Involvement of brain-derived neurotrophic factor in early retinal neuropathy of streptozotocin-induced diabetes in rats: therapeutic potential of brain-derived neurotrophic factor for dopaminergic amacrine cells

Exploring ocular disorders in Parkinson's disease: A comprehensive review and future perspectives

Parkinson's disease (PD) is a multifaceted neurodegenerative disorder characterized by predominantly motor symptoms. However, recent research has broadened our understanding of PD by revealing its impact on non-motor functions, including ocular manifestations. This review explored the intricate relationship between PD and ocular health, shedding light on the mechanisms underlying common ocular diseases such as dry eye disease, cataract, glaucoma, age-related macular degeneration, and diabetic retinopathy. It also underscores the importance of recognizing ocular manifestations as potential early markers of PD, as well as their impact on patients' daily activities, necessitating prompt identification and intervention to prevent complications and enhance the overall quality of life. Furthermore, future research should prioritize unraveling the potential association between PD and other prevalent ocular diseases, such as myopia, to formulate effective treatment strategies.

Müller cells and retinal angiogenesis: critical regulators in health and disease

Müller cells are the most abundant glial cells in the mammalian retina. Their morphology and metabolism enable them to be in close contact and interact biochemically and physically with almost all retinal cell types, including neurons, pericytes, endothelial cells, and other glial cells, influencing their physiology by releasing bioactive molecules. Studies indicate that Müller glial cells are the primary source of angiogenic growth factor secretion in the neuroretina. Because of this, over the past decade, it has been postulated that Müller glial cells play a significant role in maintaining retinal vascular homeostasis, with potential implications in vasoproliferative retinopathies. This review aims to summarize the current understanding of the mechanisms by which Müller glial cells influence retinal angiogenesis in health and disease, with a particular emphasis on three of the retinopathies with the most significant impact on visual health worldwide: diabetic retinopathy, retinopathy of prematurity, and age-related macular degeneration.

Visual stimulation and brain-derived neurotrophic factor (BDNF) have protective effects in experimental autoimmune uveoretinitis

AIMS

To investigate the therapeutic potential of visual stimulation (VS) and BDNF in murine experimental autoimmune uveoretinitis (EAU).

MAIN METHODS

Mice were immunized by subcutaneous injection of interphotoreceptor retinoid-binding protein in Freund's complete adjuvant and intravenous injection of pertussis toxin, and were then exposed to high-contrast VS 12 h/day (days 1-14 post-immunization). EAU severity was assessed by examining clinical score, visual acuity, inflammatory markers, and immune cells in the retina. The transcriptome of activated retinal cells was determined by RNA-seq using RNA immunoprecipitated in complex with phosphorylated ribosomal protein S6. The retinal levels of protein products of relevant upregulated genes were quantified. The effect of BDNF on EAU was tested in unstimulated mice by its daily topical ocular administration (days 8-14 post-immunization).

KEY FINDINGS

VS attenuated EAU development and decreased the expression of pro-inflammatory cytokines/chemokines and numbers of immune cells in the retina (n = 10-20 eyes/group for each analysis). In activated retinal cells of control mice (n = 30 eyes/group), VS upregulated genes encoding immunomodulatory neuropeptides, of which BDNF and vasoactive intestinal peptide (VIP) also showed increased mRNA and protein levels in the retina of VS-treated EAU mice (n = 6-10 eyes/group for each analysis). In unstimulated EAU mice, BDNF treatment mimicked the protective effects of VS by modulating the inflammatory and stem cell properties of Müller cells (n = 5 eyes/group for each analysis).

SIGNIFICANCE

VS effectively suppresses EAU, at least through enhancing retinal levels of anti-inflammatory and neuroprotective factors, VIP and BDNF. Our findings also suggest BDNF as a promising therapeutic agent for uveitis treatment.

Serum brain-derived neurotrophic factor and macular perfusion in type 2 diabetes mellitus using optical coherence tomography angiography

PURPOSE

To investigate the relationship between serum brain-derived neurotrophic factor (BDNF) and changes in macular perfusion in different stages of diabetic retinopathy (DR) using optical coherence tomography angiography (OCTA).

MATERIALS AND METHODS

The study was conducted on 72 eyes of people with type 2 diabetes mellitus (DM). They were divided into five groups based on their DR stage: no DR (nDR), mild and moderate nonproliferative DR, severe nonproliferative DR, active proliferative DR (aPDR), and stable PDR. The presence or absence of diabetic maculopathy was also used to categorize the cases. All patients underwent a complete history, ophthalmological examination, OCTA imaging, and evaluation of BDNF and glycated hemoglobin A1c levels.

RESULTS

The mean blood BDNF levels in the aPDR group were considerably lower than those in the nDR group (P = 0.023). In comparison to eyes without maculopathy, eyes with maculopathy had considerably decreased mean blood BDNF levels (P = 0.0004). Comparing NPDR and PDR groups to nDR as well as NPDR and PDR, a substantial decrease in average and parafoveal vessel density (VD) of the retina and choriocapillaries was seen (P = 0.02). The Foveal Avascular Zone (FAZ) acircularity index and VD were found to be significantly impacted by deteriorating DR (P = 0.001 and 0.017, respectively). It was discovered that there is a positive correlation between BDNF and the FAZ fractal dimension (P = 0.03). In diabetic eyes, there was a statistically favorable correlation between BDNF levels and best corrected visual acuity (P = 0.002). Furthermore, there was a negative relationship between DM duration and BDNF (P = 0.021).

CONCLUSION

Serum BDNF levels decreased with the progression of DR and in patients with maculopathy. BDNF was found to be related to macular perfusion, particularly in the fovea.

Medicinal utilization and nutritional properties of drumstick (Moringa oleifera)-A comprehensive review

The tropical and subtropical regions of the world support the growth of the Indian plant Moringa oleifera. It usually goes by the name drumstick tree or horseradish tree and thrives in warm climates. The leaves of the M. oleifera tree are now frequently used as nutrients and nutraceuticals due to their availability of various minerals. While having only very minor antinutritional effects, the leaves are abundant in many beneficial compounds. A recent review of the bioactive components and activity of moringa leaves has focused on both in vivo and in vitro studies. Drumstick leaves have antidiabetic qualities, anti-inflammatory, anticancer, and antibacterial qualities among other health benefits. Phytochemicals, in addition to minerals and vitamins, are abundant in this vegetable. The majority of these effects, according to a review in the literature, are mostly brought on by the presence of carotenoids, glucosinolates, and phytochemicals. As a value-added component in the production of wholesome meals, moringa is becoming more popular. Despite extensive research into locating and quantifying these advantageous elements in drumstick leaves, bioavailability and bioaccessibility studies were carried out. Beneficial photochemicals are absorbed and digested through incredibly intricate processes that involve several physicochemical and physiological interactions. Therefore, the biological impact of food may be attributed to its various metabolites that can access particular areas of action rather than its original substances. This body of literature offers the most recent findings in scientific research on the bioavailability, health advantages, nutritional profiles, and bioactive activities of moringa leaves as they relate to their use in a range of food products. Drumsticks are frequently used as a food element that promotes health because of their potent protection against a variety of ailments and the presence of environmental pollutants.

Cell and molecular targeted therapies for diabetic retinopathy

Diabetic retinopathy (DR) stands as a prevalent complication in the eye resulting from diabetes mellitus, predominantly associated with high blood sugar levels and hypertension as individuals age. DR is a severe microvascular complication of both type I and type II diabetes mellitus and the leading cause of vision impairment. The critical approach to combatting and halting the advancement of DR lies in effectively managing blood glucose and blood pressure levels in diabetic patients; however, this is seldom achieved. Both human and animal studies have revealed the intricate nature of this condition involving various cell types and molecules. Aside from photocoagulation, the sole therapy targeting VEGF molecules in the retina to prevent abnormal blood vessel growth is intravitreal anti-VEGF therapy. However, a substantial portion of cases, approximately 30-40%, do not respond to this treatment. This review explores distinctive pathophysiological phenomena of DR and identifiable cell types and molecules that could be targeted to mitigate the chronic changes occurring in the retina due to diabetes mellitus. Addressing the significant research gap in this domain is imperative to broaden the treatment options available for managing DR effectively.

