The effect of dietary vitamin E supply and a moderately oxidized oil on activities of hepatic lipogenic enzymes in rats

Dietary oxidized frying oil activates hepatic stellate cells and accelerates the severity of carbon tetrachloride- and thioacetamide-induced liver fibrosis in mice

Deep-frying is a common cooking practice worldwide, and after repeated heating's, the oil undergoes various chemical reactions, including hydrolysis, polymerization, lipid oxidation, and the Maillard reaction. Studies have pointed out that oxidized dietary frying oil may cause teratogenesis in mice and increase cancer and cardiovascular risks. The liver is the main organ involved in dietary nutrient catabolism, detoxification, bile production, and lipid metabolism. Nevertheless, the effects of oxidized frying oil exposure on the activation of hepatic stellate cells (HSCs) and liver fibrosis are still unclear. In this study, we showed that exposure to oxidized frying oil enhanced the sensitivity of HSCs to transforming growth factor (TGF)-β1-induced α-smooth muscle actin (α-SMA), collagen 1a2, collagen 1a1, metalloproteinase-2, and phosphorylated smad2/3 activation. In both carbon tetrachloride (CCl₄)- and thioacetamide (TAA)-induced liver fibrosis mouse models, we showed that long-term administration of a 10% fried oil-containing diet significantly upregulated fibrogenesis genes expression and deposition of hepatic collagen. Furthermore, long-term fried oil exposure not only promoted macrophage infiltration and increased inflammatory-related gene expression, but also accumulated excess cholesterol and lipid peroxidation in the liver tissues. In conclusion, our study demonstrated that feeding a fried oil-containing diet may trigger TGF-β1-induced HSCs activation and thereby promote liver damage and fibrosis progression through enhancing the inflammatory response and lipid peroxidation.

Saltwater fish but not freshwater fish consumption is positively related to handgrip strength: The TCLSIH Cohort Study

Fish contain many important nutrients and are primarily known for high n-3 polyunsaturated fatty acids (n-3 PUFA) content. Studies have shown that supplementation of fish oil-derived n-3 PUFA improves muscle mass and strength. Here, we hypothesized that fish consumption might improve muscle strength. To test this hypothesis, we performed this cross-sectional study (n = 29,084) in Tianjin, China. The frequency of fish consumption was assessed using a valid self-administered food frequency questionnaire. Handgrip strength (HGS) was used as the indicator of muscle strength, and was measured using a handheld digital dynamometer. Analysis of covariance was used to examine the relationship between fish consumption and HGS. In men, after adjusted potential confounding factors, the least square means (95% confidence intervals) of HGS across saltwater fish consumption categories were 41.5 (41.1, 43.7) kg for <1 time/week, 44.6 (43.2, 45.8) kg for 1 time/week, and 44.7 (43.3, 46.1) kg for ≥2 to 3 times/week (P for trend <0.001). In men, the least square means (95% confidence intervals) of HGS across the ascending quartiles of dietary n-3 PUFA intake were 43.6 (43.2, 44.4) kg, 43.7 (43.2, 44.6) kg, 44.4 (43.0, 45.8) kg, and 44.6 (43.1, 46.0) kg (P for trend <0.01). The results showed that saltwater fish consumption was positively related to HGS in men, but not in women, suggesting that saltwater fish contain nutrients that may be used to improve HGS.

High α-tocopherol dosing increases lipid metabolism by changing redox state in damaged rat gastric mucosa and liver after ethanol treatment

Regeneration of ethanol-injured rat gastric mucosa must undergo changes in major metabolic pathways to achieve DNA replication and cell proliferation. These events are highly dependent on glucose utilization and inhibited by vitamin E (VE) (α-tocopherol) administration. Therefore, the present study aimed at assessing lipid metabolism in the gastric mucosa and ethanol-induced gastric damage and the effect of α-tocopherol administration. For this, rates of fatty acid β-oxidation and lipogenesis were tested in gastric mucosa samples. Through histological analysis, we found loss of the mucosa's superficial epithelium, which became gradually normalized during the recovery period. Proliferation of gastric mucosa occurred with augmented formation of β-oxidation by-products, diminished synthesis of triacylglycerols (TGs), as well as of phospholipids, and a reduced cytoplasmic NAD/NADH ratio, whereas the mitochondrial redox NAD/NADH ratio was much less affected. In addition, α-tocopherol increased palmitic acid utilization in the gastric mucosa, which was accompanied by the induction of 'mirror image' effects on the cell redox state, reflected in an inhibited cell gastric mucosa proliferation by the vitamin administration. In conclusion, the present study shows, for the first time, the role of lipid metabolism in the adaptive cell gastric mucosa changes that drive proliferation after a chronic insult. Moreover, α-tocopherol increased gastric mucosa utilization of palmitic acid associated with energy production. These events could be associated with its antioxidant properties in co-ordination with regulation of genes and cell pathways, including changes in the cell NAD/NADH redox state.

