A review of the evidence for in vivo corneal endothelial regeneration

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.

Alginate Hydrogel Integrated with a Human Fibroblast-Derived Extracellular Matrix Supports Corneal Endothelial Cell Functionality and Suppresses Endothelial-Mesenchymal Transition

Human corneal transplantation is still the only option to restore the function of corneal endothelial cells (CECs). Therefore, there is an urgent need for hCEC delivery systems to replace the human donor cornea. Here, we propose an alginate hydrogel (AH)-based delivery system, where a human fibroblast-derived, decellularized extracellular matrix (ECM) was physically integrated with AH. This AH securely combined with the ECM (ECM-AH) was approximately 50 μm thick, transparent, and permeable. The surface roughness and surface potential provided ECM-AH with a favorable microenvironment for CEC adhesion and growth in vitro. More importantly, ECM-AH could support the structural (ZO-1) and functional (Na+/K+-ATPase) markers of hCECs, as assessed via western blotting and quantitative polymerase chain reaction, which were comparable with those of a ferritic nitrocarburizing (FNC)-coated substrate (a positive control). The cell density per unit area was also significantly better with ECM-AH than the FNC substrate at day 7. A simulation test of cell engraftment in vitro showed that hCECs were successfully transferred into the decellularized porcine corneal tissue, where they were mostly alive. Furthermore, we found out that the endothelial-mesenchymal transition (EnMT)-inductive factors (Smad2 and vimentin) were largely declined with the hCECs grown on ECM-AH, whereas the EnMT inhibitory factor (Smad7) was significantly elevated. The difference was statistically significant compared to that of the FNC substrate. Moreover, we also observed that TGF-β1-treated hCECs showed faster recovery of cell phenotype on the ECM. Taken together, our study demonstrates that ECM-AH is a very promising material for hCEC culture and delivery, which endows an excellent microenvironment for cell function and phenotype maintenance.

"Keep on ROCKIn": Repurposed ROCK inhibitors to boost corneal endothelial regeneration

The global shortage of corneal endothelial graft tissue necessitates the exploration of alternative therapeutic strategies. Rho-associated protein kinase inhibitors (ROCKi), recognized for their regenerative potential in cardiology, oncology, and neurology, have shown promise in corneal endothelial regeneration. This study investigates the repurposing potential of additional ROCKi compounds. Through screening a self-assembled library of ROCKi on B4G12 corneal endothelial cells, we evaluated their dose-dependent effects on proliferation, migration, and toxicity using live-cell imaging. Nine ROCKi candidates significantly enhanced B4G12 proliferation compared to the basal growth rate. These candidates were further assessed for their potential to accelerate wound closure as another indicator for tissue regeneration capacity, with most demonstrating notable efficacy. To assess the potential impact of candidate ROCKi on key corneal endothelial cell markers related to cell proliferation, leaky tight junctions and ion efflux capacity, we analyzed the protein expression of cyclin E1, CDK2, p16, ZO-1 and Na+/K+-ATPase, respectively. Immunocytochemistry and western blot analysis confirmed the preservation of corneal endothelial markers post-treatment with ROCKi hits. However, notable cytoplasm enlargement and nuclear fragmentation were detected after the treatment with SR-3677 and Thiazovivin, indicating possible cellular stress. In compared parameters, Chroman-1 at a concentration of 10 nM outperformed other ROCKi, requiring significantly 1000-fold lower effective concentration than established ROCKi Y-27632 and Fasudil. Altogether, this study underscores the potential of repurposing ROCKi for treating corneal endothelial dysfunctions, offering a viable alternative to conventional grafting methods, and highlights Chroman-1 as a promising candidate structure for hit-to-lead development.

The proliferative effects of stem cells from apical papilla-conditioned medium on rat corneal endothelial cells

The cornea, positioned at the forefront of the eye, refracts the light for focusing images on the retina. Damage to this transparent structure can lead to various visual disorders. The corneal endothelial cells (CECs) are crucial for transparency and homeostasis, but lack the ability to reproduce. Significant damage results in structure destruction and vision impairment. While extensive research has aimed at the restoring the corneal endothelial layer, including endothelial proliferation for functional monolayers remains challenging. Our previous studies confirmed the proliferative activity of stem cells from apical papilla-conditioned medium (SCAP-CM) on the retinal pigmented epithelium as a single cell layer. This study investigates how SCAP-CM influences the proliferation and migration of CECs. Our results introduced Matrigel, as a new matrix component for in vitro culture of CECs. Moreover, 60% of SCAP-CM was able to stimulate CEC proliferation as well as migrate to repair wound healing during 24 h. Confluent CECs also expressed specific markers, ATP1a1, ZO-1 and CD56, indicative of CEC characteristics, aligning with the recapitulation of differentiation when forming a homogenous monolayer at the same level of isolated CECs without in vitro culture. These findings suggested that SCAP-CM administration could be useful for future preclinical and clinical applications.

Corneal endothelial changes seven years after phacoemulsification cataract surgery

PURPOSE

To evaluate long-term postoperative corneal changes after phacoemulsification cataract surgery.

METHODS

Twenty patients who participated in a previous study regarding corneal endothelial changes after phacoemulsification cataract surgery were examined after 7 years. The patients were divided in three groups based on their initial increase in central corneal thickness day one after the surgery: < 5% increase, 6-20% increase and ≥ 20% increase. The primary outcome measures were corneal endothelial cell loss (ECL), endothelial cell count (ECC) and endothelial morphology.

RESULTS

After 7 years, a difference in cell loss between the groups was observed, except for groups 1 and 2. Endothelial cell count (ECC) differed significantly between groups 1 and 3 at 3 months. At 7 years, there was no difference in ECC between the three groups. Cell loss was found exclusively in group 1 between 3 months and 7 years. Endothelial cell morphology showed a converging pattern between 3 months and 7 years.

CONCLUSION

After phacoemulsification cataract surgery, long-term ECC and morphology appear to converge towards a comparable steady state regardless of initial corneal swelling and endothelial cell loss.

Narrative review after post-hoc trial analysis of factors that predict corneal endothelial cell loss after phacoemulsification: Tips for improving cataract surgery research

PURPOSE

Identifying pre/perioperative factors that predict corneal endothelial-cell loss (ECL) after phacoemulsification may reveal ways to reduce ECL. Our literature analysis showed that 37 studies have investigated one or several such factors but all have significant limitations. Therefore, the data of a large randomized controlled trial (PERCEPOLIS) were subjected to post-hoc multivariate analysis determining the ability of nine pre/perioperative variables to predict ECL.

METHODS

PERCEPOLIS was conducted in 2015-2016 to compare two phacoemulsification techniques (subluxation and divide-and-conquer) in terms of 3-month ECL. Non-inferiority between the techniques was found. In the present study, post-hoc univariate and multivariate analyses were conducted to determine associations between ECL and age, sex, cataract density, preoperative endothelial-cell density, phacoemulsification technique, effective phaco time (EPT), and 2-hour central-corneal thickness. The data are presented in the context of a narrative review of the literature.

RESULTS

Three-month data were available for 275 patients (94% of the randomized cohort; mean age, 74 years; 58% women). Mean LOCSIII cataract grade was 3.2. Mean EPT was 6 seconds. Mean ECL was 13%. Only an older age (beta = 0.2%, p = 0.049) and higher EPT (beta = 1.2%, p = 0.0002) predicted 3-month ECL. Cataract density was significant on univariate (p = 0.04) but not multivariate analysis. The other variables did not associate with ECL.

CONCLUSIONS

Older age may amplify ECL due to increased endothelial cell fragility. EPT may promote ECL via cataract density-dependent and -independent mechanisms that should be considered in future phacoemulsification research aiming to reduce ECL. Our literature analysis showed that the average ECL for relatively unselected consecutively-sampled cohorts is 12%.

Applications of Imaging Technologies in Fuchs Endothelial Corneal Dystrophy: A Narrative Literature Review

Fuchs endothelial corneal dystrophy (FECD) is a complex genetic disorder characterized by the slow and progressive degeneration of corneal endothelial cells. Thus, it may result in corneal endothelial decompensation and irreversible corneal edema. Moreover, FECD is associated with alterations in all corneal layers, such as thickening of the Descemet membrane, stromal scarring, subepithelial fibrosis, and the formation of epithelial bullae. Hence, anterior segment imaging devices that enable precise measurement of functional and anatomical changes in the cornea are essential for the management of FECD. In this review, the authors will introduce studies on the application of various imaging modalities, such as anterior segment optical coherence tomography, Scheimpflug corneal tomography, specular microscopy, in vitro confocal microscopy, and retroillumination photography, in the diagnosis and monitoring of FECD and discuss the results of these studies. The application of novel technologies, including image processing technology and artificial intelligence, that are expected to further enhance the accuracy, precision, and speed of the imaging technologies will also be discussed.

