Nonnutritive effects of glutamine

Glutamine supplementation for critically ill adults

BACKGROUND

Glutamine is a non-essential amino acid which is abundant in the healthy human body. There are studies reporting that plasma glutamine levels are reduced in patients with critical illness or following major surgery, suggesting that glutamine may be a conditionally essential amino acid in situations of extreme stress. In the past decade, several clinical trials examining the effects of glutamine supplementation in patients with critical illness or receiving surgery have been done, and the systematic review of this clinical evidence has suggested that glutamine supplementation may reduce infection and mortality rates in patients with critical illness. However, two recent large-scale randomized clinical trials did not find any beneficial effects of glutamine supplementation in patients with critical illness.

OBJECTIVES

The objective of this review was to:1. assess the effects of glutamine supplementation in critically ill adults and in adults after major surgery on infection rate, mortality and other clinically relevant outcomes;2. investigate potential heterogeneity across different patient groups and different routes for providing nutrition.

SEARCH METHODS

We searched the Cochrane Anaesthesia Review Group (CARG) Specialized Register; Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (2013, Issue 5); MEDLINE (1950 to May 2013); EMBASE (1980 to May 2013) and Web of Science (1945 to May 2013).

SELECTION CRITERIA

We included controlled clinical trials with random or quasi-random allocation that examined glutamine supplementation versus no supplementation or placebo in adults with a critical illness or undergoing elective major surgery. We excluded cross-over trials.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted the relevant information from each included study using a standardized data extraction form. For infectious complications and mortality and morbidity outcomes we used risk ratio (RR) as the summary measure with the 95% confidence interval (CI). We calculated, where appropriate, the number needed to treat to benefit (NNTB) and the number needed to treat to harm (NNTH). We presented continuous data as the difference between means (MD) with the 95% CI.

MAIN RESULTS

Our search identified 1999 titles, of which 53 trials (57 articles) fulfilled our inclusion criteria. The 53 included studies enrolled a total of 4671 participants with critical illness or undergoing elective major surgery. We analysed seven domains of potential risk of bias. In 10 studies the risk of bias was evaluated as low in all of the domains. Thirty-three trials (2303 patients) provided data on nosocomial infectious complications; pooling of these data suggested that glutamine supplementation reduced the infectious complications rate in adults with critical illness or undergoing elective major surgery (RR 0.79, 95% CI 0.71 to 0.87, P ＜ 0.00001, I² = 8%, moderate quality evidence). Thirty-six studies reported short-term (hospital or less than one month) mortality. The combined rate of mortality from these studies was not statistically different between the groups receiving glutamine supplement and those receiving no supplement (RR 0.89, 95% CI 0.78 to 1.02, P = 0.10, I² = 22%, low quality evidence). Eleven studies reported long-term (more than six months) mortality; meta-analysis of these studies (2277 participants) yielded a RR of 1.00 (95% CI 0.89 to 1.12, P = 0.94, I² = 30%, moderate quality evidence). Subgroup analysis of infectious complications and mortality outcomes did not find any statistically significant differences between the predefined groups. Hospital length of stay was reported in 36 studies. We found that the length of hospital stay was shorter in the intervention group than in the control group (MD -3.46 days, 95% CI -4.61 to -2.32, P < 0.0001, I² = 63%, low quality evidence). Slightly prolonged intensive care unit (ICU) stay was found in the glutamine supplemented group from 22 studies (2285 participants) (MD 0.18 days, 95% CI 0.07 to 0.29, P = 0.002, I² = 11%, moderate quality evidence). Days on mechanical ventilation (14 studies, 1297 participants) was found to be slightly shorter in the intervention group than in the control group (MD - 0.69 days, 95% CI -1.37 to -0.02, P = 0.04, I² = 18%, moderate quality evidence). There was no clear evidence of a difference between the groups for side effects and quality of life, however results were imprecise for serious adverse events and few studies reported on quality of life. Sensitivity analysis including only low risk of bias studies found that glutamine supplementation had beneficial effects in reducing the length of hospital stay (MD -2.9 days, 95% CI -5.3 to -0.5, P = 0.02, I² = 58%, eight studies) while there was no statistically significant difference between the groups for all of the other outcomes.

AUTHORS' CONCLUSIONS

This review found moderate evidence that glutamine supplementation reduced the infection rate and days on mechanical ventilation, and low quality evidence that glutamine supplementation reduced length of hospital stay in critically ill or surgical patients. It seems to have little or no effect on the risk of mortality and length of ICU stay, however. The effects on the risk of serious side effects were imprecise. The strength of evidence in this review was impaired by a high risk of overall bias, suspected publication bias, and moderate to substantial heterogeneity within the included studies.

L-glutamine supplementation prevents the development of experimental diabetic cardiomyopathy in streptozotocin-nicotinamide induced diabetic rats

The objective of the present investigation was to evaluate the effect of L-glutamine on cardiac myopathy in streptozotocin-nicotinamide induced diabetic rats. Diabetes was induced in overnight fasted Sprague Dawely rats by using intraperitonial injection of streptozotocin (55 mg/kg). Nicotinamide (100 mg/kg, i.p.) was administered 20 min before administration of streptozotocin. Experimental rats were divided into Group I: non-diabetic control (distilled water; 10 ml/kg, p.o.), II: diabetic control (distilled water, 10 ml/kg, p.o.), III: L-glutamine (500 mg/kg, p.o.) and IV: L-glutamine (1000 mg/kg, p.o.). All groups were diabetic except group I. The plasma glucose level, body weight, electrocardiographic abnormalities, hemodynamic changes and left ventricular contractile function, biological markers of cardiotoxicity, antioxidant markers were determined after 4 months after STZ with nicotinamide injection. Histopathological changes of heart tissue were carried out by using H and E stain. L-glutamine treatment improved the electrocardiographic, hemodynamic changes; LV contractile function; biological markers; oxidative stress parameters and histological changes in STZ induced diabetic rats. Results from the present investigation demonstrated that L-glutamine has seemed a cardioprotective activity.

Glutamine deprivation induces interleukin-8 expression in ataxia telangiectasia fibroblasts

OBJECTIVE

To investigate whether glutamine deprivation induces expression of inflammatory cytokine interleukin-8 (IL-8) by determining NF-κB activity and levels of oxidative indices (ROS, reactive oxygen species; hydrogen peroxide; GSH, glutathione) in fibroblasts isolated from patients with ataxia telangiectasia (A-T).

MATERIALS

We used A-T fibroblasts stably transfected with empty vector (Mock) or with human full-length ataxia telangiectasia mutated (ATM) cDNA (YZ5) and mouse embryonic fibroblasts (MEFs) transiently transfected with ATM small interfering RNA (siRNA) or with non-specific control siRNA.

TREATMENT

The cells were cultured with or without glutamine or GSH.

