Abstract
Dicationic alkylammonium bromide gemini surfactants represent a class of amphiphiles potentially effective as skin permeation enhancers. However, only a limited number of studies has been dedicated to the evaluation of the respective cytotoxicity, and none directed to skin irritation endpoints. Supported on a cell viability study, the cytotoxicity of gemini surfactants of variable tail and spacer length was assessed. For this purpose, keratinocyte cells from human skin (NCTC 2544 cell line), frequently used as a model for skin irritation, were employed. The impact of the different gemini surfactants on the permeability and morphology of model vesicles was additionally investigated by measuring the leakage of calcein fluorescent dye and analyzing the NMR spectra of 31P, respectively. Detail on the interaction of gemini molecules with model membranes was also provided by a systematic differential scanning calorimetry (DSC) and molecular dynamics (MD) simulation. An irreversible impact on the viability of the NCTC 2544 cell line was observed for gemini concentrations higher than 25 mM, while no cytotoxicity was found for any of the surfactants in a concentration range up to 10 mM. A higher cytotoxicity was also found for gemini surfactants presenting longer spacer and shorter tails. The same trend was obtained in the calorimetric and permeability studies, with the gemini of longest spacer promoting the highest degree of membrane destabilization. Additional structural and dynamical characterization of the various systems, obtained by 31P NMR and MD, provide some insight on the relationship between the architecture of gemini surfactants and the respective perturbation mechanism.
Highlights
Transdermal drug delivery has been indicated as one of the most promising routes for drug administration
Very few chemical enhancers for transdermal drug delivery have been approved for clinical use, due to lack of efficiency or toxicity concerns
Cytotoxicity Since cationic surfactants are known to disturb membrane integrity[4,6], it is important to determine the extent of damage caused by cationic gemini surfactants
Summary
Transdermal drug delivery has been indicated as one of the most promising routes for drug administration. Regarding the latter concentration results, from which the cytotoxicity trend becomes distinguishable for the different surfactants, it is clear that toxicity is higher for the gemini than for the corresponding single tail surfactant. As presented, indicate that for a surfactant concentration higher than 25 mM, the toxic effect is irreversible, i.e. cell viability does not increase 48 h after removing the surfactant from the culture medium.
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