Structure determination of glycosphingolipids of cultured human keratinocytes

From cultured human keratinocytes, seven glycolipid fractions were isolated by DEAE and silica-gel column chromatographies, and further by HPLC on a silica-gel column. By means of 1H-NMR spectroscopy, fast atom bombardment mass spectrometry and GLC-mass spectrometry, one fraction was determined to contain acylglucosylceramides, which consist of amide linked omega-hydroxy fatty acids (C30:0, C30:1, C32:1 and C34:1), fatty acids linked to the omega-hydroxy fatty acids through ester linkages (C14:1, C16:1, C18:1 and C18:2), a long-chain base (d18-sphingenine), and beta-glucose. Five of the other fractions contained glucosylceramides, and the seventh fraction contained a mixture of glucosylceramides and galactosylceramides. Glucosylceramides containing long-chain omega-hydroxy fatty acids, which are assumed to be immediate precursors of the acylglucosylceramides, were hardly detected in these glycolipid fractions. Six glucosylceramide fractions were separated due to differences in their fatty acids and sphingosines. On comparison with the results reported in our previous paper, the acylglucosylceramide content of the cultured human keratinocytes was about half that of human epidermis. Under the culture conditions used, the human keratinocytes did not differentiate into granular or horny cells. Taken together, the results suggest that the synthesis of acylglucosylceramides is not activated much in the cultured keratinocytes, but would be more activated in differentiated cells.