Pharmacotherapy for diabetic retinopathy

Recent Updates on Nanocarriers for Drug Delivery in Posterior Segment Diseases with Emphasis on Diabetic Retinopathy

In recent years, various conventional formulations have been used for the treatment and/or management of ocular medical conditions. Diabetic retinopathy, a microvascular disease of the retina, remains the leading cause of visual disability in patients with diabetes. Currently, for treating diabetic retinopathy, only intraocular, intravitreal, periocular injections, and laser photocoagulation are widely used. Frequent administration of these drugs by injections may lead to serious complications, including retinal detachment and endophthalmitis. Although conventional ophthalmic formulations like eye drops, ointments, and suspensions are available globally, these formulations fail to achieve optimum drug therapeutic profile due to immediate nasolacrimal drainage, rapid tearing, and systemic tearing toxicity of the drugs. To achieve better therapeutic outcomes with prolonged release of the therapeutic agents, nano-drug delivery materials have been investigated. These nanocarriers include nanoparticles, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), dendrimers, nanofibers, in-situ gel, vesicular carriers, niosomes, and mucoadhesive systems, among others. The nanocarriers carry the potential benefits of site-specific delivery and controlled and sustained drug release profile. In the present article, various nanomaterials explored for treating diabetic retinopathy are reviewed.

Edema and lymphatic clearance: molecular mechanisms and ongoing challenges

Resolution of edema remains a significant clinical challenge. Conditions such as traumatic shock, sepsis, or diabetes often involve microvascular hyperpermeability, which leads to tissue and organ dysfunction. Lymphatic insufficiency due to genetic causes, surgical removal of lymph nodes, or infections, leads to varying degrees of tissue swelling that impair mobility and immune defenses. Treatment options are limited to management of edema as there are no specific therapeutics that have demonstrated significant success for ameliorating microvascular leakage or impaired lymphatic function. This review examines current knowledge about the physiological, cellular, and molecular mechanisms that control microvascular permeability and lymphatic clearance, the respective processes for interstitial fluid formation and removal. Clinical conditions featuring edema, along with potential future directions are discussed.

Protective antioxidant effects of saffron extract on retinas of streptozotocin-induced diabetic rats

Objective: Oxidative stress plays an important role in the pathogenesis of diabetic retinopathy. The aim of the present study was to investigate the effect of Crocus sativus L. styles (saffron) extract on oxidative stress indices of retina in streptozotocin (STZ)-induced diabetic rats. Methods: Adult male Wistar rats (n=20) were randomized into the following 4 groups (n=6-7/ group): Control group (C): normal, Control + Saffron group (CS): non-diabetic rats treated with 60 mg/ kg of saffron extract, Diabetic group (D) and Diabetic + Saffron group (DS): diabetic rats treated with 60 mg/ kg saffron extract. We determined the activity of superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) as markers of antioxidant response, as well as malondialdehyde (MDA) as a marker of lipid peroxidation. Results: Induction of diabetes caused a significant decline in the activities of CAT (76.43%), SOD (53.43%) and GPx (77.58%). MDA levels were significantly lower in the DS group (0.878 ± 0.375 nmol MDA/ mg protein) as compared to D group (1.950 ± 0.299 nmol MDA/ mg protein, p<0.01) and in the CS group (0.503 ± 0.221) in comparison to C group (1.699 ± 0.454, p<0.01). Moreover, SOD and GPx activities were significantly higher (more than 1.5 and 3.5-fold respectively) after treatment with saffron (p<0.01). Regarding the retinas of non-diabetic animals, the administration of the extract caused an > 1.8-fold increase in the activity of CAT (p<0.05) and a 3-fold decrease in MDA levels (p<0.01). Conclusions: This study showed that saffron extract has a protective antioxidant action in retinas of diabetic rats. Abbreviations: C = Control group, CS = non-diabetic rats diabetic rats treated with 60 mg/ kg saffron extract, D = diabetic group, DS = diabetic rats treated with 60 mg/ kg saffron extract, SOD = superoxide dismutase, GPx = glutathione peroxidase, CAT = catalase, MDA = malondialdehyde, DM = diabetes mellitus, DR = diabetic retinopathy, ROS = reactive oxygen species, STZ = streptozotocin, GSH = reduced glutathione.

COMP-Ang1 Stabilizes Hyperglycemic Disruption of Blood-Retinal Barrier Phenotype in Human Retinal Microvascular Endothelial Cells

Purpose

Current treatments for diabetic retinopathy (DR) have considerable limitations, underpinning the need for new therapeutic options. In this article, the ability of an engineered angiopoietin-1 variant (COMP-Ang1) to ameliorate the injurious effects of hyperglycemia on barrier integrity in a human retinal microvascular endothelial cell (HRMvEC) model is comprehensively investigated.

Methods

Confluent HRMvECs were treated (0–72 hours) with d-glucose (5 or 30 mM) in the absence and presence of COMP-Ang1 (10–200 ng/mL). l-glucose (30 mM) was used as osmotic control. Posttreatment, intact cell monolayers were monitored for permeability to FITC-dextran 40 kDa. Cells were also harvested for analysis of interendothelial junction targets by RT-qPCR and Western blotting. The impact of receptor tyrosine kinase Tie2 gene silencing on COMP-Ang1 efficacy was also evaluated.

Results

Treatment with 30 mM d-glucose (but not l-glucose) demonstrated a time-dependent elevation in the mean rate of FITC-dextran diffusion across intact HRMvEC monolayers, in parallel with significant reductions in mRNA/protein levels of occludin, claudin-5, ZO-1, and VE-Cadherin. These effects were all attenuated by COMP-Ang1 in a concentration-dependent fashion, with 200 ng/mL recovering barrier function by ∼88%, and recovering reduced interendothelial junction protein levels by more than 50%. Finally, Tie2 knockdown by small interfering RNA silencing blocked the ability of COMP-Ang1 to mitigate against hyperglycemia-induced permeabilization of HRMvECs and depletion of junctional expression levels.

