Stimulation of cystine uptake by nitric oxide: regulation of endothelial cell glutathione levels

Hydrogen sulfide and its potential as a possible therapeutic agent in male reproduction

Hydrogen sulfide (H2S) is an endogenously produced signaling molecule that belongs to the group of gasotransmitters along with nitric oxide (NO) and carbon monoxide (CO). H2S plays a pivotal role in male reproductive processes. It is produced in various tissues and cells of the male reproductive system, including testicular tissue, Leydig and Sertoli cells, epididymis, seminal plasma, prostate, penile tissues, and sperm cells. This review aims to summarize the knowledge about the presence and effects of H2S in male reproductive tissues and outline possible therapeutic strategies in pathological conditions related to male fertility, e. g. spermatogenetic disorders and erectile dysfunction (ED). For instance, H2S supports spermatogenesis by maintaining the integrity of the blood-testicular barrier (BTB), stimulating testosterone production, and providing cytoprotective effects. In spermatozoa, H2S modulates sperm motility, promotes sperm maturation, capacitation, and acrosome reaction, and has significant cytoprotective effects. Given its vasorelaxant effects, it supports the erection of penile tissue. These findings suggest the importance and therapeutic potential of H2S in male reproduction, paving the way for further research and potential clinical applications.

The role of sulfur compounds in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common respiratory disease that brings about great social and economic burden, with oxidative stress and inflammation affecting the whole disease progress. Sulfur compounds such as hydrogen sulfide (H₂S), thiols, and persulfides/polysulfides have intrinsic antioxidant and anti-inflammatory ability, which is engaged in the pathophysiological process of COPD. Hydrogen sulfide mainly exhibits its function by S-sulfidation of the cysteine residue of the targeted proteins. It also interacts with nitric oxide and acts as a potential biomarker for the COPD phenotype. Thiols’ redox buffer such as the glutathione redox couple is a major non-enzymatic redox buffer reflecting the oxidative stress in the organism. The disturbance of redox buffers was often detected in patients with COPD, and redressing the balance could delay COPD exacerbation. Sulfane sulfur refers to a divalent sulfur atom bonded with another sulfur atom. Among them, persulfides and polysulfides have an evolutionarily conserved modification with antiaging effects. Sulfur compounds and their relative signaling pathways are also associated with the development of comorbidities in COPD. Synthetic compounds which can release H₂S and persulfides in the organism have gradually been developed. Naturally extracted sulfur compounds with pharmacological effects also aroused great interest. This study discussed the biological functions and mechanisms of sulfur compounds in regulating COPD and its comorbidities.

Delayed Impact of 2-Oxoadipate Dehydrogenase Inhibition on the Rat Brain Metabolism Is Linked to Protein Glutarylation

Background

The DHTKD1-encoded 2-oxoadipate dehydrogenase (OADH) oxidizes 2-oxoadipate—a common intermediate of the lysine and tryptophan catabolism. The mostly low and cell-specific flux through these pathways, and similar activities of OADH and ubiquitously expressed 2-oxoglutarate dehydrogenase (OGDH), agree with often asymptomatic phenotypes of heterozygous mutations in the DHTKD1 gene. Nevertheless, OADH/DHTKD1 are linked to impaired insulin sensitivity, cardiovascular disease risks, and Charcot-Marie-Tooth neuropathy. We hypothesize that systemic significance of OADH relies on its generation of glutaryl residues for protein glutarylation. Using pharmacological inhibition of OADH and the animal model of spinal cord injury (SCI), we explore this hypothesis.

Methods

The weight-drop model of SCI, a single intranasal administration of an OADH-directed inhibitor trimethyl adipoyl phosphonate (TMAP), and quantification of the associated metabolic changes in the rat brain employ established methods.

Results

The TMAP-induced metabolic changes in the brain of the control, laminectomized (LE) and SCI rats are long-term and (patho)physiology-dependent. Increased glutarylation of the brain proteins, proportional to OADH expression in the control and LE rats, represents a long-term consequence of the OADH inhibition. The proportionality suggests autoglutarylation of OADH, supported by our mass-spectrometric identification of glutarylated K155 and K818 in recombinant human OADH. In SCI rats, TMAP increases glutarylation of the brain proteins more than OADH expression, inducing a strong perturbation in the brain glutathione metabolism. The redox metabolism is not perturbed by TMAP in LE animals, where the inhibition of OADH increases expression of deglutarylase sirtuin 5. The results reveal the glutarylation-imposed control of the brain glutathione metabolism. Glutarylation of the ODP2 subunit of pyruvate dehydrogenase complex at K451 is detected in the rat brain, linking the OADH function to the brain glucose oxidation essential for the redox state. Short-term inhibition of OADH by TMAP administration manifests in increased levels of tryptophan and decreased levels of sirtuins 5 and 3 in the brain.

Conclusion

Pharmacological inhibition of OADH affects acylation system of the brain, causing long-term, (patho)physiology-dependent changes in the expression of OADH and sirtuin 5, protein glutarylation and glutathione metabolism. The identified glutarylation of ODP2 subunit of pyruvate dehydrogenase complex provides a molecular mechanism of the OADH association with diabetes.

Aryl Hydrocarbon Receptor and Cysteine Redox Dynamics Underlie (Mal)adaptive Mechanisms to Chronic Intermittent Hypoxia in Kidney Cortex

We hypothesized that an interplay between aryl hydrocarbon receptor (AhR) and cysteine-related thiolome at the kidney cortex underlies the mechanisms of (mal)adaptation to chronic intermittent hypoxia (CIH), promoting arterial hypertension (HTN). Using a rat model of CIH-HTN, we investigated the impact of short-term (1 and 7 days), mid-term (14 and 21 days, pre-HTN), and long-term intermittent hypoxia (IH) (up to 60 days, established HTN) on CYP1A1 protein level (a sensitive hallmark of AhR activation) and cysteine-related thiol pools. We found that acute and chronic IH had opposite effects on CYP1A1 and the thiolome. While short-term IH decreased CYP1A1 and increased protein-S-thiolation, long-term IH increased CYP1A1 and free oxidized cysteine. In addition, an in vitro administration of cystine, but not cysteine, to human endothelial cells increased Cyp1a1 expression, supporting cystine as a putative AhR activator. This study supports CYP1A1 as a biomarker of obstructive sleep apnea (OSA) severity and oxidized pools of cysteine as risk indicator of OSA-HTN. This work contributes to a better understanding of the mechanisms underlying the phenotype of OSA-HTN, mimicked by this model, which is in line with precision medicine challenges in OSA.

Biological properties and development of hypoxia in a breast cancer 3D model generated by hanging drop technique

Hanging drop represents a simple approach designed for the generation of 3D models that have potential to be used for the study of solid tumors characteristics. The aim of the study was to develop and characterize the breast cancer 3D cellular models obtained through hanging drop technique using MDA-MB-231 cells. The biological characteristics such as: morphology, cellular viability, proliferation capacity and hypoxia, were monitored for a six-day time period. The morphological evaluation indicated that the 3D models presented the aspect of compact (seeding density of 2500 and 5000 cells/drop) and loose (seeding density of 8000 cells/drop) aggregates, with a decrease in diameter and an increase of their circularity. The cellular viability and proliferation capacity decreased in time and the level of lactate dehydrogenase (LDH) increased in a time-dependent manner, suggesting the presence of necrotic cells that were dispersed in the cellular aggregates. The occurrence of hypoxia process was suggested by the up-regulation of Hsp70 protein expression and increased level of nitric oxide (NO). Moreover, the up-regulation of HIF-1α and poli-ubiquitinated Nrf2 protein expressions and decreased level of reduced glutathione (GSH) indicated the presence of an acute hypoxic environment in MDA-MB-231 3D aggregates. In conclusion, the MDA-MB-231 3D models generated through hanging drop are compact and loose aggregates characterized by an acute hypoxic condition.

