Study of the oxidation products of the VO(dmpp)2 complex in aqueous solution under aerobic conditions: comparison with the vanadate–dmpp system

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.

Experimental and molecular topology-based biological implications of Schiff base complexes: a concise review

This review is a gentle introduction toward Schiff bases with special attention to bioinorganic aspects. Depending on the nature of condensation moieties (ketonic or aldehydic) with primary amine, a large number of novel compounds are reported every year with applicability in various material science aspects. Herein, a burgeoning literature overview is presented to provide a salient discussion of the current status of these molecular systems. Schiff bases are designed depending on the particular desirable properties. For instance, to enlighten a biologically relevant molecule, it is always appreciated when a prepared compound shows biological membrane crossing and nucleic acid linking potential. Under such purview, the Schiff base functional group can serve as an enhancer of biomembrane traversing capability. In addition to various other catalytic aspects, the type of disease to be encountered also matters. Nowadays, theoretical chemistry is applied before synthesizing a compound of this sort and fruitful results are first depicted and, if found feasible, a suitable synthetic route is followed to synthesize Schiff base compounds. Molecular charge topology analysis under theoretical expression is analyzed generally to predict the biological relevance of a molecule.

Metabolic effects of VO(dmpp)2– anex vivo1H-HRMAS NMR study to unveil its pharmacological properties

VO(dmpp)₂ameliorates liver metabolic profile of obese pre-diabetic Zucker rats after 4 weeks of treatment, as demonstrated byex vivo¹H-HRMAS NMR study.

EPR and 51V NMR studies of prospective anti-diabetic bis(3-hydroxy-4-pyridinonato)oxidovanadium(iv) complexes in aqueous solution and liposome suspensions

EPR/⁵¹V-NMR parallel studies of [VO(3,4-HPO)₂] complexes in MOPS buffer and POPC liposome suspensions provide information regarding solvents for oral administration.

In vitro effects of bis(1,2-dimethyl-3-hydroxy-4-pyridinonato)oxidovanadium(IV), or VO(dmpp)2, on insulin secretion in pancreatic islets of type 2 diabetic Goto-Kakizaki rats

Vanadium compounds have been explored as therapy of diabetes, and most studies have focussed on insulin mimetic effects, i.e. reducing hyperglycemia by improving glucose sensitivity and thus glucose uptake in sensitive tissues. We have recently shown that bis(1,2-dimethyl-3-hydroxy-4-pyridinonato)oxidovanadium(IV), VO(dmpp)2, has promising effects when compared to another vanadium compound, bis(maltolato)oxidovanadium(IV), BMOV, and insulin itself, in isolated adipocytes and in vivo in Goto-Kakizaki (GK) rats, an animal model of hereditary type 2 diabetes (T2D).We now have investigated in GK rats whether VO(dmpp)2 also modulates another important defect in T2D, impaired insulin secretion. VO(dmpp)2, but not BMOV, stimulated insulin secretion from isolated GK rat pancreatic islets at high, 16.7mM, but not at low–normal, 3.3 mM, glucose concentration. Mechanistic studies demonstrate that the insulin releasing effect of VO(dmpp)2 is due to its interaction with several steps in the stimulus-secretion coupling for glucose, including islet glucose metabolism and K-ATP channels, L-type Ca2+ channels, modulation by protein kinases A and C, as well as the exocytotic machinery. In conclusion, VO(dmpp)2 exhibits properties of interest for treatment of the insulin secretory defect in T2D, in addition to its well-described insulin mimetic activity.

VO(dmpp)2 normalizes pre-diabetic parameters as assessed by in vivo magnetic resonance imaging and spectroscopy

Type 2 diabetes mellitus has been associated with obesity, metabolic syndrome, cardiovascular diseases and cancer. Attempts have been made for early diagnosis and finding effective drugs to prevent severe consequences and ameliorate the symptoms of this disorder. In this work, the pharmacological properties of VO(dmpp)(2), [bis(1,2-dimethyl-3-hydroxy-4-pyridinonato)oxovanadium(IV)], were in vivo evaluated. For 4 weeks fatty Zucker rats were subjected to a daily dose of VO(dmpp)(2) (44 μmol/kg) and their metabolic profile was followed by assessing different biological parameters at established time points: body weight, subcutaneous fat width and hepatic triglyceride content determined by magnetic resonance imaging and spectroscopy, respectively. A glucose tolerance test was performed at the end of the experiment. After treatment, treated obese rats presented a weight significantly lower than the non-treated obese animals (359.0±11.1 vs. 433.5±6.2g, P<0.05), a thinner subcutaneous fat width, and a statistically significant decrease in hepatic triglyceride content (5.41±0.59 vs. 21.03±1.40%, P<0.0005). Additionally, the glucose intolerant profile of fatty Zucker rats was completely reversed in treated animals (102.3±2.1 vs. 172.4±1.3 mg/100 mL; P<0.0005). These results reinforce the therapeutic action of VO(dmpp)(2) which shows particular effects on lipid metabolism.

