Branch-chain amino acids: their metabolism and clinical utility

Aspartic Acid in Health and Disease

Aspartic acid exists in L- and D-isoforms (L-Asp and D-Asp). Most L-Asp is synthesized by mitochondrial aspartate aminotransferase from oxaloacetate and glutamate acquired by glutamine deamidation, particularly in the liver and tumor cells, and transamination of branched-chain amino acids (BCAAs), particularly in muscles. The main source of D-Asp is the racemization of L-Asp. L-Asp transported via aspartate-glutamate carrier to the cytosol is used in protein and nucleotide synthesis, gluconeogenesis, urea, and purine-nucleotide cycles, and neurotransmission and via the malate-aspartate shuttle maintains NADH delivery to mitochondria and redox balance. L-Asp released from neurons connects with the glutamate-glutamine cycle and ensures glycolysis and ammonia detoxification in astrocytes. D-Asp has a role in brain development and hypothalamus regulation. The hereditary disorders in L-Asp metabolism include citrullinemia, asparagine synthetase deficiency, Canavan disease, and dicarboxylic aminoaciduria. L-Asp plays a role in the pathogenesis of psychiatric and neurologic disorders and alterations in BCAA levels in diabetes and hyperammonemia. Further research is needed to examine the targeting of L-Asp metabolism as a strategy to fight cancer, the use of L-Asp as a dietary supplement, and the risks of increased L-Asp consumption. The role of D-Asp in the brain warrants studies on its therapeutic potential in psychiatric and neurologic disorders.

Dietary Supplementation With Branched Chain Amino Acids to Improve Sleep in Veterans With Traumatic Brain Injury: A Randomized Double-Blind Placebo-Controlled Pilot and Feasibility Trial

Study Objectives

Traumatic brain injury (TBI) is associated with chronic sleep disturbances and cognitive impairment. Our prior preclinical work demonstrated dietary supplementation with branched chain amino acids (BCAA: leucine, isoleucine, and valine), precursors to de novo glutamate production, restored impairments in glutamate, orexin/hypocretin neurons, sleep, and memory in rodent models of TBI. This pilot study assessed the feasibility and preliminary efficacy of dietary supplementation with BCAA on sleep and cognition in Veterans with TBI.

Methods

Thirty-two Veterans with TBI were prospectively enrolled in a randomized, double-blinded, placebo-controlled trial comparing BCAA (30 g, b.i.d. for 21-days) with one of two placebo arms (microcrystalline cellulose or rice protein, both 30 g, b.i.d. for 21-days). Pre- and post-intervention outcomes included sleep measures (questionnaires, daily sleep/study diaries, and wrist actigraphy), neuropsychological testing, and blood-based biomarkers related to BCAA consumption.

Results

Six subjects withdrew from the study (2/group), leaving 26 remaining subjects who were highly adherent to the protocol (BCAA, 93%; rice protein, 96%; microcrystalline, 95%; actigraphy 87%). BCAA were well-tolerated with few side effects and no adverse events. BCAA significantly improved subjective insomnia symptoms and objective sleep latency and wake after sleep onset on actigraphy.

Conclusion

Dietary supplementation with BCAA is a mechanism-based, promising intervention that shows feasibility, acceptability, and preliminary efficacy to treat insomnia and objective sleep disruption in Veterans with TBI. A larger scale randomized clinical trial is warranted to further evaluate the efficacy, dosing, and duration of BCAA effects on sleep and other related outcome measures in individuals with TBI.

Clinical Trial Registration

[http://clinicaltrials.gov/], identifier [NCT03990909].

The Food Energy/Protein Ratio Regulates the Rat Urea Cycle but Not Total Nitrogen Losses

Nitrogen balance studies have shown that a portion of the N ingested but not excreted is not accounted for. We compared several diets (standard, high-fat, high-protein, and self-selected cafeteria) to determine how diet-dependent energy sources affect nitrogen handling, i.e., the liver urea cycle. Diet components and rat homogenates were used for nitrogen, lipid, and energy analyses. Plasma urea and individual amino acids, as well as liver urea cycle enzyme activities, were determined. Despite ample differences in N intake, circulating amino acids remained practically unchanged in contrast to marked changes in plasma urea. The finding of significant correlations between circulating urea and arginine-succinate synthase and lyase activities supported their regulatory role of urea synthesis, the main N excretion pathway. The cycle operation also correlated with the food protein/energy ratio, in contraposition to total nitrogen losses and estimated balance essentially independent of dietary energy load. The different regulation mechanisms observed have potentially important nutritional consequences, hinting at nitrogen disposal mechanisms able to eliminate excess nitrogen under conditions of high availability of both energy and proteins. Their operation reduces urea synthesis to allow for a safe (albeit unknown) mechanism of N/energy excess accommodation.

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.