Silva H, P. de Carvalho R, Ventura ALM, Calaza KC, Silveira MS, Kubrusly RCC, de Melo Reis RA. The Healthy and Diseased Retina Seen through Neuron-Glia Interactions

The retina is the sensory tissue responsible for the first stages of visual processing, with a conserved anatomy and functional architecture among vertebrates. To date, retinal eye diseases, such as diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, glaucoma, and others, affect nearly 170 million people worldwide, resulting in vision loss and blindness. To tackle retinal disorders, the developing retina has been explored as a versatile model to study intercellular signaling, as it presents a broad neurochemical repertoire that has been approached in the last decades in terms of signaling and diseases. Retina, dissociated and arranged as typical cultures, as mixed or neuron- and glia-enriched, and/or organized as neurospheres and/or as organoids, are valuable to understand both neuronal and glial compartments, which have contributed to revealing roles and mechanisms between transmitter systems as well as antioxidants, trophic factors, and extracellular matrix proteins. Overall, contributions in understanding neurogenesis, tissue development, differentiation, connectivity, plasticity, and cell death are widely described. A complete access to the genome of several vertebrates, as well as the recent transcriptome at the single cell level at different stages of development, also anticipates future advances in providing cues to target blinding diseases or retinal dysfunctions.

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.

Brain-derived neurotrophic factor in degenerative retinal diseases: Update and novel perspective

Dysfunction and death of neuronal cells are cardinal features of degenerative retinal diseases that are known to arise as the disease progresses. Increasingly evidence suggests that abnormal expression of brain-derived neurotrophic factor (BDNF) may serve as an obligatory relay of the dysfunction and death of neuronal cells in degenerative retinal diseases. Although disorder of BDNF, whether depletion or augmentation, has been connected with neuronal apoptosis and neuroinflammation, the exact mechanisms underlying the effect of impaired BDNF expression on degenerative retinal diseases remain unclear. Here, we present an overview of how BDNF is linked to pathological mechanism of retinal degenerative diseases, summarize BDNF-based treatment strategies, and discuss possible research perspectives in the future.

Retinal Neurodegeneration in Euglycemic Hyperinsulinemia, Prediabetes, and Diabetes

Diabetic retinopathy (DR) is a challenging public health problem mainly because of its growing prevalence and risk of blindness. In general, our current knowledge and practice have failed to prevent the onset or progression of DR to sight-threatening complications. While there are treatment options for sight-threatening complications of DR, it is crucial to pay more attention to the early stages of DR to decrease its prevalence. Growing evidence suggests many pathologic changes occur before clinical presentations of DR in euglycemic hyperinsulinemia, prediabetes, and diabetes. These pathological changes occur in retinal neurons, glia, and microvasculature. A new focus on these preclinical pathologies - especially on hyperinsulinemia - may provide further insight into disease mechanisms, endpoints for clinical trials, and druggable targets in early disease. Here, we review the current evidence on the pathophysiological changes reported in preclinical DR and appraise preventive and treatment options for DR.

Systemic Beta-Hydroxybutyrate Affects BDNF and Autophagy into the Retina of Diabetic Mice

Background: Diabetic retinopathy (DR) is a neurovascular disease, characterized by a deficiency of brain-derived neurotrophic factor (BDNF), a regulator of autophagy. Beta-hydroxybutyrate (BHB), previously reported as a protective agent in DR, has been associated with BDNF promotion. Here, we investigated whether systemic BHB affects the retinal levels of BDNF and local autophagy in diabetic mice with retinopathy; Methods: C57BL/6J mice were administered with intraperitoneal (i.p.) streptozotocin (STZ) (75 mg/kg) injection to develop diabetes. After 2 weeks, they received i.p. injections of BHB (25−50−100 mg/kg) twice a week for 10 weeks. Retinal samples were collected in order to perform immunofluorescence, Western blotting, and ELISA analysis; Results: BHB 50 mg/kg and 100 mg/kg significantly improved retinal BDNF levels (p < 0.01) in diabetic mice. This improvement was negatively associated with autophagosome−lysosome formations (marked by LC3B and ATG14) and to higher levels of connexin 43 (p < 0.01), a marker of cell integrity. Moreover, BHB administration significantly reduced M1 microglial activation and autophagy (p < 0.01); Conclusions: The systemic administration of BHB in mice with DR improves the retinal levels of BDNF, with the consequent reduction of the abnormal microglial autophagy. This leads to retinal cell safety through connexin 43 restoration.

Diabetic macular ischaemia- a new therapeutic target?

Diabetic macular ischaemia (DMI) is traditionally defined and graded based on the angiographic evidence of an enlarged and irregular foveal avascular zone. However, these anatomical changes are not surrogate markers for visual impairment. We postulate that there are vascular phenotypes of DMI based on the relative perfusion deficits of various retinal capillary plexuses and choriocapillaris. This review highlights several mechanistic pathways, including the role of hypoxia and the complex relation between neurons, glia, and microvasculature. The current animal models are reviewed, with shortcomings noted. Therefore, utilising the advancing technology of optical coherence tomography angiography (OCTA) to identify the reversible DMI phenotypes may be the key to successful therapeutic interventions for DMI. However, there is a need to standardise the nomenclature of OCTA perfusion status. Visual acuity is not an ideal endpoint for DMI clinical trials. New trial endpoints that represent disease progression need to be developed before irreversible vision loss in patients with DMI. Natural history studies are required to determine the course of each vascular and neuronal parameter to define the DMI phenotypes. These DMI phenotypes may also partly explain the development and recurrence of diabetic macular oedema. It is also currently unclear where and how DMI fits into the diabetic retinopathy severity scales, further highlighting the need to better define the progression of diabetic retinopathy and DMI based on both multimodal imaging and visual function. Finally, we discuss a complete set of proposed therapeutic pathways for DMI, including cell-based therapies that may provide restorative potential.

Recent Advances in Drumstick (Moringa oleifera) Leaves Bioactive Compounds: Composition, Health Benefits, Bioaccessibility, and Dietary Applications

Based on the availability of many nutrients, Moringa oleifera tree leaves have been widely employed as nutrients and nutraceuticals in recent years. The leaves contain a small amount of anti-nutritional factors and are abundant in innumerable bioactive compounds. Recently, in several in vivo and in vitro investigations, moringa leaves’ bioactive components and functionality are highlighted. Moringa leaves provide several health advantages, including anti-diabetic, antibacterial, anti-cancer, and anti-inflammatory properties. The high content of phytochemicals, carotenoids, and glucosinolates is responsible for the majority of these activities as reported in the literature. Furthermore, there is growing interest in using moringa as a value-added ingredient in the development of functional foods. Despite substantial study into identifying and measuring these beneficial components from moringa leaves, bioaccessibility and bioavailability studies are lacking. This review emphasizes recent scientific evidence on the dietary and bioactive profiles of moringa leaves, bioavailability, health benefits, and applications in various food products. This study highlights new scientific data on the moringa leaves containing nutrient and bioactive profiles, bioavailability, health benefits, and uses in various food items. Moringa has been extensively used as a health-promoting food additive because of its potent protection against various diseases and the widespread presence of environmental toxins. More research is needed for utilization as well as to study medicinal effects and bioaccesibility of these leaves for development of various drugs and functional foods.

