A Critical Evaluation of Predicting Ocular lrritancy Potential from an in Vitro Cytotoxicity Assay

A Critical Evaluation of Predicting Ocular Irritancy Potentialfrom an in Vitro Cytotoxicity Assay. KENNAH, H. E., II, ALBULESCU,D., HIGNET, S., AND BARROW. C. S. (1989) Fundam Appl. Toxicol12,281-290. Numerous in vitro cytotoxicity assays have beenproposed as potential alternatives to the Draize eye irritancytest. The results reported, based upon the rank correlationof ocular irritancy with cytotoxicity, have been encouraging.However. direct calibration of in vivo to in vitro data utilizingseveral categories of chemicals has not been reported. Thisstudy evaluated the use of in vitro cytotoxicity data for predictingthe ocular irritancy potential of 24 chemicals(six surfactants,seven alcohols four ketones, four acetates and three aromatics).BALB/c 3T3 cells were grown overnight, then exposed for 30 minto at least four different concentrations of each chemical (expressedas volume percentage). Linear regression analysis of the logconcentration versus percentage of control growth was used tocalculate the concentration of toxicant that inhibited the normalgrowth rate by 50% (G150). The rank ordering of cytotoxicitybased upon the GI50s was surfactants > aromatics > alcohols> ketones or acetates. The larger molecular weight representativeof each senes (i.e., 2-ethyl-I-hexanol for alcohols) had lowerGI50 values than those of the lower molecular weight substances.The GI50 values were then directly calibrated against in vivoocular irritancy quantitated as percentage corneal swellingfollowing exposure of rabbits to the same test chemicals. Asignificant linear correlation between cytotoxicity and ocularirritancy was established only for surfactants and alcohols.For acetates, ketones, and aromatics there was little correlation.The overall poor correlation between cytotoxicity and ocularirritancy was attributed to differences in mechanisms of irritancy.The lack of correlation illustrates that in vitro cytotoxicitydata cannot be used to predict the ocular irritancy potentialof a broad spectrum of chemicals.