Lorraine M. Leader

Glutamine and the gastrointestinal tract.

The amino acid glutamine has become one of the most intensively studied nutrients in the field of nutrition and metabolic support. A variety of studies in cell culture systems, animal models of gut mucosal atrophy, injury/repair and adaptation and a limited number of clinical trials demonstrate trophic and cytoprotective effects of glutamine in small bowel and colonic mucosal cells. Although the routine clinical use of glutamine-enriched parenteral and enteral nutrient solutions remains controversial, available data demonstrate both the safety and metabolic and clinical efficacy of glutamine treatment in selected patient groups. Basic investigations are elucidating underlying mechanisms of glutamine action in intestinal cells. These will inform preclinical and clinical investigations designed to determine glutamine efficacy in selected gastrointestinal disorders. Emerging clinical trials will further define the utility of adjunctive glutamine supplementation as a component of specialized nutrition support in gastrointestinal disease.

Metabolic effects of enteral versus parenteral alanyl-glutamine dipeptide administration in critically ill patients receiving enteral feeding: a pilot study.

BACKGROUND Glutamine (Gln) may become conditionally indispensable during critical illness. The short-term metabolic effects of enteral versus parenteral Gln supplementation are unknown in this clinical setting. OBJECTIVES We studied metabolic effects of intravenous (i.v.) alanyl-Gln dipeptide (AG) supplementation and enteral (e.n.) AG supplementation on plasma Gln concentration, antioxidant status, plasma lymphocyte subset number, gut permeability and nitrogen balance in adult critically ill patients requiring tube feeding compared to a control group not receiving Gln supplementation. METHODS In a double-blind, pilot clinical trial, 44 medical and surgical ICU patients received identical Gln-free tube feedings 24 h/day and were randomized to either isonitrogenous control (n=15), e.n. AG (n=15) or i.v. AG (n=14) groups (AG). Twelve patients were discontinued from the study. The goal AG dose was 0.5 g/kg/day. Biochemical and metabolic endpoints were measured at baseline and on day 9 (plasma Gln, antioxidant indices, lymphocyte subsets; serum IGF-1 and IGF-binding protein-3; intestinal permeability). Nitrogen balance was determined between study days 6 and 8. RESULTS Illness severity indices, clinical demographics, enteral energy and nitrogen intake and major biochemical indices were similar between groups during study. Plasma Gln was higher in the i.v. AG (565+/-119 microM, mean+/-SEM) vs the e.n. AG (411+/-27 microM) group by day 9 (p=0.039); however, subjects in the i.v. AG group received a higher dose of AG (i.v. AG 0.50 versus e.n. AG 0.32+/-0.02 g/kg/day; p<0.001). E.n. AG subjects showed a significant increase in plasma alpha-tocopherol levels over time and maintained plasma gamma-tocopherol concentrations. There were no differences between groups for plasma concentrations of vitamin C, glutathione, malondialdehyde (MDA), T-lymphocyte subsets, intestinal permeability or nitrogen balance. CONCLUSIONS This study showed that alanyl-Gln administration by enteral or parenteral routes did not appear to affect antioxidant capacity or oxidative stress markers, T-lymphocyte subset (CD-3, CD-4, CD-8) number, gut barrier function or whole-body protein metabolism compared to unsupplemented ICU patients requiring enteral tube feeding. Enteral Gln appeared to maintain plasma tocopherol levels in this pilot metabolic study.

Severe villus atrophy and chronic malabsorption induced by azathioprine

Azathioprine is commonly prescribed for autoimmune hepatitis and inflammatory bowel disease. An acute gastroenteritis-like syndrome has been ascribed to azathioprine use, but chronic diarrhea has not. We report a patient with autoimmune hepatitis who developed severe small-bowel villus atrophy and chronic diarrhea after azathioprine was initiated (50 mg/day). We present a case report of a patient followed up prospectively. Duodenal mucosal histology and expression of brush border enzyme dipeptidyl peptidase IV and peptide transporter PepT1 messenger RNA levels were determined before and after azathioprine discontinuation. Chronic diarrhea developed several weeks after the initiation of azathioprine and resulted in micronutrient depletion and severe protein-calorie malnutrition, which was unresponsive to oral pancreatic enzyme therapy or a gluten-free diet. Severe malabsorption required parenteral nutrition support for longer than 1.5 years; this was complicated by unstable blood glucose control, acute calculous cholecystitis, catheter sepsis, and severe venous thrombosis. When the temporal association between azathioprine and diarrhea was identified, the drug was tapered while the patient consumed an unrestricted diet. Within 2 weeks after azathioprine was discontinued, diarrhea had completely resolved, and parenteral nutrition was discontinued. Mucosal biopsies obtained before and 4 months after azathioprine discontinuation showed complete reversal of severe duodenal villus atrophy and marked up-regulation of mucosal dipeptidyl peptidase IV and PepT1 messenger RNA. The patient has subsequently maintained normal liver function tests on low-dose prednisone alone, with normal stools and stable nutritional status for longer than 4 years. Azathioprine can induce severe small-bowel villus atrophy, diarrhea, and malabsorption that is reversible with drug discontinuation.

