Effects of dietary polyunsaturated n-3 fatty acids on dyslipidemia and insulin resistance in rodents and humans. A review

Omega-3 improves glucose tolerance but increases lipid peroxidation and DNA damage in hepatocytes of fructose-fed rats

The high consumption of fructose is linked to the increase in various characteristics of the metabolic syndrome. Fish oil is beneficial for the treatment of these comorbidities, such as insulin resistance, dyslipidemia, and hepatic steatosis. The objective of this study was to evaluate the consequences of the administration of fish oil concomitant to fructose ingestion during the experiment (45 days) and during the final 15 days in high-fructose-fed rats. Male Wistar rats were divided into 5 groups: control; those receiving 10% fish oil (FO); those receiving 60% fructose (Fr); those receiving 60% fructose and 10% fish oil for 45 days (FrFO); and those receiving fructose plus soybean oil for 30 days and fish oil for the final 15 days of the study (FrFO15). There was an increase in triacylglycerol, serum total cholesterol, and hepatic volume in the Fr group. The FO and FrFO groups experienced an increase in lipid peroxidation and a decrease in serum reduced glutathione. The FrFO group suffered greater hepatic injury, with increased alanine aminotransferase levels and DNA damage. Marked n-3 incorporation occurred in the groups receiving fish oil, favoring a better response to the oral glucose tolerance test. Fructose induced comorbidities of the metabolic syndrome, and the use of fish oil promoted a better glucose tolerance, although it was accompanied by more hepatocyte damage.

Fish oil normalizes plasma glucose levels and improves liver carbohydrate metabolism in rats fed a sucrose-rich diet

A sucrose-rich diet (SRD) induces insulin resistance and dyslipidemia with impaired hepatic glucose production and gluconeogenesis, accompanied by altered post-receptor insulin signaling steps. The aim of this study was to examine the effectiveness of fish oil (FO) to reverse or improve the impaired hepatic glucose metabolism once installed in rats fed 8 months a SRD. In the liver of rats fed SRD in which FO replaced corn-oil during the last 2 months, as dietary fat, several key enzyme activities and metabolites involved in glucose metabolisms (phosphorylation, glycolysis, gluconeogenesis and oxidative and non oxidative glucose pathway) were measured. The protein mass levels of IRS-1 and αp85 PI-3K at basal conditions were also analyzed. FO improved the altered activities of some enzymes involved in the glycolytic and oxidative pathways observed in the liver of SRD fed rats but was unable to restore the impaired capacity of glucose phosphorylation. Moreover, FO reversed the increase in PEPCK and G-6-Pase and reduced the G-6-Pase/GK ratio. Glycogen concentration and GSa activity returned to levels similar to those observed in the liver of the control-fed rats. Besides, FO did not modify the altered protein mass levels of IRS-1 and αp85 PI-3K. Finally, dietary FO was effective in reversing or improving the impaired activities of several key enzymes of hepatic carbohydrate metabolism contributing, at least in part, to the normalization of plasma glucose levels in the SRD-fed rats. However, these positive effects of FO were not observed under basal conditions in the early steps of insulin signaling transduction.

The importance of the long-chain polyunsaturated fatty acid n-6/n-3 ratio in development of non-alcoholic fatty liver associated with obesity

Non-alcoholic fatty liver disease (NAFLD) is the most important cause of chronic liver disease that is characterized by hepatocyte triacylglycerol accumulation (steatosis), which can progress to inflammation, fibrosis, and cirrhosis (steatohepatitis). Overnutrition triggers the onset of oxidative stress in the liver due to higher availability and oxidation of fatty acids (FA), with development of hyperinsulinemia and insulin resistance (IR), and n-3 long-chain polyunsaturated FA (n-3 LCPUFA) depletion, with enhancement in the n-6/n-3 LCPUFA ratio favouring a pro-inflammatory state. These changes may lead to hepatic steatosis by different mechanisms, namely, (i) IR-dependent higher peripheral lipolysis and FA flux to the liver, (ii) n-3 LCPUFA depletion-induced changes in DNA binding activity of sterol regulatory element-binding protein 1c (SREBP-1c) and peroxisome proliferator-activated receptor α (PPAR-α) favouring lipogenesis over FA oxidation, and (iii) hyperinsulinemia-induced activation of lipogenic factor PPAR-γ. Supplementation with n-3 LCPUFA appears to reduce nutritional hepatic steatosis in adults, however, other histopathologic features of NAFLD remain to be studied.

Glucose tolerance and insulin resistance in Indian children: relationship to infant feeding pattern

AIMS/HYPOTHESIS

Our objective was to examine whether longer duration of breast-feeding and later introduction of complementary foods are associated with lower glucose concentrations and insulin resistance (IR-HOMA) in Indian children.

METHODS

Breast-feeding duration (six categories from <3 to ≥18 months) and age at introduction of complementary foods (four categories from <4 to ≥6 months) were recorded at 1, 2 and 3 year follow-up of 568 children from a birth cohort in Mysore, India. At 5 and 9.5 years of age, 518 children were assessed for glucose tolerance and IR-HOMA.

RESULTS

All the children were initially breast-fed; 90% were breast-fed for ≥6 months and 56.7% started complementary foods at or before the age of 4 months. Each category increase in breast-feeding duration was associated with lower fasting insulin concentration (β = -0.05 pmol/l [95% CI -0.10, -0.004]; p = 0.03) and IR-HOMA (β = -0.05 [95% CI -0.10, -0.001]; p = 0.046) at 5 years, adjusted for the child's sex, age, current BMI, socioeconomic status, parent's education, rural/urban residence, birthweight and maternal gestational diabetes status. Longer duration of breastfeeding was associated with higher 120-min glucose concentration at 5 years (β = 0.08 mmol/l [95% CI 0.001, 0.15; p = 0.03]) but lower 120-min glucose concentration at 9.5 years (β = -0.09 [95% CI -0.16, -0.03]; p = 0.006). Age at starting complementary foods was unrelated to the children's glucose tolerance and IR-HOMA.

CONCLUSIONS/INTERPRETATION

Within this cohort, in which prolonged breast-feeding was the norm, there was evidence of a protective effect of longer duration of breast-feeding against glucose intolerance at 9.5 years. At 5 years longer duration of breast-feeding was associated with lower IR-HOMA.

Promoting wellness for patients on androgen deprivation therapy: why using numerous drugs for drug side effects should not be first-line treatment

The controversy over androgen deprivation therapy (ADT) for prostate cancer seems to have shifted over the past decade. The issue of adverse events or side effects now seems to dominate over that of clinical efficacy. However, this article provides evidence that questions the treatment of these side effects with numerous prescription medications that have their own unique toxicity profile in patients with nonmetastatic disease. The hope is that patients will no longer be considered passive participants in the prevention and treatment of ADT side effects, now that information is available to help mitigate many of these effects.

n-3 PUFA prevent metabolic disturbances associated with obesity and improve endothelial function in golden Syrian hamsters fed with a high-fat diet

