Interactions between hyperglycemia and hypoxia: implications for diabetic retinopathy

Nutraceuticals for Diabetic Retinopathy: Recent Advances and Novel Delivery Systems

Diabetic retinopathy (DR) is a major vision-threatening disease among the working-age population worldwide. Present therapeutic strategies such as intravitreal injection of anti-VEGF and laser photocoagulation mainly target proliferative DR. However, there is a need for early effective management in patients with early stage of DR before its progression into the more severe sight-threatening proliferative stage. Nutraceuticals, natural functional foods with few side effects, have been proposed to be beneficial in patients with DR. Over the decades, many studies, either in vitro or in vivo, have demonstrated the advantages of a number of nutraceuticals in DR with their antioxidative, anti-inflammatory, neuroprotective, or vasoprotective effects. However, only a few clinical trials have been conducted, and their outcomes varied. The low bioavailability and instability of many nutraceuticals have indeed hindered their utilization in clinical use. In this context, nanoparticle carriers have been developed to deliver nutraceuticals and to improve their bioavailability. Despite its preclinical nature, research of interventive nutraceuticals for DR may yield promising information in their clinical applications.

The impact of blood lactic acid levels on retinopathy of prematurity morbidity

BACKGROUND

Retinopathy of prematurity (ROP) is a common disease in premature infants. In recent years, most researchers have used lactic acid as poor prognosis marker in premature infants. This study aims to explore investigate the impact of blood lactic acid levels on ROP.

METHODS

A retrospective case-control study was conducted, and infants with severe ROP born with birth weight (BW) ≤ 1500 g and gestational age (GA) ≤ 32 weeks were enrolled from November 2016 to November 2021. Infants without any stage ROP were included as controls and were matched with ROP infants (1:2) by GA and BW. All selected preterm infants were tested for heel terminal trace blood gas analysis within two weeks of life. Changes in blood lactic acid levels in the two groups were compared and analyzed by using multivariate logistic regression analysis. Sensitivity and specificity were analyzed by receiver operating characteristic (ROC) curve.

RESULTS

There were 79 infants in ROP group, and 158 infants in control group. The levels of blood lactic acid were significantly higher in the ROP group on days 1, 3, 5, and 7 compared with control group (all p < 0.05). The blood lactic acid levels on day 5 was an independent risk factor for ROP (p = 0.017). The area under the curve (AUC), sensitivity and specificity were highest on day 5 (AUC 0.716, sensitivity 77.2% and specificity 62.0%, respectively, p < 0.001), and higher on days 1, 3, and 7.

CONCLUSION

A high blood lactic acid level in the first seven days of life may be associated with increases ROP occurrence in very preterm infants, and suggest blood lactic acid level may impact the occurrence of ROP.

Effects of photoperiod and food on glucose intolerance and subsequent ocular pathology in the fat sand rat

Type 2 diabetes mellitus (T2DM) and its ocular complications, such as cataract and diabetic retinopathy (DR) have been linked to circadian rhythm-disturbances. Using a unique diurnal animal model, the sand rat (Psammomys obesus) we examined the effect of circadian disruption by short photoperiod acclimation on the development of T2DM and related ocular pathologies. We experimented with 48 male sand rats. Variables were day length (short photoperiod, SP, vs. neutral photoperiod NP) and diet (standard rodent diet vs. low-energy diet). Blood glucose, the presence of cataract and retinal pathology were monitored. Histological slides were examined for lens opacity, retinal cell count and thickness. Animals under SP and fed standard rodent diet (SPSR) for 20 weeks had higher baseline blood glucose levels and lower glucose tolerance compared with animals kept under NP regardless of diet, and under SP with low energy diet (SPLE). Animals under SPSR had less cells in the outer nuclear layer, a lower total number of cells in the retina, and a thickened retina. Higher blood glucose levels correlated with lower number of cells in all cellular layers of the retina and thicker retina. Animals under SPSR had higher occurrence of cataract, and a higher degree of cataract, which correlated with higher blood glucose levels. Sand rats kept under SPSR develop cataract and retinal abnormalities indicative of DR, whereas sand rats kept under NP regardless of diet, or under SPLE, do not. These ocular abnormalities significantly correlate with hyperglycemia.

Selenium-More than Just a Fortuitous Sulfur Substitute in Redox Biology

Living organisms use selenium mainly in the form of selenocysteine in the active site of oxidoreductases. Here, selenium's unique chemistry is believed to modulate the reaction mechanism and enhance the catalytic efficiency of specific enzymes in ways not achievable with a sulfur-containing cysteine. However, despite the fact that selenium/sulfur have different physicochemical properties, several selenoproteins have fully functional cysteine-containing homologues and some organisms do not use selenocysteine at all. In this review, selected selenocysteine-containing proteins will be discussed to showcase both situations: (i) selenium as an obligatory element for the protein's physiological function, and (ii) selenium presenting no clear advantage over sulfur (functional proteins with either selenium or sulfur). Selenium's physiological roles in antioxidant defence (to maintain cellular redox status/hinder oxidative stress), hormone metabolism, DNA synthesis, and repair (maintain genetic stability) will be also highlighted, as well as selenium's role in human health. Formate dehydrogenases, hydrogenases, glutathione peroxidases, thioredoxin reductases, and iodothyronine deiodinases will be herein featured.

PECULIARITIES OF PULMONARY VENTILATION RESPONSE TO DOSED HYPOXIA IN ELDERLY PEOPLE WITH IMPAIRED GLUCOSE TOLERANCE

OBJECTIVE

The aim: To determine the peculiarities of the response of pulmonary ventilation to hypoxia in elderly people with impaired glucose tolerance.

PATIENTS AND METHODS

Materials and methods: Forty-three elderly people were examined, including 20 patients with impaired glucose tolerance and 23 healthy individuals with preserved glucose tolerance. Fasting plasma glucose and insulin concentrations were determined, and the HOMA-IR insulin resistance index was calculated. Under conditions of normoxia and during a dosed hypoxic test (12% oxygen, duration 20 min), blood saturation and lung ventilation parameters were monitored.

RESULTS

Results: Under conditions of normoxia, the indicators of lung ventilation function did not differ between the groups of elderly people with impaired and preserved glucose tolerance. Under conditions of hypoxia, elderly people with impaired glucose tolerance had a less significant increase in ventilation, despite the development of more severe arterial hypoxemia. This leads to a decrease in the ventilatory response to hypoxia in case of impaired carbohydrate metabolism.

CONCLUSION

Conclusions: In people with impaired glucose tolerance, a less significant ventilatory response to hypoxia is combined with more pronounced insulin resistance.

Mechanisms of Cardiorenal Protection With SGLT2 Inhibitors in Patients With T2DM Based on Network Pharmacology

Purpose

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have cardiorenal protective effects regardless of whether they are combined with type 2 diabetes mellitus, but their specific pharmacological mechanisms remain undetermined.

Materials and Methods

We used databases to obtain information on the disease targets of “Chronic Kidney Disease,” “Heart Failure,” and “Type 2 Diabetes Mellitus” as well as the targets of SGLT2 inhibitors. After screening the common targets, we used Cytoscape 3.8.2 software to construct SGLT2 inhibitors' regulatory network and protein-protein interaction network. The clusterProfiler R package was used to perform gene ontology functional analysis and Kyoto encyclopedia of genes and genomes pathway enrichment analyses on the target genes. Molecular docking was utilized to verify the relationship between SGLT2 inhibitors and core targets.

Results

Seven different SGLT2 inhibitors were found to have cardiorenal protective effects on 146 targets. The main mechanisms of action may be associated with lipid and atherosclerosis, MAPK signaling pathway, Rap1 signaling pathway, endocrine resistance, fluid shear stress, atherosclerosis, TNF signaling pathway, relaxin signaling pathway, neurotrophin signaling pathway, and AGEs-RAGE signaling pathway in diabetic complications were related. Docking of SGLT2 inhibitors with key targets such as GAPDH, MAPK3, MMP9, MAPK1, and NRAS revealed that these compounds bind to proteins spontaneously.

Conclusion

Based on pharmacological networks, this study elucidates the potential mechanisms of action of SGLT2 inhibitors from a systemic and holistic perspective. These key targets and pathways will provide new ideas for future studies on the pharmacological mechanisms of cardiorenal protection by SGLT2 inhibitors.

MicroRNA-5195-3p alleviates high glucose‑induced injury in human ARPE-19 cells by targeting GMFB

Hyperglycemia is generally considered to be an important cause of diabetic retinopathy (DR). The aim of the present study was to investigate the role of miR-5195-3p in high glucose (HG)-induced human retinal pigment epithelial ARPE-19 cell injury. Here, we first found that the expression level of miR-5195-3p was significantly downregulated in HG-stimulated ARPE-19 cells using reverse transcription quantitative PCR. Overexpression of miR-5195-3p attenuated the impaired cell viability, increased apoptosis and pro-inflammatory cytokines secretion in ARPE-19 cells under HG condition using CCK-8 assay, flow cytometry and ELISA assay, respectively. Luciferase reporter assay showed that miR-5195-3p could specifically bind to the 3’UTR of glia maturation factor-β (GMFB). GMFB overexpression reversed, while knockdown enhanced the protective effects of miR-5195-3p overexpression against HG-induced ARPE-19 cell injury. In summary, miR-5195-3p targeting GMFB might be a potential therapeutic target for DR.

