Regression activity that is naturally present in vitreous becomes ineffective as patients develop proliferative diabetic retinopathy.

AIMS/HYPOTHESIS: The realisation that targeting agents in the vitreous is an effective approach to treating patients with diabetic retinopathy (DR) has increased awareness that changes in the composition/bioactivity of the vitreous is a contributor to the pathogenesis of DR. The overall goal of this study was to test the hypothesis that the vitreous has regression activity, and that lysophosphatidic acid (LPA) contributes to such activity. LPA is a bioactive phospholipid present in many biological fluids, and has been recently appreciated for its ability to promote regression of blood vessels. METHODS: Vitreous-mediated regression was monitored on tubes organised from primary retinal endothelial cells or neovessels that sprouted from retinal explants. LPA was quantified radioenzymatically. RESULTS: Bovine and human vitreous promoted regression of retinal explant vessels and of tubes organised from primary retinal endothelial cells. LPA was a substantial component of this regression activity. Comparing the regression activities of vitreous from patients with different stages of DR revealed that, as patients developed proliferative diabetic retinopathy (PDR), vitreous lost its ability to promote regression, even though the amount of LPA did not change. The underlying mechanism was a PDR-vitreous-mediated insensitivity to LPA, which could be overcome pharmacologically. CONCLUSIONS/INTERPRETATION: Our findings suggest that a decline in the responsiveness to regression factors such as LPA, which are naturally present in the vitreous, contributes to the pathogenesis of PDR.

Angiotensin II induces plasminogen activator inhibitor-1 and -2 expression in vascular endothelial and smooth muscle cells.

Angiotensin II (AII)- and Arg8-vasopressin (AVP)-regulated gene expression in vascular cells has been reported to contribute to vascular homeostasis and hypertrophy. In this report, AVP-induced expression of plasminogen activator inhibitor (PAI)-2 mRNA in rat microvessel endothelial (RME) cells was identified using differential mRNA display. Further characterization of vasoactive peptide effects on PAI expression revealed that AII stimulated a 44.8 +/- 25.2-fold and a 12.4 +/- 3.2-fold increase in PAI-2 mRNA in RME cells and rat aortic smooth muscle cells (RASMC), respectively. AII also stimulated a 10- and 48-fold increase in PAI-1 mRNA in RME cells and RASMC, respectively. These AII effects were inhibited by either Sar1, Ile8-angiotensin or the AT1 antagonist DuP 735, but were not significantly altered in the presence of the AT2 antagonist PD123319. AII stimulation of RASMC and RME cells also significantly increased both PAI-1 protein and PAI activity released to the culture medium. Inhibition of protein kinase C completely blocked PMA-stimulated induction of PAI-2 mRNA in both cell types and inhibited the AII-stimulated increase in RASMC by 98.6 +/- 2.8%. In contrast, protein kinase C inhibition only partially decreased the AII-stimulated PAI-2 expression in RME cells by 68.8 +/- 11.1%, suggesting that a protein kinase C-independent mechanism contributes to a 6.9 +/- 1.5-fold AII induction of PAI-2 expression in endothelial cells. AII and PMA also stimulated protein tyrosine phosphorylation in RME cells, and the tyrosine kinase inhibitor genistein partially blocked their induction of PAI-2 mRNA. These findings suggest that AII may regulate plasminogen activation in the vasculature by inducing both PAI-1 and PAI-2 expression.

Characterization of vascular endothelial growth factor's effect on the activation of protein kinase C, its isoforms, and endothelial cell growth.

Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen which mediates its effects by binding to tyrosine kinase receptors. We have characterized the VEGF-activated intracellular signal transduction pathway in bovine aortic endothelial cells and correlated this to its mitogenic effects. VEGF induced concentration- and time-dependent increases in protein kinase C (PKC) activation with a maximum of 2.2-fold above the basal level at 5 x 10(-10) M within 10 min as measured both by in situ and translocation assays. Immunoblotting analysis of PKC isoforms in cytosolic and membrane fractions indicated that after VEGF stimulation the content of Ca(2+)-sensitive PKC isoforms (alpha and betaII) was increased in the membrane fractions, whereas no changes were observed for PKC isoforms delta and epsilon. The stimulation of PKC activity by VEGF was preceded by the activation of phospholipase Cgamma (PLCgamma). This was demonstrated by parallel increases in PLCgamma tyrosine phosphorylation, [3H]inositol phosphate production, and [3H]arachidonic acid-labeled diacylglycerol formation in bovine aortic endothelial cells. In addition, VEGF increased phosphatidylinositol 3-kinase activity 2.1-fold which was inhibited by wortmannin, a phosphatidylinositol 3-kinase inhibitor, without decreasing the VEGF-induced increase in PKC activity or endothelial cell growth. Interestingly, genistein, a tyrosine kinase inhibitor, and GFX or H-7, PKC inhibitors, abolished both VEGF-induced PKC activation and endothelial cell proliferation. VEGF's mitogenic effect was inhibited by a PKC isoform beta-selective inhibitor, LY333531, in a concentration-dependent manner. In contrast, antisense PKC-alpha oligonucleotides enhanced VEGF-stimulated cell growth with a simultaneous decrease of 70% in PKC-alpha protein content. Thus, VEGF appears to mediate its mitogenic effects partly through the activation of the PLCgamma and PKC pathway, involving predominately PKC-beta isoform activation in endothelial cells.

Identification and characterization of a gene regulating enzymatic glycosylation which is induced by diabetes and hyperglycemia specifically in rat cardiac tissue.

Primary cardiac abnormalities have been frequently reported in patients with diabetes probably due to metabolic consequences of the disease. Approximately 2,000 mRNA species from the heart of streptozotocin-induced diabetic and control rats were compared by the mRNA differential display method, two of eight candidate clones thus isolated (DH1 and 13) were confirmed by Northern blot analysis. The expression of clone 13 was increased in the heart by 3.5-fold (P < 0.05) and decreased in the aorta by twofold (P < 0.05) in diabetes as compared to control. Sequence analysis showed that clone 13 is a rat mitochondrial gene. DH1 was predominantly expressed in the heart with an expression level 6.8-fold higher in the diabetic rats than in control (P < 0.001). Insulin treatment significantly (P < 0.001) normalized the expression of DH1 in the hearts of diabetic rats. DH1 expression was observed in cultured rat cardiomyocytes, but not in aortic smooth muscle cells or in cardiac derived fibroblasts. The expression in cardiomyocytes was regulated by insulin and glucose concentration of culture media. The full length cDNA of DH1 had a single open-reading frame with 85 and 92% amino acid identity to human and mouse UDP-GlcNAc:Gal beta 1-3GalNAc alpha R beta 1-6 N-acetylglucosaminyltransferase (core 2 GlcNAc-T), respectively, a key enzyme determining the structure of O-linked glycosylation. Transient transfection of DH1 cDNA into Cos7 cells conferred core 2 GlcNAc-T enzyme activity. In vivo, core 2 GlcNAc-T activity was increased by 82% (P < 0.05) in diabetic hearts vs controls, while the enzymes GlcNAc-TI and GlcNAc-TV responsible for N-linked glycosylation were unchanged. These results suggest that core 2 GlcNAc-T is specifically induced in the heart by diabetes or hyperglycemia. The induction of this enzyme may be responsible for the increase in the deposition of glycoconjugates and the abnormal functions found in the hearts of diabetic rats.

Retinal expression, regulation, and functional bioactivity of prostacyclin-stimulating factor.

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.

Randomized trial of peribulbar triamcinolone acetonide with and without focal photocoagulation for mild diabetic macular edema: a pilot study.

