Determination of Oxidized Lipids in Commonly Consumed Foods and a Preliminary Analysis of Their Binding Affinity to PPARγ.

Foods rich in poly unsaturated fatty acids (PUFA) are vulnerable to oxidation. While it is well established that endogenously derived oxidized lipids are ligands of the transcription factor PPARγ, the binding ability of diet-derived oxidized lipids is unknown. Our two-fold objective was to determine the oxidized lipid content and PPARγ binding ability of commonly consumed foods. Extracted food lipids were assayed for the peroxide value, conjugated dienes, and aldehydes, and PPARγ binding was assessed by an in vitro PPARγ ligand screening assay. Oxidized lipids were present in all foods tested at the time of purchase, and oxidation did not increase during storage. The peroxide values for walnuts, sunflower seeds, and flax meal were significantly lower at the end of three months as compared to the day of purchase (peroxide value: 1.26 ± 0.13 vs. 2.32 ± 0.4; 1.65 ± 0.23 vs. 2.08 ± 0.09; 3.07 ± 0.22 vs. 9.94 ± 0.75 mEq/kg fat, p ≤ 0.05, respectively). Lipids extracted from French fries had the highest binding affinity (50.87 ± 11.76%) to PPARγ compared to other foods. Our work demonstrates that oxidized lipids are present in commonly consumed foods when purchased, and for the first time demonstrates that some contain ligands of PPARγ.

A Novel Technique for Redox Lipidomics Using Mass Spectrometry: Application on Vegetable Oils Used to Fry Potatoes.

Vegetables oils, rich in polyunsaturated fatty acids, are vulnerable to oxidation during manufacturing, processing, and food preparation. Currently, individual oxidation products are not well characterized, and hence, the health impacts of these unique lipid species remain unknown. Here, we introduce an extensive oxidized lipidomics in silico tandem mass spectrometry library and integrate these libraries within a user-friendly software covering a comprehensive redox lipidomics workflow. We apply this workflow to olive, soy, and walnut cooking oil; comparing unheated oil, oil after deep frying potatoes, and oil after oven frying potatoes. We annotated over a thousand oxidized triglycerides across 273 features (many coeluted). This software was validated against traditional chemical assays of oxidation, known oxidized lipids in castor oil, synthesized standards, and an alternate software LPPtiger. Development of these new software programs for redox lipidomics opens the door to characterize health implications of individual oxidation products.

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

BACKGROUND: Our previous work showed that dietary oxidized linoleic acid given, as a single fatty acid, to LDL receptor knockout mice decreased weight gain as compared to control mice. Other studies have also reported that animals fed oils heated for 24 h or greater showed reduced weight gain. These observations, while important, have limited significance since fried foods in the typical human diet do not contain the extreme levels of oxidized lipids used in these studies. The main goal of this study was to investigate the effects of a diet containing soybean oil heated for 3 h on weight gain and fat pad mass in mice. Additionally, because PPARγ and UCP-1 mediate adipocyte differentiation and thermogenesis, respectively, the effect of this diet on these proteins was also examined. FINDINGS: Four to six week old male C57BL/6 J mice were randomly divided into three groups and given either a low fat diet with heated soybean oil (HSO) or unheated soybean oil (USO) or pair fed for 16 weeks. Weight and food intake were monitored and fat pads were harvested upon the study's termination. Mice consuming the HSO diet had significantly increased fat pad mass but gained less weight as compared to mice in the USO group despite a similar caloric intake and similar levels of PPARγ and UCP1. CONCLUSION: This is the first study to show that a diet containing soybean oil heated for a short time increases fat mass despite a decreased weight gain in C57BL/6 J mice. The subsequent metabolic consequences of this increased fat mass merits further investigation.

Nutraceuticals as Ligands of PPARγ.

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated nuclear receptors that respond to several exogenous and endogenous ligands by modulating genes related to lipid, glucose, and insulin homeostasis. PPARγ, expressed in adipose tissue and liver, regulates lipid storage and glucose metabolism and is the target of type 2 diabetes drugs, thiazolidinediones (TZDs). Due to high levels of toxicity associated with the first generation TZDs, troglitazone (Rezulin), rosiglitazone (Avandia), and pioglitazone (Actos), there is a renewed search for newer PPAR drugs that exhibit better efficacy but lesser toxicity. In recent years, there has been a definite increase in the consumption of dietary supplements among diabetics, due to the possible health benefits associated with these nutraceutical components. With this impetus, investigations into alternative natural ligands of PPARs has also risen. This review highlights some of the dietary compounds (dietary lipids, isoflavones, and other flavanoids) that bind and transactivate PPARγ. A better understanding of the physiological effects of this PPAR activation by nutraceuticals and the availability of high-throughput technologies should lead to the discovery of less toxic alternatives to the PPAR drugs currently on the market.

