Dietary hydroxy fatty acids are absorbed in humans: implications for the measurement of 'oxidative stress' in vivo

Plasma fatty acid esters of hydroxy fatty acids and surrogate fatty acid esters of hydroxy fatty acids hydrolysis activity in children with or without obesity and in adults with or without coronary artery disease

AIM

Fatty acid esters of hydroxy fatty acids (FAHFA) are a class of bioactive lipids with anti-inflammatory, antidiabetic and cardioprotective properties. FAHFA hydrolysis into its fatty acid (FA) and hydroxy fatty acid (HFA) constituents can affect the bioavailability of FAHFA and its subsequent biological effects. We aimed to investigate FAHFA levels and FAHFA hydrolysis activity in children with or without obesity, and in adults with or without coronary artery disease (CAD).

MATERIALS AND METHODS

Our study cohort included 20 children without obesity, 40 children with obesity, 10 adults without CAD and 28 adults with CAD. We quantitated plasma levels of four families of FAHFA [palmitic acid hydroxy stearic acid (PAHSA), palmitoleic acid hydroxy stearic acid (POHSA), oleic acid hydroxy stearic acid (OAHSA), stearic acid hydroxy stearic acid] and their corresponding FA and HFA constituents using liquid chromatography-tandem mass spectrometry analysis. Surrogate FAHFA hydrolysis activity was estimated as the FA/FAHFA or HFA/FAHFA ratio.

RESULTS

Children with obesity had lower plasma PAHSA (p = .001), OAHSA (p = .006) and total FAHFA (p = .011) levels, and higher surrogate FAHFA hydrolysis activity represented by PA/PAHSA (p = .040) and HSA/OAHSA (p = .025) compared with children without obesity. Adults with CAD and a history of myocardial infarction (MI) had lower POHSA levels (p = .026) and higher PA/PAHSA (p = .041), POA/POHSA (p = .003) and HSA/POHSA (p = .038) compared with those without MI.

CONCLUSION

Altered FAHFA metabolism is associated with obesity and MI, and inhibition of FAHFA hydrolysis should be studied further as a possible therapeutic strategy in obesity and MI.

Characterization of oxylipins in Antarctic krill oil (Euphausia superba) during storage based on RPLC-MS/MS analysis

Antarctic krill oil (AKO) is rich in polyunsaturated fatty acids (PUFAs), but is prone to oxidative degradation, resulting in the formation of oxylipins, which compromise AKO quality. Herein, we used reversed-phase-high performance liquid chromatography-tandem mass spectrometry (RPLC-MS/MS) to perform qualitative and semi-quantitative analyses of oxylipins in AKO during storage. A total of 27 oxylipins were identified. A notable decrease in epoxy oxylipins (from 41.8 % to 26.9 % of the total oxylipins) was observed, whereas the content of dihydro oxylipins initially increased and then decreased with 48 h, as a pivotal point for AKO quality decline during storage. We suspected that the ratio of dihydroxyl and epoxy oxylipins could be a novel oxidative index to evaluate the oxidation of AKO. Statistical analysis allowed the identification of five oxylipins which showed unique correlations with various indexes. The findings discussed herein provide important new insights into mechanisms of oxidation occurring in AKO during storage.

Do meals contain a relevant amount of oxylipins? LC-MS-based analysis of oxidized fatty acids in food

Several oxylipins are potent lipid mediators and are discussed to be absorbed after oral intake. However, information about their concentrations in oils and processed foods are scarce. Here, we analyzed the concentrations of mono-, di- and multihydroxy- as well as epoxy-PUFA in virgin and refined oils as well as in different foods/meals. Oil refining causes hydrolysis of epoxy-PUFA and thus high dihydroxy-PUFA concentrations (e.g. 15,16-DiHODE 290 µg/g in refined vs. 15 µg/g in virgin rapeseed oil), making the epoxy-to-diol ratio a potential marker for refined oils. Low oxylipin levels were found in foods with high amounts of saturated fatty acids such as Hamburger patties (around 30 µg/g). High concentrations (up to 1200 µg/g, 80 mg per serving) and high oxylipin/precursor-PUFA ratios were found in fried falafel and processed foods such as vegetarian sausage/fish fingers. Our study provides first insights in the oxylipin concentrations of our daily food, indicating a relevant intake.

Lipid Structure Influences the Digestion and Oxidation Behavior of Docosahexaenoic and Eicosapentaenoic Acids in the Simulated Digestion System

Omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are essential for human health but prone to oxidation. While esterification location is known to influence the stability of omega-3 in triacylglycerols (TAGs) in oxidation trials, their oxidative behavior in the gastrointestinal tract is unknown. Synthesized ABA- and AAB-type TAGs containing DHA and EPA were submitted to static in vitro digestion for the first time. Tridocosahexaenoin and DHA as ethyl esters were similarly digested. Digesta were analyzed by gas chromatography, liquid chromatography-mass spectrometry, and nuclear magnetic resonance spectroscopy. Besides the formation of di- and monoacylglycerols, degradation of hydroperoxides was detected in ABA- and AAB-type TAGs, whereas oxygenated species increased in tridocosahexaenoin. Ethyl esters were mainly unaffected. EPA was expectedly less susceptible to oxidation prior to and during the digestion process, particularly in sn-2. These results are relevant for the production of tailored omega-3 structures to be used as supplements or ingredients.

