Effects of AMD3100 subconjunctival injection on alkali burn induced corneal neovascularization in mice

Pharmacological Potential of Small Molecules for Treating Corneal Neovascularization

Under healthy conditions, the cornea is an avascular structure which allows for transparency and optimal visual acuity. Its avascular nature is maintained by a balance of proangiogenic and antiangiogenic factors. An imbalance of these factors can result in abnormal blood vessel proliferation into the cornea. This corneal neovascularization (CoNV) can stem from a variety of insults including hypoxia and ocular surface inflammation caused by trauma, infection, chemical burns, and immunological diseases. CoNV threatens corneal transparency, resulting in permanent vision loss. Mainstay treatments of CoNV have partial efficacy and associated side effects, revealing the need for novel treatments. Numerous natural products and synthetic small molecules have shown potential in preclinical studies in vivo as antiangiogenic therapies for CoNV. Such small molecules include synthetic inhibitors of the vascular endothelial growth factor (VEGF) receptor and other tyrosine kinases, plus repurposed antimicrobials, as well as natural source-derived flavonoid and non-flavonoid phytochemicals, immunosuppressants, vitamins, and histone deacetylase inhibitors. They induce antiangiogenic and anti-inflammatory effects through inhibition of VEGF, NF-κB, and other growth factor receptor pathways. Here, we review the potential of small molecules, both synthetics and natural products, targeting these and other molecular mechanisms, as antiangiogenic agents in the treatment of CoNV.

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.

Observation on ultrastructure and histopathology of cornea following femtosecond laser-assisted deep lamellar keratoplasty for acute corneal alkaline burns

AIM

To demonstrate the changes in ultrastructure and histopathology of the cornea in acute corneal alkaline burns after femtosecond laser-assisted deep lamellar keratoplasty.

METHODS

The New Zealand white rabbits treated with alkaline corneal burn were randomized into two groups, Group A (16 eyes) with femtosecond laser-assisted deep lamellar keratoplasty 24h after burn and Group B (16 eyes) without keratoplasty as controls. All eyes were evaluated with transmission electron microscopy (TEM) at 1, 2, 3, and 4wk follow-up, then all corneas were tested by hematoxylin and eosin staining histology.

RESULTS

The corneal grafts in Group A were transparent, while those in Group B showed corneal stromal edema and loosely arranged collagen fibers. One week after treatment, TEM revealed the intercellular desmosomes in the epithelial layers and intact non-dissolving nuclei in Group A. At week 4, the center of the corneas in Group A was transparent with regularly arranged collagen fibers and fibroblasts in the stroma. In Group B, squamous cells were observed on the corneal surface and some epithelial cells were detached.

CONCLUSION

Femtosecond laser-assisted deep lamellar keratoplasty can suppress inflammatory responses, prevent toxic substance-induced injury to the corneal endothelium and inner tissues with quicker recovery and better visual outcomes.

Augmented anti-angiogenesis activity of polysulfated heparin-endostatin and polyethylene glycol-endostatin in alkali burn-induced corneal ulcers in rabbits

Endostatin (ES) is an endogenous angiogenesis inhibitor that has the ability to inhibit tumor growth and metastasis. However, its clinical application is limited by a number of disadvantages, such as poor stability, short half-life and the requirement of high doses to maintain its efficacy. The chemical modification on ES may offer a solution to these disadvantages. The aim of the present study was to evaluate the effects of ES, polysulfated heparin-endostatin (PSH-ES) and polyethylene glycol-endostatin (PEG-ES) on the endothelial cell proliferation and angiogenesis associated with corneal neovascularization (CNV) and to determine their mechanisms of action. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) was used to study the effects of ES and its derivatives on endothelial cell proliferation in vitro, and rabbits were used to evaluate the effects of ES and its derivatives on CNV in vivo. In the evaluation of CNV, the expression of vascular endothelial growth factor in the cornea was measured via immunohistochemistry and microvessels were counted. ES and its derivatives significantly inhibited endothelial cell proliferation in vitro (P<0.05) and suppressed CNV in vivo. Among the compounds examined, ES most effectively inhibited endothelial cell proliferation in vitro (P<0.05); however, PSH-ES and PEG-ES most effectively inhibited CNV in vivo (P<0.05). These results indicate that PSH-ES and PEG-ES are candidate anti-angiogenesis drugs.

Inhibitory effects of 90Sr/90Y β-irradiation on alkali burn-induced corneal neovascularization in rats

The aim of the present study was to investigate the inhibitory effects of ⁹⁰Sr-⁹⁰Y β-irradiation in a rat model of alkali burn-induced corneal neovascularization (CNV). Alkali burn-induced CNV was induced in the right eyes of 30 female Wistar rats, which were randomly divided into the following three groups (n=10/group): i) The alkali burn control group, which received a balanced salt solution treatment; ii) group 1, which received treatment with angiogenesis inhibitors; and iii) group 2, which received ⁹⁰Sr-⁹⁰Y β-irradiation treatment. A further 10 female Wistar rats comprised a blank control group and received only balanced salt solution. Digital photographs of the corneas were acquired and the area of NV was calculated. In addition, the expression levels of matrix metalloproteinase (MMP)-9, vascular endothelial growth factor (VEGF), VEGF receptor (VEGFR)-1 and VEGFR-2 in alkali-burned rat corneas were determined using western blot analysis. The results suggested that the number of new vessels and the area of CNV were significantly decreased in groups 1 and 2, as compared with the alkali burn group at each time point (P<0.05). In addition, the number of inflammatory cells and the degree of edema were decreased in groups 1 and 2, as compared with the alkali burn group, with group 2 exhibiting the most marked reduction. Western blot analysis demonstrated that the expression levels of MMP-9, VEGF, VEGFR-1 and VEGFR-2 were significantly decreased in groups 1 and 2, as compared with the alkali burn control group, with group 2 exhibiting the most significant reduction (P<0.05). The results of the present study suggested that ⁹⁰Sr-⁹⁰Y β-irradiation and angiogenesis inhibitor treatments were able to inhibit alkali burn-induced CNV, although ⁹⁰Sr-⁹⁰Y β-irradiation may be more effective.

