Insulin-like Effects of Vanadium: Mechanisms of Action,Clinical and Basic Implications

Summary Most or all mammalian cells contain vanadium at a concentration of 20 nM. The bulk of the vanadium in cells is probably in the reduced vanadyl (IV) form. Although this element is essential and should be present in the diet in minute quatities, no known physiological role for vanadium has been found thus far. In the years 1975–1980 the vanadate ion was shown to act as an efficient inhibitor of Na⁺, K⁺-ATPase and of other related phosphohydrolases as well. In 1980 it was observed that vanadate and vanadyl, when added to intact rat adipocytes, mimic the biological actions of insulin in stimulating hexose uptake and glucose oxidation. This initiated a long, currently active, field of research among basic scientists and diabetologists. Several of the aspects studied are reviewed here.     

Insulin-like Effects of Vanadium: Mechanisms of Action, Clinical and Basic Implications

Most or all mammalian cells contain vanadium at a concentration of 20 nM. The bulk of the vanadium in cells is probably in the reduced vanadyl (IV) form. Although this element is essential and should be present in the diet in minute quantities, no known physiological role for vanadium has been found thus far. In the years 1975–1980 the vanadate ion was shown to act as an efficient inhibitor of Na⁺,K⁺-ATPase and of other related phosphohydrolases as well. In 1980 it was observed that vanadate and vanadyl, when added to intact rat adipocytes, mimic the biological actions of insulin in stimulating hexose uptake and glucose oxidation. This initiated a long, currently active, field of research among basic scientists and diabetologists. Several of the aspects studied are reviewed here.     

Peroxovanadium compounds: Biolgoical actions and mechanism of insulin-mimesis

When used alone, both vanadate and hydrogen peroxide (H₂O₂) are weakly insulin-mimetic, while in combination they are strongly synergistic due to the formation of aqueous peroxovanadium species pV_(aq). Administration of these pV_(aq) species leads to activation of the insulin receptor tyrosine kinase (IRK), autophosphorylation at tyrosine residues and inhibition of phosphotyrosine phosphatases (PTPs). We therefore undertook to synthesize a series of peroxovanadium (pV) compounds containing one or two peroxo anions, an oxo anion and an ancillary ligand in the inner co-ordination sphere of vanadium, whose properties and insulin-mimetic potencies could be assessed. These pV compounds were shown to be the most potent inhibitors of PTPs yet described. Their PTP inhibitory potency correlated with their capacity to stimulate IRK activity. Some pV compounds showed much greater potency as inhibitors of insulin receptor (IR) dephosphorylation than epidermal growth factor receptor (EGFR) dephosphorylation, implying relative specificity as PTP inhibitors. Replacement of vanadium with either molybdenum or tungsten resulted in equally potent inhibition of IR dephosphorylation. However IRK activation was reduced by greater than 80% suggesting that these compounds did not access intracellular PTPs. The insulin-like activity of these pV compounds were demonstrablein vivo. Intra venous (i.v.) administration of bpV(pic) and bpV(phen) resulted in the lowaring of plasma glucose concentrations in normal rats in a dose dependent manner. The greater potency of bpV(pic) compared to bpV(phen) was explicable, in part, by the capacity of the former but not the latter to act on skeletal muscle as well as liver. Finally administration of bpV(phen) and insulin led to a synergism, where tyrosine phosphorylation of the IR -subunit increased by 20-fold and led to the appearance of four insulin-dependentin vivo substrates. The insulin-mimetic properties of they pV compounds raises the possibility for their use as insulin replacements in the management of diabetes mellitus.     

Role of antioxidant defenses in the tolerance of severe dehydration by anurans. The case of the leopard frog Rana pipiens

Protein tyrosine phosphatases (PTPs) play a critical role in regulating insulin action in part through dephosphorylation of the active (autophosphorylated) form of the insulin receptor (IRK) and attenuation of its tyrosine kinase activity. Following insulin binding the activated IRK is rapidly internalized into the endosomal apparatus, a major site at which the IRK is dephosphorylated in vivo. Studies in rat liver suggest a complex regulatory process whereby PTPs may act, via selective IRK tyrosine dephosphorylation, to modulate IRK activity in both a positive and negative manner. Use of peroxovanadium (pV) compounds, shown to be powerful PTP inhibitors, has been critical in delineating a close relationship between the IRK and its associated PTP(s) in vivo. Indeed the in vivo administration of pV compounds effected activation of IRK in parallel with an inhibition of IRK-associated PTP activity. This process was accompanied by a lowering of blood glucose levels in both normal and diabetic rats thus implicating the IRK-associated PTP(s) as a suitable target for defining a novel class of insulin mimetic agents. Identification of the physiologically relevant IRK-associated PTP(s) should facilitate the development of drugs suitable for managing diabetes mellitus.     

