Oxidized Frying Oil Research Articles

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

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. The aim of present study was to test the hypothesis that OFO is an anti-androgen. In experiment 1, male progeny of Sprague Dawley female rats fed fresh oil or an OFO diet (10g fat/100g, 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; 10g fried and 20g fresh soybean oil/100g) 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. 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, haddelayed preputial separation (4.9 d)andreductions inserum 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. The anti-androgenic effect of OFO in Sprague Dawley rats was attributed to decreased testicular concentrations of cholesterol (testosterone precursor) and notbody-weight loss.

Teratogenic effects of polar compounds in oxidized frying oil

Although deep-fried foods are very popular, the safety of oxidized frying oil (OFO), which is ingested with fried food, is a concern. Consequently, food safety regulations in many countries set an upper limit of 25% polar compounds (PC). The PC comprises all oxidatively altered components in used oils; they may be regarded as a xenobiotic or endocrine-disrupting chemical, as they activate PPARa and induce expression of detoxifying cytochrome P450 monoxygenase and phase II conjugation enzymes to facilitate their own catabolism. Recently, we reported that pregnant C57BL/6J mice fed PC had a higher incidence of fetuses with congenital malformations. This review summarizes the chemical reactions and PC composition in OFO, effects of PC on modulating transcriptional activity of xenobiotic receptors including aryl hydrocarbon receptor, constitutive androstane receptor, pregnane X receptor and PPARa, the importance of retinoic acid (RA) in organogenesis of developing embryos, as well as teratogenic effects of PC. Plausible underlying mechanisms are also discussed. We speculate that the pathogenesis of congenital malformations is disturbed RA metabolism via crosstalks between xenobiotic receptors.

Oxidized frying oil and its polar fraction fed to pregnant mice are teratogenic and alter mRNA expressions of vitamin A metabolism genes in the liver of dams and their fetuses

We previously observed a higher incidence of congenital malformations in the fetuses of dams fed an oxidized frying oil (OFO)-containing diet during pregnancy. In this study, we hypothesized that, during pregnancy, maternal ingestion of OFO, specifically the oxidized components (i.e. the polar fraction), modulates peroxisome proliferator-activated receptor (PPARα) or aryl hydrocarbon receptor (AhR) transactivity, altering the metabolism of retinoic acid (RA), a well-characterized morphogen, resulting in teratogenesis. Pregnant C57BL/6J mice were divided into four groups which, from d1 (conception) to d18, were fed a diet containing 10 g/100 g of fresh soybean oil (SO), OFO or the non-polar (NP) or polar (PO) fraction of OFO. Reporter assays testing the transactivity of PPARα and AhR showed that free fatty acids from OFO, specifically the PO fraction, up-regulated PPARα transactivity and down-regulated AhR transactivity. In vivo study showed that the PO fraction group had a significantly higher number of dead fetuses and resorptions per litter than the SO and NP fraction groups. The incidence of abnormalities in terms of gross morphology and skeletal ossification of the fetus was greatest in the PO fraction group, followed by the OFO group, both values being significantly higher than in the other two groups. Hepatic expression of genes encoding enzymes associated with RA synthesis and catabolism in dams and fetuses was differentially affected by PO fraction assault. We conclude that OFO-mediated teratogenesis is associated with disturbed RA metabolism in the dams and fetuses caused, at least in part, by modulation of PPARα and AhR transactivity by the oxidized components in OFO.

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.

Effects of Oxidized Frying Oil on Proteins Related to α-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 α-tocopherol acetate and thus contained twice as much vitamin E as that of the OF group. After six weeks on these diets, liver α-tocopherol levels in the OF group were the significantly lowest among the three groups. Excretion of the α-tocopherol metabolite, α-carboxyethyl hydroxychroman (α-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 α-tocopherol transfer protein (α-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.

Effects of Oxidized Frying Oil on Proteins Related to α-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.

Impairment of glucose metabolism in mice induced by dietary oxidized frying oil is different from that induced by conjugated linoleic acid

Objective We previously reported that a diet high in oxidized frying oil (OFO) is less adipogenic but induces glucose intolerance in rodents, a situation somewhat is similar to that in conjugated linoleic acid (CLA)–fed mice. The present study compared the lipid and glucose metabolism effects of dietary OFO and CLA to clarify how the OFO diet compromises glucose tolerance. Methods C57BL/6J mice were divided into four groups in which the CLA and CLA control (CC) groups received a low-fat diet supplemented with or without 1 g/100 g of CLA (1:1 mixture of cis-9, trans-11 and trans-10, cis-12), and the OFO and OFO control (CO) groups received a high-fat diet containing 20 g/100 g of OFO or fresh soybean oil, respectively. Results When compared with their respective controls (CLA versus CC and OFO versus CO), the OFO and CLA diets resulted in deprivation of adipose and downregulation of adipocyte marker genes, but a totally different response of lipid metabolism in the liver was observed, i.e., anabolism was enhanced by the CLA diet but catabolism was enhanced by the OFO diet. In contrast to the insulin resistance that occurred in CLA-fed mice, the glucose intolerance induced by the OFO diet was accompanied by decreases in insulin and C-peptide levels during an oral glucose tolerance test. Analysis of vitamin E and thiobarbituric acid–reactive substances in the liver showed the OFO diet, but not the CLA diet, compromised vitamin E status. Conclusion The impaired glucose metabolism resulting from OFO feeding is not related to CLA. In contrast to the hyperinsulinemia and insulin resistance induced by the CLA diet, the OFO diet-induced glucose intolerance is mediated by impairment of insulin secretion.

