Graduate Thesis Or Dissertation
 

Aflatoxin B₁ metabolism by rainbow trout (Salmo gairdneri)

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  • Aflatoxins B₁, Q₁ and aflatoxicol, R [subscript o] F, but not B₂ were activated in the presence of NADPH by the 105,000 x g pellet from rainbow trout (Salmo gairdneri), Mt. Shasta strain, liver to products lethal to Bacillus subtilis GSY 1057 (metB4, hisAl, uvr-1). Electron microscopy confirmed the microsomal fraction primarily contained smooth endoplasmic reticulum. An NADPH mixed function oxidase with neo-tetrazolium reductase and aldrin epoxidase activity was present in the microsonaes. The activity of the oxidase was reduced parallel to a decrease in lethal factor production by piperonyl butoxide, NADPH deprivation, heat treatment and certain diets. After incubation of microsomes with ¹⁴C labeled B₁, the activity was found in unaltered B₁ and three extremely polar metabolites designated NM (3. 6-5. 3%), B [subscript 2a] A (1-5%) and M₁A (< 1%). They were eliminated or reduced along with microbial lethality when cytosine and cysteine were added to the incubation media. The structural requirement for the vinyl ether of B₁, R [subscript o] F and Q₁ and the nature of the enzymatic reaction were consistent with the hypothesis that the conapounds were metabolized to highly reactive and unstable electrophilic products which bound to nucleophiles such as cytosine and were lethal to B. subtilis. Aflatoxicol, R [subscript o] F, was isolated from liver homogenates and was apparently fornaed by an NADPH-dependent soluble enzyme of the 105,000 x g supernatant from rainbow trout. R [subscript o] F and its diastereomer, R [subscript o] R, were prepared by chemical reduction of B₁. Their identity was confirmed by UV and mass spechrometry. The ten-day LD50 value was 0.66 mg/kg for R [subscript o] F compared to 0.46 mg/kg for B₁. No mortality was observed, from R [subscript o] R at equivalent doses. Similar gross and microscopic pathological changes were observed for B₁, R [subscript o] F and R [subscript o] R. The degree of damage paralleled the LD50 values. After eight months of feeding, 20 ppb of B₁ and R [subscript o] F and 36.6 ppb R [subscript o] R gave 56.3%, 26.2% and 0% incidence of hepatoma. Addition of 50 ppm of cyclopropenoid fatty acids increased the incidence to 96.3%, 93.8% and 55% for B₁, R [subscript o] F and R [subscript o] R. It was concluded that aflatoxicol was not an effective means of detoxication of B₁, but instead extended the presence of a potentially toxic and carcinogenic compound.
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