Hyperlipidemia and the development of diabetic retinopathy: Comparison between type 1 and type 2 animal models

Nrf-2-dependent antioxidant and anti-inflammatory effects underlie the protective effect of esculeoside A against retinal damage in streptozotocin-induced diabetic rats

Esculeoside A (ESA) is a tomato-derived glycoside with antioxidant and anti-inflammatory properties. The protective effect of ESA against diabetic retinopathy is not well-investigated and was the core objective of this study. In addition, we tested if such protection involves the activation of Nrf2 signaling. Type 1 diabetes mellitus (T1DM) was induced in adult Wistar male rats by an intraperitoneal injection of streptozotocin (65 mg/kg). Non-diabetic and T1DM rats were divided into two subgroup groups given either the vehicle or ESA (100 mg)/kg. An additional T1DM group was given ESA (100 mg/kg) and an Nrf2 inhibitor (2 mg/kg) (n=8 rats/group). Treatments continued for 12 weeks. In this study, according to the histological features, ESA improved the structure of ganglionic cells and increased the number of cells of the inner nuclear and plexiform layers in the retinas of T1DM rats. Concomitantly, it reduced the retina levels of malondialdehyde (lipid peroxides), vascular endothelial growth factor, interleukin-6, tumor necrosis factor-α, Bax, and caspase-3. In the retinas of the control and diabetic rats, ESA boosted the levels of total glutathione, superoxide dismutase, heme-oxygenase-1, and Bcl2, reduced the mRNA levels of REDD1, and enhanced cytoplasmic and nuclear levels of Nrf2. However, ESA failed to alter the mRNA levels of Nrf2 and keap1, protein levels of keap1, plasma glucose, plasma insulin, serum triglycerides, cholesterol, and LDL-c in both the control and T1DM rats. In conclusion, ESA alleviates retinopathy in T1DM rats by suppressing REDD1-associated degradation and inhibiting the Nrf2/antioxidant axis.

A new direction in Chinese herbal medicine ameliorates for type 2 diabetes mellitus: Focus on the potential of mitochondrial respiratory chain complexes

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetes is a common chronic disease. Chinese herbal medicine (CHM) has a history of several thousand years in the treatment of diabetes, and active components with hypoglycemic effects extracted from various CHM, such as polysaccharides, flavonoids, terpenes, and steroidal saponins, have been widely used in the treatment of diabetes.

AIM OF THE STUDY

Research exploring the potential of various CHM compounds to regulate the mitochondrial respiratory chain complex to improve type 2 diabetes mellitus (T2DM).

MATERIALS AND METHODS

The literature data were primarily obtained from authoritative databases such as PubMed, CNKI, Wanfang, and others within the last decade. The main keywords used include "type 2 diabetes mellitus", "Chinese medicine", "Chinese herbal medicine", "mitochondrial respiratory chain complex", and "mitochondrial dysfunction".

RESULTS

Chinese herbal medicine primarily regulates the activity of mitochondrial respiratory chain complexes in various tissues such as liver, adipose tissue, skeletal muscle, pancreatic islets, and small intestine. It improves cellular energy metabolism through hypoglycemic, antioxidant, anti-inflammatory and lipid-modulating effects. Different components of CHM can regulate the same mitochondrial respiratory chain complexes, while the same components of a particular CHM can regulate different complex activities. The active components of CHM target different mitochondrial respiratory chain complexes, regulate their aberrant changes and effectively improve T2DM and its complications.

CONCLUSION

Chinese herbal medicine can modulate the function of mitochondrial respiratory chain complexes in various cell types and exert their hypoglycemic effects through various mechanisms. CHM has significant therapeutic potential in regulating mitochondrial respiratory chain complexes to improve T2DM, but further research is needed to explore the underlying mechanisms and conduct clinical trials to assess the safety and efficacy of these medications. This provides new perspectives and opportunities for personalized improvement and innovative developments in diabetes management.

Homocysteine and mitochondrial quality control in diabetic retinopathy

BACKGROUND

Diabetic retinopathy is a progressive disease, and one of the key metabolic abnormalities in the pathogenesis of diabetic retinopathy, mitochondrial damage, is also influenced by the duration of hyperglycemia. Mitochondrial quality control involves a coordination of mitochondrial dynamics, biogenesis and removal of the damaged mitochondria. In diabetes, these processes are impaired, and the damaged mitochondria continue to produce free radicals. Diabetic patients also have high homocysteine and reduced levels of hydrogen sulfide, and hyperhomocysteinemia is shown to exacerbate diabetes-induced mitochondrial damage and worsen their dynamics. This study aims to investigate the temporal relationship between hyperhomocysteinemia and retinal mitochondrial quality control in diabetic retinopathy.

METHODS

Human retinal endothelial cells incubated in 20 mM D-glucose for 24 to 96 h, in the absence or presence of 100 µM homocysteine, with/without a hydrogen sulfide donor GYY4137, were analyzed for mitochondrial ROS (MitoSox fluorescence), DNA damage (transcripts of mtDNA-encoded ND6 and CytB), copy numbers, oxygen consumption rate (Seahorse XF analyzer) and mitophagy (mitophagosomes immunofluorescence labeling and flow cytometry). Results were confirmed in the retina from mice genetically manipulated for hyperhomocysteinemia (cystathionine β-synthase deficient mice, Cbs+/-), streptozotocin-induced diabetic for 8 to 24 weeks. At 24 weeks of diabetes, vascular health was evaluated by counting acellular capillaries in the trypsin digested retinal vasculature and by fluorescein angiography.

RESULTS

Homocysteine, in high glucose medium, exacerbated mitochondrial ROS production, mtDNA damage and impaired mitochondrial respiration within 24 h, and slowed down/worsened mitochondrial biogenesis and mitophagy, as compared to 48 to 96 h in high glucose alone. GYY4137 supplementation ameliorated homocysteine + high glucose-induced mitochondrial damage and impairment in biogenesis and mitophagy. Similar results were obtained from Cbs+/- mice-mitochondrial ROS, mtDNA damage and decline in biogenesis and mitophagy were observed within eight weeks of diabetes vs. 16 to 24 weeks of diabetes in Cbs+/+ mice, and at 24 weeks of diabetes, Cbs+/- mice had significantly higher acellular capillaries and vascular leakage.

CONCLUSIONS

Hyperhomocysteinemia, in a hyperglycemic environment, overwhelms the mitochondria, accelerating and exacerbating their dysfunction, and also delays/worsens their removal, augmenting the development of diabetic retinopathy. Thus, our results strengthen the importance of maintaining homocysteine-hydrogen sulfide balance during the early stages of diabetes for a patient to prevent/retard vision loss.

Insulin resistance is associated with the presence and severity of retinopathy in patients with type 2 diabetes

BACKGROUND

To assess the relationship between novel insulin resistance (IR) indices and the presence and severity of diabetic retinopathy (DR) in patients with type 2 diabetes.

METHODS

This is a cross-sectional study involving 2211 patients. The study outcomes were DR events. The study exposures were IR indices including estimated glucose disposal rate (eGDR), natural logarithm of glucose disposal rate (lnGDR), metabolic insulin resistance score (METS-IR), triglyceride glucose index-body mass index (TyG-BMI), triglyceride glucose index-waist-to-hip ratio (TyG-WHR), and triglyceride/high-density lipoprotein cholesterol(TG/HDL-c ratio). We used binary and multivariate ordered logistic regression models to estimate the association between different IR indices and the presence and severity of DR. Subject work characteristic curves were used to assess the predictive power of different IR indices for DR.

RESULTS

DR was present in 25.4% of participants. After adjusting for all covariates, per standard deviation (SD) increases in eGDR (ratio [OR] 0.38 [95% CI 0.32-0.44]), lnGDR (0.34 [0.27-0.42]) were negatively associated with the presence of DR. In contrast, per SD increases in METS-IR (1.97 [1.70-2.28]), TyG-BMI (1.94 [1.68-2.25]), TyG-WHR (2.34 [2.01-2.72]) and TG/HDL-c ratio (1.21 [1.08-1.36]) were positively associated with the presence of DR. eGDR was strongly associated with severity of DR. Of all variables, eGDR had the strongest diagnostic value for DR (AUC = 0.757).

CONCLUSIONS

Of the six IR indices, eGDR was significantly associated with the presence and severity of DR in patients with type 2 diabetes. eGDR has a good predictive value for DR. Thus, eGDR maybe a stronger marker of DR.

