Re-epithelialization in cornea organ culture after chemical burns and excimer laser treatment

Activation of Wnt/β-Catenin Signaling Involves 660 nm Laser Radiation on Epithelium and Modulates Lipid Metabolism

Research has proven that light treatment, specifically red light radiation, can provide more clinical benefits to human health. Our investigation was firstly conducted to characterize the tissue morphology of mouse breast post 660 nm laser radiation with low power and long-term exposure. RNA sequencing results revealed that light exposure with a higher intervention dosage could cause a number of differentially expressed genes compared with a low intervention dosage. Gene ontology analysis, protein–protein interaction network analysis, and gene set enrichment analysis results suggested that 660 nm light exposure can activate more transcription-related pathways in HC11 breast epithelial cells, and these pathways may involve modulating critical gene expression. To consider the critical role of the Wnt/T-catenin pathway in light-induced modulation, we hypothesized that this pathway might play a major role in response to 660 nm light exposure. To validate our hypothesis, we conducted qRT-PCR, immunofluorescence staining, and Western blot assays, and relative results corroborated that laser radiation could promote expression levels of β-catenin and relative phosphorylation. Significant changes in metabolites and pathway analysis revealed that 660 nm laser could affect nucleotide metabolism by regulating purine metabolism. These findings suggest that the Wnt/β-catenin pathway may be the major sensor for 660 nm laser radiation, and it may be helpful to rescue drawbacks or side effects of 660 nm light exposure through relative interventional agents.

Establishment of a Robust and Simple Corneal Organ Culture Model to Monitor Wound Healing

The use of in vitro systems to investigate the process of corneal wound healing offers the opportunity to reduce animal pain inflicted during in vivo experimentation. This study aimed to establish an easy-to-handle ex vivo organ culture model with porcine corneas for the evaluation and modulation of epithelial wound healing. Cultured free-floating cornea disks with a punch defect were observed by stereomicroscopic photo documentation. We analysed the effects of different cell culture media and investigated the impact of different wound sizes as well as the role of the limbus. Modulation of the wound healing process was carried out with the cytostatic agent Mitomycin C. The wound area calculation revealed that after three days over 90% of the lesion was healed. As analysed with TUNEL and lactate dehydrogenase assay, the culture conditions were cell protecting and preserved the viability of the corneal tissue. Wound healing rates differ dependent on the culture medium used. Mitomycin C hampered wound healing in a concentration-dependent manner. The porcine cornea ex vivo culture ideally mimics the in vivo situation and allows investigations of cellular behaviour in the course of wound healing. The effect of substances can be studied, as we have documented for a mitosis inhibitor. This model might aid in toxicological studies as well as in the evaluation of drug efficacy and could offer a platform for therapeutic approaches based on regenerative medicine.

Development and assessment of a novel ex vivo corneal culture technique involving an agarose-based dome scaffold for use as a model of in vivo corneal wound healing in dogs and rabbits

OBJECTIVE

To develop and assess a novel ex vivo corneal culture technique involving an agarose-based dome scaffold (ABDS) for use as a model of in vivo corneal wound healing in dogs and rabbits.

SAMPLE

Corneas from clinically normal dogs (paired corneas from 8 dogs and 8 single corneas) and rabbits (21 single corneas).

PROCEDURES

8 single dog corneas (DCs), 1 DC from each pair, and 10 rabbit corneas (RCs) were wounded with an excimer laser; 1 DC from each pair and 11 RCs remained unwounded. Corneas were cultured for 21 days on ABDSs (8 pairs of DCs and all RCs) or on flat-topped scaffolds (8 single DCs). The surface area of corneal fluorescein retention was measured every 6 (DCs) or 12 (RCs) hours until full corneal epithelialization was detected. Changes in corneal clarity were evaluated at 0, 7, 14, and 21 days.

RESULTS

Median time to full epithelialization for wounded dog and rabbit corneas was 48 and 60 hours, respectively; among wounded DCs, time to full epithelization did not differ by scaffold type. After 21 days of culture on ABDSs, all DCs and RCs that epithelialized developed a circular, diffuse, cloud-like pattern of optical haze, whereas DCs cultured on flat-topped scaffolds developed a focal, crater-like region of optical haze. All corneas on the ABDSs maintained convex curvature throughout the study.

CONCLUSIONS AND CLINICAL RELEVANCE

Wounded ex vivo DCs and RCs cultured on ABDSs reliably epithelialized, formed optical haze (consistent with in vivo wound healing), and maintained convex curvature. This culture technique may be adaptable to other species.

