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

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.

Limitation and Potential Effects of Different Levels of Aging Corn on Performance, Antioxidative Capacity, Intestinal Health, and Microbiota in Broiler Chickens

Simple Summary

Corn is an important ingredient and staple food in China; thus, corn storage has a certain importance to ensure domestic food resources. Normally, corn has been stored for 3 or more years under the proper storage conditions in national barns before it is used as a feed ingredient. This study aimed to investigate the effect of different levels of aging corn (AC) on performance, antioxidative capacity, intestinal health, and microbiota in broilers. In the present study, AC grains were stored for 4 years under the proper storage conditions at the national storage facility. The results indicated that a lower level of AC diet showed improved performance and overall bird health than a higher level of AC, and comparable with a normal corn diet. However, antioxidative capacity is reduced by AC diets.

Abstract

Three-hundred and sixty-day-old male broilers underwent three treatments with six replicates of 20 birds per treatment. The experimental diets included NC: normal corn diet; ACL: lower level (39.6–41.24%) of AC; and ACH: a higher level (56.99–59.12%) of AC. During phase 1 (0–21 d), broilers fed on AC showed lower (p < 0.05) body weight (BW), body weight gain (BWG), and feed conversion ratio (FCR) as compared with the NC group. During phase 2 (22–42 d), the NC group and ACL group showed better (p < 0.05) BW, BWG, and FCR than the ACH group. The footpad lesion score (p = 0.05) and litter moisture percentage (p < 0.05) were found to be higher in the ACH group. During phase 1, the ACL group showed a lower level of malondialdehyde (MDA) contents (p < 0.05) in serum; moreover, catalase (CAT) (p < 0.05) and glutathione peroxidase (GSH-Px) activities (p < 0.05) were found lower in both AC-containing groups. During phase 2, CAT activity in serum was found higher (p < 0.05) in the ACH group. During phase 1, the NC group showed higher CAT (p = 0.05), GSH-Px (p < 0.05), and superoxide dismutase (SOD) activity (p = 0.03); however, it showed lower MDA (p < 0.05) and total-antioxidative capability (T-AOC) (p < 0.05) in the liver. During phase 1, in breast muscle, CAT, SOD, and T-AOC were higher (p < 0.05) in the NC group. During phase 1, total cholesterol and high-density lipoprotein were found to be lower (p < 0.05) in the ACL group. Similarly, triglyceride and low-density lipoprotein were found to be lower (p < 0.05) in the ACL group than the ACH group. During phase 1, villus height was found to be higher (p < 0.05) in the ACH group. Moreover, the goblet cell (GC) was found to be higher (p < 0.05) in the NC group than the ACL group. During phase 2, GC was found to be higher (p < 0.05) in the ACL group. In ileal digesta, during phase 1, acetic acid, propionic acid, and butyric acid (BA) levels were found to be higher (p < 0.05) in the ACL group. In cecal digesta, BA was significantly lower (p < 0.05) in the NC group.

Consuming oxidative frying oil impairs cardiac energy production and calcium recycling, causing cardiac hypertrophy, fibrosis and diastolic dysfunction in male Sprague Dawley rats

With regards to cardiovascular health, frequent consumption of fried foods is discouraged, despite a lack of clear evidence of a direct link between eating oxidative frying oil (OFO) and cardiovascular diseases. In this study, male Sprague Dawley rats were exposed to diets containing fresh or fried soybean oil (groups C and O, respectively) from in utero to 28 weeks of age. A subset of rats in group O was supplemented with vitamin E (500 mg/kg of DL-α-tocopherol acetate; group OE) from 8 week of age onward to mitigate oxidative stress associated with OFO ingestion. Echocardiography, cardiac histology and indices associated with ATP production and calcium cycling in cardiac tissues were measured. Compared to group C, there was cardiac hypertrophy, fibrosis and diastolic dysfunction, in groups O and OE, with no differences between the latter two groups. Although cardiac mRNA levels of genes associated with mitochondrial biogenesis and function were increased, there were lower ATP concentrations and higher transcripts of uncoupling proteins in groups O and OE than in group C. In addition, decreases in phosphorylation of phospholamban and Ca²⁺/calmodulin-dependent protein kinase II activity, plus increased protein phosphatase 2A activity in groups O and OE, implied calcium cycling required for cardiac function was disrupted by OFO consumption. We concluded that long-term OFO exposure resulted in cardiac hypertrophy, fibrosis and diastolic dysfunction that was not mitigated by vitamin E supplementation. Underlying mechanisms were partly attributed to inefficient energy production via uncoupled phosphorylation and disrupted calcium cycling.

The formation, determination and health implications of polar compounds in edible oils: Current status, challenges and perspectives

To effectively control the quality of edible oil, polar compounds in edible oils have been studied extensively in the past few decades, particularly in the field of frying. This article critically reviews the formation, determination, and health implications of the polar compounds in edible oils via comprehensive literature research. The challenges and perspectives of polar compounds in edible oils are also discussed. Three chemical reactions, including oxidation, hydrolysis, and polymerization, elaborate polar compound formation. Many techniques are used to determine the total polar compound content of edible oils, with comparative analysis; Fourier transform infrared technique is a relatively ideal method. A major obstacle for nutritional studies focused on polar compounds formed during frying is that few pure compounds have been quantified. To inhibit the formation of the polar compounds effectively, investigations into the applications of enzymatic method in developing new lipophilized antioxidants may be a new direction in research.

