Low blood and vitreal BDNF, LXA4 and altered Th1/Th2 cytokine balance are potential risk factors for diabetic retinopathy

Oxidative Stress, Endothelial Dysfunction, and N-Acetylcysteine in Type 2 Diabetes Mellitus

Significance: Cardiovascular diseases (CVDs) remain the leading cause of morbidity and mortality globally. Endothelial dysfunction is closely associated with the development and progression of CVDs. Patients with diabetes mellitus (DM) especially type 2 DM (T2DM) exhibit a significant endothelial cell (EC) dysfunction with substantially increased risk for CVDs. Recent Advances: Excessive reactive oxygen species (ROS) and oxidative stress are important contributing factors to EC dysfunction and subsequent CVDs. ROS production is significantly increased in DM and is critically involved in the development of endothelial dysfunction in diabetic patients. In this review, efforts are made to discuss the role of excessive ROS and oxidative stress in the pathogenesis of endothelial dysfunction and the mechanisms for excessive ROS production and oxidative stress in T2DM. Critical Issues: Although studies with diabetic animal models have shown that targeting ROS with traditional antioxidant vitamins C and E or other antioxidant supplements provides promising beneficial effects on endothelial function, the cardiovascular outcomes of clinical studies with these antioxidant supplements have been inconsistent in diabetic patients. Future Directions: Preclinical and limited clinical data suggest that N-acetylcysteine (NAC) treatment may improve endothelial function in diabetic patients. However, well-designed clinical studies are needed to determine if NAC supplementation would effectively preserve endothelial function and improve the clinical outcomes of diabetic patients with reduced cardiovascular morbidity and mortality. With better understanding on the mechanisms of ROS generation and ROS-mediated endothelial damages/dysfunction, it is anticipated that new selective ROS-modulating agents and effective personalized strategies will be developed for the management of endothelial dysfunction in DM.

The Severity of Diabetic Retinopathy Corresponds with Corneal Nerve Alterations and Ocular Discomfort of the Patient

Diabetic retinopathy (DR) remains the leading cause of blindness in the working-age population. Its progression causes gradual damage to corneal nerves, resulting in decreased corneal sensitivity (CS) and disruption of anterior-eye-surface homeostasis, which is clinically manifested by increased ocular discomfort and dry eye disease (DED). This study included 52 DR patients and 52 sex- and age-matched controls. Ocular Surface Disease Index (OSDI) survey, tear film-related parameters, CS, and in vivo corneal confocal microscopy (IVCM) of the subbasal plexus were performed. Furthermore, all patients underwent tear sampling for neurotrophin and cytokine analysis. OSDI scores were greater in DR patients than in controls (p = 0.00020). No differences in the Schirmer test score, noninvasive tear film-break-up time (NIBUT), tear meniscus or interferometry values, bulbar redness, severity of blepharitis or meibomian gland loss were found. In the DR group, both the CS (p < 0.001), and the scotopic pupil diameter (p = 0.00008) decreased. IVCM revealed reduced corneal nerve parameters in DR patients. The stage of DR was positively correlated with the OSDI (Rs = +0.51, 95% CI: + 0.35-+0.64, p < 0.001) and negatively correlated with IVCM corneal nerve parameters and scotopic pupillometry (Rs = -0.26, 95% CI: -0.44--0.06, p = 0.0097). We found negative correlations between the OSDI and IVCM corneal innervation parameters. The DR group showed lower tear film-brain-derived neurotrophic factor (BDNF) levels (p = 0.0001) and no differences in nerve growth factor (NGF)-β, neurotrophin (NT)-4, vascular endothelial growth factor (VEGF), interleukin (IL)-1β, IL-4, IL-5, IL-6, or IL-12 concentrations. Tumor necrosis factor (TNF)-α, IL-2, IL-8, IL-10, granulocyte macrophage colony-stimulating factor (GM-CSF), and interferon (IFN)-γ levels were decreased among patients with DR. Corneal innervation defects have a direct impact on patients' subjective feelings. The evolution of DR appears to be associated with corneal nerve alterations, emphasizing the importance of IVCM.

hsa_circ_0087100/hsa-miR-6743-5p affects Th1 cell differentiation by regulating STAT1 in diabetic retinopathy

Objective: To elucidate the role of the competitive endogenous RNA (ceRNA) network in immune infiltration of diabetic retinopathy (DR). Methods: We obtained differentially expressed (DE) circRNAs, miRNAs and mRNAs from the Gene Expression Omnibus database. Then, we identified immune infiltration by CIBERSORT and single-sample gene set enrichment analysis and discovered co-expression genes by weighted gene co-expression network analysis. Furthermore, STAT1-mediated Th1 differentiation was determined in DR cell models, DR patients and DR mouse models. Results: hsa_circ_0087100/hsa-miR-6743-5p/STAT1 was involved in immune infiltration of Th1 cells. Aberrant expression of the ceRNA network and STAT1-mediated Th1 differentiation was thus verified in vitro and in vivo. Conclusion: hsa_circ_0087100/hsa-miR-6743-5p/STAT1 may affect Th1 cell differentiation in DR.

The association between interleukin family and diabetes mellitus and its complications: An overview of systematic reviews and meta-analyses

OBJECTIVE

To evaluate and summarize the association between interleukin (IL) concentrations and diabetes mellitus (DM) and its complications.

METHODS

Meta-analyses and eligible individual studies of observational studies investigating the associations between IL and DM and its complications were included. The random-effects model was used to estimate the summary effect, and the heterogeneity among studies was assessed using the Q-statistic and the I2 metric; The Egger's regression and the χ2 test were used to test for small study effects and excess significance bias.

RESULTS

This overview identified 34 meta-analyses that investigated the association between IL concentrations and DM and its complications. Meta-analyses of prospective studies indicated that elevated circulating IL-6 and IL-1β had predictive value for the incident of type 2 diabetes mellitus (T2DM), type 1 diabetes mellitus (T1DM) as well as gestational diabetes mellitus (GDM), and the overall Hazard Ratio (HR) of T2DM was 1.28 (95 % CI: 1.17, 1.40; P＜0.001) per 1 log pg/ml increment in IL-6 levels, however, there was no correlation between circulating IL-10 levels and DM. Meanwhile, the increased level of IL-6 was significantly associated several diabetic complications (Diabetic kidney disease[DKD], diabetic peripheral neuropathy[DPN], and cognitive impairment[CI]), and for the diabetic retinopathy (DR), the levels of IL-1β, IL-8 and IL-10 in the aqueous humor and vitreous humor, but not the blood were significantly correlated with it.

CONCLUSION

Multiple ILs, such as the IL-6 and IL-1β, are definitively linked to DM and its complications, and they may be new targets for the diagnosis and treatment, but stronger evidence needs to be confirmed by prospective studies with larger sample sizes and longer observation periods.

Effects and potential mechanisms of exercise and physical activity on eye health and ocular diseases

In the field of eye health, the profound impact of exercise and physical activity on various ocular diseases has become a focal point of attention. This review summarizes and elucidates the positive effects of exercise and physical activities on common ocular diseases, including dry eye disease (DED), cataracts, myopia, glaucoma, diabetic retinopathy (DR), and age-related macular degeneration (AMD). It also catalogues and offers exercise recommendations based on the varying impacts that different types and intensities of physical activities may have on specific eye conditions. Beyond correlations, this review also compiles potential mechanisms through which exercise and physical activity beneficially affect eye health. From mitigating ocular oxidative stress and inflammatory responses, reducing intraocular pressure, enhancing mitochondrial function, to promoting ocular blood circulation and the release of protective factors, the complex biological effects triggered by exercise and physical activities reveal their substantial potential in preventing and even assisting in the treatment of ocular diseases. This review aims not only to foster awareness and appreciation for how exercise and physical activity can improve eye health but also to serve as a catalyst for further exploration into the specific mechanisms and key targets through which exercise impacts ocular health. Such inquiries are crucial for advancing innovative strategies for the treatment of eye diseases, thereby holding significant implications for the development of new therapeutic approaches.

