J. H. Wales

NEOPLASMS IN RAINBOW TROUT, A SENSITIVE ANIMAL MODEL FOR ENVIRONMENTAL CARCINOGENESIS*

The following topics are discussed: susceptibility of rainbow trout (Salmo gairdneri) to aflatoxins and other mycotoxins; the Oregon test diet; carcinogenic effects of cyclopropenoid fatty acids; carcinogenic response of the rainbow trout embryo; metabolism of mycotoxins by rainbow trout; and pathogenesis of rainbow trout liver cancer. (HLW)

Acute intraperitoneal toxicity of ochratoxins A and B in rainbow trout (Salmo gairdneri)

Abstract The acute intraperitoneal toxicities of two metabolites of Aspergillus ochraceus , ochratoxins A and B, and their dihydroisocoumarin derivatives, ochratoxins a and b , were studied in 6-month-old Mt. Shasta strain rainbow trout ( Salmo gairdneri ). Ochratoxin A was the only compound found to be lethal to trout at the levels administered, its acute intraperitoneal LD 50 being 4·67 mg/kg. Pathological changes in the liver and kidneys were produced by ochratoxins A and B but not by ochratoxin a or b . Ochratoxin A produced degenerative changes in the hepatic parenchymal cells, including nuclear swelling and cytoplasmic and nuclear lipid vacuolation, necrosis in the proximal tubules, haematopoietic tissue and glomeruli of the kidneys and pycnotic nuclei, cast formation and lipid vacuolation in the renal tubules. Ochratoxin B administered at levels up to 66·7 mg/kg caused no deaths but the highest dose induced pathological changes in the liver and kidneys similar to those produced by relatively low levels of ochratoxin A. Ochratoxins a and b administered at levels up to 28·0 and 26·7 mg/kg, respectively, failed to cause any deaths or induce any microscopic lesions that were not seen in control trout dosed with 0·1 n -sodium bicarbonate. It is suggested that ochratoxins A and B are metabolized to their non-toxic water-soluble dihydroisocoumarin moieties, which are readily excreted.

The effect of dietary sterculic acid on the hepatic lipids of rainbow trout.

Groups of young rainbow trout (5 g) were fed a basal diet containing 9% salmon oil and 1% tristearin with 0, 100 or 200 ppm methyl sterculate. Liver lipids were separated into polar and nonpolar fractions and the fatty acids quantitatively analyzed. Significant elevations of the stearic-oleic and the palmiticpalmitoleic ratios were found in liver fatty acid composition 10 days after the feeding trial began. Liver triglycerides of fish fed methyl sterculate for 87 days contained only 2–3% docosahexenoic acid as compared to 10.69% in control trout, suggesting an effect on the biosynthesis of long chain polyunsaturates. Dietary cyclopropenoid fatty acids (CPFA) suppressed growth rate during the first part of the 200 day feeding trial. After 90 days no differences in the rate of weight gain were observed between the control and CPFA groups. A seven day feeding trial with 0, 5, 20, 50 and 100 ppm CPFA resulted in a maximum change in the stearic-oleic ratio at 50 and 100 ppm levels. All levels of CPFA increased this ratio and caused marked alterations in the cellular morphology of the liver.

Effect of subacute toxic levels of dietary cyclopropenoid fatty acids upon membrane function and fatty acid composition in the rat.

The effect of subacute toxicity levels of dietary cyclopropenoid fatty acids upon several physiological parameters was determined in the rat. Diets containing 2% corn oil, 2%Sterculia foetida oil or 2% hydrogenatedSterculia foetida oil were fed.Sterculia foetida oil (50% cyclopropenoid fatty acids) fed rats exhibited retarded growth, elevated organ to body wt ratios, increased saturation of tissue lipid, and abnormal histopathology when compared to corn oil and hydrogenatedSterculia foetida oil fed rats. Growth was retarded 50%, liver/body wt doubled, and the percentage of saturated fatty acids in adipose tissue increased 2.5-fold forSterculia foetida oil vs. corn oil comparisons. Three membrane systems were examined in corn oil andSterculia foetida oil fed rats. Erythrocyte hemolysis rate in 0.3 M glycerol was increased by 30%; induction of mitochondrial swelling by reduced glutathione was inhibited completely and microsomal codeine demethylase activity was depressed nearly 50% inSterculia foetida oil fed rats. The ability of cyclopropenoid fatty acids to inhibit fatty acyl desaturase and influence tissue and membrane lipid composition is discussed. Most of the detrimental effects observed in cyclopropenoid fatty acids fed rats may be associated with alteration of normal lipid metabolism and membrane function.

Cholesterol levels, atherosclerosis and liver morphology in rabbits fed cyclopropenoid fatty acids**

Abstract Male New Zealand rabbits were fed diets containing either 0.27% cyclopropenoid fatty acids (CPFA) or 0.5% cholesterol or both in combination. Compared with control animals, those receiving CPFA tended to have higher plasma- and liver-cholesterol levels and a higher incidence of aortic atherosclerosis. A similar pattern was seen when animals fed cholesterol and CPFA were compared with animals fed cholesterol alone. The observed increases in liver cholesterol, plasma cholesterol and plasma triglycerides indicated a wide range of sensitivity to CPFA. Some animals had plasma-cholesterol levels eight to ten times as high as normal after feeding had continued for 3 wk, while others showed only slight changes after 5 wk. Liver cells from all CPFA-fed animals had altered morphology and often showed extensive damage.

Null carcinogenic effect of large doses of nitrosoproline and nitrosohydroxyproline in Wistar rats.

Summary The nitrosamino acids, nitrosoproline or nitrosohydroxyproline, were given orally to weanling rats in four weekly doses totalling 290 mg/animal and the rats were observed for their lifetime. Negative controls received water and positive controls were given diethylnitrosamine. The rats were maintained on a basal semi-purified diet or a basal diet containing cyclopropenoid fatty acids. No tumorigenic effect was seen in rats given nitrosoproline or nitrosohydroxyproline. Diethylnitrosamine produced a high incidence of hepatomas, as expected. Cyclopropenoid fatty acids had no significant effect on the carcinogenicity of the nitrosamino acids.

Liver composition and histology of rainbow trout fed cyclopropenoid fatty acids

Rainbow trout were fed 200 ppm cyclopropenoid fatty acids (CPFA) in a semipurified casein-gelatin-dextrin diet for 8 months. Liver weights, liver fat, and glycogen levels were measured during the course of the exepriment and compared with those of control fish. The effect of CPFA on liver histology was also monitored and was found to produce necrosis of hepatocytes, unusual glycogen deposition, appearance of “fibers” in the cytoplasm of many cells, and fibrotic bile ducts and blood vessels. Most of these histological abberations remained after MS was removed from the diet. Liver size, expressed as a percentage of body weight, in CPFA-fed fish became significantly larger (P < 0.05) after 7 months and remained higher until the feeding trial was terminated. Percentage of liver lipids was significantly higher (P < 0.05) in CPFA-fed fish, but returned to normal when the fish were returned to control diet.