FIRST-ORDER TOXICITY ASSAYS FOR EYE IRRITATION USING CELL-LINES - PARAMETERS THAT AFFECT IN-VITRO EVALUATION

First-order toxicity assays can be used to rapidly screen test agents. Investigators in many laboratories have used cultured cell lines to o btain correlations between first-order assay endpoints and in vivo eye irritation (Draize test) for a wide variety of compounds. Since valid ation is a key step in assay acceptance, it is important to understand which factors alter the responses of cell-line-based assays. In this study we examine: (1) the presence and configuration of a type I colla gen gel; (2) the responses of epithelial (Sf-1-Ep) and fibroblast (Sir e and 3T3) cell lines; (3) the total glutathione content, ATP content, methionine incorporation, and neutral red absorption endpoint assays; (4) alcohol(C-2-C-8), surfactant (Tween 20), and heavy metal (NiCl) t est agents; and (5) test agent exposure time (1 to 24 hr). The presenc e of a collagen gel and the cell type did not significantly affect end point assay R50 (test agent concentration that decreases assay respons e by 50%) values for a 1-hr exposure to hexanol. The ATP and glutathio ne endpoints (after 1-hr exposure) are able to distinguish between the relative in vivo toxicities of C-2-C-8 normal alcohols. All four endp oint assays detected sublethal damage, with the ATP and methionine end points being the most sensitive. The type of test agent affects the en dpoint response, as shown by the lack of a glutathione R50 value for a l-hr exposure to Tween 20 or NiCl. Even for a single test agent, endp oint assay R50 values may decrease continuously (ATP), decrease and th en stabilize (glutathione), or remain unchanged (methionine incorporat ion) during a 24-hr exposure. (C) 1995 Society of Toxicology.