Effects of antioxidant gene therapy on the development of diabetic retinopathy and the metabolic memory phenomenon

DJ-1 regulates mitochondrial function and promotes retinal ganglion cell survival under high glucose-induced oxidative stress

Purpose

This study aimed to investigate the antioxidative and neuroprotective effects of DJ-1 in mitigating retinal ganglion cell (RGC) damage induced by high glucose (HG).

Methods

A diabetic mouse model and an HG-induced R28 cell model were employed for loss- and gain-of-function experiments. The expression levels of apoptosis and oxidative stress-related factors, including Bax, Bcl-2, caspase3, Catalase, MnSOD, GCLC, Cyto c, and GPx-1/2, were assessed in both animal and cell models using Western blotting. Retinal structure and function were evaluated through HE staining, electroretinogram, and RGC counting. Mitochondrial function and apoptosis were determined using JC-1 and TUNEL staining, and reactive oxygen species (ROS) measurement.

Results

In the mouse model, hyperglycemia resulted in reduced retinal DJ-1 expression, retinal structural and functional damage, disrupted redox protein profiles, and mitochondrial dysfunction. Elevated glucose levels induced mitochondrial impairment, ROS generation, abnormal protein expression, and apoptosis in R28 cells. Augmenting DJ-1 expression demonstrated a restoration of mitochondrial homeostasis and alleviated diabetes-induced morphological and functional impairments both in vivo and in vitro.

Conclusion

This study provides novel insights into the regulatory role of DJ-1 in mitochondrial dynamics, suggesting a potential avenue for enhancing RGC survival in diabetic retinopathy.

The impact of sestrin2 on reactive oxygen species in diabetic retinopathy

Diabetic retinopathy (DR) is a significant complication of diabetes that often leads to blindness, impacting Müller cells, the primary retinal macroglia involved in DR pathogenesis. Reactive oxygen species (ROS) play a crucial role in the development of DR. The objective of this study was to investigate the involvement of sestrin2 in DR using a high-glucose (HG)-induced Müller cell model and assessing cell proliferation with 5-ethynyl-2-deoxyuridine (EdU) labeling. Following this, sestrin2 was upregulated in Müller cells to investigate its effects on ROS, tube formation, and inflammation both in vitro and in vivo, as well as its interaction with the nuclear factor erythroid2-related factor 2 (Nrf2) signaling pathway. The findings demonstrated a gradual increase in the number of EdU-positive cells over time, with a subsequent decrease after 72 h of exposure to high glucose levels. Additionally, the expression of sestrin2 exhibited a progressive increase over time, followed by a decrease at 72 h. The rh-sestrin2 treatment suppressed the injury of Müller cells, decreased ROS level, and inhibited the tube formation. Rh-sestrin2 treatment enhanced the expression of sestrin2, Nrf2, heme oxygenase-1 (HO-1), and glutamine synthetase (GS); however, the ML385 treatment reversed the protective effect of rh-sestrin2. Finally, we evaluated the effect of sestrin2 in a DR rat model. Sestrin2 overexpression treatment improved the pathological injury of retina and attenuated the oxidative damage and inflammatory reaction. Our results highlighted the inhibitory effect of sestrin2 in the damage of retina, thus presenting a novel therapeutic sight for DR.

Maresin-1 inhibits high glucose induced ferroptosis in ARPE-19 cells by activating the Nrf2/HO-1/GPX4 pathway

BACKGROUND

Maresin-1 plays an important role in diabetic illnesses and ferroptosis is associated with pathogenic processes of diabetic retinopathy (DR). The goal of this study is to explore the influence of maresin-1 on ferroptosis and its molecular mechanism in DR.

METHODS

ARPE-19 cells were exposed to high glucose (HG) condition for developing a cellular model of DR. The CCK-8 assay and flow cytometry were used to assess ARPE-19 cell proliferation and apoptosis, respectively. Furthermore, the GSH content, MDA content, ROS level, and Fe2+ level were measured by using a colorimetric GSH test kit, a Lipid Peroxidation MDA Assay Kit, a DCFH-DA assay and the phirozine technique, respectively. Immunofluorescence labelling was used to detect protein levels of ACSL4 and PTGS2. Messenger RNA and protein expression of HO-1, GPX4 and Nrf2 was evaluated through western blotting and quantitative real time-polymerase chain reaction (qRT-PCR). To establish a diabetic mouse model, mice were intraperitoneally injected 150 mg/kg streptozotocin. The MDA content, ROS level and the iron level were detected by using corresponding commercial kits.

