Dietary supplementation of very long-chain n-3 fatty acids decreases whole body lipid utilization in the rat

Variability in the Clinical Effects of the Omega-3 Polyunsaturated Fatty Acids DHA and EPA in Cardiovascular Disease-Possible Causes and Future Considerations

Cardiovascular disease (CVD) that includes myocardial infarction and stroke, is the leading cause of mortality worldwide. Atherosclerosis, the primary underlying cause of CVD, can be controlled by pharmacological and dietary interventions, including n-3 polyunsaturated fatty acid (PUFA) supplementation. n-3 PUFA supplementation, primarily consisting of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), has shown promise in reducing atherosclerosis by modulating risk factors, including triglyceride levels and vascular inflammation. n-3 PUFAs act by replacing pro-inflammatory fatty acid types in cell membranes and plasma lipids, by regulating transcription factor activity, and by inducing epigenetic changes. EPA and DHA regulate cellular function through shared and differential molecular mechanisms. Large clinical studies on n-3 PUFAs have reported conflicting findings, causing confusion among the public and health professionals. In this review, we discuss important factors leading to these inconsistencies, in the context of atherosclerosis, including clinical study design and the differential effects of EPA and DHA on cell function. We propose steps to improve clinical and basic experimental study design in order to improve supplement composition optimization. Finally, we propose that understanding the factors underlying the poor response to n-3 PUFAs, and the development of molecular biomarkers for predicting response may help towards a more personalized treatment.

Impact of Obesity-Related Inflammation on Cardiac Metabolism and Function

This review focuses on the role of adipose tissue in obese individuals in the development of metabolic diseases, and their consequences for metabolic and functional derangements in the heart. The general idea is that the expansion of adipocytes during the development of obesity gives rise to unhealthy adipose tissue, characterized by low-grade inflammation and the release of proinflammatory adipokines and fatty acids (FAs). This condition, in turn, causes systemic inflammation and elevated FA concentrations in the circulation, which links obesity to several pathologies, including impaired insulin signaling in cardiac muscle and a subsequent shift in myocardial substrate oxidation in favor of FAs and reduced cardiac efficiency. This review also argues that efforts to prevent obesity-related cardiometabolic disease should focus on anti-obesogenic strategies to restore normal adipose tissue metabolism.

Fish oil reverses metabolic syndrome, adipocyte dysfunction, and altered adipokines secretion triggered by high-fat diet-induced obesity

The effect of fish oil (FO) treatment on high-fat (HF) diet-induced obesity and metabolic syndrome was addressed by analyzing dysfunctions in cells of different adipose depots. For this purpose, mice were initially induced to obesity for 8 weeks following a treatment with FO containing high concentration of EPA compared to DHA (5:1), for additional 8 weeks (by gavage, 3 times per week). Despite the higher fat intake, the HF group showed lower food intake but higher body weight, glucose intolerance and insulin resistance, significant dyslipidemia and increased liver, subcutaneous (inguinal-ING) and visceral (retroperitoneal-RP) adipose depots mass, accompanied by adipocyte hypertrophy and decreased cellularity in both adipose tissue depots. FO treatment reversed all these effects, as well as it improved the metabolic activities of isolated adipocytes, such as glucose uptake and lipolysis in both depots, and de novo synthesis of fatty acids in ING adipocytes. HF diet also significantly increased both the pro and anti-inflammatory cytokines expression by adipocytes, while HF + FO did not differ from control group. Collectively, these data show that the concomitant administration of FO with the HF diet is able to revert metabolic changes triggered by the diet-induced obesity, as well as to promote beneficial alterations in adipose cell activities. The main mechanism underlying all systemic effects involves direct and differential effects on ING and RP adipocytes.

The composition of dietary fat alters the transcriptional profile of pathways associated with lipid metabolism in the liver and adipose tissue in the pig

