Alkylphosphocholines as a potential pharmacologic prophylaxis for posterior capsule opacification

Long-term prevention of capsular opacification after lens-refilling surgery in a rabbit model

Purpose

To reduce capsular opacification by a peri‐surgical treatment of the lens capsule with drugs in an in vivo rabbit model. Lens‐refilling surgery is a potential therapeutic intervention to treat patients with a cataract lens. The lens material is replaced with an injectable (bio)polymer that retains the natural mechanical and optical lens properties, therewith allowing accommodation. The occurrence of capsular opacification mediated by lens epithelial cells negatively affects accommodation and vision and should be avoided in this lens restoration approach.

Methods

An in vivo rabbit animal model was used with lens replacement with a silicone‐based gel‐like polymer and concurrent treatment of the lens epithelium with drugs. A case‐study approach was applied as both drug combinations and implantation times were varied. The following drugs were investigated for their potential to prevent capsular opacification long‐term: actinomycin D, methotrexate, paclitaxel and Tween‐20. All were administered in a hyaluronic acid vehicle. The rabbits were clinically followed for periods up to 4 years postimplantation. Eyes, corneas and lenses were analysed post‐mortem using MRI and confocal microscopy.

Results

Treatment combinations containing actinomycin D generally led to the least appearance of capsular fibrosis. The use of Tween‐20 or paclitaxel without actinomycin D resulted in much earlier and pronounced fibrotic responses. The aspect of capsular opacification was highly variable in individual animals. Application of the drugs in a hyaluronic acid vehicle appeared to be a safe method that spared the corneal endothelium.

Conclusion

The feasibility of long‐term prevention of fibrosis over a period of more than 4 years has been demonstrated in lens refilling in the rabbit model.

EGFR-blockade with erlotinib reduces EGF and TGF-β2 expression and the actin-cytoskeleton which influences different aspects of cellular migration in lens epithelial cells

INTRODUCTION

After cataract surgery, residual lens epithelial cells migrate and proliferate within the capsular bag resulting in posterior capsule opacification (PCO). The up-regulation of TGF-β2, EGF and FGF-2 has been identified as a key factor in PCO pathogenesis leading to actin fiber assembly and alterations in the migration pattern. In this in vitro study, the influence of Erlotinib as a selective EGFR inhibitor is investigated on the cellular features indicated, which might promote a future clinical application.

METHODS

Expression of EGF, FGF-2 and TGF-β2 was measured using RT-PCR and ELISA in human lens epithelial cells (HLEC). Computational data of an in vitro time lapse microscopy assay were used for statistical analysis of single cell migration with a particular focus on cell-cell interaction; cell velocity distribution; and displacement before, during and after mitosis. The effect of Erlotinib on the actin-cytoskeleton was evaluated using Alexa Fluor 488 Phalloidin and epifluorescence microscopy.

RESULTS

EGF and TGF-β2 mRNA expression and protein levels are reduced by Erlotinib, while FGF-2 expression remained stable. Overall fluidity of cell-cell interaction is less in the presence of Erlotinib compared to the control and the velocity distribution across all cells becomes less uniform within the cell cluster. After mitosis, HLEC move significantly faster without EGFR inhibition, which can be completely blocked by Erlotinib. Furthermore, Erlotinib diminishes the amount of actin stress fibers and the stress fiber diameter.

CONCLUSION

As a novel effect of Erlotinib on HLEC, we describe the down-regulation of EGF and TGF-β2 expression, both are crucial factors for PCO development. Cellular movement displays complex alterations under EGFR inhibition, which is partly explained by actin fiber depletion. These findings further underline the role of Erlotinib in pharmacologic PCO prophylaxis.

Attenuation of human lens epithelial cell spreading, migration and contraction via downregulation of the PI3K/Akt pathway

BACKGROUND

Posterior capsule opacification (PCO) represents a major challenge in the postoperative management of cataract patients. Spreading, migration and contraction of residual human lens epithelial cells play a pivotal role in the pathogenesis of PCO. Therefore, we analyzed the effect of the alkylphosphocholine (APC) erufosine on these cellular features as well as on PI3K/Akt, a crucial pathway in PCO pathogenesis.