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

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

Systematic review registration

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

Mitochondrial Genome-Encoded Long Noncoding RNA Cytochrome B and Mitochondrial Dysfunction in Diabetic Retinopathy

Aims: Mitochondrial dysfunction is closely associated with the development of diabetic complications. In diabetic retinopathy, electron transport chain is compromised and mitochondrial DNA (mtDNA) is damaged, downregulating transcription of mtDNA-encoded cytochrome B (CYTB) and its antisense long noncoding RNA, long noncoding RNA cytochrome B (LncCytB). Our goal was to investigate the role of LncCytB in the regulation of CYTB and mitochondrial function in diabetic retinopathy. Methods: Using human retinal endothelial cells, genetically manipulated for LncCytB (overexpression or silencing), the effect of high glucose (20 mM d-glucose) on LncCytB-CYTB interactions (by chromatin isolation by RNA purification), CYTB gene expression (by real-time quantitative polymerase chain reaction), complex III activity, mitochondrial free radicals, and oxygen consumption rate (OCR, by Seahorse XF analyzer) was investigated. Key results were confirmed in the retinal microvessels from streptozotocin-induced diabetic mice. Results: High glucose decreased LncCytB-CYTB interactions, and while LncCytB overexpression ameliorated glucose-induced decrease in CYTB gene transcripts, complex III activity and OCR and increase in mitochondrial reactive oxygen species, LncCytB-siRNA further attenuated CYTB gene transcription, complex III activity, and OCR. Similar decrease in LncCytB-CYTB interactions and CYTB transcription was observed in diabetic mice. Furthermore, maintenance of mitochondrial homeostasis by overexpressing superoxide dismutase or sirtuin 1 in mice ameliorated diabetes-induced decrease in LncCytB-CYTB interactions and CYTB gene transcripts, and also improved complex III activity and mitochondrial respiration. Innovation and Conclusion: LncCytB downregulation in hyperglycemic milieu downregulates CYTB transcription, which inhibits complex III activity and compromises mitochondrial stability and OCR. Thus, preventing LncCytB downregulation in diabetes has potential of inhibiting the development of diabetic retinopathy, possibly via maintaining mitochondrial respiration. Antioxid. Redox Signal. 39, 817-828.

Diabetic retinopathy: a comprehensive update on in vivo, in vitro and ex vivo experimental models

Diabetic retinopathy (DR), one of the leading causes of visual impairment and blindness worldwide, is one of the major microvascular complications in diabetes mellitus (DM). Globally, DR prevalence among DM patients is 25%, and 6% have vision-threatening problems among them. With the higher incidence of DM globally, more DR cases are expected to be seen in the future. In order to comprehend the pathophysiological mechanism of DR in humans and discover potential novel substances for the treatment of DR, investigations are typically conducted using various experimental models. Among the experimental models, in vivo models have contributed significantly to understanding DR pathogenesis. There are several types of in vivo models for DR research, which include chemical-induced, surgical-induced, diet-induced, and genetic models. Similarly, for the in vitro models, there are several cell types that are utilised in DR research, such as retinal endothelial cells, Müller cells, and glial cells. With the advancement of DR research, it is essential to have a comprehensive update on the various experimental models utilised to mimic DR environment. This review provides the update on the in vitro, in vivo, and ex vivo models used in DR research, focusing on their features, advantages, and limitations.

Klotho: A new therapeutic target in diabetic retinopathy?

Klotho (Kl) is considered an antiaging gene, mainly for the inhibition of the insulin-like growth factor-1 signaling. Kl exists as full-length transmembrane, which acts as co-receptor for fibroblast growth factor receptor, and in soluble forms (sKl). The sKl may exert pleiotropic effects on organs and tissues by regulating several pathways involved in the pathogenesis of diseases associated with oxidative and inflammatory state. In diabetic Patients, serum levels of Kl are significantly decreased compared to healthy subjects, and are related to duration of diabetes. In diabetic retinopathy (DR), one of the most common microvascular complications of type 2 diabetes, serum Kl levels are negatively correlated with progression of the disease. A lot of evidences showed that Kl regulates several mechanisms involved in maintaining homeostasis and functions of retinal cells, including phagocytosis, calcium signaling, secretion of vascular endothelial growth factor A (VEGF-A), maintenance of redox status, and melanin biosynthesis. Experimental data have been shown that Kl exerts positive effects on several mechanisms involved in onset and progression of DR. In particular, treatment with Kl: (1) Prevents apoptosis induced by oxidative stress in human retinal endothelial cells and in retinal pigment epithelium (RPE) cells; (2) reduces secretion of VEGF-A by RPE cells; and (3) decreases subretinal fibrosis and preserves autophagic activity. Therefore, Kl may become a novel biomarker and a good candidate for the treatment of DR.

Duration of the diabetic state altered platelet indices from baseline values in a streptozotocin-induced rat model for type 1 diabetes mellitus

BACKGROUND

Changes in platelet indices in naturally occurring type I diabetes mellitus (T1DM) have been described in several studies. In this study, platelet indices such as platelet count (PLT), plateletcrit (PCT), mean platelet volume (MPV), platelet distribution width (PDW), and MPV to PLT ratio were investigated according to diabetic duration after streptozotocin (STZ)-induced T1DM, as well as for their correlation with glucose.

METHODS

Forty healthy adult Wistar rats were randomly assigned to four experimental groups of ten (5 rats of each sex), including the control group, the 7, 14, and 28 days diabetic groups (D7, D14, and D28, respectively).

RESULTS

In diabetic groups, plasma glucose was significantly higher than in control (P < 0.01). D7, D14, and D28 groups presented significantly lower PLT than the control (P < 0. 01). A significant decrease in PCT was observed in D14 and D28 females (P < 0.05). Mean platelet volume was significantly higher in the D28 group than in to control. D28 females also showed a significant difference in PLT, MPV, and the MPV-to-PLT ratio compared with D7 females (P < 0.05). A comparison between D28 females and males showed a significant difference in PDW (P < 0.05). Both females and males showed a significant correlation between glucose and PLT, PCT, MPV, and the MPV-to-PLT ratio.

CONCLUSIONS

Platelet indices change significantly with the duration of diabetes compared with the baseline values, and female and male rats did not have significant differences in platelet indices in any period except the 28 days.

Efficiency co-delivery of ellagic acid and oxygen by a non-invasive liposome for ameliorating diabetic retinopathy

Diabetic retinopathy (DR) is one of the serious complications of diabetes, which has become the fourth leading cause of vision loss worldwide. Current treatment of DR relies on intravitreal injections of antiangiogenic agents, which has made considerable achievements in reducing visual impairment. However, long-term invasive injections require advanced technology and can lead to poor patient compliance as well as the incidence of ocular complications including bleeding, endophthalmitis, retinal detachment and others. Hence, we developed non-invasive liposomes (EA-Hb/TAT&isoDGR-Lipo) for efficiency co-delivery of ellagic acid and oxygen, which can be administered intravenously or by eye drops. Among that, ellagic acid (EA), as an aldose reductase inhibitor, could remove excessive reactive oxygen species (ROS) induced by high glucose for preventing retinal cell apoptosis, as well as reduce retinal angiogenesis through the blockage of VEGFR2 signaling pathway; carried oxygen could ameliorate DR hypoxia, and further enhanced the anti-neovascularization efficacy. Our results showed that EA-Hb/TAT&isoDGR-Lipo not only effectively protected retinal cells from high glucose-induced damage, but also inhibited VEGF-induced vascular endothelial cells migration, invasion, and tube formation in vitro. In addition, in a hypoxic cell model, EA-Hb/TAT&isoDGR-Lipo could reverse retinal cell hypoxia, thereby reducing the expression of VEGF. Significantly, after being administered as an injection or eye drops, EA-Hb/TAT&isoDGR-Lipo obviously ameliorated the structure (central retinal thickness and retinal vascular network) of retina by eliminating ROS and down-regulating the expression of GFAP, HIF-1α, VEGF and p-VEGFR2 in a DR mouse model. In summary, EA-Hb/TAT&isoDGR-Lipo holds great potentials in improvement of DR, which provides a novel approach for the treatment of DR.

Nanoformulations for the Delivery of Dietary Anthocyanins for the Prevention and Treatment of Diabetes Mellitus and Its Complications

Diabetes mellitus (DM) is a metabolic disease characterized by abnormal blood glucose levels-hyperglycemia, caused by a lack of insulin secretion, impaired insulin action, or a combination of both. The incidence of DM is increasing, resulting in billions of dollars in annual healthcare costs worldwide. Current therapeutics aim to control hyperglycemia and reduce blood glucose levels to normal. However, most modern drugs have numerous side effects, some of which cause severe kidney and liver problems. On the other hand, natural compounds rich in anthocyanidins (cyanidin, delphinidin, malvidin, pelargonidin, peonidin, and petunidin) have also been used for the prevention and treatment of DM. However, lack of standardization, poor stability, unpleasant taste, and decreased absorption leading to low bioavailability have hindered the application of anthocyanins as therapeutics. Therefore, nanotechnology has been used for more successful delivery of these bioactive compounds. This review summarizes the potential of anthocyanins for the prevention and treatment of DM and its complications, as well as the strategies and advances in the delivery of anthocyanins using nanoformulations.

Rodent Models of Diabetic Retinopathy as a Useful Research Tool to Study Neurovascular Cross-Talk

Diabetes is a group of metabolic diseases leading to dysfunction of various organs, including ocular complications such as diabetic retinopathy (DR). Nowadays, DR treatments involve invasive options and are applied at the sight-threatening stages of DR. It is important to investigate noninvasive or pharmacological methods enabling the disease to be controlled at the early stage or to prevent ocular complications. Animal models are useful in DR laboratory practice, and this review is dedicated to them. The first part describes the characteristics of the most commonly used genetic rodent models in DR research. The second part focuses on the main chemically induced models. The authors pay particular attention to the streptozotocin model. Moreover, this section is enriched with practical aspects and contains the current protocols used in research in the last three years. Both parts include suggestions on which aspect of DR can be tested using a given model and the disadvantages of each model. Although animal models show huge variability, they are still an important and irreplaceable research tool. Note that the choice of a research model should be thoroughly considered and dependent on the aspect of the disease to be analyzed.

