Albumin binding as a potential biomarker of exposure to moderately low levels of organophosphorus pesticides

Revealing the mechanistic interactions of profenofos and captan pesticides with serum protein via biophysical and computational investigations

Profenofos (PF) and captan (CT) are among the most utilized organophosphorus insecticides and phthalimide fungicides, respectively. To elucidate the physicochemical and influential toxicokinetic factors, the mechanistic interactions of serum albumin and either PF or CT were carried out in the current study using a series of spectroscopy and computational analyses. Both PF and CT could bind to bovine serum albumin (BSA), a representative serum protein, with moderate binding constants in a range of 103-104 M-1. The bindings of PF and CT did not induce noticeable BSA's structural changes. Both pesticides bound preferentially to the site I pocket of BSA, where the hydrophobic interaction was the main binding mode of PF, and the electrostatic interaction drove the binding of CT. As a result, PF and CT may not only induce direct toxicity by themselves, but also compete with therapeutic drugs and essential substances to sit in the Sudlow site I of serum albumin, which may interfere with the pharmacokinetics and equilibrium of drugs and other substances causing consequent adverse effects.

Evaluating binding and interaction of selected pesticides with serum albumin proteins by Raman, 1H NMR, mass spectrometry and molecular dynamics simulation

Addressing the acute pesticide poisoning and toxicity to humans, is a global challenge of top priority. Serum albumin is the most abundant plasma protein, capable of binding with herbicide and pesticide residues. This study reports multifaceted approaches for in-depth and robust investigation of the molecular interactions of selected pesticides, including propanil (PPL), bromoxynil (BXL), metolachlor (MLR) and glyphosate (GPE) with bovine serum albumin (BSA) proteins using experimental (Raman and FTIR spectroscopy, native mass spectrometry and high field 1H NMR), molecular dynamics (MD) simulation and principal component analysis (PCA). The binding of pesticides with BSA resulted in BSA amide I and amide II Raman spectral shifts. PCA of Raman spectra of serum-pesticide complexes showed the grouping of pesticides on the score plot based on the similarities and differences in pesticides' chemical structures. Native mass spectrometry results revealed strong adduct formation of the pesticides with the protein. The observed changes in chemical shifts, peak broadening or peak disappearance of characteristic proton signals of the pesticides, indicated altered chemical environments due to binding BSA-pesticides interactions. The results of MD simulation conducted for over 500 ns revealed strong pesticides interaction with LEU197, LEU218, LEU237, TRP213, SER286 and ILE289 residues to the site I of BSA. Free energy landscapes provided insights into the conformational changes in BSA on the binding of pesticides. Overall, the experimental and computational results are in consonant and indicate the binding of pesticides into the site I and site II (sub-domain IIA) of the BSA via hydrogen bonding, non-covalent and hydrophobic interactions.Communicated by Ramaswamy H. Sarma.

Comprehensive insight on protein modification by V-type agent: A chemical proteomic approach employing bioorthogonal reaction

Organophosphorus compounds (OPs) such as chemical agents and pesticides are posing critical threats to civilians due to their irreversible phosphonylation of diverse amino acids residues forming different protein adducts. However, traditional analytical approaches are quite limited in capturing the myriad of post-translational events that affect protein functions, especially in identifying the low-abundance OP adducts. Herein a systematic proteomic strategy based on a typical click-enrich-release-identify bioorthogonal operation was firstly developed by employing an alkynyl-tagged V-type agent probe (AVP) and a biotin-based azido-enrichment linker (BTP-N3 ). AVP targeting peptides from human serum albumin (HSA) or plasma were captured by BTP-N3 via CuAAC click reaction, enriched by streptavidin beads, released by selective alkaline hydrolysis of phenacyl ester bond, and subsequently sequenced by LC-MS/MS. This strategy has helped identifying 1115 unique OP adduction sites on 163 proteins in human plasma, and covers lots of OP adducts that cannot be achieved by traditional detection methods. The comprehensive coverage of novel OP substrates provided a general and sensitive approach to retrospective verification and/or dose assessment of toxic OPs.

Investigating the relationship between non-occupational pesticide exposure and metabolomic biomarkers

The relationship between pesticide exposures and metabolomics biomarkers is not well understood. We examined the changes in the serum metabolome (early biomarkers) and the metabolic pathways associated with various pesticide exposure scenarios (OPE: overall exposure, PEM: exposure in months, PEY: exposure in years, and PEU: reported specific pesticides use) using data from the Northern Finland Birth Cohort 1966 31-year cross-sectional examination. We utilized questionnaire data on pesticide exposures and serum samples for nuclear magnetic resonance (NMR)-based metabolomics analyses. For exposures and metabolites associations, participants size varied between 2,361 and 5,035. To investigate associations between metabolomics biomarkers and exposure to pesticide scenarios compared to those who reported no exposures multivariable regression analyses stratified by sex and adjustment with covariates (season of pesticide use, socioeconomic position (SEP), alcohol consumption, BMI, and latitude of residence) were performed. Multiple testing by Benjamini-Hochberg false discovery rate (FDR) correction applied. Pesticide exposures differed by sex, season of pesticide use, alcohol, SEP, latitude of residence. Our results showed that all pesticide exposure scenarios were negatively associated with decreased HDL concentrations across all lipoprotein subclasses in women. OPE, PEY, and PEU were associated with decreased branched-chain amino acid concentrations in men and decreased albumin concentrations in women. OPE, PEY and PEU were also associated with changes in glycolysis metabolites and ketone bodies in both sexes. Specific pesticides exposure was negatively associated with sphingolipids and inflammatory biomarkers in men. In women, OPE, PEM, and PEU were associated with decreased apolipoprotein A1 and increased apolipoprotein B/apolipoprotein A1 ratio. Our findings suggest that identification of early biomarkers of disease risk related to pesticide exposures can inform strategies to reduce exposure and investigate causal pathways. Women may be more susceptible to non-occupational pesticide exposures when compared to men, and future sex-specific studies are warranted.

