Effects of chronic wound fluid on the structure and biological activity of becaplermin (rhPDGF-BB) and becaplermin gel

Protease-Resistant Growth Factor Formulations for the Healing of Chronic Wounds

Objective: Chronic wounds are long-term nonhealing wounds that are refractory to treatment. These wounds can present elevated protease levels, leading to rapid degradation of native and exogenously added growth factors. This work focused on developing a protease-resistant growth factor formulation for treatment of chronic wounds presented with high protease activity. Approach: This study developed protease-resistant growth factor formulations comprising elastin-like peptides (ELPs) fused with a known protease inhibitor peptide or growth factor. The ELP component of the fusion proteins allows assembly of heterogeneous nanoparticles (NPs) putting the inhibitor in close proximity to the growth factor to be protected. Results: We show successful preservation of growth factor activity in high human neutrophil elastase (HNE) environment and in human chronic wound fluid derived from patients. We further show that these NPs result in enhanced collagen remodeling and resolution of inflammation in a full thickness wound supplemented with HNE in genetically diabetic mice. Innovation: Development of heterogeneous NPs that put the protease inhibitor in close proximity of the growth factor. Moreover, the modular nature of the NPs allows for protection of multiple growth factors by the same inhibitor without changing the amino acid sequence of the growth factor. Conclusion: Our results indicate that the developed NPs hold tremendous promise in chronic wound healing therapy and may further help the translation of growth factor therapies to clinic. The customizable template for the NP design allows for multifaceted use across several fields in research and medicine.

PDGF Restores the Defective Phenotype of Adipose-Derived Mesenchymal Stromal Cells from Diabetic Patients

Diabetes is a chronic metabolic disorder that affects 415 million people worldwide. This pathology is often associated with long-term complications, such as critical limb ischemia (CLI), which increases the risk of limb loss and mortality. Mesenchymal stromal cells (MSCs) represent a promising option for the treatment of diabetes complications. Although MSCs are widely used in autologous cell-based therapy, their effects may be influenced by the constant crosstalk between the graft and the host, which could affect the MSC fate potential. In this context, we previously reported that MSCs derived from diabetic patients with CLI have a defective phenotype that manifests as reduced fibrinolytic activity, thereby enhancing the thrombotic risk and compromising patient safety. Here, we found that MSCs derived from diabetic patients with CLI not only exhibit a prothrombotic profile but also have altered multi-differentiation potential, reduced proliferation, and inhibited migration and homing to sites of inflammation. We further demonstrated that this aberrant cell phenotype is reversed by the platelet-derived growth factor (PDGF) BB, indicating that PDGF signaling is a key regulator of MSC functionality. These findings provide an attractive approach to improve the therapeutic efficacy of MSCs in autologous therapy for diabetic patients.

Preclinical and clinical evidence for stem cell therapies as treatment for diabetic wounds

Diabetic wounds remain a global unsolved problem and the cost of diabetes-related amputations and diabetic wound treatment is approximately US$3 billion and US$9 billion per year, respectively. Diabetic foot ulcers (DFUs) occur in 15% of all patients with diabetes and precede 84% of all diabetes-related lower leg amputations. Currently, there is no satisfying treatment for these hard-to-heal-wounds. However, as we discuss here, experimental preclinical evidence for the successful use of adult stem cell therapies for diabetic wounds gives new hope for the development of effective treatments for use in the clinic.

Acute and impaired wound healing: pathophysiology and current methods for drug delivery, part 2: role of growth factors in normal and pathological wound healing: therapeutic potential and methods of delivery

This is the second of 2 articles that discuss the biology and pathophysiology of wound healing, reviewing the role that growth factors play in this process and describing the current methods for growth factor delivery into the wound bed.

The mechanism of protracted wound healing on oral mucosa in diabetes. Review

Diabetic patients increase their body's susceptibility to infection and diabetes is a risk factor for periodontal diseases and oral infection. Although many studies showed the mechanism of impaired wound healing in diabetes, there are still arguments to shed light on what kind of factors, including local and systemic factors are involved in the protracted wound healing. This review article summarizes reports on the wound healing in diabetes and discusses the mechanism of the protracted wound healing of the oral mucosa in diabetes. Delayed vascularization, reduction in blood flow, decline in innate immunity, decreases in growth factor production, and psychological stresses may be involved in the protracted wound healing of the oral mucosa in diabetics.

