Vascular endothelial growth factor plays a role in hyperpermeability of diabetic retinal vessels

Anti-VEGF therapy for the long-term management of diabetic macular edema: a treat-to-target strategy based on macular morphology

In an aging population, the prevalence and burden of diabetes mellitus, diabetic retinopathy, and vision-threatening diabetic macular edema (DME) are only expected to rise around the world. Similarly to other complications of diabetes mellitus, DME requires long-term management. This article aims to review the current challenges associated with the long-term management of DME, opportunities to improve outcomes for patients, and to develop a treat-to-target strategy based on macular morphology. At present, intravitreal anti-vascular endothelial growth factor (VEGF) therapy is the standard of care for the management of DME; however, best-achievable vision outcomes with treatment are reliant on frequent injections and close monitoring, which are difficult to maintain in current clinical practice because of the burden this imposes on patients. Achieving and maintaining good vision with treatment are the most important factors for patients with DME. Landmark trials have shown that vision gains with anti-VEGF therapy are typically accompanied by anatomical improvements (e.g., reductions in retinal thickness); therefore, multimodal imaging measures of macular morphology are often used in patients with DME to guide real-world treatment decisions. We would like to propose a hypothetical treat-to-target algorithm to guide physicians on treatment strategies for the long-term management of DME. Alternative measures of retinal fluid (e.g., persistence, stability, location) may be stronger predictors of visual acuity in DME, although further research is required to confirm whether alternate quantifiable biomarkers such as subretinal fluid and intraretinal fluid volumes can be used as a biomarker of clinical improvement. Identifying novel biomarkers and treatments that target neuroinflammation and neurodegeneration, improving patient-physician communication around treatment adherence, and using treat-to-target measures may help to ensure that the long-term benefits of treatment are realized.

Faricimab Treat-and-Extend for Diabetic Macular Edema: Two-Year Results from the Randomized Phase 3 YOSEMITE and RHINE Trials

PURPOSE

To evaluate the 2-year efficacy, durability, and safety of dual angiopoietin-2 and vascular endothelial growth factor (VEGF) A pathway inhibition with intravitreal faricimab according to a personalized treat-and-extend (T&E)-based regimen with up to every-16-week dosing in the YOSEMITE and RHINE (ClinicalTrials.gov identifiers, NCT03622580 and NCT03622593, respectively) phase 3 trials of diabetic macular edema (DME).

DESIGN

Randomized, double-masked, noninferiority phase 3 trials.

PARTICIPANTS

Adults with visual acuity loss (best-corrected visual acuity [BCVA] of 25-73 letters) due to center-involving DME.

METHODS

Patients were randomized 1:1:1 to faricimab 6.0 mg every 8 weeks, faricimab 6.0 mg T&E (previously referred to as personalized treatment interval), or aflibercept 2.0 mg every 8 weeks. The T&E up to every-16-week dosing regimen was based on central subfield thickness (CST) and BCVA change.

MAIN OUTCOME MEASURES

Included changes from baseline in BCVA and CST, number of injections, durability, absence of fluid, and safety through week 100.

RESULTS

In YOSEMITE and RHINE (n = 940 and 951, respectively), noninferior year 1 visual acuity gains were maintained through year 2; mean BCVA change from baseline at 2 years (weeks 92, 96, and 100 average) with faricimab every 8 weeks (YOSEMITE and RHINE, +10.7 letters and +10.9 letters, respectively) or T&E (+10.7 letters and +10.1 letters, respectively) were comparable with aflibercept every 8 weeks (+11.4 letters and +9.4 letters, respectively). The median number of study drug injections was lower with faricimab T&E (YOSEMITE and RHINE, 10 and 11 injections, respectively) versus faricimab every 8 weeks (15 injections) and aflibercept every 8 weeks (14 injections) across both trials during the entire study. In the faricimab T&E arms, durability was improved further during year 2, with > 60% of patients receiving every-16-week dosing and approximately 80% receiving every-12-week or longer dosing at week 96. Almost 80% of patients who achieved every-16-week dosing at week 52 maintained every-16-week dosing without an interval reduction through week 96. Mean CST reductions were greater (YOSEMITE/RHINE weeks 92/96/100 average: faricimab every 8 weeks -216.0/-202.6 µm, faricimab T&E -204.5/-197.1 µm, aflibercept every 8 weeks -196.3/-185.6 µm), and more patients achieved absence of DME (CST < 325 μm; YOSEMITE/RHINE weeks 92-100: faricimab every 8 weeks 87%-92%/88%-93%, faricimab T&E 78%-86%/85%-88%, aflibercept every 8 weeks 77%-81%/80%-84%) and absence of intraretinal fluid (YOSEMITE/RHINE weeks 92-100: faricimab every 8 weeks 59%-63%/56%-62%, faricimab T&E 43%-48%/45%-52%, aflibercept every 8 weeks 33%-38%/39%-45%) with faricimab every 8 weeks or T&E versus aflibercept every 8 weeks through year 2. Overall, faricimab was well tolerated, with a safety profile comparable with that of aflibercept.

CONCLUSIONS

Clinically meaningful visual acuity gains from baseline, anatomic improvements, and extended durability with intravitreal faricimab up to every 16 weeks were maintained through year 2. Faricimab given as a personalized T&E-based dosing regimen supports the role of dual angiopoietin-2 and VEGF-A inhibition to promote vascular stability and to provide durable efficacy for patients with DME.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

OCT-angiography based artificial intelligence-inferred fluorescein angiography for leakage detection in retina [Invited]

Optical coherence tomography angiography (OCTA) covers most functions of fluorescein angiography (FA) when imaging the retina but lacks the ability to depict vascular leakage. Based on OCTA, we developed artificial intelligence-inferred-FA (AI-FA) to delineate leakage in eyes with diabetic retinopathy (DR). Training data of 19,648 still FA images were prepared from FA-photo and videos of 43 DR eyes. AI-FA images were generated using a convolutional neural network. AI-FA images achieved a structural similarity index of 0.91 with corresponding real FA images in DR. The AI-FA generated from OCTA correctly depicted vascular occlusion and associated leakage with enough quality, enabling precise DR diagnosis and treatment planning. A combination of OCT, OCTA, and AI-FA yields more information than real FA with reduced acquisition time without risk of allergic reactions.

Effect of chlorpyrifos on VEGF gene expression

Chlorpyrifos (CPF; 0,0-diethyl 0-(3,5,6-trichloro-2-pyridinyl)-phosphorothioate), a cholinesterase inhibitor, compromised the integrity of the blood-brain barrier (BBB) when used at low concentrations during our previous experiments in vitro. To determine if BBB leakage would also occur in vivo, we used FITC-dextrans to evaluate BBB permeability in CPF-dosed mice. Results indicated BBB leakages that were evident at 2 h after treatment with 70 mg/kg CPF ip. Since vascular endothelial growth factor (VEGF), a potent vasopermeability factor, is a signaling protein that promotes the growth of new blood vessels, we investigated the possible involvement of VEGF in BBB disruption by CPF. We found that VEGF serum concentration was significantly increased at 24 h after CPF exposure. To further explore VEGF involving BBB disruption by CPF treatment, the receptor antagonist for VEGF (sFlt-1) was used for pretreatment before CPF exposure. After sFlt-1 pretreatment, gene expressions of the tight junction (TJ) proteins claudin5 and occludin were significantly downregulated at 1, 2, and 3 h, but returned to control levels at 24 h after CPF treatment. These results suggest that VEGF is involved in BBB disruption by CPF through BBB-TJs regulation.