The objective was to investigate the of effect chemical composition of dietary fat on transcription of genes involved in lipid metabolism in adipose tissue and the liver via transcriptional profiling in growing pigs. A total of 48 Genetiporc 6.0 × Genetiporc F25 (PIC, Inc., Hendersonville, TN) barrows (initial BW of 44.1 ± 1.2 kg) were randomly allotted to 1 of 6 dietary treatments. Each experimental diet included 95% of a corn-soybean meal basal diet and 5% cornstarch (control; CNTR), animal-vegetable blend (AV), coconut oil (COCO), corn oil (COIL), fish oil (FO), or tallow (TAL). Pigs were sacrificed on d 10 (final BW of 51.2 ± 1.7 kg) to collect tissues. Expression normalization across samples was performed by calculating a delta cycle threshold (ΔCt) value using . Delta delta cycle threshold (ΔΔCt) values were expressed relative to the CNTR treatment. In adipose tissue, adding dietary fat, regardless of the source, decreased the mRNA abundance of compared with the CNTR ( = 0.014). Pigs fed a COIL-based diet tended to have greater adipose tissue expression of ( = 0.071) than pigs fed the other dietary fat sources tested. Abundance of mRNA was greater in adipose tissue of barrows a fed COIL-based diet than barrows fed CNTR or FO-based diets ( = 0.047). In the liver, adding dietary fat, regardless of source, increased the mRNA abundance of , , , , , and ( ≤ 0.020) and tended to increase the abundance of ( = 0.071) and ( = 0.086) compared with the CNTR. Pigs fed a TAL-based diet had greater hepatic transcription of than pigs fed CNTR-, COCO-, or FO-based diets ( = 0.013). Hepatic transcription of tended to be greater in pigs fed COCO than in pigs fed other dietary fat sources ( = 0.074). Dietary omega-3 fatty acid content tended to negatively correlate with mRNA abundance of ( = 0.065) in adipose tissue and ( = 0.063) in the liver. Dietary fat SFA content was negatively correlated with in the liver ( ≤ 0.039). Dietary fat MUFA content tended to be positively correlated with , , and mRNA abundance in the liver ( ≤ 0.100). To conclude, the intake of omega-3 fatty acids suppressed the mRNA abundance of genes involved in lipolysis in both adipose tissue and the liver. Dietary SFA are greater inhibitors of lipogenesis in adipose tissue than omega-6 fatty acids. Intake of medium-chain fatty acids alters hepatic lipid metabolism differently than intake of long-chain fatty acids.

CMPF, a Metabolite Formed Upon Prescription Omega-3-Acid Ethyl Ester Supplementation, Prevents and Reverses Steatosis

Prescription ω-3 fatty acid ethyl ester supplements are commonly used for the treatment of hypertriglyceridemia. However, the metabolic profile and effect of the metabolites formed by these treatments remain unknown. Here we utilized unbiased metabolomics to identify 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) as a significant metabolite of the ω-3-acid ethyl ester prescription Lovaza™ in humans. Administration of CMPF to mice before or after high-fat diet feeding at exposures equivalent to those observed in humans increased whole-body lipid metabolism, improved insulin sensitivity, increased beta-oxidation, reduced lipogenic gene expression, and ameliorated steatosis. Mechanistically, we find that CMPF acutely inhibits ACC activity, and induces long-term loss of SREBP1c and ACC1/2 expression. This corresponds to an induction of FGF21, which is required for long-term steatosis protection, as FGF21KO mice are refractory to the improved metabolic effects. Thus, CMPF treatment in mice parallels the effects of human Lovaza™ supplementation, revealing that CMPF may contribute to the improved metabolic effects observed with ω-3 fatty acid prescriptions.

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CMPF is an abundant metabolite resultant from supplementation with the ω-3-acid ethyl ester prescription Lovaza™ in humans

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Treatment with CMPF reverses hepatic lipid accumulation in diet-induced and genetically obese mouse models

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CMPF treatment prior to high fat diet feeding prevents development of steatosis through an FGF21-dependent mechanism

Fish oil is commonly prescribed for treating dyslipidemia and metabolic syndrome. Here, we identify CMPF as a significant metabolite in humans supplemented with ω-3-acid ethyl esters. CMPF treatment reversed liver lipid accumulation and improved insulin sensitivity in obese mice, while treatment of lean mice prior to high fat diet feeding prevented the development of fatty liver and insulin resistance. We find that CMPF acutely enhances fatty acid utilization and decreases lipid synthesis in the liver, while the preventative action is dependent on FGF21, which potentiates a feedback loop activated by CMPF. Thus, CMPF may contribute to the improved metabolic effects associated with fish oil supplementation.

