Triamcinolone acetonide suppresses interleukin-1 beta-mediated increase in vascular endothelial growth factor expression in cultured rat Müller cells

GMFB/AKT/TGF-β3 in Müller cells mediated early retinal degeneration in a streptozotocin-induced rat diabetes model

Retinal degeneration, characterized by Müller cell gliosis and photoreceptor apoptosis, is considered an early event in diabetic retinopathy (DR). Our previous study proposed that GMFB may mediate diabetic retinal degeneration. This study identified GMFB as a sensitive and functional gliosis marker for DR. Compared to the wild type (WT) group, Gmfb knockout (KO) significantly improved visual function, attenuated gliosis, reduced the apoptosis of neurons, and decreased the mRNA levels of tumor necrosis factor α (Tnf-α) and interleukin-1β (Il-1β) in diabetic retinas. Tgf-β3 was enriched by hub genes using RNA sequencing in primary WT and KO Müller cells. Gmfb KO significantly upregulated the transforming growth factor (TGF)-β3 protein level via the AKT pathway. The protective effect of TGF-β3 in the vitreous resulted in significantly improved visual function and decreased the number of apoptotic cells in the diabetic retina. The protection of Gmfb KO in primary Müller cells against high glucose (HG)-induced photoreceptor apoptosis was partially counteracted by TGF-β3 antibody and administration of TGFBR1/2 inhibitors. Nuclear receptor subfamily 3 group C member 1 (NR3C1) binds to the promoter region of Gmfb and regulates Gmfb mRNA at the transcriptional level. NR3C1 was increased in the retinas of early diabetic rats but decreased in the retinas of late diabetic rats. N'-[(1E)-(3-Methoxyphenyl)Methylene]-3-Methyl-1H-Pyrazole-5-Carbohydrazide (DS-5) was identified as an inhibitor of GMFB, having a protective role in DR. We demonstrated that GMFB/AKT/TGF-β3 mediated early diabetic retinal degeneration in diabetic rats. This study provides a novel therapeutic strategy for treating retinal degeneration in patients with DR.

The glucocorticoid receptor as a master regulator of the Müller cell response to diabetic conditions in mice

Diabetic retinopathy (DR) is considered a primarily microvascular complication of diabetes. Müller glia cells are at the centre of the retinal neurovascular unit and play a critical role in DR. We therefore investigated Müller cell-specific signalling pathways that are altered in DR to identify novel targets for gene therapy. Using a multi-omics approach on purified Müller cells from diabetic db/db mice, we found the mRNA and protein expression of the glucocorticoid receptor (GR) to be significantly decreased, while its target gene cluster was down-regulated. Further, oPOSSUM TF analysis and ATAC- sequencing identified the GR as a master regulator of Müller cell response to diabetic conditions. Cortisol not only increased GR phosphorylation. It also induced changes in the expression of known GR target genes in retinal explants. Finally, retinal functionality was improved by AAV-mediated overexpression of GR in Müller cells. Our study demonstrates an important role of the glial GR in DR and implies that therapeutic approaches targeting this signalling pathway should be aimed at increasing GR expression rather than the addition of more ligand.

Diabetic retinopathy progression 6 months post-cataract surgery with intravitreous bevacizumab vs triamcinolone: A secondary analysis of the DiMECAT trial

IMPORTANCE

Diabetic retinopathy (DR) may progress following cataract surgery due to surgery-induced inflammation. The effect of intravitreal bevacizumab (BVB) and triamcinolone acetonide (TCA), which have differing anti-inflammatory properties, on DR progression following cataract surgery has not been reported.

BACKGROUND

To report the progression of DR in diabetic patients undergoing cataract extraction treated with intravitreal BVB or TCA during the surgery.

DESIGN

Post hoc analysis of 6-month data from a prospective, randomized, double-masked clinical trial.

PARTICIPANTS

Diabetic patients with clinically significant cataract and fovea involving diabetic macular oedema (DME), or a recent history of DME.

METHODS

Participants were randomly allocated 1:1 to receive intravitreal BVB 1.25 mg or TCA 4 mg during and post-cataract surgery as needed. The rate of DR progression between groups was compared.

MAIN OUTCOME MEASURES

DR progression.

