Identification of Novel Endogenous Anti(lymph)angiogenic Factors in the Aqueous Humor.

Purpose: The avascular cornea is in direct contact with aqueous humor (AqH). Here we investigate whether AqH exerts anti(lymph)angiogenic effects and thereby may contribute to corneal (lymph)angiogenic privilege. Methods: Using the murine model of suture-induced inflammatory corneal hem- and lymphangiogenesis, the potential anti(lymph)angiogenic effect of AqH was analyzed by applying murine AqH as eyedrops. Anti(lymph)angiogenic effects were measured using morphometric analysis of flat mounts stained with CD31 as panendothelial and LYVE-1 as specific lymphatic endothelial marker. The potential antilymphangiogenic effect of immunomodulatory factors contained in AqH such as vasoactive intestinal peptide (VIP) and α-melanocyte stimulating hormone (α-MSH) was analyzed in lymphatic and blood vascular endothelial cell proliferation assays in vitro. Results: Topically applied AqH significantly inhibited corneal hemangiogenesis and even more so lymphangiogenesis in vivo and directly in vitro. The immunoregulatory factors VIP and α-MSH significantly inhibited lymphatic endothelial cell proliferation in vitro. Depletion of VIP or α-MSH from AqH diminished its anti-hem- and lymphangiogenic potential. Conclusions: Aqueous humor exerts significant antilymphangiogenic effects in vivo. This is at least partially mediated by the known immunomodulatory factors VIP and α-MSH present in the AqH. Therefore, AqH not only contributes to corneal lymphangiogenic privilege and is a new tool to identify novel endogenous regulators of lymphangiogenesis but also may have therapeutic applications.

Efficient and safe gene delivery to human corneal endothelium using magnetic nanoparticles.

AIM: To develop a safe and efficient method for targeted, anti-apoptotic gene therapy of corneal endothelial cells (CECs). MATERIALS & METHODS: Magnetofection (MF), a combination of lipofection with magnetic nanoparticles (MNPs; PEI-Mag2, SO-Mag5, PalD1-Mag1), was tested in human CECs and in explanted human corneas. Effects on cell viability and function were investigated. Immunocompatibility was assessed in human peripheral blood mononuclear cells. RESULTS: Silica iron-oxide MNPs (SO-Mag5) combined with X-tremeGENE-HP achieved high transfection efficiency in human CECs and explanted human corneas, without altering cell viability or function. Magnetofection caused no immunomodulatory effects in human peripheral blood mononuclear cells. Magnetofection with anti-apoptotic P35 gene effectively blocked apoptosis in CECs. CONCLUSION: Magnetofection is a promising tool for gene therapy of corneal endothelial cells with potential for targeted on-site delivery.

Blockade of the VEGF isoforms in inflammatory corneal hemangiogenesis and lymphangiogenesis.

BACKGROUND: The VEGF-A family plays a crucial role in the induction of pathological corneal neovascularization. The role of the different VEGF-A isoforms during lymphangiogenesis is only little-known. Current anti-angiogenic therapies in the eye and other organs inhibit all VEGF-A isoforms, and have effects on both blood and lymphatic vessels. Here we investigate whether selective targeting of the isoform VEGF 165 is able to inhibit corneal lymphangiogenesis under inflammatory conditions. METHODS: The mouse model of suture-induced corneal neovascularization was used to assess the antihem- and antilymphangiogenic effect of topically applied pegaptanib. Corneal blood and lymph vascularized areas were analyzed morphometrically. Furthermore, we analyzed the proliferative effects of VEGF A 121, 165, and 189 on blood and lymphatic endothelial cells (BEC/LEC) via a cell-proliferation assay. RESULTS: Pegaptanib significantly inhibited inflammatory corneal hemangiogenesis (p < 0.01), but not lymphangiogenesis in vivo (p > 0.05), both topically as well as systemically, in the inflamed cornea. In vitro, BECs were more susceptible to pegaptanib than LECs. CONCLUSIONS: Targeting VEGF-A 165 significantly inhibits hem- but not lymphangiogenesis, suggesting VEGF-A 165 to be critical for hem-, but dispensable for lymphangiogenesis, at least in the inflamed cornea.

Topical Ranibizumab inhibits inflammatory corneal hem- and lymphangiogenesis.

