Xanthine oxidase converts nitric oxide to nitroxyl that inactivates the enzyme

CoenzymeQ in cellular redox regulation and clinical heart failure

Coenzyme Q (CoQ) is ubiquitously embedded in lipid bilayers of various cellular organelles. As a redox cycler, CoQ shuttles electrons between mitochondrial complexes and extramitochondrial reductases and oxidases. In this way, CoQ is crucial for maintaining the mitochondrial function, ATP synthesis, and redox homeostasis. Cardiomyocytes have a high metabolic rate and rely heavily on mitochondria to provide energy. CoQ levels, in both plasma and the heart, correlate with heart failure in patients, indicating that CoQ is critical for cardiac function. Moreover, CoQ supplementation in clinics showed promising results for treating heart failure. This review provides a comprehensive view of CoQ metabolism and its interaction with redox enzymes and reactive species. We summarize the clinical trials and applications of CoQ in heart failure and discuss the caveats and future directions to improve CoQ therapeutics.

Dual-Colored Fluorescence Imaging of Mitochondrial HNO and Golgi-HNO in Mice with DILI

Drug-induced liver injury (DILI) is the most common reason for the post-marketing withdrawal of drugs. Poor understanding of the mechanisms of DILI presents a large challenge in clinical diagnosis. Previous evidences indicate a potential relationship between reactive nitrogen species (RNS) and DILI. Hence, we developed two specific probes, Golgi-HNO and Mito-HNO, for the multicolored and simultaneous in situ imaging of nitroxyl (HNO) in the Golgi apparatus and mitochondria, respectively. We discovered a significant rise in HNO levels in the livers of mice with DILI, which means that for the first time, we revealed a positive correlation between HNO levels and DILI. Based on changes in the HNO level, we also successfully explored the extent of liver damage induced by an anticarcinogen, bleomycin. In addition, we uncovered catalase was involved in HNO synthesis, which is the unprecedented function of catalase. These findings demonstrate that HNO is an ideal biomarker for DILI diagnosis, and Golgi-HNO and Mito-HNO are ideal fluorescent probes to study in situ HNO changes in various physiological and biochemical processes.

Interaction among Hydrogen Sulfide and Other Gasotransmitters in Mammalian Physiology and Pathophysiology

Hydrogen sulfide (H₂S), nitric oxide (NO), carbon monoxide (CO), and sulfur dioxide (SO₂) were previously considered as toxic gases, but now they are found to be members of mammalian gasotransmitters family. Both H₂S and SO₂ are endogenously produced in sulfur-containing amino acid metabolic pathway in vivo. The enzymes catalyzing the formation of H₂S are mainly CBS, CSE, and 3-MST, and the key enzymes for SO₂ production are AAT1 and AAT2. Endogenous NO is produced from L-arginine under catalysis of three isoforms of NOS (eNOS, iNOS, and nNOS). HO-mediated heme catabolism is the main source of endogenous CO. These four gasotransmitters play important physiological and pathophysiological roles in mammalian cardiovascular, nervous, gastrointestinal, respiratory, and immune systems. The similarity among these four gasotransmitters can be seen from the same and/or shared signals. With many studies on the biological effects of gasotransmitters on multiple systems, the interaction among H₂S and other gasotransmitters has been gradually explored. H₂S not only interacts with NO to form nitroxyl (HNO), but also regulates the HO/CO and AAT/SO₂ pathways. Here, we review the biosynthesis and metabolism of the gasotransmitters in mammals, as well as the known complicated interactions among H₂S and other gasotransmitters (NO, CO, and SO₂) and their effects on various aspects of cardiovascular physiology and pathophysiology, such as vascular tension, angiogenesis, heart contractility, and cardiac protection.

Fluorescent probes for the detection of nitroxyl (HNO)

Nitroxyl (HNO), which according to the IUPAC recommended nomenclature should be named azanone, is the protonated one-electron reduction product of nitric oxide. Recently, it has gained a considerable attention due to the interesting pharmacological effects of its donors. Although there has been great progress in the understanding of HNO chemistry and chemical biology, it still remains the most elusive reactive nitrogen species, and its selective detection is a real challenge. The development of reliable methodologies for the direct detection of azanone is essential for the understanding of important signaling properties of this reactive intermediate and its pharmacological potential. Over the last decade, there has been considerable progress in the development of low-molecular-weight fluorogenic probes for the detection of HNO, and therefore, in this review, we have focused on the challenges and limitations of and perspectives on nitroxyl detection based on the use of such probes.

An evaluation of the effects of perioperatively administered fluids on ischemia/reperfusion injury

Objective:

To investigate the effects of normal saline (0.9% NaCl) and 6% Hydroxyethyl Starch 130/0.4(HES) solution on Ischemia/Reperfusion (I/R) injury in patients undergoing knee arthroscopy operations with spinal anesthesia using a tourniquet.

