Pharmacological inhibition of diabetic retinopathy: aminoguanidine and aspirin

ASCEND-Eye: Effects of Aspirin on Diabetic Retinopathy

PURPOSE

Preclinical studies support a protective role for aspirin in early diabetic retinopathy (DR), but the findings from randomized trials are limited. We present randomized evidence for the efficacy and safety of aspirin on DR outcomes.

DESIGN

A substudy of the A Study of Cardiovascular Events in Diabetes (ASCEND) double-masked, randomized, placebo-controlled trial of 100 mg aspirin daily for the primary prevention of serious cardiovascular events in people with diabetes.

PARTICIPANTS

Fifteen thousand four hundred eighty United Kingdom adults at least 40 years of age with diabetes.

METHODS

Linkage to electronic National Health Service Diabetic Eye Screening Programme records in England and Wales and confirmation of participant-reported eye events via medical record review were carried out. Log-rank methods were used for intention-to-treat analyses of time until the first primary efficacy and safety outcomes.

MAIN OUTCOME MEASURES

The primary efficacy end point was the first record of referable disease after randomization, a composite of referable retinopathy or referable maculopathy based on the grading criteria defined by the United Kingdom National Screening Committee. The primary safety outcome was the first sight-threatening eye bleed, defined as clinically significant bleeding in the eye that resulted in unresolved visual loss or required an urgent intervention such as laser photocoagulation, vitreoretinal surgery, intraocular injection, or a combination thereof.

RESULTS

Linkage data were obtained for 7360 participants (48% of those randomized in ASCEND). During the mean follow-up of 6.5 years, 539 participants (14.6%) experienced a referable disease event in the aspirin group, compared with 522 participants (14.2%) in the placebo group (rate ratio, 1.03; 95% confidence interval [CI], 0.91-1.16; P = 0.64). No statistically significant between-group difference was found in the proportions of sight-threatening eye bleed events (57 participants [0.7%] and 64 participants [0.8%], respectively; rate ratio, 0.89; 95% CI, 0.62-1.27).

DISCUSSION

These data exclude any clinically meaningful benefits of aspirin for DR, but give reassurance regarding the ophthalmologic safety of aspirin.

FINANCIAL DISCLOSURE(S)

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

Effect of advanced glycation end-products in a wide range of medical problems including COVID-19

Glycation is a physiological process that determines the aging of the organism, while in states of metabolic disorders it is significantly intensified. High concentrations of compounds such as reducing sugars or reactive aldehydes derived from lipid oxidation, occurring for example in diabetes, atherosclerosis, dyslipidemia, obesity or metabolic syndrome, lead to increased glycation of proteins, lipids and nucleic acids. The level of advanced glycation end-products (AGEs) in the body depends on rapidity of their production and the rate of their removal by the urinary system. AGEs, accumulated in the extracellular matrix of the blood vessels and other organs, cause irreversible changes in the biochemical and biomechanical properties of tissues. As a consequence, micro- and macroangiopathies appear in the system, and may contribute to the organ failure, like kidneys and heart. Elevated levels of AGEs also increase the risk of Alzheimer's disease and various cancers. In this paper, we propose a new classification due to modified amino acid residues: arginyl-AGEs, monolysyl-AGEs and lysyl-arginyl-AGEs and dilysyl-AGEs. Furthermore, we describe in detail the effect of AGEs on the pathogenesis of metabolic and old age diseases, such as diabetic complications, atherosclerosis and neurodegenerative diseases. We summarize the currently available data on the diagnostic value of AGEs and present the AGEs as a therapeutic goal in a wide range of medical problems, including SARS-CoV-2 infection and so-called long COVID.

Diabetic retinopathy: emerging concepts of current and potential therapy

Diabetic retinopathy (DR) is one of the leading causes of permanent central blindness worldwide. Despite the complexity and inadequate understanding of DR pathogenesis, many of the underlying pathways are currently partially understood and may offer potential targets for future treatments. Anti-VEGF medications are currently the main medication for this problem. This article provides an overview of the established pharmacological treatments and those that are being developed to cure DR. We firstly reviewed the widely utilized approaches including pan-retinal photocoagulation therapy, anti-VEGF therapy, corticosteroid therapy, and surgical management of DR. Next, we discussed the mechanisms of action and prospective benefits of novel candidate medications. Current management are far from being a perfect treatment for DR, despite mild-term favorable efficiency and safety profiles. Pharmacological research should work toward developing longer-lasting treatments or new drug delivery systems, as well as on identifying new molecular targets in the pathogenetical mechanism for DR. In order to find a treatment that is specifically designed for each patient, it is also necessary to properly characterize patients, taking into account elements like hereditary factors and intraretinal neovascularization stages for effective utilization of drugs. The current and potential approaches for diabetic retinopathy. Image was constructed using Biorender.com.

ASCEND-Eye: Rationale, design and baseline characteristics for a sub-study of the ASCEND randomised trial, exploring the effects of aspirin and omega-3 fatty acids on diabetic retinopathy and age-related macular degeneration

Background

Aspirin and omega-3 fatty acids (FAs) have potential disease-modifying roles in diabetic retinopathy (DR) and age-related macular degeneration (AMD), but randomized evidence of these effects is limited. We present the rationale and baseline characteristics of ASCEND-Eye, a sub-study of the double-blind, 2x2 factorial design, randomized placebo-controlled ASCEND (A Study of Cardiovascular Events iN Diabetes) trial of 100 mg aspirin daily and, separately, 1g omega-3 FAs daily for the primary prevention of serious cardiovascular events, in 15,480 British adults, aged 40 years or older with diabetes.

Methods

Eye events will be derived from three sources: 1) participant follow-up questionnaires from ASCEND, 2) electronic NHS Diabetic Eye Screening Programme (DESP) data and 3) responses to the National Eye Institute's Visual Function Questionnaire-25 (NEI-VFQ-25) sent to a subset of participants after the main trial ended. Analytic cohorts and outcomes relevant to these data sources are described. The primary outcome is referable diabetic eye disease, a secondary outcome is incident AMD events.

Results

Participant-reported events were ascertained for the full cohort of randomized individuals who were followed up over 7.4 years in ASCEND (n = 15,480). Linked DESP data were available for 48% of those (n = 7360), and 57% completed the NEI-VFQ-25 (n = 8839). The baseline characteristics of these three cohorts are presented.

Discussion

Establishing the risks and benefits of drugs commonly taken by people with diabetes, the elderly, or both, and finding new treatments for DR and AMD is important. ASCEND-Eye provides the opportunity to evaluate the effect of aspirin and, separately, omega-3 FAs for both conditions.

Study registration

Eudract No. 2004-000991-15; Multicentre Research Ethics Committee Ref No. 03/8/087; ClinicalTrials.gov No. NCT00135226; ISRCTN No. ISRCTN60635500.

Activated cGAS/STING signaling elicits endothelial cell senescence in early diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of blindness in working-age adults and remains an important public health issue worldwide. Here we demonstrate that the expression of stimulator of interferon genes (STING) is increased in patients with DR and animal models of diabetic eye disease. STING has been previously shown to regulate cell senescence and inflammation, key contributors to the development and progression of DR. To investigate the mechanism whereby STING contributes to the pathogenesis of DR, diabetes was induced in STING-KO mice and STINGGT (loss-of-function mutation) mice, and molecular alterations and pathological changes in the retina were characterized. We report that retinal endothelial cell senescence, inflammation, and capillary degeneration were all inhibited in STING-KO diabetic mice; these observations were independently corroborated in STINGGT mice. These protective effects resulted from the reduction in TBK1, IRF3, and NF-κB phosphorylation in the absence of STING. Collectively, our results suggest that targeting STING may be an effective therapy for the early prevention and treatment of DR.

