Wound Debridement by Continuous Streaming of Proteolytic Enzyme Solutions: Effects on Experimental Chronic Wound Model in Porcin
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Chronic limb wounds are associated with tissue ischemia and are typical in patients with diabetes. Such wounds can lead to serious infection, gangrene, and limb loss. Chronic wounds are characterized by the presence of devitalized tissue that enhances bacterial growth, reduces host resistance to infection, and inhibits the formation of granulation tissue.1–3 Debridement of necrotic tissue is therefore, an essential and crucial step in chronic wound management.4–7 The main approaches to wound debridement are based on surgical, mechanical, enzymatic, or biological methods.3,6,8,9
Enzymatic removal of necrotic tissue from chronic wounds and burns by proteases primarily offers selectivity of debridement without impairing adjacent healthy tissue.10,11 Proteolytic enzymes for wound debridement are commercially available as ointments.10 The most frequently used products that contain papain are Accuzyme9 (Healthpoint, Fort Worth, Tex) and Panafil11,12 (Healthpoint, Fort Worth, Tex). Comparative preclinical and clinical studies on the efficacy of papain versus other enzyme ointments indicated that papain was the more effective enzyme from this group. 9,12-14
Papain is a proteolytic enzyme derived from the fruit of Carica papaya, and has been employed for decades in the food and pharmaceutical industries. Furthermore, it was used for many years for wound healing by natives in tropical countries.11,15 Papain is the best studied and most applied protease from the thiol protease family (proteases that have a thiol group playing an essential role in their catalytic mechanism). Therefore, the efficacy of papain’s proteolytic activity is dependent on maintaining its active site’s thiol group in its active form (protection from oxidation, complexation with certain metal ions, or regeneration and pH adjustment to 6–8 are commonly employed means). In many cases, thiol-containing compounds may restore reduced papain activity due to reactions involving its thiol group.
Wound debridement using papain-containing ointments is currently practiced with repeated topical applications over a period of 1–3 weeks. The procedure is both labor intensive and time consuming.12,14 A potential explanation for the reported low efficacy of this mode of papain application for wound debridement is that the environmental conditions created within wounds treated this way are suboptimal or inhibitory to full expression of its potential activity. These conditions include acidic pH values, competitive metal ions, proteases secreted in wound exudate, as well as diffusional limitations imposing limited access of papain to its targeted substrate sites.
The authors previously proposed and demonstrated feasibility of an alternative mode of delivery and application of proteolytic enzymes for wound debridement and cleansing: continuous controlled streaming of protease solutions onto a targeted treated area, providing optimal and controlled environmental conditions for full exploitation of the protease’s potential debridement activity.16 The efficacy of the streaming approach was successfully demonstrated in removal of coagulated blood and debridement of experimental burn wounds in small lab animals by a series of proteases.16
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