Production, characterization, and cross-reactivity studies of monoclonal antibodies against the coccidiostat nicarbazin

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.

Design, Synthesis, and Characterization of Tracers and Development of a Fluorescence Polarization Immunoassay for Rapid Screening of 4,4'-Dinitrocarbanilide in Chicken Muscle

The compound, 4,4′-dinitrocarbanilide (DNC), is the marker residue of concern in edible tissues of broilers fed with diets containing anticoccidial nicarbazin (NIC). In this study, 25 fluorescein-labeled DNC derivatives (tracers) are synthesized and characterized to develop a rapid fluorescence polarization immunoassay (FPIA) for the detection of DNC in chickens using DNC monoclonal antibodies (mAbs). The effect of the tracer structure on the sensitivity of the FPIA is investigated. Our results show that after optimization, the half maximal inhibitory concentrations (IC₅₀) and limit of detection (LOD) of the FPIA in the buffer are 28.3 and 5.7 ng mL⁻¹, respectively. No significant cross-reactivity (CR < 0.89%) with 15 DNC analogues is observed. The developed FPIA is validated for DNC detection in spiked chicken homogenates, and recoveries ranged from 74.2 to 85.8%, with coefficients of variation <8.6%. Moreover, the total time needed for the detection procedure of the FPIA, including sample pretreatment, is <40 min, which has not been achieved in any other immunoassays for DNC from literature. Our results demonstrate that the FPIA developed here is a simple, sensitive, specific, and reproducible screening method for DNC residues in chickens.

Current research, regulation, risk, analytical methods and monitoring results for nicarbazin in chicken meat: A perspective review

This review presents up-to-date information about current research on nicarbazin, one of the most used anticoccidials in poultry production. The focus is to elucidate regulation concerning nicarbazin, limits for its residues in food, how maximum residue limits in different countries are calculated regarding edible chicken tissues and the possible implications in human health. Analytical methods to extract and quantify this residue, expressed as dinitrocarbanilide (DNC) are presented and discussed, including qualitative screening and quantitative/confirmatory analytical methods. Monitoring results and occurrence of DNC residues in chicken meat are discussed. Additionally, the causes of eventual chicken meat contamination and possible solutions to reduce or eliminate DNC residue in tissues are also presented. The paper concludes with perspectives, the current state of DNC residue analysis and suggestions for future research, especially considering the gap in the study of residue recycling effect due to continuous chicken litter use.

Establishment of a sandwich enzyme-linked immunosorbent assay for specific detection of Bacillus thuringiensis (Bt) Cry1Ab toxin utilizing a monoclonal antibody produced with a novel hapten designed with molecular model

Cry1Ab toxin is commonly expressed in genetically modified crops in order to control chewing pests. At present, the detection method with enzyme-linked immunosorbent assay (ELISA) based on monoclonal antibody cannot specifically detect Cry1Ab toxin for Cry1Ab's amino acid sequence and spatial structure are highly similar to Cry1Ac toxin. In this study, based on molecular design, a novel hapten polypeptide was synthesized and conjugated to keyhole limpet hemocyanin (KLH). Then, through animal immunization with this antigen, a monoclonal antibody named 2C12, showing high affinity to Cry1Ab and having no cross reaction with Cry1Ac, was produced. The equilibrium dissociation constant (K _D) value of Cry1Ab toxin with MAb 2C12 was 1.947 × 10^-8 M. Based on this specific monoclonal antibody, a sandwich enzyme-linked immunosorbent assay (DAS-ELISA) was developed for the specific determination of Cry1Ab toxin and the LOD and LOQ values were determined as 0.47 ± 0.11 and 2.43 ± 0.19 ng mL^-1, respectively. The average recoveries of Cry1Ab from spiked rice leaf and rice flour samples ranged from 75 to 115%, with coefficient of variation (CV) less than 8.6% within the quantitation range (2.5-100 ng mL^-1), showing good accuracy for the quantitative detection of Cry1Ab toxin in agricultural samples. In conclusion, this study provides a new approach for the production of high specific antibody and the newly developed DAS-ELISA is a useful method for Cry1Ab monitoring in agriculture products. Graphical Abstract Establishment of a DAS-ELISA for the specific detecting of Bacillus thuringiensis (Bt) Cry1Ab toxin.

Synthesis of hapten and development of immunoassay based on monoclonal antibody for the detection of Dufulin in agricultural samples

An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was developed for the quantitative detection of the antiviral agent against tobacco mosaic virus (TMV). Hapten 6-[2-((methyllbenzothiazol-2-yl)-1-(2-ethoxy)-O, O-diethyl-α-aminophosphonate)acetamido)] hexanoic acid (DHS) was prepared from commercial chemicals and incorporated into the spacer arm through a carbon-carbon single bond. The prepared hapten was then coupled to carrier proteins keyhole limpet hemocyanin (KLH) to be used as an immunogen for monoclonal antibody (mAb) production together with ELISA development. This assay was further optimized by the assessment of the dependence of assay parameters on organic solvents, pH, and ionic strength. The IC50 values of the optimized assay for Dufulin and the calculated limit of detection in phosphate-buffered saline (PBS) were 9.6 ± 0.59 and 0.3 ± 0.05 ng/mL, respectively. Using the optimized assays Dufulin residues in soil and tobacco samples were determined with recovery values ranging from 81.5 to 95.3%, intra-assay variation ranging from 2.88 to 6.10%, and interassay variation ranging from 6.11 to 9.42%.

