Human S-Nitroso Oxymyoglobin Is a Store of Vasoactive Nitric Oxide

The chemistry of hydropersulfides (RSSH) as related to possible physiological functions

Hydropersulfides (RSSH) are oxidized thiol (RSH) derivatives that have been shown to be biologically prevalent with likely important functions (along with other polysulfur compounds). The functional utility of RSSH can be gleaned from their unique chemical properties. That is, RSSH possess chemical reactivity not present in other biologically relevant sulfur species that should allow them to be used in specific ways in biology as effector/signaling molecules. For example, compared to RSH, RSSH are considered to be superior nucleophiles, reductants and metal ligands. Moreover, unlike RSH, RSSH can be either reductants/nucleophiles or oxidants/electrophiles depending on the protonated state. It has also become clear that studies related to the chemical biology and physiology of hydrogen suflide (H₂S) must also consider the effects of RSSH (and related polysulfur species) as they are biochemically linked. Herein is a discussion of the relevant chemistry of RSSH that can serve as a basis for understanding how RSSH can be used by cells to, for example, combat stresses and used in signaling. Also, discussed are some current experimental studies regarding the biological activity of RSSH that can be explained by their chemical properties.

NO and Heme Proteins: Cross-Talk between Heme and Cysteine Residues

Heme proteins are a diverse group that includes several unrelated families. Their biological function is mainly associated with the reactivity of the heme group, which-among several other reactions-can bind to and react with nitric oxide (NO) and other nitrogen compounds for their production, scavenging, and transport. The S-nitrosylation of cysteine residues, which also results from the reaction with NO and other nitrogen compounds, is a post-translational modification regulating protein activity, with direct effects on a variety of signaling pathways. Heme proteins are unique in exhibiting this dual reactivity toward NO, with reported examples of cross-reactivity between the heme and cysteine residues within the same protein. In this work, we review the literature on this interplay, with particular emphasis on heme proteins in which heme-dependent nitrosylation has been reported and those for which both heme nitrosylation and S-nitrosylation have been associated with biological functions.

The antioxidant and oxidant properties of hydropersulfides (RSSH) and polysulfide species

It has become apparent that hydrogen sulfide (H2S), hydropersulfides (RSSH) and other polysulfide species are all intimately linked biochemically. Indeed, at least some of the biological activity attributed to hydrogen sulfide (H2S) may actually be due to its conversion to RSSH and derived polysulfur species (and vice-versa). The unique chemistry associated with the hydropersulfide functional group (-SSH) predicts that it possesses possible protective properties that can help a cell contend with oxidative and/or electrophilic stress. However, since RSSH and polysulfides possess chemical properties akin to disulfides (RSSR), they can also be sources of oxidative/electrophilic stress/signaling as well. Herein are discussed the unique chemistry, possible biochemistry and the physiological implications of RSSH (and polysulfides), especially as it pertains to their putative cellular protection properties against a variety of stresses and/or as possible stressors/signaling agents themselves.

The reaction of hydropersulfides (RSSH) with S-nitrosothiols (RS-NO) and the biological/physiological implications

S-Nitrosothiol (RS-NO) generation/levels have been implicated as being important to numerous physiological and pathophysiological processes. As such, the mechanism(s) of their generation and degradation are important factors in determining their biological activity. Along with the effects on the activity of thiol proteins, RS-NOs have also been reported to be reservoirs or storage forms of nitric oxide (NO). That is, it is hypothesized that NO can be released from RS-NO at opportune times to, for example, regulate vascular tone. However, to date there are few established mechanisms that can account for facile NO release from RS-NO. Recent discovery of the biological formation and prevalence of hydropersulfides (RSSH) and their subsequent reaction with RS-NO species provides a possible route for NO release from RS-NO. Herein, it is found that RSSH is capable of reacting with RS-NO to liberate NO and that the analogous reaction using RSH is not nearly as proficient in generating NO. Moreover, computational results support the prevalence of this reaction over other possible competing processes. Finally, results of biological studies of NO-mediated vasorelaxation are consistent with the idea that RS-NO species can be degraded by RSSH to release NO.

Nitric Oxide Production and Regulation in the Teleost Cardiovascular System

Nitric Oxide (NO) is a free radical with numerous critical signaling roles in vertebrate physiology. Similar to mammals, in the teleost system the generation of sufficient amounts of NO is critical for the physiological function of the cardiovascular system. At the same time, NO amounts are strictly controlled and kept within basal levels to protect cells from NO toxicity. Changes in oxygen tension highly influence NO bioavailability and can modulate the mechanisms involved in maintaining the NO balance. While NO production and signaling appears to have general similarities with mammalian systems, the wide range of environmental adaptations made by fish, particularly with regards to differing oxygen availabilities in aquatic habitats, creates a foundation for a variety of in vivo models characterized by different implications of NO production and signaling. In this review, we present the biology of NO in the teleost cardiovascular system and summarize the mechanisms of NO production and signaling with a special emphasis on the role of globin proteins in NO metabolism.