Major dietary lipids in nutrition and health

In this chapter, an overview of the major lipids in the diet with emphasis in nutritional aspects is provided. Triacylglycerols, i.e., glycerol esterified with three fatty acids, are the predominant constituents in dietary lipids. Therefore, this chapter focuses on the nature and nutritional significance of the main fatty acids in the diet and their possible modifications during food processing and commercialization. The main fatty acids in dietary lipids are grouped into saturated, monounsaturated and polyunsaturated fatty acids. Nutritional implications, the latest intervention trials and health recommendations will be discussed. A brief description of the major sources of lipids in the diet is included, oils and fats standing out. Other food sources shortly commented are milk and dairy products, meat, poultry and eggs, fish, and structured lipids designed to improve functional and nutritional properties. Modifications of fatty acids as a result of processing and commercialization are discussed because of their great relevance for their health implications, especially oxidation compounds and trans fatty acids.

Feeding mice a diet high in oxidized linoleic acid metabolites does not alter liver oxylipin concentrations

The oxidation of dietary linoleic acid (LA) produces oxidized LA metabolites (OXLAMs) known to regulate multiple signaling pathways in vivo. Recently, we reported that feeding OXLAMs to mice resulted in liver inflammation and apoptosis. However, it is not known whether this is due to a direct effect of OXLAMs accumulating in the liver, or to their degradation into bioactive shorter chain molecules (e.g. aldehydes) that can provoke inflammation and related cascades. To address this question, mice were fed a low or high LA diet low in OXLAMs, or a low LA diet supplemented with OXLAMs from heated corn oil (high OXLAM diet). Unesterified oxidized fatty acids (i.e. oxylipins), including OXLAMs, were measured in liver after 8 weeks of dietary intervention using ultra-high pressure liquid chromatography coupled to tandem mass-spectrometry. The high OXLAM diet did not alter liver oxylipin concentrations compared to the low LA diet low in OXLAMs. Significant increases in several omega-6 derived oxylipins and reductions in omega-3 derived oxylipins were observed in the high LA dietary group compared to the low LA group. Our findings suggest that dietary OXLAMs do not accumulate in liver, and likely exert pro-inflammatory and pro-apoptotic effects via downstream secondary metabolites.

Chemical Changes of Hydroperoxy-, Epoxy-, Keto- and Hydroxy-Model Lipids under Simulated Gastric Conditions

Chemical changes occurring in dietary lipid oxidation compounds throughout the gastrointestinal tract are practically unknown. The first site for potential chemical modifications is the stomach due to the strong acidic conditions. In this study, model lipids representative of the most abundant groups of dietary oxidation compounds were subjected to in vitro gastric conditions. Thus, methyl linoleate hydroperoxides were used as representative of the major oxidation compounds formed in food storage at low and moderate temperatures. Methyl 9,10-epoxystearate, 12-oxostearate and 12-hydroxystearate were selected as model compounds bearing the oxygenated functional groups predominantly found in oxidation compounds formed at the high temperatures of frying. Analyses were performed using gas-liquid chromatography/flame ionization detection/mass spectrometry and high performance-liquid chromatography/ultraviolet detection. Losses of methyl 9,10-epoxystearate and linoleate hydroperoxides in the ranges 17.8–58.8% and 42.3–61.7% were found, respectively, whereas methyl 12-oxostearate and methyl 12-hydroxystearate remained unaltered. Although quantitative data of the compounds formed after digestion were not obtained, methyl 9,10-dihydroxystearate was detected after digestion of methyl 9,10-epoxystearate, and some major volatiles were detected after digestion of linoleate hydroperoxides. Overall, the results showed that significant modifications of dietary oxidized lipids occurred during gastric digestion and supported that the low pH of the gastric fluid played an important role.

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.

Effects of epoxy stearic acid on lipid metabolism in HepG2 cells

In the present study, effects of cis-9,10-epoxystearic acid (ESA) generated by the thermal oxidation of oleic acid on HepG2 cells, including intracellular lipid accumulation, fatty acid composition, and lipid metabolism, were investigated. Our results revealed that ESA increased the number and size of cellular lipid droplets. Intracellular triacylglycerol and total cholesterol content demonstrated that ESA induced lipid accumulation in HepG2 cells in a dose- and time-dependent manner. Results of fatty acid composition further indicated that ESA could lead to intracellular lipid accumulation. Our results also revealed that ESA may suppress the fatty acid oxidation in peroxisomes and mitochondria, including PPARα, Cpt1α, and Acox1, whereas the expression of genes involved in lipid synthesis, including Srebp-1c and Scd1, was enhanced. These findings provide critical information on the effects of ESA on HepG2 cells, particularly lipid accumulation and metabolism, which is important for evaluating the biosafety of the oxidative product of oleic acid. PRACTICAL APPLICATION: The administration of cis-9,10-epoxystearic acid to HepG2 cells could lead to disorder of lipid metabolism of cells by enhancing the intracellular lipid content, as well as suppressing the fatty acid oxidation in peroxisomes and mitochondria. These findings could provide information for the evaluation of the biosafety of the oxidative product of oleic acid.

