The functional nitrite reductase activity of the heme-globins

Functional metalloenzymes based on myoglobin and neuroglobin that exploit covalent interactions

Globins, such as myoglobin (Mb) and neuroglobin (Ngb), are ideal protein scaffolds for the design of functional metalloenzymes. To date, numerous approaches have been developed for enzyme design. This review presents a summary of the progress made in the design of functional metalloenzymes based on Mb and Ngb, with a focus on the exploitation of covalent interactions, including coordination bonds and covalent modifications. These include the construction of a metal-binding site, the incorporation of a non-native metal cofactor, the formation of Cys/Tyr-heme covalent links, and the design of disulfide bonds, as well as other Cys-covalent modifications. As exemplified by recent studies from our group and others, the designed metalloenzymes have potential applications in biocatalysis and bioconversions. Furthermore, we discuss the current trends in the design of functional metalloenzymes and highlight the importance of covalent interactions in the design of functional metalloenzymes.

Influence of acute dietary nitrate supplementation on oxygen delivery/consumption and critical impulse during maximal effort forearm exercise in males: a randomized crossover trial

Beetroot juice supplementation (BRJ) should increase nitric oxide bioavailability under conditions of muscle deoxygenation and acidosis that are a normal consequence of the maximal effort exercise test used to identify forearm critical impulse. We hypothesized BRJ would improve oxygen delivery:demand matching and forearm critical impulse performance. Healthy males (20.8 ± 2.4 years) participated in a randomized crossover trial between October 2017 and May 2018 (Queen's University, Kingston, ON). Participants completed 10 min of rhythmic maximal effort forearm handgrip exercise 2.5 h post placebo (PL) vs. BRJ (9 completed PL/BRJ vs. 4 completed BRJ/PL) within a 2 week period. Data are presented as mean ± SD. There was a main effect of drink (PL > BRJ) for oxygen extraction (P = 0.033, ηp2 = 0.351) and oxygen consumption/force (P = 0.017, ηp2 = 0.417). There was a drink × time interaction (PL > BRJ) for oxygen consumption/force (P = 0.035, ηp2 = 0.216) between 75 and 360 s (1.25-6 min) from exercise onset. BRJ did not influence oxygen delivery (P = 0.953, ηp2 = 0.000), oxygen consumption (P = 0.064, ηp2 = 0.278), metabolites ((lactate) (P = 0.196, ηp2 = 0.135), pH (P = 0.759, ηp2 = 0.008)) or power-duration performance parameters (critical impulse (P = 0.379, d = 0.253), W' (P = 0.733, d = 0.097)). BRJ during all-out handgrip exercise does not influence oxygen delivery or exercise performance. Oxygen cost of contraction with BRJ is reduced as contraction impulse is declining during maximal effort exercise resulting in less oxygen extraction.

Effects of Acute Beetroot Juice Supplementation and Exercise on Cardiovascular Function in Healthy Men in Preliminary Study: A Randomized, Double-Blinded, Placebo-Controlled, and Crossover Trial

Nitrate-rich beetroot juice (NRBRJ) can potentially enhance exercise performance and improve cardiovascular function, leading to an increased use of NRBRJ over the years. However, the combined effects of NRBRJ supplementation and exercise on cardiovascular function remain unclear. Therefore, this study compared cardiovascular function responses to submaximal exercise with either placebo (PLA) or NRBRJ supplementation in healthy men. Twelve healthy men (aged 25.2 ± 2.3 years) completed the 30-min submaximal cycle ergometer exercise trials corresponding to 70% maximal heart rate (HRmax) with either PLA or NRBRJ supplementation in a random order. The mean exercise load, heart rate (HR), stroke volume (SV), cardiac output (CO), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and total peripheral resistance (TPR) were measured during exercise. The brachial-ankle pulse wave velocity (baPWV) and flow-mediated dilation (FMD) were measured before and after exercise. NRBRJ supplementation was more effective than PLA in increasing the mean exercise load and decreasing DBP and MAP during submaximal exercise. Furthermore, baPWV decreased in the NRBRJ trial and was considerably lower after exercise in the NRBRJ-supplemented group than in the PLA-supplemented group. FMD significantly increased in the PLA and NRBRJ trials; however, NRBRJ supplementation demonstrated a significantly higher FMD before and after exercise than PLA supplementation. In conclusion, acute NRBRJ supplementation and exercise were more effective than PLA supplementation and exercise in improving aerobic exercise capacity and cardiovascular function in healthy men.

The Nitrate-Nitrite-Nitric Oxide Pathway: Potential Role in Mitigating Oxidative Stress in Hypertensive Disorders of Pregnancy

Hypertensive diseases of pregnancy (HDPs) represent a global clinical challenge, affecting 5-10% of women and leading to complications for both maternal well-being and fetal development. At the heart of these complications is endothelial dysfunction, with oxidative stress emerging as a pivotal causative factor. The reduction in nitric oxide (NO) bioavailability is a vital indicator of this dysfunction, culminating in blood pressure dysregulation. In the therapeutic context, although antihypertensive medications are commonly used, they come with inherent concerns related to maternal-fetal safety, and a percentage of women do not respond to these therapies. Therefore, alternative strategies that directly address the pathophysiology of HDPs are required. This article focuses on the potential of the nitrate-nitrite-NO pathway, abundantly present in dark leafy greens and beetroot, as an alternative approach to treating HDPs. The objective of this review is to discuss the prospective antioxidant role of nitrate. We hope our discussion paves the way for using nitrate to improve endothelial dysfunction and control oxidative stress, offering a potential therapy for managing HDPs.

The circularly permuted globin domain of androglobin exhibits atypical heme stabilization and nitric oxide interaction

In the decade since the discovery of androglobin, a multi-domain hemoglobin of metazoans associated with ciliogenesis and spermatogenesis, there has been little advance in the knowledge of the biochemical and structural properties of this unusual member of the hemoglobin superfamily. Using a method for aligning remote homologues, coupled with molecular modelling and molecular dynamics, we have identified a novel structural alignment to other hemoglobins. This has led to the first stable recombinant expression and characterization of the circularly permuted globin domain. Exceptional for eukaryotic globins is that a tyrosine takes the place of the highly conserved phenylalanine in the CD1 position, a critical point in stabilizing the heme. A disulfide bond, similar to that found in neuroglobin, forms a closed loop around the heme pocket, taking the place of androglobin's missing CD loop and further supporting the heme pocket structure. Highly unusual in the globin superfamily is that the heme iron binds nitric oxide as a five-coordinate complex similar to other heme proteins that have nitric oxide storage functions. With rapid autoxidation and high nitrite reductase activity, the globin appears to be more tailored toward nitric oxide homeostasis or buffering. The use of our multi-template profile alignment method to yield the first biochemical characterisation of the circularly permuted globin domain of androglobin expands our knowledge of the fundamental functioning of this elusive protein and provides a pathway to better define the link between the biochemical traits of androglobin with proposed physiological functions.

