Copper chelation-induced reduction of the biological activity of S-nitrosothiols

A novel method of rapid detection for heavy metal copper ion via a specific copper chelator bathocuproinedisulfonic acid disodium salt

The extensive usage and production of copper may lead to toxic effects in organisms due to its accumulation in the environment. Traditional methods for copper detection are time consuming and infeasible for field usage. It is necessary to discover a real-time, rapid and economical method for detecting copper to ensure human health and environmental safety. Here we developed a colorimetric paper strip method and optimized spectrum method for rapid detection of copper ion based on the specific copper chelator bathocuproinedisulfonic acid disodium salt (BCS). Both biological assays and chemical methods verified the specificity of BCS for copper. The optimized reaction conditions were 50 mM Tris-HCl pH 7.4, 200 µM BCS, 1 mM ascorbate and less than 50 µM copper. The detection limit of the copper paper strip test was 0.5 mg/L by direct visual observation and the detection time was less than 1 min. The detection results of grape, peach, apple, spinach and cabbage by the optimized spectrum method were 0.91 μg/g, 0.87 μg/g, 0.19 μg/g, 1.37 μg/g and 0.39 μg/g, respectively. The paper strip assays showed that the copper contents of grape, peach, apple, spinach and cabbage were 0.8 mg/L, 0.9 mg/L, 0.2 mg/L, 1.3 mg/L and 0.5 mg/L, respectively. These results correlated well with those determined by inductively coupled plasma-mass spectrometry (ICP-MS). The visual detection limit of the paper strip based on Cu-BCS-AgNPs was 0.06 mg/L. Our study demonstrates the potential for on-site, rapid and cost-effective copper monitoring of foods and the environment.

Peptides Derived from Angiogenin Regulate Cellular Copper Uptake

The angiogenin protein (ANG) is one of the most potent endogenous angiogenic factors. In this work we characterized by means of potentiometric, spectroscopic and voltammetric techniques, the copper complex species formed with peptide fragments derived from the N-terminal domain of the protein, encompassing the sequence 1-17 and having free amino, Ang1-17, or acetylated N-terminus group, AcAng1-17, so to explore the role of amino group in metal binding and cellular copper uptake. The obtained data show that amino group is the main copper anchoring site for Ang1-17. The affinity constant values, metal coordination geometry and complexes redox-potentials strongly depend, for both peptides, on the number of copper equivalents added. Confocal laser scanning microscope analysis on neuroblastoma cells showed that in the presence of one equivalent of copper ion, the free amino Ang1-17 increases cellular copper uptake while the acetylated AcAng1-17 strongly decreases the intracellular metal level. The activity of peptides was also compared to that of the protein normally present in the plasma (wtANG) as well as to the recombinant form (rANG) most commonly used in literature experiments. The two protein isoforms bind copper ions but with a different coordination environment. Confocal laser scanning microscope data showed that the wtANG induces a strong increase in intracellular copper compared to control while the rANG decreases the copper signal inside cells. These data demonstrate the relevance of copper complexes' geometry to modulate peptides' activity and show that wtANG, normally present in the plasma, can affect cellular copper uptake.

Enhancement of NO release from S-nitrosoalbumin by pollution derived metal ions

S-Nitrosothiols act as a comparatively long-lived reservoir of releasable nitric oxide (NO) present in vivo in a variety of body fluids. Soluble constituents of air-borne particulate matter (PM) can affect S-nitrosothiol stability and deregulate NO-based biological signaling. PM aqueous extracts of standard urban dust (SRM 1648a) were prepared, and their effect on human serum S-nitrosoalbumin (HSA-NO) stability was studied. The results indicated that PM extracts induced a release of NO from HSA-NO in a dose-dependent manner. To identify the inorganic components of urban PM responsible for HSA-NO decomposition, the effects of individual metal ions and metal ion mixtures, detected in the SRM 1648a aqueous extract, were examined. The dominant role of copper ions (specifically Cu+) was confirmed, but the results did not exclude the influence of other water-soluble PM components. Measurements with the application of several common metal ion chelators confirmed that Cu2+ may participate in NO release from HSA-NO and that reduction to monovalent Cu+ (responsible for S-NO bond breaking) may occur with the participation of S-nitrosoalbumin. The addition of ascorbic acid (AscA) significantly enhanced the effectiveness of NO release by PM extracts both kinetically and quantitatively, by inducing an increase in the reduction of Cu2+ to Cu+. These results indicate that AscA present in the respiratory tract lining fluids and plasma may amplify the activity of inorganic components of PM in S-nitrosothiol decomposition.

Biological Mechanisms of S-Nitrosothiol Formation and Degradation: How Is Specificity of S-Nitrosylation Achieved?

The modification of protein cysteine residues underlies some of the diverse biological functions of nitric oxide (NO) in physiology and disease. The formation of stable nitrosothiols occurs under biologically relevant conditions and time scales. However, the factors that determine the selective nature of this modification remain poorly understood, making it difficult to predict thiol targets and thus construct informatics networks. In this review, the biological chemistry of NO will be considered within the context of nitrosothiol formation and degradation whilst considering how specificity is achieved in this important post-translational modification. Since nitrosothiol formation requires a formal one-electron oxidation, a classification of reaction mechanisms is proposed regarding which species undergoes electron abstraction: NO, thiol or S-NO radical intermediate. Relevant kinetic, thermodynamic and mechanistic considerations will be examined and the impact of sources of NO and the chemical nature of potential reaction targets is also discussed.

Expression, S-Nitrosylation, and Measurement of S-Nitrosylation Ratio of Recombinant Galectin-2

S-nitrosylation, which involves the coupling of an NO group to the reactive thiol of Cys residue(s) in a polypeptide, is an important posttranslational modification detected in a variety of proteins. Here, we present the S-nitrosylation of recombinant galectin-2 (Gal-2) using S-nitrosocysteine and the measurement of the molecular ratio of S-nitrosylation of Cys residues in the Gal-2 protein.

S-Nitrosothiols: Materials, Reactivity and Mechanisms

The article provides a comprehensive view of S-nitrosothiols, chemical behaviour, the pathways leading to their synthesis, their spectral properties, analytical methods of detection and determination, chemical and photochemical reactivity, kinetic aspects and suggested mechanisms. The structure parameters of S-nitrosothiols and the parent thiols are analysed with respect to their effect on the strengthening or weakening the S–NO bond, and in consequence on the S-nitrosothiol stability. This depends also on the ease of S–S bond formation in the product disulphide. These structural features seem to be crucial both to spontaneous as well as to Cu-catalysed decomposition. Principal emphasis is given here to the S-nitrosothiols’ ability to act as ligands and to the effect of coordination on the ligand properties. The chemical and photochemical behaviours of the complexes are described in more detail and their roles in chemical and biochemical systems are discussed.

