Nitric Oxide Abstracts 3

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Nitrite and nitric oxide metabolism in peripheral artery disease

         (Allen, Giordano et al. 2012) Download

Peripheral artery disease (PAD) represents a burgeoning form of cardiovascular disease associated with significant clinical morbidity and increased 5 year cardiovascular disease mortality. It is characterized by impaired blood flow to the lower extremities, claudication pain and severe exercise intolerance. Pathophysiological factors contributing to PAD include atherosclerosis, endothelial cell dysfunction, and defective nitric oxide metabolite physiology and biochemistry that collectively lead to intermittent or chronic tissue ischemia. Recent work from our laboratories is revealing that nitrite/nitrate anion and nitric oxide metabolism plays an important role in modulating functional and pathophysiological responses during this disease. In this review, we discuss experimental and clinical findings demonstrating that nitrite anion acts to ameliorate numerous pathophysiological events associated with PAD and chronic tissue ischemia. We also highlight future directions for this promising line of therapy.

Evaluation of nitric oxide metabolites in a group of subjects with metabolic syndrome

         (Caimi, Hopps et al. 2012) Download

AIM: To evaluate the concentration of metabolites (NO(2)(-), NO(3)(-)) of nitric oxide (NO) in metabolic syndrome (MS). MATERIALS AND METHODS: We enrolled 106 subjects (45 women and 61 men) with MS of which 43 (14 women and 27 men) with diabetes mellitus and 63 (31 women and 32 men) without diabetes mellitus, and 54 subjects (19 women and 35 men) as control group. The nitric oxide metabolites (nitrite+nitrate=NOx) were evaluated employing the Griess reagent. RESULTS: In the whole group of MS subjects was evident, in comparison with control group, a significant increase in NOx. The same finding was also present between control group and diabetic subjects with MS and between control group and nondiabetic subjects with MS. No difference was observed between the two subgroups (diabetic and nondiabetic subjects with MS) about NOx. Contrasting information were obtained examining the linear regression among NOx, age, anthropometric profile, blood pressure values and glycometabolic pattern of subjects with MS. CONCLUSIONS: In MS subjects we found a significant increase in NOx not influenced by diabetes mellitus. The NOx is a parameter that must be considered in MS keeping in mind that its behavior is related to chronic inflammation that accompanies this clinical condition.

Beware of the pickle: health effects of nitrate intake

         (Derave and Taes 2009) Download

In a recent paper by Bailey et al. (2), dietary nitrate supplementation was shown to reduce the oxygen cost during submaximal exercise and to increase the time to ex- haustion during high-intensity exercise. These data confirm and expand on the surprising and original findings by Larsen et al. (4) of nitrate-induced improvement of exercise efficiency in humans. This newly discovered ergogenic potential of di- etary nitrate will certainly inspire athletes to boost their performance and nutriceutical companies to boost their sales. But what are the safety concerns of nitrate supplementation?

High serum nitric oxide metabolites and incident metabolic syndrome

         (Ghasemi, Zahediasl et al. 2012) Download

BACKGROUND: Endothelial dysfunction, synonymous with reduced biological activity of nitric oxide, is related to all cardiovascular risk factors. Association between metabolic syndrome and nitric oxide metabolites (nitrite + nitrate = NO(x)) has been previously shown in cross-sectional studies. The aim of this study was to determine the ability of serum NO(x) levels in predicting the incidence of metabolic syndrome in a population-based study. METHODS: Serum NO(x) levels measured in 2098 adult subjects, participants of Tehran Lipid and Glucose Study, without metabolic syndrome at baseline. After 3.3 years follow-up, logistic regression analysis was used to calculate the odds ratio (OR) and 95% confidence interval for developing metabolic syndrome, with serum NO(x) quartiles as independent variables. RESULTS: Incident metabolic syndrome was diagnosed in 23.0% of men and 16.3% of women after 3.3 years. Age-adjusted risk for developing metabolic syndrome in women who had higher NO(x) values (above 75th percentile vs. lower 75th percentile) at baseline, was significantly higher [OR: 1.59 (1.11-2.27), p = 0.011]; OR remained significant after multivariable-adjustment including adjustment for components of metabolic syndrome [OR: 1.75 (1.19-2.59), p = 0.005]. Serum NO(x) could not predict the incidence of metabolic syndrome in men. CONCLUSIONS: High serum NO(x) level is an independent predictor of incident metabolic syndrome in women, but not in men, a finding which presents serum NO(x) level as a potential biomarker for assessing cardiometabolic disturbances.