Use of a food frequency questionnaire to fulfill the research competency requirement for dietetics students.

This article describes a research project developed by the Nutrition Division at Georgia State University (GSU). The project involved students' development of a food frequency questionnaire (FFQ) and satisfied the research competency requirements of the American Dietetic Association's accrediting body. Both Coordinated Program students and Dietetic Interns from a variety of research training backgrounds were trained as a single group on topics related to the research requirements and that would prepare them to develop and use a FFQ. Students completed a literature review on a nutrient or food group of interest and received training on human subject research, subject recruitment, and data analysis with statistical methods. They then developed, administered, and analyzed the results of a FFQ and compared it to a gold standard FFQ. GSU nutrition professors conducted pre- and post-session surveys to gauge whether students gained the research skills they need. Students' evaluation of the assignment strongly suggests that they felt more capable of calculating and interpreting results from survey data after completing the project. The present article provides a framework other nutrition educators can follow. Other allied health educators can consider designing similar research projects that: (a) are uniquely relevant to their professional competency requirements, (b) are feasible for students from a variety of research training backgrounds, and (c) allow students to practice using research tools and skills frequently used in their profession.

Skeletal muscle lipid peroxidation and insulin resistance in humans.

OBJECTIVE: The relationships among skeletal muscle lipid peroxidation, intramyocellular lipid content (IMCL), and insulin sensitivity were evaluated in nine insulin-sensitive (IS), 13 insulin-resistant (IR), and 10 adults with type 2 diabetes (T2DM). DESIGN: Insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp [glucose disposal rate (GDR)]. Lipid peroxidation was assessed by 4-hydroxynonenal (HNE)-protein adducts and general oxidative stress by protein carbonyl content. All patients were sedentary. RESULTS: Protein-HNE adducts were elevated 1.6-fold in T2DM compared with IS adults, whereas IR showed intermediate levels of HNE-modified proteins. Protein-HNE adducts correlated with GDR, waist circumference, and body mass index. IMCL was increased by 4.0- and 1.9-fold in T2DM and IR patients, respectively, compared with IS, and was correlated with GDR and waist circumference but not BMI. Protein carbonyls were not different among groups and did not correlate with any of the measured variables. Correlations were detected between IMCL and protein-HNE. CONCLUSION: Our data show for the first time that skeletal muscle protein-HNE adducts are related to the severity of insulin resistance in sedentary adults. These results suggest that muscle lipid peroxidation could be involved in the development of insulin resistance.

Modulation of leptin levels by oxidized linoleic acid: a connection to atherosclerosis?

The objective of the study was to determine the effects of oxidized linoleic acid (Ox-LA) on plasma leptin and to determine the relationship between plasma leptin levels and atherosclerosis in animals treated with Ox-LA. Low-density lipoprotein (LDL) receptor knockout (LDL r(-/-)) mice were fed a high fat diet with or without Ox-LA for 11 weeks. Plasma leptin levels in the high fat group consuming Ox-LA were significantly higher (14,052 ± 601 pg/mL vs. 10,950 ± 541 pg/mL; P < .01) compared to the group receiving the high fat diet alone. There was a highly significant correlation between the plasma leptin levels and aortic atherosclerotic lesions. From this we conclude that chronic exposure to dietary Ox-LA increases the plasma levels of leptin in LDL r(-/-) mice on a high fat diet. Considering our previous finding that dietary Ox-LA increased atherosclerosis, the current findings emphasize the need to reduce dietary intake of oxidized fat.

Librarian involvement in a nutrition undergraduate research course: preparing nutrition students for evidence-based practice.

Given the foundational importance of literature searching skills to later stages of research and, ultimately, evidence-based practice, the authors wanted to assess a unique strategy for teaching such skills. This pilot study describes the results of an undergraduate nutrition research course in which a librarian lead several class sessions. The goal of this study was to assess students' perceptions, attitudes and use of research literature and resources before and after a course partially taught by a librarian. Twenty-seven students enrolled in an undergraduate Introduction to Research course at Georgia State University were given pre- and post-test questionnaires at the beginning and end of a course that included three librarian-led class sessions. Most of the results indicate that the repeated involvement of a librarian enriched this particular undergraduate research course. By the end of the course, students were more comfortable in libraries and with using library resources; they used the campus library more frequently; they were more confident in their ability to find high-quality information on nutrition-related topics and identify strengths and weaknesses of different information sources; and they felt they gained skills that will help them achieve their educational and career goals.

Temporal changes in trying to lose weight and recommended weight-loss strategies among overweight and obese Americans, 1996-2003.

