Gastroprotective and blood pressure lowering effects of dietary nitrate are abolished by an antiseptic mouthwash

Single-dose pharmacokinetics of different oral sodium nitrite formulations in diabetes patients

BACKGROUND

Diabetic foot ulcers, although associated with macrovascular disease and neuropathy, have a microvascular disease causing ischemia not amenable to surgical intervention. Nitrite selectively releases nitric oxide in ischemic tissues, and diabetes subjects have low nitrite levels that do not increase with exercise. This study explores the safety and pharmacokinetics of a single dose of sodium nitrite in subjects with diabetic foot ulcers.

SUBJECTS AND METHODS

Using a blinded, randomized crossover study design, 12 subjects with diabetes mellitus and active or healed foot ulcers received a single dose of sodium nitrite on two occasions 7-28 days apart, once with an immediate release (IR) formulation and once with an enteric-coated (EC) formulation for delayed release. Serum nitrite, nitrate, methemoglobin, sulfhemoglobin, blood pressure, pulse rate, complete blood count, chemistry panel, electrocardiogram, and adverse events were followed for up to 6 h after each dose. The IR and EC nitrite levels were analyzed by one-way analysis of variance and by pharmacokinetic modeling.

RESULTS

The IR formulation elevated nitrite levels between 0.25 and 0.75 h (P<0.05). The EC formulation did not elevate nitrite levels significantly, but both formulations gave plasma nitrite levels previously suggested to be therapeutic (approximately 2-5 μM). The IR formulation gave an asymptomatic blood pressure drop of 10/6 mm Hg (P<0.003), and two subjects experienced mild flushing. There was no elevation of methemoglobin or other safety concerns. Pharmacokinetic modeling of plama nitrite levels gave r(2) values of 0.81 and 0.97 for the fits for IR and EC formulations, respectively.

CONCLUSIONS

Oral sodium nitrite administration is well tolerated in diabetes patients.

Nitrate causes a dose-dependent augmentation of nitric oxide status in healthy women

Green leafy vegetables, high in dietary nitrate, may contribute to cardiovascular health by augmenting nitric oxide status. The exogenous enterosalivary pathway of nitrate reduction to nitrite appears to be a critical determinant of the effects of nitrate. Our primary objective was to investigate the dose-response of nitrate intake on nitric oxide status and nitrate reduction in the mouth. We also assessed whether antibacterial toothpaste can inhibit nitrate reduction and blunt subsequent increases in circulating nitric oxide. A randomised, controlled, crossover trial with healthy women (n = 16) was conducted. The acute effects of four doses of nitrate (0 mg, 100 mg, 200 mg, 400 mg, as well as 400 mg plus antibacterial toothpaste), administered in random order, were compared. Measurements included biomarkers of plasma nitric oxide status, assessed by measuring S-nitrosothiols + other nitroso species (RXNO) and nitrite, and a biomarker of nitrate reduction in the mouth, assessed by measuring salivary nitrite. Compared to 0 mg, all doses of nitrate resulted in higher plasma RXNO and nitrite, and salivary nitrite (P < 0.05). A linear dose-response to nitrate intake was observed with plasma RXNO and nitrite, and salivary nitrite (P < 0.001). Antibacterial toothpaste did not alter nitrate reduction in the mouth (P > 0.9) or blunt the increase in nitric oxide status (P > 0.9). Thus, our study has demonstrated that increasing nitrate intake results in a dose-related increase in nitrate reduction in the mouth and nitric oxide status, and that use of antibacterial toothpaste does not inhibit nitrate reduction or blunt increases in circulating nitric oxide.