Exposure to oxidized soybean oil induces mammary mitochondrial injury in lactating rats and alters the intestinal barrier function of progeny

Similar to other food contaminants, dietary oxidized soybean oil (OSO) is also a toxic xenobiotic for animal and human nutrition. This research evaluated the effects of maternal OSO exposure during lactation on mammary mitochondrial injury and intestinal barrier of sucking progeny. Twenty-four female adult SD rats were fed a fresh soybean oil (FSO) homozygous diet (7%) or an OSO homozygous diet (7%) during lactation. On day 21 of lactation, upregulated mRNA expression of Sirt3 and PRDX3 and downregulated mRNA expression of Mfn2 were observed in mammary tissues in the OSO group compared to the control group (P < 0.05). Maternal OSO consumption increased the FasL transcriptional level in the mammary glands of rat dams (P < 0.05), while the mRNA expression of Bax, Bcl-2, Caspase3, and Fas was not different from that in the control group (P > 0.05). OSO enhanced the Nrf2 transcriptional level and decreased the expression of Keap1 and PPARα in mammary tissues (P < 0.05). In addition, the contents of CAT, MDA, SOD were not affected by dietary OSO (P > 0.05), while the concentration of H2O2 was significantly decreased in the OSO-treated mammary glands of rat dams (P < 0.05). Maternal OSO exposure during lactation did not affect the organ coefficients of pups (P > 0.05). However, maternal OSO consumption influenced the intestinal tight junction protein expression of progeny (P < 0.05). In summary, the present study demonstrated that dietary OSO may aggravate mammary injury and mitochondria dysfunction, but the OSO-induced damage was self-alleviating via the promotion of Sirt3 and PRDX3 expression and further scavenging of oxidative products.

Methanolic Extract of Lysimachia Candida Lindl. Prevents High-Fat High-Fructose-Induced Fatty Liver in Rats: Understanding the Molecular Mechanism Through Untargeted Metabolomics Study

Fatty liver is one of the most common metabolic syndrome affecting the global population. Presently, limited treatment modalities with symptomatic approach are available for alleviating fatty liver. Traditional and herbal treatment modalities have shown evidence to improve the disease pathology. In the present research work, evaluation of a selected medicinal plant Lysimachia candida Lindl. was carried out to investigate its beneficial effects on fatty liver disease in rats. Male Sprague Dawley (SD) rats were fed with high-fat high-fructose diet to induce fatty liver phenotypes. After induction for 15 weeks, methanolic extract of Lysimachia candida Lindl. (250 mg/kg b. w. p. o.) was administrated to the rats daily for the next 17 weeks. Blood samples were collected at different time points to analyze fasting blood glucose levels and relevant biochemical parameters important for the assessment of metabolic disease phenotypes. Liquid chromatography-mass spectrometry (LC-MS) based metabolomics was done to study the dynamics of metabolic changes in the serum during disease progression and how the medicinally important plant extract treatment reversed the metabolic diseases. Multivariate data analysis approaches have been employed to understand the metabolome changes and disease pathology. This study has identified the interplay of some metabolic pathways that alter the disease progression and their reversal after administration of the plant extract. Different group of metabolites mainly bile acids, fatty acids, carnitines, and their derivatives were found to be altered in the diseased rats. However, all the metabolites identified between control and disease groups are mainly related to lipid metabolism. The results depict that the treatment with the above-mentioned plant extract improves the regulation of aberrant lipid metabolism, and reverses the metabolic syndrome phenotype. Therefore, the present study reveals the potential mechanism of the herbal extract to prevent metabolic syndrome in rats.

Vitamin E improves antioxidant status but not lipid metabolism in laying hens fed a aged corn-containing diet

OBJECTIVE

The objective of this study was to determine whether a dietary vitamin E (VE) supplement could alleviate any detrimental effects of aged corn on lipid metabolism and antioxidant status in laying hens.

METHODS

The experiment consisted of a 2×3 factorial design with two corn types (normal corn and aged corn (stored for 4 yr) and three concentrations of VE (0, 20, and 100 IU/kg). A total of 216 Lohmann laying hens (50 wk of age) were randomly allocated into six treatment diets for 12 wk. Each treatment had 6 replicates of 6 hens per replicate.

RESULTS

The results show that aged corn significantly decreased the content of low-density lipoprotein cholesterol (p<0.05), and reduced chemokine-like receptor 1 (CMKLR1) mRNA expression (p<0.05) in the liver compared to controls. Diet with VE did not alter the content of crude fat and cholesterol (p>0.05), or acetyl-CoA carboxylase, lipoprotein lipase, fatty acid synthase or CMKLR1 mRNA expression (p>0.05) in the liver among treatment groups. Aged corn significantly increased the content of malondialdehyde (MDA) (p<0.05) and decreased superoxide dismutase (SOD) activity (p<0.05) in the liver. The VE increased the content of MDA (p<0.05) but decreased glutathione peroxidase (GSH-Px) activity in serum (p<0.01) and in the ovaries (p<0.05). Adding VE at 20 and 100 IU/kg significantly increased GSH-Px activity (p<0.05) in liver and in serum (p<0.01), 100 IU/kg VE significantly increased SOD activity (p<0.05) in serum. Aged corn had no significant effects on GSH-Px mRNA or SOD mRNA expression (p<0.01) in the liver and ovaries. Addition of 100 IU/kg VE could significantly increase SOD mRNA expression (p<0.01) in the liver and ovary.

CONCLUSION

Aged corn affected lipid metabolism and decreased the antioxidant function of laying hens. Dietary VE supplementation was unable to counteract the negative effects of aged corn on lipid metabolism. However, addition of 100 IU/kg VE prevented aged corninduced lipid peroxidation in the organs of laying hens.

Oxidized Oils and Oxidized Proteins Induce Apoptosis in Granulosa Cells by Increasing Oxidative Stress in Ovaries of Laying Hens

The storage and preparation of corn for animal feed inevitably lead to lipid and protein peroxidation. Granulosa cells play an important role in follicular development in the ovaries, and hen laying productivity is likely to be dependent on follicle health and number. We hypothesized that oxidized oil and protein induce apoptosis via oxidative stress in laying hen granulosa cells. A sample of 360 38-week-old Lohmann commercial laying hens was used in a 2 × 2 factorial design for 8 weeks. Dietary treatments included dietary oil (fresh corn oil (FO) or oxidized corn oil (OO)) and corn gluten meal (fresh corn gluten meal (FP) or oxidized corn gluten meal (OP)). Productivity, ovarian histology, granulosa cell apoptosis, and indicators of oxidative stress were evaluated in all groups. Both dietary OO and OP decreased egg production and the average daily feed intake (ADFI) of laying hens. Flow cytometry, TUNEL, and real-time PCR revealed that both dietary OO and OP induced granulosa cell apoptosis in prehierarchical and hierarchical follicles. Furthermore, dietary OO and OP caused oxidative stress in prehierarchical and hierarchical follicles, as indicated by the downregulation of antioxidant-related-gene expression. Moreover, forkhead box O1 (FoxO1), extracellular regulated protein kinase (ERK), and c-Jun NH₂ kinase (JNK) are involved in potential apoptosis regulation pathways in the granulosa cells of laying hens fed OO and OP, as indicated by the upregulation of FoxO1 expression and downregulation of ERK/JNK expression. These results indicate that OO and OP induce granulosa cell apoptosis via oxidative stress, and the combined use of OO and OP aggravates the adverse effects of oxidative stress in laying hens.