New Insights on Dietary Polyphenols for the Management of Oxidative Stress and Neuroinflammation in Diabetic Retinopathy

Diabetic retinopathy (DR) is a neurodegenerative and vascular pathology that is considered one of the leading causes of blindness worldwide, resulting from complications of advanced diabetes mellitus (DM). Current therapies consist of protocols aiming to alleviate the existing clinical signs associated with microvascular alterations limited to the advanced disease stages. In response to the low resolution and limitations of the DR treatment, there is an urgent need to develop more effective alternative therapies to optimize glycemic, vascular, and neuronal parameters, including the reduction in the cellular damage promoted by inflammation and oxidative stress. Recent evidence has shown that dietary polyphenols reduce oxidative and inflammatory parameters of various diseases by modulating multiple cell signaling pathways and gene expression, contributing to the improvement of several chronic diseases, including metabolic and neurodegenerative diseases. However, despite the growing evidence for the bioactivities of phenolic compounds, there is still a lack of data, especially from human studies, on the therapeutic potential of these substances. This review aims to comprehensively describe and clarify the effects of dietary phenolic compounds on the pathophysiological mechanisms involved in DR, especially those of oxidative and inflammatory nature, through evidence from experimental studies. Finally, the review highlights the potential of dietary phenolic compounds as a prophylactic and therapeutic strategy and the need for further clinical studies approaching the efficacy of these substances in DR management.

Retinal Cell Damage in Diabetic Retinopathy

Diabetic retinopathy (DR), the most common microvascular complication that occurs in diabetes mellitus (DM), is the leading cause of vision loss in working-age adults. The prevalence of diabetic retinopathy is approximately 30% of the diabetic population and untreated DR can eventually cause blindness. For decades, diabetic retinopathy was considered a microvascular complication and clinically staged by its vascular manifestations. In recent years, emerging evidence has shown that diabetic retinopathy causes early neuronal dysfunction and neurodegeneration that may precede vascular pathology and affect retinal neurons as well as glial cells. This knowledge leads to new therapeutic strategies aiming to prevent dysfunction of retinal neurons at the early stage of DR. Early detection and timely treatment to protect retinal neurons are critical to preventing visual loss in DR. This review provides an overview of DR and the structural and functional changes associated with DR, and discusses neuronal degeneration during diabetic retinopathy, the mechanisms underlying retinal neurodegeneration and microvascular complications, and perspectives on current and future clinic therapies.

RAGE signaling regulates the progression of diabetic complications

Diabetes, the ninth leading cause of death globally, is expected to affect 642 million people by 2040. With the advancement of an aging society, the number of patients with diabetes having multiple underlying diseases, such as hypertension, obesity, and chronic inflammation, is increasing. Thus, the concept of diabetic kidney disease (DKD) has been accepted worldwide, and comprehensive treatment of patients with diabetes is required. Receptor for advanced glycation endproducts (RAGE), a multiligand receptor, belonging to the immunoglobulin superfamily is extensively expressed throughout the body. Various types of ligands, including advanced glycation endproducts (AGEs), high mobility group box 1, S100/calgranulins, and nucleic acids, bind to RAGE, and then induces signal transduction to amplify the inflammatory response and promote migration, invasion, and proliferation of cells. Furthermore, the expression level of RAGE is upregulated in patients with diabetes, hypertension, obesity, and chronic inflammation, suggesting that activation of RAGE is a common denominator in the context of DKD. Considering that ligand–and RAGE–targeting compounds have been developed, RAGE and its ligands can be potent therapeutic targets for inhibiting the progression of DKD and its complications. Here, we aimed to review recent literature on various signaling pathways mediated by RAGE in the pathogenesis of diabetic complications. Our findings highlight the possibility of using RAGE–or ligand–targeted therapy for treating DKD and its complications.

Integrated Metabolomics and Transcriptomics Reveal Metabolic Patterns in Retina of STZ-Induced Diabetic Retinopathy Mouse Model

Diabetic retinopathy (DR), as the leading cause of vision loss in the working-age population, exhibits unique metabolite profiles in human plasma and vitreous. However, those in retina are not fully understood. Here, we utilized liquid and gas chromatography-tandem mass spectrometry technology to explore metabolite characteristics of streptozotocin (STZ)-induced diabetic mice retina. A total of 145 metabolites differed significantly in diabetic retinas compared with controls. These metabolites are mainly enriched in the Warburg effect, and valine, leucine and isoleucine degradation pathways. To further identify underlying regulators, RNA sequencing was performed to integrate metabolic enzyme alterations with metabolomics in STZ-induced diabetic retina. Retinol metabolism and tryptophan metabolism are the shared pathways enriched by metabolome and transcriptome. Additionally, transcriptomic analysis identified 71 differentially expressed enzyme-related genes including Hk2, Slc7a5, Aldh1a3 and Tph integrated with altered metabolic pathways. In addition, single nucleotide polymorphisms within 6 out of 71 genes are associated with increased diabetes risk. This study lays the foundation for mechanism research and the therapeutic target development of DR.

Reducing Akt2 in retinal pigment epithelial cells causes a compensatory increase in Akt1 and attenuates diabetic retinopathy

The retinal pigment epithelium (RPE) plays an important role in the development of diabetic retinopathy (DR), a leading cause of blindness worldwide. Here we set out to explore the role of Akt2 signaling-integral to both RPE homeostasis and glucose metabolism-to DR. Using human tissue and genetically manipulated mice (including RPE-specific conditional knockout (cKO) and knock-in (KI) mice), we investigate whether Akts in the RPE influences DR in models of diabetic eye disease. We found that Akt1 and Akt2 activities were reciprocally regulated in the RPE of DR donor tissue and diabetic mice. Akt2 cKO attenuated diabetes-induced retinal abnormalities through a compensatory upregulation of phospho-Akt1 leading to an inhibition of vascular injury, inflammatory cytokine release, and infiltration of immune cells mediated by the GSK3β/NF-κB signaling pathway; overexpression of Akt2 has no effect. We propose that targeting Akt1 activity in the RPE may be a novel therapy for treating DR.

Effect of anticoagulant/antiplatelet therapy on the development and progression of diabetic retinopathy

Background

We investigated whether antiplatelet/anticoagulant (APAC) therapy can protect patients with type 2 diabetes mellitus (T2DM) from the development or progression of diabetic retinopathy (DR).

Methods

This is a retrospective cohort study using Longitudinal Health Insurance Database in Taiwan. A total of 73,964 type 2 diabetic patients older than 20 years old were included. Hazard ration (HR) of non-proliferative DR (NPDR), proliferative DR (PDR), and diabetic macular edema (DME) were analyzed with APAC usage as a time-dependent covariate. Age, sex, comorbidities, and medicines were further adjusted in a multi-variable model. Contributions of respective APAC was investigated with sensitivity analysis.

