sodium-nitrite and Hypertension

Nitric oxide (NO) has numerous important functions in the kidney, and long-term blockage of nitric oxide synthases in rats by L-NAME results in severe hypertension and progressive kidney damage. On the other hand, NO production seems to be low in patients with chronic kidney disease (CKD), and NO deficiency may play a role in CKD progression. In this review, we summarized the mechanisms of amelioration of renal injury induced by L-NAME treated rats by treatment of nitrite. First, we demonstrate whether orally-administrated nitrite-derived NO can shift to the circulation. When 3mg/kg body weight Na(15)NO(2) was orally administered to rats, an apparent EPR signal derived from Hb(15)NO (A(z)=23.4 gauss) appeared in the blood, indicating that orally ingested nitrite can be a source of NO in vivo. Next, in order to clarify the capacity of nitrite to prevent renal disease, we administered low-dose nitrite (LDN: 0.1mg of sodium nitrite in 1L of drinking water), medium-dose nitrite (MDN: 1mg sodium nitrite/L, which corresponds to the amount of nitrite ingested by vegetarians), or high-dose nitrite (HDN: 10mg sodium nitrite/L) to rats simultaneously with L-NAME (1 g l-NAME/L) for 8 weeks, then examined the blood NO level as a hemoglobin-NO adduct (iron-nitrosyl-hemoglobin) using electron paramagnetic resonance spectroscopy, urinary protein excretion, and renal histological changes at the end of the experiment. It was found that oral administration of MDN and HDN but not LDN increased the blood iron-nitrosyl-hemoglobin concentration to the normal level, ameliorated the L-NAME-induced proteinuria, and reduced renal histological damage. The findings demonstrate that chronic administration of a mid-level dietary dose of nitrite restores the circulating iron-nitrosyl-hemoglobin levels reduced by L-NAME and that maintenance of the circulating iron-nitrosyl-hemoglobin level in a controlled range protects against L-NAME-induced renal injury. Taking these findings together, we propose that dietary supplementation of nitrite is a potentially useful nonpharmacological strategy for maintaining circulating NO level in order to prevent or slow the progression of renal disease. It had been believed that nitrite could result in intragastric formation of nitrosamines, which had been linked to esophageal and other gastrointestinal cancers. However, there is no positive association between the intake of nitrate or nitrite and gastric and pancreatic cancer by recent researches. Furth

Topics: Animals; Diet; Hypertension; Kidney Diseases; NG-Nitroarginine Methyl Ester; Rats; Sodium Nitrite

The nitrate-nitrite-NO pathway regulates NO synthase-independent vasodilation and NO signaling. Ingestion of inorganic nitrite has vasodilatory and blood pressure-lowering effects. Preclinical studies in rodent models suggest there may be a benefit of nitrite in lowering serum triglyceride levels and improving the metabolic syndrome. In a phase 2 study, we evaluated the safety and efficacy of chronic oral nitrite therapy in patients with hypertension and the metabolic syndrome. Twenty adult subjects with stage 1 or 2 hypertension and the metabolic syndrome were enrolled in an open-label safety and efficacy study. The primary efficacy end point was blood pressure reduction; secondary end points included insulin-dependent glucose disposal and endothelial function measured by flow-mediated dilation of the brachial artery and intima-media diameter of the carotid artery. Chronic oral nitrite therapy (40 mg/3× daily) was well tolerated. Oral nitrite significantly lowered systolic, diastolic, and mean arterial pressures, but tolerance was observed after 10 to 12 weeks of therapy. There was significant improvement in the intima-media thickness of the carotid artery and trends toward improvements in flow-mediated dilation of the brachial artery and insulin sensitivity. Chronic oral nitrite therapy is safe in patients with hypertension and the metabolic syndrome. Despite an apparent lack of enzymatic tolerance to nitrite, we observed tolerance after 10 weeks of chronic therapy, which requires additional mechanistic studies and possible therapeutic dose titration in clinical trials. Nitrite may be a safe therapy to concominantly improve multiple features of the metabolic syndrome including hypertension, insulin resistance, and endothelial dysfunction. Registration- URL: https://www.clinicaltrials.gov; Unique identifier: NCT01681810.

Topics: Adult; Antihypertensive Agents; Blood Pressure; Brachial Artery; Carotid Intima-Media Thickness; Endothelium, Vascular; Female; Humans; Hypertension; Insulin Resistance; Male; Metabolic Syndrome; Sodium Nitrite; Treatment Outcome; Triglycerides; Vasodilation

On the basis of earlier executed studies of hypotensive effect of dinitrosyl iron complexes (DNIC) with glutathione, the drug has been created in industrial conditions named oxacom. Preliminary pharmacological studies of oxacom have not revealed negative qualities. The drug has been now tested in 14 healthy men in whom at single intravenous introduction it caused typical response - a decrease of diastolic as well as systolic arterial pressure on 24-27 mmHg through 3-4 min with subsequent very slow restoration in 8-10 hours. The heart rate after initial rise was quickly normalized. Echocardiography revealed unaltered cardiac output in spite of reduced cardiac filling by 28%. The multilateral analysis of clinical and biochemical data has revealed an absence of essential alterations which could lead to pathological consequences. The drug is recommended for carrying out of the second phase of clinical trial. The comparative study of the efficiency of hypotensive action of oxacom, S-nitrosoglutathione (GS-NO) and sodium nitrite (NO2) in rats has shown that the duration of effect was the greatest at oxacom action.

