Neurovascular Unit: A New Target for Treating Early Stages of Diabetic Retinopathy

Retinopatía diabética; Neurodegeneración; Unidad neurovascularRetinopatia diabètica; Neurodegeneració; Unitat neurovascularDiabetic retinopathy; Neurodegeneration; Neurovascular unitThe concept of diabetic retinopathy as a microvascular disease has evolved and is now considered a more complex diabetic complication in which neurovascular unit impairment plays an essential role and, therefore, can be considered as a main therapeutic target in the early stages of the disease. However, neurodegeneration is not always the apparent primary event in the natural story of diabetic retinopathy, and a phenotyping characterization is recommendable to identify those patients in whom neuroprotective treatment might be of benefit. In recent years, a myriad of treatments based on neuroprotection have been tested in experimental models, but more interestingly, there are drugs with a dual activity (neuroprotective and vasculotropic). In this review, the recent evidence concerning the therapeutic approaches targeting neurovascular unit impairment will be presented, along with a critical review of the scientific gaps and problems which remain to be overcome before our knowledge can be transferred to clinical practice.This research was funded by grants from the Instituto de Salud Carlos III (DTS18/0163, PI19/01215, and ICI20/00129). The funders had no role in the design of the study; in the collection, analyses, or the interpretation of the data; in the writing of the manuscript, or in the decision to publish the results

Transcriptomic Analysis Reveals That Retinal Neuromodulation Is a Relevant Mechanism in the Neuroprotective Effect of Sitagliptin in an Experimental Model of Diabetic Retinopathy

Diabetic retinopathy; Sitagliptin; Synaptic signal transmissionRetinopatia diabètica; Sitagliptina; Transmissió del senyal sinàpticRetinopatía diabética; Sitagliptina; Transmisión de señal sinápticaSynaptic dysfunction and neuronal damage have been extensively associated with diabetic retinopathy (DR). Our group evidenced that chronic hyperglycemia reduces the retinal expression of presynaptic proteins, which are crucial for proper synaptic function. The aim of the study was to explore the effect of topically administered sitagliptin, an inhibitor of the enzyme dipeptidyl peptidase-4, on the retinal expression patterns of an experimental model of DR. Transcriptome analysis was performed, comparing the retinas of 10 diabetic (db/db) mice randomly treated with sitagliptin eye drops (10 mg/mL) twice daily and the retinas of 10 additional db/db mice that received vehicle eye drops. Ten non-diabetic mice (db/+) were used as a control group. The Gene Ontology (GO) and Reactome databases were used to perform the gene set enrichment analysis (GSEA) in order to explore the most enriched biological pathways among the groups. The most differentiated genes of these pathways were validated through quantitative RT-PCR. Transcriptome analysis revealed that sitagliptin eye drops have a significant effect on retinal expression patterns and that neurotransmission is the most enriched biological process. Our study evidenced enriched pathways that contain genes involved in membrane trafficking, transmission across chemical synapses, vesicle-mediated transport, neurotransmitter receptors and postsynaptic signal transmission with negative regulation of signaling as a consequence of neuroprotector treatment with sitagliptin. This improves the modulation of the macromolecule biosynthetic process with positive regulation of cell communication, which provides beneficial effects for the neuronal metabolism. This study suggests that topical administration of sitagliptin ameliorates the abnormalities on presynaptic and postsynaptic signal transmission during experimental DR and that this improvement is one of the main mechanisms behind the previously demonstrated beneficial effects.This research was funded by grants from the Ministerio de Economía y Competitividad (PID2019-104225RB-I00) and the Instituto de Salud Carlos III (DTS18/0163, PI19/01215 and ICI20/00129). The study funder was not involved in the design of the study

Caffeine and the Risk of Diabetic Retinopathy in Type 2 Diabetes Mellitus: Findings from Clinical and Experimental Studies

