Neural apoptosis in the retina during experimental and human diabetes. Early onset and effect of insulin

Impairment of Oogenesis and Folliculogenesis in Neonatal Rats after Maternal Exposure to Mobile Phones

Today's lifestyle has led to an increase in infertility. The study investigated the effects of cell phone radiation on oogenesis, folliculogenesis, and gestation stage. Also, its impact on neonates' ovarian hormones and their ovarian development during gestation was investigated. Fifty-four virgin female Wistar rats were randomly divided into three groups: the study group (conversation and stand-by mode, n = 24), the control group (stand-by mode, n = 24), and the sham (turn off, n = 6). The study and control groups were separated into 4 subgroups, including early stage (1st week), mid-stage (2nd week), late stage (3rd week), and all stages (3 weeks). The results showed that the concentration of plasma estrogen and progesterone, ovarian primordial follicle/primary oocyte, the number of primordial follicles, and nuclei diameters in the study and control subgroups decreased significantly in comparison with the sham group. The most significant reduction was observed in subgroups in which mothers were exposed to radiation for a long period during their pregnancy. Compared to the control and sham groups, the number of primordial follicle apoptosis markedly increased in the study subgroups. The pregnant rats showed significant effects in the entire stages of pregnancy, especially during the first stage (the first week) of development, which has not been reported previously. Exposure to cell phones during the different gestation stages probably decreases ovarian hormone secretion and may harm oogenesis. It also inversely increases the apoptosis of primordial follicles. Therefore, the gestational stages and duration of exposure to cell phone radiation affect the risk of ovarian harm.

Neurotrophins of the retina and their involvement in early-stage diabetic retinopathy in an animal model of type 1 diabetes mellitus

IntroductionDiabetic retinopathy (DR) is a blindness-causing disease which belongs to the group of neurodegenerative diseases. Neurodegeneration of the retina is a process, in which retinal neurons suffer irreversible damage. This study aimed to assess the involvement of neurotrophins (brain-derived neurotrophic factor [BDNF] and nerve growth factor [NGF]) in the pathogenesis of DR.MethodsThe study was performed using male Lewis rats with type 1 diabetes mellitus induced by streptozotocin, and the control group included rats without drug administration. In vivo examinations performed over four weeks included eye fundus imaging, measurement of intraocular pressure, and glycemia. After sacrifice, serum and eyeballs were harvested. Post-mortem analyses included a histopathological analysis of the retina and the measurement of BDNF and NGF levels in the serum and eyeball homogenate.ResultsIn the experimental group, early-stage DR was confirmed, and changes in the retina were observed: diabetic rats had relatively thicker outer nuclear layers and relatively thinner inner plexiform layers. A lower level of BDNF was observed in the serum of rats with DR, while the level of NGF in the eyeball homogenate positively correlated with vascular changes.ConclusionsThe observed changes in the levels of neurotrophins in early-stage DR may indicate their involvement in the disease pathogenesis.

Circulating Cell-Free DNA as an Epigenetic Biomarker for Early Diabetic Retinopathy: A Narrative Review

Diabetic retinopathy (DR), a complication of type 2 diabetes mellitus (T2DM), is typically asymptomatic in its early stages. Diagnosis typically relies on routine fundoscopy for the clinical detection of microvascular abnormalities. However, permanent retinal damage may occur well before clinical signs are appreciable. In the early stages of DR, the retina undergoes distinct epigenetic changes, including DNA methylation and histone modifications. Recent evidence supports unique epigenetic 'signatures' in patients with DR compared to non-diabetic controls. These DNA 'signature' sequences may be specific to the retina and may circulate in peripheral blood in the form of cell-free DNA (cfDNA). In this review, we explore the literature and clinical application of cfDNA sampling as an early, non-invasive, accessible assessment tool for early DR detection. First, we summarize the known epigenetic signatures of DR. Next, we review current sequencing technologies used for cfDNA detection, such as magnetic bead-based enrichment, next-generation sequencing, and bisulfite sequencing. Finally, we outline the current research limitations and emerging areas of study which aim to improve the clinical utility of cfDNA for DR evaluation.

Correlation between macular sensitivity and kidney function in patients with diabetes

PurposeThe aim of this study is to investigate the correlation between kidney function in patients with diabetes and macular sensitivity at central 10° using microperimetry.MethodsA cross-sectional study was carried out on 30 diabetic patients (58 eyes). A full-threshold microperimetry of the central 10° of retina (the macula) was performed on all subjects, consisting of 37 measurement points, using a 4-2 representation strategy. Macular sensitivity was expressed as the average threshold value in decibels for the entire field tested. The correlation between macular sensitivity and GFR, as well as microalbuminuria, blood glucose and HbA1c, was calculated using Pearson correlation rank.ResultsA significant positive correlation was observed between GFR and macular sensitivity among both male and female study subjects. For male participants, the correlation was measured to r([16]) = [.615], p = [<.007] and r([15]) = [.844], p = [<.001] for the left and right eyes, respectively. As for female participants, the correlation was r ([9]) = [.903], p = [<.001] and r([10]) = [.941], p = [<.001] for the left and right eyes, respectively. The correlation between macular sensitivity and the following variables was statistically insignificant: microalbuminuria, blood glucose, and HbA1c.ConclusionDespite intact visual acuity measured on standard ophthalmic examination, patients with impaired kidney function had decreased macular sensitivity. This emphasizes the importance of microperimetry in preventative care and detection of early signs of diabetic retinopathy. Furthermore, we should consider the use of microperimetry as an auxiliary tool for monitoring kidney function in diabetics.

Peripapillary Bruch's membrane Opening-Minimum Rim Width (BMO-MRW) and microvascular changes in early diabetic retinopathy

BACKGROUND

To evaluate changes in peripapillary Bruch's Membrane Opening-Minimum Rim Width (BMO-MRW) and its association with peripapillary microvascular in patients with early diabetic retinopathy (DR).

METHODS

This observational cross-sectional study included 105 eyes from 105 diabetic patients, comprising 55 eyes without diabetic retinopathy (No-DR group) and 50 eyes with mild diabetic retinopathy (Mild-DR group). An additional 50 eyes from 50 healthy individuals served as the Control group. All eyes underwent optical coherence tomography (OCT) radial scanning to assess Bruch's membrane opening-minimum rim width (BMO-MRW) and OCT-angiography (OCTA) with a 6 mm × 6 mm scan centered on the optic disc to evaluate perfusion density (PD) and vessel density (VD). OCTA measurements were calibrated based on the FoBMO axis and analyzed using the ETDRS grid. The associations between BMO-MRW and PD/VD were subsequently investigated.

RESULTS

The mean BMO-MRW values were significantly lower in the No-DR (305.78 ± 35.12 μm) and Mild-DR groups (299.42 ± 37.33 μm) compared to the control group (323.56 ± 40.33 μm, P = 0.005), with significant thinning in the superotemporal and inferotemporal quadrants (P = 0.039, 0.047). PD in the inner ETDRS grid decreased from (56.01 ± 10.53)% in the control group to (52.16 ± 8.75)% in the No-DR group and (47.91 ± 12.95)% in the Mild-DR group (P = 0.001), while in the outer ETDRS grid, it declined from (42.92 ± 6.70)% to (40.20 ± 7.24)% and (38.13 ± 8.78)%, respectively (P = 0.008). VD in the inner ETDRS grid showed a reduction from (15.41 ± 2.68) mm⁻¹ in the control group to (14.39 ± 2.17) mm⁻¹ in the No-DR group and (13.55 ± 2.98) mm⁻¹ in the Mild-DR group (P = 0.001), while in the outer ETDRS grid, it decreased from (13.74 ± 2.26)mm⁻¹ to (12.78 ± 2.53)mm⁻¹ and (12.09 ± 2.83)mm⁻¹, respectively (P = 0.006). Significant reductions in PD were observed in the nasal quadrant of the inner ring and the supratemporal quadrant of the outer ring, while VD showed significant decreases in the nasal quadrants of the inner ring and the supratemporal and inferotemporal quadrant of the outer ring. Moreover, BMO-MRW was positively correlated with PD (r = 0.583, P = 0.001) and VD (r = 0.499, P = 0.001) in the inner ring, with positive correlations observed between BMO-MRW and inner PD and VD in the counterpart quadrants.

CONCLUSIONS

Peripapillary BMO-MRW is significantly reduced in early DR, particularly in the superotemporal and inferotemporal quadrants, alongside declines in PD and VD. The positive correlation between BMO-MRW and microvascular parameters suggests its potential as a biomarker for early DR detection and monitoring.

