Study on the interaction of phthalate esters to human serum albumin by steady-state and time-resolved fluorescence and circular dichroism spectroscopy

Decontamination promotes the release of incorporated organic contaminants in hair: Novel insights into non-invasive biomonitoring

Human hair is increasingly employed as a non-invasive biomonitoring matrix for exposure to organic contaminants (OCs). Decontamination procedures are generally needed to remove external contamination from hair prior to analysis of OCs. Despite various existing decontamination protocols, their impacts on internally incorporated (endogenous) OCs in hair remain poorly understood. This study aims to quantitatively assess the impact of decontamination procedures on endogenous OCs in hair, and investigate optimal decontamination processes and factors influencing the removal of endogenous OCs. In this study, guinea pig was exposed to 6 OCs (triphenyl phosphate (TPHP), tris(1,3-dichloro-2-propyl) phosphate (TDCPP), and tri-n-butyl phosphate (TNBP), bisphenol A (BPA), perfluorooctanoic acid (PFOA), and phenanthrene (PHE)), and 6 decontamination procedures with different solvents (methanol, n-hexane, acetone, ultrapure water, Triton X-100, and sodium dodecyl sulfate) were used to rinse exposed guinea pig hair. All OCs and three metabolites (diphenyl phosphate (DPHP), dibutyl phosphate (DBP), and bis(1,3-dichloro-2-propyl) phosphate (BDCPP)) were detected in the majority of washing solutions. The decontamination procedures apparently resulted in the release of endogenous OCs from hair. The percentages of residual OCs in hair exhibited a linear or exponential decrease with more washing cycles. Furthermore, the residuals of OCs in hair washed with organic and aqueous solvents showed negative correlations with molecular weight, polarizability, and their initial concentrations. Although these findings need to be validated with a broader range of OCs, the results obtained in this study provide compelling evidence that current hair decontamination procedures have significant impacts on the analysis of endogenous OCs in hair. Therefore, it is important to interpret quantitative data on hair OC concentrations with caution and to thoroughly consider each decontamination procedure during analysis.

Activated DBP degradation and relevant signal transduction path via quorum sensing autoinducers in Streptomyces sp. SH5

Microbe-mediated DBP (dibutyl phthalate) mineralization is acknowledged to be affected by diverse extracellular factors. However, little is known about the regulatory effects from quorum sensing (QS) signals. In this study, extracellularly applied QS signals A-like (hydroxymethyl dihydrofuran) was discovered to significantly enhance DBP degradation efficiency in Streptomyces sp. SH5. Monobutyl phthalate, protocatechuic acid and beta-ketoadipate were discovered as degradation intermediates by HPLC-TOF-MS/MS. Multi-omics analysis revealed the up-regulation of multiple hydrolases, transferases and decarboxylases that potentially contributed to A-like accelerated DBP degradation. Transcription of Orf2708, an orthologue of global transcriptional activator, was significantly induced by A-like. Orf2708 was demonstrated to interact specifically with the promoter of hydrolase orf2879 gene by EMSA, and the overexpression of orf2879 led to an enhanced DBP degradation in SH5. Taken together with the molecular docking studies showing the stability of ligand-receptor complex of A-like and its potential receptor Orf3712, a hierarchical regulatory cascade underlying the QS signal mediated DBP degradation was proposed as A-like/Orf3712 duplex formation, enhanced orf2708 expression and the downstream specific activation of hydrolase Orf2879. Our study presents the first evidence of GBLs-type promoted DBP degradation among bacteria, and the elucidated signal transduction path indicates a universal application potential of this activation strategy.

Investigating the effect of pH on the interaction of cypermethrin with human serum albumin: Insights from spectroscopic and molecular dynamics simulation studies

To efficiently combat the negative consequences of the utilization of pesticides and hazardous substances with biomolecules, it is crucial to comprehend the features of the corresponding compounds. In this study, interactions between cypermethrin (CYP) and HSA at neutral and acidic pH were investigated using a set of spectroscopic and computational tools, such as UV/VIS's absorption spectroscopy, fluorescence, Fourier-transform infrared (FTIR) spectroscopy, molecular docking, and molecular dynamics. Furthermore, the effect of CYP on the HSA thermal stability was investigated. The increase in the CYP concentration at acidic and neutral pH resulted in static HSA fluorescence quenching. In the interaction between HSA and CYP at both pH, increasing the temperature led to a decrease in the Stern-Volmer quenching constant and the binding constant. We also revealed that with increasing CYP concentration, the melting temperature of HSA increases at both pH values.

A physiologically based pharmacokinetic model of diethyl phthalates in humans

Phthalates are a family of industrial and consumer product chemicals, among which diethyl phthalate (DEP) has been widely used. DEP is metabolized into the active metabolite monoethyl phthalate (MEP) and exposure to DEP may induce male reproductive toxicity, developmental toxicity and hepatotoxicity. To better assess the toxicity of DEP and MEP, it is important to understand and predict their internal concentrations, especially in reproductive organs. Here we present a human physiologically based pharmacokinetic (PBPK) model of DEP. Implemented in R, the PBPK model consists of seven tissue compartments, including blood, gut, liver, fat, skin, gonad, and rest of body (RB). In the blood both DEP and MEP partition into free and bound forms, and tissue distribution is considered as blood flow-limited. DEP is metabolized in the gut and liver into MEP which is further glucuronidated and cleared through the urine. The chemical-specific parameters of the model were predicted in silico or estimated based on published human urinary MEP data after exposure to DEP in the air at 250 or 300 μg/m3 for 3 or 6 h through inhalation and dermal absorption. Sensitivity analysis identified important parameters including partition coefficients of DEP for fat, RB, and skin compartments, and the rate constants for glucuronidation of MEP and urinary excretion, with regard to Cmax, area under the curve (AUC), and clearance half-lives of DEP and MEP. A subset of the sensitive parameters was then included in hierarchical population Bayesian Markov chain Monte Carlo (MCMC) simulations to characterize the uncertainty and variability of these parameters. The model is consistent with the notion that dermal absorption represents a significant route of exposure to DEP in ambient air and clothing can be an effective barrier. The developed human PBPK model can be utilized upon further refinement as a quantitative tool for DEP risk assessment.

