rapid scan electron paramagnetic resonance (RS EPR) is a novel technique that has shown higher signal-to-noise ratio than conventional continuous-wave EPR in in vitro studies. Here we used RS EPR to acquire rapid three-dimensional images of the thiol redox status of tumors in living mice. This work presents, for the first time, in vivo RS EPR images of the kinetics of the reaction of 2H,15N-substituted disulfide-linked dinitroxide (PxSSPx) spin probe with intracellular glutathione. The cleavage rate is proportional to the intracellular glutathione concentration. Feasibility was demonstrated in a FSa fibrosarcoma tumor model in C3H mice. Similar to other in vivo and cell model studies, decreasing intracellular glutathione concentration by treating mice with l-buthionine sulfoximine (BSO) markedly altered the kinetic images.

Renal Tumor Necrosis Factor α Contributes to Hypertension in Dahl Salt-Sensitive Rats

Tumor necrosis factor α (TNFα) is a major proinflammatory cytokine and its level is elevated in hypertensive states. Inflammation occurs in the kidneys during the development of hypertension. We hypothesized that TNFα specifically in the kidney contributes to the development of hypertension and renal injury in Dahl salt-sensitive (SS) rats, a widely used model of human salt-sensitive hypertension and renal injury. SS rats were chronically instrumented for renal interstitial infusion and blood pressure measurement in conscious, freely moving state. Gene expression was measured using real-time PCR and renal injury assessed with histological analysis. The abundance of TNFα in the renal medulla of SS rats, but not the salt-insensitive congenic SS.13^BN26 rats, was significantly increased when rats had been fed a high-salt diet for 7 days (n = 6 or 9, p < 0.01). The abundance of TNFα receptors in the renal medulla was significantly higher in SS rats than SS.13^BN26 rats. Renal interstitial administration of Etanercept, an inhibitor of TNFα, significantly attenuated the development of hypertension in SS rats on a high-salt diet (n = 7–8, p < 0.05). Glomerulosclerosis and interstitial fibrosis were also significantly ameliorated. These findings indicate intrarenal TNFα contributes to the development of hypertension and renal injury in SS rats.

Disulfide-Linked Dinitroxides for Monitoring Cellular Thiol Redox Status through Electron Paramagnetic Resonance Spectroscopy

Intracellular thiol-disulfide redox balance is crucial to cell health, and may be a key determinant of a cancer's response to chemotherapy and radiation therapy. The ability to assess intracellular thiol-disulfide balance may thus be useful not only in predicting responsiveness of cancers to therapy, but in assessing predisposition to disease. Assays of thiols in biology have relied on colorimetry or fluorimetry, both of which require UV-visible photons, which do not penetrate the body. Low-frequency electron paramagnetic resonance imaging (EPRI) is an emerging magnetic imaging technique that uses radio waves, which penetrate the body well. Therefore, in combination with tailored imaging agents, EPRI affords the opportunity to image physiology within the body. In this study, we have prepared water-soluble and membrane-permeant disulfide-linked dinitroxides, at natural isotopic abundance, and with D,(15)N-substitution. Thiols such as glutathione cleave the disulfides, with simple bimolecular kinetics, to yield the monomeric nitroxide species, with distinctive changes in the EPR spectrum. Using the D,(15)N-substituted disulfide-dinitroxide and EPR spectroscopy, we have obtained quantitative estimates of accessible intracellular thiol in cultured human lymphocytes. Our estimates are in good agreement with published measurements. This suggests that in vivo EPRI of thiol-disulfide balance is feasible. Finally, we discuss the constraints on the design of probe molecules that would be useful for in vivo EPRI of thiol redox status.

Targeting of Gamma-Glutamyl-Cysteine Ligase by miR-433 Reduces Glutathione Biosynthesis and Promotes TGF-β-Dependent Fibrogenesis

AIMS

Glutathione (GSH) is the main antioxidant against cell damage. Several pathological states course with reduced nucleophilic tone and perturbation of redox homeostasis due to changes in the 2GSH/GSSG ratio. Here, we investigated the regulation of the rate-limiting GSH biosynthetic heterodimeric enzyme γ-glutamyl-cysteine ligase (GCL) by microRNAs (miRNAs).

RESULTS

"In silico" analysis of the 3'- untranslated regions (UTRs) of both catalytic (GCLc) and regulatory (GCLm) subunits of GCL enabled an identification of miR-433 as a strong candidate for the targeting of GCL. Transitory overexpression of miR-433 in human umbilical vein endothelial cells (HUVEC) showed a downregulation of both GCLc and GCLm in a nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-independent manner. Increases in pro-oxidant stimuli such as exposure to hydrogen peroxide or GSH depletion in endothelial and hepatic cells caused an expected increase in GCLc and GCLm protein expression and abrogation of miR-433 levels, thus supporting a cross-regulation of these pathways. Treatment of HUVEC with miR-433 resulted in reduced antioxidant and redox potentials, increased S-glutathionylation, and reduced endothelial nitric oxide synthase activation. In vivo models of renal and hepatic fibrosis were associated with transforming growth factor β1 (TGF-β1)-related reduction of GCLc and GCLm levels that were miR-433 dependent.

INNOVATION AND CONCLUSION

We describe for the first time an miRNA, miR-433, capable of directly targeting GCL and promoting functional consequences in endothelial physiology and fibrotic processes by decreasing GSH levels.

The protection mechanism of proline from D-galactosamine hepatitis involves the early activation of ROS-eliminating pathway in the liver

The oral pre-administration of proline, one on the non-essential amino acids, has been shown to effectively protect the liver from D-galactosamine (GalN)-induced liver injury and dramatically improve the survival rate. In the previous study, we reported that protective effect of proline involves the early activation of IL-6/STAT-3 pathway, an anti-inflammatory and regenerative signaling in the liver. Reactive oxygen species (ROS) are mediator of cellular injury and play an important role in hepatic damage during GalN-induced hepatitis. The aim of this study is to investigate the effect of proline on ROS-eliminating system. The activities of major ROS-detoxifying enzymes, i.e., glutathione peroxidase (GP), glutathione reductase (GR), catalase, and the level of glutathione in the liver were determined. Catalase activity was significantly upregulated in proline group from 0 to 3 h after GalN-injection, although GP and GR were downregulated during this period, compared with control group. From 6 to 12 h, the level of reduced glutathione (GSH) was significantly higher and the ratio of GSH/oxidized glutathione (GSSG) tended to be higher in proline group. Consistently with this, at 6 h, the GR activity in the proline group was significantly higher, followed with the higher tendency of GP activity at 12 h. Catalase activity was also significantly higher at 12 h. Taken together, catalase was activated at the beginning, followed with the significant activation of glutathione redox system around 6 to 12 h in proline group. These results suggest that the elimination of ROS in the liver was accelerated in proline group compared with control group at the very early stage of GalN-induced hepatitis.

The metabolic function of hepatocytes differentiated from human mesenchymal stem cells is inversely related to cellular glutathione levels

Differentiation of mesenchymal stem cells (MSCs) to hepatocytes-like cells is associated with alteration in the level of reactive oxygen species (ROS) and antioxidant defense system. Here, we report the role of glutathione in the functions of hepatocytes derived from MSCs. The stem cells undergoing differentiation were treated with glutathione modifiers [buthionine sulfoxide (BSO) or N-acetyl cysteine (NAC)], and hepatocytes were collected on day 14 of differentiation and analysed for their biological and metabolic functions. Differentiation process has been performed in presence of glutathione modifiers viz. BSO and NAC. Depending on the level of cellular glutathione, the proliferation rate of MSCs was affected. Glutathione depletion by BSO resulted in increased levels of albumin and ROS in hepatocytes. Whereas, albumin and ROS were inhibited in cells treated with glutathione precursor (NAC). The metabolic function of hepatocytes was elevated in BSO-treated cells as judged by increased urea, transferrin, albumin, alanine transaminase and aspartate transaminase secretions in the media. However, the metabolic activity of the hepatocytes was inhibited when glutathione was increased by NAC. We conclude that the efficiency of metabolic function of hepatocytes is inversely related to the levels of cellular glutathione. These data may suggest a novel role of glutathione in regulation of metabolic function of hepatocytes.

