Abstract
Free sphingosine, a material with multiple and potent biological activities, is known to occur in high concentration in mammalian epidermis. In the present study, thin-layer chromatography showed that in lipid extracts of human and pig stratum corneum, sphingosine forms a relatively stable compound with endogenous cholesteryl sulfate. NMR spectrometry of sphingosine and its hydrochloride, sulfate, and mixtures with cholesteryl or dodecyl sulfate showed that interaction with the organic sulfates constituted simple salt formation. Under neutral or weakly acidic conditions, such salts were only slightly dissociated and migrated on thin-layer chromatograms as discrete compounds. Thin-layer chromatography revealed undissociated salt formation between several long-chain bases and organic sulfates, and showed that their interaction is stoichiometric. However, undissociated salts were not formed between long-chain bases and fatty acids or phosphatidic acid. Undissociated salt formation may therefore be specific for organic bases and sulfates. It was concluded that the free sphingosine in the stratum corneum may be present as its cholesteryl sulfate salt and in this form be unavailable for permeation into the viable epidermal cells.
Highlights
Free sphingosine, a material with multiple and potent biological activities, is known to occur in high concentration in mammalian epidermis
In view of its broad biological activity [14], it was interesting to find that free sphingosine is present in relatively high concentration in mammalian epidermis [15, 16], especially the stratum corneum, where it appears to be produced by a ceramidase acting on the abundant ceramides in the tissue [17]
Interaction between cholesteryl sulfate and sphingosine in epidermal lipids When subjected to thin-layer chromatography in neutral or weakly acidic solvents, lipids from pig stratum corneum (Fig. 1A) or from human skin surface (Fig. 2A) usually revealed little material migrating in the regions expected for either cholesteryl sulfate or sphingosine
Summary
A material with multiple and potent biological activities, is known to occur in high concentration in mammalian epidermis. Thin-layer chromatography showed that in lipid extracts of human and pig stratum corneum, sphingosine forms a relatively stable compound with endogenous cholesteryl sulfate. Thin-layer chromatography revealed undissociated salt formation between several long-chain bases and organic sulfates, and showed that their interaction is stoichiometric. In the present study it was found that the sphingosine in epidermal stratum corneum may largely be sequestered as an undissociated salt with cholesteryl sulfate. This may have implications for the biological activity of sphingosine and for the role of cholesteryl sulfate in epidermal function, and might help to explain the variable specificity in biological activity that has been reported for long-chain bases. The stoichiometry of the interaction between long-chain bases and organic sulfates was examined by quantitative thin-layer chromatography
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