The Influence of Cholesterol on the Mechanism of Stabilization of Phospholipid Bilayers by Sucrose

Sugars are widely utilized to preserve cells during desiccation and freezing because their addition results in a decrease of the main phase transition temperature of phospholipid bilayers. This has been explained by two opposing models: the water replacement hypothesis, involving direct sugar–phospholipid interaction at the bilayer interface, and the hydration forces explanation, involving an entropy-driven phase transition with sugar molecules accumulating away from the bilayer interface. However, biological membranes contain substantial sterol content, and the influence of cholesterol (CHOL) on these mechanisms remains poorly defined. We conducted molecular dynamics simulations of sucrose (SUC) interactions with pure 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 2DOPC:1CHOL, and 1DOPC:1CHOL bilayers at full hydration and under dehydration. SUC expanded bilayers, reduced lipid tail order, and formed direct hydrogen bonds with DOPC headgroups, with the strongest protective effect observed under dehydration. CHOL condensed the bilayers and limited SUC-driven expansion, producing a saturation-limited response at high SUC concentration. SUC remains interfacially associated at low concentration but increasingly accumulates in the interbilayer aqueous region at high concentration, particularly under dehydration conditions. Thus, CHOL modulates the magnitude of SUC-mediated protection without changing the concentration- and hydration-dependent balance between mechanisms.