Corneal epithelial wound healing

The combined effect of epidermal growth factor and keratinocyte growth factor delivered by hyaluronic acid hydrogel on corneal wound healing

This study strategically incorporates epidermal growth factor (EGF) and keratinocyte growth factor (KGF) within a hyaluronic acid (HA) hydrogel to enhance corneal wound healing. The controlled release of EGF and KGF from the HA hydrogel is engineered to promote the regeneration of both the epithelial and stromal layers. Specifically, EGF plays a pivotal role in the regeneration of the epithelial layer, while KGF exhibits efficacy in the regeneration of the stromal layer. The combination of these growth factors facilitates efficient regeneration of each layer and demonstrates the capability to modulate each other's regenerative effects. The interplay between EGF and KGF provides an understanding of their cooperative influence on the dynamics of corneal wound healing. The results of this study contribute to the development of advanced strategies for corneal wound management and offer insights into the complex process of corneal regeneration.

PAX6/CXCL14 regulatory axis promotes the repair of corneal injury by enhancing corneal epithelial cell proliferation

BACKGROUND

Corneal injuries, often leading to severe vision loss or blindness, have traditionally been treated with the belief that limbal stem cells (LSCs) are essential for repair and homeostasis, while central corneal epithelial cells (CCECs) were thought incapable of such repair. However, our research reveals that CCECs can fully heal and maintain the homeostasis of injured corneas in rats, even without LSCs. We discovered that CXCL14, under PAX6's influence, significantly boosts the stemness, proliferation, and migration of CCECs, facilitating corneal wound healing and homeostasis. This finding introduces CXCL14 as a promising new drug target for corneal injury treatment.

METHODS

To investigate the PAX6/CXCL14 regulatory axis's role in CCECs wound healing, we cultured human corneal epithelial cell lines with either increased or decreased expression of PAX6 and CXCL14 using adenovirus transfection in vitro. Techniques such as coimmunoprecipitation, chromatin immunoprecipitation, immunofluorescence staining, western blot, real-time PCR, cell colony formation, and cell cycle analysis were employed to validate the axis's function. In vivo, a rat corneal epithelial injury model was developed to further confirm the PAX6/CXCL14 axis's mechanism in repairing corneal damage and maintaining corneal homeostasis, as well as to assess the potential of CXCL14 protein as a therapeutic agent for corneal injuries.

RESULTS

Our study reveals that CCECs naturally express high levels of CXCL14, which is significantly upregulated by PAX6 following corneal damage. We identified SDC1 as CXCL14's receptor, whose engagement activates the NF-κB pathway to stimulate corneal repair by enhancing the stemness, proliferative, and migratory capacities of CCECs. Moreover, our research underscores CXCL14's therapeutic promise for corneal injuries, showing that recombinant CXCL14 effectively accelerates corneal healing in rat models.

CONCLUSION

CCECs play a critical and independent role in the repair of corneal injuries and the maintenance of corneal homeostasis, distinct from that of LSCs. The PAX6/CXCL14 regulatory axis is pivotal in this process. Additionally, our research demonstrates that the important function of CXCL14 in corneal repair endows it with the potential to be developed into a novel therapeutic agent for treating corneal injuries.

Topical Insulin Eye Drops: Stability and Safety of Two Compounded Formulations for Treating Persistent Corneal Epithelial Defects

Compounded insulin eye drops were prepared at 1 IU/mL from commercially available subcutaneous insulin by dilution in saline solution or artificial tears. Physicochemical characterization and in vitro tolerance testing in human and conjunctival cells were followed by a 28-day short-term stability study under various conditions. The formulations were isotonic (280-300 mOsm/L), had a pH close to neutral (7-8), medium surface-tension values (<56 MN/m-1), and low (≈1 mPa·s) and medium (≈5 mPa·s) viscosities (compounded normal saline solution and artificial tear-based preparation, respectively). These values remained stable for 28 days under refrigeration. Microbiological stability was also excellent. Insulin potency remained in the 90-110% range in the compounded formulations containing normal saline solution when stored at 2-8 °C for 28 days, while it decreased in those based on artificial tears. Although both formulations were well tolerated in vitro, the compounded insulin diluted in a normal saline solution exhibited better cell tolerance. Preliminary data in humans showed that insulin in saline solution was an effective and safe treatment for persistent corneal epithelial defects. Compounded insulin eye drops diluted in normal saline solution could, therefore, constitute an emergent therapy for the treatment of persistent corneal epithelial defects.

The role of topical insulin in ocular surface restoration: A review

Corneal epithelial defects are one of the most common ocular disorders. Restoring corneal integrity is crucial to reduce pain and regain function, but in cases of neurotrophic or desensitized corneas, healing can be significantly delayed. Treating neurotrophic corneas is challenging for ophthalmologists, and surgical intervention is often indicated to manage refractory cases that are unresponsive to medical therapy. Over the last decade, as more expensive therapeutics reach the market, topical insulin has returned to the forefront as an affordable option to improve corneal wound healing. There is still a paucity of data on the use and the efficacy of topical insulin, with no consensus regarding its indications, preparation, or posology. Here we review the literature on topical insulin for corneal and ocular surface pathologies, with a focus on the current evidence, its mechanisms of action, and its safety profile. Additionally, we share our experience in the field and provide a potential framework for future research.

Methylation in cornea and corneal diseases: a systematic review

Corneal diseases are among the primary causes of blindness and vision loss worldwide. However, the pathogenesis of corneal diseases remains elusive, and diagnostic and therapeutic tools are limited. Thus, identifying new targets for the diagnosis and treatment of corneal diseases has gained great interest. Methylation, a type of epigenetic modification, modulates various cellular processes at both nucleic acid and protein levels. Growing evidence shows that methylation is a key regulator in the pathogenesis of corneal diseases, including inflammation, fibrosis, and neovascularization, making it an attractive potential therapeutic target. In this review, we discuss the major alterations of methylation and demethylation at the DNA, RNA, and protein levels in corneal diseases and how these dynamics contribute to the pathogenesis of corneal diseases. Also, we provide insights into identifying potential biomarkers of methylation that may improve the diagnosis and treatment of corneal diseases.

Investigation of corneal epithelial thickness and irregularity by optical coherence tomography after transepithelial photorefractive keratectomy

CLINICAL RELEVANCE

Corneal epithelial healing after refractive surgery is a clinically significant issue, especially for surface ablation procedures, and this can be monitored using optical coherence tomography (OCT).

BACKGROUND

The aim of this work is to investigate the corneal epithelial thickness and irregularity by OCT after transepithelial photorefractive keratectomy (t-PRK) and analyse its correlation with visual and refractive outcomes.

METHODS

Patients aged ≥18 years with myopia, with or without astigmatism, who underwent t-PRK between May 2020 and August 2021 were included. All participants were subjected to complete ophthalmic examinations and OCT pachymetry at every follow-up visit. Patients were followed up at 1 week and 1, 3, and 6 months postoperatively.

RESULTS

A total of 67 patients (126 eyes) were enrolled in this study. One month postoperatively, spherical equivalent refraction and visual acuity achieved preliminary stability. However, central corneal epithelial thickness (CCET) and standard deviation of the corneal epithelial thickness (SDcet) took 3-6 months to progressive recovery. Patients with higher baseline spherical equivalent refraction were associated with slower epithelial recovery. At every follow-up time point, a significant superior-inferior difference in the minimum corneal epithelial thickness area was observed. Higher stromal haze was correlated with higher spherical equivalent refraction (both baseline and residual) but had no relation with visual outcomes. There was a significant correlation between higher CCET with a better uncorrected distance visual acuity and lower corneal epithelial thickness irregularity.

CONCLUSIONS

CCET and SDcet measured by OCT seem to be a good auxiliary indicator for reflecting the status of corneal wound recovery after t-PRK surgery. However, a well-designed randomised control study is needed to confirm the study results.

