Angiogenic and antiangiogenic factors in proliferative diabetic retinopathy

Advanced glycation end-products stimulate basic fibroblast growth factor expression in cultured Müller cells

Accumulating evidence points to a causal role for advanced glycation end-products (AGEs) in the development of diabetic vascular complications, including diabetic retinopathy (DR). To assess the reciprocal correlation between AGEs and basic fibroblast growth factor (bFGF), the effects of AGEs on the production of bFGF by Müller cells were investigated. Müller cells were cultured from adult rabbit retinas. The AGEs were prepared with highly glycated bovine serum albumin (BSA) and the control non‑glycated BSA (BSA control) was incubated under the same conditions without glucose. Cultured Müller cells were exposed to AGEs or BSA control (volume percentages were 4, 8, 16, 32 and 64%) for a time course of 1, 3, 6 and 9 days in their desired medium. The expression of bFGF in Müller cells was evaluated by immunocytochemistry. Quantification was performed by densitometry using computerized image analysis with dedicated software. AGEs in a volume percentage of 16 and 32% on day 1 and in a volume percentage of 16, 32 and 64% on days 3, 6 and 9 increased the bFGF expression in Müller cells (P<0.05). Additionally, AGEs upregulated bFGF expression in Müller cells in a time‑dependent manner. In conclusion, the treatment of Müller cells with AGEs resulted in a dose- and time‑dependent elevation of bFGF in the culture medium. The results from this study suggest that the increased formation of AGEs in the vitreous may be involved in the development of DR by inducing the production of bFGF by retinal Müller cells.

Role of hyaluronan in angiogenesis and its utility to angiogenic tissue engineering

Angiogenesis represents the outgrowth of new blood vessels from existing ones, a physiologic process that is vital to supply nourishment to newly forming tissues during development and tissue remodeling and repair (wound healing). Regulation of angiogenesis in the healthy body occurs through a fine balance of angiogenesis-stimulating factors and angiogenesis inhibitors. When this balance is disturbed, excessive or deficient angiogenesis can result and contribute to development of a wide variety of pathological conditions. The therapeutic stimulation or suppression of angiogenesis could be the key to abrogating these diseases. In recent years, tissue engineering has emerged as a promising technology for regenerating tissues or organs that are diseased beyond repair. Among the critical challenges that deter the practical realization of the vision of regenerating functional tissues for clinical implantation, is how tissues of finite size can be regenerated and maintained viable in the long-term. Since the diffusion of nutrients and essential gases to cells, and removal of metabolic wastes is typically limited to a depth of 150-250 microm from a capillary (3-10 cells thick), tissue constructs must mandatorily permit in-growth of a blood capillary network to nourish and sustain the viability of cells within. The purpose of this article is to provide an overview of the role and significance of hyaluronan (HA), a glycosaminoglycan (GAG) component of connective tissues, in physiologic and pathological angiogenesis, its applicability as a therapeutic to stimulate or suppress angiogenesis in situ within necrotic tissues in vivo, and the factors determining its potential utility as a pro-angiogenic stimulus that will enable tissue engineering of neo-vascularized and functional tissue constructs for clinical use.

Usefulness of the vitreous fluid analysis in the translational research of diabetic retinopathy

Diabetic retinopathy (DR) is the major cause of acquired blindness in working-age adults. Current treatments for DR (laser photocoagulation, intravitreal corticosteroids, intravitreal antivascular endothelial growth factor (VEGF) agents, and vitreo-retinal surgery) are applicable only at advanced stages of the disease and are associated with significant adverse effects. Therefore, new pharmacological treatments for the early stages of the disease are needed. Vitreous fluid obtained from diabetic patients undergoing vitreoretinal surgery is currently used to explore the events that are taking place in the retina for clinical research. However, several confounding factors such as vitreous haemorrhage and concentration of vitreous proteins should be considered in the analysis of the results. In this paper we will focus on the vitreous fluid as a tool for exploring the mediators of DR and in particular the molecules related to inflammatory pathways. In addition, their role in the pathogenesis of DR will be discussed. The usefulness of new technologies such as flow cytometry and proteomics in identifying new candidates involved in the inflammatory process that occurs in DR will be overviewed. Finally, a more personalized treatment based on vitreous fluid analysis aiming to reduce the burden associated with DR is suggested.

Alternative pathways in the development of diabetic retinopathy: the renin-angiotensin and kallikrein-kinin systems

Diabetic retinopathy is a common complication of both type 1 and type 2 diabetes and is the leading cause of blindness in people of working age. Current treatment strategies are mostly limited to laser photocoagulation, which restricts proliferative retinopathic changes but also causes irreversible damage to the retina. This review examines two important pathways involved in regulating vascular function and their role in the development of diabetic retinopathy. One, the renin-angiotensin system, is well known and has established angiogenic effects on the retina that increase in diabetic retinopathy. The other, the kallikrein-kinin system, has recently been found to be important in the development of diabetic retinal complications. This review describes the components of the two signalling networks, examines the current animal model studies investigating the role of these pathways in diabetic retinopathy and reviews the clinical studies that have been undertaken examining systemic inhibition of different points in these pathways. These systems are promising targets for therapies aimed at inhibiting the development of diabetic retinopathy and in the future, combination therapies that take advantage of both pathways might result in new treatment options for this debilitating complication of diabetes.

Imbalanced levels of angiogenic and angiostatic factors in vitreous, plasma and postmortem retinal tissue of patients with proliferative diabetic retinopathy

A role for vascular endothelial growth factor (VEGF) has been clearly implicated in the pathogenesis of proliferative diabetic retinopathy (PDR). However, other molecules and mechanisms may be operating independently, or in conjunction with VEGF in the pathogenesis of this disease. Therefore, we made an attempt to comparatively investigate the levels of angiogenic and angiostatic factors in vitreous, plasma and postmortem retinal tissue of subjects with Proliferative Diabetic Retinopathy (PDR) compared to control subjects. The vitreous and plasma concentrations of VEGF, EPO (Erythropoietin) and PEDF (Pigment Epithelium Derived Factor) were measured using Enzyme Linked Immunosorbent Assay (ELISA) and the postmortem retinal tissue was subjected to Western blot analysis. The mean vitreous and plasma levels of VEGF and EPO in patients with PDR were significantly (p<0.001) higher than those in subjects without diabetes. Conversely, the vitreous and plasma levels of PEDF were significantly (p<0.001) lower in the PDR patients compared to control subjects. Multivariate logistic-regression analyses indicated that EPO was more strongly associated with PDR than VEGF. The protein expression of the VEGF and EPO in the retinal tissue was significantly higher in PDR and diabetes without complication groups compared to controls. Compared to controls, the protein expression of PEDF was significantly lower in retinal tissues from diabetes patients without complications and in patients with PDR. The fact that the vitreous and plasma levels and the retinal tissue protein expression of EPO were strongly associated with PDR implies a definite role of 'hypererythropoietinemia' in neovascularization processes.

Prevention of VEGF-induced growth and tube formation in human retinal endothelial cells by aldose reductase inhibition

OBJECTIVE

Since diabetes-induced vascular endothelial growth factor (VEGF) is implicated in retinal angiogenesis, we aimed to examine the role of aldose reductase (AR) in VEGF-induced human retinal endothelial cells (HREC) growth and tube formation.

MATERIALS AND METHODS

HRECs were stimulated with VEGF and cell-growth was determined by MTT assay. AR inhibitor, fidarestat, to block the enzyme activity and AR siRNA to ablate AR gene expression in HREC were used to investigate the role of AR in neovascularization using cell-migration and tube formation assays. Various signaling intermediates and angiogenesis markers were assessed by Western blot analysis. Immuno-histochemical analysis of diabetic rat eyes was performed to examine VEGF expression in the retinal layer.

