Effects of glutamine supplementation, GH, and IGF-I on glutamine metabolism in critically ill patients

N. C. Jackson1, P. V. Carroll3, D. L. Russell-Jones1, P. H. Sönksen2, D. F. Treacher1, and A. M. Umpleby1

1 Departments of Diabetes, Endocrinology and Metabolic Medicine and 2 Intensive Care, St. Thomas' Hospital, London SE1 7EH; and 3 Department of Medicine, Greenwich District Hospital, Greenwich, London SE10 9HE, United Kingdom


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

During critical illness glutamine deficiency may develop. Glutamine supplementation can restore plasma concentration to normal, but the effect on glutamine metabolism is unknown. The use of growth hormone (GH) and insulin-like growth factor I (IGF-I) to prevent protein catabolism in these patients may exacerbate the glutamine deficiency. We have investigated, in critically ill patients, the effects of 72 h of treatment with standard parenteral nutrition (TPN; n = 6), TPN supplemented with glutamine (TPNGLN; 0.4 g · kg-1 · day-1, n = 6), or TPNGLN with combined GH (0.2 IU · kg-1 · day-1) and IGF-I (160 µg · kg -1 · day-1) (TPNGLN+GH/IGF-I; n = 5) on glutamine metabolism using [2-15N]glutamine. In patients receiving TPNGLN and TPNGLN+GH/IGF-I, plasma glutamine concentration was increased (338 ± 22 vs. 461 ± 24 µmol/l, P < 0.001, and 307 ± 65 vs. 524 ± 71 µmol/l, P < 0.05, respectively) and glutamine uptake was increased (5.2 ± 0.5 vs. 7.4 ± 0.7 µmol · kg-1 · min-1, P < 0.05 and 5.2 ± 1.1 vs. 7.6 ± 0.8 µmol · kg-1 · min-1, P < 0.05). Glutamine production and metabolic clearance rates were not altered by the three treatments. These results suggest that there is an increased requirement for glutamine in critically ill patients. Combined GH/IGF-I treatment with TPNGLN did not have adverse effects on glutamine metabolism.

stable isotopes; nutritional support; catabolism; postoperative care


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

DURING CRITICAL ILLNESS amino acids are mobilized from peripheral tissue, such as muscle, and are used by organs in the splanchnic area for gluconeogenesis, oxidation, ureagenesis, protein synthesis, and also as substrates for the immune system and wound healing (9). This is thought to lead to the wasting of lean body mass characteristic of critical illness, which often persists despite nutritional support. Because maintenance of body protein stores and the integrity of the gut mucosa may have an impact on morbidity and mortality, several strategies are currently being investigated to prevent the loss of lean tissue. These include the use of specialized nutrition and the use of anabolic hormones, such as growth hormone (GH) and insulin-like growth factor I (IGF-I).

Glutamine is the most abundant amino acid in the body and is traditionally classified as a nonessential amino acid because it is synthesized endogenously (2). However, marked decreases in free glutamine concentrations have been reported in a variety of catabolic states (1, 37). This suggests that during serious illness a deficiency in glutamine availability may develop and has led to the idea that glutamine is a conditionally essential amino acid (22).

At present, glutamine is not routinely added to parenteral nutrition solutions, but recent clinical trials suggest that glutamine supplementation improves both nitrogen balance and gut mucosal integrity and decreases the number of infections, length of hospital stay, and 6-mo mortality in critically ill patients (13, 36, 41). In a previous study we showed that, despite a fall in plasma glutamine concentration and an increase in glutamine clearance, plasma glutamine flux was unchanged in critically ill patients compared with matched healthy controls (18). Despite the current clinical interest in the potential benefits of glutamine supplementation, there have been no tracer studies investigating the effects of glutamine supplementation on glutamine metabolism in critically ill patients.

The availability of recombinant human GH (rhGH) and IGF-I (rhIGF-I) has led to considerable interest in their use, either alone or in combination, to reduce protein catabolism in a variety of catabolic states. However, evidence from recent multicenter trials has linked GH treatment with increased mortality in intensive care unit (ICU) patients (34). In these trials the patients did not receive routine glutamine supplementation. Because during periods of illness glutamine is mobilized from protein stores (sketetal muscle), an increase in protein anabolism may exacerbate the glutamine depletion seen in these patients. It is possible that this may have contributed to the increased mortality observed in these trials.

The aim of the present study was to use [2-15N]glutamine to investigate the effects of standard total parenteral nutrition (TPN) and parenteral nutrition supplemented with glutamine (TPNGLN) on whole body glutamine metabolism in critically ill patients. We also studied the addition of combined treatment with GH plus IGF-I and TPNGLN (TPNGLN+GH/IGF-I) on glutamine metabolism.


    METHODS
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Materials. L-[2-15N]glutamine [99 atom percent (AP)] and L-[1-13C]leucine (99 AP) were purchased from Tracer Technologies (Somerville, MA). Sterile solutions of the tracers were prepared in 0.9% saline with an aseptic technique by the Pharmacy Department of Guy's and St Thomas' Hospital (London, UK). The standard TPN consisted of 50% dextrose, Intralipid 20% (Kabivitrum, Stockholm, Sweden), and a mixed amino acid solution (Vamin 14; Pharmacia & Upjohn, Milton Keynes, UK). L-Glutamine solution was purchased from Oxford Nutrition (Oxford, UK) and was stored at -20°C until use. GH and IGF-I were supplied by Pharmacia & Upjohn.