Biological effects of stored platelet-rich plasma eye-drops in corneal wound healing

BACKGROUND/AIMS

This study aimed to assess the efficacy and sterility of stored platelet-rich plasma (PRP) eye-drops for corneal epithelial wound healing compared with those of autologous serum (AS) eye-drops.

METHODS

At our single institution, PRP and AS eye-drops were prepared using peripheral blood obtained from six healthy volunteers and stored at 4°C. Platelet and leucocyte counts and transforming growth factor (TGF)-β1, epidermal growth factor (EGF), and fibronectin levels were assessed during storage for up to 4 weeks. Sterility was assessed by culturing 4-week poststorage samples. PRP, AS, and phosphate-buffered saline (PBS) eye-drop efficacies were compared using corneal epithelial wound healing assays in vitro and in vivo and monitoring wound areas under a microscope every 3 hours.

RESULTS

Higher platelet and lower leucocyte counts were seen in PRP than in whole blood on the day of preparation. After storage, TGF-β1, EGF, and fibronectin levels were significantly higher in PRP than in AS eye-drops. In vitro and in vivo, PRP eye-drops used on the day of preparation significantly promoted corneal epithelial wound healing compared with PBS. Moreover, PRP eye-drops stored for 4 weeks significantly promoted corneal wound healing compared with PBS and AS eye-drops.

CONCLUSION

PRP eye-drops stored at 4°C for 4 weeks promoted corneal epithelial wound healing with higher levels of growth factors than those observed in AS eye-drops, while maintaining sterility, suggesting that this preparation satisfies the unmet medical needs in the treatment of refractory keratoconjunctival epithelial disorders.

Nano Self-Assemblies of Caffeic Acid-Fibronectin Mimic a Peptide Conjugate for the Treatment of Corneal Epithelial Injury

Rapid corneal re-epithelialization is important for corneal wound healing. Corneal epithelial cell motility and oxidative stress are important targets for therapeutic intervention. In this study, we covalently conjugated the antioxidant caffeic acid (CA) with a bioactive peptide sequence (PHSRN) to generate a CA-PHSRN amphiphile, which was formulated into nanoparticular eye drops with an average size of 43.21 ± 16 nm. CA-PHSRN caused minimal cytotoxicity against human corneal epithelial cells (HCECs) and RAW264.7 cells, exhibited an excellent free radical scavenging ability, and remarkably attenuated reactive oxygen species (ROS) levels in H2O2-stimulated HCECs. The antioxidant and anti-inflammatory activities of CA-PHSRN were assessed in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. The results show that CA-PHSRN treatment effectively prevented LPS-induced DNA damage and significantly reduced the levels of LPS-induced pro-inflammatory cytochemokines (i.e., iNOS, NO, TNF-α, IL-6, and COX-2) in a dose-dependent manner. Moreover, using a rabbit corneal epithelial ex vivo migration assay, we demonstrated that the proposed CA-PHSRN accelerated corneal epithelial cell migration and exhibited high ocular tolerance and ocular bioavailability after topical instillation. Taken together, the proposed CA-PHSRN nanoparticular eye drops are a promising therapeutic formulation for the treatment of corneal epithelial injury.

Enhanced adipose-derived stem cells with IGF-1-modified mRNA promote wound healing following corneal injury

The cornea serves as an important barrier structure to the eyeball and is vulnerable to injuries, which may lead to scarring and blindness if not treated promptly. To explore an effective treatment that could achieve multi-dimensional repair of the injured cornea, the study herein innovatively combined modified mRNA (modRNA) technologies with adipose-derived mesenchymal stem cells (ADSCs) therapy, and applied IGF-1 modRNA (modIGF1)-engineered ADSCs (ADSCmodIGF1) to alkali-burned corneas in mice. The therapeutic results showed that ADSCmodIGF1 treatment could achieve the most extensive recovery of corneal morphology and function when compared not only with simple ADSCs but also IGF-1 protein eyedrops, which was reflected by the healing of corneal epithelium and limbus, the inhibition of corneal stromal fibrosis, angiogenesis and lymphangiogenesis, and also the repair of corneal nerves. In vitro experiments further proved that ADSCmodIGF1 could more significantly promote the activity of trigeminal ganglion cells and maintain the stemness of limbal stem cells than simple ADSCs, which were also essential for reconstructing corneal homeostasis. Through a combinatorial treatment regimen of cell-based therapy with mRNA technology, this study highlighted comprehensive repair in the damaged cornea and showed the outstanding application prospect in the treatment of corneal injury.

Recent Approaches to the Modification of Collagen Biomatrix as a Corneal Biomatrix and Its Cellular Interaction

Over the last several decades, numerous modifications and advancements have been made to design the optimal corneal biomatrix for corneal epithelial cell (CECs) or limbal epithelial stem cell (LESC) carriers. However, researchers have yet to discover the ideal optimization strategies for corneal biomatrix design and its effects on cultured CECs or LESCs. This review discusses and summarizes recent optimization strategies for developing an ideal collagen biomatrix and its interactions with CECs and LESCs. Using PRISMA guidelines, articles published from June 2012 to June 2022 were systematically searched using Web of Science (WoS), Scopus, PubMed, Wiley, and EBSCOhost databases. The literature search identified 444 potential relevant published articles, with 29 relevant articles selected based on inclusion and exclusion criteria following screening and appraising processes. Physicochemical and biocompatibility (in vitro and in vivo) characterization methods are highlighted, which are inconsistent throughout various studies. Despite the variability in the methodology approach, it is postulated that the modification of the collagen biomatrix improves its mechanical and biocompatibility properties toward CECs and LESCs. All findings are discussed in this review, which provides a general view of recent trends in this field.

Transglutaminase-2 is critical for corneal epithelial barrier function via positive regulation of Claudin-1

PURPOSE

Transglutaminase (TG)-2 is a ubiquitous multi-functional protein expressed in all living cells. The purpose of the current study was to investigate the role of TG-2 in corneal barrier function and its potential regulation of epithelial junctional proteins and transcription factors.

METHODS

Corneal barrier function to ions in TG-2-/- and TG-2+/+ mice was assessed by Ussing chamber assay. Hypo-osmolar water or FITC-dextran was applied on top of mouse eyes to evaluate the corneal barrier function to water and macromolecules. Western blots, qPCR and immunofluorescent staining were used to investigate the expression of tight junction proteins in TG-2-/- and TG-2+/+ mouse corneas, and also in TG-2 knockdown human corneal epithelial cells.

RESULTS

Corneal explants from TG-2-/- mice had a lower trans-epithelial electrical resistance compared to TG-2+/+ mice. When challenged by hypo-osmolar water, the central corneal thickness of TG-2-/- mice increased faster, and these mice had a faster rise of fluorescence in the anterior chamber after ocular exposure to FITC-dextran, compared to TG-2+/+. Claudin-1 protein and transcript levels were reduced in the cornea of TG-2-/- mice and in TG-2 knockdown human corneal epithelial cells. Slug which previously reported suppressing Claudin-1 transcription, was increased at both protein and transcript level in TG-2 knockdown cells. TG-2 and Claudin-1 protein levels were unchanged in shRNA and shTG cells after MG132 treatment, while Slug accumulated in treated cells.

CONCLUSION

TG-2 may positively regulate Claudin-1 through repressing Slug at transcript level, and thus it is critical for normal corneal barrier function.

