Increased expression of endothelial antigen PAL-E in human diabetic retinopathy correlates with microvascular leakage

Aims/hypothesis. The Pathologische Anatomie Leiden-Endothelium (PAL-E) antigen is a marker for loss of the blood-brain barrier function in brain tumours. It is endothelium specific and is associated with the endothelial plasmalemmal vesicles (caveolae) involved in transcellular transport. To test whether blood-retinal barrier loss in diabetic retinopathy is associated with cellular changes in the endothelium, the expression of antigen PAL-E in relation to microvascular leakage in human diabetic retinopathy was investigated. Methods. Immunohistochemical staining of frozen tissue sections of postmortem eyes obtained from 30 persons without and 41 persons with diabetes mellitus was carried out with monoclonal antibodies against PAL-E and CD31 and with antibodies against endogenous fibrinogen, albumin and IgG as indicators of vascular leakage. Results. Patchy or uniform microvascular PAL-E staining was observed in the retina of 17 of the 41 eyes of diabetic patients and in 2 of the 30 normal control eyes. In the diabetic eyes, PAL-E staining co-localized with microvascular staining for endogenous fibrinogen, albumin and IgG. Strong staining for PAL-E was observed in sites without blood-tissue barriers, like the choroid. Conclusions/interpretation. In microvessels with an intact blood-retina barrier the endothelial antigen PAL-E is absent. Its expression is increased in retinal vessels of patients with diabetic retinopathy and correlates with microvascular leakage of plasma proteins. This phenotypic shift involving an antigen associated with caveolae suggests that dysfunction of the endothelium forms the cellular basis for microvascular leakage in diabetic retinopathy, rather than passive endothelial damage. [Diabetologia (1999) 42: 596–602] Received: 10 September 1998 and in final revised form: 26 November 1998     

Screening for diabetic retinopathy

Concurrent with the increasing incidence of diabetes mellitus, the incidence of diabetic retinopathy is also rising. Timely recognition with the aid of screening, followed by laser therapy, can prevent the greater part of the resulting visual impairment and blindness. However, many patients with diabetes are not screened or not screened adequately. The necessary screening frequency is annually or biannually, depending on the degree of retinopathy and the presence of risk factors, of which glycaemic control, duration of diabetes, blood pressure, lipid profile, and race are the most important. Digital 2-field fundus photography, preferably in mydriasis, is of sufficient quality for routine screening. The impact of screening programmes can be further improved by applying the optimal method and by initiating an active implementation strategy.     

The original Pathologische Anatomie Leiden-Endothelium monoclonal antibody recognizes a vascular endothelial growth factor binding site within neuropilin-1

For two decades, the antigen recognized by the Pathologische Anatomie Leiden-Endothelium (PAL-E) monoclonal antibody, a standard vascular endothelial cell marker, has remained elusive. Here, we used a combinatorial phage display-based approach ("epitope mapping") to select peptides binding to the original PAL-E antibody. We found that a subset of the selected panel of peptides had motifs with strong homology to an exposed site within the b1 domain of human neuropilin-1 (NRP-1). We confirmed peptide binding by ELISA and by surface plasmon resonance. We also showed that the PAL-E antigen colocalizes with NRP-1 staining in endothelial cells. Crystal structure of the b1 domain in NRP-1 suggests that the PAL-E binding site overlaps with a vascular endothelial growth factor (VEGF) binding site. Taken together, these results indicate that NRP-1 is an endothelial cell antigen recognized by the true PAL-E antibody. The consistent biochemical, morphologic, and functional features between the PAL-E antigen and NRP-1 support our interpretation. Given that NRP-1 is a VEGF receptor, these results explain the attributes of the PAL-E antibody as a marker of vascular permeability and angiogenesis.     

Guidance for the treatment of neovascular age-related macular degeneration

Neovascular age-related macular degeneration is becoming an increasing socio-medical problem as the proportion of the aged population is continuously increasing. However, new insights in the pathogenesis of the disease offer the opportunity to develop targeted therapies that attack the disease process more successfully than ever. This review article will focus on summarizing the actual options in the management of neovascular age-related macular degeneration and provide a short overview about recent therapeutic options in clinical and preclinical evaluation. The recent development of anti-VEGF substances for use in clinical routine has markedly improved the prognosis of patients with neovascular AMD. Intravitreal treatment with substances targeting all isotypes of vascular endothelial growth factor (VEGF), for the first time in the history of AMD treatments, results in a significant increase in visual acuity in patients with neovascular AMD. Overall, antiangiogenic approaches provide vision maintenance in over 90% and substantial improvement in 25-40% of patients. The combination with occlusive therapies like photodynamic therapy (PDT) potentially offers a reduction of re-treatment frequency and long-term maintenance of the treatment benefit. Further developments interacting with various steps in the angiogenic cascade are under clinical or preclinical evaluation and may soon become available. Nevertheless, the growing number of novel therapeutic options will have to provide proof of concept in randomized controlled clinical trials, a major challenge in view of the rapidly evolving field. For those therapies, which are already in clinical use, reasonable diagnostic tools for follow-up need to be developed, as the burden of continuous clinical monitoring of all patients and all indications is significant for patients and doctors. Ultimately, economic issues will be the limiting factor for the clinical availability of different treatment options.     