Hydropersulfides (RSSH) and Nitric Oxide (NO) Signaling: Possible Effects on S-Nitrosothiols (RS-NO)

S-Nitrosothiol (RS-NO) formation in proteins and peptides have been implicated as factors in the etiology of many diseases and as possible regulators of thiol protein function. They have also been proposed as possible storage forms of nitric oxide (NO). However, despite their proposed functions/roles, there appears to be little consensus regarding the physiological mechanisms of RS-NO formation and degradation. Hydropersulfides (RSSH) have recently been discovered as endogenously generated species with unique reactivity. One important reaction of RSSH is with RS-NO, which leads to the degradation of RS-NO as well as the release of NO. Thus, it can be speculated that RSSH can be a factor in the regulation of steady-state RS-NO levels, and therefore may be important in RS-NO (patho)physiology. Moreover, RSSH-mediated NO release from RS-NO may be a possible mechanism allowing RS-NO to serve as a storage form of NO.

Expression and characterization of rainbow trout Oncorhynchus mykiss recombinant myoglobin

Recombinant expression system was established for rainbow trout myoglobin (Mb) considering its unique primary structure of having one unusual deletion and two cysteine residues in contrast to the other fish Mbs. The obtained recombinant Mb without His-tag showed non-cooperative thermal denaturation profile. The presence of free cysteine residue(s) in rainbow trout Mb was demonstrated by reacting with a sulfhydryl agent, 4, 4´-dithiodipyridine, which ultimately resulted in the oxidation of Mb with characteristic changes in visible absorption spectra. Besides, the recombinant Mb displayed steady peroxidase reactivity indicating in vivo roles of Mb as a reactive oxygen species scavenger. The findings of the present study indicate that the solitary rainbow trout Mb, which ultimately manifest typical secondary structure pattern and corroborate characteristic functionality, can be over expressed in recombinant system devoid of fusion tag.

Thermal denaturation and autoxidation profiles of carangid fish myoglobins

Although myoglobin (Mb) has been considered to be one of the well-characterized proteins, screening of post-genomic era databases revealed the lack of adequate information on teleost Mbs. The present study was aimed to investigate stability and functional features of Mbs from three teleosts of the same family. To unfold how primary structure influences the stability and function of proteins, Mbs were purified from the dark muscles of three carangids, namely, yellowtail, greater amberjack, and silver trevally. Thermostabilities measured by circular dichroism (CD) spectrometry revealed species-specific thermal denaturation pattern, i.e., silver trevally > yellowtail > greater amberjack Mbs. On the other hand, autoxidation rate constants of the ferrous forms of those three carangid Mbs showed positive correlation between the ferrous state of the heme iron and rising temperature. The order of autoxidation rate was in the order of greater amberjack > yellowtail > silver trevally Mbs. The finding of the present study denotes that the thermal stability is not necessarily correlated with the functional stability of carangid Mbs even though their primary structures shared high homology (84-94%).

Nitric oxide release by deoxymyoglobin nitrite reduction during cardiac ischemia: A mathematical model

Interactions between cardiac myoglobin (Mb), nitrite, and nitric oxide (NO) are vital in regulating O₂ storage, transport, and NO homeostasis. Production of NO through the reduction of endogenous myocardial nitrite by deoxygenated myoglobin has been shown to significantly reduce myocardial infarction damage and ischemic injury. We developed a mathematical model for a cardiac arteriole and surrounding myocardium to examine the hypothesis that myoglobin switches functions from being a strong NO scavenger to an NO producer via the deoxymyoglobin nitrite reductase pathway. Our results predict that under ischemic conditions of flow, blood oxygen level, and tissue pH, deoxyMb nitrite reduction significantly elevates tissue and smooth muscle cell NO. The size of the effect is consistent at different flow rates, increases with decreasing blood oxygen and tissue pH and, in extreme pathophysiological conditions, NO can even be elevated above the normoxic levels. Our simulations suggest that cardiac deoxyMb nitrite reduction is a plausible mechanism for preserving or enhancing NO levels using endogenous nitrite despite the rate-limiting O₂ levels for endothelial NO production. This NO could then be responsible for mitigating deleterious effects under ischemic conditions.