l-Arginine supplementation in severe asthma

BACKGROUNDDysregulation of l-arginine metabolism has been proposed to occur in patients with severe asthma. The effects of l-arginine supplementation on l-arginine metabolite profiles in these patients are unknown. We hypothesized that individuals with severe asthma with low fractional exhaled nitric oxide (FeNO) would have fewer exacerbations with the addition of l-arginine to their standard asthma medications compared with placebo and would demonstrate the greatest changes in metabolite profiles.METHODSParticipants were enrolled in a single-center, crossover, double-blind l-arginine intervention trial at UCD. Subjects received placebo or l-arginine, dosed orally at 0.05 mg/kg (ideal body weight) twice daily. The primary end point was moderate asthma exacerbations. Longitudinal plasma metabolite levels were measured using mass spectrometry. A linear mixed-effect model with subject-specific intercepts was used for testing treatment effects.RESULTSA cohort of 50 subjects was included in the final analysis. l-Arginine did not significantly decrease asthma exacerbations in the overall cohort. Higher citrulline levels and a lower arginine availability index (AAI) were associated with higher FeNO (P = 0.005 and P = 2.51 × 10-9, respectively). Higher AAI was associated with lower exacerbation events. The eicosanoid prostaglandin H2 (PGH2) and Nα-acetyl-l-arginine were found to be good predictors for differentiating clinical responders and nonresponders.CONCLUSIONSThere was no statistically significant decrease in asthma exacerbations in the overall cohort with l-arginine intervention. PGH2, Nα-acetyl-l-arginine, and the AAI could serve as predictive biomarkers in future clinical trials that intervene in the arginine metabolome.TRIAL REGISTRATIONClinicalTrials.gov NCT01841281.FUNDINGThis study was supported by NIH grants R01HL105573, DK097154, UL1 TR001861, and K08HL114882. Metabolomics analysis was supported in part by a grant from the University of California Tobacco-Related Disease Research Program program (TRDRP).

A Review of Hydrogen Sulfide Synthesis, Metabolism, and Measurement: Is Modulation of Hydrogen Sulfide a Novel Therapeutic for Cancer?

Significance: Hydrogen sulfide (H2S) has been recognized as the third gaseous transmitter alongside nitric oxide and carbon monoxide. In the past decade, numerous studies have demonstrated an active role of H2S in the context of cancer biology. Recent Advances: The three H2S-producing enzymes, namely cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (3MST), have been found to be highly expressed in numerous types of cancer. Moreover, inhibition of CBS has shown anti-tumor activity, particularly in colon cancer, ovarian cancer, and breast cancer, whereas the consequence of CSE or 3MST inhibition remains largely unexplored in cancer cells. Intriguingly, H2S donation at high amounts or a long time duration has also been observed to induce cancer cell apoptosis in vitro and in vivo while sparing noncancerous fibroblast cells. Therefore, a bell-shaped model has been proposed to explain the role of H2S in cancer development. Specifically, endogenous H2S or a relatively low level of exogenous H2S may exhibit a pro-cancer effect, whereas exposure to H2S at a higher amount or for a long period may lead to cancer cell death. This indicates that inhibition of H2S biosynthesis and H2S supplementation serve as two distinct ways for cancer treatment. This paradoxical role of H2S has stimulated the enthusiasm for the development of novel CBS inhibitors, H2S donors, and H2S-releasing hybrids. Critical Issues: A clear relationship between H2S level and cancer progression remains lacking. The possibility that the altered levels of these byproducts have influenced the cell viability of cancer cells has not been excluded in previous studies when modulating H2S producing enzymes. Future Directions: The consequence of CSE or 3MST inhibition in cancer cells need to be examined in the future. Better portrayal of the crosstalk among these gaseous transmitters may not only lead to an in-depth understanding of cancer progression but also shed light on novel strategies for cancer therapy.

Influence of Matrigel on Single- and Multiple-Spheroid Cultures in Breast Cancer Research

This study aimed to develop and compare single and multiple 3D models such as multicellular tumor spheroids and to investigate the influence of Matrigel on their morphological and functional behavior. MDA-MB-231 3D models were generated in the presence and absence of Matrigel and their key biological properties within 6 days of culture were monitored. Our results revealed the formation of well-defined 3D models in the presence of Matrigel, with a uniform morphology, increased diameter, good circularity, and increased expression of a proliferation marker (PCNA). In comparison, 3D models generated without Matrigel were characterized by an irregular border, reduced dimensions and circularity, and a decrease of PCNA expression. Similarities between the single and multiple 3D cultures were found in their viability, Nrf2 expression, and glutathione (GSH) content. The influence of Matrigel on MDA-MB-231 spheroids metabolism under hypoxic conditions was highlighted by released lactate dehydrogenase and nitric oxide, GSH levels and expression of Nrf2 and Hsp70 proteins. Based on the increased expression of PCNA and the development of the hypoxia process in the presence of extracellular matrix, our study showed that the addition of Matrigel improves the growing environment of tumor spheroids, making it closer to that of in vivo tumor conditions.

Reactive oxygen species modulate Na+-coupled neutral amino acid transporter 1 expression in piglet pulmonary arterial endothelial cells

We have previously shown that Na⁺-coupled neutral amino acid transporter 1 (SNAT1) modulates nitric oxide (NO) production in pulmonary arterial endothelial cells (PAECs) from newborn piglets. Specifically, the ability to increase NO production in response to the l-arginine-NO precursor l-citrulline is dependent on SNAT1 expression. Elucidating factors that regulate SNAT1 expression in PAECs could provide new insights and therapeutic targets relevant to NO production. Our major goals were to determine if reactive oxygen species (ROS) modulate SNAT1 expression in PAECs from newborn piglets and to evaluate the role of NADPH oxidase 1 (NOX1) and uncoupled endothelial NO synthase, enzymatic sources of ROS, in hypoxia-induced increases in SNAT1 expression. Treatment with either H₂O₂ or xanthine plus xanthine oxidase increased SNAT1 expression in PAECs from newborn piglets cultured under normoxic conditions. Hypoxia-induced increases in SNAT1 expression were inhibited by treatments with the ROS-removing agents catalase and superoxide dismutase, NOX1 siRNA, and the NO synthase inhibitor N^G-nitro-l-arginine methyl ester. Both tetrahydropbiopterin (BH₄) and l-citrulline, two therapies that decrease ROS by recoupling endothelial NO synthase, reduced the hypoxia-induced increase in SNAT1 expression. BH₄ and l-citrulline treatment improved NO production in hypoxic PAECs despite a reduction in SNAT1 expression. In conclusion, SNAT1 expression is modulated by ROS in PAECs from newborn piglets. However, ROS-mediated decreases in SNAT1 expression per se do not implicate a reduction in NO production. Although SNAT1 may be critical to l-citrulline-induced increases in NO production, therapies designed to alter SNAT1 expression may not lead to a concordant change in NO production. NEW & NOTEWORTHY Na⁺-coupled neutral amino acid transporter 1 (SNAT1) modulates nitric oxide (NO) production in piglet pulmonary arterial endothelial cells. Factors that regulate SNAT1 expression in pulmonary arterial endothelial cells are unclear. Here, we show that ROS-reducing strategies inhibit hypoxia-induced increases in SNAT1 expression. l-Citrulline and tetrahydropbiopterin decrease SNAT1 expression but increase NO production. Although SNAT1 is modulated by ROS, changes in SNAT1 expression may not cause a concordant change in NO production.

Role of asthma and intolerance to acetylsalicylic acid on the redox profile in nasal polyp tissue

PURPOSE

Nasal polyposis is a chronic inflammatory disease of the mucosa of the nasal cavity and paranasal sinuses. The etiology of nasal polyposis is unclear; however, it may be associated with asthma and intolerance to acetylsalicylic acid, possibly altering the redox profile. The study intends to compare the redox profile in polyps surgically removed from three clinical groups of patients with nasal polyposis who were divided according to the presence of asthma and intolerance to acetylsalicylic acid.

