Therapeutic uses of inorganic nitrite and nitrate: from the past to the future

A phase 1, first-in-human, open label, single ascending dose study to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of stabilized isoamyl nitrite nasal spray in healthy adult participants

Stabilized isoamyl nitrite (SIAN) is a novel small molecule, therapeutic candidate for the treatment of cyanide poisoning. SIAN improves survival and has a demonstrated pharmacodynamic (PD) effect in cyanide challenged nonhuman primates. Here, we report results of phase 1, first-in-human study evaluating the safety, tolerability, pharmacokinetic (PK), and PD of SIAN nasal spray in healthy human subjects (NCT05194358). SIAN was intranasally administered in ascending doses at 2 sites in Texas and Tennessee in the United States. A total of 47 subjects were enrolled across 7 dose cohorts evaluating single doses from 20 to 300 μL. Following the dosing of sentinels in each cohort, safety, PK, and PD data were interpreted by a Safety Monitoring Committee to permit dosing of additional subjects in the cohort or escalation to the next dose level. Isoamyl alcohol peak plasma concentrations were reached within 2 minutes and were highest after a 250 μL dose (125 μL/nostril). This trend was also observed for PD parameters, including a metHB peak at 2 minutes with associated increase in heart rate and systolic and diastolic blood pressure. SIAN was generally well tolerated, no serious or severe drug-related effects were observed, and there were no clinically significant changes in vitals or laboratory parameters. We conclude that SIAN, a potential new treatment for cyanide poisoning, was safe, well tolerated, and showed a relationship between PK and PD parameters at the doses tested. SIGNIFICANCE STATEMENT: This is the first-in-human clinical study to evaluate intranasal stabilized isoamyl nitrite, which was shown to be safe, well tolerated, and to elicit a measurable pharmacokinetic and pharmacodynamic response in healthy human subjects at the doses tested. This study paves the way for investigating stabilized isoamyl nitrite further as a potential emergency treatment for cyanide poisoning.

Rare cases of nitrite poisoning by accidental ingestion: Clinical and medico-legal aspects

This paper reports three rare cases of accidental sodium nitrite poisoning, including one fatality, caused by the consumption of aspic purchased from a private vendor. Clinical symptoms included cyanosis, hypotension, and respiratory distress, with methemoglobin (MetHb) levels ranging from 5 % to 41.7 %. Toxicological analysis, performed using gas chromatography coupled with a mass spectrometry in the negative chemical ionization mode (GC-NCI-MS), revealed nitrite concentrations in blood samples ranging from 4.2 to 44 µg/mL and nitrate concentrations from 36 to 256 µg/mL. Urine analysis in the fatal case showed nitrite levels exceeding 100 µg/mL. The patients received symptomatic and supportive care, and methylene blue administration was considered in cases with elevated MetHb levels. One patient died despite aggressive resuscitation efforts, highlighting the rapid progression of severe nitrite poisoning. Postmortem findings included characteristic chocolate-brown discoloration of the blood and brown organ tissues, indicative of methemoglobinemia. This study emphasizes the clinical and toxicological importance of early diagnosis and intervention in nitrite poisoning and discusses the medico-legal implications of such cases, including the forensic challenges in interpreting postmortem toxicology results.

Chronic inorganic nitrate supplementation does not improve metabolic health and worsens disease progression in mice with diet-induced obesity

Inorganic nitrate (NO3-) has been proposed to be of therapeutic use as a dietary supplement in obesity and related conditions including the metabolic syndrome (MetS), type II diabetes, and metabolic dysfunction-associated steatotic liver disease (MASLD). Administration of NO3- to endothelial nitric oxide synthase-deficient mice reversed aspects of MetS; however, the impact of NO3- supplementation in diet-induced obesity is not well understood. Here we investigated the whole body metabolic phenotype and cardiac and hepatic metabolism in mice fed a high-fat, high-sucrose (HFHS) diet for up to 12 mo of age, supplemented with 1 mM NaNO3 (or NaCl) in their drinking water. HFHS feeding was associated with a progressive obesogenic and diabetogenic phenotype, which was not ameliorated by NO3-. Furthermore, HFHS-fed mice supplemented with NO3- showed elevated levels of cardiac fibrosis and accelerated progression of MASLD including development of hepatocellular carcinoma in comparison with NaCl-supplemented mice. NO3- did not enhance mitochondrial β-oxidation capacity in any tissue assayed and did not suppress hepatic lipid accumulation, suggesting it does not prevent lipotoxicity. We conclude that NO3- is ineffective in preventing the metabolic consequences of an obesogenic diet and may instead be detrimental to metabolic health against the background of HFHS feeding. This is the first report of an unfavorable effect of long-term nitrate supplementation in the context of the metabolic challenges of overfeeding, warranting urgent further investigation into the mechanism of this interaction.NEW & NOTEWORTHY Inorganic nitrate has been suggested to be of therapeutic benefit in obesity-related conditions, as it increases nitric oxide bioavailability, enhances mitochondrial β-oxidation, and reverses metabolic syndrome in eNOS-/- mice. However, we here show that over 12 months nitrate was ineffective in preventing metabolic consequences in high fat, high sucrose-fed mice and worsened aspects of metabolic health, impairing cholesterol handling, increasing cardiac fibrosis, and exacerbating steatotic liver disease progression, with acceleration to hepatocellular carcinoma.

Bariatric surgery blunts nitrate-mediated improvements in cardiovascular function of overweight women by interfering with gastric S-nitrosothiol formation

Inorganic nitrate (NO3-) and nitrate-rich foods have been shown to exert antioxidative effects and lower blood pressure in experimental animal models and human clinical studies. The specific handling of nitrate, including its enterosalivary recirculation, secretion into saliva, oral microbial reduction to nitrite (NO2-), and the pH-dependent nitrosative capacity in the stomach have all been recognized as being important for nitrate's beneficial effects. Obesity is of major health concern worldwide and associated with increased cardiovascular risk; whether nitrate lowers blood pressure and improves endothelial function in this setting has not been investigated. We here tested the hypotheses that i) nitrate elicits cardiovascular benefits in overweight women; and ii) these beneficial effects would be diminished in women who underwent bariatric Roux-en-Y gastric bypass (RYGB) surgery. Our controlled clinical trial included 15 women with prior RYGB surgery and 15 overweight female controls. All participants received a single dose of 0.1 mmol/kg/day nitrate in the form of a beetroot extract for 14 days. Blood collection, 24-h ambulatory blood pressure measurements and endothelial function tests were performed before and after nitrate treatment. Plasma nitrite, nitrate, and S-nitrosothiol (RSNO) concentrations were determined by ozone-based reductive chemiluminescence while thiobarbituric acid reactive substances (TBARS) and total antioxidant capacity (TAC) were measured using plate-reader based assays. Nitrate reduced blood pressure and improved endothelial function in controls, but not in women with prior bariatric surgery. Nitrate also increased circulating nitrate/nitrite and RSNO levels in controls, but the latter was blunted following RYGB surgery despite even larger increases in nitrite concentrations. Similarly, nitrate increased antioxidant responses in controls but not in women with prior bariatric surgery. This is the first study to show that nitrate exerts beneficial cardiovascular effects in obesity and that the morphological/functional modifications elicited by RYGB surgery abrogates nitrate's effectiveness by preventing gastric RSNO formation.

