An Overview of Serum Albumin Interactions with Biomedical Alloys

Understanding the interactions between biomedical alloys and body fluids is of importance for the successful and safe performance of implanted devices. Albumin, as the first protein that comes in contact with an implant surface, can determine the biocompatibility of biomedical alloys. The interaction of albumin with biomedical alloys is a complex process influenced by numerous factors. This literature overview aims at presenting the current understanding of the mechanisms of serum albumin (both Bovine Serum Albumin, BSA, and Human Serum Albumin, HSA) interactions with biomedical alloys, considering only those research works that present a mechanistic description of the involved phenomena. Widely used biomedical alloys, such as 316L steel, CoCrMo and Titanium alloys are specifically addressed in this overview. Considering the literature analysis, four albumin-related phenomena can be distinguished: adsorption, reduction, precipitation, and protein-metal binding. The experimental techniques used to understand and quantify those phenomena are described together with the studied parameters influencing them. The crucial effect of the electrochemical potential on those phenomena is highlighted. The effect of the albumin-related phenomena on corrosion behavior of biomedical materials also is discussed.

Biological sulfur in the blood cells of Ascidia ceratodes: XAS spectroscopy and a cellular-enzymatic hypothesis for vanadium reduction in the ascidians

Two samples of living blood cells and of cleared blood plasma from the Phlebobranch tunicate Ascidia ceratodes from Bodega Bay, California, and one of fresh Henze solution from A. ceratodes of Monterey Bay, California, have been examined using sulfur K-edge x-ray absorption spectroscopy (XAS). Biological sulfur included sulfate esters, sulfate and bisulfate ions, benzothiazole, thianthrene, epi-sulfide, thiol and disulfide. Glutathione dominated reduced sulfur, from which an average intracellular Voltage of -0.21 V was calculated. Sulfate-bisulfate ratios yielded blood cell pH values of 2.0 and 2.8. Total blood cell [sulfur] was 373±9 mM or 296±73 mM from BaSO4 gravimetry. Two plasma samples (pH 6.9 or 7.0; [S] = 33±6 mM or 26±4 mM) were dominated by sulfate and disulfide. Fresh Henze solution evidenced a sulfur inventory similar to blood cells, with calculated pH = 2.7. A V(III)-sulfonate fraction varied systematically with intracellular pH across six independent blood cell samples, implying a vanadium mobilization pathway. Bodega Bay and Monterey Bay A. ceratodes appear to maintain alternative suites of low-valent sulfur. The significance of the vanabins to vanadium metabolism is critically examined in terms of known protein - V(IV) biochemistry. Finally, a detailed hypothesis for the reduction of [VO4]3- to V(III) in ascidians is introduced. A vanadium oxido-reductase is proposed to span the signet ring membrane and to release V(III) into the inner acidic vacuole. The V(V) to V(III) reduction is predicted require an inner-sphere mechanism, a thiol reductant, 7-coordinate V(III), a biologically accessible Voltage, and proton-facilitated release of V(III).

Towards the functional high-resolution coordination chemistry of blood plasma human serum albumin

Human serum albumin (HSA) is a monomeric, globular, multi-carrier and the most abundant protein in the blood. HSA displays multiple ligand binding sites with extraordinary binding capacity for a wide range of ions and molecules. For decades, HSA's ability to bind to various ligands has led many scientists to study its physiological properties and protein structure; indeed, a better understanding of HSA-ligand interactions in human blood, at the atomic level, will likely foster the development of more potent, and overall more performant, diagnostic and therapeutic tools against serious human disorders such as diabetes, cardiovascular disorders, and cancer. Here, we present a concise overview of the current knowledge of HSA's structural characteristics, and its coordination chemistry with transition metal ions, within the scope and limitations of current techniques and biophysical methods to reach atomic resolution in solution and in blood serum. We also highlight the overwhelming need of a detailed atomistic understanding of HSA dynamic structures and interactions that are transient, weak, multi-site and multi-step, and allosterically affected by each other. Considering the fact that HSA is a current clinical tool for drug delivery systems and a potential contender as molecular cargo and nano-vehicle used in biophysical, clinical and industrial fields, we underline the emerging need for novel approaches to target the dynamic functional coordination chemistry of the human blood serum albumin in solution, at the atomic level.

