Effects of dietary heated fats on rat liver enzyme activity

The objective of this study was to evaluate the effects of dietary heated fats from a commercial deep-fat frying operation on rat liver enzyme activity. The fats, partially hydrogenated soybean oil (PHSBO) used for four days and for 7 days (7-DH) for frying foodstuffs in a commercial restaurant, were fed to rats in either free access to food or by pair-feeding graded doses. All diets were isocaloric and contained 15 g/100 g of diet. Experiments were conducted with control rats fed nonheated (NH) PHSBO diet. Animals fed 7-DH diet in each set of experiments had larger amounts of cytochromes P₄₅₀ and b₅ and greater activity of NADPH-cytochrome P₄₅₀ reductase when compared to controls. The activities of carnitine palmitoyltransferase-I and isocitrate dehydrogenase were significantly lower in rats fed test diets in comparison to controls. A significantly depressed activity of glucose 6-phosphate dehydrogenase was also noticed for these animals when compared to those fed NH. In addition, liver and microsomal protein concentrations were significantly greater in rats fed the used oils in comparison to controls, and liver glycogen was significantly lower.     

Cyclic fatty acid monomers from dietary heated fats affect rat liver enzyme activity

This study was conducted to investigate the effects of dietary cyclic fatty acid monomers (CFAM), contained in heated fat from a commercial deep-fat frying operation, on rat liver enzyme activity. A partially hydrogenated soybean oil (PHSBO) used 7 d (7-DH) for frying foodstuffs, or 0.15% methylated CFAM diets was fed to male weanling rats in comparison to a control group fed a nonheated PHSBO (NH) diet in a 10-wk experiment. All diets were isocaloric with 15% fat. Animals fed either CFAM or 7-DH diets showed increased hepatic content of cytochrome (cyt.) b₅ and P₄₅₀ and increased activity of (E.C. 1.6.2.4) NADPH-cyt. P₄₅₀ reductase in comparison to the control rats. In addition, the activities of (E.C. 2.3.1.21) carnitine palmitoyltransferase-l and (E.C. 1.1.1.42) isocitrate dehydrogenase were significantly decreased when compared to that of rats fed the NH diet. A significantly depressed activity of (E.C. 1.1.1.49) glucose 6-phosphate dehydrogenase was also observed for these animals compared to the control rats fed NH diet. Moreover, liver and microsomal proteins were significantly increased when CFAM or 7-DH diets were fed to animals in comparison to controls while liver glycogen was decreased significantly in experimental groups of rats. The results obtained in this study indicate that the CFAM in the diet from either synthetic sources or used fats increase the activity of liver enzyme systems that detoxify them.     

Adenylate cyclase and β-receptors in salivary glands of rats fed diets containingtrans fatty acids

The effects oftrans fatty acids on adenylate cyclase were determined in the submandibular salivary glands (SMSG) of rats fed diets containing 20% corn oil, 20% partially hydrogenated soybean oil (PHSBO) or 18% PHSBO + 2% corn oil. The fluoride-and isoproterenol-stimulated adenylate cyclase activities were higher in the SMSG from rats fed 20% PHSBO than in the control group fed 20% corn oil. The feeding of 2% corn oil with the diet containing 18% PHSBO resulted in a complete restoration of isoproterenol-stimulated and a partial restoration of fluoride-stimulated adenylate cyclase activity. There was no significant difference in the concentration of the β-adrenergic receptor or in the receptor-binding affinity constants among the three dietary groups as measured by [³H]dihydroalprenolol (DHA)-binding. Higher fluorescence polarization of diphenyl hexatriene (DPH) was observed in SMSG membranes of rats fed diet containing 20% PHSBO than in the other two oils, suggesting that membrane fluidity may play a role in adenylate cyclase activity.     