Metabolic profiling of goldfish (Carassius auratis) after long-term glyphosate-based herbicide exposure

Glyphosate is an efficient herbicide widely used worldwide. However, its toxicity to non-targeted organisms has not been fully elucidated. In this study, the toxicity of glyphosate-based herbicide was evaluated on goldfish (Carassius auratus) after long-term exposure. Tissues of brains, kidneys and livers were collected and submitted to NMR-based metabolomics analysis and histopathological inspection. Plasma was collected and the blood biochemical indexes of AST, ALT, BUN, CRE, LDH, SOD, GSH-Px, GR and MDA were measured. Long-term glyphosate exposure caused disorders of blood biochemical indexes and renal tissue injury in goldfish. Metabolomics analysis combined with correlation network analysis uncovered significant perturbations in oxidative stress, energy metabolism, amino acids metabolism and nucleosides metabolism in glyphosate dosed fish, which provide new clues to the toxicity of glyphosate. This integrated metabolomics approach showed its applicability in discovering the toxic mechanisms of pesticides, which provided new strategy for the assessment of the environmental risk of herbicides to non-target organisms.

Sarcopenia in Patients with Chronic Liver Disease: Can It Be Altered by Diet and Exercise?

Sarcopenia, a loss of muscle mass, is being increasingly recognized to have a deleterious effect on outcomes in patients with chronic liver disease. Factors related to diet and the inflammatory nature of chronic liver disease contribute to the occurrence of sarcopenia in these patients. Sarcopenia adversely influences quality of life, performance, morbidity, success of transplantation, and even mortality. Specific deficiencies in macronutrients (protein, polyunsaturated fatty acids) and micronutrients (vitamins C, D, and E, carotenoids, and selenium) have been linked to sarcopenia. Lessons learned from nutritional therapy in geriatric patient populations may provide strategies to manage sarcopenia in patients with liver disease. Combining diet modification and nutrient supplementation with an organized program of exercise may help ameliorate or even reverse the effects of sarcopenia on an already complex disease process.

Serum Amino Acid Profiles in Childhood Predict Triglyceride Level in Adulthood: A 7-Year Longitudinal Study in Girls

CONTEXT

Branched-chain and aromatic amino acids are associated with high risk of developing dyslipidemia and type II diabetes in adults.

OBJECTIVE

This study aimed to examine whether serum amino acid profiles associate with triglyceride concentrations during pubertal growth and predict hypertriglyceridemia in early adulthood.

DESIGN

This was a 7.5-year longitudinal study.

SETTING

The study was conducted at the Health Science Laboratory, University of Jyväskylä.

PARTICIPANTS

A total of 396 nondiabetic Finnish girls aged 11.2 ± 0.8 years at the baseline participated in the study.

MAIN OUTCOME MEASURES

Body composition was assessed by dual-energy x-ray absorptiometry; serum concentrations of glucose, insulin, and triglyceride by enzymatic photometric methods; and amino acids by nuclear magnetic resonance spectroscopy.

RESULTS

Serum leucine and isoleucine correlated significantly with future triglyceride, independent of baseline triglyceride level (P < .05 for all). In early adulthood (at the age of 18 years), these amino acids were significantly associated with hypertriglyceridemia, whereas fat mass and homeostasis model assessment of insulin resistance were not. Leucine was the strongest determinant discriminating subjects with hypertriglyceridemia from those with normal triglyceride level (area under the curve, 0.822; 95% confidence interval, 0.740-0.903; P = .000001).

CONCLUSIONS

Serum leucine and isoleucine were associated with future serum triglyceride levels in girls during pubertal growth and predicted hypertriglyceridemia in early adulthood. Therefore, these amino acid indices may serve as biomarkers to identify individuals at high risk for developing hypertriglyceridemia and cardiovascular disease later in life. Further studies are needed to elucidate the role these amino acids play in the lipid metabolism.

Metabolomics in dyslipidemia

Hyperlipidemia is an important public health problem with increased incidence and prevalence worldwide. Current clinical biomarkers, triglyceride, total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol lack the necessary specificity and sensitivity and only increase significantly after serious dyslipidemia. Therefore, sensitive biomarkers are needed for hyperlipidemia. Hyperlipidemia-specific biomarkers would improve clinical diagnosis and therapeutic treatment at early disease stages. The aim of metabolomics is to identify untargeted and global small-molecule metabolite profiles from cells, biofluids, and tissues. This method offers the potential for a holistic approach to improve disease diagnoses and our understanding of underlying pathologic mechanisms. This review summarizes analytical techniques, data collection and analysis for metabolomics, and metabolomics in hyperlipidemia animal models and clinical studies. Mechanisms of hypolipemia and antilipemic drug therapy are also discussed. Metabolomics provides a new opportunity to gain insight into metabolic profiling and pathophysiologic mechanisms of hyperlipidemia.

Metabolic and Physiological Roles of Branched-Chain Amino Acids

Branch chain amino acids (BCAAs) have unique properties with diverse physiological and metabolic roles. They have functions other than simple nutrition. Different diseases including metabolic disease lead to protein loss, especially muscle protein. Supplementation of BCAAs promotes protein synthesis and reduces break down, as well as improving disease conditions. They are important regulators of mTOR signaling pathway and regulate protein synthesis as well as protein turnover. BCAAs facilitate glucose uptake by liver and SK muscle and also enhance glycogen synthesis. Oxidation of BCAAs seems to be beneficial for metabolic health as their catabolism increases fatty acid oxidation and reduces risk of obesity. BCAAs are also important in immunity, brain function, and other physiological aspects of well-being. All three BCAAs are absolutely required for lymphocyte growth and proliferation. They are also important for proper immune cell function. BCAAs may influence brain protein synthesis, and production of energy and may influence synthesis of different neurotransmitters. BCAAs can be used therapeutically and future studies may be directed to investigating the diverse effects of BCAAs in different tissues and their signaling pathways.

