Assessment of Ocular Irritation by Image Processed Quantification of Cell Injury in Human Corneal Cell Cultures and in Corneal Constructs

Currently, there are no accepted alternative tests for the replacement of animals in ocular irritation testing. This study focused on the quantification of cellular viability as a measure of toxic events in immortalised human corneal cell cultures and a three-dimensional corneal construct. Simultaneous vital dye staining by calcein AM and ethidium homodimer-1 was used to provide "live" and "dead" probes, respectively. For further quantification, we have developed image processing tools to evaluate digital images obtained from confocal fluorescence scanning microscopy measurements. Based on the finding that ocular irritation can be related to the extent of cell injury at the various cell layers of the cornea, we extended our studies from corneal cell cultures to an in vitro human corneal equivalent system comprising epithelial, stromal keratocyte and endothelial layers. Our results showed that the microscopic measurement of cellular injury by using either cell cultures or in vitro corneal constructs, combined with image processed quantification, can provide insight into the extent of the toxic effects.

A Human Corneal Equivalent Constructed from SV40-immortalised Corneal Cell Lines

Within the last decade, extensive research in the field of tissue and organ engineering has focused on the development of in vitro models of the cornea. The use of organotypic, three-dimensional corneal equivalents has several advantages over simple monolayer cultures. The aim of this study was to develop a corneal equivalent model composed of the same cell types as in the natural human tissue, but by using immortalised cell lines to ensure reproducibility and to minimise product variation. We report our success in the establishment of an SV40-immortalised human corneal keratocyte cell line (designated HCK). A collagen matrix, built up with these cells, displayed the morphological characteristics of the human stromal tissue and served as a biomatrix for the immortalised human corneal epithelial and endothelial cells. Histological cross-sections of the whole-cornea equivalents resemble human corneas in tissue structure. This organotypic in vitro model may serve as a research tool for the ophthalmic science community, as well as a model system for testing for eye irritancy and drug efficacy.

Comparison of human corneal cell cultures in cytotoxicity testing

The cytotoxic pattern of cosmetic or pharmaceutical compounds within different layers of the human cornea is of special interest with respect to ocular safety testing. The aim of this study was to evaluate the ability of a newly developed human corneal keratocyte (HCK) cell line as an in vitro model to predict toxicity towards keratocytes in the corneal stroma. The cytotoxic response of immortalised HCK cultures towards different surfactants was compared to that of primary cultures of human corneal keratocytes. Our studies revealed comparable results for immortalised and primary keratocytes. Furthermore, we quantified surfactant-induced cytotoxic effects on immortalised cultures of corneal epithelium and endothelium. In conclusion, the HCK cell line represents an appropriate model to test keratocyte-specific toxicity and may serve as a useful building block in the construction of three-dimensional human cornea equivalent models.

Staurosporine-induced apoptosis in human cornea epithelial cells in vitro

BACKGROUND

Apoptosis is a an important process in corneal development, homeostasis, and disease. This study was performed to determine for the first time basic temporal apoptotic features of SV-40 immortalized human corneal epithelial (HCE) cells. Additionally, we introduce a sensitive analysis of confocal microscopic images to measure the kinetics of staurosporine (STS) induced phosphatidylserine (PS) membrane translocation and early nuclear morphological changes.

METHODS

HCE cells were cultured in the presence of STS to induce apoptosis. Caspase-3 activity was measured with the fluorogenic substrate z-DEVD-rhodamine 110. We determined mitochondrial viability with a 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzenedisulfonate reduction assay, and chromatin degradation with a fluorometric method using 4,6-diamidino-2-phenylindole (DAPI). Membrane translocation of PS and nuclear alterations were assessed by quantitative fluorescence microscopy. Image processing routines were written in interactive data language (IDL).

RESULTS

Nuclear alterations like hyperchromicity, pyknosis, and active chromatin reorganization evolved instantly after STS induction. They were followed by PS translocation, DNA fragmentation, mitochondrial breakdown, and caspase-3 activation, which were detected between approximately 90 min and 4 h.

CONCLUSIONS

Morphological and texture sensitive descriptors proved to be highly susceptible for the quantification of early apoptotic nuclear characteristics in HCE cells. We propose this method to be considered for the detection of subtle nuclear reorganization in cellular studies.

Tamoxifen induces changes in the lipid composition of the retinal pigment epithelium cell line D407

Tamoxifen, the antioestrogenic drug prescribed for long-term, low-dose therapy of breast cancer, induces retinopathy. This study evaluates the effects of tamoxifen on the human retinal pigment epithelial cell line D407, attempting to identify the underlying mechanisms on tamoxifen-induced retinopathy and the involvement of cellular membranes in the cytotoxic action mechanism. We demonstrate that the tamoxifen-induced decrease in the cell growth of the D407 cell line results from pyknosis and cell cycle arrest rather than from necrosis. Furthermore, D407 cells influence the lipid composition of both plasma membrane and intracellular membranes in response to tamoxifen. Tamoxifen increases the physical order of the lipid bilayer. We observed a compensatory decrease in the cholesterol content of the plasma membrane which results in an increase of the plasma membrane fluidity. In intracellular membranes the phosphatidylcholine content is reduced to 50% of the controls. This reduction may be related to the formation of a second messenger via phospholipase pathway and sustained activation of protein kinase C. Since increased plasma membrane fluidity as well as sustained activation of protein kinase C influence the rod outer segments binding and/or ingestion by retinal pigment epithelial cells, our results suggest that membrane-mediated pathways contribute to the tamoxifen-induced retinopathy.