Dietary oxidized fatty acids may enhance intestinal apolipoprotein A-I production

Adverse effects of linoleic acid: Influence of lipid oxidation on lymphatic transport of citrus flavonoid and enterocyte morphology

Lipids usually contain a large ratio of polyunsaturated fatty acids (PUFAs), which are highly susceptible to oxidation. Presence of oxidized lipids in foods may affect the bioavailability of lipophilic bioactive components after ingestion. In this study, the effect of oxidized and unoxidized linoleic acid (LA) on the transport of a highly lipophilic bioactive citrus flavonoid (5-hydroxy - 6, 7, 8, 4' tetramethoxylflavone or 5-DMT) was determined using a Caco-2 cell model. Results demonstrated that compared to free 5-DMT, unoxidized LA improved the trans-enterocyte absorption of 5-DMT by stimulating the production of lipid droplets and chylomicrons. Although the amount of 5-DMT transported across the enterocyte doubled by oxidized LA compared to free 5-DMT, it significantly induced reactive oxygen species (ROS), affected the function of tight junction and caused damages to the morphology of enterocyte monolayer. This study re-emphasized the importance of preventing lipid oxidation in foods.

Intestinal and Hepatic Uptake of Dietary Peroxidized Lipids and Their Decomposition Products, and Their Subsequent Effects on Apolipoprotein A1 and Paraoxonase1

Both pro- and antiatherosclerotic effects have been ascribed to dietary peroxidized lipids. Confusion on the role of peroxidized lipids in atherosclerotic cardiovascular disease is punctuated by a lack of understanding regarding the metabolic fate and potential physiological effects of dietary peroxidized lipids and their decomposition products. This study sought to determine the metabolic fate and physiological ramifications of 13-hydroperoxyoctadecadienoic acid (13-HPODE) and 13-HODE (13-hydroxyoctadecadienoic acid) supplementation in intestinal and hepatic cell lines, as well as any effects resulting from 13-HPODE or 13-HODE degradation products. In the presence of Caco-2 cells, 13-HPODE was rapidly reduced to 13-HODE. Upon entering the cell, 13-HODE appears to undergo decomposition, followed by esterification. Moreover, 13-HPODE undergoes autodecomposition to produce aldehydes such as 9-oxononanoic acid (9-ONA). Results indicate that 9-ONA was oxidized to azelaic acid (AzA) rapidly in cell culture media, but AzA was poorly absorbed by intestinal cells and remained detectable in cell culture media for up to 18 h. An increased apolipoprotein A1 (ApoA1) secretion was observed in Caco-2 cells in the presence of 13-HPODE, 9-ONA, and AzA, whereas such induction was not observed in HepG2 cells. However, 13-HPODE treatments suppressed paraoxonase 1 (PON1) activity, suggesting the induction of ApoA1 secretion by 13-HPODE may not represent functional high-density lipoprotein (HDL) capable of reducing oxidative stress. Alternatively, AzA induced both ApoA1 secretion and PON1 activity while suppressing ApoB secretion in differentiated Caco-2 cells but not in HepG2. These results suggest oxidation of 9-ONA to AzA might be an important phenomenon, resulting in the accumulation of potentially beneficial dietary peroxidized lipid-derived aldehydes.

Ellagic Acid Suppresses ApoB Secretion and Enhances ApoA-1 Secretion from Human Hepatoma Cells, HepG2

The effect of ellagic acid (EA), a naturally occurring polyphenolic compound, on the secretion of apolipoproteins from human hepatocytes, HepG2, was investigated. The levels of apoB and apoA-1 secreted in the cell culture medium were determined by sandwich ELISA. EA did not affect cell viability at the tested concentrations (up to 50 µM). EA suppressed the secretion of apoB and enhanced that of apoA-1 from HepG2 cells. However, cellular apoB levels were increased, suggesting that EA inhibited the trafficking of apoB during the process of secretion. In contrast, the increase in the cellular levels of apoA-1 was consistent with its secreted levels. These results indicate that EA inhibits the secretion of apoB from hepatocytes and increases the secretion of apoA-1. Both of these effects are beneficial for lipoprotein metabolism in the prevention of lifestyle-related diseases. The detailed mechanism underlying these effects of EA on lipoprotein metabolism should be elucidated in the future, but this naturally occurring polyphenolic compound might be antihyperlipidemic. Based on these results, EA is suggested as a candidate food-derived compound for the prevention of hyperlipidemia.

