Use of a serum-free medium for long-term storage of human corneas. Influence on endothelial cell density and corneal metabolism

Comparison of the structural integrity and quality of corneal endothelium stored in organ culture storage medium versus Eusol-C

In this experimental study, we compared the structural integrity and cell quality of corneal endothelium stored in organ culture medium (OCS) and Eusol-C. The experiment included rabbit and human cornea experiments in vitro. Thirty rabbit corneas and thirty-two human corneas were collected and divided into two groups. All right corneas were allocated in experiment group and left corneas were placed in control group. The corneas in experimental group were stored in OCS at 34 °C, and the corneas in control group were stored in Eusol-C at 4 °C for 7, 14, 21, 28, and 35 days, respectively. Endothelial cell morphology, cell count, and trypan blue staining for viability were assessed before storage (Day 0) and at days 7, 14, 21, 28 and 35. The structural integrity of human corneal endothelial cell was analyzed using immunohistochemistry. The samples of storage solution for microbial culture were collected on the third day and at the end of storage. The results show that no bacterial and fungal infections were found in both groups. After 14 days of storage, the morphology of endothelial cell was better in the experimental group than in the control group. The endothelial cell stored in OCS were better than those stored in Eusol-C at the end of storage times, except human cornea 14 days storage group. The ZO-1 protein staining showed the typical polygonal morphology of endothelial cell stored in the OCS. Corneal endothelial cells stored in the OCS had better quality up to 28 days. It can be applied to Chinese eye banks as a method of corneal preservation.

Novel treatment of infectious keratitis in canine corneas using ultraviolet C (UV-C) light

OBJECTIVE

To investigate the therapeutic effect of 275 nm wavelength ultraviolet C (UV-C) light for treatment of bacterial keratitis in canine corneas using an affordable, broadly available modified handheld device.

METHODS

UV-C therapy (UVCT) was evaluated in two experiments: in vitro using triplicates of three bacterial genera (Staphylococcus, Streptococcus, Pseudomonas spp., and a mix of all species) where the UVCT was performed at a distance of 10, 15, and 20 mm with 1 or 2 doses (4 h apart) for 5, 15, or 30 s; ex vivo model where healthy canine corneal buttons were inoculated superficially and deep (330 μm) with the same bacterial isolates and treated at a 10 mm distance for 15 s with one dose of 22.5 mJ/cm2. Fluorescent marker (STYO9-PI) was used to label (green = live bacteria, red = dead bacteria), and confocal microscopy was used to image the bacteria.

RESULTS

In vitro results showed all plates treated with UVCT had 100% bactericidal effect for all isolates with single dose of 15 s at 10 mm distance or two doses, 4 h apart at 15 mm and was ineffective with single dose at 15-20 mm. The ex vivo results confirmed a significant decrease in bacterial load for all isolates on samples inoculated superficially but were inconclusive for intrastromal ones.

CONCLUSIONS

UVCT confirmed the therapeutic potential for all tested isolates, for both in vitro and ex vivo experiments using a single exposure of 15 s. While safety studies are underway, clinical trials are warranted.

The landscape of clinical trials in corneal regeneration: A systematic review of tissue engineering approaches in corneal disease

The limited availability of a healthy donor cornea and the incidence of allograft failure led researchers to seek other corneal substitutes via tissue engineering. Exploring the trend of clinical trials of the cornea with the vision of tissue engineering provides an opportunity to reveal future potential corneal substitutes. The results of this clinical trial are beneficial for future study designs to overcome the limitations of current therapeutic approaches. In this study, registered clinical trials of bio-based approaches were reviewed for corneal regeneration on March 22, 2024. Among the 3955 registered trials for the cornea, 392 trials were included in this study, which categorized in three main bio-based scaffolds, stem cells, and bioactive macromolecules. In addition to the acellular cornea and human amniotic membrane, several bio-based materials have been introduced as corneal substrates such as collagen, fibrin, and agarose. However, some synthetic materials have been introduced in recent studies to improve the desired properties of bio-based scaffolds for corneal substitutes. Nevertheless, new insights into corneal regenerative medicine have recently emerged from cell sheets with autologous and allogeneic cell sources. In addition, the future perspective of corneal regeneration is described through a literature review of recent experimental models.

Therapeutic effects of equine amniotic membrane suspension on corneal re-epithelialization and haze in a modified lagomorph ex vivo wound healing model

OBJECTIVE

To investigate the therapeutic effects of topical equine amniotic membrane (eAM) suspension following corneal wounding in a controlled experimental setting.

