Inhibition of human and rat sucrase and maltase activities to assess antiglycemic potential: optimization of the assay using acarbose and polyphenols

We optimized the assays used to measure inhibition of rat and human alpha-glucosidases (sucrase and maltase activities), intestinal enzymes which catalyze the final steps of carbohydrate digestion. Cell-free extracts from fully differentiated intestinal Caco-2/TC7 monolayers were shown to be a suitable source of sucrase-isomaltase, with the same sequence as human small intestine, and were compared to a rat intestinal extract. The kinetic conditions of the assay were optimized, including comparison of enzymatic and chromatographic methods to detect the monosaccharide products. Human sucrase activity was more susceptible than the rat enzyme to inhibition by acarbose (IC50 (concentration required for 50% inhibition) = 2.5 +/- 0.5 and 12.3 +/- 0.6 muM, respectively), by a polyphenol-rich green tea extract, and by pure (-)-epigallocatechin gallate (EGCG) (IC50 = 657 +/- 150 and 950 +/- 86 muM respectively). In contrast, the reverse was observed when assessing maltase activity (e.g. , EGCG: IC50 = 677 +/- 241 and 14.0 +/- 2.0 muM for human and rat maltase, respectively). 5-Caffeoylquinic acid did not significantly inhibit maltase and was only a very weak inhibitor of sucrase. The data show that for sucrase and maltase activities, inhibition patterns of rat and human enzymes are generally qualitatively similar but can be quantitatively different.