Diabetic retinopathy: recent advances towards understanding neurodegeneration and vision loss

Serum Globulin and Albumin-to-Globulin Ratio are Associated with Diabetic Kidney Disease but Not Diabetic Retinopathy in Type 2 Diabetes Mellitus Patients: A Cross-Sectional Study

Purpose

This study aimed to explore the association of globulin and albumin-to-globulin ratio (AGR) with diabetic kidney disease (DKD) and diabetic retinopathy (DR) in patients with type 2 diabetes mellitus (T2DM).

Methods

This study used data from the China National Diabetic Chronic Complications Study in Shaanxi Province. From April to May 2019, T2DM patients at disease surveillance sites in Shaanxi Province were investigated using a stratified multi-stage sampling method. The participants completed questionnaire surveys, anthropometric and blood pressure measurements, laboratory tests, and fundus photograph examinations. Multivariate Logistic regression and restricted cubic spline model were used to analyze the association of globulin and AGR with DKD and DR, and subgroup analysis was performed according to age, sex, and diabetes duration to test the stability of the results.

Results

A total of 1494 T2DM patients were enrolled in this study, including 495 patients with DKD (33.1%) and 341 patients with DR (22.8%). After adjusting for all covariates, globulin and AGR were linearly associated with DKD. For every 1g/L increase in globulin level, the risk of DKD increased by 7% (OR=1.07, 95% CI=1.04, 1.10). For every 1 unit increase in AGR, the risk of DKD was reduced by 55% (OR=0.45, 95% CI=0.28, 0.72). Subgroup analysis showed that the association between globulin and DKD was consistent across all subgroups, and the association between AGR and DKD was consistent across subgroups of age and diabetes duration; however, only in males, higher AGR was associated with a reduced risk of DKD. No association was found between globulin and AGR with DR.

Conclusion

Globulin is an independent risk factor and AGR is an independent protective factor for DKD. Screening for DKD should be performed in T2DM patients with high globulin and low AGR levels, especially in men.

Prolonged Photobiomodulation with Deep Red Light Mitigates Incipient Retinal Deterioration in a Mouse Model of Type 2 Diabetes

Diabetic retinopathy is a prevalent complication of type 2 diabetes mellitus, characterized by progressive damage to the retinal structure and function. Photobiomodulation therapy, using red or near-infrared light, has been proposed as a non-invasive intervention to mitigate retinal damage, but has been tested generally with short-term stimuli. This study aimed to evaluate the effects of prolonged photobiomodulation with deep red light on retinal structure and function in a type 2 diabetes mouse model. Transgenic LepRdb/J (db/db) mice were exposed to photobiomodulation therapy via LED devices emitting 654 nm light for 12 h daily over ten weeks and compared to untreated mice. Retinal function was evaluated by flash electroretinography, while structural changes were assessed through histology and immunohistochemistry to detect astro- and microgliosis. At 33 weeks of age, db/db mice were obese and severely diabetic, but exhibited only incipient indicators of retinal deterioration. Electroretinogram b-wave peak latencies were prolonged at intermediate flash intensities, while the outer plexiform layer displayed significantly elevated IBA1 expression. Photobiomodulation therapy prevented these two markers of early retinal deterioration but had no effect on other morphological and functional parameters. Photobiomodulation is well-tolerated and maintains potential as a complementary treatment option for diabetic retinopathy but requires further optimization of therapeutic settings and combinatory treatment approaches.

Nuclear proteins and diabetic retinopathy: a review

Diabetic retinopathy (DR) is an eye disease that causes blindness and vision loss in diabetic. Risk factors for DR include high blood glucose levels and some environmental factors. The pathogenesis is based on inflammation caused by interferon and other nuclear proteins. This review article provides an overview of DR and discusses the role of nuclear proteins in the pathogenesis of the disease. Some core proteins such as MAPK, transcription co-factors, transcription co-activators, and others are part of this review. In addition, some current advanced treatment resulting from the role of nuclear proteins will be analyzes, including epigenetic modifications, the use of methylation, acetylation, and histone modifications. Stem cell technology and the use of nanobiotechnology are proposed as promising approaches for a more effective treatment of DR.

Anti-vascular endothelial growth factor drugs combined with laser photocoagulation maintain retinal ganglion cell integrity in patients with diabetic macular edema: study protocol for a prospective, non-randomized, controlled clinical trial

The integrity of retinal ganglion cells is tightly associated with diabetic macular degeneration that leads to damage and death of retinal ganglion cells, affecting vision. The major clinical treatments for diabetic macular edema are anti-vascular endothelial growth factor drugs and laser photocoagulation. However, although the macular thickness can be normalized with each of these two therapies used alone, the vision does not improve in many patients. This might result from the incomplete recovery of retinal ganglion cell injury. Therefore, a prospective, non-randomized, controlled clinical trial was designed to investigate the effect of anti-vascular endothelial growth factor drugs combined with laser photocoagulation on the integrity of retinal ganglion cells in patients with diabetic macular edema and its relationship with vision recovery. In this trial, 150 patients with diabetic macular edema will be equally divided into three groups according to therapeutic methods, followed by treatment with anti-vascular endothelial growth factor drugs, laser photocoagulation therapy, and their combination. All patients will be followed up for 12 months. The primary outcome measure is retinal ganglion cell-inner plexiform layer thickness at 12 months after treatment. The secondary outcome measures include retinal ganglion cell-inner plexiform layer thickness before and 1, 3, 6, and 9 months after treatment, retinal nerve fiber layer thickness, best-corrected visual acuity, macular area thickness, and choroidal thickness before and 1, 3, 6, 9, and 12 months after treatment. Safety measure is the incidence of adverse events at 1, 3, 6, 9, and 12 months after treatment. The study protocol hopes to validate the better efficacy and safety of the combined treatment in patients with diabetic macula compared with the other two monotherapies alone during the 12-month follow-up period. The trial is designed to focus on clarifying the time-effect relationship between imaging measures related to the integrity of retinal ganglion cells and best-corrected visual acuity. The trial protocol was approved by the Medical Ethics Committee of the Affiliated Hospital of Beihua University with approval No. (2023)(26) on April 25, 2023, and was registered with the Chinese Clinical Trial Registry (registration number: ChiCTR2300072478, June 14, 2023, protocol version: 2.0).

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.

Cellular and Molecular Mechanisms of Neuronal Degeneration in Early-Stage Diabetic Retinopathy

BACKGROUND

Studies on the early retinal changes in Diabetic Retinopathy (DR) have demonstrated that neurodegeneration precedes vascular abnormalities like microaneurysms or intraretinal hemorrhages. Therefore, there is a growing field of study to analyze the cellular and molecular pathways involved to allow for the development of novel therapeutics to prevent the onset or delay the progression of DR. Molecular Mechanisms: Oxidative stress and mitochondrial dysfunction contribute to neurodegeneration through pathways involving polyol, hexosamine, advanced glycation end products, and protein kinase C. Potential interventions targeting these pathways include aldose reductase inhibitors and protein kinase C inhibitors. Neurotrophic factor imbalances, notably brain-derived neurotrophic factor and nerve growth factor, also play a role in early neurodegeneration, and supplementation of these neurotrophic factors show promise in mitigating neurodegeneration. Cellular Mechanisms: Major cellular mechanisms of neurodegeneration include caspase-mediated apoptosis, glial cell reactivity, and glutamate excitotoxicity. Therefore, inhibitors of these pathways are potential therapeutic avenues. Vascular Component: The nitric oxide pathway, critical for neurovascular coupling, is disrupted in DR due to increased reactive oxygen species. Vascular Endothelial Growth Factor (VEGF), a long-known angiogenic factor, has demonstrated both damaging and neuroprotective effects, prompting a careful consideration of long-term anti-VEGF therapy.