Effect of dietary vitamin E and selenium supplementation on growth, body composition, and antioxidant defense mechanism in juvenile largemouth bass (Micropterus salmoides) fed oxidized fish oil

Six oxidized fish oil contained diets were formulated to investigate the effect of graded levels of vitamin E (V(E)) (α-tocopherol acetate: 160, 280, and 400 mg kg(-1)) associated with either 1.2 or 1.8 mg kg(-1) selenium (Se) on growth, body composition, and antioxidant defense mechanism of juvenile largemouth bass. Another control diet containing fresh fish oil with 160 mg kg(-1) V(E) and 1.2 mg kg(-1) Se was also prepared. Over a 12-week feeding trial, about 5 % of Micropterus salmoide fed diet OxSe1.2/V(E)160 showed inflammation and hemorrhage symptoms at the base of dorsal, pectoral, and tail fin. Fish in all treatments survived well (above 90 %). Feed intakes (88.42-89.58 g fish(-1)) of all treatments were comparable. Growth performances (weight gain and specific growth rate) and feed utilization (feed and protein efficiency ratio) were significantly impaired by dietary oil oxidation, and they did not benefit from neither V(E) nor Se supplementation. Regardless of dietary V(E) and Se supplementation, oxidized oil ingestion resulted in markedly decreased hepatosomatic index and intraperitoneal fat ratio. Oxidized oil ingestion also induced markedly lower liver and muscle lipid contents, and these effects could be alleviated by dietary Se supplementation. Dietary oil oxidation stimulated hepatic catalase activities relative to the control, and supplementation of V(E) abrogated this effect. Hepatic reduced glutathione content in the control was markedly higher than that of treatment OxSe1.2/V(E)160, without any significant differences comparing with the other oxidized oil receiving groups. Hepatic glutathione peroxidase activity and liver Se concentration reflected dietary Se profile, whereas liver V(E) level reflected dietary V(E) profile. Compared with the control, fish fed diet OxSe1.2/V(E)160 obtained markedly higher serum, liver and muscle malondialdehyde contents, which droppe significantly with increasing either V(E) or Se supplementation. In conclusion, the overall results in this study suggested that both V(E) and Se inclusion could protect largemouth bass from the oxidative damage challenged by dietary oil oxidation.

Gestational ingestion of oxidized frying oil by C57BL/6J mice differentially affects the susceptibility of the male and female offspring to diet-induced obesity in adulthood

The aim of this study was to investigate whether maternal ingestion of oxidized frying oil (OFO) during pregnancy influences the susceptibility to diet-induced obesity (DIO) of the adult offspring. Pregnant C57BL/6J mice were fed either a control diet [10% fresh soybean oil (SO)] or an OFO-containing diet (10% OFO) throughout the entire gestational period. After parturition, all pups were nursed by SO-fed dams for 3 wk, weaned onto a nonpurified standard diet for 4 wk, and shifted to a high-fat diet (29% butter + 1% SO) for 5 wk. Consequently, 4 groups of offspring were obtained, consisting of the male (m) or female (f) offspring of dams fed the OFO diet (OFO-m and OFO-f) or the SO diet (SO-m and SO-f). At pregnancy d 18, higher amounts (P < 0.05) of mRNA for PPARα target genes were found in the liver of the OFO-fed dams and their fetuses than in their SO controls. Although all pups were raised under the same conditions in postnatal life, a comparison based on the gender of pups from dams fed the different diets showed that adult OFO-f mice were prone to DIO, whereas adult OFO-m mice were resistant. The adult OFO-m mice also had higher expression of PPARα target genes in the liver and white adipose tissue (WAT) and of thermogenic genes in the WAT than adult SO-m mice, whereas adult OFO-f and SO-f mice did not differ. We conclude that uterine PPARα activation caused by maternal OFO ingestion affects hepatic PPARα activity and adipose thermogenic capacity and contributes to the differential susceptibility to DIO in the male and female offspring in adulthood.

Fatty acid composition and cholesterol content of muscles as related to genotype and vitamin E treatment in crossbred lambs

Various factors (weight, sex, diet and breed) influence meat lamb fatty acid composition. The present study was undertaken to evaluate the lipid profile in two different lamb types. Sixty crossbred lambs (Ile de France×Pagliarola and Gentile di Puglia×Sopravissana) were used to determine cholesterol, lipid content and fatty acid profile of Longissimus dorsi, Semimembranosus and Gluteobiceps muscles. Moreover, the effect of vitamin E treatment in vivo on propensity of the lamb meat to lipoperoxidation was assessed. In both crossbreeds total muscle lipids ranged between 2.4 and 4.0 mg/100 g. In the Ile de France×Pagliarola lambs a lower percentage of saturated fatty acids and a low atherogenic index were found. The vitamin E treatment reduced significantly the lipoperoxidation, without difference between the two crossbreeds.

Dietary moderately oxidized oil induces expression of fibroblast growth factor 21 in the liver of pigs

Background

Fibroblast growth factor 21 (FGF21), whose expression is induced by peroxisome proliferator-activated receptor α (PPARα), has been recently identified as a novel metabolic regulator which plays a crucial role in glucose homeostasis, lipid metabolism, insulin sensitivity and obesity. Previous studies have shown that administration of oxidized fats leads to an activation of PPARα in the liver. Therefore, the present study investigated the hypothesis that feeding of oxidized fats causes an induction of FGF21 in the liver.

Methods

Twenty four crossbred pigs were allocated to two groups of 12 pigs each and fed nutritionally adequate diets with either fresh rapeseed oil or oxidized rapeseed oil prepared by heating at a temperature of 175°C for 72 h.

Results

In pigs fed the oxidized fat mRNA abundance and protein concentrations of FGF21 in liver were significantly increased (P < 0.05), and the protein concentrations of FGF21 in plasma tended to be increased (P < 0.1) in comparison to control pigs. Moreover, pigs fed the oxidized fat had increased transcript levels of the PPARα target genes acyl-CoA oxidase, carnitine palmitoyltransferase-1 and novel organic cation transporter 2 in the liver (P < 0.05), indicative of PPARα activation.

Conclusion

The present study shows for the first time that administration of an oxidized fat induces the expression of FGF21 in the liver, probably mediated by activation of PPARα. Induction of FGF21 could be involved in several effects observed in animals administered an oxidized fat.