Pre-treatment with the synthetic antioxidant T-butyl bisphenol protects cerebral tissues from experimental ischemia reperfusion injury

Treatments to inhibit or repair neuronal cell damage sustained during focal ischemia/reperfusion injury in stroke are largely unavailable. We demonstrate that dietary supplementation with the antioxidant di-tert-butyl-bisphenol (BP) before injury decreases infarction and vascular complications in experimental stroke in an animal model. We confirm that BP, a synthetic polyphenol with superior radical-scavenging activity than vitamin E, crosses the blood-brain barrier and accumulates in rat brain. Supplementation with BP did not affect blood pressure or endogenous vitamin E levels in plasma or cerebral tissue. Pre-treatment with BP significantly lowered lipid, protein and thiol oxidation and decreased infarct size in animals subjected to middle cerebral artery occlusion (2 h) and reperfusion (24 h) injury. This neuroprotective action was accompanied by down-regulation of hypoxia inducible factor-1α and glucose transporter-1 mRNA levels, maintenance of neuronal tissue ATP concentration and inhibition of pro-apoptotic factors that together enhanced cerebral tissue viability after injury. That pre-treatment with BP ameliorates oxidative damage and preserves cerebral tissue during focal ischemic insult indicates that oxidative stress plays at least some causal role in promoting tissue damage in experimental stroke. The data strongly suggest that inhibition of oxidative stress through BP scavenging free radicals in vivo contributes significantly to neuroprotection. We demonstrate that pre-treatment with ditert-butyl bisphenol(Di-t-Bu-BP) inhibits lipid, protein, and total thiol oxidation and decreases caspase activation and infarct size in rats subjected to middle cerebral artery occlusion (2 h) and reperfusion (24 h) injury. These data suggest that inhibition of oxidative stress contributes significantly to neuroprotection.

Oxygen-linked S-nitrosation in fish myoglobins: a cysteine-specific tertiary allosteric effect

The discovery that cysteine (Cys) S-nitrosation of trout myoglobin (Mb) increases heme O₂ affinity has revealed a novel allosteric effect that may promote hypoxia-induced nitric oxide (NO) delivery in the trout heart and improve myocardial efficiency. To better understand this allosteric effect, we investigated the functional effects and structural origin of S-nitrosation in selected fish Mbs differing by content and position of reactive cysteine (Cys) residues. The Mbs from the Atlantic salmon and the yellowfin tuna, containing two and one reactive Cys, respectively, were S-nitrosated in vitro by reaction with Cys-NO to generate Mb-SNO to a similar yield (∼0.50 SH/heme), suggesting reaction at a specific Cys residue. As found for trout, salmon Mb showed a low O₂ affinity (P₅₀ = 2.7 torr) that was increased by S-nitrosation (P₅₀ = 1.7 torr), whereas in tuna Mb, O₂ affinity (P₅₀ = 0.9 torr) was independent of S-nitrosation. O₂ dissociation rates (k_off) of trout and salmon Mbs were not altered when Cys were in the SNO or N-ethylmaleimide (NEM) forms, suggesting that S-nitrosation should affect O₂ affinity by raising the O₂ association rate (k_on). Taken together, these results indicate that O₂-linked S-nitrosation may occur specifically at Cys107, present in salmon and trout Mb but not in tuna Mb, and that it may relieve protein constraints that limit O₂ entry to the heme pocket of the unmodified Mb by a yet unknown mechanism. UV-Vis and resonance Raman spectra of the NEM-derivative of trout Mb (functionally equivalent to Mb-SNO and not photolabile) were identical to those of the unmodified Mb, indicating that S-nitrosation does not affect the extent or nature of heme-ligand stabilization of the fully ligated protein. The importance of S-nitrosation of Mb in vivo is confirmed by the observation that Mb-SNO is present in trout hearts and that its level can be significantly reduced by anoxic conditions.

Selenium inhibits renal oxidation and inflammation but not acute kidney injury in an animal model of rhabdomyolysis

Acute kidney injury (AKI) is a manifestation of rhabdomyolysis (RM). Extracellular myoglobin accumulating in the kidney after RM promotes oxidative damage, which is implicated in AKI.

AIM

To test whether selenium (Se) supplementation diminishes AKI and improves renal function.

RESULTS

Dietary selenite increased Se in the renal cortex, as demonstrated by X-ray fluorescence microscopy. Experimental RM-stimulated AKI as judged by increased urinary protein/creatinine, clusterin, and kidney injury molecule-1 (KIM-1), decreased creatinine clearance (CCr), increased plasma urea, and damage to renal tubules. Concentrations of cholesterylester (hydro)peroxides and F₂-isoprostanes increased in plasma and renal tissues after RM, while aortic and renal cyclic guanidine monophosphate (cGMP; marker of nitric oxide (NO) bioavailability) decreased. Renal superoxide dismutase-1, phospho-P65, TNFα gene, MCP-1 protein, and the 3-chloro-tyrosine/tyrosine ratio (Cl-Tyr/Tyr; marker of neutrophil activation) all increased after RM. Dietary Se significantly decreased renal lipid oxidation, phospho-P65, TNFα gene expression, MCP-1 and Cl-Tyr/Tyr, improved NO bioavailability in aorta but not in the renal microvasculature, and inhibited proteinuria. However, CCr, plasma urea and creatinine, urinary clusterin, and histopathological assessment of AKI remained unchanged. Except for the Se++ group, renal angiotensin-receptor-1/2 gene/protein expression increased after RM with parallel increases in MEK1/2 inhibitor-sensitive MAPkinase (ERK) activity.