CONCLUSION

Current DR treatments primarily address vascular symptoms but fall short of preventing or halting the disease. Insights into the mechanisms of retinal neurodegeneration in the setting of diabetes mellitus not only enhance our understanding of DR but also pave the way for future therapeutic interventions aimed at preventing disease progression and preserving vision.

Protective effects and mechanisms of Momordica charantia polysaccharide on early-stage diabetic retinopathy in type 1 diabetes

Momordica charantia polysaccharide (MCP) is a potential drug for the prevention and alleviation of diabetes mellitus (DM) and diabetic retinopathy (DR). This study aimed to investigate the potential protective effects of MCP on early-stage DR and explore the underlying mechanisms. The model group (DM group) and treatment group (D+H group) were established by inducing type 1 DM using a single dose of streptozotocin (STZ) at 60 mg/kg. After modeling, the D+H group was orally administered a 500 mg/kg dose of MCP solution once daily for 12 weeks. Monitoring of systemic indicators (FBG, body weight, general condition) and retinal tissue inflammation and apoptosis (HE staining, IL-6, MCP-1, TNF-α, VEGF, NF-κB, Caspase-3) in this study demonstrated that MCP intervention alleviated both DM and DR. MCP improved the body weight and general condition of DM rats by reducing FBG levels. It also enhanced the anti-inflammatory and anti-apoptotic capabilities of retinal neurons and microvessels by modulating the actions of cytokines, thereby further regulating the inflammation and apoptosis of retinal neurons and microvessels. The underlying mechanisms may be associated with the downregulation of NF-κB and Caspase-3 pathway protein expression, as well as the downregulation of mRNA expression of NF-κB and Caspase-3 pathway genes. Further research is needed to elucidate the potential mechanisms underlying the protective effects of MCP on DR. MCP may emerge as a selective medication for the prevention and alleviation of DM and a novel natural medicine for the prevention and alleviation of DR.

Cross-species scRNA-seq reveals the cellular landscape of retina and early alterations in type 2 diabetes mice

Single-cell RNA sequencing (scRNA-seq) analysis have provided an unprecedented resolution for the studies on diabetic retinopathy (DR). However, the early changes in the retina in diabetes remain unclear. A total of 8 human and mouse scRNA-seq datasets, containing 276,402 cells were analyzed individually to comprehensively delineate the retinal cell atlas. The neural retinas were isolated from the type 2 diabetes (T2D) and control mice, and scRNA-seq analysis was conducted to evaluate the early effects of diabetes on the retina. Bipolar cell (BC) heterogeneity were identified. We found some stable BCs across multiple datasets, and explored their biological functions. A new RBC subtype (Car8_RBC) in the mouse retina was validated using the multi-color immunohistochemistry. AC149090.1 was significantly upregulated in the rod cells, ON cone BCs (CBCs), OFF CBCs, and RBCs in T2D mice. Additionally, the interneurons, especially BCs, were the most vulnerable cells to diabetes by integrating scRNA-seq and genome-wide association studies (GWAS) analyses. In conclusion, this study delineated a cross-species retinal cell atlas and uncovered the early pathological alterations in the retina of T2D mice.

The Molecular Mechanism of Long Non-Coding RNA (LncRNA) Regulation of Notch Signaling in Glucose-Induced Apoptosis of Human Retinal Vascular Endothelial Cell

Diabetes, a global health concern, affects the health of more than 500 million adults. The absence of Notch protein can cause an imbalance in the retinal vascular environment and cause retinal vascular disease. Long noncoding RNA (lncRNA) is known to be involved in the regulation of many signaling pathways. We hope to understand the specific mechanism of apoptosis in retinal vascular endothelial cells (RVECs) by exploring the regulatory effect of lncRNA on the Notch pathway. In this study, we found that RVECs treated with glucose showed increased levels of Notch transcript and protein expression. The lentiviral interference with Notch RNAi reversed this response. When Notch activity decreased, oxidative stress also decreased, accompanied by increased levels of Caspase-9 and Caspase-3 and an increased rate of apoptosis. Therefore, we believe that Notch is involved in the development of diabetic retinopathy and loss of expression promotes apoptosis of human RVECs. By inhibiting the Notch pathway, lncRNA promotes apoptosis of human RVECs in a high-glucose environment.

[Modern concepts of pathogenesis of diabetic retinopathy]

This literature review presents modern view on the pathogenesis of diabetic retinopathy (DR) paying particular attention to the molecular mechanisms leading to its development, as well as the manifestations of retinal neurodegeneration in such patients. Assessment of this condition and its clinical manifestations makes it possible to diagnose DR at the stage of absent initial vascular changes. Investigating the neurodegeneration mechanisms could supplement the existing understanding of the disease pathogenesis and could possibly help find new ways of treatment and prevention of DR.

Recent Advancements in the Medical Treatment of Diabetic Retinal Disease

Diabetic retinal disease remains one of the most common complications of diabetes mellitus (DM) and a leading cause of preventable blindness. The mainstay of management involves glycemic control, intravitreal, and laser therapy. However, intravitreal therapy commonly requires frequent hospital visits and some patients fail to achieve a significant improvement in vision. Novel and long-acting therapies targeting a range of pathways are warranted, while evidence to support optimal combinations of treatments is currently insufficient. Improved understanding of the molecular pathways involved in pathogenesis is driving the development of therapeutic agents not only targeting visible microvascular disease and metabolic derangements, but also inflammation and accelerated retinal neurodegeneration. This review summarizes the current and emerging treatments of diabetic retinal diseases and provides an insight into the future of managing this important condition.

PET Imaging of Vesicular Monoamine Transporter 2 in Early Diabetic Retinopathy Using [18F]FP-(+)-DTBZ

PURPOSE

Diabetic retinopathy (DR) is characterized by dopaminergic neuron loss in the retina of the eyes. [¹⁸F]fluoropropyl-(+)-dihydrotetrabenazine ([¹⁸F]FP-(+)-DTBZ) positron emission tomography (PET) has been shown to detect dopaminergic neuron loss. The study is to investigate the feasibility of PET imaging with [¹⁸F]FP-(+)-DTBZ for early diagnosis of diabetic retinopathy (DR) in diabetes mellitus (DM) rat models.

METHODS

The DM rat model was established by a single intraperitoneal injection of streptozotocin (STZ) (65 mg/kg). After 4 weeks, 8 weeks, and 12 weeks of STZ injection, the retinas of the rats were evaluated by electroretinogram (ERG), color fundus photography (CFP), fundus fluorescein angiography (FFA), and small animal PET scan with [¹⁸F]FP-(+)-DTBZ by targeting vesicular monoamine transporter 2 (VMAT2). [¹⁸F]FP-(+)-DTBZ uptake in retina was quantified as standardized uptake value (SUV). Immunofluorescence staining and Western blot were also performed to confirm the expression level of VMAT2 in retina.

RESULTS

ERG dysfunction was observed at 8 weeks in STZ-diabetic rats, evidenced by smaller amplitudes of oscillatory potentials (OPs) when compared with OPs in normal rats. CFP and FFA showed no significant difference in vascular leakage and neovascularization between STZ-diabetic retinas and normal ones until 8 weeks. PET imaging revealed that the SUV of [¹⁸F]FP-(+)-DTBZ was significantly lower in the STZ-diabetic retinas compared with the normal ones as early as of week 4. The results from immunofluorescence staining and Western blots confirmed the early findings in PET imaging studies.