The Top 5 Can't-Miss Sport Supplements

Background/Objectives: Sports supplements have become popular among fitness enthusiasts for enhancing the adaptive response to exercise. This review analyzes five of the most effective ergogenic aids: creatine, beta-alanine, nitrates, caffeine, and protein. Methods: We conducted a narrative review of the literature with a focus on the sport supplements with the most robust evidence for efficacy and safety. Results: Creatine, one of the most studied ergogenic aids, increases phosphocreatine stores in skeletal muscles, improving ATP production during high-intensity exercises like sprinting and weightlifting. Studies show creatine supplementation enhances skeletal muscle mass, strength/power, and muscular endurance. The typical dosage is 3-5 g per day and is safe for long-term use. Beta-alanine, when combined with the amino acid histidine, elevates intramuscular carnosine, which acts as a buffer in skeletal muscles and delays fatigue during high-intensity exercise by neutralizing hydrogen ions. Individuals usually take 2-6 g daily in divided doses to minimize paresthesia. Research shows significant performance improvements in activities lasting 1-4 min. Nitrates, found in beetroot juice, enhance aerobic performance by increasing oxygen delivery to muscles, enhancing endurance, and reducing oxygen cost during exercise. The recommended dosage is approximately 500 milligrams taken 2-3 h before exercise. Caffeine, a central nervous system stimulant, reduces perceived pain while enhancing focus and alertness. Effective doses range from 3 to 6 milligrams per kilogram of body weight, typically consumed an hour before exercise. Protein supplementation supports muscle repair, growth, and recovery, especially after resistance training. The recommended intake for exercise-trained men and women varies depending on their specific goals. Concluions: In summary, creatine, beta-alanine, nitrates, caffeine, and protein are the best ergogenic aids, with strong evidence supporting their efficacy and safety.

Nitrosative Stress in Astronaut Skeletal Muscle in Spaceflight

Long-duration mission (LDM) astronauts from the International Space Station (ISS) (>180 ISS days) revealed a close-to-normal sarcolemmal nitric oxide synthase type-1 (NOS1) immunoexpression in myofibers together with biochemical and quantitative qPCR changes in deep calf soleus muscle. Nitro-DIGE analyses identified functional proteins (structural, metabolic, mitochondrial) that were over-nitrosylated post- vs. preflight. In a short-duration mission (SDM) astronaut (9 ISS days), s-nitrosylation of a nodal protein of the glycolytic flux, specific proteins in tricarboxylic acid (TCA) cycle, respiratory chain, and over-nitrosylation of creatine kinase M-types as signs of impaired ATP production and muscle contraction proteins were seen. S-nitrosylation of serotransferrin (TF) or carbonic anhydrase 3 (CA3b and 3c) represented signs of acute response microgravity muscle maladaptation. LDM nitrosoprofiles reflected recovery of mitochondrial activity, contraction proteins, and iron transporter TF as signs of muscle adaptation to microgravity. Nitrosated antioxidant proteins, alcohol dehydrogenase 5/S-nitrosoglutathione reductase (ADH5/GSNOR), and selenoprotein thioredoxin reductase 1 (TXNRD1) levels indicated signs of altered redox homeostasis and reduced protection from nitrosative stress in spaceflight. This work presents a novel spaceflight-generated dataset on s-nitrosylated muscle protein signatures from astronauts that helps both to better understand the structural and molecular networks associated to muscular nitrosative stress and to design countermeasures to dysfunction and impaired performance control in human spaceflight missions.

Nitric oxide as a double-edged sword in pulmonary viral infections: Mechanistic insights and potential therapeutic implications

In the face of the global pandemic caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), researchers are tirelessly exploring novel therapeutic approaches to combat coronavirus disease 2019 (COVID-19) and its associated complications. Nitric oxide (NO) has appeared as a multifaceted signaling mediator with diverse and often contrasting biological activities. Its intricate biochemistry renders it a crucial regulator of cardiovascular and pulmonary functions, immunity, and neurotransmission. Perturbations in NO production, whether excessive or insufficient, contribute to the pathogenesis of various diseases, encompassing cardiovascular disease, pulmonary hypertension, asthma, diabetes, and cancer. Recent investigations have unveiled the potential of NO donors to impede SARS-CoV- 2 replication, while inhaled NO demonstrates promise as a therapeutic avenue for improving oxygenation in COVID-19-related hypoxic pulmonary conditions. Interestingly, NO's association with the inflammatory response in asthma suggests a potential protective role against SARS-CoV-2 infection. Furthermore, compelling evidence indicates the benefits of inhaled NO in optimizing ventilation-perfusion ratios and mitigating the need for mechanical ventilation in COVID-19 patients. In this review, we delve into the molecular targets of NO, its utility as a diagnostic marker, the mechanisms underlying its action in COVID-19, and the potential of inhaled NO as a therapeutic intervention against viral infections. The topmost significant pathway, gene ontology (GO)-biological process (BP), GO-molecular function (MF) and GO-cellular compartment (CC) terms associated with Nitric Oxide Synthase (NOS)1, NOS2, NOS3 were arginine biosynthesis (p-value = 1.15 x 10-9) regulation of guanylate cyclase activity (p-value = 7.5 x 10-12), arginine binding (p-value = 2.62 x 10-11), vesicle membrane (p-value = 3.93 x 10-8). Transcriptomics analysis further validates the significant presence of NOS1, NOS2, NOS3 in independent COVID-19 and pulmonary hypertension cohorts with respect to controls. This review investigates NO's molecular targets, diagnostic potentials, and therapeutic role in COVID-19, employing bioinformatics to identify key pathways and NOS isoforms' significance.

Recent Progress of Spectroscopic Probes for Peroxynitrite and Their Potential Medical Diagnostic Applications

Peroxynitrite (ONOO-) is a crucial reactive oxygen species that plays a vital role in cellular signal transduction and homeostatic regulation. Determining and visualizing peroxynitrite accurately in biological systems is important for understanding its roles in physiological and pathological activity. Among the various detection methods, fluorescent probe-based spectroscopic detection offers real-time and minimally invasive detection, high sensitivity and selectivity, and easy structural and property modification. This review categorizes fluorescent probes by their fluorophore structures, highlighting their chemical structures, recognition mechanisms, and response behaviors in detail. We hope that this review could help trigger novel ideas for potential medical diagnostic applications of peroxynitrite-related molecular diseases.

Guideline-Directed Medical Therapies for Heart Failure with a Reduced Ejection Fraction in Older Adults: A Narrative Review on Efficacy, Safety and Timeliness

Heart failure is a prevalent syndrome among older adults, with a major impact on morbidity and mortality. Higher age is correlated with underuse of guideline-directed medical therapies which, in turn, has been linked to worse clinical outcomes. Importantly, most evidence so far has been collected in adults who were younger, less multi-morbid and polymedicated compared with those who are commonly treated in daily clinical practice. Hence, we aimed to assess and describe the evidence base for pharmacotherapy in older adults with heart failure with a reduced ejection. First, a narrative review was undertaken using Medline, from inception to January 2023. Four foundational therapies were selected based on the latest European Society of Cardiology clinical practice guideline: angiotensin-converting enzyme inhibitors/angiotensin receptor neprilysin inhibitors, beta blockers, mineralocorticoid receptor antagonists and sodium-glucose cotransporter-2 inhibitors. Post hoc analyses from landmark heart failure drug trials were searched and included if they contained data on the impact of age on efficacy, safety and/or timeliness of therapies in the management of heart failure with a reduced ejection fraction. Second, a proposal was developed to support and promote the use of evidence-based heart failure pharmacotherapy in complex, older adults. In total, 11 articles were selected: 4 meta-analyses, 6 post hoc analyses and 1 review paper. No attenuation of efficacy for any of the foundational agents was found in older adults. Regarding safety, dedicated analyses showed that beta blockers, mineraloid receptor antagonists, sacubitril-valsartan, dapagliflozin and empagliflozin retained their overall benefit-risk profile regardless of age. Time to benefit was short and occurred generally within 1 month. Consensus was achieved on a five-step proposal to manage complex medication regimens in older adults suffering from heart failure. In conclusion, older adults suffering from heart failure with a reduced ejection fraction should not be denied treatment based on their age.

