Neurodegeneration in the diabetic eye: new insights and therapeutic perspectives

Functional diabetic retinopathy: A new concept to improve management of diabetic retinal diseases

Multifocal functional tests are not routinely performed in diabetic retinopathy (DR) and diabetic macular edema (DME) management. We emphasise their importance and coin the term functional diabetic retinopathy (FDR). We reviewed current guidelines on management of DR/DME, and literature on diabetic retinal neurodegeneration (DRN) and functional deficits in DR/DME. Functional visual loss due to DRN precedes vasculopathy and clinical DR; however, currently the diagnosis and management of DR/DME are based on classical signs of retinal vasculopathy and structural changes shown by funduscopy, fundus photographs, and optical coherence tomography (OCT). Furthermore, DME can mask DRN-based retinal layer thinning by OCT and is focussed on the macular region. The only functional test recommended in national and international guidelines on DR/DME is best-corrected visual acuity, a test of foveal function (<1 % of retina). Multifocal functional tests can objectively characterize both foveal and extrafoveal, localized and global, function. Current recommendations for DR/DME screening are inadequate to detect FDR affecting the greater retina. Early detection of FDR using multifocal functional tests could bring DR/DME management strategies forward enabling prevention of the later stage vision-threatening complications. After all, the end point of patient care is functional outcomes.

The adaptive immune system in the retina of diabetics

As the prevalence of diabetes mellitus increases each year, its most common microvascular complication, diabetic retinopathy (DR), is also on the rise. DR is now regarded as an inflammatory disease in which innate immunity plays a crucial role, and a large number of innate immune cells with associated cytokines are involved in the pathologic process of DR. The role of adaptive immunity in DR is seldom mentioned, probably due to the general perception of the immune privileged environment of the retina; however, in recent years there has been a gradual increase in research on the role of adaptive immunity in DR, and with the discovery of the retinal lymphatic system, it seems that the role of adaptive immunity can no longer be ignored. Here, we discuss the immunosuppressive environment of the retina, the phenomenon and potential mechanisms of lymphocyte infiltration in DR, and the role of the adaptive immune system in the diabetic retina, which may point the way for future research.

Inhibition of Vascular Endothelial Growth Factor Reduces Photoreceptor Death in Retinal Neovascular Disease via Neurotrophic Modulation in Müller Glia

VEGF is not only the most potent angiogenic factor, but also an important neurotrophic factor. In this study, vitreous expression of six neurotrophic factors were examined in proliferative diabetic retinopathy (PDR) patients with prior anti-VEGF therapy (n = 48) or without anti-VEGF treatment (n = 41) via ELISA. Potential source, variation and impact of these factors were further investigated in a mouse model of oxygen-induced retinopathy (OIR), as well as primary Müller cells and 661W photoreceptor cell line under hypoxic condition. Results showed that vitreous levels of NGF, NT-3, NT-4, BDNF, GDNF and CNTF were significantly higher in eyes undergoing anti-VEGF therapy compared with PDR controls. Statistical correlation between vitreous VEGF and each trophic factor was found. Hypoxia significantly induced the expressions of these neurotrophic factors, whereas application of anti-VEGF agent in OIR model could further upregulate retinal NGF, NT-3, NT-4, together with downregulation of BDNF, GDNF, CNTF, especially in Müller glia. Inhibition of Müller cell-derived VEGF would result in similar neurotrophic changes under hypoxia. With changes of corresponding neurotrophic receptors in the cocultured photoreceptor cells, their synergic effect could protect hypoxic photoreceptor from apoptosis when VEGF inhibition was present. These findings demonstrated that regulation of Müller cell-derived neurotrophic factors might be one of the possible mechanisms by which anti-VEGF therapy produced neuroprotective effects on PDR. These results provided new evidence for the therapeutic strategy of PDR.

Impact of hypertension on changes in peripapillary retinal nerve fiber layer thickness in type 2 diabetes patients

To determine longitudinal changes in the peripapillary retinal nerve fiber layer (pRNFL) thickness in type 2 diabetes mellitus (T2DM) patients with hypertension (HTN). Participants were divided into three groups: normal controls (Group 1), patients with T2DM (Group 2), and patients with both T2DM and HTN (Group 3). Following the initial examination, patients underwent three additional examinations at 1-year intervals. Linear mixed models were used to identify significant changes in pRNFL thickness over time. The baseline mean pRNFL thickness was 95.4 ± 7.9, 93.6 ± 7.8, and 90.7 ± 10.1 μm in Group 1, Group 2, and Group 3, respectively, (P = 0.046). The reduction rate for mean pRNFL thickness was - 0.15 μm/y in Group 1, - 0.54 μm/y in Group 2, and - 1.06 μm/y in Group 3, respectively (P = 0.026). In Group 2, T2DM duration (estimate = - 0.63, P = 0.002) was a significant factor associated with changes in pRNFL thickness in multivariate analysis. In Group 3, HTN duration (estimate = - 0.59, P = 0.036) and HbA1c levels (estimate = - 4.44, P = 0.019) were significantly associated with pRNFL changes. Under ischemic conditions caused by HTN, pRNFL damage due to diabetic retinal neurodegeneration is considered to be more severe. In such patients, the duration of ischemic damage caused by HTN appears to have a significant impact on pRNFL damage, and stricter blood glucose level control could help reduce pRNFL damage.

Targeting tRNA-Derived Non-Coding RNA Alleviates Diabetes-Induced Visual Impairment through Protecting Retinal Neurovascular Unit

Diabetes is a major risk factor for compromised visual health, leading to retinal vasculopathy and neuropathy, both of which are hallmarks of neurovascular unit dysfunction. Despite the critical impact of diabetic retinopathy, the precise mechanism underlying neurovascular coupling and effective strategies to suppress neurovascular dysfunction remain unclear. In this study, the up-regulation of a tRNA-derived stress-induced RNA, 5'tiRNA-His-GTG, in response to diabetic stress is revealed. 5'tiRNA-His-GTG directly regulates Müller glia action and indirectly alters endothelial angiogenic effects and retinal ganglion cell (RGC) survival in vitro. Downregulation of 5'tiRNA-His-GTG alleviates diabetes-induced retinal neurovascular dysfunction, characterized by reduced retinal vascular dysfunction, decreased retinal neurodegeneration, and improved visually-guided behaviors in vivo. Mechanistically, 5'tiRNA-His-GTG acts as a key regulator of retinal neurovascular dysfunction, primarily by modulating arachidonic acid (AA) metabolism via the CYPs pathway. The 5'tiRNA-His-GTG-CYP2E1-19(S)-HETE signaling axis is identified as a key driver of retinal neurovascular dysfunction. Thus, targeting 5'tiRNA-His-GTG presents a promising therapeutic strategy for treating vasculopathy and neuropathy associated with diabetes mellitus. Modulating this novel signaling pathway can open up new avenues for intervention in diabetic retinopathy and its related complications.

Diabetic retinopathy: A review on its pathophysiology and novel treatment modalities

Diabetes mellitus (DM) is a chronic metabolic non-communicable disease with the ability to cause serious microvascular and macrovascular complications throughout the body, including in the eye. Diabetic retinopathy (DR), present in one-third of patients with diabetes, is a vision-threatening complication caused by uncontrolled diabetes, which greatly affects the retinal blood vessels and the light-sensitive inner retina, eventually leading to blindness. Several epidemiological studies elucidate that DR can vary by age of onset, duration, types of diabetes, and ethnicity. Recent studies show that the pathogenesis of diabetic retinopathy has spread its roots beyond merely being the result of hyperglycemia. The complexity of its etiopathology and diagnosis makes therapeutic intervention challenging. This review throws light on the pathological processes behind DR, the cascade of events that follow it, as well as the available and emerging treatment options.

Cost-Effectiveness of a Telemedicine Optometric-Based Assessment for Screening Diabetic Retinopathy in a Country with a Universal Public Health System

Objective: To determine the cost-effectiveness of a new telemedicine optometric-based screening program of diabetic retinopathy (DR) compared with traditional models' assessments in a universal European public health system. Methods: A new teleophthalmology program for DR based on the assessment of retinographies (3-field Joslin Vision Network by a certified optometrist and a reading center [IOBA-RC]) was designed. This program was first conducted in a rural area 40 km from the referral hospital (Medina de Rioseco, Valladolid, Spain). The cost-effectiveness was compared with telemedicine based on evaluations by primary care physicians and general ophthalmologists, and to face-to-face examinations conducted by ophthalmologists. A decision tree model was developed to simulate the cost-effectiveness of both models, considering public and private costs. The effectiveness was measured in terms of quality of life. Results: A total of 261 patients with type 2 diabetes were included (42 had significant DR and required specific surveillance by the RC; 219 were undiagnosed). The sensitivity and specificity of the detection of DR were 100% and 74.1%, respectively. The telemedicine-based DR optometric screening model demonstrated similar utility to models based on physicians and general ophthalmologists and traditional face-to-face evaluations (0.845) at a lower cost/patient (€51.23, €71.65, and €86.46, respectively). Conclusions: The telemedicine-based optometric screening program for DR in a RC demonstrated cost savings even in a developed country with a universal health care system. These results support the expansion of this kind of teleophthalmology program not only for screening but also for the follow-up of diabetic patients.

