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Nitrosyl iron complexes (NICs) are natural depots of NO. NICs are formed by the interaction of endogenous nitric oxide (NO) and non‒heme [2Fe–2S] proteins. Their synthetic analogues are promising compounds in medicines for the treatment of socially significant diseases. In this paper, the effect of bovine serum albumin (BSA) and reduced glutathione (GSH) on the decomposition of a nitrosyl iron complex with N,N'-dimethylthiourea ligands [Fe(SC(NHCH3)2)2(NO)2]BF4 (complex 1) under aerobic conditions are studied. In the absorption spectra complex 1 in the presence of albumin a wide band appears at 370–410 nm, which indicates the coordination of the aerobic decay product of the complex in the hydrophobic pocket of the protein with Cys34 and His39. The quenching of albumin's intrinsic fluorescence during titration with complex 1 is studied by fluorescence spectroscopy. The Stern–Volmer constant K = (2.3 ± 0.2) × 105 М–1 and the Förster radius 22.4 Å are calculated. The UV-spectrum of complex 1 in the presence of GSH has two peaks at 312 and 363 nm, characteristic of glutathione binuclear NICs. [ABSTRACT FROM AUTHOR]

Two new 4-methylcoumarin derivatives (3a–f and 4a–f) were designed, synthesized, and evaluated for their cytotoxic activity. Different spectroscopic methods and elemental analyses confirmed all the synthesized derivatives' characterization. All the prepared compounds were biologically screened against four cancer cell lines (hepatocellular carcinoma HepG-2, colon cancer cell lines HCT-116, breast cancer cell lines MCF-7, and prostate cancer cell lines PC3). The in vitro antiproliferative activity of the target analogues 4b, 4c, 4f, 3b, and 3d against the MCF-7 cancer cell line was significant, with IC50 values of 3.98, 7.80, 10.94, 17.7, and 24.07 μM, respectively. Furthermore, the potent cytotoxic oxime derivative 4b was evaluated for cell cycle analysis showing a significant substantial disruption in cell cycle profile and cell cycle arrest at the S phase boundary with a time-dependent rise in a pre-G cell population, as well as a 22-fold increase in MCF-7 apoptosis compared to control cells. Accordingly, the Bax/Bcl-2 ratio, a critical ratio in controlling cell sensitivity to apoptosis, increased upon treatment with the oxime analog 4b. A docking investigation was conducted within the BcL-2 binding site to explore and anticipate the binding modes of the synthesized compounds. Thus, synthesizing these novel coumarin/nitric oxide hybrids may aid in developing promising antiproliferative agents. [ABSTRACT FROM AUTHOR]

Fluorescent probes: 8-anilino-1-naphthalenesulfonate (ANS), eosin Y, and pyrene were used to study the interaction between liposomes and three nitrosyl iron complexes that are promising anti-inflammatory agents and cardioprotectors. It was shown that the studied complexes compete with ANS molecules for the bonding sites in a bilayer of liposomes. The incorporation of the complexes into the lipid bilayer was also studied according to the quenching of eosin Y and pyrene fluorescence. The data suggest that iron nitrosyl complexes interact with the phospholipids headgroups and can penetrate deeper into the hydrophobic center of a lipid bilayer, where they affect the packing of fatty acid chains. The pronounced membranotropic properties of the complexes correlated with their ability to inhibit lipid peroxidation. Complexes with high constants of pyrene bonding are the most effective antioxidants. [ABSTRACT FROM AUTHOR]

Renovascular hypertension is one of the most relevant causes of secondary hypertension, mostly caused by atherosclerotic renovascular stenosis or fibromuscular dysplasia. The increase in angiotensin II production, oxidative stress, and formation of peroxynitrite promotes the decrease in nitric oxide (NO) availability and the development of hypertension, renal and endothelial dysfunction, and cardiac and vascular remodeling. The NO produced by nitric oxide synthases (NOS) acts as a vasodilator; however, endothelial NOS uncoupling (eNOS) also contributes to NO reduced availability in renovascular hypertension. NO donors and NO-derived metabolites have been investigated in experimental renovascular hypertension and have shown promissory effects in attenuating blood pressure and organ damage in this condition. Therefore, understanding the role of decreased NO in the pathophysiology of renovascular hypertension promotes the study and development of NO donors and molecules that can be converted into NO (such as nitrate and nitrite), contributing for the treatment of this condition in the future. [ABSTRACT FROM AUTHOR]

Novel both symmetric and asymmetric polyoxymethylene derivatives of bis(oxytriazene N-oxides) were synthesized by the nucleophilic substitution of bis(chloromethyl) ether with salts of oxytriazene N-oxides, their pharmacological properties were preliminary evaluated. [ABSTRACT FROM AUTHOR]

The reaction of the tetranitrosyl iron complex containing the thiosulfate ligand (TNIC) (NO donor) with phosphoenolpyruvic acid (PEP), which is one of the main biological macroergic compounds, was studied by mass spectrometry. The use of mass spectrometry made it possible to perform studies in an aqueous medium, separate the substances, and quantitatively correlate the peak intensities with the concentrations of the substances. The products of the reaction of PEP with TNIC were identified by IR spectroscopy and mass spectrometry. The reaction product was found to have a Fe–O–C bond. Among the reaction products, the ions with m/z = 318 and 256 belong to the compounds [O3S2–Fe–PEP]–2, and [S-Fe–PEP]–2, respectively. [ABSTRACT FROM AUTHOR]

