L-Glutamine Aids Gastrointestinal Function
L-glutamine is the most prevalent amino acid in the bloodstream and because human cells readily synthesize it, it is usually considered a non-essential amino acid.
It is found in high concentration in skeletal muscle, lung, liver, brain, and stomach tissue. Skeletal muscle contains the greatest intracellular concentration of glutamine, comprising up to 60 percent of total body glutamine stores, and is considered the primary storage depot and exporter of glutamine to other tissues. Under certain pathological circumstances the body's tissues need more glutamine than the amount supplied by diet and biosynthesis. During catabolic stress intracellular glutamine levels can drop more than 50 percent, and it is under these circumstances that supplemental glutamine becomes necessary. In times of metabolic stress, glutamine is released into circulation, where it is transported to the tissue in need. Intracellular skeletal muscle glutamine concentration is affected by various insults, including injury, sepsis, prolonged stress, starvation, and the use of glucocorticoids. Therefore, glutamine has been re-classified as a conditionally essential amino acid.
Research demonstrates glutamine supplementation may be beneficial when added to total parenteral nutrition (TPN) for surgery, trauma, and cancer patients. In addition, evidence suggests it may provide benefit for certain gastrointestinal conditions, wound healing, critically ill neonates, HIV/AIDS patients, immune enhancement in endurance athletes, and prevention of complications associated with chemotherapy, radiation, and bone marrow transplant.
Biochemistry
L-glutamine accounts for 30-35 percent of the amino acid nitrogen in the plasma. It contains two ammonia groups, one from its precursor, glutamate, and the other from free ammonia in the bloodstream. One of glutamine's roles is to protect the body from high levels of ammonia by acting as a "nitrogen shuttle." Thus, glutamine can act as a buffer, accepting, then releasing excess ammonia when needed to form other amino acids, amino sugars, nucleotides, and urea. This capacity to accept and donate nitrogen makes glutamine the major vehicle for nitrogen transfer among tissues. Glutamine is one of the three amino acids involved in glutathione synthesis. Glutathione, an important intracellular antioxidant and hepatic detoxifier, is comprised of glutamic acid, cysteine, and glycine.
Clinical Indications
Gastrointestinal Disease
The gastrointestinal tract is by far the greatest user of glutamine in the body, as enterocytes in the intestinal epithelium use glutamine as their principal metabolic fuel. Most of the research on glutamine and its connection to intestinal permeability has been conducted in conjunction with the use of TPN. Commercially available TPN solutions do not contain glutamine, which can result in atrophy of the mucosa and villi of the small intestine. Addition of glutamine to the TPN solution reverses mucosal atrophy associated with various gastrointestinal conditions. Research has demonstrated glutamine-enriched TPN decreases villous atrophy, increases jejunal weight, and decreases intestinal permeability. Trauma, infection, starvation, chemotherapy, and other stressors are all associated with a derangement of normal intestinal permeability. One potential consequence of increased intestinal permeability is microbial translocation. Bacteria, fungi, and their toxins may translocate across the mucosal barrier into the bloodstream and cause sepsis. In numerous animal studies of experimentally induced intestinal hyperpermeability, the addition of glutamine or glutamine dipeptides (stable dipeptides of glutamine with alanine or glycine) to TPN improved gut barrier function, as well as immune activity in the gut. Conditions characterized by increased intestinal permeability that might benefit from glutamine supplementation include food allergies and associated conditions, Crohn's disease, ulcerative colitis, and irritable bowel syndrome. A clinical study of ulcerative colitis patients demonstrated that feeding 30 g daily of glutamine-rich germinated barley foodstuff (GBF) for four weeks resulted in significant clinical and endoscopic improvement, independent of disease state. Disease exacerbation returned when GBF treatment was discontinued. It has also been suggested that cabbage juice consumption may provide benefit to patients with gastric ulcers and gastritis, by virtue of its high glutamine content.
Wound Healing
The gastrointestinal tract has a large number of immune cells along its length -- fibroblasts, lymphocytes, and macrophages. The ability of glutamine to nourish these immune cells may account for its positive impact on the gastrointestinal tract and immunity. Healing of surgical wounds, trauma injuries, and bums is accomplished in part by the actions of these immune cells. Their proper functioning is dependent on glutamine as a metabolic fuel for growth and proliferation. Therefore, a depletion of intracellular glutamine can slow growth of these cells, and ultimately prolong healing. A small clinical study conducted recently in Poland demonstrated glutamine-supplemented TPN rapidly improved a number of immune parameters in malnourished surgical patients with sepsis. Additional clinical trials also suggest that glutamine supplementation, as well as arginine and omega-3 fatty acids, may promote restoration of normal tissue function and intestinal permeability in post-operative patients.
