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

Endogenous production of glutamine and plasma glutamine concentration in critically ill patients

BACKGROUND

Glutamine plasma concentrations outside the normal range at intensive care unit (ICU) admission are associated with unfavorable outcomes. Based on the hypothesis that hypoglutaminemia in the ICU is the result of an increased utilization of glutamine which cannot be fully met by endogenous production, extra glutamine supplementation has been advocated to ICU patients with hypoglutaminemia. However, it is still unclear whether there is a causal relation between hypo- and hyperglutaminemia and outcomes. Present guidelines advise against supplementation, although there is no evidence available for patients with hypoglutaminemia. The pathophysiology of abnormal glutamine levels and whether glutamine production or glutamine utilization is compromised is largely unknown. Therefore, the aim of this study was to elucidate the relationship between plasma glutamine levels and the endogenous glutamine production in ICU patients.

METHOD

In this observational study, a technique using a small bolus of intravenous glutamine with an isotopic label was used to measure glutamine production.

RESULTS

There was a statistically significant correlation between de novo endogenous production of glutamine (not emanating directly from protein breakdown) and plasma glutamine concentrations in the low and normal range in circulatory stabilized ICU patients (n = 19), R² = 0.35 (P ≤ 0.01).

CONCLUSION

The predictive value of a low plasma glutamine concentration at ICU admission on outcomes may thus be related to a low endogenous production, which may need to be supplemented in the best interest of this cohort of patients.

Glutamine dipeptide and cortisol change the liver glucose metabolism and reduce the severity of insulin-induced hypoglycaemia in untreated T1DM Swiss mice

CONTEXT

Glutamine is conditionally essential in type 1 diabetes mellitus, and might be useful to counteract hypoglycaemia.

OBJECTIVE

To investigate the systemic and hepatic effects of counter-regulatory hormones and glutamine dipeptide (GDP) during hypoglycemic episodes.

MATERIALS AND METHODS

Diabetic Swiss mice made hypoglycaemic by insulin injection (1 U/kg) were given counter-regulatory hormones and/or GDP. Sixty minutes later, liver histology, liver glucose metabolism and plasma were assessed.

RESULTS

Combined, cortisol and GDP improved the hypoglycemic profile. During liver perfusion, gluconeogenesis was possibly the major pathway leading to glucose release. Perfusion with gluconeogenic precursors after glycogen depletion by adrenaline increased liver glucose and urea release.

DISCUSSION

The less severe hypoglycaemia could result from cortisol stimulating periportal gluconeogenesis and GDP inhibiting pericentral glycogenolysis, both favouring liver glucose release.

CONCLUSIONS

At least some benefits of GDP and cortisol during hypoglycaemia came from their hepatic actions, and their use in diabetic patients should be explored.

Enteral glutamine supplementation in critically ill patients: a systematic review and meta-analysis

Introduction

Glutamine (GLN) has been suggested to have a beneficial influence on outcomes of critically ill patients. However, recent large-scale trials have suggested harm associated with GLN supplementation. Recently, systematic reviews on the use of parenteral GLN have been published; however, less information is available on the role of enteral GLN. Therefore, the aim of this systematic review was to study the effects of enteral GLN supplementation in patients with critical illness.

Methods

We identified randomized controlled trials conducted from 1980 to 2014 with enterally administered GLN in adult critically ill patients. Studies of parenteral GLN only or combined enteral-parenteral GLN were excluded. The methodological quality of studies was scored, and trial data were statistically combined. We examined a priori the treatment effects in subgroups of trials of burn and trauma patients.

