Jean-Pascal De Bandt

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.

Napping Reverses the Salivary Interleukin-6 and Urinary Norepinephrine Changes Induced by Sleep Restriction

CONTEXT Neuroendocrine and immune stresses imposed by chronic sleep restriction are known to be involved in the harmful cardiovascular effects associated with poor sleep. OBJECTIVES Despite a well-known beneficial effect of napping on alertness, its effects on neuroendocrine stress and immune responses after sleep restriction are largely unknown. DESIGN This study was a strictly controlled (sleep-wake status, light environment, caloric intake), crossover, randomized design in continuously polysomnography-monitored subjects. SETTING The study was conducted in a laboratory-based study. PARTICIPANTS The subjects were 11 healthy young men. INTERVENTION We investigated the effects on neuroendocrine and immune biomarkers of a night of sleep restricted to 2 h followed by a day without naps or with 30 minute morning and afternoon naps, both conditions followed by an ad libitum recovery night starting at 20:00. MAIN OUTCOME MEASURES Salivary interleukin-6 and urinary catecholamines were assessed throughout the daytime study periods. RESULTS The increase in norepinephrine values seen at the end of the afternoon after the sleep-restricted night was not present when the subjects had the opportunity to take naps. Interleukin-6 changes observed after sleep deprivation were also normalized after napping. During the recovery day in the no-nap condition, there were increased levels of afternoon epinephrine and dopamine, which was not the case in the nap condition. A recovery night after napping was associated with a reduced amount of slow-wave sleep compared to after the no-nap condition. CONCLUSIONS Our data suggest that napping has stress-releasing and immune effects. Napping could be easily applied in real settings as a countermeasure to the detrimental health consequences of sleep debt.

Overexpression of ornithine aminotransferase: consequences on amino acid homeostasis.

Ornithine aminotransferase (OAT) is a reversible enzyme expressed mainly in the liver, kidney and intestine. OAT controls the interconversion of ornithine into glutamate semi-aldehyde, and is therefore involved in the metabolism of arginine and glutamine which play a major role in N homeostasis. We hypothesised that OAT could be a limiting step in glutamine-arginine interconversion. To study the contribution of the OAT enzyme in amino acid metabolism, transgenic mice that specifically overexpress human OAT in the liver, kidneys and intestine were generated. The transgene expression was analysed by in situ hybridisation and real-time PCR. Tissue (liver, jejunum and kidney) OAT activity, and plasma and tissue (liver and jejunum) amino acid concentrations were measured. Transgenic male mice exhibited higher OAT activity in the liver (25 (sem 4) v. 11 (sem 1) nmol/min per microg protein for wild-type (WT) mice; P < 0.05) but there were no differences in kinetic parameters (i.e. Km and maximum rate of reaction (Vmax)) between WT and transgenic animals. OAT overexpression decreased plasma and liver ornithine concentrations but did not affect glutamine or arginine homeostasis. There was an inverse relationship between ornithine levels and OAT activity. We conclude that OAT overexpression has only limited metabolic effects, probably due to the reversible nature of the enzyme. Moreover, these metabolic modifications had no effect on phenotype.

Preventive effects of citrulline on Western diet-induced non-alcoholic fatty liver disease in rats.