RESULTS

Stimulation of primary HREC with VEGF caused increased cell growth and migration, and AR inhibition with fidarestat or ablation with siRNA significantly prevented it. VEGF-induced tube formation in HREC was also significantly prevented by fidarestat. Treatment of HREC with VEGF also increased the expression of VCAM, AR, and phosphorylation and activation of Akt and p38-MAP kinase, which were prevented by fidarestat. VEGF-induced expression of VEGFRII in HREC was also prevented by AR inhibition or ablation.

CONCLUSIONS

Our results indicate that inhibition of AR in HREC prevents tube formation by inhibiting the VEGF-induced activation of the Akt and p38-MAPK pathway and suggest a mediatory role of AR in ocular neovascularization generally implicated in retinopathy and AMD.

Neuroprotection in diabetic retinopathy

Diabetic retinopathy (DR) has been considered to be a microcirculatory disease of the retina. However, there is emerging evidence to suggest that retinal neurodegeneration is an early event in the pathogenesis of DR, which may antedate, and also participates in, the microcirculatory abnormalities that occur in DR. Therefore, the study of the underlying mechanisms that lead to neurodegeneration will be essential for identifying new therapeutic targets in the early stages of DR. Elevated levels of glutamate, oxidative stress, the overexpression of the renin-angiotensin system and the upregulation of RAGE play an essential role in the retinal neurodegeneration induced by diabetes. Finally, the balance between the neurotoxic and neuroprotective factors is crucial in determining the survival of retinal neurons. In this review we will focus on neurotrophic factors already synthesized by the retina in physiological conditions as a new therapy strategy for neuroprotection.

Role of matrix metalloproteinase-2 and -9 in the development of diabetic retinopathy

Diabetic retinopathy represents the most common causes of vision loss in patients affected by diabetes mellitus. The cause of vision loss in diabetic retinopathy is complex and remains incompletely understood. One of the earliest changes in the development of retinopathy is the accelerated apoptosis of retinal microvascular cells and the formation of acellular capillaries by unknown mechanism. Results of a recent research suggest an important role of matrix metalloproteinases (MMPs) in the development of diabetic retinopathy. MMPs are a large family of proteinases that remodel extracellular matrix components, and under pathological condition, its induction is considered as a negative regulator of cell survival; and in diabetes, latent MMPs are activated in the retina and its capillary cells, and activation of MMP-2 and -9 induces apoptosis of retinal capillary cells. This review will focus on the MMP-2 and MMP-9 in the diabetic retina with special reference to oxidative stress, mitochondria dysfunction, inflammation and angiogenesis, as well as summarizing the current information linking these proteins to pathogenesis of diabetic retinopathy.

Activation of AMP-activated protein kinase inhibits the proliferation of human endothelial cells

AMP-activated protein kinase (AMPK) is an evolutionary conserved energy-sensing enzyme that regulates cell metabolism. Emerging evidence indicates that AMPK also plays an important role in modulating endothelial cell function. In the present study, we investigated whether AMPK modulates endothelial cell growth. Treatment of cultured human umbilical vein endothelial cells with the AMPK activators 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR), 6,7-dihydro-4-hydroxy-3-(2'-hydroxy[1,1'-biphenyl]-4-yl)-6-oxo-thieno[2,3-b]pyridine-5-carbonitrile (A-769662), or metformin inhibited cell proliferation and DNA synthesis. The antiproliferative action of AICAR was largely prevented by the adenosine kinase inhibitor 5'-iodotubercidin and mimicked by infecting endothelial cells with an adenovirus expressing constitutively active AMPK. In contrast, pharmacological blockade of endothelial nitric oxide synthase or heme oxygenase-1 activity failed to reverse the inhibition of endothelial cell growth by AICAR. Flow cytometry experiments revealed that pharmacological activation of AMPK arrested endothelial cells in the G₀/G₁ phase of the cell cycle, and this was associated with increases in p53 phosphorylation and p53, p21, and p27 protein expression and decreases in cyclin A protein expression and retinoblastoma protein phosphorylation. In addition, silencing p21 and p27 expression partially restored the mitogenic response of AMPK-activated cells. Finally, activation of AMPK by AICAR blocked the migration of endothelial cells after scrape injury and stimulated tube formation by endothelial cells plated onto Matrigel-coated plates. In conclusion, these studies demonstrate that AMPK activation inhibits endothelial cell proliferation by elevating p21 and p27 expression. In addition, they show that AMPK regulates endothelial cell migration and differentiation and identify AMPK as an attractive therapeutic target in treating diseases associated with aberrant endothelial cell growth.

TMP prevents retinal neovascularization and imparts neuroprotection in an oxygen-induced retinopathy model

PURPOSE

To evaluate the effects of tetramethylpyrazine (TMP) on retinal neovascularization (NV) and neuroprotection in an oxygen-induced retinopathy (OIR) model.

METHODS

Neonatal C57BL/6J mice were subjected to 75% oxygen from postnatal day 7 (P7) to P12 and then returned to room air. TMP (200 mg/kg) or normal saline was given daily from P12 to P17. Immunostaining, HE staining, TUNEL assay, and RT-PCR were used to assess the effects of TMP on retinal neurovascular repair.

RESULTS

TMP effectively prevented pathologic NV and accelerated physiologic revascularization by enhancing the formation of endothelial tip cells at the edges of the repairing capillary networks and preserving the astrocytic template in the avascular retina. TMP also prevented morphologic changes and significantly decreased TUNEL-positive cells in the avascular retina by rescuing neurons such as amacrine, rod bipolar, horizontal, and Müller cells. In TMP-treated mice retinas, there was a less obvious loss of amacrine cell bodies and their distinct bands; the number of both rod bipolar and horizontal cell bodies, as well as the density of their dendrites in the outer plexiform layer, was greater than that in OIR control mice. TMP not only decreased the loss of alignment of Müller cell bodies and distortion of processes but reduced the reactive expression of GFAP in Müller cells. Furthermore, HIF-1α and VEGF mRNA expression were downregulated in TMP-treated mice retinas.

CONCLUSIONS

TMP improved neurovascular recovery by preventing NV and protecting retinal astroglia cells and neurons from ischemia-induced cell death partially due to its downregulation of HIF-1α and VEGF mRNA expression.

Quercetin-4'-O-β-D-glucopyranoside (QODG) inhibits angiogenesis by suppressing VEGFR2-mediated signaling in zebrafish and endothelial cells

BACKGROUND

Angiogenesis plays an important role in many physiological and pathological processes. Identification of small molecules that block angiogenesis and are safe and affordable has been a challenge in drug development. Hypericum attenuatum Choisy is a Chinese herb medicine commonly used for treating hemorrhagic diseases. The present study investigates the anti-angiogenic effects of quercetin-4'-O-β-D-glucopyranoside (QODG), a flavonoid isolated from Hypericum attenuatum Choisy, in vivo and in vitro, and clarifies the underlying mechanism of the activity.

METHODOLOGY/PRINCIPAL FINDINGS

Tg(fli1:EGFP) transgenic zebrafish embryos were treated with different concentrations of quercetin-4'-O-β-D-glucopyranoside (QODG) (20, 60, 180 µM) from 6 hours post fertilisation (hpf) to 72 hpf, and adult zebrafish were allowed to recover in different concentrations of QODG (20, 60, 180 µM) for 7 days post amputation (dpa) prior morphological observation and angiogenesis phenotypes assessment. Human umbilical vein endothelial cells (HUVECs) were treated with or without VEGF and different concentrations of QODG (5, 20, 60, 180 µM), then tested for cell viability, cell migration, tube formation and apoptosis. The role of VEGFR2-mediated signaling pathway in QODG-inhibited angiogenesis was evaluated using quantitative real-time PCR (qRT-PCR) and Western blotting.