Vanadium in Biosphere and Its Role in Biological Processes

Ultra-trace elements or occasionally beneficial elements (OBE) are the new categories of minerals including vanadium (V). The importance of V is attributed due to its multifaceted biological roles, i.e., glucose and lipid metabolism as an insulin-mimetic, antilipemic and a potent stress alleviating agent in diabetes when vanadium is administered at lower doses. It competes with iron for transferrin (binding site for transportation) and with lactoferrin as it is secreted in milk also. The intracellular enzyme protein tyrosine phosphatase, causing the dephosphorylation at beta subunit of the insulin receptor, is inhibited by vanadium, thus facilitating the uptake of glucose inside the cell but only in the presence of insulin. Vanadium could be useful as a potential immune-stimulating agent and also as an antiinflammatory therapeutic metallodrug targeting various diseases. Physiological state and dose of vanadium compounds hold importance in causing toxicity also. Research has been carried out mostly on laboratory animals but evidence for vanadium importance as a therapeutic agent are available in humans and large animals also. This review examines the potential biochemical and molecular role, possible kinetics and distribution, essentiality, immunity, and toxicity-related study of vanadium in a biological system.

A Spectroscopy Approach for the Study of the Interaction of Oxovanadium(IV)-Salen Complexes with Proteins

Oxovanadium(IV)-salen complexes bind with bovine serum albumin (BSA) and ovalbumin (OVA) strongly with binding constant in the range 10(4)-10(7) M(-1) at physiological pH (7.4) confirmed using UV-visible absorption, fluorescence spectral and circular dichroism (CD) study. CD results show that the binding of oxovanadium(IV) complexes induces the conformational change with the loss of α-helicity in the proteins. Docking studies indicate that mode of binding of oxovanadium(IV)-salen complexes with proteins is hydrophobic in nature.

Chemical, biochemical, and biological behaviors of vanadate and its oligomers

Vanadate is widely used as an inhibitor of protein tyrosine phosphatases (PTPase) and is routinely applied in cell lysis buffers or immunoprecipitations of phosphotyrosyl proteins. Additionally, vanadate has been extensively studied for its antidiabetic and anticancer effects. In most studies, orthovanadate or metavanadate was used as the starting compound, whereas these "vanadate" solutions may contain more or less oligomerized species. Whether and how different species of vanadium compounds formed in the biological media exert specific biological effect is still a mystery. In the present commentary, we focus on the chemical, biochemical, and biological behaviors of vanadate. On the basis of species formation of vanadate in chemical and biological systems, we compared the biological effects and working mechanism of monovanadate with that of its oligomers, especially the decamer. We propose that different oligomers may exert a specific biological effect, which depends on their structures and the context of the cell types, by different modes of action.

New vanadium-based magnetic resonance imaging probes: clinical potential for early detection of cancer

We have developed a magnetic resonance imaging (MRI) method for improved detection of cancer with a new class of cancer-specific contrast agents, containing vanadyl (VO(2+))-chelated organic ligands, specifically bis(acetylacetonato)oxovanadium(IV) [VO(acac)(2)]. Vanadyl compounds have been found to accumulate within cells, where they interact with intracellular glycolytic enzymes. Aggressive cancers are metabolically active and highly glycolytic; an MRI contrast agent that enters cells with high glycolytic activity could provide high-resolution functional images of tumor boundaries and internal structure, which cannot be achieved by conventional contrast agents. The present work demonstrates properties of VO(acac)(2) that may give it excellent specificity for cancer detection. A high dose of VO(acac)(2) did not cause any acute or short-term adverse reactions in murine subjects. Calorimetry and spectrofluorometric methods demonstrate that VO(acac)(2) is a blood pool agent that binds to serum albumin with a dissociation constant K (d) ~ 2.5 +/- 0.7 x 10(-7) M and a binding stoichiometry n = 1.03 +/- 0.04. Owing to its prolonged blood half-life and selective leakage from hyperpermeable tumor vasculature, a low dose of VO(acac)(2) (0.15 mmol/kg) selectively enhanced in vivo magnetic resonance images of tumors, providing high-resolution images of their interior structure. The kinetics of uptake and washout are consistent with the hypothesis that VO(acac)(2) preferentially accumulates in cancer cells. Although VO(acac)(2) has a lower relaxivity than gadolinium-based MRI contrast agents, its specificity for highly glycolytic cells may lead to an innovative approach to cancer detection since it has the potential to produce MRI contrast agents that are nontoxic and highly sensitive to cancer metabolism.