Efficacy, Durability, and Safety of Faricimab in Patients From Asian Countries With Diabetic Macular Edema: 1-Year Subgroup Analysis of the Phase III YOSEMITE and RHINE Trials

PURPOSE

To assess the 1-year efficacy, durability, and safety of faricimab in patients with diabetic macular edema from Asian and non-Asian countries.

DESIGN

Global, multicenter, randomized, double-masked, active comparator-controlled, phase III trials.

METHODS

Subgroup analysis of patients from Asian (N=144) and non-Asian (N=1747) countries randomized to faricimab 6.0 mg every 8 weeks (Q8W), faricimab per personalized treatment interval (PTI), or aflibercept 2.0 mg Q8W in the YOSEMITE/RHINE (NCT03622580/NCT03622593) trials. Primary endpoint: best-corrected visual acuity (BCVA) changes from baseline at 1 year, averaged over weeks 48, 52, and 56.

RESULTS

Mean BCVA change from baseline at 1 year in the Asian country subgroup was similar between arms: faricimab Q8W (n=50), +10.9 (95% CI: 8.6-13.2); faricimab PTI (n=48) +10.0 (7.7-12.4) letters; aflibercept Q8W (n=46) +9.0 (6.6-11.4) letters. BCVA gains in the non-Asian country subgroup (n=582, 584, 581) were +11.3 (10.5-12.1), +11.2 (10.5-12.0), and +10.7 (9.9-11.5) letters, respectively. At 1 year, 49% of Asian country patients in the faricimab PTI arm achieved Q16W dosing (vs. 52% non-Asian) and 78% achieved ≥Q12W dosing (vs. 72% non-Asian). Anatomic improvementswere generally greater with faricimab versus aflibercept and similar between the Asian and non-Asian country subgroups. Faricimab was well tolerated, with no new safety signals.

CONCLUSIONS

Vision, durability, anatomic, and safety outcomes were generally similar between the Asian and non-Asian country subgroups, suggesting that global YOSEMITE/RHINE results may be generalized to the Asian population. These data support the benefit-risk profile of faricimab for treating Asian patients with diabetic macular edema.

Identifying Hyperreflective Foci in Diabetic Retinopathy via VEGF-Induced Local Self-Renewal of CX3CR1+ Vitreous Resident Macrophages

Intraretinal hyperreflective foci (HRF) are significant biomarkers for diabetic macular edema. However, HRF at the vitreoretinal interface (VRI) have not been examined in diabetic retinopathy (DR). A prospective observational clinical study with 162 consecutive eyes using OCT imaging showed significantly increased HRF at the VRI during DR progression (P < 0.01), which was reversed by anti-vascular endothelial growth factor (VEGF) therapy. F4/80+ macrophages increased significantly at the VRI in Kimba (vegfa+/+) or Akimba (Akita × Kimba) mice (both P < 0.01), but not in diabetic Akita (Ins2+/-) mice, indicating macrophage activation was modulated by elevated VEGF rather than the diabetic milieu. Macrophage depletion significantly reduced HRF at the VRI (P < 0.01). Furthermore, BrdU administration in Ccr2rfp/+Cx3cr1gfp/+vegfa+/- mice identified a significant contribution of M2-like tissue-resident macrophages (TRMs) at the VRI. Ki-67+ and CD11b+ cells were observed in preretinal tissues of DR patients, while exposure of vitreal macrophages to vitreous derived from PDR patients induced a significant proliferation response in vitro (P < 0.01). Taken together, the evidence suggests that VEGF drives a local proliferation of vitreous resident macrophages (VRMs) at the VRI during DR. This phenomenon helps to explain the derivation and disease-relevance of the HRF lesions observed through OCT imaging in patients.

Serine-arginine-rich protein kinase-1 inhibition for the treatment of diabetic retinopathy

Angiogenic VEGF isoforms are upregulated in diabetic retinopathy (DR), driving pathological growth and fluid leakage. Serine-arginine-rich protein kinase-1 (SRPK1) regulates VEGF splicing, and its inhibition blocks angiogenesis. We tested the hypothesis that SRPK1 is activated in diabetes, and an SRPK1 inhibitor (SPHINX31) switches VEGF splicing in DR and prevents increased vascular permeability into the retina. SRPK1 was activated by high glucose (HG), in a PKC-dependent manner, and was blocked by SPHINX31. HG induced release of SRSF1 from the nuclear speckles, which was also SRPK1 dependent, and increased retinal pigment epithelial (RPE) monolayer admittance, which was reversed by SRPK1 inhibition (P < 0.05). Diabetes increased retinal permeability and thickness after 14 days which was blocked by treatment with SPHINX31 eye drops (P < 0.0001). These results show that SRPK1 inhibition, administered as an eye drop, protected the retinal barrier from hyperglycemia-associated loss of integrity in RPE cells in vitro and in diabetic rats in vivo. A clinical trial of another SRPK1 inhibitor has now been initiated in patients with diabetic macular edema.NEW & NOTEWORTHY VEGF-A₁₆₅b splicing is induced by hyperglycemia through PKC-mediated activation of SRPK1 in RPE cells, increasing their permeability and angiogenic capability. SRPK1 inhibitors can be given as eye drops to reduce retinal permeability and edema in diabetic retinopathy.

Endostatin Inhibits Blood-Retinal Barrier Breakdown in Diabetic Rats by Increasing the Expression of ICAM-1 and VCAM-1 and Decreasing the Expression of VEGF

Objective

Endostatin has become the strongest endogenous angiogenesis inhibitor due to suppressing VEGF expression. The purpose of this study was to assess the impact of endostatin on the blood-retinal barrier (BRB) in diabetic rats.

Methods

SD rats were induced to develop diabetes by streptozotocin, and endostatin was administrated by intravitreal injection. The body weight, the level of blood glucose, the expressions of C-reactive protein (CRP), adhesion molecules intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), junction proteins (occludin, claudin-5, and zonula occluden-1), and VEGF were measured in rats' retinas of diabetes. The BRB breakdown was evaluated using Evans blue.

Results

The level of CRP and adhesion molecules (ICAM-1 and VCAM-1) was increased in retinas of diabetic rats, while endostatin significantly inhibited the upregulation of these. Diabetes increased the BRB permeability and retinal thickness. Diabetes also decreased the levels of occludin, claudin-5, and ZO-1 in retinals. These changes were inhibited by endostatin treatment. Upregulation of vascular endothelial growth factor (VEGF), transforming growth factor-β (TGF-β), and protein kinase C- (PKC-) β2 was also reversed by endostatin in retinas of diabetic rats.

Conclusions

Endostatin provides protection against diabetic retinopathy, which may involve its barrier-enhancing effects.

Prospective Clinical Trial of Intravitreal Aflibercept Treat-and-extend Regimen for Diabetic Macular Edema: 1-Year Outcomes

Purpose

To investigate the efficacy of aflibercept for the treatment of diabetic macular edema via a treat-and-extend regimen.

