Beetroot juice supplementation reduces whole body oxygen consumption but does not improve indices of mitochondrial efficiency in human skeletal muscle.

KEY POINTS: Oral consumption of nitrate (NO3(-)) in beetroot juice has been shown to decrease the oxygen cost of submaximal exercise; however, the mechanism of action remains unresolved. We supplemented recreationally active males with beetroot juice to determine if this altered mitochondrial bioenergetics. Despite reduced submaximal exercise oxygen consumption, measures of mitochondrial coupling and respiratory efficiency were not altered in muscle. In contrast, rates of mitochondrial hydrogen peroxide (H2O2) emission were increased in the absence of markers of lipid or protein oxidative damage. These results suggest that improvements in mitochondrial oxidative metabolism are not the cause of beetroot juice-mediated improvements in whole body oxygen consumption. ABSTRACT: Ingestion of sodium nitrate (NO3(-)) simultaneously reduces whole body oxygen consumption (V̇O2) during submaximal exercise while improving mitochondrial efficiency, suggesting a causal link. Consumption of beetroot juice (BRJ) elicits similar decreases in V̇O2 but potential effects on the mitochondria remain unknown. Therefore we examined the effects of 7-day supplementation with BRJ (280 ml day(-1), ∼26 mmol NO3(-)) in young active males (n = 10) who had muscle biopsies taken before and after supplementation for assessments of mitochondrial bioenergetics. Subjects performed 20 min of cycling (10 min at 50% and 70% V̇O2 peak) 48 h before 'Pre' (baseline) and 'Post' (day 5 of supplementation) biopsies. Whole body V̇O2 decreased (P < 0.05) by ∼3% at 70% V̇O2 peak following supplementation. Mitochondrial respiration in permeabilized muscle fibres showed no change in leak respiration, the content of proteins associated with uncoupling (UCP3, ANT1, ANT2), maximal substrate-supported respiration, or ADP sensitivity (apparent Km). In addition, isolated subsarcolemmal and intermyofibrillar mitochondria showed unaltered assessments of mitochondrial efficiency, including ADP consumed/oxygen consumed (P/O ratio), respiratory control ratios and membrane potential determined fluorometrically using Safranine-O. In contrast, rates of mitochondrial hydrogen peroxide (H2O2) emission were increased following BRJ. Therefore, in contrast to sodium nitrate, BRJ supplementation does not alter key parameters of mitochondrial efficiency. This occurred despite a decrease in exercise V̇O2, suggesting that the ergogenic effects of BRJ ingestion are not due to a change in mitochondrial coupling or efficiency. It remains to be determined if increased mitochondrial H2O2 contributes to this response.

Inflammation and metabolism gene sets in subcutaneous abdominal adipose tissue are altered 1 hour after exercise in adults with obesity.

Although the health benefits of exercise in adults with obesity are well described, the direct effects of exercise on adipose tissue that may lead to improved metabolic health are poorly understood. The primary aims of this study were to perform an unbiased analysis of the subcutaneous abdominal adipose tissue transcriptomic response to acute exercise in adults with obesity, and to compare the effects of moderate-intensity continuous exercise versus high-intensity interval exercise on this response. Twenty-nine adults with obesity performed a session of either high-intensity interval exercise (HI; 10 × 1 min at 90%HRpeak, 1 min recovery between intervals; n = 14) or moderate-intensity continuous exercise (MI; 45 min at 70%HRpeak; n = 15). Groups were well matched for BMI (HI 33 ± 3 vs. MI 33 ± 4 kg/m2), sex (HI: 9 women vs. MI: 10 women), and age (HI: 32 ± 6 vs. MI: 29 ± 5). Subcutaneous adipose tissue was collected before and 1 h after the session of HI or MI, and samples were processed for RNA sequencing. Gene set enrichment analysis revealed 7 of 21 gene sets enriched postexercise overlapped between HI and MI. Interestingly, both HI and MI upregulated gene sets involved in inflammation (IL6-JAK-STAT3 signaling, allograft rejection, TNFα signaling via NFκB, and inflammatory response; FDR q value < 0.25). Exercise also downregulated adipogenic and oxidative metabolism gene sets in both groups. Overall, these data suggest genes involved in subcutaneous adipose tissue metabolism and inflammation may be an important part of the initial response after a session of exercise.NEW & NOTEWORTHY This study compared the effects of a single session of high-intensity interval exercise versus moderate-intensity continuous exercise on transcriptional changes in subcutaneous abdominal adipose tissue collected from adults with obesity. Our novel findings indicate exercise upregulated inflammation-related gene sets, while it downregulated metabolism-related gene sets - after both high-intensity and moderate-intensity exercise. These data suggest exercise can alter the adipose tissue transcriptome 1 h after exercise in ways that may impact inflammation and metabolism.