Glaucoma is a progressive and degenerative disease of the retina and one of the leading causes of vision loss in the world, with estimates suggesting it will affect approximately 111.8 million people by 2040 (Tham et al., 2014). With the rapid aging of the population in developing countries, the number of individuals with glaucoma tends to increase, worsening the socioeconomic burden of the disease. Elevated intraocular pressure (IOP) is a major risk factor in glaucoma, particularly for optic nerve damage and the death of retinal ganglion cells (RGCs). Topical administration of drugs aimed at controlling IOP is currently the first line of treatment. However, these treatments are limited by poor patient compliance, low bioavailability, and the potential to cause local and systemic side effects, reinforcing the urgent need to identify new drug delivery platforms. Additionally, current therapy has low efficacy, as patients continue to lose vision despite efficient IOP control. Therefore, new and more effective treatments are needed, and the neuroprotection of RGCs may have potential as an additional therapy (Cordeiro and Levin, 2011).
Adenosine is a neuromodulator in the central nervous system that acts on adenosine A1, A2A, A2B, and A3 receptors (Gomes et al., 2011). The activation of the adenosine A3 receptor (A3R) confers protection against various insults. In the retina, RGCs express A3R and the activation of this receptor confers protection to RGCs after an excitotoxic stimulus (Zhang et al., 2006a; Zhang et al., 2010). In our laboratory, results have also been obtained showing the neuroprotective potential of A3R activation. Our results show that A3R activation confers protection to mixed retinal and organotypic cultures (Figs. 1-2). Furthermore, we observed protection of RGCs after a single intravitreal injection of 2-Cl-IB-MECA (a selective A3R agonist) in animal models of RGC degeneration (intravitreal DMSO, retinal ischemia-reperfusion, and partial optic nerve transection) (Figs. 3-5). Moreover, in the retinas of animals with ocular hypertension (OHT), a decrease in A3R expression was observed, and the intravitreal administration of 2-Cl-IB-MECA decreased the IOP in these animals (Fig. 6). Overall, our results clearly support the protection of RGCs by A3R activation against glaucomatous damage. However, since glaucoma is a chronic disease, this treatment would require multiple intravitreal injections. This route of administration presents potential side effects, limiting its use, especially in the treatment of chronic diseases. Controlled drug release mechanisms have been developed to overcome these limitations; such systems can achieve prolonged therapeutic drug concentrations in target ocular tissues, limiting systemic exposure and side effects. Ultimately, in clinical use, these systems can improve patient adherence to therapy.
In this project, the main objective is to investigate the neuroprotective potential of A3R activation in glaucoma, using in vitro and in vivo models. RGC and retinal organotypic cultures will be exposed to elevated hydrostatic pressure (to mimic increased IOP). Furthermore, we intend to investigate the effects of A3R activation in a chronic animal model of glaucoma. To reduce side effects and improve the half-life of 2-Cl-IB-MECA, implants composed of poly(ε-caprolactone) (PCL) with 2-Cl-IB-MECA will be prepared. This preparation will be carried out using a supercritical CO2 extraction method and will be fully characterized by a wide variety of analytical techniques and in vitro assays in order to select the most promising implant. The efficacy and safety of the PCL implants with 2-Cl-IB-MECA will be evaluated in vitro before surgical implantation into the vitreous of animals with OHT. RGC death and optic nerve degeneration, two characteristics of glaucoma, will be evaluated in vivo using non-invasive techniques.
The electrical activity of the retina will be evaluated by electroretinography, allowing for the functional assessment of the retina through a non-invasive approach. Histological analysis of the retina will be performed by immunohistochemistry on cryosections. The efficacy and safety of the implants will also be evaluated in human retinal organotypic cultures. This is an innovative interdisciplinary project aimed at investigating the neuroprotective properties of A3R activation in glaucoma models. Furthermore, a new approach involving an intravitreal implant for controlled drug release will be used to overcome the limitations of repeated intravitreal injections. This project involves a multidisciplinary team and may result in the development of new therapeutic strategies for treating glaucoma patients, in addition to IOP-lowering therapy.
