Isabel Tomaz

Transport of therapeutic vanadium and ruthenium complexes by blood plasma components.

Low molecular weight and high molecular weight metal ion binders present in blood plasma are shortly described. The binding of vanadium and ruthenium complexes by these components has received much attention, namely their interactions with human serum albumin and transferrin, and these studies are critically reviewed. The influence of the protein binding on the bioavailability of the prospective drugs, namely on the transport by blood plasma and uptake by cells is also discussed. It is concluded that vanadium compounds are mainly transported in blood by transferrin, but that no study has properly addressed the influence of albumin and transferrin in the vanadium uptake by cells. Ruthenium complexes bind strongly to HSA, most likely at the level of His residues, leading to the formation of stable adducts. If the kinetics of binding to this protein is fast enough, probably they are mainly transported by this serum protein. Nevertheless, at least for a few Ru(III)-complexes, hTf seems to play an active role in the uptake of ruthenium, while HSA may provide selectivity and higher activity for the compounds due to an enhanced permeability effect.

Preparation and characterisation of new oxovanadium(IV) Schiff base complexes derived from amino acids and aromatic o-hydroxyaldehydes

Abstract A range of mostly new oxovanadium(IV) complexes is described. They contain coordinated Schiff bases, made from natural amino acids (glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, threonine, aspartic acid, and histidine) and salicylaldehyde or such derivatives as 3-, 4-, or 5-methoxy-salicylaldehyde. The coordination sphere is completed by simple ligands like water, 2,2′-bipyridyl or pyridine. The compounds are characterised and the nature of their coordination spheres shown by analysis, TLC, and by appropriate spectroscopy (EPR, IR, electronic and circular dichroism of solution and solids). In a few cases, magnetic properties are described to establish oxidation state. In several cases, the solubility of the compounds from racemic amino acids differs markedly from those containing the single enantiomer. The crystal and molecular structure of the related (and novel) compound with N-pyridoxylidene- d , l -isoleucinate, [VO(pyr- d , l -Ile)(bipy)]·H2O is described. It contains two diastereomers. Denoting the chiral vanadium centres as A or C, these are and [A(pyr- l -Ile)(bipy)] [C(pyr- d -Ile)(bipy)].

Oxovanadium(IV) complexes with aromatic aldehydes.

The synthesis, structure and spectroscopic properties of complexes with the formula [V(IV)O(dsal)2(H2O)], where Hdsal = salicylaldehyde, o-vanillin and 3-ethoxysalicylaldehyde, are presented. The crystal and molecular structures of [V(IV)O(o-van)2(H2O)] (1) (o-Hvan = o-vanillin = 3-methoxysalicylaldehyde) is studied by single-crystal X-ray diffraction. Each molecule exhibits an octahedral geometry with the two o-van ligands coordinated cis to the V(IV)O2+ group. 1 is the first example of a structurally characterized vanadium complex involving O(aldehyde) as the donor atom and this enables a comparison between the bonding characteristics and the contributions of O(aldehyde), O(amide), O(carboxylate) and O(ketone) (in acetylacetone) to the parallel hyperfine coupling constant in VOL2 complexes.

Vanadium compounds as therapeutic agents: Some chemical and biochemical studies

The behaviour of three vanadium(V) systems, namely the pyridinone (V(V)-dmpp), the salicylaldehyde (V(V)-salDPA) and the pyrimidinone (V(V)-MHCPE) complexes, is studied in aqueous solutions, under aerobic and physiological conditions using (51)V NMR, EPR and UV-Visible (UV-Vis) spectroscopies. The speciations for the V(V)-dmpp and V(V)-salDPA have been previously reported. In this work, the system V(V)-MHCPE is studied by pH-potentiometry and (51)V NMR. The results indicate that, at pH ca. 7, the main species present are (V(V)O(2))L(2) and (V(V)O(2))LH(-1) (L=MHCPE(-)) and hydrolysis products, similar to those observed in aqueous solutions of V(V)-dmpp. The latter species is protonated as the pH decreases, originating (V(V)O(2))L and (V(V)O(2))LH. All the V(V)-species studied are stable in aqueous media with different compositions and at physiological pH, including the cell culture medium. The compounds were screened for their potential cytotoxic activity in two different cell lines. The toxic effects were found to be incubation time and concentration dependent and specific for each compound and type of cells. The HeLa tumor cells seem to be more sensitive to drug effects than the 3T3-L1 fibroblasts. According to the IC(50) values and the results on reversibility to drug effects, the V(V)-species resulting from the V(V)-MHCPE system show higher toxicity in the tumor cells than in non-tumor cells, which may indicate potential antitumor activity.