Influence of acute dietary nitrate supplementation on oxygen delivery/consumption and limit of tolerance during progressive forearm exercise in men: a randomized crossover trial

Beetroot juice (BRJ) supplementation increases nitric oxide bioavailability with hypoxia and acidosis, characteristics of high-intensity exercise. We investigated whether BRJ improved forearm oxygen delivery:demand matching in an intensity-dependent manner. Healthy men (21 ± 2.5 years) participated in a randomized crossover trial between October 2017 and May 2018 (Queen's University, Kingston, ON, Canada). Participants completed a forearm incremental exercise test to limit of tolerance (IET-LOT) 2.5 h post placebo (PL) versus BRJ (2 completed PL/BRJ vs. 9 completed BRJ/PL) within a 2-week period. Data are presented as mean ± standard deviation. There was a significant main effect of drink (PL < BRJ; P = 0.042, ηp2 = 0.385) and drink × intensity interaction for arteriovenous oxygen difference (PL < BRJ; P = 0.03; ηp2= 0.197; 20%-50% and 90% LOT). BRJ did not influence oxygen delivery (P = 0.893, ηp2 = 0.002), forearm blood flow (P = 0.589, ηp2 = 0.03) (forearm vascular conductance (P = 0.262, ηp2 = 0.124), mean arterial pressure (P = 0.254,ηp2 = 0.128)), oxygen consumption (P = 0.194, ηp2 = 0.179) or LOT (P = 0.432, d = 0.247). In healthy men, BRJ did not improve forearm oxygen delivery (vasodilatory or pressor response) during IET-LOT. Increased arteriovenous oxygen difference at submaximal intensities did not significantly influence oxygen consumption or performance across the entire range of forearm exercise intensities. This study adds to the growing body of evidence that BRJ does not influence small muscle mass blood flow in humans regardless of exercise intensity.

Safety of dietary nitrate supplementation by calcium nitrate for finishing pigs as measured by methemoglobin and serum and tissue nitrate levels

Nitrate supplementation has been studied as a beneficial constituent of the human diet, particularly for its effects on vascular health through vasodilation. Recent studies have focused on the benefits of nitrate supplementation in animals, especially in swine. Up to 1,200 mg/kg dietary nitrate supplementation from Ca nitrate was beneficial in farrowing and lactating sows and their offspring, and up to 6,000 mg/kg supplemental nitrate showed no adverse health effects in sows or piglets. Controlled study data evaluating the safety of nitrate supplementation to growing swine of any weight class is scant. Therefore, an experiment was conducted to test the hypothesis that increased inclusion rates of dietary nitrate through the addition of Ca nitrate in diets would not influence concentrations of nitrate or nitrite in serum and tissue, nor blood hemoglobin and methemoglobin. Forty-eight individually housed pigs (initial weight 119.1 ± 5.3 kg) were randomly allotted to four dietary treatments containing 0, 500, 1,000, or 2,000 mg/kg dietary nitrate and fed experimental diets for 28 d. Growth performance was not influenced (P > 0.10) by dietary treatment. The most sensitive safety endpoint, methemoglobin, did not change (P > 0.10) with dietary nitrate exposure up to 2,000 mg/kg. Serum and tissue nitrate and nitrite levels, myoglobin, and hemoglobin were not adversely affected (P > 0.10). Total myoglobin in the loin linearly increased (P < 0.05) with greater dietary nitrate in the diet, which is correlated with the red color of meat. This work established the safety of up to 2,000 mg/kg dietary nitrate from Ca nitrate as an ingredient in food for finishing pigs.

How Nitric Oxide Hindered the Search for Hemoglobin-Based Oxygen Carriers as Human Blood Substitutes

The search for a clinically affordable substitute of human blood for transfusion is still an unmet need of modern society. More than 50 years of research on acellular hemoglobin (Hb)-based oxygen carriers (HBOC) have not yet produced a single formulation able to carry oxygen to hemorrhage-challenged tissues without compromising the body's functions. Of the several bottlenecks encountered, the high reactivity of acellular Hb with circulating nitric oxide (NO) is particularly arduous to overcome because of the NO-scavenging effect, which causes life-threatening side effects as vasoconstriction, inflammation, coagulopathies, and redox imbalance. The purpose of this manuscript is not to add a review of candidate HBOC formulations but to focus on the biochemical and physiological events that underly NO scavenging by acellular Hb. To this purpose, we examine the differential chemistry of the reaction of NO with erythrocyte and acellular Hb, the NO signaling paths in physiological and HBOC-challenged situations, and the protein engineering tools that are predicted to modulate the NO-scavenging effect. A better understanding of two mechanisms linked to the NO reactivity of acellular Hb, the nitrosylated Hb and the nitrite reductase hypotheses, may become essential to focus HBOC research toward clinical targets.

Mechanisms and physiological function of daily haemoglobin oxidation rhythms in red blood cells

Cellular circadian rhythms confer temporal organisation upon physiology that is fundamental to human health. Rhythms are present in red blood cells (RBCs), the most abundant cell type in the body, but their physiological function is poorly understood. Here, we present a novel biochemical assay for haemoglobin (Hb) oxidation status which relies on a redox-sensitive covalent haem-Hb linkage that forms during SDS-mediated cell lysis. Formation of this linkage is lowest when ferrous Hb is oxidised, in the form of ferric metHb. Daily haemoglobin oxidation rhythms are observed in mouse and human RBCs cultured in vitro, or taken from humans in vivo, and are unaffected by mutations that affect circadian rhythms in nucleated cells. These rhythms correlate with daily rhythms in core body temperature, with temperature lowest when metHb levels are highest. Raising metHb levels with dietary sodium nitrite can further decrease daytime core body temperature in mice via nitric oxide (NO) signalling. These results extend our molecular understanding of RBC circadian rhythms and suggest they contribute to the regulation of body temperature.

Ligand Control of Dinitrosyl Iron Complexes for Selective Superoxide-Mediated Nitric Oxide Monooxygenation and Superoxide-Dioxygen Interconversion

Through nitrosylation of [Fe-S] proteins, or the chelatable iron pool, a dinitrosyl iron unit (DNIU) [Fe(NO)2] embedded in the form of low-molecular-weight/protein-bound dinitrosyl iron complexes (DNICs) was discovered as a metallocofactor assembled under inflammatory conditions with elevated levels of nitric oxide (NO) and superoxide (O2-). In an attempt to gain biomimetic insights into the unexplored transformations of the DNIU under inflammation, we investigated the reactivity toward O2- by a series of DNICs [(NO)2Fe(μ-MePyr)2Fe(NO)2] (1) and [(NO)2Fe(μ-SEt)2Fe(NO)2] (3). During the superoxide-induced conversion of DNIC 1 into DNIC [(K-18-crown-6-ether)2(NO2)][Fe(μ-MePyr)4(μ-O)2(Fe(NO)2)4] (2-K-crown) and a [Fe3+(MePyr)x(NO2)y(O)z]n adduct, stoichiometric NO monooxygenation yielding NO2- occurs without the transient formation of peroxynitrite-derived •OH/•NO2 species. To study the isoelectronic reaction of O2(g) and one-electron-reduced DNIC 1, a DNIC featuring an electronically localized {Fe(NO)2}9-{Fe(NO)2}10 electronic structure, [K-18-crown-6-ether][(NO)2Fe(μ-MePyr)2Fe(NO)2] (1-red), was successfully synthesized and characterized. Oxygenation of DNIC 1-red leads to the similar assembly of DNIC 2-K-crown, of which the electronic structure is best described as paramagnetic with weak antiferromagnetic coupling among the four S = 1/2 {FeIII(NO-)2}9 units and S = 5/2 Fe3+ center. In contrast to DNICs 1 and 1-red, DNICs 3 and [K-18-crown-6-ether][(NO)2Fe(μ-SEt)2Fe(NO)2] (3-red) display a reversible equilibrium of "3 + O2- ⇋ 3-red + O2(g)", which is ascribed to the covalent [Fe(μ-SEt)2Fe] core and redox-active [Fe(NO)2] unit. Based on this study, the supporting/bridging ligands in dinuclear DNIC 1/3 (or 1-red/3-red) control the selective monooxygenation of NO and redox interconversion between O2- and O2 during reaction with O2- (or O2).