Subjects. Nineteen severely ill patients in the ICU of St Thomas' Hospital were initially studied. Two patients died before completion of the second study; thus data are presented only from the 17 patients who survived to complete both studies. However, as indicated in Table 1, one patient later died in the ICU. The patients were all newly admitted to the ICU, and the majority had undergone emergency abdominal surgery. All required mechanical ventilation and intravenous nutritional support. Further details of their clinical and metabolic characteristics are summarized in Table 1. The severity of illness was evaluated on the day of the study by use of the APACHE II and TISS score systems (5, 21).

                              
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Table 1.   Clinical and metabolic characteristics of patients

The protocol was approved by the Ethics Committee, Guy's and St. Thomas' National Health Service Trust. Written informed consent was obtained from relatives of the patients.

Study protocol. All of the patients were fasted for >= 12 h before the start of the first study. Indwelling arterial and central venous lines were used for blood sampling and for the tracer infusion, respectively. After baseline sampling, a priming bolus of [1-13C]leucine (1 mg/kg) was injected, and 4-h constant infusions of [2-15N]glutamine (2.5 mg · kg-1 · h-1) and [1-13C]leucine (1 mg · kg-1 · h-1) were started. Blood samples were taken at 210, 215, 220, 225, 230, and 240 min for steady-state measurement of plasma glutamine and alpha -ketoisocaproic acid (alpha -KIC) enrichment and glutamine concentration. Samples were also taken at steady state for the measurement of routine biochemistry, metabolite, and hormone levels [glucose, insulin, IGF-I, IGF-binding protein-1 (IGFBP-1), cortisol, glucagon, thyroid hormones, and amino acids]. For glutamine analysis, 0.5-ml lithium heparin plasma ali-quots were mixed with 100 µl internal standard (100 nmol L-[U-13C5]glutamine). All samples were stored at -70oC until analysis.

At the end of the baseline study, patients were randomized to receive either standard TPN, TPN with additional intravenous glutamine (TPNGLN: 0.4 g · kg-1 · day-1), or TPNGLN with rhGH (0.2 IU · kg-1 · day-1) and rhIGF-I (160 µg · kg-1 · day-1). The patients randomized to TPNGLN received additional nitrogen in the form of the glutamine infusion (~0.06 g N · kg-1 · day-1). The nutritional support was not made isonitrogenous because this could have limited the availability of other amino acids. A continuous insulin infusion (Actrapid; Novo Nordisk, Copenhagen, Denmark) was provided if required to maintain plasma glucose concentration at or below 7 mmol/l. The GH was administered as a single subcutaneous injection; the dose of IGF-I was split into two equal twice daily subcutaneous injections.

After 72 h of treatment, a second turnover study was performed using the same tracers and infusion rates as the initial study. In this second study the patients were not fasted, as nutritional support was continued throughout the protocol (Fig. 1). The patients were all sedated and mechanically ventilated (Servo 900; Siemens, Berlin, Germany) throughout both studies.


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Fig. 1.   Schematic representation of study protocol. All patients were initially studied in the fasting state and were then randomized to receive either total parenteral nutrition (TPN, n = 6), TPN + Gln (TPNGLN, n = 6), or TPNGLN + growth hormone (GH) + insulin-like growth factor (IGF-I) (TPNGLN+GH/IGF-I, n = 5). After 72 h of nutritional ± hormonal treatment, a second tracer study was performed during which nutritional support was continued. Hatched areas represent tracer studies. Infusion protocol is shown at bottom of diagram.

Experimental methods. The isotopic enrichment and concentration of glutamine were determined from the tert-butyldimethylsilyl derivative by use of a method modified from Wolfe (40). Glutamine concentration was determined by reverse isotope dilution using L-[U-13C5]glutamine (Bioquote, North Yorkshire, UK) as the internal standard. Analysis by gas chromatography-mass spectrometry (GC-MS; MSD 5971A, Hewlett-Packard, Berkshire, UK) used electron impact ionization with selected ion monitoring of the [M-butyl]+ ions at mass-to-charge ratios (m/z) 431, 432, and 436. The isotopic enrichment of alpha -KIC was measured as the quinoxalinol- tert-butyldimethylsilyl derivative by use of a method modified from Ford and co-workers (8). GC-MS analysis used electron impact ionization with selected ion monitoring of the [M-butyl]+ ions at m/z 259 and 260. Plasma glucose concentrations were measured on a model 23AM glucose analyzer (YSI, Hampshire, UK). Serum insulin concentrations were measured by an in-house double-antibody RIA (32). Total IGF-I was measured by RIA after acid ethanol extraction. Total IGFBP-1 was measured by a coated-tube immunoradiometric assay (Diagnostic Systems Laboratories, Webster, TX). Cortisol was measured by ELISA using the Enzymun-Test cortisol kit (Boehringer Mannheim, Sussex, UK). Glucagon was measured using a commercially available RIA kit (Linco Research, St Louis, MO). Free thyroid hormones were measured by a competitive immunoassay using chemiluminescence (Chiron Diagnostics, Essex, UK). Plasma amino acid concentrations were measured on an Alpha II+ automated amino acid analyzer (Pharmacia, Hertfordshire, UK). Plasma albumin and C-reactive protein were measured using an automated method (Kodak 250, Ortho Clinical Diagnostics, Amersham, UK).