Role of glycolysis in retinal vascular endothelium, glia, pigment epithelium, and photoreceptor cells and as therapeutic targets for related retinal diseases

Glycolysis produces large amounts of adenosine triphosphate (ATP) in a short time. The retinal vascular endothelium feeds itself primarily through aerobic glycolysis with less ATP. But when it generates new vessels, aerobic glycolysis provides rapid and abundant ATP support for angiogenesis, and thus inhibition of glycolysis in endothelial cells can be a target for the treatment of neovascularization. Aerobic glycolysis has a protective effect on Müller cells, and it can provide with a target for visual protection and maintenance of the blood-retinal barrier. Under physiological conditions, the mitochondria of RPE can use lactic acid produced by photoreceptor cells as an energy source to provide ATP for survival. In pathological conditions, because RPE cells avoid their oxidative damage by increasing glycolysis, a large number of glycolysis products accumulate, which in turn has a toxic effect on photoreceptor cells. This shows that stabilizing the function of RPE mitochondria may become a target for the treatment of diseases such as retinal degeneration. The decrease of aerobic glycolysis leads to the decline of photoreceptor cell function and impaired vision; therefore, aerobic glycolysis of stable photoreceptor cells provides a reliable target for delaying vision loss. It is of great significance to study the role of glycolysis in various retinal cells for the targeted treatment of ocular fundus diseases.

Diabetes Promotes Retinal Vascular Endothelial Cell Injury by Inducing CCN1 Expression

Purpose: Diabetic retinopathy (DR) is one of the most common diabetic microvascular complications. However, the pathogenesis of DR has not yet been fully elucidated. This study aimed to discover novel and key molecules involved in the pathogenesis of DR, which could potentially be targets for therapeutic DR intervention.

Methods: To identify potential genes involved in the pathogenesis of DR, we analyzed the public database of neovascular membranes (NVMs) from patients with proliferative diabetic retinopathy (PDR) and healthy controls (HCs) (GSE102485, https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE102485). Further, we compared these findings by performing RNA-sequencing analysis of peripheral blood mononuclear cells (PBMC) from patients with DR, control patients with non-complicated diabetes mellitus (DMC), and HCs. To determine the critical role of candidate genes in DR, knockdown or knockout was performed in human retinal vascular endothelial cells (HRVECs). The oxidative stress pathway, as well as tight junction integrity, was analyzed.

Results: Transcriptional profiles showed distinct patterns between the NVMs of patients with DR and those of the HCs. Those genes enriched in either extracellular matrix (ECM)-receptor interaction or focal adhesion pathways were considerably upregulated. Both pathways were important for maintaining the integrity of retinal vascular structure and function. Importantly, the gene encoding the matricellular protein CCN1, a key gene in cell physiology, was differentially expressed in both pathways. Knockdown of CCN1 by small interfering RNA (siRNA) or knockout of CCN1 by the CRISPR-Cas9 technique in HRVECs significantly increased the levels of VE-cadherin, reduced the level of NADPH oxidase 4 (NOX4), and inhibited the generation of reactive oxygen species (ROS).

Conclusion: The present study identifies CCN1 as an important regulator in the pathogenesis of DR. Increased expression of CCN1 stimulates oxidative stress and disrupts tight junction integrity in endothelial cells by inducing NOX4. Thus, targeting the CCN1/NOX4 axis provides a therapeutic strategy for treating DR by alleviating endothelial cell injury.

The Role of HIF1α-PFKFB3 Pathway in Diabetic Retinopathy

Diabetic retinopathy (DR) is the leading cause of blindness for adults in developed countries. Both microvasculopathy and neurodegeneration are implicated in mechanisms of DR development, with neuronal impairment preceding microvascular abnormalities, which is often underappreciated in the clinic. Most current therapeutic strategies, including anti-vascular endothelial growth factor (anti-VEGF)-antibodies, aim at treating the advanced stages (diabetic macular edema and proliferative diabetic retinopathy) and fail to target the neuronal deterioration. Hence, new therapeutic approach(es) intended to address both vascular and neuronal impairment are urgently needed. The hypoxia-inducible factor 1α (HIF1α)-6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) pathway is critically implicated in the islet pathology of diabetes. Recent evidence highlighted the pathway relevance for pathologic angiogenesis and neurodegeneration, two key aspects in DR. PFKFB3 is key to the sprouting angiogenesis, along with VEGF, by determining the endothelial tip-cell competition. Also, PFKFB3-driven glycolysis compromises the antioxidative capacity of neurons leading to neuronal loss and reactive gliosis. Therefore, the HIF1α-PFKFB3 signaling pathway is unique as being a pervasive pathological component across multiple cell types in the retina in the early as well as late stages of DR. A metabolic point-of-intervention based on HIF1α-PFKFB3 targeting thus deserves further consideration in DR.

Retinal Inflammation, Oxidative Stress, and Vascular Impairment Is Ablated in Diabetic Mice Receiving XMD8-92 Treatment

The global number of diabetics continues to rise annually. As diabetes progresses, almost all of Type I and more than half of Type II diabetics develop diabetic retinopathy. Diabetic retinopathy is a microvascular disease of the retina, and is the leading cause of blindness in the working-age population worldwide. With such a significant health impact, new drugs are required to halt the blinding threat posed by this visual disorder. The cause of diabetic retinopathy is multifactorial, and an optimal therapeutic would halt inflammation, cease photoreceptor cell dysfunction, and ablate vascular impairment. XMD8-92 is a small molecule inhibitor that blocks inflammatory activity downstream of ERK5 (extracellular signal-related kinase 5) and BRD4 (bromodomain 4). ERK5 elicits inflammation, is increased in Type II diabetics, and plays a pathologic role in diabetic nephropathy, while BRD4 induces retinal inflammation and plays a role in retinal degeneration. Further, we provide evidence that suggests both pERK5 and BRD4 expression are increased in the retinas of our STZ (streptozotocin)-induced diabetic mice. Taken together, we hypothesized that XMD8-92 would be a good therapeutic candidate for diabetic retinopathy, and tested XMD8-92 in a murine model of diabetic retinopathy. In the current study, we developed an in vivo treatment regimen by administering one 100 μL subcutaneous injection of saline containing 20 μM of XMD8-92 weekly, to STZ-induced diabetic mice. XMD8-92 treatments significantly decreased diabetes-mediated retinal inflammation, VEGF production, and oxidative stress. Further, XMD8-92 halted the degradation of ZO-1 (zonula occludens-1), which is a tight junction protein associated with vascular permeability in the retina. Finally, XMD8-92 treatment ablated diabetes-mediated vascular leakage and capillary degeneration, which are the clinical hallmarks of non-proliferative diabetic retinopathy. Taken together, this study provides strong evidence that XMD8-92 could be a potentially novel therapeutic for diabetic retinopathy.

Extracellular Vesicle Transmission of Chemoresistance to Ovarian Cancer Cells Is Associated with Hypoxia-Induced Expression of Glycolytic Pathway Proteins, and Prediction of Epithelial Ovarian Cancer Disease Recurrence

Simple Summary

Ovarian cancer is one of the most lethal cancers affecting women worldwide. Its high mortality rate is often attributed to the non-specific nature of early symptoms of the disease. Developing a better understanding of the disease progression and identifying clinically useful biomarkers that aid in clinical management are requisite to reducing the mortality rate of ovarian cancer. Reduced oxygen tension (i.e., hypoxia) is not only a characteristic of solid tumors but may also enhance the metastatic capacity of tumors by inducing the release of tumor growth promoting factors. Recently, it has been proposed that small tumor-derived extracellular vesicles (sEVs) facilitate cancer progression. In this study, we established that sEVs produced under low oxygen tension induce a metabolic switch in ovarian cancer cells associated with changes in glycolytic pathway proteins that promote resistance to carboplatin. Significantly, we identified a suite of sEV-associated glycolysis pathway proteins that are present in patients with ovarian cancer that can predict disease recurrence with over 90% accuracy.

Abstract

Hypoxia is a key regulator of cancer progression and chemoresistance. Ambiguity remains about how cancer cells adapt to hypoxic microenvironments and transfer oncogenic factors to surrounding cells. In this study, we determined the effects of hypoxia on the bioactivity of sEVs in a panel of ovarian cancer (OvCar) cell lines. The data obtained demonstrate a varying degree of platinum resistance induced in OvCar cells when exposed to low oxygen tension (1% oxygen). Using quantitative mass spectrometry (Sequential Window Acquisition of All Theoretical Fragment Ion Mass Spectra, SWATH) and targeted multiple reaction monitoring (MRM), we identified a suite of proteins associated with glycolysis that change under hypoxic conditions in cells and sEVs. Interestingly, we identified a differential response to hypoxia in the OvCar cell lines and their secreted sEVs, highlighting the cells’ heterogeneity. Proteins are involved in metabolic reprogramming such as glycolysis, including putative hexokinase (HK), UDP-glucuronosyltransferase 1–6 (UD16), and 6-phosphogluconolactonase (6 PGL), and their presence correlates with the induction of platinum resistance. Furthermore, when normoxic cells were exposed to sEVs from hypoxic cells, platinum-resistance increased significantly (p < 0.05). Altered chemoresistance was associated with changes in glycolysis and fatty acid synthesis. Finally, sEVs isolated from a clinical cohort (n = 31) were also found to be enriched in glycolysis-pathway proteins, especially in patients with recurrent disease. These data support the hypothesis that hypoxia induces changes in sEVs composition and bioactivity that confers carboplatin resistance on target cells. Furthermore, we propose that the expression of sEV-associated glycolysis-pathway proteins is predictive of ovarian cancer recurrence and is of clinical utility in disease management.