Results

Compared with nonusers, APAC users had a lower cumulative incidence of NPDR (P < 0.001), overall incidence of NPDR (10.7 per 1000 person-years), and risk of developing NPDR (adjusted HR = 0.78, 95% CI = 0.73–0.83). However, no significant differences were observed between APAC users and nonusers in the risks of PDR or DME. Hypertension, diabetic nephropathy and diabetic neuropathy were risk factors for NDPR development, while heart disease, cardiovascular disease, peripheral arterial occlusive disease, and statin usage were covariates decreasing NPDR development. Aspirin and Dipyridamole showed significant protection against NPDR development. Clopidogrel, Ticlopidine, and warfarin showed enhanced protection in combination with aspirin usage.

Conclusions

APAC medications have a protective effect against NPDR development. Diabetic patients benefit from single use of aspirin or dipyridamole on prevention of NPDR.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-022-02323-z.

Propofol protects against high glucose-mediated endothelial injury via inhibition of COX2 and iNOS expressions

Perioperative hyperglycemia is a common metabolic disorder in the clinic. Hyperglycemia, via upregulation of E74-like ETS transcription factor 3 (ELF3), induces cyclooxygenase 2 (COX2) and inducible nitric oxide synthase (iNOS) expressions, thus leading to endothelial apoptosis and vascular endothelial injury. Propofol is a widely used anesthetic. In the present study, we explored whether and how propofol protects against high glucose-induced COX2 and iNOS expressions in human umbilical vein endothelial cells (HUVECs). We found that high glucose level decreases cell viability and increases COX2 and iNOS expressions in HUVECs. Our data also indicated that ELF3 overexpression participates in high glucose-mediated cell viability reduction and high glucose-induced COX2 and iNOS expressions. Moreover, propofol treatment improves high glucose-mediated reduction in cell viability and decreases COX2 and iNOS expressions via inhibition of ELF3 expressions. Furthermore, specificity protein 1 (SP1) was found to regulate ELF3 expression, thus mediating endothelial injury. Propofol inhibits high glucose-induced SP1 expression. High glucose increases the abundance of SP1 bound to the ELF3 promoter, which can be reversed by propofol treatment. The protective effect of propofol is reversed by SP1 overexpression. In conclusion, propofol downregulates high glucose-induced SP1 expression, thus attenuating high glucose-induced ELF3 expression, inhibiting high glucose-induced COX2 and iNOS expressions, and improving high glucose-mediated cell viability reduction in HUVECs.

A Systematic Review of Carotenoids in the Management of Diabetic Retinopathy

Diabetic retinopathy, which was primarily regarded as a microvascular disease, is the leading cause of irreversible blindness worldwide. With obesity at epidemic proportions, diabetes-related ocular problems are exponentially increasing in the developed world. Oxidative stress due to hyperglycemic states and its associated inflammation is one of the pathological mechanisms which leads to depletion of endogenous antioxidants in retina in a diabetic patient. This contributes to a cascade of events that finally leads to retinal neurodegeneration and irreversible vision loss. The xanthophylls lutein and zeaxanthin are known to promote retinal health, improve visual function in retinal diseases such as age-related macular degeneration that has oxidative damage central in its etiopathogenesis. Thus, it can be hypothesized that dietary supplements with xanthophylls that are potent antioxidants may regenerate the compromised antioxidant capacity as a consequence of the diabetic state, therefore ultimately promoting retinal health and visual improvement. We performed a comprehensive literature review of the National Library of Medicine and Web of Science databases, resulting in 341 publications meeting search criteria, of which, 18 were found eligible for inclusion in this review. Lutein and zeaxanthin demonstrated significant protection against capillary cell degeneration and hyperglycemia-induced changes in retinal vasculature. Observational studies indicate that depletion of xanthophyll carotenoids in the macula may represent a novel feature of DR, specifically in patients with type 2 or poorly managed type 1 diabetes. Meanwhile, early interventional trials with dietary carotenoid supplementation show promise in improving their levels in serum and macular pigments concomitant with benefits in visual performance. These findings provide a strong molecular basis and a line of evidence that suggests carotenoid vitamin therapy may offer enhanced neuroprotective effects with therapeutic potential to function as an adjunct nutraceutical strategy for management of diabetic retinopathy.

Dysfunction of retinal neurons and glia during diabetes

Diabetic retinopathy is the leading cause of blindness in those of working age. It is well known that the retinal vasculature is altered during diabetes. More recently, it has emerged that neuronal and glial dysfunction occurs in those with diabetes. Current research is directed at understanding these neuronal and glial changes because they may be an early manifestation of disease processes that ultimately lead to vascular abnormality. This review will highlight the recent advances in our understanding of the neuronal and glial changes that occur during diabetes.

Extracellular Vesicles and MicroRNA: Putative Role in Diagnosis and Treatment of Diabetic Retinopathy

Diabetic retinopathy (DR) is a complex, progressive, and heterogenous retinal degenerative disease associated with diabetes duration. It is characterized by glial, neural, and microvascular dysfunction, being the blood-retinal barrier (BRB) breakdown a hallmark of the early stages. In advanced stages, there is formation of new blood vessels, which are fragile and prone to leaking. This disease, if left untreated, may result in severe vision loss and eventually legal blindness. Although there are some available treatment options for DR, most of them are targeted to the advanced stages of the disease, have some adverse effects, and many patients do not adequately respond to the treatment, which demands further research. Oxidative stress and low-grade inflammation are closely associated processes that play a critical role in the development of DR. Retinal cells communicate with each other or with another one, using cell junctions, adhesion contacts, and secreted soluble factors that can act in neighboring or long-distance cells. Another mechanism of cell communication is via secreted extracellular vesicles (EVs), through exchange of material. Here, we review the current knowledge on deregulation of cell-to-cell communication through EVs, discussing the changes in miRNA expression profiling in body fluids and their role in the development of DR. Thereafter, current and promising therapeutic agents for preventing the progression of DR will be discussed.

Regulation of blood flow in diabetic retinopathy

Blood flow in the retina increases in response to light-evoked neuronal activity, ensuring that retinal neurons receive an adequate supply of oxygen and nutrients as metabolic demands vary. This response, termed "functional hyperemia," is disrupted in diabetic retinopathy. The reduction in functional hyperemia may result in retinal hypoxia and contribute to the development of retinopathy. This review will discuss the neurovascular coupling signaling mechanisms that generate the functional hyperemia response in the retina, the changes to neurovascular coupling that occur in diabetic retinopathy, possible treatments for restoring functional hyperemia and retinal oxygen levels, and changes to functional hyperemia that occur in the diabetic brain.

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.

