Chronic nonhealing wounds are a major health problem for patients in the United States and worldwide. Diabetes and ischemia are two major risk factors behind impaired healing of chronic lower extremity wounds. Poly-ADP-ribose polymerase (PARP) is found to be overactivated with both ischemic and diabetic conditions. This study seeks a better understanding of the role of PARP in ischemic and diabetic wound healing, with a specific focus on angiogenesis and vasculogenesis.Methods:
Ischemic and diabetic wounds were created in FVB/NJ mice and an in vitro scratch wound model. PARP inhibitor PJ34 was delivered to the animals at 10 mg/kg/d through implanted osmotic pumps or added to the culture medium, respectively. Animal wound healing was assessed by daily digital photographs. Animal wound tissues, peripheral blood, and bone marrow cells were collected at different time points for further analysis with Western blot and flow cytometry. Scratch wound migration and invasion angiogenesis assays were performed using human umbilical vein endothelial cells (HUVECs). Measurements were reported as mean ± standard deviation. Continuous measurements were compared by t-test. P < .05 was considered statistically significant.Results:
A significant increase in PARP activity was observed under ischemic and diabetic conditions that correlated with delayed wound healing and slower HUVEC migration. The beneficial effect of PARP inhibition with PJ34 on ischemic and diabetic wound healing was observed in both animal and in vitro models. In the animal model, the percentage of wound healing was significantly enhanced from 43% ± 6% to 71% ± 9% (P < .05) by day 7 with the addition of PJ34. PARP inhibition promoted angiogenesis at the ischemic and diabetic wound beds as evidenced by significantly higher levels of endothelial cell markers (vascular endothelial growth factor receptor 2 [VEGFR2] and endothelial nitric oxide synthase) in mice treated with PJ34 compared with controls. Flow cytometry analysis of peripheral blood mononuclear cells showed that PARP inhibition increased mobilization of endothelial progenitor cells (VEGFR2+/CD133+ and VEGFR2+/CD34+) into the systemic circulation. Furthermore, under in vitro hyperglycemia and hypoxia conditions, PARP inhibition enhanced HUVEC migration and invasion in Boyden chamber assays by 80% and 180% (P < .05), respectively.Conclusions:
Delayed healing in ischemic and diabetic wounds is caused by PARP hyperactivity, and PARP inhibition significantly enhanced ischemic and diabetic wound healing by promoting angiogenesis.Clinical Relevance:
Chronic nonhealing wounds, a major health problem in the United States, affect 6.5 million people and cost $25 billion annually. The two major risk factors of poor wound healing are arterial occlusive disease and diabetes. Because 40% of diabetics also have arterial occlusive disease, the people with combined ischemic and diabetic wounds have the highest risk for limb loss. Biologic treatment to enhance angiogenesis through gene and cellular therapy has been studied extensively to promote limb salvage. A better understanding of the mechanisms behind poor healing in diabetic and ischemic wounds is needed for the identification of new treatment targets.