PROCEDURES

Equine amniotic membrane was collected, gamma irradiated, homogenized for topical suspension preparation, and cryopreserved. Corneoscleral rims harvested from fresh rabbit globes were wounded via keratectomy and were maintained in an air-liquid interface ex vivo corneal culture model. Treatment groups included topical gamma irradiated eAM suspension (n = 20) and a control group (n = 20). Re-epithelialization of the wound was assessed with daily photographic evaluation of area of fluorescein uptake (mm² ). Corneal wound haze after a 21-day period was assessed by photographic analysis of haze area (mm² ) and pixel intensity (0-255). Histologic processing of corneal tissue was performed, and protein identification of eAM suspension using Liquid chromatography-mass spectrometry (LC-MS).

RESULTS

The average day of complete corneal re-epithelialization in controls (5.5 ± 1.1) and topically treated (5.5 ± 0.6) corneas, and rates of reduction in area of fluorescein uptake over time did not significantly differ (p = .44). The corneal wound haze was significantly reduced in mean area by approximately 52% and intensity by 57% in corneas treated with topical eAM suspension (p < .05), compared to controls 21 days following wounding. Protein analysis identified numerous proteins, specifically decorin, dermatopontin, and lumican, which have previously been documented in eAM.

CONCLUSIONS

Area and intensity of corneal wound haze were significantly reduced in corneas treated with gamma irradiated eAM suspension, which may be due to previously identified therapeutic proteins which promote corneal clarity.

Synthetic media for preservation of corneal tissues deemed for endothelial keratoplasty and endothelial cell culture

PURPOSE

To compare the difference between various endothelial graft preparation methods and endothelial cell culture from tissues that are preserved in serum-based and synthetic medium.

METHODS

In a randomized masked study, the tissues (n = 64) were preserved in Cornea Max (serum-based) and Cornea Syn (synthetic) series for 36 days at their respective preservation conditions. Following organ culture, corneal tissues (n = 48) were used to prepareDescemet stripping automated endothelial keratoplasty (DSAEK), preloaded ultra-thin (UT) -DSAEK, prestripped Descemet membrane endothelial keratoplasty (DMEK), free-floating DMEK, and preloaded DMEK with endothelium inward and outward grafts. These tissues were preserved for another 4days at room temperature in dextran supplemented media following which they were subjected to trypan blue, alizarin red, live/dead and Zonula Occludens-1 (ZO-1) staining. A separate set of tissues (n = 16) from both the series was used for human corneal endothelial cell (HCEnC) culture. At confluence, the proliferation and cell doubling rate was calculated and the cultured cells were subjected to live/dead, ZO-1, 2A12 and Ki-67 staining. Mann-Whitney test was performed with p < 0.05 deemed statistically significant.

RESULTS

After preparation and preservation of the tissues for endothelial keratoplasty, alizarin red showed standard endothelial morphology from both the groups. Endothelial cell loss, hexagonality and uncovered areas did not show statistically significant differences (p > 0.05) between both groups. For HCEnC, cell doubling rate was 4.7 days (p > 0.05). All the antibodies were expressed in both the groups. Hexagonality, polymorphism, cell area, viable/dead cells and Ki-67 positivity were not statistically significant (p > 0.05).

CONCLUSIONS

Complete synthetic organ culture series is safe and advantageous for carrying out advanced endothelial keratoplasty graft preparation procedures and for HCEnC culture as it is free from animal or animal-derived products.

A new storage solution for the hypothermic preservation of corneal grafts: an experimental study

In this experimental study we used for the first time Tiprotec^® as a solution for corneal preservation and cold storage. We compared the resultant endothelial cell morphology and viability with this obtained after preservation of the ex-vivo corneas with both usual standard techniques: conventional cold storage (using Eusol-C) and organ culture. This prospective, in vitro, 3-armed parallel study was performed with the use of 90 porcine corneas (examined for their endothelial quality and transparency) randomly selected for preservation in three storage methods (each 30 corneas): organ culture, standard cold storage (Eusol-C) and experimental cold storage (Tiprotec^®) Endothelium cell quantity and quality as well as corneal opacification were assessed. The degree of endothelial transparency was significantly reduced over time with all preservation media, without any significant difference among the three groups at any point of time. A reduction in endothelial cell density was also observed with all three preservation media after 30 days of storage without statistically significant differences between groups. The number of hexagonal and pentagonal endothelium cells was significantly reduced overtime in all media with significantly more hexagonal and pentagonal in the organ culture group compared to the cold storage groups. We could show that the cryopreservation medium Tiprotec^®, used until now for the preservation of vascular grafts, was of similar quality compared to the medium Eusol-C for the hypothermic storage of corneal tissue for an extended period of time up to 30 days. In comparison to organic culture with culture medium KII, both Tiprotec^® and Eusol-C were found less effective in preserving endothelial cell quality, as assessed by the morphometric analysis, and viability, as assessed by the degree of vacuolization at least up to the 30th day of storage. However, both, Tiprotec^®- and Eusol-C-preserved corneas demonstrated a certain capacity to recover after their submission in organ culture.

