A new salicylic acid-derivatized kojic acid vanadyl complex: Synthesis, characterization and anti-diabetic therapeutic potential

Vanadium Compounds with Antidiabetic Potential

Over the last four decades, vanadium compounds have been extensively studied as potential antidiabetic drugs. With the present review, we aim at presenting a general overview of the most promising compounds and the main results obtained with in vivo studies, reported from 1899-2023. The chemistry of vanadium is explored, discussing the importance of the structure and biochemistry of vanadate and the impact of its similarity with phosphate on the antidiabetic effect. The spectroscopic characterization of vanadium compounds is discussed, particularly magnetic resonance methodologies, emphasizing its relevance for understanding species activity, speciation, and interaction with biological membranes. Finally, the most relevant studies regarding the use of vanadium compounds to treat diabetes are summarized, considering both animal models and human clinical trials. An overview of the main hypotheses explaining the biological activity of these compounds is presented, particularly the most accepted pathway involving vanadium interaction with phosphatase and kinase enzymes involved in the insulin signaling cascade. From our point of view, the major discoveries regarding the pharmacological action of this family of compounds are not yet fully understood. Thus, we still believe that vanadium presents the potential to help in metabolic control and the clinical management of diabetes, either as an insulin-like drug or as an insulin adjuvant. We look forward to the next forty years of research in this field, aiming to discover a vanadium compound with the desired therapeutic properties.

The antihyperglycemic and hypolipidemic activities of a sulfur-oxidovanadium(IV) complex

This study describes the synthesis, characterization, and biological activity of a new class of antidiabetic oxidovanadium(IV)-complexes with S₂O₂ coordination mode. The target complex 3,6-dithio-1,8-octanediolatooxidovanadium(IV), abbreviated as ([V^IVO(octd)]), where octd = 3,6-dithio-1,8-octanediol, is formed from the reaction between the 3,6-dithio-1,8-octanediol and vanadyl sulfate (V^IVOSO₄). The effects of treatment with ([V^IVO(octd)] on blood glucose, lipidic profile, body weight, food intake, water intake, urinary volume, glycogen levels, and biomarkers for liver toxicity were investigated using a streptozotocin (STZ)-induced diabetic Wistar rats model. The results have shown that the [V^IVO(octd)] complex caused a significant decrease in blood glucose (247.6 ± 19.3 mg/dL vs 430.1 ± 37.6 mg/dL diabetic group, p < 0.05), triglycerides (TG, 50%) and very low-density cholesterol (VLDL-C, 50%) levels in STZ-diabetic rats after 3 weeks of treatment. The [V^IVO(octd)] has shown antihyperglycemic activity in diabetic rats as well as a reduction in elevated lipid levels. Time-dependent studies using EPR and ⁵¹V NMR spectroscopy of [V^IVO(octd)] were done in aqueous solutions to determine the complex stability and species present in the oral gavage solution used for complex administration. The spectroscopic studies have shown that the antidiabetic/hypolipidemic activity could be attributed to [V^IVO(octd)], vanadium species resulting from redox processes, the hydrolysis of [V^IVO(octd)] and its decomposition products, or some combination of these factors. In summary, the oxidovanadium(IV) complex containing the S₂O₂ donor ligand has desirable antidiabetic properties eliminating the symptoms of Diabetes mellitus and its comorbidities.

Technologies for Solubility, Dissolution and Permeation Enhancement of Natural Compounds

The current review is based on the advancements in the field of natural therapeutic agents which could be utilized for a variety of biomedical applications and against various diseases and ailments. In addition, several obstacles have to be circumvented to achieve the desired therapeutic effectiveness, among which limited dissolution and/or solubility and permeability are included. To counteract these issues, several advancements in the field of natural therapeutic substances needed to be addressed. Therefore, in this review, the possible techniques for the dissolution/solubility and permeability improvements have been addressed which could enhance the dissolution and permeability up to several times. In addition, the conventional and modern isolation and purification techniques have been emphasized to achieve the isolation and purification of single or multiple therapeutic constituents with convenience and smarter approaches. Moreover, a brief overview of advanced natural compounds with multiple therapeutic effectiveness have also been anticipated. In brief, enough advancements have been carried out to achieve safe, effective and economic use of natural medicinal agents with improved stability, handling and storage.