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.

Significance of alterations in the metabolomics of sulfur-containing amino acids during liver regeneration

It has been known that liver regeneration is accompanied with a profound change in the metabolomics of sulfur-containing substances in liver. However, its physiological significance in the liver regenerative process is still unclear. Our previous work showed that buthioninesulfoximine and phorone, both widely used to deplete intracellular glutathione (GSH) in biological experiments, induced contrasting changes in the sulfur-containing amino acid metabolism in liver. In this study we employed these GSH-depleting agents to evaluate the role of sulfur-containing substances in the early phase of liver regeneration. Male rats treated with buthioninesulfoximine or phorone were subjected to two-thirds partial hepatectomy (PHx). At the doses used, the magnitude of GSH depletion after PHx was comparable, but buthioninesulfoximine administration inhibited the progression of liver regeneration as determined by liver weight increase, elevation of serum alanine aminotransferase activity, and cyclin D1 and proliferating cell nuclear antigen (PCNA) protein expressions, whereas liver recovery was significantly accelerated in the phorone-treated rats, suggesting that the role of GSH in this process is minimal. Hepatic concentrations of methionine, S-adenosylmethionine, cysteine, taurine and GSH were all elevated by PHx. Methionine adenosyltransferase activity was also induced in the remnant liver. Buthioninesulfoximine administration depressed the elevation of S-adenosylmethionine, but increased the catabolism of cysteine to taurine. In contrast, S-adenosylmethionine elevation was augmented whereas cysteine, hypotaurine and taurine were decreased in the phorone-treated rats. PHx elevated hepatic putrescine and spermidine, but lowered spermine concentrations. Buthioninesulfoximine administration increased putrescine further, but decreased spermidine and spermine concentrations. On the contrary, both spermidine and spermine concentrations were elevated in the rats treated with phorone. The results suggest that the availability of S-adenosylmethionine plays a critical role in the progression of liver regeneration via enhancement of polyamine synthesis. These findings raise the possibility that regulating hepatic transsulfuration reactions may be capable of modifying the recovery process after liver injury.

Glutathione synthesis

BACKGROUND

Glutathione (GSH) is present in all mammalian tissues as the most abundant non-protein thiol that defends against oxidative stress. GSH is also a key determinant of redox signaling, vital in detoxification of xenobiotics, and regulates cell proliferation, apoptosis, immune function, and fibrogenesis. Biosynthesis of GSH occurs in the cytosol in a tightly regulated manner. Key determinants of GSH synthesis are the availability of the sulfur amino acid precursor, cysteine, and the activity of the rate-limiting enzyme, glutamate cysteine ligase (GCL), which is composed of a catalytic (GCLC) and a modifier (GCLM) subunit. The second enzyme of GSH synthesis is GSH synthetase (GS).

SCOPE OF REVIEW

This review summarizes key functions of GSH and focuses on factors that regulate the biosynthesis of GSH, including pathological conditions where GSH synthesis is dysregulated.

MAJOR CONCLUSIONS

GCL subunits and GS are regulated at multiple levels and often in a coordinated manner. Key transcription factors that regulate the expression of these genes include NF-E2 related factor 2 (Nrf2) via the antioxidant response element (ARE), AP-1, and nuclear factor kappa B (NFκB). There is increasing evidence that dysregulation of GSH synthesis contributes to the pathogenesis of many pathological conditions. These include diabetes mellitus, pulmonary and liver fibrosis, alcoholic liver disease, cholestatic liver injury, endotoxemia and drug-resistant tumor cells.

GENERAL SIGNIFICANCE

GSH is a key antioxidant that also modulates diverse cellular processes. A better understanding of how its synthesis is regulated and dysregulated in disease states may lead to improvement in the treatment of these disorders. This article is part of a Special Issue entitled Cellular functions of glutathione.

Metabolomic analysis of sulfur-containing substances and polyamines in regenerating rat liver

We studied the significance of alterations in the metabolomics of sulfur-containing substances in rapidly regenerating rat livers. Male rats were subjected to two-thirds partial hepatectomy (PHx), and the changes in hepatic levels of major sulfur-containing amino acids and related substances were monitored for 2 weeks. Liver weight began to increase from 24 h after the surgery, and appeared to recover fully in 2 weeks. Serum alanine aminotransferase and aspartate aminotransferase activities were elevated immediately after the surgery and returned slowly to normal levels in 2 weeks. Methionine, S-adenosylmethionine (SAM), cystathionine and cysteine were increased rapidly and remained elevated for longer than 1 week. Hepatic glutathione concentration was increased gradually for 24 h, and then decreased thereafter, whereas hypotaurine was elevated drastically right after the surgery. Hepatic concentrations of polyamines were altered significantly by PHx. In the hepatectomized livers putrescine concentration was elevated rapidly, reaching a level 40- to 50-fold greater than normal in 6-12 h. Ornithine, the metabolic substrate for putrescine synthesis, was also elevated markedly. Spermidine was increased significantly, whereas spermine was depressed below normal, which appeared to be due to the increased consumption of decarboxylated SAM for spermidine biosynthesis. The results show that the metabolomics of sulfur-containing amino acids and related substances is altered profoundly in regenerating rat livers until the original weight is recovered. Hepatic concentrations of polyamines after PHx are closely associated with the alteration in the metabolomics of sulfur-containing substances. The implication of these changes in the progression of liver regeneration is discussed.

The relationship between cisplatin-induced reactive oxygen species, glutathione, and BCL-2 and resistance to cisplatin

Cisplatin (cDDP) is an anticancer agent that is widely used in the treatment of many solid tumors. A major obstacle to successful cDDP-based chemotherapy, however, is the intrinsic and acquired resistance of tumor cells to this drug. Greater insight into the molecular mechanisms underlying the modulation of cellular responses to cDDP will aid in the development and optimization of new therapeutic strategies. Apart from induction of DNA damage, recent data have suggested that cDDP also induces the formation of reactive oxygen species that can trigger cell death. Cell death occurs as the result of several simultaneously activated signaling pathways. The specific pathway responsible for cell death depends on the cell type and the treatment conditions. This review focuses on the relationship between glutathione and BCL-2 and their protective role in cDDP-induced reactive oxygen species formation and cDDP resistance.