Gliotic Response and Reprogramming Potential of Human Müller Cell Line MIO-M1 Exposed to High Glucose and Glucose Fluctuations

Retinal neurodegeneration (RN), an early marker of diabetic retinopathy (DR), is closely associated with Müller glia cells (MGs) in diabetic subjects. MGs play a pivotal role in maintaining retinal homeostasis, integrity, and metabolic support and respond to diabetic stress. In lower vertebrates, MGs have a strong regenerative response and can completely repair the retina after injuries. However, this ability diminishes as organisms become more complex. The aim of this study was to investigate the gliotic response and reprogramming potential of the human Müller cell line MIO-M1 cultured in normoglycemic (5 mM glucose, NG) and hyperglycemic (25 mM glucose, HG) conditions and then exposed to sustained high-glucose and glucose fluctuation (GF) treatments to mimic the human diabetic conditions. The results showed that NG MIO-M1 cells exhibited a dynamic activation to sustained high-glucose and GF treatments by increasing GFAP and Vimentin expression together, indicative of gliotic response. Increased expression of SHH and SOX2 were also observed, foreshadowing reprogramming potential. Conversely, HG MIO-M1 cells showed increased levels of the indexes reported above and adaptation/desensitization to sustained high-glucose and GF treatments. These findings indicate that MIO-M1 cells exhibit a differential response under various glucose treatments, which is dependent on the metabolic environment. The in vitro model used in this study, based on a well-established cell line, enables the exploration of how these responses occur in a controlled, reproducible system and the identification of strategies to promote neurogenesis over neurodegeneration. These findings contribute to the understanding of MGs responses under diabetic conditions, which may have implications for future therapeutic approaches to diabetes-associated retinal neurodegeneration.

Effect of Danggui Buxue decoction on hypoxia-induced injury of retinal Müller cells in vitro

Retinopathy is a common complication of diabetes mellitus and the leading cause of visual impairment. Danggui Buxue decoction (RRP) has been used as a traditional drug for the treatment of diabetic nephropathy for many years. The aim of this study was to investigate the effects of RRP on hypoxia-induced retinal Müller cell injury. A model of retinal Müller cell damage was created using high glucose levels (25 mmol/L) and/or exposure to low oxygen conditions (1% O2). RRP was given to rats by continuous gavage for 7 days to obtain drug-containing serum. After sterilization, the serum was added to the culture medium at a ratio of 10%. Cell viability, apoptosis, and cell proliferation were assessed using the CCK-8 kit, Annexin V-FITC/propidium iodide apoptosis kit, and EdU kit. The mRNA levels of angiogenesis factors (ANGPTL4, VEGF) and inflammatory factors (IL-1B, ICAM-1) were detected by RT-qPCR. Western blot analysis was employed to assess the levels of proteins related to the ATF4/CHOP pathway. Following hypoxia for 48 h and 72 h, there was a significant decrease in cell viability and proliferation, as well as a notable increase in apoptosis compared to the control group (21% O2). However, high glucose stimulation had no significant effect, and high glucose combined with hypoxia had no further damage to cells. After 48 h of exposure to low oxygen levels, the mRNA expression levels of ANGPTL4, VEGF, IL-1B, and ICAM-1 in retinal Müller cells were significantly higher than in the control group (21% O2). RRP treatment significantly alleviated the increase of cell apoptosis and the upregulation of IL-1B and-1 in retinal Müller cells induced by hypoxia. RRP has the potential to reduce the suppression of the ATF4/CHOP pathway in hypoxia-induced retinal Müller cells, and it significantly alleviates cell apoptosis through regulating inflammatory factors and the ATF4/CHOP pathway.

Incidence of Diabetic Retinopathy in Individuals with Type 2 Diabetes: A Study Using Real-World Data

Background/Objectives: This study aimed to assess the incidence of diabetic retinopathy (DR) in patients with type 2 diabetes (T2DM) treated in primary-care settings in Catalonia, Spain, and identify key risk factors associated with DR development. Methods: A retrospective cohort study was conducted using the SIDIAP (System for Research and Development in Primary Care) database. Patients aged 30-90 with T2DM who underwent retinal screening between 2010 and 2015 were included. Multivariable Cox regression analysis was used to assess the impact of clinical variables, including HbA1c levels, diabetes duration, and comorbidities, on DR incidence. Results: This study included 146,506 patients, with a mean follow-up time of 6.96 years. During this period, 4.7% of the patients developed DR, resulting in an incidence rate of 6.99 per 1000 person-years. Higher HbA1c levels were strongly associated with an increased DR risk, with patients with HbA1c > 10% having more than four times the risk compared to those with HbA1c levels < 7% (hazard ratio: 4.23; 95% CI: 3.90-4.58). Other significant risk factors for DR included greater diabetes duration, male sex, ex-smoker status, macrovascular disease, and chronic kidney disease. In contrast, obesity appeared to be a protective factor against DR, with an HR of 0.93 (95% CI: 0.89-0.98). Conclusions: In our real-world setting, the incidence rate of DR was 6.99 per 1000 person-years. Poor glycemic control, especially HbA1c > 10%, and prolonged diabetes duration were key risk factors. Effective management of these factors is crucial in preventing DR progression. Regular retinal screenings in primary care play a vital role in early detection and reducing the DR burden for T2DM patients.

In Vitro Models of Diabetes: Focus on Diabetic Retinopathy

Diabetic retinopathy is a major eye complication in patients with diabetes mellitus, and it is the leading cause of blindness and visual impairment in the world. Chronic hyperglycemia induces endothelial damage with consequent vascular lesions, resulting in global vasculitis, which affects the small vessels of the retina. These vascular lesions cause ischemic conditions in certain areas of the retina, with a consequent increase in the release of pro-angiogenic mediators. In addition to pharmacological interventions for controlling the blood glycaemic level, the main strategies for treating diabetic retinopathy are the intravitreal injections of drugs, surgical treatments, and vitrectomies. The complexity of diabetic retinopathy is due to its close interactions with different cell types (endothelial cells, astrocytes, and Müller cells). The evaluation of the efficacy of novel pharmacological strategies is mainly performed through in vivo models. However, the use of different animal species leads to heterogenic results and ethical concerns. For these reasons, the development of new and reliable in vitro models, such as cell co-cultures and eye organoids, represents an urgent need in this area of research. This review features an overview of the in vitro models used to date and highlights the advances in technology used to study this pathology.

Ocular adverse events associated with GLP-1 receptor agonists: a real-world study based on the FAERS database and network pharmacology

OBJECTIVE

This study evaluates the risk of ocular adverse events (AEs) associated with glucagon-like peptide-1 receptor agonists (GLP-1 RAs) using data from the FDA Adverse Event Reporting System (FAERS) and network pharmacology methods.

METHODS

FAERS data from 2004 to 2024 were analyzed for ocular AEs linked to GLP-1 RA treatments. Disproportionality analysis (Reporting Odds Ratio, ROR) was used to identify signals, and a drug-gene interaction network explored potential mechanisms.

RESULTS

Among 17,785,793 FAERS reports, semaglutide and lixisenatide were significantly associated with ocular AEs, with RORs of 1.25 (95% CI, 1.20-1.31) and 1.96 (95% CI, 1.70-2.27), respectively. Commonly reported AEs included blurred vision, visual impairment, and diabetic retinopathy, with some AEs occurring as early as 10 days after treatment initiation. Gene enrichment analysis highlighted potential links between GLP-1-related genes and ocular AEs.

CONCLUSION

The widespread use of GLP-1 RAs has raised concerns regarding their ophthalmic safety. This study contributes new evidence from real-world data, suggesting that semaglutide and lixisenatide are associated with significant risks of ocular AEs. Further experimental studies are warranted to elucidate the underlying mechanisms and confirm these associations.

TIN2 modulates FOXO1 mitochondrial shuttling to enhance oxidative stress-induced apoptosis in retinal pigment epithelium under hyperglycemia

Progressive dysfunction of the retinal pigment epithelium (RPE) and the adjacent photoreceptor cells in the outer retina plays a pivotal role in the pathogenesis of diabetic retinopathy (DR). Here, we observed a marked increase in oxidative stress-induced apoptosis in parallel with higher expression of telomeric protein TIN2 in RPE cells under hyperglycemia in vivo and in vitro. Delving deeper, we confirm that high glucose-induced elevation of mitochondria-localized TIN2 compromises mitochondrial activity and weakens the intrinsic antioxidant defense, thereby leading to the activation of mitochondria-dependent apoptotic pathways. Mechanistically, mitochondrial TIN2 promotes the phosphorylation of FOXO1 and its relocation to the mitochondria. Such translocation of transcription factor FOXO1 not only promotes its binding to the D-loop region of mitochondrial DNA-resulting in the inhibition of mitochondrial respiration-but also hampers its availability to nuclear target DNA, thereby undermining the intrinsic antioxidant defense. Moreover, TIN2 knockdown effectively mitigates oxidative-induced apoptosis in diabetic mouse RPE by preserving mitochondrial homeostasis, which concurrently prevents secondary photoreceptor damage. Our study proposes the potential of TIN2 as a promising molecular target for therapeutic interventions for diabetic retinopathy, which emphasizes the potential significance of telomeric proteins in the regulation of metabolism and mitochondrial function. Created with BioRender ( https://www.biorender.com/ ).

