Diabetic Retinal and Choroidal Edema in SDT Rats

Elucidating glial responses to products of diabetes-associated systemic dyshomeostasis

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. DR has non-proliferative stages, characterized in part by retinal neuroinflammation and ischemia, and proliferative stages, characterized by retinal angiogenesis. Several systemic factors, including poor glycemic control, hypertension, and hyperlipidemia, increase the risk of DR progression to vision-threatening stages. Identification of cellular or molecular targets in early DR events could allow more prompt interventions pre-empting DR progression to vision-threatening stages. Glia mediate homeostasis and repair. They contribute to immune surveillance and defense, cytokine and growth factor production and secretion, ion and neurotransmitter balance, neuroprotection, and, potentially, regeneration. Therefore, it is likely that glia orchestrate events throughout the development and progression of retinopathy. Understanding glial responses to products of diabetes-associated systemic dyshomeostasis may reveal novel insights into the pathophysiology of DR and guide the development of novel therapies for this potentially blinding condition. In this article, first, we review normal glial functions and their putative roles in the development of DR. We then describe glial transcriptome alterations in response to systemic circulating factors that are upregulated in patients with diabetes and diabetes-related comorbidities; namely glucose in hyperglycemia, angiotensin II in hypertension, and the free fatty acid palmitic acid in hyperlipidemia. Finally, we discuss potential benefits and challenges associated with studying glia as targets of DR therapeutic interventions. In vitro stimulation of glia with glucose, angiotensin II and palmitic acid suggests that: 1) astrocytes may be more responsive than other glia to these products of systemic dyshomeostasis; 2) the effects of hyperglycemia on glia are likely to be largely osmotic; 3) fatty acid accumulation may compound DR pathophysiology by promoting predominantly proinflammatory and proangiogenic transcriptional alterations of macro and microglia; and 4) cell-targeted therapies may offer safer and more effective avenues for DR treatment as they may circumvent the complication of pleiotropism in retinal cell responses. Although several molecules previously implicated in DR pathophysiology are validated in this review, some less explored molecules emerge as potential therapeutic targets. Whereas much is known regarding glial cell activation, future studies characterizing the role of glia in DR and how their activation is regulated and sustained (independently or as part of retinal cell networks) may help elucidate mechanisms of DR pathogenesis and identify novel drug targets for this blinding disease.

Differences in the Effects of Pentobarbital Anesthetic and Combination of Medetomidine Hydrochloride, Midazolam, and Butorphanol Tartrate Anesthetic on Electroretinogram in Spontaneously Diabetic Torii Fatty Rats

Purpose

The aim of this study was to investigate the effects of different anesthetic agents on electroretinograms (ERGs) in Spontaneously Diabetic Torii fatty rats (SDT fatty rats).

Methods

The ERG recordings were measured under general anesthesia using pentobarbital or a combination of medetomidine hydrochloride, midazolam, and butorphanol (MMB) tartrate anesthesia in 12 9-week-old normal Sprague-Dawley rats (Jcl:SD rats) and 16 SDT fatty rats. Each animal model was divided into 2 groups, the pentobarbital group and MMB group. The amplitudes and peak times of the a- and b-waves and oscillatory potentials (OPs) were measured from 0.0001 candela per square meter (cd.s/m²) to 10.0 cd.s/m².

Results

The amplitude of the a-wave was significantly higher in the MMB group of Jcl:SD rats, but there was no significant difference in amplitude between the two groups of SDT fatty rats. There was no significant difference in the OP1 amplitude between both groups of Jcl:SD rats, but the OP1 amplitude was significantly higher in the MMB group of SDT fatty rats. The OP2 amplitude was significantly higher in the pentobarbital group in both the Jcl:SD rats and SDT fatty rats. There was no significant difference in the OP3 amplitude between the Jcl:SD and SDT fatty rat groups. The amplitude of the OP4 waves was significantly higher in the MMB group for both Jcl:SD and SDT fatty rats. There was no significant difference in the sums of the OP1 to OP4 (ΣOPs) amplitudes between the Jcl:SD and SDT fatty rat groups. There was no significant difference in the b-wave amplitude between the Jcl:SD rat groups, but the b-wave amplitude was significantly higher in the SDT fatty rats that received pentobarbital. The peak times for a-wave, OP1, OP2, OP3, OP4, and ΣOPs were significantly longer in the pentobarbital group of SD rats. The peak time of the b-wave was significantly longer in the MMB group of Jcl:SD rats, but the same result was obtained in the SDT fatty rats except that there was no significant difference in the a-wave.

