One-pot green synthesis of ZIF-8/IgG composite for the precise orientation and protection of antibody and its application in purification and detection of aflatoxins in peanut oil

This study presents a novel approach toward the one-pot green synthesis of ZIF-8/IgG composite, focusing on its precise orientation and protection of the anti-aflatoxins antibody. The antibody orientation is achieved through the specific binding of IgG to the Fc region of the antibody, while the antibody protection is accomplished by the structural change restriction of ZIF-8 framework to the antibody. Consequently, the antibody exhibits enhanced target capability and significantly improved tolerance to organic solvents. The ZIF-8/IgG/anti-AFT was employed for the purification and detection of AFTs by coupling with UPLC. Under optimized conditions, the recoveries of spiked AFTs in peanut oils are between 86.1% and 106.4%, with relative standard deviations (RSDs) ranging from 0.8% to 8.8%. The linearity range is 0.5-20.0 ng for AFB1 and AFG1, 0.125-5.0 ng for AFB2 and AFG2, the limit of detection is 0.1 ng for AFB1 and AFG1, 0.03 ng for AFB2 and AFG2.

Development of Anti-Idiotypic Nanobody-Phage Based Immuno-Loop-Mediated Isothermal Amplification Assay for Aflatoxins in Peanuts

Aflatoxin contamination in agricultural products has posed serious health hazards and brought huge economic loss in the food and feed industries. Monitoring aflatoxins in various foods and feeds has become a crucial means to protect public health. This study aimed to report an immuno-loop-mediated isothermal amplification (iLAMP) assay by using an anti-idiotypic nanobody-phage for on-site and rapid detection of aflatoxin in real samples. The iLAMP method was developed on the basis of a competitive immunoassay and LAMP reaction performed in a simple water bath. This method can provide visualized test results: violet color represents positive samples while sky blue represents negative. The visual detection limits of iLAMP for aflatoxin B₁, B₂, G₁, and G₂ in peanut samples were 1.6, 1.6, 3.2, and 16 μg/kg, respectively. The developed assay was verified with high performance liquid chromatography (HPLC) for the analysis of aflatoxins in peanuts, which demonstrated that the iLAMP method can be applied to the detection of aflatoxin in real samples. The novel iLAMP assay eliminates the need for aflatoxin conjugates, the antibody labeling process, and special equipment, and offers an alternative to existing methods with advantages of time-saving, cost-effectiveness, and ease-of-use.

The effects of aflatoxin exposure on Hepatitis B-vaccine induced immunity in Kenyan children

BACKGROUND

Globally, approximately three million children die each year from vaccine preventable infectious diseases mainly in developing countries. Despite the success of the expanded immunization program, not all infants and children around the world develop the same protective immune response to the same vaccine. A vaccine must induce a response over the basal immune response that may be driven by population-specific, environmental or socio-economic factors. Mycotoxins like aflatoxins are immune suppressants that are confirmed to interfere with both cell-mediated and acquired immunity. The mechanism of aflatoxin toxicity is through the binding of the bio-activated AFB1-8, 9-epoxide to cellular macromolecules.

METHODS

We studied Hepatitis B surface antibodies [anti-HBs] levels to explore the immune modulation effects of dietary exposure to aflatoxins in children aged between one and fourteen years in Kenya. Hepatitis B vaccine was introduced for routine administration for Kenyan infants in November 2001. To assess the effects of aflatoxin on immunogenicity of childhood vaccines Aflatoxin B1-lysine in blood serum samples were determined using High Performance Liquid Chromatography with Fluorescence detection while anti-HBs were measured using Bio-ELISA anti-HBs kit.

RESULTS

The mean ± SD of AFB1-lysine adducts in our study population was 45.38 ± 87.03 pg/mg of albumin while the geometric mean was 20.40 pg/mg. The distribution of AFB1-lysine adducts was skewed to the right. Only 98/205 (47.8%) of the study population tested positive for Hepatitis B surface antibodies. From regression analysis, we noted that for every unit rise in serum aflatoxin level, anti-HBs dropped by 0.91 mIU/ml (-0.9110038; 95% C.I -1.604948, -0.21706).

CONCLUSION

Despite high coverage of routine immunization, less than half of the study population had developed immunity to HepB. Exposure to aflatoxin was high and weakly associated with low anti-HBs antibodies. These findings highlight a potentially significant role for environmental factors that may contribute to vaccine effectiveness warranting further research.

Feasibility of A Novel On-Site Detection Method for Aflatoxin in Maize Flour from Markets and Selected Households in Kampala, Uganda

In sub-Saharan Africa, there is a high demand for affordable and accessible methods for on-site detection of aflatoxins for appropriate food safety management. In this study, we validated an electrochemical immunosensor device by the on-site detection of 60 maize flour samples from six markets and 72 samples from households in Kampala. The immunosensor was successfully validated with a linear range from 0.7 ± 0.1 to 11 ± 0.3 µg/kg and limit of detection (LOD) of 0.7 µg/kg. The maize flour samples from the markets had a mean total aflatoxin concentration of 7.6 ± 2.3 µg/kg with approximately 20% of the samples higher than 10 µg/kg, which is the maximum acceptable level in East Africa. Further down the distribution chain, at the household level, approximately 45% of the total number contained total aflatoxin levels higher than the acceptable limit. The on-site detection method correlated well with the established laboratory-based HPLC and ELISA-detection methods for aflatoxin B₁ with the correlation coefficients of 0.94 and 0.98, respectively. This study shows the feasibility of a novel on-site detection method and articulates the severity of aflatoxin contamination in Uganda.

Development of an Enzyme-Linked Immunosorbent Assay Method Specific for the Detection of G-Group Aflatoxins

To detect and monitor G-group aflatoxins in agricultural products, we generated class-specific monoclonal antibodies that specifically recognized aflatoxins G₁ and G₂. Of the final three positive and stable hybridomas obtained, clone 2G6 produced a monoclonal antibody that had equal sensitivity to aflatoxins G₁ and G₂, and did not cross-react with aflatoxins B₁, B₂, or M₁. Its IC50 values for aflatoxins G₁ and G₂ were 17.18 ng·mL(-1) and 19.75 ng·mL(-1), respectively. Using this new monoclonal antibody, we developed a competitive indirect enzyme-linked immunosorbent assay (CI-ELISA); the method had a limit of detection of 0.06 ng·mL(-1). To validate this CI-ELISA, we spiked uncontaminated peanut samples with various amounts of aflatoxins G₁ and G₂ and compared recovery rates with those determined by a standard HPLC method. The recovery rates of the CI-ELISA ranging from 94% to 103% were comparable to those of the HPLC (92% to 102%). We also used both methods to determine the amounts of G-group aflatoxins in five peanut samples contaminated by aflatoxin B₁-positive, and their relative standard deviations ranged from 8.4% to 17.7% (under 20%), which demonstrates a good correlation between the two methods. We further used this CI-ELISA to assess the ability of 126 fungal strains isolated from peanuts or field soils to produce G-group aflatoxins. Among these, seven stains producing different amounts of G-group aflatoxins were identified. Our results showed that the monoclonal antibody 2 G6-based CI-ELISA was suitable for the detection of G-group aflatoxins present in peanuts and also those produced by fungi.

