Inorganic Nitrate Mimics Exercise-Stimulated Muscular Fiber-Type Switching and Myokine and γ-Aminobutyric Acid Release

Investigation of the effect of nitrate and L-arginine intake on aerobic, anaerobic performance, balance, agility, and recovery in elite taekwondo athletes

BACKGROUND

Taekwondo is a complex martial art that requires speed, balance, agility, and endurance. This study aims to examine the effects of nitrate and L-arginine supplementation on acute aerobic and anaerobic performance, balance, agility, and recovery in elite taekwondo athletes.

METHOD

This study was conducted as a double-blind, randomized, crossover study with the participation of 15 experienced taekwondo athletes aged 19.06 ± 0.96 years and 8.93 ± 1.27 years of training experience. Participants visited the laboratory a total of nine times, including a practice session and anthropometric measurements. These visits consisted of eight experimental sessions conducted at 72-hour intervals. The experimental sessions were conducted with nitrate, L-arginine, and a combination of both supplements (NIT*L-ARG) and placebo. Nitrate supplementation was provided by homogenizing fresh spinach (837.40 mg/kg), while L-ARG was given as a single dose of 6 g in powder form three hours before exercise.

RESULTS

NIT*L-ARG supplementation significantly improved the anaerobic performance of athletes in Wingate peak power and peak power (w/kg) compared to placebo and in mean power compared to NIT, L-ARG, and PLA. In addition, NIT*L-ARG supplementation significantly improved blood lactate levels and agility performance immediately after Wingate and Shuttle run tests.

CONCLUSION

The combined intake of NIT*L-ARG was found to be effective in improving aerobic, anaerobic, and agility performances as well as fatigue levels of athletes. It was determined that taking NIT and L-ARG supplements alone contributed to the improvement of improving athletes' performance in Wingate mean power values and subsequent fatigue level compared to PLA.

Melatonin induces fiber switching by improvement of mitochondrial oxidative capacity and function via NRF2/RCAN/MEF2 in the vastus lateralis muscle from both sex Zücker diabetic fatty rats

The positive role of melatonin in obesity control and skeletal muscle (SKM) preservation is well known. We recently showed that melatonin improves vastus lateralis muscle (VL) fiber oxidative phenotype. However, fiber type characterization, mitochondrial function, and molecular mechanisms that underlie VL fiber switching by melatonin are still undefined. Our study aims to investigate whether melatonin induces fiber switching by NRF2/RCAN/MEF2 pathway activation and mitochondrial oxidative metabolism modulation in the VL of both sex Zücker diabetic fatty (ZDF) rats. 5-Weeks-old male and female ZDF rats (N = 16) and their age-matched lean littermates (ZL) were subdivided into two subgroups: control (C) and orally treated with melatonin (M) (10 mg/kg/day) for 12 weeks. Interestingly, melatonin increased oxidative fibers amounts (Types I and IIa) counteracting the decreased levels found in the VL of obese-diabetic rats, and upregulated NRF2, calcineurin and MEF2 expression. Melatonin also restored the mitochondrial oxidative capacity increasing the respiratory control ratio (RCR) in both sex and phenotype rats through the reduction of the proton leak component of respiration (state 4). Melatonin also improved the VL mitochondrial phosphorylation coefficient and modulated the total oxygen consumption by enhancing complex I, III and IV activity, and fatty acid oxidation (FAO) in both sex obese-diabetic rats, decreasing in male and increasing in female the complex II oxygen consumption. These findings suggest that melatonin treatment induces fiber switching in SKM improving mitochondrial functionality by NRF2/RCAN/MEF2 pathway activation.

Preworkout dietary nitrate magnifies training-induced benefits to physical function in late postmenopausal women: a randomized pilot study

To inform end points for future work, we explored the utility of preworkout (i.e., an acute dose before training) beetroot juice (BRJ) combined with exercise (BRJ + EX) to augment indices of physical function in postmenopausal women compared with exercise only (EX). A two-arm pilot study was used to compare 24 postmenopausal women following an 8-wk, circuit-based exercise intervention. Participants were randomized to BRJ + EX (n = 12) or EX (n = 12). BRJ + EX participants consumed 140 mL of BRJ 120-180 min (only) before training for 7 wk, then discontinued during the final week to mitigate carryover effects. Physical function indices were 6-min walk test (6MWT), estimated V̇o2peak, heart rate recovery (HRR), and maximal knee extensor power (Pmax). A treadmill task was used to measure V̇o2 on-kinetics wherein mean response time (MRT) coincided with the duration to reach 63% of steady-state V̇o2. Results showed greater changes (Δ) among BRJ + EX participants for 6MWT distance (40 ± 23 m vs. 8 ± 25 m; P = 0.003, d = 1.35), ΔV̇o2peak (1.5 ± 0.9 mL·kg-1·min-1 vs. 0.3 ± 1.0 mL·kg-1·min-1; P = 0.008, d = 1.20), and ΔHRR (-10 ± 6 beats/min vs. -1 ± 9 beats/min; P = 0.017, d = 1.05). Large and medium effect sizes favoring BRJ + EX were detected for ΔPmax (P = 0.07, d = 0.83) and ΔMRT (P = 0.257, d = 0.50), respectively. In postmenopausal women, BRJ + EX appears to magnify some adaptive benefits to physical function including aerobic capacity and recovery beyond that of training without BRJ. Investigation into contributing mechanisms is needed.NEW & NOTEWORTHY Though exercise training represents the principal strategy to combat age-related decline, the attendant effects of menopause weaken aspects of exercise adaptation compared with premenopausal women and age-matched men. Here we provide important initial evidence that preworkout (i.e., an acute dose before training) beetroot juice coupled with an 8-wk, circuit-based exercise training intervention may uniquely benefit late postmenopausal women by enhancing indices of physical function including aerobic capacity and recovery.

Impairment of Skeletal Muscle Contraction by Inhibitors of GABA Transporters

γ-Aminobutyric acid (GABA) has a significant impact on the functioning of not only the central but also the peripheral part of the nervous system. Recently, various elements of the GABAergic signaling system have been discovered in the area of the neuromuscular junction of mammals. At the same time, the functional activity of membrane-bound GABA transporters (GATs) and their role in neuromuscular transmission have not been identified. In the present study, performed on a neuromuscular preparation of the mouse diaphragm, the effect of GABA transporter inhibitors (nipecotic acid and β-alanine) on the force of muscle contraction was assessed. It was found that in the presence of both compounds in the bathing solution, the force of contractions caused by stimulation of the motor nerve dropped by 30-50%. However, when the muscle was stimulated directly, no effect of GABA transporter inhibitors on the contractile force was observed. The depressant effect of β-alanine induced by nerve stimulation was completely abolished by the GABAB receptor blocker CGP 55845. GABA transporters were detected at the neuromuscular junction using immunohistochemistry. Thus, our results indicate that GABA transporters are localized in the area of the neuromuscular junction, and their activity affects the muscle contraction force. This influence is most likely due to the removal of GABA released during nerve stimulation and activating GABA receptors, which leads to a decrease in the contraction force of the striated muscles.