Peroxidized Linoleic Acid, 13-HPODE, Alters Gene Expression Profile in Intestinal Epithelial Cells

Lipid peroxides (LOOHs) abound in processed food and have been implicated in the pathology of diverse diseases including gut, cardiovascular, and cancer diseases. Recently, RNA Sequencing (RNA-seq) has been widely used to profile gene expression. To characterize gene expression and pathway dysregulation upon exposure to peroxidized linoleic acid, we incubated intestinal epithelial cells (Caco-2) with 100 µM of 13-hydroperoxyoctadecadienoic acid (13-HPODE) or linoleic acid (LA) for 24 h. Total RNA was extracted for library preparation and Illumina HiSeq sequencing. We identified 3094 differentially expressed genes (DEGs) in 13-HPODE-treated cells and 2862 DEGs in LA-treated cells relative to untreated cells. We show that 13-HPODE enhanced lipid metabolic pathways, including steroid hormone biosynthesis, PPAR signaling, and bile secretion, which alter lipid uptake and transport. 13-HPODE and LA treatments promoted detoxification mechanisms including cytochrome-P450. Conversely, both treatments suppressed oxidative phosphorylation. We also show that both treatments may promote absorptive cell differentiation and reduce proliferation by suppressing pathways involved in the cell cycle, DNA synthesis/repair and ribosomes, and enhancing focal adhesion. A qRT-PCR analysis of representative DEGs validated the RNA-seq analysis. This study provides insights into mechanisms by which 13-HPODE alters cellular processes and its possible involvement in mitochondrial dysfunction-related disorders and proposes potential therapeutic strategies to treat LOOH-related pathologies.

Are Fried Foods Unhealthy? The Dietary Peroxidized Fatty Acid, 13-HPODE, Induces Intestinal Inflammation In Vitro and In Vivo

Inflammatory Bowel Disease (IBD) is a chronic inflammatory disorder characterized by progressive inflammation and the erosion of the gut mucosa. Although the exact cause of IBD is unknown, multiple factors contribute to its complex pathogenesis. Diet is one such factor and a strong correlation exists between the western-style, high fat diets (HFDs) and IBD incidence rates. In this study, we propose that the peroxidized fatty acid components of HFDs could contribute to inflammation of the gut. The inflammatory nature of peroxidized linoleic acid (13-HPODE), was confirmed in vitro by analyzing pro-inflammatory gene expression in Caco-2 cells via RT-PCR and ELISA. Additionally, peroxide induced apoptosis was tested by Annexin-V fluorescent staining, while permeability was tested by FITC-dextran flux and TEER. The 13-HPODE-induced inflammation of intestinal epithelium was evaluated in vivo by analyzing pro-inflammatory cytokines under acute and chronic conditions after feeding 13-HPODE to C57BL/6J mice. Our data show that 13-HPODE significantly induced pro-inflammatory gene expression of TNF-α and MCP-1 in vitro, most notably in differentiated Caco-2 cells. Further, acute and chronic 13-HPODE treatments of mice similarly induced pro-inflammatory cytokine expression in the epithelium of both the proximal and distal small intestines, resident immune cells in Peyer's patches and peritoneal macrophages. The results of this study not only confirm the pro-inflammatory properties of peroxidized fats on the gut mucosa, but for the first time demonstrate their ability to differentially induce pro-inflammatory gene expression and influence permeability in the intestinal epithelium and mucosal cells. Collectively, our results suggest that the immunogenic properties of HFD's in the gut may be partly caused by peroxide derivatives, providing potential insight into how these diets contribute to exacerbations of IBD.

A Novel Mechanism for Atherosclerotic Calcification: Potential Resolution of the Oxidation Paradox

AIM

In this study, we tested the hypothesis that lipid peroxide-derived dicarboxylic acids (DCAs), by virtue of their ability to bind to calcium (Ca), might be involved in atherosclerotic calcification. We determined the ability of azelaic acid (AzA) to promote calcification in human aortic smooth muscle cells (HASMCs), identified AzA in human calcified atherosclerotic lesions, and compared its levels with control and noncalcified atherosclerotic lesions.