Vaccination of heifers with anaflatoxin improves the reduction of aflatoxin b1 carry over in milk of lactating dairy cows

It was previously reported that injection of anaflatoxin B1 (AnAFB1) conjugated to keyhole limpet hemocyanin (KLH), together with Freund's adjuvant, was effective in inducing in cows a long lasting titer of anti-aflatoxin B1 (AFB1) antibodies (Abs), cross-reacting with other aflatoxins, which were able to hinder, proportionally to their titer, the secretion of aflatoxin M1 (AFM1) into the milk of cows continuously fed with AFB1. According to anti-AFB1 Ab titer, 50% of the vaccinated cows were recognized as high responder animals. In an attempt to prepare a more effective formulation for vaccination of cows, it was compared the immunogenicity, in Holstein Friesian heifers, of AnAFB1 covalently conjugated to KLH or to recombinant diphtheria toxin (CRM197) molecules, and injected together with various adjuvants. This study demonstrated that injection of AnAFB1 conjugated to KLH and mixed with complete (priming) and incomplete Freund's adjuvant (boosters), as in the previous schedule of immunization, was the most effective regimen for inducing Ab responses against AFB1, although pre-calving administration could increase the effectiveness of vaccination, resulting in 100% high responder animals. After one booster dose at the beginning of the milk production cycle, anti-AFB1 Ab titers were comparable to those recorded at the end of the immunization schedule, and proved to be effective in reducing significantly AFB1 carry over, as AFM1, from feed to milk. Pre-calving vaccination of dairy heifers with conjugated AnAFB1, adjuvated with complete and incomplete Freund's adjuvant, may represent the most effective tool for preventing the public health hazard constituted by milk and cheese contaminated with aflatoxins.

[Using HTS-ELISA method to make anti-aflatoxin M1 monoclonal antibody]

OBJECTIVE

To prepare high-affinity anti-aflatoxin M1 monoclonal antibodies by High Throughput Screening ELISA (HTS-ELISA) METHODS: Balb/C mice were immunized by aflatoxin M1-bovine serum albumin conjugate, and screen secret anti-aflatoxin M1 monoclonal antibody hybridoma by HTS-ELISA. The antibody was characterized.

RESULTS

Fourteen hybridoma cell lines which could secret high activity anti-aflatoxin M1 monoclonal antibodies were obtained. The affinity of the purified monoclonal antibody was 5.5 x 10(-10) mol/L. The cross-reactivity of the monoclonal antibody clone against aflatoxin M1, aflatoxin M2, aflatoxin B1, aflatoxin B2, aflatoxin G1, aflatoxin G2, deoxynivalenol and BSA was 100%, 4.5%, 21.5%, 1.0%, 16.6%, 1.0%, 0%, 0%, respectively. The sensitivity of the anti-AFM1 monoclonal antibody binding to aflatoxin M1 was 0.01 microg/L and the linear range for developed indirect competitive ELISA was 0.1 - 10 microg/L aflatoxin M1. The binding inhibition IC50 of the anti-aflatoxin M1 monoclonal antibody was 0.82 microg/L. Assays of milk samples mixed with AFM1 ranging in concentration from 0.25 to 5.0 microg/L gave mean indirect competitive ELISA recovery of 60.3% - 152.8%.

CONCLUSION

HTS-ELISA can be used for the preparation of the high-affinity anti-aflatoxin M1 monoclonal antibodies. The anti-aflatoxin M1 monoclonal antibody could be provided as the high quality material in the system of aflatoxin M1 immune detection.

Human aflatoxicosis in developing countries: a review of toxicology, exposure, potential health consequences, and interventions

Aflatoxins are well recognized as a cause of liver cancer, but they have additional important toxic effects. In farm and laboratory animals, chronic exposure to aflatoxins compromises immunity and interferes with protein metabolism and multiple micronutrients that are critical to health. These effects have not been widely studied in humans, but the available information indicates that at least some of the effects observed in animals also occur in humans. The prevalence and level of human exposure to aflatoxins on a global scale have been reviewed, and the resulting conclusion was that approximately 4.5 billion persons living in developing countries are chronically exposed to largely uncontrolled amounts of the toxin. A limited amount of information shows that, at least in those locations where it has been studied, the existing aflatoxin exposure results in changes in nutrition and immunity. The aflatoxin exposure and the toxic affects of aflatoxins on immunity and nutrition combine to negatively affect health factors (including HIV infection) that account for >40% of the burden of disease in developing countries where a short lifespan is prevalent. Food systems and economics render developed-country approaches to the management of aflatoxins impractical in developing-country settings, but the strategy of using food additives to protect farm animals from the toxin may also provide effective and economical new approaches to protecting human populations.

Development of an immunosensor based on pressure transduction

Traditional strategies for signal transduction in immunosensors are based on piezoelectric, thermometric, electrochemical, magnetic and optical methods. The use of pressure as a signal transduction method in immunosensors has not been reported previously. An immunosensor incorporating the detection of a change in pressure as the signal-transducing mechanism was investigated. A commercially available ultra-low pressure sensor was used in conjunction with a sealed chamber to assess the feasibility of this strategy. A key feature of the current approach is the use of a thin membrane (or film) in which to perform an immunoassay and subsequently to detect production of gas. The thinness contributes to efficient gas evolution and minimizes the effect of liquid acting as a "sink" for gas molecules. This feature also simplifies measurement of evolved gas, which traditionally was based on the use of bulk solutions, shaking and pH changes to "release" dissolved gas (especially carbon dioxide). Gas generation in the current approach is achieved by the coupling of catalase to haptens or antibodies for use in competitive or sandwich immunoassays, respectively. Hydrogen peroxide is used as the substrate. Performance characteristics of the sensor apparatus were assessed in several ways. Injection of various volumes of air from a gas-tight syringe produced an essentially linear relationship from 0.2 to 2.0 microl of injected volume, with a slope of approximately 5 V/microl. Depending on the duration of the sampling period, specific signals in excess of 2 V have been obtained for 0.01 units of catalase (approximately 0.4 ng of protein). Development and use of this sensing apparatus will be described for both competitive and sandwich immunoassays.

