Improvement of hyperglycaemia and metabolic syndromes in type 2 diabetic KKAy mice by oral treatment with [meso-tetrakis(4-sulfonatophenyl) porphyrinato]oxovanadium(IV)(4-) complex

Kinetics, Equilibrium, and Thermodynamics for Conjugation of Chitosan with Insulin-Mimetic [meso-Tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4-) in an Aqueous Solution

This study investigated the conjugation of chitosan with the insulin-mimetic [meso-tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4-), VO(tpps), in an aqueous medium as a function of conjugation time, VO(tpps) concentrations, and temperatures. To validate the synthesis of chitosan-VO(tpps) conjugate, UV-visible and Fourier transform infrared spectrophotometric techniques were utilized. Conjugate formation is ascribed to the electrostatic interaction between the NH3+ units of chitosan and the SO3- units of VO(tpps). Chitosan enhances the stability of VO(tpps) in an aqueous medium (pH 2.5). VO(tpps) conjugation with chitosan was best explained by pseudo-second-order kinetic and Langmuir isotherm models based on kinetic and isotherm studies. The Langmuir equation determined that the maximal ability of VO(tpps) conjugated with each gram of chitosan was 39.22 μmol at a solution temperature of 45 °C. Activation energy and thermodynamic studies (Ea: 8.78 kJ/mol, ΔG: -24.52 to -27.55 kJ/mol, ΔS: 204.22 J/(mol K), and ΔH: 37.30 kJ/mol) reveal that conjugation is endothermic and physical in nature. The discharge of VO(tpps) from conjugate was analyzed in freshly prepared 0.1 mol/L phosphate buffer (pH 7.4) at 37 °C. The release of VO(tpps) from the conjugate is a two-phase process best explained by the Higuchi model, according to a kinetic analysis of the release data. Taking into consideration all experimental findings, it is proposed that chitosan can be used to formulate both solid and liquid insulin-mimetic chitosan-VO(tpps) conjugates.

Oxidovanadium(IV) sulfate-induced glucose uptake in HepG2 cells through IR/Akt pathway and hydroxyl radicals

The insulin-mimetic and anti-diabetic properties of vanadium and related compounds have been well documented both in vitro and in vivo. However, the molecular basis of the link between vanadium and the insulin signaling pathway in diabetes mellitus is not fully described. We investigated the effects of reactive oxygen species (ROS) induced by oxidovanadium(IV) sulfate (VOSO4) on glucose uptake and the insulin signaling pathway in human hepatoma cell line HepG2. Exposure of cells to VOSO4 (5-50 μM) resulted in an increase in glucose uptake, insulin receptor (IR) and protein kinase B (Akt) phosphorylation and intracellular ROS generation. Using Western blot, we found that catalase and sodium formate, but not superoxide dismutase, prevented the increase of hydroxyl radical (·OH) generation and significantly decreased VOSO4-induced IR and Akt phosphorylation. These results suggest that VOSO4-induced ·OH radical, which is a signaling species, promotes glucose uptake via the IR/Akt signaling pathway.

A new oxovanadium complex enhances renal function by improving insulin signaling pathway in diabetic mice

AIM

Since vanadium complexes have insulin-mimetic effects and can be used to treat complications of diabetes, we aimed to screen a new oxovanadium complex with a low toxicity, and investigate its insulin-mimetic effects, as well as the mechanism of improvement to diabetic mouse renal function.

METHODS

Cells were treated with oxovanadium complexes, and viability was assessed by MTT assay. Diabetic mouse model was established using alloxan. Blood urea nitrogen (BUN) and serum creatinine (SCr) in the mice were measured using an automatic biochemical analyzer, and blood glucose was measured using a Glucoval Compact meter. Expression of proteins related to the insulin signaling pathway in the renal cortex of mice was measured by Western blot analysis.