METHODS

ROS levels were determined using a fluorescence reader and confocal microscopy. IL-8 or murine IL-8 homolog, keratinocyte chemoattractant (KC), and hydrogen peroxide levels in the medium were determined by enzyme-linked immunosorbent assay and colorimetric assay. GSH level was assessed by enzymatic assay, while IL-8 (KC) mRNA level was measured by reverse transcription-polymerase chain reaction (RT-PCR) and/or quantitative real-time PCR. NF-κB DNA-binding activity was determined by electrophoretic mobility shift assay. Catalase activity and ATM protein levels were determined by O2 generation and Western blotting.

RESULTS

While glutamine deprivation induced IL-8 expression and increased NF-κB DNA-binding activity in Mock cells, both processes were decreased by treatment of cells with glutamine or GSH or both glutamine and GSH. Glutamine deprivation had no effect on IL-8 expression or NF-κB DNA-binding activity in YZ5 cells. Glutamine-deprived Mock cells had higher oxidative stress indices (increases in ROS and hydrogen peroxide, reduction in GSH) than glutamine-deprived YZ5 cells. In Mock cells, glutamine deprivation-induced oxidative stress indices were suppressed by treatment with glutamine or GSH or both glutamine and GSH. GSH levels and catalase activity were lower in Mock cells than YZ5 cells. MEFs transfected with ATM siRNA and cultured without glutamine showed higher levels of ROS and IL-8 than those transfected with negative control siRNA; increased levels of ROS and IL-8 were suppressed by the treatment of glutamine.

CONCLUSION

Glutamine deprivation induces ROS production, NF-κB activation, and IL-8 expression as well as a reduction in GSH in A-T fibroblasts, all of which are attenuated by glutamine supplementation.

[Activity of the glutathione system of antioxidant defense in rats under the action of L-glutamic acid]

The data on the effects of glutamic acid (L-Glu), which is one of three amino acid - precursors ofglutathione on animals organism is quite controversial because research in this area remain relevant. The aim of our research was to find out what impact the additional introduction of L-Glu on the activity glutathione system of antioxidant defence and the content of lipid peroxidation products in various organs and tissues of rats. The effect of additional (285 and 715 mg/kg, respectively) introduction to the diet of L-Glu on the activity of antioxidant enzymes and intensity of peroxidation processes in various tissues of rats was studied. It is shown that in the liver, spleen and kidneys of rats which received additional 715 mg/kg of L-Glu content of reduced glutathione and glutathione peroxidase activity increased. A decrease of the content of lipid hydroperoxides and TBA-active products in tissues of animals which received additional 285 and 715 mg/kg of L-Glu into the diet was found. We have also found that the enrichment of rat's diet by L-Glu during 30 days resulted in a change of glutathione part of antioxidant system and intensity of lipid peroxidation. More intensive changes in these indices were observed in animals which received additional 715 mg/kg of L-Glu into the diet.

Combined effects of tauroursodeoxycholic Acid and glutamine on bacterial translocation in obstructive jaundiced rats:

BACKGROUND

Bacterial Translocation is believed to be an important factor on mortality and morbidity in Obstructive Jaundiced.

AIMS

We investigated the probable or estimated positive effects of tauroursodeoxycholic acid, which has antibacterial and regulatory effects on intestinal flora, together with glutamine on BT in an experimental obstructive jaundiced rat model.

STUDY DESIGN

Animal experimentation.

METHODS

Forty adult, male, Sprague Dawley rats were used in this study. Animals were randomised and divided into five groups of eight each: sham (Sh); control (common bile duct ligation, CBDL); and supplementation groups administered tauroursodeoxycholic acid (CBDL+T), glutamine (CBDL+G), or tauroursodeoxycholic acid plus glutamine (CBDL+TG). Blood and liver, spleen, MLN, and ileal samples were taken via laparotomy under sterile conditions for investigation of bacterial translocation and intestinal mucosal integrity and hepatic function tests on the tenth postoperative day.

RESULTS

There were statistically significant differences in BT rates in all samples except the spleen of the CBDL+TG group compared with the CBDL group (p=0.041, p=0.026, and p=0.041, respectively).

CONCLUSION

It is essential to protect hepatic functions besides maintaining intestinal mucosal integrity in the active struggle against BT occurring in obstructive jaundice. The positive effect on intestinal mucosal integrity can be increased if glutamine is used with tauroursodeoxycholic acid, which also has hepatoprotective and immunomodulatory features.

Plasma kinetic of ingested essential amino acids in healthy elderly people

The purpose of this study was to investigate whether the documented difficulties of physiological amounts of essential amino acids (EAAs) (7 g) to induce protein synthesis could be reflected in a simple method adaptable to a clinical setting. Sixteen healthy individuals, nine elderly (75.3 ± 3.5 years), and seven young (28 ± 2.5 years) were enrolled in the study. Five minutes before EAA ingestion (baseline) and 20, 40, 60, 90, 120, 180 min after EAA ingestion, venous blood samples were taken from the ante-cubital vein to determine the concentrations of EAAs (μmol/L). The results show that plasma EAA increases were significantly higher in old than in young persons at the considered time points (from p < 0.004 to p < 0.001) (unpaired Student t test). However, the velocity rate of the increasing was slower in old subjects than in young group. The study shows that EAAs ingestion by old subject is associated with reduced muscle EAA uptake.

Glutamine-free condition inhibits lipopolysaccharide-induced invasion of BV2 microglial cells by suppressing of matrix metalloproteinase-9 expression

Studies showing the mechanisms involved in glutamine (Gln) starvation and regulation of matrix metalloproteinase-9 (MMP-9) expression in microglia are rare, even though MMP-9 plays a crucial role in the proinflammatory microenvironment by degrading the blood-brain barrier. We investigated the effects of Gln on the expression of MMP-9 in lipopolysaccharide (LPS)-stimulated BV2 microglial cells. Our findings showed that MMP-9 activity is significantly increased in response to LPS under Gln conditions. However, the Gln-free condition substantially inhibited LPS-induced MMP-9 activity and the expression of its corresponding gene. A matrigel invasion assay demonstrated that the Gln-free condition attenuates LPS-induced invasion of BV2 microglial cells. In addition, our results showed that the Gln-free condition diminishes LPS-induced nuclear factor-kappa B (NF-κB) and activator protein (AP)-1 activity, which are transcription factors that potentially regulate the expression of the MMP-9 gene. Taken together, these data suggest that the Gln-free condition inhibits LPS-induced invasion of BV2 microglial cells by suppressing MMP-9 expression, mainly via inhibition of the NF-κB and AP-1 pathway.