CONCLUSION/SIGNIFICANCE

Quercetin-4'-O-β-D-glucopyranoside (QODG) was shown to inhibit angiogenesis in human umbilical vein endothelial cells (HUVECs) in vitro and zebrafish in vivo via suppressing VEGF-induced phosphorylation of VEGFR2. Our results further indicate that QODG inhibits angiogenesis via inhibition of VEGFR2-mediated signaling with the involvement of some key kinases such as c-Src, FAK, ERK, AKT, mTOR and S6K and induction of apoptosis. Together, this study reveals, for the first time, that QODG acts as a potent VEGFR2 kinase inhibitor, and exerts the anti-angiogenic activity at least in part through VEGFR2-mediated signaling pathway.

Vascular endothelial growth factor in plasma and vitreous fluid of patients with proliferative diabetic retinopathy patients after intravitreal injection of bevacizumab

PURPOSE

To investigate plasma and vitreous vascular endothelial growth factor (VEGF) levels after intravitreal bevacizumab (IVB) injection into eyes with proliferative diabetic retinopathy (PDR).

DESIGN

Retrospective, interventional, nonrandomized, comparative study.

METHODS

Fifty-six eyes of 56 patients with PDR and 13 eyes of 13 patients with nondiabetic ocular diseases were enrolled. Analysis included evaluation of basic clinical conditions and measurement of vitreous and plasma VEGF concentrations using enzyme-linked immunosorbent assays.

RESULTS

PDR eyes without IVB had the highest vitreous VEGF levels; the levels were significant compared with those in the recent IVB group (previous injection within 1 week), the prolonged IVB group (injection more than 1 week previously), and the nondiabetic control group (P = .001, P = .035, P < .001, respectively). The vitreous VEGF level in the recent IVB group was higher than that in prolonged IVB group (P = .035). PDR eyes without IVB had the highest plasma VEGF level, and the level was significant compared with those in the recent IVB group, the prolonged IVB group, and the nondiabetic control group (P < .001, P = .003, P < .001, respectively). The plasma VEGF level in the recent IVB group was lower than that in the prolonged IVB group (P = .003). The vitreous VEGF level was associated significantly with the plasma VEGF level (P = .002).

CONCLUSIONS

Vitreous and plasma VEGF levels were increased markedly in patients with PDR. VEGF concentrations in vitreous and plasma were decreased significantly after IVB into PDR eyes, and the effect lasted from 4.4 ± 2.2 days to 34.8 ± 33.7 days after injection.

Axitinib modulates hypoxia-induced blood-retina barrier permeability and expression of growth factors

This study investigates the effects of the multikinase inhibitor axitinib on the expression of vascular endothelial growth factor (VEGF) receptors 1/2 (VEGFR-1/2) and platelet-derived growth factor (PDGF) receptor beta (PDGFR-β), hypoxia-induced increased tissue permeability, occludin, zonula occludens protein 1 (ZO-1), VEGF-A, and PDGF expression of human retinal pigment epithelial (RPE) cells and human umbilical vein endothelial cells (HUVECs). Primary human RPE cells and HUVECs were exposed to hypoxia and axitinib. Viability of cells, tissue permeability, and expression of occludin, ZO-1, VEGF, PDGF, VEGFR-1/2 and PDGFR-β, and their mRNAs, were investigated by reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting, and immunohistochemistry. Treatment with axitinib reduced expression of VEGFR-1/2 and PDGFR-β. Hypoxia decreased cell viability, occludin, and ZO-1 expression and increased tissue permeability, expression, and secretion of VEGF and PDGF. Axitinib significantly reduced hypoxia-induced effects on HUVEC and RPE cells. Our in vitro results suggest that axitinib may have promising properties as a potential treatment for diabetic macular edema.

Vascular complications and diabetes: current therapies and future challenges

Diabetic retinal complications, including macular edema (DME) and proliferative diabetic retinopathy (PDR), are the leading cause of new cases of blindness among adults aged 20–74. Chronic hyperglycemia, considered the underlying cause of diabetic retinopathy, is thought to act first through violation of the pericyte-endothelial coupling. Disruption of microvascular integrity leads to pathologic consequences including hypoxia-induced imbalance in vascular endothelial growth factor (VEGF) signaling. Several anti-VEGF medications are in clinical trials for use in arresting retinal angiogenesis arising from DME and PDR. Although a review of current clinical trials shows promising results, the lack of large prospective studies, head-to-head therapeutic comparisons, and potential long-term and systemic adverse events give cause for optimistic caution. Alternative therapies including targeting pathogenic specific angiogenesis and mural-cell-based therapeutics may offer innovative solutions for currently intractable clinical problems. This paper describes the mechanisms behind diabetic retinal complications, current research supporting anti-VEGF medications, and future therapeutic directions.

Effects of Selected Anionic β-Cyclodextrins on Persistence of Blood Glucose Lowering by Insulin Glargine after Subcutaneous Injection to Rats

Insulin glargine is a synthetic long-acting insulin product used for patients with diabetes mellitus. In this study, to obtain the further desirable blood-glucose lowering profile of insulin glargine, we investigated the effects of β-cyclodextrin sulfate (Sul-β-CyD) and sulfobutylether β-cyclodextrin (SBE7-β-CyD) on physicochemical properties of insulin glargine and pharmacokinetics/pharmacodynamics of insulin glargine after subcutaneous injection to rats. Sul-β-CyD and SBE7-β-CyD increased solubility of insulin glargine. SBE7-β-CyD suppressed the formation of oligomer and enhanced the dissolution rate of insulin glargine from its precipitate, compared to that of Sul-β-CyD. Additionally, we revealed that after subcutaneous administration of an insulin glargine solution, SBE7-β-CyD, but not Sul-β-CyD, increased bioavailability and sustained the blood-glucose lowering effect, possibly due to the inhibitory effects of SBE7-β-CyD on the enzymatic degradation at the injection site. These results suggest that SBE7-β-CyD could be a useful excipient for sustained release of insulin glargine.

Intraocular expression of serum amyloid a and interleukin-6 in proliferative diabetic retinopathy

PURPOSE

Because serum amyloid A can regulate angiogenesis, we searched for an association between serum amyloid A and interleukin-6 (IL-6), as proinflammatory factors, and proliferative diabetic retinopathy (PDR).

DESIGN

Retrospective, comparative study.

METHODS

Seventy-six patients (76 eyes) with PDR and 31 patients (31 eyes) with nondiabetic ocular disease (control group), including idiopathic epiretinal membranes (8 eyes) and idiopathic macular holes (23 eyes), were enrolled. Enzyme-linked immunosorbent assay, dual-color immunofluorescence staining, and semiquantitative reverse-transcription polymerase chain reaction were used to examine the serum amyloid A and IL-6 levels in vitreous and plasma, expression of protein and mRNA of serum amyloid A in the excised membranes, respectively.

RESULTS

Vitreous serum amyloid A and IL-6 levels in the study group were significantly higher than those in the control group (both P < .001), whereas the plasma concentrations of serum amyloid A and IL-6 did not vary significantly between the groups (P = .555 and P = .621, respectively). A significant correlation was observed between the vitreous and plasma levels of serum amyloid A in subjects with PDR (r = 0.525; P < .001). In fibrovascular membranes of the study group, colocalization of endothelial marker CD31 with serum amyloid A and colocalization of fibrillar structure markers fibronectin with serum amyloid A were observed. Expression of serum amyloid A mRNA was significantly higher in fibrovascular membranes with PDR than in idiopathic epiretinal membranes (P = .004).

CONCLUSIONS

Serum amyloid A and IL-6 may be involved with the inflammatory process in the development of PDR. Local expression of serum amyloid A may exist in PDR.

Fenofibric acid reduces fibronectin and collagen type IV overexpression in human retinal pigment epithelial cells grown in conditions mimicking the diabetic milieu: functional implications in retinal permeability

PURPOSE

To determine whether fenofibric acid (FA) reduces high glucose (HG)-induced basement membrane component overexpression and hyperpermeability in human retinal pigment epithelial (RPE) cells.

