Iron diethyldithiocarbamate as spin trap for nitric oxide detection

Antiviral Activity of Nitrosonium Cations against SARS-CoV-2 on a Syrian Hamster Model

The antiviral action of binuclear dinitrosyl iron complexes with glutathione along with diethyldithiocarbamate against the SARS-CoV-2 virus has been demonstrated on a Syrian hamster model after aerosol exposure of SARS-CoV-2-infected animals to the solutions of said compounds. EPR assays in analogous experiments on intact hamsters have demonstrated that the iron complexes and diethyldithiocarbamate are predominantly localized in lung tissues. These results have been compared with similar measurements on intact mice, which have shown the equal localization of these agents in both the lungs and liver. We assume that the release of the nitrosonium cations from the binuclear dinitrosyl iron complexes with glutathione occurs during their contact with diethyldithiocarbamate in the animal body. These cations caused S-nitrosation of host and viral cell proteases, leading to suppression of SARS-CoV-2 infection.

Physico-Chemistry of Dinitrosyl Iron Complexes as a Determinant of Their Biological Activity

In this article we minutely discuss the so-called "oxidative" mechanism of mononuclear form of dinitrosyl iron complexes (M-DNICs) formations proposed by the author. M-DNICs are proposed to be formed from their building material-neutral NO molecules, Fe2+ ions and anionic non-thiol (L-) and thiol (RS-) ligands based on the disproportionation reaction of NO molecules binding with divalent ion irons in pairs. Then a protonated form of nitroxyl anion (NO-) appearing in the reaction is released from this group and a neutral NO molecule is included instead. As a result, M-DNICs are produced. Their resonance structure is described as [(L-)2Fe2+(NO)(NO+)], in which nitrosyl ligands are represented by NO molecules and nitrosonium cations in equal proportions. Binding of hydroxyl ions with the latter causes conversion of these cations into nitrite anions at neutral pH values and therefore transformation of DNICs into the corresponding high-spin mononitrosyl iron complexes (MNICs) with the resonance structure described as [(L-)2Fe2+(NO)]. In case of replacing L- by thiol-containing ligands, which are characterized by high π-donor activity, electron density transferred from sulfur atoms to iron-dinitrosyl groups neutralizes the positive charge on nitrosonium cations, which prevents their hydrolysis, ensuring relatively a high stability of the corresponding M-DNICs with the resonance structure [(RS-)2Fe2+ (NO, NO+)]. Therefore, M-DNICs with thiol-containing ligands, as well as their binuclear analogs (B-DNICs, respective resonance structure [(RS-)2Fe2+2 (NO, NO+)2]), can serve donors of both NO and NO+. Experiments with solutions of B-DNICs with glutathione or N-acetyl-L-cysteine (B-DNIC-GSH or B-DNIC-NAC) showed that these complexes release both NO and NO+ in case of decomposition in the presence of acid or after oxidation of thiol-containing ligands in them. The level of released NO was measured via optical absorption intensity of NO in the gaseous phase, while the number of released nitrosonium cations was determined based on their inclusion in S-nitrosothiols or their conversion into nitrite anions. Biomedical research showed the ability of DNICs with thiol-containing ligands to be donors of NO and NO+ and produce various biological effects on living organisms. At the same time, NO molecules released from DNICs usually have a positive and regulatory effect on organisms, while nitrosonium cations have a negative and cytotoxic effect.

Comparison of Free Radical Levels in the Aerosol from Conventional Cigarettes, Electronic Cigarettes, and Heat-Not-Burn Tobacco Products

Aerosols from electronic cigarettes and heat-not-burn tobacco products have been found to contain lower levels of almost all compounds from the list of Harmful and Potentially Harmful Constituents known to be present in tobacco products and tobacco smoke than smoke from conventional cigarettes. Free radicals, which also pose potential health risks, are not considered in this list, and their levels in the different product types have not yet been compared under standardized conditions. We compared the type and quantity of free radicals in mainstream aerosol of 3R4F research cigarettes, two types of electronic cigarettes, and a heat-not-burn tobacco product. Free radicals and NO in the gas phases were separately spin trapped and quantified by electron paramagnetic resonance (EPR) spectroscopy by using a smoking machine for aerosol generation and a flow-through cell to enhance reproducibility of the quantification. Particulate matter was separated by a Cambridge filter and extracted, and persistent radicals were quantified by EPR spectroscopy. Levels of organic radicals for electronic cigarettes and the heat-not-burn product, as measured with the PBN spin trap, did not exceed 1% of the level observed for conventional cigarettes and were close to the radical level observed in air blanks. The radicals found in the smoke of conventional cigarettes were oxygen centered, most probably alkoxy radicals, whereas a signal for carbon-centered radicals near the detection limit was observed in aerosol from the heat-not-burn product and electronic cigarettes. The NO level in aerosol produced by electronic cigarettes was below our detection limit, whereas for the heat-not-burn product, it reached about 7% of the level observed for whole smoke from 3R4F cigarettes. Persistent radicals in particulate matter could be quantified only for 3R4F cigarettes. Aerosols from vaping and heat-not-burn tobacco products have much lower free radical levels than cigarette smoke, however, the toxicological implications of this finding are as yet unknown.