Effects of trace acrylamide intake in Wistar rats

Frying oil in use of cooking may contain acrylamide formed from frying foodstuffs. We have reported that administration of a diet containing 7% practically used frying oil for 12 weeks damaged liver and kidneys severely in Wistar rats. Then, male Wistar rats were fed ad libitum for 12 weeks a powdered diet (AIN93G; no fat) containing 7 wt% of fresh oil (control group) or frying oil heated with Asn + glucose for 20 h at 180 degrees C under a nitrogen flow in order to form acrylamide under the least thermal deterioration (experimental group). The rats were subjected to anthropometric measurements, hematological analyses, and observations of the liver and kidneys. All of the rats grew well, and no gross symptoms attributable to the experimental oil were observed. But the experimental rats had significantly low insulin and triacylglycerol levels. The liver and kidneys from the experimental rats had damages, but the degree of the histological changes looked lighter than that of the rats fed practically used frying oil described above. The serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were also not much increased. Thus, it was suggested that continuous intake of trace acrylamide induced characteristically low serum insulin level and that the effects of the used frying oil on the liver and kidneys were hardly attributable to acrylamide possibly contained therein.     

Effect of dietarytrans fatty acids on some membrane-associated enzymes and receptors in rat heart

Three groups of male weanling Sprague-Dawley rats were fed diets containing 20% corn oil, 20% partially hydrogenated soybean oil (PHSBO) or 18% PHSBO +2% corn oil. PHSBO contained about 48% of its total fatty acids astrans-octadecenoate. Rats were killed after 16–18 weeks of feeding the various diets, hearts were dissected and crude sarcolemma was prepared by differential centrifugation. The activities of ouabain-sensitive (Na⁺+K⁺)ATPase were significantly lower in membranes of rats fed 20% PHSBO than the control rats fed 20% corn oil. The feeding of 2% corn oil with 18% PHSBO resulted in partial restoration of the enzyme activity. The maximum number of [³H]ouabain-binding sites (B_max) was also lower in cardiac membranes of rats fed 20% PHSBO than those fed 20% corn oil. Similar to (Na⁺+K⁺)ATPase activity, some restoration of the number of [³H]ouabain-binding sites was observed when 2% corn oil was fed with 18% PHSBO-containing diet. There was no difference in the binding affinity of the radioligand for the receptor among the 3 dietary groups. Adenylate cyclase activities (fluoride-, isoproterenol- and forskolinstimulated) were lower in membranes of rats fed 20% PHSBO or 18% PHSBO +2% corn oil than in the control group fed 20% corn oil. Density of the β-adrenergic receptor was the lowest in cardiac membranes of rats fed 20% PHSBO. The feeding of 2% corn oil with 18% PHSBO resulted in partial restoration of the maximum number of [³H]dihydroalprenolol (DHA)-binding sites. The affinity of the binding sites was, however, not affected by the type of the dietary fat. The results of this study suggest that dietarytrans fatty acids can affect the activities of (Na⁺+K⁺)ATPase and adenylate cyclase and the density of digitalis and β-adrenergic receptors in rat heart.     

Chemical properties and cytotoxicity of thermally oxidized oil

Heated frying oils with different chemical properties in terms of AV (acid value), POV (peroxide value), COV (carbonyl value), and contents of polar compounds (PC) and triacylglycerol (TG), as well as color and odor, were obtained. Male Wistar rats were fed ad libitum for 12 weeks a powdered diet (AIN93G; no fat) containing 7 wt% of fresh oil (control) or one of the frying oils described above. The rats were subjected to anthropometric measurements, hematological analyses, and observations of the liver and kidneys. All of the rats grew well, and no gross symptoms attributable to the experimental oils were observed. However, the rats fed a diet containing the heated oil developed apparent liver damage to different degrees regardless of the chemical properties of the ingested oils. Thus, it was suggested that the chemical properties evaluated here had little to do with the cytotoxicity of heated oil, although the properties express quality of oil. Volatile compounds seem to be major candidates for the toxic agents in heated oil because oils with rancid and deteriorated odor show strong toxicity.     

