Impact of glutamine supplementation on glucose homeostasis during and after exercise

Cystine/Glutamine Mixture Supplementation Attenuated Fatigue during Endurance Exercise in Healthy Young Men by Enhancing Fatty Acid Utilization

Exercise-induced fatigue is a multi-origin physical and mental phenomenon. Efforts to diminish the above predisposition may contribute to endurance, along with athletic well-being, while development of nutritional strategies to optimize condition and exercise performance are essential issues for athletes and trainers. Dietary amino acids are being discussed for their specific health-promoting properties beyond their role as building blocks of proteins. Glutamine, along with cysteine, are two kinds of amino acids that are reported extensively for their anti-oxidation, anti-inflammation, and immune-regulation properties, and are promising in sport applications. In the present study, we designed a randomized, placebo-controlled, crossover trial to examine effects of 7-day supplementation of cystine/glutamine mixture (Cys2/Gln) on self-reporting fatigue index (ratings of perceived exertion, RPE), energy metabolism, and inflammation. We also employed a C2C12 myotube model to examine the capacity of cystine for fatty acid utilization. Cys2/Gln supplementation alleviated fatigue by decreasing RPE and enhanced fatty acid oxidation during a 60 min endurance exercise in human trials, while cystine increased fatty acid utilization in C2C12 myotubes by enhancing mitochondrial respiration. In summary, Cys2/Gln supplementation exerts positive effects on ameliorating exercise-induced fatigue, mechanisms of which can be attributed to enhancement of fatty acid utilization.

Metabolomics approach to investigate the ergogenic effect of Morinda citrifolia L. leaf extract on obese Sprague Dawley rats

INTRODUCTION

Natural products are obtaining much acceptance as ergogenic aid, not only among athletes but also among the general population including people with excess body fat. Under normal circumstances, an obese person will have the desire and ability to exercise reduced; mainly because they are easily fatigued. Thus, they need to boost their energy production so that they can be more active and healthier.

OBJECTIVE

In this present work, Morinda citrifolia L. leaf extract (MLE) which is believed to possess ergogenic property, was evaluated on its effect on an obese animal model using ¹ H-NMR based metabolomics.

MATERIAL AND METHODS

Rats were fed with high fat diet (HFD) for 12 weeks for obese development. Once this was achieved, all the rats underwent endurance exercise (forced swimming test) every 2 weeks for 8 weeks together with treatment. The time to exhaustion was recorded for each rat. Three different dosages of MLE: 50 mg/kg, 100 mg/kg and 200 mg/kg of body weight were used together with two positive controls: 5 mg/kg caffeine and 100 mg/kg green tea. Blood was collected before and after treatments for metabolomics study.

RESULTS

Findings showed that feeding the rats at a dose of 200 mg/kg body weight MLE significantly prolonged the exhaustive swimming time of the rats, and altered the metabolites present in their serum. Discriminating metabolites involved were the product of various metabolic pathways, including carbohydrate, lipids metabolism and energy metabolism. Treatment with 200 mg/kg body weight MLE resulted in significant improvement in the metabolic perturbations where the proximity of the obese exercised treated group to that of normal exercised group in the partial least squares discriminant analysis score plot was observed.

CONCLUSION

The present work demonstrated ergogenic property of MLE based on the improved metabolic perturbation in exercised obese rats.

Metabolome-Wide Association Study of the Relationship Between Habitual Physical Activity and Plasma Metabolite Levels

We identified plasma metabolites associated with habitual physical activity among 5,197 US participants from the Nurses' Health Study (NHS), Nurses' Health Study II (NHS II), and the Health Professionals Follow-up Study (HPFS). Physical activity was assessed every 2-4 years via self-report questionnaires. Blood was collected in the NHS in 1989-1990, in NHS II during 1996-1999, and in the HPFS during 1993-1995. Metabolic profiling was conducted by liquid chromatography-mass spectrometry. Our study included 337 known metabolites, with 256 of them classified as lipids. We corrected for multiple testing by controlling the tail probability of the proportion of false positives (TPPFP) and accounted for correlated tests using bootstrapping. Physical activity was significantly associated with 20 metabolites after correction for multiple testing (TPPFP < 0.05), and positive associations were found for most of the metabolites, including 2 amino acids (citrulline and glycine), 4 cholesteryl esters (C18:2, C18:1, C16:0, C18:3), 8 phosphocholines (PCs) (C36:4 PC-A, C34:3 PC plasmalogen, C36:3 PC plasmalogen, C34:2 PC plasmalogen, C36:2 PC) and lysophosphatidylcholines (C18:2, C20:5, C18:1), and 3 phosphatidylethanolamines (PEs) (C38:3 PE plasmalogen) and lysophosphatidylethanolamines (C18:2, C18:1). We independently replicated the 20 metabolites among 2,305 women in the Women's Health Initiative using 1993 data, and half of the metabolites were replicated. Our study may help identify biomarkers of physical activity and provide insight into biological mechanisms underlying the beneficial effect of being physically active on cardiometabolic health.