Association between thyroid stimulating hormone levels and nonproliferative diabetic retinopathy: a cross-sectional study

BACKGROUND

The association between thyroid-stimulating hormone (TSH) and type 2 diabetes mellitus (T2DM) is well known. However, whether TSH is related to nonproliferative diabetic retinopathy (NPDR) has not been studied. This study aimed to explore the relationship between TSH and NPDR in Chinese patients with T2DM.

METHODS

In this cross-sectional study, 427 patients with T2DM were enrolled. The individuals were classified into two groups according to the fundus oculi examination: the non-diabetic retinopathy (NDR) group (n = 224) and the non-proliferative diabetic retinopathy (NPDR) group (n = 203). The individuals' demographic and clinical data were collected by reviewing medical records and direct interviews. The demographic data and biochemical parameters were compared between groups using the Student's t - test or the Mann‒Whitney U test, anthropometric measurements, thyroid function, and NPDR were evaluated, and the associations between TSH and NPDR were assessed using logistic regression models.

RESULTS

No significant differences in age, sex, body mass index (BMI), incidence of alcohol consumption, and duration of diabetes were found between these two groups. The systolic blood pressure (SBP), incidence of smoking, TSH, blood urea nitrogen (BUN), and urinary micro-albumin (mALB) were significantly higher in the NPDR group than in the NDR group (P < 0.05). Individuals in the NDR group had higher levels of thyroxine (T4), glutamic pyruvic transaminase (ALT), fasting C-peptide (FCP), and 2-hour C-peptide (2hCP) than individuals in the NPDR group (P < 0.05). Spearman's correlation analysis revealed that the serum TSH levels were negatively associated with the HbA1c levels in all patients (r=-0.11, P < 0.05). Serum TSH levels were negatively correlated with HbA1c levels (r = -0.19, P < 0.01) and positively correlated with diabetes duration (r = 0.14, P < 0.05) in the NPDR group. Multivariate logistic regression analysis revealed that high TSH levels, sex, diabetes duration, high-density lipoprotein cholesterol (HDL-C), glycosylated hemoglobin (HbA1c), FCP, and SBP were associated with NPDR [odds ratio (OR) > 1, P < 0.05]. Receiver operating characteristic curve analysis revealed that the optimal cutoff point of TSH for predicting NPDR was 2.235 mIU/L.

CONCLUSION

The TSH level is independently associated with NPDR in the Chinese population with T2DM. A high serum TSH level may be a potential risk factor for NPDR and an indicator for screening for diabetic microangiopathy.

TRIAL REGISTRATION

This study is registered with the Chinese Clinical Trial Registry (02/21/2025 ChiCTR2500097614).

Genetic mechanisms of dynamic functional connectivity density in diabetic retinopathy brains: a combined transcriptomic and resting-state functional magnetic resonance imaging study

Background

Diabetic retinopathy (DR) is a condition characterized by fundus lesions resulting from retinal microvascular leakage and obstruction linked to chronic progressive diabetes mellitus. Previous neuroimaging research has revealed both structural and functional changes in the brains of DR patients. Nevertheless, the variations in dynamic functional connectivity density (dFCD) within the brains of DR patients, along with the underlying molecular mechanisms connected to these changes, have yet to be fully understood.

Methods

Forty-seven diabetic retinopathy (DR) patients and 46 healthy controls (HCs) matched for sex, age, and education were recruited for this study from the Department of Ophthalmology at the Jiangxi Provincial People's Hospital. All subjects underwent resting-state functional magnetic resonance imaging scans to analyze the differences in dFCD between the two groups. Utilizing the Allen Human Brain Atlas, we conducted spatial correlation analyses integrating transcriptomic and neuroimaging data to pinpoint genes showing correlated expression levels with dFCD alterations in DR patients. Subsequently, we carried out gene enrichment, specific expression, and protein-protein interaction analyses.

Results

In comparison to the HC group, the DR group exhibited significantly reduced dFCD variability in the left anterior cingulum, left superior occipital gyrus, and right postcentral gyrus. The abnormal dFCD variability is linked to 1,318 positively and 1,318 negatively associated genes, primarily enriched for biological functions such as ion channels, synapses, and cellular junctions. Specific expression analysis revealed that these genes were distinctly expressed in Purkinje neurons, cortex, and striatum brain regions. Furthermore, protein-protein interaction (PPI) analyses indicated that these positive and negative genes could organize PPI networks with the support of respective hub genes.

Conclusion

our study identified altered dFCD variability in brain regions linked to visual and cognitive functions in DR patients. Moreover, transcriptome-neuroimaging correlation analyses revealed a spatial association between these dFCD changes and the genes with unique functional profiles. These genes were enriched in biologically significant functions and pathways, specific to certain cells and brain areas. Our research offers novel understandings of the genetic mechanisms influencing dFCD alterations in DR.

Chronic intermittent hypoxia disrupts protective microgliosis in ischemic proliferative retinopathy

Sleep apnea that leads to chronic intermittent hypoxia (CIH) is an independent risk factor for advanced, debilitating ischemic proliferative retinopathies, such as diabetic retinopathy (DR) and retinopathy of prematurity (ROP). The underlying mechanisms are unknown. Here we investigated the consequences of CIH on the ischemic retina of the oxygen-induced retinopathy model. We show that experimental CIH inhibited colony stimulating factor 1 (CSF1) expression, blunting the reactive microgliosis during the ischemic phase of OIR. CIH severely delayed beneficial revascularization of the ischemic retina and increased pathological neovascularization. CIH also induced photoreceptor segment thinning and accentuated OIR-induced inner and outer retinal functional deficits. Mechanistically we demonstrated that local CSF1R inhibition during ischemic retinopathy reduced the number of microglial cells, inhibited revascularization, and exacerbated pathological neovascularization, recapitulating the effects of CIH. Our findings provide a novel mechanism by which sleep apnea and CIH aggravate ischemic retinopathies, underscoring the importance of treating apnea in DR and ROP to help prevent sight threatening severe disease.

Role of Tau Protein Hyperphosphorylation in Diabetic Retinal Neurodegeneration

Diabetic retinal neurodegeneration (DRN) is an early manifestation of diabetic retinopathy (DR) characterized by neurodegeneration that precedes microvascular abnormalities in the retina. DRN is characterized by apoptosis of retinal ganglion cells (involves alterations in retinal ganglion cells [RGCs], photoreceptors, amacrine cells and bipolar cells and so on), reactive gliosis, and reduced retinal neuronal function. Tau, a microtubule-associated protein, is a key mediator of neurotoxicity in neurodegenerative diseases, with functions in phosphorylation-dependent microtubule assembly and stabilization, axonal transport, and neurite outgrowth. The hyperphosphorylated tau (p-tau) loses its ability to bind to microtubules and aggregates to form paired helical filaments (PHFs), which further form neurofibrillary tangles (NFTs), leading to abnormal cell scaffolding and cell death. Studies have shown that p-tau can cause degeneration of RGCs in DR, making tau pathology a new pathophysiological model for DR. Here, we review the mechanisms by which p-tau contribute to DRN, including insulin resistance or lack of insulin, mitochondrial damage such as mitophagy impairment, mitochondrial axonal transport defects, mitochondrial bioenergetics dysfunction, and impaired mitochondrial dynamics, Abeta toxicity, and inflammation. Therefore, this article proposes that tau protein hyperphosphorylation plays a crucial role in the pathogenesis of DRN and may serve as a novel therapeutic target for combating DRN.

Extracellular Mitochondria Exacerbate Retinal Pigment Epithelium Degeneration in Diabetic Retinopathy

Advancements in fundus imaging are revealing disruptions in the neurovascular unit in diabetic retinopathy (DR). In the era of anti-vascular endothelial growth factor treatment, a thorough characterization of neurodegeneration is imperative until patients with DR are sufficiently treated. Here, we demonstrate that extracellular mitochondria exacerbate retinal pigment epithelium (RPE) degeneration and inflammation in DR. Extracellular mitochondria increased in the vitreous of patients with DR and were associated with visual impairment but not with proliferative diabetic retinopathy or diabetic macular edema. Animal experiments demonstrated detrimental effects of extracellular mitochondria on RPE and photoreceptors. Lysosomal cell death induced by extracellular mitochondria in RPE cells required mitochondrial DNA but not its pattern recognition receptors. Furthermore, biochemical screening identified candidates for DNA receptors. Among them, DNA-dependent protein kinase was necessary for extracellular mitochondria-induced cell death in both in vitro and in vivo experiments. Extracellular mitochondria further induced interleukin-1β and tumor necrosis factor-α expression in RPE cells in a Toll-like receptor 9-dependent manner. RNA sequencing suggested that extracellular mitochondria exacerbate inflammation by promoting the proliferation and migration of macrophages, at least in part. In summary, extracellular mitochondria are designated as a novel exacerbating factor of RPE degeneration in DR.