[Products of spontaneous conjugation of aflatoxins with bovine serum albumin: immunochemical properties]

Products of spontaneous conjugation of aflatoxins B1, G1, and G2 with bovine serum albumin (BSA) were shown to interact with antibodies against aflatoxins. Solid-phase BSA conjugates inhibited the binding of aflatoxins by anti-aflatoxin antibodies. Antisera against BSA-B1, BSA-G1, and BSA-G2 were obtained and their specificity, determined. The mechanisms of spontaneous binding of aflatoxins by proteins are discussed.

Immunosuppression in broiler chicks fed aflatoxin and inoculated with fowl adenovirus serotype-4 (FAV-4) associated with hydropericardium syndrome

A total of 240 unvaccinated day-old broiler chicks, which had been found to be negative for antibodies against FAV-4, were divided into four groups of 60 chicks each. Group A was fed aflatoxin at 1 ppm from 7 days to 7 weeks of age. Group V was infected intra-abdominally at 14 days of age with 0.2 ml of FAV-4, having a titre of 10(5.5) TCID50 per 0.2 ml. The combined group AV was given the aflatoxin and infected with FAV-4. The fourth group C served as the control. More pronounced clinical signs, a higher mortality rate (56.7%), and reductions in body weight gain and in the organ to body weight ratios of the bursa and spleen were recorded in group AV. A significant (p < 0.01) reduction in the HI antibody titre following vaccination against Newcastle disease, and of skin thickness in the delayed hypersensitivity test following sensitization with DNCB, indicated an additive immunosuppressive effect from aflatoxin and FAV-4 on the humoral and cell-mediated immune responses in group AV compared to groups A and V. Microscopically, marked depletion and degeneration of lymphocytes in the thymus, bursa, spleen and caecal tonsils were observed in group AV up to 5 weeks PI.

[Specific features of albumin interactions with hemiacetals of aflatoxins and sterigmatocystin]

Aflatoxin B2a (AB2a), aflatoxin G2a (AG2a), and hemiacetal of sterigmatocystin have been shown to form immunoreactive conjugates with albumin. The conjugates were formed following incubation of solution mixtures at room temperature for 1 h, as demonstrated by spectrophotometry and enzyme immunoassay. Anti-AB2a antibodies reacted with AB2a, aflatoxin B1, and aflatoxin AB2 (100, 8.8, and 5.9%, respectively); a similar result was obtained for anti-AG2a antibodies reacting with AG2a, aflatoxin G1, and aflatoxin AG@2 (100, 2.5, and < 1.0%, respectively). Binding of anti-AB2a and anti-AG2a antibodies to solid-phase conjugates of AB2a or AG2a exhibited similar analytical characteristics.

Production of ultrasensitive antibodies against aflatoxin B1

AIMS

To produce specific antibodies against the haptenic fungal toxin aflatoxin B1 (AFB1) and apply these antibodies in immunochemical assays for aflatoxins.

METHODS AND RESULTS

Rabbits were immunized using an AFB1-bovine serum albumin conjugate and serum titres determined by double-antibody enzyme immunoassay. High titres of antibodies with very high affinity for AFB1 were obtained 15 and 4 weeks after the initial immunization and the first booster immunization respectively. The antibodies were employed in enzyme immunoassay (EIA) and immunoaffinity chromatography (IAC) methods for aflatoxins. With a detection limit of 15.8 pg ml(-1) for AFB1, the EIA employing these antibodies is the most sensitive test for AFB1 described so far. In IAC columns, these antibodies provided high binding capacity for all major aflatoxins, including AFB1, AFB2, AFG1 and AFG2.

CONCLUSION

The antibodies described here are useful for the analysis of trace levels of aflatoxins.

SIGNIFICANCE AND IMPACT OF THE STUDY

Polyclonal antibody-based EIA and IAC methods for aflatoxin analysis offer a suitable alternative to the more expensive monoclonal antibody-based methods.

Comparison between inhibitory indirect ELISA and HPLC methods to quantify free and adducted aflatoxins in human urine

HPLC and Inhibitory Indirect ELISA (I.I. ELISA) methods for quantitation of aflatoxins (AF) in human urine were compared in terms of specificity, sensitivity, easiness and cost. I.I. ELISA was optimized in kind of antibody in use, type of plastic plate, adduct synthesis technique, peroxidase and antibody dilutions, etc. Both polyclonal (Cuban) and monoclonal (British) anti-AF antibodies were statistically studied and the process was standardized. HPLC and electrophoresis were performed while synthetizing AFB(1)-DNA and AFB(1)-Cl-Ovalbumin (AFB(1)-Cl-Ov) adducts. Costar polystyrene plate had the best adherence. Optimum coating dilution was 10 ng of AFB(1)-Cl-Ov per well. Dilutions of 1:1000 of monoclonal antibody from purified culture or 1:300 from monoclonal antibody from tissue culture and 1:1000 of peroxidase anti-mouse conjugate were the best. Optimum separation with HPLC was obtained isocratically with 60% MeOH and 40% distilled water mobile phase. ELISA had a sensitivity of 1 pg mL(-1) AFB(1) and HPLC sensitivity was 0.1 ng mL(-1) AFB(1) with fluorescence detector and 4.5 ng mL(-1) with UV detector. Monoclonal antibody gave more accurate results for determination of free and adducted AFB(1) in urine analysis.

Effect of aflatoxin on performance, hematology, and clinical immunology in lambs

Twenty-four female lambs were intoxicated with a diet contaminated with 2 ppm aflatoxin for a period of 37 d. Twelve lambs were maintained as the control group. After this period, the lambs were left for 35 d without aflatoxin in their feed. Performance, hematology and clinical immunology were examined in the intoxicated lambs. A non-significant decrease in body weight was observed in the intoxicated lambs during the intoxication period, whereas a significant decrease (P<0.001) in average daily gain was noted on the last day of intoxication and during the clearance period. No significant differences were observed in erythrocyte count, white blood cell count or differential leukocyte count between the groups. Bacteriostatic activity of the serum was lower in the intoxicated lambs, however, there was no effect on serum opsonic activity. Phagocytosis by the neutrophils was higher during the intoxication period and the levels of IgG were elevated in the intoxicated lambs. In vivo cellular immunity was assessed by intradermal injection of phytohemagglutinin; the response was lower during intoxication period. These results indicate that a lowering in the average daily gain was the most sensitive indicator of aflatoxicosis in lambs, and that the immune response was altered, which could render the animals more susceptible to infectious diseases.