RESULTS

Diabetic mice developed high blood glucose, BUN and SCr levels compared with control mice. The new oxovanadium complex with 3,5-dimethyl-pyrazolyl ligand, VO(HB(3,5-Me2pz)3)(3,5-Me2pz)(SCN)(SCNH)2, showed low toxicity and significantly reduced blood glucose, BUN and SCr levels in the diabetic mice. Additionally, p42/p44MAPK and Akt phosphorylation was markedly increased in diabetic mice and was decreased by treatment with the new oxovanadium complex. Caveolin-1 (Cav-1) expression was greatly decreased in diabetic mice and significantly increased after treatment with the new oxovanadium complex.

CONCLUSIONS

The new oxovanadium complex, with 3,5-dimethyl-pyrazolyl ligand, improves kidney function in diabetic mice, and its mechanism may involve regulation of the insulin signaling pathway.

Bis(α-furancarboxylato)oxovanadium(IV) exerts durable antidiabetic effects and suppresses matrix metalloproteinase-2 activity in spontaneous type 2 diabetic KKAy mice

Vanadium compounds maintain euglycemic effects in diabetic rats long after drug withdrawal and bis(α-furancarboxylato)oxovanadium(IV) (BFOV) possesses potent antidiabetic effects in diabetic rats. Here, we investigated the treatment and posttreatment effects of BFOV in diabetic Kuo Kondo [1, 2] with Ay gene (KKAy) mice, and whether these effects were associated with changes in matrix metalloproteinases (MMPs). KKAy mice received normal saline or BFOV initially at 70 μmol/kg/day for 1 month, which was tapered to 17 μmol/kg/day in the next 2 months and discontinued thereafter. Compared to diabetic controls, fasting plasma glucose (FPG) was reduced by 46 and 19 % in KKAy mice after 70 μmol/kg BFOV for 1 month and 3 months after BFOV withdrawal, respectively. OGTT and ITT showed improved glucose tolerance and a better response of FPG to insulin with a significant decrease in HOMA-IR and a marked rise in the insulin sensitivity index after 70 μmol/kg BFOV for 1 month and 4 months after BFOV withdrawal (P <0.05 in all vs. diabetic controls). BFOV treatment resulted in a moderate but significant reduction in body weight and systolic blood pressure (SBP) at 1 month of treatment and 4 months following BFOV withdrawal (P <0.05 in all vs. diabetic controls). Gelatin zymography showed that serum MMP2 activity was significantly reduced and immunoblotting assays further showed that MMP2 expression was markedly downregulated in the liver after 1 month of treatment with 70 μmol/kg and 4 months after BFOV withdrawal (P <0.05 in all vs. diabetic controls). These results suggested that BFOV possessed potent treatment and posttreatment effects in KKAy mice with improved metabolic profile and reduced body weight and SBP. Furthermore, these effects were associated with decreased MMP2 expression and activity in diabetic KKAy mice.

The discovery of vanadyl and zinc complexes for treating diabetes and metabolic syndromes

The incidence of diabetes mellitus has increased over the decades because of lifestyle changes. The number of people with diabetes mellitus worldwide is expected to increase from 150 million to 220 million by 2010 and to 300 million by 2025. There are two main types of diabetes mellitus. Type 1 diabetes mellitus is due to the autoimmune-mediated destruction of pancreatic β cells, resulting in absolute insulin deficiency; the patients require exogenous insulin injections. Type 2 is characterized by insulin resistance and abnormal insulin secretion and the patients require exercise, diet control and/or oral hypoglycemics. However, each treatment has some adverse effects, including physical burden, formation of self-antibodies for insulin injections, the severe side effects of hypoglycemics and the discontinuation of insulin synthesis in the pancreas. To overcome these adverse effects and replace the use of these agents, the author attempted to develop new antidiabetic agents with novel structures and mechanisms. This review focuses on the authors' recent development of vanadium and zinc complexes for antidiabetic and antimetabolic syndromes.