Glucose intolerance and dyslipidaemia are independent risk factors for endothelium dysfunction and CVD. The aim of the present study was to analyse the preventive effect of n-3 PUFA (EPA and DHA) on lipid and carbohydrate disturbances and endothelial dysfunction. Three groups of adult hamsters were studied for 20 weeks: (1) control diet (Control); (2) high-fat diet (HF); (3) high-fat diet enriched with n-3 PUFA (HFn-3) groups. The increase in body weight and fat mass in the HF compared to the Control group (P < 0.05) was not found in the HFn-3 group. Muscle TAG content was similar in the Control and HF groups, but significantly lower in the HFn-3 group (P = 0.008). Glucose tolerance was impaired in the HF compared to the Control group, but this impairment was prevented by n-3 PUFA in the HFn-3 group (P < 0.001). Plasma TAG and cholesterol were higher in the HF group compared to the Control group (P < 0.001), but lower in the HFn-3 group compared to the HF group (P < 0.001). HDL-cholesterol was lower in the HFn-3 group compared to the Control and HF groups (P < 0.0005). Hepatic secretion of TAG was lower in the HFn-3 group compared to the HF group (P < 0.005), but did not differ from the Control group. Hepatic gene expression of sterol regulatory element-binding protein-1c, diacylglycerol O-acyltransferase 2 and stearyl CoA desaturase 1 was lower in the HFn-3 group, whereas carnitine palmitoyl transferase 1 and scavenger receptor class B type 1 expression was higher (P < 0.05). In adipocytes and adipose macrophages, PPARγ and TNFα expression was higher in the HF and HFn-3 groups compared to the Control group. Endothelium relaxation was higher in the HFn-3 (P < 0.001) than in the HF and Control groups, and was correlated with glucose intolerance (P = 0.03) and cholesterol (P = 0.0003). In conclusion, n-3 PUFA prevent some metabolic disturbances induced by high-fat diet and improve endothelial function in hamsters.

Relationship of electrophilic stress to aging

This review begins with the premise that an organism's life span is determined by the balance between two countervailing forces: (i) the sum of destabilizing effects and (ii) the sum of protective longevity-assurance processes. Against this backdrop, the role of electrophiles is discussed, both as destabilizing factors and as signals that induce protective responses. Because most biological macromolecules contain nucleophilic centers, electrophiles are particularly reactive and toxic in a biological context. The majority of cellular electrophiles are generated from polyunsaturated fatty acids by a peroxidation chain reaction that is readily triggered by oxygen-centered radicals, but propagates without further input of reactive oxygen species (ROS). Thus, the formation of lipid-derived electrophiles such as 4-hydroxynon-2-enal (4-HNE) is proposed to be relatively insensitive to the level of initiating ROS, but to depend mainly on the availability of peroxidation-susceptible fatty acids. This is consistent with numerous observations that life span is inversely correlated to membrane peroxidizability, and with the hypothesis that 4-HNE may constitute the mechanistic link between high susceptibility of membrane lipids to peroxidation and shortened life span. Experimental interventions that directly alter membrane composition (and thus their peroxidizability) or modulate 4-HNE levels have the expected effects on life span, establishing that the connection is not only correlative but causal. Specific molecular mechanisms are considered, by which 4-HNE could (i) destabilize biological systems via nontargeted reactions with cellular macromolecules and (ii) modulate signaling pathways that control longevity-assurance mechanisms.

Polyunsaturated fatty acids: From diet to binding to ppars and other nuclear receptors

Dietary polyunsaturated fatty acids (PUFAs) function not only by altering membrane lipid composition, cellular metabolism, signal transduction, but possess also effects on gene expression by regulating the activity/abundance of different nuclear transcription factors: peroxisome proliferator activated receptors, retinoid X receptors, liver X receptors, hepatic nuclear factors-4a, and sterol regulatory binding proteins 1 and 2. PUFAs regulate the expression of genes in various tissues, including the liver, heart, adipose tissue, and brain, playing a major role in carbohydrate, fatty acid, triglyceride, and cholesterol metabolism. Before binding to transcription factors, PUFAs must be absorbed in the intestine and delivered to cells, and then they must enter the cell and the nucleus. PUFA concentration within the cell depends on many different factors, and regulate their possibility to act as transcription modulators. The aim of this review is to summarize recent knowledge about PUFAs destiny from dietto nuclear factors binding, examining the different variables which can modulate their interaction with nuclear factors themselves and therefore their effect on gene expression.

Low fish oil intake improves insulin sensitivity, lipid profile and muscle metabolism on insulin resistant MSG-obese rats

BACKGROUND

Obesity is commonly associated with diabetes, cardiovascular diseases and cancer. The purpose of this study was to determinate the effect of a lower dose of fish oil supplementation on insulin sensitivity, lipid profile, and muscle metabolism in obese rats.

METHODS

Monosodium glutamate (MSG) (4 mg/g body weight) was injected in neonatal Wistar male rats. Three-month-old rats were divided in normal-weight control group (C), coconut fat-treated normal weight group (CO), fish oil-treated normal weight group (FO), obese control group (Ob), coconut fat-treated obese group (ObCO) and fish oil-treated obese group (ObFO). Obese insulin-resistant rats were supplemented with fish oil or coconut fat (1 g/kg/day) for 4 weeks. Insulin sensitivity, fasting blood biochemicals parameters, and skeletal muscle glucose metabolism were analyzed.

RESULTS

Obese animals (Ob) presented higher Index Lee and 2.5 fold epididymal and retroperitoneal adipose tissue than C. Insulin sensitivity test (Kitt) showed that fish oil supplementation was able to maintain insulin sensitivity of obese rats (ObFO) similar to C. There were no changes in glucose and HDL-cholesterol levels amongst groups. Yet, ObFO revealed lower levels of total cholesterol (TC; 30%) and triacylglycerol (TG; 33%) compared to Ob. Finally, since exposed to insulin, ObFO skeletal muscle revealed an increase of 10% in lactate production, 38% in glycogen synthesis and 39% in oxidation of glucose compared to Ob.

CONCLUSIONS

Low dose of fish oil supplementation (1 g/kg/day) was able to reduce TC and TG levels, in addition to improved systemic and muscle insulin sensitivity. These results lend credence to the benefits of n-3 fatty acids upon the deleterious effects of insulin resistance mechanisms.

Plasma phospholipids n-3 polyunsaturated fatty acid is associated with metabolic syndrome

The relationship between n-3 PUFA and metabolic syndrome (MS) is not clear. The aim of this study was to examine relationships between plasma phospholipids (PL) n-3 PUFA and MS in Chinese subjects. Nine hundred and twenty-nine subjects were recruited in Hangzhou, China. Two hundred and ten (183 males, 27 females) with MS and 719 (545 males, 174 females) healthy subjects were identified in this cross-sectional study. The prevalence of MS in females (24.56%) was significantly higher than that in males (10.04%) in this population. Total PUFA (p<0.001), n-3 PUFA (p<0.001), and n-3:n-6 (p<0.001) were significantly lower in MS subjects compared to healthy subjects. Plasma phospholipid (PL), n-3 PUFA was significantly inversely associated with MS (p = 0.013). In addition, subjects with high levels of PL total fatty acids (FA) had a more than threefold higher likelihood of MS (OR = 3.44, 95% CI = 1.60-7.39) than the subjects with low levels of PL total FA. Our results suggest that plasma PL n-3 PUFA was significantly inversely associated with MS, while high total FA were positively associated with MS in Chinese.

Dietary omega-3 fatty acid supplementation increases the rate of muscle protein synthesis in older adults: a randomized controlled trial

BACKGROUND

Loss of muscle mass with aging is a major public health concern. Omega-3 (n-3) fatty acids stimulate protein anabolism in animals and might therefore be useful for the treatment of sarcopenia. However, the effect of omega-3 fatty acids on human protein metabolism is unknown.

OBJECTIVE

The objective of this study was to evaluate the effect of omega-3 fatty acid supplementation on the rate of muscle protein synthesis in older adults.

DESIGN

Sixteen healthy, older adults were randomly assigned to receive either omega-3 fatty acids or corn oil for 8 wk. The rate of muscle protein synthesis and the phosphorylation of key elements of the anabolic signaling pathway were evaluated before and after supplementation during basal, postabsorptive conditions and during a hyperaminoacidemic-hyperinsulinemic clamp.

