Regulation of iNOS mRNA levels in endothelial cells by glutathione, a double-edged sword

Glutathione and Nitric Oxide: Key Team Players in Use and Disuse of Skeletal Muscle

Glutathione (GSH) is the main non-enzymatic antioxidant playing an important role in detoxification, signal transduction by modulation of protein thiols redox status and direct scavenging of radicals. The latter function is not only performed against reactive oxygen species (ROS) but GSH also has a fundamental role in buffering nitric oxide (NO), a physiologically-produced molecule having-multifaceted functions. The efficient rate of GSH synthesis and high levels of GSH-dependent enzymes are characteristic features of healthy skeletal muscle where, besides the canonical functions, it is also involved in muscle contraction regulation. Moreover, NO production in skeletal muscle is a direct consequence of contractile activity and influences several metabolic myocyte pathways under both physiological and pathological conditions. In this review, we will consider the homeostasis and intersection of GSH with NO and then we will restrict the discussion on their role in processes related to skeletal muscle function and degeneration.

N-Acetylcysteine increases corneal endothelial cell survival in a mouse model of Fuchs endothelial corneal dystrophy

The present study evaluated survival effects of N-acetylcysteine (NAC) on cultured corneal endothelial cells exposed to oxidative and endoplasmic reticulum (ER) stress and in a mouse model of early-onset Fuchs endothelial corneal dystrophy (FECD). Cultured bovine corneal endothelial cell viability against oxidative and ER stress was determined by CellTiter-Glo(®) luminescent reagent. Two-month-old homozygous knock-in Col8a2(L450W/L450W) mutant (L450W) and C57/Bl6 wild-type (WT) animals were divided into two groups of 15 mice. Group I received 7 mg/mL NAC in drinking water and Group II received control water for 7 months. Endothelial cell density and morphology were evaluated with confocal microscopy. Antioxidant gene (iNos) and ER stress/unfolded protein response gene (Grp78 and Chop) mRNA levels and protein expression were measured in corneal endothelium by real time PCR and Western blotting. Cell viability of H2O2 and thapsigargin exposed cells pre-treated with NAC was significantly increased compared to untreated controls (p < 0.01). Corneal endothelial cell density (CD) was higher (p = 0.001) and percent polymegathism was lower (p = 0.04) in NAC treated L450W mice than in untreated L450W mice. NAC treated L450W endothelium showed significant upregulation of iNos, whereas Grp78 and Chop were downregulated compared to untreated L450W endothelium by real time PCR and Western blotting. NAC increases survival in cultured corneal endothelial cells exposed against ER and oxidative stress. Systemic NAC ingestion increases corneal endothelial cell survival which is associated with increased antioxidant and decreased ER stress markers in a mouse model of early-onset FECD. Our study presents in vivo evidence of a novel potential medical treatment for FECD.

Effect of lipopolysaccharide on the production of prostaglandin E2 and inhibition of uterine contractions by nitric oxide in pregnant inducible nitric oxide synthase knockout mice

AIM

The aim of the present study was to evaluate the effect of lipopolysaccharide (LPS) on the production of prostaglandin E2 (PGE2) and inhibition by nitric oxide (NO) of spontaneous contractions of uterine rings from pregnant inducible isoform of nitric oxide synthase knockout (iNOS KO) mice.

MATERIAL AND METHODS

iNOS KO and wild-type mice were sacrificed 6 h after intraperitoneal (i.p.) administration of LPS on day 14 of gestation. Uterine rings were equilibrated in Krebs-Henseleit solution for isometric tension recording. In part of the uterine rings, placental tissues were left attached. The bathing solution was analyzed for PGE2 by radioimmunoassay. Changes in spontaneous contractions in response to cumulative concentrations of L-arginine, diethylamine/nitric oxide (DEA/NO), and 8-bromo-cyclic guanosine monophosphate (8-br-cGMP) were determined.

