Vitis vinifera L. grape skin extract activates the insulin-signalling cascade and reduces hyperglycaemia in alloxan-induced diabetic mice

Objectives This study examined the effect of Vitis vinifera grape skin extract (ACH09) on hyperglycaemia and the insulin‐signalling cascade in alloxan‐treated mice. Methods Glycaemia, serum insulin and Western blot analysis of insulin cascade proteins were evaluated in the gastrocnemius muscles of four groups of adult mice: control, ACH09 (200 mg/kg per day, p.o.), alloxan (300 mg/kg, i.p.) and alloxan + ACH09. Insulin secretion in isolated pancreatic islets was also studied. Key findings Glycaemia values in the alloxan + ACH09 and ACH09 groups were significantly lower than in the alloxan‐treated and control groups, respectively. Increased insulin resistance (HOMA index) was observed in the alloxan‐treated group but not in the alloxan + ACH09 group. Insulin receptor content and Akt phosphorylation were significantly greater in the alloxan + ACH09 group compared with the alloxan‐treated group. The glucose transporter (GLUT‐4) content was reduced in alloxan‐treated mice compared with the control group, while alloxan + ACH09 and ACH09‐treated mice showed a significant increase in GLUT‐4 content. ACH09 treatment did not change glucose‐induced insulin secretion in isolated pancreatic islets. Conclusions The results suggest that ACH09 has hypoglycaemic and antihyperglycaemic effects that are independent of an increase in insulin release but are probably dependent on an increase in insulin sensitivity resulting from an activation of the insulin‐signalling cascade in skeletal muscle.     

Evidence for a direct stimulatory effect of cibenzoline on insulin secretion in rats.

The effect of cibenzoline succinate, a new antiarrhythmic agent, was studied on insulin secretion in rats. Experiments were performed both in vivo and in vitro using two preparations: the isolated perfused pancreas and isolated islets. In anaesthetized rats, cibenzoline was able to increase plasma insulin levels and to reduce glycaemia. These effects were observed at 1 mg/kg i.v. in fed rats and at 3 mg/kg i.v. in fasted rats. In the isolated pancreas perfused in the presence of a slightly stimulating glucose concentration (8.3 mM), cibenzoline (2 and 6 microM) elicited a progressive and sustained insulin response in a concentration-dependent manner. In the presence of a non-stimulating glucose concentration (4.2 mM), cibenzoline was ineffective at 2 microM and slightly increased basal insulin release at 6 microM. In isolated islets incubated with 8.3 mM glucose, cibenzoline (6 and 20 microM) caused a concentration-dependent stimulation of insulin release. It is concluded that cibenzoline stimulates insulin secretion by a direct action on pancreatic B cells in rats.     

Hypoglycemic effect of Ganoderma lucidum polysaccharides

AIM: To investigate the hypoglycemic effect of Ganoderma lucidum polysaccharides (Gl-PS) in the normal fasted mice and its possible mechanism. METHODS: Normal fasted mice were given a single dose of Gl-PS 25, 50, and 100mg/kg by ip and the serum glucose was measured at 0, 3, and 6h after administration. Gl-PS 100mg/kg were also given by ip and the serum glucose and insulin levels were measured at 0min, 30min, 1h, 3h, 6h, and 12h Pancreatic islets were isolated and incubated with glucose 5.6mmol/L and different concentration of Gl-PS, the insulin content of islets and insulin release were examined. The islets fluorescent intensity of [Ca^2 ]i was also studied with a confocal microscope. Verapamil and egtazic acid were used to testify whether the insulin-releasing effect of Gl-PS was mediated by its ability to raise the Ca^2 influx. RESULTS: Gl-PS dose-dependently lowered the serum glucose levels at 3h and 6h after administration. Gl-PS 100mg/kg raised the circulating insulin levels at 1h after administration. In vitro, Gl-PS had no effect on islets insulin content, but it stimulated the insulin release after incubation with glucose 5.6mmol/L. Confocal microscope showed that Gl-PS 100mg/L had the capacity toraise the [Ca^2 ]i. The insulin-releasing effect of Gl-PS was inhibited by verapamil/egtazic acid. CONCLUSION:Gl-PS possesses the hypoglycemic effect on normal mice; one mechanism is through its insulin-releasing activity due to a facilitation of Ca^2 inflow to the pancreatic β cells.     