Conclusions

In summary, this article presents a reproducible in vitro cell study that quantifies the concentration-dependent efficacy of COMP-Ang1 to mitigate the injurious effects of hyperglycemic challenge on HRMvEC barrier properties via Tie2-mediated signaling.

Molecular and Pathophysiological Mechanisms of Diabetic Retinopathy in Relation to Adhesion Molecules

Diabetic Retinopathy (DR) is considered as a most common microvascular complication of diabetes affected by one in three people who are suffered for diabetes. Several pathophysiological mechanisms and adhesion molecules may play an etiologic role in the development of diabetes and its complications. The adhesion molecules located on both leucocytes and endothelial cells and considered as important molecules which can assessed the endothelial function. The functions of adhesion molecules involved in the cellular margination, slow rolling and transmigration of leukocytes. Hyperglycemia and its immediate biochemical sequelae or the low-grade inflammation directly alter endothelial function or influence endothelial cell functioning indirectly by induce oxidative stress and activates leukocytosis and leukocyte-endothelial cell interactions by the increased expression of adhesion molecules, growth factors, inflammatory factors, chemokines etc. and results DR. This review summarized the several pathophysiological mechanisms and role of adhesion molecules in disruption of homeostasis of vasculature by leukocytes in the development of diabetic retinopathy.

Diabetic retinopathy: a complex pathophysiology requiring novel therapeutic strategies

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Efficiency of fenofibrate in facilitating the reduction of central macular thickness in diabetic macular edema

PURPOSE

The purpose of this study is to study the benefit of addition of oral fenofibrate to the current regimen of diabetic macular edema (DME) management and quantify its effect on macular thickness and visual function in DME.

METHODS

Fifty-three eyes of 50 patients were randomized into treatment (Group A) (oral fenofibrate 160 mg/day) and control groups (Group B). Both groups underwent treatment of DME as per the standard treatment protocol of our hospital including intravitreal injections (anti-vascular endothelial growth factor/steroid) and grid laser. Patients were followed up every 2 months to note the visual acuity and central macular thickness (CMT) for 6 months.

RESULTS

Our groups were matched with respect to age (P = 0.802), mean diabetic age (P = 0.878), serum HbA1C levels (P = 0.523), and serum triglyceride levels (P = 0.793). The mean reduction in CMT was 136 μ in Group A and 83 μ in Group B at the end of 6 months. This difference was statistically significant (P = 0.031). Visual acuity improvement was 0.15 in Group A and 0.11 in Group B at the end of 6 months (P = 0.186). On subgroup analysis in Group A, we found that there was no difference in reduction of CMT between hypertensives and normotensives (P = 0.916), in patients with normal triglyceride levels and increased triglyceride levels (P = 0.975).

CONCLUSION

Addition of fenofibrate to the standard protocol of DME management seems to facilitate reduction of CMT and probably have an added benefit on the visual functions.

Cellular retinoic acid bioavailability in various pathologies and its therapeutic implication

Retinoic acid (RA), an active metabolite of vitamin A, is a critical signaling molecule in various cell types. We found that RA depletion caused by expression of the RA-metabolizing enzyme CYP26A1 promotes carcinogenesis, implicating CYP26A1 as a candidate oncogene. Several studies of CYP26s have suggested that the biological effect of RA on target cells is primarily determined by "cellular RA bioavailability", which is defined as the RA level in an individual cell, rather than by the serum concentration of RA. Consistently, stellate cells store approximately 80% of vitamin A in the body, and the state of cellular RA bioavailability regulates their function. Based on the similarities between stellate cells and astrocytes, we demonstrated that retinal astrocytes regulate tight junction-based endothelial integrity in a paracrine manner. Since diabetic retinopathy is characterized by increased vascular permeability in its early pathogenesis, RA normalized retinal astrocytes that are compromised in diabetes, resulting in suppression of vascular leakiness. RA also attenuated the loss of the epithelial barrier in murine experimental colitis. The concept of "cellular RA bioavailability" in various diseases will be directed at understanding various pathologies caused by RA insufficiency, implying the potential feasibility of a therapeutic strategy targeting the stellate cell system.

Regulatory SNPs Alter the Gene Expression of Diabetic Retinopathy Associated Secretary Factors

OBJECTIVES

Diabetic retinopathy (DR) is a common microvascular complication in both type I and type II diabetes. Several previous reports indicated the serum centration of some secretary factors were highly associated with DR. Therefore, we hypothesis regulatory SNPs (rSNPs) genotype in secretary factors may alter these gene expression and lead to DR.

METHODS

At first, pyrosequencing were applying to screen the SNPs which present allele frequency different in DR and DNR. Then individual genotyping was processed by Taqman assays in Taiwanese DR and DNR patients. To evaluate the effect of SNP allele on transcriptional activity, we measured promoter activity using luciferase reporter constructs.

RESULTS

We found the frequencies of the CC, CG, and GG genotype of the rs2010963 polymorphism were 15.09%, 47.14%, and 37.74% in DR and 12.90%, 19.35%, and 67.74% in DNR, respectively (p = 0.0205). The prevalence of DR was higher (p = 0.00793) in patients with the CC or CG genotype (62.26% and 32.26% for DR and DNR, respectively) compared with the patients with the GG genotype. To evaluate the effect of rs2010963-C allele on transcriptional activity, we measured promoter activity using luciferase reporter constructs. The rs2010963-C reporter showed 1.6 to 2-fold higher luciferase activity than rs2010963-G in 3 cell lines.

CONCLUSION

Our data proposed rs2010963-C altered the expression level of VEGFA in different tissues. We suggested small increase but long term exposure to VEGFA may lead to DR finally.

Effects of intravitreal injection of netrin-1 in retinal neovascularization of streptozotocin-induced diabetic rats

Background

In a previous study, we confirmed that netrin-1 acts as an antiangiogenic factor by inhibiting alkali burn-induced corneal neovascularization in rats. Here, we continue working on the role of netrin-1 in retinal neovascularization.

