Nitrite is an alternative source of NO in vivo

Facilitating Nitrite-Derived S-Nitrosothiol Formation in the Upper Gastrointestinal Tract in the Therapy of Cardiovascular Diseases

Cardiovascular diseases (CVDs) are often associated with impaired nitric oxide (NO) bioavailability, a critical pathophysiological alteration in CVDs and an important target for therapeutic interventions. Recent studies have revealed the potential of inorganic nitrite and nitrate as sources of NO, offering promising alternatives for managing various cardiovascular conditions. It is now becoming clear that taking advantage of enzymatic pathways involved in nitrite reduction to NO is very relevant in new therapeutics. However, recent studies have shown that nitrite may be bioactivated in the acidic gastric environment, where nitrite generates NO and a variety of S-nitrosating compounds that result in increased circulating S-nitrosothiol concentrations and S-nitrosation of tissue pharmacological targets. Moreover, transnitrosation reactions may further nitrosate other targets, resulting in improved cardiovascular function in patients with CVDs. In this review, we comprehensively address the mechanisms and relevant effects of nitrate and nitrite-stimulated gastric S-nitrosothiol formation that may promote S-nitrosation of pharmacological targets in various CVDs. Recently identified interfering factors that may inhibit these mechanisms and prevent the beneficial responses to nitrate and nitrite therapy were also taken into consideration.

Spin Trapping of Nitric Oxide by Hemoglobin and Ferrous Diethyldithiocarbamate in Model Tumors Differing in Vascularization

Animal tumors serve as reasonable models for human cancers. Both human and animal tumors often reveal triplet EPR signals of nitrosylhemoglobin (HbNO) as an effect of nitric oxide formation in tumor tissue, where NO is complexed by Hb. In search of factors determining the appearance of nitrosylhemoglobin (HbNO) in solid tumors, we compared the intensities of electron paramagnetic resonance (EPR) signals of various iron-nitrosyl complexes detectable in tumor tissues, in the presence and absence of excess exogenous iron(II) and diethyldithiocarbamate (DETC). Three types of murine tumors, namely, L5178Y lymphoma, amelanotic Cloudman S91 melanoma, and Ehrlich carcinoma (EC) growing in DBA/2 or Swiss mice, were used. The results were analyzed in the context of vascularization determined histochemically using antibodies to CD31. Strong HbNO EPR signals were found in melanoma, i.e., in the tumor with a vast amount of a hemorrhagic necrosis core. Strong Fe(DETC)2NO signals could be induced in poorly vascularized EC. In L5178Y, there was a correlation between both types of signals, and in addition, Fe(RS)2(NO)2 signals of non-heme iron-nitrosyl complexes could be detected. We postulate that HbNO EPR signals appear during active destruction of well-vascularized tumor tissue due to hemorrhagic necrosis. The presence of iron-nitrosyl complexes in tumor tissue is biologically meaningful and defines the evolution of complicated tumor-host interactions.

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.

Nitric Oxide Oxygenation Reactions of Cobalt-Peroxo and Cobalt-Nitrosyl Complexes

Here, we report a comparative study of nitric oxide oxidation (NOO) reactions of Co^III-peroxo (Co^III-O₂^2-) and Co-nitrosyl ({CoNO}⁸) complexes bearing the same N₄-donor ligand (HMTETA) framework. In this regard, we prepared and characterized two new [(HMTETA)Co^III(O₂^2-)]⁺ (2, S = 2) and [(HMTETA)Co(NO)]²⁺ (3, S = 1) complexes from [(HMTETA)Co^II(CH₃CN)₂]²⁺ (1). Both complexes (2 and 3) are characterized by different spectroscopic measurements, including their DFT-optimized structures. Complex 2 produces Co^II-nitrato [(HMTETA)Co^II(NO₃^-)]⁺ (Co^II-NO₃^-, 4) complex in the presence of NO. In contrast, when 3 reacted with a superoxide (O₂^•-) anion, it generated Co^II-nitrito [(HMTETA)Co^II(NO₂^-)]⁺ (Co^II-NO₂^-, 5) with O₂ evolution. Experiments performed using ^18/16O-labeled superoxide (¹⁸O₂^•-/¹⁶O₂^•-) showed that O₂ originated from the O₂^•- anion. Both the NOO reactions are believed to proceed via a presumed peroxynitrite (PN) intermediate. Although we did not get direct spectral evidence for the proposed PN species, the mechanistic investigation using 2,4-di-tert-butylphenol indirectly suggests the formation of a PN intermediate. Furthermore, tracking the source of the N-atom in the above NOO reactions using ¹⁵N-labeled nitrogen (¹⁵NO) revealed N-atoms in 4 (Co^II-¹⁵NO₃^-) and 5 (Co^II-¹⁵NO₂^-) derived from the ¹⁵NO moiety.

Acid-induced nitrite reduction of nonheme iron(ii)-nitrite: mimicking biological Fe-NiR reactions

Nitrite reductase (NiR) catalyzes nitrite (NO₂ ^-) to nitric oxide (NO) transformation in the presence of an acid (H⁺ ions/pH) and serves as a critical step in NO biosynthesis. In addition to the NiR enzyme, NO synthases (NOSs) participate in NO production. The chemistry involved in the catalytic reduction of NO₂ ^-, in the presence of H⁺, generates NO with a H₂O molecule utilizing two H⁺ + one electron from cytochromes and is believed to be affected by the pH. Here, to understand the effect of H⁺ ions on NO₂ ^- reduction, we report the acid-induced NO₂ ^- reduction chemistry of a nonheme Fe^II-nitrito complex, [(12TMC)Fe^II(NO₂ ^-)]⁺ (Fe^II-NO₂ ^-, 2), with variable amounts of H⁺. Fe^II-NO₂ ^- upon reaction with one-equiv. of acid (H⁺) generates [(12TMC)Fe(NO)]²⁺, {FeNO}⁷ (3) with H₂O₂ rather than H₂O. However, the amount of H₂O₂ decreases with increasing equivalents of H⁺ and entirely disappears when H⁺ reaches ≅ two-equiv. and shows H₂O formation. Furthermore, we have spectroscopically characterized and followed the formation of H₂O₂ (H⁺ = one-equiv.) and H₂O (H⁺ ≅ two-equiv.) and explained why bio-driven NiR reactions end with NO and H₂O. Mechanistic investigations, using ¹⁵N-labeled-¹⁵NO₂ ^- and ²H-labeled-CF₃SO₃D (D⁺ source), revealed that the N atom in the {Fe^14/15NO}⁷ is derived from the NO₂ ^- ligand and the H atom in H₂O or H₂O₂ is derived from the H⁺ source, respectively.