Current Trends in Diagnosis and Treatment Approach of Diabetic Retinopathy during Pregnancy: A Narrative Review

Diabetes mellitus during pregnancy and gestational diabetes are major concerns worldwide. These conditions may lead to the development of severe diabetic retinopathy during pregnancy or worsen pre-existing cases. Gestational diabetes also increases the risk of diabetes for both the mother and the fetus in the future. Understanding the prevalence, evaluating risk factors contributing to pathogenesis, and identifying treatment challenges related to diabetic retinopathy in expectant mothers are all of utmost importance. Pregnancy-related physiological changes, including those in metabolism, blood flow, immunity, and hormones, can contribute to the development or worsening of diabetic retinopathy. If left untreated, this condition may eventually result in irreversible vision loss. Treatment options such as laser therapy, intravitreal anti-vascular endothelial growth factor drugs, and intravitreal steroids pose challenges in managing these patients without endangering the developing baby and mother. This narrative review describes the management of diabetic retinopathy during pregnancy, highlights its risk factors, pathophysiology, and diagnostic methods, and offers recommendations based on findings from previous literature.

Effect of Glycemic Disorders and Habits on the Concentration of Selected Neurotrophic Factors in Patients with Lumbosacral Intervertebral Disc Degeneration

BACKGROUND

Unhealthy habits, such as overeating processed and high-calorie foods, alcohol abuse, and smoking, negatively impact human health. It has been suggested that the inflammatory process and the resulting growth of nerve fibers within the intervertebral disc (IVD) fissures is the main reason for the pain accompanying IVD degeneration (IVDD).

OBJECTIVES

The aim of this study was to determine whether smoking, alcohol consumption, overweight/obesity, or diabetes comorbidity contribute to the development of IVDD and how the aforementioned factors affect the levels of brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), and growth associated protein 43 (GAP-43) in the study and control groups (intervertebral discs, IVDs from cadavers, and serum samples from voluntary blood donors).

METHODS

The study group comprised 113 patients diagnosed with IVDD who qualified for microdiscectomy. Two control groups (I and II) were used in this study. The first included 81 IVDs obtained from Caucasian human cadavers. Control group II, on the other hand, included serum samples obtained from 113 voluntary blood donors. The expression profiles of BDNF, GDNF, and GAP-43 were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Our statistical analysis confirmed that patients who were overweight/obese, smoked tobacco, consumed alcohol, or had diabetes had a higher risk of IVDD (OR > 1). Statistical analysis showed that BDNF, GAP-43, and GDNF concentrations were significantly higher in the IVDs and serum samples obtained from the study group compared to the control group (p < 0.05). In addition, higher levels of BDNF, GDNF, and GAP-43 were noted in IVDD patients who consumed alcohol, smoked tobacco, were overweight/obese, or had comorbid diabetes compared to patients without these risk factors (p < 0.05).

CONCLUSION

We showed that changes in energy metabolism, habits, and lifestyle, as well as the degenerative process of IVD in the lumbosacral spine contribute to changing the concentration profile of the analyzed neurotrophic factors.

Downregulation of BDNF-TrkB signaling may contribute to the colonic motility disorders in mice with streptozocin-induced diabetes

BACKGROUND

Brain-derived neurotrophic factor (BDNF) acts as a neuromodulator to regulate gut motility, but the role of BDNF in diabetes-related dysmotility is uncertain. The aim of this study was to investigate the possible involvement of BDNF and its receptor TrkB in the colonic hypomotility of mice with streptozotocin (STZ)-induced diabetes.

METHODS

A single intraperitoneal injection of STZ was used to establish a type 1 diabetes model. An organ bath system was applied to observe the contractile activities of colonic muscle strips. Immunofluorescence and western blotting were performed to evaluate the expression of BDNF and TrkB in the colon. ELISA was used to detect BDNF and SP levels in the serum and colon. The patch-clamp technique was applied to record the currents of L-type calcium channels and large conductance Ca2+ -activated K+ channels on smooth muscle cells.

KEY RESULTS

Compared with healthy controls, diabetic mice showed attenuated colonic muscle contraction (p < 0.001), which was partly reversed by BDNF supplementation. TrkB protein expression was significantly reduced in diabetic mice (p < 0.05). In addition, both BDNF and substance P (SP) levels were decreased, and exogenous administration of BDNF increased SP levels in diabetic mice (p < 0.05). Both the TrkB antagonist and the TrkB antibody inhibited the spontaneous contraction of colonic muscle strips (p < 0.01). Moreover, the BDNF-TrkB signaling system enhanced SP-induced muscle contraction.

CONCLUSIONS

Downregulation of BDNF/TrkB signaling and reduced SP release from the colon may contribute to the colonic hypomotility associated with type 1 diabetes. Brain-derived neurotrophic factor supplementation may have therapeutic potential for diabetes-related constipation.

A review on the relationship between Arachidonic acid 15-Lipoxygenase (ALOX15) and diabetes mellitus

Arachidonic acid 15-lipoxygenase (ALOX15), as one of the lipoxygenase family, is mainly responsible for catalyzing the oxidation of various fatty acids to produce a variety of lipid components, contributing to the pathophysiological processes of various immune and inflammatory diseases. Studies have shown that ALOX15 and its related products are widely distributed in human tissues and related to multiple diseases such as liver, cardiovascular, cerebrovascular diseases, diabetes mellitus and other diseases. Diabetes mellitus (DM), the disease studied in this article, is a metabolic disease characterized by a chronic increase in blood glucose levels, which is significantly related to inflammation, oxidative stress, ferroptosis and other mechanisms, and it has a high incidence in the population, accompanied by a variety of complications. Figuring out how ALOX15 is involved in DM is critical to understanding its role in diseases. Therefore, ALOX15 inhibitors or combination therapy containing inhibitors may deliver a novel research direction for the treatment of DM and its complications. This article aims to review the biological effect and the possible function of ALOX15 in the pathogenesis of DM.

Circulating Biomarkers to Predict Diabetic Retinopathy in Patients with Diabetic Kidney Disease

The purpose of this review is to outline the currently available circulating biomarkers to predict diabetic retinopathy (DR) in patients with diabetic kidney disease (DKD). Studies have extensively reported the association between DR and DKD, suggesting the presence of common pathways of microangiopathy. The presence of other ocular complications including diabetic cataracts may hinder the detection of retinopathy, which may affect the visual outcome after surgery. Unlike DKD screening, the detection of DR requires complex, costly machines and trained technicians. Recognizing potential biological markers related to glycation and oxidative stress, inflammation and endothelial dysfunction, basement membrane thickening, angiogenesis, and thrombosis as well as novel molecular markers involved in the microangiopathy process may be useful as predictors of retinopathy and identify those at risk of DR progression, especially in cases where retinal visualization becomes a clinical challenge. Further investigations could assist in deciding which biomarkers possess the highest predictive power to predict retinopathy in clinical settings.

Is fat the future for saving sight? Bioactive lipids and their impact on glaucoma

Glaucoma is characterized by a continuous loss of retinal ganglion cells. The cause of glaucoma is associated with an increase in intraocular pressure (IOP), but the underlying pathophysiology is diverse and, in most cases, unknown. There is an indisputable unmet need to identify new pathways involved in glaucoma pathogenesis. Increasing evidence suggests that bioactive lipids may be critical in the development and progression of glaucoma. Preclinical and clinical bioactive lipid targets exist and are being developed. In this review, we aim to shed light on the potential of bioactive lipids for the prevention, diagnosis, prognosis, and treatment of glaucoma by asking the question "is fat the future for saving sight".

Brain-derived neurotrophic factor in diabetes mellitus: A systematic review and meta-analysis

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor expressed in several tissues, including the brain, gut, and pancreas. Activation of the BDNF/TrkB/CREB reduces hepatic gluconeogenesis, induces hepatic insulin signal transduction, and protects against pancreatic beta-cell loss in diabetes mellitus (DM). Several studies have investigated the possible association between BDNF and DM and its complications, but the results have been conflicting.

AIM

In the present study, we aimed at systematically reviewing the literature on the serum and plasma levels of BDNF in DM and its subgroups such as T2DM, DM patients with depression, and patients with retinopathy.

METHODS

A comprehensive search was conducted in PubMed, Scopus, and Web of Science. We identified 28 eligible studies and calculated the standardized mean difference (SMD) of outcomes as an effect measure.