Inhibitory effect of polysulfated heparin endostatin on alkali burn induced corneal neovascularization in rabbits

AIM

To investigate anti-angiogenic effects of polysulfated heparin endostatin (PSH-ES) on alkali burn induced corneal neovascularization (NV) in rabbits.

METHODS

An alkali burn was made on rabbit corneas to induce corneal NV in the right eye of 24 rabbits. One day after burn creation, a 0.2 mL subconjunctival injection of 50 µg/mL PSH-ES, 50 µg/mL recombinant endostatin (ES), or normal saline was administered every other day for a total of 14d (7 injections). Histology and immunohistochemisty were used to examine corneas. Corneal NV growth was evaluated as microvessel quantity and corneal vascular endothelial growth factor (VEGF) expression was measured by immunohistochemical assay.

RESULTS

Subconjunctival injection of ES and PSH-ES resulted in significant corneal NV suppression, but PSH-ES had a more powerful anti-angiogenic effect than ES. Mean VEGF concentration in PSH-ES treated corneas was significantly lower than in ES treated and saline treated corneas. Histological examination showed that corneas treated with either PSH-ES or ES had significantly fewer microvessels than eyes treated with saline. Additionally corneas treated with PSH-ES had significantly fewer microvessels than corneas treated with ES.

CONCLUSION

Both PSH-ES and recombinant ES effectively inhibit corneal NV induced by alkali burn. However, PSH-ES is a more powerful anti-angiogenic agent than ES. This research has the potential to provide a new treatment option for preventing and treating corneal NV.

The effect of TC14012 on alkali burn-induced corneal neovascularization in mice

AIMS

To observe the effect of TC14012 (a CXCR4 antagonist and CXCR7 agonist) on alkali burn-induced corneal neovascularization (CNV) in a mouse model.

METHODS

CNV was induced in vivo by alkali burns on the corneas of BALB/c mice. A total of 54 mice treated with alkali burns were randomly divided into 3 groups, each of which received one of the following treatments: bilateral subconjunctival injections of TC14012 for 3 consecutive days, bilateral subconjunctival injections of balanced saline (BS) for 3 consecutive days or no treatment (blank control). The areas of CNV were measured on days 3, 7 and 14 after the alkali burns. CXCR4, CXCR7, vascular endothelial growth factor (VEGF) and matrix metalloproteinase (MMP) mRNAs were detected and quantified by real-time reverse transcription PCR on days 7 and 14. Additionally, the expression of the proteins CXCR4, CXCR7, VEGF, β-arrestin 2, total ERK1/2 and phospho-ERK1/2 was determined by Western blotting.

RESULTS

On day 7 after the alkali burns, the CNV area, VEGF, MMP-2 and MMP-9 mRNA levels, and VEGF, β-arrestin 2 and phospho-ERK1/2 protein levels were increased in the TC14012 group compared with the nontreatment and BS groups. However, on day 14, the CNV area, CXCR4, CXCR7, VEGF, MMP-2 and MMP-9 mRNA levels, and the CXCR4, CXCR7, VEGF and β-arrestin 2 protein levels were significantly decreased in the TC14012 group.

CONCLUSIONS

TC14012 initially enhanced alkali burn-induced CNV but reduced CNV in later stages. In addition to CXCR4, CXCR7 is involved in the pathogenesis of CNV.

TREM-2 promotes host resistance against Pseudomonas aeruginosa infection by suppressing corneal inflammation via a PI3K/Akt signaling pathway

PURPOSE

To explore the role of triggering receptor expressed on myeloid cells 2 (TREM-2) in Pseudomonas aeruginosa (PA) keratitis.

METHODS

BALB/c mice were routinely infected with PA and evaluated at various postinfection time points for corneal expression of TREM-2, by real-time PCR, Western blot, and flow cytometry. Next, BALB/c and C57BL/6 mice were respectively treated with TREM-2 siRNA or agonistic anti-TREM-2 antibody, to determine the role of TREM-2 in PA keratitis. Bacterial load and neutrophil infiltration were tested by plate count and myeloperoxidase assay, respectively. Th1-/Th2-type and proinflammatory cytokine expression were tested by real-time PCR and ELISA after in vivo and in vitro silencing of TREM-2. Moreover, phosphorylated Akt levels were tested by Western blot in murine macrophages after treatment with agonistic anti-TREM-2 antibody. mRNA levels of proinflammatory cytokines were examined in murine macrophages after TREM-2 activation and lipopolysaccharide stimulation, following pretreatment with inhibitors for PI3K or Akt, to determine whether PI3K/Akt is required in TREM-2-mediated immune modulation. In addition, BALB/c mice were treated with wortmannin and analyzed for bacterial load and proinflammatory cytokine expression.

RESULTS

TREM-2 expression was elevated in the infected BALB/c corneas at 3 or 5 days postinfection. Silencing of TREM-2 accelerated disease progression by enhancing bacterial load and corneal inflammation, whereas activation of TREM-2 promoted host resistance to PA keratitis. PI3K/Akt signaling is required in the TREM-2-mediated immune modulation, and inhibition of PI3K resulted in worsened disease after PA corneal infection.

CONCLUSIONS

TREM-2 promoted host resistance to PA infection by suppressing corneal inflammation via activation of the PI3K/Akt pathway.