Ocular angiogenesis: mechanisms and recent advances in therapy

Sphingosine-1-phosphate receptor 1/5 selective agonist alleviates ocular vascular pathologies

Ocular abnormal angiogenesis and edema are featured in several ocular diseases. S1P signaling via S1P1 likely is part of the negative feedback mechanism necessary to maintain vascular health. In this study, we conducted pharmacological experiments to determine whether ASP4058, a sphingosine 1-phosphate receptor 1/5 (S1P1/5) agonist, is useful in abnormal vascular pathology in the eye. First, human retinal microvascular endothelial cells (HRMECs) were examined using vascular endothelial growth factor (VEGF)-induced cell proliferation and hyperpermeability. ASP4058 showed high affinity and inhibited VEGF-induced proliferation and hyperpermeability of HRMECs. Furthermore, S1P1 expression and localization changes were examined in the murine laser-induced choroidal neovascularization (CNV) model, a mouse model of exudative age-related macular degeneration, and the efficacy of ASP4058 was verified. In the CNV model mice, S1P1 tended to decrease in expression immediately after laser irradiation and colocalized with endothelial cells and Müller glial cells. Oral administration of ASP4058 also suppressed vascular hyperpermeability and CNV, and the effect was comparable to that of the intravitreal administration of aflibercept, an anti-VEGF drug. Next, efficacy was also examined in a retinal vein occlusion (RVO) model in which retinal vascular permeability was increased. ASP4058 dose-dependently suppressed the intraretinal edema. In addition, it suppressed the expansion of the perfusion area observed in the RVO model. ASP4058 also suppressed the production of VEGF in the eye. Collectively, ASP4058 can be a potential therapeutic agent that normalizes abnormal vascular pathology, such as age-related macular degeneration and RVO, through its direct action on endothelial cells.

The Association between Diabetic Retinopathy and Macular Degeneration: A Nationwide Population-Based Study

OBJECTIVE

Age-related macular degeneration (AMD), particularly its exudative form, is a primary cause of vision impairment in older adults. As diabetes becomes increasingly prevalent in aging, it is crucial to explore the potential relationship between diabetic retinopathy (DR) and AMD. This study aimed to assess the risk of developing overall, non-exudative, and exudative AMD in individuals with DR compared to those without retinopathy (non-DR) based on a nationwide population study in Taiwan.

METHODS

A retrospective cohort study was conducted using the Taiwan National Health Insurance Database (NHIRD) (2000-2013). A total of 3413 patients were placed in the study group (DR) and 13,652 in the control group (non-DR) for analysis. Kaplan-Meier analysis and the Cox proportional hazards model were used to calculate the hazard ratios (HRs) and adjusted hazard ratios (aHRs) for the development of AMD, adjusting for confounding factors, such as age, sex, and comorbid conditions.

RESULTS

Kaplan-Meier survival analysis indicated a significantly higher cumulative incidence of AMD in the DR group compared to the non-DR group (log-rank test, p < 0.001). Adjusted analyses revealed that individuals with DR faced a greater risk of overall AMD, with an aHR of 3.50 (95% CI = 3.10-3.95). For senile (unspecified) AMD, the aHR was 3.45 (95% CI = 3.04-3.92); for non-exudative senile AMD, it was 2.92 (95% CI = 2.08-4.09); and for exudative AMD, the aHR was 3.92 (95% CI = 2.51-6.14).

CONCLUSION

DR is a significant risk factor for both overall, senile, exudative, and non-exudative AMD, even after adjusting for demographic and comorbid conditions. DR patients tend to have a higher prevalence of vascular comorbidities; however, our findings indicate that the ocular pathologies inherent to DR might have a more significant impact on the progression to AMD. Early detection and appropriate treatment of AMD is critically important among DR patients.

Therapeutic applications of CRISPR/Cas9 gene editing technology for the treatment of ocular diseases

Ocular diseases are a highly heterogeneous group of phenotypes, caused by a spectrum of genetic variants and environmental factors that exhibit diverse clinical symptoms. As a result of its anatomical location, structure and immune privilege, the eye is an ideal system to assess and validate novel genetic therapies. Advances in genome editing have revolutionized the field of biomedical science, enabling researchers to understand the biology behind disease mechanisms and allow the treatment of several health conditions, including ocular pathologies. The advent of clustered regularly interspaced short palindromic repeats (CRISPR)-based gene editing facilitates efficient and specific genetic modifications in the nucleic acid sequence, resulting in permanent changes at the genomic level. This approach has advantages over other treatment strategies and is promising for the treatment of various genetic and non-genetic ocular conditions. This review provides an overview of the CRISPR/CRISPR-associated protein 9 (Cas9) system and summarizes recent advances in the therapeutic application of CRISPR/Cas9 for the treatment of various ocular pathologies, as well as future challenges.

A drug-incorporated-microparticle-eggshell-membrane-scaffold (DIMES) dressing: A novel biomaterial for localised wound regeneration

Chronic wounds affect millions of people annually and have emotional and financial implications in addition to health issues. The current treatment for chronic wounds involves the repeated use of bandages and drugs such as antibiotics over an extended period. A cost-effective and convenient solution for wound healing is the development of drug-incorporated bandages. This study aimed to develop a biocompatible bandage made of drug-incorporated poly (lactic-co-glycolic acid) (PLGA) microparticles (MPs) and eggshell membrane (ESM) for cornea wound healing. ESM has desirable properties for wound healing and can be isolated from eggshells using acetic acid or ethylenediaminetetraacetic acid (EDTA) protocols. Fluorescein isothiocyanate-labelled Bovine Serum Albumin (FITC-BSA) was used as a model drug, and the PLGA MPs were fabricated using a solvent extraction method. The MPs were successfully attached to the fibrous layer of the ESM using NaOH. The surface features of the ESM samples containing MPs were studied using a field emission scanning electron microscope (FESEM) and compared with blank ESM images. The findings indicated that the MPs were attached to the ESM fibres and had similar shapes and sizes as the control MPs. The fibre diameters of the MPs samples were assessed using Fiji-ImageJ software, and no significant changes were observed compared to the blank ESM. The surface roughness, Ra values, of the MPs incorporated ESM samples were evaluated and compared to the blank ESM, and no significant changes were found. Fourier transform infrared (FTIR) spectroscopy was used to analyse the chemical Composition of the bandage, and the spectra showed that the FBM were effectively incorporated into the ESM. The FTIR spectra identified the major peaks of the natural ESM and the PLGA polymer in the bandage. The bandage was transparent but had a reduced visibility in the waterproof test card method. The bandage achieved sustained drug release up to 10 days and was found to be biocompatible and non-toxic in a chorioallantoic membrane (CAM) assay. Overall, the drug-incorporated PLGA MPs-ESM bandage has great potential for treating chronic wounds.

