Regulation of protein turnover by glutamine in heat-shocked skeletal myotubes

Zhou X, Thompson JR
Department of Animal Science, The University of British Columbia, Vancouver, Canada.
Biochim Biophys Acta 1997 Jun 27;1357(2):234-42

Skeletal muscle accounts for approximately one-half of the protein pool in the whole body. Regulation of protein turnover in skeletal muscle is critical to protein homeostasis in the whole body. Glutamine has been suggested to exert an anabolic effect on protein turnover in skeletal muscle. In the present work, we characterized the effect of glutamine on the rates of protein synthesis and degradation in cultured rat skeletal myotubes under both normal and heat-stress conditions. We found that glutamine has a stimulatory effect on the rate of protein synthesis in stressed myotubes (21%, P < 0.05) but not in normal-cultured myotubes. Glutamine shows a differential effect on the rate of degradation of short-lived and long-lived proteins. In both normal-cultured and stressed myotubes, the half-life of short-lived proteins was not altered while the half-life of long-lived proteins increased with increasing concentrations of glutamine in a concentration-dependent manner. In normal-cultured myotubes, when glutamine concentration increased from 0 to 15 mM, the half-life of long-lived proteins increased 35% (P < 0.001) while in stressed myotubes, it increased 27% (P < 0.001). We also found that glutamine can significantly (P < 0.001) increase the levels of heat-shock protein 70 (HSP70) in stressed myotubes, indicating that HSP70 may participate in the mechanism underlying the effect of glutamine on protein turnover. We conclude that in cultured skeletal myotubes the stimulatory effect of glutamine on the rate of protein synthesis is condition-dependent, and that the inhibitory effect of glutamine on the rate of protein degradation occurs only on long-lived proteins.

Effect of glutamine on leucine metabolism in humans

Hankard RG, Haymond MW, Darmaun D
Nemours Children's Clinic, Jacksonville, Florida 32247, USA.
Am J Physiol 1996 Oct;271(4 Pt 1):E748-54

The aim of this study was to determine whether the putative protein anabolic effect of glutamine:

1) is mediated by increased protein synthesis or decreased protein breakdown and

2) is specific to glutamine.

Seven healthy adults were administered 5-h intravenous infusions of L-(1-14C)leucine in the postabsorptive state while receiving in a randomized order an enteral infusion of saline on one day or L-glutamine (800 micromol . kg-1 . h-1, equivalent to 0.11 g N/kg) on the other day. Seven additional subjects were studied using the same protocol except they received isonitrogenous infusion of glycine. The rates of leucine appearance (R(a Leu)), an index of protein degradation, leucine oxidation (Ox(Leu)), and nonoxidative leucine disposal (NOLD), an index of protein synthesis, were measured using the 14C specific activity of plasma alpha-ketoisocaproate and the excretion rate of 14CO2 in breath. During glutamine infusion, plasma glutamine concentration doubled (673 plus or minus 66 vs. 1,184 plus or minus 37 microM, P < 0.05), whereas R(a Leu) did not change (122 plus or minus 9 vs. 122 plus or minus 7 micromol . kg-1 . h-1), Ox(Leu) decreased (19 plus or minus 2 vs. 11 plus or minus 1 micromol kg-1 . h-1, P < 0.01), and NOLD increased (103 plus or minus 8 vs. 111 plus or minus 6 micromol . kg-1 . h-1, P < 0.01). During glycine infusion, plasma glycine increased 14-fold (268 plus or minus 62 vs. 3,806 plus or minus 546 microM, P < 0.01), but, in contrast to glutamine, R(a Leu) (124 plus or minus 6 vs. 110 plus or minus 4 micromol . kg- 1 . h-1, P = 0.02), Ox(Leu) (17 plus or minus 1 vs. 14 plus or minus 1 micromol . kg-1 . h- 1, P = 0.03), and NOLD (106 plus or minus 5 vs. 96 plus or minus 3 micromol . kg-1 . h-1, P < 0.65) all decreased. We conclude that glutamine enteral infusion may exert its protein anabolic effect by increasing protein synthesis, whereas an isonitrogenous amount of glycine merely decreases protein turnover with only a small anabolic effect resulting from a greater decrease in proteolysis than protein synthesis.