Relevance of Peptide Homeostasis in Metabolic Retinal Degenerative Disorders: Curative Potential in Genetically Modified Mice

The mammalian retina contains approximately 30 neuropeptides that are synthetized by different neuronal cell populations, glia, and the pigmented epithelium. The presence of these neuropeptides leaves a mark on normal retinal molecular processes and physiology, and they are also crucial in fighting various pathologies (e.g., diabetic retinopathy, ischemia, age-related pathologies, glaucoma) because of their protective abilities. Retinal pathologies of different origin (metabolic, genetic) are extensively investigated by genetically manipulated in vivo mouse models that help us gain a better understanding of the molecular background of these pathomechanisms. These models offer opportunities to manipulate gene expression in different cell types to help reveal their roles in the preservation of retinal health or identify malfunction during diseases. In order to assess the current status of transgenic technologies available, we have conducted a literature survey focused on retinal disorders of metabolic origin, zooming in on the role of retinal neuropeptides in diabetic retinopathy and ischemia. First, we identified those neuropeptides that are most relevant to retinal pathologies in humans and the two clinically most relevant models, mice and rats. Then we continued our analysis with metabolic disorders, examining neuropeptide-related pathways leading to systemic or cellular damage and rescue. Last but not least, we reviewed the available literature on genetically modified mouse strains to understand how the manipulation of a single element of any given pathway (e.g., signal molecules, receptors, intracellular signaling pathways) could lead either to the worsening of disease conditions or, more frequently, to substantial improvements in retinal health. Most attention was given to studies which reported successful intervention against specific disorders. For these experiments, a detailed evaluation will be given and the possible role of converging intracellular pathways will be discussed. Using these converging intracellular pathways, curative effects of peptides could potentially be utilized in fighting metabolic retinal disorders.

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.

Retinal Neurodegeneration in Diabetes: an Emerging Concept in Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR), the leading cause of blindness in working-aged adults, remains clinically defined and staged by its vascular manifestations. However, early retinal neurodegeneration may precede vascular pathology, suggesting that this neuronal damage may contribute to disease pathogenesis and represent an independent target for intervention. This review will discuss the evidence and implications for diabetic retinal neurodegeneration.

RECENT FINDINGS

A growing body of literature has identified progressive retinal thinning and visual dysfunction in patients with diabetes even prior to the onset of DR, though advances in retinal vascular imaging suggest that vascular remodeling and choroidal changes occur during these early stages as well. Animal models of diabetes and in vitro studies have also suggested that diabetes may directly affect the retinal neural and glial tissue, providing support to the concept that diabetic retinal neurodegeneration occurs early in the disease and suggesting potentially relevant molecular pathways. Diabetic retinal neurodegeneration may represent a "preclinical" manifestation of diabetic retinal disease and remains an active area of investigation. As the natural history and molecular mechanisms become increasingly understood, it may lead to upcoming developments in not only the treatment options but also the clinical definition of DR.

Diabetes mellitus among adults on highly active anti-retroviral therapy and its associated factors in Ethiopia: Systematic review and meta-analysis

BACKGROUND

Diabetes mellitus occurs as a comorbid illness among people living with HIV and, in particular those on Highly Active Anti-retroviral therapies (HAART). Previous studies have documented the prevalence of diabetes mellitus among adults on HAART; however, there is lack of comprehensive estimation. Hence, this study was aimed to estimate the pooled prevalence and associated factors of diabetes mellitus among adults on HAART in Ethiopia.

METHODS

Primary studies were exhaustively searched using Cochrane, PubMed, Google Scholar, Scopus and Web of science databases until February 2021. Eligible studies were selected and critically appraised for quality using the Joanna Briggs Institute (JBI) quality appraisal checklist. The required data were extracted and exported to Stata version 16 for meta-analysis. The overall prevalence of diabetes mellitus among adults on HAART was estimated using a weighted inverse random effect model. Sensitivity and sub-group analysis were conducted for evidence of heterogeneity. Trim and fill analysis was performed after Egger's test and funnel plot were indicating the presence of publication bias.

RESULTS

A total of 17 studies with 6,052 subjects on HAART were included. The pooled prevalence of diabetes mellitus among patients on HAART was 16.04% [95% Confidence Interval (CI); 11.6, 20.92]. Abnormal High Density Lipoprotein Cholesterol (HDL-C) [Adjusted Odd Ratio (AOR) = 4.68, 95% CI; 2.54, 6.82], Body Mass Index (BMI) ≥ 25 kg/m² [AOR = 7.41, 95% CI; 2.75, 12.08], ≥6 years ART [AOR = 8.14, 95% CI; 5.85, 30.43], hypertension [AOR = 3.29, 95% CI; 2.13, 4.45], age 35-44 years [AOR = 6.28; 95% CI; 4.20, 8.37, BMI ≥ 30 kg/m² [AOR = 7.81, 95% CI; 4.97, 10.64], educational status above diploma [AOR = 6.42, 95% CI; 1.28, 11.57] and age 45-55 years [AOR = 4.46, 95% CI; 2.81, 6.10] were positively associated with diabetes mellitus comorbidity among adults on HAART.

CONCLUSION

The higher prevalence of diabetes mellitus was observed for adults on HAART. HDL-C, duration of ART, hypertension, overweight, obesity, age and educational status of participants increases the prevalence of diabetes mellitus. The study highlights the importance of timely screening of HDL-C level, blood pressure and BMI for adults on HAART.

Diurnal efficacy of alpha-lipoic acid/nifedipine/glimepiride combination mitigates diabetic neuropathies in rats

OBJECTIVES

Time-dependent effects of alpha-lipoic acid/nifedipine/glimepiride combination on diabetic neuropathies were investigated in rats. 7 groups (N=9) of rats were used.

MATERIALS AND METHODS

First and second groups were apparently normal and diabetic rats respectively, and were administered 1 mL/kg distilled water. The rest of the groups were diabetic and administered 10 mg/kg glimepiride at night-time (8:00 pm). Groups 4-7 were administered additional 20 mg/kg nifedipine at morning-time (8:00 am), while groups 5-7 were also administered 100 mg/kg alpha-lipoic acid (ALA) in the morning, afternoon and night-time respectively (8:00 am, 2:00 pm and 8:00 pm). During the 28 days of oral treatment, paw pressure, tail immersion and motor coordination tests were conducted. The rats were euthanized on the 29^th day after a charcoal meal. The small intestines were excised to determine intestinal transit while the brain was collected, homogenised and used to determine levels of oxidative stress.

RESULTS

Data show that treatment with ALA at 8:00 am or 2:00 pm significantly (p ≤ 0.01) produced a delay in the onset and improved prognosis of neuropathies. Treatment with ALA at 8:00 pm prevented manifestation of neuropathies throughout the study with positive antioxidant effects.

CONCLUSION

Time-dependent ALA treatment in combination with nifedipine and glimepiride should be studied in humans with an approximately similar circadian timing. This may provide additional clinical therapeutic options for diabetic neuropathies.

Association Between Diabetes, Diabetic Retinopathy, and Glaucoma

PURPOSE OF REVIEW

The strength of the relationship between diabetes, diabetic retinopathy (DR), and glaucoma remains controversial. We review evidence supporting and refuting this association and explore mechanistic pathological and treatment relationships linking these diseases.

RECENT FINDINGS

While studies have shown diabetes/DR may increase the risk for glaucoma, this remains inconsistently demonstrated. Diabetes/DR may contribute toward glaucomatous optic neuropathy indirectly (either by increasing intraocular pressure or vasculopathy) or through direct damage to the optic nerve. However, certain elements of diabetes may slow glaucoma progression, and diabetic treatment may concurrently be beneficial in glaucoma management. Diabetes plays a significant role in poor outcomes after glaucoma surgery. While the relationship between diabetes/DR and glaucoma remains controversial, multiple mechanistic links connecting pathophysiology and management of diabetes, DR, and glaucoma have been made. However, a deeper understanding of the causes of disease association is needed.