A method for synthesizing new compounds capable of releasing NO within living organisms, namely, 2-azidoethyl derivatives of methylenebis(1-oxytriaz-1-ene 2-oxides) bearing one or few 2-azidoethyl moieties, was developed. The synthesis involves nucleophilic substitution of the bromine atoms of the parent 2-bromoethyl derivatives of methylenebis(1-oxytriaz-1-ene 2-oxides) with the azide group. Some of the synthesized compounds are of interest as promising energetic materials. [ABSTRACT FROM AUTHOR]

Synthesis of new potential NO donors in living organisms, 1,1’-[methylenebis(oxy)]bis(triaz- 1-ene 2-oxides) bearing from two to four 2-nitroxyethyl groups at the nitrogen atoms was accomplished. The developed synthetic approaches involves either nucleophilic substitution of the bromine atoms of the corresponding N-2-bromoethyl derivatives of 1,1’-[methylenebis(oxy)]-bis(triaz-1-ene 2-oxides) or nitration of its 2-hydroxyethyl analogs. Some of the synthesized compounds are of interest as promising energetic materials. [ABSTRACT FROM AUTHOR]

3,3-Bis(2-nitroxyethyl) derivatives of 1,1′-[methylenebis(oxy)]bis(triaz-1-ene 2-oxides) were synthesized by either nucleophilic substitution of the bromine atoms of parent 3,3-bis(2- bromoethyl) compounds or nitration of structurally related 3,3-bis(2-hydroxyethyl) derivatives. The synthesized compounds comprise two different NO donating moieties, namely, oxytriaz- 1-ene 2-oxide and nitrate groups, and, therefore, can be regarded as a new type of NO-donating agents. [ABSTRACT FROM AUTHOR]

The decomposition of two neutral binuclear nitrosyl iron complexes (NICs) of the µ-S structural type and general composition [Fe(SR)(NO)] was studied in comparison. The exchange reaction of the thiophenol or 2-aminothiophenol thiolate ligand by glutathione (GSH) in neutral NICs was studied. The reaction system was analyzed by spectrophotometry to prove the presence of a new NICs with the GS ligand in it. It was found that, unlike the earlier studied binuclear cationic NICs of the µ-S type and general composition [Fe(µ-SR)(NO)]SO• nHO with cysteamine and penicillamine ligands in which both thiolate ligands exchange by GS, in these neutral complexes both thiolate ligands are de-tached by only one GSH ligand is attached. A water molecule is inserted into the second free site. It is assumed that the antitumor activity of the neutral NICs can be determined not only by their NO-donor activity but also by their ability to exchange the thiolate ligand by GS, i.e., "to remove" GSH from the medium as in the case of cationic NICs. The discovered reaction can prevent, most likely, the S-glutathionylation of important metabolites in the presence of GSH and is very significant for metabolism of NICs. [ABSTRACT FROM AUTHOR]

Reaction between the nitric oxide donor, tetranitrosyl iron complex with thiosulfate ligand (TNIC), and phosphoenolpyruvic acid (PEP) was studied. Formation of products of the reaction between PEP and TNIC was confirmed by UV-, IR-spectroscopy, and mass spectrometry methods. Also, ions with mass numbers m/z 318 and m/z 256 were identi-fied among the reaction products, belonging to the compounds [OS-Fe-PEP] and [S-Fe-PEP], respectively. [ABSTRACT FROM AUTHOR]

Generation of nitrite (NO2¯) and non-thiolate nitroso compounds in human blood during leukocyte activation mainly occurred due to destruction of NO donors in the plasma, but not due to intensifi cation of NO synthesis. We proposed a mechanism of production of nitrite and non-thiolate nitroso compounds in the blood during infl ammation. [ABSTRACT FROM AUTHOR]

Chrysin is one of flavones constituents of Orocylumineicum vent. It has been a hot spot as a potential chemopreventive agent and as a natural molecule with numerous biological activities such as antioxidant, antitumor, antiviral, anti-hypertension, anti-diabetic, antibacterial, and so on in recent years. Because of its poor solubility, small intestinal absorption, and the rapid metabolism of glycosylation, a large number of efforts had been made by domestic and foreign researchers on designing its analogs and conjugates to obtain compounds with improved efficacy and selectivity for developing more active drugs for clinic. This article reviews the current research of studying on chrysin derivatives including their properties and possible applications. Additionally, this article also presents the basic information concerning chemical reactivity of chrysin, relevant to the synthesis of its derivatives. [ABSTRACT FROM AUTHOR]

