Effects of dietary methionine and cystine on lipid metabolism in hepatoma-bearing rats with hyperlipidemia

Abnormal lipid metabolism and its restoration by dietary methionine (Met) and cystine (Cys) were studied in Donryu rats subcutaneously implanted with an ascites hepatoma cell line of AH109A. The hepatoma-bearing rats exhibited byperlipidemia characterized by rises in serum triglyceride and cholesterol levels. Decreased lipoprotein lipase (LPL) activities in epididymal adipose tissue, cardiac muscle, and gastrocnemius as well as increased fatty acid mobilization from adipose tissue were considered to be responsible for the hepatoma-induced hypertriglyceridemia, while increased hepatic cholesterogenesis and decreased steroid excretion into feces were thought to be responsible for the hepatoma-induced hypercholesterolemia. Dietary-supplemented Met or Cys reduced the AH109A-induced hypertriglyceridemia with suppression of fatty acid synthesis in the host liver. Met restored the fall of LPL activities, while Cys did not. Dietary Met or Cys also reduced the hypercholesterolemia with restoration of decreased bile acid excretion into feces. These results suggest that dietary Met or Cys is hypolipidemic in the hepatoma-bearing rats with slight differences in their modes of action.     

Effect of a diet rich in sunflower oil on aspects of lipid metabolism in the genetically-obese rat

Aspects of the lipid metabolism of male, obese and lean Zucker rats were compared using animals which had been fed ad libitum for 32 days on a diet (HS) which contained 200 g sunflowerseed oil/kg or one (LS) which contained 50 g/kg of the oil. When compared with the LS diet, the HS diet decreased the characteristic lipid accretion in the liver of obese rats from 126 mg (LS) to 81 mg (HS)/g wet weight; corresponding values for the lean rats were 39 mg and 56 mg/g wet weight of liver, respectively. The HS diet depressed lipid synthesis de novo by liver homogenates and decreased the Δ9-desaturase activity of liver microsomes from obese and clean rats by about 50%. Δ9-Desaturase activity in vitro was also depressed by the addition of linoleic acid to liver microsomes from both obese and lean rats fed ad libitum on a standard laboratory diet. Depressed Δ9-desaturase activity, due to ingestion of the HS diet, was reflected in lower ratios of 16∶1/16∶0 and 18∶1/18∶0 fatty acids in tissue lipids from obese and lean rats. Ingestion of the HS compared with the LS diet resulted in increased proportions of 18∶2ω6 in liver lipids and adipose tissue triacylglycerols of obese and lean rats. The HS diet also increased the proportions of 20∶4ω6 in adipose triacylglycerols of obese and lean rats and in liver lipids of obese animals but not in their lean littermates.     

Effects of dietary linseed oil and marine oil on lipid peroxidation in monkey liverin vivo andin vitro

Diets rich in linoleic acid (CO) from corn oil, or in linoleic acid and either α-linolenic acid (LO) based on linseed oil or n−3 fatty acids (MO) from menhaden oil were fed to male and female Cynomolgus monkeys for 15 wk. In the liver a 40% reduction of α-tocopherol occurred in the MO group relative to the CO and LO groups followed by increased formation of lipofuscinin vivo. A four-fold increase of α-tocopherol in the MO diet (MO+E) brought the level in the liver to that found with CO and LO. The increased peroxidation in the MO group in the liver phospholipids was associated with the replacement of 60% of the n−6 fatty acids by n−3 fatty acids from menhaden oil. Similar fatty acid profiles were found in groups fed MO and MO+E, respectively. Compared to the CO fed group, feeding α-linolenic acid only resulted in a slight incorporation of n−3 fatty acids in the liver membranes mainly due to a direct incorporation of α-linolenic acid. However, in monkeys fed menhaden oil more than 30% of the total fatty acids in the liver phospholipids were n−3 fatty acids. The various diets did not influence the activity of liver catalase (EC 1.11.1.6) nor superoxide dismutase (EC 1.15.1.1), but glutathione-peroxidase activity (EC 1.11.1.9) was higher in monkeys fed the MO diet. The catalase activity in females was 20% higher than in males. In anin vitro assay, liver microsomes from monkeys fed the MO diet or the MO diet supplemented with tocopherol produced similar amounts of thiobarbituric acid reactive substances and at a much higher rate than microsomes from the CO and LO groups. It appeared that α-tocopherol did not protect long-chain n−3 C₂₀ and C₂₂ fatty acids as well as n−6 fattya acids against peroxidation. The present data showed that monkeys were not fully able to compensate for increased peroxidative stress but a four-fold supplement of vitamin E to the diets reduced the oxidation.     