Integrative analysis of whole genome bisulfite and transcriptome sequencing reveals the effect of sodium butyrate on DNA methylation in the differentiation of bovine skeletal muscle satellite cells

Butyric acid as a short-chain fatty acid (SCFA) is one of the key microbial metabolites of ruminants. Numerous studies indicate that butyrate is crucial in muscle growth and development, and plays an important molecular regulatory role mainly by inhibiting histone deacetylation. DNA methylation, a major epigenetic modification, is involved in cell differentiation. Butyrate, in addition to its role in acetylation modifications, can alter the DNA methylation status of cells. However, the impact of butyrate on the DNA methylation of bovine skeletal muscle satellite cells (SMSCs) remains unclear. In this study, we developed a differentiation model of SMSCs and employed RNA sequencing (RNA-seq) alongside whole genome bisulfite sequencing (WGBS) to explore the effects of butyrate treatment on DNA methylation status and its relationship with gene expression. Treatment of SMSCs with sodium butyrate (NaB) at 1.0 mM for 2 days significantly inhibited the expression of DNA methyltransferases (DNMT1, DNMT2, DNMT3A) at the mRNA and protein levels while promoting the expression of demethylases (TET1, TET2, TET3) at mRNA levels. WGBS identified 4292 differentially methylated regions (DMRs), comprising 2294 hypermethylated and 1998 hypomethylated regions. These DMRs were significantly enriched in the MAPK, cAMP, and Wnt signaling pathways, all of which are implicated in myogenesis and development. Combining RNA-seq and WGBS data revealed a total of 130 overlapping genes, including MDFIC, CREBBP, DMD, LTBP2 and KLF4. These genes are predominantly involved in regulating the FoxO, MAPK, PI3K-Akt, and Wnt signaling pathways. This study provides new insights into the effects of butyrate-mediated DNA methylation on SMSC development and enhances our understanding of butyrate as an epigenetic modifier beyond its role in acetylation.

The therapeutic potential of irisin to mitigate the risk of metabolic syndrome in postmenopausal women

Oestradiol withdrawal at menopause predisposes women to metabolic syndrome, a cluster of interrelated conditions including obesity, insulin resistance, dyslipidaemia and hypertension that together confer an increased risk of developing type 2 diabetes mellitus and cardiovascular disease. Hormone replacement therapies are commonly used to treat acute symptoms of the perimenopausal period, and whilst they have been associated with metabolic improvements in many studies, long-term use is considered unviable. Novel approaches are required to mitigate the risk of postmenopausal metabolic syndrome. In 2012, the exercise-inducible myokine irisin was isolated from the skeletal muscle of mice and identified to have anti-obesity and antidiabetic effects in vivo. Irisin is now recognised to exert pleiotropic action on cognitive, bone and metabolic health. There is accumulating evidence from in vitro and in vivo rodent studies that irisin can mitigate each component condition of metabolic syndrome. In postmenopausal women, independent associations have been observed between (a) exercise and plasma irisin concentration and (b) plasma irisin concentration and reduced incidence of metabolic syndrome. To date, however, no study has considered the mechanistic basis by which irisin, whether exercise-induced or exogenously administered, could reduce the incidence or severity of metabolic syndrome in postmenopausal women. This review aims to analyse the literature concerning the metabolic actions of irisin, with a focus on its therapeutic potential for metabolic syndrome driven by a state of oestradiol depletion. It evaluates the practicality of exercise as a therapy and discusses other irisin-based therapeutic strategies that may alleviate postmenopausal metabolic syndrome. Finally, it highlights areas where future research is required to advance knowledge of irisin's biological action such that it could be considered a viable candidate for clinical application.

The metabolome as a diagnostic for maximal aerobic capacity during exercise in type 1 diabetes

AIMS/HYPOTHESIS

Our aim was to characterise the in-depth metabolic response to aerobic exercise and the impact of residual pancreatic beta cell function in type 1 diabetes. We also aimed to use the metabolome to distinguish individuals with type 1 diabetes with reduced maximal aerobic capacity in exercise defined byV ˙ O 2peak .

METHODS

Thirty participants with type 1 diabetes (≥3 years duration) and 30 control participants were recruited. Groups did not differ in age or sex. After quantification of peak stimulated C-peptide, participants were categorised into those with undetectable (<3 pmol/l), low (3-200 pmol/l) or high (>200 pmol/l) residual beta cell function. Maximal aerobic capacity was assessed byV ˙ O 2peak test and did not differ between control and type 1 diabetes groups. All participants completed 45 min of incline treadmill walking (60%V ˙ O 2peak ) with venous blood taken prior to exercise, immediately post exercise and after 60 min recovery. Serum was analysed using targeted metabolomics. Metabolomic data were analysed by multivariate statistics to define the metabolic phenotype of exercise in type 1 diabetes. Receiver operating characteristic (ROC) curves were used to identify circulating metabolomic markers of maximal aerobic capacity (V ˙ O 2peak ) during exercise in health and type 1 diabetes.

RESULTS

Maximal aerobic capacity (V ˙ O 2peak ) inversely correlated with HbA1c in the type 1 diabetes group (r2=0.17, p=0.024). Higher resting serum tricarboxylic acid cycle metabolites malic acid (fold change 1.4, p=0.001) and lactate (fold change 1.22, p=1.23×10-5) differentiated people with type 1 diabetes. Higher serum acylcarnitines (AC) (AC C14:1, F value=12.25, p=0.001345; AC C12, F value=11.055, p=0.0018) were unique to the metabolic response to exercise in people with type 1 diabetes. C-peptide status differentially affected metabolic responses in serum ACs during exercise (AC C18:1, leverage 0.066; squared prediction error 3.07). The malic acid/pyruvate ratio in rested serum was diagnostic for maximal aerobic capacity (V ˙ O 2peak ) in people with type 1 diabetes (ROC curve AUC 0.867 [95% CI 0.716, 0.956]).

CONCLUSIONS/INTERPRETATION

The serum metabolome distinguishes high and low maximal aerobic capacity and has diagnostic potential for facilitating personalised medicine approaches to manage aerobic exercise and fitness in type 1 diabetes.

Metabolic small talk during exercise: The role of metabokines and lipokines in interorgan signalling

Metabolites in exercise have traditionally been viewed as a fuel source, waste product, or anabolic components required for exercise-induced biosynthetic processes. However, it is now recognised that metabolites and lipids may act as mediators of interorgan crosstalk to coordinate the local and systemic physiological adaptations required to meet the complex system-wide challenge of exercise. These bioactive metabolite and lipid signals have been termed metabokines and lipokines, respectively. There is emerging evidence that metabokines and lipokines contribute to the health benefits of exercise. This review highlights several of the key recent discoveries related to metabokine and lipokine signalling during exercise. The discovery of these metabokines and lipokines, and their signalling targets, may provide the basis of future therapies for human disease.

γ-Aminobutyric acids (GABA) and serum GABA/AABA (G/A) ratio as potential biomarkers of physical performance and aging

Declining physical performance with age and disease is an important indicator of declining health. Biomarkers that identify declining physical performance would be useful in predicting treatment outcomes and identifying potential therapeutics. γ-aminobutyric acid (GABA), a muscle autocrine factor, is a potent inhibitor of muscle function and works as a muscle relaxant. L-α-aminobutyric acid (L-AABA) is a biomarker for malnutrition, liver damage, and depression. We sought to determine if GABA and L-AABA may be useful for predicting physical performance. Serum levels of GABA and L-AABA were quantified in 120 individuals divided by age, sex, and physical capacity into low, average, and high performer groups. Analyses explored correlations between serum levels and physical performance. Both GABA and the ratio of GABA/AABA (G/A), but not AABA, were highly positively associated with age (Pearson correlations r = 0.35, p = 0.0001 for GABA, r = 0.31, p = 0.0007 for G/A, n = 120). GABA showed negative associations in the whole cohort with physical performance [fast gait speed, 6 min walk test (6MWT), PROMIS score, and SF36PFS raw score] and with subtotal and femoral neck bone mineral density. L-AABA was positively associated with usual gait speed, 6MWT, total SPPB score, and SF36PFS raw score in the total cohort of 120 human subjects, also with 6MWT and SF36PFS raw score in the 60 male subjects, but no associations were observed in the 60 females. As both GABA and L-AABA appear to be indicative of physical performance, but in opposite directions, we examined the G/A ratio. Unlike GABA, the G/A ratio showed a more distinct association with mobility tests such as total SPPB score, usual and fast gait speed, 6MWT, and SF36PFS raw score in the males, regardless of age and metabolic status. Serum G/A ratio could be potentially linked to physical performance in the male population. Our findings strongly suggest that GABA, L-AABA, and the G/A ratio in human serum may be useful markers for both age and physical function. These new biomarkers may significantly enhance the goal of identifying universal biomarkers to accurately predict physical performance and the beneficial effects of exercise training for older adults.