Hydrolysis of oxidized phosphatidylcholines by crude enzymes from chicken, pork and beef muscles

Crude enzymes were extracted from beef, pork and chicken and were employed to hydrolyze 1-palmitoyl-2-linoleoyl-phosphatidylcholine (PLPC) and oxidized PLPC, i.e. hydroperoxide of PLPC (PLPC-OOH) and hydroxide of PLPC (PLPC-OH). HPLC-ELSD and ESI-MS were used to characterize and determinate hydrolytic products. After hydrolysis at 37 °C for 180 min, 26.8 ~ 27.4%, 21.6 ~ 22.8% and 17.8 ~ 19.0% of substrates were hydrolyzed by crude enzymes from beef, pork and chicken, respectively. Phospholipase A₂ (PLA₂) was the major contributor to hydrolysis, which accounted for 47.8 ~ 49.6%, 45.8 ~ 48.7% and 46.6 ~ 46.8% of hydrolysis of PLPC, PLPC-OOH and PLPC-OH, respectively. Crude enzymes demonstrated almost same specificities towards PLPC, PLPC-OOH and PLPC-OH. Under actions of crude enzymes, hydroperoxyoctadecadienoic acids (HpODE) and hydroxyoctadecadienoic acids (HODE) were yielded as hydrolytic products of PLPC-OOH and PLPC-OH, respectively. These finding would be helpful to better understand the fate of hydroperoxides of phospholipids and formation of HODE during meat products manufacturing.

Potential Adverse Public Health Effects Afforded by the Ingestion of Dietary Lipid Oxidation Product Toxins: Significance of Fried Food Sources

Exposure of polyunsaturated fatty acid (PUFA)-rich culinary oils (COs) to high temperature frying practices generates high concentrations of cytotoxic and genotoxic lipid oxidation products (LOPs) via oxygen-fueled, recycling peroxidative bursts. These toxins, including aldehydes and epoxy-fatty acids, readily penetrate into fried foods and hence are available for human consumption; therefore, they may pose substantial health hazards. Although previous reports have claimed health benefits offered by the use of PUFA-laden COs for frying purposes, these may be erroneous in view of their failure to consider the negating adverse public health threats presented by food-transferable LOPs therein. When absorbed from the gastrointestinal (GI) system into the systemic circulation, such LOPs may significantly contribute to enhanced risks of chronic non-communicable diseases (NCDs), e.g. cancer, along with cardiovascular and neurological diseases. Herein, we provide a comprehensive rationale relating to the public health threats posed by the dietary ingestion of LOPs in fried foods. We begin with an introduction to sequential lipid peroxidation processes, describing the noxious effects of LOP toxins generated therefrom. We continue to discuss GI system interactions, the metabolism and biotransformation of primary lipid hydroperoxide LOPs and their secondary products, and the toxicological properties of these agents, prior to providing a narrative on chemically-reactive, secondary aldehydic LOPs available for human ingestion. In view of a range of previous studies focused on their deleterious health effects in animal and cellular model systems, some emphasis is placed on the physiological fate of the more prevalent and toxic α,β-unsaturated aldehydes. We conclude with a description of targeted nutritional and interventional strategies, whilst highlighting the urgent and unmet clinical need for nutritional and epidemiological trials probing relationships between the incidence of NCDs, and the frequency and estimated quantities of dietary LOP intake.

Sequestration of 9-Hydroxystearic Acid in FAHFA (Fatty Acid Esters of Hydroxy Fatty Acids) as a Protective Mechanism for Colon Carcinoma Cells to Avoid Apoptotic Cell Death

Hydroxy fatty acids are known to cause cell cycle arrest and apoptosis. The best studied of them, 9-hydroxystearic acid (9-HSA), induces apoptosis in cell lines by acting through mechanisms involving different targets. Using mass spectrometry-based lipidomic approaches, we show in this study that 9-HSA levels in human colorectal tumors are diminished when compared with normal adjacent tissue. Since this decrease could be compatible with an escape mechanism of tumors from 9-HSA-induced apoptosis, we investigated different features of the utilization of this hydroxyfatty acid in colon. We show that in colorectal tumors and related cell lines such as HT-29 and HCT-116, 9-HSA is the only hydroxyfatty acid constituent of branched fatty acid esters of hydroxyfatty acids (FAHFA), a novel family of lipids with anti-inflammatory properties. Importantly, FAHFA levels in tumors are elevated compared with normal tissue and, unlike 9-HSA, they do not induce apoptosis of colorectal cell lines over a wide range of concentrations. Further, the addition of 9-HSA to colon cancer cell lines augments the synthesis of different FAHFA before the cells commit to apoptosis, suggesting that FAHFA formation may function as a buffer system that sequesters the hydroxyacid into an inactive form, thereby restricting apoptosis.

Effects of diets enriched in linoleic acid and its peroxidation products on brain fatty acids, oxylipins, and aldehydes in mice

BACKGROUND

Linoleic acid (LA) is abundant in modern industrialized diets. Oxidized LA metabolites (OXLAMs) and reactive aldehydes, such as 4-hydroxy-2-nonenal (4-HNE), are present in heated vegetable oils and can be endogenously synthesized following consumption of dietary LA. OXLAMs have been implicated in cerebellar degeneration in chicks; 4-HNE is linked to neurodegenerative conditions in mammals. It unknown whether increasing dietary LA or OXLAMs alters the levels of oxidized fatty acids (oxylipins), precursor fatty acids, or 4-HNE in mammalian brain.

OBJECTIVES

To determine the effects of increases in dietary OXLAMs and dietary LA, on levels of fatty acids, oxylipins, and 4-HNE in mouse brain tissues.

METHODS

Mice (n = 8 per group) were fed one of three controlled diets for 8 weeks: (1) a low LA diet, (2) a high LA diet, or (3) the low LA diet with added OXLAMs. Brain fatty acids, oxylipins, and 4-HNE were quantified in mouse cerebellum and cerebral cortex by gas chromatography-flame ionization detection, liquid chromatography-tandem mass spectrometry, and immunoblot, respectively.

