Incorporation of orally applied (13)C-galactose into milk lactose and oligosaccharides

Biosynthesis and functions of human milk oligosaccharides (HMO) are not well known. A typical housekeeping enzyme, beta1,4-galactosyltransferase, links galactose to glucose to form lactose which is then used as backbone for the assembly of HMO. We investigated whether milk lactose and HMO may be lab...

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Bibliographic Details
Published in:Glycobiology (Oxford) 2006-06, Vol.16 (6), p.477-487
Main Authors: Rudloff, Silvia, Obermeier, Susanne, Borsch, Christian, Pohlentz, Gottfried, Hartmann, Rudolf, Brösicke, Herbert, Lentze, Michael J, Kunz, Clemens
Format: Article
Language:English
Subjects:
Administration, Oral
Breath Tests
Carbon Radioisotopes
Chromatography, Ion Exchange
Chromatography, Thin Layer
Female
Galactose - administration & dosage
Galactose - metabolism
Humans
Lactation - metabolism
Lactose - biosynthesis
Lactose - urine
Milk, Human - chemistry
Milk, Human - metabolism
Oligosaccharides - biosynthesis
Oligosaccharides - urine
Pregnancy
Spectrometry, Mass, Fast Atom Bombardment
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Summary:Biosynthesis and functions of human milk oligosaccharides (HMO) are not well known. A typical housekeeping enzyme, beta1,4-galactosyltransferase, links galactose to glucose to form lactose which is then used as backbone for the assembly of HMO. We investigated whether milk lactose and HMO may be labeled in vivo by an orally given (13)C-galactose bolus. Eleven exclusively breastfeeding mothers were given a (13)C-galactose bolus at the end of their breakfast. Milk and urine samples from each nursing up to 36 h were analyzed for carbohydrate composition by high-performance thin-layer chromatography, high-pH anion-exchange chromatography, and fast atom bombardment mass spectrometry. (13)C enrichment of milk fractions, urinary carbohydrates, lactose, and oligosaccharides as well as of breath CO(2) was determined by isotope ratio mass spectrometry. Up to 10% of the orally given galactose bolus was directly transported to the mammary gland and incorporated into milk components. Characteristic for most milk samples was the appearance of two (13)C-peaks, the first immediately after the (13)C-bolus was taken and the second on the next morning. The highest (13)C enrichment was found in lactose followed by neutral and acidic oligosaccharides. In breath samples, the (13)C-excretion followed the same pattern as in milk. (13)C nuclear magnetic resonance of isolated lactose revealed (13)C only at C(1)-atom of galactose and C(1)-atom of glucose. This label was without any exception at the same position as the (13)C-label of the orally applied galactose. Neutral and acidic HMO can easily be (13)C-labeled in vivo which facilitates investigations of their metabolic fate in infants.
ISSN:0959-6658