Charged beads enhance cutaneous wound healing in rhesus non-human primates

Mast cells: an unexpected finding in the modulation of cutaneous wound repair by charged beads

Increased numbers of mast cells are affiliated with a broad spectrum of pathologic skin conditions, including ulcers, atopic dermatitis, neurofibromatosis, hemangiomas, keloids, and hypertrophic scars. It has been proposed that mast cells play a primary pathophysiologic role in these disorders and that their presence represents not merely a secondary event. While investigating their recent hypothesis that positively charged cross-linked diethylaminoethyl dextran (CLDD) beads potentiate cutaneous wound healing, the authors serendipitously observed increased numbers of mast cells in the deep dermis of wounds treated with CLDD beads. The authors propose that mast cells may play an important role in the modulation of healing seen with CLDD beads. Incisional wounds were studied in 30 Sprague-Dawley rats partitioned into two groups that were killed 7 or 14 days after wounding. The wounds were treated with positively, negatively, or neutrally charged CLDD beads. Physiologic saline served as a control. At the designated times after incisional wounding, biopsy specimens were tested for wound breaking strength or processed for histologic testing, fixed in 4% paraformaldehyde, and stained with Giemsa and Goldner-Masson trichrome. Mast cells were counted under light microscopy in a blinded fashion and were expressed as the number of cells per millimeter squared. Significant increases in the number of mast cells were observed in the deep dermis of incisional wounds after implantation with positively or negatively charged CLDD beads. In contrast, neutrally charged beads had no effect on mast cell numbers. At 7 days, the incisions treated with positively charged beads averaged 2.1 times more mast cells compared with those treated with physiologic saline or neutrally charged beads, whereas the incisions treated with negatively charged beads displayed 3.2 times more mast cells. By day 14, the incisions treated with positively charged beads averaged 2.5 times more mast cells than those wounds treated with saline or neutrally charged beads; the incisions treated with negatively charged CLDD beads had 3.4 times more mast cells. The 7-day tensiometric data indicated that wounds treated with negatively charged CLDD beads had increased breaking strength compared with wounds treated with neutrally charged beads or saline (1.8 and 1.7 times, respectively; p = 0.01 and p = 0.02). Wounds treated with positively charged beads also showed increased breaking strength compared with wounds treated with neutrally charged beads or saline (1.5 and 1.4 times greater); however, this did not reach statistical significance. There was no apparent difference in breaking strength when neutrally charged beads were compared with those treated with saline. At 14 days, there was no statistically significant difference in wound breaking strength between different treatments. These findings are clinically germane to the assessment of proposed therapeutic applications of CLDD beads for a variety of impaired wound-healing states. Furthermore, if increased mast cell populations are intimately linked to hypertrophic scar and keloid formation, the results of the authors' study suggest that CLDD bead therapy of cutaneous wounds may lead to pathologic wound healing in humans.

Increase in wound breaking strength in rats in the presence of positively charged dextran beads correlates with an increase in endogenous transforming growth factor-beta1 and its receptor TGF-betaRI in close proximity to the wound

We have previously shown that positively charged beads (DEAE A25) increase wound breaking strength in linear incisions in rats and nonhuman primates at days 10-14 post-wounding. The increased wound strength may result in part from a stimulation of cells adjacent to the DEAE A25 beads to produce growth factors important for wound healing. In this report, we investigate this hypothesis by comparing the relative expression levels of transforming growth factor-beta1 and its receptor transforming growth factor-beta receptor type I in DEAE A25-treated and contralateral untreated rat linear incisions. DEAE A25-treated incisions were stronger than untreated control wounds at 3 days post-wounding, and the difference in breaking strength reached statistical significance at days 5, 7 and 10. Immunohistochemical analysis revealed a significant increase in transforming growth factor-beta1 and transforming growth factor-beta receptor type I expression in DEAE A25-treated incisions, up to 7 days post-wounding, as compared to untreated control wounds. FACS analysis revealed that macrophage cell lines exposed to DEAE A25 in vitro upregulate transforming growth factor-beta1 and transforming growth factor-beta receptor type I expression by 2-3 fold. Therefore, the increase in expression of transforming growth factor-beta1 and transforming growth factor-beta receptor type I in DEAE A25-treated incisions may be due to an increase in the concentration of macrophages adjacent to DEAE A25 beads, as well as the stimulation of individual macrophages to produce greater amounts of transforming growth factor-beta1 and transforming growth factor-beta receptor type I. This study also supports the significance of transforming growth factor-beta1 in wound healing.

Treatment of facial wounds with botulinum toxin A improves cosmetic outcome in primates

Surgeons have constantly sought to achieve the most aesthetic scar. A major factor determining the final cosmetic appearance of a cutaneous scar is the tension acting on the wound edges during the healing phase. Since Theodor Kocher pioneered the alignment of skin incisions with Langer's lines in 1892, surgical techniques that attempt to overcome closing tension have become standard. Yet, no treatment has been available to minimize underlying muscle contractions, which are the major cause of this tension. Botulinum toxin A is a potent drug that produces temporary muscular paralysis when injected locally. It has proven to be safe and effective in the treatment of a variety of disorders, including hyperkinetic facial lines. The objective of this randomized, double-blind, placebo-controlled primate study was to investigate the efficacy of a single injection of botulinum toxin A to improve the cosmetic appearance of cutaneous scars. Symmetric pairs of standardized excisions were performed on either side of the forehead of six primates. The half foreheads were randomized to the botulinum toxin A treatment side versus the placebo injection side. A panel of three blinded facial surgeons assessed the cosmetic appearance of the mature scars 3 months postoperatively. The wounds that had been immobilized with botulinum toxin A were rated as significantly better in appearance than the control wounds (p < 0.01). Histologic examination confirmed that all scars were mature. Blinded, randomized, placebo-controlled human clinical trials are presently under way at the Mayo Clinic.

Stimulation of wound healing by positively charged dextran beads depends upon clustering of beads and cells in close proximity to the wound

We have previously shown that positively charged dextran (DEAE A25) increases wound breaking strength in linear incisions in rats and nonhuman primates at days 10-14 postwounding. In this article, we examined the cellular responses to different types of charged dextran beads (DEAE A50 and Cytodex-1) in culture studies and in rat incisional wounds. We show that Cytodex 1 and DEAE A50 beads also increased wound breaking strength in a rat linear incisional model. However, the increase was approximately 30-40% less than that observed in wounds treated with DEAE A25 beads. The main distinction between the three types of beads was the presence of bead clusters observed in tissue sections. Wounds treated with DEAE A25 beads formed distinct clusters while both Cytodex 1 and DEAE A50 beads clustered to a lesser extent or failed to cluster at all. We propose that the different types of charged dextran beads improve healing by promoting cell adhesion and encouraging proliferation in close proximity to the wound. We also hypothesize that the 30-40% improvement in wound breaking strength seen with DEAE A25 beads compared to other types of charged dextran beads (DEAE A50 and Cytodex-1) originates from the unique characteristic of DEAE A25 beads in forming cell-bead aggregates adjacent to the wounded area. This clustering, in turn, affects the distribution of cells infiltrating the wounded area (such as macrophages) during the healing process and, as a consequence, alters the distribution of matrix molecules and growth factors secreted by these cells.