Nitric oxide and oxidative stress is associated with severity of diabetic retinopathy and retinal structural alterations

Association between the triglyceride glucose index and diabetic retinopathy in type 2 diabetes: a meta-analysis

The triglyceride-glucose (TyG) index is an accessible and reliable surrogate indicator of insulin resistance and is strongly associated with diabetes. However, its relationship with diabetic retinopathy (DR) remains controversial. This meta-analysis aimed to assess the relationship between the TyG index and the prevalence of DR. Initial studies were searched from PubMed, Embase, Web of Science, and China National Knowledge Infrastructure (CNKI) electronic databases. The retrieval time range was from the establishment of the database to June 2023. Pooled estimates were derived using a random-effects model and reported as odds ratio (OR) with 95% confidence intervals (CIs). Two researchers independently assessed the methodological quality of the included studies. The Newcastle-Ottawa Quality Scale (NOS) was utilized to assess cohort studies or case-control studies. The Agency for Healthcare Research and Quality (AHRQ) methodology checklist was applied to assess cross-sectional studies. Ten observational studies encompassing 13716 patients with type 2 diabetes were included in the meta-analysis. The results showed that a higher TyG index increased the risk of DR compared with a low TyG index (OR: 2.34, 95% CI: 1.31-4.19, P < 0.05). When the index was analyzed as a continuous variable, consistent results were observed (OR: 1.48, 95% CI: 1.12-1.97, P < 0.005). There was no significant effect on the results of the sensitivity analyses excluding one study at a time (P all < 0.05). A higher TyG index may be associated with an increased prevalence of DR in patients with type 2 diabetes. However, high-quality cohort or case-control studies are needed to further substantiate this evidence.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42023432747.

A correlation between oxidative stress and diabetic retinopathy: An updated review

Oxidative stress (OS) is a cytopathic outcome of excessively generated reactive oxygen species (ROS), down regulated antioxidant defense signaling pathways, and the imbalance between the produced radicals and their clearance. It plays a role in the genesis of several illnesses, especially hyperglycemia and its effects. Diabetic retinal illness, a micro vascular side effect of the condition, is the prime reason of diabetic related blindness. The OS (directly or indirectly) is associated with diabetic retinopathy (DR) and related consequences. The OS is responsible to induce and interfere the metabolic signaling pathways to enhance influx of the polyol cascades and hexosamine pathways, stimulate Protein Kinase-C (PKC) variants, and accumulate advanced glycation end products (AGEs). Additionally, the inequity between the scavenging and generation of ROS is caused by the epigenetic alteration caused by hyperglycemia that suppresses the antioxidant defense system. Induced by an excessive buildup of ROS, retinal changes in structure and function include mitochondrial damage, cellular death, inflammation, and lipid peroxidation. Therefore, it is crucial to comprehend and clarify the mechanisms connected to oxidative stress that underlie the development of DR.

Malondialdehyde levels in diabetic retinopathy patients: a systematic review and meta-analysis

BACKGROUND

It remains unclear whether circulating malondialdehyde (MDA) levels change in people with diabetic retinopathy (DR). This systematic review compared circulating MDA levels in diabetic people with and without DR.

METHODS

PubMed, Medline (Ovid), Embase (Ovid), and Web of Science were searched for case-control studies conducted before May 2022 in English that compared circulating MDA levels in people with and without DR. The following MeSH search terms were used: ("malondialdehyde" or "thiobarbituric acid reactive substances [TBARS]" or "lipid peroxidation" or "oxidative stress") and "diabetic retinopathy." Newcastle-Ottawa Quality Assessment Scale was used to evaluate the quality of the included studies. Random-effects pairwise meta-analysis pooled the effect size with standardized mean difference (SMD) and 95% confidence intervals (CIs).

RESULTS

This meta-analysis included 29 case-control studies with 1680 people with DR and 1799 people with diabetes but not DR. Compared to people without DR, the circulating MDA levels were higher in those with DR (SMD, 0.897; 95% CI, 0.631 to 1.162; P  < 0.001). The study did not identify credible subgroup effects or publication bias and the sensitivity analysis confirmed the robustness of the study.

CONCLUSIONS

Circulating MDA levels are higher in people with DR compared to those without. Future comparative studies that use more specific methods are required to draw firm conclusions.

REGISTRATION

PROSPERO; https://www.crd.york.ac.uk/PROSPERO/ ; No. CRD42022352640.

Anti-Vegf therapy leads to an improvement in grade of retinal pigment epithelium alterations on single layer retinal pigment epithelium map in diabetic macular edema

PURPOSE

In bovine retinal pigment epithelium (RPE) cells, increased secretion of vascular endothelial growth factor (VEGF) has a positive linear association with proliferation of RPE. Spectral domain optical coherence tomography (SD-OCT) based improvement in grades of topographic retinal pigment epithelium alterations (RPE-A), were evaluated after intravitreal anti-VEGF therapy, in diabetic macular edema (DME), for the first time.

METHODS

A tertiary care center-based, prospective study. Forty-four consecutive patients, 40-65 years of age with type 2 diabetes mellitus (DM) with DME, were administered three doses of anti-VEGF therapy at monthly intervals. Pre- and post-intervention SD-OCT was done and central sub field thickness (CST), cube average thickness (CAT) and topographic grades of RPE-A were assessed using single layer RPE map (SL-RPE) as; Grade 0: No alterations, Grade 1: Alteration in two quadrants, Grade 2: Alteration in more than two quadrants.

RESULTS

CST decreased from 354.2 ± 16.0 µm pre-intervention to 233.2 ± 7.9 µm post-intervention. CAT reduced from 340.6 ± 6.5 µm pre-intervention to 274.1 ± 5.1 µm post-intervention. Significant improvement in grades of RPE-A pre- v/s post-intervention were observed. (Grade 0: 0 v/s 39; Grade 1: 17 v/s 3; Grade 2: 27 v/s 2) (p < 0.001).

CONCLUSION

Anti-VEGF therapy is associated with an improvement in grades of RPE-A in DME.The study was registered with the Clinical Trial Registry of India (CTRI/2019/03/018135).

Oxidative Stress Implication in Retinal Diseases-A Review

Oxidative stress (OS) refers to an imbalance between free radicals (FRs), namely highly reactive molecules normally generated in our body by several pathways, and intrinsic antioxidant capacity. When FR levels overwhelm intrinsic antioxidant defenses, OS occurs, inducing a series of downstream chemical reactions. Both reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced by numerous chemical reactions that take place in tissues and organs and are then eliminated by antioxidant molecules. In particular, the scientific literature focuses more on ROS participation in the pathogenesis of diseases than on the role played by RNS. By its very nature, the eye is highly exposed to ultraviolet radiation (UVR), which is directly responsible for increased OS. In this review, we aimed to focus on the retinal damage caused by ROS/RNS and the related retinal pathologies. A deeper understanding of the role of oxidative and nitrosative stress in retinal damage is needed in order to develop targeted therapeutic interventions to slow these pathologies.

Comparison of catalase, glutathione peroxidase and malondialdehyde levels in tears among diabetic patients with and without diabetic retinopathy

Background

Various studies suggest that oxidative stress has a role in the etiology of diabetes mellitus (DM) and its complications. Detection of antioxidant enzymes and malondialdehyde (MDA) level in ocular fluid may provide the possible biomarkers for monitoring the progression of diabetic retinopathy (DR). The aim of this study was to compare catalase, glutathione peroxidase (GPx) and MDA levels in tears among diabetic patients with and without DR.

Methods

A cross-sectional study was conducted among type 2 DM patients. The patients were divided into three groups: no DR, non-proliferative DR (NPDR) and proliferative DR (PDR). Tears samples were collected using Schirmer strips for measurement of catalase, GPx and MDA.

Results

A total of 171 patients were recruited in this study (no DR, 58 patients; NPDR, 57 patients; PDR, 56 patients). There was significant difference in the mean level of GPx in tears between the three groups (no DR, 658.08 ± 115.70 U/L; NPDR, 653.78 ± 87.90 U/L; PDR, 605.31 ± 107.47 U/L, respectively) before and after adjustment for covariates (p = 0.013 and p = 0.001, respectively). Bonferroni post-hoc analysis showed PDR group had significantly lower mean GPx level than in no DR (p=0.001) and NPDR (p=0.037) after adjustment for covariates. There was no significant difference of mean catalase and MDA in the tears between the three groups before and after adjustment for covariates.

Conclusion

This study demonstrated that diabetic patient with DR is associated with low level of GPx in tears, suggesting that this antioxidant enzyme is a potential biomarker for predicting the presence of DR.