Myoglobin in Brown Adipose Tissue: A Multifaceted Player in Thermogenesis

Brown adipose tissue (BAT) plays an important role in energy homeostasis by generating heat from chemical energy via uncoupled oxidative phosphorylation. Besides its high mitochondrial content and its exclusive expression of the uncoupling protein 1, another key feature of BAT is the high expression of myoglobin (MB), a heme-containing protein that typically binds oxygen, thereby facilitating the diffusion of the gas from cell membranes to mitochondria of muscle cells. In addition, MB also modulates nitric oxide (NO•) pools and can bind C16 and C18 fatty acids, which indicates a role in lipid metabolism. Recent studies in humans and mice implicated MB present in BAT in the regulation of lipid droplet morphology and fatty acid shuttling and composition, as well as mitochondrial oxidative metabolism. These functions suggest that MB plays an essential role in BAT energy metabolism and thermogenesis. In this review, we will discuss in detail the possible physiological roles played by MB in BAT thermogenesis along with the potential underlying molecular mechanisms and focus on the question of how BAT-MB expression is regulated and, in turn, how this globin regulates mitochondrial, lipid, and NO• metabolism. Finally, we present potential MB-mediated approaches to augment energy metabolism, which ultimately could help tackle different metabolic disorders.

Recent insights into mechanisms of hypoxia-induced vasodilatation in the human brain

The cerebral vasculature manages oxygen delivery by adjusting arterial blood in-flow in the face of reductions in oxygen availability. Hypoxic cerebral vasodilatation, and the associated hypoxic cerebral blood flow reactivity, involve many vascular, erythrocytic and cerebral tissue mechanisms that mediate elevations in cerebral blood flow via micro- and macrovascular dilatation. This contemporary review focuses on in vivo human work - with reference to seminal preclinical work where necessary - on hypoxic cerebrovascular reactivity, particularly where recent advancements have been made. We provide updates with the following information: in humans, hypoxic cerebral vasodilatation is partially mediated via a - likely non-obligatory - combination of: (1) nitric oxide synthases, (2) deoxygenation-coupled S-nitrosothiols, (3) potassium channel-related vascular smooth muscle hyperpolarization, and (4) prostaglandin mechanisms with some contribution from an interrelationship with reactive oxygen species. And finally, we discuss the fact that, due to the engagement of deoxyhaemoglobin-related mechanisms, reductions in O2 content via haemoglobin per se seem to account for ∼50% of that seen with hypoxic cerebral vasodilatation during hypoxaemia. We further highlight the issue that methodological impediments challenge the complete elucidation of hypoxic cerebral reactivity mechanisms in vivo in healthy humans. Future research is needed to confirm recent advancements and to reconcile human and animal findings. Further investigations are also required to extend these findings to address questions of sex-, heredity-, age-, and disease-related differences. The final step is to then ultimately translate understanding of these mechanisms into actionable, targetable pathways for the prevention and treatment of cerebral vascular dysfunction and cerebral hypoxic brain injury.

Modulation of red blood cell nitric oxide synthase phosphorylation in the quiescent and exercising human forearm

In vitro investigations demonstrate that human erythrocytes synthesize nitric oxide via a functional isoform of endothelial nitric oxide synthase (NOS) (RBC-NOS). We tested the hypothesis that phosphorylation of RBC-NOS at serine residue 1177 (RBC-NOS1177) would be amplified in blood draining-active skeletal muscle. Furthermore, given hypoxemia modulates local blood flow and thus shear stress, and nitric oxide availability, we performed duplicate experiments under normoxia and hypoxia. Nine healthy volunteers performed rhythmic handgrip exercise at 60% of individualized maximal workload for 3.5 min while breathing room air (normoxia) and after being titrated to an arterial oxygen saturation ≈80% (hypoxemia). We measured brachial artery blood flow by high-resolution duplex ultrasound, while continuously monitoring vascular conductance and mean arterial pressure using finger photoplethysmography. Blood was sampled during the final 30 s of each stage from an indwelling cannula. Blood viscosity was measured to facilitate calculation of accurate shear stresses. Erythrocytes were assessed for levels of phosphorylated RBC-NOS1177 and cellular deformability from blood collected at rest and during exercise. Forearm exercise increased blood flow, vascular conductance, and vascular shear stress, which coincided with a 2.7 ± 0.6-fold increase in RBC-NOS1177 phosphorylation (P < 0.0001) and increased cellular deformability (P < 0.0001) under normoxia. When compared with normoxia, hypoxemia elevated vascular conductance and shear stress (P < 0.05) at rest, while cellular deformability (P < 0.01) and RBC-NOS1177 phosphorylation (P < 0.01) increased. Hypoxemic exercise elicited further increases in vascular conductance, shear stress, and cell deformability (P < 0.0001), although a subject-specific response in RBC-NOS1177 phosphorylation was observed. Our data yield novel insights into the manner that hemodynamic force and oxygen tension modulate RBC-NOS in vivo.

The effect of pH and nitrite on the haem pocket of GLB-33, a globin-coupled neuronal transmembrane receptor of Caenorhabditis elegans

Out of the 34 globins in Caenorhabditis elegans, GLB-33 is a putative globin-coupled transmembrane receptor with a yet unknown function. The globin domain (GD) contains a particularly hydrophobic haem pocket, that rapidly oxidizes to a low-spin hydroxide-ligated haem state at physiological pH. Moreover, the GD has one of the fastest nitrite reductase activity ever reported for globins. Here, we use a combination of electronic circular dichroism, resonance Raman and electron paramagnetic resonance (EPR) spectroscopy with mass spectrometry to study the pH dependence of the ferric form of the recombinantly over-expressed GD in the presence and absence of nitrite. The competitive binding of nitrite and hydroxide is examined as well as nitrite-induced haem modifications at acidic pH. Comparison of the spectroscopic results with data from other haem proteins allows to deduce the important effect of Arg at position E10 in stabilization of exogenous ligands. Furthermore, continuous-wave and pulsed EPR indicate that ligation of nitrite occurs in a nitrito mode at pH 5.0 and above. At pH 4.0, an additional formation of a nitro-bound haem form is observed along with fast formation of a nitri-globin.

Red Blood Cell Metabolism In Vivo and In Vitro

Red blood cells (RBC) are the most abundant cell in the human body, with a central role in oxygen transport and its delivery to tissues. However, omics technologies recently revealed the unanticipated complexity of the RBC proteome and metabolome, paving the way for a reinterpretation of the mechanisms by which RBC metabolism regulates systems biology beyond oxygen transport. The new data and analytical tools also informed the dissection of the changes that RBCs undergo during refrigerated storage under blood bank conditions, a logistic necessity that makes >100 million units available for life-saving transfusions every year worldwide. In this narrative review, we summarize the last decade of advances in the field of RBC metabolism in vivo and in the blood bank in vitro, a narrative largely influenced by the authors' own journeys in this field. We hope that this review will stimulate further research in this interesting and medically important area or, at least, serve as a testament to our fascination with this simple, yet complex, cell.

Transport of nitrite from large arteries modulates regional blood flow during stress and exercise

Background

Acute cardiovascular stress increases systemic wall shear stress (WSS)-a frictional force exerted by the flow of blood on vessel walls-which raises plasma nitrite concentration due to enhanced endothelial nitric oxide synthase (eNOS) activity. Upstream eNOS inhibition modulates distal perfusion, and autonomic stress increases both the consumption and vasodilatory effects of endogenous nitrite. Plasma nitrite maintains vascular homeostasis during exercise and disruption of nitrite bioavailability can lead to intermittent claudication.

