Modifications of protein and amino acid metabolism during inflammation and immune system activation

Abstract

Metabolic changes associated with inflammatory processes and infectious diseases can modify protein and amino acid requirements. In such circumstances, depressed food intake and growth and muscle wasting are frequently observed. This is thought to be the consequence of an increase in the production of cytokines such as interleukin 1 (IL-1), interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) acting to alter protein metabolism. During immunological stress, amino acids are redistributed away from protein production (growth, lactation, etc.) towards tissues involved in inflammation and immune response. They are used for the synthesis of inflammatory and immune proteins, to support immune cell proliferation, and for the synthesis of other compounds important for body defense functions. As a consequence, stimulation of the immune system disturbs normal body processes and in turn is able to induce specific amino acid requirements. Some experimental data obtained in humans, laboratory or farm animals have clearly shown that the metabolism of some amino acids is modified by immune response. In this context, we question whether an adequate supply of exogenous amino acids provided by the diet, drinking water or an intravenous infusion could prevent or at least limit the consequences of inflammation and immune system activation on muscle protein metabolism and production of farm animals. The second question concerns the effects of an exogenous amino acid supply on the immune system. While the benefit of specific amino acid supplementation for immune response has been established for certain amino acids like glutamine, cysteine and arginine, it needs to be considered for other amino acids like tryptophan.