Results

A total of 11 studies involving 1079 adult critically ill patients and enteral GLN supplementation were identified. Enteral GLN supplementation was not associated with a reduction of hospital mortality (risk ratio [RR] 0.94, 95 % confidence interval [CI] 0.65–1.36; p =0.74), infectious complications (RR 0.93, 95 % CI 0.79–1.10; p =0.39) or stay in the intensive care unit (weighted mean difference [WMD] −1.36 days, 95 % CI −5.51 to 2.78; p =0.52). However, there was a significant reduction in hospital stay (WMD 4.73 days, 95 % CI −8.53 to −0.90; p =0.02). In the subset of studies of patients with burns, enteral GLN supplementation was associated with significant reductions in hospital mortality (RR 0.19, 95 % 0.06–0.67; p =0.010) and hospital stay (WMD −9.16, 95 % CI −15.06 to −3.26; p =0.002). There was no effect in trauma patients.

Conclusions

Enteral GLN supplementation does not confer significant clinical benefit in critically ill patients, with the exception of reduced hospital stay. There may be a significant benefit in patients with burns, but data are sparse and larger randomized trials are warranted to confirm this effect.

Endogenous glutamine production in critically ill patients: the effect of exogenous glutamine supplementation

Introduction

Glutamine rate of appearance (R_a) may be used as an estimate of endogenous glutamine production. Recently a technique employing a bolus injection of isotopically labeled glutamine was introduced, with the potential to allow for multiple assessments of the glutamine R_a over time in critically ill patients, who may not be as metabolically stable as healthy individuals. Here the technique was used to evaluate the endogenous glutamine production in critically ill patients in the fed state with and without exogenous glutamine supplementation intravenously.

Methods

Mechanically ventilated patients (n = 11) in the intensive care unit (ICU) were studied on two consecutive days during continuous parenteral feeding. To allow the patients to be used as their own controls, they were randomized for the reference measurement during basal feeding without supplementation, before or after the supplementation period. Glutamine R_a was determined by a bolus injection of ¹³C-glutamine followed by a period of frequent sampling to establish the decay-curve for the glutamine tracer. Exogenous glutamine supplementation was given by intravenous infusion of a glutamine containing dipeptide, L-alanyl-L-glutamine, 0.28 g/kg during 20 hours.

Results

A 14% increase of endogenous glutamine R_a was seen at the end of the intravenous supplementation period as compared to the basal measurements (P = 0.009).

Conclusions

The bolus injection technique to measure glutamine R_a to estimate the endogenous production of glutamine in critically ill patients was demonstrated to be useful for repetitive measurements. The hypothesized attenuation of endogenous glutamine production during L-alanyl-L-glutamine infusion given as a part of full nutrition was not seen.

Insulin-like Growth Factor I and its binding protein 3 in sepsis

OBJECTIVE

To investigate the Growth Hormone (GH)/Insulin-like Growth Factor-I (IGF-I) axis and identify the factors that determine IGF-I levels in adult septic patients of variable severity, i.e., with sepsis, severe sepsis or septic shock, in the acute phase of disease.

DESIGN

In 107 consecutive septic patients (44 with sepsis, 13 with severe sepsis, and 50 with septic shock), GH, IGF-I, Insulin-like Growth Factor Binding Protein-3 (IGFBP-3), insulin, cortisol, albumin, thyroid hormones, C-reactive protein and interleukin-6 serum levels were measured once within 48 h after onset of a septic episode. Twenty-nine healthy volunteers served as controls.

RESULTS

IGF-I and IGFBP-3 levels were decreased in patients with sepsis and severe sepsis (versus controls), decreasing further in patients with septic shock (versus sepsis). IGF-I levels were positively related to IGFBP-3, albumin, triiodothyronine and thyroxine, and inversely related to cortisol, sepsis severity, C-reactive protein, interleukin-6 and age. In multiple regression analysis, IGF-I levels were independently related to IGFBP-3 and albumin (lower in patients with decreased IGFBP-3 and albumin levels) (p<0.001 and p=0.01, respectively), and cortisol (lower in patients with increased cortisol levels) (p=0.04). IGFBP-3 accounted for most of the variance explained by the model (R(2)=0.519). GH levels were not related to IGF-I levels or mortality. IGF-I and IGFBP-3 levels were not associated with mortality.

CONCLUSIONS

The GH/IGF-I axis is severely disrupted in septic patients. IGFBP-3 is the major determinant of IGF-I levels.

