Evaluation of vitreous levels of advanced glycation end products and angiogenic factors as biomarkers for severity of diabetic retinopathy

Advanced glycation end products and reactive oxygen species: uncovering the potential role of ferroptosis in diabetic complications

Advanced glycation end products (AGEs) are a diverse range of compounds that are formed when free amino groups of proteins, lipids, and nucleic acids are carbonylated by reactive carbonyl species or glycosylated by reducing sugars. Hyperglycemia in patients with diabetes can cause an overabundance of AGEs. Excess AGEs are generally acknowledged as major contributing factors to the development of diabetic complications because of their ability to break down the extracellular matrix directly and initiate intracellular signaling pathways by binding to the receptor for advanced glycation end products (RAGE). Inflammation and oxidative stress are the two most well-defined pathophysiological states induced by the AGE-RAGE interaction. In addition to oxidative stress, AGEs can also inhibit antioxidative systems and disturb iron homeostasis, all of which may induce ferroptosis. Ferroptosis is a newly identified contributor to diabetic complications. This review outlines the formation of AGEs in individuals with diabetes, explores the oxidative damage resulting from downstream reactions of the AGE-RAGE axis, and proposes a novel connection between AGEs and the ferroptosis pathway. This study introduces the concept of a vicious cycle involving AGEs, oxidative stress, and ferroptosis in the development of diabetic complications.

Changes in aqueous and vitreous inflammatory cytokine levels in nonproliferative diabetic retinopathy: systematic review and meta-analysis

OBJECTIVE

Diabetic retinopathy is a complication of diabetes mellitus with the potential for significant patient morbidity. Although changes to intraocular inflammatory cytokines are integral to disease pathogenesis, studies have been inconsistent about which exact cytokines are associated with diabetic retinopathy. We aimed to quantitatively summarize proangiogenic and proinflammatory cytokines in nonproliferative diabetic retinopathy (NPDR), given its frequency among those with diabetes mellitus.

METHODS

A systematic literature search without year limitation to February 21, 2022, identified 59 studies assessing vitreous or aqueous cytokine levels in NPDR, encompassing 1378 eyes with NPDR and 1288 eyes from nondiabetic controls. Effect sizes were generated as standardized mean differences (SMD) of cytokine concentrations between patients with NPDR and controls.

RESULTS

Concentrations (SMD, 95% confidence interval, and p value) of aqueous interleukin-6 (IL-6) (2.58, 1.17‒3.99; p = 0.0003), IL-8 (1.56, 0.39‒2.74; p = 0.009), IL-17 (13.55, 7.50‒19.59; p < 0.001), transforming growth factor beta (TGF-β) (2.44, 1.02‒3.85; p = 0.0007) and vascular endothelial growth factor (VEGF) (1.35, 0.76‒1.93; p < 0.00001), and vitreous VEGF (1.49, 0.60‒2.37; p = 0.001) were significantly higher in patients with NPDR when compared with those of healthy controls.

CONCLUSIONS

These cytokines may serve as disease markers of the biochemical alterations seen in NPDR and may guide interventions, as we move into an era of more targeted therapeutics.

Genetic context modulates aging and degeneration in the murine retina

Background

Age is the principal risk factor for neurodegeneration in both the retina and brain. The retina and brain share many biological properties; thus, insights into retinal aging and degeneration may shed light onto similar processes in the brain. Genetic makeup strongly influences susceptibility to age-related retinal disease. However, studies investigating retinal aging have not sufficiently accounted for genetic diversity. Therefore, examining molecular aging in the retina across different genetic backgrounds will enhance our understanding of human-relevant aging and degeneration in both the retina and brain-potentially improving therapeutic approaches to these debilitating conditions.

Methods

Transcriptomics and proteomics were employed to elucidate retinal aging signatures in nine genetically diverse mouse strains (C57BL/6J, 129S1/SvlmJ, NZO/HlLtJ, WSB/EiJ, CAST/EiJ, PWK/PhK, NOD/ShiLtJ, A/J, and BALB/cJ) across lifespan. These data predicted human disease-relevant changes in WSB and NZO strains. Accordingly, B6, WSB and NZO mice were subjected to human-relevant in vivo examinations at 4, 8, 12, and/or 18M, including: slit lamp, fundus imaging, optical coherence tomography, fluorescein angiography, and pattern/full-field electroretinography. Retinal morphology, vascular structure, and cell counts were assessed ex vivo.

Results

We identified common molecular aging signatures across the nine mouse strains, which included genes associated with photoreceptor function and immune activation. Genetic background strongly modulated these aging signatures. Analysis of cell type-specific marker genes predicted age-related loss of photoreceptors and retinal ganglion cells (RGCs) in WSB and NZO, respectively. Fundus exams revealed retinitis pigmentosa-relevant pigmentary abnormalities in WSB retinas and diabetic retinopathy (DR)-relevant cotton wool spots and exudates in NZO retinas. Profound photoreceptor dysfunction and loss were confirmed in WSB. Molecular analyses indicated changes in photoreceptor-specific proteins prior to loss, suggesting photoreceptor-intrinsic dysfunction in WSB. In addition, age-associated RGC dysfunction, loss, and concomitant microvascular dysfunction was observed in NZO mice. Proteomic analyses revealed an early reduction in protective antioxidant processes, which may underlie increased susceptibility to DR-relevant pathology in NZO.

Conclusions

Genetic context is a strong determinant of retinal aging, and our multi-omics resource can aid in understanding age-related diseases of the eye and brain. Our investigations identified and validated WSB and NZO mice as improved preclinical models relevant to common retinal neurodegenerative diseases.