METHODS

Retinal pigment epithelial cells (ARPE-19) were cultured for 18 days in normal glucose (5 mM) or HG (25 mM) medium and studied for the effects of FA on fibronectin (FN) and collagen IV (Coll IV) expression. During last 3 days of the experiment, 100 μM FA was added to cells grown in HG medium or in HG medium plus IL-1β (HG + IL-1β) to mimic, at least in part, the inflammatory aspect of the diabetic milieu. Real-time RT-PCR was performed to determine FN and Coll IV mRNA levels, whereas protein levels were assessed by Western blot analyses. Cell monolayer morphology and barrier function were analyzed by confocal microscopy using specific antibodies against tight junction proteins, ZO-1, and claudin-1 and by measuring apical-basolateral movements of FITC-dextran, respectively.

RESULTS

FN and Coll IV expression were significantly increased in RPE cells grown in HG or HG + IL-1β medium compared with cells grown in normal medium. When cells grown in HG or HG + IL-1β medium were treated with FA, significant reductions in FN and Coll IV expression were observed. In addition, exposure to FA decreased excess permeability in a dose-dependent manner in cells grown in HG + IL-1β medium. This effect was unrelated to changes in tight junction protein content.

CONCLUSIONS

Findings from this study suggest that the downregulation of basement membrane components by FA may have a protective effect against outer blood-retinal barrier leakage associated with diabetic retinopathy.

Intraocular expression of thymosin β4 in proliferative diabetic retinopathy

PURPOSE

To examine an association between thymosin β4 as potentially angioproliferative factor and proliferative diabetic retinopathy.

METHODS

The clinical study part included 62 patients with proliferative diabetic retinopathy (PDR) (study group) and 24 patients with non-diabetic pre-retinal membranes (control group). All patients underwent pars plana vitrectomy. We examined the thymosin β4 concentration in vitreous and plasma; and the expression of thymosin β4, glial fibrillary acidic protein (GFAP) and CD31 (PECAM-1 or Platelet Endothelial Cell Adhesion Molecule) and the levels of thymosin β4 mRNA and vascular endothelial growth factor (VEGF) mRNA in the excised membranes. The experimental study part consisted of 24 Sprague--Dawley rats with streptozotocin-induced diabetes mellitus and 24 age-matched control animals without diabetes. We determined the mRNA concentrations of thymosin β4, VEGF and GFAP in the rat retinas.

RESULTS

In the clinical study part, the vitreal and plasma thymosin β4 concentrations were significantly higher in the study group than control group (p =0.04 and p=0.01, respectively), and were significantly (p=0.028) correlated with each other. Co-expression of thymosin β4 and CD31 was observed in the diabetic fibrovascular membranes. Thymosin β4 mRNA and VEGF mRNA levels were significantly (p<0.01) higher in diabetic membranes than in non-diabetic membranes. In the experimental study part, the diabetic retinas showed co-localization of thymosin β4 and GFAP. The mRNA levels of thymosin β4, VEGF and GFAP were significantly (p<0.01) higher in diabetic rats than in control animals.

CONCLUSIONS

Thymosin β4 was produced in intraocular fibrovascular membranes of patients with PDR and in rats with experimental diabetes mellitus. Thymosin β4 may play a role in diabetic retinal neovascularization.

The α7-nicotinic acetylcholine receptor and MMP-2/-9 pathway mediate the proangiogenic effect of nicotine in human retinal endothelial cells

PURPOSE

Nicotine, the active component of cigarette smoke, has been found to stimulate angiogenesis in several experimental systems. In this study, the Matrigel duplex assay (Matrigel; BD Biosciences, Franklin Lakes, NJ) and the rat retinal explant assay were used to explore the molecular mechanisms underlying the proangiogenic effects of nicotine in endothelial cells.

METHODS

Western blot analysis was performed to determine the nicotinic acetylcholine receptor (nAChR) subtypes expressed on primary human retinal microvascular endothelial cells (HRMECs). The angiogenic effect of nicotine in the retina was evaluated with the duplex assay. The results obtained from the assay were confirmed by the rat retinal explant angiogenesis assay. ELISAs were used to measure MMP-2, -9, and -13 levels in HRMEC culture supernatants. The role of α7-nAChRs in nicotine-induced angiogenesis was examined by siRNA techniques.

RESULTS

Nicotine-induced angiogenesis required nAChR function and was associated with the upregulation of MMP-2 and -9 in HRMECs. Specifically, α7-nAChRs mediated the stimulatory effects of nicotine on retinal angiogenesis and MMP levels. Treatment of HRMECs with α7-nAChR antagonists ablated nicotine-induced angiogenesis. The inhibitory actions of α7-nAChR antagonists correlated with the suppression of MMP-2 and -9 levels in HRMECs.

CONCLUSIONS

The α7-nAChR is vital for the proangiogenic activity of nicotine. The α7-nAChRs expressed on HRMECs upregulate levels of MMP-2 and -9, which stimulate retinal angiogenesis. The data also suggest that α7-nAChR antagonists could be useful agents for the therapy of angiogenesis-related retinal diseases.

Decreased prothrombin time after intravitreal bevacizumab in the early period in patients with proliferative diabetic retinopathy

PURPOSE

To evaluate the effect of intravitreal bevacizumab (Avastin; Genentech, Inc., San Francisco, CA, USA) (IVB) injection on prothrombin time (PT) in patients with proliferative diabetic retinopathy (PDR) and nondiabetic patients.

METHODS

Eighty-nine patients received primary IVB (1.25 mg) in one eye were investigated. The patients were divided into three groups: 34 PDR (diabetic group), 26 nondiabetic (nondiabetic group) patients received IVB and 29 PDR patients without IVB (control group). The levels of PT were detected before and after IVB in study groups and at corresponding time-points in the control group. Paired samples t-test was conducted to compare the statistical differences of PT in each group.

RESULTS

Significant difference (p < 0.001) of the levels of PT before and after IVB was observed in diabetic group in the early period, and the PT changes (11.0 ± 0.56 before and 10.6 ± 0.45 after IVB) were in fact within the normal range. There were no significant differences in other groups and other time-points (all p > 0.05).

CONCLUSIONS

Intravitreal bevacizumab may lead to a decrease in the levels of PT in the early period after IVB in PDR patients, suggesting a temporarily potential effect of IVB on the extrinsic clotting pathway of blood coagulation cascade in diabetic patients.

Fenofibric acid prevents retinal pigment epithelium disruption induced by interleukin-1β by suppressing AMP-activated protein kinase (AMPK) activation

AIMS/HYPOTHESIS

The mechanisms involved in the beneficial effects of fenofibrate on the development and progression of diabetic macular oedema (DMO) remain to be elucidated. To shed light on this issue we have explored the effect of fenofibric acid on the barrier function of human retinal pigment epithelium (RPE) cells.

METHODS

ARPE-19 cells (a human RPE line) were cultured for 18 days under standard conditions and under conditions leading to the disruption of the monolayer (D-glucose, 25 mmol/l, with IL-1β, 10 ng/ml, added at days 16 and 17). Fenofibric acid, 25 μmol/l and 100 μmol/l, was added on the last 3 days of the experiment (one application/day). RPE cell permeability was evaluated by measuring apical-basolateral movements of FITC-dextran (40 kDa). The production of tight junction proteins and AMP-activated protein kinase (AMPK) phosphorylation was assessed by western blot. Immunohistochemical studies of tight junction proteins and small interfering RNA transfection to AMPK were also performed in ARPE-19 monolayers.