Butyl benzyl phthalate as a key component of phthalate ester in relation to cognitive impairment in NHANES elderly individuals and experimental mice

Phthalates are a group of neurotoxicants with cognitive-disrupting potentials. Given the structural diversity of phthalates, the corresponding neurotoxicity is dramatically altered. To identify the potential contributions of different phthalates on the process of cognitive impairment, data of 836 elders from the NHANES 2011-2014 cycles were used. Survey-weighted logistic regression and principal component analysis-weighted quantile sum regression (PCA-WQSR) models were applied to estimate the independent and combined associations of 11 urinary phthalate metabolites with cognitive deficit (assessed by 4 tests: Immediate Recall (IR), Delayed Recall (DR), Animal Fluency (AF), and Digit Symbol Substitution Test (DSST)) and to identify the potential phthalate with high weight. Laboratory mice were further used to examine the effect of phthalates on cognitive function and to explore the potential mechanisms. In logistic regression models, MBzP was the only metabolite positively correlated with four tests, with ORs of 2.53 (quartile 3 (Q3)), 2.26 (Q3), 2.89 (Q4) and 2.45 (Q2), 2.82 (Q4) for IR, DR, AF, and DSST respectively. In PCA-WQSR co-exposure models, low-molecular-weight (LMW) phthalates were the only PC positively linked to DSST deficit (OR: 1.93), which was further validated in WQSR analysis (WQS OR7-phthalates: 1.56 and WQS OR8-phthalates: 1.55); consistent with the results of logistic regression, MBzP was the dominant phthalate. In mice, butyl benzyl phthalate (BBP), the parent phthalate of MBzP, dose-dependently reduced cognitive function and disrupted hippocampal neurons. Additionally, the hippocampal transcriptome analysis identified 431 differential expression genes, among which most were involved in inhibiting the neuroactive ligand-receptor interaction pathway and activating the cytokine-cytokine receptor interaction pathway. Our study indicates the critical role of BBP in the association of phthalates and cognitive deficits among elderly individuals, which might be speculated that BBP could disrupt hippocampal neurons, activate neuroinflammation, and inhibit neuroactive receptors. Our findings provide new insight into the cognitive-disrupting potential of BBP.

Impact of formaldehyde, acetaldehyde, and N-(3-(Dimethylamino)propyl)methacrylamide on the efficacy of the human derived coagulation factor IX

Polymer-borne leachables such as formaldehyde, acetaldehyde, and N-3-(Dimethylamino)propyl)methacrylamide (DMAPMA) may interact with therapeutic proteins. In this study, the leachables were spiked into human derived coagulation factor IX (FIX) at concentrations of 1, 10, 50, 100, and 500 µg/mL, corresponding to a leachable - FIX ratio of 0.5, 5, 25, 50 and 250 %, respectively. The spiked samples were visually inspected, and pH was measured. No visual effects were observed, and pH was within the drug product's specified range. Recovery experiments were performed and no loss of leachables was identified. Protein structure analysis revealed that formaldehyde reacted with lysine contained in two different positions of FIX, in a concentration-dependent manner starting at 10 µg/mL (5 %). The clotting activity of FIX was measured. The activity of the samples spiked with 500 µg/mL (250 %) of formaldehyde dropped by more than half. The activity of the samples spiked with acetaldehyde began to drop at 50 µg/mL (25 %) and continued to decline in concentration-dependent manner. DMAPMA did not impair the activity of FIX. The findings conclude that depending on the concentration, some leachables may react with or modify therapeutic proteins, potentially causing an undesired pharmacological effect however, this is specific to each protein.

Using fluorescence and circular dichroism (CD) spectroscopy to investigate the interaction between di-n-butyl phthalate and bovine serum albumin

The interaction between di-n-butyl phthalate (DBP) and bovine serum albumin (BSA) in physiological Tris-HCl buffer at pH 7.4 was investigated by fluorescence quenching technique. By analyzing the fluorescence spectrum and intensity, it was observed that the DBP had a strong ability to quench the intrinsic fluorescence of BSA through a static quenching procedure. The binding constants K and the number of binding sites n of DBP with BSA were calculated to be 0.11 × 10² L·mol^-1 and 0.52 at 298 K, respectively. The thermodynamic parameters of enthalpy change (ΔH) and entropy change (ΔS) were also calculated to be positive showing that hydrophobic forces might play a major role in the binding of DBP to BSA. The binding process was spontaneous in which Gibbs free energy change (ΔG) was negative. The distance (r) between the donor (BSA) and acceptor (DBP) was calculated to be 2.02 nm based on Forster's non-radiative energy transfer theory, which indicated that the energy transfer from BSA to DBP occurs with a high possibility. The synchronous fluorescence, three-dimensional fluorescence, and circular dichroism (CD) spectra showed that the binding of di-n-butyl phthalate to BSA induced conformational changes in BSA. The interaction between DBP and BSA can help researchers better understand the nature of poisons and serve people in the right way with first aid and detoxification.

Interactions between hydroxylated polycyclic aromatic hydrocarbons and serum albumins: Multispectral and molecular docking analyses

Hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) can bind to serum albumin and influence their distribution and elimination in organisms. Herein, multispectral analysis and molecular docking methods were used to investigate the binding mechanism of two OH-PAHs, 1-hydroxyphenanthrene (1-OHPhe) and 9-hydroxyphenanthrene (9-OHPhe), with two homologous serum albumins, human serum albumin (HSA) and bovine serum albumin (BSA). The quenching constants of HSA with 1-OHPhe and 9-OHPhe were much larger than those for BSA. Energy transfer from the tryptophan (Trp) residues in HSA to 1-OHPhe and 9-OHPhe was more probable than from Trp in BSA. The interactions of 1-OHPhe and 9-OHPhe with Trp in HSA and BSA altered the microenvironment of Trp. Molecular docking results revealed that the binding modes and binding forces of 1-OHPhe and 9-OHPhe with HSA and BSA were different. The two OH-PAHs were used as fluorescent probes to analyze the microenvironmental hydrophobicities of HSA and BSA, which were distinctly different. The structural difference between HSA and BSA induced significant variations in their binding behavior with 1-OHPhe and 9-OHPhe. Moreover, HSA was more susceptible to 1-OHPhe and 9-OHPhe than BSA. This work suggests that the differences between the two serum albumins should be considered in related studies.