Methods

This prospective, single-center, open-label, interventional study involved 30 patients with a best-corrected visual acuity (BCVA) ≤0.6 and a central retinal thickness (CRT) ≥300 µm. The enrolled eyes each received a monthly intravitreal aflibercept injection until the CRT decreased below 300 µm, upon which the administration interval was extended for 1 month until the CRT once again increased to ≥300 µm. Main outcome measures were median BCVA and CRT at 6 and 12 months after initiation of treatment via last observation carried forward analysis, the median number of injections over the 12 months, and the effects on the diabetic retinopathy severity scale (DRSS) score of the patients who completed the 12-month follow-up period.

Results

Of the 30 enrolled patients, 29 and 25 respectively completed the 6- and 12-month follow-up examinations. From baseline to 6 and 12 months after treatment initiation, the median BCVA (logarithm of the minimum angle of resolution) significantly improved from 0.52 to 0.30 and 0.35, respectively, and the median CRT significantly decreased from 439.5 to 268.5 and 249.0 µm, respectively. The median number of injections over the 12-month follow-up period was 6.0. Compared to baseline, the DRSS score at 12 months was improved by 2 steps in 16% of patients; in no cases did the DRSS score worsen or improve by three steps or more.

Conclusions

When administered in a treat-and-extend regimen, aflibercept is an effective treatment option for diabetic macular edema.

Primaquine Diphosphate, a Known Antimalarial Drug, Blocks Vascular Leakage Acting Through Junction Stabilization

Endothelial barrier integrity is important for vascular homeostasis, and hyperpermeability participates in the progression of many pathological states, such as diabetic retinopathy, ischemic stroke, chronic bowel disease, and inflammatory disease. Here, using drug repositioning, we discovered that primaquine diphosphate (PD), previously known as an antimalarial drug, was a potential blocker of vascular leakage. PD inhibited the linear pattern of vascular endothelial growth factors (VEGF)-induced disruption at the cell boundaries, blocked the formation of VEGF-induced actin stress fibers, and stabilized the cortactin actin rings in endothelial cells. PD significantly reduced leakage in the Miles assay and mouse model of streptozotocin (STZ)-induced diabetic retinopathy. Targeted prediction programs and deubiquitinating enzyme activity assays identified a potential mechanism of action for PD and demonstrated that this operates via ubiquitin specific protease 1 (USP1). USP1 inhibition demonstrated a conserved barrier function by inhibiting VEGF-induced leakage in endothelial permeability assays. Taken together, these findings suggest that PD could be used as a novel drug for vascular leakage by maintaining endothelial integrity.

Therapeutic Efficacy of a Novel Acetylated Tetrapeptide in Animal Models of Age-Related Macular Degeneration

It has been shown previously that a novel tetrapeptide, Arg-Leu-Tyr-Glu (RLYE), derived from human plasminogen inhibits vascular endothelial growth factor (VEGF)-induced angiogenesis, suppresses choroidal neovascularization in mice by an inhibition of VEGF receptor-2 (VEGFR-2) specific signaling pathway. In this study, we report that a modified tetrapeptide (Ac-RLYE) showed improved anti-choroidal neovascularization (CNV) efficacy in a number of animal models of neovascular age-related macular degeneration (AMD) which include rat, rabbit, and minipig. The preventive and therapeutic in vivo efficacy of Ac-RLYE via following intravitreal administration was determined to be either similar or superior to that of ranibizumab and aflibercept. Assessment of the intraocular pharmacokinetic and toxicokinetic properties of Ac-RLYE in rabbits demonstrated that it rapidly reached the retina with minimal systemic exposure after a single intravitreal dose, and it did not accumulate in plasma during repetitive dosing (bi-weekly for 14 weeks). Our results suggested that Ac-RLYE has a great potential for an alternative therapeutics for neovascular (wet) AMD. Since the amino acids in human VEGFR-2 targeted by Ac-RLYE are conserved among the animals employed in this study, the therapeutic efficacies of Ac-RLYE evaluated in those animals are predicted to be observed in human patients suffering from retinal degenerative diseases.

Involvement of Cytokines in the Pathogenesis of Diabetic Macular Edema

Diabetic macular edema (DME) is a critical complication of diabetic retinopathy, a condition that arises from the breakdown of the blood–retinal barrier and the consequent increase in vascular permeability. Over the years, attempts have been made to treat DME by various approaches, including laser photocoagulation, steroid triamcinolone acetonide, and vitrectomy. However, treatment was unsatisfactory until research identified vascular endothelial growth factor (VEGF) as a factor in the pathogenesis of DME. Intraocular anti-VEGF agents show good efficacy in DME. Nevertheless, in some patients the condition recurs or becomes resistant to treatment, suggesting that other factors may be involved. Because inflammation and retinal hypoxia are seen in DME, research has examined the potential role of cytokines and other inflammatory mediators. In this review, we provide an overview of this research and describe feedback mechanisms that may represent a target for novel treatments.

Human plasminogen-derived N-acetyl-Arg-Leu-Tyr-Glu antagonizes VEGFR-2 to prevent blood-retinal barrier breakdown in diabetic mice

Targeting the vascular endothelial growth factor (VEGF)/its receptor-2 (VEGFR-2) system has become a mainstay of treatment for many human diseases, including retinal diseases. We examined the therapeutic effect of recently developed N-acetylated Arg-Leu-Tyr-Glu (Ac-RLYE), a human plasminogen kringle-5 domain-derived VEGFR-2 antagonists, on the pathogenesis of diabetic retinopathy. Ac-RLYE inhibited VEGF-A-mediated VEGFR-2 activation and endothelial nitric oxide synthase (eNOS)-derived NO production in the retinas of diabetic mice. In addition, Ac-RLYE prevented the disruption of adherens and tight junctions and vascular leakage by inhibiting S-nitrosylation of β-catenin and tyrosine nitration of p190RhoGAP in the retinal vasculature of diabetic mice. Peptide treatment preserved the pericyte coverage of retinal capillaries by upregulating angiopoietin-2. These results suggest that Ac-RLYE potentially prevents blood-retinal barrier breakdown and vascular leakage by antagonizing VEGFR-2; Ac-RLYE can be used as a potential therapeutic drug for the treatment of diabetic retinopathy.

The randomized ZIPANGU trial of ranibizumab and adjunct laser for macular edema following branch retinal vein occlusion in treatment-naïve patients

The ZIPANGU study assessed the efficacy and safety of ranibizumab as a one loading dose + pro re nata (one + PRN) regimen with/without focal/grid laser among treatment-naïve patients suffering from macular edema (ME) following branch retinal vein occlusion (BRVO). ZIPANGU was a phase IV, prospective, randomized, open-label, active-controlled, 12-month, two-arm, multicenter study. Treatment-naïve patients with visual impairment (19–73 letters) caused by ME, defined as central subfield thickness (CSFT) > 300 µm, due to BRVO were randomly assigned to ranibizumab monotherapy (n = 29) or combination therapy (ranibizumab + focal/grid short-pulse laser, n = 30). The primary endpoint was the number of ranibizumab injections. Secondary endpoints were mean changes in best-corrected visual acuity (BCVA) and CSFT, and safety. There were no statistically significant differences in the mean number of ranibizumab injections between monotherapy (4.3 injections) vs. combination (4.1 injections) therapy, or in CSFT. BCVA improvement in the monotherapy arm (22.0 letters) was better than the combination therapy arm (15.0 letters) (p = 0.035). Overall, both regimens appeared to be safe and well tolerated. One + PRN ranibizumab is safe and efficacious in treatment-naïve patients with ME secondary to BRVO. A conjunctive laser treatment did not lead to better functional outcomes or fewer ranibizumab injections.

