A NEW HPLC-BASED METHOD FOR THE QUANTITATIVE-ANALYSIS OF INNER STRATUM-CORNEUM LIPIDS WITH SPECIAL REFERENCE TO THE FREE FATTY-ACID FRACTION

The inner stratum corneum is likely to represent the location of the i ntact skin barrier, unperturbed by degradation processes. In our studi es of the physical skin barrier a new high-performance liquid chromato graphy (HPLC)-based method was developed for the quantitative analysis of lipids of the inner stratum corneum. All main lipid classes were s eparated and quantitated by HPLC/light scattering detection (LSD) and the free fatty acid fraction was further analysed by gas-liquid chroma tography (GLC). Mass spectrometry (MS) was used for peak identificatio n and flame ionization detection (FID) for quantitation, Special atten tion was paid to the free fatty acid fraction since unsaturated free f atty acids may exert a key function in the regulation of the skin barr ier properties by shifting the physical equilibrium of the multilamell ar lipid bilayer system towards a noncrystalline state. Our results in dicated that the endogenous free fatty acid fraction of the stratum co rneum barrier lipids in essence exclusively consisted of saturated lon g-chain free fatty acids. This fraction was characterized as a very st able population (low interindividual peak variation) dominated by satu rated lignoceric acid (C24:0, 39 molar%) and hexacosanoic acid (C26:0, 23 molar%). In addition, trace amounts of very long-chain (C32-C36) s aturated and monounsaturated free fatty acids mere detected in human f orearm inner stratum corneum. Our analysis method gives highly accurat e and precise quantitative information on the relative composition of all major lipid species present in the skin barrier. Such data mill ev entually permit skin barrier model systems to be created which will al low a more detailed analysis of the physical nature of the human skin barrier.