Bioactivity-Guided Fractionation and Identification of Antidiabetic Compound of Syzygium polyanthum (Wight.)'s Leaf Extract in Streptozotocin-Induced Diabetic Rat Model

(1) Background: An earlier study on the hypoglycemic activity of S. polyanthum (Wight.) leaf methanol extract identified squalene as the major chemical compound. The present study was conducted to assess the hypoglycemic effect of fractions and subfractions of the methanol extract of S. polyanthum compared to the squalene using a bioassay-guided in vivo study. (2) Methods: The methanol extract was fractionated using the liquid−liquid fractionation method. Streptozotocin-induced type 1 diabetic rat was used to study the hypoglycemic effect. (3) Results: The findings showed that chloroform fraction significantly (p < 0.05) lowered blood glucose levels of diabetic rats as compared to the control. Further fractionation of chloroform fraction yielded subfraction-1 and -2, whereby subfraction-1 exhibited a higher blood-glucose-lowering effect. The lipid profile test showed that the total cholesterol level of subfraction-1 and squalene-treated groups decreased significantly (p < 0.05). An immunohistochemistry study revealed that none of the treatments regenerated pancreatic β-cells. Gas chromatography−mass spectrophotometer analysis identified the presence of squalene in the active methanol extract, chloroform fraction, and subfraction-1. In silico analysis revealed a higher affinity of squalene against protein receptors that control lipid metabolism than metformin. (4) Conclusions: Data obtained from the present work suggested the crude methanol extract exerted the highest hypoglycemic effect compared to fraction, subfraction, and squalene, confirming synergistic effect may be responsible for the hypoglycemic activity of S. polyanthum.

Regulation of serine palmitoyl-transferase and Rac1-Nox2 signaling in diabetic retinopathy

Hyperlipidemia is considered as one of the major systemic factors associated with the development of diabetic retinopathy, and animal models have documented that its presence in a hyperglycemic environment exacerbates cytosolic ROS production (via activation of the Rac1–Nox2 axis) and mitochondrial damage. Hyperglycemia also accelerates Rac1 transcription via dynamic DNA methylation–hydroxymethylation of its promoter. In diabetes, ceramide metabolism in the retina is impaired and its accumulation is increased. Our aim was to investigate the effect of inhibition of the rate limiting enzyme of the de novo ceramide biosynthesis, serine palmitoyl-transferase (SPT), on Rac1 activation in diabetic retinopathy. Using human retinal endothelial cells, transfected with SPT-siRNA, and incubated in 20 mM d-glucose in the presence or absence of 50 µM palmitate (glucolipotoxic and glucotoxic, respectively), activities of Rac1 and Nox2, and ROS levels were quantified. For Rac1 transcriptional activation, 5 hydroxymethyl cytosine (5hmC) levels at its promoter were quantified. Key parameters were confirmed in retinal microvessels from streptozotocin-induced diabetic mice on a normal diet (type 1 diabetic model) or on a high-fat diet (45% kcal, type 2 diabetic model), injected intravitreally with SPT-siRNA. Compared to normal glucose, cells in high glucose, with or without palmitic acid, had increased Rac1–Nox2–ROS signaling, Rac1 transcripts and 5hmC levels at its promoter. Inhibition of SPT by SPT-siRNA or myriocin prevented glucotoxic- and glucolipotoxic-induced increase in Rac1–Nox2–ROS signaling and 5hmC at the Rac1 promoter. Similarly, in both type 1 and type 2 diabetic mouse models, SPT-siRNA attenuated the increase in the Rac1–Nox2–ROS axis and 5hmC at the Rac1 promoter. Thus, inhibition of the rate limiting enzyme of ceramide de novo biosynthesis, SPT, regulates activation of DNA methylation–hydroxymethylation machinery and prevents increased Rac1 transcription. This ameliorates the activation of Rac1–Nox2 signaling and protects the mitochondria from damaging cytosolic ROS, which prevents accelerated capillary cell loss. These results further raise the importance of regulating lipid levels in diabetic patients with dyslipidemia.

Ferulic acid attenuates high glucose-induced apoptosis in retinal pigment epithelium cells and protects retina in db/db mice

Background

Herein, we aimed to present evidence that Ferulic acid (FA), a phenolic acid, can alleviate high glucose (HG)-induced retinal pigment epithelium (RPE) cell apoptosis and protect retina in db/db mice.

Methods

ARPE-19 cells (a human RPE cell line) were divided into four groups: control group; HG group (30 mmol/L glucose); HG+FA group (30 mmol/L glucose and 10 mmol/L FA). Cell viability and apoptosis were detected using CCK-8 and Annexin-5 staining, respectively. Apoptosis-related markers including P53, BAX and Bcl2 were examined by RT-qPCR, western blot and immunohistochemistry. Totally, 30 male db/db mice were randomly divided into db/db group (5 ml/kg saline) and FA group (0.05 g/kg FA). After treatment for 2 months, retinal samples were subjected to hematoxylin and eosin (H&E) and Masson staining. Moreover, immunofluorescence was used to detect apoptosis-related markers. Blood samples were collected for measuring cholesterol, triglyceride (TG), low-density lipoprotein (LDL) and high-density lipoprotein (HDL) levels.

Results

FA treatment markedly increased cell viability and suppressed cell apoptosis of ARPE-19 cells compared to the HG-exposed group. Furthermore, FA ameliorated the abnormal expression levels of P53, BAX and Bcl2 in HG-induced ARPE-19 cells. In animal models, FA attenuated pathological changes in the retina tissues of diabetic mice. Consistent with in vitro models, FA significantly ameliorated the expression of apoptosis-related markers in retina tissues. Biochemical test results showed that FA reduced hyperlipidemia in diabetic mice.

Conclusion

Our findings suggest that FA alleviates HG-induced apoptosis in RPE cells and protects retina in db/db mice, which can be associated with P53 and BAX inactivation and Bcl2 activation.

Monosodium Glutamate-Induced Mouse Model With Unique Diabetic Retinal Neuropathy Features and Artificial Intelligence Techniques for Quantitative Evaluation

Objective

To establish an artificial intelligence-based method to quantitatively evaluate subtle pathological changes in retinal nerve cells and synapses in monosodium glutamate (MSG) mice and provide an effective animal model and technique for quantitative evaluation of retinal neurocytopathies.

Methods

ICR mice were subcutaneously injected with MSG to establish a model of metabolic syndrome. We then established a mouse model of type 1 diabetes, type 2 diabetes, and KKAy mouse model as control. The HE sections of the retina were visualized using an optical microscope. AI technology was used for quantitative evaluation of the retinal lesions in each group of rats. The surface area custom parameters of the retinal nerve fiber layer (RNFL), inner plexiform layer (IPL), inner nuclear layer (INL), and outer plexiform layer (OPL) were defined as SR, SIPL, SINL, and SOPL, respectively. Their heights were defined as HR, HIPL, HINL, and HOPL, and the number of ganglion cells was defined as A. Then, the attention-augmented fully convolutional Unet network was used to segment the retinal HE images, and AI technology to identify retinal neurocytopathies quantitatively.

Results

The attention-augmented fully convolutional Unet network increased PA and IOU parameters for INL, OPL, RNFL, and ganglion cells and was superior in recognizing fine structures. A quantitative AI identification of the height of each layer of the retina showed that the heights of the IPL and INL of the MSG model were significantly less than those of the control groups; the retinas of the other diabetic models did not exhibit this pathological feature. The RNFLs of type 2 diabetes were thinner, and the characteristics of retinopathy were not obvious in the other animal models. The pathological changes seen on HE images were consistent with the results of the quantitative AI evaluation. Immunohistochemistry results showed that NMDAR2A, GluR2, and NRG1 were significantly downregulated in the retina of MSG mice.

Conclusions

The MSG retinopathy model is closely associated with neurotransmitter abnormalities and exhibits important characteristics of retinal neurodegeneration, making it suitable for studying retinal neurocytopathies. The AI recognition technology for retinal images established in the present study can be used for the quantitative and objective evaluation of drug efficacy.

Biological Potential of Polyphenols in the Context of Metabolic Syndrome: An Analysis of Studies on Animal Models

Metabolic syndrome (MetS) is a disease that has a complex etiology. It is defined as the co-occurrence of several pathophysiological disorders, including obesity, hyperglycemia, hypertension, and dyslipidemia. MetS is currently a severe problem in the public health care system. As its prevalence increases every year, it is now considered a global problem among adults and young populations. The treatment of choice comprises lifestyle changes based mainly on diet and physical activity. Therefore, researchers have been attempting to discover new substances that could help reduce or even reverse the symptoms when added to food. These attempts have resulted in numerous studies. Many of them have investigated the bioactive potential of polyphenols as a "possible remedy", stemming from their antioxidative and anti-inflammatory effects and properties normalizing carbohydrate and lipid metabolism. Polyphenols may be supportive in preventing or delaying the onset of MetS or its complications. Additionally, the consumption of food rich in polyphenols should be considered as a supplement for antidiabetic drugs. To ensure the relevance of the studies on polyphenols' properties, mechanisms of action, and potential human health benefits, researchers have used laboratory animals displaying pathophysiological changes specific to MetS. Polyphenols or their plant extracts were chosen according to the most advantageous mitigation of pathological changes in animal models best reflecting the components of MetS. The present paper comprises an overview of animal models of MetS, and promising polyphenolic compounds whose bioactive potential, effect on metabolic pathways, and supplementation-related benefits were analyzed based on in vivo animal models.

