Terry E. Wright

Comparative evaluation of silver-containing antimicrobial dressings and drugs

Wound dressings containing silver as antimicrobial agents are available in various forms and formulations; however, little is understood concerning their comparative efficacy as antimicrobial agents. Eight commercially available silver‐containing dressings, Acticoat® 7, Acticoat® Moisture Control, Acticoat® Absorbent, Silvercel™, Aquacel® Ag, Contreet® F, Urgotol® SSD and Actisorb®, were tested to determine their comparative antimicrobial effectiveness in vitro and compared against three commercially available topical antimicrobial creams, a non treatment control, and a topical silver‐containing antimicrobial gel, Silvasorb®. Zone of inhibition and quantitative testing was performed by standard methods using Escherichia coli, Pseudomonas aeruginosa, Streptococcus faecalis and Staphylococcus aureus. Results showed all silver dressings and topical antimicrobials displayed antimicrobial activity. Silver‐containing dressings with the highest concentrations of silver exhibited the strongest bacterial inhibitive properties. Concreet® F and the Acticoat® dressings tended to have greater antimicrobial activity than did the others. Topical antimicrobial creams, including silver sulfadiazine, Sulfamylon and gentamicin sulfate, and the topical antimicrobial gel Silvasorb® exhibited superior bacterial inhibition and bactericidal properties, essentially eliminating all bacterial growth at 24 hours. Silver‐containing dressings are likely to provide a barrier to and treatment for infection; however, their bactericidal and bacteriostatic properties are inferior to commonly used topical antimicrobial agents.

Use of the wound healing trajectory as an outcome determinant for acute wound healing.

Accurate and clinically practical methods for measuring the progress of acute wound healing is necessary before interventions designed to optimize and even accelerate acute wound healing can be applied. Complete wound closure rates and operative wound closure severity are irrelevant to most acute wounds since most are closed at the time of primary tissue repair and remain closed throughout healing. Analogous to chronic wound closure, the rate of increase of incision tensile strength progressively decreases as time passes and 100% unwounded tissue strength is never achieved making the endpoint definition of “healed” vague. Conceptualizing acute wound healing in terms of its design elements with reintegration into a final outcome lends itself to the description of acute wound healing as a mathematical trajectory. Frequently such an equation is a rate expressing the change in an acute healing parameter, most often tensile strength, over time. Such an approach also normalizes misinterpretations in analysis or errors in theory developed by measuring healing parameters at fixed points in time. Distributions of fractional strength gain times (e.g., 85% normal strength) can be determined using statistical methodology similar that used for failure time of survival analysis. Preclinical studies show that acute wound healing trajectories can be shifted to the left from a “normal” or “impaired” curve to an accelerated or more “ideal” curve. A useful method for measuring acute wound healing outcomes is therefore required before the basic science of acute wound healing is inevitably applied to the problem of acute surgical wounds.

In vivo characterization of keratinocyte growth factor-2 as a potential wound healing agent.

Human keratinocyte growth factor‐2 exerts a proliferative effect on epithelial cells and mediates keratinocyte migration. It has also been shown to increase both deposition of granulation tissue and collagen and maturation of collagen. Because these properties should affect the healing trajectory of wounds, this study set out to investigate the effects of keratinocyte growth factor‐2 on the healing of three different types of wounds. Human meshed skin grafts explanted to athymic “nude” rats, surgical incisions in Sprague‐Dawley rats, and acute excisional rat wounds inoculated with Escherichia coli were used. Two concentrations of recombinant human keratinocyte growth factor‐2 were compared to a vehicle control and keratinocyte growth factor‐1. Keratinocyte growth factor‐2 significantly accelerated the rate of epithelialization in the meshed skin graft model and effected a modestly more rapid gain in breaking strength of surgical incisions than keratinocyte growth factor‐1 or the vehicle control treatment. Neither keratinocyte growth factors accelerated wound closure by contraction of the excisional wounds. Based on these data, keratinocyte growth factor‐2 may be useful in accelerating healing in wounds healing mainly by the process of epithelialization such as venous stasis ulcers, partial thickness burn wounds, and skin graft donor sites. It might also accelerate the gain in incisional wound strength in acute surgical or traumatic wounds.