Hypothesis

During acute cardiovascular stress or strenuous exercise, we hypothesize enhanced production of nitric oxide (NO) by vascular endothelial cells raises nitrite concentrations in near-wall layers of flowing blood, resulting in cumulative NO concentrations in downstream arterioles sufficient for vasodilation.

Confirmation and implications

Utilizing a multiscale model of nitrite transport in bifurcating arteries, we tested the hypothesis for femoral artery flow under resting and exercised states of cardiovascular stress. Results indicate intravascular transport of nitrite from upstream endothelium could result in vasodilator-active levels of nitrite in downstream resistance vessels. The hypothesis could be confirmed utilizing artery-on-a-chip technology to measure NO production rates directly and help validate numerical model predictions. Further characterization of this mechanism may improve our understanding of symptomatic peripheral artery occlusive disease and exercise physiology.

Protective role of nitric oxide donors on endothelium in ischemia-reperfusion injury: a meta-analysis of randomized controlled trials

BACKGROUND

Decreased bioavailability of nitric oxide (NO) under hypoxic conditions can lead to endothelial dysfunction. NO supplementation may protect endothelial function in ischemia-reperfusion (IR) injury. Therefore, a meta-analysis of randomized controlled trials (RCTs) was performed to verify the protective effect of NO donors on endothelium in IR injury.

METHODS

Medline, Embase, Cochrane Library, and Web of Science databases were searched from inception to April 1, 2023. The specific inclusion criteria were as follows: (1) RCTs; (2) trials comparing NO donors with placebo control groups; and (3) trials reporting the effects of these interventions on vascular endothelial functional outcomes in IR injury. Random-effects models were used to assess pooled effect sizes, which were expressed as standardized mean differences (SMD).

RESULTS

Seven studies satisfied the inclusion criteria and consisted of a total of 149 participants. NO donors were protective of endothelial function in IR injury (SMD: - 1.60; 95% confidence interval [CI]: - 2.33, - 0.88, P < 0.0001; heterogeneity [I² = 66%, P = 0.001]). Results of the subgroup analysis showed the following: absence of protective effect of NO donor use following ischemia on endothelial function in IR injury - 1.78 (95% CI: - 2.50, - 1.07) and loss of protective effect on endothelial function after prolonged NO donor use - 0.89 (95% CI: - 2.06, 0.28).

CONCLUSION

The short-period use of NO donors before the onset of ischemia can protect endothelial function in IR injury.

Nitrate and Nitrite Metabolism in Aging Rats: A Comparative Study

Nitric oxide (NO) (co)regulates many physiological processes in the body. Its short-lived free radicals force synthesis in situ and on-demand, without storage possibility. Local oxygen availability determines the origin of NO-either by synthesis by nitric oxide synthases (NOS) or by the reduction of nitrate to nitrite to NO by nitrate/nitrite reductases. The existence of nitrate reservoirs, mainly in skeletal muscle, assures the local and systemic availability of NO. Aging is accompanied by changes in metabolic pathways, leading to a decrease in NO availability. We explored age-related changes in various rat organs and tissues. We found differences in nitrate and nitrite contents in tissues of old and young rats at baseline levels, with nitrate levels being generally higher and nitrite levels being generally lower in old rats. However, there were no differences in the levels of nitrate-transporting proteins and nitrate reductase between old and young rats, with the exception of in the eye. Increased dietary nitrate led to significantly higher nitrate enrichment in the majority of old rat organs compared to young rats, suggesting that the nitrate reduction pathway is not affected by aging. We hypothesize that age-related NO accessibility changes originate either from the NOS pathway or from changes in NO downstream signaling (sGC/PDE5). Both possibilities need further investigation.

Myoglobinemia, Peripheral Arterial Disease, and Patient Mortality

BACKGROUND

Peripheral arterial disease (PAD) causes leg muscle damage due to inadequate perfusion and increases cardiovascular events and mortality 2- to 3-fold. It is unclear if PAD is a biomarker for high-risk cardiovascular disease or if skeletal muscle injury harms arterial health. The objective of this work is to test if serum myoglobin levels (myoglobinemia) are a marker of PAD, and if so, whether myoglobin impairs vascular health.

STUDY DESIGN

Patient blood samples were collected from PAD and control (no PAD) patients and interrogated for myoglobin concentrations and nitric oxide bioavailability. Patient mortality over time was captured from the medical record. Myoglobin activity was tested on endothelial cells and arterial function.

RESULTS

Myoglobin is a biomarker for symptomatic PAD and was inversely related to nitric oxide bioavailability; 200 ng/mL myoglobin in vitro increased endothelial cell permeability in vitro and decreased nitrate bioavailability. Ex vivo, 100 ng/mL myoglobin increased vascular tone in naive murine aortas approximately 1.5 times, impairing absolute vessel relaxation. In vivo, we demonstrated that myoglobinemia caused impaired flow-mediated dilation in a porcine model. Patients presenting with myoglobin levels of 100 ng/mL or greater had significantly more deaths than those with myoglobin levels of less than 100 ng/mL.

CONCLUSIONS

Using a combination of patient data, in vitro, ex vivo, and in vivo testing, we found that myoglobin is a biomarker for symptomatic PAD and a potent regulator of arterial health that can increase vascular tone, increase vascular permeability, and cause endothelial dysfunction, all of which may contribute to the vulnerability of PAD patients to cardiovascular events and death.

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.

How abundant are superoxide and hydrogen peroxide in the vasculature lumen, how far can they reach?

Paracrine superoxide (O₂^•−) and hydrogen peroxide (H₂O₂) signaling critically depends on these substances' concentrations, half-lives and transport ranges in extracellular media. Here we estimated these parameters for the lumen of human capillaries, arterioles and arteries using reaction-diffusion-advection models. These models considered O₂^•− and H₂O₂ production by endothelial cells and uptake by erythrocytes and endothelial cells, O₂^•− dismutation, O₂^•− and H₂O₂ diffusion and advection by the blood flow. Results show that in this environment O₂^•− and H₂O₂ have half-lives <60. ms and <40. ms, respectively, the former determined by the plasma SOD3 activity, the latter by clearance by endothelial cells and erythrocytes. H₂O₂ concentrations do not exceed the 10 nM scale. Maximal O₂^•− concentrations near vessel walls exceed H₂O₂'s several-fold when the latter results solely from O₂^•− dismutation. Cytosolic dismutation of inflowing O₂^•− may thus significantly contribute to H₂O₂ delivery to cells. O₂^•− concentrations near vessel walls decay to 50% of maximum 12 μm downstream from O₂^•− production sites. H₂O₂ concentrations in capillaries decay to 50% of maximum 22 μm (6.0 μm) downstream from O₂^•− (H₂O₂) production sites. Near arterioles' (arteries') walls, they decay by 50% within 6.0 μm (4. μm) of H₂O₂ production sites. However, they reach maximal values 50 μm (24 μm) downstream from O₂^•− production sites and decrease by 50% over 650 μm (500 μm). Arterial/olar endothelial cells might thus signal over a mm downstream through O₂^•−-derived H₂O₂, though this requires nM-sensitive H₂O₂ transduction mechanisms.

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Physiological local H₂O₂ concentrations in vasculature lumen are up to 10's of μM.

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H₂O₂ transport range in capillaries is just ≈20 μm.

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Faster blood flow in arteri(ol)es transports O₂^•−-derived H₂O₂ over 100's of μm

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Similar H₂O₂ abundances and distribution near arterioles' and arteries' walls, likewise for O₂^•−.

