Alternative Source Of Nitric Oxide Research Articles

Enhanced Nitrite-Mediated Relaxation of Placental Blood Vessels Exposed to Hypoxia Is Preserved in Pregnancies Complicated by Fetal Growth Restriction.

Nitric oxide (NO) is essential in the control of fetoplacental vascular tone, maintaining a high flow−low resistance circulation that favors oxygen and nutrient delivery to the fetus. Reduced fetoplacental blood flow is associated with pregnancy complications and is one of the major causes of fetal growth restriction (FGR). The reduction of dietary nitrate to nitrite and subsequently NO may provide an alternative source of NO in vivo. We have previously shown that nitrite induces vasorelaxation in placental blood vessels from normal pregnancies, and that this effect is enhanced under conditions of hypoxia. Herein, we aimed to determine whether nitrite could also act as a vasodilator in FGR. Using wire myography, vasorelaxant effects of nitrite were assessed on pre-constricted chorionic plate arteries (CPAs) and veins (CPVs) from normal and FGR pregnancies under normoxic and hypoxic conditions. Responses to the NO donor, sodium nitroprusside (SNP), were assessed in parallel. Nitrate and nitrite concentrations were measured in fetal plasma. Hypoxia significantly enhanced vasorelaxation to nitrite in FGR CPAs (p < 0.001), and in both normal (p < 0.001) and FGR (p < 0.01) CPVs. Vasorelaxation to SNP was also potentiated by hypoxia in both normal (p < 0.0001) and FGR (p < 0.01) CPVs. However, compared to vessels from normal pregnancies, CPVs from FGR pregnancies showed significantly lower reactivity to SNP (p < 0.01). Fetal plasma concentrations of nitrate and nitrite were not different between normal and FGR pregnancies. Together, these data show that nitrite-mediated vasorelaxation is preserved in FGR, suggesting that interventions targeting this pathway have the potential to improve fetoplacental blood flow in FGR pregnancies.

흰쥐에서 고용량 아질산이온 함유 마늘 발효농축액에 의한 뇌혈류 변화

Nitrate–nitrite–nitric oxide (NO) pathway is a major alternative source of NO and is essential for NO - dependent physiological functions in body. Food supplements having nitrate/nitrite can improve metabolic syndromes including hypertension through antioxidant activity or vasodilation. The purpose of this study was to observe the effects of fermented garlic (F. garlic) having high concentration of NO₂ SUP-/SUP on changes in blood flow and nitric oxide synthesis in the cerebral cortex of rodents. The generation of nitric oxide detected by a chemi-luminescence detector was higher in F. Garlic compared with NaNO₂ solution under artificial gastric juice with pH 2.0. Ether F. garlic or NaNO₂ diluted with artificial cerebrospinal fluid was directly applied into around the needle probe of laser Doppler flow meter that was located on epidural surface of the cortex. Direct application of F. garlic resulted in increase of cerebral blood flow detected by a laser Doppler flow meter with a dose-dependent manner. Compared with NaNO₂ solution, F. garlic produced changes in cerebral blood flow at lower concentration of NO₂SUP-/SUP. Pretreatment of methylene blue, a guanylyl cyclase inhibitor prevented upregulation of cerebral blood flow by the treatment of F. garlic. In addition, the application of F. garlic with 250, 500ppm of NO₂SUP-/SUP caused significantly the production of NO in the cortical tissue but NaNO₂ solution with 500ppm of NO₂SUP-/SUP did not. In summary, these results suggested that F. garlic with high content of NO₂SUP-/SUP induce increase in cerebral blood flow through nitric oxide-dependent signal pathway.

Nitrite in breast milk: roles in neonatal pathophysiology.