The Pathogenesis and Therapeutic Approaches of Diabetic Neuropathy in the Retina

Diabetic retinopathy is a major retinal disease and a leading cause of blindness in the world. Diabetic retinopathy is a neurovascular disease that is associated with disturbances of the interdependent relationship of cells composed of the neurovascular units, i.e., neurons, glial cells, and vascular cells. An impairment of these neurovascular units causes both neuronal and vascular abnormalities in diabetic retinopathy. More specifically, neuronal abnormalities including neuronal cell death and axon degeneration are irreversible changes that are directly related to the vision reduction in diabetic patients. Thus, establishment of neuroprotective and regenerative therapies for diabetic neuropathy in the retina is an emergent task for preventing the blindness of patients with diabetic retinopathy. This review focuses on the pathogenesis of the neuronal abnormalities in diabetic retina including glial abnormalities, neuronal cell death, and axon degeneration. The possible molecular cell death pathways and intrinsic survival and regenerative pathways are also described. In addition, therapeutic approaches for diabetic neuropathy in the retina both in vitro and in vivo are presented. This review should be helpful for providing clues to overcome the barriers for establishing neuroprotection and regeneration of diabetic neuropathy in the retina.

Melatonin protects inner retinal neurons of newborn mice after hypoxia-ischemia

Retinopathy of prematurity is a vision-threatening disease associated with retinal hypoxia-ischemia, leading to the death of retinal neurons and chronic neuronal degeneration. During this study, we used the oxygen-induced retinopathy mice model to mimic retinal hypoxia-ischemia phenotypes to investigate further the neuroprotective effect of melatonin on neonatal retinal neurons. Melatonin helped maintain relatively normal inner retinal architecture and thickness and preserve inner retinal neuron populations in avascular areas by rescuing retinal ganglion and bipolar cells, and horizontal and amacrine neurons, from apoptosis. Meanwhile, melatonin recovered visual dysfunction, as reflected by the improved amplitudes and implicit times of a-wave, b-wave, and oscillatory potentials. Additionally, elevated cleaved caspase-3 and Bax protein levels and reduced Bcl-2 protein levels in response to hypoxia-ischemia were diminished after melatonin treatment. Moreover, melatonin increased BDNF and downstream phospho-TrkB/Akt/ERK/CREB levels. ANA-12, a TrkB receptor antagonist, antagonized these melatonin actions and reduced melatonin-induced neuroprotection. Furthermore, melatonin rescued the reduction in melatonin receptor expression. This study suggests that melatonin exerted anti-apoptotic and neuroprotective effects in inner retinal neurons after hypoxia-ischemia, at least partly due to modulation of the BDNF-TrkB pathway.

A Systematic Review of Carotenoids in the Management of Diabetic Retinopathy

Diabetic retinopathy, which was primarily regarded as a microvascular disease, is the leading cause of irreversible blindness worldwide. With obesity at epidemic proportions, diabetes-related ocular problems are exponentially increasing in the developed world. Oxidative stress due to hyperglycemic states and its associated inflammation is one of the pathological mechanisms which leads to depletion of endogenous antioxidants in retina in a diabetic patient. This contributes to a cascade of events that finally leads to retinal neurodegeneration and irreversible vision loss. The xanthophylls lutein and zeaxanthin are known to promote retinal health, improve visual function in retinal diseases such as age-related macular degeneration that has oxidative damage central in its etiopathogenesis. Thus, it can be hypothesized that dietary supplements with xanthophylls that are potent antioxidants may regenerate the compromised antioxidant capacity as a consequence of the diabetic state, therefore ultimately promoting retinal health and visual improvement. We performed a comprehensive literature review of the National Library of Medicine and Web of Science databases, resulting in 341 publications meeting search criteria, of which, 18 were found eligible for inclusion in this review. Lutein and zeaxanthin demonstrated significant protection against capillary cell degeneration and hyperglycemia-induced changes in retinal vasculature. Observational studies indicate that depletion of xanthophyll carotenoids in the macula may represent a novel feature of DR, specifically in patients with type 2 or poorly managed type 1 diabetes. Meanwhile, early interventional trials with dietary carotenoid supplementation show promise in improving their levels in serum and macular pigments concomitant with benefits in visual performance. These findings provide a strong molecular basis and a line of evidence that suggests carotenoid vitamin therapy may offer enhanced neuroprotective effects with therapeutic potential to function as an adjunct nutraceutical strategy for management of diabetic retinopathy.

Antihyperglycemic effect and phytochemical investigation of Rubia cordifolia (Indian Madder) leaves extract

Medicinal plants are used as an important source of medicines in pharmaceutical industry. Rubia cordifolia is widely used to cure diabetes mellitus. Present study was aimed to investigate the antihyperglycemic effects of different fractions of R. cordifolia leaves and to analyze its antioxidant effect and phytochemical composition. Male albino mice were randomly distributed into seven groups (n = 7). Group-I was normal control, group-II was Alloxan (100 mg/kg)-induced diabetic control, and group-III was standard drug (Glibenclamide 0.5 mg/kg)-treated group. Animals in groups IV–VII were treated with n-hexane fraction, ethyl acetate fraction, n-butanol fraction and aqueous fraction of R. cordifolia, orally administered (100 mg/kg) once daily up to 28 days after Alloxan induction, respectively. Methanolic extract (ME) and fractions of R. cordifilia were analyzed for antioxidant activity and quantification of total phenolic content and total flavonoid content. HPLC of ME and most active fractions were performed. The results showed that RCEF (G-V) and RCBF (G-VI) have significantly (P < 0.05) reduced the increased level of glucose as compared to toxicant control group. It was further revealed that EF and BF have higher antioxidant activity (having IC50 34.9, 36.86 (µg/mL)) owing to phenolic and flavonoid identified by HPLC.

Diabetic retinal neurodegeneration as a form of diabetic retinopathy

PURPOSE

To review the evidence supporting diabetic retinal neurodegeneration (DRN) as a form of diabetic retinopathy.

METHOD

Review of literature.

RESULTS

DRN is recognized to be a part of retinopathy in patients with diabetes mellitus (DM), in addition to the well-established diabetic retinal vasculopathy (DRV). DRN has been noted in the early stages of DM, before the onset of clinically evident diabetic retinopathy. The occurrence of DRN has been confirmed in animal models of DM, histopathological examination of donor's eyes from diabetic individuals and assessment of neural structure and function in humans. DRN involves alterations in retinal ganglion cells, photoreceptors, amacrine cells and bipolar cells, and is thought to be driven by glutamate, oxidative stress and dysregulation of neuroprotective factors in the retina. Potential therapeutic options for DRN are under evaluation.

CONCLUSIONS

Literature is divided on the temporal relation between DRN and DRV, with evidence of both precedence and simultaneous occurrence. The relationship between DRN and multi-system neuropathy in DM is yet to be evaluated critically.

Neurovascular unit in diabetic retinopathy: pathophysiological roles and potential therapeutical targets

Diabetic retinopathy (DR), one of the common complications of diabetes, is the leading cause of visual loss in working-age individuals in many industrialized countries. It has been traditionally regarded as a purely microvascular disease in the retina. However, an increasing number of studies have shown that DR is a complex neurovascular disorder that affects not only vascular structure but also neural tissue of the retina. Deterioration of neural retina could precede microvascular abnormalities in the DR, leading to microvascular changes. Furthermore, disruption of interactions among neurons, vascular cells, glia and local immune cells, which collectively form the neurovascular unit, is considered to be associated with the progression of DR early on in the disease. Therefore, it makes sense to develop new therapeutic strategies to prevent or reverse retinal neurodegeneration, neuroinflammation and impaired cell-cell interactions of the neurovascular unit in early stage DR. Here, we present current perspectives on the pathophysiology of DR as a neurovascular disease, especially at the early stage. Potential novel treatments for preventing or reversing neurovascular injuries in DR are discussed as well.