PGC1α: an emerging therapeutic target for chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN)-mediated paresthesias are a common complication in cancer patients undergoing chemotherapy. There are currently no treatments available to prevent or reverse CIPN. Therefore, new therapeutic targets are urgently needed to develop more effective analgesics. However, the pathogenesis of CIPN remains unclear, and the prevention and treatment strategies of CIPN are still unresolved issues in medicine. More and more studies have demonstrated that mitochondrial dysfunction has become a major factor in promoting the development and maintenance of CIPN, and peroxisome proliferator-activated receptor gamma (PPARγ) coactivator 1α (PGC1α) plays a significant role in maintaining the mitochondrial function, protecting peripheral nerves, and alleviating CIPN. In this review, we highlight the core role of PGC1α in regulating oxidative stress and maintaining normal mitochondrial function and summarize recent advances in its therapeutic effects and mechanisms in CIPN and other forms of peripheral neuropathy. Emerging studies suggest that PGC1α activation may positively impact CIPN mitigation by modulating oxidative stress, mitochondrial dysfunction, and inflammation. Therefore, novel therapeutic strategies targeting PGC1α could be a potential therapeutic target in CIPN.

Long-term GABA administration improves FNDC5, TFAM, and UCP3 mRNA expressions in the skeletal muscle and serum irisin levels in chronic type 2 diabetic rats

In this study, we aimed to investigate whether the anti-diabetic effects of γ-aminobutyric acid (GABA) and insulin can be mediated through the regulation of gene expression related to irisin production and mitochondrial biogenesis in type 2 diabetic mellitus (T2DM) rats. Four groups (n = 6) were used in this study: control, T2DM, T2DM + insulin, and T2DM + GABA groups. After T2DM induction for 3 months (high-fat diet + 35 mg/kg streptozotocin) and treatment with GABA or insulin for 3 months, circulating levels of FBG, triglyceride, LDL, Ox-LDL, and insulin as well as hepatic and serum irisin levels were measured. The mRNA expressions of fibronectin type III domain-containing protein 5 (FNDC5), mitochondrial transcription factor A (TFAM), and mitochondrial uncoupling protein 3 (UCP3) were also evaluated in the skeletal muscle of all groups. GABA therapy improved the FBG and insulin levels in diabetic rats. Insulin treatment significantly reduced FBG and failed to maintain glucose close to the control level. Insulin or GABA therapy significantly decreased the levels of LDL, Ox-LDL, and HOMA-IR index. Circulating irisin levels were markedly decreased in insulin-treated group, while irisin levels did not show significant changes in GABA-treated group compared with control group. GABA or insulin therapy increased mRNA expressions of TFAM and UCP3 in diabetic rats. GABA therapy also led to a significant increase in FNDC5 mRNA. Our findings suggest that the anti-diabetic effect of GABA may be mediated, in part, by a decrease in Ox-LDL levels and an increase in the levels of irisin as well as FNDC5, TFAM, and UCP3 gene expression in T2DM rats.

An anthracene-based Hydrogen-bonded Organic Framework as Bifunctional Fluorescent Sensor for the Detection of γ-Aminobutyric Acid and Nitrofurazone

Intelligent fluorescence detection for disease diagnosis has become a research hotspot. In the era of big data, machine learning (ML) for analyzing data and mining will be widely used in...

Exercise Inhibits NLRP3 Inflammasome Activation in Obese Mice via the Anti-Inflammatory Effect of Meteorin-like

Obesity is associated with chronic low-grade inflammation. The benefits of exercise are partly attributed to its anti-inflammatory effect, but whether exercise can regulate NLRP3 inflammasome activation in obese adipose tissue remains unknown. Meteorin-like (METRNL), a recently discovered myokine, has been implicated in mediating the effect of exercise on metabolism. Herein, we examined the effect of exercise and METRNL on NLRP3 inflammasome activation. High-fat diet (HFD)-induced obese mice were subjected to treadmill exercise for 8 weeks. A subgroup of HFD mice was switched to normal chow with the exercise intervention. Exercise and diet attenuated weight gain, fat accumulation, and insulin resistance in obese mice. In addition, exercise downregulated gene and protein levels of inflammasome markers, including NLRP3 and caspase-1, in adipose tissue. In isolated bone marrow-derived macrophages, activation of NLRP3 inflammasome was suppressed in the exercise group, as confirmed by the downregulation of IL-1β and IL-18. Exercise significantly enhanced the expression of METRNL in various muscle depots, and further in vitro analysis revealed that recombinant METRNL treatment inhibited IL-1β secretion in macrophages. In conclusion, exercise exerts its anti-inflammatory action by suppressing adipose tissue NLRP3 inflammasome, and this is, in part, associated with METRNL induction in muscle and its anti-inflammatory effects in macrophages.

Nitrate-induced improvements in exercise performance are coincident with exuberant changes in metabolic genes and the metabolome in zebrafish (Danio rerio) skeletal muscle

Dietary nitrate supplementation improves exercise performance by reducing the oxygen cost of exercise and enhancing skeletal muscle function. However, the mechanisms underlying these effects are not well understood. The purpose of this study was to assess changes in skeletal muscle energy metabolism associated with exercise performance in a zebrafish model. Fish were exposed to sodium nitrate (60.7 mg/L, 303.5 mg/L, 606.9 mg/L), or control water, for 21 days and analyzed at intervals (5, 10, 20, 30, 40 cm/s) during a 2-h strenuous exercise test. We measured oxygen consumption during an exercise test and assessed muscle nitrate concentrations, gene expression, and the muscle metabolome before, during, and after exercise. Nitrate exposure reduced the oxygen cost of exercise and increased muscle nitrate concentrations at rest, which were reduced with increasing exercise duration. In skeletal muscle, nitrate treatment upregulated expression of genes central to nutrient sensing (mtor), redox signaling (nrf2a), and muscle differentiation (sox6). In rested muscle, nitrate treatment increased phosphocreatine (P = 0.002), creatine (P = 0.0005), ATP (P = 0.0008), ADP (P = 0.002), and AMP (P = 0.004) compared with rested-control muscle. Following the highest swimming speed, concentration of phosphocreatine (P = 8.0 × 10-5), creatine (P = 6.0 × 10-7), ATP (P = 2.0 × 10-6), ADP (P = 0.0002), and AMP (P = 0.004) decreased compared with rested nitrate muscle. Our data suggest nitrate exposure in zebrafish lowers the oxygen cost of exercise by changing the metabolic programming of muscle prior to exercise and increasing availability of energy-rich metabolites required for exercise.NEW & NOTEWORTHY We show that skeletal muscle nitrate concentration is higher with supplementation at rest and was lower in groups with increasing exercise duration in a zebrafish model. The higher availability of nitrate at rest is associated with upregulation of key nutrient-sensing genes and greater availability of energy-producing metabolites (i.e., ATP, phosphocreatine, glycolytic intermediates). Overall, nitrate supplementation may lower oxygen cost of exercise through improved fuel availability resulting from metabolic programming of muscle prior to exercise.

