Milk glucosidase activity enables suckled pup starch digestion

ᅟ: Starch 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. Objective: The 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. Methods: Maltase-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. Results: Four 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.