The lack of Irs2 induces changes in the immunocytochemical expression of aromatase in the mouse retina

Insulin receptor substrate (Irs) belongs to a family of proteins that mediate the intracellular signaling of insulin and IGF-1. Insulin receptor substrate 2 (Irs2) is necessary for retinal function, since its failure in Irs2-deficient mice in hyperglycemic situation promotes photoreceptor degeneration and visual dysfunction, like in diabetic retinopathy. The expression of P450 aromatase, which catalyzes androgen aromatization to form 17ß-estradiol, increases in some neurodegenerative diseases thus promoting the local synthesis of neuroestrogens that exert relevant neuroprotective functions. Aromatase is also expressed in neurons and glial cells of the central nervous system (CNS), including the retina. To further understand the role of Irs2 at the retinal level, we performed an immunocytochemical study in adult normoglycemic Irs2-deficient mice. For this aim, the retinal immunoexpression of neuromodulators, such as aromatase, glutamine synthetase (GS), and tyrosine hydroxylase (TH) was analyzed, joint to a morphometric and planimetric study of the retinal layers. Comparing with wild-type (WT) control mice, the Irs2-knockout (Irs2-KO) animals showed a significant increase in the immunopositivity to aromatase in almost all of the retinal layers. Besides, Irs2-KO mice exhibited a decreased immunopositive reaction for GS and TH, in Müller and amacrine cells, respectively; morphological variations were also found in these retinal cell types. Furthermore, the retina of Irs2-KO mice displayed alterations in the structural organization, and a generalized decrease in the retinal thickness was observed in each of the layers, except for the inner nuclear layer. Our findings suggest that the absence of Irs2 induces retinal neurodegenerative changes in Müller and amacrine cells that are unrelated to hyperglycemia. Accordingly, in the Irs2-KO mice, the increased retinal immunocytochemical reactivity of aromatase could be associated with an attempt to repair such neural retina injuries by promoting local neuroprotective mediators.

Apocynin ameliorates NADPH oxidase 4 (NOX4) induced oxidative damage in the hypoxic human retinal Müller cells and diabetic rat retina

NADPH oxidase (NOX) is a main producers of reactive oxygen species (ROS) that may contribute to the early pathogenesis of diabetic retinopathy (DR). ROS has harmful effects on endogenous neuro-survival factors brain-derived neurotrophic factor (BDNF) and sirtuin 1 (SIRT1) are necessary for the growth and survival of the retina. The role of NOX isoforms NOX4 in triggering ROS in DR is not clear. Here we determine the protective effects of a plant-derived NOX inhibitor apocynin (APO) on NOX4-induced ROS production which may contribute to the depletion of survival factors BDNF/SIRT1 or cell death in the diabetic retinas. Human retinal Müller glial cells (MGCs) were treated with hypoxia mimetic agent cobalt chloride (CoCl₂) in the absence or presence of APO. Molecular analysis demonstrates that NOX4 is upregulated in CoCl₂-treated MGCs and in the diabetic retinas. Increased NOX4 was accompanied by the downregulation of BDNF/SIRT1 expression or in the activation of apoptotic marker caspase-3. Whereas, APO treatment downregulates NOX4 and subsequently upregulates BDNF/SIRT1 or alleviate caspase-3 expression. Accordingly, in the diabetic retina we found a positive correlation in NOX4 vs ROS (p = 0.025; R² = 0.488) and caspase-3 vs ROS (p = 0.04; R² = 0.428); whereas a negative correlation in BDNF vs ROS (p = 0.009; R² = 0.596) and SIRT1 vs ROS (p = 0.0003; R² = 0.817) respectively. Taken together, NOX4-derived ROS could be a main contributor in downregulating BDNF/SIRT1 expression or in the activation of caspase-3. Whereas, APO treatment may minimize the deleterious effects occurring due to hyperglycemia and/or diabetic mimic hypoxic condition in early pathogenesis of DR.

Recent advances in intraocular and novel drug delivery systems for the treatment of diabetic retinopathy

Introduction: Diabetic retinopathy (DR) is associated with damage to the retinal blood vessels that lead eventually to vision loss. The existing treatments of DR are invasive, expensive, and cumbersome. To overcome challenges associated with existing therapies, various intraocular sustained release and novel drug delivery systems (NDDS) have been explored.Areas covered: The review discusses recently developed intraocular devices for sustained release of drugs as well as novel noninvasive drug delivery systems that have met a varying degree of success in local delivery of drugs to retinal circulation.Expert opinion: The intraocular devices have got very good success in providing sustained release of drugs in patients. The development of NDDS and their application through the ocular route has certainly provided an edge to treat DR over existing therapies such as anti-VEGF administration but their success rate is quite low. Moreover, most of them have proved to be effective only in animal models. In addition, the extent of targeting the drug to the retina still remains variable and unpredictable. The toxicity aspect of the NDDS has generally been neglected. In order to have successful commercialization of nanotechnology-based innovations well-designed clinical research studies need to be conducted to evaluate their clinical superiority over that of the existing formulations.

Potential neuroprotective biomolecules in ophthalmology

PURPOSES

Retinal neurodegenerative diseases are responsible for a huge number of ocular problems worldwide. It seems that the progression of these diseases can be managed by the application of neuroprotective molecules particularly in the early stages. This article focuses on the most common neuroprotective bioagents under investigation in ophthalmology.

METHODS

We searched the web of science, PubMed and Scopus databases with these keywords: "glaucoma," "diabetic retinopathy," "age-related macular degeneration," "optic neuropathy and retinal degeneration" and/or "neuroprotection."

RESULTS

The most commonly utilized neuroprotective drugs for ophthalmology diseases were introduced in this study. It seems that these agents can be divided into three categories according to their mechanism of action: (A) neurotrophins, (B) decreasing effect on intraocular pressure and (C) inhibition of retinal neuron apoptosis.

CONCLUSION

A broad range of drugs has been illustrated in the literature for treatment of neuro-ophthalmic diseases. A good classification of the most applied drugs in this field can help specialists to prescribe the best matched drug considering the stage and progression of disease. However, controlled clinical trials are needed for better evaluation of the effects of these products.

The role of reactive oxygen species in the pathogenesis and treatment of retinal diseases

Reactive oxygen species (ROS) normally play an important physiological role in health regulating cellular processes and signal transduction. The amount of ROS is usually kept in fine balance with the generation of ROS largely being offset by the body's antioxidants. A tipping of this balance has increasingly been recognised as a contributor to human disease. The retina, as a result of its cellular anatomy and physical location, is a potent generator of ROS that has been linked to several major retinal diseases. This review will provide a summary of the role of oxidative stress in the pathogenesis of diabetic retinopathy, age-related macular degeneration, myopia, retinal vein occlusion, retinitis pigmentosa and retinopathy of prematurity. Therapies aimed at controlling oxidative stress in these diseases are also examined.

The effects of early diabetes on inner retinal neurons

Diabetic retinopathy is now well understood as a neurovascular disease. Significant deficits early in diabetes are found in the inner retina that consists of bipolar cells that receive inputs from rod and cone photoreceptors, ganglion cells that receive inputs from bipolar cells, and amacrine cells that modulate these connections. These functional deficits can be measured in vivo in diabetic humans and animal models using the electroretinogram (ERG) and behavioral visual testing. Early effects of diabetes on both the human and animal model ERGs are changes to the oscillatory potentials that suggest dysfunctional communication between amacrine cells and bipolar cells as well as ERG measures that suggest ganglion cell dysfunction. These are coupled with changes in contrast sensitivity that suggest inner retinal changes. Mechanistic in vitro neuronal studies have suggested that these inner retinal changes are due to decreased inhibition in the retina, potentially due to decreased gamma aminobutyric acid (GABA) release, increased glutamate release, and increased excitation of retinal ganglion cells. Inner retinal deficits in dopamine levels have also been observed that can be reversed to limit inner retinal damage. Inner retinal targets present a promising new avenue for therapies for early-stage diabetic eye disease.

