Demonstration of vasoproliferative activity from mammalian retina

Angiogenesis-Inflammation Cross Talk in Diabetic Retinopathy: Novel Insights From the Chick Embryo Chorioallantoic Membrane/Human Vitreous Platform

Pathological angiogenesis of the retina is a key component of irreversible causes of blindness, as observed in proliferative diabetic retinopathy (PDR). The pathogenesis of PDR is complex and involves vascular, inflammatory, and neuronal mechanisms. Several structural and molecular alterations associated to PDR are related to the presence of inflammation that appears to play a non-redundant role in the neovascular response that characterizes the retina of PDR patients. Vascular endothelial growth factor (VEGF) blockers have evolved over time for the treatment of retinal neovascularization. However, several limitations to anti-VEGF interventions exist. Indeed, the production of other angiogenic factors and pro-inflammatory mediators may nullify and/or cause resistance to anti-VEGF therapies. Thus, appropriate experimental models are crucial for dissecting the mechanisms leading to retinal neovascularization and for the discovery of more efficacious anti-angiogenic/anti-inflammatory therapies for PDR patients. This review focuses on the tight cross talk between angiogenesis and inflammation during PDR and describe how the chick embryo chorioallantoic membrane (CAM) assay may represent a cost-effective and rapid in vivo tool for the study of the relationship between neovascular and inflammatory responses elicited by the vitreous humor of PDR patients and for the screening of novel therapeutic agents.

Vascular progenitors generated from tankyrase inhibitor-regulated naïve diabetic human iPSC potentiate efficient revascularization of ischemic retina

Here, we report that the functionality of vascular progenitors (VP) generated from normal and disease-primed conventional human induced pluripotent stem cells (hiPSC) can be significantly improved by reversion to a tankyrase inhibitor-regulated human naïve epiblast-like pluripotent state. Naïve diabetic vascular progenitors (N-DVP) differentiated from patient-specific naïve diabetic hiPSC (N-DhiPSC) possessed higher vascular functionality, maintained greater genomic stability, harbored decreased lineage-primed gene expression, and were more efficient in migrating to and re-vascularizing the deep neural layers of the ischemic retina than isogenic diabetic vascular progenitors (DVP). These findings suggest that reprogramming to a stable naïve human pluripotent stem cell state may effectively erase dysfunctional epigenetic donor cell memory or disease-associated aberrations in patient-specific hiPSC. More broadly, tankyrase inhibitor-regulated naïve hiPSC (N-hiPSC) represent a class of human stem cells with high epigenetic plasticity, improved multi-lineage functionality, and potentially high impact for regenerative medicine.

The impact of central foveal thickness on the efficacy of subthreshold micropulse yellow laser photocoagulation in diabetic macular edema

To evaluate the efficacy of short-term subthreshold micropulse yellow laser photocoagulation (SMYLP) on eyes with diabetic macular edema (DME) with different central foveal thicknesses (CFT). Eighty eyes of 40 patients who had previously undergone ranibizumab treatment for DME and who subsequently had recurrent macular edema were included to the study. The study subjects were divided into four groups according to their initial CFT values (group 1, 250-300 μm; group 2, 301-400 μm; group 3, > 401 μm; group 4, 250-300 μm untreated control subjects). Patients were treated with SMYLP for one session and followed for 6 months. All patients underwent complete ophthalmologic evaluation. The alteration from baseline in CFT and the best corrected visual acuity (BCVA) were measured. Patients with a pretreatment CFT ≤ 300 μm experienced the statistically significant reduction in CFT and gain in BCVA at 2 months (p < 0.05), whereas patients with baseline CFT > 300 μm experienced no significant change (p > 0.05). Hyperautofluorescence lesions, that were not previously described, were detected in fundus autofluorescence imaging in the early period after SYMLP laser and these lesions were regressed with time. Our study indicates that the SYMLP provides a statistically significant improvement in BCVA and a reduction in CFT in the patients with a pretreatment CFT of 300 μm or less in DME and can be safe and effective in mild DME treatment.

Pathophysiology, screening and treatment of ROP: A multi-disciplinary perspective

The population of infants at risk for retinopathy of prematurity (ROP) varies by world region; in countries with well developed neonatal intensive care services, the highest risk infants are those born at less than 28 weeks gestational age (GA) and less than 1 kg at birth, while, in regions where many aspects of neonatal intensive and ophthalmological care are not routinely available, more mature infants up to 2000 g at birth and 37 weeks GA are also at risk for severe ROP. Treatment options for both groups of patients include standard retinal laser photocoagulation or, more recently, intravitreal anti-VEGF drugs. In addition to detection and treatment of ROP, this review highlights new opportunities created by telemedicine, where screening and diagnosis of ROP in remote locations can be undertaken by non-ophthalmologists using digital fundus cameras. The ophthalmological care of the ROP infant is undertaken in the wider context of neonatal care and general wellbeing of the infant. Because of this context, this review takes a multi-disciplinary perspective with contributions from retinal vascular biologists, pediatric ophthalmologists, an epidemiologist and a neonatologist. This review highlights the latest insights regarding cellular and molecular mechanisms in the formation of the retinal vasculature in the human infant, pathogenesis of ROP, detection and treatment of severe ROP, the risks and benefits of anti-VEGF therapy, the identification of new therapies over the horizon, and the optimal neonatal care regimen for best ROP outcomes, and the benefits and pitfalls of telemedicine in the remote screening and diagnosis of ROP, all of which have the potential to improve ROP outcomes.

