Generating and Reversing Chronic Wounds in Diabetic Mice by Manipulating Wound Redox Parameters

Abstract

By 2025, more than 500 M people worldwide will suffer from diabetes; 125 M will develop foot ulcer(s) and 20 M will undergo an amputation, creating a major health problem. Understanding how these wounds become chronic will provide insights to reverse chronicity. We hypothesized that oxidative stress (OS) in wounds is a critical component for generation of chronicity. We used the db/db mouse model of impaired healing and inhibited, at time of injury, two major antioxidant enzymes, catalase and glutathione peroxidase, creating high OS in the wounds. This was necessary and sufficient to trigger wounds to become chronic. The wounds initially contained a polymicrobial community that with time selected for specific biofilm-forming bacteria. To reverse chronicity we treated the wounds with the antioxidants α-tocopherol and N-acetylcysteine and found that OS was highly reduced, biofilms had increased sensitivity to antibiotics, and granulation tissue was formed with proper collagen deposition and remodeling. We show for the first time generation of chronic wounds in which biofilm develops spontaneously, illustrating importance of early and continued redox imbalance coupled with the presence of biofilm in development of wound chronicity. This model will help decipher additional mechanisms and potentially better diagnosis of chronicity and treatment of human chronic wounds.

Platelet Hyperactivity inTNFSF14/LIGHTKnockout Mouse Model of Impaired Healing

“…35 Furthermore, collagen-induced platelet activation in wounds can produce high amounts of H 2 O 2 that could stimulate platelet aggregation pathways. 36 We recently showed that TNFSF14/LIGHT -/-mice have high levels of oxidative stress early in wound healing with increased presence of H 2 O 2 and isoprostanes, 18 suggesting the enhancement of the platelet activation we now report here. Moreover, reactive oxygen species frequently observed in impaired and chronic wounds have increasingly been shown to be major players in the activation of platelets and to cause thrombus formation.…”

“…The procedure used was performed as previously described. 18 Briefly, mice were anesthetized with a single intraperitoneal injection of ketamine (80 mg/kg body weight)/xylazine (16 mg/kg body weight). Fullthickness 7 mm punch wounds (excision of the skin and the underlying panniculus carnosus) were made on the back of the mice 24 h after nairing and shaving the hair.…”

Challenges in the Treatment of Chronic Wounds

“…17 It has been suggested in an animal model that application of strong antioxidants reduces ROS to normal levels, which results in the reverse of the chronicity of wounds and improves healing. 18 Furthermore, chronic wounds are characterized by senescent cell populations with impaired proliferative and secretory capacities, rendering them unresponsive to typical wound healing signals. 15 It has been reported that fibroblasts from venous and PUs are senescent and have a diminished ability to proliferate.…”

Biofilm Models of Polymicrobial Infection

“…In one chronic mouse model, db/db mice (diabetic mice that have a spontaneous mutation in the leptin receptor, resulting in insulin tolerance) were given a full thickness excision wound, and over time were infected with bacterial species considered to be part of the mouse native skin flora: S. aureus, coagulase-negative Staphylococcus sp., Enterococcus sp., Enterobacter cloacae and Pseudomonas sp. [115]. The microbes developed biofilms on the wound and notably impaired wound healing compared with the noninfected mice, thus creating a chronic infection [116].…”