Deoxyhemoglobin (Hb) stabilizes the cationic nitrosyl iron complex with cysteamine {Fe[S(CH)NH](NO)}SO·2.5HO (CysAm), by slowing down its hydrolysis. In the absence of Hb, the electrochemical detection of NO release in the course of the hydrolysis using a sensor electrode gave the rate constant of (5.2±0.2)·10 s. The release of NO is a reversible process, and the amount of released NO is 1.4% of the CysAm concentration. In the presence of Hb, NO is released much more slowly, and the reaction is more intense than that in the absence of Hb. The adsorption of CysAm by an Hb molecule results in NO release from the CysAm-Hb complex with a rate constant of 1·10 s. The analysis of the Hb surface revealed the possible location of the cation-binding sites, which reversibly bind the cationic CysAm complex. The kinetic parameters of NO release from CysAm in the absence and in the presence of Hb were studied by the kinetic modeling. [ABSTRACT FROM AUTHOR]

Studies with the use of a highly specific enzymatic sensor demonstrated that, contrary to the common opinion, normally nitrate is in fact not present in the most important physiological fluids. NO metabolites in the amniotic fluid and semen are mainly presented by NO donor compounds. Therefore, the intensity of NO synthesis can be evaluated by the total content of all its metabolites, but not by the widely used summary nitrite+nitrate content. [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) and CO-releasing molecules (CO-RMs) inhibit platelet aggregation in vitro. Herein, we compare the anti-platelet action of CORM-3, which releases CO rapidly ( t 1 min), and CORM-A1, which slowly releases CO (t = 21 min). The anti-platelet effects of NO donors with various kinetics of NO release were studied for comparison. The effects of CO-RMs and NO donors were analyzed in washed human platelets (WP), platelets rich plasma (PRP), or whole blood (WB) using aggregometry technique. CORM-3 and CORM-A1 inhibited platelet aggregation in human PRP, WP, or WB, in a concentration-dependent manner. In all three preparations, CORM-A1 was more potent than CORM-3. Inhibition of platelets aggregation by CORM-A1 was not significantly affected by a guanylate cyclase inhibitor (ODQ) and a phosphodiesterase-5 inhibitor, sildenafil. In contrast, inhibition of platelet aggregation by NO donors was more potent with a fast NO releaser (DEA-NO, t = 2 min) than slow NO releasers such as PAPA-NO ( t = 15 min) or other slow NO donors. Predictably, the anti-platelet effect of DEA-NO and other NO donors was reversed by ODQ while potentiated by sildenafil. In contrast to NO donors which inhibit platelets proportionally to the kinetics of NO released via activation of soluble guanylate cyclase (sGC), the slow CO-releaser CORM-A1 is a superior anti-platelet agent as compared to CORM-3 which releases CO instantly. The anti-platelet action of CO-RMs does not involve sGC activation. Importantly, CORM-A1 or its derivatives representing the class of slow CO releasers display promising pharmacological profile as anti-platelet agents. [ABSTRACT FROM AUTHOR]

Decomposition products of [FeS(CHCHNH)(NO)]SO·2.5HO ( 1′) were studied by electrochemistry and mass spectrometry. The structures of the dicationic tetranitrosyl iron complex with cysteamine of the composition [FeS(CHCHNH)(NO)] ( 1) and possible products of its decomposition and NO replacement by an aqua ligand were studied by quantum chemical methods at the density functional theory level. Taking into account the solvation effects, the replacement of the nitrosyl ligand in dication 1 by an aqua ligand was found to be less favorable in aqueous solution than in the gas phase. The p K value was calculated for the proton abstraction from the NH group of compound 1 (7.2), and the removal of NO from the deprotonated form of the complex was found to be much easier. This result is consistent with the experimental data on an increase in the rate of NO formation in aqueous solutions of 1 with increasing pH from 6 to 8 assuming that the increase in pH is accompanied by an increase in the percentage of the less stable deprotonated form of the complex and that OH does not participate in the elementary step of NO formation. The kinetic curves of NO formation are well described by a two-step scheme of consecutive first-order reactions of the NO formation and consumption. In the gas phase, dication 1 was found to be unstable to decomposition into two mononuclear cationic dinitrosyl iron complexes with cysteamine. This result is consistent with the fact that these cations are observed in the electrospray ionization mass spectrometric experiment. The major peak in the mass spectra is associated with the [FeS(CHCHNH)(NO) − H] ion. As follows from the calculations, this is due to the deprotonation of the dication as it gets rid of the hydration shell, because even the dimer of water molecules is more basic than dication 1. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) plays diverse roles in the growth and development of plants and in their responses to various abiotic and biotic stresses. It has also been reported to repress flowering in Arabidopsis thaliana. In the present study, NO donors sodium nitroprusside (SNP), S-nitroso- N-acetyl penicillamine (SNAP), and 3-morpholinosydnonimine (SIN-1) induced flowering in Lemna aequinoctialis 6746 (a short-day strain) and in L. aequinoctialis LP (a photoperiod-insensitive strain) under noninductive conditions. Nitrate and nitrite, two stable metabolites of NO, did not induce flowering. On the other hand, cyanide donors potassium ferricyanide {K[Fe(CN)]} and potassium cyanide (KCN) induced flowering in both strains under noninductive conditions. The flowering induced under a 8-h daily photoperiod regime in the short-day strain L. aequinoctialis 6746 was inhibited by NO and cyanide donors. Vegetative multiplication of both strains was adversely affected by NO and cyanide donors, irrespective of the photoperiod conditions. The observed effects of NO donors on flowering were substantially negated by NO scavengers c-PTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] and methylene blue. This confirmed the role of NO in induction of flowering. The inductive effect of CN also appeared to be partly mediated through NO as NO scavengers partially negated the effect of CN. [ABSTRACT FROM AUTHOR]