Revisiting the mouse model of oxygen-induced retinopathy

Abnormal blood vessel growth in the retina is a hallmark of many retinal diseases, such as retinopathy of prematurity (ROP), proliferative diabetic retinopathy, and the wet form of age-related macular degeneration. In particular, ROP has been an important health concern for physicians since the advent of routine supplemental oxygen therapy for premature neonates more than 70 years ago. Since then, researchers have explored several animal models to better understand ROP and retinal vascular development. Of these models, the mouse model of oxygen-induced retinopathy (OIR) has become the most widely used, and has played a pivotal role in our understanding of retinal angiogenesis and ocular immunology, as well as in the development of groundbreaking therapeutics such as anti-vascular endothelial growth factor injections for wet age-related macular degeneration. Numerous refinements to the model have been made since its inception in the 1950s, and technological advancements have expanded the use of the model across multiple scientific fields. In this review, we explore the historical developments that have led to the mouse OIR model utilized today, essential concepts of OIR, limitations of the model, and a representative selection of key findings from OIR, with particular emphasis on current research progress.

VEGF: From Discovery to Therapy: The Champalimaud Award Lecture

Purpose

Intraocular vascular diseases are leading causes of adult vision loss, and in the mid-1900s, I. C. Michaelson postulated that the retina releases a soluble, diffusible factor that causes abnormal vascular growth and leakage. What became known as “Factor X” eluded investigators for decades.

Methods

The field of cancer research, where Judah Folkman pioneered the concept of angiogenesis, provided the inspiration for the work honored by the 2014 Champalimaud Vision Award. Recognizing that tumors recruit their own blood supply to achieve critical mass, Dr Folkman proposed that angiogenic factors could be therapeutic targets in cancer. Napoleone Ferrara identified vascular endothelial growth factor (VEGF) as such an angiogenic agent: stimulated by hypoxic tumor tissue, secreted, and able to induce neovascularization. VEGF also was a candidate for Factor X, and the 2014 Champalimaud Laureates and colleagues worked individually and collaboratively to identify the role of VEGF in ocular disease.

Results

The Champalimaud Laureates correlated VEGF with ocular neovascularization in animal models and in patients. Moreover, they showed that VEGF not only was sufficient, but it also was required to induce neovascularization in normal animal eyes, as VEGF inhibition abolished ocular neovascularization in key animal models.

Conclusions

The identification of VEGF as Factor X altered the therapeutic paradigms for age-related macular degeneration (AMD), diabetic retinopathy, retinal vein occlusion, and other retinal disorders.

Translational Relevance

The translation of VEGF from discovery to therapy resulted in the most successful applications of antiangiogenic therapy to date. Annually, over one million patients with eye disease are treated with anti-VEGF agents.

Diabetic Retinopathy: Vascular and Inflammatory Disease

Diabetic retinopathy (DR) is the leading cause of visual impairment in the working-age population of the Western world. The pathogenesis of DR is complex and several vascular, inflammatory, and neuronal mechanisms are involved. Inflammation mediates structural and molecular alterations associated with DR. However, the molecular mechanisms underlying the inflammatory pathways associated with DR are not completely characterized. Previous studies indicate that tissue hypoxia and dysregulation of immune responses associated with diabetes mellitus can induce increased expression of numerous vitreous mediators responsible for DR development. Thus, analysis of vitreous humor obtained from diabetic patients has made it possible to identify some of the mediators (cytokines, chemokines, and other factors) responsible for DR pathogenesis. Further studies are needed to better understand the relationship between inflammation and DR. Herein the main vitreous-related factors triggering the occurrence of retinal complication in diabetes are highlighted.

Efficacy of subthreshold micropulse laser in the treatment of diabetic macular edema is influenced by pre-treatment central foveal thickness

PURPOSE

To determine if the severity of diabetic macular edema influences the effectiveness of subthreshold micropulse (STMP) laser treatment.

METHODS

A total of 63 eyes of 58 patients with diabetic macular edema were divided into two groups based on their initial central foveal thickness (CFT). Group 1 had CFT ≤400 μm, group 2 had CFT >400 μm. The change from baseline in CFT and visual acuity were compared at 3, 6 and 12 months follow-up. Patients were considered for retreatment with micropulse laser at 3 months if macular edema had not improved. Patients were considered for rescue anti-VEGF injections if there was clinically significant macular edema at 6 months follow-up. Number of laser retreatments, injections, and any adverse effects from STMP laser were recorded.

RESULTS

Group 1 (n=33) experienced an average of 55 μm reduction in CFT and 0.2 log MAR gain in visual acuity at 12 months (P<0.001). No patient required rescue anti-VEGF injections. Group 2 (n=30) experienced no significant change in CFT or visual acuity by 6 months despite retreatment with STMP in 19 eyes. From 6 to 12 months follow-up, all the patients in group 2 received rescue Bevacizumab injections that resulted in 307 μm reduction in CFT and 0.3 log MAR improvement in visual acuity (P<0.001). No adverse effects from STMP laser were recorded.

CONCLUSION

Severity of edema can influence the effects of STMP laser. STMP monotherapy is safe and effective in treating edema of mild to moderate severity.

Tamponade or filling effect: changes of forces in myopic eyes

Myopia is the most common ocular abnormality. Its high and growing prevalence has contributed to a recent surge in surgical interest in the disorder, since retinal detachment in eyes with high myopia differs from that in emmetropic eyes or eyes with low myopia. The myopic eye, because of its specific anatomy, poses special challenges that need to be overcome to ensure the appropriate use of vitreous substitutes. However, intraocular tamponades have shown great potential for revolutionizing retinal detachment surgery and vitreomacular surgery in general in myopic eyes. We provide an updated review of the clinical use of vitreous substitutes in the myopic eye, paying particular attention to analyzing the ideal function of endotamponade agents and comparing the effects of these agents on the physical and biological properties of the eye.

Vascular progenitors from cord blood-derived induced pluripotent stem cells possess augmented capacity for regenerating ischemic retinal vasculature

BACKGROUND

The generation of vascular progenitors (VPs) from human induced pluripotent stem cells (hiPSCs) has great potential for treating vascular disorders such as ischemic retinopathies. However, long-term in vivo engraftment of hiPSC-derived VPs into the retina has not yet been reported. This goal may be limited by the low differentiation yield, greater senescence, and poor proliferation of hiPSC-derived vascular cells. To evaluate the potential of hiPSCs for treating ischemic retinopathies, we generated VPs from a repertoire of viral-integrated and nonintegrated fibroblast and cord blood (CB)-derived hiPSC lines and tested their capacity for homing and engrafting into murine retina in an ischemia-reperfusion model.