Phthalate metabolites in paired human serum and whole blood

Presence of phthalate metabolites (PMs) in human serum has been well documented. However, the distribution pattern of PMs in different human blood matrixes remains not well known. To investigate this, paired serum and whole blood samples were collected from 145 adults (76 males and 69 females) in Quzhou, China, and analyzed for nine PMs in this study. All PMs had high detection frequencies (> 70%) in human serum and whole blood, except mono benzyl phthalate. Total concentrations of detected PMs in serum and whole blood were 0.70-61 ng/mL (mean 12 ng/mL) and 1.6-33 ng/mL (7.5 ng/mL), respectively. Mono methyl phthalate (MMP), mono (2-ethylhexyl) phthalate, and mono butyl phthalate were consistently the predominant PMs in human serum and whole blood, with the mean concentrations of 3.4 and 2.0 ng/mL, 3.3 and 2.1 ng/mL, and 2.8 and 1.8 ng/mL, respectively. Females had higher mean serum concentrations of PMs, except MBP, than males. Youngest age group (20-30 years) consistently had the lowest mean whole blood levels of all PMs. For the first time, the distribution pattern of PMs in human blood was evaluated based on the calculated partitioning coefficient (K_p) between serum and whole blood. MMP had the highest mean K_p value (1.6; 10th-90th percentile: 1.0-2.2), while mono (2-ethyl-5-oxohexyl) phthalate had the lowest mean K_p value (0.63; 10th-90th percentile: 0.25-1.3). These results help better understand the occurrence of PMs in human blood.

The mechanism of interaction between lotus rhizome polyphenol oxidase and ascorbic acid: Inhibitory activity, thermodynamics, and conformation analysis

In this study, the interaction between lotus rhizome polyphenol oxidase (PPO) and ascorbic acid (AA) was discussed from the aspects of inhibitory activity, thermodynamics, and conformation. Results showed that PPO was purified from lotus rhizome by DEAE-52 anion exchange chromatography and Sephadex G-100 gel filtration chromatography, with its optimum substrate being determined as pyrogallic acid. Spectrophotometric and polarographic assays demonstrated that AA exhibited strong inhibitory activity against PPO. Thermodynamics, fluorescence, and circular dichroism spectral analysis showed that hydrophobic interactions caused the formation of AA-PPO complex, leading to the remarkable fluorescence quenching and conformational change of PPO. Atomic force microscopic analysis revealed that binding to AA induced significant changes in the surface morphology and molecular aggregation of PPO molecules. In this study, the interaction mechanism between PPO and AA was proposed for the first time, which provided a theoretical basis for AA to inhibit lotus rhizome browning. PRACTICAL APPLICATIONS: Lotus rhizome, an aquatic vegetable, is prone to enzymatic browning in processing operations, which leads to a decrease in market value and economic loss. At present, ascorbic acid (AA) is widely used in industries as an excellent antioxidant because of its good antibrowning effect and relatively low cost. However, the interaction between the enzymatic browning-related polyphenol oxidase (PPO) from lotus rhizome and ascorbic acid has not been clearly studied. Understanding the mechanism of inhibiting PPO will help to prevent vegetable browning, especially fresh-cut products. The inhibitory effect of AA on PPO in lotus rhizome favors simultaneous use with other types of PPO inhibitors because of their likely synergistic effects.

Probing the Role of Cu(II) Ions on Protein Aggregation Using Two Model Proteins

Copper is an essential trace element for human biology where its metal dyshomeostasis accounts for an increased level of serum copper, which accelerates protein aggregation. Protein aggregation is a notable feature for many neurodegenerative disorders. Herein, we report an experimental study using two model proteins, bovine serum albumin (BSA) and human serum albumin (HSA), to elucidate the mechanistic pathway by which serum albumins get converted from a fully folded globular protein to a fibril and an amorphous aggregate upon interaction with copper. Steady-state fluorescence, time-resolved fluorescence studies, and Raman spectroscopy were used to monitor the unfolding of serum albumin with increasing copper concentrations. Steady-state fluorescence studies have revealed that the fluorescence quenching of BSA/HSA by Cu(II) has occurred through a static quenching mechanism, and we have evaluated both the quenching constants individually. The binding constants of BSA-Cu(II) and HSA-Cu(II) were found to be 2.42 × 104 and 0.05 × 104 M-1, respectively. Further nanoscale morphological changes of BSA mediated by oligomers to fibril and HSA to amorphous aggregate formation were studied using atomic force microscopy. This aggregation process correlates with the Stern-Volmer plots in the absence of discernible lag phase. Raman spectroscopy results obtained are in good agreement with the increase in antiparallel β-sheet structures formed during the aggregation of BSA in the presence of Cu(II) ions. However, an increase in α-helical fractions is observed for the amorphous aggregate formed from HSA.