RESULTS

Treatment of ARPE-19 cells with fenofibric acid significantly reduced the increment of permeability and the breakdown of the ARPE-19 cell monolayer induced by D-glucose, 25 mmol/l, and IL-1β, 10 ng/ml, in a dose-dependent manner. This effect was unrelated to changes in the content of tight junction proteins. Fenofibric acid prevented the activation of AMPK induced by IL-1β and the hyperpermeability induced by IL-1β was blocked by silencing AMPK.

CONCLUSIONS/INTERPRETATION

Disruption of RPE induced by IL-1β is prevented by fenofibric acid through its ability to suppress AMPK activation. This mechanism could be involved in the beneficial effects of fenofibrate on DMO development.

Placental growth factor contributes to micro-vascular abnormalization and blood-retinal barrier breakdown in diabetic retinopathy

Objective

There are controversies regarding the pro-angiogenic activity of placental growth factor (PGF) in diabetic retinopathy (DR). For a better understanding of its role on the retina, we have evaluated the effect of a sustained PGF over-expression in rat ocular media, using ciliary muscle electrotransfer (ET) of a plasmid encoding rat PGF-1 (pVAX2-rPGF-1).

Materials and Methods

pVAX2-rPGF-1 ET in the ciliary muscle (200 V/cm) was achieved in non diabetic and diabetic rat eyes. Control eyes received saline or naked plasmid ET. Clinical follow up was carried out over three months using slit lamp examination and fluorescein angiography. After the control of rPGF-1 expression, PGF-induced effects on retinal vasculature and on the blood-external barrier were evaluated respectively by lectin and occludin staining on flat-mounts. Ocular structures were visualized through histological analysis.

Results

After fifteen days of rPGF-1 over-expression in normal eyes, tortuous and dilated capillaries were observed. At one month, microaneurysms and moderate vascular sprouts were detected in mid retinal periphery in vivo and on retinal flat-mounts. At later stages, retinal pigmented epithelial cells demonstrated morphological abnormalities and junction ruptures. In diabetic retinas, PGF expression rose between 2 and 5 months, and, one month after ET, rPGF-1 over-expression induced glial activation and proliferation.

Conclusion

This is the first demonstration that sustained intraocular PGF production induces vascular and retinal changes similar to those observed in the early stages of diabetic retinopathy. PGF and its receptor Flt-1 may therefore be looked upon as a potential regulatory target at this stage of the disease.

Role of intravitreal bevacizumab (Avastin) injected at the end of diabetic vitrectomy in preventing postoperative recurrent vitreous hemorrhage

PURPOSE

The purpose of this study was to evaluate the role of bevacizumab (Avastin), an antivascular endothelial growth factor agent, injected at the end of surgery for preventing postoperative recurrent vitreous hemorrhage in patients undergoing vitrectomy for diabetic eye disease.

METHODS

This was a retrospective, comparative, and nonrandomized study on a consecutive series of patients who underwent vitrectomy for diabetic eye disease. Recurrence of postoperative vitreous hemorrhage was compared in patients with and without intravitreal 1.25 mg bevacizumab given at the end of surgery.

RESULTS

During the study period, 58 patients had vitrectomy for diabetic disease. In 33 patients (the control group), no intravitreal bevacizumab was injected at the end of surgery, and in 25 patients (the intervention group) intravitreal bevacizumab 1.25 mg/0.05 mL was injected at the end of surgery. Both groups were matched for the number of patients, age, sex, diagnosis, and status of systemic disease. Recurrent postoperative vitreous hemorrhage was noted in 14 patients in the control group (14 of 33, 42.40%) and in 1 patient in the intervention group (1 of 25, 4.0%). The difference in postoperative vitreous hemorrhage between the 2 groups was statistically significant (P = 0.001). There was no statistical difference in the mean postoperative visual acuity between the 2 groups during the follow-up period (P = 0.410).

CONCLUSION

Intravitreal injection of 1.25 mg bevacizumab given at the end of vitrectomy appears safe and effective for reducing the incidence of recurrent postoperative vitreous hemorrhage after diabetic vitrectomy. Further randomized studies should be performed to evaluate the potential of this therapy in preventing postoperative recurrent vitreous hemorrhage after diabetic vitrectomy.

Measuring permeability in human retinal epithelial cells (ARPE-19): implications for the study of diabetic retinopathy

The retinal pigment epithelium (RPE) is a specialized epithelium lying in the interface between the -neural retina and the choriocapillaris where it forms the outer blood-retinal barrier (BRB). The tight junctions (TJ)s expressed in the outer BRB control fluids and solutes that enter the retina and this sealing function, which is essential for the retinal homeostasis, is impaired in diabetic retinopathy. In this -chapter, we provide the methods to explore the function of the RPE barrier by measuring Transepithelial electrical resistance (TER) and paracellular permeability to dextran in cultures of ARPE-19 cells (an immortalized RPE cell line). A method for inducing a lesion mimicking which occurs in diabetic retinopathy is described. In addition, methods for assessing mRNA expression and protein content of the main TJ proteins (occludin, zonula occludens-1 [ZO-1]) are detailed. Finally, we provide the methods required for confocal immunofluorescence detection of the TJ proteins, as well as for assessing the capacity of ARPE-19 cells to retain their functional properties.

Expression profile and regulation of telomerase reverse transcriptase on oxygen-induced retinal neovascularization

PURPOSE

Telomerase is critical for the control of replicative capacity, which plays a major role in proliferative retinal neovascularization. In this study, we investigated the expression profiles of telomerase reverse transcriptase (Tert) in a mouse model of oxygen-induced retinal neovascularization and explored the possibility of inhibiting a retinal Tert expression with small interfering RNAs (SiRNA) as a novel potential approach to suppress proliferative retinopathy.

METHODS

The mouse oxygen-induced retinal neovascularization model was used to examine expression profiles in different developmental phases and to assess the anti-angiogenic activity of Tert-SiRNA. Recombinant SiRNA plasmids were injected intravitreously into mice with or without pathological retinal neovascularization. Fluorescein angiography, vessel counting, and the expression levels of Tert mRNA and protein were used to evaluate the anti-angiogenic effects.

RESULTS

Retinal Tert expression, as assessed by both mRNA and protein levels, was significantly up-regulated during the proliferative phase of oxygen-induced retinal neovascularization. Intravitreous injection of Tert-SiRNA effectively suppressed the expression of Tert mRNA and proteins and inhibited retinal neovascularization, as confirmed by retinal flat angiography and vessel counting.

CONCLUSIONS

The expression of Tert was up-regulated during the development of oxygen-induced retinal neovascularization. Inhibiting Tert expression with SiRNA is effective in suppressing retinal neovascularization, suggesting that telomerase may be a potential therapeutic target for treating proliferative retinopathy.

[Diabetic maculopathy and retinopathy. Functional and sociomedical significance]

OBJECTIVE

The incidence of diabetic microvascular complications is expected to increase by 20-50% in the coming years. Diabetic macular edema (DME) is already a leading cause of blindness in the working-age population in developed countries, and its impact is expected to increase dramatically.

METHODS

Recent literature on the epidemiology and impact of diabetic microangiopathy (maculopathy) on visual function was reviewed to provide a comprehensive overview of the functional and socioeconomic consequences of diabetic retinal microangiopathy and new therapeutic strategies.

RESULTS

The first changes indicating diabetic microangiopathy are detectable shortly after the development of hyperglycemia, and in the long term they induce severe organ damage. More resources are used for this condition's treatment than for the treatment of hyperglycemia, corresponding to an enormous sociomedical burden of disease. Early detection of increased retinal vascular permeability may help control treatment effects. The control of recognized risk factors for the development and progression of DME, namely hyperglycemia and hyperlipidemia, as well as of hypertension has remained the cornerstone of therapy and serves as the basis for preserving visual function.

