although the current pharmacological and clinical data are still of a relatively preliminary nature, corosolic acid treatment in humans led to a decrease in post challenge plasma glucose levels. Interestingly, corosolic acid suppresses the differentiation and down-regulates the expression of peroxisome proliferator-activated receptor (PPAR-γ) as well as enhancer binding protein (C/EBP-α) mRNA in 3T3-L1 adipocytes. Also, it promotes glucose uptake . This suggests that unlike most other anti-diabetic drugs, corosolic acid,without increasing adiposity,reduces blood glucose.Moreover,in a KK-Ay mouse study,corosolic acid treatment reduced blood glucose and lowered plasma levels, indicating improved glucose metabolism by reducing insulin resistance.The mechanism for this decrease in insulin resistance on treatment with corosolic acid involved an increase in mouse muscle GLUT4 (a glucose transporter) translocation from the low-density microsomal membran. These results indicate that corosolic acid can improve hyperinsulinemia in type-2 diabetes. In addition, after an oral administration of sucrose in a ddY mouse study, treatment with corosolic acid (1 mg/kg body weight) improved hyperglycemia and significantly reduced the hydrolysis of sucrose in the small intestine. In other words, corosolic acid inhibited increasing disaccharide concentrations in the small intestine . More recently, it was demonstrated that, in CHO/hIR cells, corosolic acid stimulates glucose uptake via enhancement of insulin receptor β phosphorylation by inhibiting certain protein tyrosine phosphatases enzymes . In addition, an anti-diabetic action of corosolic acid was shown in rat liver where it increased glycolysis and decreased glycogenolysis in hepatocytes
In a clinical study,a standardized treatment with 1% corosolic acid (called Glucosol),administered as a 32 or 48 mg daily dose, caused significant reductions in glucose levels in the blood of type-2 diabetics over 2 weeks.In a similar study it was further shown that a soft-gel capsule formulation of Glucosol resulted in the greatest reduction of blood glucose levels.
This study suggests that the maximum dose before a reaching a plateau was not achieved, and that doses greater than 48 mg per day may further decrease blood glucose levels.
Reported that corosolic acid is not the primary inducer of glucose uptake in KKAy/Ta Jcl mouse cells. They found that when tannins were removed from the banaba leaf extracts, glucose uptake was not affected on treatment.Additionally, increasing concentrations of pure corosolic acid did not lead to an increase in glucose uptake. They concluded that, unlike insulin, any anti-diabetic properties of corosolic acid were due to an indirect mechanism. These results correlate with a study that demonstrated that the gallotannin penta-O-galloyl-glucopyranose (PGG) was able to lower glucose levels in the blood and increase glucose tolerance.