Specific transport of S-nitrosocysteine in human red blood cells: Implications for formation of S-nitrosothiols and transport of NO bioactivity within the vasculature

Role of Erythrocytes in Nitric Oxide Metabolism and Paracrine Regulation of Endothelial Function

Emerging studies provide new data shedding some light on the complex and pivotal role of red blood cells (RBCs) in nitric oxide (NO) metabolism and paracrine regulation of endothelial function. NO is involved in the regulation of vasodilatation, platelet aggregation, inflammation, hypoxic adaptation, and oxidative stress. Even though tremendous knowledge about NO metabolism has been collected, the exact RBCs’ status still requires evaluation. This paper summarizes the actual knowledge regarding the role of erythrocytes as a mobile depot of amino acids necessary for NO biotransformation. Moreover, the complex regulation of RBCs’ translocases is presented with a particular focus on cationic amino acid transporters (CATs) responsible for the NO substrates and derivatives transport. The main part demonstrates the intraerythrocytic metabolism of L-arginine with its regulation by reactive oxygen species and arginase activity. Additionally, the process of nitrite and nitrate turnover was demonstrated to be another stable source of NO, with its reduction by xanthine oxidoreductase or hemoglobin. Additional function of hemoglobin in NO synthesis and its subsequent stabilization in steady intermediates is also discussed. Furthermore, RBCs regulate the vascular tone by releasing ATP, inducing smooth muscle cell relaxation, and decreasing platelet aggregation. Erythrocytes and intraerythrocytic NO metabolism are also responsible for the maintenance of normotension. Hence, RBCs became a promising new therapeutic target in restoring NO homeostasis in cardiovascular disorders.

Red Blood Cell-Mediated S-Nitrosohemoglobin-Dependent Vasodilation: Lessons Learned from a β-Globin Cys93 Knock-In Mouse

Significance: Red blood cell (RBC)-mediated vasodilation plays an important role in oxygen delivery. This occurs through hemoglobin actions, at least in significant part, to convert heme-bound nitric oxide (NO) (in tense [T]/deoxygenated-state hemoglobin) into vasodilator S-nitrosothiol (SNO) (in relaxed [R]/oxygenated-state hemoglobin), convey SNO through the bloodstream, and release it into tissues to increase blood flow. The coupling of hemoglobin R/T state allostery, both to NO conversion into SNO and to SNO release (along with oxygen), under hypoxia supports the model of a three-gas respiratory cycle (O2/NO/CO2). Recent Advances: Oxygenation of tissues is dependent on a single, strictly conserved Cys residue in hemoglobin (βCys93). Hemoglobin couples SNO formation/release at βCys93 to O2 binding/release at hemes ("thermodynamic linkage"). Mice bearing βCys93Ala hemoglobin that is unable to generate SNO-βCys93 establish that SNO-hemoglobin is important for R/T allostery-regulated vasodilation by RBCs that couple blood flow to tissue oxygenation. Critical Issues: The model for RBC-mediated vasodilation originally proposed by Stamler et al. in 1996 has been largely validated: SNO-βCys93 forms in vivo, dilates blood vessels, and is hypoxia-regulated, and RBCs actuate vasodilation proportionate to hypoxia. Numerous compensations in βCys93Ala animals to alleviate tissue hypoxia (discussed herein) are predicted to preserve vasodilatory responses of RBCs but impair linkage to R/T transition in hemoglobin. This is borne out by loss of responsivity of mutant RBCs to oxygen, impaired blood flow responses to hypoxia, and tissue ischemia in βCys93-mutant animals. Future Directions: SNO-hemoglobin mediates hypoxic vasodilation in the respiratory cycle. This fundamental physiology promises new insights in vascular diseases and blood disorders.