RESULTS

There were 61 eyes included. Patients receiving BVB were older than those receiving TCA (70.2 vs 64.3 years; P < .05). Three participants (10.7%) in the BVB and three (9.09%) in the TCA group had a one-step progression, while none in BVB and only one (3%) in the TCA group demonstrated two-step DR progression. In the majority of these patients, DR progression was from mild to moderate non-proliferative diabetic retinopathy.

CONCLUSION AND RELEVANCE

In this study, BVB and TCA groups had a similar, and lower rate of DR progression compared to previous studies where no adjunctive treatment was administered, suggesting that patients with DME may benefit from either intraoperative intravitreous BVB or TCA injection to reduce the risk of DR progression following cataract surgery.

The role of Müller cell glucocorticoid signaling in diabetic retinopathy

Diabetic retinopathy (DR) is a sight-threatening complication associated with the highly prevalent diabetes disorder. Both the microvascular damage and neurodegeneration detected in the retina caused by chronic hyperglycemia have brought special attention to Müller cells, the major macroglia of the retina that are responsible for retinal homeostasis. Given the role of glucocorticoid signaling in anti-inflammatory responses and the almost exclusive expression of glucocorticoid receptors (GRs) in retinal Müller cells, administration of corticosteroid agonists as a potential treatment option has been widely studied. Although these approaches have been moderately efficacious in treating or de-escalating DR pathomechanisms, there are various side effects and gaps of knowledge with regard to introducing exogenous glucocorticoids to the diseased retina. In this paper, we provide a review of the literature concerning the available evidence for the role of Müller cell glucocorticoid signaling in DR and we discuss previously investigated approaches in modulating this system as possible treatment options. Furthermore, we propose a novel alternative to the available choices of treatment by using gene therapy as a tool to regulate the expression of GR in retinal Müller cells. Upregulating GR expression allows for induced glucocorticoid signaling with more enduring effects compared to injection of agonists. Hence, repetitive injections would no longer be required. Lastly, side effects of glucocorticoid therapy such as glucocorticoid resistance of GR following chronic exposure to excess ligands or agonists can be avoided.

Müller cells in pathological retinal angiogenesis

Müller cells are the major glial cells spanning the entire layer of the retina and maintaining retinal structure. Under pathological conditions, Müller cells are involved in retinal angiogenesis, a process of growing new blood vessels from pre-existing capillaries. In response to hypoxia, high glucose, and inflammation conditions, multiple signaling pathways are activated in Müller cells, followed by the increased production of proangiogenic factors including vascular endothelial growth factor, basic fibroblast growth factor, matrix metalloproteinases, Netrin-4, and angiopoietin-like 4. Expression of antiangiogenic factors is also downregulated in Müller cells. Besides, proliferation and dedifferentiation of Müller cells facilitates retinal angiogenesis. In this review, we summarized molecular mechanisms of Müller cells-related retinal angiogenesis. The potential of Müller cells as a therapeutic target for retinal angiogenesis was also discussed.

Effect of glucocorticoids on neuronal and vascular pathology in a transgenic model of selective Müller cell ablation

Retinal diseases such as macular telangiectasis type 2 (MacTel), age-related macular degeneration (AMD) and diabetic retinopathy (DR) affect both neurons and blood vessels. Treatments addressing both at the same time might have advantages over more specific approaches, such as vascular endothelial growth factor (VEGF) inhibitors, which are used to treat vascular leak but are suspected to have a neurotoxic effect. Here, we studied the effects of an intravitreal injection of triamcinolone acetonide (TA) in a transgenic model in which patchy Müller cell ablation leads to photoreceptor degeneration, vascular leak, and intraretinal neovascularization. TA was injected 4 days before Müller cell ablation. Changes in photoreceptors, microglia and Müller cells, retinal vasculature, differential expression of p75 neurotrophin receptor (p75(NTR) ), tumor necrosis factor-α (TNFα), the precursor and mature forms of neurotrophin 3 (pro-NT3 and mature NT3) and activation of the p53 and p38 stress-activated protein kinase (p38/SAPK) signaling pathways were examined. We found that TA prevented photoreceptor degeneration and inhibited activation of microglial and Müller cells. TA attenuated Müller cell loss and inhibited overexpression of p75(NTR) , TNFα, pro-NT, and the activation of p53 and p38/SAPK signaling pathways. TA not only prevented the development of retinal vascular lesions but also inhibited fluorescein leakage from established vascular lesions. TA inhibited overexpression of VEGF in transgenic mice but without affecting its basal level expression in the normal retina. Our data suggest that glucocorticoid treatment may be beneficial for treatment of retinal diseases such as MacTel, AMD, and DR that affect both neurons and the vasculature.