Topics: Adult; Animals; Biological Availability; Blood Pressure; Drug Evaluation, Preclinical; Drug Monitoring; Glutathione; Humans; Hypertension; Hypotension; Infusions, Intravenous; Iron; Male; Nitric Oxide; Nitrogen Oxides; Rats; Rats, Wistar; S-Nitrosoglutathione; Sodium Nitrite; Therapeutic Equivalency; Therapies, Investigational; Treatment Outcome

The unsatisfactory rates of adequate blood pressure control among patients receiving antihypertensive treatment calls for new therapeutic strategies to treat hypertension. Several studies have shown that oral sodium nitrite exerts significant antihypertensive effects, but the mechanisms underlying these effects remain unclear. While these mechanisms may involve nitrite-derived S-nitrosothiols, their implication in important alterations associated with hypertension, such as aberrant α1-adrenergic vasoconstriction, has not yet been investigated. Here, we examined the effects of oral nitrite treatment on vascular responses to the α1-adrenergic agonist phenylephrine in two-kidney, one clip (2K1C) hypertensive rats and investigated the potential underlying mechanisms. Our results show that treatment with oral sodium nitrite decreases blood pressure and prevents the increased α1-adrenergic vasoconstriction in 2K1C hypertensive rats. Interestingly, we found that these effects require vascular protein S-nitrosylation, and to investigate the specific S-nitrosylated proteins we performed an unbiased nitrosoproteomic analysis of vascular smooth muscle cells (VSMCs) treated with the nitrosylating compound S-nitrosoglutathione (GSNO). This analysis revealed that GSNO markedly increases the nitrosylation of calcium/calmodulin-dependent protein kinase II γ (CaMKIIγ), a multifunctional protein that mediates the α1-adrenergic receptor signaling. This result was associated with reduced α1-adrenergic receptor-mediated CaMKIIγ activity in VSMCs. We further tested the relevance of these findings in vivo and found that treatment with oral nitrite increases CaMKIIγ S-nitrosylation and blunts the increased CaMKIIγ activity induced by phenylephrine in rat aortas. Collectively, these results are consistent with the idea that oral sodium nitrite treatment increases vascular protein S-nitrosylation, including CaMKIIγ as a target, which may ultimately prevent the increased α1-adrenergic vasoconstriction induced by hypertension. These mechanisms may help to explain the antihypertensive effects of oral nitrite and hold potential implications in the therapy of hypertension and other cardiovascular diseases associated with abnormal α1-adrenergic vasoconstriction.

Topics: Adrenergic Agents; Animals; Antihypertensive Agents; Calcium; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Hypertension; Phenylephrine; Rats; Receptors, Adrenergic; Receptors, Adrenergic, alpha-1; Sodium Nitrite; Vasoconstriction

Proton pump inhibitors (PPI) are suppressors of gastric acid secretion (SGAS) that decrease gastric nitric oxide (NO) formation from nitrite and increase the cardiovascular risk. However, H2 receptor antagonists (H2RA) are considered safer than PPIs. We challenged this notion and hypothesized that both omeprazole (PPI) and ranitidine (H2RA) attenuate the responses to oral nitrite because both drugs increase gastric pH and therefore could decrease nitrite-derived NO formation in the stomach. We examined the blood pressure responses to oral nitrite in hypertensive rats treated with omeprazole, ranitidine, or vehicle. Chemiluminensce-based assays were used to measure gastric NO formation, plasma and gastric concentrations of nitrite, nitrate, and nitrosylated species (RXNO) to clarify the mechanism involved in the effects of SGAS on the responses to oral nitrite. Both drugs increased gastric pH, impaired oral nitrite-induced hypotensive responses, gastric NO formation, and blunted the increases in circulating RXNO concentrations, but not in circulating nitrite and nitrate concentrations. These findings were reproduced in a second study using sodium acetate buffers at pH 3.5, 4.5, and 5.5 to mimic gastric pH found with vehicle, ranitidine, and omeprazole, respectively. Increasing gastric pH impaired oral nitrite-induced hypotensive responses, gastric NO formation, and blunted the increases in circulating RXNO concentrations, but not in circulating nitrite and nitrate concentrations. Our results clearly indicate that SGAS impair nitrite-induced gastric formation of NO and vasoactive RXNO in a pH-dependent manner, thus resulting in impaired responses to oral nitrite. These findings may have several clinical implications, particularly to patients with cardiovascular diseases.