Extra-platelet low-molecular-mass thiols mediate the inhibitory action of S-nitrosoalbumin on human platelet aggregation via S-transnitrosylation of the platelet surface

Nitrosylation of sulfhydryl (SH) groups of cysteine (Cys) moieties is an important post-translational modification (PTM), often on a par with phosphorylation. S-Nitrosoalbumin (ALB-Cys³⁴SNO; SNALB) in plasma and S-nitrosohemoglobin (Hb-Cys^β93SNO; HbSNO) in red blood cells are considered the most abundant high-molecular-mass pools of nitric oxide (NO) bioactivity in the human circulation. SNALB per se is not an NO donor. Yet, it acts as a vasodilator and an inhibitor of platelet aggregation. SNALB can be formed by nitrosation of the sole reduced Cys group of albumin (Cys³⁴) by nitrosating species such as nitrous acid (HONO) and nitrous anhydride (N₂O₃), two unstable intermediates of NO autoxidation. SNALB can also be formed by the transfer (S-transnitrosylation) of the nitrosyl group (NO⁺) of a low-molecular-mass (LMM) S-nitrosothiol (RSNO) to ALB-Cys³⁴SH. In the present study, the effects of LMM thiols on the inhibitory potential of ALB-Cys³⁴SNO on human washed platelets were investigated. ALB-Cys³⁴SNO was prepared by reacting n-butylnitrite with albumin after selective extraction from plasma of a healthy donor on HiTrapBlue Sepharose cartridges. ALB-Cys³⁴SNO was used in platelet aggregation measurements after extended purification on HiTrapBlue Sepharose and enrichment by ultrafiltration (cutoff, 20 kDa). All tested LMM cysteinyl thiols (R-CysSH) including L-cysteine and L-homocysteine (at 10 µM) were found to mediate the collagen-induced (1 µg/mL) aggregation of human washed platelets by SNALB (range, 0-10 µM) by cGMP-dependent and cGMP-independent mechanisms. The LMM thiols themselves did not affect platelet aggregation. It is assumed that the underlying mechanism involves S-transnitrosylation of SH groups of the platelet surface by LMM RSNO formed through the reaction of SNALB with the thiols: ALB-Cys³⁴SNO + R-CysSH ↔ ALB-Cys³⁴SH + R-CysSNO. Such S-transnitrosylation reactions may be accompanied by release of NO finally resulting in cGMP-dependent and cGMP-independent mechanisms.

Results, meta-analysis and a first evaluation of UNOxR, the urinary nitrate-to-nitrite molar ratio, as a measure of nitrite reabsorption in experimental and clinical settings

We recently found that renal carbonic anhydrase (CA) is involved in the reabsorption of inorganic nitrite (NO₂^-), an abundant reservoir of nitric oxide (NO) in tissues and cells. Impaired NO synthesis in the endothelium and decreased NO bioavailability in the circulation are considered major contributors to the development and progression of renal and cardiovascular diseases in different conditions including diabetes. Isolated human and bovine erythrocytic CAII and CAIV can convert nitrite to nitrous acid (HONO) and its anhydride N₂O₃ which, in the presence of thiols (RSH), are further converted to S-nitrosothiols (RSNO) and NO. Thus, CA may be responsible both for the homeostasis of nitrite and for its bioactivation to RSNO/NO. We hypothesized that enhanced excretion of nitrite in the urine may contribute to NO-related dysfunctions in the renal and cardiovascular systems, and proposed the urinary nitrate-to-nitrite molar ratio, i.e., U_NOxR, as a measure of renal CA-dependent excretion of nitrite. Based on results from clinical and experimental animal studies, here, we report on a first evaluation of U_NOxR. We determined U_NOxR values in preterm neonates, healthy children, and adults, in children suffering from type 1 diabetes mellitus (T1DM) or Duchenne muscular dystrophy (DMD), in elderly subjects suffering from chronic rheumatic diseases, type 2 diabetes mellitus (T2DM), coronary artery disease (CAD), or peripheral arterial occlusive disease (PAOD). We also determined U_NOxR values in healthy young men who ingested isosorbide dinitrate (ISDN), pentaerythrityl tetranitrate (PETN), or inorganic nitrate. In addition, we tested the utility of U_NOxR in two animal models, i.e., the LEW.1AR1-iddm rat, an animal model of human T1DM, and the APOE*3-Leiden.CETP mice, a model of human dyslipidemia. Mean U_NOxR values were lower in adult patients with rheumatic diseases (187) and in T2DM patients of the DALI study (74) as compared to healthy elderly adults (660) and healthy young men (1500). The intra- and inter-variabilities of U_NOxR were of the order of 50% in young and elderly healthy subjects. U_NOxR values were lower in black compared to white boys (314 vs. 483, P = 0.007), which is in line with reported lower NO bioavailability in black ethnicity. Mean U_NOxR values were lower in DMD (424) compared to healthy (730) children, but they were higher in T1DM children (1192). ISDN (3 × 30 mg) decreased stronger U_NOxR compared to PETN (3 × 80 mg) after 1 day (P = 0.046) and after 5 days (P = 0.0016) of oral administration of therapeutically equivalent doses. In healthy young men who ingested NaNO₃ (0.1 mmol/kg/d), U_NOxR was higher than in those who ingested the same dose of NaCl (1709 vs. 369). In LEW.1AR1-iddm rats, mean U_NOxR values were lower than in healthy rats (198 vs. 308) and comparable to those in APOE*3-Leiden.CETP mice (151).

