Mechanisms of Impaired Wound Healing Due to Ischemia

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PROJECT SUMMARY/ABSTRACT Treatment of chronic, non-healing wounds is a major public health issue that is growing as our population ages. It is estimated that 5 million Americans suffer from chronic wounds, costing the US health system $20 to 25 billion a year. Chronic wounds currently affect about 15% of older Americans. However, because the number of individuals 65 and older is the fastest growing population and co-morbid conditions that result in tissue ischemia, such as heart disease, peripheral arterial disease and diabetes, are more common in the elderly, this figure is expected to steadily increase. The central hypothesis of this project is that tissue ischemia disrupts the delicate balance between the production of reactive oxygen species and their removal by endogenous antioxidants, resulting in oxidative stress, altered composition of the extracellular matrix and impaired healing. We will also explore the hypothesis that despite physiologic changes associated with aging that affect wound healing, the primary reason for the increased prevalence of impaired wound healing in the elderly is tissue ischemia. Using a rat ischemic flap model we will: 1) Test the hypothesis that dysregulation of the endogenous antioxidant system results in a net excess of reactive oxygen species in the ischemic wound, 2) Test the hypothesis that manipulating the redox balance in ischemic wounds can improve healing. 3) Test the hypothesis that the redox balance affects matrix metalloproteinase activity. Procedures to be Used: The rat model of tissue ischemia developed and validated by Dr. Gould (Wound Repair and Regeneration, 2005) will be used to measure oxidative stress, endogenous antioxidants, proteases, and protease inhibitors in ischemic and non-ischemic wounds of young, middle aged and old rats, comparing these factors to the extracellular matrix composition. Exogenous antioxidant mimetics will be tested for their ability to alter the redox balance and improve wound healing. The contribution of specific cell populations in redox homeostasis will be characterized using a novel live tissue assay. To further characterize the mechanisms that impair cellular function during oxidative stress and verify that these mechanisms are consistent between species, primary human fibroblasts from donors of different ages will be grown under conditions of hypoxia, normoxia and hyperoxia. Utilizing specific inhibitors of endogenous antioxidants, levels of inflammatory mediators, proteases, matrix production and destruction and the impact on cell migration will be determined. Significance: Our long term goal is to elucidate the cellular mechanisms that result in chronic wounds so that rational therapies can be developed to improve healing or prevent these wounds altogether. The molecular changes that occur in wound healing, particularly in the elderly who more commonly have tissue ischemia, are poorly understood.