Integrating molecular and cellular components of endothelial shear stress mechanotransduction

The lining of blood vessels is constantly exposed to mechanical forces exerted by blood flow against the endothelium. Endothelial cells detect these tangential forces (i.e., shear stress), initiating a host of intracellular signaling cascades that regulate vascular physiology. Thus, vascular health is tethered to the endothelial cells' capacity to transduce shear stress. Indeed, the mechanotransduction of shear stress underlies a variety of cardiovascular benefits, including some of those associated with increased physical activity. However, endothelial mechanotransduction is impaired in aging and disease states such as obesity and type 2 diabetes, precipitating the development of vascular disease. Understanding endothelial mechanotransduction of shear stress, and the molecular and cellular mechanisms by which this process becomes defective, is critical for the identification and development of novel therapeutic targets against cardiovascular disease. In this review, we detail the primary mechanosensitive structures that have been implicated in detecting shear stress, including junctional proteins such as platelet endothelial cell adhesion molecule-1 (PECAM-1), the extracellular glycocalyx and its components, and ion channels such as piezo1. We delineate which molecules are truly mechanosensitive and which may simply be indispensable for the downstream transmission of force. Furthermore, we discuss how these mechanosensors interact with other cellular structures, such as the cytoskeleton and membrane lipid rafts, which are implicated in translating shear forces to biochemical signals. Based on findings to date, we also seek to integrate these cellular and molecular mechanisms with a view of deciphering endothelial mechanotransduction of shear stress, a tenet of vascular physiology.

Inorganic nitrate supplementation and blood flow restricted exercise tolerance in post-menopausal women

Exercise tolerance appears to benefit most from dietary nitrate (NO3-) supplementation when muscle oxygen (O2) availability is low. Using a double-blind, randomized cross-over design, we tested the hypothesis that acute NO3- supplementation would improve blood flow restricted exercise duration in post-menopausal women, a population with reduced endogenous nitric oxide bioavailability. Thirteen women (57-76 yr) performed rhythmic isometric handgrip contractions (10% MVC, 30 per min) during progressive forearm blood flow restriction (upper arm cuff gradually inflated 20 mmHg each min) on three study visits, with 7-10 days between visits. Approximately one week following the first (familiarization) visit, participants consumed 140 ml of NO3- concentrated (9.7 mmol, 0.6 gm NO3-) or NO3-depleted beetroot juice (placebo) on separate days (≥7 days apart), with handgrip exercise beginning 100 min post-consumption. Handgrip force recordings were analyzed to determine if NO3- supplementation enhanced force development as blood flow restriction progressed. Nitrate supplementation increased plasma NO3- (16.2-fold) and NO2- (4.2-fold) and time to volitional fatigue (61.8 ± 56.5 s longer duration vs. placebo visit; p = 0.03). Nitrate supplementation increased the rate of force development as forearm muscle ischemia progressed (p = 0.023 between 50 and 75% of time to fatigue) with non-significant effects thereafter (p = 0.052). No effects of nitrate supplementation were observed for mean duration of contraction or relaxation rates (all p > 0.150). These results suggest that acute NO3- supplementation prolongs time-to-fatigue and speeds grip force development during progressive forearm muscle ischemia in postmenopausal women.

Effects of Chewing Gum on Nitric Oxide Metabolism, Markers of Cardiovascular Health and Neurocognitive Performance after a Nitrate-Rich Meal

OBJECTIVES

Cardiovascular and neurocognitive responses to chewing gum have been reported, but the mechanisms are not well understood. Chewing gum after a nitrate-rich meal may upregulate the reduction of oral nitrate to nitrite and increase nitric oxide (NO), a molecule important to cardiovascular and neurocognitive health. We aimed to explore effects of chewing gum after a nitrate-rich meal on nitrate metabolism (through the enterosalivary nitrate-nitrite-NO pathway), endothelial function, blood pressure (BP), neurocognitive performance, mood and anxiety.