Computer-aided molecular modeling study on antibody recognition of small molecules: an immunoassay for triazine herbicides

Most immunoassays for determination of small molecules are still designed on the basis of the "trial and error" method, due to the lack of understanding of antibody recognition. In the present study, we developed a heterologous indirect competitive enzyme-linked immunosorbent assay for determination of triazine herbicides, with limits of detection for 11 triazines ranging from 0.05 to 29.4 μg/L. Mechanisms of the antigen-antibody interaction were studied by computer-aided molecular modeling (CAMM)-based quantitative structure-activity relationship analyses. Co-effects of the analytes' substructural hydrophobic, electrostatic, and steric fields on antibody recognition were further revealed. Hydrophobicity of the antigens was demonstrated to have the most important impact. Even less exposed substituents provided hydrophobic force to the antigen-antibody interaction. Dislocated orientation of analyte functional groups could lead to steric hindrance and hydrophobic misleading of antibody recognition. This may happen even when the antigens contained the same substituent as the hapten. Frontier orbital energies also affect the reaction significantly. This study highlights of the power of CAMM-based analyses, providing insights into antibody recognition of small molecules.

Immunoassay for phenylurea herbicides: application of molecular modeling and quantitative structure-activity relationship analysis on an antigen-antibody interaction study

An indirect competitive enzyme-linked immunosorbent assay (icELISA) for 12 phenylurea herbicides (PUHs) was established with the half-maximum inhibition concentration (IC(50)) of 1.7-920.7 μg L(-1). A method of computer-aided molecular modeling was established in quantitative structure-activity relationship (QSAR) studies to obtain a deeper insight into the PUHs' antibody interactions on how and which molecular properties of the analytes quantitatively affect the antibody recognition. A two-dimensional (2D)-QSAR model based on the Hansch equation and a hologram QSAR (HQSAR) model were constructed, and both showed highly predictive abilities with cross-validation q(2) values of 0.820 and 0.752, respectively. It was revealed that the most important impact factor of the antibody recognition was the PUHs' hydrophobicity (log P), which provided a quadratic correlation to the antibody recognition. Hapten-carrier linking groups were less exposed to antibodies during immunization; thus, groups of the analytes in the same position were generally considered to be less contributive to antibody recognition during immunoassay. But the results of substructure-level analysis showed that these groups played an important role in the antigen-antibody interaction. In addition, the frontier-orbital energy parameter E(LUMO) was also demonstrated as a related determinant for this reaction. In short, the result demonstrated that the hydrophobicity and the lowest unoccupied molecular orbital energy (E(LUMO)) of PUH molecules were mainly responsible for antibody recognition.

Isolation and affinity maturation of hapten-specific antibodies

More and more recombinant antibodies specific for haptens such as drugs of abuse, dyes and pesticides are being isolated from antibody libraries. Thereby isolated antibodies tend to possess lower affinity than their parental, full-size counterparts, and therefore the isolation techniques must be optimized or the antibody genes must be affinity-matured in order to reach high affinities and specificities required for practical applications. Several strategies have been explored to obtain high-affinity recombinant antibodies from antibody libraries: At the selection level, biopanning optimization can be performed through elution with free hapten, analogue pre-incubation and subtractive panning. At the mutagenesis level, techniques such as random mutagenesis, bacterial mutator strains passaging, site-directed mutagenesis, mutational hotspots targeting, parsimonious mutagenesis, antibody shuffling (chain, DNA and staggered extension process) have been used with various degrees of success to affinity mature or modify hapten-specific antibodies. These techniques are reviewed, illustrated and compared.

Development of a monoclonal antibody-based broad-specificity ELISA for fluoroquinolone antibiotics in foods and molecular modeling studies of cross-reactive compounds

A competitive indirect enzyme-linked immunosorbent assay (ciELISA) using monoclonal antibodies (Mabs) having broad specificity for fluoroquinolone (FQ) antibiotics is described. Four FQs, ciprofloxacin (CIP), enrofloxacin (ENR), norfloxacin (NOR), and ofloxacin (OFL), were conjugated to bovine serum albumin for immunogens and to ovalbumin for coating antigens. A Mab C4A9H1 raised against the CIP hapten exhibited high cross-reactivity (35-100%) with 12 of 14 FQs and detected these FQs in a ciELISA below their maximum residue levels (MRLs) with good sensitivity at 50% binding inhibition (IC50). The quantitative structure-activity relationship (QSAR) between Mab C4A9H1 and various FQs by comparative molecular field analysis (CoMFA) showed a high predictive ability with a cross-validation q2 value of 0.866. Using a simple purification process and the broad-specificity ciELISA adapted for analysis of FQs in chicken muscle, chicken liver, honey, shrimp, and whole egg samples demonstrated recoveries of 60-93% for CIP, ENR, NOR, OFL, flumequine, and danofloxacin.