The RAGE Axis: A Relevant Inflammatory Hub in Human Diseases

In 1992, a transcendental report suggested that the receptor of advanced glycation end-products (RAGE) functions as a cell surface receptor for a wide and diverse group of compounds, commonly referred to as advanced glycation end-products (AGEs), resulting from the non-enzymatic glycation of lipids and proteins in response to hyperglycemia. The interaction of these compounds with RAGE represents an essential element in triggering the cellular response to proteins or lipids that become glycated. Although initially demonstrated for diabetes complications, a growing body of evidence clearly supports RAGE's role in human diseases. Moreover, the recognizing capacities of this receptor have been extended to a plethora of structurally diverse ligands. As a result, it has been acknowledged as a pattern recognition receptor (PRR) and functionally categorized as the RAGE axis. The ligation to RAGE leads the initiation of a complex signaling cascade and thus triggering crucial cellular events in the pathophysiology of many human diseases. In the present review, we intend to summarize basic features of the RAGE axis biology as well as its contribution to some relevant human diseases such as metabolic diseases, neurodegenerative, cardiovascular, autoimmune, and chronic airways diseases, and cancer as a result of exposure to AGEs, as well as many other ligands.

Serum and Vitreous Levels of Placenta Growth Factor in Diabetic Retinopathy Patients: Correlation With Disease Severity and Optical Coherence Tomographic Parameters

Purpose The primary objective of this study was to compare placenta growth factor (PlGF) levels in the serum and vitreous of diabetic retinopathy (DR) patients to non-diabetic controls. Additionally, the study aimed to establish associations between serum and vitreous PlGF concentrations and to examine the correlation between vitreous PlGF in DR patients and morphological parameters. Methods This study included serum and vitreous samples from 38 patients, including 21 patients with DR and 17 non-diabetic controls. The control group included non-diabetic patients with rhegmatogenous retinal detachment with retinal tears secondary to posterior vitreous detachment or trauma. PlGF levels were quantified in vitreous and serum samples using an enzyme-linked immunosorbent assay (ELISA). Optical coherence tomography (OCT) scans from DR patients were evaluated to measure the central retinal thickness (CRT) and macular volume (MV). Results DR patients had significantly higher mean vitreous PlGF levels compared to non-DR patients (70.0±39.2 vs. 46.47±9.7 pg/mL, p-value=0.004). However, no significant increase in mean serum PlGF levels was observed in DR patients (p-value=0.232). Within the DR group, proliferative DR (PDR) patients presented significantly higher vitreous PlGF levels than non-PDR (NPDR) patients (76.5±41.0 vs. 42.5±5.0 pg/mL, p-value=0.009). There was no association between serum and vitreous PlGF levels. The correlation between vitreous PlGF levels and morphological parameters was rsp=0.175, p-value=0.488 for CRT, and rsp=0.288, p-value=0.262 for MV. Conclusion This study emphasizes the important role of PlGF in neovascularization, specifically highlighting its overexpression exclusively in vitreous from PDR patients. The observed increase in PlGF levels may be indicative of disease severity. The lack of correlation between vitreous and serum PlGF levels suggests a potential dissociation between intravitreal and systemic PlGF synthesis. Consequently, targeting PlGF in therapeutic approaches may offer an additional strategy for ocular pathologies with a neovascular component.

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.

Association between adipocytokines and diabetic retinopathy: a systematic review and meta-analysis

Background

Diabetic retinopathy (DR) is a common complication of diabetes. The adipocytokines are closely associated with the occurrence and development of diabetes and its related complications. Literature confirms that the level of adiponectin in patients with DR is significantly higher; however, the relationship between other adipocytokines (leptin, chemerin, apelin, and omentin-1) and DR remains unclear.

Aim

This study aimed to systematically evaluate the association between adipocytokines (leptin, chemerin, apelin, and omentin-1) and DR.

Methods

The PubMed, Web of Science, Embase, EBSCO and Willy databases were used to search for potential studies with keywords such as "diabetic retinopathy" or "DR" in combination with the terms "leptin," "chemerin", "apelin" or "omentin-1" in the search titles or abstracts. Standardized mean differences (SMD) with corresponding 95% confidence intervals (CIs) were determined as the results of the meta-analysis.

Results

After screening, 18 articles were included in the meta-analysis including 750 DR cases and 993 controls. Leptin and chemerin levels in patients with DR were significantly higher than those in the control group (SMD: 0.68, 95% CI [0.1, 1.26]; SMD: 0.79, 95% CI [0.35, 1.23]). The omentin-1 levels in patients with DR were significantly lower than those in the controls (SMD: -0.85, 95% CI [-1.08, -0.62]).

Conclusions

To the best of our knowledge, this is the first meta-analysis to evaluate the leptin, chemerin, apelin, and omentin-1 levels in patients with DR. Further high-quality studies are warranted to support the association between these adipocytokines and DR.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=443770, identifier CRD42023443770.

Pharmacological mechanism and clinical study of Qiming granules in treating diabetic retinopathy based on network pharmacology and literature review

ETHNOPHARMACOLOGY RELEVANCE

Diabetic retinopathy (DR) is a general complication of diabetes, which has become a serious threat to human health worldwide. However, the best treatment is still under development. Qiming (QM) granules are mainly composed of Astragalus membranaceus, Pueraria lobata, Rehmannia Glutinosa, Lycium barbarum, Cassiae Semen, Fructus Leonuri, Pollen Typhae, and Leech, which are beneficial to qi, nourish liver and kidney, and clear collaterals and eyes. The treatment of DR is a comprehensive application based on the above traditional Chinese medicine. In recent years, satisfactory results have been achieved for DR.

AIM OF THE STUDY

Through the traditional application analysis, network pharmacology analysis and clinical research summary of QM granules, to review the effectiveness and advantages of QM granules in the treatment of DR comprehensively.