Decavanadate (V10 O28 6-) and oxovanadates: oxometalates with many biological activities

The decameric vanadate species V(10)O(28)(6-), also referred to as decavanadate, impact proteins, lipid structures and cellular function, and show some effects in vivo on oxidative stress processes and other biological properties. The mode of action of decavanadate in many biochemical systems depends, at least in part, on the charge and size of the species and in some cases competes with the simpler oxovanadate species. The orange decavanadate that contains 10 vanadium atoms is a stable species for several days at neutral pH, but at higher pH immediately converts to the structurally and functionally distinct lower oxovanadates such as the monomer, dimer or tetramer. Although the biological effects of vanadium are generally assumed to derive from monomeric vanadate or the vanadyl cation, we show in this review that not all effects can be attributed to these simple oxovanadate forms. This topic has not previously been reviewed although background information is available [D.C. Crans, Comments Inorg. Chem. 16 (1994) 35-76; M. Aureliano (Ed.), Vanadium Biochemistry, Research Signpost Publs., Kerala, India, 2007]. In addition to pumps, channels and metabotropic receptors, lipid structures represent potential biological targets for decavanadate and some examples have been reported. Decavanadate interact with enzymes, polyphosphate, nucleotide and inositol 3-phosphate binding sites in the substrate domain or in an allosteric site, in a complex manner. In mitochondria, where vanadium was shown to accumulate following decavanadate in vivo administration, nM concentration of decavanadate induces membrane depolarization in addition to inhibiting oxygen consumption, suggesting that mitochondria may be potential targets for decameric toxicity. In vivo effects of decavanadate in piscine models demonstrated that antioxidant stress markers, lipid peroxidation and vanadium subcellular distribution is dependent upon whether or not the solutions administered contain decavanadate. The present review summarizes the reports on biological effects of decavanadate and highlights the importance of considering decavanadate in evaluations of the biological effects of vanadium.

Bioanalytical interaction studies executed by preincubation affinity capillary electrophoresis

The versatility of CE is beneficial for the study of many types of molecular interactions, because different experimental designs can be made to suit the characteristics of a particular interaction. A very versatile starting point is the preequilibration type of affinity CE that has been used extensively for characterizing biomolecular interactions in the last 15 years. We review this field here and include a comprehensive overview of the existing preincubation ACE modes including their advantages and limitations as well as the methodological developments and applications within the bioanalytical field.

New insights into the interactions of serum proteins with bis(maltolato)oxovanadium(IV): transport and biotransformation of insulin-enhancing vanadium pharmaceuticals

Significant new insights into the interactions of the potent insulin-enhancing compound bis(maltolato)oxovanadium(IV) (BMOV) with the serum proteins, apo-transferrin and albumin, are presented. Identical reaction products are observed by electron paramagnetic resonance (EPR) with either BMOV or vanadyl sulfate (VOSO4) in solutions of human serum apo-transferrin. Further detailed study rules out the presence of a ternary ligand-vanadyl-transferrin complex proposed previously. By contrast, differences in reaction products are observed for the interactions of BMOV and VOSO4 with human serum albumin (HSA), wherein adduct formation between albumin and BMOV is detected. In BMOV-albumin solutions, vanadyl ions are bound in a unique manner not observed in comparable solutions of VOSO4 and albumin. Presentation of chelated vanadyl ions precludes binding at the numerous nonspecific sites and produces a unique EPR spectrum which is assigned to a BMOV-HSA adduct. The adduct species cannot be produced, however, from a solution of VOSO4 and HSA titrated with maltol. Addition of maltol to a VOSO4-HSA solution instead results in formation of a different end product which has been assigned as a ternary complex, VO(ma)(HSA). Furthermore, analysis of solution equilibria using a model system of BMOV with 1-methylimidazole (formation constant log K1 = 4.5(1), by difference electronic absorption spectroscopy) lends support to an adduct binding mode (VO(ma)2-HSA) proposed herein for BMOV and HSA. This detailed report of an in vitro reactivity difference between VOSO4 and BMOV may have bearing on the form of active vanadium metabolites delivered to target tissues. Albumin binding of vanadium chelates is seen to have a potentially dramatic effect on pharmacokinetics, transport, and efficacy of these antidiabetic chelates.