Glutathione in Cancer Biology and Therapy

The glutathione (GSH) content of cancer cells is particularly relevant in regulating mutagenic mechanisms, DNA synthesis, growth, and multidrug and radiation resistance. In malignant tumors, as compared with normal tissues, that resistance associates in most cases with higher GSH levels within these cancer cells. Thus, approaches to cancer treatment based on modulation of GSH should control possible growth-associated changes in GSH content and synthesis in these cells. Despite the potential benefits for cancer therapy of a selective GSH-depleting strategy, such a methodology has remained elusive up to now. Metastatic spread, not primary tumor burden, is the leading cause of cancer death. For patient prognosis to improve, new systemic therapies capable of effectively inhibiting the outgrowth of seeded tumor cells are needed. Interaction of metastatic cells with the vascular endothelium activates local release of proinflammatory cytokines, which act as signals promoting cancer cell adhesion, extravasation, and proliferation. Recent work shows that a high percentage of metastatic cells with high GSH levels survive the combined nitrosative and oxidative stresses elicited by the vascular endothelium and possibly by macrophages and granulocytes. ?-Glutamyl transpeptidase overexpression and an inter-organ flow of GSH (where the liver plays a central role), by increasing cysteine availability for tumor GSH synthesis, function in combination as a metastatic-growth promoting mechanism. The present review focuses on an analysis of links among GSH, adaptive responses to stress, molecular mechanisms of invasive cancer cell survival and death, and sensitization of metastatic cells to therapy. Experimental evidence shows that acceleration of GSH efflux facilitates selective GSH depletion in metastatic cells.

Regulation of glutathione synthesis

Glutathione (GSH) is a ubiquitous intracellular peptide with diverse functions that include detoxification, antioxidant defense, maintenance of thiol status, and modulation of cell proliferation. GSH is synthesized in the cytosol of all mammalian cells in a tightly regulated manner. The major determinants of GSH synthesis are the availability of cysteine, the sulfur amino acid precursor, and the activity of the rate-limiting enzyme, glutamate cysteine ligase (GCL). GCL is composed for a catalytic (GCLC) and modifier (GCLM) subunit and they are regulated at multiple levels and at times differentially. The second enzyme of GSH synthesis, GSH synthase (GS) is also regulated in a coordinated manner as GCL subunits and its up-regulation can further enhance the capacity of the cell to synthesize GSH. Oxidative stress is well known to induce the expression of GSH synthetic enzymes. Key transcription factors identified thus far include Nrf2/Nrf1 via the antioxidant response element (ARE), activator protein-1 (AP-1) and nuclear factor kappa B (NFkappaB). Dysregulation of GSH synthesis is increasingly being recognized as contributing to the pathogenesis of many pathological conditions. These include diabetes mellitus, pulmonary fibrosis, cholestatic liver injury, endotoxemia and drug-resistant tumor cells. Manipulation of the GSH synthetic capacity is an important target in the treatment of many of these disorders.

Effects of hepatocyte growth factor on glutathione synthesis, growth, and apoptosis is cell density-dependent

Hepatocyte growth factor (HGF) is a potent hepatocyte mitogen that exerts opposing effects depending on cell density. Glutathione (GSH) is the main non-protein thiol in mammalian cells that modulates growth and apoptosis. We previously showed that GSH level is inversely related to cell density of hepatocytes and is positively related to growth. Our current work examined whether HGF can modulate GSH synthesis in a cell density-dependent manner and how GSH in turn influence HGF's effects. We found HGF treatment of H4IIE cells increased cell GSH levels only under subconfluent density. The increase in cell GSH under low density was due to increased transcription of GSH synthetic enzymes. This correlated with increased protein levels and nuclear binding activities of c-Jun, c-Fos, p65, p50, Nrf1 and Nrf2 to the promoter region of these genes. HGF acts as a mitogen in H4IIE cells under low cell density and protects against tumor necrosis factor alpha (TNFalpha)-induced apoptosis by limiting JNK activation. However, HGF is pro-apoptotic under high cell density and exacerbates TNFalpha-induced apoptosis by potentiating JNK activation. The increase in cell GSH under low cell density allows HGF to exert its full mitogenic effect but is not necessary for its anti-apoptotic effect.

Effect of hepatocyte growth factor on methionine adenosyltransferase genes and growth is cell density-dependent in HepG2 cells

Hepatocyte growth factor (HGF) is a potent hepatocyte mitogen but its effect in liver cancer is conflicting. Methionine adenosyltransferase (MAT) is an essential enzyme encoded by two genes (MAT1A and MAT2A), while a third gene (MAT2beta) encodes for a subunit that regulates the MAT2A-encoded isoenzyme. MAT1A is silenced while MAT2A and MAT2beta are induced in hepatocellular carcinoma (HCC). The current work examined expression of HGF/c-met in HCC and whether HGF regulates MAT genes and growth in HepG2 cells. We found the mRNA levels of HGF and c-met are markedly increased in HCC. To study the influence of cell density, HepG2 cells were plated under high-density (HD) or low-density (LD) and treated with HGF (10 ng/ml). Cell density had a dramatic effect on MAT1A expression, being nearly undetectable at LD to a ninefold induction under HD. Cell density also determined the effect of HGF. At HD, HGF increased the mRNA levels of p21 and p27, while lowering the levels of MAT genes, cyclin A, and c-met. At LD, HGF increased the mRNA levels of cyclin A, MAT2A, MAT2beta, and c-met. Consistently, HGF inhibits growth under HD but stimulates growth under LD. HGF induced sustained high ERK activation under HD as compared to LD. In summary, HGF induces genes favoring growth and is mitogenic when HepG2 cells are plated under LD; however, the opposite occurs under HD. This involves cell density-dependent differences in HGF-induced ERK activation. This may explain why HGF is mitogenic only when there is loss of cell-cell contact in vivo.

Tumour necrosis factor alpha induces co-ordinated activation of rat GSH synthetic enzymes via nuclear factor kappaB and activator protein-1

GSH synthesis occurs via two enzymatic steps catalysed by GCL [glutamate-cysteine ligase, made up of GCLC (GCL catalytic subunit), and GCLM (GCL modifier subunit)] and GSS (GSH synthetase). Co-ordinated up-regulation of GCL and GSS further enhances GSH synthetic capacity. The present study examined whether TNFalpha (tumour necrosis factor alpha) influences the expression of rat GSH synthetic enzymes. To facilitate transcriptional studies of the rat GCLM, we cloned its 1.8 kb 5'-flanking region. TNFalpha induces the expression and recombinant promoter activities of GCLC, GCLM and GSS in H4IIE cells. TNFalpha induces NF-kappaB (nuclear factor kappaB) and AP-1 (activator protein 1) nuclear-binding activities. Blocking AP-1 with dominant negative c-Jun or NF-kappaB with IkappaBSR (IkappaB super-repressor, where IkappaB stands for inhibitory kappaB) lowered basal expression and inhibited the TNFalpha-mediated increase in mRNA levels of all three genes. While all three genes have multiple AP-1-binding sites, only GCLC has a NF-kappaB-binding site. Overexpression with p50 or p65 increased c-Jun mRNA levels, c-Jun-dependent promoter activity and the promoter activity of GCLM and GSS. Blocking NF-kappaB also lowered basal c-Jun expression and blunted the TNFalpha-mediated increase in c-Jun mRNA levels. TNFalpha treatment resulted in increased c-Jun and Nrf2 (nuclear factor erythroid 2-related factor 2) nuclear binding to the antioxidant response element of the rat GCLM and if this was prevented, TNFalpha no longer induced the GCLM promoter activity. In conclusion, both c-Jun and NF-kappaB are required for basal and TNFalpha-mediated induction of GSH synthetic enzymes in H4IIE cells. While NF-kappaB may exert a direct effect on the GCLC promoter, it induces the GCLM and GSS promoters indirectly via c-Jun.