RESULTS

Maresin-1 promoted cell proliferation while reducing the apoptotic process in HG-induced ARPE-19 cells. Maresin-1 significantly reduced ferroptosis induced by HG in ARPE-19 cells, as demonstrated as a result of decreased MDA content, ROS level, Fe2+ level, PTGS2 expression, ACSL4 expression and increased GSH content. With respect to mechanisms, maresin-1 treatment up-regulated the mRNA expression and protein expression of HO-1, GPX4 and Nrf2 in HG-induced ARPE-19 cells. Nrf2 inhibitor reversed the inhibitory effects of maresin-1 on ferroptosis in HG-induced ARPE-19 cells. In vivo experiments, we found that Maresin-1 evidently repressed ferroptosis a mouse model of DR, as evidenced by the decreased MDA content, ROS level and iron level in retinal tissues of mice.

CONCLUSION

Maresin-1 protects ARPE cells from HG-induced ferroptosis via activating the Nrf2/HO-1/GPX4 pathway, suggesting that maresin-1 prevents DR development.

Unconventional avenues to decelerated diabetic retinopathy

Diabetic retinopathy (DR) is an important microvascular complication of diabetes mellitus (DM), causing significant visual impairment worldwide. Current gold standards for retarding the progress of DR include blood sugar control and regular fundus screening. Despite these measures, the incidence and prevalence of DR and vision-threatening DR remain high. Given its slowly progressive course and long latent period, opportunities to contain or slow DR before it threatens vision must be explored. This narrative review assesses the recently described unconventional strategies to retard DR progression. These include gut-ocular flow, gene therapy, mitochondrial dysfunction-oxidative stress, stem cell therapeutics, neurodegeneration, anti-inflammatory treatments, lifestyle modification, and usage of phytochemicals. These therapies impact DR directly, while some of them also influence DM control. Most of these strategies are currently in the preclinical stage, and clinical evidence remains low. Nevertheless, our review suggests that these approaches have the potential for human use to prevent the progression of DR.

Experiment-Based Interventions to Diabetic Retinopathy: Present and Advances

Diabetic retinopathy is the major blinding disease among working-age populations, which is becoming more significant due to the growth of diabetes. The metabolic-induced oxidative and inflammatory stress leads to the insult of neovascular unit, resulting in the core pathophysiology of diabetic retinopathy. Existing therapies focus on the inflammation, oxidation, and angiogenesis phenomena of diabetic retinopathy, without effect to radically cure the disease. This review also summarizes novel therapeutic attempts for diabetic retinopathy along with their advantages and disadvantages, mainly focusing on those using cellular and genetic techniques to achieve remission on a fundamental level of disease.

DNMT1-mediated PPARα methylation aggravates damage of retinal tissues in diabetic retinopathy mice

Background

Peroxisome proliferator-activated receptor alpha (PPARα) is associated with diabetic retinopathy (DR), and the underlying mechanism is still unclear. Aim of this work was to investigate the mechanism of PPARα in DR.

Methods

Human retinal capillary pericytes (HRCPs) were treated with high glucose (HG) to induce DR cell model. DR mouse model was established by streptozotocin injection, and then received 5-Aza-2-deoxycytidine (DAC; DNA methyltransferase inhibitor) treatment. Hematoxylin–eosin staining was performed to assess retinal tissue damage. PPARα methylation was examined by Methylation-Specific PCR. Flow cytometry and DCFH-DA fluorescent probe was used to estimate apoptosis and reactive oxygen species (ROS). The interaction between DNA methyltransferase-1 (DNMT1) and PPARα promoter was examined by Chromatin Immunoprecipitation. Quantitative real-time PCR and western blot were performed to assess gene and protein expression.

Results

HG treatment enhanced the methylation levels of PPARα, and repressed PPARα expression in HRCPs. The levels of apoptotic cells and ROS were significantly increased in HRCPs in the presence of HG. Moreover, DNMT1 was highly expressed in HG-treated HRCPs, and DNMT1 interacted with PPARα promoter. PPARα overexpression suppressed apoptosis and ROS levels of HRCPs, which was rescued by DNMT1 up-regulation. In DR mice, DAC treatment inhibited PPARα methylation and reduced damage of retinal tissues.