Paracoccidioidomycosis (PCM) is a granulomatous disease caused by a dimorphic fungus, Paracoccidioides brasiliensis (Pb). To determine the influence of nitric oxide (NO) on this disease, we tested cis-[Ru(bpy)2(NO)SO3](PF6), ruthenium nitrosyl, which releases NO when activated by biological reducing agents, in BALB/c mice infected intravenously with Pb 18 isolate. In a previous study by our group, the fungicidal activity of ruthenium nitrosyl was evaluated in a mouse model of acute PCM, by measuring the immune cellular response (DTH), histopathological characteristics of the granulomatous lesions (and numbers), cytokines, and NO production. We found that cis-[Ru(bpy)2(NO)SO3](PF6)-treated mice were more resistant to infection, since they exhibited higher survival when compared with the control group. Furthermore, we observed a decreased influx of inflammatory cells in the lung and liver tissue of treated mice, possibly because of a minor reduction in fungal cell numbers. Moreover, an increased production of IL-10 and a decrease in TNF-α levels were detected in lung tissues of infected mice treated with cis-[Ru(bpy)2(NO)SO3](PF6). Immunohistochemistry showed that there was no difference in the number of VEGF- expressing cells. The animals treated with cis-[Ru(bpy)2(NO)SO3](PF6) showed high NO levels at 40 days after infection. These results show that NO is effectively involved in the mechanism that regulates the immune response in lung of Pb-infected mice. These data suggest that NO is a resistance factor during paracoccidioidomycosis by controlling fungal proliferation, influencing cytokine production, and consequently moderating the development of a strong inflammatory response. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations of the structure and solvation energies of mono- and dianions of Roussin's red salt esters [Fe(μ-RS)(NO)] (R = Me, Et, Pr, Bu) in solutions in THF and acetonitrile were carried out. In monoanions, an additional electron is localized on one Fe(NO) fragment, which leads to significant structural distortion of the anion compared to neutral molecule. The second electron is localized on the other Fe(NO) fragment; this causes symmetrization of the dianion geometry. There are good linear correlations between the calculated and experimental redox potentials of these systems. A relationship was proposed for estimation of the redox potentials of related iron-nitrosyl complexes. The standard redox potentials of the complex with R = Ph in water, DMSO, and acetonitrile evaluated using this expression lie between −0.5 and −0.6 V. [ABSTRACT FROM AUTHOR]

The review summarizes the results of studies aimed at developing the fundamentals for the design of a new class of nitric oxide donors, viz., iron nitrosyl complexes with functionalized sulfur-containing ligands, which are structural analogs of the active sites of non-heme nitrosyl iron-sulfur proteins. The structures, reactivities, and pharmacological activity in vitro and in vivo of these complexes are considered. [ABSTRACT FROM AUTHOR]

The effects of nitric oxide (NO) on caulogenesis, shoot organogenesis and rhizogenesis from hypocotyl explants of Linum usitatissimum were investigated. Exogenously supplied NO donors, 5 μM sodium nitroprusside (SNP), 2 μM S-nitroso- N-acetylpenicillamine (SNAP) and 2 μM 3-morpholinosydnonimine (SIN-1), significantly promoted shoot differentiation from the hypocotyl explants of L. usitatissimum excised from its in vitro raised seedlings. Potassium ferrocyanide, a structural analogue of SNP, lacking NO group, did not promote shoot organogenesis. Likewise, products of NO, $$ {\text{NO}}_{2}^{ - } $$ and $$ {\text{NO}}_{3}^{ - } $$ supplied as 5 μM NaNO and 5 μM NaNO did not enhance shoot differentiation. Another source of NO, a mixture of sodium nitrite (SN) provided along with ascorbic acid (AsA), also caused significant promotion in the average number of shoots per responding explant. SNP also augmented the rhizogenic response of the microshoots in terms of percentage of responding explants, number of roots per responding explant and average root length. The NO scavengers, 2-(4-carboxy-phenyl)-4, 4, 5, 5-tetramethylimideazoline-1-oxyl-3-oxide (cPTIO) or methylene blue (MB), provided along with SNP, SNAP, SIN-1 or SN + AsA, at concentrations equimolar to the optimum concentration of the donors, reversed the promotory influence, thereby, confirming the role of NO in promotion of in vitro morphogenesis. However, NO scavengers individually did not affect the observed morphogenic processes. Morphological and histological studies of hypocotyl segments cultured on BM or BM + SNP for 4, 8 and 12 days demonstrated that SNP enhanced shoot differentiation by inducing a higher number of shoot primordia, each of which develops into a single shoot. [ABSTRACT FROM AUTHOR]

