Nitric oxide (NO) is a gaseous, diatomic free-radical that is essential for a variety of physiological functions, including tissue perfusion, mitochondrial function, and glucose regulation. Patients with cardiovascular disease (CVD) are often marked by decreased NO bioavailability due to disruptions in the endothelium through a variety of CVD risk factors including hypertension, diabetes, and inflammation. Recently, an alternative exogenous route to increase NO bioavailability in patients with CVD has been explored via oral supplementation of inorganic nitrate (NO3-) and the subsequent elevation of plasma nitrite (NO2-). This approach has been applied across a range of human healthy and clinical conditions. Several comprehensive reviews on the role of nitrate in cardiovascular health have been published, and there have been more than 60 randomized controlled trials (RCTs) investigating the effects of dietary nitrate from plant sources on markers of cardiovascular health (blood pressure, endothelial function, arterial stiffness, platelet reactivity and platelet aggregation).
There is a consensus on the principal pathways and primary mechanisms involved in the conversion of oral NO3- to circulating NO2- and NO, however, there remains significant variation in the levels of NO metabolites attained in the plasma that is dependent upon the type of oral inorganic nitrate supplementation. Reduction of inorganic nitrate to bioavailable NO is a two-cycle process:
1. Inorganic nitrate is swallowed and absorbed into the circulation, where a proportion is then sequestered and concentrated in the salivary glands and slowly released into the oral cavity. At this stage commensal bacteria reduce nitrate to nitrite in the oral cavity;
2. Nitrite is swallowed and absorbed into the circulation. This circulating nitrite is readily reduced to nitric oxide by a variety of pathways involving single-electron transfer reactions with protons (H+) and hemeproteins (i.e., hemoglobin, myoglobin) during deoxygenation.
Given the dearth of other ways in human physiology to reduce nitrate to nitrite this process is highly reliant on the bacterial species within the oral microbiome. The investigators of this study (and others) have also shown that disruption of the oral microbiome via commercially available anti-bacterial mouthwash abolished increases in plasma nitrite following oral inorganic nitrate supplementation (in the form of beetroot juice) and blunted reductions in blood pressure, compared to placebo control conditions. Additionally, the investigators of this study have also shown that circulating levels of nitrite in healthy volunteers were higher compared with patients with diabetes and/or peripheral artery disease.
The potential for reduced endogenous NO and associated circulating plasma NO2- in populations at risk for cardiovascular disease (older, hypertensive, obese) make the exogenous pathway of oral supplementation and bacterial reduction of NO3- to NO2- (and subsequently NO), a potentially novel therapeutic approach to increase vascular health.
The purpose of the current proposal is to examine the single dose pharmacokinetics (the relationship between supplement plasma concentration and the time elapsed since the supplement's administration) of "Berkeley Life Pro Capsules" (Chicago, IL). Specifically, plasma and salivary nitrate and nitrite concentrations will be collected and measured at baseline (0) and 2, 4, 8 and 24 hours following two different doses of "Berkeley Life Pro Capsules" 314mg inorganic nitrate (2 capsules) (n=12) and 167mg inorganic nitrate (1 capsule) (n=6).
