Effect of N-benzoyl-D-phenylalanine and metformin on insulin receptors in neonatal streptozotocin-induced diabetic rats: studies on insulin binding to erythrocytes

In the present study, we focused on the insulin-receptor binding in circulating erythrocytes of N-benzoyl-D-phenylalanine (NBDP) and metformin in neonatal streptozotocin (nSTZ)-induced male Wistar rats. We measured blood levels of glucose and plasma insulin and the binding of insulin to cell-membrane ER receptors in NBDP and metformin-treated diabetic rats. The mean specific binding of insulin to ER was significantly lower in diabetic control rats (DC) (53.0 +/- 3.1%) than in NBDP (62.0 +/- 3.1%), metformin (66.0 +/- 3.3%) and NBDP and metformin combination-treated (72.0 +/- 4.2%) diabetic rats, resulting in a significant decrease in plasma insulin. Scatchard plot analysis demonstrated that the decrease in insulin binding was accounted for by a lower number of insulin receptor sites per cell in DC rats when compared with NBDP and metformin-treated rats. High-affinity (Kd1), low-affinity (Kd2), and kinetic analysis revealed an increase in the average receptor affinity in ER from NBDP and metformin-treated diabetic rats having NBDP 2.0 +/- 0.10 x 10(-10) M(-1) (Kd1); 12.0 +/- 0.85 x 10(-8) M(-1) (Kd2), Metformin 2.1 +/- 0.15 x 10(-10) M(-1) (Kd1); 15.0 +/- 0.80 x 10(-8) M(-1) (Kd2), NBDP and metformin 2.7 +/- 0.10 x 10(-10) M(-1) (Kd1); 20.0 +/- 1.2 x 10(-8) M(-1) (Kd2) compared with 0.9 +/- 0.06 x 10(-10) M(-1) (Kd1); 6.0 +/- 0.30 x 10(-8) M(-1) (Kd2) in DC rats. The results suggest an acute alteration in the number of insulin receptors on ER membranes in nSTZ induced diabetic control rats. Treatment with NBDP along with metformin significantly improved specific insulin binding, with receptor number and affinity binding reaching almost normal non-diabetic levels. The data presented here show that NBDP along with metformin increase total ER membrane insulin binding sites with a concomitant significant increase in plasma insulin.     

Increased insulin receptor binding in erythrocytes from growth hormone-deficient children

Erythrocytes from growth hormone-deficient children (GHd-children) (n=10) showed a statistically significant increase in insulin binding at low unlabeled insulin concentrations, together with a threefold decrease in apparent receptor affinity, as compared to control children (C) (n=11). Scatchard analysis of the binding data using the two-site model revealed that both the receptor concentration R₁ [GHd-children 0.10±0.01 ng/ml and C 0.03±0.002 ng/ml] and the dissociation constant K_D1 [GHd-children (0.48±0.05)×10^–9M and C (0.19±0.01)×10^–9M] for high affinitylow capacity sites were significantly increased in erythrocytes from GHd-children, while neither receptor concentrations (R₂) nor the dissociation constant (K_D2) for low affinity-high capacity sites proved to be altered. These events were accompanied by a normal sensitivity to insulin as well as glucose tolerance in the GHd-group. The meaning of the increased insulin binding with normal insulin sensitivity in GH-deficiency is discussed.     

The insulin-binding domain of insulin receptor is encoded by exon 2 and exon 3.

