Tacrolimus action pathways in an ointment base for hypertrophic scar prevention in a rabbit ear model()()

BACKGROUND: Tacrolimus is used to prevent unaesthetic scars due to its action on fibroblast activity and collagen production modulation. OBJECTIVES: To evaluate the action pathways, from the histopathological point of view and in cytokine control, of tacrolimus ointment in the prevention of hypertrophic scars. METHODS: Twenty-two rabbits were submitted to the excision of two 1-cm fragments in each ear, including the perichondrium. The right ear received 0.1% and 0.03% tacrolimus in ointment base twice a day in the upper wound and in the lower wound respectively. The left ear, used as the control, was treated with petrolatum. After 30 days, collagen fibers were evaluated using special staining, and immunohistochemistry analyses for smooth muscle actin, TGF-β and VEGF were performed. RESULTS: The wounds treated with 0.1% tacrolimus showed weak labeling and a lower percentage of labeling for smooth muscle actin, a higher proportion of mucin absence, weak staining, fine and organized fibers for Gomori's Trichrome, strong staining and organized fibers for Verhoeff when compared to controls. The wounds treated with 0.03% tacrolimus showed weak labeling for smooth muscle actin, a higher proportion of mucin absence, strong staining for Verhoeff when compared to the controls. There was absence of TGF-β and low VEGF expression. STUDY LIMITATIONS: The analysis was performed by a single pathologist. Second-harmonic imaging microscopy was performed in 2 sample areas of the scar. CONCLUSIONS: Both drug concentrations were effective in suppressing TGF-β and smooth muscle actin, reducing mucin, improving the quality of collagen fibers, and the density of elastic fibers, but only the higher concentration influenced elastic fiber organization.