High Glucose Induces Endothelial COX2 and iNOS Expression via Inhibition of Monomethyltransferase SETD8 Expression

Cyclooxygenase 2 (COX2) and inducible nitric oxide synthase (iNOS) overexpression results in endothelial apoptosis, thus mediating vascular endothelial injury in hyperglycaemia. E26 transformation-specific sequence transcription factor-1 (ESE-1), which belongs to the E26 transformation-specific family of transcription factors, has been demonstrated to be involved in COX2 and iNOS gene transcription. Our previous study indicated that SET domain-containing protein 8 (SETD8) downregulation is involved in high glucose-mediated endothelial inflammation in human umbilical vein endothelial cells (HUVECs). Here, we report that SETD8 plays a major role in hyperglycaemia-induced COX2 and iNOS expression. In HUVECs, upregulation of ESE-1 expression was related to high glucose-mediated apoptosis and COX2 and iNOS expression. High glucose inhibited SETD8 expression, and overexpression of SETD8 diminished the effects of high glucose treatment. Consistently, RNA silencing of SETD8 led to the opposite effect. Furthermore, SETD8 was found to interact with specificity protein 1 (SP1). Blockade of SP1 protected against high glucose-mediated endothelial injury. Mechanistically, we showed that H4K20me1, a downstream target of SETD8, and SP1 were enriched at the ESE-1 promoter region by ChIP assay. Luciferase reporter assays indicated that SETD8 overexpression attenuated ESE-1 promoter activity and augmented the inhibitory effect of siSP1 on ESE-1 promoter activity. In general, our data indicate that SETD8 interacts with SP1 to coregulate ESE-1 expression, which is involved in hyperglycaemia-mediated endothelial apoptosis in HUVECs.

Effects of sodium-glucose cotransporter-2 inhibitors and dipeptidyl peptidase-4 inhibitors on diabetic retinopathy and its progression: A real-world Korean study

The sodium-glucose cotransporter-2 inhibitors (SGLT2is) reduce the incidence of macrovascular complications of diabetes, while their effect on diabetic retinopathy has not been clarified. We compared the effects of SGLT2is with those of dipeptidyl peptidase-4 inhibitors (DPP4is) on the risk of diabetic retinopathy and its progression in people with type 2 diabetes. We performed a retrospective cohort study among people with type 2 diabetes who started on a SGLT2i or DPP4i from 2014 to 2016 according to the Korean National Health Insurance Service database. Subjects initiated on a SGLT2i or DPP4i were matched on a 1:1 basis according to their propensity scores, and Cox proportional hazards regression models were used to calculate the hazard ratios for the risk of diabetic retinopathy and its progression. After propensity score-matching, 41,430 patients without a history of diabetic retinopathy were identified as new users of a SGLT2i (n = 20,175) or DPP4i (n = 20,175). The hazard ratio (95% CI) for diabetic retinopathy was 0.89 (0.83–0.97) for SGLT2i initiators compared with DPP4i initiators. In patients with a history of diabetic retinopathy (n = 4,663 pairs), there was no significant difference in diabetic retinopathy progression between SGLT2i initiators and DPP4i initiators (hazard ratio 0.94, 95% CI 0.78–1.13). This real-world cohort study showed that SGLT2is might be associated with lower risk of diabetic retinopathy compared with DPP4is. Randomized controlled trials are needed to investigate the long-term effect of SGLT2is in diabetic retinopathy in people with diabetes.

Pathophysiology of Diabetic Retinopathy: Contribution and Limitations of Laboratory Research

Preclinical models of diabetic retinopathy are indispensable in the drug discovery and development of new therapies. They are, however, imperfect facsimiles of diabetic retinopathy in humans. This chapter discusses the advantages, limitations, and physiological and pathological relevance of preclinical models of diabetic retinopathy. The judicious interpretation and extrapolation of data derived from these models to humans and a correspondingly greater emphasis placed on translational medical research in early-stage clinical trials are essential to more successfully inhibit the development and progression of diabetic retinopathy in the future.

Aldose reductase regulates hyperglycemia-induced HUVEC death via SIRT1/AMPK-α1/mTOR pathway

Although hyperglycemia-mediated death and dysfunction of endothelial cells have been reported to be a major cause of diabetes associated vascular complications, the mechanisms through which hyperglycemia cause endothelial dysfunction is not well understood. We have recently demonstrated that aldose reductase (AR, AKR1B1) is an obligatory mediator of oxidative and inflammatory signals induced by growth factors, cytokines and hyperglycemia. However, the molecular mechanisms by which AR regulates hyperglycemia-induced endothelial dysfunction is not well known. In this study, we have investigated the mechanism(s) by which AR regulates hyperglycemia-induced endothelial dysfunction. Incubation of human umbilical vein endothelial cells (HUVECs) with high glucose (HG) decreased the cell viability and inhibition of AR prevented it. Further, AR inhibition prevented the HG-induced ROS generation and expression of BCL-2, BAX and activation of Caspase-3 in HUVECs. AR inhibition also prevented the adhesion of THP-1 monocytes on HUVECs, expression of iNOS and eNOS and adhesion molecules ICAM-1 and VCAM-1 in HG-treated HUVECs. Further, AR inhibition restored the HG-induced depletion of SIRT1 in HUVECs and increased the phosphorylation of AMPKα1 along-with a decrease in phosphorylation of mTOR in HG-treated HUVECs. Fidarestat decreased SIRT1 expression in HUVECs pre-treated with specific SIRT1 inhibitor but not with the AMPKα1 inhibitor. Similarly, knockdown of AR in HUVECs by siRNA prevented the HG-induced HUVECs cell death, THP-1 monocyte adhesion and SIRT1 depletion. Furthermore, fidarestat regulated the phosphorylation of AMPKα1 and mTOR, and expression of SIRT1 in STZ-induced diabetic mice heart and aorta tissues. Collectively, our data suggest that AR regulates hyperglycemia-induced endothelial death and dysfunction by altering the ROS/SIRT1/AMPKα1/mTOR pathway.

Advanced Glycation End Products in Chinese Medicine Mediated Aging Diseases: A Review

Aging has become a worldwide problem. During this process, the incidence of related diseases such as diabetes and atherosclerosis increases dramatically. Studies within the most recent two decades suggest a pivotal role of Advanced Glycation End Products (AGEs) in the aging process. This review aims to systemically summarize the effects and potential mechanism of Chinese Medicines on inhibiting AGEs-related aging diseases.

Diabetic retinopathy, a vascular and inflammatory disease: Therapeutic implications

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes and the leading cause of visual impairment in the working-age population in the Western world. Diabetic macular oedema (DME) is one of the major complications of DR. Therapy with intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) drugs has become the gold standard treatment for DR and its complications. However, these drugs have no effect on the pathogenesis of DR and must be administered frequently via invasive intravitreal injections over many years. Thus, there is a pressing need to develop new therapeutic strategies to improve the treatment of this devastating disease. Indeed, an increasing volume of data supports the role of the inflammatory process in the pathogenesis of DR itself and its complications, including both increased retinal vascular permeability and neovascularization. Inflammation may also contribute to retinal neurodegeneration. Evidence that low-grade inflammation plays a critical role in the pathogenesis of DME has opened up new pathways and targets for the development of improved treatments. Anti-inflammatory compounds such as intravitreal glucocorticoids, topical non-steroidal anti-inflammatory drugs (NSAIDs), antioxidants, inflammatory molecule inhibitors, renin-angiotensin system (RAS) blockers and natural anti-inflammatory therapies may all be considered to reduce the rate of administration of antineovascularization agents in the treatment of DR. This report describes the current state of knowledge of the potential role of anti-inflammatory drugs in controlling the onset and evolution of DR and DME.