The prognostic outcome of 'type 2 diabetes mellitus and breast cancer' association pivots on hypoxia-hyperglycemia axis

Type 2 diabetes mellitus and breast cancer are complex, chronic, heterogeneous, and multi-factorial diseases; with common risk factors including but not limited to diet, obesity, and age. They also share mutually inclusive phenotypic features such as the metabolic deregulations resulting from hyperglycemia, hypoxic conditions and hormonal imbalances. Although, the association between diabetes and cancer has long been speculated; however, the exact molecular nature of this link remains to be fully elucidated. Both the diseases are leading causes of death worldwide and a causal relationship between the two if not addressed, may translate into a major global health concern. Previous studies have hypothesized hyperglycemia, hyperinsulinemia, hormonal imbalances and chronic inflammation, as some of the possible grounds for explaining how diabetes may lead to cancer initiation, yet further research still needs to be done to validate these proposed mechanisms. At the crux of this dilemma, hyperglycemia and hypoxia are two intimately related states involving an intricate level of crosstalk and hypoxia inducible factor 1, at the center of this, plays a key role in mediating an aggressive disease state, particularly in solid tumors such as breast cancer. Subsequently, elucidating the role of HIF1 in establishing the diabetes-breast cancer link on hypoxia-hyperglycemia axis may not only provide an insight into the molecular mechanisms underlying the association but also, illuminate on the prognostic outcome of the therapeutic targeting of HIF1 signaling in diabetic patients with breast cancer or vice versa. Hence, this review highlights the critical role of HIF1 signaling in patients with both T2DM and breast cancer, potentiates its significance as a prognostic marker in comorbid patients, and further discusses the potential prognostic outcome of targeting HIF1, subsequently establishing the pressing need for HIF1 molecular profiling-based patient selection leading to more effective therapeutic strategies emerging from personalized medicine.

Mangiferin inhibits cell migration and angiogenesis via PI3K/AKT/mTOR signaling in high glucose‑ and hypoxia‑induced RRCECs

Mangiferin is a prominent active component that can be derived from several traditional herbs, including Mangifera indica L., Anemarrhena asphodeloides Bge., and Belamcanda chinensis (L.) DC., which displays antidiabetic properties. Diabetic retinopathy (DR), a serious complication caused by diabetes, is the leading cause of blindness. The present study aimed to evaluate the beneficial effects of mangiferin on high glucose (HG)/hypoxia‑induced rat retinal capillary endothelial cell (RRCEC) angiogenesis, as well as the underlying mechanisms. To establish an in vitro model of DR, RRCECs were exposed to 30 mM glucose and hypoxia. Following treatment with different doses of mangiferin (0.05, 0.1 or 0.2 µM), RRCEC viability, migration and angiogenesis were assessed by performing Cell Counting Kit 8, immunofluorescence, wound healing, Transwell and tube formation assays. Western blotting was conducted to evaluate protein expression levels. Furthermore, LY294002 and IGF‑1, an inhibitor and activator of the PI3K/AKT/mTOR signaling pathway, respectively, were used to verify the potential mechanisms underlying mangiferin. The results demonstrated that mangiferin notably inhibited HG/hypoxia‑induced RRCEC migration and angiogenesis. HG/hypoxia‑induced upregulation of hypoxia‑inducible factor‑1α, vascular endothelial growth factor, matrix metallopeptidase (MMP)2 and MMP9 expression levels and the phosphorylation of PI3K, AKT and mTOR in RRCECs was significantly reversed following treatment with mangiferin. Additionally, further activation of the PI3K/AKT signaling pathway by IGF‑1 inhibited the beneficial effects of mangiferin on RRCECs, whereas deactivation of the PI3K/AKT signaling pathway by LY294002 displayed the opposite results. Collectively, the results of the present study suggested that mangiferin suppressed RRCEC angiogenesis via modulating the PI3K/AKT/mTOR signaling pathway, which could serve as an effective treatment strategy for DR.

Does Hyperglycemia Cause Oxidative Stress in the Diabetic Rat Retina?

Diabetes, being a metabolic disease dysregulates a large number of metabolites and factors. However, among those altered metabolites, hyperglycemia is considered as the major factor to cause an increase in oxidative stress that initiates the pathophysiology of retinal damage leading to diabetic retinopathy. Diabetes-induced oxidative stress in the diabetic retina and its damaging effects are well known, but still, the exact source and the mechanism of hyperglycemia-induced reactive oxygen species (ROS) generation especially through mitochondria remains uncertain. In this study, we analyzed precisely the generation of ROS and the antioxidant capacity of enzymes in a real-time situation under ex vivo and in vivo conditions in the control and streptozotocin-induced diabetic rat retinas. We also measured the rate of flux through the citric acid cycle by determining the oxidation of glucose to CO2 and glutamate, under ex vivo conditions in the control and diabetic retinas. Measurements of H2O2 clearance from the ex vivo control and diabetic retinas indicated that activities of mitochondrial antioxidant enzymes are intact in the diabetic retina. Short-term hyperglycemia seems to influence a decrease in ROS generation in the diabetic retina compared to controls, which is also correlated with a decreased oxidation rate of glucose in the diabetic retina. However, an increase in the formation of ROS was observed in the diabetic retinas compared to controls under in vivo conditions. Thus, our results suggest of diabetes/hyperglycemia-induced non-mitochondrial sources may serve as major sources of ROS generation in the diabetic retina as opposed to widely believed hyperglycemia-induced mitochondrial sources of excess ROS. Therefore, hyperglycemia per se may not cause an increase in oxidative stress, especially through mitochondria to damage the retina as in the case of diabetic retinopathy.

Skin Complications of Diabetes Mellitus Revealed by Polarized Hyperspectral Imaging and Machine Learning

Aging and diabetes lead to protein glycation and cause dysfunction of collagen-containing tissues. The accompanying structural and functional changes of collagen significantly contribute to the development of various pathological malformations affecting the skin, blood vessels, and nerves, causing a number of complications, increasing disability risks and threat to life. In fact, no methods of non-invasive assessment of glycation and associated metabolic processes in biotissues or prediction of possible skin complications, e.g., ulcers, currently exist for endocrinologists and clinical diagnosis. In this publication, utilizing emerging photonics-based technology, innovative solutions in machine learning, and definitive physiological characteristics, we introduce a diagnostic approach capable of evaluating the skin complications of diabetes mellitus at the very earlier stage. The results of the feasibility studies, as well as the actual tests on patients with diabetes and healthy volunteers, clearly show the ability of the approach to differentiate diabetic and control groups. Furthermore, the developed in-house polarization-based hyperspectral imaging technique accomplished with the implementation of the artificial neural network provides new horizons in the study and diagnosis of age-related diseases.

mTOR-dependent dysregulation of autophagy contributes to the retinal ganglion cell loss in streptozotocin-induced diabetic retinopathy

BACKGROUND

Neurodegeneration, an early event in the pathogenesis of diabetic retinopathy (DR), precedes clinically detectable microvascular damage. Autophagy dysregulation is considered a potential cause of neuronal cell loss, however underlying mechanisms remain unclear. The mechanistic target of rapamycin (mTOR) integrates diverse environmental signals to coordinate biological processes, including autophagy. Here, we investigated the role of mTOR signaling in neuronal cell death in DR.

METHODS

Diabetes was induced by a single intraperitoneal injection of streptozotocin and tissue samples were harvested at 1, 2, 3, 4, and 6 months of diabetes. Early-stage of DR was investigated in 1-month-diabetic mice treated with phlorizin (two daily subcutaneous injections at a dose of 200 mg/kg of body weight during the last 7 full days of the experiment and the morning of the 8th day, 3 h before sacrifice) or rapamycin (daily intraperitoneal injections, at a dose of 3 mg/kg for the same period as for phlorizin treatment). The effect of autophagy modulation on retinal ganglion cells was investigated in 3-months-diabetic mice treated with phlorizin (two daily subcutaneous injections during the last 10 full days of the experiment and the morning of the 11th day, 3 h before sacrifice) or MHY1485 (daily i.p. injections, at a dose of 10 mg/kg for the same period as for phlorizin treatment). Tissue samples obtained from treated/untreated diabetic mice and age-matched controls were used for Western blot and histologic analysis.

RESULTS

mTOR-related proteins and glucose transporter 1 (GLUT1) was upregulated at 1 month and downregulated in the following period up to 6 months. Diabetes-induced neurodegeneration was characterized by an increase of apoptotic marker-cleaved caspase 3, a decrease of the total number of cells, and NeuN immunoreactivity in the ganglion cell layer, as well as an increase of autophagic protein. Insulin-independent glycemic control restored the mTOR pathway activity and GLUT1 expression, along with a decrease of autophagic and apoptotic proteins in 3-months-diabetic mice neuroretina. However, blockade of autophagy using MHY1485 resulted in a more protective effect on ganglion cells compared with phlorizin treatment.

CONCLUSION

Collectively, our study describes the mechanisms of neurodegeneration through the hyperglycemia/ mTOR/ autophagy/ apoptosis pathway. Video Abstract.

Metabolic Dysregulation and Neurovascular Dysfunction in Diabetic Retinopathy

Diabetic retinopathy is a major cause of ocular complications in patients with type 1 and type 2 diabetes in developed countries. Due to the continued increase in the number of people with obesity and diabetes in the United States of America and globally, the incidence of diabetic retinopathy is expected to increase significantly in the coming years. Diabetic retinopathy is widely accepted as a combination of neurodegenerative and microvascular changes; however, which change occurs first is not yet understood. Although the pathogenesis of diabetic retinopathy is very complex, regulated by numerous signaling pathways and cellular processes, maintaining glucose homeostasis is still an essential component for normal physiological functioning of retinal cells. The maintenance of glucose homeostasis is finely regulated by coordinated interplay between glycolysis, Krebs cycle, and oxidative phosphorylation. Glycolysis is the most conserved metabolic pathway in biology and is tightly regulated to maintain a steady-state concentration of glycolytic intermediates; this regulation is called scheduled or regulated glycolysis. However, an abnormal increase in glycolytic flux generates large amounts of intermediate metabolites that can be shunted into different damaging pathways including the polyol pathway, hexosamine pathway, diacylglycerol-dependent activation of the protein kinase C pathway, and Amadori/advanced glycation end products (AGEs) pathway. In addition, disrupting the balance between glycolysis and oxidative phosphorylation leads to other biochemical and molecular changes observed in diabetic retinopathy including endoplasmic reticulum-mitochondria miscommunication and mitophagy dysregulation. This review will focus on how dysregulation of glycolysis contributes to diabetic retinopathy.