Structure-Dependent Mechanism of Organophosphate Release from Albumin and Butyrylcholinesterase Adducts When Exposed to Fluoride Ion: A Comprehensive In Silico Study

The most favorable targets for retrospectively determining human exposure to organophosphorus pesticides, insecticides, retardants, and other industrial organophosphates (OPs) are adducts of OPs with blood plasma butyrylcholinesterase (BChE) and human serum albumin (HSA). One of the methods for determining OP exposure is the reactivation of modified BChE using a concentrated solution of KF in an acidic medium. It is known that under the action of fluoride ion, OPs or their fluoroanhydrides can be released not only from BChE adducts but also from the adducts with albumin; however, the contribution of albumin to the total pool of released OPs after plasma treatment with KF has not yet been studied. The efficiency of OP release can be affected by many factors associated with the experimental technique, but first, the structure of the adduct must be taken into account. We report a comparative analysis of the structure and conformation of organophosphorus adducts on HSA and BChE using molecular modeling methods and the mechanism of OP release after fluoride ion exposure. The conformational analysis of the organophosphorus adducts on HSA and BChE was performed, and the interaction of fluoride ions with modified proteins was studied by molecular dynamics simulation. The geometric and energy characteristics of the studied adducts and their complexes with fluoride ion were calculated using molecular mechanics and semiempirical approaches. The structural features of modified HSA and BChE that can affect the efficiency of OP release after fluoride ion exposure were revealed. Using the proposed approach, the expediency of using KF for establishing exposure to different OPs, depending on their structure, can be assessed.

Differentiated Neurons Are More Vulnerable to Organophosphate and Carbamate Neurotoxicity than Undifferentiated Neurons Due to the Induction of Redox Stress and Accumulate Oxidatively-Damaged Proteins

Organophosphate (OP) and carbamate pesticides are toxic to pests through targeted inhibition of acetylcholinesterase (AChE). However, OPs and carbamates may be harmful to non-target species including humans and could induce developmental neurotoxicity if differentiated or differentiating neurons are particularly vulnerable to neurotoxicant exposures. Hence, this study compared the neurotoxicity of OPs, chlorpyrifos-oxon (CPO), and azamethiphos (AZO) and the carbamate pesticide, aldicarb, to undifferentiated versus differentiated SH-SY5Y neuroblastoma cells. OP and carbamate concentration-response curves for cell viability were undertaken using 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays and cellular bioenergetic capacity assessed via quantitation of cellular ATP levels. Concentration-response curves for inhibition of cellular AChE activity were also generated and the production of reactive oxygen species (ROS) was monitored using a 2',7'-dichlorofluorescein diacetate (DCFDA) assay. The OPs and aldicarb reduced cell viability, cellular ATP levels, and neurite outgrowth in a concentration-dependent fashion, from a threshold concentration of ≥10 µM. Neurotoxic potency was in the order AZO > CPO > aldicarb for undifferentiated cells but CPO > AZO > aldicarb for differentiated cells and this toxic potency of CPO reflected its more extensive induction of reactive oxygen species (ROS) and generation of carbonylated proteins that were characterized by western blotting. Hence, the relative neurotoxicity of the OPs and aldicarb in part reflects non-cholinergic mechanisms that are likely to contribute to developmental neurotoxicity.

The interaction analysis between human serum albumin with chlorpyrifos and its derivatives through sub-atomic docking and molecular dynamics simulation techniques

Chlorpyrifos (CPF) is an extensively used organophosphate pesticide for crop protection. However, there are concerns about it contaminating the environment and human health, with estimated three lakh deaths annually. The molecular modeling protocol was assisted in redesigning thirteen well-known CPF linkers and inserting them at five selectable CPF (R1-R5) positions of CPF to get 258 CPF derivatives. CPF and its derivatives were optimized using LigPrep and docked to a grid centralized on Trp214 using extra precision glide docking. The Binding free energy of complexes was calculated using molecular mechanics/generalized born surface area (MM-GBSA). CPF and CPFD-225 have glide scores of - 3.08 and - 6.152 kcal/mol, respectively, with human serum albumin and ΔG bind for CPF (- 33.041817 kcal/mol) (- 52.825 kcal/mol) for CPF-D225. The top ten CPF derivatives showed at least ninefold better binding free energy than the CPF proposed for polyclonal antibody production. Subsequently, molecular docking studies revealed that CPF and its derivatives could bind to human serum albumin (HSA). Furthermore, using the Desmond package, a 100-ns molecular dynamics (MD) simulation was performed on the potential binding site. The final systems of CPF-HSA and CPF-222D complexes consist of 76,014 and 76,026 atoms, respectively. The physical stability of both the systems (CPF-HSA and CPF-222D) was analyzed by considering the overall potential energy, RMSF, RMSD, Hydrophobic interactions, and water-mediated patterns, which showed total energy of - 141,610 kcal/mol and - 140,150 kcal/mol, respectively.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03344-7.