Atorvastatin-loaded peptide amphiphiles against corneal neovascularization

Background: Corneal neovascularization is a sight-threatening disease. It can be treated using antiangiogenic and anti-inflammatory compounds. Therefore, atorvastatin (ATV) constitutes a suitable candidate to be administered topically. To attain suitable efficacy, ATV can be encapsulated into custom-developed nanocarriers such as peptide amphiphiles. Methods: Three peptide amphiphiles bearing one, two or four C16-alkyl groups (mC16-Tat47-57, dC16-Tat47-57 and qC16-Tat47-57) were synthesized, characterized and loaded with ATV. Drug release and ocular tolerance were assessed as well as anti-inflammatory and antiangiogenic properties. Results: ATV-qC16-Tat47-57 showed higher encapsulation efficiency than mC16-Tat47-57 and dC16-Tat47-57 and more defined nanostructures. ATV-qC16-Tat47-57 showed ATV prolonged release with suitable ocular tolerance. Moreover, ATV-qC16-Tat47-57 was antiangiogenic and prevented ocular inflammation. Conclusion: ATV-qC16-Tat47-57 constitutes a promising topical medication against corneal neovascularization.

Predicting effectiveness of anti-VEGF injection through self-supervised learning in OCT images

Anti-vascular endothelial growth factor (Anti-VEGF) therapy has become a standard way for choroidal neovascularization (CNV) and cystoid macular edema (CME) treatment. However, anti-VEGF injection is a long-term therapy with expensive cost and may be not effective for some patients. Therefore, predicting the effectiveness of anti-VEGF injection before the therapy is necessary. In this study, a new optical coherence tomography (OCT) images based self-supervised learning (OCT-SSL) model for predicting the effectiveness of anti-VEGF injection is developed. In OCT-SSL, we pre-train a deep encoder-decoder network through self-supervised learning to learn the general features using a public OCT image dataset. Then, model fine-tuning is performed on our own OCT dataset to learn the discriminative features to predict the effectiveness of anti-VEGF. Finally, classifier trained by the features from fine-tuned encoder as a feature extractor is built to predict the response. Experimental results on our private OCT dataset demonstrated that the proposed OCT-SSL can achieve an average accuracy, area under the curve (AUC), sensitivity and specificity of 0.93, 0.98, 0.94 and 0.91, respectively. Meanwhile, it is found that not only the lesion region but also the normal region in OCT image is related to the effectiveness of anti-VEGF.

Targeting endothelial cell metabolism in cancerous microenvironment: a new approach for anti-angiogenic therapy

Anti-angiogenic therapy is a practical approach to managing diseases with increased angiogenesis, such as cancer, maculopathies, and retinopathies. Considering the fundamental gaps in the knowledge of the vital pathways involved in angiogenesis and its inhibition and the insufficient efficiency of existing angiogenesis inhibitors, there is an increasing focus on the emergence of new therapeutic strategies aimed at inhibiting pathological angiogenesis. Angiogenesis is forming a new vascular network from existing vessels; endothelial cells (ECs), vascular lining cells, are the main actors of angiogenesis in physiological or pathological conditions. Switching from a quiescent state to a highly migratory and proliferative state during new vessel formation called "angiogenic switch" is driven by a "metabolic switch" in ECs, angiogenic growth factors, and other signals. As the characteristics of ECs change by altering the surrounding environment, they appear to have a different metabolism in a tumor microenvironment (TME). Therefore, pathological angiogenesis can be inhibited by targeting metabolic pathways. In the current review, we aim to discuss the EC metabolic pathways under normal and TME conditions to verify the suitability of targeting them with novel therapies.

Therapeutic siRNA: State-of-the-Art and Future Perspectives

The highly specific induction of RNA interference-mediated gene knockdown, based on the direct application of small interfering RNAs (siRNAs), opens novel avenues towards innovative therapies. Two decades after the discovery of the RNA interference mechanism, the first siRNA drugs received approval for clinical use by the US Food and Drug Administration and the European Medicines Agency between 2018 and 2022. These are mainly based on an siRNA conjugation with a targeting moiety for liver hepatocytes, N-acetylgalactosamine, and cover the treatment of acute hepatic porphyria, transthyretin-mediated amyloidosis, hypercholesterolemia, and primary hyperoxaluria type 1. Still, the development of siRNA therapeutics faces several challenges and issues, including the definition of optimal siRNAs in terms of target, sequence, and chemical modifications, siRNA delivery to its intended site of action, and the absence of unspecific off-target effects. Further siRNA drugs are in clinical studies, based on different delivery systems and covering a wide range of different pathologies including metabolic diseases, hematology, infectious diseases, oncology, ocular diseases, and others. This article reviews the knowledge on siRNA design and chemical modification, as well as issues related to siRNA delivery that may be addressed using different delivery systems. Details on the mode of action and clinical status of the various siRNA therapeutics are provided, before giving an outlook on issues regarding the future of siRNA drugs and on their potential as one emerging standard modality in pharmacotherapy. Notably, this may also cover otherwise un-druggable diseases, the definition of non-coding RNAs as targets, and novel concepts of personalized and combination treatment regimens.

Ocular inflammation after agitation of siliconized and silicone oil-free syringes: a randomized, double-blind, controlled clinical trial

Background

Noninfectious endophthalmitis may be misdiagnosed, leading to serious clinical implications. So far, its causative factors remain unknown. Therefore, this study assessed the role of silicone oil and syringe agitation in the development of inflammation after intravitreal injection of aflibercept.

Methods

A randomized, double-blind, controlled clinical trial included subjects with an indication of intravitreal antiangiogenic therapy prior to vitrectomy for proliferative diabetic retinopathy. Aflibercept was injected 48 h before surgery. The control group received the injection without agitation, while the intervention group was injected with a previously agitated syringe by flicking with either a siliconized or silicone oil-free syringe. The primary endpoint was the presence of anterior chamber reaction (ACR) at 48 h. Aqueous samples were collected and underwent cytometric bead array analysis for quantification of interleukins and chemokines.

Results

Forty-one individuals were included (21 in the agitation group and 20 in the no-agitation group). None of the included eyes showed baseline signs of AC cells, hyperemia or pain complaint, while 10% of control group and 80% of agitation group showed AC cells 48 h after injection of aflibercept with SR syringe. There were no differences in the mean variations of all cytokines and chemokines by agitation status. However, there was a marginally significant increase between the mean variations of IP-10 (p = 0.057) and IL-8 (p = 0.058) in the siliconized one.

Conclusion

This clinical trial discloses a potential role of agitation and siliconized syringes in the development of inflammation after an intravitreal injection of aflibercept. These findings have important clinical implications for all healthcare practitioners who perform intravitreal injections.

Trial Registration: Brazilian Registry of Clinical Trials, RBR-95ddhp. Registered 12 May 2019, http://www.ensaiosclinicos.gov.br/rg/RBR-95ddhp/

Analysis of optical coherence tomography angiographic findings of prematurely born children and its relationship with macular edema of prematurity

PURPOSE

To compare foveal avascular zone (FAZ) area, foveal vascular density (VD), and foveal thickness in pre- and full-term children and to evaluate their relationship with cystoid macular edema (CME) in the prematurity period using spectral domain optical coherence tomography angiography (SD-OCTA).

METHODS

OCTA imaging was performed at 4-6 years of age in 90 eyes of 45 prematurely born children and 50 eyes of 25 term children. Subjects were divided into three groups: prematurely born with CME (group 1); prematurely born without CME (group 2); healthy, term children (group 3). Imaging results in the three groups were compared.

RESULTS

FAZ area was significantly larger in group 3 than in groups 1 and 2 (P < 0.001 [ANOVA]). FAZ area was found to be correlated with birth weight (r = 0.511; P < 0.001) and gestational age (r = 0.532; P < 0.001). No significant relationship was found between history of CME and FAZ area.