Tangeretin Ameliorates Glucose-Induced Podocyte Injury through Blocking Epithelial to Mesenchymal Transition Caused by Oxidative Stress and Hypoxia

Podocyte injury inevitably results in leakage of proteins from the glomerular filter and is vital in the pathogenesis of diabetic nephropathy (DN). The underlying mechanisms of podocyte injury facilitate finding of new therapeutic targets for DN treatment and prevention. Tangeretin is an O-polymethoxylated flavone present in citrus peels with anti-inflammatory and antioxidant properties. This study investigated the renoprotective effects of tangeretin on epithelial-to-mesenchymal transition-mediated podocyte injury and fibrosis through oxidative stress and hypoxia caused by hyperglycemia. Mouse podocytes were incubated in media containing 33 mM glucose in the absence and presence of 1–20 μM tangeretin for up to 6 days. The in vivo animal model employed db/db mice orally administrated with 10 mg/kg tangeretin for 8 weeks. Non-toxic tangeretin inhibited glucose-induced expression of the mesenchymal markers of N-cadherin and α-smooth muscle actin in podocytes. However, the reduced induction of the epithelial markers of E-cadherin and P-cadherin was restored by tangeretin in diabetic podocytes. Further, tangeretin enhanced the expression of the podocyte slit diaphragm proteins of nephrin and podocin down-regulated by glucose stimulation. The transmission electron microscopic images revealed that foot process effacement and loss of podocytes occurred in diabetic mouse glomeruli. However, oral administration of 10 mg/kg tangeretin reduced urine albumin excretion and improved foot process effacement of diabetic podocytes through inhibiting loss of slit junction and adherenes junction proteins. Glucose enhanced ROS production and HIF-1α induction in podocytes, leading to induction of oxidative stress and hypoxia. Similarly, in diabetic glomeruli reactive oxygen species (ROS) production and HIF-1α induction were observed. Furthermore, hypoxia-evoking cobalt chloride induced epithelial-to-mesenchymal transition (EMT) process and loss of slit diaphragm proteins and junction proteins in podocytes, which was inhibited by treating submicromolar tangeretin. Collectively, these results demonstrate that tangeretin inhibited podocyte injury and fibrosis through blocking podocyte EMT caused by glucose-induced oxidative stress and hypoxia.

MicroRNA-15b Targets VEGF and Inhibits Angiogenesis in Proliferative Diabetic Retinopathy

BACKGROUND

Vascular endothelial growth factor (VEGF)-induced angiogenesis is a critical compensatory response to microvascular rarefaction in the diabetic retina that contributes to proliferative diabetic retinopathy (PDR). In this study, we sought to determine the role of specific micro ribonucleic acids (RNAs) (miRs) associated with VEGF in patients with PDR pathology.

METHODS

RNA sequencing was employed to detect differentially circulating miR associated with VEGF in patients with diabetes mellitus (DM), nonproliferative diabetic retinopathy (NPDR) and PDR. Quantitative real-time polymerase chain reaction was performed to measure the concentration of miR-15b in the serum of patients with DM (n = 115), NPDR (n = 47), or PDR (n = 76). The effects of miR-15b on DR and regulation of VEGF and endothelial cell function were also characterized.

RESULTS

We demonstrated that circulating miR-15b was directly associated with VEGF compared with other miRs in patients with PDR. We found a significant inverse relationship between low levels of miR-15b and high levels of VEGF in patients with PDR when compared with the DM or NPDR groups. We found that miR-15b regulates the expression of VEGF by targeting the 3'-untranslated regions to inhibit its transcription. Similarly, overexpression of miR-15b suppressed vascular abnormalities in vivo in diabetic GK rats, inhibiting endothelial tube formation and VEGF expression.

CONCLUSION

Circulating miR-15b is associated with PDR and may be targeted to regulate VEGF expression and angiogenesis.

A human retinal microvascular endothelial-pericyte co-culture model to study diabetic retinopathy in vitro

This human primary co-culture model using human retinal microvascular endothelial cells (hREC) and human retinal pericyte cells (hRP) aims to improve current understanding of the cellular changes occurring in the retinal microvasculature during diabetic retinopathy (DR). Currently, patients often present in clinic with late-stage DR, only when vision becomes impaired. Therefore, new strategies for earlier detection in clinic, combined with novel pharmaceutical and cellular interventions are essential in order to slow or halt the progression of DR from background to sight-threatening stage. This co-culture model can be used as a simple, replicable in vitro tool to discover and assess novel drug therapies and improve fundamental understanding of alterations to cell behaviour in the human retinal microvasculature during DR. hRP and hREC were cultured for up to 21 days in normoxic (20%) or hypoxic (2%) oxygen levels and physiological (5.5 mM) or very high (33 mM) glucose, to maintain a healthy, or induce a diabetic-like phenotype in vitro. Mono- or co-cultured hREC and hRP were seeded 1:1 in healthy (20% oxygen and 5.5 mM glucose) or diabetic-like (2% oxygen and 33 mM glucose) conditions, on either side of untreated polyethylene terephthalate (PET) transwell inserts, and cultured for 21 days. Mono- and co-cultures were analysed for changes in metabolic activity, angiogenic response and junctional protein expression, using immunofluorescence antibody labelling, flow cytometry and multiplex ELISA technology. hRP and hREC were successfully co-cultured, and the glucose and oxygen concentrations selected for the in vitro healthy and diabetic-like conditions were sufficient for cell viability and EC monolayer integrity, with evidence of an angiogenic response in diabetic-like conditions within the 21 day timeframe. Angiopoietin-2 (Ang-2), vascular endothelial growth factor (VEGF), and platelet-derived growth factor (PDGF) secretion were all increased, whilst hepatocyte growth factor (hHGF), tissue inhibitor for metalloproteinase-2 (TIMP-2) and interleukin-8 (IL-8) secretion were all reduced in the in vitro diabetic-like conditions. The secretion profile of co-cultures was different to mono-cultures, highlighting the importance of using co-culture models to collect data more reflective of the close relationship between hRP-hREC in vivo. Previous groups have developed useful co-culture models utilising non-human, immortalised or large vessel-sourced cells to explore changes to the vasculature during hypoxia and/or high glucose insult. In this study the use of human primary, retina-specific microvascular cells, mono- and co-cultured, collected over a longer culture period, has enabled detection of changes that may have been missed in previous models.

Intraoperative hyperglycemia in patients with an elevated preoperative C-reactive protein level may increase the risk of acute kidney injury after cardiac surgery

PURPOSE

The effect of hyperglycemia on acute kidney injury (AKI) in patients undergoing cardiac surgery is unclear and may involve as yet unexplored factors. We hypothesized differential effects of intraoperative hyperglycemia on AKI after cardiac surgery depending on baseline inflammatory status, as reflected by the C-reactive protein (CRP) level.

METHODS

This retrospective study included patients who underwent cardiac surgery seen at our hospital from 2008 to 2018. Patients were classified into four groups according to their preoperative CRP level (≥ 1 or < 1 mg/dl) and their intraoperative time-weighted average glucose concentration (> 140 or ≤ 140 mg/dl): low CRP and normoglycemia, low CRP and hyperglycemia, high CRP and normoglycemia, and high CRP and hyperglycemia. The data were analyzed by multivariable logistic regression analysis.

RESULTS

The data of 3625 patients were analyzed. The logistic regression showed that patients in the high CRP and hyperglycemia group had a significantly higher risk of AKI than patients in the low CRP and normoglycemia group [odds ratio (OR), 1.58; 95% confidence interval (CI) 1.10-2.27], low CRP with hyperglycemia group (OR, 1.69; 95% CI 1.16-2.47) and high CRP with normoglycemia group (OR, 1.50; 95% CI 1.01-2.23).

CONCLUSIONS

Intraoperative hyperglycemia in patients with an elevated preoperative CRP level was significantly related to an increased risk of AKI after cardiac surgery. Individualized perioperative glycemic control may therefore be necessary in these patients.

Impaired nicotinamide adenine dinucleotide (NAD+ ) metabolism in diabetes and diabetic tissues: Implications for nicotinamide-related compound treatment

One of the biochemical abnormalities found in diabetic tissues is a decrease in the cytosolic oxidized to reduced forms of the nicotinamide adenine dinucleotide ratio (NAD⁺/NADH also known as pseudohypoxia) caused by oxidation of excessive substrates (glucose through the polyol pathway, free fatty acids and lactate). Subsequently, a decline in NAD⁺ levels as a result of the activation of poly adenine nucleotide diphosphate‐ribose polymerase (mainly in type 1 diabetes) or the inhibition of adenine nucleotide monophosphate‐activated protein kinase (in type 2 diabetes). Thus, replenishment of NAD⁺ levels by nicotinamide‐related compounds could be beneficial. However, these compounds also increase nicotinamide catabolites that cause oxidative stress. This is particularly troublesome for patients with diabetes, because they have impaired nicotinamide salvage pathway reactions at the level of nicotinamide phosphoribosyl transferase and phosphoribosyl pyrophosphate, which occurs by the following mechanisms. First, phosphoribosyl pyrophosphate synthesis from pentose phosphate pathway is compromised by a decrease in plasma thiamine and transketolase activity. Second, nicotinamide phosphoribosyl transferase expression is decreased because of reduced adenosine monophosphate‐activated protein kinase activity, which occurs in type 2 diabetes. The adenosine monophosphate‐activated protein kinase inhibition is caused by an activation of protein kinase C and D1 as a result of enhanced diacylglycerol synthesis caused by pseudohypoxia and increased fatty acids levels. In this regard, nicotinamide‐related compounds should be given with caution to treat diabetes. To minimize the risk and maximize the benefit, nicotinamide‐related compounds should be taken with insulin sensitizers (for type 2 diabetes), polyphenols, benfotiamine, acetyl‐L‐carnitine and aldose reductase inhibitors. The efficacy of these regimens can be monitored by measuring serum NAD⁺ and urinary nicotinamide catabolites.