Nitric oxide metabolism in asthma pathophysiology

         (Ghosh and Erzurum 2011) Download

BACKGROUND: Asthma, a chronic inflammatory disease is typically characterized by bronchoconstriction and airway hyper-reactivity. SCOPE OF REVIEW: A wealth of studies applying chemistry, molecular and cell biology to animal model systems and human asthma over the last decade has revealed that asthma is associated with increased synthesis of the gaseous molecule nitric oxide (NO). MAJOR CONCLUSION: The high NO levels in the oxidative environment of the asthmatic airway lead to greater formation of reactive nitrogen species (RNS) and subsequent oxidation and nitration of proteins, which adversely affect protein functions that are biologically relevant to chronic inflammation. In contrast to the high levels of NO and nitrated products, there are lower levels of beneficial S-nitrosothiols (RSNO), which mediate bronchodilation, due to greater enzymatic catabolism of RSNO in the asthmatic airways. GENERAL SIGNIFICANCE: This review discusses the rapidly accruing data linking metabolic products of NO as critical determinants in the chronic inflammation and airway reactivity of asthma. This article is part of a Special Issue entitled Biochemistry of Asthma.

Acute ingestion of beetroot bread increases endothelium-independent vasodilation and lowers diastolic blood pressure in healthy men: a randomized controlled trial

         (Hobbs, Goulding et al. 2013) Download

Dietary nitrate, from beetroot, has been reported to lower blood pressure (BP) by the sequential reduction of nitrate to nitrite and further to NO in the circulation. However, the impact of beetroot on microvascular vasodilation and arterial stiffness is unknown. In addition, beetroot is consumed by only 4.5% of the UK population, whereas bread is a staple component of the diet. Thus, we investigated the acute effects of beetroot bread (BB) on microvascular vasodilation, arterial stiffness, and BP in healthy participants. Twenty-three healthy men received 200 g bread containing 100 g beetroot (1.1 mmol nitrate) or 200 g control white bread (CB; 0 g beetroot, 0.01 mmol nitrate) in an acute, randomized, open-label, controlled crossover trial. The primary outcome was postprandial microvascular vasodilation measured by laser Doppler iontophoresis and the secondary outcomes were arterial stiffness measured by Pulse Wave Analysis and Velocity and ambulatory BP measured at regular intervals for a total period of 6 h. Plasma nitrate and nitrite were measured at regular intervals for a total period of 7 h. The incremental area under the curve (0-6 h after ingestion of bread) for endothelium-independent vasodilation was greater (P = 0.017) and lower for diastolic BP (DBP; P = 0.032) but not systolic (P = 0.99) BP after BB compared with CB. These effects occurred in conjunction with increases in plasma and urinary nitrate (P < 0.0001) and nitrite (P < 0.001). BB acutely increased endothelium-independent vasodilation and decreased DBP. Therefore, enriching bread with beetroot may be a suitable vehicle to increase intakes of cardioprotective beetroot in the diet and may provide new therapeutic perspectives in the management of hypertension.

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

         (Machha and Schechter 2011) Download

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.


Nitric oxide: a new concept in chronic sinusitis pathogenesis

         (Naraghi, Deroee et al. 2007) Download

PURPOSE: Exhaled NO is produced mainly in paranasal sinuses and nasal mucosa. Nasal NO has been suggested to have a variety of effects in nasal cavity. Decreased exhaled NO is found in chronic sinusitis, and NO metabolite levels are increased in animal models of chronic sinusitis, suggesting a role for them in sinusitis pathogenesis. There was no data available on human NO metabolite level. MATERIALS AND METHODS: We lavaged maxillary sinuses in a control and 2 patient groups. The control group was patients who underwent functional endoscopic sinus surgery (FESS) due to any other reason than chronic sinusitis. The patient groups had chronic rhinosinusitis with and without polyposis who underwent FESS. Maxillary sinuses were lavaged during FESS, and NO metabolites (nitrate and nitrite) were lavaged in the lavage fluid. RESULTS: Nitric oxide metabolite levels (mean +/- SEM) were 8.085 +/- 1.43 mumol/L in healthy maxillary sinus lavage fluid and 18.04 +/- 3.51 and 16.78 +/- 2.91 mumol/L in chronic rhinosinusitis with and without polyposis, respectively. Lavage fluid of sinuses with chronic sinusitis had elevated levels of NO metabolites, which were significantly higher than the control group. The difference between the chronic sinusitis with and without polyposis groups was not significant. CONCLUSIONS: Nitric oxide metabolites were significantly higher in maxillary sinuses of patients with chronic sinusitis. Elevated levels of NO and NO metabolites in sinusitis might damage healthy sinus epithelium. NO metabolites may have an important role in sinusitis pathogenesis.

