Brassica campestris var. Span: II. Cardiopathogenicity of fractions isolated from span rapeseed oil when fed to male rats

Food safety and health effects of canola oil

Canola oil is a newly marketed vegetable oil for use in salads and for cooking that contains 55% of the monounsaturated fatty acid; oleic acid, 25% linoleic acid and 10% alpha-linolenate [polyunsaturated fatty acid (PUFA)], and only 4% of the saturated fatty acids (SFAs) that have been implicated as factors in hypercholesterolemia. It is expressed from a cultivar of rapeseed that was selectively bred from old varieties in Canada to be very low in erucic acid--a fatty acid suspected to have pathogenic potential in diets high in the original rapeseed oil in experimental animals. Canola oil is free of those problems. It is the most widely consumed food oil in Canada, and has been approved for Generally Recognized as Safe (GRAS) status by the Food and Drug Administration (FDA) of the United States Department of Health and Human Services. The fatty acid composition of canola oil is consistent with its use as a substitute for SFAs, in meeting the dietary goals recommended by many health associations: an average diet containing about 30% of calories as fat made up of less than 10% SFAs, 8-10% PUFAs in a ratio of linoleic to linolenic acids between 4:1 and 10:1, the remainder being monounsaturated fatty acids. No single oil meets these current recommendations for ratios of PUFA/monounsaturated/polyunsaturated fatty acid ratios as the sole source of cooking and salad oil.

The methionine and choline status of rat diets and their effects on nutrition and myocardial lesions

This study evaluated for rats the nutritional adequacy of casein-based diets routinely used to test the cardiopathogenicity of vegetable oils. Diets were formulated containing 20% by weight casein, 20% soybean oil and graded levels of choline with and without methionine and were fed to male Sprague-Dawley rats for 16 weeks. Rats fed methionine-supplemented diets had improved growth and food consumption, increased liver lipids mainly in the form of triglycerides and normal amino acid metabolism. On the other hand, choline supplementation reduced liver lipids but had no effect on growth and feed consumption. The results would indicate that diets including 20% casein and 20% oil require methionine supplementation to assure the nutritional adequacy of this high caloric diet. However, in this study there was no evidence to indicate that choline or methionine supplementation affected the heart lesion incidence in male rats. It was therefore concluded that the amount and type of fat in the diet, not the choline and methionine status of the diet, is related to heart lesions in male rats.

Reduction of myocardial necrosis in male albino rats by manipulation of dietary fatty acid levels

A comprehensive statistical analysis had shown a significant correlation between the incidence of myocardial lesions in male albino rats and the concentration of certain dietary fatty acids. To test this result under controlled conditions, male rats were fed for 16 weeks diets containing 20% by weight soybean oil or a low erucic acid rapeseed (LEAR) oil. Both dietary oils contained substantial amounts of linolenic acid, and both groups developed a high incidence of myocardial necrosis. The addition of dietary saturated fatty acids to the oil in the form of cocoa butter significantly lowered the incidence of heart lesions in both groups. The addition of cocoa butter resulted in increased absorption of saturates and increased growth. Replacement of the cocoa butter by at least an equal amount of synthetic triolein resulted in no significant changes in the cardiopathogenic response compared to the original oils, thus ensuring that the reduction in heart lesions associated with the addition of cocoa butter was not due to dilution of cardiopathogenic compounds in the original vegetable oils. These results support the hypothesis that myocardial lesions in male rats are related to the balance of dietary fatty acids and not to cardiotoxic contaminants in the oils. Changes in the dietary fatty acids did not appear to influence the proportion of the cardiac phospholipids, but their fatty acid composition was markedly influenced. Dietary linolenic acid affected the C22 polyunsaturated fatty acids (PUFA) and dietary saturates increased the level of saturates in cardiac phospholipids. The level of arachidonic acid and total C22 PUFA did not appear to be affected by diet.

Comparative studies on composition of cardiac phospholipids in rats fed different vegetable oils

Male Sprague-Dawley rats were fed diets for 1 or 16 weeks, containing 20% by weight vegetable oils differing widely in their oleic, linoleic and linolenic acid content. No significant changes were observed in the level of the cardiac lipid classes. The fatty acid composition of the 2 major phospholipids, phosphatidylcholine and phosphatidylethanolamine, showed a remarkable similarity between diets in the concentration of total saturated, C22 polyunsaturated and arachidonic acids. Monounsaturated acids were incorporated depending on their dietary concentration, but the increases were moderate. Dietary linolenic acid rapidly substituted C22 polyunsaturated fatty acids of the linoleic acid family (n-6) with those from the linolenic acid family (n-3). The results suggest that dietary linolenic acid of less than 15% does not inhibit the conversion of linoleic to arachidonic acid but the subsequent conversion of arachidonic acid to the C22 polyunsaturates was greatly reduced. Significant amounts of dietary monounsaturated fatty acids were incorporated into cardiac cardiolipin accompanied by increases in polyunsaturated fatty acids, apparently to maintain an average of 2 double bonds/molecule. The cardiac sphingomyelins also accumulated monounsaturated fatty acids depending on the dietary concentration. It is quite evident from the results of this study that the incorporation of oleic acid and the substitution of linolenic for linoleic acid-derived C22 polyunsaturated fatty acids into cardiac phospholipids was related to the dietary concentration of these fatty acids and was not peculiar to any specific oil. Even though it is impossible to estimate the effect of such changes in cardiac phospholipids on membrane structure and function, results are discussed which suggest that the resultant membrane in the Spragu-Dawley male rat is more fragile, leading to greater cellular breakdown and focal necrosis.