Regulation of NADPH-dependent Nitric Oxide and reactive oxygen species signalling in endothelial and melanoma cells by a photoactive NADPH analogue

Nitric Oxide (NO) and Reactive oxygen species (ROS) are endogenous regulators of angiogenesis-related events as endothelial cell proliferation and survival, but NO/ROS defect or unbalance contribute to cancers. We recently designed a novel photoactive inhibitor of NO-Synthases (NOS) called NS1, which binds their NADPH site in vitro. Here, we show that NS1 inhibited NO formed in aortic rings. NS1-induced NO decrease led to an inhibition of angiogenesis in a model of VEGF-induced endothelial tubes formation. Beside this effect, NS1 reduced ROS levels in endothelial and melanoma A375 cells and in aorta. In metastatic melanoma cells, NS1 first induced a strong decrease of VEGF and blocked melanoma cell cycle at G2/M. NS1 decreased NOX₄ and ROS levels that could lead to a specific proliferation arrest and cell death. In contrast, NS1 did not perturb melanocytes growth.

Altogether, NS1 revealed a possible cross-talk between eNOS- and NOX₄ –associated pathways in melanoma cells via VEGF, Erk and Akt modulation by NS1 that could be targeted to stop proliferation. NS1 thus constitutes a promising tool that modulates NO and redox stresses by targeting and directly inhibiting eNOS and, at least indirectly, NADPH oxidase(s), with great potential to control angiogenesis.

Electronic and spatial structures of water-soluble dinitrosyl iron complexes with thiol-containing ligands underlying their ability to act as nitric oxide and nitrosonium ion donors

The ability of mononuclear dinitrosyl iron commplexes (M-DNICs) with thiolate ligands to act as NO donors and to trigger S-nitrosation of thiols can be explain only in the paradigm of the model of the [Fe(+)(NO(+))(2)] core ({Fe(NO)(2)}(7) according to the Enemark-Feltham classification). Similarly, the {(RS(-))(2)Fe(+)(NO(+))(2)}(+) structure describing the distribution of unpaired electron density in M-DNIC corresponds to the low-spin (S = 1/2) state with a d(7) electron configuration of the iron atom and predominant localization of the unpaired electron on MO(d(z2)) and the square planar structure of M-DNIC. On the other side, the formation of molecular orbitals of M-DNIC including orbitals of the iron atom, thiolate and nitrosyl ligands results in a transfer of electron density from sulfur atoms to the iron atom and nitrosyl ligands. Under these conditions, the positive charge on the nitrosyl ligands diminishes appreciably, the interaction of the ligands with hydroxyl ions or with thiols slows down and the hydrolysis of nitrosyl ligands and the S-nitrosating effect of the latter are not manifested. Most probably, the S-nitrosating effect of nitrosyl ligands is a result of weak binding of thiolate ligands to the iron atom under conditions favoring destabilization of M-DNIC.

Exposure to nitric oxide increases the nitrosyl-iron complexes content in sorghum embryonic axes

This work was aimed to investigate nitrosyl-Fe complexes formation by reaction of endogenous ligands and Fe, in sorghum embryonic axes exposed to NO-donors. Electron paramagnetic resonance (EPR) was employed to detect the presence of nitrosyl-Fe complexes in plant embryos, as well as changes in labile iron pool (LIP). Nitrosyl-Fe complexes formation was detected in sorghum embryonic axes homogenates incubated in vitro in the presence of 1 mM of NO donors: diethylenetriamine NONOate (DETA NONOate), S-nitrosoglutathione (GSNO) and sodium nitroprusside (SNP). In axes isolated from seeds incubated in vivo in the presence of 1 mM SNP for 24 h, the content of NO was increased by 2-fold, and the EPR spectrum from mononitrosyl-Fe complexes (MNIC) was observed with a concomitant increase in the fresh weight of sorghum axes. The simultaneous exposure to deferoxamine and the NO donor precluded the increase in fresh weight observed in the presence of excess NO. While total Fe content in the axes isolated from seeds exposed to 1mM SNP was not significantly affected as compared to control axes, the LIP was increased by over 2-fold.The data reported suggest a critical role for the generation of complexes between Fe and NO when cells faced a situation leading to a significant increase in NO content. Moreover, demonstrate the presence of MNICs as one of the important components of the LIP, which could actively participate in Fe cellular mobilization.