Immunotoxicological effects on piglets of feeding sows diets containing aflatoxins

Three groups of four Large White sows were fed diets containing either 800 ppb purified aflatoxin B1 (group 1), 800 ppb purified aflatoxin G1 (group 2) or 400 ppb B1 and 400 ppb G1 (group 3) throughout gestation and lactation. A control group of four sows was fed a diet free of aflatoxins. Aflatoxins B1 and M1 were found in milk samples taken five and 25 days after parturition from the sows of group 1, aflatoxin G1 was present in the milk of the sows of group 2 and all three aflatoxins were present in samples from the sows of group 3. The concentration of aflatoxin in the milk was about 1000-fold lower than that in the feed, but increased over the 25 days after parturition. The piglet suckling on a central teat was selected from each sow, given sow milk until the fourth day of age, and was then free to eat prepared feed while suckling. At the 25th day of age the selected piglets were removed from the sow and sacrificed. Blood samples were collected from each piglet and cellular populations were separated for immunological measurements: an in vitro lymphocyte proliferation test, and tests to derive the phagocytic activity, phagocytic index and superoxide anion production of monocyte-derived macrophages were carried out along with studies on the motility, differential chemotaxis and chemotactic index of circulating granulocytes. The lymphoproliferative response to mitogens was reduced and monocyte-derived macrophages failed to efficiently produce superoxide anions after oxidative burst stimulation in vitro, while their ability to phagocytose red blood cells was not compromised. Granulocytic cells showed a reduction of chemotactic response in vitro to chemoattractant bacteria factor and casein.

Serological serum protein fraction and responses to Brucella melitensis in lambs fed aflatoxins

Twenty-four lambs were given 2 ppm aflatoxins (AF) in their diet for 37 d and 12 were kept as a control group. After this time, toxic feed was removed for a further 35 days (clearance period). On day 17 all lambs were vaccinated with B melitensis strain Rev-1, and blood samples were taken regularly to determine the levels of antibodies and serum proteins. Aflatoxins decreased titers of Rose Bengal test and optical densities of ELISA, both in the intoxicated and clearance periods. Complement fixation titers were lower in intoxicated lambs, except on the 23rd day of intoxication, but not statistically different (P > 0.05). No effect of AF was noted on total serum proteins, but albumin and alfa-globulin levels were lower for intoxicated lambs than for the control group. Beta-globulin concentration did not change, and increases in gamma-globulins levels in dosed lambs were observed throughout the experiment. These results suggest that AF causes a failure in the acquired immunity system of lambs by decreasing antibody production and altering serum profile proteins.

Production and characterization of a monoclonal antibody against sterigmatocystin

A monoclonal antibody, McAb-ST, specific for sterigmatocystin (ST) was produced in vitro and in vivo by a hybridoma anti-ST1. Anti-ST1 was prepared by fusion of SP2/0 murine myeloma cells with spleen cells isolated from BALB/c mouse that had been immunized with a complete antigen BSA-ST (ST conjugated to bovine serum albumin). Analysis revealed that McAb-ST was of the IgG1 type, the molecular weight of McAb-ST was 168,000 daltons (53,000 for each heavy chain, 31,000 for each light chain), and the apparent affinity constant of McAb-ST with H-ST (Hemocyanin and ST conjugate) was 1.29 x 10(9) mol/L. The relative cross reactivities of McAb-ST with ST analogs were less than 2% when determined by a competitive indirect enzyme-linked immunosorbent assay (CI-ELISA). The minimal 0.5 pg of ST in 50 microliters of solution could be detected with CI-ELISA using McAb-ST, with a linear range of 0.1-10 ng/mL.

Molecular dosimetry in rat urine of aflatoxin-N7-guanine and other aflatoxin metabolites by multiple monoclonal antibody affinity chromatography and immunoaffinity/high performance liquid chromatography

The development of molecular dosimetry methods will simplify the identification of people at high risk for cancer. A combined monoclonal antibody immunoaffinity chromatography/high performance liquid chromatography method has been devised to isolate and quantify aflatoxin-DNA adducts and other metabolites in rat urine samples. We report the production of 11 different monoclonal antibodies recognizing aflatoxin B1, aflatoxin Q1, aflatoxin G1, aflatoxicol, and aflatoxin M1 and the application of these antibodies to a multiple monoclonal antibody affinity chromatography technique. Using the multiple monoclonal antibody affinity column with rat urines obtained from dosed animals, between 90 and 95% of total aflatoxin metabolites can be bound to the column and isolated. Analytical immunoaffinity chromatography/high performance liquid chromatography analysis of these isolated aflatoxins reveals that more than 55% of the aflatoxins in rat urine are aflatoxin-dihydrodiol, aflatoxin-N7-guanine, aflatoxin Q1, aflatoxin M1, aflatoxin P1, and aflatoxin B1, accounting for 1.5, 9.6, 1.8, 34.5, 8.0, and 1.0% of the total aflatoxins, respectively. Further, a perchloric acid digestion of the aflatoxin-N7-guanine peak was used to confirm its identity by its conversion to guanine. The measurement of aflatoxin-N7-guanine excretion in rat urine was examined to assess its utility as a marker of DNA adduct formation in the liver, and a dose-dependent excretion in urine was found with a correlation coefficient of 0.99. A comparison of the dose-dependent residual levels of aflatoxin binding to liver DNA with the amount of aflatoxin-N7-guanine excreted in urine showed a correlation coefficient of 0.98. Besides the nucleic acid adduct excretion data, aflatoxin M1 and aflatoxin P1 were evaluated as molecular dosimeters in the urine. Aflatoxin M1 was found to be an excellent marker, whereas no linear relationship between dose and aflatoxin P1 excretion in urine was found.

Automated aflatoxin analysis of foods and animal feeds using immunoaffinity column clean-up and high-performance liquid chromatographic determination

A commercially available system is described for the fully automated clean-up and high-performance liquid chromatographic (HPLC) analysis of aflatoxins in foods and animal feeds. The system marketed primarily for handling solid-phase extraction columns has modified software to facilitate use with immunoaffinity columns. Sample extract clean-up followed by injection onto an HPLC column with post-column iodination and fluorescence detection is carried out completely unattended. A coefficient of variation of 5.1% for aflatoxin B1 analysis was obtained, and the accuracy of the system was demonstrated by the analysis of peanut butter certified reference material.

