Vanadyl bisacetylacetonate protects β cells from palmitate-induced cell death through the unfolded protein response pathway

Combination therapy enhances efficacy and overcomes toxicity of metal-based anti-diabetic agent

BACKGROUND AND PURPOSE

Metal-based therapeutic agents are limited by the required concentration of metal-based agents. Hereby, we determined if combination with 17β-oestradiol (E2) could reduce such levels and the therapy still be effective in type 2 diabetes mellitus (T2DM).

EXPERIMENTAL APPROACH

The metal-based agent (vanadyl acetylacetonate [VAC])- 17β-oestradiol (E2) combination is administered using the membrane-permeable graphene quantum dots (GQD), the vehicle, to form the active GQD-E2-VAC complexes, which was characterized by fluorescence spectra, infrared spectra and X-ray photoelectron spectroscopy. In db/db type 2 diabetic mice, the anti-diabetic effects of GQD-E2-VAC complexes were evaluated using blood glucose levels, oral glucose tolerance test (OGTT), serum insulin levels, homeostasis model assessment (homeostasis model assessment of insulin resistance [HOMA-IR] and homeostasis model assessment of β-cell function [HOMA-β]), histochemical assays and western blot.

KEY RESULTS

In diabetic mice, GQD-E2-VAC complex had comprehensive anti-diabetic effects, including control of hyperglycaemia, improved insulin sensitivity, correction of hyperinsulinaemia and prevention of β-cell loss. Co-regulation of thioredoxin interacting protein (TXNIP) activation by the combination of metal complex and 17β-oestradiol contributed to the enhanced anti-diabetic effects. Furthermore, a potent mitochondrial protective antioxidant, coniferaldehyde, significantly potentiates the protective effects of GQD-E2-VAC complexes.

CONCLUSION AND IMPLICATIONS

A metal complex-E2 combinatorial approach achieved simultaneously the protection of β cells and insulin enhancement at an unprecedented low dose, similar to the daily intake of dietary metals in vitamin supplements. This study demonstrates the positive effects of combination and multi-modal therapies towards type 2 diabetes treatment.

An Adequate Supply of Bis(ethylmaltolato)oxidovanadium(IV) Remarkably Reversed the Pathological Hallmarks of Alzheimer's Disease in Triple-Transgenic Middle-Aged Mice

Alzheimer's disease (AD) is a complex and progressive neurodegenerative disease with impaired synapse, imbalanced mineral metabolism, protein mis-folding and aggregation. Bis(ethylmaltolato)oxidovanadium(IV) (BEOV), an organic bioactive vanadium compound with low toxicity and high bioavailability, has been studied as therapeutic agent against tuberculosis and diabetes. However, its neuroprotective effects have rarely been reported. Therefore, in this study, the potential application of BEOV in intervening AD cognitive dysfunction and neuropathology was evaluated. Both low- and high-dose of BEOV (0.2 mmol/L and 1.0 mmol/L) supplementation for 2 months improved the spatial learning and memory deficits of the triple-transgenic AD (3 × Tg AD) mice and mitigated the loss of synaptic proteins and synaptic dysfunction. By inhibiting the expression of amyloid-β precursor protein and β-secretase, and the phosphorylation of tau protein at Ser262, Ser396, Ser404, and Ser202/Thr205 residues, BEOV reduced the amyloid-β deposition and neurofibrillary tangle formation in AD mouse brains and primarily cultured neurons. Further analysis of the brain ionome revealed that BEOV supplementation could significantly affect the concentrations of a variety of metals, most of which, including several AD risk metals, showed reduced levels, particularly with a high-dose intake. Additionally, the elemental correlation network identified both conserved and specific elemental correlations, implying a highly complex and dynamic crosstalk between vanadium and other elements during long-term BEOV supplementation. Overall, our results suggest that BEOV is effective in AD intervention via both ameliorating the disease related pathology and regulating metal homeostasis.