Oxidative stress, nitric oxide and prostaglandin E2 levels in the gastrointestinal tract of aging rats

Objectives

To evaluate the presence of oxidative stress and alterations in the levels of two cytoprotective agents, prostaglandin E2 and nitric oxide, in the gastrointestinal tract of aging rats.

Methods

The production of superoxide anion, lipid peroxides, levels of superoxide dismutase and catalase, and production of prostaglandin E2 and nitric oxide in the stomach and duodenum of rats were determined at 1.5, 3, 12, 18 and 24 months of age.

Key findings

Oxidative stress was present in the stomach of the old rats (24 months), whereas prostaglandin E2 and nitric oxide production remained stable at 18 and 24 months. In the duodenum, no oxidative stress was observed at 24 months, but at 18 months, an increase in superoxide anion levels was detected. Prostaglandin E2 remained constant in the aged rats but nitric oxide decreased significantly at 24 months.

Conclusions

The absence of macroscopic gastric injury throughout the gastrointestinal tract indicates that the oxidative stress in the stomach and the significant decrease of nitric oxide in the duodenum in the old rats are not sufficient to disrupt the mucosal defence network. The results support the notion that the disruption of the mucosal network is essentially regulated by the cytoprotective agents prostaglandin E2 and nitric oxide, and that injury appears only when both substances are concurrently reduced.

Analytical chemistry of nitric oxide

Nitric oxide (NO) is the focus of intense research primarily because of its wide-ranging biological and physiological actions. To understand its origin, activity, and regulation, accurate and precise measurement techniques are needed. Unfortunately, analytical assays for monitoring NO are challenged by NO's unique chemical and physical properties, including its reactivity, rapid diffusion, and short half-life. Moreover, NO concentrations may span the picomolar-to-micromolar range in physiological milieus, requiring techniques with wide dynamic response ranges. Despite such challenges, many analytical techniques have emerged for the detection of NO. Herein, we review the most common spectroscopic and electrochemical methods, with a focus on the underlying mechanism of each technique and on approaches that have been coupled with modern analytical measurement tools to create novel NO sensors.

Certain progestins prevent the enhancing effect of 17beta-estradiol on NO-mediated inhibition of platelet aggregation by endothelial cells

OBJECTIVE

Estro-progestin treatments have been associated with an increased risk of thromboembolic events in postmenopausal women. This study examined whether progestins affect the stimulatory effect of estrogens on the endothelial formation of nitric oxide (NO), a potent antithrombotic factor.

METHODS AND RESULTS

Experiments were performed with human endothelial cells. Endothelial NO synthase (eNOS) and GTP cyclohydrolase I (GTPCH I) mRNA expression was assessed by RT-PCR, eNOS protein by Western blotting, NO formation by electron spin resonance spectroscopy, and platelet aggregation by an aggregometer. Medroxyprogesterone acetate (MPA), progesterone, levonorgestrel, and nomegestrol acetate prevented the 17beta-estradiol (17beta-E)-induced expression of eNOS mRNA and protein. MPA and progesterone reduced the 17beta-E-induced formation of NO and potentiation of the inhibitory effect of endothelial cells on platelet aggregation whereas levonorgestrel and nomegestrol acetate were without effect. Moreover, MPA and progesterone prevented the 17beta-E-induced expression of GTPCH I mRNA. Mifepristone, a glucocorticoid and progesterone receptor antagonist, and L-sepiapterin prevented the inhibitory effect of MPA and progesterone on platelet aggregation.

CONCLUSIONS

Certain progestins, including MPA, attenuate the 17beta-E-induced NO-mediated inhibition of platelet aggregation by endothelial cells through preventing both eNOS and GTPCH I expression most likely via activation of glucocorticoid receptors.

Long-chainn-3 polyunsaturated fatty acid from fish oil modulates aortic nitric oxide and tocopherol status in the rat

In spite of their high oxidisability, long-chainn-3 PUFA protect against CVD. Dietary fatty acids modulate the fatty acid composition of lipoproteins involved in atherosclerosis. We thought that if long-chainn-3 PUFA were able to increase NO production by the aorta, then by its antioxidant activity the NO will prevent lipid peroxidation. However, the beneficial effect of NOin vivoon VLDL+LDL oxidation would only be possible if NO could diffuse to their lipidic core. Rats were fed maize oil- or fish oil as menhaden oil- (MO) rich diets for 8 weeks, to study the effects of MO on aortic NO production, NO diffusion into VLDL+LDL, the extent of oxidation in native VLDL+LDL and their oxidisabilityex vivo. Aortic NO production and its α-tocopherol content were increased andn-3 PUFA were incorporated into the VLDL+LDL. In spite of the higher peroxidisability and the low α-tocopherol in native VLDL+LDL from rats fed MO, native VLDL+LDL from the two groups shared similar electrophoretic patterns, conjugated dienes, thiobarbituric acid-reactive substances, total antioxidant capacity, and NO diffusibility on VLDL+LDL, indicative of anin vivoprotection against oxidation. However, these results do not correlate with theex vivooxidisability of VLDL+LDL, as NO is lacking. Thus, thein vivobeneficial effects can be explained by increased α-tocopherol in aorta and by a compensatory effect of NO on VLDL+LDL against the low α-tocopherol levels, which may contribute to the anti-atherogenic properties of fish oil.