Glutamine supplementation alleviates vasculopathy and corrects metabolic profile in an in vivo model of endothelial cell dysfunction

Endothelial Cell Dysfunction (ECD) is a recognized harbinger of a host of chronic cardiovascular diseases. Using a mouse model of ECD triggered by treatment with L-Nω-methylarginine (L-NMMA), we previously demonstrated that renal microvasculature displays a perturbed protein profile, including diminished expression of two key enzymes of the Krebs cycle associated with a Warburg-type suppression of mitochondrial metabolism. We hypothesized that supplementation with L-glutamine (GLN), that can enter the Krebs cycle downstream this enzymatic bottleneck, would normalize vascular function and alleviate mitochondrial dysfunction. To test this hypothesis, mice with chronic L-NMMA-induced ECD were co-treated with GLN at different concentrations for 2 months. Results confirmed that L-NMMA led to a defect in acetylcholine-induced relaxation of aortic rings that was dose-dependently prevented by GLN. In caveolin-1 transgenic mice characterized by eNOS inactivation, L-NMMA further impaired vasorelaxation which was partially rescued by GLN co-treatment. Pro-inflammatory profile induced by L-NMMA was blunted in mice co-treated with GLN. Using an LC/MS platform for metabolite profiling, we sought to identify metabolic perturbations associated with ECD and offset by GLN supplementation. 3453 plasma molecules could be detected with 100% frequency in mice from at least one treatment group. Among these, 37 were found to be differentially expressed in a 4-way comparison of control vs. LNMMA both with and without GLN. One of such molecules, hippuric acid, an “uremic toxin” was found to be elevated in our non-uremic mice receiving L-NMMA, but normalized by treatment with GLN. Ex vivo analysis of hippuric acid effects on vasomotion demonstrated that it significantly reduced acetylcholine-induced vasorelaxation of vascular rings. In conclusion, functional and metabolic profiling of animals with early ECD revealed macrovasculopathy and that supplementation GLN is capable of improving vascular function. Metabolomic analyses reveal elevation of hippuric acid, which may further exacerbate vasculopathy even before the development of uremia.

Oral L-glutamine increases active GLP-1 (7-36) amide secretion and improves glycemic control in stretpozotocin-nicotinamide induced diabetic rats

L-glutamine is a non-essential amino acid. It decreased blood sugar, stimulated insulin secretion in type 2 diabetic patients. The objective of the present investigation was to evaluate L-glutamine increases glucagon like peptide-1 (GLP-1) (7-36) amide secretion in streptozotocin-nicotinamide (STZ-NTM) induced diabetic Sprague Dawley rats. Molecular docking study was performed to elucidate the molecular basis for GLP-1 receptor agonistic activity. Type 2 diabetes was induced in overnight fasted Sprague Dawley rats pre-treated with nicotinamide (100 mg/kg, i.p.) followed by 20 min after administration of streptozotocin (55 mg/kg, i.p.). The rats were divided into; I - nondiabetic, II - diabetic control, III - sitagliptin (5 mg/kg, p.o.), IV - L-glutamine (250 mg/kg, p.o.), V - L-glutamine (500 mg/kg, p.o.) and VI - L-glutamine (1000 mg/kg, p.o.). The L-glutamine and sitagliptin treatment was 8 week. Plasma glucose was estimated every week. Body weight, food and water intake were recorded daily. Glycosylated haemoglobin, lipid profile, plasma and colonic active (GLP-1) (7-36) amide, mRNA expression of proglucagon GLP-1, plasma and pancreatic insulin, histology of pancreata and biomarkers of oxidative stress (superoxidase dismutase, reduced glutathione, malondialdehyde, glutathione peroxidase, glutathione S transferase) were measured after 8 week. In acute study, the rats were divided into I - glucose (2.5 g/kg, p.o.), II - sitagliptin (5 mg/kg, p.o.), III - L-glutamine (250 mg/kg, p.o.), IV - L-glutamine (500 mg/kg, p.o.) and V - L-glutamine (1000 mg/kg, p.o.). Plasma glucose, active GLP-1 (7-36) amide concentration and insulin levels were measured after glucose loading. The docking data indicated that l-glutamine bind to the GLP-1 receptor. L-glutamine decreased plasma glucose, increased plasma and pancreatic insulin, increased plasma and colonic active GLP-1 (7-36) amide secretion as well as decreased oxidative stress in streptozotocin-nicotinamide induced diabetic rats.

The anti-oxidant effects are not the main mechanism for glutamine's protective effects on acute kidney injury in mice

Acute kidney injury (AKI) is a common problem characterized by an inflammatory response in the kidney and oxidative stress. However, there are no interventions to prevent AKI. Glutamine is an important precursor of glutathione and has also been shown to induce heat shock proteins (HSP). Thus, glutamine may affect both oxidative stress and inflammation. This study was to explore the effects of glutamine pretreatment on nephrotoxic AKI and to investigate the underlying mechanisms. First, the effects of alternate doses of glutamine were compared in CD-1 mice with AKI induced with folic acid intra-peritoneal injection. Then the effects of glutamine quercetin (an HSP inhibitor), and quercetin+glutamine, were compared in the same AKI model. AKI were assessed with plasma creatinine, urine neutrophil gelatinase-associated lipocalin, and renal histology. Inflammatory response was monitored with renal tumor necrosis factor (TNF-α), chemkines (CXCL1 and CCL2) contents, and neutrophil infiltration. Oxidative injury was detected with reduced glutathione, malondialdehyde, and protein thiol. Glutamine provided dose-dependent renal protection. Pretreatment with quercetin, which was showed to inhibit HSP-70 expression, abolished glutamine's renal-protective effects. Quercetin also abrogated glutamine's beneficial effects on renal TNF-α, chemokines, and neutrophil infiltration. However, quercetin did not affect glutamine's anti-oxidative effects. These results suggest that glutamine's renal-protective effects are mainly related to its activation of HSP-70, which mitigates inflammatory response, renal neutrophil infiltration and subsequent AKI. Regulating neutrophil infiltration might be a potential therapeutic target for AKI.

Does glutamine promote benefits for patients with diabetes mellitus scheduled for cardiac surgery?

BACKGROUND

We hypothesised, that perioperative use of N(2)-L-alanyl-L-glutamine confers cardioprotection and improves insulin resistance in diabetic patients with coronary artery disease operated under cardiopulmonary bypass.

METHODS

This double-blind, placebo-controlled, randomised study included 64 patients with diabetes mellitus type 2 who were scheduled for on-pump coronary artery bypass graft surgery. The protocol group (32 patients) and the control group (32 patients) glutamine (0.4 g/kg/day of 20% solution of N(2)-L-alanyl-L-glutamine ("Dipeptiven(®)" Fresenius Kabi, Germany)) and placebo (0.9% NaCl), respectively. Perioperative concentration of troponin I in plasma was considered as the primary end-point. Whereas the secondary end-points were insulin resistance, insulin sensitivity, β-cell function, blood glucose, plasma triglycerides and free fatty acids concentrations. Insulin resistance, insulin sensitivity and β-cell function were measured using HOMA equation. Thermodilution method was used to measure haemodynamics in all the patients.