CONCLUSIONS

In our study cohort, FAZ area was smaller in prematurely born children and was correlated with older gestational age and higher birth weight. CME in the neonatal period did not seem to affect retinal microvascular development in premature infants.

Targeting circular RNA-MET for anti-angiogenesis treatment via inhibiting endothelial tip cell specialization

Endothelial tip cell specialization plays an essential role in angiogenesis, which is tightly regulated by the complicated gene regulatory network. Circular RNA (circRNA) is a type of covalently closed non-coding RNA that regulates gene expression in eukaryotes. Here, we report that the levels of circMET expression are significantly upregulated in the retinas of mice with oxygen-induced retinopathy, choroidal neovascularization, and diabetic retinopathy. circMET silencing significantly reduces pathological angiogenesis and inhibits tip cell specialization in vivo. circMET silencing also decreases endothelial migration and sprouting in vitro. Mechanistically, circMET regulates endothelial sprouting and pathological angiogenesis by acting as a scaffold to enhance the interaction between IGF2BP2 and NRARP/ESM1. Clinically, circMET is significantly upregulated in the clinical samples of the patients of diabetic retinopathy. circMET silencing could reduce diabetic vitreous-induced endothelial sprouting and retinal angiogenesis in vivo. Collectively, these data identify a circRNA-mediated mechanism that coordinates tip cell specialization and pathological angiogenesis. circMET silencing is an exploitable therapeutic approach for the treatment of neovascular diseases.

Inhibitory effect of miR‑182‑5p on retinal neovascularization by targeting angiogenin and BDNF

Retinal neovascularization (RNV) is a type of serious vision-threating disease, commonly induced by hypoxia of ischemic retinopathy, which happens in various ocular diseases including diabetic retinopathy and retinopathy of prematurity. In clinical work, anti-VEGF therapy is the preferred strategy for treating RNV. However, not all cases are sensitive to anti-VEGF injection. It is urgent and necessary to develop novel targets for inhibiting neovascularization in ocular diseases. Angiogenin (ANG) and brain-derived neurotrophic factor (BDNF) are implicated in angiogenesis, although their regulation and effects in RNV remain to be elucidated. microRNA (miRNA) is a type of small non-coding RNA, which can modulate targets by degrading transcripts or inhibiting protein translation. In the present study, miRNA-mediated modulation of ANG and BDNF was explored in an oxygen-induced retinopathy mouse model and human retinal microvascular endothelial cells (HRECs) under hypoxia. The results showed that downregulation of miR-182-5p and upregulation of ANG and BDNF were found in vivo and in vitro. Overexpression of miR-182-5p suppressed the expression of ANG and BDNF significantly in HRECs under hypoxia. In addition, knockdown of ANG and BDNF by miR-182-5p transfection significantly improved hypoxia-induced HRECs dysfunctions, including enhancing cell viability, reducing cell migration and improved tube integrity. In conclusion, miRNA-dependent regulation on ANG and BDNF indicates a critical role in hypoxia-induced retinal microvascular response. miR-182-5p-based therapy can influence the expression of ANG and BDNF, which demonstrates the potential for treating RNV diseases.

Silibinin Regulates Tumor Progression and Tumorsphere Formation by Suppressing PD-L1 Expression in Non-Small Cell Lung Cancer (NSCLC) Cells

Recently, natural compounds have been used globally for cancer treatment studies. Silibinin is a natural compound extracted from Silybum marianum (milk thistle), which has been suggested as an anticancer drug through various studies. Studies on its activity in various cancers are undergoing. This study demonstrated the molecular signaling behind the anticancer activity of silibinin in non-small cell lung cancer (NSCLC). Quantitative real-time polymerase chain reaction and Western blotting analysis were performed for molecular signaling analysis. Wound healing assay, invasion assay, and in vitro angiogenesis were performed for the anticancer activity of silibinin. The results indicated that silibinin inhibited A549, H292, and H460 cell proliferation in a concentration-dependent manner, as confirmed by the induction of G0/G1 cell cycle arrest and apoptosis and the inhibition of tumor angiogenesis, migration, and invasion. This study also assessed the role of silibinin in suppressing tumorsphere formation using the tumorsphere formation assay. By binding to the epidermal growth factor receptor (EGFR), silibinin downregulated phosphorylated EGFR expression, which then inhibited its downstream targets, the JAK2/STAT5 and PI3K/AKT pathways, and thereby reduced matrix metalloproteinase, PD-L1, and vascular endothelial growth factor expression. Binding analysis demonstrated that STAT5 binds to the PD-L1 promoter region in the nucleus and silibinin inhibited the STAT5/PD-L1 complex. Altogether, silibinin could be considered as a candidate for tumor immunotherapy and cancer stem cell-targeted therapy.

Comparing vision and macular thickness in neovascular age-related macular degeneration, diabetic macular oedema and retinal vein occlusion patients treated with intravitreal antivascular endothelial growth factor injections in clinical practice

Objective

To compare the visual outcomes of intravitreal antivascular endothelial growth factor (anti-VEGF) injections in neovascular age-related macular degeneration (nAMD), diabetic macular oedema (DMO) and retinal vein occlusion (RVO) in a real-world setting.

Methods and analysis

Retrospective analysis of data from the Tasmanian Ophthalmic Biobank database. The median change in best-corrected visual acuity (BCVA) between baseline and 12 months post initiating intravitreal anti-VEGF treatment were compared between the three diseases. Final BCVA, central macular thickness (CMT), cumulative number of injections and overall predictors of change in BCVA and CMT were also determined.

Results

At 12 months, change in BCVA was significantly different between nAMD, DMO and RVO cohorts (p=0.032), with lower median change for DMO (2 letters, range −5 to 20) than for RVO (11 letters, range −20 to 35). Likewise, CMT change was significantly different between the three cohorts (p=0.022), with a smaller reduction in CMT in DMO (−54 µm, range −482 to 50) than RVO patients (−137 µm, range −478 to 43; p=0.033). Total number of injections received (p=0.028) and final BCVA score (p=0.024) were also significantly different between the groups. Baseline BCVA was a negative predictor (p=0.042) and baseline CMT a positive predictor (p<0.001) of outcome. After adjusting for baseline BCVA and CMT, diagnosis of nAMD or RVO was a predictor of visual improvement compared with the DMO.

Conclusions

At the end of 12 months, nAMD and RVO cohorts had the greatest improvement in BCVA, however the final BCVA for DMO was significantly better than for nAMD.

Extraction, Purification, Characterization, and Antiangiogenic Activity of Acidic Polysaccharide from Buddleja officinalis

Firstly, optimal parameters of crude polysaccharide from Buddleja officinalis were obtained as follows: ratio of water to raw material of 26 : 1, ultrasonic power of 240 W, ultrasonic time of 45 min, and ultrasonic temperature of 62°C. Secondly, acidic polysaccharide (APBOM) from Buddleja officinalis was successfully acquired with the yield of 9.57% by using DEAE-52 cellulose and Sephadex G-100 gel column chromatography. Then, we found that total polysaccharide content of APBOM was 94.37% with a sulfuric acid group of 1.68%, uronic acid content of 17.41%, and average molecular weight of 165.4 kDa. Finally, APBOM was confirmed to have significant antiangiogenic effects.