Fish oil prevents changes induced by a high-fat diet on metabolism and adipokine secretion in mice subcutaneous and visceral adipocytes

KEY POINTS

Fish oil (FO), rich in omega-3 polyunsaturated fatty acids, has beneficial effects on changes induced by obesity and partially prevents associated comorbidities. The effects of FO on adipocytes from different adipose tissue depots in high-fat (HF) diet induced obese mice have not been uninvestigated. This is the first study to examine the effects of FO on changes in metabolism and adipokine production in adipocytes from s.c. (inguinal; ING) or visceral (retroperitoneal; RP) white adipose depots in a HF diet-induced obese mice. Unlike most studies performed previously, FO supplementation was initiated 4 weeks before the induction of obesity. HF diet caused marked changes in ING (glucose uptake and secretion of adiponectin, tumour necrosis factor-α and interleukin-6 in ING) and RP (lipolysis, de novo lipogenesis and secretion of pro-inflammatory cytokines) adipose depots. Previous and concomitant FO administration prevented the changes in ING and RP adipocytes induced by the HF diet.

ABSTRACT

In the present study, we investigated the effect of fish oil (FO) on metabolism and adipokine production by adipocytes from s.c. (inguinal; ING) and visceral (retroperitoneal; RP) white adipose depots in high-fat (HF) diet-induced obese mice. Mice were divided into CO (control diet), CO+FO, HF and HF+FO groups. The HF group presented higher body weight, glucose intolerance, insulin resistance, higher plasma total and low-density lipoprotein cholesterol levels, and greater weights of ING and RP adipose depots accompanied by hypertrophy of the adipocytes. FO exerted anti-obesogenic effects associated with beneficial effects on dyslipidaemia and insulin resistance in mice fed a HF diet (HF+FO group). HF raised RP adipocyte lipolysis and the production of pro-inflammatory cytokines and reduced de novo synthesis of fatty acids, whereas, in ING adipocytes, it decreased glucose uptake and adiponectin secretion but did not change lipolysis. Therefore, the adipose depots play different roles in HF diet-induced insulin resistance according to their location in the body. Concerning cytokine secretion, adipocytes per se in addition to white adopise tissue infiltrated leukocytes have to be considered in the aetiology of the comorbidities associated with obesity. Evidence is presented showing that previous and concomitant administration of FO can prevent changes in metabolism and the secretion of hormones and cytokines in ING and RP adipocytes induced by HF.

Obesity development in neuron-specific lipoprotein lipase deficient mice is not responsive to increased dietary fat content or change in fat composition

We have previously reported that mice with neuron-specific LPL deficiency (NEXLPL-/-) become obese by 16weeks of age on chow. Moreover, these mice had reduced uptake of triglyceride (TG)-rich lipoprotein-derived fatty acids and lower levels of n-3 long chain polyunsaturated fatty acids (n-3 PUFAs) in the hypothalamus. Here, we asked whether increased dietary fat content or altered dietary composition could modulate obesity development in NEXLPL-/- mice. Male NEXLPL-/- mice and littermate controls (WT) were randomly assigned one of three synthetic diets; a high carbohydrate diet (HC, 10% fat), a high-fat diet (HF, 45% fat), or a HC diet supplemented with n-3 PUFAs (HCn-3, 10% fat, Lovaza, GSK®). After 42weeks of HC feeding, body weight and fat mass were increased in the NEXLPL-/- mice compared to WT. WT mice fed a HF diet displayed typical diet-induced obesity, but weight gain was only marginal in HF-fed NEXLPL-/- mice, with no significant difference in body composition. Dietary n-3 PUFA supplementation did not prevent obesity in NEXLPL-/- mice, but was associated with differential modifications in hypothalamic gene expression and PUFA concentration compared to WT mice. Our findings suggest that neuronal LPL is involved in the regulation of body weight and composition in response to either the change in quantity (HF feeding) or quality (n-3 PUFA-enriched) of dietary fat. The precise role of LPL in lipid sensing in the brain requires further investigation.

α-Linolenic acid increases the G0/G1 switch gene 2 mRNA expression in peripheral blood mononuclear cells from obese patients: a pilot study

Background

Recent evidence has demonstrated that the G0/G1 switch gene 2 (G0S2) is an important negative regulator of the rate-limiting lipolytic enzyme adipose triglyceride lipase-mediated lipolysis. It has been revealed that α-linolenic acid (ALA), a plant-based essential omega-3 polyunsaturated fatty acids, reduces adipose tissue lipolysis. However, it is not known whether G0S2 is implicated in ALA-induced inhibition of lipolysis. The purpose of this pilot study is to investigate the effect of ALA on G0S2 gene expression in peripheral blood mononuclear cells (PBMC) of obese patients and the potential influence of G0S2 gene expression in ALA-induced inhibition of lipolysis.