Reduced Expression of VEGF-A in Human Retinal Pigment Epithelial Cells and Human Muller Cells Following CRISPR-Cas9 Ribonucleoprotein-Mediated Gene Disruption

Purpose

To evaluate the effects of vascular endothelial growth factor-A (VEGF-A) gene editing in human retinal pigment epithelial (RPE) cells and human Muller cells, which are the main VEGF-A producing cells in the eye.

Methods

CRISPR-Cas9 ribonucleoprotein was used to target exon 1 in VEGF-A gene. Lipofectamine CRISPRMAX was used as a vehicle. In vitro gene editing efficiency was assessed on oligonucleotides and genomic DNAs. Sanger sequencing was performed to detect indels. VEGF-A messenger RNA and protein expressions were assessed using quantitative polymerase chain reaction and enzyme-linked immunosorbent assay.

Results

In vitro cleavage assay on a 60-nucleotide DNA duplex showed 88% cleavage of the precursor. The cleavage efficiency was 40% in RPE cells and 32% in Muller cells. Sanger sequencing in the CRISPR-Cas9 treated RPE and Muller cells showed indels at the predicted cut site in both cells. After the VEGF-A gene disruption, VEGF-A protein levels decreased 43% in RPE cells (P < 0.0001) and 38% in Muller cells (P < 0.0001).

Conclusions

CRISPR-Cas9–mediated gene disruption resulted in a significant decrease in the VEGF-A gene protein expression in human RPE and Muller cells. CRISPR-Cas9 ribonucleoprotein may allow simultaneous targeting of multiple VEGF-A producing cells.

Translational Relevance

VEGF-A gene disruption using CRISPR-Cas9 ribonucleoprotein has a potential in treating retinal vascular diseases.

[Effect of acute insulin therapy on the concentration of vascular endothelial growth factor A (VEGF-A) in the intraocular fluid in an experiment]

PURPOSE

To study the effect of insulin therapy on the concentration of vascular endothelial growth factor A (VEGF-A) in the intraocular fluid of rats with alloxan model of diabetes mellitus.

MATERIAL AND METHODS

The experiment was conducted on 80 mongrel rats. In 65 rats, the alloxan model of diabetes mellitus was simulated by a single intraperitoneal injection of 100 mg/kg alloxan hydrate saluted in 0.4 ml of citrate buffer. 72 hours after intraperitoneal administration of alloxan monohydrate, these animals were divided into 2 groups. The main group (group 1) consisted of animals with alloxan model of diabetes mellitus, who started daily single intraperitoneal administration of prolonged-acting insulin at a therapeutic dose of 0.9 U/kg Body weight. The comparison group (group 2) consisted of animals with alloxan model of diabetes mellitus who did not receive specific therapy. 15 healthy rats constituted the control group (group 3). Experimental animals were removed from the study on day 31 of insulin therapy. The concentration of VEGF-A was determined in 80-90 μl of intraocular fluid collected from both eyes of each animal.

RESULTS

In the main group, the median of VEGF-A concentration [25th; 75th percentiles] in the intraocular fluid was 140 [136; 210] pg/ml, which is 1.94 times higher than in the comparison group (72 [58; 86] pg/ml) and 1.84 times higher than in the control group (76 [62.5; 88] pg/ml). The concentration of VEGF-A in the intraocular fluid in the main group was statistically significantly higher, as compared with the comparison group (p_m-u<0.0004), and compared with the control group (p_m-u=0.0045). The comparison group had no statistically significant differences when compared with the control group (p_m-u=0.9979).

CONCLUSION

Insulin therapy for 31 days increases the concentration of VEGF-A in the intraocular fluid of rats with alloxan model of diabetes mellitus.

Serous retinal detachment accompanied by pachychoroid in hypotony maculopathy after trabeculectomy for diabetic neovascular glaucoma

Purpose

Two diabetic case reports of serous retinal detachment (SRD) accompanied by pachychoroid in hypotony maculopathy after trabeculectomy for neovascular glaucoma (NVG).

Observations

Case 1: A 66-year-old female with stage 3 NVG and decreased vision acuity in the left eye. After trabeculectomy, postoperative laser suture lysis (LSL) resulted in development of hypotony maculopathy, followed by pachychoroid and SRD. Injection of C3F8 gas in the anterior chamber was unsuccessful and transconjunctival scleral re-suturing was performed. Intraocular pressure (IOP) consequently increased and SRD improved. Case 2: A 60-year-old man with stage 2 NVG and decreased vision acuity in the right eye. Trabeculectomy was uneventful, but postoperative LSL also resulted in development of hypotony maculopathy followed by pachychroid and SRD. Intravitreal bevacizumab injection had no effect and transconjunctival flap re-suturing was performed. IOP consequently increased and SRD improved.

Conclusions

SRD accompanied by pachychoroid was observed in hypotony maculopathy in diabetic cases. VEGF-independent exudative change in hypotony maculopathy may be due to hydrostatic pressure elevation in choroidal blood vessels based on Starling's hypothesis with the consequent breakdown of retinal pigment epithelium barrier in diabetic patients.

Activation of Notch signaling by soluble Dll4 decreases vascular permeability via a cAMP/PKA-dependent pathway

The Notch ligand delta-like ligand 4 (Dll4), upregulated by VEGF, is a key regulator of vessel morphogenesis and function, controlling tip and stalk cell selection during sprouting angiogenesis. Inhibition of Dll4 results in hypersprouting, nonfunctional, poorly perfused vessels, suggesting a role for Dll4 in the formation of mature, reactive, functional vessels, with low permeability and able to restrict fluid and solute exchange. We tested the hypothesis that Dll4 controls transvascular fluid exchange. A recombinant protein expressing only the extracellular portion of Dll4 [soluble Dll4 (sDll4)] induced Notch signaling in endothelial cells (ECs), resulting in increased expression of vascular-endothelial cadherin, but not the tight junctional protein zonula occludens 1, at intercellular junctions. sDll4 decreased the permeability of FITC-labeled albumin across EC monolayers, and this effect was abrogated by coculture with the γ-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester. One of the known molecular effectors responsible for strengthening EC-EC contacts is PKA, so we tested the effect of modulation of PKA on the sDll4-mediated reduction of permeability. Inhibition of PKA reversed the sDll4-mediated reduction in permeability and reduced expression of the Notch target gene Hey1. Knockdown of PKA reduced sDLL4-mediated vascular-endothelial cadherin junctional expression. sDll4 also caused a significant decrease in the hydraulic conductivity of rat mesenteric microvessels in vivo. This reduction was abolished upon coperfusion with the PKA inhibitor H89 dihydrochloride. These results indicate that Dll4 signaling through Notch activation acts through a cAMP/PKA pathway upon intercellular adherens junctions, but not tight junctions, to regulate endothelial barrier function. NEW & NOTEWORTHY Notch signaling reduces vascular permeability through stimulation of cAMP-dependent protein kinase A.

CHANGES IN PLASMA VASCULAR ENDOTHELIAL GROWTH FACTOR LEVEL AFTER INTRAVITREAL INJECTION OF BEVACIZUMAB, AFLIBERCEPT, OR RANIBIZUMAB FOR DIABETIC MACULAR EDEMA

PURPOSE

The aim of this study was to investigate the changes in plasma vascular endothelial growth factor (VEGF) level depending on the severity of diabetic retinopathy (DR) or diabetic macular edema (DME) and after intravitreal injection of bevacizumab, aflibercept, or ranibizumab for treatment of DME.