Methods:

The study comprised 48 ASA I-II patients undergoing knee arthroscopy with spinal anesthesia using a tourniquet. The patients were randomised into two groups and after standard monitoring two venous lines were introduced to obtain blood samples and to give intravenous therapy. In the control group (Group A) (n=21) 0.9% NaCl, 10 ml/kg/hours and in the study group (Group B) (n=19) 6% Hydroxyethyl Starch 130/0.4, 10 ml/kg/hours infusion were administered. Spinal anesthesia was applied with 12.5 mg hyperbaric bupivacaine to all patients. The tourniquet was applied and the operation was started when the sensorial block level reached T10 dermatome. Blood xanthine oxidase (XO) and malondialdehyde (MDA) levels as an indicator of ischemia and reperfusion injury were measured in samples before fluid infusion (t1), before tourniquet application (t2), 1 minute before tourniquet release (t3), and at 5 (t4) and 15 (t5) minutes after tourniquet release.

Results:

No difference was observed between the two groups in respect of demographic parameters, the highest block level, duration before tourniquet application and tourniquet duration (p>0.05). The MDA level after tourniquet application and 15 minutes after tourniquet release was lower in Group B (p<0.05). XO levels were not different (p>0.05).

Conclusion:

In this study 6% Hydroxyethyl Starch 130/0.4 solution reduced MDA level which is an indicator of lipid peroxidation. 6% Hydroxyethyl Starch 130/0.4 solution may be beneficial for Ischemia/reperfusion injuries.

Biological signaling by small inorganic molecules

Small redox active molecules such as reactive nitrogen and oxygen species and hydrogen sulfide have emerged as important biological mediators that are involved in various physiological and pathophysiological processes. Advancement in understanding of cellular mechanisms that tightly regulate both generation and reactivity of these molecules is central to improved management of various disease states including cancer and cardiovascular dysfunction. Imbalance in the production of redox active molecules can lead to damage of critical cellular components such as cell membranes, proteins and DNA and thus may trigger the onset of disease. These small inorganic molecules react independently as well as in a concerted manner to mediate physiological responses. This review provides a general overview of the redox biology of these key molecules, their diverse chemistry relevant to physiological processes and their interrelated nature in cellular signaling.

Nitroxyl (HNO): A Reduced Form of Nitric Oxide with Distinct Chemical, Pharmacological, and Therapeutic Properties

Nitroxyl (HNO), the one-electron reduced form of nitric oxide (NO), shows a distinct chemical and biological profile from that of NO. HNO is currently being viewed as a vasodilator and positive inotropic agent that can be used as a potential treatment for heart failure. The ability of HNO to react with thiols and thiol containing proteins is largely used to explain the possible biological actions of HNO. Herein, we summarize different aspects related to HNO including HNO donors, chemistry, biology, and methods used for its detection.

Interaction of Hydrogen Sulfide with Nitric Oxide in the Cardiovascular System

Historically acknowledged as toxic gases, hydrogen sulfide (H₂S) and nitric oxide (NO) are now recognized as the predominant members of a new family of signaling molecules, “gasotransmitters” in mammals. While H₂S is biosynthesized by three constitutively expressed enzymes (CBS, CSE, and 3-MST) from L-cysteine and homocysteine, NO is generated endogenously from L-arginine by the action of various isoforms of NOS. Both gases have been transpired as the key and independent regulators of many physiological functions in mammalian cardiovascular, nervous, gastrointestinal, respiratory, and immune systems. The analogy between these two gasotransmitters is evident not only from their paracrine mode of signaling, but also from the identical and/or shared signaling transduction pathways. With the plethora of research in the pathophysiological role of gasotransmitters in various systems, the existence of interplay between these gases is being widely accepted. Chemical interaction between NO and H₂S may generate nitroxyl (HNO), which plays a specific effective role within the cardiovascular system. In this review article, we have attempted to provide current understanding of the individual and interactive roles of H₂S and NO signaling in mammalian cardiovascular system, focusing particularly on heart contractility, cardioprotection, vascular tone, angiogenesis, and oxidative stress.

Nitroxyl (HNO) reacts with molecular oxygen and forms peroxynitrite at physiological pH. Biological Implications

Nitroxyl (HNO), the protonated one-electron reduction product of NO, remains an enigmatic reactive nitrogen species. Its chemical reactivity and biological activity are still not completely understood. HNO donors show biological effects different from NO donors. Although HNO reactivity with molecular oxygen is described in the literature, the product of this reaction has not yet been unambiguously identified. Here we report that the decomposition of HNO donors under aerobic conditions in aqueous solutions at physiological pH leads to the formation of peroxynitrite (ONOO(-)) as a major intermediate. We have specifically detected and quantified ONOO(-) with the aid of boronate probes, e.g. coumarin-7-boronic acid or 4-boronobenzyl derivative of fluorescein methyl ester. In addition to the major phenolic products, peroxynitrite-specific minor products of oxidation of boronate probes were detected under these conditions. Using the competition kinetics method and a set of HNO scavengers, the value of the second order rate constant of the HNO reaction with oxygen (k = 1.8 × 10(4) m(-1) s(-1)) was determined. The rate constant (k = 2 × 10(4) m(-1) s(-1)) was also determined using kinetic simulations. The kinetic parameters of the reactions of HNO with selected thiols, including cysteine, dithiothreitol, N-acetylcysteine, captopril, bovine and human serum albumins, and hydrogen sulfide, are reported. Biological and cardiovascular implications of nitroxyl reactions are discussed.