Dynamic changes in protein concentrations of keratins in crop milk and related gene expression in pigeon crops during different incubation and chick rearing stages

1. The objective of this study was to examine the keratin composition of crop milk, the variation of epithelial thickness and keratin (K) gene expression in samples from young pigeon during incubation and chick rearing.2. Crop milk was collected from 1-, 3- and 5-day-old squab crops for keratin content analysis. Results showed that K4 accounted for the highest proportion of all detected keratins.3. In total, 42 pairs of adult pigeons were allocated to seven groups according to different stages to collect crop samples. Gene expression studies showed that the K3 gene expression was maximised at rearing Day 15 (15) and R1 in males and females, respectively. K6a gene level was the greatest at R15 in females, whereas it peaked at incubation Day 4 (I4) in males. The K12, K13, K23 and K80 gene levels were inhibited at the peak period of crop milk formation in comparison with I4. In females, K cochleal expression peaked at I10, whereas it was the greatest at R25 in males. K4 and K14 gene expression was the highest at I10 in females, while K4 and K14 were minimised at I17 and R7 in males, respectively. Gene expressions of K5, K8, K19 and K20 in males and K19 in females were maximised at R1. The K5, K20 and K75 gene levels in females peaked at R7. K75 and K8 expressions in males and females reached a maximum value at R25 and I17, respectively.4. The epithelial thickness of male and female crops reached their greatest levels at R1 and had the highest correlation with K19.5. These results emphasised the importance of keratinisation in crop milk formation, and different keratins probably play various roles during this period. The K19 was probably a marker for pigeon crop epithelium development. The sex of the parent pigeon affected keratin gene expression profiles.

Laser-induced microinjury of the corneal basal epithelium and imaging of resident macrophage responses in a live, whole-eye preparation

The corneal epithelium is continuously subjected to external stimuli that results in varying degrees of cellular damage. The use of live-cell imaging approaches has facilitated understanding of the cellular and molecular mechanisms underlying the corneal epithelial wound healing process. Here, we describe a live, ex vivo, whole-eye approach using laser scanning confocal microscopy to simultaneously induce and visualize short-term cellular responses following microdamage to the corneal epithelium. Live-cell imaging of corneal cell layers was enabled using the lipophilic fluorescent dyes, SGC5 or FM4-64, which, when injected into the anterior chamber of enucleated eyes, readily penetrated and labelled cell membranes. Necrotic microdamage to a defined region (30 μm x 30 μm) through the central plane of the corneal basal epithelium was induced by continuously scanning for at least one minute using high laser power and was dependent on the presence of lipophilic fluorescent dye. This whole-mount live-cell imaging and microdamage approach was used to examine the behavior of Cx3cr1:GFP-expressing resident corneal stromal macrophages (RCSMs). In undamaged corneas, RCSMs remained stationary, but exhibited a constant extension and retraction of short (~5 μm) semicircular, pseudopodia-like processes reminiscent of what has previously been reported in corneal dendritic cells. Within minutes of microdamage, nearby anterior RCSMs became highly polarized and extended projections towards the damaged region. The extension of the processes plateaued after about 30 minutes and remained stable over the course of 2-3 hours of imaging. Retrospective immunolabeling showed that these responding RCSMs were MHC class II+. This study adds to existing knowledge of immune cell behavior in response to corneal damage and introduces a simple corneal epithelial microdamage and wound healing paradigm.

Collagen as a Biomaterial for Skin and Corneal Wound Healing

The cornea and the skin are two organs that form the outer barrier of the human body. When either is injured (e.g., from surgery, physical trauma, or chemical burns), wound healing is initiated to restore integrity. Many cells are activated during wound healing. In particular, fibroblasts that are stimulated often transition into repair fibroblasts or myofibroblasts that synthesize extracellular matrix (ECM) components into the wound area. Control of wound ECM deposition is critical, as a disorganized ECM can block restoration of function. One of the most abundant structural proteins in the mammalian ECM is collagen. Collagen type I is the main component in connective tissues. It can be readily obtained and purified, and short analogs have also been developed for tissue engineering applications, including modulating the wound healing response. This review discusses the effect of several current collagen implants on the stimulation of corneal and skin wound healing. These range from collagen sponges and hydrogels to films and membranes.

Corneal Epithelial Regeneration: Old and New Perspectives

Corneal blindness is the fifth leading cause of blindness worldwide, and therapeutic options are still often limited to corneal transplantation. The corneal epithelium has a strong barrier function, and regeneration is highly dependent on limbal stem cell proliferation and basement membrane remodeling. As a result of the lack of corneal donor tissues, regenerative medicine for corneal diseases affecting the epithelium is an area with quite advanced basic and clinical research. Surgery still plays a prominent role in the treatment of epithelial diseases; indeed, innovative surgical techniques have been developed to transplant corneal and non-corneal stem cells onto diseased corneas for epithelial regeneration applications. The main goal of applying regenerative medicine to clinical practice is to restore function by providing viable cells based on the use of a novel therapeutic approach to generate biological substitutes and improve tissue functions. Interest in corneal epithelium rehabilitation medicine is rapidly growing, given the exposure of the corneal outer layers to external insults. Here, we performed a review of basic, clinical and surgical research reports on regenerative medicine for corneal epithelial disorders, classifying therapeutic approaches according to their macro- or microscopic target, i.e., into cellular or subcellular therapies, respectively.

The Impact of Different Oxygen Delivery Methods on Corneal Epithelial Repair after Injury

The hyperbaric oxygen therapy is often used in the management of acid and base burns of the eyes. However, oxygen is rarely supplied locally through goggles or face mask in ophthalmology. Therefore, in this study, we aim to investigate how oxygen delivery affects eye recovery after injury. We used a rabbit model with corneal epithelial injury to examine the effects of local oxygen supply via goggles or face mask on the recovery of cornea. A total of 75 healthy New Zealand white rabbits were randomly divided into three groups, A, B, and C, with 25 rabbits in each group. Then, on each rabbit eye (150 eyes in total), a circle of corneal epithelium with 5 mm in diameter was scraped off from the center of the cornea with a corneal epithelial scraper. Group A was given oxygen goggles every day (the oxygen flow rate was 3 L/min, once a day, 2 hours each time); group B was given nasal inhalation of oxygen every day (the oxygen flow rate was 3 L/min, once a day, 2 hours each time); and group C did not receive any treatment and was healed naturally. We found that the group A, which received oxygen supply via goggles, showed the best eye recovery. Transmission electron microscopy showed that the cornea with local oxygen supply via goggles or face mask exhibited intact capillary structure and obvious desmosome/hemidesmosome connections between cells. Moreover, the protein and RNA levels of hypoxia-related genes were lower in group A and B, suggesting that the hypoxia factor is a sensitive and early regulator in the low oxygen environment.

Acute Foggy Corneal Epithelial Disease: Seeking Clinical Features and Risk Factors

(1) Purpose: Here, we describe the clinical characteristics and predisposing factors of acute foggy corneal epithelial disease, a rare disease newly found during COVID-19 pandemic; (2) Methods: In this single-arm, ambispective case series study, ten patients with acute foggy corneal epithelial disease admitted between May 2020 and March 2021 were enrolled. Their detailed medical history and clinical and ophthalmic findings were recorded and analyzed; (3) Results: All the patients were female (100%), aged from 28 to 61 years (mean age of 40.4 ± 9.3 years). Seven cases (70%) had excessive eye use, and six cases (60%) had stayed up late and were overworked. Ten subjects (100%) presented with acute onset and a self-healing tendency. There was a mild-to-moderate decrease in the corrected visual acuity (0.35 ± 0.21 (LogMAR)). Slit-lamp examination showed diffuse dust-like opacity and edema in the epithelial layer of the cornea. By in vivo confocal microscope, epithelial cells presented characteristically a “relief-like” appearance. Anterior segment optical coherence tomography examination revealed that the mean epithelial thickness was increased (69.25 ± 4.31 μm, p < 0.01); (4) Conclusions: Acute foggy corneal epithelial disease is a rare disease in clinic, which tends to occur in young and middle-aged females. The typical clinical symptom is sudden foggy vision, which occurs repeatedly and can be relieved without treatment. Sex, an abnormal menstrual cycle, overuse of the eyes, fatigue and pressure might be risk factors. Changes in lifestyle and eye use habit during the COVID-19 pandemic may have possibly contributed to this disease incidence.

