Branched-Chain Amino Acids and Insulin Resistance, from Protein Supply to Diet-Induced Obesity.

For more than a decade, there has been a wide debate about the branched-chain amino acids (BCAA) leucine, valine, and isoleucine, with, on the one hand, the supporters of their anabolic effects and, on the other hand, those who suspect them of promoting insulin resistance. Indeed, the role of leucine in the postprandial activation of protein synthesis has been clearly established, even though supplementation studies aimed at taking advantage of this property are rather disappointing. Furthermore, there is ample evidence of an association between the elevation of their plasma concentrations and insulin resistance or the risk of developing type 2 diabetes, although there are many confounding factors, starting with the level of animal protein consumption. After a summary of their metabolism and anabolic properties, we analyze in this review the factors likely to increase the plasma concentrations of BCAAs, including insulin-resistance. After an analysis of supplementation or restriction studies in search of a direct role of BCAAs in insulin resistance, we discuss an indirect role through some of their metabolites: branched-chain keto acids, C3 and C5 acylcarnitines, and hydroxyisobutyrate. Overall, given the importance of insulin in the metabolism of these amino acids, it is very likely that small alterations in insulin sensitivity are responsible for a reduction in their catabolism long before the onset of impaired glucose tolerance.

Citrulline production and protein homeostasis.

PURPOSE OF REVIEW: Protein homeostasis is crucial for maintaining cell functions. Citrulline, an endogenous amino acid, is considered as an efficient source of arginine at systemic and cellular level. Accumulating evidence, obtained from citrulline supplementation studies, suggest anabolic properties especially in malnourished rodents and human. Although these studies might suggest a key role for citrulline in protein homeostasis, the supraphysiological concentrations of citrulline do not allow to conclude on a physiological role. This review aimed to assess the role of endogenous citrulline production on protein homeostasis. RECENT FINDINGS: According to recent studies, endogenous citrulline, through its regulating effect on nitric oxide production, seems to play a key role in regulating endothelial and immune functions. We can assume that citrulline-dependent endothelial vasodilation could improve organ perfusion and thus amino acid and insulin supply. Furthermore, citrulline regulates immune cells and thus could regulate inflammation and indirectly protein metabolism. SUMMARY: Although we have currently no direct evidence of a regulating role of endogenous citrulline production on protein homeostasis, we can hypothesize that physiologically through its role in endothelial and immune function, citrulline could indirectly participate to protein homeostasis.

Effects of a Carbohydrate-, Glutamine-, and Antioxidant-Enriched Oral Nutrition Supplement on Major Surgery-Induced Insulin Resistance: A Randomized Pilot Study.

BACKGROUND: Insulin resistance after surgery hampers recovery. Oxidative stress is shown to be involved in the occurrence of postoperative insulin resistance. Preoperative carbohydrate-rich oral nutrition supplements reduce but do not prevent insulin resistance. The aim of the present study was to investigate the effect of a carbohydrate-, glutamine-, and antioxidant-enriched preoperative oral nutrition supplement on postoperative insulin resistance. METHODS: A double-blind randomized controlled pilot study in 18 patients with rectal cancer, who received either the supplement (S) or the placebo (P) 15, 11, and 4 hours preoperatively, was conducted. Insulin sensitivity was studied prior to surgery and on the first postoperative day using a hyperinsulinemic euglycemic 2-step clamp. RESULTS: Hepatic insulin sensitivity (insulin-mediated suppression of glucose production) decreased significantly after surgery in both groups, with no differences between the groups. Peripheral insulin sensitivity (glucose rate of disappearance, Rd) was significantly decreased after surgery in both groups (S: 37.2 [19.1-50.9] vs 20.6 [13.9-27.9]; P: 23.8 [15.7-35.5] vs 15.3 [12.6-19.1] µmol/kg·min) but less pronounced in the supplemented group (P = .04). The percentage decrease in glucose Rd did not differ between the groups. Adipose tissue insulin sensitivity (insulin-mediated suppression of plasma free fatty acids) decreased to the same extent after surgery in both groups. CONCLUSION: Rectal cancer surgery induced profound insulin resistance, affecting glucose and fatty acid metabolism. The preoperative nutrition supplement somewhat attenuated but did not prevent postoperative peripheral insulin resistance.

