Cornea and Sclera

An Update on Strategies to Deliver Protein and Peptide Drugs to the Eye

In the past few decades, advancements in protein engineering, biotechnology, and structural biochemistry have resulted in the discovery of various techniques that enhanced the production yield of proteins, targetability, circulating half-life, product purity, and functionality of proteins and peptides. As a result, the utilization of proteins and peptides has increased in the treatment of many conditions, including ocular diseases. Ocular delivery of large molecules poses several challenges due to their high molecular weight, hydrophilicity, unstable nature, and poor permeation through cellular and enzymatic barriers. The use of novel strategies for delivering protein and peptides such as glycoengineering, PEGylation, Fc-fusion, chitosan nanoparticles, and liposomes have improved the efficacy, safety, and stability, which consequently expanded the therapeutic potential of proteins. This review article highlights various proteins and peptides that are useful in ocular disorders, challenges in their delivery to the eye, and strategies to enhance ocular bioavailability using novel delivery approaches. In addition, a few futuristic approaches that will assist in the ocular delivery of proteins and peptides were also discussed.

Sterile corneal necrosis after bowman layer transplantation

Purpose: To report sterile corneal necrosis as a severe and rare complication after Bowman Layer Transplantation (BTL). Methods: A 35-year-old woman with Down syndrome and advanced progressive keratoconus in her left eye was scheduled for a BLT. The patient rubbed her eyes and did not tolerate contact lenses. Following standard technique, a 8mm Bowman layer graft was placed into a intrastromal pocket with no intraoperative complications. Results: Postoperatively, the patient remained stable and topography showed notable central flattening but 17 days after the BTL was performed she developed a sterile corneal necrosis. Conclusions: Many studies have proven the efficacy of this technique as a potential treatment for stabilizing progressive and advanced keratoconus in selected cases. Few complications associated with BTL have been reported, including Bowman Layer tears or buttonholes when obtaining the tissue, very thick grafts or postoperative hydrops but no sterile necrosis described to the date. A combination of the hypotheses raised in this paper may explain this undesirable event.

Application of Collagen I and IV in Bioengineering Transparent Ocular Tissues

Collagens represent a major group of structural proteins expressed in different tissues and display distinct and variable properties. Whilst collagens are non-transparent in the skin, they confer transparency in the cornea and crystalline lens of the eye. There are 28 types of collagen that all share a common triple helix structure yet differ in the composition of their α-chains leading to their different properties. The different organization of collagen fibers also contributes to the variable tissue morphology. The important ability of collagen to form different tissues has led to the exploration and application of collagen as a biomaterial. Collagen type I (Col-I) and collagen type IV (Col-IV) are the two primary collagens found in corneal and lens tissues. Both collagens provide structure and transparency, essential for a clear vision. This review explores the application of these two collagen types as novel biomaterials in bioengineering unique tissue that could be used to treat a variety of ocular diseases leading to blindness.

Role of therapeutic contact lens following Descemet's stripping automated endothelial keratoplasty: A randomized control trial

Purpose

Therapeutic contact lenses (TCL) are known to help in epithelial healing and decreasing pain after various corneal surgeries. However, literature lacks any data describing their use following Descemet's stripping automated endothelial keratoplasty (DSAEK) where intraoperative epithelial debridement is commonly performed. Here we study the efficacy and safety of TCL in patients undergoing DSAEK.

Methods

In this prospective, randomized, controlled clinical trial. 40 eyes of 40 patients of pseudophakic bullous keratopathy undergoing DSAEK were enrolled and randomized into two groups, control (no TCL) and test (TCL). Primary outcome was time taken for epithelial healing and secondary outcomes were postoperative pain score, graft attachment, best spectacle-corrected visual acuity, and endothelial cell loss at 3 months.

Results

Average time taken for epithelial healing was 3.35 ± 0.49 days in the test group and 4.95 ± 1.05 days in the control group (P < 0.001). Average pain scores in first operative week were significantly lower in the test group as compared to control (P < 0.001). Graft detachment occurred in eight patients in control group and two in test group (P = 0.03). Both rebubbling rates and average endothelial cell loss at 3 months were higher in the control group with P = 0.07 and 0.06 respectively. No contact lens-related adverse effects were noted during the study period.

Conclusion

Use of TCL in DSAEK leads to faster epithelial healing and lesser postoperative pain. In addition, it may also contribute to lower rebubbling rates and endothelial cell loss.