Arabinoxylan-Based Microcapsules Being Loaded with Bee Products as Bioactive Food Components Are Able to Modulate the Cell Migration and Inflammatory Response-In Vitro Study

The aim of the research was to use bioactive heteropolysaccharides isolated from rye bran to obtain innovative systems for the controlled release of bioactive compounds. The core of the obtained encapsulates was honey and royal jelly. It was shown for the first time that preparations effectively ameliorated inflammatory response in lipopolysaccharide (LPS)-treated RAW 264.7 macrophages, decreasing the secretion of interleukin 6 (IL-6), tumor necrosis factor α (TNF-α) and nitric oxide (NO). The in vitro digestion process revealed that bee products’ encapsulates were stronger oxidative stress reducers and had sustained ability to reduction in inflammation state mediators. The lack of inhibitory effect on migration rate of human microvascular endothelial cells (HMEC-1) endothelial cells and mouse embryonic fibroblasts (NIH-3T3), both cell models involved in wound healing process, additionally identified these preparations as agents potentially used in the management of inflammatory response. In the process of a simulated digestion in vitro, the innovative microcapsules showed 85% higher biostability and two to ten times better bioavailability, compared to natural bee products.

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.

Multifunctional Baicalin-Modified Contact Lens for Preventing Infection, Regulating the Ocular Surface Microenvironment and Promoting Corneal Repair

Corneal injury inevitably leads to disruption of the ocular surface microenvironment, which is closely associated with delayed epithelial cell repair and the development of infection. Recently, drug-loaded therapeutic contact lenses have emerged as a new approach to treating corneal injury due to their advantages of relieving pain, promoting corneal repair, and preventing infection. However, few therapeutic contact lenses could modulate the ocular surface’s inflammation and oxidative stress microenvironment. To address this, in this study, we covalently immobilized multifunctional baicalin (BCL), a flavon molecular with anti-inflammatory, anti-oxidative stress, and antibacterial capabilities, onto the surface of the contact lens. The BCL-modified contact lens showed excellent optical properties, powerful antibacterial properties, and non-toxicity to endothelial cells. Furthermore, the BCL-modified contact lens could significantly modulate the ocular surface microenvironment, including inhibition of macrophage aggregation and resistance to epithelium damage caused by oxidative stress. In animal models, BCL-modified corneal contact lens effectively promoted corneal epithelial cells repair. These excellent properties suggested that multifunctional BCL molecules had great application potential in the surface engineering of ophthalmic medical materials.

dsRNA Induced IFNβ-MMP13 Axis Drives Corneal Wound Healing

Purpose

Cornea, the outermost transparent layer of the eye, is the first line of defense against external threats. Following injury, the wound healing response is crucial to corneal repair and regeneration, yet its underlying mechanism is poorly understood. Our study was designed to investigate the role of dsRNA and its regulatory network in corneal wound healing.

Methods

A corneal wound healing model was established via the surgical removal of half of the corneal surface and adjoining limbus. RNase III was then used to clarify the role of dsRNA in corneal wound closure and RNA-seq was performed to investigate the mechanism of dsRNA in the healing process. Related gene expression was assessed using immunofluorescence staining, qPCR, and Western blot. Flow cytometry and scratch assay were used to analyze the proliferation and migration of limbal stem/progenitor cells (LSCs) in vitro and functional analysis of the target genes was completed using the corneal wound healing model.

Results

Corneal wound healing was delayed and impaired when the dsRNAs were removed or damaged following RNase III digestion. The dsRNAs released following corneal damage activate type I interferon (IFN-I) signaling, primarily IFNβ, via the corneal epithelium and neutralizing IFNβ or blocking IFN-I signaling delays corneal wound closure. Moreover, our data identified MMP13 as a downstream effector of IFNβ where its expression promotes LSC proliferation and enhances corneal epithelial reconstruction in vivo.

Conclusions

The dsRNA induced IFNβ-MMP13 axis plays a key role in corneal wound healing.

Impact of Different Oxygen Supply Methods on the Healing of Corneal Epithelial Wound and the Level of Acetylcholine

Purpose

To investigate the impact of different oxygen supply methods on corneal epithelial wound healing and acetylcholine level during wound healing.

Methods

We randomly divided 75 rabbits into three groups: A, B, and C, with 25 rabbits in each group. The central corneal epithelium was removed from all eyes of the rabbits using a 5 mm trephine. Group A rabbits were given low flow oxygen (3 L/min; concentration: 33%) for 2 h per day through goggles. Group B rabbits were given low flow oxygen (3 L/min; concentration: 33%) for 2 h per day via oxygen masks for inhalation. Group C rabbits healed naturally. The area of healed corneal epithelium and acetylcholine content in corneal epithelium were determined at 12 h, 24 h, and 36 h after injury.

Results

At 12 h, 24 h, and 36 h after injury, the healing area of corneal epithelium in the three groups was in the order group A > group B > group C (P < 0.05). At all timepoints, the acetylcholine level in corneal epithelium was in the order of group A > group B > group C (P < 0.05). In all three groups, the acetylcholine content in corneal epithelium showed the order 12 h > 24 h > 36 h (P < 0.05). There was a correlation between acetylcholine expression and the area of unhealed corneal epithelium, and the correlation coefficients of groups A, B, and C were 0.80, 0.83, and 0.85 respectively.

Conclusion

Increasing oxygen concentration through inhalation or via goggles can promote corneal epithelial wound healing, but increasing local oxygen concentration of the eye showed a better effect. Acetylcholine may play an important role in the early process of corneal epithelial wound healing.

Drug delivery to the anterior segment of the eye: A review of current and future treatment strategies

Research in the development of ophthalmic drug formulations and innovative technologies over the past few decades has been directed at improving the penetration of medications delivered to the eye. Currently, approximately 90% of all ophthalmic drug formulations (e.g. liposomes, micelles) are applied as eye drops. The major challenge of topical eye drops is low bioavailability, need for frequent instillation due to the short half-life, poor drug solubility, and potential side effects. Recent research has been focused on improving topical drug delivery devices by increasing ocular residence time, overcoming physiological and anatomical barriers, and developing medical devices and drug formulations to increase the duration of action of the active drugs. Researchers have developed innovative technologies and formulations ranging from sub-micron to macroscopic size such as prodrugs, enhancers, mucus-penetrating particles (MPPs), therapeutic contact lenses, and collagen corneal shields. Another approach towards the development of effective topical drug delivery is embedding therapeutic formulations in microdevices designed for sustained release of the active drugs. The goal is to optimize the delivery of ophthalmic medications by achieving high drug concentration with prolonged duration of action that is convenient for patients to administer.

In-situ porcine corneal matrix hydrogel as ocular surface bandage

PURPOSE

Bioactive substrates can be used therapeutically to enhance wound healing. Here, we evaluated the effect of an in-situ thermoresponsive hydrogel from decellularized porcine cornea ECM, COMatrix (COrnea Matrix), for application as an ocular surface bandage for corneal epithelial defects.

METHODS

COMatrix hydrogel was fabricated from decellularized porcine corneas. The effects of COMatrix hydrogel on attachment and proliferation of human corneal epithelial cells (HCECs) were evaluated in vitro. The effect of COMatrix on the expressions of the inflammatory genes, IL-1β, TNF-α, and IL-6 was assessed by RT-PCR. The in-situ application and also repairing effects of COMatrix hydrogel as an ocular bandage was studied in a murine model of corneal epithelial wound. The eyes were examined by optical coherence tomography (OCT) and slit-lamp microscopy in vivo and by histology and immunofluorescence post-mortem.