The Changes of Lipidomic Profiles Reveal Therapeutic Effects of Exenatide in Patients With Type 2 Diabetes

OBJECTIVE

Exenatide has been demonstrated beneficial effects on patients with type 2 diabetes mellitus (T2DM) regarding lipid metabolism. However, the potential mechanism remains unclear. We used a lipidomic approach to evaluate lipid changes in response to treatment with exenatide in T2DM patients.

METHODS

Serum lipidomic profiles of 35 newly diagnosed T2DM patients (before and after exenatide treatment) and 20 age-matched healthy controls were analyzed by ultrahigh-performance liquid chromatography-tandem quadrupole time-of-flight mass spectrometry.

RESULTS

A total of 45 lipid species including sphingomyelins (SMs), ceramides (CERs), lysophosphatidylcholines (LPCs), phosphatidylethanolamines (PEs), lysophosphatidylethanolamines (LPEs) and phosphatidylcholines (PCs) were identified in all participants. Compared to the healthy controls, 13 lipid species [SM (d18:1/18:0, d18:1/18:1), Cer (d18:1/18:0, d18:1/16:0, d18:1/20:0, d18:1/24:1), LPC (15:0, 16:0, 17:0), PC (19:0/19:0), LPE (18:0) and PE (16:0/22:6, 18:0/22:6)] were markedly increased in the T2DM group, while PE (17:0/17:0) and PC (18:1/18:0) were decreased (P < 0.05). The serum SM (d18:1/18:0, d18:1/18:1), LPC (16:0), and LPE (18:0) were significantly decreased after exenatide treatment, which was accompanied by the amelioration of lipids and glycemic parameters (TC, LDL-C, ApoA-I, FCP and HbA_1c) in T2DM patients. The chord diagrams showed distinct correlation patterns between lipid classes and subclasses among healthy controls, T2DM patients before and after exenatide treatment.

CONCLUSION

Our results revealed that the therapeutic benefits of exenatide on T2DM might be involved in the improved lipid metabolism, especially SM, LPC, and LPE.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, identifier NCT03297879.

Antipsychotics With Different Chemical Structures Cause Different Degrees of Functional Impairments in the Primary Visual Cortex in a Murine Model: A Pilot Study

Background

Antipsychotic medications can impair vision in patients with schizophrenia. However, little is known regarding the pharmacodynamics of antipsychotics in the primary visual cortex. We aimed to study the pharmacodynamics of antipsychotics in the visual cortex in a murine model.

Methods

We used an adapted 2-photon imaging technique to observe changes in calcium dynamics induced by 4 antipsychotics (olanzapine, risperidone, aripiprazole, and amisulpride) in the primary visual cortex of healthy and schizophrenic C57BL/6 mice. Visual function was further assessed by using a novel object recognition test.

Results

All 4 antipsychotics decreased calcium activity in the primary visual cortex and reduced visual recognition test scores in healthy and schizophrenic mice. The most potent drug was olanzapine, followed by risperidone, aripiprazole, and amisulpride. All drugs showed significant differences between groups.

Conclusion

Our pilot study demonstrated that antipsychotics impair visual cortical function. This finding underscores the importance of monitoring for visual adverse events in patients receiving antipsychotic medications to treat schizophrenia.

Therapeutic effect of Keap1-Nrf2-ARE pathway-related drugs on age-related eye diseases through anti-oxidative stress

Age-related eye diseases, including cataract, glaucoma, diabetic retinopathy (DR), and age-related macular degeneration (AMD), are the leading causes of vision loss in the world. Several studies have shown that the occurrence and development of these diseases have an important relationship with oxidative stress in the eye. The Keap1-Nrf2-ARE pathway is a classical pathway that resists oxidative stress and inflammation in the body. This pathway is also active in the development of age-related eye diseases. A variety of drugs have been shown to treat age-related eye diseases through the Keap1-Nrf2-ARE (Kelch-like ECH-Associating protein 1- nuclear factor erythroid 2 related factor 2-antioxidant response element) pathway. This review describes the role of oxidative stress in the development of age-related eye diseases, the function and regulation of the Keap1-Nrf2-ARE pathway, and the therapeutic effects of drugs associated with this pathway on age-related eye diseases.

High-Fat Diet Induces Inflammation of Meibomian Gland

Purpose

To determine if a high-fat diet (HFD) induces meibomian gland (MG) inflammation in mice.

Methods

Male C57BL/6J mice were fed a standard diet (SD), HFD, or HFD supplemented with the peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist rosiglitazone for various durations. Body weight, blood lipid levels, and eyelid changes were monitored at regular intervals. MG sections were subjected to hematoxylin and eosin staining, LipidTox staining, TUNEL assay, and immunostaining. Quantitative RT-PCR and western blot analyses were performed to detect relative gene expression and signaling pathway activation in MGs.

Results

MG acinus accumulated more lipids in the mice fed the HFD. Periglandular CD45-positive and F4/80-positive cell infiltration were more evident in the HFD mice, and they were accompanied by upregulation of inflammation-related cytokines. PPAR-γ downregulation accompanied activation of the mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) signaling pathways in the HFD mice. There was increased acini cell apoptosis and mitochondria damage in mice fed the HFD. MG inflammation was ameliorated following a shift to the standard diet and rosiglitazone treatment in the mice fed the HFD.

Conclusions

HFD-induced declines in PPAR-γ expression and MAPK and NF-κB signaling pathway activation resulted in MG inflammation and dysfunction in mice.

Dehydrozingerone inhibits renal lipotoxicity in high-fat diet-induced obese mice

Ectopic fat accumulation in the kidneys causes oxidative stress, inflammation and cell death. Dehydrozingerone (DHZ) is a curcumin analog that exhibits antitumour, antioxidant and antidiabetic effects. However, the efficacy of DHZ in diabetic nephropathy (DN) is unknown. Here, we verified the efficacy of DHZ on DN. We divided the experimental animals into three groups: regular diet, 60% high‐fat diet (HFD) and HFD with DHZ for 12 weeks. We analysed levels of renal triglycerides and urinary albumin and albumin‐creatinine ratio, renal morphological changes and molecular changes via real‐time polymerase chain reaction and immunoblotting. Furthermore, high glucose (HG)‐ or palmitate (PA)‐stimulated mouse mesangial cells or mouse podocytes were treated with DHZ for 24 h. As a result, DHZ markedly reduced renal glycerol accumulation and albuminuria excretion through improvement of thickened glomerular basement membrane, podocyte loss and slit diaphragm reduction. In the renal cortex in the HFD group, phospho‐AMPK and nephrin expression reduced, whereas arginase 2 and CD68 expression increased; however, these changes were recovered after DHZ administration. Increased reactive oxygen species (ROS) stimulated by HG or PA in podocytes was inhibited by DHZ treatment. Collectively, these findings indicate that DHZ ameliorates DN via inhibits of lipotoxicity‐induced inflammation and ROS formation.

NR4A1 enhances MKP7 expression to diminish JNK activation induced by ROS or ER-stress in pancreatic β cells for surviving

Under adverse conditions, such as sustained or chronic hyperglycemia or hyperlipidemia, ROS (reactive oxygen species) or/and ER-stress (endoplasmic reticulum stress) will be induced in pancreatic β cells. ROS or ER-stress damages β-cells even leads to apoptosis. Previously we found ROS or ER-stress resulted in JNK activation in β cells and overexpressing NR4A1 in MIN6 cells reduced JNK activation via modulating cbl-b expression and subsequent degrading the upstream JNK kinase (MKK4). To search other possible mechanisms, we found the mRNA level and protein level of MKP7 (a phosphatase for phospho-JNK) were dramatic reduced in pancreatic β cells in the islets from NR4A1 KO mice compared with that from wild type mice. To confirm what we found in animals, we applied pancreatic β cells (MIN6 cells) and found that the expression of MKP7 was increased in NR4A1-overexpression MIN6 cells. We further found that knocking down the expression of MKP7 increased the p-JNK level in pancreatic β cells upon treatment with TG or H₂O₂. After that, we figured out that NR4A1 did enhance the transactivation of the MKP7 promoter by physical association with two putative binding sites. In sum, NR4A1 attenuates JNK phosphorylation incurred by ER-stress or ROS partially via enhancing MKP7 expression, potentially decreases pancreatic β cell apoptosis induced by ROS or ER-stress. Our finding provides a clue for diabetes prevention.

Diabetic Retinopathy and NADPH Oxidase-2: A Sweet Slippery Road

Diabetic retinopathy remains the leading cause of vision loss in working-age adults. The multi-factorial nature of the disease, along with the complex structure of the retina, have hindered in elucidating the exact molecular mechanism(s) of this blinding disease. Oxidative stress appears to play a significant role in its development and experimental models have shown that an increase in cytosolic Reacttive Oxygen Speies (ROS) due to the activation of NADPH oxidase 2 (Nox2), is an early event, which damages the mitochondria, accelerating loss of capillary cells. One of the integral proteins in the assembly of Nox2 holoenzyme, Rac1, is also activated in diabetes, and due to epigenetic modifications its gene transcripts are upregulated. Moreover, addition of hyperlipidemia in a hyperglycemic milieu (type 2 diabetes) further exacerbates Rac1-Nox2-ROS activation, and with time, this accelerates and worsens the mitochondrial damage, ultimately leading to the accelerated capillary cell loss and the development of diabetic retinopathy. Nox2, a multicomponent enzyme, is a good candidate to target for therapeutic interventions, and the inhibitors of Nox2 and Rac1 (and its regulators) are in experimental or clinical trials for other diseases; their possible use to prevent/halt retinopathy will be a welcoming sign for diabetic patients.

