Effect of Collagen Cross-Linking on Alkali Burn-Induced Corneal Neovascularization in Rabbits

Cell therapy in the cornea: The emerging role of microenvironment

The cornea is an ideal testing field for cell therapies. Its highly ordered structure, where specific cell populations are sequestered in different layers, together with its accessibility, has allowed the development of the first stem cell-based therapy approved by the European Medicine Agency. Today, different techniques have been proposed for autologous and allogeneic limbal and non-limbal cell transplantation. Cell replacement has also been attempted in cases of endothelial cell decompensation as it occurs in Fuchs dystrophy: injection of cultivated allogeneic endothelial cells is now in advanced phases of clinical development. Recently, stromal substitutes have been developed with excellent integration capability and transparency. Finally, cell-derived products, such as exosomes obtained from different sources, have been investigated for the treatment of severe corneal diseases with encouraging results. Optimization of the success rate of cell therapies obviously requires high-quality cultured cells/products, but the role of the surrounding microenvironment is equally important to allow engraftment of transplanted cells, to preserve their functions and, ultimately, lead to restoration of tissue integrity and transparency of the cornea.

Management of corneal neovascularization: Current and emerging therapeutic approaches

Corneal neovascularization (CoNV) is a sight-threatening condition affecting an estimated 1.4 million people per year, and the incidence is expected to rise. It is a complication of corneal pathological diseases such as infective keratitis, chemical burn, corneal limbal stem cell deficiency, mechanical trauma, and immunological rejection after keratoplasties. CoNV occurs due to a disequilibrium in proangiogenic and antiangiogenic mediators, involving a complex system of molecular interactions. Treatment of CoNV is challenging, and no therapy thus far has been curative. Anti-inflammatory agents such as corticosteroids are the mainstay of treatment due to their accessibility and well-studied safety profile. However, they have limited effectiveness and are unable to regress more mature neovascularization. With the advent of advanced imaging modalities and an expanding understanding of its pathogenesis, contemporary treatments targeting a wide array of molecular mechanisms and surgical options are gaining traction. This review aims to summarize evidence regarding conventional and emerging therapeutic options for CoNV.

Scleral Remolding-Related Gene Expression After Scleral Collagen Cross-Linking Using Ultraviolet A and Riboflavin in Myopic Guinea Pig Model

PURPOSE

This study was conducted to evaluate scleral remolding-related gene expression after scleral collagen cross-linking (SCXL) using ultraviolet A (UVA) and riboflavin in lens-induced myopia (LIM) guinea pigs.

METHODS

A total of 100 4-week-old pigmented guinea pigs were randomly divided into five groups (n = 20): SCXL + LIM, LIM, SCXL, Sham, and Control. Refraction, anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), and axial length (AL) were measured using streak retinoscope and A-scan ultrasonography. SCXL was performed using 0.1% riboflavin solution and 365 nm UVA irradiation. Lens-induced myopia was achieved by wearing -10 D concave lenses. Quantitative real-time PCR (qPCR) and western blot were used to measure mRNA and protein levels, respectively.

RESULTS

Myopia was successfully induced in the LIM group, while myopic refraction was higher and ACD and AL were shorter in SCXL + LIM compared with LIM, suppressing myopia progression. The scleral COL1A1 mRNA levels were significantly decreased and MMP2 and ACTA2 mRNA levels were significantly increased in LIM compared with other groups, while COL1A1 mRNA levels were increased and MMP2 and ACTA2 mRNA levels were decreased in SCXL + LIM compared with LIM. The scleral COL1A1 protein levels were significantly increased at 1 week and 4 weeks and MMP2 protein levels were significantly decreased at 1 week in SCXL compared with SCXL + LIM, LIM and Control. MMP2 protein levels were significantly decreased in SCXL + LIM and SCXL compared with LIM at 4 weeks. The differences in TGFB1, BMP2, CCN2, ITGA2, and ITGB1 mRNA levels and ACTA2 protein levels between the five groups were not significantly different.

CONCLUSION

SCXL using UVA and riboflavin could influence the expression of scleral remolding-related genes, including COL1A1, MMP2, TIMP2, and ACTA2, and thus contribute to improving collagen synthesis and reducing collagen degradation and might have an effect on slowing myopia progression.