桑的药理研究(Ⅰ)──桑叶降血糖有效组分对糖尿病动物糖代谢的影响

自桑叶中提取的桑叶总多糖（TPM），腹腔注谢给药（50，100，200mg／kg），对四氧嘧啶糖尿病小鼠有显著的降血糖作用．TPM还可提高糖尿病小鼠的耐糖能力，增加肝糖元含量而降低肝葡萄糖．TPM腹腔注射给药100mg／kg．）可以提高正常大鼠血中胰岛素水平．上述结果表明：TPM对糖尿病小鼠糖代谢有调整作用，并可促进正常大鼠胰岛素的分泌．     

The inhibitory effect of DDT on insulin secretion in mice.

A single oral dose of 50 mg/kg of DDT administered to mice 18 hr prior to experimentation was found to reduce glucose tolerance without affecting the basal blood concentration of glucose. Also, the treatment inhibited both d-glucose and tolbutamide-stimulated insulin release by isolated pancreatic islets. Hyperglycemia was not noted during the 18-hr period after DDT. The effect of DDT on glucose tolerance persisted for at least 1 week. Reduced pancreatic secretory activity after DDT administration is consistent with the increased activity of gluconeogenic enzymes as well as decreased glycogen synthetase activity reported by earlier workers.     

Furosemide-induced glucose intolerance in mice is associated with reduced insulin secretion

The effect of furosemide on carbohydrate metabolism was studied in ob/ob mice. Intraperitoneal injection of a single dose of furosemide (200 mg/kg body weight) into fasted mice resulted in acute hyperglycaemia and two days after such a single dose, the mice showed fasting hyperglycaemia and glucose intolerance. Pancreatic islets from mice that had been injected with furosemide (200 mg/kg body weight) two days prior to the in vitro experiments showed increased basal (3 mmol/1 D-glucose) and decreased glucose-stimulated (20 mmol/1) insulin release. Islets from furosemide- or saline-injected animals showed no difference in islet insulin content. The results show that furosemide has both acute and long-term effects on carbohydrate metabolism in ob/ob mice. It is suggested that this, at least in part, is due to an effect on the pancreatic beta-cells.     

水芹黄酮的抗糖尿病作用(英文)

目的:研究水芹黄酮(OjF)的抗糖尿病作用。方法:给小鼠尾静脉注射四氧嘧啶90mg·kg~(-1),造成高血糖动物模型。用自动生化分析仪测定血糖、血脂和胰淀粉酶。放免法测定血清胰岛素。光镜下观察胰腺和胰岛的组织学变化。结果:一次ig OjF 200mg·kg~(-1)后0.5-6h,可使正常动物血糖降低。重复给药10天,OjF 200mg·kg~(-1)和400mg·kg~(-1)均使四氧嘧啶糖尿病动物血糖明显降低(P<0.05,P<0.01)。并促进正常动物及高血糖动物胰岛素释放。OjF还能明显降低血清甘油三酯(P<0.01)及升高糖尿病动物降低的胰淀粉酶水平(P<0.01)。组织学观察OjF治疗组胰岛损伤的变化与对照组相似,但程度较轻。结论:OjF具有降低血糖和甘油三酯作用,并对胰腺损伤有一定的拮抗作用。OjF降血糖作用主要是由于促进了胰岛B细胞释放胰岛素。     