Reduction enhances yields of nitric oxide trapping by iron–diethyldithiocarbamate complex in biological systems

The mechanism of NO trapping by iron-diethylthiocarbamate complexes was investigated in cultured cells and animal and plant tissues. Contrary to common belief, the NO radicals are trapped by iron-diethylthiocarbamates not only in ferrous but in ferric state also in the biosystems. When DETC was excess over endogenous iron ligands like citrate, ferric DETC complexes were directly observed with EPR spectroscopy at g=4.3. This was the case when isolated spinach leaves, endothelial cultured cells were incubated in the medium with 2.5mM DETC or mouse liver was perfused with 100mM DETC solution. After trapping NO, the nitrosylated Fe-DETC adducts are mostly in diamagnetic ferric state, with only a minor fraction having been reduced to paramagnetic ferrous state by endogenous biological reductants. In actual in vivo trapping experiments with mice, the condition of excess DETC was not met. The substantial quantities of iron in animal tissues were bound to ligands other than DETC, in particular citrate. These non-DETC complexes appear as roughly equal mixtures of ferric and ferrous iron. The presence of NO favors the replacement of non-DETC ligands by DETC. In all biological systems considered here, the nitrosylated Fe-DETC adducts appear as mixture of diamagnetic and paramagnetic states. The diamagnetic ferric nitrosyl complexes may be reduced ex vivo to paramagnetic form by exogenous reductants like dithionite. The trapping yields are significantly enhanced upon exogenous reduction, as proven by NO trapping experiments in plants, cell cultures and mice.

Complex inhibition of tyrosinase by thiol-composed Cu2+ chelators: a clue for designing whitening agents

The inhibition of tyrosinase has attracted considerable attention for potential medicinal and cosmetic applications, as well as in agriculture. This study investigated the inhibition effects of thiol-associated Cu(2+) chelators and deduced a strategy for designing and/or selecting tyrosinase inhibitors. Among the several compounds tested, dithioglycerine (DTGC) was selected for further experiments on the inhibition kinetics on tyrosinase. Different types of tyrosinases derived from mushroom and from the transient overexpression in HEK293 cells were tested individually. The results showed that DTGC significantly inhibited human tyrosinase in a complex manner (slope-parabolic mixed-type inhibition), which was comparable to mushroom tyrosinase. The affinity of DTGC affinity to human tyrosinase was evaluated by setting up a K(i slope) equation. The results suggest that a Cu(2+) chelator modified with thiol groups has potential as a whitening agent. In addition, a strategy for designing and/or selecting tyrosinase inhibitors that target the active enzyme site was also suggested.

Why iron–dithiocarbamates ensure detection of nitric oxide in cells and tissues

The in vivo mechanism of NO trapping by iron-dithiocarbamate complexes is considered. Contrary to common belief, we find that in biological systems the NO radicals are predominantly trapped by ferric iron-dithiocarbamates. Therefore, the trapping leads to ferric mononitrosyl complexes which are diamagnetic and cannot be directly detected with Electron Paramagnetic Resonance spectroscopy. The ferric mononitrosyl complexes are far easily reduced to ferrous state with L-cysteine, glutathione, ascorbate or dithiocarbamate ligands than their non-nitrosyl counterpart. When trapping NO in oxygenated biological systems, the majority of trapped nitric oxide is found in diamagnetic ferric mononitrosyl iron complexes. Only a minority fraction of NO is trapped in the form of paramagnetic ferrous mononitrosyl iron complexes with dithiocarbamate ligands. Subsequent ex vivo reduction of biological samples sharply increases the total yield of the paramagnetic mononitrosyl iron complexes. Reduction also eliminates the overlapping EPR spectrum from Cu(2+)-dithiocarbamate complexes. This facilitates the quantification of yields from NO trapping.