Nitric oxide-induced resistance to hydrogen peroxide stress is a glutamate cysteine ligase activity-dependent process

Nitric oxide (*NO) is a reactive nitrogen species known to be involved in cytotoxic processes. Cells respond to cytotoxic injury by stress response induction leading to the development of cellular resistance. This report describes an *NO-induced stress response in Chinese hamster fibroblasts (HA1), which leads to glutathione synthesis-dependent resistance to H2O2-mediated oxidative stress. The development of resistance to H2O2 was completely abolished by the inhibition of glutamate cysteine ligase (GCL) during the first 8 h of recovery after *NO exposure. Altered thiol metabolism was observed immediately after *NO exposure as demonstrated by up to 75% decrease in intracellular thiol pools (glutathione, gamma-glutamylcysteine, and cysteine), which then reaccumulated during the *NO-mediated development of resistance. Immunoreactive protein and activity associated with GCL decreased immediately after exposure to *NO and then reaccumulated during the development of resistance to H2O2 challenge. Moreover, compared to N2 controls the activity levels of GCL in *NO-exposed cells increased approximately twofold 24 h after H2O2 challenge. These results demonstrate that *NO exposure is capable of inducing an adaptive response to H2O2-mediated oxidative stress in mammalian cells, which involves alterations in thiol metabolism and is dependent upon glutathione synthesis and increased GCL activity.

Effects of TVE application during 70% hepatectomy on regeneration capacity of rats1

BACKGROUND

For adequate control of excess bleeding during liver resection, total vascular exclusion (TVE) is preferred by surgeons, especially when the tumor is located in the posterior liver lobes or near the cava. To the authors' knowledge, the effects of TVE technique on the postoperative liver regeneration process have not thus far been evaluated yet in the literature. This study was planned to compare the effects of liver resections performed either with portal pedicle clamping or with TVE on the regeneration process.

MATERIALS AND METHODS

Seventy percent hepatectomy was performed with portal pedicle clamping (n=10, Group A) or with TVE (n=10, Group B) in rats. At 48 h after resection, sampling was performed for the measurement of serum transaminase, alkaline phosphatase (ALP), tissue malondialdehyde (MDA), and glutathione (GSH) levels. Liver regeneration rate, proliferating cell nuclear antigen (PCNA) labeling, and mitotic indices were also evaluated.

RESULTS

Liver injury determinants (serum transaminases, ALP, and tissue MDA levels) were found significantly higher in group B than in group A. Liver regeneration rate, liver GSH levels, PCNA labeling index, and mitotic index were significantly lower in group B than in group A.

CONCLUSIONS

The injury during TVE seems to be greater than during resection with portal pedicle clamping. The negative effect of this oxidative damage may influence the regenerative capacity of the remnant liver tissue.

Increased expression of 19-kD interacting protein-3-like protein and the relationship to apoptosis in the lung of rats with severe acute pancreatitis

OBJECTIVE

The aim of the present study was to determine the underlying cellular mechanisms in the pancreas after acute pancreatitis and to study the pathogenesis of pancreatitis-associated lung injury. We applied a differential display analysis to normal pancreas and to the pancreas with acute pancreatitis in rats, and we examined the expression of the identified gene in the lung as well as the pancreas after acute pancreatitis.

DESIGN

Controlled animal study.

SETTING

Research laboratory of an academic institution.

SUBJECTS

Ninety male Wistar rats.

INVESTIGATIONS

Pancreatitis was induced by retrograde intraductal infusion of 4% sodium taurocholate (100 microL/100 g of body weight). Data were compared with data from controls (sham).

MEASUREMENTS AND MAIN RESULTS

We cloned some expressed sequence tags and identified one complementary DNA fragment. The deduced protein was a polypeptide of 218 amino acids, which was almost identical to human 19-kD interacting protein-3-like (NIP3L) protein. The expression of rat NIP3L identified in this study increased slightly in the pancreas after induction of acute pancreatitis but showed a marked increase in the lung by both Northern and Western blot analysis. NIP3L immunoreactivity was noted in alveolar and epithelial cells of the control (sham) lung, and the immunoreactivity in these cells was elevated after induction of acute pancreatitis. Moreover, acute pancreatitis increased terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive alveolar and bronchiolar cells in the lung.

CONCLUSION

NIP3L may be involved in lung injury, which is one of the major causes of death in cases of severe acute pancreatitis.

Effect of increasing selenite concentrations, vitamin E supplementation and different fetal calf serum content on GPx1 activity in primary cultured rabbit hepatocytes

Primary rabbit hepatocytes from 6 week old female New Zealand White rabbits (3.0 x 10(6) viable hepatocytes per treatment) were incubated for 24 h or 48 h with two basic variants of the selenium and vitamin E free DMEM/F12-HAM nutrition medium containing 2.5% or 10% fetal calf serum (FCS). Selenium and vitamin E concentrations of the media were varied by the addition of 0, 10, 50 and 100 ng Se/mL medium as sodium selenite and 100 microg alpha-tocopheryl acetate/mL. Lactic dehydrogenase (LDH) leakage of the hepatocytes was not influenced by the various selenium concentrations of the media, whereas vitamin E addition significantly inhibited LDH release. The activity of cellular glutathione peroxidase (GPx1) was markedly induced by increasing the selenium supplementation of the culture media. Vitamin E supply further enhanced GPx1 induction. In hepatocytes cultivated at the lower serum concentration (2.5% FCS), increasing the selenite concentration of the media raised GPx1 and reduced the intracellular levels of the reduced tripeptide glutathione (GSH). No vectored relation between the selenium concentration of the media and the activity of superoxide dismutase (SOD) could be observed. After both incubation periods (24 h and 48 h) SOD activity was significantly higher in the cytosol of hepatocytes grown in media containing 10% FCS as compared to cells incubated at the 2.5% FCS level. Furthermore, SOD activity was reduced by the addition of vitamin E to the media. In conclusion the results indicate an effective metabolism of rabbit hepatocytes for selenite even in amounts as low as nanograms. A general cytoprotective role for vitamin E can be shown by its ability to decrease LDH leakage and by the reduction of SOD activity.

Glutathione and thioredoxin redox during differentiation in human colon epithelial (Caco-2) cells

Cellular redox, maintained by the glutathione (GSH)- and thioredoxin (Trx)-dependent systems, has been implicated in the regulation of a variety of biological processes. The redox state of the GSH system becomes oxidized when cells are induced to differentiate by chemical agents. The aim of this study was to determine the redox state of cellular GSH/glutathione disulfide (GSH/GSSG) and Trx as a consequence of progression from proliferation to contact inhibition and spontaneous differentiation in colon carcinoma (Caco-2) cells. Results showed a significant decrease in GSH concentration, accompanied by a 40-mV oxidation of the cellular GSH/GSSG redox state and a 28-mV oxidation of the extracellular cysteine/cystine redox state in association with confluency and increase in differentiation markers. The redox state of Trx did not change. Thus the two central cellular antioxidant and redox-regulating systems (GSH and Trx) were independently controlled. According to the Nernst equation, a 30-mV oxidation is associated with a 10-fold change in the reduced/oxidized ratio of a redox-sensitive dithiol motif. Therefore, the measured 40-mV oxidation of the cellular GSH/GSSG couple or the 28-mV oxidation of the extracellular cysteine/cystine couple should be sufficient to function in signaling or regulation of differentiation in Caco-2 cells.

Regulation of carbachol-induced c-fos mRNA expression in AR42J cells by somatostatin receptor subtypes 1, 2, and 3

INTRODUCTION

Somatostatin is an inhibitory peptide that exerts its effects tissue-specifically by activating one or more of five receptors (SSTR 1-5). Although several studies have examined which SSTR subtypes control gastrointestinal function, effects of somatostatin on pancreatic gene expression are not well defined.