An Investigation of the Neurotoxic Effects of Malathion, Chlorpyrifos, and Paraquat to Different Brain Regions

Acute or chronic exposures to pesticides have been linked to neurotoxicity and the potential development of neurodegenerative diseases (NDDs). This study aimed to consider the neurotoxicity of three widely utilized pesticides: malathion, chlorpyrifos, and paraquat within the hippocampus (HC), corpus striatum (CS), cerebellum (CER), and cerebral cortex (CC). Neurotoxicity was evaluated at relatively low, medium, and high pesticide dosages. All pesticides inhibited acetylcholinesterase (AChE) and neuropathy target esterase (NTE) in each of the brain regions, but esterase inhibition was greatest in the HC and CS. Each of the pesticides also induced greater disruption to cellular bioenergetics within the HC and CS, and this was monitored via inhibition of mitochondrial complex enzymes I and II, reduced ATP levels, and increased lactate production. Similarly, the HC and CS were more vulnerable to redox stress, with greater inhibition of the antioxidant enzymes catalase and superoxide dismutase and increased lipid peroxidation. All pesticides induced the production of nuclear Nrf2 in a dose-dependent manner. Collectively, these results show that pesticides disrupt cellular bioenergetics and that the HC and CS are more susceptible to pesticide effects than the CER and CC.

Non-occupational exposure to pesticides and health markers in general population in Northern Finland: Differences between sexes

BACKGROUND

Occupational exposure to pesticides has been reported among general population worldwide. However, little is known about the associations between non-occupational exposure to pesticides, and biological markers of health and their response by sex.

OBJECTIVES

We aimed to assess the associations between non-occupational overall pesticide exposure, length of exposure and specific pesticides reported with 35 biological markers of health representing cardiometabolic, haematological, lung function, sex hormones, liver and kidney function profiles, and vitamin D in Finnish cohort.

METHODS

31-year cross-sectional examination of the Northern Finland Birth Cohort 1966 provided blood samples for biomarker measurements in 1997-1998. Number of subjects varied between 2361 and 5037 for given exposures and certain outcome associations. Multivariable regression analyses were performed to examine associations between overall pesticide exposure (OPE), length of pesticide exposure in months (PEM), in years (PEY), and specific pesticides use (PEU) or not with cardiometabolic [SBP, DBP, TC, LDL, HDL, triglycerides, fasting glucose, insulin, HOMA-IR, HOMA-B, HOMA-S, hs-CRP], hematological [WBC, RBC, Hb, HCT, MCV, MCH, MCHC, platelets], lung function (FVC, FEV1), sex hormones [luteinizing hormone (LH), testosterone (TT), sex-hormone binding globulin (SHBG)], liver and kidney function profiles [total protein, albumin, globulin, ALP, ALT, GGT, urea, creatinine], and vitamin D adjusting for sex, BMI, socioeconomic position (SEP) and season of pesticide use.

RESULTS

This cohort study on up to 5037 adults with non-occupational OPE, PEM, PEY and PEU differed by sex and SEP. In regression analyses, all the exposures were positively associated with total cholesterol and low-density lipoprotein cholesterol, and PEU was negatively associated with high-density lipoprotein cholesterol in females. OPE and PEM were positively associated with haematocrit in females and PEU with platelets in males. PEU was negatively associated with mean corpuscular haemoglobin. OPE and PEM were positively associated with LH in males. OPE was negatively associated with total protein and albumin in males.

DISCUSSION

In Finnish young adults, non-occupational overall pesticide exposure, length of exposure and specific pesticides were associated with multiple biological markers of health. The biological markers seem to be indicative of adverse effects of pesticides and warrant for further studies to replicate the findings and determine the underlying mechanisms.

Organophosphorus pesticide exposure biomarkers in a Mexican population

The organophosphate (OP) pesticides are neurotoxic compounds widely used around the world. Evaluation of OP exposure in human studies is important for enabling adequate data analyses and drawing accurate conclusions. The aim of this study was to analyze OP exposure biomarkers and their relationships in a Mexican population with different exposure levels. Dialkylphosphates (DAP) were determined through gas chromatography-mass spectrometry (GC-MSD); acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), arylesterase (AREase), basal paraoxonase 1 (PONase), and β-glucuronidase activities were detected using spectrophotometric methods. The albumin content was determined in a certified clinical laboratory. The DMTP metabolite was found in the highest concentration, and a negative and significant correlation between DAP and cholinesterase activity was observed. Our results suggested that BuChE is a considerably more sensitive biomarker than AChE. In addition, β-glucuronidase was positively correlated with albumin, BuChE, and PONase. In conclusion, our data strongly support the use of two or more biomarkers of exposure in human monitoring and the application of a strong and validated questionnaire.

Prognostic nomogram for the severity of acute organophosphate insecticide self-poisoning: a retrospective observational cohort study

OBJECTIVE

To develop a convenient nomogram for the bedside evaluation of patients with acute organophosphorus poisoning (AOPP).

DESIGN

This was a retrospective study.

SETTING

Two independent hospitals in northern China, the First Hospital of Jilin University and the Lequn Hospital of the First Hospital of Jilin University.

PARTICIPANTS

A total of 1657 consecutive patients admitted for the deliberate oral intake of AOPP within 24 hours from exposure and aged >18 years were enrolled between 1 January 2013 and 31 December 2018. The exclusion criteria were: normal range of plasma cholinesterase, exposure to any other type of poisonous drug(s), severe chronic comorbidities including symptomatic heart failure (New York Heart Association III or IV) or any other kidney, liver and pulmonary diseases. Eight hundred and thirty-four patients were included.