RESULTS

The meta-analysis included 2734 patients with DM and 6004 controls. Serum BDNF levels were significantly lower in patients with DM vs. controls (SMD = -1.00, P<0.001). Plasma BDNF levels were not different in patients with DM compared with controls. When conducting subgroup analysis, serum BDNF levels were lower among patients with T2DM (SMD = -1.26, P<0.001), DM and depression (SMD = -1.69, P<0.001), and patients with diabetic retinopathy (DR) vs. controls (SMD = -1.03, P = 0.01).

CONCLUSIONS

Serum BDNF levels were lower in patients with DM, T2DM, DM with depression, and DM and DR than the controls. Our findings are in line with the hypothesis that decreased BDNF levels might impair glucose metabolism and contribute to the pathogenesis of DM and its complications.

Comparison of brain-derived neurotrophic factor among subtypes of exudative age-related macular degeneration

PURPOSE

To compare the levels of brain-derived neurotrophic factor (BDNF) in serum and aqueous humor (AH) in eyes with typical neovascular age-related macular degeneration (tAMD), polypoidal choroidal vasculopathy (PCV), and retinal angiomatous proliferation (RAP).

METHODS

This prospective study included 20 patients with tAMD, 20 patients with PCV, 20 patients with RAP, and 20 healthy controls. BDNF levels in the serum and AH were assessed using enzyme-linked immunosorbent assay.

RESULTS

Serum and AH BDNF levels were significantly lower in the age-related macular degeneration groups (tAMD, PCV, and RAP) than in the control group (p < 0.05). There was no significant difference in the mean BDNF levels in the serum and AH among the different nAMD subtypes (p = 0.538).

CONCLUSIONS

We confirmed that serum and AH BDNF levels were independent of the nAMD subtype.

Emerging role of neutrophil extracellular traps in the complications of diabetes mellitus

Immune dysfunction is widely regarded as one of the central tenants underpinning the pathophysiology of diabetes mellitus (DM) and its complications. When discussing immunity, the role of neutrophils must be accounted for: neutrophils are the most abundant of the circulating immune cells and are the first to be recruited to sites of inflammation, where they contribute to host defense via phagocytosis, degranulation, and extrusion of neutrophil extracellular traps (NETs). NETs are composed of DNA associated with nuclear and cytosolic neutrophil proteins. Although originally reported as an antimicrobial strategy to prevent microbial dissemination, a growing body of evidence has implicated NETs in the pathophysiology of various autoimmune and metabolic disorders. In these disorders, NETs propagate a pathologic inflammatory response with consequent tissue injury and thrombosis. Many diabetic complications—such as stroke, retinopathy, impaired wound healing, and coronary artery disease—involve these mechanisms. Therefore, in this review, we discuss laboratory and clinical data informing our understanding of the role of NETs in the development of these complications. NET markers, including myeloperoxidase, citrullinated histone H3, neutrophil elastase, and cell-free double-stranded DNA, can easily be measured in serum or be detected via immunohistochemical/immunocytochemical staining of tissue specimens. Therefore, NET constituents potentially constitute reliable biomarkers for use in the management of diabetic patients. However, no NET-targeting drug is currently approved for the treatment of diabetic complications; a candidate drug will require the outcomes of well-designed, robust clinical trials assessing whether NET inhibition can benefit patients in terms of morbidity, quality of life, health expenditures, and mortality. Therefore, much work remains to be done in translating these encouraging pieces of data into clinical trials for NET-targeting medications to be used in the clinic.

Assessment of macular findings by OCT angiography in patients without clinical signs of diabetic retinopathy: radiomics features for early screening of diabetic retinopathy

This cross-sectional study aimed to quantitatively analyze the optical coherence tomography angiography (OCTA) images using MATLAB-based software and evaluate the initial changes in macular vascular density and the distortion of the foveal avascular zone (FAZ), before the clinical appearance of diabetic retinopathy. For this purpose, 21 diabetic patients without any clinical features indicating DR, and 21 healthy individuals matched with patients based on their demographic characteristics were included. Macular thickness, macular vascular density, and morphological changes of FAZ were assessed using OCTA. The diagnostic ability of morphological parameters was evaluated by receiver operating curve analysis. The intraclass correlation coefficient (ICCC) index was used to check the consistency of the extracted values. There was no significant difference in age, gender, LogMAR visual acuity, spherical equivalent, and intra-ocular pressure amongst patients and controls. No correlation was found between age and the FAZ area as well as vascular density. The vascular structure of the superficial layer showed FAZ enlargement, reduced vascular density in the macular area, and significant deviations of FAZ shape parameters (convexity and Frequency Domain Irregularity) in patients compared with healthy individuals. Measurements were highly correlated between separate imaging sessions with ICCC of over 0.85 for all parameters. The represented data suggests that radiomics parameters can be applied as both an early screening tool and guidance for better follow-up of diabetic patients who have not had any sign of DR in fundoscopic exams.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Correlation between the progression of diabetic retinopathy and inflammasome biomarkers in vitreous and serum – a systematic review

Activation of the NOD-like receptor protein 3 (NLRP3) inflammasome pathway has been implicated in Diabetic retinopathy (DR) pathogenesis, but its impact on DR development and progression remains unclear. Therefore, the primary aim of this systematic literature review was to determine the role of the inflammasome in DR development. Furthermore, the secondary aim was to determine whether systemic inflammasome activity can be used to predict DR progression. Studies measuring vitreous and/or serum inflammasome biomarkers in DR patients with Type 2 Diabetes Mellitus (T2DM) were searched systematically using online databases EMBASE, PubMed and Web of Science with the last search conducted on 29^th of September 2021. The risk of bias was assessed using the Newcastle Ottawa Scale and 20 studies were eligible for narrative analysis. Limitations included the heterogeneity in detection assays used, the small and uneven sample size, a lack of vitreous data in earlier disease stages, and not accounting for patients with other systemic co-morbidities. Analysis showed that inflammasome biomarkers IL-1β and IL-18 increased significantly from non-proliferative DR to proliferative DR in both vitreous and serum, suggesting the inflammasome pathway is activated as DR progresses and that serum inflammasome levels could be explored as potential biomarkers for DR progression.

Diagnostic circulating biomarkers to detect vision-threatening diabetic retinopathy: Potential screening tool of the future?

With the increasing prevalence of diabetes in developing and developed countries, the socio-economic burden of diabetic retinopathy (DR), the leading complication of diabetes, is growing. Diabetic retinopathy (DR) is currently one of the leading causes of blindness in working-age adults worldwide. Robust methodologies exist to detect and monitor DR; however, these rely on specialist imaging techniques and qualified practitioners. This makes detecting and monitoring DR expensive and time-consuming, which is particularly problematic in developing countries where many patients will be remote and have little contact with specialist medical centres. Diabetic retinopathy (DR) is largely asymptomatic until late in the pathology. Therefore, early identification and stratification of vision-threatening DR (VTDR) is highly desirable and will ameliorate the global impact of this disease. A simple, reliable and more cost-effective test would greatly assist in decreasing the burden of DR around the world. Here, we evaluate and review data on circulating protein biomarkers, which have been verified in the context of DR. We also discuss the challenges and developments necessary to translate these promising data into clinically useful assays, to detect VTDR, and their potential integration into simple point-of-care testing devices.

Resolution of Inflammation in Retinal Disorders: Briefly the State

The most frequent retinal diseases, such as diabetic retinopathy, age-related macular degeneration and posterior uveitis, are underlined by oxidative stress or aging-induced retinal inflammation, which contributes to vision impairing or loss. Resolution of inflammation is emerging as a critical phase able to counteract the inflammatory process leading to the progression of retinal damage. Particularly, pro-resolving mediators (PMs) play a key role in the modulation of inflammatory exudates and could be considered a new target to be investigated in different inflammatory-autoimmune pathologies. Here, we highlight the most recent studies concerning the role of the main PMs (lipoxins, resolvins, prtectins, maresins and annexins) in retinal inflammation, in order to collect the best evidence in the field of inflammatory retinal damage resolution and to propose novel pharmacological approaches in the management of the most common retinal diseases.