METHODS AND RESULTS

VPs from human embryonic stem cells and hiPSCs were generated with an optimized vascular differentiation system. Fluorescence-activated cell sorting purification of human embryoid body cells differentially expressing endothelial/pericytic markers identified a CD31(+)CD146(+) VP population with high vascular potency. Episomal CB-induced pluripotent stem cells (iPSCs) generated these VPs with higher efficiencies than fibroblast-iPSC. Moreover, in contrast to fibroblast-iPSC-VPs, CB-iPSC-VPs maintained expression signatures more comparable to human embryonic stem cell VPs, expressed higher levels of immature vascular markers, demonstrated less culture senescence and sensitivity to DNA damage, and possessed fewer transmitted reprogramming errors. Luciferase transgene-marked VPs from human embryonic stem cells, CB-iPSCs, and fibroblast-iPSCs were injected systemically or directly into the vitreous of retinal ischemia-reperfusion-injured adult nonobese diabetic-severe combined immunodeficient mice. Only human embryonic stem cell- and CB-iPSC-derived VPs reliably homed and engrafted into injured retinal capillaries, with incorporation into damaged vessels for up to 45 days.

CONCLUSIONS

VPs generated from CB-iPSCs possessed augmented capacity to home, integrate into, and repair damaged retinal vasculature.

The Harvard angiogenesis story

I shall discuss the work of researchers at Harvard Medical School who came together in the early 1990s. Scattered across various Harvard-affiliated hospitals and research centers, these individuals were unified by their interest in ocular neovascularization. Together and separately, they investigated models of ocular neovascularization, exploring tumor angiogenesis in eye development and disease.

Biomaterials and biotechnology: from the discovery of the first angiogenesis inhibitors to the development of controlled drug delivery systems and the foundation of tissue engineering

This paper describes the discovery of the first inhibitors of angiogenesis; the discoveries that led to the development of the first biocompatible controlled release systems for macromolecules, and findings that helped to create the field of tissue engineering. In addition, new paradigms for creating biomaterials, early work on nanotechnology in medicine and intelligent drug delivery systems are discussed.

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.

Inhibition of neovascularization by a cartilage factor

Neovascularization of developing, repairing or neoplastic tissues is regulated, at least partially, by a family of proteins of low molecular mass (1000 less than mol mass less than 50 000 Da) which can be extracted from avascular tissues, such as hyaline cartilage, aorta or bladder epithelium, by mild salt solutions. These extractable proteins, functionally defined as anti-invasion factor (AIF), act as local regulators for some of the major mechanistic pathways by which endothelial cells are thought to invade tissues during neovascularization, mainly by matrix-degrading enzymes and by increased rates of migration and proliferation. AIF contains a spectrum of proteinase (collagenase) inhibitory activities, as well as an endothelial cell growth inhibitor. The endothelial cell growth inhibitor is directed against actively dividing endothelial cells in culture but has no effect on endothelial cell monolayers or any other cell lines tested. In tumours, the AIF-derived endothelial cell growth inhibitor may limit tumour growth to less than 2 mm in diameter by inhibiting tumour neovascularization.

Degradation of basement membrane components by vascular endothelial cells: role in neovascularization

A retina-derived substance (or substances) has been identified that stimulates vascular endothelial cells to degrade three structural components of basement membrane: type IV collagen, fibronectin and laminin. In basement membrane surrounding existing blood vessels, endothelial cells stimulated in this way can presumably migrate through the resulting gaps and form new vascular sprouts. These events may therefore represent the earliest steps in the formation of new blood vessels.

Clinical electrophysiology in quinine induced retinal toxicity

A 43-year-old woman was evaluated 9 months after a deliberate overdose of quinine. The patient's visual acuity was 20/20, but she had lost all peripheral vision beyond approximately 30 degrees eccentricity. The multifocal electroretinography (mfERG) and optical coherence tomography are described for the first time in this condition. The mfERG shows electronegative waveforms beyond 6 degrees . The mfERG response density is reduced at all retinal locations. Optical coherence tomography shows thinning of the middle and inner retina by 25 to 35%, with preservation of the photoreceptor layer. Recent regulatory restrictions in off-label uses of quinine products should help to reduce the incidence of adverse toxic reactions.

Subthreshold micropulse diode laser photocoagulation for clinically significant diabetic macular oedema: a three-year follow up

PURPOSE

To report the long-term visual outcome of subthreshold micropulse diode laser photocoagulation for clinically significant diffuse diabetic macular oedema (CSME).

DESIGN

Non-comparative case-series.

METHODS

The main outcome measures of this 3-year follow-up study of infrared (810 nm) subthreshold diode micropulse laser photocoagulation for CSME were visual outcome and the angiographic CSME status of 19 patients (25 eyes).

RESULTS

Visual acuity stabilized or improved in 84% of treated eyes by the end of the first year. The result was maintained in the second year and by the third year, 92% maintained vision. However, more patients needed supplementary grid laser in the third year than in the second year. CSME decreased in 92% of the eyes and resolved in 88% in the first year. By the second year, 92% showed complete resolution. However, in the third year, recurrent CSME was noted in 28% of patients.

CONCLUSION

This study has the longest follow up reported so far and demonstrating that subthreshold micropulse diode laser photocoagulation has a beneficial long-term effect on visual acuity and resolution of CSME with minimal chorio-retinal damage.