Berberine Recovered Oxidative Stress Induced by Sodium Nitrite in Rat Erythrocytes

OBJECTIVE

Berberine, a plant derived alkaloid, present in Berberis species is well known as one of the most important antioxidants. The current research aimed to study the heamatoprotective characteristics of berberine and clarify its plausible mechanisms against sodium nitrite.

METHODS

Forty numbers of male Sprague Dawley rats were categorized into five equal groups, including group 1: control (normal saline); group 2: berberine (100 mg/kg); group 3: sodium nitrite (80 mg/kg); group 4: sodium nitrite (80 mg/kg) plus berberine (50 mg/kg) and group 5: sodium nitrite (80 mg/kg) plus berberine (100 mg/kg) groups. All animals were orally administrated for two months once daily. At the end of the 60th day, blood samples were withdrawn by cardiac puncture and collected in test vials when the animals had been anesthetized with ketamine (70 mg/kg). Then, hemolysate was prepared and the oxidative stress biomarkers, lipid peroxidation, and antioxidant capacity of erythrocytes were evaluated.

RESULTS

Feeding of rats with sodium nitrite remarkably enhanced malondialdehyde (MDA) (p=0.001) levels and considerably reduced the levels of glutathione (GSH) (p=0.001), and also reduced the enzymatic activities of glutathione peroxidase (GPx) (p=0.02), superoxide dismutase (SOD) (p=0.001), glutathione reductase (GR) (p=0.02), and catalase (CAT) (p=0.01). However, the co-administration of these animals with 100 mg/kg of berberine remarkably reverted the values to reach nearly a normal level. While 50 mg/kg berberine failed to restore significantly all of these antioxidant biomarkers at a normal level.

CONCLUSION

Our results clearly demonstrated that berberine in a dose-dependent manner led to protection against sodium nitrite-induced oxidative injury in rat erythrocytes, which possibly reflects the antioxidant ability of this alkaloid.

Impact of nutraceuticals and dietary supplements on mitochondria modifications in healthy aging: a systematic review of randomized controlled trials

BACKGROUND

To date, the mitochondrial function has been related to several pathways involved in the cellular aging process. Dietary supplements might have reciprocal and multilevel interactions with mitochondria network; however, no systematic review assessed the role of different nutraceuticals in mitochondria modification of healthy older adults.

AIM

To assess the effects of different dietary supplements on mitochondria modifications in older adults.

METHODS

On February 22, 2022, PubMed, Scopus, Web of Science, and Cochrane were systematically searched from inception for randomized controlled trials (RCTs). According to PICO model, we considered healthy older adults as participants, nutraceutical treatment as intervention, any treatment as comparator, mitochondrial modifications as outcome. Jadad scale was used for the quality assessment.

RESULTS

Altogether, 8489 records were identified and screened until 6 studies were included. A total of 201 healthy older adults were included in the systematic review (mean age ranged from 67.0 ± 1.0 years to 76.0 ± 5.6 years). The dietary supplements assessed were sodium nitrite, N-3 polyunsaturated fatty acids, hydrogen-rich water, nicotinamide riboside, urolithin A, and whey protein powder. Positive effects were reported in terms of mitochondrial oxidative and antioxidant capacity, volume, bioenergetic capacity, and mitochondrial transcriptome based on the nutritional supplements. The quality assessment underlined that all the studies included were of good quality.

DISCUSSION

Although dietary supplements might provide positive effects on mitochondria modifications, few studies are currently available in this field.

CONCLUSION

Further studies are needed to better elucidate the reciprocal and multilevel interactions between nutraceuticals, mitochondria, and environmental stressors in healthy older adults.

Skeletal Muscle Contractile Function in Heart Failure With Reduced Ejection Fraction-A Focus on Nitric Oxide

Despite advances over the past few decades, heart failure with reduced ejection fraction (HFrEF) remains not only a mortal but a disabling disease. Indeed, the New York Heart Association classification of HFrEF severity is based on how much exercise a patient can perform. Moreover, exercise capacity-both aerobic exercise performance and muscle power-are intimately linked with survival in patients with HFrEF. This review will highlight the pathologic changes in skeletal muscle in HFrEF that are related to impaired exercise performance. Next, it will discuss the key role that impaired nitric oxide (NO) bioavailability plays in HFrEF skeletal muscle pathology. Lastly, it will discuss intriguing new data suggesting that the inorganic nitrate 'enterosalivary pathway' may be leveraged to increase NO bioavailability via ingestion of inorganic nitrate. This ingestion of inorganic nitrate has several advantages over organic nitrate (e.g., nitroglycerin) and the endogenous nitric oxide synthase pathway. Moreover, inorganic nitrate has been shown to improve exercise performance: both muscle power and aerobic capacity, in some recent small but well-controlled, cross-over studies in patients with HFrEF. Given the critical importance of better exercise performance for the amelioration of disability as well as its links with improved outcomes in patients with HFrEF, further studies of inorganic nitrate as a potential novel treatment is critical.

Tolerance of Rodents to an Intravenous Bolus Injection of Sodium Nitrate in a High Concentration

Simple Summary

Nitrate is found in many foods and is a common metabolite that is supplied mostly through the diet. Recently, we have found that an analog of this compound, labeled with the stable isotope (non-radioactive) nitrogen-15, is a potentially useful contrast agent for magnetic resonance imaging (MRI), as it does not include a metal component as most other MRI contrast agents. This analog was previously shown with a very high magnetic resonance signal, which is relatively long-lasting, when combined with the new adjunct technology to MRI called hyperpolarization. Prior to serving as a contrast agent for MRI in patients, this agent needs to be tested and validated in small animals. As a prerequisite to such studies, one must ensure that the injection of the naturally abundant agent (not labeled with any isotopes) will be tolerated by the animals. The purpose of the current study was to evaluate the tolerance to an intravenous injection of sodium nitrate in rats and mice, as MRI contrast agents are routinely administered in this way. We have found that a high dose of sodium nitrate can be safely injected into rats and mice. This result opens the way for preclinical MRI studies with sodium nitrate.

Abstract

Nitrate, the inorganic anion NO₃⁻, is found in many foods and is an endogenous mammalian metabolite, which is supplied mostly through the diet. Although much is known about the safety of sodium nitrate when given per os, methodological safety data on intravenous bolus injection of sodium nitrate to rodents are lacking. Recently, we have proposed a new use for nitrate, as a contrast agent for magnetic resonance imaging that will be metal free and leave no traces in the body and the environment further to the imaging examination. It was shown that a stable isotope-labelled analog of this ion (¹⁵NO₃⁻), in a sodium nitrate solution form and hyperpolarized state, produces a high magnetic resonance signal with prolonged visibility. Therefore, sodium nitrate was targeted for further preclinical development in this context. In the absence of methodological safety data on the potential effects of a high concentration sodium nitrate bolus intravenous injection into rodents, we carried out such an investigation in mice and rats (n = 12 of each, 6 males and 6 females in each group, altogether 24 animals). We show here that an intravenous bolus administration of sodium nitrate at a concentration of 150 mM and a dose of 51 mg/Kg does not lead to adverse effects in mice and rats. This is the first investigation of the tolerance of rodents to an intravenous injection of sodium nitrate.

