Mechanisms of ocriplasmin uptake by retinal cells

Purpose Retinal cells participate in the transport and clearance of therapeutics. In this study, we used in vitro retinal cell models to investigate the uptake and transport of ocriplasmin, a protease used for the treatment of vitreomacular traction. Methods Cultures of primary porcine Müller and human ARPE‐19 cells were incubated with Alexa488‐labeled ocriplasmin or its inactive form for up to 3 h. Spatial distribution and colocalization with vesicle transport proteins were assessed at several time points. Results Ocriplasmin was rapidly detected in Müller and RPE cells. Uptake was observed as cytoplasmic foci and confirmed by confocal microscopy. In contrast, enzymatically inactive ocriplasmin was taken up at a significantly slower rate. Given its focal cytoplasmic distribution, we investigated whether ocriplasmin was present in cellular transport organelles. In Müller cells, ocriplasmin colocalized partly with Rab5‐positive early endosomes and Rab7‐positive lysosomes but with very few Rab11‐positive recycling endosomes. In RPE cells, ocriplasmin also colocalized in part with early endosomes and lysosomes, but to a larger extent with recycling endosomes. Conclusions Taken together, our data indicate that ocriplasmin can be taken up by Müller and RPE cells and that this uptake depends in part on its enzymatic activity. Ocriplasmin was found in transport vesicles, indicating active transport mainly through the degradation pathway in Müller cells whereas in RPE cells, outward transport is preferred. It is described that RPE cells transport anti‐VEGFs which emphasizes their role in retinal drug clearance. Our study suggests that retinal cells might participate in ocriplasmin drug clearance. Further in vivo studies will need to assess the ocriplasmin transport in the retina as well as the impact of uptake on ocriplasmin activity.