Alzheimer's Disease and Diabetes Mellitus in Comparison: The Therapeutic Efficacy of the Vanadium Compound

Alzheimer’s disease (AD) is an intractable neurodegenerative disease that leads to dementia, primarily in elderly people. The neurotoxicity of amyloid-beta (Aβ) and tau protein has been demonstrated over the last two decades. In line with these findings, several etiological hypotheses of AD have been proposed, including the amyloid cascade hypothesis, the oxidative stress hypothesis, the inflammatory hypothesis, the cholinergic hypothesis, et al. In the meantime, great efforts had been made in developing effective drugs for AD. However, the clinical efficacy of the drugs that were approved by the US Food and Drug Association (FDA) to date were determined only mild/moderate. We recently adopted a vanadium compound bis(ethylmaltolato)-oxidovanadium (IV) (BEOV), which was originally used for curing diabetes mellitus (DM), to treat AD in a mouse model. It was shown that BEOV effectively reduced the Aβ level, ameliorated the inflammation in brains of the AD mice, and improved the spatial learning and memory activities of the AD mice. These finding encouraged us to further examine the mechanisms underlying the therapeutic effects of BEOV in AD. In this review, we summarized the achievement of vanadium compounds in medical studies and investigated the prospect of BEOV in AD and DM treatment.

Trace elements concentration in adipose tissue and the risk of incident type 2 diabetes in a prospective adult cohort

The aim of this work was to study the associations of adipose tissue trace element concentrations with type 2 diabetes (T2DM) incidence over a 16-year follow-up period in an adult cohort from Southern Spain. 16-year T2DM incidence was gathered from hospital records. Chemical analyses of Cr, V, Zn, Fe, Cu and Se in adipose tissue were performed using inductively coupled plasma mass spectrometry. Multivariable Cox-regression models were used. Complementary cross-sectional analyses with markers of glucose homeostasis at recruitment were performed by multivariable linear regression. Out of 214 participants, 39 developed T2DM during the follow-up. Adipose tissue concentrations of Fe (HR = 1.97, 95% CI: 0.99 to 2.58, p = 0.057), Cr (HR = 1.58, 95% CI: 1.07-2.33, p = 0.022) and Cu (HR = 1.61, 95% CI: 1.01-2.58, p = 0.046) were individually associated with T2DM incidence. When Fe, Cr and Cu were simultaneously entered in a model, only Cr was significantly associated with T2DM incidence (HR = 1.68, 95% CI: 1.02-2.76, p = 0.041). Furthermore, adipose tissue V (β = 0.283, p = 0.004) and Zn (β = 0.217, p = 0.028) concentrations were positively associated with β-pancreatic cell function (HOMA-β), while Se showed an inverse association (β = -0.049, p = 0.027). Although further research is warranted on the potential mechanisms of action, our results suggest that adipose tissue concentrations of certain trace elements (particularly Fe, Cr and Cu) are associated with the risk of incident T2DM, while V and Zn might have a protective effect. These biomarkers might complement prediction algorithms and contribute to identify patients with an increased risk of T2DM.

Bis(ethylmaltolato)oxidovanadium (IV) alleviates neuronal apoptosis through regulating peroxisome proliferator-activated receptor γ in a triple transgenic animal model of Alzheimer's disease

Endoplasmic reticulum stress (ER stress) plays a critical role in neuronal apoptosis along with the aggravation of Alzheimer's disease (AD). Nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated transcription factor that is involved in regulating ER stress in Alzheimer's disease (AD), therefore, this protein could be a promising therapeutic target for AD. Vanadium compounds, such as vanadyl acetylacetonate, sodium metavanadate and bis(maltolato)oxovanadium, are well-known as puissant PPARγ modulators. Thus, we are curious whether bis(ethylmaltolato)oxidovanadium (IV) (BEOV) can ameliorate ER stress and subsequent neuronal apoptosis by regulating PPARγ in AD models. To this end, we determined the effect of BEOV on behavioral performance, ER stress and neuronal apoptosis in the triple transgenic mouse AD model (3×Tg-AD). Our results showed that BEOV improved cognitive abilities and reduced the ER stress- and apoptosis-associated proteins in the brains of 3×Tg-AD mice. In vitro administration of BEOV in primary hippocampal neurons and N2asw cells achieved similar results in repressing ER stress. In addition, cotreatment with GW9662 (an antagonist of PPARγ) effectively blocked these neuroprotective effects of BEOV, which provided strong evidence that PPARγ-dependent signaling plays a key role in protecting against ER stress and neuronal apoptosis in AD. In conclusion, our data demonstrated that BEOV alleviated neuronal apoptosis triggered by ER stress by regulating PPARγ in a 3×Tg-AD model.