MATERIALS AND METHODS

Analysis of main active components of QM granules by network pharmacology and prediction of mechanism of action of QM granules on DR. Further, PubMed, Web of Science, and China National Knowledge Infrastructure were used to search literature, using the keywords of "Qiming granules", "diabetic retinopathy", "clinical research" and their combinations, mainly from 1999 to 2022.

RESULTS

Traditional pharmacological analysis, Network pharmacological analysis, animal experiments, and clinical studies have confirmed that QM granules plays a role in the treatment of DR through multiple components, multiple targets, and multiple channels.

CONCLUSIONS

This systematic review for the first time provides meaningful information for the further study of the pharmacodynamic material basis and pharmacological mechanism of QM granules, and also provides a basis for further study of quality markers and quality control of QM granules.

Epigenetics in Obesity and Diabetes Mellitus: New Insights

A long-term complication of obesity is the development of type 2 diabetes (T2D). Patients with T2D have been described as having epigenetic modifications. Epigenetics is the post-transcriptional modification of DNA or associated factors containing genetic information. These environmentally-influenced modifications, maintained during cell division, cause stable changes in gene expression. Epigenetic modifications of T2D are DNA methylation, acetylation, ubiquitylation, SUMOylation, and phosphorylation at the lysine residue at the amino terminus of histones, affecting DNA, histones, and non-coding RNA. DNA methylation has been shown in pancreatic islets, adipose tissue, skeletal muscle, and the liver. Furthermore, epigenetic changes have been observed in chronic complications of T2D, such as diabetic nephropathy, diabetic retinopathy, and diabetic neuropathy. Recently, a new drug has been developed which acts on bromodomains and extraterminal (BET) domain proteins, which operate like epigenetic readers and communicate with chromatin to make DNA accessible for transcription by inhibiting them. This drug (apabetalone) is being studied to prevent major adverse cardiovascular events in people with T2D, low HDL cholesterol, chronic kidney failure, and recent coronary events. This review aims to describe the relationship between obesity, long-term complications such as T2D, and epigenetic modifications and their possible treatments.

Changes in aqueous and vitreous inflammatory cytokine levels in proliferative diabetic retinopathy: a systematic review and meta-analysis

BACKGROUND

Diabetic retinopathy is a major complication of diabetes mellitus, where in its most advanced form ischemic changes lead to the development of retinal neovascularization, termed proliferative diabetic retinopathy (PDR). While the development of PDR is often associated with angiogenic and inflammatory cytokines, studies differ on which cytokines are implicated in disease pathogenesis and on the strength of these associations. We therefore conducted a systematic review and meta-analysis to quantitatively assess the existing body of data on intraocular cytokines as biomarkers in PDR.

METHODS

A comprehensive search of the literature without year limitation was conducted to January 18, 2021, which identified 341 studies assessing vitreous or aqueous cytokine levels in PDR, accounting for 10379 eyes with PDR and 6269 eyes from healthy controls. Effect sizes were calculated as standardized mean differences (SMD) of cytokine concentrations between PDR and control patients.

RESULTS

Concentrations (SMD, 95% confidence interval, and p-value) of aqueous IL-1β, IL-6, IL-8, MCP-1, TNF-α, and VEGF, and vitreous IL-2, IL-4, IL-6, IL-8, angiopoietin-2, eotaxin, erythropoietin, GM-CSF, GRO, HMGB-1, IFN-γ, IGF, IP-10, MCP-1, MIP-1, MMP-9, PDGF-AA, PlGF, sCD40L, SDF-1, sICAM-1, sVEGFR, TIMP, TNF-α, and VEGF were significantly higher in patients with PDR when compared to healthy nondiabetic controls. For all other cytokines no differences, failed sensitivity analyses or insufficient data were found.

CONCLUSIONS

This extensive list of cytokines speaks to the complexity of PDR pathogenesis, and informs future investigations into disease pathogenesis, prognosis, and management.

Circ_0001897 regulates high glucose-induced angiogenesis and inflammation in retinal microvascular endothelial cells through miR-29c-3p/transforming growth factor beta 2 axis

Diabetic retinopathy (DR) has become the leading cause of blindness among adults at working age. Previous studies have implicated circ_0001897 in the development of DR. In this study, we investigated the functional roles and mechanisms of circ_0001897 in high glucose-induced angiogenesis and inflammation. Peripheral blood samples from DR patients and healthy controls were collected to examine circ_0001897 expression, which demonstrated a significant upregulation of circ_0001897 in DR patients. To investigate the functional role and mechanisms of circ_0001897, human retinal microvascular endothelial cells (HRECs) were treated with high glucose (HG) to establish an in vitro DR model of endothelial cells. HG treatment induced the upregulation of circ_0001897 in HRECs, and enhanced cell proliferation, inflammatory responses, as well as in vitro angiogenesis. Circ_0001897 knockdown significantly attenuated the cell proliferation, inflammatory responses, and angiogenesis induced by HG treatment. Mechanistically, circ_0001897 sponged and inhibited the activity of mir-29c-3p, which in turn regulates the downstream target transforming growth factor beta 2 (TGFB2). The effects of circ_0001897 knockdown could be rescued by mir-29c-3p inhibitor or TGFB2 overexpression. Collectively, our data demonstrated the novel role of circ_0001897/mir-29c-3p/TGFB2 axis in regulating HG-induced inflammation and angiogenesis of HRECs. These findings suggest that targeting circ_0001897 could serve as an intervention strategy to ameliorate DR.