RESULTS

No differences have been found in perioperative dynamics of troponin I, insulin resistance, insulin sensitivity, β-cell function, blood glucose, plasma triglycerides free fatty acids concentrations and haemodynamics.

CONCLUSION

Our results have failed to confirm the cardioprotective properties and modulatory effect on perioperative insulin resistance that are thought to be attributable to parenteral glutamine administration in dose 0.4 g/kg/day among cardiac patients with DM operated on under CPB.

Glutamine treatment decreases plasma and lymph cytotoxicity during sepsis in rats

Glutamine (Gln) is considered as a conditionally essential amino acid. Pharmacological supplementation of Gln helps to maintain the intestinal mucosal barrier, modulate cytokine production, and prevent organ injury during sepsis. Our previous study demonstrated the different effects of Gln on macrophage cytokine production in vitro or in vivo. The purpose of this study was to investigate the potential mechanism of Gln treatment to protect cells and modulate inflammation during sepsis in vivo. The results showed that administration of Gln significantly attenuated plasma-induced macrophage cytokine production and endothelial cell necrosis after cecal ligation and puncture in rats. In addition, it preserved human umbilical vein endothelial cell (HUVEC) viability and migration ability. Gln treatment also reduced lymph cytotoxicity by restoring macrophage tumor necrosis factor-α production, maintaining HUVEC viability, and decreasing endothelial cell necrosis. Mesenteric lymph duct ligation did not alleviate plasma cytotoxicity. Plasma lipopolysaccharide and d-lactate levels were suppressed after Gln treatment. Taken together, these results indicated that Gln administration can protect cells by attenuating the cytotoxicity of plasma and mesenteric lymph during sepsis.

Effect of parenteral l-alanyl-l-glutamine administration on phagocytic responses of polymorphonuclear neutrophilic leukocytes in dogs undergoing high-dose methylprednisolone sodium succinate treatment

OBJECTIVE

To determine whether parenteral l-alanyl-l-glutamine (Ala-Gln) administration modulated phagocytic responses of polymorphonuclear neutrophilic leukocytes (PMNs) from dogs undergoing high-dose methylprednisolone sodium succinate (MPSS) treatment.

ANIMALS

15 healthy Beagles.

PROCEDURES

Dogs were randomly assigned to 3 treatment groups (n = 5/group): 38-hour IV infusion of saline (0.9% NaCl) solution (control group), saline solution with 8.5% amino acids (2.3 g/kg/d), or saline solution with 8.5% amino acids (1.8 g/kg/d) and 20% l-alanyl-l-glutamine (Ala-Gln; 0.5 g/kg/d). High-dose MPSS treatment was initiated at the same time that IV infusions began, such that a total dose of 85 mg of MPSS/kg was administered through multiple IV injections over a 26-hour period. The infusions were maintained until 12 hours after the last MPSS injection. Blood samples collected before MPSS injections began and 2, 12, and 24 hours after injections ceased were used to evaluate PMN function.

RESULTS

MPSS injections resulted in an increase in the total number of circulating leukocytes and increases in neutrophil and monocyte counts but did not affect lymphocyte, eosinophil, or basophil counts. Lymphocyte counts in the Ala-Gln group were higher than in the control group 12 hours after MPSS injections finished. Relative to preinfusion values, phagocytic capacity, oxidative burst activity, and filamentous actin polymerization of PMNs were suppressed in all dogs except those that received Ala-Gln.

CONCLUSIONS AND CLINICAL RELEVANCE

Parenteral Ala-Gln administration in dogs resulted in an increase in PMN phagocytic responses that were suppressed by high-dose MPSS treatment.

L-glutamine is a key parameter in the immunosuppression phenomenon

Suppression of tumour-specific T-cell functions by myeloid-derived suppressor cells (MDSCs) is a dominant mechanism of tumour escape. MDSCs express two enzymes, i.e. inducible nitric oxide synthase (iNOS) and arginase (ARG1), which metabolize the semi-essential amino acid L-arginine (L-Arg) whose bioavailability is crucial for T-cell proliferation and functions. Recently, we showed that glutaminolysis supports MDSC maturation process by ensuring the supply of intermediates and energy. In this work, we used an immortalized cell line derived from mouse MDSCs (MSC-1 cell line) to further investigate the role of L-glutamine (L-Gln) in the maintenance of MDSC immunosuppressive activity. Culturing MSC-1 cells in L-Gln-limited medium inhibited iNOS activity, while ARG1 was not affected. MSC-1 cells inhibited Jukat cell growth without any noticeable effect on their viability. The characterization of MSC-1 cell metabolic profile revealed that L-Gln is an important precursor of lactate production via the NADP(+)-dependent malic enzyme, which co-produces NADPH. Moreover, the TCA cycle activity was down-regulated in the absence of L-Gln and the cell bioenergetic status was deteriorated accordingly. This strongly suggests that iNOS activity, but not that of ARG1, is related to an enhanced central carbon metabolism and a high bioenergetic status. Taken altogether, our results suggest that the control of glutaminolysis fluxes may represent a valuable target for immunotherapy.

The proline regulatory axis and cancer

Studies in metabolism and cancer have characterized changes in core pathways involving glucose and glutamine, emphasizing the provision of substrates for building cell mass. But recent findings suggest that pathways previously considered peripheral may play a critical role providing mechanisms for cell regulation. Several of these mechanisms involve the metabolism of non-essential amino acids, for example, the channeling of glycolytic intermediates into the serine pathway for one-carbon transfers. Historically, we proposed that the proline biosynthetic pathway participated in a metabolic interlock with glucose metabolism. The discovery that proline degradation is activated by p53 directed our attention to the initiation of apoptosis by proline oxidase/dehydrogenase. Now, however, we find that the biosynthetic mechanisms and the metabolic interlock may depend on the pathway from glutamine to proline, and it is markedly activated by the oncogene MYC. These findings add a new dimension to the proline regulatory axis in cancer and present attractive potential targets for cancer treatment.

Glutamine is cardioprotective in patients with ischemic heart disease following cardiopulmonary bypass

BACKGROUND

The aim of the present study was to investigate the cardioprotective effects of the perioperative use of N(2)-L-alanyl-L-glutamine (GLN) in patients with ischemic heart disease (IHD) who undergo their operations under cardiopulmonary bypass (CPB).