METHODS

Plasma VEGF level was evaluated in 72 patients with DR and changes were measured in 42 patients with DME receiving intravitreal injections of bevacizumab, aflibercept, or ranibizumab at the initial injection.

RESULTS

There were no correlations between plasma VEGF level and the severity of DME or DR. Baseline plasma VEGF level (51.9 pg/mL) was significantly reduced using bevacizumab to 11.9 pg/mL after 1 week and 24.1 pg/mL after 4 weeks (P = 0.0130 and 0.0201, respectively). In aflibercept-treated eyes, plasma VEGF decreased from 52.2 pg/mL to 7.8 pg/mL and 12.6 pg/mL, respectively, at the same time points (both P < 0.001). No such reductions were observed in patients receiving ranibizumab.

CONCLUSION

Baseline plasma VEGF level showed no correlations with DR or DME severity, whereas intravitreal injection of bevacizumab or aflibercept significantly reduced plasma VEGF for up to 4 weeks and ranibizumab produced no such effects. Changes in plasma VEGF level seemed not to be critical in progression or treatment of DME and DR.

THE RELATIONSHIP BETWEEN FOVEAL AVASCULAR ZONE AREA, VESSEL DENSITY, AND CYSTOID CHANGES IN DIABETIC RETINOPATHY: AN OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY STUDY

PURPOSE

To measure the foveal avascular zone (FAZ) areas and vessel densities of patients with diabetic retinopathy and to study their relationship with diabetic cystoid changes and retinal thickness.

METHODS

Prospective case series of 51 eyes of 31 patients with diabetic retinopathy. The eyes were grouped based on the presence or absence of cystoid edema and evaluated using optical coherence tomography angiography. The FAZ areas and vessel density were compared.

RESULTS

The FAZ area at the superficial capillary plexus level was equal between the eyes with and without cystoid edema. Vessel density did not differ as well. There was no correlation with retinal thickness. In eyes with cystoid changes, FAZ area changes at the deep capillary plexus level were difficult to interpret.

CONCLUSION

The FAZ area and vessel density at the superficial capillary plexus level are reproducible and independent of the presence of cystoid edema.

Vitreous IL-8 and VEGF levels in diabetic macular edema with or without subretinal fluid

PURPOSE

To determine the cytokine levels in vitreous samples of diabetic macular edema (DME) patients in comparison with nondiabetic patients, and to evaluate the effect of subretinal fluid on the cytokine levels of vitreous samples.

METHODS

In this prospective case-control study, 11 eyes of 11 patients with DME and subretinal fluid, 11 eyes of 11 patients with DME without subretinal fluid, and 14 eyes of 14 patients who had undergone vitreoretinal surgery for the epiretinal membrane or a macular hole (control group) were evaluated. The blood glycated hemoglobin (HbA1c) level, vitreous vascular endothelial growth factor (VEGF), and interleukin-8 (IL-8) levels were determined.

RESULTS

The vitreous VEGF level of patients in DME groups was significantly higher than the control group (p < 0.001) without significant difference between DME patients with and without subretinal fluid (p = 0.796). The vitreous IL-8 level of DME patients with subretinal fluid was significantly higher than both control (p = 0.002) and DME without subretinal fluid groups (p = 0.019). The blood HbA1c level was significantly higher in DME group with subretinal fluid than those without subretinal fluid (8.7 ± 1.32 and 7.1 ± 1.13%, respectively, p = 0.010). The only significant correlation was between vitreous VEGF level and blood HbA1c level in DME patients without subretinal fluid (r = 0.813, p = 0.002).

CONCLUSIONS

IL-8 level in vitreous samples was higher in DME patients with subretinal fluid than those without subretinal fluid, suggesting that inflammation is an important factor in the progression of DME leading to the subretinal fluid formation in diabetic patients.

Management of diabetic macular edema in Japan: a review and expert opinion

Diabetic retinopathy is a frequent cause of visual impairment in working-age adults (≥ 30 years) and in Japan is most commonly observed in those aged 50-69 years. Diabetic macular edema (DME) is one of the main causes of vision disturbance in diabetic retinopathy, which is a clinically significant microvascular complication of diabetes. Anti-vascular endothelial growth factor (VEGF) therapy is becoming the mainstay of treatment for DME. However, to achieve sustained long-term improvement in visual acuity, conventional laser photocoagulation, vitrectomy and steroid therapy are also expected to play a role in the treatment of DME. This review summarizes the epidemiology and pathology of diabetic retinopathy and DME, evaluates the findings regarding the diagnosis and treatment of DME, and underscores the importance of systemic management of the disease in the context of the current health care situation in Japan. Finally, the unmet needs of patients with DME and prospects for research are discussed. The weight of evidence suggests that it is important to establish a multipronged treatment strategy centered on anti-VEGF therapy.

EGHB010, a Standardized Extract of Paeoniae Radix and Glycyrrhizae Radix, Inhibits VEGF-Induced Tube Formation In Vitro and Retinal Vascular Leakage and Choroidal Neovascularization In Vivo

EGHB010 is a hot water extract of the rhizome mixture of Paeonia lactiflora Pallas and Glycyrrhiza uralensis Fisch. Choroidal neovascularization (CNV) and vascular leakage are the common pathophysiologies of age-related macular degeneration. In this study, we aimed to evaluate the effect of EGHB010 on retinal vascular leakage and laser-induced CNV in a rat model. Vascular endothelial growth factor- (VEGF-) induced tube formation was assayed in human retinal microvascular endothelial cells. Intravitreal VEGF-induced blood-retinal barrier breakdown was assayed in Sprague-Dawley rats. Experimental CNV was induced by laser photocoagulation in Brown Norway rats. EGHB010 (50 and 100 mg/kg/day) was administered orally for 10 days after laser photocoagulation. Choroidal flat mounts were prepared to measure the lesion size of CNV. Incubation of retinal vascular endothelial cells with EGHB010 (12.5 and 25 μg/mL) resulted in the inhibition of VEGF-induced tube formation in a dose-dependent manner. VEGF-mediated retinal vascular leakage was blocked by the oral administration of EGHB010. The CNV area was significantly lower in EGHB010-treated rats than in vehicle-treated rats. These results suggest that EGHB010 is a potent antiangiogenic agent. Thus, the oral administration of EGHB010 may have a beneficial effect in the treatment of vascular leakage and CNV in patients with age-related macular degeneration.

INCREASED SERUM LEVELS OF UREA AND CREATININE ARE SURROGATE MARKERS FOR DISRUPTION OF RETINAL PHOTORECEPTOR EXTERNAL LIMITING MEMBRANE AND INNER SEGMENT ELLIPSOID ZONE IN TYPE 2 DIABETES MELLITUS

PURPOSE

To evaluate the role of serum urea and creatinine as surrogate markers for disruption of retinal photoreceptor external limiting membrane (ELM) and inner segment ellipsoid zone (EZ) in Type 2 diabetic retinopathy (DR) using spectral-domain optical coherence tomography, for the first time.