Sonochemistry in an organocatalytic domino reaction: an expedient multicomponent access to structurally functionalized dihydropyrano[3,2-b]pyrans, spiro-pyrano[3,2-b]pyrans, and spiro-indenoquinoxaline-pyranopyrans under ambient conditions

A highly convenient and sustainable one-pot approach for the diversely-oriented synthesis of a variety of medicinally privileged amino-substituted 4,8-dihydropyrano[3,2-b]pyran-3-carbonitriles, and spiro[indoline-3,4'-pyrano[3,2-b]pyran]-3-carbonitrile/carboxylate derivatives on the basis of a domino three-component reaction of readily available carbonyl compounds including aryl aldehydes or isatins, active methylene compounds, and kojic acid as a Michael donor using secondary amine catalyst l-proline under ultrasound irradiation in aqueous ethanolic solution at ambient temperature has been developed. This methodology can involve the assembly of C-C, C[double bond, length as m-dash]C, C-O, C-N bonds via a one-pot operation, and following this protocol, a series of novel amino-substituted spiro[indeno[1,2-b]quinoxaline-11,4-pyrano[3,2-b]pyran]-3-carbonitrile/carboxylates have been synthesized. The practical utility of this method was found to be very efficient for scale-up reaction and other useful transformations. The methodology provides significant advantages including mild reaction conditions, energy-efficiency, short reaction time, fast reaction, simple work-up procedure, broad functional group tolerances, utilization of reusable catalyst, green solvent system, being metal-free, ligand-free, waste-free, inexpensive, etc. Excellent chemical yields have been achieved without using column chromatography. To address the issues of green and more sustainable chemistry, several metrics including Atom Economy (AE), Reaction Mass Efficiency (RME), Atom efficiency, E-factor, Process Mass Intensity (PMI), and Carbon Efficiency (CE) have been quantified for the present methodology that indicates the greenness of the present protocol.

Antioxidative and Anti-inflammatory Effects of Kojic Acid in Aβ-Induced Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a common cause of dementia that is clinically characterized by the loss of memory and cognitive functions. Currently, there is no specific cure for the management of AD, although natural compounds are showing promising therapeutic potentials because of their safety and easy availability. Herein, we evaluated the neuroprotective properties of kojic acid (KA) in an AD mouse model. Intracerebroventricular injection (i.c.v) of Aβ_1-42 (5 μL/5 min/mouse) into wild-type adult mice induced AD-like pathological changes in the mouse hippocampus by increasing oxidative stress and neuroinflammation, affecting memory and cognitive functions. Interestingly, oral treatment of kojic acid (50 mg/kg/mouse for 3 weeks) reversed the AD pathology by reducing the expression of amyloid-beta (Aβ) and beta-site amyloid precursor protein cleaving enzyme1 (BACE-1). Moreover, kojic acid reduced oxidative stress by enhancing the expression of nuclear factor erythroid-related factor 2 (Nrf2) and heme oxygenase 1 (HO1). Also, kojic acid reduced the lipid peroxidation and reactive oxygen species in the Aβ + kojic acid co-treated mice brains. Moreover, kojic acid decreased neuroinflammation by inhibiting Toll-like receptor 4, phosphorylated nuclear factor-κB, tumor necrosis factor-alpha, interleukin 1-beta (TLR-4, p-NFκB, TNFα, and IL-1β, respectively), and glial cells. Furthermore, kojic acid enhanced synaptic markers (SNAP-23, SYN, and PSD-95) and memory functions in AD model mice. Additionally, kojic acid treatment also decreased Aβ expression, oxidative stress, and neuroinflammation in vitro in HT-22 mouse hippocampal cells. To the best of our knowledge, this is the first study to show the neuroprotective effects of kojic acid against an AD mouse model. Our findings could serve as a favorable and alternative strategy for the discovery of novel drugs to treat AD-related neurodegenerative conditions.

Zn(II) and Cd(II) thiosemicarbazones for stimulation/inhibition of kojic acid biosynthesis from Aspergillus flavus and the fungal defense behavior against the metal complexes' excesses

The complexes {[ZnL¹Cl] C1, [ZnL²Cl].0.5H₂O C2, [CdL¹Cl] C3, and [CdL²Cl] C4} were prepared from tridentate thiosemicarbazones {HL¹ = 4-(3-nitrophenyl)-1-((pyridin-2-yl)methylene) thiosemicarbazide and HL² = 4-(2,4-dimethoxyphenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide} and identified by elemental CHNS, spectroscopic {IR and UV-Vis.}, thermal and DMF solution electrical conductivity data. On another hand, kojic acid (KA) which represents important secondary metabolite with numerous hot spot applications was successfully biosynthesized from Aspergillus flavus and structurally analyzed by single crystal analysis. The Zn(II) complexes C1&C2 (0.3 mM) enhanced the KA biosynthesis by 70.87% and 42.26%, while 76.09% of C1 and 72.78% of C2 were absorbed by the fungal cells. The Cd(II) complexes C3&C4 at 0.3 mM inhibited KA production by 87.95% and 97.03% with Cd(II) consumption reaching to 40.09% & 37.3%, while 0.4 mM of C3&C4 resulted in 100% inhibition of kojic acid biosynthesis. Light microscopic analysis showed the fungal structural abnormalities and the cell antioxidant behavior was detected. These complexes could be highly applicable as new stimulators and inhibitors of kojic acid production.

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.

