The influence of surfactants and hydrolyzed proteins on keratinocytes viability and elasticity Tomasz Kobiela 1 , Karolina Lelen-Kaminska 2 , Michal Stepulak 2 , Malgorzata Lekka 3 , Magdalena Malejczyk 4 , Jacek Arct 2 and Slawomir Majewski 2,4 1 Institute of Biotechnology, Faculty of Chemistry, Warsaw University of Technology, Warszawa, Poland, 2 Academy of Cosmetics and Health Care, Warszawa, Poland, 3 The H. Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland and 4 Department of Dermatology and Venerology, Medical University of Warsaw, Warszawa, Poland Background/purpose: The knowledge how surfactants and hydrolyzed proteins influence the elastic properties of living epidermal keratinocytes is sparse. We demonstrate that the stiffness of cells measured by atomic force microscope (AFM) can be correlated with viability test. Methods and materials: The effects of sodium lauryl sulphate (SLS) and hydrolyzed collagen (HK) of molecular weight 9 kDa were examined with respect to human keratinocytes viability and elasticity. MTT assay was applied to determine the sur- vival fraction of keratinocytes treated with SLS and HK solu- tions of various molar ratios. The AFM measurements of the keratinocytes stiffness were carried out immediately after the exposure of cells to the SLS and HK, respectively. Results: The increase of the SLS concentration resulted in the decrease of cells proliferation and this effect was inhibited by addition of HK. The strongest inhibition was observed for the SLS:HK molar ratio equals to 2:1. AFM study shows decrease in the cell stiffness for cells treated with SLS. Fluorescence microscopy reveals remodeling of actin filaments of SLS-treated cells. SLS:HK mixture treatment results in mechanical stiffness close to untreated cells. Conclusion: These results provide possible correlations between mechanical properties and viability of keratinocytes when the chemical stress occurs. Key words: atomic force microscopy – keratinocyte stiffness – cytoskeleton – sodium lauryl sulphate – hydrolyzed collagen Ó 2012 John Wiley & Sons A/S Accepted for publication 26 April 2012 S ODIUM LAURYL sulphate (SLS) is regularly used as a reference irritant because it is fast acting, non-allergic compound, and consistent in its toxicity (1). SLS is easy available in a very pure form, so that different laboratories can work on the same material to investigate irritant skin reactions (2, 3). The research on cytokine produc- tion in epidermal response to SLS and other irri- tants showed the release of several inflammatory mediators. The response was dependent on the chemical structure of the applied substance (4). The release of inflammatory mediator IL-1, induced by SLS, has been also measured in kerat- inocytes in monolayer (5) and reconstructed epi- dermis (6). Recently, it was confirmed in in vitro studies that there is a concentration-dependent effect of SLS on inflammatory mediators and keratinocyte differentiation markers (7). Wei et al. (8) showed that detergents have variable effects on lipid synthesis and keratino- cyte differentiation, resulting in the destruction of the normal function of the skin. It is well known that SLS can penetrate and interact with the skin, producing large alterations in barrier properties (1). Recently many systems have been developed to minimize the risks of intoler- ance of surfactant-based products (3). It has been reported that addition of proteins to deter- gents can reduce their adverse effects by form- ing complexes with surfactants within the detergent formulation, which produces larger micelles and consequently lowers the critical micelle concentration (CMC) of the system (9). Despite the fact that skin in its physiological state is continuously exposed to stretching and bending forces, epidermal keratinocytes are less characterized in terms of their response to mechanical stresses (10). Studies of the mechan- ical properties of cells are important for the understanding of many physiologic processes e200 Skin Research and Technology 2013; 19: e200–e208 Printed in Singapore Á All rights reserved doi: 10.1111/j.1600-0846.2012.00628.x © 2012 John Wiley & Sons A / S Skin Research and Technology