Intermittent high glucose enhances cell proliferation and VEGF expression in retinal endothelial cells: the role of mitochondrial reactive oxygen species

Short-term Glycemic Variability and Its Association With Macrovascular and Microvascular Complications in Patients With Diabetes

The introduction of continuous glucose monitoring inaugurated a new era in clinical practice by shifting the characterization of glycemic control from HbA1c to novel metrics. The one that gained widespread attention over the past decades was glycemic variability (GV), which typically refers to peaks and nadirs of blood glucose measured over a given time interval. GV can be dichotomized into two main categories: short-term and long-term. Short-term GV reflects within-day and between-day glycemic oscillations, and its contribution to diabetic complications remains an enigma. In this review, we summarize the available data about short-term GV and its possible association with both microvascular and macrovascular complications, evaluating different pathogenic mechanisms and demonstrating nonpharmaceutical, as well as pharmaceutical, therapeutic interventions.

Anti-angiogenic and antioxidant effects of axitinib in human retinal endothelial cells: implications in diabetic retinopathy

Diabetic retinopathy is a secondary microvascular complication of diabetes mellitus. This disease progresses from two stages, non-proliferative and proliferative diabetic retinopathy, the latter characterized by retinal abnormal angiogenesis. Pharmacological management of retinal angiogenesis employs expensive and invasive intravitreal injections of biologic drugs (anti-vascular endothelial growth factor agents). To search small molecules able to act as anti-angiogenic agents, we focused our study on axitinib, which is a tyrosine kinase inhibitor and represents the second line treatment for renal cell carcinoma. Axitinib is an inhibitor of vascular endothelial growth factor receptors, and among the others tyrosine kinase inhibitors (sunitinib and sorafenib) is the most selective towards vascular endothelial growth factor receptors 1 and 2. Besides the well-known anti-angiogenic and immune-modulatory functions, we hereby explored the polypharmacological profile of axitinib, through a bioinformatic/molecular modeling approach and in vitro models of diabetic retinopathy. We showed the anti-angiogenic activity of axitinib in two different in vitro models of diabetic retinopathy, by challenging retinal endothelial cells with high glucose concentration (fluctuating and non-fluctuating). We found that axitinib, along with inhibition of vascular endothelial growth factor receptors 1 (1.82 ± 0.10; 0.54 ± 0.13, phosphorylated protein levels in fluctuating high glucose vs . axitinib 1 µM, respectively) and vascular endothelial growth factor receptors 2 (2.38 ± 0.21; 0.98 ± 0.20, phosphorylated protein levels in fluctuating high glucose vs . axitinib 1 µM, respectively), was able to significantly reduce (p < 0.05) the expression of Nrf2 (1.43 ± 0.04; 0.85 ± 0.01, protein levels in fluctuating high glucose vs . axitinib 1 µM, respectively) in retinal endothelial cells exposed to high glucose, through predicted Keap1 interaction and activation of melanocortin receptor 1. Furthermore, axitinib treatment significantly (p < 0.05) decreased reactive oxygen species production (0.90 ± 0.10; 0.44 ± 0.06, fluorescence units in high glucose vs . axitinib 1 µM, respectively) and inhibited ERK pathway (1.64 ± 0.09; 0.73 ± 0.06, phosphorylated protein levels in fluctuating high glucose vs . axitinib 1 µM, respectively) in HRECs exposed to high glucose. The obtained results about the emerging polypharmacological profile support the hypothesis that axitinib could be a valid candidate to handle diabetic retinopathy, with ancillary mechanisms of action.

Oxidative stress in the eye and its role in the pathophysiology of ocular diseases

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

What is Glycaemic Variability and which Pharmacological Treatment Options are Effective? A Narrative Review

Glycated haemoglobin is currently used for diagnosis and follow-up of diabetes mellitus. However, it has important limitations; as it only reflects the average glycaemia over the last 3 months, it does not allow the identification of crucial events, such as episodes of hypoglycaemia and hyperglycaemia. Strict control of hyperglycaemia can result in severe hypoglycaemia that can be life threatening and can have important sequelae. Recently, the concept of glycaemic variability has been developed to provide information about the magnitude of glycaemic excursions and the duration of these fluctuations. This new approach has the potential to improve outcomes, decrease the risk of hypoglycaemia, and decrease cardiovascular risk. This review describes the most commonly prescribed non-insulin anti-diabetic drugs for diabetes management, their mechanism of action, and the existing evidence about their effectiveness in improving glycaemic variability and diabetes control.

Endogenous and Exogenous Regulation of Redox Homeostasis in Retinal Pigment Epithelium Cells: An Updated Antioxidant Perspective

The retinal pigment epithelium (RPE) performs a range of necessary functions within the neural layers of the retina and helps ensure vision. The regulation of pro-oxidative and antioxidant processes is the basis for maintaining RPE homeostasis and preventing retinal degenerative processes. Long-term stable changes in the redox balance under the influence of endogenous or exogenous factors can lead to oxidative stress (OS) and the development of a number of retinal pathologies associated with RPE dysfunction, and can eventually lead to vision loss. Reparative autophagy, ubiquitin-proteasome utilization, the repair of damaged proteins, and the maintenance of their conformational structure are important interrelated mechanisms of the endogenous defense system that protects against oxidative damage. Antioxidant protection of RPE cells is realized as a result of the activity of specific transcription factors, a large group of enzymes, chaperone proteins, etc., which form many signaling pathways in the RPE and the retina. Here, we discuss the role of the key components of the antioxidant defense system (ADS) in the cellular response of the RPE against OS. Understanding the role and interactions of OS mediators and the components of the ADS contributes to the formation of ideas about the subtle mechanisms in the regulation of RPE cellular functions and prospects for experimental approaches to restore RPE functions.

Association Between the Variability of Glycated Hemoglobin and Retinopathy in Patients with Type 2 Diabetes Mellitus: A Meta-Analysis

Visit-to-visit variability of glycated hemoglobin (HbA1c) is a marker of long-term glycemic fluctuation, which has been related to increased risk of macrovascular complications in patients with type 2 diabetes mellitus (T2DM). The association between HbA1c variability and retinopathy in patients with T2DM, however, has been inconsistent in previous studies. In order to fully evaluate the above association, we conducted a meta-analysis. Observational studies related to the aim of the meta-analysis were identified by search of PubMed, Web of Science, and Embase databases. Studies with HbA1c variability evaluated as the standard deviation (SD) and/or the coefficients of variation (CV) of HbA1c were included. The results were analyzed using a random-effects model that incorporated potential heterogeneity between studies. Twelve observational studies involving 44 662 T2DM patients contributed to the meta-analysis. Overall, 5150 (11.5%) patients developed retinopathy. Pooled results showed that compared to patients with lower HbA1c variability, T2DM patients with higher HbA1c-SD (relative risk [RR]: 1.48, 95% confidence interval [CI]: 1.24 to 1.78, p<0.001, I2=34%) and higher HbA1c-CV (RR: 1.29, 95% CI: 1.05 to 1.59, p=0.02, I2=0%) were both associated with higher risk of DR. For studies with HbA1c-SD, the association was not significantly affected by study characteristics such as country, study design, mean age, disease duration, adjustment of mean HbA1c, or quality scores (p for subgroup difference all>0.05). In conclusion, higher HbA1c variability may be associated with an increased risk of retinopathy in patients with T2DM.

Serum Metabolomics Reveals a Potential Benefit of Methionine in Type 1 Diabetes Patients with Poor Glycemic Control and High Glycemic Variability

Glycemic variability (GV) in some patients with type 1 diabetes (T1D) remains heterogeneous despite comparable clinical indicators, and whether other factors are involved is yet unknown. Metabolites in the serum indicate a broad effect of GV on cellular metabolism and therefore are more likely to indicate metabolic dysregulation associated with T1D. To compare the metabolomic profiles between high GV (GV-H, coefficient of variation (CV) of glucose ≥ 36%) and low GV (GV-L, CV < 36%) groups and to identify potential GV biomarkers, metabolomics profiling was carried out on serum samples from 17 patients with high GV, 16 matched (for age, sex, body mass index (BMI), diabetes duration, insulin dose, glycated hemoglobin (HbA1c), fasting, and 2 h postprandial C-peptide) patients with low GV (exploratory set), and another 21 (GV-H/GV-L: 11/10) matched patients (validation set). Subsequently, 25 metabolites were significantly enriched in seven Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways between the GV-H and GV-L groups in the exploratory set. Only the differences in spermidine, L-methionine, and trehalose remained significant after validation. The area under the curve of these three metabolites combined in distinguishing GV-H from GV-L was 0.952 and 0.918 in the exploratory and validation sets, respectively. L-methionine was significantly inversely related to HbA1c and glucose CV, while spermidine was significantly positively associated with glucose CV. Differences in trehalose were not as reliable as those in spermidine and L-methionine because of the relatively low amounts of trehalose and the inconsistent fold change sizes in the exploratory and validation sets. Our findings suggest that metabolomic disturbances may impact the GV of T1D. Additional in vitro and in vivo mechanistic studies are required to elucidate the relationship between spermidine and L-methionine levels and GV in T1D patients with different geographical and nutritional backgrounds.