The aim of the article is to demonstrate that the contribution of S-nitrosothiols to chemical and biochemical processes is more diverse than supposed hitherto. Nevertheless, their role is predictable and, based on the correlation between structure and reactivity, many important mechanisms of biochemical processes can be interpreted and various applications designed.

Exploiting the vulnerable active site of a copper-only superoxide dismutase to disrupt fungal pathogenesis

Copper-only superoxide dismutases (SODs) represent a new class of SOD enzymes that are exclusively extracellular and unique to fungi and oomycetes. These SODs are essential for virulence of fungal pathogens in pulmonary and disseminated infections, and we show here an additional role for copper-only SODs in promoting survival of fungal biofilms. The opportunistic fungal pathogen Candida albicans expresses three copper-only SODs, and deletion of one of them, SOD5, eradicated candidal biofilms on venous catheters in a rodent model. Fungal copper-only SODs harbor an irregular active site that, unlike their Cu,Zn-SOD counterparts, contains a copper co-factor unusually open to solvent and lacks zinc for stabilizing copper binding, making fungal copper-only SODs highly vulnerable to metal chelators. We found that unlike mammalian Cu,Zn-SOD1, C. albicans SOD5 indeed rapidly loses its copper to metal chelators such as EDTA, and binding constants for Cu(II) predict that copper-only SOD5 has a much lower affinity for copper than does Cu,Zn-SOD1. We screened compounds with a variety of indications and identified several metal-binding compounds, including the ionophore pyrithione zinc (PZ), that effectively inhibit C. albicans SOD5 but not mammalian Cu,Zn-SOD1. We observed that PZ both acts as an ionophore that promotes uptake of toxic metals and inhibits copper-only SODs. The pros and cons of a vulnerable active site for copper-only SODs and the possible exploitation of this vulnerability in antifungal drug design are discussed.

Evaluation of promoting effect of a novel Cu-bearing metal stent on endothelialization process from in vitro and in vivo studies

Drug eluting stents (DES) have been extensively applied nowadays and reduce the incidence of in-stent restenosis (ISR) greatly as compared with bare metal stents (BMS). However, the development of DES is hindered by the risk of late stent thrombosis (LST) due to delayed re-endothelialization, while endothelialization is an important process related to ISR and LST after implantation. 316L is a traditional stent material without bioactivity and have a high risk of ISR. Cu is recognized for angiogenesis stimulation in these years. Hence a copper bearing 316L stainless steel (316L-Cu) was prepared and evaluated about its effect on endothelialization in this paper. Compared with traditional 316L, it was proved that 316L-Cu increased the proliferation of co-cultured human umbilical vein endothelial cells (HUVECs) at first day. Moreover, HUVECs stretched better on the surface of 316L-Cu. It also improved the expression of angiogenesis related genes and tube formation ability in vitro. 316L-Cu-BMS, DES and 316L-BMS were implanted in swine to evaluate the re-endothelialization ability in vivo. And 316L-Cu-BMS showed the best effect on endothelialization with good biosafety. Consequently, 316L-Cu is a kind of promising BMS material for coronary field.

Kinetics of ABTS derived radical cation scavenging by bucillamine, cysteine, and glutathione. Catalytic effect of Cu(2+) ions

Kinetics of reduction of the stable radical cation derived from 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) in reaction with the anti-rheumatic drug bucillamine (BUC) and two reference thiols - cysteine (Cys) and glutathione (GSH) was followed spectrophotometrically in acidic medium with 10-fold molar excess of the reductant. Decay of the radical is governed by pseudo-first order kinetics with small deviation in the case of GSH. H(+) ions displayed second order inhibition of the reaction with all the studied compounds. The reaction of BUC exhibits zero order kinetics to the radical at lower acidities with a moderate acceleration of the reaction rate by H(+) ions. A significant catalytic effect of Cu(2+) ions on the reactions with all the reductants was observed. The most sensitive to Cu(2+)-catalysis was the reaction of BUC with the radical cation, while Cu(2+) ions showed much lower effect on the reaction with GSH. The presence of EDTA strongly inhibited the reactions and equalized the reaction rates for all the reductants. A Cu(I) selective chelator bathocuproine disulfonate reduced the reaction rate with Cys, but accelerated the reaction with BUC at the lower acidities. The experimental results were rationalized in the framework of the mechanism of reductive chelation. The conclusions may have important consequences for interpretation of antioxidant capacity assays, such as TEAC, utilizing the ABTS derived radical cation.

Endogenous cellular prion protein regulates contractility of the mouse ileum

BACKGROUND

Cellular prion protein (PrP(C) ) is expressed in the enteric nervous system (ENS), however, its physiological role has not been identified. Studies suggest that PrP(C) can function as a metal-binding protein, as absence of the protein has been linked to altered copper metabolism and atypical synaptic activity. Because copper is known to modulate smooth muscle relaxation, we tested the hypothesis that PrP(C) deficiency would alter intestinal contractility.

METHODS

We examined electrically evoked ileal contractility in Prnp(-/-) or wild type littermate mice and the effects of copper or copper chelation. PrP(C) expression was studied in whole mount ileal preparations of mice and guinea pigs by immunohistochemistry.

KEY RESULTS

Relative to wild type mice, ileal tissues of Prnp(-/-) mice exhibited reduced electrical field stimulation (EFS)-evoked contractility. Furthermore, EFS-induced relaxation, as a percentage of that induced by a nitric oxide donor, was enhanced. Addition of a copper donor to the organ bath increased, whereas the addition of a copper chelator inhibited, nitric oxide donor-induced ileal relaxation in Prnp(-/-) mice. PrP(C) was expressed on nerve fibers or terminals, and some cell bodies in the myenteric and submucosal plexuses of wild type mice. PrP(C) colocalized with a neuron-specific ectonucleotidase, nucleoside triphosphate diphosphohydrolase 3 (NTPDase3), but to only a limited extent with GFAP, a marker of enteric glia. Guinea pigs expressed PrP(C) in nerve fibers or terminals and enteric glia in the myenteric and submucosal plexuses.

CONCLUSIONS & INFERENCES

Our findings suggest that PrP(C) , which is abundant in the ENS, has a role in the regulation of ileal contractility.

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.

