| Research Abstract |
As to the etiology of the aging of the nervous system, we have studied on the effects of endogenous toxic substance. In this project, we looked at the lysosphingolipids, especially sphingosine, which are devoid of fatty acids in the sphingolipid molecule, abundant lipids in the nervous tissues. Lysosphingolipids are so toxic because of the absence of fatty acids and the presence of free amino base, that cells are killed by a few uM of the lipids. Recently we have developed a sensitive assay method of these lysosphingolipids including sphingosine, galactosylsphingosine and lysosulfatide, using high-performance liquid chromatography, and demonstrated the natural occurrence of these compounds in normal nervous tissues. Among them, sphingosine was the most abundant and the tissue concentration was about 100 pmol/mg protein. We investigated the detoxication mechanism of this highly toxic substance and found that sphingosine is very rapidly acylated to form ceramide which is no longer cytoto
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xic. When the sphingosine was incubated with UDP-glucose or UDP-galactose in the presence of microsomes, glucosylsphingosine and galactosylsphingosine were synthesized, respectively, which are still toxic, buy the reaction rate was very slow and the Km values were high, indicating that the main pathway of the sphingosine metabolism was acylation rather than glycosylation.
It has been known that lysoganglioside GM2 is accumulated in the brain of patients with GM2 gangliosidosis. We have developed a sensitive assay method of monosialo lysogangliosides using HPLC. This method is essentially the same as for the assay method of sphingosine. Using the method, We found the natural occurrence of lysoganglioside GM1 in human, murine and bovine brain at a concentration of 0.2-2 pmol/mg protein. In the brain from patients with GM1 and GM2 gangliosidosis, several hundred times more accumulation of lyso GM1 and GM2, respectively, were observed.
Chronological study of the concentration of the lysosphingolipids revealed that galactosylsphingosine concentration increased with age but that of sphingosine did not change with age. Less
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