Interactions Between Nutrients and Peptide Growth Factors in Intestinal Growth, Repair, and Function

Several lines of evidence demonstrate that general nutritional status, specific nutrients (eg, zinc, glutamine), and certain trophic growth factors (eg, growth hormone, insulin-like growth factor I, keratinocyte growth factor, and glucagon-like peptide-2) have important interactions relevant for intestinal growth and function. Adequate nutritional status is critical for endogenous growth factor synthesis in the gut and other tissues and is an important mediator of organ responsiveness to exogenous growth factor administration. Both endogenously synthesized and exogenously administered growth factors upregulate nutrient uptake and utilization by gut mucosa, skeletal muscle, and other organs. Emerging data from both animal and human studies indicate that combinations of selected growth factors and specific nutrients may improve the growth, adaptation, and repair of the intestinal mucosa. Additional studies to determine basic mechanisms of nutrient-growth factor interactions and the safety and efficacy of treatment with combinations of specific nutrients and recombinant growth factors are needed. Results of these investigations should define new methods for support of the intestinal tract during short bowel syndrome (SBS), catabolic illness, and malnutrition.

Glutamine : From basic science to clinical applications

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

Adjunctive therapies in nutritional support

The need for new therapeutic approaches to improve the metabolic and clinical efficacy of nutritional therapy has been increasingly emphasized. The field of nutrition support of catabolic, malnourished, or hospitalized patients is rapidly evolving in response to the beneficial effects observed with adjunctive therapies in animal models and in emerging clinical investigations. Enteral nutrition is being increasingly administered, and enteral diets are being tested to improve gut structure and function. Adjunctive therapies in enteral and parenteral nutrition are being actively investigated. These include administration of recombinant growth factors and anabolic steroid hormones (e.g., growth hormone, oxandrolone); conditionally essential amino acids (e.g., arginine, glutamine); novel lipid products (e.g., structured lipids, fish oils); nutrient antioxidants (e.g., vitamins C and E); and combinations of these approaches. It is likely that current methods of enteral and parenteral nutrition support will evolve in response to the results of these research studies.

Growth Hormone Favorably Affects Bone Turnover and Bone Mineral Density in Patients With Short Bowel Syndrome Undergoing Intestinal Rehabilitation

BACKGROUND Patients with short bowel syndrome (SBS) have a high prevalence of metabolic bone disease due to nutrient malabsorption and potential effects of parenteral nutrition (PN). Human growth hormone (hGH) has been shown in some studies to have anabolic effects on bone, but hGH effects on bone in patients with SBS are unknown. METHODS Adults with PN-dependent SBS underwent a 7-day period of baseline studies while receiving usual oral diet and PN and then began receiving modified diets designed to improve nutrient absorption and daily oral calcium/vitamin D supplements (1500 mg elemental calcium and 600 IU vitamin D, respectively). Subjects were randomized to receive in a double-blind manner either subcutaneous (sc) saline placebo as the control or hGH (0.1 mg/kg/d for 3 weeks, then 0.1 mg/kg 3 days a week for 8 subsequent weeks). Open-label hGH was given from week 13 to week 24 in subjects who required PN after completion of the 12-week double-blind phase. Markers of bone turnover (serum osteocalcin and urinary N-telopeptide [NTX]), vitamin D nutriture (serum calcium, 25-hydroxyvitamin D [25-OH D] and parathyroid hormone [PTH] concentrations), and intestinal calcium absorption were measured at baseline and at weeks 4 and 12. Dual x-ray absorptiometry (DXA) of the hip and spine was performed to determine bone mineral density (BMD) at baseline and weeks 12 and 24. RESULTS The majority of subjects in each group exhibited evidence of vitamin D deficiency at baseline (25-OH D levels<30 ng/mL; 78% and 79% of control and hGH-treated subjects, respectively). Subjects treated with hGH demonstrated a significant increase from baseline in serum osteocalcin levels at 12 weeks (+62%; p<.05). The levels of NTX were increased over time in the hGH-treated group; however, this did not reach statistical significance. Both NTX and osteocalcin remained unchanged in control subjects. BMD of the spine and total hip was unchanged in subjects treated with placebo or hGH at 24 weeks. However, femoral neck BMD was slightly but significantly decreased in the placebo group at this time point but remained unchanged from baseline in the hGH-treated subjects. CONCLUSIONS hGH therapy significantly increased markers of bone turnover during the initial 3 months of therapy and stabilized femoral neck bone mass over a 6-month period in patients with severe SBS undergoing intestinal rehabilitation.