Oxidative Regulation of Vascular Cav1.2 Channels Triggers Vascular Dysfunction in Hypertension-Related Disorders

Blood pressure is determined by cardiac output and peripheral vascular resistance. The L-type voltage-gated Ca²⁺ (Ca_v1.2) channel in small arteries and arterioles plays an essential role in regulating Ca²⁺ influx, vascular resistance, and blood pressure. Hypertension and preeclampsia are characterized by high blood pressure. In addition, diabetes has a high prevalence of hypertension. The etiology of these disorders remains elusive, involving the complex interplay of environmental and genetic factors. Common to these disorders are oxidative stress and vascular dysfunction. Reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria are primary sources of vascular oxidative stress, whereas dysfunction of the Ca_v1.2 channel confers increased vascular resistance in hypertension. This review will discuss the importance of ROS derived from NOXs and mitochondria in regulating vascular Ca_v1.2 and potential roles of ROS-mediated Ca_v1.2 dysfunction in aberrant vascular function in hypertension, diabetes, and preeclampsia.

Effect of troxerutin in counteracting hyperglycemia-induced VEGF upregulation in endothelial cells: a new option to target early stages of diabetic retinopathy?

Diabetic retinopathy (DR), one of the most common complications of diabetes mellitus, is characterized by degeneration of retinal neurons and neoangiogenesis. Until today, the pharmacological approaches for DR are limited and focused on counteracting the end-stage of this neurodegenerative disease, therefore efforts should be carried out to discover novel pharmacological targets useful to prevent DR development. Hyperglycemia is a major risk factor for endothelial dysfunction and vascular complication, which subsequently may trigger neurodegeneration. We previously demonstrated that, in the rat retina, hyperglycemia activates a new molecular cascade implicating, up-stream, protein kinase C βII (PKC βII), which in turn leads to a higher expression of vascular endothelial growth factor (VEGF), via the mRNA-binding Hu-antigen R (HuR) protein. VEGF is a pivotal mediator of neovascularization and a well-known vasopermeability factor. Blocking the increase of VEGF via modulation of this cascade can thus represent a new pharmacological option to prevent DR progression. To this aim, proper in vitro models are crucial for drug discovery, as they allow to better identify promising effective molecules. Considering that endothelial cells are key elements in DR and that hyperglycemia triggers the PKCβII/HuR/VEGF pathway, we set up two distinct in vitro models applying two different stimuli. Namely, human umbilical vein endothelial cells were exposed to phorbol 12-myristate 13-acetate, which mimics diacylglycerol whose synthesis is triggered by diabetic hyperglycemia, while human retinal endothelial cells were treated with high glucose for different times. After selecting the optimal experimental conditions able to determine an increased VEGF production, in search of molecules useful to prevent DR development, we investigated the capability of troxerutin, an antioxidant flavonoid, to counteract not only the rise of VEGF but also the activation of the PKCβII/HuR cascade in both in vitro models. The results show the capability of troxerutin to hinder the hyperglycemia-induced increase in VEGF in both models through PKCβII/HuR pathway modulation. Further, these data confirm the key engagement of this cascade as an early event triggered by hyperglycemia to promote VEGF expression. Finally, the present findings also suggest the potential use of troxerutin as a preventive treatment during the early phases of DR.

Retinitis Pigmentosa (RP): The Role of Oxidative Stress in the Degenerative Process Progression

Purpose: Retinitis Pigmentosa is a term that includes a group of inherited bilateral and progressive retinal degenerations, with the involvement of rod photoreceptors, which frequently leads to blindness; oxidative stress may be involved in the degeneration progression as proposed by several recent studies. The goal of this study is to evaluate whether circulating free radicals taken from capillary blood are related to one of the most important features of Retinitis pigmentosa that can affect frequently patients: cystoid macular oedema (CME). Materials: A total of 186 patients with Retinitis Pigmentosa (range: 25−69 years) were enrolled; all patients completed an ophthalmologic examination and SD-OCT at baseline and were divided into three subgroups according to the SD-OCT features. ROS blood levels were determined using FORT with monitoring of free oxygen radicals. Results: Test levels of free oxygen radicals were significantly increased, almost twice, in RP patients showing cystoid macular oedema and significantly increased compared to the control group. (p < 0.001). Discussion: Our findings suggest that oxidative stress may speed cone photoreceptors’ morphological damage (CMT); because long lasting oxidative stress in the RP may cause oxidative damage, with animal models of RP suggesting this is a micromolecular mechanism of photoreceptors’ (cone) death, it can be similar to cone damage in human RP eyes. The limitations of this paper are the relatively small sample, the horizontal design of the study, and the lack of data about the levels of ROS in the vitreous body.

Association between Variability of Metabolic Risk Factors and Cardiometabolic Outcomes

Despite strenuous efforts to reduce cardiovascular disease (CVD) risk by improving cardiometabolic risk factors, such as glucose and cholesterol levels, and blood pressure, there is still residual risk even in patients reaching treatment targets. Recently, researchers have begun to focus on the variability of metabolic variables to remove residual risks. Several clinical trials and cohort studies have reported a relationship between the variability of metabolic parameters and CVDs. Herein, we review the literature regarding the effect of metabolic factor variability and CVD risk, and describe possible mechanisms and potential treatment perspectives for reducing cardiometabolic risk factor variability.

The Role of Glycemic Variability in Cardiovascular Disorders

Diabetes mellitus (DM) is one of the most common and costly disorders that affect humans around the world. Recently, clinicians and scientists have focused their studies on the effects of glycemic variability (GV), which is especially associated with cardiovascular diseases. In healthy subjects, glycemia is a very stable parameter, while in poorly controlled DM patients, it oscillates greatly throughout the day and between days. Clinically, GV could be measured by different parameters, but there are no guidelines on standardized assessment. Nonetheless, DM patients with high GV experience worse cardiovascular disease outcomes. In vitro and in vivo studies showed that high GV causes several detrimental effects, such as increased oxidative stress, inflammation, and apoptosis linked to endothelial dysfunction. However, the evidence that treating GV is beneficial is still scanty. Clinical trials aiming to improve the diagnostic and prognostic accuracy of GV measurements correlated with cardiovascular outcomes are needed. The present review aims to evaluate the clinical link between high GV and cardiovascular diseases, taking into account the underlined biological mechanisms. A clear view of this challenge may be useful to standardize the clinical evaluation and to better identify treatments and strategies to counteract this DM aspect.

Glucose Variability: How Does It Work?

A growing body of evidence points to the role of glucose variability (GV) in the development of the microvascular and macrovascular complications of diabetes. In this review, we summarize data on GV-induced biochemical, cellular and molecular events involved in the pathogenesis of diabetic complications. Current data indicate that the deteriorating effect of GV on target organs can be realized through oxidative stress, glycation, chronic low-grade inflammation, endothelial dysfunction, platelet activation, impaired angiogenesis and renal fibrosis. The effects of GV on oxidative stress, inflammation, endothelial dysfunction and hypercoagulability could be aggravated by hypoglycemia, associated with high GV. Oscillating hyperglycemia contributes to beta cell dysfunction, which leads to a further increase in GV and completes the vicious circle. In cells, the GV-induced cytotoxic effect includes mitochondrial dysfunction, endoplasmic reticulum stress and disturbances in autophagic flux, which are accompanied by reduced viability, activation of apoptosis and abnormalities in cell proliferation. These effects are realized through the up- and down-regulation of a large number of genes and the activity of signaling pathways such as PI3K/Akt, NF-κB, MAPK (ERK), JNK and TGF-β/Smad. Epigenetic modifications mediate the postponed effects of glucose fluctuations. The multiple deteriorative effects of GV provide further support for considering it as a therapeutic target in diabetes.

Polyphenols from Penthorum chinense Pursh. Attenuates high glucose-induced vascular inflammation through directly interacting with Keap1 protein

ETHNOPHARMACOLOGICAL RELEVANCE

Penthorum chinense Pursh is used for promoting diuresis and alleviating "heat"-associated disorders, which were considered to be related to diabetic in Traditional Chinese Medicine (TCM).

AIMS OF THIS STUDY

Here, we aimed to evaluate the ability and underlying mechanism of the ethyl acetate fraction of Penthorum chinense Pursh stems (PSE) to inhibit vascular inflammation in high glucose (HG)-induced human umbilical vein endothelial cells (HUVEC cells).

MATERIALS AND METHODS

HUVEC cells were pre-treated with PSE following HG treatment. The cell viability, mitochondrial membrane potential (MMP), lactate dehydrogenase (LDH) levels, reactive oxygen species (ROS) generation were analyzed. Inflammatory, and antioxidant,-related proteins were analyzed using western blotting. Molecular docking and drug affinity targeting experiments (DARTS) were utilized to analyze and verify the binding of the Keap1 protein and polyphenols of PSE.

RESULTS

HG can significantly increase the activity of lactic dehydrogenase (LDH), destroy the mitochondrial membrane potential (MMP), and promote the generation of reactive oxygen species (ROS), while PSE treatment reversed these changes. Mechanistically, PSE inhibited NF-κB and inflammatory cytokines activation induced by HG through activating the expression of Nrf2 and its downstream antioxidant proteins Heme oxygenase-1 (HO-1), NAD (P)H Quinone Dehydrogenase 1 (NQO1), Glutamate cysteine ligase catalytic subunit (GCLC), Glutamate-cysteine ligase modifier (GCLM). Further study indicated that PSE activated Nrf2 antioxidant pathway mainly by the binding of primary polyphenols from PSE and the Keap1 protein.