Effects of dietary peanut oil on serum lipoprotein patterns of rats

Oils prepared from two varieties of peanuts and from a hybrid corn having linoleic acid concentrations substantially different from the respective commercial oils were compared with commercial oils for their effects on serum lipids of weanling female rats. In the first experiment, serum lipid patterns appeared to reflect linoleic acid content of the dietary oil. However, with a longer feeding period in the second experiment, serum lipid patterns were determined by the plant source of the dietary oil rather than its linoleic acid content; all peanut oils differed from both corn oils in their physiological effects. Diets containing triglyceride, hydrocarbon and sterol fractions obtained by liquid chromatography of peanut and corn oils were fed to female rats. The data provide no evidence that the hydrocarbon or sterol fractions of peanut oil are responsible for its unusual atherogenicity when fed as the sole fat source or that similar fractions from corn oil are protective against the effects of peanut oil.     

Effects of dietary triglyceride on the properties and lipid composition of plasma lipoproteins: Acute experiments in rats fed safflower oil

Male rats were administered 1.5 ml safflower oil by gastric intubation 0, 4, and 8 hr after a 16 hr fast. Plasma, liver, and adipose tissue were collected 16 hr after the last fatty meal. Rats fasted for 16 hr served as controls. Following fat feeding, the fatty acid composition of the very low density lipoprotein, triglyceride, and hepatic triglyceride were similar, as were the percentages of 18:2 in the very low density lipoprotein and hepatic cholesteryl esters. The phospholipids of liver and plasma lipoproteins were similar in the control groups, except that more 16:0 was present in the plasma lipoproteins. After fat feeding, the plasma lipoproein phospholipids were enriched with 18:2 more than were the hepatic phospholipids. Furthermore, the percentage of 18:2 in phospholipid was much less than in triglyceride or cholesteryl esters. Clearly, esterified lipids of liver and plasma lipoproteins (very low density lipoprotein, low density lipoprotein, and high density lipoprotein), and to a lesser extent, adipose tissue, were enriched with 18:2 derived from dietary triglyceride fatty acid even 16 hr after the terminal meal. A major proportion of the very low density lipoprotein isolated by ultracentrifugation in zonal rotors from plasma of fat fed animals had a faster rate-zonal mobility than did the very low density lipoprotein isolated from plasma of control animals. The very low density lipoprotein isolated from plasma of fat fed rats contained fewer moles of phospholipids, cholesterol, and cholesteryl esters, relative to triglyceride than did the very low density lipoprotein from plasma of animals not receiving safflower oil. The molar ratio triglyceride:phospholipid:cholesterol:cholesterol esters in the very low denity lipoprotein was 100:42.0:22.1:44.5 in the control group and 100:35.4:17.8:19.5 in the fat fed animals. It is postulated that an important biochemical mechanism by which dietary triglyceride fatty acids consumed by the animal over a long period of time alter plasma concentrations of triglyceride, phospholipids, and cholesterol esters is the directive influence of plasma free fatty acid, derived from dietary triglyceride, on the secretion of very low density lipoprotein lipids by the liver.     