Effects of growth hormone and insulin-like growth factor-1 on postoperative muscle and substrate metabolism

This study explored if a combined supplementation of GH and IGF-1 had an additive effect on whole body nitrogen economy, energy, substrate and skeletal muscle metabolism following surgical trauma. Patients were randomized to controls (C; n = 10), to GH (0.15 IU/kg/injection) (GH; n = 7) or GH combined with IGF-1 (40 μg/kg/injection) subcutaneously twice a day (GH-IGF-1; n = 9) together with standardized parenteral nutrition. Muscle amino acids, glutathione and the ribosomal pattern reflecting protein synthesis, and nitrogen balance were measured. GH- and GH-IGF-1 groups showed lower urea and higher plasma glucose concentrations. Energy expenditure increased in the GH-group. GH-IGF-1 prevented a decrease in muscle polyribosomes indicating a preserved muscle protein synthesis. In the GH group unaltered BCAA and AAA levels were seen in muscle indicating an unchanged protein breakdown, while the other groups showed increased muscle concentrations postoperatively. Without statistically difference GH marginally improved the nitrogen balance, in terms of higher values, and growth factors improved the nitrogen balance when the shift in urea was taken into account. To conclude, growth factors influences urea metabolism, protein degradation and protein synthesis. There was no clearcut additional effect when combining GH and IGF-1 but the study was probably underpowered to outrule this and effects on nitrogen balance.

The pattern of amino acid exchange across the brain is unaffected by intravenous glutamine supplementation in head trauma patients

BACKGROUND & AIMS

Exogenous intravenous glutamine supplementation to head trauma patients leaves intracerebral glutamate concentration unaffected. The effect of an exogenous supply upon glutamine and glutamate exchange across the brain has still not been characterised.

METHODS

A prospective randomised cross-over study, where i.v. glutamine dipeptide was compared with placebo. Arterio-venous concentration differences of free amino acids across the brain and amino acid flux across the leg were measured. In addition, the endogenous glutamine production was calculated. Fifteen mechanically ventilated head trauma patients with GCS < or =8 were included and studied during two consecutive 24-h periods on days 2-5 following head trauma.

RESULTS

Glutamine was continuously released from both the brain and the leg. The arterio-venous (a-v) concentration differences over the brain were calculated to be -49+/-26 and -27+/-14 micromol/L during the treatment and control periods respectively, showing a continuous release of glutamine (p<0.0001). On the other hand, the a-v difference of glutamate was not different from zero (p>0.2). The whole-body glutamine rate of appearance (R(a)) was calculated to be 218+/-75micromol/kg body weight/h.

CONCLUSION

Intravenous glutamine supplementation to head trauma patients was associated with an unaffected amino acid exchange pattern across head and leg, without any measurable uptake of glutamate across the brain. Endogenous glutamine production was in the normal range despite the low plasma glutamine concentration. This pilot study opens the possibility to perform prospective clinical trials in head trauma patients to evaluate the clinical efficacy of exogenous glutamine supplementation.

Exogenous glutamine: The clinical evidence

We know that critically ill patients suffering from undernutrition with a limited nutritional reserve have a poorer outcome. Furthermore, having a low body mass index has been shown to be an independent predictor of excess mortality in multiple organ failure. Therefore, nutritional support has gained increasing interest in critical illness with the hope of preventing or attenuating the effects of malnutrition. A negative nitrogen balance is the characteristic metabolic feature in critical illness, with the major protein loss derived from skeletal muscle. In particular, glutamine concentrations are rapidly reduced in plasma and muscle. Over the last 20 yrs or so, increasing evidence is emerging to support the use of glutamine supplementation in critical illness. Clinical trials have found a mortality and morbidity advantage with glutamine supplementation. The advantage appears to be greater the more glutamine is given and greater again when given parenterally. Various modes of action have been postulated. Glutamine seems to have an effect on the immune system, antioxidant status, glucose metabolism, and heat shock protein response. However, the benefit of exogenous glutamine on morbidity and mortality is not universally accepted. This review critically appraises the current clinical evidence regarding glutamine supplementation in critical illness.