Possible roles of anti-type II collagen antibody and innate immunity in the development and progression of diabetic retinopathy

The pathogenesis of both diabetic retinopathy (DR) and rheumatoid arthritis (RA) has recently been considered to involve autoimmunity. Serum and synovial fluid levels of anti-type II collagen antibodies increase early after the onset of RA, thus inducing immune responses and subsequent hydrarthrosis and angiogenesis, which resemble diabetic macular edema and proliferative DR (PDR), respectively. We previously reported that DR is also associated with increased serum levels of anti-type II collagen antibodies. Retinal hypoxia in DR may induce pericytes to express type II collagen, resulting in autoantibody production against type II collagen. As the result of blood-retinal barrier disruption, anti-type II collagen antibodies in the serum come into contact with type II collagen around the retinal vessels. A continued loss of pericytes and type II collagen around the retinal vessels may result in a shift of the immune reaction site from the retina to the vitreous. It has been reported that anti-inflammatory M2 macrophages increased in the vitreous of PDR patients, accompanied by the activation of the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, a key regulator of innate immunity. M2 macrophages promote angiogenesis and fibrosis, which might be exacerbated and prolonged by dysregulated innate immunity.

Genetic Modification as a New Approach to Ameliorate the Therapeutic Efficacy of Stem Cells in Diabetic Retinopathy

Over the last decades, the strategy of using stem cells has gained a lot of attention in treating many diseases. Recently, DR was identified as one of the common complications experienced by diabetic patients around the world. The current treatment strategy needs to be addressed since the active progression of DR may lead to permanent blindness. Interestingly, varieties of stem cells have emerged to optimize the therapeutic effects. It is also known that stem cells possess multilineage properties and are capable of differentiating, expanding in vitro and undergoing genetic modification. Moreover, modified stem cells have shown to be an ideal resource to prevent the degenerative disease and exhibit promising effects in conferring the migratory, anti-apoptotic, anti-inflammatory and provide better homing for cells into the damaged tissue or organ as well promoting healing properties. Therefore, the understanding of the functional properties of the stem cells may provide the comprehensive guidance to understand the manipulation of stem cells making them useful for long-term therapeutic applications. Hence in this review the potential use and current challenges of genetically modified stem cells to treat DR will be discussed along with its future perspectives.

Insights in diabetes: Molecular mechanisms-Protectin DX, an anti-inflammatory and a stimulator of inflammation resolution metabolite of docosahexaenoic acid, protects against the development of streptozotocin-induced type 1 and type 2 diabetes mellitus in male Swiss albino mice

Our previous studies revealed that certain endogenous low molecular weight lipids have potent anti-diabetic actions. Of all, arachidonic acid (AA) and its anti-inflammatory and inflammation resolving metabolite lipoxin A4 (LXA4) are the most potent anti-diabetic molecules. Similar anti-diabetic action is also shown by resolvins. In our efforts to identify other similar lipid based anti-diabetic molecules, we investigated potential anti-diabetic action of protectin DX that also has anti-inflammatory and inducer of inflammation resolution action(s) like LXA4. Protectin DX {10(S),17(S)-dihydroxy-4Z,7Z,11E,13Z,15E,19Z-docosahexaenoic acid, also called as 10(S),17(S)-DiHDoHE)} prevented the development of streptozotocin-induced type 1 and type 2 diabetes mellitus in Swiss male albino mice. Protectin DX showed potent anti-inflammatory, antioxidant and anti-apoptotic actions that could explain its anti-diabetic action. In view of these beneficial actions, efforts need to be developed to exploit PDX and other similar compounds as potential anti-diabetic molecule in humans.

Neurovascular Impairment and Therapeutic Strategies in Diabetic Retinopathy

Diabetic retinopathy has recently been defined as a highly specific neurovascular complication of diabetes. The chronic progression of the impairment of the interdependence of neurovascular units (NVUs) is associated with the pathogenesis of diabetic retinopathy. The NVUs consist of neurons, glial cells, and vascular cells, and the interdependent relationships between these cells are disturbed under diabetic conditions. Clinicians should understand and update the current knowledge of the neurovascular impairments in diabetic retinopathy. Above all, neuronal cell death is an irreversible change, and it is directly related to vision loss in patients with diabetic retinopathy. Thus, neuroprotective and vasoprotective therapies for diabetic retinopathy must be established. Understanding the physiological and pathological interdependence of the NVUs is helpful in establishing neuroprotective and vasoprotective therapies for diabetic retinopathy. This review focuses on the pathogenesis of the neurovascular impairments and introduces possible neurovascular protective therapies for diabetic retinopathy.

ALDH2/SIRT1 Contributes to Type 1 and Type 2 Diabetes-Induced Retinopathy through Depressing Oxidative Stress

Clinical observations found vision-threatening diabetic retinopathy (DR) occurs in both type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) patients, but T1DM may perform more progressive retinal abnormalities at the same diabetic duration with or without clinical retinopathy. In the present study, T1DM and T2DM patients without manifestations of DR were included in our preliminary clinical retrospective observation study to investigate the differentiated retinal function at the preclinical stage. Then, T1DM and T2DM rat models with 12-week diabetic duration were constructed to explore the potential mechanism of the discrepancy in retinal disorders. Our data demonstrated T1DM patients presented a poor retinal function, a higher allele frequency for ALDH2GA/AA, and a depressed aldehyde dehydrogenase 2 (ALDH2) activity and silent information regulator 1 (SIRT1) level, compared to T2DM individuals. In line with this, higher amplitudes of neurovascular function-related waves of electroretinograms were found in T2DM rats. Furthermore, the retinal outer nuclear layers were reduced in T1DM rats. The levels of retinal oxidative stress biomarkers including total reactive oxygen species, NADPH oxidase 4 and mitochondrial DNA damage, and inflammatory indicators covering inducible/endothelial nitric acid synthase ratio, interleukin-1, and interleukin-6 were obviously elevated. Notably, the level of retinal ALDH2 and SIRT1 in T1DM rats was significantly diminished, while the expression of neovascularization factors was dramatically enhanced compared to T2DM. Together, our data indicated that the ALDH2/SIRT1 deficiency resulted in prominent oxidative stress and was in association with DR progression. Moreover, a differentiating ALDH2/SIRT1 expression may be responsible for the dissimilar severity of DR pathological processes in chronic inflammatory-related T1DM and T2DM.

Serum and aqueous humor levels of brain-derived neurotrophic factor in patients with primary open-angle glaucoma and normal-tension glaucoma

PURPOSE

This study was designed to compare the levels of brain-derived neurotrophic factor (BDNF) in the serum and aqueous humor (AH) of patients with primary open-angle glaucoma (POAG) and normal-tension glaucoma (NTG).

METHODS

This prospective, observational study consists of 30 patients with POAG, 30 patients with NTG, and 30 healthy controls. The serum and AH BDNF levels were assessed using an enzyme-linked immunosorbent assay.

RESULTS

BDNF levels in serum and AH were markedly lower in the glaucoma groups (POAG and NTG) than in the control group (p < 0.05). When comparing the NTG and POAG groups, the average serum BDNF level was significantly lower in the NTG group than in the POAG group (p < 0.05). The difference in the mean BDNF levels in AH between the POAG and NTG groups was not statistically significant. (p = 0.538).

CONCLUSION

We confirmed that serum BDNF levels were lower in patients with NTG than in those with POAG. BDNF could be a causative systemic biomarker in NTG.

Differential Expression of BDNF and BIM in Streptozotocin-induced Diabetic Rat Retina After Fluoxetine Injection

BACKGROUND

Chronic diabetic retinopathy (DR) is a diabetic complication that causes blindness. Brain-derived neurotrophic factor (BDNF) expression is induced by fluoxetine. We observed the effects of fluoxetine on a streptozotocin (STZ)-induced diabetic rat model in this study.

MATERIALS AND METHODS

Rats were divided into three groups: Control, diabetic (65 mg/kg STZ injection), and diabetic with fluoxetine injection (20 mg/kg/week, six times). Western blotting was performed using anti-BDNF and anti-hexaribonucleotide-binding protein-3. Expression of BCL2 apoptosis regulator-like protein 11 (BIM) was analysed using a reverse transcription-polymerase chain reaction.

RESULTS

BDNF levels were significantly higher in the diabetic group treated with fluoxetine than in the untreated diabetic group. BIM expression was higher in the diabetic group than in the control group. BIM gene expression was lower in fluoxetine-treated diabetic group than in the untreated diabetic group.