The nitroxyl donor, Angeli's salt, inhibits inflammatory hyperalgesia in rats

Nitric oxide modulates pain development. However, there is no evidence on the effect of nitroxyl (HNO/NO⁻) in nociception. Therefore, we addressed whether nitroxyl inhibits inflammatory hyperalgesia and its mechanism using the nitroxyl donor Angeli's salt (AS; Na₂N₂O₃). Mechanical hyperalgesia was evaluated using a modified Randall and Selitto method in rats, cytokine production by ELISA and nitroxyl was determined by confocal microscopy in DAF (a cell permeable reagent that is converted into a fluorescent molecule by nitrogen oxides)-treated dorsal root ganglia neurons in culture. Local pre-treatment with AS (17-450 μg/paw, 30 min) inhibited the carrageenin-induced mechanical hyperalgesia in a dose- and time-dependent manner with maximum inhibition of 97%. AS also inhibited carrageenin-induced cytokine production. AS inhibited the hyperalgesia induced by other inflammatory stimuli including lipopolysaccharide, tumor necrosis factor-α, interleukin-1β and prostaglandin E2. Furthermore, the analgesic effect of AS was prevented by treatment with ODQ (a soluble guanylate cyclase inhibitor), KT5823 (a protein kinase G [PKG] inhibitor) or glybenclamide (an ATP-sensitive K⁺ channel blocker), but not with naloxone (an opioid receptor antagonist). AS induced concentration-dependent increase in fluorescence intensity of DAF-treated neurons in a l-cysteine (nitroxyl scavenger) sensitive manner. l-cysteine did not affect the NO⁺ donor S-Nitroso-N-acetyl-DL- penicillamine (SNAP)-induced anti-hyperalgesia or fluorescence of DAF-treated neurons. This is the first study to demonstrate that nitroxyl inhibits inflammatory hyperalgesia by reducing cytokine production and activating the cGMP/PKG/ATP-sensitive K⁺ channel signaling pathway in vivo.

Potential biological chemistry of hydrogen sulfide (H2S) with the nitrogen oxides

Hydrogen sulfide, an important gaseous signaling agent generated in numerous biological tissues, influences many physiological processes. This biological profile seems reminiscent of nitric oxide, another important endogenously synthesized gaseous signaling molecule. Hydrogen sulfide reacts with nitric oxide or oxidized forms of nitric oxide and nitric oxide donors in vitro to form species that display distinct biology compared to both hydrogen sulfide and NO. The products of these interesting reactions may include small-molecule S-nitrosothiols or nitroxyl, the one-electron-reduced form of nitric oxide. In addition, thionitrous acid or thionitrite, compounds structurally analogous to nitrous acid and nitrite, may constitute a portion of the reaction products. Both the chemistry and the biology of thionitrous acid and thionitrite, compared to nitric oxide or hydrogen sulfide, remain poorly defined. General mechanisms for the formation of S-nitrosothiols, nitroxyl, and thionitrous acid based upon the ability of hydrogen sulfide to act as a nucleophile and a reducing agent with reactive nitric oxide-based intermediates are proposed. Hydrogen sulfide reactivity seems extensive and could have an impact on numerous areas of redox-controlled biology and chemistry, warranting more work in this exciting and developing area.

Endothelium-dependent nitroxyl-mediated relaxation is resistant to superoxide anion scavenging and preserved in diabetic rat aorta

The aim of the study was to investigate whether diabetes-induced oxidant stress affects the contribution of nitroxyl (HNO) to endothelium-dependent relaxation in the rat aorta. Organ bath techniques were employed to determine vascular function of rat aorta. Pharmacological tools (3mM l-cysteine, 5mM 4-aminopyridine (4-AP), 200μM carboxy-PTIO and 100μM hydroxocobalamin, HXC) were used to distinguish between NO and HNO-mediated relaxation. Superoxide anion levels were determined by lucigenin-enhanced chemiluminescence. In the diabetic aorta, where there is increased superoxide anion production, responses to the endothelium-dependent relaxant ACh were not affected when the contribution of NO to relaxation was abolished by either HXC or carboxy-PTIO, indicating a preserved HNO-mediated relaxation. Conversely, when the contribution of HNO was inhibited with l-cysteine or 4-AP, the sensitivity and maximum relaxation to ACh was significantly decreased, suggesting that the contribution of NO was impaired by diabetes. Furthermore, whereas HNO appears to be derived from eNOS in normal aorta, in the diabetic aorta it may also arise from an eNOS-independent source, perhaps derived from nitrosothiol stores. Similarly, exposure to the superoxide anion generator, pyrogallol (100μM) significantly reduced the sensitivity to the NO donor, DEANONOate and ACh-induced NO-mediated relaxation but had no effect on responses to the HNO donor, Angeli's salt and ACh-induced HNO-mediated relaxation in the rat aorta. These findings demonstrate that NO-mediated relaxation is impaired during oxidative stress but the HNO component of relaxation is preserved under those conditions.