Dietary moderately oxidized oil activates the Nrf2 signaling pathway in the liver of pigs

Background

Previous studies have shown that administration of oxidized oils increases gene expression and activities of various enzymes involved in xenobiotic metabolism and stress response in the liver of rats and guinea pigs. As these genes are controlled by nuclear factor erythroid-derived 2-like 2 (Nrf2), we investigated the hypothesis that feeding of oxidized fats causes an activation of that transcription factor in the liver which in turn activates the expression of antioxidant, cytoprotective and detoxifying genes.

Methods

Twenty four crossbred pigs were allocated to two groups of 12 pigs each and fed nutritionally adequate diets with either fresh rapeseed oil (fresh fat group) or oxidized rapeseed oil prepared by heating at a temperature of 175°C for 72 h (oxidized fat group).

Results

After 29 days of feeding, pigs of the oxidized fat group had a markedly increased nuclear concentration of the transcription factor Nrf2 and a higher activity of cellular superoxide dismutase and T4-UDP glucuronosyltransferase in liver than the fresh fat group (P < 0.05). In addition, transcript levels of antioxidant and phase II genes in liver, like superoxide dismutase 1, heme oxygenase 1, glutathione peroxidase 1, thioredoxin reductase 1, microsomal glutathione-S-transferase 1, UDP glucuronosyltransferase 1A1 and NAD(P)H:quinone oxidoreductase 1 in the liver were higher in the oxidized fat group than in the fresh fat group (P < 0.05). Moreover, pigs of the oxidized fat group had an increased hepatic nuclear concentration of the transcription factor NF-κB which is also an important transcription factor mediating cellular stress response.

Conclusion

The present study shows for the first time that administration of an oxidized fat activates the Nrf2 in the liver of pigs which likely reflects an adaptive mechanism to prevent cellular oxidative damage. Activation of the NF-κB pathway might also contribute to this effect of oxidized fat.

The effects of moderately oxidised dietary oil with or without vitamin E supplementation on performance, nutrient digestibility, some blood traits, lipid peroxidation and antioxidant defence of male broilers

BACKGROUND

The experiment was conducted to determine the effects of dietary supplementation of oxidised oil with or without vitamin E on performance, nutrient digestibility, some blood traits, lipid peroxidation and antioxidant defence system of male broilers.

RESULTS

The supplementation of oxidised oil with or without vitamin E to the grower diets did not significantly affect performance, the pH and viscosity values of excreta and nutrient digestibilities in male broilers. Oxidised oil supplementation slightly increased plasma triglyceride and cholesterol concentrations but did not alter plasma glucose concentration. Although malondialdehyde (MDA) and nitric oxide concentrations tended to be higher in the oxidised oil group, these increases were not significant. Birds fed the diet containing oxidised oil had significantly lower superoxide dismutase (SOD) activity. However, no differences were observed in glutathione peroxidase (GSH-Px) activity and uric acid concentrations of broilers fed oxidised oil as compared to the control group. Dietary vitamin E supplementation decreased MDA concentration whereas increasing SOD activity, suggesting that vitamin E supplementation reduced susceptibility to lipid peroxidation.

CONCLUSION

The results showed that a milder oxidative stress occurred by supplementation of moderately oxidised oil to the diet of broilers and vitamin E supplementation had been helpful in alleviating lipid peroxidation.

Feeding a thermally oxidised fat inhibits atherosclerotic plaque formation in the aortic root of LDL receptor-deficient mice

Activators of PPARα have been demonstrated to inhibit atherosclerosis development due to lipid lowering in plasma and direct protective effects on the vasculature. Because dietary oxidised fats (OF) have strong PPARα-activating and lipid-lowering properties, we hypothesised that dietary OF has also an inhibitory influence on atherosclerosis development. To verify our hypothesis, we investigated the effect of feeding diets containing an OF (a 92 : 8 mixture of heated (170°C, 48 h) hydrogenated palm fat and fresh sunflower oil) compared with a fresh fat (fresh hydrogenated palm fat) on the development of atherosclerotic lesions in LDL receptor-deficient (LDLR- / - ) mice. We observed that a dietary OF caused a strong up-regulation of PPARα-regulated genes in the liver and a marked reduction in plasma concentrations of cholesterol and TAG (P < 0·05). Cross-sectional lesion area and the lipids and collagen levels in the aortic root were approximately 40-50 % lower in mice fed diets containing OF than in those fed diets containing fresh fat (P < 0·05). Immunohistochemical analysis of aortic root sections revealed an about 8-fold increased expression of PPARα and a markedly reduced expression of the proinflammatory vascular cell adhesion molecule-1 and smooth muscle cell (SMC)-specific marker α-actin in LDLR- / - mice fed OF (P < 0·05). We postulate that OF exert anti-atherogenic effects by activation of PPARα both in the liver, which contributes to lipid lowering in plasma, and in the vasculature, which inhibits pro-atherogenic events such as monocyte recruitment and SMC proliferation and migration.

