Maintenance of small bowel mucosa with glutamine-enriched parenteral nutrition

Small bowel transplantation: an overview

Small bowel transplantation (SBT) would, in theory, be the treatment of choice for patients suffering from the short bowel syndrome. Although SBT has been done with a considerable degree of success in some centers [36, 145], it is by no means an established or widely applicable therapy for those with short bowel syndrome. The small bowel is unique among vascularized organ grafts because it not only elicits a vigorous rejection reaction but is also capable of inducing graft-versus-host disease (GVHD). Rejection of the graft does not only lead to loss of function but also to bacterial translocation. The risk of fatal sepsis is aggravated by the immunosuppression given to prevent rejection. Here, the history of SBT is described, and recent developments in experimental and clinical SBT, as well as future prospects for this theoretically optimal treatment modality for patients dependent on total parenteral nutrition (TPN) for life, are outlined.

Glutamine supplementation does not prevent small bowel mucosal atrophy after total parenteral nutrition in the rat

Glutamine supplementation to non-lipid parenteral nutrition has been demonstrated to attenuate villus atrophy and increase mucosal DNA content in the rat. This study was performed in order to determine the effects of glutamine supplementation to a balanced TPN mixture (including lipids) on epithelial cell kinetics using autoradiography. Male Sprague-Dawley rats were used. Group 1 (control) received food and an intravenous saline infusion. Group 2 received an intravenous TPN mixture including lipids but without glutamine. The same TPN mixture, glutamine replacing an isonitrogenous amount of non-essential amino acids, was given to Group 3. Animals were fed for 7 days, whereafter blood and intestinal samples were taken 1 h after injection of tritiated thymidine. Microscopy of specimens from proximal jejunum revealed a significant reduction in the number of cells in crypts and villi in both TPN groups (2 and 3) compared to orally fed animals (p < 0.001). Epithelial cell numbers were not significantly different in Group 2 and 3. Similarly, the labelling index (number of labelled cells/number of crypt cells) was not affected by glutamine administration. In plasma, glucagon concentrations in Group 2 (TPN without glutamine) seemed to decrease compared to Group 1 and 3 (p = 0.06). In this study, glutamine supplementation did not affect apithelial atrophy or cell proliferation. It is concluded, that the effects of glutamine on mucosal atrophy and renewal in jejunum may depend on the composition of the TPN mixture supplied during parenteral feeding.

Short bowel syndrome: metabolic and surgical management

The management of short bowel syndrome requires long-term nutritional support and monitoring, medication, and occasionally additional surgical procedures. Constant attention is required to ensure adequate adaptation of the gut. This article reviews the normal function of the small bowel, adaptation following resection, total parenteral and enteral nutrition, and the role of adjunctive surgical procedures in the management of short bowel syndrome.

Glutamine-supplemented parenteral nutrition improves gut mucosa integrity and function in endotoxemic rats

The effects of glutamine-supplemented parenteral nutrition on protein metabolism, small intestinal mucosal metabolism, morphology, and barrier function were studied in endotoxin-treated rats. Forty-six male Wistar rats were randomized to two groups of 23 animals each and received total parenteral nutrition solutions supplemented with either glutamine (GLN group) or glycine (GLY group) at 2% wt/vol. Endotoxemia was induced by continuous intravenous infusion of endotoxin at a dose of 2 mg/kg per day throughout the 4-day study period. The GLN group had a less-negative cumulative nitrogen balance (-14.0 +/- 132.8 mg of nitrogen in the GLN group and -86.8 +/- 161.7 mg of nitrogen in the GLY group, p < .05) and less cumulative excretion of urinary 3-methylhistidine (2910 +/- 593 nmol) than the GLY group (4447 +/- 933 nmol, p < .01). Jejunal mucosal glutaminase activity and the arterio-portal venous blood glutamine concentration differences were significantly higher in the GLN group compared with the GLY group (15.6 +/- 2.3 vs 11.1 +/- 1.9 mumol/g per minute, p < .05, and 181 +/- 52 vs 147 +/- 36 nmol/mL, p < .05, respectively). The morphology of the jejunal mucosa in the GLN group was significant for having greater mucosal weight (23.4 +/- 3.1 vs 17.6 +/- 2.5 mg/cm), villus height (445 +/- 75 vs 357 +/- 57 microns), crypt depth (197 +/- 34 vs 161 +/- 28 microns), and wall thickness (751 +/- 77 vs 648 +/- 102 microns) than the GLY group (p < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of L-glutamine on hepatic lipids at different energy levels in rats receiving total parenteral nutrition

The effect of glutamine on hepatic steatosis and serum amino acid pattern was studied in rats receiving total parenteral nutrition (TPN) with different levels of caloric intake. Rats were divided into four groups; a control group (n = 10) was fed a chow diet and infused with saline only. Three experimental groups (n = 8 to 10) received TPN solutions at energy levels of 25 kcal, 30 kcal, and 35 kcal/100 g body weight, respectively. The experimental groups were maintained with TPN for a period of 6 days. Each experimental group was divided into two subgroups, one of which was supplemented with glutamine, replacing 40% of the total amino acid nitrogen. All of the basal TPN solutions were isonitrogenous and identical in nutrient composition, except for the difference in energy level, which was adjusted with glucose. The results demonstrated that liver fat increased in accordance with the increase of glucose supply, and this increase was mainly due to triglyceride accumulation. Very-low-density lipoprotein-triglyceride and serum free fatty acid were significantly higher in the 30-kcal groups. There were no differences in hepatic lipid content, very-low-density lipoprotein-triglyceride secretion, or hepatic uptake of fatty acids between subgroups with and without glutamine supplementation. It was concluded that glutamine enrichment of a TPN solution did not have any effect on hepatic steatosis in normal rats.

Small bowel transplantation: an overview

Small bowel transplantation (SBT) would, in theory, be the treatment of choice for patients suffering from the short bowel syndrome. Although SBT has been done with a considerable degree of success in some centers [36, 145], it is by no means an established or widely applicable therapy for those with short bowel syndrome. The small bowel is unique among vascularized organ grafts because it not only elicits a vigorous rejection reaction but is also capable of inducing graft-versus-host disease (GVHD). Rejection of the graft does not only lead to loss of function but also to bacterial translocation. The risk of fatal sepsis is aggravated by the immunosuppression given to prevent rejection. Here, the history of SBT is described, and recent developments in experimental and clinical SBT, as well as future prospects for this theoretically optimal treatment modality for patients dependent on total parenteral nutrition (TPN) for life, are outlined.