中药治疗糖尿病的研究概况

从单味中药及有效成分、有效部位,中药复方,作用机制等方面对近年来中药治疗糖尿病的研究概况进行综述,为进一步从中药中研制治疗糖尿病的创新药物提供参考。     

糖尿病中蛋白酪氨酸磷酸酶的研究进展

糖尿病是由于胰岛素分泌不足或胰岛素抵抗引起的以血糖升高为特征的代谢性疾病。有研究发现一些蛋白酪氨酸磷酸酶(proteintyrosine phosphatases,PTP)在胰岛素受体信号途径、胰岛素分泌和胰腺β细胞受自身免疫细胞攻击等生理或病理过程中起重要作用。以PTP1B、TCPTP和LYP为代表的PTP通过将底物去磷酸化,拮抗激酶催化的磷酸化反应,在一些信号通路中起到负相调节的作用。在糖尿病患者中发现这些PTP的单核苷酸突变使蛋白表达增加或酶活力增强,因而施用这些潜在靶蛋白的小分子抑制剂成为治疗1型或2型糖尿病可能的新疗法。而PTPIA-2/IA-2β的胞内磷酸酶结构域被发现是大量1型糖尿病患者的自身免疫原,因此可针对PTPIA-2/IA-2β发展早期诊断并预防1型糖尿病的试剂盒。     

硫化氢在糖尿病及其并发症中作用的研究进展

糖尿病及其并发症是覆盖全球的常见疾病,发病率逐年增高。硫化氢是继一氧化氮和一氧化碳之后的第三种气体信号分子,发挥重要病理生理学效应。目前研究发现,硫化氢在调节胰岛β细胞功能、胰岛素抵抗和糖尿病并发症中发挥着重要作用,已经成为糖尿病及其并发症的研究热点。本篇综述就H_2S在糖尿病及其并发症中发挥的病理生理学作用及机制进行了阐述。     

门冬胰岛素与人普通胰岛素及胰岛素泵在2型糖尿病患者围手术期的疗效比较

目的：探讨速效胰岛素类似物（门冬胰岛素,诺和锐）与人普通胰岛素（诺和灵R）及胰岛素泵在2型糖尿病（T2DM）围手术期治疗中的有效性和安全性。方法：158例围手术期T2DM患者随机分为胰岛素泵输注门冬胰岛素治疗CSII组52例,门冬胰岛素多次皮下注射治疗MSII（A）组56例,人普通胰岛素多次皮下注射治疗MSII（B）组50例。观察各组患者治疗前后空腹和餐后2h血糖变化、血糖迭标时间、胰岛素用量、低血糖发生率及术后并发症发生率。结果：3组治疗后血糖均明显低于抬疗前,CSII组治疗后血糖低于MSII（A）组（P〈o．05）,MSII（A）组治疗后血糖低于MSII（B）组（P〈0．05）;术后并发症CSII组低于MSII（A）组（P〈0．05）,MSII㈧组低于MSII（B）组（P〈0．05）。结论：门冬胰岛素对T2DM围手术期血糖控制有较好的有效性、安全性和顺应性,胰岛素泵是2型糖尿病患者围手术期胰岛素输注的最佳模式。     

Modulation of Glucose Transporter Protein by Dietary Flavonoids in Type 2 Diabetes Mellitus

Diabetes mellitus (DM) is a metabolic diseases characterized by hyperglycemia due to insufficient or inefficient insulin secretory response. This chronic disease is a global problem and there is a need for greater emphasis on therapeutic strategies in the health system. Phytochemicals such as flavonoids have recently attracted attention as source materials for the development of new antidiabetic drugs or alternative therapy for the management of diabetes and its related complications. The antidiabetic potential of flavonoids are mainly through their modulatory effects on glucose transporter by enhancing GLUT-2 expression in pancreatic β cells and increasing expression and promoting translocation of GLUT-4 via PI3K/AKT, CAP/Cb1/TC10 and AMPK pathways. This review highlights the recent findings on beneficial effects of flavonoids in the management of diabetes with particular emphasis on the investigations that explore the role of these compounds in modulating glucose transporter proteins at cellular and molecular level.     