Glutamine metabolism and transport in skeletal muscle and heart and their clinical relevance

Rennie MJ, Ahmed A, Khogali SE, Low SY, Hundal HS, Taylor PM
Department of Anatomy and Physiology, University of Dundee, Scotland, United Kingdom.
J Nutr 1996 Apr;126(4 Suppl):1142S-9S

The glutamine and glutamate transporters in skeletal muscle and heart appear to play a role in control of the steady-state concentration of amino acids in the intracellular space and, in the case of skeletal muscle at least, in the rate of loss of glutamine to the plasma and to other organs and tissues. This article reviews what is currently known about transporter characteristics and mechanisms in skeletal muscle and heart, the alterations in transport activity in pathophysiological conditions and the implications for anabolic processes and cardiac function of altering the availability of glutamine. The possibilities that glutamine pool size is part of an osmotic signaling mechanism to regulate whole body protein metabolism is discussed and evidence is shown from work on cultured muscle cells. The possible uses of glutamine in maintaining cardiac function perioperatively and in promoting glycogen metabolism are discussed.

Inhibition of lipolysis and muscle protein degradation by EPA in cancer cachexia

Tisdale MJ
Pharmaceutical Sciences Institute, Aston University, Birmingham, United Kingdom.
Nutrition 1996 Jan;12(1 Suppl):S31-3

Depletion of muscle and adipose tissue in cancer cachexia appears to arise not only from decreased food intake but also from the production of catabolic factors by certain tumours. Experiments with the cachexia-inducing MAC16 tumour in mice showed that when part of the carbohydrate calories were replaced by fish oil, host body weight loss was inhibited. The effect occurred without an alteration of either the total calorie consumption or nitrogen intake. Instead, one of the polyunsaturated fatty acids (PUFA) in fish oil, eicosapentaenoic acid (EPA), was found directly to inhibit tumour- induced lipolysis. The effect was structurally specific, as two related PUFA, docosahexaenoic acid (DHA) and gamma-linolenic acid (GLA), were without effect. The antilipolytic effect of EPA arose from an inhibition of the elevation of cyclic AMP in adipocytes in response to the lipid mobilizing factor. The increased protein degradation in the skeletal muscle of cachectic animals was also inhibited by EPA. This effect was due to the inhibition of the rise in muscle prostaglandin E2 in response to a tumour-produced proteolytic factor by EPA. Thus, reversal of cachexia by EPA in this mouse model results from its capacity to interfere with tumour-produced catabolic factors. Similar factors have been detected in human cancer cachexia.

Glutamine: From basic science to clinical applications

Ziegler TR, Szeszycki EE, Estivariz CF, Puckett AB, Leader LM
Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, USA.
Nutrition 1996 Nov-Dec;12(11-12 Suppl):S68-70

Glutamine (Gln) has been one of the most intensively studied nutrients in the field of nutrition support in recent years. Interest in provision of Gln derives from animal studies in models of catabolic stress, primarily in rats. Enteral or parenteral Gln supplementation improved organ function and/or survival in most of these investigations. These studies have also supported the concept that Gln is a critical nutrient for the gut mucosa and immune cells. Recent molecular and protein chemistry studies are beginning to define the basic mechanism involved in Gln action in the gut, liver and other cells and organs. Double-blind prospective clinical investigations to date suggest that Gln-enriched parenteral or enteral feedings are generally safe and effective in catabolic patients. Intravenous Gln (either as the L-amino acid or as Gln-dipeptides) has been shown to increase plasma Gln levels, exert protein anabolic effects, improve gut structure and/or function and reduce important indices of morbidity, including infection rates and length of hospital stay in selected patients subgroups. Additional blinded studies of Gln administration in catabolic patients and increasing clinical experience with Gln-enriched nutrient products will determine whether routine Gln supplementation should be given in nutrition support, and to whom. Taken together, the data obtained over the past decade or so of intensive research on Gln nutrition demonstrate that this amino acid is an important dietary nutrient and is probably conditionally essential in humans in certain catabolic conditions.

Glutamine: Effects on the immune system, protein metabolism and intestinal function

Roth E, Spittler A, Oehler R
Chirurgisches Forschungslaboratorium, Universitatsklinik fur Chirurgie, Allgemeines Krankenhaus, Wien.
Wien Klin Wochenschr 1996;108(21):669-76