METHODS

Patients were divided into three groups: nasal polyposis only (n = 30); nasal polyposis and asthma (n = 19); and nasal polyposis, asthma and intolerance to acetylsalicylic acid (n = 10). The following redox evaluations were performed: enzymatic antioxidant activity of superoxide dismutase, glutathione peroxidase, hydrogen peroxide consumption and glutathione S-transferase; non-enzymatic antioxidant levels of vitamin C, vitamin E and glutathione; levels of the oxidative damage biomarkers carbonyl groups (measuring protein damage) and malondialdehyde (measuring lipid peroxidation); and nitrite and nitrate levels.

RESULTS

Compared with the polyposis only group, hydrogen peroxide consumption, glutathione S-transferase, vitamin E and malondialdehyde were lower in the asthma group. Total glutathione (0.12 ± 0.01 vs. 33.34 ± 10.48 µmol/mg) and nitrite and nitrate (0.06 ± 0.01 vs. 15.95 ± 1.38 nmol/mg) levels were higher in the nasal polyposis, asthma and intolerance to acetylsalicylic acid group.

CONCLUSIONS

In patients with nasal polyposis, asthma may alter the redox profile associated with the hydrogen peroxide and lipid damage pathways, whereas asthma and intolerance to acetylsalicylic acid increase nitrite and nitrate and total glutathione levels.

Experimental evidence on interaction between xenon and bovine serum albumin

Xenon gas interacts with bovine serum albumin (BSA) dissolved in a physiological buffer solution. The fluorescence quenching related to the Trp emission is reversible and depends linearly on the time of saturation by Xe. The most probable site of this interaction is Trp212. The common emission of all BSA fluorophores is also influenced by Xe but this quenching is more complex and suggests: (i) at least two sites occupied by Xe and related to the Tyr and Trp residues; (ii) structural variations of BSA induced by the Xe guest atoms.

Hydrogen sulfide chemical biology: pathophysiological roles and detection

Hydrogen sulfide (H2S) is the most recent endogenous gasotransmitter that has been reported to serve many physiological and pathological functions in different tissues. Studies over the past decade have revealed that H2S can be synthesized through numerous pathways and its bioavailability regulated through its conversion into different biochemical forms. H2S exerts its biological effects in various manners including redox regulation of protein and small molecular weight thiols, polysulfides, thiosulfate/sulfite, iron-sulfur cluster proteins, and anti-oxidant properties that affect multiple cellular and molecular responses. However, precise measurement of H2S bioavailability and its associated biochemical and pathophysiological roles remains less well understood. In this review, we discuss recent understanding of H2S chemical biology, its relationship to tissue pathophysiological responses and possible therapeutic uses.

A tale of two gases: NO and H2S, foes or friends for life?

Nitric oxide (NO) and hydrogen sulfide (H₂S) have emerged as dominant redox regulators of numerous aspects of cellular and physiological functions within several organ systems included cardiovascular, immune and neurological tissues. Recent studies have begun to reveal that these two gaseous molecules may have redundant or overlapping pathophysiological functions often involving similar molecular targets. However, it remains less clear when and how NO and H₂S may interact under biological and disease processes. In this graphical review, we discuss the current understanding of NO and H₂S interactions and how they may functionally influence each other and what this may mean for biology and mechanisms of disease.

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H₂S and NO are important gaseous regulators of numerous physiological responses.

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H₂S and NO may target both similar and divergent signaling and molecular pathways.

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H₂S and NO react with protein free thiols that differentially affect protein function.

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H₂S and NO metabolites can react together to yield novel biochemical products.

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The presence and physiological importance of these novel products remains unknown.

Enhanced expression of cystine/glutamate transporter in the lung caused by the oxidative-stress-inducing agent paraquat

In mammalian cultured cells, the activity of a cystine/glutamate transporter, designated System xc(-), has been shown to be essential for maintaining intracellular glutathione levels and the extracellular cystine/cysteine redox balance. The substrate-specific subunit of this transporter, xCT, is strongly induced by various stimuli, including oxidative stress, which suggests that xCT is one of the adaptive cellular defense systems against these types of stress. Embryonic fibroblasts from xCT-deficient mice fail to survive unless a cysteine precursor, N-acetylcysteine, is present. However, it is unclear whether xCT has similar functions in vivo because xCT-deficient mice are apparently normal. In this study, we investigated the phenotype of the xCT-deficient mice under paraquat-induced oxidative stress. At a paraquat dose of 45mg/kg, the survival rate of the xCT-deficient mice was significantly lower than that of the wild-type mice. Under this condition, total glutathione (the reduced form of glutathione (GSH)+the oxidized form of GSH) levels in the lungs of the xCT-deficient mice were lower than those in the lungs of the wild-type mice. Histopathological examinations showed that paraquat administration worsened the alveolar structure of the xCT-deficient mice compared with the wild-type mice. After paraquat treatment, obvious 8-hydroxy-2'-deoxyguanosine and 4-hydroxy-2-nonenal reactivity was detected in the lungs of the xCT-deficient mice. Although xCT expression was slightly detectable in the lungs of the normal wild-type mice, paraquat administration induced xCT mRNA expression in the lung. Constitutive expression of xCT mRNA was detected in alveolar macrophages isolated from the pulmonary lavage fluid of the wild-type mice, and paraquat administration strongly enhanced xCT mRNA expression in these cells. GSH levels in bronchoalveolar lavage fluid were significantly higher in the paraquat-treated wild-type mice than in the paraquat-treated xCT-deficient mice. These results suggest that xCT contributes to the maintenance of glutathione levels in lungs and the glutathione redox state as a protective system against paraquat toxicity in vivo.

Mechanisms and management of doxorubicin cardiotoxicity

Doxorubicin is an effective anti-tumor agent with a cumulative dose-dependent cardiotoxicity. In addition to its principal toxic mechanisms involving iron and redox reactions, recent studies have described new mechanisms of doxorubicin-induced cell death, including abnormal protein processing, hyper-activated innate immune responses, inhibition of neuregulin-1 (NRG1)/ErbB(HER) signalling, impaired progenitor cell renewal/cardiac repair, and decreased vasculogenesis. Although multiple mechanisms involved in doxorubicin cardiotoxicity have been studied, there is presently no clinically proven treatment established for doxorubicin cardiomyopathy. Iron chelator dexrazoxane, angiotensin converting enzyme (ACE) inhibitors, and β-blockade have been proposed as potential preventive strategies for doxorubicin cardiotoxicity. Novel approaches such as anti-miR-146 or recombinant NRG1 to increase cardiomyocyte resistance to toxicity may be of interest in the future.

Sulfurous gases as biological messengers and toxins: comparative genetics of their metabolism in model organisms

Gasotransmitters are biologically produced gaseous signalling molecules. As gases with potent biological activities, they are toxic as air pollutants, and the sulfurous compounds are used as fumigants. Most investigations focus on medical aspects of gasotransmitter biology rather than toxicity toward invertebrate pests of agriculture. In fact, the pathways for the metabolism of sulfur containing gases in lower organisms have not yet been described. To address this deficit, we use protein sequences from Homo sapiens to query Genbank for homologous proteins in Caenorhabditis elegans, Drosophila melanogaster, and Saccharomyces cerevisiae. In C. elegans, we find genes for all mammalian pathways for synthesis and catabolism of the three sulfur containing gasotransmitters, H₂S, SO₂ and COS. The genes for H₂S synthesis have actually increased in number in C. elegans. Interestingly, D. melanogaster and Arthropoda in general, lack a gene for 3-mercaptopyruvate sulfurtransferase, an enzym for H₂S synthesis under reducing conditions.

Effects of hydrogen sulfide on erectile function and its possible mechanism(s) of action

INTRODUCTION

The current pharmacotherapy for erectile dysfunction (ED) relies significantly on the use of phosphodiesterase type 5 (PDE5) inhibitors, but quite a proportion of ED patients are resistant to this therapy, necessitating a search for an alternative treatment. We reviewed available published data to analyze current evidence of hydrogen sulfide (H(2) S) as a novel pharmacotherapeutic agent with supportive role in sexual function.