Topics: Administration, Oral; Animals; Antihypertensive Agents; Blood Pressure; Disease Models, Animal; Gastric Acid; Gastric Mucosa; Histamine H2 Antagonists; Hydrogen-Ion Concentration; Hypertension; Male; Nitrates; Nitric Oxide; Nitrites; Omeprazole; Proton Pump Inhibitors; Ranitidine; Rats; Rats, Wistar; Sodium Nitrite; Treatment Outcome

Sodium nitrite is used as a coloring agent or preservative in food, as well as an antimicrobial agent in meat and fish and some cheeses. In high amounts it can be toxic for humans, causing methemoglobinemia. This is an unusual and potentially fatal condition in which hemoglobin is oxidized to methemoglobin (MHb), reducing the amount of oxygen that is released from hemoglobin, similar to carbon monoxide poisoning. MHb levels of 70% are generally lethal, but the existence of underlying anemia, acidosis, respiratory compromise, and cardiac disease may exacerbate the toxicity of MHb. We present a case of poisoning with sodium nitrite in three family members after eating homemade sausages given to them by their neighbor who was a butcher. According to the findings of the veterinary inspectorate in charge of food control in this case, the concentration of sodium nitrite in the homemade sausages was about 3.5 g per 1 kg of meat, almost 30 times higher than allowed according to legislation. In this case report, a 70-year-old man died about 7 h after consuming the meal, while two women, 53 and 67 years of age, respectively, were admitted to a toxicology clinic the following day due to food poisoning, with the maximum concentration of MHb in blood of 33.7 and 20.4%, respectively. They were discharged 3 days later. The autopsy of the deceased man showed sodium nitrite poisoning with a relatively low concentration of MHb in his blood - 9.87%. Death was attributed to the exacerbation of hypertensive and ischemic heart disease, resulting from accidental sodium nitrite poisoning. The presented cases illustrate the necessity of close cooperation between the authorities, medical staff, veterinary inspectorate, and forensic pathologists in determining the source of poisoning, the cause of death of the victim, and preventing the outbreak of poisoning among a greater number of consumers.

Topics: Accidents, Home; Aged; Female; Food Preservatives; Foodborne Diseases; Humans; Hypertension; Male; Meat Products; Methemoglobinemia; Middle Aged; Myocardial Ischemia; Sodium Nitrite

Although nitrite improves vascular function and lowers blood pressure, its cardiac effects are not completely known. We investigated whether nitrite improves the cardiac function in normotensive and in hypertensive rats. Two-kidney, one-clip hypertension model (2K1C) was induced in Wistar rats. Blood pressure was evaluated by tail-cuff plethysmography over 6 weeks. By the end of week 2, hypertensive and normotensive rats received nitrite (daily dose of 1 or 15 mg/kg) by gavage for 4 weeks. Cardiac morphology and function were performed by transthoracic echocardiography. Intrinsic heart function was evaluated using the isolated heart model (Langendorff's preparation). Starling curves were generated under nitrite (1 μmol/L) and/or ascorbate (1 mmol/L) or vehicle. Cardiac tissue was collected and snap frozen for biochemical analysis. Nitrite treatment (15 mg/kg) lowered both systolic blood pressure and the increases in left ventricular (LV) mass found in 2K1C rats (P < .05). In addition, nitrite treatment restored the decreased cardiac output in 2K1C rats (P < .05) and improved the cardiac function. These findings were associated with increased nitrite, S-nitrosothiols, and protein S-nitrosylation (all P < .05) assessed in heart tissue. The cardiac effects of nitrite were further investigated in the isolated heart model, and nitrite infusion (1 μmol/L) enhanced cardiac contractility and relaxation. This infusion increased S-nitrosothiols concentrations and protein S-nitrosylation in the heart. Ascorbate completely blunted all nitrite-induced effects. These findings show that treatment with oral nitrite improves cardiac function by mechanisms involving increased S-nitrosothiols generation and S-nitrosylation of cardiac proteins. Pharmacological strategies promoting cardiac S-nitrosylation may be useful to improve myocardial function in heart diseases.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Cardiomyopathies; Heart; Hypertension; Male; Myocardium; Nitrates; Nitrosation; Oxidative Stress; Rats; Rats, Wistar; Sodium Nitrite

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.. 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.. 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.. 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.

Topics: Administration, Oral; Angiotensin II; Animals; Antihypertensive Agents; Antioxidants; Aorta, Thoracic; Arterial Pressure; Cyclic GMP; Disease Models, Animal; Endothelium, Vascular; Hypertension; Male; Mice, Inbred C57BL; NADPH Oxidase 2; NADPH Oxidase 4; Nitric Oxide; Oxidative Stress; Renal Artery; Sodium Nitrite; Tyrosine; Vasodilation

Alterations in the synthesis and bioavailability of NO are central to the pathogenesis of cardiovascular and metabolic disorders. Although endothelial NO synthase-derived (eNOS-derived) NO affects mitochondrial long-chain fatty acid β-oxidation, the pathophysiological significance of this regulation remains unclear. Accordingly, we determined the contributions of eNOS/NO signaling in the adaptive metabolic responses to fasting and in age-induced metabolic dysfunction. Four-month-old eNOS-/- mice are glucose intolerant and exhibit serum dyslipidemia and decreased capacity to oxidize fatty acids. However, during fasting, eNOS-/- mice redirect acetyl-CoA to ketogenesis to elevate circulating levels of β-hydroxybutyrate similar to wild-type mice. Treatment of 4-month-old eNOS-/- mice with nitrite for 10 days corrected the hypertension and serum hyperlipidemia and normalized the rate of fatty acid oxidation. Fourteen-month-old eNOS-/- mice exhibited metabolic derangements, resulting in reduced utilization of fat to generate energy, lower resting metabolic activity, and diminished physical activity. Seven-month administration of nitrite to eNOS-/- mice reversed the age-dependent metabolic derangements and restored physical activity. While the eNOS/NO signaling is not essential for the metabolic adaptation to fasting, it is critical for regulating systemic metabolic homeostasis in aging. The development of age-dependent metabolic disorder is prevented by low-dose replenishment of bioactive NO.