METHODS

This double-blind, placebo-controlled, randomized study included 50 patients who underwent cardiac surgery with CPB. Exclusion criteria were a left ventricular ejection fraction <50%, diabetes mellitus, <3 months since the onset of myocardial infarction, and emergency surgery. Patients in the study group (n = 25) received 0.4 g/kg GLN (Dipeptiven, 20% solution) per day. Patients in the control group (n = 25) were administered a placebo (0.9% NaCl). The primary end point was the dynamics of troponin I at the following stages: (1) prior to anesthesia, (2) 30 minutes after CPB, (3) 6 hours after CPB, (4) 24 hours after surgery, and (5) 48 hours after surgery. Secondary end points included measurements of hemodynamics with a Swan-Ganz catheter.

RESULTS

On the first postoperative day after the surgery, the median troponin I level was significantly lower in the study group than in the placebo group: 1.280 ng/mL (interquartile range [IQR], 0.840-2.230 ng/mL) versus 2.410 ng/mL (IQR, 1.060-6.600 ng/mL) (P = .035). At 4 hours after cardiopulmonary bypass (CPB), the median cardiac index was higher in the patients in the study group: 2.58 L/min per m2 (IQR, 2.34-2.91 L/min per m2) versus 2.03 L/min per m2 (IQR, 1.76-2.32 L/min per m2) (P = .002). The median stroke index also was higher in the patients who received GLN: 32.8 mL/m2 (IQR, 27.8-36.0 mL/m2) versus 26.1 mL/m2 (IQR, 22.6-31.8 mL/m2) (P = .023). The median systemic vascular resistance index was significantly lower in the study group than in the placebo group: 1942 dyn·s/cm5 per m2 (IQR, 1828-2209 dyn·s/cm5 per m2) versus 2456 dyn·s/cm5 per m2 (IQR, 2400-3265 dyn·s/cm5 per m2) (P = .001).

CONCLUSION

Perioperative administration of GLN during the first 24 hours has cardioprotective effects in IHD patients following CPB. This technique enhances the troponin concentration at 24 hours after surgery and is associated with improved myocardial function.

Metabolite profiling identifies pathways associated with metabolic risk in humans

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Glutamine and whey protein improve intestinal permeability and morphology in patients with Crohn's disease: a randomized controlled trial

BACKGROUND

Increased intestinal permeability (IP) has been implicated in the etiopathogenesis, disease activity and relapse of Crohn's disease (CD). Glutamine, the major fuel for the enterocytes, may improve IP.

AIM

We evaluated the effect of oral glutamine on IP and intestinal morphology in patients with CD.

METHODS

In a randomized controlled trial, consecutive patients with CD in remission phase with an abnormal IP were randomized to a glutamine group (GG) or active control group (ACG) and were given oral glutamine or whey protein, respectively, as 0.5 g/kg ideal body weight/day for 2 months. IP was assessed by the lactulose mannitol excretion ratio (LMR) in urine, and morphometry was performed by computerized image analysis system.

RESULTS

Patients (age 34.5 ± 10.5 years; 20 males) were assigned to the GG (n = 15) or ACG (n = 15). Fourteen patients in each group completed the trial. The LMR [median (range)] in GG and ACG at 2 months was 0.029 (0.006-0.090) and 0.033 (0.009-0.077), respectively, with P = 0.6133. IP normalized in 8 (57.1%) patients in each group (P = 1.000). The villous crypt ratio (VCR) [mean (SD)] in GG and ACG at 2 months was 2.68 (1.02) and 2.49 (0.67), respectively, (P = 0.347). At the end of 2 months LMR improved significantly in GG from 0.071 (0.041-0.254) to 0.029 (0.006-0.090) (P = 0.0012) and in ACG from 0.067 (0.040-0.136) to 0.033 (0.009-0.077) (P = 0.0063). VCR improved in the GG from 2.33 (0.77) to 2.68 (1.02) (P = 0.001), and in ACG from 2.26 (0.57) to 2.49 (0.67) (P = 0.009).

CONCLUSIONS

Intestinal permeability and morphology improved significantly in both glutamine and ACG.

Na-glutamine co-transporters B(0)AT1 in villus and SN2 in crypts are differentially altered in chronically inflamed rabbit intestine

Glutamine is a major nutrient utilized by the intestinal epithelium and is primarily assimilated via Na-glutamine co-transport (NGcT) on the brush border membrane (BBM) of enterocytes. Recently we reported that B(0)AT1 (SLC6A19) mediates glutamine absorption in villus while SN2 (SLC38A5) does the same in crypt cells. However, how B(0)AT1 and SN2 are affected during intestinal inflammation is unknown. In the present study it was shown that during chronic enteritis NGcT was inhibited in villus cells, however, it was stimulated in crypt cells. Our studies also demonstrated that the mechanism of inhibition of NGcT during chronic enteritis was secondary to a reduction in the number of B(0)AT1 co-transporters in the villus cell BBM without a change in the affinity of the co-transporter. In contrast, stimulation of NGcT in crypt cells was secondary to an increase in the affinity of SN2 for glutamine without an alteration in the number of co-transporters. Thus, glutamine assimilation which occurs via distinct transporters in crypt and villus cells is altered in the chronically inflamed intestine.

Oral glutamine attenuates cyclophosphamide-induced oxidative stress in the bladder but does not prevent hemorrhagic cystitis in rats

Cyclophosphamide (CP) is widely used in the treatment of cancer and non-malignant disease states such as rheumatoid arthritis. Hemorrhagic cystitis is a major dose-limiting side effect of CP. The incidence of this side effect is related to the dosage and can be as high as 75%. Elimination of the side effects of CP can lead to better tolerance of the drug, and a more efficient therapy can be achieved for patients in need of CP treatment. Several studies have demonstrated that oxidative stress and neutrophil infiltration play important roles in CP-induced bladder damage. Glutamine is utilized under clinical conditions for preventing chemotherapeutic drug-induced side effects, based on its ability to attenuate oxidative stress. The aim of the study is to verify whether glutamine prevents CP-induced oxidative stress and bladder damage using a rat model. Adult male rats were administered 150 mg/kg body weight of CP intraperitoneally. Glutamine pretreated rats were administered 1 g/kg body weight of glutamine orally 2 h before the administration of CP. Vehicle/glutamine-treated rats served as controls. All the rats were killed 16 h after the dose of CP/vehicle. The urinary bladders were removed and used for light microscopic and biochemical studies. The markers of oxidative stress including malondialdehyde content, protein carbonyl content, protein thiol, and myeloperoxidase activity, a marker of neutrophil infiltration, were measured in bladder homogenates. CP treatment induced hemorrhagic cystitis in the rats. Pretreatment with glutamine significantly reduced CP-induced lipid peroxidation (p < 0.01), protein oxidation (p < 0.01), and increase in myeloperoxidase activity (p < 0.05). However, it did not prevent CP-induced bladder damage. The results of the present study show that glutamine pretreatment does not attenuate CP-induced hemorrhagic cystitis, although it prevents CP-induced oxidative stress and neutrophil infiltration significantly. It is therefore necessary to clarify the utility of glutamine as a chemoprotective agent before it is recommended in the market as a nutrient supplement.