RESULTS

Corn oil supplementation had no effect on the muscle protein synthesis rate and the extent of anabolic signaling element phosphorylation in muscle. Omega-3 fatty acid supplementation had no effect on the basal rate of muscle protein synthesis (mean ± SEM: 0.051 ± 0.005%/h compared with 0.053 ± 0.008%/h before and after supplementation, respectively; P = 0.80) but augmented the hyperaminoacidemia-hyperinsulinemia-induced increase in the rate of muscle protein synthesis (from 0.009 ± 0.005%/h above basal values to 0.031 ± 0.003%/h above basal values; P < 0.01), which was accompanied by greater increases in muscle mTOR(Ser2448) (P = 0.08) and p70s6k(Thr389) (P < 0.01) phosphorylation.

CONCLUSION

Omega-3 fatty acids stimulate muscle protein synthesis in older adults and may be useful for the prevention and treatment of sarcopenia. This trial was registered at clinical trials.gov as NCT00794079.

Chronic dietary n-3 PUFA intervention improves dyslipidaemia and subsequent cardiovascular complications in the JCR:LA-cp rat model of the metabolic syndrome

There is increasing interest in the potential chronic beneficial effects of dietary n-3 PUFA on the metabolic syndrome (MetS) and associated cardiovascular complications. We have recently established that increased dietary n-3 PUFA has a profound acute benefit on fasting lipids and the postprandial pro-inflammatory response in the JCR:LA-cp rat, a model of the MetS. However, it is unclear to what extent chronic dietary n-3 PUFA intervention can modulate the progression of end-stage metabolic and vascular complications. The present study aimed to determine the chronic effects of dietary n-3 PUFA supplementation on fasting and non-fasting dyslipidaemia, insulin resistance and vascular complications in the JCR:LA-cp rodent model. JCR:LA-cp rats were fed an isoenergetic lipid-balanced diet supplemented with 5 % n-3 PUFA (w/w) of the total fat (fish oil-derived EPA/DHA) for 16 weeks. Fasting and non-fasting (postprandial) plasma lipid profile was assessed. Hepatic and adipose tissue was probed for the expression of lipogenic proteins (acyl-CoA carboxylase (ACC), fatty acid synthase (FAS) and sterol regulatory element-binding protein-1 (SREBP-1)), while the activity of Jun N-terminal kinase (JNK) was assessed via Western blot to target phosphorylated JNK protein in primary enterocytes. The frequency of myocardial lesions was assessed by haematoxylin and eosin staining. Increased dietary n-3 PUFA improved both the fasting and postprandial lipid profiles (TAG, cholesterol and apoB48) in the JCR:LA-cp rat, potentially via the down-regulation of the hepatic or adipose tissue expression of lipogenic enzymes (ACC, FAS and SREBP-1). Rats fed the 5 % n-3 PUFA diet had lower (58·2 %; P < 0·01) enterocytic phosphorylated JNK protein and secreted less cholesterol (30 %; P < 0·05) into mesenteric lymph compared with the control. The chronic metabolic benefits of dietary n-3 PUFA may underlie the potential to reduce vascular complications during the MetS, including the observed reduction in the frequency (approximately 80 %) of late-stage 3 myocardial lesions.

Vaccinium arctostaphylos, a common herbal medicine in Iran: molecular and biochemical study of its antidiabetic effects on alloxan-diabetic Wistar rats

AIM OF THE STUDY

The purpose of this study was to define antidiabetic effects of fruit of Vaccinium arctostaphylos L. (Ericaceae) which is traditionally used in Iran for improving of health status of diabetic patients.

MATERIALS AND METHODS

Firstly, we examined the effect of ethanolic extract of Vaccinium arctostaphylos fruit on postprandial blood glucose (PBG) after 1, 3, 5, 8, and 24h following a single dose administration of the extract to alloxan-diabetic male Wistar rats. Also oral glucose tolerance test was carried out. Secondly, PBG was measured at the end of 1, 2 and 3 weeks following 3 weeks daily administration of the extract. At the end of treatment period the pancreatic INS and cardiac GLUT-4 mRNA expression and also the changes in the plasma lipid profiles and antioxidant enzymes activities were assessed. Finally, we examined the inhibitory activity of the extract against rat intestinal α-glucosidase.

RESULTS

The obtained results showed mild acute (18%) and also significant chronic (35%) decrease in the PBG, significant reduction in triglyceride (47%) and notable rising of the erythrocyte superoxide dismutase (57%), glutathione peroxidase (35%) and catalase (19%) activities due to treatment with the extract. Also we observed increased expression of GLUT-4 and INS genes in plant extract treated Wistar rats. Furthermore, in vitro studies displayed 47% and 56% inhibitory effects of the extract on activity of intestinal maltase and sucrase enzymes, respectively.

CONCLUSIONS

Findings of this study allow us to establish scientifically Vaccinium arctostaphylos fruit as a potent antidiabetic agent with antihyperglycemic, antioxidant and triglyceride lowering effects.

Fructose and NAFLD: metabolic implications and models of induction in rats

PURPOSE: The increase in fructose consumption is paralleled by a higher incidence of obesity worldwide. This monosaccharide is linked to metabolic syndrome, being associated with hypertriglyceridemia, hypertension, insulin resistance and diabetes mellitus. It is metabolized principally in the liver, where it can be converted into fatty acids, which are stored in the form of triglycerides leading to NAFLD. Several models of NAFLD use diets high in simple carbohydrates. Thus, this study aimed to describe the major metabolic changes caused by excessive consumption of fructose in humans and animals and to present liver abnormalities resulting from high intakes of fructose in different periods of consumption and experimental designs in Wistar rats. METHODS: Two groups of rats were fasted for 48 hours and reefed for 24 or 48 hours with a diet containing 63% fructose. Another group of rats was fed an diet with 63% fructose for 90 days. RESULTS: Refeeding for 24 hours caused accumulation of large amounts of fat, compromising 100% of the hepatocytes. The amount of liver fat in animals refed for 48 hours decreased, remaining mostly in zone 2 (medium-zonal). In liver plates of Wistar rats fed 63% fructose for 45, 60 and 90 days it's possible to see that there is an increase in hepatocytes with fat accumulation according to the increased time; hepatic steatosis, however, is mild, compromising about 20% of the hepatocytes. CONCLUSIONS: Fructose is highly lipogenic, however the induction of chronic models in NAFLD requires long periods of treatment. The acute supply for 24 or 48 hours, fasted rats can cause big changes, liver steatosis with macrovesicular in all lobular zones.

Benefits versus risks associated with consumption of fish and other seafood

Fish provide nutrition for much of the world's population, and when not contaminated with chemicals, fish is a very good food. A major benefit of fish is that they are high in polyunsaturated fatty acids (PUFAs), low in saturated fat, and they contain other critical nutrients. Much of the benefit of fish consumption derives from their high levels of long chain omega-3 PUFAs, which are produced by aquatic microorganisms and bioconcentrate in the aquatic food supply. The PUFAs are essential, in that humans and other vertebrates are not able to synthesize them and therefore must obtain them from the diet. The PUFAs particularly concentrate in the nervous system, alter immune system function reduce serum triglyceride levels and have been reported to reduce the risk of sudden death after a myocardial infarction. But the problem is that most fish have at least some degree of chemical contamination with methylmercury, (which binds to muscle) and/or with persistent organic pollutants such as dioxins, polychlorinated biphenyls, polybrominated diphenyl ethers, chlorinated pesticides (which concentrate in fish fat). These chemicals have adverse effects on nervous system function, modulate the immune system, and are associated with elevations in risk of cardiovascular disease. Thus the question of benefits and risk from fish consumption is complex but very important.

