[Epitheliotrophic capacity of serum and plasma eyedrops. Influence of centrifugation]

Effects of Vitamin A on Expressions of Apoptosis Genes Bax and Bcl-2 in Epithelial Cells of Corneal Tissues Induced by Benzalkonium Chloride in Mice with Dry Eye

Background

The apoptosis of corneal epithelial cells participates in the pathological processes of dry eye, which is expected to be a treatment target for dry eye. The aim of this study was to investigate the effects of vitamin A (VA) on apoptosis of corneal epithelial cells in a mouse model with dry eye induced by benzalkonium chloride (BAC).

Material/Methods

We randomly divided 60 male BALB/c mice aged 8–10 weeks into 3 groups: the blank control group, the dry eye+vehicle group, and the dry eye+drug group. On the 7^th day after the dry eye model successfully induced, the mouse eyeballs removed, and the mouse corneal tissues were isolated. The expression levels of Bax and Bcl-2 in corneal tissues were detected via reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. The apoptotic corneal epithelial cells were quantified using terminal deoxynucleotidyl transferase (TdT) deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) staining technique.

Results

VA suppressed the upregulation of the Bax gene at the mRNA and protein levels, and upregulated the expression of the Bcl-2 gene (P<0.05). TUNEL results revealed that the number of apoptotic epithelial cells in the dry eye group was 40 times larger as that in the blank control group. After the intervention of VA at an appropriate concentration, the number of apoptotic corneal epithelial cells was remarkably reduced to about 10 times that in the blank control group (P<0.05).

Conclusions

VA can inhibit upregulation of the expressions of Bax and Bcl-2 in the epithelial cells of mice with dry eye induced by BAC, so as to suppress the apoptosis of epithelial cells in mice with dry eye.

[Toxicity of a new moistening agent and preservative in vitro]

PURPOSE

The use of preservatives such as benzalkonium chloride (BAC) usually increases the toxicity of pharmaceutical tear substitutes. HP-guar has been recently introduced as a new artificial tear substitute and includes the preservative Polyquad (0.001%), which is considered to be non-toxic. We therefore examined the effect of preserved (cetrimide 0.01%) and unpreserved HPMC (hydroxypropylmethyl cellulose) and HP-guar in dose and time-response experiments in a human corneal and conjunctival epithelial cell culture model.

METHODS

Immortalized human conjunctival and corneal epithelial cells were cultured in 96-well plates at 37 degrees C with 5% CO(2) and exposed to the test solutions. The ATP content was quantified by means of a luminescence-based ATP assay, intracellular esterase activity by double fluorescent viability staining (calcein AM/ethidium homodimer D-1) and cell migration by a colony dispersion assay. All experiments were performed in triplicate and repeated at least once. The significance of differences was determined with an unpaired two-sided t-test.

RESULTS

HPMC with preservative severely reduced the ATP content at all concentrations tested. Unpreserved HPMC, however, showed an inhibition of ATP production only at 100% and good esterase activity. HP-guar with and without preservative were found to reduce ATP activity more than unpreserved HPMC, but the unpreserved solution was found to reduce cellular ATP levels significantly more than the preserved solution.

CONCLUSIONS

The new preservative Polyquad induced significantly less cytotoxicity than cetrimide. However, even unpreserved HP-guar can induce cytotoxicity in vitro, while unpreserved HPMC remains a good alternative tear substitute with low cytotoxicity.

Autologous serum eye drops for ocular surface disorders

Tears have antimicrobial, nourishing, mechanical, and optical properties. They contain components such as growth factors, fibronectin, and vitamins to support proliferation, migration, and differentiation of the corneal and conjunctival epithelium. A lack of these epitheliotrophic factors--for example, in dry eye, can result in severe ocular surface disorders such as persistent epithelial defects. Recently, the use of autologous serum in the form of eye drops has been reported as a new treatment for severe ocular surface disorders. Serum eye drops may be produced as an unpreserved blood preparation. They are by nature non-allergenic and their biomechanical and biochemical properties are similar to normal tears. In vitro cell culture experiments showed that corneal epithelial cell morphology and function are better maintained by serum than by pharmaceutical tear substitutes. Clinical cohort studies have reported its successful use for severe dry eyes and persistent epithelial defects. However, the protocols to prepare and use autologous serum eye drops varied considerably between the studies. As this can result in different biochemical properties protocol variations may also influence the epitheliotrophic effect of the product. Before the definitive role of serum eye drops in the management of severe ocular surface disease can be established in a large randomised controlled trial this has to be evaluated in more detail. In view of legislative restrictions and based upon the literature reviewed here a preliminary standard operating procedure for the manufacture of serum eye drops is proposed.