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

Electrospun Nanofiber Membrane for Cultured Corneal Endothelial Cell Transplantation

The corneal endothelium, comprising densely packed corneal endothelial cells (CECs) adhering to Descemet's membrane (DM), plays a critical role in maintaining corneal transparency by regulating water and ion movement. CECs have limited regenerative capacity within the body, and globally, there is a shortage of donor corneas to replace damaged corneal endothelia. The development of a carrier for cultured CECs may address this worldwide clinical need. In this study we successfully manufactured a gelatin nanofiber membrane (gelNF membrane) using electrospinning, followed by crosslinking with glutaraldehyde (GA). The fabricated gelNF membrane exhibited approximately 80% transparency compared with glass and maintained a thickness of 20 µm. The gelNF membrane demonstrated desirable permeability and degradability for a Descemet's membrane analog. Importantly, CECs cultured on the gelNF membrane at high densities showed no cytotoxic effects, and the expression of key CEC functional biomarkers was verified. To assess the potential of this gelNF membrane as a carrier for cultured CEC transplantation, we used it to conduct Descemet's membrane endothelial keratoplasty (DMEK) on rabbit eyes. The outcomes suggest this gelNF membrane holds promise as a suitable carrier for cultured CEC transplantation, offering advantages in terms of transparency, permeability, and sufficient mechanical properties required for successful transplantation.

Gomes J, Güell JL, Casaroli-Marano RP. Corneal Endothelial Cell Cultures from Organotypic Preservation of Older Donor Corneas Are Suitable for Advanced Cell Therapy

INTRODUCTION

The purpose of this work was to evaluate the in vitro growth capacity and functionality of human corneal endothelial cells (hCEC) expanded from corneas of elderly (>60 years) donors that were preserved using an organotypic culture method (>15 days, 31°C) and did not meet the clinical criteria for keratoplasty.

METHODS

Cell cultures were obtained from prior descemetorhexis (≥10 mm) and a controlled incubation with collagenase type I followed by recombinant trypsin. Cells were seeded on coated plates (fibronectin-albumin-collagen I) and cultures were expanded using the dual supplemented medium approach (maintenance medium and growth medium), in the presence of a 10 μm Rho-associated protein kinase inhibitor (Y-27632). Cell passages were obtained at culture confluency (∼2 weeks). A quantitative colorimetric WST-1 cell growth assay was performed at different time points of the culture. Morphometric analysis (area assessment and circularity), immunocytochemistry (ZO-1, Na+/K+-ATPase α, Ki67), and transendothelial electrical resistance (TEER) were performed on confluent monolayers.

RESULTS

There was no difference between the cell growth profiles of hCEC cultures obtained from corneas older than 60 years, whether preserved cold or cultivated organotypic corneas. Primary cultures were able to maintain a certain cell circularity index (around 0.8) and morphology (hexagonal) similar to corneal endothelial mosaic. The ZO-1 and Na+/K+-ATPase pump markers were highly positive in confluent cell monolayers at 21 days after isolation (passage 0; P0), but significantly decreased in confluent monolayers after the first passage (P1). A weak expression of Ki67 was observed in both P0 and P1 monolayers. The P0 monolayers showed a progressive increase in TEER values between days 6 and 11 and remained stable until day 18 of culture, indicating a state of controlled permeability in monolayers. The P1 monolayers also showed some functional ability but with decreased TEER values compared to monolayers at P0.

CONCLUSIONS

Our results indicate that it is possible to obtain functional hCEC cultures in eye banks, using simplified and standardized protocols, from older donor corneas (>60 years of age), previously preserved under organotypic culture conditions. This tissue is more readily available in our setting, due to the profile of the donor population or due to the low endothelial count (<2,000 cells/mm2) of the donated cornea.

Plasma fibrin membranes loaded with bone marrow mesenchymal stem cells and corneal epithelial cells promote corneal injury healing via attenuating inflammation and fibrosis after corneal burns

The shortage of corneal donors has prompted the development of tissue-engineered corneal grafts as an alternative solution. Currently, amniotic membranes with good biocompatibility are widely used as scaffolds for loading stem cells in the treatment of corneal injury. However, this approach has its limitations. In this study, BMSCs were induced to differentiate into corneal epithelial cells via direct contact co-culture, and platelet-poor plasma was used to prepare fibrin gels, which were compressed to remove excess liquid and then lyophilized to obtain plasma fibrin membranes (PFMs). A tissue-engineered corneal implant with PFMs as a scaffold loaded with BMSCs and corneal epithelial cells was designed and obtained. Scanning electron microscopy showed that PFMs have a uniformly distributed microporous surface that facilitates cell attachment and nutrient transport. The rheological results showed that the freeze-dried and rehydrated PFMs were more rigid than fresh membranes, which makes it easier to use them for transplantation after cell loading. The experimental results of a rat alkali burn cornea injury model showed that PFMs effectively reduced the inflammatory reaction, inhibited fibrosis, and accelerated the healing of corneal wounds. It was also found that some of the BMSCs were successfully implanted into the corneal injury site in rats and differentiated into corneal epithelial cells. These results demonstrate the potential of tissue-engineered corneal implants using BMSCs and corneal epithelial cells and PFMs as scaffolds as a new treatment option for corneal injury.

Advances in the applications of mesenchymal stem cell-conditioned medium in ocular diseases

Mesenchymal stem cell-conditioned medium (MSC-CM), also known as secretome, is secreted by MSC and contains a variety of bioactive factors with anti-inflammatory, anti-apoptotic, neuroprotection, and proliferation effects. Increasing evidence proved that MSC-CM plays an important role in various diseases, including skin, bone, muscle, and dental diseases. However, the role of MSC-CM in ocular diseases is not quite clear, Therefore, this article reviewed the composition, biological functions, preparation, and characterization of MSC-CM and summarized current research advances in different sources of MSC-CM in corneal and retinal diseases, including dry eye, corneal epithelial damage, chemical corneal injury, retinitis pigmentosa (RP), anterior ischemic optic neuropathy (AION), diabetic retinopathy (DR), and other retinal degenerative changes. For these diseases, MSC-CM can promote cell proliferation, reduce inflammation and vascular leakage, inhibit retinal cell degeneration and apoptosis, protect corneal and retinal structures, and further improves visual function. Hence, we summarize the production, composition and biological functions of MSC-CM and focus on describing its mechanisms in the treatment of ocular diseases. Furthermore, we look at the unexplored mechanisms and further research directions for MSC-CM based therapy in ocular diseases.

Effects of Rho-Associated Kinase (Rock) Inhibitors (Alternative to Y-27632) on Primary Human Corneal Endothelial Cells

(1) Rho-associated coiled-coil protein kinase (ROCK) signaling cascade impacts a wide array of cellular events. For cellular therapeutics, scalable expansion of primary human corneal endothelial cells (CECs) is crucial, and the inhibition of ROCK signaling using a well characterized ROCK inhibitor (ROCKi) Y-27632 had been shown to enhance overall endothelial cell yield. (2) In this study, we compared several classes of ROCK inhibitors to both ROCK-I and ROCK-II, using in silico binding simulation. We then evaluated nine ROCK inhibitors for their effects on primary CECs, before narrowing it down to the two most efficacious compounds-AR-13324 (Netarsudil) and its active metabolite, AR-13503-and assessed their impact on cellular proliferation in vitro. Finally, we evaluated the use of AR-13324 on the regenerative capacity of donor cornea with an ex vivo corneal wound closure model. Donor-matched control groups supplemented with Y-27632 were used for comparative analyses. (3) Our in silico simulation revealed that most of the compounds had stronger binding strength than Y-27632. Most of the nine ROCK inhibitors assessed worked within the concentrations of between 100 nM to 30 µM, with comparable adherence to that of Y-27632. Of note, both AR-13324 and AR-13503 showed better cellular adherence when compared to Y-27632. Similarly, the proliferation rates of CECs exposed to AR-13324 were comparable to those of Y-27632. Interestingly, CECs expanded in a medium supplemented with AR-13503 were significantly more proliferative in (i) untreated vs. AR-13503 (1 μM; * p < 0.05); (ii) untreated vs. AR-13503 (10 μM; *** p < 0.001); (iii) Y-27632 vs. AR-13503 (10 μM; ** p < 0.005); (iv) AR-13324 (1 μM) vs. AR-13503 (10 μM; ** p < 0.005); and (v) AR-13324 (0.1 μM) vs. AR-13503 (10 μM; * p < 0.05). Lastly, an ex vivo corneal wound healing study showed a comparable wound healing rate for the final healed area in corneas exposed to Y-27632 or AR-13324. (4) In conclusion, we were able to demonstrate that various classes of ROCKi compounds other than Y-27632 were able to exert positive effects on primary CECs, and systematic donor-match controlled comparisons revealed that the FDA-approved ROCK inhibitor, AR-13324, is a potential candidate for cellular therapeutics or as an adjunct drug in regenerative treatment for corneal endothelial diseases in humans.