Possible Effects of Beetroot Supplementation on Physical Performance Through Metabolic, Neuroendocrine, and Antioxidant Mechanisms: A Narrative Review of the Literature

Athletes often seek to use dietary supplements to increase performance during exercise. Among various supplements, much attention has been paid to beetroot in recent years. Beetroot is a source of carbohydrates, fiber, protein, minerals, and vitamins; also, it is a natural source of nitrate and associated with improved sports performance. Nitrates can the modification of skeletal muscle contractile proteins or calcium handling after translation. The time to reach the peak plasma nitrate is between 1 and 3 h after consumption of a single dose of nitrate. Nitrate is metabolized by conversion to nitrite and subsequently nitric oxide. Beetroot can have various effects on athletic performance through nitric oxide. Nitric oxide is an intracellular and extracellular messenger for regulating certain cellular functions and causes vasodilation of blood vessels and increases blood flow. Nitric oxide seems to be effective in improving athletic performance by increasing oxygen, glucose, and other nutrients for better muscle fueling. Nitric oxide plays the main role in anabolic hormones, modulates the release of several neurotransmitters and the major mediators of stress involved in the acute hypothalamic-pituitary-adrenal response to exercise. Beetroot is an important source of compounds such as ascorbic acid, carotenoids, phenolic acids, flavonoids, betaline, and highly active phenolics and has high antioxidant properties. Beetroot supplement provides an important source of dietary polyphenols and due to the many health benefits. Phytochemicals of Beetroot through signaling pathways inhibit inflammatory diseases. In this study, the mechanisms responsible for these effects were examined and the research in this regard was reviewed.

Multiple Roles in Neuroprotection for the Exercise Derived Myokine Irisin

Exercise has multiple beneficial effects on health including decreasing the risk of neurodegenerative diseases. Such effects are thought to be mediated (at least in part) by myokines, a collection of cytokines and other small proteins released from skeletal muscles. As an endocrine organ, skeletal muscle synthesizes and secretes a wide range of myokines which contribute to different functions in different organs, including the brain. One such myokine is the recently discovered protein Irisin, which is secreted into circulation from skeletal muscle during exercise from its membrane bound precursor Fibronectin type III domain-containing protein 5 (FNDC5). Irisin contributes to metabolic processes such as glucose homeostasis and browning of white adipose tissue. Irisin also crosses the blood brain barrier and initiates a neuroprotective genetic program in the hippocampus that culminates with increased expression of brain derived neurotrophic factor (BDNF). Furthermore, exercise and FNDC5/Irisin have been shown to have several neuroprotective effects against injuries in ischemia and neurodegenerative disease models, including Alzheimer's disease. In addition, Irisin has anxiolytic and antidepressant effects. In this review we present and summarize recent findings on the multiple effects of Irisin on neural function, including signaling pathways and mechanisms involved. We also discuss how exercise can positively influence brain function and mental health via the "skeletal muscle-brain axis." While there are still many unanswered questions, we put forward the idea that Irisin is a potentially essential mediator of the skeletal muscle-brain crosstalk.

Brown and beige adipose tissue regulate systemic metabolism through a metabolite interorgan signaling axis

Brown and beige adipose tissue are emerging as distinct endocrine organs. These tissues are functionally associated with skeletal muscle, adipose tissue metabolism and systemic energy expenditure, suggesting an interorgan signaling network. Using metabolomics, we identify 3-methyl-2-oxovaleric acid, 5-oxoproline, and β-hydroxyisobutyric acid as small molecule metabokines synthesized in browning adipocytes and secreted via monocarboxylate transporters. 3-methyl-2-oxovaleric acid, 5-oxoproline and β-hydroxyisobutyric acid induce a brown adipocyte-specific phenotype in white adipocytes and mitochondrial oxidative energy metabolism in skeletal myocytes both in vitro and in vivo. 3-methyl-2-oxovaleric acid and 5-oxoproline signal through cAMP-PKA-p38 MAPK and β-hydroxyisobutyric acid via mTOR. In humans, plasma and adipose tissue 3-methyl-2-oxovaleric acid, 5-oxoproline and β-hydroxyisobutyric acid concentrations correlate with markers of adipose browning and inversely associate with body mass index. These metabolites reduce adiposity, increase energy expenditure and improve glucose and insulin homeostasis in mouse models of obesity and diabetes. Our findings identify beige adipose-brown adipose-muscle physiological metabokine crosstalk.

Irisin inhibits osteocyte apoptosis by activating the Erk signaling pathway in vitro and attenuates ALCT-induced osteoarthritis in mice

Moderate exercise can alleviate symptoms of osteoarthritis (OA) such as pain, stiffness, and joint deformities that are associated with progressive cartilaginous degeneration, osteophyte formation, subchondral bone changes, and synovial inflammation. Irisin is an exercise-related myokine that reportedly plays a crucial role in bone remodeling. However, its role in OA remains unknown. This study aimed to determine whether irisin can attenuate OA progression and the mechanism of its therapeutic effect. Three-month-old male C57BL/6J mice were randomized to groups that underwent sham operation, and anterior cruciate ligament transection (ACLT) intraperitoneally injected with vehicle or irisin in vivo. Apoptosis was induced by stretching murine osteocyte-like MLO-Y4 cells in vitro. Irisin reduced wear, maintained the proportion of hyaline cartilage, a more complete cartilage structure, and lower Osteoarthritis Research Society International (OARSI) scores at 4 weeks after ACLT. Irisin reduced the expression of matrix metalloproteinase (MMP)-13 in cartilage and caspase 3 in the subchondral bone. Irisin exerted rescue effects in microstructural parameters of subchondral trabecular bone including bone volume fraction (BV/TV), trabecular number (Tb.N), connection density (Conn. D), and the structure model index (SMI) compared with ACLT-vehicle group. Bone histomorphometry showed that irisin increased subchondral bone remodeling. The decreasing ratio (%) of the eroded surface (ES/BS) was reversed by irisin in the ACLT+vehicle group. Staining with tartrate-resistant acid phosphatase showed a decreased number of osteoclasts. Irisin significantly increased the proliferation of osteocytes, protected them from apoptosis, and maintained cellular activity by regulating the expression of Bax, Bcl-2, and osteoprotegerin/receptor activator of nuclear factor (NF)-kB-ligand (OPG/Rankl). Irisin activated serine/threonine-selective protein kinases (Erk) and p38 signaling, and its anti-apoptosis function depended on the Erk signaling pathway. Irisin attenuated OA progression by decreasing osteocyte apoptosis and improving the microarchitecture of subchondral bone. Activation of the Erk pathway by irisin plays an important role in reducing osteocyte apoptosis in vitro.