A Western diet induces insulin resistance, liver steatosis (non-alcoholic fatty liver disease (NAFLD)) and intestinal dysbiosis, leading to increased gut permeability and bacterial translocation, thus contributing to the progression of NAFLD to non-alcoholic steatohepatitis. In the present study, we sought, in a model of Western diet-induced NAFLD, to determine whether citrulline (Cit), an amino acid that regulates protein and energy metabolism, could decrease Western diet-induced liver injuries, as well as the mechanisms involved. Sprague-Dawley rats were fed a high-fat diet (45 %) and fructose (30 %) in drinking water or a control diet associated with water (group C) for 8 weeks. The high-fat, high-fructose diet (Western diet) was fed either alone (group WD) or with Cit (1 g/kg per d) (group WDC) or an isonitrogenous amount of non-essential amino acids (group WDA). We evaluated nutritional and metabolic status, liver function, intestinal barrier function, gut microbiota and splanchnic inflammatory status. Cit led to a lower level of hepatic TAG restricted to microvesicular lipid droplets and to a lower mRNA expression of CCAAT-enhancer-binding protein homologous protein, a marker of endoplasmic reticulum stress, of pro-inflammatory cytokines Il6 (P<0·05) and Tnfα, and of toll-like receptor 4 (Tlr4) (P<0·05). Cit also improved plasma TAG and insulin levels. In the colon, it decreased inflammation (Tnfα and Tlr4 expressions) and increased claudin-1 protein expression. This was associated with higher levels of Bacteroides/Prevotella compared with rats fed the Western diet alone. Cit improves Western diet-induced liver injuries via decreased lipid deposition, increased insulin sensitivity, lower inflammatory process and preserved antioxidant status. This may be related in part to its protective effects at the gut level.

Protective effects of glutamine dipeptide and α-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.

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 reviewTo 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 findingsSome 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. SummaryGlutamine 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.

Enteral administration of alanyl-[2-15N]glutamine contributes more to the de novo synthesis of arginine than does intravenous infusion of the dipeptide in humans

BACKGROUND We previously confirmed in humans the existence of a pathway of glutamine into citrulline and arginine, which is preferentially stimulated by luminally provided glutamine. However, because glutamine is unstable, we tested this pathway with a stable dipeptide of glutamine. OBJECTIVES The objectives were to explore whether alanyl-glutamine contributes to the synthesis of arginine in humans and whether this depends on the route of administration. DESIGN The study was conducted under postabsorptive conditions during surgery. Sixteen patients received alanyl-[2-(15)N]glutamine enterally or intravenously together with intravenously administered stable-isotope tracers of citrulline and arginine. Blood was collected from an artery, the portal vein, a hepatic vein, and the right renal vein. Arterial and venous enrichments and (tracer) net balances of alanyl-glutamine and glutamine, citrulline, and arginine across the portal-drained viscera, liver, and kidneys were determined. Parametric tests were used to test results (mean +/- SEM). P < 0.05 was considered significant. RESULTS Twice as much exogenous glutamine was used for the synthesis of citrulline when alanyl-glutamine was provided enterally (5.9 +/- 0.6%) than when provided intravenously (2.8 +/- 0.3%) (P < 0.01). Consequently, twice as much exogenous glutamine was used for the synthesis of arginine when alanyl-glutamine was provided enterally (5 +/- 0.7%) than when provided intravenously (2.4 +/- 0.2%) (P < 0.01). However, results at the organ level did not explain the differences due to route of administration. CONCLUSIONS Alanyl-glutamine contributes to the de novo synthesis of arginine, especially when provided enterally. A stable-isotope study using a therapeutic dose of alanyl-glutamine is needed to investigate the clinical implications of this finding.

Fructose and NAFLD: The Multifaceted Aspects of Fructose Metabolism

Among various factors, such as an unhealthy diet or a sedentarity lifestyle, excessive fructose consumption is known to favor nonalcoholic fatty liver disease (NAFLD), as fructose is both a substrate and an inducer of hepatic de novo lipogenesis. The present review presents some well-established mechanisms and new clues to better understand the pathophysiology of fructose-induced NAFLD. Beyond its lipogenic effect, fructose intake is also at the onset of hepatic inflammation and cellular stress, such as oxidative and endoplasmic stress, that are key factors contributing to the progression of simple steatosis to nonalcoholic steatohepatitis (NASH). Beyond its hepatic effects, this carbohydrate may exert direct and indirect effects at the peripheral level. Excessive fructose consumption is associated, for example, with the release by the liver of several key mediators leading to alterations in the communication between the liver and the gut, muscles, and adipose tissue and to disease aggravation. These multifaceted aspects of fructose properties are in part specific to fructose, but are also shared in part with sucrose and glucose present in energy–dense beverages and foods. All these aspects must be taken into account in the development of new therapeutic strategies and thereby to better prevent NAFLD.

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.