Inorganic nitrite therapy: historical perspective and future directions

From nitrate to NO: potential effects of nitrate-reducing bacteria on systemic health and disease

Current research has described improving multisystem disease and organ function through dietary nitrate (DN) supplementation. They have provided some evidence that these floras with nitrate (NO3-) reductase are mediators of the underlying mechanism. Symbiotic bacteria with nitrate reductase activity (NRA) are found in the human digestive tract, including the mouth, esophagus and gastrointestinal tract (GT). Nitrate in food can be converted to nitrite under the tongue or in the stomach by these symbiotic bacteria. Then, nitrite is transformed to nitric oxide (NO) by non-enzymatic synthesis. NO is currently recognized as a potent bioactive agent with biological activities, such as vasodilation, regulation of cardiomyocyte function, neurotransmission, suppression of platelet agglutination, and prevention of vascular smooth muscle cell proliferation. NO also can be produced through the conventional L-arginine-NO synthase (L-NOS) pathway, whereas endogenous NO production by L-arginine is inhibited under hypoxia-ischemia or disease conditions. In contrast, exogenous NO3-/NO2-/NO activity is enhanced and becomes a practical supplemental pathway for NO in the body, playing an essential role in various physiological activities. Moreover, many diseases (such as metabolic or geriatric diseases) are primarily associated with disorders of endogenous NO synthesis, and NO generation from the exogenous NO3-/NO2-/NO route can partially alleviate the disease progression. The imbalance of NO in the body may be one of the potential mechanisms of disease development. Therefore, the impact of these floras with nitrate reductase on host systemic health through exogenous NO3-/NO2-/NO pathway production of NO or direct regulation of floras ecological balance is essential (e.g., regulation of body homeostasis, amelioration of diseases, etc.). This review summarizes the bacteria with nitrate reductase in humans, emphasizing the relationship between the metabolic processes of this microflora and host systemic health and disease. The potential effects of nitrate reduction bacteria on human health and disease were also highlighted in disease models from different human systems, including digestive, cardiovascular, endocrine, nervous, respiratory, and urinary systems, providing innovative ideas for future disease diagnosis and treatment based on nitrate reduction bacteria.

Bringing Nitric Oxide to the Molybdenum World-A Personal Perspective

Molybdenum-containing enzymes of the xanthine oxidase (XO) family are well known to catalyse oxygen atom transfer reactions, with the great majority of the characterised enzymes catalysing the insertion of an oxygen atom into the substrate. Although some family members are known to catalyse the "reverse" reaction, the capability to abstract an oxygen atom from the substrate molecule is not generally recognised for these enzymes. Hence, it was with surprise and scepticism that the "molybdenum community" noticed the reports on the mammalian XO capability to catalyse the oxygen atom abstraction of nitrite to form nitric oxide (NO). The lack of precedent for a molybdenum- (or tungsten) containing nitrite reductase on the nitrogen biogeochemical cycle contributed also to the scepticism. It took several kinetic, spectroscopic and mechanistic studies on enzymes of the XO family and also of sulfite oxidase and DMSO reductase families to finally have wide recognition of the molybdoenzymes' ability to form NO from nitrite. Herein, integrated in a collection of "personal views" edited by Professor Ralf Mendel, is an overview of my personal journey on the XO and aldehyde oxidase-catalysed nitrite reduction to NO. The main research findings and the path followed to establish XO and AO as competent nitrite reductases are reviewed. The evidence suggesting that these enzymes are probable players of the mammalian NO metabolism is also discussed.

Dithiol-Activated Bioorthogonal Chemistry for Endoplasmic Reticulum-Targeted Synergistic Chemophototherapy

The controlled intracellular release of nitrite is still an unmet challenge due to the lack of bio-friendly donors, and the antitumor effect of nitrite is limited by its physiologically inert activity. Herein, we designed benzothiadiazole-based organic nitrite donors that are stable against bio-relevant species but selectively respond to dithiol species through S_N Ar/intramolecular cyclization tandem reactions in the aqueous media. The bioorthogonal system was established to target the endoplasmic reticulum (ER) of liver cancer HepG2 cells. The nitrite and nonivamide were coupled to induce elevation of intracellular levels of calcium ions as well as reactive oxygen/nitrogen species, which resulted in ER stress and mitochondrial dysfunction. We demonstrated that a combination of photoactivation and "click to release" strategy could enhance antitumor effect in cellular level and show good potential for cancer precision therapy.

White matter damage as a consequence of vascular dysfunction in a spontaneous mouse model of chronic mild chronic hypoperfusion with eNOS deficiency

Vascular cognitive impairment and dementia (VCID) is the second most common form of dementia after Alzheimer's disease (AD). Currently, the mechanistic insights into the evolution and progression of VCID remain elusive. White matter change represents an invariant feature. Compelling clinical neuroimaging and pathological evidence suggest a link between white matter changes and neurodegeneration. Our prior study detected hypoperfused lesions in mice with partial deficiency of endothelial nitric oxide (eNOS) at very young age, precisely matching to those hypoperfused areas identified in preclinical AD patients. White matter tracts are particularly susceptible to the vascular damage induced by chronic hypoperfusion. Using immunohistochemistry, we detected severe demyelination in the middle-aged eNOS-deficient mice. The demyelinated areas were confined to cortical and subcortical areas including the corpus callosum and hippocampus. The intensity of demyelination correlated with behavioral deficits of gait and associative recognition memory performances. By Evans blue angiography, we detected blood-brain barrier (BBB) leakage as another early pathological change affecting frontal and parietal cortex in eNOS-deficient mice. Sodium nitrate fortified drinking water provided to young and middle-aged eNOS-deficient mice completely prevented non-perfusion, BBB leakage, and white matter pathology, indicating that impaired endothelium-derived NO signaling may have caused these pathological events. Furthermore, genome-wide transcriptomic analysis revealed altered gene clusters most related to mitochondrial respiratory pathways selectively in the white matter of young eNOS-deficient mice. Using eNOS-deficient mice, we identified BBB breakdown and hypoperfusion as the two earliest pathological events, resulting from insufficient vascular NO signaling. We speculate that the compromised BBB and mild chronic hypoperfusion trigger vascular damage, along with oxidative stress and astrogliosis, accounting for the white matter pathological changes in the eNOS-deficient mouse model. We conclude that eNOS-deficient mice represent an ideal spontaneous evolving model for studying the earliest events leading to white matter changes, which will be instrumental to future therapeutic testing of drug candidates and for targeting novel/specific vascular mechanisms contributing to VCID and AD.