Conclusion

DNMT1-mediated PPARα methylation promotes apoptosis and ROS levels of HRCPs and aggravates damage of retinal tissues in DR mice. Thus, this study may highlight novel insights into DR pathogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40659-021-00347-1.

A Review on Mesenchymal Stem Cells for Treatment of Retinal Diseases

Mesenchymal Stem Cells (MSCs) have been studied extensively for the treatment of several retinal diseases. The therapeutic potential of MSCs lies in its ability to differentiate into multiple lineages and secretome enriched with immunomodulatory, anti-angiogenic and neurotrophic factors. Several studies have reported the role of MSCs in repair and regeneration of the damaged retina where the secreted factors from MSCs prevent retinal degeneration, improve retinal morphology and function. MSCs also donate mitochondria to rescue the function of retinal cells and exosomes secreted by MSCs were found to have anti-apoptotic and anti-inflammatory effects. Based on several promising results obtained from the preclinical studies, several clinical trials were initiated to explore the potential advantages of MSCs for the treatment of retinal diseases. This review summarizes the various properties of MSCs that help to repair and restore the damaged retinal cells and its potential for the treatment of retinal degenerative diseases.

Engineering carotenoid production in mammalian cells for nutritionally enhanced cell-cultured foods

Metabolic engineering of mammalian cells has to-date focused primarily on biopharmaceutical protein production or the manipulation of native metabolic processes towards therapeutic aims. However, significant potential exists for expanding these techniques to diverse applications by looking across the taxonomic tree to bioactive metabolites not synthesized in animals. Namely, cross-taxa metabolic engineering of mammalian cells could offer value in applications ranging fromfood and nutrition to regenerative medicine and gene therapy. Towards the former, recent advances in meat production through cell culture suggest the potential to produce meat with fine cellular control, where tuning composition through cross-taxa metabolic engineering could enhance nutrition and food-functionality. Here we demonstrate this possibility by engineering primary bovine and immortalized murine muscle cells with prokaryotic enzymes to endogenously produce the antioxidant carotenoids phytoene, lycopene and β-carotene. These phytonutrients offer general nutritive value and protective effects against diseases associated with red and processed meat consumption, and so offer a promising proof-of-concept for nutritional engineering in cultured meat. We demonstrate the phenotypic integrity of engineered cells, the ability to tune carotenoid yields, and the antioxidant functionality of these compounds in vitro towards both nutrition and food-quality objectives. Our results demonstrate the potential for tailoring the nutritional profile of cultured meats. They further lay a foundation for heterologous metabolic engineering of mammalian cells for applications outside of the clinical realm.

Importance of the Use of Oxidative Stress Biomarkers and Inflammatory Profile in Aqueous and Vitreous Humor in Diabetic Retinopathy

Diabetic retinopathy is one of the leading causes of visual impairment and morbidity worldwide, being the number one cause of blindness in people between 27 and 75 years old. It is estimated that ~191 million people will be diagnosed with this microvascular complication by 2030. Its pathogenesis is due to alterations in the retinal microvasculature as a result of a high concentration of glucose in the blood for a long time which generates numerous molecular changes like oxidative stress. Therefore, this narrative review aims to approach various biomarkers associated with the development of diabetic retinopathy. Focusing on the molecules showing promise as detection tools, among them we consider markers of oxidative stress (TAC, LPO, MDA, 4-HNE, SOD, GPx, and catalase), inflammation (IL-6, IL-1ß, IL-8, IL-10, IL-17A, TNF-α, and MMPs), apoptosis (NF-kB, cyt-c, and caspases), and recently those that have to do with epigenetic modifications, their measurement in different biological matrices obtained from the eye, including importance, obtaining process, handling, and storage of these matrices in order to have the ability to detect the disease in its early stages.

Updates on Gene Therapy for Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR), a leading cause of visual impairment in the developed country, is characterized by vascular lesions and neuronal damage of the retina. Treatment options for this condition are currently limited. The advent of therapy targeting vascular endothelial growth factor (VEGF) demonstrated significant benefits to patients with DR. However, this treatment is limited by its short half-life and requirement for frequent invasive intravitreal injections. In addition, many patients failed to achieve clinically significant improvement in visual function. Gene therapy has the potential to provide an alternative treatment for DR with distinct advantages, such as longer therapeutic effect, less injection frequency, ability to intervene at disease onset, and potentially fewer side effects.

