Hapten-antibody recognition studies in competitive immunoassay of α-zearalanol analogs by computational chemistry and Pearson Correlation analysis

Antibody Production, Immunoassay Establishment, and Specificity Study for Flunixin and 5-Hydroxyflunixin

Flunixin (FLU) is a nonsteroidal drug that is widely used in animals, causing severe drug residues in animal-derived foods and environment. The development of antibody-based rapid immunoassay methods is of great significance for the monitoring of FLU and its metabolite 5-hydroxyflunixin (5-FLU). We prepared monoclonal antibodies (mAbs) with different recognition spectra through FLU-keyhole limpet hemocyanin conjugates as immunogen coupled with antibody screening strategies. mAb5E6 and mAb6D7 recognized FLU with high affinity, and mAb2H5 and mAb4A4 recognized FLU and 5-FLU with broad specificity. Through evaluating the recognition of these mAbs against more than 11 structural analogues and employing computational chemistry, molecular docking, and molecular dynamics methodologies, we preliminarily determined the recognition epitope and recognition mechanism of these mAbs. Finally, an indirect competitive enzyme-linked immunosorbent assay for FLU based on mAb6D7 was developed, which exhibited limits of detection as low as 0.016-0.042 μg kg -1 (L-1) in milk and muscle samples.

Development of epitopephore-based rational hapten design strategy: A combination of theoretical evidence and experimental validation

Antibody is the key biomolecule that governing the sensitivity and specificity of an immunoassay for chemical compound, also named hapten molecule. Obviously, predication of hapten effectiveness before chemical synthesis is beneficial to boost success, save cost and improve controllability. Here, we proposed and evaluated an epitopephore based rational hapten design (ERHD) to assist antibody production to chemical compound, combining theoretical evidence and then experimental validation by using dinitrocarbanilide (DNC) as a model analyte. Briefly, epitopephores of DNC were firstly generated by HipHop algorithm after features mapping. A homemade drug database also containing reported fragment haptens (HFR) and new designed full hapten (HFU) were constructed, and then was virtually screened by using generated epitopephore followed by structural analysis and visual inspection. The DNC haptens based on the selected hits were further identified by Density Functional Theory before total synthesis. To prove and clarify the usability of the ERHD, two retrieved HFU haptens, one non-retrieved HFU hapten and three non-retrieved HFR haptens were all selected to produce monoclonal antibodies (mAbs) for comparison purpose. A maximal 6000-fold increased affinity of mAb from retrieved HFU than HFR was observed, while, non-retrieved HFU failed to produce antibody to DNC. More importantly, mAbs from HFU haptens provided highly specificity to DNC, while, mAbs from HFR haptens could recognize 15 others analogues. We then constructed antibody structure and investigated molecular recognition of the mAbs to DNC, well supporting the rationality of the ERHD. Lastly, an icELISA was developed for DNC with an IC₅₀ value as low as 0.19 ng mL^-1 with high specificity, which has never achieved before.

Hapten Synthesis and Monoclonal Antibody Preparation for Simultaneous Detection of Albendazole and Its Metabolites in Animal-Origin Food

Albendazole (ABZ) is one of the benzimidazole anthelmintics, and the overuse of ABZ in breeding industry can lead to drug resistance and a variety of toxic effects in humans. Since the residue markers of ABZ are the sum of ABZ and three metabolites (collectively referred to as ABZs), albendazole-sulfone (ABZSO₂), albendazole-sulfoxide (ABZSO), and albendazole-2-amino-sulfone (ABZNH₂SO₂), an antibody able to simultaneously recognize ABZs with high affinity is in urgent need to develop immunoassay for screening purpose. In this work, an unreported hapten, 5-(propylthio)-1H-benzo[d]imidazol-2-amine, was designed and synthesized, which maximally exposed the characteristic sulfanyl group of ABZ to the animal immune system to induce expected antibody. One monoclonal antibody (Mab) that can simultaneously detect ABZs was obtained with IC₅₀ values of 0.20, 0.26, 0.77, and 10.5 μg/L for ABZ, ABZSO₂, ABZSO, and ABZNH₂SO₂ in ic-ELISA under optimized conditions respectively, which has been never achieved in previous reports. For insight into the recognition profiles of the Mab, we used computational chemistry method to parameterize cross-reactive molecules in aspects of conformation, electrostatic fields, and hydrophobicity, revealing that the hydrophobicity and conformation of characteristic group of molecules might be the key factors that together influence antibody recognition with analytes. Furthermore, the practicability of the developed ic-ELISA was verified by detecting ABZs in spiked milk, beef, and liver samples with recoveries of 60% to 108.8% and coefficient of variation (CV) of 1.0% to 15.9%.