CONCLUSION

Fluoxetine had an anti-apoptotic effect with upregulation of BDNF expression in retina of rats with STZ-induced diabetes.

VEGF Mediates Retinal Müller Cell Viability and Neuroprotection through BDNF in Diabetes

To investigate the mechanism of vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF) in Müller cell (MC) viability and neuroprotection in diabetic retinopathy (DR), we examined the role of VEGF in MC viability and BDNF production, and the effect of BDNF on MC viability under diabetic conditions. Mouse primary MCs and cells of a rat MC line, rMC1, were used in investigating MC viability and BDNF production under diabetic conditions. VEGF-stimulated BDNF production was confirmed in mice. The mechanism of BDNF-mediated MC viability was examined using siRNA knockdown. Under diabetic conditions, recombinant VEGF (rVEGF) stimulated MC viability and BDNF production in a dose-dependent manner. rBDNF also supported MC viability in a dose-dependent manner. Targeting BDNF receptor tropomyosin receptor kinase B (TRK-B) with siRNA knockdown substantially downregulated the activated (phosphorylated) form of serine/threonine-specific protein kinase (AKT) and extracellular signal-regulated kinase (ERK), classical survival and proliferation mediators. Finally, the loss of MC viability in TrkB siRNA transfected cells under diabetic conditions was rescued by rBDNF. Our results provide direct evidence that VEGF is a positive regulator for BDNF production in diabetes for the first time. This information is essential for developing BDNF-mediated neuroprotection in DR and hypoxic retinal diseases, and for improving anti-VEGF treatment for these blood-retina barrier disorders, in which VEGF is a major therapeutic target for vascular abnormalities.

RELATIONSHIP BETWEEN STAGES OF DIABETIC RETINOPATHY AND LEVELS OF BRAIN-DERIVED NEUROTROPHIC FACTOR IN AQUEOUS HUMOR AND SERUM

PURPOSE

The aim of the study was to determine aqueous humor and serum levels of brain-derived neurotrophic factor (BDNF) in diabetic patients with and without retinopathy.

METHODS

The study included diabetic patients with or without retinopathy, who had an indication for cataract surgery. The study groups were diabetic patients without retinopathy (Group 2), with nonproliferative diabetic retinopathy (Group 3), and with proliferative retinopathy (Group 4). To quantitatively determine the amount of BDNF in samples, the RayBio Human BDNF ELISA kit (Norcross, GA), based on an enzyme-labeled immunosorbent assay was used.

RESULTS

The median serum BDNF levels were significantly lower in all the study groups than in the control group (P values: 0.038 Group 2, 0.02 Group 3, and 0.002 Group 4). Serum BDNF was lower in Group 4 than in Group 3 (P = 0.030), and in Group 3 than in Group 2 (P = 0.04). The median aqueous humor BDNF levels were significantly decreased in all groups (P values: 0.047 Group 2, 0.021 Group 3, and 0.007 Group 4). There was no significant difference between Groups 2, 3, and 4 (P = 0.214).

CONCLUSION

The serum and aqueous humor BDNF levels decreased in patients with diabetes mellitus (DM) before the emergence of clinical signs of retinopathy.

A Safe GDNF and GDNF/BDNF Controlled Delivery System Improves Migration in Human Retinal Pigment Epithelial Cells and Survival in Retinal Ganglion Cells: Potential Usefulness in Degenerative Retinal Pathologies

We assessed the sustained delivery effect of poly (lactic-co-glycolic) acid (PLGA)/vitamin E (VitE) microspheres (MSs) loaded with glial cell-derived neurotrophic factor (GDNF) alone (GDNF-MSs) or combined with brain-derived neurotrophic factor (BDNF; GDNF/BDNF-MSs) on migration of the human adult retinal pigment epithelial cell-line-19 (ARPE-19) cells, primate choroidal endothelial (RF/6A) cells, and the survival of isolated mouse retinal ganglion cells (RGCs). The morphology of the MSs, particle size, and encapsulation efficiencies of the active substances were evaluated. In vitro release, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability, terminal deoxynucleotidyl transferase (TdT) deoxyuridine dUTP nick-end labelling (TUNEL) apoptosis, functional wound healing migration (ARPE-19; migration), and (RF/6A; angiogenesis) assays were conducted. The safety of MS intravitreal injection was assessed using hematoxylin and eosin, neuronal nuclei (NeuN) immunolabeling, and TUNEL assays, and RGC in vitro survival was analyzed. MSs delivered GDNF and co-delivered GDNF/BDNF in a sustained manner over 77 days. The BDNF/GDNF combination increased RPE cell migration, whereas no effect was observed on RF/6A. MSs did not alter cell viability, apoptosis was absent in vitro, and RGCs survived in vitro for seven weeks. In mice, retinal toxicity and apoptosis was absent in histologic sections. This delivery strategy could be useful as a potential co-therapy in retinal degenerations and glaucoma, in line with future personalized long-term intravitreal treatment as different amounts (doses) of microparticles can be administered according to patients’ needs.

Clinical symptoms, comorbidities and complications in severe and non-severe patients with COVID-19: A systematic review and meta-analysis without cases duplication

BACKGROUND

The pandemic of COVID-19 poses a challenge to global healthcare. The mortality rates of severe cases range from 8.1% to 38%, and it is particularly important to identify risk factors that aggravate the disease.

METHODS

We performed a systematic review of the literature with meta-analysis, using 7 databases to identify studies reporting on clinical characteristics, comorbidities and complications in severe and non-severe patients with COVID-19. All the observational studies were included. We performed a random or fixed effects model meta-analysis to calculate the pooled proportion and 95% confidence interval (CI). Measure of heterogeneity was estimated by Cochran's Q statistic, I index and P value.

RESULTS

A total of 4881 cases from 25 studies related to COVID-19 were included. The most prevalent comorbidity was hypertension (severe: 33.4%, 95% CI: 25.4%-41.4%; non-severe 21.6%, 95% CI: 9.9%-33.3%), followed by diabetes (severe: 14.4%, 95% CI: 11.5%-17.3%; non-severe: 8.5%, 95% CI: 6.1%-11.0%). The prevalence of acute respiratory distress syndrome, acute kidney injury and shock were all higher in severe cases, with 41.1% (95% CI: 14.1%-68.2%), 16.4% (95% CI: 3.4%-29.5%) and 19.9% (95% CI: 5.5%-34.4%), rather than 3.0% (95% CI: 0.6%-5.5%), 2.2% (95% CI: 0.1%-4.2%) and 4.1% (95% CI: -4.8%-13.1%) in non-severe patients, respectively. The death rate was higher in severe cases (30.3%, 95% CI: 13.8%-46.8%) than non-severe cases (1.5%, 95% CI: 0.1%-2.8%).

CONCLUSION

Hypertension, diabetes and cardiovascular diseases may be risk factors for severe COVID-19.

Increased vitreal levels of interleukin-10 in diabetic retinopathy: a Meta-analysis

AIM

To conduct a Meta-analysis for the change of interleukin-10 (IL-10) concentration in vitreous samples of patients with diabetic retinopathy (DR).

METHODS

Systemic search for literature was conducted from the databases of PubMed, Web of Science and Cochrane Library by August 2019. Statistical analyses including standard mean difference (SMD) and its 95% confidence interval (CI) were performed by using RevMan 5.3 software.

RESULTS

Totally 194 studies were screened and finally 11 studies were included in the Meta-analysis. The concentration of IL-10 in the DR group was higher than in the control group (P=0.003, SMD: 0.77, 95%CI: 0.25-1.28). Significant heterogeneity was found among all studies (P<0.00001, I ²=92%). The subgroup analysis showed that the concentration of IL-10 increased in vitreous samples from patients with DR compared to the non-DR controls (P=0.004, SMD: 1.44, 95%CI: 0.46-2.42). Moreover, the concentration of IL-10 in samples of proliferative diabetic retinopathy (PDR) patients was significantly higher than that of non-proliferative diabetic retinopathy (NPDR) patients (P=0.01, SMD: 0.61, 95%CI: 0.13-1.08).

CONCLUSION

The vitreal concentration of IL-10 is significantly increased in patients with DR. Further studies are needed to reveal the mechanisms of IL-10 in DR.