RESULTS

In vitro, COMatrix hydrogel significantly enhanced the attachment and proliferation of HCECs relative to control. HCECs exposed to COMatrix had less induced expression of TNF-α (P < 0.05). In vivo, COMatrix formed a uniform hydrogel that adhered to the murine ocular surface after in-situ curing. Corneal epithelial wound closure was significantly accelerated by COMatrix hydrogel compared to control (P < 0.01). There was significant increase in the expression of proliferation marker Ki-67 in wounded corneal epithelium by COMatrix hydrogel compared to control (P < 0.05).

CONCLUSIONS

COMatrix hydrogel is a naturally derived bioactive material with potential application as an ocular surface bandage to enhance epithelial wound healing.

Edible Bird's Nest: The Functional Values of the Prized Animal-Based Bioproduct From Southeast Asia-A Review

Edible Bird's Nest (EBN) is the most prized health delicacy among the Chinese population in the world. Although some scientific characterization and its bioactivities have been studied and researched, no lights have been shed on its actual composition or mechanism. The aim of this review paper is to address the advances of EBN as a therapeutic animal bioproduct, challenges and future perspectives of research involving EBN. The methodology of this review primarily involved a thorough search from the literature undertaken on Web of Science (WoS) using the keyword "edible bird nest". Other information were obtained from the field/market in Malaysia, one of the largest EBN-producing countries. This article collects and describes the publications related to EBN and its therapeutic with diverse functional values. EBN extracts display anti-aging effects, inhibition of influenza virus infection, alternative traditional medicine in athletes and cancer patients, corneal wound healing effects, stimulation of proliferation of human adipose-derived stem cells, potentiate of mitogenic response, epidermal growth factor-like activities, enhancement of bone strength and dermal thickness, eye care, neuroprotective and antioxidant effects. In-depth literature study based on scientific findings were carried out on EBN and its properties. More importantly, the future direction of EBN in research and development as health-promoting ingredients in food and the potential treatment of certain diseases have been outlined.

Human platelet lysate delivered via an ocular wound chamber for the treatment of corneal epithelial injuries

Current strategies to address corneal surface defects are insufficient to successfully resolve damage caused by injury and/or disease. To address this issue, we have developed an ocular wound chamber (OWC) that creates a fluid-filled environment by encompassing damaged ocular and periocular tissues allowing for the continuous delivery of therapeutics. This study tested human platelet lysate (hPL) as a treatment for corneal epithelial defects when used with the OWC. Corneal epithelial injuries were created in anesthetized guinea pigs by debridement of the central cornea. An OWC was placed over the injured eye and animals randomly grouped followed by injection of either 20% hPL, 100% hPL, or vehicle (balanced salt solution, BSS) into the chamber. Eyes were assessed at 0, 24, 48, and 72 h using intraocular pressure (IOP), optical coherence tomography (OCT), and fluorescein imaging. Whole globes were histologically processed, and hematoxylin and eosin (H&E) stained. No differences in IOP were recorded as a result of corneal wounding, chamber placement, and/or therapeutic application. OCT images demonstrated increased corneal swelling at 48 h and 72 h in the vehicle group compared to 20% hPL. Fluorescein staining showed increased corneal re-epithelialization in the 20% and 100% hPL groups at 48 h compared to vehicle only. H&E staining revealed increased stromal cellular infiltrate in the BSS group. This study demonstrates the delivery of hPL via the OWC improves corneal re-epithelialization and supports the expanded usage of the chamber in combination with hPL to manage a variety of corneal surface injuries, diseases and/or periocular conditions.

The role of topical timolol in wound healing and the treatment of vascular lesions: A narrative review

Beta-2 adrenergic receptors are the only subgroup of beta-adrenergic receptors expressed in the membrane of large cells, including skin keratinocytes, fibroblasts, and melanocytes. Alterations in the function or concentration of β2 adrenoreceptors related to keratinocytes are associated with some skin conditions. Some findings suggest the role of β2 adrenoreceptors in maintaining the function and integrity of the epidermis. Beta-receptor antagonists can be systemically and topically effective in healing hemangioma, paronychia, vasculitis ulcer, tufted angioma, acute and chronic wounds. Most studies with a strong design on this subject deal with the systemic form, but recently, numerous case and group reports and smaller studies have focused on topical forms, especially topical timolol. The present comprehensive review study surveys the role of topical timolol in acute and chronic wound healing in the field of dermatology.

Progress on the Function and Application of Thymosin β4

Thymosin β4 (Tβ4) is a multifunctional and widely distributed peptide that plays a pivotal role in several physiological and pathological processes in the body, namely, increasing angiogenesis and proliferation and inhibiting apoptosis and inflammation. Moreover, Tβ4 is effectively utilized for several indications in animal experiments or clinical trials, such as myocardial infarction and myocardial ischemia-reperfusion injury, xerophthalmia, liver and renal fibrosis, ulcerative colitis and colon cancer, and skin trauma. Recent studies have reported the potential application of Tβ4 and its underlying mechanisms. The present study reveals the progress regarding functions and applications of Tβ4.

Heparin-Modified Amniotic Membrane Combined With Growth Factors for Promoting Corneal Wound Healing After Alkali Burn

Ocular chemical burns are potentially blinding ocular injuries and require urgent management. Amniotic membrane (AM) transplantation is an effective surgical treatment, one of the reasons is because AM is a rich source of growth factors that can promote epithelialization and wound healing. However, growth factors will be gradually lost and insufficient after preparation process and long-time storage, leading to unsatisfactory therapeutic effects. Herein, we present a modified AM (AM-HEP) for the supplement and sustained release of growth factor by surface grafting heparin for treatment of ocular chemical burns. Heparin grafting rate and stability, microstructure, physical property, and sustained release of epithelial growth factor (EGF) of AM-HEP were characterized. Biocompatibility and ability to promote corneal epithelial cell growth and migration were evaluated and compared with a biological amnion, which is available on the market in vitro. The therapeutic effects of AM-HEP combined with EGF (AM-HEP@EGF) in vivo had been evaluated in a model of mouse corneal alkali burn. The results indicated that heparin was introduced into AM and maintain stability over 3 weeks at 37°C. The modification process of AM-HEP did not affect microstructure and physical property after comparing with non-modified AM. EGF could be combined quickly and effectively with AM-HEP; the sustained release could last for more than 14 days. AM-HEP@EGF could significantly promote corneal epithelial cell growth and migration, compared with non-modified AM and control group. Faster corneal epithelialization was observed with the transplantation of AM-HEP@EGF in vivo, compared with the untreated control group. The corneas in the AM-HEP@EGF group have less inflammation and were more transparent than those in the control group. The results from in vitro and in vivo experiments demonstrated that AM-HEP@EGF could significantly enhance the therapeutic effects. Taken together, AM-HEP@EGF is exhibited to be a potent clinical application in corneal alkali burns through accelerating corneal epithelial wound healing.

Stem cell-based therapeutic strategies for corneal epithelium regeneration

Any significant loss of vision or blindness caused by corneal damages is referred to as corneal blindness. Corneal blindness is the fourth most common cause of blindness worldwide, representing more than 5% of the total blind population. Currently, corneal transplantation is used to treat many corneal diseases. In some cases, implantation of artificial cornea (keratoprosthesis) is suggested after a patient has had a donor corneal transplant failure. The shortage of donors and the side effects of keratoprosthesis are limiting these approaches. Recently, researchers have been actively pursuing new approaches for corneal regeneration because of these limitations. Nowadays, tissue engineering of different corneal layers (epithelium, stroma, endothelium, or full thickness tissue) is a promising approach that has attracted a great deal of interest from researchers and focuses on regenerative strategies using different cell sources and biomaterials. Various sources of corneal and non-corneal stem cells have shown significant advantages for corneal epithelium regeneration applications. Pluripotent stem cells (embryonic stem cells and iPS cells), epithelial stem cells (derived from oral mucus, amniotic membrane, epidermis and hair follicle), mesenchymal stem cells (bone marrow, adipose-derived, amniotic membrane, placenta, umbilical cord), and neural crest origin stem cells (dental pulp stem cells) are the most promising sources in this regard. These cells could also be used in combination with natural or synthetic scaffolds to improve the efficacy of the therapeutic approach. As the ocular surface is exposed to external damage, the number of studies on regeneration of the corneal epithelium is rising. In this paper, we reviewed the stem cell-based strategies for corneal epithelium regeneration.

