In vivo conversions of cerebroside and ceramide in rat brain

Abstract

Lignoceric acid-1-C14 was used to make lignoceroyl psychosine (kerasin) and stearic acid-1-C14 to make stearoyl sphingosine (ceramide). Emulsions of the labeled sphingolipids were injected directly into the brains of young rats and the resultant lipoidal metabolic products were examined for radioactivity.Most of the metabolized C14 was found in the ester-linked fatty acids, particularly in the acids corresponding to the ones injected. This shows that the lignocerate and stearate were released from amide linkage and incorporated into other lipids. Activity was found also in other fatty acids and cholesterol, showing that the released fatty acids were partially degraded to acetate. Ceramide and sphingomyelin showed relatively high activities, and the fatty acids of these lipids were labeled primarily in the carboxyl group. This suggests that ceramide is formed directly from cerebroside via a galactosidase, and that the ceramide is converted to free fatty acids as well as sphingomyelin. Little activity was found in the hydroxy cerebrosides and sulfatides, suggesting that neither of the injected lipids is directly converted to these glycolipids. Ester-linked lignocerate was found to occur naturally in brain.