Comparison of cultured keratinocytes and fibroblasts as models for irritancy testing in vitro

Surfactants are widely used and often cause irritation to human skin. Three groups of surfactants, the trimethylammonium bromides (cationic), sodium dodecyl sulphate (anionic) and the polyoxyethylene sorbitans (Tweens, nonionic) were tested on a rat keratinocyte line (RTE) and an established fibroblast line (3T3-L1) to assess their potential as models for skin irritancy testing. Acid phosphatase (AP) release seems to parallel the development of signs of irritation in vivo and therefore AP activity was assayed after 4 hours' treatment to give an early indication of toxicity. AP activity in RTE keratinocytes rose to a peak and fell sharply, whereas in 3T3-L1 it did not change with treatment. Therefore AP may be a specific indicator of toxicity in keratinocytes. Neutral red (NR) uptake and kenacid blue (KB) staining were both assayed after 3 days' treatment as an indicator of cell proliferation. RTE and 3T3-L1 were equally sensitive in terms of NR and KB-ID(50) values for the anionic and nonionic compounds; however, 3T3 was more sensitive to the cationic compounds.