Platelet-rich plasma is an autologous source of platelet-derived growth factor and transforming growth factor beta that is obtained by sequestering and concentrating platelets by gradient density centrifugation. This technique produced a concentration of human platelets of 338% and identified platelet-derived growth factor and transforming growth factor beta within them. Monoclonal antibody assessment of cancellous cellular marrow grafts demonstrated cells that were capable of responding to the growth factors by bearing cell membrane receptors. The additional amounts of these growth factors obtained by adding platelet-rich plasma to grafts evidenced a radiographic maturation rate 1.62 to 2.16 times that of grafts without platelet-rich plasma. As assessed by histomorphometry, there was also a greater bone density in grafts in which platelet-rich plasma was added (74.0% +/- 11%) than in grafts in which platelet-rich plasma was not added (55.1% +/- 8%; p = 0.005).

Platelet-rich plasma: Growth factor enhancement for bone grafts

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

https://www.physiology.org/doi/pdf/10.1152/physrev.1999.79.4.1283

Mechanism of Action and In Vivo Role of Platelet-Derived Growth Factor

Wound healing remains a challenging clinical problem and correct, efficient wound management is essential. Much effort has been focused on wound care with an emphasis on new therapeutic approaches and the development of technologies for acute and chronic wound management. Wound healing involves multiple cell populations, the extracellular matrix and the action of soluble mediators such as growth factors and cytokines. Although the process of healing is continuous, it may be arbitrarily divided into four phases: (i) coagulation and haemostasis; (ii) inflammation; (iii) proliferation; and (iv) wound remodelling with scar tissue formation. The correct approach to wound management may effectively influence the clinical outcome. This review discusses wound classification, the physiology of the wound healing process and the methods used in wound management.

https://journals.sagepub.com/doi/pdf/10.1177/147323000903700531

The wound healing process: an overview of the cellular and molecular mechanisms.

Understanding wound healing today involves much more than simply stating that there are three phases: "inflammation, proliferation, and maturation." Wound healing is a complex series of reactions and interactions among cells and "mediators." Each year, new mediators are discovered and our understanding of inflammatory mediators and cellular interactions grows. This article will attempt to provide a concise report of the current literature on wound healing by first reviewing the phases of wound healing followed by "the players" of wound healing: inflammatory mediators (cytokines, growth factors, proteases, eicosanoids, kinins, and more), nitric oxide, and the cellular elements. The discussion will end with a pictorial essay summarizing the wound-healing process.

The basic science of wound healing.

Transforming growth factor-β (TGF-β) is generally acknowledged to be the cytokine with the broadest range of activities in repair of injured tissue, based both on the variety of cell types that produce and/or respond to it and on the spectrum of its cellular responses (Roberts and Sporn, 1990). TGF-β is released from degranulating platelets and secreted by all of the major cell types participating in the repair process, including lymphocytes, macrophages, endothelial cells, smooth muscle cells, epithelial cells, and fibroblasts (see Fig. 1). A unique feature of this molecule is that its autoinduction results in sustained expression at the site of a wound and extends the effectiveness of both the initial burst of endogenous TGF-β released upon injury and exogenous TGF-β that might be applied to a wound. The ability of TGF-β to improve and/or accelerate tissue repair has been studied extensively in a variety of animal models of both normal and impaired healing. A limited number of clinical trials are in progress, but it is anticipated that many new applications for TGF-β will ultimately be found, once problems with appropriate timing and formulation can be solved.

Transforming Growth Factor-β

Platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) markedly potentiate tissue repair in vivo. In the present experiments, both in vitro and in vivo responses to PDGF and TGF-beta were tested to identify mechanisms whereby these growth factors might each enhance the wound-healing response. Recombinant human PDGF B-chain homodimers (PDGF-BB) and TGF-beta 1 had identical dose-response curves in chemotactic assays with monocytes and fibroblasts as the natural proteins from platelets. Single applications of PDGF-BB (2 micrograms, 80 pmol) and TGF-beta 1 (20 micrograms, 600 pmol) were next applied to linear incisions in rats and each enhanced the strength required to disrupt the wounds at 5 d up to 212% of paired control wounds. Histological analysis of treated wounds demonstrated an in vivo chemotactic response of macrophages and fibroblasts to both PDGF-BB and to TGF-beta 1 but the response to TGF-beta 1 was significantly less than that observed with PDGF-BB. Marked increases of procollagen type I were observed by immunohistochemical staining in fibroblasts in treated wounds during the first week. The augmented breaking strength of TGF-beta 1 was not observed 2 and 3 wk after wounding. However, the positive influence of PDGF-BB on wound breaking strength persisted through the 7 wk of testing. Furthermore, PDGF-BB-treated wounds had persistently increased numbers of fibroblasts and granulation tissue through day 21, whereas the enhanced cellular influx in TGF-beta 1-treated wounds was not detectable beyond day 7. Wound macrophages and fibroblasts from PDGF-BB-treated wounds contained sharply increased levels of immunohistochemically detectable intracellular TGF-beta. Furthermore, PDGF-BB in vitro induced a marked, time-dependent stimulation of TGF-beta mRNA levels in cultured normal rat kidney fibroblasts. The results suggest that TGF-beta transiently attracts fibroblasts into the wound and may stimulate collagen synthesis directly. In contrast, PDGF is a more potent chemoattractant for wound macrophages and fibroblasts and may stimulate these cells to express endogenous growth factors, including TGF-beta, which, in turn, directly stimulate new collagen synthesis and sustained enhancement of wound healing over a more prolonged period of time.