Early diabetes impairs ON sustained ganglion cell light responses and adaptation without cell death or dopamine insensitivity

Retinal signaling under dark-adapted conditions is perturbed during early diabetes. Additionally, dopamine, the main neuromodulator of retinal light adaptation, is diminished in diabetic retinas. However, it is not known if this dopamine deficiency changes how the retina responds to increased light or dopamine. Here we determine whether light adaptation is impaired in the diabetic retina, and investigate potential mechanism(s) of impairment. Diabetes was induced in C57BL/6J male mice via 3 intraperitoneal injections of streptozotocin (75 mg/kg) and confirmed by blood glucose levels more than 200 mg/dL. After 6 weeks, whole-cell recordings of light-evoked and spontaneous inhibitory postsynaptic currents (IPSCs) or excitatory postsynaptic currents (EPSCs) were made from rod bipolar cells and ON sustained ganglion cells, respectively. Light responses were recorded before and after D1 receptor (D1R) activation (SKF-38393, 20 μM) or light adaptation (background of 950 photons·μm^-2 ·s^-1). Retinal whole mounts were stained for either tyrosine hydroxylase and activated caspase-3 or GAD65/67, GlyT1 and RBPMS and imaged. D1R activation and light adaptation both decreased inhibition, but the disinhibition was not different between control and diabetic rod bipolar cells. However, diabetic ganglion cell light-evoked EPSCs were increased in the dark and showed reduced light adaptation. No differences were found in light adaptation of spontaneous EPSC parameters, suggesting upstream changes. No changes in cell density were found for dopaminergic, glycinergic or GABAergic amacrine cells, or ganglion cells. Thus, in early diabetes, ON sustained ganglion cells receive excessive excitation under dark- and light-adapted conditions. Our results show that this is not attributable to loss in number or dopamine sensitivity of inhibitory amacrine cells or loss of dopaminergic amacrine cells.

Association Between Pathophysiological Mechanisms of Diabetic Retinopathy and Parkinson's Disease

Diabetic retinopathy, the most common complication of diabetes, is a neurodegenerative disease in the eye. And Parkinson's disease, affecting the health of 1-2% of people over 60 years old throughout the world, is the second largest neurodegenerative disease in the brain. As the understanding of diabetic retinopathy and Parkinson's disease deepens, the two diseases are found to show correlation in incidence, similarity in clinical presentation, and close association in pathophysiological mechanisms. To reveal the association between pathophysiological mechanisms of the two disease, in this review, the shared pathophysiological factors of diabetic retinopathy and Parkinson's disease are summarized and classified into dopaminergic system, circadian rhythm, neurotrophic factors, α-synuclein, and Wnt signaling pathways. Furthermore, similar and different mechanisms so far as the shared pathophysiological factors of the two disorders are discussed systematically. Finally, a brief summary and new perspectives are presented to provide new directions for further efforts on the association, exploration, and clinical prevention and treatment of diabetic retinopathy and Parkinson's disease.

Low brain-derived neurotrophic factor protein levels and single-nucleotide polymorphism Val66Met are associated with peripheral neuropathy in type II diabetic patients

BACKGROUND

Studies by our group demonstrated brain-derived neurotrophic factor (BDNF) levels in blood and BDNF-Val66met-SNP as potential biomarkers in chemotherapy-induced peripheral neuropathy. Here, we evaluate symptoms of peripheral neuropathy (PN) and depression in patients with type II diabetes mellitus in search of an association with serum BDNF levels and the Val66Met-SNP.

METHODS

In total, 90 patients enrolled in the study; 23 (25.6%) had known PN, as determined by nerve conduction studies (NCS-PN), and 67 (74.4%) were not diagnosed with PN (U-PN). PN symptoms were assessed and graded in these groups using the total neuropathy score (TNSr) and DN4 scales. Small nerve fiber testing of sensitivity thresholds to cold, warm and hot pain signals was performed using the Q-sense device. Depression was assessed using the PHQ9 questionnaire. BDNF protein levels and Val66Met-SNP were determined with ELISA and Sanger sequencing, respectively.

RESULTS

NCS-PN patients showed lower serum BDNF levels alongside significantly higher TNSr, DN4 and PHQ9 scores and lower hot pain sensitivity thresholds as compared to U-PN patients. Patients with Met-BDNF-SNP showed increased TNSr scores and lower hot pain sensitivity thresholds as compared to patients with Val-BDNF-SNP. Depression showed a weaker correlation with sensitivity thresholds to hot pain signals as compared to TNSr and DN4 scores.

CONCLUSIONS

Diminished peripheral BDNF resources and Met-BDNF-SNP genotype are associated with augmented symptoms of PN in patients with type II diabetes mellitus. Sensitivity thresholds to hot pain signals may be less influenced by depression and possibly more accurately detect PN symptoms in diabetic patients.

Protective effect of Soluble Epoxide Hydrolase Inhibition in Retinal Vasculopathy associated with Polycystic Kidney Disease

Rationale: Vasoregression secondary to glial activation develops in various retinal diseases, including retinal degeneration and diabetic retinopathy. Photoreceptor degeneration and subsequent retinal vasoregression, characterized by pericyte loss and acellular capillary formation in the absence diabetes, are also seen in transgenic rats expressing the polycystic kidney disease (PKD) gene. Activated Müller glia contributes to retinal vasodegeneration, at least in part via the expression of the soluble epoxide hydrolase (sEH). Given that an increase in sEH expression triggered vascular destabilization in diabetes, and that vasoregression is similar in diabetic mice and PKD rats, the aim of the present study was to determine whether sEH inhibition could prevent retinal vasoregression in the PKD rat.

Methods: One-month old male homozygous transgenic PKD rats were randomly allocated to receive vehicle or a sEH inhibitor (sEH-I; Sar5399, 30 mg/kg) for four weeks. Wild-type Sprague-Dawley (SD) littermates received vehicle as controls. Retinal sEH expression and activity were measured by Western blotting and LC-MS, and vasoregression was quantified in retinal digestion preparations. Microglial activation and immune response cytokines were assessed by immunofluorescence and quantitative PCR, respectively. 19,20-dihydroxydocosapentaenoic acid (19,20-DHDP) mediated Notch signaling, microglial activation and migration were assessed in vivo and in vitro.

Results: This study demonstrates that sEH expression and activity were increased in PKD retinae, which led to elevated production of 19,20-DHDP and the depression of Notch signaling. The latter changes elicited pericyte loss and the recruitment of CD11b⁺/CD74⁺ microglia to the perivascular region. Microglial activation increased the expression of immune-response cytokines, and reduced levels of Notch3 and delta-like ligand 4 (Dll4). Treatment with Sar5399 decreased 19,20-DHDP generation and increased Notch3 expression. Sar5399 also prevented vasoregression by reducing pericyte loss and suppressed microglial activation as well as the expression of immune-response cytokines. Mechanistically, the activation of Notch signaling by Dll4 maintained a quiescent microglial cell phenotype, i.e. reduced both the surface presentation of CD74 and microglial migration. In contrast, in retinal explants, 19,20-DHDP and Notch inhibition both promoted CD74 expression and reversed the Dll4-induced decrease in migration.

Conclusions: Our data indicate that 19,20-DHDP-induced alterations in Notch-signaling result in microglia activation and pericyte loss and contribute to retinal vasoregression in polycystic kidney disease. Moreover, sEH inhibition can ameliorate vasoregression through reduced activity of inflammatory microglia. sEH inhibition is thus an attractive new therapeutic approach to prevent retinal vasoregression.