Dietary Exposure to Oxidized Frying Oil from Fetus to Adulthood Suppresses Male Reproductive Development by Altering Testicular Cholesterol and Testosterone Homeostasis in Sprague Dawley Rats

BACKGROUND

Dietary frying oil may have endocrine-disrupting effects, as a feminization effect was observed in cohorts of C57BL/6J male mice fetuses from dams consuming oxidized frying oil (OFO) during pregnancy.

OBJECTIVE

The aim of present study was to test the hypothesis that OFO is an anti-androgen.

METHODS

In experiment 1, male progeny of Sprague Dawley female rats fed fresh oil or an OFO diet (10 g fat/100 g, from fresh or 24-h-fried soybean oil; [control diet (C) and OFO groups, respectively] from midgestation through lactation were studied. Pups were weaned at 3 wk of age and then consumed their mothers' diet until 9 wk of age. In addition, a group of dams and pups that consumed a high-fat diet (HF; 10 g fried and 20 g fresh soybean oil/100 g) was included to counteract body-weight loss associated with OFO ingestion. Indices of male reproductive development and testosterone homeostasis were measured. In experiment 2, male rats were allocated to C and OFO groups (treated as above) and indices of male fertility compared at 9-10 wk of age.

RESULTS

In experiment 1, final body weights of the HF group were lower (17%) than the C group but higher (14%) than the OFO group (P < 0.0001 for each). In addition to abnormalities in seminiferous tubules, HF and OFO groups did not differ from one another, but, compared with the C group, had delayed preputial separation (4.9 d) and reductions in serum testosterone concentrations (17-74%), anogenital distance (8-20%), weights of androgen-dependent tissues (8-30%), testicular testosterone and cholesterol concentrations (30-40%), and mRNA levels of genes involved in steroidogenesis and cholesterol homeostasis (30-70%). In experiment 2, OFO-exposed males had 20% lower sperm motility (P < 0.05); however, when mated to normal females, pregnancy rates and litter sizes did not differ between OFO and C groups.

CONCLUSIONS

The anti-androgenic effect of OFO in Sprague Dawley rats was attributed to decreased testicular concentrations of cholesterol (testosterone precursor) and not body-weight loss.

Is frying oil a dietary source of an endocrine disruptor? Anti-estrogenic effects of polar compounds from frying oil in rats

The objective was to investigate endocrine-disrupting effects of polar compounds from oxidized frying oil. Estrogenicity of polar compounds was tested with a rat uterotrophic bioassay. Dietary oxidized frying oil (containing 51% polar compounds) or polar compounds isolated from it were incorporated into feed (in lieu of fresh soybean oil) and fed to ovariectomized rats, with or without treatment with exogenous ethynyl estradiol. Exogenous estrogen restored uterine weight, and caused histological abnormalities (stratified epithelia and conglomerate glands) as well as proliferation of uterine epithelial cells. However, tamoxifen or polar compounds reduced these effects. Furthermore, tamoxifen or polar compounds down-regulated uterine mRNA expression of estrogen receptor (ER)-target genes, implicating reduced ER activity in this hypo-uterotrophic effect. Inhibition of ER signaling and mitosis by polar compounds were attributed to reduced MAPK and AKT activation, as well as a reduced ligand binding domain-transactivity of ERα/β. We concluded polar compounds from frying oil are potential endocrine-disrupting chemicals, with implications for food and environmental safety.

Ellagic Acid Suppresses the Oxidative Stress Induced by Dietary-Oxidized Tallow

Dietary tallow was thermally oxidized at 180°C in an open fryer. The oxidized tallow (OT) and unoxidized tallow were characterized for oxidation parameters and fatty acid composition using GC-MS. Tallow samples were fed to rabbits along with 50, 100, and 150 mg/kg/day of ellagic acid (EA) for three weeks. Results revealed that the peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) significantly increased, while radical scavenging activity (RSA) of the tallow decreased significantly with oxidation. GC-MS analysis showed eight fatty acids in the tallow samples, where palmitic acid (48.5-49.7 g/100 g), linoleic acid (18.7-23.7 g/100 g), stearic acid (13.5-15.6 g/100 g), and margaric acid (6.32-6.42 g/100 g) were the major fatty acids. Animal studies showed that oxidized tallow (OT) alone or in combination with EA significantly altered the body weight of the rabbits. Serum biochemical parameters and renal function tests were affected by OT and ameliorated by EA. The toxic effects of OT on haematological indices were minimized by EA. The supplementation of OT alone had significant effects on the liver structure and functions. The coadministration of EA reduced the toxic properties of OT on the liver, by increasing the antioxidant (GSH) system. The rabbit heart was also affected by the OT, which was ameliorated by EA supplementation. These results suggested that the supplementation of EA was beneficial against the OT-induced oxidative stress and may be considered for foods containing oxidized lipids.

Lactic Acid Bacteria With Antioxidant Activities Alleviating Oxidized Oil Induced Hepatic Injury in Mice

In order to screening new Lactic acid bacteria (LAB) strains to alleviating liver injury induced by oxidized oil, we isolated and screened LAB from Chinese fermented foods. Lactobacillus plantarum AR113, Pediococcus pentosaceus AR243, and Lactobacillus plantarum AR501 showed higher scavenging activity of α, α-Diphenyl-β-Picrylhydrazyl (DPPH) free radical and hydrogen radical, stronger inhibition of lipid peroxidation, and better protective effect on yeast cells in vitro. In vivo, oral administration of L. plantarum AR501 improved the antioxidant status of injury mice induced by oxidized oil including decreasing lipid peroxidation, recovering activities of antioxidant enzymes. Meanwhile, the gene expression of Nuclear factor erythroid 2-related factor 2 (Nrf2) of L. plantarum AR501 group was markedly elevated, and several antioxidant genes such as glutathione S-transferase (GSTO1), heme oxygenase-1 (HO-1), Glutamate cysteine ligase (GCL), and NAD(P)H:quinone oxidoreductase-l (NQO1) were subsequently up regulated in mice liver. Therefore, L. plantarum AR501 could be considered as potential candidates for production of functional foods that can alleviate the oxidative damage induced by oxidized oil.