ARTICLE HIGHLIGHTS

A therapeutic strategy for retinal pigment epithelium degeneration should be developed in diabetic retinopathy. We investigated the molecular mechanisms underpinning retinal pigment epithelium degeneration by extracellular mitochondria in diabetic retinopathy. Extracellular mitochondria were found in the vitreous humor of patients with diabetic retinopathy and exacerbated retinal pigment epithelium degeneration through DNA-dependent protein kinase, cytokine expression via Toll-like receptor 9, and macrophage activation. Extracellular mitochondria are designated as an aggravating factor of neurodegeneration and inflammation in diabetic retinopathy.

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.

Retinal and Choriocapillaris Thickness Changes in Spontaneously Diabetic Macaques

Purpose

Beyond the clinically apparent damage to the retinal vasculature, diabetes affects the neuroretina and choroid. Nonhuman primates (NHPs) serve as valuable models for human retinal diseases, including diabetic retinopathy. This study aimed to investigate changes in the thickness of the retina, RPE, and choriocapillaris in spontaneously diabetic cynomolgus macaques.

Methods

Optical coherence tomography (OCT) images were obtained from 25 diabetic macaques and 26 age-matched nondiabetic macaques. The thickness of individual retinal layers in the macula, along with RPE and choriocapillaris, was measured manually. Choriocapillaris thickness was assessed in postmortem human globes from diabetic and nondiabetic individuals.

Results

Diabetes predominantly affected the inner retina more than the outer retina in macaques. Notably, the nasal retina showed greater thinning compared to the temporal retina. A slight but significant thickening of the inner nuclear layer was observed. No changes were detected in the thickness of RPE/Bruch's membrane complex via OCT. However, a significant increase in choriocapillaris thickness was noted in the diabetic macaques. Postmortem human specimens from patients with nonproliferative diabetic retinopathy (NPDR) also demonstrated thickening of choriocapillaris/Bruch's membrane.

Conclusions

Consistent with humans, early diabetes in cynomolgus macaques results in notable alterations in retinal thickness, particularly affecting the nasal inner retina. The observed increase in choriocapillaris thickness in both diabetic macaques and human patients with NPDR likely indicates pathologic changes and remodeling due to diabetes. Cynomolgus macaque presents a valuable NHP model for studying diabetic retinopathy.

Hepatic Satellite Cell Activation and Alteration of Vitamin A Status Are Relevant to the Aggravation of Retinopathy by T2DM

Purpose

Type 2 diabetes mellitus (T2DM) leads to diabetic retinopathy (DR) and hepatic impairments. The potential mutual interaction and the intermediator between these two injuries are not well elucidated. Both the retina and liver are involved in vitamin A metabolism, suggesting a potential involvement of vitamin A and its metabolites in this mutual interaction. This study aimed to elucidate the impact of either DR or hepatic impairment on the pathogenesis and vitamin A status of each during injury progression.

Methods

A streptozotocin (STZ)-high-fat diet (HFD)-induced T2DM rodent model was applied to examine via electroretinography (ERG) retinal and hepatic histopathology at 0, 12, 16, 20, 24, 28, and 30 weeks after T2DM induction. The levels of retinol in the retina, liver, serum, all-trans-retinal in the retina, and retinyl palmitate in the liver were measured at various time points after T2DM induction.

Results

Retinal dysfunction, evidenced by reduced ERG responses, appeared at week 12, followed by photoreceptor and ganglion cell damage after the 16th week. Hepatic impairments began with hepatic stellate cell activation and decreased retinyl palmitate storage, concurrent with reduced retinal retinol and increased all-trans-retinal. Serum retinol levels remained stable, but reductions in transthyretin (TTR) and retinol-binding protein 4 (RBP4) were found, likely disrupting vitamin A transport in the serum.

Conclusions

These results provide novel insights into hepatic injury and vitamin A status, implicating both in the aggravation of retinopathy under the influence of T2DM. The current results may raise clinical awareness on hepatic issues and vitamin A involvement during DR progression.

Characterization of the Disorganization of the Inner Retinal Layers in Diabetics Using Increased Axial Resolution Optical Coherence Tomography

Purpose

To compare a novel high-resolution optical coherence tomography (OCT) with improved axial resolution (High-Res OCT) with conventional spectral-domain OCT (SD-OCT) with regard to their capacity to characterize the disorganization of the retinal inner layers (DRIL) in diabetic maculopathy.

Methods

Diabetic patients underwent multimodal retinal imaging (SD-OCT, High-Res OCT, and color fundus photography). Best-corrected visual acuity and diabetes characteristics were recorded. DR was graded using the international clinical diabetic retinopathy severity scale (DRSS). In each OCT B-scan, retinal layers were segmented and the loss of discernibility was annotated. DRIL areas were analyzed in en face projection using FIJI plugins. The Wilcoxon test and regression models were used for statistical analysis.

Results

In 93 eyes of 93 patients (mean age, 61.8 ± 12.9 years) DRIL was identified in 48 eyes. DRIL was most frequent in the central subfield (27%). In DRIL eyes, DRSS was significantly higher (4.43 ± 1.01 vs. 2.12 ± 1.66; P < 0.001), BCVA was significantly worse (0.34 ± 0.38 vs. 0.13 ± 0.22; P < 0.001), and the loss of discernibility of the individual inner retinal layers was significantly smaller in High-Res OCT compared with SD-OCT (0.21 ± 0.29 vs. 1.21 ± 1.21 mm2; P < 0.001). The discernibility loss was greatest in the retinal nerve fiber layer and ganglion cell layer.

Conclusions

DRIL occurs in eyes with advanced diabetic retinopathy, with a characteristic spread: from the inner toward the outer retina. High-Res OCT shows significantly smaller DRIL areas compared with SD-OCT, because of a more precise delineation of the inner retinal layers.

Translational Relevance

Using OCT with increased axial resolution could enhance our understanding of DRIL development and progression, providing deeper insights into pathophysiological aspects, including malperfusion in the inner capillary plexus.

Retinal OCT-Derived Texture Features as Potential Biomarkers for Early Diagnosis and Progression of Diabetic Retinopathy

Purpose

Diabetic retinopathy (DR) is usually diagnosed many years after diabetes onset. Indeed, an early diagnosis of DR remains a notable challenge, and, thus, developing novel approaches for earlier disease detection is of utmost importance. We aim to explore the potential of texture analysis of optical coherence tomography (OCT) retinal images in detecting retinal changes in streptozotocin (STZ)-induced diabetic animals at "silent" disease stages when early retinal molecular and cellular changes that cannot be clinically detectable are already occurring.

Methods

Volume OCT scans and electroretinograms were acquired before and 1, 2, and 4 weeks after diabetes induction. Automated OCT image segmentation was performed, followed by retinal thickness and texture analysis. Blood-retinal barrier breakdown, glial reactivity, and neuroinflammation were also assessed.

Results

Type 1 diabetes induced significant early changes in several texture metrics. At week 4 of diabetes, autocorrelation, correlation, homogeneity, information measure of correlation II (IMCII), inverse difference moment normalized (IDN), inverse difference normalized (INN), and sum average texture metrics decreased in all retinal layers. Similar effects were observed for correlation, homogeneity, IMCII, IDN, and INN at week 2. Moreover, the values of those seven-texture metrics described above decreased throughout the disease progression. In diabetic animals, subtle retinal thinning and impaired retinal function were detected, as well as an increase in the number of Iba1-positive cells (microglia/macrophages) and a subtle decrease in the tight junction protein immunoreactivity, which did not induce any physiologically relevant effect on the blood-retinal barrier.

Conclusions

The effects of diabetes on the retina can be spotted through retinal texture analysis in the early stages of the disease. Changes in retinal texture are concomitant with biological retinal changes, thus unlocking the potential of texture analysis for the early diagnosis of DR. However, this requires to be proven in clinical studies.

Induction of a Müller Glial Cell-Specific Protective Pathway Safeguards the Retina From Diabetes-Induced Damage

Diabetes can lead to cell type-specific responses in the retina, including vascular lesions, glial dysfunction, and neurodegeneration, all of which contribute to retinopathy. However, the molecular mechanisms underlying these cell type-specific responses, and the cell types that are sensitive to diabetes have not been fully elucidated. Using single-cell transcriptomics, we profiled the transcriptional changes induced by diabetes in different retinal cell types in rat models as the disease progressed. Rod photoreceptors, a subtype of amacrine interneurons, and Müller glial cells (MGs) exhibited rapid responses to diabetes at the transcript levels. Genes associated with ion regulation were upregulated in all three cell types, suggesting a common response to diabetes. Furthermore, focused studies revealed that although MG initially increased the expression of genes playing protective roles, they cannot sustain this beneficial effect. We explored one of the candidate protective genes, Zinc finger protein 36 homolog (Zfp36), and observed that depleting Zfp36 in rat MGs in vivo using adeno-associated virus-based tools exacerbated diabetes-induced phenotypes, including glial reactivation, neurodegeneration, and vascular defects. Overexpression of Zfp36 slowed the development of these phenotypes. This work unveiled retinal cell types that are sensitive to diabetes and demonstrated that MGs can mount protective responses through Zfp36.

