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The renin angiotensin system is emerging as a potential therapeutic target for diabetic retinopathy. This study examines the effects of angiotensin-converting-enzyme inhibition by captopril and angiotensin AT(1) receptor antagonism using candesartan-cilexetil on retinal blood flow and acetylcholine-stimulated vasodilatation in normotensive diabetic rats.Non-diabetic or streptozotocin-induced diabetic rats were treated for 2 weeks with captopril (100 mg/kg/day) or candesartan cilexetil (2 mg/kg/day). Retinal haemodynamics were measured using video fluorescein angiography. Effects of exogenous acetylcholine on retinal haemodynamics were examined following intravitreal injection. Total retinal diacylglycerol was labelled using diacylglycerol kinase, separated by thin-layer chromatography, and quantified using autoradiography.Diabetic rats had prolonged retinal mean circulation time and decreased retinal blood flow compared with non-diabetic rats. Treatment of diabetic rats with either captopril or candesartan blocked the development of these blood flow abnormalities. Intravitreal injection of acetylcholine (10(-5) mol/l) in non-diabetic rats increased retinal blood flow by 53.9+/-22.0% relative to baseline whereas this response to acetylcholine was blunted in diabetic rats (4.4+/-19.6%, p0.001). Candesartan treatment of diabetic rats restored the acetylcholine-stimulated retinal blood flow response to 60.0+/-18.7% compared with a 56.2+20.1% response in candesartan-treated non-diabetic rats. Total retinal diacylglycerol levels were increased in diabetic rats (3.75+/-0.98 nmol/mg, p0.05) compared with non-diabetic rats (2.13+/-0.25 nmol/mg) and candesartan-treatment of diabetic rats normalized diacylglycerol levels (2.10+/-0.25 nmol/mg, p0.05).This report provides evidence that angiotensin-converting enzyme inhibition and AT(1) receptor antagonism ameliorates retinal haemodynamic dysfunctions in normotensive diabetic rats.

Prostacyclin-stimulating factor (PSF) acts on vascular endothelial cells to stimulate the synthesis of the vasodilatory molecule prostacyclin (PGI2). We have examined the expression, regulation, and hemodynamic bioactivity of PSF both in whole retina and in cultured cells derived from this tissue. PSF was expressed in all retinal cell types examined in vitro, but immunohistochemical analysis revealed PSF mainly associated with retinal vessels. PSF expression was constitutive in retinal pericytes (RPCs) but could be modulated in bovine retinal capillary endothelial cells (RECs) by cell confluency, hypoxia, serum starvation, high glucose concentrations, or inversely by soluble factors present in early vs. late retinopathy, such as TGF-beta, VEGF, or bFGF. In addition, RPC-conditioned media dramatically increased REC PGI2 production, a response inhibited by blocking PSF with a specific antisense oligodeoxynucleotide (ODN). In vivo, PGI2 increased retinal blood flow (RBF) in control and diabetic animals. Furthermore, the early drop in RBF during the initial weeks after inducing diabetes in rats, as well as the later increase in RBF, both correlated with levels of retinal PSF. RBF also responded to treatment with RPC-conditioned media, and this effect could be partially blocked using the antisense PSF ODN. We conclude that PSF expressed by ocular cells can induce PGI2, retinal vascular dilation, and increased retinal blood flow, and that alterations in retinal PSF expression may explain the biphasic changes in RBF observed in diabetes.