Proteomic analysis of hypothalamus and liver proteins affected by dietary l-arginine supplementation in laying hens

The goal of this study was to investigate the influence of l-arginine (l-Arg) supplementation on diet-induced changes in hypothalamus and liver proteome of laying hens. Layers were fed either an isonitrogenous control diet or a l-Arg diet. The test included a 2-week acclimation period and a 12-week experimental period. Eight layers per group were sacrificed at terminal of the experiment underwent 12 fasting. Blood and tissue samples of hypothalamus and liver were collected for further analysis. The levels of serum nitric oxide and hypothalamus neuropeptide Y of layers in l-Arg group were increased in comparison with those in control group. Quantitative proteomic analyses showed that a total of 3,715 hypothalamus proteins (235 differentially expressed) and 3797 liver proteins (373 differentially expressed) were detected between control and l-Arg-fed groups. A further enriched Gene Ontology term analysis of proteins found that 17 hypothalamus proteins (11 upregulated and six downregulated) and 29 liver proteins (14 upregulated and 15 downregulated) were altered differentially between the two groups. Our findings revealed the changes in metabolic and hormonal signals in central nervous system and peripheral tissues by responding to l-Arg feeding, which provides a possible way to gain a better understanding of l-Arg function in laying hens.

Identification of activation of tryptophan-NAD+ pathway as a prominent metabolic response to thermally oxidized oil through metabolomics-guided biochemical analysis

Consumption of thermally oxidized oil is associated with metabolic disorders, but oxidized oil-elicited changes in the metabolome are not well defined. In this study, C57BL/6 mice were fed the diets containing either control soybean oil or heated soybean oil (HSO) for 4 weeks. HSO-responsive metabolic events were examined through untargeted metabolomics-guided biochemical analysis. HSO directly contributed to the presence of new HSO-derived metabolites in urine and the decrease of polyunsaturated fatty acid-containing phospholipids in serum and the liver. HSO disrupted redox balance by decreasing hepatic glutathione and ascorbic acid. HSO also activated peroxisome proliferator-activated receptors, leading to the decrease of serum triacylglycerols and the changes of cofactors and products in fatty acid oxidation pathways. Most importantly, multiple metabolic changes, including the decrease of tryptophan in serum; the increase of NAD⁺ in the liver; the increases of kynurenic acid, nicotinamide and nicotinamide N-oxide in urine; and the decreases of the metabolites from pyridine nucleotide degradation in the liver indicated that HSO activated tryptophan-NAD⁺ metabolic pathway, which was further confirmed by the upregulation of gene expression in this pathway. Because NAD⁺ and its metabolites are essential cofactors in many HSO-induced metabolic events, the activation of tryptophan-NAD⁺ pathway should be considered as a central metabolic response to the exposure of HSO.

Prenatal PPARα activation by clofibrate increases subcutaneous fat browning in male C57BL/6J mice fed a high-fat diet during adulthood

We tested the hypothesis that prenatal administration of PPARα agonist clofibrate may permanently increase browning capacity of developing white adipose tissue (WAT). Pregnant C57BL/6J mice were fed a basal diet, without (C) or with 0.5% clofibrate (CF, a PPARα agonist) throughout pregnancy. After parturition, only male offspring were used; all suckled their mothers (who were eating the C diet) and after weaning, they ate a standard chow diet for 4 wk, followed by a high-fat diet (HFD) for 5 wk. Administration of CF up-regulated serum concentrations and hepatic expression of FGF21 in fetuses, with a return to basal levels after CF withdrawal. At postnatal day 84 (P84), CF-offspring had significantly higher expression of thermogenic genes (Ucp1, Cidea, Ppara Ppargc1a, Cpt1b) and UCP1 protein levels in response to HFD in inguinal fat, but not in retroperitoneal (combined with perirenal) or epididymal fat. Based on UCP1 levels in inguinal fat on P7, P14, and P21, appearance of the transient brown-adipocyte phenotype seemed to be hastened by CF exposure. We concluded that giving CF to pregnant mice programmed greater HFD-induced WAT browning in subcutaneous, but not in visceral fat, in their male offspring at adulthood.

Effects of dietary green tea (Camellia sinensis L.) supplementation on growth performance, lipid metabolism, and antioxidant status in a sturgeon hybrid of Sterlet (Huso huso ♂ × Acipenser ruthenus ♀) fed oxidized fish oil

Lipid content of diet is very susceptible to oxidation, especially when stored for a long time, so for evaluating protective effects of green tea in fish received oxidized oil, this study was done. Lipid content of diet was replaced by oxidized fish oil (OFO) in 0, 50, and 100%. Green tea extract (GTE) was added to diet in three levels, 0, 5, and 100 mg/kg giving a total of nine experimental diets. Two hundred and seventy sturgeon hybrid of Sterlet (Huso huso ♀ × Acipenser ruthenus ♂) with initial weight of 212.6 ± 0.7 g after 2 weeks adaptation randomly divided in 27 fiberglass tanks with 700 L volume. Fish were fed satiated three times daily. After 6 weeks, biometry was done to evaluate growth performance and blood samples were taken for biochemical analysis. The result showed that feeding with oxidized oil had no effects on growth. However, in fish fed GTE, growth indices improved slightly. Feeding with OFO reduced serum total cholesterol, triacylglycerol, and low-density lipoprotein, while increased high density lipoprotein. Dietary GTE moderated the effects of OFO on lipid metabolism. Feeding with the OFO increased activity of serum superoxide dismutase, catalase, glutathione peroxidase, and malondialdehyde contents. In fish received both OFO and GTE, reduced activity of serum antioxidant enzymes and malondialdehyde content was recorded in compare to fish fed only OFO. According to the result of the present study, it can be argued that feeding of sturgeon hybrid of Sterlet with OFO has negative effects on lipid metabolism and antioxidant status, whereas GTE dosages used in this study have protective effects on fish from the adverse effects of oxidized oil.