Further evidence for the role of fibrosis in the pathobiology of rhinophyma.

Recent evidence suggests that fibrosis may play an important role in the pathobiology of rhinophyma. The fibrogenic cytokine transforming growth factor (TGF)-&bgr;2 has been reported to be up-regulated in rhinophyma tissue. Of the three common isoforms of TGF-&bgr;, TGF-&bgr;1 and TGF-&bgr;2 are considered fibrogenic, whereas TGF-&bgr;3 has antiscarring properties. To provide further evidence for the role of fibrosis in the pathobiology of rhinophyma, specimens from 8 patients with rhinophyma were compared with nine specimens of normal nasal skin. Immunohistochemistry was used to compare intensity levels of TGF&bgr;1 and TGF&bgr;3 proteins, and quantitative reverse transcription–polymerase chain reaction was used to determine messenger ribonucleic acid (mRNA) expression levels of TGF&bgr;1 and TGF&bgr;3. TGF-&bgr;1 was elevated significantly in rhinophyma tissue (p < 0.001), whereas TGF-&bgr;3 was no different in the rhinophyma specimens compared with normal nasal skin (p = 0.06). TGF&bgr;1 mRNA expression was five-fold higher in rhinophyma tissue compared with normal skin (p < 0.001). The mRNA expression of TGF-&bgr;3 was the same for both pathological and normal tissue (p < 0.09). These data, together with previously published observations, present further evidence that fibrosis mediated by the fibrogenic cytokines TGF&bgr;1 and TGF&bgr;2 play a role in the pathobiology of rhinophyma and suggest a means of treatment by neutralizing or down-regulating these cytokines.

Down-regulating causes of fibrosis with tamoxifen: a possible cellular/molecular approach to treat rhinophyma.

Fibrosis and proliferative scarring are prominent features of the severe forms of rhinophyma. Up-regulation of growth and fibroblast kinetics are hallmarks of fibrosis. Persistent overexpression or dysregulated activation of the fibrogenic isoforms of transforming growth factor β (TGF-β) is associated with the increased fibroblast function leading to fibrotic conditions such as rhinophyma. Tamoxifen, a synthetic nonsteroidal antiestrogen, can neutralize or down-regulate TGF-β. Fibroblast-populated collagen lattices (FPCLs) were constructed from fibroblasts cultured from rhinophyma or normal nasal skin. One-half of each set of FPCLs was treated with Tamoxifen. Lattice contraction was serially measured over 5 days, and the supernatants of the cultures were analyzed for TGF-β-2 by immunoassay. Tamoxifen significantly decreased fibroblast activity by decreasing contraction of the treated lattices (P < 0.05) and significantly decreased the production/secretion of TGF-β-2 by rhinophyma fibroblasts (P < 0.001). These results suggest a possible new cellular/molecular approach to the treatment of the fibrotic varieties of rhinophyma.

Amnion-derived cellular cytokine solution (ACCS) promotes migration of keratinocytes and fibroblasts.

Amnion-derived Multipotent Progenitor cells appear to be useful as adjuvants in wound healing. Amnion-derived multipotent progenitor cells secrete a unique combination of cytokines and growth factors, known as amnion-derived cellular cytokine solution (ACCS). In the skin, a cytokine communication network between mesenchymal and epithelial cells tightly controls keratinocyte and fibroblast migration, proliferation and differentiation–key determinants of wound healing. To evaluate the influence of ACCS on the migratory behavior of keratinocytes and fibroblasts, cell migration was assayed quantitatively using a Boyden chamber. Chemotactic migration activity of fibroblasts or keratinocytes through the membrane determined the influence of ACCS. In the presence of ACCS, fibroblasts and keratinocytes demonstrated a statistically significant (P < 0.05) increase in migration when compared with controls. These cell types, critical to normal wound healing, may be influenced to accelerate migration in wounds, thus accelerating wound repair/healing.