Interleaved Optical Coherence Tomography: Clinical and Laboratory Biomarkers in Patients with Diabetic Macular Edema

(1) Background: The global burden of diabetes mellitus (DM) has been estimated to reach 600 million patients worldwide by 2040. Approximately 200 million people will develop diabetic retinopathy within this time frame. Diabetic macular edema (DME) is a severe, vision-threatening complication that can develop at any stage of diabetic retinopathy, and it represents the main cause of vision loss in patients with DM. Its harmful consequences on visual function could be prevented with timely recognition and treatment. (2) Methods: This study assessed the clinical (demographic characteristics, diabetic evolution, and systemic vascular complications); laboratory (glycated hemoglobin, metabolic parameters, capillary oxygen saturation, and renal function); ophthalmologic exam; and spectral-domain optical coherence tomography (SD–OCT) (macular volume, central macular thickness, maximal central thickness, minimal central thickness, foveal thickness, superior inner, inferior inner, nasal inner, temporal inner, inferior outer, superior outer, nasal outer, and temporal outer thicknesses, disruption of the ellipsoid zone, and disruption of the inner retinal layers (DRIL) parameters in three groups of individuals: healthy controls (HC), patients with DME and type 1 DM (T1DM—group A), and patients with DME and type 2 DM (T2DM—group B) to identify novel correlations between them that would open a path to new pathogenetic hypotheses and, implicitly, to the identification of new therapeutic methods, as part of a tailored treatment within the concept of precision medicine. (3) Results: The duration of DM was significantly longer in group A as compared with group B, as were the prevalence of smoking and systemic vascular complications. Capillary oxygen saturation and estimated glomerular filtration rates were significantly lower, and serum creatinine levels were significantly higher in group A as compared to group B. Regarding the OCT findings, DME had a predominantly eccentric pattern, and the right eye was more severely affected in both groups of patients. Significantly higher values were obtained in group B as compared to group A for the following OCT biomarkers: macular volume, central macular thickness, maximal central thickness, minimal central thickness, foveal thickness, superior inner, inferior inner, nasal inner, inferior outer and nasal outer thickness. The disruption of the ellipsoid zone was significantly more prevalent within group A, whereas the overall disruption of the retinal inner layers (DRIL) was identified significantly more frequently in group B. (4) Conclusions: Whereas systemic and laboratory biomarkers were more severely affected in patients with DME and T1DM, the OCT quantitative biomarkers revealed significantly higher values in patients with DME and T2DM.

Plasma Arginine and Citrulline are Elevated in Diabetic Retinopathy

PURPOSE

To determine if plasma levels of six arginine-related and citrulline-related metabolites (arginine, citrulline, asymmetric dimethylarginine [ADMA], ornithine, proline, and argininosuccinate) differ between patients with type 2 diabetes and diabetic retinopathy (DR) and type 2 diabetic controls or between patients with proliferative DR (PDR) and non-proliferative DR (NPDR).

DESIGN

Cross-sectional study.

METHODS

Adults with type 2 diabetes were recruited from the Vanderbilt Eye Institute. Exclusion criteria included non-diabetic retinal disease. Plasma metabolite levels were quantified in 159 diabetic controls and 156 DR patients (92 NPDR, 64 PDR) using isotope dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS). Metabolite levels were compared using Wilcoxon Rank Sum test and logistic regressions adjusting for age, sex, hemoglobin A1c, diabetes duration, statin use, and angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker use. A secondary analysis that included creatinine in the regression model was performed for the subset of patients with available creatinine values (135 diabetic controls, 100 DR patients [58 NPDR, 42 PDR]).

RESULTS

Multivariable logistic regression analyses determined that arginine (OR = 1.20, [1.06-1.38], P = .0067) and citrulline (OR = 1.53, [1.20-1.98], P = .0025) were significantly elevated in DR patients compared to diabetic controls. While ADMA differed between NPDR and PDR patients in the primary analysis (OR = 1.56, [1.15-2.16], P = .0051), it was not significantly different when adjusting for creatinine (OR = 1.30, [0.90-1.91], P = .15).

CONCLUSIONS

Plasma arginine and citrulline were significantly elevated in type 2 diabetic patients with DR compared to diabetic controls. None of the tested metabolites significantly differed between NPDR and PDR patients in the adjusted analysis.

External Limiting Membrane, Photoreceptor Ellipsoid Zone Disruption, and Retinal Pigment Epithelium Alterations in Diabetic Retinopathy

Objective Diabetic retinopathy (DR), a microvascular complication of diabetes, is a leading cause of preventable blindness. Spectral domain optical coherence tomography (SD-OCT) provides cross-sectional and topographical imaging of the retina. SD-OCT resolves outer retinal layers into three hyperreflective bands—external limiting membrane (ELM), ellipsoid zone (EZ), and retinal pigment epithelium (RPE). In this article, we have studied the role of these outer retinal layers in structural and molecular changes taking place in DR.

Materials and Methods Articles with clinical features, pathogenesis, diagnosis, and treatment of DR were thoroughly studied. Articles were searched on PubMed, MEDLINE, and Cochrane Library from 2000 to 2020. Studies focusing on the role of ELM, EZ, and RPE in pathogenesis of DR based on SD-OCT were included.

Results The long-standing hyperglycemia leads to protein glycosylation resulting in formation of advanced glycation end products (AGEs). AGEs have an impact through their effect on retinal microvasculature, vascular endothelial growth factor (VEGF), intercellular adhesion molecule-1, nitrosative and oxidative stress, and vitamin D and calcium metabolism. All these factors have been linked with disruption of outer retinal layers. AGEs lead to vascular endothelial dysfunction and release of proangiogenic factors by increasing the expression of VEGF in retinal pericytes and RPE cells. This leads to leakage and fluid accumulation resulting in diabetic macular edema (DME). In DME, there is sequential disruption of ELM and EZ and decrease in visual acuity (VA). The RPE alterations have been reported to be associated with the severity of DR and decrease in VA. Anti-VEGF therapy, most common treatment of DME, leads to restoration of barrier effect of ELM, it was found to be restored first followed by EZ restoration. Newer anti-AGEs agents and their receptor blockers are being developed which have a positive effect on maintaining the health of RPE.

Conclusion A complex molecular association exists between the structural changes in ELM, EZ, and RPE in DR. SD-OCT is an indispensable tool to study these changes as integrity of these outer layers of retina is essential for maintaining visual function of retina in DR.

Elevated advanced glycation end products are associated with subfoveal ellipsoid zone disruption in diabetic macular edema

Purpose:

Advanced glycation end products (AGEs), due to increased production and a slow turnover rate, serve as mediators of “metabolic memory” even after the resolution of hyperglycemia. A prospective study was undertaken to evaluate the association of AGEs with subfoveal ellipsoid zone (EZ) disruption in diabetic macular edema (DME).

Methods:

A tertiary-care-center-based cross-sectional study included 40 consecutive cases with DME and 20 healthy controls in the age group of 40–65 years. All the study subjects underwent spectral-domain optical coherence tomography (SD-OCT) for cross-sectional imaging of the retina. The EZ was defined as a hyperreflective band below the external limiting membrane. The disruption of EZ was graded as intact EZ and disrupted EZ. Serum AGEs were assessed by assay of N^ε-carboxymethyl-lysine (N^ε-CML) using the standard protocol. Data were analyzed statistically.

Results:

Subfoveal EZ disruption was noted in 80% (32/40) of the cases of DME. In the cases without EZ disruption, visual acuity (LogMAR VA) was 0.60 ± 0.52, whereas in cases with EZ disruption, LogMAR VA was 0.96 ± 0.56 (P < 0.001). In the cases without EZ disruption, N^ε-CML was 94.31 ± 57 ng/mL, whereas in cases with EZ disruption N^ε-CML was 120.64 ± 71.98 ng/mL (P < 0.001).

Conclusion:

In DME, increased levels of AGEs are significantly associated with EZ disruption on SD-OCT.

Increased serum cortisol is associated with alterations in cross-sectional and topographic OCT parameters in diabetic retinopathy: a preliminary study

PURPOSE

Cortisol, a steroid hormone, plays an essential role in metabolic processes of diabetes mellitus. This study for the first time evaluated the association of serum cortisol with spectral domain optical coherence tomography (SD-OCT)-based cross-sectional and topographic parameters with severity of diabetic retinopathy (DR).

METHODS

A tertiary care center-based preliminary study was undertaken. Fourteen consecutive cases of DR and fifteen healthy controls were included. Cases were graded according to ETDRS classification: non-proliferative DR (NPDR, n = 8) and proliferative DR (PDR, n = 6). All study subjects underwent complete ophthalmological evaluation. Serum cortisol was analyzed using chemiluminescence microparticle assay method. Central subfield thickness (CST), cube average thickness (CAT), cube volume (CV), retinal nerve fiber layer (RNFL) thickness, disorganization of inner retinal layers (DRIL), grade of retinal photoreceptor ellipsoid zone (EZ) disruption and grade of retinal pigment epithelium (RPE) alterations were evaluated using SD-OCT. Statistical analysis was done using ANOVA and Pearson's correlation analysis.

RESULTS

Mean serum cortisol levels (µg/dL) were NPDR = 11.59 ± 0.42, PDR = 14.50 ± 0.26 and controls = 8.22 ± 0.77. With increasing severity of DR, mean CST, CAT, CV showed positive correlation, whereas mean RNFL thickness showed negative correlation with serum cortisol levels (p < 0.01). DRIL, EZ disruption and RPE alterations showed positive correlation with serum cortisol levels (p < 0.001).