Optimisation of Storage and Transportation Conditions of Cultured Corneal Endothelial Cells for Cell Replacement Therapy

As the cornea is one of the most transplanted tissues in the body it has placed a burden on the provision of corneas from cadaveric donors. Corneal endothelial dysfunction is the leading indication for cornea transplant. Therefore, tissue engineering is emerging as an alternative approach to overcome the global shortage of transplant-grade corneas. The propagation and expansion of corneal endothelial cells has been widely reported. However, one obstacle to overcome is the transport and storage of corneal endothelial cells. In this study we investigated whether tissue engineered corneal endothelial cells can be preserved in hypothermic conditions. Human corneal endothelial cells (HCEnCs) were exposed to various temperatures (4 °C, 23 °C, and 37 °C) in both adherent and suspension storage models. Optimal storage media and storage duration was tested along with post-storage viability. Following storage and subsequent recovery at 37 °C, cell phenotype was assessed by immunofluorescence, gene and protein expression, and proliferative capacity analysis. Functionality was also assessed within a rabbit model of bullous keratopathy. Our data support our hypothesis that functional HCEnCs can be preserved in hypothermic conditions.

Recombinant human serum albumin for corneal preservation

PURPOSE

To study the performance of a completely synthetic organ culture (OC) preservation system containing recombinant human serum albumin (rHSA) for preservation of human donor corneas.

METHODS

Twenty-four paired donor corneas were randomly collected, and one cornea from each donor was preserved in synthetic (experimental) and serum-based media (control). The tissues were assessed at day 0; after 6 days of preservation at room temperature (RT) in Cornea Trans^® and Cornea Prep II^® ; after 28 days at 31°C in Cornea Syn^® [with rHSA] and Cornea Max^® [with foetal calf serum (FCS)] and; 4-day post deswelling in Cornea Trans^® and Cornea Jet^® . Thickness was determined with optical coherence tomography (OCT) and transparency with a validated, custom device. Morphology, endothelial cell density (ECD) and mortality were observed after treating the tissues with Trypan blue and sucrose. Glucose uptake by the cells was analysed. Data were compared using non-parametric paired Wilcoxon tests with p < 0.05 deemed significant. Histology using periodic acid-schiff (PAS), expressions of p63, CK12, αSMA and ZO-1 were analysed, and cell apoptosis postpreservation was studied.

RESULTS

Corneas stored in synthetic media showed a higher and statistically significant value as compared to serum-based media in terms of viable endothelial cell density (VECD), mortality, morphology and glucose uptake postpreservation. Histology showed presence of all the layers, all the markers were expressed, and no apoptosis was observed in either media.

CONCLUSION

The new synthetic preservation system containing rHSA (and other confidential constituents) showed better preservation effects than traditional media containing serum.

Optimized human platelet lysate as novel basis for a serum-, xeno-, and additive-free corneal endothelial cell and tissue culture

The expansion of donor-derived corneal endothelial cells (ECs) is a promising approach for regenerative therapies in corneal diseases. To achieve the best Good Manufacturing Practice standard the entire cultivation process should be devoid of nonhuman components. However, so far, there is no suitable xeno-free protocol for clinical applications. We therefore introduce a processed variant of a platelet lysate for the use in corneal cell and tissue culture based on a Good Manufacturing Practice-grade thrombocyte concentrate. This processed human platelet lysate (phPL), free of any animal components and of anticoagulants such as heparin with a physiological ionic composition, was used to cultivate corneal ECs in vitro and ex vivo in comparison to standard cultivation with fetal calf serum (FCS). Human donor corneas were cut in quarters while 2 quarters of each cornea were incubated with the respective medium supplement. Three fields of view per quarter were taken into account for the analysis. Evaluation of phPL as a medium supplement in cell culture of immortalized EC showed a superior viability compared with FCS control with reduced cell proliferation. Furthermore, the viability during the expansion of primary cells is significantly (3-fold ±0.5) increased with phPL compared with FCS standard medium. Quartering donor corneas was traumatic for the endothelium and therefore resulted in increased EC loss. Interestingly, however, cultivation of the quartered pieces for 2 weeks in 0.1-mg/ml pHPL in Biochrome I showed a 21 (±10) % EC loss compared with 67 (±12) % EC loss when cultivated in 2% FCS in Biochrome I. The cell culture protocol with pHPL as FCS replacement seems to be superior to the standard FCS protocols with respect to EC survival. It offers a xeno-free and physiological environment for corneal endothelial cells. This alternative cultivation protocol could facilitate the use of EC for human corneal cell therapy.