Methods

Using an in vitro angiogenesis assay, we detected the effects of netrin-1 on human umbilical vein endothelial cell tube formation, viability and proliferation, migration, and invasion at concentrations of 0.1 μg/mL or 5 μg/mL. We intravitreally injected 0.1 μg/mL or 5 μg/mL netrin-1 into streptozotocin-induced rats to assess retinal neovascularization using retinal electrophysiology and electroretinography, enzyme-linked immunosorbent assay, fundus fluoresce in angiography, measurement of inner blood retinal barrier, retinal hematoxylin-eosin staining, and retinal flat-mount fluorescence assays.

Results

Human umbilical vein endothelial cell tube formation, viability and proliferation, migration, and invasion were upregulated by netrin-1 at a concentration of 0.1 μg/mL (P<0.05), while 5 μg/mL netrin-1 had an opposite effect (P<0.05) in our in vitro angiogenesis assay. Retinal electrophysiology testing revealed that intravitreal injection of netrin-1 affected the amplitude of a- and b-waves (a-wave: 0.1 μg/mL netrin-1 =17.67±3.39 μm, 5 μg/mL netrin-1 =28.50±1.31 μm, phosphate-buffered saline [PBS]-treated =17.67±3.39 μm; b-wave: 0.1 μg/mL netrin-1 =44.67±4.80 μm, 5 μg/mL netrin-1 =97.17±9.63 μm, PBS-treated =44.67±4.80 μm) and the expression of VEGF-A (no-treatment rats, 9.29±0.80 pg/mL; PBS-treated rats, 19.64±3.77 pg/mL; 0.1 μg/mL netrin-1 treated rats, 21.37±3.64 pg/mL; 5 μg/mL netrin-1 treated rats, 9.85±0.54 pg/mL, at 6 weeks after induction). By comparing fluoresce in angiography, level of inner blood retinal barrier breakdown (% of control), retinal hematoxylin-eosin staining, and collagen-IV fluorescence assays in the retinas of PBS-treated rats, netrin-1 was found to suppress and reverse retinal neovascularization at a concentration of 5 μg/mL (P<0.05), while 0.1 μg/mL netrin-1 (P<0.05) led to an increase in the number of new retinal blood vessels, after 6 weeks’ injection.

Conclusion

Netrin-1 could play a significant role in retinal neovascularization by dual-direction regulating angiogenesis dependent on dosage.

Optical coherence tomography-guided ranibizumab injection for cystoid macular edema in well-controlled uveitis: twelve-month outcomes

PURPOSE

To determine whether serial ranibizumab injections are effective in the treatment of cystoid macular edema in patients with chronic controlled noninfectious uveitis.

METHODS

Five eyes of 5 patients were included in a prospective noncomparative therapeutic trial. They received intravitreal injections of ranibizumab at Day 0 and were followed monthly for 1 year. Injections were repeated monthly if persistent or new cystic edema manifested on optical coherence tomography. The primary outcome measure was the mean change in best-corrected visual acuity from baseline at 12 months. Secondary outcome measures included mean percentage change in central subfield retinal thickness (CST) and incidence of adverse events through Month 24.

RESULTS

Thirty-two injections were performed over the study period. At 1 year, the mean increase in acuity was 12.2 Early Treatment for Diabetic Retinopathy Study letters (P = 0.015). There was a statistically significant increase in visual acuity over time (P = 0.002). The CST decreased by 31.4%, 46.0%, 37.6%, and 45.4% relative to baseline at 3, 6, 9, and 12 months, respectively (P = 0.003). One patient experienced recurrence of uveitis with subsequent cataract and glaucoma progression.

CONCLUSION

Optical coherence tomography-guided monthly intravitreal ranibizumab injections delivered over the course of 1 year resulted in improved vision and reduced central retinal thickness.

Age-related macular degeneration and changes in the extracellular matrix

Age-related macular degeneration (AMD) is the leading cause of permanent, irreversible, central blindness (scotoma in the central visual field that makes reading and writing impossible, stereoscopic vision, recognition of colors and details) in patients over the age of 50 years in European and North America countries, and an important role is attributed to disorders in the regulation of the extracellular matrix (ECM). The main aim of this article is to present the crucial processes that occur on the level of Bruch’s membrane, with special consideration of the metalloproteinase substrates, metalloproteinase, and tissue inhibitor of metalloproteinase (TIMP).

A comprehensive review of the literature was performed through MEDLINE and PubMed searches, covering the years 2005–2012, using the following keywords: AMD, extracellular matrix, metalloproteinases, tissue inhibitors of metalloproteinases, Bruch’s membrane, collagen, elastin.

In the pathogenesis of AMD, a significant role is played by collagen type I and type IV; elastin; fibulin-3, -5, and -6; matrix metalloproteinase (MMP)-2, MMP-9, MMP-14, and MMP-1; and TIMP-3. Other important mechanisms include: ARMS2 and HTR1 proteins, the complement system, the urokinase plasminogen activator system, and pro-renin receptor activation.

Continuous rebuilding of the extracellular matrix occurs in both early and advanced AMD, simultaneously with the dysfunction of retinal pigment epithelium (RPE) cells and endothelial cells. The pathological degradation or accumulation of ECM structural components are caused by impairment or hyperactivity of specific MMPs/TIMPs complexes, and is also endangered by the influence of other mechanisms connected with both genetic and environmental factors.

Intravitreal bevacizumab in the treatment of diabetic ocular neovascularization

PURPOSE

To evaluate the efficacy of intravitreal bevacizumab for treating diabetic retinal and/or iris neovascularization.

METHODS

Consecutive, prospective, interventional case series study of 60 eyes with diabetic retinal and/or iris neovascularization. Patients had a complete ocular examination before receiving 1.25 mg (0.05 mL) of intravitreal bevacizumab. Abnormal new vessels elsewhere in the retina, optic disk, or iris were graded by size and associated hemorrhage or glaucoma. Patients had complete postinjection ophthalmic evaluations with regrading of the abnormal new vessels at 3 months and 6 months. The main outcome measures included clinical partial or total regression of abnormal new vessels, changes in visual acuity, and complications related to the intravitreal injections.