Vanadium coordination compounds loaded on graphene quantum dots (GQDs) exhibit improved pharmaceutical properties and enhanced anti-diabetic effects

Vanadium compounds are promising anti-diabetic agents, and graphene quantum dots (GQDs) are emerging as potential drug delivery systems to improve drug solubility in water and membrane transport. Using highly dispersible and water-soluble GQDs, we herein prepared a novel GQD-VO (p-dmada) complex, in which vanadium coordination compounds [VO(p-dmada)] were packed closely on one side of the GQD sheets possibly via the π-π stacking mechanism. The in vitro tests showed that GQD-VO(p-dmada) exhibited membrane permeability (Papp) as good as that of GQDs with reduced cytotoxicity. In vivo tests on type 2 diabetic mice demonstrated that GQD-VO(p-dmada) exhibited a delayed glucose lowering profile but more profound effects on insulin enhancement and β-cell protection after three-week treatment compared to VO(p-dmada) alone. In addition, GQD alone was observed for the first time to effectively lower the blood lipid levels of the db/db mice. Overall, GQD-VO(p-dmada) showed improved pharmacokinetic performance and hypoglycemic effects, and using GQD as a nanoplatform for drug delivery may provide vast opportunities for the further design of metal-based pharmaceutical agents.

Bis(ethylmaltolato)oxidovanadium (IV) mitigates neuronal apoptosis resulted from amyloid-beta induced endoplasmic reticulum stress through activating peroxisome proliferator-activated receptor γ

Neuronal apoptosis caused by amyloid-beta (Aβ) overproduction is one of the most important pathological features in Alzheimer's disease (AD). Endoplasmic reticulum (ER) stress induced by Aβ overload plays a critical role in this process. Bis(ethylmaltolato)oxidovanadium (IV) (BEOV), a vanadium compound which had been regarded as peroxisome proliferator-activated receptor γ (PPARγ) agonist, was reported to exert an antagonistic effect on ER stress. In this study, we tested whether BEOV could ameliorate the Aβ-induced neuronal apoptosis by inhibiting ER stress. It was observed that BEOV treatment ameliorated both tunicamycin-induced and/or Aβ-induced ER stress and neurotoxicity in a dose-dependent manner through downgrading ER stress-associated and apoptosis-associated proteins in primary hippocampal neurons. Consistent with in vitro results, BEOV also reduced ER stress and inhibited neuronal apoptosis in hippocampi and cortexes of transgenic AD model mice. Moreover, by adopting GW9662 and salubrinal, the inhibitor of PPARγ and hyperphosphorylated eukaryotic translation initiation factor 2α, respectively, we further confirmed that BEOV alleviated Aβ-induced ER stress and neuronal apoptosis in primary hippocampal neurons by activating PPARγ. Taken together, these results provided scientific evidences to support the concept that BEOV ameliorates Aβ-induced ER stress and neuronal apoptosis through activating PPARγ.

Vanadium in Biological Action: Chemical, Pharmacological Aspects, and Metabolic Implications in Diabetes Mellitus

Vanadium compounds have been primarily investigated as potential therapeutic agents for the treatment of various major health issues, including cancer, atherosclerosis, and diabetes. The translation of vanadium-based compounds into clinical trials and ultimately into disease treatments remains hampered by the absence of a basic pharmacological and metabolic comprehension of such compounds. In this review, we examine the development of vanadium-containing compounds in biological systems regarding the role of the physiological environment, dosage, intracellular interactions, metabolic transformations, modulation of signaling pathways, toxicology, and transport and tissue distribution as well as therapeutic implications. From our point of view, the toxicological and pharmacological aspects in animal models and humans are not understood completely, and thus, we introduced them in a physiological environment and dosage context. Different transport proteins in blood plasma and mechanistic transport determinants are discussed. Furthermore, an overview of different vanadium species and the role of physiological factors (i.e., pH, redox conditions, concentration, and so on) are considered. Mechanistic specifications about different signaling pathways are discussed, particularly the phosphatases and kinases that are modulated dynamically by vanadium compounds because until now, the focus only has been on protein tyrosine phosphatase 1B as a vanadium target. Particular emphasis is laid on the therapeutic ability of vanadium-based compounds and their role for the treatment of diabetes mellitus, specifically on that of vanadate- and polioxovanadate-containing compounds. We aim at shedding light on the prevailing gaps between primary scientific data and information from animal models and human studies.