RESULTS

Treatment with LPS increased PGE2 production by uterine rings from wild-type and iNOS-KO mice. DEA/NO and 8-br-cGMP inhibited spontaneous contractions in uterine rings in the absence or presence of placenta, in both LPS-treated and LPS-untreated animals. LPS treatment attenuated maximal inhibition induced by the agents, both in the absence and presence of placental tissues in iNOS KO and wild-type mice.

CONCLUSION

LPS induces PG production in mice myometrium that is not dependent on the integrity of iNOS, while LPS could induce pathophysiological iNOS obstruct uterine quiescence by physiological iNOS. Infection affects uterine contractile activity through PG production, as well as through placental and genetic factors. NO may be a double-edged sword in pregnant mice myometrium.

A new model of cystic fibrosis pathology: Lack of transport of glutathione and its thiocyanate conjugates

Many of the symptoms of cystic fibrosis are not explained by the current disease mechanisms. Therefore, the authors conducted an extensive literature review and present a new model of cystic fibrosis pathology, which is the culmination of this research. Understanding that the cystic fibrosis transmembrane conductance regulator (CFTR) is responsible for glutathione (GSH) transport, the authors hypothesize that mutations of the CFTR, which create abnormal GSH transport, will lead to aberrations of GSH levels in both the intracellular as well as the extracellular milieu. These alterations in normal cellular GSH levels affect the redox state of the cell, thereby affecting the intracellular stress protein, metallothionein. The authors describe how this disruption of the redox state caused by excess cellular GSH, will naturally prevent the delivery of zinc as a cofactor for various enzymatic processes, and how these disruptions in normal redox may cause alterations in both humoral and cell-mediated immunity. Moreover, the symptom of thick sticky mucus in these patients might be explained through the understanding that oversulfation of mucus is a direct result of elevated cellular GSH and cysteine. The issues of hyperinflammation, altered pH and the imbalance of fatty acids that are typical in cystic fibrosis are addressed-all of which may also be linked to disruptions in GSH homeostasis. Additionally, this new model of cystic fibrosis pathology, clarifies the relationship between the CFTR and the multi-drug resistance proteins, and the lack of cell-mediated immunity by predicting that the substrate of these proteins is a glutathione adduct of thiocyanate. Finally, a new therapeutic strategy by using isothiocyanates to rectify the GSH imbalance and restore the immune system is suggested for the treatment of cystic fibrosis patients.

Antioxidant and anti-inflammatory efficacy of NAC in the treatment of COPD: discordant in vitro and in vivo dose-effects: a review

In order to develop efficient therapeutic regimes for chronic obstructive pulmonary disease (COPD), N-acetylcysteine (NAC) has been tested as a medication which can suppress various pathogenic processes in this disease. Besides its well-known and efficient mucolytic action, NAC meets these needs by virtue of its antioxidant and anti-inflammatory modes of action. NAC is a thiol compound which by providing sulfhydryl groups, can act both as a precursor of reduced glutathione and as a direct ROS scavenger, hence regulating the redox status in the cells. In this way it can interfere with several signaling pathways that play a role in regulating apoptosis, angiogenesis, cell growth and arrest and inflammatory response. Overall, the antioxidant effects of NAC are well documented in in vivo and in vitro studies. It successfully inhibits oxidative stress at both high and low concentrations, under acute (in vitro) and chronic administration (in vivo). With regard to its anti-inflammatory action, in contrast, the effects of NAC differ in vivo and in vitro and are highly dose-dependent. In the in vitro settings anti-inflammatory effects are seen at high but not at low concentrations. On the other hand, some long-term effectiveness is reported in several in vivo studies even at low dosages. Increasing the dose seems to improve NAC bioavailability and may also consolidate some of its effects. In this way, the effects that are observed in the clinical and in vivo studies do not always reflect the success of the in vitro experiments. Furthermore, the results obtained with healthy volunteers do not always provide incontrovertible proof of its usefulness in COPD especially when number of exacerbations and changes in lung function are chosen as the primary outcomes. Despite these considerations and in view of the present lack of effective therapies to inhibit disease progression in COPD, NAC and its derivatives, because of their multiple molecular modes of action, remain promising medication once doses and route of administration are optimized.