Interactions of Diabetogenic Compounds: Cyproheptadine and Alloxan

Pretreatment with an oral dose (45 mg/kg) of cyproheptadine(CPH), a drug that inhibits secretion and synthesis of insulin,3 hr before alloxan (100 mg/kg, iv) protects mice from the permanentdiabetes produced by alloxan. Pretreated animals at the timeof alloxan adminisisation were hyperglycemic. Therefore, thepossibility that CPH-induced hyperglycemia protected mice fromalloxan was investigated. This was accomplished by giving mannoheptulose(a glucose antagonist) or insulin (to lower blood glucose) afterCPH and before alloxan. These interventions eliminated CPH-inducedprotection from alloxan, indicating a role for CPH-induced hyperglycemiain the protective effect. To confirm that CPH does not protectmice from alloxan-induced diabetes by a direct action, in vitroexperiments using isolated pancreatic islets were conducted.Mouse islets were pretreated with CPH, its metabolite desmethylcyproheptadine(DMCPH), or an equal mixture of the two and/or various concentrationsof glucose prior to an acute exposure to a toxic concentrationof alloxan. Glucose- stimulated insulin release was used asa measure of pancreatic ß-cell function after alloxanexposure. CPH or DMCPH (alone or in combination) pretreatmentdid not provide protection against alloxan-induced inhibitionof insulin release nor did pretreatments potentiate the protectiveaction of glucose against in vitro alloxan toxicity. The resultsindicate that the protective action of CPH when given to micebefore alloxan is due to drug-induced hyperglycemia and notto a direct effect of CPH or its metabolite.     

Assessment of benzene induced oxidative impairment in rat isolated pancreatic islets and effect on insulin secretion

Benzene (C₆H₆) is an organic compound used in petrochemicals and numerous other industries. It is abundantly released to our environment as a chemical pollutant causing widespread human exposure. This study mainly focused on benzene induced toxicity on rat pancreatic islets with respect to oxidative damage, insulin secretion and glucokinase (GK) activity. Benzene was dissolved in corn oil and administered orally at doses 200, 400 and 800 mg/kg/day, for 4 weeks. In rats, benzene significantly raised the concentration of plasma insulin. Also the effect of benzene on the release of glucose-induced insulin was pronounced in isolated islets. Benzene caused oxidative DNA damage and lipid peroxidation, and also reduced the cell viability and total thiols groups, in the islets of exposed rats.In conclusion, the current study revealed that pancreatic glucose metabolism is susceptible to benzene toxicity and the resultant oxidative stress could lead to functional abnormalities in the pancreas.     

Effects of selenium on the serum glucose and insulin levels in diabetic rats]

We investigated the effects of selenium (Se) on the serum glucose and insulin levels in rats with diabetes induced by streptozotocin (STZ, 75 mg/kg, i.p.) and pancreatectomized rats. Moreover, the direct action of Se on insulin release from the isolated pancreatic islets using a slight diabetic rat was studied. The following results were obtained: 1) Selenite at a dose of 173 micrograms/kg (78.9 micrograms/kg of Se base equivalent) drastically reduced the very high level of serum glucose in acute diabetic rats within 5 to 30 min after treatment. During this time period, the insulin level in the serum showed an increasing tendency. 2) The high serum glucose level in chronic diabetic rats returned to the original level with injection of selenite for 4 days, once a day. However, Se did not elicit a significant increase in serum insulin level. 3) Although there was a tendency for the serum glucose level to decrease when selenite was administered into pancreatectomized rats, no secretion of insulin into the serum was observed. 4) Insulin release from isolated pancreatic islets was dose-dependently accelerated by the addition of selenite. These data present the new finding that Se reduced the high level of serum glucose in diabetic rats.     

Potentiation of glucose-induced insulin release by thiourea and thiourea derivatives

Summary The effect of thiourea and its derivatives, including methyl- and propylthiouracil as well as the imidazole derivative thiamazole on glucose-induced insulin secretion from incubated rat pancreatic islets was studied. Additionally, the effect of a single oral dose of propylthiouracil on plasma insulin and glucose tolerance was tested in anaesthetized rats.In the presence of 2.8 mM glucose, neither thiourea nor methylthiouracil, propylthiouracil or thiamazole stimulated the secretion of insulin from pancreatic islets. However, in the presence of 11.1 mM glucose all of the above compounds augmented the insulin-releasing properties of glucose in a concentration-related manner-propylthiouracil being the most potent drug. Propylthiouracil (100 and 200 mg/kg body weight) significantly augmented insulin secretion in vivo in response to i.v. glucose (0.5 g/kg). Accordingly, the rate constant of glucose elimination (K-value) was increased.The data suggest that thiourea-containing chemical compounds sensitize pancreatic islets to the insulin-triggering action of glucose.     