Vitreous Humor Proteome: Targeting Oxidative Stress, Inflammation, and Neurodegeneration in Vitreoretinal Diseases

Oxidative stress is defined as an unbalance between pro-oxidants and antioxidants, as evidenced by an increase in reactive oxygen and reactive nitrogen species production over time. It is important in the pathophysiology of retinal disorders such as diabetic retinopathy, age-related macular degeneration, retinal detachment, and proliferative vitreoretinopathy, which are the focus of this article. Although the human organism's defense mechanisms correct autoxidation caused by endogenous or exogenous factors, this may be insufficient, causing an imbalance in favor of excessive ROS production or a weakening of the endogenous antioxidant system, resulting in molecular and cellular damage. Furthermore, modern lifestyles and environmental factors contribute to increased chemical exposure and stress induction, resulting in oxidative stress. In this review, we discuss the current information about oxidative stress and the vitreous proteome with a special focus on vitreoretinal diseases. Additionally, we explore therapies using antioxidants in an attempt to rescue the body from oxidation, restore balance, and maximize healthy body function, as well as new investigational therapies that have shown significant therapeutic potential in preclinical studies and clinical trial outcomes, along with their goals and strategic approaches to combat oxidative stress.

Protective role of vitamin D against oxidative stress in diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular complication of diabetes mellitus. There is much evidence showing that a high level of mitochondrial overproduction of reactive oxygen species in the diabetic retina contributes in modifying cellular signalling and leads to retinal cell damage and finally to the development of DR pathogenesis. In the last few decades, it has been reported that vitamin D is involved in DR pathogenesis. Vitamin D, traditionally known as an essential nutrient crucial in bone metabolism, has also been proven to be a very effective antioxidant. It has been demonstrated that it modulates the production of advanced glycosylated end products, as well as several pathways including protein kinase C, the polyol pathway leading to the reduction of free radical formation. It prevents the translocation of nuclear factor kappa B, preventing the inflammatory response, acting as an immunomodulator, and modulates autophagy and apoptosis. In this review, we explore the molecular mechanisms by which vitamin D protects the eye from oxidative stress, in order to evaluate whether vitamin D supplementation may be useful to mitigate the deleterious effects of free radicals in DR.

Correlations Between Different Angiogenic and Inflammatory Factors in Vitreous Fluid of Eyes With Proliferative Diabetic Retinopathy

Purpose: To investigate the expression of various angiogenesis and inflammation mediators in the vitreous fluid of eyes with proliferative diabetic retinopathy (PDR).

Methods: A total of 38 eyes with PDR and 37 control eyes were included. Vitreous fluid was collected during vitrectomy. Vitreous levels of colony stimulating factor-1 receptor (CSF-1R), syndecan-1, placental growth factor (PIGF), and angiopoietin-like protein 4 (ANGPTL-4) were measured by multiplex immunoassay. Vitreous levels of vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), interleukin-8 (IL-8), monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), and intercellular adhesion molecule-1 (ICAM-1) were measured by cytometric beads array. Levels of these mediators were compared between the PDR and control eyes. Correlations between levels of different mediators and between these mediators and kidney function metrics in the PDR group were also analyzed.

Results: Vitreous levels of syndecan-1, PIGF, ANGPTL-4, VEGF, and IL-8 were significantly higher in the PDR group compared to the control group (all p < 0.05). Levels of VEGF were significantly correlated with levels of syndecan-1, PIGF, and ANGPTL-4 (r = 0.370 to 0.497, all p < 0.05). Significant positive correlations were detected between levels of any two of the following mediators including syndecan-1, PIGF, ANGPTL-4, and IL-8 (r = 0.370 to 0.906, all p < 0.05). Apart from VEGF, levels of these mediators were positively correlated with serum creatinine and blood urea nitrogen (r = 0.328 to 0.638, all p < 0.05), and negatively correlated with fasting blood glucose and estimated glomerular filtration rate (r = −0.325 to −0.603, all p < 0.05).

Conclusions: Correlations between different angiogenesis and inflammation mediators were observed in eyes with PDR, suggesting cross-talks of different angiogenesis and inflammation pathways in the pathogenesis of PDR. The levels of angiogenesis and inflammation in PDR are correlated with kidney damage, indicating possible common pathways in diabetic retinopathy and nephropathy.

Intraocular fluid biomarkers (liquid biopsy) in human diabetic retinopathy

Purpose

This article aims to review the impact of detecting and quantifying intraocular biomarkers (liquid biopsy) in both aqueous and vitreous humor in eyes of people affected by diabetes mellitus.

Methods

This is a detailed review about aqueous and/or vitreous humor sampling in human diabetic eyes for proteomic and/or metabolomic analysis contributing to the understanding of the pathophysiology and treatment effects of diabetic retinopathy.

Results

Aqueous and vitreous humor molecular biomarkers proved to be directly correlated to each other and valuable to study retinal conditions. Moreover, proteomic and metabolomic analysis showed that the biomarkers of neuroinflammation, neurodegeneration, and vasculopathy are detectable in intraocular fluids and that their concentration changes in different stages of disease, and in response to treatment of all diabetic retinopathy aspects, mainly diabetic macular edema and proliferative retinopathy.

Conclusions

Liquid biopsy offers the possibility to improve our knowledge of intraocular eye disease induced by diabetes mellitus. The exact quantification of intraocular biomarkers contributes to the precision medicine approach even in the diabetic retinopathy scenario. The diffusion of this approach should be encouraged to have quantifiable information directly from the human model, which may be coupled with imaging data.

The Vitreous Ecosystem in Diabetic Retinopathy: Insight into the Patho-Mechanisms of Disease

Diabetic retinopathy is one of the leading causes of blindness in the world with the incidence of disease ever-increasing worldwide. The vitreous humor represents an extensive and complex interactive arena for cytokines in the diabetic eye. In recent decades, there has been significant progress in understanding this environment and its implications in disease pathophysiology. In this review, we investigate the vitreous ecosystem in diabetic retinopathy at the molecular level. Areas of concentration include: the current level of knowledge of growth factors, cytokine and chemokine mediators, and lipid-derived metabolites in the vitreous. We discuss the molecular patho-mechanisms of diabetic retinopathy based upon current vitreous research.