Conclusion

The overall ERG results vary depending on the anesthetic agent used. The OPs can be observed in detail when using MMB. Since the SDT fatty rat is a diabetic model animal, we recommend MMB as the anesthesia of choice when studying the OP waves in detail.

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

Background

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

Methods

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

Results

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

Conclusion

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

Glucagon-like peptide-1 receptor agonist, liraglutide, attenuated retinal thickening in spontaneously diabetic Torii fatty rats

BACKGROUND

This study aims to investigate the effect of the glucagon-like peptide-1 (GLP-1) receptor agonist (GLP-1RA) liraglutide on retinal pathological findings as compared with insulin and hydralazine using an animal model of type 2 diabetes with obesity, hypertension, and hyperlipidemia.

METHODS

Male spontaneously diabetic Torii (SDT) fatty rats at 8 weeks of age were randomly assigned to three groups: the liraglutide group (SDT-lira, n = 6) received a subcutaneous injection of liraglutide from the age of 8 to 16 weeks, the SDT-ins-hyd group (n = 6) was provided both insulin against hyperglycemia and hydralazine against hypertension to match levels of both blood glucose and blood pressure to those of the liraglutide group, and the control group of SDT fatty rats (SDT-vehicle, n = 7) and a nondiabetic control group of Sprague-Dawley rats (SD, n = 7) were injected with vehicle only. Both eyeballs of all groups were collected at the age of 16 weeks.

RESULTS

Retinal thickness, which was found in the SDT-vehicle group, was significantly prevented to similar levels in both the SDT-lira and SDT-ins-hyd groups. Immunohistological analysis revealed that GLP-1 receptor was not expressed in the retina of all rats. The ocular protein expression of monocyte chemoattractant protein-1, which causes a proinflammatory situation, was significantly upregulated in all SDT fatty rats as compared to SD rats, but the expression levels were similar between all SDT fatty rats. With regard to neovascularization in the eyes, there were no significant differences in protein expressions of vascular endothelial growth factor, CD31, or endothelial nitric oxide synthase in all rats.

CONCLUSIONS

The present study indicates that liraglutide prevents retinal thickening, dependent on blood glucose and blood pressure levels in SDT fatty rats without ocular neovascularization. However, the effects did not improve the ocular proinflammatory state.

The role of hesperidin in ameliorating retinal changes in rats with experimentally induced type 1 diabetes mellitus and the active role of vascular endothelial growth factor and glial fibrillary acidic protein

Patients with type 1 diabetes mellitus (T₁DM) are vulnerable to developing diabetic retinopathy even under insulin therapy. Thus, this study was designed to evaluate the efficacy of hesperidin and insulin in rats with T₁DM compared with insulin alone in improving diabetic retinal changes. Eighty rats were divided into four equal groups: group I, control rats without diabetes; group II, untreated rats with diabetes; group III, rats with diabetes treated daily with subcutaneous (SC) doses of long-acting insulin; and group IV, a rat with diabetes in which hesperidin was orally administered with SC insulin. The animals were assessed histologically, morphometrically, and biochemically. In group II, the thickness of all retinal layers decreased histologically. Ultrastructurally, degenerated retinal neurons and congested blood vessels were observed. Immunostaining detected elevated gene expression of advanced glycation end products. Gene expression of vascular endothelial growth factor, and glial fibrillary acidic protein were elevated. In this study, hesperidin supplementation with insulin significantly improved the retinal histological changes, supported by morphometric findings, compared with insulin alone. Moreover, treatment with hesperidin significantly reduced malondialdehyde and elevated serum antioxidant markers, including superoxide dismutase and catalase; furthermore, glutathione peroxidase decreased. Hesperidin might be an effective supplement for improving diabetic retinal complications occurring even with insulin treatment.