METHODS

Twenty healthy men (n = 6) and women (n = 14) with a mean age of 48 years (range: 23-69) were recruited to a randomized controlled cross-over trial. After consumption of a nitrate-rich meal (180 mg of nitrate), we assessed the acute effects of chewing gum, compared to no gum chewing, on (i) salivary nitrate, nitrite and the nitrate reductase ratio (100 x [nitrite]/([nitrate] + [nitrite]); (ii) plasma nitrite, S-nitrosothiols and other nitroso species (RXNO); (iii) endothelial function (measured by flow mediated dilatation); (iv) BP; (v) neurocognitive performance; (vi) mood; and (vii) anxiety.

RESULTS

Consumption of the nitrate-rich meal resulted in a significant increase in markers of nitrate metabolism. A significantly higher peak flow mediated dilatation was observed with chewing compared to no chewing (baseline adjusted mean difference: 1.10%, 95% CI: 0.06, 2.14; p = 0.038) after the nitrate-rich meal. A significant small increase in systolic BP, diastolic BP and heart rate were observed with chewing compared to no chewing after the nitrate-rich meal. The study did not observe increased oral reduction of nitrate to nitrite and NO, or improvements in neurocognitive performance, mood or anxiety with chewing compared to no chewing.

CONCLUSION

Chewing gum after a nitrate-rich meal resulted in an acute improvement in endothelial function and a small increase in BP but did not result in acute effects on neurocognitive function, mood or anxiety.

The role of dietary nitrate and the oral microbiome on blood pressure and vascular tone

There is increasing evidence for the health benefits of dietary nitrates including lowering blood pressure and enhancing cardiovascular health. Although commensal oral bacteria play an important role in converting dietary nitrate to nitrite, very little is known about the potential role of these bacteria in blood pressure regulation and maintenance of vascular tone. The main purpose of this review is to present the current evidence on the involvement of the oral microbiome in mediating the beneficial effects of dietary nitrate on vascular function and to identify sources of inter-individual differences in bacterial composition. A systematic approach was used to identify the relevant articles published on PubMed and Web of Science in English from January 1950 until September 2019 examining the effects of dietary nitrate on oral microbiome composition and association with blood pressure and vascular tone. To date, only a limited number of studies have been conducted, with nine in human subjects and three in animals focusing mainly on blood pressure. In general, elimination of oral bacteria with use of a chlorhexidine-based antiseptic mouthwash reduced the conversion of nitrate to nitrite and was accompanied in some studies by an increase in blood pressure in normotensive subjects. In conclusion, our findings suggest that oral bacteria may play an important role in mediating the beneficial effects of nitrate-rich foods on blood pressure. Further human intervention studies assessing the potential effects of dietary nitrate on oral bacteria composition and relationship to real-time measures of vascular function are needed, particularly in individuals with hypertension and those at risk of developing CVD.

Assessment of nitric oxide metabolites concentrations in plasma, saliva, and breast milk and their relationship in lactating women

Nitric oxide (NO) plays a role in many biological mechanisms. The amounts of physiologically produced NO are associated with the concentrations of its metabolites nitrate and nitrite. This study investigated whether there is any association between the concentrations of NO metabolites nitrate, nitrite, and nitrosylated species (RXNO) in mature breast milk, saliva, and plasma in healthy lactating women (N = 30). We hypothesized that the NO metabolites concentrations in plasma are associated with those found in saliva and in breast milk. NO metabolites concentrations were measured using chemiluminensce-based assays. Nitrate concentrations in breast milk are twice as much as plasma concentrations, whereas nitrate concentrations in saliva are about eightfold higher (both P < 0.001). Similar differences were found when nitrite concentrations were taken into consideration. RXNO concentrations in breast milk were negligible, and RXNO concentrations in saliva were approximately sixfold higher than those found in plasma samples (P < 0.0001). Nitrate concentrations in plasma are associated with nitrate concentrations in saliva (rs = 0.474, P = 0.004). However, no significant association was found between nitrate concentrations in breast milk and in plasma (P > 0.05). Our results show a significant association between nitrate concentrations in plasma with those found in saliva, whereas all other relationships were not significant. In conclusion, this report shows for the first time that the physiological concentrations of NO metabolites in human breast milk are probably independent of circulating NO metabolites concentrations and may depend mostly on endogenous NO synthesis in the breast. These findings may have clinical implications for newborns and lactating women.