CONCLUSION

Taken together, the present data highlight the health benefits of polyphenols from Penthorum chinense Pursh. regarding diabetes, proving it to be an important source of health care products. Besides, binding of the Keap1 protein may be an effective strategy to activate Nrf2 antioxidant pathway and prevent diabetes.

Combination therapy with semaglutide and rosiglitazone as a synergistic treatment for diabetic retinopathy in rodent animals

OBJECTIVE

To investigate the protective efficacies and potent mechanisms of combination therapy with semaglutide and rosiglitazone (RSG) on the high-glucose incubated human ARPE-19 cells and diabetic retinopathy (DR) model rats.

MAIN METHODS

The CCK-8 methods were used to evaluate the protective effects of semaglutide and RSG alone or combination on the cell viability of high-glucose treated ARPE-19 cells. After the DR rat model was established, the effects of combined treatment on general indexes, retinal morphological changes, retinal Müller cells as well as PI3K/Akt/MTOR related factors of DR model rats were investigated.

RESULTS

The CCK-8 assay showed obviously enhanced protective efficacies of combination therapy with semaglutide and RSG on the ARPE-19 with oxidative stress induced by high-glucose with combination index all below 1.5 demonstrating obvious synergistic effects. Combined incubation could also effectively decrease the expression of inflammatory factors, including TNF-α, IL-1β, IL-6, and the increase of ROS content in ARPE cell culture supernatant induced by high-glucose. Combined use of the antioxidant, PI3K/Akt and mTOR inhibitors, we further demonstrated that combined incubation of semaglutide and RSG could effectively by reduce high glucose-induced inflammatory injury inhibiting ROS/PI3K/Akt/mTOR signaling. Furthermore, chronic combination treatment effectively improved the histopathological characteristics and down-regulated the GFAP expression in Müller cells as well as PI3K/Akt/MTOR signaling pathway-related factors in retina which was better than any monomer treatment group.

CONCLUSIONS

Combined semaglutide with RSG exhibited synergistically protective efficacies on retinal cells by decreasing the GFAP expression, inhibiting oxidative stress and PI3K/Akt/MTOR signaling-transduction in DR model rats.

The relationship between glycemic variability and blood pressure variability in normoglycemic normotensive individuals

BACKGROUND AND AIM

Glycemic fluctuations around a mean glucose level, referred as glycemic variability and blood pressure variability (BPV) are considered as independent risk factors for cardiovascular diseases, all-cause mortality, and cardiovascular disease-mortality. With this background in mind, we aimed to investigate the association between glycemic variability and BPV and their association in normoglycemic and normotensive individuals.

MATERIALS AND METHOD

Twenty-seven normotensive normoglycemic individuals were recruited. Twenty-four hour Holter devices were utilized to measure ambulatory blood pressure (BP) while continuous glucose monitoring (CGM) devices were applied to measure glycemic variability simultaneously to the subjects. These devices were kept on for 48 h. For BP recordings, daytime, nighttime, and 24-h BP determinations, their mean and SD were calculated. From CGM measurements, mean blood glucose (MBG), SD of blood glucose, the mean amplitude of glycemic excursions (MAGE), the mean of daily differences (MODD), coefficient of variation (correction of variability for the MBG), and daytime and nighttime blood glucose were determined.

RESULTS

The mean age of the subjects was 23.8 ± 2.7 years and 66% were women (18/27). In the correlation analysis between glycemic variability parameters and BPV parameters, SD of 24-h SBP was correlated with the SD of MBG (r = 0.52, P = 0.006), MAGE (r = 0.49, P = 0.009), and MODD (r = 0.46, P = 0.015). SD of daytime SBP was correlated with, MAGE (r = 0.42, P = 0.03) and MODD (r = 0.43, P = 0.02).

CONCLUSION

We report correlation between glycemic variability and BPV variables in normoglycemic and normotensive healthy individuals.

The effect of a low glycaemic index diet on reducing day-long glycaemia in healthy young adults: A randomized crossover trial

AIM

To compare the effect of a low glycaemic index (LGI) diet on reducing day-long glycaemia with a macronutrient-matched high glycaemic index (HGI) diet, using customized meal delivery to ensure compliance.

MATERIALS AND METHODS

We conducted a single-blinded, randomized crossover trial in 14 healthy adults (57% female) with a mean ± SD age of 21.6 ± 1.7 years. A flash glucose monitoring sensor was installed on the subjects on day 1 to capture the interstitial glucose level every 15 minutes for 14 days. Subjects were randomized to receive an LGI (dietary GI = 40) or HGI (dietary GI = 60) diet (three meals and two snacks) from day 2 for 5 consecutive days, followed by a 2-day washout, then switched to the alternative diet for another 5 days. A paired t-test was used to test the differences in the incremental area under the curve (iAUC) of glucose, postprandial glucose (PPG) concentration and maximum postprandial glucose rise (MPGR) between the LGI and HGI periods.

RESULTS

Subjects had lower iAUC for average day-long glycaemia during the LGI intervention period compared with the HGI period (mean ± SD, 865 ± 297 vs. 1024 ± 267 mmol x min/L; P = .047). PPG for breakfast and snack 2, and MPGR for breakfast, snack 2 and dinner, were lower in the LGI period.

CONCLUSIONS

In young healthy adults, following an LGI diet resulted in lower average day-long glycaemia compared with a macronutrient-matched HGI diet. Our results support the use of LGI diets to reduce the risk of developing glucose intolerance.

NGF receptors and PI3K/AKT pathway involved in glucose fluctuation-induced damage to neurons and α-lipoic acid treatment

BACKGROUND

Glucose fluctuation promotes neuronal apoptosis, which plays a central role in diabetic encephalopathy (DE). Nerve growth factor (NGF), and its interaction with high-affinity (TrkA) and low-affinity (p75NTR) receptors, are involved in neuronal survival. NGF/TrkA contributes to the activation of the PI3K/AKT pathway, which is beneficial for neuronal survival, and α-Lipoic acid (ALA) exerts clinically favorable neuroprotective effects in the periphery. Whether NGF receptors and the PI3K/AKT pathway are involved in glucose fluctuation-induced neuronal damage, as well as the potential molecular mechanism of ALA in protecting glucose fluctuation-induced neuronal damage, remain unclear.

RESULTS

The results indicated that constant high glucose (CHG) and intermittent high glucose (IHG) significantly increased the expression of Bax and caspase-3, and decreased the expression of TrkA/p75NTR and p-AKT/AKT, while ALA stimulation reversed the above proteins in PC12 cells. IHG stimulates apoptosis more effectively than CHG in PC12 cells, which is related to the PI3K/AKT pathway but not to the TrkA/p75NTR. Furthermore, neuronal apoptosis induced by IHG was aggravated by the TrkA inhibitor K252a or the PI3K/AKT inhibitor LY294002, but this effect was alleviated by the p75NTR inhibitor TAT-pep5.

CONCLUSION

Glucose fluctuation induced cell apoptosis by regulating the TrkA/p75NTR and PI3K/AKT pathway, meanwhile ALA exhibited neuroprotective effects in response to IHG and CHG. These observations indicated that the PI3K/AKT pathway and the balance of TrkA/p75NTR are likely to serve as potential therapeutic targets for DE. In addition, ALA could be a possible therapeutic drug for DE.

Repetitive Intermittent Hyperglycemia Drives the M1 Polarization and Inflammatory Responses in THP-1 Macrophages Through the Mechanism Involving the TLR4-IRF5 Pathway

Repetitive intermittent hyperglycemia (RIH) is an independent risk factor for complications associated with type-2 diabetes (T2D). Glucose fluctuations commonly occur in T2D patients with poor glycemic control or following intensive therapy. Reducing blood glucose as well as glucose fluctuations is critical to the control of T2D and its macro-/microvascular complications. The interferon regulatory factor (IRF)-5 located downstream of the nutrient sensor toll-like receptor (TLR)-4, is emerging as a key metabolic regulator. It remains unclear how glucose fluctuations may alter the IRF5/TLR4 expression and inflammatory responses in monocytes/macrophages. To investigate this, first, we determined IRF5 gene expression by real-time qRT-PCR in the white adipose tissue samples from 39 T2D and 48 nondiabetic individuals. Next, we cultured THP-1 macrophages in hypo- and hyperglycemic conditions and compared, at the protein and transcription levels, the expressions of IRF5, TLR4, and M1/M2 polarization profile and inflammatory markers against control (normoglycemia). Protein expression was assessed using flow cytometry, ELISA, Western blotting, and/or confocal microscopy. IRF5 silencing was achieved by small interfering RNA (siRNA) transfection. The data show that adipose IRF5 gene expression was higher in T2D than nondiabetic counterparts (p = 0.006), which correlated with glycated hemoglobin (HbA1c) (r = 0.47/p < 0.001), homeostatic model assessment of insulin resistance (HOMA-IR) (r = 0.23/p = 0.03), tumor necrosis factor (TNF)-α (r = 0.56/p < 0.0001), interleukin (IL)-1β (r = 0.40/p = 0.0009), and C-C motif chemokine receptor (CCR)-2 (r = 0.49/p < 0.001) expression. IRF5 expression in macrophages was induced/upregulated (p < 0.05) by hypoglycemia (3 mM/L), persistent hyperglycemia (15 mM/L–25 mM/L), and RIH/glucose fluctuations (3–15 mM/L) as compared to normoglycemia (5 mM/L). RIH/glucose fluctuations also induced M1 polarization and an inflammatory profile (CD11c, IL-1β, TNF-α, IL-6, and monocyte chemoattractant protein (MCP)-1) in macrophages. RIH/glucose fluctuations also drove the expression of matrix metalloproteinase (MMP)-9 (p < 0.001), which is a known marker for cardiovascular complication in T2D patients. Notably, all these changes were counteracted by IRF5 silencing in macrophages. In conclusion, RIH/glucose fluctuations promote the M1 polarization and inflammatory responses in macrophages via the mechanism involving TLR4-IRF5 pathway, which may have significance for metabolic inflammation.

