Corneal angiogenesis and lymphangiogenesis

Corneal Lymphangiogenesis: Current Pathophysiological Understandings and Its Functional Role in Ocular Surface Disease

The cornea is a transparent and avascular tissue that plays a central role in light refraction and provides a physical barrier to the external environment. Corneal avascularity is a unique histological feature that distinguishes it from the other parts of the body. Functionally, corneal immune privilege critically relies on corneal avascularity. Corneal lymphangiogenesis is now recognized as a general pathological feature in many pathologies, including dry eye disease (DED), corneal allograft rejection, ocular allergy, bacterial and viral keratitis, and transient corneal edema. Currently, sizable data from clinical and basic research have accumulated on the pathogenesis and functional role of ocular lymphangiogenesis. However, because of the invisibility of lymphatic vessels, ocular lymphangiogenesis has not been studied as much as hemangiogenesis. We reviewed the basic mechanisms of lymphangiogenesis and summarized recent advances in the pathogenesis of ocular lymphangiogenesis, focusing on corneal allograft rejection and DED. In addition, we discuss future directions for lymphangiogenesis research.

Ocular Graft-versus-Host Disease in a Chemotherapy-Based Minor-Mismatch Mouse Model Features Corneal (Lymph-) Angiogenesis

Ocular graft-versus-host disease (oGVHD) is a fast progressing, autoimmunological disease following hematopoietic stem cell transplantation, leading to severe inflammation of the eye and destruction of the lacrimal functional unit with consecutive sight-threatening consequences. The therapeutic “window of opportunity” is narrow, and current treatment options are limited and often insufficient. To achieve new insights into the pathogenesis and to develop new therapeutic approaches, clinically relevant models of oGVHD are desirable. In this study, the ocular phenotype was described in a murine, chemotherapy-based, minor-mismatch GVHD model mimicking early-onset chronic oGVHD, with corneal epitheliopathy, inflammation of the lacrimal glands, and blepharitis. Additionally, corneal lymphangiogenesis was observed as part of oGVHD pathogenesis for the first time, thus opening up the investigation of lymphangiogenesis as a potential therapeutic and diagnostic tool.

The Role of Inflammatory Cytokines in Neovascularization of Chemical Ocular Injury

Aim: Chemical injuries can potentially lead to the necrosis anterior segment of the eye, and cornea in particular. Inflammatory cytokines are the first factors produced after chemical ocular injuries. Inflammation via promoting the angiogenesis factor tries to implement the wound healing mechanism in the epithelial and stromal layer of the cornea. Methods: Narrative review.Results: In our review, we described the patterns of chemical injuries in the cornea and their molecular mechanisms associated with the expression of inflammatory cytokines. Moreover, the effects of inflammation signals on angiogenesis factors and CNV were explained. Conclusion: The contribution of inflammation and angiogenesis causes de novo formation of blood vessels that is known as the corneal neovascularization (CNV). The new vascularity interrupts cornea clarity and visual acuity. Inflammation also depleted the Limbal stem cells (LSCs) in the limbus causing the failure of normal corneal epithelial healing and conjunctivalization of the cornea.

Immune reactions after modern lamellar (DALK, DSAEK, DMEK) versus conventional penetrating corneal transplantation

In the past decade, novel lamellar keratoplasty techniques such as Deep Anterior Lamellar Keratoplasty (DALK) for anterior keratoplasty and Descemet stripping automated endothelial keratoplasty (DSAEK)/Descemet membrane endothelial keratoplasty (DMEK) for posterior keratoplasty have been developed. DALK eliminates the possibility of endothelial allograft rejection, which is the main reason for graft failure after penetrating keratoplasty (PK). Compared to PK, the risk of endothelial graft rejection is significantly reduced after DSAEK/DMEK. Thus, with modern lamellar techniques, the clinical problem of endothelial graft rejection seems to be nearly solved in the low-risk situation. However, even with lamellar grafts there are epithelial, subepithelial and stromal immune reactions in DALK and endothelial immune reactions in DSAEK/DMEK, and not all keratoplasties can be performed in a lamellar fashion. Therefore, endothelial graft rejection in PK is still highly relevant, especially in the "high-risk" setting, where the cornea's (lymph)angiogenic and immune privilege is lost due to severe inflammation and pathological neovascularization. For these eyes, currently available treatment options are still unsatisfactory. In this review, we will describe currently used keratoplasty techniques, namely PK, DALK, DSAEK, and DMEK. We will summarize their indications, provide surgical descriptions, and comment on their complications and outcomes. Furthermore, we will give an overview on corneal transplant immunology. A specific focus will be placed on endothelial graft rejection and we will report on its incidence, clinical presentation, and current/future treatment and prevention options. Finally, we will speculate how the field of keratoplasty and prevention of corneal allograft rejection will develop in the future.