Nutritional evaluation of medium-chain triglycerides in the rat

Nutritional evaluation of a medium-chain triglyceride (MCT) preparation, containing about 75% octanoic acid and 25% decanoic acid, was carried out in short- and long-term experiments in rats. A casein diet containing 19.6% MCT and 2.5% safflower oil, the latter to supply essential fatty acids, was compared with similar diets containing conventional dietary fats. Data obtained in a 47-week study showed that the MCT diet supported normal growth and development. At autopsy, carcass protein and ash levels, vital organ weights and composition were similar to those in rats fed conventional fats. Histological study showed that intestinal and liver sections were normal after 47 weeks on the MCT-containing diet. In general, rats fed MCT had slightly lower growth rates and caloric efficiency values, less carcass fat and smaller epididymal fat pads than animals fed conventional dietary fats. Little C₈ and C₁₀ were found in depot fat. The MCT diet also supported normal reproducton, as indicated by litter size and number. During lactation the volume of milk secreted by the rats receiving the MCT diet was smaller and contained a lower level of fat than that secreted by the rats receiving an oleo oil diet, resulting in slower gains in weight in the MCT group. After weaning, growth of the rats fed MCT compared favorably with that attained by the animals on the diet containing oleo oil.     

Thermal deterioration of oil and frying foodstuffs

Male Wistar rats were fed ad libitum for 12 weeks a powdered diet (AIN93G; no fat) containing 7 wt% of fresh oil (control), and frying oils heated for 20 h at 180 degrees C with amino acids, gluten, sugar, and wheat starch, respectively. The rats were subjected to anthropometric measurements, hematological analyses, and observations of the liver and kidneys. All of the rats grew well, and no gross symptoms attributable to the experimental oils were observed. The serum of all the experimental groups showed a tendency toward lower levels of triacylglycerol and free fatty acids and higher levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) than that of the control group. Among experimental groups, the rats fed a diet containing oil heated with gluten were least influenced by thermally deteriorated oil in terms of serum levels of glucose, triacylglycerol, phospholipids, cholesterol, and insulin; histological evaluations; and number of dark-red patches found on the surface of the liver.     

The up-regulation of hepatic acyl-coA oxidase and cytochrome P<Subscript>450</Subscript> 4A1 mRNA expression by dietary oxidized frying oil is comparable between male and female rats

We previously demonstrated that oxidized frying oil (OFO) activates peroxisome proliferator-activated receptor α (PPARα) and up-regulates hepatic acyl-CoA oxidase (ACO) and cytochrome P₄₅₀ 4A1 (CYP4A1) genes in male rats. As female rats were shown to be less responsive to some peroxisome proliferators (PP), this study compared the expression of a few PPARα target genes in male and female rats fed diets containing OFO. Male and female rats were fed a diet containing 20 g/100 g OFO (O diet) or fresh soybean oil (F diet) for 6 wk. Both male and female rats fed the O diet showed significantly higher liver weight, hepatic ACO and catalase activities, CYP4A protein, and expression of ACO and CYP4A1 mRNA (P<0.05) compared with their control groups. The mRNA expression of two other PPARα target genes, FA-binding protein and HMG-CoA synthase, were marginally increased by dietary OFO (P=0.0669 and 0,0521, respectively). Female rats fed the O diet had significantly lower CYP4A protein than male rats fed the same diet. The remaining OFO-induced effects were not significantly different between male and female rats fed the O diet. These results indicate that dietary OFO, unlike clofibrate or other PP, had minimal sexual dimorphic effect on the induction of hepatic PPARα target gene expression.     

Effect of diet handling on nutritional studies with used frying fats

A four-week experiment to study the significance of careful diet handling was carried out with weanling rats fed purified rations containing 15% of various fats. Fresh soybean oil was the fat in the control diet and the other fats, which had been used to prepare food by a commercial-type deep-frying operation, were soybean oil, partially hydrogenated soybean oil with iodine value (I.V.) 70, partially hydrogenated soybean oil with I.V. 108, and cotton-seed oil. A purified diet was fed ad libitum. Treatment of the dietary groups in regard to preparation and handling of the rations proved to be highly significant. That is, as opposed to weekly mixing and twice weekly feeding of the diets, daily preparation and feeding along with the use of antioxidants and refrigeration of the ingredients resulted in a much superior growth rate and a higher efficiency of feed conversion. Since this very significant response became apparent in less than four weeks, the importance of careful handling to minimize secondary effects within the diet must be emphasized. The fresh soybean oil control, and all of the used frying fats gave similar results. Presented at the AOCS Meeting, Toronto, Ontario, October 1962.     