CONCLUSIONS

Early DR can be non-invasively detected with PET imaging using [¹⁸F]FP-(+)-DTBZ targeting VMAT2. The expression level of VMAT2 in retina may act as a new biomarker for early DR diagnosis.

Correlation of serum delta-like ligand-4 level with the severity of diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) is one of the most serious microvascular complications of type 2 diabetes mellitus (T2DM). Delta-like ligand-4 (DLL4) maintains the normal physiological microenvironment of the retina. However, the relationship between the level of DLL4 and the severity of DR remains unclear.

METHODS

We retrospectively analyzed serum DLL4 levels and other laboratory and clinical data in 94 T2DM patients (35 patients without DR [NDR], 32 with non-proliferative DR [NPDR], 27 with proliferative DR [PDR]), and 30 healthy controls.

RESULTS

The serum DLL4 level was significantly greater in the NDR group (43.38 ± 16.23 pg/mL), NPDR group (56.57 ± 25.89 pg/mL), and PDR group (74.97 ± 25.28 pg/mL) than in the healthy controls (29.9 ± 8.92 pg/mL; all p < 0.05). Among T2DM patients, the level of DLL4 increased as the severity of DR increased (p < 0.05). Logistic regression analysis demonstrated that DR was positively associated with DLL4, glycosylated hemoglobin (HbA1c), fasting blood glucose (FBG), and duration of T2DM (all p < 0.05). Consistently, receiver operating characteristic (ROC) curve analysis also indicated that DLL4 was a potential candidate biomarker for identifying the severity of DR.

CONCLUSIONS

T2DM patients, especially those with DR, have increased serum levels of DLL4. DLL4 may be used as a biomarker and an independent risk factor for DR, and targeting DLL4 may be a potential therapy in patients with DR.

Correlation of Retinal Structure and Visual Function Assessments in Mouse Diabetes Models

Purpose

Diabetic retinopathy results in vision loss with changes to both retinal blood vessels and neural retina. Recent studies have revealed that animal models of diabetes demonstrate early loss of visual function. We explored the time course of retinal change in three different mouse models of diabetes in a longitudinal study using in vivo measures of retinal structure (optical coherence tomography [OCT]) and visual function (optomotor and pupillary responses).

Methods

OCT analysis of retinal microstructure, optokinetic response as a measure of visual acuity, and pupillary response to light stimulation were compared among the db/db, Ins2^Akita, and streptozotocin (STZ)-induced mouse models of diabetes at 1.5, 3, 6, and 9 months of diabetes.

Results

The db/db, Ins2^Akita, and STZ-induced models of diabetes all exhibited vision loss and retinal thinning as disease progressed. Both structural changes and functional measures were significantly correlated with the blood glucose levels. Despite this, vision loss and retinal thinning were not consistently correlated, except for the inner retinal layer thickness at 6 months of diabetes.

Conclusions

This longitudinal study compiled structural measures and functional outcome data for type 1 and 2 diabetes mouse models commonly used for diabetes studies and demonstrated an overall decline in retinal-related health in conjunction with weight change and blood glucose alterations. The relationship between the structural change and functional outcome could be correlative but is not necessarily causative, as retinal thinning was not sufficient to explain visual acuity decline.

Nuclear PKR in retinal neurons in the early stage of diabetic retinopathy in streptozotocin‑induced diabetic rats

Retinal neuron apoptosis is a key component of diabetic retinopathy (DR), one of the most common complications of diabetes. Stress due to persistent hyperglycaemia and corresponding glucotoxicity represents one of the primary pathogenic mechanisms of diabetes and its complications. Apoptosis of retinal neurons serves a critical role in the pathogenesis of DR observed in patients with diabetes and streptozotocin (STZ)‑induced diabetic rats. Retinal neuron apoptosis occurs one month after STZ injection, which is considered the early stage of DR. The molecular mechanism involved in the suppression of retinal neuron apoptosis during the early stage of DR remains unclear. RNA‑dependent protein kinase (PKR) is a stress‑sensitive pro‑apoptotic kinase. Our previous study indicated that PKR‑associated protein X, a stress‑sensitive activator of PKR, is upregulated in the early stage of STZ‑induced diabetes. In order to assess the role of PKR in DR prior to apoptosis of retinal neurons, immunofluorescence and western blotting were performed to investigate the cellular localization and expression of PKR in the retina in the early stage of STZ‑induced diabetes in rats. PKR activity was indirectly assessed by expression levels of phosphorylated eukaryotic translation initiation factor 2α (p‑eIF2‑α) and the presence of apoptotic cells in the retina was investigated by TUNEL assay. The findings revealed that PKR was localized in the nucleus of retinal ganglion and inner nuclear layer cells from normal and diabetic rats. To the best of our knowledge, the present study is the first to demonstrate nuclear localization of PKR in retinal neurons. Immunofluorescence analysis demonstrated that PKR was expressed in the nuclei of retinal neurons at 3 and 6 days and its expression was decreased at 15 days after STZ treatment. In addition, p‑eIF2‑α expression and cellular localization followed the trend of PKR, suggesting that this pro‑apoptotic kinase was active in the nuclei of retinal neurons. These findings are consistent with the hypothesis that nuclear translocation of PKR may be a mechanism to sequester active PKR, thus preventing upregulation of cytosolic signalling pathways that induce apoptosis in retinal neurons. Apoptotic cells were not detected in the retina in the early stage of DR. A model was proposed to explain the mechanism by which apoptosis of retinal neurons by PKR is suppressed in the early stage of DR. The possible role of mitochondrial RNA (mtRNA) and Alu RNA in this phenomenon is also discussed since it was demonstrated that the cellular stress due to prolonged hyperglycaemia induces the release of mtRNA and transcription of Alu RNA. Moreover, it mtRNA activates PKR, whereas Alu RNA inhibits the activation of this protein kinase.

Diabetic retinopathy and diabetic macular oedema pathways and management: UK Consensus Working Group

The management of diabetic retinopathy (DR) has evolved considerably over the past decade, with the availability of new technologies (diagnostic and therapeutic). As such, the existing Royal College of Ophthalmologists DR Guidelines (2013) are outdated, and to the best of our knowledge are not under revision at present. Furthermore, there are no other UK guidelines covering all available treatments, and there seems to be significant variation around the UK in the management of diabetic macular oedema (DMO). This manuscript provides a summary of reviews the pathogenesis of DR and DMO, including role of vascular endothelial growth factor (VEGF) and non-VEGF cytokines, clinical grading/classification of DMO vis a vis current terminology (of centre-involving [CI-DMO], or non-centre involving [nCI-DMO], systemic risks and their management). The excellent UK DR Screening (DRS) service has continued to evolve and remains world-leading. However, challenges remain, as there are significant variations in equipment used, and reproducible standards of DMO screening nationally. The interphase between DRS and the hospital eye service can only be strengthened with further improvements. The role of modern technology including optical coherence tomography (OCT) and wide-field imaging, and working practices including virtual clinics and their potential in increasing clinic capacity and improving patient experiences and outcomes are discussed. Similarly, potential roles of home monitoring in diabetic eyes in the future are explored. The role of pharmacological (intravitreal injections [IVT] of anti-VEGFs and steroids) and laser therapies are summarised. Generally, IVT anti-VEGF are offered as first line pharmacologic therapy. As requirements of diabetic patients in particular patient groups may vary, including pregnant women, children, and persons with learning difficulties, it is important that DR management is personalised in such particular patient groups. First choice therapy needs to be individualised in these cases and may be intravitreal steroids rather than the standard choice of anti-VEGF agents. Some of these, but not all, are discussed in this document.

