Pollen typhae total flavone suppresses A7r5 cell proliferation promoted by insulin involving the MEK1/2-ERK1/2 cascades.

Pollen typhae, a traditional medicine in China, performs an anti-diabetic function and has anti-atherosclerosis effects involving suppression of vascular smooth muscle cell proliferation. However, the potential mechanisms keep to be revealed. The present study intended to investigate the influences of Pollen typhae extract named Pollen typhae total flavone (PTF) on A7r5 cell proliferation promoted by insulin and to uncover the underlying mechanisms. Proliferation and viability were evaluated by CCK-8 method. Western blotting was adopted to analyze the protein expression. Insulin promoted A7r5 cell proliferation, while PTF suppressed insulin-promoted proliferation in a concentration-dependent fashion. Although PTF did not change c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (p38MAPK) or MAPK kinase 1/2 (MEK1/2) protein expression and failed to affect the phosphorylation of JNK and p38MAPK, PTF remarkably inhibited extracellular signal-regulated kinase 1 and 2 (ERK1/2) protein expression and reduced ERK1/2 and MEK1/2 phosphorylation in A7r5 cells stimulated by insulin. Insulin-induced proliferation of A7r5 cells was abolished by inhibiting ERK1/2, which was in line with PTF. These findings indicate that PTF suppresses insulin-promoted proliferation of A7r5 cells involving the MEK1/2-ERK1/2 cascades, providing new insight into the potential uses of PTF for treatment of diabetic atherosclerosis.

Protective role of Pollen Typhae total flavone against the palmitic acid-induced impairment of glucose-stimulated insulin secretion involving GPR40 signaling in INS-1 cells.

Prolonged elevated levels of free fatty acids (FFAs) contribute to the impairment of insulin secretion function of pancreatic ß cells, a hallmark of type 2 diabetes, which is partly attributed to the dysfunction of G-protein-coupled receptor 40 (GPR40) signaling. Pollen Typhae total flavone (PTF), an extract from a Chinese herbal medicine named Pollen Typhae, has been reported to effectively treat type 2 diabetes, but the underlying mechanisms remain to be fully elucidated. In the present study, palmitic acid (PA), a saturated fatty acid, severely impaired glucose-stimulated insulin secretion (GSIS) in a time-dependent manner in INS-1 cells, and PTF treatment prevented the impairment in a dose-dependent manner. Moreover, PTF improved insulin secretion function in rats presenting with type 2 diabetes induced by a high-fat diet and low-dose streptozotocin. Furthermore, PA exposure for 24 h decreased the protein expression of GPR40, phospholipase C (PLC)ß1, PLCß3, and protein kinase C (PKC), and inhibited the activity of PLC and PKC stimulated by GW9508, a GPR40 agonist. In addition, PTF enhanced the protein expression of GPR40 and to a certain extent strengthened the protein expression of PKC, increased cellular levels of triphosphoinositide (IP3) and diacylglycerol (DAG), and promoted GW9508-stimulated activity of PLC and PKC reduced by PA in INS-1 cells, which were blocked by PLC inhibitor U-73122 and PKC inhibitor staurosporine, respectively. Additionally, the improvement in PA-induced impairment of GSIS by PTF in INS-1 cells was restrained by U-73122, staurosporine, and calcium channel inhibitor nifedipine, respectively. The results indicate that PTF exerts a protective role against PA-induced impairment of GSIS involving GPR40 signaling in INS-1 cells.