Differential effect of neocuproine, a copper(I) chelator, on contractile activity in isolated ovariectomized non-pregnant rat, pregnant rat and pregnant human uterus

The study was conducted to examine effects of a selective copper(I) chelator, neocuproine on the spontaneous or oxytocin-induced contractions in isolated ovariectomized non-pregnant rat, pregnant rat and pregnant human uterus. Uterus activity was evaluated in tissues obtained from bilaterally ovariectomized non-pregnant rats on the 21st day of the operation (n = 24), pregnant rats on the 19-21st day of gestation (n = 24) and women undergoing caesarean section at 38-42 weeks of pregnancy (n = 15). Neocuproine (100 microM) significantly suppressed the amplitude and frequency of the spontaneous contractions in the ovariectomized non-pregnant rat uterus while this agent facilitated the frequency of the spontaneous or oxytocin-induced contractions in the pregnant rat and human uterus without altering the amplitude of these contractions. At high concentration of 200 microM, neocuproine could enhance the amplitude of the contractions in the pregnant uterus. These effects were blocked by a purinergic receptor antagonist, suramin (100 microM) and did not occur following the administration of neocuproine-copper(I) complex or copper(II) chelator cuprizone. alpha, beta-methylene ATP increased the amplitude and frequency of contractions in the pregnant uterus, but not affected the contractions in the ovariectomized non-pregnant rat uterus, and neocuproine potentiated this facilitation effect. However, the suppressive effect of neocuproine on the ovariectomized non-pregnant rat uterus increased in the presence of alpha,beta-methylene ATP. Beta-adrenoceptor blocker, propranolol or nitric oxide synthase inhibitor, L-nitroarginine did not affect the responses to neocuproine. These findings suggest that neocuproine can affect the uterus contractile activity by modulation purinergic excitatory responses and that copper(I)-sensitive mechanisms may play a role in this effect.

Oxidation by trace Cu2+ ions underlies the ability of ascorbate to induce vascular dysfunction in the rat perfused mesentery

Ascorbate has both antioxidant and pro-oxidant activities. We have previously shown that plasma levels of ascorbate induce constriction and blockade of dilatation mediated by endothelium-derived hyperpolarizing factor (EDHF). In this study we sought to determine if these detrimental actions were mediated by a prooxidant action of ascorbate. Since trace levels of transition metal ions including, Cu2+ and Fe3+, promote oxidation of ascorbate, we examined the effects of the chelating agents, cuprizone and deferoxamine, and of CuSO4 and FeCl3 on ascorbate-induced constriction and blockade of EDHF in the perfused rat mesentery. Cuprizone abolished and Cu2+ but not Fe3+ ions enhanced both ascorbate (50 microM)-induced constriction and blockade of EDHF. The blockade of EDHF produced by ascorbate in the presence of CuSO4 (0.5 microM) was abolished by the hydrogen peroxide scavenger, catalase, but unaffected by the scavengers of hydroxyl radical or superoxide anion, mannitol and superoxide dismutase (SOD), respectively. Consistent with these observations, the oxidation of ascorbate by CuSO4 led to the rapid production of hydrogen peroxide. Catalase, mannitol and SOD had no effect on ascorbate-induced constriction. Thus, in the rat perfused mesentery, both the constrictor and EDHF-blocking actions of ascorbate arise from its oxidation by trace Cu2+ ions. The blockade of EDHF results from the consequent generation of hydrogen peroxide, but the factor producing constriction remains unidentified. These detrimental actions of ascorbate may help explain the disappointing outcome of clinical trials investigating dietary supplementation with the vitamin on cardiovascular health.

Potential Benefits of Peroxynitrite

Peroxynitrite (PN) is generated by the reaction of nitric oxide (NO) and superoxide in one of the most rapid reactions in biology. Studies have reported that PN is a cytotoxic molecule that contributes to vascular injury in a number of disease states. However, it has become apparent that PN has beneficial effects including vasodilation, inhibition of platelet aggregation, inhibition of inflammatory cell adhesion, and protection against ischemia/reperfusion injury in the heart. It is our hypothesis that PN may serve to inactivate superoxide and prolong the actions of NO in the circulation. This manuscript reviews the beneficial effects of PN in the cardiovascular system.

Protein disulfide-isomerase mediates delivery of nitric oxide redox derivatives into platelets

S-nitrosothiol compounds are important mediators of NO signalling and can give rise to various redox derivatives of NO: nitrosonium cation (NO+), nitroxyl anion (NO-) and NO* radical. Several enzymes and transporters have been implicated in the intracellular delivery of NO from S-nitrosothiols. In the present study we have investigated the role of GPx (glutathione peroxidase), the L-AT (L-amino acid transporter) system and PDI (protein disulfide-isomerase) in the delivery of NO redox derivatives into human platelets. Washed human platelets were treated with inhibitors of GPx, L-AT and PDI prior to exposure to donors of NO redox derivatives (S-nitrosoglutathione, Angeli's salt and diethylamine NONOate). Rapid delivery of NO-related signalling into platelets was monitored by cGMP accumulation and DAF-FM (4-amino-5-methylamino-2'7'-difluorofluorescein) fluorescence. All NO redox donors produced both a cGMP response and DAF-FM fluorescence in target platelets. NO delivery was blocked by inhibition of PDI in a dose-dependent manner. In contrast, inhibition of GPx and L-AT had only a minimal effect on NO-related signalling.PDI activity is therefore required for the rapid delivery into platelets of NO-related signals from donors of all NO redox derivatives. GPx and the L-AT system appeared to be unimportant in rapid NO signalling by the compounds used in the present study. This does not, however, exclude a possible role during exposure of cells to other S-nitrosothiol compounds, such as S-nitrosocysteine. These results further highlight the importance of PDI in mediating the action of a wide range of NO-related signals.

S-nitrosoglutathione and hypoxia-inducible factor-1 confer chemoresistance against carbamoylating cytotoxicity of BCNU in rat C6 glioma cells

BCNU (1,3-bis[2-chloroethyl]-1-nitrosourea) is the mainstay in glioblastoma multiform chemotherapy with only minimal effects. BCNU may kill tumor cells via carbamoylating cytotoxicity, which irreversibly inhibits glutathione reductase with resultant accumulation of oxidized form of glutathione causing oxidative stress. S-nitrosoglutathione (GSNO) is a product of glutathione and nitric oxide interaction. We report that GSNO formation may underlie carbamoylating chemoresistance mediated by activation of inducible nitric oxide synthase. Transactivation of hypoxia-inducible factor-1 (HIF-1)-responsive genes reduces oxidative stress caused by glutathione depletion. We also noted that preconditioning of C6 glioma cells to induce HIF-1 and its downstream genes confers chemoresistance against carbamoylating cytotoxicity of BCNU.