Dietary Nitrate Supplementation Does Not Alter Exercise Efficiency at High Altitude - Further Results From the Xtreme Alps Study

Introduction

Nitrate supplementation in the form of beetroot juice (BRJ) ingestion has been shown to improve exercise tolerance during acute hypoxia, but its effect on exercise physiology remains unstudied during sustained terrestrial high altitude exposure. We hypothesized that performing exercise at high altitude would lower circulating nitrate and nitrite levels and that BRJ ingestion would reverse this phenomenon while concomitantly improving key determinants of aerobic exercise performance.

Methods

Twenty seven healthy volunteers (21 male) underwent a series of exercise tests at sea level (SL, London, 75 m) and again after 5-8 days at high altitude (HA, Capanna Regina Margherita or "Margherita Hut," 4,559 m). Using a double-blind protocol, participants were randomized to consume a beetroot/fruit juice beverage (three doses per day) with high levels of nitrate (∼0.18 mmol/kg/day) or a nitrate-depleted placebo (∼11.5 μmoles/kg/day) control drink, from 3 days prior to the exercise trials until completion. Submaximal constant work rate cycle tests were performed to determine exercise efficiency and a maximal incremental ramp exercise test was undertaken to measure aerobic capacity, using breath-by-breath pulmonary gas exchange measurements throughout. Concentrations of nitrate, nitrite and nitrosation products were quantified in plasma samples collected at 5 timepoints during the constant work rate tests. Linear mixed modeling was used to analyze data.

Results

At both SL and HA, plasma nitrate concentrations were elevated in the nitrate supplementation group compared to placebo (P < 0.001) but did not change throughout increasing exercise work rate. Delta exercise efficiency was not altered by altitude exposure (P = 0.072) or nitrate supplementation (P = 0.836). V̇O₂peak decreased by 24% at high altitude (P < 0.001) and was lower in the nitrate-supplemented group at both sea level and high altitude compared to placebo (P = 0.041). Dietary nitrate supplementation did not alter other peak exercise variables or oxygen consumption at anaerobic threshold. Circulating nitrite and S-nitrosothiol levels unexpectedly rose in a few individuals right after cessation of exercise at high altitude.

Conclusion

Whilst regularly consumed during an 8 days expedition to terrestrial high altitude, nitrate supplementation did not alter exercise efficiency and other exercise physiological variables, except decreasing V̇O₂peak. These results and those of others question the practical utility of BRJ consumption during prolonged altitude exposure.

Borate Ameliorates Sodium Nitrite-Induced Oxidative Stress Through Regulation of Oxidant/Antioxidant Status: Involvement of the Nrf2/HO-1 and NF-κB Pathways

The widespread industrial use of nitrite in preservatives, colorants, and manufacturing rubber products and dyes increases the possibilities of organ toxicity. Lithium borate (LB) is known as an antioxidant and an oxidative stress reliever. Therefore, this study is aimed at examining the effect of LB on nitrite-induced hepatorenal dysfunction. Twenty-eight male Swiss mice were divided into four equal groups. Group 1, the control group, received saline. Group 2 received LB orally for 5 consecutive days at a dose of 15 mg/kg bw. Group 3, the nitrite group, received sodium nitrite (NaNO₂) on Day 5 (60 mg/kg bw intraperitoneally). Group 4, the protective group (LB + NaNO₂ group), received LB for 5 days and then a single dose of NaNO₂ intraperitoneally on Day 5, the same as in Groups 2 and 3, respectively. Samples of blood and kidney were taken for serum analysis of hepatorenal biomarkers, levels of antioxidants and cytokines, and the expression of genes associated with oxidative stress and inflammation. NaNO₂ intoxication increased markers of liver and kidney functions yet decreased reduced glutathione (GSH), superoxide dismutase (SOD), and catalase activities in blood. NaNO₂ also increased the expression of tumor necrosis factor (TNF-α), interleukin-1β and interleukin-6 (IL-1β and IL-6). Pre-administration of LB protected mice from oxidative stress, lipid peroxidation, and the decrease in antioxidant enzyme activity. Moreover, LB protected mice from cytokine changes, which remained within normal levels. LB ameliorated the changes induced by NaNO₂ on the mRNA of nuclear factor erythroid 2-related factor 2 (Nfr2), heme oxygenase-1 (HO-1), nuclear factor-kappa B (NF-κB), transforming growth factor-beta 2 (TGF-β2), and glutathione-S-transferase (GST) as determined using quantitative real-time PCR (qRT-PCR). These results collectively demonstrate that LB ameliorated NaNO₂-induced oxidative stress by controlling the oxidative stress biomarkers and the oxidant/antioxidant state through the involvement of the Nrf2/HO-1 and NF-κB signaling pathways.

Plasma Nitrate Levels Are Related to Metabolic Syndrome and Are Not Altered by Treatment with DPP-4 Inhibitor Linagliptin: A Randomised, Placebo-Controlled Trial in Patients with Early Type 2 Diabetes Mellitus

The depletion of nitrate and nitrite, stable nitric oxide (NO) end-products, promotes adipose tissue dysfunction and insulin resistance (IR). Dipeptidyl peptidase-4 (DPP-4) inhibitors have the potentially beneficial side effect of increasing NO availability. In this study, nitrate and nitrite levels and the effects of DPP-4 inhibitor linagliptin were investigated in relation to metabolic syndrome (MetS) markers. Treatment-naive patients with early type 2 diabetes mellitus (T2DM) (n = 40, median age 63 IQR (55–67) years, 63% male, mean HbA1c 45 ± 4.4 mmol/mol) were randomized (1:1) to linagliptin (5 mg/day) or placebo. MetS-related markers (body mass index (BMI), triglycerides, HOMA-IR, gamma-glutamyltransferase (GGT), C-reactive protein (CRP), and adiponectin), plasma levels of nitrate, nitrite, total free thiols (TFT) and vegetable intake were estimated at baseline and after 4 and 26 weeks of treatment. Plasma nitrate, but not nitrite, correlated positively with vegetable intake (r = 0.38, p = 0.018) and was inversely associated with HOMA-IR (r = −0.44, p = 0.006), BMI (r = −0.35, p = 0.028), GGT (r = −0.37, p = 0.019) and CRP (r = −0.34, p = 0.034). The relationship between nitrate and HOMA-IR remained significant after adjusting for BMI, CRP, vegetable intake and GGT. With stable vegetable intake, nitrate and nitrite, TFT, adipokines and CRP did not change after 26 weeks of linagliptin treatment. While plasma nitrate is inversely associated with MetS, linagliptin treatment does not significantly influence nitrate and nitrite concentrations, oxidative stress, adipose tissue function and systemic inflammation.

RETRACTED: Proof of concept efficacy study of intranasal stabilized isoamyl nitrite (SIAN) in rhesus monkeys against acute cyanide poisoning

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editors-in-Chief as the authors were unable to provide documentation of approval for the interinstitutional assurance /vertebrate animal section of the paper by the relevant authority, Public Health Service (PHS) Office of Laboratory Animal Welfare (OLAW) in the time that was provided.