CONCLUSION

Serum cortisol levels are significantly associated with severity of DR and correlate positively with CST, CAT, CV, DRIL, EZ disruption and RPE alterations and negatively with RNFL thickness.

Neurovascular unit in diabetic retinopathy: pathophysiological roles and potential therapeutical targets

Diabetic retinopathy (DR), one of the common complications of diabetes, is the leading cause of visual loss in working-age individuals in many industrialized countries. It has been traditionally regarded as a purely microvascular disease in the retina. However, an increasing number of studies have shown that DR is a complex neurovascular disorder that affects not only vascular structure but also neural tissue of the retina. Deterioration of neural retina could precede microvascular abnormalities in the DR, leading to microvascular changes. Furthermore, disruption of interactions among neurons, vascular cells, glia and local immune cells, which collectively form the neurovascular unit, is considered to be associated with the progression of DR early on in the disease. Therefore, it makes sense to develop new therapeutic strategies to prevent or reverse retinal neurodegeneration, neuroinflammation and impaired cell-cell interactions of the neurovascular unit in early stage DR. Here, we present current perspectives on the pathophysiology of DR as a neurovascular disease, especially at the early stage. Potential novel treatments for preventing or reversing neurovascular injuries in DR are discussed as well.

A Novel Approach to Quantitative Evaluation of Outer Retinal Lesions Via a New Parameter "Integral" in Spectral Domain Optical Coherence Tomography

Purpose

The purpose of this study was to design a new parameter "integral" to quantitatively evaluate the spatial cumulative reflectivity of the outer retinal layers in optical coherence tomography (OCT), and to investigate its role in the detection of outer retinal diseases.

Methods

This was a cross-sectional study. Fovea-centered line OCT scans were performed on 60 eyes of 60 healthy volunteers and 44 eyes of 44 patients diagnosed with outer retinal diseases. The integrals of the ellipsoid zone (EZ) and interdigitation zone (IZ) were measured by respectively accumulating the grayscale values of all the pixels within the EZ and IZ at specified locations on the scanning lines, and were then adjusted by calculating their percentages on the outer retina. The integrals of the EZ and IZ were compared between the two groups.

Results

The integrals of the EZ and IZ were stably and normally distributed in the healthy eyes, and were significantly lower in eyes with outer retinal lesions than in healthy ones (P < 0.05). Moreover, the integrals of the EZ and IZ were correlated with best corrected visual acuity (BCVA; adjusted R² = 0.620) and the presence of outer retinal lesions (Nagelkerke R² = 0.767). The area under the receiver operating characteristic (ROC) curve was 0.954 (95% confidence interval [CI] = 0.918-0.990) when the integral was selected as a diagnostic variable.

Conclusions

Obtained from this novel quantification method, the new parameter integral was comparable between different individuals and had the potential to detect outer retinal abnormalities in reflectivity through OCT.

Translational Relevance

Our work verified the feasibility of the new image analysis technique in the detection of the diseases affecting the outer retina.

Diabetic photoreceptors: Mechanisms underlying changes in structure and function

Based on clinical findings, diabetic retinopathy (DR) has traditionally been defined as a retinal microvasculopathy. Retinal neuronal dysfunction is now recognized as an early event in the diabetic retina before development of overt DR. While detrimental effects of diabetes on the survival and function of inner retinal cells, such as retinal ganglion cells and amacrine cells, are widely recognized, evidence that photoreceptors in the outer retina undergo early alterations in diabetes has emerged more recently. We review data from preclinical and clinical studies demonstrating a conserved reduction of electrophysiological function in diabetic retinas, as well as evidence for photoreceptor loss. Complementing in vivo studies, we discuss the ex vivo electroretinography technique as a useful method to investigate photoreceptor function in isolated retinas from diabetic animal models. Finally, we consider the possibility that early photoreceptor pathology contributes to the progression of DR, and discuss possible mechanisms of photoreceptor damage in the diabetic retina, such as enhanced production of reactive oxygen species and other inflammatory factors whose detrimental effects may be augmented by phototransduction.

Retinal Physiology and Circulation: Effect of Diabetes

In this article, we present a discussion of diabetes and its complications, including the macrovascular and microvascular effects, with the latter of consequence to the retina. We will discuss the anatomy and physiology of the retina, including aspects of metabolism and mechanisms of oxygenation, with the latter accomplished via a combination of the retinal and choroidal blood circulations. Both of these vasculatures are altered in diabetes, with the retinal circulation intimately involved in the pathology of diabetic retinopathy. The later stages of diabetic retinopathy involve poorly controlled angiogenesis that is of great concern, but in our discussion, we will focus more on several alterations in the retinal circulation occurring earlier in the progression of disease, including reductions in blood flow and a possible redistribution of perfusion that may leave some areas of the retina ischemic and hypoxic. Finally, we include in this article a more recent area of investigation regarding the diabetic retinal vasculature, that is, the alterations to the endothelial surface layer that normally plays a vital role in maintaining physiological functions. © 2020 American Physiological Society. Compr Physiol 10:933-974, 2020.

Nitrosative Stress and Its Association with Cardiometabolic Disorders

Reactive nitrogen species (RNS) are formed when there is an abnormal increase in the level of nitric oxide (NO) produced by the inducible nitric oxide synthase (iNOS) and/or by the uncoupled endothelial nitric oxide synthase (eNOS). The presence of high concentrations of superoxide anions (O₂⁻) is also necessary for their formation. RNS react three times faster than O₂⁻ with other molecules and have a longer mean half life. They cause irreversible damage to cell membranes, proteins, mitochondria, the endoplasmic reticulum, nucleic acids and enzymes, altering their activity and leading to necrosis and to cell death. Although nitrogen species are important in the redox imbalance, this review focuses on the alterations caused by the RNS in the cellular redox system that are associated with cardiometabolic diseases. Currently, nitrosative stress (NSS) is implied in the pathogenesis of many diseases. The mechanisms that produce damage remain poorly understood. In this paper, we summarize the current knowledge on the participation of NSS in the pathology of cardiometabolic diseases and their possible mechanisms of action. This information might be useful for the future proposal of anti-NSS therapies for cardiometabolic diseases.

Spectral domain optical coherence tomography based imaging biomarkers for diabetic retinopathy

To evaluate the role of central subfield thickness (CST), cube average thickness (CAT), and cube volume (CV) as imaging biomarkers for severity of diabetic retinopathy within the ETDRS-based grades of retinopathy using spectral domain optical coherence tomography (SD-OCT). This study aims to evaluate the role of macular CST, CAT, and CV on SD-OCT as imaging biomarkers for severity of DR. One hundred ninety-four consecutive cases of type 2 diabetes mellitus were divided according to ETDRS classification: diabetes mellitus without retinopathy (No DR; n = 65), nonproliferative diabetic retinopathy (NPDR; n = 66), and proliferative diabetic retinopathy (PDR; n = 63). Sixty-three healthy controls were included. CST, CAT, and CV were analyzed using SD-OCT. Data were analyzed statistically. Analysis of variance revealed a significant increase in levels of CST, CAT, CV, and LogMAR visual acuity with the increase in severity of DR. Independent t-test revealed significant difference in CST, CAT, and CV between cases with DME and cases without DME. On multivariate linear regression analysis, increase in CST, CAT, and CV were found to indicate the increase in severity of DR. SD-OCT-based imaging biomarkers CST, CAT, and CV are effective tools for documenting the severity of diabetic retinopathy. These imaging biomarkers serve as significant indicators of severity of disease.

Rubeosis faciei diabeticorum is not associated with oxidative stress and skin autofluorescence

Background

Rubeosis faciei diabeticorum is a persistent facial erythema in patients with diabetes mellitus. The actual pathogenesis has not been studied. However, it is speculated to be a cutaneous diabetic microangiopathy.

Objective

Examine the correlation between the severity of facial erythema and the possible causes of microvascular diabetic complications, namely oxidative stress, hyperglycemia, and cutaneous accumulation of advanced glycation end-products .

Methods

Patients diagnosed with Type 2 diabetes mellitus (n = 32) were enrolled in the study. The facial erythema index was measured using the Mexameter MX18; cutaneous accumulation of advanced glycation end-products was estimated by measuring skin auto fluorescence with the AGE Reader (DiagnOptics Technologies B.V. – Groningen, Netherlands). Glycated haemoglobin, total antioxidant status, and malondialdehyde were measured in blood by TBARS assay. The correlation between the selected variables was assessed by Spearman's rank test; p ≤ 0.05 was considered statistically significant.

Results

There was a statistically significant correlation between total antioxidant status and the facial erythema index (ρ = 0.398, p = 0.024). Malondialdehyde, skin autofluorescence, glycated haemoglobin, body mass index, duration of diabetes, and age did not demonstrate statistically significant correlation with the facial erythema index.

Study limitations

This is an observational study. Elevation of total antioxidant status could have been caused by several factors that might have also influenced the development of rubeosis faciei, including hyperbilirubinemia and hyperuricemia.