Peroxisome Proliferation in Liver of Rats Fed Oxidized Frying Oil

Oxidized frying oil (OFO) activates peroxisome proliferator-activated receptor a (PPAR alpha) in vitro and in vivo. As most PPARalpha activators are also peroxisome proliferators (PP), this study was aimed at exploring whether OFO induces peroxisome proliferation in the liver of rats. Four groups of male weanling Sprague-Dawley rats were fed the following diets for 6 wk: a basal diet containing 5 g/100 g fresh soybean oil (LSB), high-fat diets containing 20 g/100 g of fresh soybean oil (HSB as a control). OFO (HO) or fish oil (HF, as a positive control). Hepatomegaly and peroxisome proliferation in the liver of the HO group of rats were higher than those of the HF group. In addition, the acyl-CoA oxidase (ACO) activity, as well as cytochrome P450 4A (CYP4A) protein content in the livers of the HO group were 6 fold those of the HSB group, but were 2.5 fold in those of the HF group. These results indicated that dietary OFO induced typical responses to PPARalpha signaling. Moreover. as a dietary source, the OFO prepared under our frying conditions appears to be a more potent peroxisome proliferator than fish oil.

Effects of frying oil andHouttuynia cordatathunb on xenobiotic-metabolizing enzyme system of rodents

To evaluate the effects of frying oil and Houttuynia cordata Thunb (H. cordata), a vegetable traditionally consumed in Taiwan, on the xenobiotic-metabolizing enzyme system of rodents. Forty-eight Sprague-Dawley rats were fed with a diet containing 0%, 2% or 5% H. cordata powder and 15% fresh soybean oil or 24-h oxidized frying oil (OFO) for 28 d respectively. The level of microsomal protein, total cytochrome 450 content (CYP450) and enzyme activities including NADPH reductase, ethoxyresorufin O-deethylase (EROD), pentoxyresorufin O-dealkylase (PROD), aniline hydroxylase (ANH), aminopyrine demethylase (AMD), and quinone reductase (QR) were determined. QR represented phase II enzymes, the rest of the enzymes tested represented phase I enzymes. The oxidized frying oil feeding produced a significant increase in phase I and II enzyme systems, including the content of CYP450 and microsomal protein, and the activities of NADPH reductase, EROD, PROD, ANH, AMD and QR in rats (P<0.05). In addition, the activities of EROD, ANH and AMD decreased and QR increased after feeding with H. cordata in OFO-fed group (P<0.05). The feeding with 2% H. cordata diet showed the most significant effect. The OFO diet induces phases I and II enzyme activity, and the 2% H. cordata diet resulted in a better regulation of the xenobiotic-metabolizing enzyme system.

Oxidized Frying Oil Up-Regulates Hepatic Acyl-CoA Oxidase and Cytochrome P450 4 A1 Genes in Rats and Activates PPARα

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.

Forms of cytochrome P450 in the liver microsome of oxidized frying oil-fed guinea pigs.

The aim of this study is to investigate the influence of oxidized frying oil (OFO) on the induction of individual forms of cytochrome P450 (CYP450) in guinea pigs. The OFO samples were obtained by frying potato chips in soybean oil at 200+/-5 degrees C for 24 h. Sixteen male weaning guinea pigs were fed for 12 wk on a diet which included 15% of either OFO or fresh soybean oil supplemented with 300 ppm ascorbic acid. It was demonstrated that guinea pigs fed with the OFO diet (D300) exhibited inferior growth rates and lower feed efficiency than the control group (F300). The vitamin C contents of plasma, liver, and kidney in the D300 group were lower than those in the F300 group. Further, the thiobarbituric acid-reactive substance content in D300 liver and kidney was higher than that in the F300 equivalent. The liver UDP-glucuronyl-transferase activity in the D300 group was higher than that in the F300 group, and there was no difference in comparing the glutathione-S-transferase activity levels of the two groups. Notably, the total CYP450 content and the NADPH-cytochrome c reductase activity were significantly elevated in the D300 group. The ethoxyresorufin O-deethylase activity, which mainly represents CYP1A1 activity, for the detection of CYP450 isozyme characteristics was elevated more in the D300 than in the F300 group. There was no difference in the pentoxyresorufin O-dealkylase activity, which mainly reflects the CYP2B isozyme, between the two groups. However, the quantity of CYP1A1 isoform determined in the D300 group did not differ from that in the F300 group, as revealed by SDS-PAGE and Western blot testing. Our results demonstrate that the relative enzyme activity to CYP1A1-like activity of the guinea pig hepatic xenobiotic metabolizing enzyme system may be induced by OFO feeding, but more advanced research is needed to identify the predominant form of CYP450 isozyme induced as a result of this condition.