Dietary inorganic nitrate alleviates doxorubicin cardiotoxicity: mechanisms and implications

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

Decreased leukocyte recruitment by inorganic nitrate and nitrite in microvascular inflammation and NSAID-induced intestinal injury

Nitric oxide (NO) generated by vascular NO synthases can exert anti-inflammatory effects, partly through its ability to decrease leukocyte recruitment. Inorganic nitrate and nitrite, from endogenous or dietary sources, have emerged as alternative substrates for NO formation in mammals. Bioactivation of nitrate is believed to require initial reduction to nitrite by oral commensal bacteria. Here we investigated the effects of inorganic nitrate and nitrite on leukocyte recruitment in microvascular inflammation and in NSAID-induced small-intestinal injury. We show that leukocyte emigration in response to the proinflammatory chemokine MIP-2 is reduced by 70% after 7 days of dietary nitrate supplementation as well as by acute intravenous nitrite administration. Nitrite also reduced leukocyte adhesion to a similar extent and this effect was inhibited by the soluble guanylyl cyclase inhibitor ODQ, whereas the effect on emigrated leukocytes was not altered by this treatment. Further studies in TNF-α-stimulated endothelial cells revealed that nitrite dose-dependently reduced the expression of ICAM-1. In rats and mice subjected to a challenge with diclofenac, dietary nitrate prevented the increase in myeloperoxidase and P-selectin levels in small-intestinal tissue. Antiseptic mouthwash, which eliminates oral nitrate reduction, markedly blunted the protective effect of dietary nitrate on P-selectin levels. Despite attenuation of the acute immune response, the overall ability to clear an infection with Staphylococcus aureus was not suppressed by dietary nitrate as revealed by noninvasive IVIS imaging. We conclude that dietary nitrate markedly reduces leukocyte recruitment to inflammation in a process involving attenuation of P-selectin and ICAM-1 upregulation. Bioactivation of dietary nitrate requires intermediate formation of nitrite by oral nitrate-reducing bacteria and then probably further reduction to NO and other bioactive nitrogen oxides in the tissues.

Flavonoid-rich apples and nitrate-rich spinach augment nitric oxide status and improve endothelial function in healthy men and women: a randomized controlled trial

Flavonoids and nitrates in fruits and vegetables may protect against cardiovascular disease. Dietary flavonoids and nitrates can augment nitric oxide status via distinct pathways, which may improve endothelial function and lower blood pressure. Recent studies suggest that the combination of flavonoids and nitrates can enhance nitric oxide production in the stomach. Their combined effect in the circulation is unclear. Here, our objective was to investigate the independent and additive effects of flavonoid-rich apples and nitrate-rich spinach on nitric oxide status, endothelial function, and blood pressure. A randomized, controlled, crossover trial with healthy men and women (n=30) was conducted. The acute effects of four energy-matched treatments (control, apple, spinach, and apple+spinach), administered in random order, were compared. Measurements included plasma nitric oxide status, assessed by measuring S-nitrosothiols+other nitrosylated species (RXNO) and nitrite, blood pressure, and endothelial function, measured as flow-mediated dilatation of the brachial artery. Results are means and 95% CI. Relative to control, all treatments resulted in higher RXNO (control, 33 nmol/L, 26, 42; apple, 51 nmol/L, 40, 65; spinach, 86 nmol/L, 68, 110; apple+spinach, 69 nmol/L, 54, 88; P<0.01) and higher nitrite (control, 35 nmol/L, 27, 46; apple, 69 nmol/L, 53, 90; spinach, 99 nmol/L, 76, 129; apple+spinach, 80 nmol/L, 61, 104; P<0.01). Compared to control, all treatments resulted in higher flow-mediated dilatation (P<0.05) and lower pulse pressure (P<0.05), and apple and spinach resulted in lower systolic blood pressure (P<0.05). No significant effect was observed on diastolic blood pressure. The combination of apple and spinach did not result in additive effects on nitric oxide status, endothelial function, or blood pressure. In conclusion, flavonoid-rich apples and nitrate-rich spinach can independently augment nitric oxide status, enhance endothelial function, and lower blood pressure acutely, outcomes that may benefit cardiovascular health.