Influence of an ω3-fatty acid-enriched enteral diet with and without added glutamine on the metabolic response to injury in a rat model of prolonged acute catabolism.

OBJECTIVE: In critically ill patients, acute injury alters gut function, causing greater risk for sepsis and malnutrition. Peptide-enriched diets may promote nitrogen absorption, whereas ω3-enriched diets reduce alterations in gut barrier function. The aim of this study was to assess the effectiveness of a peptide- and ω3-enriched diet on the metabolic response to injury and the gut barrier function in a model of prolonged catabolism in the rat. Given the intestinal trophic effect of glutamine, we tested for a synergistic effect of glutamine. METHODS: We randomized 40 male Sprague-Dawley rats (250 g) into four groups to enterally receive a standard high-protein diet (S), or a peptide- and ω3-enriched diet either alone (IMN) or supplemented with glutamine and alanine supplied as dipeptide (DIP) or as free amino acids (AAs) for 4 d. Metabolic response to injury was induced by turpentine injections on days 1 and 3. At sacrifice, nutritional and inflammatory biomarkers and intestinal and liver function were assessed. RESULTS: Weight gain (+45-62%) and nitrogen balance (+33-56%) were significantly higher in all groups than in the S group. In jejunal mucosa, total glutathione was significantly higher (+20-30%) and myeloperoxidase activity significantly lower in all groups compared with the S group. Hepatic triacylglycerol content was significantly lower in the AA (0.30 ± 0.04 µM/g) and DIP (0.43 ± 0.08 µM/g) groups than in the S group (0.71 ± 0.08 µM/g). CONCLUSIONS: In this model of prolonged catabolism, compared with a standard diet, a peptide- and ω3-enriched diet improved metabolic response to injury, with better nitrogen balance and weight recovery, and decreased intestinal myeloperoxidase activity. Only marginal additional effects of glutamine supplementation were observed with decreased hepatic fat content.

Citrulline decreases hepatic endotoxin-induced injury in fructose-induced non-alcoholic liver disease: an ex vivo study in the isolated perfused rat liver.

Steatosis can sensitise the liver to various challenges and favour the development of non-alcoholic fatty liver disease (NAFLD). In this context, fructose feeding promotes endotoxin translocation from the gut, contributing to disease progression via an inflammatory process. Citrulline is protective against fructose-induced NAFLD; we hypothesised that this property might be related to its anti-inflammatory and antioxidative action against endotoxin-induced hepatic injuries. This hypothesis was evaluated in a model of perfused liver isolated from NAFLD rats. Male Sprague-Dawley rats (n 30) were fed either a standard rodent chow or a 60 % fructose diet alone, or supplemented with citrulline (1 g/kg per d) for 4 weeks. After an evaluation of their metabolic status, fasted rats received an intraperitoneal injection of lipopolysaccharide (LPS) (2·5 mg/kg). After 1 h, the livers were isolated and perfused for 1 h to study liver function and metabolism, inflammation and oxidative status. In vivo, citrulline significantly decreased dyslipidaemia induced by a high-fructose diet and insulin resistance. In the isolated perfused rat livers, endotoxaemia resulted in higher cytolysis (alanine aminotransferase release) and higher inflammation (Toll-like receptor 4) in livers of fructose-fed rats, and it was prevented by citrulline supplementation. Oxidative stress and antioxidative defences were similar in all three groups. Amino acid exchanges and metabolism (ammonia and urea release) were only slightly different between the three groups. In this context of mild steatosis, our results suggest that fructose-induced NAFLD leads to an increased hepatic sensitivity to LPS-induced inflammation. Citrulline-induced restriction of the inflammatory process may thus contribute to the prevention of NAFLD.

Oral arginine supplementation protects female mice from the onset of non-alcoholic steatohepatitis.