The Emerging Role of l-Glutamine in Cardiovascular Health and Disease

Emerging evidence indicates that l-glutamine (Gln) plays a fundamental role in cardiovascular physiology and pathology. By serving as a substrate for the synthesis of DNA, ATP, proteins, and lipids, Gln drives critical processes in vascular cells, including proliferation, migration, apoptosis, senescence, and extracellular matrix deposition. Furthermore, Gln exerts potent antioxidant and anti-inflammatory effects in the circulation by inducing the expression of heme oxygenase-1, heat shock proteins, and glutathione. Gln also promotes cardiovascular health by serving as an l-arginine precursor to optimize nitric oxide synthesis. Importantly, Gln mitigates numerous risk factors for cardiovascular disease, such as hypertension, hyperlipidemia, glucose intolerance, obesity, and diabetes. Many studies demonstrate that Gln supplementation protects against cardiometabolic disease, ischemia-reperfusion injury, sickle cell disease, cardiac injury by inimical stimuli, and may be beneficial in patients with heart failure. However, excessive shunting of Gln to the Krebs cycle can precipitate aberrant angiogenic responses and the development of pulmonary arterial hypertension. In these instances, therapeutic targeting of the enzymes involved in glutaminolysis such as glutaminase-1, Gln synthetase, glutamate dehydrogenase, and amino acid transaminase has shown promise in preclinical models. Future translation studies employing Gln delivery approaches and/or glutaminolysis inhibitors will determine the success of targeting Gln in cardiovascular disease.

Effects of Glutamine and Alanine Supplementation on Adiposity, Plasma Lipid Profile, and Adipokines of Rats Submitted to Resistance Training

Glutamine and alanine are lipogenic and could prevent the effects of resistance training (RT) in reducing adiposity and modulating lipid profile. Thus, we aimed to investigate the effects of RT and glutamine and alanine supplementation, in their free or conjugated form, on relative epididymal adipose tissue (EAT) and brown adipose tissue (BAT) weight, plasma lipid profile, and adipokines in EAT. Thirty Wistar rats, aged two months, were distributed into five groups: control (CTRL), trained (TRN), trained and supplemented with alanine (ALA), glutamine and alanine in their free form (GLN+ALA), or L-alanyl-L-glutamine (DIP). Trained groups underwent a ladder-climbing exercise for eight weeks, with progressive load increase. Supplementations were offered in a solution with a concentration of 4% in the last 21 days of training. Food consumption and body weight gain were decreased in the TRN group compared with CTRL. RT also reduced relative EAT and BAT weight, while supplementations, especially with ALA, increased adipose tissue mass. RT reduced total cholesterol (TC), triglycerides (TG), and low-density lipoprotein cholesterol (LDL-c) (TRN vs. CTRL), whereas glutamine and alanine supplementation increased TC and LDL-c, impairing lipid profile modulation by physical exercise. RT did not affect the concentrations of adipokines in EAT, but DIP supplementation increased interleukin- (IL-) 6 and IL-10. In conclusion, RT reduced adiposity and modulated lipid profile, whereas glutamine and alanine supplementation increased adiposity and impaired lipid profile but increased the concentration of the anti-inflammatory cytokines IL-6 and IL-10 in EAT.

Effects of Glutamine and Alanine Supplementation on Central Fatigue Markers in Rats Submitted to Resistance Training

Recent evidence suggests that increased brain serotonin synthesis impairs performance in high-intensity intermittent exercise and specific amino acids may modulate this condition, delaying fatigue. This study investigated the effects of glutamine and alanine supplementation on central fatigue markers in rats submitted to resistance training (RT). Wistar rats were distributed in: sedentary (SED), trained (CON), trained and supplemented with alanine (ALA), glutamine and alanine in their free form (G + A), or as dipeptide (DIP). Trained groups underwent a ladder-climbing exercise for eight weeks, with progressive loads. In the last 21 days, supplementations were offered in water with a 4% concentration. Albeit without statistically significance difference, RT decreased liver glycogen, and enhanced the concentrations of plasma glucose, free fatty acids (FFA), hypothalamic serotonin, and ammonia in muscle and the liver. Amino acids affected fatigue parameters depending on the supplementation form. G + A prevented the muscle ammonia increase by RT, whereas ALA and DIP augmented ammonia and glycogen concentrations in muscle. DIP also increased liver ammonia. ALA and G + A reduced plasma FFA, whereas DIP increased this parameter, free tryptophan/total tryptophan ratio, hypothalamic serotonin, and the serotonin/dopamine ratio. The supplementations did not affect physical performance. In conclusion, glutamine and alanine may improve or impair central fatigue markers depending on their supplementation form.