Supplementation of SK1 from Platycodi radix ameliorates obesity and glucose intolerance in mice fed a high-fat diet

This study investigated the beneficial effects of SK1 on obesity and insulin resistance in C57BL/6 mice, which were fed a high-fat diet (37% calories from fat). SK1 is an edible saponin-rich compound from Platycodi radix. The mice were supplemented with two doses of SK1 (0.5% and 1.0%, wt/wt) for 9 weeks. The body weight, visceral fat mass, and adipocyte area were significantly decreased in the SK1 supplemented-groups in a dose-dependent manner compared to the high-fat group. The SK1 supplement significantly lowered plasma triglycerides, total cholesterol, and free fatty acid levels, whereas it significantly elevated the fecal excretion of lipids in the diet-induced obese mice. Supplementation of SK1 decreased the triglyceride and cholesterol levels and the accumulation of lipid droplets in the liver compared to the high-fat control group. High-fat diet induced glucose intolerance and insulin resistance with the elevation of blood glucose levels compared to the normal group; however, the SK1 supplement significantly improved postprandial glucose levels and insulin resistance index. After 9 weeks of being fed a high-fat diet, the mice presented with significantly increased activities of hepatic fatty acid synthase, fatty acid beta-oxidation, and glucokinase; however, both 0.5% and 1.0% SK1 supplementation normalized these activities. Notably, SK1 supplementation effectively diminished the ratio of fatty acid biosynthesis to fatty acid oxidation compared to the high-fat group. These results indicate that SK1 exhibits a potential anti-obesity effect and may prevent glucose intolerance by reducing body weight and fat accumulation, increasing fecal lipid excretions, and regulating hepatic lipid and glucose metabolism in high-fat fed mice.

Effects of Oxidized Frying Oil on Proteins Related to alpha-Tocopherol Metabolism in Rat Liver

An oxidized frying oil (OFO) diet has been reported to induce an increase in lipid peroxidation and a reduction in vitamin E status in animal tissues. This study was performed to investigate how vitamin E metabolism is influenced by OFO. Male Wistar rats were divided into three groups, a control group (CO) and two OFO-fed groups (OF and OFE). The diet of the OFE group was supplemented with an extra 50 mg/kg of alpha-tocopherol acetate and thus contained twice as much vitamin E as that of the OF group. After six weeks on these diets, liver alpha-tocopherol levels in the OF group were the significantly lowest among the three groups. Excretion of the alpha-tocopherol metabolite, alpha-carboxyethyl hydroxychroman (alpha-CEHC) in the urine was significantly lower in the OF group than in the other two groups. There were no significant differences in protein levels of alpha-tocopherol transfer protein (alpha-TTP) and multidrug resistance protein among the three groups. Protein levels of cytochrome P450 monooxygenase (CYP) 3A, CYP4A, and catalase were markedly increased in both groups on the OFO diet. This suggests that an OFO diet may interfere with medicine metabolism and needs further investigation.

Effect of an oil byproduct from conjugated linoleic acid (CLA) purification on CLA accumulation and lipogenic gene expression in broilers

A previous study showed that supplementing broilers with an oil byproduct obtained during the purification process of conjugated linoleic acid (CLA) from safflower oil could result in CLA-enriched egg yolks more efficiently than feeding purified CLA (free fatty acid form). On this basis, this study evaluated whether dietary CLA byproduct (CBP) supplementation would enhance CLA accumulation in broiler muscle and its lipogenic mRNA expression in the liver. A total of 456 1-day-old male broiler chicks were randomly assigned to four groups, each of which was given one of the following 2% dietary supplements for 4 weeks: soybean oil (control), safflower oil (SAF), purified CLA, and CBP. During the feeding trial, little alteration in broiler performance was observed among the test groups. CLA accumulation efficiency in the breast muscle did not differ significantly between the CLA- and CBP-fed groups after feeding of the test diet for 3 weeks. CLA supplementation also induced lipogenesis in the livers of the broilers, and it significantly increased the relative mRNA levels of sterol regulatory element binding protein 1 (SREBP1), as well as its target genes: fatty acid synthase (FAS) and acetyl coenzyme A carboxylase (ACC) (p < 0.05). However, in the CBP-fed group, SREBP1 and ACC mRNA levels were not significantly different from the controls (p > 0.05). These results suggest that CBP could be an efficient dietary source that promotes CLA accumulation in broiler muscle without inducing lipogenesis in the liver or compromising performance and meat quality in the birds.

Hepatic steatosis in n-3 fatty acid depleted mice: focus on metabolic alterations related to tissue fatty acid composition

Background

There are only few data relating the metabolic consequences of feeding diets very low in n-3 fatty acids. This experiment carried out in mice aims at studying the impact of dietary n-3 polyunsaturated fatty acids (PUFA) depletion on hepatic metabolism.

Results

n-3 PUFA depletion leads to a significant decrease in body weight despite a similar caloric intake or adipose tissue weight. n-3 PUFA depleted mice exhibit hypercholesterolemia (total, HDL, and LDL cholesterol) as well as an increase in hepatic cholesteryl ester and triglycerides content. Fatty acid pattern is profoundly modified in hepatic phospholipids and triglycerides. The decrease in tissue n-3/n-6 PUFA ratio correlates with steatosis. Hepatic mRNA content of key factors involved in lipid metabolism suggest a decreased lipogenesis (SREBP-1c, FAS, PPARγ), and an increased β-oxidation (CPT1, PPARα and PGC1α) without modification of fatty acid esterification (DGAT2, GPAT1), secretion (MTTP) or intracellular transport (L-FABP). Histological analysis reveals alterations of liver morphology, which can not be explained by inflammatory or oxidative stress. However, several proteins involved in the unfolded protein response are decreased in depleted mice.

Conclusion

n-3 PUFA depletion leads to important metabolic alterations in murine liver. Steatosis occurs through a mechanism independent of the shift between β-oxidation and lipogenesis. Moreover, long term n-3 PUFA depletion decreases the expression of factors involved in the unfolded protein response, suggesting a lower protection against endoplasmic reticulum stress in hepatocytes upon n-3 PUFA deficiency.