Insulin receptors are disulfide-linked oligotetramers composed of two heterodimers each containing a 130-kDa alpha subunit and a 90-kDa beta subunit. Insulin binds to the extracellular alpha subunit, and in the process stimulates the autophosphorylation of the beta subunit and the expression of tyrosine kinase activity. Studies combining the use of photoaffinity labeling and immunoprecipitation with anti-peptide antibody have directly demonstrated that the cysteine-rich domain, encoded by exon 3, in the alpha subunit is part of the insulin-binding site of the receptor. Experiments with chimeric insulin receptors and chimeric insulin-like growth factor I receptors have confirmed that the cysteine-rich domain constitutes a part of the insulin-binding site. In addition, results from these experiments suggest that the N-terminal sequence, encoded by exon 2, in the alpha subunit also participates in insulin binding. In this review it is proposed that, assuming two insulin-binding sites per each holoreceptor oligotetramer, each insulin-binding domain may contain respectively two sub-domains for hydrophobic and charge contact with insulin, and that high-affinity binding would require the interaction of both subunits with the possibility of each subunit reciprocally contributing one of the sub-domains.     

黄连素对糖尿病大鼠胰岛素抵抗的治疗作用

目的:探讨黄连素对链脲佐菌素所致糖尿病大鼠胰岛素抵抗的治疗作用。方法:采用链脲佐菌素腹腔注射的方式建立大鼠糖尿病模型,将实验大鼠分为5组:分别为模型组、黄连素低(100 mg/kg)、黄连素中(200 mg/kg)、黄连素高(300 mg/kg)剂量组和阳性对照组(二甲双胍:50 mg/kg),每组10只。另取10只正常大鼠作为正常组。黄连素低、中、高剂量组小鼠每天分别灌胃100、200和300 mg/kg黄连素;对照组每天灌胃二甲双胍50 mg/kg;正常组和模型组每天给予相同体积的生理盐水进行灌胃; 1次/天,连续灌胃4周。通过测定大鼠血FBG、果糖胺水平,OGTT实验,胰岛素(FINS)水平,并计算大鼠胰岛素抵抗指数(HOMA-IR)来评价黄连素对糖尿病大鼠胰岛素抵抗作用。结果:与正常组相比,给药前模型组大鼠静脉血FBG含量显著升高(P<0.05);与模型组比较,给药2周及以后给药4周后阳性对照组、黄连素中剂量组和高剂量组大鼠静脉血FBG含量均显著下降(P<0.05);给药4周后,阳性对照组、黄连素低、中、高剂量组OGTT实验结果显示在不同时间节点的血糖值均显著低于模...     

Effect of acute zinc deficiency on insulin receptor binding in rat adipocytes

Considerable data have been reported on the relationship between insulin resistance and zinc deficiency. In this study, insulin receptor binding was measured in isolated rat adipocytes. Two assays were carried out at 37°C (binding and internalization) and 16°C (binding) using¹²⁵I insulin 0.05–20 nM. A decreased insulin receptor binding was observed in zinc-deficient rat adipocytes, but we could not make any distinction between the specific zinc depletion effects and the effects of the caloric restriction induced by zinc deficiency.     

Comparison of insulin receptor binding to monocytes and erythrocytes in newly diagnosed type II diabetes mellitus

Insulin binding to circulating monocytes and erythrocytes was studied in 20 healthy volunteers and in 25 obese hyperinsulinemic newly diagnosed type-II diabetics. In type-II diabetics insulin binding to monocytes as well as to erythrocytes was significantly decreased in comparison with healthy individuals. The lowered insulin binding of the diabetics was mainly caused by a loss of receptor number. Individual analysis of the binding data, however, shows a marked discrepancy between receptor binding to circulating monocytes compared with erythrocytes. Since insulin binding to erythrocytes shows a great variation and seems to be influenced by other factors beside insulin concentrations it is suggested that insulin receptors on monocytes should be preferred for evaluation of peripheral insulin sensitivity.     

