Search PubMed⌕ Search

Biomedical subjects

F S Chu

Publications and source records attributed to F S Chu.

At least 73 records · Page 4Linked to original sources
PubMed1982

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.

Aflatoxin B1↗
PubMed1981

Production and characterization of aflatoxin B2a antiserum.

The specificity and sensitivity of antiserum elicited from rabbits against aflatoxin B2a-bovine serum albumin conjugates were characterized with a radioimmunoassay (RIA) and an enzyme-linked immunosorbent assay (ELISA). Aflatoxin B1 was first converted to aflatoxin B2a and then conjugated to bovine serum albumin and horseradish peroxidase by a reductive alkylation method. The antiserum was developed in New Zealand white rabbits by multiple-site injection with the aflatoxin B2a-bovine serum albumin conjugate. Antibody titers were determined by both RIA and ELISA. Competitive RIAs with various aflatoxin analogs indicated that the antiserum was most reactive with aflatoxin B1 and slightly cross-reactive with aflatoxins B2a, B2, and M1. Competitive ELISAs showed the antiserum to be equally specific for aflatoxins B2a and B12 and less reactive with aflatoxins B2 and M1. The relative sensitivities of RIA and ELISA for aflatoxin B1 quantitation were 100 and 10 pg per assay, respectively.

Aflatoxins↗
PubMed1981

Enzyme-linked immunosorbent assay for detection of ochratoxin A.

A simple microtest plate enzyme-linked immunosorbent assay was developed for the detection of ochratoxin A at levels as low as 25 pg per assay. The relative cross-reactivities of the antibody in this system with ochratoxin A (OA), OB, OC, and Oalpha were found to be 1.0, 0.14, 0.44, and 0.01, respectively.

Cross Reactions↗
PubMed1981

Comparison of radioimmunoassay and enzyme-linked immunosorbent assay for determining aflatoxin M1 in milk.

Using a highly specific antibody against aflatoxin M1, a radioimmunoassay (RIA) and an enzyme-linked immunosorbent assay (ELISA) were developed for the quantitation of M1 in milk. RIA was sensitive in the range of 5-50 ng per assay but was subject to interference by whole milk. Extraction and cleanup were therefore necessary for the detection of M1 in milk at 0.5 ng/mL. An ELISA procedure was developed by using an aflatoxin M1-carboxymethyl-horseradish peroxidase conjugate as the ligand. Competitive assays revealed that this system was relatively more sensitive for M1 than for B1, and had a much lower degree of cross-reactivity for aflatoxins B2, G1, G2, B2a, and aflatoxicol. As low as 0.25 ng M1/mL in artificially contaminated milk (raw, whole, skim) could be detected by ELISA in 3 h without extraction or cleanup. Because of its simplicity, sensitivity, and specificity, ELISA is the preferred method for monitoring aflatoxin M1 in milk.

Aflatoxin M1↗
PubMed1981

Determination of aflatoxin B1 in corn, wheat, and peanut butter by enzyme-linked immunosorbent assay and solid phase radioimmunoassay.

Determinations of aflatoxin B1 in corn, wheat, and peanut butter by an enzyme-linked immunoassay (ELISA) and a solid-phase radioimmunoassay (RIA) were compared. Samples spiked with 2.9-43.2 ppb B1 were subjected to AOAC extraction procedure 26.017 or 26.023. The extracts were concentrated, redissolved in methanol, diluted in phosphate-buffered saline with Tween 20, and directly analyzed for B1 by either ELISA or RIA. At 5.8 ppb or greater, recoveries for B1 in corn, wheat, and peanut butter samples were 80.0, 86.6, and 94.8% by ELISA and 61.0, 93.3, and 110.0% by RIA, respectively. Recoveries greater than 120% were obtained for the wheat and peanut butter samples spiked with 2.9 ppb aflatoxin B1 by the RIA method but not by ELISA. Overall results indicated that ELISA gave more consistent data, relatively lower standard deviations, and lower coefficients of variation than did RIA. Analysis of 3 samples naturally contaminated with aflatoxins revealed that the ELISA data were comparable to those obtained by other established chemical methods.

Aflatoxin B1↗
PubMed1981

Radioimmunoassay of T-2 toxin in corn and wheat.

