Amino acids in surgical nutrition. Principles and practice

Burns: modified metabolism and the nuances of nutrition therapy

OBJECTIVE

To review the effects of burn injury on nutritional requirements and how this can best be supported in a healthcare setting.

METHOD

A literature search for articles discussing nutrition and/or metabolism following burn injury was carried out. PubMed, Embase and Web of Science databases were searched using the key search terms 'nutrition' OR 'metabolism' AND 'burn injury' OR 'burns'. There was no limitation on the year of publication.

RESULTS

A total of nine articles met the inclusion criteria, the contents of which are discussed in this manuscript.

CONCLUSION

Thermal injury elicits the greatest metabolic response, among all traumatic events, in critically ill patients. In order to ensure burn patients can meet the demands of their increased metabolic rate and energy expenditure, adequate nutritional support is essential. Burn injury results in a unique pathophysiology, involving alterations in endocrine, inflammatory, metabolic and immune pathways and nutritional support needed during the inpatient stay varies depending on burn severity and idiosyncratic patient physiologic parameters.

The combined effects of glutamine and growth hormone on intestinal anastomosis in the rat intra-abdominal sepsis model

AIM

Intestinal anastomoses are always risky in patients who develop intra-abdominal sepsis. In this study, the effects of combined glutamine and growth hormone (GH) on healing of intestinal anastomosis following intestinal repair in the rat intra-abdominal sepsis was induced.

MATERIAL AND METHODS

Forty Sprague Dawley Albino rats at 10 weeks weighing between 180 and 240 g were included in the study. All the animals were divided into five groups comprising eight rats each. In the control group, no treatment was given in addition to the routine oral nutrition before and after surgery. In the other groups, following surgery, oral glutamine was given at a dose of 1 mg/kg/d in the glutamine group, subcutaneous GH was given at a dose of 1 mg/kg/d in the GH group, and combined glutamine and GH were administered at the same doses in the glutamine + GH group. In rats, a clinical model mimicking intestinal fistula was generated and fistula repair was performed, and the bursting pressure of the repair area and tissue hydroxyproline level of the repair area were calculated.

RESULTS

Compared with the control group, glutamine, GH, and combined groups displayed significantly higher mean bursting pressures and tissue hydroxyproline levels.

CONCLUSION

In order to decrease the risks originating from impaired mechanisms due to intra-abdominal sepsis, and to make anastomosis safer, combined use of glutamine and GH increases the bursting pressure of anastomosis. While the use of either of these two substances alone is effective, combined use makes this effect more prominent.

The safety of oral use of L-glutamine in middle-aged and elderly individuals

OBJECTIVE

To evaluate the safety of nutraceutical oral administration of L-glutamine (L-Gln) in middle-aged and elderly individuals.

METHODS

In this randomized, crossover, double-blind clinical study, 30 residents of a long-term-care institution, selected according to a modified SENIEUR protocol (Working Party of the EURAGE Concerted Action Programme on Ageing of the European Community), were studied. Fourteen subjects received orally 0.5 g kg(-1) d(-1) of L-Gln and 16 received calcium caseinate for 14 d, followed by a 5-d washout. Supplements were switched for the second 14-d trial. Laboratory tests for hepatic and renal functions and ammonemia were performed and the estimated glomerular filtration rate (eGFR) was calculated.

RESULTS

Of the 30 subjects, 16 were men, mean age was 69+/-8.8 y, average weight was 61.8+/-14.2 kg, and mean serum albumin was 4.0+/-0.3g/dL. Neither adverse clinical effects nor clinically significant laboratory changes were noted during L-Gln supplementation. There was no difference in ammonemia between the groups. There were statistically but not clinically significant increases in plasma urea nitrogen and creatinine concentrations. There was no significant decrease in eGFR during calcium caseinate supplementation (-2.9%). The eGFR decreased significantly after L-Gln supplementation (-13.3%) but well below the 25% limit for biologic significance.

CONCLUSION

Increases in serum urea nitrogen and creatinine and decrease in eGFR are probably due to difficulties by older kidneys in metabolizing the supplemented protein sources. Although not clinically significant, those alterations impose a rigorous control on the evaluation parameters of renal function during oral L-Gln supplementation, with doses of 0.5 g kg(-1) d(-1) in middle-aged and elderly individuals.

Enhanced fracture and soft-tissue healing by means of anabolic dietary supplementation

BACKGROUND

Malnutrition is common in hospitalized injured patients. It contributes to delayed fracture-healing and increased morbidity. However, relatively little attention has been directed toward nutritional strategies for augmenting musculoskeletal recovery after a fracture. This animal study was designed to examine the effects of dietary protein intake and the role of conditionally essential amino acids in muscle and bone-healing after a fracture.