Dietary nitrate has beneficial effects on health maintenance and prevention of lifestyle-related diseases in adulthood by serving as an alternative source of nitric oxide (NO) through the enterosalivary nitrate-nitrite-NO pathway, particularly when endogenous NO generation is lacking due to vascular endothelial dysfunction. However, this pathway is not developed in the early postnatal period due to a lack of oral commensal nitrate-reducing bacteria and less saliva production than in adults. To compensate for the decrease in nitrite during this period, colostrum contains the highest amount of nitrite compared with transitional, mature, and even artificial milk, suggesting that colostrum plays an important role in tentatively replenishing nitrite, in addition to involving a nutritional aspect, until the enterosalivary nitrate-nitrite-NO pathway is established. Increasing evidence demonstrates that breast milk rich in nitrite can be effective in the prevention of neonatal infections and gastrointestinal diseases such as infantile hypertrophic pyloric stenosis and necrotizing enterocolitis, suggesting that breastfeeding is advantageous for newborns at risk, given the physiological role of nitrite in the early postnatal period. IMPACT: The aim of this review is to discuss the physiological roles of nitrite in breast milk and its implications for neonates. Nitrite in breast milk may compensate for the decrease in nitrite during the early neonatal period until the enterosalivary nitrate-nitrite-nitric oxide pathway is established. Breast milk rich in nitrite may be effective in the prevention of neonatal infections and gastrointestinal diseases by providing nitric oxide bioavailability.

Sodium Nitrite Attenuates Hepatic Ischemia-Reperfusion Injury in Rats.

Nitrite as an alternative source of nitric oxide has been proposed, as it can mediate the protective response in the presence of ischemia or hypoxic conditions and inorganic nitrite can be reduced to nitric oxide by xanthine oxidoreductase. Here, we investigated whether pretreatment with sodium nitrite can attenuate liver damage in hepatic ischemia-reperfusion injury and identified the possible mechanism of nitrite reduction using 2-(4-carboxyphenyl)-4,5dihydro-4,4,5,5-tetramethyl-1H-imidazolyl-1-oxy-3oxide (C-PTIO), a nitric oxide scavenger, and allopurinol, a xanthine oxidoreductase inhibitor. In experiment 1, 30 male Sprague-Dawley rats were divided into 5 groups: (1) sham-operated; (2) hepatic ischemia-reperfusion injury; and (3-5) sodium nitrite administered intra-peritoneally 30 minutes before ischemia at 2.5, 25, and 250 μmol/kg, respectively. In experiment 2, 24 male Sprague-Dawley rats were divided into 4 groups: (1) hepatic ischemia-reperfusion injury; (2) sodium nitrite + hepatic ischemia-reperfusion injury; (3) C-PTIO + sodium nitrite + hepatic ischemia-reperfusion injury; and (4) allopurinol + sodium nitrite + hepatic ischemia-reperfusion injury. Sodium nitrite (25 μmol/kg) was then administered 30 minutes before hepatic ischemia, and C-PTIO or allopurinol was administered 5 minutes before sodium nitrite administration. Blood aspartate aminotransferase, alanine aminotransferase, hepatic tissue malondialdehyde, histologic changes, and expression of mitogen-activated protein kinase family members were evaluated. Sodium nitrite limited serum elevation of alanine aminotransferase and aspartate aminotransferase induced by hepatic ischemia-reperfusion with a peak effect occurring at 25 μmol/kg sodium nitrite. Pre-treatment with allopurinol abolished the protective effect of sodium nitrite, and C-PTIO treatment attenuated the hepatoprotection of sodium nitrite in rats with hepatic ischemia-reperfusion injury. Liver malondialdehyde activity after ischemia-reperfusion decreased in sodium nitrite-treated rats. Sodium nitrite also prevented hepatic ischemia-reperfusion-induced c-Jun N-terminal kinase and extracellular signal-regulated kinase phosphorylation. Exogenous sodium nitrite had protective effects against hepatic ischemia-reperfusion injury. Catalytic reduction to nitric oxide and attenuation of hepatic ischemia-reperfusion is dependent on xanthine oxidoreductase.

Dietary nitrite reverses features of postmenopausal metabolic syndrome induced by high-fat diet and ovariectomy in mice.