Measurement of S -Nitrosoglutathione in Plasma by Liquid Chromatography-Tandem Mass Spectrometry

This chapter describes an ultraperformance liquid chromatographic-tandem mass spectrometric (UPLC-MS/MS) method for the quantitative determination of S-nitrosoglutathione (GSNO) in human plasma. S-[¹⁵N]Nitrosoglutathione (GS¹⁵NO) serves as the internal standard. The protocol involves inactivation of plasma γ-glutamyltransferase activity by serine-borate, stabilization of GSNO with EDTA, and avoidance of S-transnitrosylation reactions by blocking SH groups with N-ethylmaleimidide (NEM). Fresh blood is treated with NEM/serine-borate/EDTA, plasma is spiked with GS¹⁵NO (50 nM), ultrafiltered (cutoff 10 kDa) and 10-μL aliquots of ultrafiltrate are analyzed by UPLC-MS/MS in the positive electrospray ionization (ESI+) mode. LC is performed on a Nucleoshell column using isocratic (0.5 mL/min) elution with acetonitrile-20 mM ammonium formate (70:30, v/v), pH 7. Quantification is performed by selected-reaction monitoring the mass transition m/z 337 ([M+H]⁺) → m/z 307 ([M+H-¹⁴NO]^+●) for GSNO and m/z 338 ([M+H]⁺) → m/z 307 ([M+H-¹⁵NO]^+●) for GS¹⁵NO. Matrix effects are outweighed by the internal standard GS¹⁵NO. The lower limit of quantitation (LOQ) is 2.8 nM.

S-Nitroso-N-acetyl-L-cysteine ethyl ester (SNACET) and N-acetyl-L-cysteine ethyl ester (NACET)-Cysteine-based drug candidates with unique pharmacological profiles for oral use as NO, H2S and GSH suppliers and as antioxidants: Results and overview