Mechanistic Insights into Inorganic Nitrite-Mediated Vasodilation of Isolated Aortic Rings under Oxidative/Hypertensive Conditions and S-Nitros(yl)ation of Proteins in Germ-Free Mice

The prevalence and clinical importance of arterial hypertension are still growing. Inorganic nitrite (NO₂^-) represents an attractive dietary antihypertensive agent, but its metabolism and mode of action, which we aimed to investigate with the present study, are not completely understood. Isolated aortic rings from rats were treated ex vivo with oxidants, and rats were infused in vivo with angiotensin-II. Vascular responses to acetylcholine (ACh) and nitrite were assessed by isometric tension recording. The loss of vasodilatory potency in response to oxidants was much more pronounced for ACh as compared to nitrite ex vivo (but not in vivo with angiotensin-II). This effect may be caused by the redox regulation of conversion to xanthine oxidase (XO). Conventionally raised and germ-free mice were treated with nitrite by gavage, which did not improve ACh-mediated vasodilation, but did increase the plasma levels of S-nitros(yl)ated proteins in the conventionally-raised, but not in the germ-free mice. In conclusion, inorganic nitrite represents a dietary drug option to treat arterial hypertension in addition to already established pharmacological treatment. Short-term oxidative stress did not impair the vasodilatory properties of nitrite, which may be beneficial in cardiovascular disease patients. The gastrointestinal microbiome appears to play a key role in nitrite metabolism and bioactivation.

Significance of Inorganic Nitrate Supplement in Cardiovascular Health

BACKGROUND & OBJECTIVES

Nitric Oxide (NO) is frequently produced by the enzyme nitric oxide synthase (NOS) and is crucial for the control and effectiveness of the cardiovascular system. However, there is a substantial reduction in NOS activity with aging that can lead to the development of hypertension and other cardiovascular obstacles. Fortunately, NO can also be produced by sequential reduction of inorganic nitrates supplementation. This proves that NO from inorganic nitrate supplements can compensate for inadequate NOS activity, thus providing cardio protective benefits.

DISCUSSION

This review focuses on the general information about nitrous oxide, its types and mechanism of action and the fact that overview of inadequate NOS activity for cardio protective benefits was often studied for cardiovascular treatments.

CONCLUSION

We concluded that the natural plant NO is essential for cardiovascular activity to target site with desired concentration. Moreover, the researchers focused on evidence that suggested that nitrate supplementation could help regulate blood pressure, limit progression of atherosclerosis, and improve myocardial contractility in both healthy individuals and those with cardiovascular diseases.

Knockdown of Salusin-β Improves Cardiovascular Function in Myocardial Infarction-Induced Chronic Heart Failure Rats

Salusin-β is a biologically active peptide with 20 amino acids that exerts several cardiovascular activity-regulating effects, such as regulating vascular endothelial function and the proliferation of vascular smooth muscle cells. However, the regulatory effects of salusin-β in myocardial infarction-induced chronic heart failure (CHF) are still unknown. The current study is aimed at investigating the effects of silencing salusin-β on endothelial function, cardiac function, vascular and myocardial remodeling, and its underlying signaling pathways in CHF rats induced by coronary artery ligation. CHF and sham-operated (Sham) rats were subjected to tail vein injection of adenoviral vectors encoding salusin-β shRNA or a control-shRNA. The coronary artery (CA), pulmonary artery (PA), and mesenteric artery (MA) were isolated from rats, and isometric tension measurements of arteries were performed. Compared with Sham rats, the plasma salusin-β, leptin and visfatin levels and the salusin-β protein expression levels of CA, PA, and MA were increased, while the acetylcholine- (ACh-) induced endothelium-dependent vascular relaxation of CA, PA, and MA was attenuated significantly in CHF rats and was improved significantly by salusin-β gene knockdown. Salusin-β knockdown also improved cardiac function and vascular and myocardial remodeling, increased endothelial nitric oxide synthase (eNOS) activity and nitric oxide (NO) levels, and decreased NAD(P)H oxidase activity, NOX-2 and NOX-4 expression, and reactive oxygen species (ROS) levels in arteries in CHF rats. The effects of salusin-β knockdown in CHF rats were attenuated significantly by pretreatment with the NOS inhibitor L-NAME. These results indicate that silencing salusin-β contributes to the improvement of endothelial function, cardiac function, and cardiovascular remodeling in CHF by inhibiting NAD(P)H oxidase-ROS generation and activating eNOS-NO production.

Nitric oxide for the prevention and treatment of viral, bacterial, protozoal and fungal infections

Although the antimicrobial potential of nitric oxide (NO) is widely published, it is little used clinically. NO is a key signalling molecule modulating vascular, neuronal, inflammatory and immune responses. Endogenous antimicrobial activity is largely mediated by high local NO concentrations produced by cellular inducible nitric oxide synthase, and by derivative reactive nitrogen oxide species including peroxynitrite and S-nitrosothiols. NO may be taken as dietary substrate (inorganic nitrate, L-arginine), and therapeutically as gaseous NO, and transdermal, sublingual, oral, intranasal and intravenous nitrite or nitrate. Numerous preclinical studies have demonstrated that NO has generic static and cidal activities against viruses (including β-coronaviruses such as SARS-CoV-2), bacteria, protozoa and fungi/yeasts  in vitro. Therapeutic effects have been seen in animal models  in vivo, and phase II trials have demonstrated that NO donors can reduce microbial infection. Nevertheless, excess NO, as occurs in septic shock, is associated with increased morbidity and mortality. In view of the dose-dependent positive and negative effects of NO, safety and efficacy trials of NO and its donors are needed for assessing their role in the prevention and treatment of infections. Trials should test dietary inorganic nitrate for pre- or post-exposure prophylaxis and gaseous NO or oral, topical or intravenous nitrite and nitrate for treatment of mild-to-severe infections, including due to SARS-CoV-2 (COVID-19). This review summarises the evidence base from  in vitro, in vivo and early phase clinical studies of NO activity in viral, bacterial, protozoal and fungal infections.

Nitric oxide for the prevention and treatment of viral, bacterial, protozoal and fungal infections

Although the antimicrobial potential of nitric oxide (NO) is widely published, it is little used clinically. NO is a key signalling molecule modulating vascular, neuronal, inflammatory and immune responses. Endogenous antimicrobial activity is largely mediated by high local NO concentrations produced by cellular inducible nitric oxide synthase, and by derivative reactive nitrogen oxide species including peroxynitrite and S-nitrosothiols. NO may be taken as dietary substrate (inorganic nitrate, L-arginine), and therapeutically as gaseous NO, and transdermal, sublingual, oral, intranasal and intravenous nitrite or nitrate. Numerous preclinical studies have demonstrated that NO has generic static and cidal activities against viruses (including β-coronaviruses such as SARS-CoV-2), bacteria, protozoa and fungi/yeasts  in vitro. Therapeutic effects have been seen in animal models  in vivo, and phase II trials have demonstrated that NO donors can reduce microbial infection. Nevertheless, excess NO, as occurs in septic shock, is associated with increased morbidity and mortality. In view of the dose-dependent positive and negative effects of NO, safety and efficacy trials of NO and its donors are needed for assessing their role in the prevention and treatment of infections. Trials should test dietary inorganic nitrate for pre- or post-exposure prophylaxis and gaseous NO or oral, topical or intravenous nitrite and nitrate for treatment of mild-to-severe infections, including due to SARS-CoV-2 (COVID-19). This review summarises the evidence base from  in vitro, in vivo and early phase clinical studies of NO activity in viral, bacterial, protozoal and fungal infections.