Improved Survival and Retinal Function of Aging ZDF Rats in Long-Term, Uncontrolled Diabetes by BGP-15 Treatment

Retinal complications of diabetes often lead to deterioration or even loss of vision. This hastens discovery of pharmacological agents able to counterbalance diabetic retinopathy. BGP-15, an emerging small molecule agent, was formerly proven by our workgroup to be retinoprotective on nonobese diabetic animals, Goto-Kakizaki rats. In the present study, we aimed to examine its long-term tolerability or incidental side effects on obese-prone Zucker diabetic fatty (ZDF) rats to further increase the rationale for a future human translation. To make terminal visual status comparable with our other investigations, we also carried out electroretinography (ERG) at the end of the experiment. Our study was started on 16-week-old ZDF rats and lasted for 52 weeks, while BGP was administered daily by gavage. During the 12 months of treatment, 100% of BGP-treated animals survived compared to the non-treated ZDF group, where 60% of the animals died, which was a statistically significant difference. Based on ERG results, BGP-15 was able to counterbalance visual deterioration of ZDF rats caused by long-term diabetes. Some moderate but significant changes were seen in OGTT results and some relationship to oxidative stress by the western blot method: BGP-15 was able to increase expression of HSP70 and decrease that of NFkB in eyes of rats. These were in concert with our previous observations of SIRT1 increment and MMP9 decrement in diabetic eyes by BGP. In summary, not only is BGP-15 not harmful in the long run but it is even able to reduce the related mortality and the serious consequences of diabetes. BGP-15 is an excellent candidate for future drug development against diabetic retinopathy.

Therapeutic potential of curcumin in diabetic retinopathy (Review)

Diabetic retinopathy (DR) is a type of retinal microangiopathy caused by diabetes mellitus. It has become the leading cause of blindness among working individuals worldwide. DR is becoming increasingly common among younger diabetic patients and there is a need for lifelong treatment. The pathogenic mechanisms of DR are influenced by a number of factors, such as hyperglycemia, hyperlipidemia, inflammatory response and oxidative stress, among others. Currently, the treatment methods for DR mainly include retinal photocoagulation, vitrectomy, or anti‑vascular endothelial growth factor (VEGF) therapy. However, these methods have some disadvantages and limitations. Therefore, it is a matter of great interest and urgency to discover drugs that can target the pathogenesis of DR. Since ancient times, traditional Chinese medicine practitioners have accumulated extensive experiences in the use of Chinese herbal medicine for the prevention and treatment of diseases. In the theory of traditional Chinese medicine, curcumin has the effects of promoting blood circulation and relieving pain. A number of studies have also demonstrated that curcumin has multiple biological activities, including exerting anti‑apoptotic, anti‑inflammatory, antioxidant and antitumor properties. In recent years, studies have also confirmed that curcumin can prevent a variety of diabetic complications, including diabetic nephropathy (DN). However, the preventive and curative effects of curcumin on DR and its mechanisms of action have not yet been fully elucidated. The present review aimed to explore the therapeutic potential of curcumin in diabetes mellitus and DR.

Emerging Roles of Dyslipidemia and Hyperglycemia in Diabetic Retinopathy: Molecular Mechanisms and Clinical Perspectives

Diabetic retinopathy (DR) is a significant cause of vision loss and a research subject that is constantly being explored for new mechanisms of damage and potential therapeutic options. There are many mechanisms and pathways that provide numerous options for therapeutic interventions to halt disease progression. The purpose of the present literature review is to explore both basic science research and clinical research for proposed mechanisms of damage in diabetic retinopathy to understand the role of triglyceride and cholesterol dysmetabolism in DR progression. This review delineates mechanisms of damage secondary to triglyceride and cholesterol dysmetabolism vs. mechanisms secondary to diabetes to add clarity to the pathogenesis behind each proposed mechanism. We then analyze mechanisms utilized by both triglyceride and cholesterol dysmetabolism and diabetes to elucidate the synergistic, additive, and common mechanisms of damage in diabetic retinopathy. Gathering this research adds clarity to the role dyslipidemia has in DR and an evaluation of the current peer-reviewed basic science and clinical evidence provides a basis to discern new potential therapeutic targets.

Identification of aberrantly expressed circular RNAs in hyperlipidemia-induced retinal vascular dysfunction in mice

Hyperlipidemia-induced retinal vascular dysfunction is a complex pathological process. circRNAs are important regulators of biological processes and disease progression. However, the expression pattern of circRNAs in hyperlipidemia-induced retinal vascular dysfunction remains unclear. Herein, we used a murine model of hyperlipidemia and identified 317 differentially expressed circRNAs between hyperlipidemic retinas and normolipidemic retinas by circRNA microarrays. GO analysis indicated that the host genes of dysregulated circRNAs were targeted to cell differentiation (ontology: biological process), cytoplasm (ontology: cellular component), and protein binding (ontology: molecular function). Pathway analysis revealed that circRNAs-mediated network was mostly enriched in focal adhesion signaling. Notably, circLDB1 was significantly up-regulated in the serum of coronary artery disease patients and aqueous humor of age-related macular degeneration patients. circLDB1 regulated endothelial cell viability, proliferation, and apoptosis in vitro. Thus, circRNAs are the promising targets for the prediction and diagnosis of hyperlipidemia-induced vascular diseases.

Diabetic Retinopathy: The Role of Mitochondria in the Neural Retina and Microvascular Disease

Diabetic retinopathy (DR), a common chronic complication of diabetes mellitus and the leading cause of vision loss in the working-age population, is clinically defined as a microvascular disease that involves damage of the retinal capillaries with secondary visual impairment. While its clinical diagnosis is based on vascular pathology, DR is associated with early abnormalities in the electroretinogram, indicating alterations of the neural retina and impaired visual signaling. The pathogenesis of DR is complex and likely involves the simultaneous dysregulation of multiple metabolic and signaling pathways through the retinal neurovascular unit. There is evidence that microvascular disease in DR is caused in part by altered energetic metabolism in the neural retina and specifically from signals originating in the photoreceptors. In this review, we discuss the main pathogenic mechanisms that link alterations in neural retina bioenergetics with vascular regression in DR. We focus specifically on the recent developments related to alterations in mitochondrial metabolism including energetic substrate selection, mitochondrial function, oxidation-reduction (redox) imbalance, and oxidative stress, and critically discuss the mechanisms of these changes and their consequences on retinal function. We also acknowledge implications for emerging therapeutic approaches and future research directions to find novel mitochondria-targeted therapeutic strategies to correct bioenergetics in diabetes. We conclude that retinal bioenergetics is affected in the early stages of diabetes with consequences beyond changes in ATP content, and that maintaining mitochondrial integrity may alleviate retinal disease.

Epigenetics and Mitochondrial Stability in the Metabolic Memory Phenomenon Associated with Continued Progression of Diabetic Retinopathy

Retinopathy continues to progress even when diabetic patients try to control their blood sugar, but the molecular mechanism of this 'metabolic memory' phenomenon remains elusive. Retinal mitochondria remain damaged and vicious cycle of free radicals continues to self-propagate. DNA methylation suppresses gene expression, and diabetes activates DNA methylation machinery. Our aim was to investigate the role of DNA methylation in continued compromised mitochondrial dynamics and genomic stability in diabetic retinopathy. Using retinal endothelial cells, incubated in 20 mM glucose for four days, followed by 5 mM glucose for four days, and retinal microvessels from streptozotocin-induced diabetic rats in poor glycemia for four months, followed by normal glycemia for four additional months, DNA methylation of mitochondrial fusion and mismatch repair proteins, Mfn2 and Mlh1 respectively, was determined. Retinopathy was detected in trypsin-digested microvasculature. Re-institution of good glycemia had no beneficial effect on hypermethylation of Mfn2 and Mlh1 and retinal function (electroretinogram), and the  retinopathy continued to progress. However, intervention of good glycemia directly with DNA methylation inhibitors (Azacytidine or Dnmt1-siRNA), prevented Mfn2 and Mlh1 hypermethylation, and ameliorated retinal dysfunction and diabetic retinopathy. Thus, direct regulation of DNA methylation can prevent/reverse diabetic retinopathy by maintaining mitochondrial dynamics and DNA stability, and prevent retinal functional damage.

Retinopathy in a Diet-Induced Type 2 Diabetic Rat Model and Role of Epigenetic Modifications

Type 2 diabetes accounts for 90% of the population with diabetes, and these patients are generally obese and hyperlipidemic. In addition to hyperglycemia, hyperlipidemia is also closely related with diabetic retinopathy. The aim was to investigate retinopathy in a model closely mimicking the normal progression and metabolic features of the population with type 2 diabetes and elucidate the molecular mechanism. Retinopathy was evaluated in rats fed a 45% kcal as fat diet for 8 weeks before administering streptozotocin, 30 mg/kg body weight (T2D), and compared with age- and duration-matched type 1 diabetic rats (T1D) (60 mg/kg streptozotocin). The role of epigenetic modifications in mitochondrial damage was evaluated in retinal microvasculature. T2D rats were obese and severely hyperlipidemic, with impaired glucose and insulin tolerance compared with age-matched T1D rats. While at 4 months of diabetes, T1D rats had no detectable retinopathy, T2D rats had significant retinopathy, their mitochondrial copy numbers were lower, and mtDNA and Rac1 promoter DNA methylation was exacerbated. At 6 months, retinopathy was comparable in T2D and T1D rats, suggesting that obesity exaggerates hyperglycemia-induced epigenetic modifications, accelerating mitochondrial damage and diabetic retinopathy. Thus, maintenance of good lifestyle and BMI could be beneficial in regulating epigenetic modifications and preventing/retarding retinopathy in patients with diabetes.