Glutamine is the most abundant free amino acid of the human body. In catabolic stress situations such as after operations, trauma and during sepsis the enhanced transport of glutamine to splanchnic organs and to blood cells results in an intracellular depletion of glutamine in skeletal muscle. Glutamine is an important metabolic substrate for cells cultivated under in vitro conditions and is a precursor for purines, pyrimidines and phospholipids. Increasing evidence suggests that glutamine is a crucial substrate for immunocompetent cells. Glutamine depletion in the cultivation medium decreases the mitogen-inducible proliferation of lymphocytes, possibly by arresting the cells in the G0-G1 phase of the cell cycle. Glutamine depletion in lymphocytes prevents the formation of signals necessary for late activation. In monocytes glutamine deprivation downregulates surface antigens responsible for antigen preservation and phagocytosis. Glutamine is a precursor for the synthesis of glutathionine and stimulates the formation of heat-shock proteins. Moreover, there are suggestions that glutamine plays a crucial role in osmotic regulation of cell volume and causes phosphorylation of proteins, both of which may stimulate intracellular protein synthesis. Experimental studies revealed that glutamine deficiency causes a necrotising enterocolitis and increases the mortality of animals subjected to bacterial stress. First clinical studies have demonstrated a decrease in the incidence of infections and a shortening of the hospital stay in patients after bone marrow transplantation by supplementation with glutamine. In critically ill patients parenteral glutamine reduced nitrogen loss and caused a reduction of the mortality rate. In surgical patients glutamine evoked an improvement of several immunological parameters. Moreover, glutamine exerted a trophic effect on the intestinal mucosa, decreased the intestinal permeability and thus may prevent the translocation of bacteria. In conclusion, glutamine is an important metabolic substrate of rapidly proliferating cells, influences the cellular hydration state and has multiple effects on the immune system, on intestinal function and on protein metabolism. In several disease states glutamine may consequently, become an in dispensable nutrient, which should be provided exogenously during artificial nutrition.

The emerging role of glutamine as an indicator of exercise stress and overtraining

Rowbottom DG, Keast D, Morton AR
Department of Microbiology, University of Western Australia, Perth.
Sports Med 1996 Feb;21(2):80-97

Glutamine is an amino acid essential for many important homeostatic functions and for the optimal functioning of a number of tissues in the body, particularly the immune system and the gut. However, during various catabolic states, such as infection, surgery, trauma and acidosis, glutamine homeostasis is placed under stress, and glutamine reserves, particularly in the skeletal muscle, are depleted. With regard to glutamine metabolism, exercise stress may be viewed in a similar light to other catabolic stresses. Plasma glutamine responses to both prolonged and high intensity exercise are characterised by increased levels during exercise followed by significant decreases during the post-exercise recovery period, with several hours of recovery required for restoration of pre-exercise levels, depending on the intensity and duration of exercise. If recovery between exercise bouts is inadequate, the acute effects of exercise on plasma glutamine level may be cumulative, since overload training has been shown to result in low plasma glutamine levels requiring prolonged recovery. Athletes suffering from the overtraining syndrome (OTS) appear to maintain low plasma glutamine levels for months or years. All these observations have important implications for organ functions in these athletes, particularly with regard to the gut and the cells of the immune system, which may be adversely affected. In conclusion, if methodological issues are carefully considered, plasma glutamine level may be useful as an indicator of an overtrained state.

[The role of glutamine in nutrition in clinical practice]

Campos FG, Waitzberg DL, Logulo AF, Mucerino DR, Habr-Gama A
Departamento de Gastroenterologia, Faculdade de Medicina, Universidade de Sao Paulo
Arq Gastroenterol 1996 Apr-Jun;33(2):86-92

Nutritional therapy using nutrients with pharmacological properties has been intensively discussed in the recent literature. Among these nutrients, glutamine has gained special attention. Glutamine is the most abundant amino acid in the blood stream of the mammals and, besides it has been considered a non-essential amino acid, glutamine is a non-dispensable nutrient in catabolic states. In this situation, there are alterations in its inter-organic flux, leading to lower plasmatic concentrations. Glutamine is the main fuel to enterocytes and it has an important role in the maintenance of intestinal structure and functions. Moreover, supplementation with glutamine has proved to be beneficial to the immunological system functions, improves nitrogen balance and nutritional parameters in the post-operative period and lessens protein loss in severe catabolic states. For these reasons, glutamine enriched-diets must be considered in the nutritional support of many diseases; new controlled, prospective and randomized studies will help to define what group of patients can really benefit from glutamine supplementation. (47 Refs.)