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

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

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.

Oral nitrite treatment increases S-nitrosylation of vascular protein kinase C and attenuates the responses to angiotensin II

Nitrate and nitrite supplement deficient endogenous nitric oxide (NO) formation. While these anions may generate NO, recent studies have shown that circulating nitrite levels do not necessarily correlate with the antihypertensive effect of oral nitrite administration and that formation of nitrosylated species (RXNO) in the stomach is critically involved in this effect. This study examined the possibility that RXNO formed in the stomach after oral nitrite administration promotes target protein nitrosylation in the vasculature, inhibits vasoconstriction and the hypertensive responses to angiotensin II. Our results show that oral nitrite treatment enhances circulating RXNO concentrations (measured by ozone-based chemiluminescence methods), increases aortic protein kinase C (PKC) nitrosylation (measured by resin-assisted capture SNO-RAC method), and reduces both angiotensin II-induced vasoconstriction (isolated aortic ring preparation) and hypertensive (in vivo invasive blood pressure measurements) effects implicating PKC nitrosylation as a key mechanism for the responses to oral nitrite. Treatment of rats with the nitrosylating compound S-nitrosoglutathione (GSNO) resulted in the same effects described for oral nitrite. Moreover, partial depletion of thiols with buthionine sulfoximine prevented PKC nitrosylation and the blood pressure effects of oral nitrite. Further confirming a role for PKC nitrosylation, preincubation of aortas with GSNO attenuated the responses to both angiotensin II and to a direct PKC activator, and this effect was attenuated by ascorbate (reverses GSNO-induced nitrosylation). GSNO-induced nitrosylation also inhibited the increases in Ca2+ mobilization in angiotensin II-stimulated HEK293T cells expressing angiotensin type 1 receptor. Together, these results are consistent with the idea that PKC nitrosylation in the vasculature may underlie oral nitrite treatment-induced reduction in the vascular and hypertensive responses to angiotensin II.

•

Oral nitrite treatment exerts antihypertensive effects.

•

The mechanisms explaining such effects are not entirely known.

•

Oral nitrite treatment increases circulating concentrations of nitrosylating species.

•

Vascular PKC nitrosylation attenuates the vascular responses to angiotensin II.

The nitric oxide dependence of cutaneous microvascular function to independent and combined hypoxic cold exposure

When separated from local cooling, whole body cooling elicited cutaneous reflex vasoconstriction via mechanisms independent of nitric oxide removal. Hypoxia elicited cutaneous vasodilatation via mechanisms mediated primarily by nitric oxide synthase, rather than xanthine oxidase-mediated nitrite reduction. Cold-induced vasoconstriction was blunted by the opposing effect of hypoxic vasodilatation, whereas the underpinning mechanisms did not interrelate in the absence of local cooling. Full vasoconstriction was restored with nitric oxide synthase inhibition.

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.

Circulating markers of nitric oxide homeostasis and cardiometabolic diseases: insights from population-based studies

Emerging data suggest that impaired nitric oxide (NO) homeostasis has a key role in development of cardiometabolic disorders. The association between circulating levels of NO metabolites, i.e. nitrate and nitrite (NOx), and risk of chronic diseases has not yet been fully clarified. This work aims to address epidemiologic aspects of NO metabolism and discusses different physiologic and pathophysiologic conditions influencing circulating NOx. Further, cross-sectional associations of serum NOx with metabolic disorders are described and along the way, potential short-term and long-term power of serum NOx for predicting cardiometabolic outcomes are reviewed. Results from population-based studies show that circulating NOx is affected by aging, smoking habits, pregnancy, menopause status, thyroid hormones, and various pathologic conditions including type 2 diabetes, insulin resistance, hypertension, and renal dysfunction. Lifestyle factors, especially dietary habits, but also smoking habits and the degree of physical activity influence NO homeostasis and the circulating levels of NOx. Elevated serum NOx, due to increased iNOS activity, is associated with increased incidence of metabolic syndrome, different obesity phenotypes, and cardiovascular events.

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.

Nutrients, Nutraceuticals, and Xenobiotics Affecting Renal Health

Chronic kidney disease (CKD) affects 8–16% of the population worldwide. In developed countries, the most important risk factors for CKD are diabetes, hypertension, and obesity, calling into question the importance of educating and acting on lifestyles and nutrition. A balanced diet and supplementation can indeed support the maintenance of a general health status, including preservation of renal function, and can help to manage and curb the main risk factors for renal damage. While the concept of protein and salt restriction in nephrology is historically acknowledged, the role of some nutrients in renal health and the importance of nutrition as a preventative measure for renal care are less known. In this narrative review, we provide an overview of the demonstrated and potential actions of some selected nutrients, nutraceuticals, and xenobiotics on renal health and function. The direct and indirect effects of fiber, protein, fatty acids, curcumin, steviol glycosides, green tea, coffee, nitrates, nitrites, and alcohol on kidney health are reviewed here. In view of functional and personalized nutrition, understanding the renal and systemic effects of dietary components is essential since many chronic conditions, including CKD, are related to systemic dysfunctions such as chronic low-grade inflammation.

Regulation of vascular tone homeostasis by NO and H2S: Implications in hypertension

Nitric oxide (NO) and hydrogen sulfide (H2S) are two gasotransmitters that are produced in the vasculature and contribute to the regulation of vascular tone. NO and H2S are synthesized in both vascular smooth muscle and endothelial cells; NO functions primarily through the sGC/cGMP pathway, and H2S mainly through activation of the ATP-dependent potassium channels; both leading to relaxation of vascular smooth muscle cells. A deficit in the NO/H2S homeostasis is involved in the pathogenesis of various cardiovascular diseases, especially hypertension. It is now becoming increasingly clear that there are important interactions between NO and H2S and that have a profound impact on vascular tone and this may provide insights into the new therapeutic interventions. The aim of this review is to provide a better understanding of individual and interactive roles of NO and H2S in vascular biology. Overall, available data indicate that both NO and H2S contribute to vascular (patho)physiology and in regulating blood pressure. In addition, boosting NO and H2S using various dietary sources or donors could be a hopeful therapeutic strategy in the management of hypertension.