The biguanide compound metformin prevents desensitization of human pancreatic islets induced by high glucose

Pancreatic islet desensitization by high glucose concentrations is a temporary and reversible state of beta-cell refractoriness to glucose (and possibly other secretagogues), due to repeated or prolonged pre-exposure to increased glucose concentrations. We evaluated whether the oral antidiabetic agent metformin affects this phenomenon in isolated, human pancreatic islets, and whether the possible effects of the biguanide are influenced by the presence of a sulphonylurea, glyburide. Islets prepared from five human pancreases were incubated for 24 h in M199 culture medium containing either 5.5 or 22.2 mmol/l glucose, with or without a therapeutic concentration (2.4 μg/ml) of metformin. Then, the islets were challenged with either 3.3 mmol/l glucose, 16.7 mmol/l glucose, or 3.3 mmol/l glucose+10 mmol/l arginine, and insulin release was measured. After incubation in the absence of metformin, the human islets exposed to 22.2 mmol/l glucose showed no significant increase in insulin release when challenged with 16.7 mmol/l glucose (confirming that hyperglycemia desensitizes pancreatic beta-cells). In the presence of metformin, the islets fully maintained the ability to significantly increase their insulin release in response to glucose, even when previously exposed to 22.2 mmol/l glucose. No major effect on arginine-induced insulin release was observed, whatever the culture conditions. The protective action of metformin was observed also when glyburide was present in the incubation medium, whereas the sulphonylurea alone did not affect insulin release from the islets previously exposed to high glucose concentrations. These in vitro results suggest that metformin can prevent the desensitization of human pancreatic islets induced by prolonged exposure to increased glucose concentrations.     

Alteration of pancreatic B-cells in Wistar rats treated with non-diabetogenic doses of cyclosporin A.

We have investigated the effect of non-immunosuppressive cyclosporin A (CS-A) doses on glucose tolerance, pancreatic insulin content, insulin content of isolated islets and insulin secretion in vitro in response to glucose. Within 12 weeks animals treated permanently with a dose of 2.5 mg CS-A/kg b.wt. developed glucose intolerance (but not hyperglycaemia) accompanied by a decrease of pancreatic insulin content due to a decrease of islet insulin content, whereas the relative B-cell volume density was not changed. Isolated islets obtained from rats treated for 4 weeks had a diminished sensitivity for glucose, whereas islets obtained from animals treated for greater than 4 weeks showed a diminished half-maximum and maximum secretion rate. Rats treated for 12 weeks with 1.25 mg CS-A/kg b.wt. developed an impaired glucose tolerance after 8 weeks accompanied by a diminished pancreatic insulin content. Despite continued treatment the pancreatic insulin content was able to increase and the glucose tolerance to normalize, indicating an adaptation of pancreatic B-cells to CS-A. The results support the theory that a potential toxic effect of cyclosporin A can be diagnosed by functional tests (e.g. insulin secretion in response to a stepwise increase of glucose) before the irreversible (e.g. morphological) alterations occur.     

Alteration of Pancreatic B-Cells in Wistar Rats Treated with Non-Diabetogenic Doses of Cyclosporin A