Caffeine intake; Tea consumption; Type 2 diabetesConsumo de cafeína; Consumo de té; Diabetes tipo 2Consum de cafeïna; Consum de te; Diabetis tipus 2The aim of this study was to assess the potential benefits of caffeine intake in protecting against the development of diabetic retinopathy (DR) in subjects with type 2 diabetes (T2D). Furthermore, we tested the effect of topical administration of caffeine on the early stages of DR in an experimental model of DR. In the cross-sectional study, a total of 144 subjects with DR and 147 individuals without DR were assessed. DR was assessed by an experienced ophthalmologist. A validated food frequency questionnaire (FFQ) was administered. In the experimental model, a total of 20 mice were included. One drop (5 μL) of caffeine (5 mg/mL) (n = 10) or vehicle (5 μL PBS, pH 7.4) (n = 10) was randomly administered directly onto the superior corneal surface twice daily for two weeks in each eye. Glial activation and retinal vascular permeability were assessed using standard methods. In the cross-sectional study in humans, the adjusted-multivariable model showed that a moderate and high (Q2 and Q4) caffeine intake had a protective effect of DR (odds ratio (95% confidence interval) = 0.35 (0.16–0.78); p = 0.011 and 0.35 (0.16–0.77); p = 0.010, respectively). In the experimental model, the administration of caffeine did not improve either reactive gliosis or retinal vascular permeability. Our results suggest a dose-dependent protective effect of caffeine in the development of DR, while the potential benefits of antioxidants in coffee and tea should also be considered. Further research is needed to establish the benefits and mechanisms of caffeinated beverages in the development of DR.This research was funded by grant PS09/01035 from Instituto de Salud Carlos III. N.A. and M.G-C. held a predoctoral fellowship from ISCIII (FI11/0008) and Ministerio de Educación, Cultura y Deporte (FPU15/03005), respectively. CIBER of Diabetes and Associated Metabolic Diseases (CIBERDEM; the current study was led by group CB15/00071) and CIBER Epidemiología y Salud Pública (CIBERESP) are an initiative from the Instituto de Salud Carlos III (Plan Nacional de I + D + I and Fondo Europeo de Desarrollo Regional)

Neuromodulation Induced by Sitagliptin: A New Strategy for Treating Diabetic Retinopathy

Presynaptic proteins; Retinal neurodegeneration; SitagliptinProteínas presinápticas; Neurodegeneración retiniana; SitagliptinaProteïnes presinàptiques; Neurodegeneració retiniana; SitagliptinaDiabetic retinopathy (DR) involves progressive neurovascular degeneration of the retina. Reduction in synaptic protein expression has been observed in retinas from several diabetic animal models and human retinas. We previously reported that the topical administration (eye drops) of sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, prevented retinal neurodegeneration induced by diabetes in db/db mice. The aim of the present study is to examine whether the modulation of presynaptic proteins is a mechanism involved in the neuroprotective effect of sitagliptin. For this purpose, 12 db/db mice, aged 12 weeks, received a topical administration of sitagliptin (5 μL; concentration: 10 mg/mL) twice per day for 2 weeks, while other 12 db/db mice were treated with vehicle (5 μL). Twelve non-diabetic mice (db/+) were used as a control group. Protein levels were assessed by western blot and immunohistochemistry (IHC), and mRNA levels were evaluated by reverse transcription polymerase chain reaction (RT-PCR). Our results revealed a downregulation (protein and mRNA levels) of several presynaptic proteins such as synapsin I (Syn1), synaptophysin (Syp), synaptotagmin (Syt1), syntaxin 1A (Stx1a), vesicle-associated membrane protein 2 (Vamp2), and synaptosomal-associated protein of 25 kDa (Snap25) in diabetic mice treated with vehicle in comparison with non-diabetic mice. These proteins are involved in vesicle biogenesis, mobilization and docking, membrane fusion and recycling, and synaptic neurotransmission. Sitagliptin was able to significantly prevent the downregulation of all these proteins. We conclude that sitagliptin exerts beneficial effects in the retinas of db/db mice by preventing the downregulation of crucial presynaptic proteins. These neuroprotective effects open a new avenue for treating DR as well other retinal diseases in which neurodegeneration/synaptic abnormalities play a relevant role.This research was funded by grants from the Ministerio de Economía y Competitividad (PID2019-104225RB-I00) and the Instituto de Salud Carlos III (DTS18/0163, PI19/01215, and ICI20/00129). The study funder was not involved in the design of the study