Derek Walter Silcock

Mechanism of action of PROMOGRAN, a protease modulating matrix, for the treatment of diabetic foot ulcers

Proteases play a critical role in many of the physiologic processes of wound repair. However, if their activity becomes uncontrolled proteases can mediate devastating tissue damage and consequently they have been implicated in chronic wound pathophysiology. Previous studies have shown that chronic wound fluid contains elevated protease levels that have deleterious effects, degrading de novo granulation tissue and endogenous biologically active proteins such as growth factors and cytokines. Therefore, we have proposed that an effective therapeutic approach for chronic wounds would be to modify this hostile environment and redress this proteolytic imbalance. Using an ex vivo wound fluid model, we show the ability of a proprietary new wound treatment to bind and inactivate proteases. We have shown that the addition of this test material to human chronic wound fluid obtained from diabetic foot ulcer patients resulted in a significant reduction in the activities of neutrophil‐derived elastase, plasmin, and matrix metalloproteinase when compared to wet gauze. This study provides mechanistic evidence to support the hypothesis that this novel treatment modality for chronic wounds physically modifies the wound microenvironment, and thereby promotes granulation tissue formation and stimulates wound repair.

The role of oxidised regenerated cellulose/collagen in chronic wound repair and its potential mechanism of action

Normal wound healing is a carefully controlled balance of destructive processes necessary to remove damaged tissue and repair processes which lead to new tissue formation. Proteases and growth factors play a pivotal role in regulating this balance, and if disrupted in favour of degradation then delayed healing ensues; a trait of chronic wounds. Whilst there are many types of chronic wounds, biochemically they are thought to be similar in that they are characterised by a prolonged inflammatory phase, which results in elevated levels of proteases and diminished growth factor activity. This increase in proteolytic activity and subsequent degradation of growth factors is thought to contribute to the net tissue loss associated with these chronic wounds. In this study, we describe a new wound treatment, comprising oxidised regenerated cellulose and collagen (ORC/collagen), which can redress this imbalance and modify the chronic wound environment. We demonstrate that ORC/collagen can inactivate potentially harmful factors such as proteases, oxygen free radicals and excess metal ions present in chronic wound fluid, whilst simultaneously protecting positive factors such as growth factors and delivering them back to the wound. These characteristics suggest a beneficial role for this material in helping to re-balance the chronic wound environment and therefore promote healing.

The role of oxidised regenerated cellulose/collagen in wound repair: effects in vitro on fibroblast biology and in vivo in a model of compromised healing.

Irrespective of underlying chronic wound pathology, delayed wound healing is normally characterised by impaired new tissue formation at the site of injury. It is thought that this impairment reflects both a reduced capacity to synthesize new tissue and the antagonistic activities of high levels of proteinases within the chronic wound environment. Historically, wound dressings have largely been passive devices that offer the wound interim barrier function and establish a moist healing environment. A new generation of devices, designed to interact with the wound and promote new tissue formation, is currently being developed and tested. This study considers one such device, oxidised regenerated cellulose (ORC) /collagen, in terms of its ability to promote fibroblast migration and proliferation in vitro and to accelerate wound repair in the diabetic mouse, a model of delayed wound healing. ORC/collagen was found to promote both human dermal fibroblasts proliferation and cell migration. In vivo studies considered the closure and histological characteristics of diabetic wounds treated with ORC/collagen compared to those of wounds given standard treatment on both diabetic and non-diabetic mice. ORC/collagen was found to significantly accelerate diabetic wound closure and result in a measurable improvement in the histological appearance of wound tissues. As the diabetic mouse is a recognised model of impaired healing, which may share some characteristics of human chronic wounds, the results of this in vivo study, taken together with those relating the positive effects of ORC/collagen in vitro, may predict the beneficial use of this device in the clinical setting.