INNOVATION

We employed synchrotron radiation to identify Se distribution in kidneys, in addition to assessing reno-protection after RM.

CONCLUSION

Se treatment has some potential as a therapeutic for AKI as it inhibits oxidative damage and inflammation and decreases proteinuria, albeit histopathological changes to the kidney and some plasma and urinary markers of AKI remain unaffected after RM.

Expression patterns and adaptive functional diversity of vertebrate myoglobins

Recent years have witnessed a new round of research on one of the most studied proteins - myoglobin (Mb), the oxygen (O2) carrier of skeletal and heart muscle. Two major discoveries have stimulated research in this field: 1) that Mb has additional protecting functions, such as the regulation of in vivo levels of the signaling molecule nitric oxide (NO) by scavenging and generating NO during normoxia and hypoxia, respectively; and 2) that Mb in vertebrates (particularly fish) is expressed as tissue-specific isoforms in other tissues than heart and skeletal muscle, such as vessel endothelium, liver and brain, as found in cyprinid fish. Furthermore, Mb has also been found to protect against oxidative stress after hypoxia and reoxygenation and to undergo allosteric, O2-linked S-nitrosation, as in rainbow trout. Overall, the emerging evidence, particularly from fish species, indicates that Mb fulfills a broader array of physiological functions in a wider range of different tissues than hitherto appreciated. This new knowledge helps to better understand how variations in Mb structure and function may correlate with differences in animals' lifestyles and hypoxia-tolerance. This review integrates old and new results on Mb expression patterns and functional properties amongst vertebrates and discusses how these may relate to adaptive variations in different species. This article is part of a special issue entitled: Oxygen Binding and Sensing Proteins.

Assessment of the functional diversity of human myoglobin

Myoglobin is presumably the most studied protein in biology. Its functional properties as a dioxygen storage and facilitator of dioxygen transport are widely acknowledged. Experimental evidence also implicates an essential role for myoglobin in the heart in regulating nitric oxide homeostasis. Under normoxia, oxygenated myoglobin can scavenge excessive nitric oxide, while under hypoxia, deoxygenated myoglobin can reduce nitrite, an oxidative product of nitric oxide, to bioactive nitric oxide. Myoglobin-driven nitrite reduction can protect the heart from ischemia and reperfusion injury. While horse and mouse myoglobin have been previously described to reduce nitrite under these conditions, a comparable activity has not been detected in human myoglobin. We here show that human myoglobin is a fully functional nitrite reductase. To study the role of human myoglobin for nitric oxide homeostasis we used repeated photometric wavelength scans and chemiluminescence based experiments. The results revealed that oxygenated human myoglobin reacts with nitrite-derived nitric oxide to form ferric myoglobin and that deoxygenated human myoglobin acts as a nitrite reductase in vitro and in situ. Rates of both nitric oxide scavenging and nitrite reduction were significantly higher in human compared to horse myoglobin. These data extend the existing knowledge about the functional properties of human myoglobin and are the basis for further translational studies towards the importance of myoglobin for nitric oxide metabolism in humans.

Functional differentiation of myoglobin isoforms in hypoxia-tolerant carp indicates tissue-specific protective roles

Because of a recent whole genome duplication, the hypoxia-tolerant common carp and goldfish are the only vertebrates known to possess two myoglobin (Mb) paralogs. One of these, Mb1, occurs in oxidative muscle but also in several other tissues, including capillary endothelial cells, whereas the other, Mb2, is a unique isoform specific to brain neurons. To help understand the functional roles of these diverged isoforms in the tolerance to severe hypoxia in the carp, we have compared their O(2) equilibria, carbon monoxide (CO) and O(2) binding kinetics, thiol S-nitrosation, nitrite reductase activities, and peroxidase activities. Mb1 has O(2) affinity and nitrite reductase activity comparable to most vertebrate muscle Mbs, consistent with established roles for Mbs in O(2) storage/delivery and in maintaining nitric oxide (NO) homeostasis during hypoxia. Both Mb1 and Mb2 can be S-nitrosated to similar extent, but without oxygenation-linked allosteric control. When compared with Mb1, Mb2 displays faster O(2) and CO kinetics, a lower O(2) affinity, and is slower at converting nitrite into NO. Mb2 is therefore unlikely to be primarily involved in either O(2) supply to mitochondria or the generation of NO from nitrite during hypoxia. However, Mb2 proved to be significantly faster at eliminating H(2)O(2,) a major in vivo reactive oxygen species (ROS), suggesting that this diverged Mb isoform may have a specific protective role against H(2)O(2) in the carp brain. This property might be of particular significance during reoxygenation following extended periods of hypoxia, when production of H(2)O(2) and other ROS is highest.