OBJECTIVES: We examined whether the reported prevalence of trying to lose weight among overweight and obese individuals has changed over time, and whether those trying to lose weight report using recommended weight-loss strategies. METHODS: We used Behavioral Risk Factor Surveillance System data from 50 states and the District of Columbia during 1996, 1998, 2000, and 2003. The sample included participants with a self-reported Body Mass Index (BMI) of > or =25.0 kg/m(2) (N=333,378). The prevalence of trying to lose weight and eating fewer calories, using physical activity, or both, were examined for endpoint change and linear trends. RESULTS: Between 1996 and 2003, the prevalence of trying to lose weight among obese individuals increased significantly, while it remained stable among overweight individuals. The prevalence of eating fewer calories, using physical activity and using a combination of both increased significantly over time among the overweight and obese individuals trying to lose weight. CONCLUSION: Despite a rise in the number of overweight and obese people, there was little change among overweight adults in trying to lose weight over time, and a modest-but significant-change among obese adults in trying to lose weight over time. Among those who reported trying to lose weight, there were significant increases in their efforts to use recommended strategies.

Incorporating a new bioinformatics component into genetics at a historically black college: outcomes and lessons.

Many students at minority-serving institutions are underexposed to Internet resources such as the human genome project, PubMed, NCBI databases, and other Web-based technologies because of a lack of financial resources. To change this, we designed and implemented a new bioinformatics component to supplement the undergraduate Genetics course at Clark Atlanta University. The outcomes of the Bioinformatics course were assessed. During the first week of the semester, students were assigned the Felder-Soloman's Index of Learning Styles Inventory. The overwhelming majority of students were visual (82.1%) and sequential (75.0%) learners. Furthermore, pre- and postcourse surveys were administered during the first and the last week of the course to assess learning, confidence level, and mental activity. These indicated students increased the number of hours spent using computers and doing homework. Students reported confidence in using computers to study genetics increased, enabling them to better visualize and understand genetics. Furthermore, students were more mentally engaged in a more social learning environment. Although the students appreciated the value of the bioinformatics component, they reported the additional work load was substantial enough to receive additional course credit.

Inhibition of atherosclerosis in low-density lipoprotein receptor-negative mice by sesame oil.

Diet has profound effects on the development of atherosclerosis. Fatty acid composition, antioxidants, and other components such as lignans have major effects on the atherosclerotic process. Sesame oil has both mono- and polyunsaturated fatty acid constituents in equal proportions. In addition, it also has high levels of numerous antioxidants and inducers of peroxisome proliferator-activated receptor. The objective of this study was to determine the anti-atherosclerotic effects of sesame oil. In this study, male low-density lipoprotein (LDL) receptor (LDLR) -/- mice were fed atherogenic diet or atherogenic diet reformulated with the same level of sesame oil (sesame oil diet). Plasma lipids and atherosclerotic lesions were quantified after 3 months of feeding. Sesame oil-containing diet significantly reduced the atherosclerotic lesion formation and plasma cholesterol, triglyceride, and LDL cholesterol levels in LDLR -/- mice. These findings suggest that sesame oil could inhibit atherosclerosis lesion formation effectively, perhaps because of the synergistic actions of fatty acid and nonsaponifiable components.

Exercise might favor reverse cholesterol transport and lipoprotein clearance: potential mechanism for its anti-atherosclerotic effects.

Livers of C57 BL/6 mice exercised for 2 weeks showed a dramatic increase in scavenger receptor B1 (SR-B1), CD36 and low density lipoprotein (LDL) receptor and a decrease in acetyl LDL receptor gene expression. These effects on lipoprotein receptors are reminiscent of the effects mediated by peroxisome proliferator-activated receptor (PPARgamma) ligands.

Exercise reduces preexisting atherosclerotic lesions in LDL receptor knock out mice.

Exercise is recommended both as a prophylactic and also as a therapeutic approach for patients with established coronary artery disease. In this study, we investigated the effect of a normal chow diet, with or without exercise in LDL r-/- mice with preexisting atherosclerotic lesions. A total of 28 LDL r-/- mice (LDL receptor knock out mice, 4-6 weeks old) were fed a high fat, high cholesterol diet (inductive phase). At the end of the 3 months, eight mice were sacrificed, and plasma autoantibodies to oxidatively modified proteins, cholesterol levels, and surface area of the lesions in the aorta were determined. The remaining mice were divided into two groups, and placed on a normal chow diet alone, or normal chow and exercise for three more months (regressive phase). Plasma autoantibodies to oxidatively modified proteins and cholesterol were measured along with the lesion size. Compared to the group of animals at the end of the inductive phase, both the groups of animals in the regressive phase had very low levels of plasma cholesterol and autoantibodies, and almost a 50% reduction in the aortic lesion area. The group that was exercised had the lowest levels of autoantibodies and aortic lesions as compared to the group without the exercise. However, the plasma cholesterol levels were comparable in both groups. This study demonstrates that reduction of preexisting atherosclerotic lesions is accelerated dramatically by exercise in LDL r-/- mice.