Protective potential of klotho protein on diabetic retinopathy: Evidence from clinical and in vitro studies

AIMS/INTRODUCTION

The purpose of the present study was to observe the relationship between serum α-klotho (KL) protein level and diabetic retinopathy (DR), and to further examine the effects of KL protein on apoptosis induced by palmitic acid (PA) in human retinal endothelial cells.

MATERIALS AND METHODS

A total of 17 healthy people and 60 type 2 diabetes patients were included. According to the results from fundus fluorescein angiography, the diabetes patients were divided into three subgroups: without DR, non-proliferative DR and proliferative DR. Serum KL level was measured by enzyme-linked immunosorbent assay. In vitro, human retinal endothelial cells were exposed to PA with or without KL protein. Apoptosis rates were analyzed by flow cytometry analysis. Apoptotic-related protein expressions were detected by western blotting analysis.

RESULTS

Serum KL level was lower in diabetes patients than that in healthy participants (P = 0.007), and was gradually decreased among the without DR, non-proliferative DR and proliferative DR subgroups (P = 0.045). A logistic regression analysis showed that after adjusting for the other confounding factors, serum KL level was independently and negatively related with DR (P = 0.049). Furthermore, the increased apoptosis rates induced by PA were inhibited with the addition of KL protein. Consistently, KL protein reversed the expression levels of the increased pro-apoptotic protein Bax and the decreased anti-apoptotic protein Bcl-2 induced by PA. However, the anti-apoptotic effect of KL protein was attenuated by LY294002 through the phosphatidylinositol 3 kinase-serine∕threonine kinase pathway.

CONCLUSIONS

The data suggested that KL protein was probably a potential protective factor against retinopathy in type 2 diabetes patients.

Functional Regulation of an Oxidative Stress Mediator, Rac1, in Diabetic Retinopathy

PURPOSE

Early activation of cytosolic NADPH oxidase-2 (Nox2) in diabetes increases retinal ROS production, damaging their mitochondria. The assembly of Nox2 holoenzyme requires activation of a small molecular weight G protein Rac1. Rac1 activation is regulated by guanine exchange factors and guanine nucleotide-dissociation inhibitors, and post-translational modifications assist in its association with exchange factors and dissociation inhibitors. The goal of this study is to investigate the mechanisms of Rac1 activation in the development of diabetic retinopathy.

METHODS

The levels of the dissociation inhibitor, prenylating enzyme (farnesyltransferase, FNTA), and exchange factor Vav2 were quantified in human retinal endothelial cells, incubated in normal or high glucose for 96 h. The roles of prenylation and Vav2 in Rac1-Nox2-ROS mitochondrial damage were confirmed in FNTA-siRNA-transfected cells and using the Vav2 inhibitor EHop, respectively. Retinal histopathology and functional changes associated with diabetic retinopathy were analyzed in diabetic mice receiving EHop for 6 months. Key parameters of Rac1 activation were confirmed in the retinal microvasculature from human donors with diabetic retinopathy.

RESULTS

In HRECs, glucose increased FNTA and Vav2 and decreased the dissociation inhibitor. FNTA-siRNA and EHop inhibited glucose-induced activation of Rac1-Nox2-ROS signaling. In diabetic mice, EHop ameliorated the development of retinopathy and functional/structural abnormalities and attenuated Rac1-Nox2-mitochondrial damage. Similar alterations in Rac1 regulators were observed in retinal microvasculature from human donors with diabetic retinopathy. In diabetes, Rac1 prenylation and its interactions with Vav2 contribute to Nox2-ROS-mitochondrial damage, and the pharmacological inhibitors to attenuate Rac1 interactions with its regulators could have the potential to halt/inhibit the development of diabetic retinopathy. Graphical Abstract Activation of prenylating enzyme farnesyltransferase (FNTA) in diabetes, prenylates Rac1. The binding of Rac1 with guanine nucleotide-dissociation inhibitor (GDI) is decreased, but its association with the guanine exchange factor, Vav2, is increased, resulting in Rac1 activation. Active Rac1 helps in the assembly of Nox2 holoenzyme, and Nox2 activation increases cytosolic ROS production, damaging the mitochondria. Damaged mitochondria accelerate capillary cell apoptosis, and ultimately, results in the development of diabetic retinopathy.

Retinal Deficits Precede Cognitive and Motor Deficits in a Rat Model of Type II Diabetes

Purpose

To investigate the temporal appearance of retinal, cognitive, and motor deficits in Goto-Kakizaki (GK) rats, a spontaneously occurring, polygenic model of type II diabetes. GK rats develop impaired insulin secretion at 2 weeks and fasting hyperglycemia at 4 weeks.

Methods

In male and female GK rats and Wistar controls, glucose tolerance test (hyperglycemia) and electroretinogram (ERG, retinal function) were performed at 4 and 8 weeks of age. Spectral domain-optical coherence tomography (retinal structure) was assessed at 6 weeks. Spatial alternation (cognitive function) and number of entries (exploratory behavior) were assessed via Y-maze at 4, 5, 6, 7, and 8 weeks. Rotarod (motor function) was performed at 4, 6, and 8 weeks.

Results

By 4 weeks, the GK rats exhibited significant glucose intolerance (P < 0.001) and retinal deficits, including delays in ERG implicit times (flicker, P < 0.01; oscillatory potentials, P < 0.001). In addition, the GK rats showed greater ERG amplitudes (P < 0.001) and thinner retinas (P < 0.001). At 7 weeks, the GK rats showed deficits in cognitive function (P < 0.001) and exploratory behavior (P < 0.01). However, no motor function deficits were observed by 8 weeks. Interestingly, the male GK rats showed greater hyperglycemia (P < 0.05), but the female rats showed greater ERG delays (P < 0.001).

Conclusions

In GK rats, retinal function deficits developed prior to cognitive or motor deficits. Future studies will investigate common mechanistic links, long-term functional and vascular changes, and whether early retinal deficits can predict cognitive dysfunction or late-stage retinal disease.

Neuroprotective effect of levetiracetam in mouse diabetic retinopathy: Effect on glucose transporter-1 and GAP43 expression

AIMS

Retinopathy is a neurodegenerative complication associating diabetes mellitus. Diabetic retinopathy (DR) is the primary reason of visual loss during early adulthood. DR has a complicated multifactorial pathophysiology initiated by hyperglycaemia-induced ischaemic neurodegenerative retinal changes, followed by vision-threatening consequences. The main therapeutic modalities for DR involve invasive delivery of intravitreal antiangiogenic agents as well as surgical interventions. The current work aimed to explore the potential anti-inflammatory and retinal neuroprotective effects of levetiracetam.

MAIN METHODS

This study was performed on alloxan-induced diabetes in mice (n: 21). After 10 weeks, a group of diabetic animals (n: 7) was treated with levetiracetam (25 mg/kg) for six weeks. Retinal tissues were dissected and paraffin-fixed for examination using (1) morphometric analysis with haematoxylin and eosin (HE), (2) immunohistochemistry (GLUT1, GFAP and GAP43), and (3) RT-PCR-detected expression of retinal inflammatory and apoptotic mediators (TNF-α, IL6, iNOS, NF-κB and Tp53).

KEY FINDINGS

Diabetic mice developed disorganized and debilitated retinal layers with upregulation of the gliosis marker GFAP and downregulation of the neuronal plasticity marker GAP43. Additionally, diabetic retinae showed increased transcription of NF-κB, TNF-α, IL6, iNOS and Tp53. Levetiracetam-treated mice showed downregulation of retinal GLUT1 with relief and regression of retinal inflammation and improved retinal structural organization.

SIGNIFICANCE

Levetiracetam may represent a potential neuroprotective agent in DR. The data presented herein supported an anti-inflammatory role of levetiracetam. However, further clinical studies may be warranted to confirm the effectiveness and safety of levetiracetam in DR patients.