The effect of dietary nitrate on salivary, plasma, and urinary nitrate metabolism in humans

         (Pannala, Mani et al. 2003) Download

Dietary nitrate is metabolized to nitrite by bacterial flora on the posterior surface of the tongue leading to increased salivary nitrite concentrations. In the acidic environment of the stomach, nitrite forms nitrous acid, a potent nitrating/nitrosating agent. The aim of this study was to examine the pharmacokinetics of dietary nitrate in relation to the formation of salivary, plasma, and urinary nitrite and nitrate in healthy subjects. A secondary aim was to determine whether dietary nitrate increases the formation of protein-bound 3-nitrotyrosine in plasma, and if dietary nitrate improves platelet function. The pharmacokinetic profile of urinary nitrate excretion indicates total clearance of consumed nitrate in a 24 h period. While urinary, salivary, and plasma nitrate concentrations increased between 4- and 7-fold, a significant increase in nitrite was only detected in saliva (7-fold). High dietary nitrate consumption does not cause a significant acute change in plasma concentrations of 3-nitrotyrosine or in platelet function.

Total salivary nitrates and nitrites in oral health and periodontal disease

         (Sanchez, Miozza et al. 2014) Download

It is well known that nitrites are increased in saliva from patients with periodontal disease. In the oral cavity, nitrites may derive partly from the reduction of nitrates by oral bacteria. Nitrates have been reported as a defence-related mechanism. Thus, the aim of the present study was to determine the salivary levels of total nitrate and nitrite and their relationship, in unstimulated and stimulated saliva from periodontal healthy subjects, and from patients with chronic periodontal disease. Nitrates and nitrites were determined in saliva from thirty healthy subjects and forty-four patients with periodontal disease. A significant increase in salivary nitrates and nitrites was observed. Nitrates and nitrites concentration was related to clinical attachment level (CAL). A positive and significant Pearson's correlation was found between salivary total nitrates and nitrites. Periodontal treatment induced clinical improvement and decreased nitrates and nitrites. It is concluded that salivary nitrates and nitrites increase, in patients with periodontal disease, could be related to defence mechanisms. The possibility that the salivary glands respond to oral infectious diseases by increasing nitrate secretion should be explored further.

Elevated nitric oxide metabolite levels in chronic sinusitis

         (Schlosser, Spotnitz et al. 2000) Download

Decreased exhaled nitric oxide (NO) is found in chronic sinusitis. NO metabolites (nitrates, nitrites, and S-nitrosothiols) were measured in sinus lavages with a rabbit model of chronic sinusitis. NO metabolite levels (mean +/- SD) were 3.0+/-1.6 micromol/L in uninfected rabbits, 10.7+/-11.4 micromol/L in infected animals, and 7.6+/-5.4 micromol/L in postantrostomy recovering animals. Infected sinuses had elevated levels of NO metabolites that were statistically significant (P<0.01) when compared with uninfected sinuses. Mucociliary transport velocity was measured in uninfected (16.0+/-5.7 mm/minute), infected (5.2+/-1.3 mm/minute), and recovery phases (3.0 mm/minute). Endoscopic appearance, light and electron microscopy, and bacterial cultures improved during recovery. Elevated levels of NO metabolites were found during chronic sinusitis and began to return to normal levels during recovery. The possible link between NO in epithelial autotoxicity and host defense mechanisms warrants further investigation.

Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism

         (Schwedhelm, Maas et al. 2008) Download

AIMS: Oral L-arginine supplementation has been used in several studies to improve endothelium-dependent, nitric oxide (NO)-mediated vasodilation. L-Arginine treatment is hampered by extensive presystemic elimination due to intestinal arginase activity. In contrast, L-citrulline is readily absorbed and at least in part converted to L-arginine. The aim of our study was to assess this metabolic conversion and its subsequent pharmacodynamic effects. METHODS: In a double-blind, randomized, placebo-controlled cross-over study, 20 healthy volunteers received six different dosing regimes of placebo, citrulline, and arginine. Pharmacokinetic parameters (C(max), T(max), C(min), AUC) were calculated after 1 week of oral supplementation. The ratio of plasma L-arginine over asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase (arginine/ADMA ratio), urinary cyclic guanosine monophosphate (cGMP) and nitrate excretion rates, and flow-mediated vasodilation (FMD) was measured to assess pharmacodynamic effects. RESULTS: L-Citrulline dose-dependently increased AUC and C(max) of plasma L-arginine concentration more effectively than L-arginine (P < 0.01). The highest dose of citrulline (3 g bid) increased the C(min) of plasma L-arginine and improved the L-arginine/ADMA ratio from 186 +/- 8 (baseline) to 278 +/- 14 [P < 0.01, 95% confidence interval (CI) 66, 121]. Moreover, urinary nitrate and cGMP were increased from 92 +/- 10 to 125 +/- 15 micromol mmol(-1) creatinine (P = 0.01, 95% CI 8, 58) and from 38 +/- 3.3 to 50 +/- 6.7 nmol mmol(-1) creatinine (P = 0.04, 95% CI 0.4, 24), respectively. No treatment improved FMD over baseline. However, pooled analysis of all FMD data revealed a correlation between the increase of arginine/ADMA ratio and improvement of FMD. CONCLUSION: Our data show for the first time that oral L-citrulline supplementation raises plasma L-arginine concentration and augments NO-dependent signalling in a dose-dependent manner.


Inorganic nitrate and beetroot juice supplementation reduces blood pressure in adults: a systematic review and meta-analysis

         (Siervo, Lara et al. 2013) Download

Diets including food products rich in inorganic nitrate are associated with lower blood pressure (BP). The evidence for the BP-lowering effects of inorganic nitrate and beetroot in randomized clinical trials has not been systematically assessed. The objective was to conduct a systematic review and meta-analysis of randomized clinical trials that examined the effects of inorganic nitrate and beetroot supplementation on BP. Medline, EMBASE, and Scopus databases were searched from inception to February 2013. The specific inclusion criteria were: 1) randomized clinical trials; 2) trials reporting effects on systolic or diastolic BP or both; and 3) trials comparing inorganic nitrate or beetroot juice supplementation with placebo control groups. Random-effects models were used to assess the pooled BP effect sizes. Sixteen trials met the eligibility criteria for the systematic review. All studies had a crossover study design. The trials were conducted between 2006 and 2012 and included a total of 254 participants with 7-30 participants/study. The duration of each intervention ranged from 2 h to 15 d. Inorganic nitrate and beetroot juice consumption were associated with greater changes in systolic BP [-4.4 mm Hg (95% CI: -5.9, -2.8); P < 0.001] than diastolic BP [-1.1 mm Hg (95% CI: -2.2, 0.1); P = 0.06]. The meta-regression showed an association between daily dose of inorganic nitrate and changes in systolic BP (P < 0.05). Inorganic nitrate and beetroot juice supplementation was associated with a significant reduction in systolic BP. These findings need to be tested in long-term trials and in individuals at greater cardiovascular risk.

Acute blood pressure lowering, vasoprotective, and antiplatelet properties of dietary nitrate via bioconversion to nitrite

         (Webb, Patel et al. 2008) Download

Diets rich in fruits and vegetables reduce blood pressure (BP) and the risk of adverse cardiovascular events. However, the mechanisms of this effect have not been elucidated. Certain vegetables possess a high nitrate content, and we hypothesized that this might represent a source of vasoprotective nitric oxide via bioactivation. In healthy volunteers, approximately 3 hours after ingestion of a dietary nitrate load (beetroot juice 500 mL), BP was substantially reduced (Delta(max) -10.4/8 mm Hg); an effect that correlated with peak increases in plasma nitrite concentration. The dietary nitrate load also prevented endothelial dysfunction induced by an acute ischemic insult in the human forearm and significantly attenuated ex vivo platelet aggregation in response to collagen and ADP. Interruption of the enterosalivary conversion of nitrate to nitrite (facilitated by bacterial anaerobes situated on the surface of the tongue) prevented the rise in plasma nitrite, blocked the decrease in BP, and abolished the inhibitory effects on platelet aggregation, confirming that these vasoprotective effects were attributable to the activity of nitrite converted from the ingested nitrate. These findings suggest that dietary nitrate underlies the beneficial effects of a vegetable-rich diet and highlights the potential of a "natural" low cost approach for the treatment of cardiovascular disease.

