LC-MS/MS quantification of N-acetylneuraminic acid, N-glycolylneuraminic acid and ketodeoxynonulosonic acid levels in the urine and potential relationship with dietary sialic acid intake and disease in 3- to 5-year-old children

AbstractRed meat and dairy products contain high sialic acid (Sia) levels, but the metabolic fate and health impact in children remain unknown. Theaims of the present study were to quantify the levels of urinary Sia N-acetylneuraminic acid (Neu5Ac), N-glycolylneuraminic acid (Neu5Gc)and ketodeoxynonulosonic acid (KDN) and to determine their relationship with dietary Sia intake. Spot urine samples were collected from386 healthy children aged 3 (n 108), 4 (n 144) and 5 (n 134) years at 06.30–07.00, 11.30–12.00 and 16.30–17.00 hours. Food intake levelswere recorded on the day of urine sample collection. Sia levels were quantified using LC–MS/MS with [ 13 C 3 ]Sia as an internal standard. Wefound that (1) total urinary Sia levels in healthy pre-school children ranged from 40 to 79mmol Sia/mol creatinine; (2) urinary Sia levelswere independent of age and consisted of conjugated Neu5Ac (approximately 70·8%), free Neu5Ac (approximately 21·3%), conjugatedKDN (approximately 4·2%) and free KDN (approximately 3·7%); Neu5Gc was detected in the urine of only one 4-year-old girl; (3)total urinary Sia levels were highest in the morning and declined over time in 4- and 5-year-old children (P,0·05), but not in 3-year-old children; (4) Sia intake levels at breakfast and lunch were approximately 2·5 and 0·16mg Sia/kg body weight; and (5) there was nosignificant correlation between dietary Sia intake levels and urinary Sia levels. Urinary Sia levels varied with age and time of day, butdid not correlate with Sia intake in 3- to 5-year-old children. The difference in urinary Sia levels in children of different age groups suggeststhat the metabolism and utilisation rates of dietary Sia are age dependent.Key words: LC–MS/MS: Urinary sialic acids: Pre-school children: Dietary sialic acids