Calculations. Measurements of glutamine metabolism were calculated using standard isotope dilution equations. Glutamine appearance rate (RaGln; µmol · min-1 · kg-1) was calculated as RaGln = F[1/(APEGln · 0.01)-1], where F is the isotope infusion rate (µmol · min-1 · kg-1), and APEGln is the plasma glutamine enrichment. In the postabsorptive state, the endogenous glutamine rate of appearance in plasma (Endo RaGln) is equal to the calculated RaGln. At steady state, the rate of disappearance of glutamine from plasma (glutamine uptake: RdGln) was assumed to be equal to RaGln. Leucine appearance rate was calculated using an analogous equation but with use of the plasma enrichment of alpha -KIC as a measure of intracellular leucine enrichment (27). Glutamine metabolic clearance rate (MCR; ml · min-1 · kg-1) was calculated as MCR = RdGln/[Gln], where [Gln] is the steady-state plasma glutamine concentration (µmol/ml).

Because glutamine is a nonessential amino acid in the fasting state, RaGln is derived from both protein breakdown (BGln) and de novo glutamine synthesis (DGln). BGln was estimated as 0.78 × RaLeu (7), and DGln was calculated as DGln = RaGln - BGln (15).

Nutritional support was maintained throughout the second study. Because the patients were not in the postabsorptive state, the equations given above were corrected for the known exogenous rates of leucine and glutamine infusion. In all three treatment groups, the exogenous rate of infusion of leucine (ILeu) was calculated from the TPN regimen, and the endogenous leucine rate of appearance in plasma from protein breakdown (Endo RaLeu) was estimated as Endo RaLeu = RaLeu - ILeu. In the group of patients receiving TPN without glutamine supplementation, BGln was estimated using Endo RaLeu, and DGln was calculated as shown above.

For the two groups of patients receiving TPNGLN, the exogenous rate of glutamine infusion (IGln) was calculated, and the endogenous glutamine rate of appearance in plasma (Endo RaGln) was estimated as Endo RaGln = RaGln - IGln. BGln was estimated using Endo RaLeu, and DGln was calculated using Endo RaGln.

Statistics. All data are presented as means ± SE. "Steady state" for plasma glutamine and alpha -KIC enrichments was confirmed as an insignificant correlation with time (P > 0.05) by use of repeated-measures ANOVA (NCSS 6.0, Dr. J. Hintze, Kaysville, UT). Comparisons between groups were made using ANOVA, and comparisons between study 1 and study 2 were made by standard two-tailed paired t-tests. The insulin, IGFBP-1, cortisol, and glucagon data were log transformed before analysis.


    RESULTS
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Table 1 shows the details of the 17 ICU patients studied. There were no significant differences in age, weight, height, or body mass index among the three treatment groups. The severity of illness is indicated by the APACHE II and TISS scores, which identify the patients as being severely ill and dependent on cardiorespiratory and nutritional support (5, 21). There were no significant differences in the APACHE II and TISS scores among the three groups of ICU patients at the start of the study. None of the patients was acidemic, and there were no differences in the arterial pH values among the patient groups in study 1 (TPN, 7.43 ± 0.03; TPNGLN, 7.44 ± 0.02; TPNGLN+GH/IGF-I, 7.39 ± 0.02). In addition, bicarbonate concentrations indicated no depletion of alkaline reserves (TPN, 26 ± 2 mmol/l; TPNGLN, 26 ± 1.5 mmol/l; TPNGLN+GH/IGF-I, 25 ± 2.3 mmol/l). There were no significant changes in arterial blood gas analysis between study 1 and study 2. Plasma urea concentrations were elevated in all groups in study 1, indicating a high rate of protein catabolism (TPN, 13.0 ± 2.3 mmol/l; TPNGLN, 12.9 ± 2.5 mmol/l; TPNGLN+GH/IGF-I, 9.3 ± 1.4 mmol/l; normal reference range 4-7 mmol/l).

