Reply to the ‘Comment on “Cholesterol Solubility Limit in Lipid Membranes probed by Small Angle Neutron Scattering and MD simulations”’ by R. Epand, Soft Matter, 2015, 11, DOI: 10.1039/C4SM02819H

Abstract

In the comment by Epand et al. on our recent article, it is stated that the term “cholesterol solubility limit” is misused. As Epand et al. point out, there is extensive literature on cholesterol phase separation in phospholipid bilayers and this term is used to define the appearance of cholesterol crystals. Moreover, as they state, this does not preclude them from existing as bilayered crystals or cholesterol-only domains within the membrane itself. Since our SANS data directly measured the maximum amount of cholesterol harboured by POPC and POPS membranes, it may have been more appropriate to use the term “cholesterol saturation limit”. Nonetheless, we stated that the saturation and solubility limits of cholesterol coincide in both POPC and POPS. Epand and et al. suggest that the data shown was insufficient to uphold this claim. Herein, we present data that supports the coincidence of cholesterol’s saturation limit with cholesterol’s solubility limit in 100 nm POPS unilamellar vesicles, where previously it has been reported to not be the case.