Topics: Administration, Oral; Aging; Animals; Disease Models, Animal; Drug Evaluation, Preclinical; Fasting; Homeostasis; Humans; Hyperlipidemias; Hypertension; Male; Mice; Mice, Knockout; Nitric Oxide; Nitric Oxide Synthase Type III; Signal Transduction; Sodium Nitrite; Time Factors; Treatment Outcome

Hypotensive effects of oral sodium nitrite have been reported as alternative sources of nitric oxide (NO) formation in animals and human beings. Reductions in NO bioavailability were observed in lead-induced hypertension. However, no previous study has examined whether a single daily dose of sodium nitrite prevents the reductions in the NO bioavailability in lead-induced hypertension. Then, we expanded previous reports and evaluated the effects of sodium nitrite in 7-day lead-treated rats. Wistar rats were divided into four experimental groups: Pb+sodium nitrite group received intraperitoneally (i.p.) 1st dose 8 µg/100 g of lead acetate and a subsequent dose of 0.1 µg/100 g, and daily treatment with sodium nitrite (45 mg/kg/day) or water (Pb group) by gavage for 7 days; Sodium nitrite group received i.p. 1st dose 8 µg/100 g of sodium acetate and a subsequent dose of 0.1 µg/100 g, and daily treatment with sodium nitrite (45 mg/kg/day) or water (saline group) by gavage for 7 days. Similar and higher whole-blood lead levels (11.5 ± 1.2 and 13.2 ± 0.7 µg/dL) were found in lead-exposed rats treated with either water or sodium nitrite (Pb or Pb+sodium nitrite, respectively; both p  <  0.05 versus control groups). We found lower NO markers such as plasma nitrite and nitrite + nitrate (NOx) levels (both p < 0.05 versus controls) in lead-exposed rats compared with normotensive (sodium acetate)-treated controls (Pb group versus saline group; p  <  0.05). Lead induced increases in systolic blood pressure (from 130 ± 2 to 164 ± 6 mmHg in Pb group; p  <  0.05); however, both lead-induced decreases in NO markers and hypertension (Pb+sodium nitrite group versus Pb group; both p  <  0.05) were prevented by a single daily dose of sodium nitrite. In conclusion, these findings are consistent with the idea that impaired NO bioavailability contributes to the maintenance of elevated blood pressure in lead-induced hypertension. Additionally, our results show that sodium nitrite exerts antihypertensive effects in lead-induced hypertension and provide evidence that sodium nitrite prevents the impairment of NO, thus, reaffirming the relevance of nitrite as alternative source of recycling back to NO.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Hypertension; Lead; Male; Nitric Oxide; Rats; Rats, Wistar; Sodium Nitrite

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.

Topics: Acetylcholine; Animals; Antihypertensive Agents; Aorta; Arterial Pressure; Cyclic GMP; Endothelium, Vascular; Enzyme Activation; HSP90 Heat-Shock Proteins; Hypertension; Male; Nitrates; Nitric Oxide; Nitric Oxide Synthase Type III; Nitrites; Phosphorylation; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Sprague-Dawley; Sodium Nitrite

Ingestion of dietary nitrites lowers arterial blood pressure in experimental animals and in humans. However, the exact mechanism underlying the hypotensive effect of nitrite remains unclear. The present study compared nitrite-induced responses in rings (with or without endothelium) of aortae of 18-20weeks old Wistar-Kyoto Rats (WKY) and spontaneously hypertensive (SHR) rats and investigated the underlying mechanism. Relaxations of aortae from WKY and SHR to increasing concentrations (1nM-100μM) of sodium nitrite (NaNO2) were determined during sustained contractions to phenylephrine, in the absence and presence of pharmacological agents. The nitrite-induced relaxations were concentration-dependent and larger in SHR than in WKY aortic rings. Inhibition of endothelial nitric oxide synthase (eNOS) and the absence of endothelium decreased nitrite-induced relaxations in both WKY and SHR aortae, indicating the role of endothelium-derived nitric oxide (NO) in the response. The involvement of eNOS was further confirmed by increases in phosphorylation of eNOS at ser1177 in HUVEC cells following treatment with sodium nitrite. The presence of NO scavengers decreased the relaxation to nitrite in both WKY and SHR preparations while inhibition of soluble guanylyl cyclase (sGC) abolished the response, indicating that besides producing NO, nitrite also induces relaxation by directly activating the enzyme. Thus, the present study demonstrates that the sensitivity to exogenous nitrite is increased in the aorta of the SHR compared to that of the WKY. The endothelium-dependent component of the relaxation to nitrite involves activation of eNOS with production of endothelium-derived NO, while the endothelium-independent component is due to stimulation of sGC.

Topics: Animals; Aorta; Cells, Cultured; Endothelium, Vascular; Guanylate Cyclase; Human Umbilical Vein Endothelial Cells; Humans; Hypertension; Male; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase Type III; Phenylephrine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Cytoplasmic and Nuclear; Sodium Nitrite; Soluble Guanylyl Cyclase; Vasodilation; Vasodilator Agents

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.