Cardiopathogenicity of soybean oil and tower rapeseed oil triglycerides when fed to male rats

The triglycerides of soybean oil were purified by molecular distillation and those of Tower rapeseed oil by molecular distillation and adsorption chromatography. The original oils and the purified triglycerides were incorporated in semisynthetic diets at 20% by weight and fed for 16 weeks to weanling male Sprague-Dawley rats to compare the nutritional and pathological effects of the oils and their triglyceride fractions on rats. The study was carried out at two independent laboratories. No significant differences were observed between the results of the two establishments. The incidence of myocardial lesions was significantly higher in rats fed Tower rapeseed oil than in those fed soybean oil. Purification of the triglycerides by molecular distillation and adsorption chromatography appeared to have no major effect on the incidence of myocardial lesions. This supports our previous findings that the cardiopathogenicity appeared to have no major effect on the incidence of myocardial lesions. This supports our previous findings that the cardiopathogenicity of the test oils to rats resides in the triglycerides of these oils.

Effects of rapeseed oil on fatty acid oxidation and lipid levels in rat heart and liver

The comparative rates of oxidation of erucic and oleic acids and of their CoA esters were studied in heart and liver mitochondria of rats fed a standard diet or semisynthetic diets containing 25% of the calories as either rapeseed oil (46.6% erucic and 10.4% eicosenoic acid) or olive oil, for a period of 5 months. The long exposure to the diet containing 25% rapeseed oil did not alter the oxidative activity of mitochondria and did not induce morphological changes in the heart. It is confirmed that erucic acid is oxidized in mitochondria at lower rates than other long chain fatty acids and that its activation as CoA derivative may be one of the rate limiting steps of the overall oxidationprocess. Total lipids and triglycerides do not significantly change in the heart whereas they increase in the liver of rats fed the diet containing rapeseed oil.

Cardiopathogenicity of rapeseed oils and oil blends differing in erucic, linoleic, and linolenic acid content

Male Wistar rats were fed semipurifed diets containing 20% fat for 25 weeks. Ten different oils or oil blends were employed, including rapessed oils, simulated rapeseed-type oils, and modified rapeseed-type oils. Safflower, soybean, and hydrogenated coconut oils served as control oils. Histopathological examination of the cardiac tissue was conducted at the end of the study and an incidenceseverity rating assigned to the lesions induced by each fat. Oils containing high levels of erucic acid (26-30%) induced the most severe cardiac necrosis, irrespective of the source of erucic acid (rapeseed oil or nasturtium oil). Increasing the linoleic: :linolenic acid ratio of the high erucic oils to that of soybean oil failed to reduce necrosis, but the absence of linolenic acid from a high erucic acid oil blend resulted in a markedly reduced lesion incidenceseverity rating, comparable to those obtained for low erucic acid rapessed oil and soybean oil which were similar. Lowest lesion incidence was obtained with safflower oil and hydrogenated coconut oil. We have postulated that linolenic acid plays a role in the etiology of cardiac necrosis observed when rats are fed diets containing low erucic acid rapeseed oils.

Relationship between erucic acid and myocardial changes in male rats

The back and belly fat of pigs fed a diet containing 20% by wt rapeseed oil (22% erucic acid) for 16 weeks was rendered into oil. This rendered pig fat, which contained 5.6% erucic acid, was fed to male rats in three separate experiments at 20% by wt of the diet for 16 weeks. In experiment I rendered pig fat was compared only to Brassica campestris var. Span rapeseed oil containing 4.8% erucic acid. In experiments II and III, rendered pig fat was compared to commercial lard containing 0.2% docosenoic acid, commercial lard to which 5.4% free erucic acid was added, and Span rapeseed oil. There was no significant (P less than 0.01) differences observed in the level of erucic acid in the hearts of rats fed diets of rendered pig fat, Span rapeseed oil, or commercial lard plus erucic acid. However, the incidence (P less than 0.001) and severity (P less than 0.01) of cardiac lesions were significantly higher in Span rapeseed oil fed rats compared to rats fed control diets. The number of rats affected or the severity of lesions in the rendered pig fat fed group was not significantly different from controls. The results of this study indicate that the myocardial lesions associated with feeding 20% rapeseed oil diets are not related to the content of erucic acid per se. The possible reasons why rapeseed oil causes cardiac lesions in rats are discussed. It is suggested that a triglyceride imbalance in the oil might play an important role in causing these lesions in rats.

Brassica compestris var. Span: I. Fractionation of rapeseed oil by molecular distillation and adsorption chromatography

Procedures for the large scale isolation of pure triglycerides and fractions rich in nontriglyceride components from Span rapeseed oil are described. Fractionation of Brassica campestris var. Span rapeseed oil by molecular distillation yielded 4 triglyceride fractions, all of which contained traces of sterol esters. An additional triglyceride fraction rich in free and esterified sterols and other volatile components was obtained from the oil. Separation by adsorption chromatography of Span rapeseed oil yielded three fractions; A) a pure triglyceride ffaction; B) a triglyceride fraction rich in sterol esters; and C) another fraction containing free sterols and other polar components.