Establish an In Vitro Cell Model to Explore the Impacts of UVA on Human Corneal Endothelial Wound Healing

PURPOSE

To provide scientific data for clinical practice in making strategies for accelerating corneal endothelial wound healing, we investigated the impact of UVA on the corneal endothelial wound healing process and the underlying mechanism using an in vitro cell model.

MATERIALS AND METHODS

An in vitro cell model for corneal endothelial wound healing was established by scratching the in vitro cultured human corneal endothelial cell (HCEnC) confluent layer. Then, we investigated the impacts of UVA irradiation and Ascorbic acid-2-phosphate (Asc-2p) on the wound healing process of the in vitro HCEnC model by examining wound-healing index, F-actin⁺ rate, Ki-67⁺ rate, and ROS production.

RESULTS

After scratching, the Ki-67⁺ and F-actin⁺ HCEnCs occupied the scratching gap. Furthermore, the F-actin⁺ rates were significantly higher than Ki-67⁺ rates in the wound closure area. After irradiated with UVA, the wound-healing indexes, Ki-67⁺ rates and F-actin⁺ rates of the wound-healing model significantly reduced, whereas the ROS production significantly increased in a dose-dependent manner. Pretreatment with Asc-2p significantly reduced the ROS production as well as increased the wound-healing indexes, Ki-67⁺rates and F-actin⁺ rates of the UVA irradiated wound-healing model.

CONCLUSION

The migration of HCEnC plays a major role in the wound healing process of the established cell model, which is like the wound healing process in vivo. UVA decreases the wound closure of the in vitro HCEnC model dose-dependently, while antioxidant Asc-2p can attenuate the damage to UVA to HCEnCs probably via reducing ROS to improve their migration.

Regeneration of the Corneal Endothelium

Penetrating keratoplasty was the only therapeutic choice for the treatment of corneal endothelial decompensation until the introduction of evolutional endothelial keratoplasties, namely Descemet's stripping automated endothelial keratoplasty (DSAEK) and Descemet's membrane endothelial keratoplasty (DMEK). Although now in widespread use, DSAEK and DMEK still have associated problems, such as difficulty of the surgical technique, acute and chronic cell loss, and shortage of donor corneas. Therefore, regeneration of the corneal endothelium by tissue engineering techniques is being researched to overcome these problems. The concept of transplantation of cultured corneal endothelial cells (CECs) was proposed in the 1970s. However, cultivation of human CECs (HCECs) in sufficient quantity and with acceptable quality for clinical use has proven surprisingly difficult, and the development of methods for transplanting cultured HCECs has been necessary. Numerous research groups have developed culture protocols and techniques that are now bringing corneal endothelial regeneration closer to real-world therapy. For instance, we started a clinical trial in 2013 involving the injection of cultured HCECs into the anterior chamber of patients with corneal endothelial decompensation. This review outlines the rapid progression of this research field, including clinical trial results, and is also intended to identify topics that still require further research or discussion.

Review: corneal endothelial cell derivation methods from ES/iPS cells

Globally, approximately 12.7 million people are awaiting a transplantation, while only 185,000 cases of corneal transplantation are performed in a year. Corneal endothelial dysfunction (bullous keratopathy) due to Fuchs’ corneal endothelial dystrophy, or insults associated with intraocular surgeries, shared half of all indications for corneal transplantation. Regenerative therapy for corneal endothelium independent of eye bank eyes has great importance to solve the large supply-demand mismatching in corneal transplantation and reduce the number of worldwide corneal blindness. If corneal endothelial cells could be derived from ES or iPS cells, these stem cells would be the ideal cell source for cell therapy treatment of bullous keratopathy. Four representative corneal endothelial cell derivation methods were reviewed. Components in earlier methods included lens epithelial cell-conditioned medium or fetal bovine serum, but the methods have been improved and materials have been chemically more defined over the years. Conditioned medium or serum is replaced to recombinant proteins and small molecule compounds. These improvements enabled to open the corneal endothelial developmental mechanisms, in which epithelial-mesenchymal and mesenchymal-endothelial transition by TGF beta, BMP, and Wnt signaling have important roles. The protocols are gradually approaching clinical application; however, proof of efficacy and safety of the cells by adequate animal models are the challenges for the future.

Effect of a p38 Mitogen-Activated Protein Kinase Inhibitor on Corneal Endothelial Cell Proliferation

Purpose

We have performed clinical research on cell-based therapy for corneal endothelial decompensation since 2013. The purpose of this study was to investigate the usefulness of a p38 MAPK inhibitor for promoting proliferation of human corneal endothelial cells (HCECs).