Microbiota in the oral subgingival biofilm is associated with obesity in adolescence

To test the hypothesis whether microbiota in oral biofilm is linked with obesity in adolescents we designed this cross-sectional study. Obese adolescents (n = 29) with a mean age of 14.7 years and normal weight subjects (n = 58) matched by age and gender were examined with respect to visible plaque index (VPI%) and gingival inflammation (bleeding on probing (BOP%)). Stimulated saliva was collected. They answered a questionnaire concerning medical history, medication, oral hygiene habits, smoking habits, and sociodemographic background. Microbiological samples taken from the gingival crevice was analyzed by checkerboard DNA-DNA hybridization technique. The sum of bacterial cells in subgingival biofilm was significantly associated with obesity (P < 0.001). The link between sum of bacterial cells and obesity was not confounded by any of the studied variables (chronic disease, medication, VPI%, BOP%, flow rate of whole saliva, or meal frequency). Totally 23 bacterial species were present in approximately threefold higher amounts, on average, in obese subjects compared with normal weight controls. Of the Proteobacteria phylum, Campylobacter rectus and Neisseria mucosa were present in sixfold higher amounts among obese subjects. The association between obesity and sum of bacterial cells in oral subgingival biofilm indicates a possible link between oral microbiota and obesity in adolescents.

Nitrate and nitrite content of human, formula, bovine, and soy milks: implications for dietary nitrite and nitrate recommendations

BACKGROUND

Estimation of nitrate and nitrite concentrations of milk sources may provide insight into potential health risks and benefits of these food sources for infants, children, and adults. The World Health Organization and American Academy of Pediatrics recommends exclusive consumption of human milk for the first 6 months of life. Human milk is known to confer significant nutritional and immunological benefits for the infant. Consumption of formula, cow's, and soy milk may be used as alternatives to human milk for infants.

METHODS

We sought to estimate potential exposure to nitrate and nitrite in human, formula, bovine, and soy milk to inform total dietary exposure estimates and recommendations. Using sensitive quantitative methodologies, nitrite and nitrate were analyzed in different samples of milk.

RESULTS

Human milk concentrations of colostrum (expressed days 1-3 postpartum; n=12), transition milk (expressed days 3-7 postpartum; n=17), and mature milk (expressed >7 days postpartum; n=50) were 0.08 mg/100 mL nitrite and 0.19 mg/100 mL nitrate, 0.001 mg/100 mL nitrite and 0.52 mg/100 mL nitrate, and 0.001 mg/100 mL nitrite and 0.3 mg/100 mL nitrate, respectively, revealing that the absolute amounts of these anions change as the composition of milk changes. When expressed as a percentage of the World Health Organization's Acceptable Daily Intake limits, Silk® Soy Vanilla (WhiteWave Foods, Broomfield, CO) intake could result in high nitrate intakes (104% of this standard), while intake of Bright Beginnings Soy Pediatric® formula (PBM Nutritionals, Georgia, VT) could result in the highest nitrite intakes (383% of this standard).

CONCLUSIONS

The temporal relationship between the provision of nitrite in human milk and the development of commensal microbiota capable of reducing dietary nitrate to nitrite supports a hypothesis that humans are adapted to provide nitrite to the gastrointestinal tract from birth. These data support the hypothesis that the high concentrations of breastmilk nitrite and nitrate are evidence for a physiologic requirement to support gastrointestinal and immune homeostasis in the neonate.

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

PURPOSE

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

RESULTS

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

CONCLUSION

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

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

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

Nitrite and nitrate: cardiovascular risk-benefit and metabolic effect

PURPOSE OF REVIEW

To review the most recent published literature on the biological effects of nitrite and nitrate in order to establish the context for potential health benefits vs. potential risks or adverse effects. Nitrite and nitrate are indigenous to our diet and are formed naturally within our body from the oxidation of nitric oxide. Emerging health benefits from dietary sources of nitrite and nitrate contradict decades of epidemiological research that have suggested an association of nitrite and nitrate in foods, primarily cured and processed meat, with certain cancers.

RECENT FINDINGS

The major source of exposure of nitrite and nitrate comes from the consumption of nitrate-enriched vegetables. The preponderance of epidemiological studies shows a very weak association with consumption of meats and certain cancers, which contain very little nitrite and nitrate. Nitrite and nitrate in certain foods and diets can be metabolized to nitric oxide and promote cardiovascular benefits and cytoprotection.