By an example of the iron cysteamine nitrosyl complex {Fe[S(CH)NH](NO)}SO··2.5HO (CAC), it was shown for the first time that the hydrolysis of this NO donor in the presence of ferrocytochrome c (cyt c) affords the iron nitrosyl complex NO-cyt c, which serves as the NO depot. The rate constant of NO release from CAC was determined from the kinetics of the formation of NO-cyt c. At pH 3.0 the rate constant is (2.7±0.1)·10 s. Ferrocytochrome c produces a less stabilizing effect on CAC than deoxyhemoglobin (Hb). Thus in the presence of cyt c, the reaction is completed in 1 h, whereas NO is released from a solution of CAC (2·10 mol L) in the presence of Hb during 40 h. The previously unknown stabilization of iron nitrosyl complexes by hemoglobin was found. [ABSTRACT FROM AUTHOR]

By an example of cysteamine iron nitrosyl complex {Fe[S(CH)NH](NO)}SO • 2.5HO (CAC) it was shown for the first time that the NO donor hydrolysis in the presence of ferricytochrome c (cyt c) affords the iron nitrosyl complex NO-cyt c. It was found that cyt c can serve as a depot for NO evolved during the hydrolysis of CAC. In the presence of CAC, the rate of NO-cyt c complex decomposition to NO and cyt c depends on the molar ratio [cyt c]: [CAC] and at [cyt c]: [CAC] = 0.3 it was found to be lower than that in decomposition of CAC in the absence of cyt c. As a result, the total NO evolving process becomes 5.6 times more prolonged. The number of NO groups evolved from CAC can be determined by the reaction of CAC with cyt c in the presence of ferricyanide: at most one NO group is evolved to a solution in the spontaneous hydrolysis of CAC (pH 7.0), and no less than three of them are evolved from oxidized CAC. [ABSTRACT FROM AUTHOR]

Dinuclear iron tetranitrosyl complex with the composition [Fe(SPh)(NO)] ( 1) was synthesized and its single crystals and polycrystals were studied by X-ray diffraction, IR spectroscopy, and elemental analysis. The decomposition products of complex 1 were investigated by electrochemical method and mass spectrometry. The mass spectrum of a solution of complex 1 shows two groups of ions: the primary decomposition products of 1 in solution (the complex ions [Fe(SPh)(NO)(NO)], [Fe(SPh)(NO)], and [Fe(SPh)(NO)]) and a series of the ions [FeO + n(NO)] and [FeO + n(NO)] ( n = 0-4), which are formed in secondary reactions. The structures of the complexes, which were formed through the Fe-NO bond dissociation and the replacement of the NO ligand by aqua and oxygen ligands in complex 1, and the structure of the complex [FeO] were studied by quantum chemical modeling. [ABSTRACT FROM AUTHOR]

The reactions of glycine hydroxamic and DL-alanine hydroxamic acids with triacetonamine are chemoselective and afford 1-hydroxy-7,7,9,9-tetramethyl-1,4,8-triazaspiro[4.5]decan-2-one ( 3) and (±)-1-hydroxy-3,7,7,9,9-pentamethyl-1,4,8-triazaspiro[4.5]decan-2-one ( 4), respectively. The X-ray diffraction study showed that compound 3 crystallizes as a solvate with MeCN (1: 1). As shown by ESR measurements, spiro hydroxamic acids 3 and 4 are NO donors in in vitro biological systems. The NO-donor activity of compounds 3 and 4 was found to be substantially higher in the presence of DMSO. Homologue 4 is a stronger NO donor than 3. Compound 4 also exhibits high antimetastatic activity (81%) on the B16-melanoma model. [ABSTRACT FROM AUTHOR]

New binuclear tetranitrosyl iron complex with pyrimidin-2-yl of the μ2-S type [Fe2(SC4H3N2)2(NO)4] ( 1) was synthesized by the exchange reaction of thiosulfate ligands in the [Fe(S2O3)2(NO)2]3s- anion for pyrimidin-2-yl ligands. The crystal structure of complex 1 was studied by single-crystal X-ray diffraction analysis. According to the X-ray diffraction data, pyrimidin-2-yl is coordinated to the iron atom in the thiol form. According to the quantum chemical calculations, the low stability of complex 1 is related to a possibility of formation of the coordination bond of the iron atom with the atom of the pyrimidine cycle of the ligand after NO group detachment. The ability of complex 1 to donate NO and the kinetics of its hydrolysis in aqueous solutions were studied by electrochemical analysis using sensor electrodes ami NO-700, by spectrophotometry in the pH interval from 6.0 to 7.76, and in the reaction with hemoglobin. Complex 1 is most stable in a neutral medium and more vigorously evolves NO in acidic and alkaline media. [ABSTRACT FROM AUTHOR]

