The toxic effects of surfactants were also tested in confluent HeLa cell cultures as described for polarized epithelial cells. This cell line was chosen since it is a human cervical cell line. Despite the fact that these cells have epithelial origin, they are usually Dexrazoxane hydrochloride referred to as epithelial-like cells because they do not completely polarize and do not establish tight junctions between them. Despite the fact that clinical trials using surfactant-based gels have failed, it has been shown that several quaternary ammonium compounds, with various alkyl chain lengths and polar head groups, exert antibacterial activity against both Gram positive and Gram negative bacteria, as well as against some pathogenic species of fungi and protozoa, at concentration that are not harmful to mammalian epithelial cells. The study of the relation between cationic surfactant structure and its toxic effects is crucial to understand the mechanisms involved in surfactant toxicity and make predictions of the impact that new surfactants will have in cell viability. For this reason we tested the effects of the hydrocarbon chain length and polar head group structure of the cationic surfactants upon cell viability. Surfactant toxicity is dependent upon the ability to partition 
between the aqueous phase and the cell membrane and may also depend upon their ability to subsequently cross the membrane and enter the cytoplasm. The fact that amphiphile partition coefficients as well as the rate constants for their insertion into membranes and translocation across them are lower for more ordered membranes explains why HeLa cells, that are neither polarized nor have well-formed tight junctions to make their less ordered membrane domains less accessible, may be more susceptible to surfactant toxicity than fully polarized and confluent epithelial cells such as MDCK and Caco-2 cell lines. The first criterion to be considered in the evaluation of the safety of topical vaginal Orbifloxacin microbicides is their toxicity to the cervicovaginal mucosa. On ethical grounds any such evaluation should begin with an in vitro screening before using animal models and human studies. In this work we have screened the in vitro effects of concentration, exposure-time and surfactant structure on the viability of mammalian cells with characteristics mimicking the different cell types that exist in the human cervicovaginal mucosa. Earlier studies identified vaginal columnar epithelial cells as the most important site of damage caused by the surfactants Nonoxynol-9 and C31G in humans. Our studies were thus performed on two laboratory models of mammalian columnar epithelial cells, namely, fully polarized MDCK and Caco-2 cells grown to confluence. These cell cultures have wellformed tight junctions and are commonly used as models of ”tight epithelia” in laboratory trans-epithelial drug transport studies. Non-polarized cells, in particular dendritic cells, have previously been identified as the primary sites of viral infection in the vagina. We, therefore, also studied surfactant toxicity to dendritic cells under non-confluent conditions. As a model for confluent but non-polarized cells, vaginal ”epithelial-like” HeLa cells were also included in this study. A comparison of these two cell types is in itself instructive since the exposed cell surfaces are expected to be significantly different in membrane order and, therefore, with regard to surfactant partition into and translocation across them. The results reported here indicate that all surfactants used in this study revealed concentration and time-dependent toxic effects but exhibited different degrees of toxicity depending on the chemical nature of their polar head, which is in agreement with previous in vitro and in vivo studies. For Triton X-100, DDPS and SDS, cytotoxicity was not observed up to concentrations close to the Critical Micelle Concentration, in both non-polarized and polarized epithelial cell lines, whereas the toxicity of cationic surfactants occurred at concentrations very much lower than the surfactant CMC.