Mitochondrial fusion and maintenance of mitochondrial homeostasis in diabetic retinopathy

Mitochondria are dynamic in structure, and undergo continuous fusion-fission to maintain their homeostasis. In diabetes, retinal mitochondria are swollen, their membrane is damaged and mitochondrial fusion protein, mitofusin 2 (Mfn2), is decreased. DNA methylation machinery is also activated and methylation status of genes implicated in mitochondrial damage and biogenesis is altered. This study aims to investigate the role of mitochondrial fusion in the development of diabetic retinopathy, and to illustrate the molecular mechanism responsible for Mfn2 suppression. Using human retinal endothelial cells, manipulated for Mfn2, we investigated the role of fusion in mitochondrial structural and functional damage in diabetes. The molecular mechanism of its suppression in diabetic milieu was determined by investigating Mfn2 promoter DNA methylation, and confirmed using molecular and pharmacological inhibitors of DNA methylation. Similar studies were performed in the retinal microvasculature (prepared by hypotonic shock method) of diabetic rats, and human donors with documented diabetic retinopathy. Overexpression of Mfn2 prevented glucose-induced increase in mitochondrial fragmentation, decrease in complex III activity and increase in membrane permeability, mtDNA damage and apoptosis. High glucose hypermethylated Mfn2 promoter and decreased transcription factor (SP1) binding, and Dnmt inhibition protected Mfn2 promoter from these changes. In streptozotocin-induced diabetic rats, intravitreal administration of Dnmt1-siRNA attenuated Mfn2 promoter hypermethylation and restored its expression. Human donors with diabetic retinopathy confirmed Mfn2 promoter DNA hypermethylation. Thus, regulating Mfn2 and its epigenetic modifications by molecular/pharmacological means will protect mitochondrial homeostasis in diabetes, and could attenuate the development of retinopathy in diabetic patients.

Elevated serum OxLDL is associated with progression of type 2 Diabetes Mellitus to diabetic retinopathy

Hyperlipidemia is associated with the progression of diabetic retinopathy (DR). Paraoxonase 1 (PON1), an esterase is known to prevent systemic LDL oxidation. This study assessed if serum oxLDL is associated with the progression of Type 2 DM to DR. This study is part of a three-year hospital based prospective study where 87 subjects were recruited. This included T2DM without DR (n = 22); Non-Proliferative (NPDR) (n = 21) and Proliferative DR (PDR) (n = 22) along with age/sex matched controls (n = 22). Serum oxLDL-Ab was estimated by ELISA. Serum PON esterase activity and plasma Malondialdehyde (MDA) level were estimated by spectrophotometry and the serum Advanced Glycation End products (AGE) level by spectroflourimetry. The systemic levels of oxLDL, AGE and MDA were increased with the progression of T2DM without DR to DR as seen by ANOVA (P < 0.05). Serum oxLDL-Ab levels showed a positive correlation to total cholesterol (P = 0.04) as evaluated in the DR group. Statin intake was found to lower PON esterase activity (P < 0.05). Based on this pilot study, it is proposed that elevated serum oxLDL should be validated in larger cohort studies to ensure it could be potential risk factor for the progression of T2DM to DR.

Adaptor Protein p66Shc: A Link Between Cytosolic and Mitochondrial Dysfunction in the Development of Diabetic Retinopathy

AIMS

Diabetes increases oxidative stress in the retina and dysfunctions their mitochondria, accelerating capillary cell apoptosis. A 66 kDa adaptor protein, p66Shc, is considered as a sensor of oxidative stress-induced apoptosis. In the pathogenesis of diabetic retinopathy, a progressive disease, reactive oxygen species (ROS) production by activation of a small molecular weight G-protein (Ras-related C3 botulinum toxin substrate 1 [Rac1])-Nox2 signaling precedes mitochondrial damage. Rac1 activation is facilitated by guanine exchange factors (GEFs), and p66Shc increases Rac1-specific GEF activity of Son of Sevenless 1 (Sos1). p66Shc also possesses oxidoreductase activity and can directly stimulate mitochondrial ROS generation. Our aim was to investigate the role of p66Shc in the development of diabetic retinopathy and mechanism of its transcription.

RESULTS

High glucose increased p66Shc expression in human retinal endothelial cells, and elevated acetylated histone 3 lysine 9 (H3K9) levels and transcriptional factor p53 binding at its promoter. Glucose also augmented interactions between Rac1 and Sos1 and activated Rac1-Nox2. Phosphorylation of p66Shc was increased, allowing it to interact with peptidyl prolyl isomerase to facilitate its localization inside the mitochondria, culminating in mitochondrial damage. P66shc-small interfering RNA (siRNA) inhibited glucose-induced Rac1 activation and mitochondrial damage. Similar results are observed in retinal microvessels from diabetic rats.

INNOVATION

This is the first report identifying the role of p66Shc in the development of diabetic retinopathy and implicating increased histone acetylation in its transcriptional regulation.

CONCLUSION

Thus, p66Shc has dual role in the development of diabetic retinopathy; its regulation in the early stages of the disease should impede Rac1-ROS production and, in the later stages, prevent mitochondrial damage and initiation of a futile cycle of free radicals.

Salvianolic Acid B Attenuates Apoptosis of HUVEC Cells Treated with High Glucose or High Fat via Sirt1 Activation

High glucose and high fat are important inducements for the development and progression of diabetic cardiopathy. Salvianolic acid B (SAB), which is the most abundant and bioactive compound in Danshen, attenuates oxidative stress-related disorders, such as cardiovascular diseases, cerebral ischemia, and diabetes. However, the effect of SAB on diabetic cardiopathy is not clear. The aim of study was to investigate the effect and the underlying molecular mechanisms of SAB on diabetic cardiopathy in vitro model. The human umbilical vein endothelial (HUVEC) cells were treated with high glucose (HG, 30 mM) or high fat (palmitic acid, PA, 0.75 mM) in the presence or absence of SAB (100, 200, and 400 mg/L) and incubated for 24 h. We found that HG or PA induced apoptosis of HUVEC cells, while treatment with SAB inhibited the apoptosis. We also found that SAB reversed HG- or PA-induced oxidative stress, apoptosis cell cytokines production, and expression of thioredoxin-interacting protein (TXNIP). Moreover, SAB increased HG- or PA-induced expression of Sirtuin 1 (Sirt1), a nicotinamide adenine dinucleotide- (NAD⁺-) dependent histone deacetylase. Exposure of HUVEC cells to Ex527 (Sirt1 inhibitor) suppressed the effect of SAB on acetyl-p53 and procaspase-3 expressions. In conclusion, the results suggested that SAB could attenuate HUVEC cells damage treated with HG or PA via Sirt1 and might be a potential therapy agent for the diabetic cardiopathy treatment.

The Status of Metabolic Control in Patients With Type 2 Diabetes Attending Dasman Diabetes Institute, Kuwait

Purpose: To evaluate metabolic control in patients with type 2 diabetes at Dasman Diabetes Institute (DDI, Kuwait), a specialist diabetes clinic and research center, and to investigate its association with patient demographics and clinical characteristics. Methods: Data from 963 patients with type 2 diabetes were retrospectively collected from the Knowledge Based Health Records maintained at DDI for patients who attended DDI during 2011-2014. The collected data included patient demographics, clinical characteristics, and anti-diabetic medications. Student's t-test was used to evaluate the differences in mean values between poor and good glycemic control groups. Categorical variables were assessed using chi-square analysis with Fisher's exact test for small data sets. Results: The patients' mean age was 53.0 ± 9.5 years with equal number of males and females. Females (34.4 ± 7.2 kg/m²) had a higher mean body mass index than males (32.1 ± 6.4 kg/m²). The mean fasting blood glucose and HbA1c levels were 9.6 ± 3.8 mmol/L and 8.5 ± 1.8%, respectively. Dyslipidemia (46%) and hypertension (40%) were the most common comorbidities, whereas nephropathy (36%) and neuropathy (35%) were the most common diabetic complications. The most commonly used anti-diabetic medication was metformin (55%). Factors significantly associated with poor glycemic control (HbA1c level ≥ 7%) included insulin use; neuropathy or foot ulcers as diabetic complications; and elevated systolic blood pressure and total cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides, and fasting blood glucose levels. Factors significantly associated with good glycemic control included metformin use and elevated high-density lipoprotein cholesterol level. The proportion of patients with good glycemic control (HbA1c level < 7%) was 29.5%. A large proportion of the patients with poor glycemic control were only administered monotherapy drugs, and two-thirds of the patients were obese. Further, the American Diabetes Association (ADA) recommendations for blood pressure and LDL cholesterol level were met (62 and 63%, respectively) by follow-up year 4. Conclusion: The therapeutic management of type 2 diabetes in Kuwait is suboptimal. Therapeutic strategies should ensure better adherence to ADA guidelines, evaluate the high obesity rates, and adherence to lifestyle recommendations by patients, and continually promote diabetes education and self-empowerment.

Sirt1: A Guardian of the Development of Diabetic Retinopathy

Diabetic retinopathy is a multifactorial disease, and the exact mechanism of its pathogenesis remains obscure. Sirtuin 1 (Sirt1), a multifunctional deacetylase, is implicated in the regulation of many cellular functions and in gene transcription, and retinal Sirt1 is inhibited in diabetes. Our aim was to determine the role of Sirt1 in the development of diabetic retinopathy and to elucidate the molecular mechanism of its downregulation. Using Sirt1-overexpressing mice that were diabetic for 8 months, structural, functional, and metabolic abnormalities were investigated in vascular and neuronal retina. The role of epigenetics in Sirt1 transcriptional suppression was investigated in retinal microvessels. Compared with diabetic wild-type mice, retinal vasculature from diabetic Sirt1 mice did not present any increase in the number of apoptotic cells or degenerative capillaries or decrease in vascular density. Diabetic Sirt1 mice were also protected from mitochondrial damage and had normal electroretinography responses and ganglion cell layer thickness. Diabetic wild-type mice had hypermethylated Sirt1 promoter DNA, which was alleviated in diabetic Sirt1 mice, suggesting a role for epigenetics in its transcriptional suppression. Thus strategies targeted to ameliorate Sirt1 inhibition have the potential to maintain retinal vascular and neuronal homeostasis, providing opportunities to retard the development of diabetic retinopathy in its early stages.

