Cytotoxicity evaluation of multipurpose contact lens solutions using an in vitro test battery

Many in vitro alternatives to eye irritation testing are not mechanism-specific and do not employ ocular cell lines. We have developed an effective and reliable test battery that reveals toxicity mechanisms of contact lens solutions on cell metabolism and proliferation.

Cytotoxicity endpoints were quantified using bovine corneal epithelial cultures in 96-well microplates. A kenacid blue assay provided information on total cell protein, while lactate production and alamarBlue assays served as indicators of aerobic/anaerobic metabolism and redox state of cells grown in serum-free Dulbecco's modified Eagle's/Ham's F12 medium (DMEM/F12). Concentrations (% v/v) causing 10-90% inhibition of the control assay responses were used for correlations with in vivo data.

Cytotoxicities of contact lens solutions correlated better with irritant symptoms than with corneal staining, and were ranked as follows: Lens Plus << Opti-Free < or = ContaClair < or = ReNu. Lens Plus was not toxic to cell glycolysis, respiration, and proliferation for up to 20% v/v. However, the multi-purpose solutions inhibited these endpoints in a concentration-dependent manner. Opti-Free and ReNu, containing Dymed and Polyquad (ammonium surfactants), showed non-specific cell inhibition. The lactate production assay had a flatter log concentration-response curve than the other two assays.

The proposed biochemically-based test battery using the target corneal epithelium has the potential to be a simple and effective method for screening and defining toxicity profiles of contact lens care solutions. The model can be applicable to small- or large-scale testing programs and research and development of new ocular products.