The Effects And Mechanisms Of Baicalein On Insulin Secretion In Pancreatic Islets

Objective:Baicalein is extracted from the root of scutellaria baicalensis,which is a traditional Chinese medicine.Baicalein is one of the most abundant flavonoids and main active ingredient in scutellaria.It has a wide range of function including anti-inflammatory,antibacterial,antivirus,antitumor,protecting liver,scavenging free radicals as well as protecting nerves.To investigate the effects of baicalein on insulin secretion and its role of antidiabetic in rats and its mechanisms,the following experiments were done.Methods:(1)Male Wistar rats were aseptically dissected,then intestines and surrounding structures of the rats were fully exposed.Syringe filled with 1mg/ml collagenase P was injected into the pancreas,and then completely separated the wholepancreas tissue;Put this material in water bath vessel in which the water’s tempreture was38 °C.We shaked the centrifuge tube until the liquid was homogenized after digestion in 11 minutes’.Histopaque 1077 was separated by gradient centrifugation to obtain islets.Digested with dispase II for 5 minutes followed by hand sorting,an appropriate amount of islets were difused into individual islet cells.(2)Insulin release experiment:round,peripheral intact Pancreatic islets were picked under a microscope.Rat islets insulin secretion was measured by radioimmunoassay when baicalein and related blockers were intervened.(3)Patch-clamp technique was used to record the potassium channel,calcium channel current and action potential in different experimental groups.(4)Under baicalein intervention condition,using fluorescence imaging system andfluorescence microscope to record intracellular concentration of calcium ion.Result:Insulin secretion experiments showed different concentrations of baicalein(20,50,100 μmol/L)stimulated insulin secretion in a dose-dependent manner under 2.8mmol/L and 16.7 mmol/L glucose conditions.On the glucose condition of 16.7mmol/L,the maximum secretory effect was showed with baicalein at 50 μmol/L(the baicalein group,408.44±21.88 μIU/ml;the control group,233.46.33±44.87 μIU/ml).(2)Adenylate cyclase(AC)inhibitor SQ22536(10 μmol/L)can not limite insulin secretory effect of baicalein.The enzyme C(PLC)inhibitor U-73122(1 μmol/L)can eliminate insulin secretory effect of baicalein.ERK inhibitor PD98059(20 μmol/L)can not develop the same inhibition effect as U-73122.(4)Patch clamp experiments showed that baicalein shut down ATP-dependent potassium channel KATP and decrease KATP current(negative control group,-64.17±9.53 p A/p F;baicalein group,-35.74 ± 8.16 p A/p F).Safrole inhibited voltage-dependent potassium channel(Kv)current in a dose-dependent manner,reaching a maximum inhibitory effect at 50μmol/L(safrole group,82.66±9.40 p A/p F;control group,143.33±11.46 p A/p F).PLC inhibitor U-73122(1 μmol/L)reversed the inhibitory effect of baicalein on Kv,whereas ERK inhibitor PD98059(20 μmol/L)did not.(5)The results of calcium ion imaging experiments indicated 50 μmol/L baicalein increased intracellular calcium concentration.Conclusion:Baicalein stimulate insulin secretion in isolated rat pancreatic islets.One of its mechanisms is the direct inhibition of KATP channels.In addition,PLC signaling pathway is also involved in baicalein-promoted insulin secretion by inhibiting Kv channels and increasing the intracellular calcium concentration in β-cells.