METHODS

One hundred and seventeen consecutive cases of Type 2 diabetes mellitus (diabetes without retinopathy [No DR; n = 39], nonproliferative diabetic retinopathy [NPDR; n = 39], proliferative diabetic retinopathy [PDR; n = 39]) and 40 healthy control subjects were included. Serum levels of urea and creatinine were assessed using standard protocol. Spectral-domain optical coherence tomography was used to grade the disruption of ELM and EZ as follows: Grade 0, no disruption of ELM and EZ; Grade 1, ELM disrupted, EZ intact; Grade 2, ELM and EZ disrupted. Data were analyzed statistically.

RESULTS

Increase in serum levels of urea (F = 22.93) and creatinine (F = 15.82) and increased grades of disruption of ELM and EZ (γ = 116.3) were observed with increased severity of DR (P < 0.001). Increase in serum levels of urea (F = 10.45) and creatinine (F = 6.89) was observed with increased grades of disruption of ELM and EZ (P = 0.001).

CONCLUSION

Serum levels of urea and creatinine are surrogate markers for disruption of retinal photoreceptor ELM and EZ on spectral-domain optical coherence tomography in DR.

Treatment of Leukoencephalopathy With Calcifications and Cysts With Bevacizumab

BACKGROUND

Leukoencephalopathy with calcifications and cysts is a rare, autosomal recessive cerebral microangiopathy that causes progressive white matter disease, calcifications, and cysts within the brain. It is typically associated with slowly progressive psychomotor regression, seizures, and movement disorders. Although leukoencephalopathy with calcifications and cysts affects only the central nervous system, it demonstrates remarkable neuropathologic and radiologic overlap with Coats plus, a disorder of small vessels of the brain, eyes, gastrointestinal tract, and bone. Coats disease without extraocular involvement, a genetically distinct disorder from Coats plus, is characterized by retinal telangiectasias and exudative retinopathy, accompanied by neovascularization. Inhibition of vascular endothelial growth factor (VEGF) signaling with the monoclonal anti-VEGF antibody bevacizumab can improve retinal edema and exudates in Coats disease. Given these observations, we reasoned that VEGF inhibition might also be effective in treating leukoencephalopathy with calcifications and cysts and Coats plus, neither of which has any known therapy.

METHODS

We treated an 18-year-old man with leukoencephalopathy with calcifications and cysts using biweekly infusions of the VEGF inhibitor bevacizumab for more than one year and performed clinical examinations and brain imaging at three month intervals.

RESULTS

After treatment for more than one year, the patient showed improved bradykinesia and range of motion, and brain magnetic resonance imaging demonstrated a marked reduction in cyst volume and white matter lesions.

CONCLUSIONS

Further studies in a cohort of patients are warranted to investigate the efficacy of VEGF inhibition as a treatment for leukoencephalopathy with calcifications and cysts.

Application of multiplex immunoassay technology to investigations of ocular disease

Eye-derived fluids, including tears, aqueous humour and vitreous humour often contain molecular signatures of ocular disease states. These signatures can be composed of cytokines, chemokines, growth factors, proteases and soluble receptors. However, the small quantities (<10 µl) of these fluids severely limit the detection of these proteins by traditional enzyme-linked immunosorbent assay or Western blot. To maximise the amount of information generated from the analysis of these specimens, many researchers have employed multiplex immunoassay technologies for profiling the expression or modification of multiple proteins from minute sample volumes.

Cost-utility of ranibizumab versus aflibercept for treating Greek patients with visual impairment due to diabetic macular edema

Background

To conduct a cost-utility analysis of ranibizumab versus aflibercept for the treatment of patients with visual impairment due to diabetic macular edema (DME) in the Greek setting.

Methods

A Markov model was adapted to compare the use of ranibizumab 0.5 mg (pro re nata-PRN and treat and extend-T&E) to aflibercept 2 mg (every 8 weeks after five initial doses) in DME. Patients transitioned at a 3-month cycle among nine specified health states (including death) over a lifetime horizon. Transition probabilities, utilities, as well as DME-related mortality were extracted from relevant clinical trials, a network meta-analysis and other published studies. The analysis was conducted from payer perspective and as such only costs reimbursed by the payer were considered (year 2014). The incremental cost per quality-adjusted life year (QALY) gained and the net monetary benefit was the main outcome measures.

Results

Τhe use of PRN and T&E ranibizumab regimens were shown to be cost saving comparing to aflibercept (by €2824 and €22, respectively), and more beneficial in terms of QALYs gained (+0.05) and time without visual impairment (0.031 and 0.034 years), thereby dominating aflibercept. Moreover, ranibizumab used as PRN or T&E resulted in a net monetary benefit of €3984 and €1278, respectively.

Conclusions

Both PRN and T&E ranibizumab regimens were more beneficial and less costly compared to aflibercept for the management of DME. Hence, ranibizumab seems to be a dominant option for the treatment of visual impairment due to DME in the Greek setting.

Electronic supplementary material

The online version of this article (doi:10.1186/s12962-016-0056-1) contains supplementary material, which is available to authorized users.

Protective Effects of Melatonin on Retinal Inflammation and Oxidative Stress in Experimental Diabetic Retinopathy

Oxidative stress and inflammation are important pathogenic factors contributing to the etiology of diabetic retinopathy (DR). Melatonin is an endogenous hormone that exhibits a variety of biological effects including antioxidant and anti-inflammatory functions. The goals of this study were to determine whether melatonin could ameliorate retinal injury and to explore the potential mechanisms. Diabetes was induced by a single intraperitoneal (i.p.) injection of STZ (60 mg/kg) in Sprague-Dawley rats. Melatonin (10 mg kg(-1) daily, i.p.) was administered from the induction of diabetes and continued for up to 12 weeks, after which the animals were sacrificed and retinal samples were collected. The retina of diabetic rats showed depletion of glutathione and downregulation of glutamate cysteine ligase (GCL). Melatonin significantly upregulated GCL by retaining Nrf2 in the nucleus and stimulating Akt phosphorylation. The production of proinflammatory cytokines and proteins, including interleukin 1β, TNF-α, and inducible nitric oxide synthase (iNOS), was inhibited by melatonin through the NF-κB pathway. At 12 weeks, melatonin prevented the significant decrease in the ERG a- and b-wave amplitudes under the diabetic condition. Our results suggest potent protective functions of melatonin in diabetic retinopathy. In addition to being a direct antioxidant, melatonin can exert receptor-mediated signaling effects to attenuate inflammation and oxidative stress of the retina.

Combination of Angiotensin Converting Enzyme Insertion/Deletion (I/D) (rs4646994) and VEGF Polymorphism (+405G/C; rs2010963) Synergistically Associated With the Development, of Albuminuria in Iranian Patients With Type 2 Diabetes

BACKGROUND

Angiotensin-converting enzyme (ACE) insertion/deletion (I/D) and vascular endothelial growth factor (VEGF) polymorphisms have been shown to associate with diabetic nephropathy (DN).

OBJECTIVES

We examined the hypothesis that ACE-D and VEGF-G alleles act synergistically in association with DN, in patients with type 2 diabetes mellitus (T2DM).

PATIENTS AND METHODS

The VEGF (rs2010963) and ACE (rs4646994) genotypes were detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 490 T2DM patients. Diabetic patients were classified as T2DM patients with and without albuminuria (control). The PCR and RFLP were used to detect the VEGF and ACE alleles.