CONCLUSIONS

Modern treatment options, begun early, may result in a remarkably delayed occurrence of irreversible diabetic microvascular pathologies, particularly diabetic retinopathy and maculopathy. Ophthalmological screening nowadays aims at earlier recognition of at-risk individuals to optimize the therapeutic strategy--that is, before visual impairment is imminent. Close interdisciplinary medical cooperation and implementation of new therapeutic options may provide the foundation for success in terms of maintaining visual function.

Investigation of the potential utility of a linomide analogue for treatment of choroidal neovascularization

The aim of this study was to test the selectivity, in-vivo effectiveness, and potential mechanism of action of a linomide analogue (N-phenyl-1,2-dihydro-4-hydroxyl-2-oxo-quinoline-3-carboxamide, Lin05) for inhibition of choroidal neovascularization. The selectivity of Lin05 was tested in cell proliferation assays with human umbilical vein endothelial cells (HUVEC) and a retinal pigmented epithelial cell line(ARPE-19). In-vivo anti-angiogenic effect of Lin05 was investigated utilizing an experimental laser-induced choroidal neovascularization (ECNV) model in adult Brown Norway rats. Western blot and/or reverse transcriptase-PCR was used to test the effect of Lin05 on potential targets. Our results indicate that Lin05 is at least an 8-fold more selective inhibitor of endothelial cell proliferation compared to RPE cells. Systemic administration of Lin05 in an ECNV model was associated with a significant decrease in both vascular leakage on fluorescein angiography and lesion size by histopathology (p = 0.02). No systemic toxicity was detected for Lin05 in major organs such as the liver, lung and kidneys. Lin05 did not inhibit VEGF-induced VEGFR2 (KDR) phosphorylation in HUVEC nor was associated with decreased VEGF gene expression. Also it did not inhibit insulin-like growth factor (IGF-1) and Epidermal Growth Factor (EGF) induced activation of p42/p44 MAPK activation. It inhibited both PDGF- and bFGF-induced p42/p44 MAPK phosphorylation. However, the effect on PDGF was variable in different HUVEC cells. In conclusion, Lin05 is a potential anti-angiogenic agent for the treatment of eye diseases associated with pathological neovascularization. The anti-angiogenic effect of Lin05 is likely through inhibition of bFGF but not through inhibition of the VEGF/KDR pathway.

Maternal immune system adaptation to pregnancy--a potential influence on the course of diabetic retinopathy

BACKGROUND

Progression of diabetic retinopathy occurs at least temporarily during pregnancy. Although the cause of this progression is not entirely understood, the immune phenomenon and chronic inflammation may play a significant role. During pregnancy in order to avoid fetus rejection, certain components of the immune system that are knowingly implicated in the pathogenesis of diabetic retinopathy are activated including generalized leukocyte activation and an increase in certain cytokine plasma levels. Activated leukocytes with up regulated adhesion molecules have an increased potential to bind to the endothelium cells of blood vessels. Leukocyte-endothelial interaction and the consequent leukostasis with capillary occlusion, ischemia and vascular leakage have a substantial role in the development of diabetic retinopathy. Furthermore, certain increased cytokines are known to cause blood-retinal-barrier breakdown whilst others promote angiogenic and fibrovascular proliferation and thereby can also be implicated in the pathogenesis of this diabetic complication.

PRESENTATION OF THE HYPOTHESIS

We hypothesized that the activation of the immune system during gestation may have an influence on the course of retinopathy in pregnant diabetic women.

TESTING THE HYPOTHESIS

We suggest two prospective follow up studies conducted on women with type 1 diabetes mellitus. The first study would include a group of non-pregnant women and a group of diabetic women undergoing normal pregnancy matched for age and duration of diabetes. In the second study pregnant women would be divided into two groups: one with normal pregnancy and the other with preeclampsia. The procedure and data collection in both studies will be identical: a complete ophthalmological examination, glycaemic control, blood pressure measurement and venous blood samples for the determination of plasma levels of cytokines (TNF-alpha, IL-1beta, IL-6, IL-8) and adhesion molecules (ICAM-1, VCAM-1).

IMPLICATIONS OF THE HYPOTHESIS

Considering the present assumption, the gestational immune activation could be suggested as a potential risk factor for the development and progression of retinopathy in diabetic women. A better understanding of immunomodulatory effects of pregnancy on diabetic retinopathy pave the way for further investigations of the mechanism of its pathogenesis and could be essential for novel approaches to the treatment of this serious sight threatening complication of diabetes mellitus.

Iron overload in diabetic retinopathy: a cause or a consequence of impaired mechanisms?

Iron is an essential ion for life, playing a central role in many metabolic processes. The most important property of free iron is its capacity to be reversibly oxidized and reduced, but at same time this make it highly pro-oxidant molecule. In this regard, iron is able to generate powerful reactive oxygen species (ROS). For this reason, careful control on iron availability is central to the maintenance of normal cell function in the retina. In the diabetic eye there is an impairment of iron homeostasis, thus leading to iron overload. The mechanisms involved in this process include: (1) Destruction of heme molecules induced by hyperglycemia (2) Intraretinal and vitreal hemorrhages (3) Overexpression of the renin-angiotensin system. The main consequences of iron overload are the following: (1) Retinal neurodegeneration due to the increase of oxidative stress (2) Increase of AGE-RAGE binding (3) Defective phagocytosis of retinal pigment epithelium, which generates the accumulation of autoantigens and the synthesis of proinflammatory cytokines. Further studies addressed to explore not only the role of iron in the pathogenesis of diabetic retinopathy, but also to design novel therapeutic strategies based on the regulation of iron homeostasis are needed.

The PKCbeta/HuR/VEGF pathway in diabetic retinopathy

We investigated whether the diabetes-related PKCbeta activation affects VEGF expression through the mRNA-stabilizing human embryonic lethal abnormal vision (ELAV) protein, HuR, in the retina of streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in rats by STZ injection. Retinal tissues were processed to detect PKCbetaI, PKCbetaII, VEGF and HuR contents, as well as HuR phosphorylation. Immunoprecipitation coupled to RT-PCR was employed to evaluate HuR binding to VEGF mRNA in RiboNucleoProteic (RNP) complexes. Statistical analysis was performed by ANOVA followed by an appropriate post hoc comparison test. Following experimental diabetes PKCbetaI and PKCbetaII levels were increased compared to sham; there was also a PKC-mediated phosphorylation/activation of HuR. These effects were blunted by the in vivo co-administration of a selective PKCbeta inhibitor. A specific binding between the HuR protein and the VEGF mRNA was also detected. The PKCbeta/HuR activation was accompanied by enhanced VEGF protein expression that was, again, blunted by the PKCbeta inhibitor. These findings first demonstrate the activation, in the retina, of the PKCbeta/HuR/VEGF pathway following experimental diabetes and disclose a new potential pharmacological target to counteract pathologies implicating VEGF deregulation, such as diabetic retinopathy.

Profile of lipid and protein autacoids in diabetic vitreous correlates with the progression of diabetic retinopathy

OBJECTIVE

This study was aimed at obtaining a profile of lipids and proteins with a paracrine function in normal and diabetic vitreous and exploring whether the profile correlates with retinal pathology.

RESEARCH DESIGN AND METHODS

Vitreous was recovered from 47 individuals undergoing vitreoretinal surgery: 16 had nonproliferative diabetic retinopathy (NPDR), 15 had proliferative diabetic retinopathy, 7 had retinal detachments, and 9 had epiretinal membranes. Protein and lipid autacoid profiles were determined by protein arrays and mass spectrometry-based lipidomics.