[The metabolic role of glutamine]

Balzola FA, Boggio-Bertinet D
Dipartimento Sperimentale di Gastroenterologia, Ospedale Molinette, Torino.
Minerva Gastroenterol Dietol 1996 Mar;42(1):17-26

Glutamine is a non essential amino acid. Nevertheless it has to be considered a "conditionally essential" amino acid for several metabolic reactions in which it is involved. Glutamine is the most abundant amino acid in human plasma and muscle. Because glutamine is highly unsteady, it was never used for enteral and parenteral nutrition in the past. It appears to be a unique amino acid for rapidly proliferating cells serving as a preferred fuel compared to glucose. It seems to be essential for cellular replication such as a "nitrogen carrier" between the tissues. A deficiency state of glutamine causes morphology and functional changing and negative nitrogen metabolism. The need for glutamine is particularly high when metabolism is increased as in the critically ill (surgical stress, sepsis, inflammatory states, fasten, burns) especially in the tissues with a rapid cell turn-over. In these conditions the body requirements of glutamine appear to exceed the individual's muscle deposits (muscle is the most important place of synthesis and storage), causing an increased synthesis with a high energy waste and loss of muscle mass. Glutamine is essential for bowel mucosa trophism and its deficiency in all the catabolic states allows bacterial translocation. In these cases feeding is not sufficient to restore basal conditions. At present enteral or parenteral glutamine supplementations are of high interest for the feeding of critically ill patients. (96 Refs.)

Glutamine and arginine metabolism in tumor-bearing rats receiving total parenteral nutrition

Yoshida S, Ishibashi N, Noake T, Shirouzu Y, Oka T, Shirouzu K
First Department of Surgery, School of Medicine, Kurume University, Fukuoka, Japan.
Metabolism 1997 Apr;46(4):370-3

Arginine supplementation increases glutamine levels in muscle and plasma. Since glutamine production is increased in catabolic states, these observations prompted us to investigate whether the flux of arginine to glutamine was increased in tumor-bearing (TB) rats, and we measured the synthesis rate of glutamine from arginine in control versus TB rats receiving standard total parenteral nutrition (TPN) solution. Male Donryu rats (N = 36; body weight, 200 to 225 g) were divided into two groups, control and TB rats. Yoshida sarcoma cells (1 x 106) were inoculated into the back of the rats (n = 18) subcutaneously on day 0. The rats were given free access to water and rat chow. On day 5, all animals, including non-TB rats (n = 18), were catheterized at the jugular vein and TPN was begun. On day 10, TPN solution containing either U-14C-glutamine (2.0 microCi/h) or U-14C-arginine (2.0 microCi/h) was infused as a 6-hour constant infusion. At the end of the isotope infusion, plasma was collected to determine the glutamine production rate in rats receiving U-14C-glutamine, and the ratio of specific activity of glutamine to specific activity of arginine was measured in rats receiving U- 14C-arginine. Only 2 g tumor caused a decrease in glutamine levels and an increase in glutamine and arginine production. The low flux rate of arginine to glutamine was observed in control rats (Arg to Gln, 41.0 plus or minus 11.9 micromol/kg/h). On the other hand, TB caused a significant increase in Arg to Gln compared with the control (213.3 plus or minus 66.1 micromol/kg/h, P < .01 v control). An increase in the flux rate of Arg to Gln was associated with an enhancement in the ratio of specific activity of ornithine to specific activity of arginine in TB rats (control 51.5% plus or minus 10.9% v 77.4% plus or minus 8.9%, P < .05). We conclude that (1) glutamine and arginine metabolism is altered with very small tumors, (2) although the flux of Arg to Gln was increased in TB and rats, the small increase in Arg to Gln cannot explain the observed large increase in Gln production.

Ornithine alpha-ketoglutarate metabolism after enteral administration in burn patients: Bolus compared with continuous infusion

Le Bricon T, Coudray-Lucas C, Lioret N, Lim SK, Plassart F, Schlegel L, De Bandt JP, Saizy R, Giboudeau J, Cynober L
Service de Biochimie A, Hopital St-Antoine, Paris, France.
Am J Clin Nutr 1997 Feb;65(2):512-8

Ornithine alpha-ketoglutarate (OKG) has been successfully used as an enteral supplement in the treatment of catabolic states, including burn injury. However, specific questions remain unanswered concerning burn patients, including OKG metabolism and metabolite production, appropriate mode of administration, and dose. We thus performed a kinetic study and followed plasma ornithine and OKG metabolite concentrations on day 7 postburn in 42 (35 men, 7 women) consecutive burn patients aged 33 plus or minus 2 y with a mean (plus or minus SEM) total burn surface area (TBSA) of 31 plus or minus 1%. Patients were randomly assigned to receive OKG as a single bolus (10 g; n = 13) or in the form of a continuous gastric infusion (10, 20, or 30 g/d over 21 h; n = 13) or an isonitrogenous control (n = 16). Plasma pharmacokinetics of ornithine followed a one-compartment model with first-order input (r = 0.993, P < 0.005). OKG was extensively metabolized in these patients (absorption constant = 0.028 min-1, elimination half-life = 89 min), with the production of glutamine, arginine, and proline; proline was quantitatively the main metabolite (in OKG bolus, area under the curve (AUC)(0-7h): proline, 41.4 plus or minus 5.6 nmol . min/L; glutamine, 20.4 plus or minus 5.7 mmol . min/L; and arginine, 7.3 plus or minus 1.9 mmol . min/L). Proline production was dose-dependent and quantitatively similar between modes of OKG administration. Glutamine and arginine production were not dose-dependent and were higher in the bolus group than in the infusion group. Overall, the bolus mode of OKG administration appeared to be associated with higher metabolite production compared with continuous infusion in burn patients, especially for glutamine and arginine.

