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PurposeTo determine if dietary administration of the dual ETA/ ETB receptor antagonist, macitentan, could protect retinal ganglion cells (RGCs) following endothelin-1 (ET-1) mediated vasoconstriction in Brown Norway rats.MethodsAdult male and female Brown Norway rats were either untreated or treated with macitentan (5 mg/kg body weight) once a day for 3 days followed by intravitreal injection of either 4 μl of 500 μM ET-1 (2 nmole/eye) or vehicle in one eye. Imaging of the retinal vasculature using fluorescein angiography was carried out at various time points, including, 5, 10, 15, 25 and 30 minutes. Following the imaging of the vasculature, rats were either treated with macitentan (5 mg/kg/body weight in dietary gels) or untreated (control gels without medication). Following treatments, rats were euthanized, retinal flat mounts were prepared, immunostained for RGC marker Brn3a, imaged and surviving RGCs were counted in a masked manner.ResultsVasoconstrictive effects following intravitreal ET-1 injection were greatly reduced in rats administered with macitentan in the diet prior to the ET-1 administration. ET-1 intravitreal injection produced a 31% loss of RGCs which was significantly reduced in macitentan-treated rats. Following ET-1 administration, GFAP immunostaining was increased in the ganglion cell layer as well as in the retrolaminar region, suggestive of astrocytic activation by ET-1 administration. RGC numbers in macitentan treated and ET-1 injected rats were similar to that observed in control retinas.ConclusionsET-1-mediated neurodegeneration could occur through both vascular and cellular mechanisms. The endothelin receptor antagonist, macitentan, has neuroprotective effects in retinas of Brown Norway rats that occurs through different mechanisms, including, enhancement of RGC survival and reduction ET-1 mediated vasoconstriction.

Purpose Glaucoma is a neurodegenerative disease of the eye with an estimated prevalence of more than 111.8 million patients worldwide by 2040, with at least 6 to 8 million projected to become bilaterally blind. Clinically, the current method of slowing glaucomatous vision loss is to reduce intraocular pressure (IOP). In this manuscript, we describe the in vitro cytoprotective and in vivo long lasting IOP-lowering activity of the poly D, L-lactic-co-glycolic acid (PLGA) nanoparticle-encapsulated hybrid compound SA-2, possessing nitric oxide (NO) donating and superoxide radical scavenging functionalities. Methods Previously characterized primary human trabecular meshwork (hTM) cells were used for the study. hTM cells were treated with SA-2 (100 µM, 200 µM, and 1,000 µM), SA-2 PLGA-loaded nanosuspension (SA-2 NPs, 0.1%), or vehicle for 30 min. Cyclic guanosine monophosphate (cGMP) and super oxide dismutase (SOD) levels were analyzed using commercial kits. In another experiment, hTM cells were pretreated with tert-butyl hydrogen peroxide (TBHP, 300 µM) for 30 min followed by treatment with escalating doses of SA-2 for 24 h, and CellTiter 96 cell proliferation assay was performed. For the biodistribution study, the cornea, aqueous humor, vitreous humor, retina, choroid, and sclera were collected after 1 h of administration of a single eye drop (30 μl) of SA-2 NPs (1% w/v) formulated in PBS to rat (n = 6) eyes. Compound SA-2 was quantified using high performance liquid chromatography /mass spectrometry (HPLC/MS). For the IOP-lowering activity study, a single SA-2 NPs (1%) eye drop was instilled in normotensive rats eyes and in the IOP-elevated rat eyes (n = 3/group, in the Morrison model of glaucoma), or Ad5TGFβ2-induced ocular hypertensive (OHT) mouse eyes (n = 5/group). IOP was measured at various time points up to 72 h, and the experiment was repeated in triplicate. Mouse aqueous humor outflow facility was determined with multiple flow-rate infusion and episcleral venous pressure estimated with manometry. Results SA-2 upregulated cGMP levels (six- to ten-fold) with an half maximal effective concentration (EC50) of 20.3 µM in the hTM cells and simultaneously upregulated (40-fold) the SOD enzyme when compared with the vehicle-treated hTM cells. SA-2 also protected hTM cells from TBHP-induced decrease in cell survival with an EC50 of 0.38 µM. A single dose of slow-release SA-2 NPs (1% w/v) delivered as an eye drop significantly lowered IOP (by 30%) in normotensive and OHT rodent eyes after 3 h post-dose, with the effect lasting up to 72 h. A statistically significant increase in aqueous outflow facility and a decrease in episcleral venous pressure was observed in rodents at this dose at 54 h. Conclusions Hybrid compound SA-2 upregulated cGMP in hTM cells, increased outflow facility and decreased IOP in rodent models of OHT. Compound SA-2 possessing an antioxidant moiety provided additive cytoprotective activity to oxidatively stressed hTM cells by scavenging reactive oxygen species (ROS) and increasing SOD enzyme activity. Additionally, the PLGA nanosuspension formulation (SA-2 NPs) provided longer duration of IOP-lowering activity (up to 3 days) in comparison with the free non-encapsulated SA-2 drug. The data have implications for developing novel, non-prostaglandin therapeutics for IOP-lowering and cytoprotective effects with the possibility of an eye drop dosing regimen of once every 3 days for patients with glaucoma.