Diminished light sensitivities of ON alpha retinal ganglion cells observed in a mouse model of hyperglycemia

This study aimed to investigate potential functional changes in retinal ganglion cells (RGCs) in a mouse model of hyperglycemia and explore possible therapeutic approaches. Hyperglycemia resembling type 1 diabetes mellitus (DM) was induced in C57BL/6 mice through intraperitoneal injection of streptozotocin (STZ). Blood glucose levels were confirmed to be elevated after 1 week and 4 weeks of injection. Mice with blood glucose levels above 350 mg/mL after 4 weeks of one-dose STZ injection were considered hyperglycemic. The light sensitivity of ON alpha (α) retinal ganglion cells (RGCs), not OFF αRGCs, was reduced in the hyperglycemic mouse model. The number of apoptotic cells, RGCs, and amacrine cells (ACs) remained unaffected at this stage. Similarly, the eletroretinogram (ERG) and optokinetic test results showed no significant differences. The application of picrotoxin (PTX) to block GABA receptors could increase the light sensitivity of ON αRGCs by 1 log unit in hyperglycemic mice. The results show that ON αRGCs may be more susceptible to microenvironmental changes caused by hyperglycemia than OFF αRGCs. This decline in light sensitivity may occur before cell apoptosis during the early stages of the hyperglycemic mouse model but has the potential to be reversed.

Ganglion cell-derived LysoPS induces retinal neovascularisation by activating the microglial GPR34-PI3K-AKT-NINJ1 axis

Retinal neovascularisation is a major cause of blindness in patients with proliferative diabetic retinopathy (PDR). It is mediated by the complex interaction between dysfunctional ganglion cells, microglia, and vascular endothelial cells. Notably, retinal microglia, the intrinsic immune cells of the retina, play a crucial role in the pathogenesis of retinopathy. In this study, we found that lysophosphatidylserines (LysoPS) released from injured ganglion cells induced microglial extracellular trap formation and retinal neovascularisation. Mechanistically, LysoPS activated the GPR34-PI3K-AKT-NINJ1 signalling axis by interacting with the GPR34 receptor on the microglia. This activation upregulated the expression of inflammatory cytokines, such as IL-6, IL-8, VEGFA, and FGF2, and facilitated retinal vascular endothelial cell angiogenesis. As a result, inhibition of the GPR34-PI3K-AKT-NINJ1 axis significantly decreased microglial extracellular trap formation and neovascularisation by suppressing LysoPS-induced microglial inflammatory responses, both in vitro and in vivo. This study reveals the crucial role of apoptotic ganglion cells in activating microglial inflammation in PDR, thereby enhancing our understanding of the pathogenesis of retinal neovascularisation.

Docosahexaenoic acid eliminates endoplasmic reticulum stress and inflammatory pathways in diabetic rat keratopathy

Diabetic keratopathy, characterized by corneal structural changes, is a common complication of diabetes mellitus (DM). Docosahexaenoic acid (DHA), an omega-3 fatty acid, has shown potential therapeutic benefits in various diabetic complications. This study aimed to investigate the protective effect of DHA on corneal tissue in streptozotocin (STZ)-induced type 2 DM in rats. Forty male Sprague-Dawley rats were randomly assigned to four groups (n = 10 per group): Control, DHA, DM, and DM + DHA. The DHA group received DHA by oral gavage at a dose of 100 mg/kg daily for 10 days. In the DM group, diabetes was induced by a single intraperitoneal injection of STZ at 50 mg/kg. Confirmation of diabetes induction was based on monitoring fasting blood glucose levels on the third day post-injection. The DM + DHA group underwent the same diabetes induction protocol with STZ and received DHA at 100 mg/kg daily via oral gavage for 10 consecutive days. Corneal tissue samples were collected at the end of the study period for histopathological, immunohistochemical, qRT-PCR, and ELISA analyses. Histopathological analysis showed significant edema, angiogenesis, and degeneration in the DM group compared to the control (p < 0.001). DHA treatment significantly mitigated these changes, approaching control levels (p < 0.01). Immunohistochemistry showed increased VEGFR2 and iNOS expression in the DM group, which was significantly reduced in the DM + DHA group (p < 0.01). qRT-PCR results indicated a significant decrease in Bcl-2 expression (p < 0.001) and an increase in ATF-6, IRE1, NF-κB, TNF-α, IL-1β, NLRP3, Bax, and Caspase-3 expressions in the DM group (p < 0.001). ELISA analyses revealed significantly elevated levels of inflammatory markers NF-κB, TNF-α, IL-1β, and IL-6 in the DM group compared to the control (p < 0.001). DHA treatment significantly upregulated Bcl-2 and downregulated apoptotic and inflammatory markers (p < 0.01). DHA demonstrated significant protective effects against STZ-induced corneal damage in diabetic rats by modulating apoptotic and inflammatory pathways. These findings suggest that DHA may be a promising therapeutic agent for preventing diabetic keratopathy.

The Role of Immune Cells and Signaling Pathways in Diabetic Eye Disease: A Comprehensive Review

Diabetic eye disease (DED) encompasses a range of ocular complications arising from diabetes mellitus, including diabetic retinopathy, diabetic macular edema, diabetic keratopathy, diabetic cataract, and glaucoma. These conditions are leading causes of visual impairments and blindness, especially among working-age adults. Despite advancements in our understanding of DED, its underlying pathophysiological mechanisms remain incompletely understood. Chronic hyperglycemia, oxidative stress, inflammation, and neurodegeneration play central roles in the development and progression of DED, with immune-mediated processes increasingly recognized as key contributors. This review provides a comprehensive examination of the complex interactions between immune cells, inflammatory mediators, and signaling pathways implicated in the pathogenesis of DED. By delving in current research, this review aims to identify potential therapeutic targets, suggesting directions of research for future studies to address the immunopathological aspects of DED.

Insights to Ang/Tie signaling pathway: another rosy dawn for treating retinal and choroidal vascular diseases

Retinal neurovascular unit (NVU) is a multi-cellular structure that consists of the functional coupling between neural tissue and vascular system. Disrupted NVU will result in the occurrence of retinal and choroidal vascular diseases, which are characterized by the development of neovascularization, increased vascular permeability, and inflammation. This pathological entity mainly includes neovascular age-related macular degeneration (neovascular-AMD), diabetic retinopathy (DR) retinal vein occlusion (RVO), and retinopathy of prematurity (ROP). Emerging evidences suggest that the angopoietin/tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (Ang/Tie) signaling pathway is essential for the development of retinal and choroidal vascular. Tie receptors and their downstream pathways play a key role in modulating the vascular development, vascular stability, remodeling and angiogenesis. Angiopoietin 1 (Ang1) is a natural agonist of Tie2 receptor, which can promote vascular stability. On the other hand, angiopoietin 2 (Ang2) is an antagonist of Tie2 receptor that causes vascular instability. Currently, agents targeting the Ang/Tie signaling pathway have been used to inhibit neovascularization and vascular leakage in neovascular-AMD and DR animal models. Particularly, the AKB-9778 and Faricimab have shown promising efficacy in improving visual acuity in patients with neovascular-AMD and DR. These experimental and clinical evidences suggest that activation of Ang/Tie signaling pathway can inhibit the vascular permeability, neovascularization, thereby maintaining the normal function and structure of NVU. This review seeks to introduce the versatile functions and elucidate the modulatory mechanisms of Ang/Tie signaling pathway. Recent pharmacologic therapies targeting this pathway are also elaborated and summarized. Further translation of these findings may afford a new therapeutic strategy from bench to bedside.

Peripapillary microvasculature and retinal nerve fiber layer damage according to the severity of diabetic retinopathy

PURPOSE

To identify damage to the inner retinal layer and microvasculature in the peripapillary area according to the severity of diabetic retinopathy (DR).

METHODS

Patients were divided into four groups: control (group 1), type 2 diabetes (T2DM) without DR (group 2), mild to moderate nonproliferative DR (NPDR) (group 3), and severe NPDR (group 4). The peripapillary retinal nerve fiber layer (pRNFL) thickness and peripapillary vessel density (VD) were compared. Linear regression analysis was performed to identify factors associated with the DR severity.

RESULTS

The average pRNFL thicknesses were 96.2 ± 7.1, 94.1 ± 9.6, 92.0 ± 9.9, and 90.3 ± 12.4 μm in groups 1, 2, 3, and 4, respectively (P = 0.003) (post hoc analyses: group 1 vs. group 2, P = 0.529; group 2 vs. group 3, P = 0.627; group 2 vs. group 4, P = 0.172; group 3 vs. group 4, P = 0.823). The VDs of the outer ring were 18.9 ± 0.6, 18.4 ± 0.8, 17.9 ± 1.1, and 17.3 ± 1.6 mm-1 in groups 1, 2, 3 and 4, respectively (P < 0.001) (all pairwise comparisons, P < 0.050). In multivariate analysis, the VD of the outer ring (B = - 0.35, P < 0.001) was significantly associated with the DR severity.