Dietary modulation of amino acid transport in rat and human liver

Espat NJ, Watkins KT, Lind DS, Weis JK, Copeland EM, Souba WW
Department of Surgery, University of Florida, Gainesville 32601, USA.
J Surg Res 1996 Jun;63(1):263-8

Specialized diets enriched in the amino acids glutamine and arginine have been shown to benefit surgical patients. In the liver, glutamine supports glutathione biosynthesis, arginine regulates nitric oxide synthesis, and both of these amino acids serve as precursors for ureagenesis, gluconeogenesis, and acute phase protein synthesis. The effects of a diet enriched with glutamine and arginine on hepatic plasma membrane transport activity have not been studied in humans. We hypothesized that feeding supradietary amounts of these nutrients would enhance the activities of the specific carriers which mediate their transmembrane transport in the liver. We fed surgical patients (n = 8) and rats (n = 6) one of three diets: a) a regular diet, b) an enteral liquid diet containing arginine and glutamine, or c) an enteral diet supplemented with pharmacologic amounts of glutamine and arginine. Diets were isocaloric and were administered for 3 days. Hepatic plasma membrane vesicles were prepared from rat liver and from human wedge biopsies obtained at laparotomy. The transport of glutamine and arginine by rat and human vesicles was assayed. Vesicle integrity and functionality were verified by osmolarity plots, enzyme marker enrichments, and time courses. Provision of both a standard enteral liquid diet and one enriched with glutamine and arginine increased the activities of Systems N (glutamine) and y' (arginine) in rat and human liver compared to a control diet. The diet supplemented with glutamine and arginine was the most effective in increasing transport activity. We conclude that the liver responds to diets enriched with specific amino acids by increasing membrane transport activity. This adaptive response provides essential precursors for hepatocytes which may enhance hepatic synthetic functions during catabolic states. This study provides insights into the mechanisms by which enteral nutrition regulates nutrient transport at the cellular level and may provide a biochemical rationale for the use of formulas which are enriched with conditionally essential nutrients.

The increased synthesis of inducible nitric oxide inhibits IL-1ra synthesis by human articular chondrocytes: Possible role in osteoarthritic cartilage degradation

Pelletier JP, Mineau F, Ranger P, Tardif G, Martel-Pelletier J
Louis-Charles Simard Research Center, Notre-Dame Hospital, Department of Medicine, University of Montreal, Quebec, Canada.
Osteoarthritis Cartilage 1996 Mar;4(1):77-84

The degradation of osteoarthritic (OA) cartilage is likely related to the synthesis and the release of catabolic factors by chondrocytes. Nitric oxide (NO) has recently been suggested as playing a role in cartilage degradation. Since NO production is largely dependent on stimulation by IL-1, its effects on factors regulating the IL-1 biological activity, such as IL-1ra, are of the utmost importance. This study examined and compared the level of NO production by normal and OA cartilage and chondrocytes, as well as studied the effect of IL-1-induced NO production on the synthesis and steady-state mRNA of interleukin-l receptor antagonist (IL-1ra). The NO baseline production by normal cartilage explants was undetectable but inducible by rhIL-1beta. OA cartilage spontaneously produced NO. About a two-fold increase in NO production was found in OA rhIL-1beta-stimulated (0.5-100 units/ml) cartilage as compared with the similarly stimulated normal cartilage. On chondrocytes rhIL-1beta-stimulation (0.5-100 units/ml) produced a dose-dependent enhancement of both NO production and IL-1ra synthesis. Treatment with 200 microM N(g)-monomethyl-L-arginine (L-NMA), a well known NO synthase inhibitor, induced over 70% inhibition of the NO production and a marked increased IL-1ra synthesis (average of 84%) and expression (mRNA level). Inhibition of prostaglandin synthesis by indomethacin had no effect on both the NO production or the IL-1ra level. In the present study, we demonstrated the capacity of OA cartilage to produce a larger amount of NO than the normal controls, both in spontaneous and IL-1-stimulated conditions. These data support the notion that, in vivo, OA chondrocytes are stimulated by factors, possibly IL-1, which in turn may induce the expression of NO synthase, thus the synthesis of NO itself. Importantly, our results showed that the elevation of NO production may be an important factor in the pathophysiology of OA since it can reduce IL-1ra synthesis by chondrocytes. As such, an increased level of IL-1, associated with a decreased IL-1ra level, may be responsible for the stimulation of OA chondrocytes by this cytokine, leading to an enhancement of cartilage matrix degradation.