Topics: Animals; Antihypertensive Agents; Antioxidants; Blood Pressure; Desoxycorticosterone; Dinoprost; Disease Models, Animal; Hypertension; Lipid Peroxides; Male; NADPH Oxidases; Nitrites; Nitrogen Oxides; Oxidative Stress; Rats; Rats, Wistar; Reactive Oxygen Species; Sodium Nitrite; Xanthine Oxidase

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 N(ω)-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.

Topics: Aldehyde Dehydrogenase; Aldehyde Dehydrogenase, Mitochondrial; Animals; Antihypertensive Agents; Blood Pressure; Disease Models, Animal; Dose-Response Relationship, Drug; Hydrazines; Hypertension; Male; Mitochondrial Proteins; NG-Nitroarginine Methyl Ester; Nitrates; Nitric Oxide; Nitroglycerin; Rats; Rats, Sprague-Dawley; Sodium Nitrite; Time Factors

Nitrate and nitrite have emerged as an important novel source of nitric oxide (NO). We have previously demonstrated that sodium nitrite is an antihypertensive compound that exerts antioxidant effects in experimental hypertension. These unpredicted antioxidant effects of nitrite raised the question whether the beneficial effects found were caused by its conversion to NO or simply due to reversal of endothelial dysfunction as a consequence of its antioxidant effects. Here, we evaluated the antihypertensive effects of a daily dose of sodium nitrite for 4 weeks in L-NAME-induced hypertension in rats. We studied the effects of nitrite on markers of NO bioavailability, vascular oxidative stress, and expression of xanthine oxidoreductase. Moreover, we tested if xanthine oxidoreductase inhibition could attenuate the acute hypotensive effects of sodium nitrite in L-NAME hypertensive rats. We found that a single pharmacological dose of sodium nitrite exerts antihypertensive effects in L-NAME-induced hypertension. While the beneficial antihypertensive properties of nitrite were associated with increased levels of NO metabolites, hypertension increased vascular xanthine oxidoreductase expression by approximately 40%, with minor increases in vascular superoxide production. The inhibition of xanthine oxidoreductase by oxypurinol attenuated the acute hypotensive effects of nitrite. Taken together, our results show that nitrite exerts antihypertensive effects in L-NAME hypertensive rats and provide evidence that xanthine oxidoreductase plays an important role in this antihypertensive effect.

Topics: Animals; Antihypertensive Agents; Endothelium, Vascular; Hypertension; Male; NG-Nitroarginine Methyl Ester; Random Allocation; Rats; Rats, Wistar; Sodium Nitrite; Xanthine Dehydrogenase

Nitrite-derived nitric oxide (NO) formation exerts antihypertensive effects. Because NO inhibits angiotensin converting enzyme (ACE) activity, we carried a comprehensive series of experiments in rats to test the hypothesis that sodium nitrite exerts antihypertensive effects by inhibiting ACE. We examined whether sodium nitrite (15 mg/kg; or vehicle; by gavage): (I) attenuates the pressor responses to angiotensin I at doses of 0.03, 0.1, 0.3, 1, 3, and 10 μg/kg intravenously; (II) attenuates the acute hypertension induced by L-NAME (100 mg/kg; or vehicle; by gavage); (III) attenuates the chronic hypertension induced by L-NAME (1 g/L in drinking water; or vehicle) administered for 6 weeks; (IV) attenuates the hypertension in the 2 kidney-1 clip (2K1C) chronic hypertension model. Blood samples were collected at the end of each study and plasma angiotensin converting enzyme (ACE) activity was measured with a fluorimetric assay using Hippuryl-His-Leu as substrate. ACE inhibitors were used as positive controls. Plasma nitrite concentrations were measured by ozone-based reductive chemiluminescence. The in vitro effects of sodium nitrite (0, 1, 3, 10, 30, 100 μmol/L) on plasma ACE activity were also determined. We found that sodium nitrite did not affect the pressor responses to angiotensin I. Moreover, while sodium nitrite exerted significant antihypertensive effects in acute and chronic hypertension models, no significant effects on plasma ACE activity were found. In vitro experiments showed no effects of sodium nitrite on plasma ACE activity. This is the first study to demonstrate that the acute and chronic antihypertensive effects of sodium nitrite are not associated with significant inhibition of circulating ACE activity.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Antihypertensive Agents; Disease Models, Animal; Dose-Response Relationship, Drug; Hypertension; Male; NG-Nitroarginine Methyl Ester; Peptidyl-Dipeptidase A; Rats; Rats, Wistar; Sodium Nitrite; Structure-Activity Relationship

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.

