The Effects of TGF-b3 Modulation on Scar Tissue Formation in the Pig

Nathan D. Schwade, PhD, James J. Fowler, MD, Joseph Leach, MD, Department of Otolaryngology - Head and Neck Surgery, University of Texas Southwestern Medical Center, Dallas, Texas

Disclosures

Wounds. 2000;12(2) 

In This Article

Abstract and Introduction

Transforming growth factor beta (TGF-b) is a product of platelets, macrophages and fibroblasts that is instrumental in modulating the healing process. Of the three distinct subtypes of TGF-b present in humans, TGF-b3 has been noted to reduce cutaneous scarring in rats. In an effort to investigate the effects of TGF-b3 on skin more closely resembling that of humans, TGF-b3 and its antibody were injected serially into porcine cutaneous wounds. Exogenous administration of antibody to TGF-b3 significantly increases the breaking strength of porcine wounds seven and fourteen days post injury. A significant elevation in the breaking strength of wounds treated with higher doses of TGF-b3 antibody at seven and fourteen days post injury was noted compared to controls. Histologic examination revealed substantially greater fibroplasia in the dermis of wounds treated with higher doses of antibody to TGF-b3 fourteen days post injury when compared to control. Exogenous administration of antibody to TGF-b3 significantly increases the breaking strength of porcine wounds seven and fourteen days post injury.

Despite major advances in wound care this century, much of the dynamic of wound healing remains beyond the immediate control of the surgeon. Some wounds, particularly in the elderly, the diabetic, or the cachectic patient heal slowly or not at all. Other wounds heal too robustly, producing keloids or hypertrophic scars. More remarkably, wounds produced in the fetal model heal without a trace of scarring at all. Evidence is accumulating to indicate that growth factors play a major role in mediating successful wound healing. With the advent of recombinant gene technology, growth factors are available at less expense and in greater quantity. This allows the researcher the ability to test a multitude of growth factors for their effects on wound healing. Growth factor families that have known effects on wound healing include epidermal growth factor, fibroblast growth factors, transforming growth factors, platelet-derived growth factors, insulin like growth factors and interleukins.

Transforming growth factor beta (TGF-b) has gained the attention of many researchers recently due to its widely ranging effects on wound healing. Prior to the delineation of the various subtypes, TGF-b was found to inhibit or stimulate growth of many cell types depending on the presence of other growth factors.[1] TGF-b has been noted to be a potent chemoattractant for macrophages, in addition to modulating collagen synthesis and causing tissue fibrosis.[2,3,4] It is also known to increase granulation tissue formation and breaking strength in healing dermal wounds.[5,6] In wounds where healing has been impaired by steroids and Adriamycin, TGF-b has even been found to reverse the impairment in healing.[7,8,9]

The TGF-b gene superfamily is now known to consist of 19 different proteins, including TGF-b1-5, the inhibin family, bone morphogenic protein, and Müllerian inhibiting substances.[10] Although five distinct subtypes of TGF-b have been identified in nature, only three subtypes have been discovered in humans: TGF-b1, TGF-b2 and TGF-b3. All TGF-b precursors share a region of high homology near the n-terminus. Their effects on tissue growth both in vivo and in vitro, however, vary widely. The delineation of the various subtypes of TGF-b has brought forth a wealth of information regarding their effects on tissue growth. TGF-b3 and TGF-b2 are significantly more potent in inducing mesoderm formation than TGF-b1 in frog embryos.[11] TGF-b3 is a significantly better inhibitor of DNA synthesis in human keratinocyte cells than either TGF-b1 or TGF-b2.[12]

More recently, researchers have investigated the role of TGF-b isomers in cutaneous scarring. Mustoe, et al., demonstrated an increase in the breaking strength of wounds after the application of TGF-b1 to incisional wounds in rats.[6] In 1992, Shah, et al., applied antibodies to TGF-b to fresh skin defects in rats. Assessment revealed lower collagen content but identical breaking strength in antibody-treated wounds.[13] In 1994, Shah demonstrated that application of neutralizing antibody to TGF-b1 and TGF-b2 reduced extracellular matrix deposition in the early stages of wound healing without a reduction in breaking strength.[14] Shah, et al., went on to show that neutralization of TGF-b1 and TGF-b2 or the addition of TGF-b3 to cutaneous wounds not only improved architecture of the neodermis but also reduced scarring.[15]

To our knowledge, no studies have been performed to date to investigate the effect of TGF-b3 modulation on wound healing in larger mammals. This study was designed, therefore, to quantify the effects of TGF-b3 and its neutralizing antibody on scar tissue formation in the porcine model. The breaking strength of the experimental wounds was measured after varying doses of TGF-b3 or its antibody were injected into the wound edges. A dose response curve was then formulated to determine the effects of varying dosages of isomer and antibody on breaking strength. Histologic examination of treated wounds was performed to determine differences between treated and control wounds with respect to fibroblastic response and inflammatory cell infiltrate.

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