Role of superoxide-nitric oxide interactions in the accelerated age-related loss of muscle mass in mice lacking Cu,Zn superoxide dismutase

Mice lacking Cu,Zn superoxide dismutase (SOD1) show accelerated, age-related loss of muscle mass. Lack of SOD1 may lead to increased superoxide, reduced nitric oxide (NO), and increased peroxynitrite, each of which could initiate muscle fiber loss. Single muscle fibers from flexor digitorum brevis of wild-type (WT) and Sod1^−/− mice were loaded with NO-sensitive (4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate, DAF-FM) and superoxide-sensitive (dihydroethidium, DHE) probes. Gastrocnemius muscles were analyzed for SOD enzymes, nitric oxide synthases (NOS), and 3-nitrotyrosine (3-NT) content. A lack of SOD1 did not increase superoxide availability at rest because no increase in ethidium or 2-hydroxyethidium (2-HE) formation from DHE was seen in fibers from Sod1^−/− mice compared with those from WT mice. Fibers from Sod1^−/− mice had decreased NO availability (decreased DAF-FM fluorescence), increased 3-NT in muscle proteins indicating increased peroxynitrite formation and increased content of peroxiredoxin V (a peroxynitrite reductase), compared with WT mice. Muscle fibers from Sod1^−/− mice showed substantially reduced generation of superoxide in response to contractions compared with fibers from WT mice. Inhibition of NOS did not affect DHE oxidation in fibers from WT or Sod1^−/− mice at rest or during contractions, but transgenic mice overexpressing nNOS showed increased DAF-FM fluorescence and reduced DHE oxidation in resting muscle fibers. It is concluded that formation of peroxynitrite in muscle fibers is a major effect of lack of SOD1 in Sod1^−/− mice and may contribute to fiber loss in this model, and that NO regulates superoxide availability and peroxynitrite formation in muscle.

The synthetic polyphenol tert-butyl-bisphenol inhibits myoglobin-induced dysfunction in cultured kidney epithelial cells

Abstract Rhabdomyolysis caused by severe burn releases extracellular myoglobin (Mb) that accumulates in the kidney and urine (maximum [Mb] approximately 50 microM) (termed myoglobinuria). Extracellular Mb can be a pro-oxidant. This study cultured Madin-Darby-canine-kidney-Type-II (MDCK II) cells in the presence of Mb and tested whether supplementation with a synthetic tert-butyl-polyphenol (tert-butyl-bisphenol; t-BP) protects these renal cells from dysfunction. In the absence of t-BP, cells exposed to 0-100 microM Mb for 24 h showed a dose-dependent decrease in ATP and the total thiol (TSH) redox status without loss of viability. Gene expression of superoxide dismutases-1/2, haemoxygenase-1 and tumour necrosis factor increased and receptor-mediated endocytosis of transferrin and monolayer permeability decreased significantly. Supplementation with t-BP before Mb-insult maintained ATP and the TSH redox status, diminished antioxidant/pro-inflammatory gene responses, enhanced monolayer permissiveness and restored transferrin uptake. Overall, bolstering the total antioxidant capacity of the kidney may protect against oxidative stress induced by experimental myoglobinuria.

Allosteric modulation by S-nitrosation in the low-O₂ affinity myoglobin from rainbow trout

Myoglobin (Mb) serves in the facilitated diffusion and storage of O₂ in heart and skeletal muscle, where it also regulates O₂ consumption via nitric oxide (NO) scavenging or generation. S-nitrosation at reactive cysteines may generate S-nitroso Mb (Mb-SNO) and contribute further to NO homeostasis. In being a monomer, Mb is commonly believed to lack allosteric control of heme reactivity. Here, we test whether in rainbow trout, a fast swimmer living in well-aerated water, the Mb-O₂ affinity is regulated by ionic cofactors and S-nitrosation. O₂ equilibria showed the lowest O₂ affinity ever reported among vertebrate Mbs (P₅₀ = 4.92 ± 0.29 mmHg, 25°C), a small overall heat of oxygenation (ΔH = -12.03 kcal/mol O₂), and no effect of chloride, pH, or lactate. Although the reaction with 4,4'-dithiodipyridine (4-PDS) showed 1.3-1.9 accessible thiols per heme, the reaction of Mb with S-nitroso cysteine (Cys-NO) and S-nitrosoglutathione (GSNO) to generate Mb-SNO yielded ∼0.3-0.6 and ∼0.1 SNO/heme, respectively, suggesting S-nitrosation at only one cysteine (likely Cys¹⁰). At ∼60% S-nitrosation, trout Mb-SNO showed a higher O₂ affinity (P₅₀ = 2.23 ± 0.19 mmHg, 20°C) than unmodified Mb (3.36 ± 0.11 mmHg, 20°C). Total SNO levels measured by chemiluminescence in trout myocardial preparations decreased after hypoxia, but not significantly, indicating that transnitrosation reactions between thiols may occur in vivo. Our data reveal a novel, S-nitrosation-dependent allosteric mechanism in this low-affinity Mb that may contribute to targeted O₂-linked SNO release in the hypoxic fish heart and be of importance in preserving cardiac function during intense exercise.

