The Inhibiting Effect Of Botulinum Toxin Type A On Scar Contracture In Rabbit Ears Model

OBJECTIVE Some studies have suggested that BTXA has certain therapeutic effect, can promote apoptosis of fibroblasts, reduce collagen synthesis in hypertrophic scar. Through the establishment of rabbit ear hypertrophic scar model , early injection of BTXA in wound, dynamic observation of effect of BTXA on wound contraction﹑scar formation and proliferation of myofibroblasts (or a-Smactin expression) , this study is aimed to investigate the mechanism of scar contractrue and provide theoretical basis and a effective way of preventing sar contractrue.METHODS①twenty-four healthy purebred adult New Zealand rabbits of either weighting 2.5±0.3 kg,were taken as experimental animals and divided randomly into saline group,BTXA group and triamcinolone acetonide group .Each group contained 8 rabbits with 32 wounds.②The scar models in rabbit ears were reproduced after one week when the rabbits were fed for. Two wounds with 2㎝×2㎝ areas were created down to bare cartilage on the ventral surface of each ear .There were 32 wounds surfaces in each group.Each scar in saline group was received saline solution injection with dose of 0.3ml ,and in triamcinolone acetonide group triamcinolone acetonide injection with dose of 0.3ml(2mg) at 1,2,3,4 weeks after operation respectively.Eath scar in BTXA group was received BTXA injection with dose of 0.3ml(3IU) at 1,2 weeks after operation。③On days 16,30,40,60 after modeling ,the color of scar tissue ,change of texture and healing of wound surface were observed , the hypertrophic index (HI) and scar areas were measured,the a-Smactin expression of myofibroblasts were detected by immunohistochemical method in each scar tissue.RESULTS twenty-four experimental rabbits were involved in the final analysis.①BTXA and triamcinolone acetonide may reduce the scar formation of rabbit ears. There were significant difference to compare hypertrophic index (HI) beteen the saline group and the two others(P <0.05), there were significant difference to compare hypertrophic index (HI) beteen the BTXA group and the triamcinolone acetonide group (P <0.05) .②BTXA and triamcinolone acetonide can reduce the scar contraction of rabbit ears. There were significant difference to compare the scar area beteen the saline group and the two others(P <0.05), there were significant difference to compare scar area beteen the BTXA group and the triamcinolone acetonide group (P <0.05).③The proliferation of fibroblasts and myofibroblasts was obviously inhibited and the contents of collagen fiber were decreased in TXA group and triamcinolone acetonide group than that of collagen fiber in saline group under a optical microscope in Hematoxylin-eosin (HE),Van Gieson(VG) and immunohistochemical staining. Compared with the saline group,the dermise of the scar in BTXA group and triamcinolone acetonide group was thinner,collagen fibers well-arranged and no significant collagen node. Meanwhile , a great deal of fibroblasts,myofibroblasts,collagen fibers and collagen node were found in the saline group .④The optical density of theα-SMA protein (brown-yellow granules) in each scar slice were measured after 16 and 60 day ,the results show that theα- SMA protein expression is high in saline group, less in BTXA group, lowest in the triamcinolone acetonide group. The difference was statistically significant to compare the optical density of theα-SMA protein among three groups (P <0.05).CONCLUSION BTXA could inhibit the formation and contracture of hypertrophic scar in rabbit ears through inhibiting the proliferation of fibroblast and myofibroblasts ,decreasing the contents of collagen fibers . The inhibiting effect of BTXA is less than that of triamcinolone acetonide on scar contracture in rabbit ear.