Plasma and lipoprotein lipid peroxidation in humans on sunflower and rapessed oil diets

The effects of natural mixed diets on lipid peroxidation were investigated in humans. In the first study, 59 subjects were fed a rapeseed oil-based diet rich in monounsaturated fatty acids (MUFA) and a sunflower oil-based diet rich in polyunsaturated fatty acids (PUFA) in a cross-over manner for three and a half weeks. The lipid peroxidation products in plasma were determined by measuring conjugated dienes and malondialdehyde (MDA). In a second study, plasma thiobarbituric acid reactive substances (TBARS), lipid hydroperoxides, and the susceptibility of very low density lipoprotein + low-density lipoprotein (LDL) toin vitro oxidation were measured from subjects fed similar MUFA and PUFA diets for six week diets. No significant differences in plasma MDA or conjugated diene concentrations were found after the rapeseed oil diet or the sunflower oil diet in Study 1. In the second study, a small but significant decrease (P<0.05) in both lipid hydroperoxides and TBARS was observed in the LDL fraction after the sunflower oil diet. Thein vitro oxidation gave opposite results, showing increased oxidation after the sunflower oil diet. Despite a high intake of α-tocopherol during the oil peroids, no increase in plasma α-tocopherol was noticed in either study. The results suggest that moderate changes in the fatty acid composition in the Western-type diet may be adequate to affect lipoprotein susceptibility to oxidationin vitro, but there is considerable disparity with some indices ofin vivo lipid peroxidation.     

Effects of triton WR 1339 and orotic acid on lipid metabolism in rats

In order to investigate the effect of hepatic cholesterol flux on biliary bile acids, Triton WR 1339 and orotic acid were administered to rats, and the biliary cholesterol, phospholipids and bile acids were analyzed together with serum lipoproteins and hepatic lipids. Triton, which raised serum very low density lipoprotein and lipid levels and decreased serum high density lipoprotein liver lipid levels, increase the biliary cholic acid group/chenodeoxycholic acid group ratio (CA/CDCA) in the bile without affecting the total amount of bile acids and the other biliary lipids. Orotic acid, which decreased serum lipid and lipoprotein concentrations and increased liver lipid levels, increased the biliary excretion of cholesterol and phospholipids, but produced no significant change in the total amount of bile acids and in the CA/CDCA ratio in bile.     

The combined effects of dietary proteins and fish oil on cholesterol metabolism in rats of different ages

Male Sprague-Dawley rats at the ages of four weeks and nine months were fed purified diets containing 20% proteins either as casein (CAS), milk whey protein (WHY), or soybean protein (SOY) with 5% sardine oil for four weeks. The hypocholesterolemic effect of SOY was not statistically evident as compared to milk proteins at both ages, although serum cholesterol tended to be low in the SOY groups. A significant agedependent increase in serum cholesterol was observed in all dietary groups. Liver cholesterol concentrations were comparable in young rats, whereas in adults they were significantly lower in the SOY than in the CAS or WHY groups. At both ages, the activity of liver 3-hydroxy-3-methylglutaryl coenzyme A reductase tended to be higher in the SOY than in the other groups. Fecal steroid excretion was significantly higher in rats fed SOY than those fed either CAS or WHY, especially in adult rats. Significant age- and dietary protein-effects were observed in fatty acid profiles of liver microsomal phospholipids. Thus, the effects of dietary proteins on various lipid parameters were essentially maintained even when fish oil served as the source of dietary fat.     

Effects of deteriorated frying oil and dietary protein levels on liver microsomal enzymes in rats