Resistant starch attenuates impaired lipid biosynthesis induced by dietary oxidized oil via activation of insulin signaling pathways

The current study found that deep-frying process led to an increased content of oxidized triacylglycerols in canola oil, 3.5 times higher than that of fresh canola oil (not used for frying).

Roles of Peroxisome Proliferator-Activated Receptor α in Bitter Melon Seed Oil-Corrected Lipid Disorders and Conversion of α-Eleostearic Acid into Rumenic Acid in C57BL/6J Mice

We previously reported that bitter melon seed oil (BMSO) was an effective anti-steatosis and antiobesity agent. Since the major fatty acid α-eleostearic acid (α-ESA) in BMSO is a peroxisome proliferator-activated receptor α (PPARα) activator, the objective was to investigate the role of PPARα in BMSO-modulated lipid disorders and α-ESA metabolism. C57BL/6J wild (WD) and PPARα knockout (KO) mice were fed a high-fat diet containing BMSO (15% soybean oil + 15% BMSO, HB) or not (30% soybean oil, HS) for 5 weeks. The HB diet significantly reduced hepatic triglyceride concentrations and increased acyl-CoA oxidase activity in WD, but not in KO mice. However, regardless of genotype, body fat percentage was lowered along with upregulated protein levels of uncoupling protein 1 (UCP1) and tyrosine hydroxylase, as well as signaling pathway of cAMP-dependent protein kinase and AMP-activated protein kinase in the white adipose tissue of HB-treated groups compared to HS cohorts. In WD-HB and KO-HB groups, white adipose tissue had autophagy, apoptosis, inflammation, and browning characteristics. Without PPARα, in vivo reduction of α-ESA into rumenic acid was slightly but significantly lowered, along with remarkable reduction of hepatic retinol saturase (RetSat) expression. We concluded that BMSO-mediated anti-steatosis depended on PPARα, whereas the anti-adiposity effect was PPARα-independent. In addition, PPARα-dependent enzymes may participate in α-ESA conversion, but only have a minor role.

Dietary supplementation of pyrroloquinoline quinone disodium protects against oxidative stress and liver damage in laying hens fed an oxidized sunflower oil-added diet

The protective effects of dietary pyrroloquinoline quinone disodium (PQQ.Na2) supplementation against oxidized sunflower oil-induced oxidative stress and liver injury in laying hens were examined. Three hundred and sixty 53-week-old Hy-Line Gray laying hens were randomly allocated into one of the five dietary treatments. The treatments included: (1) a diet containing 2% fresh sunflower oil; (2) a diet containing 2% thermally oxidized sunflower oil; (3) an oxidized sunflower oil diet with 100 mg/kg of added vitamin E; (4) an oxidized sunflower oil diet with 0.08 mg/kg of PQQ.Na2; and (5) an oxidized sunflower oil diet with 0.12 mg/kg of PQQ.Na2. Birds fed the oxidized sunflower oil diet showed a lower feed intake compared to birds fed the fresh oil diet or oxidized oil diet supplemented with vitamin E (P=0.009). Exposure to oxidized sunflower oil increased plasma malondialdehyde (P<0.001), hepatic reactive oxygen species (P<0.05) and carbonyl group levels (P<0.001), but decreased plasma glutathione levels (P=0.006) in laying hens. These unfavorable changes induced by the oxidized sunflower oil diet were modulated by dietary vitamin E or PQQ.Na2 supplementation to levels comparable to the fresh oil group. Dietary supplementation with PQQ.Na2 or vitamin E increased the activities of total superoxide dismutase and glutathione peroxidase in plasma and the liver, when compared with the oxidized sunflower oil group (P<0.05). PQQ.Na2 or vitamin E diminished the oxidized sunflower oil diet induced elevation of liver weight (P=0.026), liver to BW ratio (P=0.001) and plasma activities of alanine aminotransferase (P=0.001) and aspartate aminotransferase (P<0.001) and maintained these indices at the similar levels to the fresh oil diet. Furthermore, oxidized sunflower oil increased hepatic DNA tail length (P<0.05) and tail moment (P<0.05) compared with the fresh oil group. Dietary supplementation of PQQ.Na2 or vitamin E decreased the oxidized oil diet induced DNA tail length and tail moment to the basal levels in fresh oil diet. These results indicate that PQQ.Na2 is a potential antioxidant and is as effective against oxidized oil-related liver injury in laying hens as vitamin E. The protective effects of PQQ.Na2 against liver damage induced by oxidized oil may be partially due to its role in the scavenging of free radicals, inhibiting of lipid peroxidation and enhancing of antioxidant defense systems.

Possible adverse effects of frying with vegetable oils

The question of whether heated fats in the diet may be detrimental to health is nowadays of the upmost concern, but finding an answer is not easy and requires careful consideration of different aspects of lipid oxidation. This review is divided into two sections. The first part deals with the nature of the new compounds formed at high temperature in the frying process as well as their occurrence in the diet while the second part focuses on their possible nutritional and physiological effects. Oxidation products present in abused frying fats and oils are the compounds most suspected of impairing the nutritional properties of the oils or involving adverse physiological effects. The recent studies on their health implications include those related to their fate and those focused on their effects in metabolic pathways and the most prevalent diseases.

Chemistry and liquid chromatography methods for the analyses of primary oxidation products of triacylglycerols

Triacylglycerols (TAGs) are one of the major components of the cells in higher biological systems, which can act as an energy reservoir in the living cells. The unsaturated fatty acid moiety is the key site of oxidation and formation of oxidation compounds. The TAG free radical generates several primary oxidation compounds. These include hydroperoxides, hydroxides, epidioxides, hydroperoxy epidioxides, hydroxyl epidioxides, and epoxides. The presence of these oxidized TAGs in the cell increases the chances of several detrimental processes. For this purpose, several liquid chromatography (LC) methods were reported in their analyses. This review is therefore focused on the chemistry, oxidation, extraction, and the LC methods reported in the analyses of oxidized TAGs. The studies on thin-layer chromatography were mostly focused on the total oxidized TAGs separation and employ hexane as major solvent. High-performance LC (HPLC) methods were discussed in details along with their merits and demerits. It was found that most of the HPLC methods employed isocratic elution with methanol and acetonitrile as major solvents with an ultraviolet detector. The coupling of HPLC with mass spectrometry (MS) highly increases the efficiency of analysis as well as enables reliable structural elucidation. The use of MS was found to be helpful in studying the oxidation chemistry of TAGs and needs to be extended to the complex biological systems.