Metabolomics and biomarkers in ocular matrix: beyond ocular diseases

According to the recent report, there are 870 million people suffer from ocular diseases worldwide. The present approaches for diagnosis are morphological examination, imaging examination and immunological examination, regrettably, they lack of sensitivity and difficult to make a definite diagnosis in the early stage. Systemic biology as an effective method has been used in clinical diagnosis and treatment for diseases, especially metabolomics which is more attractive with high sensitivity and accuracy. Although previous researches had been confirmed that endogenous metabolites in the ocular matrix play a crucial role in the progress of diseases related diseases, the standard protocols and systematic summary about the biomarker researches based on ocular matrix has not been established. This review article highlights the pretreatment for ocular matrix and the new biomarkers expressed by the eye diseases, expected to promote the application of biomarkers in the diagnosis and treatment of eye diseases.

The hypoxic expression of the glucose transporter RAG1 reveals the role of the bHLH transcription factor Sck1 as a novel hypoxic modulator in Kluyveromyces lactis

Glucose is the preferred nutrient for most living cells and is also a signaling molecule that modulates several cellular processes. Glucose regulates the expression of glucose permease genes in yeasts through signaling pathways dependent on plasma membrane glucose sensors. In the yeast Kluyveromyces lactis, sufficient levels of glucose induction of the low-affinity glucose transporter RAG1 gene also depends on a functional glycolysis, suggesting additional intracellular signaling. We have found that the expression of RAG1 gene is also induced by hypoxia in the presence of glucose, indicating that glucose and oxygen signaling pathways are interconnected. In this study we investigated the molecular mechanisms underlying this crosstalk. By analyzing RAG1 expression in various K. lactis mutants, we found that the bHLH transcriptional activator Sck1 is required for the hypoxic induction of RAG1 gene. The RAG1 promoter region essential for its hypoxic induction was identified by promoter deletion experiments. Taken together, these results show that the RAG1 glucose permease gene is synergistically induced by hypoxia and glucose and highlighted a novel role for the transcriptional activator Sck1 as a key mediator in this mechanism.

Dysregulation of 2-oxoglutarate-dependent dioxygenases by hyperglycaemia: does this link diabetes and vascular disease?

The clinical, social and economic burden of cardiovascular disease (CVD) associated with diabetes underscores an urgency for understanding the disease aetiology. Evidence suggests that the hyperglycaemia associated with diabetes is, of itself, causal in the development of endothelial dysfunction (ED) which is recognised to be the critical determinant in the development of CVD. It is further recognised that epigenetic modifications associated with changes in gene expression are causal in both the initiation of ED and the progression to CVD. Understanding whether and how hyperglycaemia induces epigenetic modifications therefore seems crucial in the development of preventative treatments. A mechanistic link between energy metabolism and epigenetic regulation is increasingly becoming explored as key energy metabolites typically serve as substrates or co-factors for epigenetic modifying enzymes. Intriguing examples are the ten-eleven translocation and Jumonji C proteins which facilitate the demethylation of DNA and histones respectively. These are members of the 2-oxoglutarate-dependent dioxygenase superfamily which require the tricarboxylic acid metabolite, α-ketoglutarate and molecular oxygen (O2) as substrates and Fe (II) as a co-factor. An understanding of precisely how the biochemical effects of high glucose exposure impact upon cellular metabolism, O2 availability and cellular redox in endothelial cells (ECs) may therefore elucidate (in part) the mechanistic link between hyperglycaemia and epigenetic modifications causal in ED and CVD. It would also provide significant proof of concept that dysregulation of the epigenetic landscape may be causal rather than consequential in the development of pathology.

Cardiorenal protection with SGLT2: Lessons from the cardiovascular outcome trials

Sodium glucose cotransporter 2 (SGLT2) inhibitors are a class of drugs that were primarily developed for the treatment of type 2 diabetes mellitus. However, these agents have shown to provide additional beneficial effects. We will discuss three main topics regarding the use of SGLT2 inhibitors: noncardiovascular effects, cardiovascular benefits, and novel clinical indications. Multiple clinical trials and preliminary studies across varying disciplines have shown that these agents exhibit cardiorenal-protective benefits, retinoprotective benefits, and may aid in weight loss without causing marked hypoglycemia. Therefore, these agents represent an avenue in clinical practice to manage comorbid conditions in the hyperglycemic patient. Because of their multifaceted effects and robust action, SGLT2 inhibitors represent therapy options for providers that not only provide beneficial clinical results but also reduce total patient drug burden.

Context-Dependent Regulation of Nrf2/ARE Axis on Vascular Cell Function during Hyperglycemic Condition

Diabetes mellitus is associated with an increased risk of micro and macrovascular complications. During hyperglycemic conditions, endothelial cells and vascular smooth muscle cells are exquisitely sensitive to high glucose. This high glucose-induced sustained reactive oxygen species production leads to redox imbalance, which is associated with endothelial dysfunction and vascular wall remodeling. Nrf2, a redox-regulated transcription factor plays a key role in the antioxidant response element (ARE)-mediated expression of antioxidant genes. Although accumulating data indicate the molecular mechanisms underpinning the Nrf2 regulated redox balance, understanding the influence of the Nrf2/ARE axis during hyperglycemic condition on vascular cells is paramount. This review focuses on the context-dependent role of Nrf2/ARE signaling on vascular endothelial and smooth muscle cell function during hyperglycemic conditions. This review also highlights improving the Nrf2 system in vascular tissues, which could be a potential therapeutic strategy for vascular dysfunction.

Myocardial Adaptation in Pseudohypoxia: Signaling and Regulation of mPTP via Mitochondrial Connexin 43 and Cardiolipin

Therapies intended to mitigate cardiovascular complications cannot be applied in practice without detailed knowledge of molecular mechanisms. Mitochondria, as the end-effector of cardioprotection, represent one of the possible therapeutic approaches. The present review provides an overview of factors affecting the regulation processes of mitochondria at the level of mitochondrial permeability transition pores (mPTP) resulting in comprehensive myocardial protection. The regulation of mPTP seems to be an important part of the mechanisms for maintaining the energy equilibrium of the heart under pathological conditions. Mitochondrial connexin 43 is involved in the regulation process by inhibition of mPTP opening. These individual cardioprotective mechanisms can be interconnected in the process of mitochondrial oxidative phosphorylation resulting in the maintenance of adenosine triphosphate (ATP) production. In this context, the degree of mitochondrial membrane fluidity appears to be a key factor in the preservation of ATP synthase rotation required for ATP formation. Moreover, changes in the composition of the cardiolipin’s structure in the mitochondrial membrane can significantly affect the energy system under unfavorable conditions. This review aims to elucidate functional and structural changes of cardiac mitochondria subjected to preconditioning, with an emphasis on signaling pathways leading to mitochondrial energy maintenance during partial oxygen deprivation.

Fetal hypoxia and hyperglycemia in the formation of phenytoin-induced cleft lip and maxillary hypoplasia

OBJECTIVE

Phenytoin exposure during the first trimester of pregnancy increases the risk of maxillary hypoplasia and cleft lip. The etiology of phenytoin embryopathy is unknown. Interestingly, phenytoin is also known to induce hyperglycemia in humans as well as rats. This study uses a rat model of fetal phenytoin syndrome to examine the role of hyperoxia, hyperglycemia, and arachidonic acid deficiency in the development of cleft lip and maxillary hypoplasia.

METHODS

Pregnant rats were dosed with phenytoin during the critical period of lip development (day 11 of pregnancy) with or without supplemental oxygen, insulin, or arachidonic acid. The fetuses from all studies were examined at term.

RESULTS

The frequency of cleft lip and maxillary hypoplasia was reduced by treating dams at the time of phenytoin exposure with either increased oxygen or insulin. However, in fetuses from phenytoin-treated dams dosed with arachidonic acid, the incidence of severe lip deformities remained the same although there was an increase in normal and mildly affected fetuses. Interestingly, this occurred in embryos from hyperglycemic dams.

SIGNIFICANCE

Together, the results from these experiments suggest phenytoin-induced malformations may be a multifactorial process as malformations were not solely linked to a hyperglycemic state of the dam.

NFE2/miR-423-5p/TFF1 axis regulates high glucose-induced apoptosis in retinal pigment epithelial cells

Background

A study has shown that miR-423-5p is highly expressed in proliferative diabetic retinopathy. However, the exact biological functions and mechanisms of miR-423-5p in diabetic retinopathy (DR) progression are currently unclear. This study aimed to investigate the role of miR-423-5p in DR and the underlying mechanism.