Anti-diabetic vanadyl complexes reduced Alzheimer's disease pathology independent of amyloid plaque deposition

Association of Alzheimer's disease (AD) with cerebral glucose hypometabolism, likely due to impairments of insulin signaling, has been reported recently, with encouraging results when additional insulin is provided to AD patients. Here, we tested the potential effects of the anti-diabetic vanadium, vanadyl (IV) acetylacetonate (VAC), on AD in vitro and in vivo models. The experimental results showed that VAC at sub-micromolar concentrations improved the viability of neural cells with or without increased β-amyloid (Aβ) burden; and in APP/PS1 transgenic mice, VAC treatment (0.1 mmol kg^-1 d^-1) preserved cognitive function and attenuated neuron loss, but did not reduce brain Aβ plaques. Further studies revealed that VAC attenuated Aβ pathogenesis by (i) activation of the PPARγ-AMPK signal transduction pathway, leading to improved glucose and energy metabolism; (ii) up-regulation of the expression of glucose-regulated protein 75 (Grp75), thus suppressing p53-mediated neuronal apoptosis under Aβ-related stresses; and (iii) decreasing toxic soluble Aβ peptides. Overall, our work suggested that vanadyl complexes may have great potential for effective therapeutic treatment of AD.

Vanadyl complexes discriminate between neuroblastoma cells and primary neurons by inducing cell-specific apoptotic pathways

Vanadium compounds have arisen as potential therapeutic agent for the treatment of cancers over the past decades. A few studies suggested that vanadyl complexes may discriminate between the cancerous and the normal cells. Here, we reported the investigation on the pro-apoptotic effect and the underlying mechanism of bis(acetylacetonato) oxovanadium(IV) ([VO(acac)₂]) on SH-SY5Y neuroblastoma cells in comparison with that of mouse primary cortex neurons. The experimental results revealed that [VO(acac)₂] showed about 10-fold higher cytotoxicity (IC50 ~16 μM) on the neuroblastoma cells than on normal neurons (IC50 ~250 μM). Further analysis indicated that the vanadyl complex suppressed the growth of neuroblastoma cells via different pathways depending on its concentration. It induced a special cyclin D-mediated and p53-independent cell apoptosis at <50 μM but cell cycle arrests at >50 μM. In contrast, [VO(acac)₂] promoted cell viability of primary neurons in the concentration range of 0-150 μM; while [VO(acac)₂] at hundreds of μM would cause neuronal death possibly via the reactive oxygen species (ROS)-mediated signal pathways. The extraordinary discrimination between neuroblastoma cells and primary neurons suggests potential application of vanadyl complexes for therapeutic treatment of neuroblastoma. In addition, the p53-independent apoptotic pathways induced by vanadyl complexes may provide new insights for future discovery of new anticancer drugs overcoming the chemo-resistance due to p53 mutation.

Synthesis and characterization of oxidovanadium complexes as enzyme inhibitors targeting dipeptidyl peptidase IV

Two oxidovanadium(IV) complexes carrying Schiff base ligands obtained from the condensation of 4,5-dichlorobenzene-1,2-diamine and salicylaldehyde derivatives were synthesised and characterised, including their X-ray crystallographic structures. They were evaluated as dipeptidyl peptidase IV (DPP-IV) inhibitors for the treatment of type 2 diabetes. These compounds were moderate inhibitors of DPP-IV, with IC₅₀ values of ca. 40μM. In vivo tests showed that complexes 1 and 2 could lower significantly the level of glucose in the blood of alloxan-diabetic mice at doses of 22.5mgV·kg^-1 and 29.6mgV·kg^-1, respectively. Moreover, molecular modeling studies suggested that the oxidovanadium complexes 1 and 2 could fit well into the active-site cleft of the kinase domain of DPP-IV. To the best of our knowledge, this is the first report of vanadium complexes capable of inhibiting DPP-IV.