Therapeutic targets for altering mitochondrial dysfunction associated with diabetic retinopathy

INTRODUCTION

Retinopathy remains as one of the most feared blinding complications of diabetes, and with the prevalence of this life-long disease escalating at an alarming rate, the incidence of retinopathy is also climbing. Although the cutting edge research has identified many molecular mechanisms associated with its development, the exact mechanism how diabetes damages the retina remains obscure, limiting therapeutic options for this devastating disease. Areas covered: This review focuses on the central role of mitochondrial dysfunction/damage in the pathogenesis of diabetic retinopathy, and how damaged mitochondria initiates a self-perpetuating vicious cycles of free radicals. We have also reviewed how mitochondria could serve as a therapeutic target, and the challenges associated with the complex double mitochondrial membranes and a well-defined blood-retinal barrier for optimal pharmacologic/molecular approach to improve mitochondrial function. Expert opinion: Mitochondrial dysfunction provides many therapeutic targets for ameliorating the development of diabetic retinopathy including their biogenesis, DNA damage and epigenetic modifications. New technology to enhance pharmaceuticals uptake inside the mitochondria, nanotechnology to deliver drugs to the retina, and maintenance of mitochondrial homeostasis via lifestyle changes and novel therapeutics to prevent epigenetic modifications, could serve as some of the welcoming avenues for a diabetic patient to target this sight-threatening disease.

Herba Artemisiae Capillaris Extract Prevents the Development of Streptozotocin-Induced Diabetic Nephropathy of Rat

Diabetic nephropathy (DN) is a major cause of end-stage renal disease throughout the world; until now there is no specific drug available. In this work, we use herba artemisiae capillaris extract (HACE) to alleviate renal fibrosis characterized by the excessive accumulation of extracellular matrix (ECM) in rats, aiming to investigate the protective effect of the HACE on DN. We found that the intragastric treatment of high-dose HACE could reverse the effect of streptozotocin not only to decrease the level of blood glucose and blood lipid in different degree but also further to improve renal functions. It is worth mentioning that the effect of HACE treatment was comparable to the positive drug benazepril. Moreover, we found that HACE treatment could on one hand inhibit oxidative stress in DN rats through regulating enzymatic activity for scavenging reactive oxygen species and on the other hand increase the ECM degradation through regulating the activity of metalloproteinase-2 (MMP-2) and the expression of tissue transglutaminase (tTG), which explained why HACE treatment inhibited ECM accumulation. On the basis of above experimental results, we conclude that HACE prevents DN development in a streptozotocin-induced DN rat model, and HACE is a promising candidate to cure DN in clinic.

Fenofibrate attenuates fatty acid-induced islet β-cell dysfunction and apoptosis via inhibiting the NF-κB/MIF dependent inflammatory pathway

BACKGROUND

Fatty acid-induced lipotoxicity and macrophage migration inhibitory factor (MIF) affect pancreatic β-cell function, and may promote the development of diabetes mellitus. However, the association of lipotoxicity with MIF and the effect of Fenofibrate on β-cell function remain unknown.

METHODS

LPL+/- mice and MIN6 cells stimulated with palmitic acid (PA) were utilized as models of lipid metabolism disorders. Factors associated with insulin secretion and apoptosis were assessed in the presence or absence of Fenofibrate. The possible mechanisms of lipotoxicity-induced β-cell dysfunction were also explored.

RESULTS

Fenofibrate effectively improved lipid accumulation in pancreatic β-cells, increased glucose-stimulated insulin secretion and β-cell mass, and significantly downregulated pro-apoptotic molecules, at the gene and protein levels, both in vivo and in vitro. Additionally, elevated MIF levels in serum from LPL+/- mice and PA-treated MIN6 cells were starkly decreased after Fenofibrate administration. Mechanistic analysis indicated that NF-κB signaling was remarkably triggered, which could further activate MIF transcription. Furthermore, Fenofibrate exerted beneficial effects on fatty acid-induced β-cell dysfunction likely by inhibiting the NF-κB/MIF dependent inflammatory response.

CONCLUSIONS

Fenofibrate ameliorates lipotoxicity-induced β-cell dysfunction and apoptosis by inhibiting the NF-κB/MIF inflammatory pathway. These findings provide novel insights into the treatment of lipotoxicity-induced metabolic disorders.

Effects of calcium dobesilate on Nrf2, Keap1 and HO-1 in the lenses of D-galactose-induced cataracts in rats

This study investigated the effects of calcium dobesilate on Nrf2, Keap1 and HO-1 in the lenses of D-galactose-induced cataracts in rats. Thirty Sprague-Dawley rats were randomly divided into three groups: a blank control group, a model control group and a model administration group. A normal diet was given to the rats in the blank control group and the rats with D-galactose-induced cataracts of the model control group. Calcium dobesilate was also given to the rats with D-galactose-induced cataracts of the model administration group. A slit lamp microscope was used to check the degree of lens opacity. RT-PCR and western blot analysis were used to detect the mRNA and protein expression of Nrf2, Keap1 and HO-1 in the lenses of the three groups. There was a significant difference in the degree of lens opacity among the three groups (P<0.05). The model control group was the most turbid of the three groups, followed by the model administration group. Moreover, the mRNA and protein expression of Nrf2, Keap1 and HO-1 in the lenses of the three groups were also significantly different (P<0.05). The mRNA levels of Nrf2 and HO-1 were the highest in the model control group, followed by the model administration group, and were the lowest in the blank control group. However, the mRNA expression level of Keap1 among the three groups had an opposite trend. In conclusion, calcium dobesilate can effectively increase the levels of Nrf2 and HO-1 in the lenses of diabetic cataract rats and inhibit the level of Keap1. Therefore, the therapeutic effect of calcium dobesilate against cataracts is related to the improvement of the Nrf2-Keap1 signaling pathway.

Homonoia riparia and its major component, myricitrin, inhibit high glucose-induced apoptosis of human retinal pericytes

Background

The loss of retinal pericytes is one of the earliest changes associated with diabetic retinopathy (DR). Chronic hyperglycemia induces apoptosis of these cells, leading to the onset and progression of DR. In this study, we investigated the effects of Homonoia riparia (H. riparia) and its major component, myricitrin, on high glucose (HG)-induced apoptosis of primary human retinal pericytes (HRPs).

Methods

The effects of an ethanol extract of H. riparia leaves and of myricitrin on HRP viability and apoptosis were investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. Reactive oxygen species (ROS) levels were measured using 2′,7′-dichlorofluorescein diacetate. The activity of specificity protein 1 (Sp1), a transcription factor, was measured using a luciferase reporter assay and western blot analyses were performed to measure the expression of proteins involved in signaling and apoptosis.

Results

HG produced cytotoxic effects on HRPs, which showed increased Sp1 expression and ROS levels. H. riparia extract and myricitrin significantly inhibited HG-induced apoptosis and ROS generation, and also inhibited Sp1 activity. This was evidenced by an attenuation of the HG-mediated increase in extracellular signal-regulated kinase phosphorylation.

Conclusion

These data indicate that HG-mediated induction of Sp1 is one of a number of key signaling pathways involved in HRP apoptosis, and that H. riparia extracts or myricitrin may provide useful approaches to preventing and treating DR.

Diabetic retinopathy, metabolic memory and epigenetic modifications

Retinopathy, a sight-threatening disease, remains one of the most feared complications of diabetes. Although hyperglycemia is the main initiator, progression of diabetic retinopathy continues even after re-institution of normal glycemic control in diabetic patients, and the deleterious effects of prior hyperglycemic insult depend on the duration and the severity of this insult, suggesting a 'metabolic memory' phenomenon. Metabolic memory phenomenon is successfully duplicated in the experimental models of diabetic retinopathy. Hyperglycemia, in addition to initiating many other biochemical and functional abnormalities and altering expression of genes associated with them, also increases oxidative stress. Increased production of cytosolic reactive oxygen species dysfunctions the mitochondria, and a compromised antioxidant defense system becomes overwhelmed to neutralize free radicals. With the duration of diabetes extending, mitochondrial DNA (mtDNA) is also damaged, and transcription of mtDNA-encoded genes, important for function of the electron transport chain, is compromised. This fuels into a 'self-propagating' vicious cycle of free radicals, and retinopathy continues to progress. Hyperglycemic insult also affects the enzymatic machinery responsible for epigenetic modifications; these modifications alter gene expression without affecting the DNA sequence. Histones and/or DNA modifications of many enzymes, important in mitochondrial homeostasis, affect their activities and disturb mitochondrial homeostasis. Experimental models have shown that these epigenetic modifications have potential to halt only if normal glycemia is maintained from the day of induction of diabetes (streptozotocin) in rats, but if hyperglycemia is allowed to proceed even for couple months before initiation of normal glycemia, these epigenetic modification resist reversal. Supplementation of a therapy targeted to prevent increased oxidative stress or epigenetic modifications, during the normal glucose phase, which has followed high glucose insult, however, helps ameliorate these abnormalities and prevents the progression of diabetic retinopathy. Thus, without undermining the importance of tight glycemic control for a diabetic patient, supplementation of their 'best possible' glycemic control with such targeted therapies has potential to retard further progression of this blinding disease.