Dietary arginine (Arg) supplementation has been proposed to have positive effects on the development of liver diseases. In the present study, we investigate if an oral Arg supplementation in diet protects mice fed a fructose, fat and cholesterol enriched Western-style diet (WSD) from the development of non-alcoholic steatohepatitis (NASH). Female C57BL/6J mice were fed a liquid control diet or a liquid WSD ± Arg (2.49 g/kg body weight/day) for 6 weeks. Indices of liver injury, glucose metabolism and intestinal permeability were determined. While Arg supplementation had no effects on body weight gain, fasting blood glucose levels were significantly lower in WSD+Arg-fed mice than in C+Arg-fed animals. WSD-fed mice developed liver steatosis accompanied with inflammation, both being significantly attenuated in WSD+Arg-fed mice. These effects of Arg supplementation went along with a protection against WSD-induced decreased tight junction protein levels in the upper parts of the small intestine, increased levels of bacterial endotoxin in portal plasma as well as increased hepatic toll-like receptor-4 mRNA and 4-hydroxynonenal protein adduct levels. In conclusion, Arg supplementation may protect mice from the development of NASH.

Oral citrulline supplementation protects female mice from the development of non-alcoholic fatty liver disease (NAFLD).

PURPOSE: Impairments of intestinal barrier function are discussed as risk factors for the development and progression of non-alcoholic fatty liver disease (NAFLD). Studies suggest an association between arginine/citrulline homeostasis and the development of liver damages. Here, the effect of an oral L-citrulline (Cit) supplement on the development of a Western-style diet (WSD)-induced NAFLD was determined in mice. METHODS: Female 6- to 8-week-old C57BL/6J mice were either pair-fed a liquid Western-style or control diet (C) ± 2.5 g/kg bodyweight Cit for 6 weeks (C + Cit or WSD + Cit). Indices of liver damage, glucose metabolism, intestinal barrier function and NO synthesis were measured. RESULTS: While bodyweight gain was similar between groups, markers of glucose metabolism like fasting blood glucose and HOMA index and markers of liver damage like hepatic triglyceride levels, number of neutrophils and plasminogen activator inhibitor-1 protein levels were significantly lower in WSD + Cit-fed mice when compared to WSD-fed mice only. Protein levels of the tight junction proteins occludin and zonula occludens-1 in duodenum were significantly lower in mice fed a WSD when compared to those fed a WSD + Cit (-~70 and -~60 %, respectively, P < 0.05), whereas portal endotoxin levels, concentration of 3-nitrotyrosine protein adducts in duodenum and toll-like receptor-4 mRNA expression in livers of WSD + Cit-fed mice were markedly lower than in WSD-fed mice (-~43 %, P = 0.056; -~80 and -~48 %, respectively, P < 0.05). CONCLUSION: Our data suggest that the protective effects of supplementing Cit on the development of NAFLD in mice are associated with a decreased translocation of endotoxin into the portal vein.

Indications and contraindications for infusing specific amino acids (leucine, glutamine, arginine, citrulline, and taurine) in critical illness.

PURPOSE OF REVIEW: The review assesses the utility of supplementing parenteral or enteral nutrition of ICU patients with each of five specific amino acids that display pharmacological properties. Specifying indications implies also stating contraindications.Combined supplementation of amino acids with ω3-fatty acids and/or trace elements (immune-enhancing diets) will not be considered in this review because these mixtures do not allow the role of amino acids in the effect (positive or negative) of the mixture to be isolated, and so cannot show whether or not supplementation of a given amino acid is indicated. RECENT FINDINGS: After decades of unbridled use of glutamine (GLN) supplementation in critically ill patients, recent large trials have brought a note of caution, indicating for example that GLN should not be used in patients with multiple organ failure. Yet these large trials do not change the conclusions of recent meta-analyses. Arginine (ARG), as a single dietary supplement, is probably not harmful in critical illness, in particular in a situation of ARG deficiency syndrome with low nitric oxide production. Citrulline supplementation strongly improves microcirculation in animal models with gut injury, but clinical studies are lacking. Taurine has a potent protective effect against ischemic reperfusion injury. SUMMARY: Amino acid-based pharmaconutrition has displayed familiar 'big project' stages: enthusiasm (citrulline and taurine), doubt (GLN), hunt for the guilty (ARG), and backpedalling (leucine). Progress in this field is very slow, and sometimes gives way to retreat, as demonstrated by recent large trials on GLN supplementation.

