Vanadium in diabetes: 100 years from Phase 0 to Phase I

A little over one hundred years ago, a vanadium-containing compound was assessed clinically for use in treatment of human diabetic patients. The results were somewhat ambiguous, but nonetheless, intriguing. In 2000, the first Phase I clinical trial of a designed vanadium-based pharmaceutical agent (bis(ethylmaltolato)oxovanadium(IV), BEOV), was completed by Medeval Ltd., Manchester, UK. Results here, too, were promising, but not without some difficult remaining questions. In this review, we look back at the many questions asked and answered regarding vanadium’s glucose-enhancing potential, its biodistribution and biomolecular transformation, and its mechanism(s) of action, and consider some of the newest developments in the field, including novel delivery methods for vanadium in diabetes treatment.     

Calorimetric studies of the interaction between the insulin-enhancing drug candidate bis(maltolato)oxovanadium(IV) (BMOV) and human serum apo-transferrin

Bis(maltolato)oxovanadium(IV) (BMOV), and its ethylmaltol analog, bis(ethylmaltolato)oxovanadium(IV) (BEOV), are candidate insulin-enhancing agents for the treatment of type 2 diabetes mellitus; in mid-2008, BEOV advanced to phase II clinical testing. The interactions of BMOV and its inorganic congener, vanadyl sulfate (VOSO₄), with human serum apo-transferrin (hTf) were investigated using differential scanning calorimetry (DSC). Addition of BMOV or VOSO₄ to apo-hTf resulted in an increase in thermal stability of both the C- and N-lobes of transferrin as a result of binding to either vanadyl compound. A series of DSC thermograms of hTf solutions containing different molar ratios of BMOV and VOSO₄ were used to determine binding constants; at 25 °C the binding constants of BMOV to the C- and N-lobes of apo-hTf were found to be 3 (±1) × 10⁵ and 1.8 (±0.7) × 10⁵ M⁻¹, respectively. The corresponding values for VOSO₄ were 1.7 (±0.3) × 10⁵ and 7 (±2) × 10⁴ M⁻¹. The results show that the vanadium species initially presented as either BMOV or VOSO₄ had similar affinities for human serum transferrin due to oxidation of solvated vanadyl(IV) prior to complexation to transferrin. Binding of metavanadate () was confirmed by DSC and isothermal titration calorimetry (ITC) experiments of the interaction between sodium metavanadate (NaVO₃) and hTf.     

Metallokinetic characteristics of antidiabetic bis(allixinato)oxovanadium(IV)-related complexes in the blood of rat

The antidiabetic effect of vanadium is a widely accepted phenomenon; some oxovanadium(IV) complexes have been found to normalize high blood glucose levels in both type 1 and type 2 diabetic animals. In light of the future clinical use of these complexes, the relationship among their chemical structures, physicochemical properties, metallokinetics, and antidiabetic activities must be closely investigated. Recently, we found that among bis(3-hydroxypyronato)oxovanadium(IV) [VO(3hp)₂] related complexes, bis(allixinato)oxovanadium(IV) [VO(alx)₂] exhibits a relatively strong hypoglycemic effect in diabetic animals. Next, we examined its metallokinetics in the blood of rats that received five VO(3hp)₂-related complexes by the blood circulation monitoring–electron paramagnetic resonance method. The metallokinetic parameters were obtained from the blood clearance curves based on a two-compartment model; most parameters, such as area under the concentration curve and mean residence time, correlated significantly with the in vitro insulinomimetic activity in terms of 1/IC₅₀ (IC₅₀ is the 50% inhibitory concentration of the complex required for the release of free fatty acids in adipocytes) and the lipophilicity of the complex (log P _com). The oxovanadium(IV) concentration was significantly higher and the species resided longer in the blood of rats that received VO(alx)₂ than in the blood of rats that received VO(3hp)₂ or bis(kojato)oxovanadium(IV); VO(alx)₂ also exhibited higher log P _com and 1/IC₅₀ values. On the basis of these results, we propose that the introduction of lipophilic groups at the C2 and C6 positions of the 3hp ligand is an effective method to enhance the hypoglycemic effect of the complexes, as supported by the observed in vivo exposure and residence in the blood.     