Menopausal women are at greater risk of developing metabolic syndrome with reduced endothelial nitric oxide synthase (eNOS) activity. Hormone replacement therapy increases eNOS activity and normalizes some characteristics of metabolic syndrome. We hypothesized that nitric oxide (NO) supplementation should have a therapeutic effect on this syndrome. We examined the effect of dietary nitrite in a mouse model with postmenopausal metabolic syndrome induced by ovariectomy (OVX) and a high fat diet (HF). C57BL/6 female mice were divided into five groups, sham+normal fat diet (NF), sham+ HF, OVX+HF with or without sodium nitrite (50 mg and 150 mg/l) in the drinking water. Daily food intake and weekly body weight were monitored for 18 wk. OVX and HF significantly reduced plasma levels of nitrate/nitrite (NOx), and mice developed obesity with visceral hypertrophic adipocytes and increased transcriptional levels of monocyte chemoattractant protein-1, TNF-α, and IL-6 in visceral fat tissues. The proinflammatory state in the adipocytes provoked severe hepatosteatosis and insulin resistance in OVX+HF group compared with sham+NF group. However, dietary nitrite significantly suppressed adipocyte hypertrophy and transcriptions of proinflammatory cytokines in visceral fat in a dose-dependent manner. The improvement of visceral inflammatory state consequently reversed the hepatosteatosis and insulin resistance observed in OVX+HF mice. These results suggest that an endogenous NO defect might underlie postmenopausal metabolic syndrome and that dietary nitrite provides an alternative source of NO, subsequently compensating for metabolic impairments of this syndrome.

Dietary nitrite supplementation improves insulin resistance in type 2 diabetic KKAy mice

BackgroundBecause insulin signaling is essential for endothelial nitric oxide synthase (eNOS)-derived nitric oxide (NO) production, the loss of bioavailable NO might be a common molecular mechanism underlying the development of insulin resistance and endothelial dysfunction. Although dietary nitrite acts as a substrate for systemic NO generation, thereby serving as a physiological alternative source of NO for signaling, it is not precisely known how dietary nitrite affects type 2 diabetes mellitus. Here we report the therapeutic effects of dietary nitrite on the metabolic and histological features of KKAy diabetic mice. MethodsKKAy mice were divided into three groups (without nitrite, and with 50 mg/L and 150 mg/L nitrite in drinking water), and two groups of C57BL/6J mice served as controls (without nitrite and with 150 mg/L nitrite in drinking water). After 10 weeks, blood samples, visceral adipose tissues, and gastrocnemius muscles were collected after a 16-hour fast to assess the homeostasis model assessment of insulin resistance (HOMA-IR) levels, the histology of the adipose tissue, insulin-stimulated sequential signaling to glucose transporter 4 (GLUT4), and nitrite and nitrate contents in the muscle using an HPLC system. ResultsKKAy mice developed obesity with enhanced fasting plasma levels of glucose and insulin and exhibited increased HOMA-IR scores compared with the C57BL/6J control mice. Dietary nitrite dose-dependently reduced the size of the hypertrophic adipocytes and TNF-α transcription in the adipose tissue of KKAy diabetic mice, which also restored the insulin-mediated signal transduction, including p85 and Akt phosphorylation, and subsequently restored the GLUT4 expression in the skeletal muscles. ConclusionsThese results suggest that dietary nitrite provides an alternative source of NO, and subsequently improves the insulin-mediated signaling and the metabolic and histological features in KKAy diabetic mice.

Aldehyde dehydrogenase 2 partly mediates hypotensive effect of nitrite on l-NAME-induced hypertension in normoxic rat

Nitrite has become a topic of interest in the field of medical research because of its potential therapeutic role as an alternative source of nitric oxide (NO). While the bioconversion of nitrite to NO occurs via either nonenzymatic or enzymatic reduction under acidic or hypoxic conditions, little is known about its conversion to NO under normoxic conditions. Because of a recent report of aldehyde dehydrogenase 2 (ALDH2)-catalyzed glyceryl trinitrate (GTN) vasorelaxation by denitration of GTN to 1,2-glyceryl dinitrate (1,2-GDN) and nitrite, we therefore investigated a catalytic activity of ALDH2 for nitrite reduction and subsequent effect on Nω-nitro-l-arginine methyl ester (l-NAME)-induced hypertension in normoxic rat. Male Sprague–Dawley rats treated with l-NAME in drinking water for 3 weeks developed hypertension with significantly reduced plasma levels of nitrite and nitrate. The intravenous injection of sodium nitrite lowered the arterial pressure in a dose-dependent manner (17, 50 and 150 μmol/kg). Pretreatment with ALDH2 inhibitors (cyanamide and chloral hydrate) partially inhibited the hypotensive responses to sodium nitrite. In addition, cyanamide significantly delayed the nitrite clearance from plasma and most of the organs examined during the experimental period. These results suggest that ALDH2 may be at least in part involved in nitrite-mediated hypotensive effects and nitrite catalysis in many organs of normoxic rats.