Plasma metabolic biomarkers for syndrome of phlegm and blood stasis in hyperlipidemia and atherosclerosis

OBJECTIVE

To explore the plasma metabolite profiles in patients with the syndrome of phlegm and blood stasis in hyperlipidemia and atherosclerosis (As), and to search for the metabolic biomarkers of the syndrome.

METHODS

The plasma metabolite profiles of 31 patients with the syndrome of phlegm and blood stasis in hyperlipidemia and As, 6 patients with syndromes without phlegm and blood stasis, and 10 healthy subjects were analyzed by gas chromatography-mass spectrometry (GC-MS). Partial least squares-discriminant analyses (PLS-DA) were used to carry out the pattern-recognition analyses of the data. The plasma metabolic biomarkers of patients were obtained by variable importance plot value (VIP value) and Student's t-test. The structures of biomarkers were defined by the National Institute of Standards and Technology (NIST) database.

RESULTS

PLS-DA score plots of plasma metabolomes did not show overlap between the phlegm-blood stasis syndrome group and syndromes without phlegm and blood stasis group, whereas significant differences in the concentrations in the plasma of 5 metabolites were found (P < 0.05). They were identified as urine, isoleucine, glucuronic acid, palmitic acid and glycerol by searching in NIST database. The concentrations of four metabolites in the plasma of patients with syndrome of phlegm and blood stasis were higher than those with syndromes without phlegm and blood stasis, whereas the glycerol concentration was lower.

CONCLUSION

Compared with patients with syndromes without phlegm and blood stasis, five metabolites showed abnormal levels in patients with the syndrome of phlegm and blood stasis. These metabolites could be diagnostic and prognostic biomarkers.

Parenteral nutrition in liver resection

Albeit a very large number of experiments have assessed the impact of various substrates on liver regeneration after partial hepatectomy, a limited number of clinical studies have evaluated artificial nutrition in liver resection patients. This is a peculiar topic because many patients do not need artificial nutrition, while several patients need it because of malnutrition and/or prolonged inability to feeding caused by complications. The optimal nutritional regimen to support liver regeneration, within other postoperative problems or complications, is not yet exactly defined. This short review addresses relevant aspects and potential developments in the issue of postoperative parenteral nutrition after liver resection.

Supplements and the endocrine system in athletes

In the world of athletes' nutrition, there are many ethical concerns, because there is the suspicion that in practice, large doses of supplements in athletes are not taken for nutritional purposes. It is beyond the scope of this article to highlight the possible roles of supplements or methods of supplementation in the improvement of athletic performance in elite athletes. Instead, the author briefly reviews some of the substances taken by athletes, with particular attention to their mechanisms of action and the pathways involved. Very often, the effects of many supplements are hormone-related, or supplements influence hormone secretion. Examples of possible links between "supplements or ergogenic compounds" and the endocrine/metabolic system are addressed.

Relationship of taurine and other amino acids in plasma and in neutrophils of septic trauma patients

Recently, an interdependency of plasma taurine and other amino acids as well as metabolic and clinical variables implicating therapeutic options was reported. This result may be an indication that plasma taurine levels are directly related to intracellular levels. Therefore, the aim of this study was to analyse the possible relationship between taurine levels in plasma and in neutrophils, the relationship to other amino acids, and variables quantifying metabolic impairment and severity of sepsis in multiple trauma patients developing sepsis. After multiple trauma taurine decreased significantly in plasma in thirty-two patients as well as within the neutrophil and does not recover in sepsis. Lower individual levels in the neutrophil did not follow lower individual levels in plasma and no correlation of taurine in plasma and in the neutrophils could be observed. In sepsis, only plasma showed an interdependency of taurine, aspartate, and glutamate. No association between taurine plasma or intracellular levels and SOFA score as indicator for severity of sepsis or metabolic variables was observed. After multiple trauma and in sepsis, taurine uptake in cells (which is regulated in different ways), and intracellular taurine (which serves e.g. as an osmolyte) can be influenced. Therefore a prediction of the neutrophil taurine pool seems not fully possible from taurine plasma levels. Intracellular taurine has some unique properties explaining the missing interdependency despite some similarities in osmoregulation and metabolic interactions to other amino acids. The association of taurine, aspartate, and glutamate in plasma cannot be simply transferred to the neutrophils intracellular level. The clinical meaning of the plasma correlation remains unclear. A dependency of plasma and neutrophil taurine to severity of sepsis and to metabolic variables seems not possible because of the multifactorial pathophysiology of sepsis.

The effects of standard and branched chain amino acid enriched solutions on thermogenesis and energy expenditure in unconscious intensive care patients

BACKGROUND & AIMS

This study aims to compare the effects of standard and branched chain amino acid enriched solutions on thermogenesis and energy expenditure in unconscious and mechanically ventilated intensive care patients.