S-Nitrosothiols or thionitrites with the general formula RSNO are formally composed of the nitrosyl cation (NO⁺) and a thiolate (RS⁻), the base of the corresponding acids RSH. The smallest S-nitrosothiol is HSNO and derives from hydrogen sulfide (HSH, H₂S). The most common physiological S-nitrosothiols are derived from the amino acid L-cysteine (CysSH). Thus, the simplest S-nitrosothiol is S-nitroso-L-cysteine (CysSNO). CysSNO is a spontaneous potent donor of nitric oxide (NO) which activates soluble guanylyl cyclase to form cyclic guanosine monophosphate (cGMP). This activation is associated with multiple biological actions that include relaxation of smooth muscle cells and inhibition of platelet aggregation. Like NO, CysSNO is a short-lived species and occurs physiologically at concentrations around 1 nM in human blood. CysSNO can be formed from CysSH and higher oxides of NO including nitrous acid (HONO) and its anhydride (N₂O₃). The most characteristic feature of RSNO is the S-transnitrosation reaction by which the NO⁺ group is reversibly transferred to another thiolate. By this way numerous RSNO can be formed such as the low-molecular-mass S-nitroso-N-acetyl-L-cysteine (SNAC) and S-nitroso-glutathione (GSNO), and the high-molecular-mass S-nitrosol-L-cysteine hemoglobin (HbCysSNO) present in erythrocytes and S-nitrosol-L-cysteine albumin (AlbCysSNO) present in plasma at concentrations of the order of 200 nM. All above mentioned RSNO exert NO-related biological activity, but they must be administered intravenously. This important drawback can be overcome by lipophilic charge-free RSNO. Thus, we prepared the ethyl ester of SNAC, the S-nitroso-N-acetyl-L-cysteine ethyl ester (SNACET), from synthetic N-acetyl-L-cysteine ethyl ester (NACET). Both NACET and SNACET have improved pharmacological features over N-acetyl-L-cysteine (NAC) and S-nitroso-N-acetyl-L-cysteine (SNAC), respectively, including higher oral bioavailability. SNACET exerts NO-related activities which can be utilized in the urogenital tract and in the cardiovascular system. NACET, with high oral bioavailability, is a strong antioxidant and abundant precursor of GSH, unlike its free acid N-acetyl-L-cysteine (NAC). Here, we review the chemical and pharmacological properties of SNACET and NACET as well as their analytical chemistry. We also report new results from the ingestion of S-[¹⁵N]nitroso-N-acetyl-L-cysteine ethyl ester (S¹⁵NACET) demonstrating the favorable pharmacological profile of SNACET.

HbE/β-Thalassemia and Oxidative Stress: The Key to Pathophysiological Mechanisms and Novel Therapeutics

SIGNIFICANCE

Oxidative stress and generation of free radicals are fundamental in initiating pathophysiological mechanisms leading to an inflammatory cascade resulting in high rates of morbidity and death from many inherited point mutation-derived hemoglobinopathies. Hemoglobin (Hb)E is the most common point mutation worldwide. The βE-globin gene is found in greatest frequency in Southeast Asia, including Thailand, Malaysia, Indonesia, Vietnam, Cambodia, and Laos. With the wave of worldwide migration, it is entering the gene pool of diverse populations with greater consequences than expected.

CRITICAL ISSUES

While HbE by itself presents as a mild anemia and a single gene for β-thalassemia is not serious, it remains unexplained why HbE/β-thalassemia (HbE/β-thal) is a grave disease with high morbidity and mortality. Patients often exhibit defective physical development, severe chronic anemia, and often die of cardiovascular disease and severe infections. Recent Advances: This article presents an overview of HbE/β-thal disease with an emphasis on new findings pointing to pathophysiological mechanisms derived from and initiated by the dysfunctional property of HbE as a reduced nitrite reductase concomitant with excess α-chains exacerbating unstable HbE, leading to a combination of nitric oxide imbalance, oxidative stress, and proinflammatory events.

FUTURE DIRECTIONS

Additionally, we present new therapeutic strategies that are based on the emerging molecular-level understanding of the pathophysiology of this and other hemoglobinopathies. These strategies are designed to short-circuit the inflammatory cascade leading to devastating chronic morbidity and fatal consequences. Antioxid. Redox Signal. 26, 794-813.

