Effects of activated omental cells on rat limbal corneal alkali injury

Trimebutine prevents corneal inflammation in a rat alkali burn model

Alkaline burns to the cornea lead to loss of corneal transparency, which is essential for normal vision. We used a rat corneal alkaline burn model to investigate the effect of ophthalmic trimebutine solution on healing wounds caused by alkaline burns. Trimebutine, an inhibitor of the high-mobility group box 1-receptor for advanced glycation end products, when topically applied to the burned cornea, suppressed macrophage infiltration in the early phase and neutrophil infiltration in the late phase at the wound site. It also inhibited neovascularization and myofibroblast development in the late phase. Furthermore, trimebutine effectively inhibited interleukin-1β expression in the injured cornea. It reduced scar formation by decreasing the expression of type III collagen. These findings suggest that trimebutine may represent a novel therapeutic strategy for corneal wounds, not only through its anti-inflammatory effects but also by preventing neovascularization.

Animal Models for Limbal Stem Cell Deficiency: A Critical Narrative Literature Review

This literature review will provide a critical narrative overview of the highlights and potential pitfalls of the reported animal models for limbal stem cell deficiency (LSCD) and will identify the neglected aspects of this research area. There exists significant heterogeneity in the literature regarding the methodology used to create the model and the predefined duration after the insult when the model is supposedly fully fit for evaluations and/or for testing various therapeutic interventions. The literature is also replete with examples wherein the implementation of a specific model varies significantly across different studies. For example, the concentration of the chemical, as well as its duration and technique of exposure in a chemically induced LSCD model, has a great impact not only on the validity of the model but also on the severity of the complications. Furthermore, while some models induce a full-blown clinical picture of total LSCD, some are hindered by their ability to yield only partial LSCD. Another aspect to consider is the nature of the damage induced by a specific method. As thermal methods cause more stromal scarring, they may be better suited for assessing the anti-fibrotic properties of a particular treatment. On the other hand, since chemical burns cause more neovascularisation, they provide the opportunity to tap into the potential treatments for anti-neovascularisation. The animal species (i.e., rats, mice, rabbits, etc.) is also a crucial factor in the validity of the model and its potential for clinical translation, with each animal having its unique set of advantages and disadvantages. This review will also elaborate on other overlooked aspects, such as the anaesthetic(s) used during experiments, the gender of the animals, care after LSCD induction, and model validation. The review will conclude by providing future perspectives and suggestions for further developments in this rather important area of research.

Concise Review: Bioengineering of Limbal Stem Cell Niche

The corneal epithelium is composed of nonkeratinized stratified squamous cells and has a significant turnover rate. Limbal integrity is vital to maintain the clarity and avascularity of the cornea as well as regeneration of the corneal epithelium. Limbal epithelial stem cells (LESCs) are located in the basal epithelial layer of the limbus and preserve this homeostasis. Proper functioning of LESCs is dependent on a specific microenvironment, known as the limbal stem cell niche (LSCN). This structure is made up of various cells, an extracellular matrix (ECM), and signaling molecules. Different etiologies may damage the LSCN, leading to limbal stem cell deficiency (LSCD), which is characterized by conjunctivalization of the cornea. In this review, we first summarize the basics of the LSCN and then focus on current and emerging bioengineering strategies for LSCN restoration to combat LSCD.

Evaluating the clinical translational relevance of animal models for limbal stem cell deficiency: A systematic review

PURPOSE

Animal models are pivotal for elucidating pathophysiological mechanisms and evaluating novel therapies. This systematic review identified studies that developed or adapted animal models of limbal stem cell deficiency (LSCD), assessed their reporting quality, summarized their key characteristics, and established their clinical translational relevance to human disease.

METHODS

The protocol was prospectively registered (PROSPERO CRD42020203937). Searches were conducted in PubMed, Ovid EMBASE and Web of Science in August 2020. Two authors screened citations, extracted data, assessed the reporting quality of eligible studies using the ARRIVE guidelines, and judged the clinical translational relevance of each model using a custom matrix.

RESULTS

105 studies were included. Rabbits were the most common animal species. Overall, 97% of studies recapitulated LSCD to a clinical etiology, however 62% did not provide sufficient methodological detail to enable independent reproduction of the model. Adverse events and/or exclusion of animals were infrequently (20%) reported. Approximately one-quarter of studies did not produce the intended severity of LSCD; 34% provided insufficient information to assess the fidelity of disease induction. Adjunctive diagnostic confirmation of LSCD induction was performed in 13% of studies.