AIM

To examine the effects of somatostatin and newly synthesized selective SSTR agonists on the cholinergically stimulated expression of the immediate early response gene

METHODOLOGY AND RESULTS

In pancreatic acinar AR42J cells, polymerase chain reaction analysis revealed that mRNAs for SSTR 1, 2, and 3 were expressed. SSTR 4 and 5 were not detected. When AR42J cells were exposed to the cholinergic agonist carbachol in the presence of somatostatin or selective SSTR agonists, significant and dose-dependent reductions in agonist-induced levels of mRNA were noted. Pretreatment with agonists specific for SSTR 4 or 5 had no inhibitory effects. The inhibitory actions of somatostatin were pertussis toxin-sensitive. In addition, since somatostatin did not affect intracellular calcium homeostasis, the inhibitory actions of somatostatin are independent of calcium signaling.

CONCLUSION

The current studies demonstrate that somatostatin inhibits carbachol-induced increases in expression by interacting with somatostatin receptor subtypes 1, 2, and 3. In addition, because somatostatin did not affect intracellular calcium homeostasis, it can be concluded that SSTR actions are independent of carbachol-stimulated calcium signaling.

Cloning and characterization of the 5'-flanking region of the rat glutamate-cysteine ligase catalytic subunit

Glutamate-cysteine ligase (GCL), the rate-limiting enzyme in glutathione synthesis, is made up of two subunits, a catalytic (heavy) subunit (GCLC) and a modifier (light) subunit (GCLM), which are differentially regulated. Increased hepatic GCLC expression occurs during rapid growth, oxidative stress and after ethanol treatment. To facilitate studies of GCLC transcriptional regulation, we have cloned and characterized a 1.8 kb 5'-flanking region of the rat GCLC (GenBank accession number AF218362). A consensus TATA box and one transcriptional start site are located at 302 and 197 nucleotides upstream of the translational start site, respectively. The promoter contains consensus binding sites for many transcription factors including nuclear factor kappaB (NF-kappaB) and activator protein 1 (AP-1). The rat GCLC promoter was able to efficiently drive luciferase expression in H4IIE cells. Sequential deletion analysis revealed that three DNA regions, -595 to -111, -1108 to -705 and -705 to -595, are involved in positive (the first two regions) and negative (the latter region) gene regulation. Specific protein binding to these regions was confirmed by DNase I footprinting and electrophoretic mobility-shift assays (EMSAs). Ethanol-fed livers exhibit increased protein binding to region -416 to -336 on DNase I footprinting analysis, which was found to be NF-kappaB and AP-1 on EMSA and supershift analysis. Acetaldehyde treatment of H4IIE cells led to a time- and dose-dependent increase in GCLC mRNA levels, binding of NF-kappaB and AP-1 to the GCLC promoter, and luciferase activity driven by the GCLC promoter fragment containing these binding sites.

The biological lifetime of nitric oxide: Implications for the perivascular dynamics of NO and O2

Endothelial nitric oxide (nitrogen monoxide) is synthesized at the intravascular/extravascular interface. We previously have reported the intravascular half-life of NO, as a result of consumption by erythrocytes, as approximately 2 ms. We report here studies designed to estimate the lifetime of NO in the parenchymal (extravascular) tissue and describe the implications of these results for the distribution of NO and oxygen concentration gradients away from the blood vessel. The rate of consumption of NO by parenchymal cells (hepatocytes) linearly depends on both NO and O(2) concentration. We estimate that the extravascular half-life of NO will range from 0.09 to > 2 s, depending on O2 concentration and thus distance from the vessel. Computer modeling reveals that this phenomenon, coupled with reversible NO inhibition of cellular mitochondrial oxygen consumption, substantially extends the zone of adequate tissue cellular oxygenation away from the blood vessel, with an especially dramatic effect during conditions of increased tissue work (oxygen consumption). This represents a second action of NO, in addition to vasodilation, in enhancing tissue cellular respiration and provides a possible physiological function for the known reversible inhibition of mitochondrial respiration by low concentrations of NO.

The biological lifetime of nitric oxide: implications for the perivascular dynamics of NO and O2

Endothelial nitric oxide (nitrogen monoxide) is synthesized at the intravascular/extravascular interface. We previously have reported the intravascular half-life of NO, as a result of consumption by erythrocytes, as approximately 2 ms. We report here studies designed to estimate the lifetime of NO in the parenchymal (extravascular) tissue and describe the implications of these results for the distribution of NO and oxygen concentration gradients away from the blood vessel. The rate of consumption of NO by parenchymal cells (hepatocytes) linearly depends on both NO and O(2) concentration. We estimate that the extravascular half-life of NO will range from 0.09 to > 2 s, depending on O2 concentration and thus distance from the vessel. Computer modeling reveals that this phenomenon, coupled with reversible NO inhibition of cellular mitochondrial oxygen consumption, substantially extends the zone of adequate tissue cellular oxygenation away from the blood vessel, with an especially dramatic effect during conditions of increased tissue work (oxygen consumption). This represents a second action of NO, in addition to vasodilation, in enhancing tissue cellular respiration and provides a possible physiological function for the known reversible inhibition of mitochondrial respiration by low concentrations of NO.

Mechanism and significance of increased glutathione level in human hepatocellular carcinoma and liver regeneration

Increased glutathione (GSH) level occurs early during liver regeneration and in many drug and/or radiation-resistant tumors. Whether GSH level is elevated in liver cancer is unknown. GSH levels and expression of GSH synthetic enzymes were measured in hepatocellular carcinoma (HCC) and normal liver. GSH levels doubled in HCC. The mRNA levels of g-glutamylcysteine synthetase heavy subunit (GCS-HS) and GSH synthetase (GS) doubled, whereas the expression of GCS light subunit was unchanged. Nuclear run-on assay showed that the rate of gene transcription doubled for both GCS-HS and GS. In HCC, there is increased binding to anti-oxidant response, AP-1 and NF-kB, three cis-acting elements in the 5'-flanking region of the human GCS-HS important for its transcriptional regulation. The role of GSH in cell growth was examined by using HepG2 cells. Cell GSH level was varied by treating cells with cystine (0 to 0.2 mM) with or without GSH ester or buthionine sulfoximine. Cell GSH level correlated directly with growth rate. Finally, preventing the increase in GSH after two-thirds partial hepatectomy blunted liver regeneration. Thus, GSH level is increased during liver growth as a result of up-regulation of GCS-HS and GS. This increase, in turn, facilitates growth.

Cholecystokinin does not affect the pancreatic contents of epidermal growth factor or its receptor

Cholecystokinin (CCK) is a hormone with well-known secretory and trophic effects on the pancreas. This also is true for epidermal growth factor (EGF), which acts in a paracrine and autocrine way. The aim was to study the influence of CCK on cell proliferation in rat pancreas with special reference to the expression of EGF, the EGF receptor, and phosphorylated tyrosine. Twenty-four male Sprague-Dawley rats received either one single injection, or injections twice daily for 3 days of 6 microg sulfated CCK-8 (CCK-8S) subcutaneously in the neck. The same number of rats received injections of 1% bovine serum albumin (BSA) in the same way. The rats were killed 1, 3, or 6 hours after the last injection. One hour before killing, they received 50 mg/kg of bromodeoxyuridine (BrdU) intraperitoneally. Plasma was collected for analysis of CCK. The pancreas was dissected, and in situ hybridization using a probe for EGF mRNA was performed for semiquantification of gene expression. Immunocytochemistry using antibodies against the EGF receptor and phosphotyrosine was performed to examine the expression of the proteins, and against BrdU for measuring the cell proliferation. A single injection of CCK-8S led to hyperCCKemia at 1 and 3 hours afterward. After 6 hours, plasma CCK had returned to the same levels as in control rats. The cell proliferation was unaffected. The rats that received CCK-8S injections for 3 days still had hyperCCKemia 6 hours after the last injection. The cell proliferation was increased by CCK, as indicated by the BrdU labeling. However, neither body weight nor pancreatic weight was affected. In controls, EGF was expressed all over the gland, but its receptor and phosphotyrosine were expressed only in ductal cells and in the islet cells of endocrine pancreas. There was no difference in the pancreatic staining of EGF, its receptor, or phosphotyrosine at the different time points studied. There was no difference in the staining of EGF and its receptor between CCK-8S- and BSA-treated animals, but phosphotyrosine staining was detectable in acinar cells after 3 days of CCK-8S injections. Thus CCK-8S causes hyperCCKemia with ensuing enhanced cell proliferation in rat pancreas. This effect on the cell proliferation seems to be a direct effect of CCK and not mediated by changes in the tissue levels of EGF or its receptor.

