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

Ingested inorganic nitrate (NO(3)?) has multiple effects in the human body including vasodilation, inhibition of platelet aggregation, and improved skeletal muscle function. The functional effects of oral NO(3)? involve the in vivo reduction of NO(3)? to nitrite (NO(2)?) 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 NO(3)?-rich beetroot juice ingestion. In healthy human volunteers, we tested the effect of dietary supplementation with NO(3)?-rich beetroot juice (BR) or NO(3)?-depleted beetroot juice (placebo; PL) on [RSNO], [NO(3)?] and [NO(2)?] 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 NO(3)?) 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 NO(3)? over two days, p < 0.01) compared to PL. In conclusion, RBC and plasma [RSNO] are increased by BR ingestion. In addition to NO(2)?, RSNO may be involved in dietary NO(3)? metabolism/actions.The article is available via Open Access. Click on the 'Additional link' above to access the full-text.Published version, accepted version, submitted versio