Dimeric dinitrosyl iron complexes (DNIC) with cysteine or glutathione as NO donors accelerated the healing of experimental skin wound in rats, as demonstrated by histological and histochemical examination. After two injections of an aqueous DNIC solution into the wound (total 5 μmol) on days 1 and 2 after surgery, the granulocyte volume in wound tissue on day 4 was 3–4 times greater than in the control. Higher DNIC doses provoked inflammation in the wound. Similar experiments with another NO donor S-nitrosoglutathione in equivalent amounts (10 μmol) adversely affected the wound. Addition of 2.5 μmol glutathione DNIC for 40 min produced EPR-detectable protein-bound DNIC (2.5 nmol) in wound tissue. Under the same conditions, 5 μmol S-nitrosoglutathione produced less than 10 pmol of protein-bound DNIC; an EPR-active nitrosyl hemoglobin complex was mainly formed (1.5–2.0 nmol) in this case. The beneficial effect of DNIC on the wound was suggested to be due to the delivery of NO to its targets without pronounced formation of cytotoxic peroxynitrite in wound tissue. In contrast, peroxynitrite could form upon administration of rapidly decomposed S-nitrosoglutathione, thereby aggravating the wound condition. [ABSTRACT FROM AUTHOR]

Geometric and electronic structures of the iron thiolate tetranitrosyl complexes Fe2(µ-SC6− n H5− n Nn)2(NO)4, n = 0, 1, 2) were calculated using the B3LYP and PBE density functional methods. The geometric structures of the complexes found by the both theoretical approaches well agree with experiment, and a divergence of bond lengths is at most several hundredths of angstrom. According to the experimental data, the ground state of the system is diamagnetic, with the antiparallel orientation of the local spins 1/2 of the Fe(NO)2 fragments. The NO group bears a small negative charge mostly concentrated on the O atom, and the Fe-NO bond should be considered as homopolar. The formal electronic configuration of Fe is d7, which corresponds to the oxidation state 1+. However, in view of the presence of two homopolar bonds, the Fe atoms in the complexes should be trivalent. The both methods used well reproduce the experimental structure of the IR spectrum, but the PBE functional gives somewhat better description of the absolute position of the lines and the B3LYP functional better describes their relative intensities. The shifts of the vibrational bands of the thiolate ligand in the spectra of the complexes to both long-and short-wavelength regions are theoretically reproduced both qualitatively and semiquantitatively. Comparison of the calculated and measured splittings of the doublet of the stretching NO vibrations made it possible to attribute the appreciable disorder of splitting (15–55 cm−1) to the structural nonequivalence of the NO groups in the complexes. Due to peculiarities of NO binding, even a small difference in the N-O and Fe-N distances (∼0.01 Å) affects the frequency of the NO vibrations. [ABSTRACT FROM AUTHOR]

Background. After the discovery that nitric oxide (NO) plays a major role in the regulation of vascular tone, this substance moved into the focus of interest with regard to vasospasm after subarachnoid haemorrhage (SAH). A multitude of interactions were discovered and some concepts of therapeutic intervention were developed. Method. The present review is based on a Medline search with the terms “nitric oxide” and “subarachnoid haemorrhage”. Findings. SAH and particularly liberated oxyhaemoglobin sequestrate the physiologically produced NO. Reactivity to NO appears to be principally preserved. As other types of injury, SAH leads to induction of inducible NO synthase (iNOS). The NO produced by this pathway cannot compensate for the lack of the physiological NO and may even lead to tissue damage by oxidative stress. Experimental therapeutic attempts use stimulation of NO production and delivery of NO donors. NO donors were also used in some small clinical trials. A final assessment of efficacy and safety is not yet possible. Conclusion. NO physiology and pathophysiology are important in the genesis of vasospasm after subarachnoid haemorrhage. NO directed therapeutic strategies enlarge the spectrum of available instruments, but complete elimination of the problem of vasospasm cannot be expected. [ABSTRACT FROM AUTHOR]

We examined the contribution of K+ channels to the relaxation responses induced by different redox forms of nitric oxide (NO•, NO– and NO+) in comparison with those evoked by electrical field stimulation (EFS) of nitrergic nerves in the sheep urethra. K+ channel blockers with different selectivity profile were used. Sodium nitroprusside (SNP) and different S-nitrosothiols were used as NO+ donors, Angeli's salt as an NO– donor and nitroglycerin (GTN) was chosen as a representative compound known to require metabolic activation in the target tissue. Pure NO gas was used to prepare NO• solutions. Relaxation evoked by EFS of nitrergic nerves or by exogenous NO• was not inhibited by any of the K+ channel blockers, but was enhanced by 4-aminopyridine [inhibitor of voltage-dependent K+ (Kv) channels]. This suggests that, whereas K+ channel activation and hyperpolarization of the postsynaptic membrane do not contribute to relaxation, prejunctional modulation of the nitrergic neurotransmission by Kv channels may be relevant. Relaxation induced by NO+ or NO– donors was not affected by K+ channel blockade with the following exceptions: glybenclamide, a blocker of ATP-sensitive K+ channels (KATP), enhanced responses to SNP and Angeli's salt, 4-aminopyridine inhibited relaxation evoked by Angeli's salt and GTN, and charybdotoxin, a blocker of large-conductance, Ca2+-activated K+ channels (BKCa) inhibited those induced by the S-nitrosothiol S-nitrosoglutathione. These results do not suggest the existence of a general mechanism of action on K+ channels for compounds releasing either NO+ or NO– in the sheep urethra. None of the K+ channel blockers affected relaxation induced by the membrane-permeable analogue of cGMP, 8-bromo-cGMP. However, the fact that the addition of the phosphodiesterase inhibitor zaprinast (0.1 mM) enhanced the relaxation to Angeli's salt, while preventing the inhibition induced by 4-aminopyridine, suggests that involvement of guanylate cyclase activation in the action of NO donors on K+ channels can not be excluded. Accordingly, the guanylate cyclase inhibitors 1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ, 10 µM) and 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one (NS 2028, 10 µM) almost abolished relaxations to EFS and Angeli's salt. In contrast, ODQ only moderately inhibited relaxations to NO•. In addition, the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl imidazoline-1-oxyl 3-oxide (carboxy-PTIO) effectively inhibited responses to NO• whilst not affecting those to EFS or NO–, suggesting a close similarity between the nitrergic transmitter and nitroxyl ion. We conclude that nitrergic relaxation induced either by the endogenous transmitter or by exogenous NO donors in the ovine urethra is not mediated by postsynaptic alterations in the K+ conductance; only a prejunctional modulation through Kv channels seems to be significant. In addition, the production and/or release of alternative redox forms of NO, such as NO–, may be involved in neurotransmission processes in the urethra. [ABSTRACT FROM AUTHOR]