Ingestion of thermally oxidized sunflower oil decreases postprandial lipemia mainly in younger individuals

Animal studies have shown that diets rich in thermally oxidized fat increase glucose and decrease insulin and triglyceride (TG) concentrations in the blood. We hypothesized that ingestion of a potato meal rich in thermally oxidized sunflower oil (TOSO) would decrease postprandial concentrations of insulin, incretins, and TG and increase plasma glucose concentrations. Twenty healthy subjects aged 22 to 70 years consumed meals rich in TOSO or unheated sunflower oil and containing paracetamol (1.5 g) in a randomized, crossover trial. Blood samples were taken at baseline and 10, 20, 30, 60, 90, and 120 minutes after the meals and glucose, insulin, TG, nonesterified fatty acids, glucagon-like polypeptide-1, glucose-independent polypeptide, and paracetamol (as a marker of gastric emptying) were measured in plasma or serum. The incremental areas under the curve of glucose, insulin, nonesterified fatty acid, incretins, and paracetamol levels were not significantly different between the meals. Plasma TG incremental area under the curve was 44% lower after the TOSO meal at a marginal level of significance (P = .06) in the total study population and was significantly (P = .04) and 61% lower in those of median age and younger (n = 11). These data suggest that ingestion of TOSO may acutely decrease plasma TG mainly in younger individuals and does not acutely affect glucose and insulin metabolism or gastric emptying in healthy subjects.

A diet containing soybean oil heated for three hours increases adipose tissue weight but decreases body weight in C57BL/6 J mice

Background

Our previous work showed that dietary oxidized linoleic acid given, as a single fatty acid, to LDL receptor knockout mice decreased weight gain as compared to control mice. Other studies have also reported that animals fed oils heated for 24 h or greater showed reduced weight gain. These observations, while important, have limited significance since fried foods in the typical human diet do not contain the extreme levels of oxidized lipids used in these studies. The main goal of this study was to investigate the effects of a diet containing soybean oil heated for 3 h on weight gain and fat pad mass in mice. Additionally, because PPARγ and UCP-1 mediate adipocyte differentiation and thermogenesis, respectively, the effect of this diet on these proteins was also examined.

Findings

Four to six week old male C57BL/6 J mice were randomly divided into three groups and given either a low fat diet with heated soybean oil (HSO) or unheated soybean oil (USO) or pair fed for 16 weeks. Weight and food intake were monitored and fat pads were harvested upon the study’s termination. Mice consuming the HSO diet had significantly increased fat pad mass but gained less weight as compared to mice in the USO group despite a similar caloric intake and similar levels of PPARγ and UCP1.

Conclusion

This is the first study to show that a diet containing soybean oil heated for a short time increases fat mass despite a decreased weight gain in C57BL/6 J mice. The subsequent metabolic consequences of this increased fat mass merits further investigation.

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.

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.

13-hydroxy linoleic acid increases expression of the cholesterol transporters ABCA1, ABCG1 and SR-BI and stimulates apoA-I-dependent cholesterol efflux in RAW264.7 macrophages

BACKGROUND

Synthetic activators of peroxisome proliferator-activated receptors (PPARs) stimulate cholesterol removal from macrophages through PPAR-dependent up-regulation of liver × receptor α (LXRα) and subsequent induction of cholesterol exporters such as ATP-binding cassette transporter A1 (ABCA1) and scavenger receptor class B type 1 (SR-BI). The present study aimed to test the hypothesis that the hydroxylated derivative of linoleic acid (LA), 13-HODE, which is a natural PPAR agonist, has similar effects in RAW264.7 macrophages.

METHODS

RAW264.7 macrophages were treated without (control) or with LA or 13-HODE in the presence and absence of PPARα or PPARγ antagonists and determined protein levels of LXRα, ABCA1, ABCG1, SR-BI, PPARα and PPARγ and apolipoprotein A-I mediated lipid efflux.

RESULTS

Treatment of RAW264.7 cells with 13-HODE increased PPAR-transactivation activity and protein concentrations of LXRα, ABCA1, ABCG1 and SR-BI when compared to control treatment (P < 0.05). In addition, 13-HODE enhanced cholesterol concentration in the medium but decreased cellular cholesterol concentration during incubation of cells with the extracellular lipid acceptor apolipoprotein A-I (P < 0.05). Pre-treatment of cells with a selective PPARα or PPARγ antagonist completely abolished the effects of 13-HODE on cholesterol efflux and protein levels of genes investigated. In contrast to 13-HODE, LA had no effect on either of these parameters compared to control cells.

CONCLUSION

13-HODE induces cholesterol efflux from macrophages via the PPAR-LXRα-ABCA1/SR-BI-pathway.

Wild bitter gourd extract up-regulates mRNA expression of PPARα, PPARγ and their target genes in C57BL/6J mice

ETHNOPHARMACOLOGICAL RELEVANCE

Wild bitter gourd (Momordica charantia Linn. var. abbreviata ser.) was commonly used as a medicinal herb in Asia, Africa, and South America because of its anti-diabetic, antibacterial, anti-viral, and chemopreventive functions.

MATERIALS AND METHODS

C57BL/6J mice were orally administered with 250, 500 or 1000mg/kg BW of WBGE in 0.2mL/mouse of olive oil daily for 2 weeks.