RESULTS

Twenty-six patients (47.3%) were men (mean age, 59 years). Abnormal new vessel regression at 6 months occurred in 65% of new vessels of the iris (P = 0.001), 45% of new vessels of the optic disk (P = 0.009), and 43% of new vessels elsewhere (P = 0.008). The visual acuity improved in 20% of eyes, which was not significant (P = 0.235); the visual acuity deteriorated in 23% of eyes (P = 0.163). No systemic or ocular side effects developed except for postinjection hypotony in one eye.

CONCLUSION

Intravitreal bevacizumab is a well-tolerated medication that causes regression of abnormal diabetic neovascularization. New vessels of the iris responded more than new vessels of the optic disk and new vessels elsewhere.

Microvascular complications and diabetic retinopathy: recent advances and future implications

Retinal microvascular alterations have been observed during diabetic retinopathy (DR) due to the retinal susceptibility towards subtle pathological alterations. Therefore, retinal microvascular pathology is essential to understand the nature of retinal degenerations during DR. In this review, the role of retinal microvasculature complications during progression of DR, along with recent efforts to normalize such alterations for better therapeutic outcome, will be underlined. In addition, current therapeutics and future directions for advancement of standard treatment for DR patients will be discussed.

Diabetic retinopathy and VEGF

Diabetic retinopathy remains the leading vascular-associated cause of blindness throughout the world. Its treatment requires a multidisciplinary interventional approach at both systemic and local levels. Current management includes laser photocoagulation, intravitreal steroids, and anti-vascular endothelial growth factor (VEGF) treatment along with systemic blood sugar control. Anti-VEGF therapies, which are less destructive and safer than laser treatments, are being explored as primary therapy for the management of vision-threatening complications of diabetic retinopathy such as diabetic macular edema (DME). This review provides comprehensive information related to VEGF and describes its role in the pathogenesis of diabetic retinopathy, and in addition, examines the mechanisms of action for different antiangiogenic agents in relation to the management of this disease. Medline (Pubmed) searches were carried out with keywords “VEGF”, “diabetic retinopathy”, and “diabetes” without any year limitation to review relevant manuscripts used for this article.

Pathophysiology of diabetic retinopathy

Diabetes is now regarded as an epidemic, with the population of patients expected to rise to 380 million by 2025. Tragically, this will lead to approximately 4 million people around the world losing their sight from diabetic retinopathy, the leading cause of blindness in patients aged 20 to 74 years. The risk of development and progression of diabetic retinopathy is closely associated with the type and duration of diabetes, blood glucose, blood pressure, and possibly lipids. Although landmark cross-sectional studies have confirmed the strong relationship between chronic hyperglycaemia and the development and progression of diabetic retinopathy, the underlying mechanism of how hyperglycaemia causes retinal microvascular damage remains unclear. Continued research worldwide has focussed on understanding the pathogenic mechanisms with the ultimate goal to prevent DR. The aim of this paper is to introduce the multiple interconnecting biochemical pathways that have been proposed and tested as key contributors in the development of DR, namely, increased polyol pathway, activation of protein kinase C (PKC), increased expression of growth factors such as vascular endothelial growth factor (VEGF) and insulin-like growth factor-1 (IGF-1), haemodynamic changes, accelerated formation of advanced glycation endproducts (AGEs), oxidative stress, activation of the renin-angiotensin-aldosterone system (RAAS), and subclinical inflammation and capillary occlusion. New pharmacological therapies based on some of these underlying pathogenic mechanisms are also discussed.

Retinopathy in diabetes

With the incidence, and prevalence of diabetes mellitus increasing worldwide, diabetic retinopathy is expected to reach epidemic proportions. The aim of this chapter is to introduce diabetic retinopathy, a leading cause of blindness in people of the working age. The clinical course of retinopathy, anatomical changes, its pathogenesis and current treatment are described, followed by an overview of the emerging drug therapies for the potential treatment of this sight-threatening complication of diabetes.

Regenerative therapies for diabetic microangiopathy

Hyperglycaemia occurring in diabetes is responsible for accelerated arterial remodeling and atherosclerosis, affecting the macro- and the microcirculatory system. Vessel injury is mainly related to deregulation of glucose homeostasis and insulin/insulin-precursors production, generation of advanced glycation end-products, reduction in nitric oxide synthesis, and oxidative and reductive stress. It occurs both at extracellular level with increased calcium and matrix proteins deposition and at intracellular level, with abnormalities of intracellular pathways and increased cell death. Peripheral arterial disease, coronary heart disease, and ischemic stroke are the main causes of morbidity/mortality in diabetic patients representing a major clinical and economic issue. Pharmacological therapies, administration of growth factors, and stem cellular strategies are the most effective approaches and will be discussed in depth in this comprehensive review covering the regenerative therapies of diabetic microangiopathy.

Role of Peoxisome Proliferator Activator Receptor gamma on Blood Retinal Barrier Breakdown

The retinal vessels have two barriers: the retinal pigment epithelium and the retinal vascular endothelium. Each barrier exhibits increased permeability under various pathological conditions. This condition is referred to as blood retinal barrier (BRB) breakdown. Clinically, the most frequently encountered condition causing BRB breakdown is diabetic retinopathy. In recent studies, inflammation has been linked to BRB breakdown and vascular leakage in diabetic retinopathy. Biological support for the role of inflammation in early diabetes is the adhesion of leukocytes to the retinal vasculature (leukostasis) observed in diabetic retinopathy. PPARγ is a member of a ligand-activated nuclear receptor superfamily and plays a critical role in a variety of biological processes, including adipogenesis, glucose metabolism, angiogenesis, and inflammation. There is now strong experimental evidence to support the theory that PPARγ inhibits diabetes-induced retinal leukostasis and leakage, playing an important role in the pathogenesis of diabetic retinopathy. Therapeutic targeting of PPARγ may be beneficial to diabetic retinopathy.