Effects of oral amino acid supplementation on long-term-care-acquired infections in elderly patients

The very high general infection rate (IRI) observed in our Geriatric Intensive Rehabilitation Center (GIRC) led us to investigate whether patient supplementation with essential amino acids (EAAs), modulators of immuno-competence, could reduce IRI. Eighty elderly patients admitted to our GIRC (n=40; age 79.5 ± 7.71; male/female 14/26) or placebo (n=40; age 82.13 ± 6.15; male/female 13/27) were allocated to an 8 g/day oral EAAs group and were surveyed for infections (>48 h from admission) over the first month of their hospital stay. The IRI was 67% for the entire population of patients, 82.5% (33/40 patients) in the placebo group and 52% (21/40 patients) in the EAA group (p<0.02). When patients were divided into infection group (IG) and without-infection group (WIG), independently of post randomization allocation, the WIG had higher levels of serum albumin (p<0.001), blood hemoglobin (Hb) concentration (p=0.01), dietary protein (p=0.008) calorie intakes (p=0.05) but lower serum C-reactive protein (CRP) (p<0.001). The factor of CRP>0.8 mg/dl and Hb ≤ 12 in females, ≤13 in males was associated 4 times and 3.6 times risk of infection, respectively, by sex. EAAs supplementation may lower the risk of infection by 30% in the rehabilitative elderly population. CRP and blood hemoglobin levels can be considered risk markers of future infection.

Lack of effect of glutamine administration to boost the innate immune system response in trauma patients in the intensive care unit

Introduction

The use of glutamine as a dietary supplement is associated with a reduced risk of infection. We hypothesized that the underlying mechanism could be an increase in the expression and/or functionality of Toll-like receptors (TLR), key receptors sensing infections. The objective of this study was to evaluate whether glutamine supplementation alters the expression and functionality of TLR2 and TLR4 in circulating monocytes of trauma patients admitted to the intensive care unit (ICU).

Methods

We designed a prospective, randomized and single-blind study. Twenty-three patients received parenteral nutrition (TPN) with a daily glutamine supplement of 0.35 g/kg. The control group (20 patients) received an isocaloric-isonitrogenated TPN. Blood samples were extracted before treatment, at 6 and 14 days. Expression of TLR2 and TLR4 was determined by flow cytometry. Monocytes were stimulated with TLR specific agonists and cytokines were measured in cell culture supernatants. Phagocytic ability of monocytes was also determined.

Results

Basal characteristics were similar in both groups. Monocytes from patients treated with glutamine expressed the same TLR2 levels as controls before treatment (4.9 ± 3.5 rmfi vs. 4.3 ± 1.9 rmfi, respectively; P = 0.9), at Day 6 (3.8 ± 2.3 rmfi vs. 4.0 ± 1.7 rmfi, respectively; P = 0.7) and at Day 14 (4.1 ± 2.1 rfim vs. 4.6 ± 1.9 rmfi, respectively; P = 0.08). TLR4 levels were not significantly different between the groups before treatment: (1.1 ± 1 rmfi vs 0.9 ± 0.1 rmfi respectively; P = 0.9), at Day 6 (1.1 ± 1 rmfi vs. 0.7 ± 0.4 rmfi respectively; P = 0.1) and at Day 14 (1.4 ± 1.9 rmfi vs. 1.0 ± 0.6 rmfi respectively; P = 0.8). No differences in cell responses to TLR agonists were found between groups. TLR functionality studied by phagocytosis did not vary between groups.

Conclusions

In trauma patients in the intensive care unit, TPN supplemented with glutamine does not improve the expression or the functionality of TLRs in peripheral blood monocytes.

Trial registration

ClinicalTrials.gov Identifier: NCT01250080.

Proline metabolism and microenvironmental stress

Proline, the only proteinogenic secondary amino acid, is metabolized by its own family of enzymes responding to metabolic stress and participating in metabolic signaling. Collagen in extracellular matrix, connective tissue, and bone is an abundant reservoir for proline. Matrix metalloproteinases degrading collagen are activated during stress to make proline available, and proline oxidase, the first enzyme in proline degradation, is induced by p53, peroxisome proliferator-activated receptor gamma (PPARgamma) and its ligands, and by AMP-activated protein kinase downregulating mTOR. Metabolism of proline generates electrons to produce ROS and initiates a variety of downstream effects, including blockade of the cell cycle, autophagy, and apoptosis. The electrons can also enter the electron transport chain to produce adenosine triphosphate for survival under nutrient stress. Pyrroline-5-carboxylate, the product of proline oxidation, is recycled back to proline with redox transfers or is sequentially converted to glutamate and alpha-ketoglutarate. The latter augments the prolyl hydroxylation of hypoxia-inducible factor-1alpha and its proteasomal degradation. These effects of proline oxidase, as well as its decreased levels in tumors, support its role as a tumor suppressor. The mechanism for its decrease is mediated by a specific microRNA. The metabolic signaling by proline oxidase between oxidized low-density lipoproteins and autophagy provides a functional link between obesity and increased cancer risk.

Effect of dietary glutamine supplementation on Salmonella colonization in the ceca of young broiler chicks

Live poultry is an important vehicle for transmitting Salmonella Typhimurium to humans that have salmonellosis. It is therefore imperative to reduce Salmonella Typhimurium levels in the gastrointestinal tract of live chickens. Glutamine is an established immunonutrient that is capable of alleviating disease conditions in humans and rats. Thus, 2 experiments that used Ross broiler chicks were conducted to evaluate the effect of glutamine supplementation at 1% level of the diet on cecal Salmonella Typhimurium levels in young broiler chicks. Experiment 1 consisted of i) treatment 1 (control, CN), in which chicks were given an unmedicated corn-soybean meal basal starter diet without glutamine supplementation or Salmonella Typhimurium challenge; ii) treatment 2 (CST), in which chicks were given the same diet as CN but challenged with 3.6 x 10(6) cfu Salmonella Typhimurium/mL at 3 d of age; and iii) treatment 3 (GST), in which chicks were given the unmedicated corn-soybean meal basal starter diet supplemented with glutamine at 1% level, and challenged with 3.6 x 10(6) cfu at 3 d of age. Experiment 2 used similar treatments (CN, CST, and GST), except that chicks in CST and GST were challenged with 7.4 x 10(7) cfu Salmonella Typhimurium/mL, and a fourth treatment was added. The fourth treatment consisted of chicks that were not challenged with Salmonella Typhimurium but given the same diet as in GST. Duration of each experiment was 14 d. Growth performance of chicks was monitored weekly, and cecal Salmonella Typhimurium concentration was microbiologically enumerated on d 4, 10, or 11 postchallenge. Results showed that glutamine supplementation improved BW and BW gain in experiment 2 (P < 0.05) but did not reduce cecal Salmonella Typhimurium levels in either experiment (P > 0.05). The optimum supplemental level of glutamine that will enhance intestinal resistance to Salmonella Typhimurium colonization should be determined.