Non-Oxido-Vanadium(IV) Metalloradical Complexes with Bidentate 1,2-Dithienylethene Ligands: Observation of Reversible Cyclization of the Ligand Scaffold in Solution

Derivatives of 1,2‐dithienylethene (DTE) have superb photochromic properties due to an efficient reversible photocyclization reaction of their hexatriene structure and, thus, have application potential in materials for optoelectronics and (multi‐responsive) molecular switches. Transition‐metal complexes bearing switchable DTE motifs commonly incorporate their coordination site rather distant from the hexatriene system. In this work the redox active ligand 1,2‐bis(2,5‐dimethylthiophen‐3‐yl)ethane‐1,2‐dione is described, which reacts with [V(TMEDA)₂Cl₂] to give a rare non‐oxido vanadium(IV) species 3(M,M/P,P). This blue complex has two bidentate en‐diolato ligands which chelate the V^IV center and give rise to two five‐membered metallacycles with the adjacent hexatriene DTE backbone bearing axial chirality. Upon irradiation with UVA light or prolonged heating in solution, the blue compound 3(M,M/P,P) converts into the purple atropisomer 4(para,M/para,P). Both complexes were isolated and structurally characterized by single‐crystal X‐ray diffraction analysis (using lab source and synchrotron radiation). The antiparallel configuration (M or P helicity) present in both 3(M,M/P,P) and 4(para,M/para,P) is a prerequisite for (reversible) 6π cyclization reactions. A CW EPR spectroscopic study reveals the metalloradical character for 3(M,M/P,P) and 4(para,M/para,P) and indicates dynamic reversible cyclization of the DTE backbone in complex 3(M,M/P,P) at ambient temperature in solution.

Oxovanadium(IV) Coordination Compounds with Kojic Acid Derivatives in Aqueous Solution

Hydroxypyrone derivatives have a good bioavailability in rats and mice and have been used in drug development. Moreover, they show chelating properties towards vanadyl cation that could be used in insulin-mimetic compound development. In this work, the formation of coordination compounds of oxovanadium(IV) with four kojic acid (5-hydroxy-2-(hydroxymethyl)-4-pyrone) derivatives was studied. The synthetized studied ligands (S2, S3, S4, and SC) have two or three kojic acid units linked through diamines or tris(2-aminoethyl)amine chains, respectively. The chemical systems were studied by potentiometry (25 °C, ionic strength 0.1 mol L^-1 with KCl), and UV-visible and EPR spectroscopy. The experimental data were analyzed by a thermodynamic and a chemometric (Multivariate Curve Resolution-Alternating Least Squares) approach. Chemical coordination models were proposed, together with the species formation constants and the pure estimated UV-vis and EPR spectra. In all systems, the coordination of the oxovanadium(IV) starts already under acidic conditions (the cation is totally bound at pH higher than 3-4) and the metal species remain stable even at pH 8. Ligands S3, S4, and SC form three coordination species. Two of them are probably due to the successive insertion of the kojate units in the coordination shell, whereas the third is most likely a hydrolytic species.

Consistent production of kojic acid from Aspergillus sojae SSC-3 isolated from rice husk

A consistent kojic acid producing fungal strain has been isolated from rice husk using glucose-peptone medium. The isolate was identified as Aspergillus sojae SSC-3 on 18S rDNA analysis. A. sojae was capable of producing substantially good amount of kojic acid, however the production was varying from batch to batch. In order to obtain consistent, repeated and high levels of kojic acid, monospore isolation procedures was adopted. The highest production of kojic acid obtained was 12 ± 2 g/L in 120 h with sucrose (10%) and yeast extract (0.5%) as carbon and nitrogen source respectively. The process was scale up to 10 L fermenter size which repeatedly resulted in the production of 18 ± 2 g/L of kojic acid in 96 h. Kojic acid was recovered (> 82%) from the fermentation broth with > 99% purity. Best to our knowledge this is the first report were kojic acid production is reported from Aspergillus sojae strain.

Chemistry of mixed-ligand oxidovanadium(IV) complexes of aroylhydrazones incorporating quinoline derivatives: Study of solution behavior, theoretical evaluation and protein/DNA interaction

A series of eight hexacoordinated mixed-ligand oxidovanadium(IV) complexes [VO(L^x)(L^N-N)] (1-8), where L^x = L¹ - L⁴ are four differently substituted ONO donor aroylhydrazone ligands and L^N-N are N,N-donor bases like 2,2'-bipyridine (bipy) (1, 3, 5 and 7) and 1,10-phenanthroline (phen) (2, 4, 6 and 8), have been reported. All synthesized complexes have been characterized by various physicochemical techniques and molecular structures of 1 and 6 were determined by X-ray crystallography. With a view to evaluate the biological activity of the V^IVO species, the behavior of the systems V^IVO²⁺/L^x, V^IVO²⁺/L^x/bipy and V^IVO²⁺/L^x/phen was studied as a function of pH in a mixture of H₂O/DMSO 50/50 (v/v). DFT calculations allowed finding out the relative stability of the tautomeric forms of the ligands, and predicting the structure of vanadium complexes and their EPR parameters. To study their interaction with proteins, firstly the ternary systems V^IVO²⁺/L^1,2 with 1-methylimidazole, which is a good model for histidine binding, were examined. Subsequently the interaction of the complexes with lysozyme (Lyz), cytochrome c (Cyt) and bovine serum albumin (BSA) was studied. The results indicate that the complexes showed moderate binding affinity towards BSA, while no interaction takes place with lysozyme and cytochrome c. This could be explained with the higher number of accessible coordinating and polar residues for BSA than for Lyz and Cyt. Further, the complexes were also evaluated for their DNA binding propensity through UV-vis absorption titration and fluorescence spectral studies. These results were consistent with BSA binding affinity and showed moderate binding affinity towards CT-DNA.