Topics: Administration, Oral; Animals; Anti-Ulcer Agents; Antihypertensive Agents; Aorta; Benzoates; Blood Pressure; Free Radical Scavengers; Gastric Juice; Hydrogen-Ion Concentration; Hypertension; Imidazoles; In Vitro Techniques; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Omeprazole; Rats; Rats, Wistar; S-Nitrosothiols; Sodium Nitrite; Vasodilation

Arterial hypertension is a major risk factor that can lead to complication of peripheral vascular disease due, in part, to endothelial dysfunction. Because sodium nitrite (SN) can be converted to nitric oxide (NO), which counteracts endothelial dysfunction, we explored the effect of nitrite on neovascularization following hind limb ischemia in different models of hypertension (HT). Chronic delivery of angiotensin II (Ang II, 400 ng/kg/min) or N(omega)-nitro-L-arginine-methyl-ester (L-NAME, 0.1 g/L) was used for a 2-week period to induce hypertension. Mice were subjected to femoral artery ligation-induced ischemia in the hind limb followed by treatment with SN (50 mg/L) for 2 weeks. SN significantly reduced systolic arterial blood pressure in mice receiving Ang II and L-NAME but had no effect in sham animals. After 2 weeks, blood flow and microangiography showed 60 % ± 1.0 recovery in sham compared with 40 % ± 1.3 in HT mice. Importantly, sham and HT mice treated with SN showed a 100 % blood flow recovery associated with normalization in capillary density. The inhibition of xanthine-oxido-reductase (allopurinol) or VEGFR (SU-5416) prevented the neovascularization in HT mice treated with SN. Cyclic GMP (cGMP) content in the hind limb was significantly increased in mice treated with SN compared with non-treated mice. Nitrite/nitrate content was only increased in the sham group treated with SN. Immunoprecipitation and Western blot analysis revealed an increase in eNOS/Akt/VEGFR phosphorylation in skeletal muscle from mice treated with SN compared with non-treated mice. Our findings indicate that SN therapy rescues the neovascularization and blood flow recovery in the ischemic hind limb of sham and HT mice likely through the Akt/NO/cGMP and VEGFR pathways.

Topics: Allopurinol; Angiotensin II; Animals; Arterial Pressure; Capillaries; Cyclic AMP; Cyclic GMP; Femoral Artery; Hindlimb; Hypertension; Indoles; Ischemia; Male; Mice; Mice, Inbred C57BL; Muscle, Skeletal; Neovascularization, Pathologic; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase Type III; Proto-Oncogene Proteins c-akt; Pyrroles; Receptors, Vascular Endothelial Growth Factor; Regional Blood Flow; Sodium Nitrite; Xanthine Dehydrogenase

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.

Topics: Animals; Antihypertensive Agents; Antioxidants; Blood Pressure; Dinoprost; Down-Regulation; Hypertension; Lipid Peroxides; NADPH Oxidases; Nitric Oxide; Nitrites; Oxidative Stress; Rats; Reactive Oxygen Species; Sodium Nitrite; Xanthine Oxidase

Hypertension secondary to scavenging of NO remains a limitation in the use of HBOCs (haemoglobin-based oxygen carriers). Recent studies suggest that nitrite reduction to NO by deoxyhaemoglobin supports NO signalling. In the present study we tested whether nitrite would attenuate HBOC-mediated hypertension using HBOC-201 (Biopure), a bovine cross-linked, low-oxygen-affinity haemoglobin. In a similar way to unmodified haemoglobin, deoxygenated HBOC-201 reduced nitrite to NO with rates directly proportional to the extent of deoxygenation. The functional importance of HBOC-201-dependent nitrite reduction was demonstrated using isolated aortic rings and a murine model of trauma, haemorrhage and resuscitation. In the former, HBOC-201 inhibited NO-donor and nitrite-dependent vasodilation when oxygenated. However, deoxygenated HBOC-201 failed to affect nitrite-dependent vasodilation but still inhibited NO-donor dependent vasodilation, consistent with a model in which nitrite-reduction by deoxyHBOC-201 counters NO scavenging. Finally, resuscitation using HBOC-201, after trauma and haemorrhage, resulted in mild hypertension ( approximately 5-10 mmHg). Administration of a single bolus nitrite (30-100 nmol) at the onset of HBOC-201 resuscitation prevented hypertension. Nitrite had no effect on mean arterial pressure during resuscitation with LR (lactated Ringer's solution), suggesting a role for nitrite-HBOC reactions in attenuating HBOC-mediated hypertension. Taken together these data support the concept that nitrite can be used as an adjunct therapy to prevent HBOC-dependent hypertension.

Topics: Animals; Antihypertensive Agents; Aorta; Blood Substitutes; Disease Models, Animal; Hemoglobins; Hypertension; Male; Mice; Mice, Inbred C57BL; Nitric Oxide; Nitric Oxide Donors; Nitrite Reductases; Rats; Rats, Sprague-Dawley; Sodium Nitrite; Vasodilation

One of the major obstacles hindering the clinical development of a cell-free, hemoglobin-based oxygen carrier (HBOC) is systemic vasoconstriction.. Experiments were performed in healthy mice and lambs by infusion of either murine tetrameric hemoglobin (0.48 g/kg) or glutaraldehyde-polymerized bovine hemoglobin (HBOC-201, 1.44 g/kg). We observed that intravenous infusion of either murine tetrameric hemoglobin or HBOC-201 induced prolonged systemic vasoconstriction in wild-type mice but not in mice congenitally deficient in endothelial nitric oxide (NO) synthase (NOS3). Treatment of wild-type mice by breathing NO at 80 ppm in air for 15 or 60 minutes or with 200 ppm NO for 7 minutes prevented the systemic hypertension induced by subsequent intravenous administration of murine tetrameric hemoglobin or HBOC-201 and did not result in conversion of plasma hemoglobin to methemoglobin. Intravenous administration of sodium nitrite (48 nmol) 5 minutes before infusion of murine tetrameric hemoglobin also prevented the development of systemic hypertension. In awake lambs, breathing NO at 80 ppm for 1 hour prevented the systemic hypertension caused by subsequent infusion of HBOC-201.. These findings demonstrate that HBOC can cause systemic vasoconstriction by scavenging NO produced by NOS3. Moreover, in 2 species, inhaled NO administered before the intravenous infusion of HBOC can prevent systemic vasoconstriction without causing methemoglobinemia.