CONCLUSIONS

The peripapillary microvasculature reflects retinal damage following DR progression better than the structure of the pRNFL.

Mesenchymal Stem Cells Regulate Microglial Polarization via Inhibition of the HMGB1/TLR4 Signaling Pathway in Diabetic Retinopathy

Diabetic retinopathy (DR) is recognized as the most prevalent retinal degenerative disorder. Inflammatory response usually precedes microvascular alteration and is the primary factor of diabetic retinopathy. Activated microglia express many pro-inflammatory cytokines that exacerbate retina inflammation and disruption. In the present study, we found that MSCs alleviated blood-retina barrier (BRB) breakdown in diabetic rats, as evidenced by reduced retinal edema, decreased vascular leakage, and increased occludin expression. The MSC-treated retinal microglia exhibited reduced expression of M1-phenotype markers in the diabetic rats, including inducible nitric oxide synthase (iNOS), CD16, and pro-inflammatory cytokines. On the other hand, MSCs increased the expression of M2-phenotype markers, such as arginase-1 (Arg-1), CD206, and anti-inflammatory cytokines. HMGB1/TLR4 signaling pathway is activated in DR and inhibited after MSC treatment. Consistent with in vivo evidence, MSCs drove BV2 microglia toward M2 phenotype in vitro. Overexpression of HMGB1 in microglia reversed the effects of MSC treatment, suggesting HMGB1/TLR4 pathway is necessary for MSCs' regulatory effects on microglia polarization. Collectively, MSCs exert beneficial effects on DR by polarizing microglia from M1 toward M2 phenotype via inhibiting the HMGB1/TLR4 signaling pathway.

High-normal serum bilirubin is a useful indicator to assess the risk of diabetic retinopathy in type 2 diabetes: A real-world study

Background

To investigate the association of serum bilirubin within normal range, especially unconjugated bilirubin (UCB), with diabetic retinopathy (DR) in patients with type 2 diabetes mellitus (T2DM).

Methods

In this cross-sectional, real-world study, 7617 T2DM patients were stratified into quartiles based on serum UCB levels. DR was determined by digital fundus photography and further classified into non-proliferative diabetic retinopathy (NPDR) and PDR. The associations of serum bilirubin levels and UCB quartiles with DR were investigated by logistic regression analysis.

Results

After controlling for age, sex, and diabetes duration, the DR prevalence was significantly decreased across the serum UCB quartiles (40.4 %, 33.4 %, 29.7 %, 26.6 % for each quartile, respectively, p < 0.001 for trend). The subjects with DR had lower serum total bilirubin (TB) and UCB, rather than conjugated bilirubin (CB), compared with those without DR (p = 0.003 for TB, p < 0.001 for UCB, and p = 0.528 for CB, respectively), while all three types of serum bilirubin in the subjects with PDR were obviously lower than those with NPDR (p = 0.006 for TB, and p < 0.001 for UCB and CB, respectively). After adjustment for confounding factors, logistic regression demonstrated negative associations of serum TB and UCB levels, rather than CB, with the presence of DR (OR: 0.844, 95%CI: 0.774-0.920, p < 0.001 for TB; OR: 0.828, 95%CI: 0.763-0.899, p < 0.001 for UCB; and OR: 0.984, 95%CI: 0.900-1.074, p = 0.713 for CB, respectively). Additionally, a fully-adjusted analysis revealed a negative correlation between UCB quartiles and DR (p < 0.001).

Conclusion

High-normal serum TB and UCB were closely associated with the decreased odds of DR, while all types of serum bilirubin were negatively correlated with the severity of DR in T2DM patients. Serum bilirubin may be used as a potential indicator to assess the risk and severity of DR in T2DM.

Neuroprotective Effects of Sodium-Glucose Cotransporter-2 (SGLT2) Inhibitors (Gliflozins) on Diabetes-Induced Neurodegeneration and Neurotoxicity: A Graphical Review

Diabetes is a chronic endocrine disorder that negatively affects various body systems, including the nervous system. Diabetes can cause or exacerbate various neurological disorders, and diabetes-induced neurodegeneration can involve several mechanisms such as mitochondrial dysfunction, activation of oxidative stress, neuronal inflammation, and cell death. In recent years, the management of diabetes-induced neurodegeneration has relied on several types of drugs, including sodium-glucose cotransporter-2 (SGLT2) inhibitors, also called gliflozins. In addition to exerting powerful effects in reducing blood glucose, gliflozins have strong anti-neuro-inflammatory characteristics that function by inhibiting oxidative stress and cell death in the nervous system in diabetic subjects. This review presents the molecular pathways involved in diabetes-induced neurodegeneration and evaluates the clinical and laboratory studies investigating the neuroprotective effects of gliflozins against diabetes-induced neurodegeneration, with discussion about the contributing roles of diverse molecular pathways, such as mitochondrial dysfunction, oxidative stress, neuro-inflammation, and cell death. Several databases-including Web of Science, Scopus, PubMed, Google Scholar, and various publishers, such as Springer, Wiley, and Elsevier-were searched for keywords regarding the neuroprotective effects of gliflozins against diabetes-triggered neurodegenerative events. Additionally, anti-neuro-inflammatory, anti-oxidative stress, and anti-cell death keywords were applied to evaluate potential neuronal protection mechanisms of gliflozins in diabetes subjects. The search period considered valid peer-reviewed studies published from January 2000 to July 2023. The current body of literature suggests that gliflozins can exert neuroprotective effects against diabetes-induced neurodegenerative events and neuronal dysfunction, and these effects are mediated via activation of mitochondrial function and prevention of cell death processes, oxidative stress, and inflammation in neurons affected by diabetes. Gliflozins can confer neuroprotective properties in diabetes-triggered neurodegeneration, and these effects are mediated by inhibiting oxidative stress, inflammation, and cell death.

Correlation of glycosylated hemoglobin (HbA1c) with retinal nerve fiber layer (RNFL) thickness and central macular thickness (CMT) in the diabetic population in North India

PURPOSE

The current study was aimed to find correlation of glycosylated hemoglobin with retinal nerve fiber layer thickness (RNFLT) and central macular thickness (CMT) in the diabetic population in North India.

METHODS

This was a cross-sectional observational study of 300 diabetic patients divided equally in two groups with and without retinopathy, and 150 people were included as control. The study was conducted from October 2020 to August 2022. All patients underwent slitlamp fundoscopy with a +78 D lens, and spectral-domain (SD) optical coherence tomography was performed to measure the RNFLT and CMT, and the staging of retinopathy was done as per the ETDRS classification. Along with that, blood investigations were ordered, including fasting (FBS) and post-prandial (PPBS) blood sugar and glycosylated hemoglobin (HbA1c). Quantitative variables were compared using one-way analysis of variance, or Kruskal-Wallis test was applied for inter-group comparison, followed by a Student Newman Keuls Test.

RESULTS

The mean age of the patients in the diabetic group with retinopathy was 52.62 ± 9.38 years. The overall male: female ratio was 3:2. The mean FBS in the diabetic group with retinopathy was 146.54 ± 45.40mg/dl; the PPBS and HbA1c in the same were 210.39 ± 63.71mg/dl and 7.85 ± 1.33%, respectively. RNFL thinning was found in all four quadrants in diabetics irrespective of the status of retinopathy (P-value = 0.000) with a significant weak negative (r<0.4) correlation of glycosylated hemoglobin values with RNFLT in the inferior (r value = -0.300, P-value = 0.000) and superior (r value = -0.236, P-value = 0.004) quadrants of right eyes and in inferior (r value = -0.176, p- value = 0.031), superior (r value = -0.222, P value = 0.006), and nasal quadrants (r value = -0.166, p- value = 0.043) of left eyes in diabetics with retinopathy. However, in diabetics without retinopathy, no correlation was found. On correlating HbA1c with CMT, a weak positive (r<0.3) association existed in both eyes in the diabetic group without retinopathy (r = 0.020 and 0.048 for OD and OS, respectively) and diabetics with retinopathy (r = 0.152 and 0.127 for OD and OS, respectively). However, the association was not found to be significant in either of the groups (P-value > 0.05).

CONCLUSION

The study concluded that neurodegeneration occurs in diabetic retinopathy as evident with nerve fiber layer thinning, and it is negatively correlated with glycosylated hemoglobin (HbA1c).

Myopia and Rate of Peripapillary Retinal Nerve Fiber Layer Thickness in Diabetic Patients Without Retinopathy: A 2-Year Longitudinal Study

PURPOSE

The aim of this study was to investigate the association between myopia and longitudinal changes in peripapillary retinal nerve fiber layer (pRNFL) thickness in type 2 diabetic patients without diabetic retinopathy (DR).