Renal cyclic 3',5'-guanosine monophosphate and sodium excretion in Dahl salt-resistant and Dahl salt-sensitive rats: comparison of the roles of bradykinin and nitric oxide

OBJECTIVE

The purpose of this study was to determine the relative importance of bradykinin and nitric oxide (NO) in mediating renal responses to altered sodium intake in Dahl salt-resistant (Dahl-SR) and salt-sensitive (Dahl-SS) rats.

DESIGN AND METHODS

Dahl-SR and Dahl-SS rats consumed a diet containing 0.15% (low) or 4.0% (high) sodium chloride for 10 days. A microdialysis technique was then used to measure renal cortical interstitial fluid (RIF) cyclic 3',5'-guanosine monophosphate (cGMP) production in anesthetized rats, under baseline conditions and during acute cortical infusion of either the bradykinin B2 receptor antagonist icatibant or the NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME). Urine sodium excretion was monitored simultaneously by ureter cannulation. Results Baseline sodium excretion was similar in the two types of rats, but RIF cGMP was significantly elevated in Dahl-SR compared to Dahl-SS rats on both low and high sodium diets. Icatibant infusion significantly reduced both RIF cGMP and sodium excretion in Dahl-SR rats during low sodium intake, but had no effect in Dahl-SS rats on either diet L-NAME infusion significantly reduced sodium excretion in Dahl-SR and Dahl-SS rats, during both low and high sodium intake. L-NAME infusion caused a significant reduction in RIF cGMP in Dahl-SR and Dahl-SS rats on low sodium diet, but reduced RIF cGMP only in Dahl-SR rats on high sodium diet. Conclusion These data suggest a potential role for cortical bradykinin, but not NO, in mediating the differences in the renal response to low sodium intake between Dahl-SR and Dahl-SS rats.

Growth-associated changes in glutathione content correlate with liver metastatic activity of B16 melanoma cells

B16 melanoma (B16M) was used to study the relationship between glutathione (GSH) metabolism and the metastatic activity of malignant cells. GSH content increased in B16M cells during the initial period of exponential growth in vitro, to reach a maximum of 37 +/- 3 nmol/10(6) cells 12 h after plating, and then gradually decreased to control values (10 +/- 2 nmol/10(6) cells) when cultures approached confluency. On the contrary, glutathione disulphide (GSSG) levels (0.5 +/- 0.2 nmol/10(6) cells) and the rate of glutathione efflux (GSH + GSSG) (2.5 +/- 0.4 nmol/10(6) cells per h) remained constant as B16M grew. Changes in enzyme activities involved in GSH synthesis or the glutathione redox cycle did not explain shifts in the glutathione status (GSH/GSSG). However, two facts contributed to explain why GSH levels changed within B16M cells: a) high intracellular levels of GSH induced a feed-back inhibition of its own synthesis in B16M cells from cultures with low cellular density (LD cells); b) transport of cyst(e)ine, whose availability is the major rate-limiting step for GSH synthesis, was limited by cell-cell contact in cultures with high cellular density (HD cells). Intrasplenic injection of B16M cells with high GSH content (exponentially-growing cultures) showed higher metastatic activity in the liver than cells with low GSH content (cells at confluency). However, when low GSH-content cells (HD cells) were incubated in the presence of GSH ester, which rapidly enters the cell and delivers free GSH, their metastatic activity significantly increased. Our results demonstrate that changes in GSH content regulate the metastatic behaviour of B16M cells.

Modulation of glutathione synthetic enzymes by acidic fibroblast growth factor

Increasing evidence suggests that glutathione (GSH) synthesis is a regulated process. Documented increases in gamma-glutamylcysteine synthetase (GCS) occur in response to oxidants, in tumors, on plating cells at a low cell density, and with nerve growth factor stimulation, suggesting that GSH synthesis may be related to the cell growth and transformation. Previously, extracellular acidic fibroblast growth factor (FGF-1) has been demonstrated to cause transformation and aggressive cell growth in murine embryonic fibroblasts. In the present investigation, we sought to determine whether FGF-1, with its growth inducing properties, resulted in the modulation of GSH biosynthetic enzymes, GCS and GSH synthetase. Murine fibroblasts transduced with (hst/KS)FGF-1, a chimeric human FGF-1 gene containing a signal peptide sequence for secretion, displayed elevated gene expression of both heavy and light subunits of GCS. Activity of GSH synthetase was also elevated in these cells compared with control cells. Nonetheless, GSH was decreased in the FGF-1-transduced cells along with high energy phosphates, adenine nucleotides, NADH, and the redox poise. However, GSSG was not elevated in these cells. Fibroblasts stably expressing human immunodeficiency virus type 1 Tat, which induces intrinsic FGF-1 secretion, resulted in similar changes in GCS, GS, and GSH. The results suggest that although increases in the enzymes of GSH synthesis are a common response to growth factors, an increase in GSH content per se is not required for altered cell growth.

Heparin-binding EGF-like growth factor contributes to reduced glomerular filtration rate during glomerulonephritis in rats

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a member of the epidermal growth factor (EGF) family, is expressed during inflammatory and pathological conditions. We have cloned the rat HB-EGF and followed the expression of HB-EGF in rat kidneys treated with anti- glomerular basement membrane (anti-GBM) antibody (Ab) to induce glomerulonephritis (GN). We observed glomerular HB-EGF mRNA and protein within 30 minutes of Ab administration and showed by in situ hybridization that glomerular HB-EGF mRNA expression was predominantly in mesangial and epithelial cells. Expression of HB-EGF correlated with the onset of decreased renal function in this model. To test the direct effect of HB-EGF on renal function, we infused the renal cortex with active rHB-EGF, prepared from transfected Drosophila melanogaster cells. This treatment induced a significant decrease in single nephron GFR (SNGFR), single nephron plasma flow, and glomerular ultrafiltration coefficient and an increase in the glomerular capillary hydrostatic pressure gradient. In addition, anti-HB-EGF Ab administered just before anti-GBM Ab blocked the fall in SNGFR and GFR at 90 minutes without any change in the glomerular histologic response. These studies suggest that HB-EGF expressed early in the anti-GBM Ab GN model contributes to the observed acute glomerular hemodynamic alterations.