Selective and pan-blockade agents in the anti-angiogenic treatment of proliferative diabetic retinopathy: a literature summary

Diabetes mellitus is a major health concern in the modern world. Several sight-threatening ocular conditions are included in the array of health problems associated with this disease. Understandably, 2 of the more sight-threatening problems, proliferative diabetic retinopathy (PDR) and diabetic macular edema (DME), have received a great deal of attention in recent years. Pivotal studies, such as the Early Treatment Diabetic Retinopathy Study and the Diabetic Retinopathy Study, have established laser photocoagulation as the accepted treatment modality. The last decade has seen a surge in clinical data supporting the use of pharmacologic therapy in place of the often damaging laser therapy. Supporting data are based on the establishment of vascular endothelial growth factor (VEGF) as a key facilitator of disease progression in diabetic retinopathy. We will discuss the advantages and disadvantages of both selective and pan-blockade anti-VEGF agents available today in an effort to help guide physicians wishing to use these agents to treat PDR and DME.

Protective effects of triamcinolone acetonide upon the upregulation and phosphorylation of GAP 43 in an animal model of retinopathy of prematurity

PURPOSE

The aim of the current study was to investigate the effects of triamcinolone acetonide (TA) upon the expression and phosphorylation of growth-associated protein 43 (GAP 43) in the retinas of oxygen-induced retinopathy (OIR) rats.

METHODS

Oxygen-induced retinopathy was induced by exposing Sprague-Dawley rats to hyperoxia (80% oxygen) from postnatal (P) days 2-14 and then returning the rats to normoxic conditions. Triamcinolone acetonide or a conditioned saline (control) was injected intravitreally into the right or left eye, respectively, of OIR rats at P15. We then assessed the molecular and histological changes in the expression of GAP 43 and phospho-GAP 43 in OIR and control rat retinas, and also after treatment with TA by RT-PCR, Western blotting and immunohistochemistry.

RESULTS

Growth-associated protein 43 mRNA levels were found to be increased by 1.6-fold (p=0.001, n=5) in the retinas of P18 OIR rats compared with the control rats. The protein levels of GAP 43 and phospho-GAP43 were found to be elevated in the retina of P18 OIR rats (2.40- and 2.39-fold greater than each control, p<0.001, n=5, respectively). Immunoreactivities of GAP 43 and phospho-GAP 43 were stronger in the inner plexiform layer in OIR rat retinas compared with the control. However, treatment with TA attenuated GAP 43 and phospho-GAP 43 upregulation in the OIR retinas.

CONCLUSION

Our results indicate that GAP 43 and phospho-GAP 43 participate in retinal (potentially pathologic) changes following oxygen-induced damage. Triamcinolone acetonide protects the retinal damage in relatively hypoxic retinas of OIR rats. Therefore, TA treatment does not induce the expression and phosphorylation of GAP 43 in OIR rat retinas.

Hypoxia-inducible factor and vascular endothelial growth factor in the neuroretina and retinal blood vessels after retinal ischemia

Retinal ischemia arises from circulatory failure. As the retinal blood vessels are key organs in circulatory failure, our aim was to study the retinal vasculature separately from the neuroretina to elucidate the role of hypoxia-inducible factor (HIF) 1α and 1β and vascular endothelial growth factor (VEGF) in retinal ischemia. Retinal ischemia was induced in porcine eyes by applying an intraocular pressure, followed by 12 h of reperfusion. HIF-1α mRNA expression was not affected by ischemia, while immunofluorescence staining was higher after ischemia in the neuroretina. HIF-1β immunoreactivity and mRNA expression were unaffected. VEGF protein levels in the vitreous humor and VEGF staining in the neuroretina were more pronounced in eyes subjected to ischemia than in the sham eyes. VEGF may be activated downstream of HIF-1 and is known to stimulate retinal neovascularization, which causes sight-threatening complications. These results emphasize the need for pharmacological treatment to block the HIF and VEGF signaling pathways in retinal ischemia.

Can an intraoperative bevacizumab injection prevent recurrent postvitrectomy diabetic vitreous hemorrhage?

PURPOSE

To evaluate the recurrence of vitreous hemorrhage (VH) in patients treated with intravitreal bevacizumab (IVB) injection (2.5 mg/0.1 mL) intraoperatively at the end of vitrectomy for treatment of diabetic nonclearing VH.

METHODS

A prospective pilot study of 30 eyes of 28 consecutive diabetic patients who underwent pars plana vitrectomy and IVB injection intraoperatively at the end of vitrectomy was performed. The amount of VH was graded with slit lamp biomicroscopy by three masked retinal specialists from grade 0 to grade 3. Main outcome measures were rate of recurrence of the VH, improvement in visual acuity, incidence of cataract formation, and postoperative complications through a follow-up of 6 months.

RESULTS

The percentage of severe recurrent VH with no fundus details (grade 3) was 7%, 13%, 27%, and 30%, respectively, at 7 days and 1-, 3-, and 6-month follow-up. At 6-month followup, the best-corrected visual acuity improved from 1.00 to 0.4 logMAR (p=0.01) in 21 out of 30 eyes (70%). Nine out 20 (40%) phakic patients developed cataract during the follow-up period, and 7 (31%) of them underwent cataract surgery.

CONCLUSIONS

The study suggests that intravitreal bevacizumab injection cannot prevent rebleeding in eyes undergoing pars plana vitrectomy for treatment of diabetic vitreous hemorrhage.

Rapid resolution of severe retinal neovascularisation in proliferative diabetic retinopathy following adjunctive intravitreal bevacizumab (Avastin)

A 23-year-old aboriginal woman with severe bilateral proliferative diabetic retinopathy and left rubeotic glaucoma received bilateral pan-retinal photocoagulation with adjunctive intravitreal bevacizumab. Six days post-injection, there was almost complete resolution of new vessels.