Results

Our data demonstrate that the expression of miR-423-5p is significantly increased in HG-induced RPE cells and DR patient plasma. Moreover, the overexpression of miR-423-5p exacerbates HG-induced apoptosis. Mechanistically, our results provide evidence that miR-423-5p directly targets TFF1. MiR-423-5p exerts its effect on HG-induced apoptosis in RPE cells through TFF1, and the NF-κB pathway is involved in the regulatory mechanism. Further analysis revealed that the transcription factor NFE2 regulates miR-423-5p promoter activity. In addition, NFE2 regulates the levels of TFF1 and NF-κB pathway-associated proteins by regulating the expression of miR-423-5p.

Conclusion

The NFE2-miR-423-5p-TFF1 axis is a novel molecular mechanism and provides a new direction for the study and treatment of DR.

Hexokinase-2 Glycolytic Overload in Diabetes and Ischemia-Reperfusion Injury

Hexokinase-2 (HK2) was recently found to produce increased metabolic flux through glycolysis in hyperglycemia without concurrent transcriptional or other functional regulation. Rather, stabilization to proteolysis by increased glucose substrate binding produced unscheduled increased glucose metabolism in response to high cytosolic glucose concentration. This produces abnormal increases in glycolytic intermediates or glycolytic overload, driving cell dysfunction and vulnerability to the damaging effects of hyperglycemia in diabetes, explaining tissue-specific pathogenesis. Glycolytic overload is also activated in ischemia-reperfusion injury and cell senescence. A further key feature is HK2 displacement from mitochondria by increased glucose-6-phosphate concentration, inducing mitochondrial dysfunction and oxidative stress. This pathogenic mechanism suggested new targets for therapeutics development that gave promising outcomes in initial clinical evaluation.

Metabolic characterization of diabetic retinopathy: An 1H-NMR-based metabolomic approach using human aqueous humor

Patients with a long duration of diabetes mellitus (DM) usually have accompanied complications such as diabetic retinopathy (DR), which is a leading cause of blindness and visual impairment among working-age persons in developed countries; nevertheless, some patients have no complications. Thus, various studies, including genomic, transcriptomic, and proteomic studies, have been conducted to identify potential biomarkers for predicting DR and to reveal the underlying disease mechanism. Although metabolomics could be a powerful tool for characterizing aqueous eye fluids and revealing the metabolic signatures of common ocular diseases such as DR, studies about its relationship with DR are limited. Moreover, to our knowledge, no previous study has applied a metabolomic approach to investigate the aqueous humor in DR. Therefore, we performed an NMR-based metabolomic study of the aqueous humor of patients with DM and cataract (DM, n = 13), DR and cataract (DR, n = 14), and senile cataract (CON, n = 7) to investigate the metabolic alterations accompanying the development of DR. Principal component analysis, average change analysis, and heatmap analysis revealed that lactate, succinate, 2-hydroxybutyrate, asparagine, dimethylamine, histidine, threonine, and glutamine were the most altered metabolites that potentially play roles in the development and progression of DR. The highly activated alanine, aspartate, and glutamate metabolic pathway was selected using pathway analysis. The phenotypic metabolomic analyses of the aqueous humor indicated an alteration in the metabolic pathways of energy metabolism and amino acids in DR patients which was to some extent suggestive of the pathophysiological process of mitochondrial dysfunction and oxidative stress/endothelial damage. It provides a proof of concept that metabolomic analysis using the aqueous humor of DM patients may be a reliable method to improve the accuracy of predicting the development and progression of DR.

Enhanced ROBO4 is mediated by up-regulation of HIF-1α/SP1 or reduction in miR-125b-5p/miR-146a-5p in diabetic retinopathy

Retinal cell damage caused by diabetes leads to retinal microvascular injury. Roundabout 4 (ROBO4) is involved in angiogenesis, which varies with the development of diabetic retinopathy (DR). Here, we explored the transcriptional regulation and microRNA‐mediated modulation of ROBO4 expression and related retinal cell function in DR. A streptozotocin‐induced type I diabetic animal model was established to detect the expression of hypoxia inducible factor‐1α (HIF‐1α), specificity protein 1 (SP1) and ROBO4. Retinal pigment epithelium (RPE) cells were cultured under hyperglycaemia or hypoxia and used for mechanistic analysis. Furthermore, roles of miR‐125b‐5p and miR‐146a‐5p were evaluated, and their targets were identified using luciferase assays. The cell functions were evaluated by MTS assays, permeability analysis and migration assays. The development of DR increased the levels of HIF‐1α, SP1 and ROBO4 both in the DR model and in hyperglycaemic/hypoxic RPE cells. They were co‐expressed and up‐regulated in diabetic retinas and in RPE cells under hyperglycaemia/hypoxia. Knockdown of HIF‐1α significantly inhibited SP1 and ROBO4, whereas SP1 down‐regulation abolished ROBO4 expression in RPE cells under hyperglycaemia/hypoxia. miR‐125b‐5p and miR‐146a‐5p were down‐regulated by hyperglycaemia and/or hypoxia. Up‐regulation of miRNAs reversed these changes and resulted in recovery of target gene expression. Moreover, luciferase assays confirmed miR‐125b‐5p targeted SP1 and ROBO4, and miR‐146a‐5p targeted HIF‐1α and ROBO4 directly. The decreased cell viability, enhanced permeability, and increased cell migration under DR conditions were mitigated by knockdown of HIF‐1α/SP1/ROBO4 or up‐regulation of miR‐125b‐5p/miR‐146a‐5p. In general, our results identified a novel mechanism that miR‐125b‐5p/miR‐146a‐5p targeting HIF‐1α/SP1‐dependent ROBO4 expression could retard DR progression.

miRNA-451a regulates RPE function through promoting mitochondrial function in proliferative diabetic retinopathy

The purpose of this study was to explore the role of microRNA-451a (miR-451a) in diabetic retinopathy through activating transcription factor 2 (ATF2). The epiretinal membrane samples from patients with proliferative diabetic retinopathy (PDR) were immunolabeled with an antibody for Ki-67 to identify the proliferative cells. The expression of miR-451a was measured by qRT-PCR in the retina of Akita mice and in RPE cells under diabetic conditions. The potential downstream targets of miR-451a were predicted by bioinformatics and confirmed by dual luciferase assay, qRT-PCR, and Western blotting. Mitochondrial function, cell proliferation, and migration assays were used to detect the functional change after transfection of miR-451a mimic and inhibitor. Proliferative RPE cells were identified in the epiretinal membrane from PDR patients. The expression of miR-451a was downregulated both in the retina of Akita mice and 4-hydroxynonenal (4-HNE)-treated RPE cells. Bioinformatic analysis and luciferase assay identified ATF2 as a potential target of miR-451a. miR-451a inhibited proliferation and migration of RPE cells. The mitochondrial function was enhanced by miR-451a mimic, but suppressed by miR-451a inhibitor. In diabetic conditions, miR-451a showed a protective effect on mitochondrial function. The results of qRT-PCR and Western blotting revealed that overexpression of miR-451a downregulated the expression of ATF2 and its downstream target genes CyclinA1, CyclinD1, and MMP2. In conclusion, miR-451a/ATF2 plays a vital role in the regulation of proliferation and migration in RPE cells through regulation of mitochondrial function, which may provide new perspectives for developing effective therapies for PDR.

Imbalance between pro-apoptotic and pro-survival factors in human retinal pericytes in diabetic-like conditions

PURPOSE

Loss of pericytes is one the key events in the pathogenesis of diabetic retinopathy. We have previously demonstrated that human retinal pericytes (HRP) are more vulnerable to intermittent than stable high glucose concentrations, with an increase in apoptosis. Our aim was to explore the expression of molecules involved in pro-apoptotic and survival pathways in pericytes cultured in stable/intermittent high glucose and/or hypoxia, to clarify the mechanisms of action of these diabetic-like stressing stimuli.

METHODS

Human retinal pericytes (HRP) were exposed intermittently at 48-hr intervals to high/physiological glucose for 8 days (intHG) and/or hypoxia over the last 48 hr. Control cells were kept in stable physiological and high glucose. Cell proliferation and apoptosis were assessed. The expression of pro-apoptotic and pro-survival molecules was evaluated by Western blotting. Caspase-8 translocation from the cytoplasm into the nucleus was checked by Western blotting of nuclear versus cytoplasmic fractions and immunofluorescence.

RESULTS

Hypoxia, alone and combined with intHG, increased HRP apoptosis and decreased proliferation. Pro-apoptotic molecules increased in HRP cultured in these conditions, while some survival markers decreased. Conversely, in stable HG, pro-apoptotic molecules were stable or even decreased, and survival factors increased. Translocation of caspase-8 from cytoplasm into nucleus indicates a primary role for this molecule in inducing apoptosis.

CONCLUSION

Diabetic-like conditions are able to stimulate pericyte apoptosis through activation of pro-apoptotic molecules, leading to an imbalance between pro-apoptotic and survival signalling pathways, with caspase-8 playing a pivotal role. Our identification of such intermediates could help finding new therapeutic approaches for the prevention of diabetic retinopathy.

