Effect of protein cationicity on inhibition of in vitro epidermis curling by alkylbenzene sulfonate

Dilute solutions of linear alkylbenzene sulfonate (LAS), an anionic detergent, caused strips of epidermis to twist and curl. Four commercially available protein hydrolysate mixtures and a synthetic peptide, when added to the LAS solution, countered this to varying degrees, from the epidermis being as distorted as the LAS control to as flat as the water control. A study to determine the contribution of these materials’ positive charge (isoionic point) to in vitro epidermis flatness demonstrated a direct linear relationship, i.e., the more positive the charge the flatter the epidermis. This effect was even discernible in a 1 to 30 ratio of a highly cationic protein to detergent. One of the protein mixtures, which was then fractionated according to charge, showed a linear regression correlation coefficient of 0.86 for this relationship. Because the twisting and curling of epidermis has been demonstrated to be related to human skin irritation, these results suggest that positively charged proteins might increase the mildness of solutions containing anionic detergents.