Inorganic nitrite alters mitochondrial dynamics without overt changes in cell death and mitochondrial respiration in cardiomyoblasts under hyperglycemia

Inorganic nitrate or nitrite supplementation has been reported to demonstrate positive outcomes in rodent models of obesity and diabetes as well as in type 2 diabetic humans and even included in clinical trials pertaining to cardiovascular diseases in the recent decade. However, there are contrasting data regarding the useful and toxic effects of the anions. The primary scope of this study was to analyze the beneficial/detrimental alterations in redox status, mitochondrial dynamics and function, and cellular fitness in cardiomyoblasts inflicted by nitrite under hyperglycemic conditions compared with normoglycemia. Nitrite supplementation in H9c2 myoblasts under high glucose diminishes the Bcl-x_L expression and mitochondrial ROS levels without significant initiation of cell death or decline in total ROS levels. Concomitantly, there are tendencies towards lowering of mitochondrial membrane potential, but without noteworthy changes in mitochondrial biogenesis and respiration. The study also revealed that under high glucose stress, nitrite may alter mitochondrial dynamics by Drp1 activation possibly via Akt1-Pim1 axis. Moreover, the study revealed differential effects of Drp1 silencing and/or nitrite under the above glycemic conditions. Overall, the study warrants more research regarding the effects of nitrite therapy in cardiac cells exposed to hyperglycemia.

Irisin Gene Delivery Ameliorates Burn-Induced Sensory and Motor Neuropathy

Burn-related neuropathy is common and often involves pain, paresthesia, or muscle weakness. Irisin, an exercise-induced myokine after cleavage from its membrane precursor fibronectin type III domain-containing 5 (FNDC5), exhibits neuroprotective and anti-inflammatory activities. A rat model of third-degree burn on the right hind paw was used to investigate the therapeutic role of irisin/FNDC5. Rats received burn injury and were treated with intrathecal recombinant adenovirus containing the irisin sequence (Ad-irisin) at 3 weeks postburn. One week later, mechanical allodynia was examined. The expression of irisin in cerebrospinal fluid (CSF) was detected. Ipsilateral gastrocnemius muscle and lumbar spinal cord were also obtained for further investigation. Furthermore, the anti-apoptotic effect of recombinant irisin in SH-SY5Y cells was evaluated through tumor necrosis factor alpha (TNFα) stimulus to mimic burn injury. We noted intrathecal Ad-irisin attenuated pain sensitization and gastrocnemius muscle atrophy by modulating the level of irisin in CSF, and the expression of neuronal FNDC5/irisin and TNFα in the spinal cord. Ad-irisin also ameliorated neuronal apoptosis in both dorsal and ventral horns. Furthermore, recombinant irisin attenuated TNFα-induced SH-SY5Y cell apoptosis. In summary, irisin attenuated allodynia and muscle wasting by ameliorating neuroinflammation-induced neuronal apoptosis.

Synergetic Effect of NO Precursor Supplementation and Exercise Training

INTRODUCTION

Nitric oxide (NO) precursor supplementation has been shown to increase NO bioavailability and can potentially improve vascular function and exercise performance. It remains unclear whether the combination of NO precursor supplementation and exercise training has synergic effects on exercise performance. This study aims to assess the effect of chronic nitrate and citrulline intake on exercise training adaptations in healthy young individuals.

METHODS

In this randomized, double-bind trial, 24 healthy young (12 females) subjects performed vascular function assessment (blood pressure, pulse wave velocity, postischemia vasodilation, and cerebrovascular reactivity) and both local (submaximal isometric unilateral knee extension) and whole-body (incremental cycling) exercise tests to exhaustion before and after a 2-month exercise training program and daily intake of a placebo or a nitrate-rich salad and citrulline (N + C, 520 mg nitrate and 6 g citrulline) drink. Prefrontal cortex and quadriceps oxygenation was monitored continuously during exercise by near-infrared spectroscopy.

RESULTS

N + C supplementation had no effect on vascular function and muscle and cerebral oxygenation during both local and whole-body exercise. N + C supplementation induced a significantly larger increase in maximal knee extensor strength (+5.1 ± 3.5 vs +0.2 ± 5.5 kg, P = 0.008) as well as a trend toward a larger increase in knee extensor endurance (+35.2 ± 26.1 vs +24.0 ± 10.4 contractions, P = 0.092) than placebo, but no effect on exercise training-induced maximal aerobic performance improvement.

CONCLUSION

These results suggest that chronic nitrate and citrulline supplementation enhances the effect of exercise training on quadriceps muscle function in healthy active young individuals, but this does not translate into improved maximal aerobic performances.

Sodium nitrate co-supplementation does not exacerbate low dose metronomic doxorubicin-induced cachexia in healthy mice

The purpose of this study was to determine whether (1) sodium nitrate (SN) treatment progressed or alleviated doxorubicin (DOX)-induced cachexia and muscle wasting; and (2) if a more-clinically relevant low-dose metronomic (LDM) DOX treatment regimen compared to the high dosage bolus commonly used in animal research, was sufficient to induce cachexia in mice. Six-week old male Balb/C mice (n = 16) were treated with three intraperitoneal injections of either vehicle (0.9% NaCl; VEH) or DOX (4 mg/kg) over one week. To test the hypothesis that sodium nitrate treatment could protect against DOX-induced symptomology, a group of mice (n = 8) were treated with 1 mM NaNO₃ in drinking water during DOX (4 mg/kg) treatment (DOX + SN). Body composition indices were assessed using echoMRI scanning, whilst physical and metabolic activity were assessed via indirect calorimetry, before and after the treatment regimen. Skeletal and cardiac muscles were excised to investigate histological and molecular parameters. LDM DOX treatment induced cachexia with significant impacts on both body and lean mass, and fatigue/malaise (i.e. it reduced voluntary wheel running and energy expenditure) that was associated with oxidative/nitrostative stress sufficient to induce the molecular cytotoxic stress regulator, nuclear factor erythroid-2-related factor 2 (NRF-2). SN co-treatment afforded no therapeutic potential, nor did it promote the wasting of lean tissue. Our data re-affirm a cardioprotective effect for SN against DOX-induced collagen deposition. In our mouse model, SN protected against LDM DOX-induced cardiac fibrosis but had no effect on cachexia at the conclusion of the regimen.

Metabolic communication during exercise

The coordination of nutrient sensing, delivery, uptake and utilization is essential for maintaining cellular, tissue and whole-body homeostasis. Such synchronization can be achieved only if metabolic information is communicated between the cells and tissues of the entire organism. During intense exercise, the metabolic demand of the body can increase approximately 100-fold. Thus, exercise is a physiological state in which intertissue communication is of paramount importance. In this Review, we discuss the physiological processes governing intertissue communication during exercise and the molecules mediating such cross-talk.

Effects of Dietary Supplements on Adaptations to Endurance Training

Endurance training leads to a variety of adaptations at the cellular and systemic levels that serve to minimise disruptions in whole-body homeostasis caused by exercise. These adaptations are differentially affected by training volume, training intensity, and training status, as well as by nutritional choices that can enhance or impair the response to training. A variety of supplements have been studied in the context of acute performance enhancement, but the effects of continued supplementation concurrent to endurance training programs are less well characterised. For example, supplements such as sodium bicarbonate and beta-alanine can improve endurance performance and possibly training adaptations during endurance training by affecting buffering capacity and/or allowing an increased training intensity, while antioxidants such as vitamin C and vitamin E may impair training adaptations by blunting cellular signalling but appear to have little effect on performance outcomes. Additionally, limited data suggest the potential for dietary nitrate (in the form of beetroot juice), creatine, and possibly caffeine, to further enhance endurance training adaptation. Therefore, the objective of this review is to examine the impact of dietary supplements on metabolic and physiological adaptations to endurance training.