METHODS

One hundred adult male rats were used. Ten rats served as controls and received a 15% protein diet throughout the study. The remaining ninety rats received a 6% protein diet for five weeks to induce protein malnutrition. The rats underwent intramedullary nailing and closed midshaft fracture of one femur. After the fracture, they were separated into three isocaloric dietary groups. Group P6 received a diet with 6% protein; Group P15, a diet with 15% protein; and group P30, a diet with 30% protein with conditionally essential amino acids. At two, four, and six weeks after surgery, ten animals from each group were killed and the femora were evaluated with dual x-ray absorptiometry, histomorphometric assessment of callus, and torsional testing. The quadriceps muscles were analyzed for total mass, total protein content, and for mRNA expression of insulin-like growth factor-1 (IGF-1), IGF-2, IGF receptors, actin, myosin, and vascular endothelial growth factor (VEGF).

RESULTS

The P30 group demonstrated elevations in albumin, body mass, muscle mass, total protein content of muscle, and bone mineral density in the fracture callus compared with the P6 diet group at six weeks (p < 0.05). Molecular analysis of muscle revealed that IGF-1, IGF-2, IGF receptors, myosin, actin, and VEGF gene expression were significantly (p < 0.001) higher in the P6 group compared with the P30 group. Biomechanical testing of the femora, however, showed no significant differences.

CONCLUSIONS

Dietary supplementation with conditionally essential amino acids in malnourished animals had anabolic effects on bone mineralization, body mass, and muscle mass.

Controlled study of enteral arginine supplementation in burned children: impact on immunologic and metabolic status

OBJECTIVE

We compared the effects of an arginine-supplemented diet with those of an isocaloric isonitrogenous diet on immune and metabolic response of children with burns.

METHODS

This was a double-blind, randomized, placebo-controlled trial in a burn treatment center of a pediatric hospital in Santiago, Chile. All children (1-5 y of age) admitted within 48 h of a moderate to deep burn injury covering 10% to 40% of total body surface area were evaluated. Twenty-eight children met the criteria and were randomly assigned to receive an arginine-supplemented diet (AG; n = 14) or an isocaloric isonitrogenous diet (CG; control, n = 14) for 14 d. Samples were collected at admission (baseline) and on days 7 and 14 for lymphoproliferative response to mitogens, plasma interleukins (interleukin-1, interleukin-6, tumor necrosis factor-alpha), plasma arginine and ornithine levels, serum C-reactive protein, prealbumin, albumin, glucose, and total urinary nitrogen.

RESULTS

The AG enhanced lymphoproliferative responses (analysis of variance, P < 0.05), which were 72% of normal at baseline in both groups; by day 7 responses increased to 144% in the AG group and decreased to 56% in the CG group; both groups returned to normal by day 14. Baseline interleukin-6 was significantly increased in all children. There were no differences in plasma concentrations of interleukin-1, interleukin-6, tumor necrosis factor-alpha, C-reactive protein, prealbumin, albumin, or glucose between the AG and CG groups. On day 7 plasma ornithine levels increased significantly in the AG versus CG group (P < 0.05); arginine levels showed no change.

CONCLUSIONS

An exclusively AG improves mitogen-stimulated lymphocyte proliferation in burned children. The benefits of arginine for the immune system do not appear to be related to a metabolic response. The biological significance of this finding remains to be determined.

High-intensity dynamic human muscle performance enhanced by a metabolic intervention

PURPOSE

The purpose of this study was to quantify the effects of a metabolic treatment on human muscle dynamic performance (strength, work, and fatigue) measured under conditions of acute, exhaustive high-intensity anaerobic isokinetic exercise.

METHODS

Unilateral prefatigue and postfatigue peak torque and work values were measured in the quadriceps femoris of 13 subjects using a computer-controlled isokinetic dynamometer, over a 23-d interval. The two experimental treatments were: 1) a glycine and L-arginine salt of alpha-ketoisocaproic acid calcium ("GAKIC"); and 2) isocaloric sucrose (control). Based on a randomized double-blind cross-over repeated measures design, measurements were made before and during an exhaustive anaerobic fatigue protocol to calculate a Fatigue Resistance Index (FRI = [peri-exhaustion torque]\[baseline peak torque]), as well as total work.