The glucose and insulin data are shown in Fig. 2. There was a trend toward increased plasma glucose levels in the second studies for all three treatment groups. However, this increase only reached significance in the TPN and TPNGLN+GH/IGF-I groups (P < 0.05). Plasma insulin levels increased in study 2 for all three treatment groups (TPN, P < 0.01; TPNLGLN, P < 0.05); however, this failed to reach significance in the TPNGLN+GH/IGF-I group (P = 0.13). Insulin infusion rates in study 2 were 1.0 ± 0.4 U/h in the TPN (n = 4) and 1.5 ± 0.6 U/h in the TPNGLN (n = 4) patient groups. In the TPNGLN+GH group only one patient received 2 U/h insulin during study 2. The measured total IGF-I concentrations were similar in all three groups in study 1 (TPN, 13.6 ± 1.8 nmol/l; TPNGLN, 12.1 ± 0.9 nmol/l; TPNGLN+GH/IGF-I, 10.3 ± 0.8 nmol/l), and these values were lower than those reported from healthy control subjects of a similar age (16.5 ± 1.7 nmol/l; see Ref. 18). Total IGF-I was unchanged after both TPN and TPNGLN; however, as expected, there was a significant increase in study 2 (48.1 ± 9.1 nmol/l) in the TPNGLN+GH/IGF-I group (P < 0.05). IGFBP-1 was significantly decreased in study 2 in the TPN group (231 ± 79 vs. 39 ± 12 ng/ml, P < 0.05); however, the changes in the TPNGLN (87 ± 35 vs. 132 ± 86 ng/ml) and TPNGLN+GH/IGF-I (134 ± 59 vs. 58 ± 15 ng/ml) groups were not significant. There were no significant changes in cortisol, free thyroxine, free triiodothyronine, or glucagon levels between studies 1 and 2 for the three treatment groups.


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Fig. 2.   Glucose (A) and insulin concentrations (B) in study 1 (open bars) and study 2 (filled bars). Values are means ± SE.

Plasma amino acid profiles are shown in Table 2. In the group receiving TPN there were significant increases in plasma serine (P < 0.05), glycine (P < 0.05), alanine (P < 0.05), methionine (P < 0.01), and ornithine (P < 0.05) levels in study 2. However, the increase in total amino acids did not reach significance (P = 0.07). Plasma serine (P < 0.05), glutamate (P < 0.05), glutamine (P < 0.001), glycine (P < 0.05), alanine (P < 0.001), methionine (P < 0.05), histidine (P < 0.01), and total amino acids (P < 0.01) were all significantly increased in the second study in the patients receiving TPNGLN. In the group receiving TPNGLN+GH/IGF-I, the plasma profiles were similar in studies 1 and 2, apart from increases in glutamine (P < 0.05) and phenylalanine concentrations (P < 0.05).

                              
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Table 2.   Plasma amino acid profiles

Figure 3 shows the plasma glutamine enrichments and concentrations from studies 1 and 2 for the TPNGLN patient group during the final 30 min of tracer infusion, indicating that steady state was achieved. Similar glutamine enrichment and concentration steady states were achieved for the other two patient groups (data not shown). The glutamine metabolic data are summarized in Fig. 4. Glutamine production rate and MCR were not affected by any of the three treatments. Glutamine uptake was significantly increased in the second study in both the TPNGLN (5.2 ± 0.5 vs. 7.4 ± 0.7 µmol · kg-1 · min-1, P < 0.05) and TPNGLN+GH/IGF-I (5.2 ± 1.1 vs. 7.6 ± 0.8 µmol · kg-1 · min-1, P < 0.05) groups but was unchanged in the TPN group.


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Fig. 3.   Plasma glutamine enrichment (atom percent excess, APE; A) and concentration (µmol/l, B) for total parenteral nutrition + Gln (TPNGLN) patients in study 1 (open circle ) and study 2 (). Values are means ± SE; n = 6.



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Fig. 4.   Glutamine production rate (A), glutamine metabolic clearance rate (MCR; B), and glutamine uptake (C) in study 1 (open bars) and study 2 (filled bars). Values are means ± SE.

BGln was significantly decreased in study 2 in the TPN group (2.5 ± 0.2 vs. 2.1 ± 0.2 µmol · kg-1 · min-1, P < 0.01), and although a similar trend was observed in the TPNGLN group, this failed to reach significance (2.0 ± 0.1 vs. 1.7 ± 0.2 µmol · kg-1 · min-1, P = 0.08). When expressed as a percentage of Endo RaGln, protein-derived glutamine release was decreased after treatment with TPN (44 ± 4 vs. 40 ± 3%, P < 0.05) and TPNGLN (40 ± 3 vs. 32 ± 3%, P < 0.05; Fig. 5). In the TPNGLN+GH/IGF-I group there was no significant change in BGln (2.1 ± 0.3 vs. 1.9 ± 0.2 µmol · kg-1 · min-1). The decrease in the percentage of the glutamine Ra derived from proteolysis also failed to reach significance in this group (46 ± 6 vs. 35 ± 4%, P = 0.08; Fig. 5).


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Fig. 5.   Percentage of endogenous glutamine appearance rate derived from protein breakdown (A) and de novo synthesis (B) in study 1 (open bars) and study 2 (filled bars). Values are means ± SE.

DGln was not significantly altered by treatment with TPN (3.2 ± 0.5 vs. 3.3 ± 0.5 µmol · kg-1 · min-1), TPNGLN (3.1 ± 0.5 vs. 3.8 ± 0.5 µmol · kg-1 · min-1), or TPNGLN+GH/IGF-I (3.0 ± 1.0 vs. 3.9 ± 0.7 µmol · kg-1 · min-1). However, the percentage of the glutamine Ra arising from DGln was significantly increased after treatment with TPN (56 ± 4 vs. 60 ± 3%, P < 0.05) and TPNGLN (60 ± 3 vs. 68 ± 3%, P < 0.05; Fig. 5). Although a similar trend was seen in the TPNGLN+GH/IGF-I group, this failed to reach significance (54 ± 6 vs. 65 ± 4%, P = 0.08; Fig. 5).