Preparation of highly sensitive monoclonal antibody against α-zearalanol based on the similar antigen determinant structure to zearalanone

In this study, we report a new method to prepare highly sensitive monoclonal antibody against α-zearalanol (ZAL) based on a similar antigen determinant structure. Zearalanone (ZAN), structural analogs of ZAL, was modified by oximation to obtain ZAN-O. ZAN-O was then coupled with bovine serum albumin using 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide (EDC) to synthesise the artificial complete antigen ZAN-O-BSA. ZAN-O-BSA was used to immunise the BALB/c mice. The splenocytes of the immunised mice were fused with myeloma NS0 cells. During the process of cell fusion, ZAL was used as an inhibitor instead of ZAN to screen the hybridoma cell lines that can secrete monoclonal antibodies against ZAL. The sensitivity (half inhibitory concentration, IC50) of the prepared monoclonal antibody was 0.475 ng/ml, the limit of detection (LOD) was 0.050 ng/ml, the linear range of detection was 0.066-3.399 ng/ml, the affinity constant Kaff was 6.18×107 l/mol, the cross-reactivity rate with structural analogues, such as β-zearalanol, α-zearalenol, β-zearalenol, ZAN and zearalenone were 28.07, 13.16, 15.83, 60.28 and 7.95% respectively. The cross-reactivity with other mycotoxin and carrier proteins were all less than 0.05%. The prepared monoclonal antibody can be used to establish a highly sensitive immunoassay for the detection of ZAL.

Data-Driven Real-Time Online Taxi-Hailing Demand Forecasting Based on Machine Learning Method

The development of the intelligent transport system has created conditions for solving the supply–demand imbalance of public transportation services. For example, forecasting the demand for online taxi-hailing could help to rebalance the resource of taxis. In this research, we introduced a method to forecast real-time online taxi-hailing demand. First, we analyze the relation between taxi demand and online taxi-hailing demand. Next, we propose six models containing different information based on backpropagation neural network (BPNN) and extreme gradient boosting (XGB) to forecast online taxi-hailing demand. Finally, we present a real-time online taxi-hailing demand forecasting model considering the projected taxi demand (“PTX”). The results indicate that including more information leads to better prediction performance, and the results show that including the information of projected taxi demand leads to a reduction of MAPE from 0.190 to 0.183 and an RMSE reduction from 23.921 to 21.050, and it increases R2 from 0.845 to 0.853. The analysis indicates the demand regularity of online taxi-hailing and taxi, and the experiment realizes real-time prediction of online taxi-hailing by considering the projected taxi demand. The proposed method can help to schedule online taxi-hailing resources in advance.

Application of quantitative structure-activity relationship analysis on an antibody and alternariol-like compounds interaction study

The antigen-antibody interaction determines the sensitivity and specificity of competitive immunoassay for hapten detection. In this paper, the specificity of a monoclonal antibody against alternariol-like compounds was evaluated through indirect competitive ELISA. The results showed that the antibody had cross-reactivity with 33 compounds with the binding affinity (expressed by IC₅₀ ) ranging from 9.4 ng/mL to 12.0 μg/mL. All the 33 compounds contained a common moiety and similar substituents. To understand how this common moiety and substituents affected the recognition ability of the antibody, a three-dimensional quantitative structure-activity relationship (3D-QSAR) between the antibody and the 33 alternariol-like compounds was constructed using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) methods. The q² values of the CoMFA and CoMSIA models were 0.785 and 0.782, respectively, and the r² values were 0.911 and 0.988, respectively, indicating that the models had good predictive ability. The results of 3D-QSAR showed that the most important factor affecting antibody recognition was the hydrogen bond mainly formed by the hydroxyl group of alternariol, followed by the hydrophobic force mainly formed by the methyl group. This study provides a reference for the design of new hapten and the mechanisms for antibody recognition.