Nitrite Prevents Right Ventricular Failure and Remodeling Induced by Pulmonary Artery Banding

BACKGROUND

Nitrite has been shown to reduce right ventricle (RV) remodeling in experimental pulmonary hypertension. However, whether this effect is due to a reduction in RV afterload (ie, reduction in pulmonary artery pressure) or a direct effect on the RV itself remains unanswered. We hypothesize that nitrite has direct effects on RV remodeling and studied its effects in mice with pulmonary artery banding (PAB).

METHODS AND RESULTS

PAB decreased exercise tolerance and reduced RV systolic and diastolic function. Nitrite treatment attenuated the decrease in RV systolic function and improved the RV diastolic function. Nitrite-treated mice with PAB had similar exercise tolerance compared with a control group. PAB induced RV hypertrophy and fibrosis which were associated with increased expression of phospho-Akt. Interestingly, nitrite treatment attenuated PAB-induced RV hypertrophy and reduced the expression of phospho-Akt in RV tissue from mice with PAB. In neonatal rat cardiac fibroblast, nitrite also attenuated hypoxia-induced increase in expression of phospho-Akt.

CONCLUSION

Our study indicates that nitrite treatment has direct beneficial effects on RV and improves function and attenuates remodeling in RV exposed to chronic pressure overload. These beneficial effects, at least in part, could be due to the inhibition of the phospho-Akt (p-Akt) pathway activation.

Chronic administration of sodium nitrite prevents hypertension and protects arterial endothelial function by reducing oxidative stress in angiotensin II-infused mice

AIM

Endothelial dysfunction accompanied by an increase in oxidative stress is a key event leading to hypertension. As dietary nitrite has been reported to exert antihypertensive effect, the present study investigated whether chronic oral administration of sodium nitrite improves vascular function in conduit and resistance arteries of hypertensive animals with elevated oxidative stress.

METHODS

Sodium nitrite (50mg/L) was given to angiotensin II-infused hypertensive C57BL/6J (eight to ten weeks old) mice for two weeks in the drinking water. Arterial systolic blood pressure was measured using the tail-cuff method. Vascular responsiveness of isolated aortae and renal arteries was studied in wire myographs. The level of nitrite in the plasma and the cyclic guanosine monophosphate (cGMP) content in the arterial wall were determined using commercially available kits. The production of reactive oxygen species (ROS) and the presence of proteins (nitrotyrosine, NOx-2 and NOx-4) involved in ROS generation were evaluated with dihydroethidium (DHE) fluorescence and by Western blotting, respectively.

RESULTS

Chronic administration of sodium nitrite for two weeks to mice with angiotensin II-induced hypertension decreased systolic arterial blood pressure, reversed endothelial dysfunction, increased plasma nitrite level as well as vascular cGMP content. In addition, sodium nitrite treatment also decreased the elevated nitrotyrosine and NOx-4 protein level in angiotensin II-infused hypertensive mice.

CONCLUSIONS

The present study demonstrates that chronic treatment of hypertensive mice with sodium nitrite improves impaired endothelium function in conduit and resistance vessels in addition to its antihypertensive effect, partly through inhibition of ROS production.

The potential of stimulating nitric oxide formation in the treatment of hypertension

INTRODUCTION

Hypertension is a leading cause of morbidity and mortality worldwide. A major pathophysiological factor contributing to hypertension is reduced nitric oxide (NO) bioavailability. Strategies to address this pathophysiological mechanism could offer significant advantages. Areas covered: In this review we aimed at examining a variety of drugs (statins, beta-adrenergic receptor blockers, calcium channel blockers, angiotensin converting enzyme inhibitors, angiotensin II type-1 receptor blockers) used to treat hypertension and other cardiovascular diseases, particularly with respect to their potential of increasing NO bioavailability and activity in the cardiovascular system. There is now evidence supporting the notion that many cardiovascular drugs activate NO signaling or enhance NO bioavailability as a contributing mechanism to their beneficial cardiovascular effects. Moreover, other drugs may attenuate NO inactivation by superoxide and other reactive oxygen species by exerting antioxidant effects. More recently, the NO oxidation products nitrite and nitrate have been acknowledged as sources of NO after recycling back to NO. Activation of the nitrate-nitrite-NO pathway is an alternate pathway that may generate NO from both anions and exert antihypertensive effects. Expert opinion: In this review, we provide an overview of the possible mechanisms by which these drugs enhance NO bioavailability and help in the therapy of hypertension.

Oral nitrite circumvents antiseptic mouthwash-induced disruption of enterosalivary circuit of nitrate and promotes nitrosation and blood pressure lowering effect

The nitric oxide (NO^•) metabolites nitrite and nitrate exert antihypertensive effects by mechanisms that involve gastric formation of S-nitrosothiols. However, while the use of antiseptic mouthwash (AM) is known to attenuate the responses to nitrate by disrupting its enterosalivary cycle, there is little information about whether AM attenuates the effects of orally administered nitrite. We hypothesized that the antihypertensive effects of orally administered nitrite would not be prevented by AM because, in contrast to oral nitrate, oral nitrite could promote S-nitrosothiols formation in the stomach without intereference by AM. Chronic effects of oral nitrite or nitrate were studied in two-kidney, one-clip (2K1C) hypertensive rats (and normotensive controls) treated with AM (or vehicle) once/day. We found that orally administered nitrite exerts antihypertensive effects that were not affected by AM. This finding contrasts with lack of antihypertensive responses to oral nitrate in 2K1C hypertensive rats treated with AM. Nitrite and nitrate treatments increased plasma nitrites, nitrates, and S-nitrosothiols concentrations. However, while treatment with AM attenuated the increases in plasma nitrite concentrations after both nitrite and nitrate treatments, AM attenuated the increases in S-nitrosothiols in nitrate-treated rats, but not in nitrite-treated rats. Moreover, AM attenuated vascular S-nitrosylation (detected by the SNO-RAC method) after nitrate, but not after nitrite treatment. Significant correlations were found between the hypotensive responses and S-nitrosothiols, and vascular S-nitrosylation levels. These results show for the first time that oral nitrite exerts antihypertensive effects notwithstanding the fact that antiseptic mouthwash disrupts the enterosalivary circulation of nitrate. Our results support a major role for S-nitrosothiols formation resulting in vascular S-nitrosylation as a key mechanism for the antihypertensive effects of both oral nitrite and nitrate.

