Temple University School of Podiatric Medicine Journal Review Club
Editor's note: This post is part of the Temple University School of Podiatric Medicine (TUSPM) journal review club blog series. In each blog post, a TUSPM student will review a journal article relevant to wound management and related topics and provide their evaluation of the clinical research therein.

Article Title: A Modified Collagen Gel Dressing Promotes Angiogenesis in a Pre-Clinical Swine Model of Chronic Ischemic Wounds
Authors: Haytham Elgharably, MD, Kasturi Ganesh, MD, Jennifer Dickerson, RVT, Savita Khanna, PhD, Motaz Abas, BS, Piya Das Ghatak, MS, Sriteja Dixit, MS, Valerie Bergdall, DVM, Sashwati Roy, PhD, and Chandan K. Sen, PhD (Departments of Surgery, Davis Heart & Lung Research Institute, Center for Regenerative Medicine and Cell based Therapies and Comprehensive Wound Center, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210).
Journal: Wound Repair Regen.
Reviewed by: Zoha Khan, Class of 2020, Temple University School of Podiatric Medicine

Introduction

Chronic wounds are seen mainly in those individuals who are already patients (not healthy individuals). Ischemia involves lowered blood supply to the wound that decreases the amount of oxygen available to help the healing process. Peripheral vascular disease commonly causes ischemia, as does diabetes mellitus, renal failure, hypertension, and inflammatory diseases. Collagen dressings give structural support and promote granulation tissue formation. Proteolytic enzymes degrade extracellular matrix proteins (a major constituent of dermal extracellular matrix), thus slowing or stopping wound healing. Modified collagen gel (MCG) is used in the study to test its effects on wound angiogenesis in the porcine model of chronic ischemic wounds.

Methods

In this porcine ischemic flap model, six pigs were used in the study. Four skin flaps were created on each animal, and silicone sheets were placed under the flaps. Both the flap and silicone sheet edges were sutured to the adjacent skin. Doppler imaging of the flaps verified blood flow and ischemia status. In the center of each flap, a full-thickness excisional wound was created. The wounds on one side were treated with an MCG, followed by dressing with Tegaderm. The wounds in the contralateral flaps were covered with just Tegaderm as a control. The dressing was changed every five to seven days, and on days seven and 21 post-wounding, the entire wound tissue was harvested for analyses. The Moor LDI-Mark 2 laser Doppler blood flow scanner was used to study tissue perfusion. This scanner was used after the surgical procedure and at day 21 post-wounding.

Results

Macrophage infiltration to the wound-edge tissue was significantly higher in MCG-treated ischemic wounds at day seven post-wounding compared with untreated control wounds. This led the researchers to investigate the effect of MCG on macrophage function in vitro. THP-1 –derived macrophages that were treated with MCG were up-regulated with Mrc-1 gene expression (a marker for M2 reparative macrophage). In addition, MCG induced interleukin-10 and basic fibroblast growth factor. To validate the M2 macrophage marker found, the phenotype of the wound macrophage in MCG-treated wounds was studied. Expression of CCR2 (M2 macrophage marker) was found in the macrophages from MCG-treated wounds. In the MCG-treated wounds at day seven post-wounding, there was also an increase in expression of vascular endothelial growth factor (promotes angiogenesis), von Willebrand factor (endothelial cell marker), and transforming growth factor-β (growth factor for fibroblast recruitment and collagen expression in healing wounds). On day 21 post-wounding, the MCG-treated wound displayed more mature and thick vascular formations, as well as increased blood flow to the wound tissue compared with the control. Vimentin (marker for dermal fibroblasts) expression was also significantly higher on day 21 post-wounding in the MCG-treated wounds. Histological staining showed a significant increase of the ratio of collagen type I (thick fibers) to type III (thin fibers) deposition in the MCG-treated wounds.

Conclusion

The report shows the efficacy of MCG in chronic ischemic wounds by stimulating inflammation (which resolved in due time) and promoting wound angiogenesis. Failure to resolve the inflammation in due time leads to tissue necrosis with risk of complications. MCG-enhanced macrophage recruitment to the ischemic wound in the early phase is indicative of a strong inflammatory response. Increased expression of M2 macrophages (CCR2 and Mrc-1 ) strongly suggests a potential role of MCG in macrophage polarization in wounds. Interleukin-10 is an anti-inflammatory agent that promotes scar-minimized regenerative healing of fetal wounds. Basic fibroblast growth factor promotes wound angiogenesis, fibroblast proliferation, and migration. Ischemic wounds show delayed macrophage recruitment to the wound site. The study shows that even under ischemia, MCG promotes macrophage recruitment to wounds. The MCG-treated wounds also showed increased expression of factors such as vascular endothelial growth factor, Willebrand factor, and transforming growth factor-β, as well as an increase in blood flow and fibroblasts, all important factors in wound healing. The increase in the ratio of collagen type I to type III by MCG proved the advanced ability of MCG to heal wounds because the increase in this ratio thickens the associated dermal fibers. Previous porcine ischemic wound models have shown that wounds have a prolonged inflammatory phase and poor angiogenesis. The study overall shows that an MCG collagen–based dressing, even under conditions of ischemia, can promote an inflammatory response and vascularization. The studies warrant further clinical testing of MCG in ischemic chronic wounds.

About the Author
Zoha Khan is a third-year podiatric medical student at Temple University School of Podiatric Medicine (TUSPM) in Philadelphia, Pennsylvania. She graduated from the University of Maryland, College Park in 2016 with a Bachelor of Science in Neurobiology and Physiology. Over the course of six years, Zoha worked at numerous labs at the National Institutes of Health as a research intern. These labs included the National Institute of Allergies and Infectious Diseases (NIAID), the National Mental Health Institute (NIMH) and the National Heart, Lung, and Blood Institute (NHLBI). During her time at the National Institutes of Health is where her interest in becoming a physician and eventually a podiatrist began. In college, Zoha was very active in Student Council, where she served as the Events and Scholarship committee leader for two years. She also held leadership positions in the Biology Council of Majors, Student Events Board, and Science Café.

Dr. James McGuire is the director of the Leonard S. Abrams Center for Advanced Wound Healing and an associate professor of the Department of Podiatric Medicine and Orthopedics at the Temple University School of Podiatric Medicine in Philadelphia.