Preparation of Monoclonal Antibodies Specifically Reacting with the Trichothecene Mycotoxins Nivalenol and 15-Acetylnivalenol via the Introduction of a Linker Molecule into Its C-15 Position

Nivalenol (NIV) is a trichothecene mycotoxin that is more toxic than deoxynivalenol. It accumulates in grains due to infection with Fusarium species, which are the causative agents of scab or Fusarium head blight. An immunoassay, which is a rapid and easy analytical method, is necessary for monitoring NIV in grains. However, a specific antibody against NIV has not been prepared previously. To establish an immunoassay, we prepared NIV, introduced a linker, and generated antibodies against it. NIV was prepared from a culture of Fusarium kyushuense obtained from pressed barley through chromatographic procedures with synthetic adsorbents and silica gel. NIV was reacted with glutaric anhydride, and the reaction was stopped before mono-hemiglutaryl-NIV was changed to di-hemiglutaryl-NIV. 15-O-Hemiglutaryl-NIV was isolated via preparative HPLC and bound to keyhole limpet hemocyanin (KLH) using the active ester method. Two different monoclonal antibodies were prepared by immunizing mice with the NIV-KLH conjugate. The 50% inhibitory concentration values were 36 and 37 ng/mL. These antibodies also showed high reactivity in a direct competitive enzyme-linked immunosorbent assay and specifically reacted with NIV and 15-acetyl-NIV but not with deoxynivalenol and 4-acetyl-NIV.

Risks to human and animal health related to the presence of deoxynivalenol and its acetylated and modified forms in food and feed

Deoxynivalenol (DON) is a mycotoxin primarily produced by Fusarium fungi, occurring predominantly in cereal grains. Following the request of the European Commission, the CONTAM Panel assessed the risk to animal and human health related to DON, 3-acetyl-DON (3-Ac-DON), 15-acetyl-DON (15-Ac-DON) and DON-3-glucoside in food and feed. A total of 27,537, 13,892, 7,270 and 2,266 analytical data for DON, 3-Ac-DON, 15-Ac-DON and DON-3-glucoside, respectively, in food, feed and unprocessed grains collected from 2007 to 2014 were used. For human exposure, grains and grain-based products were main sources, whereas in farm and companion animals, cereal grains, cereal by-products and forage maize contributed most. DON is rapidly absorbed, distributed, and excreted. Since 3-Ac-DON and 15-Ac-DON are largely deacetylated and DON-3-glucoside cleaved in the intestines the same toxic effects as DON can be expected. The TDI of 1 μg/kg bw per day, that was established for DON based on reduced body weight gain in mice, was therefore used as a group-TDI for the sum of DON, 3-Ac-DON, 15-Ac-DON and DON-3-glucoside. In order to assess acute human health risk, epidemiological data from mycotoxicoses were assessed and a group-ARfD of 8 μg/kg bw per eating occasion was calculated. Estimates of acute dietary exposures were below this dose and did not raise a health concern in humans. The estimated mean chronic dietary exposure was above the group-TDI in infants, toddlers and other children, and at high exposure also in adolescents and adults, indicating a potential health concern. Based on estimated mean dietary concentrations in ruminants, poultry, rabbits, dogs and cats, most farmed fish species and horses, adverse effects are not expected. At the high dietary concentrations, there is a potential risk for chronic adverse effects in pigs and fish and for acute adverse effects in cats and farmed mink.

Enzyme-Linked Immunosorbent Assay (ELISA)

Food allergy is a public health concern especially after recognizing its constantly increased prevalence and severity. Despite careful reading of food ingredient statements, food allergic individuals may experience reactions caused by "hidden", "masked", or "contaminated" proteins that are known major allergens. Many techniques have been developed to detect even small traces of food allergens, for clinical or laboratory purposes. Enzyme-linked immunosorbent assay (ELISA) is one of the best validated and most routinely used immunoassay in allergy research, in allergy diagnosis in allergy-related quality control in various industries. Although as a technique it has been implemented for the last 45 years, the evolution in biochemistry allowed the development of ultrasensitive ELISA variations that are capable of measuring quantities in the scale of picograms, rendering ELISA attractive, robust, and very famous.

Immunoaffinity clean-up of mycotoxins with organic solvent-free elution

A novel immunoaffinity (IA) clean-up procedure for the isolation of mycotoxins from maize extracts is described. Commonly, mycotoxins are eluted with organic solvents from IA columns after isolation. The new procedure uses water at 70 °C as alternative. The resulting eluate is suitable for direct and complete injection onto a reversed-phase liquid-chromatography column. Evaporation, reconstitution or dilution are not required. The procedure has been tested for a variety of mycotoxins, including deoxynivalenol (DON) zearalenone, T-2 and HT-2 toxins, aflatoxins and ochratoxin A in an array of different matrices. The example of DON in maize is discussed in more detail and evaluated for repeatability (5%, n=10) and recovery (95%, n=10).

