Sialic Acid Content of the Brain

The human brain is extremely rich in sialic acids (9 carbon back bone acidic amino sugars). The predominant form of sialic acid in the mammalian brain is N-Acetylneuraminic acid (Neu5Ac), even in most mammals where other tissues can be rich in a different form called N-Glycolylneuraminic acid (Neu5Gc). Most brain sialic acids are found on gangliosides which are enriched on the membrane of neurons near synapses. Early in development, long chains of sialic acid polymers (polysialic acid) are also found on neuronal cell adhesion molecules (NCAM). These reappear in adults during neuronal remodeling in places such as the hippocampus. Human cerebellar gray matter has a sialic acid content 3 X hat of cerebellar white matter and 15 x higher than the many other large organs. The sialic acid concentration in the left lobe is 22% higher than that in the right lobe. The total sialic acid concentration in the human brain is 2 to 4 times higher than that in eight other mammalian species analyzed, including chimpanzees, which were the only other hominid species. These  findings need to be confirmed in lager sample sizes which include other great ape species.