Effect of insulin on exocrine pancreatic secretion in healthy and diabetic anaesthetised rats

This investigation characterised the effects of exogenous insulin on exocrine pancreatic secretion in anaesthetised healthy and diabetic rats. Animals were rendered diabetic by a single injection of streptozotocin (STZ, 60 mg kg^–1 I.P.). Age-matched controls were injected citrate buffer. Rats were tested for hyperglycaemia 4 days after STZ injection and 7–8 weeks later when they were used for the experiments. Following anaesthesia (1 g kg^–1 urethane I.P.), laparotomy was performed and the pancreatic duct cannulated for collection of pure pancreatic juice. Basal pancreatic juice flow rate in diabetic rats was significantly (p < 0.001) increased whereas protein and amylase outputs were significantly (p < 0.001) decreased compared to control rats. Insulin (1 IU, I.P.) produced in healthy rats significant increases in pancreatic flow rate, amylase secretion and protein output compared to basal (p < 0.05). Insulin action also included a reduction in blood glucose (152.7 ± 16.9 mg dl^–1, n= 6, prior to insulin and 42.0 ± 8.4 mg dl^–1, n= 4, 100 min later). In fact, flow rate and glycaemia showed a strong negative correlation (p < 0.01, Pearson). Pretreatment with atropine (0.2 mg kg^–1, I.V.) abolished the effects of insulin on secretory parameters despite a similar reduction in glycaemia; in this series of experiments the correlation between flow rate and blood glucose was lost. In diabetic rats, insulin (4 IU, I.P.) did not modify exocrine pancreatic secretion. There was a fall in blood glucose (467.6 ± 14.0 mg dl^–1, n= 10, prior to insulin and 386.6 ± 43.6 mg dl^–1, n= 7, 120 min later). Rats, however, did not become hypoglycaemic. Similar results were observed in diabetic atropinized rats. The results of this study indicate that the effects of insulin on exocrine pancreatic secretion in anaesthetised healthy rats are mediated by hypoglycaemia-evoked vagal cholinergic activation. (Mol Cell Biochem 261: 105–110, 2004)     

姜黄素及其类似物J7对2型糖尿病大鼠睾丸氧化应激损伤的干预作用*

目的: 研究姜黄素(CUR)及其类似物J7对糖尿病大鼠睾丸氧化应激损伤的干预作用。方法: 60只SD大鼠随机分组,其中10只作为正常(NC)组,余50只通过高脂饮食和腹腔注射链脲佐菌素诱导建立糖尿病大鼠模型,造模成功后将其再分为4组:糖尿病(DM,n=12)组、姜黄素治疗(CUR,n=10)组、J7高剂量治疗(J+,n=10)组、J7低剂量治疗(J-,n=10)组。CUR组大鼠每天予以姜黄素20 mg/kg灌胃治疗,J+及J-组分别予以J7 20 mg/kg、10 mg/kg灌胃治疗,8周后处死大鼠,测量各组大鼠体重、空腹血糖,羟胺法和硫代巴比妥酸法分别检测超氧化物歧化酶(SOD)活性和丙二醛(MDA)含量,Western blot法检测tNrf2、pNrf2、CAT、NQO1蛋白表达水平,qRT-PCR检测CAT、NQO1、HO1 mRNA表达水平,光镜下观察大鼠睾丸形态学改变,免疫组化检测Nrf2及CAT蛋白表达情况。结果: DM组血糖、MDA水平升高(P＜0.05),体重、SOD活性、pNrf2/tNrf2、CAT、NQO1蛋白及CAT、NQO1、HO1 mRNA水平均有下降(P＜0.05);光镜下见睾丸各级生精细胞减少、排列紊乱;免疫组化显示Nrf2蛋白核周表达量下降,CAT蛋白表达水平降低。经姜黄素及J7治疗后,三个治疗组的MDA水平均下降(P＜0.05),SOD活性、pNrf2/tNrf2、CAT、NQO1蛋白及NQO1、HO1 mRNA水平均上升(P＜0.05),J+及J-组血糖显著下降(P＜0.05),J+组CAT mRNA水平显著上升(P＜0.05);J+组pNrf2/tNrf2比值明显高于CUR组及J-组(P＜0.05),J+组CAT蛋白水平也明显高于J-组(P＜0.05),其余指标在三个治疗组间不具有显著性差异。光镜下见三个治疗组睾丸形态学病变减轻;免疫组化显示Nrf2蛋白核周表达量上升,CAT蛋白表达水平升高。提示高剂量J7抗糖尿病大鼠睾丸的氧化应激损伤的能力较强。结论: 姜黄素及J7可在一定程度上对抗糖尿病大鼠睾丸的氧化应激损伤,其机制可能与Nrf2-ARE信号通路的激活相关。     