Mobile ultra-clean unidirectional airflow screen reduces air contamination in a simulated setting for intra-vitreal injection

The aim of this study is to determine whether the use of a mobile ultra-clean laminar airflow screen reduces the air-borne particle counts in the setting of a simulated procedure of an intra-vitreal injection. A mobile ultra-clean unidirectional airflow (UDF) screen was tested in a simulated procedure for intra-vitreal injections in a treatment room without mechanical ventilation. One UDF was passed over the instrument tray and the surgical area. The concentration of particles was measured in the background, over the instrument table, and next to the ocular area. The degree of protection was calculated at the instrument table and at the surgical site. Use of the UDF mobile screen reduced the mean particle concentration (particles > 0.3 microns) on the instrument table by a factor of at least 100.000 (p < 0.05), and over the patient’s eye by at least a factor of 436 (p < 0.05), which in clinical practice translates into significantly reduced air contamination. Mobile UDF screen reduces the mean particle concentration substantially. The mobile UDF screen may therefore allow for a safer procedural environment for ambulatory care procedures such as intra-vitreal injections in treatment rooms.     

Longstanding symptomatic choroidal hemangioma managed with limited PDT as initial or salvage therapy

Purpose To describe the use of limited, low-irradiance, single-spot photodynamic therapy (PDT) with verteporfin for the treatment of symptomatic choroidal hemangiomas.Methods Thirteen consecutive patients with a circumscribed choroidal hemangioma were treated with limited PDT 6 min following a 1-min infusion with verteporfin (6 mg/m² body surface area), using a diode laser (692 nm) and a single spot large enough to cover only the most prominent part of the tumor. Exposure time was 166 s in the first three patients and 83 s in the last ten patients, resulting in a radiance exposure of respectively 100 and 50 J/cm².Results In all 11 not previously conventionally treated patients, visual acuity improved following PDT treatment. The two remaining patients with prior radiation treatment both reported widening of the visual field and sharper vision, but did not show an increase in ETDRS vision. In all but four patients the tumor became ultrasonographically undetectable by the first follow-up visit at 6 weeks, with only a slight irregularity at the level of the previous tumor remaining. In four patients the residual tumor was still detectable, and they received a second treatment, following which the tumor flattened completely. In all patients the retinal detachment disappeared.Conclusion The present series demonstrates that even limited, low-irradiance, single-spot photodynamic therapy with verteporfin is an effective first-line treatment for choroidal hemangiomas.Financial support/proprietary interest: none     

Lack of blood-brain barrier properties in microvessels of the prelaminar optic nerve head

PURPOSE: To define the blood-brain barrier (BBB) characteristics of microvessels in the optic nerve head (ONH). METHODS: Immunohistochemical staining of different regions of the ONH, retro-laminar optic nerve, and retina of human and monkey eyes was carried out, using antibodies against BBB markers (glucose transporter 1, transferrin receptor, and P-glycoprotein), the non-BBB marker PAL-E, and against plasma proteins fibrinogen and IgG, which serve as endogenous markers of nonspecific microvascular permeability. In the ONH of monkey eyes, the number of transport-related endothelial pinocytotic vesicles and their cellular distribution within the microvessels were determined by electron microscopy. RESULTS: In both human and monkey eyes, only microvessels in the prelaminar region of the ONH were positive for the PAL-E antigen. The prelaminar region microvessels showed either no or weak expression of the transferrin receptor and P-glycoprotein but stained positive for glucose transporter 1. In human ONH, fibrinogen and IgG were present around microvessels in the prelaminar region but not in other parts of the optic nerve or retina. By electron microscopy, endothelial cells of prelaminar region microvessels contained a higher number of pinocytotic vesicles, located at the luminal and abluminal side of the endothelial cell membrane, in contrast to a mainly abluminal localization in microvessels of the retina and other parts of the optic nerve. CONCLUSIONS: Microvessels in the prelaminar region of the ONH lack classical BBB characteristics and display nonspecific permeability, possibly mediated by vesicular transport.     

Altered expression patterns of VEGF receptors in human diabetic retina and in experimental VEGF-induced retinopathy in monkey

PURPOSE: The vascular endothelial growth factor (VEGF) family is involved in vascular leakage and angiogenesis in diabetic retinopathy (DR) in the eye, but may also have physiological functions. Based on the hypothesis that differential VEGF receptor (VEGFR) expression in the retina is an important determinant of effects of VEGF, this study was conducted to investigate VEGFR expression in the diabetic retina and in an experimental monkey model of VEGF-A-induced retinopathy. METHODS: In retinas of 27 eyes of diabetic donors, 18 eyes of nondiabetic control donors, and 4 monkey eyes injected with PBS or VEGF-A, expression patterns of VEGFR-1, -2, and -3 in relation to leaky microvessels, as identified by the marker pathologische anatomie Leiden-endothelium (PAL-E) were studied by immunohistochemistry. RESULTS. In control human retinas and retinas of PBS-injected monkey eyes, all three VEGFRs were expressed in nonvascular areas, but only VEGFR-1 was constitutively expressed in retinal microvessels. In diabetic eyes, increased microvascular VEGFR-2 expression was found in association with PAL-E expression, whereas microvascular VEGFR-3 was present in a subset of PAL-E-positive cases. In VEGF-A-injected monkey eyes, VEGFR-1, -2, and -3 and PAL-E were expressed in retinal microvessels. CONCLUSIONS: The VEGFR-1, -2, and -3 expression patterns in control retinas suggest physiological functions of VEGFs that do not involve the vasculature. Initial vascular VEGF signaling may act primarily through VEGFR-1. In diabetic eyes, expression of retinal VEGFR-2 and -3 is increased, mainly in leaky microvessels, and VEGF-A induces vascular expression of the VEGF-A receptor VEGFR-2 and the VEGF-C/D receptor VEGFR-3. These findings indicate a dual role of VEGFs in the physiology and pathophysiology of the retina and suggest that microvascular VEGFR-2 and -3 signaling by VEGFs occurs late in the pathogenesis of DR, possibly initiated by high levels of VEGF-A in established nonproliferative DR.