Importance of specific amino acids

The role of single amino acids in promoting wound healing has gained interest over the past several decades. Arginine and glutamine have been the focus of most current research. Details on these two amino acids are discussed elsewhere (Chapter 5 and Chapter 6). Several other amino acids may influence wound healing. Methionine functions in fibroblast proliferation and collagen synthesis. Cysteine participates in collagen synthesis as a cofactor.27 Historical trials showed a positive effect of sulfur amino acids, such as methionine and cysteine, on wound healing in protein-deficient rats.29,38 However, clinical data have not been obtained in human subjects so far to support these findings.

Nutritional support enriched with valine, leucine, and isoleucine, the branched-chain amino acids, has been used to treat liver disease, and also to protect liver function during sepsis, trauma, and burns. Branched-chain amino acids are the major nitrogen source for glutamine and alanine synthesis in muscle. Following injury, branched-chain amino acids support protein synthesis and decrease protein catabolism. Although branched-chain amino acids have been shown to retain nitrogen during sepsis, trauma, and burns,30-32 there appears to be no benefit for wound healing.33

Conventional guidelines for protein intake to promote wound healing aim at promoting positive nitrogen balance or, at the very least, maintaining nitrogen balance. Protein kinetic studies provide greater insight into protein dynamics with respect to protein synthesis and protein breakdown. More specifically, protein breakdown is less amenable to exogenous protein during inflammation. Therefore, some lean body mass loss can be expected despite adequate protein intake. However, dietary protein can improve protein economy by increasing the rate of protein synthesis. This, in turn, can enhance increased structural and functional protein synthesis.

Recommended protein intakes for healthy adults and children as well as those with specific clinical conditions are presented in Table 4.1. Major surgery can increase protein requirements by 10%, and pressure ulcers can increase protein requirements by 56 to 88%.34 Specifically, the National Pressure Ulcer Advisory Panel recommends 1.25 to 1.5 g/kg/d for patients with severe pressure ulcers.35

Severe injuries, such as multiple traumas or burns, are characterized by an increased amino acid efflux from the skeletal muscle36 to accommodate amino acid needs for tissue repair, acute-phase protein production, cellular immunity, and gluconeogenesis. Inadequate protein intake compromises wound healing, muscle

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