Cinchonain Ib isolated from Eriobotrya japonica induces insulin secretion in vitro and in vivo

Aims of the studyEriobotrya japonica leaves had been used traditionally for the treatment of diabetes mellitus by immersing the dried leaves in a hot water drink. Few studies have shown the hypoglycemic effect of Eriobotrya japonica using crude alcoholic extract and isolated methanolic compounds. These studies proposed that the mechanism of action could be by stimulating the β-islets of Langerhans to secrete insulin, however with no scientific evidence.MethodsEriobotrya japonica water extract (EJWE) and the compounds derived from it: cinchonain Ib, procyanidin B-2, chlorogenic acid and epicatechin, were tested for their effects on insulin secretion from INS-1 cells and following oral administration in rats.ResultsThe present study showed that EJWE increased significantly (p < 0.05) insulin secretion from INS-1 cells in dose-dependent manner. Oral administration of EJWE at 230 mg/kg to rats, however, decreased plasma insulin level for as long as 240 min post-administration and caused a transient drop of blood glucose at 15 and 30 min post-administration. On the other hand, cinchonain Ib enhanced significantly (p < 0.05) insulin secretion from INS-1 cells, whereas epicatechin inhibited significantly (p < 0.05) insulin secretion from INS-1 cells. In addition, cinchonain Ib enhanced significantly (150%: p < 0.05) plasma insulin level in rats for as long as 240 min after 108 mg/kg oral administration but did not induce any change in blood glucose level.ConclusionThese data indicate that cinchonain Ib has an insulinotropic effect and suggest the possible use of cinchonain Ib for managing type 2 diabetes.