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Inflowing O₂^•− may significantly feed H₂O₂ to the cytosol of endothelial cells

Redox and spectroscopic properties of mammalian nitrite reductase-like hemoproteins

Besides the canonical pathway of L-arginine oxidation to produce nitric oxide (NO) in vivo, the nitrate-nitrite-NO pathway has been widely accepted as another source for circulating NO in mammals, especially under hypoxia. To date, there have been at least ten heme-containing nitrite reductase-like proteins discovered in mammals with activities mainly identified in vitro, including four globins (hemoglobin, myoglobin, neuroglobin (Ngb), cytoglobin (Cygb)), three mitochondrial respiratory chain enzymes (cytochrome c oxidase, cytochrome bc₁, cytochrome c), and three other heme proteins (endothelial nitric oxide synthase, cytochrome P450 and indoleamine 2,3-dioxygenase 1 (IDO1)). The pathophysiological functions of these proteins are closely related to their redox and spectroscopic properties, as well as their protein structure, although the physiological roles of Ngb, Cygb and IDO1 remain unclear. So far, comprehensive summaries of the redox and spectroscopic properties of these nitrite reductase-like hemoproteins are still lacking. In this review, we have mainly summarized the published data on the application of ultraviolet-visible, electron paramagnetic resonance, circular dichroism and resonance Raman spectroscopies, and X-ray crystallography in studying nitrite reductase-like activity of these 10 proteins, in order to sort out the relationships among enzymatic function, structure and spectroscopic characterization, which might help in understanding their roles in redox biology and medicine.

Endothelial alpha globin is a nitrite reductase

Resistance artery vasodilation in response to hypoxia is essential for matching tissue oxygen and demand. In hypoxia, erythrocytic hemoglobin tetramers produce nitric oxide through nitrite reduction. We hypothesized that the alpha subunit of hemoglobin expressed in endothelium also facilitates nitrite reduction proximal to smooth muscle. Here, we create two mouse strains to test this: an endothelial-specific alpha globin knockout (EC Hba1Δ/Δ) and another with an alpha globin allele mutated to prevent alpha globin's inhibitory interaction with endothelial nitric oxide synthase (Hba1WT/Δ36-39). The EC Hba1Δ/Δ mice had significantly decreased exercise capacity and intracellular nitrite consumption in hypoxic conditions, an effect absent in Hba1WT/Δ36-39 mice. Hypoxia-induced vasodilation is significantly decreased in arteries from EC Hba1Δ/Δ, but not Hba1WT/Δ36-39 mice. Hypoxia also does not lower blood pressure in EC Hba1Δ/Δ mice. We conclude the presence of alpha globin in resistance artery endothelium acts as a nitrite reductase providing local nitric oxide in response to hypoxia.

Stimulation of Akt Phosphorylation and Glucose Transport by Metalloporphyrins with Peroxynitrite Decomposition Catalytic Activity

Iron porphyrin molecules such as hemin and iron(III) 4,4′,4″,4‴-(porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid) (FeTBAP) have previously been shown to influence insulin signaling and glucose metabolism. We undertook this study to determine whether a catalytic action of iron porphyrin compounds would be related to their stimulation of insulin signaling and glucose uptake in C2C12 myotubes. FeTBAP did not display nitrite reductase activity or alter protein S-nitrosylation in myotubes, eliminating this as a candidate mode by which FeTBAP could act. FeTBAP displayed peroxynitrite decomposition catalytic activity in vitro. Additionally, in myotubes FeTBAP decreased protein nitration. The peroxynitrite decomposition catalyst Fe(III)5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato chloride (FeTPPS) also decreased protein nitration in myotubes, but the iron porphyrin Fe(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachlorideporphyrin pentachloride (FeTMPyP) did not. FeTBAP and FeTPPS, but not FeTMPyP, showed in vitro peroxidase activity. Further, FeTBAP and FeTPPs, but not FeTMPyP, increased Akt phosphorylation and stimulated glucose uptake in myotubes. These findings suggest that iron porphyrin compounds with both peroxynitrite decomposition activity and peroxidase activity can stimulate insulin signaling and glucose transport in skeletal muscle cells.

Piezo1 regulates shear-dependent nitric oxide production in human erythrocytes

Mature circulating red blood cells (RBC) are classically viewed as passive participants in circulatory function, given erythroblasts eject their organelles during maturation. Endogenous production of nitric oxide (NO) and its effects are of particular significance; however, the integration between RBC sensation of the local environment and subsequent activation of mechano-sensitive signaling networks that generate NO remain poorly understood. The present study investigated endogenous NO-production via the RBC-specific nitric oxide synthase-isoform (RBC-NOS), connecting membrane strain with intracellular enzymatic processes. Isolated RBC were obtained from apparently healthy humans. Intracellular NO was compared at rest and following shear (cellular deformation) using semi-quantitative fluorescent imaging. Concurrently, RBC-NOS phosphorylation at its Serine¹¹⁷⁷ (ser¹¹⁷⁷) residue was measured. The contribution of cellular deformation to shear-induced NO-production in RBC was determined by rigidifying RBC with the thiol-oxidizing agent diamide; rigid RBC exhibited significantly impaired (up to 80%) capacity to generate NO via RBC-NOS during shear. Standardizing membrane strain of rigid RBC by applying increased shear did not normalize NO-production, or RBC-NOS activation. Calcium-imaging with Fluo-4 revealed that diamide-treated RBC exhibited a 42%-impairment in Piezo1-mediated calcium-movement when compared with untreated RBC. Pharmacological inhibition of Piezo1 with GsMTx4 during shear inhibited RBC-NOS activation in untreated RBC, while Piezo1-activation with Yoda1 in the absence of shear stimulated RBC-NOS activation. Collectively, a novel, mechanically-activated signaling pathway in mature RBC is described. Opening of Piezo1 and subsequent influx of calcium appears to be required for endogenous production of NO in response to mechanical shear, which is accompanied by phosphorylation of RBC-NOS at ser¹¹⁷⁷.

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.

Tri-iodide and vanadium chloride based chemiluminescent methods for quantification of nitrogen oxides

Nitric Oxide (NO) is an important signaling molecule that plays roles in controlling vascular tone, hemostasis, host defense, and many other physiological functions. Low NO bioavailability contributes to pathology and NO administration has therapeutic potential in a variety of diseases. Thus, accurate measurements of NO bioavailability and reactivity are critical. Due to its short lifetime in vivo and many in vitro conditions, NO bioavailability and reactivity are often best determined by measuring NO congeners and metabolites that are more stable. Chemiluminescence-based detection of NO following chemical reduction of these compounds using the tri-iodide and vanadium chloride methods have been widely used in a variety of clinical and laboratory studies. In this review, we describe these methods used to detect nitrite, nitrate, nitrosothiols and other species and discuss limitations and proper controls.

Tissue-Engineered Constructions in Biophysics, Neurology and Other Fields and Branches of Medicine

This paper describes the gangliopexy method, a method for creating a new center of local neurohumoral regulation, based on the formation of new connections discovered between the nervous system and the vascular system. The prospects for the development of this method are studied. At the same time, novel concepts about the cycles of nitric oxide and the superoxide anion radical are introduced. A possible role of these cycles is examined in the protection of cells and the body as a whole against oxidative and nitrosative stress, which develops when (in 5-30% of cases) destructive changes in the displaced ganglion lead to vascular complications and an increased risk of mortality. Mechanisms that can protect nerve cells, prevent the development of destructive changes in these cells and reduce the risk of mortality are also investigated.