ARTICLE HIGHLIGHTS

Therapeutic Potential of Dimethyl Sulfoxide via Subconjunctival Injection in a Diabetic Retinopathy Rat Model

BACKGROUND/AIM

Diabetic retinopathy (DR), a complication of diabetes, causes damage to retinal blood vessels and can lead to vision impairment. Persistent high blood glucose levels contribute to this damage, and despite ongoing research, effective treatment options for DR remain limited. Dimethyl sulfoxide (DMSO) has shown anti-inflammatory and antioxidant properties in both in vivo and in vitro studies; however, its potential as an anti-inflammatory agent in the context of DR has not yet been explored. This study aimed to assess the effects of subconjunctival injection of DMSO on the progression of DR.

MATERIALS AND METHODS

DR was induced in rats using intraperitoneal injections of streptozotocin (55 mg/kg), confirmed by measuring blood glucose levels and electroretinography (ERG). The rats were divided into five groups: a normal control group (CON), a DR control group receiving PBS injections (DMSO 0), and three DR groups receiving different concentrations of DMSO (98%, 50%, and 10%). Retinal function was evaluated using ERG at weeks 10 and 14, and histological analysis at week 16.

RESULTS

The DMSO 50 group had significantly higher B-wave amplitude in ERG compared to the DMSO 0 group (p<0.05). Flicker response amplitudes were also significantly greater in the DMSO 50 and DMSO 10 groups compared to DMSO 0 (p<0.05). Histological examination revealed thinner retinal layers in the DMSO 0 group compared to the CON group, while the DMSO-treated groups showed improved retinal thickness.

CONCLUSION

Subconjunctival injection of 50% DMSO appears to improve retinal function in a rat model of DR.

[A modern perspective on the pathogenesis of proliferative diabetic retinopathy]

This article reviews the pathogenic mechanisms underlying proliferative diabetic retinopathy (DR), focusing on the development of angio-fibrotic switch, neurodegeneration, pro-inflammatory and pro-angiogenic biomarkers, emphasizes the modern perspectives on the role of the vitreous body and mechanical traction in DR progression. Understanding of these pathogenic mechanisms will provide new opportunities for improvement and development of treatments for DR at earlier stages, before significant and persistent functional impairment occurs.

Modular Architecture of Retinal Layers in Diabetic Patients Without Retinopathy

Purpose Diagnosing diabetic retinopathy (DR) in the pre-clinical stage is crucial to reversing DR. This study aimed to compare the retinal thickness changes between healthy controls (HCs) and diabetics without retinopathy (DWORs). For the first time, we would like to introduce the concept of network modularity analysis in studying retinal networks to demonstrate disrupted retinal layer organization as evidence of subclinical retinopathy. Methods This was a cross-sectional study on 156 eyes of HCs and 78 eyes of DWORs. Retinal layer thickness was measured on Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany). Average thickness values from the outer ring of the ETDRS grid (Avg_O) and the inner ring (Avg_I) were calculated for each layer. Mean retinal thicknesses for each layer between the two groups were compared using the t-test. Age-related thickness changes were compared between the groups using Fisher's r-to-z transform. Group-based structural covariance networks were estimated for both DWORs and HCs. Optimal community architecture was estimated using Louvain's modularity. Results Inner retinal layers, namely RNFL_C (HC: 10.16 ± 2.48 µm versus DWOR: 10.85 ± 2.23 µm; p=0.023) and INL_Avg_I (HC: 39.9 ± 3.7 µm versus DWOR: 40.9 ± 3.16 µm; p=0.035), were thicker in the DWOR group compared to the HC group. Outer retinal layers, namely OR_C (HC: 89.9 ± 3.8 µm versus DWOR: 88.7 ± 3.6 µm; p=0.017) and OR_Avg_I (HC: 81.4 ± 3.16 µm versus DWOR: 80.5 ± 2.28 µm; p=0.02), were thinner in the DWOR group compared to the HC group. The central sub-field showed an age-related thickening in retinal nerve fiber layer (RNFL) (r=0.117, p=0.04), GCL (r=0.078, p=0.17), inner plexiform layer (r=0.137, p=0.01), inner nuclear layer (INL) (r=0.29, p≤0.001), outer plexiform layer (r=0.256, p<0.001), and outer nuclear layer (r=0.197, p=0.001) layers in the HC group, which was not seen in the DWOR group. There was an abnormal increase in modularity among DWORs compared to HCs (Qhc=0.47, Qdowr=0.51, p=1.6x10-8). In the DWOR group, we noted a disruption in the community architecture and minimal inter-community interactions compared to HCs. Conclusion RNFL and INL are thicker in DWORs compared to HCs. Outer retinal layers are thinner in DWORs compared to HCs. On modularity analysis, we noted a disruption in the community architecture in the DWOR group compared to the HC group.

Severity Scale of Diabetic Macular Ischemia Based on the Distribution of Capillary Nonperfusion in OCT Angiography

Purpose

To evaluate the severity scales of diabetic macular ischemia (DMI) by analyzing the quantity and distribution of capillary nonperfusion using OCT angiography (OCTA) images.

Design

A single-center, prospective case series.

Participants

Three hundred one eyes from 301 patients with diabetic retinopathy.

Methods

We acquired 3 × 3-mm swept-source OCTA images and created en face images within a central 2.5-mm circle. The circle was divided into 15 × 15-pixel squares and nonperfusion squares (NPSs) were defined as those without retinal vessels. Eyes with high-dimensional spatial data were arranged on a 2-dimensional space using the uniform manifold approximation and projection (UMAP) algorithm and classified by clustering into 5 groups: Initial, Mild, Superficial, Moderate, and Severe.

Main Outcome Measures

Development of a severity scale for DMI.

Results

Eyes arranged on a 2-dimensional UMAP space were divided into 5 clusters, based on the similarity of nonperfusion area distribution. Nonperfusion square counts in the deep layer increased in eyes of the Initial, Mild, Moderate, and Severe groups in a stepwise manner. In contrast, there were no significant changes in superficial NPS counts between eyes of the Initial and Mild groups. In the intermediate stage, eyes of the Superficial group exhibited higher NPS counts in the central sector of the superficial layer compared with those of the Moderate group. The foveal avascular zone extended into the temporal subfield of the deep layer in eyes of the Moderate group. Eyes of the Severe group had significantly poorer visual acuity that was more frequently accompanied with proliferative diabetic retinopathy.

Conclusions

The application of dimensionality reduction and clustering has facilitated the development of a novel severity scale for DMI based on the distribution of capillary nonperfusion in OCTA images.

Financial Disclosures

The authors have no proprietary or commercial interest in any materials discussed in this article.

Diabetic Retinopathy - Pathophysiology to Treatment: A Review

Diabetic retinopathy (DR) is a microvascular disease affecting the eyes of diabetic patients, and is the most prevalent complication of diabetes mellitus. Vision improvement is not possible in the majority of DR patients. Several studies have indicated that microvascular changes, inflammation, oxidative stress, and retinal neurodegeneration are involved in the pathogenesis of DR. Therefore, there is an urgent need for the development of new and effective treatment for DR. Understanding the molecular mechanisms involved in the pathogenesis of disease will pave a way for better treatment and management of DR. This article has emphasized the molecular pathogenesis and treatment of DR.

Ultrastructural imaging biomarkers in diabetic macular edema: A major review

Diabetic macular edema (DME) is a vision-threatening complication of diabetic retinopathy and causes significant morbidity in patients. Anti-vascular endothelial growth factor (VEGF) agents are the mainstay of treatment for DME, with steroid implants being used for the treatment of anti-VEGF resistant eyes. Over the years, several classification systems have been devised to describe the patterns of DME using optical coherence tomography (OCT). With the advent of effective treatments, it has become imperative that imaging cues are not merely used for classifying the disease but also as biomarkers for prognostication of disease activity and treatment response. In this aspect, newer imaging findings such as hyperreflective dots, photoreceptor integrity, and disorganization of retinal inner layers have been characterized in detail by several authors. Macular perfusion analysis using OCT angiography is the latest in the armamentarium for imaging DME. In this narrative review, we have summarized all relevant literature related to the ultrastructural imaging-based biomarkers of DME and their correlation to treatment.