Corneal epithelium tissue engineering: recent advances in regeneration and replacement of corneal surface

Currently, many corneal diseases are treated by corneal transplantation, artificial corneal implantation or, in severe cases, keratoprosthesis. Owing to the shortage of cornea donors and the risks involved with artificial corneal implants, such as infection transmission, researchers continually seek new approaches for corneal regeneration. Corneal tissue engineering is a promising approach that has attracted much attention from researchers and is focused on regenerative strategies using various biomaterials in combination with different cell types. These constructs should have the ability to mimic the native tissue microenvironment and present suitable optical, mechanical and biological properties. In this article, we review studies that have focused on the current clinical techniques for corneal replacement. We also describe tissue-engineering and cell-based approaches for corneal regeneration.

The Need for Improved Therapeutic Approaches to Protect the Cornea Against Chemotoxic Injuries

Cornea, a highly specialized transparent tissue, is the major refractive element of the eye. The cornea is highly susceptible to chemotoxic injury through topical exposure to vapors, microparticles, and aqueous drops, as well as through systemically absorbed chemicals that access the cornea via tear film, aqueous humor, and limbal vasculature. Corneal injury activates a carefully orchestrated series of repair processes capable of resolving minor lesions over time, but it often fails to overcome the menace of moderate, severe, and chronic injuries and secondary pathophysiologies that permanently impair vision. The most serious complications of chemical injuries-persistent corneal edema, neovascularization, scarring/haze, limbal stem cell deficiency, and corneal melting-often manifest over months to years, suggesting that a better understanding of endogenous regenerative mechanisms of corneal repair can lead to the development of improved treatments that may attenuate or prevent corneal defects and protect vision.

Transcriptional profiles along cell programming into corneal epithelial differentiation

Using the rabbit corneal epithelial cell line RCE1(5T5) as a model, we analyzed three differentiation stages, distinguished on basis to the growth state of cultured cells and after studying the expression of transcription factors such as Oct4, Pax6 and ΔNp63α, selected differentiation markers, and signaling or epigenetic markers such as Notch receptors and Prdm3. Namely, proliferative non-differentiated cells, committed cells, and cells that constitute a stratified epithelium with a limbal epithelial-like structure. RNAseq based transcriptome analysis showed that 4891 genes were differentially expressed among these stages displaying distinctive gene signatures: proliferative cells had 1278 genes as gene signature, and seem to be early epithelial progenitors with an Oct4⁺, KLF4⁺, Myc⁺, ΔNp63α⁺, ABCG2⁺, Vimentin⁺, Zeb1⁺, VANGL1⁺, Krt3^-, Krt12^- phenotype. Committed cells had a gene signature with 417 genes and displayed markers indicative of the beginning of corneal differentiation, and genes characteristic of proliferative cells; we found the possible participation of Six3 and Six4 transcription factors along this stage. The third stage matches with a stratified corneal epithelium (gene signature comprising 979 genes) and is typified by an increase in the expression of WNT10A and NOTCH 2 and 3 signaling and Cux1 transcription factor, besides Pax6, KLF4 or Sox9. The differentiated cells express about 50% of the genes that belong to the Epidermal Differentiation Complex (EDC). Analysis of the differences between corneal epithelium and epidermis could be crucial to understand the regulatory mechanisms that lead to the expression of the differentiated phenotype.

Acetylsalicylic Acid Promotes Corneal Epithelium Migration by Regulating Neutrophil Extracellular Traps in Alkali Burn

Neutrophils are the first cells to migrate into the cornea in response to alkali burns, and excessive neutrophil infiltration is associated with inflammatory injury and a poorer prognosis. In an effort to understand the mechanisms underlying the inflammation mediated by neutrophils after alkali burns, we examined the role of alkali-activated neutrophils on human corneal epithelial cells (HCEs) proliferation and migration, as well as the effects of acetylsalicylic acid (ASA) and dexamethasone (DXM) on NETosis. We stimulated human neutrophils with sodium hydroxide (NaOH) and observed dose- and time-dependent neutrophil extracellular traps (NETs) formation. We also observed that ASA, but not DXM, significantly inhibited NaOH-induced NETosis. Furthermore, the activation of nuclear factor (NF)-κB, but not the production of reactive oxygen species, was involved in ASA-regulated NETosis. Moreover, NETs were found to be involved in alkali-activated neutrophils (ANs) induced neutrophil-HCE adhesion. ANs enhanced HCEs proliferation via phagocytosis. Meanwhile, ANs inhibited HCEs migration through the release of NETs, which was partially rescued by 5 mM ASA. In conclusion, ANs may interfere with HCEs proliferation and migration by phagocytosis and NETs formation, respectively. ASA may enhance HCEs migration by decreasing NETs formation through inhibition of NF-κB activation and could be a promising strategy for improving the prognosis of corneal alkali burns.

Perfluorooctanoic acid in indoor particulate matter triggers oxidative stress and inflammation in corneal and retinal cells

To investigate the particle size distribution of particulate matter and the concentration of specific perfluorinated compounds in indoor dust samples from several locations. Then, we used cell-based assays to investigate the effect of perfluorinated compounds on human corneal epithelial (HCEpiC), endothelial cells (HCEC) and retinal pigment epithelial cells (RPE). Indoor dust samples were collected at five different locations and PM_50–10, PM_10–2.5, and PM_2.5–1 were fractionized. The presence and levels of 8:2 fluorotelomer alcohol, 10:2 fluorotelomer alcohol, and perfluorooctanoic acid were detected by gas chromatography–mass spectrometry. The effect of perfluorooctanoic acid on the activation of reactive oxygen species, transepithelial resistance as well as the expression of interleukin (IL)-6 and IL-8 were determined. The basolateral media of human corneal epithelial or human corneal endothelial cells were used to treat human corneal endothelial or retinal pigment epithelial cells, respectively to indicate the potential of ocular surface inflammation may result in retinal inflammation. Among perfluorinated compounds, only perfluorooctanoic acid was detected in all indoor dust samples. Perfluorooctanoic acid had the highest concentration among all perfluorinated compounds in the samples. Exposure to perfluorooctanoic acid impaired tight junction sealing and increased the levels of reactive oxygen species in human corneal epithelial cells. In human corneal epithelial cells, secretion of IL-6 and IL-8 in both apical and basolateral media was promoted significantly by perfluorooctanoic acid treatment. Stimulation with the basolateral media from perfluorooctanoic acid-treated human corneal epithelial cells induced inflammation in human corneal endothelial cells. The treatment of retinal pigment epithelial cells with the basolateral media from stimulated human corneal endothelial cells also elicited the secretion of proinflammatory cytokines. The results indicate that perfluorooctanoic acid exposure impaired the tight junction of corneal cells and caused inflammatory reactions in the retina. Exposure of the cornea to perfluorooctanoic acid contained in particulate matter might induce oxidative stress and inflammation in the retina and represent a risk factor for age-related macular degeneration.

