Metabolic fate and organ distribution of 13C-3′-sialyllactose and 13C-N-acetylneuraminic acid in wild-type mice – No evidence for direct incorporation into the brain

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.

Keywords

• 3′ sialyllactose
• N-acetylneuraminic acid
• Stable isotopes
• Metabolism
• Brain
• Wildtype mice