Methods

HCECs were cultured in media supplemented with various low-molecular-weight compounds to screen for the effect of those compounds on cell proliferation. Activation of substrates of p38 MAPK and cell cycle regulatory proteins were evaluated by western blotting. Corneal endothelial wounds were created in a rabbit model, and p38 MAPK was applied in eye drop form, followed by evaluation of cell proliferation in the corneal endothelium by Ki67-immunostaining.

Results

HCECs cultured with SB203580 exhibited hexagonal morphology and similar size and morphology, whereas control HCECs cultured without inhibitor exhibited monolayer morphology and varied in size and morphology. Flow cytometry demonstrated that cell proliferation was significantly increased by SB203580. Western blotting showed activation of ATF2 and HSP27 (substrates of p38 MAPK), and upregulation of cyclin D and downregulation of p27 were induced by inhibiting p38 MAPK. In the rabbit model, promotion of wound healing of the corneal endothelium was associated with significant upregulation of Ki67-positive proliferating cells following topical administration of SB203580 when compared with untreated endothelium (50.9% and 36.1%, respectively).

Conclusions

Activation of p38 MAPK signaling due to culture stress might suppress the proliferation of HCECs, whereas a p38 MAPK inhibitor can counteract this activation and enable efficient in vitro HCEC expansion.

Safety of Using Matrix Metalloproteinase Inhibitor in Experimental Glaucoma Filtration Surgery

We evaluated the safety of matrix metalloproteinase (MMP) inhibitor in experimental glaucoma filtration surgery in an animal model. Fifteen New Zealand white rabbits underwent an experimental trabeculectomy and were randomly allocated into 3 groups according to the adjuvant agent: no treatment group (n = 5), 0.02% mitomycin C (MMC) soaking group (n = 5), and MMP inhibitor (ilomastat) subconjunctival injection group (n = 5). Slit lamp examination with Seidel testing, pachymetry, and specular microscopy was performed preoperatively and postoperatively. The conjunctiva and ciliary body toxicity were evaluated with scores according to the pathologic grading systems. Electron microscopy was used to examine the structural changes in cornea, conjunctiva, and ciliary body. In the ilomastat-treated group, there was no statistically significant change in central corneal thickness preoperatively and at 28 days postoperatively (P = 0.655). There were also no significant changes in specular microscopy findings over the duration of the study in the ilomastat-treated group. The conjunctival toxicity score was 1 in the control group, 1.5 in the ilomastat-treated group, and 2 in the MMC-treated group. When assessing ciliary body toxicity scores, the ilomastat-treated group score was 0.5 and the MMC-treated group score was 1.5. Transmission electron microscopy did not show structural changes in the cornea and ciliary body whereas the structural changes were noticed in MMC group. A single subconjunctival injection of MMP inhibitor during the experimental trabeculectomy showed a less toxic affect in the rabbit cornea, conjunctiva, and ciliary body compared to MMC.

Functional corneal endothelium derived from corneal stroma stem cells of neural crest origin by retinoic acid and Wnt/β-catenin signaling

Corneal endothelial dysfunction remains a major indication for corneal transplantation. Both corneal endothelial cells and stromal cells originate from the neural crest, but have distinct phenotypes and function in the adult cornea. We previously reported that stem cells isolated from the adult corneal stroma [cornea-derived precursors (COPs)] show characteristics of multipotent neural crest-derived stem cells. In this study, we report the induction of functional tissue-engineered corneal endothelium (TECE) from mouse and human COPs. TECE was engineered from Wnt1-Cre/Floxed EGFP mouse COPs in a medium containing retinoic acid and glycogen synthase kinase (GSK) 3β inhibitor (activator of Wnt/β-catenin signaling). The expression levels of major markers characterizing corneal endothelial function (Atp1a1, Slc4a4, Car2, Col4a2, Col8a2, and Cdh2) were significantly upregulated. Both retinoic acid and GSK 3β inhibitor upregulated the expression of Pitx2, a homeobox gene involved in the development of the anterior segment of the eye. GSK 3β inhibitor increased Atp1a1 expression and Na,K-ATPase pump activity of TECE, which was significantly higher than COPs or control 3T3 cells, and 2.6-fold higher than cultured mouse corneal endothelial cells. Mouse TECE transplanted into rabbit corneas maintained transparency and corneal thickness, whereas control corneas without TECE showed marked edema and increased corneal thickness. Furthermore, we successfully induced TECE from human COPs, and human TECE transplanted into rabbit corneas also maintained corneal transparency and thickness. This protocol enables efficient production of corneal endothelium from corneal stromal stem cells by direct induction, which may lead to a novel stem cell therapy for corneal endothelial dysfunction.