Can a preoperative bevacizumab injection prevent recurrent postvitrectomy diabetic vitreous haemorrhage?

AIMS

To evaluate the recurrence rate of vitreous haemorrhage (VH) in patients treated with one intravitreal bevacizumab (IVB) injection (2.5 mg/0.1 ml) before planned pars plana vitrectomy for treatment of diabetic non-clearing VH.

METHODS

Prospective pilot study of 32 eyes of 31 consecutive diabetic patients who underwent IVB injection within 1 week before surgery for persistent VH in the presence of active proliferative diabetic retinopathy. Three masked retinal specialists graded the amount of VH from grade 0 to grade 3 with slit-lamp biomicroscopy. Main outcome measures were the rate of recurrence of the VH, improvement in visual acuity, incidence of cataract formation, and postoperative complications through a follow-up of 6 months.

RESULTS

The percentage of severe recurrent VH with no fundus details (grade 3) was 3% at 1 week follow-up and 3, 6, and 6% respectively at 1-, 3-, and 6-month follow-up. The mean best-corrected visual acuity (BCVA) improved from 1.6 (1/60) to 0.40 (6/15) logMAR (P=0.02) in 29 out of 32 eyes (91%). In all, 12 out of 22 (54%) phakic eyes developed cataract during the follow-up period, and 10 (31%) of them underwent cataract surgery.

CONCLUSIONS

Our study suggests that IVB injection few days before planned surgery seems to be efficacious and safe as an adjuvant treatment to prevent rebleeding in eyes undergoing pars plana vitrectomy for treatment of diabetic vitreous haemorrhage. IVB facilitates the surgery and reduces the need for extensive delamination and segmentation, decreasing the possibility of significant early active postoperative VH.

MRI retinovascular studies in humans: research in patients with diabetes

PURPOSE

To review existing applications of MRI for detecting blood-retinal barrier (BRB) damage and retinal oxygenation response abnormalities in patients with diabetes and highlight new information available from such applications.

METHODS

BRB studies were accomplished using dynamic contrast-enhanced MRI, and the retinal oxygenation response studies were accomplished by monitoring changes in the MRI signal associated with hyperoxic provocation. Participants were patients with diabetes and macular edema, with either no detectable or mild to moderate background retinopathy, as well as non-diabetic individuals of similar age (controls). Single-slice FLASH images were obtained using a Siemens Sonata, 1.5 T together with a Siemens 'Loop Small' surface coil fixed in place over the eye. Time-dependent changes in image contrast in the pre-retinal vitreous were quantified, and differences between patients and controls were assessed statistically.

RESULTS

The BRB breakdown studies showed a significant difference in the temporal evolution of the MRI signal enhancement post-contrast injection between the controls and the patients with diabetic macular edema. The retinal oxygenation studies revealed a supernormal oxygenation response in the pre-retinal vitreous in patients with diabetes who had no evidence of retinopathy, as well as in patients with background diabetic retinopathy. A nasal-temporal asymmetry in the evolution of retinal oxygenation response was found in patients with diabetes that was not present in healthy subjects.

CONCLUSIONS

These studies show that subtle differences in retinovascular function between patients with diabetes and non-diabetic individuals, including changes that occur in advance of the clinical appearance of diabetic retinopathy, can be detected with MRI. These results, together with previous extensive preclinical data, establish MRI as a powerful non-invasive method for measuring spatial and temporal changes in the same key retinovascular metrics in both animals and humans. Wide application of these techniques for diagnosis and evaluation of treatment efficacy in a variety of human retinopathies, including diabetic retinopathy, is expected.

Intravitreal bevacizumab in active progressive proliferative diabetic retinopathy

BACKGROUND

Vitreous concentration of vascular endothelial growth factor (VEGF) rises significantly during proliferative diabetic retinopathy (PDR). Bevacizumab (Avastin) is a humanized monoclonal antibody to VEGF. Intravitreal administration of bevacizumab (IVB) has recently been shown to be effective in some ocular neovascularizations, including PDR. In this study we evaluate the efficacy of IVB in eyes with active, progressive PDR.

METHODS

In an interventional prospective case series, eyes with active, progressive PDR underwent one to three IVB injections (1.25 mg) at intervals of either 6 or 12 weeks. Complete ophthalmic examinations and color fundus photography were performed at baseline and 1, 6, 12, and 20 weeks after the first injection. Fluorescein angiography (FA) was performed before injection and 20 weeks after. The primary outcome measures were clearing of vitreous hemorrhage (VH) and regression of active fibrovascular tissue (FVT). The secondary outcomes were any change in best-corrected visual acuity (BCVA) and any incidence of adverse events.

RESULTS

Thirty eight eyes of 38 patients with a mean age of 54.7 +/- 10.1 years were included in the study. VH resolved significantly after 1 week (P = 0.014), 12 weeks (P = 0.0001), and 20 weeks (P = 0.002). The vascular component of FVT regressed, though the FVT area did not change. Mean BCVA improved significantly compared to baseline at all follow-up examinations. Two cases showing moderate fibrous proliferation developed traction retinal detachment (TRD).

CONCLUSIONS

IVB has significant therapeutic effect on eyes with active, progressive PDR: the treatment causes a significant amount of VH resolution and neovessel regression. At the same time, this procedure may increase the risk of TRD in eyes with fibrous proliferation.

Vitamin C and superoxide dismutase (SOD) for diabetic retinopathy

BACKGROUND

There is increasing evidence that diabetic retinopathy is caused by the action of free radicals. Radical scavengers like vitamin C and superoxide dismutase (SOD) may influence the outcome and progression of diabetic retinopathy, but no systematic review of the literature has been published to examine this hypothesis.

OBJECTIVES

The aim of the current research was to review the literature in a standard systematic way in order to assess the effects of vitamin C and superoxide dismutase on diabetic retinopathy in methodologically robust trials.

SEARCH STRATEGY

We tried to obtain studies from computerised searches of MEDLINE, EMBASE, CINAHL, Web of Science and The Cochrane Library.

