Discussion

Apoptosis is probably the main form ofβ-cell death in T1DM and T2DM.In this study，we selected two of the main stimuli forβ-cell apoptosis—high glucose and cytokines to construct apoptotic cell models.It has been reported that high glucose concentration impairs islet function by disturbing glucose metabolism in the mitochondria of β-cell and could induce apoptosis.48 50)In addition，high glucose could increaseβ-cell vulnerability to toxic damage by increasing the expression of potential autoantigens on the cell membrane surface.51)Cytokines(IL-1β，TNF-αand IFN-γ)may be directly cytotoxic toβ-cells by inducing NOand oxygen free radicals，inhibiting insulin synthesis and secretion，destroyingβ-cells.52)Meanwhile，cytokines may sensitizeβ-cells to T cellmediated cytotoxicity in vivo by up-regulating MHC class Iexpression on theβ-cells(an action of IFN-γ)，and inducing Fas expression ofβ-cells(actions of IL-1β，and possibly TNF-αand IFN-γ).13)Cytokines cause additional production of chemokines，further increasing insulitis and the consequent dysfunction and damage ofβ-cells.53，54)

In this study，we observed the loss ofβ-cells and reduction of cell function，which indicated the success of apoptoticβ-cell model construction.Mechanisms underlying high glucose/cytokine-inducedβ-cell apoptosis include increasing NO production together with up and down-regulation of apoptosis-related gene expressions.Among these genes，Bax，Fas and Caspase-3 gene expression were up-regulated by high glucose，whereas only Bax and Caspase-3 gene expression were elevated by cytokines.In addition，cytokines instead of high glucose down-regulated Bcl-2 gene expression.As a conclusion，Fas signal pathway is important in high glucoseinduced apoptosis，while mitochondria pathway plays a key role in cytokine-induce apoptosis.(https://www.daowen.com)

Ginsenoside Rg1/Rb1，separately or in combination，protected pancreaticβ-cell from high glucose/cytokine-induced cell loss and function reduction.Both ginsenosides reduced i NOS gene expression and consequent NO production.However，the apoptosis-related genes involved in the protective function of the two agents are different.In high glucoseinduced apoptotic cells，Rg1 down-regulated Fas gene expression，while Rb1 decreased Caspase-3 gene expression.Similar result was observed in the cytokinesinduced apoptotic cells.Of note，in these cells，the impaired Bcl-2/Bax ratio(0.53)was protected by Rg1 with the value 1.04，which is comparable to control condition.

In conclusion，high glucose and cytokine induce pancreaticβ-cells apoptosis via promoting NO production and regulating apoptosis-related genes.Both ginsenoside Rg1 and Rb1 protectβ-cells from these two stimuli-induced apoptosis.The mechanism of anti-apoptotic effects of Rg1 is mostly related with Fas signal pathway and mitochondria stress，whereas Caspase-3 pathway is essential when Rb1 is present.