Comprehensive insights into the interactions of dicyclohexyl phthalate and its metabolite to human serum albumin

Phthalate esters (PAEs) are a type of persistent organic pollutants and have received widespread concerns due to their adverse effects on human health. Dicyclohexyl phthalate (DCHP) and its metabolite monocyclohexyl phthalate (MCHP) were selected to explore the mechanism for interaction of PAEs with human serum albumin (HSA) through molecular docking and several spectroscopic techniques. The results showed that DCHP/MCHP can spontaneously occupy site I to form a binary complex with HSA, and DCHP exhibited higher binding affinity to HSA than MCHP. At 298 K, the binding constants (K_b) of DCHP and MCHP to HSA were 24.82 × 10⁴ and 1.04 × 10⁴ M^-1, respectively. Hydrogen bonds and van der Waals forces were the major driving forces in DCHP/MCHP-HSA complex. The presence of DCHP/MCHP induced the secondary structure changes in HSA, and the pi electrons of the benzene ring skeleton of DCHP/MCHP played a key role in this binding processes. Exposure of DCHP/MCHP to TM4 cells revealed that interactions between PAEs and serum albumin can affect their cytotoxicity; DCHP showed higher toxicity than MCHP. The binding affinity of PAEs with HSA may be a valuable parameter for rapid assessment of their toxicity to organisms.

Mono-n-Butyl Phthalate Distributes to the Mouse Ovary and Liver and Alters the Expression of Phthalate-Metabolizing Enzymes in Both Tissues

Humans are exposed to phthalates daily via items such as personal care products and medications. Reproductive toxicity has been documented in mice exposed to di-n-butyl phthalate (DBP); however, quantitative evidence of its metabolite, mono-n-butyl phthalate (MBP), reaching the mouse ovary and its effects on hepatic and ovarian biotransformation enzymes in treated mice is still lacking. Liquid chromatography/tandem mass spectrometry (LC-MS/MS) was employed to quantify MBP levels in liver, serum, and ovary from mice treated with a single or repeated exposure to the parent compound, DBP. Adult CD-1 females were pipet fed once or for 10 days with vehicle (tocopherol-stripped corn oil) or DBP at 1, 10, and 1000 mg/kg/day. Tissues and serum were collected at 2, 6, 12, and 24 h after the single or final dose and subjected to LC-MS/MS. Ovaries and livers were processed for qPCR analysis of selected phthalate-associated biotransformation enzymes. Regardless of duration of exposure (single vs repeated), MBP was detected in the tissues of DBP-treated mice. In single dose mice, MBP levels peaked at ≤6 h and fell close to background levels by 24 h post-exposure. Following the last repeated dose, MBP levels peaked at ≤2 h and fell to background levels by 12 h. Hepatic and ovarian expression of Lpl, Aldh1a1, Adh1, Ugt1a6a, and Cyp1b1 were altered in DBP-treated mice in a time- and dose-specific manner. These findings confirm that MBP reaches the mouse liver and ovary after oral exposure to DBP and influences the expression of hepatic and ovarian phthalate-associated biotransformation enzymes.

Spectroscopic studies of simultaneous binding of cyclophosphamide and imatinib mesylate to human holo-transferrin

The interactions of proteins with drugs are very important from a pharmacological point of view. Holo-transferrin is a blood-plasma glycoprotein whose main function is iron-binding and the transport of other ligands. Additionally, the protein is only transferrin-form recognized by TfR1 and TfR2 receptors at the surface of rapidly proliferating malignant cells. Imatinib mesylate is a tyrosine-kinase inhibitor mainly used in the treatment of blood cancers, frequently in multidrug therapy with cyclophosphamide. In this study the effect of cyclophosphamide on the interaction of imatinib mesylate with human holo-transferrin has been investigated. Using spectroscopic techniques such as fluorescence, circular dichroism, ultraviolet-visible and electrophoretic light scattering additive parameters, system stability and the effect of the ligands on the protein conformation at varying pH values have been defined. Calculated quenching constants are in the order of 2 × 10⁴ M^-1 and the type of interaction depends on the reaction medium. Under physiological conditions binding constant is 1.329 × 10⁶ M^-1 whereas in an environment similar to that of cancer cells the constant is significantly lower, K_a = 6.060 × 10⁴ M^-1. N values are approximate to 1 in all cases. Moreover, some changes are observed in the α-helical structure of the protein after interaction with the drugs and the presence of cyclophosphamide slightly stabilizes the protein secondary structure. All collected data proves the effect of cyclophosphamide on the interaction between imatinib mesylate and human holo-transferrin. It is of great clinical interest due to anticancer, multidrug therapies including both imatinib mesylate and cyclophosphamide.

Mechanistic insight into esterase-catalyzed hydrolysis of phthalate esters (PAEs) based on integrated multi-spectroscopic analyses and docking simulation

A novel PAE-hydrolyzing esterase (named Hyd) gene was screened from the genomic library of Rhodococcus sp. 2G and was successfully expressed in heterologous E. coli, which was defined as a new family of esterolytic enzymes. The purified Hyd could efficiently degrade various PAEs, displaying high activity and stability with a broad range of pH (4-10) and temperature (20-60 °C). Interaction mechanism of Hyd with dibutyl phthalate (DBP) was investigated by integrated multi-spectroscopic and docking simulation methods. Fluorescence and UV-vis spectra revealed that DBP could quench the fluorescence of Hyd through a static quenching mechanism. The results from synchronous fluorescence and CD spectra confirmed that the DBP binding to Hyd triggered conformational and micro-environmental changes of Hyd, which were characterized by increased stretching extent and random coil, and decreased α-helix and β-sheet. Molecular docking study showed that DBP could be bound to the cavity of Hyd with hydrogen bonding and hydrophobic interaction. A novel and distinctive catalytic mechanism was proposed: two key residues Thr¹⁹⁰ and Ser¹⁹¹ might catalyze the hydrolysis of DBP, instead of the conserved catalytic triad (Ser-His-Asp) reported elsewhere, which was confirmed by site-directed mutagenesis.