Glutathione redox potential in response to differentiation and enzyme inducers

The reduced glutathione (GSH)/oxidized glutathione (GSSG) redox state is thought to function in signaling of detoxification gene expression, but also appears to be tightly regulated in cells under normal conditions. Thus it is not clear that the magnitude of change in response to physiologic stimuli is sufficient for a role in redox signaling under nontoxicologic conditions. The purpose of this study was to determine the change in 2GSH/GSSG redox during signaling of differentiation and increased detoxification enzyme activity in HT29 cells. We measured GSH, GSSG, cell volume, and cell pH, and we used the Nernst equation to determine the changes in redox potential Eh of the 2GSH/GSSG pool in response to the differentiating agent, sodium butyrate, and the detoxification enzyme inducer, benzyl isothiocyanate. Sodium butyrate caused a 60-mV oxidation (from -260 to -200 mV), an oxidation sufficient for a 100-fold change in protein dithiols:disulfide ratio. Benzyl isothiocyanate caused a 16-mV oxidation in control cells but a 40-mV oxidation (to -160 mV) in differentiated cells. Changes in GSH and mRNA for glutamate:cysteine ligase did not correlate with Eh; however, correlations were seen between Eh and glutathione S-transferase (GST) and nicotinamide adenine dinucleotide phosphate (NADPH):quinone reductase activities (N:QR). These results show that 2GSH/GSSG redox changes in response to physiologic stimuli such as differentiation and enzyme inducers are of a sufficient magnitude to control the activity of redox-sensitive proteins. This suggests that physiologic modulation of the 2GSH/GSSG redox poise could provide a fundamental parameter for the control of cell phenotype.

Gamma-glutamylcysteine synthetase activity in human lung epithelial (A549) cells: factors influencing its measurement

Despite the central role of gamma-glutamylcysteine synthetase (gammaGCS) in lung antioxidant defenses, the limited studies of the activity of this enzyme in respiratory cells have produced variable results. This study has examined the factors, which may influence the measurement of gammaGCS activity in cultured human lung epithelial cells (A549). Although a source of potential error, gammaGCS activity in A549 cell extracts did not vary significantly when appropriately assayed by three different methods or after removal of the endogenous inhibitor, glutathione (GSH). However, gammaGCS activity did increase significantly during the early stages of cell proliferation (3.50 +/- 0.31 vs. 2.35 +/- 0.16 nmol/min/10(6) cells for baseline, p < .001) and thereafter returned to baseline levels during the later stages of cell growth. Variations in initial plating density also significantly altered gammaGCS activity (3.11 +/- 0.14 vs. 4.04 +/- 0.50 nmol/min/10(6) cells, at 0.25 x 10(5) and 0.58 x 10(5) cells/cm2, respectively, p < .001) and GSH content (45.43 +/- 4.43 vs. 63.64 +/- 3.28 nmol/10(6) cells at 0.25 x 10(5) and 0.58 x 10(5) cells/cm2, respectively, p < .001) during the early stages of cell proliferation. In addition, gammaGCS activity and GSH content were highest in A549 cells grown in medium containing cystine as the predominant sulfur-containing amino acid. These results suggest that gammaGCS activity of A549 cells is strongly dependent on initial plating density, stage of cell growth and sulfur amino acid content of the medium and may account for some of the variation in values reported by different investigators. Whether gammaGCS has an important role in the early phase of cell proliferation needs further investigation.

Use of antisense techniques in rat renal medulla

The experiments outlined in this chapter utilized a novel infusion technique to deliver an antisense oligonucleotide (and an enzyme inhibitor) directly into the renal medullary interstitial space of conscious rats. Antisense treatment led to a selective decrease in nNOS protein and reduced total NOS enzymatic activity in the renal medulla of the infused rats while three other gene products found in the renal medulla (iNOS, eNOS, and beta-actin) were unaltered. Physiological studies in rats demonstrated that infusion of the antisense oligonucleotide into the renal medullary interstitial space increased mean arterial pressure. The increase in blood pressure was dependent on the sodium intake of the rats, was not mimicked when a scrambled oligonucleotide was infused, and was reversible when the antisense infusion was stopped. To confirm the functional data obtained with the antisense oligonucleotide, renal medullary interstitial infusion of the nNOS enzyme inhibitor 7-NI was also shown to lead to a similar increase in arterial pressure and decrease in total NOS activity in the renal medulla. Together, the antisense oligonucleotide, the enzyme inhibitor, and the interstitial infusion technique were used to demonstrate that nNOS found in the renal medulla is important in the chronic regulation of arterial pressure. The experiments summarized in this chapter outline a strategy that can potentially be used to examine the functional effects of many different proteins in this region of the body. Through the use of antisense oligonucleotides and other pharmacological agents, we can hope to gain a more comprehensive understanding of the factors that control renal medullary tubular and vascular function and consequently fluid and electrolyte homeostasis and blood pressure.

Cholecystokinin activates PYK2/CAKbeta by a phospholipase C-dependent mechanism and its association with the mitogen-activated protein kinase signaling pathway in pancreatic acinar cells

PYK2/CAKbeta is a recently described cytoplasmic tyrosine kinase related to p125 focal adhesion kinase (p125(FAK)) that can be activated by a number of stimuli including growth factors, lipids, and some G protein-coupled receptors. Studies suggest PYK2/CAKbeta may be important for coupling various G protein-coupled receptors to the mitogen-activated protein kinase (MAPK) cascade. The hormone neurotransmitter cholecystokinin (CCK) is known to activate both phospholipase C-dependent cascades and MAPK signaling pathways; however, the relationship between these remain unclear. In rat pancreatic acini, CCK-8 (10 nM) rapidly stimulated tyrosine phosphorylation and activation of PYK2/CAKbeta by both activation of high affinity and low affinity CCK(A) receptor states. Blockage of CCK-stimulated increases in protein kinase C activity or CCK-stimulated increases in [Ca(2+)](i), inhibited by 40-50% PYK2/CAKbeta but not p125(FAK) tyrosine phosphorylation. Simultaneous blockage of both phospholipase C cascades inhibited PYK2/CAKbeta tyrosine phosphorylation completely and p125(FAK) tyrosine phosphorylation by 50%. CCK-8 stimulated a rapid increase in PYK2/CAKbeta kinase activity assessed by both an in vitro kinase assay and autophosphorylation. Total PYK2/CAKbeta under basal conditions was largely localized (77 +/- 7%) in the membrane fraction, whereas total p125(FAK) was largely localized (86 +/- 3%) in the cytosolic fraction. With CCK stimulation, both p125(FAK) and PYK2/CAKbeta translocated to the plasma membrane. Moreover CCK stimulation causes a rapid formation of both PYK2/CAKbeta-Grb2 and PYK2/CAKbeta-Crk complexes. These results demonstrate that PYK2/CAKbeta and p125(FAK) are regulated differently by CCK(A) receptor stimulation and that PYK2/CAKbeta is probably an important mediator of downstream signals by CCK-8, especially in its ability to activate the MAPK signaling pathway, which possibly mediates CCK growth effects in normal and neoplastic tissues.