Improvement of diabetes, obesity and hypertension in type 2 diabetic KKAy mice by bis(allixinato)oxovanadium(IV) complex

Previously, we found that bis(allixinato)oxovanadium(IV) (VO(alx)(2)) exhibits a potent hypoglycemic activity in type 1-like diabetic mice. Since the enhancement of insulin sensitivity is involved in one of the mechanisms by which vanadium exerts its anti-diabetic effects, VO(alx)(2) was further tested in type 2 diabetes with low insulin sensitivity. The effect of oral administration of VO(alx)(2) was examined in obesity-linked type 2 diabetic KKA(y) mice. Treatment of VO(alx)(2) for 4 weeks normalized hyperglycemia, glucose intolerance, hyperinsulinemia, hypercholesterolemia and hypertension in KKA(y) mice; however, it had no effect on hypoadiponectinemia. VO(alx)(2) also improved hyperleptinemia, following attenuation of obesity in KKA(y) mice. This is the first example in which a vanadium compound improved leptin resistance in type 2 diabetes by oral administration. On the basis of these results, VO(alx)(2) is proposed to enhance not only insulin sensitivity but also leptin sensitivity, which in turn improves diabetes, obesity and hypertension in an obesity-linked type 2 diabetic animal.     

Reduction of vanadium(V) with ascorbic acid and isolation of the generated oxovanadium(IV) species

The interaction of sodium metavanadate and VOCl₃ with ascorbic acid, one of the possible natural reducing agents of vanadium(V) to oxovanadium(IV), has been investigated. Three new VO²⁺ complexes could be isolated as microcrystalline powders. One of them, of composition K_1.5Na_0.5[VO(HAsc)(OH)₃], contains ascorbic acid as a monodentate ligand. In the other two, K[VO(Diketo)(OH)]·H₂O and Na₃[VO(Diketo)₂(OH)], the enolized form of 2,3-diketogulonic acid (one of the oxidation products of ascorbic acid), acts as a bidentate ligand. The complexes were characterized by means of electronic (absorption and reflectance) and infrared spectroscopy and magnetic susceptibility measurements. Their thermal behavior was investigated by thermogravimetric and differential thermal analyses. The interest of the investigated system in relation to vanadium detoxification is also discussed.     

Inhibition of protein tyrosine phosphatase 1B and alkaline phosphatase by bis(maltolato)oxovanadium (IV)

Vanadate has been recognized as a specific and potent phosphatase inhibitor since its structure is similar to that of phosphate. In this study, we measured the inhibition of glutathione S-transferase-tagged protein tyrosine phosphatase 1B (GST-PTP1B) and alkaline phosphatase (ALP) by the insulin enhancing compounds, bis(maltolato)oxovanadium(IV) (BMOV). The results showed that the activity of GST-PTP1B was reversibly inhibited by solutions of BMOV with an IC₅₀ value of 0.86 ± 0.02 μM. Steady state kinetic studies showed that inhibition of GST-PTP1B by BMOV was of a mixed competitive and noncompetitive type. In addition, incubation of GST-PTP1B with BMOV showed a time-dependent biphasic inactivation of the protein. On the other hand, the inhibitory behavior of BMOV on ALP activity was reversible and competitive with an IC₅₀ value of 32.1 ± 0.6 μM. Incubation with BMOV did not show biphasic inactivation of ALP. The reversible inhibition of GST-PTP1B by BMOV is more potent than that of ALP, but solutions of BMOV inhibited both enzymes. This data support the suggestion that mechanisms for the inhibitory effects of BMOV on GST-PTP1B and ALP are very different.     