Typical organic pollutant-protein interactions studies through spectroscopy, molecular docking and crystallography: A review

With the development of industry and human society, more attention was paid for the toxic effects of organic pollutants that are closely related to human daily life. Previous studies mainly focused on the dose-response relationship and cytotoxic effects of pollutants to organisms，while little research focused on pollutant-protein interactions at molecular level. However, the binding of organic pollutants to biomolecules, especially proteins like transporters, membrane receptor and nuclear receptors, is often the first step of toxic effects. It can make a series of endocrine disrupting and genotoxic effects through cell signaling pathway by binding specific target proteins including serum albumin, thyroid transporter, estrogen receptor, androgen receptor, and aryl hydrocarbon receptor. Thus, the research of interactions between organic pollutants and proteins is helpful and necessary to understand the distribution, metabolism and toxicity mechanism of compounds in organisms at the molecular level. This paper reviewed the latest research progress of the interaction types of persistent organic pollutants (POPs), emerging pollutants and some other pollutants with targeted proteins. In addition, we summarized several main experimental techniques for studying pollutant-protein interactions including ultraviolet/visible absorption spectrometry (UV-vis), fluorescence, infrared spectrometry, circular dichroic spectra (CD), molecular docking and X-ray crystallography. This review contributes to the molecular mechanism of the interaction between organic pollutants and biomolecules.

Potential involvement of environmental triggers in protein aggregation with mercuric chloride as a model

Heavy metal based toxicity has a direct relation with the perturbation of protein structure. We have investigated the progressive unfolding of ovalbumin, in the presence of increasing concentration mercury (0-6.25 μM) using different spectroscopic techniques. Formation of amorphous aggregate has been observed at the physiological pH. Initial addition of HgCl₂ resulted in the association of monomers to oligomers that proceeded to non-fibrillar aggregates on further addition. The sigmoidal curve obtained from the Stern-Volmer plot clearly divided into three stage transition. A strong lag phase is observed indicating the time dependence for the association of competent monomers. The second stage was resolved into non-cooperative binding. These results match very well with the data from atomic force microscopy and the free energy change observed in the regions. Raman spectroscopic studies indicated toxic antiparallel β-sheets structure. Time dependent atomic force microscopy study revealed the off-pathway nature of amorphous aggregates. At molten globular state, similar quenching behaviour is observed. The atomic force microscopy images clearly indicate at pH 2.2 the initiation of fibril formation occurs at lower concentration of HgCl₂ itself. Our results revealed the conformation switch of ovalbumin upon the contact of an environmental toxin and its possible way of toxicity.

Revealing the toxicity of dimethyl phthalate (DMP) to the oxygen-carrying function of red blood cells (RBCs): The iron release mechanism

Phthalic acid esters (PAEs), as typical hormone pollutants, do harms to human health after enrichment over a long term exposure, causing the loss of oxygen-carrying function of red blood cells (RBCs). This study has investigated the mechanism for the toxicity of dimethyl phthalate (DMP) on the oxygen-carrying function of RBCs by measuring the iron release content of hemoglobin (Hb) in vivo and in vitro. The hematologic examination showed that the high dose of DMP at 1000 mg/kg significantly reduced the Hb content and increased the granulocyte content, whereas such toxicity was not relatively observed at a low (50 mg/kg) or a medium (250 mg/kg) dose of DMP. The in vitro experiments showed that DMP, incubated with RBCs, increased the iron release content as a function of DMP concentration. Interestingly, such a phenomenon was not observed when DMP was incubated with Hb alone, indicating that the release of hemoglobin iron could not directly caused by the combination of DMP and hemoglobin. The in vivo experiments indicated that DMP induced iron release and oxidative stress for rat RBCs. Moreover, vitamin C and E was found to reduce the level of iron release by recovering erythrocytes from the oxidative stress induced by DMP. This work has revealed that the oxidative stress induced by DMP, causing the release of Hb iron from RBCs, is the reason for the toxicity of DMP to the oxygen-carrying function.

Insights into the binding interaction of substrate with catechol 2,3-dioxygenase from biophysics point of view

This study aims to clarify the interaction mechanism of substrate with catechol 2,3-dioxygenase (C23O) through multi-technique combination. A novel C23O (named C23O-2G) was cloned, heterogeneously expressed, and identified as a new member in subfamily I.2 of extradiol dioxygenases. Based on the simulations of molecular docking and dynamics, the exact binding sites of catechol on C23O-2G were identified, and the catalytic mechanism mediated by key residues was proposed. The roles of the predicted residues during catalysis were confirmed by site-directed mutagenesis, and the mutation of Thr254 could significantly increase catalytic efficiency and substrate specificity of C23O-2G. The binding and thermodynamic parameters obtained from fluorescence spectra suggested that catechol could effectively quench the intrinsic fluorescence of C23O-2G via static and dynamic quenching mechanisms and spontaneously formed C23O-2G/catechol complex by the binding forces of hydrogen bond and van der Waals force. The results of UV-vis spectra, synchronous fluorescence, and CD spectra revealed obvious changes in the microenvironment and conformation of C23O-2G, especially for the secondary structure. The atomic force microscope images further demonstrated the changes from an appearance point of view. This study could improve our mechanistic understanding of representative dioxygenases involved in aromatic compound degradation.

Elucidation of binding mechanism of dibutyl phthalate on bovine serum albumin by spectroscopic analysis and molecular docking method

Dibutyl phthalate has been illegally used in beverages and directly affects the human health. Herein, the interaction occurred between dibutyl phthalate and bovine serum albumin was studied. The experimental results demonstrated that dibutyl phthalate could bind to bovine serum albumin and statically quench the intrinsic fluorescence of this protein. Circular dichroism measurements proved that the binding of dibutyl phthalate would lead to an obvious decrease of α-helix content in the bovine serum albumin. Molecular docking analysis clarified the fluorescence quenching mechanism, size distribution and zeta potential variation, conformational change of BSA, the site marker competitive fluorescence quenching and the interaction mechanism of dibutyl phthalate to bovine serum albumin. This work provided a useful information for the binding of dibutyl phthalate to protein.