Higher urinary nitrate was associated with lower prevalence of congestive heart failure: results from NHANES

Background

Some studies have reported that nitrate intake from vegetables was inversely associated with many vascular diseases, but few studies have paid attention to the relationship between urinary nitrate and cardiovascular diseases (CVDs). This cross-sectional study aimed to explore the connections between urinary nitrate and prevalence of CVDs.

Methods

The data of this study was collected from National Health and Nutrition Examination Survey (NHANES). Finally, several years’ data of NHANES were merged into 14,894 observations. Logistic regression models were used to examine the associations between urinary nitrate and CVDs by using the “survey” package in R software (version 3.2.3).

Results

In the univariable logistic analysis, significant association was discovered between urinary nitrate and congestive heart failure, coronary heart disease, angina pectoris, myocardial infarction (all P < 0.001). By adjusting related covariates, the multivariable logistic analysis showed that the significant association only existed between urinary nitrate and congestive heart failure (OR = 0.651, 95% CI 0.507–0.838, P < 0.001). Compared to Q1 urinary nitrate level as reference, the risk for prevalent heart failure diminished along with increasing levels of urinary nitrates, (OR of Q2 level = 0.633, 95% CI 0.403–0.994), (OR of Q3 level = 0.425, 95% CI 0.230–0.783), (OR of Q4 level = 0.375, 95% CI 0.210–0.661), respectively. Moreover, urinary nitrate levels were associated with congestive heart failure in a dose-dependent manner in both 20–60 years group, 60+ years group and male, female group (P < 0.001, P = 0.011 and P = 0.009, P = 0.004).

Conclusions

Independent of related covariates, higher urinary nitrate was associated with lower prevalent congestive heart failure.

Modification of diet, exercise and lifestyle (MODEL) study: a randomised controlled trial protocol

INTRODUCTION

Most cardiovascular disease (CVD)-related events could be prevented or substantially delayed with improved diet and lifestyle. Providing information on structural vascular disease may improve CVD risk factor management, but its impact on lifestyle change remains unclear. This study aims to determine whether providing visualisation and pictorial representation of structural vascular disease (abdominal aortic calcification (AAC)) can result in healthful diet and lifestyle change.

METHODS AND ANALYSIS

This study, including men and women aged 60-80 years, is a 12-week, two-arm, multisite randomised controlled trial. At baseline, all participants will have AAC assessed from a lateral spine image captured using a bone densitometer. Participants will then be randomised to receive their AAC results at baseline (intervention group) or a usual care control group that will receive their results at 12 weeks. All participants will receive information about routinely assessed CVD risk factors and standardised (video) diet and lifestyle advice with three simple goals: (1) increase fruit and vegetable (FV) intake by at least one serve per day, (2) improve other aspects of the diet and (3) reduce sitting time and increase physical activity. Clinical assessments will be performed at baseline and 12 weeks.

OUTCOMES

The primary outcome is a change in serum carotenoid concentrations as an objective measure of FV intake. The study design, procedures and treatment of data will adhere to Standard Protocol Items for Randomized Trials guidelines.

ETHICS AND DISSEMINATION

Ethics approval for this study has been granted by the Edith Cowan University and the Deakin University Human Research Ethics Committees (Project Numbers: 20513 HODGSON and 2019-220, respectively). Results of this study will be published in peer-reviewed academic journals and presented in scientific meetings and conferences. Information regarding consent, confidentiality, access to data, ancillary and post-trial care and dissemination policy has been disclosed in the participant information form.