Noble Metals and Soft Bio-Inspired Nanoparticles in Retinal Diseases Treatment: A Perspective

We are witnessing an exponential increase in the use of different nanomaterials in a plethora of biomedical fields. We are all aware of how nanoparticles (NPs) have influenced and revolutionized the way we supply drugs or how to use them as therapeutic agents thanks to their tunable physico-chemical properties. However, there is still a niche of applications where NP have not yet been widely explored. This is the field of ocular delivery and NP-based therapy, which characterizes the topic of the current review. In particular, many efforts are being made to develop nanosystems capable of reaching deeper sections of the eye such as the retina. Particular attention will be given here to noble metal (gold and silver), and to polymeric nanoparticles, systems consisting of lipid bilayers such as liposomes or vesicles based on nonionic surfactant. We will report here the most relevant literature on the use of different types of NPs for an efficient delivery of drugs and bio-macromolecules to the eyes or as active therapeutic tools.

A Systematic Investigation on Complement Pathway Activation in Diabetic Retinopathy

The complement system plays a crucial role in retinal homeostasis. While the proteomic analysis of ocular tissues in diabetic retinopathy (DR) has shown the deposition of complement proteins, their exact role in the pathogenesis of DR is yet unclear. We performed a detailed investigation of the role of the complement system by evaluating the levels of major complement proteins including C3, C1q, C4b, Complement Factor B (CFB), and Complement Factor H (CFH) and their activated fragments from both the classical and alternative pathways in vitreous humor and serum samples from proliferative DR (PDR) patients and controls. Further, the expressions of complements and several other key pro- and anti-angiogenic genes in the serum and vitreous humor were analyzed in the blood samples of PDR and non-PDR (NPDR) patients along with controls without diabetes. We also assessed the pro-inflammatory cytokines and matrix metalloproteinases in the vitreous humor samples. There was a significant increase in C3 and its activated fragment C3bα' (110 kDa) along with a corresponding upregulation of CFH in the vitreous of PDR patients, which confirmed the increased activation of the alternative complement pathway in PDR. Likewise, a significant upregulation of angiogenic genes and downregulation of anti-angiogenic genes was seen in PDR and NPDR cases. Increased MMP9 activity and upregulation of inflammatory markers IL8 and sPECAM with a downregulation of anti-inflammatory marker IL-10 in PDR vitreous indicated the possible involvement of microglia in DR pathogenesis. Further, a significantly high C3 deposition in the capillary wall along with thickening of basement membranes and co-localization of CFH expression with CD11b^+ve activated microglial cells in diabetic retina suggested microglia as a source of CFH in diabetic retina. The increased CFH levels could be a feedback mechanism for arresting excessive complement activation in DR eyes. A gradual increase of CFH and CD11b expression in retina with early to late changes in epiretinal membranes of DR patients indicated a major role for the alternative complement pathway in disease progression.

STAT3-mediated activation of miR-21 is involved in down-regulation of TIMP3 and neovascularization in the ischemic retina

Retinal neovascularization (RNV) is a sight threatening complication of ischemic retinopathies with limited therapeutic options. The transcription factor signal transducer and activator of transcription 3 (STAT3) has been shown to play a crucial role in promoting RNV. However, manipulating of STAT3 activity can cause significant adverse side effects due to its neurotrophic properties. In this study, we identified microRNA-21 (miR-21) as a downstream effector of STAT3 activity in the ischemic retinas and determined its role in promoting RNV through inhibition of its molecular target, the tissue inhibitor of matrix metalloproteinases 3 (TIMP3). Using human retinal endothelial cells (HREC) exposed to hypoxia and a mouse model of oxygen-induced retinopathy (OIR), we found that TIMP3 expression was significantly decreased at both mRNA and protein levels and this paralleled the activation of STAT3 and up-regulation of miR-21. Moreover, TIMP3 expression was restored by knockdown of STAT3 or blocking of miR-21 in HREC, thus, confirming TIMP3 as a downstream target of STAT3/miR-21 pathway. Finally, in a mouse model of OIR, blockade of miR-21 by a specific antisense (a.miR-21), halted RNV and this effect was associated with rescuing of TIMP3 expression. Our data show that miR-21 mediates STAT3 pro-angiogenic effects in the ischemic retina, thus suggesting its blockade as a potential therapy to prevent/halt RNV.

Aquaporins: Novel Targets for Age-Related Ocular Disorders

Aquaporins (AQPs), a large family of membrane protein channels that facilitate transport of water and other small solutes, play important roles in physiological functions and human diseases. Up till now, 13 types of AQPs, numbered 0 through 12, have been identified in various mammalian tissues. Homologous genes for AQPs in amphibians, insects, and bacteria highlight the evolutionary conservation and, thus, the importance of these membrane channels. Many members of the AQP family are expressed in the eye. AQP1, which is a water-selective channel, is expressed in the anterior chamber (cornea, ciliary body, trabecular meshwork) and posterior chamber (retina and microvessels in choroid), controlling the fluid homeostasis in the eye. Mice knockout studies have indicated that AQP1 plays an important function in the eye by suggesting its role in aqueous humor dynamics and retina angiogenesis. This review will focus on the role of AQP1 as a novel target for ocular disorders such as glaucoma and age-related macular degeneration, and it will discuss challenges and advances in identifying modulators of AQP1 function that could be useful in clinical applications.

Detection of aqueous VEGF concentrations before and after intravitreal injection of anti-VEGF antibody using low-volume sampling paper-based ELISA

Intraocular vascular endothelial growth factor (VEGF) levels play an important role in the pathogenesis of blindness-related diseases, such as age-related macular degeneration (AMD). Here, we aimed to develop a paper-based enzyme-linked immunosorbent assay (P-ELISA) to analyze the suppression of aqueous VEGF concentrations following intravitreal injection (IVI) of anti-VEGF antibody (bevacizumab or ranibizumab). A total of 25 eyes with wet AMD, one with myopic neovascularization, and one with polypoidal choroidal vasculopathy were enrolled in this study. The limit of detection using P-ELISA was 0.03 pg/mL. Forty-six consecutive samples of aqueous humor were acquired. From all samples, 66.67% (10/15) achieved complete VEGF suppression (below the detection limit) within 5 weeks of receiving IVI of anti-VEGF antibody. Only 13.33% of samples (2/15) achieved complete VEGF suppression 5 weeks after receiving treatment. In some patients, elevated VEGF was still detected 5 weeks after receipt of anti-VEGF antibody, and all samples (10/10) were found to have elevated VEGF levels 49 days after treatment. Thus, we suggest that monthly IVI of anti-VEGF antibody may be required to ensure durable VEGF inhibition. Ultrasensitive P-ELISA can detect elevated VEGF at an earlier time point and may facilitate decision-making regarding appropriate treatment strategies.

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.