Pollen Typhae total flavone improves insulin resistance in high-fat diet and low-dose streptozotocin-induced type 2 diabetic rats

Pollen Typhae total flavone (PTF), the extract from Pollen Typhae, is reported to enhance glucose uptake in C2C12 myotubes in vitro, but the convincing evidence is lacking in vivo. In this study, PTF ameliorated insulin resistance and dyslipidemia, but failed to significantly increase body weight in type 2 diabetic rats induced by high-fat diet and low-dose streptozotocin.     

槟榔碱对2型糖尿病大鼠肝脏胰岛素抵抗的作用

目的：探讨槟榔碱对2型糖尿病大鼠肝脏胰岛素抵抗的影响及其机制。方法：采用高果糖饲料饲养Wistar大鼠12周制备2型糖尿病大鼠模型,实验动物随机分为5组（n=8）：对照组、模型组、模型＋不同浓度的槟榔碱（0,0．5,1,5mg／kg）组。4周后通过检测血糖、血脂、胰岛素、RT-PCR检测肝脏组成型雄甾烷受体（CAR）、孕甾烷x受体（PXR）、糖代谢相关基因：葡萄糖-6-磷酸酶（G6Pase）、磷酸烯醇式丙酮酸羧激酶（PEPCK）和炎症相关因子：白细胞介素-6（IL-6）、肿瘤坏死因子α（TNF-α）mRNA表达,Western blot检测大鼠肝内p-AKT和葡萄糖转运体4（GLUT4）蛋白表达。结果：1,5mg／kg槟榔碱显著降低糖尿病大鼠体重、空腹血糖、空腹胰岛素、血脂和糖代谢相关基因及炎症相关因子mRNA水平,提高CAR、PXR mRNA水平及p-AKT、GLUT4蛋白水平。结论：槟榔碱可能通过提高CAR和PXR的表达,导致肝脏糖代谢关键酶PEPCK、G6Pase基因表达或者炎性因子肿瘤坏死因子-α（TNF-α）、白介素-6（n-6）表达降低,改善2型糖尿病大鼠肝脏胰岛素抵抗。     

Effect of long-term nickel ingestion on insulin binding and antilipolytic response in rat adipocytes

Male Wistar rats of the third generation of rats drinking 200 micrograms Ni2+/mL as NiCl2 in their drinking water were studied. Basal plasma glucose and insulin levels were unchanged. Epididymal adipocytes from Ni2(+)-fed rats showed an increased insulin binding with a slight increase in apparent insulin affinity (ED50: Ni2(+)-fed rats 2.8 x 10(-9) M and controls 5 x 10(-9) M) with no change in insulin receptor numbers (Ni2(+)-fed rats 143,000 +/- 12,000 (6) receptors/cell and controls 126,000 +/- 13,000 (5]. Moreover, a decreased sensitivity to the antilipolytic response of insulin was also observed in adipocytes from Ni2(+)-fed rats. These events could represent actions of Ni2+ both at the receptor and post-receptor insulin levels. Several possible mechanisms involved in the process are suggested.     

