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).