Natural compounds derived from foods modulate nitric oxide production and oxidative status in epithelial lung cells

The effects of natural antioxidants on nitric oxide (NO) modulation and oxidative status were determined in rat epithelial lung cells (L-2). Cells were stimulated with cytokines and treated with one of the following: resveratrol, soybean saponin group B (SSB), quercetin, genistein, olive leaf polyphenol concentrate (OLPC), or N-acetyl-L-cystein (NAC). NAC had no effect on NO levels, whereas resveratrol and OLPC were found to be effective in reducing nitrite levels, modifying iNOS mRNA, and decreasing free radical production. OLPC affected the levels of MnSOD while resveratrol did not, indicating that they act via different pathways. Quercetin and genistein reduced nitrite levels without affecting iNOS levels, presumably by scavenging NO. SSB did not affect nitrite levels, but exposure did reduce iNOS mRNA expression and protein levels, possibly due to antioxidant activity. Naturally occurring antioxidants, in particular resveratrol and OLPC, may have therapeutic potential in the treatment of inflammatory diseases.

Triacylglycerol-mediated oxidative stress inhibits nitric oxide production in rat isolated hepatocytes

This study was designed to evaluate the effects of triacylglycerol (TG) on nitric oxide (NO) production, expression of endothelial (e) and inducible (i) nitric oxide synthase (NOS) and variables related to oxidative stress in rat isolated hepatocytes. Hepatocytes were isolated and exposed to TG in the form of a lipid emulsion (0.01-0.1% LE). Exposure to LE dose dependently decreased nitrite levels. Nitrite levels were inhibited 67% and intracellular reactive oxygen species (ROS) levels were increased 250% at 0.1% LE. The decline in nitrite levels was accompanied by 37 and 67% reductions in iNOS and eNOS expressions, respectively. To evaluate whether the increased oxidative stress inhibited NOS synthesis, cells were treated for 48 h with rotenone (a mitochondrial complex 1 inhibitor) or buthionine sulfoximine (a glutathione synthesis inhibitor). Both compounds elevated ROS production, which was followed by inhibition of nitrite production. To determine whether there is an association between LE-mediated ROS production and the inhibition of NO synthesis by the LE, hepatocytes were treated with antioxidants. N-Acetyl-l-cysteine (NAC), ascorbate, and resveratrol attenuated the reduction of nitrite levels due to LE alone. NAC inhibited the reductions in eNOS and iNOS transcription and protein levels. Nuclear factor-kappaB (NF-kappaB), one of the transcription factors involved in eNOS and iNOS transcriptional regulation, was decreased 15% in the nucleus by LE treatment. These results suggest that TG reduces nitrite production by elevating intracellular ROS levels (prolonged oxidative stress), and the downregulation of NOS enzymes may occur at least in part via the NFkappaB pathway.

Effect of dietary restriction and N-acetylcysteine supplementation on intestinal mucosa and liver mitochondrial redox status and function in aged rats

The age-related changes of glutathione (GSH) levels and the effect of hypocaloric regimen and N-acetylcysteine (NAC) supplementation were investigated in intestinal mucosa and liver mitochondria of 28 months rats. Old rats exhibited lower proteins, GSH and protein sulphydrils (PSH) concentrations, higher GSH-peroxidase (GSH-Px) activity and protein carbonyl deposit, partial inhibition of succinate stimulated mitochondrial state III respiration and decreased mitochondrial nitrosothiols (RSNO) concentration. Lower electric potential and current intensity were found in the colonic mucosa. Old rats undergone hypocaloric regimen showed higher intestinal concentrations of GSH, lower oxidized protein accumulation and GSH-Px activity and higher mitochondrial RSNO levels. Mitochondrial state III respiration and intestinal transport were improved. NAC supplementation enhanced GSH and PSH levels in the ileal but not in the colonic mucosa, GSH and RSNO in liver mitochondria, while GSH-Px and protein carbonyls were decreased everywhere. Mitochondrial respiration ameliorated. In conclusion, ageing is characterized by a spread decrease of GSH concentrations, increased protein oxidation and decreased mitochondrial NO content. Hypocaloric diet ameliorated intestinal transport and, as well as NAC, was effective in enhancing GSH levels but at different extent according to the investigated districts. Both interventions reduced the age-associated increase of GSH-Px and protein carbonyls and improved mitochondrial respiration.