Vanadium detoxification: on the interaction of oxovanadium(IV) and other vanadium species with 2,3-dimercapto-1-propanesulfonate

The interaction of the VO²⁺ cation with the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS) was investigated by electron absorption spectroscopy in aqueous solution, in the pH range between 4 and 12. The spectral behavior points to the generation of a [VO(DMPS)₂]⁴⁻ complex in which the oxocation interacts with two pairs of deprotonated –SH groups of the ligand. By spectrophotometric monitoring it was found that DMPS rapidly reduces vanadates(V) to VO²⁺ which may be chelated by an excess of the acid. DMPS produces also the slow reduction of a V₂O₅ suspension at pH 7.1. The results of this study suggest that DMPS may be a potentially useful detoxification agent for vanadium.     

Haptoglobin2-2 phenotype is an additional risk factor of retinopathy in type 2 diabetes mellitus

AIMS:

The aim of this study was to investigate the association between haptoglobin (Hp) phenotypes and risk of the development of diabetic retinopathy (DR) in patients of type 2 diabetes mellitus.

MATERIALS AND METHODS:

This cross-sectional study included 45 normotensive type 2 diabetic patients (duration more than 5 years) admitted in the hospital divided into two groups (with and without DR) on the basis of fundus examination by direct ophthalmoscopy. Serum samples of all patients were subjected for Hp phenotyping by polyacrylamide gel electrophoresis.

RESULTS:

DR was associated significantly in diabetic patients with Hp2-2 phenotype (79.31%) than diabetic patients with Hp2-1 phenotype (43.75%) and Hp2-2 had higher odds ratio (OR) for DR in univariate analysis (OR 4.929, [95% confidence interval [CI] (1.297-18.733)], P = 0.016) and multivariate analysis (OR 7.704 [95% CI (0.887-66.945)], P = 0.064). Furthermore, Hp2-2 was associated significantly with severe forms of DR.

CONCLUSION:

Hp2-2 phenotype is associated with susceptibility to DR showing a graded risk relationship to the number of Hp2 alleles. Determination of Hp phenotype may be useful in the risk assessment and management of DR.     

Some biologically active oxovanadium(IV) complexes of triazole derived Schiff bases: their synthesis,characterization and biological properties

A series of biologically active oxovanadium(IV) complexes of triazole derived Schiff bases L₁–L₅ have been synthesized and characterized by their physical, analytical, and spectral data. The synthesized ligands potentially act as bidentate, in which the oxygen of furfural and nitrogen of azomethine coordinate with the oxovanadium atom to give a stoichiometry of vanadyl complexes 1:2 (M:L) in a square-pyramidal geometry. In vitro antibacterial and antifungal activities on different species of pathogenic bacteria (E. coli, S. flexneri, P. aeruginosa, S. typhi, S. aureus, and B. subtilis) and fungi (T. longifusus, C. albicans, A. flavus, M. canis, F. solani, and C. glabrata) have been studied. All compounds showed moderate to significant antibacterial activity against one or more bacterial strains and good antifungal activity against most of the fungal strains. The brine shrimp bioassay was also carried out to check the cytotoxicity of coordinated and uncoordinated synthesized compounds.     

The future of protein biomarker research in type 2 diabetes mellitus

Introduction: The onset of type 2 diabetes mellitus (T2DM) is strongly associated with obesity and subsequent perturbations in immuno-metabolic responses. To understand the complexity of these systemic changes and better monitor the health status of people at risk, validated clinical biomarkers are needed. Omics technologies are increasingly applied to measure the interplay of genes, proteins and metabolites in biological systems, which is imperative in understanding molecular mechanisms of disease and selecting the best possible molecular biomarkers for clinical use.

Areas covered: This review describes the complex onset of T2DM, the contribution of obesity and adipose tissue inflammation to the T2DM disease mechanism, and the output of current biomarker strategies. A new biomarker approach is described that combines published and new self-generated data to merge multiple -omes (i.e. genome, proteome, metabolome etc.) toward understanding of mechanism of disease on the individual level and design multiparameter biomarker panels that drive significant impacts on personalized healthcare.