RESULTS

Compared to control (vehicle treated) mice, mice receiving WBGE showed significantly higher PPARα, ACO (acyl-CoA oxidase) and L-FABP (liver-fatty acid binding protein) mRNA expression, ACO activity and protein in the liver (P<0.05), as clofibrate-treated mice. WBGE treatment also resulted in significantly higher PPARγ and LPL (lipoprotein lipase) mRNA (P<0.05) in the epididymal adipose tissue. Liver triglyceride and non-esterified fatty acid concentration in WBGE treated mice were significantly lower than those of control mice (P<0.05). Plasma adiponectin level was significantly higher in mice receiving WBGE than in control mice (P<0.05), as the rosiglitazone treated mice.

CONCLUSION

Results of this study demonstrated that WBGE also activates PPARα and PPARγ signaling pathway in vivo.

Dietary oxidised frying oil causes oxidative damage of pancreatic islets and impairment of insulin secretion, effects associated with vitamin E deficiency

We previously reported that, in rodents, a diet with a high oxidised frying oil (OFO) content leads to glucose intolerance associated with a reduction in insulin secretion. The present study aimed at investigating the impairment of pancreatic islets caused by dietary OFO. C57BL/6J mice were divided into three groups to receive a low-fat basal diet containing 5 g/100 g of fresh soyabean oil (LF group) or a high-fat diet containing 20 g/100 g of either fresh soyabean oil (HF group) or OFO (HO group). After 8 weeks, mice in the HO group showed glucose intolerance and hypoinsulinaemia, and their islets showed impaired glucose-stimulated insulin secretion (P < 0·05; HO group v. LF and HF groups). Significantly higher oxidative stress and a lower mitochondrial membrane potential were observed in the islets in the HO group compared with the LF and HF groups. Immunoblots showed that the reduction in insulin levels in HO islets was associated with activation of the c-Jun NH2-terminal kinase and a reduction in levels of pancreatic and duodenal homeobox factor-1. In a second study, when dietary OFO-induced tissue vitamin E depletion was prevented by large-dose vitamin E supplementation (500 IU(1·06 mmol all-rac-α-tocopherol acetate)/kg diet; HO+E group), the OFO-mediated reduction in islet size and impairment of glucose tolerance and insulin secretion were significantly attenuated (P < 0·05; HO group v. HO+E group). We conclude that a high level of dietary OFO ingestion impairs glucose metabolism by causing oxidative damage and compromising insulin secretion in pancreatic islets, and that these effects can be prevented by vitamin E supplementation.

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.

A novel body weight-loss promoting oil prepared with vegetable protein

It has been reported that oil thermally processed with wheat gluten (gluten oil) exhibited safe weight-loss promoting effects in animal experiments. However, as the oil has a high color index, and its chemical properties and smell differ from those of fresh oil, it is uncertain if the oil will find market acceptance. In order to resolve the issue, frying oil was heated with soybean protein under reduced pressure (soybean protein oil), resulting in a product with an appearance, chemical properties and smell comparable to those of fresh oil. This improved oil was mixed (7 wt%) with powdered AIN93G no fat, defined standard diet and fed to 10-week-old Wistar rats ad libitum. The experimental rats grew normally, ingesting the same amount as that of the control rats; however, there was a negative correlation between body weight increases and fecal weight increases. After the 12-week feeding period, all the rats were sacrificed to obtain blood and organs. In the experimental group, liver weight, retroperitoneal fat tissue weight and serum triacylglycerol (TG) levels decreased significantly. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), and histological analysis supported the safety of the improved oil. In conclusion, it was found that soybean protein oil inhibited body weight increases without any adverse effects in animal experiments. The oil holds promise as a novel dieting oil that steadily decreases body weight at an appropriate rate.

Administration of tomato and paprika beverages modifies hepatic glucose and lipid metabolism in mice: a DNA microarray analysis

To examine whether the expression of hepatic genes, including biomarkers, is affected by the ingestion of tomato or paprika, mice were given tomato beverage (TB), paprika beverage (PB), or water (control) ad libitum for 6 weeks. The body weights in the TB and PB groups were significantly lower than those in the control group. Administration of PB significantly increased the plasma high-density lipoprotein-cholesterol level. Hepatic gene expression was investigated using DNA microarrays. The ingestion of TB or PB up-regulated the expression of 687 and 1045 genes and down-regulated the expression of 841 and 653 genes, respectively (false discovery rate<0.05). These changes in gene expression suggest that TB ingestion promotes glycogen accumulation and stimulates some specific steps in fatty acid oxidation. PB ingestion promoted the entire glucose and fatty acid metabolic pathways to improve lipid profiles. These results provide useful genetic information about a variety of biochemical processes by which vegetables can contribute to good health.

PPARα Mediates Transcriptional Upregulation of Novel Organic Cation Transporters-2 and -3 and Enzymes Involved in Hepatic Carnitine Synthesis

We tested the hypothesis that transcription of novel organic cation transporters (OCTNs) is directly regulated by peroxisome proliferator–activated receptor (PPAR)-α. Therefore, wild-type mice and mice deficient in PPARα (PPARα−/−) were treated with the PPARα agonist WY 14,643. Wild-type mice treated with WY 14,643 had a greater abundance of OCTN2 mRNA in their liver, muscle, kidney, and small intestine and a greater abundance of OCTN3 mRNA in kidney and small intestine than did untreated wild-type mice ( P < 0.05). Moreover, wild-type mice treated with WY 14,643 had greater mRNA abundances of enzymes involved in hepatic carnitine synthesis (4-N-trimethylaminobutyraldehyde dehydrogenase, γ-butyrobetaine dioxygenase) and increased carnitine concentrations in liver and muscle than did untreated wild-type mice ( P < 0.05). Untreated PPARα−/− mice had a lower abundance of OCTN2 mRNA in liver, kidney, and small intestine and lower carnitine concentrations in plasma, liver, and kidney than did untreated wild-type mice ( P < 0.05). In PPARα−/− mice, treatment with WY 14,643 did not influence mRNA abundance of OCTN2 and OCTN3 and carnitine concentrations in all tissues analyzed. The abundance of OCTN1 mRNA in all the tissues analyzed was not changed by treatment with WY 14,643 in wild-type or PPARα−/− mice. In conclusion, this study shows that transcriptional upregulation of OCTN2 and OCTN3 in tissues and of enzymes involved in hepatic carnitine biosynthesis are mediated by PPARα. It also shows that PPARα mediates changes of whole-body carnitine homeostasis in mice by upregulation of carnitine transporters and enzymes involved in carnitine synthesis.