The role of nitric oxide in proteoglycan turnover by bovine articular cartilage organ cultures

Stefanovic-Racic M, Morales TI, Taskiran D, McIntyre LA, Evans CH
Ferguson Laboratory, Department of Orthopedic Surgery, University of Pittsburgh School of Medicine, PA 15261, USA.
J Immunol 1996 Feb 1;156(3):1213-20

Monolayer cultures of articular chondrocytes synthesize large amounts of nitric oxide (NO) following exposure to IL-1. The latter has antianabolic and procatabolic activities on these cells, but little is known about the role, if any, of NO in the integrated metabolic pathways of the chondrocyte. In the present study, the role of endogenously produced NO in both the synthesis and degradation of proteoglycans was investigated for the first time. Bovine articular cartilage slices exposed to 20 U/ml human rIL-1beta (hrIL-1beta) synthesized large amounts of NO for 1 to 2 days, after which production fell to a steady state level similar20% of the peak value for the remainder of the 14- day incubation. The NO synthase inhibitor, N-monomethyl L-arginine (L-NMA, 1 mM), blocked NO production and enhanced the acute catabolic effects of hrIL- 1beta in cartilage derived from both calves and adult animals. However, in late cultures, release of proteoglycans was reduced in the presence of L-NMA. The proteolytic activity in conditioned medium of these cultures (measured as caseinolytic activity) was enhanced by L-NMA; however, this inhibitor did not affect the rates of synthesis of proteoglycans. Although NO is widely assumed to be a mediator of cartilage catabolism, our data suggest that it may instead have an acute protective effect. Whether this effect is maintained chronically is less clear.

Alanylglutamine-enriched total parenteral nutrition improves protein metabolism more than branched chain amino acid-enriched total parenteral nutrition in protracted peritonitis

Naka S, Saito H, Hashiguchi Y, Lin MT, Furukawa S, Inaba T, Fukushima R, Wada N, Muto T
Department of Surgery, The University of Tokyo, Japan.
J Trauma 1997 Feb;42(2):183-90

Branched chain amino acids (BCAAs) and glutamine are both recommended in catabolic states. The object of this study was to compare the efficacies of alanylglutamine (Ala-Gln)-enriched and BCAA-enriched total parenteral nutrition (TPN) on the protein kinetics in peritonitis. Rats were divided into Ala-Gln and BCAA groups after intraperitoneal implantation of an osmotic pump, delivering a continuous infusion of Escherichia coli. Glutamine composed 30.0% (w/v) of the total amino acids in the Ala-Gln group, and BCAA composed 30.5% (w/v) of the total amino acids in the BCAA group. The two solutions were isocaloric and isonitrogenous. Whole body protein turnover and organ fractional protein synthetic rates (FSR) were measured on days 3 and 5. Serum amino acid levels and mucosal morphology were determined. Ala-Gln group had higher rates of whole body protein turnover, and hepatic FSR on both days. Serum glutamine levels correlated with hepatic and muscle FSR. Ala-Gln TPN group had greater mucosal thickness, numbers of mitoses per crypt, and FSR in distal intestine. Ala-Gln-enriched TPN may be a useful nutritional treatment modality in sepsis.

The effect of branched-chain amino acid-enriched parenteral nutrition on gut permeability

McCauley R, Heel KA, Barker PR, Hall J
University Department of Surgery, Royal Perth Hospital, Australia.
Nutrition 1996 Mar;12(3):176-9

In situations of catabolic stress, the gut becomes atrophic and has a diminished barrier function as evidenced by an increased permeability to a variety of molecules. It is known that the parenteral administration of branched-chain amino acids (BCAA) reduce gut atrophy. The aim of this study was to examine the effect of BCAA-enriched solutions of parenteral nutrients on gut permeability. A secondary aim was to observe the association between gut permeability and variables that have been used to assess jejunal atrophy. Central venous lines were inserted into 30 rats before randomization to receive nutritional support with: (1) a conventional parenteral solution (CPN), (2) A 2.0% BCAA-enriched solution (BCAA), or (3) rat food ad lib (Rat Food). The rats were assessed after 7 d for nutritional status, gut morphology, and gut permeability ratio (ratio of the permeability to 14C raffinose and 3H mannitol). We found that rats in the Rat Food Group lost the least amount of weight, had the least amount of jejunal atrophy, and had better preservation of harrier function as determined by gut permeability. When compared with the CPN Group, the BCAA Group had better preservation of jejunal morphology and protein content (p < 0.05), but a similar gut permeability. A cross-correlation matrix demonstrated a significant negative correlation between permeability to mannitol and mucosal weight, mucosal protein content and mucosal DNA content. Branched-chain amino acid-enriched parenteral nutrition reduced gut atrophy but not the gut permeability associated with parenteral nutrition. In the parenterally nourished rat model, atrophy of the jejunum is associated with increased permeability to small molecules.