Determination of binding constants and stoichiometries for platinum anticancer drugs and serum transport proteins by capillary electrophoresis using the Hummel-Dreyer method

A CE method has been developed to evidence and quantitatively characterize the interaction between platinum-based antitumor drugs and human serum proteins. This method is a variant of affinity CE modified regarding both experimental setup and data treatment so as to measure the peaks (or vacancies) that correspond to the bound drug when it slowly binds to the protein. Using the formalism of the Hummel-Dreyer method and cisplatin and oxaliplatin as test compounds, a protocol for determining albumin and transferrin binding constants and stoichiometries, including (and distinguished by) 48 hours of incubation of the reaction mixture, was elaborated. Relative affinities of drugs toward different proteins in aqueous solution at physiological pH, chloride concentration, and temperature were compared in terms of overall binding constants and numbers of drug molecules attached to the protein. The results indicate that both platinum drugs bind to albumin more strongly than to transferrin, supporting the concept that the albumin fraction is a major drug supply route for chemotherapeutical needs. From a comparison with the binding parameters measured previously for cisplatin by other methods, conclusions were drawn about the validity of CE as a simple and convenient method for assaying protein-drug reactions with slow kinetics.

3?-Azido-3?-deoxythymidine binding to ribonuclease A: Model for drug-protein interaction

Ribonuclease A (RNase A) with several high affinity binding sites is a possible target for many organic and inorganic molecules. 3'-Azido-3'-deoxythymidine (AZT) is the first clinically effective drug for the treatment of human immunodeficiency virus (HIV) infection. The drug interactions with protein and nucleic acids are associated with its mechanism of action in vivo. This study was designed to examine the interaction of AZT with RNase A under physiological conditions. Reaction mixtures of constant protein concentration (2%) and different drug contents (0.0001-0.1 mM) are studied by UV-visible, FTIR, and circular dichroism spectroscopic methods in order to determine the drug binding mode, the drug binding constant, and the effects of drug complexation on the protein and AZT conformations in aqueous solution. The spectroscopic results showed one major binding for the AZT-RNase complexes with an overall binding constant of 5.29 x 10(5) M(-1). An increase in the protein alpha helicity was observed upon AZT interaction, whereas drug sugar pucker remained in the C2'-endo/anti conformation in the AZT-RNase complexes.

Pharmacokinetics of vanadium in humans after intravenous administration of a vanadium containing albumin solution

AIMS

Vanadium is currently undergoing clinical trials as an oral drug in patients with noninsulin-dependent diabetes mellitus. Furthermore, vanadium occurs in elevated concentrations in the blood of patients receiving intravenous albumin solutions containing large amounts of the metal ion as an impurity. The present study was performed to examine the pharmacokinetics of vanadium in humans following a single intravenous (i.v.) dose of a commercial albumin solution containing a high amount of vanadium.

METHODS

The study was conducted in five healthy volunteer subjects who received intravenously 90 ml of a commercial 20% albumin infusion solution containing 47.6 micro g vanadium as an impurity. Vanadium concentrations in serum and urine were determined by electrothermal atomic absorption spectrometry.

RESULTS

Vanadium serum concentrations after i.v. administration were measured for 31 days. The data could be fitted by a triexponential function corresponding formally to a three-compartment model. There was an initial rapid decrease in serum concentrations with half-lives of 1.2 and 26 h. This was followed by a long-terminal half-life time of 10 days. The terminal phase accounted for about 80% of the total area under the serum concentration-time curve (AUC). The mean apparent volume of distribution of the central compartment was found to be 10 l. The volume of distribution at steady state was 54 l, and total clearance was 0.15 l h(-1). Vanadium was mainly excreted by the kidneys. About 52% of the dose was recovered in the urine after 12 days.

CONCLUSIONS

This study provides data on vanadium pharmacokinetics in healthy humans.