This study was conducted to investigate the effects of deteriorated used frying oil (DUFO) and dietary protein levels upon the hepatic microsomal drugmetabolizing enzyme system. Fresh soybean oil was subjected to a deep-frying process at 205±5°C for four six-hr periods. The resultant DUFO was incorporated into high protein (HU) (27% lactalbumin) or low protein (LU) (8% lactalbumin) test diets at a 15% level. High protein (HF) and low protein (LF) diets containing fresh soybean oil served as the control. Male Long-Evans young rats fed the test diets for eight weeks showed decreased fat absorption and increased red blood cell (RBC) in vitro hemolysis. The activities of hepatic aminopyrine N-demethylase (AD), aniline hydroxylase (AH), NADPH-cytochrome C reductase (NCD), UDP-glucuronyl transferase (UDPGT) and glutathione S-transferase (GST) as well as cytochrome P-450 content were significantly increased in rats fed the HU diet. However, the AD, AH and GST activities, as well as the cytochrome P-450 content of the LU group, were increased to a lesser extent and significantly lower than those of the HU group. Rats fed the LU diet were the only group that showed significantly elevated serum GOT (E.C. 2.6.1.1, glutamate-oxaloacetate transaminase) and GPT (E.C. 2.6.1.2, glutamatepyruvate transaminase) values. Supplementation of 0.3% DL-methionine to the HU diet further increased GST activity. Unexpectedly, rats fed the low protein control diet (LF) also had raised levels of AD, AH and UDPGT activities as well as in vitro RBC hemolysis. It was concluded that rat hepatic microsomal enzymes are induced by dietary DUFO and that the level of induction is influenced by dietary protein level.     

Effect of varying levels of dietary protein on tumor development and lipid metabolism in rats exposed to aflatoxin

Reports in the literature concerning the relationship of protein nutrition to aflatoxicosis are contradictory. In an attempt to elucidate this relationship more clearly, we have examined the effects of low, normal, and high protein-containing diets on tumor incidence and development, as well as on several biochemical indices, in rats which have been exposed to low levels of aflatoxin in a “chronic” rather than “acute” situation. In our study, male weanling rats were place for 3 months on otherwise adequate diets containing either 8, 22, or 30% casein with and without aflatoxin B₁ at 1.7 ppm. Half of the animals in each group received diets which were further supplemented with the amino acid, cystine, at 0.6% of the diet. (Sulfur-containing amino acids are the most limiting amino acids in casein, and the addition of cystine to the diet serves to improve the biological quality of the protein source.) After 3 months the animals were fed control diets without aflatoxin until they were killed at 1 year. Weight gain was markedly decreased and liver weights increased in response to aflatoxin in all groups except those on the low protein diets, where aflatoxin had no effect on these protein diets, where aflatoxin had no effect on these indices. No tumors were found in the livers of rats fed the low protein, aflatoxin-supplemented diet. In the other groups, the severity of the liver involvement increased progressively with increased protein levels in the diet. When cystine was included in the diet, tumors were observed also in the animals fed the low protein diet; furthermore, the livers of those animals on “normal” and high protein diets were much more severely involved than were the livers of animals on non-cystine supplemented diets. Plasma cholesterol levels were increased in response to aflatoxin when the diets containing 22 and 30% protein were fed and when cystine was included in the 8% protein diet. Liver cholesterol levels were increased in response to aflatoxin in all groups except in those receiving the low protein diets. Among these latter animals, aflatoxin administration had no effect on liver cholesterol values. Changes as a result of aflatoxin administration were also observed in the fatty acid composition of sterol esters, triglycerides, and phospholipids of liver and tumor tissue.     

Effects of dietary palm oil on arterial thrombosis,platelet responses and platelet membrane fluidity in rats

Wistar rats were fed a control diet containing 5 energy % (en %) sunflowerseed oil or diets containing 50 en % of either palm oil, rich in saturated fatty acids, or sunflowerseed oil, high in linoleic acid, for at least eight weeks. Arterial thrombosis tendency, measured by the aorta loop technique, tended to be lowered by the palm oil diet and was lowered significantly by the sunflowerseed oil diet, compared with the control. Aggregation of platelets in whole blood activated with collagen was not altered by palm oil feeding, but was enhanced in the sunflowerseed oil group, compared with the control. The concomitant formation of thromboxane A₂ was decreased by palm oil feeding, although formation of prostacyclin did not change; the ratio of thromboxane/prostacyclin formed was decreased significantly in the palm oil group. Compared with the control diet, platelet membrane fluidity, measured by fluorescence polarization, was not altered in the palm oil group and was significantly increased only by sunflowerseed-oil feeding. Thus, although palm oil contains about 50% saturated fatty acids, it did not increase arterial thrombosis tendency and tended to decrease platelet aggregation, as compared with highly polyunsaturated sunflowerseed oil.     