RECENT FINDINGS

Strategies for gene therapy in DR, stemming from the current understanding of the disease pathogenesis, focus on the inhibition of neovascularization and protection of neurovascular degeneration in the retina. Studies with promising results have mainly focussed on animal models due to efficacy and safety concerns, despite a number of successful preclinical studies using adeno-associated virus-mediated transduction to treat both vascular dysfunction and neuronal degeneration. With the optimization of delivery vectors, transgene regulation, and outcome measure, gene therapy will potentially become available for patients with DR. This review provides an update on the current strategies utilized in DR gene therapy research. Several barriers to the clinical application of gene therapy for DR are highlighted, and future directions for this research are proposed.

DJ-1 protects retinal pericytes against high glucose-induced oxidative stress through the Nrf2 signaling pathway

Oxidative stress has been associated with the etipathogenesis of Diabetic retinopathy (DR). Studies have shown that DJ-1 plays an important role in regulating the reactive oxygen species (ROS) production and resistance to oxidative stress-induced apoptosis. This study aimed to investigate whether DJ-1 upregulates oxidative stress and prevents damage to retinal capillary pericytes by increasing antioxidant capacity through the Nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway. Nrf2 is a redox-sensitive transcription factor that encode antioxidant enzymes and phase II metabolic enzymes, activation of Nrf2 functions is one of the critical defensive mechanisms against oxidative stress in many tissues. Our results showed after DJ-1 overexpression, apoptosis of rat retinal pericytes (RRPs) decreased, the ratio of B-cell lymphoma-2 (Bcl-2) to BCL2-Associated X Protein (BAX) increased, the production of ROS decreased, and the protein expression and activity of manganese superoxide dismutase (MnSOD, also called SOD2) and catalase (CAT) increased. DJ-1 overexpression activated Nrf2 expression, however, after Nrf2 silencing, apoptosis of RRPs increased, the ratio of Bcl-2 to BAX decreased, the production of ROS increased, the protein expression of MnSOD and CAT decreased, and the expression of heme oxygenase-1 (HO-1), NADP(H) quinone oxidoreductase (NQO1), glutamate-cysteine ligase catalytic subunit (GCLC) and modifier subunit (GCLM) decreased. These data suggest that enhancement of the Nrf2 pathway is a potential protective strategy for the treatment of DR. Therefore, DJ-1 may prevent high glucose-induced oxidative stress and RRPs apoptosis through the Nrf2 signaling pathway, thereby preventing the early onset and progression of DR.

DJ-1/PARK7 inhibits high glucose-induced oxidative stress to prevent retinal pericyte apoptosis via the PI3K/AKT/mTOR signaling pathway

Reactive oxygen species (ROS) act through multiple pathways to induce apoptosis of retinal capillary pericytes, which is an early marker and the primary cause of the progression of diabetic retinopathy. However, the specific molecular mechanisms behind ROS-induced retinal capillary pericyte loss in diabetic retinopathy remains elusive. In this study, we investigated the molecular regulation and effects of DJ-1/PARK7 on oxidative stress and injury of rat retinal pericytes (RRPs). To perform the research, RRPs were isolated from rat retina and cultured in medium with for 2 days: control group (5.6 mM glucose), high glucose group (30 mM glucose), hypertonic group (5.6 mM glucose + 24.4 mM mannitol). We found decreased expression of DJ-1 and increased apoptosis of RRPs in high glucose group. To further study the role of DJ-1, four groups were divided as follows: normal control group (5.6 mM glucose), high glucose (30 mM glucose), empty vector control group (pcDNA3.1,30 mM glucose), DJ-1 overexpression group (pcDNA3.1-myc-DJ-1,30 mM glucose). DJ-1, P53, p-P53, cleaved caspase-3, manganese superoxide dismutase (MnSOD), catalase (CAT) and PI3K/Akt/mTOR signaling pathway in each group was detected by Western Blot. RRPs apoptosis was detected by Terminal-deoxynucleoitidyl Transferase mediated Nick End Labeling (TUNEL) and 4'6- diamidino-2-phenylindole (DAPI). Mitochondrial function was detected by jc-1 and fluorescent probes DCFH-DA was used to determine reactive oxygen species (ROS). We found that high glucose (30 mM) lasting two days can induce significant apoptosis of RRPs, increase ROS production and expressions of p-p53 and active caspase-3, impair mitochondrial function, decrease the activities of MnSOD and CAT, and decrease expression of DJ-1, p-AKT and p-mTOR. In contrast, DJ-1/PARK7 overexpression significantly increases expression of DJ-1, p-AKT and p-mTOR, increases expression and activities of MnSOD and CAT, improves mitochondrial function, decreases expression of apoptotic gene protein p-p53 and active caspase-3, reduces ROS production and reduces the apoptotic rate of RRPs induced by high glucose. These results suggest that DJ-1 may play a role in protecting RRPs from high glucose induced-oxidative injury. DJ-1 might improve mitochondrial function, inhibit ROS production and enhance antioxidant capacity to reduce apoptosis of retinal pericytes through the PI3K/AKT/mTOR signaling pathway which may be related to early pathogenesis of diabetic retinopathy.