A self-healing hydrogel eye drop for the sustained delivery of decorin to prevent corneal scarring

Scarring/Opacity on the surface of the eye and vascularisation following infectious diseases, inflammation and corneal trauma are often a leading cause of blindness. The 'gold standard' treatment to prevent corneal scarring is the application of amniotic membrane (AM) to the ocular surface in the acute stage of injury. Although clinically effective, the use of the AM is associated with biological variability and unpredictable responses. Potential health risks including disease transmission, significant ethical issues surrounding the tissue donation process and stringent regulations/storage conditions, preclude widespread use. Consequently, there is a demand for the development of a new, synthetic alternative, that is stable at room temperature, capable of protecting the wound and has the capacity to deliver anti-scarring and anti-inflammatory mediators. Here we have developed a micro-structured fluid gel eye drop, to deliver a potent anti-scarring molecule, decorin. We have compared the release of decorin from the formulated dressing to a typical gel film, demonstrating enhanced release for the fluid gel eye-drops. Therefore, we have investigated the effect of the fluid gel system in 2D human corneal fibroblast culture models, as well as shown the retention of the gellan fluid gel in an in vivo rat model. At the same time the efficacy of the fluid gel eye drop was studied in an organ culture model, whereby the fluid gel containing decorin, significantly (P < 0.05) increased re-epithelialisation within 4 days of treatment.

Enhanced wound healing of tissue-engineered human corneas through altered phosphorylation of the CREB and AKT signal transduction pathways

The cornea is a transparent organ, highly specialized and unique that is continually subjected to abrasive forces and occasional mechanical or chemical trauma because of its anatomical localization. Upon injury, the extracellular matrix (ECM) rapidly changes to promote wound healing through integrin-dependent activation of specific signal transduction mediators whose contribution is to favor faster closure of the wound by altering the adhesive and migratory properties of the cells surrounding the damaged area. In this study, we exploited the human tissue-engineered cornea (hTECs) as a model to study the signal transduction pathways that participate to corneal wound healing. By exploiting both gene profiling and activated kinases arrays, we could demonstrate the occurrence of important alterations in the level of expression and activation of a few mediators from the PI3K/Akt and CREB pathways in response to the ECM remodeling taking place during wound healing of damaged hTECs. Pharmacological inhibition of CREB with C646 considerably accelerated wound closure compared to controls. This process was considerably accelerated further when both C646 and SC79, an Akt agonist, were added together to wounded hTECs. Therefore, our study demonstrate that proper corneal wound healing requires the activation of Akt together with the inhibition of CREB and that wound healing in vitro can be altered by the use of pharmacological inhibitors (such as C646) or agonists (such as SC79) of these mediators.

STATEMENT OF SIGNIFICANCE

Corneal wounds account for a large proportion of all visual disabilities in North America. To our knowledge, this is the first time that a tissue-engineered human cornea (hTEC) entirely produced using normal untransformed human cells is used as a biomaterial to study the signal transduction pathways that are critical to corneal wound healing. Through the use of this biomaterial, we demonstrated that human corneal epithelial cells engaged in wound healing reduce phosphorylation of the signal transduction mediator CREB while, in the mean time, they increase that of AKT. By increasing the activation of AKT together with a decrease in CREB activation, we could considerably reduce wound closure time in our punch-damaged hTECs. Considering the increasing interest given to the reconstruction of different types of tissues, we believe these results will have a strong impact on the field of tissue-engineering and biomaterials. Altering the activation status of the Akt and CREB proteins might prove to be a therapeutically interesting avenue and may also find applications in wound healing of other tissues beside the cornea, such as the skin.

