LAUSR

Abstract Milk sialyllactose (SL) and sialic acids (SA) are considered to be crucial for brain composition and development. To investigate their metabolic fate, we administered 13C-labelled 3′SL (13C-3′SL) and 13C-N-acetylneuraminic acid (13C-Neu5Ac) to NMRI mice. From per oral and intravenous (i.v.) applications, an organ specific 13C-enrichment can be excluded. The 13C-enrichment after oral application (o.a.) was lowest in brain tissue and not detectable after i.v. in any organ. The presence of 13C-Neu5Ac in urine after the o.a. of both labelled components demonstrated that 13C-Neu5Ac was taken up by gut epithelial cells. Because plasma 13C-enrichment increased over time, when the oral 13C-bolus had reached the lower gastrointestinal tract, an involvement of intestinal epithelial cells and/or gut microbiota in the metabolism of 13C-3′SL and/or 13C-Neu5Ac could be assumed. Hence, SL or Neu5Ac might influence the gut brain axis by effects within the gastrointestinal tract rather than being directly incorporated into the brain.