Memantine mitigates ROS/TXNIP/NLRP3 signaling and protects against mouse diabetic retinopathy: Histopathologic, ultrastructural and bioinformatic studies.

Diabetic retinopathy (DRET) triggers vision loss in adults, however, little therapeutic options are existing. Memantine is an anti-Alzheimer drug that antagonizes the activity of glutamate at N-methyl-D-aspartate (NMDA) receptors. Glutamate and thioredoxin-interacting protein (TXNIP) are known to be overexpressed in diabetic retinas and can produce activation of NOD-like receptor protein 3 (NLRP3) with subsequent secretion of interlukin-1ß. This study repurposed memantine for its neuroprotective effect in experimental DRET and tested its impact on ROS/TXNIP/NLRP3. In addition, KEGG pathway database and STRING database identified the protein-protein interaction between glutamate receptors and TXNIP/NLRP3. Male Swiss albino mice received alloxan (180 mg/kg) to induce DRET. After 9 weeks, we divided the mice into groups: (a) saline, (ii) DRET, (iii and iv) DRET + oral memantine (5 or 10 mg per kg) for 28 days. Then, mice were euthanized, and eyeballs were removed. Retinal samples were utilized for biochemical, histopathological, and electron microscopy studies. Retinal levels of glutamate, TXNIP, NLRP3 and interlukin-1ß were estimated using ELISA technique as well as retinal malondialdehyde. Histopathological and ultrastructural examination demonstrated that oral memantine attenuated vacuolization and restored normal retinal cell layers. Moreover, memantine reduced TXNIP, NLRP3, interleukin-1ß and MDA concentrations. These results provide evidence demonstrating memantine' efficacy in alleviating DRET via suppressing reactive oxygen species/TXNIP/NLRP3 signaling cascade. Therefore, memantine might serve as a potential therapy for retinopathy after adequate clinical research.

Protective Effect of Topiramate against Diabetic Retinopathy and Computational Approach Recognizing the Role of NLRP3/IL-1ß/TNF-α Signaling.

The possible impact of topiramate against diabetic retinopathy (DREN) and its molecular mechanisms in relation to the nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome has not been studied before. Thus, in the present study, we aimed to utilize a computational approach to investigate the possible protective effect of topiramate on experimental DREN and explore its impact on NLRP3/interlukin-1ß signaling and brain-derived neurotrophic factor (BDNF) expression. Male albino mice were distributed to four experimental groups and assigned the following categorizations: (i) saline, (ii) diabetic, (iii) diabetic + topiramate 10 mg/kg and (iv) diabetic + topiramate 30 mg/kg. We observed shrinkage of total retinal thickness and elevation in retinal glutamate, malondialdehyde, NLRP3 and interlukin-1ß but decreased glutathione (GSH) levels in the diabetic mice. Additionally, retinal ultra-structures in the diabetic group showed abnormalities and vacuolations in the pigmented epithelium, the photoreceptor segment, the outer nuclear layer, the inner nuclear layer and the ganglion cell layer (GCL). Mice treated with topiramate 10 or 30 mg/kg showed downregulation in retinal malondialdehyde, NLRP3 and interlukin-1ß levels; improvements in the retinal pathologies; enhanced immunostaining for BDNF and improved ultra-structures in different retinal layers. Overall, the current results suggest topiramate as a neuroprotective agent for DREN, and future studies are warranted to further elucidate the mechanism of its protective action.

Protective effect of metformin on rat diabetic retinopathy involves suppression of toll-like receptor 4/nuclear factor-k B expression and glutamate excitotoxicity.

Microvascular complications of diabetes mellitus are progressively significant reasons for mortality. Metformin (MET) is considered as the first-line therapy for type 2 diabetes patients, and may be especially beneficial in cases of diabetic retinopathy although the precise mechanisms of MET action are not fully elucidated. The current study was designed to inspect the antioxidant and modulatory actions of MET on DRET in streptozotocin-induced diabetic rats. The effect of MET on the toll-like receptor 4/nuclear factor kappa B (TLR4/NFkB), inflammatory burden and glutamate excitotoxicity was assessed. Twenty-four male rats were assigned to four experimental groups: (1) Vehicle group, (2) Diabetic control: developed diabetes by injection of streptozotocin (60 mg/kg, i.p.). (3&4) Diabetic + MET group: diabetic rats were left for 9 weeks without treatment and then received oral MET 100 and 200 mg/kg for 6 weeks. Retinal samples were utilized in biochemical, histological, immunohistochemical and electron microscopic studies. MET administration significantly decreased retinal level of insulin growth factor and significantly suppressed the diabetic induced increase of malondialdehyde, glutamate, tumor necrosis factor-α and vascular endothelial growth factor (VEGF). Further, MET decreased the retinal mRNA expression of NFkB, tumor necrosis factor-α and TLR4 in diabetic rats. The current findings shed the light on MET's efficacy as an adjuvant therapy to hinder the development of diabetic retinopathy, at least partly, via inhibition of oxidative stress-induced NFkB/TLR4 pathway and suppression of glutamate excitotoxicity.

