Disaccharidase Inhibitory Activity of Thai Plant Extracts

<b>Background/Objectives</b>: Intestinal α-glucosidases, including maltase, sucrase, and trehalase, are key enzymes responsible for the final steps of carbohydrate digestion. Although Thai medicinal plants possess diverse bioactivities, most previous studies on plant-derived α-glucosidase inhibitors have focused on single-enzyme assays, primarily maltase, and lack systematic comparison of the three major intestinal disaccharidases-maltase, sucrase, and trehalase. This study aimed to determine the kinetic properties of rat intestinal α-glucosidases and evaluate the inhibitory potential of selected Thai plant extracts. <b>Methods</b>: Rat small-intestinal S9 fractions, post-mitochondrial supernatant obtained by centrifugation at 9000× <i>g</i>, containing soluble enzymes and microsomal components responsible for disaccharidase activity, were prepared and disaccharidase activities were quantified using the glucose oxidase-peroxidase method. Kinetic parameters were obtained from Eadie-Hofstee plots using maltose, sucrose, and trehalose as substrates. Fourteen Thai plant extracts (<i>Oryza sativa</i>, <i>Cratoxylum formosum</i>, <i>Garcinia cawa</i>, <i>Aganosma marginata</i>, <i>Polyalthia evecta</i>, <i>Ellipeiopsis cherrevensis</i>, <i>Ancistrocladus tectorius</i>, <i>Micromelum minutum</i>, and <i>Microcos tomentosa</i>) and isolated compounds (Bergapten, Eurycomalactone, Lupinifolin, Osthole) were assessed at 100 and 250 µg/mL for inhibition of maltase, sucrase, and trehalase. <b>Results</b>: Maltase exhibited the highest substrate affinity based on the lowest Km value. Among the tested samples, the 80% ethanol extract of <i>Microcos tomentosa</i> (MT80) inhibited maltase, sucrase, and trehalase activities by approximately 10-60% at 250 µg/mL, and was the only extract showing consistent inhibition across all three enzymes. Other extracts showed selective inhibition toward one or two enzymes. <b>Conclusions</b>: These findings indicate that MT80 possesses a broad-spectrum inhibitory profile against major intestinal α-glucosidases, suggesting a potential advantage for comprehensive regulation of postprandial glucose excursions and supporting its candidacy as a source of novel α-glucosidase inhibitors.