Modulation of pattern recognition receptor-mediated inflammation and risk of chronic diseases by dietary fatty acids

Chronic inflammation is known to promote the development of many chronic diseases. Pattern recognition receptors (PRRs), Toll-like receptors (TLRs), and nucleotide-binding oligomerization domain proteins (NODs) mediate both infection-induced inflammation and sterile inflammation by recognizing pathogen- associated molecular patterns and endogenous molecules, respectively. PRR-mediated inflammation is an important determinant in altering the risk of many chronic diseases. Saturated fatty acids (SFAs) can activate PRRs, leading to enhanced expression of pro-inflammatory target gene products. However, n-3 polyunsaturated fatty acids (PUFAs) inhibit agonist-induced activation of PRRs. These results suggest that SFAs and n-3 PUFAs can reciprocally modulate PRR-mediated inflammation, and that PRRs and their downstream signaling components are molecular targets for dietary strategies to reduce chronic inflammation and subsequent risk of chronic diseases. This advancement in knowledge provides a new paradigm for understanding the mechanism by which different dietary fatty acids modify risk of chronic diseases including insulin resistance, atherosclerosis, and cancer.

Nuclear receptors and hepatic lipidogenic enzyme response to a dyslipidemic sucrose-rich diet and its reversal by fish oil n-3 polyunsaturated fatty acids

A sucrose-rich diet (SRD), compared with a starch diet, induces time-dependent metabolic disorders and insulin resistance with hypertriglyceridemia, similar to type 2 diabetes. In this study, we examined the effect of SRD, after 8 mo, on nuclear receptors peroxisome proliferator-activated receptor-alpha (PPARalpha), and liver X receptor-alpha (LXRalpha), stearoyl-CoA desaturase-1 (SCD-1), and Delta6 and Delta5 desaturases mRNA and activity, hepatic enzymes involved in lipid metabolism, and fatty acid (FA) composition as well as the reversal produced by cod liver oil. SRD induced triglyceride increase in plasma and liver, increasing the anabolic FA synthase, malic enzyme, and glucose-6-phosphate dehydrogenase, but not the prooxidative enzymes FA oxidase and carnitine palmitoyltransferase I, and correspondingly decreased PPARalpha and increased LXRalpha expressions. Results suggest a contribution of both nuclear receptors' interaction on these enzymatic activities. SRD depressed SCD-1 without altering oleic acid proportion and increased Delta6 and Delta5 desaturases and the proportion of n-6 arachidonic acid. Therefore, the data do not support that SRD hypertriglyceridemia is produced by increased SCD-1-dependent oleic acid biosynthesis. The administration of 7% cod liver oil for 2 mo depressed LXRalpha, enhancing PPARalpha in control and SRD-fed rats, reversing the activity of the hepatic enzymes involved in lipid metabolism and therefore the hyperlipidemia produced by the SRD. Fish oil increased n-3 PUFA and depressed n-6 PUFA of liver lipids without altering the 18:1/18:0 ratio, suggesting that its effects were produced mainly by competition of dietary n-6 and n-3 FA and not through desaturase activity modification.

Highly purified eicosapentaenoic acid ethyl ester prevents development of steatosis and hepatic fibrosis in rats

BACKGROUND AND AIMS

Pathogenesis of nonalcoholic steatohepatitis (NASH) is considered to be involved in fat accumulation, oxidative stress, inflammation, and fibrosis in liver, but no drug therapy has been established as yet. Eicosapentaenoic acid (EPA) is an agent used clinically to treat hypertriglyceridemia, and has been reported to suppress reactive oxygen species and inflammation. Here, we aimed to assess the effect of EPA on progression of hepatic fibrosis in an animal model of NASH.

METHODS

Wistar rats were fed a methionine- and choline-deficient (MCD) diet and given EPA ethyl ester (EPA-E) (1,000 mg/kg/day) or vehicle by gavage for 8 or 20 weeks.

RESULTS

The MCD diet caused development of hepatic fibrosis and nodule formation at 20 weeks. EPA-E treatment significantly suppressed MCD-induced increase in fibrosis and hepatic hydroxyproline, and inhibited nodule formation. EPA-E treatment also decreased hepatic transforming growth factor (TGF)-beta1, and messenger RNA (mRNA) levels of connective tissue growth factor. EPA-E suppressed MCD-induced elevation of serum levels of ferritin, 8-isoprostane, soluble tumor necrosis factor receptor 1 (sTNFR1), and sTNFR2 at 20 weeks, and hepatic triglyceride accumulation at 8 weeks.

CONCLUSIONS

EPA-E prevents progression of hepatic fibrosis in an MCD-induced NASH model with reduction of oxidative stress, inflammation, and initial hepatic steatosis. Thus, EPA-E treatment may be a potential therapy to treat NASH.

Dietary supplementation of n-3 PUFA reduces weight gain and improves postprandial lipaemia and the associated inflammatory response in the obese JCR:LA-cp rat

BACKGROUND

Postprandial dyslipidaemia occurs in obesity and insulin resistance (IR), and is associated with an increased risk of developing cardiovascular disease. We have recently established that the JCR:LA-cp rodent model develops postprandial dyslipidaemia concomitant with complications of the metabolic syndrome. Dietary n-3 polyunsaturated fatty acids (n-3 PUFAs) are proposed to modulate plasma lipids, serum hormone levels, lipoprotein metabolism and the inflammatory state; however, results remain inconsistent during conditions of IR.

AIM

To assess the acute metabolic and inflammatory effects of dietary fish oil supplementation on existing postprandial dyslipidaemia in the JCR:LA-cp model.

METHODS

JCR:LA-cp rats (14 weeks of age) were fed either a control, isocaloric, lipid balanced diet (15% w/w total fat, 1.0% cholesterol, P:S ratio 0.4), a lipid balanced diet with 5% n-3 PUFA [fish oil derived eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA)] or a lipid balanced diet with 10% n-3 PUFA for 3 weeks. Fasting plasma lipid, cytokine levels, postprandial chylomicron (apoB48) metabolism and the postprandial inflammatory response [haptoglobin and lipopolysaccharide binding protein (LBP)] were assessed following a standardized 'oral fat challenge'.

RESULTS

n-3 PUFA treatment resulted in a significant improvement (i.e. decrease) in the postprandial response for triglyceride (45%) (p < 0.05), apoB48 (45%) (p < 0.03) and LBP (33%) (p < 0.05) compared to controls (measured as area under the clearance curve). In contrast, we observed a significant elevation in postprandial haptoglobin (165%) (p < 0.001) in obese rats supplemented with 10% n-3 PUFA. Treatment with 5% n-3 PUFA in the JCR:LA-cp obese animals resulted in a complementary decrease in total body weight gain (6%) (p < 0.001) and an increase (i.e. improvement) in adiponectin (33%) (p < 0.05) compared to controls, without a concomitant reduction in food intake.

CONCLUSION

Acute dietary n-3 PUFA dietary supplementation can improve fasting as well as postprandial lipid metabolism and components of the associated inflammatory response in the JCR:LA-cp rat. Further, moderate dose n-3 PUFA supplementation may reduce corresponding body weight during conditions of hypercholesterolaemia and/or modulate inflammation associated with obesity and the metabolic syndrome.