Silencing of S100A4, a metastasis-associated protein, inhibits retinal neovascularization via the downregulation of BDNF in oxygen-induced ischaemic retinopathy

BackgroundTo investigate the underlying mechanism of S100A4 function and whether it has a role in retinal neovascularization (RNV) in a mouse model of oxygen-induced retinopathy (OIR).MethodsRetinas from a mouse model of OIR were treated with and without an intravitreous injection of adenoviral-S100A4-RNAi or adenoviral green fluorescence protein (GFP) at postnatal day 12 (P12). At P17, the efficacy of adenoviral gene transfer was assessed using fluorescence microscopy and western blot analysis. RNV was evaluated by whole-mount immunofluorescence staining of the mouse retina and by counting the number of pre-retinal neovascular cells. Protein and mRNA expression levels of S100A4, brain-derived growth factor (BDNF), and vascular endothelial growth factor (VEGF) were measured using western blot analysis and real-time PCR.ResultsRetinal S100A4 levels were positively correlated with the progression of RNV. In the OIR-S100A4-RNAi group, both protein and mRNA expression levels of S100A4 in the retina significantly decreased at P17 compared with those in the OIR group. Ad-S100A4-RNAi transfer was clearly demonstrated by GFP fluorescence in many layers of the retina 5 days after the Ad-S100A4-RNAi transfer. Whole-mount immunofluorescence staining of the retina and quantification of the pre-retinal neovascular cells demonstrated that RNV was significantly inhibited. Meanwhile, the levels of the transcription and translation of BDNF, VEGF, and hypoxia-inducible factor-1α (HIF-1α) significantly decreased in the OIR-S100A4-RNAi group.ConclusionsAd-S100A4-RNAi transfer ameliorates RNV. The related mechanism may involve silencing S100A4 to decrease the activation of BDNF, which downregulates VEGF expression via HIF-1α. This finding could provide a new therapeutic target for the treatment of ocular neovascularization diseases.

Anti-VEGF Therapy and the Retina: An Update

Ocular angiogenesis and macular oedema are major causes of sight loss across the world. Aberrant neovascularisation, which may arise secondary to numerous disease processes, can result in reduced vision as a result of oedema, haemorrhage, and scarring. The development of antivascular endothelial growth factor (anti-VEGF) agents has revolutionised the treatment of retinal vasogenic conditions. These drugs are now commonly employed for the treatment of a plethora of ocular pathologies including choroidal neovascularisation, diabetic macular oedema, and retinal vein occlusion to name a few. In this paper, we will explore the current use of anti-VEGF in a variety of retinal diseases and the impact that these medications have had on visual outcome for patients.

Thrombospondin-1-Based Antiangiogenic Therapy

Ocular angiogenesis is one of the underlying causes of blindness and vision impairment and may occur in a spectrum of disorders, including diabetic retinopathy, neovascular age-related macular degeneration, retinal artery or vein occlusion, and retinopathy of prematurity. As such, strategies to inhibit angiogenesis by suppressing vascular endothelial growth factor activity have proven to be effective in the clinic for the treatment of eye diseases. A complementary approach would be to increase the level of naturally occurring inhibitors of angiogenesis, such as thrombospondin (TSP)-1. This article summarizes the development of TSP-1-based inhibitors of angiogenesis.

The effects of topical everolimus and sunitinib on corneal neovascularization

PURPOSE

To evaluate the effects of topical everolimus and sunitinib on corneal neovascularization (CNV).

METHODS

CNV was induced by application of silver nitrate to the cornea for all groups. Rats were divided into four groups of 10 rats each, and two corneas were obtained from each rat. Group I received 1 mg/ml everolimus, Group II received 0.5 mg/ml sunitinib, Group IV received no treatment (control group) and Group IV received 1% Dimethylsulfoxide (DMSO). All treatments were administrated twice daily for 2 weeks. The right corneas were used for extracellular signal-regulated kinase 1/2 (ERK 1/2) protein analysis by western blot analysis and the left corneas were used for ERK 1/2 and vascular endothelial growth factor-receptor (VEGFR-2) gene expression analysis by quantitative real-time PCR.

RESULTS

VEGFR-2 mRNA expression levels (ΔCt, median, min-max) were reduced in the everolimus 1.0 (0.25-1.81) and sunitinib 1.06 (0.24-2.68) treated groups compared with the control 4.74 (1.02-14.74) and DMSO groups 7.41 (0.72-13.10). The expression of ERK 1/2 protein and mRNA levels were reduced in everolimus group compared with the control group (p < 0.05). These differences were not seen between the sunitinib and control groups.

CONCLUSION

Topical administration of both everolimus and sunitinib reduced VEGFR-2 levels and inhibited CNV. In additon, everolimus reduced ERK 1/2 levels and seems to be more effective than sunitinib on CNV.

Seeing through VEGF: innate and adaptive immunity in pathological angiogenesis in the eye

The central role of vascular endothelial growth factor (VEGF) signaling in regulating normal vascular development and pathological angiogenesis has been documented in multiple studies. Ocular anti-VEGF therapy is highly effective for treating a subset of patients with blinding eye disorders such as diabetic retinopathy and neovascular age-related macular degeneration (AMD). However, chronic VEGF suppression can lead to adverse effects associated with poor visual outcomes due to the loss of prosurvival and neurotrophic capacities of VEGF. In this review, we discuss emerging evidence for immune-related mechanisms that regulate ocular angiogenesis in a VEGF-independent manner. These novel molecular and cellular pathways may provide potential therapeutic avenues for a multitarget strategy, preserving the neuroprotective functions of VEGF in those patients whose disease is unresponsive to VEGF neutralization.

miRNA-dependent cross-talk between VEGF and Ang-2 in hypoxia-induced microvascular dysfunction

Ocular neovascularization is a vision-threatening complication of ischemic retinopathy that develops in various ocular disorders, such as retinopathy of prematurity (ROP) and diabetic retinopathy. Both Ang-2 and VEGF are implicated in this pathogenesis. However, their inter-regulation still remains elusive. Competitive endogenous RNAs (ceRNAs) are messenger RNA (mRNA) molecules that affect each other expression through the competition for the shared miRNA. Herein, we assessed whether the expression of Ang-2 and VEGF is interdependent through the sequestration of common miRNAs. Bioinformatics prediction and 3'-UTR luciferase assay revealed that Ang-2 and VEGF is commonly targeted by miR-351. Silencing either Ang-2 or VEGF increases the availabilities of shared miR-351, therefore reduces the activity of Luc-Ang-2 3'-UTR. The interdependence of VEGF and Ang-2 is miRNA- and 3'-UTR dependent, as silencing Dicer abolishes the interdependence. We also found that miR-351 dependency of VEGF-Ang-2 crosstalk occurs in retinal endothelial cells and rat retinas. miR-351 over-expression significantly reduces the level of VEGF and Ang-2 expression in vivo and in vitro. Overall, miRNA-dependent crosstalk between Ang-2 and VEGF plays a role in hypoxia-induced microvascular response. miRNA-based therapy can affect the expression of Ang-2 and VEGF, which represents a therapeutic potential for the treatment of vascular disease.