Conclusions

The results contradicted expectations. Total antioxidant status correlated positively with facial erythema index; however, there was no correlation with oxidative stress and skin autofluorescence. Further investigations should be conducted to reveal the cause of total antioxidant status elevation in patients with rubeosis faciei.

Resistive index of central retinal artery is a bioimaging biomarker for severity of diabetic retinopathy

BACKGROUND

The present study was undertaken to assess the resistive index (RI) of central retinal artery (CRA) as a bioimaging biomarker for the severity of diabetic retinopathy (DR), for the first time.

METHODS

Eighty-one consecutive patients of type 2 diabetes mellitus between the ages of 40 and 70 years were included in a tertiary care center-based cross sectional study. Severity of retinopathy was assessed according to Early Treatment Diabetic Retinopathy Study (ETDRS) classification: diabetes mellitus with no retinopathy (No DR) (n = 26); non-proliferative diabetic retinopathy (NPDR) (n = 29); and proliferative diabetic retinopathy (PDR) (n = 26). Twenty-six healthy controls of similar age were also included. Resistive index of CRA was studied using color Doppler and gray scale sonography. Central subfield thickness (CST), cube average thickness (CAT), retinal photoreceptor ellipsoid zone (EZ) disruption, and retinal nerve fiber layer (RNFL) thickness were evaluated using spectral domain optical coherence tomography. Sensitivity and specificity were assessed by receiver operating characteristic (ROC) curve.

RESULTS

Mean RI of CRA for the study groups revealed significant increase with severity of diabetic retinopathy (F = 10.24, P < 0.001). The ROC curve analysis showed diagnostic accuracy of RI of CRA (area under curve = 0.841-0.999; sensitivity = 76-100%, specificity = 95.45-100%, P < 0.001) in discriminating controls and patients. Univariate regression analysis revealed significant association between the study groups and RI of CRA (P < 0.001). RI of CRA correlated positively with CST (r = 0.37), CAT (r = 0.45), EZ disruption (r = 0.43) and negatively with RNFL thickness (r = - 0.35) (P < 0.001).

CONCLUSIONS

Resistive index of CRA is a reliable bioimaging biomarker for the severity of DR.

Nitrosative Stress in Retinal Pathologies: Review

Nitric oxide (NO) is a gas molecule with diverse physiological and cellular functions. In the eye, NO is used to maintain normal visual function as it is involved in photoreceptor light transduction. In addition, NO acts as a rapid vascular endothelial relaxant, is involved in the control of retinal blood flow under basal conditions and mediates the vasodilator responses of different substances such as acetylcholine, bradykinin, histamine, substance P or insulin. However, the retina is rich in polyunsaturated lipid membranes and is sensitive to the action of reactive oxygen and nitrogen species. Products generated from NO (i.e., dinitrogen trioxide (N₂O₃) and peroxynitrite) have great oxidative damaging effects. Oxygen and nitrogen species can react with biomolecules (lipids, proteins and DNA), potentially leading to cell death, and this is particularly important in the retina. This review focuses on the role of NO in several ocular diseases, including diabetic retinopathy, retinitis pigmentosa, glaucoma or age-related macular degeneration (AMD).

Serum vitamin D is a biomolecular biomarker for proliferative diabetic retinopathy

BACKGROUND

Vitamin D is a multi-functional fat-soluble metabolite essential for a vast number of physiological processes. Non-classical functions are gaining attention because of the close association of vitamin D deficiency with diabetes, and its complications. The present study was undertaken to evaluate the role of vitamin D as a biomarker for proliferative diabetic retinopathy.

METHODS

A tertiary care center based cross-sectional study was undertaken. Seventy-two consecutive cases of type 2 diabetes mellitus were included. Diagnosis of diabetes mellitus was made using American Diabetes Association guidelines. Study subjects included: diabetes mellitus with no retinopathy (No DR) (n = 24); non-proliferative diabetic retinopathy (n = 24); and proliferative diabetic retinopathy (n = 24) and healthy controls (n = 24). All of the study subjects underwent complete ophthalmological evaluation. Best Corrected Visual Acuity (BCVA) was measured on the logarithm of the minimum angle of resolution (logMAR) scale. Serum 25-OH Vitamin D assay was done using chemiluminescent microparticle immunoassay technology. Diagnostic accuracy of vitamin D was assessed using receiver operating characteristics curve analysis and area under curve (AUC) was determined for the first time.

RESULTS

ANOVA revealed a significant decrease in serum vitamin D levels with severity of diabetic retinopathy (F = 8.95, p < 0.001). LogMAR BCVA was found to increase significantly with the severity of DR (F = 112.64, p < 0.001). On AUC analysis, a cut off value of 18.6 ng/mL for Vitamin D was found to be significantly associated with proliferative diabetic retinopathy [sensitivity = 86.36% (95% CI 65.1-96.9); specificity = 81.82% (95% CI 59.7-94.7); AUC = 0.91 (excellent); and Z value = 8.17].

CONCLUSIONS

Serum vitamin D levels of ≤ 18.6 ng/mL serve as sensitive and specific indicator for proliferative disease, among patients of DR.

Fushiming Capsule Attenuates Diabetic Rat Retina Damage via Antioxidation and Anti-Inflammation

Aims

Diabetic retinopathy (DR) remains one of the leading causes of acquired blindness. Fushiming capsule (FSM), a compound traditional Chinese medicine, is clinically used for DR treatment in China. The present study was to investigate the effect of FSM on retinal alterations, inflammatory response, and oxidative stress triggered by diabetes.

Main Methods

Diabetic rat model was induced by 6-week high-fat and high-sugar diet combined with 35 mg/kg streptozotocin (STZ). 30 days after successful establishment of diabetic rat model, full field electroretinography (ffERG) and optical coherence tomography (OCT) were performed to detect retinal pathological alterations. Then, FSM was administered to diabetic rats at different dosages for 42-day treatment and diabetic rats treated with Calcium dobesilate (CaD) capsule served as the positive group. Retinal function and structure were observed, and retinal vascular endothelial growth factor-α (VEGF-α), glial fibrillary acidic (GFAP), and vascular cell adhesion protein-1 (VCAM-1) expressions were measured both on mRNA and protein levels, and a series of blood metabolic indicators were also assessed.

Key Findings

In DR rats, FSM (1.0 g/kg and 0.5 g/kg) treatment significantly restored retinal function (a higher amplitude of b-wave in dark-adaptation 3.0 and OPs2 wave) and prevented the decrease of retinal thickness including inner nuclear layer (INL), outer nuclear layer (ONL), and entire retina. Additionally, FSM dramatically decreased VEGF-α, GFAP, and VCAM-1 expressions in retinal tissues. Moreover, FSM notably improved serum antioxidative enzymes glutathione peroxidase, superoxide dismutase, and catalase activities, whereas it reduced serum advanced glycation end products, methane dicarboxylic aldehyde, nitric oxide, and total cholesterol and triglycerides levels.

Significance

FSM could ameliorate diabetic rat retina damage possibly via inhibiting inflammation and improving antioxidation.

Interplay between IDO1 and iNOS in human retinal pigment epithelial cells

Human retinal pigment epithelial (hRPE) cells form a selectively permeable monolayer between the neural retina and the highly permeable choroidal vessels. Thus, hRPE cells bear important regulatory functions and are potential targets of pathogens in vivo. Endogenous bacterial endophthalmitis (EBE) is frequently caused by infections with the Gram-positive bacterium Staphylococcus aureus (S. aureus). Upon microbial infection, interferon gamma (IFN-γ), a major cytokine of the adaptive immune response, induces a broad spectrum of effector molecules, such as the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase-1 (IDO1). We stimulated human RPE (hRPE) cells in vitro with proinflammatory cytokines and analyzed the expression levels and enzymatic activities of IDO1 and inducible nitric oxide synthase (iNOS), another antimicrobial effector molecule. The antimicrobial capacity was analyzed in infection experiments using S. aureus and Toxoplasma gondii (T. gondii). Our aim was to characterize the particular importance of IDO1 and iNOS during EBE. We found that an IFN-γ stimulation of hPRE cells induced the expression of IDO1, which inhibited the growth of T. gondii and S. aureus. A co-stimulation with IFN-γ, interleukin-1 beta, and tumor necrosis factor alpha induced a strong expression of iNOS. The iNOS-derived nitric oxide production was dependent on cell-culture conditions; however, it could not cause antimicrobial effects. iNOS did not act synergistically with IDO1. Instead, iNOS activity inhibited IDO1-mediated tryptophan degradation and bacteriostasis. This effect was reversible by the addition of the iNOS inhibitor N^G-monomethyl-l-arginine. In conclusion, iNOS mediates anti-inflammatory effects in hRPE cells stimulated with high amounts of IFN-γ together with tumor necrosis factor alpha and Interleukin-1 beta and prevents potential IDO1-dependent tissue damage.