"Immunonutrition" Has Failed to Improve Peritonitis-Induced Septic Shock in Rodents.

BACKGROUND: Immunonutrition in sepsis, including n-3 poly-unsaturated fatty acids (PUFAs) or L-arginine supplementation, is a controversial issue that has yielded a great number of studies for the last thirty-five years, and the conclusions regarding the quantity and quality of this support in patients are deceiving. The aim of the present experimental study is to investigate the effects of a pretreatment with enteral nutrition enriched with n-3 PUFAs or L-arginine on vascular dysfunctions, inflammation and oxidative stress during septic shock in rats. DESIGN: Rats were fed with enteral Peptamen® HN (HN group), Peptamen® AF containing n-3 PUFAs (AF group) or Peptamen® AF enriched with L-arginine (AFA group). On day 4, peritonitis by cecal ligation and puncture (CLP) was performed. Rats were resuscitated (H18) once septic shock was established. After a 4-hour resuscitation, vessels and organs were harvested to assess inflammation, superoxide anion, nitric oxide and prostacyclin levels. Ex-vivo vascular reactivity was also performed. RESULTS: Compared to CLP-AF or CLP-HN groups, 47.6% of CLP-AFA rats died before the beginning of hemodynamic measurements (vs. 8.0% and 20.0% respectively, p<0.05). AF and AFA rats required significantly increased norepinephrine infusion rates to reach the mean arterial pressure objective, compared to CLP-HN rats. Both CLP-AF and CLP-AFA reduced mesenteric resistance arterial contractility, decreased vascular oxidative stress, but increased NF-κB (0.40±0.15 in CLP-AF and 0.69±0.06 in CLP-AFA vs. 0.09±0.03 in SHAM rats and 0.30±0.06 in CLP-HN, ß-actin ratio, p<0.05) and pIκB expression (0.60±0.03 in CLP-AF and 0.94±0.15 in CLP-AFA vs. 0.04±0.01 in SHAM rats and 0.56±0.07 in CLP-HN, ß-actin ratio, p<0.05), nitric oxide and prostacyclin production in septic rats. CONCLUSIONS: Although n-3 PUFAs or L-arginine supplementation exhibited an antioxidant effect, it worsened the septic shock-induced vascular dysfunction. Furthermore, mortality was higher after L-arginine supplementation.

Effect of specific amino acids on hepatic lipid metabolism in fructose-induced non-alcoholic fatty liver disease.

BACKGROUND & AIM: Fructose diets have been shown to induce insulin resistance and to alter liver metabolism and gut barrier function, ultimately leading to non-alcoholic fatty liver disease. Citrulline, Glutamine and Arginine may improve insulin sensitivity and have beneficial effects on gut trophicity. Our aim was to evaluate their effects on liver and gut functions in a rat model of fructose-induced non-alcoholic fatty liver disease. METHODS: Male Sprague-Dawley rats (n = 58) received a 4-week fructose (60%) diet or standard chow with or without Citrulline (0.15 g/d) or an isomolar amount of Arginine or Glutamine. All diets were made isonitrogenous by addition of non-essential amino acids. At week 4, nutritional and metabolic status (plasma glucose, insulin, cholesterol, triglycerides and amino acids, net intestinal absorption) was determined; steatosis (hepatic triglycerides content, histological examination) and hepatic function (plasma aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, bilirubin) were assessed; and gut barrier integrity (myeloperoxidase activity, portal endotoxemia, tight junction protein expression and localization) and intestinal and hepatic inflammation were evaluated. We also assessed diets effects on caecal microbiota. RESULTS: In these experimental isonitrogenous fructose diet conditions, fructose led to steatosis with dyslipidemia but without altering glucose homeostasis, liver function or gut permeability. Fructose significantly decreased Bifidobacterium and Lactobacillus and tended to increase endotoxemia. Arginine and Glutamine supplements were ineffective but Citrulline supplementation prevented hypertriglyceridemia and attenuated liver fat accumulation. CONCLUSION: While nitrogen supply alone can attenuate fructose-induced non-alcoholic fatty liver disease, Citrulline appears to act directly on hepatic lipid metabolism by partially preventing hypertriglyceridemia and steatosis.