Bioactive lipids in intervertebral disc degeneration and its therapeutic implications

Intervertebral disc (IVD) degeneration is not uncommon. It is estimated that approximately >60% of individuals above the age of 40 years suffer from IVD degeneration. Shan et al. showed that hyperglycemia can enhance apoptosis of anulus fibrosis cells in a JNK pathway and p38 mitogen-activated protein kinase (MAPK) pathway dependent fashion. Recent studies showed that IVD degeneration could be an inflammatory condition characterized by increased production of matrix metalloproteinases, TNF-α, nitric oxide, IL-6, IL-17, IL-9, and prostaglandin E2, and decreased formation of anti-inflammatory molecules such as lipoxin A4. This imbalance between pro- and anti-inflammatory molecules seem to activate JNK pathway and p38 MAPK pathway to induce apoptosis of anulus fibrosis and nucleus pulposus cells. The activation of production of PGE2 (due to activation of COX-2 pathway) seems to be dependent on p38/c-Fos and JNK/c-Jun activation in an AP-1-dependent manner. These results imply that suppressing pro-inflammatory events in the disc by either augmenting anti-inflammatory events or suppressing production of pro-inflammatory molecules or both may form a logical step in the prevention and management of IVD degeneration.

Efficacy and safety of intravitreal dexamethasone implant in treatment naïve eyes with diabetic macular edema: Real world experience

PURPOSE

To evaluate the efficacy and safety of intravitreal dexamethasone implant in treatment naïve eyes with diabetic macular edema (DME).

METHODS

A retrospective analysis of treatment naïve eyes with DME which received intravitreal dexamethasone implant between January 2016 and March 2018 was done. Demographic details of the patients, ocular examination findings at baseline and on follow up visits were noted. Morphological features of DME and central macular thickness were noted on optical coherence tomography at each visit. The details regarding additional treatment for macular edema on follow up were noted.

RESULTS

Sixty five eyes were included in the study. The mean age was 59.14 ± 9.59 years. The follow up ranged from 6 to 48 months. Psuedophakic eyes showed visual improvement whereas the phakic eyes showed stable vision. The central foveal thickness showed significant reduction (p = 0.05) in all the eyes. The best corrected visual acuity at final follow up (+0.65 logMAR) was slightly less as compared to baseline (+0.62 logMAR). Retreatment was needed in 37% eyes and antiglaucoma medications in 8% eyes. Cataract progression was noted in 24 eyes (37%); 17 eyes (26.1%) underwent surgery. Notably, 27 eyes (41.5%) had some degree of macular ischemia at baseline. And five eyes (7.7%) showed progression of retinopathy leading to vitreous hemorrhage.

CONCLUSION

Dexamethasone implant is helpful in reducing the macular thickness and stabilizing the vision in treatment naïve DME; requiring less number of treatment sessions. However, it does not prevent progression of diabetic retinopathy. The visual improvement may be affected by cataract and macular ischemia.

Relationship between Serum Vascular Endothelial Growth Factor Levels and Stages of Diabetic Retinopathy and Other Biomarkers

Aim

This study aims to measure serum vascular endothelial growth factor (VEGF) levels in a sample of Jordanian patients and to determine their relationship with the different stages of diabetic retinopathy. It also explores the correlation between VEGF concentrations and different biochemical and demographic findings.

Materials and Methods

A total of 167 adults participated in the study. Participants were divided into two main categories: patients with diabetes mellitus (DM) type 2 without diabetic retinopathy (DR) (N = 62) and patients with DM type 2 affected by DR (N = 105). DR patients were further subclassified into nonproliferative (N = 41) and proliferative (N = 64). Basic laboratory tests were measured to correlate with VEGF levels. Irisin, a hormone linked to diabetic retinopathy was also measured and correlated with VEGF.

Results

Serum VEGF was found to positively correlate with the severity of diabetic retinopathy. The means of VEGF serum concentrations were 60 pg/mL for controls, 133 pg/mL for nonproliferative DR patients, and 229 pg/mL for proliferative DR patients. We found a significant positive correlation with glycosylated hemoglobin (HbA1c), and a significant negative correlation with high-density lipoprotein (HDL) levels, age, and irisin.

Conclusion

In this cohort of Jordanian diabetics, serum VEGF concentrations strongly correlated with the presence and stages of diabetic retinopathy, suggesting it as an appropriate indicator for diabetic retinopathy early detection and management in this society. VEGF levels also significantly correlated with HbA1c, HDL, and irisin levels. Further studies are encouraged to explore these relationships in other ethnic groups and with different diabetic complications.

Brain-derived neurotrophic factor in non-proliferative diabetic retinopathy with diabetic macular edema

PURPOSE

To investigate aqueous humor (AH) and serum levels of brain-derived neurotrophic factor (BDNF) in non-proliferative diabetic retinopathy (NPDR) patients with diabetic macular edema (DME).

METHODS

The prospective study consists of 20 patients with DME NPDR, 20 patients with no-DME NPDR, and 20 healthy control subjects. Serum and AH samples were obtained during cataract surgery and intravitreal injection. Serum and AH levels of BDNF were measured by enzyme-linked immunosorbent assay.

RESULTS

The mean serum levels of BDNF were lower in both NPDR groups compared to the control group (DME NPDR group, p = 0.015; no-DME NPDR group, p = 0.024). Furthermore, the mean serum level of BDNF was lower in the DME NPDR group compared to the no-DME NPDR group (p = 0.041). The mean AH levels of BDNF were significantly reduced in both NPDR groups compared to the control group (DME NPDR group, p < 0.001; no-DME NPDR group, p = 0.006). Further, the mean AH level of BDNF was significantly lower in the DME NPDR group compared to the no-DME NPDR group (p = 0.037).

CONCLUSION

Serum and AH levels of BDNF were reduced in NPDR patients with DME than without DME.

Diabetic Retinopathy and BDNF: A Review on Its Molecular Basis and Clinical Applications

Impairment of neuroprotection and vasculopathy are the main reasons for the progression of diabetic retinopathy. In this review, we decided to illustrate the molecular and clinical aspects of diabetic retinal neuro-vasculopathy. We searched the Web of Science, PubMed, and Scopus databases with these keywords: “brain-derived neurotrophic factor” and “vascular endothelial growth factor” and/or “diabetic retinopathy.” The most relevant in vitro and clinical trial studies were then extracted for final interpretation. Brain-derived neurotrophic factor and the vascular endothelial growth factor have pivotal roles in the pathogenesis of diabetic retinopathy. They have neuroprotective effects on the retina. However, there are controversial results on the relation between these two factors. Reviewing available articles, we have concluded that various concentrations of these molecules at different stages of retinopathy may exert different effects. Optimal doses of the brain-derived neurotrophic factor at the early stages of retinopathy may have a neuroprotective effect. In contrast, higher concentrations of brain-derived neurotrophic factor might induce inflammatory responses. Damage to the retinal cells due to metabolic alterations associated with diabetes and its consequence vasculopathy may also lead to changes in the ocular microenvironment and cytokines. Changes in cytokines result in the modification of neural cell receptors and the overproduction of vascular endothelial growth factor. It seems that controlling the optimal levels of neuroprotective molecules in the retinal tissue is the main step to halter diabetic retinopathy.

n-3 Fatty Acid and Its Metabolite 18-HEPE Ameliorate Retinal Neuronal Cell Dysfunction by Enhancing Müller BDNF in Diabetic Retinopathy

Diabetic retinopathy (DR) is a widespread vision-threatening disease, and neuroretinal abnormality should be considered as an important problem. Brain-derived neurotrophic factor (BDNF) has recently been considered as a possible treatment to prevent DR-induced neuroretinal damage, but how BDNF is upregulated in DR remains unclear. We found an increase in hydrogen peroxide (H₂O₂) in the vitreous of patients with DR. We confirmed that human retinal endothelial cells secreted H₂O₂ by high glucose, and H₂O₂ reduced cell viability of MIO-M1, Müller glia cell line, PC12D, and the neuronal cell line and lowered BDNF expression in MIO-M1, whereas BDNF administration recovered PC12D cell viability. Streptozocin-induced diabetic rats showed reduced BDNF, which is mainly expressed in the Müller glia cell. Oral intake of eicosapentaenoic acid ethyl ester (EPA-E) ameliorated BDNF reduction and oscillatory potentials (OPs) in electroretinography (ERG) in DR. Mass spectrometry revealed an increase in several EPA metabolites in the eyes of EPA-E-fed rats. In particular, an EPA metabolite, 18-hydroxyeicosapentaenoic acid (18-HEPE), induced BDNF upregulation in Müller glia cells and recovery of OPs in ERG. Our results indicated diabetes-induced oxidative stress attenuates neuroretinal function, but oral EPA-E intake prevents retinal neurodegeneration via BDNF in Müller glia cells by increasing 18-HEPE in the early stages of DR.

