Inhibition of ocular neovascularization by a novel peptide derived from human placenta growth factor-1

Loss of miR-673-5p expression in the cornea promotes rat corneal allograft rejection by promoting Th17 cell differentiation mediated by JAK2/STAT3

Background

Cluster of differentiation 4 positive (CD4⁺) T cells play an important role in corneal graft rejection, especially the dynamic balance between regulatory T cells and helper T cells. This study aims to explore the upstream and downstream regulatory mechanisms of Th17 cell differentiation-mediated corneal allograft rejection.

Methods

By establishing rat corneal allograft transplantation model, transcriptome analysis was carried out to screen the differentially expressed genes related to T helper 17 (Th17) cell differentiation, and then cell experiments were used to verify the effect of miR-673-5p/Janus Kinase 2 (JAK2) signal on naïve CD4⁺ T cell differentiation and the proliferation, migration, and tube formation ability of human umbilical vein endothelial cells (HUVECs). Finally, the role of miR-673-5p/JAK2 signal in corneal allograft rejection was verified by animal model in vivo.

Results

The results showed that JAK2/STAT3 signaling activation-mediated Th17 cell differentiation was significantly up-regulated during corneal allograft rejection, and miR-673-5p expression was down-regulated after corneal allograft rejection. Low expression of miR-673-5p promoted Th17 cell differentiation by up-regulating JAK2, and then promoted placental growth factor (PLGF)mediated corneal neovascularization (CNV).

Conclusions

The results of this study suggested that low expression of miR-673-5p is a promoter of corneal allograft rejection. Overexpression of miR-673-5p can improve the survival rate of corneal allografts by inhibiting the differentiation and maturation of Th17 cells mediated by JAK2/STAT3 signaling.

Efficacy of a new automated method for quantification of corneal neovascularisation

BACKGROUND/AIMS

To evaluate the efficacy of a new automated method for quantification of corneal neovascularisation (NV).

METHODS

An in-house software for automated measurement of corneal NV was developed. Anterior segment photographs (ASPs) of 81 consecutive patients with corneal NV were analysed using our newly developed software. Manual measurements were performed by three independent examiners using ImageJ software V.1.48 (National Institute of Health, Bethesda, Maryland, USA). Interobserver reliability of the automated and manual methods, and correlations between the results of both methods were evaluated.

RESULTS

The automated method showed a strong interexaminer reliability (intraclass correlation coefficient (ICC)=0.994), which was slightly better than the manual method (ICC=0.958). A significant correlation was found between the results of both methods (p<0.001 for all three examiners). The time spent for analysis of each ASP was significantly reduced in the automated method compared with the manual method (p<0.001 for all three examiners).

CONCLUSIONS

Our newly developed automated method for quantification of corneal NV was more reproducible and time-saving compared with the manual method. Our method can be useful for diagnosis and monitoring diseases causing corneal NV.

The role of placental growth factor (PlGF) and its receptor system in retinal vascular diseases

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family. Upon binding to VEGF- and neuropilin-receptor sub-types, PlGF modulates a range of neural, glial and vascular cell responses that are distinct from VEGF-A. As PlGF expression is selectively associated with pathological angiogenesis and inflammation, its blockade does not affect the healthy vasculature. PlGF actions have been extensively described in tumor biology but more recently there has been accumulating preclinical evidence that indicates that this growth factor could have an important role in retinal diseases. High levels of PlGF have been found in aqueous humor, vitreous and/or retina of patients exhibiting retinopathies, especially those with diabetic retinopathy (DR) and neovascular age-related macular degeneration (nvAMD). Expression of this growth factor seems to correlate closely with many of the key pathogenic features of early and late retinopathy in preclinical models. For example, studies using genetic modification and/or pharmacological treatment to block PlGF in the laser-induced choroidal neovascularization (CNV) model, oxygen-induced retinopathy model, as well as various murine diabetic models, have shown that PlGF deletion or inhibition can reduce neovascularization, retinal leakage, inflammation and gliosis, without affecting vascular development or inducing neuronal degeneration. Moreover, an inhibitory effect of PlGF blockade on retinal scarring in the mouse CNV model has also been recently demonstrated and was found to be unique for PlGF inhibition, as compared to various VEGF inhibition strategies. Together, these preclinical results suggest that anti-PlGF therapy might have advantages over anti-VEGF treatment, and that it may have clinical applications as a standalone treatment or in combination with anti-VEGF. Additional clinical studies are clearly needed to further elucidate the role of PlGF and its potential as a therapeutic target in ocular diseases.