The role of cytokines and trophic factors in epiretinal membranes: Involvement of signal transduction in glial cells

Idiopathic epiretinal membranes (ERMs) in the macular region can cause a reduction in vision and sometimes recurs after surgical removal, but its pathogenic mechanisms are still unknown. On the other hand, the presence of secondary ERMs has been associated with various clinical conditions including proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). Recent studies have shown a significant association between clinical grades of PDR or PVR, and the expression levels of specific cytokines and/or growth factors in the vitreous fluid. Expression of these factors and their receptors are also observed in secondary ERMs. ERMs are composed of many cell types such as retinal pigment epithelial cells and vascular endothelial cells, however the role of glial cells is yet unclear. Interestingly, glial cells in ERMs express some trophic factor receptors and transcription factors, such as NF-kappaB, suggesting an involvement of glial signal transduction in the pathogenesis of ERMs. In this review, we summarize recent progress regarding the clinical and laboratory findings of ERMs.

Effect of Müller cell co-culture on in vitro permeability of bovine retinal vascular endothelium in normoxic and hypoxic conditions

Müller cell dysfunction may contribute to the early pathological changes associated with conditions such as diabetes, that cause breakdown of the blood-retinal barrier. In this study we used an in vitro model of the blood-retinal barrier to investigate Müller cell effects on retinal vascular endothelial cell monolayer permeability under normoxic (20% oxygen) and hypoxic (1% oxygen) conditions. Second passage bovine retinal capillary endothelial cells were co-cultured with retinal Müller cells on opposite sides of a 0.4 microm pore size polycarbonate Transwell filter or in medium that was continually conditioned by Müller cells. Permeability changes were observed for up to 24h of hypoxia by measurement of [(3)H]-inulin and [(14)C]-albumin flux across the endothelial cell monolayer. Endothelial cell barrier function was enhanced by co-culturing with Müller cells under normoxic conditions. Under hypoxic conditions however, the barrier was significantly impaired after 12h of co-culture with Müller cells. These results shed more light on the trophic effect of Müller cells on the blood-retinal barrier, suggesting a critical role in the maintenance and regulation of the barrier in health and during disease.

Use of viscodissection and silicone oil in vitrectomy for severe diabetic retinopathy

Improvement in surgical techniques has led to improved anatomic and functional success rates following surgery for severe complications of proliferative diabetic retinopathy (PDR). We compared the anatomic and functional outcomes of surgery in a non-randomized, consecutive case series of patients with severe PDR. We found that viscodissection using Healon provides outcomes comparable to conventional pick and scissors dissection. We also found that adjunctive use of silicone oil can salvage selected cases with particularly severe manifestations of PDR (e.g., the fibrinoid syndrome). With proper selection of patients and techniques, the anatomic success rate can exceed 80% even in the most severe cases. The goal of this paper is to show the applicability of using viscodissection and silicone oil infusion during vitrectomy in eyes with severe PDR.

Vitrectomy with silicone oil infusion in severe diabetic retinopathy

AIMS

To determine the results of pars plana vitrectomy (PPV) and silicone oil infusion (SOI) in severe proliferative diabetic retinopathy (PDR).

METHODS

The records of 23 eyes (21 patients: 12 males, nine females) with PDR who had undergone PPV and SOI were reviewed retrospectively.

RESULTS

Average follow up was 5.4 months (range 1-25). Surgical indications were tractional retinal detachment (TRD) (17.4%), traction-rhegmatogenous retinal detachment (TRRD) (8.7%), TRD with vitreous haemorrhage (VH) (48%), TRD with neovascular glaucoma (NVG) (8.6%), TRD with fibrinoid syndrome (FS) (17.3%). With one operation, the retinal reattachment rate was 17/23 (74%). Among these 23 eyes, 11 (48%) had previously failed vitrectomy, and the retina was attached in 8/11 (73%) with a single procedure. With additional surgery employing PPV and SOI, the final reattachment rate was 20/23 (87%). The only cases with intraocular pressure <5 mm Hg had retinal detachment. Postoperative visual acuity (VA) improved in 10 eyes (44%), was unchanged in three (12%), and decreased in 10 eyes (44%).

CONCLUSION

SO tamponade is useful in severely diseased eyes with PDR, even in the presence of rubeosis iridis (RI) and NVG, FS, or in cases with previously failed vitrectomy, especially in the presence of RI.

Up-Regulation of Glial Fibrillary Acidic Protein in Response to Retinal Injury: Its Potential Role in Glial Remodeling and a Comparison to Vimentin Expression

Intermediate filament proteins are a heterogeneous group of proteins that form 10-nm-diameter filaments, a highly stable cytoskeletal component occurring in various cell types. The up-regulation of one of these intermediate filament proteins, glial fibrillary acidic protein (GFAP), historically has been an indicator of "stress" in central nervous system (CNS) astrocytes. The retina also responds similarly to "stress" but the up-regulation of intermediate filaments occurs primarily in the Müller cells, the radial glia of the retina. This is a remarkably ubiquitous response in that a similar up-regulation can be observed in numerous forms of retinal degeneration. As a consequence of retinal detachment, a "mechanical" injury to the retina, GFAP, and another intermediate filament protein, vimentin, dramatically increase in Müller cells. Concomitant with this up-regulation is the hypertrophy of these cells both within the retina and onto the photoreceptor and vitreal surfaces of the retina. The function of this distinctive intermediate filament up-regulation in glial cells is unknown, but in the retina their expression is differentially regulated in a polarized manner as the Müller cells hypertrophy, suggesting that they play some role in this process. Moreover the response of intermediate filaments and the Müller cells differs depending on whether the retina has been detached or reattached to the retinal pigment epithelium. The differential expression of these proteins may give insight into their role in the formation of glial scars in the retina and elsewhere in the CNS.