Glutamine Supplementation Increases Postprandial Energy Expenditure and Fat Oxidation in Humans

BACKGROUND

Glutamine interacts with insulin-mediated glucose disposal, which is a component of the increase in energy expenditure (EE) after a meal. The study aim was to examine if glutamine supplementation alters postmeal nutrient oxidation.

METHODS

Ten healthy young adults consumed a mixed meal (6.5 kcal/kg, 14%:22%:64% = protein:fat:carbohydrate) containing either glutamine (GLN:1.05 kcal/kg) or an isocaloric amino acid mixture (alanine: glycine:serine = 2:1:0.5; CON). GLN and CON treatments were administered on separate days in random order for each subject. EE, nonprotein respiratory quotient (RQ), and fat and carbohydrate oxidation rates were assessed using indirect calorimetry for 30 minutes before and for 360 minutes after meal ingestion.

RESULTS

Premeal EE and RQ were similar between treatments. The increase in EE above basal during both early (0-180 minutes) and late (180-360 minutes) postmeal phases was greater in GLN than in CON (p < .05), resulting in postmeal EE being 49% greater during the total postmeal phase (p < .05). Net change of carbohydrate oxidation was 38% higher during the early phase with GLN (p < .05), whereas it was 71% lower during the later phase (p < .05). GLN enhanced fat oxidation by approximately 42 kcal compared with CON during the late phase (p < .05).

CONCLUSIONS

Glutamine supplementation with a mixed meal alters nutrient metabolism to increase postmeal EE by increasing carbohydrate oxidation during the early postmeal phase and fat oxidation during the late postmeal phase. Consideration must be given to the potential that these postprandial changes in EE are related to glutamine-mediated changes in insulin action and consequently glucose disposal.

Does oral glutamine improve insulin sensitivity in adolescents with type 1 diabetes?

OBJECTIVE

The decline in insulin sensitivity (S_I) associated with puberty increases the difficulty of achieving glycemic control in adolescents with type 1 diabetes (T1D). The aim of this study was to determine whether glutamine supplementation affects blood glucose by enhancing S_I in adolescents with T1D.

METHODS

Thirteen adolescents with T1D (HbA1C 8.2 ± 0.1%) were admitted to perform afternoon exercise (four 15-min treadmill/5-min rest cycles of exercise) on two occasions within a 4-wk period. They were randomized to receive a drink containing either glutamine (0.25 g/kg) or placebo before exercise, at bedtime, and early morning in a double-blind, crossover design. Blood glucose was monitored overnight, and a hyperinsulinemic-euglycemic clamp was performed the following morning.

RESULTS

Blood glucose concentration dropped comparably during exercise on both days. However, the total number of nocturnal hypoglycemic events (17 versus 7, P = 0.045) and the cumulative probability of overnight hypoglycemia (50% versus 33%, P = 0.02) were higher on the glutamine day than on the placebo day. During clamp, glucose infusion rate was not affected by glutamine supplementation (7.7 ± 1 mg • kg^-1 • min^-1 versus 7.0 ± 1; glutamine versus placebo; P = 0.4).

CONCLUSIONS

Oral glutamine supplementation decreases blood glucose in adolescents with T1D after exercise. Insulin sensitivity, however, was unaltered during the euglycemic clamp. Although the mechanisms involved remain to be elucidated, studies to explore the potential use of glutamine to improve blood glucose control are needed.

Metabolites of Glutamate Metabolism Are Associated With Incident Cardiovascular Events in the PREDIMED PREvención con DIeta MEDiterránea (PREDIMED) Trial

BACKGROUND

Glutamate metabolism may play a role in the pathophysiology of cardiometabolic disorders. However, there is limited evidence of an association between glutamate-related metabolites and, moreover, changes in these metabolites, and risk of cardiovascular disease (CVD).

