Human milk oligosaccharides are resistant to enzymatic hydrolysis in the upper gastrointestinal tract

Abstract

Background: Human milk oligosaccharides (HMOs) show a complexity and variety not found in milk of any other species. Although progress has been made in the past 3 decades with regard to identification and structural characterization of HMOs, not much is known about the physiologic functions of HMOs. Objective: As a prerequisite for biological activity in infant metabolism, HMOs have to resist enzymatic hydrolysis in the gastrointestinal tract. To assess the extent to which selected HMOs are hydrolyzed, we carried out in vitro digestion studies using enzyme preparations of human and porcine pancreas and intestinal brush border membranes (BBMs). Design: Fractions of HMOs, including structurally defined isolated oligosaccharides, were digested for up to 20 h with human pancreatic juice and BBMs prepared from human or porcine intestinal tissue samples. HMOs were incubated by using a porcine pancreatic homogenate and BBMs as enzyme sources. HMOs and digestion products were identified by mass spectrometry and anion-exchange chromatography. Additionally, free D-glucose, L-fucose, and N-acetylneuraminic acid were determined enzymatically. Results: Whereas maltodextrin (control) was rapidly and completely hydrolyzed, neutral and acidic HMOs showed a profound resistance against pancreatic juice and BBM hydrolases. However, cleavage of most of the HMOs was achieved by using a pancreatic homogenate containing intracellular, including lysosomal, enzymes in addition to secreted enzymes. Conclusions:The results of this study strongly suggest that HMOs are not hydrolyzed by enzymes in the upper small intestine. Although intact HMOs may be absorbed, we postulate that a majority of HMOs reach the large intestine, where they serve as substrates for bacterial metabolism. Therefore, HMOs might be considered the soluble fiber fraction of human milk.Am J Clin Nutr 2000;71:1589-96. KEY WORDSHuman milk, oligosaccharides, enzymatic hydrolysis, pancreatic enzymes, brush border membranes, matrix-assisted laser desorption ionization mass spectrometry, MALDI-MS

The role and potential of sialic acid in human nutrition

“…However, Brand-Miller et al (1998) demonstrated with breath hydrogen methodology that most HMOs resist digestion in the small intestine of breast-fed infants and undergo fermentation in the colon. Studies in vitro have also confirmed that sialic acid is not released from the incubation of HMOs with pancreatic and mucosal enzyme mixtures (Engfer et al, 2000). The quantities of oligosaccharides in the urine and feces of breast-fed infants are also much higher than those in formula-fed infants (about 9:1 in urine and 62:1 in feces) (Newburg, 2000).…”

Evolution of milk oligosaccharides and lactose: a hypothesis

“…Much less is known about the exact fate of eutherian milk oligosaccharides. Human milk oligosaccharides (HMOs) are resistant to enzymatic hydrolysis by brush border intestinal lactase (Engfer et al, 2000) and the majority appears to survive passage through the small intestine and to enter the colon, where they are subjected to fermentation by colonic bacteria (Brand-Miller et al, 1998).…”

Biome engineering‐2020

“…HMO is of no energetic value for the infant since it resists enzymatic hydrolysis by host enzymes (Engfer et al ., 2000). This seemingly wasteful biosynthesis represents a paradox.…”