A Novel Model of Chronic Wounds: Importance of Redox Imbalance and Biofilm-Forming Bacteria for Establishment of Chronicity

Abstract

Chronic wounds have a large impact on health, affecting ∼6.5 M people and costing ∼$25B/year in the US alone [1]. We previously discovered that a genetically modified mouse model displays impaired healing similar to problematic wounds in humans and that sometimes the wounds become chronic. Here we show how and why these impaired wounds become chronic, describe a way whereby we can drive impaired wounds to chronicity at will and propose that the same processes are involved in chronic wound development in humans. We hypothesize that exacerbated levels of oxidative stress are critical for initiation of chronicity. We show that, very early after injury, wounds with impaired healing contain elevated levels of reactive oxygen and nitrogen species and, much like in humans, these levels increase with age. Moreover, the activity of anti-oxidant enzymes is not elevated, leading to buildup of oxidative stress in the wound environment. To induce chronicity, we exacerbated the redox imbalance by further inhibiting the antioxidant enzymes and by infecting the wounds with biofilm-forming bacteria isolated from the chronic wounds that developed naturally in these mice. These wounds do not re-epithelialize, the granulation tissue lacks vascularization and interstitial collagen fibers, they contain an antibiotic-resistant mixed bioflora with biofilm-forming capacity, and they stay open for several weeks. These findings are highly significant because they show for the first time that chronic wounds can be generated in an animal model effectively and consistently. The availability of such a model will significantly propel the field forward because it can be used to develop strategies to regain redox balance that may result in inhibition of biofilm formation and result in restoration of healthy wound tissue. Furthermore, the model can lead to the understanding of other fundamental mechanisms of chronic wound development that can potentially lead to novel therapies.

Platelet Hyperactivity inTNFSF14/LIGHTKnockout Mouse Model of Impaired Healing

“…14 We have previously shown that TNFSF14/ LIGHT -/-mice display marked abnormalities in wound healing processes, including increased inflammation, oxidative and nitrosative stress, excessive coagulation and fibrin cuffs, vascular defects, and abnormal ECM deposition. 5,16 Furthermore, we also showed that the basement membrane of the blood vessels was not continuous, the microvessels had very few associated a-smooth muscle actin-expressing periendothelial cells, and contained significant intravascular coagulation, 16 resulting in immature/ defective vessels. Moreover, we have recently shown that in these mice with impaired healing, platelets have enhanced aggregation as well as shorter bleeding time.…”

“…[2][3][4] Prediction of healing outcomes remains elusive due to the lack of understanding of the mechanisms involved in the etiology of impaired and chronic wounds, and often the coexisting morbidities. Furthermore, although a murine model for chronic wounds has been developed recently, 5,6 mechanistic studies are still lacking, thereby hindering the advancement in the development of diagnostics and therapeutics to treat these wounds. [7][8][9] Tissue injury causes the disruption of blood vessels and extravasation of blood constituents.…”

Photosynthetic biomaterials: A pathway towards autotrophic tissue engineering

“…The importance of oxygen as a key mediator promoting wound healing has been addressed in several review articles [7][8][9][10]. Moreover, as a product of anaerobic metabolism, the accumulation of lactic acid causes additional toxicity in hypoxic tissues [11][12].…”

Myeloid Cells in Cutaneous Wound Repair

“…Ultimately this repetitive cycle overloads endogenous antioxidant machinery, resulting in elevated oxidative stress and a profoundly proinflammatory and tissue-destructive state, with damage inflicted to host cell proteins, lipids, and DNA (25,(143)(144)(145)(146)(147)(148)(149). Indeed, the first truly chronic wound model in the mouse hinges on locally elevating oxidative stress at the wound site, demonstrating the devastating potential of dysregulation of oxidative balance (150,151).…”