Elevated hepatic gamma-glutamylcysteine synthetase activity and abnormal sulfate levels in liver and muscle tissue may explain abnormal cysteine and glutathione levels in SIV-infected rhesus macaques I

Gross A, Hack V, Stahl-Hennig C, Droge W
Department of Immunochemistry, Deutsches Krebsforschungszentrum, Heidelberg, Germany.
AIDS Res Hum Retroviruses 1996 Nov 20;12(17):1639-41

To establish whether the low cysteine and glutathione levels in HIV-infected patients and SIV-infected rhesus macaques may be consequences of an abnormal cysteine catabolism, we analyzed sulfate and glutathione levels in macaques. Muscle tissue (m. vastus lateralis and m. gastrocnemius) of SIV- infected macaques (n = 25) had higher sulfate and lower glutathione and glutamate levels than that of uninfected controls (n = 9). Hepatic tissue, in contrast, showed decreased sulfate and glutathione disulfide (GSSG) levels, and increased gamma-glutamylcysteine synthetase (gamma-GCS) activity. These findings suggest drainage of the cysteine pool by increased cysteine catabolism in skeletal muscle tissue, and by increased hepatic glutathione biosynthesis. Cachectic macaques also showed increased urea levels and decreased glutamine/urea ratios in the liver, which are obviously related to the abnormal urea excretion and negative nitrogen balance commonly observed in cachexia. As urea production and net glutamine synthesis in the liver are strongly influenced by proton-generating processes, the abnormal hepatic urea production may be the direct consequence of the cysteine deficiency and the decreased catabolic conversion of cysteine into sulfate and protons in the liver.

Development of an intravenous glutamine supply through dipeptide technology

Langer K
Department of Research and Development, Pharmacia & Upjohn, Erlangen, Germany.
Nutrition 1996 Nov-Dec;12(11-12 Suppl):S76-7

Glutamine is considered as semi-essential amino acid during catabolic stress. Due to its chemical instability in aqueous solutions during heat sterilization and long term storage, it could not be added to infusion solutions so far. In contrast, the dipeptide glycl-L-glutamine exhibits all properties needed for use as glutamine derivative in parenteral nutrition. It is freely soluble in water and does not decompose during heat sterilization. The peptide undergoes rapid enzymatic hydrolysis after infusion. This results in perfect utilization. Glycyl-L-glutamine is already produced in large amounts by chemical synthesis techniques. Both chemical and optical purity of the dipeptide can be controlled by modem chromatographic methods. Glamin, a newly developed complete amino acid solution, contains 20 g of glutamine per liter in form of glycyl-L-glutamine. Since no additional free glycine is added, no imbalances are created by the amino-terminal amino acid of the peptide structure.

Alanyl-glutamine prevents muscle atrophy and glutamine synthetase induction by glucocorticoids

Hickson RC, Wegrzyn LE, Osborne DF, Karl IE
School of Kinesiology, University of Illinois at Chicago 60608-1516, USA.
Am J Physiol 1996 Nov;271(5 Pt 2):R1165-72