PURPOSE: Ranibizumab (Lucentis(®) ) is a Fab-Fragment of a recombinant, humanized, monoclonal VEGF (anti-vascular endothelial growth factor) antibody. This study analyzed the ability of topical Ranibizumab to inhibit lymphangiogenesis in addition to hemangiogenesis after acute corneal inflammation in vivo. In addition, the effect of Ranibizumab on the proliferation of human lymphatic endothelial cells (LECs) and blood endothelial cells (BECs) in vitro was studied. METHODS: The inhibitory effect of Ranibizumab on LECs and BECs was studied in vitro using a proliferation enzyme-linked immunosorbent assay (ELISA) assay. To study the in vivo effects of Ranibizumab, the mouse model of suture induced inflammatory corneal neovascularization was used. Study mice received topical Ranibizumab as eye drops. After 1 week excised corneas were stained with LYVE-1 and CD31. Hemangiogenesis and lymphangiogenesis were analyzed morphometrically by using a semiautomatic method based on the image analyzing program Cell^F. RESULTS: An antiproliferative effect of Ranibizumab was seen in vitro on both human BECs and LECs with a significance of p < 0.0001 and p < 0.0004, respectively. In vivo experiments showed that topical application of Ranibizumab significantly inhibits both hemangiogenesis (p = 0.0026) and lymphangiogenesis (p = 0.0026) in the cornea. CONCLUSION: Ranibizumab is a potent inhibitor of inflammatory corneal hemangiogenesis and lymphangiogenesis in vivo with a direct inhibitory effect on both endothelial cell types in vitro. This study for the first time demonstrates an inhibitory effect of Ranibizumab on lymphatic vessels which could have a wider range of clinical applications.

Topical application of soluble CD83 induces IDO-mediated immune modulation, increases Foxp3+ T cells, and prolongs allogeneic corneal graft survival.

Modulation of immune responses is one of the main research aims in transplant immunology. In this study, we investigate the local immunomodulatory properties of soluble CD83 (sCD83) at the graft-host interface using the high-risk corneal transplantation model. In this model, which mimics the inflammatory status and the preexisting vascularization of high-risk patients undergoing corneal transplantation, allogeneic donor corneas are transplanted onto sCD83-treated recipient animals. This model allows the direct and precise application of the immune modulator at the transplantation side. Interestingly, sCD83 was able to prolong graft survival after systemic application as well as after topical application, which is therapeutically more relevant. The therapeutic effect was accompanied by an increase in the frequency of regulatory T cells and was mediated by the immune-regulatory enzyme IDO and TGF-ß. In vitro, sCD83 induced long-term IDO expression in both conventional and plasmacytoid dendritic cells via autocrine or paracrine production of TGF-ß, a cytokine previously shown to be an essential mediator of IDO-dependent, long-term tolerance. These findings open new treatment avenues for local immune modulation after organ and tissue transplantation.

Blockade of insulin receptor substrate-1 inhibits corneal lymphangiogenesis.

PURPOSE: To analyze whether insulin receptor substrate (IRS-1) is involved in lymphatic vessel development and whether IRS-1 blockade can inhibit lymphangiogenesis in vivo. METHODS: The impact of IRS-1 blockade by GS-101 (Aganirsen), an antisense oligonucleotide against IRS-1, on lymphatic endothelial cell (LEC) proliferation was assessed by ELISA. Furthermore, the effect of IRS-1 blockade on prolymphangiogenic growth factor expression by LECs and macrophages (peritoneal exudate cells) was tested by real-time PCR. The mouse model of inflammatory corneal neovascularization was used to analyze the effect of IRS-1 blockade in vivo: after corneal suture placement, mice were treated with GS-101 eye drops (twice daily afterwards for 1 week, 5 µL per drop; 50, 100, or 200 µM). Afterward, corneal wholemounts were prepared and stained for blood and lymphatic vessels. RESULTS: Blockade of IRS-1 by GS-101 inhibited LEC proliferation dose dependently. GS-101 led to decreased VEGF-A expression levels in LECs, whereas VEGF-C, VEGF-D, and VEGFR3 showed no significant change. In macrophages, VEGF-A expression levels were also inhibited by IRS-1 blockade. Additionally, GS-101 strongly inhibited macrophage-derived VEGF-C, VEGF-D, and VEGFR3 expression. In vivo, corneal hemangiogenesis was significantly inhibited when used at a concentration of 200 µM (by 17%; P < 0.01). Corneal lymphangiogenesis was significantly inhibited when used at a dose of 100 µM (by 21%; P < 0.01), and the highest used dose (200 µM) showed an even stronger inhibition (by 28%; P < 0.001). CONCLUSIONS: Blockade of IRS-1 inhibits not only hemangiogenesis but also lymphangiogenesis. To the authors' knowledge, this is the first evidence that IRS-1 is involved in the molecular pathway leading to lymphangiogenesis.