Dietary n-3 HUFA affects mitochondrial fatty acid beta-oxidation capacity and susceptibility to oxidative stress in Atlantic salmon

Atlantic salmon (Salmo salar) (90 g) were fed four different diets for 21 weeks (final weight 344 g). The levels of n-3 highly unsaturated fatty acids (HUFA) ranged from 11% of the total fatty acids (FA) in the low n-3 diet to 21% in the intermediate n-3 diet, to 55 and 58% in the high n-3 diets. The high n-3 diets were enriched with either docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA). Increasing dietary levels of n-3 HUFA led to increasing percentages (from 31 to 52%) of these FA in liver lipids. The group fed the highest level of DHA had higher expressions of peroxisome proliferator-activated receptor (PPAR) beta and the FA beta-oxidation genes acyl-CoA oxidase (ACO) and carnitine palmitoyltransferase (CPT)-II, compared to the low n-3 groups. The high n-3 groups had reduced activity of mitochondrial cytochrome c oxidase and beta-oxidation capacity, together with increased activities of superoxide dismutase (SOD) and caspase-3 activities. In the group fed the highest level of n-3 HUFA, decreased percentages of major phospholipids (PL) in the mitochondrial and microsomal membranes of the liver were also apparent. The percentage of mitochondrial cardiolipin (Ptd(2)Gro) was 3.1 in the highest n-3 group compared to 6.6 in the intermediate group. These data clearly show an increased incidence of oxidative stress in the liver of fish fed the high n-3 diets.

Thermally oxidized oil increases the expression of insulin-induced genes and inhibits activation of sterol regulatory element-binding protein-2 in rat liver

Administration of oxidized oils to rats or pigs causes a reduction of their cholesterol concentrations in liver and plasma. The reason for this effect is unknown. We tested the hypothesis that oxidized oils lower cholesterol concentrations by inhibiting the proteolytic activation of sterol regulatory element-binding protein (SREBP)-2 in the liver and transcription of its target genes involved in cholesterol synthesis and uptake through an upregulation of gene expression of insulin-induced genes (Insig). For 6 d, 18 rats were orally administered either sunflower oil (control group) or an oxidized oil prepared by heating sunflower oil. Rats administered the oxidized oil had higher messenger RNA (mRNA) concentrations of acyl-CoA oxidase and cytochrome P450 4A1 in the liver than control rats (P < 0.05), indicative of activation of PPARalpha. Furthermore, rats administered the oxidized oil had higher mRNA concentrations of Insig-1 and Insig-2a, a lower concentration of the mature SREBP-2 in the nucleus, lower mRNA concentrations of the SREBP-2 target genes 3-hydroxy-3-methylglutaryl CoA reductase and LDL receptor in their livers, and a lower concentration of cholesterol in liver, plasma, VLDL, and HDL than control rats (P < 0.05). In conclusion, this study shows that reduced cholesterol concentrations in liver and plasma of rats administered an oxidized oil were due to an inhibition of the activation of SREBP-2 by an upregulation of Insig, which in turn inhibited transcription of proteins involved in hepatic cholesterol synthesis and uptake.

Feeding of a deep-fried fat causes PPARα activation in the liver of pigs as a non-proliferating species

Recent studies have shown that dietary oxidised fats influence the lipid metabolism in rats by activation of PPARα. In this study, we investigated whether a mildly oxidised fat causes activation of PPARα in pigs which are non-proliferators like man. Eighteen pigs were assigned to two groups and received either a diet containing 90 g/kg of a fresh fat or the same diet with 90 g/kg of an oxidised fat prepared by heating for 24 h at 180°C in a deep fryer. Pigs fed the oxidised fat had a higher peroxisome count, a higher activity of catalase and a higher mRNA concentration of mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase in the liver and a higher concentration of 3-hydroxybutyrate in plasma than pigs fed the fresh fat (P < 0·05). Hepatic mRNA concentrations of acyl-CoA oxidase and carnitine palmitoyltransferase-1 tended to be increased in pigs fed the oxidised fat compared to pigs fed the fresh fat (P < 0·10). Pigs fed the oxidised fat, moreover, had higher mRNA concentrations of sterol regulatory element-binding protein (SREBP)-1 and its target genes acetyl-CoA carboxylase and stearoyl-CoA desaturase in the liver and higher mRNA concentrations of SREBP-2 and its target genes 3-hydroxy-3-methylglutary-CoA reductase and LDL receptor in liver and small intestine. In conclusion, this study shows that even a mildly oxidised fat causes activation of PPARα in the liver of pigs. Up-regulation of SREBP and its target genes in liver and small intestine suggests that the oxidised fat could stimulate synthesis of cholesterol and TAG in these tissues.

Effects of peroxidation products in thermoxidised dietary oil in female rats during rearing, pregnancy and lactation on their reproductive performance and the antioxidative status of their offspring

The present study was performed to investigate whether lipid peroxidation products in thermoxidised dietary oil fed during rearing, pregnancy and lactation influences the reproductive performance of female rats and the antioxidant status of their offspring. Twenty-four female rats were divided into two groups at 4 weeks of age. They were fed diets containing fresh or oxidised oil (the latter prepared by heating at a temperature of 50°C for 16 d) for 14 weeks. At the age of 12 weeks female rats were mated. The number of total pups and pups born alive was not different between both groups. However, individual pups and litters of dams fed oxidised oil were lighter at birth and gained less weight during the suckling period than those of dams fed fresh oil (P>0·05). Pups of dams fed oxidised oil contained less protein and more fat in their carcasses than those of dams fed fresh oil (P>0·05). The milk of dams fed oxidised oil had a lower concentration of triacylglycerols and a lower energy content than that of dams fed the fresh oil (P>0·05). The pups of dams fed oxidised oil had higher concentrations of lipid peroxidation products in the liver at birth and day 19 of lactation than those of dams fed fresh oil (P>0·05). In conclusion, the present study shows that feeding oxidised oil with a high concentration of lipid peroxidation products to female rats during rearing, pregnancy and lactation influences the development and antioxidant status of fetus and suckling pups.

