Date of Award

1998

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Nutrition and Food Sciences

First Advisor

Douglas L. Park

Abstract

The current study evaluated interactions between the mycotoxins aflatoxin B$\sb1$ (AFB$\sb1$) and fumonisin B$\sb1$ (FB$\sb1$) in pure systems as well as in corn. During storage at 25$\sp\circ$C with high moisture (ca. 50%), corn contaminated with Aspergillus flavus (L13) and/or Fusarium moniliforme (A00102) presented different aflatoxin and fumonisin levels. Toxin production/degradation varied over storage time (0-45 days). Evaluation of the mutagenicity of unifungal or bifungal corn extracts with the Salmonella/microsomal assay (tester strains TA-100 and TA-98) with metabolic activation (S9) showed positive mutagenic responses. Different ratios of pure AFB$\sb1$/FB$\sb1$ produced divergent mutagenic responses (tester strains TA-100 and TA-98) with S9. The mutagenicity of 10$\sp3$ ng AFB$\sb1$/plate was reduced by addition of 1 to 10$\sp2$ ng FB$\sb1$/plate. Higher FB$\sb1$ concentrations (10$\sp3$ to 10$\sp5$ ng/plate) caused an opposite effect. The mutagenic potential of 2-aminofluorene (2-AF) was also affected by FB$\sb1.$ This suggested that FB$\sb1$ affects the enzyme systems responsible for activating AFB$\sb1$ and 2-AF. Analysis by liquid chromatography of AFB$\sb1$/AFB$\sb1$-metabolites after reaction with FB$\sb1$ and S9 showed decreased recovery when 10$\sp3$ ng AFB$\sb1$ were exposed to 1 to 10$\sp2$ ng FB$\sb1$, but at higher FB$\sb1$ levels (10$\sp3$ to 10$\sp5$ ng), recovery was increased. Thin layer chromatography analysis of these samples suggested that unidentified AFB$\sb1$-metabolites derivatized with trifluoroacetic acid were indirectly detected as AFB$\sb1.$. FB$\sb1$ (1 to 10$\sp5$ ng/plate) inhibited gap-junction intercellular communication of Clone-9 rat liver cells. This could be a possible mechanism by which FB$\sb1$ acts as a non-genotoxic carcinogen. Addition of 1 to 10$\sp3$ ng AFB$\sb1$ to 10$\sp5$ ng FB$\sb1$ did not change the effect of FB$\sb1.$ An increase in the uptake of neutral red by Clone-9 rat liver cells exposed to AFB$\sb1$/FB$\sb1$ implied that peroxisome proliferation and oxidative metabolism may be involved in AFB$\sb1$/FB$\sb1$ interactions. H$\sb2$O$\sb2$ (3%) and NaHCO$\sb3$ (2%) were effective in decontaminating/detoxifying aflatoxin-fumonisin naturally co-contaminated corn without generating mutagenic by-products. This study showed preliminary evidence that simultaneous exposure to AFB$\sb1$/FB$\sb1$ can give different toxicological responses than single exposure to either of these compounds. More research is needed to better assess the toxicological impact of AFB$\sb1$/FB$\sb1$ co-contamination and to develop possible control strategies.

ISBN

9780591997897

Pages

278

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