S-Nitrosothiols: cellular formation and transport

This review will focus on the transport and intracellular formation of S-nitrosothiols in cell culture models. The major points made in this article are: (1) S-Nitrosothiols are actively metabolized by cells. (2) S-Nitrosothiols affect cells in ways distinctly different from those of nitric oxide and can act through mechanisms that do not involve the intermediacy of nitric oxide. (3) Some S-nitrosothiols (S-nitrosocysteine, S-nitrosohomocysteine) can be taken up into cells via amino acid transport system L, whereas others (S-nitrosoglutathione, S-nitroso-N-acetylpenicillamine) are not directly transported, but require the presence of cysteine and/or cystine before the nitroso functional group is transported. (4) Proteomic detection of intracellular S-nitrosothiols is currently possible only if cells are loaded with high levels of S-nitrosothiols, and methodological advances are required in order to examine the S-nitrosated proteome after exposure of cells to physiological levels of nitric oxide.

Nitric oxide and blood: a review

Nitric oxide (NO) was identified as a physiological mediator of vascular tone in 1987. NO produced by endothelial cells causes vasodilatation and also inhibits platelet aggregation and leucocyte adhesion. Red cells metabolize NO to nitrate but may possibly carry and release, or even produce, NO in hypoxic conditions. NO physiology may have important implications for transfusion medicine, ranging from adverse effects of haemoglobin substitutes to preservation of stored platelets and to detrimental effects of stored red cells.

Detection and characterization of protein nitrosothiols

Protein S-nitrosylation is a post-translational modification of cysteine residues elicited by nitric oxide (NO). Detection and quantification of protein nitrosothiols remains a challenge because of the lability of the nitrosothiol moiety. Here, we describe approaches for labeling S-nitrosylated proteins with affinity and radioactive tags to facilitate their detection, purification, and identification.

Nitric oxide and BCNU chemoresistance in C6 glioma cells: role of S-nitrosoglutathione

Inducible nitric oxide synthase (iNOS or NOS2) is expressed in malignant glioma. Previously we noted that C6 glioma cells overexpressing NOS2 displayed chemoresistance against 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and other chloroethylnitrosourea derivatives with carbamoylating action. Herein we report experimental evidence supporting the contention that this NOS2 effect is mediated, at least in part, by S-nitrosoglutathione (GSNO), a potent antioxidant derived from interaction of NO and glutathione. Out of three NO donors tested, only GSNO was effective in protecting glioma cells against BCNU cytotoxicity. Furthermore, the protective effect of GSNO, similar to that of NOS2, was confined to carbamoylating, but not alkylating action. Experimental manipulations that were expected to increase or decrease cellular GSNO stores, as confirmed by immunocytochemical staining using a GSNO-specific antibody and HPLC analysis of GSNO contents in culture medium, led respectively to enhanced or reduced chemoresistance against carbamoylating cytotoxicity. Finally, neocuproine, a selective cuprous ion chelator known to neutralize GSNO actions, abolished NOS2-mediated chemoresistance against carbamoylating agents. Our results reveal a novel action of NOS2/GSNO that may potentially contribute to the development of chemoresistance against BCNU, which remains a mainstay in chemotherapy for glioblastoma multiforme.

Neocuproine inhibits the decomposition of endogenous S-nitrosothiol by ultraviolet irradiation in the mouse gastric fundus

In the present study, we investigated whether copper ions are involved in the decomposition of endogenous S-nitrosothiols by ultraviolet (UV) light irradiation in the mouse gastric fundus. The effects of copper ions and chelators of copper(I) and copper(II), neocuproine and cuprozine, respectively, were studied on relaxations in response to S-nitrosoglutathione, UV irradiation, exogenous nitric oxide (NO), added as acidified NaNO(2), and isoproterenol. UV irradiation of smooth muscle strips induced fast and transient relaxations which were mimicked by exogenous NO. S-Nitrosoglutathione induced concentration-dependent relaxations, which were more sustained than those elicited by UV irradiation or NO. CuCl(2) did not affect relaxations elicited by UV irradiation, exogenous NO and isoproterenol but enhanced those elicited by S-nitrosoglutathione. CuSO(4) but not FeSO(4) mimicked the effect of CuCl(2) on relaxations elicited by S-nitrosoglutathione. Neocuproine, the copper(I)-specific chelator, inhibited both photorelaxation and S-nitrosoglutathione-induced relaxation, and this inhibition was prevented by CuCl(2). In contrast, neocuproine significantly enhanced the relaxations in response to exogenous NO, without affecting the relaxations elicited by isoproterenol. Cuprizone, a specific copper(II) chelator, did not affect relaxations in response to S-nitrosoglutathione, UV irradiation, exogenous NO and isoproterenol. These results suggest that copper(I) and not copper(II) may play a role in the NO release evoked by the light-induced decomposition of endogenous S-nitrosothiols in mouse gastric fundus. Also, results with the selective copper(I) chelator, neocuproine, confirmed our recent findings that the endogenous "store" of S-nitrosoglutathione, rather than NO, acts as an intermediate in photorelaxation of the mouse gastric fundus, and that photorelaxation may be a suitable model to elucidate the nature of endogenous S-nitrosothiols.

Role of copper in the relaxant action of S-nitrosothiols in the rat anococcygeus muscle

1. The effects of copper chelators were investigated on the relaxant actions of the S-nitrosothiols S-nitrosoglutathione (GSNO) and S-nitroso-N-acetyl-d,l-penicillamine (SNAP), the non-S-nitrosothiol nitric oxide (NO) donor sodium nitroprusside (SNP), free radical NO (NO.) and the nitrergic neurotransmitter in rat isolated anococcygeus muscle. 2. Cumulative additions of GSNO (0.01-100 micro mol/L), SNAP (0.001-10 micro mol/L), SNP (0.001-1 micro mol/L) and NO. (0.5-5 micro mol/L) and electrical field stimulation (EFS; 1-5 Hz, 10 s) of nitrergic nerves in preparations precontracted with guanethidine (10-30 micro mol/L) and clonidine (0.01-0.3 micro mol/L) produced concentration-dependent relaxations. 3. The Cu[I] chelator neocuproine (10-30 micro mol/L) produced concentration-dependent inhibitions of the relaxations to GSNO and SNAP. At 30 micro mol/L, neocuprinone had no effect on relaxations to SNP (0.001-1 micro mol/L), NO. (0.5-5 micro mol/L) or EFS (1-5 Hz, 10 s). 4. The Cu[II] chelator cuprizone (30 micro mol/L) slightly and significantly enhanced relaxations to GSNO and NO., but had no effect on relaxations to SNAP, SNP or EFS. 5. In conclusion, the results indicate that Cu[I], but not Cu[II], may be involved in the relaxant actions of GSNO and SNAP in the rat anococcygeus muscle.