Comparison of femtosecond laser-assisted cataract surgery and conventional phacoemulsification on corneal impact: A meta-analysis and systematic review

This meta-analysis aims to compare corneal injuries and function after femtosecond laser-assisted cataract surgery (FLACS) and conventional phacoemulsification surgery (CPS). A comprehensive literature search of PubMed, EMBASE, and the Cochrane Controlled Trials Register was conducted to identify randomized controlled trials (RCT) and high-quality prospective comparative cohort studies comparing FLACS with CPS. Endothelial cell loss percentage (ECL%), central corneal thickness (CCT), endothelial cell density (ECD), endothelial cell loss (ECL), percentage of the hexagonal cell (6A), and coefficient of variance (CoV) were used as an indicator of corneal injury and function. Totally 42 trials (23 RCTs and 19 prospective cohort studies), including 3916 eyes, underwent FLACS, and a total of 3736 eyes underwent CPS. ECL% is significantly lower in the FLACS group at 1-3 days (P = 0.005), 1 week (P = 0.004), 1 month (P<0.0001), 3 months (P = 0.001), and 6 months (P = 0.004) after surgery compared to CPS. ECD and ECL appeared no statistically significant difference between the two groups, except for the significant reduction of ECD at 3 months in the CPS group (P = 0.002). CCT was significantly lower in the FLACS group at 1 week (P = 0.05) and 1 month (P = 0.002) early postoperatively. While at 1-3 days (P = 0.50), 3 months (P = 0.18), and 6 months (P = 0.11), there was no difference between the FLACS group and the CPS group. No significant difference was found in the percentage of hexagonal cells and the coefficient of variance. FLACS, compared with CPS, reduces corneal injury in the early postoperative period. Corneal edema recovered faster in the FLACS group in the early postoperative period. In addition, FLACS may be a better option for patients with corneal dysfunction.

Modified gellan gum-based hydrogel with enhanced mechanical properties for application as a cell carrier for cornea endothelial cells

Recently, the number of people suffering from visual loss due to eye diseases is increasing rapidly around the world. However, due to the severe donor shortage and the immune response, corneal replacement is needed. Gellan gum (GG) is biocompatible and widely used for cell delivery or drug delivery, but its strength is not suitable for the corneal substitute. In this study, a GM hydrogel was prepared by blending methacrylated gellan gum with GG (GM) to give suitable mechanical properties to the corneal tissue. In addition, lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), a crosslinking initiator, was added to the GM hydrogel. After the photo-crosslinking treatment, it was named GM/LAP hydrogel. GM and GM/LAP hydrogels were analyzed for physicochemical properties, mechanical characterization, and transparency tests to confirm their applicability as carriers for corneal endothelial cells (CEnCs). Also, in vitro studies were performed with cell viability tests, cell proliferation tests, cell morphology, cell-matrix remodeling analysis, and gene expression evaluation. The compressive strength of the GM/LAP hydrogel was improved compared to the GM hydrogel. The GM/LAP hydrogel showed excellent cell viability, proliferation, and cornea-specific gene expression than the GM hydrogel. Crosslinking-improved GM/LAP hydrogel can be applied as a promising cell carrier in corneal tissue engineering.

GSK-3 inhibition reverts mesenchymal transition in primary human corneal endothelial cells

Human corneal endothelial cells are organized in a tight mosaic of hexagonal cells and serve a critical function in maintaining corneal hydration and clear vision. Regeneration of the corneal endothelial tissue is hampered by its poor proliferative capacity, which is partially retrieved in vitro, albeit only for a limited number of passages before the cells undergo mesenchymal transition (EnMT). Although different culture conditions have been proposed in order to delay this process and prolong the number of cell passages, EnMT has still not been fully understood and successfully counteracted. In this perspective, we identified herein a single GSK-3 inhibitor, CHIR99021, able to revert and avoid EnMT in primary human corneal endothelial cells (HCEnCs) from old donors until late passages in vitro (P8), as shown from cell morphology analysis (circularity). In accordance, CHIR99021 reduced expression of α-SMA, an EnMT marker, while restored endothelial markers such as ZO-1, Na⁺/K⁺ ATPase and N-cadherin, without increasing cell proliferation. A further analysis on RNA expression confirmed that CHIR99021 induced downregulation of EnMT markers (α-SMA and CD44), upregulation of the proliferation repressor p21 and revealed novel insights into the β-catenin and TGFβ pathways intersections in HCEnCs. The use of CHIR99021 sheds light on the mechanisms involved in EnMT, providing a substantial advantage in maintaining primary HCEnCs in culture until late passages, while preserving the correct morphology and phenotype. Altogether, these results bring crucial advancements towards the improvement of the corneal endothelial cells based therapy.

A Framework for Human Corneal Endothelial Cell Culture and Preliminary Wound Model Experiments with a New Cell Tracking Approach

Cell injection therapy is emerging as an alternative to treat corneal endothelial dysfunction (CED) and to avoid corneal scarring due to bullous keratopathy. However, establishing a standardized culture procedure that provides appropriate cell yield while retaining functional features remains a challenge. Here, we describe a detailed framework obtained from in vitro culture of human corneal endothelial cells (HCECs) and comparative in vivo experimental models for CED treatment with a new cell tracking approach. Two digestion methods were compared regarding HCEC morphology and adhesion. The effect of Y-27632 (ROCKi) supplementation on final cell yield was also assessed. Cell adhesion efficacy with two cell delivery systems (superparamagnetic embedding and cell suspension) was evaluated in an ex vivo human cornea model and in an in vivo rabbit CED model. The injection of supplemented culture medium or balanced salt solution (BSS) was used for the positive and negative controls, respectively. HCEC isolation with collagenase resulted in better morphology and adhesion of cultured HCEC when compared to EDTA. Y-27632 supplementation resulted in a 2.6-fold increase in final cell yield compared to the control. Ex vivo and in vivo adhesion with both cell delivery systems was confirmed by cell tracker fluorescence detection. Corneal edema and opacity improved in both animal groups treated with cultured HCEC. The corneas in the control groups remained opaque. Both HCEC delivery systems seemed comparable as treatments for CED and for the prevention of corneal scarring.

DMEK graft: One size does not fit all

Descemet membrane endothelial keratoplasty (DMEK) is a popular procedure for the treatment of corneal endothelial diseases mainly targeting Fuchs endothelial corneal dystrophy (FECD) and pseudophakic bullous keratopathy (PBK). Although DMEK has multiple advantages, it is challenging in terms of graft preparation and delivery. One of the crucial factors of DMEK graft preparation is determining the size of the graft. Evaluating risks and benefits of transplanting larger or smaller grafts compared with the descemetorhexis performed following a standard DMEK procedure thus becomes important. Advanced techniques like pre-loaded DMEK requires pre-selection of graft diameter without physical examination of the eye making it more challenging. Therefore, recognizing the benefits of graft size and the number of transplanted endothelial cells becomes essential. Smaller DMEK grafts have been preferred and accepted for grafting. Larger diameter grafts have advantages but can be challenging due to higher detachment rates. We thus aim to review the challenges of preparing and delivering DMEK tissues with small or large diameter based on selected descemetorhexis area, discuss the outcomes based on different graft sizes, highlight related complications and suggest which cases may benefit from adopting smaller or larger graft size.

