Glutamine (symbol Gln or Q) is an ?-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral, polar amino acid. It is non-essential and conditionally essential in humans, meaning the body can usually synthesize sufficient amounts of it, but in some instances of stress, the body's demand for glutamine increases, and glutamine must be obtained from the diet. It is encoded by the codons CAA and CAG.
Glutamine is produced industrially using mutants of Brevibacterium flavum, which gives ca. 40 g/L in 2 days using glucose as a carbon source.
Glutamine is synthesized by the enzymeglutamine synthetase from glutamate and ammonia. The most relevant glutamine-producing tissue is the muscle mass, accounting for about 90% of all glutamine synthesized. Glutamine is also released, in small amounts, by the lungs and brain. Although the liver is capable of relevant glutamine synthesis, its role in glutamine metabolism is more regulatory than producing, since the liver takes up large amounts of glutamine derived from the gut.
The most eager consumers of glutamine are the cells of intestines, the kidney cells for the acid-base balance, activated immune cells, and many cancer cells.
Glutamine is the most abundant naturally occurring, nonessential amino acid in the human body, and one of the few amino acids that can directly cross the blood-brain barrier. Humans obtain glutamine through catabolism of proteins in foods they eat. In states where tissue is being built or repaired, like growth of babies, or healing from wounds or severe illness, glutamine becomes conditionally essential.
Sickle cell disease
In 2017, the U.S. Food and Drug Administration (FDA) approved L-glutamine oral powder, marketed as Endari, to reduce severe complications of sickle cell disease in people aged 5 years and older with the disorder.
Glutamine is marketed as medical food and is prescribed when a medical professional believes a person in their care needs supplementary glutamine due to metabolic demands beyond what can be met by endogenous synthesis or diet.
Glutamine is safe in adults and in preterm infants. Although glutamine is metabolized to glutamate and ammonia, both of which have neurological effects, their concentrations are not increased much, and no adverse neurological effects were detected. The observed safe level for supplemental L-glutamine in normal healthy adults is 14 g/day.
Adverse effects of glutamine have been described for people receiving home parenteral nutrition and those with liver-function abnormalities.
Although glutamine has no effect on the proliferation of tumor cells, it is still possible that glutamine supplementation may be detrimental in some cancer types.
Ceasing glutamine supplementation in people adapted to very high consumption may initiate a withdrawal effect, raising the risk of health problems such as infections or impaired integrity of the intestine.
Glutamine can exist in either of two enantiomeric forms, L-glutamine and D-glutamine. The L-form is found in nature. Glutamine contains an ?-amino group which is in the protonated -NH3+ form under biological conditions and a carboxylic acid group which is in the deprotonated -COO- form, known as carboxylate, under physiological conditions.
Glutamine zwitterionic forms at neutral pH: L-glutamine (left) and D-glutamine
Consequences of glutamine depletion in critically ill individuals
Glutamine mouthwash may be useful to prevent oral mucositis in people undergoing chemotherapy but intravenous glutamine does not appear useful to prevent mucositis in the GI tract.
Glutamine supplementation was thought to have potential to reduce complications in people who are critically ill or who have had abdominal surgery but this was based on poor quality clinical trials. Supplementation does not appear to be useful in adults or children with Crohn's disease or inflammatory bowel disease, but clinical studies as of 2016 were underpowered. Supplementation does not appear to have an effect in infants with significant problems of the stomach or intestines.
Some athletes use L-glutamine as supplement. Studies support the positive effects of the chronic oral administration of the supplement on the injury and inflammation induced by intense aerobic and exhaustive exercise, but the effects on muscle recovery from weight training are unclear.
^Dietary Reference Intakes: The Essential Guide to Nutrient Requirements, published by the Institute of Medicine's Food and Nutrition Board, currently available online at "Archived copy". Archived from the original on 5 July 2014. Retrieved 2014.CS1 maint: archived copy as title (link)
^Newsholme, P.; Lima, M. M. R.; Procopio, J.; Pithon-Curi, T. C.; Doi, S. Q.; Bazotte, R. B.; Curi, R. (2003). "Glutamine and glutamate as vital metabolites". Brazilian Journal of Medical and Biological Research. 36 (2): 153-163. doi:10.1590/S0100-879X2003000200002. PMID12563517.
^Newsholme, P. (2001). "Why is L-glutamine metabolism important to cells of the immune system in health, postinjury, surgery or infection?". The Journal of Nutrition. 131 (9 Suppl): 2515S-2522S, discussion 2522S-4S. doi:10.1093/jn/131.9.2515S. PMID11533304.
^Buchman AL (2001). "Glutamine: commercially essential or conditionally essential? A critical appraisal of the human data". The American Journal of Clinical Nutrition. 74 (1): 25-32. doi:10.1093/ajcn/74.1.25. PMID11451714.
^Raizel, Raquel; Tirapegui, Julio (5 December 2018). "Role of glutamine, as free or dipeptide form, on muscle recovery from resistance training: a review study". Nutrire. 43 (1): 28. doi:10.1186/s41110-018-0087-9. ISSN2316-7874.