The increases in diacylglycerol (DAG) level and protein kinase C (PKC) activity have been characterized biochemically and functionally in the retina and the brain of diabetic rats as well as in cultured vascular cells. PKC specific activities were increased in the membraneous fraction of retina from streptozotocin (STZ)-induced diabetic rats and the genetically determined diabetic BB rats, respectively, after 1 or 2 wk of diabetes, compared with control. The ratio of total PKC activities from membraneous and cytosol fractions was also increased in the retina of diabetic rats. With diabetes, all the isoenzymes and the total DAG level were increased in the rat retina, whereas no changes were found in the rat brain. Insulin treatment normalized plasma glucose levels and partially prevented the increases in the membraneous PKC activity and all the isoenzymes in the retina. In the retinal endothelial cells, the total DAG level and PKC specific activities are increased by 36 and 22%, respectively, in the membraneous pool when the glucose levels are changed from 5.5 to 22 mM. Activation of PKC activity and isoform beta II by the vitreal injection of phorbol dibutyrate mimicked the abnormal retinal blood circulation observed in diabetic rats (2.22 +/- 0.24 vs. 1.83 +/- 0.40 s). Thus diabetes and elevated glucose levels will increase DAG level and PKC activities and its isoenzyme specifically in vascular cells and may affect retinal hemodynamics.

The alpha(V) integrins are key receptors involved in mediating cell migration and angiogenesis. In age-related macular degeneration (AMD) and diabetic retinopathy, angiogenesis plays a critical role in the loss of vision. These ocular vasculopathies might be treatable with a suitable alpha(V) antagonist, and an oral drug would offer a distinct advantage over current therapies. (3,S,beta,S)-1,2,3,4-Tetrahydro-beta-[[1-[1-oxo-3-(1,5,6,7-tetrahydro-1,8-naphthyridin-2-yl)propyl]-4-piperidinyl]methyl]-3-quinolinepropanoic acid (JNJ-26076713) is a potent, orally bioavailable, nonpeptide alpha(V) antagonist derived from the arginine-glycine-asparagine binding motif in the matrix protein ligands (e.g., vitronectin). This compound inhibits alpha(V)beta(3) and alpha(V)beta(5) binding to vitronectin in the low nanomolar range, it has excellent selectivity over integrins alpha(IIb)beta(3) and alpha(5)beta(1), and it prevents adhesion to human, rat, and mouse endothelial cells. JNJ-26076713 blocks cell migration induced by vascular endothelial growth factor, fibroblast growth factor (FGF), and serum, and angiogenesis induced by FGF in the chick chorioallantoic membrane model. JNJ-26076713 is the first alpha(V) antagonist reported to inhibit retinal neovascularization in an oxygen-induced model of retinopathy of prematurity after oral administration. In diabetic rats, orally administered JNJ-26076713 markedly inhibits retinal vascular permeability, a key early event in diabetic macular edema and AMD. Given this profile, JNJ-26076713 represents a potential therapeutic candidate for the treatment of age-related macular degeneration, macular edema, and proliferative diabetic retinopathy.

PURPOSE. Although vascular endothelial growth factor (VEGF) is a key mediator of retinal vascular permeability (RVP), there may be additional humoral contributors. Hepatocyte growth factor (HGF) induces endothelial cell separation, regulates expression of cell adhesion molecules and is increased in the vitreous fluid of patients with proliferative diabetic retinopathy. The purpose of this study was to evaluate the in vivo effects of HGF on RVP and retinal hemodynamics and delineate the signaling pathways. METHODS. RVP was assessed by vitreous fluorescein fluorophotometry in rats. Time course and dose-response were determined after intravitreal HGF injection. MAP kinase (MAPK), phosphatidylinositol 3-kinase (PI-3 kinase), and protein kinase C (PKC) involvement were examined by using selective inhibitors. Retinal blood flow (RBF) and mean circulation time (MCT) were evaluated by video fluorescein angiography. RESULTS. HGF increased RVP in a time- and dose-dependent manner. HGF-induced RVP was evident 5 minutes after injection, and reached maximal levels after 25 minutes (+107% versus vehicle, P = 0.002). This effect was comparable to that of maximum VEGF stimulation (134% ± 128% at 25 ng/mL). Selective inhibitors of MAPK (PD98059) and PI-3 kinase (LY294002) suppressed HGF-induced RVP by 86% ± 44% (P = 0.015) and 97% ± 59% (P = 0.021), respectively. Non-isoform-selective inhibition of PKC did not significantly decrease HGF-induced RVP. Although VEGF increases RBF and reduces MCT, HGF did not affect either. CONCLUSIONS. HGF increases RVP in a time- and dose-dependent manner at physiologically relevant concentrations with a magnitude and profile similar to that of VEGF, without affecting retinal hemodynamics. Thus, HGF may represent another clinically significant contributor to retinal edema distinct from the actions of VEGF.

