Isotopic labeling of milk disialogangliosides (GD3)

The most abundant ganglioside group in both human milk and bovine milk during the first postnatal week is ganglioside GD3. This group of disialogangliosides forms up to 80% of the total ganglioside content of colostrum. Although dietary gangliosides have shown biological activity such as improvement of cognitive development, gastrointestinal health, and immune function, there is still a gap in our understanding of the molecular mechanisms governing its uptake and the metabolic processes affecting its bioavailability. The use of isotopically labeled ganglioside to track the bioavailability, absorption, distribution, and metabolism of gangliosides may provide key information to bridge this gap. However, isotope labeled GD3 is not commercially available and its preparation has not been described. We report for the first time the preparation of labeled GD3 with stable isotopes. Using alkaline hydrolysis, we were able to selectively remove both acetyl groups from the tetrasaccharide portion of GD3 without promoting significant hydrolysis of the ceramide portion of the molecule to generate N-deacetyl-GD3 (Neu5α2-8Neu5-GD3). The N-deacetyl-GD3 was then chemoselectively re-acetylated in aqueous medium using deuterated acetic anhydride in the presence of Triton X 100 to produce ²H₆-GD3 {GD3[(Neu5Ac-11-²H₃)-(Neu5Ac-11-²H₃)]}. This method provided ²H₆-GD3 with approximately 60% yield. This compound was characterized by proton nuclear magnetic resonance (¹H NMR) and liquid chromatography mass spectrometry (LC-MS). The oral absorption of the ²H₆-GD3 was demonstrated using a Sprague-Dawley weaning rats. Our results indicate that some ingested labeled milk gangliosides are absorbed and transported into the bloodstream without modification.