Detergent cytotoxicity: simplified assay of cytolysis by measuring LDH activity

A simple assay protocol has been developed for measuring release of lactate dehydrogenase (LDH) activity into the medium from cultured human cells after detergent treatment. This method allows highly sensitive determination of lysed cells with simultaneous measurement of residual unlysed cells. The effective doses of 10 detergents for 50% cell lysis (ED(50)) and for 1% cell lysis (ED(1)) were determined in 96-well culture plates on their addition to five human cell lines for 20 min. The ED(50) values of these detergents correlated with their reported concentrations, giving Draize scores of 20 (DS(20)). However, the ratios of the ED(50) to the ED(1) for each detergent on the various cell lines showed scatters of 1.44 (for polyoxyethylene(10)nonyl phenyl ether with human carcinoma SQ-5 cells) to 21.43 (for stearyl trimethyl ammonium chloride with human gastric cancer KATO-III cells). These results suggest that some commonly used detergents may show relatively higher cytotoxicities than those deduced from their ED(50) values at lower concentrations. ED(1) values and the ratio of ED(50) to ED(1) are suggested as simple markers of low-dose cytotoxicity of detergents.