L-Glutamine is the most abundant amino acid in the bloodstream and in the body. It is involved in more metabolic processes than any other amino acid, fulfilling a number of biochemical needs. It operates as a nitrogen shuttle, taking up excess ammonia and forming urea. Ammonia, a by-product of certain normal biochemical reactions in the body (including the brain) is toxic to the human body and thus glutamine serves an important function in helping to convert ammonia into urea, a non toxic end product, which the body can easily eliminate. L-Glutamine can contribute to the production of other amino acids, glucose, nucleotides, protein and glutathione. It is the principal metabolic fuel for the epithelial cells that line the small intestine (enterocytes), and for certain immune cells, namely lymphocytes, macrophages, and fibroblasts.1
Glutamine intake has been shown to enhance glutathione stores in conjunction with N-acetylcysteine, which may forestall the progression of HIV infection to AIDS in afflicted patients.2 Glutamine supplementation has been shown to help protect the gastrointestinal tract from damage by certain chemotherapy drugs (i.e. fluorouracil) and also prevents diarrhea that these drugs are known to produce.1,3
Glutamine supplementation has been shown to enhance immune system function and result in a lower level of infection and a shorter stay in hospital following surgery, radiation treatment, bone marrow transplantation, and in patients suffering from injury, compared with patients receiving Glutamine-free parenteral nutrition.4,5,6
Glutamine is a non-essential amino acid in that the body can synthesize it from the amino acid glutamic acid via the Glutamine synthase enzyme.7
However, during periods of fasting, starvation, critical illness, cancer, AIDS and following trauma, radiation treatment, surgery, bone marrow transplantation or in patients with a weakened immune system or catabolic stress, extra Glutamine replenishment has been shown to be beneficial to re-establish homeostatis.7
Glutamine is also a main anti-catabolic agent in muscle, which when supplemented, may help preserve muscle tissue (preventing its breakdown), during and after exercise. The heavier one trains, the greater the stress on the muscle and the greater is the use of Glutamine.8
Glutamine May Help Athletes Reduce Exercise-Induced Muscle Catabolism
During and following exercise or trauma, large amounts of alanine and Glutamine are released from muscle. They then travel through the blood stream to the liver where they can be used to form glucose and glycogen. The total loss of alanine and Glutamine induced by exercise is above the amount available in muscle and represents more than 50 percent of the total loss of muscle amino acids and nitrogen loss from muscle tissue during exercise. Studies show that during exercise other muscle amino acids (branched-chain amino acids) are used to donate their carbon skeletons to make alanine and certain alpha ketoacids and amino acids, such as alpha ketogluturate and glutamic acid are converted within the muscle to glutamine. Most notably, the branched-chain amino acid, leucine, isoleucine and valine serve as a substrate for alanine synthesis, but higher levels of intramuscular glutamine (via supplementation) may help to stop the catabolism of branched chain-amino acids, as glutamine can diffuse from the muscle and become a source of glucose in the liver to help maintain blood glucose and liver glycogen levels during periods of stress (i.e. exercise)8,9,10 This is also the role played by alanine, and thus, higher glutamine concentrations may reduce the requirement for alanine synthesis in the muscle, and thereby spare the breakdown of muscle tissue (branched-chain amino acid catabolism) during exercise and under other periods of catabolic stress (burn victims, infection, post surgery etc). 8,9,10
Supplementation Studies and Clinical Applications
Glutamine supplementation plus N-acetylcysteine supplementation enhances glutathione levels in HIV patients. Higher glutathione status correlates with a slowing of the progression of HIV to AIDS. Glutathione depletion is common in these patients due to increased free radical production. Glutathione is a first line antioxidant in the quenching of free radicals and participates in Phase I and Phase II liver detoxification functions.2
These patients have been shown to benefit from additional Glutamine, although it may be required as part of parenteral nutrition requiring medical prescription and supervision.4
Oral Glutamine has been shown to maintain muscle mass in catabolic patients.11 However, Glutamine supplementation may increase ammonia levels and add to the ammonia burden of certain patients and athletes, jeopardizing recovery and performance respectively.8 To overcome this burden the use of alpha-ketogluturate has been shown to act as a Glutamine precursor, without contributing to ammonia build up. However, L-glutamine at a dose of up to 2,000-5,000 mg per day appears to be safe.
Oral ornithine alpha-ketogluturate reduces muscle catabolism in burn and surgery patients and is known to increase muscle Glutamine levels. Ornithine alpha-ketogluturate also stimulates the release of growth hormone and may thereby further provide an anti-catabolic and indirect anabolic effect on muscle tissue and lean mass, in general. A daily dosage of 2-4 mg per day of ornithine alpha-ketogluturate is required to increase growth hormone levels. 12,13,14
Glutamine supplementation in endurance athletes has been shown to reduce the incidence of infections in this population, who are known to have their immune system suppressed by excess training of this nature. A double-blind, placebo-controlled study showed that Glutamine supplementation at a dose of 5 gm, taken after the end of exercise, in 151 endurance athletes resulted in a significantly lower incidence of infections (19%) compared to the placebo group (51%), during the study period.24 It has been suggested that the immune system suppression associated with endurance exercise, may be in part, due to reduction in Glutamine that results from intensive training.25 Another study, using the same protocol, demonstrated that 81% of athletes taking Glutamine had no subsequent infection during the study period compared to 49% in the placebo group.24
Side Effects and Toxicity
Supplementation with L-Glutamine has been shown to reduce side effects associated with the use of methotrexate, paclitaxel and chemotherapy drugs. It may also improve the efficacy of some chemotherapy drugs.
Use of Glutamine in these applications should be implemented in collaboration with the attending medical physician.20,21
There are no well-known drug interactions with ornithine alpha-ketogluturate.22
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