Morinda Citrifolia (Noni): Its Effect on Insulin Secretion by G-Protein-Coupled Receptor Systems

摘要

The American Diabetes Association estimates that 14 millions people in the USA are known to have diabetes, with 9% being type 1 diabetes and 91% being type 2 diabetes. Type 2 diabetes occurs when insulin secretion is no longer sufficient from the degenerated or diseased beta cells in the islet of langerhans. At the molecular level, remedies which may influence insulin secretion include 1) functioning through the ion channels of beta cell, 2) functioning through the second messenger pathways, in which G-Protein-Coupled Receptor Systems are the most important. Increased content of cAMP inside the beta cell, adenosine 3,5-cyclic monophosphate and a second messenger generated in the G-Protein-Coupled Receptor Systems, has been found by much research to be positively related to the increased insulin secretion. Morinda citrifolia (L) (Noni), a natural plant growing in tropical areas such as Tahiti and Hawaii has historical uses and anecdotal reputations in treating type 2 diabetes. In this study, we found that the dried form of Noni fruit was an inhibitor of PDE3, phosphodiesterase 3 which hydrolyzes cAMP, and an agonsit of P2Y receptor which was a G-Protein-Coupled receptor on the beta cell. The agonists of P2Y might increase the secretion of insulin by stimulating the cAMP production, as indicated by other previous research results. Therefore, our findings suggested that one of the mechanisms of Noni fruit anti-diabetic effects might be through the G-Protein-Coupled Receptor Systems.