Use of the cytosensor microphysiometer to predict results of a 21-day cumulative irritation patch test in humans

The cytosensor™ microphysiometer (μϕ) was investigated as a rapid, relatively inexpensive test to predict performance of skin cleansing wipes on the human 21-day cumulative irritation patch test (21CIPT). It indirectly measures metabolic rate changes in L929 cells as a function of test article dose, by measuring the acidification rate in a low-buffer medium. The dose producing a 50% reduction in metabolic rate (MRD 50), relative to the baseline rate, is used as a measure of toxicity. The acute toxicity of the μϕ assay can be compared to the chronic toxicity of the 21CIPT, which is based largely on the exposure of test agents to the epidermal cells, resulting in damage and penetration of the stratum corneum leading to cell toxicity. Two series of surfactant-based cleansing wipe products were tested via the μϕ assay and 21CIPT. The first series, consisting of 20 products, was used to determine a prediction model. The second series of 38 products consisted of routine product development formulas or marketed products. Comparing the results from both tests, samples with an MRD 50 greater than 50 mg/ml provided a 21CIPT score consistent with a product that performs satisfactorily in the market. When the MRD 50 was greater than 78 mg/ml, the 21CIPT score was usually zero. The μϕ may be more sensitive than the 21CIPT for ranking minimally irritating materials. The μϕ assay is useful as a screen for predicting the performance of a wet wipes formula on the 21CIPT, and concurrently reduces the use of animals for safety testing in a product development program for cleansing wipes.