Diverse natural phenolic compounds show inhibition activity of intestinal α-glucosidases, which may constitute the molecular basis for their ability to control systemic glycemia. Additionally, phenolics can modify mRNA expression for proteins involved in nutritional, metabolic or immune processes. To explore the possibility that phenolics can regulate the mRNA expression, enzymatic activity, and protein synthesis/processing of intestinal Maltase-Glucoamylase (MGAM) and Sucrase-Isomaltase (SI), small intestinal explants from Balb/c mice were cultured for 24 h in the presence or absence of gallic acid, caffeic acid, and (+)-catechin at 0.1, 0.5, and 1 mM. We measured the levels of MGAM and SI mRNA expression by qRT-PCR, maltase and sucrase activities by a standard colorimetric method and the molecular size distribution of MGAM and SI proteins by western blotting. mRNA expression for MGAM was induced by the three phenolic compounds at 0.1 mM. mRNA expression for SI was induced by caffeic and gallic acids, but not by (+)-catechin. Caffeic acid was the most effective inducer of mRNA expression of these enzymes. Total maltase and sucrase activities were not affected by treatment with phenolics. The proportion of high molecular size forms of MGAM was significantly increased by two of the three phenolic compounds, but little effect was observed on SI proteins. Thus, changes in the protein synthesis/processing, affecting the proportions of the different molecular forms of MGAM, may account for the lack of correlation between mRNA expression and enzymatic activity.

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. 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. 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. 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. (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.