Nutrient Intake From Habitual Oral Diet in Patients With Severe Short Bowel Syndrome Living in the Southeastern United States

OBJECTIVES Little data are published on the habitual home oral diet of patients with short bowel syndrome (SBS). METHODS We assessed nutrient intake from oral food and beverages in 19 stable patients with severe SBS who live in the southeastern United States. Intestinal absorption of energy, fat, nitrogen (N), and carbohydrate (CHO) was determined in a metabolic ward. RESULTS We studied 12 women and 7 men, age 48 +/- 3 y of age (mean +/- SE) receiving parenteral nutrition for 31 +/- 8 mo following massive small bowel resection (118 +/- 25 cm residual small bowel). The patients demonstrated severe malabsorption of energy (59 +/- 3% of oral intake), fat (41 +/- 5%), N (42 +/- 5%) and CHO (76 +/- 3%). Oral energy intake was 2656 +/- 242 kcal/d (39 +/- 3 kcal/kg/d) and oral protein intake was 1.4 +/- 0.1 g/kg/d. Food/beverage intake constituted 49 +/- 4% of total (enteral plus parenteral) daily fluid intake, 66 +/- 4% of total daily kcal and 58 +/- 5% of total daily N intake. Oral fat intake averaged 92 +/- 11 g/day ( approximately 35% of total oral energy). Oral fluid intake averaged 2712 +/- 240 ml/d, primarily from water, soft drinks, sweet tea and coffee. Simple sugars comprised 42 +/- 3% of oral CHO intake. Usual dietary intake of multiple micronutrients were below the Recommended Dietary Allowances (RDA) in a large percentage of patients: vitamin A (47%), vitamin D (79%), vitamin E (79%), vitamin K (63%), thiamine (42%), vitamin B6 (68%), vitamin B12 (11%), vitamin C (58%), folate (37%), iron (37%), calcium (63%), magnesium (79%) and zinc (68%). Only seven patients (37%) were taking oral multivitamin-mineral supplements and only six subjects (32%) were taking oral iron and calcium supplements, respectively. CONCLUSION In these SBS patients, an oral diet provided a significant proportion of daily nutrient intake. The types of foods and fluids consumed are likely to worsen malabsorption and thus increase PN requirements. Oral intake of essential micronutrients was very low in a significant proportion of these individuals.

Prospective analysis of serum carotenoids, vitamin A, and tocopherols in adults with short bowel syndrome undergoing intestinal rehabilitation.

OBJECTIVE Carotenoids, vitamin A, and tocopherols serve important roles in many key body functions. However, availability of these compounds may be decreased in patients with short bowel syndrome (SBS) due to decreased oral intake of fruits and vegetables and/or decreased intestinal absorption. Little information is available on serum concentrations of carotenoids, vitamin A, and tocopherols during chronic parenteral nutrition (PN) or during PN weaning. The aim of this study was to prospectively examine serum concentrations of a wide variety of carotenoids, vitamin A, and tocopherols in patients with SBS undergoing an intensive 12-wk intestinal rehabilitation program. METHODS Twenty-one PN-dependent adult patients with SBS were enrolled in a 12-wk intestinal rehabilitation program, which included individualized dietary modification, multivitamin supplementation, and randomization to receive subcutaneous placebo (n = 9) or human growth hormone (0.1 mg . kg(-1) . d(-1); n = 12). PN weaning was initiated after week 4 and advanced as tolerated. Serum concentrations of carotenoids, vitamin A, and tocopherols were determined at baseline and at weeks 4 and 12. RESULTS A significant percentage of subjects exhibited low serum concentrations for carotenoids and alpha-tocopherol at study entry, and a few subjects had low concentrations of retinol (5%). Carotenoid and vitamin A valves did not improve over time, while alpha-tocopherol levels rose. Serum alpha-tocopherol concentration was negatively associated with PN lipid dose (r = -0.34, P < 0.008). CONCLUSION Patients with SBS are depleted in diet-derived carotenoids despite oral and intravenous multivitamin supplementation and dietary adjustment during intestinal rehabilitation and PN weaning. Reduction of PN lipid infusion may improve serum alpha-tocopherol concentrations.