Corosolic acid (CRA) is a substance extracted from Lagerstroemia speciosa L. and has been reported to have biological activities in invitro and experimental animal studies. In this study, 31 subjects were orally administered 10 mg CRA or a placebo, on different occasions, in a capsule 5 min before the 75-g oral glucose tolerance test (OGTT) in a double-blind and cross-over design. Nineteen subjects had diabetes, seven had impaired glucose tolerance, one had impaired fasting glucose, and four had normal glucose tolerance according to the 1998 WHO criteria. There were no significant differences in plasma glucose levels before and 30 min after the administration. CRA treatment subjects showed lower glucose levels from 60 min until 120 min and reached statistical significance at 90 min. In this study, we have shown for the first time that CRA has a lowering effect on postchallenge plasma glucose levels in vivo in humans.
Corosolic acid (CRA) is a substance extracted from Lagerstroemia speciosa L. (Banaba) and has been reported to have biological activities in in vitro and experimental animal studies, In a study using KK-Ay mice (a model of type 2 diabetes), elevation of plasma glucose levels in the group fed with a diet containing the extract from the leaf of L. speciosa was significantly suppressed compared to the control group .In studies using Ehrlich ascites tumour cells and 3T3-L1 cells, glucose uptake was stimulated by the extract from the leaf of L. speciosa, Recently, Judy et al. described the anti-diabetic activity of the leaf extract (including 1% CRA) in humans in a dosedependent manner,It is known that the main content of the plant leaf extract is polyphenol, which has a blood glucose lowering effect. Screening of the compounds with blood glucose lowering activities.from the crude extract of L. speciosa leaf elucidated lagerstroemin (a kind of polyphenol) as the fraction with glucose lowering activity, but it was not enough to explain the glucose lowering effect of the total leaf extract in vivo CRA is contained in the leaf of L. speciosa, but it is still unclear whether CRA per se has an effect on a glucose challenge in humans. In this study, we have clarified the effect of CRA on postchallenge plasma glucose levels in vivo in humans.