[T-786C endothelial nitric oxide gene polymorphism and type 1 diabetic retinopathy in the Algerian population]

INTRODUCTION

Diabetic retinopathy (DR) results from interactions between genetic and environmental factors. We were interested in the endothelial nitric oxide gene (eNOS), given the involvement of this enzyme in functional alterations in the retinal microvasculature in diabetes. The goal of our study was to assess the association of T-786C endothelial nitric oxide synthase (eNOS) gene polymorphism with diabetic retinopathy in the Algerian population.

PATIENTS AND METHODS

Our study enrolled 110 patients with and without DR. All subjects were genotyped for the T786C eNOS polymorphism using the PCR-RFLP method. We also investigated the association between this polymorphism and certain clinical and laboratory characteristics of patients with DR.

RESULTS

A significant increase in the frequency of the CC genotype is noted in subjects without DR (P=0.03). We also report a significant increase in the frequencies of the TT+TC genotypes in individuals with DR (P=0.03). However, the association between the different genotypes and clinical or laboratory profiles in patients with DR reveals that the NO level is lower in subjects carrying the TT genotype (P=0.039).

CONCLUSION

Our preliminary results suggest that the CC genotype could confer protection from type 1 diabetic retinopathy in the Algerian population, while the T allele seems to confer susceptibility.

Perturbed Biochemical Pathways and Associated Oxidative Stress Lead to Vascular Dysfunctions in Diabetic Retinopathy

Diabetic retinopathy (DR) is a vascular insult that accompanies the hyperglycemic state. Retinal vasculature holds a pivotal role in maintaining the integrity of the retina, and any alteration to retinal vasculature affects retinal functions. The blood retinal barrier, a prerequisite to vision acuity, is most susceptible to damage during the progression of DR. This is a consequence of impaired biochemical pathways such as the polyol, advanced end glycation products (AGE), hexosamine, protein kinase C (PKC), and tissue renin-angiotensin system (RAS) pathways. Moreover, the role of histone modification and altered miRNA expression is also emerging as a major contributor. Epigenetic changes create a link between altered protein function and redox status of retinal cells, creating a state of metabolic memory. Although various biochemical pathways underlie the etiology of DR, the major insult to the retina is due to oxidative stress, a unifying factor of altered biochemical pathways. This review primarily focuses on the critical biochemical pathways altered in DR leading to vascular dysfunctions and discusses antioxidants as plausible treatment strategies.

Retinal photoreceptor apoptosis is associated with impaired serum ionized calcium homeostasis in diabetic retinopathy: An in-vivo analysis

PURPOSE

The aim of this work was to study the association of serum ionized calcium with retinal photoreceptor apoptosis on spectral domain optical coherence tomography (SD-OCT) in diabetic retinopathy (DR).

METHODS

Sixty consecutive cases with Type 2 diabetes mellitus were categorized into three groups: no diabetic retinopathy; non-proliferative DR; proliferative DR. The eye with more severe form of the disease was considered. Twenty healthy controls were also included. Best corrected visual acuity (BCVA) was measured on logMAR scale. Retinal photoreceptor apoptosis was defined as disruption of retinal photoreceptor ellipsoid zone (EZ). Ellipsoid zone disruption was assessed using SD-OCT. Serum levels of total and ionized calcium were measured using standard protocol.

RESULTS

EZ disruption was found to be positively associated with serum total calcium and ionized calcium. Also, EZ disruption was found to be positively associated with logMAR BCVA.

CONCLUSION

Increased serum ionized calcium induces retinal photoreceptor apoptosis resulting in increased EZ disruption in DR.

Ginsenoside Rg1 protects human retinal pigment epithelial ARPE-19 cells from toxicity of high glucose by up-regulation of miR-26a

AIMS

The therapeutic strategies for diabetic retinopathy (DR) are disappointing. Ginsenoside Rg1 (Rg1) extracted from Panax ginseng can induce glucose uptake and lower oxidative stress. We aimed to explore the effect of Rg1 on DR using human retinal pigment epithelium cells (ARPE-19).

MAIN METHODS

ARPE-19 cells were grown in high glucose (HG) to simulate DR. Cell viability, apoptosis, ROS generation and miR-26a level were examined by CCK-8 assay, flow cytometry assay, DCFH-DA staining and RT-qPCR, respectively. Expression of proteins associated with viability, apoptosis and oxidative stress was measured by Western blot analysis. Effects of Rg1 on HG-induced alteration were assessed. Moreover, whether miR-26a was involved in Rg1-associated modulation was verified. Finally, the involvements of the ERK and Wnt/β-catenin pathways were analyzed by Western blot analysis.

KEY FINDINGS

HG reduced cell viability while promoted apoptosis and oxidative stress in ARPE-19 cells. Rg1 ameliorated HG-induced cell injury. The expression of miR-26a was up-regulated by Rg1 in HG-treated cells, and miR-26a inhibition obviously reversed the effects of Rg1 on HG-treated cells. Finally, we found the ERK and Wnt/β-catenin pathways were inhibited by Rg1 through up-regulation of miR-26a.

SIGNIFICANCE

Rg1 protected ARPE-19 cells against HG-induced injury through up-regulating miR-26a, along with inhibition of the ERK and Wnt/β-catenin pathways. Rg1 might be a potential therapeutic drug for DR.

Hyperglycemia potentiates the effect of ionic calcium in photoreceptor ellipsoid zone disruption in diabetic retinopathy

PURPOSE

To study the association of serum ionic calcium and glycated hemoglobin (HbA1c) with retinal photoreceptor ellipsoid zone (EZ) disruption in diabetic retinopathy (DR).

METHODS

This is a tertiary care center-based observational cross-sectional study. Sixty-three consecutive cases, divided into 21 cases each with no diabetic retinopathy, non-proliferative diabetic retinopathy and proliferative diabetic retinopathy were included. Twenty-one healthy controls were also included. Ellipsoid zone disruption was assessed using spectral-domain optical coherence tomography. Serum ionic calcium and HbA1c were measured using standard protocol. Patient data from cases were divided into two groups according to their HbA1c levels: group 1 (HbA1c < 7, n = 26) and group 2 (HbA1c > 7, n = 37). Data were analyzed statistically.

RESULTS

Mean ionic calcium levels in group 1 and group 2 were 1.131 ± 0.073 mmol/dL and 1.170 ± 0.070 mmol/dL, respectively. In group 1, 11 out of 26 had EZ disruption (42.3%). Similarly, in group 2, 29 out of 37 had EZ disruption (78.4%). On logistic regression analysis, as compared to group 1, ellipsoid zone disruption was found to be positively associated with serum ionic calcium (p = 0.01) in group 2 cases.

CONCLUSION

Increased levels of serum ionic calcium are associated with increased EZ disruption in patients with HbA1c > 7 in DR.

Central subfield thickness and cube average thickness as bioimaging biomarkers for ellipsoid zone disruption in diabetic retinopathy

BACKGROUND

To evaluate the association of central subfield thickness (CST) and cube average thickness (CAT) with ellipsoid zone (EZ) disruption on spectral domain optical coherence tomography (SD-OCT) in patients of diabetic retinopathy (DR).

METHODS

Cross sectional study including consecutive patients of type 2 diabetes mellitus [without DR (No DR, n = 97); non-proliferative DR (NPDR, n = 91); proliferative DR (PDR, n = 83)] and healthy controls (n = 82) was undertaken. CST and CAT values were measured using SD-OCT. Data was analyzed using Chi square test, ANOVA and multivariate analysis. Discriminant values of CST and CAT for EZ disruption were evaluated using receiver operator characteristic curve. Area under curve (AUC) was computed.

RESULTS

Mean CAT and CST values in the study subjects showed an incremental trend. Multivariate ordinal logistic regression analysis showed increase in CST (OR = 1.022, p < 0.001) and CAT (OR = 1.029, p < 0.001) as significant independent predictors of EZ disruption. Area under curve showed excellent predictive results of CST (AUC = 0. 943 ± 0.021, 95% CI, 0.902-0.984, p < 0.05) and CAT (AUC = 0.959 ± 0.012, 95% CI 0.936-0.982, p < 0.05), as bioimaging biomarkers, for EZ disruption.

CONCLUSION

Increase in CST and CAT is associated with increased odds of EZ disruption and these macular parameters serve as bioimaging biomarkers for EZ disruption in DR.

Nitric oxide in the pathophysiology of retinopathy: evidences from preclinical and clinical researches

Retinopathy is the leading cause of blindness and visual disability in working-aged people. The pathogenesis of retinopathy is an actual and still open query. Alterations contributing to oxidative and nitrosative stress, including elevated nitric oxide and superoxide production, changes in the expression of different isoforms of nitric oxide synthase or endogenous antioxidant system, have been implicated in the mechanisms how this ocular disease develops. In addition, it was documented that renin-angiotensin system has been implicated in the progression of retinopathy. Based on comprehensive preclinical and clinical researches in this area, the role of above-mentioned factors in the pathogenesis of diabetic retinopathy, hypertensive retinopathy and ischaemic proliferative retinopathy is reviewed in this study. Moreover, the genetic susceptibility factors involved in the development of the retinopathy and possible strategies that utilize antioxidants as additive therapy are also highlighted here.