Placental growth factor and its potential role in diabetic retinopathy and other ocular neovascular diseases

The role of vascular endothelial growth factor (VEGF), including in retinal vascular diseases, has been well studied, and pharmacological blockade of VEGF is the gold standard of treatment for neovascular age‐related macular degeneration, retinal vein occlusion and diabetic macular oedema. Placental growth factor (PGF, previously known as PlGF), a homologue of VEGF, is a multifunctional peptide associated with angiogenesis‐dependent pathologies in the eye and non‐ocular conditions. Animal studies using genetic modification and pharmacological treatment have demonstrated a mechanistic role for PGF in pathological angiogenesis. Inhibition decreases neovascularization and microvascular abnormalities across different models, including oxygen‐induced retinopathy, laser‐induced choroidal neovascularization and in diabetic mice exhibiting retinopathies. High levels of PGF have been found in the vitreous of patients with diabetic retinopathy. Despite these strong animal data, the exact role of PGF in pathological angiogenesis in retinal vascular diseases remains to be defined, and the benefits of PGF‐specific inhibition in humans with retinal neovascular diseases and macular oedema remain controversial. Comparative effectiveness research studies in patients with diabetic retinal disease have shown that treatment that inhibits both VEGF and PGF may provide superior outcomes in certain patients compared with treatment that inhibits only VEGF. This review summarizes current knowledge of PGF, including its relationship to VEGF and its role in pathological angiogenesis in retinal diseases, and identifies some key unanswered questions about PGF that can serve as a pathway for future basic, translational and clinical research.

A Critical Analysis of the Available In Vitro and Ex Vivo Methods to Study Retinal Angiogenesis

Angiogenesis is a biological process with a central role in retinal diseases. The choice of the ideal method to study angiogenesis, particularly in the retina, remains a problem. Angiogenesis can be assessed through in vitro and in vivo studies. In spite of inherent limitations, in vitro studies are faster, easier to perform and quantify, and typically less expensive and allow the study of isolated angiogenesis steps. We performed a systematic review of PubMed searching for original articles that applied in vitro or ex vivo angiogenic retinal assays until May 2017, presenting the available assays and discussing their applicability, advantages, and disadvantages. Most of the studies evaluated migration, proliferation, and tube formation of endothelial cells in response to inhibitory or stimulatory compounds. Other aspects of angiogenesis were studied by assessing cell permeability, adhesion, or apoptosis, as well as by implementing organotypic models of the retina. Emphasis is placed on how the methods are applied and how they can contribute to retinal angiogenesis comprehension. We also discuss how to choose the best cell culture to implement these methods. When applied together, in vitro and ex vivo studies constitute a powerful tool to improve retinal angiogenesis knowledge. This review provides support for researchers to better select the most suitable protocols in this field.

Influences of placental growth factor on mouse retinal vascular development

BACKGROUND

Placental growth factor (PGF) is important for wound-healing and vascular collaterogenesis. PGF deficiency is associated with preeclampsia, a hypertensive disease of human pregnancy. Offspring born to preeclamptic mothers display cognitive impairments and brain vascular and neurostructural deviations. Low PGF production during development may contribute to alterations in offspring cerebrovascular beds. Retina is a readily accessible part of the central nervous system with a well-described pattern of vascular development in mice. Impacts of PGF deficiency were addressed during mouse retinal vascularization.

RESULTS

Retinal vessels were compared between Pgf^-/- and congenic C57BL/6 (B6) mice. PGF deficiency altered neonatal retinal vascularization patterns. Some anatomic alterations persisted into adulthood, particularly in males. Greater arterial wall collagen IV expression was found in adult Pgf^-/- females. Pregnancy (studied in adult females at gestational days 11.5 or 18.5) induced subtle changes upon the mother's retinal vasculature but these pregnancy-induced changes did not differ between genotypes. Significant sex-related differences occurred between adult male and female B6 although sexually dimorphic retinal vascular differences were absent in B6 neonates.

CONCLUSIONS

Overall, PGF has a role in retinal vascular angiogenesis and vessel organization during development but does not affect retinal vessel adaptations in adult females during pregnancy. Developmental Dynamics 246:700-712, 2017. © 2017 Wiley Periodicals, Inc.

