Production of a high-affinity monoclonal antibody specific for 7-(benzo[alpha]pyren-6-yl) guanine and its application in a competitive enzyme-linked immunosorbent assay

Purification and characterization of mouse single-chain antibody against polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAH) such as benzo[a]pyren mainly induce lung cancer in humans. We characterized the mouse single chain antibody against benzo[a]pyren (pSh). pSh was expressed and purified as cellulose binding domain fusion (pSh-CBD). The pSh-CBD bound five different PAH with high affinity. The 18 amino acid linker connected pSh-CBD heavy and light chains provided correct protein folding. The KDs for pSh-CBD and polycyclic aromatic hydrocarbons were similar to KDs for monoclonal antibody, approximately 10(-8). Separately heavy and light chains of pSh-CBD did not interact with benzo[a]pyren. Previously defined eleven pSh-CBD aa involved to benzo[a]pyren binding were confirmed by mutagenesis.

Selective immunoclean-up followed by liquid chromatography for the monitoring of a biomarker of exposure to polycyclic aromatic hydrocarbons in urine at the ngl−1 level

A selective clean-up procedure using an immunosorbent (IS) was developed for the trace-level determination, in water and urine samples, of 3-benzo(a)pyrene-glucuronide (3-BP-G), a biomarker of exposure to carcinogenic polycyclic aromatic hydrocarbons (PAHs). First, three sorbents used for the immobilization of antibodies were evaluated for their ability to limit the risk of non-specific interactions and to provide a high bonding density. The best sorbent, i.e. sepharose, was used for the immobilization of two different monoclonal antibodies. The most specific antibody for 3-BP-G was applied to the selective extraction from urine providing a clean extract, an easy and reliable quantification by comparison with a classical SPE process. The sensitivity of the fluorescence associated with the selectivity of the IS provides a limit of detection up to 1.2 ng l(-1) in urine for 3-BP-G.

Development of a highly sensitive monoclonal antibody based ELISA for detection of benzo[a]pyrene in potable water

In Europe, a limit value of 10 ng L(-1) was set by the European Commission for benzo[a]pyrene (B[a]P) in water intended for human consumption (Council Directive 98/83/EC) and, therefore, sensitive and reliable methods are needed to evaluate its presence. We report here on the development of a highly sensitive indirect competitive ELISA for the detection of B[a]P in potable water. Fourteen monoclonal antibodies were generated in mice using novel B[a]P derivatives. The immunoassay with the least interference and the best sensitivity was optimized and characterized. As co-solvent, ten percent methanol (v/v) was determined as the optimum concentration for B[a]P solubilization for use with the developed ELISA. With the purified antibody (clone 22F12) the average IC50 for B[a]P and corresponding detection limit at a signal:noise (S/N) ratio of 3 was 65 ng L(-1) and 24 ng L(-1), respectively. From the 16 EPA-designated PAHs, only chrysene, indeno[1,2,3-cd]pyrene, and benzo[b]fluoranthene showed a cross-reactivity (CR) higher than 20%. No CR was observed for two- and three-ringed aromatics as well as dibenz[ah]anthracene and benzo[ghi]perylene. The effect of pH value (range 6.5-9.5), ionic strength (specific electric conductivity 1 microS cm(-1)-2.5 mS cm(-1)), and inorganic ions (sodium, copper, iron, aluminium, manganese, chloride, sulfate, nitrate, and nitrite at maximum permissible levels according to the Council Directive) on both signal and sensitivity of the ELISA was studied. No significant influence of these parameters on the ELISA competition curve was found. We suggest that the optimized ELISA can be used to monitor potable water samples without previous extraction from the samples. The assay should facilitate the cleanup of B[a]P contaminated sites where B[a]P levels fall close to the limit value of the new drinking water directive.

Probing the Interaction of Benzo[a]pyrene Adducts and Metabolites with Monoclonal Antibodies Using Fluorescence Line-Narrowing Spectroscopy

A new approach for studying antibody-antigen interactions of DNA adducts and metabolites of polycyclic aromatic hydrocarbons (PAHs) is demonstrated in which fluorescence line-narrowing spectroscopy (FLNS) is used. It is based on the fact that in an FLN spectrum the relative intensities of the line-narrowed bands (that correspond to the excited-state vibrations) are, in general, strongly dependent on the local environment of the fluorophore. Information on the nature of the interactions can be obtained by comparing the FLN spectra of the antigen-antibody complexes to the spectra of the antigen in different types of solvents (H-bonding, aprotic, and pi-electron-containing solvent molecules) recorded under the same conditions. The antigens used were the DNA adduct 7-(benzo[a]pyren-6-yl)guanine (BP-6-N7Gua) and the metabolite (+)-trans-anti-7,8,9,10-benzo[a]pyrenetetrol (BP-tetrol) of benzo[a]pyrene; two monoclonal antibodies (MAbs) have been developed to selectively bind these compounds. It is shown that, for BP-tetrol, H-bonding solvents have a pronounced effect on the FLN spectra. The presence of pi electrons in the solvent molecules results in relatively small but still significant changes in the spectra. When BP-tetrol is bound to its MAb, however, neither of these effects is observed; its spectrum is very similar to the one obtained with an aprotic solvent, methylcyclohexane. Therefore, we can conclude that this MAb has an internal binding site in which the interaction with BP-tetrol is of a hydrophobic character. For BP-6-N7Gua, however, there is a strong effect of the presence of pi electrons in the solvent molecules. The FLN spectrum of this antigen bound to its MAb is very similar to its spectrum in acetone, indicating that pi-pi interactions play an important role in the binding.