PRIMARY OUTCOME MEASURE

The existence of severely poisoned cases, defined as patients with any of the following complications: cardiac arrest, respiratory failure requiring ventilator support, hypotension or in-hospital death.

RESULTS

440 patients from one hospital were included in the study to develop a nomogram of severe AOPP, whereas 394 patients from the other hospital were used for the validation. Associated risk factors were identified by multivariate logistic regression. The nomogram was validated by the area under the receiver operating characteristic curve (AUC). A nomogram was developed with age, white cells, albumin, cholinesterase, blood pH and lactic acid levels. The AUC was 0.875 (95% CI 0.837 to 0.913) and 0.855 (95% CI 0.81 to 0.9) in the derivation and validation cohorts, respectively. The calibration plot for the probability of severe AOPP showed an optimal agreement between the prediction by nomogram and actual observation in both derivation and validation cohorts.

CONCLUSION

A convenient severity evaluation nomogram for patients with AOPP was developed, which could be used by physicians in making clinical decisions and predicting patients' prognosis.

Spectrofluorimetric analysis of the binding of a target molecule to serum albumin: tricky aspects and tips

Protein binding heavily modulates drug activity. Therefore, the binding features need to be elucidated when chemistry researchers study new molecules (metal complexes) to be used as drugs. This paper concerns the experimental and data treatment aspects of the mechanistic analysis of the binding to a fluorescent protein (the golden standard serum albumin) by using direct fluorescence titrations. Fluorescence data are not rarely only qualitatively used, neglecting further treatments which could offer a precious detailed picture of the behavior of the drug. We aim to spread a mechanistic approach, discussing the critical aspects for correctly designing the experiments and treating the data. The researcher may confirm adduct formation and evaluate binding constants (Stern-Volmer K_SV or other types of K). Also, we discuss here, with the help of literature examples, the correct use of temperature dependence of K to extract thermodynamic parameters, comment on enthalpy-entropy compensation, together with the use of synchronous spectra and exchange experiments to gain information on the binding type and site. We think that this tutorial/critical synopsis can be of help for the increasing community dealing with these experiments, which are valuable but often much more tricky than it might appear at first sight.

The Universal Soldier: Enzymatic and Non-Enzymatic Antioxidant Functions of Serum Albumin

As a carrier of many biologically active compounds, blood is exposed to oxidants to a greater extent than the intracellular environment. Serum albumin plays a key role in antioxidant defence under both normal and oxidative stress conditions. This review evaluates data published in the literature and from our own research on the mechanisms of the enzymatic and non-enzymatic activities of albumin that determine its participation in redox modulation of plasma and intercellular fluid. For the first time, the results of numerous clinical, biochemical, spectroscopic and computational experiments devoted to the study of allosteric modulation of the functional properties of the protein associated with its participation in antioxidant defence are analysed. It has been concluded that it is fundamentally possible to regulate the antioxidant properties of albumin with various ligands, and the binding and/or enzymatic features of the protein by changing its redox status. The perspectives for using the antioxidant properties of albumin in practice are discussed.

Mechanism of interactions between organophosphorus insecticides and human serum albumin: Solid-phase microextraction, thermodynamics and computational approach

Organophosphates insecticides (OPs) are one of the major environmental pollutants and their interaction with human serum albumin (HSA) has been shown to have significant effects on their bioavailability which is related to toxicokinetics and toxicodynamics in human body. In this research, solid-phase microextraction methods were developed to analyse the free concentrations of three OPs (chlorpyrifos, parathion-methyl and malathion) in buffered HSA solution and that provide a useful method for the determination of binding affinity constants (K_a), binding forces and binding location. Polydimethylsiloxane fibers were selected for analysing the free concentrations of OPs, with an external calibration approach. Good linearities conducted in PBS solution were observed in the range of 0.0025-1.7 μmol L^-1 (R² = 0.9975) for chlorpyrifos, 1.0-27 μmol L^-1 (R² = 0.9974) for parathion-methyl, and 0.5-70 μmol L^-1 (R² = 0.9973)for malathion, respectively. The LODs for instrument response were 1 ng, 5 ng and 10 ng for chlorpyrifos, parathion-methyl and malathion, respectively. The K_a values for chlorpyrifos, parathion-methyl and malathion showed that they were positively correlated with hydrophobicity and negatively correlated with temperature. The OP binding sites on HSA were confirmed by site marker competition test and further proven by computational approaches. The recognition region of parathion-methyl was situated within residues 199-292 in subdomain IIA. Malathion bonded to residues 404-558 in subdomain IIIA. The mode of action between HSA-parathion-methyl and HSA-malathion is found to involve mainly by H-bonds, π-π stacking and hydrophobic effects. These results clearly demonstrate the noncovalent binding of OPs with HSA and provide new insight into solid-phase microextraction, thermodynamics and computational approaches.