Cell-cell interactions in vascular development

Research into areas as divergent as hemangiopoiesis and cardiogenesis as well as investigations of diseases such as cancer and diabetic retinopathy have converged to form the face of research in vascular development today. This convergence of disparate topics has resulted in rapid advances in many areas of vascular research. The focus of this review has been the role of cell-cell interactions in the development of the vascular system, but we have included discussions of pathology where the mechanism of disease progression may have parallels with developmental processes. A number of intriguing questions remain unanswered. For example, what triggers abnormal angiogenesis in the disease state? Are the mechanisms similar to those that control developmental neovascularization? Perhaps the difference in development in angiogenesis versus in disease is context driven, that is, an adult versus an embryonic organism. If this is the case, can the controls that curtail developmental vessel formation be applied in pathologies? Can cell-cell interactions be targeted as a control point for new vessel formation? For instance, can perivascular cells be stimulated or eliminated to result in increased vessel stability or instability, respectively? If the hypothesis that mural cell association is required for vessel stabilization is accurate, are there mechanisms to promote or inhibit mural cell recruitment and differentiation as needed? These and other questions lie in wait for the next generation of approaches to discern the mechanisms and the nature of the cell-cell interactions and the influence of the microenvironment on vascular development.

Fetal hemoglobin in sickle cell anemia: relationship to erythrocyte adhesion markers and adhesion

To assess whether fetal hemoglobin (HbF) modulates the adhesion of sickle erythrocytes to endothelium, children with homozygous sickle cell anemia (SS disease) were studied, using this physiologically crucial period to evaluate the relationships between HbF and the major erythrocyte adhesion markers. The mean level of CD36(+) erythrocytes was 2.59% +/- 2.15% (+/- SD, n = 40) with an inverse relationship between CD36 positivity and F cells (R = -0.76, P < .000 00 002). In univariate analyses, significant correlations with various hematologic parameters and age were noted. Multiple regression analyses, however, revealed a relationship solely with F cells. Minimal levels of very late activation antigen-4(+) (VLA4(+)) erythrocytes (0.31% +/- 0.45%, n = 40) with relationships similar to those noted for CD36(+) cells were also observed. The subpopulation of strongly adhesive stress reticulocytes was further assessed, using CD71 as their marker. The mean level of CD71(+) erythrocytes was 5.81% +/- 4.21%, with statistical correlates in univariate and multivariate analyses similar to those discussed above. When adhesion ratios were evaluated, inverse correlations were noted between basal and plasma-induced adhesion and F-cell numbers (R = -0.54, P < .0005; R = -0.53, P < .0006, n = 39). In addition, in analyses where basal or plasma-induced adhesion was the dependent variable and the independent variables included F cells and the various adhesion-related parameters, significant relationships solely with F cells were noted. The results demonstrate that SS patients with higher levels of F cells have concomitant decreases in the numbers of CD36(+), VLA4(+), and CD71(+) erythrocytes and that these findings translate into less adherent erythrocytes. These findings extend knowledge regarding the protective effects of HbF in the pathophysiology of sickle cell disease.

Pathogenic mechanism of mouse brain damage caused by oral infection with Shiga toxin-producing Escherichia coli O157:H7

In a previous study, we showed that infection with Shiga toxin (Stx)-producing Escherichia coli O157:H7 (strain Sm(r)N-9) caused neurologic symptoms in malnourished mice with positive immunoreactions of Stx2 in brain tissues. The present study explores the mechanism of how Stx injures the vascular endothelium to enter the central nervous system in mice. Oral infection with strain Sm(r)N-9 elicited a tumor necrosis factor alpha (TNF-alpha) response in the blood as early as 2 days after infection, while Stx was first detected at 3 days postinfection. In the brain, TNF-alpha was detected at day 3, and its quantity was increased over the next 3 days. Frozen sections of the brains from moribound mice contained high numbers of apoptotic cells. Glycolipids recognized by an anti-Gb3 monoclonal antibody were extracted from the brain, and purified Stx2 was able to bind to the glycolipids. In human umbilical vascular endothelial cells (HUVEC) cultured with fluorescein-labeled Stx2 (100 ng/ml), TNF-alpha (20 U/ml) significantly facilitated the intracellular compartmentalization of fluorescence during 24 h of incubation, suggesting the enhanced intracellular processing of Stx2. Consequently, higher levels of apoptosis in HUVEC were found at 48 h. Short-term exposure of HUVEC to Stx2 abrogated their apoptotic response to subsequent incubation with TNF-alpha alone or TNF-alpha and Stx2. In contrast, primary exposure of HUVEC to TNF-alpha followed by exposure to Stx2 alone or TNF-alpha and Stx2 induced apoptosis at the same level as obtained after 48-h incubation with these two agents. These results suggest that the rapid production of circulating TNF-alpha after infection induces a state of competence in vascular endothelial cells to undergo apoptosis, which would be finally achieved by subsequent elevation of Stx in the blood. In this synergistic action, target cells must be first exposed to TNF-alpha. Such cell injury may be a prerequisite to brain damage after infection with Stx-producing E. coli O157:H7.

Integrins alpha(v)beta3 and alpha5beta1 mediate attachment of lyme disease spirochetes to human cells

Borrelia burgdorferi (sensu lato), the agent of Lyme disease, is able to cause chronic, multisystemic infections in human and animal hosts. Attachment of the spirochete to host cells is likely to be important for the colonization of diverse tissues. The platelet-specific integrin alpha(IIb)beta3 was previously identified as a receptor for all three species of Lyme disease spirochetes (B. burgdorferi sensu stricto, B. garinii, and B. afzelii). Here we show that B. burgdorferi also recognizes the widely expressed integrins alpha(v)beta3 and alpha5beta1, known as the vitronectin and fibronectin receptors, respectively. Three representatives of each species of Lyme disease spirochete were tested for the ability to bind to purified alpha(v)beta3 and alpha5beta1. All of the strains tested bound to at least one integrin. Binding to one integrin was not always predictive of binding to other integrins, and several different integrin preference profiles were identified. Attachment of the infectious B. burgdorferi strain N40 to purified alpha(v)beta3 and alpha5beta1 was inhibited by RGD peptides and the appropriate receptor-specific antibodies. Binding to alpha(v)beta3 was also shown by using a transfected cell line that expresses this receptor but not alpha(IIb)beta3. Attachment of B. burgdorferi N40 to human erythroleukemia cells and to human saphenous vein endothelial cells was mediated by both alpha5beta1 and alpha(v)beta3. Our results show that multiple integrins mediate attachment of Lyme disease spirochetes to host cells.