METHODS

A total of 1069 participants with a median follow-up time of 1.9 years were included in this study. The participants were categorized into four groups based on the presence of myopia (≤ -0.5 diopter [D]) and diabetes without DR, including a control group (n = 412), diabetes group (n = 416), myopia group (n = 115), and diabetes + myopia group (n = 126). Peripapillary average and sectoral RNFL measurements were obtained using 6 × 6 mm swept-source optical coherence tomography (SS-OCT) scans centered at the optic disc. The change rate of pRNFL, adjusted for age and sex, was calculated and compared among the four groups to investigate the impact of myopia and diabetes.

RESULTS

The baseline estimated pRNFL thickness after adjustment for covariates was 113.7 μm, 116.2 μm, 108.0 μm, and 105.6 μm in the control, diabetes, myopia, and diabetes + myopia group, respectively (diabetes > control > myopia = diabetes + myopia, p < 0.001). The respective average pRNFL loss in the four groups was -0.48 μm/year, -1.11 μm/year, -1.23 μm/year, and -2.62 μm/year (all p < 0.01). The diabetes + myopia group exhibited a greater rate of average pRNFL reduction compared to the other groups (all p < 0.001). Multivariate analysis using a linear mixed-effects model showed that age, diabetes, axial length (AL), and baseline pRNFL thickness were significantly associated with the rate of average pRNFL reduction.

CONCLUSIONS

The diabetes group showed a faster rate of average pRNFL thickness reduction compared to healthy controls, regardless of the presence of myopia. The average pRNFL thickness decreased more rapidly when diabetes and myopia were present simultaneously than in the individual diabetes or myopia group. Both diabetes and myopia were associated with accelerated pRNFL loss.

Resilience to diabetic retinopathy

Chronic elevation of blood glucose at first causes relatively minor changes to the neural and vascular components of the retina. As the duration of hyperglycemia persists, the nature and extent of damage increases and becomes readily detectable. While this second, overt manifestation of diabetic retinopathy (DR) has been studied extensively, what prevents maximal damage from the very start of hyperglycemia remains largely unexplored. Recent studies indicate that diabetes (DM) engages mitochondria-based defense during the retinopathy-resistant phase, and thereby enables the retina to remain healthy in the face of hyperglycemia. Such resilience is transient, and its deterioration results in progressive accumulation of retinal damage. The concepts that co-emerge with these discoveries set the stage for novel intellectual and therapeutic opportunities within the DR field. Identification of biomarkers and mediators of protection from DM-mediated damage will enable development of resilience-based therapies that will indefinitely delay the onset of DR.

The association of islet autoantibodies with the neural retinal thickness and microcirculation in type 1 diabetes mellitus with no clinical evidence of diabetic retinopathy

OBJECTIVE

To examine the association between islet autoantibodies (IAbs) and the retinal neurovascular changes in type 1 diabetes mellitus (T1DM) with no diabetic retinopathy (NDR).

METHODS

This cross-sectional study measured the neural retinal structure and microvascular density of 118 NDR eyes using spectral-domain optical coherence tomography angiography. Retinal structure parameters included retinal thickness (RT), inner retinal thickness (iRT), retina never fibral layer thickness (RNFL thickness), ganglion cell complex thickness (GCC thickness), and loss volume of GCC. Microvascular parameters included vessel density of superficial capillary plexus (sVD), vessel density of deep capillary plexus, and vessel density of choroid capillary plexus. Comparison and correlation analyses of these OCTA parameters were made with various IAbs, including glutamic acid decarboxylase antibody (GADA), tyrosine phosphatase-related islet antigen 2 antibody (IA2A), and zinc transporter 8 antibody (ZnT8A). A general linear model was used to understand the association of IAbs with the retina parameters.

RESULTS

The IAb positive (IAbs +) group, which included 85 patients, had thinner RT (235.20 ± 18.10 mm vs. 244.40 ± 19.90 mm at fovea, P = 0.021) and thinner iRT (120.10 ± 9.00 mm vs. 124.70 ± 6.90 mm at parafovea, P = 0.015), compared with the IAb negative (IAbs-) group comprising 33 patients. Furthermore, a more severe reduction of RT was demonstrated in the presence of multiple IAbs. Among the three IAbs, GADA was the most significant independent risk factor of all-round RT decrease (β = -0.20 vs. -0.27 at fovea and parafovea, respectively, P < 0.05), while titers of IA2A negatively affect sVD in the parafovea (β = -0.316, P = 0.003).

CONCLUSIONS

IAbs are associated with neural retinal thinning and microcirculation reduction in T1DM patients before the clinical onset of diabetic retinopathy.

Optical coherence tomography and contrast sensitivity in early diabetic retinopathy

PURPOSE

This study used contrast sensitivity (CS) and optical coherence tomography (OCT) to assess the functional and structural alterations of the macula and the optic nerve head (ONH) in diabetic patients with no retinopathy and those with mild nonproliferative diabetic retinopathy (NPDR).

MATERIALS AND METHODS

In this study, 40 eyes of 20 diabetic patients with no diabetic retinopathy (DR), 40 eyes of 20 diabetic patients with mild NPDR, and 36 eyes of 18 healthy individuals were examined. Best-corrected visual acuity (VA) and CS were performed using early treatment DR study charts and the Pelli-Robson chart, respectively. The macula and ONH were evaluated using OCT, which provided data on the entire retina, inner retinal layer, outer retinal layer, retinal nerve fiber layer (RNFL), and the macula zone-ellipsoid zone-retinal pigment epithelium layer.

RESULTS

VA and CS were significantly different between the three groups (P < 0.001). The entire thickness of the retina and the internal thickness of the retina in the 3-6 mm subfields of the macular region, as well as the thickness of the ganglion cell layer + inner plexiform layer (GCL + IPL) and GCL + IPL + RNFLs, differed significantly across the groups (P < 0.013).

CONCLUSION

In diabetic subjects with no retinopathy, the reduced thickness of the GCL + IPLs is possibly indicative of early neurodegenerative changes in the inner retina. Furthermore, in the diabetic groups, a decrease in CS was observed compared to the control group.

O-GlcNAc Modification Is a Promising Therapeutic Target for Diabetic Retinopathy

Diabetic retinopathy (DR) is a very serious diabetes complication. Changes in the O-linked N-acetylglucosamine (O-GlcNAc) modification are associated with many diseases. However, its role in DR is not fully understood. In this research, we explored the effect of O-GlcNAc modification regulation by activating AMP-activated protein kinase (AMPK) in DR, providing some evidence for clinical DR treatment in the future. Bioinformatics was used to make predictions from the database, which were validated using the serum samples of diabetic patients. As an in vivo model, diabetic mice were induced using streptozotocin (STZ) injection with/without an AMPK agonist (metformin) or an AMPK inhibitor (compound C) treatment. Electroretinogram (ERG) and H&E staining were used to evaluate the retinal functional and morphological changes. In vitro, 661 w cells were exposed to high-glucose conditions, with or without metformin treatment. Apoptosis was evaluated using TUNEL staining. The protein expression was detected using Western blot and immunofluorescence staining. The angiogenesis ability was detected using a tube formation assay. The levels of O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) in the serum changed in the DR patients in the clinic. In the diabetic mice, the ERG wave amplitude and retinal thickness decreased. In vitro, the apoptotic cell percentage and Bax expression were increased, and Bcl2 expression was decreased in the 661 w cells under high-glucose conditions. The O-GlcNAc modification was increased in DR. In addition, the expression of GFAT/TXNIP O-GlcNAc was also increased in the 661 w cells after the high-glucose treatment. Additionally, the Co-immunoprecipitation(CO-IP) results show that TXNIP interacted with the O-GlcNAc modification. However, AMPK activation ameliorated this effect. We also found that silencing the AMPKα1 subunit reversed this process. In addition, the conditioned medium of the 661 w cells may have affected the tube formation in vitro. Taken together, O-GlcNAc modification was increased in DR with photoreceptor cell degeneration and neovascularization; however, it was reversed after activating AMPK. The underlying mechanism is linked to the GFAT/TXNIP-O-GlcNAc modification signaling axis. Therefore, the AMPKα1 subunit plays a vital role in the process.

YAP in development and disease: Navigating the regulatory landscape from retina to brain

The distinctive role of Yes-associated protein (YAP) in the nervous system has attracted widespread attention. This comprehensive review strategically uses the retina as a vantage point, embarking on an extensive exploration of YAP's multifaceted impact from the retina to the brain in development and pathology. Initially, we explore the crucial roles of YAP in embryonic and cerebral development. Our focus then shifts to retinal development, examining in detail YAP's regulatory influence on the development of retinal pigment epithelium (RPE) and retinal progenitor cells (RPCs), and its significant effects on the hierarchical structure and functionality of the retina. We also investigate the essential contributions of YAP in maintaining retinal homeostasis, highlighting its precise regulation of retinal cell proliferation and survival. In terms of retinal-related diseases, we explore the epigenetic connections and pathophysiological regulation of YAP in diabetic retinopathy (DR), glaucoma, and proliferative vitreoretinopathy (PVR). Lastly, we broaden our exploration from the retina to the brain, emphasizing the research paradigm of "retina: a window to the brain." Special focus is given to the emerging studies on YAP in brain disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD), underlining its potential therapeutic value in neurodegenerative disorders and neuroinflammation.