Effect of postprandial hyperglycemia at clinic visits on the incidence of retinopathy in patients with type 2 diabetes: An analysis using real-world long-term follow-up data

AIMS/INTRODUCTION

There is little evidence on the role of postprandial glycemia in the incidence of diabetic retinopathy (DR) in a real-world setting. We aimed to assess the effect of postprandial hyperglycemia at clinic visits on the incidence of DR in patients with type 2 diabetes, and whether its effect differs depending on glycated hemoglobin (HbA1c) values and age.

MATERIALS AND METHODS

Intrapersonal mean blood glucose levels at 1-2 h post-breakfast (1-2h-PBBG), post-lunch (1-2 h-PLBG) and both (1-2h-PBLBG) during 2 years from the first visit were used as baseline data. This retrospective cohort study enrolled 487, 323 and 406 patients who had 1-2h-PBLBG, 1-2h-PBBG and 1-2h-PLBG measurements, respectively. These three groups were followed from 1999 up through 2017.

RESULTS

DR occurred in 145, 92 and 126 patients in the 1-2h-PBLBG, 1-2h-PBBG and 1-2h-PLBG groups, respectively. Multivariate Cox regression analysis showed that the mean 1-2h-PBLBG, 1-2h-PBBG and 1-2h-PLBG levels were significant predictors of DR, independent of mean HbA1c. In patients with mean HbA1c <7.0% and those with a baseline age <60 years, the mean 1-2h-PBLBG, 1-2h-PBBG and 1-2h-PLBG levels were significant predictors.

CONCLUSIONS

Postprandial hyperglycemia at clinic visits might predict the incidence of DR, independent of HbA1c. The effect of postprandial hyperglycemia on DR is obvious in patients with well-controlled HbA1c and in younger patients. Even with the lower HbA1c level, correcting postprandial hyperglycemia is important for preventing DR, especially in middle-aged adults with type 2 diabetes.

Identification of potential molecular targets associated with proliferative diabetic retinopathy

BACKGROUND

This study aimed to identify and evaluate potential molecular targets associated with the development of proliferative diabetic retinopathy (DR).

METHODS

The microarray dataset "GSE60436" generated from fibrovascular membranes (FVMs) associated with proliferative DR was downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) from the active FVMs and control or inactive FVMs and control were evaluated and co-DEGs were identified using VEEN analysis. Functional enrichment analysis, and protein-protein interactions (PPI) network and module analyses were performed on the upregulated and downregulated coDEGs. Finally, several predictions regarding microRNAs (miRNAs) and transcription factors (TFs) were made to construct a putative TF-miRNA-target network.

RESULTS

A total of 1475 co-DEGs were screened in active/inactive FVM samples, including 461 upregulated and 1014 downregulated genes, which were enriched for angiogenesis [Hypoxia Inducible Factor 1 Subunit Alpha (HIF1A) and Placental Growth Factor (PGF)] and visual perception, respectively. In the case of the upregulated co-DEGs, Kinesin Family Member 11 (KIF11), and BUB1 Mitotic Checkpoint Serine/Threonine Kinase (BUB1) exhibited the highest values in both the PPI network and module analyses, as well as the genes related to mitosis. In the case of downregulated co-DEGs, several G protein subunits, including G Protein Subunit Beta 3 (GNB3), exhibited the highest values in both the PPI network and module analyses. The genes identified in the module analysis were found to be from the signal transduction-related pathways. In addition, we were able to identify four miRNAs and five TFs, including miR-136 and miR-374.

CONCLUSIONS

In brief, HIF1A, PGF, KIF11, G protein subunits, and miR-136, miR-374 may all be involved in angiogenesis, retinal endothelial cell proliferation, and visual signal transduction in proliferative DR. This study provides a number of novel insights that may aid the development of future studies dedicated to discovering novel therapeutic targets in proliferative DR.

Adipose-derived mesenchymal stromal cells reverse high glucose-induced reduction of angiogenesis in human retinal microvascular endothelial cells

BACKGROUND AIMS

Diabetic retinopathy (DR) is characterized by a progressive alteration of the retinal microvasculature, arising from microaneurysms to leaky vessels and finally abnormal neovascularization. The hyperglycemia-mediated loss of pericytes is a key event in vessel degeneration causing vascular destabilization. To overcome this, mesenchymal stromal cells (MSCs) have been tested as pericyte replacement in several animal models showing repair and regeneration of DR-damaged vasculature.

METHODS

We hypothesized that adipose-derived mesenchymal stromal cells (ASCs) resist high glucose-induced challenges and protect human retinal microvascular endothelial cells (HRMVECs) from glucose-mediated injury. ASCs and HRMVECs were cultured under normal-glucose (NG; 1 g/L) and high-glucose (HG; 4.5 g/L) conditions comparing their phenotype and angiogenic potential.

RESULTS

Whereas ASCs were generally unaffected by HG, HG caused a reduction of the angiogenic potential in HRMVEC. Indeed, HG-treated HRMVECs formed fewer vascular tube structures in a basement membrane angiogenesis assay. However, this was not observed in a direct ASC and HRMVEC coculture angiogenesis assay. Increased oxidative stress levels appeared to be linked to the HG-induced reduction of angiogenesis, which could be restored by ASC-conditioned medium and antioxidant treatment.

CONCLUSIONS

These findings suggest that ASC resist HG-stress whereas endothelial cell angiogenic capacity is reduced. Thus, ASC may be potentially therapeutically active in DR by restoring angiogenic deficits in retinal endothelial cells by the secretion of proangiogenic factors. However, these data also inquire for a thorough risk assessment about the timing of the ASC-based cell therapy, which can be considered advantageous at early stage of DR, but possibly detrimental at the late neo-angiogenic stage of DR.

Effect of basal insulin supplement therapy on diabetic retinopathy in short-duration type 2 diabetes: A one-year randomized parallel-group trial

BACKGROUND

In this study, we compared the effect on diabetic retinopathy (DR) between oral antidiabetic drugs (OADs) alone and in combination with basal insulin-supported OADs therapy (BOT). [Correction added on 11 November 2019, after first online publication: In Abstract under Background section, "DR" has been corrected into "diabetic retinopathy (DR)".] METHODS: Between January 2015 and January 2018, this study enrolled 290 patients (age 18-65 years) with diabetes duration between 0 and 5 years. Patients were randomly assigned to receive OADs or BOT after 14 days intensive insulin treatment. Examinations were performed at the beginning and end of the study.

RESULTS

Fewer patients developed DR in the BOT than OADs group (8 [6.06%] vs 12 [8.3%], respectively), and all cases of DR were non-proliferative. Blood glucose concentrations were higher in the BOT than OADs group at the 3rd month, but lower in the former at the 6th and 12th month. The rate of reaching target HbA1c ≤7% was lower in the BOT than OADs group at the 3rd month (63.6% vs 72.2%, respectively), similar between the two groups at the 6th month (60.6% vs 66.6%, respectively) and higher in the BOT group at the 12th month (75.0% vs 61.1%, respectively). The SD of fasting blood glucose (FBG), coefficient of variation of FBG, SD of blood glucose (SDBG), and mean amplitude of glycemic excursions were lower in the BOT than OADs group. Changes in the levels of three cytokines (interleukin [IL]-1β, IL-6, and IL-17α) were significantly less in the BOT than OADs group.

CONCLUSIONS

Twelve months of BOT decreased the incidence of DR in short-duration type 2 diabetes by reducing glycemia more effectively, stably, and completely than OADs alone.

Activation of retinal Müller cells in response to glucose variability

PURPOSE

In the earliest stages of diabetic retinopathy (DR), a dysfunction of Müller cells, characterized by high levels of glial fibrillary acidic protein (GFAP), and aquaporins (AQP), has been observed. Although chronic hyperglycemia causes the activation of Müller cells, the effect of glycemic fluctuations is yet unknown. The aim of the study was to analyze the impact of glucose variability on rat retinal Müller cells (rMC-1) adapted to either normal (5 mM) or high (25 mM) glucose levels.