AIM

To discuss the role of H(2) S in erectile function, its possible mechanism of action, and how this knowledge may be exploited for therapeutic use.

METHODS

Pubmed and Medline search was conducted to identify original articles and reviews.

MAIN OUTCOME MEASURES

Data from peer-reviewed publications.

RESULTS

Animal studies using different species, including in vitro study done in humans, show evidence of H(2) S's pro-erectile effects. The mechanism behind is still unclear, but evidence in literature points out the involvement of K(+) (ATP) channel, modulation of protein with anti-erectile effects, as well as involvement of the nitrergic pathway through a complex cross-talk. A new drug called H(2) S-donating sildenafil (ACS6), which incorporated an H(2) S-donating moiety in sildenafil, has been developed. While more studies are still needed, this heralded a new pharmacotherapeutical approach, which is multipronged in nature.

CONCLUSIONS

Given the mounting evidence of H(2) S's role in erectile function and how it appears to achieve its pro-erectile effects through different mechanisms, H(2) S represents a potentially important treatment alternative or adjunct to PDE5 inhibitors.

Mechanisms of anthracycline cardiotoxicity and strategies to decrease cardiac damage

Anthracyclines are common chemotherapeutic agents used to treat many different types of cancer. Unfortunately, the use of anthracyclines is limited by their cardiotoxic effects, which may become manifest as late as 20 years from initial exposure. Studies in cells and animals suggest that the mechanism of anthracycline-induced cardiotoxicity (AIC) is multifactorial. Anthracyclines induce multiple forms of cellular injury by free radical production. In addition, anthracyclines alter nucleic acid biology by intercalation into DNA and modulate intracellular signaling, leading to cell death and the disruption of homeostatic processes such as sarcomere maintenance. In an effort to decrease AIC, many strategies have been tested, but no specific therapies are universally acknowledged to prevent or treat anthracycline-induced cardiac dysfunction. Newer imaging modalities and cardiac biomarkers may be useful in improving early detection of cardiac injury and dysfunction. As long as there is no cardiac-specific therapy for AIC, evidence suggests that high-risk patients will benefit from prophylactic treatment with neurohormonal blockade by angiotensin-converting enzyme inhibitors and beta-adrenergic receptor blockers.

Oxidative stress increases SNAT1 expression and stimulates cysteine uptake in freshly isolated rat cardiomyocytes

Intracellular cysteine availability is an important rate-limiting factor governing glutathione synthesis in the heart. This is also dependent on the magnitude and rate of cysteine uptake into cardiomyocytes, which has been little studied. This study investigated the hypothesis that changes to cysteine transporter expression and activity during oxidative stress influence cardiomyocyte glutathione levels. The uptake of 0-3 mM L-[(35)S]cysteine into ventricular cardiomyocytes isolated from adult male Wistar rats was measured using oil filtration. Cysteine transporter expression was investigated by conventional and real-time quantitative reverse-transcription polymerase chain reaction and Western blotting. Glutathione levels were measured enzymatically. Oxidative stress was induced via 0-6 h incubation with 0.05 mM H(2)O(2). Cysteine uptake was greatest in sodium-containing media and was inhibited by glutamine, 2-(methylamino)-isobutyric acid (αMeAIB), serine or alanine. The K(m) and V(max) of the αMeAIB insensitive and sensitive portions were 0.133 ± 0.01 mM and 468.11 ± 9.04 pmol/μl cell vol/min, and 0.557 ± 0.096 mM and 279.87 ± 16.06 pmol/μl cell vol/min, respectively. Cardiomyocytes expressed ASCT2, SNAT1 and SNAT2 but not ASCT1. Oxidative stress significantly enhanced cysteine uptake, which was attenuated by αMeAIB. This was accompanied by significantly enhanced SNAT1 expression, whilst SNAT2 and ASCT2 were unaffected. Incubation with cysteine significantly reduced the oxidative-stress-induced decline in cardiomyocyte glutathione as compared to cells incubated without cysteine or cells incubated with cysteine and αMeAIB. In conclusion, under control conditions SNAT transporters aid in the delivery of cysteine for cardiomyocyte GSH synthesis, whilst oxidative stress increases cardiomyocyte cysteine uptake and stimulates cardiomyocyte SNAT1 expression.

Bacterial nitric oxide detoxification prevents host cell S-nitrosothiol formation: a novel mechanism of bacterial pathogenesis

S-nitrosylation is an important mediator of multiple nitric oxide-dependent biological processes, including eukaryotic cellular events such as macrophage apoptosis and proinflammatory signaling. Many pathogenic bacteria possess NO detoxification mechanisms, such as the nitric oxide reductase (NorB) of Neisseria meningitidis and the flavohemoglobins (Hmp) of Salmonella enterica and Escherichia coli, which serve to protect the microorganism from nitrosative stress within the intracellular environment. In this study, we demonstrate that expression of meningococcal NorB increases the rate at which low-molecular-weight S-nitrosothiol (SNO) decomposes in vitro. To determine whether this effect occurs in cells during infection by bacteria, we induced SNO formation in murine macrophages by activation with lipopolysaccharide and γ-interferon and observed a reduced abundance of SNO during coincubation with N. meningitidis, S. enterica, or E. coli. In each case, this effect was shown to be dependent on bacterial NO detoxification genes, which act to prevent SNO formation through the removal of NO. This may represent a novel mechanism of host cell injury by bacteria.—Laver, J. R., Stevanin, T. M., Messenger, S. L., Dehn Lunn, A., Lee, M. E., Moir, J. W. B., Poole, R. K., Read, R. C. Bacterial nitric oxide detoxification prevents host cell S-nitrosothiol formation: a novel mechanism of bacterial pathogenesis.

Role of Nrf2-mediated heme oxygenase-1 upregulation in adaptive survival response to nitrosative stress

Nitrosative stress caused by reactive nitrogen species such as nitric oxide and peroxynitrite overproduced during inflammation leads to cell death and has been implicated in the pathogenesis of many human ailments. However, relatively mild nitrosative stress may fortify cellular defense capacities, rendering cells tolerant or adaptive to ongoing and subsequent cytotoxic challenges, a phenomenon known as 'preconditioning' or 'hormesis'. One of the key components of cellular stress response is heme oxygenase-1 (HO-1), the rate limiting enzyme in the process of degrading potentially toxic free heme into biliverdin, free iron and carbon monoxide. HO-1 is upregulated by a wide array of stimuli and has antioxidant, anti-inflammatory and other cytoprotective functions. This review is intended to provide readers with a welldocumented account of the research done in the area of cellular adaptive survival response against nitrosative stress with special focus on the role of HO-1 upregulation, especially through activation of the transcription factor, Nrf2.

The x(c)- cystine/glutamate antiporter: a potential target for therapy of cancer and other diseases

The x(c) (-) cystine/glutamate antiporter is a major plasma membrane transporter for the cellular uptake of cystine in exchange for intracellular glutamate. Its main functions in the body are mediation of cellular cystine uptake for synthesis of glutathione essential for cellular protection from oxidative stress and maintenance of a cystine:cysteine redox balance in the extracellular compartment. In the past decade it has become evident that the x(c) (-) transporter plays an important role in various aspects of cancer, including: (i) growth and progression of cancers that have a critical growth requirement for extracellular cystine/cysteine, (ii) glutathione-based drug resistance, (iii) excitotoxicity due to excessive release of glutamate, and (iv) uptake of herpesvirus 8, a causative agent of Kaposi's sarcoma. The x(c) (-) transporter also plays a role in certain CNS and eye diseases. This review focuses on the expression and function of the x(c) (-) transporter in cells and tissues with particular emphasis on its role in disease pathogenesis. The potential use of x(c) (-) inhibitors (e.g., sulfasalazine) for arresting tumor growth and/or sensitizing cancers is discussed.

