Pharmacokinetics of Ocriplasmin in Vitreous

PURPOSE. Ocriplasmin contains the active moiety of plasmin enzyme. At a physiologic pH, ocriplasmin is highly proteolytic and autolytic, limiting its duration of activity. Specific inhibitors of plasmin are present in the vitreous under normal and disease conditions and could affect its activity. Each may contribute to its mode of action. METHODS. Degradation characteristics were determined in porcine, human vitreous, and PBS under reducing conditions with different incubation periods between 0 and 24 hours on SDS-PAGE Tris-glycine gels. Residual activity was determined by spectrophotometry of p-nitroaniline release through hydrolysis of L-pyroglutamyl-L-phenylalanyl-L-lysine-p-nitroaniline hydrochloride. The presence of endogenous inactivators of ocriplasmin in human vitreous was determined in a series of vitreous samples using an ELISA specific for alpha(2)-antiplasmin, antithrombin, and antitrypsin. RESULTS. Degradation productions from autolysis are similar between vitreous and PBS with a significant prolongation of the effect in vitreous. Both follow a nonlinear pattern over time. The degradation corresponds best to a second-order kinetic process. The resulting rate constants were 207 +/- 60 M-1 s(-1) in PBS, 81 +/- 15 M-1 s(-1) in porcine vitreous, and 195 M-1 s(-1) in human vitreous natural inhibitors were identified in samples of donor vitreous. Amounts differed significantly between samples, which may help explain the observed variability in human subjects. CONCLUSIONS. Ocriplasmin is autolytic in vitreous. Biologic activity extends to several days following injection. The exact duration will vary based on the presence and concentration of serine protease inhibitors. (Invest Ophthalmol Vis Sci. 2012; 53: 8208-8213) DOI:10.1167/iovs.12-10148