Efficacy of an organophosphorus hydrolase enzyme (OpdA) in human serum and minipig models of organophosphorus insecticide poisoning

Objectives: Current therapeutic options for organophosphorus (OP) insecticide self-poisoning including atropine and oximes are inadequate and case fatality may exceed 20%. An OP hydrolase enzyme, OpdA, has been used for environmental cleansing of OP insecticides and prevented death in rat and non-human primate models of OP insecticide poisoning if given very quickly after exposure. We here tested OpdA's ability to break down OP insecticides in human serum and in clinically relevant minipig models of OP insecticide poisoning.Methods: Human serum was spiked with seven diverse WHO Class II OP insecticides (chlorpyrifos, quinalphos, diazinon, dimethoate, fenthion, phenthoate, and profenofos) and the effect of OpdA on degradation measured. The pharmacodynamic and clinical effects of OpdA treatment were studied in Gottingen minipigs orally poisoned with agricultural formulations of dimethoate EC40 or methyl parathion EC60; pharmacodynamic effects were also assessed in profenofos EC50-poisoned pigs.Results: OpdA effectively hydrolysed OP insecticides in human serum, with rates varying from 856 (SD 44) down to 0.107 (SD 0.01) moles of substrate hydrolysed/mole of enzyme/sec (k_cat) for quinalphos and phenthoate, respectively, although at rates 2-3 log orders less than found in vitro in buffered solution. It showed clinical benefit in minipig models, reducing the dose of noradrenaline required to sustain an adequate mean arterial pressure after dimethoate (mean 0.149 [SD 0.10] μg/kg/h vs. 1.07 [SD 0.77] μg/kg/h, p < .0001) and methyl parathion (mean 0.077 [SD 0.08] μg/kg/h vs. 0.707 [SD 0.49] μg/kg/h, p < .0001) poisoning. OpdA reduced blood OP insecticide concentration and acetylcholinesterase inhibition after poisoning by dimethoate, methyl parathion, and profenofos insecticides.Conclusions: In vitro incubation of OpdA in human serum showed hydrolysis of diverse OP insecticides, although at lower rates than found in buffer solutions. This activity results in clinical and pharmacodynamic efficacy in vivo against several OP insecticides. These results support the testing of OpdA in further animal models before considering human trials to determine whether it may become an urgently required novel therapeutic agent for OP insecticide self-poisoning.

Positron emission tomography studies of organophosphate chemical threats and oxime countermeasures

There is a unique in vivo interplay involving the mechanism of inactivation of acetylcholinesterase (AChE) by toxic organophosphorus (OP) compounds and the restoration of AChE activity by oxime antidotes. OP compounds form covalent adducts to this critical enzyme target and oximes are introduced to directly displace the OP from AChE. For the most part, the in vivo inactivation of AChE leading to neurotoxicity and antidote-based therapeutic reversal of this mechanism are well understood, however, these molecular-level events have not been evaluated by dynamic imaging in living systems at millimeter resolution. A deeper understanding of these critically, time-dependent mechanisms is needed to develop new countermeasures. To address this void and to help accelerate the development of new countermeasures, positron-emission tomography (PET) has been investigated as a unique opportunity to create platform technologies to directly examine the interdependent toxicokinetic/pharmacokinetic and toxicodynamic/pharmacodynamic features of OPs and oximes in real time within live animals. This review will cover two first-in-class PET tracers representing an OP and an oxime antidote, including their preparation, requisite pharmacologic investigations, mechanistic interpretations, biodistribution and imaging.

Streptozocin; a GLUT2 binding drug, interacts with human serum albumin at loci h6DOM3-h7DOM3

Streptozocin (STZ) is a broad range antibiotic, highly genotoxic, antineoplastic and hyperglycemic. HSA is the most abundant protein in physiology and it binds to almost all exogenic and endogenic ligands, including drugs. STZ-induced fluorescence quenching of HSA has been done at pH 7.4, pH 3.5 and at pH 7.4 with 4.5 M urea at temperatures 286 K, 291 K, and 306 K. K_sv found to be 10³ M^-1, binding constant 1.5X10³M^-1 and binding sites ~1. But, K_sv for HSA and glucopyranose interaction was found lesser than that of HSA-STZ binding. Binding of STZ/glucopyranose on HSA seems to result in complex formation as calculated K_q > 10¹⁰ M^-1 s^-1. The number of binding sites, binding constants, and binding energies were increased with temperature. The ΔG⁰, ΔH⁰, and ΔS⁰ for HSA-STZ interaction were found to be -17.7 × 10³ J·mol^-1; 2.34 × 10⁵ J·mol^-1 and 841 JK^-1 mol^-1 respectively at pH 7.4 and 291 K. The comparative bindings of N, F and I states of HSA with STZ and their molecular docking analyses indicate that IIIA-B junction (i.e., inter-helix h6_DOM3-h7_DOM3) is the probable binding site, a locus close to fatty acid binding site-5. These results could be useful for therapeutic and analytical exploitation of STZ, as albumin used as the vehicle for drug delivery.

Application of lanthanum stearate monolayers as a metal-affinity sorbent for the selective sorption of soman adducts to human serum albumin

A new metal-affinity sorbent based on lanthanum stearate monolayers has been developed and characterized. The prospect of its application to specific extraction of organophosphorous compound (OP) adducts of blood proteins was demonstrated. For this, the patterns of soman adducts of human serum albumin (HSA) were comprehensively characterized by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS).