CONCLUSIONS

This is the first systematic review to assess the reporting quality and clinical translational relevance of animal models of LSCD. Models of LSCD have evolved over time, resulting in variable reporting of the characteristics of animals, experimental procedures and adverse events. In most studies, validation of LSCD was made using clinical tests; newer adjunctive techniques would enhance diagnostic validation. As most studies sought to evaluate novel therapies for LSCD, animal models should ideally recapitulate all features of the condition that develop in patients.

Autologous Activated Omental versus Allogeneic Adipose Tissue-Derived Mesenchymal Stem Cells in Corneal Alkaline Injury: An Experimental Study

Purpose:

To compare the effects of two types of mesenchymal stem cells (MSCs), activated omental cells (AOCs), and adipose tissue-derived stem cells (ADSCs) in the healing process of animal model of ocular surface alkali injury.

Methods:

An alkaline burn was induced on the ocular surfaces of eighteen rats divided randomly into three groups. The first and second groups received subconjunctival AOCs and ADSCs, respectively. The control group received normal saline subconjunctival injection. On the 90^th day after the injury, the eyes were examined using slit-lamp biomicroscopy. Corneal neovascularization and scarring were graded in a masked fashion. Histological evaluation of the corneal scar was performed, and the number of inflammatory cells was evaluated.

Results:

Corneal neovascularization scores revealed higher neovascularization in the control (0.49 ± 0.12) than the AOC (0.80 ± 0.20, P = 0.01) and ADSC groups (0.84 ± 0.24, P = 0.007). There were no statistically significant differences between the neovascularization score of the AOC and ADSC groups (P > 0.05). According to histologic evaluation, stromal infiltration was significantly more in the control group compared to AOC and ADSC groups (P < 0.05).

Conclusions:

Our results suggest that MSCs, even with different sources, can be used to promote wound healing after corneal chemical burns. However, the ease of harvesting ADSC from more superficial fat sources makes this method more clinically applicable.

Stem Cell Niche Microenvironment: Review

The cornea comprises a pool of self-regenerating epithelial cells that are crucial to preserving clarity and visibility. Limbal epithelial stem cells (LESCs), which live in a specialized stem cell niche (SCN), are crucial for the survival of the human corneal epithelium. They live at the bottom of the limbal crypts, in a physically enclosed microenvironment with a number of neighboring niche cells. Scientists also simplified features of these diverse microenvironments for more analysis in situ by designing and recreating features of different SCNs. Recent methods for regenerating the corneal epithelium after serious trauma, including burns and allergic assaults, focus mainly on regenerating the LESCs. Mesenchymal stem cells, which can transform into self-renewing and skeletal tissues, hold immense interest for tissue engineering and innovative medicinal exploration. This review summarizes all types of LESCs, identity and location of the human epithelial stem cells (HESCs), reconstruction of LSCN and artificial stem cells for self-renewal.

Evaluation of Anti-Inflammatory and Antiapoptotic Effects of Bone Marrow and Adipose-Derived Mesenchymal Stem Cells in Acute Alkaline Corneal Burn

Purpose: The aim of the present study is to comparatively evaluate the anti-inflammatory and antiapoptotic effects of bone marrow and adipose-derived mesenchymal stem cells (MSCs) applied subconjunctivally after alkaline corneal burn. Methods: Thirty-two rats were divided into 4 groups and included in the study (n = 8). While no intervention was made in the control group, a chemical burn was created by applying 4 μL of NaOH soaked in 6 mm filter paper to the right eye of each subject in the other groups under general anesthesia. While only subconjunctival 0.1 mL phosphate-buffered saline (PBS) was injected to in the group 1, 2 × 106 adipose or bone marrow-derived MSC in 0.1 mL PBS was applied subconjunctivally to the subjects in the remaining groups (Group 2 and 3, respectively). Tissue samples were collected for histological analysis on the third day after the burn. Tissue samples were evaluated light microscopically and immunohistochemically stained for interleukin-1 beta (IL-1β), tumor necrosis factor alpha (TNF-α), caspase-3 (Cas-3), and CD68. Results: The IL-1β and TNF-α staining scores and the number of CD68- and Cas-3-positive stained cells were significantly lower in the groups given bone marrow and adipose-derived MSC compared to the alkaline burn group (P < 0.0001, for all parameters). Epithelial IL-1β and TNF-α staining scores were significantly lower in the bone marrow-derived MSC group compared to the adipose-derived MSC group (P < 0.0001, for all parameters). Conclusions: The presented study shows that both bone-marrow and adipose-derived MSCs support wound healing in the corneal tissue and strongly suppress the inflammation occured in the tissue.