RESULTS

Increasing dietary LA significantly increased omega-6 fatty acids, decreased omega-3 fatty acids, and increased OXLAMs in brain. Dietary OXLAMs had minimal effect on oxidized lipids but did decrease both omega-6 and omega-3 fatty acids. Neither dietary LA nor OXLAMs altered 4-HNE levels.

CONCLUSION

Brain fatty acids are modulated by both dietary LA and OXLAMs, while brain OXLAMs are regulated by endogenous synthesis from LA, rather than incorporation of preformed OXLAMs.

Lipidomic Analysis of Oxidized Fatty Acids in Plant and Algae Oils

Linoleic acid (LA) and α-linolenic acid (ALA) in plant or algae oils are precursors to oxidized fatty acid metabolites known as oxylipins. Liquid chromatography tandem mass spectrometry was used to quantify oxylipins in soybean, corn, olive, canola, and four high-oleic acid algae oils at room temperature or after heating for 10 min at 100 °C. Flaxseed oil oxylipin concentrations were determined in a follow-up experiment that compared it to soybean, canola, corn, and olive oil. Published consumption data for soybean, canola, corn, and olive oil were used to estimate daily oxylipin intake. The LA and ALA fatty acid composition of the oils was generally related to their respective oxylipin metabolites, except for olive and flaxseed oil, which had higher LA derived monohydroxy and ketone oxylipins than other oils, despite their low LA content. Algae oils had the least amount of oxylipins. The change in oxylipin concentrations was not significantly different among the oils after short-term heating. The estimated oxylipin intake from nonheated soybean, canola, corn, and olive oil was 1.1 mg per person per day. These findings suggest that oils represent a dietary source of LA and ALA derived oxylipins and that the response of oils to short-term heating does not differ among the various oils.

The importance of antioxidants which play the role in cellular response against oxidative/nitrosative stress: current state

Remarkable interest has risen in the idea that oxidative/nitrosative stress is mediated in the etiology of numerous human diseases. Oxidative/Nitrosative stress is the result of an disequilibrium in oxidant/antioxidant which reveals from continuous increase of Reactive Oxygen and Reactive Nitrogen Species production. The aim of this review is to emphasize with current information the importance of antioxidants which play the role in cellular responce against oxidative/nitrosative stress, which would be helpful in enhancing the knowledge of any biochemist, pathophysiologist, or medical personnel regarding this important issue. Products of lipid peroxidation have commonly been used as biomarkers of oxidative/nitrosative stress damage. Lipid peroxidation generates a variety of relatively stable decomposition end products, mainly α, β-unsaturated reactive aldehydes, such as malondialdehyde, 4-hydroxy-2-nonenal, 2-propenal (acrolein) and isoprostanes, which can be measured in plasma and urine as an indirect index of oxidative/nitrosative stress. Antioxidants are exogenous or endogenous molecules that mitigate any form of oxidative/nitrosative stress or its consequences. They may act from directly scavenging free radicals to increasing antioxidative defences. Antioxidant deficiencies can develop as a result of decreased antioxidant intake, synthesis of endogenous enzymes or increased antioxidant utilization. Antioxidant supplementation has become an increasingly popular practice to maintain optimal body function. However, antoxidants exhibit pro-oxidant activity depending on the specific set of conditions. Of particular importance are their dosage and redox conditions in the cell.

Does IV Iron Induce Plasma Oxidative Stress in Critically Ill Patients? A Comparison With Healthy Volunteers

OBJECTIVE

To compare the oxidative stress induced by IV iron infusion in critically ill patients and in healthy volunteers.

DESIGN

Multicenter, interventional study.

SETTING

Two ICUs and one clinical research center.

SUBJECTS

Anemic critically ill patients treated with IV iron and healthy volunteers.

INTERVENTIONS

IV infusion of 100 mg of iron sucrose.

MEASUREMENTS AND MAIN RESULTS

Thirty-eight anemic patients (hemoglobin, median [interquartile range] = 8.4 g/dL [7.7-9.2]) (men, 25 [66%]; aged 68 yr [48-77]; Simplified Acute Physiology Score II, 48.5 [39-59]) and 39 healthy volunteers (men, 18 [46%]; aged 42.1 yr [29-50]) were included. Blood samples were drawn before (H0) and 2, 6, and 24 hours (H2, H6, and H24) after a 60-minute iron infusion for the determination of nontransferrin bound iron, markers of lipid peroxidation-8α-isoprostanes, protein oxidation-advanced oxidized protein product, and glutathione reduced/oxidized. Iron infusion had no effect on hemodynamic parameter in patients and volunteers. At baseline, patients had much higher interleukin-6, C-reactive protein, and hepcidin levels. 8α-isoprostanes was also higher in patients at baseline (8.5 pmol/L [6.5-12.9] vs 4.6 pmol/L [3.5-5.5]), but the area under the curve above baseline from H0 to H6 was not different (p = 0.38). Neither was it for advanced oxidized protein product and nontransferrin bound iron. The area under the curve above baseline from H0 to H6 (glutathione reduced/oxidized) was lower in volunteers (p = 0.009). Eight patients had a second set of dosages (after the fourth iron infusion), showing higher increase in 8α-isoprostanes.