Postprandial effects of a lipid-rich meal in the rat are modulated by the degree of unsaturation of 18C fatty acids

The fatty acid composition of high-fat diets is known to influence the magnitude of postprandial events that increase the risk of metabolic syndrome. These variations in magnitude may be directly ascribed to differences in the channeling of lipids toward oxidation or storage. A study was designed to compare the effects of 4 dietary fats on postprandial energy expenditure and on some risk factors of the metabolic syndrome. To avoid usual confounding factors due to simultaneous variations in chain length and double-bounds number of fatty acids, dietary fats were chosen to provide mainly 18-carbon fatty acids with 0 (stearic acid [SA]), 1 (oleic acid [OA]), 2 (linoleic acid [LA]), or 3 (alpha-linolenic acid [ALA]) double bounds. They were given as single high-fat test meals to 4 different groups of male rats. The resting metabolic rate and the lipid and carbohydrate oxidation were measured from oxygen consumption and carbon dioxide production using indirect calorimetry 2 hours before and 6.5 hours after the test meal. Plasma glucose, triglyceride, and chylomicron concentrations were determined at 0, 1.5, and 4 hours after the test meal. Postprandial concentration of glucose and triglyceride did not vary with the nature of the test meals, whereas that of chylomicrons was the highest after the LA test meal and the lowest after the SA test meal. Postprandial increase in resting metabolic rate was the highest after the LA and OA test meals, and the lowest after the SA and ALA test meals. Compared with the 3 other diets, the ALA test meal enhanced lipid oxidation and decreased glucose oxidation during the early postprandial period (0.25-3.25 hours). This suggests that stearic acid may not induce all the adverse effects classically described for other saturated fatty acids and that alpha-linolenic acid may beneficially influence energy partitioning, especially during the early postprandial state.

Nutritional fatty acid quality of raw and cooked farmed and wild sea bream (Sparus aurata)

The effects of steaming, grilling, and frying in corn and sunflower oils, respectively, on the fatty acid compositions of farmed and wild sea bream were evaluated. The lipid content increased with frying in both oil types. The maximum moisture value was found in steamed fish (P<0.05). Fried sea bream in corn and sunflower oils contained a lower content of n-3 polyunsaturated fatty acids (P<0.05) (3.87 and 5.32% of total fatty acids (TFA) in farmed fish and 2.96 and 2.14% TFA in wild fish). The n-3/n-6 ratio decreased significantly after cooking, particularly after frying in corn and sunflower oils, respectively: from 2.51 to 0.08 and 0.12 in farmed fish and from 0.94 to 0.06 and 0.04 in wild fish. The trans fatty acid levels remain stable after steaming and grilling, but they were significantly affected by frying. Our results reveal that the cooking process has considerable effect on the fatty acid compositions of farmed and wild sea bream.

Effect of a dietary intervention and n-3 fatty acid supplementation on measures of serum lipid and insulin sensitivity in persons with HIV

BACKGROUND

Elevated serum triglyceride and low HDL-cholesterol concentrations have been reported in persons with HIV.

OBJECTIVE

The effect of a dietary intervention plus n-3 (omega-3) fatty acid supplementation on serum triglycerides and markers of insulin sensitivity was investigated.

DESIGN

Fifty-four persons with HIV and elevated serum triglycerides (>150 mg/dL) and/or abnormal Quantitative Insulin Sensitivity Check Index values (<0.35 but >0.30) were recruited for a dietary intervention in which total fat, type of fat, fiber, and glycemic load were controlled along with supplementation with n-3 fatty acids to achieve an intake of 6 g/d. The subjects were randomly assigned to an intervention or control group, and serum lipids, markers of insulin sensitivity, and serum phospholipid fatty acids were measured in both groups at baseline, 3 wk, and 13 wk.

RESULTS

Triglycerides in the intervention group decreased from a median of 180 mg/dL (interquartile range: 141, 396) to 114 mg/dL (interquartile range: 84, 169) from baseline to 3 wk, whereas they remained stable in the control group (P = 0.003). Serum phospholipid fatty acids indicated a decrease in de novo lipogenesis and a decrease in arachidonic acid (% nmol; P <or= 0.001) in the intervention group. At 3 wk, the insulin area under the curve decreased but not significantly.

CONCLUSIONS

Diet and n-3 fatty acid supplementation dramatically reduced serum triglycerides, decreased arachidonic acid in the phospholipids fraction, and appeared to decrease the de novo lipogenesis associated with the metabolic syndrome in the intervention group.

Combined effects of endurance training and dietary unsaturated fatty acids on physical performance, fat oxidation and insulin sensitivity

Endurance training improves exercise performance and insulin sensitivity, and these effects may be in part mediated by an enhanced fat oxidation. Since n-3 and n-9 unsaturated fatty acids may also increase fat oxidation, we hypothesised that a diet enriched in these fatty acids may enhance the effects of endurance training on exercise performance, insulin sensitivity and fat oxidation. To assess this hypothesis, sixteen normal-weight sedentary male subjects were randomly assigned to an isoenergetic diet enriched with fish and olive oils (unsaturated fatty acid group (UFA): 52 % carbohydrates, 34 % fat (12 % SFA, 12 % MUFA, 5 % PUFA), 14 % protein), or a control diet (control group (CON): 62 % carbohydrates, 24 % fat (12 % SFA, 6 % MUFA, 2 % PUFA), 14 % protein) and underwent a 10 d gradual endurance training protocol. Exercise performance was evaluated by measuring VO2max and the time to exhaustion during a cycling exercise at 80 % VO2max; glucose homeostasis was assessed after ingestion of a test meal. Fat oxidation was assessed by indirect calorimetry at rest and during an exercise at 50 % VO2max. Training significantly increased time to exhaustion, but not VO2max, and lowered incremental insulin area under the curve after the test meal, indicating improved insulin sensitivity. Those effects were, however, of similar magnitude in UFA and CON. Fat oxidation tended to increase in UFA, but not in CON. This difference was, however, not significant. It is concluded that a diet enriched with fish- and olive oil does not substantially enhance the effects of a short-term endurance training protocol in healthy young subjects.

n-3 PUFA and lipotoxicity

Excess lipid accumulation in nonadipose tissues may occur in the setting of high levels of plasma free fatty acids or triglycerides (TGs) in a process called "lipotoxicity". Evidence from human studies and animal models suggests that lipid accumulation in the heart, skeletal muscle, pancreas, and liver play an important role in the pathogenesis of heart failure, obesity, metabolic syndrome, and type 2 diabetes mellitus (T2DM). During the past few years, several studies have shown that n-3 polyunsaturated fatty acids (PUFA) have potentially cardioprotective effects, especially in high-risk patients with dyslipidemia, and might therefore be expected to be of benefit in T2DM. Moreover, new information has demonstrated the beneficial effects of consuming n-3 PUFA in preventing the complications of lipotoxicity. n-3 PUFA dietary intake thus had positive effects on fatty liver in patients with non-alcoholic fatty liver disease (NAFLD), with an improvement in liver echotexture and a significant regression of hepatic brightness, associated with improved liver hemodynamics. The n-3 PUFA also had beneficial effects on ectopic fat accumulation inside the heart, with stabilization of cardiac myocytes and antiarrhythmic effects. On the other hand, recent data from animal models suggest that oral dosing of eicosapentaenoic acid (EPA) could contribute to protect against beta-cell lipotoxicity. This review discusses the latest hypotheses regarding lipotoxicity, concentrating on the impact of the n-3 PUFA that contribute to ectopic lipid storage, affecting organ function. Further human studies are needed to test the evidence and elucidate the mechanisms involved in this process.