TRIAL REGISTRATION NUMBER

Australian New Zealand Clinical Trial Registry (ACTRN12618001087246).

A randomised controlled crossover trial investigating the short-term effects of different types of vegetables on vascular and metabolic function in middle-aged and older adults with mildly elevated blood pressure: the VEgetableS for vaScular hEaLth (VESSEL) study protocol

Background

A diet rich in fruits and vegetables is recommended for cardiovascular health. However, the majority of Australians do not consume the recommended number of vegetable servings each day. Furthermore, intakes of vegetables considered to have the greatest cardiovascular benefit are often very low. Results from prospective observational studies indicate that a higher consumption of cruciferous vegetables (e.g. broccoli, cabbage, cauliflower) is associated with lower cardiovascular disease risk. This may be due to the presence of specific nutrients and bioactive compounds found almost exclusively, or at relatively high levels, in cruciferous vegetables. Therefore, the aim of this randomised controlled crossover trial is to determine whether regular consumption of cruciferous vegetables results in short-term improvement in measures related to cardiovascular disease risk, including ambulatory blood pressure, arterial stiffness, glycaemic control, and circulating biomarkers of oxidative stress and inflammation.

Methods

Twenty-five participants (50–75 years) with mildly elevated blood pressure (systolic blood pressure 120–160 mmHg) will complete two 2-week intervention periods in random order, separated by a 2-week washout period. During the intervention period, participants will consume 4 servings (~ 300 g) of cruciferous vegetables per day as a soup (~ 500–600 mL/day). The ‘control’ soup will consist of other commonly consumed vegetables (potato, sweet potato, carrot, pumpkin). Both soups will be approximately matched for energy, protein, fat, and carbohydrate content. All measurements will be performed at the beginning and end of each intervention period.

Discussion

The findings of this study will provide evidence regarding the potential cardiometabolic health benefits of cruciferous vegetables, which may contribute to the revision of dietary and clinical guidelines.

Trial registration

The trial was registered with the Australian New Zealand Clinical Trial Registry on 19th September 2019 (ACTRN12619001294145).

Nitrate, the oral microbiome, and cardiovascular health: a systematic literature review of human and animal studies

Background

Dietary nitrate is an important source of nitric oxide (NO), a molecule critical for cardiovascular health. Nitrate is sequentially reduced to NO through an enterosalivary nitrate-nitrite-NO pathway that involves the oral microbiome. This pathway is considered an important adjunct pathway to the classical l-arginine-NO synthase pathway.

Objective

The objective of this study was to systematically assess the evidence for dietary nitrate intake and improved cardiovascular health from both human and animal studies.

Design

A systematic literature search was performed according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines by using key search terms in Medline and EMBASE databases and defined inclusion and exclusion criteria.

Results

Thirty-seven articles on humans and 14 articles on animals were included from 12,541 screened references. Data on the effects of dietary nitrate on blood pressure, endothelial function, ischemic reperfusion injury, arterial stiffness, platelet function, and cerebral blood flow in both human and animal models were identified. Beneficial effects of nitrate on vascular health have predominantly been observed in healthy human populations, whereas effects in populations at risk of cardiovascular disease are less clear. Few studies have investigated the long-term effects of dietary nitrate on cardiovascular disease clinical endpoints. In animal studies, there is evidence that nitrate improves blood pressure and endothelial function, particularly in animal models with reduced NO bioavailability. Nitrate dose seems to be a critical factor because there is evidence of cross-talk between the 2 pathways of NO production.

Conclusions

Evidence for a beneficial effect in humans at risk of cardiovascular disease is limited. Furthermore, there is a need to investigate the long-term effects of dietary nitrate on cardiovascular disease clinical endpoints. Further animal studies are required to elucidate the mechanisms behind the observed effects.

