Effect of dietary protein on the response of rainbow trout (Salmo gairdneri) to aflatoxin B1.

Diets containing either 49.5% or 32% casein or fish protein concentrate (FPC) were fed to young rainbow trout (Salmo gairdneri) for 12 months. Five levels [0, 2, 6, 18, and 54 parts per billion (ppb)] of aflatoxin B1 (AFB1) were given in each of four different diets. A 30-fish sample was taken at 6, 9, and 12 months to determine the influence of diet on the carcinogenicity of AFB1. Both levels of casein produced similar hepatoma incidences at each level of AFB1. The diet high in FPC produced more tumours than did the casein diets at 2, 6, and 18 ppb AFB1, whereas fish fed the diet low in FPC had a significantly (P less than 0.05) lower hepatoma incidence than did the other three groups. The liver size (percent body wt) was smaller at higher toxin levels in all instances. The growth of fish given 32% casein was less than that of the other groups.

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 0.5-ppm aqueous suspension of ST for 1 hour produced a 13% incidence of hepatocellular carcinomas among survivors 1 year later. Similar exposure of trout eggs to a 0.5-ppm solution of AFB1 produced a 53% incidence among survivors. Subsequent exposure of 21-day rainbow trout embryos to 5- and 25-ppm solutions of VA resulted in hepatocellular carcinoma incidences among survivors of 42 and 68%, respectively, at 12 months. A 0.5-ppm AFB1 positive control group had a 68% incidence among survivors of hepatocellular carcinomas at 1 year. These results established the carcinogenicity of VA for the first time and confirmed previous reports of ST carcinogenicity. Both compounds were of sufficient potencies to warrant caution as possible human health hazards.

Aflatoxin B1 induction of hepatocellular carcinoma in the embryos of rainbow trout (Salmo gairdneri).

Liver cancer in rainbow trout was induced by exposure of fertile eggs to an aqueous, 0.5 ppm (microgram/ml) solution of aflatoxin B1 (AFB1) for 1 hour. Single treatments, given on alternate days during the embryonic period, produced a low cancer incidence (less than 20%) prior to formation of the embryonic liver on day 14, but a steadily increasing incidence from day 15 (31.7%) until day 23 (58.3%), in fish examined 1 year later. Treatment of trout eggs with [14C]AFB1 was used to quantitate the amount of AFB1 absorbed by the eggs. Twenty-one-day-old rainbow trout eggs absorbed approximately 30 ng of [14C]AFB1 during a 1-hour exposure to 0.5 ppm aqueous [14C]AFB1. After 1 day 85-90% of the [14C]AFB1 was either metabolized and excreted or leached from the egg. The residual [14C]AFB1 remained constant until hatching when an additional 50% was lost. Comparison of the amount of AFB1 absorbed by eggs with the amount of AFB1 consumed per fish during a 1-year feeding trial at 4 ppb in the diet indicates that the trout embryo is even more sensitive than juvenile trout to the carcinogenic properties of AFB1.

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 10.6% incidence of hepatocellular carcinomas at the end of 1 year. Administration of 50 ppm methyl sterculate, a cyclopropenoid fatty acid, in combination with 100 ppb AFQ1 resulted in a synergistic tumor response similar to that previously noted with administration of AFB1 plus aflatoxin M1. The tumor incidence was 89.1% in the fish on the combined diet. These results indicated that AFQ1 was approximately 100 times less carcinogenic than was AFB1. This comparison of carcinogenic potencies was very similar to the comparison of the relative mutagenicities of the two compounds in the Ames bacterial mutagen assay system.

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. In the same manner, additional duplicate groups received one of the following: no toxicant; AFB1; the diastereomer of AFL (AFL'); cyclopropenoid fatty acids (CPFA); and CPFA plus AFB1, AFL, and AFL'. Eight months after the initiation of the study, the following incidences of carcinoma were observed: control (0%); 20 ppb AFB1 (56%); 29 ppb AFL (26%); 61 ppb AFL' (0%); 50 ppm CPFA (3%); 20 ppb AFB1 plus 50 ppm CPFA (96%); 29 ppb AFL plus 50 ppm CPFA (94%); and 61 ppb AFL' plus 50 ppm CPFA (55%), showing both the carcinogenicity of AFL and the synergistic effects of CPFA. Twelve-month incidences were correspondingly higher in all cases. Aflatoxin M1, another metabolite of AFB1 in rainbow trout, was reported previously to be carcinogenic in trout. These results support the hypothesis that metabolism in rainbow trout does not effectively detoxify AFB1, but rather the formation of AFL extends the carcinogenicity of AFB1 and may contribute to the high sensitivity of rainbow trout to AFB.

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 0.5 ppm aqueous solution of AFB1 for 30 minutes, rinsing the eggs in water, and allowing hatching, swim-up and the onset of feeding to proceed as usual. Resulting fish are fed a control diet for 1 year at which time approximately two-thirds of the population will have developed hepatocellular carcinoma of the liver. Variables, such as embryo age of greatest sensitivity, carcinogen concentration, and length of exposure, have been defined for AFB1 exposures. Sensitivity to AFB1 increased with increasing age of the embryo, the model system showed a dose-response to increasing carcinogen concentrations, and one-half hour exposures appeared to be optimum for AFB1. Experiments with other carcinogens have shown the embryo model system to be sensitive to the hepatocarcinogenicity of AFB1 metabolites (aflatoxicol, aflatoxin M1, and aflatoxin G1), sterigmatocystin, versicolorin A, dimethylnitrosamine, and N-methyl-N'-nitro-N-nitrosoguanidine. The latter compound also initiated nephroblastomas of the kidneys. The results demonstrate the potential for the trout embryo to be developed into a convenient, economical, and sensitive whole animal model system for experimental carcinogenesis.

Aflatoxin in corn: ammonia inactivation and bioassay with rainbow trout.

Four samples of corn were compared with respect to their hepatocarcinogenicity in rainbow trout. One corn sample was found by chemical analysis to contain no detectable aflatoxin. A second sample was contaminated with aflatoxins at a level of 180 microgram/kg. Each of the above-mentioned samples was divided, and one-half of each was ammoniated. These four samples were added to a semipurified basal diet and fed to a sensitive strain of rainbow trout. It was found that ammoniation inactivated the aflatoxins and reduced the carcinogenicity of the contaminated corn to a level that was not significantly different from that with the basal control diet. It was also found that the ammoniation process did not reduce the nutritive value of the corn.

Neurological and adrenal dysfunction in the adrenal insufficiency/alacrima/achalasia (3A) syndrome.

Review of 20 patients with glucocorticoid deficiency (three cases also with salt loss) associated with absent tear secretion (19 cases) and achalasia of the cardia (15 cases) revealed neurological abnormalities in 17 including hyper-reflexia, muscle weakness, dysarthria, and ataxia together with impaired intelligence and abnormal autonomic function, particularly postural hypotension. These findings indicate that significant neurological problems are common in this multisystem disorder.