Abstract: We have investigated the effect of non-immunosuppressive cyclosporin A (CS-A) doses on glucose tolerance, pancreatic insulin content, insulin content of isolated islets and insulin secretion in vitro in response to glucose. Within 12 weeks animals treated permanently with a dose of 2.5 mg CS-A/kg b.wt. developed glucose intolerance (but not hyperglycaemia) accompanied by a decrease of pancreatic insulin content due to a decrease of islet insulin content, whereas the relative B-cell volume density was.not changed. Isolated islets obtained from rats treated for 4 weeks had a diminished sensitivity for glucose, whereas islets obtained from animals treated for > 4 weeks showed a diminished half-maximum and maximum secretion rate. Rats treated for 12 weeks with 1.25 mg CS-A/kg b.wt. developed an impaired glucose tolerance after 8 weeks accompanied by a diminished pancreatic insulin content. Despite continued treatment the pancreatic insulin content was able to increase and the glucose tolerance to normalize, indicating an adaptation of pancreatic B-cells to CS-A. The results support the theory that a potential toxic effect of cyclosporin A can be diagnosed by functional tests (e.g. insulin secretion in response to a stepwise increase of glucose) before the irreversible (e.g. morphological) alterations occur.     

Effect of beta-sitosterol-3-beta-D-glucoside on insulin secretion in vivo in diabetic rats and in vitro in isolated rat islets of Langerhans

Beta-Sitosterol-3-beta-D-glucoside (1) has been reported to be the active antidiabetic agent of Centaurea seridis L. var. maritima. The present study examines the effect of oral administration of this compound on plasma insulin and glucose levels in streptozotocin-induced diabetic rats and its influence on insulin release from isolated rat islets. The results indicate that 1 did not change insulin and glucose levels in rats with severe diabetes. 1 stimulated insulin release from isolated rat islets in the presence of a non-stimulatory glucose concentration but did not increase the insulin releasing capacity of glucose (16 mmol/l). These data suggest that 1 exerts its action on intact pancreatic beta-cells by stimulating insulin secretion.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced impairment of glucose-stimulated insulin secretion in isolated rat pancreatic islets

We have explored the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) administration on the secretory function of isolated rat pancreatic islets. Twenty-four hours after TCDD administration (1 microg/kg b.w., i.p.), rats showed no significant differences in plasma glucose, insulin, triglycerides and leptin levels whereas plasma-free fatty acids were significantly increased with respect to untreated controls. In isolated islets, DNA and protein content were unchanged, whereas insulin content was significantly decreased in TCDD-treated rats. Incubation with different concentrations of glucose demonstrated a significant impairment of glucose-stimulated insulin secretion in islets isolated from TCDD-treated rats, whereas insulin release was better preserved upon alpha-ketoisocaproate stimulation. A significant reduction of [3H]-2-deoxy-glucose uptake was observed in pancreatic tissue of TCDD-treated rats, whereas no significant reduction in GLUT-2 protein levels was detectable by immunoblotting in islets from TCDD-treated rats. We concluded that low-dose TCDD could rapidly induce significant alterations of the pancreatic endocrine function in the rat.     

Effects of (-)15-deoxyspergualin on pancreatic islet B-cell function in vitro and on the development of diabetes after multiple low dose streptozotocin administration

The effects of (-)15-deoxyspergualin (15-DS), a newly described immunosuppressive drug, have been investigated on diabetes induced in mice treated with multiple low-dose streptozotocin (multiple SZ). Male C3D2F1 mice were treated with either intraperitoneal injections of saline or 15-DS (2.5 mg/kg body weight) for a total of 10 days, starting during the first day of SZ administration (5 days; 40 mg/kg body weight). On day 14, 15-DS-treated animals were still normoglycaemic, whilst on day 21 there was only a partial reduction in the hyperglycaemia compared to that found in the saline treated animals receiving SZ. 15-DS did not prevent hyperglycaemia in the long run (day 35-63). Furthermore, morphological examinations of pancreatic glands suggested that the insulitis in the pancreatic islets was delayed in the 15-DS-treated animals. In control experiments mice were treated with 15-DS+ the vehicle for SZ. This regimen did not hamper the glucose homeostasis of the animals. In vitro effects of 15-DS were also examined. Isolated islets from C3D2F1 mice were cultured at different concentrations of 15-DS (0.1-10.0 mg/l). After one week in culture, islet insulin release, islet insulin and DNA content were measured. The islets looked fluffy after culture at the higher 15-DS concentrations (4.0-10.0 mg/l) and at 10 mM almost all of the islets disappeared. A dose-dependent reduction of glucose-stimulated insulin release could also be seen. In other experiments islets were exposed to SZ and subsequently cultured in the presence of 0.5 mM 15-DS, however, 15-DS could not prevent the reduction in insulin release due to SZ exposure. Since 15-DS influences macrophage functions, the presently observed protective effects against the multiple SZ-treatment could reflect a reduced local interleukin-1 production in the islet vicinity. Alternatively, a lowered interleukin-1 secretion could prevent the activation of other immune cells involved in the destruction of B-cells.     