Arginine metabolism: nitric oxide and beyond

         (Wu and Morris 1998) Download

Arginine is one of the most versatile amino acids in animal cells, serving as a precursor for the synthesis not only of proteins but also of nitric oxide, urea, polyamines, proline, glutamate, creatine and agmatine. Of the enzymes that catalyse rate-controlling steps in arginine synthesis and catabolism, argininosuccinate synthase, the two arginase isoenzymes, the three nitric oxide synthase isoenzymes and arginine decarboxylase have been recognized in recent years as key factors in regulating newly identified aspects of arginine metabolism. In particular, changes in the activities of argininosuccinate synthase, the arginases, the inducible isoenzyme of nitric oxide synthase and also cationic amino acid transporters play major roles in determining the metabolic fates of arginine in health and disease, and recent studies have identified complex patterns of interaction among these enzymes. There is growing interest in the potential roles of the arginase isoenzymes as regulators of the synthesis of nitric oxide, polyamines, proline and glutamate. Physiological roles and relationships between the pathways of arginine synthesis and catabolism in vivo are complex and difficult to analyse, owing to compartmentalized expression of various enzymes at both organ (e.g. liver, small intestine and kidney) and subcellular (cytosol and mitochondria) levels, as well as to changes in expression during development and in response to diet, hormones and cytokines. The ongoing development of new cell lines and animal models using cDNA clones and genes for key arginine metabolic enzymes will provide new approaches more clearly elucidating the physiological roles of these enzymes.


References

Allen, J. D., T. Giordano, et al. (2012). "Nitrite and nitric oxide metabolism in peripheral artery disease." Nitric Oxide 26(4): 217-22. [PMID: 22426034]

Caimi, G., E. Hopps, et al. (2012). "Evaluation of nitric oxide metabolites in a group of subjects with metabolic syndrome." Diabetes Metab Syndr 6(3): 132-5. [PMID: 23158975]

Derave, W. and Y. Taes (2009). "Beware of the pickle: health effects of nitrate intake." J Appl Physiol (1985) 107(5): 1677; author reply 1678. [PMID: 19890035]

Ghasemi, A., S. Zahediasl, et al. (2012). "High serum nitric oxide metabolites and incident metabolic syndrome." Scand J Clin Lab Invest 72(7): 523-30. [PMID: 23050497]

Ghosh, S. and S. C. Erzurum (2011). "Nitric oxide metabolism in asthma pathophysiology." Biochim Biophys Acta 1810(11): 1008-16. [PMID: 21718755]

Hobbs, D. A., M. G. Goulding, et al. (2013). "Acute ingestion of beetroot bread increases endothelium-independent vasodilation and lowers diastolic blood pressure in healthy men: a randomized controlled trial." J Nutr 143(9): 1399-405. [PMID: 23884387]

Machha, A. and A. N. Schechter (2011). "Dietary nitrite and nitrate: a review of potential mechanisms of cardiovascular benefits." Eur J Nutr 50(5): 293-303. [PMID: 21626413]

Naraghi, M., A. F. Deroee, et al. (2007). "Nitric oxide: a new concept in chronic sinusitis pathogenesis." Am J Otolaryngol 28(5): 334-7. [PMID: 17826536]

Pannala, A. S., A. R. Mani, et al. (2003). "The effect of dietary nitrate on salivary, plasma, and urinary nitrate metabolism in humans." Free Radic Biol Med 34(5): 576-84. [PMID: 12614846]

Sanchez, G. A., V. A. Miozza, et al. (2014). "Total salivary nitrates and nitrites in oral health and periodontal disease." Nitric Oxide 36: 31-5. [PMID: 24211765]

Schlosser, R. J., W. D. Spotnitz, et al. (2000). "Elevated nitric oxide metabolite levels in chronic sinusitis." Otolaryngol Head Neck Surg 123(4): 357-62. [PMID: 11020168]

Schwedhelm, E., R. Maas, et al. (2008). "Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism." Br J Clin Pharmacol 65(1): 51-9. [PMID: 17662090]

Siervo, M., J. Lara, et al. (2013). "Inorganic nitrate and beetroot juice supplementation reduces blood pressure in adults: a systematic review and meta-analysis." J Nutr 143(6): 818-26. [PMID: 23596162]

Webb, A. J., N. Patel, et al. (2008). "Acute blood pressure lowering, vasoprotective, and antiplatelet properties of dietary nitrate via bioconversion to nitrite." Hypertension 51(3): 784-90. [PMID: 18250365]

Wu, G. and S. M. Morris, Jr. (1998). "Arginine metabolism: nitric oxide and beyond." Biochem J 336 ( Pt 1): 1-17. [PMID: 9806879]