Suppression of inflammatory corneal lymphangiogenesis by application of topical corticosteroids.

OBJECTIVES: To analyze whether topical application of corticosteroids inhibits inflammatory corneal lymphangiogenesis and to study the potential underlying antilymphangiogenic mechanisms. METHODS: Inflammatory corneal neovascularization was induced by suture placement, and the corneas were then treated with topical fluorometholone, prednisolone acetate, or dexamethasone sodium phosphate. After 1 week, the corneas were stained with lymphatic vessel endothelial hyaluronan receptor 1 for detection of pathological corneal lymphangiogenesis. The effect of these corticosteroids on macrophage recruitment was assessed via fluorescence-activated cell sorting analysis. The effect of these corticosteroids on proinflammatory cytokine expression by peritoneal exudate cells was tested via real-time polymerase chain reaction. Furthermore, the effect of steroid treatment on the proliferation of lymphatic endothelial cells was assessed via enzyme-linked immunosorbent assay. RESULTS: Treatment with corticosteroids resulted in a significant reduction of inflammatory corneal lymphangiogenesis. The antilymphangiogenic effect of fluorometholone was significantly weaker than that of prednisolone and dexamethasone. Corneal macrophage recruitment was also significantly inhibited by the application of topical steroids. Treatment of peritoneal exudate cells with corticosteroids led to a significant downregulation of the RNA expression levels of tumor necrosis factor and interleukin 1ß. Additionally, proliferation of lymphatic endothelial cells was also inhibited. CONCLUSIONS: Corticosteroids are strong inhibitors of inflammatory corneal lymphangiogenesis, with significant differences between various corticosteroids in terms of their antilymphangiogenic potency. The main mechanism of the antilymphangiogenic effect seems to be through the suppression of macrophage infiltration, proinflammatory cytokine expression, and direct inhibition of proliferation of lymphatic endothelial cells. CLINICAL RELEVANCE: Steroids block corneal lymphangiogenesis, the main risk factor for immune rejections after corneal transplantation. The different antilymphangiogenic potency of these drugs should be taken into account when using steroids in clinical practice (eg, after keratoplasty).

Genetic heterogeneity of lymphangiogenesis in different mouse strains.

Lymphangiogenesis plays an important role in tumor metastasis, wound healing, and immune reactions, such as after organ transplantation. Furthermore, novel antilymphangiogenic drugs are moving into clinical medicine, but so far nothing is known about a potential genetic heterogeneity influencing lymphangiogenesis. Using the mouse cornea micropocket assay (VEGF-C) and the suture-induced corneal neovascularization model in different inbred and wild-derived mouse strains (Balb/cAnNCrl, C57BL/6NCrl, 129S1/SvImJ, SJL/JCrl, Cast/EiJ, FVB/NCrl), significant differences in the lymphangiogenic response were detected: the lymphvascularized area varied up to 1.9-fold in the micropocket assay and up to 1.7-fold in the suture-induced neovascularization model between the "low-responder" strain BALB/c and the "high-responder" strain FVB in response to the same stimulus. Furthermore, the number of physiological lymphatic vascular extensions into the marginal zone of the normally alymphatic cornea in untreated eyes again showed a difference of 1.6-fold between low- and high-responders. An anti-inflammatory (prednisolone acetate) and a specific anti(lymph)angiogenic therapy (blocking anti-VEGFR-3 antibody) had different effects on the lymphvascularized area in BALB/c mice and FVB mice, suggesting a different responsiveness to antilymphangiogenic treatments. These data for the first time demonstrate significant differences in the lymphangiogenic response of several mouse strains and suggest underlying genetic factors influencing the lymphangiogenic response. These considerations need to be taken into account when using different mouse strains to study lymphangiogenesis and may also explain different success of antilymphangiogenic treatments in tumor patients.

Safety profile of topical VEGF neutralization at the cornea.

