J. H. Chen1,2, M. M. Kebede2, S. E. Epstein3, T. E. Travis1,2, L. T. Moffatt2, J. W. Shupp1,2 1Washington Hospital Center,Department Of Surgery, The Burn Center,Washington, DC, USA 2MedStar Health Research Institute,Firefighters’ Burn And Surgical Research Laboratory,Washington, DC, USA 3MedStar Health Research Institute,Cardiovascular Research Institute,Washington, DC, USA
Introduction: Severe burn injuries often require grafting, resulting in a second wound, the donor site. Patients with large burns may have limited options for harvesting. Decreasing time to re-epithelialization would allow for more frequent re-harvesting and therefore earlier wound closure. The regenerative properties of stem cells are thought to be secondary to secreted products including various cytokines and growth factors. We have developed a gel-matrix conditioned-media (CM)-based product from stem cells. Previous studies using a mouse model of limb ischemia-reperfusion demonstrated potent angiogenic responses, including greater total vessels present in CM-treated vs. VEGF-treated animals. We hypothesized that similar effects may be seen in donor sites treated with CM. In this study, we use an established model of donor site healing to investigate these effects.
Methods: Stem cell-derived molecules, obtained by concentrating stem cell growth media supernatants, were embedded in a biodegradable polymer and formulated to be gradually released. Wounds measuring 3" x 3" were created on Duroc pigs with a dermatome (0.06” depth) in triplicate on the flank of five animals. These wounds were treated with conventional dressings to protect from infection. Digital photos, laser Doppler imaging (LDI), and biopsies were taken pre- and post- wounding and every 48 hours until re-epithelialized (16 days). Subsequently, a set of identical wounds were created on the contralateral flank of each animal, treated with CM dressing, and assessed using the same metrics. Formalin-fixed biopsies were paraffin-embedded and stained for VEGF. RNA was isolated and qRT-PCR was used to examine differential gene expression of VEGF and other markers of wound healing over time.
Results:Using paired comparisons of sham and treated wounds on each animal (n = 5 pigs and 15 lesion pairs) CM treatment significantly accelerated healing. In the treatment arm, time to complete healing of 50% of the wound surface area was decreased by 12% (from 8.3 to 7.1 days; p = 0.04) and final degree of healing was increased by 14% (from 77 to 88%; p = 0.002). Three days after treatment with CM, IHC revealed elevated VEGF levels that exceeded those of sham wounds. By day seven, treated wounds continued to have higher VEGF levels compared to sham. Wound perfusion as measured by LDI was significantly higher in treated wounds than in control wounds by day four (784 ± 62 vs 680 ± 46 PU; p = 0.04). Differential expression of growth factors was assessed using qRT-PCR.
Conclusion:We conclude that topical application of conditioned media, the secreted products of stem cells, is a novel and potentially potent means for accelerating wound healing of burn-related donor sites by promoting VEGF-induced angiogenesis. Further study is warranted to elucidate the key components of conditioned media responsible for this effect and to assess other metrics of neovascularization and angiogenesis.