Fish oil diets do not improve insulin sensitivity and secretion in healthy adult male pigs

The effects of long-term dietary supplementation of fish oil (n-3 PUFA-rich) in adult male pigs on body condition as well as insulin sensitivity and secretion were examined. Fifteen Duroc boars aged 204·5 (sd 9·4) d (body weight 145·8 (sd 16·8) kg) received daily 2·5 kg basal diet with a supplement of: (1) 62 g hydrogenated animal fat (n 5); (2) 60 g menhaden oil containing 10·8 g DHA and 9·0 g EPA (n 6); (3) 60 g tuna oil containing 19·8 g DHA and 3·9 g EPA (n 4). Rations were balanced to be isoenergetic. After 7 months of treatments, oral glucose and meal tolerance tests were conducted after insertion of a catheter into the jugular vein. Dietary supplementation with n-3 PUFA altered the blood plasma profile: DHA and EPA increased whereas arachidonic acid decreased (P < 0·01). Plasma glucose, insulin and C-peptide responses to oral glucose and the test meal were not affected by treatments (P>0·34). For all animals, total body fat estimated from body weight and back fat thickness was correlated with both β-cell function (by homeostasis model assessment (HOMA); r+0·63) and insulin sensitivity (index of whole-body insulin sensitivity and by HOMA; r − 0·63 and r+0·66, respectively). In conclusion, long-term supplementation with dietary n-3 PUFA did not affect insulin metabolism in healthy adult male pigs. The relationship between body fat and insulin sensitivity, well documented in human subjects, suggests that the adult male pig could be a promising animal model for studies on insulin metabolism.

Enhancement in liver SREBP-1c/PPAR-alpha ratio and steatosis in obese patients: correlations with insulin resistance and n-3 long-chain polyunsaturated fatty acid depletion

Sterol receptor element-binding protein-1c (SREBP-1c) and peroxisome proliferator-activated receptor-alpha (PPAR-alpha) mRNA expression was assessed in liver as signaling mechanisms associated with steatosis in obese patients. Liver SREBP-1c and PPAR-alpha mRNA (RT-PCR), fatty acid synthase (FAS) and carnitine palmitoyltransferase-1a (CPT-1a) mRNA (real-time RT-PCR), and n-3 long-chain polyunsaturated fatty acid (LCPUFA)(GLC) contents, plasma adiponectin levels (RIA), and insulin resistance (IR) evolution (HOMA) were evaluated in 11 obese patients who underwent subtotal gastrectomy with gastro-jejunal anastomosis in Roux-en-Y and 8 non-obese subjects who underwent laparoscopic cholecystectomy (controls). Liver SREBP-1c and FAS mRNA levels were 33% and 70% higher than control values (P<0.05), respectively, whereas those of PPAR-alpha and CPT-1a were 16% and 65% lower (P<0.05), respectively, with a significant 62% enhancement in the SREBP-1c/PPAR-alpha ratio. Liver n-3 LCPUFA levels were 53% lower in obese patients who also showed IR and hipoadiponectinemia over controls (P<0.05). IR negatively correlated with both the hepatic content of n-3 LCPUFA (r=-0.55; P<0.01) and the plasma levels of adiponectin (r=-0.62; P<0.005). Liver SREBP-1c/PPAR-alpha ratio and n-3 LCPUFA showed a negative correlation (r=-0.48; P<0.02) and positive associations with either HOMA (r=0.75; P<0.0001) or serum insulin levels (r=0.69; P<0.001). In conclusion, liver up-regulation of SREBP-1c and down-regulation of PPAR-alpha occur in obese patients, with enhancement in the SREBP-1c/PPAR-alpha ratio associated with n-3 LCPUFA depletion and IR, a condition that may favor lipogenesis over FA oxidation thereby leading to steatosis.

Lipogenic enzyme activities and glucose uptake in fat tissue of dyslipemic, insulin-resistant rats: effects of fish oil

OBJECTIVE

The purposes of the present work were twofold: (1) investigate same mechanisms involved in the development of fat cell hypertrophy in the experimental model of dyslipidemia and whole-body insulin resistance induced in rats chronically fed a sucrose-rich diet (SRD); and (2) analyze the possible beneficial effect of fish oil on these mechanisms.

METHODS

For 6 mo, male Wistar rats received a sucrose-rich diet (62.5% w/w sucrose, 8% corn oil) or a control diet in which sucrose was replaced by starch. After this period, the sucrose-fed animals were divided randomly into two groups: the first one continued with the same diet up to 8 mo and the second one received the same diet, but with corn oil replaced by 7% fish oil+1 % corn oil. Rats were fed with this diet for the next 2 mo.

RESULTS

Although an enlarged fat cell lipolysis and an impaired insulin-stimulated glucose uptake were present in the fat cells of SRD-fed rats, an increase of several key enzymes of the novo lipogenesis could be one of the possible mechanisms involved in visceral adiposity. The addition of dietary fish oil restored or improved the above abnormalities.

CONCLUSION

This study shows possible mechanisms conditioning the influence of nutrients on the development and management of dyslipidemia, insulin sensitivity, and fat cell accretion, all abnormalities present in the metabolic syndrome.

Antihyperglycemic effects of total flavonoids from Polygonatum odoratum in STZ and alloxan-induced diabetic rats

AIM OF THE STUDY

Total flavonids of Polygonatum(P) odoratum (TFP) were tested for anti-diabetic activity in streptozotocin (STZ)-induced diabetic mice and alloxan-induced diabetic rats.

MATERIALS AND METHODS

Rhizoma Polygonati Odorati, well-known Chinese traditional medicine, is widely used for treatment of diverse diseases for example diabetes. In our study, TFP was extracted by 70% ethanol and purified by macroreticular resin. The experiments were designed to detect the anti-diabetic activity of TFP by determination of blood glucose (BG) using one touch gluco-meter and insulin levels by using a radioimmunoassay kit in streptozotocin (STZ)-induced diabetic mice and alloxan-induced diabetic rats and alpha-amylase inhibitory activity by alpha-amylase inhibition assay in vitro.

RESULTS

TFP had beneficial effects on regulation of blood glucose. Daily administration with 50-200 mg/kg body weight of TFP for 9 days can reduce significantly hyperglycemia in STZ-induced diabetic mice. Thirtieth day administration with TFP (50-200 mg/kg body weight) also decreased significantly fasting blood glucose in alloxan-induced diabetic rats. The hypoglycemic effect of TFP at 50 and 100 mg/kg is less than that of acarbose 20 mg/kg and gliclazide 15 mg/kg. The hypoglycemic effects of TFP at 200 mg/kg is similar to that of acarbose 20 mg/kg and gliclazide 15 mg/kg. TFP also could increase significantly the insulin level in alloxan-induced type 2 diabetic rats (P<0.05) compared with control. Alpha-amylase inhibition assay in vitro showed that TFP inhibited significantly alpha-amylase activity in a dose-dependent manner.

CONCLUSIONS

TFP possess significant dose-dependent anti-diabetic activity. TFP is one of the primary hypoglycemic active compounds of Polygonatum odoratum which would worth further study and development.

Controle da adipogênese por ácidos graxos

A obesidade é um dos principais problemas de saúde pública. Indivíduos obesos são mais suscetíveis a desenvolver doenças cardiovasculares e diabetes melito tipo 2. A obesidade resulta do aumento no tamanho e no número de adipócitos. O balanço entre adipogênese e adiposidade determina o grau de obesidade do indivíduo. Adipócitos maduros secretam adipocinas, tais como TNFα, IL-6, leptina e adiponectina, e lipocina, o ácido palmitoleico ω-7. A produção de adipocinas é maior na obesidade, o que contribui para o estabelecimento de resistência periférica à insulina. O conhecimento dos eventos moleculares que regulam a diferenciação dos pré-adipócitos e de células-tronco mesenquimais em adipócitos (adipogênese) é importante para o entendimento da gênese da obesidade. A ativação do fator de transcrição PPARγ é essencial na adipogênese. Certos ácidos graxos são ligantes de PPARγ e podem, assim, controlar a adipogênese. Além disso, alguns ácidos graxos atuam como moléculas sinalizadoras em adipócitos, regulando sua diferenciação ou morte. Dessa forma, a composição lipídica da dieta e os agonistas de PPARγ podem regular o balanço entre adipogênese e morte de adipócitos e, portanto, a obesidade.