Effects of thermally processed oil on weight loss in rats

We have previously proposed that thermally processed oil holds promise as a dietary supplement intended for weight loss. We employed a thermal process whereby oil was heated to 180 degrees C for 10 h in the absence and presence of gluten. We compared the effects of three diets, untreated oil, heated oil, heated oil and gluten on body weight, retroperitoneal weight and lipid composition and fecal lipid contents. Ten week-old male Wistar rats were fed ad libitum a diet containing 7 wt% of the oil for 12 weeks. The oil heated with gluten showed low levels of food efficiency and oil absorption ratios, and high levels of fecal oil excretion, oil content and bile acid content. Diets containing thermally treated oils resulted in significantly lower retroperitoneal tissue weights and lipid contents as compared to the control group; the groups fed the heated oil and gluten diets showed a general decrease in the fatty acid (especially linoleic acid) amount. In conclusion, oil heated with gluten was not fully digested and thus excreted without showing any detrimental effects on either the organs or feces. This resulted in safe and effective weight loss in growing adult rats.     

Effect of dietary palm oil and its fractions on rat plasma and high density lipoprotein lipids

Male Sprague Dawley rats were fed semipurified diets containing 20% fat for 15 weeks. The dietary fats were corn oil, soybean oil, palm oil, palm olein and palm stearin. No differences in the body and organ weights of rats fed the various diets were evident. Plasma cholesterol levels of rats fed soybean oil were significantly lower than those of rats fed corn oil, palm oil, palm olein or palm stearin. Significant differences between the plasma cholesterol content of rats fed corn oil and rats fed the three palm oils were not evident. HDL cholesterol was raised in rats fed the three palm oil diets compared to the rats fed either corn oil or soybean oil. The cholesterol-phospholipid molar ratio of rat platelets was not influenced by the dietary fat type. The formation of 6-keto-PGF_1α was significantly enhanced in palm oil-fed rats compared to all other dietary treatments. Fatty acid compositional changes in the plasma cholesterol esters and plasma triglycerides were diet regulated with significant differences between rats fed the polyunsaturated corn and soybean oil compared to the three palm oils.     

Iron accumulation in oil during the deep-fat frying of meat

Iron accumulation in oil is a potential problem when frying food containing substantial amounts of iron. Selected meat products (skinless chicken breast, beef liver, and lean beef) were ground and fried (ca. 2-cm spheres, ca. 10 g/sphere) in partially hydrogenated soybean oil (PHSBO). Samples (450 g) of ground meat were fried 3 times/h for 8 h/d for 3 d. Oil samples were collected for analysis for iron (every 8 h) and oil degradation (every 4 h) and replaced with fresh oil. The iron contents of oil samples after 3 d of frying were approximately 0.11, 0.48, and 4.01 mg of iron/kg of PHSBO for the oil used to fry chicken, beef, and liver, respectively. There was a notable darkening in color and an increased tendency to foam for the beef liver oil sample compared with the other samples. After frying, the acid values were 0.9, 1.1, and 1.4 for the oil samples for chicken, beef, and liver, respectively. After frying, the p-anisidine values were 11.5, 12.8, and 32.6 for the oil samples for chicken, beef, and liver, respectively; the food oil sensor values were 0.96, 0.96, and 0.83 for the oil samples for chicken, beef, and liver, respectively.     

Nutritional and metabolic studies of distillable fractions from fresh and thermally oxidized corn oil and olive oil

A semisynthetic diet containing 15% by weight of dietary fat was fed to six groups of male Wistar rats for 28 days. Two groups received the distilable fraction of fresh corn oil (DCO) or fresh olive oil (DOO), two groups the distillable fraction of the thermally oxidized fats (OCO,OOO), and two groups received the respective fresh fats as controls (FCO, FOO). Substantial changes in the fatty acid composition occurred in the fats upon thermal oxidation. Only the rats that received OOO showed overt symptoms of heated fat toxicity. This was reflected in the histological scores of these animals, with the liver sustaining the most numerous and severe lesions. Tissue fatty acid changes of any significance were confined largely to the polar liver lipids of the rats that were fed OCO or OOO. The results of this study would suggest that the relatively greater toxicity of OOO, compared to OCO, may in part be due to the high oleic:linoleic acid ratio of the fresh olive oil and in part to a higher tocopherol content of the corn oil.     

