Identification and characterization of N-acetyl-2,3-dehydro-2-deoxyneuraminic acid as a metabolite in mammalian brain

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Abstract
N-acetyl-2,3-didehydro-2-deoxyneuraminic acid (NADNA) was identified in bovine and in rat brain. Identification was made by mass spectrometric and GLC analysis of the per(trimethylsilyl) derivative of the purified brain compound. CNS NADNA hitherto has escaped detection; it behaves chromogenically and chromatographically during purification on ion-exchange chromatography as free N-acetylneuraminic acid (NANA) that also occurs in brain. Although NADNA is a dehydro analog of NANA, brain NANA does not give rise to NADNA as an artifact during its purification from brain. Three hours after intracranial injection of [14C]-N-acetylmannosamine ([14C]ManNAc) [14C]NANA was detected but no [14C]NADNA in rat brain. ManNAc is a brain NANA precursor, and at this time, formation of CMP-[14C]NANA from [14C]ManNAc is at a maximum. This finding precludes decomposition of CMP-NANA as a source of brain NADNA. Upon intracranial injection of [14C]ManNAc, [14C]NADNA became detectable at 19 h and reached a maximum level around 40 h later; this maximum of labeling of NADNA coincides with the maximum label in brain sialo conjugate-NANA. The occurrence of NADNA in mammalian brain is demonstrated and may derive enzymatically from brain sialo conjugates.

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