The role of glutamine
Glutamine is one of the most abundant amino acid in the human organism and it is mostly present in the muscle tissue (about 60%). It is particularly involved in a variety of processes for maintaining body homeostasis: redox processes, acid-base balance and glucose metabolism. Glutamine can become essential and have a positive effect in critically ill patients (e.g. in hospital stay). The effect of Glutamine seems to depend on the route of administration for which the parental one is proven to be the most effective so far. An excessive inflammatory response, oxidative stress, comorbidity such as malnutrition and a catabolic state, could lead to a severe depletion of glutamine. Respiratory diseases are mostly associated with a glutamine increase. Unlike skeletal muscle, which contains significant quantities of free glutamine, the lung synthesizes it ex novo from glutamate and ammonia by means of the enzyme glutamine-synthetase. The release of glutamine in stressed lungs is a consequence of the release of glucocorticoids and other mechanical mechanisms and becomes significant due to the massive pulmonary perfusion. Glutamine is synthesized from cytosolic glutamine synthetase (GS) in many tissues, but degraded by mitochondrial glutaminase (GA) and used in large quantities by other tissues that do not synthesize it. The beneficial effects of glutamine on critical diseases is thought to depend on a better expression of thermal shock proteins (HSP). In critically ill patients, the increase in mortality was associated with a decrease in plasma Gln concentration. It is proven that during catabolic stress, the consumption rate of Gln exceeds the supply and both the plasma pools and the skeletal muscle pools present severely reduced free Gln levels. Experimental studies have reported that Gln can protect cells, tissues and whole organisms from stress and injury through the following mechanisms: attenuation of activation of NF (nuclear factor) -κB, a balance between pro and anti-inflammatory cytokines, reduction of neutrophils accumulation, improvement of intestinal integrity and immune cell function and enhancement of heat shock protein sex pression. In conclusion, high doses of parenteral Gln (> 0.50 g / kg / day) show a greater benefit potential in critically ill patients, although the pathophysiological mechanisms of Gln require clarification (16-17).