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

This study demonstrates that supplementation of TPN with glutamine in critically ill patients restores plasma glutamine concentration to nearly normal levels and increases glutamine uptake. A similar increase in plasma glutamine concentration and glutamine uptake was found when combined GH/IGF-I therapy was added to TPN with glutamine supplementation. This suggests that combined GH/IGF-I therapy does not have adverse effects on glutamine metabolism in these patients.

Marked decreases in free glutamine concentrations have been reported in catabolic states associated with protein wasting. To date it has not been established whether this fall in glutamine concentration is a true glutamine deficiency or an alteration in glutamine homeostasis related to severe illness. Several studies have shown that the addition of glutamine or its analogs to TPN improves nitrogen balance and reduces the fall in muscle glutamine concentration and protein synthesis in postoperative patients (3, 14, 30, 33, 39). In the present study, we found that glutamine supplementation to TPN increased plasma glutamine concentration. The patients were fasted for >= 12 h before the first study, but nutritional support was continued throughout the second study. By using an isotopic tracer of glutamine to measure glutamine metabolism, we were also able to demonstrate that whole body glutamine uptake was increased. This increased uptake may be for use by tissues with high metabolic demands for glutamine, such as the immune system and the gastrointestinal tract. TPN without glutamine supplementation failed to normalize glutamine concentration and had no effect on glutamine uptake, suggesting that glutamine supplementation may be important to meet the increased metabolic demands of glutamine-requiring tissues in the catabolic state.

In a previous study we showed that, despite a marked decrease in plasma glutamine concentration, plasma glutamine flux was unchanged in critically ill patients compared with matched healthy controls. We also found that glutamine MCR was increased in these patients, suggesting that the primary mechanism for the reduced concentration may be an increased efficiency of glutamine transport (18). In the present study when exogenous glutamine was provided, with or without GH/IGF-I treatment, glutamine MCR remained elevated. The increased glutamine uptake would thus have been facilitated by the increased efficiency of glutamine transport.

Acute glutamine depletion induced by phenylbutyrate in healthy adults has also been shown not to affect the glutamine appearance rate (7). However, Gore and Jahoor (12) reported an increased glutamine flux (60%) in burns patients compared with controls. In the present study there was a decrease in the proportion of endogenous glutamine production derived from protein breakdown when the patients were receiving nutritional support, although this decrease did not achieve significance in the TPNGLN+GH/IGF-I-treated patients.

Exogenous insulin was given when necessary to maintain the patients' blood glucose at or below 7 mmol/l, a standard procedure in the ICU at St Thomas' Hospital. This treatment contributed to the observed increase in plasma insulin concentration in the TPN and TPNGLN groups. The increase in insulin concentration was not statistically significant in the TPNGLN+ GH/IGF-I group; this may be related to the fact that only one patient received exogenous insulin in this group. Because insulin plays a central role in protein metabolism by reducing protein breakdown (10), this may account for some of the decrease in glutamine production derived from protein breakdown in the TPN and TPNGLN groups. Similarly, the insulin deficiency of type 1 diabetes mellitus has been shown to increase the proportion of the glutamine appearance from protein breakdown (6). The fact that glutamine production rate was unchanged in the present study suggests that there was a shift to de novo synthesis of glutamine from the exogenous supply of amino acids.

Many of the early studies on the effects of glutamine supplementation assessed nitrogen balance and protein synthesis using ribosomal analysis. The improvement in nitrogen balance with glutamine supplementation led to the assumption that some of the benefits associated with glutamine supplementation were mediated through alterations in protein metabolism and the preservation of muscle mass. In addition, experiments using animal models had indicated a positive relationship between protein synthesis and glutamine concentration (20, 26). More recently, enteral glutamine infusions in healthy adults have been shown to increase protein synthesis (16). However, there is no direct evidence from studies in humans that increased muscle glutamine concentration enhances protein synthesis in catabolic states. Whole body protein metabolism in critically ill patients was not affected by glutamine supplementation of enteral nutrition (24). Interpretation of the improvement in nitrogen balance needs caution, as a significant proportion of this balance may be due to replenishment of the muscle glutamine pool rather than synthesis of glutamine-containing proteins (38).

The benefits of glutamine supplementation may be mediated through other tissues and pathways rather than via a direct effect on muscle and protein. Glutamine supplementation has been reported to have a beneficial effect on intestinal function and the intestinal mucosa in patients receiving intravenous nutrition (35, 36). A decrease in the number of infections and reduced hospital stay and costs have been reported in bone marrow transplant patients receiving TPN supplemented with glutamine (25, 41), suggesting possible effects on immune function, and glutamine is recognized to be a substrate for immunocytes (29). An improvement in 6-mo survival has also been reported in critically ill patients receiving glutamine-supplemented TPN, but the mechanism(s) for this improvement remain unclear (13).

