角质层脂质双分子层水渗透的原子模拟
Water permeation through stratum corneum lipid bilayers from atomistic simulations
摘要：
角质层是皮肤的最外层，由被多层脂质包围的角质填充的刚性非活性角质细胞组成。脂质层负责皮肤的屏障性质。我们计算过量的化学势和扩散系数的水作为一个功能的深度在脂质双层与角质层的组成代表使用原子分子动力学模拟。在脂质双层内的水的过剩自由能的最大值被发现是两倍的水在磷脂双层在相同的温度下。与磷脂双层相比，渗透性随自由能势垒呈指数下降，降低了几个数量级。水分子穿过双层所需的平均时间通过在存在自由能垒的情况下求解Smoluchowski方程来计算。在300 K下，对于神经酰胺NS、胆固醇和游离脂肪酸的摩尔比为2：2：1的双层膜，我们估计了渗透率P=3.7e-9 cm/s，平均通过时间τ_{av}=0.69 ms，比已有的哺乳动物皮肤切片实验结果小30倍。
英文摘要：
Stratum corneum, the outermost layer of skin, consists of keratin filled rigid non-viable corneocyte cells surrounded by multilayers of lipids. The lipid layer is responsible for the barrier properties of the skin. We calculate the excess chemical potential and diffusivity of water as a function of depth in lipid bilayers with compositions representative of the stratum corneum using atomistic molecular dynamics simulations. The maximum in the excess free energy of water inside the lipid bilayers is found to be twice that of water in phospholipid bilayers at the same temperature. Permeability, which decreases exponentially with the free energy barrier, is reduced by several orders of magnitude as compared to with phospholipid bilayers. The average time it takes for a water molecule to cross the bilayer is calculated by solving the Smoluchowski equation in presence of the free energy barrier. For a bilayer composed of a 2:2:1 molar ratio of ceramide NS 24:0, cholesterol and free fatty acid 24:0 at 300K, we estimate the permeability P=3.7e-9 cm/s and the average crossing time τ_{av}=0.69 ms. The permeability is about 30 times smaller than existing experimental results on mammalian skin sections.
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