DESIGNS

The study was carried out at multidisciplinary intensive care unit. Twenty unconscious and mechanically ventilated patients (18-65 years of age) were included in the study. Patients were hemodynamically stable and all received continuous enteral nutrition. Energy expenditure was calculated using the Harris-Benedict Equation for all of the patients. Patients were randomly assigned to receive a 4h infusion of 0.4 g/kg protein as amino acid solution. Group I (n = 10) received standard amino acid solution and group II (n = 10) received branched chain amino acid enriched solution. Energy expenditure, oxygen consumption and carbon dioxide production were measured by indirect calorimetric method every 30 min during the 4h infusion period and 3h thereafter. Rectal temperature was recorded concomitantly with the metabolic measurements throughout the study.

RESULTS

There was a statistically significant increase in body temperature during the infusion of amino acid solution between 30 and 210 min in group I and between 30 and 120 min in group II (P <0.05). We observed a significant increase in energy expenditure at 30, 150, 180 and 210 min in group I and at 30-240 min in group II (P <0.05). There were no differences between the two groups in terms of thermogenesis or energy expenditure values during the study (P >0.05).

CONCLUSION

Thermogenesis and energy expenditure values were increased during the parenteral infusion of both standard amino acid and branched chain amino acid enriched solutions in unconscious intensive care patients without any significance in between.

The branched-chain amino acid requirement of parenterally fed neonatal piglets is less than the enteral requirement

The requirements for branched-chain amino acids (BCAA), isoleucine, leucine and valine, in neonates have not been determined previously. Furthermore, the BCAA are considered to be catabolized primarily in the muscle and their metabolism in the small intestine has received little attention. In this study, the parenteral and enteral BCAA requirements were determined by the indicator amino acid oxidation (IAAO) technique. Male Yorkshire piglets (n = 32) received amino acid-based diets containing adequate nutrients for 5 d. On d 6 and 8, the piglets were randomly assigned to one of the test diets containing a fixed ratio of BCAA (1:1.8:1.2; isoleucine/leucine/valine). Diets were infused continuously via intravenous catheters for parenterally fed piglets or via gastric catheters for enterally fed piglets. Phenylalanine kinetics and oxidation were determined from a 4-h primed, constant infusion of L-[1-(14)C]phenylalanine. Phenylalanine oxidation (% of dose) decreased linearly (P < 0.05) as the BCAA intake increased from 0.2 to 1.53 g/(kg. d) and from 0.2 to 2.64 g/(kg. d) for parenterally and enterally fed piglets, respectively, after which the phenylalanine oxidation was low and the slope was not different from zero. Using breakpoint analysis, the mean total BCAA requirements were determined to be 1.53 and 2.64 g/(kg. d) for parenterally and enterally fed piglets, respectively. Thus, the parenteral requirement for total BCAA is 56% of the enteral requirement, suggesting that 44% of total BCAA is extracted by first-pass splanchnic metabolism.

Metabolic approach of absence seizures in a genetic model of absence epilepsy, the GAERS: study of the leucine-glutamate cycle

We suggest that a dysregulation of energy metabolism in the brain of genetic absence epilepsy rats from Strasbourg (GAERS) could create a specific cerebral environment that would favor the expression of spike-and-wave discharges (SWD) in the thalamocortical loop, largely dependent on glutamatergic and gamma-aminobutyric acid (GABA)-ergic neurotransmissions. We tested several aspects of metabolic activity in the brain of GAERS compared to a genetic strain of nonepileptic (NE) rats. Glucose metabolism was higher in all brain regions of GAERS compared to those of NE rats along the whole glycolytic and aerobic pathways, as assessed by regional histochemical measurement of lactate dehydrogenase and cytochrome oxidase activities. Branched-chain amino acids (BCAA) and alpha-ketoisocaproate (alpha-KIC), the ketoacid of leucine, when injected intraperitoneally, increased the number of SWD in GAERS but had only a slight effect on their duration. These data speak in favor of a BCAA- or alpha-KIC-induced change in neuronal excitability. Leucine and alpha-KIC decreased the concentration of glutamate in thalamus and cortex without affecting GABA concentrations. Thus, BCAA and alpha-KIC, by decreasing glutamatergic neurotransmission, could favor GABAergic neurotransmission, which is known to increase the occurrence of seizures in GAERS. Finally, the transport of [1-(14)C]alpha-KIC in freshly isolated cortical neurons was lower in GAERS than in NE rats, and this difference was shown to be of metabolic origin. The addition of gabapentin, a specific inhibitor of BCAA transaminase (BCAT), reduced the transport of [1-(14)C]alpha-KIC in GAERS and NE rats to a level that became identical in both strains. This strain-dependent change was not related to a difference in the activity of BCAT, which was identical in GAERS and NE rats. The exact origin of this apparent metabolic dysregulation of energy metabolism in GAERS that could underlie the origin of seizures in that strain remains to be explored further.