Expert commentary: We here propose an approach to use cross-omics analyses to contextualize published biomarker data and better understand molecular mechanisms of health and disease. This will improve the current and future innovation gaps in translation of discovered putative biomarkers to clinically applicable biomarker tests.     

Synthesis,characterization and evaluation of the suppression of insulin resistance in Type-II diabetes mellitus animals by treatment with metal complex

The present study is characterized toward thespesone isolation from Thespesia populnea (Malvaceae). Subsequently it was modified and characterized to study its effect on diabetes related symptoms. The complex is administered to diabetes induced mice with the doses of 5, 10 and 20 mg/kg, p.o. and the effect of complex on the level of body weight, lipid profile and blood glucose was studied after 22 days. The results have indicated that diabetic mice show a significant (p < 0.01) decrease in the level of serum triglyceride, plasma glucose and increase in body weight. Hence the present investigation reveals that newly synthesized complex is useful in the management of Type-II diabetes mellitus because of its ability to reduce insulin resistance.     

The design and synthesis of a potent glucagon receptor antagonist with favorable physicochemical and pharmacokinetic properties as a candidate for the treatment of type 2 diabetes mellitus

A novel and potent small molecule glucagon receptor antagonist for the treatment of diabetes mellitus is reported. This candidate, (S)-3-[4-(1-{3,5-dimethyl-4-[4-(trifluoromethyl)-1H-pyrazol-1-yl]phenoxy}butyl)benzamido]propanoic acid, has lower molecular weight and lipophilicity than historical glucagon receptor antagonists, resulting in excellent selectivity in broad-panel screening, lower cytotoxicity, and excellent overall in vivo safety in early pre-clinical testing. Additionally, it displays low in vivo clearance and excellent oral bioavailability in both rats and dogs. In a rat glucagon challenge model, it was shown to reduce the glucagon-elicited glucose excursion in a dose-dependent manner and at a concentration consistent with its rat in vitro potency. Its properties make it an excellent candidate for further investigation.     

In vivo effects of insulin and bis(maltolato)oxovanadium (IV) on PKB activity in the skeletal muscle and liver of diabetic rats

In this study, the in vivo effects of insulin and chronic treatment with bis(maltolato)oxovanadium (IV) (BMOV) on protein kinase B (PKB) activity were examined in the liver and skeletal muscle from two animal models of diabetes, the STZdiabetic Wistar rat and the fatty Zucker rat. Animals were treated with BMOV in the drinking water (0.75–1 mg/ml) for 3 (or 8) weeks and sacrificed with or without insulin injection. Insulin (5 U/kg, i.v.) increased PKB activity more than 10fold and PKB activity more than 3fold in both animal models. Despite the development of insulin resistance, insulininduced activation of PKB was not impaired in the STZdiabetic rats up to 9 weeks of diabetes, excluding a role for PKB in the development of insulin resistance in type 1 diabetes. Insulin-induced PKB activity was markedly reduced in the skeletal muscle of fatty Zucker rats as compared to lean littermates (fatty: 7fold vs. lean: 14fold). In contrast, a significant increase in insulinstimulated PKBa activity was observed in the liver of fatty Zucker rats (fatty: 15.7fold vs. lean: 7.6fold). Chronic treatment with BMOV normalized plasma glucose levels in STZdiabetic rats and decreased plasma insulin levels in fatty Zucker rats but did not have any effect on basal or insulininduced PKB and PKB activities. In conclusion (i) in STZdiabetic rats PKB activity was normal up to 9 weeks of diabetes; (ii) in fatty Zucker rats insulininduced activation of PKB (but not PKB) was markedly altered in both tissues; (iii) changes in PKB activity were tissue specific; (iv) the glucoregulatory effects of BMOV were independent of PKB activity.     