A Pilot Study of the Effect of Inhaled Buffered Reduced Glutathione on the Clinical Status of Patients With Cystic Fibrosis

STUDY OBJECTIVES

To assess the impact of inhaled, buffered reduced glutathione (GSH) on clinical indicators of cystic fibrosis (CF) pathophysiology.

DESIGN AND PATIENTS

A randomized, double-blind, placebo-controlled pilot study was conducted over an 8-week period. Nineteen subjects, age 6 to 19 years, with CF status documented by positive sweat chloride test results (> 60 mEq/L) were recruited for the trial. After matching on age and sex, 10 patients were randomly assigned to the treatment group and 9 patients to the placebo group. Primary outcomes were FEV1, FVC, forced expiratory flow at 25 to 75% of vital capacity, and peak flow; secondary outcomes were body mass index, 6-min walk distance, and self-reported cough frequency, mucus production/viscosity/color, wellness, improvement, and stamina. INTERVENTIONS AND ANALYSIS: Treatment was buffered GSH, and placebo was sodium chloride with a hint of quinine. The total daily dose of buffered GSH was approximately 66 mg/kg of body weight, and the total daily dose of placebo was approximately 15 mg/kg of body weight (quinine, 25 to 30 microg/kg). Doses were distributed across four inhalation sessions per day and spaced 3- to 4-h apart. General linear mixed models were used to analyze the data. The final sample size was nine subjects in the treatment group and seven subjects in the placebo group.

RESULTS

Mean change for peak flow was -6.5 L/min for the placebo group and +33.7 L/min for the GSH group (p = 0.04), and self-reported average improvement on a scale from 1 to 5 (1 being much worse and 5 being much better) was 2.8 for placebo and 4.7 for GSH (p = 0.004). Of the 13 primary and secondary outcomes examined, 11 outcomes favored the treatment group over the placebo group (p = 0.002), indicating a general tendency of improvement in the GSH group. No adverse events in the treatment group were noted.

CONCLUSION

This pilot study indicates the promise of nebulized buffered GSH to ameliorate CF disease, and longer, larger, and improved studies of inhaled GSH are warranted.

Apocynin prevents cyclooxygenase 2 expression in human monocytes through NADPH oxidase and glutathione redox-dependent mechanisms

In the present study we report the preventive effect of apocynin, an active constituent of the Himalayan herb Picrorhiza kurrooa, on cyclooxygenase-2 (Cox-2) synthesis and activity in human adherent monocytes exposed to serum treated zymosan (STZ) and phorbol myristate acetate (PMA). Apocynin markedly decreases the intracellular reduced/oxidized glutathione ratio (GSH/GSSG) and prevents nuclear factor-kappaB (NF-kappaB) activation in stimulated monocytes. Moreover, it reduces intracellular reactive oxygen species (ROS) generation, NADPH oxidase activity in monocyte homogenates and translocation of p47phox subunit in monocyte membranes. p47phox levels are also reduced in lysates of apocynin-treated monocytes. The inhibition of Cox-2 by apocynin is completely abrogated by GSH provision. Results from this study indicate that apocynin inhibits Cox-2 synthesis and activity induced in monocytes by an increased oxidative tone and provide an explanation for the protective effect exerted by this compound in numerous cell and animal models of inflammation. Attenuation of NADPH oxidase derived ROS coupled with GSH/GSSG reduction and suppression of NF-kappaB activation are highlighted as the molecular mechanisms responsible for Cox-2 inhibition.