OBJECTIVE: To provide pilot data on the safety and efficacy of anterior and posterior sub-Tenon injections of triamcinolone either alone or in combination with focal photocoagulation in the treatment of mild diabetic macular edema (DME). DESIGN: Prospective, phase II, multicenter, randomized clinical trial. PARTICIPANTS: One hundred nine patients (129 eyes) with mild DME and visual acuity 20/40 or better. METHODS: The participants were assigned randomly to receive either focal photocoagulation (n = 38), a 20-mg anterior sub-Tenon injection of triamcinolone (n = 23), a 20-mg anterior sub-Tenon injection followed by focal photocoagulation after 4 weeks (n = 25), a 40-mg posterior sub-Tenon injection of triamcinolone (n = 21), or a 40-mg posterior sub-Tenon injection followed by focal photocoagulation after 4 weeks (n = 22). Follow-up visits were performed at 4, 8, 17, and 34 weeks. MAIN OUTCOME MEASURES: Change in visual acuity and retinal thickness measured with optical coherence tomography (OCT). RESULTS: At baseline, mean visual acuity in the study eyes was 20/25 and mean OCT central subfield thickness was 328 mum. Changes in retinal thickening and in visual acuity were not significantly different among the 5 groups at 34 weeks (P = 0.46 and P = 0.94, respectively). There was a suggestion of a greater proportion of eyes having a central subfield thickness less than 250 mum at 17 weeks when the peribulbar triamcinolone was combined with focal photocoagulation. Elevated intraocular pressure and ptosis were adverse effects attributable to the injections. CONCLUSIONS: In cases of DME with good visual acuity, peribulbar triamcinolone, with or without focal photocoagulation, is unlikely to be of substantial benefit. Based on these results, a phase III trial to evaluate the benefit of these treatments for mild DME is not warranted.

Vascular endothelial growth factor and diabetes: the agonist versus antagonist paradox.

Much of the morbidity and mortality associated with diabetes is primarily attributable to sequelae of microvascular and macrovascular disease. Over the past decade, dramatic progress has been achieved in elucidating the fundamental processes underlying the pathogenesis of these complications. Angiogenic factors in particular now appear to play a pivotal role in the development of microvascular complications as well as the response to macrovascular disease. Hyperglycemia, other growth factors, advanced glycation end products, oxidative stress, and ischemia can increase growth factor expression. In some microvascular tissues, the result is pathologic neovascularization and increased vascular permeability. These responses account for much of the visual loss associated with diabetic retinopathy and may, in addition, serve a significant role in nephropathy and neuropathy. In contrast, recent data suggest that vascular collateralization resulting from ischemia-induced growth factor release in tissues compromised by macrovascular disease may be important in reducing clinical symptoms and tissue damage. This angiogenic response, which may be beneficial in coronary artery and peripheral limb disease, appears to be reduced in patients with diabetes. Thus, two apparently diametrically opposed therapeutic paradigms are arising for the treatment of vascular complications in diabetes. Indeed, growth factor antagonists have been used successfully in diabetes-related animal models to block angiogenic and permeability complications in the retina and kidney. Conversely, growth factor agonists have been successfully used to stimulate collateral vessel formation and reduce ischemic symptoms from macrovascular disease in the coronary arteries and peripheral limbs. Both of these approaches are currently being evaluated in clinical trials for their respective indications. Thus, as these divergent therapeutic modalities begin to enter the clinical arena, this apparent paradox necessitates careful consideration of the potential risks, benefits, and interactions of the opposing regimens. Using vascular endothelial growth factor as a classic example of growth factor involvement, we discuss the current preclinical and clinical data supporting these approaches and the implications arising from the probable coexistence of these two therapeutic modalities.

Hypoxia upregulates glucose transport activity through an adenosine-mediated increase of GLUT1 expression in retinal capillary endothelial cells.

