Phase behavior of stratum corneum lipids in mixed Langmuir-Blodgett monolayers

Abstract

The lipids found in the bilayers of the stratum corneum fulfill the vital barrier role of mammalian bodies. The main classes of lipids found in stratum corneum are ceramides, cholesterol, and free fatty acids. For an investigation of their phase behavior, mixed Langmuir-Blodgett monolayers of these lipids were prepared. Atomic force microscopy was used to investigate the structure of the monolayers as a function of the monolayer composition. Three different types of ceramide were used: ceramide extracted from pigskin, a commercially available ceramide with several fatty acid chain lengths, and two synthetic ceramides that have only one fatty acid chain length. In pigskin ceramide-cholesterol mixed monolayers phase separation was observed. This phase separation was also found for the commercially available type III Sigma ceramide-cholesterol mixed monolayers with molar ratios ranging from 1:0.1 to 1:1. These monolayers separated into two phases, one composed of the long fatty acid chain fraction of Sigma ceramide III and the other of the short fatty acid chain fraction of Sigma ceramide III mixed with cholesterol. Mixtures with a higher cholesterol content consisted of only one phase. These observations were confirmed by the results obtained with synthetic ceramides, which have only one fatty acid chain length. The synthetic ceramide with a palmitic acid (16:0) chain mixed with cholesterol, and the synthetic ceramide with a lignoceric acid (24:0) chain did not. Free fatty acids showed a preference to mix with one of these phases, depending on their fatty acid chain lengths. The results of this investigation suggest that the model system used in this study is in good agreement with those of other studies concerning the phase behavior of the stratum corneum lipids. By varying the composition of the monolayers one can study the role of each lipid class in detail.

Increase in Secretory Sphingomyelinase Activity and Specific Ceramides in the Aorta of Apolipoprotein E Knockout Mice during Aging

“…Ceramide chain length affects the physicochemical properties of lipid membranes; 33) thus, C16:0 ceramide easily mixes with cholesterol in contrast to C24 ceramide. 34) Mesicek et al 35) reported that the overexpression of ceramide synthase (CerS) 5 lead to generation of C16:0 ceramide and an increase in apoptosis, whereas overexpression of CerS2 yielded C24 ceramide and provoked pro-survival signals. Furthermore, in the liver of CerS2 null mice, elevated rOS levels are associated with an increase in C16:0 ceramide and a decrease in mitochondria complex IV activity.…”

Ceramide Enables Fas to Cap and Kill

“…A number of groups have now identified specific properties of ceramide in model membrane systems devoid of protein (57). In particular, ceramide has the propensity to spontaneously self-associate into microdomains, as detected by a variety of physical techniques including 2 H NMR (58), the combination of differential scanning calorimetry and infrared spectroscopy (59), and atomic force spectroscopy (60). If these properties are also operative in biologic membranes, locally generated ceramide might re-organize into lipid patches capable of fusing into larger platforms (29).…”

Ceramide Selectively Displaces Cholesterol from Ordered Lipid Domains (Rafts)

“…An example may be the lipid layers of the stratum corneum of skin, which are primarily composed of a cholesterol/ceramide mixture (44). The tendency of both cholesterol and ceramide to avoid excessive hydration presumably contributes functionally to the action of the stratum corneum as a barrier to water.…”