Evaluation of an indirect enzyme-linked immunosorbent assay for screening antibody against aflatoxins

Enzyme-linked immunosorbent assay screening of antibody produced against aflatoxin was accomplished by a new and simple procedure. To demonstrate the new indirect ELISA technique used, antibody against aflatoxin M1 was produced in female BALB/CJ mice by immunization with an aflatoxin M1-bovine serum albumin conjugate. Instead of coating test-plate wells with purified antibody (direct ELISA) or synthesizing a second protein-aflatoxin conjugate (aflatoxin M1-poly-L-lysine) to coat test-plate wells, wells were coated with the readily available aflatoxin M1-bovine serum albumin and aflatoxin B1-bovine serum albumin. This method, applicable for any aflatoxin conjugated by the common cyclopentano-carboxymethoxyl-oxime technique, eliminates the more time-consuming and technically difficult portions of earlier direct and indirect ELISA. The new technique can be valuable in continued efforts toward development of new and improved immunoassays against aflatoxin metabolites.

Aflatoxin monoclonals: academic development to commercial production

A monoclonal antibody (mAb) has been produced to aflatoxin B1 (AF B1) after successful immunization of mice and fusion of sensitized spleen cells with myeloma cancer cells. The mice were immunized with AF B1-oxime-protein conjugate. Positive mAbs were screened using an indirect ELISA specific for AF B1. The selected mAb was then developed in direct competitive ELISA and immunoaffinity column chromatography methods for aflatoxin detection in foods and feeds. Both assays are rapid, sensitive, specific and require only the minimum of sample preparation. Both immunological assays have now been commercialized and are produced in convenient ready-made kit formats.

Evidence for human antibodies that recognize an aflatoxin epitope in groups with high and low exposure to aflatoxins

Antibody activity against an aflatoxin epitope has been detected in serum from individuals who live in Kenya and who experience high exposure to aflatoxin B1. The activity was higher than in Danish people. The highest antibody activity was found in individuals who were recently exposed to aflatoxin B1. The ratio between IgG and IgM activities was higher in individuals with a high antibody titer. The specificity of the antibody activity differed in the serums obtained from Danish and Kenyan persons ("Danish" and "Kenyan" serum, respectively). The activity in Danish serum was inhibited by an aflatoxin-like substance isolated from human urine, whereas aflatoxin B1 did not inhibit the activity. In contrast, the activity in Kenyan serum was not inhibited by the aflatoxin-like substances. Therefore, the presence of antibodies against aflatoxin in humans indicates exposure to aflatoxin or aflatoxin-antigenic material. However, the biological consequences of these antibodies remain unknown.

Aflatoxin B1 metabolism by 3-methylcholanthrene-induced hamster hepatic cytochrome P-450s

We have studied the activation of aflatoxin B1 by hamster liver microsomes and purified hamster cytochrome P-450 isozymes using a umu mutagen test. The hamster liver microsomes or S-9 fractions were much more active than rat liver microsomes or S-9 fractions in the activation of umu gene expression by aflatoxin B1 metabolites. 3-Methyl-cholanthrene treatment increased aflatoxin B1 activation by hamster liver microsomes. Two major 3-methylcholanthrene-inducible cytochrome P-450 isozymes, P-450 MC1 (IIA) and P-450 MC4 (IA2), were purified from 3-methylcholanthrene-treated hamster liver microsomes, and the metabolism of aflatoxin B1 by these two cytochromes was studied. In the reconstituted enzyme system, both P-450 MC1 and P-450 MC4 were highly active in the activation of aflatoxin B1, and antibodies against these P-450s specifically inhibited these activities. Antibody against P-450 MC1 inhibited the activation of aflatoxin B1 by 20% in the presence of 3-methyl-cholanthrene-treated hamster liver microsomes. In contrast, antibody against P-450 MC4 stimulated the activity by 175%. These results indicated that hamster P-450 MC1 might convert aflatoxin B1 to more toxic metabolite(s), whereas P-450 MC4 might convert aflatoxin B1 to less toxic metabolite(s), than aflatoxin B1 in liver microsomes. The metabolite(s) produced by both hamster cytochrome P-450 MC1 and MC4 were genotoxic in the umu mutagen test.

Time-resolved fluoroimmunoassay of aflatoxins

Preparation of purified and Eu-labeled antibodies specific for aflatoxins is described. Their use is illustrated by a solid-phase competitive time-resolved fluoroimmunoassay, results of which were correlated with those of an enzyme-linked immunosorbent assay based on use of the unmodified antibody to aflatoxin. This procedure is discussed as a quick, sensitive, and reliable immunoassay for use in mycotoxin screening in foodstuffs and body fluids.

Production and characterization of antibodies cross-reactive with major aflatoxins

Antibodies cross-reactive with 4 major aflatoxins were demonstrated three weeks after immunization of rabbits with an immunogen which was prepared by conjugating aflatoxin B3 to bovine serum albumin. Aflatoxin B3 was first converted to its hemisuccinate before conjugation to the protein. Tritiated aflatoxin B1 (AFB1) was used as the marker ligand both for antibody titer determination as well as for analysis of antibody specificity. Competitive RIA revealed that the antibodies have good cross-reactivity with aflatoxins B1, B2, G1, and G2 when tritiated AFB1 was used as the marker ligand. The concentrations causing 50% inhibition of binding of 3H-AFB1 to the antibodies by unlabeled aflatoxins B1, B2, G1, G2 and B3 were found to be 0.25, 3.34, 0.32, 4.0 and 0.53 ng/assay, respectively. The antibodies could be used for simultaneous analysis of aflatoxins B1 and G1, two of the most important toxic metabolites produced by Aspergillus flavus and A. parasiticus.

Effects of aflatoxin B1 on murine lymphocytic functions

We recently reported on the immunotoxic effects of Aflatoxin B1 (AFB1), a secondary fungal metabolite of Aspergillus flavus in mice. The present paper describes the effect of AFB1 on cellular functions in lymphocytes after in vivo or in vitro exposures. Male BALB/c mice received 0, 0.03, 0.145 or 0.7 mg/kg body weight of AFB1 for 4 weeks. A dose-related decrease in DNA synthesis in lymphocyte cultures with or without the mitogens (lipopolysaccharide, phytohemagglutinin, pokeweed mitogen and concanavalin A) was observed. No effects on protein or ribonucleic acid synthesis were observed. There were dose-dependent decreases in peripheral leucocyte counts and natural killer cell function. Splenic lymphocytes from normal mice cultured with 10(-6) to 10(-4) M AFB1 had decreased DNA synthesis at greater than 1 X 10(-5) M, a decreased protein synthesis at 10(-4) M and decreased RNA synthesis at greater than 2.5 X 10(-5) M. In vitro addition of AFB1 (greater than 50 microM) reduced generation of concanavalin A-induced suppressor cells. The results suggest that AFB1 had a direct and complex effect on lymphocytes and there is a differential sensitivity of various subpopulations.

