Experimental lens capsular bag model for posterior capsule opacification

Influence of Lens Power on IOL/Posterior Lens Capsule Interactions and IOL's PCO Potential

Purpose

Severely myopic eyes have been associated with high posterior capsule opacification (PCO) incidence. Although it has been reported that myopic eyes have weaker or more delayed capsule adhesion than emmetropic eyes, it is unclear whether/how dioptric power and posterior curvature of IOLs affect IOLs' affinity for the posterior lens capsule (PLC) and their PCO potential.

Methods

To investigate this, acrylic foldable IOLs with increasing dioptric power of 6.0D (for high myopia), 20.0D, and 30.0D (for low/non-myopia) were tested on their binding affinity toward PLC and their ability to inhibit the proliferation and infiltration of lens epithelial cells (LECs) using an in vitro simulated human PLC (sPLC) model.

Results

We found that IOL power and posterior radius of curvature (PRC) had significant impacts on IOL/sPLC adhesion forces, which are in the following order: 20.0D ≈ 30.0D > 6.0D. Optical coherence tomography (OCT) images showed that loose binding between 6.0D IOLs and sPLC contributed to larger interface spaces and significantly greater LEC infiltration, proliferation, metabolic activity, and transdifferentiation compared to 20.0D and 30.0D IOLs. Statistical analyses showed that IOLs' PRC may have a substantial influence on IOL/sPLC physical interactions, LEC responses, and PCO incidence.

Conclusions

The overall results suggest that the high PRC of low-diopter (6.0D) IOLs reduces their binding affinity toward the PLC, facilitates LEC reactions, thus causes high PCO incidence in myopic eyes. These findings strongly support that a new design to increase IOL posterior surfaces' PLC affinity may reduce PCO potential and increase safety for myopic patients.

IL-8 promotes lens capsular residual cells migration by down-regulates expression of E-cadherin and ZO-1 via the CXCR1/2-NF-κB-RhoA signal pathway

BACKGROUND

Posterior capsular opacification is a major complication following cataract surgery, marked by proliferation, migration, epithelial-mesenchymal transition, and fibrosis of residual epithelial cells. Various inflammatory cytokines are upregulated and contribute to the development of posterior capsular opacification. The effect of interleukin-8 on residual epithelial cells has not been fully determined.

METHODS

Aqueous humor and anterior capsules samples were collected from cataract surgery. Capsular bags from rats and pigs were cultured in DMEM media. Protein and mRNA expressions were measured using immunoblot and qPCR. Cell migration was assessed using the transwell assay.

RESULTS

Interleukin-8 is an early inflammatory factor secreted by residual lens epithelial cells. Migration of lens epithelial cells in aqueous humor positively correlates with interleukin-8 levels, and this effect is inhibited by the receptors of interleukin-8 CXCR1/2 blocker Reparaxin. The expression of tight-junction protein ZO-1 and cell-adhesion protein E-cadherin were down-regulated by administrating interleukin-8, and cell migration of both SRA01/04 cell line in vitro and capsular residual epithelial cells ex vivo were up-regulated via activating RhoA expression and RhoA/GTPase activity. The loss-of- function studies demonstrate that interleukin-8 binding to its receptor CXCR1/2 activates NF-κB/p65, which then turns on the RhoA's expression and RhoA/GTPase activity, and RhoA-modulated the downexpression of E-cadherin and ZO-1 and the increase of cell migration.

CONCLUSIONS

The upregulation in interleukin-8 occurs early in posterior capsular opacification and contributes to down-regulating tight-junctions among epithelial cells and elevates cell migration via the CXCR1/2-NF-κB-RhoA signaling pathway. These demonstrated that interleukin-8 could be a potential target for preventing posterior capsular opacification.

Lens Epithelial Explants Treated with Vitreous Humor Undergo Alterations in Chromatin Landscape with Concurrent Activation of Genes Associated with Fiber Cell Differentiation and Innate Immune Response

Lens epithelial explants are comprised of lens epithelial cells cultured in vitro on their native basement membrane, the lens capsule. Biologists have used lens epithelial explants to study many different cellular processes including lens fiber cell differentiation. In these studies, fiber differentiation is typically measured by cellular elongation and the expression of a few proteins characteristically expressed by lens fiber cells in situ. Chromatin and RNA was collected from lens epithelial explants cultured in either un-supplemented media or media containing 50% bovine vitreous humor for one or five days. Chromatin for ATAC-sequencing and RNA for RNA-sequencing was prepared from explants to assess regions of accessible chromatin and to quantitatively measure gene expression, respectively. Vitreous humor increased chromatin accessibility in promoter regions of genes associated with fiber differentiation and, surprisingly, an immune response, and this was associated with increased transcript levels for these genes. In contrast, vitreous had little effect on the accessibility of the genes highly expressed in the lens epithelium despite dramatic reductions in their mRNA transcripts. An unbiased analysis of differentially accessible regions revealed an enrichment of cis-regulatory motifs for RUNX, SOX and TEAD transcription factors that may drive differential gene expression in response to vitreous.