Generic Hapten Synthesis, Broad-Specificity Monoclonal Antibodies Preparation, and Ultrasensitive ELISA for Five Antibacterial Synergists in Chicken and Milk

An antibody with broad specificity and principally depending on hapten structure and size is a key reagent for developing a class-selective immunoassay. In the present study, three new generic haptens of antibacterial synergists (ASGs) were proposed using trimethoprim as the starting molecule. These haptens contained carboxyl groups on the meta position of trimethoxybenzene for conjugating to protein, while, the common moiety of ASGs, i.e., diaminopyrimidine, was intentionally and maximally exposed to the immune system in animals in order to induce antibodies with broad specificity against ASGs. Five monoclonal antibodies (mAbs) were finally obtained, and 5C4 from the hapten with a short spacer arm, named Hapten A, showed not only uniform broad specificity but also high affinity to all five ASGs. We further determined the possible recognition mechanism of mAbs in terms of conformational and electronic aspects. An indirect competitive ELISA (icELISA)-based 5C4 was established and exhibited IC₅₀ values of 0.067-0.139 μg L^-1 with cross-reactivity of 48.2%-418.7% for the five ASGs in buffer under optimal conditions. The calculated limits of detection of the icELISA for chicken and milk were 0.06-0.8 μg kg^-1 and 0.05-0.6 μg L^-1, respectively. The recoveries in spiked chicken and milk samples were 75.2%-101.4% with a coefficient of variation less than 14.3%. In summary, we have developed, for the first time, a rapid and reliable icELISA for ASGs with significantly improved sensitivity and class selectivity.

Substructure-activity relationship studies on antibody recognition for phenylurea compounds using competitive immunoassay and computational chemistry

Based on the structural features of fluometuron, an immunizing hapten was synthesized and conjugated to bovine serum albumin as an immunogen to prepare a polyclonal antibody. However, the resultant antibody indicated cross-reactivity with 6 structurally similar phenylurea herbicides, with binding activities (expressed by IC₅₀ values) ranging from 1.67 µg/L to 42.71 µg/L. All 6 phenylurea herbicides contain a common moiety and three different substitutes. To understand how these three different chemical groups affect the antibody-phenylurea recognition activity, quantum chemistry, using density function theory (DFT) at the B3LYP/6-311++ G(d,p) level of theory, was employed to optimize all phenylurea structures, followed by determination of the 3D conformations of these molecules, pharmacophore analysis, and molecular electrostatic potential (ESP) analysis. The molecular modeling results confirmed that the geometry configuration, pharmacophore features and electron distribution in the substituents were related to the antibody binding activity. Spearman correlation analysis further elucidated that the geometrical and electrostatic properties on the van der Waals (vdW) surface of the substituents played a critical role in the antibody-phenylurea recognition process.

Fluorescence Polarization Immunoassay Based on a New Monoclonal Antibody for the Detection of the Zearalenone Class of Mycotoxins in Maize

To develop a sensitive fluorescence polarization immunoassay (FPIA) for screening the zearalenone class of mycotoxins in maize, two new monoclonal antibodies with uniform affinity to the zearalenone class and four fluorescein-labeled tracers were prepared. After careful selection of appropriate tracer-antibody pairs in terms of sensitivity and specificity, a FPIA that could simultaneously detect the zearalenone class with similar sensitivity was developed. Under optimum conditions, the half maximal inhibitory concentrations of the FPIA in buffer were 1.89, 1.97, 2.43, 1.99, 2.27, and 2.44 μg/L for zearalenone, α-zearalenol, β-zearalenol, α-zearalanol, β-zearalanol, and zearalanone, respectively. The limit of detection of FPIA for the zearalenone class was around 12 μg/kg in maize, and the recoveries ranged from 84.6 to 113.8%, with coefficients of variation below 15.3% in spiked samples. Finally, the FPIA was applied for screening naturally contaminated maize samples, and the results indicated a good correlation with that of high-performance liquid chromatography-tandem mass spectrometry.