Association of Vegetable Nitrate Intake With Carotid Atherosclerosis and Ischemic Cerebrovascular Disease in Older Women

BACKGROUND AND PURPOSE

A short-term increase in dietary nitrate (NO₃^-) improves markers of vascular health via formation of nitric oxide and other bioactive nitrogen oxides. Whether this translates into long-term vascular disease risk reduction has yet to be examined. We investigated the association of vegetable-derived nitrate intake with common carotid artery intima-media thickness (CCA-IMT), plaque severity, and ischemic cerebrovascular disease events in elderly women (n=1226).

METHODS

Vegetable nitrate intake, lifestyle factors, and cardiovascular disease risk factors were determined at baseline (1998). CCA-IMT and plaque severity were measured using B-mode carotid ultrasound (2001). Complete ischemic cerebrovascular disease hospitalizations or deaths (events) over 14.5 years (15 032 person-years of follow-up) were obtained from the West Australian Data Linkage System.

RESULTS

Higher vegetable nitrate intake was associated with a lower maximum CCA-IMT (B=-0.015, P=0.002) and lower mean CCA-IMT (B=-0.012, P=0.006). This relationship remained significant after adjustment for lifestyle and cardiovascular risk factors (P≤0.01). Vegetable nitrate intake was not a predictor of plaque severity. In total 186 (15%) women experienced an ischemic cerebrovascular disease event. For every 1 SD (29 mg/d) higher intake of vegetable nitrate, there was an associated 17% lower risk of 14.5-year ischemic cerebrovascular disease events in both unadjusted and fully adjusted models (P=0.02).

CONCLUSIONS

Independent of other risk factors, higher vegetable nitrate was associated with a lower CCA-IMT and a lower risk of an ischemic cerebrovascular disease event.

Enterosalivary nitrate metabolism and the microbiome: Intersection of microbial metabolism, nitric oxide and diet in cardiac and pulmonary vascular health

Recent insights into the bioactivation and signaling actions of inorganic, dietary nitrate and nitrite now suggest a critical role for the microbiome in the development of cardiac and pulmonary vascular diseases. Once thought to be the inert, end-products of endothelial-derived nitric oxide (NO) heme-oxidation, nitrate and nitrite are now considered major sources of exogenous NO that exhibit enhanced vasoactive signaling activity under conditions of hypoxia and stress. The bioavailability of nitrate and nitrite depend on the enzymatic reduction of nitrate to nitrite by a unique set of bacterial nitrate reductase enzymes possessed by specific bacterial populations in the mammalian mouth and gut. The pathogenesis of pulmonary hypertension (PH), obesity, hypertension and CVD are linked to defects in NO signaling, suggesting a role for commensal oral bacteria to shape the development of PH through the formation of nitrite, NO and other bioactive nitrogen oxides. Oral supplementation with inorganic nitrate or nitrate-containing foods exert pleiotropic, beneficial vascular effects in the setting of inflammation, endothelial dysfunction, ischemia-reperfusion injury and in pre-clinical models of PH, while traditional high-nitrate dietary patterns are associated with beneficial outcomes in hypertension, obesity and CVD. These observations highlight the potential of the microbiome in the development of novel nitrate- and nitrite-based therapeutics for PH, CVD and their risk factors.

Dietary Nitrate, Nitric Oxide, and Cardiovascular Health

Emerging evidence strongly suggests that dietary nitrate, derived in the diet primarily from vegetables, could contribute to cardiovascular health via effects on nitric oxide (NO) status. NO plays an essential role in cardiovascular health. It is produced via the classical L-arginine-NO-synthase pathway and the recently discovered enterosalivary nitrate-nitrite-NO pathway. The discovery of this alternate pathway has highlighted dietary nitrate as a candidate for the cardioprotective effect of a diet rich in fruit and vegetables. Clinical trials with dietary nitrate have observed improvements in blood pressure, endothelial function, ischemia-reperfusion injury, arterial stiffness, platelet function, and exercise performance with a concomitant augmentation of markers of NO status. While these results are indicative of cardiovascular benefits with dietary nitrate intake, there is still a lingering concern about nitrate in relation to methemoglobinemia, cancer, and cardiovascular disease. It is the purpose of this review to present an overview of NO and its critical role in cardiovascular health; to detail the observed vascular benefits of dietary nitrate intake through effects on NO status as well as to discuss the controversy surrounding the possible toxic effects of nitrate.