The role of red blood cell S-nitrosation in nitrite bioactivation and its modulation by leucine and glucose

Previous work has shown that red blood cells (RBCs) reduce nitrite to NO under conditions of low oxygen. Strong support for the ability of red blood cells to promote nitrite bioactivation comes from using platelet activation as a NO-sensitive process. Whereas addition of nitrite to platelet rich plasma in the absence of RBCs has no effect on inhibition of platelet activation, when RBCs are present platelet activation is inhibited by an NO-dependent mechanism that is potentiated under hypoxia. In this paper, we demonstrate that nitrite bioactivation by RBCs is blunted by physiologically-relevant concentrations of nutrients including glucose and the important signaling amino acid leucine. Our mechanistic investigations demonstrate that RBC mediated nitrite bioactivation is largely dependent on nitrosation of RBC surface proteins. These data suggest a new expanded paradigm where RBC mediated nitrite bioactivation not only directs blood flow to areas of low oxygen but also to areas of low nutrients. Our findings could have profound implications for normal physiology as well as pathophysiology in a variety of diseases including diabetes, sickle cell disease, and arteriosclerosis.

Carbonic anhydrases are producers of S-nitrosothiols from inorganic nitrite and modulators of soluble guanylyl cyclase in human platelets

Nitric oxide (NO), S-nitrosoglutathione (GSNO) and S-nitrosocysteine are highly potent signaling molecules, acting both by cGMP-dependent and cGMP-independent mechanisms. The NO metabolite nitrite (NO2 (-)) is a major NO reservoir. Hemoglobin, xanthine oxidoreductase and carbonic anhydrase (CA) have been reported to reduce/convert nitrite to NO. We evaluated the role and the physiological importance of CA for an extra-platelet CA/nitrite/NO/cGMP pathway in human platelets. Authentic NO was analyzed by an NO-sensitive electrode. GSNO and GS(15)NO were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). cGMP was determined by LC-MS/MS or RIA. In reduced glutathione (GSH) containing aqueous buffer (pH 7.4), human and bovine erythrocytic CAII-mediated formation of GSNO from nitrite and GS(15)NO from (15)N-nitrite. In the presence of L-cysteine and GSH, this reaction was accompanied by NO release. Incubation of nitrite with bovine erythrocytic CAII and recombinant soluble guanylyl cyclase resulted in cGMP formation. Upon incubation of nitrite with bovine erythrocytic CAII and washed human platelets, cGMP and P-VASP(S239) were formed in the platelets. This study provides the first evidence that extra-platelet nitrite and erythrocytic CAII may modulate platelet function in a cGMP-dependent manner. The new nitrite-dependent CA activity may be a general principle and explain the cardioprotective effects of inorganic nitrite in the vasculature. We propose that nitrous acid (ONOH) is the primary CA-catalyzed reaction product of nitrite.

Local and systemic vasodilatory effects of low molecular weight S-nitrosothiols

S-nitrosothiols (SNOs) such as S-nitroso-L-cysteine (L-cysNO) are endogenous compounds with potent vasodilatory activity. During circulation in the blood, the NO moiety can be exchanged among various thiol-containing compounds by S-transnitrosylation, resulting in SNOs with differing capacities to enter the cell (membrane permeability). To determine whether the vasodilating potency of SNOs is dependent upon membrane permeability, membrane-permeable L-cysNO and impermeable S-nitroso-D-cysteine (D-cysNO) and S-nitroso-glutathione (GSNO) were infused into one femoral artery of anesthetized adult sheep while measuring bilateral femoral and systemic vascular conductances. L-cysNO induced vasodilation in the infused hind limb, whereas D-cysNO and GSNO did not. L-cysNO also increased intracellular NO in isolated arterial smooth muscle cells, whereas GSNO did not. The infused SNOs remained predominantly in a low molecular weight form during first-passage through the hind limb vasculature, but were converted into high molecular weight SNOs upon systemic recirculation. At systemic concentrations of ~0.6 μmol/L, all three SNOs reduced mean arterial blood pressure by ~50%, with pronounced vasodilation in the mesenteric bed. Pharmacokinetics of L-cysNO and GSNO were measured in vitro and in vivo and correlated with their hemodynamic effects, membrane permeability, and S-transnitrosylation. These results suggest local vasodilation by SNOs in the hind limb requires membrane permeation, whereas systemic vasodilation does not. The systemic hemodynamic effects of SNOs occur after equilibration of the NO moiety amongst the plasma thiols via S-transnitrosylation.