METHODS AND RESULTS

Plasma levels of glutamate and glutamine were measured at baseline and 1-year follow-up in a case-cohort study including 980 participants (mean age 68 years; 46% male) from the PREvención con DIeta MEDiterránea (PREDIMED) randomized trial, which assessed a Mediterranean diet intervention in the primary prevention of CVD. During median 4.8 years of follow-up, there were 229 incident CVD events (nonfatal stroke, nonfatal myocardial infarction, or CVD death). In fully adjusted models, per 1-SD, baseline glutamate was associated with 43% (95% CI: 16% to 76%) and 81% (39% to 137%) increased risk of composite CVD and stroke alone, respectively, and baseline glutamine-to-glutamate ratio with 25% (6% to 40%) and 44% (25% to 58%) decreased risk of composite CVD and stroke alone, respectively. Associations appeared linear for stroke (both Plinear trend≤0.005). Among participants with high baseline glutamate, the interventions lowered CVD risk by 37% compared to the control diet; the intervention effects were not significant when baseline glutamate was low (Pinteraction=0.02). No significant effect of the intervention on year-1 changes in metabolites was observed, and no effect of changes themselves on CVD risk was apparent.

CONCLUSIONS

Baseline glutamate was associated with increased CVD risk, particularly stroke, and glutamine-to-glutamate ratio was associated with decreased risk. Participants with high glutamate levels may obtain greater benefits from the Mediterranean diet than those with low levels.

CLINICAL TRIAL REGISTRATION

URL: www.controlled-trials.com. Unique identifier: ISRCTN 35739639.

Metabolite profiling identifies pathways associated with metabolic risk in humans

BACKGROUND

Although metabolic risk factors are known to cluster in individuals who are prone to developing diabetes mellitus and cardiovascular disease, the underlying biological mechanisms remain poorly understood.

METHODS AND RESULTS

To identify pathways associated with cardiometabolic risk, we used liquid chromatography/mass spectrometry to determine the plasma concentrations of 45 distinct metabolites and to examine their relation to cardiometabolic risk in the Framingham Heart Study (FHS; n=1015) and the Malmö Diet and Cancer Study (MDC; n=746). We then interrogated significant findings in experimental models of cardiovascular and metabolic disease. We observed that metabolic risk factors (obesity, insulin resistance, high blood pressure, and dyslipidemia) were associated with multiple metabolites, including branched-chain amino acids, other hydrophobic amino acids, tryptophan breakdown products, and nucleotide metabolites. We observed strong associations of insulin resistance traits with glutamine (standardized regression coefficients, -0.04 to -0.22 per 1-SD change in log-glutamine; P<0.001), glutamate (0.05 to 0.14; P<0.001), and the glutamine-to-glutamate ratio (-0.05 to -0.20; P<0.001) in the discovery sample (FHS); similar associations were observed in the replication sample (MDC). High glutamine-to-glutamate ratio was associated with lower risk of incident diabetes mellitus in FHS (odds ratio, 0.79; adjusted P=0.03) but not in MDC. In experimental models, administration of glutamine in mice led to both increased glucose tolerance (P=0.01) and decreased blood pressure (P<0.05).

CONCLUSIONS

Biochemical profiling identified circulating metabolites not previously associated with metabolic traits. Experimentally interrogating one of these pathways demonstrated that excess glutamine relative to glutamate, resulting from exogenous administration, is associated with reduced metabolic risk in mice.

A randomized cross-over study of the metabolic and hormonal responses following two preoperative conditioning drinks

OBJECTIVE

Preoperative conditioning with carbohydrate-based drinks attenuates postoperative insulin resistance and leads to clinical benefits. The use of metabolic conditioning agents such as glutamine and antioxidants, in addition to carbohydrate, may benefit patients undergoing major surgery, because glutamine and antioxidant supplementation have been shown to improve gastrointestinal perfusion, immune function, morbidity, and gluco-metabolic control in critically ill patients. We investigated the postprandial responses after ingestion of a clear carbohydrate drink (CCD) containing 50 g of carbohydrate (preOp, Nutricia, Trowbridge, UK) and that of another drink containing 50 g of carbohydrate, 15 g of glutamine, and antioxidants (ONS; Fresenius Kabi, Bad Homburg, Germany).

METHODS

Twelve overnight-fasted healthy male subjects ingested one of the drinks in a randomized, double-blinded, cross-over manner, after which blood was sampled for 360 min for measurement of glucose, insulin, glucagon, non-esterified fatty acids, β-hydroxybutyrate and glutamine.