Glutamine peptide-supplemented long-term total parenteral nutrition: effects on intracellular and extracellular amino acid patterns, nitrogen economy, and tissue morphology in growing rats

Glutamine (GLN) is a nonessential amino acid that is not included in current regimens for parenteral nutrition because of its chemical instability. This study tested the hypothesis that GLN supplementation during long-term total parenteral nutrition (TPN) (3 weeks) would enhance GLN availability, thereby improving nitrogen economy and growth in a growing rat model: Standard TPN delivering 300 kcal/kg per day (lipid:carbohydrate = 1.1) including 2.1 g of nitrogen per kilogram per day in an all-in-one solution was compared with an isonitrogenous, isocaloric, and isovolemic TPN regimen with 0.29 g of nitrogen per kilogram per day substituted by GLN derived from the dipeptides glycyl-GLN and alanyl-GLN (TPN GLN). Enterally fed controls were included. Analysis was confined to nonbacteremic animals with negative blood culture, in which extracellular and intracellular amino acid concentrations including GLN, nitrogen balance, serum protein concentrations, growth, and histologic sections of liver and small-bowel mucosa (light and scanning electron microscopy) were evaluated. Hepatic intracellular GLN concentrations were significantly lower, in animals receiving GLN-free TPN (11.7 +/- 1.6 nmol/mg fat-free dry and solid tissue mass, n = 9) compared with both GLN-supplemented TPN (16.0 +/- 3.0, n = 7) and enteral feeding (18.2 +/- 1.8, n = 6) (p < .001). Corresponding results were found for intracellular GLN concentrations in skeletal muscle (TPN standard 12.5 +/- 3.1, TPN GLN 14.7 +/- 3.1, enteral control 17.3 +/- 2.3, p < .05), intestinal mucosa, and spleen as well as for plasma concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic pouchitis after ileal pouch-anal anastomosis: responses to butyrate and glutamine suppositories in a pilot study

Nonspecific, idiopathic inflammation of ileal pouch mucosa ("pouchitis") after ileal pouch-anal anastomosis is a common complication of this surgical approach. The epithelium of the pouch is ileal, but variable degrees of colonic metaplasia are natural sequelae of construction of such a pouch. One hypothesis is that pouchitis is caused by a deficiency of epithelial nutrition. Thus, a lack of butyric acid (the principal metabolic fuel of colonocytes) or of glutamine (the main fuel of enterocytes) may develop. In this study, our aims were to determine the concentration of total short-chain fatty acids in random stool samples obtained from patients with an ileal pouch-anal anastomosis with and without pouchitis and to test the therapeutic effects of butyrate and glutamine suppositories on pouchitis. During the study, all conventional therapy for pouchitis was discontinued. For 21 days, 9 patients participated in a butyrate trial, and 10 patients were treated with glutamine. Total concentrations of fecal short-chain fatty acids were significantly less in patients with pouchitis than in those without pouchitis. During treatment, 6 of the 10 patients who received glutamine had no recurrence of symptoms, but only 3 of the 9 patients who received butyrate responded similarly. Hence, further studies of glutamine in the treatment of pouchitis seem warranted.

The influence of parenteral glutamine and branched-chain amino acids on total parenteral nutrition-induced atrophy of the gut

We tested the hypothesis that the provision of glutamine and branched-chain amino acids would reverse the gut atrophy that accompanies parenteral nutrition. Three hundred seventy-five rats were randomized into 15 groups to receive either conventional parenteral nutrition, rat food, glutamine-enriched parenteral nutrition (0.5% to 2.5%), branched-chain amino acid-enriched parenteral nutrition (0.8% to 2.0%), or glutamine plus branched-chain amino acid-enriched parenteral nutrition (0.5%/0.4% to 1.25%/1/0%). When compared with effects of conventional parenteral nutrition, the infusion of either glutamine or branched-chain amino acids partially reversed, in a dose-dependent manner, atrophy of the small bowel as assessed by gut weight (p < .05), mucosal weight (p < .05), villous height (p < .05), crypt cell production rate (p < .05), and mucosal protein concentration (p < .05). There was no effect on the large bowel. These results suggest that the parenteral infusion of either glutamine or branched-chain amino acids partially reverses the small-bowel atrophy that is associated with the infusion of solutions of conventional parenteral nutrients.

Glutamine peptide does not improve gut barrier function and mucosal immunity in total parenteral nutrition

In two separate experiments, three groups of 10 (first experiment) and 12 (second experiment) rats each were catheterized for the long term via the right jugular vein and fed one of the following dietary regimens for 7 days while in individual metabolism cages. The rat food control groups were fed powdered rat food. The total parenteral nutrition (TPN) formula for one group was enriched with the stable dipeptide L-alanyl-L-glutamine (ALA-GLN) equivalent to a 1% or 2% glutamine concentration. For the control TPN groups, the dipeptide was replaced by isonitrogenous amounts of alanine (ALA). In both experiments, bacterial translocation was promoted to a similar extent by the ALA-GLN and ALA TPN formulas compared with the rat food groups. Bacterial overgrowth in the cecum and intestinal atrophy, quantitated by the mucosal protein content, did not differ between ALA-GLN and ALA groups. The nitrogen balances of the three groups showed similar values in the second experiment. The secretory immunoglobulin A was measured in washings of the jejunum and ileum (soluble fraction) and in the homogenates of the gut mucosa (insoluble fraction). The secretory immunoglobulin A values of both fractions showed no difference between the ALA and ALA-GLN groups, irrespective of whether they were normalized for gut segment length or corrected for mucosal protein content. In conclusion from these results, the supplementation of TPN with glutamine does not seem to improve gut barrier function or mucosal immunity in unstressed rats.