Interactions of the cis and trans states of an azobenzene photoswitch with lysozyme induced by red and blue light

Exploring the interaction between an azobenzene-based photoswitch and natural protein can help elucidate how the photo-control of an optical molecule participates in the transmission and delivery of proteins, as well as the effects of azo-switch trans and cis states on protein configurations. In this study, fluorescence analysis, circular dichroism spectroscopy, molecular docking, and molecular dynamics simulations were used to study the interaction among different configurations of tetra-ortho-methoxy substituted azobenzene di-maleimide (toM-ABDM), a red light-induced optical azo-switch, and lysozyme (LYZ). Results showed that toM-ABDM caused the static quenching of LYZ. The cis toM-ABDM had stronger binding affinity than trans toM-ABDM. The noncovalent interaction, hydrogen bonds and van der Waals forces, could not regulate the conformation of LYZ in photo-control. A binding model of toM-ABDM and LYZ in different forms induced by red and blue light was further established by computer simulation.

Glutathione peroxidase 6 from Arabidopsis thaliana as potential biomarker for plants exposure assessment to di-(2-ethylhexyl) phthalate

As a most abundant plasticizer, Di-(2-ethylhexyl) phthalate (DEHP) has been widely used in agriculture with an associated potential toxicity to many species including plants via the production of the excessive reactive oxygen species (ROS). However, the potential toxic mechanisms of the plasticizer DEHP-induced oxidative damage to plants remain unknown. The antioxidant enzyme glutathione peroxidase has been suggested as biomarkers to reflect over excessive oxidative stress. In this study, the effect of DEHP on AtGPX6 was evaluated by multi-spectroscopic techniques and molecular docking method. The fluorescence intensity of AtGPX6 was reduced by the static quenching mechanism upon the addition of DEHP. The predominant forces in complex formation was mainly impelled by hydrogen bonding and Van der Waals forces based on the negative ΔH and ΔS, which was in accordance with the molecular docking results. In addition, the secondary structural changes resulted from the complex formation were investigated in presence of different amounts of DEHP by the combination of fluorescence, UV-vis absorption and Circular dichroism spectra, which revealed the loosening and unfolding of the framework of AtGPX6 accompanied with the enhancement of the hydrophilicity around the tryptophan residues. The exploration of the interaction mechanism of DEHP with AtGPX6 at molecular level would help to evaluate the toxicity of the plasticizers and forecast the related adverse effects on plants.

Evaluation of single and combined effects of cadmium and micro-plastic particles on biochemical and immunological parameters of common carp (Cyprinus carpio)

The growing accumulation of microplastics (MPs) in aquatic environments is a global concern. MPs are capable to interact with other environmental contaminants, including heavy metals, altering their toxicity. The aim of the study was to investigate the sub-lethal effects of cadmium chloride (Cd) alone and in combination with MPs on common carp (Cyprinus carpio). Multi-biomarkers, including plasma biochemical parameters and intrinsic immunological factors, were measured after 30 days of exposure. Exposure to Cd or NPs reduced the plasma activities of acetylcholinesterase (AChE) and gamma-glutamyl-transferase (GGT) and increased aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) and alkaline phosphatase (ALP). Exposure to both compounds enhanced the observed effects except for AST activity and ALP at the highest concentrations, whereas evidenced an antagonistic interaction in ALT. Plasma total protein, albumin, and globulin levels were decreased, and the levels of glucose, triglyceride, and cholesterol levels increased mainly in the Cd groups with no additional effects derived from the co-exposure to both stressors. Lysozyme and alternative complement (ACH50) activities and the levels of total immunoglobulins, and complement C3 and C4 in fish exposed to Cd and MPs were lower than those in the control group and this decrease was more significant by the mixture of both compounds. These findings showed that the exposure to Cd or MPs alone is toxic to fish altering the biochemical and immunological parameters. Moreover, these alterations are even greater when the Cd and the MPS are combined suggesting synergistic effects in increasing Cd toxicity and vice versa.

Binding mechanism of maltol with catalase investigated by spectroscopy, molecular docking, and enzyme activity assay

Maltol is a flavor additive that is widely used in the daily diet of humans, and its biosafety attention is concomitantly increasing. Catalase (CAT) is an antioxidant enzyme to maintain homeostasis in the tissue's environment of human body and protect cells from oxidative damages. The adverse effects of maltol to CAT activity within mouse hepatocytes as well as the structural and functional changes of CAT on molecular level were investigated by multiple spectroscopy techniques, enzyme activity experiments, and molecular docking. Results suggested that when the maltol concentrations reached to 8 × 10^-5 mol L^-1 , the viability of hepatocytes decreased to 93%, and CAT activity was stimulated by maltol to 111% than the control group after exposure for 24 hours. Changes in CAT activity on molecular level were consistent with those on cellular level. The fluorescence quenching of CAT by maltol was static with the forming of maltol-CAT complex. Moreover, ultraviolet-visible (UV-visible) absorption, synchronous fluorescence, and circular dichroism (CD) spectra reflected that the presence of maltol caused conformational change of CAT and made the CAT molecule skeleton loose and increased α-helix of CAT. Maltol mainly bound with CAT through hydrogen bond, and binding site that is near the heme ring in the enzyme activity center did not interact with its main amino acid residues. This study explores the combination between maltol and CAT, providing references for evaluating health damages caused by maltol.

A theoretical method for the high-sensitivity fluorescence detection of PAEs through double-substitution modification

A highly sensitive method for the detection of phthalate acid ester (PAE) derivatives by fluorescence spectroscopy based on a double-substitution modification is reported. The fluorescence intensities of 18 PAE derivatives and the template PAEs after docking with the protein bovine serum albumin (BSA) are compared; the fluorescence intensities of the PAE derivatives increase significantly (28.20 to 110.00 times) with high sensitivities, but the functionalities (stability and insulation) are not affected. The persistence, mobility, and toxicity of the PAE derivatives are reduced by varying degrees, and their amounts of bioaccumulation are not significantly changed, indicating that the derivatives are more environmentally friendly. Within the wavelength range 240-420 nm in the fluorescence spectrum, there is no interference between the PAE derivatives and polycyclic aromatic hydrocarbons (PAHs), and the derivatives can be detected with good precision. Based on the analysis of fluorescence characteristics using a 2D quantitative structure-activity relationship (QSAR) model, the occupied orbital energies and Mulliken charge numbers are the main factors that influence the spectral characteristics of the PAE derivatives.