Effect of thioacetamide on the hepatic expression of gamma-glutamylcysteine synthetase subunits in the Rat

Glutathione (GSH) is the main nonprotein thiol important in antioxidant defense and maintenance of the intracellular redox state. A major determinant of the rate of GSH synthesis is the activity of the rate-limiting enzyme, gamma-glutamylcysteine synthetase (GCS). A heavy (HS) and light subunit (LS) make up GCS; oxidative stress regulates both transcriptionally. cis-Acting elements important for the oxidative stress-induced transcriptional up-regulation of both subunits are antioxidant response element (ARE) and activator protein-1 (AP-1) site. The nuclear factor-kappaB (NF-kappaB) binding site may also regulate the heavy subunit. Increased GSH and gamma-glutamyltranspeptidase are often observed in preneoplastic hepatocyte nodules and may be important in hepatocarcinogenesis. The current work examined the effect of a commonly used hepatocarcinogen, thioacetamide (TAA), on the expression of GCS subunits. After 3 weeks of TAA treatment, liver GSH level remained unchanged despite significant oxidative stress as measured by the thiobarbituric acid reactive substance assay. The mRNA levels of GCS-HS and GCS-LS increased six- and fourfold, respectively, and the protein level of GCS-HS and GCS activity all increased. Electrophorectic mobility shift assay showed binding to ARE, AP-1, and NF-kappaB probes all increased. These results suggest TAA treatment increased hepatic GCS subunit expression and GCS activity by inducing oxidative stress and increasing the binding to redox-sensitive cis-acting elements important for transcriptional up-regulation of GCS. This is the first in vivo study that examined the effect of a hepatocarcinogen on GCS expression.

Glutathione and signal transduction in the mammalian CNS

The tripeptide glutathione (GSH) has been thoroughly investigated in relation to its role as antioxidant and free radical scavenger. In recent years, novel actions of GSH in the nervous system have also been described, suggesting that GSH may serve additionally both as a neuromodulator and as a neurotransmitter. In the present article, we describe our studies to explore further a potential role of GSH as neuromodulator/neurotransmitter. These studies have used a combination of methods, including radioligand binding, synaptic release and uptake assays, and electrophysiological recording. We report here the characteristics of GSH binding sites, the interrelationship of GSH with the NMDA receptor, and the effects of GSH on neural activity. Our results demonstrate that GSH binds via its gamma-glutamyl moiety to ionotropic glutamate receptors. At micromolar concentrations GSH displaces excitatory agonists, acting to halt their physiological actions on target neurons. At millimolar concentrations, GSH, acting through its free cysteinyl thiol group, modulates the redox site of NMDA receptors. As such modulation has been shown to increase NMDA receptor channel currents, this action may play a significant role in normal and abnormal synaptic activity. In addition, GSH in the nanomolar to micromolar range binds to at least two populations of binding sites that appear to be distinct from all known excitatory amino acid receptor subtypes. GSH bound to these sites is not displaceable by glutamatergic agonists or antagonists. These binding sites, which we believe to be distinct receptor populations, appear to recognize the cysteinyl moiety of the GSH molecule. Like NMDA receptors, the GSH binding sites possess a coagonist site(s) for allosteric modulation. Furthermore, they appear to be linked to sodium ionophores, an interpretation supported by field potential recordings in rat cerebral cortex that reveal a dose-dependent depolarization to applied GSH that is blocked by the absence of sodium but not by lowering calcium or by NMDA or (S)-2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate antagonists. The present data support a reevaluation of the role of GSH in the nervous system in which GSH may be involved both directly and indirectly in synaptic transmission. A full accounting of the actions of GSH may lead to more comprehensive understanding of synaptic function in normal and disease states.

Regulation of cathepsin B activity by cysteine and related thiols

We studied the mode of regulation of the activity of mature cathepsin B (CB) by L-cysteine and some related thiols. The activity of CB with Z-Arg-Arg-NHMec as substrate was gradually inhibited over a range of increasing concentration of Cys, Cys methyl ester (CysOMe), Cys ethyl ester (CysOEt), N-acetyl-Cys (N-AcCys) and 3-mercaptopropionic acid. However, the inhibition of CB peaked at a definite value of [Cys], [CysOMe], [CysOEt] and [N-AcCys] and was gradually reversed over a range of higher concentrations of Cys and its esters. The maximum inhibitory concentrations of Cys, CysOME, CysOEt and N-AcCys showed a positive relationship to the pKa(RSH) values of the thiols and those of CysOEt and Cys decreased with increasing pH. The capability of the thiols to overcome their own inhibitory effect on CB was dependent on the concentration of their thiolate anion (RS-). However, the preincubation-dilution experiments showed that Cys and N-AcCys did not interact with active CB via a covalent mode. The inhibition of CB by N-AcCys was competitive and could be reversed by CysOMe. This activity-recovering effect of CysOMe was concentration-dependent and obeyed the Michaelis-Menten saturation kinetics over a profound increase of [RS-]. CB reacting in an environment of concurrently decreasing [RS-] and increasing [RSH], which was achieved by means of carboxylesterase-catalyzed deesterification of CysOEt to Cys, was progressively inhibited. Cys and N-AcCys also inhibited the fragmentation of histone H4 by CB and their concentration-dependent inhibitory profiles were qualitatively similar to those observed with Z-Arg-Arg-NHMec. Taken together, the results indicate that the RSH form of Cys and related thiols inhibits the activity of CB while the RS- form of these thiols counteracts or reverses the inhibitory action of the RSH form. This previously unrecognized thiol-thiolate anion regulation mechanism might be involved in a dynamic regulation of CB activity in endosomes and lysosomes and at the sites of lysosome-driven pericellular proteolysis.

Susceptibility of cultured rat hepatocytes to oxidative stress by peroxides and iron. The extracellular matrix affects the toxicity of tert-butyl hydroperoxide

The aim of this study was to set up an in vitro model for studying the importance of an altered extra-cellular matrix composition and its importance for the resistance to oxidative stress, in hepatocytes from normal and iron loaded rats. Primary cultures of hepatocytes from iron loaded and normal rats were plated on a laminin rich extracellular matrix or on collagen type I, and incubated with tert-butyl hydroperoxide (TBH). Malon dialdehyde (MDA) and the activities of lactate dehydrogenase (LDH) in cell culture medium were analyzed. The protein synthesis, the concentrations of glutathione and the expression of manganese-superoxide dismutase and ferritin genes were measured. All hepatocytes contained lower concentrations of glutathione when plated on collagen than on EHS. Ferritin H and Mn-SOD gene expression showed no difference. The rate of lipid peroxidation in iron loaded hepatocytes exposed to TBH was higher on collagen than in those plated on EHS (0.95 +/- 0.28 microM MDA vs. 1.62 +/- 0.22 microM MDA, p < 0.05). Iron loaded cells were in general more susceptible to TBH than were normal hepatocytes (MDA, LDH, protein synthesis and glutathione content). Lipid peroxidation could be prevented by adding desferrioxamine. In conclusion, we show that the combination of iron overload and collagen matrix in rat hepatocytes leads to an increased susceptibility to oxidative stress. These findings may be of interest for the further studies on effects of iron overload and the altered matrix composition in liver fibrosis.

Nitric oxide-dependent induction of glutathione synthesis through increased expression of gamma-glutamylcysteine synthetase

The nitric oxide (NO) donors S-nitrosopenicillamine or DetaNONOate, which release NO at a rate of 0-15 nM sec-1, were exposed to rat aortic vascular smooth muscle cells for a period of 0-24 h. This treatment resulted in an increase in total glutathione levels of two- to threefold under conditions where no cytotoxicity was detected. The signaling pathways do not involve activation of protein kinase G Ialpha nor are they cGMP dependent. Oxidation of reduced glutathione (GSH) was found after exposure to NO for 3-4 h at rates of formation at or above 8 nM sec-1. Increased intracellular GSH was due to enhanced expression of the rate-limiting enzyme for GSH synthesis, gamma-glutamylcysteine synthetase. Since NO has been shown previously to protect cells against oxidative stress, we propose that the increase in GSH by NO is a potential mechanism for enhancing the antioxidant defenses of the cell. This result also has important implications for identifying redox-sensitive cell signaling pathways that can be activated by NO.