Preparation of collagen/cellulose nanocrystals composite films and their potential applications in corneal repair

As the main component of the natural cornea, collagen (COL) has been widely applied to the construction of corneal repair materials. However, the applications of collagen are limited due to its poor mechanical properties. Cellulose nanocrystals (CNCs) possess excellent mechanical properties, optical transparency and good biocompatibility. Therefore, in this study, we attempted to introduce cellulose nanocrystals into collagen-based films to obtain corneal repair materials with a high strength. CNCs were incorporated at 1, 3, 5, 7 and 10 wt%. The physical properties of these composite films were characterized, and in vitro cell-based analyses were also performed. The COL/CNC films possessed better mechanic properties, and the introduction of CNCs did not affect the water content and light transmittance. The COL/CNC films demonstrated good biocompatibility toward rabbit corneal epithelial cells and keratocytes in vitro. Moreover, the collagen films with appropriate ration of CNCs effectively induced the migration of corneal epithelial cells and inhibited the myofibroblast differentiation of keratocytes. A collagen film with 7 wt% CNCs displayed the best combination of physical properties and biological performance in vitro among all the films. This study describes a nonchemical cross-linking method to enhance the mechanical properties of collagen for use in corneal repair materials and highlights potential application in corneal tissue engineering.

A Systematic Review on Cornea Epithelial-Stromal Homeostasis

INTRODUCTION

This review aims to summarise the role of different cells, genes, proteins and lipid in regulating cornea epithelial-stromal homeostasis.

METHODS

We performed an Entrez PubMed literature search using keywords "human," "cornea," "epithelial," "stromal," "homeostasis," "fibrosis response," and "pathogenesis" on 24th of September 2019, resulting in 35 papers, of which 18 were chosen after filtering for "English language" and "published within 10 years" as well as curation for relevance by the authors.

RESULTS

The 18 selected papers showed that corneal epithelial cells, fibroblasts and telocytes, together with genes such as Klf4, Pax6 and Id found in the cells, play important roles in achieving homeostasis to maintain corneal integrity and transparency. Proteins classified as pro-fibrotic ligands and anti-fibrotic ligands are responsible for regulating cornea stromal fibrosis and extracellular matrix deposition, thus regulators of scar formation during wound healing. Anti-inflammatory ligands and wound repairing ligands are critical in eliciting protective inflammation and promoting epithelial healing, respectively. Protein receptors located on cellular membrane play a role in maintaining intercellular connections as well as corneal hydration.

DISCUSSION/CONCLUSION

These studies prompt development of novel therapeutic strategies such as tear drops or ointments that target certain proteins to maintain corneal homeostasis. However, more in vitro and in vivo studies are required to prove the effectiveness of exogenous administration of molecules in improving healing outcome. Hence, future investigations of the molecular pathways highlighted in this review will reveal novel therapeutic tools such as gene or cell therapy to treat corneal diseases.

TGF-β regulation of microRNA miR-497-5p and ocular lens epithelial cell mesenchymal transition

The purpose of this study was to investigate the role of a human lens microRNA (miR-497-5p) in regulating epithelialmesenchymal transition (EMT) under the control of transforming growth factor beta (TGF-β). A microRNA array was used to evaluate the microRNA profiles of untreated and TGF-β-treated human lens epithelial cells in culture. This showed that TGF-β treatment led to the upregulation of 96 microRNAs and downregulation of 39 microRNAs. Thirteen microRNAs were predicted to be involved in the pathogenesis of posterior capsule opacification (PCO). Meanwhile, overexpression of miR-497-5p suppressed cell proliferation and EMT 48 h post-transfection, and inhibition of miR-497-5p accelerated cell proliferation and EMT. Treatment with TGF-β inhibited the expression of miR-497-5p, but not cell proliferation. miR-497-5p was also found to regulate the level of CCNE1 and FGF7, which are reported to be actively involved in EMT. CCNE1 and FGF7 were bona fide targets of miR-497-5p. The results suggest that miR-497-5p participates in the direct regulation of lens epithelial cell EMT and is regulated by TGF-β. miR-497-5p may be a novel target for PCO therapy.

Advanced Glycation End Products and Receptor (RAGE) Promote Wound Healing of Human Corneal Epithelial Cells

Purpose

We used a human corneal epithelial cell (HCE) line to determine the involvement of the advanced glycation end products (AGEs) / receptor for AGEs (RAGE) couple in corneal epithelium wound healing.

Methods

After wounding, HCE cells were exposed to two major RAGE ligands (HMGB1 and AGEs), and wound healing was evaluated using the in vitro scratch assay. Following wound healing, the HCE cells were used to study the influence of the RAGE ligands on HCE proliferation, invasion, and migration. Activation of the nuclear factor (NF)-κB signaling pathway by the AGEs/RAGE couple was tested using a luciferase reporter assay. Functional transcriptional regulation by this pathway was confirmed by quantification of expression of the connexin 43 target gene. For each experiment, specific RAGE involvement was confirmed by small interfering RNA treatments.

Results

AGEs treatment at a dose of 100 µg/mL significantly improved the wound healing process in a RAGE-dependent manner by promoting cell migration, whereas HMGB1 had no effect. No significant influence of the AGEs/RAGE couple was observed on cell proliferation and invasion. However, this treatment induced an early activation of the NF-κB pathway and positively regulated the expression of the target gene, connexin 43, at both the mRNA and protein levels.

Conclusions

Our results demonstrate that the RAGE pathway is activated by AGEs treatment and is involved in the promotion of corneal epithelial wound healing. This positive action is observed only during the early stages of wound healing, as illustrated by the quick activation of the NF-κB pathway and induction of connexin 43 expression.

Engineered metal oxide nanomaterials inhibit corneal epithelial wound healing in vitro and in vivo

Ocular exposure to metal oxide engineered nanomaterials (ENMs) is common as exemplified by zinc oxide (ZnO), a major constituent of sunscreens and cosmetics. The ocular surface that includes the transparent cornea and its protective tear film are common sites of exposure for metal ENMs. Despite the frequency of exposure of the ocular surface, there is a knowledge gap regarding the effects of metal oxide ENMs on the cornea in health and disease. Therefore, we studied the effects of metal oxide ENMs on the cornea in the presence or absence of injury. Cell viability of immortalized human corneal epithelial (hTCEpi) cells was assessed following treatment with 11 metal oxide ENMs with a concentration ranging from 0.5 to 250 μg/mL for 24 hours. An epithelial wound healing assay with a monolayer of hTCEpi cells was then performed using 11 metal oxide ENMs at select concentrations based on data from the viability assays. Subsequently, based on the in vitro results, in vivo testing of precorneal tear film (PTF) quantity and stability as well as a corneal epithelial wound healing were tested in the presence or absence ZnO or vanadium pentoxide (V₂O₅) at a concentration of 50 μg/mL. We found that WO₃, ZnO, V₂O₅ and CuO ENMs significantly reduced hTCEpi cell viability in comparison to vehicle control or the other metal oxide ENMs tested. Furthermore, ZnO and V₂O₅ ENMs also significantly decreased hTCEpi cell migration. Although ZnO and V₂O₅ did not alter PTF parameters of rabbits in vivo, corneal epithelial wound healing was significantly delayed by topical ZnO while V₂O₅ did not alter wound healing. Finally, hyperspectral images confirmed penetration of ZnO and V₂O₅ through all corneal layers and into the iris stroma. Considering the marked epithelial toxicity and corneal penetration of ZnO, further investigations on the impact of this ENM on the eye are warranted.

Treatment of Corneal Alkali Burn with Chestnut Honey, Royal Jelly, and Chestnut Honey-Royal Jelly Mixture

Objectives:

The alkaline burn of the cornea usually results in a decreased vision with opacification. In this study, we investigated the potential role of endemic chestnut honey (CH) and royal jelly on corneal healing after an alkaline burn.