P44: Nitric oxide may modulate matrix metalloproteinase-2 during renovascular hypertension

Decreased nitric oxide (NO) bioavailability and up-regulated MMP activity contribute to hypertension-induced cardiovascular hypertrophy. However, it is uncertain whether NO affects MMP activity. Dietary nitrite is an alternative source of NO and may exert antioxidant effects, thus affecting up-regulated MMP hypertension. We evaluated whether sodium nitrite treatment reduces cardiac MMP in 2-kidney, 1-clip (2K1C) hypertension. Sham and 2K1C rats were treated with vehicle or sodium nitrite (15 mg/kg orally) for 4 weeks. Systolic blood pressure was monitored weekly. Plasma nitrite concentrations were analyzed by chemiluminescence. Cardiac MMP level/activity were determined by gelatin and in situ zymography. Sodium nitrite treatment exerted antihypertensive effects in 2K1C rats ( P < 0.05). We found lower plasma nitrite concentrations in 2K1C rats when compared with the Sham group ( P < 0.05), and nitrite treatment restored these levels in 2K1C rats. 2K1C hypertension increased cardiac MMP-2 levels and MMP activity ( P < 0.05). Sodium nitrite treatment reduced hypertension-induced increases in both MMP levels and activity ( P < 0.05). Our results suggest that sodium nitrite treatment prevents 2K1C hypertension-induced MMP up-regulation, and therefore may prevent cardiac remodeling associated with hypertension. Supported by: FAPESP, CNPq. Nothing to disclose.

Treatment with a Novel Dinitroazetidine, Abdnaz, Improves Nitrite Reductase Activity of Sickle Red Blood Cells

AbstractAbstract 3246 IntroductionVaso-occlusion is a hallmark of sickle cell disease (SCD). Congestion of blood vessels by sickle red blood cells (RBC) is caused by hemoglobin polymerization (sickling), increased adhesion, and vasoconstriction due to a disregulated nitric oxide (NO) metabolism. NO generated from L-arginine by NO synthases plays a key role in vasodilation. Under hypoxia hemoglobin has been shown to be a potent alternative source of NO by reducing nitrite (NO2−). In SCD, modification of hemoglobin may reduce sickling and increase its ability to generate NO, and as such improve blood flow. In this study, we examined hemoglobin modification and consequent change in nitrite reductase capacity by 1-bromoacetyl-3,3-dinitroazetidine (ABDNAZ). This is a compound that has recently been described to bind to hemoglobin (Scicinski et al. Drug Met Disp. 2012) and has promising anticancer activity by altering blood flow in hypoxic tumors (Ning et al. Cancer Res. 2012). MethodBlood samples from SCD patients and control blood from healthy volunteers was collected with IRB approval. Red blood cells were isolated and resuspended to physiological hemactocrit in HEPES buffered saline (HBS) containing 2% bovine serum albumin (BSA). Samples were incubated with ABDNAZ, hydroxyurea (HU) or iodoacetamide at a final concentration of 3 mM for 30 minutes at room temperature. Intact RBC, hemolysates or purified hemoglobin samples were exposed to a constant nitrogen (N2) flow (200 mL/minute) at 37°C in a tonometer. At time zero, sodium nitrite was added to a final concentration of 5 mM. The influx of NO2− into the RBC was measured using Griess reagent on supernatant samples. The gas outflow from the tonometer was collected in Mylar balloons at various time points, and NO released in the gas phase was measured using a Nitric Oxide Analyzer. ResultsUpon NO2− addition under deoxygenated conditions, influx in RBC was rapid. An equilibrium between supernatant and RBC was reached within 10 minutes and indicated active recruitment of RBC rather than a simple diffusion equilibrium. Release of NO from SCD patient RBC was increased compared to normal control (HbAA) RBC. Under these conditions, hemolysates with the identical hemoglobin concentration as compared to intact RBC showed a pronounced increase in NO release. Using purified hemoglobin NO release was reduced to 50% as compared to hemolysates. Blood samples from both normal control and sickle cell patients treated with ABDNAZ, showed a significant increase in NO release as compared to untreated samples. Iodoacetamide and HU treatment, described to increase NO (Gladwin et al. Br. J. Hematol. 2002), also showed increased NO release but at a markedly lower level as compared to ABDNAZ treatment. ConclusionsEpisodes of vaso-occlusion result in pain and organ damage in SCD. Local generation of NO will improve vasodilation, and is potentially beneficial. The novel compound ABDNAZ, currently in human clinical trials, greatly increases nitrite reductase capacity of hemoglobin, in both normal and SCD blood samples. Our results indicate that this agent improves NO release from RBC and suggests that modification of sickle patient blood by ABDNAZ in the presence of plasma nitrite should be considered as a potential therapeutic approach. Disclosures:Scicinski:RadioRx, Inc: Employment. Oronsky:RadioRx, Inc: Employment.