Citrulline and Nonessential Amino Acids Prevent Fructose-Induced Nonalcoholic Fatty Liver Disease in Rats.

BACKGROUND: Fructose induces nonalcoholic fatty liver disease (NAFLD). Citrulline (Cit) may exert a beneficial effect on steatosis. OBJECTIVE: We compared the effects of Cit and an isonitrogenous mixture of nonessential amino acids (NEAAs) on fructose-induced NAFLD. METHODS: Twenty-two male Sprague Dawley rats were randomly assigned into 4 groups (n = 4-6) to receive for 8 wk a 60% fructose diet, either alone or supplemented with Cit (1 g · kg(-1) · d(-1)), or an isonitrogenous amount of NEAAs, or the same NEAA-supplemented diet with starch and maltodextrin instead of fructose (controls). Nutritional and metabolic status, liver function, and expression of genes of hepatic lipid metabolism were determined. RESULTS: Compared with controls, fructose led to NAFLD with significantly higher visceral fat mass (128%), lower lean body mass (-7%), insulin resistance (135%), increased plasma triglycerides (TGs; 67%), and altered plasma amino acid concentrations with decreased Arg bioavailability (-27%). This was corrected by both NEAA and Cit supplementation. Fructose caused a 2-fold increase in the gene expression of fatty acid synthase (Fas) and 70% and 90% decreases in that of carnitine palmitoyl-transferase 1a and microsomal TG transfer protein via a nearly 10-fold higher gene expression of sterol regulatory element-binding protein-1c (Srebp1c) and carbohydrate-responsive element-binding protein (Chrebp), and a 90% lower gene expression of peroxisome proliferator-activated receptor α (Ppara). NEAA or Cit supplementation led to a Ppara gene expression similar to controls and decreased those of Srebp1c and Chrebp in the liver by 50-60%. Only Cit led to Fas gene expression and Arg bioavailability similar to controls. CONCLUSION: In our rat model, Cit and NEAAs effectively prevented fructose-induced NAFLD. On the basis of literature data and our findings, we propose that NEAAs may exert their effects specifically on the liver, whereas Cit presumably acts at both the hepatic and whole-body level, in part via improved peripheral Arg metabolism.

Oral Glutamine Supplementation Protects Female Mice from Nonalcoholic Steatohepatitis.

BACKGROUND: Genetic factors, a diet rich in fat and sugar, and an impaired intestinal barrier function are critical in the development of nonalcoholic steatohepatitis (NASH). The nonessential amino acid glutamine (Gln) has been suggested to have protective effects on intestinal barrier function but also against the development of liver diseases of various etiologies. OBJECTIVE: The effect of oral Gln supplementation on the development of Western-style diet (WSD)-induced NASH in mice was assessed. METHODS: Female 6- to 8-wk-old C57BL/6J mice were pair-fed a control (C) diet or a WSD alone or supplemented with 2.1 g l-Gln/kg body weight for 6 wk (C+Gln or WSD+Gln). Indexes of liver damage, lipid peroxidation, and glucose metabolism and endotoxin concentrations were measured. RESULTS: Although Gln supplementation had no effect on the loss of the tight junction protein occludin, the increased portal endotoxin and fasting glucose concentrations found in WSD-fed mice, markers of liver damage (e.g., nonalcoholic fatty liver disease activity score and number of neutrophils in the liver) were significantly lower in the WSD+Gln group than in the WSD group (~47% and ~60% less, respectively; P < 0.05). Concentrations of inducible nitric oxide synthase (iNOS) protein and 3-nitrotyrosin protein adducts were significantly higher in livers of WSD-fed mice than in all other groups (~8.6- and ~1.9-fold higher, respectively, compared with the C group; P < 0.05) but did not differ between WSD+Gln-, C-, and C+Gln-fed mice. Hepatic tumor necrosis factor α and plasminogen activator inhibitor 1 concentrations were significantly higher in WSD-fed mice (~1.6- and ~1.8-fold higher, respectively; P < 0.05) but not in WSD+Gln-fed mice compared with C mice. CONCLUSION: Our data suggest that the protective effects of oral Gln supplementation on the development of WSD-induced NASH in mice are associated with protection against the induction of iNOS and lipid peroxidation in the liver.