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.

Effect of panretinal photocoagulation versus intravitreal bevacizumab injection on optic disc microcirculation in patients with diabetic retinopathy

BACKGROUND

This retrospective study aimed to compare optic disc vasculature changes in 1 and 3 months after treatment with either panretinal photocoagulation (PRP) or Intravitreal bevacizumab (IVB) in patients with diabetic retinopathy.

METHODS

A total of 50 eyes of 29 diabetic patients without severe complications were included in this comparative case series. Of these, twenty-eight eyes (15 patients) were assigned to the PRP group, while twenty-two eyes (14 patients) were treated with the biosimilar (IVB) (Stivant® CinnaGen Co., Iran). Optical tomography angiography (OCTA) was performed to measure optic disc vascular density (VD) as well as retinal nerve fiber layer (RNFL) thickness.

RESULTS

The mean age of the enrolled patients was 62.1 ± 8.3 years (40 to 78 years). During follow-up, whole disc VD, inside disc VD and peripapillary VD decreased significantly in the PRP group at month 1 (p = 0.032, p = 0.32, and p = 0.016, respectively) and month 3 (p = 0.004, p = 0.001 and p = 0.011, respectively). There was an insignificant and slight increase for these parameters in the IVB group. (p > 0.05 for all) A comparison of two treatment arms based on mean whole disc VD, inside disc VD, and peripapillary VD changes revealed a significant difference at month 1 (p = 0.009, p = 0.019, and p = 0.002, respectively) and month 3 (p = 0.002, p = 0.015, and p = 0.009, respectively). Peripapillary RNFL thickness increased in the PRP group at month 1 (p = 0.002) and then decreased at month 3 (p = 0.001). During three months of follow-up, the peripapillary RNFL thickness decreased significantly in the IVB group (p = 0.001). Peripapillary RNFL thickness changes were significantly different between treatment groups at month 1 and month 3. (p = 0.001 for both) The RNFL changes during the study did not significantly correlate with peripapillary VD changes in each group (p = 0.231 and p = 372, for PRP and IVB group, respectively).

CONCLUSION

This study demonstrated that IVB and PRP treatments produced distinct short-term microvascular changes in the optic nerve of diabetic retinopathy patients. PRP treatment significantly reduced vascular density in the optic disc and peripapillary region over 3 months, with an initial increase in RNFL thickness followed by a decrease by month 3. In contrast, IVB treatment led to a slight increase in optic disc vascular density while significantly reducing RNFL thickness. No significant correlation was found between changes in RNFL thickness and peripapillary vascular density within either treatment group.

SMOX Inhibition Preserved Visual Acuity, Contrast Sensitivity, and Retinal Function and Reduced Neuro-Glial Injury in Mice During Prolonged Diabetes

Diabetic retinopathy, a major cause of vision loss, is characterized by neurovascular changes in the retina. The lack of effective treatments to preserve vision in diabetic patients remains a significant challenge. A previous study from our laboratory demonstrated that 12-week treatment with MDL 72527, a pharmacological inhibitor of spermine oxidase (SMOX, a critical regulator of polyamine metabolism), reduced neurodegeneration in diabetic mice. Utilizing the streptozotocin-induced diabetic mouse model and MDL 72527, the current study investigated the effectiveness of SMOX inhibition on the measures of vision impairment and neuro-glial injury following 24 weeks of diabetes. Reductions in visual acuity, contrast sensitivity, and inner retinal function in diabetic mice were improved by MDL 72527 treatment. Diabetes-induced changes in neuronal-specific class III tubulin (Tuj-1), synaptophysin, glutamine synthetase, and vimentin were attenuated in response to SMOX inhibition. In conclusion, our findings show that SMOX inhibition improved visual acuity, contrast sensitivity, and inner retinal function and mitigated diabetes-induced neuroglial damage during long-term diabetes. Targeting SMOX signaling may provide a potential strategy for reducing retinal neuronal damage and preserving vision in diabetes.

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.

Role of ferroptosis in mitochondrial damage in diabetic retinopathy

Diabetic retinopathy is driven by oxidative stress-mitochondrial damage. Activation of ROS producing cytosolic NADPH oxidase 2 (Nox2) in diabetes precedes retinal mitochondrial damage, initiating a vicious cycle of free radicals. Elevated ROS levels peroxidize membrane lipids increasing damaging lipid peroxides (LPOs). While glutathione peroxidase 4 (GPx4) neutralizes LPOs, an imbalance in its generation-neutralization leads to ferroptosis, which is characterized by increased LPOs, free iron and decreased GPx4 activity. Mitochondria are rich in polyunsaturated fatty acids and iron and have mitochondrial isoform of GPx4. Our aim was to investigate mitochondrial ferroptosis in diabetic retinopathy, focusing on Nox2 mediated ROS production. Using human retinal endothelial cells, incubated in 5 mM or 20 mM D-glucose for 12-96 h, with or without Nox2 inhibitors (100 μM apocynin, 5 μM EHop-016 or 5 μM Gp91 ds-tat), or ferroptosis inhibitors (1 μM ferrostatin-1, 50 μM deferoxamine) or activator (0.1 μM RSL3), cytosolic and mitochondrial ROS, LPOs, iron, GPx4 activity, mitochondrial integrity (membrane permeability, oxygen consumption rate, mtDNA copy numbers) and cell death were quantified. High glucose significantly increased ROS, LPOs and iron levels and inhibited GPx4 activity in cytosol, and while Nox2 and ferroptosis inhibitors prevented glucose-induced increase in ferroptosis markers, mitochondrial damage and cell death, RSL3, further worsened them. Furthermore, high glucose also increased ferroptosis markers in the mitochondria, which followed their increase in the cytosol, suggesting a role of cytosolic ROS in mitochondrial ferroptosis. Thus, targeting Nox2-ferroptosis should help break down the self-perpetuating vicious cycle of free radicals, initiated by the damaged mitochondria, and could provide novel therapeutics to prevent/retard the development of diabetic retinopathy.

Autophagy-dependent ferroptosis may play a critical role in early stages of diabetic retinopathy

Diabetic retinopathy (DR), as one of the most common and significant microvascular complications of diabetes mellitus (DM), continues to elude effective targeted treatment for vision loss despite ongoing enrichment of the understanding of its pathogenic mechanisms from perspectives such as inflammation and oxidative stress. Recent studies have indicated that characteristic neuroglial degeneration induced by DM occurs before the onset of apparent microvascular lesions. In order to comprehensively grasp the early-stage pathological changes of DR, the retinal neurovascular unit (NVU) will become a crucial focal point for future research into the occurrence and progression of DR. Based on existing evidence, ferroptosis, a form of cell death regulated by processes like ferritinophagy and chaperone-mediated autophagy, mediates apoptosis in retinal NVU components, including pericytes and ganglion cells. Autophagy-dependent ferroptosis-related factors, including BECN1 and FABP4, may serve as both biomarkers for DR occurrence and development and potentially crucial targets for future effective DR treatments. The aforementioned findings present novel perspectives for comprehending the mechanisms underlying the early-stage pathological alterations in DR and open up innovative avenues for investigating supplementary therapeutic strategies.

Deciphering the Connection Between Microvascular Damage and Neurodegeneration in Early Diabetic Retinopathy

Diabetic retinopathy (DR), a common diabetes complication leading to vision loss, presents early clinical signs linked to retinal vasculature damage, affecting the neural retina at advanced stages. However, vascular changes and potential effects on neural cells before clinical diagnosis of DR are less well understood. To study the earliest stages of DR, we performed histological phenotyping and quantitative analysis on postmortem retinas from 10 donors with diabetes and without signs of DR (e.g., microaneurysms, hemorrhages), plus three control eyes and one donor eye with DR. We focused on capillary loss in the deeper vascular plexus (DVP) and superficial vascular plexus (SVP), and on neural retina effects. The eye with advanced DR had profound vascular and neural damage, whereas those of the 10 randomly selected donors with diabetes appeared superficially normal. The SVP was indistinguishable from those of the control eyes. In contrast, more than half of the retinas from donors with diabetes had capillary dropout in the DVP and increased capillary diameter. However, we could not detect any localized neural cell loss in the vicinity of dropout capillaries. Instead, we observed a subtle pan-retinal loss of inner nuclear layer cells in all diabetes cases (P < 0.05), independent of microvascular damage. In conclusion, our findings demonstrate a novel histological biomarker for early-stage diabetes-related damage in the human postmortem retina; the biomarker is common in people with diabetes before clinical DR diagnosis. Furthermore, the mismatch between capillary dropout and neural loss leads us to question the notion of microvascular loss directly causing neurodegeneration at the earliest stages of DR, so diabetes may affect the two readouts independently.