Site-specific hypochlorous acid-induced oxidation of recombinant human myoglobin affects specific amino acid residues and the rate of cytochrome b5-mediated heme reduction

Myeloperoxidase catalyzes the reaction of chloride ions with H(2)O(2) to yield hypochlorous acid (HOCl), which can damage proteins. Human myoglobin (HMb) differs from other Mbs by the presence of a cysteine residue at position 110 (Cys110). This study has (i) compared wild-type and a Cys110Ala variant of HMb to assess the influence of Cys110 on HOCl-induced amino acid modification and (ii) determined whether HOCl oxidation of HMb affects the rate of ferric heme reduction by cytochrome b(5). For wild-type HMb (HOCl:Mb ratio of 5:1 mol:mol), Cys110 was preferentially oxidized to a homodimeric or cysteic acid product-sulfenic/sulfinic acids were not detected. At a HOCl:Mb ratio 10:1 mol:mol, methionine (Met) oxidation was detected, and this was enhanced in the Cys110Ala variant. Tryptophan (Trp) oxidation was detected only in the Cys110Ala variant at the highest HOCl dose tested, with oxidation susceptibility following the order Cys>Met>Trp. Tyrosine chlorination was evident only in reactions between HOCl and the Cys110Ala variant and at a longer incubation time (24 h), consistent with the formation via chlorine-transfer reactions from preformed chloramines. HOCl-mediated oxidation of wild-type HMb resulted in a dose-dependent decrease in the observed rate constant for ferric heme reduction (approx two-fold at HOCl:Mb of 10:1 mol:mol). These data indicate that Cys110 influences the oxidation of HMb by HOCl and that oxidation of Cys, Met, and Trp residues is associated with a decrease in the one-electron reduction of ferric HMb by other proteins; such heme-Fe(3+) reduction is critical to the maintenance of function as an oxygen storage protein in tissues.

Nitric oxide stimulates myoglobin gene and protein expression in vascular smooth muscle

Mb (myoglobin) is a haemoprotein present in cardiac, skeletal and smooth muscle and is primarily responsible for the storage and 'facilitated transfer' of molecular oxygen from the cell membrane to mitochondria. Also, Mb plays a role in regulating *NO (nitric oxide) homoeostasis through (i) binding *NO (Mb-NO complex); (ii) oxidation of *NO to nitrate; and (iii) formation of vasoactive S-nitroso-Mb [Rayner, B.S., Wu, B.-J., Raftery, M., Stocker, R. and Witting, P.K. (2005) J. Biol. Chem. 280, 9985-9993]. Pathological *NO concentrations affect mitochondrial function and decrease cell viability through inducing apoptosis. Treatment of cultured rat VSMCs (vascular smooth muscle cells) with cumulative doses (0.1, 1 or 10 microM) of *NO from the donors diethylamineNONOate or spermineNONOate (N-[2-aminoethyl]-N-[2-hydroxy-3-nitrosohydrazine]-1,2-ethelenediamine) yielded a time-dependent increase in Mb gene expression. Concomitant transcriptional activation increased the concentration of Mb within cultured rat or primary human VSMCs as judged by Western blot analysis and indirect immunofluorescence microscopy. Cell viability did not decrease in these cells at the *NO doses tested. Importantly, sub-culturing isolated rat aortic segments for 7 days in the presence of L-arginine at 37 degrees C stimulated *NO production with a parallel increase in Mb in the underlying VSMCs. Overall, exposure of VSMCs (either in cell culture or intact vessels) to pathological *NO promotes an up-regulation of the Mb gene and protein, suggesting a feedback relationship between *NO and Mb that regulates the concentration of the potent cell signalling molecule in the vessel wall, similar to the role haemoglobin plays in the vessel lumen.