Effect of oral taurine on morbidity and mortality in elderly hip fracture patients: a randomized trial.

Hip fracture patients represent a large part of the elderly surgical population and face severe postoperative morbidity and excessive mortality compared to adult surgical hip fracture patients. Low antioxidant status and taurine deficiency is common in the elderly, and may negatively affect postoperative outcome. We hypothesized that taurine, an antioxidant, could improve clinical outcome in the elderly hip fracture patient. A double blind randomized, placebo controlled, clinical trial was conducted on elderly hip fracture patients. Supplementation started after admission and before surgery up to the sixth postoperative day. Markers of oxidative status were measured during hospitalization, and postoperative outcome was monitored for one year after surgery. Taurine supplementation did not improve in-hospital morbidity, medical comorbidities during the first year, or mortality during the first year. Taurine supplementation lowered postoperative oxidative stress, as shown by lower urinary 8-hydroxy-2-deoxyguanosine levels (Generalized estimating equations (GEE) analysis average difference over time; regression coefficient (Beta): -0.54; 95% CI: -1.08--0.01; p = 0.04), blunted plasma malondialdehyde response (Beta: 1.58; 95% CI: 0.00-3.15; p = 0.05) and a trend towards lower lactate to pyruvate ratio (Beta: -1.10; 95% CI: -2.33-0.12; p = 0.08). We concluded that peri-operative taurine supplementation attenuated postoperative oxidative stress in elderly hip fracture patients, but did not improve postoperative morbidity and mortality.

In vitro anti-inflammatory effects of citrulline on peritoneal macrophages in Zucker diabetic fatty rats.

In type 2 diabetes (T2D) macrophage dysfunction increases susceptibility to infection and mortality. This may result from the associated decreased plasma concentration of arginine, an amino acid that plays an important role in immunity. In vitro, increasing arginine availability leads to an improvement in macrophage function; however, arginine supplementation in diabetic obese patients may be detrimental. The aim of the present study was to assess in vitro whether citrulline, an arginine precursor, could replace arginine in the regulation of macrophage function under a condition of diabetes and obesity. Peritoneal macrophages from diabetic obese or lean rats were incubated for 6 h in an arginine-free medium, in the presence of increasing citrulline concentrations (0·1, 0·5, 1 or 2 mmol/l). Cytokine and NO production was determined. Peritoneal macrophages from either lean or diabetic obese rats produced NO, and at higher levels in the cells from lean rats. In diabetic obese rats, TNF-α production decreased with increasing citrulline concentrations, but was higher than that in the cells from lean rats. In contrast, IL-6 production increased with increasing citrulline concentrations. The present experiment shows that citrulline is effectively used for NO production and regulates cytokine production in macrophages from diabetic obese rats. This effect warrants in vivo evaluation in T2D-related inflammation.

Citrulline induces fatty acid release selectively in visceral adipose tissue from old rats.

SCOPE: During aging, increased visceral adipose tissue (AT) mass may result in impaired metabolic status. A citrulline (CIT)-supplemented diet reduces AT mass in old rats. We hypothesized that CIT could directly affect fatty acid (FA) metabolism in retroperitoneal AT. METHODS AND RESULTS: A 24-h exposure of AT explants from old (25 months) rats to 2.5 mM CIT induced a 50% rise in glycerol and FA release, which was not observed in explants from young (2 months) animals. The phosphorylated form of hormone-sensitive lipase, a key lipolytic enzyme, was 1.5-fold higher in CIT-treated explants from old and young rats, whereas glyceroneogenesis, that provides glycerol-3P requested for FA re-esterification, and its key enzyme phosphoenolpyruvate carboxykinase, were down-regulated 40-70%. Specifically in young rats, beta-oxidation capacity and gene expressions of carnitine palmitoyl transferase 1-b and very long chain acyl-CoA dehydrogenase were strongly up-regulated by CIT. In contrast, in old rats, while glyceroneogenesis was lower, beta-oxidation was not affected, enabling increased FA release. CONCLUSION: Hence, in visceral AT, CIT exerts a specific induction of the beta-oxidation capacity in young rats and a selective stimulation of FA release in old rats, therefore providing a direct mechanism of CIT action to reduce AT mass.

