S-nitrosothiols, and other products of nitrate metabolism, are increased in multiple human blood compartments following ingestion of beetroot juice

Mohammed Abu-Alghayth,Anni Vanhatalo,Lee J Wylie,Sinead Tj Mcdonagh,Christopher Thompson,Stefan Kadach,Paul Kerr,Miranda J Smallwood,Andrew M Jones,Paul G Winyard

doi:10.1016/j.redox.2021.101974

Mohammed Abu-Alghayth, Anni Vanhatalo + Show 8 more

Open Access

https://doi.org/10.1016/j.redox.2021.101974

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Abstract

Ingested inorganic nitrate (NO3⁻) has multiple effects in the human body including vasodilation, inhibition of platelet aggregation, and improved skeletal muscle function. The functional effects of oral NO3⁻ involve the in vivo reduction of NO3⁻ to nitrite (NO2⁻) and thence to nitric oxide (NO). However, the potential involvement of S-nitrosothiol (RSNO) formation is unclear. We hypothesised that the RSNO concentration ([RSNO]) in red blood cells (RBCs) and plasma is increased by NO3⁻-rich beetroot juice ingestion. In healthy human volunteers, we tested the effect of dietary supplementation with NO3⁻-rich beetroot juice (BR) or NO3⁻-depleted beetroot juice (placebo; PL) on [RSNO], [NO3⁻] and [NO2⁻] in RBCs, whole blood and plasma, as measured by ozone-based chemiluminescence. The median basal [RSNO] in plasma samples (n = 22) was 10 (5–13) nM (interquartile range in brackets). In comparison, the median values for basal [RSNO] in the corresponding RBC preparations (n = 19) and whole blood samples (n = 19) were higher (p < 0.001) than in plasma, being 40 (30–60) nM and 35 (25–80) nM, respectively. The median RBC [RSNO] in a separate cohort of healthy subjects (n = 5) was increased to 110 (93–125) nM after ingesting BR (12.8 mmol NO3⁻) compared to a corresponding baseline value of 25 (21–31) nM (Mann-Whitney test, p < 0.01). The median plasma [RSNO] in another cohort of healthy subjects (n = 14) was increased almost ten-fold to 104 (58–151) nM after BR supplementation (7 × 6.4 mmol of NO3⁻ over two days, p < 0.01) compared to PL. In conclusion, RBC and plasma [RSNO] are increased by BR ingestion. In addition to NO2⁻, RSNO may be involved in dietary NO3⁻ metabolism/actions.

Highlights

Nitric oxide (NO) is a pivotal gaseous molecule that executes mul tiple functions in the human body, such as promoting vasodilation and lowering blood pressure [1,2,3,4], inhibiting platelet aggregation [5] and enhancing exercise performance [6,7,8]
The chem iluminescence assay of the total [RSNO] in these biological samples indicated that levels of total RSNO were significantly higher in red blood cells (RBCs) and whole blood (p < 0.05) compared to matched plasma from the same individuals
The median RSNO concentrations in plasma and RBCs from healthy volunteers were significantly higher after ingesting beetroot juice (BR) compared with PL and/or baseline concentrations

Summary

Introduction

Nitric oxide (NO) is a pivotal gaseous molecule that executes mul tiple functions in the human body, such as promoting vasodilation and lowering blood pressure [1,2,3,4], inhibiting platelet aggregation [5] and enhancing exercise performance [6,7,8]. NO is synthesised in endothelial cells by a reaction catalysed by three isozymes of nitric oxide synthase (NOS). These consist of neuronal (nNOS), endothelial (eNOS) and inducible (iNOS) isoforms of NOS. Recent studies have demonstrated that, in humans, dietary NO3− may be converted to NO. This involves the entero-salivary circulation of NO3−, whereby NO3− is absorbed in the stomach and small intestine, enters the blood circulation, and is concentrated in saliva due to active uptake by the salivary glands. Swallowed NO2− is chemi cally reduced to NO under the acidic conditions of the stomach [17], as well as NO2− being absorbed in the gastrointestinal tract and entering the

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