Inhibition of
alpha-glucosidase and
alpha-amylase delays the digestion of
starch and
disaccharides to absorbable
monosaccharides, resulting in a reduction of
postprandial hyperglycemia. Finding effective mammalian
alpha-glucosidase inhibitors from natural sources can be beneficial in the prevention and treatment of
diabetes mellitus. We investigated the inhibitory activity of
cinnamic acid derivatives against rat intestinal
alpha-glucosidase and porcine
pancreatic alpha-amylase in vitro. Among 11
cinnamic acid derivatives,
caffeic acid,
ferulic acid, and
isoferulic acid were the most potent inhibitors against intestinal
maltase with IC(50) values of 0.74 +/- 0.01, 0.79 +/- 0.04, and 0.76 +/- 0.03 mM, respectively, whereas
ferulic acid (IC(50) = 0.45 +/- 0.01 mM) and
isoferulic acid (IC(50) = 0.45 +/- 0.01 mM) were effective intestinal
sucrase inhibitors. However, all
cinnamic acid derivatives were found to be inactive in
pancreatic alpha-amylase inhibition. Kinetic analysis revealed that intestinal
maltase was inhibited by
caffeic acid,
ferulic acid, and
isoferulic acid in a mixed-inhibition manner. In addition,
ferulic acid and
isoferulic acid inhibited intestinal
sucrase in a mixed type manner, whereas
caffeic acid was a non-competitive inhibitor. The combination of
isoferulic acid and
acarbose showed an additive inhibition on intestinal
sucrase. This study could provide a new insight into naturally occurring intestinal
alpha-glucosidase inhibitors that could be useful for treatment of diabetes and its complications.