Anti-inflammatory role of curcumin in retinal disorders (Review)

Curcumin [1,7-bis-(4-hydroxy-3-methoxyphenyl)-hepta-1,6-diene-3,5-dione], the main component of turmeric (Curcuma longa, a flowering plant of the ginger family, Zingiberaceae), is known to possess different pharmacological activities, particularly anti-inflammatory and antioxidant properties. Since an underlying inflammatory process exists in several ocular conditions, such as anterior uveitis, glaucoma, age-related macular degeneration (AMD) and diabetic retinopathy (DR), the aim of the present review was to summarize the pleiotropic effects exerted by this molecule, focusing in particular on its beneficial role in retinal diseases. The anti-inflammatory activity of curcumin has also been described in numerous systemic inflammatory pathologies and tumors. Specifically, the biological, pharmaceutical and nutraceutical properties of curcumin are associated with its ability to downregulate the expression of the following genes: IκBα, cyclooxygenase 2, prostaglandin E2, interleukin (IL)-1, IL-6, IL-8 and tumor necrosis factor-α. According to this finding, curcumin may be useful in the treatment of some retinal disorders. In DR, proliferative vitreoretinopathy and AMD, beneficial effects have been observed following treatment with curcumin, including slowing down of the inflammatory process. Despite the aforementioned evidence, the main disadvantage of this substance is that it possesses a low solubility, as well as poor oral bioavailability due to its reduced absorption, rapid metabolism and rapid elimination. Therefore, several curcumin analogues have been synthesized and tested over the years, in order to improve the possible obtainable therapeutic effects. The purpose of the present review was to identify new aspects that could guide future research on this important traditional medicine, which is a well-tolerated natural product, and is widely considered safe and economical.

Blood-retinal barrier as a converging pivot in understanding the initiation and development of retinal diseases

Clinical ophthalmologists consider each retinal disease as a completely unique entity. However, various retinal diseases, such as uveitis, age-related macular degeneration, diabetic retinopathy, and primary open-angle glaucoma, share a number of common pathogenetic pathways. Whether a retinal disease initiates from direct injury to the blood-retinal barrier (BRB) or a defect/injury to retinal neurons or glia that impairs the BRB secondarily, the BRB is a pivotal point in determining the prognosis as self-limiting and recovering, or developing and progressing to a clinical phenotype. The present review summarizes our current knowledge on the physiology and cellular and molecular pathology of the BRB, which underlies its pivotal role in the initiation and development of common retinal diseases.

Association between renal function and retinal neurodegeneration in Chinese patients with type 2 diabetes mellitus

Background

Chronic kidney disease (CKD) and diabetic retinopathy (DR) are two serious complications of diabetes. However, the association between retinal neurodegeneration in DR and renal function decline is still unclear. Our objective was to evaluate the association by measure estimated glomerular filtration rate (eGFR), macular ganglion cell-inner plexiform layer (GC-IPL), and ganglion cell complex (GCC) thickness in patients with type 2 diabetes mellitus (T2DM).

Methods

We analyzed the baseline data of the Guangzhou Diabetic Eye Study. T2DM patients from communities in Guangzhou were enrolled and all participants went through ophthalmic and general examinations. The thickness of the macular GC-IPL and GCC in their right eyes were measured by swept-source optical coherence tomography. CKD was defined as eGFR <60 mL/min/1.73 m².

Results

One thousand three hundred and nine patients were included (mean age 64.4±7.6 years, 59.1% female), and fifty-eight (4.4%) of them had CKD. Average macular GC-IPL thickness was significantly thinner in CKD patients (96.5±9.1 µm) than non-CKD patients (101.3±9.2 µm) (P<0.01). Average macular GCC thickness was also significantly thinner in CKD patients (123.5±13.2 µm) than non-CKD patients (129.9±12.8 µm) (P<0.01). The significant thinning of macular GC-IPL and GCC thickness presented in every gird in the macula (all, P<0.05) except for central grid (P≥0.05). In the patients without DR, the eGFR was linearly correlated with the average macular GC-IPL thickness [β=0.07 (95% CI, 0.02-0.12), P<0.01] and GCC thickness [β=0.09 (95% CI, 0.03-0.16), P<0.01] after adjustment for age, sex, axial length, intraocular pressure (IOP) and combination of hypertension. However, no linear correlation was found between eGFR and macular GC-IPL or GCC thickness in DR patients.

Conclusions

Renal function decrease is associated with the thinning of the macular GC-IPL and GCC in T2DM patients, suggesting the potential value of ganglion cell lose to detect early function decline in the kidney in diabetic patients, especially in patients without DR.

Evaluation of retinal neurovascular structures by optical coherence tomography and optical coherence tomography angiography in children and adolescents with type 1 diabetes mellitus without clinical sign of diabetic retinopathy

BACKGROUND

The aim of the study was to investigate whether retinal neurovascular structural impairment in children and adolescents with type 1 diabetes mellitus (T1D) without clinical signs of diabetic retinopathy (DR) could be detected early via optical coherence tomography (OCT) and OCT angiography (OCTA).

METHODS

In the current prospective, cross-sectional, observational clinical study children and adolescents with T1D without DR were evaluated between December 2018 and May 2019. Retinal neurovascular structures in the macular and optic disc regions were examined in detail and quantitatively assessed using OCT and OCTA. Data from subjects with T1D were compared with data from healthy controls. Whether retinal neurovascular structural changes were significantly associated with puberty stage, diabetes duration, and HbA1c level was also investigated.

RESULTS

The T1D group included 110 eyes and the control group included 84 eyes. In the T1D group the mean inside disc vessel density (VD) was significantly lower than that of the control group (p < 0.001), as was the mean superior temporal disc VD (p < 0.043). Puberty stage was significantly associated with retinal thickness, parafoveal superficial capillary plexus VD, and peripapillary retinal nerve fiber layer thickness (p < 0.05). Diabetes duration and HbA1c level was significantly correlated with retinal layer thickness, foveal avascular zone diameter, and superficial and deep capillary plexus VDs.

CONCLUSION

In children and adolescents with T1D without clinical signs of DR, the VD of the disc region is affected earlier than the macular region. In these patients, early neurovascular impairment can be detected non-invasively via OCT and OCTA.

Assessment of retinal neurodegeneration with spectral-domain optical coherence tomography: a systematic review and meta-analysis

OBJECTIVES

To comprehensively assess diabetic retinopathy neurodegeneration (DRN) as quantified by retinal neuronal and axonal layers measured with spectral-domain optical coherence tomography (SD-OCT) in subjects with diabetes mellitus (DM).

METHODS

Articles on the topic of examining macular ganglion cell-inner plexiform layer (m-GCIPL), macular retinal nerve fibre layer (m-RNFL), macular ganglion cell complex (m-GCC), and peripapillary RNFL (p-RNFL) measured with SD-OCT in DM subjects without DR (NDR) or with non-proliferative DR (NPDR) were searched in PubMed and Embase up to November 31, 2019. Standardized mean difference (SMD) as effect size were pooled using random-effects model.