Immunological detection of aflatoxin B1-DNA adducts formed in vivo

Two monoclonal antibodies (6A10 and 12F5) were obtained after fusion of mouse P3X63-AG.8.653 myeloma cells with spleen cells isolated from BALB/c mice immunized with imidazole ring-opened aflatoxin B1 (AFB1)-DNA and characterized by competitive enzyme-linked immunosorbent assays. Both antibodies are highly specific for imidazole ring opened AFB1-DNA and show some cross-reactivity with AFB1-DNA and no cross-reactivity with 8,9-dihydro-8-(7-guanyl)-9-hydroxy-AFB1, AFB1 conjugated with bovine serum albumin, aflatoxin M1 conjugated with bovine serum albumin, AFB1, or aflatoxin G1. Antibody 6A10 was further characterized and showed no cross-reactivity with DNA modified by several other carcinogens. It could detect adducts with 4-fold higher sensitivity in highly modified DNA (2.5 adducts/100 nucleotides) than in low modified DNA (4 adducts/10(5) nucleotides). With low modified DNA the limit of sensitivity is 5 adducts/10(7) nucleotides. Antibody 6A10 reliably detected adducts formed in vivo in rats and mice treated with AFB1. In a pilot study, AFB1 adducts were detected in liver tissues from individuals living in areas with suspected exposure to AFB1. Monitoring adduct levels in human tissue may provide information not only on carcinogen exposure but also on the relationship among infection with hepatitis B virus, dietary exposure to aflatoxin B1, and liver cancer.

Effect of antiserum against aflatoxin B1-bovine serum albumin complex on aflatoxin B1-induced lysogenesis

Escherichia coli K12 bacteria lysogenic for the lambda phage were used to study the effect of antiserum against aflatoxin B1-induced lysogenesis. The antiserum was obtained from rabbits immunized with water in oil emulsion of aflatoxin B1-bovine serum albumin complex (AFB1-BSA). A marked reduction in the degree of lysogenesis was observed when the antiserum was added to the reaction medium prior to microsomal enzyme activation of aflatoxin B1. There was no detectable effect when the antiserum was added after aflatoxin B1 activation. The result presented suggests that the antibodies in the AFB1-BSA antiserum can interact with aflatoxin B1 prior to its activation. This implies that an immune-protective effect can only be exerted if the antibodies intervene before activation.

Analysis of UK sera for aflatoxin by enzyme-linked immunosorbent assay

1. Aflatoxins are toxic, carcinogenic secondary fungal metabolites produced by certain moulds that commonly infest foods. Measurement of aflatoxins in human serum would give a direct measurement of exposure. 2. Twenty-seven serum samples from UK blood donors were found to contain aflatoxin levels not greater than 64 pmol/l (20 pg/ml) by an enzyme-linked immunosorbent assay. 3. These findings may indicate that present UK guideline tolerances for aflatoxin in imported food are effective in limiting human exposure to toxic aflatoxins in the UK diet, though further work would be needed to confirm this. In particular, sub-populations suspected of being at higher risk may need special considerations.

Substances with affinity to a monoclonal aflatoxin B1 antibody in Danish urine samples

Using a competitive enzyme immunoassay, one or more substances recognized by a monoclonal antibody against aflatoxin B1 were detected in human urine samples collected in Denmark. The concentration of urinary aflatoxin-like substances was equivalent to 0.0-6.5 ng aflatoxin B1/mg creatinine. A truly competitive interaction in the immunoassay was found between aflatoxin-like substances and aflatoxin B1. Aflatoxin-like substances could be isolated in small quantities from urine by affinity chromatography. The quantity of urinary aflatoxin-like compounds in the samples collected showed a skewed normal distribution (80 individuals). In order to explain the seemingly high level of aflatoxin-like material in urine samples from people living in a cold temperate climate, the source of aflatoxin-like compounds was investigated. In a dietary restriction study, potential dietary factors leading to excretion of aflatoxin-like compounds were investigated. Our data indicate that the excretion of these compounds by healthy Danes depends mainly on the food ingested 24-48 hr before urine samples were collected. In particular, the excretion of aflatoxin-like substances was increased when diets include beer, dairy products or meat. A map of the epitope recognized by the antibody was constructed from the results of competition studies with several AFB1 analogues. The epitope map was used to draw chemical structures representing the minimal requirements for antibody recognition. An on-line search was conducted among the 98.2 x 10(6) structures in the Chemical Abstracts and Registry Databases (STN, Columbus, OH) and provided strong evidence that only aflatoxins or aflatoxin derivatives are recognized by the antibody. The possible chemical structures of the aflatoxin-like substances are discussed.

Aflatoxin detected in human breast milk by immunoassay

Several epidemiological studies have shown a positive association between dietary exposure to aflatoxin (AF) and an increased incidence of primary hepatocellular carcinoma (PHC). One area in which little information is available is the exposure of newborn children to AF in human breast milk. We report the development, validation and application of an enzyme-linked immunosorbent assay (ELISA) to the detection of AF in human breast milk. The assay allows the quantitation of 2 pg AFM1 per ml of milk using less than 10 ml of sample. A good correlation was observed between ELISA and an hplc-fluorescence technique using naturally contaminated milk at levels up to 40 pg AF per ml. Of 54 samples collected from women in rural villages in Zimbabwe, 6 were found to be positive (11%) in ELISA with levels up to 50 pg AF per ml. No positive samples were detected out of 42 milk samples obtained from women in France. This sensitive and rapid methodology will be useful in examining the importance of and interaction between exposure to AF and infection with hepatitis B virus (HBV) early in life.

Hapten-protein conjugates prepared by the mixed anhydride method. Cross-reactive antibodies in heterologous antisera

Poly-L-lysine conjugates of three structurally unrelated mycotoxins were made by either a mixed anhydride intermediate (MA) or an activated N-hydroxysuccinimide ester intermediate (AE). Control conjugates, with no mycotoxin, were also prepared by each method. Antisera elicited by mycotoxin-albumin conjugates produced by the MA method bound to the three poly-L-lysine-MA mycotoxin conjugates and the MA control conjugate , but bound only to the poly-L-lysine-AE conjugates of the homologous mycotoxin. Binding of antisera to homologous poly-L-lysine conjugates was always inhibited by free hapten when the conjugate was prepared by the AE method but not by the MA method. The specific inhibition of antibody binding by various synthetic haptens indicated that the cross-reactions associated with the MA method were due to the undesired conjugation of isobutylformate during the mixed anhydride procedure.