Role of Nitric Oxide in Cardiovascular Adaptation to Intermittent Hypoxia

Hypoxia is one of the most frequently encountered stresses in health and disease. The duration, frequency, and severity of hypoxic episodes are critical factors determining whether hypoxia is beneficial or harmful. Adaptation to intermittent hypoxia has been demonstrated to confer cardiovascular protection against more severe and sustained hypoxia, and, moreover, to protect against other stresses, including ischemia. Thus, the direct and cross protective effects of adaptation to intermittent hypoxia have been used for treatment and prevention of a variety of diseases and to increase efficiency of exercise training. Evidence is mounting that nitric oxide (NO) plays a central role in these adaptive mechanisms. NO-dependent protective mechanisms activated by intermittent hypoxia include stimulation of NO synthesis as well as restriction of NO overproduction. In addition, alternative, nonenzymic sources of NO and negative feedback of NO synthesis are important factors in optimizing NO concentrations. The adaptive enhancement of NO synthesis and/or availability activates or increases expression of other protective factors, including heat shock proteins, antioxidants and prostaglandins, making the protection more robust and sustained. Understanding the role of NO in mechanisms of adaptation to hypoxia will support development of therapies to prevent and treat hypoxic or ischemic damage to organs and cells and to increase adaptive capabilities of the organism.

The Nitrate-Nitrite-NO Pathway and Its Implications for Heart Failure and Preserved Ejection Fraction

The pathogenesis of exercise intolerance in patients with heart failure and preserved ejection fraction (HFpEF) is likely multifactorial. In addition to cardiac abnormalities (diastolic dysfunction, abnormal contractile reserve, chronotropic incompetence), several peripheral abnormalities are likely to be involved. These include abnormal pulsatile hemodynamics, abnormal arterial vasodilatory responses to exercise, and abnormal peripheral O2 delivery, extraction, and utilization. The nitrate-nitrite-NO pathway is emerging as a potential target to modify key physiologic abnormalities, including late systolic left ventricular (LV) load from arterial wave reflections (which has deleterious short- and long-term consequences for the LV), arterial vasodilatory reserve, muscle O2 delivery, and skeletal muscle mitochondrial function. In a recently completed randomized trial, the administration of a single dose of exogenous inorganic nitrate has been shown to exert various salutary arterial hemodynamic effects, ultimately leading to enhanced aerobic capacity in patients with HFpEF. These effects have the potential for both immediate improvements in exercise tolerance and for long-term "disease-modifying" effects. In this review, we provide an overview of key mechanistic contributors to exercise intolerance in HFpEF, and of the potential therapeutic role of drugs that target the nitrate-nitrite-NO pathway.

Sodium nitrite exerts an antihypertensive effect and improves endothelial function through activation of eNOS in the SHR

Sodium nitrite (NaNO₂) induces relaxation in isolated arteries partly through an endothelium-dependent mechanism involving NO-eNOS-sGC-cGMP pathway. The present study was designed to investigate the effect of chronic NaNO₂ administration on arterial systolic blood pressure (SBP) and vascular function in hypertensive rats. NaNO₂ (150 mg L−1) was given in drinking water for four weeks to spontaneously (SHR) and Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME) treated hypertensive SD rats. Arterial SBP and vascular function in isolated aortae were studied. Total plasma nitrate/nitrite and vascular cyclic guanosine monophosphate (cGMP) levels were measured using commercially available assay kits. Vascular nitric oxide (NO) levels were evaluated by DAF-FM fluorescence while the proteins involved in endothelial nitric oxide synthase (eNOS) activation was determined by Western blotting. NaNO₂ treatment reduced SBP, improved the impaired endothelium-dependent relaxation, increased plasma total nitrate/nitrite level and vascular tissue NO and cGMP levels in SHR. Furthermore, increased presence of phosphorylated eNOS and Hsp-90 was observed in NaNO₂-treated SHR. The beneficial effect of nitrite treatment was not observed in L-NAME treated hypertensive SD rats. The present study provides evidence that chronic treatment of genetically hypertensive rats with NaNO₂ improves endothelium-dependent relaxation in addition to its antihypertensive effect, partly through mechanisms involving activation of eNOS.

Tempol improves xanthine oxidoreductase-mediated vascular responses to nitrite in experimental renovascular hypertension

Upregulation of xanthine oxidoreductase (XOR) increases vascular reactive oxygen species (ROS) levels and contributes to nitroso-redox imbalance. However, XOR can generate nitric oxide (NO) from nitrite, and increased superoxide could inactivate NO formed from nitrite. This study tested the hypothesis that XOR contributes to the cardiovascular effects of nitrite in renovascular hypertension, and that treatment with the antioxidant tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) improves XOR-mediated effects of nitrite. Blood pressure was assessed weekly in two-kidney one-clip (2K1C) and control rats. After six weeks of hypertension, the relaxing responses to nitrite were assessed in aortic rings in the presence of the XOR inhibitor oxypurinol (or vehicle), either in the absence or in the presence of tempol. Moreover, in vivo hypotensive responses to nitrite were also examined in the presence of oxypurinol (or vehicle) and tempol (or vehicle). Aortic XOR activity and expression were evaluated by fluorescence and Western blot, respectively. Vascular ROS production was assessed by the dihydroethidium assay. 2K1C hypertensive rats showed increased aortic XOR activity and vascular ROS production compared with control rats. Oxypurinol shifted the nitrite concentration–response curve to the right in aortic rings from 2K1C rats (but not in controls). Oxypurinol also attenuated the hypotensive responses to nitrite in 2K1C rats (but not in controls). These functional findings agree with increased aortic and plasma XOR activity found in 2K1C rats. Tempol treatment enhanced oxypurinol-induced shift of the nitrite concentration–response curve to the right. However, antioxidant treatment did not affect XOR-mediated hypotensive effects of nitrite. Our results show that XOR is important to the cardiovascular responses to nitrite in 2K1C hypertension, and XOR inhibitors commonly used by patients may cancel this effect. This finding suggests that nitrite treatment may not be effective in patients being treated with XOR inhibitors. Moreover, while tempol may improve the vascular responses to nitrite, antihypertensive responses are not affected.

•

Upregulation of xanthine oxidoreductase (XOR) is usually found in hypertension.

•

While XOR produces superoxide, it can also produce NO from nitrite.

•

This study shows that XOR mediates vasorelaxing effects of nitrite in renovascular hypertension.

•

XOR inhibition prevents against the antihypertensive effects of nitrite.

•

Antioxidant treatment improves XOR-mediated vasorelaxing effects of nitrite.