Effect of starvation on insulin production and insulin binding in Tetrahymena

Tetrahymena pyriformis GL was starved for 24 h and then the immunologically demonstrable insulin content and FITC-insulin binding were measured by flow cytometry and localization was studied by confocal microscopy. The amount of endogeneous insulin as well as FITC insulin binding, was highly significantly elevated. Glucose feeding for 30 min abolished the elevation of FITC-insulin binding. In starved cells, insulin-binding sites disappeared from the surface and FITC-insulin was bound inside the cells, within large food vacuoles. Endogeneous insulin was dispersed in the cytoplasm both in the control and starved cells and food vacuoles did not contain it. The results call attention to the stimulatory effect of starvation on insulin production in Tetrahymena, in parallel with the internal storage of insulin receptors, which points to an autocrine mechanism.     

Effect of gamma irradiation on insulin receptor interaction in rat erythrocytes

An insulin receptor interaction has been studied in rat erythrocytes after whole-body gamma irradiation (1 Gy). Specific binding of insulin was found to increase 30 days following irradiation against the background of a decreased immunoreactive insulin concentration in the blood. A change in the postirradiation activity of insulin receptors is considered as a manifestation of the homeostatic mechanism of "up" regulation in exposed animals.     

Tissue-specific expression of insulin receptor isoforms in obesity/type 2 diabetes mouse models

The two insulin receptor (IR) isoforms IR-A and IR-B are responsible for the pleiotropic actions of insulin and insulin-like growth factors. Consequently, changes in IR isoform expression and in the bioavailability of their ligands will impact on IR-mediated functions. Although alteration of IR isoform expression has been linked to insulin resistance, knowledge of IR isoform expression and mechanisms underlying tissue/cell-type-specific changes in metabolic disease are lacking. Using mouse models of obesity/diabetes and measuring the mRNA of the IR isoforms and mRNA/protein levels of total IR, we provide a data set of IR isoform expression pattern that documents changes in a tissue-dependent manner. Combining tissue fractionation and a new in situ mRNA hybridization technology to visualize the IR isoforms at cellular resolution, we explored the mechanism underlying the change in IR isoform expression in perigonadal adipose tissue, which is mainly caused by tissue remodelling, rather than by a shift in IR alternative splicing in a particular cell type, e.g. adipocytes.     

姜黄素衍生物B06对2型糖尿病大鼠心肌的保护作用及其机制探讨

目的：研究姜黄素衍生物B06对2型糖尿病大鼠心肌的保护作用及机制。方法：雄性sD大鼠35只,随机均分为正常对照组（NC组）、高脂组（肿组）、高脂治疗组（rT组）、糖尿病组（DM组）和糖尿病治疗组（DT组）（n=7）,后四组高脂喂养4周后,DM组及七rr组用低剂量链脲佐菌素（srz）诱导糖尿病,FTr组和町组用0．2mg／kg·d的姜黄素衍生物B06灌胃。用生化方法测大鼠血糖和血脂浓度,用ELISA法测血胰岛素水平,并计算胰岛素抵抗指数,用光镜和电镜观察心肌形态,用Westernblot法测心肌腺苷酸活化蛋白激酶a（AMPKa）和磷酸化腺苷酸活化蛋白激酶a（p-AMPKa）的蛋白表达。结果：HF组及DM组血糖、血脂、血胰岛素、胰岛素抵抗指数升高,经B06治疗后均下降;HF组及DM组AMPKa和p-AMPKa表达下降,经／306治疗后升高;DM纽心肌间质胶原纤维增多,心肌细胞内线粒体扩张,经B06治疗后病变减轻。结论：B06可缓解2型糖尿病大鼠心肌病变,AMPKa和p-AMPKa表达升高可能参与其中。     

Effect of metformin on insulin receptor binding and glycaemic control in type II diabetes.