Aflatoxin metabolism in humans: detection of metabolites and nucleic acid adducts in urine by affinity chromatography

A high-affinity IgM monoclonal antibody specific for aflatoxins was covalently bound to Sepharose 4B and used as a preparative column to isolate aflatoxin derivatives from the urine of people and experimental animals who had been exposed to the carcinogen environmentally or under laboratory conditions. Aflatoxin levels were quantified by radioimmunoassay and high-performance liquid chromatography after elution from the affinity column. In studies on rats injected with [14C]aflatoxin B1, we identified the major aflatoxin-DNA adduct, 2,3-dihydro-2-(N7-guanyl)-3-hydroxy-aflatoxin B1 (AFB1-N7-Gua), and the oxidative metabolites M1 and P1 as the major aflatoxin species present in the urine. When this methodology was applied to human urine samples obtained from people from the Guangxi Province of China exposed to aflatoxin B1 through dietary contamination, the aflatoxin metabolites detected were also AFB1-N7-Gua and aflatoxins M1 and P1. Therefore, affinity chromatography using a monoclonal antibody represents a useful and rapid technique with which to isolate this carcinogen and its metabolites in biochemical epidemiology and for subsequent quantitative measurements, providing exposure information that can be used for risk assessment.

Production and characterization of monoclonal antibodies against aflatoxin M1

By using an indirect enzyme-linked immunosorbent assay, four monoclonal antibodies were selected after fusion of mouse P3-NS1-Ag4-1 myeloma cells with spleen cells isolated from BALB/c mice that had been immunized with aflatoxin M1 (AFM1) conjugated to bovine serum albumin. Two of these antibodies were found to be specific for AFM1 and were designated AMW-1 and AMW-4. The specificities of AMW-1, which had higher affinity to AFM1, were determined by a competitive direct enzyme-linked immunosorbent assay with peroxidase-AFM1 as the marker. The relative cross-reactivity of each toxin (relative to AFM1) with AMW-1, as determined by the amount of aflatoxin necessary to cause 50% inhibition of enzyme activity, was 12, greater than 40, 12, and greater than 40 for B1, B2, G1, and G2, respectively.

Aflatoxin B1 dihydrodiol antibody: production and specificity

A specific antibody for 2,3-dihydro-2,3-dihydroxyaflatoxin B1 (AFB1-diol) was prepared, and its reactivity was characterized for the major aflatoxin (AF) B1 (AFB1) metabolites. Reductive alkylation was used to conjugate AFB1-diol to ethylenediamine-modified bovine serum albumin (EDA-BSA) and horseradish peroxidase for use as an immunogen and an enzyme-linked immunosorbent assay (ELISA) marker, respectively. High reactant ratios, 1:5 and 1:10, for AFB1-diol-EDA-BSA (wt/wt) resulted in precipitated conjugates which were poorly immunogenic. However, a soluble conjugate obtained by using a 1:25 ratio of AFB1-diol to EDA-BSA could be used for obtaining high-titer AFB1-diol rabbit antibody within 10 weeks. Competitive ELISAs revealed that the AFB1-diol antibody detected as little as 1 pmol of AFB1-diol per assay. Cross-reactivity of AFB1-diol antibody in the competitive ELISA with AF analogs was as follows: AFB1-diol, 100%; AFB1, 200%; AFM1, 130%; AFB2a, 100%; AFG1, 6%; AFG2, 4%; aflatoxicol, 20%; AFQ1, 2%; AFB1-modified DNA, 32%; and 2,3-dihydro-2-(N7-guanyl)-3-hydroxy AFB1, 0.6%. These data indicated that the cyclopentanone and methoxy moieties of the AF molecule were the primary epitopes for the AFB1-diol antibody. The AFB1-diol competitive ELISA was subject to substantial interference by human, rat, and mouse serum albumins but not by BSA, Tris, human immunoglobulin G, or lysozyme. By using a noncompetitive, indirect ELISA with an AFB1-modified DNA solid phase, a modification level of one AFB1 residue for 200,000 nucleotides could be determined.

Production and characterization of antibody against aflatoxin Q1

Antibodies against aflatoxin Q1 (AFQ1) were obtained from rabbits after immunization of either AFQ1-hemisuccinate or AFQ2a conjugated to bovine serum albumin. Both radioimmunoassay and enzyme-linked immunosorbent assaY (ELISA) were used for the determination of antibody titers and specificities. Antibodies obtained from rabbits after immunization with AFQ1-hemisuccinate-bovine serum albumin had the highest affinity to aflatoxin B1, whereas antibodies obtained from rabbits after immunization with AFQ2a-bovine serum albumin bound most effectively with AFQ2a. AFQ2a antibody was selected for the subsequent direct and indirect ELISA for the detection of AFQ1 in biological fluids. When AFQ2a-peroxidase and AFQ2a antibody were used, direct ELISA was able to detect as low as 2 ppb (ng/ml) of AFQ1 spiked in the urine samples that had been subjected to a Sep-Pak cleanup treatment. In indirect ELISA in which the antigen (AFQ2a-bovine serum albumin) was coated to the solid phase followed by reaction with rabbit antibody and goat anti-rabbit immunoglobulin G-peroxidase conjugate, 50-fold less antibody was used without sacrificing sensitivity. Recoveries of AFQ1 added to urine samples (2 to 40 ppb) were 46.3 to 73% and 65.8 to 85.8% for direct and indirect ELISA, respectively.

Reduction of covalent binding of aflatoxin B1 to rabbit liver DNA after immunization against this carcinogen

The covalent binding of [3H]aflatoxin B1 (AF) to liver DNA was determined, 6 h after oral administration to male rabbits. A Covalent Binding Index, CBI (mumol AF/mol DNA-P)/(mmol AF/kg b.w.) = 8,500 was found. Pretreatment of rabbits with AF coupled to bovine serum albumin in Freund's adjuvant led to the production of AF-directed antibodies. Administration of [3H]AF to such immunized rabbits resulted in a CBI of only 2,500, i.e., the immunization provided a protection by a factor of more than 3. Although this is encouraging evidence for the potential of active immunization against genotoxic carcinogens, a number of points will have to be clarified, such as the time course for the DNA binding and the question of a possible shift to other target cells.

Preparation of aflatoxin B1-BSA conjugate with high hapten/carrier molar ratio

We reported previously on the properties of an anti-aflatoxin B1 (AFB) antiserum raised with a conjugate in which AFB is coupled at the C8 position to bovine serum albumin (BSA). The hapten/carrier protein molar ratio of the conjugate was 14. We have since been able to optimize the coupling conditions, resulting in the preparation of another conjugate, with a molar ratio of 45. Comparison of the 2 conjugates by double-gel immunodiffusion analysis shows that little BSA 'activity' remains on the conjugate with a high molar ratio; on the other hand, its capacity to precipitate in the presence of anti-AFB antibodies is increased.