Downregulation of circulating miR-320a and target gene prediction in patients with diabetic retinopathy

Objective

To evaluate the expression of a set of miRNAs to identify differentially expressed miRNAs that might be considered reliable biomarkers on Diabetic Retinopathy (DR) blood samples.

Results

Expression levels of MiR-320a, MiR-342-3p, MiR-155, MiR-99a, MiR-29a and MiR-27b were analyzed in 60 healthy controls, 48 Diabetes Melitus (DM) without DR patients and 62 DR patients by qRT-PCR. MiR-320a was shown to be downregulated in the plasma of DR patients compared with DM patients without DR and healthy subjects. Target genes were predicted using miRWalk3.0, miR targeting data and target gene interaction data were imported to Cytoscape to visualize and merge networks and top ranked predicted genes were run through Ontology Genes to perform enrichment analysis on gene sets and classification system to identify biological processes and reactome pathways associated with DR. Highly scored target genes of miR-320a were categorized for various biological processes, including negative regulation of cell aging, negative regulation of cellular protein metabolic process and regulation of cellular response to stress that are critical to the development of DR. Our findings suggest that MiR-320a may have a role in the pathogenesis of DR and may represent novel biomarkers for this disease.

Molecular Basis of the Beneficial Actions of Resveratrol

Resveratrol modulates the transcription factor NF-κB, cytochrome P450 isoenzyme CYP1A1, expression and activity of cyclooxygenase (COX) enzymes, Fas/Fas ligand mediated apoptosis, p53, mTOR and cyclins and various phospho-diesterases resulting in an increase in cytosolic cAMP levels. Cyclic AMP, in turn, activates Epac1/CaMKKβ/AMPK/SIRT1/PGC-1α pathway that facilitates increased oxidation of fatty acids, mitochondrial respiration and their biogenesis and gluconeogenesis. Resveratrol triggers apoptosis of activated T cells and suppresses tumor necrosis factor-α (TNF-α), interleukin-17 (IL-17) and other pro-inflammatory molecules and inhibits expression of hypoxia inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) that may explain its anti-inflammatory actions. Polyunsaturated fatty acids (PUFAs) and their anti-inflammatory metabolites lipoxin A4, resolvins, protectins and maresins have a significant role in obesity, type 2 diabetes mellitus (T2DM), metabolic syndrome and cancer. We observed that PUFAs (especially arachidonic acid, AA) and BDNF (brain-derived neurotrophic factor) protect against the cytotoxic actions of alloxan, streptozotocin, benzo(a)pyrene (BP) and doxorubicin. Thus, there is an overlap in the beneficial actions of resveratrol, PUFAs and BDNF suggesting that these molecules may interact and augment synthesis and action of each other. This is supported by the observation that resveratrol and PUFAs modulate gut microbiota and influence stem cell proliferation and differentiation. Since resveratrol is not easily absorbed from the gut it is likely that it may act on endocannabinoid and light, odor, and taste receptors located in the gut, which, in turn, convey their messages to the various organs via vagus nerve.

Brain-Derived Neurotrophic Factor and Diabetes

Diabetes and its chronic complications still represent a great clinical problem, despite improvements made in the diagnosis and treatment of the disease. People with diabetes have a much higher risk of impaired brain function and psychiatric disorders. Neurotrophins are factors that protect neuronal tissue and improve the function of the central nervous system, and among them is brain-derived neurotrophic factor (BDNF). The level and function of BDNF in diabetes seems to be disturbed by and connected with the presence of insulin resistance. On the other hand, there is evidence for the highly beneficial impact of physical activity on brain function and BDNF level. However, it is not clear if this protective phenomenon works in the presence of diabetes. In this review, we summarize the current available research on this topic and find that the results of published studies are ambiguous.

Molecular pathobiology of scleritis and its therapeutic implications

Scleritis and other autoimmune diseases are characterized by an imbalance in the levels of pro-inflammatory and anti-inflammatory molecules with the balance tilted more towards the former due to the failure of recognition of self. The triggering of inflammatory process could be ascribed to the presence of cytoplasmic DNA/chromatin that leads to activation of cytosolic DNA-sensing cGAS-STING (cyclic GMP-AMP synthase linked to stimulator of interferon genes) pathway and enhanced expression of NF-κB that results in an increase in the production of pro-inflammatory bioactive lipids. Bioactive lipids gamma-linolenic acid (GLA), dihomo-GLA (DGLA), prostaglandin E1 (PGE1), prostacyclin (PGI2) and lipoxin A4, resolvins, protectins and maresins have anti-inflammatory actions, bind to DNA to render it non-antigenic and are decreased in autoimmune diseases. These results suggest that efforts designed to enhance the production of anti-inflammatory bioactive lipids may form a new approach to autoimmune diseases. Local injection or infusion of lipoxins, resolvins, protectins and maresins or their precursors such as arachidonic acid may be exploited in the prevention and management of autoimmune diseases including scleritis, uveitis and lupus/rheumatoid arthritis.

PUFAs, BDNF and lipoxin A4 inhibit chemical-induced cytotoxicity of RIN5F cells in vitro and streptozotocin-induced type 2 diabetes mellitus in vivo

Objective

To study whether minimal doses of arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and lipoxin A4 (LXA4) and brain-derived neurotrophic factor (BDNF), when used in combination can protect RIN5F cells from chemical-induced cytotoxicity. As a corollary, to know whether plasma BDNF and LXA4 are altered in STZ-induced type 2 DM animals.

Materials and methods

RIN5F cells, alloxan (AL), streptozotocin (STZ), doxorubicin (DB), and benzo(a)pyrene (BP) were used in this study. Chemical-induced apoptosis and changes in antioxidants, lipid peroxides and nitric oxide (NO) and LXA4 and BDNF levels in RIN5F cells were studied. Alterations in plasma concentrations of BDNF and LXA4 in STZ-induced type 2 diabetes animals was estimated.

Results

BDNF, LXA4 and AA, EPA and DHA protected (P < 0.001 and P < 0.01 respectively) against AL/STZ/DB/BP-induced toxicity to RIN5F cells in vitro. AL/ STZ/DB/BP inhibited BDNF and LXA4 production by RIN5F cells and were restored to normal by AA, EPA and DHA. Sub-optimal doses of BDNF, LXA4, AA and EPA when used in combination protected against cytotoxic action of AL/STZ/DB/BP on RIN5F cells in vitro by restoring LXA4/BDNF levels and altered antioxidant/lipid peroxides/NO levels (P < 0.01) to normal. STZ (65 mg/kg)-induced type 2 diabetes mellitus animals showed reduced plasma BDNF and LXA4 levels (P < 0.001).

Discussion

AL/STZ/DB/BP-induced cytotoxicity to RIN5F cells in vitro can be prevented by BDNF, LXA4 and AA. AL/STZ/DB/BP are cytotoxic, possibly, by suppressing the production of LXA4 and BDNF in RIN5F cells. STZ-induced type 2 DM animals have decreased plasma levels of LXA4 and BDNF.

Conclusion

The results of the present study suggest that BDNF, LXA4, EPA, DHA, AA, GLA and BDNF protect pancreatic β cells from the cytotoxic action of various chemicals and prevent development of diabetes mellitus. LXA4 seems to be the mediator of these cytoprotective actions of BDNF and PUFAs suggesting a close interaction exists among these molecules (BDNF, PUFAs and LXA4). Hence, methods developed to deliver a combination of PUFAs (especially AA), LXA4 and BDNF may prevent development of diabetes mellitus (both type 1 and type 2).