Association of dietary intake, medication and anthropometric indices with serum levels of advanced glycation end products, caspase-3, and matrix metalloproteinase-9 in diabetic patients

Background and objective

Increased serum levels of advanced glycation end products (AGEs), caspase-3 (Cas-3) and matrix metalloproteinase-9 (MMP-9) have been reported in diabetic patients. This study aimed to evaluate association of anthropometric, dietary, and therapeutic factors with serum levels of methylglyoxal (MGO), carboxymethyl lysine (CML), pentosidine (Pen), Cas-3, and MMP-9 in diabetic patients.

Methods

The current study included 36 diabetic subjects. Dietary intake of the participants was assessed using three-day 24-h recall survey and anthropometric indices were measured. Demographic factors and medication intake of every subject were obtained. Serum levels of CML, MGO, Pen, MMP-9, and Cas-3 were measured using ELISA method.

Results

Gliclazide consumption was positively correlated with MMP-9 and Cas-3, but not AGEs levels. Females had higher MGO level compared with males. Further, CML levels were negatively correlated with BMI and WHR. Dietary protein intake was positively correlated with MMP-9, Cas-3, and MGO levels. As well as dietary energy and fat intake had significant positive relationship with serum Cas-3 concentration.

Conclusion

It is concluded that anthropometric characteristics, dietary intake, and therapeutic medications are possible factors that may determine the circulating levels of AGEs, MMP-9, and Cas-3 in patients with diabetes.

A novel organic cation transporter involved in paeonol transport across the inner blood-retinal barrier and changes in uptake in high glucose conditions

Paeonol exerts various pharmacological effects owing to its antiangiogenic, antioxidant, and antidiabetic activities. We aimed to investigate the transport mechanism of paeonol across the inner blood-retinal barrier both in vitro and in vivo. The carotid artery single injection method was used to investigate the retina uptake index of paeonol. The retina uptake index (RUI) value of [³H]paeonol was dependent on both concentration and pH. This value decreased significantly in the presence of imperatorin, tramadol, and pyrilamine when compared to the control. However, para-aminohippuric acid, choline, and taurine had no effect on the RUI value. Conditionally immortalized rat retina capillary endothelial cells (TR-iBRB cell lines) were used as an in vitro model of the inner blood-retinal barrier (iBRB). The uptake of [³H]paeonol by the TR-iBRB cell lines was found to be time-, concentration-, and pH-dependent. However, the uptake was unaffected by the absence of sodium or by membrane potential disruption. Moreover, in vitro structural analog studies revealed that [³H]paeonol uptake was inhibited in the presence of organic cationic compounds including imperatorin, clonidine and tramadol. This is consistent with the results obtained in vivo. In addition, transfections with OCTN1, 2 or plasma membrane monoamine transporter (PMAT) small interfering RNA did not affect paeonol uptake in TR-iBRB cell lines. Upon pre-incubation of these cell lines with high glucose (HG) media, [³H]paeonol uptake decreased and mRNA expression levels of angiogenetic factors, such as hypoxia inducible factor-1 (HIF-1) and vascular endothelial growth factor (VEGF) increased. However, after the pretreatment of unlabeled paeonol in HG conditions, the mRNA levels of VEGF and HIF-1 were comparatively reduced, and the [³H]paeonol uptake rate was restored. After being exposed to inflammatory conditions induced by glutamate, TNF-α, and LPS, paeonol and propranolol pretreatment significantly increased the uptake of both [³H]paeonol and [³H]propranolol in TR-iBRB cell lines compared to their respective controls. Our results demonstrate that the transport of paeonol to the retina across the iBRB may involve the proton-coupled organic cation antiporter system, and the uptake of paeonol is changed by HG conditions.

MicroRNA-148a-3p alleviates high glucose-induced diabetic retinopathy by targeting TGFB2 and FGF2

AIMS

Diabetic retinopathy (DR), a common complication of type 1 or type 2 diabetes mellitus, has become the leading cause of blindness among adults in working age. The dysregulation of microRNA has been reported to be strongly related to the initiation or progression of DR. However, neither the biological role nor the molecular mechanism of miR-148a-3p has been researched in DR. This study is designed to investigate the function and mechanism of miR-148a-3p in DR.

METHODS

The bioinformatics analysis (Targetscan: https://www.targetscan.org/vert_72/ ) and numerous experiments including real-time quantitative polymerase chain reaction, terminal deoxynucleotidyltransferase dUTP nick end labeling, CCK-8, western blot, vasculogenesis and luciferase reporter assays were used to research the function and mechanism of miR-148a-3p in DR.

RESULTS

We constructed DR cell model by treating human retinal microvascular endothelial cells (HRECs) with different concentration gradients of high glucose (HG). Additionally, HG treatment reduced miR-148a-3p level in HRECs. In function, overexpression of miR-148a-3p caused an increase in cell viability and a decrease in cell apoptosis. Besides, miR-148a-3p overexpression led to a damage on blood-retinal barrier (BRB) and suppressed angiogenesis. In mechanism, miR-148a-3p specifically bound to 3' untranslated region of TGFB2 and FGF2. At least, rescue assays demonstrated that the inhibitive influence of miR-148a-3p mimics on BRB injury was offset by overexpression of TGFB2 and the attenuation of angiogenesis resulting from miR-148a-3p mimics was abrogated by overexpression of FGF2 CONCLUSIONS: In a word, we discovered that miR-148a-3p alleviated HG-induced DR by targeting TGFB2 and FGF2. This novel discovery indicated miR-148a-3p as a potential target for DR diagnosis or treatment.

