Astragaloside IV attenuates proteinuria in streptozotocin-induced diabetic nephropathy via the inhibition of endoplasmic reticulum stress.

BACKGROUND: Diabetic nephropathy (DN) is a major cause of Chronic Kidney Disease and End-Stage Renal Disease throughout the world; however, the reversibility of diabetic nephropathy remains controversial. Endoplasmic reticulum (ER) stress plays an important role in the pathogenesis of DN. Astragaloside IV (AS-IV) is derived from Astragalus membranaceus (Fisch) Bge, a widely used traditional herbal medicine in China, and has diverse pharmacological activities including the attenuation of podocyte injury and amelioration of proteinuria in idiopathic nephrotic syndrome. The present study aimed to investigate the effect and mechanism of AS-IV on proteinuria in the rat streptozotocin (STZ)-induced model of diabetes. METHODS: Male Sprague-Dawley (SD) rats were randomly divided into four groups: normal control (Normal group), diabetic nephropathy (Model group), diabetic nephropathy plus AS-IV treatment (AS-IV group) and diabetic nephropathy plus 4-phenyl butyric acid treatment (PBA group). ER stress was induced in cultured human podocytes, pretreated with or without AS-IV, with tunicamycin (TM). At the end of 8 weeks, serum creatinine (Scr), blood urea nitrogen (BUN) and 24-hour urinary protein excretion rate (UAER) were determined. Renal morphology was examined after periodic acid-Schiff staining of kidney sections. Apoptosis of podocytes was measured by flow cytometry. The total expression and phosphorylation of eIF2α, PERK and JNK, and the expression of CHOP and cleaved caspase-3 were determined by western blotting. The expression of glucose-regulated protein 78 (GRP78) and 150 kDa oxygen-regulated protein (ORP150) mRNA and protein was determined by real-time PCR and western blotting respectively. RESULTS: AS-IV treatment significantly reduced urinary albumin excretion, plasma creatinine and blood urea nitrogen levels, and prevented the mesangial matrix expansion and increase in mean mesangial induced by STZ. AS-IV also prevented the phosphorylation of eIF2α, PERK and JNK, and inhibited the expression of GRP78 and ORP150 markedly, both in vivo and in vitro. AS-IV inhibited the TM-induced apoptosis of podocytes, concomitant with decreased CHOP expression and cleaved caspase-3. CONCLUSIONS: This study supports the hypothesis that AS-IV reduces proteinuria and attenuates diabetes, which is associated with decreased ER stress. This might be an important mechanism in the renoprotective function of AS-IV in the pathogenesis of DN.

Effects of Bushen Tongmai Recipe on protein kinase Balpha expression in polycystic ovary rats with insulin resistance.

OBJECTIVE: To observe the effects of Bushen Tongmai Recipe (, BSTMR) on mRNA and protein expressions of protein kinase B alpha (PKB alpha) in hepatic, adipose, muscular, and ovarian tissues of polycystic ovary (PCO) rats with insulin resistance (IR) and to explore the possible molecular mechanism of BSTMR in treating IR and ovulation dysfunction. METHODS: Female 22-day-old SD rats were injected subcutaneously with sodium prasterone sulfate (9 mg.100g(-1).d(-1)) for 20 days and fed with high-fat diet for 80 days to induce PCO rats with IR. Then, the PCO rats were randomly divided into the model group (n=23) and the treated group (n=21). The treated group was administered with BSTMR for 2 weeks. Meanwhile, a group with 15 rats of the same age was used as the control group. The histological changes in the ovaries were examined. Fasting blood glucose (FBG) was determined by the glucose oxidase method. Serum fasting insulin (Fins) was determined by radioimmunoassay (RIA). The mRNA level of PKBalpha was measured by reverse transcription polymerase chain reaction (RT-PCR). Immunohistochemistry staining and Western blot analysis were employed to detect the protein expression in target tissues. RESULTS: Compared with the control group, the ovaries in the model group showed multiple follicular cysts, levels of FBG and Fins in the model group increased markedly (P<0.05 or P<0.01, respectively), and the insulin sensitive index (ISI) decreased obviously (P<0.01). The mRNA and protein expressions of PKBalpha in target tissues in the model group were dramatically lower than those in the control group (P<0.05 or P<0.01). Compared with the model group, the stratum granulosum of the ovarian follicle in the treated group increased markedly, the level of Fins in the treated group decreased obviously (P<0.01), ISI in the treated group improved markedly (P<0.01), and the mRNA and protein expressions of PKBalpha in target tissues of the treated rats were elevated significantly (P<0.05 or P<0.01). CONCLUSION: BSTMR could improve IR and ovulation dysfunction in PCO rats with IR, and its molecular mechanisms might be closely related with the elevation of mRNA and protein expressions of PKBalpha in target tissues of PCO rats with IR.

Berberine reduces endoplasmic reticulum stress and improves insulin signal transduction in Hep G2 cells.