Reactive oxygen species mediates a metabolic memory of high glucose stress signaling in bovine retinal pericytes

AIM

To investigate the role of reactive oxygen species (ROS) and antioxidant mechanism underlying the metabolic memory of bovine retinal pericytes (BRPs) induced by high glucose.

METHODS

Effects of high glucose levels and culture time on BRPs viability were evaluated by CCK-8. BRPs were grown in high-glucose media (30 mmol/L) for 4d followed by culture in normal glucose condition (5.6 mmol/L) for 4d in an experimental group. In contrast, in negative and positive control groups, BRPs were grown in either normal-glucose media or high-glucose media for 8d, respectively. The ROS levels, apoptosis, the expression and activity of manganese superoxide dismutase (MnSOD) in BRPs, as well as the protective effect of adeno-associated viral (AAV)-mediated over expression of MnSOD were determined separately by DCHFA, ELISA and Western blot.

RESULTS

Comparing the result of cells apoptosis, activity and protein expression of MnSOD and caspase-3, the cell culture system that exposed in sequence in 30 mmol/L and normal glucose for 4d was demonstrated as a suitable model of metabolic memory. Furthermore, delivery of antioxidant gene MnSOD can decrease BRPs apoptosis, reduce activated caspase-3, and reverse hyperglycemic memory by reducing the ROS of mitochondria.

CONCLUSION

Increased ROS levels and decreased MnSOD levels may play important roles in pericyte loss of diabetic retinopathy. BRPs cultured in high glucose for 4d followed by normal glucose for 4d could be an appropriate model of metabolic memory. rAAV-MnSOD gene therapy provides a promising strategy to inhibit this blinding disease.

ACSS2-related autophagy has a dual impact on memory

Autophagy is an intracellular degenerative pathway which is responsible for neuronal survival. Under the condition of nutrient deprivation, autophagy can lead to dysfunction in memory consolidation. AMPK/mTOR pathway is currently the most studied autophagy mechanism, while recently researchers have proved ACSS2 can also affect autophagy. ACSS2 is phosphorylated at Ser659 by AMPK and then forms a translocation complex with Importin α5 to translocate into the nucleus. This process interacts with TFEB, resulting in upregulated expression of lysosomal and autophagosomal genes. These upregulations inhibit synaptic plasticity and hence memory functions. On the other hand, ACSS2 is also recognized as a regulator of histone acetylation. After recruiting CBP/p300 and activating CBP’s HAT activity in the nucleus, ACSS2 maintains the level of localized histone acetylation by recapturing acetate from histone deacetylation to reform acetyl-CoA, providing substrates for HAT. The increase of histone acetylation locally enhanced immediate early gene transcription, including Egr2, Fos, Nr2f2, Sgk1, and Arc, to benefit neuronal plasticity and memory in many ways.

Astragalus polysaccharides suppresses high glucose-induced metabolic memory in retinal pigment epithelial cells through inhibiting mitochondrial dysfunction-induced apoptosis by regulating miR-195

BACKGROUND

Metabolic memory contributes to the development of diabetic retinopathy (DR), which is the complication of diabetes. But it's still unknown how to prevent the metabolic memory to treat the DR. In our study, we want to examine the function of Astragalus polysaccharides (APS) in the metabolic memory of retinal pigment epithelium (RPE) pretreated with high glucose (HG).

