Abnormalities of
ganglioside structure characterize the neoplastic state, and aberrant glycosylation has been implicated as underlying many new
tumor ganglioside structures. However, variations in
ceramide structure can also result in novel
tumor gangliosides. To address systematically this aspect of
ganglioside metabolism, we have initiated a study of the structures of the
ceramide species of an
oligosaccharide-homogeneous human
tumor-derived
ganglioside, GM2. The
ganglioside was isolated from
neuroblastoma tissue and purified by normal-phase high pressure liquid chromatography. Marked
ceramide heterogeneity was observed; 18 individual
ceramide species of
neuroblastoma GM2 were separated by reversed-phase high pressure liquid chromatography and collected. Their structures were determined by a combination of negative- and positive-ion fast atom bombardment mass spectrometry and collisionally activated dissociation tandem mass spectrometry of the underivatized
gangliosides. The striking finding was the detection of alpha-hydroxylation of a significant fraction of each of the major
fatty acid species (16:0, 18:0, 20:0, 22:0, and 24:1); alpha-hydroxylated species quantitatively represented almost one-fifth of the total
tumor GM2 species. Fatty acyl hydroxylation was also detected in the
ceramide of several other human
tumor gangliosides. In contrast, as previously known, fatty acyl hydroxylation was not detected in the normal human brain
gangliosides GM3, GM2, and GM1. We propose that aberrant
fatty acid alpha-hydroxylation is a novel and sometimes quantitatively significant characteristic of human
tumor ganglioside metabolism.