Progestins overcome inhibition of platelet aggregation by endothelial cells by down‐regulating endothelial NO synthase via glucocorticoid receptors

Hormone replacement therapy with estroprogestin preparations is associated with an increased risk of venous and arterial thromboembolic events in postmenopausal women. This study examined whether progestins affect the formation of NO in endothelial cells, and, if so, to determine the underlying mechanism. Experiments were performed with human umbilical vein endothelial cells. Endothelial nitric oxide synthase (eNOS) expression was assessed by real-time polymerase chain reaction (PCR) and Western blot analysis, NO formation by electron spin resonance spectroscopy, nuclear translocation of the glucocorticoid receptor by immunofluorescence microscopy, and platelet aggregation by an aggregometer. Medroxyprogesterone acetate (MPA) and progesterone markedly decreased the eNOS mRNA and protein levels, whereas levonorgestrel and nomegestrol acetate had only small effects. This effect was associated with a decreased NO formation leading to a reduced ability of endothelial cells to prevent platelet aggregation and was prevented by knockdown of the glucocorticoid receptor using siRNA. MPA and progesterone, but not levonorgestrel and nomegestrol acetate, caused nuclear translocation of the glucocorticoid receptor. The present findings indicate that certain progestins, including MPA, reduce the antiaggregatory effect of endothelial cells by decreasing the expression of eNOS and the formation of NO in endothelial cells, an effect that is mediated via activation of glucocorticoid receptors.

NO trapping in biological systems with a functionalized zeolite network

Zeolite-Y powder has been functionalized with ferric iron-diethyldithiocarbamate complexes and applied to trap nitric oxide radicals in liquids and biological systems. The complexes have been assembled in situ in the pores of zeolite-Y and act as traps for nitric oxide radicals. The resulting mononitrosyl-iron complexes form a mixture of diamagnetic ferric and paramagnetic ferrous complexes. The yield of trapped NO may be determined ex situ using electron paramagnetic resonance. The material may be anchored on solid surfaces, mixed into a composite or compressed into small pellets. The material was used to detect endogenous NO in endothelial cell cultures and spinach leaves. The sensitivity of the functionalized zeolite is significantly better than that achieved in conventional trapping of NO with iron-diethyldithiocarbamate complexes.

Endothelium-dependent vasodilator effect of Euterpe oleracea Mart. (Açaí) extracts in mesenteric vascular bed of the rat

Açai (Euterpe oleracea Mart.) a fruit from the Amazon region, largely consumed in Brazil is rich in polyphenols. Experiments were undertaken to determine whether hydro-alcoholic extract obtained from stone of açaí induces a vasodilator effect in the rat mesenteric vascular bed precontracted with norepinephrine (NE) and, if so, to elucidate the underlying mechanism. Açai stone extract (ASE, 0.3-100 microg) induced a long-lasting endothelium-dependent vasodilation that was significantly reduced by N(G)-nitro-l-arginine methyl ester (l-NAME) and (1)H-[1,2,3] oxadiazolo [4,4-a] quinoxalin-l-one (ODQ) and abolished by KCl (45 mM) plus l-NAME. In vessels precontrated with NE and KCl (45 mM) or treated with K(Ca)(+2) channel blockers (charybdotoxin plus apamin), the effect of ASE was significantly reduced. However this effect is not affect by indomethacin, glybenclamide and 4-aminopiridine. Atropine, pyrilamine, yohimbine and HOE 140 significantly reduced the vasodilator effect of acetylcholine, histamine, clonidine and bradykinin, respectively, but did not change the vasodilator effect of ASE. In cultured endothelial cells ASE (100 microg/mL) induced the formation of NO that was reduced by N(G)-nitro-l-arginine (l-NA, 100 microM). The present study demonstrates that the vasodilator effect of ASE is dependent on activation of NO-cGMP pathway and may also involve endothelium-derived hyperpolarizing factor (EDHF) release. The vasodilator effect suggest a possibility to use ASE as a medicinal plant, in the treatment of cardiovascular diseases.

Endothelial beta3-adrenoreceptors mediate nitric oxide-dependent vasorelaxation of coronary microvessels in response to the third-generation beta-blocker nebivolol

BACKGROUND

The therapeutic effects of nonspecific beta-blockers are limited by vasoconstriction, thus justifying the interest in molecules with ancillary vasodilating properties. Nebivolol is a selective beta1-adrenoreceptor antagonist that releases nitric oxide (NO) through incompletely characterized mechanisms. We identified endothelial beta3-adrenoreceptors in human coronary microarteries that mediate endothelium- and NO-dependent relaxation and hypothesized that nebivolol activates these beta3-adrenoreceptors.

