Wiedmann T S, Salmon A
University of Minnesota, College of Pharmacy, Department of Pharmaceutics, Minneapolis 55455.
Lipids. 1991 May;26(5):364-8. doi: 10.1007/BF02537200.
The interaction of cholesterol with ceramides containing alpha-hydroxy fatty acyl chains (hydroxyceramides) has been studied as a foundation for characterizing the lipid bilayers of the stratum corneum. A relatively large quantity of cerebrosides was obtained from bovine brain and converted to ceramides through removal of the carbohydrate side chain. The ceramides were separated based on the absence or presence of hydroxy fatty acyl chains. The lyophilized hydroxyceramides showed a broad melting region at 92 degrees C. Hydroxyceramides dispersed in water produced a relatively narrow, thermotropic transition at 75 degrees C. The effect of cholesterol on this thermotropic phase transition of hydroxyceramides was determined by differential scanning calorimetry. With respect to the main transition, cholesterol caused a broadening of the phase transition at relatively low levels as well as a decrease in the peak transition temperature. The presence of cholesterol at levels in excess of 7 wt% gave rise to an additional low-temperature transition at 55 degrees C. Upon immediate rescanning, this transition was exothermic, but with increasing incubation time the area under the excess heat capacity curve as a function of temperature became smaller. After two days or more, the transition observed was endothermic. At cholesterol levels between 40 and 50 wt%, multiple peaks were observed. From comparisons with related systems, the cooperative thermal transitions of hydroxyceramides with cholesterol are suggested to result from changes in hydrogen bonding or be due to phase separation. The composition of isolated brain ceramides is being compared with that reported for the stratum corneum.
胆固醇与含有α-羟基脂肪酰链的神经酰胺（羟基神经酰胺）之间的相互作用已被研究，作为表征角质层脂质双层的基础。从牛脑中获得了相对大量的脑苷脂，并通过去除碳水化合物侧链将其转化为神经酰胺。根据羟基脂肪酰链的有无对神经酰胺进行分离。冻干的羟基神经酰胺在92℃显示出较宽的熔化区域。分散在水中的羟基神经酰胺在75℃产生相对较窄的热致相变。通过差示扫描量热法测定胆固醇对羟基神经酰胺这种热致相变的影响。关于主要相变，胆固醇在相对较低水平时导致相变变宽以及相变峰值温度降低。胆固醇含量超过7 wt%时，在55℃出现额外的低温相变。立即重新扫描时，该相变是放热的，但随着孵育时间增加，过量热容曲线下面积随温度的变化变小。两天或更长时间后，观察到的相变是吸热的。在胆固醇含量为40至50 wt%之间时，观察到多个峰。通过与相关体系比较，羟基神经酰胺与胆固醇的协同热相变被认为是由氢键变化或相分离引起的。正在将分离的脑源性神经酰胺的组成与角质层报道的组成进行比较。