Hypoxia-inducible factor-1α: A promising therapeutic target for vasculopathy in diabetic retinopathy

Diabetic retinopathy (DR) is a serious condition that can cause blindness in diabetic patients. It is a neurovascular disease, but the pathogenesis leading to the onset of this disease is still not completely understood. However, hypoxia with subsequent neovascularization is a characteristic phenomenon observed with DR. Cellular response to hypoxia is mediated by the transcriptional regulator hypoxia-inducible factor (HIF). Long-term research has shown that one isotype of HIF, HIF-1α, may play a pivotal role under hypoxic conditions, and an increasing number of studies have shown that HIF-1α and its target genes contribute to retinal neovascularization. Therefore, targeting HIF-1α may lead to more effective DR treatments. This review describes the possible mechanisms of HIF-1α in neovascularization of DR. Furthermore, various inhibitors of HIF-1α that may have viable potential in the treatment of DR are also discussed.

Comparison of aqueous humor levels of PlGF and VEGF in proliferative diabetic retinopathy before and after intravitreal conbercept injection

AIMS

The aim of this paper is to observe the change of aqueous humor levels of placenta growth factor (PlGF) and vascular endothelial growth factor (VEGF) in proliferative diabetic retinopathy (PDR) patients before and one week after intravitreal conbercept injection.

METHODS

A prospective case series study was conducted in 24 active PDR patients (24 eyes). All the patients had received 0.5 mg of intravitreal conbercept followed by vitrectomy one week later. The aqueous humor was collected before conbercept injection and at the beginning of vitrectomy.

RESULTS

Before conbercept injection, the aqueous humor median levels of VEGF-A, VEGF-B and PlGF were457.0pg/mL(IQRfrom392.9to860.6pg/mL), 43.6pg/mL(IQRfrom33.6to81.6pg/mL), 37.5pg/mL(IQRfrom25.0to53.6pg/mL), respectively. One week after conbercept injection, the aqueous humor levels of VEGF-A, VEGF-B and PiGF decreased significantly. The aqueous humor VEGF-A levels in PDR patients with fibrovascular membranes were lower than those without them. There was positive correlation between aqueous humor VEGF-B and PiGF levels (P = 0.007). No significant correlation was found between VEGF-A and PiGF levels. No ocular and systemic adverse events were observed.

CONCLUSIONS

The aqueous humor levels of PlGF was correlated with VEGF-B, and levels of VEGF-A, VEGF-B, and PlGF decreased after intravitreal conbercept injection in active PDR patients.

Vitreous and Vision Degrading Myodesopsia

Macromolecules comprise only 2% of vitreous, yet are responsible for its gel state, transparency, and physiologic function(s) within the eye. Myopia and aging alter collagen and hyaluronan association causing concurrent gel liquefaction and fibrous degeneration. The resulting vitreous opacities and collapse of the vitreous body during posterior vitreous detachment are the most common causes for the visual phenomenon of vitreous floaters. Previously considered innocuous, the vitreous opacities that cause floaters sometimes impact vision by profoundly degrading contrast sensitivity function and impairing quality-of-life. While many people adapt to vitreous floaters, clinically significant cases can be diagnosed with Vision Degrading Myodesopsia based upon echographic assessment of vitreous structure and by measuring contrast sensitivity function. Perhaps due to the ubiquity of floaters, the medical profession has to date largely ignored the plight of those with Vision Degrading Myodesopsia. Improved diagnostics will enable better disease staging and more accurate identification of severe cases that merit therapy. YAG laser treatments may occasionally be slightly effective, but vitrectomy is currently the definitive cure. Future developments will usher in more informative diagnostic approaches as well as safer and more effective therapeutic strategies. Improved laser treatments, new pharmacotherapies, and possibly non-invasive optical corrections are exciting new approaches to pursue. Ultimately, enhanced understanding of the underlying pathogenesis of Vision Degrading Myodesopsia should result in prevention, the ultimate goal of modern Medicine.

Advanced glycation end products induce immature angiogenesis in in vivo and ex vivo mouse models

Proliferative diabetic retinopathy (PDR) is a progressive disease predominantly involving pathological angiogenesis and is characterized by the development of immature, fragile, and easily hemorrhagic new vessels. Advanced glycation end products (AGEs) and the receptor for AGEs (RAGE) play important roles in the progression of diabetic retinopathy. Our previous studies demonstrated that AGEs promoted HUVEC angiogenesis by inducing moesin phosphorylation via RhoA/Rho-associated protein kinase (ROCK) pathway. The aim of this study was to further confirm AGE-induced angiogenesis in vivo and the involvement of RAGE, ROCK, and moesin phosphorylation in this process. We performed the study in an AGE-treated mouse model with various angiogenesis assays in multiple in vivo and ex vivo models. The results demonstrated that AGEs promoted significant neovascularization in whole mount retina and mouse aortic ring of adult and postnatal mice and in Matrigel plug as well, which were consistently accompanied by increased moesin phosphorylation. The increase of AGE-evoked neovascularization and moesin phosphorylation were both attenuated by RAGE knockout or ROCK inhibitor Y27632 administration in mice. We also revealed the pathological characteristics of AGE-promoted angiogenesis by demonstrating the decrease of pericyte coverage and the disarranged endothelial alignment in microvessels. In conclusion, this study provides in vivo evidences that AGEs induce immature angiogenesis by binding to RAGE, activating the RhoA/ROCK signal pathway and inducing moesin phosphorylation.NEW & NOTEWORTHY Advanced glycation end product (AGE)-induced formation of neovessels and phosphorylation of moesin in retina and aortic ring required AGE receptors. AGEs increased neovessels and the phosphorylation of moesin in retina and aortic ring via RhoA/ROCK pathway. AGE-induced immature angiogenesis in AGE-treated mouse retina and aortic ring. The AGE-RAGE axis and moesin could be candidate targets for overcoming relative diseases.