Influence of glutamine on pancreatic blood flow and apoptosis of pancreatic acinar in rats with severe acute pancreatitis

OBJECTIVE

To investigate the role of glutamine on splanchnic blood flow, apoptosis of pancreatic acinar and the underlying mechanism in rats with severe acute pancreatitis.

METHODS

Forty-eight rats were randomized into two groups: the glutamine group (n = 24) and the severe acute pancreatitis group (n = 24). Jejunotomy was performed in all rats: the glutamine group also received glutamine, and the severe acute pancreatitis group received normal saline. Each group was then subdivided into three subgroups of eight rats each, with the rats be killed at 12, 24 and 36 h after the operation, respectively. A control group underwent sham operation (n = 8). The regional pancreatic microvascular blood flow was measured by Doppler ultrasound. The blood flow of the portal vein, splenic artery and superior mesenteric artery were also recorded. Apoptosis of pancreatic acinar cells was evaluated by TUNEL method.

RESULTS

The regional pancreatic microvascular blood flow (KHz) decreased significantly in the severe acute pancreatitis group (P < 0.01), and continued to decrease after 24 h (vs. 12 h, P < 0.01). The blood flow of the portal vein, splenic artery and superior mesenteric artery also decreased in the severe acute pancreatitis group. The glutamine group showed increased regional pancreatic microvascular blood flows, as well as increased blood flow of the portal vein, splenic artery and superior mesenteric artery (vs. the severe acute pancreatitis group, P < 0.01). The apoptotic index of pancreatic acinar in the glutamine group was higher than in the severe acute pancreatitis group (P < 0.01), and both were much higher than that in the control group (P < 0.01).

CONCLUSIONS

Enteral administration of glutamine increased the splanchnic blood flow in severe acute pancreatitis rats. The apoptotic index of pancreatic acinar was negatively correlated with the severity of the disease. The interrelation between glutamine and apoptosis in severe acute pancreatitis is worthy of further investigation.

Treatment with GH and IGF-1 in Critical Illness

Trauma, sepsis, and surgery are associated with global hypercatabolism and a negative nitrogen balance. When critical illness is prolonged the relentless loss of lean tissue becomes functionally important. Protein catabolism in the critically ill patient is associated with complex changes in the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis. Many small clinical studies indicate that treatment with recombinant human (rh) GH would be a safe and effective means of limiting the deleterious effects of the catabolic response. Unexpectedly, however, two large prospective randomized controlled trials (PRCTs) demonstrated that administration of rhGH to long-stay critically ill adults increases morbidity and mortality. Some progress has been made in understanding the mechanisms underlying this observation.

Review article: nutrition and adult inflammatory bowel disease

Major advances in the understanding of the aetio-pathogenesis and genetics of inflammatory bowel disease have been accompanied by an escalation in the sophistication of immunomodulatory inflammatory bowel disease therapeutics. However, the basic 'triple' therapy (5-aminosalicylates, corticosteroids, azathioprine) and nutrition have maintained their central role in the management of patients with inflammatory bowel disease over recent decades. This review provides an overview of the supportive and therapeutic perspectives of nutrition in adult inflammatory bowel disease. The objective of supportive nutrition is to correct malnutrition in terms of calorie intake or specific macro- or micronutrients. Of particular clinical relevance is deficiency in calcium, vitamin D, folate, vitamin B12 and zinc. There is justifiably a growing sense of unease amongst clinicians and patients with regard to the long-term use of corticosteroids in inflammatory bowel disease. This, rather than arguments about efficacy, should be the catalyst for revisiting the use of enteral nutrition as primary treatment in Crohn's disease. Treatment failure is usually related to a failure to comply with enteral nutrition. Potential factors that militate against successful completion of enteral nutrition are feed palatability, inability to stay on a solid-free diet for weeks, social inconvenience and transient feed-related adverse reactions. Actions that can be taken to improve treatment outcome include the provision of good support from dietitians and clinicians for the duration of treatment and the subsequent 'weaning' period. There is evidence to support a gradual return to a normal diet through exclusion-re-introduction or other dietary regimen following the completion of enteral nutrition to increase remission rates. We also review the evidence for emerging therapies, such as glutamine, growth factors and short-chain fatty acids. The future may see the evolution of enteral nutrition into an important therapeutic strategy, and the design of a 'Crohn's disease-specific formulation' that is individually tailored, acceptable to patients, cost-effective, free from adverse side-effects and combines enteral nutrition with novel pre- and pro-biotics and other factors.