Resistive index of ophthalmic artery correlates with retinal pigment epithelial alterations on spectral domain optical coherence tomography in diabetic retinopathy

Background

Retinal pigment epithelium (RPE) plays a significant role in maintenance of integrity of retinal photoreceptors and choriocapillaries. RPE derives its blood supply through ophthalmic artery (OA) via choriocapillaries. RPE topographic alterations have been observed to be associated with severity of retinopathy. The present study was undertaken to assess the correlation between resistive index (RI) of the OA with RPE topographic alterations on Spectral-Domain optical coherence tomography (SD-OCT), to our knowledge, it is for the first time.

Methods

A tertiary care center based cross-sectional study was undertaken after informed consent. Sample size was calculated using 95% confidence interval. Seventy five consecutive cases of type 2 diabetes mellitus between the ages of 40 and 70 years were included. The cases were divided into three groups according to Early Treatment Diabetic Retinopathy Study classification: diabetes mellitus with no retinopathy (No DR) (n = 24); non-proliferative diabetic retinopathy (n = 27); and proliferative diabetic retinopathy (n = 24). Healthy control subjects of similar age group were included (n = 24). RI in OA was studied using Color Doppler imaging. Grades of RPE topographic alterations and retinal photoreceptor ellipsoid zone (EZ) disruption were studied using SD-OCT. Data was analysed using Chi square (χ²) test, analysis of variance (ANOVA), Pearson correlation analysis and Neuman–Keuls test.

Results

LogMAR best corrected visual acuity was found to increase significantly with the severity of DR (F = 105.74, p < 0.001). ANOVA revealed a significant increase in RI of OA (F = 14.23, p < 0.001) with severity of diabetic retinopathy. χ² test revealed significant increase in grades of RPE alterations (χ² = 71.83, p < 0.001) and EZ disruption (χ² = 60.59, p < 0.001) with the severity of diabetic retinopathy. Pearson correlation analyses revealed a significant positive correlation between RI of OA with grades of RPE alterations (r = 0.48, p < 0.001) and also between grades of RPE alterations and EZ disruption (r = 0.82, p < 0.001).

Conclusions

Decrease in ocular blood flow resulting from an increase in RI of OA correlates with severity of DR and grades of topographic alterations in RPE. Integrity of EZ was observed to be dependent on RPE.

Shifts in renin-angiotensin system components, angiogenesis, and oxidative stress-related protein expression in the lamina cribrosa region of streptozotocin-induced diabetic mice

PURPOSE

This study aimed to analyse shifts in renin-angiotensin system (RAS) components, angiogenesis, and oxidative stress-related protein expression in the lamina cribrosa (LC) region in streptozotocin (STZ)-induced diabetic mice.

METHODS

Six months after diabetes induction, the retinal vessels of male C57BL/6 J mice were observed by colour photography, fundus fluorescein angiography (FFA), and immunofluorescent staining following incubation with CD31. Immunofluorescence for glial fibrillary acidic protein (GFAP), alpha-smooth muscle actin (α-SMA),and NG2 was also performed. Angiotensin-converting enzyme 1 (ACE1), angiotensin II type I receptor (AT1R), renin, hypoxia-inducible factor 1-alpha (HIF-1α), vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor 2 (VEGFR2), and haeme oxygenase 1 (HO-1) expression levels were confirmed by immunohistochemical and western blotting analyses.

RESULTS

Compared with control mice, diabetic mice had significantly higher blood glucose concentrations (p < 0.001) and significantly lower body weights (p < 0.001). Colour photography and FFA did not reveal any vessel abnormalities in the diabetic mice; however, immunostaining of whole-mount retinas revealed an increased number of retinal vessels. Furthermore, histopathological staining showed significant reduction in the whole retinal thickness. GFAP expression was slightly higher, whereas fewer NG2⁺ pericytes were observed in diabetic mice than in control mice. ACE1, AT1R, renin, HIF-1α, VEGF, VEGFR2, and HO-1 expression were up-regulated in the LC of the STZ-induced diabetic mice.

CONCLUSIONS

Collectively, ACE 1, AT1R, HIF-1α, VEGF, VEGFR2, and HO-1 activation in the LC region in diabetic mice may be involved in diabetes via the RAS and induction of angiogenesis and oxidative stress.

Retinal exposure to high glucose condition modifies the GABAergic system: Regulation by nitric oxide

Diabetic retinopathy is a severe retinal complication that diabetic patients are susceptible to present. Although this disease is currently characterized as a microvascular disease, there is growing evidence that neural changes occur and maybe precede vascular impairments. Using chicken retina, an avascular tissue with no direct contact with blood vessels and neural retina, this study aimed to evaluate the influence of acute exposure to high glucose concentration in the retinal GABAergic system, and the role of nitric oxide (NO) in this modulation. Therefore, in ex vivo experiments, retinas were incubated in control (10 mM glucose) or high glucose condition (35 mM) for 30 min. By using DAF-FM to evaluate NO production, it was possible to show that high glucose (HG) significantly increased NO levels in the outer nuclear layer, inner nuclear layer (outer and inner portion), and inner plexiform layer. It was also observed that HG increased GABA immunoreactivity (IR) in amacrine and horizontal cells. HG did not change glutamic acid decarboxylase-IR, whereas it decreased GABA Transporter (GAT) 1-IR and increased GAT-3-IR. The co-treatment with 7-NI, an inhibitor of neuronal nitric oxide synthase (nNOS), blocked all changes stimulated by HG exposure. The concomitant exposure with SNAP-5114, a GAT-2/3 inhibitor, blocked the increase in GABA-IR caused by HG incubation. Therefore, our data suggest that hyperglycemia induces GABA accumulation in the cytosol by modulating GABA transporters. This response is dependent on NO production and signaling.

INCREASED SERUM LEVELS OF UREA AND CREATININE ARE SURROGATE MARKERS FOR DISRUPTION OF RETINAL PHOTORECEPTOR EXTERNAL LIMITING MEMBRANE AND INNER SEGMENT ELLIPSOID ZONE IN TYPE 2 DIABETES MELLITUS

PURPOSE

To evaluate the role of serum urea and creatinine as surrogate markers for disruption of retinal photoreceptor external limiting membrane (ELM) and inner segment ellipsoid zone (EZ) in Type 2 diabetic retinopathy (DR) using spectral-domain optical coherence tomography, for the first time.

METHODS

One hundred and seventeen consecutive cases of Type 2 diabetes mellitus (diabetes without retinopathy [No DR; n = 39], nonproliferative diabetic retinopathy [NPDR; n = 39], proliferative diabetic retinopathy [PDR; n = 39]) and 40 healthy control subjects were included. Serum levels of urea and creatinine were assessed using standard protocol. Spectral-domain optical coherence tomography was used to grade the disruption of ELM and EZ as follows: Grade 0, no disruption of ELM and EZ; Grade 1, ELM disrupted, EZ intact; Grade 2, ELM and EZ disrupted. Data were analyzed statistically.

RESULTS

Increase in serum levels of urea (F = 22.93) and creatinine (F = 15.82) and increased grades of disruption of ELM and EZ (γ = 116.3) were observed with increased severity of DR (P < 0.001). Increase in serum levels of urea (F = 10.45) and creatinine (F = 6.89) was observed with increased grades of disruption of ELM and EZ (P = 0.001).

CONCLUSION

Serum levels of urea and creatinine are surrogate markers for disruption of retinal photoreceptor ELM and EZ on spectral-domain optical coherence tomography in DR.

Effects of Chinese herbal medicines on the occurrence of diabetic retinopathy in type 2 diabetes patients and protection of ARPE-19 retina cells by inhibiting oxidative stress

Diabetic retinopathy is a microvascular complication of type 2 diabetes and the leading cause of acquired blindness. In Taiwan, Chinese herbal medicine (CHM) is a popular adjunctive therapy. In this study, we investigated the CHM prescription patterns and their effects. We identified 23,701 subjects with type 2 diabetes in a database, and after matching for age and gender, 6,948 patients each were assigned to CHM and non-CHM groups. In the female subgroups, the cumulative retinopathy probability was lower for the CHM users than that for the CHM non-users (P < 0.001, log-rank test). Among the top 10 CHMs, Jia-Wei-Xiao-Yao-San (JWXYS; 52.9%), Shu-Jing-Huo-Xue-Tang (SJHXT; 45.1%), and Ge-Gen-Tang (GGT; 43.7%) were the most common herbal formulas. Yan-Hu-Suo (48.1%), Ge-Gen (42.1%), and Huang-Qin (HQin; 40.1%) were the most common single herbs. CHM network analysis showed that JWXYS was the core CHM of cluster 1. JWXYS, DS, XF, and SZRT exhibited both of the reductions of H₂O₂-induced phosphorylation of p38 MAPK and p44/42 MAPK (Erk1/2) in human ARPE-19 retina cells. In cluster 2, SJHXT was the core CHM. SJHXT and NX showed both of the phosphorylation reductions. In cluster 3, GGT was the core CHM, and it reduced the phosphorylation of both MAPKs. In cluster 4, HQin was the core CHM, and it also reduced the phosphorylation of both MAPKs. Our study suggests that adjunctive CHM therapy may reduce diabetic retinopathy via antioxidant activity of the herbs and provides information on core CHM treatments for further scientific investigations or therapeutic interventions.