Role of Moesin Phosphorylation in Retinal Pericyte Migration and Detachment Induced by Advanced Glycation Endproducts

Proliferative diabetic retinopathy (PDR) involves persistent, uncontrolled formation of premature blood vessels with reduced number of pericytes. Our previous work showed that advanced glycation endproducts (AGEs) induced angiogenesis in human umbilical vein endothelial cells, mouse retina, and aortic ring, which was associated with moesin phosphorylation. Here we investigated whether moesin phosphorylation may contribute to pericyte detachment and the development of PDR. Primary retinal microvascular pericytes (RMPs) were isolated, purified from weanling rats, and identified by cellular markers α-SMA, PDGFR-β, NG2, and desmin using immunofluorescence microscopy. Effects of AGE-BSA on proliferation and migration of RMPs were examined using CCK-8, wound healing, and transwell assays. Effects on moesin phosphorylation were examined using western blotting. The RMP response to AGE-BSA was also examined when cells expressed the non-phosphorylatable Thr558Ala mutant or phospho-mimicking Thr558Asp mutant of moesin or were treated with ROCK inhibitor Y27632. Colocalization and interaction between CD44, phospho-moesin, and F-actin were observed. Experiments with cultured primary RMPs showed that AGE-BSA inhibited the proliferation, enhanced the migration, and increased moesin phosphorylation in a dose- and time-dependent manner. AGE-BSA also triggered the rearrangement of F-actin and promoted the interaction of CD44 with phospho-moesin in RMPs. These effects were abrogated in cells expressing the non-phosphorylatable moesin mutant and the application of ROCK inhibitor Y27632 attenuated AGE-induced alteration in cultured RMPs by abolishing the phosphorylation of moesin. However, those AGE-induced pathological process occurred in RMPs expressed the phospho-mimicking moesin without AGE-BSA treatment. It is concluded that AGEs could activate ROCK to mediate moesin phosphorylation at Thr558, and resulting phospho-moesin interacts with CD44 to form CD44 cluster, which might stimulate the migration of RMPs and subsequent RMP detachment in microvessel. This pathway may provide new drug targets against immature neovessel formation in PDR.

Alteration of choroidal vascular structure in diabetic retinopathy

PURPOSE

The aim of this study was to analyse choroidal structures in normal patients and patients with diabetes with various severities of diabetic retinopathy (DR).

METHODS

This is a retrospective observation case control study. Three hundred and forty-two diabetic eyes, and age-matched 112 eyes without diabetes mellitus (DM) were enrolled in this study. Patients with DM were classified into no DR, mild/moderate non-proliferative DR (mNPDR), severe NPDR and proliferative DR (PDR). Patients with DM were further divided into two groups based on information regarding systemic DM treatment situation: DM-treated and untreated groups. Central choroidal thickness (CCT), and total choroidal area (TCA), luminal area (LA) and stromal area (SA) were determined using enhanced depth imaging optical coherence tomography and a binarisation method, respectively. The ratio of LA in the TCA was defined as L/C ratio.

RESULTS

The haemoglobin A1c (HbA1c) value was significantly higher in the DM-untreated than in the DM-treated subjects. L/C ratio was significantly lower in all the diabetic eyes than control eyes (p<0.05). TCA, LA, L/C ratio and CCT were significantly greater in the DM-untreated than treated group (each p<0.05). In the DM-untreated group, TCA and LAs (p<0.05) and L/C ratio (p<0.01) were significantly lower in mNPDR subjects than normal controls (p<0.05). PDR in the DM-untreated group showed significantly larger SA and LA, and greater CCT than normal controls (each p<0.05).

CONCLUSIONS

These results suggest that choroidal vasculature was initially involved at an early DR, whereas thickened LA and SA were noted in advanced DR.

Probucol promotes high glucose-induced proliferation and inhibits apoptosis by reducing reactive oxygen species generation in Müller cells

PURPOSE

To explore the protective effect of probucol on human retinal Müller cells cultured in high glucose.

METHODS

Primary Müller cells from human retinas were cultured in complete DMEM. Third-generation Müller cells were identified using glutamine synthetase (GS) antibody and randomly divided into three groups: normoglycemia (NG, 5.5 mmol/L); hyperglycemia (HG, 30 mmol/L); and hyperglycemia (30 mmol/L) with probucol (10 μmol/L; HGPB). After a 24-h intervention, cell proliferation, apoptosis, and cellular reactive oxygen species (ROS) were measured with a CCK-8 kit, flow cytometry, and DCFH-DA probe, respectively. Kelch-like ECH-associated protein 1 (Keap1), NF-E2-related factor 2 (Nrf2), and glutamate cysteine ligase catalytic subunit (GCLC) protein expression were detected by immunofluorescence staining.

RESULTS

For NG, HG, and HGPB, optical density (OD) values for cell proliferation were 0.98 ± 0.23, 0.58 ± 0.11, and 0.73 ± 0.11; apoptotic rates were 2.79 ± 0.52%, 7.70 ± 0.44%, and 4.00 ± 0.95%; and intracellular ROS were 20.89 ± 5.14, 55.17 ± 14.07, and 26.28 ± 4.73, respectively. Compared to NG, OD was markedly decreased (P < 0.01), apoptosis was increased (P < 0.001), and intracellular ROS level was significantly higher than in HG (P < 0.01). Compared to HG, OD was markedly increased (P < 0.01), apoptosis was meaningfully decreased (P < 0.01), and intracellular ROS level was significantly lower than in HGPB (P < 0.01). GS, Keap1, Nrf2, and GCLC had positive expression.