Emerging drugs for diabetic retinopathy

INTRODUCTION

Diabetes mellitus with its ophthalmic complications is the major cause for legal blindness in industrialized countries. Diabetic macular edema and its complex pathophysiology as part of diabetic retinopathy are the leading cause of vision loss among diabetic patients. In recent years, treatment options have developed involving the intravitreal applications of several compounds.

AREAS COVERED

Current treatment options for diabetic macular edema including laser therapy and scientific basis of new drugs are discussed. Possible benefits and drawbacks of these new approaches are addressed.

EXPERT OPINION

In recent years, new drugs against retinal diseases have been developed consisting mainly of steroid or anti-vascular endothelial growth factor compounds. Targeting macular edema, the second shows a possible therapeutic role in the proliferative form of diabetic retinopathy, requiring further investigation. New biodegradable delivery systems show an advantage in sustaining effective compound concentrations for longer times and have positive impact on safety profile and cost-effectiveness of the drug, a factor of grave importance when considering the future of any new drug in the market. All these new therapeutic approaches alone or in combination with the existing treatments have to demonstrate their efficacy and safety in diabetic retinopathy in current and future trials.

Upcoming therapeutic advances in diabetic macular edema: an intravitreal dexamethasone drug delivery system

INTRODUCTION

Diabetes mellitus, through its ophthalmic complications diabetic retinopathy and diabetic macular edema (DME), is a leading cause of vision loss in industrialized countries.

AREAS COVERED

This review covers laser treatment, which is a standard treatment strategy that has proven efficacy and safety through large clinical trials in DME. Several intravitreal drug applications currently being investigated are also discussed.

EXPERT OPINION

First results suggest that the administration of anti-VEGF compounds is effective for DME. However, frequent injections may compromise safety. In order to enhance patient compliance, sustained delivery systems are being evaluated as potential treatment approaches. So far, only steroids have been included as active in such non-biodegradable or biodegradable delivery systems. Non-biodegradable systems are more complicated to administer as surgery is required and they need to be retrieved at the end of treatment. Also, in some cases safety issues have arisen, especially around intraocular pressure control. A new biodegradable dexamethasone delivery system seems to show promising efficacy results in addition to a more favorable safety profile, which will potentially improve patient compliance. All new therapeutic approaches, alone and in combination, will need to demonstrate their efficacy and safety in DME in future trials.

Visual outcomes in five different approaches for treatment of central retinal vein occlusion

BACKGROUND AND OBJECTIVE

Four treatment methods for central retinal vein occlusion were compared with its natural course.

PATIENTS AND METHODS

In this partially prospective, comparative, interventional case series on 63 eyes with central retinal vein occlusion, five approaches were compared: intravitreal triamcinolone injection; radial optic neurotomy; combined radial optic neurotomy and intraocular triamcinolone injection; combined internal limiting membrane peeling, radial optic neurotomy, and intraocular triamcinolone; and observation.

RESULTS

Final visual acuity in the intravitreal triamcinolone group was better compared with the observation (P = .025), radial optic neurotomy (P = .037), combined radial optic neurotomy/intraocular triamcinolone injection (P = .401), and combined internal limiting membrane peeling, radial optic neurotomy, and intraocular triamcinolone injection (P = .023) groups. However, after adjustment for baseline visual acuity, the only treatment method with significant visual acuity improvement in relation to the observation group was the combined radial optic neurotomy/intraocular triamcinolone injection (P = .025, .023, and .054 at 1, 3, and 6 months, respectively).

CONCLUSION

Among the five different approaches analyzed in this study, combined radial optic neurotomy and intraocular triamcinolone injection may provide a better visual outcome in the management of central retinal vein occlusion.

