Dietary Sialic Acid and Cholesterol Influence Cortical Composition in Developing Rats

Human milk compared with infant formulas contains considerably more sialic acid (SA) and cholesterol. Because both compounds accumulate rapidly in the frontal cortex in infancy, it has been suggested these compounds may be conditionally essential nutrients for brain development. A limited number of animal studies demonstrate that dietary cholesterol and SA increase cortical cholesterol and SA concentrations, respectively, and enhance learning. No study to our knowledge has examined the effects of simultaneously increasing cholesterol and SA intake on brain cortex composition. Rats were provided with cholesterol (0 or 0.5% of diet weight) from conception until they were killed on postnatal day (P) 32. Litters were culled (P1) to 8 pups, weaned early (P17), and fed a diet (P17-32) with the same amount of cholesterol as the dam for that litter with 1 of 4 amounts of SA from casein glycomacropeptide estimated to provide 0, 20, 40, or 80 mg · kg⁻¹ · d⁻¹ SA. The brain cortex from 10-12 pups (all from different litters) was analyzed for each of the 8 cholesterol-SA groups. SA, cholesterol, and protein concentrations were measured in cortex. Cholesterol exposure from conception to P32 increased cortex weight (P = 0.003) and the concentrations of cortical cholesterol (P = 0.006), protein (P = 0.034), and ganglioside SA (P = 0.02). Independent of cholesterol feeding, SA fed from P17 to P32 increased the cortical ganglioside SA concentration (P-trend = 0.007). Dietary cholesterol and SA independently contribute to brain cortex composition during early brain development.