Rapid and Economical Drug-Eluting IOL Preparation via Thermoresponsive Agarose Coating for Effective Posterior Capsular Opacification Prevention

Posterior capsular opacification (PCO), the highest incidence complication after cataract surgery, is mainly due to the attachment, proliferation, and migration of the residual lens epithelial cells (LECs). Although the drug-eluting IOLs have been proved to be an effective way to prevent PCO incidence, its preparations are time consuming and require tedious preparation steps. Herein, the thermoreversible agarose is adopted to prepare drug-eluting IOL. Such functional coating can be obtained easily by simple immersion in the antiproliferative drug containing hot agarose and taken out for cooling, which not only does not affect the optical property but also can effectively decrease the PCO incidence after intraocular implantation. As a result, the proposed agarose coating provides a rapid and economical alternative of drug-eluting IOL fabrication for PCO prevention.

An evaluation of the inhibition effects of cell migration of Aspirin soaking 360°square-edge intraocular lens in an in vitro lens capsule model

PURPOSE

This study performs to evaluate the Hydrophobic and Hydrosmart 360°square-edge intraocular lens drug delivery of Aspirin using an in vitro lens capsular model.

METHODS

Cell counting kit-8 assay was used to calculate 50% inhibiting concentration values in both SRA01/04 and HLE-B3 cells. Hoechst staining and transwell assay were used to detect cell proliferation and cell migration. The in vitro lens capsule model was established mainly with a special transwell-col and cell climbing sheet, in which an intraocular lens and the TGF-β2 were added. The ultraviolet spectrophotometer was used to measure the drug concentrations released in vitro. Cell-exclusion zone assay was used to detect the cell migration in the in vitro capsular model.

RESULTS

It shows that cell morphology and distribution of SRA01/04 in the in vitro lens capsular model were closer to those in vivo. The results revealed that there could be significant inhibiting effects on cell migration of the hydrosmart intraocular lens with a sustained drug release in vitro in 7 days, while the hydrophobic intraocular lens drug delivery of Aspirin was mainly performed only from day 1 to day 3.

CONCLUSIONS

Results showed the developed hydrosmart intraocular lens could release Aspirin continuously in vitro to inhibit the cell migration of lens epithelial cells.

Factors Affecting Posterior Capsule Opacification in the Development of Intraocular Lens Materials

Posterior capsule opacification (PCO) is the most common complication arising from the corrective surgery used to treat cataract patients. PCO arises when lens epithelial cells (LEC) residing in the capsular bag post-surgery undergo hyper-proliferation and transdifferentiation into myofibroblasts, migrating from the posterior capsule over the visual axis of the newly implanted intraocular lens (IOL). The developmental pathways underlying PCO are yet to be fully understood and the current literature is contradictory regarding the impact of the recognised risk factors of PCO. The aim of this review is firstly to collate the known biochemical pathways that lead to PCO development, providing an up-to-date chronological overview from surgery to established PCO formation. Secondly, the risk factors of PCO are evaluated, focussing on the impact of IOLs’ properties. Finally, the latest experimental model designs used in PCO research are discussed to demonstrate the ongoing development of clinical PCO models, the efficacy of newly developed IOL technology, and potential therapeutic interventions. This review will contribute to current PCO literature by presenting an updated overview of the known developmental pathways of PCO, an evaluation of the impact of the risk factors underlying its development, and the latest experimental models used to investigate PCO. Furthermore, the review should provide developmental routes for research into the investigation of potential therapeutic interventions and improvements in IOL design in the aid of preventing PCO for new and existing patients.

Surface modification of intraocular lenses via photodynamic coating for safe and effective PCO prevention

Posterior capsular opacification (PCO) is an emerging complication in cataract phacoemulsification and intraocular lens (IOL) implantation surgery, mainly stemming from the adhesion, proliferation, and trans-differentiation of the post-surgery residual lens epithelial cells (LECs). Previous investigations have shown that an anti-proliferative drug eluting coating on the IOL surface provides an effective way to inhibit PCO. However, due to the undesirable elution of the anti-proliferative drug, the safety of such modification is one of the important issues to be solved. In this investigation, photodynamic coating was introduced into IOL surface modification. The photosensitizer chlorin e6 grafted α-cyclodextrin (α-CD-Ce6) was synthesized and self-assembled onto the poly(poly(ethylene glycol) methacrylate) (PPEGMA) brush established IOL surface via the supramolecular interaction between α-CD and poly(ethylene glycol) chains. The results of investigation into its optical properties, including transmittance, refractive index, and surface morphology, showed no obvious alterations after photodynamic coating modification on the IOL surface. The in vitro LEC behaviour investigation optimized the photodynamic therapy parameters when light illumination was used for the cell elimination on the photodynamic coating modified IOL. The results have also shown that this functional coating modification effectively eliminates the cells on the surface of the IOL material when treated with light illumination, whereas it keeps excellent cytocompatibility in the absence of light illumination. The investigation of the cell elimination mechanism shows that this kind of functional coating eliminates the adherent cells by ROS induced apoptosis. The in vivo implantation result confirms the excellent PCO inhibition effect, as well as their safety and biocompatibility to the surrounding tissues. As a result, the proposed photodynamic coating provides a safer and effective alternative of IOL modification for preventing PCO.