Danhong Huayu Koufuye Prevents Diabetic Retinopathy in Streptozotocin-Induced Diabetic Rats via Antioxidation and Anti-Inflammation

Danhong Huayu Koufuye (DHK), a traditional Chinese prescription, is used to treat central retinal vein occlusion clinically. We previously reported that DHK prevented diabetic retinopathy (DR) in rats. Moreover, we found that it protected endothelial cells from hyperglycemia-induced apoptosis through antioxidation and anti-inflammation. Here, we investigated whether antioxidative and anti-inflammatory activities of DHK contributed to its therapeutic effect on DR in streptozotocin- (STZ-) induced diabetic rats. DHK significantly blocked the breakdown of the blood-retinal barrier (BRB) and increased the thickness of the inner nuclear layer (INL), as well as suppressed the swelling of the ganglion cell layer (GCL) in diabetic retinas. DHK remarkably increased the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) in plasma, and decreased serum level of nitric oxide (NO). Moreover, DHK markedly reduced the serum levels of vascular endothelial growth factor (VEGF) and intercellular adhesion molecule-1 (ICAM-1). Furthermore, DHK significantly downregulated protein expressions of VEGF and inducible NO synthase (iNOS) and mRNA expression of ICAM-1 in retinas. These results suggest that the antioxidative and anti-inflammatory activities of DHK may be important mechanisms involved in the protective effect of DHK on DR in STZ-induced diabetic rats.

Association of serum levels of anti-myeloperoxidase antibody with retinal photoreceptor ellipsoid zone disruption in diabetic retinopathy

AIM

To study the association of serum levels of anti-myeloperoxidase (MPO) antibody with retinal photoreceptor ellipsoid zone (EZ) disruption in diabetic retinopathy.

METHODS

Consecutive patients with type 2 DM [diabetes mellitus with no retinopathy (NODR; n=20); non-proliferative diabetic retinopathy (NPDR; n=18); proliferative diabetic retinopathy (PDR; n=16)] and healthy controls (n=20) between the ages of 40 and 65years were included. Disruption of EZ was graded by spectral domain optical coherence tomography as no disruption of EZ and disrupted EZ. The serum levels of anti-MPO antibody was analyzed using standard protocol. Association between the variables was evaluated using multiple regression analysis.

RESULTS

A significant difference was found between the serum levels of anti-MPO antibody in various study groups (p<0.001). A positive association was found between EZ disruption and levels of anti-MPO antibody [adjusted odd's ratio (AOR)=1.079, CI 1.010-1.124, p=0.04]. A significant positive correlation was found between logMAR visual acuity and grade of disruption (AOR=1.008, CI 1.006-5.688, p=0.04).

CONCLUSIONS

An increased serum anti-MPO antibody levels is associated with retinal photoreceptor EZ disruption and decreased visual acuity in diabetic retinopathy.

Oxidative Stress-Related Mechanisms and Antioxidant Therapy in Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes and is the leading cause of blindness in young adults. Oxidative stress has been implicated as a critical cause of DR. Metabolic abnormalities induced by high-glucose levels are involved in the development of DR and appear to be influenced by oxidative stress. The imbalance between reactive oxygen species (ROS) production and the antioxidant defense system activates several oxidative stress-related mechanisms that promote the pathogenesis of DR. The damage caused by oxidative stress persists for a considerable time, even after the blood glucose concentration has returned to a normal level. Animal experiments have proved that the use of antioxidants is a beneficial therapeutic strategy for the treatment of DR, but more data are required from clinical trials. The aims of this review are to highlight the improvements to our understanding of the oxidative stress-related mechanisms underlying the development of DR and provide a summary of the main antioxidant therapy strategies used to treat the disease.

The potential of spectral domain optical coherence tomography imaging based retinal biomarkers

Background

Biomarker”, a merged word of “biological marker”, refers to a broad subcategory of medical signs that objectively indicate the state of health, and well-being of an individual. Biomarkers hold great promise for personalized medicine as information gained from diagnostic or progression markers can be used to tailor treatment to the individual for highly effective intervention in the disease process. Optical coherence tomography (OCT) has proved useful in identifying various biomarkers in ocular and systemic diseases.

Main body

Spectral domain optical coherence tomography imaging-based biomarkers provide a valuable tool for detecting the earlier stages of the disease, tracking progression, and monitoring treatment response. The aim of this review article is to analyze various OCT based imaging biomarkers and their potential to be considered as surrogate endpoints for diabetic retinopathy, age related macular degeneration, retinitis pigmentosa and vitreomacular interface disorder. These OCT based surrogate markers have been classified as retinal structural alterations (macular central subfield thickness and cube average thickness); retinal ultrastructural alterations (disruption of external limiting membrane and ellipsoid zone, thinning of retinal nerve fiber layer and ganglion cell layer); intraretinal microangiopathic changes; choroidal surrogate endpoints; and vitreoretinal interface endpoints.

Conclusion

OCT technology is changing very quickly and throughout this review there are some of the multiple possibilities that OCT based imaging biomarkers will be more useful in the near future for diagnosis, prognosticating disease progression and as endpoint in clinical trials.

Spectral Domain Optical Coherence Tomography Features and Classification Systems for Diabetic Macular Edema: A Review

Spectral domain optical coherence tomography (SD-OCT) is fast becoming the current standard of care for the detection and assessment of diabetic macular edema. With the application of SD-OCT for imaging of retinal microstructure and measurement of retinal thickness, new information regarding disease characteristics has been gathered, which was unrecognized previously. Retinal thickness measurements on SD-OCT have also been used for deciding the management and monitoring of the disease. Since its development, OCT has enhanced the understanding of retinal anatomical changes in diabetic retinopathy. Several authors have used SD-OCT to classify diabetic macular edema with the purpose of correlating the pathophysiology with disease severity. The classification systems have helped monitor the treatment efficacy and provide prognostic information on the treatment outcome. The following review article summarizes these classifications.

Diabetes-induced oxidative stress in the vitreous humor

Purpose

Diabetes is accompanied by fundamental rearrangements in redox homeostasis. Hyperglycemia triggers the production of reactive oxygen and nitrogen species which contributes to tissue damage in various target organs. Proliferative diabetic retinopathy (PDR) is a common manifestation of diabetic complications but information on the possible role of reactive intermediates in this condition with special regard to the involvement of the vitreous in PDR-associated redox alterations is scarce.

The aim of the study was to determine key parameters of redox homeostasis [advanced glycation endproducts (AGE); protein carbonyl and glutathione (GSH)] content in the vitreous in PDR patients.

Methods

The study population involved 10 diabetic patients undergoing surgery for complications of proliferative diabetic retinopathy and 8 control (non-diabetic) patients who were undergoing surgery for epiretinal membranes. Vitreal fluids were assayed for the above biochemical parameters.

Results

We found elevated levels of AGE in the vitreous of PDR patients (812.10 vs 491.69 ng AGE/mg protein). Extent of protein carbonylation was also higher in the samples of diabetic patients (2.08 vs 0.67 A/100 μg protein). The GSH content also increased in the vitreous of PDR patients as compared to the control group (4.54 vs 2.35 μmol/μg protein), respectively.

Conclusion

The study demonstrates that diabetes-associated redox alterations also reach the vitreous with the most prominent changes being increased protein carbonylation and increased antioxidant levels.

•

Vitreal AGE levels are elevated in PDR patients.

•

Extent of protein carbonylation is higher in the vitreal samples of PDR patients.

•

The glutathione content is increased in the vitreous of PDR patients.

Increased levels of N(ε)- Carboxy methyl lysine (N(ε)-CML) are associated with topographic alterations in retinal pigment epithelium: A preliminary study

PURPOSE

To evaluate the association of serum levels of N(ε)- Carboxy methyl lysine (N(ε)-CML), an advanced glycation end product with topographic alterations in retinal pigment epithelium (RPE) in diabetic retinopathy on spectral domain optical coherence tomography (SD-OCT).

METHOD

Consecutive cases of type 2 diabetes mellitus with no retinopathy (n=20); non-proliferative diabetic retinopathy (n=20); proliferative diabetic retinopathy (n=20) and healthy controls (n=20) between the ages of 40 and 65years were included. RPE alterations were graded on segmentation map of SD-OCT: grade 0, No RPE alterations; grade 1, RPE alterations in up to two quadrants and grade 2, RPE alterations in more than two quadrants. Serum level of N(ε)-CML and glycated hemoglobin (HbA1c) was analyzed using the standard protocol. Statistical analysis was done.