ARTICLE HIGHLIGHTS

Demographic and Metabolic Risk Factors Associated with Development of Diabetic Macular Edema among Persons with Diabetes Mellitus

Purpose

Diabetic macular edema (DME), a leading cause of visual impairment, can occur regardless of diabetic retinopathy (DR) stage. Poor metabolic control is hypothesized to contribute to DME development, although large-scale studies have yet to identify such an association. This study aims to determine whether measurable markers of dysmetabolism are associated with DME development in persons with diabetes.

Design

Retrospective cohort study.

Participants

Using data from the Sight Outcomes Research Collaborative (SOURCE) repository, patients with diabetes mellitus and no preexisting DME were identified and followed over time to see what factors associated with DME development.

Methods

Cox proportional hazard modeling was used to assess the relationship between demographic variables, diabetes type, smoking history, baseline DR status, blood pressure (BP), lipid profile, body mass index (BMI), hemoglobin A1C (HbA1C), and new onset of DME.

Main Outcome Measures

Adjusted hazard ratio (HR) of developing DME with 95% confidence intervals (CIs).

Results

Of 47 509 eligible patients from 10 SOURCE sites (mean age 63 ± 12 years, 58% female sex, 48% White race), 3633 (7.6%) developed DME in the study period. The mean ± standard deviation time to DME was 875 ± 684 days (∼2.4 years) with those with baseline nonproliferative DR (HR 3.67, 95% CI: 3.41-3.95) and proliferative DR (HR 5.19, 95% CI: 4.61-5.85) more likely to develop DME. There was no difference in DME risk between type 1 and type 2 patients; however, Black race was associated with a 40% increase in DME risk (HR 1.40, 95% CI: 1.30-1.51). Every 1 unit increase in HbA1C had a 15% increased risk of DME (HR 1.15, 95% CI: 1.13-1.17), and each 10 mmHg increase in systolic BP was associated with a 6% increased DME risk (HR 1.06, 95% CI: 1.02-1.09). No association was identified between DME development and BMI, triglyceride levels, or high-density lipoprotein levels.

Conclusions

These findings suggest that in patients with diabetes modifiable risk factors such as elevated HbA1C and BP confer a higher risk of DME development; however, other modifiable systemic markers of dysmetabolism such as obesity and dyslipidemia did not. Further work is needed to identify the underlying contributions of race in DME.

Financial Disclosures

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

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.

Dyslipidemia and reduced retinal layer thicknesses in mild to moderate non-proliferative diabetic retinopathy

OBJECTIVE

To investigate the changes in ganglion cell layer-inner plexiform layer (GCL-IPL) thickness and its association with peripheral blood indices in non-proliferative diabetic retinopathy (NPDR).

METHODS

In this cross-sectional study, 132 participants were categorized into three groups: 30 healthy volunteers (control group), 50 diabetic patients with non-diabetic retinopathy (NDR group), and 52 patients with NPDR. Optical coherence tomography (OCT) was used to measure the retinal nerve fiber layer (RNFL) and GCL-IPL thicknesses in the macula. The associations between RNFL loss and systemic risk factors for DR, such as diabetes duration, triglyceride (TG), total cholesterol (TC), high-density lipoprotein (HDL), low-density lipoprotein (LDL), and hemoglobin A1c (HbA1c) were evaluated.

RESULTS

The average, superior, and nasal thicknesses in the NDR and NPDR groups were significantly thinner compared to the control group (P=0.002, 0.020, 0.090, respectively). Similarly, GCL-IPL thicknesses in the 3 mm and 6 mm zones of the NDR and NPDR groups were thinner than those in the control group (P=0.040, 0.022, 0.037, respectively). Temporal thicknesses in the 3 mm range of the NDR and NPDR groups were also thinner than in the control group (P=0.010). Superior RNFL thickness was positively correlated with HbA1c (r=0.200, P=0.044), and negatively correlated with HDL (r=-0.198, P=0.047). The average inferior and nasal GCL-IPL thicknesses were negatively correlated with TC across the 3 mm zone (r=-0.211, P=0.033; r=-0.224, P=0.023; r=-0.227, P=0.022). Additionally, the average thickness of GCL-IPL in the 6-mm range were positively correlated with the duration of diabetes (r=0.196, P=0.048).

CONCLUSION

This study demonstrates that dyslipidemia in diabetic patients correlates with reductions in RNFL and GCL-IPL thicknesses, suggesting a role in the pathogenesis of diabetic retinopathy.

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.

Targeting the PINK1/Parkin pathway: A new perspective in the prevention and therapy of diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular complication of diabetes characterized by neurovascular impairment of the retina. The dysregulation of the mitophagy process occurs before apoptotic cell death and the appearance of vascular damage. In particular, mitochondrial alterations happen during DR development, supporting the hypothesis that mitophagy is negatively correlated to disease progression. This process is mainly regulated by the PTEN-induced putative kinase protein 1 (PINK1)/Parkin pathway whose activation promotes mitophagy. In this review, we will summarize the evidence reported in the literature demonstrating the involvement of the PINK1/Parkin pathway in diabetic retinopathy-induced retinal degeneration.

Rodent Models of Retinal Degeneration: From Purified Cells in Culture to Living Animals

Rodent models of retinal degeneration are essential for the development of therapeutic strategies. In addition to living animal models, we here also discuss models based on rodent cell cultures, such as purified retinal ganglion cells and retinal explants. These ex vivo models extend the possibilities for investigating pathological mechanisms and assessing the neuroprotective effect of pharmacological agents by eliminating questions on drug pharmacokinetics and bioavailability. The number of living rodent models has greatly increased with the possibilities to achieve transgenic modifications in animals for knocking in and out genes and mutations. The Cre-lox system has further enabled investigators to target specific genes or mutations in specific cells at specific stages. However, chemically or physically induced models can provide alternatives to such targeted gene modifications. The increased diversity of rodent models has widened our possibility to address most ocular pathologies for providing initial proof of concept of innovative therapeutic strategies.

Translational Research and Therapies for Neuroprotection and Regeneration of the Optic Nerve and Retina: A Narrative Review

Most retinal and optic nerve diseases pose significant threats to vision, primarily due to irreversible retinal neuronal cell death, a permanent change, which is a critical factor in their pathogenesis. Conditions such as glaucoma, retinitis pigmentosa, diabetic retinopathy, and age-related macular degeneration are the top four leading causes of blindness among the elderly in Japan. While standard treatments-including reduction in intraocular pressure, anti-vascular endothelial growth factor therapies, and retinal photocoagulation-can partially delay disease progression, their therapeutic effects remain limited. To address these shortcomings, a range of neuroprotective and regenerative therapies, aimed at preventing retinal neuronal cell loss, have been extensively studied and increasingly integrated into clinical practice over the last two decades. Several of these neuroprotective therapies have achieved on-label usage worldwide. This narrative review introduces several neuroprotective and regenerative therapies for retinal and optic nerve diseases that have been successfully translated into clinical practice, providing foundational knowledge and success stories that serve as valuable references for researchers in the field.

Rationale of Basic and Cellular Mechanisms Considered in Updating the Staging System for Diabetic Retinal Disease

Purpose

Hyperglycemia is a major risk factor for early lesions of diabetic retinal disease (DRD). Updating the DRD staging system to incorporate relevant basic and cellular mechanisms pertinent to DRD is necessary to better address early disease, disease progression, the use of therapeutic interventions, and treatment effectiveness.

Design

We sought to review preclinical and clinical evidence on basic and cellular mechanisms potentially pertinent to DRD that might eventually be relevant to update the DRD staging system.

Participants

Not applicable.

Methods

The Basic and Cellular Mechanisms Working Group (BCM-WG) of the Mary Tyler Moore Vision Initiative carefully and extensively reviewed available preclinical and clinical evidence through multiple iterations and classified these.

Main Outcome Measures

Classification was made into evidence grids, level of supporting evidence, and anticipated future relevance to DRD.

Results

A total of 40 identified targets based on pathophysiology and other parameters for DRD were grouped into concepts or evaluated as specific candidates. VEGFA, peroxisome proliferator-activated receptor-alpha related pathways, plasma kallikrein, and angiopoietin 2 had strong agreement as promising for use as biomarkers in diagnostic, monitoring, predictive, prognostic, and pharmacodynamic responses as well as for susceptibility/risk biomarkers that could underlie new assessments and eventually be considered within an updated DRD staging system or treatment, based on the evidence and need for research that would fit within a 2-year timeline. The BCM-WG found there was strong reason also to pursue the following important concepts regarding scientific research of DRD acknowledging their regulation by hyperglycemia: inflammatory/cytokines, oxidative signaling, vasoprotection, neuroprotection, mitophagy, and nutrients/microbiome.