Quality assessment of corneal storage media and their components

BACKGROUND

To keep the loss of endothelial cell density in donor corneas to a minimum, a storage medium which is adjusted to their nutritional needs is necessary. Different media, used either serum-supplemented or serum-free, are available. The quality of medium- and serum-batches as well as support of endothelial cell viability by the medium are to be tested with a quality assured screening system that allows routine examination.

METHODS

A screening system was developed which is based on cell-culture tests with the well-established human corneal endothelial cell line HCEC-12, and therefore can be performed without the need for donor corneas. The cells are plated at a defined density in cell-culture dishes, and are cultured for a defined period of time in the test media. Evaluation is carried out by assaying cell count, activity of cell metabolism (resazurin conversion), and determining the number of apoptotic and necrotic cells (combined vital staining with YO-PRO®-1/propidium iodide and subsequent flow cytometry).

RESULTS

Human corneal endothelial cells that are cultured in a medium which is adjusted to their nutritional needs achieve higher cell numbers and show a higher metabolic rate. Simultaneously, the percentage of apoptotic and necrotic cells is lower. The screening system developed in this study allows for easy and reliable detection of slightest differences between different media, different processing steps for same media, and different supplements, as well as different serum batches.

CONCLUSIONS

The differentiated results show that the screening system is sensitive enough to show even minor quality differences. Therefore, it is more suitable than the hitherto commonly used growth assay with primary, mostly porcine, corneal endothelial cells.

Tissue engineering of the corneal endothelium: a review of carrier materials

Functional impairment of the human corneal endothelium can lead to corneal blindness. In order to meet the high demand for transplants with an appropriate human corneal endothelial cell density as a prerequisite for corneal function, several tissue engineering techniques have been developed to generate transplantable endothelial cell sheets. These approaches range from the use of natural membranes, biological polymers and biosynthetic material compositions, to completely synthetic materials as matrices for corneal endothelial cell sheet generation. This review gives an overview about currently used materials for the generation of transplantable corneal endothelial cell sheets with a special focus on thermo-responsive polymer coatings.

Keeping an eye on decellularized corneas: a review of methods, characterization and applications

The worldwide limited availability of suitable corneal donor tissue has led to the development of alternatives, including keratoprostheses (Kpros) and tissue engineered (TE) constructs. Despite advances in bioscaffold design, there is yet to be a corneal equivalent that effectively mimics both the native tissue ultrastructure and biomechanical properties. Human decellularized corneas (DCs) could offer a safe, sustainable source of corneal tissue, increasing the donor pool and potentially reducing the risk of immune rejection after corneal graft surgery. Appropriate, human-specific, decellularization techniques and high-resolution, non-destructive analysis systems are required to ensure reproducible outputs can be achieved. If robust treatment and characterization processes can be developed, DCs could offer a supplement to the donor corneal pool, alongside superior cell culture systems for pharmacology, toxicology and drug discovery studies.

Clinical Transplantation of Individualized Recipient Serum-Adapted Cornea Reduces the Risk of Graft Rejection after Keratoplasty