Fish oil and argan oil intake differently modulate insulin resistance and glucose intolerance in a rat model of dietary-induced obesity

We investigated the potential metabolic benefits of fish oil (FO) or vegetable argan oil (AO) intake in a dietary model of obesity-linked insulin resistance. Rats were fed a standard chow diet (controls), a high-fat/high-sucrose (HFHS) diet, or an HFHS diet in which 6% of the fat was replaced by either FO or AO feeding, respectively. The HFHS diet increased adipose tissue weight and insulin resistance as revealed by increased fasting glucose and exaggerated glycemic and insulin responses to a glucose tolerance test (intraperitoneal glucose tolerance test). Fish oil feeding prevented fat accretion, reduced fasting glycemia, and normalized glycemic or insulin responses to intraperitoneal glucose tolerance test as compared with HFHS diet. Unlike FO consumption, AO intake failed to prevent obesity, yet restored fasting glycemia back to chow-fed control values. Insulin-induced phosphorylation of Akt and Erk in adipose tissues, skeletal muscles, and liver was greatly attenuated in HFHS rats as compared with chow-fed controls. High-fat/high-sucrose diet-induced insulin resistance was also confirmed in isolated hepatocytes. Fish oil intake prevented insulin resistance by improving or fully restoring insulin signaling responses in all tissues and isolated hepatocytes. Argan oil intake also improved insulin-dependent phosphorylations of Akt and Erk; and in adipose tissue, these responses were increased even beyond values observed in chow-fed controls. Taken together, these results strongly support the beneficial action of FO on diet-induced insulin resistance and glucose intolerance, an effect likely explained by the ability of FO to prevent HFHS-induced adiposity. Our data also show for the first time that AO can improve some of the metabolic and insulin signaling abnormalities associated with HFHS feeding.

High fat feeding induces hepatic fatty acid elongation in mice

Background

High-fat diets promote hepatic lipid accumulation. Paradoxically, these diets also induce lipogenic gene expression in rodent liver. Whether high expression of these genes actually results in an increased flux through the de novo lipogenic pathway in vivo has not been demonstrated.

Methodology/Principal Findings

To interrogate this apparent paradox, we have quantified de novo lipogenesis in C57Bl/6J mice fed either chow, a high-fat or a n-3 polyunsaturated fatty acid (PUFA)-enriched high-fat diet. A novel approach based on mass isotopomer distribution analysis (MIDA) following 1-¹³C acetate infusion was applied to simultaneously determine de novo lipogenesis, fatty acid elongation as well as cholesterol synthesis. Furthermore, we measured very low density lipoprotein-triglyceride (VLDL-TG) production rates. High-fat feeding promoted hepatic lipid accumulation and induced the expression of lipogenic and cholesterogenic genes compared to chow-fed mice: induction of gene expression was found to translate into increased oleate synthesis. Interestingly, this higher lipogenic flux (+74 µg/g/h for oleic acid) in mice fed the high-fat diet was mainly due to an increased hepatic elongation of unlabeled palmitate (+66 µg/g/h) rather than to elongation of de novo synthesized palmitate. In addition, fractional cholesterol synthesis was increased, i.e. 5.8±0.4% vs. 8.1±0.6% for control and high fat-fed animals, respectively. Hepatic VLDL-TG production was not affected by high-fat feeding. Partial replacement of saturated fat by fish oil completely reversed the lipogenic effects of high-fat feeding: hepatic lipogenic and cholesterogenic gene expression levels as well as fatty acid and cholesterol synthesis rates were normalized.

Conclusions/Significance

High-fat feeding induces hepatic fatty acid synthesis in mice, by chain elongation and subsequent desaturation rather than de novo synthesis, while VLDL-TG output remains unaffected. Suppression of lipogenic fluxes by fish oil prevents from high fat diet-induced hepatic steatosis in mice.

Teor lipídico da dieta, lipídios séricos e peso corporal em ratos exercitados

OBJETIVO: Analisar os efeitos de diferentes níveis de triglicerídeos fornecidos pela dieta sobre os parâmetros séricos triglicerídeos e lipoproteínas de alta densidade e o peso corporal de ratos sedentários e exercitados. MÉTODOS: Foram utilizados ratos Wistar, alimentados com dietas controle (7%peso/peso) e hiperlipídica (14% peso/peso) e subdivididos em sedentários e exercitados, por um período de 8 semanas. RESULTADOS: Verificou-se que o peso não diferiu entre os grupos, embora o consumo tenha sido reduzido nos grupos com dieta hiperlipídica. Os níveis de triglicerídeos não foram aumentados com a dieta rica em gordura e o HDL-colesterol se elevou apenas entre os animais exercitados que tiveram dieta normolipídica. CONCLUSÃO: A intensidade e o tempo de exercício físico influenciam de maneira mais aguda os níveis de HDL-colesterol em comparação aos níveis de triglicérides. Sugere-se que a dieta hiperlipídica deveria sobrepor (14%peso/peso) de gordura para que houvesse alterações relevantes nos parâmetros lipídicos e supostamente um aumento da performance física.

Relationship between n-3 and n-6 plasma fatty acid levels and insulin resistance in coronary patients with and without metabolic syndrome

BACKGROUND AND AIMS

Animal studies show that ecosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are effective for the prevention and treatment of insulin resistance (IR). Data from human studies are contradictory. We sought to determine whether the relationships between plasma n-3 and n-6 polyunsaturated fatty acid (FA) levels and IR differ according to the presence or absence of metabolic syndrome (MS) in a coronary heart disease sample.

METHOD AND RESULTS

Clinical, metabolic parameters, plasma phospholipid FA profiles and indirect measurement of IR (homeostatic model assessment-HOMA) were measured in 734 subjects, 8 weeks following acute coronary syndrome. FA levels and their correlations with IR were compared in subjects with and without MS. MS patients had higher saturated (16:0, 18:0) and n-6 (18:3n-6, 20:3n-6, 22:4n-6, 22:5n-6) FA levels, and lower EPA and DHA levels. HOMA-IR correlated positively with total saturated (r=0.13, P=0.017) and n-6 (r=0.17, P=0.001) FA levels and negatively with total n-3 FA levels (r=-0.13, P=0.012), in MS subjects only. Total n-3 and n-6 FAs and n-6/n-3 ratio were associated with HOMA-IR levels in MS subjects independent of total saturated FA levels, age, sex, sedentary behaviour, smoking, waist circumference, triglycerides, HDL-cholesterol, and systolic blood pressure.

CONCLUSIONS

Relationships between polyunsaturated FA type and IR vary according to the presence or absence of MS. N-3 FAs including EPA and DHA are associated with lower HOMA-IR, while the opposite is true for n-6 FAs. Prospective studies are required to address the potential effects of intermediate dose EPA and DHA on glucose handling in MS patients.