Modulation of absence seizures by branched-chain amino acids: correlation with brain amino acid concentrations

The occurrence of absence seizures might be due to a disturbance of the balance between excitatory and inhibitory neurotransmissions in the thalamo-cortical loop. In this study, we explored the consequences of buffering the glutamate content of brain cells on the occurrence and duration of seizures in Genetic Absence Epilepsy Rats from Strasbourg (GAERS), a genetic model of generalized non-convulsive epilepsy. Branched-chain amino acids (BCAAs) and alpha-ketoisocaproate (alpha-KIC), the ketoacid of leucine were repeatedly shown to have a critical role in brain glutamate metabolism. Thus, GAERS were injected by intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) route with these compounds, then the effects on seizures were evaluated on the electroencephalographic recording. We also measured the concentration of amino acids in thalamus and cortex after an i.p. injection of leucine or alpha-KIC. Intracerebroventricular injections of leucine or alpha-KIC did not influence the occurrence of seizures, possibly because the substances reached only the cortex. BCAAs and alpha-KIC, injected intraperitoneally, increased the number of seizures whereas they had only a slight effect on their duration. Leucine and alpha-KIC decreased the concentration of glutamate in thalamus and cortex without affecting GABA concentrations. Thus, BCAAs and alpha-KIC, by decreasing the effects of glutamatergic neurotransmission could facilitate those of GABAergic neurotransmission, which is known to increase the occurrence of seizures in GAERS.

Endotoxemia affects organ protein metabolism differently during prolonged feeding in pigs

The metabolic response after sepsis is characterized by net protein loss. Nutritional intervention often is applied to sustain whole body protein mass under such circumstances. The manner in which protein metabolism of the different organs is affected under nutrition-supported and postseptic circumstances remains ambiguous. Therefore, we explored the changes in in vivo organ and whole body protein turnover after endotoxin-induced sepsis during enteral nutrition in pigs. The use of isotopes enabled simultaneous measurements of protein synthesis, breakdown and amino acid degradation across the portal-drained viscera (PDV; approximately intestine), liver and hindquarter ( approximately 50% skeletal muscle). All pigs received a continuous enteral infusion of a liquid meal equivalent to 0.3 g protein. kg bw(-1). h(-1) 3 d before and 4 d after a 24-h endotoxemia period. Measurements were performed 1 d before and 1 and 4 d after endotoxemia that was induced by a 24-h endotoxin (3 microg. kg bw(-1). h(-1) lipopolysaccharide, n = 7) infusion. Controls received NaCl (n = 7). At 4 d after endotoxemia, hindquarter protein turnover was increased, resulting in net synthesis. The amino acid output by the PDV was increased 1 and 4 d after endotoxemia. In the liver, net protein synthesis was enhanced 1 d after endotoxemia. Increased amino acid transamination in hindquarter and PDV led to glutamine and alanine effluxes that serve as substrates for liver and, possibly, the immune system. By providing substrate, enteral nutrition can sustain elevated amino acid demand in the postendotoxemic state by hindquarter, PDV and liver for protein synthesis and transamination processes.

The relationship between plasma taurine and other amino acid levels in human sepsis

Although reports of decreased plasma taurine in trauma, sepsis and critical illness are available, very little is known about the relationships among changes in plasma taurine, other amino acid levels and metabolic variables. We analyzed a large series of plasma amino acid profiles obtained in trauma patients with sepsis who were undergoing total parenteral nutrition. The correlations between plasma taurine, other amino acid levels, parenteral substrate doses and metabolic and cardiorespiratory variables were assessed by regression analysis. Post-traumatic hypotaurinemia was followed by partial recovery toward less abnormal values when sepsis developed. Levels of taurine were directly and significantly related to levels of glutamate, aspartate, beta-alanine and phosphoethanolamine (and unrelated to other amino acids). Levels of these amino acids increased simultaneously with increasing doses of leucine, isoleucine and valine in total parenteral nutrition. Decreasing taurine was associated with increasing lactate, arteriovenous O(2) concentration difference and respiratory index, and with decreasing cholesterol and cardiac index. These results characterize the relationships between plasma taurine and other amino acid levels in sepsis, provide evidence of amino acid interactions that may support taurine availability and show more severe decreases in plasma taurine with the worsening of metabolic and cardiorespiratory patterns.

Cytokine hypothesis of overtraining: a physiological adaptation to excessive stress?

Overtraining syndrome (OTS) is a condition wherein an athlete is training excessively, yet performance deteriorates. This is usually accompanied by mood/behavior changes and a variety of biochemical and physiological alterations. Presently, there is no global hypothesis to account for OTS. The present paper will attempt to provide a unifying paradigm that will integrate previous research under the rubric of the cytokine hypothesis of overtraining. It is argued that high volume/intensity training, with insufficient rest, will produce muscle and/or skeletal and/or joint trauma. Circulating monocytes are then activated by injury-related cytokines, and in turn produce large quantities of proinflammatory IL-1beta, and/or IL-6, and/or TNF-alpha, producing systemic inflammation. Elevated circulating cytokines then co-ordinate the whole-body response by: a) communicating with the CNS and inducing a set of behaviors referred to as "sickness" behavior, which involves mood and behavior changes that support resolution of systemic inflammation: b) adjusting liver function, to support the up-regulation of gluconeogenesis, as well as de novo synthesis of acute phase proteins, and a concomitant hypercatabolic state; and c) impacting on immune function. Theoretically, OTS is viewed as the third stage of Selye's general adaptation syndrome, with the focus being on recovery/survival, and not adaptation, and is deemed to be "protective," occurring in response to excessive physical/physiological stress. Recommendations are made for potential markers of OTS, based on a systemic inflammatory condition.