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.

Effects of additional Vitamin E and selenium supply on G6PDH activity in rats treated with high doses of glucocorticoid

The aim of this work was to determine the effects of dietary intake Vitamin E and selenium (Se) on glucose-6-phosphate dehydrogenase (G6PDH) activity in rats treated with high doses of prednisolone. Two hundred and fifty adult male Wistar rats were randomly divided into five groups. The rats were fed a normal diet, but groups 3, 4, and 5 received a daily supplement in their drinking water of 20mg Vitamin E, 0.3mg Se, and a combination of Vitamin E and Se, respectively, for 30 days. For 3 days subsequently, the control group (group 1) was treated with a placebo, and the remaining four groups were injected intramuscularly with 100 mg/kg body weight prednisolone. After the last administration of prednisolone, 10 rats from each group were killed at 4, 8, 12, 24, and 48 h and the activities of G6PDH enzymes in their tissues were measured. Hepatic and spleen G6PDH activities in the prednisolone treatment group began to decrease gradually at 8 h, while enzyme activities did not change in the kidney and heart. However, the administration of Vitamin E alone did not affect G6PDH activity in any of the tissues. Se supplementation had a preventive effect on the decrease of G6PDH caused by prednisolone and improved the diminished activities of G6PDH. Therefore, the present study demonstrates that a high dose of prednisolone may alter the effects of normal dose glucocorticoids and that Se is effective in reducing damage in prednisolone-treated rats. Se may prevent the changes in G6PDH activity in various tissues caused by prednisolone in various tissues.

Differential action of 13-HPODE on PPARalpha downstream genes in rat Fao and human HepG2 hepatoma cell lines

In rats, oxidized fats activate the peroxisome proliferator-activated receptor alpha (PPARalpha), leading to reduced triglyceride concentrations in liver, plasma and very low density lipoproteins. Oxidation products of linoleic acid constitute an important portion of oxidized dietary fats. This study was conducted to check whether the primary lipid peroxidation product of linoleic acid, 13-hydroperoxy-9,11-octadecadienoic acid (13-HPODE), might be involved in the PPARalpha-activating effect of oxidized fats. Therefore, we examined the effect of 13-HPODE on the expression of PPARalpha target genes in the rat Fao and the human HepG2 hepatoma cell lines. In Fao cells, 13-HPODE increased the mRNA concentration of the PPARalpha target genes acyl-CoA oxidase (ACO), cytochrome P450 4A1 and carnitine-palmitoyltransferase 1A (CPT1A). Furthermore, the concentration of cellular and secreted triglycerides was reduced in Fao cells treated with 13-HPODE. Because PPARalpha mRNA was not influenced, we conclude that these effects are due to an activation of PPARalpha by 13-HPODE. In contrast, HepG2 cells seemed to be resistant to PPARalpha activation by 13-HPODE because no remarkable induction of the PPARalpha target genes ACO, CPT1A, mitochondrial HMG-CoA synthase and delta9-desaturase was observed. Consequently, cellular and secreted triglyceride levels were not changed after incubation of HepG2 cells with 13-HPODE. In conclusion, this study shows that 13-HPODE activates PPARalpha in rat Fao but not in human HepG2 hepatoma cells.

Suppression of hepatic fatty acid synthase by feeding alpha-linolenic acid rich perilla oil lowers plasma triacylglycerol level in rats

This study was performed to determine the effects of dietary perilla oil, a n-3 alpha-linolenic acid (ALA) source, on hepatic lipogenesis as a possible mechanism of lowering triacylglycerol (TG) levels. Male Sprague-Dawley rats were trained for a 3-hour feeding protocol and fed one of five semipurified diets as follows: 1% (w/w) corn oil control diet, or one of four diets supplemented with 10% each of beef tallow, corn oil, perilla oil, and fish oil. Two separate experiments were performed to compare the effects of feeding periods, 4 weeks and 4 days. Hepatic and plasma TG levels were decreased in rats fed perilla oil and fish oil diets, compared with corn oil and beef tallow diets. The activities of hepatic lipogenic enzymes such as fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase, and malic enzyme were suppressed in the fish oil, perilla oil, and corn oil-fed groups, and the effect was the most significant in the fish oil-fed group. Also, the activities of glycolytic enzymes, glucokinase, and L-pyruvate kinase showed the similar trend as that of lipogenic enzymes. The activity of FAS, the key regulatory enzyme in lipogenesis, was positively correlated with hepatic and plasma TG levels and reduced significantly in the perilla oil-fed group compared with corn oil-fed group. In addition, the FAS activity was negatively correlated with the hepatic microsomal content of EPA and DHA. In conclusion, suppression of FAS plays a significant role in the hypolipidemic effects observed in rats fed ALA rich perilla oil and these effects were associated with the increase of hepatic microsomal EPA and DHA contents.