RESULTS

The FRI and total work for each of the exhaustion sets measured at 0, 5, and 15 min after oral GAKIC treatment were greater than values obtained for isocaloric control treatment (P < 0.02). GAKIC treatment increased the mean resistance to fatigue (FRI) up to 28% over isocaloric control. Overall gain in total muscle work attributable to GAKIC was 10.5 +/- 0.8% greater than control, sustained for at least 15 min. After 24 h, both GAKIC and control concentric forces returned to the same absolute values (P > 0.05): mean FRI = 0.42 +/- 0.05 and mean total work = 4600 +/- 280 J. There were no significant differences attributable to random order of testing.

CONCLUSIONS

Compared with isocaloric carbohydrate, oral GAKIC treatment increased muscle torque and work sustained during intense acute anaerobic dynamic exercise; additionally, it increased overall muscle performance by delaying muscle fatigue during the early phases of anaerobic dynamic exercise.

Glutamine supplementation in catabolic patients

OBJECTIVE

To evaluate the safety and efficacy of parenteral and enteral glutamine supplementation in patients who are catabolic.

DATA SOURCES

English-language clinical trials and review articles identified by MEDLINE searches (January 1970-December 1997) and from bibliographies of selected articles were considered for possible inclusion. Key words used in the search strategy were glutamine, critical illness, stress, catabolism, injury, enteral nutrition, and parenteral nutrition.

STUDY SELECTION AND DATA EXTRACTION

Inclusion was restricted to pertinent studies that evaluated the safety of glutamine supplementation, as well as effects of glutamine on amino acid metabolism, immune function, and patient outcome. Data from 18 clinical trials and multiple review articles were compiled into a review format.

DATA SYNTHESIS

Glutamine is an important metabolic fuel for intestinal enterocytes, lymphocytes and macrophages, and metabolic precursors such as purines and pyrimidines. Although originally considered a nonessential amino acid, experimental work suggests that glutamine is essential for maintaining intestinal function, immune response, and amino acid homeostasis during periods of severe stress. In the past decade, clinical trials conducted in metabolically stressed patients indicate that glutamine improves nitrogen balance, increases cellular proliferation, decreases the incidence of infection, and shortens hospital stay in some catabolic patients.

CONCLUSIONS

Glutamine has been studied extensively over the past decade for its role during critical illness. Clinical trials conducted in humans demonstrate glutamine to be well tolerated without adverse consequences, even during times of stress. Although glutamine has shown promise in select groups of catabolic patients, additional studies are needed to define which patient populations derive the greatest benefit from supplemental glutamine and the mechanisms by which these effects are exerted.

Epidermal growth factor and human growth hormone induce two sodium-dependent arginine transport systems after massive enterectomy

BACKGROUND

A combination of epidermal growth factor (EGF) and human growth hormone (hGH) after massive enterectomy induces a 400% increase in arginine transport in the remnant distal small intestine. The kinetic mechanism(s) responsible for enhanced arginine transport under these conditions is unknown.

METHODS

New Zealand White rabbits underwent 70% midjejunoileal resection. After a 1-week recovery period, animals received hGH (0.2 mg/kg/d IM), EGF (1.5 microg/kg/h SC), hGH + EGF, or vehicle (equal volume) for 7 days. Transport of tritiated arginine into brush border membrane vesicles prepared from distal remnant small intestinal mucosa was quantified in the presence and absence of a sodium gradient over a range of arginine concentrations (25 to 5000 micromol/L).

RESULTS

Eadie-Hofstee transformation of the kinetic data demonstrates two sodium-dependent arginine transport systems, comprising a high-capacity, low-affinity system and a low-capacity, high-affinity system. A combination of EGF and hGH significantly upregulates both the high-capacity (685%) and low-capacity (350%) maximum transport velocity (Vmax). Additionally, EGF alone significantly upregulates Vmax by 200% in the low-capacity system. There were no significant changes in transport affinity (Km) in either system.

CONCLUSIONS

There are two quiescent sodium-dependent arginine transport systems in the distal small intestine. A combination of EGF and hGH after massive enterectomy increase arginine transport by Vmax upregulation in both the high-capacity/low-affinity and low-capacity/high-affinity systems.

Comparison of plasma amino acid concentrations in end-stage renal disease patients on hemodialysis and peritoneal dialysis

OBJECTIVES

Recent reports have suggested that patients treated by CAPD have a relatively increased risk of death compared to patients undergoing HD, although the cause of this discrepancy is poorly understood. Protein malnutrition is an important risk factor in ESRD. Also, amino acid concentrations, for which the physiological function differs from that of protein, may be an independent risk factor in ESRD. There is no doubt concerning the prevalence of low amino acid levels in both HD and CAPD patients. But the difference in plasma amino acid levels between these two groups has not been well defined. The purpose of this study is to compare plasma amino acid levels between patients with ESRD on HD and CAPD.