Comparison of monoclonal antibody performance characteristics for the detection of two representatives of A- and B-trichothecenes: T-2 toxin and deoxynivalenol

Mycotoxins are secondary metabolites produced by fungi belonging mainly to the Aspergillus, Penicillium and Fusarium genera. They represent a relevant source of danger to human and animal health causing food- and feedborne intoxication. One group, produced by Fusarium spp., are the trichothecenes, of which T-2 toxin belongs to the type-A trichothecenes and deoxynivalenol to the type-B trichothecenes. As these mycotoxins are ubiquitous, the testing of products is required to keep our food and feed safe. For this purpose, sensitive and reliable tests are needed to detect contaminations. One detection possibility is an immunoanalytical based test which needs antibodies as reagents. Cell culture facilities allow cell line selection and production of monoclonal antibodies for further immunological test development. Especially for mycotoxins antibody development for further use in immunoassays is a crucial task. T-2 toxin and deoxynivalenol specific monoclonal antibodies were developed and further characterised to test stability and solvent resistance properties. Especially cross-reactivities were determined to related mycotoxins also belonging to the trichothecene family, e.g. HT-2 toxin or 3-acetyldeoxynivalenol.

Magnetic nanogold microspheres-based lateral-flow immunodipstick for rapid detection of aflatoxin B2 in food

A novel membrane-based lateral-flow immunodipstick assay was developed for the fast screening of aflatoxin B(2) (AFB(2)) as a model compound in food samples. The detector reagent consisted of magnetic nanogold microspheres (MnGMs) with nano-Fe(2)O(3) particles as core and gold nanoparticles as shell, and bio-functionalized with monoclonal anti-AFB(2) antibodies. Manually spotted AFB(2)-bovine serum albumin conjugates (AFB(2)-BSA) and goat anti-mouse IgG on nitrocellulose membrane were used as test and control lines, respectively. As the major advantage, experimental results indicated that the visual detection limit (cutoff value) of the MnGM-based dipstick immunoassay with 0.9 ng/ml AFB(2) was about threefold lower compared to a conventional immunodipstick test using gold nanoparticles as detection reagent. Qualitative results (yes/no) could be obtained within 15 min without expensive equipment. The assay was evaluated with AFB(2) spiked or naturally contaminated samples (n=8), including peanuts, hazelnuts, pistacia and almonds, receiving excellent correspondance with results from high performance liquid chromatography (HPLC). Most importantly, the assay gave no false negative results. By controlling the target antibody this assay can be easily extended for use with other food relevant toxins and thus represents a versatile detection method.

Rapid test strips for analysis of mycotoxins in food and feed

An overview is given on recent trends and applications of rapid immunodiagnostic tests for screening of food and feed for mycotoxins. Different test formats are discussed, and challenges in the development of lateral-flow devices for on-site determination of mycotoxins, with requirements such as being robust, fast, and cost-effective, are briefly elucidated.

Development of polyclonal antibodies for the detection of Tribolium castaneum contamination in wheat grain

Two polyclonal antibodies (Pab) were developed for the detection of Tribolium castaneum, which is a stored product pest of medical and economical importance. Selected Pab anti- T. castaneumK51 showed low cross-reactivity to other stored product arthropods but revealed high reactivity to T. destructor, T. confusum, and partly to Tenebrio molitor. PTA-ELISA was used to detect adults, larva, and feces of T. castaneum in artificially contaminated grain samples. Calibration methods were applied to determine detection limits for each type of contaminants. Anti- T.castaneumK51 enabled detection of T. castaneum in grain samples; detection limits reached 60 and 640 individuals/kg of grain for larvae and adults, respectively, and 4 mg of feces/kg of grain. After recalculation, the detection limit for feces enables detection of 30 larvae after 5 days of feeding in optimal conditions. The main advantage of the developed assay is traceability of T. castaneum contamination, especially when the adults and larvae are removed from contaminated material, based on the detection of feces that persist in the grain.

Mycotoxin analysis: an update

Mycotoxin contamination of cereals and related products used for feed can cause intoxication, especially in farm animals. Therefore, efficient analytical tools for the qualitative and quantitative analysis of toxic fungal metabolites in feed are required. Current methods usually include an extraction step, a clean-up step to reduce or eliminate unwanted co-extracted matrix components and a separation step with suitably specific detection ability. Quantitative methods of analysis for most mycotoxins use immunoaffinity clean-up with high-performance liquid chromatography (HPLC) separation in combination with UV and/or fluorescence detection. Screening of samples contaminated with mycotoxins is frequently performed by thin layer chromatography (TLC), which yields qualitative or semi-quantitative results. Nowadays, enzyme-linked immunosorbent assays (ELISA) are often used for rapid screening. A number of promising methods, such as fluorescence polarization immunoassays, dipsticks, and even newer methods such as biosensors and non-invasive techniques based on infrared spectroscopy, have shown great potential for mycotoxin analysis. Currently, there is a strong trend towards the use of multi-mycotoxin methods for the simultaneous analysis of several of the important Fusarium mycotoxins, which is best achieved by LC-MS/MS (liquid chromatography with tandem mass spectrometry). This review focuses on recent developments in the determination of mycotoxins with a special emphasis on LC-MS/MS and emerging rapid methods.