Effect of growth hormone on muscle and liver protein synthesis in septic rats receiving glutamine-enriched parenteral nutrition

OBJECTIVE

Administration of recombinant human growth hormone (rhGH) to critically ill adults in an attempt to attenuate catabolism was associated with increased morbidity and mortality. Possible explanations included inhibition of glutamine release from skeletal muscle and consequent restriction of splanchnic glutamine supply. In this study, we examined the effects of rhGH on plasma glutamine levels and on muscle and liver glutamine concentrations and protein synthesis rates in sepsis. We investigated the possibility that administration of supplemental glutamine might ameliorate any adverse effects of rhGH.

DESIGN

Prospective study in rats rendered septic by cecal ligation and puncture.

SETTING

University hospital laboratory.

SUBJECTS

A total of 78 male Wistar rats in six groups.

INTERVENTIONS

Animals received 6-hr tail vein infusions, commencing 18 hrs after cecal ligation and puncture, of either (a) 0.9% sodium chloride, (b) a standard parenteral nutrition (PN) solution without glutamine, or (c) an isocaloric, isonitrogenous PN solution with glutamine. PN groups received 400 microg rhGH or equivolume 0.9% sodium chloride vehicle in a divided subcutaneous and intravenous dose at PN commencement. Sacrifice was at the end of the infusion period. A further group was unoperated and uninfused and killed at 24 hrs as baseline controls.

MEASUREMENTS AND MAIN RESULTS

Glutamine concentrations were measured by fluorometry. Protein synthesis in muscle and liver was measured by a "flooding-dose" technique employing L-[4-H]phenylalanine. Plasma glutamine was increased after cecal ligation and puncture except in the saline and glutamine with rhGH animals. Muscle glutamine was reduced after cecal ligation and puncture and was significantly lower in animals receiving standard PN with rhGH vs. saline alone. Liver glutamine was increased in animals receiving saline and those receiving standard PN with rhGH. PN, with or without glutamine, increased muscle protein synthesis, and the administration of rhGH tended to further increase this effect. Neither PN, glutamine, nor rhGH had an effect on the increased liver protein synthesis characteristic of sepsis.

CONCLUSIONS

In sepsis, increased muscle protein synthesis with PN and rhGH administration is not associated with increased muscle glutamine levels. Administration of rhGH does not result in reduced liver glutamine levels or rates of hepatic protein synthesis. PN containing glutamine was no more efficacious than standard PN at increasing muscle protein synthesis.

Dangers of growth hormone therapy in critically ill patients

Prolonged length of stay is the major challenge for modern intensive care because of the associated morbidity and the impact on resource utilization. Severe trauma or infection is associated with a catabolic response, which is characterized by increased protein turnover and negative nitrogen balance. Severe catabolism leads to end-organ dysfunction and muscular weakness, prolonging the need for mechanical ventilation. Catabolism cannot be prevented with standard parenteral or enteral nutritional formulas. In order to prevent the complications of catabolism in intensive care patients, recombinant growth hormone has been applied as an experimental therapy for two decades in patients requiring parenteral nutrition and in patients with respiratory failure. Administration of recombinant growth hormone has resulted in positive nitrogen balance, and studies in mechanically ventilated patients suggest that it may shorten the need for ventilatory support. In contrast to the results of these relatively small studies, a recent multinational randomized controlled trial revealed that the administration of recombinant growth hormone (with doses 10-20 times higher than used for replacement therapy) increases mortality of critically ill patients. The excessive mortality in patients treated with recombinant growth hormone was related to infections and development of multiple organ failure, leading to the conclusion that administration of high doses of recombinant growth hormone cannot be recommended for critically ill patients. This review reinforces that conclusion.