Corneal diseases cause severe visual impairment that necessitates corneal transplantation and frequently repetitive procedures due to graft rejection. We tested the hypothesis that exposure of donor corneas to recipient serum-derived factors during eye banking triggers a preoperative adaptation that is beneficial for postoperative tolerance. Donor corneas were incubated in a medium containing human serum (HS) obtained in each case from the prospective graft recipient in order to individually expose the donor cornea to the recipient's serum. All recipient serum-adapted corneas (RSACs) fulfilled the clinical criteria required by the national law and were transplanted successfully. The postoperative ophthalmological examination extended up to 8 years. All RSACs were tolerated by their recipients and did not cause postoperative complications and no rejection. Proteomic analysis of corneas cultivated in culture medium containing either fetal calf serum (FCS) that is routinely used for cornea banking or HS revealed different patterns of proteins. HS-cultured corneas showed a greater proteomic similarity with native human corneas than did the FCS-cultured corneas, indicating a differential nutrification of the cultured corneal tissue by HS-derived factors. The clinical results show for the first time that postoperative complications such as tissue intolerance and graft rejection might be managed if the corneal tissue is individually adapted to the recipient's serum trophic factors. This new donor tissue treatment procedure offers incontrovertible advantages and could be adapted for low-risk eyes as well as other transplantable tissues.

The human corneal endothelium: new insights into electrophysiology and ion channels

The corneal endothelium is a monolayer that mediates the flux of solutes and water across the posterior corneal surface. Thereby, it plays an essential role to maintain the transparency of the cornea. Unlike the epithelium, the human endothelium is an amitotic cell layer with a critical cell density and the risk of corneal decompensation. The number of endothelial cells subsequently decreases with age. Moreover, the endothelial cell loss is accelerated after various impairments such as surgical trauma (e.g. cataract extraction) and following corneal transplantation. This cell loss is associated with programmed cell death (apoptosis) and changed ion channel activity. However, little is known about the electrophysiology and ion channel expression (in particular Ca2+ channels) in corneal endothelial cells. This article reviews our current knowledge about the electrophysiology of the corneal endothelium. It highlights ion channel expression, which may have a major role in corneal cell physiology and pathological events. A better understanding of the (electro)physiological function of the cornea may lead to the development of clinical relevant new therapeutic and preventive measures.

Preserving the cornea: corneal storage media

PURPOSE OF REVIEW

The aim of this article is to review the recent literature regarding corneal storage media since the last review that discussed this topic in substantial detail in this journal.

RECENT FINDINGS

During the last few years, despite the development of new corneal storage media and the addition of new additives to established corneal storage media, Optisol GS (Bausch & Lomb, Irvine, California, USA) has continued to remain the popular choice among storage media used in the United States, and traditional organ culture methods are still used in Europe. Recognizing that persistent epithelial defects after corneal transplantation can be a serious complication, however, attention has started to focus on not only preserving the endothelium, but also the epithelium. In addition, there has been more research towards antimicrobial prophylaxis.

SUMMARY

With recent evidence suggesting that longer storage times may allow better outcomes in high-risk grafts because of the depletion of donor T cells from the donor cornea into the storage media, storage media will need to be optimized for preserving the endothelium for longer periods of time. In addition, because the epithelium is typically unable to be sustained for longer than 1 week in storage media, research toward preserving the epithelium will also be essential.

Prospects for endothelial transplantation

BACKGROUND

The human corneal endothelium has a limited proliferative capacity in vivo. Until now it has only been possible to replace damaged endothelium by transplantation of a donor cornea. After establishing methods for the isolation and in vitro cultivation of human corneal endothelial cells (HCEC), transplantation of these cells may be an alternative therapeutic option.

MATERIALS AND METHODS

In this review methods for the in vitro cultivation of HCEC and their transplantation onto the Descemet membrane of donor corneas are described.

RESULTS

In vitro proliferation of human adult corneal endothelial cells was achieved by the development of defined cell culture conditions, including supplementation of culture medium with specified growth factors. Dependent on the culture conditions, in vitro cultured endothelial cells showed phenotypic changes and different proliferative behaviour. The propagation of corneal endothelial cells in vitro offered the possibility of their transplantation onto donor corneas in an in vitro model. After transplantation, these cells formed a monolayer whose morphology and cell density depended on the differentiation status of the cells in vitro. Highest cell numbers up to 3000 cells/mm2 were achieved using a SV40-transformed HCEC-cell line. Monolayer integrity could be demonstrated by positive staining for integrins and light junction proteins, and pump function of the newly established endothelium was proven by perfusion studies.

CONCLUSIONS

Methods to transplant HCEC onto human denuded corneas have been successfully established to reconstruct human corneas. Recent developments in genetic manipulation of cells and tissue engineering will be of great help in constructing suitable corneas for keratoplasty. Thus corneal endothelial cell transplantation is one of the promising future possibilities to provide corneas of high quality for patients. Furthermore, improvement of the transplantation technique may lead to a method to directly manipulate the diseased endothelium of patients with corneal endothelial dystrophies.