Biological evaluation of hydrogenated rapeseed oil

A 91-day feeding study evaluated soybean oil, rapeseed oil, fully hydrogenated soybean oil, fully hydrogenated rapeseed oil, fully hydrogenated superglycerinated soybean oil and fully hydrogenated superglycerinated rapeseed oil at 7.5% of the diet in rats; a 16-wk feeding study evaluated soybean oil and the three rapeseed oils or fats at 15% of the diet. Each fat was fed to 40 rats as a mixture with soybean oil making up 20% of a semi-synthetic diet. No significant differences in body weight gains or diet-related pathology were seen in the 91-day study although the rats fed liquid rapeseed oil had slightly heavier hearts, kidneys and testes than the others. The rats fed the four fully hydrogenated fats ate more feed and had lower feed efficiencies than those fed oils but no differences were seen among the four hydrogenated fats. In the 16-wk feeding study, no pronounced pathology related to the diet was seen although the rats fed liquid rapeseed oil had a slightly higher incidence of histiocytic infiltration of cardiac muscle than the rats in the other groups. The female rats fed the three rapeseed oil fats gained significantly less weight and the females fed liquid rapeseed oil had enlarged hearts compared to the other groups. The absorbabilities of the six fats were measured in the 91-day study when fed as a mixture with soybean oil and as the sole source of dietary fat in a separate 15-day balance study. The four fully hydrogenated fats were poorly absorbed and the absorption of behenic acid from the two hydrogenated rapeseed oils was found to be 12% and 17% in the balance study and 8-40% in the feeding study. The adverse biological effects of unhydrogenated rapeseed oil containing erucic acid as reported in the literature do not occur with fully hydrogenated rapeseed oil. In addition, the low absorbability of the fully hydrogenated rapeseed oil is an added factor in its biological inertness.     

trans fatty acids. 4. Effects on fatty acid composition of colostrum and milk

trans Isometric fatty acids of partially hydrogenated fish oil (PHFO) consist oftrans 20∶1 andtrans 22∶1 in addition to thetrans isomers of 18∶1, which are abundant in hydrogenated vegetable oils, such as in partially hydrogenated soybean oil (PHSBO). The effects of dietarytrans fatty acids in PHFO and PHSBO on the fatty acid composition of milk were studied at 0 (colostrum) and 21 dayspostpartum in sows. The dietary fats were PHFO (28%trans), or PHSBO (36%trans) and lard. Sunflower seed oil (4%) was added to each diet. The fats were fed from three weeks of age throughout the lactation period of Experiment 1. In Experiment 2 PHFO or “fully” hydrogenated fish oil (HFO) (19%trans), in comparison with coconut oil (CF) (0%trans), was fed with two levels of dietary linoleic acid, 1 and 2.7% from conception throughout the lactation period. Feedingtrans-containing fats led to secretion oftrans fatty acids in the milk lipids. Levels oftrans 18∶1 andtrans 20∶1 in milk lipids, as percentages of totalcis+trans 18∶1 andcis+trans 20∶1, respectively, were about 60% of that of the dietary fats, with no significant differences between PHFO and PHSBO. The levels were similar for colostrum and milk. Feeding HFO gave relatively lesstrans 18∶1 andtrans 20∶1 fatty acids in milk lipids than did PHFO and PHSBO. Only low levels ofcis+trans 22∶1 were found in milk lipids. Feedingtrans-containing fat had no consistent effects on the level of polyenoic fatty acids but reduced the level of saturated fatty acids and increased the level ofcis+trans monoenoic fatty acids. Increasing the dietary level of linoleic acid had no effect on the secretion oftrans fatty acids but increased the level of linoleic acid in milk. The overall conclusion was that the effect of dietary fats containingtrans fatty acids on the fat content and the fatty acid composition of colostrum and milk in sows were moderate to minor.     