Alanyl glutamine-enriched total parenteral nutrition restores intestinal adaptation after either proximal or distal massive resection in rats

This study was designed to determine whether alanyl glutamine-containing total parental nutrition (TPN) can restore the impaired adaptive process of the remaining intestine, observed with administration of conventional TPN, after massive small-bowel resection. Seventy-four male Sprague-Dawley rats weighing 250 g were randomly divided into seven groups. Group I rats (n = 10) were killed after overnight fasting. Group II animals (n = 32) underwent massive small bowel resection (85%) with preservation of the first 15 cm of jejunum. Group III animals (n = 32) were also submitted to massive small-bowel resection with preservation of 15 cm of terminal ileum. Three different TPN solutions were prepared. Solution A was a conventional formulation that did not contain glutamine. Solution B contained 1.88 times the amino acid concentration of solution A. Solution C was prepared by adding alanyl glutamine (2 g/100 mL) to solution A. Solutions B and C were isonitrogenous and isocaloric. Each solution was infused to groups II and III, which were subdivided into groups IIA (n = 10), IIB (n = 11), IIC (n = 11), IIIA (n = 10), IIIB (n = 11), and IIIC (n = 11). After 1 week of TPN (270 kcal/kg per day), the experimental animals were killed and the intestine was taken for examination. Final body weight did not differ significantly among the groups, and there was no difference in nitrogen balance among the animals that received solution B or C.(ABSTRACT TRUNCATED AT 250 WORDS)

Intravenous administration of nucleosides and a nucleotide mixture diminishes intestinal mucosal atrophy induced by total parenteral nutrition

Total parenteral nutrition (TPN) is associated with atrophic changes in the structure and function of the intestinal mucosa. Because rapidly renewing intestinal mucosal cells may require an external source of purines and pyrimidines for their optimal growth, it can be assumed that supplementation of nucleosides and a nucleotide mixture (OG-VI) during TPN may prevent the progression of mucosal atrophy by compensating for a relatively insufficient delivery from liver. To test that hypothesis, male Wistar rats receiving TPN for 7 days were divided into four groups according to different TPN solutions. Group C (n = 10) received a standard solution, group O (n = 10) received OG-VI in addition to the standard solution, and group G (n = 10) received a glutamine-rich TPN solution containing almost the same amount of calories and nitrogen as the standard solution. Group O+G (n = 10) received OG-VI in addition to the glutamine-rich solution. Various parameters were examined on the eighth day in the jejunal and ileal segments. The following significant changes in comparison with group C were observed: total wet weight of the jejunal segment in group O was significantly greater, as was mucosal wet weight of the jejunal and ileal segments in groups O and O+G; protein contents of the ileal segment in group O as well as the DNA content of the jejunal segment in group O increased significantly; and maltase activity of the jejunal segment in group O+G increased, as did the villus height of the jejunal segment in groups O and O+G and the villus height of the ileal segment in group G.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of parenteral nutrition supplemented with L-glutamine or glutamine dipeptides

Although glutamine is an important fuel used by the intestinal mucosa and other visceral organs, it is not present in any commercially available parenteral amino acid solution. To compare the effects of L-glutamine with glutamine dipeptides, we studied the effects of each in 8 dogs and 60 Wistar rats. In the dog study, three amino acid solutions were compared: standard commercial amino acid solution (control), alanine-glutamine dipeptide-enriched solution (glutamine 3.4%), and glycine-glutamine dipeptide-enriched solution (glutamine 3.6%). Arterial and venous samples were collected to compare the effects of the three solutions on skeletal muscle amino acid exchange. In the rat study, two studies were undertaken: group 1 rats underwent only central venous catheterization; group 2 rats underwent central venous catheterization and a 50% intestinal resection. Within each group, three different solutions were infused: standard amino acid solution (control), glutamine-enriched (1.5% glutamine) solution, or glutamine dipeptide-enriched (1% glutamine) solution. After 7 days of parenteral nutrition, samples of gut, blood, and muscle were collected for determination of mucosal thickness, villus area, serum amino acid profile, liver and renal function tests, and muscle composition. When glutamine or glutamine-dipeptide solutions were administered, the dogs showed increasing serum glutamine concentrations and enhanced glutamine uptake across the hind leg muscle. Similarly, both groups of rats demonstrated significant differences in serum glutamine levels, nitrogen balance, intestinal mucosa thickness, and villus area. We conclude that both glutamine and glutamine-dipeptide infusions increase serum glutamine concentrations and result in regional tissue effects. Both exerted similar metabolic effects with no apparent complications.

Effect of glutamine-supplemented total parenteral nutrition on recovery of the small intestine after starvation atrophy

Intestinal atrophy was induced in rats by infusion of 5% dextrose for 7 days with only oral water allowed. Compared with control animals fed standard rat chow (Purina Mills, St. Louis), the starved animals lost 30.5% of their initial body weight, 34.7% mucosal wet weight, 68.3% mucosal nitrogen content, 36.7% mucosal thickness, and 38.6% villous height and had variable losses of mucosal disaccharidase activities. Three groups of depleted rats were then refed with different regimens. One group was refed with standard Purina rodent chow (n = 15); a second group with a standard total parenteral nutrition (TPN) solution containing 16% glucose, 2.8% fat, and 4.25% standard amino acids (Travasol 8.5%, Baxter Healthcare Corporation, Deerfield, IL) (n = 15); and the third group with a TPN solution of 16% glucose, 2.8% fat, 2.75% standard amino acids, and 1.5% glutamine (n = 15). After 7 days of refeeding, rats were killed to determine the degree of intestinal recovery. Animals refed with standard TPN solution showed no significant recovery of intestinal mucosal weight, mucosal nitrogen content, villous height, mucosal thickness, or mucosal disaccharidase activities. Animals refed with glutamine-supplemented TPN solution demonstrated significant recovery of all parameters but not back to normal. Oral rodent chow completely restored intestinal anatomy and function. The addition of glutamine to TPN solutions significantly improved recovery of the intestine from starvation atrophy, and additional efforts to make it commercially available are indicated. This study again confirms the preferable use of a regular oral diet when clinically feasible and safe.