Eicosanoids in sickle cell disease: potential relevance of 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid to the pathophysiology of vaso-occlusion

The monohydroxyeicosanoid 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE), which is derived from oxygenation of arachidonic acid by 12-lipoxygenase, is one of the major metabolites in platelets. In a recent study, we have showed that this eicosanoid stimulated basal sickle-red-cell-endothelial-cell adhesion. To understand the pathophysiologic significance of 12-HETE, we measured the levels of this eicosanoid in plasma and urine from children with sickle cell disease. We found that as compared with controls, plasma 12-HETE levels are increased in patients with sickle-cell disease in the steady state, and are increased further during vaso-occlusive crises. Urinary 12-HETE levels were also increased during the steady state. We also assessed plasma levels of soluble P-selectin (another potential marker for platelet activation), and found changes in the levels of this marker similar to those seen with plasma 12-HETE. In additional studies, we found that 12-HETE enhanced hypoxia-induced sickle-red-cell-endothelial adherence, and that this effect was mediated by potentiation of agonist-induced upregulation of the expression of the mRNA for vascular cell adhesion molecule-1 (VCAM-1) in endothelial cells. Because 12-HETE appears to enhance both basal and agonist-induced sickle-red-cell adhesion, this metabolite could potentially play a role in the pathogenesis of the vaso-occlusive crisis (VOC) in sickle-cell disease.

Use of dynamic capillaroscopy for studying cutaneous microcirculation in patients with diabetes mellitus

To investigate the relationship between cutaneous microcirculation and retinopathy in diabetes mellitus, we studied by dynamic capillaroscopy 35 diabetes mellitus patients, including 10 patients without retinopathy, 10 patients with background retinopathy, and 15 patients with proliferative retinopathy. We found that (1) cutaneous and retinal microcirculation in diabetes mellitus in long-term diabetes mellitus, regressional rather than proliferational changes occurred in skin vasculature as compared to that in retina; (2) functional impairments of cutaneous microcirculation, that is, decreased resting capillary blood cell velocity, peak blood cell velocity, and prolonged time to peak capillary blood cell velocity by dynamic capillaroscopy, could be detected in diabetes mellitus patients without retinopathy; (3) the degree of tortouosity of capillaries, impairment in peak capillary blood cell velocity, and time to peak capillary blood cell velocity of cutaneous microcirculation were significantly correlated with the gravity of retinopathy in diabetes mellitus patients; (4) abnormal leakage of fluorescence in cutaneous microcirculation appeared in diabetes mellitus patients with or without abnormal fluorescein angiography in retina. In conclusion, dynamic capillaroscopy used in concert with ophthalmoscopy and fluorescein angiography can facilitate a comprehensive examination of vasculopathy in diabetes mellitus.

Identifying maculopathy after neodymium: YAG membranotomy for dense diabetic premacular hemorrhage

PURPOSE

To assess the value of neodymium:YAG membranotomy in achieving rapid intravitreal dispersion of dense diabetic premacular hemorrhage and allowing the identification and treatment of maculopathy before panretinal photocoagulation (PRP).

METHODS

A pilot study, in which nine eyes with dense diabetic premacular hemorrhages were treated with neodymium:YAG membranotomy, is described. After intravitreal dispersion of premacular blood, fundus examination and fluorescein angiography were performed to identify neovascularization and macular edema. Macular photocoagulation was performed before PRP in eyes with co-existing maculopathy and neovascularization.

RESULTS

Complete intravitreal dispersion was achieved in all eyes within 1 week. Clinically significant macular edema was identified and treated, before PRP, in three eyes. No exacerbation of macular edema occurred after PRP, and visual acuity was stabilized at pre-hemorrhage levels in seven eyes and to within one line in the remaining two eyes. No traction retinal detachments or rebleeding occurred, and vitrectomy was not required in any eye.

CONCLUSIONS

Early neodymium:YAG membranotomy may obviate the need for early vitrectomy for dense diabetic premacular hemorrhage, and allows early identification and treatment of maculopathy, before PRP, thus reducing the risk of exacerbation after PRP. Further studies to evaluate this treatment modality, particularly with respect to long-term visual prognosis, appear warranted.

Sickle red blood cells stimulate endothelial cell production of eicosanoids and diacylglycerol

The effects of sickle red cell-endothelial cell interaction on endothelial cell arachidonic: acid (AA) mobilization, eicosanoid release, and diacylglycerol (DAG) production were evaluated by using bovine aortic endothelial cells. We have shown that coincubation of washed red blood cells (RBCs) from patients with sickle cell disease with endothelial cells stimulate AA release (90% increase as compared with buffer controls, n = 8, p < 0.002). Released AA was mobilized from membrane phosphatidylcholine and phosphatidylserine and was converted to eicosanoids via the cyclooxygenase and lipoxygenase pathways in increased amounts in the presence of sickle erythrocytes. The production of prostacyclin and 15-hydroxyeicosatetraenoic acid (15-HETE) were increased by 78% (p < 0.01) and 103% (p < 0.025), respectively, as shown by both chromatographic and immunoassay procedures. Sickle erythrocytes also stimulated the hydrolysis of endothelial cell phosphoinositides, including phosphatidylinositol-mono-phosphate (p < 0.03) and phosphatidylinositol-bis-phosphate (p < 0.006). This response was accompanied by a significant increase in the production of DAG (50% increase as compared with buffer control, n = 8, p < 0.025). In contrast, coincubation of washed erythrocytes from normal healthy donors with endothelial cells had no significant effect on endothelial cell phospholipid turnover. When the sickle RBC-induced biochemical changes in endothelial cells were contrasted with those observed with normal RBCs, the ability of sickle RBCs to induce AA mobilization and the production of mono-HETEs and DAG was markedly increased (p = 0.05 to p < 0.025). Because 15-HETE is a pro-adhesinogenic eicosanoid and DAG is an endogamous activator of protein kinase C, an enzyme involved in modulating cell surface adhesive properties, both 15-HETE and DAG could potentially play a role in the vascular pathophysiology of sickle cell disease.