Trans fatty acids. 1. Growth,fertility, organ weights and nerve histology and conduction velocity in sows and offspring

Effects of dietarytrans fatty acids on the pre- and postnatal growth and development in pigs were studied with special emphasis on nervous tissue. In experiment 1, female pigs were fed partially hydrogenated fish oil (PHFO) (28%trans) or soybean oil (PHSBO) (36%trans), in comparison with lard (0%trans) from weaning (3 wk) through the first reproduction cycle (up to 2 yr). In experiment 2, female pigs were fed two fish oils (33 and 19%trans) in comparison with coconut oil (0%trans) in diets with low and high levels of linoleic acid (18∶2n−6cis,cis) from gestation until their offspring were three wk old. Compared with thetrans-free fats, thetrans-containing fats had no effect on growth and development, feed consumption and utilization or on the weight of the brain, heart, kidneys, liver, lungs or spleen in the adult sows and their offspring. No effects from the experimental fats were found on histology and conduction velocity of the peroneal nerve. An increased number of the sows fed PHFO had fertility problems compared with those fed lard and PHSBO in Expt. 1, but no similar effects were seen in Expt. 2. It is concluded that consumption oftrans fatty acids with 18–22 carbon atoms from PHFO and with 18 carbon atoms from PHSBO at levels that were 5 to 12 times higher than those normally consumed by humans had no detrimental effects on female pigs or their offspring during pregnancy and lactation.     

Effects of fresh and used hydrogenated soybean oil on reproduction and teratology in rats

Groups of 25 pairs of two generations of male and female rats were fed diets containing 15% of either fresh hydrogenated soybean oil (iodine value, 107), a similar fat used 56 hr for deep frying or an unhydrogenated mixture of fats and oils with a fatty acid composition similar to the hydrogenated soybean oil. The first two litters of each generation were permitted to be born naturally. During the third pregnancy of each generation, one-half of the females were sacrificed on day 13 of gestation and inspected for early embryonic death. The remaining females were sacrificed on day 21 of gestation, and the fetuses were examined for either skeletal or softtissue abnormalities. There was no evidence of any deleterious effects on the reproductive parameters nor any teratogenic effects due to either hydrogenated soybean oil, a similar oil used for frying foods for 56 hr or an unhydrogenated mixture of fats and oils.     

Effects of fresh and used hydrogenated soybean oil on reproduction and teratology in rats

Groups of 25 pairs of two generations of male and female rats were fed diets containing 15% of either fresh hydrogenated soybean oil (iodine value, 107), a similar fat used 56 hr for deep frying or an unhydrogenated mixture of fats and oils with a fatty acid composition similar to the hydrogenated soybean oil. The first two litters of each generation were permitted to be born naturally. During the third pregnancy of each generation, one-half of the females were sacrificed on day 13 of gestation and inspected for early embryonic death. The remaining females were sacrificed on day 21 of gestation, and the fetuses were examined for either skeletal or softtissue abnormalities. There was no evidence of any deleterious effects on the reproductive parameters nor any teratogenic effects due to either hydrogenated soybean oil, a similar oil used for frying foods for 56 hr or an unhydrogenated mixture of fats and oils.     

Mild ingestion of used frying oil damages hepatic and renal cells in Wistar rats

Male Wistar rats were fed ad libitum a powdered diet (AIN93G; no fat) containing 7 wt% of fresh oil (control) or used frying oil recovered from Japanese food manufacturing companies (recovered oil) for 12 weeks and subjected to anthropometric measurements, hematological analyses, and observations of the liver and kidneys. All of the rats grew well, and no gross symptoms attributable to recovered oil were observed. There was a tendency toward higher consumption of the diet in the experimental group as compared to the control group. In the serum of the experimental group, no difference was detected in the levels of glucose, triacylglycerol, and phospholipids. But many dark-red patches, necrosis, and bleeding were found in the livers of 75% of the experimental rats; these rats had extremely high aspartate aminotransferase (AST) and alanine aminotransferase (ALT) values. Average AST and ALT values of the experimental group were significantly higher than those of the controls. The renal cells were also obviously damaged. These results raise the concern that frying oil contained in ready-made foods, snacks, etc., if deteriorated to an extent equal to or greater than that of the recovered oil, may be able to change human serum AST/ALT levels and damage the liver and kidneys.