Subconjunctival Injection of Transdifferentiated Oral Mucosal Epithelial Cells for Limbal Stem Cell Deficiency in Rats

Rat limbal niche cells (LNCs) have been proven to induce transdifferentiation of oral mucosal epithelial cells (OMECs) into corneal epithelial-like cells termed transdifferentiated oral mucosal epithelial cells (T-OMECs). This investigation aimed to evaluate the effect of subconjunctival T-OMEC injections on alkali-induced limbal stem cell deficiency (LSCD) in rats. LNCs were cocultured with OMECs in the Transwell system to obtain T-OMECs, with NIH-3T3 cells serving as a control. Subconjunctival injection of single T-OMEC or OMEC suspension was performed immediately after corneal alkali injury. T-OMECs were prelabeled with the fluorescent dye CM-DiI in vitro and tracked in vivo. Corneal epithelial defect, opacity, and neovascularization were quantitatively analyzed. The degree of corneal epithelial defect (from day 1 onward), opacity (from day 5 onward), and neovascularization (from day 2 onward) was significantly less in the T-OMEC group than in the OMEC group. Cytokeratin 12 (CK12), pigment epithelium-derived factor, and soluble fms-like tyrosine kinase-1 were expressed at a higher rate following T-OMEC injection. Some CM-DiI-labeled cells were found to be coexpressed with CK12, Pax6, and ΔNp63α in the corneal epithelium after subconjunctival injection. Subconjunctival injection of T-OMECs prevents conjunctival invasion and maintains a normal corneal phenotype, which might be a novel strategy in the treatment of LSCD.

Strategies for reconstructing the limbal stem cell niche

The epithelial cell layer that covers the surface of the cornea provides a protective barrier while maintaining corneal transparency. The rapid and effective turnover of these epithelial cells depends, in part, on the limbal epithelial stem cells (LESCs) located in a specialized microenvironment known as the limbal niche. Many disorders affecting the regeneration of the corneal epithelium are related to deficiency and/or dysfunction of LESCs and the limbal niche. Current approaches for regenerating the corneal epithelium following significant injuries such as burns and inflammatory attacks are primarily aimed at repopulating the LESCs. This review summarizes and assesses the clinical feasibility and efficacy of current and emerging approaches for reconstruction of the limbal niche. In particular, the application of mesenchymal stem cells along with appropriate biological scaffolds appear to be promising strategies for long-term revitalization of the limbal niche.

A Simple Mechanical Procedure to Create Limbal Stem Cell Deficiency in Mouse

Limbal stem cell deficiency (LSCD) is a state of malfunction or loss of limbal epithelial stem cells, after which the corneal epithelium is replaced with conjunctiva. Patients suffer from recurrent corneal defects, pain, inflammation, and loss of vision. Previously, a murine model of LSCD was described and compared to two other models. The goal was to produce a consistent mouse model of LSCD that both mimics the phenotype in humans and lasts long enough to make it possible to study the disease pathophysiology and to evaluate new treatments. Here, the technique is described in more detail. A motorized tool with a rotating burr has been designed to remove the rust rings from the corneal surface or to smooth the pterygium bed in patients. It is a suitable device to create the desired LSCD model. It is a readily available, easy-to-use tool with a fine tip that makes it appropriate for working on small eyes, as in mice. Its application prevents unnecessary trauma to the eye and it does not result in unwanted injuries, as often is the case with chemical injury models. As opposed to a blunt scraper, it removes the epithelium with the basement membrane. In this protocol, the limbal area was abraded two times, and then the whole corneal epithelium was shaved from limbus to limbus. To avoid stroma injury, care was taken not to brush the corneal surface once the epithelium was already removed.

Assessment of therapeutic options for reducing alkali burn-induced corneal neovascularization and inflammation

This article aims to review and provide the current knowledge of the possibilities of topical treatment of corneal neovascularization due to alkali burns, evidenced by laboratory experiments, in vitro studies, and clinical trials published in the specialized literature. Authors present clinically relevant treatment of corneal neovascularization used in clinical practice, potential antiangiogenic topical therapeutics against corneal neovascularization, which are under investigation, and anti-angiogenic gene-therapy.