The aims of this work were to establish whether glutamine infusion via alanyl-glutamine dipeptide provides effective therapy against muscle atrophy from glucocorticoids and whether the glucocorticoid induction of glutamine synthetase (GS) is downregulated by dipeptide supplementation. Rats were given hydrocortisone 21-acetate or the dosing vehicle and were infused with alanyl-alanine (AA) or alanyl-glutamine (AG) at the same concentrations and rates (1.15 micromol . min-1 . 100 g body wt-1, 0.75 ml/h) for 7 days. Compared with AA infusion in hormone-treated animals, AG infusion prevented total body and fast-twitch muscle mass losses by over 70%. Glucocorticoid treatment did not reduce muscle glutamine levels. Higher serum glutamine was found in the AG-infused (1.72 plus or minus 0.28 micromol/ml) compared with the AA-infused group (1.32 plus or minus 0.06 micromol/ml), but muscle glutamine concentrations were not elevated by AG infusion. Following glucocorticoid injections, GS enzyme activity was increased by two- to threefold in plantaris, fast-twitch white (superficial quadriceps), and fast-twitch red (deep quadriceps) muscle/fiber types of the AA group. Similarly, GS mRNA was elevated by 3.3- to 4.1-fold in these same muscles of hormone-treated, AA-infused rats. AG infusion diminished glucocorticoid effects on GS enzyme activity to 52-65% and on GS mRNA to 31-37% of the values with AA infusion. These results provide firsthand evidence of atrophy prevention from a catabolic state using glutamine in dipeptide form. Despite higher serum and muscle alanine levels with AA infusion than with AG infusion, alanine alone is not a sufficient stimulus to counteract muscle atrophy. The AG-induced muscle sparing is accompanied by diminished expression of a glucocorticoid-inducible gene in skeletal muscle. However, glutamine regulation of GS appears complex and may involve more regulators than muscle glutamine concentration alone.

Tissue-specific regulation of glutamine synthetase gene expression in acute pancreatitis is confirmed by using interleukin-1 receptor knockout mice

Abcouwer SF; Norman J; Fink G; Carter G; Lustig RJ; Souba WW
Department of Surgery, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Surgery (USA), 1996, 120/2 (255-264); discussion 263-4

Background. Acute pancreatitis causes a pronounced depletion of plasma and muscle glutamine pools. In several other catabolic disease states expression of the enzyme glutamine synthetase (GS) is induced in lung and muscle to support glutamine secretion by these organs. The hormonal mediators of GS induction have not been conclusively identified. We used mice deficient for the expression of the type 1 interleukin-1 receptor (IL-1R1 knockout mice) to investigate the expression of GS during acute edematous pancreatitis.

Methods. Acute edematous pancreatitis ways induced in adult male wild-type and IL-1R1 knockout mice by means of the intraperitoneal administration of cerulein, and their conditions were monitored. Five organs, including lung, liver, gastrocnemius muscle, spleen, and pancreas, were assayed for relative GS messenger RNA (mRNA) content by Northern blotting.

Results. The ultimate severity of pancreatitis was reduced by IL-1R1 deficiency. GS mRNA levels increased during progression of pancreatitis in lung, spleen, and muscle tissue from each group. No consistent increase in GS mRNA level was observed in liver. IL-1R1 deficiency did not affect GS mRNA expression in lung tissue but consistently retarded GS induction in the spleens of knockout animals. IL-1R deficiency altered the kinetics of GS induction in muscle.

Conclusions. Cerulein-induced experimental pancreatitis causes an induction in GS mRNA levels in a tissue-specific fashion. IL-1R1 deficiency reduced the ultimate severity of the condition and altered the induction of GS mRNA in the spleen and muscle.

Glutamine content of protein and peptide-based enteral products

Kuhn K.S.; Stehle P.; Furst P.
Biological Chemistry/Nutrition Inst., University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart Germany
Journal of Parenteral and Enteral Nutrition (USA), 1996, 20/4 (292-295)

Background: Glutamine is a conditionally essential amino acid for patients with severe catabolic illness, intestinal dysfunction, or immunodeficiency syndromes. Glutamine is a natural component in many enteral preparations, yet lacking methodology hampers its quantitative determination in dietary products.

Objective: The present study was assigned to assess glutamine contents in selected enteral products by using a newly developed method enabling the assessment of protein/peptide bound glutamine.

Methods: Fourteen commercially available enteral diets (10 protein based and 4 peptide based) were investigated. After removal of interfering fat and carbohydrates, the nitrogen content of the purified preparations was determined by chemiluminescence and protein/peptide bound glutamine was assessed using a three-step procedure; by using a novel prehydrolysis derivatization technique with bis(1,1-trifluoroacetoxy)iodobe nzene, glutamine is converted to acid stable diaminobutyric acid. The derivatives are hydrolyzed with a new microwave technology, and subsequently the amino acid composition is determined by reversed phase-high-performance liquid chromatography after dansyl-chloride derivatization.

Results: The content in the protein-based preparations varied between 5.2 and 8.1 g/16 g nitrogen. In the peptide- based products, considerably lower glutamine contents were measured (1.3 to 5.6 g/16 g nitrogen).

Conclusion: In the present study, we report for the first time glutamine contents in ready to use enteral products. The dally amount might be satisfactory for healthy individuals but probably not sufficient for the adequate support of the stressed patient. Reliable assessment of glutamine in enteral formulae is a prerequisite to perform clinical studies investigating glutamine requirements in the catabolic state.

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