Insulin secretion: The nitric oxide controversy

Nitric oxide (NO) is a gas that serves as a ubiquitous signaling molecule participating in physiological activities of various organ systems. Nitric oxide is produced in the endocrine pancreas and contributes to synthesis and secretion of insulin. The potential role of NO in insulin secretion is disputable - both stimulatory and inhibitory effects have been reported. Available data indicate that effects of NO critically depend on its concentration. Different isoforms of NO synthase (NOS) control this and have the potential to decrease or increase insulin secretion. In this review, the role of NO in insulin secretion as well as the possible reasons for discrepant findings are discussed. A better understanding of the role of NO system in the regulation of insulin secretion may facilitate the development of new therapeutic strategies in the management of diabetes.

Regulation of carbohydrate metabolism by nitric oxide and hydrogen sulfide: Implications in diabetes

Nitric oxide (NO) and hydrogen sulfide (H₂S) are two gasotransmitters that are produced in the human body and have a key role in many of the physiological activities of the various organ systems. Decreased NO bioavailability and deficiency of H₂S are involved in the pathophysiology of type 2 diabetes and its complications. Restoration of NO levels have favorable metabolic effects in diabetes. The role of H₂S in pathophysiology of diabetes is however controversial; H₂S production is decreased during development of obesity, diabetes, and its complications, suggesting the potential therapeutic effects of H₂S. On the other hand, increased H₂S levels disturb the pancreatic β-cell function and decrease insulin secretion. In addition, there appear to be important interactions between NO and H₂S at the levels of both biosynthesis and signaling pathways, yet clear an insight into this relationship is lacking. H₂S potentiates the effects of NO in the cardiovascular system as well as NO release from its storage pools. Likewise, NO increases the activity and the expression of H₂S-generating enzymes. Inhibition of NO production leads to elimination/attenuation of the cardioprotective effects of H₂S. Regarding the increasing interest in the therapeutic applications of NO or H₂S-releasing molecules in a variety of diseases, particularly in the cardiovascular disorders, much is to be learned about their function in glucose/insulin metabolism, especially in diabetes. The aim of this review is to provide a better understanding of the individual and the interactive roles of NO and H₂S in carbohydrate metabolism.

Inorganic Nitrate Supplementation for Cardiovascular Health

Nitric oxide (NO) is continually produced by the enzyme nitric oxide synthase (NOS) and is essential to the control and effectiveness of the cardiovascular system. However, there is a substantial reduction in NOS activity with aging that can lead to the development of hypertension and other cardiovascular complications. Fortunately, NO can also be produced by the sequential reduction of inorganic nitrate to nitrite and then to NO. Nitric oxide from inorganic nitrate supplementation has been found to have the same cardioprotective benefits of NO produced by NOS. Moreover, it can effectively compensate for declining NOS activity due to aging or NOS inhibition by oxidative stress, hypoxia, or other factors. This review covers some of the major cardiovascular regulatory actions of NO and presents evidence that NO from inorganic nitrate supplementation can provide (1) compensation when NOS activity is inadequate, and (2) cardioprotective benefits beyond that provided by a healthy NOS system. In addition, it discusses how to obtain a safe and efficacious range of inorganic nitrate.

In Situ Hydrogel-Forming/Nitric Oxide-Releasing Wound Dressing for Enhanced Antibacterial Activity and Healing in Mice with Infected Wounds

The eradication of bacteria from wound sites and promotion of healing are essential for treating infected wounds. Nitric oxide (NO) is desirable for these purposes due to its ability to accelerate wound healing and its broad-spectrum antibacterial effects. We developed an in situ hydrogel-forming/NO-releasing powder dressing (NO/GP), which is a powder during storage and forms a hydrogel when applied to wounds, as a novel NO-releasing formulation to treat infected wounds. An NO/GP fine powder (51.5 μm) was fabricated by blending and micronizing S-nitrosoglutathione (GSNO), alginate, pectin, and polyethylene glycol (PEG). NO/GP remained stable for more than four months when stored at 4 or 37 °C. When applied to wounds, NO/GP absorbed wound fluid and immediately converted to a hydrogel. Additionally, wound fluid triggered a NO release from NO/GP for more than 18 h. The rheological properties of hydrogel-transformed NO/GP indicated that NO/GP possesses similar adhesive properties to marketed products (Vaseline). NO/GP resulted in a 6-log reduction in colony forming units (CFUs) of methicillin resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa, which are representative drug-resistant gram-positive and -negative bacteria, respectively. The promotion of wound healing by NO/GP was demonstrated in mice with full-thickness wounds challenged with MRSA and P. aeruginosa. Thus, NO/GP is a promising formulation for the treatment of infected wounds.

Nitric Oxide and Hydrogen Sulfide Regulation of Ischemic Vascular Growth and Remodeling

Ischemic vascular remodeling occurs in response to stenosis or arterial occlusion leading to a change in blood flow and tissue perfusion. Altered blood flow elicits a cascade of molecular and cellular physiological responses leading to vascular remodeling of the macro- and micro-circulation. Although cellular mechanisms of vascular remodeling such as arteriogenesis and angiogenesis have been studied, therapeutic approaches in these areas have had limited success due to the complexity and heterogeneous constellation of molecular signaling events regulating these processes. Understanding central molecular players of vascular remodeling should lead to a deeper understanding of this response and aid in the development of novel therapeutic strategies. Hydrogen sulfide (H₂ S) and nitric oxide (NO) are gaseous signaling molecules that are critically involved in regulating fundamental biochemical and molecular responses necessary for vascular growth and remodeling. This review examines how NO and H₂ S regulate pathophysiological mechanisms of angiogenesis and arteriogenesis, along with important chemical and experimental considerations revealed thus far. The importance of NO and H₂ S bioavailability, their synthesis enzymes and cofactors, and genetic variations associated with cardiovascular risk factors suggest that they serve as pivotal regulators of vascular remodeling responses. © 2019 American Physiological Society. Compr Physiol 9:1213-1247, 2019.

Plasma-activated medium triggers cell death and the presentation of immune activating danger signals in melanoma and pancreatic cancer cells

Over the past decade, cold atmospheric plasmas have shown promising application in cancer therapy. The therapeutic use of plasma-activated media is a topic addressed in an emerging field known as plasma pharmacy. In oncology, plasma-activated media are  used to harness the therapeutic effects of oxidant species when they come in contact with cancer cells. Among several factors that contribute to the anticancer effect of plasma-activated liquid media (PALM), H₂O₂ and NO derivatives likely play a key role in the apoptotic pathway. Despite the significant amount of literature produced in recent years, a full understanding of the mechanisms by which PALM exert their activity against cancer cells is limited. In this paper, a sealed dielectric-barrier discharge was used to disentangle the effect of reactive nitrogen species (RNS) from that of reactive oxygen species (ROS) on cancer cells. Two cancers characterized by poor prognosis have been investigated: metastatic melanoma and pancreatic cancer. Both tumour models exposed to PALM rich in H₂O₂ showed a reduction in proliferation and an increase in calreticulin exposure and ATP release, suggesting the potential use of activated media as an inducer of immunogenic cell death via activation of the innate immune system.