A photosensitive vascular smooth muscle store of nitric oxide in mouse aorta: no dependence on expression of endothelial nitric oxide synthase

(1) Photorelaxation is the reversible relaxation of vascular smooth muscle (VSM) when irradiated with ultraviolet (UV) light resulting from the release of nitric oxide (NO). In this study we characterize the involvement of endothelial nitric oxide synthase (eNOS) in the photorelaxation response of thoracic aorta from endothelial NOS deficient (-/-) and control (C57BL/6j) mice. (2) Cirazoline contracted aortae were repeatedly exposed to 30 s of UV light every 3-4 min. Equal levels of photorelaxation (45+/-2%; n=34) was observed in both strains. (3) 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), K(+), 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), 4-aminopyridine (4-AP) and ethacrynic acid significantly reduced the photorelaxation response. In C57BL/6j mice diethyldithiocarbamate (DETCA) also reduced photorelaxation. (4) Control endothelium-intact and -denuded aorta and L-NAME (100 micro M) treated and untreated eNOS (-/-) aortae were repeatedly exposed to UV light for 5 min every 10 min until no photorelaxation response was observed. After 1 h of rest in the dark the vessels showed between 30-70% recovery of the photorelaxation response indicating regeneration of the store in the absence of the endothelium and eNOS. (5) The results of this study suggest that photorelaxation in mouse aorta VSM results from the release of NO from a stable store of RSNOs, which activates soluble guanylate cyclase (sGC), leading to cGMP-dependent relaxation that is partially mediated by an increase in K(V) channel activation and hyperpolarization. In addition, the eNOS isoform is not essential for the formation of the photorelaxation store and a non-NOS source of NO may be involved in the maintenance of this store.

The decomposition of thionitrites

The mechanism of thionitrite decomposition, both in vivo and in vitro, remains unclear. Thionitrite stability is highly variable; it is a complex function of thionitrite structure and environmental condition. Several recent advances clarify the role of unimolecular homlytic decomposition, metal-catalyzed reductive decomposition and higher-order enzymatic and non-enzymatic processes to the overall observed stability of thionitrites.

NO and the vasculature: where does it come from and what does it do?

Nitric oxide (NO) is involved in a large number of cellular processes and dysfunctions in NO production have been implicated in many different disease states. In the vasculature NO is released by endothelial cells where it modulates the underlying smooth muscle to regulate vascular tone. Due to the unique chemistry of NO, such as its reactive and free radical nature, it can interact with many different cellular constituents such as thiols and transition metal ions, which determine its cellular actions. In this review we also discuss many of the useful pharmacological tools that have been developed and used extensively to establish the involvement of NO in endothelium-derived relaxations. In addition, the recent literature identifying a potential source of NO in endothelial cells, which is not directly derived from endothelial nitric oxide synthase is examined. Finally, the photorelaxation phenomena, which mediates the release of NO from a vascular smooth muscle NO store, is discussed.

Current trends in QSAR on NO donors and inhibitors of nitric oxide synthase (NOS)*

This article evaluates the quantitative structure-activity relationships (QSAR) of nitric oxide (NO) radical donors and nitric oxide synthases (NOS) inhibitors, using the C-QSAR program of Biobyte. Furoxans, triazines, amidoximes, tetrazoles, imidazoles and N(omega)-2-nitroarylamino acid analogues were included in this survey. In nine out of seventeen cases, the clog P plays a significant part in the QSAR of the NO radical donors and of the NOS inhibition. Many of the compounds must be interacting with a hydrophobic space in a non-specific way. In some cases molecular refractivity CMR/MR as well as sterimol parameters (B(1) and L) are important. Electronic effects, with the exception of the Hammett's constant sigma and the Swain-Lupton parameter F, are not found to govern the biological activity. Stereochemical and electronic features are also found to be important. Indicator variables were used after the best model was found to account for the usual structural features.

Nitric oxide donor drugs: current status and future trends

Nitric oxide synthesised in endothelial cells that line blood vessels has a wide range of functions that are vital for maintaining a healthy cardiovascular system. Reduced nitric oxide availability is implicated in the initiation and progression of many cardiovascular diseases and delivery of supplementary nitric oxide to help prevent disease progression is an attractive therapeutic option. Nitric oxide donor drugs represent a useful means of systemic nitric oxide delivery and organic nitrates have been used for many years as effective therapies for symptomatic relief from angina. However, nitrates have limitations and a number of alternative nitric oxide donor classes have emerged since the discovery that nitric oxide is a crucial biological mediator. This review focuses on novel advances and possible future directions in nitric oxide donor drug development.

The biochemistry and physiology of S-nitrosothiols

S-nitrosothiols are biological metabolites of nitric oxide. It has often been suggested that they represent a more stable metabolite of nitric oxide that can either be stored, or transported, although the evidence for this is sparse. There are many unanswered questions concerning how S-nitrosothiols are formed, how they are metabolized and how they elicit biological responses. These questions are highlighted by the fact that the known chemistry of nitric oxide, thiols, and S-nitrosothiols cannot serve to explain their proposed biological activities. This review attempts to highlight the gulf between our chemical understanding of S-nitrosothiols and the proposed biological activities of these compounds with respect to guanylyl cyclase-independent nitric oxide bioactivity and also the control of vascular tone.

Kinetics studies of the reaction of the ruthenium porphyrin Ru(OEP)(CO) with the S-nitrosothiol N-acetyl-1-amino-2-methylpropyl-2-thionitrite

The reaction of the S-nitrosothiol compound N-acetyl-1-amino-2-methylpropyl-2-thionitrite (RSNO) with the model metalloporphyrin complex Ru(II)(OEP)(CO) (OEP = octaethylporphyrinato dianion) gives the addition product trans-Ru(II)(OEP)(NO)(SR). Here we report the details of a stopped flow kinetics investigation which demonstrates the rapid equilibrium formation of an intermediate concluded to be S-bound RSNO complex Ru(II)(OEP)(RSNO)(CO), which undergoes a rate-limiting step, presumably S-NO bond cleavage to give a second intermediate Ru(III)(OEP)(SR)(CO) too short lived for direct observation. Notably, this is different from the nitrogen coordination pathway often proposed and represents an alternative mechanism by which S-nitrosothiols may be formed or decomposed in the presence of redox active metal centers. Also reported is a brief study of the quantitative photochemistry of RSNO, the photodecomposition of which complicates the kinetics studies by spectroscopic techniques.