Screening for the coccidiostats halofuginone and nicarbazin in egg and chicken muscle: development of an ELISA

Nicarbazin and halofuginone have been widely used as coccidiostats for the prevention and treatment of coccidiosis in poultry. It has been shown that accidental cross-contamination of feed can lead to residues of these compounds in eggs and/or muscle. This paper describes a direct competitive assay for detecting halofuginone and nicarbazin, developed as qualitative screening assay. In an optimized competitive ELISA, antibodies showed 50% binding inhibition at approximately 0.08 ng ml(-1) for halofuginone and 2.5 ng ml(-1) for dinitrocarbanilide (marker residue for nicarbazin). Extraction from the matrix was carried out with acetonitrile followed by a wash with hexane. The assay's detection capability (CCbeta) for halofuginone was < 0.5 microg kg(-1) in egg and < 1 microg kg(-1) in muscle. For dinitrocarbanilide, the CCbeta was estimated at < 3 microg kg(-1) in egg and < 10 microg kg(-1) in chicken muscle.

Preparation of anti-tetracycline antibodies and development of an indirect heterologous competitive enzyme-linked immunosorbent assay to detect residues of tetracycline in milk

Tetracycline (TC) is a broad-spectrum antibiotic used increasingly in animal husbandry to treat diseases or to promote growth as feed additives. To avoid using labor-intensive instrumental methods to detect residues of TC in food and food products, a simple and convenient indirect heterologous competitive enzyme-linked immunosorbent assay (ELISA) method for TC was developed using polyclonal antibody prepared in this study. Three new immunogens, TC-o-tolidine-bovine serum albumin (BSA), TC- 4-aminobenzoic acid-cationized BSA (cBSA), and TC-1,1'-carbonyldiimidazole-cBSA, were synthesized in this research to develop anti-TC antibodies. All antibodies raised in rabbits and coating antigens synthesized were screened and characterized using homologous and heterologous ELISA formats to select the best combination. An optimized ELISA gave an IC50 value of 3.92 mug/mL toward TC in PBS buffer. The specificity of the assay was studied by measuring cross-reactivity of the antibody with the structurally closely related compounds of chlortetracycline (112%) and oxytetracycline (<2%). The recovery rates from the TC-fortified raw milk samples were in the range of 74-116%, while the intra- and interassay coefficients of variation were <14.5 and <25.0, respectively.

Production and characterization of monoclonal antibodies against the antibiotic tilmicosin

Monoclonal antibodies (Mabs) were developed that specifically bind tilmicosin. Keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) conjugates were used for the immunogen and plate coating antigen, respectively. The conjugates were synthesized by different methods, resulting in different linkages. Six hybridoma cell lines were isolated that produced Mabs that competed with tilmicosin, and have IgG1 isotype. The Til-1 and Til-5 Mabs had IC50 values for tilmicosin of 9.6 and 6.4 ng/well (48 and 32 ng/mL), respectively, and limits of detection at IC20 of 1.84 and 0.89 ng/well (9.2 and 4.45 ng/mL), respectively. The Mabs demonstrated high cross-reactivity to the macrolides containing 3,5-dimethylpiperidine at C20 and the amino sugar at C5. No cross-reactivity was observed for tylosin and other macrolides that did not contain 3,5-dimethylpiperidine. A competitive enzyme-linked immunosorbent assay (ELISA) was developed for the antibiotic tilmicosin by use of the developed Mabs. These Mabs may be excellent candidates for the determination and immunolocalization of tilmicosin.

The production and characterisation of dinitrocarbanilide antibodies raised using antigen mimics

Polyclonal antibodies were produced to detect the coccidiostat nicarbazin. Due to structural constraints of the active component of nicarbazin, dinitrocarbanilide (DNC), three different compounds that shared a common substructure with DNC were used as antigen mimics. The compounds (N-succinyl-L-alanyl-L-alanyl-L-alanine 4-nitroanilide (SAN), L-glutamic acid gamma-(p-nitroanilide) (GAN) and p-nitrosuccinanilic acid (NSA)) were conjugated to a carrier protein and used in the immunisation of rabbits. Five different polyclonal sera were produced and consequently characterised. The antibodies exhibited an IC(50) range of 2.3-7.6 ng/ml using a competitive ELISA procedure. Serum from one rabbit, R555, exhibited an IC(50) of 2.9 ng/ml for DNC and cross-reactivity studies showed that this serum was specific for DNC and did not cross-react with other coccidiostats such as halofuginone, toltrazuril or ronidazole.