Sulphur Amino Acids and the Metabolic Response to Cytokines

Abstract

The metabolic response to trauma and infection is characterised by major increases in urinary excretion of nitrogen and sulphur containing compounds. The increase arises as a consequence of qualitative and quantitative changes in protein and amino acid metabolism. The changes are mediated by the production of pro-inflammatory cytokines from macrophages, endothelial cells and fibroblasts. An increasing number of cytokines are being identified which activate and modulate the activity of the immune system. However only three, interleukins 1 and 6, and tumour necrosis factor, have been shown to have major metabolic effects. These cytokines play a pivotal role in the response to trauma and infection as they initiate processes which provide substrate for the activated immune system, and for the synthesis of substances that are important in the control of the inflammatory process (6). Such control is of major importance, as many of the materials and cellular events associated with the process have the potential to damage the host. Inappropriate or excessive production of cytokines and free radicals and other oxidant molecules have been closely associated with morbidity and mortality in a wide range of conditions in which the immune system has become activate. These include rheumatoid arthritis, inflammatory bowel disease, sepsis, adult respiratory disease, cerebral malaria and meningitis (6).