Role of Ligands in the Uptake and Reduction of V(V) Complexes in Red Blood Cells

The interaction with erythrocytes of four [V^VO₂L₂]^- complexes, with L = picolinate (pic), 5-cyanopicolinate (picCN), 3-aminopyrazine-2-carboxylate (przNH₂), and 1,2-dimethyl-3-hydroxy-4(1 H)-pyridinonate (dhp), was studied. The thermodynamic stability at physiological pH is: [V^VO₂(dhp)₂]^- > [V^VO₂(przNH₂)₂]^- > [V^VO₂(pic)₂]^- > [V^VO₂(picCN)₂]^-. With picCN and pic, V exists at physiological pH as H₂V^VO₄^-, with przNH₂ as a mixture of H₂V^VO₄^- and [V^VO₂(przNH₂)₂]^- and with dhp as [V^VO₂(dhp)₂]^-. In the systems with pic and picCN, H₂V^VO₄^- and the ligands cross the erythrocyte membrane independently, with dhp the uptake occurs by diffusion, whereas with przNH₂ both the mechanisms are active. Inside erythrocytes stable V^IVOL₂ complexes are formed, indicating that there is no relationship with the stability and redox state of the administered compounds and that, if the metal ion changes its oxidation state in the cytosol as V does, unstable complexes in the extracellular medium could become stable inside the cells and contribute to the pharmacological action.

Kojic acid applications in cosmetic and pharmaceutical preparations

Skin color disorders can be caused by various factors, such as excessive exposure to sunlight, aging and hormonal imbalance during pregnancy, or taking some medications. Kojic acid (KA) is a natural metabolite produced by fungi that has the ability to inhibit tyrosinase activity in synthesis of melanin. The major applications of KA and its derivatives in medicine are based on their biocompatibility, antimicrobial and antiviral, antitumor, antidiabetic, anticancer, anti-speck, anti-parasitic, and pesticidal and insecticidal properties. In addition, KA and its derivatives are used as anti-oxidant, anti-proliferative, anti-inflammatory, radio protective and skin-lightening agent in skin creams, lotions, soaps, and dental care products. KA has the ability to act as a UV protector, suppressor of hyperpigmentation in human and restrainer of melanin formation, due to its tyrosinase inhibitory activity. Also, KA could be developed as a chemo sensitizer to enhance efficacy of commercial antifungal drugs or fungicides. In general, KA and its derivatives have wide applications in cosmetics and pharmaceutical industries.

Synthesis, structure, solution behavior, reactivity and biological evaluation of oxidovanadium(iv/v) thiosemicarbazone complexes

The synthesis and characterization of an oxidovanadium(iv) [VIVO(L)(acac)] (1) and of two dioxidovanadium(v) [VVO2(L')] (2) and [VVO2(L)] (2a) complexes of the Schiff base formed from the reaction of 4-(p-fluorophenyl) thiosemicarbazone with pyridine-2-aldehyde (HL) are described. The oxidovanadium(iv) species [VIVO(L)(acac)] (1) was synthesized by the reaction of VIVO(acac)2 with the thiosemicarbazone HL in refluxing ethanol. The recrystallization of [VIVO(L)(acac)] (1) in DMF, CH3CN or EtOH gave the same product i.e. the dioxidovanadium(v) complex [VVO2(L)] (2a); however, upon recrystallization of 1 in DMSO a distinct compound [VVO2(L')] (2) was formed, wherein the original ligand L- is transformed to a rearranged one, L'-. In the presence of DMSO the ligand in complex 1 is found to undergo methylation at the carbon centre attached to imine nitrogen (aldimine) and transformed to the corresponding VVO2-species through in situ reaction. The synthesized HL and the metal complexes were characterized by elemental analysis, IR, UV-Vis, NMR and EPR spectroscopy. The molecular structure of [VVO2(L')] (2) was determined by single crystal X-ray crystallography. The methylation of various other ligands and complexes prepared from different vanadium precursors under similar reaction conditions was also attempted and it was confirmed that the imine methylation observed is both ligand and metal precursor specific. Complexes 1 and 2 show in vitro insulin-like activity against insulin responsive L6 myoblast cells, higher than VIVO(acac)2, with complex 1 being more potent. In addition, the in vitro cytotoxicity studies of HL, and of complexes 1 and 2 against the MCF-7 and Vero cell lines were also done. The ligand is not cytotoxic and complex 2 is significantly more cytotoxic than 1. DAPI staining experiments indicate that an increase in the time of incubation and an increase of concentration of the complexes lead to the increase in cell death.