Conclusion

Promising targets that might eventually be considered within an updated DRD staging system or treatment were identified. Although the BCM-WG recognizes that at this stage little can be incorporated into a new DRD staging system, numerous potential targets and important concepts deserve continued support and research, as they may eventually serve as biomarkers and/or therapeutic targets with measurable benefits to patients with diabetes.

Financial Disclosures

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

Tocotrienol-rich fraction (TRF) protects against retinal cell apoptosis and preserves visual behavior in rats with streptozotocin-induced diabetic retinopathy

BACKGROUND

Tocotrienol is a vitamin E analogue that is known to exert anti-inflammatory and antioxidant effects. Hence, in the current study, the effects of TRF on the expression of pro- and anti-apoptotic proteins in the streptozotocin-induced diabetic rat retinas were investigated. The effect of TRF on the visual behaviour of rats was also studied.

METHODS

Diabetes was induced in rats by intraperitoneal injection of streptozotocin and was confirmed by a blood sugar level of at least 20 mmol/L, 48 h, post-injection. Diabetic rats were divided into a group treated with vehicle (DV) and the other treated with TRF (100 mg/kg; DT). A group of non-diabetic rats treated with vehicle (N) served as the control group. All treatments were administered orally for 12 weeks. Rats were then subjected to an assessment of general behaviour in an open field arena and a two-chamber mirror test to assess their visual behaviour. At the end of the experimental period, rats were sacrificed, and their retinas were isolated to measure the expression of pro- (Casp3, Bax) and anti-apoptotic (Bcl2) markers using RT-qPCR and ELISA. TUNEL staining was used to detect the apoptotic retinal cells.

RESULTS

Treatment with TRF lowered the retinal expression of Casp3 protein by 2.26-folds (p < 0.001) and Bax protein by 2.18-fold (p < 0.001) compared to vehicle-treated rats. The retinal anti-apoptotic protein Bcl2 expression was 1.87-fold higher in DT compared to DV rats (p < 0.001). Accordingly, the Bax/Bcl2 ratio in the TRF-treated group was significantly greater in DT compared to DV rats. Retinal Casp3, Bax, and Bcl2 gene expression, as determined by RT-qPCR, also showed changes corresponding to protein expression. In the open field test, DV rats showed greater anxiety-related behaviour than group N, while the behaviour of DT rats was similar to the N group of rats. DT rats and group N rats preferred the inverse mirror chamber over the mirror-containing chamber in the two-mirror chamber test (p < 0.01).

CONCLUSION

Oral TRF therapy for 12 weeks lowers retinal cell apoptosis by decreasing pro- and increasing anti-apoptotic markers. The preservation of visual behaviour in a two-chamber mirror test supported these retinal molecular alterations in diabetic rats.

HSPB4/CRYAA Protect Photoreceptors during Retinal Detachment in Part through FAIM2 Regulation

Our previous study discussed crystallin family induction in an experimental rat model of retinal detachment. Therefore, we attempted to evaluate the role of α-crystallin in photoreceptor survival in an experimental model of retinal detachment, as well as its association with the intrinsically neuroprotective protein Fas-apoptotic inhibitory molecule 2 (FAIM2). Separation of retina and RPE was induced in rat and mouse eyes by subretinal injection of hyaluronic acid. Retinas were subsequently analyzed for the presence αA-crystallin (HSPB4) and αB-crystallin (HSPB5) proteins using immunohistochemistry and immunoblotting. Photoreceptor death was analyzed using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) staining and cell counts. The 661W cells subjected to FasL were used as a cell model of photoreceptor degeneration to assess the mechanisms of the protective effect of αA-crystallin and its dependence on its phosphorylation on T148. We further evaluated the interaction between FAIM2 and αA-crystallin using a co-immunoprecipitation assay. Our results showed that α-crystallin protein levels were rapidly induced in response to retinal detachment, with αA-crystallin playing a particularly important role in protecting photoreceptors during retinal detachment. Our data also show that the photoreceptor intrinsically neuroprotective protein FAIM2 is induced and interacts with α-crystallins following retinal detachment. Mechanistically, our work also demonstrated that the phosphorylation of αA-crystallin is important for the interaction of αA-crystallin with FAIM2 and their neuroprotective effect. Thus, αA-crystallin is involved in the regulation of photoreceptor survival during retinal detachment, playing a key role in the stabilization of FAIM2, serving as an important modulator of photoreceptor cell survival under chronic stress conditions.

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).

Hyperglycemia-independent neonatal streptozotocin-induced retinopathy (NSIR) in rats

Introduction: Chemicals, such as MNU (N-methyl-N-nitrosourea) and NaIO3 (sodium iodate), are widely used to induce retinal degeneration in rodents. Streptozotocin (STZ) is an analog of N-acetyl glucosamine in which an MNU moiety is linked to a hexose and has a special toxic effect on insulin-producing pancreatic β-cells. It is commonly used to induce hyperglycemia to model diabetes. While intracerebroventricular injection of STZ can produce Alzheimer's disease independent of hyperglycemia, most retinal studies using STZ focus on the effects of hyperglycemia on the retina, but whether STZ has any impact on retinal cells independent of hyperglycemia is unknown. We aimed to investigate the role of cytotoxicity of STZ in rat retina. Methods: Intravitreal or subcutaneous injection of STZ was performed on newborn rats. Electroretinogram (ERG) and H&E staining investigated retinal function and morphological changes. Retinal cell types, cell death, proliferation, inflammation, and angiogenesis were studied by immunostaining. RNA sequencing was performed to examine the transcriptome changes of retinal cells after intravitreal injection of STZ. Results: Intravitreal (5 μg or 10 μg) or subcutaneous (30 mg/kg) injection of STZ at the early stage of newborn rats couldn't induce hyperglycemia but caused NSIR (Neonatal STZ-induced retinopathy), including reduced ERG amplitudes, retinal rosettes and apoptosis, cell cycle arrest, microglial activation, and delayed retinal angiogenesis. STZ did not affect the early-born retinal cell types but significantly reduced the late-born ones. Short-term and long-term hyperglycemia had no significant effects on the NSIR phenotypes. RNA sequencing revealed that STZ induces oxidative stress and activates the p53 pathway of retinal cells. Locally or systemically, STZ injection after P8 couldn't induce SINR when all retinal progenitors exit the cell cycle. Conclusion: NSIR in rats is independent of hyperglycemia but due to STZ's direct cytotoxic effects on retinal progenitor cells. NSIR is a typical reaction to STZ-induced retinal oxidative stress and DNA damage. This significant finding suggests that NSIR may be a valuable model for studying retinal progenitor DNA damage-related diseases, potentially leading to new insights and treatments.

Exploring Neuroprotective Effects of Topical Brimonidine in Experimental Diabetic Retinopathy

BACKGROUND/AIM

Diabetic retinopathy is a leading cause of blindness worldwide, characterized by neurovascular dysfunction. This study aimed to investigate the impact of brimonidine, a selective adrenoceptor agonist, on diabetic retinal neurodegeneration, recognizing the critical role of neurodegeneration in diabetic retinopathy.

MATERIALS AND METHODS

Streptozotocin-induced diabetes was established in adult male Sprague-Dawley rats to mimic diabetic retinopathy. Rats, except non-diabetic control rats, received topical applications of 0.15% brimonidine tartrate (treatment group) or balanced salt solution (diabetic control group) twice daily following diabetes induction. Each group comprised six randomly assigned animals. Retinal samples were analyzed using immunofluorescence staining, apoptosis assay, and western blot.

RESULTS

Topical brimonidine treatment reduced apoptosis of retinal ganglion cells at 8 weeks after induction of diabetes (p<0.05). Glial activation induced by diabetes was reduced by brimonidine treatment. Immunoblot and immunofluorescence assay revealed that the decrease in phospho- protein kinase B (AKT) level resulting from diabetes was also attenuated by brimonidine (p<0.05). Furthermore, brimonidine alleviated the decrease in anti-apoptotic proteins [BCL2 apoptosis regulator (BCL2) and BCL-xl] induced by diabetes (p<0.05). Elevation of phospho-p38 mitogen-activated protein kinase (p38MAPK) and p53 in diabetic rats were reduced by brimonidine (p<0.05). Additionally, brimonidine treatment attenuated the upregulation of the pro-apoptotic molecule BCL-2 associated X in retinas of diabetic rats (p<0.05).

CONCLUSION

These findings suggest that topical brimonidine treatment may protect retinal ganglion cells in experimental diabetes by modulating the AKT pathway and reducing pro-apoptotic p38MAPK levels. This presents a potential neuroprotective approach in diabetes, offering the advantage of localized treatment without the added burden of oral medication.