Aorta from angiotensin II hypertensive mice exhibit preserved nitroxyl anion mediated relaxation responses

Hypertension is a disorder affecting millions worldwide, and is a leading cause of death and debilitation in the United States. It is widely accepted that during hypertension and other cardiovascular diseases the vasculature exhibits endothelial dysfunction; a deficit in the relaxatory ability of the vessel, attributed to a lack of nitric oxide (NO) bioavailability. Recently, the one electron redox variant of NO, nitroxyl anion (NO(-)) has emerged as an endothelium-derived relaxing factor (EDRF) and a candidate for endothelium-derived hyperpolarizing factor (EDRF). NO(-) is thought to exist protonated (HNO) in vivo, which would make this species more resistant to scavenging. However, no studies have investigated the role of this redox species during hypertension, and whether the vasculature loses the ability to relax to HNO. Thus, we hypothesize that aorta from angiotensin II (AngII)-hypertensive mice will exhibit a preserved relaxation response to Angeli's Salt, an HNO donor. Male C57Bl6 mice, aged 12-14 weeks were implanted with mini-osmotic pumps containing AngII (90ng/min, 14 days plus high salt chow) or sham surgery. Aorta were excised, cleaned and used to perform functional studies in a myograph. We found that aorta from AngII-hypertensive mice exhibited a significant endothelial dysfunction as demonstrated by a decrease in acetylcholine (ACh)-mediated relaxation. However, vessels from hypertensive mice exhibited a preserved response to Angeli's Salt (AS), the HNO donor. To confirm that relaxation responses to HNO were maintained, concentration response curves (CRCs) to ACh were performed in the presence of scavengers to both NO and HNO (carboxy-PTIO and L-cys, resp.). We found that ACh-mediated relaxation responses were significantly decreased in aorta from sham and almost completely abolished in aorta from AngII-treated mice. Vessels incubated with l-cys exhibited a modest decrease in ACh-mediated relaxations responses. These data demonstrate that aorta from AngII-treated hypertensive mice exhibit a preserved relaxation response to AS, an HNO donor, regardless of a significant endothelial dysfunction.

Sildenafil protects human mammary epithelial cells against ROS production induced by estradiol

Several studies suggest that xanthine dehydrogenase (XDH) and its oxidase form (XO) play an important role in various types of ischemic and vascular injuries. Recently, we have demonstrated that estradiol (E2) induces a significant decrease of the expression and activity of XDH and of its conversion to XO in human mammary epithelial cells. E2 is known to induce upregulation of eNOS gene expression in aortic endothelial cells. Because the XO-derived O2·- combines with ·NO to yield ONOO-, and considering that ONOO- converts XDH to XO, the resulting increase of XO activity and reactive oxygen species production would eventually lead to a further increase of ONOO- production, thus creating a vicious cycle of oxidative stress. Our previous study has indicated that sildenafil has a protective effect on human mammary epithelial cells as a consequence of XO inhibition and of the resulting decrease of free oxygen radicals that can impair the expression of NADPH oxidase and type 5 phosphodiesterase (PDE-5). In the present study, we report that the dual inhibitory effect exerted by sildenafil on both XO and PDE-5 is a consequence of a structural modification induced by O2·-, also consisting of the release of a piperazine group that could in turn inhibit the XO enzyme.

Playing with cardiac "redox switches": the "HNO way" to modulate cardiac function

The nitric oxide (NO(•)) sibling, nitroxyl or nitrosyl hydride (HNO), is emerging as a molecule whose pharmacological properties include providing functional support to failing hearts. HNO also preconditions myocardial tissue, protecting it against ischemia-reperfusion injury while exerting vascular antiproliferative actions. In this review, HNO's peculiar cardiovascular assets are discussed in light of its unique chemistry that distinguish HNO from NO(•) as well as from reactive oxygen and nitrogen species such as the hydroxyl radical and peroxynitrite. Included here is a discussion of the possible routes of HNO formation in the myocardium and its chemical targets in the heart. HNO has been shown to have positive inotropic/lusitropic effects under normal and congestive heart failure conditions in animal models. The mechanistic intricacies of the beneficial cardiac effects of HNO are examined in cellular models. In contrast to β-receptor/cyclic adenosine monophosphate/protein kinase A-dependent enhancers of myocardial performance, HNO uses its "thiophylic" nature as a vehicle to interact with redox switches such as cysteines, which are located in key components of the cardiac electromechanical machinery ruling myocardial function. Here, we will briefly review new features of HNO's cardiovascular effects that when combined with its positive inotropic/lusitropic action may render HNO donors an attractive addition to the current therapeutic armamentarium for treating patients with acutely decompensated congestive heart failure.