联合应用甘精胰岛素和门冬胰岛素治疗儿童1型糖尿病疗效初步观察

目的:观察联合应用甘精胰岛素和门冬胰岛素治疗儿童1型糖尿病(type1diabetes mellitus,T1DM)的临床效果。方法:比较12例采用传统治疗方案(诺和灵30R,2/3量早餐前半小时皮下注射,1/3量晚餐前半小时皮下注射)的T1DM患儿,改用3+1治疗方案(3餐前0-15分钟诺和锐皮下注射,睡前来的时皮下注射)治疗后HbA1c水平、低血糖发生和胰岛素用量变化。结果:12例T1DM患儿改用3+1方案治疗时HbA1c基础值为9.51±0.71%,治疗后3个月时为9.12±0.82%,6个月时为8.61±0.87%、9个月时为8.71±0.68%、12个月时为8.65±0.79%。换用3+1方案治疗后第6、9、12个月时HbA1c值较基础值明显降低,差异有统计学意义(P<0.05)。每日胰岛素用量由1.1±0.8U/kg降至1.0±0.5U/kg,差异无统计学意义。传统方案治疗期间,6例次发生过严重低血糖,改用3+1治疗方案后,无1例发生严重低血糖。轻中度低血糖的发生次数由2.2±0.1次/周降至1.3±0.1次/周,差异有显著统计学意义(P<0.001)。结论:采用传统治疗方案治疗的T1DM患儿,改...     

The Full-Length, Cytoplasmic C-Terminus of the β2-Adrenergic Receptor Expressed in E. coli Acts as a Substrate for Phosphorylation by Protein Kinase A, Insulin Receptor Tyrosine Kinase, GRK2, but Not Protein Kinase C and Suppresses Desensitization when Expressed in Vivo

The ability of the cytoplasmic, full-length C-terminus of the β2-adrenergic receptor (BAC1) expressed in Escherichia coli to act as a functional domain and substrate for protein phosphorylation was tested. BAC1 was expressed at high-levels, purified, and examined in solution as a substrate for protein phosphorylation. The mobility of BAC1 on SDS–PAGE mimics that of the native receptor itself, displaying decreased mobility upon chemical reduction of disulfide bonds. Importantly, the C-terminal, cytoplasmic domain of the receptor expressed in E. coli was determined to be a substrate for phosphorylation by several candidate protein kinases known to regulate G-protein-linked receptors. Mapping was performed by proteolytic degradation and matrix-assisted laser desorption ionization, time-of-flight mass spectrometry. Purified BAC1 is phosphorylated readily by protein kinase A, the phosphorylation occurring within the predicted motif RRSSSK. The kinetic properties of the phosphorylation by protein kinase A displayed cooperative character. The activated insulin receptor tyrosine kinase, which phosphorylates the beta-adrenergic receptor in vivo, phosphorylates BAC1. The Y364 residue of BAC1 was predominantly phosphorylated by the insulin receptor kinase. GRK2 catalyzed modest phosphorylation of BAC1. Phosphorylation of the human analog of BAC1 in which Cys341 and Cys378 were mutated to minimize disulfide bonding constraints, displayed robust phosphorylation following thermal activation, suggesting under standard conditions that the population of BAC1 molecules capable of assuming the “activated” conformer required by GRKs is low. BAC1 was not a substrate for protein kinase C, suggesting that the canonical site in the second cytoplasmic loop of the intact receptor is preferred. The functional nature of BAC1 was tested additionally by expression of BAC1 protein in human epidermoid carcinoma A431 cells. BAC1 was found to act as a dominant-negative, blocking agonist-induced desensitization of the beta-adrenergic receptor when expressed in mammalian cells. Thus, the C-terminal, cytoplasmic tail of this G-protein-linked receptor expressed in E. coli acts as a functional domain, displaying fidelity with regard to protein kinase action in vivo and acting as a dominant-negative with respect to agonist-induced desensitization.     

