Two ceramide subfractions detectable in Cer(AS) position by HPTLC in skin surface lipids of non-lesional skin of atopic eczema

The non-involved skin of atopic eczema (NEAE) is characterized by severe dryness and an impaired barrier function of the stratum corneum as indicated by an increased transepidermal water loss. Previous studies have demonstrated that this barrier impairment coincides with marked alterations in the amount and composition of stratum corneum ceramides. The aim of this study was to identify specific alterations in NEAE that may be used in the diagnosis of the atopic eczema. Using a classical procedure for high performance thin layer chromatography we could confirm earlier results: apart from Cer(EOH), which contains ω-hydroxy fatty acid (O) ester-linked to linoleic acid (E) and amide-linked to 6-hydroxy-4-sphingenine (H), the quantities of all ceramide fractions were significantly decreased. Furthermore, Cer(EOH)/Cer(total) was significantly increased, whereas the percentage of Cer(EOS), which contains sphingosine (S), and Cer(NP), which contains non- hydroxy fatty acid (N) amide-linked to phytosphingosine (P), were significantly decreased. Using a modified procedure for high performance thin layer chromatography we could demonstrate the formation of a double peak in the position of Cer(AS), which contains α-hydroxy fatty acid (A), in lipids of NEAE. The subfractions of the double peak comprised 15% and 12% of Cer(total). MALDITOF mass spectrometry suggested that the double peak was formed by a homologous series of mono-hydroylated and mono-unsaturated ceramides of different chain length, e.g., Cer(AS) subfractions containing either (C_16,18) or (C_22,24,26) α-hydroxy fatty acids. In contrast, in normal skin a single peak in Cer(AS) position, which comprised 22% of Cer(total), was mainly formed by the long chain subfraction. In some cases this single peak displayed a small shoulder at its right flank, but never showed a clear peak separation when developed with NEAE samples. Furthermore, even in senile xerosis, or in either non-involved skin of psoriasis or seborrhoic eczema, only a single peak occurred in Cer(AS) position. Accordingly, the double peak might be specific for NEAE and turn out to be a marker for atopic eczema.