Identification differential behavior of Gd@C82(OH)22 upon interaction with serum albumin using spectroscopic analysis

The interaction between Gd@C₈₂(OH)₂₂ and serum albumin (HSA and BSA) were investigated by spectroscopic analysis. From the characteristic feature of fluorescence quenching spectra at different temperatures, the inherent binding information including quenching mechanism, association constants, number of binding site, fraction of initial fluorescence and basic thermodynamic parameters were calculated. The binding of Gd@C₈₂(OH)₂₂ to serum albumin caused strong quenching of protein intrinsic fluorescence and the structural changes of serum albumin. At lower concentrations, Gd@C₈₂(OH)₂₂ was likely to rise fluorescence quenching of serum albumin through individual static quenching process by forming a ground-state complex, while dynamic and static coexisting quenching mechanism occurred in high concentration. Bimolecular quenching (K_q) value is twice the diffusion-controlled quenching constant (2.0 × 10¹⁰ L mol^-1 s^-1); binding sites of BSA were slightly more than those of HAS, and all of them reached to 1; the distance r between donor and acceptor was found to be 3.1494 nm and 3.6479 nm for HSA and BSA, respectively, both of which were fewer than 7 nm. It is confirmed that binding interaction for proteins in the presence of drugs was strong, the binding ratio was 1:1, and non-radiative energy transfer from protein to drug was extremely high probability in lower density. Binding process of Gd@C₈₂(OH)₂₂-HSA was driven mainly through van der Waals forces and hydrogen bonding formation, however more likely to be electrostatic interaction involved in the Gd@C₈₂(OH)₂₂-BSA binding process; Binding sites of Gd@C₈₂(OH)₂₂ to serum albumin were near tryprophan (HSA) and tyrosine residues (BSA), respectively. Moreover, a theoretical model of predicting the binding rate of drug to serum albumin was estimated, further analyzed that the binding rate was dynamically altered in various dose of protein and drug. Overall, these results provide potentially significant information for elucidating the distribution, transportation, the apparent relationship between pharmacologic activity and total plasma drug concentration as well as anti-carcinogenic activity and mechanisms in vivo.

Study on the interaction of chromate with bovine serum albumin by spectroscopic method

The interaction between two chromates [sodium chromate (Na₂CrO₄) and potassium chromate K₂CrO₄)] and bovine serum albumin (BSA) in physiological buffer (pH 7.4) was investigated by the fluorescence quenching technique. The results of fluorescence titration revealed that two chromates could strongly quench the intrinsic fluorescence of BSA through a static quenching procedure. The apparent binding constants K and number of binding sites n of chromate with BSA were obtained by the fluorescence quenching method. The thermodynamic parameters enthalpy change (ΔH), entropy change (ΔS) were negative, indicating that the interaction of two chromates with BSA was driven mainly by van der Waals forces and hydrogen bonds. The process of binding was a spontaneous process in which Gibbs free energy change was negative. The distance r between donor (BSA) and acceptor (chromate) was calculated based on Forster's non-radiative energy transfer theory. The results of UV-Vis absorption, synchronous fluorescence, three-dimensional fluorescence and circular dichroism (CD) spectra showed that two chromates induced conformational changes of BSA.

Characterizing the binding interaction between ultrafine carbon black (UFCB) and catalase: electron microscopy and spectroscopic analysis

UFCB bound close to the heme of CAT and dissolved well in tween 80, significantly inhibiting the activity of CAT.

Myricetin inhibits the generation of superoxide anion by reduced form of xanthine oxidase

Myricetin, a plant-derived flavonol, was found to inhibit the formation of uric acid in a mixed-type manner with IC₅₀ value of (8.66±0.03)×10^-6molL^-1 and more potently inhibit the generation of superoxide anion (O₂^-) catalysed by xanthine oxidase (XOD) with IC₅₀ value of (4.55±0.02)×10^-6molL^-1. Inhibiting O₂^- generation by myricetin may be attributed to the reduced form of XOD with a substantially higher reduction potential for FADH/FADH₂ couple. Moreover, molecular docking verified that myricetin bound to the site around isoalloxazine ring in the flavin adenine dinucleotide (FAD) domain to block the diffusion of O₂^- out of the FAD site, resulting in the transfer of another electron from FADH₂ to O₂^- to form hydrogen peroxide. This study has provided new insight into the role of myricetin in inhibiting XOD catalysis, which may be beneficial to improve myricetin's potential application in functional foods.

Bisphenol S Interacts with Catalase and Induces Oxidative Stress in Mouse Liver and Renal Cells

Bisphenol S (BPS) is present in multitudinous consumer products and detected in both food and water. It also has been a main substitute for bisphenol A (BPA) in the food-packaging industry. Yet, the toxicity of BPS is not fully understood. The present study of the toxicity of BPS was divided into two parts. First, oxidative stress, cell viability, apoptosis level, and catalase (CAT) activity in mouse hepatocytes and renal cells were investigated after BPS exposure. After 12 h of incubation with BPS, all of these parameters of hepatocytes and renal cells changed by >15% as the concentration of BPS ranged from 0.1 to 1 mM. Second, the direct interaction between BPS and CAT on the molecule level was investigated by multiple spectral methods and molecular docking investigations. BPS changed the structure and the activity of CAT through binding to the Gly 117 residue on the substrate channel of the enzyme. The main binding forces were hydrogen bond and hydrophobic force.