RESULTS

Significant increase in N(ε)-CML was observed with increased severity of diabetic retinopathy (F=34.1; p<0.0001). Fisher exact test revealed significant increase in grades of RPE alterations with increased severity of diabetic retinopathy (p<0.001). Univariate ordinal regression analysis was done to calculate the risk of progression in grades of RPE alteration with individual changes in variables like duration of diabetes (odds ratio=1.37; p=0.001), HbA1c (odds ratio=1.37; p=0.002) and Nε-CML (odds ratio=1.37; p<0.0001). Multivariate ordinal regression analysis for predicting progression in grades of RPE alteration revealed Nε-CML to be an independent predictor of increase in grades of RPE alteration (adjusted odds ratio=1.07; p<0.01) when duration of diabetes and HbA1c were held constant.

CONCLUSION

Increase in serum levels of N(ε)- Carboxy methyl lysine is significantly associated with topographic alterations in RPE. Grades of RPE alteration increase significantly with increased severity of diabetic retinopathy.

Antimyeloperoxidase antibody is a biomarker for progression of diabetic retinopathy

AIM

To study the correlation between serum antimyeloperoxidase (MPO) antibody levels with severity of diabetic retinopathy (DR).

METHODS

Study subjects included 60 consecutive cases of type 2 diabetes mellitus (DM): no diabetic retinopathy (NODR, n=20); nonproliferative DR (NPDR, n=20); proliferative DR (PDR, n=20) and 20 healthy controls. Best corrected visual acuity (BCVA) was measured on logMAR scale. Serum anti-MPO antibody levels were evaluated using ELISA IgG kit. Serum urea and creatinine was measured using standard protocol. Data were analysed statistically.

RESULTS

Mean serum anti-MPO antibody (RU/ml) was 16.94 ± 4.85 in controls, 17.66 ± 4.78 in NODR, 21.51 ± 5.27 in NPDR and 37.27 ± 11.92 in PDR groups. On ANOVA, significant difference in visual acuity was found among the study groups (F=73.46, p<0.001). Serum anti-MPO antibody was correlated significantly with decrease in visual acuity (F=48.40, p<0.001), increase in serum urea (F=128.13, p<0.001) and creatinine (F=77.10, p<0.001).

CONCLUSION

Increase in serum anti-MPO antibody levels correlate with increased severity of DR. Serum anti-MPO antibody may be a noteworthy biochemical marker for progression of retinopathy from nonproliferative to proliferative stage.

Association of serum N(ε)-Carboxy methyl lysine with severity of diabetic retinopathy

PURPOSE

To correlate serum levels of N-epsilon-carboxy methyl lysine (N(ε)-CML) with severity of retinopathy, in vivo macular edema and disruption of external limiting membrane (ELM) and photoreceptor ellipsoid zone in type 2 diabetes mellitus (DM).

METHODS

Consecutive cases of type 2 DM [diabetes mellitus with no retinopathy (No DR) (n=20); non- proliferative diabetic retinopathy (NPDR) with diabetic macular edema (n=20); proliferative diabetic retinopathy with diabetic macular edema (PDR) (n=20)] and healthy controls (n=20) between the ages of 40 and 65 years were included (power of study=93.8%). In vivo histology of retinal layers was assessed using spectral domain optical coherence tomography. Every study subject underwent macular thickness analysis using the macular cube 512×128 feature. Disruption of ELM and photoreceptor ellipsoid zone was graded: grade 0, no disruption of ELM and ellipsoid zone; grade 1, ELM disrupted and ellipsoid zone intact; grade 2, both ELM and ellipsoid zone disrupted. Data were statistically analyzed.

RESULTS

The mean levels of N(ε)-CML were 31.34±21.23 ng/ml, 73.88±35.01 ng/ml, 91.21±66.65 ng/ml, and 132.08±84.07 ng/ml in control, No DR, NPDR and PDR respectively. N(ε)-CML level was significantly different between the study groups (control, No DR, NPDR and PDR) (p<0.001). Mean logMAR visual acuity decreased with increased levels of N(ε)-CML (p<0.001). The association of N(Ɛ)CML with the grades of disruption was found to be statistically significant (F value=18.48, p<0.001). Univariate analysis was done with N(Ɛ)-CML as a dependent variable. The values of N(Ɛ)-CML were normalized (log10) and were subjected to univariate analysis with fasting blood glucose level, glycosylated hemoglobin, central subfield macular thickness and cube average thickness among the diseased groups (NPDR and PDR) that act as confounders. It was found that none of the variables had significant effect on N(Ɛ)-CML (fasting blood glucose p=0.12, HBA1c p=0.65, central subfield macular thickness p=0.13, cube average thickness p=0.19). N(Ɛ)-CML tends to be a significant and important predictor of grade of ELM and ellipsoid zone disruption in diabetic retinopathy.

CONCLUSIONS

Increased N(ε)-CML levels are associated with increased severity of diabetic retinopathy, macular edema and structural changes in macula that is ELM and ellipsoid zone disruption, which serves as a prognosticator of visual outcome.

Correlation of biomarkers thiobarbituric acid reactive substance, nitric oxide and central subfield and cube average thickness in diabetic retinopathy: a cross-sectional study

BACKGROUND

To evaluate the role of thiobarbituric acid reactive substance (TBARS) and nitric oxide (NO) as biochemical biomarkers and central subfield (CST) and cube average thickness (CAT) as biomarkers for medical imaging in diabetic retinopathy.

METHODS

Forty consecutive cases of diabetic retinopathy and 20 healthy controls were included. Cases were divided into two groups: non proliferative diabetic retinopathy (n = 20) and proliferative diabetic retinopathy (n = 20) according to ETDRS classification. LogMAR visual acuity was documented. Plasma levels of TBARS, NO and glycated hemoglobin (HbA1c) were measured using standard protocol. CST and CAT were analyzed on spectral domain optical coherence tomography. Data was analyzed statistically.

RESULTS

Increased severity of diabetic retinopathy was associated with an increase in plasma levels of TBARS (F = 10.92; p < 0.001), NO (F = 21.8; p < 0.001) and HbA1c (F = 5.87; p = 0.001). Increase in CST (F = 61.51; p < 0.001) and CAT (F = 60.84; p < 0.001) was also found to be associated with increased severity of diabetic retinopathy. Pearson's correlation analysis revealed a positive correlation of TBARS with CST (r = 0.29; p = 0.038) and CAT (r = 0.31; p = 0.04). A positive correlation of NO with CST (r = 0.27; p = 0.03) and CAT (r = 0.7; p = 0.001) was also observed. On univariate analysis with logMAR visual acuity as dependent variable, a significant increase in visual acuity was observed with increase in independent variables TBARS (B = 0.22; p = 0.004), NO (B = 0.006; p < 0.001), CST (B = 0.005; p < 0.001) and CAT (B = 0.005; p < 0.001). On multivariate linear regression analysis with logMAR visual acuity as dependent variable and adjusting for other factors like duration of diabetes and HbA1c, it was observed that increase in independent variables TBARS (B = 0.07), NO (B = 0.001) and CST (B = 0.004) independently predict increase in logMAR visual acuity (p < 0.001).

CONCLUSION

Thiobarbituric acid reactive substance and nitric oxide serve as potential biochemical markers whereas central subfield and cube average thickness serve as potential biomarkers for medical imaging for severity of diabetic retinopathy. In a clinical retinal setting, CAT and CST will help in early recognition of increase in severity of diabetic retinopathy.

Single nucleotide polymorphisms in the Trx2/TXNIP and TrxR2 genes of the mitochondrial thioredoxin antioxidant system and the risk of diabetic retinopathy in patients with Type 2 diabetes mellitus

BACKGROUND

Oxidative stress plays an important role in the pathogenesis of diabetes and its complications. The aim of this study was to examine the possible association between seven single nucleotide polymorphisms (SNPs) of the Trx2/TXNIP and TrxR2 genes encoding proteins involved in the thioredoxin antioxidant defence system and the risk of diabetic retinopthy (DR).

DESIGN

Cross-sectional case-control study.

PARTICIPANTS

A total of 802 Slovenian patients with Type 2 diabetes mellitus; 277 patients with DR and 525 with no DR were enrolled.

METHODS

Patients genotypes of the SNPs; including rs8140110, rs7211, rs7212, rs4755, rs1548357, rs4485648 and rs5748469 were determined by the competitive allele specific PCR method.

MAIN OUTCOME MEASURES

Each genotype of examined SNPs was regressed in a logistic model, assuming the co-dominant, dominant and the recessive models of inheritance with covariates of duration of diabetes, HbA1c, insulin therapy, total cholesterol and LDL cholesterol levels.

RESULTS

In the present study, for the first time we identified an association between the rs4485648 polymorphism of the TrxR2 gene and DR in Caucasians with Type 2 DM. The estimated ORs of adjusted logistic regression models were found to be as follows: 4.4 for CT heterozygotes, 4.3 for TT homozygotes (co-dominant genetic model) and 4.4 for CT+TT genotypes (dominant genetic model).

CONCLUSIONS

In our case-control study we were not able to demonstrate any association between rs8140110, rs7211, rs7212, rs4755, rs1548357, and rs5748469 and DR, however, our findings provide evidence that the rs4485648 polymorphism of the TrxR2 gene might exert an independent effect on the development of DR.