METHODS

ARPE-19 and PRPE cells were exposed to HG followed by normal glucose (NG) treatment with or without APS. QPCR was used to examine the levels of miR-195 and Bcl-2. MDA and SOD detection assays were used to examine the oxidative stress level. Western blotting and immunostaining were applied to detect the protein level of mitochondrial damage and apoptotic signaling pathway. Flow cytometry and TUNEL staining were used to analyze cell apoptosis. Luciferase assay was used to examine the direct target of miR-195.

RESULTS

APS treatment significantly decreased the expression of miR-195, while increased the expression of Bcl-2 with optimized dosages which were induced by HG treatment, even after replacing the HG with NG. And we found Bcl-2 was the direct target of miR-195. APS alleviated the oxidative stress, mitochondrial damage and cell apoptosis induced by HG and HG + NG treatments in RPE cells via regulating miR-195. Furthermore, we found overexpression of miR-195 abolished the alleviated effects of APS on the HG-treated RPE cells.

CONCLUSIONS

APS suppressed high glucose-induced metabolic memory in retinal pigment epithelial cells through inhibiting mitochondrial dysfunction-induced apoptosis by regulating miR-195.

Novel stem cell and gene therapy in diabetic retinopathy, age related macular degeneration, and retinitis pigmentosa

Degenerative retinal disease leads to significant visual morbidity worldwide. Diabetic retinopathy and macular degeneration are leading causes of blindness in the developed world. While current therapies for these diseases slow disease progression, stem cell and gene therapy may also reverse the effects of these, and other, degenerative retinal conditions. Novel therapies being investigated include the use of various types of stem cells in the regeneration of atrophic or damaged retinal tissue, the prolonged administration of neurotrophic factors and/or drug delivery, immunomodulation, as well as the replacement of mutant genes, and immunomodulation through viral vector delivery. This review will update the reader on aspects of stem cell and gene therapy in diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa and other less common inherited retinal dystrophies. These therapies include the use of adeno-associated viral vector-based therapies for treatment of various types of retinitis pigmentosa and dry age-related macular degeneration. Other potential therapies reviewed include the use of mesenchymal stem cells in local immunomodulation, and the use of stem cells in generating structures like three-dimensional retinal sheets for transplantation into degenerative retinas. Finally, aspects of stem cell and gene therapy in diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, and other less common inherited retinal dystrophies will be reviewed.

Diabetic retinopathy: a complex pathophysiology requiring novel therapeutic strategies

INTRODUCTION

Diabetic retinopathy (DR) is the leading cause of vision loss in the working age population of the developed world. DR encompasses a complex pathology, and one that is reflected in the variety of currently available treatments, which include laser photocoagulation, glucocorticoids, vitrectomy and agents which neutralize vascular endothelial growth factor (VEGF). Whilst these options demonstrate modest clinical benefits, none is yet to fully attenuate clinical progression or reverse damage to the retina. This has led to an interest in developing novel therapies for the condition, such as mediators of angiopoietin signaling axes, immunosuppressants, nonsteroidal anti-inflammatory drugs (NSAIDs), oxidative stress inhibitors and vitriol viscosity inhibitors. Further, preclinical research suggests that gene therapy treatment for DR could provide significant benefits over existing treatments options.

AREAS COVERED

Here we review the pathophysiology of DR and provide an overview of currently available treatments. We then outline recent advances made towards improved patient outcomes and highlight the potential of the gene therapy paradigm to revolutionize DR management.

EXPERT OPINION

Whilst significant progress has been made towards our understanding of DR, further research is required to enable the development of a detailed spatiotemporal model of the disease. In addition, we hope that improvements in our knowledge of the condition facilitate therapeutic innovations that continue to address unmet medical need and improve patient outcomes, with a focus on the development of targeted medicines.