Long-Term Follow-Up of Corneal Endothelial Cell Changes After Iris-Fixated Phakic Intraocular Lens Explantation

PURPOSE

The purpose of this study was to evaluate long-term corneal endothelial cell changes and visual outcomes after iris-fixated phakic intraocular lens (pIOL) explantation in patients with endothelial damage and to investigate potential predictors of endothelial injury.

METHODS

Consecutive patients undergoing pIOL explantation with corneal endothelial cell density (ECD) <2000 cells/mm 2 at the time of the procedure were retrospectively reviewed in a single tertiary center. All patients were treated between April 2016 and October 2020 at a high-volume referral-based tertiary hospital. The primary outcome was the change in corneal endothelial parameters, including ECD, over long-term follow-up. Secondary outcomes included changes in corrected distance visual acuity and analysis of prognostic factors.

RESULTS

This study included 44 eyes from 28 patients with an average age of 42.5 ± 7.8 years (range: 27-63). Mean ECD before explantation was 1375.4 ± 468.2 cells/mm 2 (range: 622-1996), and the average duration of follow-up after explantation was 20.5 months (6-58.2). Two years after explantation, ECD had significantly decreased by more than 25% to 1019.6 ± 368.6 (608-1689; P < 0.01). However, there was no significant change in corrected distance visual acuity (20/23-20/22, P = 0.59). Longer operation duration (odds ratio, 1.004; P = 0.04) was the only significant factor weakly associated with postoperative decreases in ECD.

CONCLUSIONS

Although ECD continuously decreased despite pIOL explantation on a long-term follow-up, patients did not experience any discomfort or showed decreases in visual acuity. Therefore, a careful follow-up is required for possible endothelial injury after pIOL explantation.

Acceleration of Regeneration of the Corneal Endothelial Layer After Descemet Stripping Induced by the Engineered FGF TTHX1114 in Human Corneas in Organ Culture

PURPOSE

Descemet stripping only (DSO, descemetorhexis without endothelial keratoplasty) is increasing in clinical use but can impose long recovery times. The objective of this research was to determine whether TTHX1114, an engineered analog of FGF1, could accelerate healing in corneas after DSO.

METHODS

Corneas obtained from eye banks were placed into suspension culture and subjected to DSO with a procedure comparable with that used clinically. The healing of the stripped area and the regeneration of the corneal endothelial cell (CEC) layer were evaluated intermittently for 14 days using trypan blue staining, alizarin red staining, and immunohistochemistry.

RESULTS

Corneas subjected to DSO showed about 30% of the stripped area healed after 14 days in culture while those treated with TTHX1114 healed 81%. The healed area was similar in both normal corneas and corneas judged by the eye banks to be dystrophic. The regeneration of the endothelial layer in the stripped area was substantially more complete in TTHX1114-treated corneas, most of which demonstrated a contiguous monolayer of CECs expressing ZO-1 at the cell-cell junctions. In corneas not subject to DSO, incorporation of EdU, a marker of proliferation, was stimulated by TTHX1114 treatment.

CONCLUSIONS

The corneal organ culture model recapitulated clinical observations of DSO, only with much more rapid recovery. Within the immediate postsurgical time frame of 2 weeks, treatment with TTHX1114 stimulated near-total regeneration of the CEC layer, suggesting that TTHX1114 may be useful as an adjunct to DSO.

Influence of the Size and Charge of Carbon Quantum Dots on Their Corneal Penetration and Permeation Enhancing Properties

Reaching the corneal endothelium through the topical administration of therapeutic drugs remains a challenge in ophthalmology. Besides, endothelial cells are not able to regenerate, and diseases at this site can lead to corneal blindness. Targeting the corneal endothelium implies efficient penetration through the three corneal layers, which still remains difficult for small molecules. Carbon quantum dots (CQDs) have demonstrated great potential for ocular nanomedicine. This study focuses on the corneal penetration abilities of differently charged CQDs and their use as permeation enhancers for drugs. Excised whole bovine eyes were used as an ex vivo model to investigate corneal penetration of CQDs derived from glucosamine using β-alanine, ethylenediamine, or spermidine as a passivation agent. It was found that negatively charged CQDs have limited corneal penetration ability, while positively charged CQDs derived from glucosamine hydrochloride and spermidine (CQD-S) penetrate the entire corneal epithelium all the way down to the endothelium. CQD-S were shown to enhance the penetration of FITC-dextran 150 kDa, suggesting that they could be used as efficient penetration enhancers for therapeutic delivery to the corneal endothelium.

Early and late-onset cell migration from peripheral corneal endothelium

In this study we describe peripheral corneal endothelial cell migration in vitro in the absence and presence of a ROCK-inhibitor. For this study, 21 corneal endothelial graft rims, with attached trabecular meshwork (TM), were prepared from Descemet membrane-endothelial cell sheets by 6.5 mm trepanation. For the initial proof-of-concept, 7 outer graft rims were cultured in a thermo-reversible hydrogel matrix for up to 47 days. To assess the effect of a ROCK-inhibitor, 14 paired outer rims were cultured either with or without ROCK-inhibitor for up to 46 days. At the end of culture, tissue was retrieved from the hydrogel matrix and examined for cell viability and expression of different endothelial cell markers (ZO-1, Na+/K+-ATPase, NCAM, glypican, and vimentin). All cultured rims remained viable and displayed either single regions (n = 5/21) or collective areas (n = 16/21) of cell migration, regardless of the presence or absence of ROCK-inhibition. Migration started after 4±2 days and continued for at least 29 days. The presence of ROCK-inhibitor seemed to contribute to a more regular cell morphology of migrating cells. In addition, 7 outer rims demonstrated a phenotypically distinct late-onset but fast-growing cell population emerging from the area close to the limbus. These cells emerged after 3 weeks of culture and appeared less differentiated compared to other areas of migration. Immunostaining showed that migrated cells maintained the expression patterns of endothelial cell markers. In conclusion, we observed 2 morphologically distinct migrating cell populations with the first type being triggered by a broken physical barrier, which disrupted contact inhibition and the second, late-onset type showing a higher proliferative capacity though appearing less differentiated. This cell subpopulation appeared to be mediated by stimuli other than loss of contact inhibition and ROCK-inhibitor presence. Further exploration of the differences between these cell types may assist in optimizing regenerative treatment options for endothelial diseases.

iPSC-Derived Corneal Endothelial Cells

The corneal endothelium is the innermost monolayer of the cornea that maintains corneal transparency and thickness. However, adult human corneal endothelial cells (CECs) possess limited proliferative capacity, and injuries can only be repaired by migration and enlargement of resident cells. When corneal endothelial cell density is lower than the critical level (400-500 cells/mm2) due to disease or trauma, corneal endothelial dysfunction will occur and lead to corneal edema. Corneal transplantation remains the most effective clinical treatment therapy but is limited by the global shortage of healthy corneal donors. Recently, researchers have developed several alternative strategies for the treatment of corneal endothelial disease, including the transplantation of cultured human CECs and artificial corneal endothelial replacement. Early-stage results show that these strategies can effectively resolve corneal edema and restore corneal clarity and thickness, but the long-term efficacy and safety remain to be further validated. Induced pluripotent stem cells (iPSCs) represent an ideal cell source for the treatment and drug discovery of corneal endothelial diseases, which can avoid the ethical-related and immune-related problems of human embryonic stem cells (hESCs). At present, many approaches have been developed to induce the differentiation of corneal endothelial-like cells from human induced pluripotent stem cells (hiPSCs). Their safety and efficacy for the treatment of corneal endothelial dysfunction have been confirmed in rabbit and nonhuman primate animal models. Therefore, the iPSC-derived corneal endothelial cell model may provide a novel effective platform for basic and clinical research of disease modeling, drug screening, mechanistic investigation, and toxicology testing.

Nanoneedles Induce Targeted siRNA Silencing of p16 in the Human Corneal Endothelium

Nanoneedles can target nucleic acid transfection to primary cells at tissue interfaces with high efficiency and minimal perturbation. The corneal endothelium is an ideal target for nanoneedle-mediated RNA interference therapy aimed at enhancing its proliferative capacity, necessary for tissue regeneration. This work develops a strategy for siRNA nanoninjection to the human corneal endothelium. Nanoneedles can deliver p16-targeting siRNA to primary human corneal endothelial cells in vitro without toxicity. The nanoinjection of siRNA induces p16 silencing and increases cell proliferation, as monitored by ki67 expression. Furthermore, siRNA nanoinjection targeting the human corneal endothelium is nontoxic ex vivo, and silences p16 in transfected cells. These data indicate that nanoinjection can support targeted RNA interference therapy for the treatment of endothelial corneal dysfunction.