Gastric S-nitrosothiol formation drives the antihypertensive effects of oral sodium nitrite and nitrate in a rat model of renovascular hypertension

Many effects of nitrite and nitrate are attributed to increased circulating concentrations of nitrite, ultimately converted into nitric oxide (NO(•)) in the circulation or in tissues by mechanisms associated with nitrite reductase activity. However, nitrite generates NO(•) , nitrous anhydride, and other nitrosating species at low pH, and these reactions promote S-nitrosothiol formation when nitrites are in the stomach. We hypothesized that the antihypertensive effects of orally administered nitrite or nitrate involve the formation of S-nitrosothiols, and that those effects depend on gastric pH. The chronic effects of oral nitrite or nitrate were studied in two-kidney, one-clip (2K1C) hypertensive rats treated with omeprazole (or vehicle). Oral nitrite lowered blood pressure and increased plasma S-nitrosothiol concentrations independently of circulating nitrite levels. Increasing gastric pH with omeprazole did not affect the increases in plasma nitrite and nitrate levels found after treatment with nitrite. However, treatment with omeprazole severely attenuated the increases in plasma S-nitrosothiol concentrations and completely blunted the antihypertensive effects of nitrite. Confirming these findings, very similar results were found with oral nitrate. To further confirm the role of gastric S-nitrosothiol formation, we studied the effects of oral nitrite in hypertensive rats treated with the glutathione synthase inhibitor buthionine sulfoximine (BSO) to induce partial thiol depletion. BSO treatment attenuated the increases in S-nitrosothiol concentrations and antihypertensive effects of oral nitrite. These data show that gastric S-nitrosothiol formation drives the antihypertensive effects of oral nitrite or nitrate and has major implications, particularly to patients taking proton pump inhibitors.

Consistent antioxidant and antihypertensive effects of oral sodium nitrite in DOCA-salt hypertension

Hypertension is a common disease that includes oxidative stress as a major feature, and oxidative stress impairs physiological nitric oxide (NO) activity promoting cardiovascular pathophysiological mechanisms. While inorganic nitrite and nitrate are now recognized as relevant sources of NO after their bioactivation by enzymatic and non-enzymatic pathways, thus lowering blood pressure, mounting evidence suggests that sodium nitrite also exerts antioxidant effects. Here we show for the first time that sodium nitrite exerts consistent systemic and vascular antioxidant and antihypertensive effects in the deoxycorticosterone-salt (DOCA-salt) hypertension model. This is particularly important because increased oxidative stress plays a major role in the DOCA-salt hypertension model, which is less dependent on activation of the renin-angiotensin system than other hypertension models. Indeed, antihypertensive effects of oral nitrite were associated with increased plasma nitrite and nitrate concentrations, and completely blunted hypertension-induced increases in plasma 8-isoprostane and lipid peroxide levels, in vascular reactive oxygen species, in vascular NADPH oxidase activity, and in vascular xanthine oxidoreductase activity. Together, these findings provide evidence that the oral administration of sodium nitrite consistently decreases the blood pressure in association with major antioxidant effects in experimental hypertension.

●

Nitrite is known to recycle back to NO under specific conditions.

●

Antihypertensive effects have been shown for sodium nitrite in some animal models.

●

The DOCA-salt hypertension model includes oxidative stress as a major pathogenetic mechanism.

●

This study shows antihypertensive effects of nitrite in the DOCA-salt hypertension model.

●

Reduction in arterial blood pressure was associated with important antioxidant effects of sodium nitrite.

Validation of a method to directly and specifically measure nitrite in biological matrices

The bioactivity of nitric oxide (NO) is influenced by chemical species generated through reactions with proteins, lipids, metals, and its conversion to nitrite and nitrate. A better understanding of the functions played by each of these species could be achieved by developing selective assays able of distinguishing nitrite from other NO species. Nagababu and Rifkind developed a method using acetic and ascorbic acids to measure nitrite-derived NO in plasma. Here, we adapted, optimized, and validated this method to assay nitrite in tissues. The method yielded linear measurements over 1-300 pmol of nitrite and was validated for tissue preserved in a nitrite stabilization solution composed of potassium ferricyanide, N-ethylmaleimide and NP-40. When samples were processed with chloroform, but not with methanol, ethanol, acetic acid or acetonitrile, reliable and reproducible nitrite measurements in up to 20 sample replicates were obtained. The method's accuracy in tissue was ≈ 90% and in plasma 99.9%. In mice, during basal conditions, brain, heart, lung, liver, spleen and kidney cortex had similar nitrite levels. In addition, nitrite tissue levels were similar regardless of when organs were processed: immediately upon collection, kept in stabilization solution for later analysis or frozen and later processed. After ip nitrite injections, rapidly changing nitrite concentrations in tissue and plasma could be measured and were shown to change in significantly distinct patterns. This validated method could be valuable for investigations of nitrite biology in conditions such as sickle cell disease, cardiovascular disease, and diabetes, where nitrite is thought to play a role.

Pharmacology and therapeutic role of inorganic nitrite and nitrate in vasodilatation

Nitrite has emerged as an important bioactive molecule that can be biotransformed to nitric oxide (NO) related metabolites in normoxia and reduced to NO under hypoxic and acidic conditions to exert vasodilatory effects and confer a variety of other benefits to the cardiovascular system. Abundant research is currently underway to understand the mechanisms involved and define the role of nitrite in health and disease. In this review we discuss the impact of nitrite and dietary nitrate on vascular function and the potential therapeutic role of nitrite in acute heart failure.

TEMPOL enhances the antihypertensive effects of sodium nitrite by mechanisms facilitating nitrite-derived gastric nitric oxide formation