RESULTS

HASMCs efficiently converted 9-oxononanoic acid (ONA), a lipid peroxide-derived monocarboxylic aldehyde, to AzA. In vitro incubations of AzA micelles with HASMC resulted in the formation of Ca deposits, which contained AzA. Liquid chromatography-mass spectrometry analysis of human control uninvolved artery, noncalcified, and calcified lesions showed significant increase of AzA in calcified lesions compared with noncalcified and control tissues. Calcified mouse atherosclerotic lesions also showed substantial presence of AzA in Ca complexes.

INNOVATION

This study identifies a DCA, AzA, as an integral part of the Ca complex. The study also demonstrates the conversion of a lipid peroxidation product, ONA, as a potential source of AzA, and establishes the presence of AzA in calcified materials isolated from human and mouse lesions.

CONCLUSION

The presence of AzA as a Ca sequestering agent in atherosclerotic lesions (i) might indicate participation of oxidized low-density lipoprotein (Ox-LDL) derived products in calcification, (ii) explain the potential correlation between calcification and overall plaque burden (as Ox-LDL has been suggested to be involved in atherogenesis), (iii) could contribute to plaque stabilization via its anti-inflammatory actions, and (iv) might explain why antioxidants failed to affect atherosclerosis in clinical studies. Antioxid. Redox Signal. 29, 471-483.

Apolipoprotein A-I inhibits experimental colitis and colitis-propelled carcinogenesis

In both humans with long-standing ulcerative colitis and mouse models of colitis-associated carcinogenesis (CAC), tumors develop predominantly in the distal part of the large intestine but the biological basis of this intriguing pathology remains unknown. Herein we report intrinsic differences in gene expression between proximal and distal colon in the mouse, which are augmented during dextran sodium sulfate (DSS)/azoxymethane (AOM)-induced CAC. Functional enrichment of differentially expressed genes identified discrete biological pathways operating in proximal vs distal intestine and revealed a cluster of genes involved in lipid metabolism to be associated with the disease-resistant proximal colon. Guided by this finding, we have further interrogated the expression and function of one of these genes, apolipoprotein A-I (ApoA-I), a major component of high-density lipoprotein. We show that ApoA-I is expressed at higher levels in the proximal compared with the distal part of the colon and its ablation in mice results in exaggerated DSS-induced colitis and disruption of epithelial architecture in larger areas of the large intestine. Conversely, treatment with an ApoA-I mimetic peptide ameliorated the phenotypic, histopathological and inflammatory manifestations of the disease. Genetic interference with ApoA-I levels in vivo impacted on the number, size and distribution of AOM/DSS-induced colon tumors. Mechanistically, ApoA-I was found to modulate signal transducer and activator of transcription 3 (STAT3) and nuclear factor-κB activation in response to the bacterial product lipopolysaccharide with concomitant impairment in the production of the pathogenic cytokine interleukin-6. Collectively, these data demonstrate a novel protective role for ApoA-I in colitis and CAC and unravel an unprecedented link between lipid metabolic processes and intestinal pathologies.

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.

Differentiated CaCo-2 cells as an in-vitro model to evaluate de-novo apolipoprotein A-I production in the small intestine

BACKGROUND

Increasing HDL cholesterol concentrations by stimulating de-novo apolipoprotein A-I (apoA-I) production in the liver and/or in the small intestine is a potential strategy to reduce coronary heart disease risk. Although there is quite some knowledge concerning regulatory effects in the liver, less is known concerning potential agents that could elevate de-novo apoA-I production in the small intestine.

METHODS

Therefore, we compared side-by-side effects of various peroxisome proliferator-activated receptor (PPAR)alpha, PPARgamma, retinoid-X-receptor alpha, and farnesoid-X-receptor agonists on de-novo apoA-I production in differentiated CaCo-2 and HepG2 cells.

RESULTS

For PPARa agonists, we showed that GW7647 elevated apoA-I concentrations in the medium of both cell models, whereas WY14643 elevated only de-novo apoA-I concentrations in differentiated CaCo-2 cells. Unexpectedly, fenofibric acid lowered apoA-I medium concentrations in both cell lines, which could not be explained by a lack of PPAR transactivation or a lack of retinoid-X-receptor a activation. For farnesoid-X-receptor agonists, chenodeoxycholic acid strongly reduced apoA-I concentrations both in differentiated CaCo-2 and HepG2 cells, whereas GW4064 and taurocholate only lowered apoA-I in CaCo-2 cells (GW4064) or in HepG2 cells (taurocholate). However, overall effects of all individual components on apoA-I production in differentiated CaCo-2 and HepG2 cells were highly correlated (r = 0.68; P = 0.037; N=9).