Sustained Action of Ceramide on the Insulin Signaling Pathway in Muscle Cells: IMPLICATION OF THE DOUBLE-STRANDED RNA-ACTIVATED PROTEIN KINASE*

In vivo, ectopic accumulation of fatty acids in muscles leads to alterations in insulin signaling at both the IRS1 and Akt steps. However, in vitro treatments with saturated fatty acids or their derivative ceramide demonstrate an effect only at the Akt step. In this study, we adapted our experimental procedures to mimic the in vivo situation and show that the double-stranded RNA-dependent protein kinase (PKR) is involved in the long-term effects of saturated fatty acids on IRS1. C2C12 or human muscle cells were incubated with palmitate or directly with ceramide for short or long periods, and insulin signaling pathway activity was evaluated. PKR involvement was assessed through pharmacological and genetic studies. Short-term treatments of myotubes with palmitate, a ceramide precursor, or directly with ceramide induce an inhibition of Akt, whereas prolonged periods of treatment show an additive inhibition of insulin signaling through increased IRS1 serine 307 phosphorylation. PKR mRNA, protein, and phosphorylation are increased in insulin-resistant muscles. When PKR activity is reduced (siRNA or a pharmacological inhibitor), serine phosphorylation of IRS1 is reduced, and insulin-induced phosphorylation of Akt is improved. Finally, we show that JNK mediates ceramide-activated PKR inhibitory action on IRS1. Together, in the long term, our results show that ceramide acts at two distinct levels of the insulin signaling pathway (IRS1 and Akt). PKR, which is induced by both inflammation signals and ceramide, could play a major role in the development of insulin resistance in muscle cells.     

Vanadium and tungsten derivatives as antidiabetic agents: a review of their toxic effects

Tungstate is an oxyanion that has biological similarities to vanadate. In recent years, a number of studies have shown the antidiabetic effects of oral tungstate in animal models of diabetes. However, because of the tissue accumulation and potential toxicity derived from chronic administration of vanadium and tungsten compounds, the pharmacological use of vanadate or tungstate in the treatment of diabetes is not necessarily exempt from concern. In the context of a potential use in the treatment of human diabetes mellitus, the most relevant toxic effects of vanadium derivatives are reviewed and compared with those reported for tungsten. Hematological and biochemical alterations, loss of body weight, nephrotoxicity, immunotoxicity, reproductive and developmental toxicity, and behavioral toxicity have been reported to occur following exposure to vanadium compounds. Moreover, vanadium also has a mitogenic activity affecting the distribution of chromosomes during mitosis and inducing aneuploidyrelated end points. In contrast to vanadate, studies about the toxic effects of tungstate are very scant. Early investigations in cats, rabbits, dogs, mice, and rats showed that tungstate was less toxic than vanadate when given intravenously. Although in vitro investigations showed a direct effect of tungstate on the embryo and fetus of mice at concentrations similar to those causing effects in vivo, information on the potential cellular toxicity of tungstate is particularly scarce. Taking into account the recent interest of tungstate as a new potential oral antidiabetic agent, an exhaustive evaluation of its toxicity in mammals is clearly necessary.     

Increased Plasma Manganese, Partially Reduced Ascorbate,1 and Absence of Mitochondrial Oxidative Stress in Type 2 Diabetes Mellitus: Implications for the Superoxide Uncoupling Protein 2 (Ucp-2) Pathway