Tributyltin-sulfhydryl interaction as a cause of immunotoxicity in phagocytes of tunicates

We reported elsewhere that tributyltin (TBT) has detrimental effects on the immune system of the colonial ascidian Botryllus schlosseri, through interaction with calmodulin and alteration of Ca2+ homeostasis. Here, we studied the capability of TBT to react with intracellular thiols. After exposure to 0.1 microM TBT, a significant decrease in B. schlosseri hemocytes stained for total thiols and reduced glutathione (GSH) was detected. Exogenous sulfhydryl and sulfide compounds can prevent TBT-induced cell morphology alterations and decrease the percentage of tin-containing hemocytes, indicating the scavenging ability of thiol peptides. No effects were observed with disulfides, N-acetylcysteine, or the GSH fragment Cys-Gly. No interactions were observed with TBT and carmustine, whereas TBT and N-ethylmaleimide (NEM) showed a combined antagonistic action, suggesting direct interaction of TBT with thiol-containing compounds. Regulation of Ca2+ efflux from internal stores seems to depend on stimulation of the inositol 1,4,5-trisphosphate (InsP3) receptor by oxidized glutathione (GSSG), which results from interactions of both TBT-GSH and TBT-GSH reductase.

Differential expression of inducible nitric oxide synthase and peroxisome proliferator-activated receptor gamma in non-small cell lung carcinoma

Both inducible nitric oxide synthase (iNOS) and peroxisome proliferator-activated receptor gamma (PPARgamma) are closely associated with the development of human cancer. Although the expression of iNOS has been studied in non-small cell lung carcinoma (NSCLC), the level of PPARgamma has not been examined in tumorous and non-tumorous tissues from NSCLC. The present study analysed the levels of both iNOS and PPARgamma in NSCLC tissues and in lung cell lines. The possible role of these two molecules in the carcinogenesis of lung cancer was investigated. The expression of iNOS was significantly higher in the tumorous tissues than in the non-tumorous ones. In contrast to this pattern of iNOS protein expression, the level of PPARgamma was much lower in the tumorous tissues than in the non-tumorous samples. A similar result was also obtained in vitro using human lung cancer cell lines and normal lung cells. Immunohistochemical examination revealed that PPARgamma expression in the non-tumorous tissues was more likely to be located in the nucleus whereas it was present in both the nucleus and cytoplasm of the tumorous tissues. The intensity of iNOS expression was stronger in the nucleus than in the cytoplasm of the tumorous tissues. More than 50% of the cases tested did not express iNOS protein in the non-tumorous tissues. Statistical analysis indicated a negative correlation between iNOS and PPARgamma levels in the NSCLC tissues. In conclusion, this study demonstrated differing expressions for iNOS and PPARgamma in NSCLC tissues. Since activated PPARgamma is able to inhibit the expression of iNOS and the generation of iNOS is particularly associated with the inflammatory and environmental factors of lung cancer risk, this discrepant expression pattern may be associated with the pathogenesis of NSCLC.

Relationship between gluconeogenesis and glutathione redox state in rabbit kidney-cortex tubules