Possible links between intestinal permeability and food processing: A potential therapeutic niche for glutamine

Increased intestinal permeability is a likely cause of various pathologies, such as allergies and metabolic or even cardiovascular disturbances. Intestinal permeability is found in many severe clinical situations and in common disorders such as irritable bowel syndrome. In these conditions, substances that are normally unable to cross the epithelial barrier gain access to the systemic circulation. To illustrate the potential harmfulness of leaky gut, we present an argument based on examples linked to protein or lipid glycation induced by modern food processing. Increased intestinal permeability should be largely improved by dietary addition of compounds, such as glutamine or curcumin, which both have the mechanistic potential to inhibit the inflammation and oxidative stress linked to tight junction opening. This brief review aims to increase physician awareness of this common, albeit largely unrecognized, pathology, which may be easily prevented or improved by means of simple nutritional changes.

Coupled amino acid deamidase-transport systems essential for Helicobacter pylori colonization

In addition to their classical roles as carbon or nitrogen sources, amino acids can be used for bacterial virulence, colonization, or stress resistance. We found that original deamidase-transport systems impact colonization by Helicobacter pylori, a human pathogen associated with gastric pathologies, including adenocarcinoma. We demonstrated that l-asparaginase (Hp-AnsB) and gamma-glutamyltranspeptidase (Hp-gammaGT) are highly active periplasmic deamidases in H. pylori, producing ammonia and aspartate or glutamate from asparagine and glutamine, respectively. Hp-GltS was identified as a sole and specialized transporter for glutamate, while aspartate was exclusively imported by Hp-DcuA. Uptake of Gln and Asn strictly relies on indirect pathways following prior periplasmic deamidation into Glu and Asp. Hence, in H. pylori, the coupled action of periplasmic deamidases with their respective transporters enables the acquisition of Glu and Asp from Gln and Asn, respectively. These systems were active at neutral rather than acidic pH, suggesting their function near the host epithelial cells. We showed that Hp-DcuA, the fourth component of these novel deamidase-transport systems, was as crucial as Hp-gammaGT, Hp-AnsB, and Hp-GltS for animal model colonization. In conclusion, the pH-regulated coupled amino acid deamidase-uptake system represents an original optimized system that is essential for in vivo colonization of the stomach environment by H. pylori. We propose a model in which these two nonredundant systems participate in H. pylori virulence by depleting gastric or immune cells from protective amino acids such as Gln and producing toxic ammonia close to the host cells.

Majority of dietary glutamine is utilized in first pass in preterm infants

Glutamine is a conditionally essential amino acid for very low-birth weight infants by virtue of its ability to play an important role in several key metabolic processes of immune cells and enterocytes. Although glutamine is known to be used to a great extent, the exact splanchnic metabolism in enterally fed preterm infants is unknown. We hypothesized that preterm infants show a high splanchnic first-pass glutamine metabolism and the primary metabolic fate of glutamine is oxidation. Five preterm infants (mean + or - SD birth weight 1.07 + or - 0.22 kg and GA 29 + or - 2 wk) were studied by dual tracer ([U-(13)C]glutamine and [(15)N(2)]glutamine) cross-over techniques on two study days (at postnatal week 3 + or - 1 wk). Splanchnic and whole-body glutamine kinetics were assessed by plasma isotopic enrichment of [U-(13)C]glutamine and [(15)N(2)]glutamine and breath (13)CO(2) enrichments. Mean fractional first-pass glutamine uptake was 73 + or - 6% and 57 + or - 17% on the study days. The splanchnic tissues contributed for a large part (57 + or - 6%) to the total amount of labeled carbon from glutamine retrieved in expiratory air. Dietary glutamine is used to a great extent by the splanchnic tissues in preterm infants and its carbon skeleton has an important role as fuel source.

Hypothesis: Muscular glutamine deficiency in sepsis--a necessary step for a hibernation-like state?

Glutamine depletion in skeletal muscle of severely ill patients is an outstanding metabolic marker related to acute skeletal muscle wasting. To date it is unclear why intracellular glutamine concentrations are lowered in skeletal muscle to such an extent when simultaneously muscular glutamine synthesis and release are stimulated. This essay introduces a hypothesis that intracellular glutamine deficiency is part of a metabolic program maintaining cell integrity. This program seems to resemble short-term hibernation, which can be observed in various mammalian species during periods of starvation. Interestingly, even in septic patients who do not survive, there are no signs of apoptosis or necrosis in affected organs. Therefore, in severe illness evolutionarily conserved energy saving programs may be switched on for protecting the organs in a mode reminiscent of hibernation. This would explain the low energy expenditure as described for septic patients and the limited success of nutrition in avoiding skeletal muscle atrophy in sepsis.

Oral glutamine protects against acute doxorubicin-induced cardiotoxicity of tumor-bearing rats

Doxorubicin (DOX), a widely used anticancer drug, has a dose-dependent cardiotoxicity, attributed mainly to free radical formation. The cardiomyocyte oxidative stress occurs rapidly after DOX treatment, resulting in harmful modifications to proteins, lipids, and DNA. Previous data showed that oral l-glutamine (Gln) prevented cardiac lipid peroxidation and maintained normal cardiac glutathione (GSH) levels in DOX-treated rats. Our aim in this study was to examine the effect of Gln on DOX-induced cardiac oxidative stress in a tumor-bearing host. Female Fisher344 rats with implanted MatBIII mammary tumors were randomized into 2 groups: a Gln group that received l-Gln (1 g.kg(-1).d(-1)) (n = 10) via a Gln-enriched diet and/or gavage with 50% Gln suspension during the whole experiment and a control group that was fed the same diet formulation without Gln and/or were gavaged with water. All rats received a single injection of 12 mg/kg DOX and were killed 3 d later. GSH levels of hearts, livers, tumors, and blood, as well as cardiac histological alterations, lipid peroxidation, peroxinitrite levels, and caspase-3 activation were determined. Cardiac physiologic alterations were assessed by ultrasound imaging before and 3 d after DOX administration. The Gln supplementation resulted in lower cardiac lipid peroxidation and peroxintrite levels and elevated cardiac catalase enzyme activity and GSH compared with the controls, without affecting those of the tumors. DOX-induced alterations of the echocardiographic parameters were significantly reduced in the Gln-supplemented rats. These data indicate that Gln is able to reduce the oxidative damage of cardiomyocytes that occurs soon after DOX administration and thus protects the heart of a tumor-bearing host from DOX-induced cardiomyopathy.

Combined infusion of glutamine and arginine: does it make sense?