NO and hypoxia: Taking nitrate to new heights

Residents of the Tibetan plateau appear to produce more nitric oxide (NO) compared to lowlanders as indicated by enhanced NO concentrations in exhaled breath and elevated levels of NO metabolites (incl. nitrite, nitrate and nitroso species) in their blood. This adaptation may help offset the consequences of life-long exposure to reduced atmospheric oxygen at high altitude by improving oxygen delivery and/or utilization and thus hypoxic tolerance. Recently, lowland participants of two independent research expeditions to Nepal have been demonstrated to also respond to environmental hypoxia with enhanced NO formation, suggesting this to be an integral part of human physiology that contributes to the process of acclimatization to reduced oxygen availability. Furthermore, dietary nitrate has been demonstrated to reduce the oxygen cost of exercise by improving mitochondrial efficiency at sea level and suggested to be sequentially reduced to nitrite and NO in hypoxia. This pathway could theoretically complement NOS-mediated l -arginine oxidation by providing an alternative source of NO under conditions of reduced oxygen availability. We hypothesized, therefore, that dietary nitrate administration may improve oxygen efficiency at high altitude, and this rationale has been tested in a randomized, double-blind field study carried out during summer 2010 at the Margherita Hut at 4,559 m ( Xtreme Alps ). This presentation will highlight some of the key results of this study and discuss their potential implications for the treatment of patients suffering from hypoxemia during critical illness.

NO-synthase independent NO generation in mammals

Inorganic nitrate ( NO 3 - ) and nitrite ( NO 2 - ) are part of the nitrogen cycle in nature. To the general public these anions are generally known as undesired residues in the food chain with potentially carcinogenic effects. Among biologists, these inorganic anions have merely been viewed as inert oxidative end products of endogenous nitric oxide (NO) metabolism. However, recent studies surprisingly show that nitrate and nitrite can be metabolized in vivo to form nitric oxide (NO) and other bioactive nitrogen oxides. This represents an important alternative source of NO especially during hypoxia when the oxygen-dependent l-arginine–NO pathway can be altered. A picture is now emerging suggesting important biological functions of the nitrate–nitrite–NO pathway with profound implications in relation to the diet and cardiovascular homeostasis. Moreover, an increasing number of studies suggest a therapeutic potential for nitrate and nitrite in diseases such as myocardial infarction, stroke, hypertension, renal failure and gastric ulcers.

