Studies On The Protection Mechanisms Of Pancreatic Beta INS-1 Cells By Silibinin

Silibinin,a polyphenolic flavonoid,has been used as a hepatoprotectant and possesses phytoestrogen effects.The effect of silibinin on the rat pancreatic β-cell line,INS-1 cells,damaged with pro-inflammatory cytokines,TNFα or IL-1β was investigated.Exposure to TNFα or IL-1β for 48 h caused INS-1 cells to reduce the production of insulin as well as cell viability.These actions of TNFa or IL-1β are associated with suppression of the expression of estrogen receptors(ERs).Further study revealed that silibinin protected the suppression in the expression of both ERα and ERβ that are involved in insulin synthesis and release,respectively.Direct cytoprotective effects of silibinin on INS-1 cells suggest that silibinin may be therapeutically beneficial for diabetes.Fibrils formed by aggregation of amylin are the major components of amyloid deposits in pancreatic islets of individuals with T2DM.Aβ effects peripheral insulin resistance and hyperglycemia,suggesting a role for Aβ in T2DM pathogenesis for individuals predisposed to AD.Investigation of the mechanism of the protective effect of silibinin on amylin/Aβ1-42-induced INS-1 cell apoptosis revealed:INS-1 cells exposed to amylin showed increased apoptosis and reduced expression of GLP-1R and PKA,and induce reactive oxygen species(ROS)and reactive nitrogen species(RNS)generation.Silibinin exerted antiapoptotic effect on and up-regulation of GLP-1R and PKA.However,in the API-42 induced INS-1 cell apoptosis,and ROS/RNS generation,while GLP-1R and PKA expressions were not changed.Our results indicate that down-regulation of GLP-1R and PKA contributes to INS-1 cell apoptosis induced with amylin.Silibinin protects INS-1 cells from amylin-induced apoptosis through activation of GLP-IR/PKA signaling.Silibinin’s inhibition of the toxic effects of Aβ1-42 is independent of GLP-1R/PKA pathway.Treatment with silibinin down-regulated amylin/Aβ1-42-induced ROS/RNS production in the cells.The binding of silibinin to ERs implies that the protective effect of silibinin on amylin/Aβ1-42-treated INS-1 cells owes to down-regulation of ROS/RNS through the activation of ERs signaling.Amylin and Aβ1-42 co-treatment furthermore enhanced ROS/RNS generation and cytotoxicity through further down-regulation of ERs signaling.Silibinin also protects INS-1 cells from amylin and Ap1-42 co-treatment.These results indicate that protective effect of silibinin is mediated by enhancement of ERs signaling that depresses ROS/RNS generation in amylin/Ap1-42-treated INS-1 cells.Extracellular matrix(ECM)molecules have multiple functions:prevention of cytotoxicity,provision of mechanical support,cell adhesive substrates and structural integrity in addition to mediation of cellular signaling.Collagen I and V are distributed in the pancreatic islets,and they affect the proliferation and survival of pancreatic β cells.In this study,we report that the proliferation of INS-1 cells cultured collagen I-coated dishes is enhanced,but it is inhibited on collagen V-coated dishes.Inhibitory proliferation on collagen V-coated is not due to apoptosis induction.Silibinin up-regulates the proliferation of cells cultured on both collagen I-and V-coated dishes.Differential effects of silibinin on collagen I mRNA and collagen V mRNA can be accounted for by the finding that silibinin enhances nuclear translocation of β-catenin on both collagen I-and V-coated dishe.