Elevation of intracellular glucose within retinal vascular cells is believed to be an important causal factor in the development of diabetic retinopathy. The intracellular glucose concentration is regulated by both the rate of glucose metabolism and glucose transport. Because retinal hypoxia often precedes proliferative diabetic retinopathy, we have studied the regulation of the glucose transport system by hypoxia in cultured bovine retinal endothelial cells (BRECs). Because retinal ischemia is known to increase intracellular adenosine levels, which subsequently regulate hypoxia-inducible genes, such as vascular endothelial growth factor and erythropoietin, the role of adenosine and its receptor-mediated pathways has also been evaluated. Hypoxia (0.5% O2, 5% CO2, and 94.5% N2) stimulated GLUT1 mRNA expression in BRECs in a time-dependent manner with an 8.9 +/- 1.5-fold (P < 0.01) increase observed after 12 h. GLUT1 mRNA expression returned to baseline (1.4 +/- 0.3-fold of control) within 12 h after reinstitution of normoxia. N6-Cyclopentyl adenosine (adenosine A1 receptor agonist, Kd = 1 nmol/l) did not affect GLUT1 mRNA expression at concentrations up to 1 micromol/l, while 2-p-(2-carboxyethyl)-phenethyl-amino-5'-N-ethylcarboxamidoadenosine and 5'-(N-ethylcalboxamido)-adenosine (adenosine A2 receptor [A2R] agonists, Kd = 15 and 16 nmol/l, respectively) increased mRNA levels at concentrations as low as 10 nmol/l. Maximal stimulation was 2.3 +/- 0.2- and 2.1 +/- 0.2-fold, respectively (P < 0.01). The adenosine A2a receptor antagonist 8-(3-chlorostyryl)caffeine (CSC) (Kd = 100 nmol/l for A2R) inhibited hypoxia-stimulated GLUT1 mRNA expression by 40 +/- 8% at 100 nmo/l. Hypoxia upregulated GLUT1 protein expression by 3.0 +/- 0.3-fold after 12 h (P < 0.01), but this response was attenuated by CSC (P < 0.05). Hypoxia increased glucose transport activity by 2.1 +/- 0.3-fold (P < 0.001) after 12 h, a response inhibited 65% by CSC (P < 0.01). A protein kinase A (PKA) inhibitor (H89, 20 micromol/l) suppressed hypoxia-induced GLUT1 mRNA expression by 42 +/- 9% (P < 0.01). These data suggest that hypoxia in BRECs upregulates glucose transport activity through an increase of GLUT1 expression that is partially mediated by adenosine, A2R, and the cAMP-PKA pathway.

Identification and characterization of vascular endothelial growth factor receptor (Flt) in bovine retinal pericytes.

Vascular endothelial growth factor (VEGF) plays an important role in the hypoxia-stimulated neovascularization of ischemic retinal diseases such as proliferative diabetic retinopathy. VEGF exerts its effect through two known high-affinity tyrosine kinase receptors, named kinase insert domain-containing receptor (KDR) and the fms-like tyrosine kinase (Flt). VEGF receptors are located primarily on endothelial cells, although receptors on a few other nonocular cell types also have been described. In the present study, we demonstrate the expression of Flt, but not KDR, in bovine retinal pericytes (BRPCs). Although KDR is expressed predominantly in retinal endothelial cells, Northern blot analysis demonstrated substantial expression of the Flt gene in BRPCs without detection of KDR despite using polyadenylated RNA. Hypoxia increased Flt gene expression in BRPCs (2.7-fold, P < 0.01). 125I-labeled VEGF binding analysis on BRPCs demonstrated two apparent high-affinity receptor subtypes (Kd = 14 and 215 pmol/l), with 2.9 x 10(4) and 1.4 x 10(5) receptors/cell, respectively. 125I-VEGF affinity cross-linking demonstrated VEGF-specific binding complexes at 150, 172, 187, and 200 kDa under reducing conditions. Western blot analysis using an anti-phosphotyrosine antibody demonstrated VEGF-induced tyrosine phosphorylation of several proteins. VEGF stimulation had little effect on initial BRPCs growth rates but significantly increased BRPCs number after 7 days. These results suggest that two classes of high-affinity VEGF receptors are present on BRPCs, at least one of which is analogous to Flt and is capable of intracellular protein phosphorylation. Thus, VEGF might regulate the function of both retinal endothelial cells and retinal pericytes to induce pathological angiogenesis and vascular remodeling during proliferative diabetic retinopathy and other ischemic retinal diseases.

Basic fibroblast growth factor induces expression of VEGF receptor KDR through a protein kinase C and p44/p42 mitogen-activated protein kinase-dependent pathway.

Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are angiogenic molecules whose combined mitogenic activity is potently synergistic. However, the molecular mechanism underlying this synergy is incompletely understood. We examined whether VEGF and bFGF affect expression of each other or alter expression of the VEGF receptor KDR in retinal capillary endothelial cells. In addition, we investigated the intracellular signaling mechanisms involved in this response. VEGF-induced [3H]thymidine uptake was tightly correlated with KDR mRNA and protein concentrations, suggesting that increased KDR expression might account for VEGF's synergistic activity in the presence of bFGF. bFGF (10 ng/ml) induced KDR mRNA expression within 4 h and attained a 4.0-fold increase after 24 h. KDR protein expression was increased 7.5-fold after 48 h. VEGF (= 50 ng/ml) did not alter bFGF, VEGF, or KDR mRNA expression under serum-deprived conditions. In contrast, VEGF increased KDR mRNA expression 87% under growth conditions and 2.9-fold under serum-deprived conditions in the presence of bFGF. The protein kinase C (PKC) agonist phorbol myristate acetate (PMA) induced KDR mRNA expression 5.1-fold at 100 nmol/l. bFGF increased p44/p42 mitogen-activated protein kinase (MAPK) phosphorylation within 5 min, reaching a maximum within 15 min and remaining significantly elevated for >6 h. bFGF-induced MAPK phosphorylation and KDR mRNA expression were almost completely inhibited by 5 micromol/l GFX, a non-isoform-selective PKC inhibitor. MAPK inhibitor PD98059 reduced KDR mRNA expression 72% at concentrations that inhibited bFGF-induced MAPK phosphorylation 100%, suggesting that pathways in addition to MAPK might also be involved. Inhibitors of the beta isoform of PKC (LY333531), protein kinase A (PKA) (H89), and phosphotidylinositol (PI) 3 kinase (wortmannin) had no significant effect. These data suggest that bFGF stimulates KDR expression through a PKC and p44/p42 MAPK-dependent pathway not primarily involving the beta isoform of PKC, PKA, or PI-3 kinase. Since bFGF induces VEGF expression and since increased KDR expression potentiates VEGF action, resulting in additional KDR expression and marked mitogenic activity, these data provide a novel mechanistic explanation for the angiogenic synergy between VEGF and bFGF.

Comparative analysis of vascular endothelial growth factor receptors on retinal and aortic vascular endothelial cells.

Ischemic eye disease often results in ocular neovascularization, presumably due to the elaboration of growth factors. Diabetic retinopathy is a classic example in which dramatic retinal neovascularization arises after ischemic retinal damage. The characterization of vascular endothelial growth factor (VEGF) as an angiogenic molecule whose expression is markedly induced by hypoxia makes it a promising candidate for mediating ischemic retinal neovascularization. Thus, we have characterized the structure, binding, and regulation of VEGF receptors in bovine retinal (BREC) and aortic endothelial cells (BAEC). VEGF stimulated a 2.1-fold increase in BREC number and DNA content at 0.6 nmol/l VEGF (P < 1 x 10(-7)). Scatchard binding analysis demonstrated specific high-affinity VEGF receptors on BREC with a Kd of 4.9 +/- 0.6 x 10(-11) mmol/l, similar to that observed for BAEC at 5.1 +/- 0.4 x 10(-11) mmol/l. BREC, however, possess 1.5 x 10(5) high-affinity receptors/cell, threefold more than BAEC (P < 0.003) and more than any cell type reported previously. 125I-VEGF affinity cross-linking revealed complexes at 220 and 170 kDa in BREC, but only a 220-kDa band of lesser intensity in BAEC. Cross-linking was displaceable in a dose-dependent manner by VEGF (P < 0.01) but not by other hormones. Hypoxia increased VEGF receptor number 50% in BREC without altering affinity. Antiphosphotyrosine immunoblotting showed VEGF-stimulated tyrosine autophosphorylation of VEGF receptor bands at 225 and 220 kDa and another band at 80 kDa within 1 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypoxia induces vascular endothelial growth factor gene and protein expression in cultured rat islet cells.

The formation of new microvasculature by capillary sprouting at the site of islet transplantation is crucial for the long-term survival and function of the graft. Vascular endothelial growth factor (VEGF), an endothelial cell-specific mitogen with potent angiogenic and vascular permeability-inducing properties, may be a key factor in modulating the revascularization of islets after transplantation. In this study, we examined the gene expression of VEGF mRNA in three tumor cell lines and in isolated whole and dispersed rat islets in vitro by Northern blot hybridization in normoxic (5% CO2, 95% humidified air) and hypoxic (1% O2, 5% CO2, 94% N2) culture conditions. Increased expression of VEGF mRNA was observed in beta-TC3, RAW 264.7, and IC-21 tumor cell lines when subjected to hypoxia. With isolated whole islets in normoxic culture, a threefold increase in VEGF mRNA (P < 0.001) was seen at 48 h as compared with freshly isolated islets. This response was similar to the 3.8-fold increase observed with islets subjected to hypoxia. Dispersed rat islet cell clusters cultured on Matrigel for 24 h under hypoxic conditions showed a 3.4-fold increase (P < 0.01) in VEGF mRNA compared with those cultured in normoxia. This correlated with increased VEGF secretion as determined by enzyme-linked immunosorbent assay. Immunohistochemical studies revealed the presence of increased expression of VEGF protein near the center of islets after 24 h of normoxic culture. Islet cell clusters on Matrigel showed intense cellular localization of VEGF in both beta-cells and non-beta-cells. These findings suggest that rat islet cells, when subjected to hypoxia during the first few days after transplantation, may act as a major source of VEGF, thereby initiating revascularization and maintaining the vascular permeability of the grafted islets.