Human cord blood-derived endothelial progenitor cells and their conditioned media exhibit therapeutic equivalence for diabetic wound healing

Transplantation of human cord blood-derived endothelial progenitor cells (EPCs) is reported to contribute to neovascularization in various ischemic diseases. However, the possible beneficial role and underlying mechanisms in diabetes-impaired wound healing have been less well characterized. In this study, EPC transplantation stimulated keratinocyte and fibroblast proliferation substantially as early as 3 days after injury, leading to significantly accelerated wound closure in streptozotocin-induced diabetic nude mice, compared to PBS control. RT-PCR analysis showed that EPCs secreted various wound healing-related growth factors. Among them, keratinocyte growth factor and platelet-derived growth factor were highly expressed in the EPCs and were present at substantial levels in the EPC-injected dermal tissue. Using EPC-conditioned medium (CM), we found that paracrine factors from EPCs directly exerted mitogenic and chemotactic effects on keratinocytes and fibroblasts. Moreover, injection of EPC-CM alone into the same diabetic wound mice promoted wound healing and increased neovascularization to a similar extent as achieved with EPC transplantation. These results indicate that the beneficial effect of EPC transplantation on diabetic wounds was mainly achieved by their direct paracrine action on keratinocytes, fibroblasts, and endothelial cells, rather than through their physical engraftment into host tissues (vasculogenesis). In addition, EPC-CM was shown to be therapeutically equivalent to EPCs, at least for the treatment of diabetic dermal wounds, suggesting that conditioned medium may serve as a novel therapeutic option that is free from allograft-associated immune rejection concern.

Altered molecular mechanisms of diabetic foot ulcers

The continuously increasing worldwide prevalence of diabetes will be accompanied by a greater incidence of diabetic foot ulcer, a complication in which many of the morphological processes involved in normal wound healing are disrupted. The highly complex and integrated process of wound healing is regulated by a large array of molecular factors. These often have overlapping functions, ensuring a certain degree of tolerance through redundancy. In diabetes, changes to the expression of a large number of molecular factors have been observed, overwhelming this inbuilt redundancy. This results in delayed healing or incomplete healing as in ulceration. Understanding the relationship between altered levels of molecular factors and the inhibited healing process in such ulcers will permit the development of targeted treatments aimed to greatly improve the quality of life of patients, at the same time helping to reduce the huge costs associated with treating this diabetic condition and its long-term consequences. This short review examines how changes in the expression of molecular factors are related to altered morphology in diabetic foot ulceration and very briefly considers treatment strategies at molecular level.

Impaired wound healing in an acute diabetic pig model and the effects of local hyperglycemia

Diabetic wounds result in significant morbidity, prolonged hospitalization, and enormous health-care expenses. Pigs have been shown to have wound healing resembling that in humans. The aim of this study was to develop a large-animal model for diabetic wound healing. Diabetes was induced by streptozotocin injection in Yorkshire pigs. Full-thickness wounds were created and dressed with a sealed chamber. Nondiabetic pigs with or without high glucose wound fluid concentration served as controls. Glucose concentration in serum and wound fluid was measured and collected. Wound contraction was monitored, and biopsies were obtained for measurement of reepithelialization. Wound fluid was analyzed for insulin-like growth factor-1 (IGF-1), platelet-derived growth factor, and transforming growth factor. Glucose concentration in wound fluid initially followed serum levels and then decreased to undetectable on day 9. Reepithelialization was significantly delayed in diabetic pigs. In nondiabetic pigs, wounds treated in a local hyperglycemic environment, and thus excluding the effects of systemic hyperglycemia, showed no difference in wound closure compared with controls. This suggests that delayed wound healing in diabetes is not induced by local high-glucose concentration itself. Analysis of growth factor expression showed a marked reduction in IGF-1 in the diabetic wounds. Diabetic pigs have impaired healing that is accompanied by a reduction of IGF-1 in the healing wound and is not due to the local hyperglycemia condition itself.

Chemokines and diabetic wound healing

Chemokines are critical for white blood cell recruitment to injured tissues and play an important role in normal wound healing processes. In contrast, impaired wound healing in diabetic patients is accompanied by decreased early inflammatory cell infiltration but persistence of neutrophils and macrophages in the chronic, nonhealing wounds. These changes in inflammatory cell recruitment occur in conjunction with alterations in chemokine and growth factor expression. In addition to leukocyte trafficking, many different cell types, including endothelial cells, fibroblasts, and keratinocytes, produce and respond to chemokines, and these interactions are altered in diabetic wounds. Thus, the chemokine system may have both direct and inflammatory-mediated effects on many different aspects of diabetic wound healing. The potential roles of chemokines and inflammatory or immune cells in nonhealing diabetic wounds, including impairments in growth factor expression, angiogenesis, extracellular matrix formation, and reepithelialization, are examined.