Bradykinin Type 1 Receptor - Inducible Nitric Oxide Synthase: A New Axis Implicated in Diabetic Retinopathy

Compelling evidence suggests a role for the inducible nitric oxide synthase, iNOS, and the bradykinin type 1 receptor (B1R) in diabetic retinopathy, including a possible control of the expression and activity of iNOS by B1R. In diabetic retina, both iNOS and B1R contribute to inflammation, oxidative stress, and vascular dysfunction. The present study investigated whether inhibition of iNOS has any impact on inflammatory/oxidative stress markers and on the B1R-iNOS expression, distribution, and action in a model of type I diabetes. Diabetes was induced in 6-week-old Wistar rats by streptozotocin (65 mg.kg^-1, i.p.). The selective iNOS inhibitor 1400W (150 μg.10 μl^-1) was administered twice a day by eye-drops during the second week of diabetes. The retinae were collected 2 weeks after diabetes induction to assess the protein and gene expression of markers by Western blot and qRT-PCR, the distribution of iNOS and B1R by fluorescence immunocytochemistry, and the vascular permeability by the Evans Blue dye technique. Diabetic retinae showed enhanced expression of iNOS, B1R, carboxypeptidase M (involved in the biosynthesis of B1R agonists), IL-1β, TNF-α, vascular endothelium growth factor A (VEGF-A) and its receptor, VEGF-R2, nitrosylated proteins and increased vascular permeability. All those changes were reversed by treatment with 1400W. Moreover, the additional increase in vascular permeability in diabetic retina induced by intravitreal injection of R-838, a B1R agonist, was also prevented by 1400W. Immunofluorescence staining highlighted strong colocalization of iNOS and B1R in several layers of the diabetic retina, which was prevented by 1400W. This study suggests a critical role for iNOS and B1R in the early stage of diabetic retinopathy. B1R and iNOS appear to partake in a mutual auto-induction and amplification loop to enhance nitrogen species formation and inflammation in diabetic retina. Hence, B1R-iNOS axis deserves closer scrutiny in targeting diabetic retinopathy.

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.

Ginseng Extract Modified by Pectin Lyase Inhibits Retinal Vascular Injury and Blood-Retinal Barrier Breakage in a Rat Model of Diabetes

GS-E3D is an enzymatically modified ginseng extract by pectin lyase. In this study, we evaluated the preventive effects of GS-E3D on blood-retinal barrier (BRB) leakage in a rat model of diabetes. To produce diabetes, rats were injected with streptozotocin. GS-E3D was orally gavaged at 25, 50, and 100 mg/kg body weight for 6 weeks. We then compared the effect of GS-E3D with that of an unmodified ginseng extract (UGE) on retinal vascular leakage. The administration of GS-E3D significantly blocked diabetes-induced BRB breakdown. Immunofluorescence staining showed that GS-E3D reduced the loss of occludin in diabetic rats. In TUNEL staining, the number of apoptotic retinal microvascular cells was dose dependently decreased by GS-E3D treatment. GS-E3D decreased the accumulations of advanced glycation end products in the retinal vessels. In addition, the inhibition potential of GS-E3D on BRB breakage was stronger compared with UGE. These results indicate that GS-E3D could be a beneficial treatment option for preventing diabetes-induced retinal vascular injury.

Role of advanced glycation end products in mobility and considerations in possible dietary and nutritional intervention strategies

Advanced glycation end products (AGEs), a group of compounds that are formed by non-enzymatic reactions between carbonyl groups of reducing sugars and free amino groups of proteins, lipids or nucleic acids, can be obtained exogenously from diet or formed endogenously within the body. AGEs accumulate intracellularly and extracellularly in all tissues and body fluids and can cross-link with other proteins and thus affect their normal functions. Furthermore, AGEs can interact with specific cell surface receptors and hence alter cell intracellular signaling, gene expression, the production of reactive oxygen species and the activation of several inflammatory pathways. High levels of AGEs in diet as well as in tissues and the circulation are pathogenic to a wide range of diseases. With respect to mobility, AGEs accumulate in bones, joints and skeletal muscles, playing important roles in the development of osteoporosis, osteoarthritis, and sarcopenia with aging. This report covered the related pathological mechanisms and the potential pharmaceutical and dietary intervention strategies in reducing systemic AGEs. More prospective studies are needed to determine whether elevated serum AGEs and/or skin autofluorescence predict a decline in measures of mobility. In addition, human intervention studies are required to investigate the beneficial effects of exogenous AGEs inhibitors on mobility outcomes.

Role of oxidative stress, inflammation, hypoxia and angiogenesis in the development of diabetic retinopathy

Diabetic retinopathy (DR) is a retinal disease which is one of the most severe complications occuring due to diabetes mellitus and is a major cause of blindness. Patients who have diabetes mellitus for number of years develop characteristic group of lesions in the retina which leads to Diabetic retinopathy. It is a multifactorial condition occuring due to complex cellular interactions between biochemical and metabolic abnormalities taking place in all retinal cells. Considerable research efforts in the past 20 years have suggested that the microvasculature of the retina responds to hyperglycemia through a number of biochemical changes, which includes polyol pathway, protein kinase C activation, upregulation of advanced glycation end products formation and renin angiotensin system activation. Various previous studies had suggest that interaction of these biochemical changes may cause a cascade of events, such as apoptosis, oxidative stress, inflammation and angiogenesis which can lead to the damage of a diabetic retina, causing DR. This highlights that oxidative stress, inflammation, angiogenesis-related factors triggers the occurrence of retinal complication in diabetes are highlighted.

Aster koraiensis extract prevents diabetes-induced retinal vascular dysfunction in spontaneously diabetic Torii rats

BACKGROUND

Aster koraiensis extract (AKE) is a standard dietary herbal supplement. The aim of this study is to investigate the inhibitory effects of AKE on diabetes-induced retinal vascular dysfunction in Spontaneously Diabetic Torii (SDT) rats.

METHODS

AKE (50 and 100 mg/kg body weight/day) was administered for 16 weeks. The effects of orally administered AKE on blood glucose levels, retinal vascular leakage, apoptosis, and accumulation of advanced glycation end products (AGEs) in the retina were evaluated.

RESULTS

SDT rats exhibited hyperglycemia and retinal vascular leakage, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was clearly detected apoptosis in the retinal microvasculature. Immunofluorescence staining revealed the accumulation of AGEs in the retinal vasculature of the SDT rats. However, oral administration of AKE for 16 weeks blocked diabetes-induced blood-retinal barrier (BRB) breakdown and the loss of occludin, which is an important tight junction protein. Apoptosis of retinal vascular cells and AGE accumulation were significantly inhibited after AKE treatment.

CONCLUSION

These results indicate that, as a dietary herbal supplement, AKE may have beneficial effects on patients with diabetic retinopathy.

TOWARDS A TREATMENT FOR DIABETIC RETINOPATHY: Intravitreal Toxicity and Preclinical Safety Evaluation of Inducible Nitric Oxide Synthase Inhibitors

BACKGROUND

The purpose of this study is to determine the maximum tolerated dose of a single intravitreal injection of aminoguanidine and 1400W, 2 inhibitors of inducible nitric oxide synthase, in rabbit eyes. Inhibition of inducible nitric oxide synthase has already been shown to be beneficial in various animal models of diabetic eye disease.

METHODS

Groups of 4 New Zealand white rabbits were injected with balanced salt solution in the right eye and a single dose of either aminoguanidine (5, 1, 0.25 mg) or 1400W (2 mg and 0.4 mg) in the left eye. Toxicity was assessed by slit-lamp and fundus examination, intraocular pressure and pachymetric measurements, and electrophysiologic and histologic analysis.