A novel role for HNO in local and spreading vasodilatation in rat mesenteric resistance arteries

Nitric oxide-mediated vasodilatation has previously been attributed to the uncharged form of the molecule (NO(•)), but increasing evidence suggests that nitroxyl (HNO) may play a significant role in endothelium-dependent relaxation. The aim of this study was to investigate the mechanisms underlying HNO-mediated vasodilatation in phenylephrine pre-constricted pressurized (70 mmHg) mesenteric arteries, and on membrane currents in isolated smooth muscle cells using whole cell and perforated patch clamp recordings. Angeli's salt (AS: nitroxyl donor), evoked concentration-dependent vasodilatation that was insensitive to the NO(•) scavengers carboxy-PTIO and hydroxocobalamin (HXC), but sensitive to either the HNO scavenger L-cysteine, K-channel blockers (4-AP and iberiotoxin), raised [K(+)](o), or inhibition of soluble guanylyl cyclase (ODQ). AS-evoked smooth muscle hyperpolarization significantly augmented K(V) current in an ODQ sensitive manner, and also increased the BK(Ca) current. Importantly, 30 μM AS initiated conducted or spreading vasodilatation, and following blockade of endothelial K-channels (TRAM-34 and apamin), ACh was able to evoke similar L-cysteine-sensitive conducted dilatation. These data show that vasodilatation induced by HNO is mediated by both K(V) and BK(Ca) channels, and suggest a physiological role in vasodilatation through the vasculature.

Hydrogen sulfide interacts with nitric oxide in the heart: possible involvement of nitroxyl

AIMS

The present study aims to investigate the interaction between nitric oxide (NO) and hydrogen sulfide (H(2)S), the two important gaseous mediators in rat hearts.

METHODS AND RESULTS

Intracellular calcium in isolated cardiomyocytes was measured with a spectrofluorometric method using Fura-2. Myocyte contractility was measured with a video edge system. NaHS (50 µM, an H(2)S donor) had no significant effect on the resting calcium level, electrically induced (EI) calcium transients, and cell contractility in ventricular myocytes. Stimulating endogenous NO production with l-arginine or exogenous application of NO donors [sodium nitroprusside (SNP) and 2-(N,N-diethylamino)-diazenolate-2-oxide] decreased myocyte twitch amplitudes accompanied by slower velocities of both cell contraction and relaxation. Surprisingly, NaHS reversed the negative inotropic and lusitropic effects of the above three NO-increasing agents. In addition, the mixture of SNP + NaHS increased, whereas SNP alone decreased, the resting calcium level and the amplitudes of EI calcium transients. Angeli's salt, a nitroxyl anion (HNO) donor, mimicked the effect of SNP + NaHS on calcium handling and myocyte contractility. Three thiols, N-acetyl-cysteine, l-cysteine, and glutathione, abolished the effects of HNO and SNP + NaHS on myocyte contraction. Neither Rp-cAMP [a protein kinase A (PKA) inhibitor] nor Rp-cGMP [a protein kinase G (PKG) inhibitor] affected the effects of SNP + NaHS, suggesting a cAMP/PKA- or cGMP/PKG-independent mechanism.

CONCLUSION

H(2)S may interact with NO to form a thiol sensitive molecule (probably HNO) which produces positive inotropic and lusitropic effects. Our findings may shed light on the interaction of NO and H(2)S and provide new clues to treat cardiovascular diseases.

Estradiol decreases xanthine dehydrogenase enzyme activity and protein expression in non-tumorigenic and malignant human mammary epithelial cells

The retinoic acid deficiency in breast tumour epithelial cells has been ascribed to an insufficient expression of either the enzyme(s) involved in its biosynthesis or the cellular retinol binding protein (CRBP) or both. In an attempt to define the mechanisms underpinning retinoic acid deficiency in these cell model systems, we have investigated the potential regulatory effect of oestrogen (17beta-estradiol) on one key player in retinoic acid biosynthesis, the xanthine dehydrogenase (XDH). This enzyme is consistently expressed and very active in non-malignant human mammary epithelial cells (HMEC), as opposed to tumour MDA-MB231 and MCF7 cells. In these latter two cell lines, as opposed to HMEC cells, we observe a residual ability of XDH to produce retinoic acid from retinaldehyde and the inability to use retinol, as a consequence of a deficit in CRBP. In addition, estradiol treatment of MDA-MB231 and MCF7 cells decreases protein expression and activity of the enzyme, with no modification of the mRNA transcript levels, eventually leading to deteriorate further retinoic acid production.

Quinone-enhanced reduction of nitric oxide by xanthine/xanthine oxidase

The quinones 1,4-naphthoquinone, methyl-1,4-naphthoquinone, tetramethyl-1,4-benzoquinone, 2,3-dimethoxy-5-methyl-1,4-benzoquinone, 2,6-dimethylbenzoquinone, 2,6-dimethoxybenzoquinone, and 9,10-phenanthraquinone enhance the rate of nitric oxide reduction by xanthine/xanthine oxidase in nitrogen-saturated phosphate buffer (pH 7.4). Maximum initial rates of NO reduction (V(max)) and the amount of nitrous oxide produced after 5 min of reaction increase with quinone one- and two-electron redox potentials measured in acetonitrile. One of the most active quinones of those studied is 9,10-phenanthraquinone with a V(max) value 10 times larger than that corresponding to the absence of quinone, under the conditions of this work. Because NO production is enhanced under hypoxia and under certain pathological conditions, the observations obtained in this work are very relevant to such conditions.