Effect of glutamine-supplemented intravenous nutrition on survival after Escherichia coli-induced peritonitis

Current solution formulations for total parenteral nutrition (TPN) do not contain glutamine (GLN). The purpose of this study was to examine whether GLN supplementation of TPN would improve survival in experimental Escherichia coli peritonitis in Fischer 344 rats (190-210 g). Initial experiments were performed to determine the degree of stress and to evaluate survival after intraperitoneal E coli injection. The E coli colony used was isolated from a culture of human blood. Graded doses were injected intraperitoneally in Fischer 344 rats (190-210 g). The response of white blood cell count, plasma insulin, glucagon, and corticosterone levels, and urinary excretion of vanillylmandelic acid reflected a significant stress response for at least 3 days. Survival was dose-dependent, with 60% mortality at 3 days after injection of 5 x 10(5) colony forming units of E coli/200 g body weight. To determine whether GLN supplementation of TPN would alter survival in this E coli peritonitis model, Fischer 344 rats were randomized to receive TPN containing 4.25% standard amino acids (group STD, n = 38) or the same solution with 1.5% of the amino acid content replaced with L-GLN (group GLN, n = 38). After 7 days of TPN, 5 x 10(5) colony forming units of E coli/200 g body weight were injected intraperitoneally under direct vision through a small laparotomy. Survival was monitored for 3 days. Surviving rats were killed to determine various nutritional parameters including plasma albumin and GLN concentration, the weight and nitrogen content of the gastrocnemius muscle, and biochemical and histological composition of the small intestine.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism and nutritional frontiers in pediatric surgical patients

The successful treatment of pediatric surgical disease requires an understanding of the acute metabolic stress response. Poor clinical outcome can result when the metabolic demands of acute injury exceed the ability of endogenous host mechanisms to compensate. Appropriate exogenous supplementation may provide the metabolic and nutritional support crucial to recovery. As knowledge in this area grows, more effective treatment strategies are evolving. The potential for further advances, especially in the infant critical care population, offers the hope for substantial progress in the near future.

Ornithine alpha-ketoglutarate and glutamine supplementation during refeeding of food-deprived rats

The aim of this study was to compare the efficiency of ornithine alpha-ketoglutarate (OKG) and glutamine supplementation in an experimental model of denutrition that provides well-characterized disturbances of amino acid patterns. Male Wistar rats (187 +/- 11 g; five in each group) were starved for 3 days and then refed for 7 days with an oral diet (192 kcal kg-1.day-1 and 2.25 g of nitrogen kg-1.day-1), supplemented with 0.19 g of nitrogen kg-1.day-1 in the form of OKG, glutamine, or casein (control group). Food deprivation induced a fall in most tissue amino acids, with the notable exception of muscle leucine and liver glutamate, which increased by 43% (p < .01), and 11% (p < .05), respectively. The main effect of OKG was seen in the viscera, with a normalization of most amino acid pools (including proline and branched-chain amino acids) in the small bowel and liver. The main effect of glutamine was observed in the muscle, with a normalization of the glutamine and leucine pools. We conclude that, in this model and with the doses used, OKG and glutamine act in different target tissues, ie, splanchnic areas and muscle, respectively.

Intravenous glutamine fails to improve gut morphology after radiation injury

Male Sprague-Dawley rats housed in individual metabolic cages received total parenteral nutrients via chronic indwelling internal jugular catheters to determine whether supplementing parenteral nutrition with glutamine would accelerate recovery of small-bowel morphology after abdominal radiation. After recovering from catheter insertion for 3 days they received either 1000 cGy gamma radiation to the abdomen only or no radiation and immediately thereafter received isonitrogenous and isocaloric intravenous solutions containing either 0% or 2% glutamine at 1.58 mL/h for the next 5 days. Intestinal segments were then assayed for whole-bowel deoxyribose nucleic acid content and villus height. Irradiation caused a 40% decrement in these parameters, which were not restored by glutamine supplementation. Therefore, intravenous glutamine supplementation failed to accelerate recovery of small-bowel morphology in this model of combined surgical and radiation injury.

Effect of glutamine-supplemented total parenteral nutrition on the small bowel of septic rats

In order to study the effect of total parenteral nutrition (TPN) with or without glutamine supplementation in septic rats, septic Wistar albino rats were randomly assigned to receive 0.23 g of nitrogen and 113 kJ (100 g BW)(-1) per day in the form of amino acids with (group 2) or without (group 1) glutamine supplementation or 10% (w/v) glucose only (group 3). After 4 days of TPN treatments, rats receiving glutamine-supplemented TPN had a cumulative nitrogen balance of -24.4 +/- 3.3 mg N, which was significantly (P < 0.001) better compared to other TPN-treated groups. Septic rats of group 2 survived sepsis significantly (P < 0.001) better than those in groups 1 and 3. Glutamine-supplemented TPN treatment resulted in significant increases in jejunal weight (P < 0.001), DNA and protein contents (P < 0.001), villous height (P < 0.001) and crypt depth (P < 0.001) when compared with septic rats of group 1. Septic rats of group 2 extracted and metabolised glutamine by the small bowel at higher rates (P < 0.001) than that observed in septic rats of group 1. Increases in jejunal glutaminase (38.2%, P < 0.001) and decreases in glutamine synthetase (41.7%, P < 0.001) activities were observed in response to glutamine-supplemented TPN treatment. It is concluded that the administration of glutamine-supplemented TPN is beneficial to the small bowel of septic rats.

Intravenous nutritional support and the surgeon: where next?