Methods:

We created an alkaline burn on the center of the corneas of four groups of Wistar rats by applying round filter paper soaked with 1 N NaOH for 30 seconds. The animals were treated with RJ, CH, RJ-CH combination and Na-Hyaluronate (Na-HA) eye drops. We performed a serial evaluation with anterior segment photography on the first, 7th, and 14th days of the experiment. Pathologic examination conducted with hematoxylin and eosin stains and immunostaining for SMA and α4β1 integrin. We evaluated the corneal healing process with a scoring system, which was estimating the degree of corneal edema, the size of the corneal ulcer, and limbal hyperemia.

Results:

There was no statistically significant difference between groups on the first, 7^th, and 14^th days concerning the healing scores (p=0.88, p=0.06, p=0.80, respectively). However, there were significantly better scores in the repeated measures of CH (p=0.012) and RJ-CH (p=0.00) groups. The RJ group and Na-HA group did not show a significant difference in repeated measures (p=0.19 and p=0.10, respectively). The α4β1 integrin levels on immunostaining showed a significant difference among groups on the 14^th day (p=0.002).

Conclusion:

We found better corneal healing after treatment with the RJ-CH containing eye drops concerning corneal healing sore and α4β1 integrin staining.

Engineering topography: Effects on corneal cell behavior and integration into corneal tissue engineering

Cell-material interactions are important to tissue engineering. Inspired by the natural topographic structures on the extracellular matrix, a growing number of studies have integrated engineering topography into investigations of cell behavior on biomaterials. Engineering topography has a significant influence on cell behaviors. These cell-topography interactions play an important role in regenerative medicine and tissue engineering. Similarly, cell-topography interactions are important to corneal reconstruction and regeneration. In this review, we primarily summarized the effects of topographic cues on the behaviors of corneal cells, including cell morphology, adhesion, migration, and proliferation. Furthermore, the integration of engineering surface topography into corneal tissue engineering was also discussed.

PM2.5 and NOx exposure promote myopia: clinical evidence and experimental proof

Myopia is caused by complex genetic and environmental factors. However, information regarding the effect of long-term exposure to air pollutants on the risk of development of myopia is lacking. We collected data from two linked databases: the Taiwan National Health Insurance Research Database (NHIRD) and the Taiwan Air Quality-Monitoring Database (TAQMD). A total of 15,822 children (16.3%) were diagnosed with myopia within the cohort. The incidence rate of myopia increased with exposure to increasing concentrations of particulate matter (PM2.5) and nitrogen oxides (NOx), increasing from 15.8 to 24.5 and from 13.7 to 34.4, per 1000 person-years, respectively. The adjusted hazard ratio for myopia increased with elevated PM2.5 and NOx exposure concentrations in Q4 to 1.57 and 2.60, respectively, compared to those exposed to the corresponding concentrations in Q1. In the animal experiments, PM2.5 induced myopia in hamsters by enhancing inflammation and was inhibited by resveratrol treatment compared to the control group. The change in axial length in the PM2.5 group was 0.386 ± 0.069 mm versus 0.287 ± 0.086 mm in the control group and 0.257 ± 0.059 mm in the PM2.5 + resveratrol group. We provide both clinical and experimental correlations that exposure to ambient air pollutants is associated with the pathogenesis of myopia.

Corneal Cells: Fine-tuning Nerve Regeneration

The cornea is a transparent outermost structure of the eye anterior segment comprising the highest density of innervated tissue. In the process of corneal innervation, trigeminal ganglion originated corneal nerves diligently traverse different corneal cell types in different corneal layers including the corneal stroma and epithelium. While crossing the stromal and epithelial cell layers during innervation, due to the existing physical contacts, close interactions occur between stromal keratocytes, epithelial cells, resident immune cells and corneal nerves. Furthermore, by producing various trophic and growth factors corneal cells assist in maintaining the growth and function of corneal nerves. Similarly, corneal nerve generated growth factors critically modify the corneal cell function in all the corneal layers. Due to their close association and contacts, on-going cross-communication between these cell types and corneal nerves play a vital role in the modulation of corneal nerve function, regeneration during wound healing. The present review highlights the influence of different corneal cell types and growth factors released from these cells on corneal nerve regeneration and function.

Hyperosmotic Stress-Induced TRPM2 Channel Activation Stimulates NLRP3 Inflammasome Activity in Primary Human Corneal Epithelial Cells

Purpose

The purpose of this study was to determine whether either a hyperosmotic or oxidative stress induces NLRP3 inflammasome activation and increases in bioactive IL-1β secretion through transient receptor potential melastatin 2 (TRPM2) activation in primary human corneal epithelial cells (PHCECs).

Methods

Real-time PCR, Western blots, and immunofluorescent staining were used to evaluate TRPM2 and NLRP3, ASC, caspase-1, and IL-1β mRNA and protein expression levels, respectively. A CCK-8 assay evaluated cell viability. Hyperosmotic 500 mOsm and oxidative 0.5 mM H2O2 stresses were imposed. TRPM2 expression was inhibited with a TRPM2 inhibitor, 20 μM N-(p-amylcinnamoyl) anthranilic acid (ACA), or TRPM2 siRNA knockdown.

Results

In the hypertonic medium, TRPM2, NLRP3, ASC, caspase-1, and IL-1β gene and protein expression levels rose after 4 hours (P ≤ 0.043), whereas ACA preincubation suppressed these rises (P ≤ 0.044). Similarly, H2O2 upregulated TRPM2 protein expression by 80%, and induced both NLRP3 inflammasome activation and increased bioactive IL-1β secretion (P ≤ 0.036), whereas ACA pretreatment suppressed these effects (P ≤ 0.029). TRPM2 siRNA transfection reduced TRPM2 gene expression by 70% (P = 0.018) in this hyperosmotic medium and inhibited the increases in NLRP3, caspase-1, and IL-1β gene (P ≤ 0.028) and protein expression (P ≤ 0.037).

Conclusions

TRPM2 activation by either a hyperosmotic or oxidative stress contributes to mediating increases in NLRP3 inflammasome activity and bioactive IL-1β expression because inhibiting TRPM2 activation or its expression blunted both of these responses in PHCECs. This association points to the possibility that TRPM2 is a viable target to suppress hyperosmotic-induced corneal epithelial inflammation.

Autologous Platelet-rich Plasma Eye Drops Accelerate Re-epithelialization of Post-keratoplasty Persistent Corneal Epithelial Defects

Purpose:

To investigate whether autologous platelet-rich plasma (PRP) eye drops accelerate re-epithelialization of post-keratoplasty persistent corneal epithelial defects (PEDs).

Methods:

A total of 34 eyes with PEDs after keratoplasty (24 penetrating keratoplasty and 10 deep anterior lamellar keratoplasty) that were refractory to conventional medical treatments were treated with PRP eye drops every 3 hours. PRP eye drops were prepared with a low- and high-speed centrifugation method and final platelet counts were 700,000-800,000 plt/μl. The mean treatment duration for complete re-epithelialization was compared with the mean treatment duration of conventionally treated corneal defects before the PRP treatment by paired t-test. The mean treatment duration was also statistically analyzed between age groups, gender, indications for keratoplasty, and types of keratoplasty using analysis of variance (ANOVA).

Results:

Treatment with autologous PRP eye drops led to rapid re-epithelialization in all eyes. The mean treatment duration for complete re-epithelialization was 2.47 ± 1.21 weeks, which was significantly shorter than the mean treatment duration of conventionally treated corneal defects before PRP treatment (6.82 ± 1.24 weeks) (P = 0.0001). There was no significant correlation between re-epithelialization time and patients' age, sex, indications for keratoplasty, and techniques of corneal transplantation.

Conclusion:

Treatment with autologous PRP eye drops is an effective and reliable approach that accelerates re-epithelialization of post-transplantation PEDs.

Microgrooved collagen-based corneal scaffold for promoting collective cell migration and antifibrosis

Microgrooved collagen membrane can effectively promote the epithelialization of corneal epithelial cells and inhibit the fibrosis of corneal stromal cells.