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.

Advances in Structural and Functional Retinal Imaging and Biomarkers for Early Detection of Diabetic Retinopathy

Diabetic retinopathy (DR), a vision-threatening microvascular complication of diabetes mellitus (DM), is a leading cause of blindness worldwide that requires early detection and intervention. However, diagnosing DR early remains challenging due to the subtle nature of initial pathological changes. This review explores developments in multimodal imaging and functional tests for early DR detection. Where conventional color fundus photography is limited in the field of view and resolution, advanced quantitative analysis of retinal vessel traits such as retinal microvascular caliber, tortuosity, and fractal dimension (FD) can provide additional prognostic value. Optical coherence tomography (OCT) has also emerged as a reliable structural imaging tool for assessing retinal and choroidal neurodegenerative changes, which show potential as early DR biomarkers. Optical coherence tomography angiography (OCTA) enables the evaluation of vascular perfusion and the contours of the foveal avascular zone (FAZ), providing valuable insights into early retinal and choroidal vascular changes. Functional tests, including multifocal electroretinography (mfERG), visual evoked potential (VEP), multifocal pupillographic objective perimetry (mfPOP), microperimetry, and contrast sensitivity (CS), offer complementary data on early functional deficits in DR. More importantly, combining structural and functional imaging data may facilitate earlier detection of DR and targeted management strategies based on disease progression. Artificial intelligence (AI) techniques show promise for automated lesion detection, risk stratification, and biomarker discovery from various imaging data. Additionally, hematological parameters, such as neutrophil-lymphocyte ratio (NLR) and neutrophil extracellular traps (NETs), may be useful in predicting DR risk and progression. Although current methods can detect early DR, there is still a need for further research and development of reliable, cost-effective methods for large-scale screening and monitoring of individuals with DM.

Network pharmacology and biochemical experiments reveal the antiapoptotic mechanism of huperzine A for treating diabetic retinopathy

BACKGROUND/AIMS

Diabetic retinopathy is the most common eye disease that causes blindness in the working population. Neurodegeneration is the early sign of diabetic retinopathy, but no drug has been approved for delaying or reversing retinal neurodegeneration. Huperzine A, a natural alkaloid isolated from Huperzia serrata, displays neuroprotective and antiapoptotic effects in treating neurodegenerative disorders. Our study aims to investigate the effect of huperzine A in preventing retinal neurodegeneration of diabetic retinopathy and its possible mechanism.

METHODS

Diabetic retinopathy model was induced by streptozotocin. H&E staining, optical coherence tomography, immunofluorescence staining and angiogenic factors were used to determine the degree of retinal pathological injury. The possible molecular mechanism was unrevealed by network pharmacology analysis and further validated by biochemical experiments.

RESULTS

In our study, we demonstrated that huperzine A has a protective effect on the diabetes retina in a diabetic rat model. Based on the network pharmacology analysis and biochemical studies, huperzine A may treat diabetic retinopathy via key target HSP27 and apoptosis-related pathways. Huperzine A may modulate the phosphorylation of HSP27 and activate the antiapoptotic signalling pathway.

CONCLUSION

Our findings revealed that huperzine A might be a potential therapeutic drug to prevent diabetic retinopathy. It is the first-time combining network pharmacology analysis with biochemical studies to explore the mechanism of huperzine A in preventing diabetic retinopathy.

Cell and molecular targeted therapies for diabetic retinopathy

Diabetic retinopathy (DR) stands as a prevalent complication in the eye resulting from diabetes mellitus, predominantly associated with high blood sugar levels and hypertension as individuals age. DR is a severe microvascular complication of both type I and type II diabetes mellitus and the leading cause of vision impairment. The critical approach to combatting and halting the advancement of DR lies in effectively managing blood glucose and blood pressure levels in diabetic patients; however, this is seldom achieved. Both human and animal studies have revealed the intricate nature of this condition involving various cell types and molecules. Aside from photocoagulation, the sole therapy targeting VEGF molecules in the retina to prevent abnormal blood vessel growth is intravitreal anti-VEGF therapy. However, a substantial portion of cases, approximately 30-40%, do not respond to this treatment. This review explores distinctive pathophysiological phenomena of DR and identifiable cell types and molecules that could be targeted to mitigate the chronic changes occurring in the retina due to diabetes mellitus. Addressing the significant research gap in this domain is imperative to broaden the treatment options available for managing DR effectively.

Reduced macular thickness and vascular density in abnormal glucose metabolism patients: A meta-analysis of optical coherence tomography (OCT) and OCT angiography studies

BACKGROUND

Alterations in macular thickness and vascular density before clinically visible diabetic retinopathy (DR) remain inconclusive. This study aimed to determine whether retinal manifestations in abnormal glucose metabolism (AGM) patients differ from those in the healthy individuals.

METHODS

PubMed, Embase, and Web of Science were searched between 2000 and 2021. The eligibility criteria were AGM patients without DR. Primary and secondary outcomes measured by optical coherence tomography (OCT) and OCT angiography (OCTA) were analyzed and expressed as standardized mean differences (SMDs) with 95% confidence intervals (CIs). A random-effects model was used in the data synthesis. The potential publication bias for the variables was evaluated using Egger's test.

RESULTS

A total of 86 observational studies involving 13,773 participants and 15,416 eyes were included. OCT revealed that compared to healthy controls, the total macular thickness of AGM patients was thinner, including the thickness of fovea (-0.24, 95% CI [-0.39, -0.08]; P  = 0.002, I2  = 87.7%), all regions of parafovea (-0.32, 95% CI [-0.54, -0.11]; P  = 0.003; I2  = 71.7%) and the four quadrants of perifovea; the thickness of peripapillary retinal nerve fiber layer (pRNFL), macular retinal nerve fiber layer (mRNFL), and ganglion cell layer (GCL) also decreased. OCTA indicated that the superficial and deep vascular density decreased, the foveal avascular zone (FAZ) area enlarged, and the acircularity index (AI) reduced in AGM individuals.

CONCLUSIONS

Retinal thinning and microvascular lesions have occurred before the advent of clinically detectable DR; OCT and OCTA may have the potential to detect these preclinical changes.

REGISTRATION

PROSPERO; http://www.crd.york.ac.uk/prospero/ ; No. CRD42021269885.

Current understanding of subclinical diabetic retinopathy informed by histology and high-resolution in vivo imaging

The escalating incidence of diabetes mellitus has amplified the global impact of diabetic retinopathy. There are known structural and functional changes in the diabetic retina that precede the fundus photography abnormalities which currently are used to diagnose clinical diabetic retinopathy. Understanding these subclinical alterations is important for effective disease management. Histology and high-resolution clinical imaging reveal that the entire neurovascular unit, comprised of retinal vasculature, neurons and glial cells, is affected in subclinical disease. Early functional manifestations are seen in the form of blood flow and electroretinography disturbances. Structurally, there are alterations in the cellular components of vasculature, glia and the neuronal network. On clinical imaging, changes to vessel density and thickness of neuronal layers are observed. How these subclinical disturbances interact and ultimately manifest as clinical disease remains elusive. However, this knowledge reveals potential early therapeutic targets and the need for imaging modalities that can detect subclinical changes in a clinical setting.

Aflibercept Off-Target Effects in Diabetic Macular Edema: An In Silico Modeling Approach

Intravitreal aflibercept injection (IAI) is a treatment for diabetic macular edema (DME), but its mechanism of action (MoA) has not been completely elucidated. Here, we aimed to explore IAI's MoA and its multi-target nature in DME pathophysiology with an in silico (computer simulation) disease model. We used the Therapeutic Performance Mapping System (Anaxomics Biotech property) to generate mathematical models based on the available scientific knowledge at the time of the study, describing the relationship between the modulation of vascular endothelial growth factor receptors (VEGFRs) by IAI and DME pathophysiological processes. We also undertook an enrichment analysis to explore the processes modulated by IAI, visualized the effectors' predicted protein activity, and specifically evaluated the role of VEGFR1 pathway inhibition on DME treatment. The models simulated the potential pathophysiology of DME and the likely IAI's MoA by inhibiting VEGFR1 and VEGFR2 signaling. The action of IAI through both signaling pathways modulated the identified pathophysiological processes associated with DME, with the strongest effects in angiogenesis, blood-retinal barrier alteration and permeability, and inflammation. VEGFR1 inhibition was essential to modulate inflammatory protein effectors. Given the role of VEGFR1 signaling on the modulation of inflammatory-related pathways, IAI may offer therapeutic advantages for DME through sustained VEGFR1 pathway inhibition.