Becaplermin gel in the treatment of diabetic neuropathic foot ulcers

Diabetic foot ulcers remain a major cause of morbidity. Significant progress has been accomplished in ulcer healing by improved management of both ischemia and neuropathy in the diabetic foot. Nevertheless, there is a vital need for further improvement. Becaplermin gel represents an important therapeutic advance for diabetic neuropathic foot ulcers with adequate blood supply. Randomized controlled trials have shown that it is effective in increasing healing rates. However, this efficacy has not translated to positive clinical experience, and the drug is not widely used. Moreover, becaplermin is an expensive medication. Even though it has repeatedly been estimated as cost-effective, its high cost may be prohibitive for some clinicians, especially in developing countries. Clearly, further work is needed to clarify whether use of becaplermin is justified in everyday clinical practice. Future research also needs to assess the potential room for improvement with becaplermin, for instance by combination with other growth factors or by exploring alternative modes of drug delivery.

Growth factors in the treatment of diabetic foot ulcers: new technologies, any promises?

Foot ulcers remain a common problem, leading to increased morbidity in patients with diabetes. Despite the progress that has been achieved in revascularization techniques as well as in off-loading to relieve high-pressure areas, diabetic foot wounds remain a clinical challenge. Growth factors are a major technological advance that promised to change the face of wound healing. The most important of growth factors are recombinant human platelet-derived growth factor-BB and granulocyte colony-stimulating factor. The former has been approved by the FDA for the treatment of neuropathic ulcers when there is adequate blood supply. The latter is less demonstrably useful. Advances include methods of delivering growth factors.

The molecular biology of chronic wounds and delayed healing in diabetes

Wound healing is a complicated and integrated process. Although there is some tolerance in terms of redundancy and interrelated control mechanisms, pushing beyond such limits may contribute to delayed wound healing, and in extreme cases lead to chronic wounds/ulcers and thus potentially to lower extremity amputation. Diabetes is associated with such disruption in wound healing. Research in humans and in animal models has identified a large number of changes associated with diabetes at the molecular level in delayed wound healing and to a lesser extent in chronic diabetic ulcers. Better overall understanding of these changes and how they are interrelated would allow for specifically targeted treatment, thus ensuring improved quality of life for patients and providing savings to the high costs that are associated with all aspects of chronic diabetic ulcers. This review examines the work done at the molecular level on chronic diabetic ulcers, as well as considering changes seen in diabetes in general, both in humans and animal models, that may in turn contribute to ulcer formation.

Bécaplermine gel (Regranex® gel)

Becaplermine gel (Regranex) is an hydrogel which contains 100 microg of Platelet Derived Growth Factor-BB (rhPDGF-BB) per gram. Regranex is presented in 15-gram multidose tubes. It has been approved as adjuvant treatment for neuropathic diabetic ulcerations of less than 5 cm2, extending into the subcutaneous tIssue, in the absence of ischemia, in conjunction with a standardised program of appropriate wound care, (control of infection, sharp debridement, provision of a moist environment and avoidance of pressure on the wound). PDGF-BB promotes cutaneous wound healing by increasing proliferation and migration of dermal fibroblasts and extracellular matrix deposition. PDGF also promotes chemotaxis of neutrophils, monocytes and smooth muscle cells in wounds. Topical application of rhPDGF-BB speeds wound healing and promotes granulation tIssue formation, synthesis of extracellular matrix and the inflammatory phase of the wound healing process in healthy and healing-impaired animal models. In clinical trials in humans, accelarated healing has been demonstrated in patients with lower extremity diabetic neuropathic ulcers and decubitus sores by increasing granulation tIssue formation and epithelialization. Local toxicity studies in humans were negative (repeated becaplermin gel application under occlusion to intact or abraded skin, dermal sensitization tests). Pharmacokinetic studies in humans have shown that systemic absorption after topical applications was minimal. In trials, systemic and local tolerance were excellent. Reported adverse effects were similar in incidence and in nature in all groups. The 0.01% Regranex gel is safe and easy to use, with single daily application. It is currently the only commercially available topical growth factor for use in cutaneous wound healing.