Colorimetric analysis of the decomposition of S-nitrosothiols on paper-based microfluidic devices

A disposable paper microfluidic device was developed to analyse different S-nitrosothiols simultaneously decomposed by Hg²⁺ as well as UV, Vis and IR lamps.

S-nitrosophytochelatins: investigation of the bioactivity of an oligopeptide nitric oxide delivery system

This study investigates the in vitro bioactivity of S-nitrosophytochelatins (SNOPCs), oligopeptide analogues of S-nitrosoglutathione (GSNO), and their mechanisms of nitric oxide (NO) delivery. SNOPCs were more potent than GSNO in inhibiting platelet aggregation and stimulating vasorelaxation. Their potency was related to the number of S-nitrosated moieties per mole compound. Transnitrosation reactions with cell membrane surface components were shown to be the primary mode of NO delivery to intracellular targets for SNOPCs, while delivery via γ-glutamyl transpeptidase was unique to GSNO. Due to rapid NO release, larger SNOPCs elicited a more transitory effect compared to smaller compounds. The duration of effect was influenced by compound molecular weight, NO release kinetics, ability to undergo transnitrosation, and incubation time with tissues. In summary, a new oligopeptide NO delivery system based on SNOPCs was shown to be biologically active and can be used to investigate the mechanisms of NO delivery to intracellular targets.

Nutritional and medicinal aspects of D-amino acids

This paper reviews and interprets a method for determining the nutritional value of D-amino acids, D-peptides, and amino acid derivatives using a growth assay in mice fed a synthetic all-amino acid diet. A large number of experiments were carried out in which a molar equivalent of the test compound replaced a nutritionally essential amino acid such as L-lysine (L-Lys), L-methionine (L-Met), L-phenylalanine (L-Phe), and L-tryptophan (L-Trp) as well as the semi-essential amino acids L-cysteine (L-Cys) and L-tyrosine (L-Tyr). The results show wide-ranging variations in the biological utilization of test substances. The method is generally applicable to the determination of the biological utilization and safety of any amino acid derivative as a potential nutritional source of the corresponding L-amino acid. Because the organism is forced to use the D-amino acid or amino acid derivative as the sole source of the essential or semi-essential amino acid being replaced, and because a free amino acid diet allows better control of composition, the use of all-amino-acid diets for such determinations may be preferable to protein-based diets. Also covered are brief summaries of the widely scattered literature on dietary and pharmacological aspects of 27 individual D-amino acids, D-peptides, and isomeric amino acid derivatives and suggested research needs in each of these areas. The described results provide a valuable record and resource for further progress on the multifaceted aspects of D-amino acids in food and biological samples.

S-nitrosothiols as selective antithrombotic agents - possible mechanisms

S-nitrosothiols have a number of potential clinical applications, among which their use as antithrombotic agents has been emphasized. This is largely because of their well-documented platelet inhibitory effects, which show a degree of platelet selectivity, although the mechanism of this remains undefined. Recent progress in understanding how nitric oxide (NO)-related signalling is delivered into cells from stable S-nitrosothiol compounds has revealed a variety of pathways, in particular denitrosation by enzymes located at the cell surface, and transport of intact S-nitrosocysteine via the amino acid transporter system-L (L-AT). Differences in the role of these pathways in platelets and vascular cells may in part explain the reported platelet-selective action. In addition, emerging evidence that S-nitrosothiols regulate key targets on the exofacial surfaces of cells involved in the thrombotic process (for example, protein disulphide isomerase, integrins and tissue factor) suggests novel antithrombotic actions, which may not even require transmembrane delivery of NO.