METHODS AND RESULTS

Nebivolol dose-dependently relaxed rodent coronary resistance microarteries studied by videomicroscopy (10 micromol/L, -86+/-6% of prostaglandin F2alpha contraction); this was sensitive to NO synthase (NOS) inhibition, unaffected by the beta(1-2)-blocker nadolol, and prevented by the beta(1-2-3)-blocker bupranolol (P<0.05; n=3 to 8). Importantly, nebivolol failed to relax microarteries from beta3-adrenoreceptor-deficient mice. Nebivolol (10 micromol/L) also relaxed human coronary microvessels (-71+/-5% of KCl contraction); this was dependent on a functional endothelium and NO synthase but insensitive to beta(1-2)-blockade (all P<0.05). In a mouse aortic ring assay of neoangiogenesis, nebivolol induced neocapillary tube formation in rings from wild-type but not beta3-adrenoreceptor- or endothelial NOS-deficient mice. In cultured endothelial cells, 10 micromol/L nebivolol increased NO release by 200% as measured by electron paramagnetic spin trapping, which was also reversed by NOS inhibition. In parallel, endothelial NOS was dephosphorylated on threonine(495), and fura-2 calcium fluorescence increased by 91.8+/-23.7%; this effect was unaffected by beta(1-2)-blockade but abrogated by beta(1-2-3)-blockade (all P<0.05).

CONCLUSIONS

Nebivolol dilates human and rodent coronary resistance microarteries through an agonist effect on endothelial beta3-adrenoreceptors to release NO and promote neoangiogenesis. These properties may prove particularly beneficial for the treatment of ischemic and cardiac failure diseases through preservation of coronary reserve.

Red wine polyphenol-induced, endothelium-dependent NO-mediated relaxation is due to the redox-sensitive PI3-kinase/Akt-dependent phosphorylation of endothelial NO-synthase in the isolated porcine coronary artery

An enhanced endothelial formation of nitric oxide (NO) by red wine polyphenolic compounds (RWPs) has been involved in the protective effect of chronic intake of red wine on coronary diseases. However, the mechanism underlying the activation of endothelial NO synthase (eNOS) remains unclear. In the presence of indomethacin and charybdotoxin plus apamin to prevent the formation of prostanoids and endothelium-derived hyperpolarizing factor, respectively, RWPs caused pronounced endothelium-dependent relaxations in porcine coronary arteries. Relaxations to RWPs were abolished by N(omega)-nitro-L-arginine (L-NA, a competitive inhibitor of NO synthase) and the membrane permeant analog of superoxide dismutase (SOD), MnTMPyP, and reduced by polyethylene glycol-SOD (PEG-SOD), PEG-catalase and inhibitors of PI3-kinase (wortmannin and LY294002). RWPs caused the L-NA-sensitive formation of NO, as assessed by electron spin resonance spectroscopy and the formation of cyclic guanosine monophosphate in coronary artery endothelial cells; these responses were reduced by MnTMPyP, PEG-catalase, and inhibitors of PI3-kinase. RWPs caused the sustained phosphorylation of Akt and eNOS at Ser1177 in endothelial cells, which were abolished by MnTMPyP and inhibitors of PI3-kinase. These data demonstrate that RWPs induce the redox-sensitive activation of the PI3-kinase/Akt pathway in endothelial cells which, in turn, causes phosphorylation of eNOS, resulting in an increased formation of NO.

Vasomotor responses in MnSOD-deficient mice

MnSOD is the only mammalian isoform of SOD that is necessary for life. MnSOD(-/-) mice die soon after birth, and MnSOD(+/-) mice are more susceptible to oxidative stress than wild-type (WT) mice. In this study, we examined vasomotor function responses in aortas of MnSOD(+/-) mice under normal conditions and during oxidative stress. Under normal conditions, contractions to serotonin (5-HT) and prostaglandin F2alpha (PGF2alpha), relaxation to ACh, and superoxide levels were similar in aortas of WT and MnSOD(+/-) mice. The mitochondrial inhibitor antimycin A reduced contraction to PGF2alpha and impaired relaxation to ACh to a similar extent in aortas of WT and MnSOD(+/-) mice. The Cu/ZnSOD and extracellular SOD inhibitor diethyldithiocarbamate (DDC) paradoxically enhanced contraction to 5-HT and superoxide more in aortas of WT mice than in MnSOD(+/-) mice. DDC impaired relaxation to ACh and reduced total SOD activity similarly in aortas of both genotypes. Tiron, a scavenger of superoxide, normalized contraction to 5-HT, relaxation to ACh, and superoxide levels in DDC-treated aortas of WT and MnSOD(+/-) mice. Hypoxia, which reportedly increases superoxide, reduced contractions to 5-HT and PGF2alpha similarly in aortas of WT and MnSOD(+/-) mice. The vasomotor response to acute hypoxia was similar in both genotypes. In summary, under normal conditions and during acute oxidative stress, vasomotor function is similar in WT and MnSOD(+/-) mice. We speculate that decreased mitochondrial superoxide production may preserve nitric oxide bioavailability during oxidative stress.

Detection of reactive oxygen and nitrogen species by EPR spin trapping

Electron paramagnetic resonance spin trapping has become an indispensable tool for the specific detection of reactive oxygen free radicals in biological systems. In this review we describe some of the advantages as well as some experimental considerations of this technique and how it can be applied to biological systems to measure oxidative stress.