Purpose. Model compounds containing NO-donor furoxan moieties at the 3-positioned basic lateral chain of 1, a 1,4-dihydropyridine related to nicardipine, were synthesized in order to study their vasodilating activity as well as their basic and lipophilic behaviour. Methods. All the compounds were obtained by a modified Hantzsch approach. Potentiometry was used to determine pKa and lipophilicity descriptors. The furoxan 4-aryl-1,4-dihydropyridines were assessed for their ability to release nitrite, in the presence of a large excess of cysteine, by the Griess reaction. Vasodilating activity of the products in the absence and in the presence of ODQ, a well-known guanylate cyclase inhibitor, was evaluated on rat thoracic aorta. Results. The compounds display low basicity values and for this reason their log Ds at physiological pH are identical to the log Ps of the neutral forms. Products 2, 3 display vasodilating action principally dependent on their Ca2+-antagonist properties, whereas 4 behaves as a well-balanced hybrid with mixed Ca2+-channel blocker and NO-dependent vasodilator activities. Conclusions. Nitrogen containing lateral chain at the 3-position of 1 is a suitable molecular region to be modified in order to obtain well-balanced furoxan NO-donor 1,4-DHPs. This manipulation produces a decrease in the basicity. General analysis of pKa and lipophilicity descriptors of these new DHPs suggest that molecular flexibility could influence both their basicity and log PI. [ABSTRACT FROM AUTHOR]

7-Aryl-4a-hydroxy-4a,6,7,7a-tetrahydroisoxazolo[4,5- b]quinuclidines have been prepared from 2-arylmethylene-3-quinuclidones and hydroxylamine and they are able to release NO upon mild oxidation with K3[Fe(CN6)] in basic medium. [ABSTRACT FROM AUTHOR]

Methods have been developed for the synthesis of mono- and bisacetyl derivatives of 2-hydroxyarylmethylene-3-quinuclidone oximes. [ABSTRACT FROM AUTHOR]

Purpose. To obtain new cardiovascular agents with mixed Ca2+-channel antagonistic and NO-donor properties, a series of “hybrid” 1,4-dihydropyridines (1,4-DHPs), bearing NO-donating furoxan moieties on the 3-positioned lateral ester chain were synthesized and pharmacologically characterized. Furazan analogues were also prepared and investigated for control purposes, because they are unable to release NO.4 Methods. Synthesis of the models was achieved by a modified Hantzsch approach. All of the final furoxan 1,4-DHPs were assessed for their ability to produce nitrite in the presence of a large excess of cysteine by the Griess reaction. Vasodilating activity was evaluated on rat aorta and expressed as EC50 and EC50 MB values, obtained in the absence and in the presence of methylene blue (MB) respectively, a well-known guanylate cyclase inhibitor. Affinities to 1,4-DHP receptor on Ca2+-channels, expressed as IC50 values, were determined through displacement experiments of [3H]-nitrendipine on rat cortex homogenates. Results. Some hybrid compounds (derivatives 15a, 15b, 16a, and 16b) displayed vasodilating activity depending predominantly on their Ca2+-channel blocker properties. By contrast, some others (derivatives 17a, 17b, and 21) behaved as well-balanced hybrids with mixed Ca2+-channel blocking and NO-dependent vasodilating activities. Conclusion. This work demonstrates the possibility of obtaining well-balanced hybrids endowed with mixed NO-donor and Ca2+-channel blocker properties using appropriate 1,4-DHP and furoxan moieties. A procedure for the individual evaluation of the NO-dependent vasodilator component and that due to Ca2+-channel blocking is proposed. [ABSTRACT FROM AUTHOR]

