Experimental Models Exploring Metabolic Processes in Skin and Whole Body In Vivo 50

In Vivo Quantitative Estimate of Collagen Turnover as an Indicator of the Dynamic Metabolic Process of Wound Healing 50

Experimental Models for Assessing the Dynamics of Skin DNA

and Protein Metabolism 51

DNA Metabolism 52

Determination of Protein Synthesis and Degradation Rates in the

Epidermis and Dermis 53

Physiological Regulation of Wound Metabolism and Wound Healing

Process in Relation to Whole Body Metabolic State 54

Effect of Low-Protein Diet on the Wound 56

Effect of High-Protein Diet on the Wound 56

Importance of Specific Amino Acids 56

Recommendations for Protein Intake to Optimize Wound Repair 57

Future Directions in Clinical Nutritional Support in Relation to

Wound Healing 58

Toxicity of Protein Excess 59

References 61

Wound healing is a dynamic, interactive process involving soluble mediators, blood cells, extracellular matrix, and parenchymal cells. The healing process of the wound can be divided into three phases — inflammation, tissue formation, and tissue remodeling — that overlap in time. Many aspects of the detailed mechanisms of this pathophysiological processes, and hence, the approaches to modulate the healing process, are still under extensive investigation. However, this complicated healing process, including the various morphological changes, can also be viewed as a complicated metabolic process (i.e., the utilization of various substrates by the cells in the area of injury for the recovery of their normal lives and functions, including the protein synthesis and degradation in the repairing of the wound and the renewal of tissues). All these regional metabolic processes are also associated with the whole body metabolic status of the host under the conditions of health and severe trauma, such as thermal injury.

Because the process of healing in different tissues is more similar than different, in this chapter the focus will be on the metabolic changes of the skin with wound healing. The mechanisms described for skin would be similar in other tissues, such as muscle, because the major protein of the healing wound is collagen (see Chapter 1). By discussing skin, one may also explore the unique aspect of skin wound healing — epithelialization.

In every living subject, the cellular and protein components of skin undergo a constant degradation and regeneration process. This self-renewal process of the skin involves two components: cell proliferation, mostly among the fibroblasts and kera-tinocytes; and protein synthesis and degradation within the cells. From the metabolic point of view, the former component is related to the metabolic turnover of DNA and the latter is associated with the turnover of skin proteins. After injury, both metabolic processes are accelerated for repairing the wounded skin and restoring its normal function. In severely injured patients, the metabolic process of wound healing proceeds under a state of the severely altered whole body energy and protein metabolism — hypermetabolic response and severe protein catabolism. Therefore, understanding the relationship between the metabolism in the regional wound and the whole body is an important aspect in managing wound healing. Such a relationship will be discussed based on clinical observations and the recent laboratory in vivo experimental data on the simultaneous measurements on both whole body and skin protein metabolism under different physiological and pathophysiological conditions.

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