Hemoglobin, nitric oxide and molecular mechanisms of hypoxic vasodilation

The protected transport of nitric oxide (NO) by hemoglobin (Hb) links the metabolic activity of working tissue to the regulation of its local blood supply through hypoxic vasodilation. This physiologic mechanism is allosterically coupled to the O(2) saturation of Hb and involves the covalent binding of NO to a cysteine residue in the beta-chain of Hb (Cys beta93) to form S-nitrosohemoglobin (SNO-Hb). Subsequent S-transnitrosation, the transfer of NO groups to thiols on the RBC membrane and then in the plasma, preserves NO vasodilator activity for delivery to the vascular endothelium. This SNO-Hb paradigm provides insight into the respiratory cycle and a new therapeutic focus for diseases involving abnormal microcirculatory perfusion. In addition, the formation of S-nitrosothiols in other proteins may regulate an array of physiological functions.

Arteriovenous differences in NO2- kinetics in anesthetized rabbits

Despite of the importance of plasma NO2- as an index of endothelial nitric oxide (NO) formation and a substrate for NO production, only a limited kinetic knowledge is available in vivo. To address this issue, we intravenously injected NaNO2 into anesthetized rabbits and quantified changes in arterial and venous plasma NO2- levels. Plasma NO2- levels in arterial blood (956 +/- 220 nM) were slightly, but significantly, higher than those in venous blood (889 +/- 214 nM) under control conditions. Although similar half-lives of the NO2- were observed in arterial and venous plasma, significant arteriovenous differences were observed in the volume of distribution of the central compartment (0.158 +/- 0.007 l/kg in arterial blood and 0.295 +/- 0.015 l/kg in venous blood) and the peripheral compartment (0.259 +/- 0.035 l/kg in arterial blood and 0.135 +/- 0.034 l/kg in venous blood). When NOR1 (authentic NO) was injected, increases in NO2- levels were greater in arterial plasma, and decreases in blood pressure significantly correlated with arterial NO2- levels only (r = 0.90, p < 0.01). These results indicate that changes in NO2- are larger and more easily detectable as an index of NO formation in arterial plasma.

Apoptosis-inducing high (.)NO concentrations are not sustained either in nascent or in developed cancers

Nitric oxide ((.)NO) induces apoptosis at high concentrations by S-nitrosating proteins such as glyceraldehyde-3-phosphate dehydrogenase. This literature analysis revealed that failure to sustain high (.)NO concentrations is common to all cancers. In cervical, gastric, colorectal, breast, and lung cancer, the cause of this failure is the inadequate expression of inducible nitric oxide synthase (iNOS), resulting from the inhibition of iNOS expression by TGF-beta1 at the mRNA level. In bladder, renal, and prostate cancer, the reason for the insufficient (.)NO levels is the depletion of arginine, resulting from arginase overexpression. Arginase competes with iNOS for arginine, catalyzing its hydrolysis to ornithine and urea. In gliomas and ovarian sarcomas, low (.)NO levels are caused by inhibition of iNOS by N-chlorotaurine, produced by infiltrating neutrophils. Stimulated neutrophils express myeloperoxidase, catalyzing H2O2 oxidation of Cl- to HOCl, which N-chlorinates taurine at its concentration of 19 mM in neutrophils. In squamous cell carcinomas of the skin, ovarian cancers, lymphomas, Hodgkin's disease, and breast cancers, low (.)NO concentrations arise from the inhibition of iNOS by N-bromotaurine, produced by eosinophil-peroxidase-expressing infiltrating eosinophils. Eosinophil peroxidase catalyzes the H2O2 oxidation of Br- to HOBr, which N-brominates taurine to N-bromotaurine at its concentration of 15 mM in eosinophils. In microvascularized tumors, the (.)NO concentration is further depleted; (.)NO is rapidly consumed by red blood cells (RBCs) through S-nitrosation of RBC glutathione and hemoglobin, and by oxidation to nitrate by RBC oxyhemoglobin. Angiogenesis-inhibiting antibodies are currently used to treat cancers; their mode of action is not, as previously thought, reduction of the tumor O2 or nutrient supply. They actually decrease the loss of (.)NO to RBCs.