SELECTION CRITERIA

Only randomized clinical trials (RCTs) that evaluated the effect of vitamin C, superoxide dismutase or both in the treatment of diabetic retinopathy were considered.

DATA COLLECTION AND ANALYSIS

Two authors independently read all abstracts, titles or both and wanted to assess risk of bias and to perform data extraction. Discrepancies were planned to be resolved by consensus or by the judgement of a third author.

MAIN RESULTS

A total of 241 publications were identified by the electronic searches. Of these, 28 were identified as potentially containing information about the treatment of patients with diabetic retinopathy using vitamin C or SOD and were read in full. No trial evaluated the treatment of diabetic retinopathy with vitamin C or SOD.

AUTHORS' CONCLUSIONS

No research to date has adequately examined the treatment of diabetic retinopathy with vitamin C or SOD in such a way as to indicate whether this form of intervention has a significant impact on the progress of this clinical condition. The potential role of these substances in the treatment of diabetic retinopathy remains open to debate, and it is suggested that future research focusing on patient-oriented outcomes should address this important issue.

Effects of stobadine and vitamin E in diabetes-induced retinal abnormalities: involvement of oxidative stress

BACKGROUND

Because hyperglycemia-induced oxidative stress may be a cause of retinopathy, this study examined the hypothesis that administration of exogenous antioxidants, stobadine (ST) and vitamin E (vitE), can restore retinal abnormalities in experimental diabetes.

METHODS

Normal and streptozotocin (STZ)-induced male Wistar rats received daily intraoral doses of ST (24.7 mg/kg) and vitE (alpha-dl-tocopherol acetate, 400-500 IU/kg) individually or in combinations for 8 months. The biochemical parameters including aldose reductase enzyme (AR) activity and lipid peroxidation (MDA), and histopathological changes such as retinal capillary basement membrane thickness (RCBMT) and vascular endothelial growth factor (VEGF) expression were evaluated.

RESULTS

A 37.99% increase in RCBMT was observed in rats after 8 months diabetes duration. The increase in RCBMT was 12.34% in diabetic rats treated with ST and 23.07% in diabetic rats treated with vitE. In diabetic rats treated with antioxidant combination, just a 4.38% increase was observed in RCBMT. The excess VEGF immunoreactivity and increased MDA and AR activity determined in diabetic retina were significantly attenuated by individual antioxidant treatments. Although both antioxidants decreased blood glucose, HbA1c, fructosamine and triglyceride levels in diabetic rats, poor glycemic control was maintained in all experimental groups during the treatment period. However, the antioxidant combination led to almost complete amelioration in retinal MDA and RCBMT in diabetic rats.

CONCLUSIONS

The ability of antioxidant combination to arrest retinal abnormalities and lipid peroxidation even in the presence of poor glycemic control might advocate the key role of direct oxidative damage and the protective action of antioxidants in retinal alterations associated with diabetic retinopathy.

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.

Glial cell-derived cytokines attenuate the breakdown of vascular integrity in diabetic retinopathy

The blood-retinal barrier (BRB) is a biological unit comprised of specialized capillary endothelial cells firmly connected by intercellular tight junctions and endothelium-surrounding glial cells. The BRB is essential for maintaining the retinal microenvironment and low permeability and is compromised in an early phase during the progression of diabetic retinopathy. Here, we demonstrate that retinoic acid receptor (RAR)alpha stimulants preferentially act on glial cells rather than endothelial cells, resulting in the enhanced expression of glial cell line-derived neurotrophic factor (GDNF) through recruitment of the RARalpha-driven trans-acting coactivator to the 5'-flanking region of the gene promoter. Conversely, RARalpha decreases expression of vascular endothelial growth factor (VEGF)/vascular permeability factor. These gene expression alterations causally limit vascular permeability by modulating the tight junction function of capillary endothelium in a paracrine manner in vitro. The phenotypic transformation of glial cells mediated by RARalpha is sufficient for significant reductions of vascular leakage in the diabetic retina, suggesting that RARalpha antagonizes the loss of tight junction integrity induced by diabetes. These findings reveal that glial cell-derived cytokines such as GDNF and VEGF regulate BRB function, implying that the glial cell can be a possible therapeutic target in diabetic retinopathy.

Lower intraocular oxygen tension in diabetic patients: possible contribution to decreased incidence of nuclear sclerotic cataract

PURPOSE

To report intraocular oxygen tension in eyes of diabetic and nondiabetic patients.

DESIGN

A prospective, interventional consecutive case series.

METHODS

Oxygen was measured with an optical oxygen sensor in patients who were undergoing vitrectomy. Before turning on the infusion fluid, intraocular oxygen tension was measured in two locations: adjacent to the lens and in the mid vitreous cavity.

RESULTS

Fifty eyes from 50 patients were included in the study. Twenty-one eyes were from diabetic patients and 29 eyes were from nondiabetic patients. The mean oxygen tension adjacent to the lens was significantly lower in diabetic than in nondiabetic patients (8.4 +/- 0.7 mm Hg vs 10.7 +/- 0.8 mm Hg; P < .05). Similarly, the mean oxygen tension in the center of the vitreous cavity was lower in diabetic than in nondiabetic patients (5.7 +/- 0.7 mm Hg vs 8.5 +/- 0.6 mm Hg; P < .001). In subgroup analyses, previous panretinal photocoagulation or cataract surgery did not affect oxygen levels significantly in the vitreous of diabetic or nondiabetic patients.

CONCLUSION

Eyes from diabetic patients have significantly lower intraocular oxygen tension than in eyes from nondiabetic patients. Because oxidative damage to the lens nucleus and increased intraocular oxygen tension have been associated with nuclear sclerotic cataract, these findings may help explain recent reports of an apparent protective effect of diabetes mellitus against nuclear sclerotic cataract.