RESULTS

The means ± standard errors for age and body mass index of participants were 21 ± 0.9 y and 23.2 ± 0.5 kg/m(2). After CCD ingestion, glucose and insulin concentrations peaked within 40 min (8.4 ± 0.4 mmol/L and 43.9 ± 3.8 mIU/L, respectively) and returned to baseline at 80 min (glucose 4.9 ± 0.3 mmol/L) and 140 min (insulin 5.5 ± 0.5 mIU/L). After ONS ingestion, peak glucose and insulin concentrations occurred within 40 min but were of a lower magnitude (6.6 ± 0.1 mmol/L and 29.6 ± 2.9 mIU/L, respectively). Glucose concentrations after ONS were higher than after CCD at 100 min.

CONCLUSION

Peak insulin and glucose concentrations were higher after CCD ingestion; in contrast, responses after ONS ingestion were "blunted" and prolonged.

Comparative effects of selected non-caffeinated rehydration sports drinks on short-term performance following moderate dehydration

BACKGROUND

The effect of moderate dehydration and consequent fluid replenishment on short-duration maximal treadmill performance was studied in eight healthy, fit (VO2max = 49.7 +/- 8.7 mL kg-1 min-1) males aged 28 +/- 7.5 yrs.

METHODS

The study involved a within subject, blinded, crossover, placebo design. Initially, all subjects performed a baseline exercise test using an individualized treadmill protocol structured to induce exhaustion in 7 to 10 min. On each of the three subsequent testing days, the subjects exercised at 70-75% VO2max for 60 min at 29-33 degrees C, resulting in a dehydration weight loss of 1.8-2.1% body weight. After 60 min of rest and recovery at 22 C, subjects performed the same treadmill test to voluntary exhaustion, which resulted in a small reduction in VO2max and a decline in treadmill performance by 3% relative to the baseline results. Following another 60 min rest and recovery, subjects ingested the same amount of fluid lost in the form of one of three lemon-flavored, randomly assigned commercial drinks, namely Crystal Light (placebo control), Gatorade(R) and Rehydrate Electrolyte Replacement Drink, and then repeated the treadmill test to voluntary exhaustion.

RESULTS

VO2max returned to baseline levels with Rehydrate, while there was only a slight improvement with Gatorade and Crystal Light. There were no changes in heart rate or ventilation with all three different replacement drinks. Relative to the dehydrated state, a 6.5% decrease in treadmill performance time occurred with Crystal Light, while replenishment with Gatorade, which contains fructose, glucose, sodium and potassium, resulted in a 2.1% decrease. In contrast, treatment with Rehydrate, which comprises fructose, glucose polymer, calcium, magnesium, sodium, potassium, amino acids, thiols and vitamins, resulted in a 7.3% increase in treadmill time relative to that of the dehydrated state.

CONCLUSIONS

The results indicate that constituents other than water, simple transportable monosaccharides and sodium are important for maximal exercise performance and effective recovery associated with endurance exercise-induced dehydration.

Glutamine and carbohydrate supplements reduce ammonemia increase during endurance field exercise

Blood ammonia concentration increases during endurance exercise and has been proposed as a cause for both peripheral and central fatigue. We examined the impact of glutamine and (or) carbohydrate supplementation on ammonemia in high-level runners. Fifteen men in pre-competitive training ran 120 min (~34 km) outdoors on 4 occasions. On the first day, the 15 athletes ran without the use of supplements and blood samples were taken every 30 min. After that, each day for 4 d before the next 3 exercise trials, we supplemented the athletes’ normal diets in bolus with carbohydrate (1 g·kg–1·d–1), glutamine (70 mg·kg–1·d–1), or a combination of both in a double-blind study. Blood ammonia level was determined before the run and every 30 min during the run. During the control trial ammonia increased progressively to approximately 70% above rest concentration. Following supplementation, independent of treatment, ammonia was not different (p > 0.05) for the first 60 min, but for the second hour it was lower than in the control (p < 0.05). Supplementation in high-level, endurance athletes reduced the accumulation of blood ammonia during prolonged, strenuous exercise in a field situation.

Determination of derivatized amino acids in human embryo culture media by gas chromatography

An adequate analytical method for determination of amino acids can provide a better insight in the metabolism of in vitro human embryo cultures, increasing the success rate of embryo implantation. Since individual amino acid amounts per embryo occur in the nanogram range, GC was the technique of choice, due to its inherent sensitivity and high sample throughput. Amino acids were analyzed as alkyl formate derivatives. The limits of detection (LOD) of all amino acids involved were in the sub-nmol range. The high risk of sample contamination proved to be the major analytical issue, but it could be overcome. For an extended method sensitivity, a simple preconcentration step could also be used.