Cyclic stretch and hypertension induce retinal expression of vascular endothelial growth factor and vascular endothelial growth factor receptor-2: potential mechanisms for exacerbation of diabetic retinopathy by hypertension.

Systemic hypertension exacerbates diabetic retinopathy and other coexisting ocular disorders through mechanisms that remain largely unknown. Increased vascular permeability and intraocular neovascularization characterize these conditions and are complications primarily mediated by vascular endothelial growth factor (VEGF). Because systemic hypertension increases vascular stretch, we evaluated the expression of VEGF, VEGF-R2 (kinase insert domain-containing receptor [KDR]), and VEGF-R1 (fms-like tyrosine kinase [Flt]) in bovine retinal endothelial cells (BRECs) undergoing clinically relevant cyclic stretch and in spontaneously hypertensive rat (SHR) retina. A single exposure to 20% symmetric static stretch increased KDR mRNA expression 3.9 +/- 1.1-fold after 3 h (P = 0.002), with a gradual return to baseline within 9 h. In contrast, BRECs exposed to cardiac-profile cyclic stretch at 60 cpm continuously accumulated KDR mRNA in a transcriptionally mediated, time-dependent and stretch-magnitude-dependent manner. Exposure to 9% cyclic stretch increased KDR mRNA expression 8.7 +/- 2.9-fold (P = 0.011) after 9 h and KDR protein concentration 1.8 +/- 0.3-fold (P = 0.005) after 12 h. Stretched-induced VEGF responses were similar. Scatchard binding analysis demonstrated a 180 +/- 40% (P = 0.032) increase in high-affinity VEGF receptor number with no change in affinity. Cyclic stretch increased basal thymidine uptake 60 +/- 10% (P < 0.001) and VEGF-stimulated thymidine uptake by 2.6 +/- 0.2-fold (P = 0.005). VEGF-NAb reduced cyclic stretch-induced thymidine uptake by 65%. Stretched-induced KDR expression was not inhibited by AT1 receptor blockade using candesartan. Hypertension increased retinal KDR expression 67 +/- 42% (P < 0.05) in SHR rats compared with normotensive WKY control animals. When hypertension was reduced using captopril or candesartan, retinal KDR expression returned to baseline levels. VEGF reacted similarly, but Flt expression did not change. These data suggest a novel molecular mechanism that would account for the exacerbation of diabetic retinopathy by concomitant hypertension, and may partially explain the principal clinical manifestations of hypertensive retinopathy itself. Furthermore, these data imply that anti-VEGF therapies may prove therapeutically effective for hypertensive retinopathy and/or ameliorating the deleterious effects of coexistent hypertension on VEGF-associated disorders such as diabetic retinopathy.

A specific increased expression of insulin receptor substrate 2 in pancreatic beta-cell lines is involved in mediating serum-stimulated beta-cell growth.

