Metipranolol promotes structure and function of retinal photoreceptors in the rd10 mouse model of human retinitis pigmentosa

Metipranolol is a β-adrenergic receptor antagonist that is given orally for the treatment of hypertension and also applied topically to the cornea for treating glaucoma. It also inhibits nitrosative stress which has previously been shown to be the cause of cone photoreceptor death in retinitis pigmentosa. In this study, we tested the hypothesis that metipranolol protects photoreceptor structure and function in the mouse model rd10. At P35, compared with vehicle-treated rd10 mice in which rod degeneration was nearly complete, rd10 mice given daily subcutaneous injections of 40 mg/kg of metipranolol had reduction in markers of nitrosative stress, fewer TUNEL-positive cells, increased outer nuclear layer thickness, and substantially more staining for rhodopsin. This was accompanied by significantly higher mean scotopic and photopic electroretinogram b-wave amplitudes indicating improved photoreceptor function. At P50, metipranolol-treated rd10 mice had decreased 3-nitrotyrosine staining in the retina, increased immunostaining for cone arrestin, a marker for cone photoreceptors, and significantly higher scotopic and photopic b-wave amplitudes at the highest stimulus intensity compared with vehicle-treated mice. At P65, cone density was significantly higher in metipranolol-treated versus vehicle-injected rd10 mice. Metipranolol applied as eye drops promoted cone photoreceptor function in retinas of rd10 mice greater than subcutaneously injected metipranolol. The reduced nitrosative damage and rescue of functional loss of photoreceptors in rd10 mice suggests that metipranolol, a drug with established ocular safety and tolerability, may have potential for treating patients with retinitis pigmentosa.

Tyrosine kinase blocking collagen IV-derived peptide suppresses ocular neovascularization and vascular leakage

Vascular endothelial growth factor (VEGF)-neutralizing proteins provide benefit in several retinal and choroidal vascular diseases, but some patients still experience suboptimal outcomes, and the need for frequent intraocular injections is a barrier to good outcomes. A mimetic peptide derived from collagen IV, AXT107, suppressed subretinal neovascularization (NV) in two mouse models predictive of effects in neovascular age-related macular degeneration (NVAMD) and inhibited retinal NV in a model predictive of effects in ischemic retinopathies. A combination of AXT107 and the current treatment aflibercept suppressed subretinal NV better than either agent alone. Furthermore, AXT107 caused regression of choroidal NV. AXT107 reduced the VEGF-induced vascular leakage that underlies macular edema in ischemic retinopathies and NVAMD. In rabbit eyes, which are closer to the size of human eyes, intraocular injection of AXT107 significantly reduced VEGF-induced vascular leakage by 86% at 1 month and 70% at 2 months; aflibercept significantly reduced leakage by 69% at 1 month and did not reduce leakage at 2 months, demonstrating the longer effectiveness of AXT107. AXT107 reduced ligand-induced phosphorylation of multiple receptors: VEGFR2, c-Met, and PDGFRβ. Optimal signaling through these receptors requires complex formation with β₃ integrin, which was reduced by AXT107 binding to α_vβ₃ AXT107 also reduced total VEGFR2 levels by increasing internalization, ubiquitination, and degradation. This biomimetic peptide is a sustained, multitargeted therapy that may provide advantages over intraocular injections of specific VEGF-neutralizing proteins.