METHODS

A cross sectional study of overnight fasting plasma amino acid concentrations was performed on 12 CAPD and 45 HD patients with ESRD, matched by age, sex and body mass index. The levels of individual plasma amino acid and TAA, EAA, NEAA and BCAA were compared for the HD and CAPD groups. In order to measure losses during HD and CAPD, amino acid and protein concentrations were measured from 10 dialysates obtained from 10 HD patients and 12 peritoneal dialysis solutions from 12 CAPD patients.

RESULTS

All of the measured amino acid concentrations were found to be lower in the CAPD group compared to the HD group. Furthermore, the levels of TAA (2017.3 +/- 781.1 vs. 903.3 +/- 316.1 mumole/L), EAA(1201.8 +/- 492.6 vs. 567.6 +/- 223.2 mumole/L), NEAA(815.5 +/- 308.6 vs. 335.7 +/- 100.2 mumole/L); and BCAA (315.0 +/- 146.0 vs. 145.2 +/- 65.0 mumole/L), were all lower in the CAPD group than in the HD group. The protein loss was 2.0 +/- 0.2 g/L in the peritoneal dialysate but was not detectable in the hemodialysates. TAA loss over a one week period was about 61.8 +/- 13.0mmole for the HD group and 38.0 +/- 13.0 mmole for the CAPD group.

CONCLUSIONS

Our results show that amino acid concentrations are lower in ESRD patients on CAPD than on HD. It seems likely that protein loss in the peritoneal dialysate is a contributing factor to lowered plasma amino acid concentrations in ESRD patients on CAPD than on HD. We believe that the lowered amino acid concentrations observed in CAPD patients may worsen the clinical outcome compared to HD patients.

Human growth hormone induces system B transport in short bowel syndrome

BACKGROUND

After massive enterectomy, remnant intestine undergoes compensatory adaptation. A combination of human growth hormone (hGH) and a glutamine-enriched modified diet induces further adaptation in patients with short bowel syndrome (SBS) on long-term total parenteral nutrition. The specific actions of each component, however, are not well-defined.

METHODS

New Zealand White rabbits were randomized to control, sham operation, or SBS (70% midjejunoileal resection) groups and treated with either hGH or saline. Sodium-dependent uptake of glucose, glutamine, alanine, leucine, and arginine into brush border membrane vesicles was quantitated. Serum insulin-like growth factor-I (IGF-I) levels were determined by immunoradiometric assay. Mucosal mRNA expression of IGF-I and IGF binding protein 4 (IGFBP-4) was evaluated by northern blot analysis using rat cDNA probes.

RESULTS

Glutamine and leucine transports were 33 and 39% greater, respectively, in the hGH-treated versus saline-treated SBS group (P < 0.05), supporting induction of system B amino acid transport. This upregulation was due, in part, to an 88% increase in glutamine carrier capacity (Vmax) with no change in carrier affinity (Km). Both hGH treatment and SBS increased serum IGF-I levels without direct correlation with increased nutrient transport. IGFBP-4 mRNA expression in small bowel mucosa of saline-treated SBS animals was significantly greater than saline-treated unoperated control values. Mucosal IGFBP-4 mRNA was not significantly altered from control in the other study groups. IGF-I mRNA expression was not detected in mucosa, but weak hybridization was noted in rabbit liver.

CONCLUSIONS

Human growth hormone accelerates early adaptation in SBS by upregulation of system B carrier capacity. Serum IGF-I levels and mucosal IGF-I and IGFBP-4 mRNA expression did not directly correlate with this enhanced nutrient transport, suggesting that hGH might exert its adaptive effects by mechanisms that are independent from the IGF system in this model.

Effects of the amino acid glutamine on frequency of chromosomal aberrations induced by gamma radiation in Wistar rats

The radiotherapy treatment of human cancer is often limited by the side effects and complications induced in normal surrounding tissues. The use of therapeutic strategies that could protect normal tissues while permitting the death of malignant neoplasm would be advantageous. Some studies have suggested that the amino acid glutamine (GLN) can serve as a conditionally essential nutrient in patients in a catabolic condition. The objective of this study was to evaluate the possible radioprotection of GLN on the frequency of chromosomal aberrations, number of metaphases with chromosomal aberrations and mitotic index in bone marrow cells of Rattus norvegicus. In this in vivo test system, GLN was administered by gavage at concentrations of 300 and 600 mg/kg body weight, in acute treatments, 30 min or 24 h before exposure to 3 Gy of whole-body gamma radiation. The results obtained in these experiments showed that GLN did not alter significantly the frequency of chromosome aberrations induced by gamma radiation under the experimental conditions used in the present study.