Branched-chain and odd-numbered fatty acids and aldehydes in the nervous system of a patient with deranged vitamin B12 metabolism

Abstract

A mixture of isomers of methylhexadecanoic acid was isolated from glycerolipids of brain, spinal cord, and sciatic nerve of a patient who died from methylmalonic aciduria, a disease in which vitamin B12 is not converted to deoxyadenosyl B12. The isomers were identified by gas–liquid chromatographic–mass spectrometric analyses, and the data indicated that the points of methyl branching are located predominantly on the even-numbered carbon atoms. The concentration of these branched-chain acids among the glycerolipid fatty acids in the patient's nervous system was at least 0.3–0.9%, while the control tissues contained no more than a trace amount, if any, of these acids. In the spinal cord, these branched acids were distributed among all phosphatides and were in highest concentration on the β position of phosphatidylcholine. On the other hand, most extraneural tissues contained these acids in much lower concentrations; there were only trace amounts in liver, kidney, muscle, and skin, and 0.2, 0.2, and 0.5% in total ester-linked fatty acids in spleen, duodenum, and lung, respectively. A second abnormality was the 6–13-fold increase in 15:0 and 17:0 fatty acids in all of the glycerolipids in the nervous system of the patient. This abnormality was also observed to a somewhat smaller extent in every extraneural tissue examined. The C17, aldehydes of phosphatidylethanolamine plasmalogens from the spinal cord of the patient were identified by converting them to the corresponding dimethylacetals. 17:0 dimethylacetal accounted for nearly 10% of total dimethylacetals. There were no abnormalities in total lipids, cholesterol, cerebrosides, and sphingomyelins.

Keywords

• gas–liquid chromatography–mass spectrometry
• dimethylacetal
• methylmalonic aciduria
• brain
• spinalcord
• sciatic nerve