RESULTS

Thirty-six studies searched from online databases and the CUHK DM cohort were included in the meta-analysis. In the comparison between NDR and control, macular measures including mean m-GCIPL (SMD = -0.26, p = 0.003), m-RNFL (SMD = -0.26, p = 0.046), and m-GCC (SMD = -0.28; p = 0.009) were significantly thinner in the NDR group. In the comparison between NPDR and NDR, only mean p-RNFL was significantly thinner in the NPDR group (SMD = -0.27; p = 0.03), but not other macular measures.

CONCLUSIONS

Thinning of retinal neuronal and axonal layers at macula as measured by SD-OCT are presented in eyes with NDR, supporting DRN may be the early pathogenesis in the DM patients without the presence of clinical signs of DR. In the future, these SD-OCT measures may be used as surrogates of DRN to stratify DM patients with a high risk of DR, and may be used as a therapeutic target if neuroprotection treatment for DR is available.

Measurable Aspects of the Retinal Neurovascular Unit in Diabetes, Glaucoma, and Controls

PURPOSE

To study the structural and angiographic optical coherence tomography (OCT) data of the macula from controls, patients with diabetes, and patients with glaucoma to evaluate neurovascular and structural relationships.

METHODS

This was a retrospective study of 89 eyes from 49 patients in a community-based retinal referral practice with diabetes, glaucoma, and normal controls. The patients were evaluated with OCT to include retinal nerve fiber layer (RNFL) thickness measurement and ganglion cell layer (GCL) volume determination. The vascular density of the radial peripapillary capillary network and the vascular plexuses in the macula were evaluated with OCT angiography. The main outcome measures were the data obtained per disease state and the interrelationships the data displayed.

RESULTS

The mean GCL volumes were significantly lower than the control group in both the diabetic (P = .016) and glaucoma (P < .001) groups. The difference between the diabetic and glaucoma groups was not significant (P = .052). The mean global vascular density was greater in the control group than the diabetic group (P = .002) and the glaucoma group (P < .001). The mean RNFL thicknesses were lowest in the glaucoma group. Both the diabetic and glaucoma groups had significantly lower radial peripapillary network and deep vascular plexus density values compared to controls.

CONCLUSIONS

Although there are important differences in disease pathogenesis between diabetes and glaucoma, they share certain similarities in the structural and angiographic abnormalities eventually produced. This suggests that, in addition to canonical pathways of disease, a component of both could represent neurodegenerative disease, offering the possibility for the development of new treatments. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Therapeutic potential of curcumin in eye diseases

Curcumin (diferuloylmethane) derived from the rhizome of Curcuma longa L. has been used for thousands of years in traditional Chinese medicine and Ayurvedic medicine in Asian countries to treat liver diseases, rheumatoid diseases, diabetes, atherosclerosis, infectious diseases and cancer. It exhibits a wide range of pharmacological properties, which include antioxidant, anti-inflammatory, antimutagenic, antimicrobial and anticancer activity. Herein the mechanisms of curcumin impact on oxidative stress, angiogenesis and inflammatory processes are described indicating that curcumin use may inhibit those pathological conditions and restore body homeostasis. Its effectiveness was also proved for major eye diseases. In this review, the influence of curcumin on eye diseases, such as glaucoma, cataract, age-related macular degeneration, diabetic retinopathy, corneal neovascularization, corneal wound healing, dry eye disease, conjunctivitis, pterygium, anterior uveitis are reported. The analysis of a number of clinical and preclinical investigations indicates that curcumin may be used as a therapeutic agent in the treatment of various eye disorders.

Longitudinal In Vivo Characterization of the Streptozotocin-Induced Diabetic Mouse Model: Focus on Early Inner Retinal Responses

Purpose

The goal of this study was to perform an extensive temporal characterization of the early pathologic processes in the streptozotocin (STZ)-induced diabetic retinopathy (DR) mouse model, beyond the vascular phenotype, and to investigate the potential of clinically relevant compounds in attenuating these processes.

Methods

Visual acuity and contrast sensitivity (CS) were studied in the mouse STZ model until 24 weeks postdiabetes onset. ERG, spectral domain optical coherence tomography (SD-OCT), leukostasis, and immunohistochemistry were applied to investigate neurodegeneration, inflammation, and gliosis during early-, mid- and late-phase diabetes. Aflibercept or triamcinolone acetonide (TAAC) was administered to investigate their efficacy on the aforementioned processes.

Results

Visual acuity and CS loss started at 4 and 18 weeks postdiabetes onset, respectively, and progressively declined over time. ERG amplitudes were diminished and OP latencies increased after 6 weeks, whereas SD-OCT revealed retinal thinning from 4 weeks postdiabetes. Immunohistochemical analyses linked these findings to retinal ganglion and cholinergic amacrine cell loss at 4 and 8 weeks postdiabetes onset, respectively, which was further decreased after aflibercept administration. The number of adherent leukocytes was augmented after 2 weeks, whereas increased micro- and macroglia reactivity was present from 4 weeks postdiabetes. Aflibercept or TAAC showed improved efficacy on inflammation and gliosis.

Conclusions

STZ-induced diabetic mice developed early pathologic DR hallmarks, from which inflammation seemed the initial trigger, leading to further development of functional and morphologic retinal changes. These findings indicate that the mouse STZ model is suitable to study novel integrative non-vascular therapies to treat early DR.

Loss of XBP1 Leads to Early-Onset Retinal Neurodegeneration in a Mouse Model of Type I Diabetes

Retinal neuronal injury and degeneration is one of the primary manifestations of diabetic retinopathy, a leading cause of vision loss in working age adults. In pathological conditions, including diabetes and some physiological conditions such as aging, protein homeostasis can become disrupted, leading to endoplasmic reticulum (ER) stress. Severe or unmitigated ER stress can lead to cell death, which in retinal neurons results in irreversible loss of visual function. X-box binding protein 1 (XBP1) is a major transcription factor responsible for the adaptive unfolded protein response (UPR) to maintain protein homeostasis in cells undergoing ER stress. The purpose of this study is to determine the role of XBP1-mediated UPR in retinal neuronal survival and function in a mouse model of type 1 diabetes. Using a conditional retina-specific XBP1 knockout mouse line, we demonstrate that depletion of XBP1 in retinal neurons results in early onset retinal function decline, loss of retinal ganglion cells and photoreceptors, disrupted photoreceptor ribbon synapses, and Müller cell activation after induction of diabetes. Our findings suggest an important role of XBP1-mediated adaptive UPR in retinal neuronal survival and function in diabetes.

Neuroprotective effect of levetiracetam in mouse diabetic retinopathy: Effect on glucose transporter-1 and GAP43 expression

AIMS

Retinopathy is a neurodegenerative complication associating diabetes mellitus. Diabetic retinopathy (DR) is the primary reason of visual loss during early adulthood. DR has a complicated multifactorial pathophysiology initiated by hyperglycaemia-induced ischaemic neurodegenerative retinal changes, followed by vision-threatening consequences. The main therapeutic modalities for DR involve invasive delivery of intravitreal antiangiogenic agents as well as surgical interventions. The current work aimed to explore the potential anti-inflammatory and retinal neuroprotective effects of levetiracetam.

MAIN METHODS

This study was performed on alloxan-induced diabetes in mice (n: 21). After 10 weeks, a group of diabetic animals (n: 7) was treated with levetiracetam (25 mg/kg) for six weeks. Retinal tissues were dissected and paraffin-fixed for examination using (1) morphometric analysis with haematoxylin and eosin (HE), (2) immunohistochemistry (GLUT1, GFAP and GAP43), and (3) RT-PCR-detected expression of retinal inflammatory and apoptotic mediators (TNF-α, IL6, iNOS, NF-κB and Tp53).

