Binding of aflatoxin by plasma albumin in vitro

Aflatoxin B1 transport in rat blood plasma. Binding to albumin in vivo and in vitro and spectrofluorimetric studies into the nature of the interaction

Binding of [3H]aflatoxin B1 to rat plasma was investigated in vivo and in vitro. Column chromatographic and polyacrylamide gel electrophoretic analyses clearly demonstrated that aflatoxin B1 bound primarily plasma albumin. Very little binding activity was shown by other plasma proteins. Spectrofluorimetric studies were undertaken to gain some insight into the nature of the aflatoxin-albumin interaction. Quenching of the lone tryptophan fluorescence intensity upon aflatoxin binding was due, at least in part, to a ligand-induced conformational change in the albumin molecule. Aflatoxin B1 binds an apolar site with an association constant of 30 mM-1 at pH 7.4 and 20 degrees C. Neither charcoal treatment of rat albumin nor the presence of 0.15 M NaCl had any significant effect on the interaction. The association constant was pH-dependent, increasing about 1.7-fold as the pH increased from 6.1 to 8.4. This pH dependence is ascribed to a pH-induced conformational change in the albumin molecule. Thermodynamic studies indicated that the aflatoxin-albumin interaction was exothermic (delta H = -29.3 kJ X mol-1), with a delta S value of -13.8 J X mol-1 X K-1.

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.

In vivo and in vitro studies on the binding nature of terreic acid with macromolecules such as protein and nucleic acids

The binding of terreic acid to macromolecules such as nucleic acids and protein was examined. In vivo studies using [14C]terreic acid showed that radioactivity was incorporated into the protein and nucleic acid fractions of the liver mice. In vitro experiments with human serum showed that [14C]terreic acid bound to the albumin component and spectral studies indicated that terreic acid also combined with hepatic DNA.

Biointeraction of sodium selenite and aflatoxin B1 in the Mongolian gerbil

The interaction of sodium selenite (Na2SeO3) and aflatoxin B1 (AFB1) was studied in 6-wk-old male Mongolian gerbils. Each of four groups of gerbils were fed one of the following diets during a 12-wk experimental period: control (commercial Chow), 5.0 ppm Na2SeO3, 12.8 ppm AFB1, or 5.09 ppm Na2SeO3 + 12.8 ppm AFB1. Animals receiving Na2SeO3 in the diet, alone and with AFB1, had a significantly lower mean total weight gain during the experiment than did control animals. Animals receiving both compounds together displayed a very high level of physical activity compared to the three other groups. Blood analysis showed no change in total leukocytes, but the relative percentage of lymphocytes increased and the percentage of neutrophils decreased concurrently in the order: control less than AFB1 less than Na2SeO3 + AFB1 les than Na2SeO3. A significant reduction in organ weight relative to body weight was observed in the liver, kidney, and lung of the animals fed AFB1 alone but only in the liver of those fed both Na2SeO3 and AFB1. No similar alterations were observed in the Na2SeO3 group. Histopathological examination revealed considerably less hepatic damage in animals fed Na2SeO3 with AFB1 than in those receiving either compound alone. Renal and intestinal damage, however, was most severe in this double-treatment group. Hepatic protein analysis revealed two protein peaks in the Na2SeO3 + AFB1 group that were absent in all other groups. It was concluded that these proteins may be selenoproteins directly or indirectly involved in the lower incidence of histopathological damage in this group.