Certain nutrients and growth factors can stimulate pancreatic beta-cell growth. However, the appropriate mitogenic signaling pathways in beta-cells have been relatively undefined. In this study, differential gene expression in NEDH rat insulinoma was compared with NEDH rat primary islet beta-cells. Differential mRNA display analysis revealed an elevated expression in insulinoma of VL30 transposons, S24 ribosomal protein, and cytochrome-C oxidaseVIIc that is typical for cells undergoing mitosis. A gene candidate approach revealed that mRNA levels of the oncogenes c-fos and c-jun were equivalently expressed in insulinoma and islet cells, as was the mRNA for the mitogenic signal transduction molecule insulin receptor substrate (IRS)-1. However, in contrast to that of IRS-1, IRS-2 gene expression was 60- to 70-fold higher in the insulinoma tissue compared with islets, which was reflected at the protein as well as the mRNA level. The specific elevated IRS-2 expression was a consistent observation across all rodent pancreatic beta-cell lines. To investigate whether IRS-2 was functional, serum-stimulated beta-cell proliferation was examined in isolated insulinoma cells. After a 48-h period of serum withdrawal, 24 h of serum refeeding rendered an 8- to 10-fold increase in [3H]thymidine incorporation into insulinoma cells. This serum-stimulated DNA synthesis was prevented by inhibitors of tyrosine protein kinase and phosphatidylinositol (PI) 3-kinase activities, as well as the activation of mitogen-activated protein (MAP) kinase and p70S6K. Examination of IRS-mediated signal transduction pathways indicated that after 10-15 min of serum refeeding, there was increased tyrosine phosphorylation of IRS-2 and pp60, and PI 3-kinase recruitment to IRS-2. Serum also increased the association of growth factor-bound protein 2/murine sons of sevenless 1 protein to a PI 3-kinase/IRS-2 protein complex. Moreover, serum also activated MAP-kinase (erk-1 and erk-2 isoforms) and 70 kD S6 kinase. Thus IRS-mediated signal transduction pathways are functional in pancreatic beta-cells. It is conceivable that IRS-2 expression in beta-cells contributes to maintaining the islet beta-cell population, complementary to observations in the IRS-2 knockout mouse in which beta-cell mass is markedly reduced.

Vascular endothelial growth factor-induced retinal permeability is mediated by protein kinase C in vivo and suppressed by an orally effective beta-isoform-selective inhibitor.

Increased vascular permeability and excessive neovascularization are the hallmarks of endothelial dysfunction, which can lead to diabetic macular edema and proliferative diabetic retinopathy in the eye. Vascular endothelial growth factor (VEGF) is an important mediator of ocular neovascularization and a known vasopermeability factor in nonocular tissues. In these studies, we demonstrate that intravitreal injection of VEGF rapidly activates protein kinase C (PKC) in the retina at concentrations observed clinically, inducing membrane translocation of PKC isoforms alpha, betaII, and delta and >threefold increases in retinal vasopermeability in vivo. The effect of VEGF on retinal vascular permeability appears to be mediated predominantly by the beta-isoform of PKC with >95% inhibition of VEGF-induced permeability by intravitreal or oral administration of a PKC beta-isoform-selective inhibitor that did not inhibit histamine-mediated effects. These studies represent the first direct demonstration that VEGF can increase intraocular vascular permeability through activation of PKC in vivo and suggest that oral pharmacological therapies involving PKC beta-isoform-selective inhibitors may prove efficacious for the treatment of VEGF-associated ocular disorders such as diabetic retinopathy.

Preventive eye care in people with diabetes is cost-saving to the federal government. Implications for health-care reform.

OBJECTIVE: Diabetic retinopathy, which leads to macular edema and retinal neovascularization, is the leading cause of blindness among working-age Americans. Previous research has demonstrated significant cost savings associated with detection of eye disease in Americans with type I diabetes. However, detection and treatment of eye disease among those with type II diabetes was previously thought not to be cost-saving. Our purpose was to estimate the current and potential federal savings resulting from the screening and treatment of retinopathy in patients with type II diabetes, based on recently available data concerning efficacy of treating both macular edema and neovascularization along with new data on federal budgetary costs of blindness. RESEARCH DESIGN AND METHODS: We used computer modeling, incorporating data from population-based epidemiological studies and multicenter clinical trials. Monte Carlo simulation was used, combined with sensitivity analysis and present value analysis of cost savings. RESULTS: Screening and treatment for eye disease in patients with type II diabetes generates annual savings of $247.9 million to the federal budget and 53,986 person-years of sight, even at current suboptimal (60%) levels of care. If all patients with type II diabetes receive recommended care, the predicted net savings (discounted at 5%) exceeds $472.1 million and 94,304 person-years of sight. Nearly all savings are associated with detection and treatment of diabetic macular edema. Enrolling each additional person with type II diabetes into currently recommended ophthalmological care results in an average net savings of $975/person, even if all costs of care are borne by the federal government. CONCLUSIONS: Our analysis indicates that prevention programs aimed at improving eye care for patients with diabetes not only reduce needless vision loss but also will provide a financial return on the investment of public funds.

von Willebrand factor and retinal circulation in early-stage retinopathy of type 1 diabetes.