KEY FINDINGS

Diabetic mice developed disorganized and debilitated retinal layers with upregulation of the gliosis marker GFAP and downregulation of the neuronal plasticity marker GAP43. Additionally, diabetic retinae showed increased transcription of NF-κB, TNF-α, IL6, iNOS and Tp53. Levetiracetam-treated mice showed downregulation of retinal GLUT1 with relief and regression of retinal inflammation and improved retinal structural organization.

SIGNIFICANCE

Levetiracetam may represent a potential neuroprotective agent in DR. The data presented herein supported an anti-inflammatory role of levetiracetam. However, further clinical studies may be warranted to confirm the effectiveness and safety of levetiracetam in DR patients.

Nutraceuticals for the Treatment of Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most common complications of diabetes mellitus and is characterized by degeneration of retinal neurons and neoangiogenesis, causing a severe threat to vision. Nowadays, the principal treatment options for DR are laser photocoagulation, vitreoretinal surgery, or intravitreal injection of drugs targeting vascular endothelial growth factor. However, these treatments only act at advanced stages of DR, have short term efficacy, and cause side effects. Treatment with nutraceuticals (foods providing medical or health benefits) at early stages of DR may represent a reasonable alternative to act upstream of the disease, preventing its progression. In particular, in vitro and in vivo studies have revealed that a variety of nutraceuticals have significant antioxidant and anti-inflammatory properties that may inhibit the early diabetes-driven molecular mechanisms that induce DR, reducing both the neural and vascular damage typical of DR. Although most studies are limited to animal models and there is the problem of low bioavailability for many nutraceuticals, the use of these compounds may represent a natural alternative method to standard DR treatments.

The Association of CEP135 rs4865047 and NPY2R rs1902491 Single Nucleotide Polymorphisms (SNPs) with Rapid Progression of Proliferative Diabetic Retinopathy in Patients with Type 1 Diabetes Mellitus

Background

Diabetic retinopathy has a varied prevalence, severity, and rate of progression. The aim of this study was to determine whether the single nucleotide polymorphisms (SNPs) of the gene encoding a 135-kD centrosomal protein CEP135 rs4865047 and the gene encoding the type 2 NPY protein NPY2R rs1902491 were associated with the development of rapidly progressive proliferative diabetic retinopathy in patients with type 1 diabetes mellitus.

Material/Methods

Patients with rapidly progressive proliferative diabetic retinopathy (n=48) were included in the study group. The control group (n=84) consisted of diabetes mellitus patients who had no proliferative diabetic retinopathy up to 15 years of diabetes duration. The reference group (n=90) included non-diabetic individuals who matched the study group by age and gender. The SNPs in the three groups were analyzed using real-time polymerase chain reaction (PCR) amplification.

Results

The analysis of the distribution of genotypes in CEP135 rs4865047 and NPY2R rs1902491 detected significant differences only in the single nucleotide polymorphism rs4865047 genotype between the case and control group in comparison to the reference group. The co-dominant model showed that CEP135 rs4865047 was significantly associated with patients with rapidly progressive proliferative diabetic retinopathy (OR 7.2, 95% CI, 2.28–22.74, p=0.001). No significant association was found for the NPY2R SNP rs1902491 genotype.

Conclusions

Our study reports a significant association of the CEP135 single nucleotide polymorphism rs4865047 genotype with rapidly progressive proliferative diabetic retinopathy and the control group. No significant association was found of the NPY2R single nucleotide polymorphism rs1902491 genotype.

Proteomics reveals ablation of PlGF increases antioxidant and neuroprotective proteins in the diabetic mouse retina

Placental growth factor (PlGF or PGF), a member of the vascular endothelial growth factor (VEGF) sub-family, plays a crucial role in pathological angiogenesis and inflammation. However, the underlying molecular mechanisms that PlGF mediates regarding the complications of non-proliferative diabetic retinopathy (DR) remain elusive. Using an LC-MS/MS-based label-free quantification proteomic approach we characterized the alterations in protein expression caused by PlGF ablation in the retinas obtained from C57BL6, Akita, PlGF-/- and Akita.PlGF-/- mice. After extraction and enzymatic digestion with Trypsin/LysC, the retinal proteins were analyzed by Q-Exactive hybrid Quadrupole-Orbitrap mass spectrometry. Differentially expressed proteins (DEPs) were identified in four comparisons based on Z-score normalization and reproducibility by Pearson's correlation coefficient. The gene ontology (GO), functional pathways, and protein-protein network interaction analysis suggested that several proteins involved in insulin resistance pathways (Gnb1, Gnb2, Gnb4, Gnai2, Gnao1, Snap2, and Gngt1) were significantly down-regulated in PlGF ablated Akita diabetic mice (Akita.PlGF-/- vs. Akita) but up-regulated in Akita vs. C57 and PlGF-/- vs. C57 conditions. Two proteins involved in the antioxidant activity and neural protection pathways, Prdx6 and Map2 respectively, were up-regulated in the Akita.PlGF-/- vs. Akita condition. Overall, we predict that down-regulation of proteins essential for insulin resistance, together with the up-regulation of antioxidant and neuroprotection proteins highlight and epitomize the potential mechanisms important for future anti-PlGF therapies in the treatment of DR.

Long noncoding RNA MALAT1 acts as a competing endogenous RNA to regulate Amadori-glycated albumin-induced MCP-1 expression in retinal microglia by a microRNA-124-dependent mechanism

OBJECTIVE

To determine whether the long noncoding RNA MALAT1 may be involved in the inflammatory effect of Amadori-glycated albumin (AGA) in retinal microglia via a microRNA-124 (miR-124)-dependent mechanism.

METHODS

Diabetes mellitus was induced by streptozotocin (STZ) injection. The expression of monocyte chemotactic protein-1 (MCP-1) in the retinas of rats was determined using quantitative reverse transcription-PCR (qRT-PCR) analyses and enzyme-linked immunosorbent assay (ELISA). Both qRT-PCR and ELISA were used to detect the levels of MCP-1 mRNA and soluble MCP-1 protein in the primary rat retinal microglia treated with AGA. The regulation of a putative target of miR-124 was validated by luciferase reporter assays.

RESULTS

MALAT1 knockdown ameliorated diabetic retinopathy (DR) and inhibited MCP-1 release in the retinas of STZ-induced diabetic rats. The cultured retinal microglial cells treated with AGA-released MCP-1 in a dose- and time-dependent manner. In addition, AGA consistently induced MALAT1 expression in the retinal microglial cells. Next, we demonstrated that the expression of MCP-1 is controlled by miR-124, which binds to the 3'-UTR of MCP-1 in microglial cells. Luciferase reporter assays and RNA-binding protein immunoprecipitation assays showed that MALAT1 targets miR-124. Finally, we demonstrated that MALAT1 acts as a competing endogenous RNA by directly binding to miR-124 to regulate AGA-induced MCP-1 expression in microglial cells.

CONCLUSIONS

MALAT1-miR-124-MCP-1 signaling pathway may be involved in AGA-induced MCP-1 expression in microglial cells, which may provide a new approach for the treatment of DR.

