Fang-Fang Tian

Spectroscopic, structural and thermodynamic properties of chlorpyrifos bound to serum albumin: A comparative study between BSA and HSA

Chlorpyrifos (CPF) is a widely used organophosphate insecticide which could bind with human serum albumin (HSA) and bovine serum albumin (BSA). The binding behavior was studied employing fluorescence, three-dimensional fluorescence, Circular dichroism (CD) spectroscopy, UV-vis absorption spectroscopy, electrochemistry and molecular modeling methods. The fluorescence spectra revealed that CPF causes the quenching of the fluorescence emission of serum albumin. Stern-Volmer plots were made and quenching constants were thus obtained. The results suggested the formation of the complexes of CPF with serum albumins, which were in good agreement with the results from electrochemical experiments. Association constants at 25°C were 3.039 × 10(5) mol L(-1) for HSA, and 0.3307 × 10(5) mol L(-1) for BSA, which could affect the distribution, metabolism, and excretion of pesticide. The alterations of protein secondary structure in the presence of CPF were confirmed by the evidences from UV and CD spectra. Site competitive experiments also suggested that the primary binding site for CPF on serum albumin is close to tryptophan residues 214 of HSA and 212 of BSA, which was further confirmed by molecular modeling.

Mitochondria as target of Quantum dots toxicity

Quantum dots (QDs) hold great promise in many biological applications, with the persistence of safety concerns about the environment and human health. The present work investigated the potential toxicity of CdTe QDs on the function of mitochondria isolated from rat livers by examining mitochondrial respiration, swelling, and lipid peroxidation. We observed that QDs can significantly affect the mitochondrial membrane properties, bioenergetics and induce mitochondrial permeability transition (MPT). These results will help us learn more about QDs toxicity at subcellular (mitochondrial) level.

Spectroscopic studies on the interactions between CdTe quantum dots coated with different ligands and human serum albumin

This paper investigates the interactions between human serum albumin (HSA) and CdTe quantum dots (QDs) with nearly identical hydrodynamic size, but capped with four different ligands (MPA, NAC, and GSH are negatively charged; CA is positively charged) under physiological conditions. The investigation was carried out using fluorescence spectroscopy, circular dichroism (CD) spectra, UV-vis spectroscopy, and dynamic light scattering (DLS). The results of fluorescence quenching and UV-vis absorption spectra experiments indicated the formation of the complex of HSA and negatively charged QDs (MPA-CdTe, NAC-CdTe, and GSH-CdTe), which was also reconfirmed by the increasing of the hydrodynamic radius of QDs. The K(a) values of the three negatively charged QDs are of the same order of magnitude, indicating that the interactions are related to the nanoparticle itself rather than the ligands. ΔH<0 and ΔS>0 implied that the electrostatic interactions play predominant roles in the adsorption process. Furthermore, it was also proven that QDs can induce the conformational changes of HSA from the CD spectra and the three-dimensional fluorescence spectra of HSA. However, our results demonstrate that the interaction mechanism between the positively charged QDs (CA-CdTe) and HSA is significantly different from negatively charged QDs. For CA-CdTe QDs, both the static and dynamic quenching occur within the investigated range of concentrations. According to the DLS results, some large-size agglomeration also emerged.

Toxicity of nano zinc oxide to mitochondria

Zinc oxide nanoparticles (ZnO NPs) are increasingly applied in a diverse array of industrial and commercial products. Therefore, it is urgently required to characterize their toxic behavior. ZnO NPs have been reported to induce toxic effects at the levels of the individual organism, tissue, cell and DNA. However, little is known about the potential impacts of ZnO NPs at a subcellular level. In the present work, we investigated the toxicity of ZnO NPs to the isolated rat liver mitochondria. We found that treatment of mitochondria with ZnO NPs resulted in collapse of mitochondrial membrane potential (Δψ), swelling, depression of respiration, inner membrane permeabilization to H+ and K+, alterations of ultrastructure, release of cytochrome c, generation of reactive oxygen species (ROS), and Zn2+ liberation from ZnO NPs. These results suggested that ZnO NPs can increase the inner membrane permeability and impair the respiratory chain, thus leading to energy dissipation, oxidative stress and even apoptosis. This putative mechanism helps us learn more about the toxicology of this nanomaterial.

The adsorption of an anticancer hydrazone by protein: an unusual static quenching mechanism

A novel hydrazone, 4-chloro-N′-(pyridin-2-ylmethylene)benzohydrazide (CPBH) has been synthesized through a one-pot synthesis method and used as a chemical probe to find the structural cause of the unusual static quenching mechanism in the interaction with serum albumin. The adsorption of CPBH by bovine/human serum albumin (BSA/HSA) has been investigated systematically by comprehensive spectroscopy, modeling, electrochemistry and microcalorimetry under physiological conditions. CPBH forms a complex with BSA/HSA with the binding site in Sudlows site I of BSA/HSA. The adverse temperature dependence in the unusual static quenching is found to be a reasonable consequence of the large activation energy requirement in the binding process, which is required to overcome the structural block and it is a direct result of the unique microstructure of the binding pocket.