Nitrate-rich beetroot juice selectively lowers ambulatory pressures and LDL cholesterol in uncontrolled but not controlled hypertension: a pilot study

BACKGROUND

Dietary nitrate has been shown to increase nitrate/nitrite levels in multiple populations, with potential blood pressure lowering effects. However, there are few reports among hypertensives.

AIMS

We aimed to assess the effect of daily nitrate in subjects with controlled hypertension vs. uncontrolled hypertension.

METHODS

On day 0, hypertensives wore an ambulatory BP monitor (ABPM) for 24 h and fasting blood was taken. Subjects then consumed concentrated beetroot juice (12.9 mmol nitrate) for 14 consecutive days. On day 14 subjects consumed their last nitrate dose after fasting blood was drawn and again had an ABPM for 24 h.

RESULTS

According to baseline ABPM, 11 subjects had controlled BP while 8 had uncontrolled BP. There were similar, significant increases in serum nitrate/nitrite in both groups. We observed little change in BP variables among controlled hypertensives. However, there were reductions in BP variables in uncontrolled hypertensives where decreases in nighttime DBP (-6 ± 4.8 mmHg), arterial stiffness (-0.08 ± 0.03 ambulatory arterial stiffness index) and LDL (-0.36 ± 0.42 mmol/L) reached significance (p = 003, 0.05 and 0.046, respectively).

CONCLUSIONS

Our results support the existing data suggesting an anti-hypertensive effect of nitrate-containing beetroot juice, but only among those with uncontrolled hypertension.

Low dose dietary nitrate improves endothelial dysfunction and plaque stability in the ApoE-/- mouse fed a high fat diet

BACKGROUND

Nitric oxide (NO) is an important vascular signalling molecule. NO is synthesised endogenously by endothelial nitric oxide synthase (eNOS). An alternate pathway is exogenous dietary nitrate, which can be converted to nitrite and then stored or further converted to NO and used immediately. Atherosclerosis is associated with endothelial dysfunction and subsequent lesion formation. This is thought to arise due to a reduction in the bioavailability and/or bioactivity of endogenous NO.

AIM

To determine if dietary nitrate can protect against endothelial dysfunction and lesion formation in the ApoE^-/- mouse fed a high fat diet (HFD).

METHODS AND RESULTS

ApoE^-/- fed a HFD were randomized to receive (i) high nitrate (10mmol/kg/day, n=12), (ii) moderate nitrate (1mmol/kg/day, n=8), (iii) low nitrate (0.1mmol/kg/day, n=8), or (iv) sodium chloride supplemented drinking water (control, n=10) for 10 weeks. A group of C57BL6 mice (n=6) received regular water and served as a healthy reference group. At 10 weeks, ACh-induced vessel relaxation was significantly impaired in ApoE^-/- mice versus C57BL6. Mice supplemented with low or moderate nitrate showed significant improvements in ACh-induced vessel relaxation compared to ApoE^-/- mice given the high nitrate or sodium chloride. Plaque collagen expression was increased and lipid deposition reduced following supplementation with low or moderate nitrate compared to sodium chloride, reflecting increased plaque stability with nitrate supplementation. Plasma nitrate and nitrite levels were significantly increased in all three groups fed the nitrate-supplemented water.

CONCLUSION

Low and moderate dose nitrate significantly improved endothelial function and atherosclerotic plaque composition in ApoE^-/- mice fed a HFD.