Evaluation of the binding of oxovanadium(IV) to human serum albumin

The understanding of the biotransformations of insulin mimetic vanadium complexes in human blood and its transport to target cells is an essential issue in the development of more effective drugs. We present the study of the interaction of oxovanadium(iv) with human serum albumin (HSA) by electron paramagnetic resonance (EPR), circular dichroism (CD) and visible absorption spectroscopy. Metal competition studies were done using Cu(II) and Zn(II) as metal probes. The results show that V(IV)O occupies two types of binding sites in albumin, which compete not only with each other, but also with hydrolysis of the metal ion. In one of the sites the resulting V(IV)O-HSA complex has a weak visible CD signal and its X-band EPR spectrum may be easily measured. This was assigned to amino acid side chains of the ATCUN site. The other binding site shows stronger signals in the CD in the visible range, but has a hardly measurable EPR signal; it is assigned to the multi metal binding site (MBS) of HSA. Studies with fatted and defatted albumin show the complexity of the system since conformational changes, induced by the binding of fatty acids, decrease the ability of V(IV)O to bind albumin. The possibility and importance of ternary complex formation between V(IV)O, HSA and several drug candidates - maltol (mal), picolinic acid (pic), 2-hydroxypyridine-N-oxide (hpno) and 1,2-dimethyl-3-hydroxy-4(1H)-pyridinone (dhp) was also evaluated. In the presence of maltol the CD and EPR spectra significantly change, indicating the formation of ternary VO-HSA-maltol complexes. Modeling studies with amino acids and peptides were used to propose binding modes. Based on quantitative RT EPR measurements and CD data, it was concluded that in the systems with mal, pic, hpno, and dhp (V(IV)OL(2))(n)(HSA) species form, where the maximum value for n is at least 6 (mal, pic). The degree of formation of the ternary species, corresponding to the reaction V(IV)OL(2) + HSA -->/<-- V(IV)OL(2)(HSA) is hpno > pic ≥ mal > dhp. (V(IV)OL)(n)(HSA) type complexes are detected exclusively with pic. Based on the spectroscopic studies we propose that in the (V(IV)OL(2))(n)(HSA) species the protein bounds to vanadium through the histidine side chains.

The systems VIVO2+-glutathione and related ligands: a potentiometric and spectroscopic study

Abstract. The equilibria in the system VIVO2+-glutathione in aqueous solution were studied in the pH range 2–11 by a combination of pH-potentiometry and spectroscopy (EPR, visible absorption and circular dichroism). The results of the various methods are consistent and the equilibrium model includes the species MLH3, MLH2, MLH, ML2H2, MLH–1, and MLH–2 and several hydrolysis products (where H4L denotes totally protonated glutathione); individual formation constants and spectra are given. ML2H2 is the predominant species at physiological pH. Plausible structures for each stoichiometry are discussed. The related VIVO2+ systems of S-methylglutathione and γ-L-glutamyl-L-cysteinyl ethyl ester were studied by means of the same spectroscopic techniques in order to support the established binding modes for the glutathione complexes. The importance of glutathione and oxidized glutathione in binding VIVO2+ in cells is assessed.

Interactions of VO(IV) with oligopeptides

Abstract The oxovanadium(IV)-binding features of various oligopeptides are reviewed in the paper. The decisive role of amide coordination and the presence of a suitable anchoring donor group in the molecules are discussed through numerous examples. It is found that the effectiveness of the anchoring donors in promoting peptide amide deprotonation and coordination follows the sequence: phenolate-O − >alcoholate-O − , thiolate-S − >carboxylate-COO − >NH 2 . This basic sequence is finely tuned by the presence of additional donors in the molecule, and also by the presence of additional binder molecules in the biological fluids.

The system VO2++oxidized glutathione: A potentiometric and spectroscopic study

The equilibria in the system VO2+ +oxidized glutathione in aqueous solution have been studied in the pH range 2-11 by a combination of pH potentiometry and spectroscopy (EPR, visible absorption and circular dichroism). The results of the various methods are self-consistent and the equilibrium model includes the species MLH4, MLH3, MLH2, MLH, ML, MLH(-1), MLH(-2) and several hydrolysis products (where H4L denotes oxidized glutathione); individual formation constants and spectra are given. Plausible structures for each stoichiometry are discussed.