AIM: Endoplasmic reticulum (ER) stress plays an important role in the pathogenesis of insulin resistance and pancreatic beta-cell dysfunction. The aim of this study is to investigate whether the insulin-sensitizing action of berberine is related to reducing ER stress. METHODS: ER stress in cultured Hep G2 cells was induced with tunicamycin. Cells were pretreated with berberine in combination with or without insulin. The concentration of glucose was measured by glucose oxidase method. The molecular markers of ER stress, including ORP150, PERK, and eIF2 alpha were analyzed by Western blot or real time PCR. The activity of JNK was also evaluated. Moreover, the insulin signaling proteins such as IRS-1 and AKT were determined by Western blot. RESULTS: The production of glucose stimulated with insulin was reduced. The expressions of ORP150 was decreased both in gene and protein levels when cells were pretreated with berberine, while the activation of JNK was blocked. The levels of phosphorylation both on PERK and eIF2 alpha were inhibited in cells pretreated with berberine. The level of IRS-1 ser(307) phosphorylation was decreased, whereas IRS-1 tyr phosphorylation was increased notablely. AKT ser(473) phosphorylation was also enhanced significantly in the presence of berberine. CONCLUSION: The antidiabetic effect of berberine in Hep G2 cells maybe related to attenuation of ER stress and improvement of insulin signal transduction.

[8-hydroxy-dihydroberberine ameliorated insulin resistance induced by high FFA and high glucose in 3T3-L1 adipocytes].

The purpose of the study is to investigate the effect of 8-hydroxy-dihydroberberine on insulin resistance induced by high free fatty acid (FFA) and high glucose in 3T3-L1 adipocytes and its possible molecular mechanism. Palmic acid or glucose in combination with insulin was used to induce insulin resistance in 3T3-L1 adipocytes. 8-Hydroxy-dihydroberberine and berberine were added to the cultured medium separately, which were considered as treated group and positive control group. The rate of glucose uptake was determined by 2-deoxy-[3H]-D-glucose method. The amount of glucose consumption in the medium was measured by glucose oxidase method. Cell growth and proliferation of 3T3-L1 adipocytes were detected with Cell Counting Kit-8 (CCK-8) assay. After incubated with palmic acid for 24 hours or glucose with insulin for 18 hours, the rate of glucose transport in 3T3-L1 adipocytes was inhibited by 67% and 58%, respectively. The amount of glucose consumption in 3T3-L1 adipose cells was decreased by 41% after cells were incubated with palmic acid for 24 h. However, the above changes were reversed by pretreatment with 8-hydroxy-dihydroberberine for 24 and 48 h. Significant difference existed between groups. Insulin resistance in 3T3-L1 adipocytes, which is induced by high FFA and high glucose, could be ameliorated by 8-hydroxy-dihydroberberine.

Facilitating effects of berberine on rat pancreatic islets through modulating hepatic nuclear factor 4 alpha expression and glucokinase activity.

AIM: To observe the effect of berberine on insulin secretion in rat pancreatic islets and to explore its possible molecular mechanism. METHODS: Primary rat islets were isolated from male Sprague-Dawley rats by collagenase digestion and treated with different concentrations (1, 3, 10 and 30 micromol/L) of berberine or 1 micromol/L Glibenclamide (GB) for 24 h. Glucose-stimulated insulin secretion (GSIS) assay was conducted and insulin was determined by radioimmunoassay. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed to evaluate cytotoxicity. The mRNA level of hepatic nuclear factor 4 alpha (HNF4alpha) was determined by reverse transcription polymerase chain reaction (RT-PCR). Indirect immunofluorescence staining and Western blot analysis were employed to detect protein expression of HNF4alpha in the islets. Glucokinase (GK) activity was measured by spectrophotometric method. RESULTS: Berberine enhanced GSIS rather than basal insulin secretion dose-dependently in rat islets and showed no significant cytotoxicity on islet cells at the concentration of 10 mumol/L. Both mRNA and protein expressions of HNF4alpha were up-regulated by berberine in a dose-dependent manner, and GK activity was also increased accordingly. However, GB demonstrated no regulatory effects on HNF4alpha expression or GK activity. CONCLUSION: Berberine can enhance GSIS in rat islets, and probably exerts the insulinotropic effect via a pathway involving HNF4alpha and GK, which is distinct from sulphonylureas (SUs).

[Effect of berberine on insulin secretion and glucokinase activity of NIT-1 cells].

To investigate the effect of berberine on insulin secretion of NIT-1 cells stimulated by glucose and the possible molecular mechanism, we used radioimmunoassay, scintillation counting technique, enzymatic method and Western blotting to measure the effects of berberine on insulin secretion, glucose utilization, the activity of glucokinase (GK) and protein level of GK and GK regulation protein (GKRP). Compared with untreated group, insulin secretion level, glucose utilization, the activity and protein level of GK in NIT-1 cells stimulated by high concentration of glucose were increased significantly in berberine group (P < 0.05), while the protein level of GKRP in berberine group decreased markedly. In conclusion, berberine can promote insulin secretion of NIT-1 cells induced by high concentration of glucose. The possible molecular mechanism may be associated with berberine acting as a GK activator, improving glucose utilization, enhancing the activity and protein expression level of GK, as well as decreased the protein level of GKRP.