Relationships between Intraocular Pressure, Effective Filtration Area, and Morphological Changes in the Trabecular Meshwork of Steroid-Induced Ocular Hypertensive Mouse Eyes

Segmental Unconventional Outflow in Mouse Eyes

Purpose

To investigate the flow pattern in unconventional outflow and its correlation with conventional outflow in mouse eyes.

Methods

Fluorescent microspheres were injected into the anterior chamber of one eye of anesthetized C57BL/6J mice (n = 4), followed by perfused fixation with 4% paraformaldehyde in situ after 45 minutes. Post-euthanasia, the injected eyes were enucleated, further immersion fixed, and dissected into 12 equal radial segments. Both sides of each segment were imaged using a confocal microscope after nuclear counterstaining. Both unconventional and conventional outflow patterns of each eye were analyzed by ImageJ and ZEN 2.3 imaging software.

Results

Segmental outflow patterns were observed in both the ciliary body (CB) and the supraciliary space and suprachoroidal space (SCS). In the CB, the tracer intensity was the lowest at 12 o'clock and highest at 9 o'clock, whereas in the SCS it was the lowest at 2 o'clock and the highest at 10 o'clock. Consequently, a segmental unconventional outflow was observed, with the lowest and highest flow regions in the superior and temporal quadrants, respectively. The overall segmental uveoscleral outflow has no correlation with trabecular outflow (P > 0.05). Four different outflow patterns were observed: (1) low-flow regions in both outflows, (2) primarily a high-flow region in conventional outflow, (3) primarily a high-flow region in unconventional outflow, and (4) high-flow regions in both outflows.

Conclusions

Uveoscleral outflow is segmental and unrelated to the trabecular segmental outflow. These findings will lead to future studies to identify the best location for the placement of drainage devices and drug delivery.

Modulation of Mitochondrial Metabolic Parameters and Antioxidant Enzymes in Healthy and Glaucomatous Trabecular Meshwork Cells with Hybrid Small Molecule SA-2

Oxidative stress (OS)-induced mitochondrial damage is a risk factor for primary open-angle glaucoma (POAG). Mitochondria-targeted novel antioxidant therapies could unearth promising drug candidates for the management of POAG. Previously, our dual-acting hybrid molecule SA-2 with nitric oxide-donating and antioxidant activity reduced intraocular pressure and improved aqueous humor outflow in rodent eyes. Here, we examined the mechanistic role of SA-2 in trabecular meshwork (TM) cells in vitro and measured the activity of intracellular antioxidant enzymes during OS. Primary human TM cells isolated from normal (hNTM) or glaucomatous (hGTM) post-mortem donors and transformed glaucomatous TM cells (GTM-3) were used for in vitro assays. We examined the effect of SA-2 on oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in vitro using Seahorse Analyzer with or without the oxidant, tert-butyl hydroperoxide (TBHP) treatment. Concentrations of total antioxidant enzymes, catalase (CAT), malondialdehyde (MDA), and glutathione peroxidase (GPx) were measured. We observed significant protection of both hNTM and hGTM cells from TBHP-induced cell death by SA-2. Antioxidant enzymes were elevated in SA-2-treated cells compared to TBHP-treated cells. In addition, SA-2 demonstrated an increase in mitochondrial metabolic parameters. Altogether, SA-2 protected both normal and glaucomatous TM cells from OS via increasing mitochondrial energy parameters and the activity of antioxidant enzymes.

Rho Kinase Inhibitor AR-12286 Reverses Steroid-Induced Changes in Intraocular Pressure, Effective Filtration Areas, and Morphology in Mouse Eyes

Purpose

We investigated mechanisms of reduction of intraocular pressure (IOP) by Rho kinase inhibitor AR-12286 in steroid-induced ocular hypertension (SIOH).

Methods

C57BL/6 mice (N = 56) were randomly divided into Saline, dexamethasone (DEX), DEX + AR-12286, and DEX-discontinuation (DEX-DC) groups. IOP was measured weekly during the first four weeks in all groups. Beginning at week 5, the DEX-DC group was followed without treatment until IOP returned to normal, and the other groups were treated as assigned with IOP measured every other day for another week. Fluorescent tracer was injected into the anterior chamber to visualize the outflow pattern in the trabecular meshwork (TM) and TM effective filtration area (EFA) was determined. Radial sections from both high- and low-tracer regions were processed for electron microscopy.

Results

AR-12286 reduced IOP in SIOH mouse eyes in one day (P < 0.01). At the end of week 5, mean IOP in the DEX + AR-12286 group was ∼4 mm Hg lower than DEX group (P < 0.001) and ∼2 mm Hg lower than DEX-DC group (P < 0.05). After one-week AR-12286 treatment (P < 0.05) or five-week DC of DEX (P < 0.01), DEX-induced reduction of EFA was rescued and DEX-induced morphological changes in the TM were partially reversed.

Conclusions

AR-12286 reversed steroid-induced morphological changes in the TM and reduced EFA, which correlated with reduced IOP in SIOH eyes. AR-12286 reduced IOP elevation in SIOH eyes more effectively than discontinuing DEX treatment even when accompanied by continuous DEX treatment. Therefore Rho kinase inhibitors may lower SIOH in patients who rely on steroid treatment.

Metformin protects trabecular meshwork against oxidative injury via activating integrin/ROCK signals

This study aimed to investigate the protective effect of metformin on trabecular meshwork (TM) and explore its molecular mechanisms in vivo and in vitro. Ocular hypertension (OHT) mouse models were induced with dexamethasone and further treated with metformin to determine the intraocular pressure (IOP)-lowering effect. Cultured human TM cells (HTMCs) were pre-stimulated with tert-butyl hydroperoxide (tBHP) to induce oxidative damage and then supplemented with metformin for another 24 hr. The expression of fibrotic markers and integrin/Rho-associated kinase (ROCK) signals, including α-smooth muscle actin (α-SMA), transforming growth factor-β (TGF-β), fibronectin, integrin beta 1, ROCK 1/2, AMP-activated protein kinase, myosin light chain 1, and F-actin were determined by western blotting and immunofluorescence. Reactive oxygen species (ROS) content was analysed using flow cytometry. Transmission electron microscopy was performed to observe microfilaments in HTMCs. It showed that metformin administration reduced the elevated IOP and alleviated the fibrotic activity of aqueous humour outflow in OHT models. Additionally, metformin rearranged the disordered cytoskeleton in the TM both in vivo and in vitro and significantly inhibited ROS production and activated integrin/ROCK signalling induced by tBHP in HTMCs. These results indicated that metformin reduced the elevated IOP in steroid-induced OHT mouse models and exerted its protective effects against oxidative injury by regulating cytoskeleton remodelling through the integrin/ROCK pathway. This study provides new insights into metformin use and preclinical evidence for the potential treatment of primary open-angle glaucoma.