Philip V. Peplow

A review of the influence of growth factors and cytokines in in vitro human keratinocyte migration.

OBJECTIVE Keratinocyte migration from the wound edge is a crucial step in the reepithelization of cutaneous wounds. Growth factors and cytokines, released from cells that invade the wound matrix, play an important role, and several in vitro assays have been performed to elucidate this. The purposes of this study were to review in vitro human studies on keratinocyte migration to identify those growth factors or cytokines that stimulate keratinocyte migration and whether these assays might serve as a screening procedure prior to testing combinations of growth factors or cytokines to promote wound closure in vivo. METHODS Research papers investigating effect of growth factors and cytokines on human keratinocyte migration in vitro were retrieved from library sources, PubMed databases, reference lists of papers, and searches of relevant journals. RESULTS Fourteen different growth factors and cytokines enhanced migration in scratch wound assay and HGF together with TGF-β, and IGF-1 with EGF, were more stimulatory than either growth factor alone. HGF with TGF-β1 had a greater chemokinetic effect than either growth factor alone in transmigration assay. TGF-β1, FGF-7, FGF-2 and AGF were chemotactic to keratinocytes. EGF, TGF-α, IL-1α, IGF and MGSA enhanced cell migration on ECM proteins. CONCLUSION Many growth factors and cytokines enhanced migration of keratinocytes in vitro, and certain combinations of growth factors were more stimulatory than either alone. These and other combinations that stimulate keratinocyte migration in vitro should be tested for effect on wound closure and repair in vivo. The scratch wound assay provides a useful, inexpensive and easy-to-perform screening method for testing individual or combinations of growth factors or cytokines, or growth factors combined with other modalities such as laser irradiation, prior to performing wound healing studies with laboratory animals.

Photodynamic Modulation of Wound Healing: A Review of Human and Animal Studies

OBJECTIVE The purpose of this study was to review studies of photodynamic therapy (PDT) on wound healing and cells in vitro, to assess the effects of such therapy. BACKGROUND DATA PDT is used to treat tumors. When activated by light of a specific wavelength, the photosensitizer produces reactive oxygen species (ROS) that kill tumor cells. Low levels of ROS may induce cellular proliferation. METHODS Research articles investigating PDT on wound healing and cells in vitro published up to August 2010 were retrieved from library sources, PubMed and Medline databases, reference lists of articles, and searches of relevant journals. RESULTS The studies indicated that use of various photosensitizers combined with laser irradiation led to improved wound outcomes. For most in vitro studies, there was a decrease in cell growth or viability. CONCLUSIONS PDT improved healing outcomes in several animal wound models, but mainly had an inhibitory effect on cells in vitro. These findings strongly support PDT for wound healing.

Osseous regeneration in the presence of oxidized cellulose and collagen.

Oxidized cellulose and collagen are two absorbable hemostatic scaffolding materials that are used widely in surgery. A histomorphological study was undertaken to determine the tissue response and extent of healing brought about by intraosseously implanting these two materials in the femur and tibia of sheep. There was no major difference in the rate of repair of the bone defects brought about by these two materials, with the bone defects being completely repaired by lamellar bone at 6–8 weeks. Therefore, our results suggest that, in most instances where collagen is presently used in surgical applications, it could be substituted by oxidized cellulose.

Gene Expression and Release of Growth Factors During Delayed Wound Healing: A Review of Studies in Diabetic Animals and Possible Combined Laser Phototherapy and Growth Factor Treatment to Enhance Healing

OBJECTIVE The purposes of this study were: to review studies of growth factors in cutaneous wounds of animals with diabetes to identify those factors with altered gene expression and content compared with nondiabetic animals; and to explore which deficiencies of growth factors in diabetic wounds may or may not be improved by laser irradiation. BACKGROUND DATA Wound healing is compromised in diabetes. Decreased production and/or increased destruction of growth factors may be responsible. Laser irradiation can increase the gene expression and release of certain growth factors by cells. METHODS Research articles investigating growth factor expression in wounds of nondiabetic and diabetic mice and rats published through September 2011 were retrieved from library sources, PubMed databases, reference lists of articles, and searches of relevant journals. RESULTS Vascular endothelial growth factor (VEGF), placental growth factor (PlGF), keratinocyte growth factor (KGF), fibroblast growth factor 1 (FGF-1), FGF-2, insulin-like growth factor 1 (IGF-1), IGF-2, transforming growth factor beta (TGF-β), and nerve growth factor (NGF) had decreased gene expression and content in early phases of healing for diabetic wounds. Gene expression of KGF, IGF-1, and IGF-2 was delayed, whereas that of FGF-1 and FGF-2 occurred earlier, in diabetic compared with nondiabetic wounds. CONCLUSIONS Growth factor administration combined with laser irradiation may provide an effective therapy to maximize healing of diabetic wounds.

Laser Photobiomodulation of Wound Healing in Diabetic and Non-Diabetic Mice: Effects in Splinted and Unsplinted Wounds

OBJECTIVE The aim of this investigation was to compare the healing of laser-irradiated and non-irradiated wounds covered by an occlusive dressing in mice. BACKGROUND DATA Many previous studies of the effects of laser irradiation of experimental wounds in mice and rats did not cover the wounds so that healing occurred mainly by contraction. Healing of covered wounds is slower and mimics more closely wound healing in humans. MATERIALS AND METHODS Forty-seven diabetic and twenty non-diabetic mice were used. A single wound (5 mm diameter) was created on the left flank of each animal and covered by Tegaderm HP dressing (Day 1). Wounds were irradiated (660 nm) for 20 s using a lower power (18 mW) or higher power (80 mW) laser starting immediately post-wounding for seven consecutive days (0.36 or 1.6 J/day); untreated wounds served as controls. Animals were euthanized on Day 8, 10, or 14. Wound specimens were cut and stained using haematoxylin and eosin, and picrosirius red, and examined by microscopy. RESULTS Results confirmed that wound healing was impaired in diabetic mice. Analysis of the data demonstrated that Tegaderm HP dressing had retarded contraction (splinted the wounds) in a large proportion of diabetic mice and, to a lesser extent, in non-diabetic mice. Healing of splinted wounds was delayed compared to unsplinted wounds, but laser irradiation (1.6 J/day, 7 days) stimulated healing by re-epithelization and granulation tissue formation. CONCLUSION These are the first findings of laser-mediated stimulation of healing in splinted wounds. Further studies are needed to assess the effects of different constellation sets of laser parameters in this wound model.