Inorganic Nitrate Promotes Glucose Uptake and Oxidative Catabolism in White Adipose Tissue Through the XOR-Catalyzed Nitric Oxide Pathway

An aging global population combined with sedentary lifestyles and unhealthy diets has contributed to an increasing incidence of obesity and type 2 diabetes. These metabolic disorders are associated with perturbations to nitric oxide (NO) signaling and impaired glucose metabolism. Dietary inorganic nitrate, found in high concentration in green leafy vegetables, can be converted to NO in vivo and demonstrates antidiabetic and antiobesity properties in rodents. Alongside tissues including skeletal muscle and liver, white adipose tissue is also an important physiological site of glucose disposal. However, the distinct molecular mechanisms governing the effect of nitrate on adipose tissue glucose metabolism and the contribution of this tissue to the glucose-tolerant phenotype remain to be determined. Using a metabolomic and stable-isotope labeling approach, combined with transcriptional analysis, we found that nitrate increases glucose uptake and oxidative catabolism in primary adipocytes and white adipose tissue of nitrate-treated rats. Mechanistically, we determined that nitrate induces these phenotypic changes in primary adipocytes through the xanthine oxidoreductase-catalyzed reduction of nitrate to NO and independently of peroxisome proliferator-activated receptor-α. The nitrate-mediated enhancement of glucose uptake and catabolism in white adipose tissue may be a key contributor to the antidiabetic effects of this anion.

Supplements and Nutritional Interventions to Augment High-Intensity Interval Training Physiological and Performance Adaptations-A Narrative Review

High-intensity interval training (HIIT) involves short bursts of intense activity interspersed by periods of low-intensity exercise or rest. HIIT is a viable alternative to traditional continuous moderate-intensity endurance training to enhance maximal oxygen uptake and endurance performance. Combining nutritional strategies with HIIT may result in more favorable outcomes. The purpose of this narrative review is to highlight key dietary interventions that may augment adaptations to HIIT, including creatine monohydrate, caffeine, nitrate, sodium bicarbonate, beta-alanine, protein, and essential amino acids, as well as manipulating carbohydrate availability. Nutrient timing and potential sex differences are also discussed. Overall, sodium bicarbonate and nitrates show promise for enhancing HIIT adaptations and performance. Beta-alanine has the potential to increase training volume and intensity and improve HIIT adaptations. Caffeine and creatine have potential benefits, however, longer-term studies are lacking. Presently, there is a lack of evidence supporting high protein diets to augment HIIT. Low carbohydrate training enhances the upregulation of mitochondrial enzymes, however, there does not seem to be a performance advantage, and a periodized approach may be warranted. Lastly, potential sex differences suggest the need for future research to examine sex-specific nutritional strategies in response to HIIT.

Quantification of aminobutyric acids and their clinical applications as biomarkers for osteoporosis

Osteoporosis is a highly prevalent chronic aging-related disease that frequently is only detected after fracture. We hypothesized that aminobutyric acids could serve as biomarkers for osteoporosis. We developed a quick, accurate, and sensitive screening method for aminobutyric acid isomers and enantiomers yielding correlations with bone mineral density (BMD) and osteoporotic fracture. In serum, γ-aminobutyric acid (GABA) and (R)-3-aminoisobutyric acid (D-BAIBA) have positive associations with physical activity in young lean women. D-BAIBA positively associated with hip BMD in older individuals without osteoporosis/osteopenia. Lower levels of GABA were observed in 60–80 year old women with osteoporotic fractures. Single nucleotide polymorphisms in seven genes related to these metabolites associated with BMD and osteoporosis. In peripheral blood monocytes, dihydropyrimidine dehydrogenase, an enzyme essential to D-BAIBA generation, exhibited positive association with physical activity and hip BMD. Along with their signaling roles, BAIBA and GABA might serve as biomarkers for diagnosis and treatments of osteoporosis.

Wang et al. develop an LC/MS based screening method to separate and quantify aminobutyric acids isoforms. Applying it to osteoporosis clinical studies, their method yields important correlations with bone mineral density and osteoporotic fracture and highlight the role of γ-aminobutyric acid and β-aminoisobutyric acid as biomarkers for osteoporosis.

NAFLD as a continuum: from obesity to metabolic syndrome and diabetes

BACKGROUND

The prevalence of non-alcoholic fatty liver disease (NAFLD) has been increasing rapidly. It is nowadays recognized as the most frequent liver disease, affecting a quarter of global population and regularly coexisting with metabolic disorders such as type 2 diabetes, hypertension, obesity, and cardiovascular disease. In a more simplistic view, NAFLD could be defined as an increase in liver fat content, in the absence of secondary cause of steatosis. In fact, the clinical onset of the disease is a much more complex process, closely related to insulin resistance, limited expandability and dysfunctionality of adipose tissue. A fatty liver is a main driver for a new recognized liver-pancreatic α-cell axis and increased glucagon, contributing to diabetes pathophysiology.

MAIN TEXT

This review will focus on the clinical and pathophysiological connections between NAFLD, insulin resistance and type 2 diabetes. We reviewed non-invasive methods and several scoring systems for estimative of steatosis and fibrosis, proposing a multistep process for NAFLD evaluation. We will also discuss treatment options with a more comprehensive view, focusing on the current available therapies for obesity and/or type 2 diabetes that impact each stage of NAFLD.

CONCLUSION

The proper understanding of NAFLD spectrum-as a continuum from obesity to metabolic syndrome and diabetes-may contribute to the early identification and for establishment of targeted treatment.

Treatment with Nitrate, but Not Nitrite, Lowers the Oxygen Cost of Exercise and Decreases Glycolytic Intermediates While Increasing Fatty Acid Metabolites in Exercised Zebrafish

BACKGROUND

Dietary nitrate improves exercise performance by reducing the oxygen cost of exercise, although the mechanisms responsible are not fully understood.

OBJECTIVES

We tested the hypothesis that nitrate and nitrite treatment would lower the oxygen cost of exercise by improving mitochondrial function and stimulating changes in the availability of metabolic fuels for energy production.

METHODS

We treated 9-mo-old zebrafish with nitrate (sodium nitrate, 606.9 mg/L), nitrite (sodium nitrite, 19.5 mg/L), or control (no treatment) water for 21 d. We measured oxygen consumption during a 2-h, strenuous exercise test; assessed the respiration of skeletal muscle mitochondria; and performed untargeted metabolomics on treated fish, with and without exercise.

RESULTS

Nitrate and nitrite treatment increased blood nitrate and nitrite levels. Nitrate treatment significantly lowered the oxygen cost of exercise, as compared with pretreatment values. In contrast, nitrite treatment significantly increased oxygen consumption with exercise. Nitrate and nitrite treatments did not change mitochondrial function measured ex vivo, but significantly increased the abundances of ATP, ADP, lactate, glycolytic intermediates (e.g., fructose 1,6-bisphosphate), tricarboxylic acid (TCA) cycle intermediates (e.g., succinate), and ketone bodies (e.g., β-hydroxybutyrate) by 1.8- to 3.8-fold, relative to controls. Exercise significantly depleted glycolytic and TCA intermediates in nitrate- and nitrite-treated fish, as compared with their rested counterparts, while exercise did not change, or increased, these metabolites in control fish. There was a significant net depletion of fatty acids, acyl carnitines, and ketone bodies in exercised, nitrite-treated fish (2- to 4-fold), while exercise increased net fatty acids and acyl carnitines in nitrate-treated fish (1.5- to 12-fold), relative to their treated and rested counterparts.

CONCLUSIONS

Nitrate and nitrite treatment increased the availability of metabolic fuels (ATP, glycolytic and TCA intermediates, lactate, and ketone bodies) in rested zebrafish. Nitrate treatment may improve exercise performance, in part, by stimulating the preferential use of fuels that require less oxygen for energy production.