Detection of Carbofuran-Protein Adducts in Serum of Occupationally Exposed Pesticide Factory Workers in Pakistan

This study was conducted to investigate the protein adducts with pesticides in a cohort of 172 factory workers that were exposed to a mixture of pesticides. The 35 samples showing considerable variation in biochemical parameters, i.e., butyrylcholinestrase (BChE), serum glutamic pyruvic transaminase (SGPT), serum glutamic oxaloacetic transaminase (SGOT), gamma-glutamyl transferase (GGT), serum glutamic pyruvic transaminase (SGPT), alkaline phosphatase (ALP/ALKP), lactate dehydrogenase (LDH), creatine phosphokinase (CPK) enzymes, and controls were analyzed by reversed-phase nanoscale liquid chromatography tandem mass spectrometry (nLC-MS/MS) on an Orbitrap mass spectrometer employing a shotgun proteomics approach. Only protein adducts with carbofuran were found on serum proteins of these workers. These adducts were of carbofuran labeled lysine (Lys-142, Lys-183, Lys-287, and Lys-467), arginine (Arg-210, Arg-242, and Arg-256) from serum albumin, and serine (Ser-07, Ser-54, and Ser-150) from immunoglobulin proteins. The arginine residues (Arg-210, Arg-242, Arg-246, and Arg-434) from albumin were also found to be glycated in serum of workers showing a high level of glucose who also had glycated arginine (Arg-1120) modified with carbofuran in their tankyrase-1-binding protein. The number of tandem mass spectra of modified peptides increased with increasing time of exposure. This is the first report to demonstrate the presence of carbofuran-labeled albumin, immunoglobulin, and glycated arginine, which shows that lysine and arginine of human albumin and serine of immunoglobulin are covalently modified in the serum of workers that were occupationally exposed to carbofuran, and the modification is detectable by tandem mass spectrometry. These peptides modified with carbofuran can potentially be used as a biomarker of carbofuran exposure.

In vitro evaluation of the conjugations of neonicotinoids with transport protein: photochemistry, ligand docking and molecular dynamics studies

The flexibility of ligand structures and the property of substituents in neonicotinoids play a pivotal role in protein–neonicotinoid and this type of biorecognition may have a great impact on the potential toxicity of these widely used agrochemicals.

Molecular and practical aspects of the enzymatic properties of human serum albumin and of albumin-ligand complexes

BACKGROUND

Human serum albumin and some of its ligand complexes possess enzymatic properties which are useful both in vivo and in vitro.

SCOPE OF REVIEW

This review summarizes present knowledge about molecular aspects, practical applications and potentials of these properties.

MAJOR CONCLUSIONS

The most pronounced activities of the protein are different types of hydrolysis. Key examples are esterase-like activities involving Tyr411 or Lys199 and the thioesterase activity of Cys34. In the first case, hydrolysis involves water and both products are released, whereas in the latter cases one of the products is set free, and the other stays covalently bound to the protein. However, the modified Cys34 can be converted back to its reduced form by another compound/enzymatic system. Among the other activities are glucuronidase, phosphatase and amidase as well as isomerase and dehydration properties. The protein has great impact on the metabolism of, for example, eicosanoids and xenobiotics. Albumin with a metal ion-containing complex is capable of facilitating reactions involving reactive oxygen and nitrogen species.

GENERAL SIGNIFICANCE

Albumin is useful in detoxification reactions, for activating prodrugs, and for binding and activating drug conjugates. The protein can be used to construct smart nanotubes with enzymatic properties useful for biomedical applications. Binding of organic compounds with a metal ion often results in metalloenzymes or can be used for nanoparticle formation. Because any compound acting as cofactor and/or the protein can be modified, enzymes can be constructed which are not naturally found and therefore can increase, often stereospecifically, the number of catalytic reactions. This article is part of a Special Issue entitled Serum Albumin.

Detection, quantification, and microlocalisation of targets of pesticides using microchannel plate autoradiographic imagers

Organophosphorus (OP) compounds are a diverse chemical group that includes nerve agents and pesticides. They share a common chemical signature that facilitates their binding and adduction of acetylcholinesterase (AChE) within nerve synapses to induce cholinergic toxicity. However, this group diversity results in non-uniform binding and inactivation of other secondary protein targets, some of which may be adducted and protein activity influenced, even when only a relatively minor portion of tissue AChE is inhibited. The determination of individual OP protein binding targets has been hampered by the sensitivity of methods of detection and quantification of protein-pesticide adducts. We have overcome this limitation by the employment of a microchannel plate (MCP) autoradiographic detector to monitor a radiolabelled OP tracer compound. We preincubated rat thymus tissue in vitro with the OP pesticides, azamethiphos-oxon, chlorfenvinphos-oxon, chlorpyrifos-oxon, diazinon-oxon, and malaoxon, and then subsequently radiolabelled the free OP binding sites remaining with 3H-diisopropylfluorophosphate (3H-DFP). Proteins adducted by OP pesticides were detected as a reduction in 3H-DFP radiolabelling after protein separation by one dimensional polyacrylamide gel electrophoresis and quantitative digital autoradiography using the MCP imager. Thymus tissue proteins of molecular weights -28 kDa, 59 kDa, 66 kDa, and 82 kDa displayed responsiveness to adduction by this panel of pesticides. The 59 kDa protein target (previously putatively identified as carboxylesterase I) was only significantly adducted by chlorfenvinphos-oxon (p < 0.001), chlorpyrifos-oxon (p < 0.0001), and diazinon-oxon (p < 0.01), the 66 kDa protein target (previously identified as serum albumin) similarly only adducted by the same three pesticides (p < 0.0001), (p < 0.001), and (p < 0.01), and the 82 kDa protein target (previously identified as acyl peptide hydrolase) only adducted by chlorpyrifos-oxon (p < 0.0001) and diazinon-oxon (p < 0.001), when the average values of tissue AChE inhibition were 30%, 35%, and 32% respectively. The -28 kDa protein target was shown to be heterogeneous in nature and was resolved to reveal nineteen 3H-DFP radiolabelled protein spots by two dimensional polyacrylamide gel electrophoresis and MCP autoradiography. Some of these 3H-DFP proteins spots were responsive to adduction by preincubation with chlorfenvinphos-oxon. In addition, we exploited the useful spatial resolution of the MCP imager (-70 mm) to determine pesticide micolocalisation in vivo, after animal dosing and autoradiography of brain tissue sections. Collectively, MCP autoradiographic imaging provided a means to detect targets of OP pesticides, quantify their sensitivity of adduction relative to tissue AChE inhibition, and highlighted that these common pesticides exhibit specific binding character to protein targets, and therefore their toxicity will need to be evaluated on an individual compound basis. In addition, MCP autoradiography afforded a useful method of visualisation of the localisation of a small radiolabelled tracer within brain tissue.