Corneal endothelial wound healing: understanding the regenerative capacity of the innermost layer of the cornea

Currently, there are very few well-established treatments to stimulate corneal endothelial cell regeneration in vivo as a cure for corneal endothelial dysfunctions. The most frequently performed intervention for a damaged or dysfunctional corneal endothelium nowadays is corneal endothelial keratoplasty, also known as lamellar corneal transplantation surgery. Newer medical therapies are emerging and are targeting the regeneration of the corneal endothelium, helping the patients regain their vision without the need for donor tissue. Alternatives to donor tissues are needed as the aging population requiring transplants, has further exacerbated the pressure on the corneal eye banking system. Significant ongoing research efforts in the field of corneal regenerative medicine have been made to elucidate the underlying pathways and effector proteins involved in corneal endothelial regeneration. However, the literature offers little guidance and selective attention to the question of how to fully exploit these pathways. The purpose of this paper is to provide an overview of wound healing characteristics from a biochemical level in the lab to the regenerative features seen in the clinic. Studying the pathways involved in corneal wound healing together with their key effector proteins, can help explain the effect on the proliferation and migration capacity of the corneal endothelial cells.

Descemet Membrane Endothelial Transfer (DMET) in Pseudophakic Bullous Keratopathy After DSEK-A Case Report and Review of Literature

PURPOSE

The purpose of this study was to report a Descemet membrane endothelial transfer (DMET) in a patient with pseudophakic bullous keratopathy (PBK) who developed graft dislocation after manual Descemet stripping endothelial keratoplasty.

METHODS

A 60-year-old man presented with defective vision in the left eye; after Descemet stripping endothelial keratoplasty, graft dislocation was noted 1 month after surgery.

RESULTS

Corneal clarity was improving slowly over 3 months without any secondary surgical intervention. The mechanism of DMET and the review of literature were enunciated.

CONCLUSIONS

DMET occurs commonly in eyes with Fuch endothelial dystrophy and rarely in patients with PBK. The mechanism of DMET in PBK probably occurs because of migration of the donor endothelial cells from partially attached Descemet stripping endothelial keratoplasty grafts to the host stroma, in contrast to Fuch endothelial dystrophy, where the endothelial cells from the periphery migrate to the center. Hence, waiting for spontaneous corneal clarity is pivotal because of DMET even in patients with PBK for at least 3 months.

Descemetorhexis Without Endothelial Keratoplasty in Fuchs Endothelial Corneal Dystrophy: A Systematic Review and Meta-Analysis

PURPOSE

Descemetorhexis without endothelial keratoplasty (DWEK) is an innovative corneal intervention and potentially effective against Fuchs endothelial corneal dystrophy (FECD). We aimed to conduct a systematic review and meta-analysis on the outcomes of DWEK, associated or not with phacoemulsification (PKE) and rho-kinase inhibitor (RHOKI) in FECD.

METHOD

PubMed, Cochrane Library, Embase, ClinicalTrials.gov , and Science Direct were searched for studies until November 29, 2020. We performed random-effects meta-analyses and meta-regressions, stratified by the type of intervention and descemetorhexis size (PROSPERO CRD42020167566).

RESULTS

We included 11 articles (mainly case series, both prospective and retrospective), representing 127 eyes of 118 patients. DWEK globally improved visual acuity (effect size = -1.11, 95% confidence interval, -1.70 to -0.52, P < 0.001) and pachymetry (-1.25, -1.92 to -0.57, P < 0.001), without significant effects on endothelial cell count (-0.59, -2.00 to 0.83, P = 0.419). The 3 types of interventions (ie, DWEK ± RHOKI, DWEK ± PKE, and DWEK ± PKE ± RHOKI) improved visual acuity and pachymetry in FECD. A descemetorhexis size ≤4 mm improved visual acuity (-0.72, -1.29 to -0.14, P < 0.001) and pachymetry (-0.68, -0.98 to -0.38, P < 0.001), whereas >4 mm did not. Overall, DWEK failure (ie, the prevalence of EK after DWEK) was 17% (7%-27%, P < 0.001), with 4% (0%-8%, P = 0.08) for a descemetorhexis size ≤4 mm.

CONCLUSIONS

Despite the lack of comparative studies, DWEK seemed to improve visual acuity and pachymetry in early stages of FECD. A descemetorhexis size ≤4 mm was associated with the best visual outcomes and pachymetry.

Scaffold-Free Strategy Using a PEG-Dextran Aqueous Two-Phase-System for Corneal Tissue Repair

Forming thin tissue constructs with minimal extracellular matrix surrounding them is important for tissue engineering applications. Here, we explore and optimize a strategy that enables rapid fabrication of scaffold-free corneal tissue constructs using the liquid-liquid interface of an aqueous two-phase system (ATPS) that is based on biocompatible polymers, dextran and polyethylene glycol. Intact tissue-like constructs, made of corneal epithelial or endothelial cells, can be formed on the interface between the two liquid phases of ATPS within hours and subsequently collected simply by removing the liquid phases. The formed corneal cell constructs express essential physiological markers and have preserved viability and proliferative ability in vitro. The corneal epithelial cell constructs are also able to re-epithelialize the corneal epithelial wound in vitro. The results suggest the promise of our reported strategy in corneal repair.

Tissue engineered scaffolds for corneal endothelial regeneration: a material's perspective

Currently, the treatment of corneal diseases caused by damage to the corneal endothelium requires a donor cornea. Because of their limited availability (1 donor cornea for 70 patients in need), researchers are investigating alternative approaches that are independent of donor tissue. One of them includes the development of a tissue engineered scaffold onto which corneal endothelial cells are seeded. In order to function as a suitable substrate, some of its essential properties including thickness, permeability, transparency and mechanical strength should meet certain demands. Additionally, the membrane should be biocompatible and allow the formation of a functional endothelium on the surface. Many materials have already been investigated in this regard including natural, semi-synthetic and synthetic polymers. In the current review, we present an overview of their characteristics and provide a critical view on the methods exploited for material characterization. Next, also the suitability of scaffolds to serve their purpose is discussed along with an overview of natural tissues (e.g. amniotic membrane and lens capsule) previously investigated for this application. Eventually, we propose a consistent approach to be exploited ideally for membrane characterization in future research. This will allow a scientifically sound comparison of materials and membranes investigated by different research groups, hence benefitting research towards the creation of a suitable/optimal tissue engineered endothelial graft.

Novel Corneal Endothelial Cell Carrier Couples a Biodegradable Polymer and a Mesenchymal Stem Cell-Derived Extracellular Matrix

Here, we report a transparent, biodegradable, and cell-adhesive carrier that is securely coupled with the extracellular matrix (ECM) for corneal endothelial cell (CEC) transplantation. To fabricate a CEC carrier, poly(lactide-co-caprolactone) (PLCL) solution was poured onto the decellularized ECM (UMDM) derived from in vitro cultured umbilical cord blood-MSCs. Once completely dried, ECM-PLCL was then peeled off from the substrate. It was 20 μm thick, transparent, rich in fibronectin and collagen type IV, and easy to handle. Surface characterizations exhibited that ECM-PLCL was very rough (54.0 ± 4.50 nm) and uniformly covered in high density by ECM and retained a positive surface charge (65.2 ± 57.8 mV), as assessed via atomic force microscopy. Human CECs (B4G12) on the ECM-PLCL showed good cell attachment, with a cell density similar to the normal cornea. They could also maintain a cell phenotype, with nicely formed cell-cell junctions as assessed via ZO-1 and N-cadherin at 14 days. This was in sharp contrast to the CEC behaviors on the FNC-coated PLCL (positive control). A function-related marker, Na⁺/K⁺-ATPase, was also identified via western blot and immunofluorescence. In addition, primary rabbit CECs showed a normal shape and they could express structural and functional proteins on the ECM-PLCL. A simulation test confirmed that CECs loaded on the ECM-PLCL were successfully engrafted into the decellularized porcine corneal tissue, with a high engraftment level and cell viability. Moreover, ECM-PLCL transplantation into the anterior chamber of the rabbit eye for 8 weeks proved the maintenance of normal cornea properties. Taken together, this study demonstrates that our ECM-PLCL can be a promising cornea endothelium graft with an excellent ECM microenvironment for CECs.

