BACKGROUND: Netarsudil, a Rho kinase and norepinephrine transport (NET) inhibitor, is a new FDA approved drug used for decreasing raised intraocular pressure (IOP) in ocular hypertensive and primary open-angle glaucoma (POAG) patients. Previous studies reported that netarsudil increased outflow facility and lowered IOP by increasing active outflow areas around the circumference of the eye and dilating the episcleral veins (ESV; Kiel and Kopczynski, 2015; Ren et al., 2016). However, the mechanisms by which netarsudil increases outflow facility have not yet been fully elucidated. Moreover, the effects of netarsudil on the inner wall (IW) endothelium I-pores and B-pores of the Schlemm’s canal (SC) have also not been investigated yet.
AIM: The goal was to determine if netarsudil-treatment increased the effective filtration areas (EFA) by increasing pore density in both high- and non-flow type areas, compared to untreated control eyes.
METHODS: In this study, the effects of netarsudil on the pore densities on IW of SC were investigated by serial block-face scanning electron microscopy (SBF-SEM). Two pairs of eyes were perfused with green fluorescent tracers in order to determine the outflow pattern prior to treatment. Then, one eye of each pair was perfused with netarsudil, while the fellow eye of each pair was perfused with vehicle solution. All eyes were then perfused with red fluorescent tracers in order to determine the outflow pattern once they were treated with netarsudil. Both pairs of eyes were perfused and fixed at 15 mmHg. Global imaging was performed for all eyes to visualize high- and non- flow areas in the trabecular meshwork (TM) and ESV’s. A SBF-SEM was used to image eight wedges of tissue including the IW of SC and TM (high- and non-flow areas from four eyes) for a total of 16,378 images. The study analyzed the percentage of pore-types (GV-associated I-pores, Non-GV associated I-pores, B-pores), the median pore spans, the GV-associated I-pore locations, and the pore densities (per IW nuclei and IW area) between the equivalent control and netarsudil-treated flow areas.
RESULTS: In global images, an increase in high-flow areas were observed in netarsudil-treated eyes due to recruitment from low-flow and non-flow areas. A greater percentage of GV-associated I-pores, B-pores, and total pores were found in high-flow in contrast to non-flow areas in both control and netarsudil-treated eyes (all P ≤ 0.05). However, the percentage of GV-associated I-pores in non-flow areas were significantly greater in treated compared to control eyes (P ≤ 0.05). Qualitative observations from two pairs of eyes showed a trend of greater I-pore, B-pore, and total pore density/per IW nucleus and density/per IW surface area in high-flow in contrast to non-flow areas for both treated and control eyes. No difference in I-pore, B-pore, and total pore density/per IW nucleus and density /per IW surface area were observed in equivalent flow-type areas when comparing control and netarsudil-treated eyes. In addition, there was a significant greater percentage of I-pores located on the side of GVs than the top of GVs in all cases (P ≤ 0.05).
CONCLUSIONS: Netarsudil increased high-flow areas. A greater pore density was found in high-flow in contrast to non-flow areas. Netarsudil also significantly increased the proportion of GV-associated I-pores in non-flow areas when compared to control eyes. Our results suggests that one mechanism of netarsudil increasing outflow facility is acting through recruiting the high-flow areas around the circumference of the eye, which is associated with higher pore density and increasing the proportion of GV-associated I-pores in non-flow areas.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/43879 |
| Date | 11 February 2022 |
| Creators | Ramirez, Justin |
| Contributors | Gong, Haiyan |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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