METHODS

rMC-1 were cultured in a medium containing either 5 mM (N cells) or 25 mM of glucose (H cells) and then incubated for 96 h in a medium containing (a) low glucose (either 1-3 or 5 mM), (b) basal glucose (either 5 or 25 mM), (c) high glucose (either 25 or 45 mM), (d) basal and high glucose alternated every 24 h; (e) low- and high glucose alternated every 24 h; (f) basal glucose with episodes of low glucose for 30 min twice a day. Müller cells activation was evaluated by measuring the levels of GFAP, AQP4, and phospho-active extracellular signal-regulated kinase (pERK).

RESULTS

Under both basal and high glucose concentrations rMC-1 were viable, but their response to glucose excursions was different. In N cells kept under normal (5 mM) glucose, a significant glial activation was measured not only in response to constant high glucose but also to alternating low/high glucose. In H cells, adapted to 25 mM glucose, a significant response was observed only after exposition to a lower (5 mM) glucose concentration.

CONCLUSION

Our results highlight Müller cells activation in response to glucose variability and a different susceptibility depending on the basal glucose conditions.

Short-term exercise training reduces glycaemic variability and lowers circulating endothelial microparticles in overweight and obese women at elevated risk of type 2 diabetes

Exercise is recognized as a frontline therapy for the prevention and treatment of type 2 diabetes (T2D) but the optimal type of exercise is not yet determined. We compared the effects of high-intensity interval training (HIIT) with moderate-intensity continuous training (MICT) for improvement of continuous glucose monitoring (CGM)-derived markers of glycaemic variability, and biomarkers of endothelial cell damage (CD31+ and CD62+ endothelial microparticles (EMPs)) within a population at elevated risk of developing T2D. Fifteen inactive overweight or obese women were randomized to 2 weeks (10-sessions) of progressive HIIT (n = 8, 4-10X 1-min @ ∼90% peak heart rate, 1-min rest periods) or MICT (n = 7, 20-50 min of continuous activity at ∼65% peak heart rate). Prior and three days post-training, fasting blood samples were collected. Both HIIT and MICT improved glycaemic variability as measured by CGM standard deviation (HIIT: 0.82 ± 0.39 vs. 0.72 ± 0.33 mmol/L; MICT: 0.82 ± 0.19 vs. 0.62 ± 0.16 mmol/L, pre vs. post) and mean amplitude of glycaemic excursions (MAGE; HIIT: 1.98 ± 0.81 vs. 1.41 ± 0.90; MICT; 1.98 ± 0.43 vs. 1.65 ± 0.48, pre vs. post) with no difference between groups. CD62+ EMPs were lower following HIIT (187.7 ± 65 vs. 174.9 ± 55, pre vs. post) and MICT (170 ± 60 vs. 160.3 ± 59, pre vs. post) with no difference between groups. There was no change in 24-h mean glucose or CD31+ EMPs. Two weeks of both HIIT or MICT similarly decreased glycaemic variability and CD62+ EMPs in overweight/obese women at elevated risk of T2D.

Molecular Mechanisms of Glucose Fluctuations on Diabetic Complications

Accumulating evidence indicates the occurrence and development of diabetic complications relates to not only constant high plasma glucose, but also glucose fluctuations which affect various kinds of molecular mechanisms in various target cells and tissues. In this review, we detail reactive oxygen species and their potentially damaging effects upon glucose fluctuations and resultant downstream regulation of protein signaling pathways, including protein kinase C, protein kinase B, nuclear factor-κB, and the mitogen-activated protein kinase signaling pathway. A deeper understanding of glucose-fluctuation-related molecular mechanisms in the development of diabetic complications may enable more potential target therapies in future.

Reactive Oxygen Species-Mediated Damage of Retinal Neurons: Drug Development Targets for Therapies of Chronic Neurodegeneration of the Retina

The significance of oxidative stress in the development of chronic neurodegenerative diseases of the retina has become increasingly apparent in recent years. Reactive oxygen species (ROS) are free radicals produced at low levels as a result of normal cellular metabolism that are ultimately metabolized and detoxified by endogenous and exogenous mechanisms. In the presence of oxidative cellular stress, ROS are produced in excess, resulting in cellular injury and death and ultimately leading to tissue and organ dysfunction. Recent studies have investigated the role of excess ROS in the pathogenesis and development of chronic neurodegenerative diseases of the retina including glaucoma, diabetic retinopathy, and age-related macular degeneration. Findings from these studies are promising insofar as they provide clear rationales for innovative treatment and prevention strategies of these prevalent and disabling diseases where currently therapeutic options are limited. Here, we briefly outline recent developments that have contributed to our understanding of the role of ROS in the pathogenesis of chronic neurodegenerative diseases of the retina. We then examine and analyze the peer-reviewed evidence in support of ROS as targets for therapy development in the area of chronic neurodegeneration of the retina.

Models of retinal diseases and their applicability in drug discovery

INTRODUCTION

The impact of vision debilitating diseases is a global public health concern, which will continue until effective preventative and management protocols are developed. Two retinal diseases responsible for the majority of vision loss in the working age adults and elderly populations are diabetic retinopathy (DR) and age-related macular degeneration (AMD), respectively. Model systems, which recapitulate aspects of human pathology, are valid experimental modalities that have contributed to the identification of signaling pathways involved in disease development and consequently potential therapies. Areas covered: The pathology of DR and AMD, which serve as the basis for designing appropriate models of disease, is discussed. The authors also review in vitro and in vivo models of DR and AMD and evaluate the utility of these models in exploratory and pre-clinical studies. Expert opinion: The complex nature of non-Mendelian diseases such as DR and AMD has made identification of effective therapeutic treatments challenging. However, the authors believe that while in vivo models are often criticized for not being a 'perfect' recapitulation of disease, they have been valuable experimentally when used with consideration of the strengths and limitations of the experimental model selected and have a place in the drug discovery process.

The Comprehensive Glucose Pentagon: A Glucose-Centric Composite Metric for Assessing Glycemic Control in Persons With Diabetes

BACKGROUND

Composite metrics have the potential to provide more complete and clinically useful information about glycemic control than traditional individual metrics such as hemoglobin A1C, %/time/area under curve of hypoglycemia and hyperglycemia.

METHODS

Using five key metrics that are derived from continuous glucose monitoring, we developed a new, multicomponent composite metric, the Comprehensive Glucose Pentagon (CGP) that demonstrates glycemic control both numerically and visually. Two of its axes are composite metrics-the intensity of hypoglycemia and intensity of hyperglycemia. This approach eliminates the use of the surrogate marker, hemoglobin A1C (A1C), and replaces it with glucose-centric metrics.

RESULTS

We reanalyzed the data from two randomized control trials, the STAR 3 and ASPIRE In-Home studies using the CGP. It provided new insights into the effect of sensor-augmented pumping (SAP) in the STAR 3 trial and sensor-integrated pumping with low-glucose threshold suspend (SIP+TS) in the ASPIRE In-Home trial.

CONCLUSIONS

The CGP has the potential to enable health care providers, investigators and patients to better understand the components of glycemic control and the effect of various interventions on the individual elements of that control. This can be done on a daily, weekly, or monthly basis. It also allows direct comparison of the effects on different interventions among clinical trials which is not possible using A1C alone. This new composite metric approach requires validation to determine if it provides a better predictor of long-term outcomes than A1C and/or better predictor of severe hypoglycemia than the low blood glucose index (LBGI).

Does the ingestion of a 24 hour low glycaemic index Asian mixed meal diet improve glycaemic response and promote fat oxidation? A controlled, randomized cross-over study

BACKGROUND

The health benefits of consuming a low glycaemic index (GI) diet to reduce the risk of type 2 Diabetes are well recognized. In recent years the GI values of various foods have been determined. Their efficacy in constructing and consuming a low GI diet over 24 h in modulating glycaemic response has not been fully documented. The translation of using single-point GI values of foods to develop a 24 h mixed meal diet can provide valuable information to consumers, researchers and dietitians to optimize food choice for glycaemic control. By using GI values of foods to develop mixed meals, our study is the first to determine how both blood glucose and substrate oxidation may be modulated over 24 h.

METHODS

The study included 11 Asian men with a BMI between 17-24 kg/m² who followed both a 1-day low GI and 1-day high GI diet in a randomized, controlled cross-over design. Test meals included breakfast, lunch, snack and dinner. Glycaemic response was measured continuously for over 24 h and postprandial substrate oxidation for 10 h inside a whole body calorimeter.

RESULTS

The low GI diet resulted in lower 24 h glucose iAUC (860 ± 440 vs 1329 ± 614 mmol/L.min; p = 0.014) with lower postprandial glucose iAUC after breakfast (p < 0.001), lunch (p = 0.009), snack (p = 0.012) and dinner (p = 0.003). Moreover, 24 h mean amplitude of glycaemic excursion was lower during the low GI vs high GI diet (1.44 ± 0.63 vs 2.33 ± 0.82 mmol/L; p < 0.001). Simultaneously, decrease in 10 h fat oxidation was less during the low vs high GI diet (-0.033 ± 0.021 vs -0.050 ± 0.017 g/min; p < 0.001), specifically after breakfast (p < 0.001) and lunch (p < 0.001).