Persimmon Leaves (Diospyros kaki) Extract Enhances the Viability of Human Corneal Endothelial Cells by Improving Na+-K+-ATPase Activity

The Na⁺/K⁺-ATPase, present in the basolateral membrane of human corneal endothelial cells (HCECs), is known to play an important role for corneal transparency. Na⁺/K⁺-ATPase dysfunction is one of the major causes of corneal decompensation. The ethanol extract of Diospyros kaki (EEDK) has been reported to increase corneal cell viability. Thus, we treated HCECs with EEDK and studied its effects on HCECs survival and Na⁺/K⁺-ATPase against cytotoxic drugs like staurosporine (ST) and ouabain (OU). Firstly, survival assays, (MTT assay and live dead-imaging) showed that decreased HCECs viability by ST and OU was significantly recovered by EEDK co-treatment. Secondly, Na⁺/K⁺-ATPase activity assays revealed that EEDK enhanced Na⁺/K⁺-ATPase enzymatic activity (* p < 0.01) with/without ST and OU. Finally, Na⁺/K⁺-ATPase expression analysis (Western Blot and confocal microscopy) demonstrated that EEDK treatment with/without ST and OU facilitates Na⁺/K⁺-ATPase expression in HCECs. Taken together, our findings led us to the conclusion that EEDK might aid HCECs survival in vitro by increasing the activity and expression of Na⁺/K⁺-ATPase enzyme. Since Na⁺/K⁺-ATPase activity is important to maintain cellular function of HCECs, we suggest that EEDK can be a potential effective agent against corneal edema and related corneal disorders.

Oxidative Stress Induces a Breakdown of the Cytoskeleton and Tight Junctions of the Corneal Endothelial Cells

Purpose: To investigate the impact of oxidative stress, which is a hallmark of Fuchs dystrophy, on the barrier function of the corneal endothelial cells. Methods: Experiments were carried out with cultured bovine and porcine corneal endothelial cells. For oxidative stress, cells were supplemented with riboflavin (Rf) and exposed to UV-A (15-30 min) to induce Type-1 photochemical reactions that release H₂O₂. The effect of the stress on the barrier function was assayed by transendothelial electrical resistance (TER) measurement. In addition, the associated changes in the organization of the microtubules, perijunctional actomyosin ring (PAMR), and ZO-1 were evaluated by immunocytochemistry, which was also repeated after direct exposure to H₂O₂ (100 μM, 1 h). Results: Exposure to H₂O₂ led to the disassembly of microtubules and the destruction of PAMR. In parallel, the contiguous locus of ZO-1 was disrupted, marking a loss of barrier integrity. Accordingly, a sustained loss in TER was induced when cells in the Rf-supplemented medium were exposed to UV-A. However, the addition of catalase (7,000 U/mL) to rapidly decompose H₂O₂ limited the loss in TER. Furthermore, the adverse effects on microtubules, PAMR, and ZO-1 were suppressed by including catalase, ascorbic acid (1 mM; 30 min), or pretreatment with p38 MAP kinase inhibitor (SB-203580; 10 μM, 1 h). Conclusions: Acute oxidative stress induces microtubule disassembly by a p38 MAP kinase-dependent mechanism, leading to the destruction of PAMR and loss of barrier function. The response to oxidative stress is reminiscent of the (TNF-α)-induced breakdown of barrier failure in the corneal endothelium.

Single cell transcriptomics reveals the heterogeneity of the human cornea to identify novel markers of the limbus and stroma

The cornea is the clear window that lets light into the eye. It is composed of five layers: epithelium, Bowman's layer, stroma, Descemet's membrane and endothelium. The maintenance of its structure and transparency are determined by the functions of the different cell types populating each layer. Attempts to regenerate corneal tissue and understand disease conditions requires knowledge of how cell profiles vary across this heterogeneous tissue. We performed a single cell transcriptomic profiling of 19,472 cells isolated from eight healthy donor corneas. Our analysis delineates the heterogeneity of the corneal layers by identifying cell populations and revealing cell states that contribute in preserving corneal homeostasis. We identified expression of CAV1, HOMER3 and CPVL in the corneal epithelial limbal stem cell niche, CKS2, STMN1 and UBE2C were exclusively expressed in highly proliferative transit amplifying cells, CXCL14 was expressed exclusively in the suprabasal/superficial limbus, and NNMT was exclusively expressed by stromal keratocytes. Overall, this research provides a basis to improve current primary cell expansion protocols, for future profiling of corneal disease states, to help guide pluripotent stem cells into different corneal lineages, and to understand how engineered substrates affect corneal cells to improve regenerative therapies.

New developments in corneal endothelial cell replacement

Corneal transplantation is currently the most effective treatment to restore corneal clarity in patients with endothelial disorders. Endothelial transplantation, either by Descemet membrane endothelial keratoplasty (DMEK) or by Descemet stripping (automated) endothelial keratoplasty (DS(A)EK), is a surgical approach that replaces diseased Descemet membrane and endothelium with tissue from a healthy donor eye. Its application, however, is limited by the availability of healthy donor tissue. To increase the pool of endothelial grafts, research has focused on developing new treatment options as alternatives to conventional corneal transplantation. These treatment options can be considered as either 'surgery-based', that is tissue-efficient modifications of the current techniques (e.g. Descemet stripping only (DSO)/Descemetorhexis without endothelial keratoplasty (DWEK) and Quarter-DMEK), or 'cell-based' approaches, which rely on in vitro expansion of human corneal endothelial cells (hCEC) (i.e. cultured corneal endothelial cell sheet transplantation and cell injection). In this review, we will focus on the most recent developments in the field of the 'cell-based' approaches. Starting with the description of aspects involved in the isolation of hCEC from donor tissue, we then describe the different natural and bioengineered carriers currently used in endothelial cell sheet transplantation, and finally, we discuss the current 'state of the art' in novel therapeutic approaches such as endothelial cell injection.

Supramolecular Host-Guest Hydrogels for Corneal Regeneration

Over 6.2 million people worldwide suffer from moderate to severe vision loss due to corneal disease. While transplantation with allogenic donor tissue is sight-restoring for many patients with corneal blindness, this treatment modality is limited by long waiting lists and high rejection rates, particularly in patients with severe tissue damage and ocular surface pathologies. Hydrogel biomaterials represent a promising alternative to donor tissue for scalable, nonimmunogenic corneal reconstruction. However, implanted hydrogel materials require invasive surgeries and do not precisely conform to tissue defects, increasing the risk of patient discomfort, infection, and visual distortions. Moreover, most hydrogel crosslinking chemistries for the in situ formation of hydrogels exhibit off-target effects such as cross-reactivity with biological structures and/or result in extractable solutes that can have an impact on wound-healing and inflammation. To address the need for cytocompatible, minimally invasive, injectable tissue substitutes, host-guest interactions have emerged as an important crosslinking strategy. This review provides an overview of host-guest hydrogels as injectable therapeutics and highlights the potential application of host-guest interactions in the design of corneal stromal tissue substitutes.

Wound healing of the corneal epithelium: a review

The corneal epithelium (CE) forms the outermost layer of the cornea. Despite its thickness of only 50 μm, the CE plays a key role as an initial barrier against any insults to the eye and contributes to the light refraction onto the retina required for clear vision. In the event of an injury, the cornea is equipped with many strategies contributing to competent wound healing, including angiogenic and immune privileges, and mechanotransduction. Various factors, including growth factors, keratin, cytokines, integrins, crystallins, basement membrane, and gap junction proteins are involved in CE wound healing and serve as markers in the healing process. Studies of CE wound healing are advancing rapidly in tandem with the rise of corneal bioengineering, which employs limbal epithelial stem cells as the primary source of cells utilizing various types of biomaterials as substrates.