Topics: Administration, Inhalation; Animals; Blood Substitutes; Blood Transfusion; Drug Evaluation, Preclinical; Hemodynamics; Hemoglobins; Hypertension; Infusions, Intravenous; Methemoglobinemia; Mice; Mice, Knockout; Nitric Oxide; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Premedication; Sheep; Sodium Nitrite; Vasoconstriction; Vasodilator Agents; Wakefulness

Treatment with tetrahydrobiopterin (BH(4)) reduces blood pressure in spontaneously hypertensive rats (SHR). In the present study, we tested the hypothesis that chronic BH(4) reduces blood pressure in male SHR by reducing testosterone biosynthesis mediated by increasing nitric oxide (NO). Male SHR, aged 17-18 wk, intact or castrated, were treated for 1 wk with BH(4) (20 mg.kg(-1).day(-1) ip). After 1 wk, mean arterial pressure (MAP), serum testosterone, and nitrate/nitrite excretion (NO(x)) were measured. MAP was significantly higher in intact males than castrated males (179 +/- 2 vs. 155 +/- 4 mmHg, P < 0.001). In intact males, BH(4) caused a 17% reduction in MAP (148 +/- 2 mmHg), had no effect on NO(x), and reduced serum testosterone by 85% (24.09 +/- 2.37 vs. 3.72 +/- 0.73 ng/dl; P < 0.001). In castrated males, BH(4) had no effect on MAP (152 +/- 5 mmHg) but increased NO(x) by 38%. When castrated males were supplemented with testosterone, MAP increased to the same level as in intact males (180 +/- 7 mmHg), and BH(4) had no effect on MAP (182 +/- 7 mmHg) or NO(x). NO has been shown to decrease testosterone biosynthesis. Chronic sodium nitrite (70 mg.kg(-1).day(-1) x 1 wk) decreased MAP in intact males (150 +/- 4 mmHg) but had no effect on serum testosterone (21.46 +/- 3.08 ng/dl). The data suggest that BH(4) reduces testosterone synthesis and thereby reduces MAP in male SHR, an androgen-dependent model of hypertension. The mechanism(s) by which BH(4) reduces serum testosterone levels are not clear, but the data do not support a role for NO as a mediator.

Topics: Animals; Biopterins; Blood Pressure; Drug Administration Schedule; Hypertension; Male; Nitric Oxide Donors; Orchiectomy; Rats; Rats, Inbred SHR; Sodium Nitrite; Testosterone

The hypothesis was studied whether the chronic administration of nitrite lowers the blood pressure of spontaneously hypertensive rats (SHR) and prevents secondary hypertension-induced organ lesions. For this purpose totally 96 SHR received 50 to 75 mmol/l NaNO2 or equimolar amounts of NaHCO3 in their drinking water during 4, 8 or 12 months. At each point of time arterial blood pressure, determined with the tail cuff method, was significantly lower in the NaNO2-group in comparison to the controls indicating that no significant tolerance towards nitrite had developed. There was also a tendency towards reduced cardiac hypertrophy and renal atrophy in the NaNO2-group, however without reaching the level of significance. Drinking water containing 75 mmol NaNO2/l was not well tolerated by young rats in contrast to 50 mmol/l. Possible beneficial effects of high dietary nitrate/nitrite levels are discussed with respect to the low frequency of hypertension observed in vegetarians.

Topics: Administration, Oral; Animals; Antihypertensive Agents; Blood Pressure; Hypertension; Male; Methemoglobin; Organ Size; Rats; Rats, Inbred SHR; Rats, Sprague-Dawley; Sodium Nitrite

Our earlier studies suggested an association between alpha-thalassemia and hypertension. We postulated that this association might involve trapping of the vasodilator nitric oxide (NO) by hemoglobin (Hb). Hb A has recently been shown to carry NO on its sulfhydryl groups in addition to its hemes. In this report we studied the interaction of purified Hb H as well as Hb A with NO. The number of reactive sulfhydryls were determined spectrophotometrically with bis-dithionitrobenzoate. Spectral studies and nitrosothiol measurements after treatment with NO or nitrosothiols indicated that all eight reactive sulfhydryls of Hb H were capable of binding NO. Hb A, however, was only able to bind and transfer two molecules of NO per tetramer. These findings support the biochemical basis for the association between alpha-thalassemia and hypertension.