Features of Metabolic Support of Physical Performance in Highly Trained Cross-Country Skiers of Different Qualifications during Physical Activity at Maximum Load

The purpose of our study was to identify the features of metabolic regulation in highly trained cross-country skiers of different qualifications at different stages of the maximum load test. We examined 124 highly trained cross-country skiers (male, ages 17–24). The group consisted of two subgroups based on their competition performance: 61 nonelite athletes (Group I) and 63 elite athletes (group II), who were current members of the national team of the Komi Republic and Russia. The bicycle ergometer test was performed by using the OxyconPro system (Erich Jaeger, Hoechberg, Germany). All the examined athletes performed the exercise test on a cycle ergometer “until exhaustion”. The results of our research indicate that the studied groups of athletes with high, but different levels of sports qualifications are a convenient model for studying the molecular mechanisms of adaptation to physical loads of maximum intensity. Athletes of higher qualifications reveal additional adaptive mechanisms of metabolic regulation, which is manifested in the independence of serum lactate indicators under conditions of submaximal and maximum power from maximal oxygen uptake, and they have an NO-dependent mechanism for regulating lactate levels during aerobic exercise, including work at the anaerobic threshold.

Conformational dynamics of myoglobin in the presence of vitamin B12: A spectroscopic and in silico investigation

Myoglobin is an essential transport protein of heart and muscle tissues that acts as a local oxygen reservoir and a marker in different diseased conditions. On the other hand, Vitamin B12 is a vital nutrient that helps synthesize red blood cells, DNA, and proteins. To understand the ability of vitamin B12 to bind to the excess of myoglobin produced in the body under certain conditions (muscle injuries, severe trauma, etc.), it is essential to dig into the interaction between them. Therefore, the present study reports the binding interaction of vitamin B12 and myoglobin employing different spectroscopic and computational methods. The myoglobin's intrinsic fluorescence is quenched by vitamin B12 via static nature as observed from steady-state as well as time-resolved fluorescence measurements. The microenvironment of myoglobin's tryptophan residue gets affected, but there is no change observed in its α-helical content by vitamin B12 as seen from synchronous fluorescence and circular dichroism measurements. The probable binding of vitamin B12 on myoglobin was elucidated through molecular docking, and the interaction stability was studied by molecular dynamics simulation. The determination of vitamin B12's affinity to myoglobin and its effect on the conformational transitions of myoglobin might afford valuable insight for clinical pharmacology.

Endogenous Hemoprotein-Dependent Signaling Pathways of Nitric Oxide and Nitrite

Interdisciplinary research at the interface of chemistry, physiology, and biomedicine have uncovered pivotal roles of nitric oxide (NO) as a signaling molecule that regulates vascular tone, platelet aggregation, and other pathways relevant to human health and disease. Heme is central to physiological NO signaling, serving as the active site for canonical NO biosynthesis in nitric oxide synthase (NOS) enzymes and as the highly selective NO binding site in the soluble guanylyl cyclase receptor. Outside of the primary NOS-dependent biosynthetic pathway, other hemoproteins, including hemoglobin and myoglobin, generate NO via the reduction of nitrite. This auxiliary hemoprotein reaction unlocks a "second axis" of NO signaling in which nitrite serves as a stable NO reservoir. In this Forum Article, we highlight these NO-dependent physiological pathways and examine complex chemical and biochemical reactions that govern NO and nitrite signaling in vivo. We focus on hemoprotein-dependent reaction pathways that generate and consume NO in the presence of nitrite and consider intermediate nitrogen oxides, including NO2, N2O3, and S-nitrosothiols, that may facilitate nitrite-based signaling in blood vessels and tissues. We also discuss emergent therapeutic strategies that leverage our understanding of these key reaction pathways to target NO signaling and treat a wide range of diseases.

Identification of the Protein Glycation Sites in Human Myoglobin as Rapidly Induced by d-Ribose

Protein glycation is an important protein post-translational modification and is one of the main pathogenesis of diabetic angiopathy. Other than glycated hemoglobin, the protein glycation of other globins such as myoglobin (Mb) is less studied. The protein glycation of human Mb with ribose has not been reported, and the glycation sites in the Mb remain unknown. This article reports that d-ribose undergoes rapid protein glycation of human myoglobin (HMb) at lysine residues (K34, K87, K56, and K147) on the protein surface, as identified by ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). Moreover, glycation by d-ribose at these sites slightly decreased the rate of the met heme (Fe^III) in reaction with H₂O₂ to form a ferryl heme (Fe^IV=O). This study provides valuable insight into the protein glycation by d-ribose and provides a foundation for studying the structure and function of glycated heme proteins.

Cysteine residues in the fourth zinc finger are important for activation of the nitric oxide-inducible transcription factor Fzf1 in the yeast Saccharomyces cerevisiae

Nitric oxide (NO) is a ubiquitous signaling molecule in various organisms. In the yeast Saccharomyces cerevisiae, NO functions in both cell protection and cell death, depending on its concentration. Thus, it is important for yeast cells to strictly regulate NO concentration. The transcription factor Fzf1, containing five zinc fingers, is reportedly important for NO homeostasis by regulating the expression of the YHB1 gene, which encodes NO dioxygenase. However, the mechanism by which NO activates Fzf1 is still unclear. In this study, we showed that NO activated Fzf1 specifically at the protein level by RT-qPCR and Western blotting. Our further transcriptional analyses indicated that cysteine residues in the fourth zinc finger (ZF4) are required for the NO-responsive activation of Fzf1. Additionally, the present results suggest that ZF4 is important for the protein stability of Fzf1. From these results, we proposed possible mechanisms underlying Fzf1 activation.

Protective Effects of Topical Application of Nitrite on Testicular Ischemia-Reperfusion Injury in Rats

Testicular torsion is a urologic emergency induced by torsion of the spermatic cord, interrupting blood circulation to the testis. Therapeutic options for testicular torsion, except surgical restoration of testis, are rarely applied in clinical practice. This study, therefore, investigated whether topical application of nitrite (NO₂⁻) is beneficial in tissue damage due to testicular ischemia-reperfusion (I/R) injury in rats. Pubertal Sprague-Dawley rats were assigned to seven groups: group A, sham-operated control group; group B, I/R with no treatment; groups C, D, and E, I/R followed by treatment with three different doses of nitrite; group F, I/R followed by administration of nitrite and a NO scavenger, C-PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt); and group G, I/R followed by administration of nitrate (NO₃⁻). Unilateral testicular ischemia was maintained for 5 h, followed by reperfusion for 24 h. Nitrite and nitrate were topically administered before reperfusion. Compared to group A, germ cell apoptosis, oxidative stress, antioxidant enzymatic function, and lipid peroxidation were significantly increased, along with abnormal morphology and impaired spermatogenesis in group B (P < 0.05). In contrast, testicular damage was generally attenuated in the nitrite treatment groups due to a reduction in superoxide and peroxynitrite levels and the inhibition of caspase-3-dependent apoptosis (P < 0.05 vs. group B). These therapeutic effects of nitrite-derived NO were suppressed after injection of C-PTIO, which showed in group F. Taken together, our results demonstrate that topical application of nitrite may be one of the therapeutic strategies for testicular ischemia-reperfusion injury.

One-electron reduction triggered nitric oxide release for ischemia-reperfusion protection

Nitric oxide donors (NODs) are indispensable in biological research and disease treatment. NODs had been utilized to treat cardiovascular diseases in clinic and many others are under trial. Thiols are typically required for these donors to release NO. Yet, their mechanism is complex and often lead to resistance. Herein, we reported that N-nitrosated electron-deficient dyes are capable of NO release with one-electron reduction. A fluorophore is generated simultaneously, whose fluorescence is harnessed to monitor the profile of NO release. Through electrochemical and spectral studies, NOD f3 was found to exhibit good biocompatibility and high reduction efficiency and its potentials in cell-protection in oxygen and glucose deprivation (OGD) models were showcased with endothelial cells. This work aims at offering a new approach to design reduction-triggered NOD, which have therapeutic potentials in ischemia-reperfusion.