Cysteine turnover in human cell lines is influenced by glyphosate

Pesticides are widely spread in the environment and there is a lack of knowledge concerning the impact of these substances on the human cell. In the present study the effect of low doses of the pesticides bentazon, metalaxyl and glyphosate on the cellular metabolism of glutathione and cysteine was examined in HeLa and hepatoma cell cultures. No effect was observed when the cells were exposed to bentazon or metalaxyl. However, significant changes in the intra- and extracellular concentration of cysteine, a precursor for glutathione synthesis, were detected when glyphosate was added to the medium. This finding was observed in the presence of micromolar concentration range of glyphosate, and is relevant when compared to concentrations observed in monitoring programmes.

The effect of modulation of gamma-glutamyl transpeptidase and nitric oxide synthase activity on GSH homeostasis in HepG2 cells

High glutathione (GSH) level and elevated gamma-glutamyl transpeptidase (gammaGT) activity are hallmarks of tumor cells. Toxicity of drugs and radiation to the cells is largely dependent on the level of thiols. In the present studies, we attempted to inhibit gammaGT activity in human hepatoblastoma (HepG2) cells to examine whether the administration of gammaGT inhibitors, acivicin (AC) and 1,2,3,4-tetrahydroisoquinoline (TIQ) influences cell proliferation and enhances cytostatic action of doxorubicin (DOX) and cisplatin (CP) on HepG2 cells. The effects of these inhibitors were determined by 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), BrdU and lactate dehydrogenase (LDH) tests and by estimation of GSH level. Additionally, we investigated the changes in caspase-3 activity, which is a marker of apoptosis. The obtained results showed that the gammaGT inhibitors introduced to the medium alone elicited cytotoxic effect, which was accompanied by an increase in GSH level in the cells. TIQ concomitantly increased caspase-3 activity. Doxorubicin and CP proved to be cytotoxic, and both inhibitors augmented this effect. As well DOX as CP radically decreased GSH levels, whereas gammaGT inhibitors had diverse effects. Therefore, the obtained results confirm that gammaGT inhibitors can enhance pharmacological action of DOX and CP, which may permit clinicians to decrease their doses thereby alleviating side effects. Aminoguanidine (nitric oxide synthase inhibitor) given alone was little cytotoxic to HepG2 cells, while its introduction to the medium together with DOX and CP significantly increased their cytotoxicity. Aminoguanidine on its own did not show any effect on GSH level in HepG2 cells, but markedly and significantly elevated its concentration when added in combination with CP but not with DOX. This indicates that when CP was used as a cytostatic, GSH level rose after treatment with its combination with both AC and aminoguanidine.

Requirement of transmembrane transport for S-nitrosocysteine-dependent modification of intracellular thiols

S-nitrosothiols have been implicated as intermediary transducers of nitric oxide bioactivity; however, the mechanisms by which these compounds affect cellular functions have not been fully established. In this study, we have examined the effect of S-nitrosothiol transport on intracellular thiol status and upon the activity of a target protein (caspase-3), in bovine aortic endothelial cells. We have previously demonstrated that the specific transport of amino acid-based S-nitrosothiols (S-nitroso-L-cysteine and S-nitrosohomocysteine) occurs via amino acid transport system L to generate high levels of intracellular protein S-nitrosothiols (Zhang, Y., and Hogg, N. (2004) Proc. Natl. Acad. Sci. U. S. A. 101, 7891-7896). In this study, we demonstrate that the transport of S-nitrosothiols is essential for these compounds to affect intracellular thiol levels and to modify intracellular protein activity. Importantly, the ability of these compounds to affect intracellular processes occurs independently of nitric oxide formation. These findings suggest that the major action of these compounds is not to liberate nitric oxide in the extracellular space but to be specifically transported into cells where they are able to modify cellular functions through nitric oxide-independent mechanisms.

The glutamate-glutamine cycle as an inducible, protective face of macrophage activation

Neuronal damage in HIV infection results mainly from chronic activation of brain tissue and involves inflammation, oxidative stress, and glutamate-related neurotoxicity. Glutamate toxicity acts via two distinct pathways: an excitotoxic one, in which glutamate receptors are hyperactivated, and an oxidative one, in which cystine uptake is inhibited, resulting in glutathione depletion, oxidative stress, and cell degeneration. A number of studies have shown that astrocytes normally take up glutamate, keeping extracellular glutamate concentration low in the brain and preventing excitotoxicity. They, in turn, provide the trophic amino acid glutamine via their expression of glutamine synthetase. These protective and trophic actions are inhibited in HIV infection, probably as a result of the effects of inflammatory mediators and viral proteins. In vitro and in vivo studies have demonstrated that activated microglia and brain macrophages (AMM) express the transporters and enzymes of the glutamate cycle. This suggests that in addition to their recognized neurotoxic properties in HIV infection, these cells exhibit some neuroprotective properties, which may partly compensate for the inhibited astrocytic function. This hypothesis might explain the discrepancy between microglial activation, which occurs early in the disease, and neuronal apoptosis and neuronal loss, which are late events. In this review, we discuss the possible neuroprotective and neurotrophic roles of AMM and their relationships with inflammation and oxidative stress.

Gene expression of phenylethanolamine N-methyltransferase in corticotropin-releasing hormone knockout mice during stress exposure

AIMS

Epinephrine (EPI) synthesizing enzyme phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28) is primarily localized in the adrenal medulla (AM). We have recently described existence of the PNMT gene expression in cardiac atria and ventricles and in sympathetic ganglia of adult rats and mice. The aim of the present work was to study regulation of the PNMT gene expression in corticotropin-releasing hormone knockout mice (CRH KO) and matched control wild-type mice (WT) under normal and stress conditions.

METHODS

Levels of the PNMT mRNA were determined by RT-PCR; PNMT immunoprotein and protein of transcription factor EGR-1 by Western Blot. Plasma EPI and corticosterone (CORT) levels were determined by radioenzymatic and RIA methods. Immobilization (IMMO) was used as a stressor.

RESULTS

Stress-induced increases in the PNMT mRNA and protein levels observed in WT mice were almost completely absent in CRH KO mouse adrenal medulla, stellate ganglia, and cardiac atria, while ventricular PNMT mRNA elevation was not CRH-dependent. Plasma EPI and CORT levels were markedly reduced in CRH KO compared to WT mice both before and after the stress. Levels of EGR-1, crucial transcription factor for regulation of the PNMT were highly increased in stressed WT and CRH KO mice in cardiac areas, but not in the adrenal medulla.

CONCLUSIONS

Data show that the CRH deficiency can markedly prevent immobilization-triggered induction of the PNMT mRNA and protein levels in the adrenal medulla and stellate ganglia. Reduced plasma epinephrine and corticosterone levels and adrenal medullary EGR-1 protein levels in CRH knockout versus WT mice during stress indicate that the HPA axis plays a crucial role in regulation of the PNMT gene expression in these organs. Cardiac atrial PNMT gene expression with stress is also dependent on intact HPA axis. However, in cardiac ventricles, especially after the single stress exposure, its expression is not impaired by CRH deficiency. Since cardiac EGR-1 protein levels in CRH KO mice are also not affected by the single stress exposure, we propose existence of different regulation of the PNMT gene expression, especially in the cardiac ventricles.Overall, our findings reveal that the PNMT gene expression is regulated through the HPA in both sympathoadrenal system and the heart and also via EGR-1 in the adrenal medulla, but apparently not in the heart. Regulation of the PNMT gene expression in various compartments of heart includes both corticosterone-dependent and independent mechanisms.

Regulated expression of sodium-dependent glutamate transporters and synthetase: a neuroprotective role for activated microglia and macrophages in HIV infection?