Glutamine in the intensive care unit.

PURPOSE OF REVIEW: To analyze the recent literature (2011-2013) on glutamine supplementation of parenteral and enteral nutrition in critically ill patients. Potential confounding factors that may explain conflicting results are suggested. RECENT FINDINGS: Some recent, prospective, multicenter trials and two small trials yielded conflicting results that weigh heavily in the conclusions of a recent meta-analysis. Heterogeneity of the patients enrolled (especially in terms of injury severity, age, and basal nutritional status) and difficulties in identifying patients truly in need of glutamine supplementation may explain the discrepancies. SUMMARY: Glutamine supplementation has been recognized as beneficial in acutely injured patients. However, recent conflicting results in either 'real-life conditions' or very severe situations suggest that its indications need to be more precisely determined.

Effects of a diabetes-specific enteral nutrition on nutritional and immune status of diabetic, obese, and endotoxemic rats: interest of a graded arginine supply.

OBJECTIVE: Obese and type 2 diabetic patients present metabolic disturbance-related alterations in nonspecific immunity, to which the decrease in their plasma arginine contributes. Although diabetes-specific formulas have been developed, they have never been tested in the context of an acute infectious situation as can be seen in intensive care unit patients. Our aim was to investigate the effects of a diabetes-specific diet enriched or not with arginine in a model of infectious stress in a diabetes and obesity situation. As a large intake of arginine may be deleterious, this amino acid was given in graded fashion. DESIGN: Randomized, controlled experimental study. SETTING: University research laboratory. SUBJECTS: Zucker diabetic fatty rats. INTERVENTIONS: Gastrostomized Zucker diabetic fatty rats were submitted to intraperitoneal lipopolysaccharide administration and fed for 7 days with either a diabetes-specific enteral nutrition without (G group, n=7) or with graded arginine supply (1-5 g/kg/day) (GA group, n=7) or a standard enteral nutrition (HP group, n=10). MEASUREMENTS AND MAIN RESULTS: Survival rate was better in G and GA groups than in the HP group. On day 7, plasma insulin to glucose ratio tended to be lower in the same G and GA groups. Macrophage tumor necrosis factor-α (G: 5.0±1.1 ng/2×106 cells·hr⁻¹; GA: 3.7±0.8 ng/2×106 cells·hr⁻¹; and HP: 1.7±0.6 ng/2×106 cells·hr⁻¹; p<.05 G vs. HP) and nitric oxide (G: 4.5±1.1 ng/2×106 cells·hr⁻¹; GA: 5.1±1.0 ng/2×106 cells·hr⁻¹; and HP: 1.0±0.5 nmol/2×106 cells·hr⁻¹; p<.05 G and GA vs. HP) productions were higher in the G and GA groups compared to the HP group. Macrophages from the G and GA groups exhibited increased arginine consumption. CONCLUSIONS: In diabetic obese and endotoxemic rats, a diabetes-specific formula leads to a lower mortality, a decreased insulin resistance, and an improvement in peritoneal macrophage function. Arginine supplementation has no additional effect. These data support the use of such disease-specific diets in critically ill diabetic and obese patients.

The 2009 ESPEN Sir David Cuthbertson. Citrulline: a new major signaling molecule or just another player in the pharmaconutrition game?