Animal models of diabetic microvascular complications: Relevance to clinical features

Diabetes has become more common in recent years worldwide, and this growth is projected to continue in the future. The primary concern with diabetes is developing various complications, which significantly contribute to the disease's mortality and morbidity. Over time, the condition progresses from the pre-diabetic to the diabetic stage and then to the development of complications. Years and enormous resources are required to evaluate pharmacological interventions to prevent or delay the progression of disease or complications in humans. Appropriate screening models are required to gain a better understanding of both pathogenesis and potential therapeutic agents. Different species of animals are used to evaluate the pharmacological potentials and study the pathogenesis of the disease. Animal models are essential for research because they represent most of the structural, functional, and biochemical characteristics of human diseases. An ideal screening model should mimic the pathogenesis of the disease with identifiable characteristics. A thorough understanding of animal models is required for the experimental design to select an appropriate model. Each animal model has certain advantages and limitations. The present manuscript describes the animal models and their diagnostic characteristics to evaluate microvascular diabetic complications.

Retinal Tropism and Transduction of Adeno-Associated Virus Varies by Serotype and Route of Delivery (Intravitreal, Subretinal, or Suprachoroidal) in Rats

Viral-mediated gene augmentation offers tremendous promise for the treatment of inherited retinal diseases. The development of effective gene therapy requires an understanding of the vector's tissue-specific behavior, which may vary depending on serotype, route of delivery, or target species. Using an ex vivo organotypic explant system, we previously demonstrated that retinal tropism and transduction of adeno-associated virus type 2 (AAV2) vary significantly depending on serotype in human eyes. However, the ex vivo system has limited ability to assess route of ocular delivery, and relatively little literature exists on tropic differences between serotypes and routes of delivery in vivo. In this study, we demonstrate that retinal tropism and transduction efficiency of five different AAV2 serotypes (AAV2/1, AAV2/2, AAV2/6, AAV2/8, and AAV2/9) expressing enhanced green fluorescent protein driven by a cytomegalovirus promoter vary greatly depending on serotype and route of delivery (intravitreal, subretinal, or suprachoroidal) in rats. With subretinal delivery, all serotypes successfully transduced the retinal pigmented epithelium and outer nuclear layer (ONL), with AAV2/1 displaying the highest transduction efficiency and AAV2/2 and AAV2/6 showing lower ONL transduction. There was minimal transduction of the inner retina through subretinal delivery for any serotype. Tropism by suprachoroidal delivery mirrored that of subretinal delivery for all AAV serotypes but resulted in a wider distribution and greater ONL transduction. With intravitreal delivery, retinal transduction was seen primarily in the inner retina (retinal nerve fiber, ganglion cell, and inner nuclear layers) for AAV2/1 and AAV2/6, with AAV2/6 showing the highest transduction. When compared with data from human explant models, there are substantial differences in tropism and transduction that are important to consider when using rats as preclinical models for the development of ocular gene therapies for humans.

Effects of an Aquaporin 4 Inhibitor, TGN-020, on Murine Diabetic Retina

PURPOSE

To investigate the effect of a selective aquaporin 4 (AQP4) inhibitor, 2-(nicotinamide)-1,3,4-thiadiazole (TGN-020), on the expression of vascular endothelial growth factor (VEGF) and reactive oxygen species (ROS) production, as well as on the retinal edema in diabetic retina.

METHODS

Intravitreal injections of bevacizumab, TGN-020, or phosphate-buffered saline (PBS) were performed on streptozotocin-induced diabetic rats. Retinal sections were immunostained for anti-glial fibrillary acidic protein (GFAP), anti-AQP4, and anti-VEGF. Protein levels of VEGF from collected retinas were determined by Western blot analysis. In addition, retinal vascular leakage of Evans Blue was observed in the flat-mounted retina from the diabetic rats in the presence or absence of TGN-020. Volumetric changes of rat retinal Müller cells (TR-MUL5; transgenic rat Müller cells) and intracellular levels of ROS were determined using flow cytometry analysis of ethidium fluorescence in the presence or absence of TGN-020 or bevacizumab under physiological and high glucose conditions.

RESULTS

In the diabetic retina, the immunoreactivity and protein levels of VEGF were suppressed by TGN-020. AQP4 immunoreactivity was higher than in the control retinas and the expressions of AQP4 were co-localized with GFAP. Similarly to VEGF, AQP4 and GFAP were also suppressed by TGN-020. In the Evans Blue assay, TGN-020 decreased leakage in the diabetic retinas. In the cultured Müller cells, the increase in cell volumes and intracellular ROS production under high glucose condition were suppressed by exposure to TGN-020 as much as by exposure to bevacizumab.

CONCLUSION

TGN-020 may have an inhibitory effect on diabetic retinal edema.

