Effect of NADPH oxidase inhibitors in an experimental retinal model of excitotoxicity

Retinal pharmacodynamic and pharmacokinetic profile of cannabidiol in an in vivo model of retinal excitotoxicity

Cannabidiol (CBD) is one of the principal constituents of Cannabis Sativa with no psychoactive properties. CBD is a promising neuroprotective compound bearing anti-inflammatory and antioxidant properties. However, considering its low solubility, CBD delivery to the retina represents an unresolved issue. The first aim was to investigate the potential neuroprotective effects of CBD in an in vivo model of retinal excitotoxicity induced by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). Rats underwent intravitreal co-injection of AMPA (42 nmol) and CBD (10-4 M). The neuroprotective effect of CBD was investigated with histology and immunohistochemical evaluation of inflammatory and oxidative stress biomarkers. CBD reversed the AMPA-induced total retinal, inner nuclear layer and inner plexiform layer shrinkage and loss of amacrine cells. Moreover, CBD decreased the AMPA induced number of cleaved caspase-3, Iba-1 and nitrotyrosine (NT) positive cells. Based on this evidence, we developed a nanotechnological formulation of CBD to overcome critical issues related to its eye delivery. Particularly, nanostructured lipid carriers (NLC) loaded with CBD were prepared, optimized and characterized. Due to the optimal physicochemical characteristics, CBD-NLC3 has been selected and the in vitro release profile has been investigated. Additionally, CBD-NLC3 was topically administered to rats, and retinal CBD levels were determined. CBD-NLC3 formulation, after a single topical administration, efficiently delivered CBD in the retina (Cmax = 98 ± 25.9 ng/mg; Tmax = 60 min), showing a high translational value. In conclusion, these findings showed a good PD/PK profile of CBD warranting further pre-clinical and clinical evaluation of the new formulation for the treatment of retinal degenerative diseases.

Immunomodulatory and Antioxidant Drugs in Glaucoma Treatment

Glaucoma, a group of diseases characterized by progressive retinal ganglion cell loss, cupping of the optic disc, and a typical pattern of visual field defects, is a leading cause of severe visual impairment and blindness worldwide. Elevated intraocular pressure (IOP) is the leading risk factor for glaucoma development. However, glaucoma can also develop at normal pressure levels. An increased susceptibility of retinal ganglion cells to IOP, systemic vascular dysregulation, endothelial dysfunction, and autoimmune imbalances have been suggested as playing a role in the pathophysiology of normal-tension glaucoma. Since inflammation and oxidative stress play a role in all forms of glaucoma, the goal of this review article is to present an overview of the inflammatory and pro-oxidant mechanisms in the pathophysiology of glaucoma and to discuss immunomodulatory and antioxidant treatment approaches.

Oxidative Stress: A Suitable Therapeutic Target for Optic Nerve Diseases?

Optic nerve disorders encompass a wide spectrum of conditions characterized by the loss of retinal ganglion cells (RGCs) and subsequent degeneration of the optic nerve. The etiology of these disorders can vary significantly, but emerging research highlights the crucial role of oxidative stress, an imbalance in the redox status characterized by an excess of reactive oxygen species (ROS), in driving cell death through apoptosis, autophagy, and inflammation. This review provides an overview of ROS-related processes underlying four extensively studied optic nerve diseases: glaucoma, Leber's hereditary optic neuropathy (LHON), anterior ischemic optic neuropathy (AION), and optic neuritis (ON). Furthermore, we present preclinical findings on antioxidants, with the objective of evaluating the potential therapeutic benefits of targeting oxidative stress in the treatment of optic neuropathies.

A small molecule inhibitor of Nox2 and Nox4 improves contractile function after ischemia-reperfusion in the mouse heart

The NADPH oxidase enzymes Nox2 and 4, are important generators of Reactive oxygen species (ROS). These enzymes are abundantly expressed in cardiomyocytes and have been implicated in ischemia-reperfusion injury. Previous attempts with full inhibition of their activity using genetically modified animals have shown variable results, suggesting that a selective and graded inhibition could be a more relevant approach. We have, using chemical library screening, identified a new compound (GLX481304) which inhibits Nox 2 and 4 (with IC50 values of 1.25 µM) without general antioxidant effects or inhibitory effects on Nox 1. The compound inhibits ROS production in isolated mouse cardiomyocytes and improves cardiomyocyte contractility and contraction of whole retrogradely (Langendorff) perfused hearts after a global ischemia period. We conclude that a pharmacological and partial inhibition of ROS production by inhibition of Nox 2 and 4 is beneficial for recovery after ischemia reperfusion and might be a promising venue for treatment of ischemic injury to the heart.

Nox4-dependent upregulation of S100A4 after peripheral nerve injury modulates neuropathic pain processing

Previous studies suggested that reactive oxygen species (ROS) produced by NADPH oxidase 4 (Nox4) affect the processing of neuropathic pain. However, mechanisms underlying Nox4-dependent pain signaling are incompletely understood. In this study, we aimed to identify novel Nox4 downstream interactors in the nociceptive system. Mice lacking Nox4 specifically in sensory neurons were generated by crossing Advillin-Cre mice with Nox4^fl/fl mice. Tissue-specific deletion of Nox4 in sensory neurons considerably reduced mechanical hypersensitivity and neuronal action potential firing after peripheral nerve injury. Using a proteomic approach, we detected various proteins that are regulated in a Nox4-dependent manner after injury, including the small calcium-binding protein S100A4. Immunofluorescence staining and Western blot experiments confirmed that S100A4 expression is massively up-regulated in peripheral nerves and dorsal root ganglia after injury. Furthermore, mice lacking S100A4 showed increased mechanical hypersensitivity after peripheral nerve injury and after delivery of a ROS donor. Our findings suggest that S100A4 expression is up-regulated after peripheral nerve injury in a Nox4-dependent manner and that deletion of S100A4 leads to an increased neuropathic pain hypersensitivity.