Acute amino acids supplementation enhances pituitary responsiveness in athletes

PURPOSE

The purpose of this study was to determine the effect of a mixture of amino acids on pituitary responsiveness to a stimulation test (GnRH + CRH) in athletes.

METHODS

In a double blinded counterbalanced experimental protocol, 10 moderately trained male athletes performed the pituitary stimulation test 60 min after a single oral administration of a placebo (P1-AS) or an amino acid mixture solution (AS) (L-arginine hydrochloride 100 mg x kg(-1) + L-ornithine hydrochloride 80 mg x kg(-1) + L-branched chain amino acids 140 mg x kg(-1): 50% L-leucine, 25% L-isoleucine, 25% L-valine) on two different occasions. Plasma ACTH, LH, FSH, GH, and cortisol were evaluated before (-60, -30, 0 min) and after (+15, +30, +45, +60, +90 min) the stimulation test.

RESULTS

The ACTH, LH and FSH response to CRH + GnRH was significantly higher in AS group both as absolute values and area under curve (AUC) values than in P1-AS group. Pre-test and post-test cortisol AUC levels were significantly higher in P1-AS group although a higher percent increase in post-test cortisol was found in AS group. The total GH-AUC was higher in AS group and, as expected, the absolute GH concentrations at different time points were not influenced by CRH + GnRH administration.

CONCLUSION

The amino acid mixture used enhanced the ACTH, LH, and FSH response to CRH + GnRH.

[Protein requirements in children during states of stress. Committee on Nutrition of the French Society of Pediatrics]

Acute and chronic stress conditions affecting critically ill children are characterized by severe protein breakdown and growth failure. This paper describes the disorders of protein metabolism, and gives recommendations for protein and energy intakes during stress conditions in children.

Branched-chain amino acid-induced hippocampal norepinephrine release is antagonized by picrotoxin: evidence for a central mode of action

Previous studies indicated that administration of a 1:1:1 mixture of the branched-chain amino acids leucine, isoleucine, and valine (BCAA) decreased the response to pain. The present study investigates the effects of BCAA on release of norepinephrine (NE) from isolated hippocampal brain slices. BCAA evoked 3H-NE release in a concentration-dependent manner. This effect was antagonized by the gamma aminobutyric acid (GABA) receptor antagonist picrotoxin, again in a concentration-dependent manner, suggesting that the effect may be mediated via a GABA receptor. Given the role of NE and of GABA receptors in the central response to pain, it is possible that the BCAA may exert their antinociceptive properties through activation of GABA receptors.

Nutrition management in the ICU

Nutrition support plays an important role in the management of nutritional deficiencies in properly selected critically ill patients. A full nutritional assessment allows the calculation of appropriate feeding goals. The route of feeding, enteral or parenteral, is determined by the presence or absence of a functioning intestine and hemodynamic status of the patient. The specific roles of carbohydrates, fats, and protein need to be considered in order to prevent overfeeding and other complications. The efficacy of certain disease-specific enteral formulas has been demonstrated in clinical trials, however, careful cost-benefit analyses are required.

Modulation of pentylenetetrazol-induced seizure activity by branched-chain amino acids and alpha-ketoisocaproate

Branched-chain amino acids, and mainly leucine act as nitrogen donors in the cerebral glutamate-glutamine cycle, thereby reducing brain excitability. Rats equipped with cortical electrodes received 300 mg/kg of leucine, isoleucine, valine or the ketoacid of leucine, alpha-ketoisocaproate at 2 h before the induction of seizures by 40 mg/kg pentylenetetrazol. Control groups received saline or a commercial mixture of amino acids, Vamine(R). Leucine and isoleucine increased the latency to absence-like and tonic-clonic seizures but did not influence the duration of the tonic-clonic seizure. Vamine(R), valine and alpha-ketoisocaproate had no effect. These data are consistent with the role of leucine in buffering brain glutamate concentration.

The effects of branched chain amino acid infusion on pain perception and plasma concentrations of monoamines

Infusions of branched chain amino acids (BCAA) have been shown to have several CNS-mediated effects including antinociceptive action. We investigated the effects of BCAA infusion on pain perception, respiratory control, and plasma monoamine concentrations. Six healthy female volunteers were given in a double-blind, random, crossover design an 8-h infusion (1.75 ml/kg/h) of either (a) Ringers lactate, (b) conventional 4% amino acid solution, or (c) 4% BCAA solution with intervals of at least 48 h. Respiratory control was evaluated with continuous capnography. Pain perception was measured using dental dolorimetry for sharp pain, and pain transmitted by afferent C-fibers was evaluated with tourniquet test. Changes in vigilance were measured using critical flicker fusion technique. Evaluations were made for baseline, and after 2.5, 5, and 8 h. Plasma samples were collected at the same time points for amino acid and monoamine analysis. BCAA infusion resulted in significant increases of plasma concentrations of all BCAAs, with a simultaneous decrease in concentrations of aromatic amino acids. Of the measured monoamines and their metabolites dihydroxyphenylacetic acid (DOPAC) decreased, showing significant treatment effect for BCAA. Despite these changes no significant effect of BCAAs on respiratory control, vigilance, or pain perception was observed. In conclusion, despite significant changes in plasma concentrations of both amino acids and DOPAC, BCAA infusion did not show any clinically relevant antinociceptive effect.

