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Kevin Wu, Ruiyi Ren, Guorong Li, Casey Kopczynski, W Daniel Stamer, Haiyan Gong; Netarsudil increases size of giant vacuoles in Schlemm’s canal of perfused human eyes. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1074.
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© ARVO (1962-2015); The Authors (2016-present)
Phase 3 clinical trials of Netarsudil, an inhibitor of Rho kinase/norepinephrine transporter, have shown promising results as a potential new treatment for glaucoma. Netarsudil lowers intraocular pressure primarily by increasing trabecular outflow facility; however, the mechanisms by which outflow facility is increased have yet to be fully elucidated. This study tested the hypothesis that one mechanism by which Netarsudil increases outflow facility is through its effects on giant vacuole (GV) formation along the inner wall of Schlemm’s Canal (SC).
Five pairs of normal human eyes were perfused with phosphate buffered saline containing 5.5mM glucose (GPBS) at 15 mmHg to establish a stable baseline. One eye of each pair was then exchanged (5mL) and perfused with 0.3μM Netarsudil-M1, the active metabolite of Netarsudil, for 3 hours, while the contralateral eye was treated with vehicle in GPBS. After tracer labeling of the outflow pattern, perfusion-fixation and sample processing, 2μm frontal sections were obtained from high and low tracer regions of each eye. Light microscope images were taken using a 40x objective along the inner wall of SC. ImageJ was used to measure the density and cross-sectional area (size) for each GV. Student T-test, nonparametric Mann-Whitney U test, linear regression and chi square test were performed with a required significance of p < 0.05.
A total of 2787 GVs were analyzed between the controls (1554 GVs) and Netarsudil treated eyes (1233 GVs). No significant difference in density of GVs was found between untreated and treated eyes (p=0.22). The average size of GVs in Netarsudil treated eyes (15.2 ± 1.3μm2) were significantly larger than in control eyes (11.0±1.3μm2, p<0.05). The percentage of GV ≥35μm2 (the size required for pore formation by another study in the lab) is significantly increased after Netarsudil treatment (9.89% vs. 5.60%, p<0.001). There is a significant positive correlation between GV size and percentage change in outflow facility (p=0.02).
Our results suggest that one of the mechanisms by which Netarsudil increases outflow facility is through increasing the size of GVs, especially the prevalence of GVs ≥ 35μm2. This is the first time a drug-induced change in SC has been directly correlated with an increase in outflow facility.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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