Synthesis and anti-diabetic activity of new N,N-dimethylphenylenediamine-derivatized nitrilotriacetic acid vanadyl complexes

Vanadium compounds are promising anti-diabetic agents. However, reducing the metal toxicity while keeping/improving the hypoglycemic effect is still a big challenge towards the success of anti-diabetic vanadium drugs. To improve the therapeutic potency using the anti-oxidative strategy, we synthesized new N,N-dimethylphenylenediamine (DMPD)-derivatized nitrilotriacetic acid vanadyl complexes ([VO(dmada)]). The in vitro biological evaluations revealed that the DMPD-derivatized complexes showed improved antioxidant capacity and lowered cytotoxicity on HK-2 cells than bis(maltolato)oxidovanadium (IV) (BMOV). In type II diabetic mice, [VO(p-dmada)] (0.15mmolkg^-1/day) exhibited better hypoglycemic effects than BMOV especially on improving glucose tolerance and alleviating the hyperglycemia-induced liver damage. These insulin enhancement effects were associated with increased expression of peroxisome proliferator-activated receptor α and γ (PPARα/γ) in fat, activation of Akt (v-Akt murine thymoma viral oncogene)/PKB (protein kinase-B) in fat and liver, and inactivation of c-Jun NH₂-terminal protein kinases (JNK) in liver. Moreover, [VO(p-dmada)] showed no tissue toxicity at the therapeutic dose in diabetic mice and the oral acute toxicity (LD50) was determined to be 1640mgkg^-1. Overall, the experimental results indicated that [VO(p-dmada)] can be a potent insulin enhancement agent with improved efficacy-over- toxicity index for further drug development. In addition, the results on brain Tau phosphorylation suggested necessary investigation on the effects of vanadyl complexes on the pathology of the Alzheimer's disease in the future.

Vanadium and zinc complexes of 5-cyanopicolinate and pyrazine derivatives: synthesis, structural elucidation and in vitro insulino-mimetic activity study

Inhibition of free fatty acid release from rat adipocytes was observed for vanadium(iv), vanadium(v) and zinc(ii) complexes.

Chemistry of Monomeric and Dinuclear Non-Oxido Vanadium(IV) and Oxidovanadium(V) Aroylazine Complexes: Exploring Solution Behavior

A series of mononuclear non-oxido vanadium(IV) [V(IV)(L(1-4))2] (1-4), oxidoethoxido vanadium(V) [V(V)O(L(1-4))(OEt)] (5-8), and dinuclear μ-oxidodioxidodivanadium(V) [V(V)2O3(L(1))2] (9) complexes with tridentate aroylazine ligands are reported [H2L(1) = 2-furoylazine of 2-hydroxy-1-acetonaphthone, H2L(2) = 2-thiophenoylazine of 2-hydroxy-1-acetonaphthone, H2L(3) = 1-naphthoylazine of 2-hydroxy-1-acetonaphthone, H2L(4) = 3-hydroxy-2-naphthoylazine of 2-hydroxy-1-acetonaphthone]. The complexes are characterized by elemental analysis, by various spectroscopic techniques, and by single-crystal X-ray diffraction (for 2, 3, 5, 6, 8, and 9). The non-oxido V(IV) complexes (1-4) are quite stable in open air as well as in solution, and DFT calculations allow predicting EPR and UV-vis spectra and the electronic structure. The solution behavior of the [V(V)O(L(1-4))(OEt)] compounds (5-8) is studied confirming the formation of at least two different types of V(V) species in solution, monomeric corresponding to 5-8, and μ-oxidodioxidodivanadium [V(V)2O3(L(1-4))2] compounds. The μ-oxidodioxidodivanadium compound [V(V)2O3(L(1))2] (9), generated from the corresponding mononuclear complex [V(V)O(L(1))(OEt)] (5), is characterized in solution and in the solid state. The single-crystal X-ray diffraction analyses of the non-oxido vanadium(IV) compounds (2 and 3) show a N2O4 binding set and a trigonal prismatic geometry, and those of the V(V)O complexes 5, 6, and 8 and the μ-oxidodioxidodivanadium(V) (9) reveal that the metal center is in a distorted square pyramidal geometry with O4N binding sets. For the μ-oxidodioxidodivanadium species in equilibrium with 5-8 in CH2Cl2, no mixed-valence complexes are detected by chronocoulometric and EPR studies. However, upon progressive transfer of two electrons, two distinct monomeric V(IV)O species are detected and characterized by EPR spectroscopy and DFT calculations.

A study of DNA/BSA interaction and catalytic potential of oxidovanadium(v) complexes with ONO donor ligands

The study of DNA/BSA interaction and the catalytic potential of five mono- and dinuclear oxidoethoxido vanadium(v) complexes.

