Transplantation of amniotic membrane improves experimental herpetic keratitis. Modulation of matrix metalloproteinase-9

Purpose. Transplantation of human amniotic membrane (AMT) accelerates the healing of experimental ulcerative herpetic keratitis. Here the expression and activity of matrix metalloproteinase (MMP)-9 was studied. Methods. BALB/c mice were corneally infected with HSV-1. Whereas the infected corneas of mice in group I were covered with AM, tarsorrhaphies were performed in others (group 2). After 2 days,the appearance of corneal ulcers and stromal inflammation was judged clinically, and the corneal PMN infiltration was studied histologically. The expression of MMP-9 in the corneas was localized by immunohistochemistry and analyzed by Western-blot technique. The MMP-9 activity in the corneas was determined by zymography. Results. On day 14,the ulcerating corneas had a dense PMN infiltration, the ulcers and the majority of PMNs were highly positive for MMP-9, and the active forms of MMP-9 were detected. Gelatinolytic activity was found in these corneas by zymography. Compared with the mice of group 2, ulceration, stromal inflammation and neovascularization markedly improved clinically and histologically within 2 days in mice of group 1. This was associated with a reduced expression of MMP-9 in corneal tissue and in PMNs. The gelatinolytic activity of MMP-9 was reduced after AMT Conclusions. These observations suggest that improvement of herpetic corneal ulcers and reduced corneal neovascularization after AMT may result from a reduced expression and activity of MMP-9.