Acetaminophen-induced alterations in pancreatic beta cells and serum insulin concentrations in B6C3F1 mice

Administration of acetaminophen (500 mg/kg) to male B6C3F1 mice resulted in alterations of pancreatic beta cell ultrastructure. These alterations were characterized by pronounced intercellular spaces, cytoplasmic vacuolization, damaged membranes of cytoplasm, secretory granules, and other organelles, and pyknotic nuclei with disrupted membranes. Concomitant with these changes, acetaminophen also caused increaes in serum insulin concentrations from 24 microU/ml at 0 time to 160 microU/ml at 8 hr and increases in serum alanine aminotransferase (ALT) concentrations from 42 to 13,279 U/liter, which indicated hepatic damage. Quantitation of 3-(cystein-S-yl)acetaminophen adducts in hepatic 10,000g supernatant protein using a particle concentration fluorescence immunochemical assay indicated a positive correlation between binding and the occurrence of the hepatotoxicity consistent with what has been previously reported; however, 3-(cystein-S-yl)acetaminophen protein adducts were not detected in pancreatic 10,000g supernatant. Immunohistochemical analysis of the liver and pancreas from acetaminophen-treated mice revealed acetaminophen-protein adducts in the centrilobular regions of the liver but not in the pancreatic islets. Doses of 100 and 200 mg/kg produced no evidence of hepatotoxicity and no increase in serum insulin; 300 mg/kg and higher doses produced both hepatotoxicity and increased serum insulin concentrations. A comparison of the time course for the increase in serum levels of ALT and insulin following a toxic dose of acetaminophen indicated that the increase in ALT preceded the increase in insulin. Thus the hepatotoxicity of acetaminophen correlates with the formation of 3-(cystein-S-yl)acetaminophen protein adducts in liver, which supports the concept that this toxicity is mediated by the reactive metabolite N-acetyl-p-benzoquinone imine; however, the toxicity of acetaminophen to beta cells in the pancreas is apparently not mediated by this mechanism.     

Multiple effector pathways regulate the insulin secretory response to the imidazoline RX871024 in isolated rat pancreatic islets.

When isolated rat islets were cultured for 18 h prior to use, the putative imidazoline binding site ligand, RX871024 caused a dose-dependent increase in insulin secretion at both 6 mM and 20 mM glucose. By contrast, a second ligand, efaroxan, was ineffective at 20 mM glucose whereas it did stimulate insulin secretion in response to 6 mM glucose. Exposure of islets to RX871024 (50 microM) for 18 h, resulted in loss of responsiveness to this reagent upon subsequent re-exposure. However, islets that were unresponsive to RX871024 still responded normally to efaroxan. The imidazoline antagonist, KU14R, blocked the insulin secretory response to efaroxan, but failed to prevent the stimulatory response to RX871024. By contrast with its effects in cultured islets, RX871024 inhibited glucose-induced insulin release from freshly isolated islets. Efaroxan did not inhibit insulin secretion under any conditions studied. In freshly isolated islets, the effects of RX871024 on insulin secretion could be converted from inhibitory to stimulatory, by starvation of the animals. Inhibition of insulin secretion by RX871024 in freshly isolated islets was prevented by the cyclo-oxygenase inhibitors indomethacin or flurbiprofen. Consistent with this, RX871024 caused a marked increase in islet PGE2 formation. Efaroxan did not alter islet PGE2 levels. The results suggest that RX871024 exerts multiple effects in the pancreatic beta-cell and that its effects on insulin secretion cannot be ascribed only to interaction with a putative imidazoline binding site.