Use of Mouse Footpad Model to Test Effectiveness of Wound Dressings

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Author(s): 
Laura K.S. Parnell, MS, CWS;1 Anthony D. Chinnah, PhD;2 Ian R. Tizard, BVMS, PhD3

Introduction

Acemannan is a complex carbohydrate isolated from the clear gel in the center of the aloe vera leaf, which consists of polymerized beta-(1,4)-linked acetylmannose. Molecular weight after purification varies from 10-1000kDa with an average of 200kDa. The precise size depends on the degree of degradation during the manufacturing process. Acemannan does not appear to be mitogenic for monocytes, macrophages, or fibroblasts and is noncytotoxic even at high concentrations.[1–3]

Many wound dressings, such as alginates and hydrocolloids, contain various forms of carbohydrates.[4] Differences in carbohydrate chemical structure can lend different properties and functions to wound dressings, such as improvement of absorption, increased binding, or improved retention of moisture. At a cellular level, some carbohydrates appear to stimulate cell functions of proliferation, migration, and cytokine production.[5–10]

Early reports in the literature indicate carbohydrates can enhance wound repair by promoting early mobilization of macrophages to a wounded area.[11] Periwound injections of macrophages activated by the carbohydrate glucan caused an increase in fibroblast proliferation, fibrogenesis, collagen synthesis, epithelialization, and an increase in the tensile strength of the wound.[11] This was presumed to be due to the effect of glucan-induced interleukin-1 (IL-1), and tumor necrosis factor alpha (TNF-apha) on the wound fibroblasts.[11,12] Topical application of glucans to wounds seems to result in more rapid angiogenesis and reepithelialization compared to controls.[12] Other carbohydrate extracts have been shown to accelerate healing of open wounds and burns.[13,14] These extracts stimulate oxygen consumption, increase angiogenesis, and increase collagen synthesis in the wounds.[13]

Because aloe vera sap and acemannan gel have been reported to enhance wound healing, the following experiments were designed to determine if acemannan could enhance healing and to investigate possible mechanisms of the activity of acemannan. The wound model used in this study was adopted and modified from the methods developed previously by others.[11,15] The method developed by these authors has the twin merits of simplicity and speed. The reader chooses which wound of a pair has healed (if any) as well as gives each wound a subjective score. When read blind, the presence of a control on the opposite foot provides an additional measure of wound healing by providing a basis for comparison as well as a control for any bias in the reader’s scoring. This model is simple, yet quick and reliable. The reproducibility and reliability come from the use of blinds and multiple controls. The basic experimental unit consisted of two groups, each of 30 mice. One group of mice in each experiment had controls in both feet, while the other group received control in one foot and treatment in the opposite foot. All experiments were performed blind.

Materials and Methods

Mice. Male Swiss-Webster mice weighing approximately 20g were obtained from Harlan Sprague Dawley, Inc. (Indianapolis, Indiana). Groups of 30 mice were wounded on the posterior tarsus of both feet after being anesthetized with 0.6mL of a mixture of sodium pentothal, propylene glycol, 90-percent ethanol, and sterile distilled water administered intraperitoneally. A 5mm incision was made through the thickness of the skin between the Achilles tendon and the external vestigial finger parallel to the posterior tarsal vein. Immediately after making the incision, one wound was treated with one drop of test material. A 2mm x 4mm piece of sterile parafilm (Parafilm™, American National Can, Chicago, Illinois) was inserted into the wounds to ensure even distribution of the solutions and to prevent rapid adhesion of the wound edges. The parafilm fell out within 24 hours without further intervention.

References: 

References

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