Correlation of Vascular Endothelial Growth Factor Production with Photochemical Reaction-induced Retinal Edema

BACKGROUND

Retinal edema is the major complication of retinal vein occlusion and diabetic retinopathy; it can damage visual function by influencing macular region. This study was to establish a rat retinal edema model and explore the related VEGF expression and observe the responses to anti-VEGF drugs in this model.

METHODS

A rat retinal edema model was established by inducing photochemical reaction using a 532 nm laser after the intravenous injection of Erythrosin B. Immediately after the laser treatment, models were given intravitreal injections of Ranibizumab or Conbercept to inhibit VEGF expression, and the changes of retinal thickness were measured. Retinal edema was observed using fundus photography (FP), optical coherence tomography (OCT), and fluoresce in fundus angiography (FFA) at 0, 1, 2, 4, 7 and 14 days after intervention. The retinal VEGF expression was measured using enzyme-linked immunosorbent assay (ELISA) and western blotting at each time point. The rat retinal edema model was also used to verify the function of anti-VEGF polypeptide ZY1.

RESULTS

Both retinal edema and vascular leakage were clearly observed at 1, 2 and 4 days after photochemical induction and the retinal thickness increased notably over the same period. The retinal VEGF expression peaked at day 1 and retina became thickening simultaneously. After the interventions, the VEGF expression of the Ranibizumab and Conbercept groups decreased at each time point compared to the edema group (26.90 ± 3.57 vs. 40.29 ± 6.68, F = 31.269 on day 1 and 22.36 ± 1.12 vs. 29.92 ± 0.93 F = 163.789 on day 2, both P < 0.01); the mean RT (278 ± 4 vs. 288 ± 3, F = 134.190 on day 1 and 274 ± 7 vs. 284 ± 6, F = 64.367 on day 2, both P < 0.05) and vascular leakage in these groups also decreased. The same results were observed in the ZY1 group, particularly at day 2 (P < 0.05).

CONCLUSIONS

This retinal edema model induced by a photochemical reaction is reliable and repeatable. Induced edema increases expression of VEGF. This model can be used to test new drugs.

Anti-angiogenesis through noninvasive to minimally invasive intraocular delivery of the peptide CC12 identified by in vivo-directed evolution

Anti-vascular endothelial growth factor (VEGF) therapies are widely used for the treatment of neovascular fundus diseases such as diabetic retinopathy. However, these agents need to be injected intravitreally, because their strong hydrophilicity and high molecular weight prevent them from penetrating cell membranes and complex tissue barriers. Moreover, the repeated injections that are required can cause infection and tissue injury. In this study, we used in vivo-directed evolution phage display technology to identify a novel dodecapeptide, named CC12, with the ability to penetrate the ocular barrier in a noninvasive (via conjunctival sac instillation) or minimally invasive (via retrobulbar injection) manner. KV11, an antiangiogenesis peptide previously demonstrated to inhibit pathological neovascularization in the retina, was then used as a model antiangiogenesis cargo for CC12. We found that conjugation of KV11 peptide with CC12 peptide facilitated the delivery of KV11 to the retina, resulting in significant inhibition of retinal neovascularization development via topical application without tissue toxicity. Collectively, our data of multilevel evaluations demonstrate that CC12 may enable the noninvasive to minimally invasive intraocular delivery of antiangiogenic therapeutics.

The peptidomimetic Vasotide targets two retinal VEGF receptors and reduces pathological angiogenesis in murine and nonhuman primate models of retinal disease

Blood vessel growth from preexisting vessels (angiogenesis) underlies many severe diseases including major blinding retinal diseases such as retinopathy of prematurity (ROP) and aged macular degeneration (AMD). This observation has driven development of antibody inhibitors that block a central factor in AMD, vascular endothelial growth factor (VEGF), from binding to its receptors VEGFR-1 and mainly VEGFR-2. However, some patients are insensitive to current anti-VEGF drugs or develop resistance, and the required repeated intravitreal injection of these large molecules is costly and clinically problematic. We have evaluated a small cyclic retro-inverted peptidomimetic, D(Cys-Leu-Pro-Arg-Cys) [D(CLPRC)], and hereafter named Vasotide, that inhibits retinal angiogenesis by binding selectively to the VEGF receptors VEGFR-1 and neuropilin-1 (NRP-1). Delivery of Vasotide via either eye drops or intraperitoneal injection in a laser-induced monkey model of human wet AMD, a mouse genetic knockout model of the AMD subtype called retinal angiomatous proliferation (RAP), and a mouse oxygen-induced model of ROP decreased retinal angiogenesis in all three animal models. This prototype drug candidate is a promising new dual receptor inhibitor of the VEGF ligand with potential for translation into safer, less-invasive applications to combat pathological angiogenesis in retinal disorders.