Pigment epithelium derived factor as an anti-inflammatory factor against decrease of glutamine synthetase expression in retinal Müller cells under high glucose conditions

BACKGROUND

The pathogenesis of diabetic retinopathy (DR) is similar to that of a chronic inflammatory disease. A predominant function of Müller cells is to regulate glutamate levels, but in DR the function is compromised. The present study was performed to investigate the role of pigment epithelial derived factor (PEDF) on the expression of glutamine synthetase (GS) in rat retinal Müller cells under high glucose conditions, and to study the possible mechanism for PEDF against decrease of GS expression in retinal Müller cells under high glucose conditions.

METHODS

The role of PEDF on the expressions of GS and interleukin-1beta (IL-1beta) in retinal Müller cells under normal and high glucose conditions was measured by western blotting, real-time RT-PCR, or immunocytochemistry. In order to confirm the effect of PEDF on GS against the role of IL-1beta, the PEDF siRNA method was used.

RESULTS

High glucose increased the expression of IL-1beta, but decreased the expressions of GS and PEDF in retinal Müller cells. PEDF increased the expression of GS and decreased the expression of IL-1beta in retinal Müller cells under high glucose conditions. The effect of IL-1beta on expression of GS was inhibited by PEDF. Moreover, down-regulation of PEDF expression by siRNA resulted in significantly increasing the expression of IL-1beta, but decreasing the expression of GS in retinal Müller cells.

CONCLUSIONS

PEDF increases expression of GS against the effect of IL-1beta in retinal Müller cells under high glucose conditions. These findings suggested that PEDF may act as an anti-inflammatory factor against decrease of GS expression in retinal Müller cells in diabetic retinopathy.

Short-term results of intravitreal bevacizumab for macular edema with retinal vein obstruction and diabetic macular edema

OBJECTIVE

The aim of this study was to identify the short-term effect, safety, and durability of intravitreally injected bevacizumab in patients with macular edema (ME) caused by retinal vein obstruction (RVO) and diabetic macular edema (DME).

METHODS

We retrospectively evaluated 39 eyes of 36 patients, 14 with ME caused by RVO and 25 with DME, who received intravitreal bevacizumab (1.25 mg) and were followed up for at least 3 months. Monthly assessments examined safety, best corrected visual acuity with an ETDRS chart (logMAR), and central retinal thickness (CRT) using optical coherence tomography.

RESULTS

No significant ocular or systemic side-effects were observed. The follow-up period was 5.4 +/- 1.1 months (mean +/- standard deviation). During follow-up, the mean number of injections was 1.4 +/- 0.5. The baseline mean logMAR was 0.91 +/- 0.51, and the mean CRT was 552.6 +/- 186.7 microm. At 1, 2, and 3 months, the mean logMAR was 0.67 +/- 0.46 (paired t test, P < 0.001), 0.66 +/- 0.46 (P < 0.001), and 0.69 +/- 0.45 (P < 0.001), respectively, and the mean CRT was 323.1 +/- 151.9 mum (P < 0.001), 324.6 +/- 136.9 mum (P < 0.001), and 382.5 +/- 130.4 microm (P < 0.001), respectively. Fourteen (14) of 34 eyes with more than 3 months of follow-up required a second injection at a mean 3.4 +/- 1.0 months after the initial injection. For both ME caused RVO and DME patients, a bevacizumab administration improved logMAR and CRT at each time point through to 6 months, except for logMAR in DME at 1 week (P = 0.081), 5 months (P = 0.130) and 6 months (P = 0.759).

CONCLUSIONS

An intravitreal bevacizumab injection for ME caused by RVO and DME was safe and effective for improving visual acuity and reducing CRT.