EPR quantification of vascular nitric oxide production in genetically modified mouse models

With increasing use of genetically modified mice to study endothelial nitric oxide (NO) biology, methods for reliable quantification of vascular NO production by mouse tissues are crucial. We describe a technique based on electron paramagnetic resonance (EPR) spectroscopy, using colloid iron (II) diethyldithiocarbamate [Fe(DETC)2], to trap NO. A signal was seen from C57BL/6 mice aortas incubated with Fe(DETC)2, that increased 4.7-fold on stimulation with calcium ionophore A23187 [3.45+/-0.13 vs 0.73+/-0.13au (arbitrary units)]. The signal increased linearly with incubation time (r(2) = 0.93), but was abolished by addition of N(G)-nitro-l-arginine methyl ester (L-NAME) or endothelial removal. Stimulated aortas from eNOS knockout mice had virtually undetectable signals (0.14+/-0.06 vs 3.17+/-0.21 au in littermate controls). However, the signal was doubled from mice with transgenic eNOS overexpression (7.17+/-0.76 vs 3.37+/-0.43 au in littermate controls). We conclude that EPR is a useful tool for direct NO quantification in mouse vessels.

Upregulation of endothelial nitric oxide synthase in rat aorta after ingestion of fish oil-rich diet

A previous study with aortic segments isolated from rats fed a fish oil-rich diet indicated an increase in acetylcholine-induced nitric oxide (.NO)-mediated relaxation. However, it remained to be elucidated whether a fish oil-rich diet affects the vascular activity per se and the point of the.NO-cGMP pathway at which fish oil acts. For this purpose, two groups of Sprague-Dawley rats were fed a semipurified diet containing 5% lipids, either corn oil (CO) or menhaden oil (MO), for 8 wk. We studied the mRNA and protein levels of endothelial NO synthase (eNOS) and NOS activity. The bioavailability of vascular.NO was assessed directly by electron spin resonance spectroscopy. The levels of cGMP, l-arginine, and l-citrulline were also evaluated in homogenates. Superoxide anion (O(2)(-).) production and related antioxidant activities were also studied in aortic segments. The aortic content of eNOS mRNA was increased in rats fed the MO-rich diet. This resulted in increases in both eNOS protein levels (70% relative to the rats fed the CO-rich diet) and NOS activity (102%);.NO production increased by 90%, cGMP levels increased by 100%, and l-arginine decreased by 30%. No change in aortic O(2)(-). production was caused by dietary MO. The upregulation of the eNOS-cGMP pathway induced by dietary MO may contribute to the maintenance of vascular homeostasis and explain its beneficial effect in the prevention of arterial diseases.

The mechanisms of S-nitrosothiol decomposition catalyzed by iron

The mechanisms of S-nitrosothiol transformation into paramagnetic dinitrosyl iron complexes (DNICs) with thiol- or non-thiol ligands or mononitrosyl iron complex (MNICs) with N-methyl-D-glucamine dithiocarbamate catalyzed by iron(II) ions under anaerobic conditions were studied by monitoring EPR or optical features of the complexes and S-nitrosothiols. The kinetic investigations demonstrated the appearance of short-living paramagnetic mononitrosyl-iron complex with L-cysteine prior to the formation of stable dinitrosyl-iron complex with cysteine in the solution of iron(II)-citrate complex (50-100 microM), S-nitrosocysteine (400 microM), and L-cysteine (20 mM) in 100 mM Hepes buffer (pH 7.4). The addition of deoxyhemoglobin (100 microM) did not influence the process, which points to a direct interaction between S-nitrosocysteine and iron(II) ions to yield DNIC. The reaction of DNIC-cysteine formation is first- and second-order in iron and S-nitrosocysteine, respectively. The third-order rate constant is (1.0 +/- 0.2) x 10(5) M(-2) s(-1) (estimated from EPR results) or (2.0 +/- 0.1) x 10(4) M(-2) s(-1) (estimated by optical method). A similar process of DNIC-cysteine formation was observed in a solution of iron(II)-citrate complex, L-cysteine, and NO-proline (200 microM) as a NO* donor. The appearance of a less stable dinitrosyl-iron complex with phosphate was detected when solutions of iron(II)-citrate containing 100 mM phosphate buffer (pH 7.4) were mixed with S-nitrosocysteine or NO-proline. The rapid formation of DNIC with phosphate was followed by its decay. When the concentration of L-cysteine in solutions was reduced from 20 to 1 mM, the life-time of the DNIC-cysteine diminished notably; this was caused by consumption of L-cysteine in the process of DNIC-cysteine formation from S-nitrosocysteine and iron. Thus, L-cysteine is consumed. Formation of DNIC with glutathione was also observed in a solution of glutathione (20 mM), S-nitrosoglutathione (400 microM), and iron(II) complex (800 microM) in 100 mM Hepes buffer (pH 7.4), but the rate of formation was about 10 times slower than the formation of the DNIC-cysteine. The rate of MNIC-MGD formation from iron(II)-MGD complexes and S-nitrosocysteine was first-order in both reactants. The second-order rate constant for this reaction, estimated from EPR measurements, was 30 +/- 5 M(-1) s(-1). Rate constants of MNIC-MGD formation from iron(II)-MGD and the more stable S-nitrosoglutathione and S-nitroso-D,L-penicillamine were equal to 3.0 +/- 0.3 and 0.3 +/- 0.05 M(-1) s(-1), respectively. Thus, the concerted mechanism of DNIC and MNIC formation from S-nitrosothiols and iron(II) ions can be suggested to be predominant.