Immunohistochemical distribution of basic fibroblast growth factor in experimental retinal ischaemia and reperfusion in the rat

It has been proposed that basic fibroblast growth factor (basic FGF) mediates the neovascular response in a variety of conditions, including diabetic retinopathy and branch retinal vein occlusion. To test the hypothesis that basic FGF was released from retinal stores as a result of retinal ischaemia, transient retinal ischaemia was induced, followed by 48 h of reperfusion, in the rat by combined central retinal vasculature and optic nerve ligation. The immunolocalization of basic FGF was studied in the retina. We found that basic FGF in the normal retina is present around the deeper retinal vessels and in the neuronal tissue of the outer plexiform layer. In the eyes that had ischaemia followed by reperfusion, there was moderate cellular oedema with retinal swelling, and mitoses in the inner nuclear and plexiform layers. There were no changes evident at the immunohistochemical level either in the intensity or distribution of stores of basic FGF. We conclude from these data that stores of basic FGF are not altered dramatically under the conditions of transient experimental ischaemia and reperfusion in the rat, despite the presence of cellular proliferation.

The angiotensin II AT2 receptor inhibits proliferation and promotes differentiation in PC12W cells

Angiotensin II (ANG II) has been implicated in cell growth and differentiation. We investigated the effect of AT2 receptor stimulation on proliferation and morphological differentiation in cells of neuronal origin by using the pheochromocytoma derived cell line, PC12W. ANG II (10(-8)-10(-6) M) inhibited fetal calf serum (FCS)-induced cell proliferation in a concentration dependent manner. In half of the experiments, the epidermal growth factor (EGF) exerted a mitogenic action which was concentration-dependently inhibited by ANG II. In the other half of the experiments, EGF had an antimitogenic effect which was further enhanced by ANG II (maximally at 10(-6) M). Treatment with nerve growth factor (NGF) induced an inhibition of [3H]thymidine incorporation, which was enhanced by ANG II, maximally 25% at the highest concentration. The effects of ANG II on [3H]thymidine incorporation were reflected by those on cell number and were prevented by the AT2 receptor antagonist, PD123177, but not influenced by the AT1 receptor antagonist, losartan. The ANG II-induced inhibition of cell proliferation was paralleled by morphological differentiation in response to daily treatment with ANG II. ANG II also enhanced low-dose NGF-induced neurite formation. Again, these effects of ANG II were abolished by the AT2 receptor antagonist, PD123177. Our data in PC12W cells show that the AT2 receptor not only inhibits growth factor-induced proliferation and enhances the NGF-mediated growth arrest but also induces morphological differentiation in cells of neuronal origin. These findings strongly support the hypothesis that the AT2 receptor promotes differentiation in neuronal cells.

Upregulated expression of vascular endothelial growth factor in proliferative diabetic retinopathy

AIMS/BACKGROUND

Vascular endothelial growth factor (VEGF) is a hypoxia induced angiogenic factor. Recent studies have shown that high levels of VEGF accumulate in the vitreous of patients with proliferative diabetic retinopathy (PDR). The purpose of the present study was to identify the retinal cells that upregulate VEGF expression in human PDR patients representing progressive stages of retina deterioration.

METHODS

Thirteen formalin fixed and paraffin embedded enucleated eyes with PDR were used (eyes were enucleated because of being blind and painful as a result of neovascular glaucoma). Thin retina sections were hybridised in situ with a VEGF specific probe, to identify cells producing VEGF mRNA.

RESULTS

All eyes with PDR showed upregulated expression of VEGF mRNA, specifically in the cells of the neurosensory retina. VEGF expression was upregulated in all three nuclear layers--namely, the ganglion cell layer, the inner nuclear layer, and the outer nuclear layer. However, in each patient, VEGF producing cells were mostly distributed in a different layer, or even confined to a specific region in that layer. For example, expression by the outer nuclear layer was mostly detected in detached (presumably hypoxic) regions of the retina.

CONCLUSIONS

Progression of PDR is distinguished by a sustained, upregulated expression of VEGF by the neurosensory retina. Cells in all retina layers can potentially contribute to augmented VEGF production. The restricted population of VEGF producing cells in each case is likely to represent cells residing in ischaemic regions of the retina. Thus, VEGF may function as a linking factor between retinal ischaemia and PDR associated neovascularisation.

Early photocoagulation in patients with either type I or type II diabetes

OBJECTIVE

To determine the benefits of early photocoagulation in patients with type I versus type II diabetes.

DESIGN

One eye of each of 3,711 patients was randomly assigned to early photocoagulation; the other was assigned to deferral of photocoagulation, with follow-up visits scheduled every 4 months and photocoagulation to be carried out promptly if high-risk proliferative retinopathy developed. Patients were categorized by age and type of diabetes.

MAIN OUTCOME MEASURES

Best corrected visual acuity was measured at each study visit scheduled at 4-month intervals. Stereoscopic fundus photographs were taken and evaluated at baseline, 4 months, and yearly thereafter. Retinopathy severity was assessed from fundus photographs. Severe visual loss was defined as visual acuity of worse than 5/200 for at least two consecutive study visits.

