Molecular and mechanistic validation of delayed healing rat wounds as a model for human chronic wounds

Abstract

The purpose of this study was to provide molecular and mechanistic evaluation of an ischemic wound model in rats to determine if it is a valid model for human chronic wounds. Compared to acute wounds, human chronic wounds contain markedly elevated levels of proinflammatory cytokines and matrix metalloproteinases, while matrix metalloproteinase inhibitors and growth factor activity are diminished. Accordingly, tissue from ischemic and normal rat wounds were analyzed for cytokine, proteases and growth factor levels. Dorsal full thickness punch wounds were created in rats using a reproducible template. The ischemic wound group (n = 10) had six uniformly placed wounds within a bipedicled dorsal flap. The control group (n = 10) had the same wounds created without elevation of a flap. On postwound days 3, 6 and 13 wounds were excised and analyzed. Protein levels for tumor necrosis factor-alpha were determined with a rat-specific enzyme-linked immunosorbent assay, while mRNA was determined by RNase protection assay. Matrix metalloproteinases and serine protease detection was done using gelatin and casein zymography, respectively. Significant delay in healing was achieved in the ischemic group: 50% healing for control wounds was at 7 days and 11 days for ischemic wounds (p < 0.001). No significant differences between wound groups were found for interleukin-1beta, and mRNA for tumor necrosis factor-alpha and interleukin-1beta. However, at day 13 ischemic wounds contained significantly more tumor necrosis factor-alpha than controls and normal skin (586 +/- 106 pg/biopsy vs. 79 +/- 7 pg/biopsy vs. 52 +/- 2 pg/biopsy; p < 0. 001). Zymography showed substantially greater quantities of matrix metalloproteinase-2, matrix metalloproteinase-9, and serine proteases in ischemic wounds. This model of delayed healing in rats shares many of the key biochemical, molecular and mechanistic characteristics found in human chronic wounds, namely elevated tumor necrosis factor-alpha and protease levels. As such, this model will likely prove to be useful in chronic wound research, particularly in developing novel therapeutics.

Role of Nitric Oxide in Extracellular Matrix Metabolism and Inflammation in Diabetic Wound Healing

“…Prior studies by others have resulted in the development of a catalog of factors (altered MMP/TIMP ratio, decreased cell proliferation and migration, changes in growth factors [TGF-, VEGF, PDGF-BB] and cytokines [IL-1, IL-6, TNF-], extracellular matrix, oxygenation, and nitric oxide) which are important in normal wound healing and demonstrate the dysregulation that exists in chronic wounds (Chen et al, 1999;Cook et al, 2000;Lobmann et al, 2002;Efron and Moldawer, 2004;Vandeberg et al, 2005). What was intriguing to us was the observation that a number of MMPs were known to be elevated in chronic wounds and that nitric oxide levels were quite low, but no one had drawn the connection that nitric oxide may regulate MMPs and promote wound healing by altering the MMP/TIMP ratio.…”

Evaluation of a bilayered, micropatterned hydrogel dressing for full-thickness wound healing

“…33,34,41 The apical layers of the wound-dressing prototypes were produced following the same procedure outlined above to make gelatin hydrogels. Then the solution-filled molds were cooled to 4 C for 1 h to solidify the gelatin.…”

“…The skin flap created was elevated to sever the underlying vasculature, repositioned, and stapled on each lateral side. 33,34 One of each of the four dressings: (1) the novel bilayer Sharklet-micropatterned apical layer with the combined Capgel neovascularization technology, (2) a smooth apical layer with Capgel, (3) Endoform, a dermal template that is currently in clinical use as a commercial competitor, and (4) no treatment. The Endoform dermal template consists of a naturally derived ovine collagen ECM.…”

Molekulare Grundlagen der Wundheilung bei diabetischem Fu�syndrom

“…Gerade in chronischen Wundsekreten (Ulcus cruris, diabetisches Fußsyndrom) ist eine deutlich erhöhte Proteasenaktivität festzustellen, die zu rund 90% den MMPs zuzuordnen ist [26,27].…”