Over the past twenty five years the development of total parenteral nutrition has in many ways revolutionised the practice of surgery. It has enhanced survival in otherwise high mortality operations such as oesophageal surgery, especially with anastomotic complications. It has changed significantly the management of fistulae, either post operative or associated with diseases such as Crohn's enteritis. Here a basic general principle is applied--that a fistula will close if there is no distal obstruction and the throughput can be diminished. This can be achieved by withholding oral feeding and using the parenteral route. It has allowed survival in the short gut syndrome from whatever cause and it is interesting to see the degree of "intestinal adaptation" that occurs once the first critical year is survived with the help of intravenous nutrition. The assessment of nutritional status is difficult and while the level of serum albumin may be taken as a clinical standard, it is obvious that many patients survive extensive surgery with low albumin levels and also that there appears to be a lag period to the restoration of albumin levels, even with otherwise successful nutritional support and with other parameters being satisfactory. Even complex formulae using a combination of laboratory and antropometric parameters is not fully satisfactory as an absolute assessment of nutritional status. It is now interesting to see that nutrition can affect both immune competence and even carcinogenesis. The lipid element in intravenous nutrition may cause dysfunction of immunity and vitamin status, gastric and platelet function with impaired oxygen diffusion leading to increased wedge pressures.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamine content of whole proteins: implications for enteral formulas

In two recent clinical trials in surgical patients, supplementation of total parenteral nutrition with daily doses of 12 or 20 g of glutamine resulted in a diminished loss of free glutamine in skeletal muscle tissue. Studies in animals exploring the use of both enteral and parenteral glutamine supplementation suggest that glutamine may be an essential nutrient in the maintenance of gut structure and function during critical illness. These findings have led to heightened interest in the glutamine content of enteral formulas. This article describes a method for estimating the glutamine content of whole-protein enteral formulas. The average amount of glutamine in selected, whole-protein formulas ranges from a minimum of 3.55 g/4200 kJ to a maximum of 5.15 g/4200 kJ. Although it is still too early to define the safest and most effective dose of glutamine, there are two points regarding glutamine supplementation that clearly merit further investigation: no clinical trials have been conducted to assess the potential benefits of glutamine supplementation of an enteral diet or to assess the effects of using diets containing protein-bound glutamine rather than free glutamine.

Outcome and intestinal adaptation in neonatal short-bowel syndrome

We reviewed 52 consecutive patients with short-bowel syndrome (SBS) treated with long-term parenteral nutrition (PN) from 1978 through 1990. The SBS etiologies included necrotizing enterocolitis (NEC) in 26 patients (50%), abdominal wall defects in 11 (22%), jejunoileal atresia in 6 (12%), midgut volvulus in 4 (8%), Hirschsprung's disease in 3 (6%), and segmental volvulus and cloacal exstrophy in 1 (2%) each. The average initial small bowel length was 48.1 cm, and only 31% of the patients retained an ileocecal valve (ICV). The mean duration of PN therapy was 16.6 months, and 39 patients (75%) were successfully weaned from it. Forty-three patients (83%) survived. Significant differences between the initial 20 patients treated from 1978 through 1984 and the next 32 from 1985 through 1990 were duration of PN therapy (25.1 v 11.4 months; P = .04), incidence of PN-associated jaundice (80% v 31%; P = .001), and survival (65% v 94%; P = .02). NEC patients had a significantly lower mean birthweight than those with other etiologies (mean, 1,367 v 2,544 g; P less than .0001) but did not differ in initial small bowel length, ICV retention rate, duration of PN treatment, incidence of successful PN weaning, or outcome. The presence of an ICV did not correlate with successful PN weaning but did affect the mean duration of PN therapy (7.2 months with ICV v 21.6 months without; P = .03).(ABSTRACT TRUNCATED AT 250 WORDS)

Altered glutamine metabolism in rat portal drained viscera and hindquarter during hyperammonemia

In normal rats, muscle is the major glutamine releasing organ and gut is the major glutamine consuming organ. It has been suggested that enhanced muscle ammonia detoxification and gut ammonia production occurs during liver insufficiency-induced hyperammonemia. Therefore, ammonia and amino acid fluxes across portal-drained viscera and hindquarter, and muscle concentrations were measured in portacaval shunted and acute liver ischemia rats. Arterial ammonia and most amino acids were increased after portacaval shunting and increased progressively during liver ischemia, but net hindquarter ammonia uptake was not observed. Net hindquarter glutamine efflux was increased during portacaval shunting, but it decreased during liver ischemia, while muscle glutamine concentrations increased. The comparable net portal drained viscera glutamine uptake in normal and portacaval shunted rats changed during liver ischemia from net uptake to release, coinciding with release of most other amino acids. These results cast doubt on the ammonia detoxifying role of muscle during acute liver ischemia-induced hyperammonemia in the rat. The portal drained viscera glutamine release during severe hyperammonemia could be due to intestinal damage.

Increased energy expenditure after intravenous administration of amino acids

Nutrient-induced thermogenesis (NIT) after parenteral administration of amino acids (AAs) was investigated in rats and compared with result obtained with intragastric administration. Resting energy expenditure was measured with a new type of open-circuit indirect calorimeter. The NIT increased shortly after parenteral AAs administration and reached a steady state in 30 minutes. The change in resting energy expenditure (the increment of resting energy expenditure over preinfusion baseline values) showed a significant relationship not only with the amount of infused AAs but also with the AA concentration in the portal vein. Furthermore, the increase in plasma AA concentrations in the portal vein was proportional to the amount of the particular AA infused. This relationship held true over the entire range tested. NIT with parenteral infusion (11% to 12%) was lower than that with intragastric infusion (20% to 23%). Plasma insulin, corticosterone, and glucagon levels increased after both parenteral and intragastric AAs administration, but the two methods did not show any significant differences in hormonal changes. The plasma aminogram of the portal vein after intragastric infusion was compared with that after parenteral infusion. Total plasma AA concentration and the levels of glutamine, lysine, arginine, glutamate, aspartate, and histidine were lower but the level of isoleucine was higher after intragastric infusion. On the basis of these results, it is believed that parenteral administration of AAs can induce thermogenesis, which may be regulated by the intraportal AA concentration. Considering the remarkable decrease in glutamine in the portal vein after intragastric infusion, the cost of intestinal metabolism may predominantly contribute to the NIT resulting from intragastric infusion.