Metabolomics reveals attenuation of the SLC6A20 kidney transporter in nonhuman primate and mouse models of type 2 diabetes mellitus

To enhance understanding of the metabolic indicators of type 2 diabetes mellitus (T2DM) disease pathogenesis and progression, the urinary metabolomes of well characterized rhesus macaques (normal or spontaneously and naturally diabetic) were examined. High-resolution ultra-performance liquid chromatography coupled with the accurate mass determination of time-of-flight mass spectrometry was used to analyze spot urine samples from normal (n = 10) and T2DM (n = 11) male monkeys. The machine-learning algorithm random forests classified urine samples as either from normal or T2DM monkeys. The metabolites important for developing the classifier were further examined for their biological significance. Random forests models had a misclassification error of less than 5%. Metabolites were identified based on accurate masses (<10 ppm) and confirmed by tandem mass spectrometry of authentic compounds. Urinary compounds significantly increased (p < 0.05) in the T2DM when compared with the normal group included glycine betaine (9-fold), citric acid (2.8-fold), kynurenic acid (1.8-fold), glucose (68-fold), and pipecolic acid (6.5-fold). When compared with the conventional definition of T2DM, the metabolites were also useful in defining the T2DM condition, and the urinary elevations in glycine betaine and pipecolic acid (as well as proline) indicated defective re-absorption in the kidney proximal tubules by SLC6A20, a Na(+)-dependent transporter. The mRNA levels of SLC6A20 were significantly reduced in the kidneys of monkeys with T2DM. These observations were validated in the db/db mouse model of T2DM. This study provides convincing evidence of the power of metabolomics for identifying functional changes at many levels in the omics pipeline.     

2型糖尿病患者乙型肝炎病毒感染率分析

目的：通过调查糖尿病患者乙型肝炎病毒（HBV）的携带率,阐明糖尿病发生是否与HBV感染有关,并观察糖尿病合并HBV感染时是否加重对肝功能的损害。方法：用ELISA方法检测533例2型糖糖尿病患者和1440例普通人群乙型肝炎表面抗原（HBsAg）以及HBV其他血清学标志,同时常规测定肝功能和血糖等。结果：2型糖尿病HBsAg阳性24例,阳性率4.50%,普通人群HBsAg阳性70例,阳性率4.86%,两组间阳性率差异无统计学意义（x2=0.110,P=0.740）。糖尿病患者感染HBV后的抗体应答与普通人群相似。糖尿病合并HBV感染者与无糖尿病HBV感染者的肝功能异常差异无统计学意义。糖尿病患者中83例（16.3%）谷氨酰转肽酶升高,在肝功能异常指标中最常见,这与HBV感染后丙氨酸转氨酶升高为主不同。结论：糖尿病发生与HBV感染无关,糖尿病合并HBV感染时不加重对肝脏的损害。     

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.     

Impact of bariatric surgery on type 2 diabetes

The management and prevention of diabetes through lifestyle modifications and weight loss should be the mainstay of therapy in appropriate candidates. Although the results from the Diabetes Prevention Trial and the Finnish Prevention Study support this approach, over 95% of patients not participating in a prevention research study are unable to achieve and maintain any significant weight loss over time. Bariatric surgery for weight loss is an emerging option for more sustainable weight loss in the severely obese subject, especially when obesity is complicated by diabetes or other co-morbidities. The two most common types of procedures currently used in the United States are adjustable gastric bands and Roux-en-Y gastric bypass. These procedures can be performed laparoscopically, further reducing the perioperative morbidity and mortality associated with the surgery. While the gastric bypass procedure usually results is greater sustained weight loss (40–50%) than adjustable gastric banding (20–30%), it also carries greater morbidity and nutritional/metabolic issues, such as deficiencies in iron, B12, calcium, and vitamin D. Following bariatric surgery most subjects experience improvements in diabetes control, hypertension, dyslipidemia, and other obesity-related conditions. In patients with impaired glucose tolerance most studies report 99–100% prevention of progression to diabetes, while in subjects with diabetes prior to surgery, resolution of the disease is reported in 64–93% of the cases. While improvements in insulin resistance and beta-cell function are related to surgically induced weight loss, the rapid post-operative improvement in glycemia is possibly due to a combination of decreased nutrient intake and changes in gut hormones as a result of the bypassed intestine. Post-prandial hyperinsulinemic hypoglycemia associated with nesidioblastosis has been described in a series of patients following gastric bypass surgery, and may be related to the described changes in GLP-1 and other gut hormones.     