RESULTS

A total of 255 consecutive patients with T2DM and microalbuminuria (Group A) and 235 patients with T2DM and normoalbuminuria (Group B) were included in the study. In univariate analysis, the groups were statistically similar for all variables, except for glycated hemoglobin (HbA1c) (P = 0.034), and the frequency of ACE (P = 0.015) and VEGF (P = 0.006) genotypes. Our study showed that the VEGF-G and ACE-D alleles are independently associated with the development of nephropathy. According to our data, the combination of these two risk factors had a significant synergistic effect on the risk of microalbuminuria development.

CONCLUSIONS

Our study indicated that ACE-D and VEGF-G alleles can be an independent risk factor for microalbominuria in T2DM patients.

Ocular complications of diabetes mellitus

Diabetes mellitus (DM) is a important health problem that induces ernestful complications and it causes significant morbidity owing to specific microvascular complications such as, retinopathy, nephropathy and neuropathy, and macrovascular complications such as, ischaemic heart disease, and peripheral vasculopathy. It can affect children, young people and adults and is becoming more common. Ocular complications associated with DM are progressive and rapidly becoming the world's most significant cause of morbidity and are preventable with early detection and timely treatment. This review provides an overview of five main ocular complications associated with DM, diabetic retinopathy and papillopathy, cataract, glaucoma, and ocular surface diseases.

Vaccinium myrtillus extract prevents or delays the onset of diabetes--induced blood-retinal barrier breakdown

Many dietary supplements have been sold through advertising their large number of beneficial effects. The aim of this study was to determine whether bilberries (Vaccinium myrtillus) help to prevent diabetes-induced retinal vascular dysfunction in vivo. V. myrtillus extract (VME; 100 mg/kg) was orally administered to streptozotocin-induced diabetic rats for 6 weeks. All diabetic rats exhibited hyperglycemia, and VME did not affect the blood glucose levels and body weight during the experiments. In the fluorescein-dextran angiography, the fluorescein leakage was significantly reduced in diabetic rats treated with VME. VME treatment also decreased markers of diabetic retinopathy, such as retinal vascular endothelial growth factor (VEGF) expression and degradation of zonula occludens-1, occludin and claudin-5 in diabetic rats. In conclusion, VME may prevent or delay the onset of early diabetic retinopathy. These findings have important implications for prevention of diabetic retinopathy using a dietary bilberry supplement.

En Face Swept-Source Optical Coherence Tomography Detecting Thinning of Inner Retinal Layers as an Indicator of Capillary Nonperfusion

Purpose

To report en face swept-source optical coherence tomography (SS-OCT) as a noninvasive detection modality for regions of retinal layer thinning that are potential indicators of retinal nonperfusion areas (NPAs) in patients with branch retinal vein occlusion (BRVO).

Methods

Thirty-one eyes of 46 patients with BRVO showing a definite retinal NPA larger than 1 disc in diameter within the vascular arcades were included in this study. We calculated the overlapping correspondence ratio between presumed NPA, which appeared as a dark area in en face SS-OCT, and definite NPA in corresponding fluorescein angiography (FA) images. The correlation between brightness in en face SS-OCT images and corresponding ganglion cell complex (GCC) thickness determined by SD-OCT GCC maps was evaluated as well.

Results

Measured NPA size in FA and presumed NPA size in en face SS-OCT showed strong correlation (r = 0.746, p<0.001) and colocalization. Reliable agreement between the 2 methods was confirmed by size comparisons (p = 0.11), with an overlapping correspondence ratio of 0.73.

Conclusions

The results suggest that en face SS-OCT is a noninvasive and relatively reliable method for delineating retinal thinning as an indicator of NPAs in eyes with BRVO. Because SS-OCT can be performed without mydriasis, this procedure may be an option for evaluating NPAs on a screening basis and during follow-up to reduce the number of FA examinations that carry very rare, but potentially fatal, allergic side effects.

Correlation between diabetic retinopathy severity and elevated skin autofluorescence as a marker of advanced glycation end-product accumulation in type 2 diabetic patients

AIMS

We evaluated skin autofluorescence (AF) as a marker of tissue advanced glycation end-product (AGE) accumulation and examined whether it was related to the prevalence and severity of diabetic retinopathy (DR) and of diabetic macular edema (DME) in patients with type 2 diabetes mellitus (DM).

METHODS

This study included 138 type 2 DM patients consisting of 31 patients with proliferative DR, 71 patients with non-proliferative DR, and 36 patients without retinopathy, in addition to 111 non-DM control subjects. At the time of skin AF and HbA1c measurement, self-assessed duration of DM was also determined. DR and DME stages were classified according to international guidelines.

RESULTS

Skin AF was significantly increased in patients with DM as compared with non-DM controls. Furthermore, skin AF was correlated with the severity of DR, whereas single measurement of HbA1c and self-assessed DM duration were not. None of these 3 factors showed a correlation with DME prevalence or severity.

CONCLUSIONS

Skin AF levels, which can be measured non-invasively on a screening basis without skin biopsy or blood sampling, have a greater predictive ability for the presence and severity of DR than single measurement of HbA1c or self-assessed DM duration in patients with type 2 DM.

Multicolor pattern scan laser for diabetic retinopathy with cataract

AIM

To evaluate the ability of various laser wavelengths in delivering sufficient burns to the retina in eyes with cataract using a new multicolor pattern scan laser with green (532 nm), yellow (577 nm), and red (647 nm) lasers.

METHODS

The relationship between the Emery-Little (EL) degree of cataract severity and the laser wavelength required to deliver adequate burns was investigated in 102 diabetic eyes. Treatment time, total number of laser shots, and intra-operative pain were assessed as well.

RESULTS

All EL-1 grade eyes and 50% of EL-2 eyes were successfully treated with the green laser, while 50% of EL-2 eyes, 96% of EL-3 eyes, and 50% of EL-4 eyes required the yellow laser. The red laser was effective in the remaining 4% of EL-3 and 50% of EL-4 eyes.

CONCLUSION

Longer wavelength lasers are more effective in delivering laser burns through cataract when we use a multicolor pattern scan laser system.

Extract of Litsea japonica ameliorates blood-retinal barrier breakdown in db/db mice

Loss of blood-retinal barrier (BRB) properties is an important feature in the pathology of diabetic retinopathy. Endothelium integrity is important for the normal vascular function. Litsea japonica (Thunb.) Jussieu is a Korean native plant that is consumed as a vegetable food. In this study, we evaluated the ability of an ethanol extract of L. japonica to prevent retinal vascular leakages in db/db mice, which is an animal model of type II diabetes. L. japonica extracts (LJE, 100 and 250 mg/kg) were administered once a day, orally, for 12 weeks. Vehicle-treated db/db mice exhibited hyperglycemia and retinal vascular leakage. LJE treatment blocked diabetes-induced BRB breakdown and decreased retinal VEGF expression in db/db mice. LJE also inhibited the degradation of occludin, which is an important tight junction protein. These findings support the potential therapeutic usefulness of L. japonica for retinal vascular permeability diseases.