Posterior capsule opacification: What's in the bag?

Cataract, a clouding of the lens, is the most common cause of blindness in the world. It has a marked impact on the wellbeing and productivity of individuals and has a major economic impact on healthcare providers. The only means of treating cataract is by surgical intervention. A modern cataract operation generates a capsular bag, which comprises a proportion of the anterior capsule and the entire posterior capsule. The bag remains in situ, partitions the aqueous and vitreous humours, and in the majority of cases, houses an intraocular lens (IOL). The production of a capsular bag following surgery permits a free passage of light along the visual axis through the transparent intraocular lens and thin acellular posterior capsule. Lens epithelial cells, however, remain attached to the anterior capsule, and in response to surgical trauma initiate a wound-healing response that ultimately leads to light scatter and a reduction in visual quality known as posterior capsule opacification (PCO). There are two commonly-described forms of PCO: fibrotic and regenerative. Fibrotic PCO follows classically defined fibrotic processes, namely hyperproliferation, matrix contraction, matrix deposition and epithelial cell trans-differentiation to a myofibroblast phenotype. Regenerative PCO is defined by lens fibre cell differentiation events that give rise to Soemmerring's ring and Elschnig's pearls and becomes evident at a later stage than the fibrotic form. Both fibrotic and regenerative forms of PCO contribute to a reduction in visual quality in patients. This review will highlight the wealth of tools available for PCO research, provide insight into our current knowledge of PCO and discuss putative management of PCO from IOL design to pharmacological interventions.

Effects of anti-vascular endothelial growth factor monoclonal antibody (bevacizumab) on lens epithelial cells

The molecular and cellular effects of anti-vascular endothelial growth factor monoclonal antibody (bevacizumab) on lens epithelial cells (LECs) were examined using both an immortalized human lens epithelial cell line and a porcine capsular bag model. After treatment with various concentrations of bevacizumab, cell viability and proliferation patterns were evaluated using the water-soluble tetrazolium salt assay and 5-bromo-2′-deoxyuridine enzyme-linked immunosorbent assay, respectively. The scratch assay and Western blot analysis were employed to validate the cell migration pattern and altered expression levels of signaling molecules related to the epithelial–mesenchymal transition (EMT). Application of bevacizumab induced a range of altered cellular events in a concentration-dependent manner. A 0.1–2 mg/mL concentration demonstrated dose-dependent increase in proliferation and viability of LECs. However, 4 mg/mL decreased cell proliferation and viability. Cell migrations displayed dose-dependent retardation from 0.1 mg/mL bevacizumab treatment. Transforming growth factor-β2 expression was markedly increased in a dose-dependent manner, and α-smooth muscle actin, matrix metalloproteinase-9, and vimentin expression levels showed dose-dependent changes in a B3 cell line. Microscopic observation of porcine capsular bag revealed changes in cellular morphology and a decline in cell density compared to the control after 2 mg/mL treatment. The central aspect of posterior capsule showed delayed confluence, and the factors related to EMT revealed similar expression patterns to those identified in the cell line. Based on these results, bevacizumab modulates the proliferation and viability of LECs and induces morphological alterations through the modulation of expression patterns of specific factors related to the EMT.

Experimental models for posterior capsule opacification research

Millions of people worldwide are blinded due to cataract formation. At present the only means of treating a cataract is through surgical intervention. A modern cataract operation involves the creation of an opening in the anterior lens capsule to allow access to the fibre cells, which are then removed. This leaves in place a capsular bag that comprises the remaining anterior capsule and the entire posterior capsule. In most cases, an intraocular lens is implanted into the capsular bag during surgery. This procedure initially generates good visual restoration, but unfortunately, residual lens epithelial cells undergo a wound-healing response invoked by surgery, which in time commonly results in a secondary loss of vision. This condition is known as posterior capsule opacification (PCO) and exhibits classical features of fibrosis, including hyperproliferation, migration, matrix deposition, matrix contraction and transdifferentiation into myofibroblasts. These changes alone can cause visual deterioration, but in a significant number of cases, fibre differentiation is also observed, which gives rise to Soemmering's ring and Elschnig's pearl formation. Elucidating the regulatory factors that govern these events is fundamental in the drive to develop future strategies to prevent or delay visual deterioration resulting from PCO. A range of experimental platforms are available for the study of PCO that range from in vivo animal models to in vitro human cell and tissue culture models. In the current review, we will highlight some of the experimental models used in PCO research and provide examples of key findings that have resulted from these approaches.