The loss of lean tissue in the critically ill has led to the investigation of treatments to preserve lean tissue by use of various protein anabolic agents. GH treatment has been shown to improve nitrogen balance, increase protein synthesis, and reduce leucine oxidation in parenterally fed catabolic patients (4, 19). The demonstration that GH had protein anabolic effects led to two European multicenter trials being conducted in ICU patients. However, rather than improving mortality, as was expected, exogenous GH resulted in a significant increase in mortality (42 vs. 18%) (34). These multicenter studies differed from the present study in that the patients were given a variety of nutritional supports excluding glutamine supplementation. In addition, in the present study the GH treatment was given only in combination with IGF-I therapy.

An increase in protein anabolism as a result of GH and IGF-I treatment may result in a decrease in glutamine availability, exacerbating the glutamine depletion seen in the critically ill. Supporting this possibility is the finding that GH reduces skeletal muscle glutamine release in catabolic states (28). It is therefore possible that decreased glutamine availability may have contributed to the increased mortality in the multicenter ICU trials. Because IGF-I has protein anabolic effects, there is also interest in the use of this hormone in the treatment of catabolic patients (11, 23). In normal subjects, combined GH/IGF-I has been shown to have a synergistic effect on protein synthesis (31). Thus, in the present study, the effect of combined treatment with GH/IGF-I was investigated. These results show that combined GH and IGF-I treatment did not decrease glutamine production rate in these critically ill patients. The increase in glutamine concentration and glutamine uptake was similar to that achieved in the TPNGLN group, suggesting that this treatment did not have adverse effects on glutamine metabolism when nutritional support was supplemented with glutamine.

Many of the clinical studies of glutamine supplementation have studied patients undergoing elective surgery. These are homogenous groups of patients undergoing standard operative traumas, and these subjects are generally less severely ill than patients admitted to the ICU. The patients for the present study were recruited in the ICU from those for whom the clinical decision had been made to use parenteral nutrition. We chose to study these patients because they represent the group in which there is considerable clinical interest in the potential benefits of glutamine supplementation, but they are a very heterogeneous group, as can be seen from the patient details in Table 1. We had originally intended to study 12 patients in each group, but unfortunately the study was terminated because of the withdrawal of GH from use in ICUs after the mortality outcome of the GH multicenter trial. Some of the trends between the studies, for example the changes in insulin and amino acid concentrations, might have reached significance if more patients had been studied.

We have previously shown in the critically ill that glutamine uptake is maintained, despite low glutamine concentrations, by an increase in the efficiency of glutamine transport as demonstrated by the increase in glutamine MCR. This is probably due to the increased metabolic demand for glutamine by tissues such as the immune system and the gastrointestinal tract in the catabolic state. In the present study we have shown that, after glutamine supplementation, glutamine concentration was restored to normal but glutamine uptake was increased. The fact that glutamine MCR remained elevated suggests that an increased efficiency of glutamine transport facilitates the increased uptake. The addition of combined GH/IGF-I therapy to nutritional support with glutamine supplementation did not affect the increase in whole body glutamine uptake or the restoration of plasma glutamine concentration, suggesting that in the presence of glutamine supplementation, this hormone treatment did not have adverse effects on glutamine metabolism.


    ACKNOWLEDGEMENTS

We are grateful to the nurses and staff of Mead Ward (ICU), St. Thomas' Hospital, for their patience and support. We are also grateful to Pharmacia & Upjohn for supplying the GH and IGF-I. We acknowledge the assistance of Dr. F. Shojaee-Moradie, A. Fofanah, and the Department of Chemical Pathology for sample analysis. We also thank P. Forsey, of the Hospital Pharmacy, for preparation of the tracer solutions.


    FOOTNOTES

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Address for reprint requests and other correspondence: N. C. Jackson, Dept. of Diabetes, Endocrinology and Metabolic Medicine, 4th Floor North Wing, St. Thomas' Hospital, London SE1 7EH, UK.

Received 30 March 1999; accepted in final form 1 October 1999.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Askanazi, J., Y. A. Carpentier, C. B. Michelsen, D. H. Elwyn, P. Furst, L. R. Kantrowitz, F. E. Gump, and M. J. Kinney. Muscle and plasma amino acids following injury: influence of intercurrent infection. Ann. Surg. 192: 78-85, 1980[ISI][Medline].

2.   Bergstöm, J., P. Fürst, L.-O. Norée, and E. Vinnars. Intracellular free amino acid concentration in human muscle tissue. J. Appl. Physiol. 36: 693-697, 1974[Free Full Text].

3.   Blomqvist, B. I., F. Hammerqvist, A. von der Decken, and J. Wernerman. Glutamine and ketoglutarate prevent the decrease in muscle free glutamine concentration and influence protein synthesis after hip replacement. Metabolism 44: 1215-1222, 1995[ISI][Medline].

