ELSEVIER Biochimica et Biophysics Acta 1212 (1994) 183-192 BiochimicaL et Biophysics &cta The lipid and protein structure of mouse stratum corneum: A wide and small angle diffraction study Joke A. Bouwstra a,*, Gert. S. Gooris a, Joop A. van der Spek b, S. Lavrijsen b, Wim Bras ‘,’ a zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Pharmaceutical Technology, Center for Bio-Pharmaceutical Sciences, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands ’ Technical Department, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands ’ SERC Daresbury Laboratory, W arrington W A4 4AD, UK (Received 20 October 1993) Abstract The structure of mouse stratum corneum was investigated using small and wide angle X-ray scattering. Diffraction patterns were collected as a function of temperature and hydration. The lipid lamellar structure is characterized by a repeat distance of 13.4 nm. Occasionally a second lipid lamellar phase has been found with a repeat distance of 6.1 nm. Upon hydration neither swelling of the lamellae nor lateral swelling of the lipids was found. On the basis of these facts it was concluded that the size of the crystallographic unit cell of the lipid structure is insensitive to the water content. The 13.4 nm lamellar phase disappeared upon heating to 55°C. At 45°C the orthorhombic lateral packing disappeared. At this temperature only an hexagonal and liquid lateral packing of the lipids was observed. The hexagonal lateral packing transformed to a liquid one between 45°C and 80°C. Model calculations were carried out to obtain the electron density profile of the lamellar structure. In all models three electron lucent regions were fitted between which electron dense regions are located indicating that the 13.4 nm lamellar structure consist of three bilayers. Key words: Lipid structure; Stratum corneum; X-ray diffraction protein structure 1. Introduction One of the routes of drugs administration, which is rapidly becoming more popular, is the transdermal route. One of the major problems in transdermal drug delivery is the slow penetration rate of drugs through the skin. The main barrier of the skin is the upper layer, the stratum corneum, which consists of corneo- cytes embedded in lipid lamellar regions. It has been found [ll that the main transport route of drugs, or other substances, is located in the lipid regions of the stratum corneum and that thus the barrier function of the skin is found in these lipid regions. In order to * Corresponding author. Fax: + 31 071 274277. ’ Sponsored by the ‘Nederlandse organisatie voor wetenschappelijk onderzoek’ (NWO). Abbreviations: d, repeat distance; IQ, intensity; n, order of the diffraction peak; N, number of unit cells; Q, scattering vector; A, wave length; 0, scattering angle; p(x), electron density; x, distance perpendicular to basal plane. obtain a better understanding of the barrier function, information on the lipid organization of the stratum corneum is of predominant importance. Besides methods such as Fourier Transform In- fraRed spectroscopy, Electron Spin Resonance and Nuclear Magnetic Resonance, the structure has also been studied with X-ray diffraction techniques. Using the latter technique, the structure of rat [2] and human stratum corneum [2-91 was studied. Swanbeck [3] and Wilkes [21 explained the diffraction patterns by a sheet of lipids surrounding the keratin filaments. However, through later electron microscopy studies [lo], it be- came clear that the lipids are arranged in lamellae in the intercellular spaces. The existence of these lamellar phases was confirmed by more recent X-ray diffraction studies [7-91. The structure of hairless mouse stratum corneum was studied by White et al. [ll], who found that the lipids are arranged in a lamellar structure with a repeat distance of 13.1 nm and that the lateral packing of the lipids is partly orthorhombic, partly hexagonal and partly liquid. When the samples were Elsevier Science B.V. SSDI 0005-2760(93)E0263-J