We have applied sputtering using a buckminsterfullerene (C 60 ) ion beam for XPS analysis. A practical sputter rate of 2.4 nm min −1 for SiO 2 was obtained for sputtering an area of 5 mm × 5 mm using a 5 kV C 60 ion beam with an energy of 83 eV per carbon atom. Extremely low sputtering degradation of polytetrafluoroethylene was observed in these conditions. The results were compared with argon ion beam energies of 500 V and 5 kV. These are the first results utilizing a C 60 ion beam for XPS analysis with limited sputtering damage.

The stratum corneum (SC), the outermost barrier of mammalian bodies, consists of layers of cornified keratinocytes with intercellular spaces sealed with lipids. The insolubility of the SC has hampered in-depth analysis, and the SC has been considered a homogeneous barrier. Here, we applied time-of-flight secondary ion mass spectrometry to demonstrate that the SC consists of three layers with distinct properties. Arginine, a major component of filaggrin-derived natural moisturizing factors, was concentrated in the middle layer, suggesting that this layer functions in skin hydration. Topical application of metal ions revealed that the outer layer allowed their passive influx and efflux, while the middle and lower layers exhibited distinct barrier properties, depending on the metal tested. Notably, filaggrin deficiency abrogated the lower layer barrier, allowing specific metal ions to permeate viable layers. These findings elucidate the multi-layered barrier function of the SC and its defects in filaggrin-deficient atopic disease patients.

Pseudo-acylceramides with different acyl properties were investigated for their capacity to restore diminished barrier function in essential fatty acid-deficient rats. Daily topical applications of synthetic pseudo-acylceramides containing ester-linked linoleic acid caused a dose-dependent, significant reduction of transepidermal water loss (TEVL). Both other pseudo-acylceramides with ester-linked oleic acid or saturated alkyl chains and ordinary ceramides exhibited a poor effect on recovery of TEWL. Furthermore, pseudoceramide containing ether-linked linoleic acid, which is biologically inactive in terms of degradation by hydrolytic enzymes, also induced a significant and similar increase in the barrier function. This restoration of barrier function by pseudo-acylceramides with linoleic acid was accompanied by suppressed DNA synthesis in the EFAD rat epidermis. In UVB-irradiated guinea pig skin, topical applications of the pseudo-acylceramides with linoleic acid immediately after the exposure significantly reduced epidermal hyperplasia, secondary to markedly diminished barrier disruption, whereas linoleic acid itself did not. A comparison of both the anti-hyperplasia and the barrier recovery effects in the series of pseudo-ceramide derivatives examined revealed that the suppressive effect on the induced epidermal hyperplasia was paralleled by the recovery of the barrier defect in EFAD rats. These findings directly suggest that acylceramide with an ester-linked linoleic acid has an essential role in the epidermal permeability barrier. (J. Clin. Invest. 1994. 94:89-96.) Key words: permeability barrier -pseudo-acylceramide * epidermal hyperplasia * linoleic acid

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