Parenteral administration of different amounts of branch-chain amino acids in septic patients: clinical and metabolic aspects

OBJECTIVE

To study the effects of a total parenteral nutrition solution changing branch-chain amino acid concentrations and/or nitrogen supply on protein metabolism, length of stay, and mortality rate; and to evaluate the unique metabolic status of sepsis that leads to a search for specific total parenteral nutrition formulas.

DESIGN

Prospective, randomized, and multicenter study.

SETTING

Intensive care units (ICUs) in seven university hospitals.

PATIENTS

Sixty-nine septic patients.

MEASUREMENTS AND MAIN RESULTS

The patients were randomized into three groups according to the total parenteral nutrition administered. Group A (n = 22) and B (n = 25) patients received 1.5 g of amino acids/kg/day with a nonprotein ratio of 100:1 calories/g of nitrogen, and a varying branch-chain amino acids percentage (group A [23%); group B [45%]). Group C patients were treated with 1.1 g/kg/day of amino acids with a nonprotein ratio of 140:1 calories/g of nitrogen and 45% branch-chain amino acids. All diets were isocaloric. Prealbumin, retinol-binding protein, nitrogen balance, and plasma amino acid profiles (24 amino acids) were determined at baseline and after 3, 7, and 11 days of total parenteral nutrition. The length of stay and the mortality rate in the ICU were recorded. At baseline (preparenteral nutrition), no differences in age, gender, severity of the condition, or clinical chemistry were found between the groups. Prealbumin and retinol-binding protein increased in groups B (p < .004, p < .002, respectively) and C (p < .001, p < .002, respectively). Plasma arginine increased significantly in group C (p < .05), and plasma valine (p < .0001, p < .04, respectively), leucine (p < .005, p < .03, respectively), and isoleucine (p < .001, p < .0001, respectively) increased significantly in groups B and C. The length of stay in the ICU did not change between the groups. The mortality rate in groups B and C was less than in group A (p < .03).

CONCLUSIONS

Our results suggest that the branch-chain amino acids-rich formulas (45%) show a beneficial effect in septic patients.

The antinociceptive effects of branched-chain amino acids: evidence for their ability to potentiate morphine analgesia

The effect of branched-chain amino acids (BCAA) on pain threshold was studied in rats. Nociception was induced by the hot-plate analgesia meter, a method measuring supraspinally organized pain responses. After a single intravenous injection of BCAA (320 mg/kg), the percent change in latency time to the pain response significantly increased by 19% in 60 min, and by 22% in 75 min (p < 0.005), as compared to an injection of an equal volume of a standard concentration of an amino acid solution or physiological saline. Subsequently, we studied the interaction of BCAA with opioid-type analgesia. In combination with intravenously injected morphine (3 mg/kg), BCAA significantly potentiated and prolonged the action of morphine using the hot-plate test. From 5 min after morphine injection, the latencies to a pain response were markedly higher with the combination of BCAA and morphine (+80% and +89% at 5 min after morphine injection, if BCAA was administered 45 or 60 min prior to morphine injection, respectively) when compared with the effect of morphine alone (+13% at 5 min; p < 0.005). BCAA demonstrated analgesic effects, which, in combination with morphine, potentiated and prolonged the antinociceptive action of morphine. BCAA may represent a new adjunct treatment modality for acute and chronic pain, and give us further insight into the mechanisms of pain control.

Arginine-enriched solution induces a marked increase in muscle glutamine concentration and enhances muscle protein synthesis in tumor-bearing rats

Using a transplantable Yoshida sarcoma in a rat model of total parenteral nutrition (TPN), we measured the effectiveness of an arginine-enriched amino acid solution (AI-82) on muscle glutamine concentration and muscle protein synthesis compared with that of a conventional amino acid solution (Proteamin12). After tumor-bearing rats had been given one of two isocaloric TPN regimens for 6 days, [15N]glycine (99 atom %) containing TPN solution was infused into animals at a constant rate of 8 mg of [15N]glycine per hour for 18 hours, after which the liver, skeletal muscle (gastrocnemius muscle), and tumor protein synthesis rates were measured. A significantly increased whole muscle protein synthesis rate was observed in the AI-82 group; there was no difference in the whole liver and tumor protein synthesis rates between the two groups. When each TPN solution was administered for 1 week, muscle concentrations of arginine, ornithine, glutamine, and glutamate were considerably higher in the AI-82 group than in the Proteamin12 group, and these differences were also accompanied by a decrease in the plasma branched-chain amino acid (BCAA) (leucine, isoleucine, and valine) levels in the AI-82 group. The high levels of muscle glutamine concentration in the AI-82 group were investigated in connection with the high use of exogenous branched-chain amino acids.