The intracellular glutathione redox state and the rate of glucose formation were studied in rabbit kidney-cortex tubules. In the presence of substrates effectively utilized for glucose formation, ie, aspartate + glycerol + octanoate, alanine + glycerol + octanoate, malate, or pyruvate, the intracellular reduced glutathione/oxidized glutathione (GSH/GSSG) ratios were significantly higher than those under conditions of negligible glucose production. Changes in the intracellular GSH/GSSG ratio corresponded to those in glucose-6-phosphate content and reduced nicotinamide adenine dinucleotide phosphate/oxidized nicotinamide adenine dinucleotide phosphate (NADPH/NADP(+)) ratio obtained from malate/pyruvate measurements. Gluconeogenesis stimulation by extracellular adenosine triphosphate (ATP) or inosine caused an elevation of the intracellular GSH/GSSG and NADPH/NADP(+) ratios, as well as glucose-6-phosphate level. Surprisingly, in the presence of 5 mmol/L glucose, both the intracellular GSH/GSSG and NADPH/NADP(+) ratios and glucose-6-phosphate content were almost as low as under conditions of negligible glucose synthesis. L-buthionine sulfoximine (BSO)-induced decline in both the intracellular glutathione level and redox state resulted in inhibition of gluconeogenesis accompanied by accumulation of phosphotrioses and a decrease in fructose-1,6-bisphosphate content, while cysteine precursors altered neither GSH redox state nor the rate of glucose formation. In view of the data, it seems likely that: (1) intensive gluconeogenesis rather than extracellular glucose is responsible for maintaining a high intracellular GSH/GSSG ratio due to effective glucose-6-phosphate delivery for NADPH generation via the pentose phosphate pathway; (2) a decline in the intracellular glutathione level and/or redox state causes a decrease in glucose synthesis resulting from a diminished flux through aldolase; (3) induced by cysteine precursors, elevation of the intracellular GSH level does not affect the rate of glucose formation, probably due to no changes in the intracellular GSH/GSSG ratio.

N-acetylcysteine ameliorates renal microcirculation: studies in rats

BACKGROUND

N-acetylcysteine (NAC) administration has been shown to ameliorate experimental acute renal failure induced by ischemia-reflow, and was found to prevent radiocontrast nephropathy in high-risk patients. While the protective effect of NAC has been primarily attributed to scavenging oxygen free radicals, improving renal microcirculation also may play a role in the prevention of acute renal failure.

METHODS

This study was designed to explore the effect of NAC on renal microcirculation. Blood pressure, total renal blood flow and selective regional cortical and outer medullary blood flow were continuously monitored in anesthetized Sprague Dawley rats with ultrasonic and laser-Doppler probes during the infusion of NAC (60 mg/kg).

RESULTS

In control intact rats blood pressure and renal microcirculation were unaffected by NAC. By contrast, following renal vasoconstriction induced by the radiocontrast agent iothalamate meglumine, NAC decreased total, cortical and medullary vascular resistance by 7 to 10% (P < 0.05). NAC also reduced renal vascular resistance by 16% when given during angiotensin II infusion (P < 0.05). Altered renal microcirculation, induced by the cyclooxygenase inhibitor indomethacin, by the nitric oxide synthase-inhibitor, Nomeganitro-l-arginine (L-NAME), or with their combination was partially restored by NAC. Nevertheless, NAC administration failed to attenuate renal function and morphology in a rat model of acute renal failure with selective outer medullary hypoxic injury, induced by indomethacin, L-NAME and iothalamate.

CONCLUSIONS

NAC ameliorates renal vasoconstriction, an effect that seems to be mediated by mechanisms other than prostaglandins and nitric oxide. The potential renoprotective outcome of NAC and the role of its vasodilating effect on the pre-constricted renal vasculature should be evaluated further.

Infection in the chronically critically ill: unique risk profile in a newly defined population

Although CCI is defined as prolonged ventilatory failure with tracheotomy stemming from preceding critical illness, the contention that multisystem debilities impact on most CCI patients' care and recovery is a central thesis of this volume. Perhaps reflecting the combined debilities inherent in CCI, infectious complications take their toll in morbidity, mortality, and persistent ventilatory insufficiency. Enhanced susceptibility to infection results from a potent admixture of barrier breakdown, exposure to virulent and resistant nosocomial pathogens, and postulated "immune exhaustion" that stems from the combined impact of comorbidities and the sequellae of critical illness. Strategies to improve outcome in CCI-related infection include standard measures of support especially nutrition, reducing environmental inoculum through pulmonary hygiene measures, skin care, and limiting barrier breaches, and appropriate antimicrobials directed at likely pathogens. Future stratification of patient risk on the basis of immune phenotype or genotype and potential immunomodulatory prophylaxis may be around the corner, as new prospects in the pharmaceutical armamentarium are presently undergoing testing.