Nitric Oxide Production in Professional Skiers During Physical Activity at Maximum Load

The purpose of this study is to assess the production of nitric oxide in professional cross-country skiers with normotensive and hypertensive responses to physical activity at maximum load. The observation group included professional cross-country skiers (22.2 ± 7.1 years, = 107) who were current members of the national team of the Komi Republic. All the examined athletes performed the exercise test on a cycle ergometer “until exhaustion.” The following parameters were determined for each participant while they were sitting at rest, while at their anaerobic threshold level, during peak load, and during the recovery period (5th min): systolic blood pressure, diastolic blood pressure, heart rate, and the level of stable nitric oxide metabolites (nitrites, nitrates) in capillary blood samples. According to the blood pressure results, the cross-country skiers were divided into two groups. Group I included athletes with a normotensive response to stress. Group II was composed of individuals with a hypertensive response to stress. During the performance of the test “until exhaustion,” a significant (p < 0.05) increase in the amount of stable metabolites of nitric oxide was observed in the group of athletes with a normotensive response to the load compared with the group with a hypertensive response to the load. In athletes with a normotensive reaction to the load during exercise at maximum load and in the early recovery period, nitrate was prioritized in the regulation of vascular tone. The exercise test on a cycle ergometer “until exhaustion,” combined with the assessment of the levels of stable nitric oxide metabolites in plasma, can be considered a test for the early diagnosis of endothelial dysfunction in professional athletes.

The analytical method to identify the nitrogen source for nitric oxide synthesis

Nitric oxide (NO) is a ubiquitous signaling molecule synthesized from various nitrogen sources. An analytical method to identify a nitrogen source for NO generation was developed using liquid chromatography with tandem mass spectrometry in combination with stable isotope labeling. Our method successfully detected the 15N-labeled NO-containing compound generated from 15N-labeled substrate nitrite in vitro and in vivo.

Multi-Omics Analysis Provides Novel Insight into Immuno-Physiological Pathways and Development of Thermal Resistance in Rainbow Trout Exposed to Acute Thermal Stress

In recent years, poikilothermic animals such as fish have increasingly been exposed to stressful high-temperature environments due to global warming. However, systemic changes in fish under thermal stress are not fully understood yet at both the transcriptome and proteome level. Therefore, the objective of this study was to investigate the immuno-physiological responses of fish under extreme thermal stress through integrated multi-omics analysis. Trout were exposed to acute thermal stress by raising water temperature from 15 to 25 °C within 30 min. Head-kidney and plasma samples were collected and used for RNA sequencing and two-dimensional gel electrophoresis. Gene enrichment analysis was performed: differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) were identified to interpret the multi-omics results and identify the relevant biological processes through pathway analysis. Thousands of DEGs and 49 DEPs were identified in fish exposed to thermal stress. Most of these genes and proteins were highly linked to DNA replication, protein processing in the endoplasmic reticulum, cell signaling and structure, glycolysis activation, complement-associated hemolysis, processing of released free hemoglobin, and thrombosis and hypertension/vasoconstriction. Notably, we found that immune disorders mediated by the complement system may trigger hemolysis in thermally stressed fish, which could have serious consequences such as ferroptosis and thrombosis. However, antagonistic activities that decrease cell-free hemoglobin, heme, and iron might be involved in alleviating the side effects of thermally induced immuno-physiological disorders. These factors may represent the major thermal resistance traits that allow fish to overcome extreme thermal stress. Our findings, based on integration of multi-omics data from transcriptomics and proteomics analyses, provide novel insight into the pathogenesis of acute thermal stress and temperature-linked epizootics.

The dual roles of a V(III) centre for substrate binding and oxygen atom abstraction; nitrite reduction mediated by a V(III) complex

A V(iii) complex bearing a tris(thiolato)phoshine derivative mediates the reduction of nitrite without the assistance of external protons or oxophilic substrates. The metal site plays dual roles for nitrite binding and deoxygenation. The reaction is monitored by spectroscopy combined with isotopic labeling experiments. The formed product, a {VNO}4 species, is isolated and characterized.

Inorganic nitrite bioactivation and role in physiological signaling and therapeutics

The bioactivation of inorganic nitrite refers to the conversion of otherwise 'inert' nitrite to the diatomic signaling molecule nitric oxide (NO), which plays important roles in human physiology and disease, notably in the regulation of vascular tone and blood flow. While the most well-known sources of NO are the nitric oxide synthase (NOS) enzymes, another source of NO is the nitrate-nitrite-NO pathway, whereby nitrite (obtained from reduction of dietary nitrate) is further reduced to form NO. The past few decades have seen extensive study of the mechanisms of NO generation through nitrate and nitrite bioactivation, as well as growing appreciation of the contribution of this pathway to NO signaling in vivo. This review, prepared for the volume 400 celebration issue of Biological Chemistry, summarizes some of the key reactions of the nitrate-nitrite-NO pathway such as reduction, disproportionation, dehydration, and oxidative denitrosylation, as well as current evidence for the contribution of the pathway to human cardiovascular physiology. Finally, ongoing efforts to develop novel medical therapies for multifarious conditions, especially those related to pathologic vasoconstriction and ischemia/reperfusion injury, are also explored.

A Novel Mechanism for Nitrosative Stress Tolerance Dependent on GTP Cyclohydrolase II Activity Involved in Riboflavin Synthesis of Yeast

The biological functions of nitric oxide (NO) depend on its concentration, and excessive levels of NO induce various harmful situations known as nitrosative stress. Therefore, organisms possess many kinds of strategies to regulate the intracellular NO concentration and/or to detoxify excess NO. Here, we used genetic screening to identify a novel nitrosative stress tolerance gene, RIB1, encoding GTP cyclohydrolase II (GTPCH2), which catalyzes the first step in riboflavin biosynthesis. Our further analyses demonstrated that the GTPCH2 enzymatic activity of Rib1 is essential for RIB1-dependent nitrosative stress tolerance, but that riboflavin itself is not required for this tolerance. Furthermore, the reaction mixture of a recombinant purified Rib1 was shown to quench NO or its derivatives, even though formate or pyrophosphate, which are byproducts of the Rib1 reaction, did not, suggesting that the reaction product of Rib1, 2,5-diamino-6-(5-phospo-d-ribosylamino)-pyrimidin-4(3 H)-one (DARP), scavenges NO or its derivatives. Finally, it was revealed that 2,4,5-triamino-1H-pyrimidin-6-one, which is identical to a pyrimidine moiety of DARP, scavenged NO or its derivatives, suggesting that DARP reacts with N₂O₃ generated via its pyrimidine moiety.

Emerging perspectives on cytoglobin, beyond NO dioxygenase and peroxidase

Cytoglobin is an evolutionary ancient hemoglobin with poor functional annotation. Rather than constrained to penta coordination, cytoglobin's heme iron may exist either as a penta or hexacoordinated arrangement when exposed to different intracellular environments. Two cysteine residues at the surface of the protein form an intramolecular disulfide bond that regulates iron coordination, ligand binding, and peroxidase activity. Overall, biochemical results do not support a role for cytoglobin as a direct antioxidant enzyme that scavenges hydrogen peroxide because the rate of the reaction of cytoglobin with hydrogen peroxide is several orders of magnitude slower than metal and thiol-based peroxidases. Thus, alternative substrates such as fatty acids have been suggested and regulation of nitric oxide bioavailability through nitric oxide dioxygenase and nitrite reductase activities has received experimental support. Cytoglobin is broadly expressed in connective, muscle, and nervous tissues. Rational for differential cellular distribution is poorly understood but inducibility in response to hypoxia is one of the most established features of cytoglobin expression with regulation through the transcription factor hypoxia-inducible factor (HIF). Phenotypic characterization of cytoglobin deletion in the mouse have indicated broad changes that include a heightened inflammatory response and fibrosis, increase tumor burden, cardiovascular dysfunction, and hallmarks of senescence. Some of these changes might be reversed upon inhibition of nitric oxide synthase. However, subcellular and molecular interactions have been seldom characterized. In addition, specific molecular mechanisms of action are still lacking. We speculate that cytoglobin functionality will extend beyond nitric oxide handling and will have to encompass indirect regulatory antioxidant and redox sensing functions.