Plasma Tissue Factor Pathway Inhibitor Levels as a Marker for Postoperative Bleeding After Enoxaparin Use in Deep Vein Thrombosis Prophylaxis in Orthopedics and General Surgery

Low-molecular-weight heparins (LMWH) are widely used as antithrombotic prophylactic pharmaceutical agents in orthopedic and general surgery. Their antithrombotic characteristics are expressed by plasma mediators such as anti-Xa, anti-Ila, and increased release of tissue factor pathway inhibitor (TFPI) from vascular endothelium. The purpose of this clinical research is to study the relation between plasma levels of these mediators and postoperative bleeding. Forty-one consecutive patients undergoing hip or knee arthroplasty (n = 36) and colectomy (n = 5) received the standard enoxaparin (a LMWH) dose preoperatively (general surgery) or immediately postoperatively (orthopedic surgery). Major bleeding was defined as a postoperative drop of ≥ 5 g/dL) of hemoglobin. The authors observed that there was a linear relationship between an increase in free/total TFPI ratio levels and postoperative bleeding. When that ratio increased by >60%, the hemoglobin dropped to >5 g/dL (n = 13). This relationship between free/total TFPI ratio increase and postoperative bleeding was statistically significant (P < 0.001). Those who did not bleed (hemoglobin drop was less than 5 g/dL) (n = 28) had a ratio increase (if any) of less than 50%. However, the authors did not observe any statistical relationship between anti-Xa, anti-IIa, or prothrombin time and postoperative bleeding in patients receiving LMWH for deep vein thrombosis prophylaxis in orthopedic and general surgery patients. The authors recommend a pre- and postoperative ratio level measurement whenever major bleeding is anticipated, as adjustments of LMWH dose or frequency might be necessary.

Minoxidil and Wound Contraction

Minoxidil has been proposed as a potential topical inhibitor of wound contraction and proliferative scarring. Suggestions for this application are derived from in vitro investigations demonstrating inhibition of various fibroblastic functions. The purpose of this study was to attempt to establish in vivo support of these effects using an established animal model of wound contraction. Standardized cutaneous wounds were created on the dorsum of Sprague-Dawley rats, which were divided equally into six treatment groups. Wounds were treated daily after tracing their unhealed areas. On complete closure of the wounds, analyses of the contraction rates and tensile strength were performed for comparison among groups. Minoxidil did not demonstrate significant inhibition of wound contraction rates relative to either an inert vehicle, an active vehicle, or no treatment. Contrarily, as previously demonstrated in this animal model, silver sulfadiazine did demonstrate significant inhibition of wound contraction rates relative to both vehicles. No significant difference in tensile strength was demonstrated among groups. These observations do not support the proposed use of minoxidil as an “antifibrotic” agent.

Individualized, targeted wound treatment based on the tissue bacterial level as a biological marker

BACKGROUND The use of biologic markers to aid in individualizing wound treatment may help improve outcomes. A biologic marker that has been demonstrated to be predictive of healing in both chronic and acute wounds is wound tissue bacterial level. The objective of this study was to determine whether tissue bacterial level can be used to individualize wound treatment regimens with a stem-like cell-derived product. METHODS Amnion-derived cellular cytokine solution (ACCS) was topically applied to rat chronic wounds, and healing rates were measured. RESULTS Experimental wounds treated with ACCS demonstrated accelerated healing regardless of the tissue level of bacteria, compared with saline. As the level of tissue bacteria increased, the frequency of ACCS application required to obtain optimal results increased. CONCLUSIONS It appears that the biologic characteristic of tissue bacterial level can serve as a marker to predict the response of open granulating wounds treated with ACCS.