Diabetic vitrectomy: risks, prognosis, future trends

PURPOSE OF REVIEW

We review the current standards, risks, prognosis, and indications for diabetic pars plana vitrectomy and consider recent developments in surgical techniques. We also examine surgery's role as a treatment modality for diabetic eye disease among the other accepted and developing treatment options, such as systemic and intravitreal pharmacotherapy.

RECENT FINDINGS

Pars plana vitrectomy for diabetic macular edema and for traction retinal detachment is addressed. Techniques to decrease retinal swelling and ischemia are showing promising results. The use of the smaller 25-gauge and 23-gauge vitrectors is gaining acceptance and offers advantages such as less trauma, less postoperative discomfort, and quicker healing. Techniques are being developed and refined to help prevent postoperative vitreous hemorrhage using cryotherapy around sclerotomy sites and/or endolaser in a near-confluent pattern in an effort to quell fibrovascular ingrowth and subsequent hemorrhage. Finally, pharmacological advances include targeting three levels of intervention: achieving the best glycemic control, correcting altered retinal metabolism secondary to increased glucose availability, and employing neuroprotective and vasoprotective agents.

SUMMARY

The combination of therapies and interventions as they improve and evolve offers the potential to revolutionize the approach to the complications of diabetic eye disease and may soon render many current interventions obsolete. Diabetic pars plana vitrectomy continues to advance with better anatomic and visual success.

A randomized, masked, cross-over trial of lisinopril for inflammatory macular edema

PURPOSE

To analyze the effect of angiotensin-converting enzyme (ACE) inhibitor lisinopril on inflammatory cystoid macular edema and visual acuity.

DESIGN

Randomized, double-blind, placebo-controlled cross-over trial.

METHODS

setting: Outpatient clinic of the Department of Ophthalmology at the University Medical Center of Utrecht. patients: Forty patients with inflammatory cystoid macular edema were included. intervention: Each patient received lisinopril (10 mg daily) or placebo for three months. After two months of a lisinopril/placebo free wash-out period, the groups received the reverse study medication for three months. Fluorescein angiography was performed to evaluate the retina. main outcome measures: Cystoid macular edema, best-corrected visual acuity and contrast sensitivity.

RESULTS

Lisinopril had no effect on cystoid macular edema, visual acuity, papillary leakage, retinal vasculitis, and choroidal leakage. In a subgroup analysis, we observed a decrease in blood pressure (lisinopril, 14 of 36 patients; placebo, 5 of 36 patients; P = .02) and a decrease in morning urinary albumin excretion (lisinopril, 23 of 35 patients; placebo 10 of 34 patients, P = .003) was observed.

CONCLUSIONS

Although lisinopril had no effect on inflammatory cystoid macular edema and visual acuity, we found a positive effect on the vascular system.

Regulators of angiogenesis and strategies for their therapeutic manipulation

Angiogenesis provides a mechanism by which delivery of oxygen and nutrients is adapted to compliment changes in tissue mass or metabolic activity. However, maladaptive angiogenesis is integral to the process of several diseases common in Western countries, including tumor growth, vascular insufficiency, diabetic retinopathy and rheumatoid arthritis. Understanding the process of capillary growth, including the identification and functional analyses of key pro- and anti-angiogenic factors, provides knowledge that can be applied to improve/reverse these pathological states. Initially, angiogenesis research focused predominantly on vascular endothelial growth factor (VEGF) as a main player in the angiogenesis cascade. It is apparent now that participation of multiple angiogenic factors and signal pathways is critical to enable effective growth and maturation of nascent capillaries. The purpose of this review is to focus on recent progress in identifying angiogenesis signaling pathways that show promise as targets for successful induction or inhibition of capillary growth. The strategies applied to achieve these contradictory tasks are discussed within the framework of our existing fundamental knowledge of angiogenesis signaling cascades, with an emphasis on comparing the employment of distinctive tactics in modulation of these pathways. Innovative developments that are presented include: (1) inducing a pleiotropic response via activation or inhibition of angiogenic transcription factors; (2) modulation of nitric oxide tissue concentration; (3) manipulating the kallikrein-kinin system; (4) use of endothelial progenitor cells as a means to either directly contribute to capillary growth or to be used as a vehicle to deliver "suicide genes" to tumor tissue.

Hyperglycemia alters PI3k and Akt signaling and leads to endothelial cell proliferative dysfunction

Diabetes mellitus is a major risk factor for the development of vascular complications. We hypothesized that hyperglycemia decreases endothelial cell (EC) proliferation and survival via phosphatidylinositol 3-kinase (PI3k) and Akt signaling pathways. We cultured human umbilical vein ECs (HUVEC) in 5, 20, or 40 mM d-glucose. Cells grown in 5, 20, and 40 mM mannitol served as a control for osmotic effects. We measured EC proliferation for up to 15 days. We assessed apoptosis by annexin V and propidium iodide staining and flow cytometry, analyzed cell lysates obtained on culture day 8 for total and phosphorylated PI3k and Akt by Western blot analysis, and measured Akt kinase activity using a GSK fusion protein. HUVEC proliferation was also tested in the presence of pharmacological inhibitors of PI3k-Akt (wortmannin and LY294002) and after transfection with a constitutively active Akt mutant. ECs in media containing 5 mM d-glucose (control) exhibited log-phase growth on days 7-10. d-Glucose at 20 and 40 mM significantly decreased proliferation versus control (P < 0.05 for both), whereas mannitol did not impair EC proliferation. Apoptosis increased significantly in HUVEC exposed to 40 mM d-glucose. d-Glucose at 40 mM significantly decreased tyrosine-phosphorylated PI3k, threonine 308-phosphorylated-Akt, and Akt activity relative to control 5 mM d-glucose. Pharmacological inhibition of PI3k-Akt resulted in a dose-dependent decrease in EC proliferation. Transfection with a constitutively active Akt mutant protected ECs by enhancing proliferation when grown in 20 and 40 mM d-glucose. We conclude that d-glucose regulates Akt signaling through threonine phosphorylation of Akt and that hyperglycemia-impaired PI3k-Akt signaling may promote EC proliferative dysfunction in diabetes.