It is now widely accepted that neuronal damage in HIV infection results mainly from microglial activation and involves apoptosis, oxidative stress and glutamate-mediated neurotoxicity. Glutamate toxicity acts via 2 distinct pathways: an excitotoxic one in which glutamate receptors are hyperactivated, and an oxidative one in which cystine uptake is inhibited, resulting in glutathione depletion and oxidative stress. A number of studies show that astrocytes normally take up glutamate, keeping extracellular glutamate concentration low in the brain and preventing excitotoxicity. This action is inhibited in HIV infection, probably due to the effects of inflammatory mediators and viral proteins. Other in vitro studies as well as in vivo experiments in rodents following mechanical stimulation, show that activated microglia and brain macrophages express high affinity glutamate transporters. These data have been confirmed in chronic inflammation of the brain, particularly in SIV infection, where activated microglia and brain macrophages also express glutamine synthetase. Recent studies in humans with HIV infection show that activated microglia and brain macrophages express the glutamate transporter EAAT-1 and that expression varies according to the disease stage. This suggests that, besides their recognized neurotoxic properties in HIV infection, these cells also have a neuroprotective function, and may partly make up for the inhibited astrocytic function, at least temporarily. This hypothesis might explain the discrepancy between microglial activation which occurs early in the disease, and neuronal apoptosis and neuronal loss which is a late event. In this review article, we discuss the possible neuroprotective and neurotrophic roles of activated microglia and macrophages that may be generated by the expression of high affinity glutamate transporters and glutamine synthetase, 2 major effectors of glial glutamate metabolism, and the implications for HIV-induced neuronal dysfunction, the underlying cause of HIV dementia.

Regulation of lens aldose reductase activity by nitric oxide

To examine the regulation of aldose reductase (AR) activity by nitric oxide (NO) in human lens epithelial cells (HLEC), cultured rat lens, and normal and diabetic rat lens, we have incubated HLEC or cultured rat lenses with 1 mm of the NO donors S-nitroso-N-acetylpenicillamine (SNAP) or S-nitrosoglutathione (GSNO), and the AR activity and sorbitol content were measured. Non-diabetic and diabetic (treated with streptozotocin 65 mg kg(-1) body wt, i.p.) rats were injected with the nitric oxide synthase (NOS) inhibitor, L-NAME (50 mg kg(-1) body wt day(-1), x 10 days i.p.) or NOS substrate, L-arginine (200 mg kg(-1) body wt day(-1), x 10 days i.p.). In a separate group of rats, a nitroglycerin (NG)-patch that releases 200 ng min(-1) NO was applied to the dorsal neck region. After 10 days of treatment, the lenses were removed and their AR activity and sorbitol content were measured. Incubation of HLEC with SNAP or GSNO reduced AR activity. A similar reduction in AR activity and sorbitol accumulation was observed when diabetic and non-diabetic rat lenses were cultured in the presence of SNAP and GSNO. Total protein-SSG in diabetic lens was lower compared to normal lens. Treatment of diabetic and non-diabetic rats with L-NAME enhanced AR activity and sorbitol accumulation, whereas NG patch and L-arginine significantly decreased AR activity and sorbitol accumulation in diabetic lenses compared to non-diabetic. Increased S-glutathiolation of AR was observed in the presence of SNAP. These results suggest that decreased glutathiolation of cellular proteins in diabetic rat lens compared to non-diabetic lens is related to decreased NO availability in diabetic rats which would decrease GSNO. Restoring the NO levels in diabetic animals increases glutathiolation of cellular proteins, inhibits AR activity and prevents sorbitol accumulation. Exogenous delivery of NO may represent a potentially useful strategy for preventing or delaying diabetic cataractogenesis and the development of other diabetic complications.

Gene therapy vectors containing CArG elements from the Egr1 gene are activated by neutron irradiation, cisplatin and doxorubicin

Combining gene therapy with radiotherapy and chemotherapy holds potential to increase the efficacy of cancer treatment, while minimizing side effects. We tested the responsiveness of synthetic gene promoters containing CArG elements from the Early Growth Response 1 (Egr1) gene after neutron irradiation, doxorubicin and cisplatin. Human MCF-7 breast adenocarcinoma and U373-MG glioblastoma cells were transfected with plasmids containing CArG promoters controlling the expression of the green fluorescent protein (GFP). Exposing the cells to neutrons, doxorubicin or cisplatin resulted in a significant induction of transgene expression. Therapeutic advantage was demonstrated by replacing the reporter with the herpes simplex virus thymidine kinase (HSVtk), able to convert the prodrug ganciclovir (GCV) into a cytotoxin. A 1.3 Gy neutron dose caused 49% growth inhibition in MCF-7 cells, which increased to 63% in irradiated CArG-HSVtk-transfectants treated with GCV. Exposure to 0.5 microM cisplatin or 0.01 microM doxorubicin induced a growth inhibition of 25-30% in MCF-7 cells. In the presence of GCV, this value increased to 65-70% in cells transfected with the CArG promoter constructs driving the expression of HSVtk. These data indicate that combining CArG-mediated HSVtk/GCV suicide gene therapy with radio- and chemotherapy can enhance antitumor toxicity, and validates future in vivo investigations.

Treatment with 1,2,3,4-tetrahydroisoquinolone affects the levels of nitric oxide, S-nitrosothiols, glutathione and the enzymatic activity of γ-glutamyl transpeptidase in the dopaminergic structures of rat brain

Depletion of glutathione (GSH), nitrosative stress and chronic intoxication with some neurotoxins have been postulated to play a major role in the pathogenesis of Parkinson's disease. This study aimed to examine the effects of acute and chronic treatments with 1,2,3,4-tetrahydroisoquinoline (TIQ), an endo-/exogenous substance suspected of producing Parkinsonism in human, on the levels of nitric oxide (NO), S-nitrosothiols and glutathione (GSH) in the whole rat brain and in its dopaminergic structures. TIQ administered at a dose of 50 mg/kg i.p. significantly increased the tissue concentrations of NO and GSH in the substantia nigra (SN), striatum (STR) and cortex (CTX) of rats receiving this compound both acutely and chronically. Moreover, it decreased the level of oxidized glutathione (GSSG) and enhanced GSH:GSSG ratio affecting in this way the redox state of brain cells. TIQ also increased the level of S-nitrosothiols when measured in the whole rat brain and CTX, although it markedly decreased their level in the STR after both treatments. Inhibition of the constitutive NO synthase by l-NAME in the presence of TIQ caused decreases in GSH and S-nitrosothiol levels in the brain. The latter effect shows that the TIQ-mediated increases in GSH and S-nitrosothiol concentrations were dependent on the enhanced NO level. The above-described results suggest that TIQ can act as a modulator of GSH, NO and S-nitrosothiol levels but not as a parkinsonism-inducing agent in the rat brain.

Increase of intracellular glutathione by low-level NO mediated by transcription factor NF-κB in RAW 264.7 cells

The mechanism underlying the elevation of intracellular glutathione (GSH) in RAW 264.7 cells exposed to low concentrations of sodium nitroprusside (SNP), a well-known nitric oxide (NO) donor, was investigated. The peak of intracellular GSH was reached at 6 h after exposure of the cells to SNP (0.1-0.5 mM), and this was preceded by the induction of mRNA for gamma-glutamylcysteine synthetase (gamma-GCS; the rate-limiting enzyme of de novo GSH synthesis), which peaked at 3 h. N-alpha-Tosyl-L-phenylalanine chloromethyl ketone (TPCK) and caffeic acid phenethyl ester (CAPE), specific inhibitors of NF-kappaB, significantly suppressed the SNP-induced elevation of GSH protein and gamma-GCS mRNA, while curcumin, an inhibitor of AP-1, was less effective. Electrophoretic mobility shift assay (EMSA) showed that SNP exposure markedly increased the DNA binding of NF-kappaB, but not that of AP-1. Deletion or mutagenesis of the NF-kappaB site in the gamma-GCS gene promoter abolished the SNP-induced up-regulation of GSH protein and gamma-GCS mRNA. These results suggest that the elevation of intracellular GSH in RAW 264.7 cells exposed to low concentrations of SNP occurs through the operation of the de novo GSH pathway, and is mediated by transcriptional up-regulation of the gamma-GCS gene, predominantly at the NF-kappaB binding site in its promoter.