CONCLUSIONS

Probucol could inhibit intracellular ROS generation, promote proliferation, and decrease apoptosis of human retinal Müller cells cultured in high glucose. This might also be associated with Keap1/Nrf2/ARE oxidative stress signaling pathway activation.

Inhibition of Diabetes-Induced Lysyl Oxidase Overexpression Prevents Retinal Vascular Lesions Associated With Diabetic Retinopathy

Purpose

The purpose of this study was to investigate the effect of reducing diabetes-induced lysyl oxidase (LOX) overexpression on vascular cell apoptosis and blood-retinal barrier (BRB) characteristics in diabetic rats.

Methods

Nondiabetic rats, diabetic rats, and diabetic rats intravitreally (IV) injected with LOX siRNA or scrambled (scram) siRNA were used in the study. One month after the onset of diabetes, intravitreal injections were initiated at monthly intervals for up to three times. At the end of study, retinal capillary networks were isolated, stained with periodic acid-Schiff (PAS) and hematoxylin, and assessed for acellular capillaries (AC) and pericyte loss (PL). To assess vascular leakage, extravasation of FITC-dextran was evaluated in retinal capillaries after tail vein injection of FITC-dextran. Western blot analysis was performed to determine retinal LOX level and confirm LOX downregulation via LOX siRNA intravitreal injection.

Results

LOX expression was significantly upregulated in retinas of diabetic rats compared with that of nondiabetic rats. Diabetic rats injected with LOX siRNA showed a significant decrease in retinal LOX expression compared with those of diabetic rats or scram siRNA-injected rats. In diabetic retinas, AC and PL were significantly increased compared with those of nondiabetic retinas. Importantly, diabetic rats treated with LOX siRNA exhibited a significant decrease in AC and PL counts compared with those of untreated diabetic rats. Furthermore, diabetic rats treated with LOX siRNA showed significant decrease in retinal vascular permeability compared with that of untreated diabetic rats.

Conclusions

Findings suggest LOX siRNA intravitreal injection may be effective against diabetes-induced LOX overexpression in preventing apoptosis and vascular leakage associated with diabetic retinopathy.

Human vitreous in proliferative diabetic retinopathy: Characterization and translational implications

Diabetic retinopathy (DR) is one of the leading causes of visual impairment in the working-age population. DR is a progressive eye disease caused by long-term accumulation of hyperglycaemia-mediated pathological alterations in the retina of diabetic patients. DR begins with asymptomatic retinal abnormalities and may progress to advanced-stage proliferative diabetic retinopathy (PDR), characterized by neovascularization or preretinal/vitreous haemorrhages. The vitreous, a transparent gel that fills the posterior cavity of the eye, plays a vital role in maintaining ocular function. Structural and molecular alterations of the vitreous, observed during DR progression, are consequences of metabolic and functional modifications of the retinal tissue. Thus, vitreal alterations reflect the pathological events occurring at the vitreoretinal interface. These events are caused by hypoxic, oxidative, inflammatory, neurodegenerative, and leukostatic conditions that occur during diabetes. Conversely, PDR vitreous can exert pathological effects on the diabetic retina, resulting in activation of a vicious cycle that contributes to disease progression. In this review, we recapitulate the major pathological features of DR/PDR, and focus on the structural and molecular changes that characterize the vitreal structure and composition during DR and progression to PDR. In PDR, vitreous represents a reservoir of pathological signalling molecules. Therefore, in this review we discuss how studying the biological activity of the vitreous in different in vitro, ex vivo, and in vivo experimental models can provide insights into the pathogenesis of PDR. In addition, the vitreous from PDR patients can represent a novel tool to obtain preclinical experimental evidences for the development and characterization of new therapeutic drug candidates for PDR therapy.

Review of Biomarkers in Ocular Matrices: Challenges and Opportunities

Biomarkers provide a powerful and dynamic approach to improve our understanding of the mechanisms underlying ocular diseases with applications in diagnosis, disease modulation or for predicting and monitoring of clinical response to treatment. Defined as measurable indicator of normal or pathological processes, biomarker evaluation has been used extensively in drug development within clinical settings to better comprehend effectiveness of treatment in ocular diseases. Biomarkers in the eye have the advantage of access to multiple ocular matrices via minimally invasive methods. Repeat sampling for biomarker assessment has enabled reproducible objective measures of disease process or biological responses to a drug treatment. This review describes the usage of biomarkers with respect to four commonly sampled ocular matrices in clinic: tears, conjunctiva, aqueous humor and vitreous. Issues that affect the evaluation of biomarkers are discussed along with opportunities to leverage biomarkers such that ultimately, they can be used for customized targeted therapy.

The Oxidative Stress and Mitochondrial Dysfunction during the Pathogenesis of Diabetic Retinopathy

Diabetic retinopathy is one of the most serious microvascular complications induced by hyperglycemia via five major pathways, including polyol, hexosamine, protein kinase C, and angiotensin II pathways and the accumulation of advanced glycation end products. The hyperglycemia-induced overproduction of reactive oxygen species (ROS) induces local inflammation, mitochondrial dysfunction, microvascular dysfunction, and cell apoptosis. The accumulation of ROS, local inflammation, and cell death are tightly linked and considerably affect all phases of diabetic retinopathy pathogenesis. Furthermore, microvascular dysfunction induces ischemia and local inflammation, leading to neovascularization, macular edema, and neurodysfunction, ultimately leading to long-term blindness. Therefore, it is crucial to understand and elucidate the detailed mechanisms underlying the development of diabetic retinopathy. In this review, we summarized the existing knowledge about the pathogenesis and current strategies for the treatment of diabetic retinopathy, and we believe this systematization will help and support further research in this area.