Mechanisms of the protective effects of nitrate and nitrite in cardiovascular and metabolic diseases

Within the body, NO is produced by nitric oxide synthases via converting _l-arginine to citrulline. Additionally, NO is also produced via the NOS-independent nitrate-nitrite-NO pathway. Unlike the classical pathway, the nitrate-nitrite-NO pathway is oxygen independent and viewed as a back-up function to ensure NO generation during ischaemia/hypoxia. Dietary nitrate and nitrite have emerged as substrates for endogenous NO generation and other bioactive nitrogen oxides with promising protective effects on cardiovascular and metabolic function. In brief, inorganic nitrate and nitrite can decrease blood pressure, protect against ischaemia-reperfusion injury, enhance endothelial function, inhibit platelet aggregation, modulate mitochondrial function and improve features of the metabolic syndrome. However, many questions regarding the specific mechanisms of these protective effects on cardiovascular and metabolic diseases remain unclear. In this review, we focus on nitrate/nitrite bioactivation, as well as the potential mechanisms for nitrate/nitrite-mediated effects on cardiovascular and metabolic diseases. Understanding how dietary nitrate and nitrite induce beneficial effect on cardiovascular and metabolic diseases could open up novel therapeutic opportunities in clinical practice.

Altered Hemorheology in Fontan Patients in Normoxia and After Acute Hypoxic Exercise

Background

The Fontan circulation is a unique palliation procedure for several congenital heart defects. Impaired exercise capacity has previously been demonstrated in these patients and also a higher risk for cardiopulmonary mortality. Hemorheology was shown to affect cardiopulmonary capacity and in turn to be affected by regular exercise and hypoxia but none of these have been investigated in Fontan patients so far. The aim of this study was to detect general differences in hemorheology in normoxia as well as possible altered hemorheological responses to hypoxia exposure and hypoxic exercise between Fontan patients and healthy controls.

Methods and Findings

26 Fontan patients and 20 healthy controls performed an acute exercise test (AET) on a bicycle ergometer under hypoxia with ambient 15.2% oxygen saturation (sO₂). Blood samples were taken at rest in normoxia (T0), at rest in hypoxia (T1), after maximum exhaustion in hypoxia (T2), and after 50 min recovery in normoxia (T3). Hemorheological and blood parameters were investigated. Additionally, arterial stiffness was tested at T0. Red blood cell (RBC) deformability, NOx, erythropoietin (EPO) concentration, RBC count, hemoglobin (Hb) concentration and hematocrit (hct) were significantly increased in Fontan patients compared to controls. Same was observed for arterial stiffness. No changes were observed for RBC aggregation, fibrinogen concentration, free radical levels and vascular endothelial growth factor (VEGF). Hypoxia exposure did not change parameters, whereas exercise in hypoxia increased aggregation and hct significantly in both groups. Fontan patients showed significantly increased aggregation-disaggregation balance compared to controls.

Conclusion

Acute hypoxia exposure and exercise under hypoxia might have similar impact on hemorheology in Fontan patients and controls and was clinically well tolerated. Nevertheless, exercise alters aggregation and possibly hemodynamics which requires special attention in Fontan patients.

Adaptations to environmental change: Globin superfamily evolution in Antarctic fishes

The ancient origins and functional versatility of globins make them ideal subjects for studying physiological adaptation to environmental change. Our goals in this review are to describe the evolution of the vertebrate globin gene superfamily and to explore the structure/function relationships of hemoglobin, myoglobin, neuroglobin and cytoglobin in teleost fishes. We focus on the globins of Antarctic notothenioids, emphasizing their adaptive features as inferred from comparisons with human proteins. We dedicate this review to Guido di Prisco, our co-author, colleague, friend, and husband of C.V. Ever thoughtful, creative, and enthusiastic, Guido spearheaded study of the structure, function, and evolution of the hemoglobins of polar fishes - this review is testimony to his wide-ranging contributions. Throughout his career, Guido inspired younger scientists to embrace polar biological research, and he challenged researchers of all ages to explore evolutionary adaptation in the context of global climate change. Beyond his scientific contributions, we will miss his warmth, his culture, and his great intellect. Guido has left an outstanding legacy, one that will continue to inspire us and our research.

Therapeutic Implications of Nitrite in Hypertension

Nitrite, an anion produced from the oxidative breakdown of nitric oxide (NO), has traditionally been viewed as an inert molecule. However, this dogma has been challenged with the findings that nitrite can be readily reduced to NO under pathological conditions, hence representing a physiologically relevant storage reservoir of NO either in the blood or tissues. Nitrite administration has been demonstrated to improve myocardial function in subjects with heart failure and to lower the blood pressure in hypertensive subjects. Thus, extensive amount of work has since been carried out to investigate the therapeutic potential of nitrite in treating cardiovascular diseases, especially hypertension. Studies done on several animal models of hypertension have demonstrated the efficacy of nitrite in preventing and ameliorating the pathological changes associated with the disease. This brief review of the current findings aims to re-evaluate the use of nitrite for the treatment of hypertension and in particular to highlight its role in improving endothelial function.

Role of Nitric Oxide Carried by Hemoglobin in Cardiovascular Physiology: Developments on a Three-Gas Respiratory Cycle

A continuous supply of oxygen is essential for the survival of multicellular organisms. The understanding of how this supply is regulated in the microvasculature has evolved from viewing erythrocytes (red blood cells [RBCs]) as passive carriers of oxygen to recognizing the complex interplay between Hb (hemoglobin) and oxygen, carbon dioxide, and nitric oxide-the three-gas respiratory cycle-that insures adequate oxygen and nutrient delivery to meet local metabolic demand. In this context, it is blood flow and not blood oxygen content that is the main driver of tissue oxygenation by RBCs. Herein, we review the lines of experimentation that led to this understanding of RBC function; from the foundational understanding of allosteric regulation of oxygen binding in Hb in the stereochemical model of Perutz, to blood flow autoregulation (hypoxic vasodilation governing oxygen delivery) observed by Guyton, to current understanding that centers on S-nitrosylation of Hb (ie, S-nitrosohemoglobin; SNO-Hb) as a purveyor of oxygen-dependent vasodilatory activity. Notably, hypoxic vasodilation is recapitulated by native S-nitrosothiol (SNO)-replete RBCs and by SNO-Hb itself, whereby SNO is released from Hb and RBCs during deoxygenation, in proportion to the degree of Hb deoxygenation, to regulate vessels directly. In addition, we discuss how dysregulation of this system through genetic mutation in Hb or through disease is a common factor in oxygenation pathologies resulting from microcirculatory impairment, including sickle cell disease, ischemic heart disease, and heart failure. We then conclude by identifying potential therapeutic interventions to correct deficits in RBC-mediated vasodilation to improve oxygen delivery-steps toward effective microvasculature-targeted therapies. To the extent that diseases of the heart, lungs, and blood are associated with impaired tissue oxygenation, the development of new therapies based on the three-gas respiratory system have the potential to improve the well-being of millions of patients.