Metabolism of S-nitrosoglutathione by endothelial cells

S-nitrosoglutathione (GSNO) is an inhibitor of platelet aggregation and has also been shown to protect the ischemic heart from reperfusion-mediated injury. Although GSNO is often used in cell culture as a source of nitric oxide, the mechanisms of GSNO metabolism are not well established. We show here that GSNO decomposition by bovine aortic endothelial cells has an absolute dependence on the presence of cystine in the cell culture medium. In addition, GSNO decay is inhibited by diethyl maleate, an intracellular glutathione scavenger, but not by buthionine sulfoximine, a glutathione synthesis inhibitor. This indicates that thiols in general, rather than specifically glutathione, are the major factors that influence GSNO decay. Only 40% of the nitroso group of GSNO could be recovered as nitrite/nitrate, suggesting that the primary route of GSNO decay is reductive and that nitric oxide is only a minor product of GSNO decay. We conclude that the intracellular thiol pool causes the reduction of extracellular disulfides to thiols, which then directly reduce GSNO.

S-nitrosation controls gating and conductance of the alpha 1 subunit of class C L-type Ca(2+) channels

Modulation of smooth muscle, L-type Ca(2+) channels (class C, Ca(V)1.2b) by thionitrite S-nitrosoglutathione (GSNO) was investigated in the human embryonic kidney 293 expression system at the level of whole-cell and single-channel currents. Extracellular administration of GSNO (2 mM) rapidly reduced whole-cell Ba(2+) currents through channels derived either by expression of alpha1C-b or by coexpression of alpha1C-b plus beta2a and alpha2-delta. The non-thiol nitric oxide (NO) donors 2,2-diethyl-1-nitroso-oxhydrazin (2 mM) and 3-morpholinosydnonimine-hydrochloride (2 mM), which elevated cellular cGMP levels to a similar extent as GSNO, failed to affect Ba(2+) currents significantly. Intracellular administration of copper ions, which promote decomposition of the thionitrite, antagonized its inhibitory effect, and loading of cells with high concentrations of dithiothreitol (2 mM) prevented the effect of GSNO on alpha1C-b channels. Intracellular loading of cells with oxidized glutathione (2 mM) affected neither alpha1C-b channel function nor their modulation by GSNO. Analysis of single-channel behavior revealed that GSNO inhibited Ca(2+) channels mainly by reducing open probability. The development of GSNO-induced inhibition was associated with the transient occurrence of a reduced conductance state of the channel. Our results demonstrate that GSNO modulates the alpha1 subunit of smooth muscle L-type Ca(2+) channels by an intracellular mechanism that is independent of NO release and stimulation of guanylyl cyclase. We suggest S-nitrosation of intracellularly located sulfhydryl groups as an important determinant of Ca(2+) channel gating and conductance.

Nitric oxide-dependent pro-oxidant and pro-apoptotic effect of metallothioneins in HL-60 cells challenged with cupric nitrilotriacetate

Intracellular safeguarding functions of metallothioneins (MTs) include sequestering transition and heavy metals, scavenging free radicals and protecting against electrophiles. We report that MT protection against Cu-induced cytotoxicity can be reversed and pro-oxidant and pro-apoptotic effects can be induced in HL-60 cells exposed to NO. We demonstrate that in ZnCl(2)-pretreated HL-60 cells loaded with copper nitrilotriacetate (Cu-NTA), exposure to an NO donor, S-nitroso-N-acetyl penicillamine, resulted in S-nitrosylation and oxidation of MT cysteines. This disruption of MT Cu-binding thiolate clusters caused loosening and release of redox-active Cu, enhanced redox-cycling activity of Cu and increased peroxidation of major classes of membrane phospholipids. We also found that Cu-induced oxidative stress in ZnCl(2)-pretreated/Cu-NTA-loaded HL-60 cells was accompanied by apoptosis documented by characteristic changes of nuclear morphology, internucleosomal DNA cleavage, externalization of phosphatidylserine, release of cytochrome c from mitochondria into cytosol and activation of caspase-3. We conclude that in Cu-challenged cells, NO can reverse the protective role of MTs and convert them into pro-oxidant, pro-apoptotic implements.

Role of copper ions and cytochrome P450 in the vasodilator actions of the nitroxyl anion generator, Angeli's salt, on rat aorta

Since copper ions catalyse the oxidation of nitroxyl anion to nitric oxide, we investigated whether this might explain the vasodilator actions of the nitroxyl generator, Angeli's salt, in rat aorta. Parallel studies were conducted with S-nitroso-N-acetyl-D,L-penicillamine (SNAP), since Cu ions catalyse the liberation of nitric oxide from this compound. Copper sulphate enhanced relaxation to Angeli's salt and SNAP but this resulted from reduced destruction of nitric oxide by superoxide rather than from enhanced generation of nitric oxide, since it was mimicked by superoxide dismutase and by the superoxide dismutase mimetic, MnCl2. Results with the selective Cu2+ chelators, neocuproine and bathocuproine disulfonate, and the Cu2+ chelators, EDTA, cuprizone and diethyldithiocarbamate, confirmed an important role for endogenous copper in mediating relaxation to SNAP but suggested only a minor role for Angeli's salt. Relaxation to Angeli's salt was, however, powerfully blocked by proadifen, suggesting an important role for cytochrome P450.

Pre- and postjunctional protective effect of neocuproine on the nitrergic neurotransmitter in the mouse gastric fundus

1. Electrical field stimulation (EFS) of non-adrenergic non-cholinergic nerves of the mouse gastric fundus induced frequency-dependent transient relaxations which were mimicked by nitric oxide (NO), added as acidified NaNO(2). The NO donors S-nitrosocysteine, S-nitrosoglutathione, SIN-1 and hydroxylamine induced sustained concentration-dependent relaxations. The NO synthase blocker L-nitro arginine (L-NOARG; 300 microM) abolished the relaxations to EFS without affecting the relaxations to NO. 2. The copper(I) chelator neocuproine (10 microM) enhanced the relaxations to EFS and NO but inhibited those to S-nitrosocysteine and S-nitrosoglutathione. Neocuproine potentiated the relaxations to SIN-1, which releases NO extracellularly, without affecting the relaxations to hydroxylamine, which releases NO intracellularly. 3. The potentiating effect of neocuproine on the relaxations to EFS was more pronounced after inhibition of catalase with 3-amino-1,2,4-triazole (1 mM) but not after inhibition of Cu/Zn superoxide dismutase (SOD) with diethyl dithiocarbamic acid (DETCA, 1 mM). The potentiating effect of neocuproine on relaxations to NO was not altered by 3-amino-1,2,4-triazole or DETCA treatment. 4. The relaxations to EFS were significantly inhibited by the oxidants hydrogen peroxide (70 microM) and duroquinone (10 microM) but only after inhibition of catalase with 3-amino-1,2,4-triazole or after inhibition of Cu/ZnSOD with DETCA respectively. 5. Our results suggest that neocuproine can act as an antioxidant in the mouse gastric fundus and that both catalase and Cu/ZnSOD protect the nitrergic neurotransmitter from oxidative breakdown. Since inhibition of catalase but not inhibition of Cu/ZnSOD potentiated the effect of neocuproine on relaxations to EFS without affecting the relaxations to NO, catalase may protect the nitrergic neurotransmitter mainly at a prejunctional site whereas Cu/ZnSOD protects at a postjunctional site.