Diethyldithiocarbamate inhibition of galactosamine-induced hepatitis in rats

Free-radical-mediated oxidant damage can contribute to acute hepatitis. Vitamin E, a classic antioxidant, has been tested as a therapy for rodent acute hepatitis, but the protection achieved has not been complete. This study demonstrated that in rats, sodium diethyldithiocarbamate (DDC), a potent antioxidant, strongly depressed galactosamine-induced hepatitis in terms of serum alanine amino transferase activities and bile acids, though not in terms of serum beta-glucuronidase activities. A potential limitation for DDC use in humans, inhibition of copper metalloenzyme activities, did occur at the DDC dose used here. However, these effects were not severe. Thus, DDC could make a useful short term therapeutic drug for acute hepatitis.

Determination of the enhancing action of HSP90 on neuronal nitric oxide synthase by EPR spectroscopy

Recent studies showed that heat shock protein 90 (HSP90) enhances nitric oxide (NO) synthesis from endothelial and neuronal NO synthase (eNOS and nNOS, respectively). However, these findings were based on indirect NO measurements. Moreover, although our previous studies showed that the action of HSP90 involves increased Ca(2+)/calmodulin (Ca(2+)/CaM) binding, quantitative measurements of the effect of HSP90 on CaM binding to nNOS have been lacking. With electron paramagnetic resonance spectroscopy, we directly measured NO signals from purified nNOS. HSP90 augmented NO formation from nNOS in a dose-dependent manner. Tryptophan fluorescence-quenching measurements revealed that HSP90 markedly reduced the K(d) of CaM to nNOS (0.5 +/- 0.1 nM vs. 9.4 +/- 1.8 nM in the presence and absence of HSP90, P < 0.01). Ca(2+) ionophore triggered strong NO production from nNOS-transfected cells, and this was significantly reduced by the HSP90 inhibitor geldanamycin. Thus these studies provide direct evidence demonstrating that HSP90 enhances nNOS catalytic function in vitro and in intact cells. The effect of HSP90 is mediated by the enhancement of CaM binding to nNOS.

Redox properties of iron-dithiocarbamates and their nitrosyl derivatives: implications for their use as traps of nitric oxide in biological systems

While the Fe(2+)-dithiocarbamate complexes have been commonly used as NO traps to estimate NO production in biological systems, these complexes can undergo complex redox chemistry. Characterization of this redox chemistry is of critical importance for the use of this method as a quantitative assay of NO generation. We observe that the commonly used Fe(2+) complexes of N-methyl-D-glucamine dithiocarbamate (MGD) or diethyldithiocarbamate (DETC) are rapidly oxidized under aerobic conditions to form Fe(3+) complexes. Following exposure to NO, diamagnetic NO-Fe(3+) complexes are formed as demonstrated by the optical, electron paramagnetic resonance and gamma-resonance spectroscopy, chemiluminescence and electrochemical methods. Under anaerobic conditions the aqueous NO-Fe(3+)-MGD and lipid soluble NO-Fe(2+)-DETC complexes gradually self transform by reductive nitrosylation into paramagnetic NO-Fe(2+)-MGD complexes with yield of up to 50% and the balance is converted to Fe(3+)-MGD and nitrite. In dimethylsulfoxide this process is greatly accelerated. More efficient transformation of NO-Fe(3+)-MGD into NO-Fe(2+)-MGD (60-90% levels) was observed after addition of reducing equivalents such as ascorbate, hydroquinone or cysteine or with addition of excess Fe(2+)-MGD. With isotope labeling of the NO-Fe(3+)-MGD with (57)Fe, it was shown that these complexes donate NO to Fe(2+)-MGD. NO-Fe(3+)-MGD complexes were also formed by reversible oxidation of NO-Fe(2+)-MGD in air. The stability of NO-Fe(3+)-MGD and NO-Fe(2+)-MGD complexes increased with increasing the ratio of MGD to Fe. Thus, the iron-dithiocarbamate complexes and their NO derivatives exhibit complex redox chemistry that should be considered in their application for detection of NO in biological systems.