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.

From the gut to the heart: L. plantarum and inulin administration as a novel approach to control cardiac apoptosis via 5-HT2B and TrkB receptors in diabetes

BACKGROUND & AIMS

Type 2 diabetes mellitus, as a metabolic disorder, can lead to diabetic cardiomyopathy, identified by cardiomyocyte apoptosis and myocardial fibrosis. Brain-derived neurotrophic factor (BDNF) and serotonin are two neurotransmitters that can control cardiomyocyte apoptosis and myocardial fibrosis through their cardiac receptors. In the present study, we investigated the impacts of L. plantarum and inulin supplementation on the inhibition of cardiac apoptosis and fibrosis by modulating intestinal, serum, and cardiac levels of serotonin and BDNF as well as their cardiac receptors.

METHODS

Diabetes was induced by a high-fat diet and streptozotocin in male Wistar rats. Rats were divided into six groups and were supplemented with L. plantarum, inulin or their combination for 8 weeks. Finally, the rats were killed and levels of intestinal, serum, and cardiac parameters were evaluated.

RESULTS

Concurrent administration of L. plantarum and inulin caused a significant rise in the expression of cardiac serotonin and BDNF receptors (P < 0.001) as well as a significant fall in cardiac interstitial and perivascular fibrosis (P < 0.001, both) and apoptosis (P = 0.01). Moreover, there was a strong correlation of cardiac 5-Hydroxytryptamine 2B (5-HT2B) and tropomyosin receptor kinase B (TrkB) receptors with interstitial/perivascular fibrosis and apoptosis (P < 0.001, both).

CONCLUSIONS/INTERPRETATION

Results revealed beneficial effects of L. plantarum, inulin or their combination on intestinal, serum, and cardiac serotonin and BDNF accompanied by higher expression of their cardiac receptors and lower levels of cardiac apoptotic and fibrotic markers. It seems that L. plantarum and inulin supplementation could be considered as a novel adjunct therapy to reduce cardiac complications of type 2 diabetes mellitus.

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.

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.

Recent Developments in Diabetic Retinal Neurodegeneration: A Literature Review

Neurodegeneration plays a significant role in the complex pathology of diabetic retinopathy. Evidence suggests the onset of neurodegeneration occurs early on in the disease, and so a greater understanding of the process is essential for prompt detection and targeted therapies. Neurodegeneration is a common pathway of assorted processes, including activation of inflammatory pathways, reduction of neuroprotective factors, DNA damage, and apoptosis. Oxidative stress and formation of advanced glycation end products amplify these processes and are elevated in the setting of hyperglycemia, hyperlipidemia, and glucose variability. These key pathophysiologic mechanisms are discussed, as well as diagnostic modalities and novel therapeutic avenues, with an emphasis on recent discoveries. The aim of this article is to highlight the crucial role of neurodegeneration in diabetic retinopathy and to review the molecular basis for this neuronal dysfunction, its diagnostic features, and the progress currently made in relevant therapeutic interventions.

Caffeic Acid Alkyl Amide Derivatives Ameliorate Oxidative Stress and Modulate ERK1/2 and AKT Signaling Pathways in a Rat Model of Diabetic Retinopathy

The purpose of this study was to examine the neuroprotective effects of caffeic acid hexyl (CAF6) and dodecyl (CAF12) amide derivatives on the early stage of retinopathy in streptozotocin-induced diabetic rats. Animals were divided in five groups (n=8/group); one group consisted of non-diabetic rats as control, while the other four were diabetic animals either non-treated or treated with CAF6, CAF12 or resveratrol intravitreally for four weeks. Retinal superoxide dismutase (SOD) activity and 8-iso-prostaglandin F_2α (iPF_2α ) levels were evaluated by an ELISA assay. Phosphorylation of ERK1/2 and AKT was determined by immunoblotting in retinal homogenates. Retinal morphology was also examined using light microscopy. Treatment with CAF6 and CAF12 increased retinal SOD activity, while it decreased iPF_2α levels in diabetic rats. Phosphorylation of ERK1/2 was increased, while AKT phosphorylation was decreased in diabetic rats compared to normal control and these alterations were significantly reversed in diabetic rats treated with CAF6 and CAF12. Furthermore, thickness of the whole retinal layer, outer nuclear layer, and ganglion cell count were decreased in diabetic rats compared to control and CAF6 and CAF12 treatments prevented these changes. CAF6 and CAF12 seem to be effective agents for treatment of diabetic retinopathy via attenuation of retinal oxidative stress and improvement of neuronal survival signaling.

ON-Type Retinal Ganglion Cells are Preferentially Affected in STZ-Induced Diabetic Mice

Purpose

We investigate morphologic and physiologic alterations of ganglion cells (GCs) in a streptozocin (STZ)-induced diabetic mouse model.

Methods

Experiments were conducted in flat-mount retinas of mice 3 months after the induction of diabetes. Changes in morphology of four subtypes of GCs (ON-type RGA2 [ON-RGA2], OFF-type RGA2 [OFF-RGA2], ON-type RGC1 [ON-RGC1], and ON-OFF type RGD2 [ON-OFF RGD2]) were characterized in Thy1-YFP transgenic mice. Using whole-cell patch-clamp recording, passive membrane properties and action potential (AP) firing properties were further investigated in transient ON- and OFF-RGA2 cells.

Results

Morphologic parameters were significantly altered in the dendrites branching in the ON sublamina of the inner plexiform layer (IPL) for ON-RGA2 cells and ON-OFF RGD2 cells. Much less significant changes, if any, were seen in those arborizing in the OFF sublamina of the IPL for OFF-RGA2 and ON-OFF RGD2 cells. No detectable changes in morphology were seen in RGC1 cells. Electrophysiologically, increased resting membrane potentials and decreased membrane capacitance were found in transient ON-RGA2 cells, but not in transient OFF-RGA2 cells. Similar alterations in AP firing properties, such as an increase in AP width and reduction in maximum spiking rate, were shared by these two subtypes. Furthermore, in response to depolarizing current injections, both cells generated more APs suggesting an enhanced excitability of these cells in diabetic conditions.

Conclusions

These differential changes in morphology and electrophysiology in subtypes of GCs may be responsible for reduced contrast sensitivity known to occur during the early stage of diabetic retinopathy.

Effects of macular xanthophyll supplementation on brain-derived neurotrophic factor, pro-inflammatory cytokines, and cognitive performance

PURPOSE

Oxidative and inflammatory processes play a major role in stress-induced neural atrophy. There is a wide body of literature linking oxidative and inflammatory stress with reductions in neurotrophic factors, stress resilience, and cognitive function. Based on their antioxidant and anti-inflammatory capacity, we investigated the effect of the dietary carotenoids lutein and zeaxanthin, along with the zeaxanthin isomer meso-zeaxanthin (collectively the "macular xanthophylls" [MXans]) on systemic brain-derived neurotrophic factor (BDNF) and anti-oxidant capacity (AOC), and the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β. To investigate higher-order effects, we assessed cognitive performance.

METHODS

59 young (18-25 yrs.), healthy subjects participated in a 6-month, double-blind, placebo-controlled trial to evaluate the effects of MXan supplementation on the aforementioned serum parameters and cognitive performance. Subjects were randomly assigned to one of three groups: placebo, 13 mg, or 27 mg/day total MXans; all measures were taken at baseline and 6 months. Blood was obtained via fasting blood draw, and MXan concentration in the retina (termed macular pigment optical density [MPOD]) was measured via customized heterochromatic flicker photometry. Serum BDNF and cytokines were assessed via ELISA. Serum antioxidant capacity (AOC) and serum MXan concentrations were quantified via colorimetric microplate assay, and high-performance liquid chromatography, respectively. Cognitive performance was measured via a computer-based assessment tool (CNS Vital Signs).