Investigation of the insulin-like properties of zinc(II) complexes of 3-hydroxy-4-pyridinones: identification of a compound with glucose lowering effect in STZ-induced type I diabetic animals

Results from an investigation in an in vivo model of STZ-induced diabetic rats demonstrate that compound bis(1,2-dimethyl-3-hydroxy-4(1H)-pyridinonate)zinc(II), Zn(dmpp)(2), significantly lowers the blood glucose levels of individuals, thus showing evidence of glucose lowering activity. The compound was selected from a set of eight zinc(II) complexes of 3-hydroxy-4-pyridinones with diverse lipophilicity that were prepared and characterized in our laboratory. Assessment of insulin-like activity of the complexes was firstly performed in vitro by measuring the inhibition of FFA release in isolated rat adipocytes. The results indicate that compounds bis(2-methyl-3-hydroxy-4-pyridinonate)zinc(II), Zn(mpp)(2) and Zn(dmpp)(2) display significantly higher activity than that of the respective positive control thus suggesting its selection for in vivo tests. Safety evaluation of the active zinc(II) compounds was performed in freshly isolated rat hepatocytes. The results support that cell viability is not significantly different from the control set after 1 and 2h of incubation with both zinc(II) complexes.

Vanadate complexes in serum: a speciation modeling study

The speciations of two drug candidate ligands, 2-hydroxypyridine-N-oxide (Hhpno) and 2-mercaptopyridine-N-oxide (Hmpno), with vanadate (V(V)) were determined at 25.0 degrees C and 0.20 mol dm(-3) KCl by pH-metric and (51)V-NMR methods. At pH 7.4, the two predominant compounds with both ligands are the VO(2)L(2) and VO(2)L(OH). NH(4)[VO(2)(hpno)(2)] x 3 H(2)O was prepared in solid form, and its crystal structure was determined by X-ray diffraction. The stabilities of the complexes VO(2)L(2) of five drug candidate ligands were compared at pH 7.4. In view of the stability sequence hpno > maltol approximately hdp (Hhdp: 3-hydroxy-1,2-dimethyl-4-pyridinone) >> mpno > picolinic acid, the first two of these ligands were chosen for equilibrium studies with apotransferrin (apoTf) competition. The V(V)-apoTf stability constants (log K(1) = 6.03 +/- 0.10; log K(2) = 5.46 +/- 0.18) determined by (51)V-NMR spectroscopy were confirmed by ultrafiltration. Both methods proved that there seems to be no hydrogencarbonate-vanadate competition for the apoTf anion-binding positions. The other potential high molecular mass V(V) binder in the serum is human serum albumin (HSA). As no interaction was detected by (51)V-NMR spectroscopy or fluorimetry, the binding properties of HSA were quantified on the basis of literature data. As a final conclusion, speciation modeling calculations suggest that, under serum conditions, apoTf is probably the primary metal ion binder, even in the presence of the most stable V(V) carrier ligands hpno and maltol and HSA plays a negligible role in V(V) binding.

Novel 3-hydroxy-4-pyridinonato oxidovanadium(IV) complexes to investigate structure/activity relationships

A previous evaluation of the insulin-like activity of three 3-hydroxy-4-pyridinonato oxidovanadium(IV) complexes raised questions about structure/activity relationships, namely the influence of the hydrophilic/lipophilic balance of the complex and the capacity of the ligand to stabilize the +4 oxidation state of vanadium ion, on achieving an positive effect. To address these questions, we synthesized six new oxidovanadium(IV) complexes with variable hydrophilic/lipophilic balance, obtained by introducing different substituents on the nitrogen atom, and used two 3-hydroxy-4-pyrones as starting reagents to provide methyl and ethyl groups in the ortho position of the ring. For the new and previously reported complexes, we studied the oxidation-reduction properties and insulin-like activity in terms of inhibitory effect on Free fatty acid (FFA) release in isolated rat adipocytes. The results obtained show that only one of the complexes, Bis(3-hydroxy-1(H)-2-methyl-4-pyridonato)oxidovanadium(IV), VO(mpp)(2), exhibits a significantly greater capacity to inhibit FFA release than VOSO(4) and consequently is worthy to be considered for further studies. The establishment of structure activity relationships was not attainable but this study brings new information about the influence of some properties of the compounds on the achievement of an insulin-like effect. The results reveal that: (i) the oxidation-reduction cycles of the complexes are identical; (ii) the presence of more lipophilic substituents on the nitrogen atom does not enhance insulin-like properties; (iii) a high solubility in water proved to be not sufficient for a positive activity in inhibiting FFA release; (iv) a small molecular size may be an important property for reaching the right targets.

Uptake and metabolic effects of insulin mimetic oxovanadium compounds in human erythrocytes

The uptake of the oxidation products of two oxovanadium(IV) compounds, [N,N'-ethylenebis(pyridoxylaminato)]oxovanadium(IV), V(IV)O(Rpyr(2)en), and bis-[3-hydroxy-1,2-dimethyl-4-pyridinonato]oxovanadium(IV), V(IV)O(dmpp)(2), by human erythrocytes was studied using (51)V and (1)H NMR and EPR spectroscopy. V(IV)O(Rpyr(2)en) in aerobic aqueous solution is oxidized to its V(V) counterpart and the neutral form slowly enters the cells by passive diffusion. In aerobic conditions, V(IV)O(dmpp)(2) originates V(V) complexes of 1:1 and 1:2 stoichiometry. The neutral 1:1 species is taken up by erythrocytes through passive diffusion in a temperature-dependent process; its depletion from the extracellular medium promotes the dissociation of the negatively charged 1:2 species, and the protonation of the negatively charged 1:1 species. The identity of these complexes is not maintained inside the cells, and the intracellular EPR spectra suggest N(2)O(2) or NO(3) intracellular coordinating environments. The oxidative stress induced by the oxovanadium compounds in erythrocytes was not significant at 1mM concentration, but was increased by both vanadate and oxidized V(IV)O(dmpp)(2) at 5mM. Only 1mM oxidized V(IV)O(dmpp)(2) significantly stimulated erythrocytes glucose intake (0.75+/-0.13 against 0.37+/-0.17mM/h found for the control, p<0.05).