Regulation of protein metabolism by glutamine: implications for nutrition and health

Abstract

Glutamine is the most abundant free alpha-amino acid in plasma and skeletal muscle. This nutrient plays an important role in regulating gene expression, protein turnover, anti-oxidative function, nutrient metabolism, immunity, and acid-base balance. Interestingly, intracellular and extracellular concentrations of glutamine exhibit marked reductions in response to infection, sepsis, severe burn, cancer, and other pathological factors. This raised an important question of whether glutamine may be a key mediator of muscle loss and negative nitrogen balance in critically ill and injured patients. Therefore, since the initial reports in late 1980s that glutamine could stimulate protein synthesis and inhibit proteolysis in rat skeletal muscle, there has been growing interest in the use of this functional amino acid to improve protein balance under various physiological and disease conditions. Although inconsistent results have appeared in the literature regarding a therapeutic role of glutamine in clinical medicine, a majority of studies indicate that supplementing appropriate doses of glutamine to enteral diets or parenteral solutions is beneficial for improving nitrogen balance in animals or humans with glutamine deficiency.

Serum Concentration of Free Amino Acids in Dogs Suffering From Perianal Tumours

“…Additionally, it should be noted that the observed reduced serum concentration of glutamine in dogs with perianal tumours is associated with higher glutamic acid level, since glutamine may be easily converted into glutamic acid (32). The decreased serum glutamine concentration in tumour-affected dogs may also result from its reduced amount in the intracellular and extracellular compartments at hypercatabolic pathological state, such as neoplastic disease (34). Furthermore, the observed differences in serum concentration of taurine, threonine, glutamic acid, glycine, alanine, GABA, valine, methionine, isoleucine, leucine, tryptophan, and arginine between the groups with benign or malignant tumours may result from diverse course of metabolic processes in dogs suffering from different tumour types in term of malignancy.…”

Functional amino acids in nutrition and health

“…Based on the foregoing lines of compelling evidence from animal and human studies, Wu (2010) proposed the new concept of functional AA, which are defined as those AA that participate in and regulate key metabolic pathways to improve health, survival, growth, development, lactation, and reproduction of the organisms. Metabolic pathways include: (1) intracellular protein turnover (synthesis and degradation) and associated events (Bertrand et al 2012;Kong et al 2012;Wauson et al 2013;Xi et al 2011Xi et al , 2012Yao et al 2012), (2) AA synthesis and catabolism (Brosnan and Brosnan 2012;Lei et al 2012a, b), (3) generation of small peptides, nitrogenous metabolites, and sulfur-containing substances [e.g., H 2 S (Mimoun et al 2012)], (4) urea cycle and uric acid synthesis (Wu 2013), (5) lipid and glucose metabolism Go et al 2012;Satterfield et al 2011Satterfield et al , 2012, (6) one-carbon unit metabolism (Wang et al 2012), and (7) cellular redox signaling (Hou et al 2012a). Functional AA can be nutritionally ''essential'', ''nonessential'', or conditionally essential AA (Table 1).…”

Effects of soybean isoflavone on intestinal antioxidant capacity and cytokines in young piglets fed oxidized fish oil

“…Oxidative stress is lessened by the antioxidants (Otani et al, 2000;Kelley, 2001). Accumulating evidence suggests that supplementation of additives with antioxidant function (such as vitamin E, selenium, glutamine, and arginine) to the feed of piglets (Ban et al, 2004;Huang et al, 2011;Xi et al, 2011;Zhan et al, 2011) can reduce the oxidative stress and protect the intestinal function. Soybean isoflavones (ISFs) are stronger antioxidants, and have been studied extensively (Yousef et al, 2004;Foti et al, 2005;Lee et al, 2005;Jiang et al, 2007;Dixit et al, 2012).…”