Impact of Thymus vulgaris extract on sodium nitrite-induced alteration of renal redox and oxidative stress: Biochemical, molecular, and immunohistochemical study

Thyme (Thymus vulgaris) is an herbal plant with pleiotropic medicinal properties. In this study, we examined the possible protective effect of an ethanolic extract of thyme leaves against the renal oxidative stress induced by sodium nitrite (NaNO₂ ). Male Swiss mice received either saline or thyme extract for 15 days (0.5 g/kg body weight, orally). NaNO₂ (60 mg/kg) was injected intraperitoneally at Day 14. The protective group received the thyme extract for 15 days and NaNO₂ on Day 14. Blood and kidney samples were taken from all groups to measure serum urea, blood urea nitrogen (BUN), creatinine, serum, tissue antioxidant activity, and the inflammatory cytokines IL-1β and IL-6. Quantitative real-time PCR (qRT-PCR) was used to examine the expression of kidney injury marker-1 (Kim-1), TNF-α, nuclear factor erythroid-2 related factor 2 (Nrf2), and hemoxygenase-1 (HO-1), all of which are associated with kidney redox and oxidative stress. Pretreatment with thyme extract reduced the effects of NaNO₂ on urea, BUN, and creatinine, and reversed its effect on tissue and serum antioxidants. NaNO₂ -induced nephritis as demonstrated by the upregulation in mRNA expression of Kim-1 and TNF-α, which was, however, recovered and protected by pretreatment with thyme extract. Expression of Nrf2 and HO-1 was upregulated by treatment with thyme extract and downregulated by NaNO₂ intoxication. NaNO₂ -induced congestion in glomeruli and dilatation of the renal tubules, conditions that were restored in the group pretreated with thyme extract. NaNO₂ upregulated Bax immunoreactivity and caused apoptosis in renal structures. Thus, thyme extract is effective in managing the renal toxicity associated with oxidative stress and renal redox. PRACTICAL APPLICATIONS: The results from this study have shown that use of thyme extract may promote better health due to its high antioxidant activity. For instance, it could be ingested to alleviate the symptoms of renal inflammation and oxidative stress associated with nitrite toxicity. Thyme extract regulated renal redox, oxidative stress, antioxidant levels, and inflammation-associated genes at the molecular, biochemical, and cellular immunohistochemical levels.

Hepatoprotective effect of Thymus vulgaris extract on sodium nitrite-induced changes in oxidative stress, antioxidant and inflammatory marker expression

The herb thyme (Thymus vulgaris) has multiple therapeutic uses. In this study, we explored how T. vulgaris leaf extract protects liver cells against sodium nitrite-(NaNO₂) induced oxidative stress. Mice were divided into four groups; each group received one of the following treatments orally: saline; T. vulgaris extract alone; NaNO₂ alone; or T. vulgaris extract + NaNO₂. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), reduced glutathione (GSH), superoxide dismutase (SOD), malondialdehyde (MDA), IL-1β, IL-6, TNF-α, and total proteins were measured in serum using standard methods. TNF-α, hemooxygenase-1 (HO-1), thioredoxin, SOD, and GSH synthase, all of which are linked to oxidative stress, were measured using quantitative real-time PCR (qRT-PCR). In mice treated with T. vulgaris extract, the effect of NaNO₂ on ALT and AST levels and total proteins was reduced, and its effect on antioxidant levels was reversed. Normally, NaNO₂ causes hepatocyte congestion and severe hepatic central vein congestion. Tissues in the mice treated with T. vulgaris were restored to normal conditions. Our results demonstrate that NaNO₂-induced hepatic injury is significantly reduced by pretreatment with T. vulgaris extract, which protects against hepatic oxidative stress and its associated genes at the biochemical, molecular, and cellular levels.

AB569, a non-toxic combination of acidified nitrite and EDTA, is effective at killing the notorious Iraq/Afghanistan combat wound pathogens, multi-drug resistant Acinetobacter baumannii and Acinetobacter spp

Multi-drug resistant (MDR) Acinetobacter baumannii (Ab) and Acinetobacter spp. present monumental global health challenges. These organisms represent model Gram-negative pathogens with known antibiotic resistance and biofilm-forming properties. Herein, a novel, nontoxic biocide, AB569, consisting of acidified nitrite (A-NO₂^-) and ethylenediaminetetraacetic acid (EDTA), demonstrated bactericidal activity against all Ab and Acinetobacter spp. strains, respectively. Average fractional inhibitory concentrations (FICs) of 0.25 mM EDTA plus 4 mM A-NO₂^- were observed across several clinical reference and multiple combat wound isolates from the Iraq/Afghanistan wars. Importantly, toxicity testing on human dermal fibroblasts (HDFa) revealed an upper toxicity limit of 3 mM EDTA plus 64 mM A-NO₂^-, and thus are in the therapeutic range for effective Ab and Acinetobacter spp. treatment. Following treatment of Ab strain ATCC 19606 with AB569, quantitative PCR analysis of selected genes products to be responsive to AB569 revealed up-regulation of iron regulated genes involved in siderophore production, siderophore biosynthesis non-ribosomal peptide synthetase module (SBNRPSM), and siderophore biosynthesis protein monooxygenase (SBPM) when compared to untreated organisms. Taken together, treating Ab infections with AB569 at inhibitory concentrations reveals the potential clinical application of preventing Ab from gaining an early growth advantage during infection followed by extensive bactericidal activity upon subsequent exposures.

Inorganic Nitrite Supplementation Improves Endothelial Function With Aging: Translational Evidence for Suppression of Mitochondria-Derived Oxidative Stress

[Figure: see text].

Nitrite and myocardial ischaemia reperfusion injury. Where are we now?

Cardiovascular disease remains the leading cause of death worldwide despite major advances in technology and treatment, with coronary heart disease (CHD) being a key contributor. Following an acute myocardial infarction (AMI), it is imperative that blood flow is rapidly restored to the ischaemic myocardium. However, this restoration is associated with an increased risk of additional complications and further cardiomyocyte death, termed myocardial ischaemia reperfusion injury (IRI). Endogenously produced nitric oxide (NO) plays an important role in protecting the myocardium from IRI. It is well established that NO mediates many of its downstream functions through the 'canonical' NO-sGC-cGMP pathway, which is vital for cardiovascular homeostasis; however, this pathway can become impaired in the face of inadequate delivery of necessary substrates, in particular L-arginine, oxygen and reducing equivalents. Recently, it has been shown that during conditions of ischaemia an alternative pathway for NO generation exists, which has become known as the 'nitrate-nitrite-NO pathway'. This pathway has been reported to improve endothelial dysfunction, protect against myocardial IRI and attenuate infarct size in various experimental models. Furthermore, emerging evidence suggests that nitrite itself provides multi-faceted protection, in an NO-independent fashion, against a myriad of pathophysiologies attributed to IRI. In this review, we explore the existing pre-clinical and clinical evidence for the role of nitrate and nitrite in cardioprotection and discuss the lessons learnt from the clinical trials for nitrite as a perconditioning agent. We also discuss the potential future for nitrite as a pre-conditioning intervention in man.