Highly sensitive and selective surface plasmon resonance sensor for detection of sub-ppb levels of benzo[a]pyrene by indirect competitive immunoreaction method

A surface plasmon resonance (SPR)-immunosensor for detection of benzo[a]pyrene (BaP) is developed by using a model BaP-hapten compound, BaP-bovine serum albumin conjugate (BaP-BSA), and an anti-BaP-BSA monoclonal antibody. BaP-BSA conjugate is immobilized on a gold thin-film sensor chip by means of simple physical adsorption. The number of BaP-hapten units in BaP-BSA conjugate is estimated to be 28 from the difference in molecular weight (MW) between BaP-BSA conjugate and BSA based on the results of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) measurement. Anti-BaP-BSA antibody on contact with the BaP-BSA conjugate immobilized sensor chip causes an increase in the incident angle of the sensor chip. Binding of anti-BaP-BSA antibody with surface-immobilized BaP-BSA conjugate is inhibited by the presence of BaP in analyte solution, because of the inhibition effect of BaP. The SPR immunosensor for BaP functioning with the indirect competitive immunoreaction of anti-BaP-BSA antibody between the analyte (BaP) in testing solution and the BaP-BSA conjugate immobilized on the sensor chip provides a rapid determination (response time: ca. 15 min) of BaP in the concentration range of 0.01-1000 ppb. The antibody anchored to the sensor chip by antigen-antibody binding is removed on treatment with a pepsin solution (pH 2.0) for few minutes. The SPR sensor chip is found to be reusable for more than 20 times with a little decrease (<7%) in the sensor response. Detection of BaP by direct competitive immunoreactions is also carried out by enzyme-linked immunosorbent assay (ELISA). The concentration of BaP could be determined as low as 0.01 ppb and 2 ppb using the SPR sensor and the ELISA method, respectively. The SPR sensor is found to detect BaP selectively in the presence of 2-hydroxybiphenyl (HBP); the incident angle shift of the SPR sensor for BaP is found to be same irrespective to the presence or the absence of a same concentration (as much as 30 ppb) of HBP together.

Monoclonal antibody--gold biosensor chips for detection of depurinating carcinogen--DNA adducts by fluorescence line-narrowing spectroscopy

A new direct readout methodology for detection and quantitation of fluorescent carcinogen-DNA adducts is described. It combines the binding specificity of an immobilized monoclonal antibody (MAb) with high-resolution, low-temperature fluorescence spectroscopy. The MAb, which is covalently bound to a gold surface via a chemisorbed disulfide coupling agent, binds the adduct of interest in an aqueous sample. Laser-induced fluorescence under nonline narrowing (FNLN) and line-narrowing (FLN) conditions was used to detect (benzo[a]pyren-6-yl)guanine (BP-6-N7Gua) bound to immobilized MAb. At room temperature, the BP-6-N7Gua fluorescence was not detected, most likely because of quenching by the gold surface and/or efficient dynamical quenching. However, fluorescence was observed at room temperature when the surface was covered with a thin layer of glycerol, and possible reasons for the fluorescence enhancement are considered. Lowering of the temperature to 77 K led to nearly an order of magnitude increase in fluorescence intensity. Highly structured FLN spectra obtained at 4.2 K allowed for definitive adduct identification. The potential of this methodology for risk assessments of individuals exposed to polycyclic aromatic hydrocarbons is discussed.

What is the significance of increases in background levels of carcinogen-derived protein and DNA adducts? Some considerations for incremental risk assessment

Improvements in analytical methodology have led to the detection and quantification of 'background' levels of a number of DNA and protein adducts. Many of these adducts are derived from 'low molecular weight' reactive species which may be generated during normal physiological processes, metabolic pathways or inflammatory processes. The adducts have been detected using gas chromatography-mass spectrometry, HPLC in combination with various detection systems, 32P-postlabelling and immunoassay methods. The reliability and accuracy of many widely used methods for adduct measurements are discussed with reference to several examples where human data is available, namely 4-aminobiphenyl, malondialdehyde, methylating agents, ethylene oxide and hydroxyl radical damage. The accurate and specific quantitation of 'background' levels of damage is essential if reliable estimates of increases in risk associated with incremental increases in exposure to exogenous agents are to be calculated. In experimental studies using low dose exposures to carcinogens, such as N-nitrosodimethylamine, adduct levels in liver correlate closely with tumour incidence. In all likelihood, such relationships need to be established for each exposure and, in order to be relevant to human risk assessment, need to take into account factors such as DNA repair and mutagenic efficiency. Finally, in order to estimate the increase in cancer attributable to a given level of external exposure, it is clearly important to establish background levels of corresponding DNA damage so that the scale of the incremental increase can be calculated.

A method for direct cross-linking of DNA bases containing aromatic amino groups to proteins

A one step method to cross-link DNA bases containing aromatic amino groups directly to proteins was developed. No chemical modification of the base is required prior to conjugation, which is performed at neutral pH. Work focused on 8-oxoguanine and the carrier protein, bovine serum albumin. Conjugates were stable after sodium dodecyl sulfate (SDS)-induced protein denaturation and were characterized by UV spectroscopy, enzyme linked immunosorbent assay (ELISA), SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot analyses. This method is a viable alternative to existing procedures for generating DNA base-protein conjugates for antibody characterization and affinity purification.