Dietary Nitrate and Physical Performance

Nitric oxide (NO) plays a plethora of important roles in the human body. Insufficient production of NO (for example, during older age and in various disease conditions) can adversely impact health and physical performance. In addition to its endogenous production through the oxidation of l-arginine, NO can be formed nonenzymatically via the reduction of nitrate and nitrite, and the storage of these anions can be augmented by the consumption of nitrate-rich foodstuffs such as green leafy vegetables. Recent studies indicate that dietary nitrate supplementation, administered most commonly in the form of beetroot juice, can ( a) improve muscle efficiency by reducing the O₂ cost of submaximal exercise and thereby improve endurance exercise performance and ( b) enhance skeletal muscle contractile function and thereby improve muscle power and sprint exercise performance. This review describes the physiological mechanisms potentially responsible for these effects, outlines the circumstances in which ergogenic effects are most likely to be evident, and discusses the effects of dietary nitrate supplementation on physical performance in a range of human populations.

Inorganic nitrate, hypoxia, and the regulation of cardiac mitochondrial respiration-probing the role of PPARα

Dietary inorganic nitrate prevents aspects of cardiac mitochondrial dysfunction induced by hypoxia, although the mechanism is not completely understood. In both heart and skeletal muscle, nitrate increases fatty acid oxidation capacity, and in the latter case, this involves up-regulation of peroxisome proliferator-activated receptor (PPAR)α expression. Here, we investigated whether dietary nitrate modifies mitochondrial function in the hypoxic heart in a PPARα-dependent manner. Wild-type (WT) mice and mice without PPARα (Ppara^−/−) were given water containing 0.7 mM NaCl (control) or 0.7 mM NaNO₃ for 35 d. After 7 d, mice were exposed to normoxia or hypoxia (10% O₂) for the remainder of the study. Mitochondrial respiratory function and metabolism were assessed in saponin-permeabilized cardiac muscle fibers. Environmental hypoxia suppressed mass-specific mitochondrial respiration and additionally lowered the proportion of respiration supported by fatty acid oxidation by 18% (P < 0.001). This switch away from fatty acid oxidation was reversed by nitrate treatment in hypoxic WT but not Ppara^−/− mice, indicating a PPARα-dependent effect. Hypoxia increased hexokinase activity by 33% in all mice, whereas lactate dehydrogenase activity increased by 71% in hypoxic WT but not Ppara^−/− mice. Our findings indicate that PPARα plays a key role in mediating cardiac metabolic remodeling in response to both hypoxia and dietary nitrate supplementation.—Horscroft, J. A., O’Brien, K. A., Clark, A. D., Lindsay, R. T., Steel, A. S., Procter, N. E. K., Devaux, J., Frenneaux, M., Harridge, S. D. R., Murray, A. J. Inorganic nitrate, hypoxia, and the regulation of cardiac mitochondrial respiration—probing the role of PPARα.

In vitro experimental models for examining the skeletal muscle cell biology of exercise: the possibilities, challenges and future developments

Exercise provides a cornerstone in the prevention and treatment of several chronic diseases. The use of in vivo exercise models alone cannot fully establish the skeletal muscle-specific mechanisms involved in such health-promoting effects. As such, models that replicate exercise-like effects in vitro provide useful tools to allow investigations that are not otherwise possible in vivo. In this review, we provide an overview of experimental models currently used to induce exercise-like effects in skeletal muscle in vitro. In particular, the appropriateness of electrical pulse stimulation and several pharmacological compounds to resemble exercise, as well as important technical considerations, are addressed. Each model covered herein provides a useful tool to investigate different aspects of exercise with a level of abstraction not possible in vivo. That said, none of these models are perfect under all circumstances, and the choice of model (and terminology) used should be informed by the specific research question whilst accounting for the several inherent limitations of each model. Further work is required to develop and optimise the current experimental models used, such as combination with complementary techniques during treatment, and thereby improve their overall utility and impact within muscle biology research.

Metabolic Effects of Dietary Nitrate in Health and Disease

Nitric oxide (NO), generated from L-arginine and oxygen by NO synthases, is a pleiotropic signaling molecule involved in cardiovascular and metabolic regulation. More recently, an alternative pathway for the formation of this free radical has been explored. The inorganic anions nitrate (NO₃^-) and nitrite (NO₂^-), originating from dietary and endogenous sources, generate NO bioactivity in a process involving seemingly symbiotic oral bacteria and host enzymes in blood and tissues. The described cardio-metabolic effects of dietary nitrate from experimental and clinical studies include lowering of blood pressure, improved endothelial function, increased exercise performance, and reversal of metabolic syndrome, as well as antidiabetic effects. The mechanisms underlying the salutary metabolic effects of nitrate are being revealed and include interaction with mitochondrial respiration, activation of key metabolic regulatory pathways, and reduction of oxidative stress. Here we review the recent advances in the nitrate-nitrite-NO pathway, focusing on metabolic effects in health and disease.

Discrete physiological effects of beetroot juice and potassium nitrate supplementation following 4-wk sprint interval training

The physiological and exercise performance adaptations to sprint interval training (SIT) may be modified by dietary nitrate ([Formula: see text]) supplementation. However, it is possible that different types of [Formula: see text] supplementation evoke divergent physiological and performance adaptations to SIT. The purpose of this study was to compare the effects of 4-wk SIT with and without concurrent dietary [Formula: see text] supplementation administered as either [Formula: see text]-rich beetroot juice (BR) or potassium [Formula: see text] (KNO3). Thirty recreationally active subjects completed a battery of exercise tests before and after a 4-wk intervention in which they were allocated to one of three groups: 1) SIT undertaken without dietary [Formula: see text] supplementation (SIT); 2) SIT accompanied by concurrent BR supplementation (SIT + BR); or 3) SIT accompanied by concurrent KNO3 supplementation (SIT + KNO3). During severe-intensity exercise, V̇o2peak and time to task failure were improved to a greater extent with SIT + BR than SIT and SIT + KNO3 ( P < 0.05). There was also a greater reduction in the accumulation of muscle lactate at 3 min of severe-intensity exercise in SIT + BR compared with SIT + KNO3 ( P < 0.05). Plasma [Formula: see text] concentration fell to a greater extent during severe-intensity exercise in SIT + BR compared with SIT and SIT + KNO3 ( P < 0.05). There were no differences between groups in the reduction in the muscle phosphocreatine recovery time constant from pre- to postintervention ( P > 0.05). These findings indicate that 4-wk SIT with concurrent BR supplementation results in greater exercise capacity adaptations compared with SIT alone and SIT with concurrent KNO3 supplementation. This may be the result of greater NO-mediated signaling in SIT + BR compared with SIT + KNO3.

NEW & NOTEWORTHY We compared the influence of different forms of dietary nitrate supplementation on the physiological and performance adaptations to sprint interval training (SIT). Compared with SIT alone, supplementation with nitrate-rich beetroot juice, but not potassium [Formula: see text], enhanced some physiological adaptations to training.

Dietary nitrate supplementation in cardiovascular health: an ergogenic aid or exercise therapeutic?