Vanadium compounds in medicine

Vanadium is a transition metal that, being ubiquitously distributed in soil, crude oil, water and air, also found roles in biological systems and is an essential element in most living beings. There are also several groups of organisms which accumulate vanadium, employing it in their biological processes. Vanadium being a biological relevant element, it is not surprising that many vanadium based therapeutic drugs have been proposed for the treatment of several types of diseases. Namely, vanadium compounds, in particular organic derivatives, have been proposed for the treatment of diabetes, of cancer and of diseases caused by parasites. In this work we review the medicinal applications proposed for vanadium compounds with particular emphasis on the more recent publications. In cells, partly due to the similarity of vanadate and phosphate, vanadium compounds activate numerous signaling pathways and transcription factors; this by itself potentiates application of vanadium-based therapeutics. Nevertheless, this non-specific bio-activity may also introduce several deleterious side effects as in addition, due to Fenton's type reactions or of the reaction with atmospheric O2, VCs may also generate reactive oxygen species, thereby introducing oxidative stress with consequences presently not well evaluated, particularly for long-term administration of vanadium to humans. Notwithstanding, the potential of vanadium compounds to treat type 2 diabetes is still an open question and therapies using vanadium compounds for e.g. antitumor and anti-parasitic related diseases remain promising.

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.

Thirty years through vanadium chemistry

The relevance of vanadium in biological systems is known for many years and vanadium-based catalysts have important industrial applications, however, till the beginning of the 80s research on vanadium chemistry and biochemistry did not receive much attention from the scientific community. The understanding of the broad bioinorganic implications resulting from the similarities between phosphate and vanadate(V) and the discovery of vanadium dependent enzymes gave rise to an enormous increase in interest in the chemistry and biological relevance of vanadium. Thereupon the last 30years corresponded to a period of enormous research effort in these fields, as well as in medicinal applications of vanadium and in the development of catalysts for use in fine-chemical synthesis, some of these inspired by enzymatic active sites. Since the 80s my group in collaboration with others made contributions, described throughout this text, namely in the understanding of the speciation of vanadium compounds in aqueous solution and in biological fluids, and to the transport of vanadium compounds in blood plasma and their uptake by cells. Several new types of vanadium compounds were also synthesized and characterized, with applications either as prospective therapeutic drugs or as homogeneous or heterogenized catalysts for the production of fine chemicals. The developments made are described also considering the international context of the evolution of the knowledge in the chemistry and bioinorganic chemistry of vanadium compounds during the last 30years. This article was compiled based on the Vanadis Award presentation at the 9th International Vanadium Symposium.

Physiological roles of peroxido-vanadium complexes: Leitmotif as their signal transduction pathway

Evidence exists that supports the various physiological roles of vanadium compounds, although the amount of vanadium in our body is limited. This limited concentration in our body does not attract much attention of the biological chemists, although the fact is present; even in the 19th century, vanadium derivatives were used for the therapeutic reagents. In the middle of the 20th century, the main focus of vanadium chemistry is mainly on the chemical and material fields. After the first discovery of vanadium compounds expressing ATPase activity, oxidovanadium(IV) sulfate was reported to have insulin mimic activity. Additionally, because some vanadium compounds possess cellular toxicity, trials were also carried out to examine the possible use of vanadium compounds as cancer therapeutics. The application of vanadium complexes was extended in recent years especially in the 21st century. In this review, we briefly explain the historical background of vanadium chemistry and also summarize the physiological role of vanadium complexes mainly focusing on the synthesis and physiological role of peroxidovanadium compounds and their interactions with insulin signal transduction pathways.

Characterization and biotransformation in the plasma and red blood cells of V(IV)O(2+) complexes formed by ceftriaxone

The coordination mode and geometry in aqueous solution of oxidovanadium(IV) complexes formed by a third-generation cephalosporin, ceftriaxone (H3cef), were studied by spectroscopic (EPR, electron paramagnetic resonance), pH-potentiometric and computational (DFT, density functional theory) methods. The behavior of the model systems containing 6-hydroxy-2-methyl-3-thioxo-3,4-dihydro-1,2,4-triazine-5(2H)-one (H2hmtdt) and 3-benzylthio-6-hydroxy-2-methyl-1,2,4-triazine-5(2H)-one (Hbhmt) was examined for comparison. The stability of the tautomers of ceftriaxone and 6-hydroxy-2-methyl-3-thioxo-3,4-dihydro-1,2,4-triazine-5(2H)-one in the neutral, mono- and bi-anionic form was calculated by DFT methods, both in the gas phase and in aqueous solution, and the electron density on the oxygen atoms of the hydroxytriazinone ring was related to the pKa of the ligands. The data demonstrate that ceftriaxone coordinates V(IV)O(2+) forming mono- and bis-chelated complexes with (Oket, O(-)) donor set and formation of five-membered chelate rings. The geometry of the bis-chelated complex, cis-[VO(Hcef)2(H2O)](2-), is cis-octahedral and this species can deprotonate, around physiological pH, to form the corresponding mono-hydroxido cis-[VO(Hcef)2(OH)](3-). The interaction of cis-[VO(Hcef)2(H2O)](2-) with apo-transferrin (apo-hTf) was studied and the results suggest that V(IV)O(2+) distributes between (VO)apo-hTf/(VO)2apo-hTf and cis-[VO(Hcef)2(H2O)](2-), whereas mixed complexes are not formed for charge and steric effects. The interaction of cis-[VO(Hcef)2(H2O)](2-) with red blood cells shows that ceftriaxone helps V(IV)O(2+) ion to cross the erythrocyte membrane. Inside the cell cis-[VO(Hcef)2(H2O)](2-) decomposes and the same species formed by inorganic V(IV)O(2+) are observed. The relationship between the biotransformation in the plasma and red blood cells and the potential pharmacological activity of V(IV)O(2+) species of ceftriaxone is finally discussed.