Orally administered nitrite exerts antihypertensive effects associated with increased gastric nitric oxide (NO) formation. While reducing agents facilitate NO formation from nitrite, no previous study has examined whether antioxidants with reducing properties improve the antihypertensive responses to orally administered nitrite. We hypothesized that TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) could enhance the hypotensive effects of nitrite in hypertensive rats by exerting antioxidant effects (and enhancing NO bioavailability) and by promoting gastric nitrite-derived NO generation. The hypotensive effects of intravenous and oral sodium nitrite were assessed in unanesthetized freely moving rats with L-NAME (N(ω)-nitro-L-arginine methyl ester; 100mg/kg; po)-induced hypertension treated with TEMPOL (18mg/kg; po) or vehicle. While TEMPOL exerted antioxidant effects in hypertensive rats, as revealed by lower plasma 8-isoprostane and vascular reactive oxygen species levels, this antioxidant did not affect the hypotensive responses to intravenous nitrite. Conversely, TEMPOL enhanced the dose-dependent hypotensive responses to orally administered nitrite, and this effect was associated with higher increases in plasma nitrite and lower increases in plasma nitrate concentrations. In vitro experiments using electrochemical and chemiluminescence NO detection under variable pH conditions showed that TEMPOL enhanced nitrite-derived NO formation, especially at low pH (2.0 to 4.0). TEMPOL signal evaluated by electron paramagnetic resonance decreased when nitrite was reduced to NO under acidic conditions. Consistent with these findings, increasing gastric pH with omeprazole (30mg/kg; po) attenuated the hypotensive responses to nitrite and blunted the enhancement in plasma nitrite concentrations and hypotensive effects induced by TEMPOL. Nitrite-derived NO formation in vivo was confirmed by using the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (C-PTIO), which blunted the responses to oral nitrite. Our results showed that TEMPOL promotes nitrite reduction to NO in the stomach and enhanced plasma nitrite concentrations and the hypotensive effects of oral sodium nitrite through mechanisms critically dependent on gastric pH. Interestingly, the effects of TEMPOL on nitrite-mediated hypotension cannot be explained by increased NO formation in the stomach alone, but rather appear more directly related to increased plasma nitrite levels and reduced nitrate levels during TEMPOL treatment. This may relate to enhanced nitrite uptake or reduced nitrate formation from NO or nitrite.

Nitric oxide and geriatrics: Implications in diagnostics and treatment of the elderly

The nation's aging population is growing rapidly. By 2030, the number of adults age 65 and older will nearly double to 70 million. Americans are living longer and older adults can now live for many years with multiple chronic illnesses but with a substantial cost to health care. Twenty percent of the Medicare population has at least five chronic conditions i.e., hypertension, diabetes, arthritis, etc. Studies in experimental models and even humans reveal that constitutive production of nitric oxide (NO) is reduced with aging and this circumstance may be relevant to a number of diseases that plague the aging population. NO is a multifunctional signaling molecule, intricately involved with maintaining a host of physiological processes including, but not limited to, host defense, neuronal communication and the regulation of vascular tone. NO is one of the most important signaling molecules in our body, and loss of NO function is one of the earliest indicators or markers of disease. Clinical studies provide evidence that insufficient NO production is associated with all major cardiovascular risk factors, such as hyperlipidemia, diabetes, hypertension, smoking and severity of atherosclerosis, and also has a profound predictive value for disease progression including cardiovascular and Alzheimers disease. Thirty plus years after its discovery and over 13 years since a Nobel Prize was awarded for its discovery, there have been no hallmark therapeutic breakthroughs or even NO based diagnostics. We will review the current state of the science surrounding NO in the etiology of a number of different diseases in the geriatric patient. From these observations, it can be concluded that enzymatic production of NO declines steadily with increasing age in healthy human subjects. Implementing strategies to diagnose and treat NO insufficiency may provide enormous benefit to the geriatric patient.

Nitrite and nitrite reductases: from molecular mechanisms to significance in human health and disease

Nitrite, previously considered physiologically irrelevant and a simple end product of endogenous nitric oxide (NO) metabolism, is now envisaged as a reservoir of NO to be activated in response to oxygen (O(2)) depletion. In the first part of this review, we summarize and compare the mechanisms of nitrite-dependent production of NO in selected bacteria and in eukaryotes. Bacterial nitrite reductases, which are copper or heme-containing enzymes, play an important role in the adaptation of pathogens to O(2) limitation and enable microrganisms to survive in the human body. In mammals, reduction of nitrite to NO under hypoxic conditions is carried out in tissues and blood by an array of metalloproteins, including heme-containing proteins and molybdenum enzymes. In humans, tissues play a more important role in nitrite reduction, not only because most tissues produce more NO than blood, but also because deoxyhemoglobin efficiently scavenges NO in blood. In the second part of the review, we outline the significance of nitrite in human health and disease and describe the recent advances and pitfalls of nitrite-based therapy, with special attention to its application in cardiovascular disorders, inflammation, and anti-bacterial defence. It can be concluded that nitrite (as well as nitrate-rich diet for long-term applications) may hold promise as therapeutic agent in vascular dysfunction and ischemic injury, as well as an effective compound able to promote angiogenesis.

Increase in gastric pH reduces hypotensive effect of oral sodium nitrite in rats

The new pathway nitrate-nitrite-nitric oxide (NO) has emerged as a physiological alternative to the classical enzymatic pathway for NO formation from l-arginine. Nitrate is converted to nitrite by commensal bacteria in the oral cavity and the nitrite formed is then swallowed and reduced to NO under the acidic conditions of the stomach. In this study, we tested the hypothesis that increases in gastric pH caused by omeprazole could decrease the hypotensive effect of oral sodium nitrite. We assessed the effects of omeprazole treatment on the acute hypotensive effects produced by sodium nitrite in normotensive and L-NAME-hypertensive free-moving rats. In addition, we assessed the changes in gastric pH and plasma levels of nitrite, NO(x) (nitrate+nitrite), and S-nitrosothiols caused by treatments. We found that the increases in gastric pH induced by omeprazole significantly reduced the hypotensive effects of sodium nitrite in both normotensive and L-NAME-hypertensive rats. This effect of omeprazole was associated with no significant differences in plasma nitrite, NO(x), or S-nitrosothiol levels. Our results suggest that part of the hypotensive effects of oral sodium nitrite may be due to its conversion to NO in the acidified environment of the stomach. The increase in gastric pH induced by treatment with omeprazole blunts part of the beneficial cardiovascular effects of dietary nitrate and nitrite.