Inhibition of human platelet aggregation by nitric oxide donor drugs: relative contribution of cGMP-independent mechanisms

Inhibition of platelet activation by nitric oxide (NO) is not exclusively cGMP-dependent. Here, we tested whether inhibition of platelet aggregation by structurally distinct NO donors is mediated by different mechanisms, partly determined by the site of NO release. Glyceryl trinitrate (GTN), sodium nitroprusside (SNP), S-nitrosoglutathione (GSNO), diethylamine diazeniumdiolate (DEA/NO), and a novel S-nitrosothiol, RIG200, were examined in ADP (8 microM)- and collagen (2.5 microgram/ml)-activated human platelet rich plasma. GTN was a poor inhibitor of aggregation whilst the other NO donors inhibited aggregation, irrespective of agonist. These effects were abolished by the NO scavenger, hemoglobin (Hb; 10 microM, P < 0.05, n = 6), except with high concentrations of DEA/NO, when NO concentrations exceeded the capacity of Hb. However, experiments with the soluble guanylate cyclase inhibitor, ODQ (100 microM), indicated that only SNP-mediated inhibition was exclusively cGMP-dependent. Furthermore, the cGMP-independent effects of S-nitrosothiols were distinct from those of DEA/NO, suggesting that different NO-related mediators (e.g., nitrosonium and peroxynitrite, respectively) are responsible for their actions.

Inhibition of human platelet aggregation by a novel S-nitrosothiol is abolished by haemoglobin and red blood cells in vitro: implications for anti-thrombotic therapy

1. S-Nitrosothiols are nitric oxide (NO) donor drugs that have been shown to inhibit platelet aggregation in platelet rich plasma (PRP) in vitro and to inhibit platelet activation in vivo. The aim of this study was to compare the platelet effects of a novel S-nitrosated glyco-amino acid, RIG200, with an established S-nitrosothiol, S-nitrosoglutathione (GSNO) in PRP, and to investigate the effects of cell-free haemoglobin and red blood cells on S-nitrosothiol-mediated inhibition of platelet aggregation. 2. The effects of GSNO and RIG200 in collagen (2.5 microg ml(-1))-induced platelet aggregation in PRP and whole blood were investigated in vitro. Both compounds were found to be powerful inhibitors of aggregation in PRP, and RIG200 was significantly more potent (IC(50)=2.0 microM for GSNO and 0.8 microM for RIG200; P=0.04). 3. Neither compound inhibited aggregation in whole blood, even at concentrations of 100 microM. Red blood cell concentrations as low as 1% of the haematocrit, and cell-free haemoglobin (> or = 2.5 microM), significantly reduced their inhibitory effects on platelets. 4. Experiments involving measurement of cyclic GMP levels, electrochemical detection of NO and electron paramagnetic resonance of haemoglobin in red blood cells, indicated that scavenging of NO generated from S-nitrosothiols by haemoglobin was responsible for the lack of effect of S-nitrosothiols on platelets in whole blood. 5. These studies suggest that scavenging of NO by haemoglobin in blood might limit the therapeutic application of S-nitrosothiols as anti-platelet agents.

A novel family of S-nitrosothiols: chemical synthesis and biological actions

S-Nitrosothiols are a class of chemical compounds that decompose to release nitric oxide and show promise in the treatment of a variety of cardiovascular diseases. Some of these are present in vivo and others have been synthesized in vitro. However, those discovered or synthesized to date have very little tissue selectivity or specificity. We synthesized a number of novel S-nitrosated dipeptides of high purity and examined their effects on vasorelaxation using rat mesenteric arteries and on inhibition of platelet aggregation using platelets from healthyhuman subjects. For comparison, we also tested the effects of S-nitroso-l-glutathione (GSNO, an S-nitrosothiol present in vivo) and S-nitroso-N-acetyl-d-beta,beta-dimethylcysteine (SNAP(D), the d-isomer of SNAP, a commonly used S-nitrosothiol previously synthesized in vitro) in these biological systems. Satisfactory elemental analyses were obtained for all compounds synthesized (less than +/- 0.3%), and all accurate mass measurements were within 1-5 ppm of the expected mass. The novel S-nitrosated dipeptides all elicited vasorelaxation with significantly higher potency, of the order of one log molar unit, than either GSNO or SNAP(D). However, all compounds inhibited U46619-induced platelet aggregation with similar potency to GSNO and SNAP(D). These findings indicate a degree of tissue selectivity which may prove to be of therapeutic usefulness.

Novel S-nitrosothiols do not engender vascular tolerance and remain effective in glyceryltrinitrate-tolerant rat femoral arteries

Organic nitrates, such as glyceryltrinitrate, are nitric oxide (NO) donor drugs that engender tolerance with long-term use. Here, we tested the hypothesis that our novel S-nitrosothiols, N-(S-nitroso-N-acetylpenicillamine)-2-amino-2-deoxy-1,3,4,6, tetra-O-acetyl-beta-D-glucopyranose (RIG200) and S-nitroso-N-valeryl-D-penicillamine (D-SNVP), do not induce vascular tolerance ex vivo. Femoral arteries from adult male Wistar rats were preconstricted with phenylephrine and perfused with the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME). Perfusion pressure was measured during 20 h treatment with supramaximal concentrations of NO donor (10 microM). Perfusion with glyceryltrinitrate caused a vasodilatation, which recovered over 2-20 h. In contrast, the S-nitrosothiols caused vasodilatations that were maintained throughout the 20 h perfusion period. Responses to S-nitrosothiols were partially reversed by the NO scavenger ferrohaemoglobin and fully reversed by the soluble guanylate cyclase inhibitor [1H-[1,2,4] oxadiazole [4,3-a]quinoxaline-1-one (ODQ). Glyceryltrinitrate-tolerant vessels were fully responsive to bolus injections of S-nitrosothiols. Resistance to tolerance is an attractive property of our novel compounds, particularly in view of their sustained activity in arteries with damaged endothelium.