RESULTS

Eyes injected with high doses of aminoguanidine (5 mg) or 1400W (2 mg) demonstrated severe retinal vascular attenuation and infarction. Lower doses of intravitreal aminoguanidine (1 mg) and 1400W (0.4 mg) caused no significant toxic ocular effects in rabbit eyes.

CONCLUSION

If the difference in vitreal volume between rabbit eyes and human eyes is taken into account, aminoguanidine (2.7 mg) and 1400W (1 mg) would be reasonable intravitreal doses to test for safety and efficacy in early clinical trials.

Epac1 Blocks NLRP3 Inflammasome to Reduce IL-1β in Retinal Endothelial Cells and Mouse Retinal Vasculature

Inflammation is an important component of diabetic retinal damage. We previously reported that a novel β-adrenergic receptor agonist, Compound 49b, reduced Toll-like receptor 4 (TLR4) signaling in retinal endothelial cells (REC) grown in high glucose. Others reported that TLR4 activates high-mobility group box 1 (HMGB1), which has been associated with the NOD-like receptor 3 (NLRP3) inflammasome. Thus, we hypothesized that Epac1, a downstream mediator of β-adrenergic receptors, would block TLR4/HMGB1-mediated stimulation of the NLRP3 inflammasome, leading to reduced cleavage of caspase-1 and interleukin-1 beta (IL-1β). We generated vascular specific conditional knockout mice for Epac1 and used REC grown in normal and high glucose treated with an Epac1 agonist and/or NLRP3 siRNA. Protein analyses were done for Epac1, TLR4, HMGB1, NLRP3, cleaved caspase-1, and IL-1β. Loss of Epac1 in the mouse retinal vasculature significantly increased all of the inflammatory proteins. Epac1 effectively reduced high glucose-induced increases in TLR4, HMGB1, cleaved caspase-1, and IL-1β in REC. Taken together, the data suggest that Epac1 reduces formation of the NLRP3 inflammasome to reduce inflammatory responses in the retinal vasculature.

Putative protective role of lutein and zeaxanthin in diabetic retinopathy

Diabetic retinopathy (DR) is one of the most important microvascular complications of diabetes and remains the leading cause of blindness in the working-age individuals. The exact aetiopathogenesis of DR remains elusive despite major advances in basic science and clinical research. Oxidative damage as one of the underlying causes for DR is increasingly being recognised. In humans, three hydroxycarotenoids, lutein (L), zeaxanthin (Z) and meso-zeaxanthin (MZ), accumulate at the central retina (to the exclusion of all other dietary carotenoids), where they are collectively known as macular pigment. These hydroxycarotenoids by nature of their biochemical structure and function help neutralise reactive oxygen species, and thereby, prevent oxidative damage to the retina (biological antioxidants). Apart from their key antioxidant function, evidence is emerging that these carotenoids may also exhibit neuroprotective and anti-inflammatory function in the retina. Since the preliminary identification of hydroxycarotenoid in the human macula by Wald in the 1940s, there has been astounding progress in our knowledge of the role of these carotenoids in promoting ocular health. While the Age-Related Eye Disease Study 2 has established a clinical benefit for L and Z supplements in patients with age-related macular degeneration, the role of these carotenoids in other retinal diseases potentially linked to oxidative damage remains unclear. In this article, we comprehensively review the literature germane to the putative protective role of two hydroxycarotenoids, L and Z, in the pathogenesis of DR.

Genetic components in diabetic retinopathy

Diabetic retinopathy (DR) is a serious complication of diabetes, which is fast reaching epidemic proportions worldwide. While tight glycemic control remains the standard of care for preventing the progression of DR, better insights into DR etiology require understanding its genetic basis, which in turn may assist in the design of novel treatments. During the last decade, genomic medicine is increasingly being applied to common multifactorial diseases such as diabetes and age-related macular degeneration. The contribution of genetics to the initiation and progression of DR has been recognized for some time, but the involvement of specific genes and genetic variants remains elusive. Several investigations are currently underway for identifying DR susceptibility loci through linkage studies, candidate gene approaches, and genome-wide association studies. Advent of next generation sequencing and high throughput genomic technologies, development of novel bioinformatics tools and collaborations among research teams should facilitate such investigations. Here, we review the current state of genetic studies in DR and discuss reported findings in the context of biochemical, cell biological and therapeutic advances. We propose the development of a consortium in India for genetic studies with large cohorts of patients and controls from limited geographical areas to stratify the impact of the environment. Uniform guidelines should be established for clinical phenotyping and data collection. These studies would permit identification of genetic loci for DR susceptibility in the Indian population and should be valuable for better diagnosis and prognosis, and for clinical management of this blinding disease.

Presence and Risk Factors for Glaucoma in Patients with Diabetes

Diabetes mellitus represents a growing international public health issue with a near quadrupling in its worldwide prevalence since 1980. Though it has many known microvascular complications, vision loss from diabetic retinopathy is one of the most devastating for affected individuals. In addition, there is increasing evidence to suggest that diabetic patients have a greater risk for glaucoma as well. Though the pathophysiology of glaucoma is not completely understood, both diabetes and glaucoma appear to share some common risk factors and pathophysiologic similarities with studies also reporting that the presence of diabetes and elevated fasting glucose levels are associated with elevated intraocular pressure-the primary risk factor for glaucomatous optic neuropathy. While no study has completely addressed the possibility of detection bias, most recent epidemiologic evidence suggests that diabetic populations are likely enriched with glaucoma patients. As the association between diabetes and glaucoma becomes better defined, routine evaluation for glaucoma in diabetic patients, particularly in the telemedicine setting, may become a reasonable consideration to reduce the risk of vision loss in these patients.

Genetic and epigenetic modifications in the pathogenesis of diabetic retinopathy: a molecular link to regulate gene expression

Intensification in the frequency of diabetes and the associated vascular complications has been a root cause of blindness and visual impairment worldwide. One such vascular complication which has been the prominent cause of blindness; retinal vasculature, neuronal and glial abnormalities is diabetic retinopathy (DR), a chronic complicated outcome of Type 1 and Type 2 diabetes. It has also become clear that "genetic" variations in population alone can't explain the development and progression of diabetes and its complications including DR. DR experiences engagement of foremost mediators of diabetes such as hyperglycemia, oxidant stress, and inflammatory factors that lead to the dysregulation of "epigenetic" mechanisms involving histone acetylation and histone and DNA methylation, chromatin remodeling and expression of a complex set of stress-regulated and disease-associated genes. In addition, both elevated glucose concentration and insulin resistance leave a robust effect on epigenetic reprogramming of the endothelial cells too, since endothelium associated with the eye aids in maintaining the vascular homeostasis. Furthermore, several studies conducted on the disease suggest that the modifications of the epigenome might be the fundamental mechanism(s) for the proposed metabolic memory' resulting into prolonged gene expression for inflammation and cellular dysfunction even after attaining the glycemic control in diabetics. Henceforth, the present review focuses on the aspects of genetic and epigenetic alterations in genes such as vascular endothelial growth factor and aldose reductase considered being associated with DR. In addition, we discuss briefly the role of the thioredoxin-interacting protein TXNIP, which is strongly induced by high glucose and diabetes, in cellular oxidative stress and mitochondrial dysfunction potentially leading to chromatin remodeling and ocular complications of diabetes. The identification of disease-associated genes and their epigenetic regulations will lead to potential new drugs and gene therapies as well as personalized medicine to prevent or slow down the progression of DR.