Oxidized fatty acids promote atherosclerosis only in the presence of dietary cholesterol in low-density lipoprotein receptor knockout mice.

Studies suggest that heated oils contribute to the presence of oxidized components in the circulating lipoproteins and to the development of atherosclerosis in animals. We evaluated the effects of 11-13 wk of consumption of a well defined dietary oxidized fatty acid, 13-hydroxylinoleic acid (13-HODE) (8 mg), on atherosclerotic lesion development and plasma cholesterol concentrations in mice fed diets varying in fat and cholesterol contents. LDL receptor knockout mice were used in two feeding studies. In study 1, oxidized fatty acid consumption in association with a high fat diet increased aortic lesion areas by >100% (P < 0.05). Surprisingly, oxidized fatty acid intake also tended to increase plasma total cholesterol (P = 0.12) and LDL cholesterol (P < 0.05) as well as oxidative stress as measured by higher levels of autoantibodies to oxidatively modified proteins (P = 0.008). However, in mice fed a nonpurified diet, oxidized fatty acids were not atherogenic and may even have been beneficial, as indicated by a lower plasma triglyceride (TG) concentration (P < 0.05). In study 2, mice were fed either a high fat, medium fat or low fat diet to evaluate whether the increase in aortic lesions due to oxidized fatty acid consumption in study 1 was a result of the associated higher plasma total and LDL cholesterol concentrations. In study 2, 13-HODE-treated mice in the medium and low fat diet groups but not those fed the high fat diet had larger atherosclerotic lesions (P < 0.05). Additionally, plasma total and LDL cholesterol as well as TG were not affected by HODE treatment. However, the total cholesterol:HDL cholesterol ratio was higher in treated mice (P < 0.05) and HDL cholesterol was lower in HODE-treated mice that were fed the low fat diet (P < 0.05). Our results suggest that, in mice fed cholesterol, oxidized fatty acids may be atherogenic, both in terms of increased oxidative stress (as seen in study 1) and by increasing the atherogenicity of the plasma cholesterol profile.

Enhanced solubilization and intestinal absorption of cholesterol by oxidized linoleic acid.

Solubilization of cholesterol in the intestinal lumen by bile acids and the subsequent formation of mixed micelles is an important step in the absorption of cholesterol. We propose that oxidized fatty acids (ox-FA) may mimic bile acids and form mixed micelles with cholesterol much more efficiently, as compared with unoxidized fatty acids, thereby increasing there absorption. In an in vitro assay at concentrations of 1, 5, and 10 mM, oxidized linoleic acid (ox-18:2) increased the solubilization of cholesterol (3.06, 8.16, and 15.46 nmol/ml) in a dose dependent manner compared with a 10 mM unoxidized linoleic acid (unox-18:2 at 0.97 nmol/ml). The uptake of cholesterol solubilized in the presence of ox-18:2 by Caco-2 cells and everted rat intestinal sacs was greater (1.78 and 1.95 nmol/ml respectively) as compared with the cholesterol solubilized in the presence of unox-18:2 (0.29 and 0.61 nmol/ml; P = 0.05). In addition, when LDL receptor deficient mice were fed a high fat diet along with ox-18:2 their plasma cholesterol levels were greater than animals fed the high fat diet alone (1290 mg/dl vs. 1549 mg/dl, P = 0.013). From these results, we suggest that ox-FA, by enhancing the solubilization of luminal cholesterol, increases the uptake of cholesterol that might lead to hypercholesterolemia and atherosclerosis.

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

Apolipoprotein (apo)A-I, the major protein component of HDL, is synthesized principally in the small intestine and liver. Recently we observed an increase in plasma apoA-I level in humans who were on an oxidized fat diet. To test whether oxidized fatty acids could affect apoA-I synthesis, we incubated day 4 (undifferentiated) and day 14 (differentiated) Caco-2 cells with varying concentrations of oxidized linoleic acid (ox-linoleic acid) (5, 10, and 25 microM) and unoxidized linoleic acid for 24 h. Ox-linoleic acid caused a dose-dependent increase in the levels of apoA-I protein in both differentiated and undifferentiated Caco-2 cells as assessed by ELISA and Western blot analysis. Whereas apoB production was not increased by ox-linoleic acid in both day 4 and day 14 Caco-2 cells. The mRNA expression for apoA-I paralleled the protein expression when measured by RT-PCR. We also found that both day 4 and day 14 Caco-2 cells did express peroxisomal proliferator-activated receptor-gamma (PPAR-gamma). mRNA and PPAR-gamma ligand could increase apoA-I secretion in these cells. Therefore we propose that the mechanism for the induction of apoA-I might include PPAR-gamma for which oxidized fatty acid is a ligand.