Reactivity and Speciation of Anti-Diabetic Vanadium Complexes in Whole Blood and Its Components: The Important Role of Red Blood Cells.

Reactions with blood components are crucial for controlling the antidiabetic, anticancer, and other biological activities of V(V) and V(IV) complexes. Despite extensive studies of V(V) and V(IV) reactions with the major blood proteins (albumin and transferrin), reactions with whole blood and red blood cells (RBC) have been studied rarely. A detailed speciation study of Na3[V(V)O4] (A), K4[V(IV)2O2(citr)2]·6H2O (B; citr = citrato(4-)); [V(IV)O(ma)2] (C; ma = maltolato(-)), and (NH4)[V(V)(O)2(dipic)] (D; dipic = pyridine-2,6-dicarboxylato(2-)) in whole rat blood, freshly isolated rat plasma, and commercial bovine serum using X-ray absorption near-edge structure (XANES) spectroscopy is reported. The latter two compounds are potential oral antidiabetic drugs, and the former two are likely to represent their typical decomposition products in gastrointestinal media. XANES spectral speciation was performed by principal component analysis and multiple linear regression techniques, and the distribution of V between RBC and plasma fractions was measured by electrothermal atomic absorption spectroscopy. Reactions of A, C, or D with whole blood (1.0 mM V, 1-6 h at 310 K) led to accumulation of ∼50% of total V in the RBC fraction (∼10% in the case of B), which indicated that RBC act as V carriers to peripheral organs. The spectra of V products in RBC were independent of the initial V complex, and were best fitted by a combination of V(IV)-carbohydrate (2-hydroxyacid moieties) and/or citrate (65-85%) and V(V)-protein (15-35%) models. The presence of RBC created a more reducing environment in the plasma fraction of whole blood compared with those in isolated plasma or serum, as shown by the differences in distribution of V(IV) and V(V) species in the reaction products of A-D in these media. At physiologically relevant V concentrations (<50 µM), this role of RBC may promote the formation of V(III)-transferrin as a major V carrier in the blood plasma. The results reported herein have broad implications for the roles of RBC in the transport and speciation of metal pro-drugs that have broad applications across medicine.

Vanadium(V) and -(IV) complexes of anionic polysaccharides: Controlled release pharmaceutical formulations and models of vanadium biotransformation products.

Uncontrolled reactions in biological media are a main obstacle for clinical translation of V-based anti-diabetic or anti-cancer pro-drugs. We investigated the use of controlled-release pharmaceutical formulations to ameliorate this issue with a series of V(V) and (IV) complexes of anionic polysaccharides. Carboxymethyl cellulose, xanthan gum, or alginic acid formulations were prepared by the reactions of [VO4](3-) with one or two molar equivalents of biological reductants, L-ascorbic acid (AA) or L-cysteine (Cys), in the presence of excess polysaccharide at pH~7 or pH~4. XANES studies with the use of a previously developed library of model V(V), V(IV) and V(III) complexes showed that reactions in the presence of AA led mostly to the mixtures of five- and six-coordinate V(IV) species, while the reactions in the presence of Cys led predominantly to the mixtures of five- and six-coordinate V(V) species. The XANES spectra of some of these samples closely matched those reported previously for [VO4](3-) biotransformation products in isolated blood plasma, red blood cells, or cultured adipocytes, which supports the hypothesis that modified polysaccharides are major binders of V(V) and V(IV) in biological systems. Studies by EPR spectroscopy suggested predominant V(IV)-carboxylato binding in complexes with polysaccharides. One of the isolated products (a V(IV)-alginato complex) showed selective release of low-molecular-mass V species at pH~8, but not at pH~2, which makes it a promising lead for the development of V-containing formulations for oral administration that are stable in the stomach, but release the active ingredient in the intestines.

Biotransformations of Antidiabetic Vanadium Prodrugs in Mammalian Cells and Cell Culture Media: A XANES Spectroscopic Study.

The antidiabetic activities of vanadium(V) and -(IV) prodrugs are determined by their ability to release active species upon interactions with components of biological media. The first X-ray absorption spectroscopic study of the reactivity of typical vanadium (V) antidiabetics, vanadate ([V(V)O4](3-), A) and a vanadium(IV) bis(maltolato) complex (B), with mammalian cell cultures has been performed using HepG2 (human hepatoma), A549 (human lung carcinoma), and 3T3-L1 (mouse adipocytes and preadipocytes) cell lines, as well as the corresponding cell culture media. X-ray absorption near-edge structure data were analyzed using empirical correlations with a library of model vanadium(V), -(IV), and -(III) complexes. Both A and B ([V] = 1.0 mM) gradually converged into similar mixtures of predominantly five- and six-coordinate V(V) species (∼75% total V) in a cell culture medium within 24 h at 310 K. Speciation of V in intact HepG2 cells also changed with the incubation time (from ∼20% to ∼70% V(IV) of total V), but it was largely independent of the prodrug used (A or B) or of the predominant V oxidation state in the medium. Subcellular fractionation of A549 cells suggested that V(V) reduction to V(IV) occurred predominantly in the cytoplasm, while accumulation of V(V) in the nucleus was likely to have been facilitated by noncovalent bonding to histone proteins. The nuclear V(V) is likely to modulate the transcription process and to be ultimately related to cell death at high concentrations of V, which may be important in anticancer activities. Mature 3T3-L1 adipocytes (unlike for preadipocytes) showed a higher propensity to form V(IV) species, despite the prevalence of V(V) in the medium. The distinct V biochemistry in these cells is consistent with their crucial role in insulin-dependent glucose and fat metabolism and may also point to an endogenous role of V in adipocytes.