Effects of bismuth subsalicylate and encapsulated calcium ammonium nitrate on ruminal fermentation of beef cattle

A replicated 5 × 5 Latin square design with a 2 × 2 + 1 factorial arrangement of treatments was used to determine the effects of bismuth subsalicylate (BSS) and encapsulated calcium ammonium nitrate (eCAN) on ruminal fermentation of beef cattle consuming bahiagrass hay (Paspalum notatum) and sugarcane molasses. Ten ruminally cannulated steers (n = 8; 461 ± 148 kg of body weight [BW]; average BW ± SD) and heifers (n = 2; 337 ± 74 kg of BW) were randomly assigned to one of five treatments as follows: 1) 2.7 g/kg of BW of molasses (NCTRL), 2) NCTRL + 182 mg/kg of BW of urea (U), 3) U + 58.4 mg/kg of BW of BSS (UB), 4) NCTRL + 538 mg/kg of BW of eCAN (NIT), and 5) NIT + 58.4 mg/kg of BW of BSS (NITB). With the exception of NCTRL, all treatments were isonitrogenous. Beginning on day 14 of each period, ruminal fluid was collected and rectal temperature was recorded 4× per day for 3 d to determine ruminal changes every 2 h from 0 to 22 h post-feeding. Ruminal gas cap samples were collected at 0, 3, 6, 9, and 12 h on day 0 of each period followed by 0 h on days 1, 2, 3, and 14. Microbial N flow was determined using Cr-Ethylenediaminetetraacetic acid, YbCl3, and indigestible neutral detergent fiber for liquid, small particle, and large particle phases, respectively. Data were analyzed using the MIXED procedure of SAS. Orthogonal contrasts were used to evaluate the effects of nonprotein nitrogen (NPN) inclusion, NPN source, BSS, and NPN source × BSS. There was no treatment effect (P > 0.05) on concentrations of H2S on day 0, 1, 2, or 14; however, on day 3, concentrations of H2S were reduced (P = 0.018) when NPN was provided. No effect of treatment (P = 0.864) occurred for ruminal pH. There was an effect of NPN source on total concentrations of VFA (P = 0.011), where a 6% reduction occurred when eCAN was provided. There were effects of NPN (P = 0.001) and NPN source (P = 0.009) on the concentration of NH3-N, where cattle consuming NPN had a greater concentration than those not consuming NPN, and eCAN reduced the concentration compared with urea. Total concentrations of VFA and NH3-N were not affected (P > 0.05) by BSS. There was an effect of BSS (P = 0.009) on rectal temperature, where cattle not consuming BSS had greater temperatures than those receiving BSS. No differences for NPN, NPN source, nor BSS (P > 0.05) were observed for microbial N flow. In conclusion, eCAN does not appear to deliver equivalent ruminal fermentation parameters compared with urea, and BSS has limited effects on fermentation.

Red Blood Cells as a "Central Hub" for Sulfide Bioactivity: Scavenging, Metabolism, Transport, and Cross-Talk with Nitric Oxide

Significance: Sulfide was revealed to be an endogenous signaling molecule regulating a plethora of cellular functions. It is involved in the regulation of fundamental processes, including blood pressure regulation, suspended animation, and metabolic activity of mitochondria, pain, and inflammation. The underlying biochemical pathways and pharmacological targets are still largely unidentified. Recent Advances: Red blood cells (RBCs) are known as oxygen transporters and were proposed to contribute to cardiovascular homeostasis by regulating nitric oxide (NO) metabolism, also via interaction of hemoglobin with nitrite and NO itself. Interestingly, recent evidence indicates that RBCs may also play a central role in systemic sulfide metabolism and homeostasis, and, potentially, in the crosstalk with NO. Heme-containing proteins such as hemoglobin were shown to be targeted by both NO and sulfide. In this article, we aim at revising and discussing the potential impact of RBCs on systemic sulfide metabolism in the cardiovascular system. Critical Issues: Although the synthetic pathways and the reactivity of hemoglobin and other heme proteins with sulfide and NO are known, the in vivo role of RBCs in sulfide metabolism, physiology, pharmacology, and its pathophysiological implications have not been characterized so far. Future Directions: To allow a better understanding of the role of RBCs in systemic sulfide metabolism and its cross-talk with NO, basic and translational science studies should be focused on dissecting the enzymatic and nonenzymatic sulfur metabolic pathways in RBCs in vivo and their impact on the cardiovascular system in animal models and clinical settings.

Sensing of electrolytes in urine using a miniaturized paper-based device

Analyzing electrolytes in urine, such as sodium, potassium, calcium, chloride, and nitrite, has significant diagnostic value in detecting various conditions, such as kidney disorder, urinary stone disease, urinary tract infection, and cystic fibrosis. Ideally, by regularly monitoring these ions with the convenience of dipsticks and portable tools, such as cellphones, informed decision making is possible to control the consumption of these ions. Here, we report a paper-based sensor for measuring the concentration of sodium, potassium, calcium, chloride, and nitrite in urine, accurately quantified using a smartphone-enabled platform. By testing the device with both Tris buffer and artificial urine containing a wide range of electrolyte concentrations, we demonstrate that the proposed device can be used for detecting potassium, calcium, chloride, and nitrite within the whole physiological range of concentrations, and for binary quantification of sodium concentration.

The Noncanonical Pathway for In Vivo Nitric Oxide Generation: The Nitrate-Nitrite-Nitric Oxide Pathway

In contrast to nitric oxide, which has well established and important roles in the regulation of blood flow and thrombosis, neurotransmission, the normal functioning of the genitourinary system, and the inflammation response and host defense, its oxidized metabolites nitrite and nitrate have, until recently, been considered to be relatively inactive. However, this view has been radically revised over the past decade and more. Much evidence has now accumulated demonstrating that nitrite serves as a storage form of nitric oxide, releasing nitric oxide preferentially under acidic and/or hypoxic conditions but also occurring under physiologic conditions: a phenomenon that is catalyzed by a number of distinct mammalian nitrite reductases. Importantly, preclinical studies demonstrate that reduction of nitrite to nitric oxide results in a number of beneficial effects, including vasodilatation of blood vessels and lowering of blood pressure, as well as cytoprotective effects that limit the extent of damage caused by an ischemia/reperfusion insult, with this latter issue having been translated more recently to the clinical setting. In addition, research has demonstrated that the other main metabolite of the oxidation of nitric oxide (i.e., nitrate) can also be sequentially reduced through processing in vivo to nitrite and then nitrite to nitric oxide to exert a range of beneficial effects-most notably lowering of blood pressure, a phenomenon that has also been confirmed recently to be an effective method for blood pressure lowering in patients with hypertension. This review will provide a detailed description of the pathways involved in the bioactivation of both nitrate and nitrite in vivo, their functional effects in preclinical models, and their mechanisms of action, as well as a discussion of translational exploration of this pathway in diverse disease states characterized by deficiencies in bioavailable nitric oxide. SIGNIFICANCE STATEMENT: The past 15 years has seen a major revision in our understanding of the pathways for nitric oxide synthesis in the body with the discovery of the noncanonical pathway for nitric oxide generation known as the nitrate-nitrite-nitric oxide pathway. This review describes the molecular components of this pathway, its role in physiology, potential therapeutics of targeting this pathway, and their impact in experimental models, as well as the clinical translation (past and future) and potential side effects.

Mechanisms Associated to Nitroxyl (HNO)-Induced Relaxation in the Intestinal Smooth Muscle

The pharmacological properties of nitroxyl (HNO) donors in the gastrointestinal tract are unknown. We investigated the properties of this molecule in the regulation of gastrointestinal contractility focusing on its possible interaction with other gaseous signaling molecules such as NO and H₂S. Organ bath, Ca²⁺ imaging, and microelectrode recordings were performed on rat intestinal samples, using Angeli’s salt as HNO donor. Angeli’s salt caused a concentration-dependent relaxation of longitudinal or circular muscle strips of the ileum and the proximal colon. This relaxation was strongly inhibited by the Rho-kinase inhibitor Y-27632 (10 μM), by the reducing agent DTT or by the inhibitor of soluble guanylate cyclase (sGC) ODQ (10 μM) alone or in combination with the inhibitors of the endogenous synthesis of H₂S β-cyano-L-alanine (5 mM) and amino-oxyacetate (5 mM). Preventing endogenous synthesis of NO by the NO synthase inhibitor L-NAME (200 μM) did not affect the relaxation induced by HNO. HNO induced an increase in cytosolic Ca²⁺ concentration in colonic myocytes. It also elicited myocyte membrane hyperpolarization that amounted to −10.6 ± 1.1 mV. ODQ (10 μM) and Apamin (1 μM), a selective inhibitor of small conductance Ca²⁺-activated K⁺ channels (SKca), strongly antagonized this effect. We conclude that HNO relaxes the gastrointestinal tract musculature by hyperpolarizing myocytes via activation of the sGC/cGMP pathway similarly to NO, not only inhibiting the RhoK and activating MLCP as do both NO and H₂S but also increasing cytosolic Ca²⁺ for activation of SK_Ca contributing to hyperpolarization.