CONCLUSION

We conclude that differentiated CaCo-2 cells are suitable models to study de-novo small intestinal apoA-I production in vitro enabling the possibility to screen for potential bioactive dietary components. This cell model may also determine small-intestinal-specific effects, as some discrepancy was found between both cell models.

Nutriomic analysis of fresh and processed fruit products. 2. During in vitro simultaneous molecular passages using Caco-2 cell monolayers

Many studies have used Caco-2 cell monolayers as human intestinal absorption models. However, only a few studied digested foods, instead of pure standard compounds. Moreover, beneficial and nutritional molecules (nutriome) have not been investigated simultaneously. The present study explored nutriome passages from digest solution of fresh, dried, and juiced tomato, mango, and papaya using Caco-2 cell monolayers in apical-->basolateral directions. A validation method using complementary TEER and P(app) values or internal standard caffeine is recommended because physiologically passive diffusion is unlikely to happen. Sugars were transported into basolateral sides, resulting in potential glucose equivalent bioavailability of 2.26-75 mg h(-1)/100 g (WB). Using sugar passage rates (DB) of juices as 100% references, the rate order was tomato (49.8% dried; 89.5% fresh) > mango (56.8% dried; 22.8% fresh) > papaya (18.7% dried; 36.7% fresh). Major indications that phytochemical absorption does not occur in the small intestine were obtained from the bioassay condition selected. Apical organic acid levels decreased, which occasionally were transported into basolateral sides, whereas the disappearances of apical carotenoids and phenolics were not. Pectin substances were predicted to be responsible for the disappearances of bioactive compounds in those pectin-rich fruits. Further investigations on the role of pectin substances in intestinal passages are recommended.

Dietary oxidized linoleic acid lowers triglycerides via APOA5/APOClll dependent mechanisms

Previously we have shown that intestinal cells efficiently take up oxidized fatty acids (OxFAs) and that atherosclerosis is increased when animals are fed a high cholesterol diet in the presence of oxidized linoleic acid. Interestingly, we found that in the absence of dietary cholesterol, the oxidized fatty acid fed low-density lipoprotein (LDL) receptor negative mice appeared to have lower plasma triglyceride (TG) levels as compared to animals fed oleic acid. In the present study, we fed C57BL6 mice a normal mice diet supplemented with oleic acid or oxidized linoleic acid (at 18 mg/animal/day) for 2 weeks. After the mice were sacrificed, we measured the plasma lipids and collected livers for the isolation of RNA. The results showed that while there were no significant changes in the levels of total cholesterol and high-density lipoprotein cholesterol (HDLc), there was a significant decrease (41.14%) in the levels of plasma TG in the mice that were fed oxidized fatty acids. The decreases in plasma TG levels were accompanied by significant increases (P<0.001) in the expressions of APOA5 and acetyl-CoA oxidase genes as well as a significant (P<0.04) decrease in APOClll gene expression. Oxidized lipids have been suggested to be ligands for peroxisome proliferator-activated receptor (PPAR*). However, there were no increases in the mRNA or protein levels of PPAR* in the oxidized linoleic acid fed animals. These results suggest that oxidized fatty acids may act through an APOA5/APOClll mechanism that contributes to lowering of TG levels other than PPAR* induction.

Changes and Effects of Dietary Oxidized Lipids in the Gastrointestinal Tract

This paper is focused on the present state-of-the art of modifications and effects of dietary oxidized lipids during their transit along the gastrointestinal tract. A survey of the literature reporting changes and effects of oxidized lipids before absorption, first in the stomach and then during enzymatic lipolysis in the small intestine, are addressed. Also, the fate of non-absorbed compounds and their potential implications at the colorectal level are discussed. Among the results found, it is shown that acidic gastric conditions and the influence of other dietary components may lead to either further oxidation or antioxidative effects in the stomach. Also, changes in oxidized functions, especially of hydroperoxy and epoxy groups, seem likely to occur. Enzymatic hydrolysis by pancreatic lipase is not effective for triacylglycerol polymers, and hence they can be found as non-absorbed oxidized lipids in the large intestine. Interactions of oxidized lipids with cholesterol absorption in the small intestine and with microflora metabolism have been also observed.