Non-invasive in vivo functional optical imaging is emonstrated using high-speed, ultrahigh resolution optical coherence tomography (UHR-OCT). A high-speed, UHR-OCT system using spectral/Fourier domain detection was developed for functional imaging experiments in the rodent retina. Using a spectrally multiplexed superluminescent diode light source, imaging was performed with 2.8 μm resolution at a rate of 24,000 axial scans per second. OCT measurement protocols were designed to minimize noise sources that cause undesired fluctuations in the measured OCT signal. A white light stimulus was applied to the retina and the average reflectivity from each intraretinal layer was monitored over time using OCT. A white light stimulus induces a response consisting of an increase in the reflectance of the photoreceptor outer segments. To our knowledge, this is the first in vivo demonstration of functional imaging using OCT in the retina. Further systematic investigation will be required to fully characterize the observed optical changes. Eventually, this may prove to be an objective method for measuring photoreceptor function in the human retina.

Telehealth holds the promise of increased adherence to evidenced-based medicine and improved consistency of care. Goals for an ocular telehealth program include preserving vision, reducing vision loss, and providing better access to medicine. Establishing recommendations for an ocular telehealth program may improve clinical outcomes and promote informed and reasonable patient expectations. This document addresses current diabetic retinopathy telehealth clinical and administrative issues and provides recommendations for designing and implementing a diabetic retinopathy ocular telehealth care program. The recommendations also form the basis for evaluating diabetic retinopathy telehealth techniques and technologies. Recommendations in this document are based on careful reviews of current evidence, medical literature and clinical practice. They do not, however, replace sound medical judgment or traditional clinical decision-making. "Telehealth Practice Recommendations for Diabetic Retinopathy" will be annually reviewed and updated to reflect evolving technologies and clinical guidelines.

Insulin receptors (IRs) on vascular endothelial cells have been suggested to participate in insulin-regulated glucose homeostasis. To directly address the role of insulin action in endothelial function, we have generated a vascular endothelial cell IR knockout (VENIRKO) mouse using the Cre-loxP system. Cultured endothelium of VENIRKO mice exhibited complete rearrangement of the IR gene and a more than 95% decrease in IR mRNA. VENIRKO mice were born at the expected Mendelian ratio, grew normally, were fertile, and exhibited normal patterns of vasculature in the retina and other tissues. Glucose homeostasis under basal condition was comparable in VENIRKO mice. Both eNOS and endothelin-1 mRNA levels, however, were reduced by approximately 30–60% in endothelial cells, aorta, and heart, while vascular EGF expression was maintained at normal levels. Arterial pressure tended to be lower in VENIRKO mice on both low- and high-salt diets, and on a low-salt diet VENIRKO mice showed insulin resistance. Thus, inactivation of the IR on endothelial cell has no major consequences on vascular development or glucose homeostasis under basal conditions, but alters expression of vasoactive mediators and may play a role in maintaining vascular tone and regulation of insulin sensitivity to dietary salt intake.

In vivo ultrahigh resolution, spectroscopic optical coherence tomography (OCT) with 3µm axial resolution allows for an unprecedented visualization of microstructure relevant to pathology in the anterior eye and retina. The visualization of retinal morphology and intraretinal structures shown here demonstrate the potential for this technique to identify early structural and functional changes associated with retinal diseases, such as diabetic retinopathy and glaucoma. Ultrahigh resolution OCT allows delineation of corneal morphology, including the corneal epithelium and endothelium. Ultrahigh resolution OCT also allows for the imaging of animal models of disease, such as transgenic mice, providing a powerful research tool to better understand disease pathogenesis and evaluate therapies.