Current and emerging therapies for corneal neovascularization

The cornea is unique because of its complete avascularity. Corneal neovascularization (CNV) can result from a variety of etiologies including contact lens wear; corneal infections; and ocular surface diseases due to inflammation, chemical injury, and limbal stem cell deficiency. Management is focused primarily on the etiology and pathophysiology causing the CNV and involves medical and surgical options. Because inflammation is a key factor in the pathophysiology of CNV, corticosteroids and other anti-inflammatory medications remain the mainstay of treatment. Anti-VEGF therapies are gaining popularity to prevent CNV in a number of etiologies. Surgical options including vessel occlusion and ocular surface reconstruction are other options depending on etiology and response to medical therapy. Future therapies should provide more effective treatment options for the management of CNV.

Cooperative Effects of Vascular Angiogenesis and Lymphangiogenesis

In this study, we modeled lymphangiogenesis and vascular angiogenesis in a microdevice using a tissue engineering approach. Lymphatic vessels (LV) and blood vessels (BV) were fabricated by sacrificial molding with seeding human lymphatic endothelial cells and human umbilical vein endothelial cells into molded microchannels (600 μm diameter). During subsequent perfusion culture, lymphangiogenesis and vascular angiogenesis were induced by addition of phorbol 12-myristate 13-acetate (PMA) and VEGF-C or VEGF-A characterized by podoplanin and Prox-1 expression. The lymphatic capillaries formed button-like junctions treated with dexamethasone. To test the potential for screening anti-angiogenic (vascular and lymphatic) factors, antagonists of VEGF were introduced. We found that an inhibitor of VEGF-R3 did not completely suppress lymphatic angiogenesis with BVs present, although lymphatic angiogenesis was selectively prevented by addition of a VEGF-R3 inhibitor without BVs. To probe the mechanism of action, we focus on matrix metalloproteinase (MMP) secretion by vascular endothelial cells and lymphatic endothelial cells under monoculture or co-culture conditions. We found that vascular angiogenesis facilitated lymphangiogenesis via remodeling of the local microenvironment by the increased secretion of MMP, mainly by endothelial cells. Applications of this model include a drug screening assay for corneal disease and models for tumorigenesis including lymphatic angiogenesis and vascular angiogenesis.

CXCL10 suppression of hem- and lymph-angiogenesis in inflamed corneas through MMP13

Though not present in the normal adult cornea, both hem- and lymph-angiogenesis can be induced in this tissue after an inflammatory, infectious, or traumatic insult. We previously showed that the chemokine CXCL10 plays a key role in eradicating invading Candida (C.) albicans in C57BL6 mouse corneas. However, even after the clearance of pathogens, infection-induced inflammation and angiogenesis continue to progress in the cornea. The aim of this study is define the role of CXCL10 as a major angiostatic factor in modulating cornea angiogenesis in B6 mouse corneas under pathogenic conditions. We showed that epithelial expression of CXCL10, driven by AAV9 vector, suppressed both infection- and inflammation-induced hem and lymph angiogenesis, whereas the neutralization of CXCL10 as well as its receptor CXCR3 greatly promoted these processes. The inhibitory effect of CXCL10 was unrelated to its antimicrobial activity, but through the suppression of the expression of many angiogenic factors, including VEGFa and c, and MMP-13 in vivo. Inhibition of MMP13 but not TIMPs, attenuated suture-induced neovascularization but had no effects on CXCL10 expression. Strikingly, topical application of CXCL10 post-C. albicans infection effectively blocked both hem- and lymph-angiogenesis and preserved the integrity of sensory nerves in the cornea. Taken together, CXCL10 has strong inhibitory effects on neovascularization, whereas MMP13 is required for neovascularization in C. albicans-infected corneas and the local application of CXCL10 or MMP13 inhibitors, alone or as adjuvant therapy, may target hem- and lymph-angiogenesis in the inflamed corneas.

Prevention of recurrent pterygium with topical bevacizumab 0.05% eye drops: a randomized controlled trial

PURPOSE

We assessed the efficacy and tolerability of topical bevacizumab 0.05% when used as an adjunctive therapy after excision of primary pterygia.

METHODS

This randomized double-masked study included 22 patients (22 eyes) with primary pterygia who underwent pterygium surgery with the use of the bare sclera technique. After pterygium excision, 22 patients were randomized to receive the topical bevacizumab 0.05% (12 eyes) or the placebo (10 eyes) with the use of the block of four randomization method. Topical bevacizumab and placebo were applied in the respective groups 4 times daily for 3 months. Follow-up evaluations for recurrence by slit-lamp photography were conducted once monthly. Ocular and systemic adverse events were assessed every 2 weeks during the 3 months of treatment. The slit-lamp photographs were masked and analyzed. The primary and secondary outcomes were the differences in the pterygial recurrence rates between the groups and adverse events at 3 months, respectively. Corneal recurrence was defined as recurrent fibrovascular tissue invading the cornea; conjunctival recurrence was defined as either recurrent vessels or fibrous tissue in the excised area without corneal invasion.