Differential expression and regulation of extracellular matrix-associated genes in fetal and neonatal fibroblasts

Adults and neonates heal wounds by a repair process associated with scarring in contrast to scar‐free wound healing in the fetus. In the present study, human dermal fetal fibroblasts, representing the scarless phenotype, and neonatal human dermal fibroblasts, representing scar‐forming phenotype, were examined for potential differences that might influence the wound healing process. Fetal fibroblasts secreted four‐ to tenfold more latent transforming growth factor‐β1 depending on the cell strains compared. Fetal fibroblasts also produced higher levels of collagen protein and mRNA for most types of collagen (particularly type III) as compared to neonatal cells. Interestingly, mRNA for type V collagen was significantly reduced in fetal cells. Neonatal fibroblasts expressed significantly higher levels of latent transforming growth factor‐β1 binding protein mRNA, in contrast to almost undetectable levels in fetal fibroblasts. By ligand blot analysis, the levels of insulin‐like growth factor binding protein‐3, a reported mediator of transforming growth factor‐β1 activity, was eightfold higher in neonatal versus fetal fibroblasts. Approximately 20 other mRNAs for various cytokines, matrix molecules and receptors were examined and found to be similar between the two cell types. The phenotypic differences described in this article may represent potentially important mechanisms to explain the differences in the quality of wound repair observed in fetal versus adult/neonatal tissues.

The differential regulation and secretion of proteinases from fetal and neonatal fibroblasts by growth factors

One of the major differences between fetal and adult wound repair is the unique ability of fetal wounds to heal without scarring. Since scar formation is a function of extracellular matrix deposition, the regulation of this component is fundamental in tissue remodeling. In this study, we have characterized the differences in the secretion of matrix-degrading proteases, namely urokinase plasminogen activator and gelatinase A and B, from fetal and neonatal fibroblasts. In addition, we examined the modulation of these protease levels by growth factors known to be important in wound repair. The results indicate that the secretion of these proteases differ significantly between the two cell types. The levels of urokinase plasminogen activator and its inhibitor were notably higher in media conditioned by neonatal fibroblasts in comparison to fetal samples. In contrast, the basal level of gelatinase A was comparable in both cell types, whilst the level of gelatinase B was elevated in the fetal fibroblasts. Transforming growth factor-beta 1 reduced the level of urokinase plasminogen activator and stimulated the secretion of plasminogen activator inhibitor-1 and progelatinase B in both neonatal and fetal fibroblasts. However, only progelatinase A and an activated form of gelatinase B were significantly elevated in fetal fibroblasts. In contrast, platelet-derived growth factor stimulated urokinase plasminogen activator, its inhibitor and both gelatinase A and B, an effect which was more apparent in fetal fibroblasts. This difference in protease regulation may be reflected in the differing rate and quality of tissue remodeling observed during adult vs fetal wound repair.

p38 MAPK inhibition reduces diabetes-induced impairment of wound healing

In healthy tissue, a wound initiates an inflammatory response characterized by the presence of a hematoma, infiltration of inflammatory cells into the wound and, eventually, wound healing. In pathological conditions like diabetes mellitus, wound healing is impaired by the presence of chronic nonresolving inflammation. p38 mitogen-activated protein kinase (MAPK) inhibitors have demonstrated anti-inflammatory effects, primarily by inhibiting the expression of inflammatory cytokines and regulating cellular traffic into wounds. The db/db mouse model of type 2 diabetes was used to characterize the time course of expression of activated p38 during impaired wound healing. The p38α-selective inhibitor, SCIO-469, was applied topically and effects on p38 activation and on wound healing were evaluated. A topical dressing used clinically, Promogran™, was used as a comparator. In this study, we established that p38 is phosphorylated on Days 1 to 7 post-wounding in db/db mice. Further, we demonstrated that SCIO-469, at a dose of 10 μg/wound, had a positive effect on wound contraction, granulation tissue formation, and re-epithelialization, and also increased wound maturity during healing. These effects were similar to or greater than those observed with Promogran™. These results suggest a novel approach to prophylactic and therapeutic management of chronic wounds associated with diabetes or other conditions in which healing is impaired.