Bis(maltolato)oxovanadium(IV) (BMOV) Attenuates Apoptosis in High Glucose-Treated Cardiac Cells and Diabetic Rat Hearts by Regulating the Unfolded Protein Responses (UPRs)

Endoplasmic reticulum stress (ERS)-induced unfolded protein response (UPR) and the subsequent cell deaths are essential steps in the pathogenesis of diabetic cardiomyopathy (DCM), a main cause of diabetics' morbidity and mortalities. The bis(maltolato)oxovanadium(IV) (BMOV), a potent oral vanadium complex with anti-diabetic properties and insulin-mimicking effects, was shown to improve cardiac dysfunctions in diabetic models. Here, we examined the effects of BMOV on UPR pathway protein expression and apoptotic cell deaths in both high glucose-treated cardiac H9C2 cells and in the hearts of diabetic rats. We show that in both the high glucose-treated cardiac cells and in the hearts of streptozotocin (STZ) diabetic rats, there was an overall activation of the UPR signaling, including both apoptotic (e.g., the cascades of PERK/EIf2α/ATF4/CHOP and of IRE1/caspase 12/caspase 3) and pro-survival (GRP78 and XBP1) signaling. A high amount of apoptotic cell deaths was also detected in both diabetic conditions. The administration of BMOV suppressed both the apoptotic and pro-survival UPR signaling and significantly attenuated apoptotic cell deaths in both conditions. The overall suppression of UPR signaling by BMOV suggests that the drug protects diabetic cardiomyopathy by counteracting reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress. Our findings lend support to promote the use of BMOV in the treatment of diabetic heart diseases.

Synthesis, characterization and anti-diabetic therapeutic potential of novel aminophenol-derivatized nitrilotriacetic acid vanadyl complexes

In the present work, we synthesized three novel aminophenol-derivatized nitrilotriacetic acid vanadyl complexes (VOohpada, VOmhpada, VOphpada) using the strategy of rational incorporation of antioxidant groups in ligand in order to balance the side effects with the therapeutic properties. The complexes were characterized by IR, UV-VIS, ESI-MS and elemental analysis. The biological evaluations in vitro revealed that the position of the hydroxyl group of aminophenol moiety regulated the antioxidant activity of the complexes as well as the cytotoxicity on HK-2 cells. The vanadyl complex of p-hydroxyl aminophenol derivative (VOphpada) exhibited better antioxidant activity and lower cytotoxicity than other analogs. In type II diabetic db/db mice, VOphpada (0.1 mmol/kg/day) effectively reduced blood glucose level, improved glucose tolerance, and alleviated stresses induced by hyperglycemia and hyperlipidemia. VOphpada treatment significantly increased expression of PPARα and γ, activated Akt, and inactivated JNK in muscle and adipose tissues. The insulin enhancement effects of VOphpada were observed more potent than BMOV. Moreover, VOphpada decreased the level of kidney injury molecule-1 marker (KIM-1), suggesting a potentially lower renal toxicity. In overall, the present results suggest VOphpada as a novel hypoglycemic agent with improved efficacy-over-toxicity index.

Is the hypoglycemic action of vanadium compounds related to the suppression of feeding?

Vanadium compounds exhibit effective hypoglycemic activity in both type I and type II diabetes mellitus. However, there was one argument that the hypoglycemic action of vanadium compounds could be attributable to the suppression of feeding-one common toxic aspect of vanadium compounds. To clarify this question, we investigated in this work the effect of a vanadyl complex, BSOV (bis((5-hydroxy-4-oxo-4H-pyran-2-yl)methyl-2-hydroxy-benzoatato) oxovanadium (IV)), on diabetic obese (db/db) mice at a low dose (0.05 mmol/kg/day) when BSOV did not inhibit feeding. The experimental results showed that this dose of BSOV effectively normalized the blood glucose level in diabetic mice without affecting the body weight growth. Western blotting assays on the white adipose tissue of db/db mice further indicated that BSOV treatment significantly improved expression of peroxisome proliferator-activated receptor γ (PPARγ) and activated AMP-activated protein kinase (AMPK). In addition, vanadium treatment caused a significant suppression of phosphorylation of c-Jun N-terminal protein kinase (JNK), which plays a key role in insulin-resistance in type II diabetes. This is the first evidence that the mechanism of insulin enhancement action involves interaction of vanadium compounds with JNK. Overall, the present work indicated that vanadium compounds exhibit antidiabetic effects irrelevant to food intake suppression but by modulating the signal transductions of diabetes and other metabolic disorders.