Critical role of endoplasmic reticulum stress in chronic endothelial activation-induced visual deficits in tie2-tumor necrosis factor mice

Diabetic retinopathy (DR) is the leading cause of vision loss among working-age adults. The interplay between hyperglycemia and endothelial activation in inducing endoplasmic reticulum (ER) stress pathways and visual deficits in DR is not fully understood. To address this, we used a mouse model of chronic vascular activation using endothelial-specific tumor necrosis factor-α (TNF-α)-expressing (tie2-TNF) mice to induce diabetes with streptozotocin. At 4 weeks post streptozotocin, a significant 2-fold to 10-fold increase in retinal neurovascular inflammatory gene transcript response in tie2-TNF mice was further increased in diabetic tie2-TNF mice. A decrease in visual acuity and scotopic b-wave amplitude in tie2-TNF mice was further accentuated in diabetic tie2-TNF mice and these changes correlated with a multi-fold increase in retinal ER stress markers and a reduction in adherens junctions. Cultured retinal endothelial cells showed a significant decrease in trans-endothelial resistance as well as VE-cadherin expression under TNF-α and high glucose stress. These changes were partly rescued by tauroursodeoxycholic acid, a potent ER stress inhibitor. Taken together, constant endothelial activation induced by TNF-α further exacerbated by hyperglycemia results in activation of ER stress and chronic proinflammation in a feed forward loop ultimately resulting in endothelial junction protein alterations leading to visual deficits in the retina. Inhibition of ER stress and endothelial activation may prove to be a novel therapeutic target in DR.

Curcumin Alleviates Diabetic Retinopathy in Experimental Diabetic Rats

PURPOSE

To investigate the potential protective effects of curcumin on the retina in diabetic rats.

METHODS

An experimental diabetic rat model was induced by a low dose of streptozotocin combined with a high-energy diet. Rats which had blood glucose levels ≥11.6 mmol/L were used as diabetic rats. The diabetic rats were randomly divided into 3 groups: diabetic rats with no treatment (DM), diabetic rats treated with 100 mg/kg curcumin (DM + Cur 100 mg/kg), and diabetic rats treated with 200 mg/kg curcumin (DM + Cur 200 mg/kg). Curcumin was orally administered daily for 16 weeks. After 16 weeks of administration, the rats were euthanized, and eyes were dissected. Retinal histology was examined, and the thickness of the retina was measured. Ultrastructural changes of retinal ganglion cells, inner layer cells, retinal capillary, and membranous disks were observed by electron microscopy. Malondialdehyde, superoxide dismutase, and total antioxidant capacity were measured by ELISA. Expression levels of vascular endothelial growth factor (VEGF) in retina tissues were examined by immunohistochemical staining and ELISA. Expression levels of Bax and Bcl-2 in retina tissues were determined by immunohistochemical staining and Western blotting.

RESULTS

Curcumin reduced the blood glucose levels of diabetic rats and decreased diabetes-induced body weight loss. Curcumin prevented attenuation of the retina in diabetic rats and ameliorated diabetes-induced ultrastructure changes of the retina, including thinning of the retina, apoptosis of the retinal ganglion cells and inner nuclear layer cells, thickening of retinal capillary basement membrane and disturbance of photoreceptor cell membranous disks. We also found that curcumin has a strong antioxidative ability in the retina of diabetic rats. It was observed that curcumin attenuated the expression of VEGF in the retina of diabetic rats. We also discovered that curcumin had an antiapoptotic effect by upregulating the expression of Bcl-2 and downregulating the expression of Bax in the retina of diabetic rats.

CONCLUSIONS

Taken together, these results suggest that curcumin may have great therapeutic potential in the treatment of diabetic retinopathy which could be attributed to the hypoglycemic, antioxidant, VEGF-downregulating and neuroprotection properties of curcumin.

Ultrastructure of neurovascular changes in human diabetic retinopathy

The previous concept regarding diabetic retinopathy assigned a primary role to hyperglycemia-induced microvascular alterations, while neuronal and glial abnormalities were considered to be secondary to either ischemia or exudation. The aim of this study was to reveal the potential role of neuronal and glial cells in initial and advanced alterations of the retinopathy in human type 2 diabetes. Electron microscopy and histochemical studies were performed on 38 surgically removed human eyes (28 obtained from diabetic patients and 10 from non-diabetic patients). Morphometric analysis of basement membrane material and lipids was performed. An accumulation of metabolic by-products was found in the capillary wall with aging: this aspect was significantly more pronounced in diabetics. Müller glial cells were found to contribute to alterations of the capillary wall and to occlusion, as well as to the development of proliferative retinopathy and cystoid degeneration of the retina. Our results showed morphological evidence regarding the role of neuronal and glial cells in the pathology of diabetic retinopathy, prior and in addition to microangiopathy. These morphological findings support a neurovascular pathogenesis at the origin of diabetic retinopathy, thus the current treatment approach should be completed by neuroprotective measures.

High glucose levels impact visual response properties of retinal ganglion cells in C57 mice-An in vitro physiological study

This study investigated visual response properties of retinal ganglion cells (RGCs) under high glucose levels. Extracellular single-unit responses of RGCs from mouse retinas were recorded. And the eyecup was prepared as a flat mount in a recording chamber and superfused with Ames medium. The averaged RF size of the ON RGCs (34.1±2.9, n=14) was significantly smaller than the OFF RGCs under the HG (49.3±0.3, n=12) (P<0.0001) conditions. The same reduction pattern was also observed in the osmotic control group (HM) between ON and OFF RGCs (P<0.0001). The averaged luminance threshold (LT) of ON RGCs increased significantly under HG or HM (HG: P<0.0001; HM: P<0.0002). OFF RGCs exhibited a similar response pattern under the same conditions (HG: P<0.01; HM: P<0.0002). The averaged contrast gain of ON cells was significantly lower than that of OFF cells with the HM treatment (P<0.015, unpaired Student's t test). The averaged contrast gain of ON cells was significantly higher than OFF cells with the HG treatment (P<0.0001). The present results suggest that HG reduced receptive field center size, suppressed luminance threshold, and attenuated contrast gain of RGCs. The impact of HG on ON and OFF RGCs may be mediated via different mechanisms.

Structural neurodegeneration correlates with early diabetic retinopathy

PURPOSE

To examine differences in structural and functional neurodegenerative measurements between patients with no and early diabetic retinopathy (DR).

METHODS

In this cross-sectional study, we examined 103 patients with type 2 diabetes mellitus. In 7-field fundus photographs acquired with Topcon TRC-NW6S, a single, certified grader determined the presence of DR according to the Early Treatment Diabetic Retinopathy Study (ETDRS) scale. Retinal neurodegeneration was evaluated by Topcon 3D OCT-2000 spectral domain optical coherence tomography (OCT) and by a RETI-scan multifocal electroretinography (mf-ERG) system in rings 1-6.

RESULTS

Median age and duration of diabetes were 63.6 and 10 years, respectively, and 46% were men. Median HbA1c was 50 mmol/mol (6.7%), and ETDRS levels were 10 (41.7%, n = 43), 20 (35.0%, n = 36), and 35 (23.3%, n = 24). The duration of diabetes increased with higher levels of DR (p = 0.04), but patients with different level of DR did not differ according to age, sex, blood pressure, HbA1c, and mf-ERG or OCT parameters. In a multiple logistic regression model, macular ganglion cell layer thickness was associated with the presence of DR (OR 1.73 per 5 μm increase, 95% CI 1.06-2.85, p = 0.03). Conversely, retinal nerve fibre layer thickness at optic disc was inversely related to DR (OR 0.69 per 5 μm increase, 95% CI 0.51-0.95, p = 0.02). There were no associations between DR and mf-ERG outcomes.