CONCLUSIONS

Our study corroborates that using low GI local foods to construct a 24 h low GI diet, is able to reduce glycaemic response and variability as recorded by continuous glucose monitoring. Our observations also confirm that a low GI diet promotes fat oxidation over carbohydrate oxidation when compared to a high GI diet. These observations provide public health support for the encouragement of healthier nutrition choices by consuming low GI foods.

TRIAL REGISTRATION

NCT 02631083 (Clinicaltrials.gov).

Redox regulation of gasotransmission in the vascular system: A focus on angiogenesis

Reactive oxygen species have emerged as key participants in a broad range of physiological and pathophysiological processes, not least within the vascular system. Diverse cellular functions which have been attributed to some of these pro-oxidants within the vasculature include the regulation of blood pressure, neovascularisation and vascular inflammation. We here highlight the emerging roles of the enzymatically-generated reaction oxygen species, O₂^- and H₂O₂, in the regulation of the functions of the gaseous signalling molecules: nitric oxide (NO), carbon monoxide (CO), and hydrogen sulphide (H₂S). These gasotransmitters are produced on demand from distinct enzymatic sources and in recent years it has become apparent that they are capable of mediating a number of homeostatic processes within the cardiovascular system including enhanced vasodilation, angiogenesis, wound healing and improved cardiac function following myocardial infarction. In common with O₂^- and/or H₂O₂ they signal by altering the functions of target proteins, either by the covalent modification of thiol groups or by direct binding to metal centres within metalloproteins, most notably haem proteins. The regulation of the enzymes which generate NO, CO and H₂S have been shown to be influenced at both the transcriptional and post-translational levels by redox-dependent mechanisms, while the activity and bioavailability of the gasotransmitters themselves are also subject to oxidative modification. Within vascular cells, the family of nicotinamide adenine dinucleotide phosphate oxidases (NAPDH oxidases/Noxs) have emerged as functionally significant sources of regulated O₂^- and H₂O₂ production and accordingly, direct associations between Nox-generated oxidants and the functions of specific gasotransmitters are beginning to be identified. This review focuses on the current knowledge of the redox-dependent mechanisms which regulate the generation and activity of these gases, with particular reference to their roles in angiogenesis.

Interpretation of metabolic memory phenomenon using a physiological systems model: What drives oxidative stress following glucose normalization?

Hyperglycemia is generally associated with oxidative stress, which plays a key role in diabetes-related complications. A complex, quantitative relationship has been established between glucose levels and oxidative stress, both in vitro and in vivo. For example, oxidative stress is known to persist after glucose normalization, a phenomenon described as metabolic memory. Also, uncontrolled glucose levels appear to be more detrimental to patients with diabetes (non-constant glucose levels) vs. patients with high, constant glucose levels. The objective of the current study was to delineate the mechanisms underlying such behaviors, using a mechanistic physiological systems modeling approach that captures and integrates essential underlying pathophysiological processes. The proposed model was based on a system of ordinary differential equations. It describes the interplay between reactive oxygen species production potential (ROS), ROS-induced cell alterations, and subsequent adaptation mechanisms. Model parameters were calibrated using different sources of experimental information, including ROS production in cell cultures exposed to various concentration profiles of constant and oscillating glucose levels. The model adequately reproduced the ROS excess generation after glucose normalization. Such behavior appeared to be driven by positive feedback regulations between ROS and ROS-induced cell alterations. The further oxidative stress-related detrimental effect as induced by unstable glucose levels can be explained by inability of cells to adapt to dynamic environment. Cell adaptation to instable high glucose declines during glucose normalization phases, and further glucose increase promotes similar or higher oxidative stress. In contrast, gradual ROS production potential decrease, driven by adaptation, is observed in cells exposed to constant high glucose.

Gene therapy for diabetic retinopathy: Are we ready to make the leap from bench to bedside?

Diabetic retinopathy (DR), a chronic and progressive complication of diabetes mellitus, is a sight-threatening disease characterized in the early stages by neuronal and vascular dysfunction in the retina, and later by neovascularization that further damages vision. A major contributor to the pathology is excess production of vascular endothelial growth factor (VEGF), a growth factor that induces formation of new blood vessels and increases permeability of existing vessels. Despite the recent availability of effective treatments for the disease, including laser photocoagulation and therapeutic VEGF antibodies, DR remains a significant cause of vision loss worldwide. Existing anti-VEGF agents, though generally effective, are limited by their short therapeutic half-lives, necessitating frequent intravitreal injections and the risk of attendant adverse events. Management of DR with gene therapies has been proposed for several years, and pre-clinical studies have yielded enticing findings. Gene therapy holds several advantages over conventional treatments for DR, such as a longer duration of therapeutic effect, simpler administration, the ability to intervene at an earlier stage of the disease, and potentially fewer side-effects. In this review, we summarize the current understanding of the pathophysiology of DR and provide an overview of research into DR gene therapies. We also examine current barriers to the clinical application of gene therapy for DR and evaluate future prospects for this approach.

Circulating levels of reactive oxygen species in patients with nonproliferative diabetic retinopathy and the influence of antioxidant supplementation: 6-month follow-up

Aims:

The aim was to evaluate circulating levels of reactive oxygen species (ROS) and changes in central macular thickness (CMT) in patients with nonproliferative diabetic retinopathy (NPDR) after antioxidant supplementation.

Materials and Methods:

A total of 68 patients (68 eyes) with NPDR were enrolled. Patients were randomly divided into two groups: Treated with antioxidant supplement (Group A) and untreated control group (Group B). Each tablet, for oral administration, containing pycnogenol 50 mg, Vitamin E 30 mg and coenzyme Q10 20 mg. CMT and free oxygen radical test (FORT) were analyzed at baseline (T0), 3 (T1) and 6 (T2) months in both groups.

Results:

In Group A, FORT levels and CMT were significantly reduced over time (P < 0.001 for both). In Group B, FORT levels were increased (P < 0.001) and CMT did not vary significantly (P = 0.81) over 3 time points.

Conclusions:

This is the first study showing the reduction of ROS levels in patients with NPDR thanks to antioxidant therapy. Moreover, our findings have suggested also an influence on retinal thickness.

Designer Leptin Receptor Antagonist Allo-aca Inhibits VEGF Effects in Ophthalmic Neoangiogenesis Models

Experimental and clinical data suggest that pro-angiogenic, pro-inflammatory and mitogenic cytokine leptin can be implicated in ocular neovascularization and other eye pathologies. At least in part, leptin action appears to be mediated through functional interplay with vascular endothelial growth factor (VEGF). VEGF is a potent regulator of neoangiogenesis and vascular leakage with a proven role in conditions such as proliferative diabetic retinopathy, age-related macular degeneration and diabetic macular edema. Accordingly, drugs targeting VEGF are becoming mainstream treatments for these diseases. The crosstalk between leptin and VEGF has been noted in different tissues, but its involvement in the development of eye pathologies is unclear. Leptin is coexpressed with VEGF during ocular neovascularization and can potentiate VEGF synthesis and angiogenic function. However, whether or not VEGF regulates leptin expression or signaling has never been studied. Consequently, we addressed this aspect of leptin/VEGF crosstalk in ocular models, focusing on therapeutic exploration of underlying mechanisms. Here we show, for the first time, that in retinal (RF/6A) and corneal (BCE) endothelial cells, VEGF (100 ng/mL, 24 h) stimulated leptin mRNA synthesis by 70 and 30%, respectively, and protein expression by 56 and 28%, respectively. In parallel, VEGF induced RF/6A and BCE cell growth by 33 and 20%, respectively. In addition, VEGF upregulated chemotaxis and chemokinesis in retinal cells by ~40%. VEGF-dependent proliferation and migration were significantly reduced in the presence of the leptin receptor antagonist, Allo-aca, at 100-250 nmol/L concentrations. Furthermore, Allo-aca suppressed VEGF-dependent long-term (24 h), but not acute (15 min) stimulation of the Akt and ERK1/2 signaling pathways. The efficacy of Allo-aca was validated in the rat laser-induced choroidal neovascularization model where the compound (5 μg/eye) significantly reduced pathological vascularization with the efficacy similar to that of a standard treatment (anti-VEGF antibody, 1 μg/eye). Cumulatively, our results suggest that chronic exposure to VEGF upregulates leptin expression and function. As leptin can in turn activate VEGF, the increased abundance of both cytokines could amplify pro-angiogenic and pro-inflammatory environement in the eye. Thus, combined therapies targeting ObR and VEGF should be considered in the treatment of ocular diseases.