Vanadium compounds modulate PPARγ activity primarily by increasing PPARγ protein levels in mouse insulinoma NIT-1 cells

Vanadium compounds are promising agents in the therapeutic treatment of diabetes; however, their mechanism of action has not been clearly elucidated. The current study investigated the effects of vanadium compounds, vanadyl acetylacetonate [V(IV)O(acac)2] and sodium metavanadate (NaV(V)O3), on peroxisome proliferator-activated receptors (PPARs), especially PPARγ, which are important targets of anti-diabetic drugs. Our experimental results revealed that treatment of NIT-1 β-pancreas cells with vanadium compounds resulted in PPARγ activation and elevation of PPARγ protein levels. Vanadium compounds did not increase PPARγ transcription but ameliorated PPARγ degradation induced by inflammatory stimulators TNF-α/IL-6. Vanadium compounds induced binding of PPARγ to heat shock protein (Hsp60). This PPARγ-Hsp60 interaction might cause inhibition of PPARγ degradation, thus elevating the PPARγ level. In addition, modulation of PPARγ phosphorylation was also observed upon vanadium treatment. The present work demonstrated for the first time that vanadium compounds are novel PPARγ modulators. The results may provide new insights for the mechanism of anti-diabetic action of vanadium compounds.

Raft localization of type I Fcε receptor and degranulation of RBL-2H3 cells exposed to decavanadate, a structural model for V2O5

Vanadium oxides (VOs) have been identified as low molecular weight sensitizing agents associated with occupational asthma and compromised pulmonary immunocompetence. Symptoms of adult onset asthma result, in part, from increased signal transduction by Type I Fcε receptors (FcεRI) leading to release of vasoactive compounds including histamine from mast cells. Exposure to (VOs) typically occurs in the form of particles which are insoluble. Upon contact with water or biological fluids, (VOs) form a series of soluble oxoanions, one of which is decavanadate, V10O28(6-) abbreviated V10, which is structurally related to a common vanadium oxide, that is vanadium pentoxide, V2O5. Here we investigate whether V10 may be initiating plasma membrane events associated with activation of FcεRI signal transduction. We show that exposure of RBL-2H3 cells to V10 causes a concentration-dependent increase in degranulation of RBL-2H3 and, in addition, an increase in plasma membrane lipid packing as measured by the fluorescent probe, di-4-ANEPPDHQ. V10 also increases FcεRI accumulation in low-density membrane fragments, i.e., lipid rafts, which may facilitate FcεRI signaling. To determine whether V10 effects on plasma membrane lipid packing were similarly observed in Langmuir monolayers formed from dipalmitoylphosphatidylcholine (DPPC), the extent of lipid packing in the presence and absence of V10 and vanadate was compared. V10 increased the surface area of DPPC Langmuir monolayers by 6% and vanadate decreased the surface area by 4%. These results are consistent with V10 interacting with this class of membrane lipids and altering DPPC packing.

Europium complexes as novel indicators of paracellular diffusion

Measurement of paracellular permeation is an important assay for tight-junction investigations of drug toxicity, especially for metal-based drugs, and routine validation of the integrity of cell monolayers for models of drug absorption. Great efforts have been made in discovery and validation of novel paracellular diffusion indicators. In the present work, we prepared three Eu complexes, i.e., [Eu(dtpa)] (dtpa=diethylenetriaminepentaacetic acid), [Eu(dtpa)(BSA)], and [Eu(dtpa)(PLL)] (PLL=poly(L-lysine)), and tested their permeation properties on Madin-Darby canine kidney (MDCK) cells. The experimental results showed that all three probes were nontoxic to MDCK cells, permeated across MDCK monolayer exclusively via the paracellular pathways, and responded well to the changes on tight junction with high correlation of P(app) values to the decrease of trans-epithelial electric resistance (TEER). In addition, time-resolved fluorescence assays were conducted in a high-sensitivity and background-free mode. All these results confirmed the Eu complexes as novel and practical paracellular indicators.