Vasoregression: A Shared Vascular Pathology Underlying Macrovascular And Microvascular Pathologies?

Vasoregression is a common phenomenon underlying physiological vessel development as well as pathological microvascular diseases leading to peripheral neuropathy, nephropathy, and vascular oculopathies. In this review, we describe the hallmarks and pathways of vasoregression. We argue here that there is a parallel between characteristic features of vasoregression in the ocular microvessels and atherosclerosis in the larger vessels. Shared molecular pathways and molecular effectors in the two conditions are outlined, thus highlighting the possible systemic causes of local vascular diseases. Our review gives us a system-wide insight into factors leading to multiple synchronous vascular diseases. Because shared molecular pathways might usefully address the diagnostic and therapeutic needs of multiple common complex diseases, the literature analysis presented here is of broad interest to readership in integrative biology, rational drug development and systems medicine.

Diabetic macular edema, retinopathy and age-related macular degeneration as inflammatory conditions

Diabetic macular edema (DME) and diabetic retinopathy (DR) are complications affecting about 25% of all patients with long-standing type 1 and type 2 diabetes mellitus and are a major cause of significant decrease in vision and quality of life. Age-related macular degeneration (AMD) is not uncommon, and diabetes mellitus affects the incidence and progression of AMD through altering hemodynamics, increasing oxidative stress, accumulating advanced glycation end products, etc. Recent studies suggest that DME, DR and AMD are inflammatory conditions characterized by a breakdown of the blood-retinal barrier, inflammatory processes and an increase in vascular permeability. Key factors that seem to have a dominant role in DME, DR and AMD are angiotensin II, prostaglandins and the vascular endothelial growth factor and a deficiency of anti-inflammatory bioactive lipids. The imbalance between pro- and anti-inflammatory eicosanoids and enhanced production of pro-angiogenic factors may initiate the onset and progression of DME, DR and AMD. This implies that bioactive lipids that possess anti-inflammatory actions and suppress the production of angiogenic factors could be employed in the prevention and management of DME, DR and AMD.

The Extract of Aster Koraiensis Prevents Retinal Pericyte Apoptosis in Diabetic Rats and Its Active Compound, Chlorogenic Acid Inhibits AGE Formation and AGE/RAGE Interaction

Retinal capillary cell loss is a hallmark of early diabetic retinal changes. Advanced glycation end products (AGEs) are believed to contribute to retinal microvascular cell loss in diabetic retinopathy. In this study, the protective effects of Aster koraiensis extract (AKE) against damage to retinal vascular cells were investigated in streptozotocin (STZ)-induced diabetic rats. To examine this issue further, AGE accumulation, nuclear factor-kappaB (NF-κB) and inducible nitric oxide synthase (iNOS) were investigated using retinal trypsin digests from streptozotocin-induced diabetic rats. In the diabetic rats, TUNEL (Terminal deoxynucleotidyl transferase mediated dUTP Nick End Labeling)-positive retinal microvascular cells were markedly increased. Immunohistochemical studies revealed that AGEs were accumulated within the retinal microvascular cells, and this accumulation paralleled the activation of NF-κB and the expression of iNOS in the diabetic rats. However, AKE prevented retinal microvascular cell apoptosis through the inhibition of AGE accumulation and NF-κB activation. Moreover, to determine the active compounds of AKE, two major compounds, chlorogenic acid and 3,5-di-O-caffeoylquinic acid, were tested in an in vitro assay. Among these compounds, chlorogenic acid significantly reduced AGE formation as well as AGE/RAGE (receptor for AGEs) binding activity. These results suggest that AKE, particularly chlorogenic acid, is useful in inhibiting AGE accumulation in retinal vessels and exerts a preventive effect against the injuries of diabetic retinal vascular cells.

Zerumbone, a Phytochemical of Subtropical Ginger, Protects against Hyperglycemia-Induced Retinal Damage in Experimental Diabetic Rats

Diabetic retinopathy (DR), the most ordinary and specific microvascular complication of diabetes, is a disease of the retina. Zerumbone (ZER) is a monocyclic sesquiterpene compound, and based on reports, it is the predominant bioactive compound from the rhizomes of Zingiber zerumbet. The aim of the current study is to evaluate the protective effect of zerumbone against DR in streptozotocin (STZ)-induced diabetic rats. STZ-diabetic rats were treated with ZER (40 mg/kg) once a day orally for 8 weeks. ZER administration significantly (p < 0.05) lowered the levels of plasma glucose (32.5% ± 5.7% lower) and glycosylated hemoglobin (29.2% ± 3.4% lower) in STZ-diabetic rats. Retinal histopathological observations indicated that disarrangement and reduction in thickness of retinal layers were reversed in ZER-treated diabetic rats. ZER downregulated both the elevated levels of advanced glycosylated end products (AGEs) and the higher levels of the receptors for AGEs (RAGE) in retinas of diabetic rats. What's more, ZER significantly (p < 0.05) ameliorated diabetes-induced upregulation of tumor necrosis factor-α, interleukin (IL)-1 and IL-6. ZER also attenuated overexpression of vascular endothelial growth factor and intercellular adhesion molecule-1, and suppressed activation of nuclear factor (NF)-κB and apoptosis in the retinas of STZ-diabetic rats. Our results suggest ZER possesses retinal protective effects, which might be associated with the blockade of the AGEs/RAGE/NF-κB pathway and its anti-inflammatory activity.

Reactive oxygen species: sources, consequences and targeted therapy in type 2 diabetes

Oxidative stress has been considered as a central mediator in the progression of diabetic complication. The intracellular reactive oxygen species (ROS) leads to oxidative stress and it is raised from the mitochondria as well as by activation of five major pathways: increased polyol pathway flux, activation of protein kinase C (PKC) pathway, increased formation of advanced glycation end products (AGEs), over activity of hexosamine pathway and increased production of angiotensin II. The increased ROS through these pathways leads to β-cell dysfunction and insulin resistance, responsible for cell damage and death. This review not only highlights the sources of ROS production and their involvement in the progression of diabetes, but also emphasizes on pharmacological interventions and targeting of ROS in type 2 diabetes. This review summarizes the ROS as potential therapeutic targets, based on a putative mechanism in the progression of the diabetes. It also summarizes current knowledge of ROS activation in type 2 diabetes as well as ROS as a possible target for its treatment. Eventually, it would be a promising target for various strategies and drugs to modulate ROS levels in diabetes.

Effect of periocular injection of celecoxib and propranolol on ocular level of vascular endothelial growth factor in a diabetic mouse model

AIM

To investigate the effects of periocular injection of propranolol and celecoxib on ocular levels of vascular endothelial growth factor (VEGF) in a diabetic mouse model.

METHODS

Forty 4-6wk BALB-C male mice weighing 20-25 g were used. The study groups included: non-diabetic control (group 1), diabetic control (group 2), diabetic propranolol (group 3), and diabetic celecoxib (group 4). After induction of type 1 diabetes by streptozotocin, propranolol (10 µg) and celecoxib (200 µg dissolved in carboxymethylcellulose 0.5%) were injected periocularly. The ocular level of VEGF was measured in all the study groups using enzyme-linked immuno sorbent assay (ELISA) method.