Identification of protein targets underlying dietary nitrate-induced protection against doxorubicin cardiotoxicity

We recently demonstrated protective effect of chronic oral nitrate supplementation against cardiomyopathy caused by doxorubicin (DOX), a highly effective anticancer drug. The present study was designed to identify novel protein targets related to nitrate-induced cardioprotection. Adult male CF-1 mice received cardioprotective regimen of nitrate (1 g NaNO₃ per litre of drinking water) for 7 days before DOX injection (15 mg/kg, i.p.) and continued for 5 days after DOX treatment. Subsequently the heart samples were collected for proteomic analysis with two-dimensional differential in-gel electrophoresis with 3 CyDye labelling. Using 1.5 cut-off ratio, we identified 36 proteins that were up-regulated by DOX in which 32 were completely reversed by nitrate supplementation (89%). Among 19 proteins down-regulated by DOX, 9 were fully normalized by nitrate (47%). The protein spots were further identified with Matrix Assisted Laser Desorption/Ionization-Time-of-Flight (MALDI-TOF)/TOF tandem mass spectrometry. Three mitochondrial antioxidant enzymes were altered by DOX, i.e. up-regulation of manganese superoxide dismutase and peroxiredoxin 3 (Prx3), and down-regulation of Prx5, which were reversed by nitrate. These results were further confirmed by Western blots. Nitrate supplementation also significantly improved animal survival rate from 80% in DOX alone group to 93% in Nitrate + DOX group 5 days after the DOX treatment. In conclusion, the proteomic analysis has identified novel protein targets underlying nitrate-induced cardioprotection. Up-regulation of Prx5 by nitrate may explain the observed enhancement of cardiac antioxidant defence by nitrate supplementation.

Dietary inorganic nitrate alleviates doxorubicin cardiotoxicity: mechanisms and implications

Doxorubicin (DOX) is one of the most powerful and widely prescribed chemotherapeutic agents to treat divergent human cancers. However, the clinical use of DOX is restricted due to its severe cardiotoxic side-effects. There has been ongoing search for cardioprotectants against DOX toxicity. Inorganic nitrate has emerged as a bioactive compound that can be reduced into nitrite and nitric oxide in vivo and in turn plays a therapeutic role in diseases associated with nitric oxide insufficiency or dysregulation. In this review, we describe a novel concept of using dietary supplementation of inorganic nitrate to reduce DOX-induced cardiac cellular damage and dysfunction, based on our recent promising studies in a mouse model of DOX cardiotoxicity. Our data show that chronic oral ingestion of sodium nitrate, at a dose equivalent to ~400% of the Acceptable Daily Intake of the World Health Organization, alleviated DOX-induced left ventricular dysfunction and mitochondrial respiratory chain damage. Such cardioprotective effects were associated with reduction of cardiomyocyte necrosis/apoptosis, tissue lipid peroxidation, and mitochondrial H(2)O(2) generation following DOX treatment. Furthermore, proteomic studies revealed enhanced cardiac expression of mitochondrial antioxidant enzyme - peroxiredoxin 5 in the nitrate-treated animals. These studies suggest that inorganic nitrate could be an inexpensive therapeutic agent for long-term oral administration in preventing DOX-induced cardiac toxicity and myopathy during the prolonged pathological process. Future clinical trials in the cancer patients undergoing DOX chemotherapy are warranted to translate these experimental findings into an effective new therapy in preventing the DOX-induced cardiomyopathy.

The problem of nitrogen disposal in the obese

Amino-N is preserved because of the scarcity and nutritional importance of protein. Excretion requires its conversion to ammonia, later incorporated into urea. Under conditions of excess dietary energy, the body cannot easily dispose of the excess amino-N against the evolutively adapted schemes that prevent its wastage; thus ammonia and glutamine formation (and urea excretion) are decreased. High lipid (and energy) availability limits the utilisation of glucose, and high glucose spares the production of ammonium from amino acids, limiting the synthesis of glutamine and its utilisation by the intestine and kidney. The amino acid composition of the diet affects the production of ammonium depending on its composition and the individual amino acid catabolic pathways. Surplus amino acids enhance protein synthesis and growth, and the synthesis of non-protein-N-containing compounds. But these outlets are not enough; consequently, less-conventional mechanisms are activated, such as increased synthesis of NO∙ followed by higher nitrite (and nitrate) excretion and changes in the microbiota. There is also a significant production of N(2) gas, through unknown mechanisms. Health consequences of amino-N surplus are difficult to fathom because of the sparse data available, but it can be speculated that the effects may be negative, largely because the fundamental N homeostasis is stretched out of normalcy, forcing the N removal through pathways unprepared for that task. The unreliable results of hyperproteic diets, and part of the dysregulation found in the metabolic syndrome may be an unwanted consequence of this N disposal conflict.

Antihypertensive and antioxidant effects of a single daily dose of sodium nitrite in a model of renovascular hypertension

Dietary nitrite and nitrate have been reported as alternative sources of nitric oxide (NO). In this regard, we reported previously that sodium nitrite added to drinking water was able to exert antihypertensive effects in an experimental model of hypertension in a dose-dependent manner. Taking into consideration that nitrite is continuously converted to nitrate in the bloodstream, here we expanded our previous report and evaluate whether a single daily dose of sodium nitrite could exert antihypertensive effects in 2 kidney-1 clip (2K1C) hypertensive rats. Sham-operated and 2K1C rats were treated with vehicle or sodium nitrite (15 mg/kg/day) for 4 weeks. We evaluated the effects induced by sodium nitrite treatment on systolic blood pressure (SBP) and NO markers such as plasma nitrite, nitrite + nitrate (NOx), cGMP, and blood levels of nitrosyl-hemoglobin. In addition, we also evaluated effects of nitrite on oxidative stress and antioxidant enzymes. Dihydroethidium (DHE) was used to evaluate aortic reactive oxygen species (ROS) production by fluorescence microscopy, and plasma levels of thiobarbituric acid-reactive species (TBARS) were measured in plasma samples from all experimental groups. Red blood cell superoxide dismutase (SOD) and catalase activity were evaluated with commercial kits. Sodium nitrite treatment reduced SBP in 2K1C rats (P < 0.05). We found lower plasma nitrite and NOx levels in 2K1C rats compared with normotensive controls (both P < 0.05). Nitrite treatment restored the lower levels of nitrite and NOx. While no change was found in the blood levels of nitrosyl-hemoglobin (P > 0.05), nitrite treatment increased the plasma levels of cGMP in 2K1C rats (P < 0.05). Higher plasma TBARS levels and aortic ROS levels were found in hypertensive rats compared with controls (P < 0.05), and nitrite blunted these alterations. Lower SOD and catalase activities were found in 2K1C hypertensive rats compared with controls (both P < 0.05). Nitrite treatment restored SOD activity (P < 0.05), whereas catalase was not affected. These data suggest that even a single daily oral dose of sodium nitrite is able to lower SBP and exert antioxidant effects in renovascular hypertension.