Pathological Features of Diabetic Retinopathy in Spontaneously Diabetic Torii Fatty Rats

OBJECTIVE

The Spontaneously Diabetic Torii (SDT) fatty rat, established by introducing the fa allele (obesity gene) of the Zucker fatty rat into the SDT rat genome, is a new model of obese type 2 diabetes. We studied the pathologic features of diabetic retinopathy (DR) in this animal.

METHODS

The eyes of SDT fatty, SDT (controls), and Sprague Dawley (SD) rats (normal controls) were enucleated at 8, 16, 24, 32, and 40 weeks of age (n = 5-6 for each rat type at each age). The retinal thicknesses, numbers of retinal folds, and choroidal thicknesses were evaluated. Immunostaining for glial fibrillary acidic protein (GFAP) and vascular endothelial growth factor (VEGF) was performed. Quantitative analyses of the immunopositive regions were performed using a cell-counting algorithm.

RESULTS

The retinas tended to be thicker in the SDT fatty rats and SDT rats than in the SD rats; the choroids tended to be thicker in the SDT fatty rats than in the SD rats. The retinal folds in the SDT fatty rats developed earlier and were more severe than in the SDT rats. Quantitative analyses showed that the GFAP- and VEGF-positive regions in the retinas of the SDT fatty rats were significantly larger than those of the SDT rats.

CONCLUSIONS

SDT fatty rats developed more severe DR earlier than the SDT rats. The SDT fatty rats might be useful as a type 2 diabetes animal model to study DR.

In Vivo Imaging of the Retina, Choroid, and Optic Nerve Head in Guinea Pigs

PURPOSE

Guinea pigs are increasingly being used as a model of myopia, and may also represent a novel model of glaucoma. Here, optical coherence tomography (OCT) imaging was performed in guinea pigs. In vivo measurements of retinal, choroidal, and optic nerve head parameters were compared with histology, and repeatability and interocular variations were assessed.

METHODS

OCT imaging and histology were performed on adult guinea pigs (n = 9). Using a custom program in MATLAB, total retina, ganglion cell/nerve fiber layer (GC/NFL), outer retina, and choroid thicknesses were determined. Additionally, Bruch's membrane opening (BMO) area and diameter, and minimum rim width were calculated. Intraobserver, interocular, and intersession coefficients of variation (CV) and intraclass correlation coefficients (ICC) were assessed.

RESULTS

Retina, GC/NFL, outer retina and choroid thicknesses from in vivo OCT imaging were 147.7 ± 5.8 μm, 59.2 ± 4.5 μm, 72.4 ± 2.4 μm, and 64.8 ± 11.6 μm, respectively. Interocular CV ranged from 1.8% to 11% (paired t-test, p = 0.16 to 0.81), and intersession CV ranged from 1.1% to 5.6% (p = 0.12 to 0.82), with the choroid showing the greatest variability. BMO area was 0.192 ± 0.023 mm², and diameter was 493.79 ± 31.89 μm, with intersession CV of 3.3% and 1.7%, respectively. Hyper reflective retinal layers in OCT correlated with plexiform and RPE layers in histology.

CONCLUSION

In vivo OCT imaging and quantification of guinea pig retina and optic nerve head parameters were repeatable and similar between eyes of the same animal. In vivo visibility of retinal cell layers correlated well with histological images.

ABBREVIATIONS

optic nerve head (ONH), retinal ganglion cell (RGC), spectral domain optical coherence tomography (SD-OCT), enhanced depth imaging (EDI), minimum rim width (MRW), hematoxylin and eosin (H & E).

Diabetic macular edema-like ocular lesions in male spontaneously diabetic torii fatty rats

Diabetic macular edema (DME) is a major factor contributing to visual disabilities in diabetic patients, and the number of patients is increasing. Animal models play a key role in the development of novel therapies. In this study, pathophysiological analyses of ocular lesions in Spontaneously Diabetic Torii (SDT) fatty rats were performed. First, vascular endothelial growth factor (VEGF) concentrations in vitreous humor, retinal vascular permeability and retinal thickness were measured in SDT fatty rats (Experiment 1). Furthermore, the pharmacological effects of two anti-diabetic drugs, phlorizin and pioglitazone, on retinal lesions were evaluated (Experiment 2). As results, the SDT fatty rats exhibited VEGF increase in vitreous humor at 8 and 16 weeks of age, and both retinal vascular hyperpermeability and retinal thickening at 16 weeks of age. In particular, the layers between the retinal internal limiting membrane and the outer nuclear layer were thickened. Phlorizin treatment from 4 to 16 weeks of age improved hyperglycemia and normalized retinal thickness; however, the effect of pioglitazone on retinal thickness was not strong despite the normalization of hyperglycemia. These data demonstrate that the male SDT fatty rat is a useful model for developing new therapeutic approaches in DME.