Quantification of Interactions between Serum Albumin and Endogenous Free Fatty Acids or Exogenous Chemicals by Stable Isotope-Coded Mass Spectrometry

As primary endogenous ligands of serum albumin, free fatty acids exert versatile effects on the albumin conformation through cooperative or competitive interactions with exogenous chemicals. Based on equilibrium partition between n-hexane and aqueous phases, we have established three indexes, defined as R A, R V, and R T, for quantitative assessment of the intrinsic binding affinity, the affinitive variation induced by exogenous chemicals, and the topological dependence of albumin affinity, respectively. When albumin molecules in the aqueous phase are in native or denatured forms, or disturbed by exogenous chemicals, corresponding changes of free fatty acids in the n-hexane phase can be quantified by an iFFAM (isotope-coded free fatty acid methylation) approach. Free fatty acids from the control and the sample are differentially derived by d0- or d3-methanol and analyzed by gas chromatography-mass spectrometry. Changes of fatty acids can be revealed by peak ratios of d0- or d3-labeled fragment ions of fatty acid methyl esters.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for detection and identification of albumin phosphylation by organophosphorus pesticides and G- and V-type nerve agents

Toxic organophosphorus compounds (OPC), e.g., pesticides and nerve agents (NA), are known to phosphylate distinct endogenous proteins in vivo and in vitro. OPC adducts of butyrylcholinesterase and albumin are considered to be valuable biomarkers for retrospective verification of OPC exposure. Therefore, we have detected and identified novel adducts of human serum albumin (HSA) by means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Pure albumin and plasma were incubated with numerous pesticides and NA of the V- and G-type in different molar ratios. Samples were prepared either by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by in-gel enzymatic cleavage using endoproteinase Glu-C (Glu-C) or by combining highly albumin-selective affinity extraction with ultrafiltration followed by reduction, carbamidomethylation, and enzymatic cleavage (Glu-C) prior to MALDI-TOF MS analysis. Characteristic mass shifts for phosphylation revealed tyrosine adducts at Y(411) (Y(401)KFQNALLVRY(411)TKKVPQVSTPTLVE(425)), Y(148) and Y(150) (I(142)ARRHPY(148)FY(150)APE(153), single and double labeled), and Y(161) (L(154)LFFAKRY(161)KAAFTE(167)) produced by original NA (tabun, sarin, soman, cyclosarin, VX, Chinese VX, and Russian VX) as well as by chlorpyrifos-oxon, diisopropyl fluorophosphate (DFP), paraoxon-ethyl (POE), and profenofos. MALDI-MS/MS of the single-labeled I(142)-E(153) peptide demonstrated that Y(150) was phosphylated with preference to Y(148). Aged albumin adducts were not detected. The procedure described was reproducible and feasible for detection of adducts at the most reactive Y(411)-residue (S/N ≥ 3) when at least 1% of total albumin was labeled. This was achieved by incubating plasma with molar HSA/OPC ratios ranging from approximately 1:0.03 (all G-type NA, DFP, and POE) to 1:3 (V-type NA, profenofos). Relative signal intensity of the Y(411) adduct correlated well with the spotted relative molar amount underlining the usefulness for quantitative adduct determination. In conclusion, the current analytical design exhibits potential as a verification tool for high-dose exposure.

Detection of adduct on tyrosine 411 of albumin in humans poisoned by dichlorvos

Studies in mice and guinea pigs have shown that albumin is a new biomarker of organophosphorus toxicant (OP) and nerve agent exposure. Our goal was to determine whether OP-labeled albumin could be detected in the blood of humans exposed to OP. Blood from four OP-exposed patients was prepared for mass spectrometry analysis by digesting 0.010 ml of serum with pepsin and purifying the labeled albumin peptide by offline high performance liquid chromatography. Dimethoxyphosphate-labeled tyrosine 411 was identified in albumin peptides VRY(411)TKKVPQVSTPTL and LVRY(411)TKKVPQVSTPTL from two patients who had attempted suicide with dichlorvos. The butyrylcholinesterase activity in these serum samples was inhibited 80%. A third patient whose serum BChE activity was inhibited 8% by accidental inhalation of dichlorvos had undetectable levels of adduct on albumin. A fourth patient whose BChE activity was inhibited 60% by exposure to chlorpyrifos had no detectable adduct on albumin. This is the first report to demonstrate the presence of OP-labeled albumin in human patients. It is concluded that tyrosine 411 of human albumin is covalently modified in the serum of humans poisoned by dichlorvos and that the modification is detectable by mass spectrometry. The special reactivity of tyrosine 411 with OP suggests that other proteins may also be modified on tyrosine. Identification of other OP-modified proteins may lead to an understanding of neurotoxic symptoms that appear long after the initial OP exposure.