Biofabrication of Artificial Stem Cell Niches in the Anterior Ocular Segment

The anterior segment of the eye is a complex set of structures that collectively act to maintain the integrity of the globe and direct light towards the posteriorly located retina. The eye is exposed to numerous physical and environmental insults such as infection, UV radiation, physical or chemical injuries. Loss of transparency to the cornea or lens (cataract) and dysfunctional regulation of intra ocular pressure (glaucoma) are leading causes of worldwide blindness. Whilst traditional therapeutic approaches can improve vision, their effect often fails to control the multiple pathological events that lead to long-term vision loss. Regenerative medicine approaches in the eye have already had success with ocular stem cell therapy and ex vivo production of cornea and conjunctival tissue for transplant recovering patients' vision. However, advancements are required to increase the efficacy of these as well as develop other ocular cell therapies. One of the most important challenges that determines the success of regenerative approaches is the preservation of the stem cell properties during expansion culture in vitro. To achieve this, the environment must provide the physical, chemical and biological factors that ensure the maintenance of their undifferentiated state, as well as their proliferative capacity. This is likely to be accomplished by replicating the natural stem cell niche in vitro. Due to the complex nature of the cell microenvironment, the creation of such artificial niches requires the use of bioengineering techniques which can replicate the physico-chemical properties and the dynamic cell-extracellular matrix interactions that maintain the stem cell phenotype. This review discusses the progress made in the replication of stem cell niches from the anterior ocular segment by using bioengineering approaches and their therapeutic implications.

Optimization of polycaprolactone - based nanofiber matrices for the cultivation of corneal endothelial cells

Posterior lamellar transplantation of the eye’ s cornea (DSAEK, DMEK) currently is the gold standard for treating patients with corneal endothelial cell and back surface pathologies resulting in functional impairment. An artificial biomimetic graft carrying human corneal endothelium could minimize the dependency on human donor corneas giving access to this vision-restoring surgery to large numbers of patients, thus reducing current long waiting lists. In this study, four groups of electrospun nanofibrous scaffolds were compared: polycaprolactone (PCL), PCL/collagen, PCL/gelatin and PCL/chitosan. Each of the scaffolds were tissue-engineered with human corneal endothelial cells (HCEC-B4G12) and analyzed with regard to their potential application as artificial posterior lamellar grafts. Staining with ZO-1 and Na⁺/K⁺-ATPase antibodies revealed intact cell functionalities. It could be shown, that blending leads to decreasing contact angle, whereby a heterogeneous blend morphology could be revealed. Scaffold cytocompatibility could be confirmed for all groups via live/dead staining, whereby a significant higher cell viability could be observed for the collagen and gelatine blended matrices with 97 ± 3% and 98 ± 2% living cells respectively. TEM images show the superficial anchoring of the HCECs onto the scaffolds. This work emphasizes the benefit of blended PCL nanofibrous scaffolds for corneal endothelial keratoplasty.

Animal models of corneal endothelial dysfunction to facilitate development of novel therapies

Progressive corneal endothelial disease eventually leads to corneal edema and vision loss due to the limited regenerative capacity of the corneal endothelium in vivo and is a major indication for corneal transplantation. Despite the relatively high success rate of corneal transplantation, there remains a pressing global clinical need to identify improved therapeutic strategies to address this debilitating condition. To evaluate the safety and efficacy of novel therapeutics, there is a growing demand for pre-clinical animal models of corneal endothelial dysfunction. In this review, experimentally induced, spontaneously occurring and genetically modified animal models of corneal endothelial dysfunction are described to assist researchers in making informed decisions regarding the selection of the most appropriate animal models to meet their research goals.

Toxicity of amantadine hydrochloride on cultured bovine cornea endothelial cells

Amantadine hydrochloride (HCl) is commonly prescribed for treating influenza A virus infection and Parkinson’s disease. Recently, several studies have indicated that the use of amantadine HCl is associated with corneal edema; however, the cytotoxic effect of amantadine HCl has not been investigated. In the present study, the effects of amantadine HCl on cell growth, proliferation, and apoptosis in bovine cornea endothelial cells, and in vitro endothelial permeability were examined. Results showed that lower doses of amantadine HCl do not affect cell growth (≤ 20 μΜ), whereas higher doses of amantadine HCl inhibits cell growth (≥ 50 μΜ), induces apoptosis (2000 μΜ), increases sub-G1 phase growth arrest (2000 μΜ), causes DNA damage (≥ 1000 μΜ), and induces endothelial hyperpermeability (≥ 1000 μΜ) in bovine cornea endothelial cells; additionally, we also found that amantadine HCl attenuates the proliferation (≥ 200 μΜ) and arrests cell cycle at G1 phase (≥ 200 μΜ) in bovine cornea endothelial cells. In the present study, we measured the cytotoxic doses of amantadine HCl on cornea endothelial cells, which might be applied in evaluating the association of corneal edema.

Tips, Tricks, and Guides in Descemet Membrane Endothelial Keratoplasty Learning Curve

Lamellar keratoplasty is fast becoming the most popular form of corneal transplantation. The adoption of Descemet membrane endothelial keratoplasty (DMEK) in the management of Fuchs endothelial dystrophy and pseudophakic bullous keratopathy is partly responsible for this shift in the paradigm of management of corneal pathology. The learning curve of DMEK, however, has been proven to be much steeper than previous endothelial keratoplasty procedures. To ease the procedure, experts have proposed multiple innovative techniques from tissue preparation to graft unfolding to aid the more novice surgeon. Here, we collate and share tips and tricks from our collective experiences to support the learning curve and outcomes in DMEK for both the novice and more experienced corneal transplant surgeons.

Spontaneous attachment of complex Descemet's membrane detachment following multiple failed interventions

We describe a case with complex Descemet membrane detachment (DMD) which persisted despite initial two failed surgical attempts to appose the ocular tissues. However, over time, tissue alignment was obtained spontaneously. A 60-year-old woman, operated trabeculectomy, had a total DMD intraoperatively during a complicated cataract surgery. Initial attempt to DM repositioning with intracameral air injection failed. Anterior Segment Optical Coherence Tomography (ASOCT) showed detachment of both DM and pre-Descemet's layer (PDL). After consultation with a corneal surgeon, patient was again attempted for Intra-operative Optical Coherence Tomography (iOCT)-guided settlement of DMD with intracameral air which again failed. So, the patient was registered for lamellar corneal transplant, but at 3 months follow-up, DM had spontaneously attached, confirmed on ASOCT. This case shows for the first time that even complex DMDs involving PDL, can spontaneously appose despite failed surgical interventions.

Long-Term Observation and Sequencing Analysis of SKPs-Derived Corneal Endothelial Cell-Like Cells for Treating Corneal Endothelial Dysfunction

Corneal endothelial dysfunction is a principal cause of visual deficiency. Corneal transplantation is the most effective treatment for corneal endothelial dysfunction. However, a severe shortage of available donor corneas or human corneal endothelial cells (HCECs) remains a global challenge. Previously, we acquired corneal endothelial cell-like cells (CEC-like cells) derived from human skin-derived precursors (SKPs). CEC-like cells were injected into rabbit and monkey corneal endothelial dysfunction models and exerted excellent therapeutic effect. In this study, we prolonged the clinical observation in the monkey experiment for 2 years. Polymerase chain reaction (PCR) and DNA sequencing were carried out to confirm the existence of CEC-like cells. Histological examinations were carried out to show the corneal morphology. Further transcriptome sequencing was also carried out on HCEC, CEC-like cells before transplantation and after transplantation. We found that the monkeys cornea remained transparent and normal thickness. The total endothelial cell density decreased gradually, but tended to be stable and remained in a normal range during 2-year observation. The CEC-like cells persist during observation and could adapt to the microenvironment after transplantation. The gene expression pattern of CEC-like cells was similar to HCEC and changed slightly after transplantation. In conclusion, this study presented a brand-new insight into CEC-like cells and further provided a promising prospect of cell-based therapy for corneal endothelial dysfunction. The renewable cell source, novel derivation method and simple treatment strategy may be clinically applied in regenerative medicine in the future.

Potential Functional Restoration of Corneal Endothelial Cells in Fuchs Endothelial Corneal Dystrophy by ROCK Inhibitor (Ripasudil)

PURPOSE

Rho-associated kinase (ROCK) inhibitors have been successfully used as a rescue strategy in eyes that failed to clear after descemetorhexis without endothelial graft for treatment of Fuchs endothelial corneal dystrophy (FECD). The functional mechanisms by which ROCK inhibitors modulate corneal endothelial cell regeneration in FECD patients have, however, not been clarified. Here, we analyzed the effect of the ROCK inhibitor ripasudil on corneal endothelial cells of FECD patients and normal donors using ex vivo tissue and in vitro cellular models.

DESIGN

Experimental study: laboratory investigation.