A comprehensive time course study of tissue nitric oxide metabolites concentrations after oral nitrite administration

Nitrite and nitrate are considered nitric oxide (NO) storage pools. The assessment of their tissue concentrations may improve our understanding of how they attenuate pathophysiological mechanisms promoting disease. We hypothesized that significant differences exist when the tissue concentrations of nitrite, nitrate, and nitrosylated species (RXNO) are compared among different tissues, particularly when nitrite is administered orally because nitrite generates various NO-related species in the stomach. We studied the different time-dependent changes in plasma and tissue concentrations of nitrite, nitrate, and RXNO after oral nitrite 15 mg/kg was administered rats, which were euthanized 15, 30, 60, 120, 240, 480 or 1440 min after nitrite administration. A control group received water. Arterial blood samples were collected and the rats were perfused with a PBS solution containing NEM/DTPA to prevent the destruction of RXNO. After perfusion, heart, aorta, mesenteric artery, brain, stomach, liver and femoral muscle were harvested and immediately stored at -70°C until analyzed for their nitrite, nitrate and RXNO contents using an ozone-based reductive chemiluminescence assay. While nitrite administration did not increase aortic nitrite or nitrate concentrations for at least 60 min, both aorta and mesenteric vessels stored nitrite from 8 to 24 h after its administration and their tissue concentrations increased from 10 to 40-fold those found in plasma. In contrast, the other studied tissues showed only transient increases in the concentrations of these NO metabolites, including RXNO. The differences among tissues may reflect differences in mechanisms regulating cellular influx of nitrite. These findings have important pharmacological and clinical implications.

Dietary Nitrate Protects Against Skin Flap Ischemia-Reperfusion Injury in Rats via Modulation of Antioxidative Action and Reduction of Inflammatory Responses

Dietary nitrate, found abundant in green vegetables, can be absorbed into the blood and be converted to nitric oxide (NO) in the body. Dietary nitrate has been proved to have many positive physiological functions in the body. Here, we evaluated the therapeutic effects of dietary nitrate on skin flap recovery following ischemia reperfusion (IR). Wistar rats were pretreated with nitrate from one week prior to ischemia to the end of reperfusion. It was found that oral administration of nitrate increased serum nitrate and nitrite levels, protected cells from apoptosis, and attenuated flap tissue edema. In the meantime, the oxidative stress marker malondialdehyde was reduced, while the activities of antioxidant enzymes were restored after nitrate treatment. Moreover, the macrophage and neutrophil infiltration in the flap was significantly attenuated by nitrate supplementation, as were the pro-inflammatory cytokines. In sum, we found that oral administration of nitrate can attenuate skin flap IR injury through the regulation of oxidative stress and inflammatory response.

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.

Acidification is an Essential Process of Cold Atmospheric Plasma and Promotes the Anti-Cancer Effect on Malignant Melanoma Cells

(1) Background: Cold atmospheric plasma (CAP) is ionized gas near room temperature. The anti-cancer effects of CAP were confirmed for several cancer types and were attributed to CAP-induced reactive species. However, the mode of action of CAP is still not well understood. (2) Methods: Changes in cytoplasmic Ca²⁺ level after CAP treatment of malignant melanoma cells were analyzed via the intracellular Ca²⁺ indicator fura-2 AM. CAP-produced reactive species were determined by fluorescence spectroscopic and protein nitration by Western Blot analysis. (3) Results: CAP caused a strong acidification of water and solutions that were buffered with the so-called Good buffers, while phosphate-buffered solutions with higher buffer capacity showed minor pH reductions. The CAP-induced Ca²⁺ influx in melanoma cells was stronger in acidic pH than in physiological conditions. NO formation that is induced by CAP was dose- and pH-dependent and CAP-treated solutions only caused protein nitration in cells under acidic conditions. (4) Conclusions: We describe the impact of CAP-induced acidification on the anti-cancer effects of CAP. A synergistic effect of CAP-induced ROS, RNS, and acidic conditions affected the intracellular Ca²⁺ level of melanoma cells. As the microenvironment of tumors is often acidic, further acidification might be one reason for the specific anti-cancer effects of CAP.

Saying NO to H2S: A Story of HNO, HSNO, and SSNO. Inorg Chem 2019;58:4039-4051. [PMID: 30883105 DOI: 10.1021/acs.inorgchem.8b02592]

Interactions between small inorganic molecules are fundamental to the understanding of basic reaction mechanisms and some of the initial processes of chemical evolution that preceded organic molecules and led to the origin of life. The kinetics of these processes are suitable for the fast generation of a variety of new chemical entities and the propagation of a cascade of chemical reactions, a property that is ideal for signaling purposes even in biological systems. NO and H₂S are such molecules that are nowadays recognized as biological gasotransmitters involved in the regulation of physiological functions through protein modifications such as S-nitrosothiol, disulfide, and persulfide formations. In this Viewpoint, we review the current understanding of interactions of NO (and organic and metal nitrosyl species) with H₂S, in both chemical and biochemical contexts. Through the formation of HNO, (H)SNO (and its isomers), (H)SSNO, and polysulfides, these two gasotransmitters initiate reaction networks with significant roles in cell signaling. The chemical reactivities and biological effects of these nitrogen and sulfur species are still unresolved, and, thus, a cross-talk between all of them represents a challenging interdisciplinary field that awaits exciting new findings. We tackle some of the intriguing and open questions and provide perspectives for future research directions.

Hyperpolarized [15N]nitrate as a potential long lived hyperpolarized contrast agent for MRI

Reports on gadolinium deposits in the body and brains of adults and children who underwent contrast-enhanced MRI examinations warrant development of new, metal free, contrast agents for MRI. Nitrate is an abundant ion in mammalian biochemistry and sodium nitrate can be safely injected intravenously. We show that hyperpolarized [¹⁵N]nitrate can potentially be used as an MR tracer. The ¹⁵N site of hyperpolarized [¹⁵N]nitrate showed a T₁ of more than 100 s in aqueous solutions, which was prolonged to more than 170 s below 20 °C. Capitalizing on this effect for polarization storage we obtained a visibility window of 9 min in blood. Conversion to [¹⁵N]nitrite, the bioactive reduced form of nitrate, was not observed in human blood and human saliva in this time frame. Thus, [¹⁵N]nitrate may serve as a long-lived hyperpolarized tracer for MR. Due to its ionic nature, the immediate applications appear to be perfusion and tissue retention imaging.

RuIII(edta)-mediated interaction of nitrite and sulphide: formation of an N-bonded thionitrous acid (HSNO) complex of RuIII(edta) in aqueous solution

It is reported for the first time that [Ru^III(edta)(NO⁺)] (edta⁴⁻ = ethylenediaminetetraacetate) generated from [Ru^III(edta)(NO₂)]²⁻ at lower pH (∼3.5) can react with NaHS to form the thionitrous acid bound Ru(edta) complex in aqueous solution.

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.