Retinal Cryo-sections, Whole-Mounts, and Hypotonic Isolated Vasculature Preparations for Immunohistochemical Visualization of Microvascular Pericytes

Retinal pericytes play an important role in many diseases of the eye. Immunohistochemical staining techniques of retinal vessels and microvascular pericytes are central to ophthalmological research. It is vital to choose an appropriate method of visualizing the microvascular pericytes. We describe retinal microvascular pericyte immunohistochemical staining in cryo-sections, whole-mounts, and hypotonic isolated vasculature using antibodies for platelet-derived growth factor receptor β (PDGFRβ) and nerve/glial antigen 2 (NG2). This allows us to highlight advantages and shortcomings of each of the three tissue preparations for the visualization of the retinal microvascular pericytes. Cryo-sections provide transsectional visualization of all retinal layers but contain only a few occasional transverse cuts of the microvasculature. Whole-mount provides an overview of the entire retinal vasculature, but visualization of the microvasculature can be troublesome. Hypotonic isolation provides a method to visualize the entire retinal vasculature by the removal of neuronal cells, but this makes the tissue very fragile.

Integrated bioinformatic changes and analysis of retina with time in diabetic rats

Diabetic retinopathy (DR) is the most common chronic complication of diabetes. It can cause impaired vision and even blindness. However, the pathological mechanism of DR is still unknown. In the present study, we use bioinformatic analysis to reveal the pathological changes of early DR in a streptozotocin (STZ) induced diabetes rat model. The dataset GSE28831 was downloaded from the Gene Expression Omnibus (GEO) database. To clarify the pathological mechanism of early DR, genes which were up-regulated (UP group) or down-regulated (DOWN group) over time were identified. One hundred eighty six genes in the UP group and 85 genes in the DOWN group were defined. There were in total 28 Gene ontology (GO) terms with a P value lower than 0.05 in UP group, including astrocyte development, neutrophil chemotaxis, neutrophil aggregation, mesenchymal cell proliferation and so on. In the DOWN group, there were totally 14 GO terms with a P value lower than 0.05, including visual perception, lens development in camera-type eye, camera-type eye development, bicellular tight junction and so on. Signaling pathways were analyzed with all genes in the UP and DOWN groups, and leukocyte transendothelial migration and tight junction were selected. Protein–protein interaction (PPI) network was constructed and six hub genes Diras3, Actn1, Tssk6, Cnot6l, Tek and Fgf4 were selected with connection degree ≥5. S100a8, S100a9 and Tek may be potential targets for DR diagnosis and treatment. This study provides the basis for the diagnosis and treatment of DR in the future.

Supplementation with Phycocyanobilin, Citrulline, Taurine, and Supranutritional Doses of Folic Acid and Biotin-Potential for Preventing or Slowing the Progression of Diabetic Complications

Oxidative stress, the resulting uncoupling of endothelial nitric oxide synthase (eNOS), and loss of nitric oxide (NO) bioactivity, are key mediators of the vascular and microvascular complications of diabetes. Much of this oxidative stress arises from up-regulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. Phycocyanobilin (PhyCB), the light-harvesting chromophore in edible cyanobacteria such as spirulina, is a biliverdin derivative that shares the ability of free bilirubin to inhibit certain isoforms of NADPH oxidase. Epidemiological studies reveal that diabetics with relatively elevated serum bilirubin are less likely to develop coronary disease or microvascular complications; this may reflect the ability of bilirubin to ward off these complications via inhibition of NADPH oxidase. Oral PhyCB may likewise have potential in this regard, and has been shown to protect diabetic mice from glomerulosclerosis. With respect to oxidant-mediated uncoupling of eNOS, high-dose folate can help to reverse this by modulating the oxidation status of the eNOS cofactor tetrahydrobiopterin (BH4). Oxidation of BH4 yields dihydrobiopterin (BH2), which competes with BH4 for binding to eNOS and promotes its uncoupling. The reduced intracellular metabolites of folate have versatile oxidant-scavenging activity that can prevent oxidation of BH4; concurrently, these metabolites promote induction of dihydrofolate reductase, which functions to reconvert BH2 to BH4, and hence alleviate the uncoupling of eNOS. The arginine metabolite asymmetric dimethylarginine (ADMA), typically elevated in diabetics, also uncouples eNOS by competitively inhibiting binding of arginine to eNOS; this effect is exacerbated by the increased expression of arginase that accompanies diabetes. These effects can be countered via supplementation with citrulline, which efficiently enhances tissue levels of arginine. With respect to the loss of NO bioactivity that contributes to diabetic complications, high dose biotin has the potential to "pinch hit" for diminished NO by direct activation of soluble guanylate cyclase (sGC). High-dose biotin also may aid glycemic control via modulatory effects on enzyme induction in hepatocytes and pancreatic beta cells. Taurine, which suppresses diabetic complications in rodents, has the potential to reverse the inactivating impact of oxidative stress on sGC by boosting synthesis of hydrogen sulfide. Hence, it is proposed that concurrent administration of PhyCB, citrulline, taurine, and supranutritional doses of folate and biotin may have considerable potential for prevention and control of diabetic complications. Such a regimen could also be complemented with antioxidants such as lipoic acid, N-acetylcysteine, and melatonin-that boost cellular expression of antioxidant enzymes and glutathione-as well as astaxanthin, zinc, and glycine. The development of appropriate functional foods might make it feasible for patients to use complex nutraceutical regimens of the sort suggested here.