The L-shape relationship between hemoglobin, albumin, lymphocyte, platelet score and the risk of diabetic retinopathy in the US population

Background

The primary aim of this study was to investigate the correlation between diabetic retinopathy (DR) and the HALP score (hemoglobin, albumin, lymphocyte, and platelet) in individuals with diabetes within the United States population.

Methods

This cross-sectional investigation was based on the National Health and Nutrition Examination Survey (NHANES) database from 2003-2018. The following module calculated the HALP score: HALP score = [lymphocytes (/L) × hemoglobin (g/L) × albumin (g/L)]/platelets (/L). By performing the receiver operating characteristic (ROC) analysis, the optimal cutoff value of HALP was ascertained. Restricted cubic splines (RCS), multivariable logistic regression analysis, sensitivity analysis, and subgroup analysis were conducted to evaluate the effect of the HALP score on DR patients. Finally, the decision curve analysis (DCA) and clinical impact curve (CIC) were conducted to estimate the predictive power and clinical utility of the HALP score with clinical indicators.

Results

According to the cutoff value (42.9) determined by the ROC curve, the participants were stratified into a lower HALP group (HALPlow) and a higher HALP group (HALPhigh). An L-shaped relationship between HALP score and DR risk was presented in the RCS model (P for nonlinearity <0.001). The DR risk sharply decreased with the increase of HALP, and the decline reached a plateau when HALP was more than 42.9. After fully adjustment, the multivariate logistic regression analysis found that HALPlow was an independent risk factor for DR (OR = 1.363, 95% CI: 1.111-1.671, P < 0.001). Besides, sensitivity analysis showed consistent results. Furthermore, the combination of HALP score and clinical indicators demonstrated predictive power and clinical utility, as shown by the ROC curve, DCA, and CIC.

Conclusion

The HALP score has an L-shaped correlation with the risk of DR, and thus, the HALP score may contribute to the timely intervention of diabetes patients.

A New Approach to Staging Diabetic Eye Disease: Staging of Diabetic Retinal Neurodegeneration and Diabetic Macular Edema

Topic

The goal of this review was to summarize the current level of evidence on biomarkers to quantify diabetic retinal neurodegeneration (DRN) and diabetic macular edema (DME).

Clinical relevance

With advances in retinal diagnostics, we have more data on patients with diabetes than ever before. However, the staging system for diabetic retinal disease is still based only on color fundus photographs and we do not have clear guidelines on how to incorporate data from the relatively newer modalities into clinical practice.

Methods

In this review, we use a Delphi process with experts to identify the most promising modalities to identify DRN and DME. These included microperimetry, full-field flash electroretinogram, spectral-domain OCT, adaptive optics, and OCT angiography. We then used a previously published method of determining the evidence level to complete detailed evidence grids for each modality.

Results

Our results showed that among the modalities evaluated, the level of evidence to quantify DRN and DME was highest for OCT (level 1) and lowest for adaptive optics (level 4).

Conclusion

For most of the modalities evaluated, prospective studies are needed to elucidate their role in the management and outcomes of diabetic retinal diseases.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Drp1-dependent mitochondrial fragmentation mediates photoreceptor abnormalities in type 1 diabetic retina

Recent studies have highlighted that retinal neurodegeneration precedes microvascular changes in diabetic retinopathy (DR), but the specific mechanisms remain unclear. Given the pivotal role of dysfunctional mitochondria and oxidative stress in early DR, our objective was to observe mitochondria-related alterations in the neural retina of type one diabetic mellitus mice with no evidence of DR (T1DM-NDR). We aimed to identify the key mitochondrial-related proteins contributing to mitochondrial injury. Our study revealed that T1DM-NDR mice exhibited outer retina thinning, including the ellipsoid zone, inner segment, and outer segment. Additionally, there was an impaired amplitude of the b-wave in electroretinogram (ERG) and a disorganized arrangement of the photoreceptor layer. In both the retina of DM mice and high glucose (HG)-treated 661w cells, mitochondria appeared swollen and fragmented, with disrupted cristae, disorganized or shortened branches in the mitochondrial network, and decreased mitochondrial membrane potential. Among the mitochondrial-related proteins, dynamin-related protein 1 (Drp1) was upregulated, and the ratio of phosphorylated Drp1 protein at serine 616 (S616) and serine 637 (S637) sites significantly increased in the retina of DM mice. The administration of Mdivi-1 ameliorated high-glucose-induced dysfunctional mitochondria, thereby protecting T1DM-NDR mice retina from morphological and functional injuries. Our findings suggest that hyperglycemia promotes Drp1-mediated mitochondrial dysfunction, which may be a significant factor in the development of DR. The inhibition of high-glucose-induced mitochondrial fission emerges as a potential and innovative intervention strategy for preventing DR.

The usefulness of the retina for identifying people with type 2 diabetes with prodromal stages of dementia

Type 2 diabetes (T2D) is associated with cognitive impairment and dementia. The detection of cognitive impairment is important because this population is at higher risk of experiencing difficulties in the self-management of diabetes. Mild cognitive impairment (MCI) often remains undiagnosed due to lack of simple tools for screening at large scale. This represents an important gap in the patients' management because subjects with diabetes and MCI are at high risk of progressing to dementia. Due to its developmental origin as a brain-derived tissue, the retina has been proposed as a potential means of non-invasive and readily accessible exploration of brain pathology. Recent evidence showed that retinal imaging and/or functional tests are correlated with the cognitive function and brain changes in T2D. Simple retinal functional tests (i.e. retinal microperimetry) have proven to be useful as reliable tool for the cognitive evaluation and monitoring in patients with T2D>65 years. This review gives an overall update on the usefulness of retinal imaging in identifying patients with T2D at risk of developing dementia.

Retinal neurodegeneration in diabetic retinopathy with systemic hypertension

PURPOSE

To identify the impact of hypertension (HTN) on inner retinal layer thickness in patients with diabetic retinopathy (DR).

METHODS

In this retrospective cross-sectional study, participants were divided into three groups: type 2 diabetes patients without DR (DM group), patients with DR (DR group), and patients with both DR and HTN (DR+HTN group). The peripapillary retinal nerve fiber layer (pRNFL) and ganglion cell-inner plexiform layer (GC-IPL) thicknesses, measured using optical coherence tomography, were compared among the groups.

RESULTS

A total of 470 eyes were enrolled: 224 eyes in the DM group, 131 eyes in the DR group, and 115 eyes in the DR+HTN group. The mean RNFL thicknesses were 95.0 ± 7.7, 92.5 ± 10.1, and 89.2 ± 11.2 μm, and the mean GC-IPL thicknesses were 84.0 ± 5.7, 82.0 ± 7.6, and 79.2 ± 8.1 μm in each group, respectively (all P < 0.001). In the DR+HTN group, the DR stage showed a significant association with pRNFL (B = - 5.38, P = 0.014) and GC-IPL (B = - 5.18, P = 0.001) thicknesses in multivariate analyses. Subgroup analyses revealed that pRNFL (P = 0.007) and GC-IPL (P = 0.005) thicknesses decreased significantly as DR progressed only in the DR+HTN group.

CONCLUSIONS

Patients with both DR and HTN exhibited much thinner pRNFL and GC-IPL, compared with patients with DR only. These results may have been related to the amplified diabetic retinal neurodegeneration and synergistic impact of ischemia in DR patients with concurrent HTN. Additionally, the progression of DR resulted in more severe inner retinal damage when combined with HTN.

Short-term effect of intravitreal dexamethasone implant in refractory diabetic macular edema

PURPOSE

To evaluate the short-term effects (hours-days) of intravitreal dexamethasone implant (IDI) in eyes with diabetic macular edema (DME) refractory to anti-vascular endothelial growth factor (VEGF) injections.

METHODS

This was a prospective, single-arm, interventional clinical series. Eyes with DME and 3-9 injections of ranibizumab without a good response were included. Patients underwent a single IDI. Best-corrected visual acuity (BCVA) measurement, complete ophthalmic evaluation, and spectral-domain optical coherence tomography (SD-OCT) were performed at baseline, 2 h, 3 h, 24 h, 7 days, and 1 month. The main outcomes were change in central retinal thickness (CRT) on SD-OCT and BCVA.

RESULTS

Fifteen eyes of 15 patients were included. Mean CRT decreased after treatment from 515.87 µm ± 220.00 µm at baseline to 489.60 µm ± 176.53 µm after 2 h (p = 0.126), and 450.13 µm ± 163.43 at 24 h (p = 0.006). Change in BCVA was from 0.85 ± 0.44 logMAR baseline to 0.58 ± 0.37 log MAR at 1 month (p = 0.003).

CONCLUSIONS

Eyes treated with IDI showed significant decrease in CRT detectable 1 day after injection. In some patients, the effect could be observed 3 h post-implantation.

TRIAL REGISTRATION

Clinicaltrials.gov NCT05736081 . Registered 20 February 2023, Retrospectively registered.