Oral consumption of inorganic nitrate, which is abundant in green leafy vegetables and roots, has been shown to increase circulating plasma nitrite concentration, which can be converted to nitric oxide in low oxygen conditions. The associated beneficial physiological effects include a reduction in blood pressure, modification of platelet aggregation, and increases in limb blood flow. There have been numerous studies of nitrate supplementation in healthy recreational and competitive athletes; however, the ergogenic benefits are currently unclear due to a variety of factors including small sample sizes, different dosing regimens, variable nitrate conversion rates, the heterogeneity of participants’ initial fitness levels, and the types of exercise tests used. In clinical populations, the study results seem more promising, particularly in patients with cardiovascular diseases who typically present with disruptions in the ability to transport oxygen from the atmosphere to working tissues and reduced exercise tolerance. Many of these disease-related, physiological maladaptations, including endothelial dysfunction, increased reactive oxygen species, reduced tissue perfusion, and muscle mitochondrial dysfunction, have been previously identified as potential targets for nitric oxide restorative effects. This review is the first of its kind to outline the current evidence for inorganic nitrate supplementation as a therapeutic intervention to restore exercise tolerance and improve quality of life in patients with cardiovascular diseases. We summarize the factors that appear to limit or maximize its effectiveness and present a case for why it may be more effective in patients with cardiovascular disease than as ergogenic aid in healthy populations.

High-Intensity Interval Training Is Equivalent to Moderate-Intensity Continuous Training for Short- and Medium-Term Outcomes of Glucose Control, Cardiometabolic Risk, and Microvascular Complication Markers in Men With Type 2 Diabetes

We sought to determine the efficacy of 12 weeks high-intensity interval training (HIIT), compared to moderate-intensity continuous training (MICT) on glucose control, cardiometabolic risk and microvascular complication markers in men living with type 2 diabetes (T2D). Both modalities were combined with resistance training (RT). Additionally, the study aimed to determine the medium-term durability of effects. After a 12-week, thrice weekly, training intervention incorporating either MICT+RT (n = 11) or HIIT+RT (n = 12), the study concluded with a 6-month follow-up analysis. The middle-aged study participants were obese, had moderate duration T2D and were taking multiple medications including insulin, statins and beta-blockers. Participants, randomized via the method of minimization, performed MICT (progressing to 26-min at 55% maximum estimated workload [eWLmax]) or HIIT (progressing to two variations in which twelve 1-min bouts at 95% eWLmax interspersed with 1-min recovery bouts, alternated with eight 30-s bouts at 120% eWLmax interspersed with 2:15 min recovery bouts) under supervision at an exercise physiology facility. To account for fixed and random effects within the study sample, mixed-effect models were used to determine the significance of change following the intervention and follow-up phases and to evaluate group^*time interactions. Beyond improvements in aerobic capacity (P < 0.001) for both groups, both training modalities elicited similar group^*time interactions (P > 0.05) while experiencing benefits for glycated hemoglobin (HbA1c; P = 0.01), subcutaneous adiposity (P < 0.001), and heart rate variability (P = 0.02) during the 12-week intervention. Adiposity (P < 0.001) and aerobic capacity (P < 0.001) were significantly maintained in both groups at the 6-month follow-up. In addition, during the intervention, participants in both MICT+RT and HIIT+RT experienced favorable reductions in their medication usage. The study reported the inter-individual variability of change within both groups, the exaggerated acute physiological responses (using exercise termination indicators) that occurred during the interventions as well as the incidence of precautionary respite afforded in such a study sample. To reduce hyperglycaemia, and prevent further deterioration of cardiometabolic risk and microvascular complication markers (in both the short- and medium-term), future strategies that integrate the adoption and maintenance of physical activity as a cornerstone in the treatment of T2M for men should (cognisant of appropriate supervision) include either structured MICT+RT, or HIIT+RT. Clinical Trials Registration Number: ACTRN12617000582358 http://www.anzctr.org.au/default.aspx.

Anti-obesity and anti-diabetic effects of nitrate and nitrite

Prevalence of obesity is increasing worldwide and type 2 diabetes to date is the most devastating complication of obesity. Decreased nitric oxide bioavailability is a feature of obesity and diabetes that links these two pathologies. Nitric oxide is synthesized both by nitric oxide synthase enzymes from l-arginine and nitric oxide synthase-independent from nitrate/nitrite. Nitric oxide production from nitrate/nitrite could potentially be used for nutrition-based therapy in obesity and diabetes. Nitric oxide deficiency also contributes to pathogeneses of cardiovascular disease and hypertension, which are associated with obesity and diabetes. This review summarizes pathways for nitric oxide production and focuses on the anti-diabetic and anti-obesity effects of the nitrate-nitrite-nitric oxide pathway. In addition to increasing nitric oxide production, nitrate and nitrite reduce oxidative stress, increase adipose tissue browning, have favorable effects on nitric oxide synthase expression, and increase insulin secretion, all effects that are potentially promising for management of obesity and diabetes. Based on current data, it could be suggested that amplifying the nitrate-nitrite-nitric oxide pathway is a diet-based strategy for increasing nitric oxide bioavailability and the management of these two interlinked conditions. Adding nitrate/nitrite to drugs that are currently used for managing diabetes (e.g. metformin) and possibly anti-obesity drugs may also enhance their efficacy.

Effects of supervised exercise and dietary nitrate in older adults with controlled hypertension and/or heart failure with preserved ejection fraction

Aerobic exercise training is an effective therapy to improve peak aerobic power (peak VO₂) in individuals with hypertension (HTN, AHA/ACC class A) and heart failure patients with preserved ejection fraction (HFpEF). High nitrate containing beetroot juice (BRJ) also improves sub-maximal endurance and decreases blood pressure in both HTN and HFpEF. We hypothesized that combining an aerobic exercise and dietary nitrate intervention would result in additive or even synergistic positive effects on exercise tolerance and blood pressure in HTN or HFpEF. We report results from two pilot studies examining the effects of supervised aerobic exercise combined with dietary nitrate in patients with controlled HTN (n = 26, average age 65 ± 5 years) and in patients with HFpEF (n = 20, average age 69 ± 7 years). All patients underwent an aerobic exercise training regimen; half were randomly assigned to consume a high nitrate-containing beet juice beverage (BRJ containing 6.1 mmol nitrate for the HFpEF study consumed three times a week and 8 mmol nitrate for the HTN study consumed daily) while the other half consumed a beet juice beverage with the nitrate removed (placebo). The main result was that there was no added benefit observed for any outcomes when comparing BRJ to placebo in either HTN or HFpEF patients undergoing exercise training (p ≥ 0.14). There were within-group benefits. In the pilot study in patients with HFpEF, aerobic endurance (primary outcome), defined as the exercise time to volitional exhaustion during submaximal cycling at 75% of maximal power output, improved during exercise training within each group from baseline to end of study, 369 ± 149 s vs 520 ± 257 s (p = 0.04) for the placebo group and 384 ± 129 s vs 483 ± 258 s for the BRJ group (p = 0.15). Resting systolic blood pressure in patients with HFpEF also improved during exercise training in both groups, 136 ± 16 mm Hg vs 122 ± 3 mm Hg for the placebo group (p < 0.05) and 132 ± 12 mm Hg vs 119 ± 9 mm Hg for the BRJ group (p < 0.05). In the HTN pilot study, during a treadmill graded exercise test, peak oxygen consumption (primary outcome) did not change significantly, but time to exhaustion (also a primary outcome) improved in both groups, 504 ± 32 s vs 601 ± 38 s (p < 0.05) for the placebo group and 690 ± 38 s vs 772 ± 95 s for the BRJ group (p < 0.05) which was associated with a reduction in supine resting systolic blood pressure in BRJ group. Arterial compliance also improved during aerobic exercise training in both the HFpEF and the HTN patients for both BRJ and placebo groups. Future work is needed to determine if larger nitrate doses would provide an added benefit to supervised aerobic exercise in HTN and HFpEF patients.