Metabolic fate of intravenously administered N-acetylneuraminic acid-6-¹⁴C in newborn piglets

Background: Sialic acid (N-acetylneuraminic acid), a component of gangliosides and sialylglycoproteins, may be a conditional nutrient in early life because endogenous synthesis is limited. The aim of this study was to investigate the metabolic fate of intravenously administrated N-acetylneuraminic acid 6¹⁴C (sialic acid) in piglets. Method: Three-day-old male domestic piglets (Sus scrofa) were injected via the jugular vein with 5 μCi (11-12x10⁶ cpm) of N-acetylneuraminic acid-6¹⁴C (specific activity of 55 mCi/mmol). Blood samples were collected at regular intervals over the next 120 min. The organs were then removed and the urine collected for determination of residual radioactivity. Results: Within 2 min of injection, 80% of the activity was removed from the blood and by 120 min the remaining activity approached 8%. At 120 min, the brain contained significantly more radioactivity (cpm/g tissue) than the liver, pancreas, heart and spleen, but less than the kidneys. Within the brain, the percentage of total injected activity was highest in the cerebrum (0.175 ± 0.008) followed by the cerebellum (0.0295 ± 0.006, p = 0.00006) and the thalamus (0.029 ± 0.006, p = 0.00003). Conclusions: An exogenous source of sialic acid is capable of crossing the blood-brain barrier and being taken up into various tissues. The findings suggest that dietary sources of sialic acid may contribute to early brain development in newborn mammals.