Abstract
Purpose: :
Dry-eye disease is associated with hyper-osmolality of the tears which can initiate on the ocular surface a deleterious cascade of reactions including inflammatory responses and cell death. The purpose of this study was to investigate whether potential osmoprotectants can defend corneal epithelial cells from this destructive pathway following exposure to increasingly hyper-osmolar solutions.
Methods: :
Human corneal epithelial cells were grown in vitro in isotonic medium. Cells were then exposed to media that was hypertonic by the addition of increasing concentrations of NaCl. This resulted in the cells being exposed to media at 300mOsm (iso-osmolar), and hyper-osmolar solutions of 375, 450 and 600 mOsm. The cells were exposed to these conditions for 24 hrs. In addition, other cells were exposed to the iso-osmolar and hyper-osmolar solutions containing increasing concentrations of carnitine or erythritol (up to 10mM). The effect of the media on cell viability was assayed using the MTT assay for mitochondrial activity and for cell proliferation by staining.
Results: :
Exposure to 375mOsm reduced cell viability by 21% (p<0.05), exposure to 450mOsm reduced cell viability by 44% (p<0.02), compared to controls in iso-osmolar media. Exposure to 600mOsm killed nearly all cells in the population. In the presence of a potential osmoprotectant (carnitine or erythritol) at 375mOsm and 450mOsm, cells remained viable and showed no decrease compared to cells incubated in iso-osmolar media (p>0.05). If cells were pre-treated with the osmoprotectant there was a significant increase in cell proliferation/survival in hyper-osmolar conditions. However, in 600mOsm cells were not protected by the presence of osmoprotectants. Cell proliferation results showed very similar levels of protection by the osmoprotectants.
Conclusions: :
The potential osmoprotectants carnitine and erythritol were able to increase the survival of human corneal epithelial cells when exposed to hyper-osmolar solutions up to 450mOsm. Thus, topical application of an eye drop containing osmoprotectants may be able to better protect the ocular surface from tear film hyperosmotic stress.
Keywords: cell survival • cornea: tears/tear film/dry eye • cornea: epithelium