Dietary modification of aflatoxin B1 carcinogenesis: mechanism studies with isolated hepatocytes from rainbow trout.

Hepatocytes were prepared from rainbow trout by perfusion in situ with collagenase and hyaluronidase. Preparations normally showed high initial viability (95 +/- 5% dye exclusion, 92 +/- 5% lactate dehydrogenase retention) and gradually decreased in viability and glutathione concentration over 5 hours. Cellular metabolism of aflatoxin B1 (AFB1), a potent hepatocarcinogen, was characterized by an investigation of the following parameters: kinetics of AFB1 metabolism and DNA adduct formation, dose response, viabilities of detoxication and activation pathways with time, influence of organic solvents, and effect of variation in cell concentration.

Inhibition of aflatoxin B1 carcinogenesis in rainbow trout by flavone and indole compounds.

Several compounds such as flavonoids, selenium, antioxidants and retinoids reportedly reduce the induction of cancer in experimental animals, and some have been suggested to function by affecting the mixed-function oxidase (MFO) system. The following compounds: 50 and 500 p.p.

Identification and mutagenicity of aflatoxicol-M1 produced by metabolism of aflatoxin B1 and aflatoxicol by liver fractions from rainbow trout (Salmo gairdneri) fed beta-naphthoflavone.

beta-Naphthoflavone (beta NF) fed to rainbow trout (Salmo gairdneri) at 50 or 500 ppm in the diet, modified the in vitro metabolism of aflatoxin B1 (AFB1) by the postmitochondrial fraction (PMF) of the liver. Production of aflatoxicol (AFL) was significantly less in the 500 ppm beta NF-fed group (33.9 ng/mg protein) than in the control group (45.

Dietary antioxidant effects on the hepatic mixed-function oxidase system of rainbow trout (Salmo Gairdneri).

Rainbow trout (Salmo gairdneri) were fed a control diet with or without an antioxidant--3,5-di-tert-butyl-4-hydroxytoluene (BHT), 2(3)-tert-butyl-4-hydroxyanisole (BHA), mono-tert-butylhydroquinone (TBHQ) or ethoxyquin (EQ)--at a level of 5.56 mmol in 100 g oil/kg diet for 6 wk. The treated trout had reduced liver weight/body weight ratios.

Effect of cyclopropenoid fatty acids on the hepatic microsomal mixed-function-oxidase system and aflatoxin metabolism in rabbits.

Male New Zealand weanling rabbits were fed a diet containing 0.25% cyclopropenoid fatty acids for 28 days. Compared with the controls, the rabbits given cyclopropenoid fatty acids showed retarded growth, some moderate liver histological damage, altered hepatic mixed-function-oxidase activities and minor variations in vitro [14C]aflatoxin B1 metabolism.

Liver DNA bound in vivo with aflatoxin B1 as a measure of hepatocarcinoma initiation in rainbow trout.

The in vivo binding of aflatoxin B1 (AFB1) to liver DNA was measured in rainbow trout subjected to various regimens and in coho salmon to determine if binding would correlate with tumor incidence and initiation of hepatocellular carcinoma. Establishment of time-course binding parameters showed no significant difference between 4, 12, 24, or 48 hours. Doses of 5, 25, 100, and 300 micrograms AFB1/kg body weight produced an almost linear increase in binding with increasing dose.

Mechanisms of dietary modification of aflatoxin B1 carcinogenesis.

Trout were fed a range of dietary components which altered their carcinogenic response to aflatoxin B1 (AFB1). Dietary protein at levels substantially exceeding nutritional requirements were synergistic with AFB1. Cyclopropene fatty acids (CPFA) were carcinogenic when fed alone at 20 or 55 ppm, and synergistic when fed with AFB1.

Comparative mutagenicity of aflatoxins using a Salmonella/trout hepatic enzyme activation system.

A modification of the Ames assay using rainbow trout (Salmo gairdneri) liver postmitochondrial fraction (PMF) was developed to investigate the relative mutagenic potential of a series of aflatoxins (AFs). Preliminary experiments revealed that the 20000 x g (S20) liver fraction contained a higher metabolic activity than either the S9 or S30 fractions, and that 5 mg of S20 protein/plate gave the highest mutagenic response. A 9-24 h preincubation period at 25 degrees C was also required.

Carcinogenicity of aflatoxicol in Fischer 344 rats.

Aflatoxicol (AFL), a metabolite of aflatoxin B1 (AFB1), is formed in vitro by liver preparations from several species including humans. A positive correlation appears to exist between the sensitivity of a species to AFB1 and the species ability to metabolize AFB1 to AFL. Conversion of AFB1 to AFL is, therefore, a questionable detoxification step.

Aflatoxicol-induced hepatocellular carcinoma in rainbow trout (Salmo gairdneri) and the synergistic effects of cyclopropenoid fatty acids.

Aflatoxicol (AFL), a major metabolite of aflatoxin B1 (AFB1) in the Mt. Shasta rainbow trout (Salmo gairdneri), was found to produce hepatocellular carcinoma in trout. It was administered in a casein diet to duplicate groups of 120 fingering trout.

Carcinogen aflatoxin B1 is located preferentially in internucleosomal deoxyribonucleic acid following exposure in vivo in rainbow trout.

