α-glucosidase inhibitors from java tea Orthosiphon aristatus Miq

Diabetes is a metabolic disorder where the body fails to utilize the ingested glucose properly. Type 2 diabetes is characterized by insulin resistance, which may be combined with relatively reduced insulin secretion. An effective strategy for type 2 diabetes therapy is to suppress glucose level through inhibition of intestinal α-glucosidase. Orthosiphon aristatus (Blume) Miq. (Java tea) known in Thai as “Ya-Nuad-Meo” have been recorded for in vivo hyperglycemia. In our research, crude extracts from leaves and twigs of O. aristatus prepared by two different extraction methods-decoction and maceration were screened for a-glucosidase inhibition. Apparently, the leave extract prepared by decoction with hot water showed more potent inhibition. Bioassay-guided fractionation of the aqueous extract from leaves led to the isolation of methyl caffeate (1), 3,4-dihydroxy benzaldehyde (2), methyl rosmarinate (3) and rosmarinic acid (4). The isolated compounds inhibited maltase and sucrase with IC50 values in the range of 0.061-0.738 mM, which are equipotent to standard antidiabetic drug acarbose. Furthermore, the kinetic investigation revealed that maltase was inhibited by methyl rosmarinate and rosmarinic acid through mixed-type whereas sucrase was inhibited through mixed-type and competitive manners.