Mechanisms impairing blood pressure responses to nitrite and nitrate

Hypertension is a multifactorial disease associated with impaired nitric oxide (NO) production and bioavailability. In this respect, restoring NO activity by using nitrite and nitrate has been considered a potential therapeutic strategy to treat hypertension. This possibility is justified by the understanding that both nitrite and nitrate may be recycled back to NO and also promote the generation of other bioactive species. This process involves a complex biological circuit known as the enterosalivary cycle of nitrate, where this anion is actively taken up by the salivary glands and converted to nitrite by nitrate-reducing bacteria in the oral cavity. Nitrite is then ingested and reduced to NO and other nitroso species under the acid conditions of the stomach, whereas reminiscent nitrite that escapes gastric reduction is absorbed systemically and can be converted into NO by nitrite-reductases in tissues. While there is no doubt that nitrite and nitrate exert antihypertensive effects, several agents can impair the blood pressure responses to these anions by disrupting the enterosalivary cycle of nitrate. These agents include dietary and smoking-derived thiocyanate, antiseptic mouthwash, proton pump inhibitors, ascorbate at high concentrations, and xanthine oxidoreductase inhibitors. In this article, we provide an overview of the physiological aspects of nitrite and nitrate bioactivation and the therapeutic potential of these anions in hypertension. We also discuss mechanisms by which agents counteracting the antihypertensive responses to nitrite and nitrate mediate their effects. These critical aspects should be taken into consideration when suggesting nitrate or nitrite-based therapies to patients.

Putting xanthine oxidoreductase and aldehyde oxidase on the NO metabolism map: Nitrite reduction by molybdoenzymes

Nitric oxide radical (NO) is a signaling molecule involved in several physiological and pathological processes and a new nitrate-nitrite-NO pathway has emerged as a physiological alternative to the "classic" pathway of NO formation from L-arginine. Since the late 1990s, it has become clear that nitrite can be reduced back to NO under hypoxic/anoxic conditions and exert a significant cytoprotective action in vivo under challenging conditions. To reduce nitrite to NO, mammalian cells can use different metalloproteins that are present in cells to perform other functions, including several heme proteins and molybdoenzymes, comprising what we denominated as the "non-dedicated nitrite reductases". Herein, we will review the current knowledge on two of those "non-dedicated nitrite reductases", the molybdoenzymes xanthine oxidoreductase and aldehyde oxidase, discussing the in vitro and in vivo studies to provide the current picture of the role of these enzymes on the NO metabolism in humans.

Does dietary nitrate say NO to cardiovascular ageing? Current evidence and implications for research

CVD are characterised by a multi-factorial pathogenesis. Key pathogenetic steps in the development of CVD are the occurrence of endothelial dysfunction and formation of atherosclerotic lesions. Reduced nitric oxide (NO) bioavailability is a primary event in the initiation of the atherosclerotic cascade. NO is a free radical with multiple physiological functions including the regulation of vascular resistance, coagulation, immunity and oxidative metabolism. The synthesis of NO proceeds via two distinct pathways identified as enzymatic and non-enzymatic. The former involves the conversion of arginine into NO by the NO synthases, whilst the latter comprises a two-step reducing process converting inorganic nitrate $({\rm NO}_3^ - )$ into nitrite and subsequently NO.

Inorganic ${\rm NO}_3^ - $ is present in water and food, particularly beetroot and green leafy vegetables. Several investigations have therefore used the non-enzymatic NO pathway as a target for nutritional supplementation (${\rm NO}_3^ - $ salts) or dietary interventions (high-${\rm NO}_3^ - $ foods) to increase NO bioavailability and impact on cardiovascular outcomes. Some studies have reported positive effects of dietary ${\rm NO}_3^ - $ on systolic blood pressure and endothelial function in patients with hypertension and chronic heart failure. Nevertheless, results have been inconsistent and the size of the effect appears to be declining in older individuals. Additionally, there is a paucity of studies for disorders such as diabetes, CHD and chronic kidney failure. Thus, whilst dietary ${\rm NO}_3^ - $ supplementation could represent an effective and viable strategy for the primary and secondary prevention of age-related cardiovascular and metabolic diseases, more large-scale, robust studies are awaited to confirm or refute this notion.

Total antioxidant capacity of the diet modulates the association between habitual nitrate intake and cardiovascular events: A longitudinal follow-up in Tehran Lipid and Glucose Study

Background

Considering the lack of data on the association between habitual dietary intakes of nitrate (NO₃⁻) and nitrite (NO₂⁻) and cardiovascular events, we assessed possible effects of dietary NO₃⁻ and NO₂⁻, in the context of total antioxidant capacity (TAC) of the diet, with the risk of cardiovascular (CVD) outcomes.

Methods

Adult men and women without CVD (n = 2369) were recruited from the Tehran Lipid and Glucose Study and were followed for a mean of 6.7 years. Dietary NO₃⁻ and NO₂⁻ intakes, as well as dietary TAC and nitric oxide (NO) index were assessed at baseline (2006–2008). Multivariable-adjusted Cox proportional hazards regression models were used to estimate risk of CVD above and below median of dietary intakes of NO₃⁻/NO₂⁻ and dietary TAC and NO index. Due to a significant interaction between NO₃⁻/NO₂⁻ intake and TAC, stratified analyses were done for < and ≥ median dietary TAC.

Results

Daily mean (SD) dietary NO₃⁻ and NO₂⁻ intakes were 460 (195) and 9.5 (3.9) mg; mean (SD) dietary TAC and NO index was 1406 (740) and 338 (197) μmol trolox equivalent (TE)/100 g. In subjects with lower dietary TAC, higher intake of NO₃⁻ (≥ 430 mg/d) was accompanied with an increased risk of CVD (HR = 3.28, 95% CI = 1.54–6.99). There were no significant associations between dietary intakes of NO₂⁻, TAC of the diet and NO index with the occurrence of CVD events during the study follow-up.

Conclusion

High habitual intake of NO₃⁻, in the context of low TAC of the food, may be associated with the risk of CVD outcomes.