Indirect immunoperoxidase localization of aflatoxin B1 in rat liver

Aflatoxin B2a (AFB2a) antibody was used as a histochemical probe in the indirect immunoperoxidase localization of aflatoxin B1 (AFB1) bound to rat liver. The efficacy of the indirect method was initially demonstrated by detecting AFB1 covalently bound to DNA in an enzyme-linked immunosorbent assay. AFB1-modified DNA was attached to a polystyrene microtissue culture plate (solid phase) and then subjected to sequential incubation with AFB2a antiserum followed by goat anti-rabbit peroxidase conjugate. Assays for bound peroxidase revealed that the AFB2a antiserum could be diluted 200,000-fold and still yield a signal-to-noise ratio of 10 when compared to an unmodified DNA control. When the same indirect immunoperoxidase protocol was applied to the light-microscopic localization of AFB1 in liver sections of rats treated in vivo with the mycotoxin, bound toxin could be identified in excellent detail in tissues fixed with periodate-lysine-paraformaldehyde and embedded in glycol methacrylate, but was detectable with only poor resolution in unfixed cryostat sections. Peroxidase-positive reactions in hepatocytes typically exhibited strong nuclear and relatively lighter cytoplasmic staining. Greater concentrations of peroxidase-positive hepatocytes were detected in the periportal area than in the area of the central vein, suggesting a circulatory pattern for AFB1 binding in the liver.

Reactivity of aflatoxin B2a antibody with aflatoxin B1-modified DNA and related metabolites

Aflatoxin B2a (AFB2a) antiserum has been previously used in an enzyme-linked immunosorbent assay (ELISA) for the quantitation of AFB1 and AFB2a. The present investigation examined the reactivity of the antiserum toward those adducts and metabolites of AFB1 believed to play a major role in aflatoxicosis and carcinogenesis. 2,3-Dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 (AFB1-N7-Gua), the putative 2,3-(N5-formyl-2-2', 5',6'-triamino-4-oxo-N5-pyrimidyl)-3-hydroxyaflatoxin B1 (AFB1-FAPyr), 2,3-dihydro-2,3-dihydroxyaflatoxin B1 (AFB1-diol), AFB1-N7-Gua-modified DNA, and AFB1-FAPyr-modified DNA were prepared by in vitro incubation or chemical methods and subjected to competitive AFB2a ELISA. The antiserum showed significant reactivity with all five compounds, indicating that it had a high degree of specificity for both the cyclopentenone and the methoxy group of the parent aflatoxin molecule. Sensitivity for AFB-N7-Gua-modified DNA, AFB1-FAPyr-modified DNA, and AFB1-diol by the ELISA method was 0.1 pmol per assay. To test the applicability of immunological detection of covalent binding of AFB1 to DNA, the ELISA was compared with a conventional radioisotopic assay in two in vitro studies. The results showed that estimates of the kinetics and substrate dependence of covalent binding to calf thymus DNA in rat microsomal incubation mixtures by both methods were comparable. The broad specificity AFB2a antibody might be of considerable value in the detection of AFB1 macromolecular adducts and related metabolites in epidemiological investigations or in the diagnosis of aflatoxicosis.

Production of monoclonal antibodies to guanine imidazole ring-opened aflatoxin B1DNA, the persistent DNA adduct in vivo

Monoclonal antibodiess were produced following immunisation of mice with guanine imidazole ring-opened aflatoxin B1 DNA (iro AFB1 DNA), coupled electrostatically to methylated keyhole limpet haemocyanin. Three monoclonal hybridoma lines producing antibodies specific for iro AFB1 DNA were grown as ascites tumours and suitable dilutions of the ascitic fluid (1:8000-1:50,000) used in a competitive enzyme linked immunosorbent assay (ELISA) to measure reactivity of the antibodies to a variety of aflatoxin and nucleic acid-related compounds. These antibodies recognise AFB1 bound to DNA at levels 10(4)-10(5) times lower concentration than unmodified calf thymus DNA or 8,9-dihydro-8,9-dihydroxy-aflatoxin B1: and show 2-5 times the affinity to iro AFB1 DNA compared to AFB1 DNA. The concentration of AFB1 in iro AFB1 DNA producing 50% inhibition in a competitive ELISA was 1.8 x 10(-7) molar. Using the most sensitive hybridoma line, levels of 1 adduct in 300,000 nucleotides would be detectable, which is the level of binding found in the rat and the hamster in vivo. These monoclonal antibodie should therefore prove useful in detecting these lesions in animal and human tissue samples exposed to aflatoxins.

Monoclonal antibody to aflatoxin B1-modified DNA detected by enzyme immunoassay

Monoclonal antibodies were obtained after fusion of mouse P3 X 63 myeloma cells with spleen cells isolated from BALB/c mice that had been immunized with aflatoxin B1-adducted DNA complexed with methylated bovine serum albumin. Selected hybridomas were found to produce monoclonal antibodies specific for aflatoxin B1-modified DNA containing both the 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 and the putative 2,3-dihydro-2-(N5-formyl-2',5',6'-triamino-4'oxo-N5-pyrimidyl) -3-hydroxyaflatoxin B1, suggesting that these DNA adducts share a common antigenic determinant. The monoclonal antibody was not reactive towards the free aflatoxin B1-guanine adducts in solution, seven other aflatoxin derivatives, or benzo[a]pyrene-adducted DNA. A noncompetitive ultrasensitive enzyme radioimmunoassay could measure 15 fmol of aflatoxin B1-DNA adducts in 10 ng of DNA and was at least 100-fold more sensitive than the standard enzyme-linked immunosorbent assay. Competitive enzyme-linked immunosorbent assay with these monoclonal antibodies reliably quantitated aflatoxin B1 adducted in vivo to rat liver DNA at adduct levels of one aflatoxin B1 residue per 250,000 nucleotides. The competitive ultrasensitive enzyme radioimmunoassay was determined to be at least 6-fold more sensitive than the competitive enzyme-linked immunosorbent assay in analysis of aflatoxin B1-adducted DNA. Therefore, enzyme immunoassay using monoclonal antibodies will be useful analytical tools for studying both the molecular interactions of aflatoxin B1 with DNA and the occurrence of aflatoxin B1-DNA adducts in biological specimens from people exposed to this environmental carcinogen.