Efficient vitreolysis by combining plasmin and sulfur hexafluoride injection in a preclinical study in rabbit eyes

PURPOSE To investigate the efficacy of plasmin and sulfur hexafluoride (SF(6)) on the vitreoretinal junction, as well as the long-term safety in the eye and effect on the recipient's general health after application in the eye. METHODS The study design included four groups of rabbits with three animals in each group. Group 1 received an intravitreal injection (IVI) of plasmin and SF(6) in the right eye; group 2 received an IVI of plasmin in the right eye; group 3 received an IVI of SF(6) in the right eye; and group 4 received an IVI of balanced salt solution in the right eye, which served as a normal control. Long-term safety (up to approximately three months) after plasmin and/or SF(6) injection was evaluated morphologically by clinical examination, histology, and immunohistochemistry, and functionally by electroretinograms (ERGs). General health evaluations after intravitreal injection included the assessment of weight gain, food intake, body temperature, and complete blood count analysis. RESULTS Plasmin plus SF(6) injection resulted in complete posterior vitreous detachment (PVD), whereas plasmin or SF(6) injection alone resulted in only partial PVD. Balanced salt solution did not induce PVD. Eighty days after intravitreal injection, there were no major differences among the eyes of the three groups of animals compared with the normal control animals upon clinical evaluation, or regarding retinal morphology and ERGs. The lenses examined remained clear for up to 80 days following the intravitreal injection of plasmin plus SF(6), except one eye in the plasmin-treated group. ERGs decreased transiently one week after intravitreal injection in groups 1 through 3, but animals recovered fully to normal status afterward. General health was not affected after the injection of plasmin plus SF(6). CONCLUSIONS Efficient vitreoretinal separation could be achieved, and an acceptable long-term safety profile was noted after plasmin plus SF(6) injection in the eye. No major ocular toxicity or systemic toxicity was found after the injection of plasmin plus SF(6). These results provide good support for the future clinical use of plasmin plus SF(6) for treatment of a variety of vitreoretinopathies.