Nitrite-Mediated Hypoxic Vasodilation Predicted from Mathematical Modeling and Quantified from in Vivo Studies in Rat Mesentery

Nitric oxide (NO) generated from nitrite through nitrite reductase activity in red blood cells has been proposed to play a major role in hypoxic vasodilation. However, we have previously predicted from mathematical modeling that much more NO can be derived from tissue nitrite reductase activity than from red blood cell nitrite reductase activity. Evidence in the literature suggests that tissue nitrite reductase activity is associated with xanthine oxidoreductase (XOR) and/or aldehyde oxidoreductase (AOR). We investigated the role of XOR and AOR in nitrite-mediated vasodilation from computer simulations and from in vivo exteriorized rat mesentery experiments. Vasodilation responses to nitrite in the superfusion medium bathing the mesentery equilibrated with 5% O₂ (normoxia) or zero O₂ (hypoxia) at either normal or acidic pH were quantified. Experiments were also conducted following intraperitoneal (IP) injection of nitrite before and after inhibiting XOR with allopurinol or inhibiting AOR with raloxifene. Computer simulations for NO and O₂ transport using reaction parameters reported in the literature were also conducted to predict nitrite-dependent NO production from XOR and AOR activity as a function of nitrite concentration, PO₂ and pH. Experimentally, the largest arteriolar responses were found with nitrite >10 mM in the superfusate, but no statistically significant differences were found with hypoxic and acidic conditions in the superfusate. Nitrite-mediated vasodilation with IP nitrite injections was reduced or abolished after inhibiting XOR with allopurinol (p < 0.001). Responses to IP nitrite before and after inhibiting AOR with raloxifene were not as consistent. Our mathematical model predicts that under certain conditions, XOR and AOR nitrite reductase activity in tissue can significantly elevate smooth muscle cell NO and can serve as a compensatory pathway when endothelial NO production is limited by hypoxic conditions. Our theoretical and experimental results provide further evidence for a role of tissue nitrite reductases to contribute additional NO to compensate for reduced NO production by endothelial nitric oxide synthase during hypoxia. Our mathematical model demonstrates that under extreme hypoxic conditions with acidic pH, endogenous nitrite levels alone can be sufficient for a functionally significant increase in NO bioavailability. However, these conditions are difficult to achieve experimentally.

Anti-obesity and anti-diabetic effects of nitrate and nitrite

Prevalence of obesity is increasing worldwide and type 2 diabetes to date is the most devastating complication of obesity. Decreased nitric oxide bioavailability is a feature of obesity and diabetes that links these two pathologies. Nitric oxide is synthesized both by nitric oxide synthase enzymes from l-arginine and nitric oxide synthase-independent from nitrate/nitrite. Nitric oxide production from nitrate/nitrite could potentially be used for nutrition-based therapy in obesity and diabetes. Nitric oxide deficiency also contributes to pathogeneses of cardiovascular disease and hypertension, which are associated with obesity and diabetes. This review summarizes pathways for nitric oxide production and focuses on the anti-diabetic and anti-obesity effects of the nitrate-nitrite-nitric oxide pathway. In addition to increasing nitric oxide production, nitrate and nitrite reduce oxidative stress, increase adipose tissue browning, have favorable effects on nitric oxide synthase expression, and increase insulin secretion, all effects that are potentially promising for management of obesity and diabetes. Based on current data, it could be suggested that amplifying the nitrate-nitrite-nitric oxide pathway is a diet-based strategy for increasing nitric oxide bioavailability and the management of these two interlinked conditions. Adding nitrate/nitrite to drugs that are currently used for managing diabetes (e.g. metformin) and possibly anti-obesity drugs may also enhance their efficacy.

Gasotransmitter Heterocellular Signaling

SIGNIFICANCE

The family of gasotransmitter molecules, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), has emerged as an important mediator of numerous cellular signal transduction and pathophysiological responses. As such, these molecules have been reported to influence a diverse array of biochemical, molecular, and cell biology events often impacting one another. Recent Advances: Discrete regulation of gasotransmitter molecule formation, movement, and reaction is critical to their biological function. Due to the chemical nature of these molecules, they can move rapidly throughout cells and tissues acting on targets through reactions with metal groups, reactive chemical species, and protein amino acids.

CRITICAL ISSUES

Given the breadth and complexity of gasotransmitter reactions, this field of research is expanding into exciting, yet sometimes confusing, areas of study with significant promise for understanding health and disease. The precise amounts of tissue and cellular gasotransmitter levels and where they are formed, as well as how they react with molecular targets or themselves, all remain poorly understood.

FUTURE DIRECTIONS

Elucidation of specific molecular targets, characteristics of gasotransmitter molecule heterotypic interactions, and spatiotemporal formation and metabolism are all important to better understand their true pathophysiological importance in various organ systems. Antioxid. Redox Signal. 26, 936-960.

Vitamin C intake modify the impact of dietary nitrite on the incidence of type 2 diabetes: A 6-year follow-up in Tehran Lipid and Glucose Study

BACKGROUND

There is no epidemiological study on the association between dietary nitrate (NO₃) and nitrite (NO₂) and intakes and the risk of type 2 diabetes (T2D).

OBJECTIVE

The aim of this study was therefore to examine the potential effect of dietary NO₃ and NO₂ on the occurrence of T2D.

DESIGN

This longitudinal study was conducted within the framework of the Tehran Lipid and Glucose Study (TLGS) on 2139 T2D-free adults, aged 20-70 years, followed for a median of 5.8 y. Dietary intakes of NO₃ and NO₂ were estimated using a 168-food items validate semi-quantitative food frequency questionnaire, at baseline. Multivariate Hazard Ratios (HR) and 95% confidence intervals (CI), adjusted for diabetes risk score (DRS), and dietary intakes of fat, fiber and vitamin C, were calculated for residual energy-adjusted NO₃ and NO₂ intakes. Since significant interaction (P = 0.024) was found between NO₂ and vitamin C intakes in the multivariable model, stratified analyses were done for < and ≥ median vitamin C intakes.

RESULTS

Median (inter quartile range; IQR) daily intake of NO₃ and NO₂ were 410 mg/d (343-499) and 8.77 mg/d (7.53-10.2). An increased risk of T2D was observed among participants who had higher intake of total and animal-based NO₂ in participants who had low vitamin C intake (HR = 2.43, 95% CI = 1.45-4.05, HR = 1.88, 95% CI = 1.12-3.15, respectively). We found no significant association between NO₃ in overall, and plant- and animal sources as well, with the risk of T2D. Plant-derived NO₂ was also unrelated to incidence of T2D.

CONCLUSION

Our findings indicated that higher intakes of total and animal-based NO₂ may be an independent dietary risk factor for development of T2D in subjects with lower vitamin C intakes.