Radiation as a risk factor for cardiovascular disease

Abstract population are ubiquitous background radiation and medical exposure of patients. From the early 1980s to 2006, the average dose per individual in the United States for all sources of radiation increased by a factor of 1.7-6.2 mSv, with this increase due to the growth of medical imaging procedures. Radiation can place individuals at an increased risk of developing cardiovascular disease. Excess risk of cardiovascular disease occurs a long time after exposure to lower doses of radiation as demonstrated in Japanese atomic bomb survivors. This review examines sources of radiation (atomic bombs, radiation accidents, radiological terrorism, cancer treatment, space exploration, radiosurgery for cardiac arrhythmia, and computed tomography) and the risk for developing cardiovascular disease. The evidence presented suggests an association between cardiovascular disease and exposure to low-to-moderate levels of radiation, as well as the well-known association at high doses. Studies are needed to define the extent that diagnostic and therapeutic radiation results in increased risk factors for cardiovascular disease, to understand the mechanisms involved, and to develop strategies to mitigate or treat radiation-induced cardiovascular disease.

Dietary nitrate supplementation protects against Doxorubicin-induced cardiomyopathy by improving mitochondrial function

OBJECTIVES

The aim of this study was to test the hypothesis that long-term dietary nitrate supplementation protects against doxorubicin-induced cardiomyopathy by improving ventricular function and reducing mitochondrial respiratory chain damage.

BACKGROUND

Doxorubicin is a powerful anthracycline antibiotic used to treat divergent human neoplasms. Its clinical use is limited because of severe cardiotoxic side effects. Dietary nitrate and nitrite are essential nutrients for maintenance of steady-state tissue levels of nitric oxide and may play a therapeutic role in diseases associated with nitric oxide insufficiency or dysregulation. Dietary nitrate and nitrite supplementation alleviates myocardial injury caused by ischemia-reperfusion and cardiac arrest-resuscitation.

METHODS

Adult male CF-1 mice were given a single dose of doxorubicin (15 mg/kg intraperitoneally), and left ventricular contractile function was assessed 5 days later using both echocardiography and pressure-volume Millar catheterization. A nitrate supplementation regimen (1 g/l sodium nitrate in drinking water) was started 7 days before doxorubicin injection and continued thereafter. Cardiomyocyte necrosis and apoptosis, tissue lipid peroxidation, and plasma nitrate and nitrite levels were assessed. In addition, mitochondrial complex I activity, oxidative phosphorylation capacity, and hydrogen peroxide generation were determined in parallel experiments.

RESULTS

Doxorubicin caused impairment of ventricular contractility and cell death, which were significantly reduced by nitrate supplementation (p < 0.05). These cardioprotective effects were associated with a significant decrease in tissue lipid peroxidation. Nitrate supplementation significantly preserved mitochondrial complex I activity and oxidative phosphorylation and attenuated hydrogen peroxide generation after doxorubicin treatment.

CONCLUSIONS

Long-term oral intake of inorganic nitrate attenuates doxorubicin-induced ventricular dysfunction, cell death, oxidative stress, and mitochondrial respiratory chain damage. Nitrate could be a promising therapeutic agent against doxorubicin-induced cardiotoxicity.

Dietary nitrite and nitrate: a review of potential mechanisms of cardiovascular benefits

PURPOSE

In the last decade, a growing scientific and medical interest has emerged toward cardiovascular effects of dietary nitrite and nitrate; however, many questions concerning their mode of action(s) remain unanswered. In this review, we focus on multiple mechanisms that might account for potential cardiovascular beneficial effects of dietary nitrite and nitrate.

RESULTS

Beneficial changes to cardiovascular health from dietary nitrite and nitrate might result from several mechanism(s) including their reduction into nitric oxide, improvement in endothelial function, vascular relaxation, and/or inhibition of the platelet aggregation. From recently obtained evidence, it appears that the longstanding concerns about the toxicity of oral nitrite or nitrate are overstated.

CONCLUSION

Dietary nitrite and nitrate may have cardiovascular protective effects in both healthy individuals and also those with cardiovascular disease conditions. A role for nitrite and nitrate in nitric oxide biosynthesis and/or in improving nitric oxide bioavailability may eventually provide a rationale for using dietary nitrite and nitrate supplementation in the treatment and prevention of cardiovascular diseases.

Sodium nitrite downregulates vascular NADPH oxidase and exerts antihypertensive effects in hypertension

Dietary nitrite and nitrate are important sources of nitric oxide (NO). However, the use of nitrite as an antihypertensive drug may be limited by increased oxidative stress associated with hypertension. We evaluated the antihypertensive effects of sodium nitrite given in drinking water for 4 weeks in two-kidney one-clip (2K1C) hypertensive rats and the effects induced by nitrite on NO bioavailability and oxidative stress. We found that, even under the increased oxidative stress conditions present in 2K1C hypertension, nitrite reduced systolic blood pressure in a dose-dependent manner. Whereas treatment with nitrite did not significantly change plasma nitrite concentrations in 2K1C rats, it increased plasma nitrate levels significantly. Surprisingly, nitrite treatment exerted antioxidant effects in both hypertensive and sham-normotensive control rats. A series of in vitro experiments was carried out to show that the antioxidant effects induced by nitrite do not involve direct antioxidant effects or xanthine oxidase activity inhibition. Conversely, nitrite decreased vascular NADPH oxidase activity. Taken together, our results show for the first time that nitrite has antihypertensive effects in 2K1C hypertensive rats, which may be due to its antioxidant properties resulting from vascular NADPH oxidase activity inhibition.

How to protect liver graft with nitric oxide

Organ preservation and ischemia reperfusion injury associated with liver transplantation play an important role in the induction of graft injury. One of the earliest events associated with the reperfusion injury is endothelial cell dysfunction. It is generally accepted that endothelial nitric oxide synthase (e-NOS) is cell-protective by mediating vasodilatation, whereas inducible nitric oxide synthase mediates liver graft injury after transplantation. We conducted a critical review of the literature evaluating the potential applications of regulating and promoting e-NOS activity in liver preservation and transplantation, showing the most current evidence to support the concept that enhanced bioavailability of NO derived from e-NOS is detrimental to ameliorate graft liver preservation, as well as preventing subsequent graft reperfusion injury. This review deals mainly with the beneficial effects of promoting “endogenous” pathways for NO generation, via e-NOS inducer drugs in cold preservation solution, surgical strategies such as ischemic preconditioning, and alternative “exogenous” pathways that focus on the enrichment of cold storage liquid with NO donors. Finally, we also provide a basic bench-to-bed side summary of the liver physiology and cell signalling mechanisms that account for explaining the e-NOS protective effects in liver preservation and transplantation.