A thermally oxidized dietary oil does not lower the activities of lipogenic enzymes in mammary glands of lactating rats but reduces the milk triglyceride concentration

It was shown that dietary thermoxidized oils suppress gene expression of lipogenic enzymes in the liver. This study was performed to investigate whether oxidized oils also influence the activities of lipogenic enzymes in the mammary gland of lactating rats. Female rats (n = 24) were divided into two groups at 4 wk of age. They were fed for 14 wk diets with either fresh oil (a mixture of sunflower oil, linseed oil, and palm oil, 73:15:12) or oxidized oil (a mixture of sunflower oil and linseed oil, 80:20) prepared by heating at a temperature of 50 degrees C for 16 d. At the age of 12 wk, the rats were mated. At birth, litters were adjusted to 7 pups/dam. Milk was sampled at d 14 of lactation; mammary glands were taken at d 19 of lactation. Rats fed the oxidized oil had a lower activity of glucose-6-phosphate dehydrogenase (G6PDH) in their mammary glands than those fed the fresh oil (P < 0.05); the activities of fatty acid synthase (FAS) and acetyl-CoA-carboxylase in mammary glands did not differ. Relative mRNA concentrations of G6PDH, FAS, and sterol-regulatory element binding protein-1, a regulator of lipogenesis, in the mammary gland did not differ between groups. The concentrations in the milk of medium-chain fatty acids (C8-C14), the major products of fatty acid synthesis in mammary glands, also did not differ. The concentrations of triglycerides and long-chain fatty acids (C18-C22), however, were lower in the milk of rats fed the oxidized oil than in the milk of rats fed the fresh oil (P < 0.05). In conclusion, this study shows that feeding oxidized oils to lactating rats does not affect lipogenic enzymes in mammary glands but reduces the triglyceride concentrations in their milk.

Suppression of fatty acid synthase by dietary polyunsaturated fatty acids is mediated by fat itself, not by peroxidative mechanism

This study examined the effect of dietary polyunsaturated fatty acids (PUFA) that were supplemented with vitamin E on lipid peroxidation, glutathione-dependent detoxifying enzyme system activity, and lipogenic fatty acid synthase (FAS) expression in rat liver. Male Sprague-Dawley rats were fed semipurified diets containing either 1% (w/w) corn oil or 10% each of beef tallow, corn oil, perilla oil, and fish oil for 4 wk. Alpha-tocopherol was supplemented in perilla oil (0.015%) and fish oil (0.019%). Hepatic thiobarbituric acid reactive substances, an estimate of lipid peroxidation, were not significantly different among the dietary groups. The glutathione peroxidase, glutathione reductase, and glutathione S-transferase activities were all elevated by the polyunsaturated fats, especially fish oil. The activity of FAS was reduced in the polyunsaturated fat-fed groups in the order of fish oil, perilla oil, and corn oil. The mRNA contents decreased in rats that were fed the 10% fat diets, particularly polyunsaturated fats, compared with the rats that were fed the 1% corn oil diet. Similarly, the inhibitory effect was the greatest in fish oil. These results suggest that lipid peroxidation can be minimized by vitamin E; PUFA in itself has a suppressive effect on lipogenic enzyme.

Effects of dietary thermoxidized fats on expression and activities of hepatic lipogenic enzymes in rats

This study was undertaken to investigate the effect of dietary oxidized fats on the relative mRNA concentrations and the activities of fatty acid synthase (FAS) and glucose-6-phosphate dehydrogenase (G6PDH) in the liver of rats treated with vitamin E or selenium. Two experiments with male Sprague-Dawley rats were carried out. The first experiment included eight groups of rats fed diets with either fresh fat or three different types of oxidized fat, prepared by heating at temperatures of 50, 105, or 190 degrees C, over a period of 6 wk. The diets contained either 25 or 250 mg alpha-tocopherol equivalents per kg. The second experiment included four groups of rats fed diets with fresh fat or oxidized fat, heated at a temperature of 55 degrees C, containing either 70 or 570 microg selenium per kg, over a period of 8 wk. Feeding the diets with oxidized fats led to a significant overall reduction of the relative mRNA concentrations and the activities of FAS and G6PDH in both experiments. The effects of the oxidized fats on mRNA concentrations and activities of these enzymes were independent of the dietary concentrations of vitamin E or selenium. Moreover, in both experiments the rats whose diet contained the oxidized fats had significantly lower concentrations of TG in liver, plasma, and VLDL than the rats whose diet contained fresh fat. The study suggests that oxidized fats contain substances that suppress gene expression of lipogenic enzymes in the liver.

Oxidized frying oil up-regulates hepatic acyl-CoA oxidase and cytochrome P450 4 A1 genes in rats and activates PPARalpha

Oxidized LDL (oxLDL) and its component hydroxy fatty acids were shown to activate peroxisome proliferator-activating receptor alpha (PPARalpha) and gamma (PPARgamma). To test the hypothesis that lipid oxidation products in oxidized frying oil (OFO) can activate PPARalpha and up-regulate its target genes, a feeding experiment and a transactivation experiment were conducted. Based on a 2 x 2 factorial design, four groups of Sprague-Dawley male weanling rats were fed diets containing either high (20 g/100 g, HO and HF) or low (5 g/100 g, LO and LF) levels of oxidized frying soybean oil (HO and LO) or fresh soybean oil (HF and LF) for 6 wk. The OFO sample was prepared by frying wheat dough sheets in soybean oil at 205 +/- 5 degrees C for 24 h. OFO dose dependently and significantly increased (P < 0.05) mRNA of acyl-CoA oxidase (ACO) and cytochrome P(450) 4A1(CYP4A1) in liver of rats. Dietary OFO also dose dependently increased liver microsomal CYP4A protein (P < 0.05). The activity of hepatic ACO of the HO group was sixfold that of the HF group (P < 0.05). Plasma total lipids, liver triglycerides, cholesterol and total lipids were reduced in rats fed the LO and HO diets (P < 0.05). Through the ligand binding domain of PPARalpha, the hydrolyzed OFO enhanced the expression of alkaline phosphatase (ALP) reporter gene to a significantly greater extent (P < 0.05) than the hydrolyzed fresh soybean oil in a transactivation assay using a clone of CHO K1 cells stably expressing Gal4-PPARalpha chimeric receptor and UAS4-ALP reporter. The results support our hypothesis that dietary OFO, by activating PPARalpha, up-regulates the expression of PPARalpha downstream genes and alters lipid metabolism in rats.