Influence of N-acetylglutamine or glutamine infusion on plasma amino acid concentrations during the early phase of small-bowel adaptation in the dog

Glutamine is a nonessential neutral amino acid that is widely consumed by the intestinal tract in catabolic states. We have followed up the plasma amino acid profile after extensive small-bowel resection in dogs receiving total parenteral nutrition (TPN) with or without glutamine (GLN) or N-acetylglutamine (aGLN) supplementation. Animals were divided into four groups according to the type of surgery (enterectomy or transection) and nutrition (TPN, TPN with aGLN, or TPN with GLN). Plasma GLN levels decreased in group I (enterectomy and TPN) on day 2 (p = .03) and significantly increased on postoperative days in groups III (enterectomy and TPN with aGLN) and IV (enterectomy and TPN with GLN). A significant increase of plasma GLN was observed in groups III and IV compared with group I on days 6 and 8 (p = .03 and p = .01). Plasma alanine decreased in groups with bowel resection, whereas no change was observed in the control group (transection) and the decrease of plasma alanine was significantly less pronounced in groups III and IV compared with group I. The increase of crypt depth and villous height was more pronounced in groups III and IV. These results suggest that GLN is a required substrate for mucosal growth and function, which could improve the intestinal adaptation encountered after enterectomy.

Glutamine preserves liver glutathione after lethal hepatic injury

Glutathione (GSH) is a major antioxidant that protects tissues from free radical injury. Glutamine augments host defenses and may be important in GSH synthesis. Acetaminophen toxicity causes hepatic GSH depletion and hepatic necrosis. The authors hypothesized that glutamine-supplemented nutrition would enhance liver GSH stores and diminish hepatic injury and death after acetaminophen overdose. Wistar rats received either a standard total parenteral nutrition (TPN) solution (STD) or an isocaloric, isonitrogenous glutamine-supplemented solution (GLN). On the 5th day of feeding, animals were given acetaminophen (400 mg/kg intraperitoneally) and then killed at various time points. Standard TPN solution animals had a rapid depletion of hepatic glutathione, whereas GLN animals were resistant to this drop and rapidly repleted hepatic GSH stores. Glutamine-supplemented animals maintained higher plasma glutamine concentrations, had lesser elevations in hepatic enzymes, and sustained significantly fewer complications compared with STD animals. The authors conclude that glutamine-supplemented nutrition preserves hepatic glutathione, protects the liver, and improves survival during acetaminophen toxicity. Glutamine may augment host defenses by enhancing antioxidant protection.

Glutamine-enhanced enteral diet improves nitrogen balance without increasing portal ammonia

Following surgical stress the jejunum actively metabolizes endogenous glutamine, a non-essential amino acid, to produce alanine and ammonia, which augments substrate flow to the liver at a time when oral intake of nutrients is decreased. Oral glutamine supplementation theoretically may modify the response to injury. This study was designed to demonstrate the role of the jejunum in postinjury glutamine metabolism and to evaluate the influence of enteral glutamine supplements on nitrogen and ammonia metabolism after laparotomy and bowel resection in dogs. Oral glutamine in the presence of an intact small bowel significantly improved nitrogen balance (461 mg kg body-weight-1 day-1) compared with a control diet (-370 mg kg-1 day-1) (P less than 0.05, analysis of variance). Removal of the proximal small bowel prevented this beneficial effect of glutamine (-507 mg kg-1 day-1). Glutamine-supplemented and control diets were associated with similar portal ammonia concentrations throughout the study.

Glutamine-enriched intravenous feedings attenuate extracellular fluid expansion after a standard stress

A double-blind, randomized controlled trial was performed to determine the effect of glutamine (GLN)-enriched intravenous feedings on the volume and distribution of body fluids in catabolic patients. Subjects with hematologic malignancies in remission underwent a standard treatment of high-dose chemotherapy and total body irradiation before bone marrow transplantation. After completion of this regimen, they were randomized to receive either standard parenteral nutrition (STD, n = 10) or an isocaloric, isonitrogenous nutrient solution enriched with crystalline L-glutamine (0.57 g/kg/day, GLN, n = 10). Extracellular water (ECW) and total body water (TBW), determined by bromide and heavy water dilution techniques, were measured before the conditioning treatment and after termination of the intravenous feedings that were administered for 27 +/- 1 days. In addition electrical resistance (R, in ohms, omega) and reactance (Xc, omega) of the body to a weak alternating current were measured at these time points. Both study groups were comparable for age, weight, height, sex, and diagnosis. Initial TBW was highly related to electrical resistance (r = -0.93, p less than 0.001). After conditioning therapy, bone marrow infusion, and intravenous feedings, a 20% expansion in ECW was observed in the STD group (ECW: 18.0 +/- 1.1 L vs. 14.9 +/- 1.0, p = 0.012), and this fluid retention was associated with a marked decrease in electrical resistance (R: 514 +/- 28 omega vs. 558 +/- 26, p less than 0.05). In contrast the extracellular fluid compartment in patients receiving GLN-supplementation did not change (ECW: 15.8 +/- 0.9 L vs. 15.4 +/- 0.8, p = 0.49), and the body's resistance was maintained (R: 552 +/- 27 omega vs. 565 +/- 23, p = 0.42). Expansion of ECW could not be related to differences in fluid or sodium intake, or to the use of diuretics or steroids. Patients receiving the STD solution, however, exhibited a greater number of positive microbial cultures (p less than 0.01) and a higher rate of clinical infection compared with the GLN patients (5/10 vs. 0/10, p less than 0.05); the fluid expansion in infected STD patients was greater compared with uninfected individuals (delta ECW: + 5.0 +/- 1.4 vs. 0.7 +/- 0.5, p = 0.007). In this model of catabolic stress, fluid retention and expansion of the extracellular fluid compartment commonly observed after standard total parenteral nutrition can be attenuated by administering glutamine-supplemented intravenous feedings, possibly by protecting the host from microbial invasion and associated infection.

Influence of glutamine and branched chain amino acids on the jejunal atrophy associated with parenteral nutrition

Infusions of conventional parenteral nutrients (CPN) are associated with gut atrophy. This may be due to the absence of glutamine in such solutions. Although glutamine is a preferred gut nutrient, it is excluded from CPN because it is unstable at room temperature. This problem may be circumvented either directly by the infusion of fresh solutions of glutamine, or indirectly by the infusion of branched chain amino acids (BCAA). We evaluated the effect of infusing either glutamine, BCAA, or glutamine plus BCAA-enriched CPN on the rat jejunum. Sixty male Wistar rats were randomized to receive 6 days of either conventional parenteral nutrition (CPN), CPN plus 1.5% glutamine (GLN), CPN plus 2% BCAA (BCAA), CPN plus 0.8% BCAA and 1.0% glutamine (GLN/BCAA), or a normal oral diet (Chow). Standardized segments of jejunum were then removed for assessment. Compared with the CPN group, both the GLN/BCAA and the BCAA groups had greater mucosal weights (P less than 0.05) and mucosal protein concentrations (P less than 0.05), the GLN/BCAA group had greater jejunal weights (P less than 0.05), and the GLN group had an increased jejunal weight (P less than 0.05) and a higher crypt cell production rate (P less than 0.05). We conclude that the infusion of glutamine or BCAA-enriched parenteral nutrition improves jejunal morphology compared with conventional parenteral nutrition.