Erianin inhibits high glucose-induced retinal angiogenesis via blocking ERK1/2-regulated HIF-1α-VEGF/VEGFR2 signaling pathway

Erianin is a natural compound found in Dendrobium chrysotoxum Lindl. Diabetic retinopathy (DR) is a serious and common microvascular complication of diabetes. This study aims to investigate the inhibitory mechanism of erianin on retinal neoangiogenesis and its contribution to the amelioration of DR. Erianin blocked high glucose (HG)-induced tube formation and migration in choroid-retinal endothelial RF/6A cells. Erianin inhibited HG-induced vascular endothelial growth factor (VEGF) expression, hypoxia-inducible factor 1-alpha (HIF-1α) translocation into nucleus and ERK1/2 activation in RF/6A and microglia BV-2 cells. MEK1/2 inhibitor U0126 blocked HG-induced HIF-1α and ERK1/2 activation in both above two cells. In addition, erianin abrogated VEGF-induced angiogenesis in vitro and in vivo, and also inhibited VEGF-induced activation of VEGF receptor 2 (VEGFR2) and its downstream cRaf-MEK1/2-ERK1/2 and PI3K-AKT signaling pathways in RF/6A cells. Furthermore, erianin reduced the increased retinal vessels, VEGF expression and microglia activation in streptozotocin (STZ)-induced hyperglycemic and oxygen-induced retinopathy (OIR) mice. In conclusion, our results demonstrate that erianin inhibits retinal neoangiogenesis by abrogating HG-induced VEGF expression by blocking ERK1/2-mediated HIF-1α activation in retinal endothelial and microglial cells, and further suppressing VEGF-induced activation of VEGFR2 and its downstream signals in retinal endothelial cells.

Identifying disrupted pathways by tracking altered modules in type 2 DM-related heart failure

BACKGROUND

This study aimed to screen disrupted pathways in type 2 diabetes mellitus (T2DM) heart failure by systematically tracking the altered modules of reweighted protein-protein interaction (PPI) networks.

METHODS

We implemented systematic identification and comparison of modules across non-T2DM and T2DM heart failure subjects by integrating gene expression data and PPI networks. The PPI networks of non-T2DM heart failure and T2DM heart failure were constructed and reweighted by means of Spearman's correlation coefficient (SCC). Subsequently, a clique-merging algorithm was used to explore the modules in the PPI network, followed by the identification of disrupted modules based on a maximum-weight bipartite matching and sorting in descending order. Finally, pathway enrichment analyses were conducted for genes in disrupted modules to determine the biological pathways in T2DM heart failure.

RESULTS

By comparing the modules of non-T2DM heart failure and T2DM heart failure, 804 disrupted modules were explored. The genes in disrupted modules were significantly enriched in 39 categories (p < 1.00E-06). Of these, the most significant pathways were the focal adhesion, vascular endothelial growth factor (VEGF) signaling, and mitogen-activated protein kinase (MAPK) signaling pathways.

CONCLUSION

The identified disrupted pathways - focal adhesion, VEGF signaling, and MAPK signaling - might play important roles in the progression of T2DM heart failure.

Oscillating glucose induces microRNA-185 and impairs an efficient antioxidant response in human endothelial cells

BACKGROUND

Intracellular antioxidant response to high glucose is mediated by Cu/Mn-superoxide dismutases (SOD-1/SOD-2), catalase (CAT) and glutathione peroxidases (GPx), particularly glutathione peroxidase-1 (GPx-1). Although oscillating glucose can induce a more deleterious effect than high glucose on endothelial cells, the mechanism by which oscillating glucose exerts its dangerous effects is incompletely understood; however, the involvement of oxidative damage has been generally accepted. In this study we sought to determine whether oscillating glucose differentially modulates antioxidant response, and to elucidate the potential regulatory mechanisms exerted by the microRNA-185 (miR-185).

METHODS

Human endothelial cells were exposed for 1 week to constant and oscillating high glucose. SOD-1, SOD-2, CAT and GPx-1, as well as two markers of oxidative stress [8-hydroxy-2'-deoxyguanosine (8-OHdG) and the phosphorylated form of H2AX (γ-H2AX)] were measured at the end of the experiment. Intracellular miR-185 was measured and loss-of function assays were performed in HUVEC. Bioinformatic tool was used to predict the link between miR-185 on 3'UTR of GPx-1 gene. Luciferase assay was performed to confirm the binding on HUVEC.

RESULTS

After exposure to constant high glucose SOD-1 and GPx-1 increased, while in oscillating glucose SOD-1 increased and GPx-1 did not. SOD-2 and CAT remained unchanged under both conditions. A critical involvement of oscillating glucose-induced miR-185 in the dysregulation of endogenous GPx-1 was found. Computational analyses predict GPx-1 as miR-185's target. HUVEC cultures were used to confirm glucose's causal role on the expression of miR-185, its target mRNA and protein and finally the activation of antioxidant response. In vitro luciferase assays confirmed computational predictions targeting of miR-185 on 3'-UTR of GPx-1 mRNA. Knockdown of miR-185, using anti-miR-185 inhibitor, was accompanied by a significant upregulation of GPx-1 in oscillating glucose. 8-OHdG and γ-H2AX increased more in oscillating glucose than in constant high glucose.

CONCLUSIONS

Glucose oscillations may exert more deleterious effects on the endothelium than high glucose, likely due to an impaired response of GPx-1, coupled by the upregulation of miR-185.

The impact of a low glycaemic index (GI) diet on simultaneous measurements of blood glucose and fat oxidation: A whole body calorimetric study

•

Blood glucose and fat oxidation were simultaneously measured in Asian males.

•

The whole body calorimetre measured fat oxidation over 10 hours.

•

Low GI meals increased fat oxidation in subjects who were in a sedentary state.

•

Low GI meals minimized large blood glucose fluctuations throughout the day.

Objective

Low glycaemic index (GI) foods are known to minimize large fluctuations in blood glucose levels and have been suggested to increase fat oxidation. The objective of this study was to simultaneously investigate glucose excursion and substrate oxidation in a whole body calorimetre when Chinese male subjects were provided a low or high GI meal.

Materials/Methods

In a randomized, controlled crossover non blind design, 12 healthy Chinese male adults (BMI 21.8 ± 1.3 kgm⁻²) attended two sessions consisting of either four low or high glycaemic meals (LGI vs HGI). Breakfast, lunch and snack were consumed in a whole body calorimetre while dinner was consumed at home. Daily changes in glycaemic response (GR) and postprandial GR responses were measured using a continuous glucose monitoring system. The GR was further calculated to obtain the incremental area under the curve (iAUC) for glucose concentrations. Glycaemic variability was calculated as mean amplitude of glycaemic excursion (MAGE). Substrate oxidation was calculated by measuring respiratory quotient and urine nitrogen excretion.

Results

After LGI meals in the whole body calorimetre, iAUC for glucose (P = 0.008) was lower compared to the HGI session. The HGI treatment produced a significantly greater MAGE than the LGI treatment over the 24 hour period (P < 0.001). Additionally, higher fat oxidation and lower carbohydrate oxidation were observed following breakfast and lunch when comparing LGI to HGI (P < 0.05)

Conclusions

Consumption of LGI meals was capable of attenuating 24-hour blood glucose profiles and decreasing postprandial glucose excursions in healthy Asian males. Additionally, LGI mixed meals were able to promote fat oxidation over carbohydrate oxidation when compared to HGI mixed meals. The consumption of low GI meals may be a strategic approach in improving overall glycaemia and increasing fat oxidation in Asians consuming a high carbohydrate diet.

MiR-18b suppresses high-glucose-induced proliferation in HRECs by targeting IGF-1/IGF1R signaling pathways

MicroRNAs (miRNAs) are important for the proliferation of endothelial cells and have been shown to be involved in diabetic retinopathy (DR). In previous study, we found that miRNAs might play a critical role in hyperglycemia-induced endothelial cell proliferation based on miRNA expression profiling. Here, the roles of microRNA-18b (miR-18b) in the proliferation of human retinal endothelial cells (HRECs) were investigated in an in vitro model of HRECs grown in high glucose. We identified that levels of miR-18b were decreased in high-glucose-induced HRECs, compared with those in cells incubated in normal glucose. However, the reduction of miR-18b up-regulated vascular endothelial growth factor (VEGF) secretion and promoted effects on in vitro proliferation of HRECs. Mechanistically, insulin growth factor-1 (IGF-1) was identified as a target of miR-18b. IGF-1 simulation could antagonize the effect induced by miR-18b up-regulation, promoting cell proliferation and increasing VEGF production. In contrast, the opposite results were observed with silencing IGF-1, which was consistent with the effects of miR-18b overexpression. MiR-18b exerted its function on VEGF synthesis and cell proliferation by suppressing the IGF-1/insulin growth factor-1 receptor (IGF1R) pathway, consequently inhibiting the downstream phosphorylation of Akt, MEK, and ERK. Hence, this may provide a new insight into understanding the mechanism of DR pathogenesis, as well as a potential therapeutic target for proliferative DR.

ROS signaling and redox biology in endothelial cells

The purpose of this review is to provide an overview of redox mechanisms, sources and antioxidants that control signaling events in ECs. In particular, we describe which molecules are involved in redox signaling and how they influence the relationship between ECs and other vascular component with regard to angiogenesis. Recent and new tools to investigate physiological ROS signaling will be also discussed. Such findings are providing an overview of the ROS biology relevant for endothelial cells in the context of normal and pathological angiogenic conditions.