Effect of neocuproine, a selective Cu(I) chelator, on nitrergic relaxations in the mouse corpus cavernosum

The effects of neocuproine and bathocuproine, Cu(I) and Cu(II) chelators, respectively, were studied on relaxations in response to electrical field stimulation, acetylcholine, S-nitrosoglutathione, acidified sodium nitrite and sodium nitroprusside in the mouse corpus cavernosum precontracted with phenylephrine. Neocuproine significantly inhibited relaxations induced by electrical field stimulation, acetylcholine and S-nitrosoglutathione, but not by acidified sodium nitrite and sodium nitroprusside. The pre-prepared neocuproine-Cu(I) complex was ineffective on the responses. The discrepancy between the shape of relaxations in response to electrical field stimulation or to acetylcholine and S-nitrosoglutathione was abolished by adding CuCl(2) into the bathing medium. The copper action was blocked by neocuproine but not by bathocuproine. However, the pre-prepared bathocuproine-Cu(II) complex did not accelerate the relaxations affected by CuCl(2). These findings suggest that a Cu(I)-dependent mechanism may play a role in the relaxation induced by the endogenous relaxant factor as well as by S-nitrosoglutathione in mouse cavernosal tissue.

Novel S-nitrosothiols do not engender vascular tolerance and remain effective in glyceryl trinitrate-tolerant rat femoral arteries

Organic nitrates, such as glyceryl trinitrate, are nitric oxide (NO) donor drugs that engender tolerance with long-term use. Here, we tested the hypothesis that our novel S-nitrosothiols, N-(S-nitroso-N-acetylpenicillamine)-2-amino-2-deoxy-1,3,4,6, tetra-O-acetyl-beta-D-glucopyranose (RIG200) and S-nitroso-N-valeryl-D-penicillamine (D-SNVP), do not induce vascular tolerance ex vivo. Femoral arteries from adult male Wistar rats were preconstricted with phenylephrine and perfused with the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME). Perfusion pressure was measured during 20-h treatment with supramaximal concentrations of NO donor (10 microM). Perfusion with glyceryltrinitrate caused a vasodilatation, which recovered over 2-20 h. In contrast, the S-nitrosothiols caused vasodilatations that were maintained throughout the 20-h perfusion period. Responses to S-nitrosothiols were partially reversed by the NO scavenger ferrohaemoglobin and fully reversed by the soluble guanylate cyclase inhibitor [1H-[1,2,4] oxadiazole [4,3-a]quinoxaline-1-one (ODQ). Glyceryltrinitrate-tolerant vessels were fully responsive to bolus injections of S-nitrosothiols. Resistance to tolerance is an attractive property of our novel compounds, particularly in view of their sustained activity in arteries with damaged endothelium.

Copper-mediated toxicity of 2,4,5-trichlorophenol: biphasic effect of the copper(I)-specific chelator neocuproine

The lipophilic copper(I)-specific chelator neocuproine has been frequently used as an inhibitor of copper-mediated damage in biological systems. In this communication we report that the copper-mediated toxicity of 2,4,5-trichlorophenol is markedly potentiated by neocuproine at levels which are near-stoichiometric with respect to the copper concentration but is inhibited at higher concentrations. However, no potentiation was observed when neocuproine was substituted by bathocuproinedisulfonic acid, a negative charged ligand with essentially the same copper-binding characteristics as neocuproine. We found that the potentiation by neocuproine was due to the formation of a lipophilic copper complex, while the inhibition by bathocuproinedisulfonic acid was due to the formation of a hydrophilic one. Caution in the use of neocuproine to study copper-mediated toxicity is advised.

Selective modifiers of glutathione biosynthesis and 'repriming' of vascular smooth muscle photorelaxation

Photorelaxation of vascular smooth muscle (VSM) is caused by the release of nitric oxide (NO) from a finite molecular store that can be depleted by irradiating pre-contracted arteries with visible light. The ability of an 'exhausted' vessel to respond to a further period of illumination is lost temporarily but then recovers slowly as the photosensitive store is reconstituted in the dark. The recovery process, termed repriming, displays an absolute requirement for endothelium-derived NO and is inhibited by pre-treating arteries with ethacrynic acid, a thiol-alkylating agent. Here we demonstrate that agents that up- or down-regulate glutathione (GSH) biosynthesis influence the extent to which the store is regenerated in the dark. Isolated rat tail arteries (RTAs) were perfused internally with Krebs solution containing phenylephrine (PE; mean [PE] +/- s.e.mean: 5. 78+/-0.46 microM) and periodically exposed to laser light (lambda=514.5 nm, 6.3 mW cm(-2) for 6 min). Photorelaxations of control RTAs were compared with those from either (a) vessels taken from animals previously injected i.p. with buthionine sulphoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase (three injections, 100 mg kg(-1) at 8 h intervals); or (b) isolated RTAs that were perfused ex vivo with oxothiazolidine (OXO), a precursor of cysteine (10(-4) M OXO for 60 min). RTAs from BSO-treated animals exhibited attenuated photorelaxations: the mean (+/-s.e.mean) amplitude of the response recorded after 72 min recovery in the dark was 12.4+/-1.6% versus 21.4+/-2.9% for control arteries (n=5; P<0. 01). Conversely RTAs treated with OXO and allowed to recover for a similar period showed enhanced photorelaxations, 32.6+/-6.3% as compared to 21.4+/-2.9% for control arteries (n=5; P<0.01). A hyperbolic curve fit to repriming curves for BSO-treated and control arteries returned asymptote values (maximum photorelaxations) of (mean +/- s.e.mean) 24.2+/-3.2% and 55.2+/-8.5%, respectively. The level of GSH in RTA extracts was measured by high-pressure liquid chromatography (HPLC). Injecting animals with BSO decreased GSH to 85% of control levels (P<0.05) while treatment of isolated vessels with OXO resulted in a 31% increase above control levels (P<0.05). Thus, drug-induced changes in RTA GSH levels were positively correlated with altered photorelaxations. The results lead us to postulate that the photosensitive store in VSM is generated, at least in part, from intracellular GSH which becomes converted to S-nitrosoglutathione (GSNO) by nitrosating species that are formed ultimately from endothelium-derived NO. The possible physiological significance of a photolabile store of NO in VSM is discussed briefly.