Long non-coding RNAs: new players in ocular neovascularization

Pathological neovascularization are the most prevalent causes of moderate or severe vision loss. Long non-coding RNAs (lncRNAs) have emerged as a novel class of regulatory molecules involved in numerous biological processes and complicated diseases. However, the role of lncRNAs in ocular neovascularization is still unclear. Here, we constructed a murine model of ocular neovascularization, and determined lncRNA expression profiles using microarray analysis. We identified 326 or 51 lncRNAs that were significantly either up-regulated or down-regulated in the vaso-obliteration or neovascularization phase, respectively. Based on Pearson correlation analysis, lncRNAs/mRNAs co-expression networks were constructed. GO enrichment analysis of lncRNAs-co-expressed mRNAs indicated that the biological modules were correlated with chromosome organization, extracellular region and guanylate cyclase activator activity in the vaso-obliteration phase, and correlated with cell proliferation, extracellular region and guanylate cyclase regulator activity in the neovascularization phase. KEGG pathway analysis indicated that MAPK signaling was the most significantly enriched pathway in both phases. Importantly, Vax2os1 and Vax2os2 were not only dynamically expressed in the vaso-obliteration and neovascularization phases, but also significantly altered in the aqueous humor of patients with neovascular age-related macular degeneration (AMD), suggesting a potential role of lncRNAs in the regulation of ocular neovascularization. Taken together, this study provided novel insights into the molecular pathogenesis of ocular neovascularization. The intervention of dysregulated lncRNA could become a potential target for the prevention and treatment of ocular vascular diseases.

Protective effects of the neuropeptides PACAP, substance P and the somatostatin analogue octreotide in retinal ischemia: a metabolomic analysis

Ischemia is a primary cause of neuronal death in retinal diseases and the somatostatin subtype receptor 2 agonist octreotide (OCT) is known to decrease ischemia-induced retinal cell death. Using a recently optimized ex vivo mouse model of retinal ischemia, we tested the anti-ischemic potential of two additional neuropeptides, pituitary adenylate cyclase activating peptide (PACAP) and substance P (SP), and monitored the major changes occurring at the metabolic level. Metabolomics analyses were performed via fast HPLC online using a microTOF-Q MS instrument, a workflow that is increasingly becoming the gold standard in the field of metabolomics. The metabolomic approach allowed detection of the most significant alterations induced in the retina by ischemia and of the significance of the protective effects exerted by OCT, PACAP or SP. All treatments were shown to reduce ischemia-induced cell death, vascular endothelial growth factor over-expression and glutamate release. The metabolomic analysis showed that OCT and, to a lesser extent, also PACAP or SP, were able to counteract the ischemia-induced oxidative stress and to promote, with various efficacies, (i) decreased accumulation of glutamate and normalization of glutathione homeostasis; (ii) reduced build-up of α-ketoglutarate, which might serve as a substrate for the enhanced biosynthesis of glutamate in response to ischemia; (iii) reduced accumulation of peroxidized lipids and inflammatory mediators; (iv) the normalization of glycolytic fluxes and thus preventing the over-accumulation of lactate or either promoting the down-regulation of the glyoxalate anti-oxidant system; (v) a reduced metabolic shift from glycolysis towards the PPP or either a blockade at the non-oxidative phase of the PPP; and (vi) tuning down of purine metabolism. In addition, OCT seemed to stimulate nitric oxide production. None of the treatments was able to restore ATP production, although ATP reservoirs were partly replenished by OCT, PACAP or SP. These data indicate that, in addition to that of somatostatin, peptidergic systems such as those of PACAP and SP deserve attention in view of peptide-based therapies to treat ischemic retinal disorders.

Molecular umbrella conjugate for the ocular delivery of siRNA

The synthesis, computer modeling, and biological activity of an octawalled molecular umbrella short interfacing RNA (siRNA) conjugate is described. This molecular umbrella–siRNA conjugate exhibited mRNA knockdown activity in vitro in the absence of a transfection reagent. Evaluation of this molecular umbrella conjugate in vivo, using the rat eye via intravitreal injection, resulted in sequence specific mRNA knockdown in the retina with no obvious signs of toxicity, as judged by ophthalmic examination.

Regional morphology and pathophysiology of retinal vascular disease

Disturbances in the retinal vascular supply are involved in the pathophysiology of the most frequent diseases causing visual impairment and blindness in the Western World. These diseases are diagnosed by noting how morphological lesions in the retina vary in shape, size, location and dynamics, and subsequently concluding the presence of a specific disease entity. This diagnostic approach can be used to identify the site of a retinal vascular occlusion, to assess whether retinal diseases are primarily due to changes in the larger retinal vessels or the microcirculation, and to differentiate the relative involvement of the choroidal and the retinal vascular systems. However, a number of morphological manifestations of retinal vascular disease cannot presently be related to the underlying pathophysiology. The review concludes that there is a need for developing new methods for assessing vascular structure and function in the ciliary vascular system supplying the choroid and the optic nerve head. Presently, the study of these structures relies on imaging techniques with limited penetration and resolution into the tissue. Secondly, there is a need for studying oscillations in retinal vascular function occurring within days to weeks, and for studying regional manifestations of retinal vascular disease. This may constitute the basis for future research in retinal vascular pathophysiology and for the development of new treatment modalities to reduce blindness secondary to retinal vascular disease.

Association between hemoglobin scavenger receptor and heme oxygenase-1-related anti-inflammatory mediators in human coronary stable and unstable plaques

Heme oxygenase-1 (HO-1) is a cytoprotective enzyme that is induced by intraplaque hemorrhage and degrades free heme and releases ferrous iron, which is rapidly sequestered by ferritin. In vitro studies have shown that binding of hemoglobin to hemoglobin scavenger receptor (CD163) induces HO-1 and the anti-inflammatory mediator interleukin (IL)-10. We immunohistochemically examined the relationship between CD163 expression in macrophages and intraplaque hemorrhage, HO-1, IL-10, and ferritin using coronary atherectomy specimens from patients with stable (SAP) or unstable angina pectoris (UAP). A total of 67 patients underwent atherectomy for SAP (n = 33) or UAP (n = 34). Samples were stained with antibodies against smooth muscle cells, macrophages, glycophorin-A (a protein specific to erythrocyte membranes), CD163, HO-1, IL-10, and ferritin. To identify cell types of HO-1-positive cells, double immunostaining was also performed. Double immunostaining for HO-1 and macrophages revealed that the vast majority of HO-1-positive cells were macrophages. Morphometric analysis demonstrated that CD163-positive macrophage score and the percentage of glycophorin-A-, HO-1-, IL-10-, and ferritin-positive areas were significantly higher in UAP than in SAP patients (CD163, P < .005; glycophorin-A, P < .0001; HO-1, P < .0001; IL-10, P < .005; ferritin, P = .0001). Moreover, CD163-positive macrophage score was positively associated with the percentage of glycophorin-A-, HO-1-, IL-10-, and ferritin-positive areas (glycophorin-A, r = 0.60, P < .0001; HO-1, r = 0.67, P < .0001; IL-10, r = 0.45, P < .0005; ferritin, r = 0.61, P < .0001). These findings suggest that enhanced expression of HO-1 and HO-1-related atheroprotective molecules plays an important role in exerting anti-inflammatory, antioxidant, and scavenging functions, which could contribute to plaque stabilization.