Diverse cell-specific expression of myoglobin isoforms in brain, kidney, gill and liver of the hypoxia-tolerant carp and zebrafish

Myoglobin (Mb) is famous as a muscle-specific protein--yet the common carp expresses the gene (cMb1) encoding this protein in a range of non-muscle tissues and also expresses a novel isoform (cMb2) in the brain. Using a homologous antibody and riboprobes, we have established the relative amounts and cellular sites of non-muscle Mb expression in different tissues. The amounts of carp myoglobin (cMb) in supernatants of different tissues were just 0.4-0.7% relative to that of heart supernatants and were upregulated by two-to-four fold in liver, gill and brain following 5 days of hypoxic treatment. Brain exhibited both cMb proteins in western analysis, whereas all other tissues had only cMb1. We have also identified cells expressing cMb protein and cMb mRNA using immunohistology and RNA in situ hybridisation (RNA-ISH), respectively. Mb was strongly expressed throughout all cardiac myocytes and a subset of skeletal muscle fibres, whereas it was restricted to a small range of specific cell types in each of the non-muscle tissues. These include pillar and epithelial cells in secondary gill lamellae, hepatocytes, some neurones, and tubular epithelial cells in the kidney. Capillaries and small blood vessels in all tissues exhibited Mb expression within vascular endothelial cells. The cMb2 riboprobe located expression to a subset of neurones but not to endothelial cells. In zebrafish, which possesses only one Mb gene, a similar expression pattern of Mb protein and mRNA was observed. This establishes a surprisingly cell-specific distribution of Mb within non-muscle tissues in both carp and zebrafish, where it probably plays an important role in the regulation of microvascular, renal and brain function.

Myocyte specific overexpression of myoglobin impairs angiogenesis after hind-limb ischemia

OBJECTIVE

In preclinical models of peripheral arterial disease the angiogenic response is typically robust, though it can be impaired in conditions such as hypercholesterolemia and diabetes where the endothelium is dysfunctional. Myoglobin (Mb) is expressed exclusively in striated muscle cells. We hypothesized that myocyte specific overexpression of myoglobin attenuates ischemia-induced angiogenesis even in the presence of normal endothelium.

METHODS AND RESULTS

Mb overexpressing transgenic (MbTg, n=59) and wild-type (WT, n=56) C57Bl/6 mice underwent unilateral femoral artery ligation/excision. Perfusion recovery was monitored using Laser Doppler. Ischemia-induced changes in muscle were assessed by protein and immunohistochemistry assays. Nitrite/nitrate and protein-bound NO, and vasoreactivity was measured. Vasoreactivity was similar between MbTg and WT. In ischemic muscle, at d14 postligation, MbTg increased VEGF-A, and activated eNOS the same as WT mice but nitrate/nitrite were reduced whereas protein-bound NO was higher. MbTg had attenuated perfusion recovery at d21 (0.37+/-0.03 versus 0.47+/-0.02, P<0.05), d28 (0.40+/-0.03 versus 0.50+/-0.04, P<0.05), greater limb necrosis (65.2% versus 15%, P<0.001), a lower capillary density, and greater apoptosis versus WT.

CONCLUSIONS

Increased Mb expression in myocytes attenuates angiogenesis after hind-limb ischemia by binding NO and reducing its bioavailability. Myoglobin can modulate the angiogenic response to ischemia even in the setting of normal endothelium.

Reductive gas-phase chemiluminescence and flow injection analysis for measurement of the nitric oxide pool in biological matrices

There is growing evidence for nitric oxide (NO.) being involved in cell signaling and pathology. Much effort has been made to elucidate and characterize the different biochemical reaction pathways of NO.in vivo. However, a major obstacle in assessing the significance of nitrosated species and oxidized metabolites often remains: a reliable analytical technique for the detection of NO. in complex biological matrices. This chapter presents refined methodologies, such as chemiluminescence detection and flow injection analysis, compared with adequate sample processing procedures to reliably quantify and assess the circulating and resident NO(.) pool, consisting of nitrite, nitrate, nitroso, and nitrosylated species.

Hydrogen peroxide promotes endothelial dysfunction by stimulating multiple sources of superoxide anion radical production and decreasing nitric oxide bioavailability

Hydrogen peroxide (H(2)O(2)) is an oxidant implicated in cell signalling and various pathologies, yet relatively little is known about its impact on endothelial cell function. Herein we studied the functional and biochemical changes in aortic vessels and cultured porcine aortic endothelial cells (PAEC) exposed to H(2)O(2). Exposure of aortic rings to 25 or 50 microM, but not 10 microM, H(2)O(2) for 60 min prior to constriction significantly decreased subsequent relaxation in response to acetylcholine (ACh), but not the nitric oxide ((.)NO) donor sodium nitroprusside. Treatment of PAEC with 50 microM H(2)O(2) significantly decreased ACh-induced accumulation of (.)NO, as measured with a (.)NO-selective electrode, yet such treatment increased nitric oxide synthase activity approximately 3-fold, as assessed by conversion of L-arginine to L-citrulline. Decreased (.)NO bioavailability was reflected in decreased cellular cGMP content, associated with increased superoxide anion radical (O(2)(-.)), and overcome by addition of polyethylene glycol superoxide dismutase. Increased cellular O(2)(-.) production was inhibited by allopurinol, diphenyliodonium and rotenone in an additive manner. The results show that exposure of endothelial cells to H(2)O(2) decreases the bioavailability of agonist-induced (.)NO as a result of increased production of O(2)(-.) likely derived from xanthine oxidase, NADPH-oxidase and mitochondria. These processes could contribute to H(2)O(2)-induced vascular dysfunction that may be relevant under conditions of oxidative stress such as inflammation.