FINDINGS

All 22 patients completed follow-up at 3 months after the start of the trial medications. After 3 months of treatment, 1 patient (8.33%) and 3 patients (30.00%) from the bevacizumab and placebo groups, respectively, had a corneal recurrence. No significant (P = 0.293) differences were found between the groups as determined by Fisher's exact test. However, conjunctival and corneal recurrences were found in 4 (33.33%) and 9 (90.00%) patients, respectively, in the bevacizumab and placebo groups, a difference that reached significance (P = 0.01). No significant adverse events developed.

IMPLICATIONS

Topical bevacizumab, as an adjunctive treatment after pterygium excision, was well tolerated. The trend for recurrence was lower in the topical bevacizumab group. ClinicalTrials.gov identifier: NCT01311960.

Imidazole-based alkaloid derivative LCB54-0009 suppresses ocular angiogenesis and lymphangiogenesis in models of experimental retinopathy and corneal neovascularization

BACKGROUND AND PURPOSE

Abnormally induced angiogenesis and lymphangiogenesis are associated with human diseases, including neovascular eye disease. Substances that inhibit these processes may have potential as an attractive therapeutic strategy for these diseases.

EXPERIMENTAL APPROACH

In vitro and in vivo angiogenesis and/or lymphangiogenesis were assessed in VEGF- or hypoxia-stimulated endothelial and retinal cells and in animal models of oxygen-induced retinopathy (OIR), streptozotocin-induced diabetic retinopathy (SIDR), suture-induced inflammatory corneal neovascularization (SICNV) and silver nitrate-induced corneal neovascularization. HUVECs and retinal cells were cultured under hypoxic conditions or incubated with VEGF to identify the molecular mechanisms involved.

KEY RESULTS

The imidazole-based alkaloid derivative LCB54-0009 inhibited capillary-like tube formation in VEGF-induced HUVECs without inducing cytotoxic effects. Intravitreal injection of LCB54-0009 into retinas suppressed the formation of the pathological neovascular tufts and increased vascular permeability in both OIR of mice and SIDR of rats. Furthermore, subconjunctival injection of LCB54-0009 into the cornea suppressed corneal inflammation and inflammation-associated angiogenesis and lymphangiogenesis in SICNV of mice and silver nitrate cauterization of rats. These pharmacological activities were associated with effects on HIF-1α protein stability and HIF-1α/NF-κB redox sensitivity through its antioxidant activities. LCB54-0009 also inhibited the hypoxia-induced expression of angiopoietin-2, and VEGF-induced VEGFR-2 activation and downstream signalling, resulting in the down-regulation of the expression of pro-angiogenic factors and pro-inflammatory mediators and an up-regulation of the expression of anti-angiogenic factors.

CONCLUSIONS AND IMPLICATIONS

LCB54-0009 is a potential candidate molecule for blocking pathological angiogenesis and lymphangiogenesis mediated by HIF-1α- angiopoietin-2 expression and VEGFR-2 activation.

Role of vascular networks in extending glucose sensor function: Impact of angiogenesis and lymphangiogenesis on continuous glucose monitoring in vivo

The concept of increased blood vessel (BV) density proximal to glucose sensors implanted in the interstitial tissue increases the accuracy and lifespan of sensors is accepted, despite limited existing experimental data. Interestingly, there is no previous data or even conjecture in the literature on the role of lymphatic vessels (LV) alone, or in combination with BV, in enhancing continuous glucose monitoring (CGM) in vivo. To investigate the impact of inducing vascular networks (BV and LV) at sites of glucose sensor implantation, we utilized adenovirus based local gene therapy of vascular endothelial cell growth factor-A (VEGF-A) to induce vessels at sensor implantation sites. The results of these studies demonstrated that (1) VEGF-A based local gene therapy increases vascular networks (blood vessels and lymphatic vessels) at sites of glucose sensor implantation; and (2) this local increase of vascular networks enhances glucose sensor function in vivo from 7 days to greater than 28 days postsensor implantation. This data provides "proof of concept" for the effective usage of local angiogenic factor (AF) gene therapy in mammalian models in an effort to extend CGM in vivo. It also supports the practice of a variety of viral and nonviral vectors as well as gene products (e.g. anti-inflammatory and anti-fibrosis genes) to engineer "implant friendly tissues" for the usage with implantable glucose sensors as well as other implantable devices.

Corneal lymphangiogenesis in herpetic stromal keratitis

Corneal lymphangiogenesis is the extension of lymphatic vessels into the normally alymphatic cornea, a process that compromises the cornea's immune-privileged state and facilitates herpetic stromal keratitis (HSK). HSK results most commonly from infection by herpes simplex virus-1 (HSV-1) and is characterized by immune- and inflammation-mediated damage to the deep layers of the cornea. Current research demonstrates the potential of anti-lymphangiogenic therapy to decrease and prevent herpes-induced lymphangiogenesis.