Neurovascular cross talk in diabetic retinopathy: Pathophysiological roles and therapeutic implications

Diabetic retinopathy (DR) is the leading cause of blindness in the working-age population in developed countries, and its prevalence will increase as the global incidence of diabetes grows exponentially. DR begins with an early nonproliferative stage in which retinal blood vessels and neurons degenerate as a consequence of chronic hyperglycemia, resulting in vasoregression and persistent retinal ischemia, metabolic disequilibrium, and inflammation. This is conducive to overcompensatory pathological neovascularization associated with advanced proliferative DR. Although DR is considered a microvascular complication, the retinal microvasculature is intimately associated with and governed by neurons and glia; neurodegeneration, neuroinflammation, and dysregulation of neurovascular cross talk are responsible in part for vascular abnormalities in both early nonproliferative DR and advanced proliferative DR. Neuronal activity directly regulates microvascular dilation and blood flow in the process of neurovascular coupling. Retinal neurons also secrete guidance cues in response to injury, ischemia, or metabolic stress that may either promote or suppress vascular outgrowth, either alleviating or exacerbating DR, contingent on the stage of disease and retinal microenvironment. Neurodegeneration, impaired neurovascular coupling, and dysregulation of neuronal guidance cues are key events in the pathogenesis of DR, and correcting these events may prevent or delay development of advanced DR. The review discusses the mechanisms of neurovascular cross talk and its dysregulation in DR, and their potential therapeutic implications.

Inhibition of Pathologic Corneal Neovascularization by Topical Application of a Novel Peptide In Vivo

PURPOSE

To investigate the antiangiogenic effect of topical application of H-KI20, a novel 20-amino acid peptide from the hepatocyte growth factor, on 2 animal models of corneal neovascularization (NV), and its possible toxic effects on the cornea and conjunctiva.

METHODS

The antiangiogenic effect of topical H-KI20 in vivo was studied on corneal NV induced by a mouse corneal micropocket assay and rat intrastromal suture model. In each model, H-KI20, scrambled control peptide H-KI20S, bevacizumab, and phosphate buffer solution (PBS) were applied topically 4 times a day. Corneal NV was examined, photographed, and analyzed. Histological analysis of the corneas was performed. Tear film breakup time and gross and histological examinations were used to study the possible toxicity of topical H-KI20.

RESULTS

Topical application of H-KI20 significantly inhibited corneal NV induced by vascular endothelial growth factor (VEGF), and intrastromal suture (P < 0.01 vs. the PBS group), and the area of corneal NV was suppressed by 80.3% and 83.6%, respectively (PBS group as 100%). No significant difference was found between 1.0 mg/mL H-KI20 and 10 mg/mL bevacizumab (P > 0.05). Both hematoxylin and eosin and CD34 staining revealed fewer new blood vessels in the H-KI20 and bevacizumab groups. Tear film breakup time and histological examinations showed that H-KI20 had no obvious toxic effects on the cornea and conjunctiva in vivo.

CONCLUSIONS

The novel peptide H-KI20 is an effective and safe inhibitor of corneal NV. It may provide a promising alternative for ocular topical antiangiogenic therapy.

Protein polymer nanoparticles engineered as chaperones protect against apoptosis in human retinal pigment epithelial cells