RESULTS

Previously published results of the Early Treatment Diabetic Retinopathy Study (ETDRS) demonstrated a statistically significant benefit of early photocoagulation in preventing severe vision loss. Further analyses demonstrate that this benefit of early photocoagulation is greater in patients with type II diabetes than in those with type I. The relative benefit of early photocoagulation in patients with type II diabetes is also seen for other outcomes (development of high-risk proliferative retinopathy, development of the combined end point [severe visual loss or vitrectomy], development of moderate visual loss, or development of legal blindness). The patients most likely to benefit from early photocoagulation had severe nonproliferative retinopathy or early proliferative retinopathy. Analyses from the Diabetic Retinopathy Study confirm the relative benefit of scatter photocoagulation for type II patients. Because of the high correlation between age and type of diabetes, analyses sub-grouped by age show similar results.

CONCLUSION

These analyses suggest that patients with type II diabetes, or older patients with diabetes, are more likely to benefit from early scatter photocoagulation than patients with type I diabetes. The current standard of care is to initiate scatter photocoagulation as the severity of retinopathy approaches or reaches the high-risk stage, Provided careful follow-up is possible, ETDRS data do not show that initiating scatter photocoagulation prior to the development of high-risk proliferative diabetic retinopathy in patients with type I diabetes will reduce the risk of severe visual loss. ETDRS analyses do indicate that for patients with type II diabetes, it is especially important to consider scatter photocoagulation at the time of the development of severe nonproliferative or early proliferative retinopathy.

The role of growth factors in the development of diabetic retinopathy

Proliferation of retinal blood vessels is one of the most striking features of advanced diabetic retinopathy. This feature has led to the conclusion that the normal balance of growth factors, which usually serves to keep angiogenesis in check, is disturbed in diabetic retinopathy. A considerable amount of work has been performed in the field of angiogenesis within the last decade. Much of this is applicable to diabetic eye disease, but due to the lack of an animal model, few studies have been performed directly on models of diabetic retinopathy. This review examines the literature as it relates to diabetic retinopathy.

Distribution of growth factors in subfoveal neovascular membranes in age-related macular degeneration and presumed ocular histoplasmosis syndrome

PURPOSE

We performed a histopathologic and immunohistologic study to determine the macromolecular and cellular components of subfoveal neovascular membranes removed at the time of submacular surgery.

METHODS

Subfoveal neovascular membranes were surgically removed from ten patients (seven with age-related macular degeneration and three with presumed ocular histoplasmosis syndrome). Tissues obtained were examined by light and electron microscopy to identify structural components. Immunohistochemical staining was then performed with monoclonal antibodies to various growth factors, including transforming growth factor-beta 1, basic fibroblast growth factor, platelet-derived growth factor, and epidermal growth factor, as well as antibodies against procollagen 1 and phosphotyrosine residues.

RESULTS

Most cells in subfoveal neovascular membranes are retinal pigment epithelial cells and cells resembling fibroblasts, with some vascular endothelial cells, lymphocytes, and macrophages. Basic fibroblasts growth factor was found in the extracellular matrix and in endothelial cells. Transforming growth factor-beta 1 was found in endothelial cells, fibroblasts, and retinal pigment epithelial cells. Procollagen 1 was found in protein-synthesizing fibroblasts, and phosphotyrosine residues were detected within fibroblasts, endothelial cells, and retinal pigment epithelial cells.

CONCLUSIONS

Subfoveal neovascular membranes are neovascular complexes composed of retinal pigment epithelial cells, fibroblasts, vascular endothelial cells, and chronic inflammatory cells. Furthermore, transforming growth factor-beta 1 and basic fibroblast growth factor are present within the major cell types, which suggests a possible pathogenic role in the development of the neovascular complex.

Electrical resistance and macromolecular permeability of retinal capillary endothelial cells in vitro

This study was undertaken to examine the ability of retinal capillary endothelial cells to retain blood-retinal barrier properties in vitro. Second passage bovine retinal capillary endothelial cells were grown to confluence on polycarbonate filters in two chamber systems coated with laminin, fibronectin and type IV collagen. The electrical resistances, permeability of 3H-insulin and expression of blood-brain barrier related enzymes by retinal cells was observed and compared with bovine aortic endothelial cells and bovine fibroblasts. The electrical resistance of retinal cells rose over the first week of culture, peaking after 5-9 days in culture. In eleven separate experiments (n = 5 for each experiment) the average peak resistance of retinal endothelial cells ranged from 89.3-186.6 with a mean average of 129.0 ohm.cm2. In one of these experiments, the peak electrical resistance of retinal cells was 149.0 +/- 10.3 compared with 34.8 +/- 6.8 for aortic cells and 37.8 +/- 3.8 ohm.cm2 for fibroblasts. The permeability coefficients of inulin were: retinal cells 0.17 +/- 0.09, aortic cells 3.47 +/- 1.58 (p = 0.015), fibroblasts 3.93 +/- 0.78 (p = 0.002) x 10(-6) cm/sec. Retinal cells expressed significantly higher activities of gamma-glutamyl transpeptidase and alkaline phosphatase than the other cell types. Treatment of the monolayers with the calcium ionophore, A23187, resulted in a reversible increase in permeability as has been described for peripheral vascular endothelium. We conclude that BRCEC retain at least some of their specialised barrier properties in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Diode laser photocoagulation for diabetic macular oedema

AIMS

This study aimed to investigate whether diode laser irradiation, which is poorly absorbed by haemoglobin, can induce closure of leaking retinal microvascular lesions in the treatment of diabetic macular oedema.

METHODS

Thirty three eyes with clinically significant diabetic macular oedema were treated with a diode laser. Fundus evaluation before and after treatment included visual acuity, stereoscopic biomicroscopy, colour photographs, and fluorescein angiography.

RESULTS

At a mean period of review of 6 months macular oedema had completely or partially resolved in 27 eyes. Visual acuity improved in three, deteriorated in one, and was unchanged in 29 eyes.

CONCLUSION

Preliminary data suggest that diode laser therapy induces closure of leaking retinal microaneurysms and is effective in the treatment of diabetic macular oedema.