CONCLUSION

In patients with type 2 diabetes, structural neurogenic characteristics were associated with DR. If confirmed by larger prospective studies, these results may indicate that a complex neurovascular interaction is an early event in the pathogenesis of DR.

Morphological evaluation of retinal ganglion cells expressing the L132C/T159C ChR2 mutant transgene in young adult cynomolgus monkeys

To characterize recombinant AAV2 (rAAV2)-mediated expression of L132C/T159C ChR2 mutant in retinal ganglion cells (RGCs) of young adult cynomolgus monkeys. rAAV2 vectors carrying a fusion construct of the ChR2 mutant and GFP (ChR2-GFP) were delivered to the vitreous chamber by intravitreal injection. Expression patterns of the ChR2 mutant in RGCs were examined by immunohistochemical methods three months after injection. The RNA-binding protein with multiple splicing (RBPMS) was used as an RGC specific marker to differentiate RGCs from other retinal neurons and non-neuronal cells. The numbers of RBPMS+ and GFP+ double-labeled RGCs in the central foveal varied with the eccentricity. The expression peaked within 100 μm from the edge of the foveola and drastically decreased to a single superficial RGC layer approximately 300 μm from the edge. On average, the ratio of the double-labeled RGCs versus RBPMS+ RGCs approached 0.32±0.15 (n=14 fields) at the central foveal region (0.1 to 0.53 mm). We observed that the ratio reached 0.78±0.16 (n=21 fields) at peripheral retinal locations (eccentricity >7 mm). This investigation demonstrates that RBPMS could serve as a valuable RGC specific marker for future investigations in this field.

Differential expression of breast cancer-resistance protein, lung resistance protein, and multidrug resistance protein 1 in retinas of streptozotocin-induced diabetic mice

AIM

To investigate the altering expression profiles of efflux transporters such as breast cancer-resistance protein (BCRP), lung resistance protein (LRP), and multidrug resistance protein 1 (MDR1) at the inner blood-retinal barrier (BRB) during the development of early diabetic retinopathy (DR) and/or aging in mice.

METHODS

Relative mRNA and protein expression profiles of these three efflux transporters in the retina during the development of early DR and/or aging in mice were examined. The differing expression profiles of Zonula occludens 1 (ZO-1) and vascular endothelial growth factor-A (VEGFA) in the retina as well as the perfusion characterization of fluorescein isothiocyanate (FITC)-dextran and Evans blue were examined to evaluate the integrity of the inner BRB.

RESULTS

There were significant alterations in these three efflux transporters' expression profiles in the mRNA and protein levels of the retina during the development of diabetes mellitus and/or aging. The development of early DR was confirmed by the expression profiles of ZO-1 and VEGFA in the retina as well as the compromised integrity of the inner BRB.

CONCLUSION

The expression profiles of some efflux transporters such as BCRP, LRP, and MDR1 in mice retina during diabetic and/or aging conditions are tested, and the attenuated expression of BCRP, LRP, and MDR1 along with the breakdown of the inner BRB is found, which may be linked to the pathogenesis of early DR.

Neurodegeneration and Neuroinflammation in Diabetic Retinopathy: Potential Approaches to Delay Neuronal Loss

In spite of the extensive research the complex pathogenesis of diabetic retinopathy (DR) has not been fully elucidated. For many years it has been thought that diabetic retinopathy manifests only with microangiopathic lesions, which are totally responsible for the loss of vision in diabetic patients. In view of the current knowledge on the microangiopathic changes in the fundus of the eye, diabetic retinopathy is perceived as a neurodegenerative disease. Several clinical tools are available to detect neuronal dysfunction at early stages of diabetes. Many functional changes in the retina can be identified before vascular pathology develops, suggesting that they result from a direct effect of diabetes on the neural retina. In the course of diabetes there is a chronic loss of retinal neurons due to increased frequency of apoptosis. The neuronal apoptosis begins very early in the course of diabetes. This observation has led to suggestions that precautions against DR should be implemented immediately after diabetes is diagnosed. Neurodegeneration cannot be reversed; therefore treatments preventing neuronal cell loss in the retina need to be developed to protect diabetic patients. This review is an attempt to summarize what is currently known about the mechanisms of neuronal apoptosis in the context of diabetic retinopathy and vascular degeneration as well as about potential treatments of DR

Retinal Neurodegeneration in the Course of Diabetes-Pathogenesis and Clinical Perspective

Diabetic retinopathy is generally considered as a microvascular disease which develops as a result of chronic hyperglycaemia. However, the neuronal apoptosis and reactive gliosis are recently postulated as early changes in diabetic retinopathy. This phenomenon is described as a neurodegeneration and suggests that diabetic retinopathy should be recognized as a neurovascular complication. In this review, we discuss the mechanisms leading to the neurodegeneration of the retina in diabetic patients including: low-grade inflammatory process, oxidative stress, activation of polymorphonuclear neutrophils, glutamate excitotoxicity and imbalance in the neuroprotective factors. Secondly, we point out the clinical significance of measuring the retinal neurodegeneration.

Retinal Neurodegeneration Associated With Peripheral Nerve Conduction and Autonomic Nerve Function in Diabetic Patients

OBJECTIVE

In this study, we evaluated the correlation of retinal thickness with peripheral nerve conduction and autonomic nerve function in diabetic patients.

DESIGN

Cross-sectional study.

METHODS

Medical records of 160 patients (mean age, 63.61 ± 12.52 years) with diabetes without diabetic retinopathy or mild nonproliferative diabetic retinopathy (NPDR) were reviewed. The mean retinal thickness of the parafoveal area and ganglion cell/inner plexiform layer (GC-IPL) thickness in 6 macular regions were measured using optical coherence tomography. Peripheral nerve conduction studies were conducted on peroneal and posterior tibial motor nerves and the sural sensory nerve. Five cardiovascular autonomic function tests were performed. We classified patients into groups by severity of peripheral neuropathy and autonomic dysfunction and analyzed the correlations with mean retinal thickness.

RESULTS

The mean retinal thickness of the parafovea was 315.05 ± 12.70 μm and mean macular GC-IPL thickness was 79.89 ± 4.70 μm. Macular GC-IPL thickness showed significant correlation with peripheral nerve conduction (no peripheral neuropathy vs definite peripheral neuropathy: 82.0 ± 4.8 μm vs 75.2 ± 3.8 μm, P < .001). GC-IPL thickness decreased with severity of autonomic nerve dysfunction (no/mild dysfunction vs severe dysfunction: 81.2 ± 6.6 μm vs 77.6 ± 5.9 μm, P = .005). There was no significant correlation between the retinal thickness of the parafovea and electrodiagnostic tests.

CONCLUSION

The decrease of GC-IPL thickness was positively correlated with both peripheral nerve conduction and autonomic nerve function in diabetic patients who presented with no diabetic retinopathy or mild NPDR.

Diabetic Retinopathy: Animal Models, Therapies, and Perspectives

Diabetic retinopathy (DR) is one of the major complications of diabetes. Although great efforts have been made to uncover the mechanisms underlying the pathology of DR, the exact causes of DR remain largely unknown. Because of multifactor involvement in DR etiology, currently no effective therapeutic treatments for DR are available. In this paper, we review the pathology of DR, commonly used animal models, and novel therapeutic approaches. Perspectives and future directions for DR treatment are discussed.