Photoreceptor avascular privilege is shielded by soluble VEGF receptor-1

Optimal phototransduction requires separation of the avascular photoreceptor layer from the adjacent vascularized inner retina and choroid. Breakdown of peri-photoreceptor vascular demarcation leads to retinal angiomatous proliferation or choroidal neovascularization, two variants of vascular invasion of the photoreceptor layer in age-related macular degeneration (AMD), the leading cause of irreversible blindness in industrialized nations. Here we show that sFLT-1, an endogenous inhibitor of vascular endothelial growth factor A (VEGF-A), is synthesized by photoreceptors and retinal pigment epithelium (RPE), and is decreased in human AMD. Suppression of sFLT-1 by antibodies, adeno-associated virus-mediated RNA interference, or Cre/lox-mediated gene ablation either in the photoreceptor layer or RPE frees VEGF-A and abolishes photoreceptor avascularity. These findings help explain the vascular zoning of the retina, which is critical for vision, and advance two transgenic murine models of AMD with spontaneous vascular invasion early in life. DOI:http://dx.doi.org/10.7554/eLife.00324.001.

CONTROLLED DELIVERY OF ANTIANGIOGENIC DRUG TO HUMAN EYE TISSUE USING A MEMS DEVICE

We demonstrate an implantable MEMS drug delivery device to conduct controlled and on-demand, ex vivo drug transport to human eye tissue. Remotely operated drug delivery to human post-mortem eyes was performed via a MEMS device. The developed curved packaging cover conforms to the eyeball thereby preventing the eye tissue from contacting the actuating membrane. By pulsed operation of the device, using an externally applied magnetic field, the drug released from the device accumulates in a cavity adjacent to the tissue. As such, docetaxel (DTX), an antiangiogenic drug, diffuses through the eye tissue, from sclera and choroid to retina. DTX uptake by sclera and choroid were measured to be 1.93±0.66 and 7.24±0.37 μg/g tissue, respectively, after two hours in pulsed operation mode (10 s on/off cycles) at 23°C. During this period, a total amount of 192 ng DTX diffused into the exposed tissue. This MEMS device shows great potential for the treatment of ocular posterior segment diseases such as diabetic retinopathy by introducing a novel way of drug administration to the eye.

Formulation approaches to short interfering RNA and MicroRNA: challenges and implications

RNA interference has emerged as a potentially powerful tool in the treatment of genetic and acquired diseases by delivering short interfering RNA (siRNA) or microRNA (miRNA) to target genes, resulting in their silencing. However, many physicochemical and biological barriers have to be overcome to obtain efficient in vivo delivery of siRNA and miRNA molecules to the organ/tissue of interest, thereby enabling their effective clinical therapy. This review discusses the challenges associated with the use of siRNA and miRNA and describes the nonviral delivery strategies used in overcoming these barriers. More specifically, emphasis has been placed on those technologies that have progressed to clinical trials for both local and systemic siRNA and miRNA delivery.

Role of matrix metalloproteinase-2 and -9 in the development of diabetic retinopathy

Diabetic retinopathy represents the most common causes of vision loss in patients affected by diabetes mellitus. The cause of vision loss in diabetic retinopathy is complex and remains incompletely understood. One of the earliest changes in the development of retinopathy is the accelerated apoptosis of retinal microvascular cells and the formation of acellular capillaries by unknown mechanism. Results of a recent research suggest an important role of matrix metalloproteinases (MMPs) in the development of diabetic retinopathy. MMPs are a large family of proteinases that remodel extracellular matrix components, and under pathological condition, its induction is considered as a negative regulator of cell survival; and in diabetes, latent MMPs are activated in the retina and its capillary cells, and activation of MMP-2 and -9 induces apoptosis of retinal capillary cells. This review will focus on the MMP-2 and MMP-9 in the diabetic retina with special reference to oxidative stress, mitochondria dysfunction, inflammation and angiogenesis, as well as summarizing the current information linking these proteins to pathogenesis of diabetic retinopathy.

Ferritin blocks inhibitory effects of two-chain high molecular weight kininogen (HKa) on adhesion and survival signaling in endothelial cells

Angiogenesis is tightly regulated through complex crosstalk between pro- and anti-angiogenic signals. High molecular weight kininogen (HK) is an endogenous protein that is proteolytically cleaved in plasma and on endothelial cell surfaces to HKa, an anti-angiogenic protein. Ferritin binds to HKa and blocks its anti-angiogenic activity. Here, we explore mechanisms underlying the cytoprotective effect of ferritin in endothelial cells exposed to HKa. We observe that ferritin promotes adhesion and survival of HKa-treated cells and restores key survival and adhesion signaling pathways mediated by Erk, Akt, FAK and paxillin. We further elucidate structural motifs of both HKa and ferritin that are required for effects on endothelial cells. We identify an histidine-glycine-lysine (HGK) -rich antiproliferative region within domain 5 of HK as the target of ferritin, and demonstrate that both ferritin subunits of the H and L type regulate HKa activity. We further demonstrate that ferritin reduces binding of HKa to endothelial cells and restores the association of uPAR with α5β1 integrin. We propose that ferritin blocks the anti-angiogenic activity of HKa by reducing binding of HKa to UPAR and interfering with anti-adhesive and anti-proliferative signaling of HKa.

Endostatin lowers blood pressure via nitric oxide and prevents hypertension associated with VEGF inhibition

Antiangiogenesis therapy has become a vital part of the armamentarium against cancer. Hypertension is a dose-limiting toxicity for VEGF inhibitors. Thus, there is a pressing need to address the associated adverse events so these agents can be better used. The hypertension may be mediated by reduced NO bioavailability resulting from VEGF inhibition. We proposed that the hypertension may be prevented by coadministration with endostatin (ES), an endogenous angiogenesis inhibitor with antitumor effects shown to increase endothelial NO production in vitro. We determined that Fc-conjugated ES promoted NO production in endothelial and smooth muscle cells. ES also lowered blood pressure in normotensive mice and prevented hypertension induced by anti-VEGF antibodies. This effect was associated with higher circulating nitrate levels and was absent in eNOS-knockout mice, implicating a NO-mediated mechanism. Retrospective study of patients treated with ES in a clinical trial revealed a small but significant reduction in blood pressure, suggesting that the findings may translate to the clinic. Coadministration of ES with VEGF inhibitors may offer a unique strategy to prevent drug-related hypertension and enhance antiangiogenic tumor suppression.

Recent advances in cellular and molecular aspects of mammalian retinal ischemia

Retinal ischemia is a common clinical entity and, due to relatively ineffective treatment, remains a common cause of visual impairment and blindness. Generally, ischemic syndromes are initially characterized by low homeostatic responses which, with time, induce injury to the tissue due to cell loss by apoptosis. In this respect, retinal ischemia is a primary cause of neuronal death. It can be considered as a sort of final common pathway in retinal diseases and results in irreversible morphological and functional changes. This review summarizes the recent knowledge on the effects of ischemia in retinal tissue and points out experimental strategies/models performed to gain better comprehension of retinal ischemia diseases. In particular, the nature of the mechanisms leading to neuronal damage (i.e., excess of glutamate release, oxidative stress and inflammation) will be outlined as well as the potential and most intriguing retinoprotective approaches and the possible therapeutic use of naturally occurring molecules such as neuropeptides. There is a general agreement that a better understanding of the fundamental pathophysiology of retinal ischemia will lead to better management and improved clinical outcome. In this respect, to contrast this pathological state, specific pharmacological strategies need to be developed aimed at the many putative cascades generated during ischemia.