S-nitrosylation of beta-arrestin regulates beta-adrenergic receptor trafficking

Signal transduction through G protein-coupled receptors (GPCRs) is regulated by receptor desensitization and internalization that follow agonist stimulation. Nitric oxide (NO) can influence these processes, but the cellular source of NO bioactivity and the effects of NO on GPCR-mediated signal transduction are incompletely understood. Here, we show in cells and mice that beta-arrestin 2, a central element in GPCR trafficking, interacts with and is S-nitrosylated at a single cysteine by endothelial NO synthase (eNOS), and that S-nitrosylation of beta-arrestin 2 is promoted by endogenous S-nitrosogluthathione. S-nitrosylation after agonist stimulation of the beta-adrenergic receptor, a prototypical GPCR, dissociates eNOS from beta-arrestin 2 and promotes binding of beta-arrestin 2 to clathrin heavy chain/beta-adaptin, thereby accelerating receptor internalization. The agonist- and NO-dependent shift in the affiliations of beta-arrestin 2 is followed by denitrosylation. Thus, beta-arrestin subserves the functional coupling of eNOS and GPCRs, and dynamic S-nitrosylation/denitrosylation of beta-arrestin 2 regulates stimulus-induced GPCR trafficking.

Functional characterization of two S-nitroso-L-cysteine transporters, which mediate movement of NO equivalents into vascular cells

System L amino acid transporters have been shown to be responsible for cellular uptake of S-nitroso-L-cysteine (l-CSNO). In this study, we examined the characteristics of L-CSNO uptake in Xenopus laevis oocytes expressing system L transporters and found that uptake increased only when both 4F2 heavy chain (4F2HC) and either L-type amino acid transporter 1 (LAT1) or LAT2 light chain were coexpressed. The K(m) for transport was 57 +/- 8 microM for 4F2HC-LAT1 and 520 +/- 52 microM for 4F2HC-LAT2. Vascular endothelial and smooth muscle cells were shown to express transcripts for 4F2HC and for both LAT1 and LAT2. Transport of L-CSNO into red blood cells, endothelial cells, and smooth muscle cells was inhibited by 2-aminobicyclo(2.2.1)heptane-2-carboxylic acid (BCH) and by large neutral amino acids demonstrating functional system L transporters in each cell type. Uptake of L-CSNO led to accumulation of cellular S-nitrosothiols and inhibition of both growth factor-induced ERK phosphorylation and TNF-alpha-mediated IkappaB degradation. Similar effects were seen when cells were incubated simultaneously with S-nitrosoalbumin and L-cysteine but not with d-cysteine or with S-nitrosoalbumin alone. In each case, nitrosylation of proteins and cellular responses were blocked by BCH. Together, these data suggest that transmembrane movement of nitric oxide (NO) equivalents from the plasma albumin NO reservoir is mediated by cysteine, which serves as a carrier. The mechanism requires transnitrosylation from S-nitrosoalbumin to free cysteine and activity of system L transporters, thereby providing a unique pathway for cellular responses to S-nitrosoalbumin.

Detection of S-nitrosothiols in biological fluids: a comparison among the most widely applied methodologies

Many different methodologies have been applied for the detection of S-nitrosothiols (RSNOs) in human biological fluids. One unsatisfactory outcome of the last 14 years of research focused on this issue is that a general consensus on reference values for physiological RSNO concentration in human blood is still missing. Consequently, both RSNO physiological function and their role in disease have not yet been clarified. Here, a summary of the values measured for RSNOs in erythrocytes, plasma, and other biological fluids is provided, together with a critical review of the most widely used analytical methods. Furthermore, some possible methodological drawbacks, responsible for the highlighted discrepancies, are evidenced.