CONCLUSIONS

In our observation, IV iron infusion does not induce more nontransferrin bound iron, lipid, or protein oxidation in patients compared with volunteers, despite higher inflammation, oxidative stress, and hepcidin levels and lower antioxidant at baseline. In contrary, iron induces a greater decrease in antioxidant, compatible with higher oxidative stress in volunteers than in critically ill patients.

Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73)

OBJECTIVE

To examine the traditional diet-heart hypothesis through recovery and analysis of previously unpublished data from the Minnesota Coronary Experiment (MCE) and to put findings in the context of existing diet-heart randomized controlled trials through a systematic review and meta-analysis.

DESIGN

The MCE (1968-73) is a double blind randomized controlled trial designed to test whether replacement of saturated fat with vegetable oil rich in linoleic acid reduces coronary heart disease and death by lowering serum cholesterol. Recovered MCE unpublished documents and raw data were analyzed according to hypotheses prespecified by original investigators. Further, a systematic review and meta-analyses of randomized controlled trials that lowered serum cholesterol by providing vegetable oil rich in linoleic acid in place of saturated fat without confounding by concomitant interventions was conducted.

SETTING

One nursing home and six state mental hospitals in Minnesota, United States.

PARTICIPANTS

Unpublished documents with completed analyses for the randomized cohort of 9423 women and men aged 20-97; longitudinal data on serum cholesterol for the 2355 participants exposed to the study diets for a year or more; 149 completed autopsy files.

INTERVENTIONS

Serum cholesterol lowering diet that replaced saturated fat with linoleic acid (from corn oil and corn oil polyunsaturated margarine). Control diet was high in saturated fat from animal fats, common margarines, and shortenings.

MAIN OUTCOME MEASURES

Death from all causes; association between changes in serum cholesterol and death; and coronary atherosclerosis and myocardial infarcts detected at autopsy.

RESULTS

The intervention group had significant reduction in serum cholesterol compared with controls (mean change from baseline -13.8%v-1.0%; P<0.001). Kaplan Meier graphs showed no mortality benefit for the intervention group in the full randomized cohort or for any prespecified subgroup. There was a 22% higher risk of death for each 30 mg/dL (0.78 mmol/L) reduction in serum cholesterol in covariate adjusted Cox regression models (hazard ratio 1.22, 95% confidence interval 1.14 to 1.32; P<0.001). There was no evidence of benefit in the intervention group for coronary atherosclerosis or myocardial infarcts. Systematic review identified five randomized controlled trials for inclusion (n=10,808). In meta-analyses, these cholesterol lowering interventions showed no evidence of benefit on mortality from coronary heart disease (1.13, 0.83 to 1.54) or all cause mortality (1.07, 0.90 to 1.27).

CONCLUSIONS

Available evidence from randomized controlled trials shows that replacement of saturated fat in the diet with linoleic acid effectively lowers serum cholesterol but does not support the hypothesis that this translates to a lower risk of death from coronary heart disease or all causes. Findings from the Minnesota Coronary Experiment add to growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid.

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.

Clinical perspective on oxidative stress in sporadic amyotrophic lateral sclerosis

Sporadic amyotrophic lateral sclerosis (ALS) is one of the most devastating neurological diseases; most patients die within 3 to 4 years after symptom onset. Oxidative stress is a disturbance in the pro-oxidative/antioxidative balance favoring the pro-oxidative state. Autopsy and laboratory studies in ALS indicate that oxidative stress plays a major role in motor neuron degeneration and astrocyte dysfunction. Oxidative stress biomarkers in cerebrospinal fluid, plasma, and urine are elevated, suggesting that abnormal oxidative stress is generated outside of the central nervous system. Our review indicates that agricultural chemicals, heavy metals, military service, professional sports, excessive physical exertion, chronic head trauma, and certain foods might be modestly associated with ALS risk, with a stronger association between risk and smoking. At the cellular level, these factors are all involved in generating oxidative stress. Experimental studies indicate that a combination of insults that induce modest oxidative stress can exert additive deleterious effects on motor neurons, suggesting that multiple exposures in real-world environments are important. As the disease progresses, nutritional deficiency, cachexia, psychological stress, and impending respiratory failure may further increase oxidative stress. Moreover, accumulating evidence suggests that ALS is possibly a systemic disease. Laboratory, pathologic, and epidemiologic evidence clearly supports the hypothesis that oxidative stress is central in the pathogenic process, particularly in genetically susceptive individuals. If we are to improve ALS treatment, well-designed biochemical and genetic epidemiological studies, combined with a multidisciplinary research approach, are needed and will provide knowledge crucial to our understanding of ALS etiology, pathophysiology, and prognosis.

Caffeoylquinic acid-rich extract from chicory seeds improves glycemia, atherogenic index, and antioxidant status in rats

OBJECTIVE

Comparison of the effects of a high-fructose diet supplemented with rutin, a phenolic compound with well-recognized bioavailability and bioactivity, and a chicory (Cichorium intybus L.) seed extract rich in caffeoylquinic acids (CQA) on gut physiology and the development of disorders related to metabolic syndrome.

METHODS

A 28-d experiment was conducted on 32 young male Wistar rats. In comparison with control rats fed a standard corn starch diet (group C), the experimental group (group E) was fed a diet with an increased content of cholesterol and fructose (to 1% and 66% of the diet, respectively), as well as with oxidized soybean oil. Rats from the other two experimental groups were administered the same diet as group E during the first 2 wk of feeding, whereas at the beginning of the last 2 wk, the diet was enriched with rutin (group ER) or the CQA-rich ethanol extract from chicory seeds (9.6% of CQA, group EC), so the amount of added phenolics was equal in both dietary groups (0.15%).