Oxidative Stress and the Role of NADPH Oxidase in Glaucoma

Glaucoma is characterised by loss of retinal ganglion cells, and their axons and many pathophysiological processes are postulated to be involved. It is increasingly understood that not one pathway underlies glaucoma aetiology, but rather they occur as a continuum that ultimately results in the apoptosis of retinal ganglion cells. Oxidative stress is recognised as an important mechanism of cell death in many neurodegenerative diseases, including glaucoma. NADPH oxidase (NOX) are enzymes that are widely expressed in vascular and non-vascular cells, and they are unique in that they primarily produce reactive oxygen species (ROS). There is mounting evidence that NOX are an important source of ROS and oxidative stress in glaucoma and other retinal diseases. This review aims to provide a perspective on the complex role of oxidative stress in glaucoma, in particular how NOX expression may influence glaucoma pathogenesis as illustrated by different experimental models of glaucoma and highlights potential therapeutic targets that may offer a novel treatment option to glaucoma patients.

The endocannabinoid 2-arachidonoylglycerol and dual ABHD6/MAGL enzyme inhibitors display neuroprotective and anti-inflammatory actions in the in vivo retinal model of AMPA excitotoxicity

The endocannabinoid system has been shown to be a putative therapeutic target for retinal disease. Here, we aimed to investigate the ability of the endocannabinoid 2-arachidonoylglycerol (2-AG) and novel inhibitors of its metabolic enzymes, α/β-hydrolase domain-containing 6 (ABHD6) and monoacylglycerol lipase (MAGL), a) to protect the retina against excitotoxicity and b) the mechanisms involved in the neuroprotection. Sprague-Dawley rats, wild type and Akt2^-/- C57BL/6 mice were intravitreally administered with phosphate-buffered saline or (RS)-α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid hydrobromide (AMPA). 2-AG was intravitreally co-administered with AMPA in the absence and presence of AM251 or AM630 (cannabinoid 1 and 2 receptor antagonists, respectively) or Wortmannin [Phosphoinositide 3-Kinase (PI3K)/Akt inhibitor]. Inhibitors of ABHD6 and dual ABHD6/MAGL (AM12100 and AM11920, respectively) were co-administered with AMPA intravitreally in rats. Immunohistochemistry was performed using antibodies raised against retinal neuronal markers (bNOS), microglia (Iba1) and macroglia (GFAP). TUNEL assay and real-time PCR were also employed. The CB2 receptor was expressed in rat retina (approx. 62% of CB1 expression). 2-AG attenuated the AMPA-induced increase in TUNEL⁺ cells. 2-AG activation of both CB1 and CB2 receptors and the PI3K/Akt downstream signaling pathway, as substantiated by the use of Akt2^-/- mice, afforded neuroprotection against AMPA excitotoxicity. AM12100 and AM11920 attenuated the AMPA-induced glia activation and produced a dose-dependent partial neuroprotection, with the dual inhibitor AM11920 being more efficacious. These results show that 2-AG has the pharmacological profile of a putative therapeutic for retinal diseases characterized by neurodegeneration and neuroinflammation, when administered exogenously or by the inhibition of its metabolic enzymes.

Effect of acute and subchronic administration of (R)-WIN55,212-2 induced neuroprotection and anti inflammatory actions in rat retina: CB1 and CB2 receptor involvement

Cannabinoids have been shown to protect the retina from ischemic/excitotoxic insults. The aim of the present study was to investigate the neuroprotective and anti-inflammatory properties of the synthetic cannabinoid (R)-WIN55,212-2 (CB1/CB2 receptor agonist) when administered acutely or subchronically in control and AMPA treated retinas. Sprague-Dawley rats were intravitreally administered (acutely) with vehicle or AMPA, in the absence or presence of (R)-WIN55,212-2 (10^-7-10^-4M) alone or in combination with AM251 [CB1 receptor antagonist/inverse agonist,10^-4M] and AM630 (CB2 receptor antagonist,10^-4M). In addition, AMPA was co-administered with the racemic (R,S)-WIN55,212 (10^-4Μ). (R)-WIN55,212-2 was also administered subchronically (25,100 μg/kg,i.p.,4d) in control and AMPA treated rats. Immunohistochemical studies were performed using antibodies against the CB1R, and retinal markers for retinal neurons (brain nitric oxide synthetase, bNOS) and microglia (ionized calcium binding adaptor molecule 1, Iba1). ELISA assay was employed to assess TNFα levels in AMPA treated retinas. Intravitreal administration of (R)-WIN55,212-2 reversed the AMPA induced loss of bNOS expressing amacrine cells, an effect that was blocked by both AM251 and AM630. (R,S)WIN55,212 had no effect. (R)-WIN55,212-2 also reduced a) the AMPA induced activation of microglia, by activating CB2 receptors that were shown to be colocalized with Iba1⁺ reactive microglial cells, and b) TNFα levels in retina. (R)-WIN55,212-2 administered subchronically led to the downregulation of CB1 receptors at the high dose of 100 μg/kg(i.p.), and to the attenuation of the WIN55,212-2 induced neuroprotection of amacrine cells. At the same dose, (R)-WIN55,212-2 did not attenuate the AMPA induced increase in the number of reactive microglia cells, suggesting CB2 receptor downregulation under subchronic conditions. This study provides new findings regarding the role of CB1 and CB2 receptor activation by the synthetic cannabinoid (R)-WIN55,212-2, administered acutely or sub-chronically, on neuron viability and microglia activation in healthy and diseased retina.