RESULTS

BDNF, MPOD, serum MXans, and AOC all increased significantly versus placebo in both treatment groups over the 6-month study period (p < .05 for all). IL-1β decreased significantly versus placebo in both treatment groups (p = .0036 and p = .006, respectively). For cognitive measures, scores for composite memory, verbal memory, sustained attention, psychomotor speed, and processing speed all improved significantly in treatment groups (p < .05 for all) and remained unchanged in the placebo group. Several measures were found to be significantly associated in terms of relational changes over the course of the study. Notably, change in BDNF was related to change in IL-1β (r = -0.47; p < .001) and MPOD (r = 0.44; p = .0086). Additionally, changes in serum MXans were strongly related to AOC (r = 0.79 & 0.61 for lutein and zeaxanthin isomers respectively; p < .001). For cognitive scores, change in BDNF was correlated to change in composite memory (r = 0.32; p = .014) and verbal memory (r = 0.35; p = .007), whereas change in MPOD was correlated with change in both psychomotor speed (r = 0.38; p = .003), and processing speed (r = 0.35; p = .007). Change in serum lutein was found to be significantly correlated to change in verbal memory (r = 0.41; p < .001), composite memory (r = 0.31; p = .009), and sustained attention (r = 0.28; p = .036). Change in serum zeaxanthin isomers was significantly correlated with change in verbal memory (r = 0.33; p = .017). Lastly, change in AOC was significantly associated with verbal memory (r = 0.34; p = .021), composite memory (r = 0.29; p = .03), and sustained attention (r = 0.35; p = .016). No significant relational changes in any cognitive parameter were found for the placebo group.

CONCLUSIONS

Six months of daily supplementation with at least 13 mg of MXans significantly reduces serum IL-1β, significantly increases serum MXans, BDNF, MPOD, and AOC, and improves several parameters of cognitive performance. Findings suggest that increased systemic antioxidant/anti-inflammatory capacity (and not necessarily deposition of the carotenoids in neural tissues), may explain many of the effects determined in this study. The significant relationship between change in BDNF and IL-1β over the course of the study suggests that regular consumption of MXans interrupts the inflammatory cascade that can lead to reduction of BDNF. Changes in MPOD and BDNF appear to account for enhancement in cognitive parameters that involve speed of processing and complex processing, respectively. ISRCTN Clinical Trial Registration: ISRCTN16156382.

Human vitreous in proliferative diabetic retinopathy: Characterization and translational implications

Diabetic retinopathy (DR) is one of the leading causes of visual impairment in the working-age population. DR is a progressive eye disease caused by long-term accumulation of hyperglycaemia-mediated pathological alterations in the retina of diabetic patients. DR begins with asymptomatic retinal abnormalities and may progress to advanced-stage proliferative diabetic retinopathy (PDR), characterized by neovascularization or preretinal/vitreous haemorrhages. The vitreous, a transparent gel that fills the posterior cavity of the eye, plays a vital role in maintaining ocular function. Structural and molecular alterations of the vitreous, observed during DR progression, are consequences of metabolic and functional modifications of the retinal tissue. Thus, vitreal alterations reflect the pathological events occurring at the vitreoretinal interface. These events are caused by hypoxic, oxidative, inflammatory, neurodegenerative, and leukostatic conditions that occur during diabetes. Conversely, PDR vitreous can exert pathological effects on the diabetic retina, resulting in activation of a vicious cycle that contributes to disease progression. In this review, we recapitulate the major pathological features of DR/PDR, and focus on the structural and molecular changes that characterize the vitreal structure and composition during DR and progression to PDR. In PDR, vitreous represents a reservoir of pathological signalling molecules. Therefore, in this review we discuss how studying the biological activity of the vitreous in different in vitro, ex vivo, and in vivo experimental models can provide insights into the pathogenesis of PDR. In addition, the vitreous from PDR patients can represent a novel tool to obtain preclinical experimental evidences for the development and characterization of new therapeutic drug candidates for PDR therapy.

Cellular Signaling in Müller Glia: Progenitor Cells for Regenerative and Neuroprotective Responses in Pharmacological Models of Retinal Degeneration

Retinal degenerative diseases are a leading cause of visual impairment or blindness. There are many therapies for delaying the progression of vision loss but no curative strategies currently. Stimulating intrinsic neuronal regeneration is a potential approach to therapy in retinal degenerative diseases. In contrast to stem cells, as embryonic/pluripotent stem cell-derived retinal progenitor cell or mesenchymal stem cells, Müller glia provided an endogenous cellular source for regenerative therapy in the retina. Müller glia are a major component of the retina and considerable evidence suggested these cells can be induced to produce the lost neurons in several species. Understanding the specific characteristic of Müller glia to generate lost neurons will inspire an attractive and alternative therapeutic strategy for treating visual impairment with regenerative research. This review briefly provides the different signal transduction mechanisms which are underlying Müller cell-mediated neuroprotection and neuron regeneration and discusses recent advances about regeneration from Müller glia-derived progenitors.

Retinal Neurodegeneration as an Early Manifestation of Diabetic Eye Disease and Potential Neuroprotective Therapies

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is a major cause of visual impairment and blindness throughout the world. Microvascular changes have long been regarded central to disease pathogenesis. In recent years, however, retinal neurodegeneration is increasingly being hypothesized to occur prior to the vascular changes classically associated with DR and contribute to disease pathogenesis.

RECENT FINDINGS

There is growing structural and functional evidence from human and animal studies that suggests retinal neurodegeneration to be an early component of DR. Identification of new therapeutic targets is an ongoing area of research with several different molecules undergoing testing in animal models for their neuroprotective properties and for possible use in humans. Retinal neurodegeneration may play a central role in DR pathogenesis. As new therapies are developed, it will be important to develop criteria for clinically defining retinal neurodegeneration. A standardization of the methods for monitoring neurodegeneration along with more sensitive means of detecting preclinical damage is also needed.

Involvement of ciliary neurotrophic factor in early diabetic retinal neuropathy in streptozotocin-induced diabetic rats

Objective

Ciliary neurotrophic factor (CNTF) has been evaluated as a candidate therapeutic agent for diabetes and its neural complications. However, its role in diabetic retinopathy has not been fully elucidated.

Methods

This is a randomized unblinded animal experiment. Wistar rats with streptozocin (STZ)-induced diabetes were regularly injected with CNTF or vehicle control in their vitreous bodies beginning at 2 weeks after STZ injection. A total of five injections were used. In diabetic rats, the levels of CNTF and neurotrophin-3 (NT-3) were evaluated by enzyme-linked immunosorbent assays (ELISA) and real-time PCR. The abundance of tyrosine hydroxylase (TH) and β-III tubulin was detected by western blot. Transferase-mediated dUTP nick-end labeling staining (TUNEL) was used to detect cell apoptosis in the retinal tissue. The activation of caspase-3 was also measured.

Results

The protein and mRNA levels of CNTF in diabetic rat retinas were reduced compared to control rats. In addition, retinal ganglion cells (RGCs) and dopaminergic amacrine cells appeared to undergo degeneration in diabetic rat retinas, as revealed by transferase-mediated dUTP nick-end labeling staining (TUNEL). Tyrosine hydroxylase (TH) and β-III tubulin protein levels also decreased significantly. Intraocular administration of CNTF rescued RGCs and dopaminergic amacrine cells from neurodegeneration and counteracted the downregulation of β-III tubulin and TH expression, thus demonstrating its therapeutic potential.

Conclusion

Our study suggests that early diabetic retinal neuropathy involves the reduced expression of CNTF and can be ameliorated by an exogenous supply of this neurotrophin.