Long-Term Visual, Refractive and Topographic Outcomes of "Epi-off" Corneal Collagen Cross-Linking in Pediatric Keratoconus: Standard versus Accelerated Protocol.

PURPOSE: To compare the visual, refractive and topographic outcomes of standard and accelerated corneal collagen cross-linking (CXL) in pediatric keratoconus patients. METHODS: Prospective, comparative observational study on 68 eyes of 35 pediatric keratoconus patients (<18 years). Patients were classified into two groups, group (I) included 34 eyes and received standard "Epi-Off" CXL (3 mW/cm2, 30 min.) and group (II) included 34 eyes and received accelerated "Epi-Off" CXL (9 mW/cm2, 10 min.). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent (SE), simulated keratometry (Sim K-1, Sim K-2, K-max, K-mean), cylindrical (CYL), pachymetry and Q-value were evaluated preoperatively and for 3 years postoperatively. RESULTS: Postoperative UDVA and CDVA did not significantly change in both groups after 3 years. Postoperative SE was increased significantly in accelerated CXL (p=0.012) with no significant change in the postoperative cylinder in both procedures. Standard CXL had greater "significant" effect in decreasing Sim K-1, K-max and K-mean. The mean reduction in postoperative corneal pachymetry (at thinnest location) was significant in standard CXL (18.4 µm) (p=0.001). No significant change was noticed in postoperative Q-value. CONCLUSION: Standard and accelerated CXL protocols are efficient in pediatric keratoconus management with better outcomes in the standard procedure.

Retinoprotective effect of donepezil in diabetic mice involves mitigation of excitotoxicity and activation of PI3K/mTOR/BCl2 pathway.

Donepezil (DNPZ) has shown neuroprotective effect in many disorders. The current study tested the putative retinoprotection provided by donepezil in mouse diabetic retinopathy. Swiss albino mice were allocated to, 1] saline control, 2] diabetic, 3&4] diabetic+DNPZ (1 or 4 mg/kg). After induction of diabetes, mice were maintained for 8 weeks then DNPZ therapy was launched for 28 days. Retinas were isolated and used for histopathology and immunohistochemistry for caspase 3 and the anti-apoptotic protein, B-cell lymphoma 2 (BCl2). Retinas were examined for glutamate, acetylcholine and oxidation markers. Western blot analysis measured inflammatory cytokines, N-methyl-d-aspartate receptors (NMDARs), phosphorylated and total phosphatidylinositol-3 kinase and mTOR, BCl2 and cleaved caspase 3. Significant histopathological changes and decreased thickness were found in diabetic retinas (125.52 ± 2.85 vs. 157.15 ± 7.55 in the saline group). In addition, retinal glutamate (2.39-fold), inflammatory cytokines and NMDARs proteins (4.9-fold) were higher in the diabetic retinas. Western blot analysis revealed low ratio of phosphorylated/total PI3K (0.21 ± 0.043 vs. 1 ± 0.005) and mTOR (0.18 ± 0.04 vs. 1 ± 0.005), low BCl2 (0.28 ± 0.06 vs. 1 ± 0.005) and upregulated cleaved caspase 3 (5.18 ± 1.27 vs. 1 ± 0.05 in the saline group) versus the saline control. DNPZ ameliorated the histopathologic manifestations and to prevent the decrease in retinal thickness. DNPZ (4 mg/kg) improved phosphorylation of PI3K (0.76 ± 0.12 vs. 0.21 ± 0.04) and mTOR (0.59 ± 0.09 vs. 0.18 ± 0.04) and increased BCl2 (0.75 ± 0.08 vs. 0.28 ± 0.06) versus the diabetic control group. This study explained the retinoprotective effect of DNPZ in mouse diabetic retinopathy and highlighted that mitigation of excitotoxicity, improving phosphorylation of PI3K/mTOR and increasing BCl2 contribute to this effect.