Milk glucosidase activity enables suckled pup starch digestion

Abstract

ᅟStarch requires six enzymes for digestion to free glucose: two amylases (salivary and pancreatic) and four mucosal maltase activities; sucrase-isomaltase and maltase-glucoamylase. All are deficient in suckling rodents.ObjectiveThe objective of this study is to test 13C-starch digestion before weaning by measuring enrichment of blood 13C-glucose in maltase-glucoamylase-null and wild-type mice.MethodsMaltase-glucoamylase gene was ablated at the N-terminal. Dams were fed low 13C-diet and litters kept on low 13C-diet. Pups were weaned at 21 days. Digestion was tested at 13 and 25 days by intragastric feeding of amylase predigested 13C-α-limit dextrins. Blood 13C-glucose enrichment was measured by gas chromatography combustion isotope ratio mass spectrometry (GCRMS) using penta-acetate derivatives.ResultsFour hours after feeding, blood 13C-glucose was enriched by 26 × 103 in null and 18 × 103 in wild-type mice at 13 days and 0.3 × 103 and 0.2 × 103 at 25 days (vs. fasting p = 0.045 and p = 0.045). By jejunal enzyme assay, immunohistochemistry, or Western blots, there was no maltase activity or brush border staining with maltase-glucoamylase antibodies at 13 days, but these were fully developed in the wild-type mice by 25 days. In 13-day null mice, luminal contents were stained by maltase-glucoamylase antibodies. Lactating the mammary gland revealed maltase-glucoamylase antibody staining of alveolar cells. Reverse transcription/polymerase chain reaction (RT/PCR) of lactating glands revealed a secreted form of maltase-glucoamylase.Conclusions(1) 13C-α-limit dextrins were rapidly digested to 13C-glucose in 13-day mice independent of maltase-glucoamylase genotype or mucosal maltase activity. (2) This experiment demonstrates that a soluble maltase activity is secreted in mouse mother’s milk which enables suckling pup starch digestion well before brush border enzyme development. (3) This experiment with 13C-α-limit dextrins needs to be repeated in human breast fed infants.

The digestion of complementary feeding starches in the young child

“…Ct‐MGAM is the last α‐glucosidase to develop and is developed fully only after birth . We have reported that α‐glucosidase is also present in milk, and enables suckling mouse pups to digest starch . Whether human milk also has α‐glucosidase activity is unknown.…”

Molecular biology of the gut

“…Unraveling of the structural-functional relationships of these components as well as their biosynthetic and processing pathways has experienced a huge progress in the last few years, so that their malfunctioning and association with the onset of intestinal disorders and symptoms can be clarified. Particularly, the cell biology and pathobiochemistry of intestinal disaccharidases has occupied a major part of this workshop by virtue of the primordial function of the sucrase-isomaltase enzyme complex in carbohydrate and human starch digestion to glucose (α-glucogenesis) [ 1 ]. Sucrase-isomaltase is the major brush border enzyme with almost 5–7 % protein content of the entire brush border membrane and is the enzyme that is responsible for the digestion of almost all disaccharides that are transported to the intestinal lumen [ 2 ].…”

Small intestine mucosal α-glucosidase: A missing feature of in vitro starch digestibility

“…Mucosal α-glucosidase, different from α-amylase, exists since birth,306 and young infants have similar amounts of mucosal α-glucosidase as adults (P. C. Lee, Werlin, Trost, & Struve, 2004). It has been shown in mice that maltase activity is 308 secreted before brush border enzyme development is completed; this enables sucking 309 pups to digest starch well(Nichols, et al, 2012a). In pigs, the activity of MGAM seems to 310 increase along with postnatal growth(Lackeyram, Nichols, & Fan, 2007).The longitudinal distribution of total maltase activity (contributed from all four domains)312 in the small intestine is even, but glucoamylase activity (mainly from CtMGAM) rises steadily and reaches its highest near the ileocecal valve(Triadou, Bataille, & Schmitz, 314 1983).…”