Topics: alpha-Thalassemia; Dithionitrobenzoic Acid; Electrophoresis, Agar Gel; Heme; Hemoglobin A; Hemoglobin H; Humans; Hypertension; Mercuribenzoates; Nitric Oxide; Nitroso Compounds; Oxygen; Oxyhemoglobins; Sodium Nitrite; Spectrophotometry; Sulfhydryl Compounds

Blood vessel responses to relaxant drugs have been reported to change with aging and with the development of hypertension. In view of the requirement of endothelial cells for the activity of many relaxant drugs, we examined the role of the endothelium in the relaxation response of vascular tissue. Aortic and mesenteric ring segments from normotensive and hypertensive rats, ages 5 to 6, 15 to 18 and 30 to 31 weeks, were examined for relaxation to sodium nitroprusside, sodium nitrite, atrial natriuretic factor and 8-bromo-cyclic GMP. Relaxation responses to the nitrovasodilators were reduced progressively with aging in ring segments of Wistar-Kyoto rats (WKYs) and spontaneously hypertensive rats (SHRs) with intact endothelium; however, intact SHR ring preparations displayed less relaxation to nitrovasodilators at 15 to 18 and 30 to 31 weeks than those of WKYs. Rubbed (endothelium denuded) ring preparations displayed greatest relaxation to nitrovasodilators with no difference being observed between SHR and WKY preparations at any age tested. Relaxation to atrial natriuretic factor and 8-bromo-cyclic GMP was not different between rubbed and unrubbed ring segments or between SHRs and WKYs, indicating no detectable impairment of the overall relaxation response in the vascular smooth muscle of SHRs. These results suggest that the total functional capacity of vascular smooth muscle to relax to nitrovasodilators is not changed with aging or hypertension. However, the endothelial cells exert modulatory influences upon the vascular smooth muscle to reduce overall responsiveness to nitrovasodilators, an effect that is enhanced with aging and the development of genetic hypertension.

Topics: Aging; Animals; Atrial Natriuretic Factor; Cyclic GMP; Dose-Response Relationship, Drug; Endothelium; Hypertension; Male; Methylene Blue; Muscle Contraction; Muscle Relaxation; Nitroprusside; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Sodium Nitrite; Vasodilator Agents

The relaxation effects of endothelium-dependent (acetylcholine, histamine) and endothelium-independent (nitroprusside, nitrite) relaxing substances were comparatively examined on contracted thoracic aortic rings from normotensive and experimental renal and desoxycorticosterone acetate (DOCA)-salt hypertensive Wistar rats. On the aorta preparations from hypertensive animals a highly significant depression of the maximal relaxation effect of histamine and acetylcholine was observed. This was not seen with nitroprusside and nitrite. By use of a bioassay technique it was demonstrated that the depression of the endothelium-mediated response is not due to a diminished release of endothelium-derived relaxing factor. Impaired coupling between the endothelium and the smooth muscle cells is suggested to be responsible for that depression.

Topics: Acetylcholine; Animals; Aorta, Thoracic; Desoxycorticosterone; Dinoprost; Endothelium; Histamine; Hypertension; In Vitro Techniques; Ligation; Male; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroprusside; Prostaglandins F; Rats; Rats, Inbred Strains; Renal Artery; Sodium Chloride; Sodium Nitrite

This study investigated the effects of altered extracellular Ca2+ on in vitro femoral arterial smooth muscle responsiveness in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Compared with controls, femoral arteries from DOCA-salt rats showed a significant increase in sensitivity to KCl and norepinephrine in normal Ca2+ (2.5 mM). Although no difference in maximal contractile response to KCl was observed between groups, there was a significant difference in maximal response to norepinephrine. Dose-response curves in low Ca2+ (0.25 mM) resulted in a significant decrease in the sensitivity of femoral arteries from DOCA-salt rats to KCl and NE so that the responses were similar to those of controls. Relaxation of femoral arteries from DOCA-salt rats after washout of the KCl contraction was significantly slower than that of controls in both low and normal Ca2+. Isoproterenol-induced relaxation of femoral arteries from DOCA-salt rats was significantly attenuated in normal Ca2+. Sensitivity of femoral arteries from DOCA-salt rats to isoproterenol increased in low Ca2+, but maximal relaxation was unaltered. Whereas no difference in maximal relaxation to NaNO2 was seen in femoral arteries from either group in normal Ca2+, a significant decrease in sensitivity to NaNO2 was observed in femoral arteries from DOCA-salt rats. In low Ca2+ the response of femoral arteries from DOCA-salt rats to NaNO2 was similar to that of controls. These results suggest that the increased vascular smooth muscle responsiveness to KCl and norepinephrine seen in DOCA-salt hypertension is due to increased sensitivity of the vascular smooth muscle to Ca2+. Extracellular Ca2+, however, plays only a minor role in the decreased vasodilator responsiveness seen in this form of hypertension.

Topics: Animals; Calcium; Desoxycorticosterone; Dose-Response Relationship, Drug; Extracellular Space; Femoral Artery; Hypertension; Isoproterenol; Male; Muscle Contraction; Muscle, Smooth, Vascular; Norepinephrine; Potassium Chloride; Rats; Rats, Inbred Strains; Sodium Chloride; Sodium Nitrite

Topics: Cerebrospinal Fluid; Cerebrospinal Fluid Pressure; Cerebrovascular Circulation; Humans; Hypertension; Intracranial Arteriosclerosis; Intracranial Embolism; Intracranial Embolism and Thrombosis; Multiple Sclerosis; Nitrites; Pharmacology; Retinal Artery; Retinal Vessels; Sodium Nitrite

Topics: Blood Pressure; Blood Pressure Determination; Humans; Hypertension; Nitrates; Sodium Nitrite