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.

Oxidized fat reduces milk triacylglycerol concentrations by inhibiting gene expression of lipoprotein lipase and fatty acid transporters in the mammary gland of rats

Feeding oxidized fats to lactating rats causes a strong reduction of triacylglycerol concentration in the milk. The reason for this, however, has not yet been elucidated. Pregnant Sprague-Dawley rats were assigned to 2 groups of 11 rats each and fed diets containing either fresh fat (FF group) or an oxidized fat (OF group) from d 1 to d 20 of lactation. Concentrations of triacylglycerols and long-chain fatty acids in the milk and weight gain of suckling pups were lower in the OF group than in the FF group (P < 0.05). Concentrations of medium-chain fatty acids in the milk and messenger RNA (mRNA) abundance of lipogenic enzymes in the mammary gland did not differ between the 2 groups of rats. However, the OF group had a lower concentration of triacylglycerols and nonesterified fatty acids (NEFA) in plasma and lower mRNA concentrations of lipoprotein lipase and fatty acid transporters in the mammary gland than the FF group (P < 0.05). Moreover, the OF group had higher mRNA concentrations of hepatic lipase, fatty acid transporters, and several genes involved in fatty acid oxidation in the liver than the FF group (P < 0.05). The present findings suggest that a dietary oxidized fat lowers the concentration of triacylglycerols in the milk by a reduced uptake of fatty acids from triacylglycerol rich-lipoproteins and NEFA into the mammary gland. The study, moreover, indicates that an oxidized fat impairs normal metabolic adaptations during lactation, which promote the utilization of metabolic substrates by the mammary gland for the synthesis of milk.

The pesticide adjuvant, Toximul™, alters hepatic metabolism through effects on downstream targets of PPARα

Previous studies demonstrated that chronic dermal exposure to the pesticide adjuvant (surfactant), Toximul (Tox), has significant detrimental effects on hepatic lipid metabolism. This study demonstrated that young mice dermally exposed to Tox for 12 days have significant increases in expression of peroxisomal acyl-CoA oxidase (mRNA and protein), bifunctional enzyme (mRNA) and thiolase (mRNA), as well as the P450 oxidizing enzymes Cyp4A10 and Cyp4A14 (mRNA and protein). Tox produced a similar pattern of increases in wild type adult female mice but did not induce these responses in PPARalpha-null mice. These data support the hypothesis that Tox, a heterogeneous blend of nonionic and anionic surfactants, modulates hepatic metabolism at least in part through activation of PPARalpha. Notably, all three groups of Tox-treated mice had increased relative liver weights due to significant accumulation of lipid. This could be endogenous in nature and/or a component(s) of Tox or a metabolite thereof. The ability of Tox and other hydrocarbon pollutants to induce fatty liver despite being PPARalpha agonists indicates a novel consequence of exposure to this class of chemicals, and may provide a new understanding of fatty liver in populations with industrial exposure.

A high oxidised frying oil content diet is less adipogenic, but induces glucose intolerance in rodents

Oxidised frying oil (OFO) and fish oil have been shown to be peroxisome proliferator-activated receptor (PPAR)α activators and their ingestion results in pleotropic peroxisome proliferator responses in rats. To examine the effect of dietary OFO on adiposity, four groups of weanling Sprague–Dawley rats were fed isoenergetically with, respectively, a low fat basal diet containing 5 g/100 g of fresh soybean oil (LSB) or a high fat diet containing 20 g/100 g of fresh soybean oil (HSB), OFO (HO) or fish oil (HF). The tissue mass, cell size and lipid/DNA ratio in the retroperitoneal fat pad and serum leptin levels were lowest in the HO group (P < 0·05), indicating that dietary OFO has a greater anti-adipogenic action than dietary fish oil. However, a tendency to hyperglycaemia was observed in the HO group (P = 0·0528). To examine the effect of dietary OFO on glucose tolerance, three groups of rats and three groups of mice were fed, respectively, the LSB, HSB or HO diet, and an oral glucose tolerance test was performed. After oral glucose load, the area under the curve for blood glucose (AUCglu) over 2 h was significantly higher, and that for serum insulin (AUCins) over 90 min was significantly lower, in the HO group than in the other two groups (P < 0·05). These results demonstrate that, in rats and mice, a high OFO diet is less adipogenic, but induces glucose intolerance.

Dietary oxidised fat up regulates the expression of organic cation transporters in liver and small intestine and alters carnitine concentrations in liver, muscle and plasma of rats

It has been shown that treatment of rats with clofibrate, a synthetic agonist of PPARalpha, increases mRNA concentration of organic cation transporters (OCTN)-1 and -2 and concentration of carnitine in the liver. Since oxidised fats have been demonstrated in rats to activate hepatic PPARalpha, we tested the hypothesis that they also up regulate OCTN. Eighteen rats were orally administered either sunflower-seed oil (control group) or an oxidised fat prepared by heating sunflower-seed oil, for 6 d. Rats administered the oxidised fat had higher mRNA concentrations of typical PPARalpha target genes such as acyl-CoA oxidase, cytochrome P450 4A1 and carnitine palmitoyltransferases-1A and -2 in liver and small intestine than control rats (P < 0.05). Furthermore, rats treated with oxidised fat had higher hepatic mRNA concentrations of OCTN1 (1.5-fold) and OCTN2 (3.1-fold), a higher carnitine concentration in the liver and lower carnitine concentrations in plasma, gastrocnemius and heart muscle than control rats (P < 0.05). Moreover, rats administered oxidised fat had a higher mRNA concentration of OCTN2 in small intestine (2.4-fold; P < 0.05) than control rats. In conclusion, the present study shows that an oxidised fat causes an up regulation of OCTN in the liver and small intestine. An increased hepatic carnitine concentration in rats treated with the oxidised fat is probably at least in part due to an increased uptake of carnitine into the liver which in turn leads to reduced plasma and muscle carnitine concentrations. The present study supports the hypothesis that nutrients acting as PPARalpha agonists influence whole-body carnitine homeostasis.

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.