OBJECTIVE: Although retinopathy is a common microvascular complication of type 1 diabetes, the mechanism for this complication is still unknown. Changes in retinal circulation have been noted before the development of overt retinal pathology. Because von Willebrand factor (vWF) is a marker for endothelial dysfunction and mediates platelet adhesion, we determined if there was an association between vWF and retinal circulation in the early stages of diabetic retinopathy. RESEARCH DESIGN AND METHODS: Twenty subjects (aged 32.4 +/- 7.8 years) with type 1 diabetes and minimal or no retinopathy were studied. The mean duration of diabetes was 4.7 +/- 2.6 years. Data were collected at baseline and after 4 months of 1,800 IU vitamin E therapy or placebo. Retinal circulation was evaluated by video fluorescein angiography. Plasma vWF antigen levels were measured by enzyme-linked immunosorbent assay and fibrinogen by the Clauss method. RESULTS: Retinal blood flow was negatively correlated with vWF levels (r = -0.44, P = 0.008), whereas retinal circulation time was positively correlated with vWF levels (r = 0.33, P = 0.048). Fibrinogen levels were not significantly associated with either retinal index. However, fibrinogen levels were positively associated with HbA1c levels (r = 0.34, P = 0.01), indicating an association between poor glycemic control and higher fibrinogen levels. CONCLUSIONS: Increased vWF was associated with a prolonged retinal circulation time and reduced retinal blood flow in early-stage retinopathy of type 1 diabetes. Reduced blood flow associated with increased vWF levels may promote stasis in the retinal circulation and lead to local hypoxemia. These changes might contribute to the microvascular complications of diabetes. Whether the vWF levels predict retinal complications deserves further investigation.

High-dose vitamin E supplementation normalizes retinal blood flow and creatinine clearance in patients with type 1 diabetes.

OBJECTIVE: To determine the effectiveness of vitamin E treatment in normalizing retinal blood flow and renal function in patients with <10 years of type 1 diabetes. RESEARCH DESIGN AND METHODS: An 8-month randomized double-masked placebo-controlled crossover trial evaluated 36 type 1 diabetic and 9 nondiabetic subjects. Subjects were randomly assigned to either 1,800 IU vitamin E/day or placebo for 4 months and followed, after treatment crossover, for a further 4 months. Retinal blood flow was measured using video fluorescein angiography, and renal function was assessed using normalized creatinine clearance from timed urine collections. RESULTS: After vitamin E treatment, serum levels of vitamin E were significantly elevated (P<0.01) in both type 1 diabetic and control patients. Hemoglobin A1c was not affected by vitamin E treatment. Diabetic patient baseline retinal blood flow (29.1+/-7.5 pixel2/s) was significantly (P = 0.030) decreased compared with that of nondiabetic subjects (35.2+/-7.2 pixel2/s). After vitamin E treatment, diabetic patient retinal blood flow (34.5+/-7.8 pixel2/s) was significantly increased (P<0.001) and was comparable with that of nondiabetic subjects. Additionally, vitamin E treatment significantly (P = 0.039) normalized elevated baseline creatinine clearance in diabetic patients. CONCLUSIONS: Oral vitamin E treatment appears to be effective in normalizing retinal hemodynamic abnormalities and improving renal function in type 1 diabetic patients of short disease duration without inducing a significant change in glycemic control. This suggests that vitamin E supplementation may provide an additional benefit in reducing the risks for developing diabetic retinopathy or nephropathy.

Diabetic eye disease.

Diabetic retinopathy accounts for most visual loss in the United States among working-age individuals. With appropriate detection, evaluation, and treatment, the risk for severe visual loss from this condition is dramatically reduced. This article details the natural history, pathophysiology, complications, grading, evaluation, and treatment for patients with diabetic retinopathy and discusses potential novel treatment modalities currently under investigation.