Secondary structural analysis of the Na(+),K(+)-ATPase and its Na(+) (E(1)) and K(+) (E(2)) complexes by FTIR spectroscopy

The Na(+),K(+)-ATPase is an integral membrane protein which transports sodium and potassium cations against an electrochemical gradient. The transport of Na(+) and K(+) ions is presumably connected to an oscillation of the enzyme between the two conformational states, the E(1) (Na(+)) and the E(2) (K(+)) conformations. The E(1) and E(2) states have different affinities for ligand interaction. However, the determination of the secondary structure of this enzyme in its sodium and potassium forms has been the subject of much controversy. This study was designed to provide a quantitative analysis of the secondary structure of the Na(+),K(+)-ATPase in its sodium (E(1)) and potassium (E(2)) states in both H(2)O and D(2)O solutions at physiological pH, using Fourier transform infrared (FTIR) with its self-deconvolution and second derivative resolution enhancement methods, as well as curve-fitting procedures. Spectroscopic analysis showed that the secondary structure of the sodium salt of the Na(+),K(+)-ATPase in H(2)O solution contains alpha-helix 19.8+/-1%, beta-sheet 25.6+/-1%, turn 9.1+/-1%, and beta-anti 7.5+/-1%, whereas in D(2)O solution, the enzyme shows alpha-helix 16.8+/-1%, beta-sheet 24.5+/-1.5%, turn 10.9+/-1%, beta-anti 9.8+/-1%, and random coil 38.0+/-2%. Similarly, the potassium salt in H(2)O solution contains alpha-helix 16.6+/-1%, beta-sheet 26.4+/-1.5%, turn 8.9+/-1%, and beta-anti 8.1+/-1%, while in D(2)O solution it shows alpha-helix 16.2+/-1%, beta-sheet 24.5+/-1.5%, turn 10.3+/-1%, beta-anti 9.0+/-1%, and random coil 40+/-2%. Thus the main differences for the sodium and potassium forms of the Na(+),K(+)-ATPase are alpha-helix 3.2% in H(2)O and 0.6% in D(2)O, beta-sheet (pleated and anti) 1.5% in H(2)O and random structure 2% (D(2)O), while for other minor components (turn structure), the differences are less than 1%.

Interaction of AZT with human serum albumin studied by capillary electrophoresis, FTIR and CD spectroscopic methods

The thymidine analog 3'-azido-3'-deoxythymidine (AZT) is still one of the effective drugs against human immunodeficiency (HIV) infection. AZT has been used as inhibitor of HIV-1 reverse transcriptase, the virus encoded enzyme which catalyzes transcription of viral RNA to DNA. The drug interaction with protein has been included in its mechanism of action. Human serum albumin (HSA) is a carrier of many drugs in vivo and thus AZT-HSA complexation can serve as a model for drug-protein interaction. This study was designed to examine the interaction of AZT with human serum albumin at physiological conditions using constant protein concentration (0.2% or 2%) and different drug contents (5 to 1000 microM). Capillary electrophoresis, FTIR and CD spectroscopic methods were used to determine the drug binding mode, the drug binding constant and the effects of drug-HSA complexation on the protein and AZT conformations in aqueous solution. Capillary electrophoresis and spectroscopic results showed two major bindings for the AZT-HSA complexes with K(1)=1.9 x 10(6) M(-1)and K(2)= 2.1 x 10(4) M(-1). Minor alterations of the protein secondary structure from that of the alpha-helix to beta-sheet were observed upon drug complexation, whereas the drug sugar pucker remained in the C2'-endo/anti conformation upon protein interaction.

Binding of vanadate to human albumin in infusion solutions, to proteins in human fresh frozen plasma, and to transferrin

The binding of vanadate (V) to human serum albumin (HSA) in infusion solutions, to human fresh frozen plasma (FFP), and to human transferrin (TF) was investigated over a wide concentration range. Free V concentrations were obtained by ultrafiltration. Total and free V concentrations were determined using electrothermal atomic absorption spectrometry (ETAAS). Binding parameters were obtained by non-linear regression. V only bound appreciably to HSA at low concentrations (<1 microM). The binding capacity of HSA was about 1000-fold lower than that of FFP and TF per mole of protein. Binding to FFP and TF in the concentration range investigated could be described by a combination of saturable and additional non-saturable binding. The respective maximal binding capacities (B(max), microM), dissociation constants (k(D), microM), and proportionality constants (C) for the non-saturable, linear binding were B(max)=27, k(D)=2.5, C=0.19 for FFP and B(max)=47, k(D)=0.47, C=0.38 for TF. The results suggest that V is predominantly bound to transferrin in FFP. It is concluded that HSA in infusion solutions represents a reservoir of readily accessible V. Nevertheless, given the high binding capacity of transferrin in plasma, the amount of vanadate delivered via the brief administration of HSA solutions is unlikely to be of major importance.