Review of lipocalin-2-mediated effects in diabetic retinopathy

BACKGROUND

Studies have uncovered LCN2 as a marker of inflammation strongly related to obesity, insulin resistance, and abnormal glucose metabolism in humans, and is involved in vascular diseases, inflammatory diseases, and neurological diseases. In recent years, studies have shown that elevated levels of LCN2 have a strong association with diabetic retinopathy (DR), but the pathogenesis is unknown. Here, we reviewed the relevant literature and compiled the pathogenesis associated with LCN2-induced DR.

METHODS

We searched PubMed and Web of Science electronic databases using "lipocalin-2, diabetic retinopathy, retinal degeneration, diabetic microangiopathies, diabetic neuropathy and inflammation" as subject terms.

RESULTS

In diabetic retinal neuropathy, LCN2 causes impaired retinal photoreceptor function and retinal neurons; in retinal microangiopathy, LCN2 induces apoptosis of retinal vascular endothelial cells and promotes angiogenesis; in retinal inflammation, increased secretion of LCN2 recruits inflammatory cells and induces pro-inflammatory cytokines. Moreover, LCN2 has the potential as a biomarker for DR. Recent studies have shown that retinal damage can be attenuated by silencing LCN2, which may be associated with the inhibition of caspase-1-mediated pyroptosis, and LCN2 may be a new target for the treatment of DR.

CONCLUSIONS

In conclusion, LCN2, involved in the development of diabetic retinopathy, is a key factor in diabetic retinal microangiopathy, neurodegeneration, and retinal inflammation. LCN2 is likely to be a novel molecular target leading to DR, and a more in-depth study of the pathogenesis of DR caused by LCN2 may provide considerable benefits for clinical research and potential drug development.

Parallelism and non-parallelism in diabetic nephropathy and diabetic retinopathy

Diabetic nephropathy (DN) and diabetic retinopathy (DR), as microvascular complications of diabetes mellitus, are currently the leading causes of end-stage renal disease (ESRD) and blindness, respectively, in the adult working population, and they are major public health problems with social and economic burdens. The parallelism between the two in the process of occurrence and development manifests in the high overlap of disease-causing risk factors and pathogenesis, high rates of comorbidity, mutually predictive effects, and partial concordance in the clinical use of medications. However, since the two organs, the eye and the kidney, have their unique internal environment and physiological processes, each with specific influencing molecules, and the target organs have non-parallelism due to different pathological changes and responses to various influencing factors, this article provides an overview of the parallelism and non-parallelism between DN and DR to further recognize the commonalities and differences between the two diseases and provide references for early diagnosis, clinical guidance on the use of medication, and the development of new drugs.

PFKFB3 in neovascular eye disease: unraveling mechanisms and exploring therapeutic strategies

BACKGROUND

Neovascular eye disease is characterized by pathological neovascularization, with clinical manifestations such as intraocular exudation, bleeding, and scar formation, ultimately leading to blindness in millions of individuals worldwide. Pathologic ocular angiogenesis often occurs in common fundus diseases including proliferative diabetic retinopathy (PDR), age-related macular degeneration (AMD), and retinopathy of prematurity (ROP). Anti-vascular endothelial growth factor (VEGF) targets the core pathology of ocular angiogenesis.

MAIN BODY

In recent years, therapies targeting metabolism to prevent angiogenesis have also rapidly developed, offering assistance to patients with a poor prognosis while receiving anti-VEGF therapy and reducing the side effects associated with long-term VEGF usage. Phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3), a key enzyme in targeted metabolism, has been shown to have great potential, with antiangiogenic effects and multiple protective effects in the treatment of neovascular eye disease. In this review, we summarize the mechanisms of common types of neovascular eye diseases; discuss the protective effect and potential mechanism of targeting PFKFB3, including the related inhibitors of PFKFB3; and look forward to the future exploration directions and therapeutic prospects of PFKFB3 in neovascular eye disease.

CONCLUSION

Neovascular eye disease, the most common and severely debilitating retinal disease, is largely incurable, necessitating the exploration of new treatment methods. PFKFB3 has been shown to possess various potential protective mechanisms in treating neovascular eye disease. With the development of several drugs targeting PFKFB3 and their gradual entry into clinical research, targeting PFKFB3-mediated glycolysis has emerged as a promising therapeutic approach for the future of neovascular eye disease.

A two-year longitudinal observational study of the peripapillary microvasculature in pediatric type 1 diabetes mellitus patients without visual impairment or diabetic retinopathy

•Neurodegeneration precede microcirculatory deterioration in DR. Early signs can be seen in DM patients without visible DR symptoms, such as glial cell apoptosis and thinner retinal nerve fiber layer.•Peripapillary microvascular abnormalities in the peripapillary region may affect the normal metabolism of neurons and eventually aggravate the process of DR.•Prompting ongoing research to monitor the peripapillary microcirculation and microvasculature among T1DM children for early detection and prevention.•In longitudinal observation, the vessel density of the peripapillary superficial capillary plexus were slightly affected, while vessel density, blood flow, vessel morphological abnormalities and flow impairment area were significantly deteriorated in the deep capillary plexus.•The peripapillary deep capillary plexus is more susceptible and vulnerable to DR progression and could be used as a target for DR screening.

A deep learning system for predicting time to progression of diabetic retinopathy

Diabetic retinopathy (DR) is the leading cause of preventable blindness worldwide. The risk of DR progression is highly variable among different individuals, making it difficult to predict risk and personalize screening intervals. We developed and validated a deep learning system (DeepDR Plus) to predict time to DR progression within 5 years solely from fundus images. First, we used 717,308 fundus images from 179,327 participants with diabetes to pretrain the system. Subsequently, we trained and validated the system with a multiethnic dataset comprising 118,868 images from 29,868 participants with diabetes. For predicting time to DR progression, the system achieved concordance indexes of 0.754-0.846 and integrated Brier scores of 0.153-0.241 for all times up to 5 years. Furthermore, we validated the system in real-world cohorts of participants with diabetes. The integration with clinical workflow could potentially extend the mean screening interval from 12 months to 31.97 months, and the percentage of participants recommended to be screened at 1-5 years was 30.62%, 20.00%, 19.63%, 11.85% and 17.89%, respectively, while delayed detection of progression to vision-threatening DR was 0.18%. Altogether, the DeepDR Plus system could predict individualized risk and time to DR progression over 5 years, potentially allowing personalized screening intervals.

[Objective functional monitoring of retinoprotective treatment in diabetic retinopathy]

In recent years, there has been a growing interest in the contribution of neuroretinal degeneration to the pathogenesis of diabetic retinopathy (DR).

PURPOSE

This study assesses the effect of the drug Retinalamin on the functional state of the retina in patients with DR using the Diopsys NOVA Vision Testing System that utilizes electrophysiological (EP) technology.

MATERIAL AND METHODS

The study included patients with type 1 and 2 diabetes mellitus (DM) with DR of any stage without macular edema. Patients underwent standard ophthalmological examination and objective functional examination of the retina using the Diopsys NOVA Vision Testing System. The control group consisted of patients with type 1 and 2 DM with DR who did not receive Retinalamin.

RESULTS

Significant changes in pattern electroretinography and flash electroretinography parameters were recorded in patients who received a course of Retinalamin. Two clinical examples are presented, which can be designated as the first experience of objective functional monitoring of treatment of patients with DR with Retinalamin.

CONCLUSION

Retinoprotective therapy is necessary already at the early stages of DR. Electroretinography is an objective tool for functional analysis of the earliest changes in retinal cells in DR. It is necessary to use the identified "therapeutic" window for the appointment of retinoprotective agents.

The lack of homology domain and leucine rich repeat protein phosphatase 2 ameliorates visual impairment in rats with diabetic retinopathy through regulation of the AKT-GSK-3β-Nrf2 signal cascade

Pleckstrin homology domain and leucine rich repeat protein phosphatase 2 (PHLPP2) is an emerging player in diverse disorders. Our previous findings have documented that reducing PHLPP2 levels in cultured retinal ganglion cells protects against cellular damage caused by high glucose, indicating a possible link between PHLPP2 and diabetic retinopathy (DR). The present work was dedicated to the investigation of PHLPP2 in DR through in vivo experiments with rat models induced by intraperitoneal injection of streptozotocin. Compared to normal rats, the retinas of rats with DR exhibited a notable increase in the level of PHLPP2. The reduction of PHLPP2 levels in the retina was achieved by the intravitreal administration of adeno-associated viruses expressing specific shRNA targeting PHLPP2. Decreasing the expression of PHLPP2 ameliorated visual function impairment and improved the pathological changes of retina in DR rats. Moreover, decreasing the expression of PHLPP2 repressed the apoptosis, oxidative stress and proinflammatory response in the retinas of rats with DR. Reduction of PHLPP2 levels led to an increase in the levels of phosphorylated AKT and glycogen synthase kinase-3β (GSK-3β). Decreasing the expression of PHLPP2 resulted in increased activation of nuclear factor erythroid 2-related factor 2 (Nrf2), which was reversed by suppressing AKT. Notably, the protective effect of reducing PHLPP2 on DR was eliminated when Nrf2 was restrained. These observations show that the down-regulation of PHLPP2 has protective effects on DR by preserving the structure and function of the retina by regulating the AKT-GSK-3β-Nrf2 signal cascade. Therefore, targeting PHLPP2 may hold promise in the treatment of DR.