Photoinitiated Reactivity of a Thiolate-Ligated, Spin-Crossover Nonheme {FeNO}(7) Complex with Dioxygen

The nonheme iron complex, [Fe(NO)(N3PyS)]BF4, is a rare example of an {FeNO}(7) species that exhibits spin-crossover behavior. The comparison of X-ray crystallographic studies at low and high temperatures and variable-temperature magnetic susceptibility measurements show that a low-spin S = 1/2 ground state is populated at 0-150 K, while both low-spin S = 1/2 and high-spin S = 3/2 states are populated at T > 150 K. These results explain the observation of two N-O vibrational modes at 1737 and 1649 cm(-1) in CD3CN for [Fe(NO)(N3PyS)]BF4 at room temperature. This {FeNO}(7) complex reacts with dioxygen upon photoirradiation with visible light in acetonitrile to generate a thiolate-ligated, nonheme iron(III)-nitro complex, [Fe(III)(NO2)(N3PyS)](+), which was characterized by EPR, FTIR, UV-vis, and CSI-MS. Isotope labeling studies, coupled with FTIR and CSI-MS, show that one O atom from O2 is incorporated in the Fe(III)-NO2 product. The O2 reactivity of [Fe(NO)(N3PyS)]BF4 in methanol is dramatically different from CH3CN, leading exclusively to sulfur-based oxidation, as opposed to NO· oxidation. A mechanism is proposed for the NO· oxidation reaction that involves formation of both Fe(III)-superoxo and Fe(III)-peroxynitrite intermediates and takes into account the experimental observations. The stability of the Fe(III)-nitrite complex is limited, and decay of [Fe(III)(NO2)(N3PyS)](+) leads to {FeNO}(7) species and sulfur oxygenated products. This work demonstrates that a single mononuclear, thiolate-ligated nonheme {FeNO}(7) complex can exhibit reactivity related to both nitric oxide dioxygenase (NOD) and nitrite reductase (NiR) activity. The presence of the thiolate donor is critical to both pathways, and mechanistic insights into these biologically relevant processes are presented.

Oxygen tension, H2S, and NO bioavailability: is there an interaction?

Molecular oxygen (O2) is an essential component for survival and development. Variation in O2 levels leads to changes in molecular signaling and ultimately affects the physiological functions of many organisms. Nitric oxide (NO) and hydrogen sulfide (H2S) are two gaseous cellular signaling molecules that play key roles in several physiological functions involved in maintaining vascular homeostasis including vasodilation, anti-inflammation, and vascular growth. Apart from the aforementioned functions, NO and H2S are believed to mediate hypoxic responses and serve as O2 chemosensors in biological systems. In this literature review, we briefly discuss NO and H2S and their roles during hypoxia.

Physiological recycling of endogenous nitrate by oral bacteria regulates gastric mucus thickness

BACKGROUND

Inorganic nitrate from exogenous and endogenous sources is accumulated in saliva, reduced to nitrite by oral bacteria and further converted to nitric oxide (NO) and other bioactive nitrogen oxides in the acidic gastric lumen. To further explore the role of oral microbiota in this process we examined the gastric mucus layer in germ free (GF) and conventional mice given different doses of nitrate and nitrite.

METHODS

Mice were given either nitrate (100mg/kg/d) or nitrite (0.55-11 mg/kg/d) in the drinking water for 7 days, with the lowest nitrite dose resembling the levels provided by swallowing of fasting saliva. The gastric mucus layer was measured in vivo.

RESULTS

GF animals were almost devoid of the firmly adherent mucus layer compared to conventional mice. Dietary nitrate increased the mucus thickness in conventional animals but had no effect in GF mice. In contrast, nitrite at all doses, restored the mucus thickness in GF mice to the same levels as in conventional animals. The nitrite-mediated increase in gastric mucus thickness was not inhibited by the soluble guanylyl cyclase inhibitor ODQ. Mice treated with antibiotics had significantly thinner mucus than controls. Additional studies on mucin gene expression demonstrated down regulation of Muc5ac and Muc6 in germ free mice after nitrite treatment.

CONCLUSION

Oral bacteria remotely modulate gastric mucus generation via bioactivation of salivary nitrate. In the absence of a dietary nitrate intake, salivary nitrate originates mainly from NO synthase. Thus, oxidized NO from the endothelium and elsewhere is recycled to regulate gastric mucus homeostasis.

Effects of nitrite infusion on skeletal muscle vascular control during exercise in rats with chronic heart failure

Chronic heart failure (CHF) reduces nitric oxide (NO) bioavailability and impairs skeletal muscle vascular control during exercise. Reduction of NO2 (-) to NO may impact exercise-induced hyperemia, particularly in muscles with pathologically reduced O2 delivery. We tested the hypothesis that NO2 (-) infusion would increase exercising skeletal muscle blood flow (BF) and vascular conductance (VC) in CHF rats with a preferential effect in muscles composed primarily of type IIb + IId/x fibers. CHF (coronary artery ligation) was induced in adult male Sprague-Dawley rats. After a >21-day recovery, mean arterial pressure (MAP; carotid artery catheter) and skeletal muscle BF (radiolabeled microspheres) were measured during treadmill exercise (20 m/min, 5% incline) with and without NO2 (-) infusion. The myocardial infarct size (35 ± 3%) indicated moderate CHF. NO2 (-) infusion increased total hindlimb skeletal muscle VC (CHF: 0.85 ± 0.09 ml·min(-1)·100 g(-1)·mmHg(-1) and CHF + NO2 (-): 0.93 ± 0.09 ml·min(-1)·100 g(-1)·mmHg(-1), P < 0.05) without changing MAP (CHF: 123 ± 4 mmHg and CHF + NO2 (-): 120 ± 4 mmHg, P = 0.17). Total hindlimb skeletal muscle BF was not significantly different (CHF: 102 ± 7 and CHF + NO2 (-): 109 ± 7 ml·min(-1)·100 g(-1) ml·min(-1)·100 g(-1), P > 0.05). BF increased in 6 (∼21%) and VC in 8 (∼29%) of the 28 individual muscles and muscle parts. Muscles and muscle portions exhibiting greater BF and VC after NO2 (-) infusion comprised ≥63% type IIb + IId/x muscle fibers. These data demonstrate that NO2 (-) infusion can augment skeletal muscle vascular control during exercise in CHF rats. Given the targeted effects shown herein, a NO2 (-)-based therapy may provide an attractive "needs-based" approach for treatment of the vascular dysfunction in CHF.

A 'green' diet-based approach to cardiovascular health? Is inorganic nitrate the answer?

Ingestion of fruit and vegetables rich in inorganic nitrate (NO(3)(-)) has emerged as an effective method for acutely elevating vascular nitric oxide (NO) levels through formation of an NO(2)(-) intermediate. As such a number of beneficial effects of NO(3)(-) and NO(2)(-) ingestion have been demonstrated including reductions in blood pressure, measures of arterial stiffness and platelet activity. The pathway for NO generation from such dietary interventions involves the activity of facultative oral microflora that facilitate the reduction of inorganic NO(3)(-), ingested in the diet, to inorganic NO(2)(-). This NO(2)(-) then eventually enters the circulation where, through the activity of one or more of a range of distinct NO(2)(-) reductases, it is chemically reduced to NO. This pathway provides an alternative route for in vivo NO generation that could be utilized for therapeutic benefit in those cardiovascular disease states where reduced bioavailable NO is thought to contribute to pathogenesis. Indeed, the cardiovascular benefits of NO(2)(-) and NO(3)(-) are now starting to be translated in patients in several clinical trials. In this review, we discuss recent evidence supporting the potential utility of delivery of NO(3)(-) or NO(2)(-) for the treatment of cardiovascular diseases.

