Analysis of galactosylsphingosine (psychosine) in the brain

A sensitive and specific analytical procedure has been developed for determination of galactosylsphingosine (psychosine) in the brain. The method takes advantage of two unusual properties of psychosine--the strong positive charge and the reactivity of the free amino group. It involves lipid extraction, separation from other lipids on a cation-exchange column (AG-50W), elimination of the last trace of galactosylceramide by silicic acid chromatography, dansylation of psychosine, Florisil and DEAE-Sephadex chromatography, and finally, fluorescent densitometry of dansylated psychosine separated by thin-layer chromatography. The detection limit is 5-10 ng/100 mg brain tissue when the standard procedure is followed exactly. Reliable determination can be made for 50 ng/100 mg or higher in the presence of 200,000-fold excess of other lipids and in the presence of 40,000-fold excess of galactosylceramide. The sensitivity can be increased fivefold by using a larger aliquot for the final determination. This analytical procedure has been successfully applied to demonstrate abnormal accumulation of psychosine in the brain in human, canine, and murine genetic galactosylceramidase deficiencies (globoid cell leukodystrophy).