Approaches in the study of ganglioside metabolism

Placental transfer of (3H)-GM1 and its distribution to maternal and fetal tissues of the rat

The demonstration that ganglioside GM1 pretreatment reduced the ethanol induced neurobehavioral effects in adult pups exposed to ethanol in utero, prompted study to examine whether GM1 crosses the placenta and penetrates fetal tissues. The present results indicate that 3H-galactose labeled GM1 not only passes the placenta but also served as a substrate for the synthesis of polysialogangliosides, and remained in various tissues up to 48 h after maternal (3H)-GM1 administration.

Formation of ganglioside GD1b-lactone in rat brain from intracisternally administered GD1b

The presence of ganglioside GD1b, in lactone form GD1b-L, was ascertained in rat brain. The possible formation of GD1b-L from GD1b in brain was explored by the intracisternal injection of GD1b, 3H-labelled at the level of the terminal galactose. This was followed by recognition of the radioactive gangliosides formed at different times (1, 3, and 7 days) after injection. Whereas at 0 time after injection the only radioactive ganglioside was GD1b, after 1, 3, and 7 days other radioactive gangliosides were also found, thus indicating GD1b penetration into the brain tissue, followed by metabolic processing. Besides GD1b, the following radioactive gangliosides were recognized: GM1 and GM2, derived from GD1b degradation; GT1b, formed by the direct sialylation of GD1b; and GD1b-L, produced by metabolic lactonization. The radioactivity carried by GD1b-L was maximal 3 days after injection; its time course was different from that of the other gangliosides, suggesting that the process of lactonization is separate from that of both degradation and glycosylation. Under the same experimental conditions, some radioactive gangliosides also appeared in the liver, although in much smaller amounts than in brain. Radioactive GD1b-L could not be detected in liver, thus indicating that metabolic lactonization is a tissue- or organ-specific process.

Mouse liver gangliosides

The major gangliosides from mouse liver were purified and characterized by t.l.c., g.l.c., sialidase treatment, and a methylation study. GM3(NeuAc), GM3(NeuGc), GM2(NeuGc), GM1(NeuGc), and GDla(NeuGc, NeuGc) were identified. The structural identification of three of the gangliosides, GM2(NeuGc), GM1(NeuGc), and GDla(NeuGc, NeuGc), was supported by the results of 1H-n.m.r. analysis, and the structures of GM3(NeuGc), GM2(NeuGc), and GM1(NeuGc) were further confirmed by negative-ion fast-atom bombardment mass spectrometry. Ganglioside mapping showed that there was polymorphic variation of gangliosides in the liver of inbred strains of mice and that the major gangliosides were GM3(NeuGc) in WHT/Ht, GM2(NeuGc) in BALB/c and C3H/He, and GM2(NeuGc), GM1(NeuGc), and GDla(NeuGc, NeuGc) in ICR mice. Gangliosides containing N-acetylneuraminic acid, except for GM3(NeuAc), were not detected as major gangliosides in the strains of mice we analyzed.