Spectroscopic and microscopic studies on the mechanisms of mitochondrial toxicity induced by different concentrations of cadmium.

The deleterious action of Cd2+ on rat liver mitochondria was investigated in this work using spectroscopic and microscopic methods. The concentration dependence of Cd2+ on mitochondrial swelling, membrane potential and membrane fluidity was studied. Our aim was to detect the active sites of Cd2+ in the mitochondrial membrane treatments with cyclosporin A (CsA) and EGTA on the mitochondrial permeability transition (MPT) induced by low and high concentrations of Cd2+. The protective effects of dithiothreitol, human serum albumin and monobromobimane+ on Cd2+-induced MPT were also monitored. All of these investigations indicated that Cd2+ can directly affect MPT at two separate localization sites at different concentrations: the classic Ca2+ triggering site and the thiol (–SH) groups of membrane proteins matched by MPT pore opening (defined as “S” site). At the high concentration of Cd2+, other free –SH groups in the mitochondrial matrix may be involved in this process. These findings were supported by transmission electron microscopy and shed light on the toxic mechanism of Cd2+ on mitochondria.

Toxicity of CdTe Quantum Dots on Yeast Saccharomyces Cerevisiae

Along with the widespread development of their bioapplications, concerns about the biosafety of quantum dots (QDs) have increasingly attracted intensive attention. This study examines the toxic effect and subcellular location of cadmium telluride (CdTe) QDs with different sizes against yeast Saccharomyces cerevisiae. The innovative approach is based on the combination of microcalorimetric, spectroscopic, electrochemical, and microscopic methods, which allows analysis of the toxic effect of CdTe QDs on S. cerevisiae and its mechanism. According to the values of the half inhibitory concentration (IC(50)), CdTe QDs exhibit marked cytotoxicity in yeast cells at concentrations as low as 80.81 nmol L(-1) for green-emitting CdTe QDs and 17.07 nmol L(-1) for orange-emitting CdTe QDs. QD-induced cell death is characterized by cell wall breakage and cytoplasm blebbing. These findings suggest that QDs with sizes ranging from 4.1 to 5.8 nm can be internalized into yeast cells, which then leads to QD-induced cytotoxicity. These studies provide valuable information for the design and development of aqueous QDs for biological applications.

Mitochondrial Permeability Transition Induced by Different Concentrations of Zinc

Zinc is one of the required trace elements in animals, and it serves an important role in biological systems. However, high levels of zinc are poisonous to organisms. So far, there exist conflicting reports about zinc ions-induced mitochondrial permeability transition (MPT). We analyzed the effects of Zn2+ on MPT by monitoring mitochondrial swelling with the ultraviolet–visible light absorption spectrum, characterizing the fluidity of the membrane with fluorescence anisotropy, detecting the transmembrane potential (Δψ) with fluorescence intensity, and observing mitochondrial ultrastructure with transmission electron microscopy. Data reveal that low concentrations of zinc ions can trigger MPT while high levels of zinc ions cannot, which implies that zinc ions’ toxicity cannot be the result of a single simple mechanism.

Direct observation of the binding process between protein and quantum dots by in situ surface plasmon resonance measurements

A layer-by-layer surface decoration technique has been developed to anchor quantum dots (QDs) onto a gold substrate and an in situ surface plasmon resonance technique has been used to study interactions between the QDs and different proteins. Direct observation of the binding of the protein onto the QDs and the kinetics of the adsorption and dissociation of different proteins on the QDs has been achieved. This would be helpful for the identification of particle-associated proteins and may offer a fundamental prerequisite for nanobiology, nanomedicine and nanotoxicology. The combination of the novel layer-by-layer surface modification method and in situ surface plasmon resonance would be powerful in studying biological systems such as DNA and cells.

Investigating the interactions of a novel anticancer delocalized lipophilic cation and its precursor compound with human serum albumin

F16 is a novel identified delocalized lipophilic cation (DLC) which has been found to inhibiting a variety of tumor cell proliferation due to its selective accumulation in the mitochondria of carcinoma cells. To gain further insight into the thermodynamic properties of this small molecule, we chose human serum albumin (HSA) as the model protein, and investigated the interactions of F16 and its precursor compound PVI with HSA by comprehensive spectroscopy, electrochemistry and molecule modeling methods. The static fluorescence quenching of HSA suggests that both F16 and PVI can form complexes with HSA, though the binding mechanisms are different. The main driving forces for F16–HSA binding are typical hydrophobic interactions, while PVI–HSA binding takes place through electrostatic interactions. F16–HSA binding shows an adverse temperature dependence recognized as the effect of the high activation energy requirement in the binding process generated by the specific structural obstacle. Both F16 and PVI can bind with HSA and thus benefit their transportation and elimination in body, however, the positive charge of F16 may have negative effect on the binding interaction.