A role for nitroxyl (HNO) as an endothelium-derived relaxing and hyperpolarizing factor in resistance arteries

BACKGROUND AND PURPOSE

Nitroxyl (HNO) is emerging as an important regulator of vascular tone as it is potentially produced endogenously and dilates conduit and resistance arteries. This study investigates the contribution of endogenous HNO to endothelium-dependent relaxation and hyperpolarization in resistance arteries.

EXPERIMENTAL APPROACH

Rat and mouse mesenteric arteries were mounted in small vessel myographs for isometric force and smooth muscle membrane potential recording.

KEY RESULTS

Vasorelaxation to the HNO donor, Angeli's salt, was attenuated in both species by the soluble guanylate cyclase inhibitor (ODQ, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one), the voltage-dependent K(+) channel inhibitor, 4-aminopyridine (4-AP) and the HNO scavenger, L-cysteine. In mouse mesenteric arteries, nitric oxide (NO) synthase inhibition (with L-NAME, N(omega)-Nitro-L-arginine methyl ester) markedly attenuated acetylcholine (ACh)-mediated relaxation. Scavenging the uncharged form of NO (NO(*)) with hydroxocobalamin (HXC) or HNO with L-cysteine, or 4-AP decreased the sensitivity to ACh, and a combination of HXC and L-cysteine reduced ACh-mediated relaxation, as did L-NAME alone. ACh-induced hyperpolarizations were significantly attenuated by 4-AP alone and in combination with L-NAME. In rat mesenteric arteries, blocking the effects of endothelium-derived hyperpolarizing factor (EDHF) (charybdotoxin and apamin) decreased ACh-mediated relaxation 10-fold and unmasked a NO-dependent component, mediated equally by HNO and NO(*), as HXC and L-cysteine in combination now abolished vasorelaxation to ACh. Furthermore, ACh-evoked hyperpolarizations, resistant to EDHF inhibition, were virtually abolished by 4-AP.

CONCLUSIONS AND IMPLICATIONS

The factors contributing to vasorelaxation in mouse and rat mesenteric arteries are NO(*) = HNO > EDHF and EDHF > HNO = NO(*) respectively. This study identified HNO as an endothelium-derived relaxing and hyperpolarizing factor in resistance vessels.

Redox variants of NO (NO{middle dot} and HNO) elicit vasorelaxation of resistance arteries via distinct mechanisms

The free radical form of nitric oxide (NO(.)) is a well-known mediator of vascular tone. What is not so well recognized is that NO(.) exists in several different redox forms. There is considerable evidence that NO(.) and its one-electron reduction product, nitroxyl (HNO), have pharmacologically distinct actions that extend into the regulation of the vasculature. The aim of this study was to compare the vasorelaxation mechanisms of HNO and NO(.), including an examination of the ability of these redox variants to hyperpolarize and repolarize vascular smooth muscle cells from rat mesenteric arteries. The HNO donor Angeli's salt (0.1 nM-10 microM) caused a concentration-dependent hyperpolarization of vessels at resting tone and a simultaneous, concentration-dependent vasorelaxation and repolarization of vessels precontracted and depolarized with methoxamine. Both vasorelaxation and repolarization responses to Angeli's salt were significantly attenuated by both the HNO scavenger l-cysteine (3 mM) and the voltage-dependent K(+) (K(v)) channel inhibitor 4-aminopyridine (4-AP; 1 mM) and virtually abolished by the soluble guanylate cyclase (sGC) inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 microM) or 30 mM K(+). In contrast, NO(.) (0.01-1 microM) repolarized arteries to a lesser extent than HNO, and these responses were resistant to inhibition by ODQ (10 microM) and 4-AP (1 mM). Blockade of K(v) channels (1 mM 4-AP) also significantly inhibited the repolarization response to YC-1 (0.1-10 microM), confirming a role for sGC/cGMP in the activation of K(v) channels in this preparation. We conclude that HNO causes vasorelaxation via a cGMP-dependent activation of K(v) channels and that there are different profiles of vasorelaxant activity for the redox siblings HNO and NO(.).

Dexmedetomidine reduces the ischemia-reperfusion injury markers during upper extremity surgery with tourniquet

PURPOSE

We examined the effect of dexmedetomidine on ischemia-reperfusion injury due to tourniquet application during upper-extremity surgery by determining blood malondialdehyde and hypoxanthine levels. Alterations in aspartate aminotransferase, alanine aminotransferase, creatine phosphokinase, lactate dehydrogenase, uric acid, and creatinine levels were also assessed.