Age-strain interrelations in lipid metabolism of rats

Various aspects of lipid metabolism were compared in Fisher 344 (F) and Sprague-Dawley (SD) rats aged 2, 6, 12, 18 and 24 months. The analyses included free and total cholesterol of serum and liver, LCAT, hepatic HMG-CoA reductase, cholesterol 7α-hydroxylase, fatty acid synthetase, acetyl CoA carboxylase and cholesterol synthesis from acetate or mevalonate. The body weight of SD rats increases with age whereas that of F rats plateaus at 9–12 months. Liver and aorta cholesterol levels were comparable for the 2 strains. Serum cholesterol varied but was usually lower in F rats. HMG-CoA reductase and cholesterol 7α-hydroxylase activities were not significantly different. Cholesterol synthesis from acetate was significantly higher only in 2-month-old F rats; synthesis from mevalonate was similar at each level. Acetyl CoA carboxylase and fatty acid synthetase activity were generally higher in F rats at every age level. The major difference between F and SD rats is in their pattern of weight gain with age. Differences in lipid metabolism are most marked between the young (2-month) rats.     

Effect of oil replenishment during deep-fat frying of frozen foods in sunflower oil and high-oleic acid sunflower oil

Frying stability of sunflower oil (SO) with 23% oleic acid and 61% linoleic acid, and of high-oleic acid sunflower oil (HOSO) with 74% oleic acid and 13% linoleic acid was studied during 20 discontinuous deep-fat fryings of various frozen foods, with or without frequent replenishment of the used oil with fresh oil. Alterations of both oils were measured by column, gas-liquid and high-performance size-exclusion chromatography. Total polar content and compounds, related to thermoxidative changes, and diacylglycerides, related to hydrolytic changes, increased in all oils during frying but reached higher levels in SO than in HOSO. Nevertheless, the increased levels of diacylglycerides observed may result from the frozen potatoes prefried in palm oil. Oleic acid in HOSO and linoleic acid in SO significantly decreased, but the fatty acid modifications that occurred during the repeated fryings were not only related to thermoxidative alteration but also to interactions between the bath oil and the fat in the fried products. Data from this study also indicated that HOSO performed more satisfactorily than SO in repeated fryings of frozen foods. Moreover, frequent addition of fresh oil throughout the deep-frying process minimized thermoxidative and hydrolytic changes in the frying oils and extended the frying life of the oils.     

Effect of aging and dietary restriction on bile acid metabolism in rats

The aim of the present study was to determine whether increased output of phospholipid in bile during aging may be due to alteration of bile acid composition and stimulated hydrophobic bile acid formation. In female Sprague-Dawley rats we examined the influence of aging and life long dietary restriction (60% of thead libitum intake) on bile flow, total bile acid secretion, bile acid composition and conjugation pattern, as well as phospholipid output. Rats were cannulated at 3.5, 8–12 and 24–27 months of age and bile collected for analysis. With age, there was a significant reduction in bile flow and total bile acid secretion, however, phospholipid output increased. Restriction of dietary intake exerted a beneficial effect on the age-related decline in bile formation. Studies of bile composition indicated that 12α-hydroxylated bile acids (cholic acid and deoxycholic acid) secretion decreased in aged rats compared to 3.5-month-old rats. This was associated with a corresponding increase in secretion of chenodeoxycholic acid and hyodeoxycholic-ursodeoxycholic acid. However, the magnitude of the change in secretion of these bile acids could not account for the increased output of phospholipid in bile.     