Water-soluble organosulfur compounds of garlic inhibit fatty acid and triglyceride syntheses in cultured rat hepatocytes

The putative hypolipidemic effect of garlic remains controversial. To gain further insight into the effect of garlic on lipid metabolism, the present study determined the inhibitory effects of water-soluble organosulfur compounds present in garlic on triglyceride (TG) and fatty acid synthesis in cultured rat hepatocytes. When incubated at 0.05 to 4.0 mmol/L with cultured hepatocytes, S-allyl cysteine (SAC) and S-propyl cysteine (SPC) decreased [2-14C]acetate incorporation into triglyceride in a concentration-dependent fashion achieving a maximal inhibition at 4.0 mmol/L of 43 and 51%, respectively. The rate of [2-14C]acetate incorporation into phosphlipids was depressed to a similar extent by SAC and SPC. SPC, SAC, S-ethyl cysteine (SEC), and gamma-glutamyl-S-methyl cysteine decreased [2-14C]acetate incorporation into fatty acid synthesis by 81, 59, 35, and 40%, respectively, at 2.0-4.0 mmol/L concentrations. Alliin, gamma-glutamyl-S-allyl cysteine, gamma-glutamyl-S-propyl cysteine S-allyl-N-acetyl cysteine, S-allylsulfonyl alanine, and S-methyl cysteine had no effect on fatty acid synthesis. The activities of lipogenic enzymes, fatty acid synthase (FAS), and glucose-6-phosphate dehydrogenase (G6PDH) were measured in cultured hepatocytes treated with the inhibitors. The activity of FAS in cells treated with 4.0 mmol/L SAC and SPC, respectively, was 32 and 27% lower than that of nontreated cells. Neither SAC nor SPC affected G6PDH activity. The results indicate that SAC, SEC, and SPC inhibit lipid biosynthesis in cultured rat hepatocytes, and further suggest that these S-alk(en)yl cysteines of garlic impair triglyceride synthesis in part due to decreased de novo fatty acid synthesis resulting from inhibition on FAS. Whether tissue concentrations of active garlic components can achieve levels required to inhibit TG synthesis in vivo warrants further investigation.

Methods to assess free radicals and oxidative stress in biological systems

Oxidative stress results from a disruption of the prooxidant/antioxidant cellular balance and monitoring free radical status becomes an interesting challenge in animal and human nutrition. In the present work, merits and limitations of different analytical techniques (HPLC, GC-MS, fluorometric and colourometric assays, ELISA, gel electrophoresis) for the measurement of radical mediated alterations in the cellular integrity of lipids (malondialdehyde, hydrocarbon gases, F2-isoprostanes) proteins (protein carbonyls, 3-nitrotyrosine) and DNA (8-hydroxy-2'-deoxyguanosine) are discussed. Besides these indirect methods, owing to the fact that free radicals are paramagnetic, electron paramagnetic resonance spectroscopy combined with spin trapping has become a valuable tool to directly assess and to better understand the mechanisms of free radical reactions. With this approach a radical that is too short-lived to be detected, adds to a spin-trapping agent to form a relatively long-lived radical adduct. Information obtained from the hyperfine splitting of the spin-trapped adduct can provide identification and quantification of the originally generated free radicals.

The effects of a dietary oxidized oil on lipid metabolism in rats

This study was carried out to investigate the effects of a dietary oxidized oil on lipid metabolism in rats, particularly the desaturation of fatty acids. Two groups of rats were fed initially for a period of 35 d diets containing 10% of either fresh oil or thermally treated oil (150 degrees C, 6 d). The dietary fats used were markedly different for lipid peroxidation products (peroxide value: 94.5 vs. 3.1 meq O2/kg; thiobarbituric acid-reactive substances: 230 vs. 7 micromol/kg) but were equalized for their fatty acid composition by using different mixtures of lard and safflower oil and for tocopherol concentrations by individual supplementation with DL-alpha-tocopherol acetate. In the second period which lasted 16 d, the same diets were supplemented with 10% linseed oil to study the effect of the oxidized oil on the desaturation of alpha-linolenic acid. During the whole period, all the rats were fed identical quantities of diet by a restrictive feeding system in order to avoid a reduced food intake in the rats fed the oxidized oil. Body weight gains and food conversion rates were only slightly lower in the rats fed the oxidized oil compared to the rats fed the fresh oil. Hence, the effects of lipid peroxidation products could be studied without a distortion by a marked reduced food intake and growth. To assess the rate of fatty acid desaturation, the fatty acid composition of liver and heart total lipids and phospholipids was determined and ratios between product and precursor of individual desaturation reactions were calculated. Rats fed the oxidized oil had reduced ratios of 20:4n-6/18:2n-6, 20:5n-3/18:3n-3, 20:4n-6/20:3n-6, and 22:6n-3/22:5n-3 in liver phospholipids and reduced ratios of 20:4n-6/18:2n-6, 22:5n-3/18:3n-3, and 22:6n-3/18:3n-3 in heart phospholipids. Those results suggest a reduced rate of desaturation of linoleic acid and alpha-linolenic acid by microsomal delta4-, delta5-, and delta6-desaturases. Furthermore, liver total lipids of rats fed the oxidized oil exhibited a reduced ratio between total monounsaturated fatty acids and total saturated fatty acids, suggesting a reduced delta9-desaturation. Besides those effects, the study observed a slightly increased liver weight, markedly reduced tocopherol concentrations in liver and plasma, reduced lipid concentrations in plasma, and an increased ratio between phospholipids and cholesterol in the liver. Thus, the study demonstrates that feeding an oxidized oil causes several alterations of lipid and fatty acid metabolism which might be of great physiologic relevance.