Immunochemical methods in health risk assessment: cross reactivity of antibodies against mycotoxin deoxynivalenol with deoxynivalenol-3-glucoside

Co-occurrence of deoxynivalenol (DON) with other DON derivatives/metabolites and other Fusarium toxins, including zearalenone, nivalenol and as well as other mycotoxins (e.g. fumonisins) is frequently observed in food and feed. DON-3beta-glucopyranoside (DON-3-glucoside) was described as detoxification product of DON in wheat. This mycotoxin conjugate was observed in maize, barley, malt, beer and wort. Digestion of this conjugate in intestine is still unclear but due to possibility to release DON after hydrolysis is considered as potential masked mycotoxin. DON is analytically quantified by various methods and also with immunochemical methods. There is no available information about specificity of anti-DON antibodies used in commercial ELISA kits with DON-3-glucoside. Preliminary testing of anti-DON monoclonal antibodies used in ELISA kits RIDASCREEN DON (R-BiopharmAG, Germany) approved a hypothesis that these antibodies have high relative cross reactivity with DON-3-glucoside. In two repeated tests cross reaction 82 and 98% were observed. Analytical results produced by these ELISA kits can be interpreted as an approximate sum of both mycotoxins. Described cross reactivity can lead to overestimating of DON concentration. Over these cross reactions immunochemical methods are mentioned still valuable for quantitative screening and even for an initial exposure assessment in situations when there are practical or economical reasons not to use another analytical method with a reasonable low limit of quantification (< 50 ppb).

Development of qualitative and semiquantitative immunoassay-based rapid strip tests for the detection of T-2 toxin in wheat and oat

Novel qualitative as well as semiquantitative rapid strip tests for screening of T-2 mycotoxin in agricultural commodities were developed. Colloidal gold particles were coated with monoclonal anti-T-2 antibodies and used as detector reagent, indicating the strip test results by formation of up to two colored lines in a competitive assay format. The test line comprises a protein conjugate of the T-2 mycotoxin and the control line an antispecies-specific antibody to confirm the correct test development. To perform the test, 5 g of sample was extracted in a ratio of 1:5 with methanol/water (70:30) by shaking for 3 min and the extract directly used without further cleanup steps. The T-2 toxin lateral flow device (LFD) presented has a cutoff level around 100 microg/kg for naturally contaminated wheat and oat. The semiquantitative test may be used in the lower micrograms per kilogram range and allows for rapid semiquantitative photometric classification of the level of sample contamination. For both tests, results were obtained within 4 min. The developed LFDs therefore allow for the first time fast and on-site screening for the determination of T-2 toxin in cereals.

Label-Free Impedance Biosensors: Opportunities and Challenges

Impedance biosensors are a class of electrical biosensors that show promise for point-of-care and other applications due to low cost, ease of miniaturization, and label-free operation. Unlabeled DNA and protein targets can be detected by monitoring changes in surface impedance when a target molecule binds to an immobilized probe. The affinity capture step leads to challenges shared by all label-free affinity biosensors; these challenges are discussed along with others unique to impedance readout. Various possible mechanisms for impedance change upon target binding are discussed. We critically summarize accomplishments of past label-free impedance biosensors and identify areas for future research.

Phospho-specific recognition by 14-3-3 proteins and antibodies monitored by a high throughput label-free optical biosensor

Label-free detection of molecular interactions has considerable potential in facilitating assay development. When combined with high throughput capability, it may be applied to small molecule screens for drug candidates. Phosphorylation is a key posttranslational process that confers diverse regulation in biological systems involving specific protein-protein interactions recognizing the phosphorylated motifs. Using a resonant waveguide grating biosensor, the Epic mark System, we have developed a generic assay to quantitatively measure phospho-specific interactions between a trafficking signal-phosphorylated SWTY peptide and 14-3-3 proteins or anti-phosphopeptide antibodies. Compared with a solution-based fluorescence anisotropy assay, our results support that the high throughput resonant waveguide grating biosensor system has favorable technical profiles in detecting protein-protein interactions that recognize phosphorylated motifs. Hence it provides a new generic HTS platform for phospho-detection.

Rapid methods for deoxynivalenol and other trichothecenes

Method development for deoxynivalenol (DON) and other trichothecenes in recent years was driven by the analytical necessities arising from its widespread (and increasing) occurrence in foods and feeds. This has resulted in the establishment of guideline levels for animal feed, tolerable daily intake (TDI) levels for humans, and most importantly, in the prospect of low-tolerance levels for these toxins in foods in the near future. In order to ensure reliable determination of the toxin content at the tolerance levels, routine analytical methods must have detection limits of less than the tolerance level. This paper intends to give an overview of current analytical developments of rapid testing for deoxynivalenol and other trichothecene mycotoxins, with a special focus on antibody-based techniques. This includes high-throughput instrumental analysis for the laboratory environment, as well as rapid visual tests for on-site testing. The applicability of rapid tests within an integrated detection system for mycotoxins in foods is discussed.