Nitric oxide regulation of microvascular oxygen

The role of nitric oxide (NO) as a highly diffusible free radical gaseous vasodilator is intrinsically linked to the control of blood flow and oxygen (O(2)) delivery to tissue. NO also is involved in regulating mitochondrial O(2) metabolism, growth of new blood vessels, and blood oxygenation through control of respiratory ventilation. Hemoglobin and myoglobin may help to conserve NO for subsequent release of a NO-related vasoactive species under hypoxic conditions. NO has a major role in regulating microvascular O(2), and dysfunctional NO signaling is associated with the pathogenesis of metabolic and cardiovascular diseases.

Distribution, adaptation and physiological meaning of thiols from vertebrate hemoglobins

In the present review, the sequences of hemoglobins (Hb) of 267 adult vertebrate species belonging to eight major vertebrate taxa are examined for the presence and location of cysteinyl residues in an attempt at correlation with their ecophysiology. Essentially, all vertebrates have surface cysteinyl residues in Hb molecules whereby their thiol groups may become highly reactive. Thiol-rich Hbs may display eight or more thiols per tetramer. In vertebrates so far examined, the cysteinyl residues occur in 44 different sequence positions in alpha chains and 41 positions in beta chains. Most of them are conservatively located and occur in only a few positions in Teleostei, Aves and Mammalia, whereas they are dispersed in Amphibia. The internal cysteinyl residue alpha104 is ubiquitous in vertebrates. Residue beta93 is highly conserved in reptiles, birds and mammals. The number of cysteine residues per tetramer with solvent access varies in vertebrates, mammalians and bony fish having the lowest number of external residues, whereas nearly all external cysteine residues in Aves and Lepidosauria are of the surface crevice type. In cartilaginous fish, amphibians, Crocodylidae and fresh water turtles, a substantial portion of the solvent accessible thiols are of the totally external type. Recent evidence shows that some Hb thiol groups are highly reactive and undergo extensive and reversible S-thiolation, and that they may be implicated in interorgan redox equilibrium processes. Participation of thiol groups in nitric oxide ((*)NO) metabolism has also been proved. The evidence argues for a new physiologically relevant role for Hb via involvement in free radical and antioxidant metabolism.

S-nitrosylation-induced conformational change in blackfin tuna myoglobin

S-nitrosylation is a post-translational protein modification that can alter the function of a variety of proteins. Despite the growing wealth of information that this modification may have important functional consequences, little is known about the structure of the moiety or its effect on protein tertiary structure. Here we report high-resolution x-ray crystal structures of S-nitrosylated and unmodified blackfin tuna myoglobin, which demonstrate that in vitro S-nitrosylation of this protein at the surface-exposed Cys-10 directly causes a reversible conformational change by "wedging" apart a helix and loop. Furthermore, we have demonstrated in solution and in a single crystal that reduction of the S-nitrosylated myoglobin with dithionite results in NO cleavage from the sulfur of Cys-10 and rebinding to the reduced heme iron, showing the reversibility of both the modification and the conformational changes. Finally, we report the 0.95-A structure of ferrous nitrosyl myoglobin, which provides an accurate structural view of the NO coordination geometry in the context of a globin heme pocket.

Oxidative stress in myocardial ischaemia reperfusion injury: a renewed focus on a long-standing area of heart research

Advances in the treatment of coronary artery disease have seen a significant drop in mortality and morbidity particularly amongst patients with acute myocardial infarction (MI). In particular, percutaneous trans-luminal balloon angioplasty (PTCA) with stenting to re-open atherosclerotic coronary arteries has yielded marked improvement in clinical outcome for patients with acute MI. Furthermore, with the advent of drug-eluting stents occurrence rates for coronary artery restenosis, one common clinical problem associated with angioplasty and stent deployment, have declined markedly. However, coronary restenosis in diabetic patients remains an on-going problem. The success of drug-eluting stents has seen a renewed focus on myocardial ischaemia reperfusion (IR) injury as this represents one area of research where many questions remain unanswered. In particular, the relationship between myocardial IR injury and decreased myocardial micro-vasculature re-flow post PTCA (that ultimately leads to poor clinical outcome and myocardial damage/dysfunction) is one area of research with the potential to decrease current complication rates further in patients suffering myocardial IR injury sustained during MI. This review discusses the role for oxidative stress, oxidant source(s) and both gene regulation and stem-cell therapy as potential strategic targets in the ischaemic myocardium, with the ultimate aim of providing significant cardioprotection in the setting of acute MI.