Electroacupuncture for control of blood glucose in diabetes: literature review.

Electrical stimulation at acupuncture points (acupoints) has been investigated for its utility in lowering blood glucose in hyperglycemic humans and animal models. Only two studies were found using electroacupuncture in human subjects, and in both of these, the participants were normal (nondiabetic) and electrical stimulation was carried out at several acupoints. It had a hypoglycemic effect in obese women with calorific restriction diet using electrical stimulation of 2 Hz for 30 minutes/day for 20 days, but no change occurred in blood glucose of fasted patients in the other study using 1 Hz for 15 minutes. Fourteen animal studies were found, of which, 11 were performed in diabetic and normal rats. A hypoglycemic effect was observed in fasted type 1 diabetic rats using the Zusanli (ST36) leg acupoint with electrical stimulation of 15 Hz for 30 minutes and 60 minutes. In fasted type 2 diabetic rats, blood glucose was lowered using the Zusanli acupoint with electrical stimulation parameters of 15 Hz and 10 mA for 30 minutes. Also, using the Zhongwan (CV12) abdomen acupoint with electrical stimulation parameters of 15 Hz and 10 mA for 90 minutes had a hypoglycemic effect in fasted type 2 diabetic rats. In fasted normal rats, electrical stimulation of 2 Hz or 15 Hz for 30 minutes at the Zusanli or Zhongwan acupoint caused a decrease in blood glucose. Future studies are required in fasted diabetic rats to determine the effect of electroacupuncture on blood levels of insulin, lipids, fatty acids and β-endorphin, and blood flow and nerve conduction velocity. Studies with fasted normal and diabetic human subjects treated by electroacupuncture are warranted using data from animal experiments to inform such studies.

Influence of growth factors and cytokines on angiogenic function of endothelial progenitor cells: a review of in vitro human studies

Abstract Growth factors and cytokines released at sites of injury and inflammation play an important role in stimulating endothelial progenitor cell (EPC) migration to these sites. A comparative analysis of the literature shows under neutral in vitro conditions (pH 7.4), several growth factors and cytokines influenced favorably indices of EPC angiogenic function. They included SDF-1, VEGF, PlGF, FGF-2, NGF and IL-1β. Others, e.g. TNF-α, have an unfavorable influence. SDF-1 and VEGF in combination increased chemotactic cell migration and reduced apoptosis caused by serum starvation. Under acidic conditions (pH 6.5), the biological activity of certain growth factors may be impaired, although TPO, SCF and IL-3 were each able to rescue EPCs from acidic exposure apoptosis, a combination of these three factors stimulated cell proliferation and prevented apoptosis. Possible combinations of growth factors and cytokines together with EPC transplantation may provide for a greater extent of vessel repair and new vessel formation.

Biocompatibility and osseointegration of reconstituted keratin in an ovine model

Reconstituted keratin has potential as a raw material for orthopaedic applications. The aim of this study was to investigate the in vivo biocompatibility and osseointegration of keratin materials in an ovine model. Six different modifications of the keratin polymer, based on porous or dense constructs, regenerated by either neutral or acidic treatment, with or without hydroxyapatite, were made as small rods and inserted into drilled round defects in the femur and tibia of sheep. Histology was carried out on samples taken at different time points up to 24 weeks postsurgery. All keratin implants showed similar histological profiles, which included granulation tissue surrounding and infiltrating the implants, followed by new bone formation radiating from the existing bone. By 8 weeks, new bone had grown to within a short distance of the implant surface, and in some places was in direct apposition to the keratin implant. In the 12 to 24-week period, there was peripheral resorption and infiltration of bony trabeculae with regard to the porous constructs only. The tissue reaction appeared to model that of a fairly inert material. Further work on improving the extent of osseointegration and acceleration of the biodegradation rate of reconstituted keratin is underway.

Laser photobiostimulation of wound healing: defining a dose response for splinted wounds in diabetic mice.

We have used a 660 nm, 80 mW laser diode in genetic diabetic mice to stimulate the healing of wounds covered with a Tegaderm HP dressing that causes a retardation of contraction (splinted wounds). The purpose of our study was to examine the effects of irradiating the wounds for different time intervals in order to determine a dose response relationship.

A study of the relationship between mass and physical strength of keratin bars in vivo

A study was undertaken of the changes in the mass and physical properties of keratin bars implanted subcutaneously in adult rats. A very gradual decrease occurred in vivo in the dry weight of the bars over the period of the study (up to 18 weeks). The elastic modulus of the bars decreased abruptly when present in vivo between 3 and 6 weeks. At the same time there was an increase in the number of cavitations and fissures at the surface of the bars, and an increase in a central internal region of the bars where there was a disorganisation in structure of the polymer. A biocompatible material showing such changes in vivo is likely to be suitable for a variety of medical and surgical applications in which it provides a framework for cell invasion.