METHODS

Forty patients of American Society of Anesthesiologists physical status I to II having hand and forearm surgery with tourniquet were randomly allocated into 2 groups. Brachial plexus anesthesia via axillary approach was performed for upper-limb block in all patients. In the dexmedetomidine group, a continuous infusion of dexmedetomidine (1 microg/kg for 10 minutes, followed by 0.5 microg kg(-1) h(-1)) was used until the end of surgery, whereas the control group received an equivalent volume of saline. Venous blood samples were obtained before brachial plexus anesthesia, at 1 minute before tourniquet release, and 15 minutes after tourniquet release for biochemical analysis.

RESULTS

Dexmedetomidine significantly attenuated plasma hypoxanthine production in the ischemia and plasma malondialdehyde production in the reperfusion periods. Blood creatine phosphokinase and uric acid levels were significantly lower in the dexmedetomidine group compared with those in the control group after reperfusion.

CONCLUSIONS

Our results suggest that dexmedetomidine may offer advantages by inhibiting lipid peroxidation in the case of anticipated ischemia-reperfusion injury, such as would occur in upper-extremity surgery requiring tourniquet application.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic II.

Chemistry of nitric oxide and related species

Nitric oxide (NO) has essential roles in a remarkable number of diverse biological processes. The reactivity of NO depends upon its physical properties, such as its small size, high diffusion rate, and lipophilicity (resulting in its accumulation in hydrophobic regions), and also on its facile but selective chemical reactivity toward a variety of cellular targets. NO also undergoes reactions with oxygen, superoxide ions, and reducing agents to give products that themselves show distinctive reactivity toward particular targets, sometimes with the manifestation of toxic effects, such as nitrosative stress. These include nitroxyl (HNO), the oxides NO2/N2O4, and N2O3, peroxynitrite, and S-nitrosothiols (RSNO). HNO is attracting considerable attention due to its pharmacological properties, which appear to be distinct from those of NO, and that may be significant in the treatment of heart failure.

Nitroxyl increases force development in rat cardiac muscle

Donors of nitroxyl (HNO), the reduced congener of nitric oxide (NO), exert positive cardiac inotropy/lusitropy in vivo and in vitro, due in part to their enhancement of Ca(2+) cycling into and out of the sarcoplasmic reticulum. Here we tested whether the cardiac action of HNO further involves changes in myofilament-calcium interaction. Intact rat trabeculae from the right ventricle were mounted between a force transducer and a motor arm, superfused with Krebs-Henseleit (K-H) solution (pH 7.4, room temperature) and loaded iontophoretically with fura-2 to determine [Ca(2+)](i). Sarcomere length was set at 2.2-2.3 microm. HNO donated by Angeli's salt (AS; Na(2)N(2)O(3)) dose-dependently increased both twitch force and [Ca(2+)](i) transients (from 50 to 1000 microm). Force increased more than [Ca(2+)](i) transients, especially at higher doses (332 +/- 33% versus 221 +/- 27%, P < 0.01 at 1000 microm). AS/HNO (250 microm) increased developed force without changing Ca(2+) transients at any given [Ca(2+)](o) (0.5-2.0 mm). During steady-state activation, AS/HNO (250 microm) increased maximal Ca(2+)-activated force (F(max), 106.8 +/- 4.3 versus 86.7 +/- 4.2 mN mm(-2), n = 7-8, P < 0.01) without affecting Ca(2+) required for 50% activation (Ca(50), 0.44 +/- 0.04 versus 0.52 +/- 0.04 microm, not significant) or the Hill coefficient (4.75 +/- 0.67 versus 5.02 +/- 1.1, not significant). AS/HNO did not alter myofibrillar Mg-ATPase activity, supporting an effect on the myofilaments themselves. The thiol reducing agent dithiothreitol (DTT, 5.0 mm) both prevented and reversed HNO action, confirming AS/HNO redox sensitivity. Lastly, NO (from DEA/NO) did not mimic AS/HNO cardiac effects. Thus, in addition to reported changes in Ca(2+) cycling, HNO also acts as a cardiac Ca(2+) sensitizer, augmenting maximal force without altering actomyosin ATPase activity. This is likely to be due to modulation of myofilament proteins that harbour reactive thiolate groups that are targets of HNO.

Electrochemistry of Xanthine Oxidase and Its Interaction with Nitric Oxide

With the help of nanocrystalline TiO2, the direct electrochemistry of xanthine oxidase (XOD) was achieved and two pairs of redox waves were observed. The interaction between XOD and nitric oxide (NO) was also investigated. The experimental results reveal that NO can be reduced at a XOD-nano TiO2 film modified electrode. When the NO concentration was low, the reduced product, HNO, would inactivate the protein. However, when the NO concentration was high, HNO would continue to react with NO to form N2O2- and N3O3-, which would not inhibit XOD, and thus the amount of active protein did not decrease any further.

NITROXYL (HNO): Chemistry, Biochemistry, and Pharmacology

Recent discoveries of novel and potentially important biological activity have spurred interest in the chemistry and biochemistry of nitroxyl (HNO). It has become clear that, among all the nitrogen oxides, HNO is unique in its chemistry and biology. Currently, the intimate chemical details of the biological actions of HNO are not well understood. Moreover, many of the previously accepted chemical properties of HNO have been recently revised, thus requiring reevaluation of possible mechanisms of biological action. Herein, we review these developments in HNO chemistry and biology.