Evaluation of clinical and histological effects of KGF-2 and NGF on corneal wound healing in an experimental alkali burn rabbit model

Endogenously produced peptide growth factors such as keratinocyte growth factor-2 (KGF-2) and nerve growth factor (NGF) play a key role in the natural corneal wound healing process. However, this self-healing ability of the corneal tissue is often impaired in cases of severe corneal damage, as in corneal alkali injuries. In the present study, we investigated the clinical and histopathological effects of topical recombinant human keratinocyte growth factor-2 and nerve growth factor treatments in a rabbit model of corneal alkali burn. After induction of an alkali burn, 24 rabbits were divided equally into three groups: control group, KGF-2 group, and NGF group. Clinical parameters including epithelial healing, opacification, neovascularization and central corneal thickness were evaluated on the first (D1), seventh (D7) and fourteenth (D14) days after injury. Corneal histology was performed using hematoxylin/eosin (H&E) and Masson's Trichrome stains. Immunohistochemical staining for matrix metalloproteinase-2 (MMP-2), MMP-9 and transforming growth factor-β (TGF-β) was performed. On D14, the percentage of epithelial defect and opacity were significantly less in the KGF-2 and NGF groups compared to the control group (p < 0.05). There was no significant difference between the groups in central corneal thickness. In the evaluation of neovascularization on D14, the NGF group was significantly less vascularized than the control group (p = 0.011). Histological examination showed a significant increase in stromal edema and inflammation in the control group compared to both treatment groups (p < 0.05). There was also a significant difference between the NGF and control groups in histological evaluation of epithelial repair and vascularization (p < 0.05). When immunoreactivity of MMP-2, MMP-9 and TGF-β was examined, there was a significant increase in the control group compared to the NGF group (p < 0.05). Taken together, both NGF and KGF-2 treatments were effective for early re-epithelialization and decrease in inflammation, opacity and neovascularization after corneal alkali burn. The inhibitory effect of NGF treatment on chemical-induced neovascularization was found to be superior to KGF-2 treatment.

Lycium barbarum polysaccharide promotes corneal Re-epithelialization after alkaline injury

Chemical injury of the cornea results in epithelial defect and subsequent stromal scarring and infection. Our study aims to evaluate the effectiveness of pre-treatment of Lycium barbarum polysaccharide (LBP) in promoting corneal re-epithelialization after alkaline burn. The corneas of C57BL/6J mice were pre-treated with topical phosphate-buffered saline or LBP (0.2/2/20 mg/mL) for 7 days, following by 0.1M sodium hydroxide injury for 30 s and washing with distilled water for another 30 s. Area of epithelial defect and thickness of cornea were evaluated. Inflammatory cytokines and water channel expression levels were assessed using immunohistochemistry and Western blot. Compared to the injury group, mice with 2 mg/mL LBP pre-treatment revealed a significant decrease in fluorescein stained area after injury (p = 0.025), with increased epithelial layer thickness (p = 0.004). The corneal opacity was significantly reduced in the group with 2 mg/mL LBP pre-treatment followed by injury (p = 0.02). The expression of matrix metalloproteinase 12 (p = 0.033), platelet derived growth factor-BB (p = 0.031), and aquaporin 5 (p = 0.022) resulted in a decrease in expression level in group with 2 mg/mL LBP pre-treatment. Our results showed that 2 mg/mL LBP, with no apoptotic effect on corneal cells, promoted corneal epithelial growth and minimized disruption of the collagen architecture after injury in vivo. We suggest that LBP, as a natural Traditional Chinese Medicine, may potentially be a novel topical pre-treatment option for patients highly susceptible to ocular injury.

Corneal Collagen Cross-Linking Inhibits Corneal Blood and Lymphatic Vessels Temporarily in Alkali-Burned Rabbits

PURPOSE

This study aimed to explore whether corneal cross-linking (CXL) could regress corneal blood vessels (CBV) and corneal lymphatic vessels (CLV) in alkali-burned rabbits.

METHODS

A total of 80 rabbits 2-3 months old weighing 1.5-2.0 kg were randomly divided into four groups: CXL7 group; CTL7 group; CXL14 group; and CTL14 group. Then, 3% sodium pentobarbital 1 ml/kg and tetracaine eye drop 5 g/L were administered before surgery. NaOH 2 mol/L was topically applied to the central cornea to establish the alkali burning model. Then CXL was administered within 2 h in groups CXL7 and CXL14. Corneal opacity and edema, CBV and CLV volume, cluster differentiation 31 (CD31), and lymphatic vessel endothelial receptor 1 (LYVE-1) expression levels were analyzed on days 7 and 14.

RESULTS

CXL reduced cornea opacity, CNV, and CLV volumes on day 7 in alkali-burned rabbits. However, CNV and CLV volumes were increased on day 14. CXL also showed down- and upregulation of CD31 and LYVE-1 expression levels on days 7 and 14, respectively.

CONCLUSIONS

CXL effectively regulated CBV and CLV in alkali-burned rabbits. The transient angioregression and lymphangioregression induced by CXL may be potentially helpful in vascularized high-risk eyes.