METHODS

Human lens epithelial cells were cultured under standard cell culture conditions. Cell spreading was analyzed on fibronectin-coated wells and chemokinetic migration was assessed by time-lapse microscopy. For evaluation of cell-mediated collagen matrix contraction, the cells were seeded into collagen gels and incubated with an APC in different non-toxic concentrations before the surface area was measured on day 6. The activity of PI3K/Akt was assessed by an ELISA kit after incubation of the cells with different APC concentrations.

RESULTS

Human lens epithelial cell spreading and migration were attenuated by APCs as follows: 7 % spreading, 48 % migration (0.1 μM APC), and 32 % spreading, 68 % migration (1.0 μM APC). APC concentrations of 0.1 μM reduced collagen gel diameter by 5 %, and 1.0 μM by less than 1 %, compared to untreated, cell-populated gels that resulted in a cell diameter contraction of 36 %. PI3K was downregulated in a concentration-dependent manner.

CONCLUSIONS

The crucial cellular features of PCO pathogenesis are attenuated by the APC erufosine via downregulation of the PI3K pathway. Thus, erufosine might become a valuable tool for pharmacologic PCO prophylaxis in the future.

[Alkylphosphocholines inhibit lens epithelial cell proliferation and attachment]

BACKGROUND

Posterior capsule opacification (PCO) is one of the major concerns in modern cataract surgery. Ten years after successful surgery, Nd:YAG capsulotomy is required in up to 42% of patients with an acrylic sharp-edged intraocular lens (IOL). Some accommodative and multifocal IOLs display even higher capsulotomy rates. Pharmacologic prophylaxis with alkylphosphocholines (APCs) could be a novel option in PCO prevention.

METHODS

The human lens epithelial cell line HLE-B3 served as an in-vitro model. After incubation with APCs in different concentrations (0.01, 0.1, and 1 mM), the trypan blue exclusion assay and the live/dead test were performed at serum concentrations of only 5%. Cell proliferation was assessed with the MTT test. Evaluation of cell attachment was done with fibronectin- and laminin-coated wells.

RESULTS

APCs can inhibit the proliferation of human lens epithelial cells in the presence of only 5% serum in a dose-dependent manner. Proliferation inhibition of 60% and attachment inhibition of about 50% were reached at concentrations of 0.1 µM.

CONCLUSION

APCs inhibit proliferation and attachment of human lens epithelial cells in nontoxic concentrations in vitro. The substance can be applied topically, and an intraoperative application for pharmacologic PCO prophylaxis is feasible.

The safety profile of alkylphosphocholines in the model of the isolated perfused vertebrate retina

BACKGROUND

Alkylphosphocholines (APCs) are synthetic phospholipid derivatives, and have been demonstrated to inhibit ocular cell proliferation in vitro and in vivo. Currently, they are applied clinically for their antitumoral and antiparasitic properties, but have not yet been implemented for clinical use in proliferative ophthalmic disorders. The purpose of this study was to assess the safety of APC in the ex vivo model of the isolated perfused vertebrate retina.

METHODS

Bovine retina preparations were perfused with an oxygen pre-equilibrated standard solution. The electroretinogram (ERG) was recorded using Ag/AgCl-electrodes. After recording stable b-wave amplitudes, an APC was applied at the following concentrations to the nutrient solution: 0.25 microM, 2.5 microM and 25 microM. To investigate the effects of APC on photoreceptor function, a test series at the same concentrations was performed to evaluate the effects of APC on the a-wave amplitude. Aspartate at a concentration of 1 mM was added to the nutrient solution to obtain stable a-wave amplitudes. Thereafter, APC was applied at the same concentrations to the nutrient solution. The recovery of the ERG amplitudes was followed up for 75 minutes.

RESULTS

No reduction of the a- and b-wave amplitude was found at the end of the exposure time with APC added in each test series. No differences were found between the ERG amplitudes before and after application of APC at the end of the washout.

CONCLUSIONS

In the ex vivo model of the isolated perfused vertebrate retina, APC has proved to be a safe compound in the concentrations applied. Thus, APCs should further be considered as promising candidates for future clinical applications in ophthalmology.