αB-Crystallin is a protein chaperone with anti-apoptotic and anti-inflammatory activity that is apically secreted in exosomes by polarized human retinal pigment epithelium. A 20 amino acid mini-peptide derived from residues 73-92 of αB-crystallin protects human retinal pigment epithelial (RPE) cells from oxidative stress, a process involved in the progression of age-related macular degeneration (AMD). Unfortunately, due to its small size, its development as a therapeutic requires a robust controlled release system. To achieve this goal, the αB-crystallin peptide was re-engineered into a protein polymer nanoparticle/macromolecule with the purpose of increasing the hydrodynamic radius/molecular weight and enhancing potency via multivalency or an extended retention time. The peptide was recombinantly fused with two high molecular weight (~40kDa) protein polymers inspired by human tropoelastin. These elastin-like polypeptides (ELPs) include the following: (i) a soluble peptide called S96 and (ii) a diblock copolymer called SI that assembles multivalent nanoparticles at physiological temperature. Fusion proteins, cryS96 and crySI, were found to reduce aggregation of alcohol dehydrogenase and insulin, which demonstrates that ELP fusion did not diminish chaperone activity. Next their interaction with RPE cells was evaluated under oxidative stress. Unexpectedly, H2O2-induced stress dramatically enhanced cellular uptake and nuclear localization of both cryS96 and crySI ELPs. Accompanying uptake, both fusion proteins protected RPE cells from apoptosis, as indicated by reduced caspase 3 activation and TUNEL staining. This study demonstrates the in vitro feasibility of modulating the hydrodynamic radius for small peptide chaperones by seamless fusion with protein polymers; furthermore, they may have therapeutic applications in diseases associated with oxidative stress, such as AMD.

Safety profiles of anti-VEGF drugs: bevacizumab, ranibizumab, aflibercept and ziv-aflibercept on human retinal pigment epithelium cells in culture

Purpose

To compare the safety profiles of antivascular endothelial growth factor (VEGF) drugs ranibizumab, bevacizumab, aflibercept and ziv-aflibercept on retinal pigment epithelium cells in culture.

Methods

Human retinal pigment epithelium cells (ARPE-19) were exposed for 24 h to four anti-VEGF drugs at 1/2×, 1×, 2× and 10× clinical concentrations. Cell viability and mitochondrial membrane potential assay were performed to evaluate early apoptotic changes and rate of overall cell death.

Results

Cell viability decreased at 10× concentrations in bevacizumab (82.38%, p=0.0001), aflibercept (82.68%, p=0.0002) and ziv-aflibercept (77.25%, p<0.0001), but not at lower concentrations. However, no changes were seen in cell viability in ranibizumab-treated cells at all concentrations including 10×. Mitochondrial membrane potential was slightly decreased in 10× ranibizumab-treated cells (89.61%, p=0.0006) and 2× and 10× aflibercept-treated cells (88.76%, 81.46%; p<0.01, respectively). A larger reduction in mitochondrial membrane potential was seen at 1×, 2× and 10× concentrations of bevacizumab (86.53%, 74.38%, 66.67%; p<0.01) and ziv-aflibercept (73.50%, 64.83% and 49.65% p<0.01) suggestive of early apoptosis at lower doses, including the clinical doses.

Conclusions

At clinical doses, neither ranibizumab nor aflibercept produced evidence of mitochondrial toxicity or cell death. However, bevacizumab and ziv-aflibercept showed mild mitochondrial toxicity at clinically relevant doses.

Inhibitory effects of regorafenib, a multiple tyrosine kinase inhibitor, on corneal neovascularization

AIM

To evaluate the inhibitory effects of regorafenib (BAY 73-4506), a multikinase inhibitor, on corneal neovascularization (NV).

METHODS

Thirty adult male Sprague-Dawley rats weighing 250-300 g, were used. Corneal NV was induced by NaOH in the left eyes of each rat. Following the establishment of alkali burn, the animals were randomized into five groups according to topical treatment. Group 1 (n = 6) received 0.9% NaCl, Group 2 (n = 6) received dimethyl sulfoxide, Group 3 (n = 6) received regorafenib 1 mg/mL, Group 4 (n =6) received bevacizumab 5 mg/mL and Group 5 (n = 6) received 0.1% dexamethasone phosphate. On the 7d, the corneal surface covered with neovascular vessels was measured on photographs as the percentage of the cornea's total area using computer-imaging analysis. The corneas obtained from rats were semiquantitatively evaluated for caspase-3 and vascular endothelial growth factor by immunostaining.

RESULTS

A statistically significant difference in the percent area of corneal NV was found among the groups (P <0.001). Although the Group 5 had the smallest percent area of corneal NV, there was no difference among Groups 3, 4 and 5 (P >0.005). There was a statistically significant difference among the groups in apoptotic cell density (P = 0.002). The staining intensity of vascular endothelial growth factor in the epithelial and endothelial layers of cornea was significantly different among the groups (P <0.05). The staining intensity of epithelial and endothelial vascular endothelial growth factor was significantly weaker in Groups 3, 4 and 5 than in Groups 1 and 2.

CONCLUSION

Topical administration of regorafenib 1 mg/mL is partly effective for preventing alkali-induced corneal NV in rats.