A radioimmunoassay (RIA) for the determination of T-2 toxin in corn and wheat was developed. The toxin was first extracted with methanol, and the methanolic extract was washed with hexane and passed through a Sep-Pak C18 reverse phase cartridge. The extract was then evaporated to remove the organic solvent, diluted with 0.1M sodium phosphate buffer (pH 7.2), and subjected to RIA using an ammonium sulfate precipitation method to separate the free T-2 toxin from the antigen-antibody complex. The recovery of T-2 toxin after the extraction and cleanup steps was 78-85% for corn and 90-95% for wheat. Sep-Pak cleanup removed a considerable amount of interfering substances from the sample, thus enabling the detection of 1 and 2.5 ppb of T-2 toxin in the wheat and corn samples, respectively. The recovery by RIA methods of T-2 toxin added to the corn and wheat samples was between 84 and 103% in the ranges of 1-20 ppb (for wheat) and 2.5-20 ppb (for corn). The new RIA proved to be a sensitive, accurate, reproducible, and relatively simple method for determining T-2 toxin.

Animals↗
PubMed1981

Radioimmunoassay of T-2 toxin in biological fluids.

A simple radioimmunoassay (RIA) for detection of T-2 toxin in biological fluids was developed. The method, which involves a Sep-Pak C18 reverse phase column cleanup step before RIA, can detect 0.5 ppb T-2 toxin in serum and 2.5 ppb T-2 toxin in urine and milk. Recoveries for toxin added to serum and urine or milk samples were 87-106% in the 0.5-20 ppb range and 88-117% in the 2.5-20ppb range, respectively. If samples were not cleaned up, false positive results prevented positive detection at concentration less than 2.5 ppb in urine and milk.

Body Fluids↗
PubMed1980

Comparison of antibody production against aflatoxin B1 in goats and rabbits.

Antibody production against aflatoxin B1 was compared in three rabbits and one goat. Titers obtained were 20 times higher in the rabbits than in the goat. The goat antiserum appeared to have a higher degree of cross-reactivity for other aflatoxins and related metabolites than did the rabbit antiserum.

Aflatoxins↗
PubMed1980

Quantitation of aflatoxin B1 and aflatoxin B1 antibody by an enzyme-linked immunosorbent microassay.

A specific microtest plate enzyme immunoassay has been developed for the rapid quantitation of aflatoxin B1 at levels as low as 25 pg per assay. Multiple-site injection of rabbits with an aflatoxin B1 carboxymethyloxime-bovine serum albumin conjugate was used for the production of hyperimmune sera. Dilutions of the purified antibody were air dried onto microplates previously treated with bovine serum albumin and glutaraldehyde and then incubated with an aflatoxin B1 carboxymethyloxime-horseradish peroxidase conjugate. The amount of enzyme bound to antibody was determined by monitoring the change in absorbance at 414 nm after the addition of a substrate solution consisting of hydrogen peroxide and 2,2'-azino-di-3-ethyl-benzthiazoline-6-sulfonate. Antibody titers determined in this manner closely correlated with those determined by radioimmunoassay. Competition assays as performed by incubation of different aflatoxin analogs with the peroxidase conjugate showed that aflatoxins B1 and B2 and aflatoxicol caused the most inhibition of conjugate binding to antibody. Aflatoxins G1 and G2 inhibited the conjugate binding to a lesser degree, whereas aflatoxins M1 and B2a had no effect of the assay.

Aflatoxins↗
PubMed1979

Production and characterization of antibody against aflatoxin M1.

Antibody against aflatoxin M1 was obtained after immunization of rabbits with bovine serum albumin-afla M1 oxime conjugate. The antibody has greatest binding efficiency for afla M1, and was less efficient for afla B1. Cross-reaction of antibody with aflatoxin Q1, aflatoxicol, and aflatoxin B2a was weak. Aflatoxin B2, G1, and G2 and afla B1-guanine adducts showed almost no cross-reaction with the antibody. The sensitivity of the binding assay for aflatoxin M1 detection is in the range of 1-10 ng per assay. Detailed methods for the preparation of the conjugate, production of immune serum, and methods for antibody determination are described.

Aflatoxins↗
PubMed1979

Characterization of byssochlamyopeptidase A.