Effects of valine, leucine, isoleucine, and a balanced amino acid solution on the seizure threshold to picrotoxin in rats

During infusion of branched-chain amino acids (BCAAs) in humans, changes in ventilatory drive, sleeping pattern, and appetite have been reported. The mechanism by which BCAA exerts their effects on CNS remains unclear. An infusion of a BCAA solution (300 mg/kg) has previously been found to increase the seizure threshold in rats to the proconvulsant drug picrotoxin, an antagonist on the GABA-benzodiazepine receptor complex. In this study, each of the BCAAs given separately (valine, leucine, isoleucine; 300 mg/kg) (n = 10) increased the mean latency time to onset of seizures vs. placebo as an indication of an increased seizure threshold. A balanced amino acid solution (Vamin-Glucose) had no effect on the seizure threshold. Thus, these CNS effects are specific for BCAAs and occur with all three.

Nutritional support for liver transplantation: identifying caloric and protein requirements

OBJECTIVE

To characterize the caloric and protein requirements of patients with end-stage liver disease before and for 28 days after liver transplantation.

DESIGN

We prospectively assessed 16 adult patients who were scheduled to undergo liver transplantation between December 1989 and September 1990.

MATERIAL AND METHODS

Nitrogen balance, 24-hour urinary creatinine, 3-methylhistidine, and resting energy expenditure were determined before transplantation and on days 1, 3, 5, 14, and 28 after transplantation. The investigators were unaware of the results of these measurements, and patients were fed in accordance with a previously established clinical protocol.

RESULTS

Resting energy expenditure did not increase from preoperative values; however, urinary nitrogen and 3-methylhistidine increased significantly after liver transplantation, an indication of protein catabolism from a myofibrillar source. A negative nitrogen balance persisted for 28 days post-operatively.

CONCLUSION

We recommend that caloric intake be determined by using the formulation provided by the Harris-Benedict equation at ideal body weight plus 20%. We also recommend that intake of protein be adjusted on the basis of preoperative nutritional assessment, perioperative hepatic and renal function, and results of tests used to measure the adequacy of administered protein. Parenterally or enterally administered protein of more than 1.2 g/kg daily should be well tolerated in most patients who have undergone liver transplantation.

Amino acid loss and plasma concentration during continuous hemodiafiltration

Amino acid loss, plasma concentration, and the relationship between amino acid intake and balance during continuous hemodiafiltration (CHD) were investigated in a prospective, nonrandomized study of trauma patients exhibiting the systemic inflammatory response with acute renal failure. Data were compared with those from a group of similar patients who had maintained renal function (control). Both groups received similar amounts of nonprotein calories (3015 +/- 753 nonprotein calories per day in the control group vs 3077 +/- 1018 nonprotein calories per day in the CHD group) and amino acids (2.24 +/- 0.36 g/kg per day in the control group vs 2.19 +/- 0.48 g/kg per day in the CHD group) via the parenteral route. Amino acid solutions were either 19% or 45% branched-chain amino acid enriched. Studies were performed every 12 hours for a maximum of 6 days. Amino acid loss was 2.5 +/- 2.3 g/12 h in the control group vs 6.6 +/- 2.4 g/12 h in the CHD group (p < .0001). Increasing the dialysate rate from 15 to 30 mL/min increased amino acid loss from 5.7 +/- 1.7 to 7.9 +/- 2.6 g/12 h (p < .0001). Amino acid loss was unrelated to amino acid intake but was directly related to plasma amino acid concentration, CHD effluent volume, and the efficiency of filtration as measured by the ratio of filtered urea nitrogen to blood urea nitrogen (R2 = .69). A linear relationship was found between amino acid intake and balance (R2 = .991). The patterns of plasma amino acid concentrations were consistent with metabolic changes wrought by a combination of sepsis and multiple organ dysfunction and type of amino acid intake but seemed unaffected by increased amino acid loss in CHD effluent. Amino acid losses were 2 to 3 times greater from CHD than from normal kidney. However, CHD amino acid losses may not be clinically significant unless amino acid intake is restricted to levels used typically in traditional hemodialysis.

A sensible approach to the nutritional support of mechanically ventilated critically ill patients

OBJECTIVES

The goal of this review is to educate physicians in the details of nutritional support of mechanically ventilated critically ill patients.

DESIGN

The subtopics of this review include: introduction, goals of nutritional treatment, assessment of nutritional status, estimation of nutritional requirements, estimation of protein requirements, recommended approach to the initial nutritional regimen, route of nutrition, and monitoring the response to nutrition.

SETTING

The information is primarily germane to the medical management of patients with acute respiratory failure superimposed on chronic lung disease and malnutrition.

CONCLUSION

Malnutrition is prevalent in mechanically ventilated critically ill patients. Undernutrition is associated with respiratory muscle weakness and may contribute to ventilator dependency. Overnutrition may increase CO2 production and increase ventilatory demands. This review advocates a titrated approach to nutritional management based on protein balance. Careful monitoring is necessary to ensure a regimen which maintains or improves body protein composition. Preliminary data exists which indicates that careful nutritional support may improve clinical outcome but more information is needed to recommend a universal approach.