Effect of Oxidized Frying Oil and Vitamin C Levels on the Hepatic Xenobiotic-Metabolizing Enzyme System of Guinea Pigs.

The influence of oxidized frying oil (OFO) on the guinea pig hepatic microsomal xenobiotic-metabolizing enzyme system in the presence of different amounts dietary vitamin C was investigated. Weanling male guinea pigs were divided into four groups and were fed 15% oxidized frying oil diets supplemented with vitamin C at 300, 600, or 1,500 mg/kg (experimental diets) or a control diet that contained 15% fresh untreated soybean oil with 300 mg/kg of vitamin C, respectively. After 60 d, guinea pigs were euthanized and phase I and phase II xenobiotic-metabolizing enzymes in the liver were determined. Compared with the fresh oil diet fed the control group, the relative liver weight was higher in the OFO-fed groups. Hepatic microsomal protein and cytochrome P450 contents were significantly higher in OFO-fed guinea pigs than in the control group. Both values increased in response to increased intake of vitamin C. The activities of phase II relative components, including UDP-glucuronyl transferase, UDP-glucuronyl dehydrogenase and beta-glucuronidase, of guinea pigs fed the OFO diets supplemented with 300 mg vitamin C/kg were significantly higher than those of guinea pigs fed the control diet. However, the phase II relative components decreased with increasing vitamin C content in the diet. The results demonstrate that both dietary OFO and vitamin C in guinea pigs induce hepatic xenobiotic-metabolizing enzymes, but the level of induction is modulated by the dietary vitamin C level.

Vitamin C Supplementation Restores the Impaired Vitamin E Status of Guinea Pigs Fed Oxidized Frying Oil ,

To investigate the effect of dietary oxidized frying oil (OFO) on tissue retention of vitamin C, and to explore the effect of vitamin C supplementation on tissue vitamin E concentrations and lipid peroxidation, male weanling guinea pigs were divided into four groups. Guinea pigs were fed 15% OFO diets supplemented with vitamin C at 300, 600 or 1500 mg/kg diet. Control animals were fed a diet containing 15% fresh untreated soybean oil with 300 mg/kg of vitamin C. After 60 d of feeding, body weight gain, food intake, feed efficiency and plasma triglyceride concentration were significantly lower in guinea pigs fed OFO diets than in controls (P< 0.05). However, plasma cholesterol concentration was highest in guinea pigs fed the OFO diet supplemented with 300 mg/kg vitamin C. Increasing vitamin C in OFO diets significantly reduced plasma cholesterol concentration. Plasma and tissue vitamins C and E concentrations were significantly lower in the OFO-fed guinea pigs receiving 300 mg/kg vitamin C than in controls. Greater levels of supplemental vitamin C increased tissue vitamins C and E. Guinea pigs fed OFO diets had significantly higher tissue levels of thiobarbituric acid reactive substances (TBARS) (P< 0.05) than controls. Our results demonstrated that OFO feeding, which impaired α-tocopherol retention and increased TBARS, could be alleviated somewhat by vitamin C supplementation. J. Nutr. 128: 116–122, 1998.

Tissue alpha-tocopherol retention in male rats is compromised by feeding diets containing oxidized frying oil.

To investigate the effect of dietary oxidized frying oil (OFO) on tissue retention of alpha-tocopherol (alpha-T). Long-Evans male weanling rats were divided to four groups based on a 2 x 2 factorial design. Two groups were fed 15% OFO diets, and the remaining two groups were fed control diets in which OFO was replaced by vitamin-E-stripped fresh soybean oil. Vitamin E as all-rac-alpha-tocopheryl acetate was added at the concentration of either 50 (normal E) or 500 (high E) mg/kg diet. The OFO sample was prepared by deepfrying sticks in fresh soybean oil at 205 +/- 5 degrees C for four 6-h periods. After 6 wks of feeding, alpha-T concentrations in most tissues were significantly lower in rats fed OFO diets (P < 0.05) than in the control groups. For rats fed the OFO diet with the normal vitamin E concentration, the alpha-T concentration is epididymal fat pad, plasma, liver, kidney, muscle, brain and lung were 29-64% those of the corresponding control group (P < 0.05). The interaction between the two dietary factors on tissue alpha-T was significant in liver, spleen, and adrenal gland. In these three tissues, the differences between the normal and high dietary vitamin E groups were less in rats fed the OFO diets than in rats fed the control diets. The tissue alpha-T concentrations of the high vitamin E OFO group were comparable with or higher (P < 0.05) than those of the normal vitamin E control group, indicating that the negative effect of OFO on tissue alpha-T concentration can be alleviated by dietary supplementation of vitamin E. Compared with the controls, rats OFO diets had significantly higher tissue thiobarbituric acid reactive substances (P < 0.05). Because the amount of alpha-T directly added into the test oil samples was not significantly decreased through an incubation (at 37 degrees C) period of up to 10 d, the inefficient absorption and/or enhanced catabolism or turnover of vitamin E may be involved in the inferior tissue alpha-T retention of OFO fed rats.