4.   Carli, F., J. D. Webster, and D. Halliday. Growth hormone modulates amino acid oxidation in the surgical patient: leucine kinetics during the fasted and fed state using moderate nitrogenous and caloric diet and recombinant human growth hormone. Metabolism 46: 23-28, 1997[ISI][Medline].

5.   Cullen, D. J., J. M. Civetta, B. A. Briggs, and L. C. Ferrara. Therapeutic intervention scoring system: a method for quantitative comparison of patient care. Crit. Care Med. 2: 57-60, 1974[Medline].

6.   Darmaun, D., M. Rongier, J. Koziet, and J.-J. Robert. Glutamine nitrogen kinetics in insulin-dependent diabetic humans. Am. J. Physiol. Endocrinol. Metab. 261: E713-E718, 1991[Abstract/Free Full Text].

7.   Darmaun, D., S. Welch, A. Rini, B. K. Sager, A. Altomare, and M. W. Haymond. Phenylbutyrate-induced glutamine depletion in humans: effect on leucine metabolism. Am. J. Physiol. Endocrinol. Metab. 274: E801-E807, 1998[Abstract/Free Full Text].

8.   Ford, G. C., K. N. Cheng, and D. Halliday. The analysis of (1-13C)leucine and (13C)KIC in plasma by capillary gas chromatography mass spectrometry in protein turnover studies. Biomed. Mass Spectrom. 12: 432-436, 1985[ISI][Medline].

9.   Gamrin, L., P. Essen, A. M. Forsberg, E. Hultman, and J. Wernerman. A descriptive study of skeletal muscle metabolism in critically ill patients: free amino acids, energy rich phosphates, protein, nucleic acids, fat, water and electrolytes. Crit. Care Med. 24: 575-583, 1996[ISI][Medline].

10.   Gelfand, R. A., and E. J. Barrett. Effect of physiologic hyperinsulinaemia on skeletal muscle protein synthesis and breakdown in man. J. Clin. Invest. 80: 1-6, 1987[ISI][Medline].

11.   Goeters, C., N. Mertes, J. Tacke, U. Bolder, M. Kuhman, P. Lawin, and D. Löhlein. Repeated administration of recombinant human insulin-like growth factor-I in patients after gastric surgery effect on metabolic and hormonal patterns. Ann. Surg. 222: 646-653, 1995[ISI][Medline].

12.   Gore, D. C., and F. Jahoor. Glutamine kinetics in burn patients, comparison with hormonally induced volunteers. Arch. Surg. 129: 1318-1323, 1994[Abstract].

13.   Griffiths, R. D. Outcome of critically ill patients after supplementation with glutamine. Nutrition 13: 752-754, 1997[ISI][Medline].

14.   Hammarqvist, F., J. Wernerman, A. Rustom, A. von der Decken, and E. Vinnars. Addition of glutamine to total parenteral nutrition after elective abdominal surgery spares free glutamine in muscle, counteracts the fall in muscle protein synthesis and improves nitrogen balance. Ann. Surg. 209: 455-461, 1989[ISI][Medline].

15.   Hankard, R. G., D. Darmaun, B. K. Sager, D. D'Amore, W. R. Parsons, and M. Haymond. Response of glutamine metabolism to exogenous glutamine in humans. Am. J. Physiol. Endocrinol. Metab. 269: E663-E670, 1995[Abstract/Free Full Text].

16.   Hankard, R. G., M. W. Haymond, and D. Darmaun. Effect of glutamine on leucine metabolism in humans. Am. J. Physiol. Endocrinol. Metab. 271: E748-E754, 1996[Abstract/Free Full Text].

18.   Jackson, N. C., P. V. Carroll, D. L. Russell-Jones, P. H. Sönksen, D. F. Treacher, and A. M. Umpleby. The metabolic consequences of critical illness: acute effects on glutamine and protein metabolism. Am. J. Physiol. Endocrinol. Metab. 276: E163-E170, 1999[Abstract/Free Full Text].

19.   Jeevanandam, M., N. J. Holaday, and S. R. Petersen. Integrated nutritional, hormonal, and metabolic effects of recombinant human growth hormone (rhGH) supplementation in trauma patients. Nutrition 12: 777-787, 1996[ISI][Medline].

20.   Jepson, M. M., P. C. Bates, P. Broadbent, J. M. Pell, and D. J. Millward. Relationship between glutamine concentration and protein synthesis in rat skeletal muscle. Am. J. Physiol. Endocrinol. Metab. 255: E166-E172, 1988[Abstract/Free Full Text].

21.   Knaus, W. A., E. A. Draper, D. P. Wagner, and J. E. Zimmerman. APACHE II: a severity of disease classification system. Crit. Care Med. 13: 818-829, 1985[ISI][Medline].

22.   Lacy, J. M., and D. W. Wilmore. Is glutamine a conditionally essential amino acid? Nutr. Rev. 48: 297-309, 1990[ISI][Medline].

23.   Liberman, S. A., G. E. Butterfield, D. Harrison, and A. R. Hoffman. Anabolic effects of recombinant insulin-like growth factor-I in cachetic patients with acquired immunodeficiency syndrome. J. Clin. Endocrinol. Metab. 78: 404-410, 1994[Abstract].