Enhanced permeability responses to inflammation in streptozotocin-induced diabetic rat venules: Rho-mediated alterations of actin cytoskeleton and VE-cadherin

Diabetes is a progressive disease that often leads to microvascular complications. This study investigates the impact of diabetes on microvessel permeability under basal and inflammatory conditions. Streptozotocin-induced diabetic rats were used to mimic type 1 diabetes. Parallel experiments were conducted in intact mesenteric venules in normal rats and diabetic rats experiencing hyperglycemia for 2-3 wk. Microvessel permeability was determined by measuring hydraulic conductivity (Lp). The correlated changes in endothelial intracellular Ca(2+) concentration ([Ca(2+)]i), adherens junctions, and cytoskeleton F-actin were examined with fluorescence imaging. Diabetic vessels showed moderately increased basal Lp, but upon platelet-activating factor (PAF) exposure, these vessels showed an ~10-fold higher Lp increase than the normal vessels. Concomitantly, we observed higher increases in endothelial [Ca(2+)]i, enhanced stress fiber formation, vascular endothelial-cadherin separation, and larger gap formation between endothelial cells than those occurring in normal vessels. PAF receptor staining showed no significant difference between normal and diabetic vessels. The application of Rho kinase inhibitor Y27632 did not affect PAF-induced increases in endothelial [Ca(2+)]i but significantly reduced PAF-induced Lp increases by 90% in diabetic vessels. The application of both Y27632 and nitric oxide (NO) synthase inhibitor attenuated PAF-induced Lp increases more than using one inhibitor alone. Our studies indicate that diabetic conditions prime endothelial cells into a phenotype with increased susceptibility to inflammation without altering receptor expression and that the increased Rho activation and NO production play important roles in exaggerated permeability increases when diabetic vessels were exposed to inflammatory mediators, which may account for the exacerbated vascular dysfunction when diabetic patients are exposed to additional inflammation.

Diabetes-induced superoxide anion and breakdown of the blood-retinal barrier: role of the VEGF/uPAR pathway

Diabetes-induced breakdown of the blood-retinal barrier (BRB) has been linked to hyperglycemia-induced expression of vascular endothelial growth factor (VEGF) and is likely mediated by an increase in oxidative stress. We have shown that VEGF increases permeability of retinal endothelial cells (REC) by inducing expression of urokinase plasminogen activator receptor (uPAR). The purpose of this study was to define the role of superoxide anion in VEGF/uPAR expression and BRB breakdown in diabetes. Studies were performed in streptozotocin diabetic rats and mice and high glucose (HG) treated REC. The superoxide dismutase (SOD) mimetic tempol blocked diabetes-induced permeability and uPAR expression in rats and the cell permeable SOD inhibited HG-induced expression of uPAR and VEGF in REC. Inhibiting VEGFR blocked HG-induced expression of VEGF and uPAR and GSK-3β phosphorylation in REC. HG caused β-catenin translocation from the plasma membrane into the cytosol and nucleus. Treatment with HG-conditioned media increased REC paracellular permeability that was blocked by anti-uPA or anti-uPAR antibodies. Moreover, deletion of uPAR blocked diabetes-induced BRB breakdown and activation of MMP-9 in mice. Together, these data indicate that diabetes-induced oxidative stress triggers BRB breakdown by a mechanism involving uPAR expression through VEGF-induced activation of the GSK3β/β-catenin signaling pathway.

Rk1, a ginsenoside, is a new blocker of vascular leakage acting through actin structure remodeling

Endothelial barrier integrity is essential for vascular homeostasis and increased vascular permeability and has been implicated in many pathological processes, including diabetic retinopathy. Here, we investigated the effect of Rk1, a ginsenoside extracted from sun ginseng, on regulation of endothelial barrier function. In human retinal endothelial cells, Rk1 strongly inhibited permeability induced by VEGF, advanced glycation end-product, thrombin, or histamine. Furthermore, Rk1 significantly reduced the vessel leakiness of retina in a diabetic mouse model. This anti-permeability activity of Rk1 is correlated with enhanced stability and positioning of tight junction proteins at the boundary between cells. Signaling experiments revealed that Rk1 induces phosphorylation of myosin light chain and cortactin, which are critical regulators for the formation of the cortical actin ring structure and endothelial barrier. These findings raise the possibility that ginsenoside Rk1 could be exploited as a novel prototype compound for the prevention of human diseases that are characterized by vascular leakage.

Antiangiogenic therapy for ischemic retinopathies

Neovascularization is a common pathological process in various retinal vascular disorders including diabetic retinopathy (DR), age-related macular degeneration (AMD) and retinal vein occlusion (RVO). The development of neovascular vessels may lead to complications such as vitreous hemorrhage, fibrovascular tissue formation, and traction retinal detachments. Ultimately, irreversible vision loss may result. Various proangiogenic factors are involved in these complex processes. Different antiangiogenic drugs have been formulated in an attempt treat these vascular disorders. One factor that plays a major role in the development of retinal neovascularization is vascular endothelial growth factor (VEGF). Anti-VEGF agents are currently FDA approved for the treatment of AMD and RVO. They are also extensively used as an off-label treatment for diabetic macular edema (DME), proliferative DR, and neovascular glaucoma. However, at this time, the long-term safety of chronic VEGF inhibition has not been extensively evaluated. A large and rapidly expanding body of research on angiogenesis is being conducted at multiple centers across the globe to determine the exact contributions and interactions among a variety of angiogenic factors in an effort to determine the therapeutic potential of antiangiogenic agent in the treatment of a variety of retinal diseases.

Treadmill exercise inhibits apoptotic neuronal cell death with suppressed vascular endothelial growth factor expression in the retinas of the diabetic rats

Diabetic retinopathy is one of the most important microvascular complications in diabetes, and it is the major cause of visual loss. Physical exercise is known to ameliorate the symptoms of metabolic syndromes such as diabetic mellitus. In the present study, we investigated the effects of treadmill exercise on vascular endothelial growth factor (VEGF) expression and apoptotic cell death in the retinas of streptozotocin (STZ)-induced diabetic rats. The male Sprague-Dawley rats were randomly divided into three groups (n = 10 in each group): control group, STZ-induce diabetes group, STZ-induced diabetes and treadmill exercise group. To induce diabetes in the experimental animals, a single intraperitioneal injection of STZ (50 mg/kg) was given to each animal. The rats in the exercise group were forced to run on a motorized treadmill for 30 min once a day during 1 week starting 6 weeks after STZ injection. In the present results, VEGF expression in the retinas was increased by induction of diabetes. The numbers of caspase-3-positive and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive cells in the retinas were also enhanced by induction of diabetes. Treadmill exercise significantly decreased VEGF expression and suppressed the number of TUNEL-positive and caspase-3-positive cells in the retinas of diabetic rats. In the present study, we have shown that treadmill exercise might alleviate the progression of diabetic retinopathy through suppressing VEGF expression and apoptotic cell death in the retinas of the diabetic rats.

Advanced glycation end products and diabetic retinopathy

Studies have established hyperglycemia as the most important factor in the progress of vascular complications. Formation of advanced glycation end products (AGEs) correlates with glycemic control. The AGE hypothesis proposes that hyperglycemia contributes to the pathogenesis of diabetic complications including retinopathy. However, their role in diabetic retinopathy remains largely unknown. This review discusses the chemistry of AGEs formation and their patho-biochemistry particularly in relation to diabetic retinopathy. AGEs exert deleterious effects by acting directly to induce cross-linking of long-lived proteins to promote vascular stiffness, altering vascular structure and function and interacting with receptor for AGE, to induce intracellular signaling leading to enhanced oxidative stress and elaboration of key proinflammatory and prosclerotic cytokines. Novel anti-AGE strategies are being developed hoping that in next few years, some of these promising therapies will be successfully evaluated in clinical context aiming to reduce the major economical and medical burden caused by diabetic retinopathy.