A Review on Diabetic Retinopathy

Diabetic retinopathy is a well-recognised microvascular complication of diabetes and is among the leading cause of blindness all over the world. Over the last decade, there have been advances in the diagnosis of diabetic retinopathy and diabetic macular edema. At the same time, newer therapies for the management of diabetic retinopathy have evolved. As a result of these advances, a decline in severe vision loss due to diabetes has been witnessed in some developing countries. However, there is a steady increase in the number of people affected with diabetes, and is expected to rise further in the coming years. Therefore, it is prudent to identify diabetic retinopathy, and timely intervention is needed to decrease the burden of severe vision loss. An effort has been made to review all the existing knowledge regarding diabetic retinopathy in this article and summarize the present treatment options for diabetic retinopathy.

Fractal Phototherapy in Maximizing Retina and Brain Plasticity

The neuroplasticity potential is reduced with aging and impairs during neurodegenerative diseases and brain and visual system injuries. This limits the brain's capacity to repair the structure and dynamics of its activity after lesions. Maximization of neuroplasticity is necessary to provide the maximal CNS response to therapeutic intervention and adaptive reorganization of neuronal networks in patients with degenerative pathology and traumatic injury to restore the functional activity of the brain and retina.Considering the fractal geometry and dynamics of the healthy brain and the loss of fractality in neurodegenerative pathology, we suggest that the application of self-similar visual signals with a fractal temporal structure in the stimulation therapy can reactivate the adaptive neuroplasticity and enhance the effectiveness of neurorehabilitation. This proposition was tested in the recent studies. Patients with glaucoma had a statistically significant positive effect of fractal photic therapy on light sensitivity and the perimetric MD index, which shows that methods of fractal stimulation can be a novel nonpharmacological approach to neuroprotective therapy and neurorehabilitation. In healthy rabbits, it was demonstrated that a long-term course of photostimulation with fractal signals does not harm the electroretinogram (ERG) and retina structure. Rabbits with modeled retinal atrophy showed better dynamics of the ERG restoration during daily stimulation therapy for a week in comparison with the controls. Positive changes in the retinal function can indirectly suggest the activation of its adaptive plasticity and the high potential of stimulation therapy with fractal visual stimuli in a nonpharmacological neurorehabilitation, which requires further study.

Early diabetic eye damage: Comparing detection methods using diagnostic power

It is now clear that retinal neuropathy precedes classical microvascular retinopathy in diabetes. Therefore, tests that underpin useful new endpoints must provide high diagnostic power well before the onset of moderate diabetic retinopathy. Hence, we compare detection methods of early diabetic eye damage. We reviewed data from a range of functional and structural studies of early diabetic eye disease and computed standardized effect size as a measure of diagnostic power, allowing the studies to be compared quantitatively. We then derived minimum performance criteria for tests to provide useful clinical endpoints. This included the criteria that tests should be rapid and easy so that children with type 1 diabetes can be followed into adulthood with the same tests. We also defined attributes that lend test data to further improve performance using Machine/Deep Learning. Data from a new form of objective perimetry suggested that the criteria are achievable.

Release of Pro-Inflammatory/Angiogenic Factors by Retinal Microvascular Cells Is Mediated by Extracellular Vesicles Derived from M1-Activated Microglia

The interactions between the neuronal and vascular sides of the retina during diabetic retinopathy (DR) have gained increasing attention. Microglia is responsible for the immune response to inflammation inside the retina, which could be mediated by paracrine signals carried by extracellular vesicles (EVs). We aimed to characterize EVs released from immortalized human microglial cells in inflammation and investigate their effects on the retinal microvasculature and the anti-inflammatory potential of thiamine in this context. M1 pro-inflammatory polarization in microglia was induced through a cytokine cocktail. EVs were isolated from the supernatants, characterized, and used to stimulate human retinal endothelial cells (HRECs) and pericytes (HRPs). Microvascular cell functions and their release of pro-inflammatory/angiogenic factors were assessed. M1-derived EVs showed increased content of miR-21, miR-155, CCL2, MMP2, and MMP9, and enhanced apoptosis, proliferation, migration, and ROS production in HRPs and HRECs. IL-1β, IL-6, MMP9, CCL2, and VEGF release increased in HRPs exposed to M1-derived EVs, while HRECs showed augmented IL-6, Ang2, VEGF, and PDFG-B. Addition of thiamine to M1-microglial cultures reverted most of these effects. In conclusion, M1-derived EVs stimulate functional changes and secretion of pro-inflammatory/angiogenic molecules in microvascular cells, exacerbating inflammatory damage and retinopathy features. Thiamine added to microglia exerts anti-inflammatory effects.

Hyperglycemia-regulated tRNA-derived fragment tRF-3001a propels neurovascular dysfunction in diabetic mice

Neurovascular dysfunction is a preclinical manifestation of diabetic complications, including diabetic retinopathy (DR). Herein, we report that a transfer RNA-derived RNA fragment, tRF-3001a, is significantly upregulated under diabetic conditions. tRF-3001a downregulation inhibits Müller cell activation, suppresses endothelial angiogenic effects, and protects against high-glucose-induced retinal ganglion cell injury in vitro. Furthermore, tRF-3001a downregulation alleviates retinal vascular dysfunction, inhibits retinal reactive gliosis, facilitates retinal ganglion cell survival, and preserves visual function and visually guided behaviors in STZ-induced diabetic mice and db/db diabetic mice. Mechanistically, tRF-3001a regulates neurovascular dysfunction in a microRNA-like mechanism by targeting GSK3B. Clinically, tRF-3001a is upregulated in aqueous humor (AH) samples of DR patients. tRF-3001a downregulation inhibits DR-induced human retinal vascular endothelial cell and Müller cell dysfunction in vitro and DR-induced retinal neurovascular dysfunction in C57BL/6J mice. Thus, targeting tRF-3001a-mediated signaling is a promising strategy for the concurrent treatment of vasculopathy and neuropathy in diabetes mellitus.

Neuroprotective role of plumbagin on eye damage induced by high-sucrose diet in adult fruit fly Drosophila melanogaster

The natural compound plumbagin has a wide range of pharmacological and potential therapeutic activities, although its role in neuroretina degeneration is unknown. Here we evaluated the effects of plumbagin on retina homeostasis of the fruit fly Drosophila melanogaster fed with high glucose diet, a model of hyperglycemia-induced eye impairment to study the pathophysiology of diabetic retinopathy at the early stages. To this aim, the visual system of flies orally administered with plumbagin has been analyzed at structural, functional, and molecular/cellular level as for instance neuronal apoptosis/autophagy dysregulation and oxidative stress-related signals. Our results demonstrated that plumbagin ameliorates the visual performance of hyperglycemic flies. Drosophila eye-structure, clearly altered by hyperglycemia, i.e. defects of the pattern of ommatidia, irregular rhabdomeres, vacuoles, damaged mitochondria, and abnormal phototransduction units were rescued, at least in part, by plumbagin. In addition, it reactivated autophagy, decreased the presence of cell death/apoptotic features, and exerted antioxidant effects in the retina. In terms of mechanisms favoring death/survival ratio, Nrf2 signaling activation may be one of the strategies by which plumbagin reduced redox unbalance mainly increasing the levels of glutathione-S-transferase. Likewise, plumbagin may act additively and/or synergistically inhibiting the mitochondrial-endoplasmic reticulum stress and unfolded protein response pathways, which prevented neuronal impairment and eye damage induced by reactive oxygen species. These results provide an avenue for further studies, which may be helpful to develop novel therapeutic candidates and drug targets against eye neurotoxicity by high glucose, a key aspect in retinal complications of diabetes.

Correlation of hemoglobin levels with diabetic retinopathy in US adults aged ≥40 years: the NHANES 2005-2008

Purpose

The aim of this study was to explore the connection between hemoglobin levels and diabetic retinopathy (DR).

Methods

Cross-sectional research used data from the National Health and Nutrition Examination Survey (NHANES) 2005-2008. A multiple logistic regression analysis was performed to investigate the association between DR and hemoglobin levels. Additionally, generalized additivity models and smoothed curve fitting were carried out.

Results

After adjusting for several covariates, there was a negative association between hemoglobin levels and DR in the study, which included 837 participants. The negative association between hemoglobin levels and DR was present in men and women, the obese (BMI > 30), and 60- to 69-year-olds in subgroup analyses stratified by sex, BMI, and age. The association between hemoglobin levels and DR in the normal weight group (BMI < 25) displayed an inverted U-shaped curve with an inflection point of 13.7 (g/dL).

Conclusion

In conclusion, our research reveals that high hemoglobin levels are related to a decreased risk of DR. Ascertaining the hemoglobin levels ought to be regarded as an integral facet of the monitoring regimen for patients with diabetic complications and that the risk of DR is reduced through the detection and management of hemoglobin levels.