The enzyme properties of byssochlamyopeptidase A, a chymosin-like enzyme produced by Byssochlamys fulva were studied. The enzyme was shown to be electrophoretically and immunochemically pure. Most metallic cations had negligible effect, whereas Hg2+ greatly suppressed the enzyme activity. N-Bromosuccinimide and I2 completely inactivated the enzyme. For milk clotting at pH 4.6-6.6, the enzyme was less sensitive to pH than pepsin. The substrate specificity of the enzyme was studied by incubation of the enzyme at 37 degrees C with whole and individual casein fractions at pH 6.6 and pH 3.0, respectively. The proteolysis by the enzyme was found to be most extensive for alphas-, less for kappa-, and least for beta-casein. Studies with different synthetic dipeptides and tripeptides revealed that byssochlamyopeptidase A exhibits specificity for Phe-Tyr and Gly-Phe-Phe, but the enzyme did not hydrolyze Ac-Phe-Tyr(I2).

Ascomycota↗
PubMed1979

Effects of temperature and time on mutagen formation in pan-fried hamburger.

Mutagenic activity generated in hamburger during pan-frying is dependent upon both temperature and time, with temperature appearing to be the more important variable. Uniformly prepared frozen hamburger pattie (115 g; 19% fat) were fried under carefully controlled conditions at 143 degrees C, 191 degrees C and 210 degrees C. Mutagenic activity assayed with the Ames test was not detected in uncooked hamburger, and in hamburger fried at 143 degrees C mutagenic activity remained low at all times studied (4--20 min). In contrast, frying at 191 degrees C or 210 degrees C for up to 10 min resulted in the generation of considerably higher levels of mutagenic activity. Mutagenic activity in fried hamburgers sold at selected restaurants ranged from very low to moderately high. Evidence is also presented for mutagenic inhibitory activity in uncooked and fried hamburger. Mutagenic inhibitory activity decreased mutagenesis mediated by liver S-9 from normal rats but not from Aroclor 1254-treated rats.

Animals↗
PubMed1979

Fate of ochratoxin A in goats.

The fate of ochratoxin A (OA) was studied in goats given a single oral dose of 3H-OA (0.5 mg/kg). More than 90% of the radioactivity was found to be excreted in 7 days and the majority (53%) was found in feces. Thirty-eight percent, 6% and 2.26% of the activity was found in urine, milk and serum, respectively. The radioactivity in the liver and kidney 6 hours after feeding amounted to 1.5 and 0.5% of the total dose administered, respectively. Subsequent fractionation of liver and kidney homogenates revealed that microsomes, ribosomes and post-ribosomal supernatant fractions contained most radioactivity. Thin layer chromatographic analyses revealed two additional radioactive spots with Rf values and fluorescent characteristics different from OA, Oalpha and 4-OH-OA. Whereas OA was found as the unaltered molecule in feces, the metabolites were primarily found in urine and milk. Less than 0.03% of free OA was found in milk during the 7-day period.

Animals↗
PubMed1979

Production of antibody against T-2 toxin.

Antibody against T-2 toxin was obtained after immunization of rabbits with bovine serum albumin-T-2 hemisuccinate conjugate. The antibody had greatest binding efficiency for T-2 toxin, less efficiency for HT-2, and least for T-2 triol. Cross-reaction of antibody with neosolaniol, T-2 tetraol, and 8-acetyl-neosolaniol was very weak. Diacetoxyscirpenol, trichodermin, vomitoxin, and verrucarin A essentially gave no cross-reaction with the antibody. The sensitivity of the binding assay for T-2 toxin detection was in the range of 1 to 20 ng per assay. Detailed methods for the preparation of the conjugate and the production of immune serum and methods for antibody determination are described.

Animals↗
PubMed1978

Modification of hepatotoxic effects of aflatoxin B1 in rabbits by immunization.

Reduction of acute toxic effect of aflatoxin B1 was achieved by immunizing the rabbits with small amounts of bovine serum albumin-aflatoxin B1 conjugate. Rabbits after immunization showed lower mortality, near normal serum isocitric dehydrogenase activity, no abnormality in livers when challenged with a single dose of aflatoxin B1. The results suggest that immunization might be used prophylactically against aflatoxicosis.

Aflatoxins↗