Hyperglycemia induced early growth response-1 regulates vascular dysfunction in human retinal endothelial cells

Early growth response-1 (Egr-1) protein upregulation is reported in diabetes and vascular disorders. This study aims at deciphering its role in hyperglycemia induced changes of retinal endothelium. Human retinal endothelial cells (hRECs) were exposed to hyperglycemia (25mM) and normoglycemia (5.5mM). Gene silencing was done using siRNA against Egr-1. Transcript and protein level analysis of Egr-1 and gene targets were done using qPCR and immunoblotting respectively in hRECs, diabetic and nondiabetic human retina and immunofluorescence for localization in retinal sections. Hyperglycemia induced Egr-1 and vascular endothelial growth factor-A (VEGF-A) but not pigment epithelium derived factor (PEDF) in hRECs. Expression of Egr-1 repressor NGFI-A binding protein-2 (NAB-2) was unaltered. Egr-1 downstream gene targets, tissue factor (TF) and intercellular adhesion molecule-1 (ICAM-1) expression were increased in hRECs which was reduced by Egr-1 silencing in hyperglycemia. Diabetic retina, showed an increase in Egr-1, VEGF-A and gene target TF, ICAM-1 but not NAB-2 and PEDF similar to the changes seen in hyperglycemic hRECs. Hyperglycemic induction of Egr-1 and absence of NAB-2 repression in retinal endothelium, up-regulates downstream genes involved in pro-thrombotic and pro-inflammatory pathways linking Egr-1 in diabetes mediated vascular aberration of retina.

Biochemical Gas Sensors (Biosniffers) Using Forward and Reverse Reactions of Secondary Alcohol Dehydrogenase for Breath Isopropanol and Acetone as Potential Volatile Biomarkers of Diabetes Mellitus

This study describes two biosniffers to determine breath acetone and isopropanol (IPA) levels and applies them for breath measurement in healthy subjects and diabetic patients. Secondary alcohol dehydrogenase (S-ADH) can reduce acetone and oxidize nicotinamide adenine dinucleotide (NADH to NAD⁺) in a weak acid environment. NADH can be excited by 340 nm excitation lights and subsequently emit 490 nm fluorescence. Therefore, acetone can be measured by the decrease in NADH fluorescence intensity. S-ADH can also oxidize IPA and reduce NAD⁺ to NADH when it is in an alkaline environment. Thus, IPA can be detected by the increase of fluorescence. The developed biosniffers show rapid response, high sensitivity and high selectivity. The breath acetone and IPA analysis in healthy subjects shows that the mean values were 750.0 ± 434.4 ppb and 15.4 ± 11.3 ppb. Both acetone and IPA did not show a statistical difference among different genders and ages. The breath acetone analysis for diabetic patients shows a mean value of 1207.7 ± 689.5 ppb, which was higher than that of healthy subjects (p < 1 × 10^-6). In particularly, type-1 diabetic (T1D) patients exhaled a much higher concentration of acetone than type-2 diabetic (T2D) patients (p < 0.01). The breath IPA also had a higher concentration in diabetic patients (23.1 ± 20.1 ppb, p < 0.01), but only T2D patients presented a statistical difference (23.9 ± 21.3 ppb, p < 0.01). These findings are worthwhile in the study of breath biomarkers for diabetes mellitus diagnosis. Additionally, the developed biosniffers provide a new technique for volatolomics research.

Effect of thiamine pyrophosphate on retinopathy induced by hyperglycemia in rats: A biochemical and pathological evaluation

Purpose:

Information is lacking on the protective effects of thiamine pyrophosphate (TPP) against hyperglycemia-induced retinopathy in rats. This study investigated the biochemical and histopathological aspects of the effect of TPP on hyperglycemia-induced retinopathy induced by alloxan in rats.

Materials and Methods:

The rats were separated into a diabetic TPP-administered group (DTPG), a diabetes control group (DCG) and a healthy group (HG). While the DTPG was given TPP, the DCG and HG were administered distilled water as a solvent at the same concentrations. This procedure was repeated daily for 3 months. At the end of this period, all of the rats were euthanized under thiopental sodium anesthesia, and biochemical and histopathological analyses of the ocular retinal tissues were performed. The results of the DTPG were compared with those of the DCG and HG.

Results:

TPP prevented hyperglycemia by increasing the amount of malondialdehyde and decreasing endogen antioxidants, including total glutathione, glutathione reductase, glutathione S-transferase and superoxide dismutase. In addition, the amounts of the DNA oxidation product 8-hydroxyguanine were significantly lower in the retinas of the DTPG compared to the DCG. In the retinas of the DCG, there was a marked increase in vascular structures and congestion, in addition to edema. In contrast, little vascularization and edema were observed in the DTPG, and there was no congestion. The results suggest that TPP significantly reduced the degree of hyperglycemia-induced retinopathy.

Conclusions:

The results of this study indicate that TPP may be useful for prophylaxis against diabetic retinopathy.

miR-15a/16 inhibits TGF-beta3/VEGF signaling and increases retinal endothelial cell barrier proteins

Hyperglycemia is a significant risk factor for diabetic retinopathy and induces multiple biochemical changes, including inflammation and endothelial dysfunction in the retina. Alterations in microRNA expression have been implicated in the pathological responses of diabetic retinopathy and the manipulation of microRNA may provide powerful strategy for therapeutics. Among the predicted targets of miR-15a and -16 are TGF-beta3, SMAD2/3, and VEGF, all of which are known to play a role in vascular endothelial functions. The purpose of this study was to investigate the hypothesis that miR-15a/16 inhibits TGF-beta3/VEGF signaling to maintain retinal endothelial cell barrier protein levels. Human primary retinal endothelial cells (REC) were maintained in normal (5mM) glucose or transferred to high glucose medium (25mM) for 3days. REC were transfected with miRNA mimics (hsa-miR-15a-5p and -16-5p). Retinal lysates from miR-15a-transgenic mice were also analyzed. We demonstrated that overexpression of miR-15a/16 resulted in decreased TGF-beta3 signaling and VEGF levels in cultured REC grown in high glucose conditions. In addition, the levels of tight junction proteins, zonula occludens-1 (ZO-1) and occludin, were elevated in REC following overexpression of miR-15a and -16. Overexpression of miR-15a and -16 played a role in reducing cellular permeability through inhibition of VEGF signaling in REC cultured under high glucose conditions. Using miR-15a-transgenic mice, we demonstrated the regulatory role of miR-15a on TGF-beta3 signaling and tight junction proteins in vivo. Our outcomes suggest that miR-15a/16 maintain the retinal endothelial cell barrier by reducing TGFbeta3/VEGF signaling and increasing levels of key tight junction proteins.

Hyperlipidemia-Mediated Increased Advanced Lipoxidation End Products Formation, an Important Factor Associated with Decreased Erythrocyte Glucose-6-Phosphate Dehydrogenase Activity in Mild Nonproliferative Diabetic Retinopathy

OBJECTIVES

The present study aimed to evaluate the role of hyperlipidemia in increased formation of advanced lipoxidation end products (ALEs) and to evaluate whether there is any relationship between ALEs generation and erythrocyte glucose-6-phosphate dehydrogenase (G6PD) activity in cases of mild nonproliferative diabetic retinopathy (MNPDR).

METHODS

In this study, we enrolled 100 patients with type 2 diabetes and MNPDR, 100 subjects with type 2 diabetes but without retinopathy (DNR) and 90 normal individuals without diabetes as healthy controls (HCs). Erythrocyte nicotinamide dinucleotide phosphate (NADPH), G6PD activity, serum total cholesterol, low- and high-density lipoprotein (LDL, HDL) and triglyceride levels were determined by photometric assay. Serum malondialdehyde (MDA) protein adduct and hexanoyl-lysine (HEL) were measured by an enzyme-linked immunosorbent assay (ELISA).

RESULTS

A robust linear relationship was observed between MDA protein adduct and LDL or cholesterol or triglyceride levels, and HEL and LDL or cholesterol or triglyceride levels in subjects with MNPDR (p=0.0001). A significant inverse association was observed between erythrocyte G6PD activity and serum MDA protein adductor HEL levels in subjects with MNPDR (p=0.0001).

CONCLUSIONS

Hyperlipidemia is an important factor that is associated with increased ALEs formation in persons with MNPDR. Increased ALEs generation was associated with decreased G6PD activity and low NADPH levels in cases of MNPDR, suggesting their detrimental role in the occurrence of early NPDR.

Gene expression and histopathological evaluation of thiamine pyrophosphate on optic neuropathy induced with ethambutol in rats

AIM

To compare the effects of thiamine pyrophosphate (TPP) and thiamine (TM) in oxidative optic neuropathy in rats induced by ethambutol.

METHODS

The animals were divided into four groups: a control group (CG), an ethambutol control (ETC) group, TM plus ethambutol group (TMG), and TPP plus ethambutol group (TPPG). One hour after intraperitoneal administration of TM 20 mg/kg to the TMG group and TPP 20 mg/kg to TPPG group, 30 mg/kg ethambutol was given via gavage to all the groups but the CG. This procedure was repeated once daily for 90d. After that period, all rats were exposed to high levels of anaesthesia in order to investigate the gene expression of malondialdehyde and glutathione in removed optic nerve tissue and histopathologically to examine these tissues.

RESULTS

Malondialdehyde gene expression significantly increased, whereas glutathione gene expression significantly decreased in the ETC group compared to the CG. TM could not prevent the increase of malondialdehyde gene expression and the decrease of glutathione, while TPP significantly could suppress. Histopathologically, significant vacuolization in the optic nerve, single-cell necrosis in the glial cells, and a decrease in oligodendrocytes were observed in the ETC group. Vacuolization in the optic nerve, a decrease in oligodendrocytes and single-cell necrosis were found in the TMG group, while no pathological finding was observed in the TPPG group except for mild vacuolization.

CONCLUSION

TPP protects the optic nerve against the ethambutol-induced toxicity but TM does not. TPP can be beneficial in prophilaxis of optic neuropathy in ethambutol therapy.

