Geniposide improves insulin production and reduces apoptosis in high glucose-induced glucotoxic insulinoma cells
Our previous work revealed that in the pancreatic β cell line, geniposide modulated ATP production and glucose-stimulated insulin secretion (GSIS) induced by the acute stimulation of high glucose concentration. However, the effects of geniposide on functional impairment and the mass of β-cells exposed to elevated levels of glucose remains unknown. In the present study, impaired GSIS and restrained proliferation were observed in the prolonged culture of insulinoma INS-1 cells with 33 mM of glucose (high glucose). Our results indicate that the glucose-induced impairment of insulin release was significantly reverted by the inclusion of 1 or 10 μM of geniposide. Moreover, induction of the phosphorylation of AMP-activated protein kinase (AMPK) was observed, which promoted the utilization of nutrient stores for energy production. AMPK phosphorylation was enhanced by an increased number of INS-1 cells, and the increased expression of AMPK downstream target heme oxygenase 1 (HO-1), under high glucose concentration. Furthermore, geniposide protected rat insulinoma cells from apoptosis in high-glucose concentrations. We have shown that these effects were associated with an increased apoptosis-related Bcl-2/BAX protein ratio. In conclusion, geniposide dose dependently improves β-cell function and increases the proliferation of β-cells exposed to prolonged hyperglycemia.