RESULTS

Vitreous lipids included lipoxygenase (LO)- and cytochrome P450 epoxygenase (CYP)-derived eicosanoids. The most prominent LO-derived eicosanoid was 5-hydroxyeicosate traenoic acid (HETE), which demonstrated a diabetes-specific increase (P = 0.027) with the highest increase in NPDR vitreous. Vitreous also contained CYP-derived epoxyeicosatrienoic acids; their levels were higher in nondiabetic than diabetic vitreous (P < 0.05). Among inflammatory, angiogenic, and angiostatic cytokines and chemokines, only vascular endothelial growth factor (VEGF) showed a significant diabetes-specific profile (P < 0.05), although a similar trend was noted for tumor necrosis factor (TNF)-alpha. Soluble VEGF receptors R1 and R2 were detected in all samples with lowest VEGF-R2 levels (P < 0.05) and higher ratio of VEGF to its receptors in NPDR and PDR vitreous.

CONCLUSIONS

This study is the first to demonstrate diabetes-specific changes in vitreous lipid autacoids including arachidonate and docosahexanoate-derived metabolites indicating an increase in inflammatory versus anti-inflammatory lipid mediators that correlated with increased levels of inflammatory and angiogenic proteins, further supporting the notion that inflammation plays a role the pathogenesis of this disease.

Mediators of ocular angiogenesis

Angiogenesis is the formation of new blood vessels from pre-existing vasculature. Pathologic angiogenesis in the eye can lead to severe visual impairment. In our review, we discuss the roles of both pro-angiogenic and anti-angiogenic molecular players in corneal angiogenesis, proliferative diabetic retinopathy, exudative macular degeneration and retinopathy of prematurity, highlighting novel targets that have emerged over the past decade.

Lipopolysaccharide-binding protein and soluble CD14 in the vitreous fluid of patients with proliferative diabetic retinopathy

PURPOSE

The purpose of this study was to compare intravitreous levels of lipopolysaccharide-binding protein and soluble CD14 (sCD14) between patients with proliferative diabetic retinopathy (PDR) and nondiabetic subjects.

METHODS

This study included 19 consecutive Type 2 diabetic patients with PDR in whom a vitrectomy was performed. Sixteen vitreous humors from nondiabetic patients matched by age, with idiopathic macular holes, were selected from our vitreous bank and used as a control group. Lipopolysaccharide-binding protein was assessed by enzyme-linked immunosorbent assay and sCD14 by a solid-phase enzyme-amplified sensitive immunoassay.

RESULTS

Lipopolysaccharide-binding protein and sCD14 levels were significantly higher in patients with PDR than in the control group (lipopolysaccharide-binding protein, P < 0.001; sCD14, P < 0.01). After correcting for vitreal proteins, the results remained significantly higher in patients with PDR. No differences in serum levels were observed, and we did not find any correlation between serum and vitreous levels. A direct correlation between lipopolysaccharide-binding protein and sCD14 was detected in the vitreous fluid (r = 0.57; P < 0.001) but not in the plasma. Finally, a significant correlation between intravitreal levels of both lipopolysaccharide-binding protein and sCD14 and interleukin-8 and monocyte chemotactic protein-1 was also detected.

CONCLUSION

Lipopolysaccharide-binding protein and sCD14 are elevated in the vitreous fluid of patients with PDR and thus may play a role in the innate immune response triggered by the inflammatory injury characteristic of PDR.

Proliferative diabetic retinopathy: predictive and preventive measures at hypoxia induced retinal changes

Retinal vasculature changes in diabetic patients are most common cause of blindness among eye diseases. Numerous studies have explored the role of the agiogenic factors in the progression of diabetic retinopathy (DR). The balance between angiogenic and antiangiogenic factors has a determining role in the DR progression. Current treatment modalities include laser photocoagulation, intravitreal drug application, and pars plana vitrectomy (ppv). These maneuvers are employed with occurrence of advanced retinal changes. New diagnostic approaches can provide better information for the initial retinal changes thereby requiring a new DR classification and treatment guidelines. The results that are expected from Diabetic Retinopathy Clinical Research Network (DRCR) are at the level where prediction and prevention can not be made. Innovative molecular-imaging technology, can pave the way for application of novel clinical approaches. Identification of pathology-specific biomarkers and their application to diagnosis and treatment, support the individualized treatment algorithms.

Antiangiogenic effects and transcriptional regulation of pigment epithelium-derived factor in diabetic retinopathy

The effects of the antiangiogenic cytokine PEDF on key steps in retinal angiogenesis, specifically endothelial cell proliferation and vascular tubule formation, and the regulation of PEDF expression in retinal capillary endothelial cells were evaluated. HUVECs were co-cultured with fibroblasts to construct a model of angiogenesis using the Angiokit assay, and image analysis software was used to measure the effects of PEDF and VEGF on vascular tubule formation. Quantitative real-time PCR analysis was used to determine the expression of PEDF in microvascular endothelial cells exposed to glucose 20 mM, insulin 100 nM and VEGF 10 ng/ml. PEDF inhibited endothelial cell proliferation and significantly decreased the number of tubules (629+93 AU vs 311+31, p=0.001), number of branching points (145+19 AU vs 46+5, p=0.03) and total tubule length (4848+748 AU vs 11,172+2353, p=0.001). In bovine retinal capillary endothelial cells (BRCECs), PEDF mRNA and protein expression was suppressed by insulin (22%) in a rapamycin-sensitive manner; wortmannin had no effect. PEDF mRNA expression was also significantly reduced in the presence of high glucose (23%) and VEGF (25%). In conclusion, PEDF inhibits key steps in the angiogenic response of BRCECs, including endothelial cell proliferation and vascular tubule formation. Gene expression of PEDF is negatively regulated by glucose, insulin (via an mTOR-dependent pathway) and VEGF.

The retinal pigment epithelium: something more than a constituent of the blood-retinal barrier--implications for the pathogenesis of diabetic retinopathy

The retinal pigment epithelium (RPE) is an specialized epithelium lying in the interface between the neural retina and the choriocapillaris where it forms the outer blood-retinal barrier (BRB). The main functions of the RPE are the following: (1) transport of nutrients, ions, and water, (2) absorption of light and protection against photooxidation, (3) reisomerization of all-trans-retinal into 11-cis-retinal, which is crucial for the visual cycle, (4) phagocytosis of shed photoreceptor membranes, and (5) secretion of essential factors for the structural integrity of the retina. An overview of these functions will be given. Most of the research on the physiopathology of diabetic retinopathy has been focused on the impairment of the neuroretina and the breakdown of the inner BRB. By contrast, the effects of diabetes on the RPE and in particular on its secretory activity have received less attention. In this regard, new therapeutic strategies addressed to modulating RPE impairment are warranted.

Predominant cone photoreceptor dysfunction in a hyperglycaemic model of non-proliferative diabetic retinopathy

Approximately 2.5 million people worldwide are clinically blind because of diabetic retinopathy. In the non-proliferative stage, the pathophysiology of this ocular manifestation of diabetes presents as morphological and functional disruption of the retinal vasculature, and dysfunction of retinal neurons. However, it is uncertain whether the vascular and neuronal changes are interdependent or independent events. In addition, the identity of the retinal neurons that are most susceptible to the hyperglycaemia associated with diabetes is unclear. Here, we characterise a novel model of non-proliferative diabetic retinopathy in adult zebrafish, in which the zebrafish were subjected to oscillating hyperglycaemia for 30 days. Visual function is diminished in hyperglycaemic fish. Significantly, hyperglycaemia disrupts cone photoreceptor neurons the most, as evidenced by prominent morphological degeneration and dysfunctional cone-mediated electroretinograms. Disturbances in the morphological integrity of the blood-retinal barrier were also evident. However, we demonstrate that these early vascular changes are not sufficient to induce cone photoreceptor dysfunction, suggesting that the vascular and neuronal complications in diabetic retinopathy can arise independently. Current treatments for diabetic retinopathy target the vascular complications. Our data suggest that cone photoreceptor dysfunction is a clinical hallmark of diabetic retinopathy and that the debilitating blindness associated with diabetic retinopathy may be halted by neuroprotection of cones.