Specialized pro-resolving mediators in diabetes: novel therapeutic strategies

Diabetes mellitus (DM) is an important metabolic disorder characterized by persistent hyperglycemia resulting from inadequate production and secretion of insulin, impaired insulin action, or a combination of both. Genetic disorders and insulin receptor disorders, environmental factors, lifestyle choices and toxins are key factors that contribute to DM. While it is often referred to as a metabolic disorder, modern lifestyle choices and nutrient excess induce a state of systemic chronic inflammation that results in the increased production and secretion of inflammatory cytokines that contribute to DM. It is chronic hyperglycemia and the low-grade chronic-inflammation that underlies the development of microvascular and macrovascular complications leading to damage in a number of tissues and organs, including eyes, vasculature, heart, nerves, and kidneys. Improvements in the management of risk factors have been beneficial, including focus on intensified glycemic control, but most current approaches only slow disease progression. Even with recent studies employing SGLT2 inhibitors demonstrating protection against cardiovascular and kidney diseases, kidney function continues to decline in people with established diabetic kidney disease (DKD). Despite the many advances and a greatly improved understanding of the pathobiology of diabetes and its complications, there remains a major unmet need for more effective therapeutics to prevent and reverse the chronic complications of diabetes. More recently, there has been growing interest in the use of specialised pro-resolving mediators (SPMs) as an exciting therapeutic strategy to target diabetes and the chronic complications of diabetes.

A systematic review on the functional role of Th1/Th2 cytokines in type 2 diabetes and related metabolic complications

The T-helper (Th1/Th2) paradigm is widely studied for its role in modulating an adaptive immune response, especially in relation to the onset of various autoimmune diseases. In fact, emerging evidence clearly shows an inverse relationship between Th1/Th2 cytokines and the development of type 2 diabetes (T2D) complications, which is accelerated by an exacerbated inflammatory state. Here, relevant studies reporting on any association between the levels of Th1/Th2 cytokines and the development of T2D were retrieved through major electronic databases such as The Cochrane Library, Embase and PubMed. Extracted evidence which mostly involved animal models and human subjects with T2D or metabolic syndrome was assessed for quality and risk of bias using the Downs and Black checklist and Animal Research: Reporting of In Vivo Experiments (ARRIVE) guidelines. Results strongly correlated raised Th1/Th2 cytokines such as interferon-gamma (IFN-γ)/interleukin (IL)-5 and IL-2/IL-5 ratios to T2D, and this was positively linked with the other complications including retinopathy and cardiovascular complications. Further, logistic regression analysis demonstrated that the Th1/Th2 ratios were significantly associated with impaired glucose homeostasis, abnormally enhanced lipid profiles, and insulin resistance. Although more studies making use of a larger sample size are required, current data suggest that optimal modulation of Th1/Th2 cytokines may be an important aspect in the management of T2D and its associated complications.

Proteomic Biomarkers of Retinal Inflammation in Diabetic Retinopathy

Diabetic retinopathy (DR), a sight-threatening neurovasculopathy, is the leading cause of irreversible blindness in the developed world. DR arises as the result of prolonged hyperglycemia and is characterized by leaky retinal vasculature, retinal ischemia, retinal inflammation, angiogenesis, and neovascularization. The number of DR patients is growing with an increase in the elderly population, and therapeutic approaches are limited, therefore, new therapies to prevent retinal injury and enhance repair are a critical unmet need. Besides vascular endothelial growth factor (VEGF)-induced vascular proliferation, several other mechanisms are important in the pathogenesis of diabetic retinopathy, including vascular inflammation. Thus, combining anti-VEGF therapy with other new therapies targeting these pathophysiological pathways of DR may further optimize treatment outcomes. Technological advancements have allowed for high-throughput proteomic studies examining biofluids such as aqueous humor, vitreous humor, tear, and serum. Many DR biomarkers have been identified, especially proteins involved in retinal inflammatory processes. This review attempts to summarize the proteomic biomarkers of DR-associated retinal inflammation identified over the last several years.

Diabetic Retinopathy, lncRNAs, and Inflammation: A Dynamic, Interconnected Network

Diabetic retinopathy (DR) is reaching epidemic levels globally due to the increase in prevalence of diabetes mellitus (DM). DR also has detrimental effects to quality of life, as it is the leading cause of blindness in the working-age population and the most common cause of vision loss in individuals with DM. Over several decades, many studies have recognized the role of inflammation in the development and progression of DR; however, in recent years, accumulating evidence has also suggested that non-coding RNAs, especially long non-coding (lncRNAs), are aberrantly expressed in diabetes and may play a putative role in the development and progression of DR through the modulation of gene expression at the transcriptional, post-transcriptional, or epigenetic level. In this review, we will first highlight some of the key inflammatory mediators and transcription factors involved in DR, and we will then introduce the critical roles of lncRNAs in DR and inflammation. Following this, we will discuss the implications of lncRNAs in other epigenetic mechanisms that may also contribute to the progression of inflammation in DR.

Lipoxin A4 delays the progression of retinal degeneration via the inhibition of microglial overactivation

BACKGROUND

Retinal degeneration (RD) is characterized by progressive photoreceptor degeneration, and emerging evidence has demonstrated that activated microglia-mediated inflammation exacerbates the progression of RD. Lipoxin A4 (LXA4) is an endogenous neuroprotective lipid mediator, but the potential therapeutic roles of LXA4 in RD have not been evaluated.

METHODS

Electroretinogram (ERG) recordings and behavioral tests were used to analyze whether the intravitreal injection (IVI) of LXA4 restored visual function in RD1 mice. Immunostaining, qPCR, western blotting and mouse cytokine arrays using an ex-vivo retinal explant model were successively performed to explore the mechanisms underlying the effects of LXA4.

RESULTS

The key rate-limiting enzyme in LXA4 biosynthesis and the LXA4 receptor were substantially downregulated in end-stage RD1 retinas. LXA4 maintained visual function in RD1 mice from postnatal days 15-21 (PN15 to PN21). Moreover, LXA4 modulated microglial activities, significantly inhibited proinflammatory gene expression, and thereby attenuated photoreceptor apoptosis.

CONCLUSIONS

LXA4 delayed the progression of RD, and thus, the use of LXA4 might be a novel approach for ameliorating dysfunction in neurodegenerative disorders.

Polygonatum sibiricum polysaccharide potentially attenuates diabetic retinal injury in a diabetic rat model

AIMS/INTRODUCTION

To investigate the protective effect of Polygonatum sibiricum polysaccharide (PSP) on the retina in diabetic rats.

MATERIALS AND METHODS

A total of 120 Sprague-Dawley rats were randomly divided into blank control, control model (meaning diabetes mellitus), and diabetes mellitus with PSP intervention of high, medium and low doses groups. The difference of retinal vascularization between groups was evaluated by fluorescein isothiocyanate-dextran perfusion. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining was used to assess apoptosis in the retinal ganglion cells; reverse transcriptase polymerase chain reaction and western blotting were utilized to evaluate the expression of Bcl2-associated X protein, B-cell lymphoma-2 factor, epidermal growth factor, p38 mitogen-activated protein kinases, transforming growth factor-β and vascular endothelial growth factor at the messenger ribonucleic acid and protein level.

RESULTS

Fluorescein isothiocyanate-dextran perfusion showed retinal vascular anomaly in diabetes mellitus rats, but vascular tortuosity and leakage were relatively alleviated after PSP intervention. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining showed numerous terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive retinal cells in the diabetes mellitus group, which then were reduced by PSP treatment. Reverse transcriptase polymerase chain reaction showed that PSP intervention decreased Bcl2-associated X protein, epidermal growth factor, p38 mitogen-activated protein kinases, vascular endothelial growth factor and transforming growth factor-β messenger ribonucleic acid expression, but increased B-cell lymphoma-2 factor messenger ribonucleic acid expression. Western blot showed that PSP intervention upregulated the expression of B-cell lymphoma-2 factor, and downregulated the expression of Bcl2-associated X protein, epidermal growth factor, p38 mitogen-activated protein kinases, vascular endothelial growth factor and transforming growth factor-β proteins.

CONCLUSIONS

Polygonatum sibiricum polysaccharide shows a protective effect against diabetes-induced retinal injury in a dose-dependent manner. The mechanism of action deserves further study and exploration.