Implications of oxidovanadium(IV) binding to actin

Oxidovanadium(IV), a cationic species (VO²⁺) of vanadium(IV), binds to several proteins, including actin. Upon titration with oxidovanadium(IV), approximately 100% quenching of the intrinsic fluorescence of monomeric actin purified from rabbit skeletal muscle (G-actin) was observed, with a V₅₀ of 131 μM, whereas for the polymerized form of actin (F-actin) 75% of quenching was obtained and a V₅₀ value of 320 μM. Stern-Volmer plots were used to estimate an oxidovanadium(IV)-actin dissociation constant, with K_d of 8.2 μM and 64.1 μM VOSO₄, for G-actin and F-actin, respectively. These studies reveal the presence of a high affinity binding site for oxidovanadium(IV) in actin, producing local conformational changes near the tryptophans most accessible to water in the three-dimensional structure of actin. The actin conformational changes, also confirmed by ¹H NMR, are accompanied by changes in G-actin hydrophobic surface, but not in F-actin. The ¹H NMR spectra of G-actin treated with oxidovanadium(IV) clearly indicates changes in the resonances ascribed to methyl group and aliphatic regions as well as to aromatics and peptide-bond amide region. In parallel, it was verified that oxidovanadium(IV) prevents the G-actin polymerization into F-actin. In the 0-200 μM range, VOSO₄ inhibits 40% of the extent of polymerization with an IC₅₀ of 15.1 μM, whereas 500 μM VOSO₄ totally suppresses actin polymerization. The data strongly suggest that oxidovanadium(IV) binds to actin at specific binding sites preventing actin polymerization. By affecting actin structure and function, oxidovanadium(IV) might be responsible for many cellular effects described for vanadium.     

On the interaction of vanadium species with meso-2,3-dimercaptosuccinic acid

The interaction of the VO²⁺ cation with meso-2,3-dimercaptosuccinic acid (DMSA) was investigated by electron absorption spectroscopy in aqueous solution at different pH values. The spectral behavior, complemented with a spectrophotometric titration, shows the generation of a [VO(DMSA)₂]²⁻ complex in which the oxocation interacts with two pairs of deprotonated-SH groups of the acid. It was also found that DMSA rapidly reduces VO₃ ⁻ to VO²⁺, which might be chelated by an excess of the acid. DMSA can also produce the partial reduction of a V₂O₅ suspension at pH=5.2. The results of this study suggest that DMSA might be a potentially useful detoxification agent for vanadium.     

锌转运蛋白8与1型和2型糖尿病的研究进展

ZnT8(zinc transporter,member8)是锌离子转运蛋白,主要定位于胰岛β细胞,能将胞浆锌离子转运至胰岛素储存/分泌性囊泡内,其转运功能降低会影响胰岛素合成、储存和分泌,能增加2型糖尿病(T2DM)的发病风险。ZnT8蛋白也可作为抗原引起β细胞自身免疫损伤,诱发1型糖尿病(T1DM)。ZnT8基因多态性是引起其锌离子转运功能和免疫原性变化的重要因素,与糖尿病的发生、发展密切相关。该文综述了ZnT8与T1DM和T2DM的研究进展,提示ZnT8可作为糖尿病防治的新药物靶点。