Reduced concentrations of angiogenesis-related factors in vitreous after vitrectomy in patients with proliferative diabetic retinopathy

BACKGROUND

The purpose of this study was to determine whether vitrectomy alters the angiogenic profile in the vitreous of eyes with proliferative diabetic retinopathy (PDR).

METHODS

We measured the levels of angiopoietin-2, HGF, bFGF, PDGF, TIMP-1, and TIMP-2 by sandwich enzyme linked immunosorbent assay (ELISA) in vitreous samples from 27 eyes of 26 patients with PDR before pars plana vitrectomy (without IOL implantation) and in 12 fluid samples from 12 patients with PDR obtained during an IOL implantation 3.5 to 9 (mean 4.9) months after an earlier vitrectomy. The levels of these factors were also measured in 12 vitreous samples obtained from 12 eyes that had undergone epiretinal membrane (ERM) or macular hole (MH) surgeries.

RESULTS

The mean vitreous levels of both angiopietin-2 (103 pg/ml) and HGF (1091 pg/ml) in the sample from eyes with PDR collected at the time of the IOL implantation were significantly lower than in those collected before the vitrectomy (P < 0.01). On the other hand, the changes in the levels of TIMP-1 and TIMP-2 were both not significant after vitrectomy.

CONCLUSION

The significant decrease of angiopietin-2 and HGF in the vitreous fluid after vitrectomy suggests that vitrectomy shifts the eye towards an anti-angiogenic environment.

Endothelial heparan sulfate in angiogenesis

Heparan sulfate (HS) is a linear polysaccharide composed of 50-200 glucosamine and uronic acid (glucuronic acid or iduronic acid) disaccharide repeats with epimerization and various sulfation modifications. HS is covalently attached to core proteins to form HS-proteoglycans. Most of the functions of HS-proteoglycans are mediated by their HS moieties. The biosynthesis of HS is initiated by chain polymerization and is followed by stepwise modification reactions, including sulfation and epimerization. These modifications generate ligand-binding sites that modulate cell functions and activities of proteinases and/or proteinase inhibitors. HS is abundantly expressed in developing and mature vasculature, and understanding its roles in vascular biology and related human diseases is an area of intense investigation. In this chapter, we summarize the significant recent advances in our understanding of the roles of HS in developmental and pathological angiogenesis with a major focus on studies using transgenic as well as gene knockout/knockdown models in mice and zebrafish. These studies have revealed that HS critically regulates angiogenesis by playing a proangiogenic role, and this regulatory function critically depends on HS fine structure. The latter is responsible for facilitating cell-surface binding of various proangiogenic growth factors that in turn mediate endothelial growth signaling. In cancer, mouse studies have revealed important roles for endothelial cell-surface HS as well as matrix-associated HS, wherein signaling by multiple growth factors as well as matrix storage of growth factors may be regulated by HS. We also discuss important mediators that may fine-tune such regulation, such as heparanase and sulfatases; and models wherein targeting HS (or core protein) biosynthesis may affect tumor growth and vascularization. Finally, the importance of targeting HS in other human diseases wherein angiogenesis may play pathophysiologic (or even therapeutic) roles is considered.

Systemic propranolol reduces b-wave amplitude in the ERG and increases IGF-1 receptor phosphorylation in rat retina

PURPOSE

To determine whether systemic application of propranolol, a nonselective beta-adrenergic receptor antagonist, with an osmotic pump will decrease the b-wave amplitude of the electroretinogram (ERG) and increase insulin-like growth factor (IGF)-1 receptor signaling.

METHODS

Young rats at 8 weeks of age were treated with saline, phentolamine, a nonselective alpha-adrenergic receptor antagonist, or propranolol, a nonselective beta-adrenergic receptor antagonist, delivered by osmotic pumps for 21 days. On the 21st day, all rats underwent electroretinographic analyses followed by collection of the retinas for protein assessment using Western blot analysis for IGF binding protein 3 (IGFBP3), IGF-1 receptor (IGF-1R), Akt, extracellular signal-related kinases 1 and 2 (ERK1/2), and vascular endothelial cell growth factor (VEGF).

RESULTS

Data indicate that 21 days of propranolol significantly decreased the b-wave amplitude of the ERG. The decrease in the b-wave amplitude occurred concurrently with a decrease in IGFBP3 levels and an increase in tyrosine phosphorylation of IGF-1 receptor on 1135/1136. This phosphorylation of IGF-1 receptor led to increased phosphorylation of Akt and ERK1/2. VEGF protein levels were also increased.

CONCLUSIONS

Overall, beta-adrenergic receptor antagonism produced a dysfunctional ERG, which occurred with an increase in IGF-1R phosphorylation and activation of VEGF. Systemic application of beta-adrenergic receptor antagonists may have detrimental effects on the retina.

Intravitreous vascular endothelial growth factor and hypoxia-inducible factor 1a in patients with proliferative diabetic retinopathy

PURPOSE

To determine vascular endothelial growth factor (VEGF) and hypoxia-inducible factor 1a (HIF-1a) in the vitreous fluid of patients with proliferative diabetic retinopathy (PDR).

DESIGN

Observational case-control study.

METHODS

Serum and vitreous fluid samples were obtained during vitrectomy from 42 eyes of diabetic patients with PDR (17 type I and 25 type II diabetes mellitus) and from 23 eyes of nondiabetic patients. Retinopathy of 19 diabetic patients was graded as active and the other 23 graded as quiescent according to retinal neovascularization. VEGF and HIF-1a of serum and vitreous fluid samples were measured by enzyme-linked immunosorbent assay.

RESULTS

Both intravitreous VEGF and HIF-1a were higher in diabetic patients with PDR than in control subjects (P < .01 and P < .01, respectively). After adjusting for total intravitreous protein (TP) concentration, intravitreous VEGF/TP and HIF-1a/TP in diabetic patients remained significantly higher too. Correlations between intravitreous VEGF and HIF-1a and intravitreous VEGF/TP and HIF-1a/TP were observed in diabetic patients with PDR (r = 0.730; P < .01; r = 0.531; P < .01, respectively) but not in control subjects. Both intravitreous VEGF and HIF-1a were higher in diabetic patients with active PDR than in those with quiescent PDR (P < .01 and P < .05, respectively). Intravitreous VEGF/TP in patients with active PDR remained higher (P < .05). Correlation between intravitreous VEGF and HIF-1a, as well as correlation between intravitreous VEGF/TP and HIF-1a/TP, were observed in diabetic patients with active PDR and those with quiescent PDR but not observed in control subjects.

CONCLUSIONS

Intravitreous VEGF and HIF-1a in diabetic patients with PDR are increased and related mutually. VEGF and HIF-1a, especially VEGF, are associated with the angiogenesis of PDR.

Phenotypic categorization of genetic skin diseases reveals new relations between phenotypes, genes and pathways

Motivation: Systematic analysis of connection between proteins, their cellular function and phenotypic manifestations in disease is a central problem of biological and clinical research. The solution to this problem requires the development of new approaches to link the rapidly growing dataset of gene–disease associations with the many complex and overlapping phenotypes of human disease.

Results: We analyze genetic skin disorders and suggest a manually designed set of elementary phenotypes whose combinations define diseases as points in a multidimensional space, providing a basis for phenotypic disease clustering. Placing the known gene–disease associations in the context of this space reveals new patterns that suggest previously unknown functional links between proteins, signaling pathways and disease phenotypes. For example, analysis of telangiectasias (spider vein diseases) reveals a previously unrecognized interplay between the TGF-β signaling pathway and pentose phosphate pathway. This interaction may mediate glucose-dependent regulation of TGF-β signaling, providing a clue to the known association between angiopathies and diabetes and implying new gene candidates for mutational analysis and drug targeting.

Contact:grishin@chop.swmed.edu

Supplementary information:Supplementary data are available at Bioinformatics online.