Development of wound healing models to study TGFβ3's effect on SMA

The goal of this study was to test the efficacy of transforming growth factor beta 3 (TGFβ3) in reducing α-smooth muscle actin (SMA) expression in two models-an ex vivo organ culture and an in vitro 3D cell construct-both of which closely mimic an in vivo environment. For the ex vivo organ culture system, a central 6.0 mm corneal keratectomy was performed on freshly excised rabbit globes The corneas were then excised, segregated into groups treated with 1.0 ng/ml TGFβ1 or β3 (T1 or T3, respectively), and cultured for 2 weeks. The corneas were assessed for levels of haze and analyzed for SMA mRNA levels. For the 3D in vitro model, rabbit corneal fibroblasts (RbCFs) were cultured for 4 weeks on poly-transwell membranes in Eagle's minimum essential media (EMEM) + 10% FBS + 0.5 mM vitamin C ± 0.1 ng/ml T1 or T3. At the end of 4 weeks, the constructs were processed for analysis by indirect-immunofluorescence (IF) and RT-qPCR. The RT-qPCR data showed that SMA mRNA expression in T3 samples for both models was significantly lower (p < 0.05) than T1 treatment (around 3-fold in ex vivo and 2-fold in constructs). T3 also reduced the amount of scarring in ex vivo corneas as compared with the T1 samples. IF data from RbCF constructs confirmed that T3-treated samples had up to 4-fold (p < 0.05) lower levels of SMA protein expression than samples treated with T1. These results show that T3 when compared to T1 decreases the expression of SMA in both ex vivo organ culture and in vitro 3D cell construct models. Understanding the mechanism of T3's action in these systems and how they differ from simple cell culture models, may potentially help in developing T3 as an anti-scarring therapy.

Assessment of anti-scarring therapies in ex vivo organ cultured rabbit corneas

The effects of a triple combination of siRNAs targeting key scarring genes were assessed using an ex vivo organ culture model of excimer ablated rabbit corneas. The central 6 mm diameter region of fresh rabbit globes was ablated to a depth of 155 microns with an excimer laser. Corneas were excised, cultured at the air-liquid interface in defined culture medium supplemented with transforming growth factor beta 1 (TGFB1), and treated with either 1% prednisolone acetate or with 22.5 μM cationic nanoparticles complexed with a triple combination of siRNAs (NP-siRNA) targeting TGFB1, TGFB Receptor (TGFBR2) and connective tissue growth factor (CTGF). Scar formation was measured using image analysis of digital images and levels of smooth muscle actin (SMA) were assessed in ablated region of corneas using qRT-PCR and immunostaining. Ex vivo cultured corneas developed intense haze-like scar in the wounded areas and levels of mRNAs for pro-fibrotic genes were significantly elevated 3-8 fold in wounded tissue compared to unablated corneas. Treatment with NP-siRNA or steroid significantly reduced quantitative haze levels by 55% and 68%, respectively, and reduced SMA mRNA and immunohistostaining. This ex vivo corneal culture system reproduced key molecular patterns of corneal scarring and haze formation generated in rabbits. Treatment with NP-siRNAs targeting key scarring genes or an anti-inflammatory steroid reduced corneal haze and SMA mRNA and protein.

Reconstruction of limbal stem cell deficient corneal surface with induced human bone marrow mesenchymal stem cells on amniotic membrane

The cornea can be damaged by a variety of clinical disorders or chemical, mechanical, and thermal injuries. The objectives of this study were to induce bone marrow mesenchymal stem cells (BMSCs) to corneal lineage, to form a tissue engineered corneal substitute (TEC) using BMSCs, and to treat corneal surface defects in a limbal stem cell deficiency model. BMSCs were induced to corneal lineage using limbal medium for 10 days. Induced BMSCs demonstrated upregulation of corneal stem cell markers; β1-integrin, C/EBPδ, ABCG2, and p63, increased protein expression of CK3 and p63 significantly compared with the uninduced ones. For TEC formation, passage 1 BMSCs were trypsinized and seeded on amniotic membrane in a transwell co-culture system and were grown in limbal medium. Limbal stem cell deficiency models were induced by alkaline injury, and the TEC was implanted for 8 weeks. Serial slit lamp evaluation revealed remarkable improvement in corneal regeneration in terms of corneal clarity and reduced vascularization. Histologic and optical coherence tomography analyses demonstrated comparable corneal thickness and achieved stratified epithelium with a compact stromal layer resembling that of normal cornea. CK3 and p63 were expressed in the newly regenerated cornea. In conclusion, BMSCs can be induced into corneal epithelial lineage, and these cells are viable for the formation of TEC, to be used for the reconstruction of the corneal surface in the limbal stem cell deficient model.

Use of topical human amniotic fluid in the treatment of acute ocular alkali injuries in mice

PURPOSE

To evaluate the efficacy of topical human amniotic fluid (HAF) in the treatment of ocular acute alkali burns in mice.

DESIGN

Experimental study.

