Effect of proteins on the assessment of surfactant cytotoxicity by an in vitro test: Possible correlations with in vivo data

Four surfactants were studied for their cytotoxic effect on human fibroblasts in culture. The surfactants were sodium dodecyl sulphate (SDS; anionic), cetyltrimethylammonium bromide (CTAB; cationic) and two nonionic compounds, octylphenoxy polyethoxyethanol (Triton X100) and polyoxyethylene (20) sorbitan monooleate (Tween 80). For each surfactant, LD 100 values were determined with varying amounts of protein—foetal calf serum (FCS) or bovine serum albumin (BSA)—in the culture medium, to evaluate the influence of protein concentration on surfactant cytotoxicity. FCS, like BSA, acted as a detoxifying agent, increasing the LD 100 values especially for SDS and Tween 80. Dialysis experiments enabled this general decrease in cytotoxicity to be correlated with a binding process. The binding of surfactants to the proteins of the culture medium could also be estimated by calculation, using the LD 100 values, and the values obtained were found to be similar to those determined by the dialysis assays. Comparison of these in vitro cytotoxicity results with those obtained by an in vivo procedure (the Draize test) showed that the protein in the culture medium was essential for the establishment of good correlations. Thus, this in vitro test can be considered a reliable alternative in the assessment of surfactant toxicity, although its applicability to other types of eye irritant remains to be determined.