The purpose of this work was to investigate the distribution in chromatin of deoxyribonucleic acid (DNA) adducts of aflatoxin B1, following exposure in vivo. Rainbow trout were injected intraperitoneally with radiolabeled aflatoxin B1, a potent procarcinogen known to readily induced hepatocellular carcinomas in these fish. After maximum incorporation, liver nuclei were prepared and digested with micrococcal nuclease.

Rainbow trout (Salmo gairdneri) embryos: a sensitive animal model for experimental carcinogenesis.

Dietary exposures have demonstrated rainbow trout to be the most sensitive experimental animal to the hepatocarcinogenicity of aflatoxin B1 (AFB1). More recently the development of an alternate exposure method has shown trout to be even more sensitive to AFB1. This method involves the single exposure of fertile rainbow trout eggs (embryos) to a 0.

Null effect of dietary Aroclor 1254 on hepatocellular carcinoma incidence in rainbow trout (Salmo gairdneri) exposed to aflatoxin B1 as embryos.

Four lots of 200 rainbow trout embryos were exposed to 200 ml solutions of aqueous 0.5 ppm aflatoxin B1 (AFB1) for 1 hr, and 4 lots of 200 rainbow trout embryos were sham-treated for 1 hr. After hatching and swimup, 100 fry from each group were selected for a feeding trial.

Hepatocarcinogenicity of sterigmatocystin and versicolorin A to rainbow trout (Salmo gairdneri) embryos.

Versicolorin A (VA) and sterigmatocystin (ST) are biosynthetic precursors of aflatoxin B1 (AFB1). The carcinogenicity of these compounds relative to AFB1 was determined with the use of rainbow trout (Salmo gairdneri) embryo exposure. Exposure of 14-day rainbow trout embryos to a 0.

Hepatocarcinogenicity of glandless cottonseeds and cottonseed oil to rainbow trout (Salmo gairdnerii).

Glandless cottonseed kernels are available for purchase and consumption by the general public. These kernels contain no gossypol but still have a full complement of naturally occurring cyclopropenoid fatty acids, which in rainbow trout are active as synergists with aflatoxins and primary liver carcinogens. Diets containing glandless cottonseed kernels or a lightly processes cottonseed oil produced significant numbers of hepatocellular carcinomas in rainbow trout after 1 year.

Carcinogenic response of rainbow trout (Salmo gairdneri) to aflatoxin Q1 and synergistic effect of cyclopropenoid fatty acids.

Aflatoxin Q1 (AFQ1), the major microsomal biotransformation product of aflatoxin B1 (AFB1) formed in vitro by monkey and human liver preparations, was fed to rainbow trout (Salmo gairdneri) in a semipurified diet at levels of 20 ppb for 1 year and 100 ppb for 10 months. As a test for carcinogenicity in hatched fish, it was also used at 1 ppm in a water solution and exposed for 1 hour to fertile trout eggs. The 20-ppb dietary exposure and 1-ppm egg exposure failed to elicit a carcinogenic response; however, the 100-ppb dietary exposure produced a 10.

Turnover of label from [1-14C]linolenic acid in phospholipids of coho salmon, Oncorhynchus kisutch.

Juvenile coho salmon were injected intraperitoneally with [1-14C] linolenic acid and sampled at 24, 120, and 240 hr. Liver, heart and gill lipids were extracted analyzed, and halflives of individual liver glycerophospholipids and n-3 fatty acids determined from rates of loss of radioactivity. Incorporation of label into gill was much less than into either heart or liver.

Investigation of covalent aflatoxin B1-DNA adducts formed in vivo in rainbow trout (Salmo gairdneri) embryos and liver.

The formation of covalent aflatoxin-DNA adducts has been studied in embryo and yearling stages of the rainbow trout (Salmo gairdneri). A linear relationship was found between the amount of aflatoxin B1 (AFB1) absorbed into 21-day-old eggs and the level of covalent modification of embryo DNA after exposure to 0.25 to 0.

Aflatoxin B1 and aflatoxicol metabolism in rainbow trout (Salmo gairdneri) and the effects of dietary cyclopropene.

Aflatoxin M1 was identified as a minor metabolite formed by the in vitro incubation of aflatoxin B1 with the postmitochondrial fraction or microsomes from rainbow trout (Salmo gairdneri) liver. Fresh, whole trout liver converted perfused aflatoxin B1 to aflatoxicol and aflatoxin M1, and converted perfused aflatoxicol to aflatoxin B1 and aflatoxin M1. AFB1 reductive activity was found in the 105,000 xg supernatant, while activity converting AFL to AFB1 was distributed about equally in the 105,000 xg supernatant and in the microsomal pellet.

Dietary protein levels and aflatoxin B metabolism in rainbow trout (Salmo gairdneri).

In an attempt to understand dietary protein effects upon aflatoxin B1-induced liver cancer in rainbow trout, the activities of several suspected aflatoxin B1 metabolizing enzyme systems were studied relative to protein intake. Fish fed diets containing 32 percent, 52 percent and 62 percent fish protein concentrate (FPC) were examined for hepatic cytochrome P-450 content and in vitro cytochrome c reductase, glutathione-S-epoxide transferase (GTr), epoxide hydrase (EH) and aldrin epoxidase (AE) activity. In addition, aflatoxin B1 conversion to aflatoxicol (AFL) was examined.