αA-crystallin in the pathogenesis and intervention of experimental murine corneal neovascularization

This study was to determine the potential roles of lens crystallins in the pathogenesis of corneal neovascularization (CorNV) and implications in therapy of CorNV-related diseases. Suture- or chemical burn-induced CorNV in different strains of mice were used. Changes of gene expression patterns were analyzed by microarray, and the results of interesting genes were confirmed by real-time quantitative PCR and Western blot. Mice deficient in αA-crystallin gene were used to evaluate the role of αA-crystallin in the development of CorNV. In some animals, exogenous αA-crystallin proteins were injected around time of CorNV induction. CorNV was assessed by slit-lamp, flat-mounts and histology. In BALB/C mice, the expression of α-, β-, and γ-crystallins were up-regulated at day 5 and returned to baseline level at day 10 of suture-induced CorNV, but remained up-regulated from day 6 to day 14 of chemical burn-induced CorNV. In chemical burn-induced CorNV in C57BL/6J mice, however, they were down-regulated at day 6. Corneal crystallins were down-regulated in both CorNV models at all time points in both BALB/c and C57BL/6J mice. Comparison of CorNV development in αA-crystallin-deficient mice and that in wild-type mice revealed no significant difference. Subconjunctival injection of αA-crystallin significantly attenuated suture-induced CorNV, and the inhibitory activity might be implemented by the increased expression of soluble VEGFR-1. In conclusion, the expression patterns of lens crystallins were time- and strain-dependent but different from that of corneal crystallins in mouse CorNV models. Exogenous αA-crystallin protein attenuated CorNV, potentially by increasing the expression of soluble VEGFR-1.

Local ischemia and increased expression of vascular endothelial growth factor following ocular dissemination of Mycobacterium tuberculosis

The pathogenesis of intraocular tuberculosis remains poorly understood partly due to the lack of adequate animal models that accurately simulate human disease. Using a recently developed model of ocular tuberculosis following aerosol infection of guinea pigs with Mycobacterium tuberculosis, we studied the microbiological, histological, and clinical features of intraocular tuberculosis infection. Viable tubercle bacilli were cultivated from all eyes by Day 56 after aerosol delivery of ∼200 bacilli to guinea pig lungs. Choroidal tuberculous granulomas showed reduced oxygen tension, as evidenced by staining with the hypoxia-specific probe pimonidazole, and expression of vascular endothelial growth factor (VEGF) was detected in the retinal pigment epithelium (RPE) and photoreceptors. Fundoscopic examination of M. tuberculosis-infected guinea pig eyes revealed altered vascular architecture and chorioretinal hemorrhage by Day 56 after infection. This model may be useful in further elucidating the pathogenesis of ocular tuberculosis, as well as in developing tools for diagnosis and assessment of antituberculosis treatment responses in the eye.

Emerging techniques to treat corneal neovascularisation

Neovascularisation is a major cause of visual loss in a number of ophthalmic diseases. This review aims to outline the basic regulators of vessel growth in corneal neovascularisation. An understanding of the underlying principles of physiological and pathophysiological vascular development helps to appreciate current approaches to prevent or treat corneal neovascularisation. Options for future interventions will be discussed in the light of recent evidence provided by animal models of corneal neovascularisation.

Normalization of the vasculature for treatment of cancer and other diseases

New vessel formation (angiogenesis) is an essential physiological process for embryologic development, normal growth, and tissue repair. Angiogenesis is tightly regulated at the molecular level. Dysregulation of angiogenesis occurs in various pathologies and is one of the hallmarks of cancer. The imbalance of pro- and anti-angiogenic signaling within tumors creates an abnormal vascular network that is characterized by dilated, tortuous, and hyperpermeable vessels. The physiological consequences of these vascular abnormalities include temporal and spatial heterogeneity in tumor blood flow and oxygenation and increased tumor interstitial fluid pressure. These abnormalities and the resultant microenvironment fuel tumor progression, and also lead to a reduction in the efficacy of chemotherapy, radiotherapy, and immunotherapy. With the discovery of vascular endothelial growth factor (VEGF) as a major driver of tumor angiogenesis, efforts have focused on novel therapeutics aimed at inhibiting VEGF activity, with the goal of regressing tumors by starvation. Unfortunately, clinical trials of anti-VEGF monotherapy in patients with solid tumors have been largely negative. Intriguingly, the combination of anti-VEGF therapy with conventional chemotherapy has improved survival in cancer patients compared with chemotherapy alone. These seemingly paradoxical results could be explained by a "normalization" of the tumor vasculature by anti-VEGF therapy. Preclinical studies have shown that anti-VEGF therapy changes tumor vasculature towards a more "mature" or "normal" phenotype. This "vascular normalization" is characterized by attenuation of hyperpermeability, increased vascular pericyte coverage, a more normal basement membrane, and a resultant reduction in tumor hypoxia and interstitial fluid pressure. These in turn can lead to an improvement in the metabolic profile of the tumor microenvironment, the delivery and efficacy of exogenously administered therapeutics, the efficacy of radiotherapy and of effector immune cells, and a reduction in number of metastatic cells shed by tumors into circulation in mice. These findings are consistent with data from clinical trials of anti-VEGF agents in patients with various solid tumors. More recently, genetic and pharmacological approaches have begun to unravel some other key regulators of vascular normalization such as proteins that regulate tissue oxygen sensing (PHD2) and vessel maturation (PDGFRβ, RGS5, Ang1/2, TGF-β). Here, we review the pathophysiology of tumor angiogenesis, the molecular underpinnings and functional consequences of vascular normalization, and the implications for treatment of cancer and nonmalignant diseases.

Decreased angiogenin concentration in vitreous and serum in proliferative diabetic retinopathy

Diabetic retinopathy is the most common cause of vision loss in young adults in developed countries. The disease therapy with anti-vascular endothelial growth factor (VEGF) agents gives some positive results, but is associated with retinal ischemia and vasoconstriction. Therefore, determination of factors involved in the physiological and pathological angiogenesis in the diabetic eye is of great importance for understanding of the pathogenesis of diabetic retinopathy and its effective treatment. Previously, we found that diabetic patients were characterized by increased serum concentration of VEGF, but decreased levels of other proangiogenic factor-angiogenin. The involvement of VEGF in pathogenesis of diabetic retinopathy is well established, but there is lack of data regarding angiogenin in retinopathy. Therefore, in the present study we measured angiogenin concentration in vitreous and serum samples of the patients with type 1 diabetes to determine its role in diabetic retinopathy. In addition, in each time, we compared the level of angiogenin with level of VEGF as a known factor involved in the pathogenesis of the disease. Angiogenin was found to be significantly more abundant in serum than in vitreous in both diabetic groups. In addition, patients with retinopathy had twofold lower vitreous angiogenin levels than diabetic individuals without complications. On the contrary, vitreous concentration of VEGF was dramatically increased only in participants with retinopathy. Patients without diabetic complications had significantly lower VEGF levels in vitreous than in serum and were characterized by high local and systemic concentration of angiogenin. These data suggest a local imbalance between two proangiogenic factors-VEGF and angiogenin in retinopathy. Low vitreous concentration of angiogenin in diabetic patients suggests that this factor is not responsible for pathological neovascularization in diabetic eye. Further studies will elucidate if angiogenin can be used to improve the insufficient angiogenesis in diabetes and prevent retinal ischemia after retinopathy treatment with anti-VEGF agents.