Ketamine Sedation During Spinal Anesthesia for Arthroscopic Knee Surgery Reduced the Ischemia-Reperfusion Injury Markers

We studied the effect of ketamine sedation on oxidative stress during arthroscopic knee surgery with tourniquet application by determining blood and tissue malonyldialdehyde (MDA) and hypoxanthine (HPX) levels. Thirty ASA I-II patients undergoing arthroscopic knee surgery with tourniquet were randomly divided into two groups. Spinal anesthesia induced with 12.5 mg bupivacaine was administered to all patients. In the ketamine group, after IV administration of 0.01 mg/kg midazolam, a continuous infusion of ketamine (0.5 mg . kg(-1) . h(-1)) was used until the end of surgery whereas the placebo group received a volume-equivalent placebo infusion. Ramsey Sedation Scale (RSS) was used for assessing the sedation level. Venous blood and synovial membrane tissue samples were obtained before ketamine infusion, at 30 min of tourniquet ischemia, and at 5 min after tourniquet deflation for MDA and HPX measurements. Tissue MDA and HPX levels were significantly less in the ketamine group than the control group after reperfusion. RSS scores were higher in the ketamine group without any adverse effect. We conclude that ketamine sedation attenuates lipid peroxidation markers in arthroscopic knee surgery with tourniquet application.

Prevention of human cancer by modulation of chronic inflammatory processes

Chronic inflammation induced by biological, chemical and physical factors has been associated with increased risk of human cancer at various sites. Inflammation facilitates the initiation of normal cells and their growth and progression to malignancy through production of pro-inflammatory cytokines and diverse reactive oxygen and nitrogen species. These also activate signaling molecules involved in inflammation and carcinogenesis such as nuclear transcription factor (NF-kappaB), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Several chemopreventive agents act through inhibition of signaling pathways (e.g. NF-kappaB), inhibition of oxidant-generating enzymes (e.g. iNOS) and mediators of inflammation (e.g. COX-2), scavenging reactive oxygen and nitrogen species, and modulation of xenobiotic-metabolizing enzymes (especially phase II enzyme induction). Some anti-inflammatory drugs have been tested in clinical trials to prevent human cancer at several sites. Better understanding of the molecular mechanisms by which chronic inflammation increases cancer risk will lead to further development of new strategies for cancer prevention at many sites.

N-Nitrosoamide-Mediated N → O Nitroso Transfer to Alcohols with Subsequent Denitroxylation

Decomposition of certain N-benzyl-N-nitrosoamides is often accompanied by small amounts of benzaldehyde whose formation was postulated to arise from in situ formation and oxidation of benzyl alcohol. Incubation of excess benzyl alcohol with thermostable N-benzyl-N-nitrosoamides at ambient temperatures in inert solvents generates benzyl nitrite, N-benzyl amides, and benzaldehyde as the major products. Benzyl nitrite formation appears to be linked to N --> O nitroso transfer between the N-benzyl-N-nitrosoamides and benzyl alcohol, which is subject to the previously observed electronic and steric features of the acyl substituent although the former appears to play a much larger role than the latter. Benzaldehyde formation evidently arises from dehydronitrosation (denitroxylation) of the nitrite via O-N bond homolysis and H-abstraction from the resultant benzyloxy radical. Although trans-nitrosation occurs with methanol, 1 degree, 2 degree, and 3 degree alcohols, the reaction is evidently subject to steric effects at both the alpha and beta carbons of the alcohol. Additionally, carbonyl formation only occurs with 2 degrees alcohols and those that can derive resonance-stabilized carbonyls.

Reduction of nitrite to nitric oxide during ischemia protects against myocardial ischemia-reperfusion damage

Nitric oxide (NO.) is thought to protect against the damaging effects of myocardial ischemia-reperfusion injury, whereas xanthine oxidoreductase (XOR) normally causes damage through the generation of reactive oxygen species. In the heart, inorganic nitrite (NO(2)(-)) has the potential to act as an endogenous store of NO., liberated specifically during ischemia. Using a detection method that we developed, we report that under ischemic conditions both rat and human homogenized myocardium and the isolated perfused rat heart (Langendorff preparation) generate NO. from NO(2)(-) in a reaction that depends on XOR activity. Functional studies of rat hearts in the Langendorff apparatus showed that nitrite (10 and 100 microM) reduced infarct size from 47.3 +/- 2.8% (mean percent of control +/- SEM) to 17.9 +/- 4.2% and 17.4 +/- 1.0%, respectively (P < 0.001), and was associated with comparable improvements in recovery of left ventricular function. This protective effect was completely blocked by the NO. scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide (carboxy-PTIO). In summary, the generation of NO. from NO(2)(-), by XOR, protects the myocardium from ischemia-reperfusion injury. Hence, if XOR is presented with NO(2)(-) as an alternative substrate, the resultant effects of its activity may be protective, by means of its production of NO. , rather than damaging.