Polyphenol Metabolite Pyrogallol-O-Sulfate Decreases Microglial Activation and VEGF in Retinal Pigment Epithelium Cells and Diabetic Mouse Retina.

(Poly)phenol-derived metabolites are small molecules resulting from (poly)phenol metabolization after ingestion that can be found in circulation. In the last decade, studies on the impact of (poly)phenol properties in health and cellular metabolism accumulated evidence that (poly)phenols are beneficial against human diseases. Diabetic retinopathy (DR) is characterized by inflammation and neovascularization and targeting these is of therapeutic interest. We aimed to study the effect of pyrogallol-O-sulfate (Pyr-s) metabolite in the expression of proteins involved in retinal glial activation, neovascularization, and glucose transport. The expression of PEDF, VEGF, and GLUT-1 were analyzed upon pyrogallol-O-sulfate treatment in RPE cells under high glucose and hypoxia. To test its effect on a diabetic mouse model, Ins2Akita mice were subjected to a single intraocular injection of the metabolite and the expression of PEDF, VEGF, GLUT-1, Iba1, or GFAP measured in the neural retina and/or retinal pigment epithelium (RPE), two weeks after treatment. We observed a significant decrease in the expression of pro-angiogenic VEGF in RPE cells. Moreover, pyrogallol-O-sulfate significantly decreased the expression of microglial marker Iba1 in the diabetic retina at different stages of disease progression. These results highlight the potential pyrogallol-O-sulfate metabolite as a preventive approach towards DR progression, targeting molecules involved in both inflammation and neovascularization.

Dysregulation of trophic factors contributes to diabetic retinopathy in the Ins2Akita mouse.

Diabetic retinopathy (DR) is considered as a diabetes-related complication that can lead to severe visual impairments. By 2030, it is expected that 1 in 5 adults will suffer from the disease. Suitable animal models for chronic DR are essential for a better understanding of the pathophysiology and to further develop new treatments. The Ins2Akita mouse is a type 1 diabetes model that shows signs of both early and late stages of DR, including pericyte loss, increased vascular permeability, increased acellular capillaries and neovascularization. To further characterize DR in the Ins2Akita mouse model, we have evaluated the protein levels of the angiogenesis inducers vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) and the angiogenesis inhibitor pigment epithelium-derived factor (PEDF). Additionally, we have analyzed the protein expression profile of the glial markers ionized calcium binding adaptor molecule 1 (Iba1) and glial fibrillary acidic protein (GFAP) as well as of the chemokine monocyte chemoattractant protein 1 (MCP-1). In this study we demonstrate that, with disease progression, there is the development of an inflammatory response and an unbalanced expression of pro- and antiangiogenic factors in the neural retina and in the retinal pigment epithelium (RPE) of Ins2Akita mice. Therefore, our data provide support for the diabetic retinopathy features detected in the Ins2Akita retina, reflecting what is observed in the human pathology.

The role of the retinal pigment epithelium and Müller cells secretome in neovascular retinal pathologies.

Secreted trophic factors are key to maintain the structural and functional integrity of the retina, as they regulate cellular pathways responsible for survival, function, and response to injury. Nevertheless, these same factors can also be involved in retinal pathologies, as a consequence of the impairment of the secretory function of cells. The cells considered as major contributors to the retinal secretome are the retinal pigmented epithelium (RPE) and Müller cells. Their role in the pathophysiology of the most common neovascular pathologies in the retina - Age-related Macular Degeneration (AMD), Diabetic Retinopathy (DR), and Retinopathy of Prematurity (ROP) - is highlighted in this short review, together with current trophic factor-based therapies, which are mainly focused on controlling inflammation, cell survival, and angiogenesis.

Aliskiren decreases oxidative stress and angiogenic markers in retinal pigment epithelium cells.

There is growing evidence on the role of ocular renin-angiotensin system (RAS) in the development of diabetic retinopathy (DR), particularly due to the trigger of oxidative stress and angiogenesis. Despite this there is no effective RAS-based therapy in DR capable of preventing retinal damage induced by RAS activation. We recently described that retinal pigment epithelium (RPE) cells express the main components of the RAS. We here propose to investigate the role of glucose upon the retinal RAS and whether aliskiren, a direct renin inhibitor, protects RPE cells from angiogenesis and oxidative stress. RPE cells were chosen as target since one of the first events in DR is the dysfunction of the RPE retinal layer, which as a key function in maintaining the integrity of the retina. We found that the RAS present in the RPE cells was deregulated by hyperglycemic glucose concentrations. Exposure of RPE cells to angiotensin II increased the levels of the main pro-angiogenic factor, vascular endothelial growth factor (VEGF) in a concentration-dependent manner. Additionally, angiotensin II also stimulated the production of reactive oxygen species in RPE cells. Treatment of RPE cells with aliskiren decreased the levels of oxidative stress and promoted the expression of anti-angiogenic factors such as the pigment epithelium-derived factor and the VEGF165b isoform. Our findings demonstrate that the RAS is deregulated in hyperglycemic conditions and that aliskiren successfully protected RPE cells from RAS over activation. These anti-angiogenic and antioxidant properties described for aliskiren over RPE cells suggest that this drug has potential to be used in the treatment of diabetic retinopathy.

Aliskiren inhibits the renin-angiotensin system in retinal pigment epithelium cells.

Observations of increased angiotensin II levels and activation of the (pro)renin receptor in retinopathies support the role of ocular renin-angiotensin system (RAS) in the development of retinal diseases. While targeting RAS presents significant therapeutic potential, current RAS-based therapies are ineffective halting the progression of these diseases. A new class of drugs, the direct renin inhibitors such as aliskiren, is a potential therapeutic alternative. However, it is unclear how aliskiren acts in the retina, in particular in the retinal pigment epithelium (RPE), the structure responsible for the maintenance of retinal homeostasis whose role is deeply compromised in retinal diseases. We firstly analyzed the expression and activity of the main RAS components in RPE cells. Time- and concentration-dependent treatments with aliskiren were performed to modulate different pathways of the RAS in RPE cells. Our data demonstrate that RPE cells express the main RAS constituents. Exposure of RPE cells to aliskiren inhibited the activity of renin and consequently decreased the levels of angiotensin II. Additionally, aliskiren reduced the translocation of the (pro)renin receptor to the cellular membrane of RPE cells preventing the activation of ERK1/2. Our findings of the RPE well-defined RAS, together with the demonstration that aliskiren effectively blocks this system at different steps of the cascade, suggest that aliskiren might be an alternative and successful drug in preventing the deleterious effects derived from the overactivation of the RAS, known to contribute to the pathogenesis of different retinal diseases.

Nitric Oxide Regulates Neurogenesis in the Hippocampus following Seizures.

Hippocampal neurogenesis is changed by brain injury. When neuroinflammation accompanies injury, activation of resident microglial cells promotes the release of inflammatory cytokines and reactive oxygen/nitrogen species like nitric oxide (NO). In these conditions, NO promotes proliferation of neural stem cells (NSC) in the hippocampus. However, little is known about the role of NO in the survival and differentiation of newborn cells in the injured dentate gyrus. Here we investigated the role of NO following seizures in the regulation of proliferation, migration, differentiation, and survival of NSC in the hippocampus using the kainic acid (KA) induced seizure mouse model. We show that NO increased the proliferation of NSC and the number of neuroblasts following seizures but was detrimental to the survival of newborn neurons. NO was also required for the maintenance of long-term neuroinflammation. Taken together, our data show that NO positively contributes to the initial stages of neurogenesis following seizures but compromises survival of newborn neurons.