Study of non-covalent interactions between MRI contrast agents and human serum albumin by NMR diffusometry

Effect of bovine serum albumin on tartrate-modified manganese ferrite nano hollow spheres: spectroscopic and toxicity study

The emerging category of magneto-fluorescent tartrate-modified MnFe₂O₄ nano hollow spheres (T-MnFe₂O₄ NHSs) can be considered as promising candidates for biomedical applications. The interaction of bovine serum albumin (BSA) with T-MnFe₂O₄ NHSs has been studied using several spectroscopic techniques, which suggest that the interaction occurs by an electrostatic mechanism. Furthermore, BSA enhances the charge transfer transition from the tartrate ligand to the metal ions along with the d-d transition of Fe³⁺ ions on NHSs surfaces at different pH. Very strong salt bridge formation occurs between the lysine of the BSA surface and the tartrate in basic medium (pH 10), followed by the acidic (pH 3) and neutral medium (pH 7), respectively. Systematic fluorescence microscopic analysis reveals that BSA significantly enhances the contrast of T-MnFe₂O₄ NHSs in UV and blue light excitation because of the extended charge transfer from BSA to T-MnFe₂O₄ NHSs. Our report demonstrates great potential in the field of nanotechnology and biomedical applications. In vitro toxicity analysis using RAW 264.7 celline and in vivo studies on Wister rats revealed that the T-MnFe₂O₄ NHSs are benign. Furthermore, T-MnFe₂O₄ NHSs also appear to be an antimicrobial agent. Therefore, T-MnFe₂O₄ NHSs can be explored for future therapeutic applications.

NMR diffusion and relaxation studies of 2-nitroimidazole and albumin interactions

Nitroimidazole derivatives are of current interest in the development of hypoxia targeting agents and show potential in the establishment of quantitative measures of tumor hypoxia. In this study, the binding of 2-nitroimidazole to albumin was probed using NMR diffusion and relaxation measurements. Binding studies were conducted at three different protein concentrations (0.23, 0.30 and 0.38mM) with drug concentrations ranging from 0.005-0.16M at 298K. Quantitative assessments of the binding model were made by evaluating the number of binding sites, n, and association constant, K. These were determined to be 21±3 and 53±4M^-1, respectively.

Reinvestigation of the mechanism of polymerization of β-butyrolactone from 1,5,7-triazabicyclo[4.4.0]dec-5-ene

The questionable mechanism initially proposed to explain how 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) allows us to ring-open β-lactones, such as β-butyrolactone (BL), is reinvestigated here.

A Comparative Study of Receptor-Targeted Magnetosome and HSA-Coated Iron Oxide Nanoparticles as MRI Contrast-Enhancing Agent in Animal Cancer Model

Magnetosomes are specialized organelles arranged in intracellular chains in magnetotactic bacteria. The superparamagnetic property of these magnetite crystals provides potential applications as contrast-enhancing agents for magnetic resonance imaging. In this study, we compared two different nanoparticles that are bacterial magnetosome and HSA-coated iron oxide nanoparticles for targeting breast cancer. Both magnetosomes and HSA-coated iron oxide nanoparticles were chemically conjugated to fluorescent-labeled anti-EGFR antibodies. Antibody-conjugated nanoparticles were able to bind the MDA-MB-231 cell line, as assessed by flow cytometry. To compare the cytotoxic effect of nanoparticles, MTT assay was used, and according to the results, HSA-coated iron oxide nanoparticles were less cytotoxic to breast cancer cells than magnetosomes. Magnetosomes were bound with higher rate to breast cancer cells than HSA-coated iron oxide nanoparticles. While 250 μg/ml of magnetosomes was bound 92 ± 0.2%, 250 μg/ml of HSA-coated iron oxide nanoparticles was bound with a rate of 65 ± 5%. In vivo efficiencies of these nanoparticles on breast cancer generated in nude mice were assessed by MRI imaging. Anti-EGFR-modified nanoparticles provide higher resolution images than unmodified nanoparticles. Also, magnetosome with anti-EGFR produced darker image of the tumor tissue in T2-weighted MRI than HSA-coated iron oxide nanoparticles with anti-EGFR. In vivo MR imaging in a mouse breast cancer model shows effective intratumoral distribution of both nanoparticles in the tumor tissue. However, magnetosome demonstrated higher distribution than HSA-coated iron oxide nanoparticles according to fluorescence microscopy evaluation. According to the results of in vitro and in vivo study results, magnetosomes are promising for targeting and therapy applications of the breast cancer cells.