RESULTS

The diet administered in group E caused hyperglycemia and increased blood serum atherogenicity in rats, but did not induce other manifestations of the metabolic syndrome, i.e., dyslipidemia and oxidative stress. Additionally, it affected gut physiology through increasing mucosal sucrase activity and disturbing fermentative processes in the cecum, such as the production of short-chain fatty acids and the activity of microbial enzymes. Similarly to rutin, the dietary addition of the chicory seed extract improved glycemia, which was comparable to that determined in group C. In addition, the extract was found to decrease the atherogenic index to the level observed in group C and to increase blood antioxidant status. Both dietary supplements reduced the content of thiobarbituric acid-reactive substances in kidney and heart tissue when compared with group E.

CONCLUSION

The potential efficacy of the CQA-rich extract from chicory seeds in improving diet-induced metabolic disturbances proved to be better than that of rutin; thus, the extract might be considered as a dietary supplement for carrying out clinical trials.

The oxidative state of chylomicron remnants influences their modulation of human monocyte activation

Chylomicron remnants (CMRs) contribute directly to human monocyte activation in vitro, by increasing reactive oxygen species (ROS) production and cell migration. In this study, the effects of the oxidative state of CMR on the degree of monocyte activation was investigated. CMR-like particles (CRLPs) were prepared in three different oxidative states, normal (CRLPs), protected from oxidation by incorporation of the antioxidant, probucol (pCRLPs), or oxidised with CuSO(4) (oxCRLPs). Lipid accumulation and ROS production were significantly increased in primary human monocytes incubated with CRLPs, whilst secretion on monocyte chemoattractant protein-1 was reduced, but oxCRLPs had no additional effect. In contrast, pCRLPs were taken up by monocytes to a lesser extent and had no significant effect on ROS or MCP-1 secretion. These studies suggest that the oxidative state of CMRs modulates their stimulation of the activation of peripheral blood human monocytes and that dietary antioxidants may provide some protection against these atherogenic effects.

Biomarkers of oxidative and nitrosative damage in Alzheimer's disease and mild cognitive impairment

Alzheimer's disease (AD) is the most common type of dementia in the elderly. Products of oxidative and nitrosative stress (OS and NS, respectively) accumulate with aging, which is the main risk factor for AD. This provides the basis for the involvement of OS and NS in AD pathogenesis. OS and NS occur in biological systems due to the dysregulation of the redox balance, caused by a deficiency of antioxidants and/or the overproduction of free radicals. Free radical attack against lipids, proteins, sugars and nucleic acids leads to the formation of bioproducts whose detection in fluids and tissues represents the currently available method for assessing oxidative/nitrosative damage. Post-mortem and in-vivo studies have demonstrated an accumulation of products of free radical damage in the central nervous system and in the peripheral tissues of subjects with AD or mild cognitive impairment (MCI). In addition to their individual role, biomarkers for OS and NS in AD are associated with altered bioenergetics and amyloid-beta (Abeta) metabolism. In this review we discuss the main results obtained in the field of biomarkers of oxidative/nitrosative stress in AD and MCI in humans, in addition to their potential role as a tool for diagnosis, prognosis and treatment efficacy in AD.

Different patterns of oxidized lipid products in plasma and urine of dengue fever, stroke, and Parkinson's disease patients: cautions in the use of biomarkers of oxidative stress

Many products of lipid oxidation have been associated with human diseases. These include F2-isoprostanes (F2-IsoPs), hydroxyeicosatetraenoic acid products (HETEs), and cholesterol oxidation products (COPs). Here we present measurements of F2-IsoPs, HETEs, COPs, and arachidonate in single plasma samples of patients with acute (dengue fever and ischemic stroke) and chronic (Parkinson's) diseases, and in age-matched study controls. Urine samples were collected for F2-IsoPs analysis. Our analysis demonstrated elevated F2-IsoPs levels in ischemic stroke, HETEs in Parkinson's disease, dengue fever, and ischemic stroke, and COPs in Parkinson's disease and dengue fever patients, as compared with those in age-matched study controls. Strong but complex correlations were observed between levels of certain oxidized lipid products and age. The relations between various oxidized lipids and dengue fever, stroke, and Parkinson's disease are discussed in relation to the selection and application of biomarkers of oxidative lipid damage, in particular the need for corrections for age and lipid levels.

Antiserum detection of reactive carbonyl species-modified DNA in human colonocytes

Polyunsaturated fats have been linked to occurrences of sporadic colon cancer. One possible cause may be degradation of polyunsaturated fats during cooking, resulting in multiple reactive carbonyl species (RCS) that can damage nuclear DNA and proteins, particularly in rapidly dividing colon crypt cells. This study describes a novel antiserum against RCS-modified DNA, with apparent order of reactivity to DNA modified with 4-hydroxy-trans-2-nonenal > glyoxal > acrolein > crotonaldehyde > malondialdehyde; some reactivity was also observed against conjugated Schiff base-type structures. Anti-(RCS-DNA) antiserum was successfully utilised to demonstrate formation of RCS-DNA in a human colon cell model, exposed to RCS insult derived from endogenous and exogenous lipid peroxidation sources. Further utilisation of the antiserum for immunohistochemical analysis confirmed RCS-modified DNA in crypt areas of 'normal' colon tissue. These results fully support a potential role for dietary lipid peroxidation products in the development of sporadic colon cancer.