Metabolic bases of amino acid requirements in acute diseases

Acute diseases are characterized by a catabolic state, resulting in a negative nitrogen balance and muscle wasting. Increasing protein intake often proves to have little effect in limiting muscle protein loss. This suggests a qualitative inadequacy of the usual nutritional supports to meet the amino acid requirements of the critically ill patient. Therefore, it can be assumed that the additional intake of limiting amino acids would allow the sparing of muscle proteins. The aim of this review is to examine whether metabolic and kinetics studies using labelled amino acids can help identify the pathways activated in injury and their specific amino acid requirements. The kinetics of cysteine, arginine and glutamine, which are mainly cited as conditionally indispensable in stress situations, are presented. Moreover, amino acids can act as mediators or signal molecules and modulate numerous functions. The optimal conditions allowing the best expression of these activities are discussed.

Combination of recombinant human growth hormone and glutamine-enriched total parenteral nutrition to surgical patients: effects on circulating amino acids

BACKGROUND & AIMS

Both recombinant human growth hormone (rhGH) and glutamine (GLN) may have beneficial anabolic actions on amino acid metabolism. The aim of this study was to evaluate the additive effects of rhGH and GLN on plasma amino acids postoperatively.

METHODS

31 females undergoing laparoscopic cholecystectomy were randomized to three groups: Group I (n=10) received 13 IU/m(2) of rhGH the morning of surgery and the following three postoperative days, together with glutamine-free TPN for the first two postoperative days. Group II (n=11) received rhGH as the first group, together with glutamine-enriched (7 g GLN/m(2)/day) TPN. Group III (n=10) received glutamine-enriched TPN as the second group, but rhGH was replaced by placebo. Daily plasma amino acid concentrations and nitrogen balance were determined.

RESULTS

In the GH treated groups, the plasma concentrations of several amino acids were decreased on the third postoperative day, compared to preoperatively. This was not observed in Group III. The changes were more pronounced in Group II. In Group II the negative AV-differences of amino acids tended to be attenuated, while the patients in Group III had increased negative AV-differences. The cumulative nitrogen balance was significantly improved in the GH groups, compared with Group III.

CONCLUSION

The combined treatment of growth hormone and glutamine has additive effects on AV-balances of amino acids postoperatively, whereas nitrogen balance is not further improved when adding glutamine to rhGH treatment.

Feeding the intensive care patient

The present review highlights recent findings (focusing on papers published between October 1999 and December 2000) in nutritional support of intensive care unit patients. During the past year, research focused on the use of enteral nutrition versus parenteral nutrition, and on the best composition of enteral nutrition and parenteral nutrition according to the clinical condition of the patient. With regard to enteral nutrition, the pH of nutritional support, the timing of administration and the technique of tube placement were debated. Immunomodulating agents and hormonal manipulations may improve outcomes of critically ill patients, but still warrant further research before they can be recommended for routine clinical use.

Nutritional support in sepsis: still skeptical?

The immediate metabolic response to a septic challenge is probably adaptive, meaning that nutritional interference, mainly via the parenteral route, during this early phase of instability can do more harm than good. During the later phases, a gradual increase in enteral nutrition, at the expense of parenteral nutrition, combined with the administration of nutraceuticals such as glutamine and omega-3 fatty acids, can counteract wasting and modulate the complex inflammatory response and immunosuppression associated with sepsis. In these times of scarce resources, there is an urgent need to clearly document the efficacy of immuno/pharmaconutrients, individually and in combination, enterally or parenterally, before proposing them for routine management of septic patients in the intensive care unit.