Triamcinolone suppresses retinal vascular pathology via a potent interruption of proinflammatory signal-regulated activation of VEGF during a relative hypoxia

We examined the effect of triamcinolone acetonide (TA), a corticosteroid, on the relationship between vascular pathophysiology and vascular endothelial growth factor (VEGF) activation in the retina of a rat model of oxygen-induced retinopathy (OIR). OIR was induced by exposure of hyperoxia (80% oxygen) to Sprague-Dawley (SD) rats from P2 to P14 and then returned to normoxic conditions. TA was intravitreal-injected once into the right eye of OIR rats at P15. Effects of TA on vascular pathophysiology or changes of various genes in response to hypoxia and/or proinflammation under hypoxic retina were assessed by the Evans-blue method, fluorescein isothiocyanate-dextran (FITC-D) infusion, immunoblotting, and ELIZA. TA not only reduced retinal neovascularization and vascular leakage in the OIR-rat retina, but also blocked the induction of hypoxia-response proinflammatory genes before it negatively controlled VEGF activation. These findings suggest a potential that TA suppresses retinal neovascular pathophysiology via proinflammation-mediated activation of VEGF during hypoxia.

Müller cells as players in retinal degeneration and edema

BACKGROUND

Under normal conditions, Müller cells support neuronal activity and the integrity of the blood-retinal barrier, whereas gliotic alterations of Müller cells under pathological conditions may contribute to retinal degeneration and edema formation. A major function of Müller cells is the fluid absorption from the retinal tissue, which is mediated by transcellular water transport coupled to currents through potassium channels.

METHODS

Alterations of retinal Müller cells under pathological conditions were investigated by immunohistochemistry and recording their behavior under osmotic stress.

RESULTS

In animal models of various retinopathies, e.g., retinal ischemia, ocular inflammation, retinal detachment, and diabetes, it was found that Müller cells decrease the expression of their major potassium channel (Kir4.1). This alteration is associated with an impairment of the rapid water transport across Müller cell membranes, as recognizable in the induction of cellular swelling under hypoosmolar conditions. Osmotic swelling of Müller cells is also induced by oxidative stress and by inflammatory mediators such as arachidonic acid and prostaglandins.

CONCLUSIONS

The data suggest that a disturbed fluid transport through Müller cells is (in addition to vascular leakage) a pathogenic factor contributing to the development of retinal edema. Pharmacological re-activation of the retinal water clearance by Müller cells may represent an approach to the development of new edema-resolving drugs. Triamcinolone acetonide, which is clinically used to resolve edema, prevents osmotic swelling of Müller cells as it induces the release of endogenous adenosine and subsequent A1 receptor activation which results in the opening of ion channels. Apparently, triamcinolone resolves edema by both inhibition of vascular leakage and stimulation of retinal fluid clearance by Müller cells.

Triamcinolone reduces neovascularization, capillary density and IGF-1 receptor phosphorylation in a model of oxygen-induced retinopathy

PURPOSE

To study the effects of intravitreous triamcinolone acetonide (TA) on neovascularization (NV), capillary density, and retinal endothelial cell (REC) viability in a model of oxygen-induced retinopathy (OIR).

METHODS

Newborn rats exposed to OIR underwent intravitreous injections (right eye) at day 14 to achieve intravitreous concentrations of: dexamethasone (DEX) (0.3 mg/mL), triamcinolone (TA; 0.4-4 mg/mL), or PBS. Animals were removed to room air and at day 18, retinal flatmounts were assayed for clock hours of NV, percent peripheral avascular retina, capillary density, apoptosis, and VEGF protein. At day 15, retinas were assayed for insulin-like growth factor (IGF)-1 receptor phosphorylation (IGF-1Rphos). Human RECs exposed to TA were assayed for trypan blue exclusion or activated caspase-3.

RESULTS

TA but not DEX or PBS reduced NV (ANOVA, P < 0.001), capillary density (ANOVA, P < 0.001), and systemic weight gain (ANOVA, P = 0.002). VEGF protein was not different between TA- and PBS-injected or noninjected groups. Apoptosis was not increased in vivo or in vitro between groups, but there was a dose-dependent toxic effect of TA on cultured RECs (P < 0.001). At day 15, retinas from the 4 mg/mL TA-injected OIR group had a trend toward reduced IGF-1Rphos compared with room air-raised PBS- or non-injected OIR groups.

CONCLUSIONS

TA caused dose-dependent reductions in NV, retinal vascularization, and systemic weight gain associated with a reduction in IGF-1Rphos. Long-term studies are needed to assess TA toxicity in vivo. TA doses should be carefully considered before administering the drug in diseases with ongoing retinal vascular development, such as retinopathy of prematurity.