SUMMARY

The cardiovascular benefits of nitrite and nitrate are beginning to be translated in humans by the increasing number of clinical trials using nitrite and nitrate. The collective body of evidence suggests that foods enriched in nitrite and nitrate provide significant health benefits with very little risk.

Biological toxicity of acid electrolyzed functional water: effect of oral administration on mouse digestive tract and changes in body weight

OBJECTIVE

Acid electrolyzed functional water has been used in a variety of ways because of its antiseptic action. In the present study, we investigated both the systemic and gastrointestinal effects of ingesting acid electrolyzed functional water, from the perspective of its use in mouthwash.

MATERIALS AND METHODS

Seventeen mice (three weeks old) were used in the experiment. Three of the mice (three-week-old group) were euthanized before having been given solid food, whilst the remaining 14 were divided into two groups, one given free access to acid electrolyzed functional water as drinking water (test group) and the other given free access to tap water as drinking water (control group). Changes in body weight, visual inspections of the oral cavity, histopathological tests, and measurements of surface enamel roughness and observations of enamel morphology were recorded after eight weeks.

RESULTS

The results showed no significant difference in changes in body weight between the test and control groups. No abnormal findings or measurements were observed for the test group in terms of visual inspections of the oral cavity, histopathological tests, or measurements of surface enamel roughness. In terms of enamel morphology, attrition was seen in the test group.

CONCLUSIONS

These findings suggest that the use of acid electrolyzed functional water has no systemic effect and is safe for use in mouthwash.

Dietary nitrate attenuates oxidative stress, prevents cardiac and renal injuries, and reduces blood pressure in salt-induced hypertension

AIMS

Reduced bioavailability of endogenous nitric oxide (NO) is a central pathophysiological event in hypertension and other cardiovascular diseases. Recently, it was demonstrated that inorganic nitrate from dietary sources is converted in vivo to form nitrite, NO, and other bioactive nitrogen oxides. We tested the hypothesis that dietary inorganic nitrate supplementation may have therapeutic effects in a model of renal and cardiovascular disease.

METHODS AND RESULTS

Sprague-Dawley rats subjected to unilateral nephrectomy and chronic high-salt diet from 3 weeks of age developed hypertension, cardiac hypertrophy and fibrosis, proteinuria, and histological as well as biochemical signs of renal damage and oxidative stress. Simultaneous nitrate treatment (0.1 or 1 mmol nitrate kg⁻¹ day⁻¹), with the lower dose resembling the nitrate content of a diet rich in vegetables, attenuated hypertension dose-dependently with no signs of tolerance. Nitrate treatment almost completely prevented proteinuria and histological signs of renal injury, and the cardiac hypertrophy and fibrosis were attenuated. Mechanistically, dietary nitrate restored the tissue levels of bioactive nitrogen oxides and reduced the levels of oxidative stress markers in plasma (malondialdehyde) and urine (Class VI F2-isoprostanes and 8-hydroxy-2-deoxyguanosine). In addition, the increased circulating and urinary levels of dimethylarginines (ADMA and SDMA) in the hypertensive rats were normalized by nitrate supplementation.

CONCLUSION

Dietary inorganic nitrate is strongly protective in this model of renal and cardiovascular disease. Future studies will reveal if nitrate contributes to the well-known cardioprotective effects of a diet rich in vegetables.

Inorganic nitrate and nitrite and control of blood pressure

Continual nitric oxide (NO) synthesis is important in the regulation of vascular tone and thus blood pressure. Whereas classically NO is provided by the enzymatic oxidation of l-arginine via endothelial NO synthase, it is now clear that NO can also be generated in mammals from the reduction of nitrite and nitrate. Thus inorganic nitrate derived either from NO oxidation or from dietary sources may be an important storage form of reactive nitrogen oxides which can be reduced back to nitrite and NO when physiologically required or in pathological conditions. The very short half-life of NO and the ready availability of stored nitrite and nitrate make for a very sensitive and responsive blood pressure control system. This review will examine processes by which these storage forms are produced and how augmentation of dietary nitrate intake may have a beneficial effect on blood pressure and other vascular function in humans.