Cysteine‑rich 61 RNA interference inhibits pathological angiogenesis via the phosphatidylinositol 3‑kinase/Akt‑vascular endothelial growth factor signaling pathway in endothelial cells

Hypoxia is a key factor in the pathogenesis of angiogenesis, and cysteine‑rich 61 (CCN1), an angiogenic factor, is involved in the development of pathological angiogenesis. The aim of the present study was to investigate the mechanism of CCN1 RNA interference (RNAi)‑induced inhibition of hypoxia‑induced pathological angiogenesis in endothelial cells. Human umbilical vein endothelial cells (HUVECs) were cultured under hypoxic conditions in vitro. The effects of inhibiting phosphoinositide 3‑kinase (PI3K)/Akt signaling using LY294002 were investigated in hypoxic HUVECs. The proliferation and apoptosis of HUVECs under hypoxia were assessed using CCN1 RNAi. The CCN1‑PI3K/Akt‑vascular endothelial growth factor (VEGF) pathway was analyzed under hypoxic conditions using reverse transcription‑quantitative polymerase chain reaction and western blotting. CCN1 RNAi inhibited the proliferation and induced the apoptosis of the HUVECs under hypoxia, with hypoxia significantly increasing the mRNA and protein expression levels of CCN1, Akt and VEGF. By contrast, CCN1 RNAi reduced the mRNA and protein expression levels of CCN1, Akt and VEGF in the HUVECs (P<0.05). Furthermore, LY294002 reduced the mRNA and protein expression levels of CCN1 in the hypoxic cells (P<0.05). These data indicated that CCN1 inhibits apoptosis and promotes proliferation in HUVECs. Therefore, CCN1 RNAi may offer a novel therapeutic strategy, which may aid in the treatment of pathological angiogenesis via inhibition of the PI3K/Akt‑VEGF pathway.

Functional Differences of Very-Low-Density Lipoprotein Receptor Splice Variants in Regulating Wnt Signaling

The very-low-density lipoprotein receptor (VLDLR) negatively regulates Wnt signaling. VLDLR has two major alternative splice variants, VLDLRI and VLDLRII, but their biological significance and distinction are unknown. Here we found that most tissues expressed both VLDLRI and VLDLRII, while the retina expressed only VLDLRII. The shed soluble VLDLR extracellular domain (sVLDLR-N) was detected in the conditioned medium of retinal pigment epithelial cells, interphotoreceptor matrix, and mouse plasma, indicating that ectodomain shedding of VLDLR occurs endogenously. VLDLRII displayed a higher ectodomain shedding rate and a more potent inhibitory effect on Wnt signaling than VLDLRI in vitro and in vivo O-glycosylation, which is present in VLDLRI but not VLDLRII, determined the differential ectodomain shedding rates. Moreover, the release of sVLDLR-N was inhibited by a metalloproteinase inhibitor, TAPI-1, while it was promoted by phorbol 12-myristate 13-acetate (PMA). In addition, sVLDLR-N shedding was suppressed under hypoxia. Further, plasma levels of sVLDLR-N were reduced in both type 1 and type 2 diabetic mouse models. We concluded that VLDLRI and VLDLRII had differential roles in regulating Wnt signaling and that decreased plasma levels of sVLDLR-N may contribute to Wnt signaling activation in diabetic complications. Our study reveals a novel mechanism for intercellular regulation of Wnt signaling through VLDLR ectodomain shedding.

Membrane flexibility, free fatty acids, and the onset of vascular and neurological lesions in type 2 diabetes

Free fatty acids released from human adipose tissue contain a limited amount of non-esterified poly-cis-unsaturated fatty acids. In cases of elevated plasma free fatty acids, this condition ultimately leads to a shift from unsaturated to saturated fatty-acyl chains in membrane phospholipids. Because this shift promotes the physical attractive van der Waals interactions between phospholipid acyl chains, it increases stiffness of both erythrocyte and endothelial membranes, which causes a reduction in both insulin-independent and insulin-dependent Class 1 glucose transporters, a reduction in cell membrane functionality, and a decreased microcirculatory blood flow which results in tissue hypoxia. Against the background of these processes, we review recently published experimental phospholipid data obtained from Drosophila melanogaster and from human erythrocytes of controls and patients with type 2 diabetes, with and without retinopathy, along the way free fatty acids interfere with eye and kidney function in patients with type 2 diabetes and give rise to endoplasmic reticulum stress, reduced insulin sensitivity, and ischemia.

Validation of RT-qPCR reference genes and determination of Robo4 expression levels in human retinal endothelial cells under hypoxia and/or hyperglycemia

Real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) has become the most common technique to investigate mRNA expression levels of target genes. In order to obtain accurate results, stable reference genes need to be selected for normalization in an experimental study. Human retinal endothelial cells (HREC) cultured in a hypoxic and hyperglycemic environment is a potential cell model to study diabetic retinopathy (DR), but the proper reference genes for RNA analysis have not yet been determined. In the present study, we evaluated the expression levels of 14 candidate housekeeping genes and selected the most suitable reference genes for RT-qPCR for HREC under hypoxic and/or hyperglycemic conditions. The results of the analyses using GeNorm, NormFinder, and BestKeeper software showed that a combination of TBP, PUM1, and ALAS1 was most suitable for this research. Based on these results, mRNA expression levels of Roundabout4 (Robo4) in HREC were determined. The RT-qPCR analysis showed that there was a significant increase in Robo4 expression under hyperglycemic conditions, while there was a decrease in expression under hypoxic and combined hypoxic and hyperglycemic conditions, suggesting that Robo4 might play different roles in various stages of DR.

Strong inhibition of the polyol pathway diverts glucose flux to protein glycation leading to rapid establishment of secondary complications in diabetes mellitus

BACKGROUND

Polyol pathway and protein glycation are implicated in establishing secondary complications in diabetes. Their relative contribution to the process needs to be evaluated. It is essential to understand why some aldose reductase inhibitors (ARIs) trials are successful while some have failed and to study their effect on protein glycation.

METHODS

Aldose reductase (AR) was assayed using xylose as substrate; protein glycation was evaluated using total and specific fluorescence, fructoseamine and protein bound carbonyl content (PCO) measurements. Long term studies were carried out on streptozotocin induced diabetic rats for evaluation of urine parameters, tissue fluorescence. Anti-cataract action was studied by lens culture studies.

RESULTS

Epalrestat, a commercial ARI was also found to possess potent glycation inhibitory action. Long term experiments revealed strong protein glycation with higher concentration of citronellol (ARI) demonstrating shift in glucose flux. Treatment with epalrestat and limonene revealed improved urine parameters and tissue fluorescence. Lens culture studies revealed cataract formation at higher inhibition of AR while no lens opacity was observed at lower citronellol concentration and with limonene and epalrestat.

CONCLUSION

Strong inhibition of AR shifts the glucose flux to protein glycation causing damage. ARIs possessing protein glycation inhibition are more useful in amelioration of secondary complications.

Diabetic complications within the context of aging: Nicotinamide adenine dinucleotide redox, insulin C-peptide, sirtuin 1-liver kinase B1-adenosine monophosphate-activated protein kinase positive feedback and forkhead box O3

Recent research in nutritional control of aging suggests that cytosolic increases in the reduced form of nicotinamide adenine dinucleotide and decreasing nicotinamide adenine dinucleotide metabolism plays a central role in controlling the longevity gene products sirtuin 1 (SIRT1), adenosine monophosphate‐activated protein kinase (AMPK) and forkhead box O3 (FOXO3). High nutrition conditions, such as the diabetic milieu, increase the ratio of reduced to oxidized forms of cytosolic nicotinamide adenine dinucleotide through cascades including the polyol pathway. This redox change is associated with insulin resistance and the development of diabetic complications, and might be counteracted by insulin C‐peptide. My research and others' suggest that the SIRT1–liver kinase B1–AMPK cascade creates positive feedback through nicotinamide adenine dinucleotide synthesis to help cells cope with metabolic stress. SIRT1 and AMPK can upregulate liver kinase B1 and FOXO3, key factors that help residential stem cells cope with oxidative stress. FOXO3 directly changes epigenetics around transcription start sites, maintaining the health of stem cells. ‘Diabetic memory’ is likely a result of epigenetic changes caused by high nutritional conditions, which disturb the quiescent state of residential stem cells and impair tissue repair. This could be prevented by restoring SIRT1–AMPK positive feedback through activating FOXO3.

miR-146a Attenuates Inflammatory Pathways Mediated by TLR4/NF-κB and TNFα to Protect Primary Human Retinal Microvascular Endothelial Cells Grown in High Glucose

Pathological mechanisms underlying diabetic retinopathy are still not completely understood. Increased understanding of potential cellular pathways responsive to hyperglycemia is essential to develop novel therapeutic strategies for diabetic retinopathy. A growing body of evidence shows that microRNA (miRNA) play important roles in pathological mechanisms involved in diabetic retinopathy, as well as possessing potential as novel therapeutic targets. The hypothesis of this study was that miR-146a plays a key role in attenuating hyperglycemia-induced inflammatory pathways through reduced TLR4/NF-κB and TNFα signaling in primary human retinal microvascular endothelial cells (REC). We cultured human REC in normal (5 mM) glucose or transferred to high glucose medium (25 mM) for 3 days. Transfection was performed on REC with miRNA mimic (hsa-miR-146a-5p). Our results demonstrate that miR-146a expression was decreased in human REC cultured in high glucose. Overexpression of miR-146a using mimics reduced the levels of TLR4/NF-κB and TNFα in REC cultured in high glucose. Both MyD88-dependent and -independent signaling were decreased by miR-146a overexpression in REC in high glucose conditions. The results suggest that miR-146a is a potential therapeutic target for reducing inflammation in REC through inhibition of TLR4/NF-κB and TNFα. Our study will contribute to understanding of diabetic retinal pathology, as well as providing important clues to develop therapeutics for clinical applications.