To investigate the effect of metformin on insulin receptor binding and diabetic control, eight obese type II diabetic patients were studied before treatment, after one and four weeks of taking metformin (500 mg thrice daily), and four weeks after withdrawal of the drug. After one and four weeks of treatment the number of erythrocyte insulin receptors had increased by 116% and 184% respectively. This was due almost entirely to an increase in the number of low affinity binding sites. The number of receptors was still raised four weeks after metformin had been withdrawn. Diabetic control as assessed by urinary glucose, glycosylated haemoglobin (HbA1), and glucose tolerance values was significantly improved during metformin treatment, while plasma insulin concentrations were not altered. These results indicate that metformin produces a rapid and protracted increase in low affinity insulin receptors in type II diabetes, associated with greater insulin sensitivity and improved diabetic control.     

Binding of SH2 containing proteins to the insulin receptor: A new way for modulating insulin signalling

Prior studies have established a role in insulin action for the tyrosine phosphorylation of substrates and their subsequent complexing with SH2 containing proteins. More recently, SH2 proteins have been identified which can tightly bind to the tyrosine phosphorylated insulin receptor. The major protein identified so far (called Grb-IR or Grb10) of this type appears to be present in at least 3 isoforms, varying in the presence of a pleckstrin homology domain and in the sequence of its amino terminus. The binding of this protein to the insulin receptor appears to inhibit signalling by the receptor. The present review will discuss the current knowledge of the structure and function of this protein.     

Effects of phorbol esters on insulin receptor function and insulin action in hepatocytes: evidence for heterogeneity

We investigated the effect of phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator on insulin receptors and insulin action in freshly isolated and primary cultures of rat hepatocytes. PMA (1 x 10^–7 M) did not alter insulin receptor numbers or affinity either acutely or chronically but within 60 minute inactivated insulin stimulated tyrosine kinase of the insulin receptor. PKC activation inhibitied insulin (1 x 10^–7M) stimulation of glycogen and lipid synthesis with a decrease or no change in basal glycogenesis and lipogenesis respectively. However, PKC activation did not alter insulin stimulated or basal amino acid transport even though PCK activation inhibited insulin stimulation of the insulin. receptor tyrosine kinase. Thus, within one tissue, PKC activation has differential effect on insulin action depending on which pathway is examined. Furthermore, insulin stimulation of the insulin receptor tyrosine kinase may not be a necessary step for all insulin signaling pathways.     

姜黄素类似物L6H4对2型糖尿病大鼠肾脏的保护作用

目的：探讨姜黄素类似物L6H4对2型糖尿病大鼠肾脏的保护作用及机制。方法：24只SPF级雄性SD大鼠,随机分成3组（n=8）：对照组（NC组）、糖尿病组（DM组）和糖尿病治疗组（DT组）,采用高脂饮食加腹腔注射低剂量链脲佐菌素诱导2型糖尿病大鼠模型。DT组按0.2 mg/kg·d剂量的L6H4灌胃8周。治疗结束后测24 h尿蛋白、空腹血糖（FBG）、甘油三酯（TG）、血肌酐（Scr）、血尿素氮（BUN）、尿酸（UA）。采用光镜和透射电镜观察大鼠肾脏的形态学改变;用免疫组化法测定大鼠肾脏组织转化生长因子-β1（TGF-β1）、纤维粘连蛋白（FN）、四型胶原（Col-IV）的表达水平。结果：DM组大鼠24 h尿蛋白、FBG、TG、Scr、BUN均明显升高（P<0.01）,肾小球体积增大、不规则,弥漫性系膜基质增多,伴基底膜不同程度的增生肥厚及足突融合现象;肾组织的TGF-β1、FN、Col-IV表达水平明显增加（P<0.05）。经L6H4治疗后,DT组的24 h尿蛋白、FBG、TG、Scr、BUN水平明显下降（P<0.01）,大鼠肾小球形态较规则,系膜区基质明显减少,足细胞肿胀、融合现象减轻;肾组织的TGF-β1、FN、Col-IV表达明显减少（P<0.05）。结论：L6H4可能通过下调TGF-β1的表达,抑制FN、Col-IV的大量分泌,减轻细胞外基质的沉积,从而起到保护2型糖尿病大鼠肾脏的作用。