METHODS

A chemical burn with 2 microl of sodium hydroxide 0.15 mol/l was created in one eye of 30 mice. The animals were divided into gender- and age-matched groups according to the topical treatment that was administered: group 1 was treated with preterm HAF (n = 10 mice); group 2 was treated with term HAF (n = 10 mice), and group 3 was treated with saline solution (n = 10 mice). Treatment consisted of one drop that was applied to the burned eye five times per day (week one), and three times per day (week two). The epithelial defect was photographed and measured on days two and four. Ocular burn damage was assessed at days two, seven, and 14 after a pre-established classification. On day 14, both eyes of each mouse were enucleated and assessed histopathologically.

RESULTS

Median epithelial defect (interquartile range [IQR], 25th, 75th percentile) at day four was 9.93% (IQR, 8.57, 11.27) for group 1, 7.30% (IQR, 5.96, 8.97) for group 2, and 18.92% (IQR, 11.71, 27.64) for group 3 (P < .0076). The overall change (difference in slope) in ocular burn score between days 2 and 14 was -0.127 (P = .009) in group 1 vs 3, -0.134 (P = .012) in group 2 vs 3, and 0.007 (P = .88) in group 1 vs 2. On histologic examination saline solution-treated corneas had more inflammatory cells and blood vessels than HAF-treated corneas.

CONCLUSION

Topical preterm/term HAF was an effective topical therapy for limiting the damage after acute alkali burns of the eye in this animal model.

An Ex-Vivo, Whole-Globe Porcine Model of Corneoepithelial Wound Healing Tested Using Immunomodulatory Drugs

BACKGROUND

An efficient epithelial wound healing is essential for the preservation of vision. Hence, the effects of novel topical drugs on the ocular surface must be ascertained before clinical use. We have tested the utility of an ex vivo, whole-globe porcine screening model to serve as a partial substitute for resource- and time-consuming animal experiments.

METHODS

Standardized corneoepithelial lesions, 5.0 mm in diameter and 40 microm in depth, were created with an Excimer laser in freshly enucleated porcine eyes. These were then exposed to control solutions (physiological saline (baseline), tissue-culture medium (positive control) and NH4 + (toxicity control)) and to three test agents (cyclosporin A, dexamethasone, and mitomycin C). The wound-healing response and toxic effects were monitored after 20-26 h by comparing lesion sizes.

RESULTS

According to baseline data obtained using physiological saline, tissue-culture medium improved wound healing. The highest doses of NH4 + (1 M) and mitomycin C (1.0 mg/mL) elicited toxic effects (confidence interval according to Scheffé's post hoc test: -0.65 to -0.07 and -0.99 to -0.60, respectively). Under the same test conditions, cyclosporin A (0.1 to 10 mg/mL) and dexamethasone (0.1 to 10 mg/mL) had no influence on corneoepithelial wound healing.

CONCLUSIONS

Drug screening with this ex vivo porcine model permits a reproducibly quantitative and time- and dose-dependent assessment of corneoepithelial wound healing. This model corresponds more closely to the clinical situation than cell culturing and may, therefore, be useful in evaluating novel pharmaceutical agents, thereby helping to cut down on the number of animal experiments performed prior to the instigation of clinical trials.

Fluorescence-guided laser removal of chemically damaged cornea

PURPOSE

To correlate the observed fluorescence spectrum with the depth of ablation during 193 nm argon-fluoride excimer laser ablation of chemically damaged corneas.

SETTING

Laser facility, Cedars-Sinai Medical Center, Los Angeles, California, USA.

METHODS

Three cadaver New Zealand white rabbit corneas were exposed to 1 N hydrogen chloride for 10 seconds. The resultant opaque corneas were ablated to perforation using the excimer laser. Laser-induced fluorescence was collected at 45 degrees from incidence and channeled into an ultraviolet-visible spectrometer coupled to an optical multichannel analyzer reading a diode array detector. The detector recorded single-shot fluorescence spectra. The data were examined by principal component analysis, and the evolution of eigenvectors and their weighting coefficients were used to compare data among corneas. The results were correlated with histopathological sections.

RESULTS

The eigenvalues of 3 principal components corresponded to 88.9%, 10.0%, and 0.4% of the data in acid-burned corneas. Compared to that in undamaged corneas, more information was stored in the first principal component and the third eigenvector was distinctly altered. Acid-scarred tissue blue shifted the dominant fluorescence peak compared to that in normal corneal tissue.

CONCLUSIONS

After severe hydrogen chloride burn to the rabbit corneal surface, monitoring the dominant peak wavelength shift of excimer-laser-induced fluorescence can detect the transition between severely acid-damaged and underlying tissue.