High glutathione turnover in human cell lines revealed by acivicin inhibition of gamma-glutamyltranspeptidase and the effects of thiol-reactive metals during acivicin inhibition

BACKGROUND

Glutathione is the most abundant nonprotein sulfhydryl-containing compound and constitutes the largest component of the endogenous thiol buffer. Glutathione is known to have multifaceted physiological functions and is a critical factor in protecting organisms against toxicity and disease. Intracellular cysteine concentration is a limiting factor for glutathione synthesis.

METHODS

In the present study, the metabolism of intra- and extracellular glutathione in HeLa and hepatoma cell cultures is investigated by using different transport inhibitors for cellular uptake of cystine/cysteine.

RESULTS

There exist several ways of cystine/cysteine transport into HeLa and hepatoma cells, and inhibition of them decreased intracellular concentration of cystine/cysteine and in some cases also of glutathione. It was also shown that a large pool of total cell culture glutathione was located extracellularly in both HeLa and hepatoma cell cultures when gamma-glutamyltranspeptidase (GT) activity was inhibited by acivicin (ACI). Furthermore, the addition of thiol-reactive metal ions significantly increased the total amount of glutathione in hepatoma cell cultures during acivicin inhibition. Thus, occasional determinations of extracellular concentrations of glutathione without GT inhibition strongly underestimate the total turnover of glutathione in a cell culture.

CONCLUSION

This finding has important implications for future research in glutathione metabolism and the understanding of its role in human health and disease.

Involvement of Mitochondrial Peroxynitrite in Nitric Oxide-Induced Glutathione Synthesis

Cells respond to oxidative stress including nitric oxide (NO) by increasing cellular glutathione concentration, as a part of adaptive response against oxidative injury. To elucidate the mechanism by which NO induces glutathione we investigated the reactive oxygen species (ROS) generated in the cell. Treatment of RAW264.7 cells with NO donor, sodium nitroprusside (SNP), resulted in a temporary increase in glutathione in a dose-dependent manner, which peaked between 6 h and 12 h after treatment, whereas expression of gamma-glutamylcysteine synthetase (gamma-GCS) mRNA peaked around 3 h after treatment. The increase was inhibited by NO scavengers, oxyhemoglobin and carboxyl-2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). N-Acetyl-L-cysteine (NAC) also reduced the increase in glutathione to some extent, whereas both peroxynitrite scavenger ebselen and hydroxyl radical scavenger DMSO inhibited the increase in glutathione in a dose-dependent manner and complete inhibition was observed. Hydrogen peroxide exogenously added to the cell did not increase either glutathione or gamma-GCS expression at any concentration, indicating that involvement of hydrogen peroxide is not likely. Flow cytometric analysis showed that SNP induced a marked dose-dependent increase in Rhodamine123 fluorescence, which was completely inhibited by ebselen in a dose-dependent manner, whereas, little increase in 2',7'-dichlorofluorescin (DCF) fluorescence was observed. Generation of peroxynitrite in mitochondria by SNP was confirmed by elevated level of nitrotyrosine in a mitochondria fraction isolated from SNP-treated cells, and the elevation was completely inhibited by ebselen as well. These results suggest that induction of glutathione (GSH) synthesis by SNP treatment is mediated by peroxynitrite generated in mitochondria.

Nitric oxide stimulates Nrf2 nuclear translocation in vascular endothelium

Vascular endothelial cells respond to nitric oxide by activating MAPK pathways and upregulating stress-activated proteins such as gamma-glutamylcysteine synthetase (gamma-GCS) and heme oxygenase-1 (HO-1). Since consensus sequences for the antioxidant response element (ARE) are found in the promoters of the gamma-GCS and HO-1 genes, we examined nuclear translocation of Nrf2, a CNC-bZIP protein which binds to and activates the ARE. We found a dramatic increase in Nrf2 nuclear translocation 1-8h following the nitric oxide donor spermine NONOate. Translocation was inhibited by pretreatment of cells with N-acetylcysteine suggesting involvement of an oxidative mechanism in this response. Translocation was also blocked by PD 98059 and SB 203580, inhibitors of ERK and p38 pathways, respectively. In addition to effects on Nrf2 subcellular localization, spermine NONOate increased Nrf2 protein levels by a mechanism which was inhibited by PD 98059. Pretreatment with N-acetylcysteine, PD 98059, and SB 203580 decreased HO-1 upregulation in spermine NONOate-treated cells. These results suggest that ERK and p38 pathways may regulate nitric oxide-mediated adaptive responses in vascular endothelium via translocation of Nrf2 and activation of the ARE.

Structural adaptation of the nuclear pore complex in stem cell-derived cardiomyocytes

Macromolecules are transported in and out of the nucleus through nuclear pores. It is poorly understood how these megadalton conduits support nucleocytoplasmic traffic during genetic reprogramming associated with cell commitment to a specific lineage. Murine embryonic stem cells were differentiated into cardiomyocytes within embryoid bodies, and contracting cells expressing myocardial-specific proteins were isolated from the mesodermal layer. Compared with postmitotic cardiac cells from heart muscle, these proliferative and differentiating stem cell-derived cardiomyocytes demonstrated a significantly lower density of nuclear pores. At nanoscale resolution, the pore channel was commonly unoccupied in heart muscle-isolated cardiac cells, yet a dense material, presumably the central transporter, protruded toward the cytosolic face of the nuclear pore complex in stem cell-derived cardiomyocytes. Stem cell-derived cardiac cells distributed the nuclear transport factor Ran in the nucleus, decreased the number of spare nuclear pore complexes from the cytosolic annulate lamellae reservoir, and expressed a set of nucleoporins, NUP214, NUP358, NUP153, and p62, involved in nuclear transport. Stem cell-derived cardiomyocytes secured transport of nuclear constitutive proteins, cardiogenic transcription factors, and cell cycle regulators, including the prototypic histone H1, myocyte enhancer binding factor 2, and p53. Thus, differentiating stem cell-derived cardiomyocytes undergo structural adaptation and mobilize nuclear transport regulators in support of nucleocytoplasmic communication during commitment to mature cardiac lineage.

Regulation of amino acid and glucose transporters in endothelial and smooth muscle cells

While transport processes for amino acids and glucose have long been known to be expressed in the luminal and abluminal membranes of the endothelium comprising the blood-brain and blood-retinal barriers, it is only within the last decades that endothelial and smooth muscle cells derived from peripheral vascular beds have been recognized to rapidly transport and metabolize these nutrients. This review focuses principally on the mechanisms regulating amino acid and glucose transporters in vascular endothelial cells, although we also summarize recent advances in the understanding of the mechanisms controlling membrane transport activity and expression in vascular smooth muscle cells. We compare the specificity, ionic dependence, and kinetic properties of amino acid and glucose transport systems identified in endothelial cells derived from cerebral, retinal, and peripheral vascular beds and review the regulation of transport by vasoactive agonists, nitric oxide (NO), substrate deprivation, hypoxia, hyperglycemia, diabetes, insulin, steroid hormones, and development. In view of the importance of NO as a modulator of vascular tone under basal conditions and in disease and chronic inflammation, we critically review the evidence that transport of L-arginine and glucose in endothelial and smooth muscle cells is modulated by bacterial endotoxin, proinflammatory cytokines, and atherogenic lipids. The recent colocalization of the cationic amino acid transporter CAT-1 (system y(+)), nitric oxide synthase (eNOS), and caveolin-1 in endothelial plasmalemmal caveolae provides a novel mechanism for the regulation of NO production by L-arginine delivery and circulating hormones such insulin and 17beta-estradiol.