Dietary glycine inhibits activation of nuclear factor kappa B and prevents liver injury in hemorrhagic shock in the rat

We investigated the effects of a glycine-containing diet (5%) on liver injury caused by hemorrhagic shock and resuscitation in rats. Anesthetized rats were bled to a mean arterial blood pressure of 35-40 mm Hg for 1 h and then resuscitated with 60% of shed blood and lactated Ringer's solution. Feeding the rats glycine significantly reduced mortality, the elevation of plasma transaminase levels and hepatic necrosis. The increase in plasma TNFalpha and nitric oxide (NO) was also blunted by glycine feeding. Hemorrhagic shock resulted in oxidative stress (significant elevations in TBARS and in the oxidized/reduced glutathione ratio) and was accompanied by a reduced activity of the antioxidant enzymes Mn- and Cu,Zn-superoxide dismutase, glutathione peroxidase and catalase, overexpression of inducible NO synthase (iNOS), and activation of nuclear factor kappa B (NF-kappaB). Glycine ameliorated oxidative stress and the impairment in antioxidant enzyme activities, inhibited NF-kappaB activation, and prevented expression of iNOS. Dietary glycine blocks activation of different mediators involved in the pathophysiology of liver injury after shock.

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.

Effect of redox modulation on xenogeneic target cells: the combination of nitric oxide and thiol deprivation protects porcine endothelial cells from lysis by IL-2-activated human NK cells

Evidence suggests that NK cells contribute to the pathogenesis of delayed rejection of vascularized xenografts, and NK cells have been suggested to participate in hyperacute xenograft rejection. Endothelial cells have been shown to be the primary target of the recipient's immune responses that mediate both hyperacute and delayed xenograft rejection. Under conditions of oxidative stress induced by thiol deprivation, but not under normal conditions, pretreatment of porcine aortic endothelial cells (PAECs) with the NO donor, S-nitroso-N-acetyl-penicillamine, dramatically inhibited killing of PAEC target cells by IL-2-activated human NK cells. This same combined treatment reduced both surface expression and mRNA levels of E-selectin. Moreover, anti-E-selectin mAb, but not Ab to VCAM-1, protected PAEC from lysis by human IL-2-activated NK cells in a dose-dependent manner. These findings suggest that expression of porcine E-selectin is important for the cytotoxicity of PAEC mediated by activated human NK cells and may be involved in the redox-mediated modulation of that cytotoxicity. It is known that NF-kappa B activation is required for transcription of E-selectin, and the current data show that the suppression of E-selectin expression by S-nitroso-N-acetyl-penicillamine pretreatment and thiol deprivation was associated with reduced NF-kappa B DNA-binding activity in PAEC. These data suggest that the regulation of porcine E-selectin may be important for modulating delayed xenograft rejection and that manipulation of cellular redox systems may provide a means to protect xenogeneic endothelial cells from NK cell-mediated cytotoxicity.

Regulation of iNOS expression and glutathione levels in rat liver by oxygen tension

Molecular oxygen (O(2)) regulates the expression of a variety of genes. We hypothesized that O(2) tension may regulate iNOS expression in rat liver through the production of reactive oxygen species (ROS) and the reduction of intracellular glutathione (GSH) levels. To investigate this hypothesis, we determined the effects of hyperoxia upon iNOS induction (both at the protein and mRNA level) and the intracellular concentration of GSH in an isolated in vitro perfused rat liver preparation. To study the potential involvement of ROS in the intracellular signaling pathway linking changes in oxygen tension to gene expression, we repeated these determinations in the presence of the thiol antioxidant N-acetyl-L-cysteine (NAC). We found that 95% O(2) tension caused a significant induction of the iNOS protein and mRNA levels paralleled by a significant fall in intracellular GSH concentration. The addition of NAC (1 mM) to the perfusate during hyperoxia blocked the induction of iNOS and restored GSH levels. These results indicate that molecular O(2) regulates the expression of iNOS in rat liver at the transcriptional level, most likely through the production of ROS and the reduction of intracellular GSH levels.