The augmentation of O-GlcNAcylation reduces glyoxal-induced cell injury by attenuating oxidative stress in human retinal microvascular endothelial cells

It has recently been reported that O-linked β-N-acetyl glucosamine (O-GlcNAc) modification (a simple intracellular serine (Ser)/threonine (Thr)-linked monosaccharide) in human retinal microvascular endothelial cells (HRECs) is related to diabetic retinopathy (DR). During O-GlcNAcylation, O-GlcNAc is added to Ser and Thr residues. As the generation of reactive oxygen species (ROS) is one of the characteristics of advanced glycation end product (AGE) injury, and the most important key pathogenic factor of DR, in the present study, we aimed to investigate the association between O-GlcNAcylation and ROS generation in order to ascertain whether O-GlcNAcylation mitigates cellular injury through the generation of ROS. For this purpose, HRECs were divided into 4 groups as follows: HRECs treated with normal glucose (5 mM), HRECs treated with glyoxal (500 µM), glyoxal-treated HRECs also treated with 200 µM PUGNAc, and glyoxal-treated HRECs infected with O-GlcNAc transferase (OGT) siRNA. We detected increased O-GlcNAc levels and increased ROS production in the glyoxal-treated HRECs. The cellular redox status was determined by cellular ROS staining and by measuring the expression levels of the antioxidant genes, superoxide dismutase (SOD) and glutathione peroxidase (GPX). While the augmentation of O-GlcNAcylation following treatment with PUGNAc significantly attenuated the production of ROS (p<0.01) and increased the expression levels of SOD and GPX, the reduction of O-GlcNAcylation following infection with OGT siRNA, exacerbated the production of ROS (p<0.01) and decreased the expression of antioxidant genes. The effects of O-GlcNAcylation on the viability of HRECs were significant (p<0.01), particularly in the hydrogen peroxide (H2O2)-treated HRECs. Treatment with PUGNAc reduced glyoxal-induced cell apoptosis and transfection with OGT siRNA increased HREC apoptosis; these results were confirmed by flow cytometry and by the assessment of mitochondrial membrane potential. The augmentation of O-GlcNAcylation exerted cytoprotective effects on the HRECs by reducing the generation of ROS, increasing the expression of antioxidant genes, preventing the dissipation of mitochondrial membrane potential and preventing HREC apoptosis. Therefore, it can be concluded that O-GlcNAcylation plays a role in the early developmental process of DR.

The impact of a low glycemic index (GI) breakfast and snack on daily blood glucose profiles and food intake in young Chinese adult males

Objective

Low glycemic index (GI) foods have been suggested to minimize large fluctuations in blood glucose levels and reduce food intake. However, the majority of studies have been conducted on Caucasian populations with limited data on Asians. The objective of this study was to investigate how the provision of a low GI breakfast and afternoon snack affected daily blood glucose profiles and food intake.

Materials and methods

In a randomized, controlled crossover non blind design, 11 healthy Chinese male adults (body mass index 22.4 ± 1.3 kg m⁻²) attended two sessions where they consumed either a high or low GI breakfast and afternoon snack, and a standardized buffet lunch. Daily changes in glycemic response (GR) were measured using the Medtronic MiniMed (Northridge, CA) iPro™2 continuous glucose monitoring system (CGMS). The GR was further calculated to obtain the incremental area under the curve (IAUC). Glycemic variability was calculated as mean amplitude of glycemic excursion (MAGE) and energy intake (kcal) was measured quantitatively at the buffet lunch.

Results

Compared to the high GI intervention, the low GI intervention significantly reduced the GR following breakfast (p = 0.02), lunch (p = 0.02) and dinner (p = 0.05). The low GI treatment showed a reduction in daily AUC (p = 0.03). There was a significant reduction in IAUC after a low GI breakfast compared to the high GI breakfast (p = 0.03). The low GI breakfast resulted in a significantly lower food intake at lunch and a resulting decreased energy intake of 285 kcal (p = 0.02). The MAGE was significantly lower during the entire low GI treatment (p = 0.03).

Conclusions

Consumption of a low GI breakfast and afternoon snack was capable of attenuating 24-h blood glucose profiles, minimize glycemic excursions and reduce food intake in healthy Asian males. This simple dietary intervention may be an acceptable approach in improving overall glycemia and energy balance in Asians.

Clinical trial registration number

NCT02340507

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The impact of low and high glycemic index foods on 24 h blood glucose profile.

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The CGMS provides detailed information on how diets affect longer term glycemia.

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Low GI breakfast and afternoon snack minimize large blood glucose fluctuations.

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Low GI foods reduce glycemic variability and total energy intake.

Saxagliptin is similar in glycaemic variability more effective in metabolic control than acarbose in aged type 2 diabetes inadequately controlled with metformin

This study compared the effects on glycaemic variability and glucose control between saxagliptin and acarbose as add-on therapies for aged T2DM inadequately controlled with metformin alone. The results showed that compared with acarbose-metformin, saxagliptin-metformin was more effective in glucose control with similar glycaemic variability.

Endothelial cell oxidative stress in diabetes: a key driver of cardiovascular complications?

Atherothrombotic disease is a well-recognized complication of diabetes and is a major contributor to the high morbidity and mortality associated with diabetes. Although there is substantial evidence linking diabetes with cardiovascular disease, the specific effect of hyper- (or hypo-) glycaemia is less well understood. The present review focuses on the impact that glycaemic dysregulation has on respiratory function and ROS (reactive oxygen species) generation in the endothelial cells that are critical in preventing several key steps in the atherothrombotic process. Endothelial cells are particularly susceptible to ROS-mediated dysfunction not only because of reduced cell viability and increased senescence, but also because one of the major endothelium-derived factors that help to protect against atherosclerosis, nitric oxide, is rapidly deactivated by superoxide radicals.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.

Efficacy of real-time continuous glucose monitoring on glycaemic control and glucose variability in type 1 diabetic patients treated with either insulin pumps or multiple insulin injection therapy: a randomized controlled crossover trial

BACKGROUND

The aim of this study was to determine the efficacy of real-time continuous glucose monitoring in T1D patients treated with insulin pump therapy or multiple daily insulin therapy.

METHODS

Twenty adult patients (ten insulin pump therapy and ten multiple daily insulin) with poor glycaemic control (HbA1c  > 8.0%) were randomized into two groups for 6 months: the continuous glucose monitoring arm (using real-time continuous glucose monitoring) and the SMBG arm. After 2 months of wash-out, the participants crossed over. The primary outcome was HbA1c reduction. The secondary outcomes were hypoglycaemia and hyperglycaemia risk assessment (area under the curve < 70 mg/dL/day and AUC > 200 mg/dL/day, respectively) and glucose variability.

RESULTS

Fourteen patients (eight multiple daily insulin, six insulin pump therapy) used continuous glucose monitoring appropriately (at least 40% of the time). In these patients, the improvement in glycaemic control was more evident during the real-time continuous glucose monitoring period (7.76% ± 0.4 vs 8.54% ± 0.4, p < 0.05) than during the self-monitoring of blood glucose period (8.42% ± 0.4 vs 8.56% ± 0.5, p = 0.2). Better results with continuous glucose monitoring were observed in patients using multiple daily insulin with greater improvement in both glycaemic control (7.71% ± 0.2 vs 8.58% ± 0.2, p < 0.05) and glucose variability and with a marked reduction in the risk of both hypoglycaemia and hyperglycaemia.

CONCLUSIONS

Appropriate use of real-time continuous glucose monitoring improved glycometabolic control in T1D patients. The effects of continuous glucose monitoring were more evident in patients under multiple daily insulin treatment, compared with insulin pump therapy. Glucose variability, in addition to glycaemic control, was improved in compliant diabetic patients.

Glycemic variability in nondiabetic morbidly obese persons: results of an observational study and review of the literature

Glycemic variability (GV) is correlated with oxidative stress which may lead to increased cardiovascular risk and poor clinical outcomes in people with prediabetes and diabetes. We sought to understand whether morbidly obese persons without diabetes by standard criteria have dysglycemia as measured by GV. We performed an observational study of GV metrics and carotid intima media thickness (CIMT) in 21 morbidly obese normoglycemic and 15 morbidly obese prediabetic applicants to The Biggest Loser television show. The results were compared to previously published studies in normoglycemic nonobese and obese individuals. Glucose was measured with a masked continuous glucose monitor (CGM) over 3 to 8 days and carotid intima media thickness (CIMT) was determined by ultrasound. CGM-derived GV metrics for GV were coefficient of variation (CV), standard deviation (SD), mean amplitude of glycemic excursions (MAGE), continuous overall net glycemic action-1 hour (CONGA1), and mean of daily differences (MODD). We found that morbidly obese subjects (n = 21) who were normoglycemic by standard criteria had higher GV (CV = 22%, SD = 24.2 mg/dl and MAGE = 48.6 mg/dl) than previous reports of normoglycemic, nonobese individuals (CV = 12-18%, SD = 11.5-15.0 mg/dl, and MAGE = 26.3-28.3 mg/dl). Morbidly obese prediabetic subjects (n = 15) had GV metrics indistinguishable from those morbidly obese subjects who were normoglycemic. CIMT was higher in both morbidly obese groups compared with historical age- and sex-matched controls. Normoglycemic and prediabetic morbidly obese individuals have higher GV compared with normal weight, nondiabetic individuals. We speculate that this may increase the risk for macrovascular disease through excessive oxidative stress.