/pdf/platelet-derived-growth-factor-and-transforming-growth-18srwslcal.pdf

Platelet-derived growth factor and transforming growth factor-beta enhance tissue repair activities by unique mechanisms.

Platelet-derived growth factor (PDGF) is a potent activator for cells of mesenchymal origin. PDGF stimulates chemotaxis, proliferation, and new gene expression in monocytes-macrophages and fibroblasts in vitro, cell types considered essential for tissue repair. Therefore, we analyzed the influence of exogenously administered recombinant B chain homodimers of PDGF (PDGF-BB) on two experimental tissue repair paradigms, incisional and excisional wounds. In both types of wounds, as little as 20-200 picomoles applied a single time to wounds significantly augmented the time dependent influx of inflammatory cells and fibroblasts and accelerated provisional extracellular matrix deposition and subsequent collagen formation. In incisional wounds, PDGF-BB augmented wound breaking strength 50-70% over the first 3 weeks; in excisional wounds, PDGF-BB accelerated time to closure by 30%. PDGF-BB exaggerated, but did not alter, the normal course of soft tissue repair, resulting in a significant acceleration of healing. Long term observations established no apparent differences between PDGF-BB treated and non-treated wounds. Thus, the vulnerary effects of PDGF-BB were transient and fully reversible in both wound healing models. Furthermore, analysis of PDGF-treated and non-treated wounds has provided important insights into mechanisms of normal and deficient tissue repair processes. PDGF appears to transduce its signal through wound macrophages and may trigger the induction of positive autocrine feedback loops and synthesis of endogenous wound PDGF and other growth factors, thereby enhancing the cascade of tissue repair processes required for a fully-healed wound. Thus, PDGF and other wound produced polypeptide growth factors may be the critical regulators of extracellular matrix deposition within healing wounds.

Role of platelet-derived growth factor in wound healing.

The roles of polypeptide growth factors in promoting wound healing and in directing the specificity and sequence of responses of different tissues in wounds are little understood. We investigated the influence of four growth factors on the rates of healing of a novel full thickness dermal ulcer placed on an avascular base in the rabbit ear. The wound model precludes significant wound contraction and requires new granulation tissue and epithelial cells for healing to originate centripetally. 5 micrograms (7-31 pmol/mm2) of platelet-derived growth factor-B chain (PDGF-BB), basic fibroblast growth factor (bFGF), and epidermal growth factor (EGF) applied locally at the time of wounding resulted in a twofold increase in complete reepithelialization of treated wounds (PDGF-BB, P = 0.02 chi square analysis; bFGF, P = 0.04; EGF, P = 0.05); transforming growth factor (TGF)-beta 1 significantly inhibited reepithelialization (P = 0.05). Both PDGF-BB and TGF-beta 1 uniquely increased the depth and area of new granulation tissue (P less than 0.005), the influx of fibroblasts, and the deposition of new matrix into wounds. Explants from 7-d old PDGF-BB-treated wounds remained metabolically far more active than controls, incorporating 473% more [3H]thymidine into DNA (P = 0.05) and significantly more [3H]leucine and [3H]proline into collagenase-sensitive protein (P = 0.04). The results establish that polypeptide growth factors have significant and selective positive influences on healing of full thickness ulcers in the rabbit.

/pdf/growth-factor-induced-acceleration-of-tissue-repair-through-1wex3nly0w.pdf

Growth factor-induced acceleration of tissue repair through direct and inductive activities in a rabbit dermal ulcer model.

Human platelet-derived growth factor (hPDGF) is likely to be important in stimulating tissue repair, based upon its in vivo chemotactic and stimulatory activities for inflammatory cells and fibroblasts and upon the presence of PDGF and related proteins in platelets, macrophages, and activated fibroblasts, cell types that make up the milieu of the healing wound. Recombinant human c-sis (rPDGF-B), homodimers of the B chain of PDGF, were compared with hPDGF in vitro. rPDGF-B was immunologically similar to hPDGF and, at identical concentrations, similar to hPDGF in stimulating fibroblast mitogenesis and chemotaxis of polymorphonuclear leukocytes, monocytes, and fibroblasts. Purified hPDGF and rPDGF-B were also tested in vivo for potency in a model of tissue repair using a linear incision wound through rat dermis. A single application of hPDGF or rPDGF-B (2-20 micrograms/wound) in a slow release vehicle at the time of wounding resulted in a dose-dependent, statistically highly significant increase of breaking strength of treated wounds. Wound healing in animals treated with rPDGF-B was 170% stronger and accelerated by 2 d during the first week over control wounds and by 4-6 d over the next 2 wk. Histologic evaluation of growth factor-treated wounds correlated the in vitro chemotactic activity and the accelerated healing of wounds with a striking inflammatory cell infiltrate early after wounding, markedly increased formation of granulation tissue by 4-d, and increased fibrosis by 14 d in comparison to control wounds. The results thus demonstrate that rPDGF-B is fully active in in vitro tests of mitogenesis and chemotaxis and, for the first time, demonstrate directly that PDGF significantly advances wound healing in incisional wounds of experimental animals.

/pdf/in-vivo-incisional-wound-healing-augmented-by-platelet-56hoou7vc5.pdf

Thomas A. Mustoe

Papers

Platelet-derived growth factor and transforming growth factor-beta enhance tissue repair activities by unique mechanisms.

Role of platelet-derived growth factor in wound healing.

Growth factor-induced acceleration of tissue repair through direct and inductive activities in a rabbit dermal ulcer model.

In vivo incisional wound healing augmented by platelet-derived growth factor and recombinant c-sis gene homodimeric proteins.

Primary intraosseous carcinoma of the mandible with probable origin in an odontogenic cyst