Genistein-Induced Potentiation Effect on Glucose-Stimulated Insulin Secretion (GSIS) in INS-1 β-cells

Impaired secretion of insulin as well as insulin resistance is a critical characteristic of type 2 diabetes. Thus, correction of the deficient secretion of insulin as well as improvement of insulin action is an important target for prevention of overt type 2 diabetes. Sulfonylureas have been used to stimulate insulin secretion in patients with type 2 diabetes. However, glucose-dependent insulinotropic molecules are required to improve diabetic hyperglycemia since sulfonylureas have glucose-independent insulinotropic effect, possibly eliciting hypoglycemia, and, moreover, are cytotoxic to beta cells under long-term exposure. Genistein, a isoflavonoid phytoestrogen isolated from soy bean seed and having tyrosin kinase inhibition activity, had a potentiation effect on GSIS (glucose-stimulated insulin secretion) in pancreatic INS-1 beta cells. Although the potentiation effect was glucose-dependent, the signal involved in potentiation effect were not intensively studied. First, to determine whether genistein has the same potentiation effect on other insulinotropic agents, potentiation effect by genistein on other insulinotropic agent-induced insulin secretion were investigated. Gesnistein had similar potentiation effect on insulin secretion by nutrients such as L-leucineLl-glutamin (Leu/Gln) and pyruvate, but little potetiation effects by simple calcium influx enhancer such as tolbutamide, KCl, and Bay K8644, suggesting that genistein may augment amplifying signals involved in insulin secretion. On the other hand, glimepiride-induced insulin secretion coulde be potentiated by genistein, suggesting that glimepiride is able to elicit another signal as well as calcium influx. Second, to determine which amplifying signals such as protein kinase A (PKA), protein kinase C (PKC) and Ca2+/Calmodulin kinase Ⅱ (CaMK II) on insulin secretion were invastigated using of pharmacological inhibitors. Studies showed that CaMK II inhibitor reduced genistein-induced potentiation effect on insulin secretion, while inhibitors of PKA and PKC did not reduce. Immunoblotting studies also demonstrated that genistien significantly enhanced phospho-CaMK II level elicited by Leu/Gln and glimepireide. whereas the same treatment did not enhance phosphorylation of PKA and PKC substrates. Third, to determine whether calcium is involved in genistein-induced CaMK II phosphorylation, we measured intracellular Ca2+ level after genistein treatment. Intracellular Ca2+ level was futhermore increased by genistein and glimepiride. Fourth, to determine whether potentiation effect of genistein-induced insulin secretion was due to phytoestrogen activity or tyrosine kinase inhibitor activity, studies of using 17β-estadiol (astrogen receptor agonist), tyrphostin25. 17β-estadiol did not potentiation effect on insulin secretion. Tyrphostin25 as other tyrosine kinase inhibitor had potentiation effect on insulin secretion by Leu/Gln, but did not potentiate effect on insulin secretion by glimepireide, suggesting that genistein may not potentiate insulin secretion by another activity instead of phytoestrogen activity and tyrosine kinase inhibitor activity. Last, over-expression CaMK Ⅱ more incresed genistein-induced potentiation effect on insulin secretion and CaMK Ⅱ activation. In conclusion, our studies suggest that geniistein potentiates insulin secretion by calcium-mediated augmentation of CaMK II activation.

Author dc:creator

• 이, 수진

Contributors dc:contributor

• 강, 엽
• 대학원 의학과
• 105644

• 인슐린 분비
• Glucose stimulated insulin secretion (GSIS)
• Genistein
• Calmodulin kinaseⅡ (CaMK Ⅱ)
• INS-1 beta cells

Language dc:language

ko

Identifier

http://dcoll.ajou.ac.kr:9080/dcollection/jsp/common/DcLoOrgPer.jsp?sItemId=000000002647
000000002647

OAI identifier oai:identifier

oai:repository.ajou.ac.kr:201003/1685