Alterations in brain glutathione homeostasis induced by the nerve gas soman

Public awareness of the dangers of chemical and biological warfare has been heightened in recent times. In particular, chemical nerve agents such as soman and its analogs have been developed and used in war as well as recent incidents, such as in Iraq and Japan. Soman, a rapid acting acetylcholinesterase inhibitor, produces a status epilepticus that leads to extensive neuropathology in vulnerable brain regions (eg, piriform cortex and hippocampus). This study was undertaken to determine whether oxidative mechanisms are involved in brain pathology during soman toxicity. Intracellular thiols such as glutathione (GSH) and protein sulfhydryls (PrSH) are among the most critical antioxidants used to combat oxidative stress. Here we report that during the seizure phase (1 h post soman exposure), PrSH levels in piriform cortex and hippocampus were decreased without changes in glutathione (GSH) levels. However, by 24 h post soman exposure (pathology phase), GSH levels were decreased by nearly 50% in the piriform cortex with a corresponding decrease in PrSH groups. The shift to a more oxidized thiol status indicates that oxygen free radicals likely participate in the neuropathology associated with soman-induced seizures.

Cerebral cystine uptake: a tale of two transporters

Transport of cystine across the cell membrane is essential for synthesis of the major cellular antioxidant glutathione. Cystine uptake in the brain occurs by both the Na(+)-independent x(c)(-) cystine-glutamate exchanger and the X(AG)(-) family of high-affinity, Na(+)-dependent glutamate transporters. New evidence concerning the role of cystine transport in the defence against oxidative stress is described.

Role of glutamate transporters in the regulation of glutathione levels in human macrophages

Cysteine is the limiting precursor for glutathione synthesis. Because of its low bioavailability, cysteine is generally produced from cystine, which may be taken up through two different transporters. The cystine/glutamate antiporter (x system) transports extracellular cystine in exchange for intracellular glutamate. The X(AG) transport system takes up extracellular cystine, glutamate, and aspartate. Both are sensitive to competition between cystine and glutamate, and excess extracellular glutamate thus inhibits glutathione synthesis, a nonexcitotoxic mechanism for glutamate toxicity. We demonstrated previously that human macrophages express the glutamate transporters excitatory amino acid transporter (EAAT)1 and EAAT2 (which do not transport cystine, X system) and overcome competition for the use of cystine transporters. We now show that macrophages take up cystine through the x and not the X(AG) system. We also found that glutamate, although competing with cystine uptake, dose-dependently increases glutathione synthesis. We used inhibitors to demonstrate that this increase is mediated by EAATs. EAAT expression in macrophages thus leads to glutamate-dependent enhancement of glutathione synthesis by providing intracellular glutamate for direct insertion in glutathione and also for fueling the intracellular pool of glutamate and trans-stimulating the cystine/glutamate antiporter.

Heteromeric amino acid transporters: biochemistry, genetics, and physiology

The heteromeric amino acid transporters (HATs) are composed of two polypeptides: a heavy subunit (HSHAT) and a light subunit (LSHAT) linked by a disulfide bridge. HSHATs are N-glycosylated type II membrane glycoproteins, whereas LSHATs are nonglycosylated polytopic membrane proteins. The HSHATs have been known since 1992, and the LSHATs have been described in the last three years. HATs represent several of the classic mammalian amino acid transport systems (e.g., L isoforms, y(+)L isoforms, asc, x(c)(-), and b(0,+)). Members of the HAT family are the molecular bases of inherited primary aminoacidurias cystinuria and lysinuric protein intolerance. In addition to the role in amino acid transport, one HSHAT [the heavy subunit of the cell-surface antigen 4F2 (also named CD98)] is involved in other cell functions that might be related to integrin activation. This review covers the biochemistry, human genetics, and cell physiology of HATs, including the multifunctional character of CD98.

Modulation of adenosine transport by insulin in human umbilical artery smooth muscle cells from normal or gestational diabetic pregnancies

1. Adenosine transport was measured in human cultured umbilical artery smooth muscle cells, isolated from non-diabetic or gestational diabetic pregnancies, under basal conditions and after pretreatment in vitro with insulin. 2. Adenosine transport in non-diabetic smooth muscle cells was significantly increased by insulin (half-maximal stimulation at 0.33 +/- 0.02 nM, 8 h) and characterized by a higher maximal rate (V(max)) for nitrobenzylthioinosine (NBMPR)-sensitive (es) saturable nucleoside transport (17 +/- 5 vs. 52 +/- 12 pmol (microg protein)(-1) min(-1), control vs. insulin, respectively) and maximal binding sites (B(max)) for [(3)H]NBMPR (0.66 +/- 0.07 vs. 1.1 +/- 0.1 fmol (microg protein)(-1), control vs. insulin, respectively), with no significant changes in Michaelis-Menten (K(m)) and dissociation (K(d)) constants. 3. In contrast, in smooth muscle cells from diabetic pregnancies, where the values of V(max) for adenosine transport (59 +/- 4 pmol (microg protein)(-1) min(-1)) and B(max) for [(3)H]NBMPR binding (1.62 +/- 0.16 fmol (microg protein)(-1)) were significantly elevated by comparison with non-diabetic cells, insulin treatment (1 nM, 8 h) reduced the V(max) for adenosine transport and B(max) for [(3)H]NBMPR binding to levels detected in non-diabetic cells. 4. In non-diabetic cells, the stimulatory effect of insulin on adenosine transport was mimicked by dibutyryl cGMP (100 nM) and reduced by inhibitors of phosphatidylinositol 3-kinase (10 nM wortmannin), nitric oxide synthase (100 microM N (G)-nitro-L-arginine methyl ester, L-NAME) or protein synthesis (1 microM cycloheximide), whereas inhibition of adenylyl cyclase (100 microM SQ-22536) had no effect. 5. Wortmannin or SQ-22536, but not L-NAME or cycloheximide, attenuated the inhibitory action of insulin on the diabetes-induced stimulation of adenosine transport. 6. Protein levels of inducible NO synthase (iNOS) were similar in non-diabetic and diabetic cells, but were increased by insulin (1 nM, 8 h) only in non-diabetic smooth muscle cells. 7. Our results suggest that adenosine transport via the es nucleoside transporter is modulated differentially by insulin in either cell type. Insulin increased adenosine transport in non-diabetic cells via NO and cGMP, but inhibited the diabetes-elevated adenosine transport via activation of adenylyl cyclase, suggesting that the biological actions of adenosine may be altered under conditions of sustained hyperglycaemia in uncontrolled diabetes.

Rethinking cystic fibrosis pathology: the critical role of abnormal reduced glutathione (GSH) transport caused by CFTR mutation

Though the cause of cystic fibrosis (CF) pathology is understood to be the mutation of the CFTR protein, it has been difficult to trace the exact mechanisms by which the pathology arises and progresses from the mutation. Recent research findings have noted that the CFTR channel is not only permeant to chloride anions, but other, larger organic anions, including reduced glutathione (GSH). This explains the longstanding finding of extracellular GSH deficit and dramatically reduced extracellular GSH:GSSG (glutathione disulfide) ratio found to be chronic and progressive in CF patients. Given the vital role of GSH as an antioxidant, a mucolytic, and a regulator of inflammation, immune response, and cell viability via its redox status in the human body, it is reasonable to hypothesize that this condition plays some role in the pathogenesis of CF. This hypothesis is advanced by comparing the literature on pathological phenomena associated with GSH deficiency to the literature documenting CF pathology, with striking similarities noted. Several puzzling hallmarks of CF pathology, including reduced exhaled NO, exaggerated inflammation with decreased immunocompetence, increased mucus viscoelasticity, and lack of appropriate apoptosis by infected epithelial cells, are better understood when abnormal GSH transport from epithelia (those without anion channels redundant to the CFTR at the apical surface) is added as an additional explanatory factor. Such epithelia should have normal levels of total glutathione (though perhaps with diminished GSH:GSSG ratio in the cytosol), but impaired GSH transport due to CFTR mutation should lead to progressive extracellular deficit of both total glutathione and GSH, and, hypothetically, GSH:GSSG ratio alteration or even total glutathione deficit in cells with redundant anion channels, such as leukocytes, lymphocytes, erythrocytes, and hepatocytes. Therapeutic implications, including alternative methods of GSH augmentation, are discussed.