PURPOSE: Bevacizumab eyedrops inhibit corneal neovascularization. The purpose of this study was to analyze the safety profile of VEGF-A neutralization at the ocular surface. METHODS: Bevacizumab eyedrops (5 mg/mL) and an antimurine VEGF-A antibody (250 microg/mL) were applied to normal murine corneas five times a day for 7 and 14 days. Subsequently, corneas were analyzed for morphologic changes by light and electron microscopy. In a mouse model of corneal epithelial abrasion, the effects of topically applied anti-VEGF antibodies on epithelial wound healing were analyzed: the treatment group received bevacizumab (5 mg/mL) or the antimurine VEGF-A antibody (250 microg/mL) as eyedrops, and the control group received an equal volume of saline solution. After 12, 18, and 24 hours, corneas were photographed in vivo with and without fluorescein staining for morphometry. Afterwards the mice were killed, and eyes were removed for histology, immunohistochemistry with Ki67/DAPI, and electron microscopy. The effect of midterm anti-VEGF therapy on corneal nerve density was assessed by staining corneas treated with an FITC-conjugated anti-neurofilament antibody and morphometric analysis. RESULTS: Murine corneas treated with two different types of anti-VEGF antibody eyedrops did not show obvious corneal morphologic changes at the light and electron microscopic levels. Furthermore, anti-VEGF antibody eyedrops had no significant impact on the wound healing process after corneal epithelial injury or on normal murine corneal nerve fiber density. CONCLUSIONS: Topical neutralization of VEGF-A at the corneal surface does not have significant side effects on normal corneal epithelial wound healing, normal corneal integrity, or normal nerve fiber density. Therefore, anti-VEGF eyedrops seem to be a relatively safe option to treat corneal neovascularization.

Inflammatory corneal (lymph)angiogenesis is blocked by VEGFR-tyrosine kinase inhibitor ZK 261991, resulting in improved graft survival after corneal transplantation.

PURPOSE: To analyze whether tyrosine kinase inhibitors blocking VEGF receptors (PTK787/ZK222584 [PTK/ZK] and ZK261991 [ZK991]) can inhibit not only hemangiogenesis but also lymphangiogenesis and whether treatment with tyrosine kinase inhibitors after corneal transplantation can improve graft survival. METHODS: Inflammatory corneal neovascularization was induced by corneal suture placement. One treatment group received PTK/ZK, and the other treatment group received ZK991. Corneas were analyzed histomorphometrically for pathologic corneal hemangiogenesis and lymphangiogenesis. The inhibitory effect of tyrosine kinase inhibitors on lymphatic endothelial cells (LECs) in vitro was analyzed with a colorimetric (BrdU) proliferation ELISA. Low-risk allogeneic (C57Bl/6 to BALB/c) corneal transplantations were performed; the treatment group received ZK991, and grafts were graded for rejection (for 8 weeks). RESULTS: Treatment with tyrosine kinase inhibitors resulted in a significant reduction of hemangiogenesis (PTK/ZK by 30%, P < 0.001; ZK991 by 53%, P < 0.001) and lymphangiogenesis (PTK/ZK by 70%, P < 0.001; ZK991 by 71%, P < 0.001) in vivo. Inhibition of proliferation of LECs in vitro was also significant and dose dependent (PTK/ZK, P < 0.001; ZK991, P < 0.001). Comparing the survival proportions after corneal transplantation, treatment with ZK991 significantly improved graft survival (68% vs. 33%; P < 0.02). CONCLUSIONS: Tyrosine kinase inhibitors blocking VEGF receptors are potent inhibitors not only of inflammatory corneal hemangiogenesis but also lymphangiogenesis in vivo. Tyrosine kinase inhibitors seem to have the ability to restrain the formation of the afferent and efferent arm of the immune reflex arc and are therefore able to promote graft survival after corneal transplantation.

Blockade of VEGFR3-signalling specifically inhibits lymphangiogenesis in inflammatory corneal neovascularisation.