Interaction of Biphenyl-Functionalized Eu(2+)-Containing Cryptate with Albumin: Implications to Contrast Agents in Magnetic Resonance Imaging

The influence of albumin on the efficacy of a Eu(2+)-containing complex capable of interacting with human serum albumin (HSA) was investigated at different field strengths (1.4, 3, 7, 9.4, and 11.7 T). Relaxometric measurements indicated that the presence of albumin at higher field strengths (>3 T) did not result in an increase in the relaxivity of the Eu(2+) complex, but a relaxation enhancement of 171 ± 11% was observed at 1.4 T. Titration experiments using different percentages (2, 4.5, 6, 10, 15, and 25% w/v) of HSA and variable-temperature (17)O NMR measurements were performed to understand the effect of albumin on the molecular properties of the biphenyl-functionalized Eu(2+) complex that are relevant to magnetic resonance imaging.

Characterizing the binding of nucleotide ATP on serum albumin by 31P NMR diffusion

The pulsed-field-gradient (PFG) 31P NMR diffusion spectra were measured under varied sample conditions to characterize the low-affinity binding of adenosine 5′-triphosphate (ATP) on human serum albumin (HSA) or bovine serum albumin (BSA). The NMR diffusion constants of ATP, ATP–HSA, or ATP–BSA were illustrated as function of ATP concentrations. The binding curves of ATP–HSA and ATP–BSA were identical but strikingly different from the ATP curve. Using a “Scatchard plot”, the apparent binding constant (K) and number of ATP binding sites (n) on serum albumin were evaluated as K = 75.25 (mol/L)–1 and n = 10, respectively. At a pH < 5.0 and a pH > 9.0 or a temperature > 45 °C, the diffusion data of ATP–HSA were found to increase remarkably, suggesting that the dissociation of ATP from HSA was largely enhanced, probably because of pH- or heat-induced protein structural change, degradation, or aggregation. In addition, our data indicated that ADP was strongly competitive with ATP for the low-affinity binding to HSA, but heptanone and Cl– were essentially noncompetitive. These results are important for further elucidating the interaction of ATP with serum albumin and its possible effect on related bioprocesses. The method can be well applied to study the binding of other nucleotides/nucleosides on proteins.

Studies on the interaction between chromium(VI) and human serum albumin: spectroscopic approach

The interaction between Cr(2)O(7)(2-) and human serum albumin (HSA) was investigated using fluorescence, UV/vis, FT-IR, CD spectroscopy, and molecular modeling method. The experimental results showed that the fluorescence quenching of HSA by Cr(2)O(7)(2-) is a result of the formation of HSA-chromium(VI) complex; static quenching was confirmed to result in the fluorescence quenching. The corresponding thermodynamic parameters showed that the process of binding Cr(2)O(7)(2-) on HSA was a spontaneous molecular interaction procedure. Ionic, H-bonds and van der Waals interactions play a major role in stabilizing the complex. The Cr(2)O(7)(2-) altered the environments of Trp and Tyr residues in HSA.

Synthesis and physicochemical characterization of Gd-C4-thyroxin-DTPA, a potential MRI contrast agent. Evaluation of its affinity for human serum albumin by proton relaxometry, NMR diffusometry, and electrospray mass spectrometry

Gd-C(4)-thyroxin-DTPA, a potential MRI contrast agent, was synthesized from Gd-DTPA and thyroxine, which interacts strongly with human serum albumin (HSA). It was characterized in water by its relaxometric properties and its stability versus zinc transmetalation. The affinity of the complex for HSA was studied by using three different methods: proton relaxometry, NMR diffusometry, and electrospray mass spectrometry. From the results, it appears that Gd-C(4)-thyroxin-DTPA exhibits a relatively high relaxivity (r(1) = 9.01 s(-1) mM(-1) at 1.5 T and 310 K), a good stability versus zinc transmetalation, and a strong interaction with HSA (K(a) approximately 10,000 M(-1) with two binding sites). The kinetics of the exchange between the bound and the free form of the complex was evaluated by the NMR diffusometry technique. Competition experiments have allowed the assignment of the chelate's binding site on HSA.