Effects of glutamine infusion on colonic anastomotic strength in the rat

Glutamine is one of the primary respiratory fuels of the colon. However, it is not included in commercial preparations of parenteral nutrients because of its short shelf life. It has been suggested that colonic atrophy induced by conventional parenteral nutrition can be reversed by the intravenous infusion of fresh solutions of glutamine. This study evaluated the hypothesis that glutamine-enriched parenteral nutrition would enhance the strength of a standard colonic anastomosis in undernourished rats. After surgery, the rats were randomized to receive 6 days of postoperative support with either rat chow, conventional parenteral nutrition, or parenteral nutrition containing 1.2% glutamine. Measurement of colonic bursting tension failed to demonstrate any significant differences between the groups under study. In conclusion, the administration of 1.2% glutamine-enriched parenteral nutrition failed to influence the healing of colonic anastomoses in undernourished rats.

Enteral alimentation: administration and complications

Tube feeding is commonly used for providing essential calories and nutrients to the patient otherwise unable to eat. In the last two decades there has been significant expansion in the number and quality of enteral formulas. In this review, we evaluate the indications for each major class of formula, and survey complications associated with formulas and devices that deliver formula. Recommendations for future research are listed.

Tumour necrosis factor increases hepatic cell mass

The effect of tumour necrosis factor (TNF) on hepatic cellularity was investigated in male Wistar rats maintained on total parenteral nutrition. Twenty-eight rats were infused with TNF (2 x 10(5) units TNF-alpha kg-1 24 h-1) or saline (controls) for 6 days. Wet and dry liver weights and nitrogen content were significantly increased by TNF (P less than 0.001), indicating an increase in liver mass. A further 81 rats were infused with TNF (2 or 4 x 10(5) units kg-1 24 h-1) or saline over 1, 3 and 6 days. Total liver DNA and protein content and counts of hepatocyte mitosis were determined. Liver DNA and protein increased with dose of TNF and time (P less than 0.001), suggesting that TNF increased hepatic cellularity. Histological examination demonstrated no significant inflammatory infiltrate to account for the increased cell mass. However, the number of hepatocyte mitoses increased with dose of TNF and time (P less than 0.05), indicating that the increase in liver cellularity was due to increased hepatocyte cell number. TNF-induced hepatic hyperplasia appears to be an additional feature of the integrated host response to injury and infection.

Short-bowel syndrome: a review of the role of nutrition support

Advances in long-term venous access devices and in parenteral nutrition solutions have made it possible for patients with severe short bowel syndrome to survive and to live in our society. The spectrum of this disease is such that some patients may be able to lessen their dependence or even become free from parenteral therapy. This review will discuss the role of nutrition support in the patient with short bowel syndrome.

Total parenteral nutrition: practical recommendations and new developments

In this article the general guidelines for a nutrition schedule and new developments in the field of parenteral nutrition are discussed. The present possibilities for parenteral nutrition do not imitate the normal physiologic diet completely. The most frequently used calculation of the energy expenditure is estimated by a formula using weight, height, and age and was developed in healthy persons. It does not always represent the real caloric demands of a patient. Complications, partly due to parenteral nutrition, are noted. In severely ill patients hyperglycaemia and liver function disorders are frequently observed. Parenteral nutrition results in atrophy of the intestinal mucosa. Deficiencies in trace elements and vitamins are diagnosed despite calculated adequate nutritional support because the demands are underestimated. New developments in parenteral nutrition include a better method to determine the nutritional demands in clinical practice, administration of hormones to improve the nitrogen balance, and development of new lipid emulsions and amino-acid solutions. Studies provide more insight into the physiologic process of trace element metabolism, and methods are being developed to define a real deficiency.

The influence of branched chain amino acids on colonic atrophy and anastomotic strength in the rat

Conventional solutions of parenteral nutrients fail to reverse the colonic atrophy caused by starvation. This may be due to the absence from these solutions of the amino acid glutamine--a fuel for rapidly dividing cells such as colonocytes and fibroblasts. Although glutamine is unstable in solution, the infusion of branched chain amino acids (BCAA) increases the rate of synthesis and release of glutamine from skeletal muscle. We evaluated the hypothesis that the infusion of BCAA into undernourished rats would reduce the extent of mucosal atrophy and enhance the healing of anastomoses in the colon. Undernourished rats were randomized to receive 6 days of either a normal diet (Chow), conventional parenteral nutrition (CPN), or CPN supplemented with 1.8% BCAA (BCAA). The BCAA group had a higher plasma glutamine concentration than the Chow group (P less than 0.05). Compared with the CPN group, the BCAA group had the greater colonic mucosal weight (P less than 0.05) and colonic mucosal protein content (P less than 0.05), but there were no significant differences between groups in the bursting wall tension of the colon or the hydroxyproline content of the anastomoses. Although the infusion of BCAA has a beneficial effect on colonic atrophy, this did not result in the more secure healing of colonic anastomoses in this experimental model.

Review article: towards safer parenteral nutrition

Central parenteral nutrition can cause serious complications, particularly in association with the feeding catheter, previously in relation to nutrient provision, and occasionally in other organ systems, notably disease of the liver and abnormalities of bone composition. Developments in catheter design, the introduction of catheter care protocols based on an understanding of the common routes of catheter infection, and the identification of factors associated with central vein thrombosis have all reduced dramatically the incidence of complications. Furthermore, problems such as catheter occlusion, catheter infection and central vein thrombosis can now be treated effectively in many patients without the loss of the feeding catheter. This review summarizes the common and important complications of parenteral feeding with emphasis on their practical prevention and management.