Background: We evaluated the contribution of endogenous and exogenous nitric oxide (NO) in ischaemia reperfusion (IR) injury and histamine release in the isolated guinea pig heart. ¶ Methods: Ischaemia reperfusion was performed in isolated Langendorff perfused guinea pig heart throughout the ligature of the left anterior descending coronary (LAD) artery for 20 min, and following the release of the ligature for a further 20 min. ¶ Results: IR promoted a linear release of lactate dehydrogenase (LDH) and a preferential release of histamine in the reperfusion phase. The amount of nitrite (NO2 -, one of the breakdown products of NO) released during IR was significantly lower than in the control hearts. These effects were accompanied by an increase in calcium levels and malonyldialdehyde (MDA) production in the left ventricle and by a decrease in cardiac mast cell metachromasia. Perfusion of the hearts with two inhibitors of the nitric oxide synthase pathway, namely NG-monomethyl-L-arginine (L-NMMA, 10-4 M) or nitroarginine methylester (L-NAME, 10-5 M) significantly enhanced histamine and LDH release; these effects were attenuated by co-infusion with L-arginine (10-4 M) but not D-arginine (10-4 M), while L-arginine (10-4 M, reduced histamine release, LDH release, calcium overload and MDA production induced by IR. These effects were amplified by concomitant perfusion with superoxide dismutase (SOD, 50 IU/ml). ¶ Conclusion: The endogenous production of NO provides significant myocardial protection from IR injury and histamine release. These effects were mimicked by various NO donors. [ABSTRACT FROM AUTHOR]-5 M, reduced histamine release, LDH release, calcium overload and MDA production induced by IR. These effects were amplified by concomitant perfusion with superoxide dismutase (SOD, 50 IU/ml). ¶ Conclusion: The endogenous production of NO provides significant myocardial protection from IR injury and histamine release. These effects were mimicked by various NO donors. [ABSTRACT FROM AUTHOR]

Purpose. To investigate the effect of benzofusion on NO donor properties and related biological activities of the furoxan system. The biological properties considered were the ability to increase the cytosolic levels of cGMP in C6 cells and vasodilation. Methods. NO donor properties were investigated either in the presence or the absence of cysteine by using the Griess reaction, chemiluminescence, and gas chromatography. Increase of cytosolic cGMP levels were evaluated by radioimmunoassay. Vasodilating activity was assessed on rat aorta strips precontracted with noradrenaline, in the presence and the absence of oxyhemoglobin (HbO2) and methylene blue (MB), respectively. Results. Benzofuroxan and its methyl and cyano derivatives were unable to release NO under the experimental conditions. Generally these compounds displayed feeble vasodilating properties and were able to weakly stimulate soluble guanylate cyclase (sGC). By contrast, benzodifuroxan and benzotrifuroxan were able to produce both NO• and its reduced form NO−, the nitroxyl anion. They displayed potent vasodilating properties and were able to increase cytosolic levels of cGMP in a concentration-dependent manner. Conclusions. The simple benzofuroxans considered here are devoid of the capability to release NO, they weakly stimulate sGC as well as manifest feeble vasodilating properties by a mechanism that does not involve a thiol-induced NO production. By contrast, benzodifuroxan and benzotrifuroxan behave as typical NO donor furoxans. [ABSTRACT FROM AUTHOR]

We have examined the mechanisms of action of a broad spectrum of nitric oxide (NO) donors, including several S-nitrosothiols, sodium nitroprusside (SNP) and nitroglycerine (GTN), in relation to their relaxant activity of urethral smooth muscle. For all the compounds examined, NO release (in solution and in the presence of urethral tissue), relaxation responses, elevations in cGMP levels and the effect of thiol modulators were evaluated and compared with the effect of NO itself. Whilst all NO donors, except GTN, released NO in solution due to photolysis or chemical catalysis, this release was not correlated with their relaxant activity in sheep urethral preparations, which were furthermore not affected by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (cPTIO; 0.3 mM). A substantial NO-generating activity was found for S-nitroso- L-cysteine (CysNO) and S-nitroso- N-acetyl- D, L-penicillamine (SNAP) in the presence of urethral cytosolic fractions, suggesting metabolic activation to NO in the cytosol of the target tissue. In contrast, NO generation from S-nitroso- N-acetyl- L-cysteine ( N-ac-CysNO), S-nitrosoglutathione (GSNO) and SNP were reduced by the presence of urethral homogenate and/or subcellular fractions, suggesting direct NO transfer to tissue constituents. NO donors and NO gas induced dissimilar degrees of cGMP accumulation in urethral tissue, while they were essentially equipotent as urethral relaxants. Furthermore, 1H-[1,2,4]-oxadiazole-[4,3- a]-quinoxalin-1-one (ODQ; 10 µM) inhibited both relaxation and cGMP accumulations, but with different potency for the different compounds. Oxidation of sarcolemmal thiol groups with 5-5´-dithio-bis[2-nitrobenzoic acid] (DTNB; 0.5 mM) enhanced relaxations to GSNO, an effect that was reversed by dithiotreitol (DTT; 1 mM), suggesting a direct effect through nitrosylation/oxidation reactions at the cell membrane, while relaxations to NO and to all the other compounds were not affected by these treatments. Finally, photodegradation of SNP induced the formation of a stable intermediate that still evoked NO-cGMP-mediated relaxations. This indicates that the assumption that SNP is fully depleted of NO by exposure to light should be revised. It can be concluded that important differences exist in the mechanisms by which distinct NO donors relax urethral smooth muscle and they cannot be regarded simply as NO-releasing prodrugs. [ABSTRACT FROM AUTHOR]