Dietary sources of nitrite as a modulator of ischemia/reperfusion injury

The nitrite anion is an endogenous product of nitric oxide (NO) metabolism, a key intermediate in the nitrogen cycle in plants and bacteria, and a constituent of many foods. Research over the past 6 years has revealed a surprising biological and cytoprotective activity of this anion. Its ability to restore NO homeostasis throughout the physiological oxygen gradient in vivo has transformed this once-thought to be inert anion into a critical molecule in health and disease. Ischemia-reperfusion (I/R) injury is a major clinical problem worldwide. NO has been shown to be one of the most important molecules for the prevention of injury from I/R. Paradoxically, however, enzymatic NO formation from NO synthase (NOS) is inactive during conditions of inadequate oxygen and substrate delivery, such as in ischemia. Nitrite has emerged as a viable alternative source of NO under ischemic conditions. As nitrite is known to be derived not only from the oxidation of NO but also through diet, understanding nitrite metabolism and mechanisms of cytoprotection may offer novel and natural means to prevent disease or at least limit injury from an I/R event. Here, we review the current body of knowledge regarding dietary sources of nitrite and its modulation of cytoprotection in an I/R injury.

The nitrate–nitrite–nitric oxide pathway in physiology and therapeutics

The inorganic anions nitrate (NO3-) and nitrite (NO2-) were previously thought to be inert end products of endogenous nitric oxide (NO) metabolism. However, recent studies show that these supposedly inert anions can be recycled in vivo to form NO, representing an important alternative source of NO to the classical L-arginine-NO-synthase pathway, in particular in hypoxic states. This Review discusses the emerging important biological functions of the nitrate-nitrite-NO pathway, and highlights studies that implicate the therapeutic potential of nitrate and nitrite in conditions such as myocardial infarction, stroke, systemic and pulmonary hypertension, and gastric ulceration.

Nitrite-derived nitric oxide formation following ischemia-reperfusion injury in kidney.

Nitric oxide (NO) is synthesized from l-arginine by nitric oxide synthase (NOS), and nitrite and nitrate are believed to be waste forms of NO. We previously reported an enzyme-independent pathway of NO generation from nitrite in acidic conditions. In this study, we show nitrite-derived NO formation in renal ischemia-reperfusion injury using electron paramagnetic resonance (EPR) spectroscopy. In this experiment, we utilized a stable isotope of [(15)N]nitrite as a source of nitrite to distinguish l-arginine-derived NO from [(15)N]nitrite-derived (15)NO. Intravenous infusion of a stable isotope of [(15)N]nitrite ((15)NO(2)(-)) facilitated the formation of Hb(15)NO during renal ischemia, which demonstrated that the origin of NO was nitrite. The EPR signal of Hb(15)NO in kidney appeared after 40 min of renal ischemia, and renal reperfusion decreased the Hb(15)NO level in the kidney and increased it in blood by contrast. In addition, the amount of HbNO was nitrite concentration dependent, and this formation was NOS independent. Our findings suggest that nitrite can be an alternative source of NO in ischemic kidney and that it binds with hemoglobin and then is spread by the circulation after reperfusion.

Nitric oxide accumulation in the nonventilated nasal cavity.

Nasal nitric oxide is present in high concentrations in the upper airway relative to the lower respiratory tract. To explore the rate of nitric oxide accumulation in the nonventilated nasal cavity. In 9 healthy subjects previously trained to close the soft palate, steady-state plateau nitric oxide levels were recorded while air was aspirated through the nasal airway in series at a constant flow rate. Nitric oxide was then allowed to accumulate in the nasal cavity by occluding both nares and keeping the velum closed. After varying occlusion times, peak nitric oxide levels and a second plateau were ascertained. While the subjects aspirated air at a constant flow, there was a slow rise to a first nitric oxide plateau. On opening to the analyzer after the accumulation period, the peak nitric oxide level was several times higher than the initial plateau (range, 2810-19008 ppb) and then slowly returned to previous plateau levels. There was no significant difference between initial and second plateau nitric oxide levels for any period. The accumulated nitric oxide peak increased in direct proportion to the accumulation time (P<.001). Nitric oxide concentrations accumulate in the nonventilated nasal cavity in proportion to the time of nonventilation. Peak nasal nitric oxide values after accumulation are similar to published sinus nitric oxide measurements obtained by direct puncture. These results suggest an important alternative source of nitric oxide in humans.