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.

Lipid peroxidation products as oxidative stress biomarkers

Oxidative stress induced by reactive oxygen and nitrogen species has been implicated in the pathogenesis of various disorders and diseases. Biomarkers are needed for assessment of oxidative stress status in vivo and also for health examination, diagnosis at early stage, prognosis, safe and efficient drug development, and evaluation of efficacy of drugs, foods, beverages, and supplements. Lipids are susceptible to oxidation and lipid peroxidation products are potential biomarkers for oxidative stress status in vivo and its related diseases. Recently, isoprostane, isoprostaglandin homologues from arachidonic acid, neuroprostanes from docosahexaenoic acid, hydroxyoctadecadienoic acid from linoleic acid, and oxysterols from cholesterol have received much attention as potential biomarkers for oxidative stress status in vivo. The physiological levels of these lipid peroxidation products and potential application as biomarkers will be reviewed.

Chromatographic and electrophoretic methods for the analysis of biomarkers of oxidative damage to macromolecules (DNA, lipids, and proteins)

Free radicals and other reactive species can cause oxidative damage to biomolecules when oxidant species exceed the antioxidant defences in the body, resulting in oxidative stress. Oxidatively damaged products have been associated with aging as well as with the development of pathologies like cancer, cardiovascular disease, neurodegenerative disorders, diabetes, inflammation, etc. Reliable measurements of biomarkers of oxidative damage to macromolecules would afford information on the pre-disposition and prognosis of certain pathologies, being of utmost importance in evaluation of the effect of intervention with antioxidants on the incidence of diseases associated to oxidative stress. This review will present and compare different analytical methods, especially those involving chromatographic and electrophoretic techniques, commonly used for the analysis of biomarkers of oxidative damage to the three main macromolecules, namely oxidised DNA, lipid peroxidation products, and protein carbonyls.

Protection of lipids from oxidation by epicatechin, trans-resveratrol, and gallic and caffeic acids in intestinal model systems

Consumption of polyphenols is associated with health promotion through diet, although many are poorly absorbed in animals and humans alike. Lipid peroxides may reach the intestine and initiate deleterious oxidation. Here we measured inhibition of the oxidation of linoleic acid (LA) in authentic fluid from rat small intestine (RIF) by two dietary polyphenols, a flavonoid, epicatechin (EC), and a stilbene, resveratrol (RV), and by gallic (GA) and caffeic (CA) acids, and their partition coefficients. Both polyphenols inhibited 80%, and CA inhibited 65%, of the production of hexanal. GA was the weakest antioxidant in this assay. Interestingly, measuring peroxides production in RIF showed that only epicatechin inhibited the first stage of oxidation. The oxidizing agent, the antioxidant comound, the solution pH and lipophilicity are known to affect the total antioxidative activity. We suggest that the mechanism of this activity changes in accord with the environment: i.e., RV may act as a free radial scavenger, but here, in protecting lipids in intestinal fluid from oxidation, it acts as a hydrogen atom donor. Since the concentration of phenolics is much higher in the intestinal fluid than is ever achieved in plasma or other body tissues, it is suggested that their antioxidant activity could be exerted in the gastrointestinal tract (GIT), breaking the propagation of lipid peroxides oxidation and production of toxic compounds.

Biomarkers of oxidative damage in human disease

Oxidative/nitrosative stress, a pervasive condition of increased amounts of reactive oxygen/nitrogen species, is now recognized to be a prominent feature of many acute and chronic diseases and even of the normal aging process. However, definitive evidence for this association has often been lacking because of recognized shortcomings with biomarkers and/or methods available to assess oxidative stress status in humans. Emphasis is now being placed on biomarkers of oxidative stress, which are objectively measured and evaluated as indicators of normal biological processes, pathogenic processes, or pharmacologic responses to therapeutic intervention. To be a predictor of disease, a biomarker must be validated. Validation criteria include intrinsic qualities such as specificity, sensitivity, degree of inter- and intraindividual variability, and knowledge of the confounding and modifying factors. In addition, characteristics of the sampling and analytical procedures are of relevance, including constraints and noninvasiveness of sampling, stability of potential biomarkers, and the simplicity, sensitivity, specificity, and speed of the analytical method. Here we discuss some of the more commonly used biomarkers of oxidative/nitrosative damage and include selected examples of human studies.

Limited effects of combined dietary copper deficiency/iron overload on oxidative stress parameters in rat liver and plasma

Copper (Cu) deficiency decreases the activity of Cu-dependent antioxidant enzymes such as Cu,zinc-superoxide dismutase (Cu,Zn-SOD) and may be associated with increased susceptibility to oxidative stress. Iron (Fe) overload represents a dietary oxidative stress relevant to overuse of Fe-containing supplements and to hereditary hemochromatosis. In a study to investigate oxidative stress interactions of dietary Cu deficiency with Fe overload, weanling male Long-Evans rats were fed one of four sucrose-based modified AIN-93G diets formulated to differ in Cu (adequate 6 mg/kg diet vs. deficient 0.5 mg/kg) and Fe (adequate 35 mg/kg vs. overloaded 1500 mg/kg) in a 2 x 2 factorial design for 4 weeks prior to necropsy. Care was taken to minimize oxidation of the diets prior to feeding to the rats. Liver and plasma Cu content and liver Cu,Zn-SOD activity declined with Cu deficiency and liver Fe increased with Fe overload, confirming the experimental dietary model. Liver thiobarbituric acid reactive substances were significantly elevated with Fe overload (pooled across Cu treatments, 0.80+/-0.14 vs. 0.54+/-0.08 nmol/mg protein; P<.0001) and not affected by Cu deficiency. Liver cytosolic protein carbonyl content and the concentrations of several oxidized cholesterol species in liver tissue did not change with these dietary treatments. Plasma protein carbonyl content decreased in Cu-deficient rats and was not influenced by dietary Fe overload. The various substrates (lipid, protein and cholesterol) appeared to differ in their susceptibility to the in vivo oxidative stress induced by dietary Fe overload, but these differences were not exacerbated by Cu deficiency.