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.

Diabetes Onset at 31-45 Years of Age is Associated with an Increased Risk of Diabetic Retinopathy in Type 2 Diabetes

This hospital-based, cross-sectional study investigated the effect of age of diabetes onset on the development of diabetic retinopathy (DR) among Chinese type 2 diabetes mellitus (DM) patients. A total of 5,214 patients with type 2 DM who were referred to the Department of Ophthalmology at the Shanghai First People’s Hospital from 2009 to 2013 was eligible for inclusion. Diabetic retinopathy status was classified using the grading system of the Early Treatment Diabetic Retinopathy Study (ETDRS). Logistic and hierarchical regression analyses were used to identify independent variables affecting the development of DR. Upon multiple logistic regression analysis, patient age at the time of diabetes onset was significantly associated with development of DR. Further, when the risk of retinopathy was stratified by patient age at the onset of diabetes, the risk was highest in patients in whom diabetes developed at an age of 31–45 years (odds ratio [OR] 1.815 [1.139–2.892]; p = 0.012). Furthermore, when patients were divided into four groups based on the duration of diabetes, DR development was maximal at a diabetes onset age of 31–45 years within each group. A diabetes onset age of 31–45 years is an independent risk factor for DR development in Chinese type 2 DM patients.

The role of pharmacogenetics and advances in gene therapy in the treatment of diabetic retinopathy

Diabetic retinopathy (DR) and its complications such as diabetic macular edema continue to remain a major cause for legal blindness in the developed world. While the introduction of anti-tVEGF agents has significantly improved visual outcomes of patients with DR, unpredictable response, largely due to genetic polymorphisms, appears to be a challenge with this therapy. With advances in identification of various genetic biomarkers, novel therapeutic strategies consisting of gene transfer are being developed and tested for patients with DR. Application of pharmacogenetic principles appears to be a promising futuristic strategy to attenuate diabetes-mediated retinal vasculopathy. In this comprehensive review, data from recent studies in the field of pharmacogenomics for the treatment of DR have been provided.

Association of bilirubin and malondialdehyde levels with retinopathy in type 2 diabetes mellitus

INTRODUCTION

Bilirubin as an antioxidant and malondialdehyde (MDA) as an oxidant have been shown to be associated with various complications of type 2 diabetes mellitus (DM).

AIMS AND OBJECTIVES

The aim was to measure the levels of serum bilirubin and MDA in type 2 DM patients with and without diabetic retinopathy (DR) and to correlate them with severity of DR.

MATERIALS AND METHODS

A total number of 120 subjects out of which 40 were controls without type 2 DM and the rest 80 were type 2 DM patients were included in the study. Of those 80 diabetics, 44 patients did not have DR and 36 patients had DR.

RESULTS

The total bilirubin, direct bilirubin, indirect bilirubin were higher in controls as compared to cases (P = 0.017, 0.033, 0.024). Serum MDA levels were found to be higher in diabetics as compared to controls (P = 0.00). The values of all the three parameters, that is, total bilirubin, direct bilirubin and indirect bilirubin were lower in patients with retinopathy as compared to those without retinopathic changes (P = 0.00, 0.020, and 0.007). Subjects were assigned to quartiles based on serum total bilirubin concentration. The prevalence of DR was significantly lower among persons with the highest bilirubin quartile compared to those with the lowest quartile. The severity of DR was inversely proportional to the total bilirubin levels (P = 0.001). The multiple logistic regression analysis showed total bilirubin to be associated with prevalence of DR (P = 0.035).

CONCLUSIONS

The levels of total bilirubin were significantly lower in patients with DR and also in the late stages of retinopathy as compared to those without retinopathy and in controls but MDA levels did not show any association with DR.