Serum albumins and detoxication of anti-cholinesterase agents

Serum albumin displays an esterase activity that is capable of hydrolysing the anti-cholinesterase compounds carbaryl, paraoxon, chlorpyrifos-oxon, diazoxon and O-hexyl, O-2,5-dichlorphenyl phosphoramidate. The detoxication of all these anti-cholinesterase compounds takes place at significant rates with substrate concentrations in the same order of magnitude as expected during in vivo exposures, even when these substrate concentrations are between 15 and 1300 times lower than the recorded K(m) constants. Our data suggest that the efficacy of this detoxication system is based on the high concentration of albumin in plasma (and in the rest of the body), and not on the catalytic efficacy itself, which is low for albumin. We conclude the need for a structure-activity relationship study into the albumin-associated esterase activities because this protein is universally present in vertebrates and could compensate for reduced levels of other esterases, i.e., lipoprotein paraoxonase, in some species. It is also remarkable that the biotransformation of xenobiotics can be reliably studied in vitro, although conditions as similar as possible to in vivo situations are necessary.

Analytical approaches to investigate protein-pesticide adducts

Organophosphorus pesticides primarily elicit toxicity via their common covalent adduction of acetylcholinesterase (AChE), but pesticide binding to additional sensitive secondary targets may also compromise health. We have utilised tritiated-diisopropylfluorophosphate ((3)H-DFP) binding to quantify the levels of active immune and brain tissue serine hydrolases, and visualise them using autoradiography after protein separation by one-dimensional and two-dimensional techniques. Preincubation of protein extracts with pesticide in vitro or dosing of rats with pesticide in vivo was followed by (3)H-DFP radiolabelling. Pesticide targets were identified by a reduction in (3)H-DFP radiolabelling relative to controls, and characterised by their tissue presence, molecular weight, and isoelectric point. Conventional column chromatography was employed to enrich pesticide targets to enable their further characterisation, and/or identification by mass spectrometry. The major in vivo pesticide targets characterised were 66 kDa, serum albumin, and 60 kDa, likely carboxylesterase 1, both of which displayed differential pesticide binding character under conditions producing approximately 30% tissue AChE inhibition. The characterisation and identification of sensitive pesticide secondary targets will enable an evaluation of their potential contribution to the ill health that may arise from chronic low-dose pesticide exposures. Additionally, secondary targets may provide useful biomonitors and/or bioscavengers of pesticide exposures.

Mass spectrometry identifies multiple organophosphorylated sites on tubulin

Acute toxicity of organophosphorus poisons (OP) is explained by inhibition of acetylcholinesterase in nerve synapses. Low-dose effects are hypothesized to result from modification of other proteins, whose identity is not yet established. The goal of the present work was to obtain information that would make it possible to identify tubulin as a target of OP exposure. Tubulin was selected for study because live mice injected with a nontoxic dose of a biotinylated organophosphorus agent appeared to have OP-labeled tubulin in brain as determined by binding to avidin beads and mass spectrometry. The experiments with live mice were not conclusive because binding to avidin beads could be nonspecific. To be convincing, it is necessary to find and characterize the OP-labeled tubulin peptide. The search for OP-labeled tubulin peptides was begun by identifying residues capable of making a covalent bond with OP. Pure bovine tubulin (0.012 mM) was treated with 0.01-0.5 mM chlorpyrifos oxon for 24 h at 37 degrees C in pH 8.3 buffer. The identity of labeled amino acids and percent labeling was determined by mass spectrometry. Chlorpyrifos oxon bound covalently to tyrosines 83, 103, 108, 161, 224, 262, 272, 357, and 399 in bovine alpha tubulin, and to tyrosines 50, 51, 59, 106, 159, 281, 310, and 340 in bovine beta tubulin. The most reactive were tyrosine 83 in alpha and tyrosine 281 in beta tubulin. In the presence of 1 mM GTP, percent labeling increased 2-fold. Based on the crystal structure of the tubulin heterodimer (PDB 1jff) tyrosines 83 and 281 are well exposed to solvent. In conclusion seventeen tyrosines in tubulin have the potential to covalently bind chlorpyrifos oxon. These results will be useful when searching for OP-labeled tubulin in live animals.

Covalent binding of organophosphorothioates to albumin: a new perspective for OP-pesticide biomonitoring?

We here report on the covalent binding of various organophosphorothioate (OPT) pesticides to albumin at in vitro exposure levels that did not give rise to butyrylcholinesterase inhibition. Adduct formation occurred at the Tyr-411 residue of albumin, as was firmly corroborated by LC-tandem MS analysis of a pepsin digest of OPT-modified albumin. It cannot be excluded that other (tyrosine) residues become modified as well. A convenient method for mass spectrometric determination of the OPT tyrosine adduct has also been developed based on the pronase digestion of albumin and subsequent LC-tandem MS analysis of the digest. The resulting tyrosine phosphorothioate ester displayed favorable chromatographic and mass spectrometric properties for sensitive analysis. In vitro exposure levels of parathion and chlorpyrifos down to 1 microM could readily be assessed. The remarkable affinity of OPTs for albumin opens the way for a more complete assessment of OP pesticide exposure.