Preparation and characterisation of vanadium complexes derived from salicylaldehyde or pyridoxal and sugar derivatives

Abstract By reaction of salicylaldehyde (Hsal) with the amino-sugars d -glucosamine (glsmN), d -galactosamine (galacN) or d -glucamine (glcN) in the presence of VOSO4 or VOCl2, Schiff base (SB) complexes were obtained. By using pyridoxal (pyr) instead of Hsal, a solid containing the SB derived from its reaction with glcN was isolated. The compounds were characterised in the solid state by elemental analyses, IR, EPR, CD and magnetic susceptibility measurements. The complexes are not simple monomers in the solid state and were formulated as {VIVO(sal– d -galacN)}n, {VIVO(sal– d -glsmN)}n, (VIVVVO3)(sal– d -glcN) and (VIVO)3(pyr– d -glcN)2, the SB ligands being coordinated through the imine–N, phenolato-O−, sugar–O− and sugar–OH moieties. The complexes 3–5 were studied in solution by UV–Vis and CD spectrophotometry. The CD band pattern and λmax are normally the same both in the solid state and in MeOH, indicating that the binding mode is mostly preserved. Complex 6 is only slightly soluble and the spectroscopic studies were not conclusive in this respect. Upon dissolution of complexes 3–6, the oxovanadium(IV) is progressively oxidized and the SB hydrolysed.

A novel VIVO–pyrimidinone complex: synthesis, solution speciation and human serum protein binding

The pyrimidinones mhcpe, 2-methyl-3H-5-hydroxy-6-carboxy-4-pyrimidinone ethyl ester (mhcpe, 1), 2,3-dimethyl-5-benzyloxy-6-carboxy-4-pyrimidinone ethyl ester (dbcpe, 2) and N-methyl-2,3-dimethyl-5-hydroxy-6-carboxyamido-4-pyrimidinone (N-MeHOPY, 3), are synthesized and their structures determined by single crystal X-ray diffraction. The acid-base properties of 1 are studied by potentiometric and spectrophotometric methods, the pK(a) values being 1.14 and 6.35. DFT calculations were carried out to determine the most stable structure for each of the H2L(+), HL and L(-) forms (HL = mhcpe) and assign the groups involved in the protonation-deprotonation processes. The mhcpe(-) ligand forms stable complexes with V(IV)O(2+) in the pH range 2 to 10, and potentiometry, EPR and UV-Vis techniques are used to identify and characterize the V(IV)O-mhcpe species formed. The results are consistent with the formation of V(IV)O, (V(IV)O)L, (V(IV)O)L2, (V(IV)O)2L2H(-2), (V(IV)O)L2H(-1), (V(IV)O)2L2H(-3), (V(IV)O)LH(-2) species and V(IV)O-hydrolysis products. Calculations indicate that the global binding ability of mhcpe towards V(IV)O(2+) is similar to that of maltol (Hmaltol = 3-hydroxy-2-methyl-4H-pyran-4-one) and lower than that of 1,2-dimethyl-3-hydroxy-4-pyridinone (Hdhp). The interaction of V(IV)O-complexes with human plasma proteins (transferrin and albumin) is studied by circular dichroism (CD), EPR and (51)V NMR spectroscopy. V(IV)O-mhcpe-protein ternary complexes are formed in both cases. The binding of V(IV)O(2+) to transferrin (hTF) in the presence of mhcpe involves mainly (V(IV)O)1(hTF)(mhcpe)1, (V(IV)O)2(hTF)(mhcpe)1 and (V(IV)O)2(hTF)(mhcpe)2 species, bound at the Fe(III) binding sites, and the corresponding conditional formation constants are determined. Under the conditions expected to prevail in human blood serum, CD data indicate that the V(IV)O-mhcpe complexes mainly bind to hTF; the formation of V(IV)O-hTF-mhcpe complexes occurs in the presence of Fe(III) as well, distinct EPR signals being clearly obtained for Fe(III)-hTF and to V(IV)O-hTF-mhcpe species. Thus this study indicates that transferrin plays the major role in the transport of V(IV)O-mhcpe complexes under blood plasma conditions in the form of ternary V(IV)-ligand-protein complexes.