PURPOSE: Inflammatory corneal hem- and lymphangiogenesis occurring both prior to as well as after penetrating keratoplasty significantly increase the risk for subsequent immune rejections. The purpose of this study was to analyze whether the blocking anti-VEGFR3 antibody mF4-31C1 is able to inhibit the outgrowth of pathologic new lymphatic vessels in a mouse model of suture-induced, inflammatory corneal neovascularisation, and whether this antibody specifically inhibits lymphangiogenesis without affecting hemangiogenesis. METHODS: Three interrupted 11-0 nylon sutures were placed into the corneal stroma of BALB/c mice (6 weeks old) and left in place for 7 days to induce neovascularisation. The treatment group (n = 9) received the anti-VEGFR3 antibody mF4-31C1 intraperitoneally on the day of surgery and 3 days later (0.5 mg/mouse). Control mice received an equal amount of control IgG solution. For immunohistochemistry, corneal flat mounts were stained with LYVE-1 as a specific lymphatic vascular endothelial marker and with CD31 as panendothelial marker. Morphometry was performed with the image analysis software analySIS;B (Soft Imaging Systems GmbH, Münster, Germany). To improve the objectivity and precision of the morphometrical analysis, we established a modified method using grey filter sampling on monochromatic pictures. RESULTS: The mF4-31C1 antibody-treated mice displayed nearly complete inhibition of lymphangiogenesis compared with IgG controls (p < 0.006). In contrast, there was no significant inhibitory effect observed with respect to blood vessel growth (p > 0.05). CONCLUSIONS: Inflammatory corneal lymphangiogenesis seems to depend on VEGFR3-signalling. By blocking this receptor the ingrowths of lymphatic vessels can be inhibited almost completely, and specifically without affecting hemangiogenesis. This may open new treatment options to promote (corneal) graft survival without affecting hemangiogenesis.

Inhibition of inflammatory lymphangiogenesis by integrin alpha5 blockade.

The interaction between endothelial cells and extracellular matrix proteins plays an important role in (hem)angiogenesis. Integrins are able to mediate the outgrowth of newly formed blood vessels. In contrast, the role of integrins in lymphangiogenesis, ie, the outgrowth of new from pre-existing lymphatic vessels, has so far been unclear. Here, expression and functional relevance of integrins on lymphatic endothelium in vivo was investigated using the mouse model of combined inflammatory corneal hemangiogenesis and lymphangiogenesis. Immunohistochemistry revealed novel expression of both integrin alpha5 and alphav on both resting and activated lymphatic vessels in vivo. Integrin alpha5-inhibiting small molecules significantly blocked the outgrowth of new lymphatic vessels into the cornea in a dose-dependent manner. The outgrowth of blood vessels was less significantly affected by this treatment, thus allowing for selective inhibition of lymphangiogenesis at lower dosages. Combined inhibition of integrin alpha5 and alphav using inhibiting molecules did not significantly increase the anti-lymphangiogenic effect in vivo, thus suggesting an important functional role of integrin alpha5 in lymphangiogenesis. In summary, our findings demonstrate novel expression of specific integrins on growing lymphatic endothelial cells in vivo and reveal their functional role during lymphangiogenesis. This opens new treatment options for selective inhibition of lymphangiogenesis, eg, in oncology and transplant immunology.

Bevacizumab as a potent inhibitor of inflammatory corneal angiogenesis and lymphangiogenesis.

PURPOSE: To analyze whether bevacizumab can inhibit inflammatory angiogenesis and lymphangiogenesis in the cornea. Bevacizumab (Avastin; Roche, Welwyn Garden City, UK) is a recombinant, humanized, monoclonal antibody against VEGF-A that has been approved by the U.S. Food and Drug Administration for the treatment of colon carcinomas. METHODS: The mouse model of suture-induced corneal neovascularization was used to assess the antihemangiogenic and antilymphangiogenic effect of bevacizumab by systemic and topical application. Corneal flatmounts were stained with LYVE-1 as a specific lymphatic vascular endothelial marker and CD31 as a pan-endothelial marker, and blood and lymph vascularized areas were analyzed morphometrically. The inhibitory effect of bevacizumab on lymphatic endothelial cells (LECs) was analyzed with a colorimetric (BrdU) proliferation ELISA. The binding ability of bevacizumab to murine VEGF-A was analyzed by Western blot, ELISA, and surface plasmon resonance. RESULTS: The systemic and topical applications of bevacizumab significantly inhibited the outgrowth of blood (P < 0.006 and P < 0.0001, respectively) and lymphatic (P < 0.002 and P < 0.0001, respectively) vessels. Inhibition of the proliferation of LECs was also significant (P < 0.0001). Western blot analysis, ELISA, and the surface plasmon resonance assay showed that bevacizumab binds murine VEGF-A. CONCLUSIONS: Topical or systemic application of bevacizumab inhibits both inflammation-induced angiogenesis and lymphangiogenesis in the cornea. This finding suggests an important role of VEGF-A in corneal lymphangiogenesis. Bevacizumab may be useful in preventing immune rejections after penetrating keratoplasty or tumor metastasis via lymphatic vessels.