Evaluation of the cell cytotoxicity and DNA/BSA binding and cleavage activity of some dioxidovanadium(V) complexes containing aroylhydrazones

Three dioxidovanadium(V) complexes [VO2L(1-3)] (1-3) [HL(1)=1-napthoyl hydrazone of 2-acetyl pyridine, HL(2)=2-furoyl hydrazone of 2-acetyl pyridine and H2L(3)=isonicotinoyl hydrazone of 2-hydroxy benzaldehyde] have been reported. All the complexes were characterized by various spectroscopy (IR, UV-visible and NMR) and the molecular structures of 1 and 2 were characterized by single crystal X-ray diffraction technique. Structural report established five-coordinate geometries, distorted toward square pyramidal for each of 1 and 2, based on a tridentate -O,N,N coordinating anion and two oxido-O atoms. The experimental results show that the complexes interact with calf-thymus DNA (CT-DNA) possibly by a groove binding mode, with binding constants of ~10(5)M(-1). All complexes show good photo-induced cleavage of pUC19 supercoiled plasmid DNA with complex 1 showing the highest photo-induced DNA cleavage activity of ~68%. 1-3 also exhibit moderate binding affinity in the range of 10(3)-10(4)M(-1) towards bovine serum albumin (BSA), while all the complexes show good photo-induced BSA cleavage activity. Moreover the antiproliferative activity of all these complexes was studied, which reveal all compounds are significantly cytotoxic towards the HeLa cell line.

Kojic acid protects C57BL/6 mice from gamma-irradiation induced damage

The radioprotective effects of a single administration of kojic acid (KA) against ionizing radiation were evaluated via assessment of 30-day survival and alterations of peripheral blood parameters of adult C57BL/6 male mice. The 30-day survival rate of mice pretreated with KA (75 or 300 mg/kg body weight, KA75 or KA300) subcutaneously 27 h prior to a lethal dose (8 Gy, 153.52 cGy/min) of gamma irradiation was higher than that of mice irradiated alone (40% or 60% vs 0%). It was observed that the white blood cell (WBC) count/the red blood cell (RBC) count, haemoglobin content, haematocrit and platelet count of mice with or without KA pretreatment as exposed to a sub-lethal dose (4 Gy, 148.14 cGy/min) of gamma irradiation decreased maximally at day 4/day 8 post-irradiation. Although the initial WBC values were low in KA300 or WR-2721 (amifostine) groups, they significantly recovered to normal at day 19, whereas in the control group they did not. The results from the cytotoxicity and cell viability assays demonstrated that KA could highly protect Chinese hamster ovary (CHO) cells against ionizing radiation with low toxicity. In summary, KA provides marked radioprotective effects both in vivo and in vitro.

Vanadium methyl-bipyridine organoligand and its influence on energy balance and organs mass

In the treatment of lifestyle diseases, including metabolic syndrome and type 2 diabetes, it is important to lower body mass and fat tissue, and consequently, to increase insulin-sensitivity. Unfortunately, it often happens that low-energy diet which would lower overweight is not observed and, thus, it does not bring the expected effects. This paper discusses the influence of three diets-control, high-fructose, and high-fatty diet-on absorption of energy from food in order to transform it into body mass. The kJ/g ratio which describes this process has been calculated. In the tested diets, the addition of fructose (79.13 ± 2.47 kJ/g) or fat (82.48 ± 2.28 kJ/g) results in higher transformation of energy into body mass than in the case of control diet (89.60 ± 1.86 kJ/g). The addition of Na[VO(O2)2(4,4′-Me2-2,2′-bpy)]•8H2O (where 4,4′-Me2-2,2′-bpy = 4,4′-dimethyl-2,2′-bipyridine) results in statistical increase of that ratio: fructose diet (86.88 ± 0.44 kJ/g), fat diet (104.68 ± 3.01 kJ/g), and control diet (115.98 ± 0.56 kJ/g), respectively. Fat diet statistically influences the decrease of kidney mass in comparison to the other diets. The application of the tested vanadium compound results also in the statistical decrease of the fatty liver caused by fructose and fat diet.