Serum nitric oxide metabolites are associated with the risk of hypertriglyceridemic-waist phenotype in women: Tehran Lipid and Glucose Study

BACKGROUND AND AIM

There are some controversial issues regarding the association of nitric oxide and obesity-related states. This study was conducted to investigate whether serum nitric oxide metabolites (NOx) could predict the occurrence of visceral lipid accumulation, defined as hypertriglyceridemic-waist (HTW) phenotype.

METHODS

We used a prospective approach for this study conducted on participants of the Tehran Lipid and Glucose Study, 2243 adult men and women were followed for a median of 6.3 years. Serum NOx concentrations were measured at baseline (2006-2008), and demographics, anthropometrics and biochemical variables were evaluated at baseline and again after a 3-year (2009-2011) and a 6-year follow-up (2012-2014). The occurrence of HTW phenotype, defined as waist circumference ≥90 cm in men and ≥85 cm in women, along with serum triglyceride levels ≥177 mg/dL, were assessed across serum NOx tertiles.

RESULTS

Mean age of participants was 41.5 ± 14.5 years at baseline and 39.4% were male. The cumulative incidence of HTW phenotype was 37.6% (33.2% in men, 40.5% in women). There was no significant association between serum NOx and the occurrence of HTW phenotype in men. After adjustment of confounding variables, risk of HTW phenotype in women, in the highest compared to the lowest tertile of serum NOx (≥30.9 vs. <19.9 μmol/L), increased by 39% (OR = 1.39, 95% CI = 1.05-1.93, P for trend = 0.053).

CONCLUSION

Serum NOx level was an independent predictor of HTW phenotype in women.

Cystathionine γ-lyase regulates arteriogenesis through NO-dependent monocyte recruitment

AIMS

Hydrogen sulfide (H2S) is a vasoactive gasotransmitter that is endogenously produced in the vasculature by the enzyme cystathionine γ-lyase (CSE). However, the importance of CSE activity and local H2S generation for ischaemic vascular remodelling remains completely unknown. In this study, we examine the hypothesis that CSE critically regulates ischaemic vascular remodelling involving H2S-dependent mononuclear cell regulation of arteriogenesis.

METHODS AND RESULTS

Arteriogenesis including mature vessel density, collateral formation, blood flow, and SPY angiographic blush rate were determined in wild-type (WT) and CSE knockout (KO) mice at different time points following femoral artery ligation (FAL). The role of endogenous H2S in regulation of IL-16 expression and subsequent recruitment of monocytes, and expression of VEGF and bFGF in ischaemic tissues, were determined along with endothelial progenitor cell (CD34/Flk1) formation and function. FAL of WT mice significantly increased CSE activity, expression and endogenous H2S generation in ischaemic tissues, and monocyte infiltration, which was absent in CSE-deficient mice. Treatment of CSE KO mice with the polysulfide donor diallyl trisulfide restored ischaemic vascular remodelling, monocyte infiltration, and cytokine expression. Importantly, exogenous H2S therapy restored nitric oxide (NO) bioavailability in CSE KO mice that was responsible for monocyte recruitment and arteriogenesis.

CONCLUSION

Endogenous CSE/H2S regulates ischaemic vascular remodelling mediated during hind limb ischaemia through NO-dependent monocyte recruitment and cytokine induction revealing a previously unknown mechanism of arteriogenesis.

Therapeutic potential of sustained-release sodium nitrite for critical limb ischemia in the setting of metabolic syndrome

Nitrite is a storage reservoir of nitric oxide that is readily reduced to nitric oxide under pathological conditions. Previous studies have demonstrated that nitrite levels are significantly reduced in cardiovascular disease states, including peripheral vascular disease. We investigated the cytoprotective and proangiogenic actions of a novel, sustained-release formulation of nitrite (SR-nitrite) in a clinically relevant in vivo swine model of critical limb ischemia (CLI) involving central obesity and metabolic syndrome. CLI was induced in obese Ossabaw swine (n = 18) by unilateral external iliac artery deployment of a full cross-sectional vessel occlusion device positioned within an endovascular expanded polytetrafluoroethylene-lined nitinol stent-graft. At post-CLI day 14, pigs were randomized to placebo (n = 9) or SR-nitrite (80 mg, n = 9) twice daily by mouth for 21 days. SR-nitrite therapy increased nitrite, nitrate, and S-nitrosothiol in plasma and ischemic skeletal muscle. Oxidative stress was reduced in ischemic limb tissue of SR-nitrite- compared with placebo-treated pigs. Ischemic limb tissue levels of proangiogenic growth factors were increased following SR-nitrite therapy compared with placebo. Despite the increases in cytoprotective and angiogenic signals with SR-nitrite therapy, new arterial vessel formation and enhancement of blood flow to the ischemic limb were not different from placebo. Our data clearly demonstrate cytoprotective and proangiogenic signaling in ischemic tissues following SR-nitrite therapy in a very severe model of CLI. Further studies evaluating longer-duration nitrite therapy and/or additional nitrite dosing strategies are warranted to more fully evaluate the therapeutic potential of nitrite therapy in peripheral vascular disease.

Effect of sodium nitrite on ischaemia and reperfusion-induced arrhythmias in anaesthetized dogs: is protein S-nitrosylation involved?

Background and Purpose

To provide evidence for the protective role of inorganic nitrite against acute ischaemia and reperfusion-induced ventricular arrhythmias in a large animal model.

Experimental Approach

Dogs, anaesthetized with chloralose and urethane, were administered intravenously with sodium nitrite (0.2 µmolkg^-1min^-1) in two protocols. In protocol 1 nitrite was infused 10 min prior to and during a 25 min occlusion of the left anterior descending (LAD) coronary artery (NaNO₂-PO; n = 14), whereas in protocol 2 the infusion was started 10 min prior to reperfusion of the occluded vessel (NaNO₂-PR; n = 12). Control dogs (n = 15) were infused with saline and subjected to the same period of ischaemia and reperfusion. Severities of ischaemia and ventricular arrhythmias, as well as changes in plasma nitrate/nitrite (NOx) levels in the coronary sinus blood, were assessed throughout the experiment. Myocardial superoxide and nitrotyrosine (NT) levels were determined during reperfusion. Changes in protein S-nitrosylation (SNO) and S-glutathionylation were also examined.

Key Results

Compared with controls, sodium nitrite administered either pre-occlusion or pre-reperfusion markedly suppressed the number and severity of ventricular arrhythmias during occlusion and increased survival (0% vs. 50 and 92%) upon reperfusion. There were also significant decreases in superoxide and NT levels in the nitrite treated dogs. Compared with controls, increased SNO was found only in NaNO₂-PR dogs, whereas S-glutathionylation occurred primarily in NaNO₂-PO dogs.

Conclusions

Intravenous infusion of nitrite profoundly reduced the severity of ventricular arrhythmias resulting from acute ischaemia and reperfusion in anaesthetized dogs. This effect, among several others, may result from an NO-mediated reduction in oxidative stress, perhaps through protein SNO and/or S-glutathionylation.