RESULTS

Ocular VEGF level was significantly increased (1.25 fold) in the diabetic control group when compared to the non-diabetic group one week after induction with streptozotocin (P=0.002). Both periocular propranolol and celecoxib significantly reduced ocular VEGF levels (P=0.047 and P<0.001, respectively). The effect was more pronounced with celecoxib.

CONCLUSION

The periocular administration of propranolol and celecoxib can significantly reduce ocular VEGF levels in a diabetic mouse model.

Epigenetic Modification of Mitochondrial DNA in the Development of Diabetic Retinopathy

PURPOSE

Retinal mitochondria are dysfunctional in diabetes, and mitochondrial DNA (mtDNA) is damaged and its transcription is compromised. Our aim was to investigate the role of mtDNA methylation in the development of diabetic retinopathy.

METHODS

Effect of high glucose (20 mM) on mtDNA methylation was analyzed in retinal endothelial cells by methylation-specific PCR and by quantifying 5-methylcytosine (5mC). Dnmt1 binding at the D-loop and Cytb regions of mtDNA was analyzed by chromatin immunoprecipitation. The role of mtDNA methylation in transcription and cell death was confirmed by quantifying transcripts of mtDNA-encoded genes (Cytb, ND6, and CoxII) and apoptosis, using cells transfected with Dnmt1-small interfering RNA (siRNA), or incubated with a Dnmt inhibitor. The key parameters were validated in the retinal microvasculature from human donors with diabetic retinopathy.

RESULTS

High glucose increased mtDNA methylation, and methylation was significantly higher at the D-loop than at the Cytb and CoxII regions. Mitochondrial accumulation of Dnmt1 and its binding at the D-loop were also significantly increased. Inhibition of Dnmt by its siRNA or pharmacologic inhibitor ameliorated glucose-induced increase in 5mC levels and cell apoptosis. Retinal microvasculature from human donors with diabetic retinopathy presented similar increase in D-loop methylation and decrease in mtDNA transcription.

CONCLUSIONS

Hypermethylation of mtDNA in diabetes impairs its transcription, resulting in dysfunctional mitochondria and accelerated capillary cell apoptosis. Regulation of mtDNA methylation has potential to restore mitochondrial homeostasis and inhibit/retard the development of diabetic retinopathy.

Retinylamine Benefits Early Diabetic Retinopathy in Mice

Recent evidence suggests an important role for outer retinal cells in the pathogenesis of diabetic retinopathy (DR). Here we investigated the effect of the visual cycle inhibitor retinylamine (Ret-NH2) on the development of early DR lesions. Wild-type (WT) C57BL/6J mice (male, 2 months old when diabetes was induced) were made diabetic with streptozotocin, and some were given Ret-NH2 once per week. Lecithin-retinol acyltransferase (LRAT)-deficient mice and P23H mutant mice were similarly studied. Mice were euthanized after 2 (WT and Lrat(-/-)) and 8 months (WT) of study to assess vascular histopathology, accumulation of albumin, visual function, and biochemical and physiological abnormalities in the retina. Non-retinal effects of Ret-NH2 were examined in leukocytes treated in vivo. Superoxide generation and expression of inflammatory proteins were significantly increased in retinas of mice diabetic for 2 or 8 months, and the number of degenerate retinal capillaries and accumulation of albumin in neural retina were significantly increased in mice diabetic for 8 months compared with nondiabetic controls. Administration of Ret-NH2 once per week inhibited capillary degeneration and accumulation of albumin in the neural retina, significantly reducing diabetes-induced retinal superoxide and expression of inflammatory proteins. Superoxide generation also was suppressed in Lrat(-/-) diabetic mice. Leukocytes isolated from diabetic mice treated with Ret-NH2 caused significantly less cytotoxicity to retinal endothelial cells ex vivo than did leukocytes from control diabetics. Administration of Ret-NH2 once per week significantly inhibited the pathogenesis of lesions characteristic of early DR in diabetic mice. The visual cycle constitutes a novel target for inhibition of DR.

Protective effect of a Chinese Medicine formula He-Ying-Qing-Re Formula on diabetic retinopathy

ETHNOPHARMACOLOGY RELEVANCE

He-Ying-Qing-Re Formula (HF) is a formula modified from "Si-Miao-Yong-An Decoction", a traditional Chinese medical classic emerged in the Qing dynasty and has been reported for treatment of vascular diseases. HF, containing 8 herbs, has been used in local hospital for decades as a complementary method for diabetic retinopathy (DR) with retinal vascular dysfunction. Clinical reports revealed HF could ameliorate vision defects, microaneurysms, hemorrhages and macular edema. The aim of this study is to investigate the anti-DR action of HF and its underlying mechanism experimentally.

METHODS

Chromatographic fingerprinting of HF and rodent model of DR were established; hypoglycemic effect of HF was measured by fasting, random blood glucose and glucose tolerance test; vascular degeneration was measured by retinal digestion; blood-retina-barrier (BRB) permeability was assessed with Evans Blue leakage assay. Advanced glycation end products (AGEs) were measured in vitro and in vivo level; Migration of retinal vascular endothelial cells were determined by wound healing and transwell chamber assays; permeability of endothelial monolayer was monitored with dextran transport. AGEs-related proteins and signaling were measured with immunoblotting and immunohistochemistry.

RESULTS

Chlorogenic acid, ferulic acid and arctin were identified as major components in HF; HF suppresses retinal vasculature degeneration and BRB permeability damage without significant inhibition on hyperglycemia; HF reduces in vitro and in vivo formation of AGEs and AGEs-induced migration as well as permeability of retinal vascular endothelial cells. Expression of tight junction proteins Zo-1 and Claudin-1 was increased while activation of AGEs receptor and downstream signaling Akt were suppressed upon HF treatment.

CONCLUSIONS

HF exhibits protective effect against diabetic retinopathy, which may be associated with inhibition on AGEs and recovery on endothelial dysfunction via modulation of tight junction and AGEs downstream signaling.

Antiglycation therapy: Discovery of promising antiglycation agents for the management of diabetic complications

CONTEXT

During diabetes mellitus, non-enzymatic reaction between amino groups of protein and carbonyl of reducing sugars (Millard reaction) is responsible for the major diabetic complications. Various efforts have been made to influence the process of protein glycation.

OBJECTIVES

This review article provides an extensive survey of various studies published in scientific literature to understand the process of protein glycation and its measurement. Moreover, evaluation and identification of potential inhibitors (antiglycation agents) of protein glycation from natural and synthetic sources and their mechanism of action in vitro and in vivo are also addressed.

METHOD

In this review article, the mechanism involved in the formation of advanced glycation end products (AGEs) is discussed, while in second and third parts, promising antiglycation agents of natural and synthetic sources have been reviewed, respectively. Finally, in vivo studies have been addressed. This review is mainly compiled from important databases such as Science, Direct, Chemical Abstracts, SciFinder, and PubMed.

RESULTS

During the last two decades, various attempts have been made to inhibit the process of protein glycation. New potent inhibitors of protein glycation belonging to different classes such as flavonoids, alkaloids, terpenes, benzenediol Schiff bases, substituted indol, and thio compounds have been identified.

CONCLUSION

Antiglycation therapy will be an effective strategy in future to prevent the formation of AGEs for the management of late diabetic complications Current review article highlighted various compounds of natural and synthetic origins identified previously to inhibit the protein glycation and formation of AGEs in vitro and in vivo.