Induction of paraoxonase 1 and apolipoprotein A-I gene expression by aspirin

Low-dose aspirin therapy has become a standard in the treatment of cardiovascular diseases. Aspirin has been shown to inhibit atherosclerosis in mouse models. To determine the mechanisms by which aspirin might inhibit atherosclerosis, we incubated HEPG2 cells and rat primary hepatocytes with aspirin or salicylic acid and noted an increase in paraoxonase 1(PON1) activity in the medium, together with an induction of PON1 and apolipoprotein A-I (apoA-I) gene expression. Mice treated with aspirin also showed a 2-fold increase in plasma PON1 activity and a significant induction of both PON1 and apoA-I gene expression in the liver. The induction of the PON1 gene in cell culture was accompanied by an increase in arylhydrocarbon receptor (AhR) gene expression. Accordingly, aspirin treatment of AhR(-/-) animals failed to induce PON1 gene expression. We previously suggested that aspirin might be hydrolyzed by serum PON1, which could account for its short plasma half-life of 10 min. Taken together with the current studies, we suggest that the antiatherosclerotic effects of aspirin might be mediated by its hydrolytic product salicylate and that the induction of PON1 and apoA-I might be important in the cardioprotective effects of aspirin.

Lipid peroxidation and decomposition--conflicting roles in plaque vulnerability and stability

The low density lipoprotein (LDL) oxidation hypothesis has generated considerable interest in oxidative stress and how it might affect atherosclerosis. However, the failure of antioxidants, particularly vitamin E, to affect the progression of the disease in humans has convinced even staunch supporters of the hypothesis to take a step backwards and reconsider alternatives. Preponderant evidence for the hypothesis came from animal antioxidant intervention studies. In this review we point out basic differences between animal and human atherosclerosis development and suggest that human disease starts where animal studies end. While initial oxidative steps in the generation of early fatty streak lesions might be common, the differences might be in the steps involved in the decomposition of peroxidized lipids into aldehydes and their further oxidation into carboxylic acids. We suggest that these steps may not be amenable to attenuation by antioxidants and antioxidants might actually counter the stabilization of plaque by preventing the formation of carboxylic acids which are anti-inflammatory in nature. The formation of such dicarboxylic acids may also be conducive to plaque stabilization by trapping calcium. We suggest that agents that would prevent the decomposition of lipid peroxides and promote the formation and removal of lipid hydroxides, such as paraoxonase (PON 1) or apo A1/high density lipoprotein (HDL) might be more conducive to plaque regression.

The effect of select nutrients on serum high-density lipoprotein cholesterol and apolipoprotein A-I levels

One of the factors contributing to the increased risk of developing premature atherosclerosis is low plasma concentrations of high-density lipoprotein (HDL) cholesterol (HDLc). Multiple potential mechanisms account for the cardioprotective effects of HDL and its main protein apolipoprotein A-I (apo A-I). The low plasma concentrations of HDL could be the result of increased fractional clearance and reduced expression of apo A-I. To this end, nutrients play an important role in modulating the fractional clearance rate, as well as the rate of apo A-I gene expression. Because medical nutrition therapy constitutes the cornerstone of management of dyslipidemias, it is essential to understand the mechanisms underlying the changes in HDL level in response to alterations in dietary intake. In this review, we will discuss the effect of select nutrients on serum HDLc and apo A-I levels. Specifically, we will review the literature on the effect of carbohydrates, fatty acids, and ketones, as well as some of the nutrient-related metabolites, such as glucosamine and the prostanoids, on apo A-I gene expression. Because there are multiple mechanisms involved in the regulation of serum HDLc levels, changes in gene transcription do not necessarily correlate with clinical observations on serum levels of HDLc.