Is dietary nitrate/nitrite exposure a risk factor for development of thyroid abnormality? A systematic review and meta-analysis

The potential effects of inorganic nitrate/nitrite on global health are a much debated issue. In addition to possible methemoglobinemia and carcinogenic properties, anti-thyroid effects of nitrate/nitrite have been suggested. Considering the growing significance of nitrate/nitrite and since there is no comprehensive review in data available, clarifying the effect of nitrate/nitrite on thyroid disorder outcomes is essential. Therefore, we conducted this systematic review of experimental and clinical studies, and a meta-analysis of relevant cohort and cross-sectional studies investigating the association of nitrate/nitrite exposure and thyroid function. Most animal studies show that high exposure (~10-600 times of acceptable daily intake) to nitrate/nitrite induces anti-thyroid effects, including decreased serum level of thyroid hormones and histomorphological changes in thyroid gland; however no similar observations have been documented in humans. Based on our meta-analysis, no significant association was observed between nitrate exposure and the risk of thyroid cancer, hyper- and hypothyroidism; findings from three cohort studies however showed a significant association between higher exposure to nitrite and the risk of thyroid cancer (risk = 1.48, 95% confidence interval = 1.09-2.02, P = 0.012). Additional research is needed to clarify the association between nitrate/nitrite exposures and both thyroid function and cancer.

H2S regulation of nitric oxide metabolism

Nitric oxide (NO) and hydrogen sulfide (H2S) are two major gaseous signaling molecules that regulate diverse physiological functions. Recent publications indicate the regulatory role of H2S on NO metabolism. In this chapter, we discuss the latest findings on H2S-NO interactions through formation of novel chemical derivatives and experimental approaches to study these adducts. This chapter also addresses potential H2S interference on various NO detection techniques, along with precautions for analyzing biological samples from various sources. This information will facilitate critical evaluation and clearer insight into H2S regulation of NO signaling and its influence on various physiological functions.

Mechanisms of human erythrocytic bioactivation of nitrite

Nitrite signaling likely occurs through its reduction to nitric oxide (NO). Several reports support a role of erythrocytes and hemoglobin in nitrite reduction, but this remains controversial, and alternative reductive pathways have been proposed. In this work we determined whether the primary human erythrocytic nitrite reductase is hemoglobin as opposed to other erythrocytic proteins that have been suggested to be the major source of nitrite reduction. We employed several different assays to determine NO production from nitrite in erythrocytes including electron paramagnetic resonance detection of nitrosyl hemoglobin, chemiluminescent detection of NO, and inhibition of platelet activation and aggregation. Our studies show that NO is formed by red blood cells and inhibits platelet activation. Nitric oxide formation and signaling can be recapitulated with isolated deoxyhemoglobin. Importantly, there is limited NO production from erythrocytic xanthine oxidoreductase and nitric-oxide synthase. Under certain conditions we find dorzolamide (an inhibitor of carbonic anhydrase) results in diminished nitrite bioactivation, but the role of carbonic anhydrase is abrogated when physiological concentrations of CO2 are present. Importantly, carbon monoxide, which inhibits hemoglobin function as a nitrite reductase, abolishes nitrite bioactivation. Overall our data suggest that deoxyhemoglobin is the primary erythrocytic nitrite reductase operating under physiological conditions and accounts for nitrite-mediated NO signaling in blood.

The concentration-determined and population-specific antimicrobial effects of free nitrous acid on Pseudomonas aeruginosa PAO1

There is great potential to use free nitrous acid (FNA/HNO2), the protonated form of nitrite, as an antimicrobial agent due to its bacteriostatic and bactericidal effects on a range of microorganisms. Here, we determine the effects of FNA on the opportunistic pathogen Pseudomonas aeruginosa PAO1, a well-studied denitrifier capable of nitrate/nitrite reduction in its anaerobic respiration. It was seen that lower FNA concentrations in the range of 0.1 to 0.2 mg N/L exerted a temporary inhibitory effect on the growth of P. aeruginosa, while respiratory inhibition was not detected until an FNA concentration of 1.0 mg N/L was applied. The FNA concentration of 5.0 mg N/L caused complete cell killing and likely cell lysis. The results suggest concentration-related and multiple antimicrobial effects of FNA. Differential killing of FNA in the P. aeruginosa subpopulations was detected, suggesting intrastrain heterogeneity, and does not support the idea of specific concentrations of FNA bringing about bacteriostatic and bactericidal effects on this species. A delayed recovery from FNA treatment suggested that FNA caused cell damage which required repair prior to the organism showing cell growth. The results of the study provide insight of the inhibitory and biocidal mechanisms of FNA on this important microorganism.

Sodium nitrite supplementation improves motor function and skeletal muscle inflammatory profile in old male mice

Aging is associated with motor declines that lead to functional limitations and disability, necessitating the development of therapies to slow or reverse these events. We tested the hypothesis that sodium nitrite supplementation attenuates declines in motor function in older C57BL/6 mice. Motor function was assessed using a battery of tests (grip strength, open-field distance, rota-rod endurance) in old animals (age 20-24 mo) at baseline and after 8 wk of sodium nitrite (old nitrite, n = 22, 50 mg/liter) or no treatment (old control, n = 40), and in young reference animals (3 mo, n = 87). Eight weeks of sodium nitrite supplementation improved grip strength (old nitrite, +12.0 ± 14.9% vs. old control, +1.5 ± 15.2%, P < 0.05) and open field distance (old nitrite, +9.5 ± 7.7%, P < 0.01 vs. old control, -28.1 ± 2.0%) and completely restored rota-rod endurance-run time (old nitrite, +3.2 ± 7.1%, P < 0.01 vs. old control, -21.5 ± 7.2%; old nitrite after treatment P > 0.05 vs. young reference). Inflammatory cytokines were markedly increased in quadriceps of old compared with young reference animals (by ELISA, interleukin-1β [IL-1β] 3.86 ± 2.34 vs. 1.11 ± 0.74, P < 0.05; interferon-gamma [INF-γ] 8.31 ± 1.59 vs. 3.99 ± 2.59, P < 0.01; tumor necrosis factor-alpha [TNF-α] 1.69 ± 0.44 vs. 0.76 ± 0.30 pg/ml, P < 0.01), but were reduced to young reference levels after treatment (old nitrite, IL-1β 0.67 ± 0.95; INF-γ 5.22 ± 2.01, TNF-α 1.21 ± 0.39 pg/ml, P < 0.05 vs. old control, P > 0.05 vs. young reference). Cytokine expression and treatment (old nitrite vs. old control) predicted strength (R(2) = 0.822, P < 0.001, IL-1β, INF-γ, group), open field distance (R(2) = 0.574, P < 0.01, IL-1β, group) and endurance run time (R(2) = 0.477, P < 0.05, INF-γ). Our results suggest that sodium nitrite improves motor function in old mice, in part by reducing low-grade inflammation in muscle.