Prevention and reversal of obesity and glucose intolerance in mice by DHA derivatives

The n-3 polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), exert hypolipidemic effects and prevent development of obesity and insulin resistance in animals fed high-fat diets. We sought to determine the efficacy of alpha-substituted DHA derivatives as lipid-lowering, antiobesity, and antidiabetic agents. C57BL/6 mice were given a corn oil-based high-fat (35% weight/weight) diet (cHF), or cHF with 1.5% of lipids replaced with alpha-methyl DHA ethyl ester (Substance 1), alpha-ethyl DHA ethyl ester (Substance 2), alpha,alpha-di-methyl DHA ethyl ester (Substance 3), or alpha-thioethyl DHA ethyl ester (Substance 4) for 4 months. Plasma markers of glucose and lipid metabolism, glucose tolerance, morphology, tissue lipid content, and gene regulation were characterized. The cHF induced obesity, hyperlipidemia, impairment of glucose homeostasis, and adipose tissue inflammation. Except for Substance 3, all other substances prevented weight gain and Substance 2 exerted the strongest effect (63% of cHF-controls). Glucose intolerance was significantly prevented (~67% of cHF) by both Substance 1 and Substance 2. Moreover, Substance 2 lowered fasting glycemia, plasma insulin, triacylglycerols, and nonesterified fatty acids (73, 9, 47, and 81% of cHF-controls, respectively). Substance 2 reduced accumulation of lipids in liver and skeletal muscle, as well as adipose tissue inflammation associated with obesity. Substance 2 also induced weight loss in dietary obese mice. In contrast to DHA administered either alone or as a component of the EPA/DHA concentrate (replacing 15% of dietary lipids), Substance 2 also reversed established glucose intolerance in obese mice. Thus, Substance 2 represents a novel compound with a promising potential in the treatment of obesity and associated metabolic disturbances.

Highly purified eicosapentaenoic acid prevents the progression of hepatic steatosis by repressing monounsaturated fatty acid synthesis in high-fat/high-sucrose diet-fed mice

Eicosapentaenoic acid (EPA) is a member of the family of n-3 polyunsaturated fatty acids (PUFAs) that are clinically used to treat hypertriglyceridemia. The triglyceride (TG) lowering effect is likely due to an alteration in lipid metabolism in the liver, but details have not been fully elucidated. To assess the effects of EPA on hepatic TG metabolism, mice were fed a high-fat and high-sucrose diet (HFHSD) for 2 weeks and were given highly purified EPA ethyl ester (EPA-E) daily by gavage. The HFHSD diet increased the hepatic TG content and the composition of monounsaturated fatty acids (MUFAs). EPA significantly suppressed the hepatic TG content that was increased by the HFHSD diet. EPA also altered the composition of fatty acids by lowering the MUFAs C16:1 and C18:1 and increasing n-3 PUFAs, including EPA and docosahexaenoic acid (DHA). Linear regression analysis revealed that hepatic TG content was significantly correlated with the ratios of C16:1/C16:0, C18:1/C18:0, and MUFA/n-3 PUFA, but was not correlated with the n-6/n-3 PUFA ratio. EPA also decreased the hepatic mRNA expression and nuclear protein level of sterol regulatory element binding protein-1c (SREBP-1c). This was reflected in the levels of lipogenic genes, such as acetyl-CoA carboxylase alpha (ACCalpha), fatty acid synthase, stearoyl-CoA desaturase 1 (SCD1), and glycerol-3-phosphate acyltransferase (GPAT), which are regulated by SREBP-1c. In conclusion, oral administration of EPA-E ameliorates hepatic fat accumulation by suppressing TG synthesis enzymes regulated by SREBP-1 and decreases hepatic MUFAs accumulation by SCD1.

Induction of lipid oxidation by polyunsaturated fatty acids of marine origin in small intestine of mice fed a high-fat diet

BACKGROUND

Dietary polyunsaturated fatty acids (PUFA), in particular the long chain marine fatty acids docosahexaenoic (DHA) and eicosapentaenoic (EPA), are linked to many health benefits in humans and in animal models. Little is known of the molecular response to DHA and EPA of the small intestine, and the potential contribution of this organ to the beneficial effects of these fatty acids. Here, we assessed gene expression changes induced by DHA and EPA in the wildtype C57BL/6J murine small intestine using whole genome microarrays and functionally characterized the most prominent biological process.

RESULTS

The main biological process affected based on gene expression analysis was lipid metabolism. Fatty acid uptake, peroxisomal and mitochondrial beta-oxidation, and omega-oxidation of fatty acids were all increased. Quantitative real time PCR, and -- in a second animal experiment -- intestinal fatty acid oxidation measurements confirmed significant gene expression differences and showed in a dose-dependent manner significant changes at biological functional level. Furthermore, no major changes in the expression of lipid metabolism genes were observed in the colon.

CONCLUSION

We show that marine n-3 fatty acids regulate small intestinal gene expression and increase fatty acid oxidation. Since this organ contributes significantly to whole organism energy use, this effect on the small intestine may well contribute to the beneficial physiological effects of marine PUFAs under conditions that will normally lead to development of obesity, insulin resistance and diabetes.

Cellular and molecular effects of n-3 polyunsaturated fatty acids on adipose tissue biology and metabolism

Adipose tissue and its secreted products, adipokines, have a major role in the development of obesity-associated metabolic derangements including Type 2 diabetes. Conversely, obesity and its metabolic sequelae may be counteracted by modulating metabolism and secretory functions of adipose tissue. LC-PUFAs (long-chain polyunsaturated fatty acids) of the n-3 series, namely DHA (docosahexaenoic acid; C(22:6n-3)) and EPA (eicosapentaenoic acid; C(20:5n-3)), exert numerous beneficial effects, such as improvements in lipid metabolism and prevention of obesity and diabetes, which partially result from the metabolic action of n-3 LC-PUFAs in adipose tissue. Recent studies highlight the importance of mitochondria in adipose tissue for the maintenance of systemic insulin sensitivity. For instance, both n-3 LC-PUFAs and the antidiabetic drugs TZDs (thiazolidinediones) induce mitochondrial biogenesis and beta-oxidation. The activation of this 'metabolic switch' in adipocytes leads to a decrease in adiposity. Both n-3 LC-PUFAs and TZDs ameliorate a low-grade inflammation of adipose tissue associated with obesity and induce changes in the pattern of secreted adipokines, resulting in improved systemic insulin sensitivity. In contrast with TZDs, which act as agonists of PPARgamma (peroxisome-proliferator-activated receptor-gamma) and promote differentiation of adipocytes and adipose tissue growth, n-3 LC-PUFAs affect fat cells by different mechanisms, including the transcription factors PPARalpha and PPARdelta. Some of the effects of n-3 LC-PUFAs on adipose tissue depend on their active metabolites, especially eicosanoids. Thus treatments affecting adipose tissue by multiple mechanisms, such as combining n-3 LC-PUFAs with either caloric restriction or antidiabetic/anti-obesity drugs, should be explored.

Dietary supplementation with conjugated linoleic acid plus n-3 polyunsaturated fatty acid increases food intake and brown adipose tissue in rats

The effect of supplementation with 1% conjugated linoleic acid and 1% n-3 long chain polyunsaturated fatty acids (CLA/n-3) was assessed in rats. Food intake increased with no difference in body weights. White adipose tissue weights were reduced whereas brown adipose tissue and uncoupling protein-1 expression were increased. Plasma adiponectin, triglyceride and cholesterol levels were reduced while leptin, ghrelin and liver weight and lipid content were unchanged. Hypothalamic gene expression measurements revealed increased expression of orexigenic and decreased expression of anorexigenic signals. Thus, CLA/n-3 increases food intake without affecting body weight potentially through increasing BAT size and up-regulating UCP-1 in rats.