Reactivity-activity relationships of oral anti-diabetic vanadium complexes in gastrointestinal media: an X-ray absorption spectroscopic study.

The reactions of oral V(V/IV) anti-diabetic drugs within the gastrointestinal environment (particularly in the presence of food) are a crucial factor that affects their biological activities, but to date these have been poorly understood. In order to build up reactivity-activity relationships, the first detailed study of the reactivities of typical V-based anti-diabetics, Na3V(V)O4 (A), [V(IV)O(OH2)5](SO4) (B), [V(IV)O(ma)2] (C, ma = maltolato(-)) and (NH4)[V(V)(O)2(dipic)] (D, dipic = pyridine-2,5-dicarboxylato(2-)) with simulated gastrointestinal (GI) media in the presence or absence of food components has been performed by the use of XANES (X-ray absorption near edge structure) spectroscopy. Changes in speciation under conditions that simulate interactions in the GI tract have been discerned using correlations of XANES parameters that were based on a library of model V(V), V(IV), and V(III) complexes for preliminary assessment of the oxidation states and coordination numbers. More detailed speciation analyses were performed using multiple linear regression fits of XANES from the model complexes to XANES obtained from the reaction products from interactions with the GI media. Compounds B and D were relatively stable in the gastric environment (pH ∼ 2) in the absence of food, while C was mostly dissociated, and A was converted to [V10O28](6-). Sequential gastric and intestinal digestion in the absence of food converted A, B and D to poorly absorbed tetrahedral vanadates, while C formed five- or six-coordinate V(V) species where the maltolato ligands were likely to be partially retained. XANES obtained from gastric digestion of A-D in the presence of typical food components converged to that of a mixture of V(IV)-aqua, V(IV)-amino acid and V(III)-aqua complexes. Subsequent intestinal digestion led predominantly to V(IV) complexes that were assigned as citrato or complexes with 2-hydroxyacidato donor groups from other organic compounds, including certain carbohydrates. The absence of strong reductants (such as ascorbate) in the food increased the V(V) component in gastrointestinal digestion products. These results can be used to predict the oral bioavailability of various types of V(V/IV) anti-diabetics, and the effects of taking such drugs with food.

Vanadium speciation by XANES spectroscopy: a three-dimensional approach.

A library of X-ray absorption near-edge structure (XANES) spectroscopic data for V(V), V(IV) and V(III) complexes with a broad range of biologically relevant ligand has been used to demonstrate that three-dimensional plots of key XANES parameters (pre-edge and edge energies; pre-edge and white line intensities) can be used for the prediction of V oxidation states and coordination numbers in biological or environmental matrices. The reliability of the technique has been demonstrated by re-analysis of the published XANES data for a V(V)-dependent bromoperoxidase.

Silicon nitride as a versatile growth substrate for microspectroscopic imaging and mapping of individual cells.

Herein is described a general sampling protocol that includes culture, differentiation and fixing of cells in their preferred morphology on the one sample substrate (Si(3)N(4)) to enable subsequent diverse modern microspectroscopic analyses. The protocol enables unprecedented correlated and complementary information on the intracellular biochemistry of metabolic processes, diseases and their treatment, which offers the opportunity to revolutionize our understanding of cell and tissue biology at a molecular level. The culture of adherent cells onto inexpensive Si(3)N(4) membranes allows microspectroscopic analyses across the electromagnetic spectrum, from hard X-ray fluorescence (both XRF and XANES), through to visible and fluorescence light microscopies, and infrared microspectroscopy without substrate interference. Adherent mammalian cell lines (3T3-L1 adipocytes and H9c2 cardiac myocytes) illustrate the in vitro application of these protocols. The cells adhered strongly to Si(3)N(4) membranes and visually displayed normal proliferative and phenotypic growth; more importantly, rapid alcohol fixation of cells did not affect their structural integrity for subsequent analyses.

Reactivity of potential anti-diabetic molybdenum(VI) complexes in biological media: a XANES spectroscopic study.

The application of Mo(VI) complexes as anti-diabetic agents is a subject of considerable recent interest. The stability and speciation of [Mo(VI)O(4)](2-) and three analogs of known anti-diabetic V(IV) complexes ([Mo(VI)O(2)L(2)]; where LH=2,4-pentanedione, l-cysteine ethyl ester or N,N-diethyldithiocarbamic acid) in natural and simulated biological fluids (including blood and its components, cell culture media, and artificial digestion systems) were studied using MoK-edge XANES (X-ray absorption near-edge structure) spectroscopy of freeze-dried samples at 20K. All of the studied [MoO(2)L(2)] complexes decomposed extensively under simulated gastric and intestinal digestion conditions (3 h at 310 K), as well as in blood plasma or in cell culture medium (24 h at 310 K). The reaction products of [MoO(4)](2-) and [MoO(2)L(2)] with biological fluids could be satisfactorily modelled (using multiple linear regression analyses) as mixtures of tetrahedral and octahedral Mo(VI) species (with O-donor ligands) in various ratios, which were dependent on the nature of the medium rather than that of the initial Mo(VI) compounds. Red blood cells take up Mo(VI) predominantly in the form of [MoO(4)](2-). Implications of these results to the development of Mo(VI)-based anti-diabetics and to the mechanisms of natural uptake and metabolism of Mo(VI) are discussed.