The potential of aldehyde dehydrogenase 2 as a therapeutic target in cardiovascular disease

INTRODUCTION

Mitochondrial aldehyde dehydrogenase (ALDH-2) plays a major role in the ethanol detoxification pathway by removing acetaldehyde. Therefore, ALDH-2 inhibitors such as disulfiram represent the first therapeutic targeting of ALDH-2 for alcoholism therapy. Areas covered: Recently, ALDH-2 was identified as an essential bioactivating enzyme of the anti-ischemic organic nitrate nitroglycerin, bringing ALDH-2 again into the focus of clinical interest. Mechanistic studies on the nitroglycerin bioactivation process revealed that during bioconversion of nitroglycerin and in the presence of reactive oxygen and nitrogen species the active site thiols of ALDH-2 are oxidized and the enzyme activity is lost. Thus, ALDH-2 activity represents a useful marker for cardiovascular oxidative stress, a concept, which has been meanwhile supported by a number of animal disease models. Mechanistic studies on the protective role of ALDH-2 in different disease processes identified the detoxification of 4-hydroxynonenal by ALDH-2 as a fundamental process of cardiovascular, cerebral and antioxidant protection. Expert opinion: The most recent therapeutic exploitation of ALDH-2 includes activators of the enzyme such as Alda-1 but also cell-based therapies (ALDH-bright cells) that deserve further clinical characterization in the future.

Inorganic Nitrate in Angina Study: A Randomized Double-Blind Placebo-Controlled Trial

Background

In this double‐blind randomized placebo‐controlled crossover trial, we investigated whether oral sodium nitrate, when added to existing background medication, reduces exertional ischemia in patients with angina.

Methods and Results

Seventy patients with stable angina, positive electrocardiogram treadmill test, and either angiographic or functional test evidence of significant ischemic heart disease were randomized to receive oral treatment with either placebo or sodium nitrate (600 mg; 7 mmol) for 7 to 10 days, followed by a 2‐week washout period before crossing over to the other treatment (n=34 placebo‐nitrate, n=36 nitrate‐placebo). At baseline and at the end of each treatment, patients underwent modified Bruce electrocardiogram treadmill test, modified Seattle Questionnaire, and subgroups were investigated with dobutamine stress, echocardiogram, and blood tests. The primary outcome was time to 1 mm ST depression on electrocardiogram treadmill test. Compared with placebo, inorganic nitrate treatment tended to increase the primary outcome exercise time to 1 mm ST segment depression (645.6 [603.1, 688.0] seconds versus 661.2 [6183, 704.0] seconds, P=0.10) and significantly increased total exercise time (744.4 [702.4, 786.4] seconds versus 760.9 [719.5, 802.2] seconds, P=0.04; mean [95% confidence interval]). Nitrate treatment robustly increased plasma nitrate (18.3 [15.2, 21.5] versus 297.6 [218.4, 376.8] μmol/L, P<0.0001) and almost doubled circulating nitrite concentrations (346 [285, 405] versus 552 [398, 706] nmol/L, P=0.003; placebo versus nitrate treatment). Other secondary outcomes were not significantly altered by the intervention. Patients on antacid medication appeared to benefit less from nitrate supplementation.

Conclusions

Sodium nitrate treatment may confer a modest exercise capacity benefit in patients with chronic angina who are taking other background medication.

Clinical Trial Registration

URL: https://www.clinicaltrials.gov/. Unique identifier: NCT02078921. EudraCT number: 2012‐000196‐17.

Nitrite Derived from Endogenous Bacterial Nitric Oxide Synthase Activity Promotes Aerobic Respiration

Macrophage-derived nitric oxide (NO·) is a crucial effector against invading pathogens. Yet, paradoxically, several bacterial species, including some pathogens, are known to endogenously produce NO· via nitric oxide synthase (NOS) activity, despite its apparent cytotoxicity. Here, we reveal a conserved role for bacterial NOS in activating aerobic respiration. We demonstrate that nitrite generated from endogenous NO· decomposition stimulates quinol oxidase activity in Staphylococcus aureus and increases the rate of cellular respiration. This not only supports optimal growth of this organism but also prevents a dysbalance in central metabolism. Further, we also show that activity of the SrrAB two-component system alleviates the physiological defects of the nos mutant. Our findings suggest that NOS and SrrAB constitute two distinct but functionally redundant routes for controlling staphylococcal respiration during aerobic growth.

Despite its potential autotoxic effects, several bacterial species, including pathogenic staphylococcal species, produce NO· endogenously through nitric oxide synthase (NOS) activity. Therefore, how endogenous NO· influences bacterial fitness remains unclear. Here we show that the oxidation of NO· to nitrite increases aerobic respiration and consequently optimizes central metabolism to favor growth. Importantly, we also demonstrate that cells have a “fail-safe” mechanism that can maintain respiratory activity through the SrrAB two-component signaling regulon should NOS-derived nitrite levels decrease. These findings identify NOS and SrrAB as critical determinants of staphylococcal respiratory control and highlight their potential as therapeutic targets.

Taurine mitigates nitrite-induced methemoglobin formation and oxidative damage in human erythrocytes

Nitrite is present as a noxious contaminant in drinking water and causes oxidative damage in various tissues of humans and animals. It is a well-known methemoglobin-forming agent that has been shown to damage blood cells. The protective effect of taurine, a semi-essential sulfur-containing amino acid, was studied on sodium nitrite (NaNO₂)-induced oxidative damage in human erythrocytes. Erythrocytes were incubated with NaNO₂, in the presence and absence of taurine, and changes in oxidative stress parameters determined. Pretreatment with taurine significantly ameliorated NaNO₂-induced oxidative damage to lipids, proteins, and plasma membrane. It also reduced the NaNO₂-induced increase in methemoglobin levels and ROS production. Taurine improved the antioxidant capacity of cells, restored the alterations in the activities of various metabolic enzymes, and prevented morphological changes in erythrocytes. Thus, taurine can be potentially used as a protective agent against the damaging effects of nitrite.

Sulfate, nitrate and blood pressure - An EPIC interaction between sulfur and nitrogen

Nitrate (NO₃⁻)-rich foods such as green leafy vegetables are not only part of a healthy diet, but increasingly marketed for primary prevention of cardiovascular disease (CVD) and used as ergogenic aids by competitive athletes. While there is abundant evidence for mild hypotensive effects of nitrate on acute application there is limited data on chronic intake in humans, and results from animal studies suggest no long-term benefit. This is important as nitrate can also promote the formation of nitrosamines. It is therefore classified as ‘probably carcinogenic to humans', although a beneficial effect on CVD risk might compensate for an increased cancer risk.

Dietary nitrate requires reduction to nitrite (NO₂⁻) by oral commensal bacteria to contribute to the formation of nitric oxide (NO). The extensive crosstalk between NO and hydrogen sulfide (H₂S) related metabolites may further affect nitrate’s bioactivity. Using nitrate and nitrite concentrations of drinking water − the only dietary source continuously monitored for which detailed data exist − in conjunction with data of >14,000 participants of the EPIC-Norfolk study, we found no inverse associations with blood pressure or CVD risk. Instead, we found a strong interaction with sulfate (SO₄²⁻). At low sulfate concentrations, nitrate was inversely associated with BP (−4 mmHg in top quintile) whereas this was reversed at higher concentrations (+3 mmHg in top quintile).

Our findings have a potentially significant impact for pharmacology, physiology and public health, redirecting our attention from the oral microbiome and mouthwash use to interaction with sulfur-containing dietary constituents. These results also indicate that nitrate bioactivation is more complex than hitherto assumed. The modulation of nitrate bioactivity by sulfate may render dietary lifestyle interventions aimed at increasing nitrate intake ineffective and even reverse potential antihypertensive effects, warranting further investigation.