A Retrospective Study of Herpetic Keratitis in Patients with Keratoconus after Crosslinking Surgery

Background: The aim of this study was to perform a retrospective analysis of patients who underwent cross-linking for keratoconus, in the Department of Ophthalmology of the Medical University of Silesia in Katowice, between 2011 and 2020, regarding the occurrence of herpetic keratitis after the procedure. Methods: We analyzed the medical history of 543 patients who underwent cross-linking surgery. Results: In the analyzed group, there were nine cases of herpetic keratitis (six men and three women), aged from 16 to 40 years (mean 26.2 years). The mean follow-up period was 49.3 months (16–82 months). The average time from surgery to the manifestation of the first symptoms of keratitis was 4.3 days (2–6 days). In two cases, iritis was observed, and in one of them, iritis was the first symptom. After systemic and topical administration of acyclovir, ulceration healed in all patients. Corneal healing time ranged from 10 days to 3 weeks (average 13.7 days). In one patient, a recurrence of the inflammation was observed after 8 months. Conclusion: Patients should be carefully observed in the early post-CXL period. Herpetic keratitis could be induced by CXL even in patients with no history of herpetic disease.

Long term observation of ocular surface alkali burn in rabbit models: Quantitative analysis of corneal haze, vascularity and self-recovery

Limbal Stem Cell Deficiency (LSCD), caused due to corneal injury, primarily by chemical/alkali burns, leads to compromised vision. Recently, several animal models of corneal alkali burn injury have become available. The majority of the studies with these animal models start interventions soon after the injury. However, in the clinical setting, there is a considerable delay before the intervention is initiated. Detailed knowledge of the molecular, histopathological, and clinical parameters associated with the progression of the injury leading to LSCD is highly desirable. In this context, we set out to investigate clinical, histopathological parameters of ocular surface alkali burn over a long period of time, post-injury. Limbal stem cell-deficient animal models of rabbits were created by alkali burn using sodium hydroxide, which was then assessed for their progression towards LSCD by grading the alkali burn, corneal haze, and vascularization. Additionally, cells present on the corneal surface after the burn was investigated by histology and immunophenotyping. Grading of rabbit eyes post-alkali burn had shown complete conjunctivalization in 80% (n = 12/15) of the rabbits with the alkali burn grade score of 3.88 ± 0.29 in three months and remained stable at four months (4.12 ± 0.24). However, ocular surface showed self-healing in 20% (n = 3/15) of the rabbits with a score of 1.67 ± 0.34 in four months irrespective of similar alkali injury. These self-healing corneas exhibited decreased opacity score from 2.51 ± 0.39 to 0.66 ± 0.22 (p = 0.002) and regressed vascularity from 1.66 ± 0.41 to 0.66 ± 0.33 in one to nine months, respectively. Restoration of the corneal phenotype (CK3+) was observed in central and mid-peripheral regions of the self-healing corneas, and histology revealed the localization of inflammatory cells to the peripheral cornea when compared to conjunctivalized and scarred LSCD eyes. Our study shows the essentiality to consider the time required for surgical intervention after the corneal alkali injury in rabbit models as evident from their tendency to self-heal and restore corneal phenotype without therapy. Such information on the possibility of self-healing should be useful in further studies as well as determining interventional timings and strategy during clinical presentation of corneal alkali burns.

Effect of ERK inhibitor on corneal neovascularization induced by alkali burn in mice and its mechanism

The objective of this study is to explore the effect of extracellular signal–regulated kinase (ERK) inhibitors on corneal neovascularization induced by alkali burn in mice and its mechanism. A total of 30 standard diet (SD) healthy mice were divided into normal group, alkali burn group, and inhibitor group. Normal group was not treated. Alkali burn group and inhibitor group were used to establish corneal neovascularization model induced by alkali burn. After successful modeling, ERK inhibitor was used to intervene in inhibitor group, and saline of equal volume was used in normal group and alkali burn group. The area of corneal neovascularization was calculated and the expression of vascular endothelial growth factor (VEGF), c-Fos, c-Jun, ERK1/2, and p-ERK1/2 protein in cornea tissue of three groups of mice was detected. The relative expression of vascular area, length, VEGF, c-Fos, c-Jun, ERK1/2, and p-ERK1/2 protein in cornea tissue of mice in alkali burn group was significantly higher than that in normal group and inhibitor group. The relative expression of vascular area, length, VEGF, c-Fos, c-Jun, ERK1/2, and p-ERK1/2 protein in cornea tissue of mice in inhibitor group was higher than that in normal group, and the expression level of PEDF was lower than that in normal group ( P < 0.05). ERK inhibitors inhibit the formation of corneal neovascularization by inhibiting the expression of VEGF, c-Fos, and c-Jun proteins through the action of ERK signaling pathway.