Oxidative stress is an important component of diabetes and its complications. Manganese (Mn), the key component of the Mitochondrial antioxidant (MnSOD), plays a key role in the superoxide uncoupling protein 2 (UCP-2) pathway in inhibiting of glucose-stimulated insulin secretion (GSIS). The interactions of Mn with ascorbate and other components of this pathway have not been defined in type-2 diabetes. Fifty established type 2 diabetics (30 males, 20 females) and 30 non-diabetics (controls; 18 males, 12 females) matched for age and sex were investigated. Dietary intake, particularly of micronutrients as assessed by 24-h dietary recall was similar between diabetics and controls. Weight and height of all subjects were determined and body mass index (BMI) computed after clinical assessment. Fasting plasma glucose, manganese, ascorbic acid, creatinine and K⁺ levels were determined; K⁺ was to assess the K⁺ channels, whereas creatinine was to assess probability of oxidative stress nephropathy. Body mass index was greater in DM than in controls (p < 0.001). Fasting plasma glucose and Mn levels (p < 0.00 and p < 0.01, respectively) were higher in diabetes than in the controls. Manganese level was greater than twice the levels in controls. Ascorbic acid was not significantly different (p > 0.05), but was 50% lower than the level in non-diabetics. Potassium like Mn and glucose was significantly higher in diabetes mellitus (DM) than in controls (p < 0.001). Creatinine was not significantly different between diabetics and controls (p > 0.05). Correlations among all parameters were not significantly different. These findings suggest absence of significant oxidative stress in the mitochondria, probably excluding a role for UCP-2-superoxide pathway in the inhibition of glucose-stimulated insulin secretion (GSIS), calling for caution in the precocious conclusion that interruption of UCP-2 activity may provide a viable strategy to improve β-cell dysfunction in type 2 diabetes mellitus.     

Diabetes mellitus caused by mutations in human insulin: analysis of impaired receptor binding of insulins Wakayama,Los Angeles and Chicago using pharmacoinformatics

Several naturally occuring mutations in the human insulin gene are associated with diabetes mellitus. The three known mutant molecules, Wakayama, Los Angeles and Chicago were evaluated using molecular docking and molecular dynamics (MD) to analyse mechanisms of deprived binding affinity for insulin receptor (IR). Insulin Wakayama, is a variant in which valine at position A3 is substituted by leucine, while in insulin Los Angeles and Chicago, phenylalanine at positions B24 and B25 is replaced by serine and leucine, respectively. These mutations show radical changes in binding affinity for IR. The ZDOCK server was used for molecular docking, while AMBER 14 was used for the MD study. The published crystal structure of IR bound to natural insulin was also used for MD. The binding interactions and MD trajectories clearly explained the critical factors for deprived binding to the IR. The surface area around position A3 was increased when valine was substituted by leucine, while at positions B24 and B25 aromatic amino acid phenylalanine replaced by non-aromatic serine and leucine might be responsible for fewer binding interactions at the binding site of IR that leads to instability of the complex. In the MD simulation, the normal mode analysis, rmsd trajectories and prediction of fluctuation indicated instability of complexes with mutant insulin in order of insulin native insulin < insulin Chicago < insulin Los Angeles < insulin Wakayama molecules which corresponds to the biological evidence of the differing affinities of the mutant insulins for the IR.     

Gastroretentive Microsponge as a Promising Tool for Prolonging the Release of Mitiglinide Calcium in Type-2 Diabetes Mellitus: Optimization and Pharmacokinetics Study

Diabetes mellitus is one of the leading causes of death due to the persistent hyperglycemia that leads to potential complications. Lack of patients’ adherence to their prescribed medication regimens, due to the requirement of frequent dosing, leads to failure of 40–50% of patients to manage their disease. Thus, microsponges of the novel short half-life mitiglinide calcium (MTG) were formulated using Quasi-emulsion solvent diffusion method, employing Eudragit RS100, ethyl cellulose, and polyvinyl alcohol, then characterized in terms of production yield, entrapment efficiency, particle size, in vitro buoyancy, in vitro drug release, and in vivo pharmacokinetics in rabbits. Optimization was done using response surface methodology; the optimized formulation was investigated by FTIR, DSC, and SEM. Results revealed that the optimized MTG microsponge was successfully formulated with high production yield (61.61%?±?0.6), entrapment efficiency (77.7% ±1.37), and particle size of 192.76 μm and it remained buoyant over simulated gastric fluid for 24 h with high percentage of in vitro buoyancy (91.01%?±?2.5). Moreover, it sustained the in vitro drug release with cumulative % release of 83.74?±?1.5 after 24 h. This microsponge was highly porous in nature with interconnected pores where MTG was entrapped with good compatibility as confirmed by SEM, DSC, and FTIR analysis; Pharmacokinetic studies showed improvement in C_max and AUC_0-∞ (1.92- and 20.68-fold, respectively) with marked prolongation in MRT and t_1/2 (7.22- and 7.97-fold, respectively) than the marketed tablet. Thus, it is a promising approach to improve diabetic patients’ compliance by eliminating the necessity of frequent dosing thus attaining better diabetes control.     