METHODS

This institutional study used endothelial cell-Descemet membrane lamellae from FECD patients (n = 450) undergoing Descemet membrane endothelial keratoplasty (FECD ex vivo model), normal research-grade donor corneas (n = 30) after scraping off central endothelial cells (ex vivo wound healing model), normal donor corneas (n = 20) without endothelial injury, and immortalized cell lines (n = 3) generated from FECD patients (FECD in vitro model). Descemet membrane lamellae were dissected into halves and incubated for 24-72 hours in storage medium with or without a single dose of 30 μM ripasudil. The effects of ripasudil on expression of genes and proteins related to endothelial cell proliferation, migration, functionality, and endothelial-to-mesenchymal transition were analyzed and complemented by functional assays on FECD cell lines.

RESULTS

A single dose of ripasudil induced significant upregulation of genes and proteins related to cell cycle progression, cell-matrix adhesion and migration, as well as endothelial barrier and pump function up to 72 hours, whereas classical markers of endothelial-to-mesenchymal transition were downregulated in both FECD and normal specimens compared to unstimulated controls ex vivo. In addition to stimulation of proliferation and migration, ripasudil-induced changes in expression of functional signature genes could be also verified in FECD cell lines in vitro.

CONCLUSIONS

These data support the concept that inhibition of ROCK signaling represents a potent tool in regenerative therapies in FECD patients through reactivation of cell proliferation and migration as well as restoration of endothelial pump and barrier function without inducing adverse phenotypic changes.

Super-resolution imaging of flat-mounted whole mouse cornea

Super-resolution microscopy revolutionized biomedical research with significantly improved imaging resolution down to the molecular scale. To date, only limited studies reported multi-color super-resolution imaging of thin tissue slices mainly because of unavailable staining protocols and incompatible imaging techniques. Here, we show the first super-resolution imaging of flat-mounted whole mouse cornea using single-molecule localization microscopy (SMLM). We optimized immunofluorescence staining protocols for β-Tubulin, Vimentin, Peroxisome marker (PMP70), and Histone-H4 in whole mouse corneas. Using the optimized staining protocols, we imaged these four intracellular protein structures in the epithelium and endothelium layers of flat-mounted mouse corneas. We also achieved simultaneous two-color spectroscopic SMLM (sSMLM) imaging of β-Tubulin and Histone-H4 in corneal endothelial cells. The spatial localization precision of sSMLM in these studies was around 20-nm. This work sets the stage for investigating multiple intracellular alterations in corneal diseases at a nanoscopic resolution using whole corneal flat-mount beyond cell cultures.

Current development of alternative treatments for endothelial decompensation: Cell-based therapy

Current treatment for corneal endothelial dysfunction consists in the replacement of corneal endothelium by keratoplasty. Owing to the scarcity of donor corneas and the increasing number of transplants, alternative treatments such as cell-based therapies are necessary. In this article, we highlight the biological aspects of the cornea and the corneal endothelium, as well as the context that surrounds the need for new alternatives to conventional keratoplasty. We then review some of those experimental treatments in more detail, focusing on the development of the in vitro and preclinical phases of two cell-based therapies: tissue-engineered endothelial keratoplasty (TE-EK) and cell injection. In the case of TE-EK graft construction, we analyse the current progress, considering all the requirements it must meet in order to be functional. Moreover, we discuss the inherent drawbacks of endothelial keratoplasties, which TE-EK grafts should overcome in order to make surgical intervention easier and to improve the outcomes of current endothelial keratoplasties. Finally, we analyse the development of preclinical trials and their limitations in terms of performing an optimal functional evaluation of cell-based therapy, and we conclude by discussing early clinical trials in humans.

Corneal Endothelial Cell Toxicity Determines Long-Term Outcome After Ocular Exposure to Sulfur Mustard Vapor

PURPOSE

Ocular exposure to sulfur mustard (SM) vapor causes acute loss of corneal endothelial cells (CECs). Persistent corneal endothelial pathologies are observed in eyes that do not recover from SM exposure, suggesting that endothelial toxicity contributes to mustard gas keratopathy (MGK). Here, we evaluated the contributions of endothelial loss to acute and chronic corneal injuries in SM-exposed eyes.

METHODS

Rabbit eyes were exposed in vivo to equivalent doses of SM using 9-, 11-, or 14-mm vapor caps. The effects of exposure area on corneal injury progression were longitudinally evaluated over 12 weeks using clinical evaluations. The effects of exposure area on CEC morphology, endothelial and epithelial ultrastructure, and endothelial barrier function were determined from 1 day to 12 weeks.

RESULTS

SM exposure caused loss of CECs and failure of endothelial barrier integrity at 1 day, independent of exposure cap size. By 3 weeks, eyes exposed with the 14-mm vapor cap exhibited increased corneal permeability, repopulation of the endothelium by cells with fibroblastic morphology, and abnormal deposition of extracellular matrix. Eyes exposed with 9- or 11-mm vapor caps exhibited transient symptoms of injury that fully resolved, with the rate of recovery correlated with cap size.

CONCLUSIONS

The nonlinear correlation between endothelial lesion size and probability of developing MGK suggests that the CEC loss is a determinative factor for emergence of MGK. These studies illustrate the importance of endothelial repair in preventing MGK. Furthermore, they exclude chemical modification of basement membrane as a mechanistic cause of recurrent epithelial erosions in MGK eyes.

Impact of surgical experience on early post-operative regional corneal thickness after phacoemulsification

Background: Currently, phacoemulsification is a very common cataract surgical procedure in which the lens is emulsified and aspirated from the eye through a small corneal incision.Aim: To compare early regional corneal thickness changes following phacoemulsification done by experienced surgeons versus trainee surgeons.Setting: A prospective cohort study was done at Ibn Al Haitham tertiary eye hospital in Baghdad, Iraq.Methods: The data were collected for 5 months, from 01 March 2018 until 31 July 2018. Adult patients undergoing phacoemulsification and intraocular lens surgery were prospectively evaluated and divided into two groups. Group 1 comprised those operated by experienced surgeons, whilst Group 2 patients were operated by trainee surgeons. Slit lamp examination and endothelial specular microscopy were assessed with the measurement of central corneal thickness (CCT) and peripheral corneal thickness (PCT), using Scheimpflug imaging (Pentacam).Results: There was a significant statistical difference in post-operative CCT between Groups 1 and 2, being 596.72 ± 50.69 µm compared to 631.54 ± 67.84 µm in Groups 1 and 2, respectively, with a mean difference of 34.82 µm (p = 0.000). More difference was observed in post-operative PCT (148.38 µm) as it was 734.8 ± 88.55 µm in the experienced group, compared to 883.18 ± 128.43 µm in the trainee group (p = 0.005).Conclusion: Phacoemulsification done by trainee surgeons was associated with higher CCT and PCT.

Preclinical testing of small diameter Descemet membrane endothelial keratoplasty grafts to increase tissue availability

In this study, we describe a process of preparing, surgically manipulating, and validating a novel “small diameter” 4mm circular Descemet membrane endothelial keratoplasty (DMEK) graft in vitro. Three small diameter DMEK grafts can be prepared from a single donor endothelium and could, therefore, potentially expand the donor pool. Prior to clinical use, however, we aimed to examine each step of the process to determine the effect on the endothelial cell loss and whether or not cells retained their capacity to migrate uniformly. For this study, circular small diameter grafts, obtained from twelve corneas of ten donors deemed ineligible for transplantation, were included. Small diameter DMEK graft preparation was successful in all cases (n = 36). Endothelial cell density (ECD), determined in the eye bank on seventeen grafts, showed an average decrease from 2413 (±189) cells/mm² before to 2240 (±413) cells/mm² after preparation. Twenty-four grafts were used to simulate DMEK-surgery in vitro and were successfully stained with 0.06% trypan blue, loaded into a straight DMEK-injector, unfolded, positioned, and centered within the circular ~ 4mm descemetorhexis. The estimated % area populated by viable cells on the grafts decreased from on average 92 (±3) % before to 78 (±10) % (n = 4) after in vitro surgery. Cells displayed a capacity for uniform cell migration from all edges of the graft (n = 4) when embedded in the 3D hydrogel system. Our data show, that by using an in vitro model of DMEK-surgery it was possible to test the 4mm circular DMEK grafts from eye bank preparation to surgical implantation. The cell loss after in vitro surgery was comparable with the in vivo ECD decline early after DMEK and the capacity of the cells to migrate to potentially cover bare stroma indicates that these small diameter grafts may be a viable clinical option to treat central endothelial disease.