Dietary inorganic nitrate reverses features of metabolic syndrome in endothelial nitric oxide synthase-deficient mice

The metabolic syndrome is a clustering of risk factors of metabolic origin that increase the risk for cardiovascular disease and type 2 diabetes. A proposed central event in metabolic syndrome is a decrease in the amount of bioavailable nitric oxide (NO) from endothelial NO synthase (eNOS). Recently, an alternative pathway for NO formation in mammals was described where inorganic nitrate, a supposedly inert NO oxidation product and unwanted dietary constituent, is serially reduced to nitrite and then NO and other bioactive nitrogen oxides. Here we show that several features of metabolic syndrome that develop in eNOS-deficient mice can be reversed by dietary supplementation with sodium nitrate, in amounts similar to those derived from eNOS under normal conditions. In humans, this dose corresponds to a rich intake of vegetables, the dominant dietary nitrate source. Nitrate administration increased tissue and plasma levels of bioactive nitrogen oxides. Moreover, chronic nitrate treatment reduced visceral fat accumulation and circulating levels of triglycerides and reversed the prediabetic phenotype in these animals. In rats, chronic nitrate treatment reduced blood pressure and this effect was also present during NOS inhibition. Our results show that dietary nitrate fuels a nitrate-nitrite-NO pathway that can partly compensate for disturbances in endogenous NO generation from eNOS. These findings may have implications for novel nutrition-based preventive and therapeutic strategies against cardiovascular disease and type 2 diabetes.

Involvement of salivary glands in regulating the human nitrate and nitrite levels

OBJECTIVE

To study the dynamic fluctuations of nitrate and nitrite content in humans following damage to major salivary glands.

METHODS

Fifteen nasopharyngeal carcinoma patients, scheduled to undergo IMRT, were recruited. The prescription dose to GTV, CTV1 and CTV2, was 68, 60 and 54 Gy, respectively, in 30 fractions, 1 fraction/day. Saliva, serum and urine samples were collected at baseline, RT10, RT20 and at endpoint of radiation. Ions concentration was determined using ion chromatography.

RESULTS

Salivary flow rates and nitrate content decreased over time (p<0.0001), whereas serum and urinary nitrite rose. Salivary nitrite increased transiently and then plateaued. Cumulative irradiation dose to salivary glands correlated with nitrate content in serum (p<0.0001), but not in saliva and urine (p=0.876 and p=0.175). The salivary flow rates correlated to the nitrate content in serum (p<0.0001), but not in saliva and urine (p=0.230 and p=0.428).

CONCLUSIONS

Nitrate and nitrite contents in saliva, serum or urine changed in response to salivary gland damage. Salivary glands are associated with the metabolism of both ions in humans. The decreased serum nitrate appears to provide adjuvant information about salivary dysfunction.

Gut Microbiota in Health and Disease

Gut microbiota is an assortment of microorganisms inhabiting the length and width of the mammalian gastrointestinal tract. The composition of this microbial community is host specific, evolving throughout an individual's lifetime and susceptible to both exogenous and endogenous modifications. Recent renewed interest in the structure and function of this “organ” has illuminated its central position in health and disease. The microbiota is intimately involved in numerous aspects of normal host physiology, from nutritional status to behavior and stress response. Additionally, they can be a central or a contributing cause of many diseases, affecting both near and far organ systems. The overall balance in the composition of the gut microbial community, as well as the presence or absence of key species capable of effecting specific responses, is important in ensuring homeostasis or lack thereof at the intestinal mucosa and beyond. The mechanisms through which microbiota exerts its beneficial or detrimental influences remain largely undefined, but include elaboration of signaling molecules and recognition of bacterial epitopes by both intestinal epithelial and mucosal immune cells. The advances in modeling and analysis of gut microbiota will further our knowledge of their role in health and disease, allowing customization of existing and future therapeutic and prophylactic modalities.