Beneficial Effects of Dietary Nitrate on Endothelial Function and Blood Pressure Levels

Poor eating habits may represent cardiovascular risk factors since high intake of fat and saturated fatty acids contributes to dyslipidemia, obesity, diabetes mellitus, and hypertension. Thus, nutritional interventions are recognized as important strategies for primary prevention of hypertension and as adjuvants to pharmacological therapies to reduce cardiovascular risk. The DASH (Dietary Approach to Stop Hypertension) plan is one of the most effective strategies for the prevention and nonpharmacological management of hypertension. The beneficial effects of DASH diet on blood pressure might be related to the high inorganic nitrate content of some food products included in this meal plan. The beetroot and other food plants considered as nitrate sources account for approximately 60-80% of the daily nitrate exposure in the western population. The increased levels of nitrite by nitrate intake seem to have beneficial effects in many of the physiological and clinical settings. Several clinical trials are being conducted to determine the broad therapeutic potential of increasing the bioavailability of nitrite in human health and disease, including studies related to vascular aging. In conclusion, the dietary inorganic nitrate seems to represent a promising complementary therapy to support hypertension treatment with benefits for cardiovascular health.

Antibacterial mouthwash blunts oral nitrate reduction and increases blood pressure in treated hypertensive men and women

BACKGROUND

Endothelial nitric oxide (NO) is fundamental to cardiovascular health. Dietary nitrate and nitrate from endothelial derived NO metabolism provides a significant contribution to the circulating NO pool through the nitrate-nitrite-NO pathway. A critical step in this pathway is the reduction of nitrate to nitrite by the oral microbiota. We aimed to assess the effects of antibacterial mouthwash use on markers of nitrate-nitrite-NO metabolism and blood pressure in treated hypertensive men and women.

METHODS

Fifteen treated hypertensive men and women (mean age 65 years) were recruited to a randomized controlled cross-over trial. The effects of 3-day use of antibacterial mouthwash on oral nitrate to nitrite reduction, salivary and plasma nitrate and nitrite, plasma cyclic guanosine monophosphate (cGMP) and systolic and diastolic blood pressure were compared to control (water).

RESULTS

Relative to control, 3-day antibacterial mouthwash use resulted in decreased oral nitrate to nitrite reduction (P = 0.02), decreased salivary nitrite (P = 0.01) and increased salivary nitrate (P < 0.001), and there was a trend toward a decrease in plasma nitrite concentration (P = 0.09). Use of antibacterial mouthwash over 3 days also resulted in higher systolic blood pressure (2.3mm Hg; 95% CI: 0.5, 4.0; P = 0.01), but not diastolic blood pressure (P = 0.4) or plasma cGMP (P = 0.7), relative to control.

CONCLUSIONS

Interruption of the nitrate-nitrite-NO pathway through the use of antibacterial mouthwash was paralleled by a small elevation of systolic blood pressure in treated hypertensive men and women.

The oral microbiome and nitric oxide homoeostasis

The tiny radical nitric oxide (NO) participates in a vast number of physiological functions including vasodilation, nerve transmission, host defence and cellular energetics. Classically produced by a family of specific enzymes, NO synthases (NOSs), NO signals via reactions with other radicals or transition metals. An alternative pathway for the generation of NO is the nitrate-nitrite-NO pathway in which the inorganic anions nitrate (NO(3)(-)) and nitrite (NO(2)(-)) are reduced to NO and other reactive nitrogen intermediates. Nitrate and nitrite are oxidation products from NOS-dependent NO generation but also constituents in our diet, mainly in leafy green vegetables. Irrespective of origin, active uptake of circulating nitrate in the salivary glands, excretion in saliva and subsequent reduction to nitrite by oral commensal bacteria are all necessary steps for further NO generation. This central role of the oral cavity in regulating NO generation from nitrate presents a new and intriguing aspect of the human microbiome in health and disease. In this review, we present recent advances in our understanding of the nitrate-nitrite-NO pathway and specifically highlight the importance of the oral cavity as a hub for its function.