Synthesis and characterization of V(IV)O complexes of picolinate and pyrazine derivatives. Behavior in the solid state and aqueous solution and biotransformation in the presence of blood plasma proteins

Oxidovanadium(IV) complexes with 5-cyanopyridine-2-carboxylic acid (HpicCN), 3,5-difluoropyridine-2-carboxylic acid (HpicFF), 3-hydroxypyridine-2-carboxylic acid (H2hypic), and pyrazine-2-carboxylic acid (Hprz) have been synthesized and characterized in the solid state and aqueous solution through elemental analysis, IR and EPR spectroscopy, potentiometric titrations, and DFT simulations. The crystal structures of the complexes (OC-6-23)-[VO(picCN)2(H2O)]·2H2O (1·2H2O), (OC-6-24)-[VO(picCN)2(H2O)]·4H2O (2·4H2O), (OC-6-24)-Na[VO(Hhypic)3]·H2O (4), and two enantiomers of (OC-6-24)-[VO(prz)2(H2O)] (Λ-5 and Δ-5) have been determined also by X-ray crystallography. 1 presents the first crystallographic evidence for the formation of a OC-6-23 isomer for bis(picolinato) V(IV)O complexes, whereas 2, 4, and 5 possess the more common OC-6-24 arrangement. The strength order of the ligands is H2hypic ≫ HpicCN > Hprz > HpicFF, and this results in a different behavior at pH 7.40. In organic and aqueous solution the three isomers OC-6-23, OC-6-24, and OC-6-42 are formed, and this is confirmed by DFT simulations. In all the systems with apo-transferrin (VO)2(apo-hTf) is the main species in solution, with the hydrolytic V(IV)O species becoming more important with lowering the strength of the ligand. In the systems with albumin, (VO)(x)HSA (x = 5, 6) coexists with VOL2(HSA) and VOL(HSA)(H2O) when L = picCN, prz, with [VO(Hhypic)(hypic)](-), [VO(hypic)2](2-), and [(VO)4(μ-hypic)4(H2O)4] when H2hypic is studied, and with the hydrolytic V(IV)O species when HpicFF is examined. Finally, the consequence of the hydrolysis on the binding of V(IV)O(2+) to the blood proteins, the possible uptake of V species by the cells, and the possible relationship with the insulin-enhancing activity are discussed.

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.

Influence of vanadium-organic ligands treatment on selected metal levels in kidneys of STZ rats

The objective of the study was to investigate the effects of five organic vanadium complexes supplement and a small dose of insulin injection on V, Fe, Cu, Zn, Mn, Ca, and K level in the streptozotocin diabetic rat's kidney during a 5-week treatment with the tested complexes. In all groups of animals, metal level in the lyophilized kidney organs was investigated by means of the proton induced X-ray emission method. Tissue vanadium level was naturally higher in vanadium-treated rats. The maximum level of vanadium was observed in the kidney (x(mean) = 16.6 μg/g). The influence of vanadium administration on other metal level in rat's tissue was also investigated. Spectacular influence of vanadium action was observed on copper and zinc level in examined tissue.

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.

A coordination chemistry study of hydrated and solvated cationic vanadium ions in oxidation states +III, +IV, and +V in solution and solid state

The coordination chemistry of hydrated and solvated vanadium(III), oxovanadium(IV), and dioxovanadium(V) ions in the oxygen-donor solvents water, dimethyl sulfoxide (DMSO), and N,N'-dimethylpropyleneurea (DMPU) has been studied in solution by extended X-ray absorption fine structure (EXAFS) and large-angle X-ray scattering (LAXS) and in the solid state by single-crystal X-ray diffraction and EXAFS. The hydrated vanadium(III) ion has a regular octahedral configuration with a mean V-O bond distance of 1.99 Å. In the hydrated and DMSO-solvated oxovanadium(IV) ions, vanadium binds strongly to an oxo group at ca. 1.6 Å. The solvent molecule trans to the oxo group is very weakly bound, at ca. 2.2 Å, while the remaining four solvent molecules, with a mean V-O bond distance of 2.0 Å, form a plane slightly below the vanadium atom; the mean O═V-O(perp) bond angle is ca. 98°. In the DMPU-solvated oxovanadium(IV) ion, the space-demanding properties of the DMPU molecule leave no solvent molecule in the trans position to the oxo group, which reduces the coordination number to 5. The O═V-O bond angle is consequently much larger, 107°, and the mean V═O and V-O bond distances decrease to 1.58 and 1.97 Å, respectively. The hydrated and DMSO-solvated dioxovanadium(V) ions display a very distorted octahedral configuration with the oxo groups in the cis position with a mean V═O bond distance of 1.6 Å and a O═V═O bond angle of ca. 105°. The solvent molecules trans to the oxo groups are weakly bound, at ca. 2.2 Å, while the remaining two have bond distances of 2.02 Å. The experimental studies of the coordination chemistry of hydrated and solvated vanadium(III,IV,V) ions are complemented by summarizing previously reported crystal structures to yield a comprehensive description of the coordination chemistry of vanadium with oxygen-donor ligands.