24.   Long, C. L., K. M. Nelson, D. B. DiRenzo, J. K. Weis, R. D. Stahl, T. D. Broussard, W. L. Theus, J. A. Clark, T. W. Pinson, J. W. Geiger, H. L. Laws, W. S. Blakemore, and R. P. Carraway. Glutamine supplementation of enteral nutrition: impact on whole body protein kinetics and glucose metabolism in critically ill patients. J. Parent. Enteral Nutr. 19: 470-476, 1995[Abstract].

25.   MacBurney, M., L. S. Young, T. R. Zeigler, and D. W. Wilmore. A cost evalutation of glutamine supplemented parenteral nutrition in adult bone marrow transplant patients. J. Am. Diet. Assoc. 94: 1263-1266, 1994[ISI][Medline].

26.   MacLennan, P. A., R. A. Brown, and M. J. Rennie. A positive relationship between protein synthetic rate and intracellular glutamine concentration in perfused rat muscle. FEBS Lett. 215: 187-191, 1987[ISI][Medline].

27.   Matthews, D. E., H. P. Schwartz, R. D. Yang, K. J. Motil, V. R. Young, and D. M. Bier. Relationship of plasma leucine and alpha -ketoisocaproate during a L-[1-13C]leucine infusion in man: a method for measuring intracellular leucine tracer enrichment. Metabolism 31: 1105-1112, 1982[ISI][Medline].

28.   Mjaaland, M., K. Unneberg, J. Larsson, L. Nilsson, and A. Revhaug. Growth hormone after abdominal surgery attenuated forearm glutamine, alanine, 3-methyl histidine, and total amino acid efflux in patients receiving total parenteral nutrition. Ann. Surg. 217: 413-422, 1993[ISI][Medline].

29.   Parry-Billings, M., J. Evans, P. C. Calderans, and E. A. Newsholme. Does glutamine contribute to immunosuppression after major burns? Lancet 336: 523-525, 1990[ISI][Medline].

30.   Petersson, B., S. O. Waller, E. Vinnars, and J. Wernerman. Long term effect of glycyl-glutamine after elective surgery on free amino acids in muscle. J. Parent. Enteral Nutr. 18: 320-325, 1994[Abstract].

31.   Ross, R. J. M., and D. W. Wilmore. Endocrinology in catabolic illness. Endocrinol. Metab. 3, Suppl. A: 115-118, 1996.

32.   Sönksen, P. H. Double antibody technique for the simultaneous assay of insulin and growth hormone. In: Hormones in Human Blood: Detection and Assay. Cambridge, MA: Harvard University Press, 1976, p. 176-199.

33.   Stehle, P., J. Zander, N. Mertens, S. Albers, C. H. Puchstein, P. Lawn, and P. Fürst. Effect of parenteral glutamine supplements on muscle glutamine loss and nitrogen balance after major surgery. Lancet 1: 221-233, 1989.

34.   Takala, J., E. Ruokonen, N. R. Webster, M. S. Nielsen, D. F. Zandstra, G. Vundelinckx, and C. J. Hinds. Increased mortality associated with growth hormone treatment in critically ill adults. N. Engl. J. Med. 341: 785-791, 1999[Abstract/Free Full Text].

35.   Tremel, H., B. Kienle, L. S. Weilemann, P. Stehle, and P. Fürst. Glutamine dipeptide supplemented parenteral nutrition maintains intestinal function in the critically ill. Gastroenterology 107: 1595-1601, 1994[ISI][Medline].

36.   Van der Hulst, R. R., B. K. van Kreel, M. F. von Meyenfeldt, R. J. M. Brummer, J.-W. Arends, N. E. P. Deutz, and P. B. Soeters. Glutamine and the preservation of gut integrity. Lancet 334: 1363-1365, 1993.

37.   Vinnars, E., J. Bergstöm, and P. Fürst. Influence of the post operative state on the intracellular free amino acids in human muscle tissue. Ann. Surg. 182: 665-671, 1975[ISI][Medline].

38.   Walser, H. Misinterpretation of nitrogen balances when glutamine stores fall or are replenished. Am. J. Clin. Nutr. 53: 1337-1338, 1991[ISI][Medline].

39.   Wernerman, J., F. Hammarqvist, and E. Vinnars. alpha -Ketoglutarate and postoperative muscle catabolism. Lancet 335: 701-703, 1990[ISI][Medline].

40.   Wolfe, R. R. Radioactive and Stable Isotope Tracers in Biomedicine: Principles and Practice of Kinetic Analysis. New York: Wiley-Liss, 1992, p. 419-420.

41.   Zeigler, T. R., L. S. Young, K. Benfell, M. Scheltinga, K. Hortos, R. Bye, F. D. Morrow, D. O. Jacobs, R. J. Smith, J. H. Antin, and D. W. Wilmore. Clinical and metabolic efficacy of glutamine supplemented parenteral nutrition after bone marrow transplantation. Ann. Intern. Med. 116: 821-828, 1992[ISI][Medline].


Am J Physiol Endocrinol Metab 278(2):E226-E233
0193-1849/00 $5.00 Copyright © 2000 the American Physiological Society




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