Citrulline (CIT) is synthesized from arginine (ARG) and glutamine in enterocytes and metabolized by the kidneys into arginine, which is available for peripheral tissues. Thus CIT, rather than ARG, could be a limiting amino acid (AA) in situations of intestinal failure. This was verified in a rat model of short bowel syndrome. The effects of CIT were further tested in renutrition of malnourished rats and in healthy volunteers fed a hypoproteic diet. CIT supplementation improved protein synthesis (PS) and ARG availability more than ARG itself, which is explained by the fact that CIT, unlike ARG, is very efficiently transported into enterocytes and escapes hepatic uptake. Action of CIT on PS is mediated through the mTOR pathway. A key issue is why CIT should stimulate PS. CIT could be a counterpart of leucine, with leucine stimulating PS in the postprandial state, while CIT acts when protein intake is low or nil to maintain PS at a minimal level compatible with life. CIT could also be a safe way to deliver ARG to endothelial and immune cells, and can certainly prevent excessive uncontrolled nitric oxide production.

Protective effects of glutamine dipeptide and alpha-tocopherol against ischemia-reperfusion injury in the isolated rat liver.

BACKGROUND & AIMS: Glutamine and vitamin E may prevent hepatic ischemia-reperfusion (I/R) injuries. Our aim was to investigate the effects of glutamine, either alone or combined with vitamin E, against I/R in the isolated perfused rat liver. METHODS: Four groups of 8 livers from male Sprague-Dawley rats were isolated and submitted to a 45-min no-flow ischemia and reperfusion in the presence of alanine 2 mM, alanine 2 mM plus vitamin E 150 microM, Alanyl-Glutamine (AlaGln) 2 mM, or AlaGln 2 mM plus vitamin E 150 microM. Six non-perfused livers were studied in parallel. Liver function, metabolic parameters, oxidative stress and inflammatory parameters have been studied. RESULTS: AlaGln was rapidly cleared from the perfusate (436+/-41 nmol min(-1) g(-1)) and lowered transaminase release during reperfusion (ALT: -59%), significantly so in the AlaGln+Vit E group (ALT: -65%, p<0.05). The association of glutamine with vitamin E led to lower degrees NO (-83%, p<0.05) production, better preserved hepatic glutathione content and, as with vitamin E alone, preserved hepatic vitamin A and significantly decreased malondialdehyde (-85%, p<0.05). CONCLUSION: Both glutamine, by attenuating inflammatory response, and vitamin E, via its antioxidative properties, showed complementary protective effects against I/R-induced hepatic injury. These data emphasize the potential benefit of combining glutamine and vitamin E supplementation in hepatic I/R injury.

Therapeutic use of branched-chain amino acids in burn, trauma, and sepsis.

Various experimental studies conducted in the 1970s demonstrated, at least in the physiological situation, the anabolic and/or anticatabolic properties of branched-chain amino acids (leucine, valine, isoleucine) or their ketoacid derivatives. This led to several clinical studies in the late 1970s and early 1980s that aimed to evaluate the potential benefits of BCAA supplementation in nutritional support of the critically ill. The data on burn, trauma, and sepsis are, however, far from convincing. Besides significant discrepancies in their results and the fact that most of these studies involved very small populations of patients, few of them meet the current standards of therapeutic evaluation. However, some positive results in specific studies suggest that the underlying concept may be correct but that interpretation has been faulty. Indeed, we know now that while the BCAAs possess regulatory properties on protein metabolism, leucine is by far the most potent, while isoleucine and valine are inefficient. However, in the above-mentioned studies, BCAA-supplemented nutrition very frequently supplied almost equivalent amounts of all 3 BCAAs. Moreover, several studies were performed without adequate basal nutritional support, which most probably hampered the correct metabolic utilization of these amino acids. Taken together, these factors mean that the demonstrations of BCAA efficacy were fortunate in the least. In contrast, more recently, leucine was demonstrated to positively affect protein synthesis in an experimental model of sepsis or burn. In parallel, 2 prospective controlled trials of BCAA supplementation in septic patients also demonstrated an improvement in patients' nutritional status and outcome. Thus, we should abandon the concept of BCAA-supplemented nutrition for a more promising leucine-supplemented nutrition that requires further evaluation.