Induction of the apolipoprotein AI promoter by Sp1 is repressed by saturated fatty acids

Insulin induces transcription of the hepatic apolipoprotein AI (apo AI) gene by increasing Sp1 binding to the promoter. To determine the effect of fatty acids on this process, HepG2 cells cotransfected with the plasmid pAI.474.CAT containing the full-length apo AI promoter and the Sp1-expressing plasmid, pCMV-Sp1, were studied. Chloramphenicol acetyl transferase (CAT) activity (% acetylation) increased 1.98-fold in cells receiving the Sp1 expression construct relative to control cells (46.4% +/- 0.6% v 23.4% +/- 1.3%, P < .05). Treatment of cells with 3 saturated fatty acids, stearic, myristic, and palmitic acid, repressed the ability of exogenous Sp1 to induce apo AI reporter gene expression (15.2% +/- 1.7%, 22.5% +/- 0.3%, 22.9% +/- 0.1%, 23.5% +/- 0.8%, respectively, P < .05). Unsaturated fatty acids, oleic, linoleic, or linolenic acid had no effect on Sp1-mediated induction of the apo AI promoter. In the presence of the trans fatty acids, CAT activity in the Sp1-transfected cells was similar to control cells (16.7% +/- 3.3%, 19.3% +/- 0.5%, and 21.0% +/- 2.1% acetylation in cells exposed to elaidic acid, linolelaidic, or linolenelaidic acid, respectively). In cells treated with an equimolar mixture of oleic acid and stearic acid, apo AI promoter activity was suppressed in a manner similar to that observed in stearic acid-treated cells. Insulin (100 microU/mL) induced apo AI promoter activity 2.9-fold (22.4% +/- 1.7% v 7.8% +/- 2.4%, P < .05). However, in the presence of stearic acid, insulin was unable to induce apo AI promoter (6.3% +/- 1.6%). Stearic acid treatment did not alter Sp1-DNA binding as measured by gel shift analysis. Therefore, saturated fatty acids blunt Sp1 induction of apo AI promoter probably at a step beyond DNA binding.

The up-regulation of hepatic acyl-coA oxidase and cytochrome P450 4A1 mRNA expression by dietary oxidized frying oil is comparable between male and female rats

We previously demonstrated that oxidized frying oil (OFO) activates peroxisome proliferator-activated receptor alpha (PPARalpha) and up-regulates hepatic acyl-CoA oxidase (ACO) and cytochrome P450 4A1 (CYP4A1) genes in male rats. As female rats were shown to be less responsive to some peroxisome proliferators (PP), this study compared the expression of a few PPARalpha target genes in male and female rats fed diets containing OFO. Male and female rats were fed a diet containing 20 g/100 g OFO (O diet) or fresh soybean oil (F diet) for 6 wk. Both male and female rats fed the O diet showed significantly higher liver weight, hepatic ACO and catalase activities, CYP4A protein, and expression of ACO and CYP4A1 mRNA (P < 0.05) compared with their control groups. The mRNA expression of two other PPARalpha target genes, FA-binding protein and HMG-CoA synthase, were marginally increased by dietary OFO (P = 0.0669 and 0.0521, respectively). Female rats fed the O diet had significantly lower CYP4A protein than male rats fed the same diet. The remaining OFO-induced effects were not significantly different between male and female rats fed the O diet. These results indicate that dietary OFO, unlike clofibrate or other PP, had minimal sexual dimorphic effect on the induction of hepatic PPARalpha target gene expression.

Oxidized fats in foods

PURPOSE OF REVIEW

Lipid oxidation is the cause of important deteriorative changes in chemical, sensory and nutritional food properties. In particular, the question of whether oxidized 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.

RECENT FINDINGS

In this review, the most recent works on the formation, nature and evaluation of oxidized dietary lipids are addressed; important issues such as the difficulties encountered in estimating their intake and the relationships between oxidants and antioxidants in the diet are discussed, and the latest studies on health implications of oxidized lipids are summarized.

SUMMARY

The current literature reflects various important points. At present, there is no information on the intake of oxidized fats, which is essential to know if the amount of oxidized lipids in normal diets is sufficient to cause the physiological effects claimed. Recently, relevant advances in analytical methodologies for quantitation of specific oxidation compounds have been reported, although their application to improve the analytical definition of the oxidized substrate used in nutritional studies is still a goal to be reached. Alternatively, one of the most promising current tendencies in this field is the study of the molecular targets by which dietary oxidized lipids can influence health. Overall, more selected research based on coordinated multidisciplinary studies is needed to define the role of dietary oxidized fats in health.