NO-synthase independent NO generation in mammals

Inorganic nitrate (NO3(-)) and nitrite (NO2(-)) 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.

Enhanced xanthine oxidoreductase expression and tissue nitrate reduction in germ free mice

The nitrate-nitrite-NO pathway is emerging as an alternative to the l-arginine/NO-synthase pathway for the generation of NO in mammals. Bioactivation of the stable nitrate anion involves initial reduction to nitrite by commensal bacteria in the gastrointestinal tract. Nitrite is then further metabolized in blood and tissues to form nitric oxide (NO) and other bioactive nitrogen oxides. In addition to nitrate reduction by bacteria, a functional mammalian nitrate reductase activity was recently explored. It was demonstrated that xanthine oxidoreductase (XOR) and possibly other enzymes can catalyze nitrate reduction under normoxic conditions in vivo. In the present study, we compared nitrate reduction in germ free (GF) and conventional mice. One aim was to see if the complete lack of bacterial nitrate reduction in the GF mice would be associated with an upregulation of mammalian nitrate reductase activity. Sodium nitrate (NaNO(3)) or placebo (NaCl) was injected intraperitoneally and blood and tissues were collected 1.5-2h later for measurements of nitrate and nitrite and in some cases analyses of protein expression. Tissue and plasma levels of nitrate increased to a similar extent in conventional and GF animals after nitrate administration. Plasma nitrite was 3-fold higher in GF mice receiving nitrate compared to placebo while this effect of nitrate was absent in the conventional mice. In GF mice pretreated with the xanthine oxidase inhibitor allopurinol the increase in nitrite was attenuated. The levels of nitrite in the liver and small intestine increased after the nitrate load in GF mice but not in the conventional mice. Anaerobic nitrate reduction to nitrite in intestinal tissue homogenates was also accelerated in GF mice. Studies of tissue protein levels revealed increased expression of XOR in the livers of GF animals. We conclude that XOR expression in tissues is enhanced in germ free mice and this may explain the apparently greater tissue nitrate reductase activity observed in these animals. Future studies will reveal if this represents a compensatory functional response to uphold nitrite homeostasis in the absence of commensal bacteria.

Mitochondria as metabolizers and targets of nitrite

Mitochondrial function is integral to maintaining cellular homeostasis through the production of ATP, the generation of reactive oxygen species (ROS) for signaling, and the regulation of the apoptotic cascade. A number of small molecules, including nitric oxide (NO), are well-characterized regulators of mitochondrial function. Nitrite, an NO metabolite, has recently been described as an endocrine reserve of NO that is reduced to bioavailable NO during hypoxia to mediate physiological responses. Accumulating data suggests that mitochondria may play a role in metabolizing nitrite and that nitrite is a regulator of mitochondrial function. Here, what is known about the interactions of nitrite with the mitochondria is reviewed, with a focus on the role of the mitochondrion as a metabolizer and target of nitrite.

Nitrate and nitrite in biology, nutrition and therapeutics

Inorganic nitrate and nitrite from endogenous or dietary sources are metabolized in vivo to nitric oxide (NO) and other bioactive nitrogen oxides. The nitrate-nitrite-NO pathway is emerging as an important mediator of blood flow regulation, cell signaling, energetics and tissue responses to hypoxia. The latest advances in our understanding of the biochemistry, physiology and therapeutics of nitrate, nitrite and NO were discussed during a recent 2-day meeting at the Nobel Forum, Karolinska Institutet in Stockholm.

Dietary nitrate--good or bad?

There has now been a great deal written about inorganic nitrate in both the popular press and in scientific journals. Papers in the 1970s warned us that inorganic nitrate could theoretically be metabolised in the human body to N-nitroso compounds, many of which are undoubtedly carcinogenic. More recently there is evidence that nitrate can undergo metabolic conversion to nitrite and nitric oxide and perform a useful protective function to prevent infection, protect our stomach, improve exercise performance and prevent vascular disease.