PURPOSE OF REVIEW

Glutamine and arginine are conditionally essential amino acids because depletion occurs in stressed conditions. Intravenous glutamine supplementation reduces morbidity and mortality in critically ill patients fed parenterally. In surgical patients, arginine-enriched diets have beneficial effects, but the use of supplemental arginine in critically ill patients should be avoided in most cases.

RECENT FINDINGS

In addition to its role as a fuel, glutamine regulates gut barrier function, immuno-inflammatory response and antioxidant status. Arginine metabolism leads to nitric oxide and/or polyamines and thus modulates the immuno-inflammatory response and wound healing. Glutamine and arginine metabolism are closely related, and therefore may give additive or antagonist effects on several pathways. The effects of combined arginine and glutamine are still poorly documented. Combined administration of arginine and glutamine resulted in additive or synergistic effects on gut barrier function and inflammatory response but arginine reduced glutamine protection against oxidative stress. Preliminary data indicate that the combination may be beneficial during intestinal inflammation, whereas data in surgical or critically ill patients are still lacking.

SUMMARY

Mostly speculative effects of combined infusion of arginine and glutamine are discussed. Future studies are needed in specific pathophysiological conditions to assess whether this combination is beneficial or detrimental.

Inborn errors of proline metabolism

l-Proline concentration is primarily related to the balance of enzymatic activities of proline dehydrogenase [proline oxidase (POX)] and Delta-1-pyrroline-5-carboxylate (P5C) reductase. As a result, P5C plays a pivotal role in maintaining the concentration of proline in body fluids and inborn errors of P5C metabolism lead to disturbance of proline metabolism. Several inborn errors of proline metabolism have been described. Hyperprolinemia type I (HPI) is a result of a deficiency in POX. The POX gene (PRODH) is located on chromosome 22 (22q11.2) and this region is deleted in velo-cardio-facial syndrome, a congenital malformation syndrome. In addition, this gene locus is related to susceptibility to schizophrenia. The other type of hyperprolinemia is HPII. It is caused by a deficiency in P5C dehydrogenase activity. Hypoprolinemia, on the other hand, is found in the recently described deficiency of P5C synthetase. This enzyme defect leads to hyperammonemia associated with hypoornithinemia, hypocitrullinemia, and hypoargininemia other than hypoprolinemia. Hyperhydroxyprolinemia is an autosomal recessive inheritance disorder caused by the deficiency of hydroxyproline oxidase. There are no symptoms and it is believed to be a benign metabolic disorder. The deficiency of ornithine aminotransferase causes transient hyperammonemia during early infancy due to deficiency of ornithine in the urea cycle. In later life, gyrate atrophy of the retina occurs due to hyperornithinemia, a paradoxical phenomenon. Finally, prolidase deficiency is a rare autosomal recessive hereditary disease. Prolidase catalyzes hydrolysis of dipeptide or oligopeptide with a C-terminal proline or hydroxyproline and its deficiency can cause mental retardation and severe skin ulcers.

Clinical use of glutamine supplementation

Endogenous production of glutamine may become insufficient during critical illness. The shortage of glutamine is reflected as a decrease in plasma concentration, which is a prognostic factor for poor outcome in sepsis. Because glutamine is a precursor for nucleotide synthesis, rapidly dividing cells are most likely to suffer from a shortage. Therefore, exogenous glutamine supplementation is necessary. In particular, when i.v. nutrition is given, extra glutamine supplementation becomes critical, because most present formulations for i.v. use do not contain any glutamine for technical reasons. The major part of endogenously produced glutamine comes from skeletal muscle. For patients staying a long time in the intensive care unit (ICU), the muscle mass decreases rapidly, which leaves a tissue of diminishing size to maintain the export of glutamine. The metabolic and nutritional adaptation in long-staying ICU patients is poorly studied and is one of the fields that needs more scientific evidence for clinical recommendations. To date, there is evidence to support the clinical use of glutamine supplementation in critically ill patients, in hematology patients, and in oncology patients. Strong evidence is presently available for i.v. glutamine supplementation to critically ill patients on parenteral nutrition. This must be regarded as the standard of care. For patients on enteral nutrition, more evidence is needed. To guide administration of glutamine, there are good arguments to use measurement of plasma glutamine concentration for guidance. This will give an indication for treatment as well as proper dosing. Most patients will have a normalized plasma glutamine concentration by adding 20-25 g/24 h. Furthermore, there are no reported adverse or negative effects attributable to glutamine supplementation.

The 7th workshop on the assessment of adequate intake of dietary amino acids: summary of general discussion

Extensive discussion sessions were held at the end of each of the 2 d of the workshop. Through the course of the workshop, it became clear that there were different opinions on how to use uncertainty factors to obtain upper levels of intake from no observed adverse effect levels of a particular nutrient and that the selection of an appropriate uncertainty factor would be rather arbitrary. Much of the discussion centered around the potential for using metabolic limits, expressed as the level of intake at which the major pathway of metabolism may approach saturation and at which the amino acid is metabolized by alternative pathways, as a measurable early or surrogate marker for amino acid excess and possible toxicity. After extensive discussion on various conditions that would need to be satisfied for metabolic limits to be used as markers of excessive intake of amino acids, there was a general consensus that methods such as measuring oxidation limits are an attractive approach that merit future investigation. It was noted that there are many data on the clinical use of glutamine, whereas data for proline are very scarce. There was recognition that regardless of the available data, there is regulatory pressure for setting upper levels of intake for amino acids and that much more data are required.

Comparative aspects of tissue glutamine and proline metabolism

The cellular metabolism of glutamine and proline are closely interrelated, because they can be interconverted with glutamate and ornithine via the mitochondrial pathway involving pyrroline-5-carboxylate (P5C). In adults, glutamine and proline are converted via P5C to citrulline in the gut, then citrulline is converted to arginine in the kidney. In neonates, arginine is a semiindispensable amino acid and is synthesized from proline completely in the gut; because of low P5C synthase activity, glutamine is not an important precursor for neonatal arginine synthesis. Thus, splanchnic metabolism of glutamine and proline is important, because both amino acids serve as key precursors for arginine synthesis with some developmental differences. Studies investigating splanchnic extraction demonstrate that about two-thirds of dietary glutamine and almost all dietary glutamate are extracted on first pass and the vast majority is oxidized in the gut. This capacity to extract glutamine and glutamate appears to be very large, so diets high in glutamine or glutamate probably have little impact on circulating concentrations and consequent potential toxicity. In contrast, it appears that very little proline is extracted by the gut and liver, at least in the neonate, which may result in hyperprolinemia and potential toxicity. Therefore, the upper limits of safe dietary intake for glutamine and proline, and other amino acids, appear to be substantially different depending on the extent of first-pass splanchnic extraction and irreversible catabolism.