The Relationship between Peripheral Nerve Conduction Velocity and Ophthalmological Findings in Type 2 Diabetes Patients with Early Diabetic Retinopathy

PURPOSE

Nerve conduction velocity (NCV) is an indicator of neuronal damage in the distal segment of the peripheral nerves. Here, we determined the association between NCV and other systemic and ocular clinical findings, in type 2 diabetes patients with early diabetic retinopathy (DR).

METHODS

This study included 42 eyes of 42 type 2 diabetes patients (median age: 54 years) with no DR or with mild nonproliferative DR. Standard statistical techniques were used to determine associations between clinical findings.

RESULTS

Sural sensory conduction velocity (SCV) and tibial motor conduction velocity (MCV) were significantly lower in mild nonproliferative DR patients than patients with no DR (P = 0.008 and P = 0.01, resp.). Furthermore, logistic regression analyses revealed that sural SCV and tibial MCV were independent factors contributing to the presence of mild nonproliferative DR (OR 0.83, P = 0.012 and OR 0.69 P = 0.02, resp.). Tibial MCV was correlated with choroidal thickness (CT) (P = 0.01), and a multiple regression analysis revealed that age, tibial MCV, and carotid intima-media thickness were independent associating factors with CT (P = 0.035, P = 0.015, and P = 0.008, resp.).

CONCLUSIONS

Our findings suggest that reduced NCV may be closely associated with early DR in type 2 diabetes patients. Thus, reduced nerve conduction is a potential early biomarker of DR.

Neuroprotective Effect of Hydroxytyrosol in Experimental Diabetic Retinopathy: Relationship with Cardiovascular Biomarkers

The aim of the study was to test the neuroprotective effect of hydroxytyrosol (HT) on experimental diabetic retinopathy. Animals were divided in four groups: (1) control nondiabetic rats, (2) streptozotocin-diabetic rats (DR), (3) DR treated with 1 mg/kg/day p.o. HT, and (4) DR treated with 5 mg/kg/day p.o. HT. Treatment with HT was started 7 days before inducing diabetes and was maintained for 2 months. In the DR group, total area occupied by extracellular matrix was increased, area occupied by retinal cells was decreased; both returned to near-control values in DR rats treated with HT. The number of retinal ganglion cells in DR was significantly lower (44%) than in the control group, and this decrease was smaller after HT treatment (34% and 9.1%). Linear regression analysis showed that prostacyclin, platelet aggregation, peroxynitrites, and the dose of 5 mg/kg/day HT significantly influenced retinal ganglion cell count. In conclusion, HT exerted a neuroprotective effect on diabetic retinopathy, and this effect correlated significantly with changes in some cardiovascular biomarkers.

Evaluation of Retinal Function in Streptozotocin-induced Diabetic Rats by Using the Electroretinography and Immunohistochemistry Methods

Streptozotocin-induced diabetic rat (STZ rat) was used in many studies for the diabetic mellitus. In this study, we demonstrated whether the electroretinograms (ERG) was changed in the retina of STZ rats. In addition, we investigated the histopathological alteration in the retina of STZ rats by using the immunological method. The 100 mg/kg of STZ was injected continuously for 2 d (100 mg/kg×2). The insulin level was decreased, and the glucose level was enhanced 14 d after the injection of STZ. Moreover, the levels of a-wave, b-wave and OP amplitude were decreased in the rat at 14 d after the injection of STZ. Although, the damage and apoptosis was not observed in the retinal ganglion cell of STZ rats by the immunological experiment using the phospho-H2A.X and cleaved caspase-3, the distance between cell and cell was increased in both of outer- and inner- nuclear (granule) layer in retina of STZ rats. In conclusion, we showed that the enhanced thickening in retina was caused by the injection of excessive STZ. The thickening in retina of STZ rats may lead to the dysfunction of retina, resulting in the decrease in ERG. These findings provide significant information that can be used in the design of a model of diabetic retinopathy.