HYS-32, a novel analogue of combretastatin A-4, enhances connexin43 expression and gap junction intercellular communication in rat astrocytes

HYS-32 [4-(3,4-dimethoxyphenyl)-3-(naphthalen-2-yl)-2(5H)-furanone] is a new analogue of the anti-tumor compound combretastatin A-4 containing a cis-stilbene moiety. In this study, we investigated its effects on Cx43 gap junction intercellular communication (GJIC) and the signaling pathway involved in rat primary astrocytes. Western blot analyses showed that HYS-32 dose- and time-dependently upregulated Cx43 expression. A confocal microscopic study and scrape-loading/dye transfer analyses demonstrated that HYS-32 (5 μM) induced microtubule coiling, accumulation of Cx43 in gap junction plaques, and increased GJIC in astrocytes. The HYS-32-induced microtubule coiling and Cx43 accumulation in gap junction plaques was reversed when HYS-32 was removed. Treatment of astrocytes with cycloheximide resulted in time-dependent degradation of by co-treatment with HYS-32 by increasing the half-life of Cx43. Co-treatment with HYS-32 also prevented the LPS-induced downregulation of Cx43 and inhibition of GJIC in astrocytes. HYS-32 induced activation of PKC, ERK, and JNK, and co-treatment with the PKC inhibitor Go6976 or the ERK inhibitor PD98059, but not the JNK inhibitor SP600125, prevented the HYS-32-induced increase in Cx43 expression and GJIC. Go6976 suppressed the HYS-32-induced PKC phosphorylation and increase in phospho-ERK levels, while PD98059 did not prevent the HYS-32-induced increase in phospho-PKC levels, suggesting that PKC is an upstream effector of ERK. In conclusion, our results show that HYS-32 increases the half-life of Cx43 and enhances Cx43 expression and GJIC in astrocytes via a PKC–ERK signaling cascade. These novel biological effects of HYS-32 on astrocyte gap junctions support its potential for therapeutic use as a protective agent for the central nervous system.     

The prevalence,type and severity of cardiovascular disease in diabetic and non-diabetic patients: A matched-paired retrospective analysis using coronary angiography as the diagnostic tool

People with diabetes mellitus have a 2–8-fold excess in cardiovascular mortality than people without diabetes. This study compared angiographically determined cardiovascular disease in 79 patients with diabetes mellitus and an equal number of matched controls without diabetes under the age of 55 years. Seventy-nine diabetic patients coming to coronary angiography during a 12-month period were reviewed retrospectively along with 79 control patients matched for age (±3 years), sex, ethnic origin and risk factors (hyperlipidemia, body mass index and smoking history). The angiographic features of a consecutive series of 62 European and 17 Asian patients and their matched-paired controls were assessed. In all study subjects had undergone elective coronary angiography and ventriculography. Angiographic findings were graded to describe severity and extent of coronary atherosclerosis. Left ventricular systolic function was assessed by ejection fraction. The diabetic group had a significantly higher arterial systolic pressure than the non-diabetic group (p < 0.008) and they were clinically obese with a body mass index of >30. Detailed analysis of the angiograms showed that prevalence and severity of coronary artery disease in diabetic patients was greater. The mean severity score was 11.66 for the diabetic group against 8.49 for the non-diabetic group (p < 0.037). Multivessel disease was more common in diabetic patients than in the controls, with three-vessel disease being the most common. Furthermore, 38 of 79 diabetic patients had three-vessel disease compared to 29 of 79 controls. Diabetic patients were also more likely to have more segments diseased in one vessel. Systolic function was reduced in the diabetic group, with a significantly lower (p < 0.05) mean ejection fraction. The present study supports the evidence that diabetic patients have more extensive coronary artery disease than non-diabetic patients and a poorer prognosis, and that the coronary arteries of the Asian patients were affected more adversely than those of the European group irrespective of the diabetic state. (Mol Cell Biochem 261: 263–269, 2004)     

The Effects of Selenium Supplementation on Gene Expression Related to Insulin and Lipid Metabolism,and Pregnancy Outcomes in Patients with Gestational Diabetes Mellitus: a Randomized,Double-Blind,Placebo-Controlled Trial

Biological Trace Element Research - To observe and compare the effects of healthy instruction and Zhiqi granules on lead, calcium, iron, and zinc levels in serum of children with moderately...