In vitro insulin-mimetic activity and in vivo metallokinetic feature of oxovanadium(IV)porphyrin complexes in healthy rats

We prepared [meso-tetrakis(4-carboxylatophenyl)porphyrinato]oxovanadium(IV) tetrasodium, ([VO(tcpp)]Na4), and investigated its in vitro insulin-mimetic activity and in vivo metallokinetic feature in healthy rats. The results were compared with those of previously proposed insulin-mimetic oxovanadium(IV)porphyrin complexes and oxovanadium(IV) sulphate. The in vitro insulin-mimetic activity and bioavailability of [VO(tcpp)]Na4 were considerably better than those of [meso-tetrakis (1-methylpyridinium-4-yl)porphyrinato]oxovanadium(IV)(4+) tetraperchlorate ([VO(tmpyp)](ClO4)4) and oxovanadium(IV) sulphate. On the other hand, [VO(tcpp)]Na4 and [meso-tetrakis(4-sulfonatophenyl) porphyrinato]oxidovanadate(IV)(4-)([VO(tpps)]) showed very similar in vitro insulin-mimetic activity and in vivo metallokinetic feature in healthy rats. In particular, the order of in vitro insulin-mimetic activity of the complexes was determined to be: [VO(tcpp)]Na4 ≈ [VO(tpps)] > ([VO(tmpyp)](ClO4)4 > oxovanadium(IV) sulphate.

Metal-based anti-diabetic drugs: advances and challenges

The current status and likely future directions of complexes of V(V/IV), Cr(III), Mo(VI), W(VI), Zn(II), Cu(II), and Mn(III) as potential oral drugs against type 2 diabetes are reviewed. We propose a unified model of extra- and intracellular mechanisms of anti-diabetic efficacies of V(V/IV), Mo(VI), W(VI), and Cr(III), centred on high-oxidation-state oxido/peroxido species that inhibit protein tyrosine phosphatases (PTPs) involved in insulin signalling. The postulated oxidative mechanism of anti-diabetic activity of Cr(III) via carcinogenic Cr(VI/V) (which adds to safety concerns) is consistent with recent clinical trials on Cr(III) picolinate, where activity was apparent only in patients with poorly controlled diabetes (high oxidative stress), and the correlation between the anti-diabetic activities and ease of oxidation of Cr(III) supplements and their metabolites in vivo. Zn(II) and Cu(II) anti-diabetics act via different mechanisms and are unlikely to be used as specific anti-diabetics due to their diverse and unpredictable biological activities. Hence, future research directions are likely to centre on enhancing the bioavailability and selectivity of V(V/IV), Mo(VI), or W(VI) drugs. The strategy of potentiating circulating insulin with metal ions has distinct therapeutic advantages over interventions that stimulate the release of more insulin, or use insulin mimetics, because of many adverse side-effects of increased levels of insulin, including increased risks of cancer and cardiovascular diseases.

Amelioration of Hyperglycemia and Metabolic Syndromes in Type 2 Diabetic KKAy Mice by Poly(γ-glutamic acid)oxovanadium(IV) Complex

Recently, we found that poly(gamma-glutamic acid)oxovanadium(IV) complex (VO(gamma-pga)) exhibits a potent antidiabetic activity in streptozotocin (STZ)-induced type 1 diabetic mice. This result prompted us to examine its ability to treat the type 2 diabetic model KKA(y) mice with insulin resistance. We studied the in vivo antidiabetic activity of VO(gamma-pga), compared with that of vanadium(IV) oxide sulfate (VS) as control. Both compounds were orally administered at doses of 5-10 mg (0.1-0.2 mmol) V kg(-1) body mass to the KKA(y) mice for 30 days. VO(gamma-pga) normalized the hyperglycemia within 21 days, whereas VS lowered the blood glucose concentration only by a small degree. In addition, the glucose intolerance, HbA(1c) level, hyperinsulinemia, hypercholesterolemia, and hyperleptinemia were significantly improved in VO(gamma-pga)-treated KKA(y) mice compared with those treated with VS. Based on these observations, VO(gamma-pga) is proposed to be the first orally active oxovanadium(IV)-polymer complex for the efficacious treatment of not only type 2 diabetes but also metabolic syndrome in animals.