Is glutamine a conditionally essential amino acid?

The nonessential amino acid glutamine has recently been the focus of extensive scientific interest because of its importance in cell and tissue cultures and its physiologic role in animals and humans. Glutamine appears to be a unique amino acid, serving as a preferred respiratory fuel for rapidly proliferating cells, such as enterocytes and lymphocytes; a regulator of acid-base balance through the production of urinary ammonia; a carrier of nitrogen between tissues; and an important precursor of nucleic acids, nucleotides, amino sugars, and proteins. Abundant evidence suggests that glutamine may become a "conditionally essential" amino acid in the critically ill. During stress the body's requirements for glutamine appear to exceed the individual's ability to produce sufficient amounts of this amino acid. Provision of supplemental glutamine in specialized enteral or parenteral feeding may enhance nutritional management and augment recovery of the seriously ill while minimizing hospital stay.

Glutamine metabolism and its physiologic importance

The amino acid glutamine has important and unique metabolic functions. It is the most abundant free amino acid in the circulation and in intracellular pools and a precursor for the synthesis of amino acids, proteins, nucleotides, and many other biologically important molecules. It is the most important precursor for ammoniagenesis in the kidney, the major end product of ammonia-trapping pathways in the liver, a substrate for gluconeogenesis, and an oxidative fuel in rapidly proliferating cells and tissues. Glutamine also may have a number of important regulatory roles, increasing protein synthesis and decreasing protein degradation in skeletal muscle and stimulating glycogen synthesis in the liver. The demonstration that glutamine concentrations decrease and tissue glutamine metabolism increases markedly in many catabolic, stressful disease states has led to a reconsideration of the classification of glutamine as a nonessential amino acid and to the alternative hypothesis that glutamine may be a conditionally essential nutrient. This hypothesis has been supported by recent studies that have shown trophic effects of glutamine-supplemented diets on the growth of specific tissues and on total body nitrogen balance. These observations form the basis for current efforts to define the clinical usefulness of glutamine-supplemented nutrition.

Safety and metabolic effects of L-glutamine administration in humans

A series of dose-response studies was conducted to evaluate the clinical safety, pharmacokinetics, and metabolic effects of L-glutamine administered to humans. Initial studies in normal individuals evaluated the short-term response to oral loads of glutamine at doses of 0, 0.1, and 0.3 g/kg. A dose-related increase in blood glutamine occurred after oral loading and elevation of amino acids known to be end products of glutamine metabolism occurred (including alanine, citrulline, and arginine). No evidence of clinical toxicity or generation of toxic metabolites (ammonia and glutamate) was observed. Glutamine was infused intravenously in normal subjects over 4 hr at doses of 0.0125 and 0.025 g/kg/hr. In addition, glutamine was evaluated as a component of parenteral nutrition solutions (0.285 and 0.570 g/kg/day) administered for 5 days to normal subjects. Intravenous administration of glutamine was well tolerated without untoward clinical or biochemical effects. Subsequent studies in patients receiving glutamine-enriched parenteral nutrition for several weeks confirmed the clinical safety of this approach in a catabolic patient population. In addition, nitrogen retention appeared to be enhanced when glutamine was administered at a dose of 0.570 g/kg/day in a balanced nutritional solution providing adequate calories (145% of basal) and protein (1.5 g/kg/day). Nitrogen balance in patients receiving lower doses of glutamine (0.285 g/kg/day) was similar to that in patients receiving standard formulations. Further controlled clinical trials of the metabolic efficacy, tolerance, and dose response of glutamine in other patient groups are necessary to determine the appropriate use of glutamine enrichment of nutrient solutions.

Glutamine nutrition and requirements

Glutamine is the most abundant free amino acid in plasma and tissue pools and an important intermediate in a number of metabolic pathways. Glutamine levels decline markedly in the course of many different catabolic disease states and it has recently been suggested that glutamine may be a conditionally essential dietary nutrient rather than a nonessential amino acid. Changes in tissue glutamine concentrations have been shown to correlate with net protein turnover, and there is evidence that glutamine may both stimulate protein synthesis and inhibit protein degradation. In experimental animals, we have shown that the fall in glutamine concentrations in plasma and tissue pools that occurs in the postoperative state can be prevented or reversed by providing large quantities of exogenous glutamine. In gastrointestinal tissues, the provision of glutamine-free total parenteral nutrition solutions is associated with atrophy of mucosal cells and pancreatic exocrine cells. Glutamine-supplemented parenteral formulas result in diminished atrophy of intestinal mucosal and pancreatic exocrine cells; both intravenous and enteral glutamine promote gastrointestinal tissue regeneration following toxic injury. In animals undergoing partial small intestine resection, glutamine feeding leads to increased adaptive hyperplasia in remaining intestinal segments and results in earlier postoperative weight gain. All of these trophic, anabolic effects of glutamine require the administration of quantities that exceed the glutamine content of normal dietary protein. These findings in experimental animals support the hypothesis that glutamine is a conditionally essential nutrient and suggest a potentially important role for glutamine-supplemented nutrition in catabolic disease states.

Glutamine prevents pancreatic atrophy and fatty liver during elemental feeding

Rats fed an elemental, enteral diet (STD) developed pancreatic atrophy and hepatic steatosis following 60% jejunoileal intestinal resection. An isonitrogenous, isocaloric 2 g/100 ml glutamine-supplemented diet (GLN) significantly attenuated the development of pancreatic atrophy and hepatic steatosis associated with elemental feeding. Pancreatic weight, DNA, and protein were 27, 22, and 40% increased, respectively, in GLN animals. The pancreata of all animals appeared normal by light and electron microscopic examination. GLN animals had 12% less total liver wet weight, 3% less hepatic water content, and 47% less hepatic fat relative to STD rats. Histologic examination of the liver revealed extensive centrilobular fatty vacuolization in STD animals whereas GLN rats had normal looking hepatic parenchyma. Glutamine should be viewed as an important nutrient in elemental diets with trophic effects on the pancreas and protective effects against the development of hepatic steatosis.