Study on the mechanism of action between dimethyl phthalate and herring sperm DNA at molecular level

Dimethyl phthalate (DMP), a typical phthalic acid ester, is widespread in the environment and causes extensive concern due to its adverse effects on human health. To understand the genotoxicity of DMP at molecular level, the toxic interaction of DMP with herring sperm (hs) deoxyribonucleic acid (DNA; hs-DNA) was investigated in vitro under simulated physiological conditions using multi-spectroscopic techniques and a molecular modeling method. The results of Ultraviolet-Visible absorption spectroscopy, fluorescence emission spectroscopy, and circular dichroism spectra indicated that DMP interacts with hs-DNA in a groove-binding mode that changes the double helical structure of DNA. The binding constant and the number of binding sites calculated from the fluorescence quenching data were 565.718 L mol(-1) and 0.7872, respectively. A molecular modeling study revealed that DMP tends to bind with DNA in the A-T-rich regions of minor groove and that hydrogen bonding and van der Waals forces play main roles in the interaction. This research can help to elucidate the mechanism of DMP toxicity in vivo.

Interactions of benzotriazole UV stabilizers with human serum albumin: Atomic insights revealed by biosensors, spectroscopies and molecular dynamics simulations

Benzotriazole UV stabilizers (BZTs) belong to one prominent group of ultraviolet (UV) stabilizers and are widely used in various plastics materials. Their large production volumes, frequent detections in the environment and potential toxicities have raised increasing public concern. BZTs can be transported in vivo by transport proteins in plasma and the binding association to transport proteins may serve as a significant parameter to evaluate the bioaccumulative potential. We utilized a novel HSA biosensor, circular dichroism spectroscopy, fluorescence spectroscopy to detect the dynamic interactions of six BZTs (UV-326, UV-327, UV-328, UV-329, UV-P, and BZT) with human serum albumin (HSA), and characterized the corresponding structure-activity relationships (SAR) by molecular dynamics simulations. All test BZTs potently bind at Sudlow site I of HSA with a binding constant of 10(4) L/mol at 298 K. Minor changes in the moieties of BZTs affect their interactions with HSA and differently induce conformations of HSA. Their binding reduced electrochemical impedance spectra and α-helix content of HSA, caused slight red-shifted emission, and changed fluorescence lifetime components of HSA in a concentration-dependent mode. UV-327 and UV-329 form hydrogen bonds with HSA, while UV-329, UV-P and BZT bind HSA with more favorable electrostatic interactions. Our in vitro and in silico study offered a significant framework toward the understanding of risk assessment of BZTs and provides guide for future design of environmental benign BZTs-related materials.

Affinity of rosmarinic acid to human serum albumin and its effect on protein conformation stability

Rosmarinic acid (RA) is a natural polyphenol contained in many aromatic plants with promising biological activities. The interaction between RA and human serum albumin (HSA) was investigated by multi-spectroscopic, electrochemistry, molecular docking and molecular dynamics simulation methods. The fluorescence emission of HSA was quenched by RA through a combined static and dynamic quenching mechanism, but the static quenching was the major constituent. Fluorescence experiments suggested that RA was bound to HSA with moderately strong binding affinity through hydrophobic interaction. The probable binding location of RA was located near site I of HSA. Additionally, as shown by the Fourier transform infrared (FT-IR) and circular dichroism (CD) spectra, RA can result in conformational and structural alterations of HSA. Furthermore, the molecular dynamics studies were used to investigate the stability of the HSA and HSA-RA system. Altogether, the results can provide an important insight for the applications of RA in the food industry.

Molecular simulation study of the specific combination between four kinds of phthalic acid esters and human serum albumin

The interaction between endocrine disruptor phthalic acid esters (PAEs) and human serum albumin (HSA) was studied by fluorescence spectroscopy and molecular modeling methods. The efficiency of energy transfer and the distance between HSA and PAEs were calculated. The results showed that all of the four kinds of PAEs could quench the intrinsic fluorescence of the HSA, with the mechanisms of static quenching and non-radiative energy transfer. Molecular docking study and thermodynamic analysis revealed that the binding behavior was mainly governed by hydrophobic force. And the results of site marker competitive experiments and modeling method suggested that the four PAEs would mainly bind to the HSA in sub-domain IIIA, which demonstrated that the experimental results could coordinate with the theoretical results. Molecular dynamic simulation (MD) revealed that HSA did have a slight conformational change when it bound with PAEs. It also verified the greater stability of HSA-PAEs complex compared to free protein.

The inhibitory kinetics and mechanism of dietary vitamins D3and B2on xanthine oxidase

Dietary guidelines to promote health are usually based on the patterns’ prediction on disease risk of foods and nutrients.

Deciphering the binding patterns and conformation changes upon the bovine serum albumin-rosmarinic acid complex

Rosmarinic acid (RA) is an importantly and naturally occurring polyphenol from plants of the mint family with potent biological activities. Here, the in vitro interaction of RA with bovine serum albumin (BSA) has been investigated using various biophysical approaches as well as molecular modeling methods, to ascertain its binding mechanism and conformational changes. The fluorescence results demonstrated that the fluorescence quenching of BSA by RA was mainly the result of the formation of a ground state BSA-RA complex, and BSA had one high affinity RA binding site with a binding constant of 4.18 × 10(4) mol L(-1) at 298 K. Analysis of thermodynamic parameters revealed that hydrophobic and hydrogen bond interactions were the dominant intermolecular force in the complex formation. The primary binding site of RA in BSA (site I) had been identified by site marker competitive experiments. The distance between RA and the tryptophan residue of BSA was evaluated at 3.12 nm based on Förster's theory of non-radiation energy transfer. The UV-vis absorption, synchronous fluorescence, three-dimensional fluorescence, 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectra confirmed that the conformation and structure of BSA were altered in the presence of RA. Moreover, the nuclear magnetic spectroscopy showed that the aromatic groups of RA took part in the binding reaction during the BSA-RA complexation. In addition, the molecular picture of the interaction mechanism between BSA and RA at the atomic level was well examined by molecular docking and dynamics studies. In brief, RA can bind to BSA with noncovalent bonds in a relatively stable way, and these findings will be beneficial to the functional food research of RA.