Effects of low-fat and/or high-fruit-and-vegetable diets on plasma levels of 8-isoprostane-F2alpha in the Nutrition and Breast Health study

Dietary patterns that involve both a decrease in fat and an increase in fruit and vegetable (FV) intake may decrease cancer risks. In this study, a total of 122 premenopausal women with a family history of breast cancer were randomized into one of four diets for 12 mo: nonintervention, low-fat (15% of energy from fat), high-FV(9 servings/d), and combination low-fat/high-FV Fasting blood samples were obtained at baseline and after 3, 6, and 12 mo. Levels of 8-isoprostane-F2a in plasma were deter-mined by immunoassay kits. Statistical analyses indicated that levels of 8-isoprostane-F2a decreased significantly with time in the low-fat arm, which is the only intervention that resulted in weight loss; there were no significant changes in the other three diet arms. It is unlikely that this is due to changes in levels of blood lipids because there was little change overtime in plasma total cholesterol, high-density lipoprotein,low-density lipoprotein (LDL), or triglyceride levels in any diet arm, although mean LDL did decrease slightly in women who reduced fat intake after adjustment for change in body mass index (BMI). Levels of baseline 8-isoprostane-F2a were significantly higher in obese women than in overweight or normal weight women, and change in BMI was significantly correlated with change in 8-isoprostane-F2a levels. These results indicate that low-fat diets or high-FV diets are unlikely to affect plasma levels of 8-isoprostane-F2a in healthy,premenopausal women who do not lose weight during dietary change.

Measuring reactive species and oxidative damage in vivo and in cell culture: how should you do it and what do the results mean?

Free radicals and other reactive species (RS) are thought to play an important role in many human diseases. Establishing their precise role requires the ability to measure them and the oxidative damage that they cause. This article first reviews what is meant by the terms free radical, RS, antioxidant, oxidative damage and oxidative stress. It then critically examines methods used to trap RS, including spin trapping and aromatic hydroxylation, with a particular emphasis on those methods applicable to human studies. Methods used to measure oxidative damage to DNA, lipids and proteins and methods used to detect RS in cell culture, especially the various fluorescent "probes" of RS, are also critically reviewed. The emphasis throughout is on the caution that is needed in applying these methods in view of possible errors and artifacts in interpreting the results.

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.

Oxidized lipid depresses canine growth, immune function, and bone formation

Dietary oxidized lipids can increase oxidative stress and potentially contribute to a variety of disease syndromes. This research describes the first use of a canine model to assess the effects of dietary oxidized lipids on growth, antioxidant status, and some immune functions. Three groups of eight, two-month old coon-hound puppies were pair fed diets for 16 weeks. The control diet contained <50 ppm aldehydes, and two additional diets contained thermally oxidized lipids targeted to contain 100 ppm aldehydes (medium-oxidation) and 500 ppm aldehydes (high-oxidation). Dogs fed the high-oxidation diet weighed less than those from the medium-oxidation (P < 0.05) and control groups (P < 0.001) at the end of the study. Oxidized lipids reduced serum vitamin E levels, total body fat content, and bone appositional rate. At different time points of the study, peripheral blood neutrophils and monocytes from dogs fed the HO diet had reduced oxidative burst capacity and produced less superoxide and hydrogen peroxide when stimulated with phorbol esters compared to the control group. Lymphocyte blastogenesis in response to concanavalin A was suppressed by dietary oxidized lipid. This study indicates that dietary oxidized lipids negatively affect the growth, antioxidant status, and some immune functions of dogs. Importantly, some effects are evident at 100 ppm aldehydes in the diet, which is a moderate level of oxidation. The rapid growth and weight gain of the dog during the first 6 months of life may also provide a better model for assessing the risks of dietary oxidized lipid in children and adolescents than previously used rodent models.

Simultaneous determination by GC-MS of epoxy and hydroxy FA as their methoxy derivatives

We report on a capillary GC-MS method for the quantitative analysis of hydroxy and epoxy FA. Catalytic hydrogenation of lipid extracts produces stable saturated lipids. Saponification followed by methylation with boron trifluoride in the presence of methanol converts FA to methyl esters and epoxy groups to methoxy-hydroxy groups. These compounds are purified from nonoxidized methyl esters using solid phase extraction. Derivatization of the hydroxy group using tetramethylammonium hydroxide forms methoxy and vicinal dimethoxy FAME. When subjected to EI-MS, fragmentation gives two characteristic ion fragments for each epoxy and hydroxy positional isomer. Quantitative measurements were achieved using uniformly labeled hydroxy and epoxy 13C FA as internal standards. Epoxy and hydroxy FA were identified in both plasma and adipose tissue of men, and the levels of hydroxy and epoxy in these tissues were related. The levels of hydroxy isomers were typical of oxidation of linoleic acid, whereas epoxy isomers were characteristic of oxidation of oleic acid.