Crystal Structure of the Fab Fragment of an Anti-ofloxacin Antibody and Exploration of Its Specific Binding

The limited knowledge on the mechanism of interactions between small contaminants and the corresponding antibodies greatly inhibits the development of enzyme-linked immunosorbent assay methods. In this study, the crystal structure of a Fab fragment specific for ofloxacin was obtained. On the basis of the crystal characteristics, the modeling of the interactions between ofloxacin and the Fab revealed that TYR31 and HIS99 of the heavy chain and MET20 and GLN79 of the light chain formed a hydrophobic region and that SER52 and ALA97 of the heavy chain and TYR35 of the light chain formed a salt bridge and two hydrogen bonds for specific binding. The key roles of SER52 and ALA97 were further confirmed by site-directed mutation. A specificity analysis using 14 ofloxacin analogues indicates that the length of the bond formed between the piperazine ring and the antibody plays key roles in specific recognition. This work helps to clarify the mechanisms through which antibodies recognize small molecules and improve immune detection methods.

Molecular modeling application on hapten epitope prediction: an enantioselective immunoassay for ofloxacin optical isomers

To deepen our understanding of the physiochemical principles that govern hapten-antibody recognition, ofloxacin enantiomers were chosen as a model for epitope prediction of small molecules. In this study, two monoclonal antibodies (mAbs) mAb-WR1 and mAb-MS1 were raised against R-ofloxacin and S-ofloxacin, respectively. The enantioselective mAbs have a high sensitivity and specificity, and the enantioselectivity is not affected by heterologous coating format reactions. The epitopes of the ofloxacin isomers were predicted using the hologram quantitative structure-activity relationship (HQSAR) and comparative molecular field analysis (CoMFA) approaches. The results consistently show that the epitope of the chiral hapten should be primarily composed of the oxazine ring and the piperazinyl ring and mAbs recognize the hapten from the side of this moiety. The enantioselectivity of mAbs is most likely due to the steric hindrance caused by the stereogenic center of the epitope. Modeling of chiral hapten-protein mimics reveals that ofloxacin isomers remain upright on the surface of the carrier protein. Suggestions to improve the enantioselectivity of antibodies against ofloxacin isomers were also proposed. This study provided a simple, efficient, and general method for predicting the epitopes of small molecules via molecular modeling. The epitope predictions for small molecules may create a theoretical guide for hapten design.

Development of an ultrasensitive immunoassay for detecting tartrazine

We have developed an ultrasensitive indirect competitive enzyme-linked immunosorbent assay for the determination of tartrazine. Two carboxylated analogues of tartrazine with different spacer lengths, and one derivative from commercial tartrazine after a little chemical modification, were synthesized as haptens in order to produce antibodies specific to tartrazine. The effect of sulfonic acid groups on the hapten structure of tartrazine was also studied carefully for the first time. A most specific monoclonal antibody against tartrazine was created and exhibited an IC50 value of 0.105 ng/mL and a limit of detection of 0.014 ng/mL, with no cross-reactivity to other structurally-related pigments. The established immunoassay was applied to the determination of tartrazine in fortified samples of orange juice and in real positive samples of carbonated beverages.

Altered of apoptotic markers of both extrinsic and intrinsic pathways induced by hepatitis C virus infection in peripheral blood mononuclear cells

Background

Chronic hepatitis C (CHC) has emerged as a leading cause of cirrhosis in the U.S. and across the world. To understand the role of apoptotic pathways in hepatitis C virus (HCV) infection, we studied the mRNA and protein expression patterns of apoptosis-related genes in peripheral blood mononuclear cells (PBMC) obtained from patients with HCV infection.

Methods

The present study included 50 subjects which plasma samples were positive for HCV, but negative for human immunodeficiency virus (HIV) or hepatitis B virus (HBV). These cases were divided into four groups according to METAVIR, a score-based analysis which helps to interpret a liver biopsy according to the degree of inflammation and fibrosis. mRNA expression of the studied genes were analyzed by reverse transcription of quantitative polymerase chain reaction (RT-qPCR) and protein levels, analyzed by ELISA, was also conducted. HCV genotyping was also determined.

Results

HCV infection increased mRNA expression and protein synthesis of caspase 8 in group 1 by 3 fold and 4 fold, respectively (p < 0.05). In group 4 HCV infection increased mRNA expression and protein synthesis of caspase 9 by 2 fold and 1,5 fold, respectively (p < 0.05). Also, caspase 3 mRNA expression and protein synthesis had level augumented by HCV infection in group 1 by 4 fold and 5 fold, respectively, and in group 4 by 6 fold and 7 fold, respectively (p < 0.05).

Conclusions

HCV induces alteration at both genomic and protein levels of apoptosis markers involved with extrinsic and intrinsic pathways.