Effect of low-to-moderate amounts of dietary fish oil on neutrophil lipid composition and function

Although essential to host defense, neutrophils are also involved in numerous inflammatory disorders including rheumatoid arthritis. Dietary supplementation with relatively large amounts of fish oil [containing >2.6 g eicosapentaenoic acid (EPA) plus 1.4 g docosahexaenoic acid (DHA) per day] can attenuate neutrophil functions such as chemotaxis and superoxide radical production. In this study, the effects of more moderate supplementation with fish oil on neutrophil lipid composition and function were investigated. The rationale for using lower supplementary doses of fish oil was to avoid adverse gastrointestinal problems, which have been observed at high supplementary concentrations of fish oil. Healthy male volunteers aged <40 yr were randomly assigned to consume one of six dietary supplements daily for 12 wk (n=8 per treatment group). The dietary supplements included four different concentrations of fish oil (the most concentrated fish oil provided 0.58 g EPA plus 1.67 g DHA per day), linseed oil, and a placebo oil. The percentages of EPA and DHA increased (both P<0.05) in neutrophil phospholipids in a dose-dependent manner after 4 wk of supplementation with the three most concentrated fish oil supplements. No further increases in EPA or DHA levels were observed after 4 wk. The percentage of arachidonic acid in neutrophil phospholipids decreased (P<0.05) after 12 wk supplementation with the linseed oil supplement or the two most concentrated fish oil supplements. There were no significant changes in N-formyl-met-leu-phe-induced chemotaxis and superoxide radical production following the dietary supplementations. In conclusion, low-to-moderate amounts of dietary fish oil can be used to manipulate neutrophil fatty acid composition. However, this may not be accompanied by modulation of neutrophil functions such as chemotaxis and superoxide radical production.     

Effects of sucrose ester on the kinetics of polymorphic transition in hydrogenated sunflower oil

The effect of a commercial emulsifier, sucrose ester, on the crystallization kinetics of hydrogenated sunflowerseed oil was studied by means of an optical method. Induction times were measured for hydrogenated oil with the addition of 0.01, 0.05, and 0.1 wt% sucrose ester. This emulsifier delayed nucleation, thus affecting the formation of critical nuclei and prolonging induction times. Kinetics of the β’→β polymorphic transition was followed by X-ray diffractometry. Addition of the emulsifier delayed the appearance of the signal at 4.6 Å. Moreover, longer times were needed to complete the transition. The kinetic model chosen to describe the transition process was based on the theory of Avrami. Avrami’s exponentn was approximately 1 in all cases. Then value was in agreement with the fact that only one β’ pattern was found. The β form could not be obtained directly from the melt, and it is unlikely that the β’→β transition occurred through a melt-mediated mechanism. Transition was hindered by the rigidity of the sucrose ester structure.     

Hyperthyroidism affects lipid metabolism in lactating and suckling rats

Two per thousand pregnant women have hyperthyroidism (HT), and although the symptoms are attenuated during pregnancy, they rebound after delivery, affecting infant development. To examine the effects of hyperthyroidism on lactation, we studied lipid metabolism in maternal mammary glands and livers of hyperthyroid rats and their pups. Thyroxine (10 μg/100 g body weight/d) or vehicle-treated rats were made pregnant 2 wk after commencement of treatment and sacrificed on days 7, 14, and 21 of lactation with the litters. Circulating triiodothyronine and tetraiodothyronine concentratins in the HT mothers were increased on all days. Hepatic esterified cholesterol (EC) and free cholesterol (FC) and triglyceride (TG) concentrations were diminished on days 14 and 21. Lipid synthesis, measured by incorporation of [³H]H₂O into EC, FC, and TG, fatty acid synthase, and acetyl CoA carboxylase activities increased at day 14, while incorporation into FC and EC decreased at days 7 and 21, respectively. Mammary FC and TG concentrations were diminished at day 14. Incorporation of [³H]H₂O into TG decreased at days 7 and 21, and incorporation of [³H]H₂O into FC increased at day 14. In the HT pups, growth rate was diminished, tetraiodothyronine concentration rose at days 7 and 14 of lactation, and triiodothyronine increased only at day 14, Liver TG concentrations increased at day 7 and fell at day 14, while FC increased at day 14 and only acetyl CoA carboxylase activity fell at day 14. Thus, hyperthyroidism changed maternal liver and mammary lipid metabolism, with decreased lipid concentration in spite of increased liver rate of synthesis and decreased in mammary synthesis. These changes, along with the mild hyperthyroidism of the litters, may have contributed to their reduced growth rate.