Methods

A total of 26 obese patients were randomly assigned to be treated with or without ALA treatment (~4.0 g daily) for 12 weeks: the ALA-treated group (n = 14) or the untreated control group (n = 12). Plasma triglyceride (TG), free fatty acids (FFA), glycerol, interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), as well as the mRNA expression levels of proliferator-activated receptor gamma (PPAR-γ), G0S2, and G protein-coupled receptor 120 (GPR120) in PBMC were repeatedly examined from fasting obese patients before and after ALA treatment.

Results

ALA significantly decreased plasma TG, FFA, glycerol, IL-6, and TNF-α levels and increased the mRNA expression levels of PPAR-γ, G0S2, and GPR120 in PBMC, compared with the untreated control group. In obese patients from the ALA-treated group, decreased plasma FFA (a biomarker for lipolysis) level was significantly correlated with increased PPAR-γ (a functional omega-3 fatty acids receptor) and G0S2 (a direct target gene of PPAR-γ) mRNA expression in PBMC, while decreased plasma FFA level was not correlated with increased GPR120 (another functional omega-3 fatty acids receptor) mRNA expression in PBMC.

Conclusion

This study shows that ALA increases G0S2 gene expression in PBMC in parallel with the decrease of plasma FFA level in obese patients. Increased G0S2 gene expression might contribute to the beneficial anti-lipolytic effect of ALA in obese patients.

Comparative actions of omega-3 fatty acids on in-vitro lipid droplet formation

Storage of fat into lipid droplets (LDs) is the key step in adipogenesis. Previously the omega-3 polyunsaturated fatty acid (n-3PUFA) eicosapentaenoic acid (EPA; C20:5n-3) has been shown to suppress LD formation, yet the actions of other n-3PUFA is unknown. Here, we examined the impact of the three major long chain n-3PUFA; EPA, docosapentaenoic acid (DPA; C22:5n-3) and docosahexaenoic acid (DHA; C22:6n-3) on LD formation in 3T3-L1 adipocytes. Cells were supplemented with 100µM fatty acid during differentiation. All n-3PUFA significantly reduced LD formation and the metabolic disorder marker, SCD1, in comparison to stearic acid (STA; C18:0). This action was more potent for DHA than either EPA or DPA. Furthermore, DHA significantly increased lipolysis and ATGL gene and protein expression but reduced the gene expression of three proteins related to LD formation (Perilipin A, Caveolin-1 and Cidea), compared with other n-3PUFA. Thus, DHA, above EPA and DPA, markedly suppressed fat storage in LDs in in-vitro adipocytes.

Effects of a diet enriched with polyunsaturated, saturated, or trans fatty acids on cytokine content in the liver, white adipose tissue, and skeletal muscle of adult mice

This study analyzed the effect of diet enriched with 30% lipids on cytokines content in different tissues. Swiss male mice were distributed into four groups treated for 8 weeks with control (C, normolipidic diet); soybean oil (S); lard (L); and hydrogenated vegetable fat (H). We observed an increase in carcass fat in groups S and L, and the total amount of fatty deposits was only higher in group L compared with C group. The serum levels of free fatty acids were lower in the L group, and insulin, adiponectin, lipid profile, and glucose levels were similar among the groups. IL-10 was lower in group L in mesenteric and retroperitoneal adipose tissues. H reduced IL-10 only in retroperitoneal adipose tissue. There was an increase in IL-6 in the gastrocnemius muscle of the L group, and a positive correlation between TNF-α and IL-10 was observed in the livers of groups C, L, and H and in the muscles of all groups studied. The results suggested relationships between the quantity and quality of lipids ingested with adiposity, the concentration of free fatty acids, and cytokine production in white adipose tissue, gastrocnemius muscle, and liver.

Oil from the marine zooplankton Calanus finmarchicus improves the cardiometabolic phenotype of diet-induced obese mice

The aim of the present study was to investigate the effects of oil extracted from the zooplankton Calanus finmarchicus (Calanus oil) on diet-induced obesity and obesity-related disorders in mice. C57BL/6J mice fed a high-fat diet (HFD, 45 % energy from fat) exhibited increased body weight and abdominal fat accumulation as well as impaired glucose tolerance compared with mice fed a normal chow diet (10 % energy from fat). Supplementing the HFD with 1·5 % (w/w) Calanus oil reduced body-weight gain, abdominal fat accumulation and hepatic steatosis by 16, 27 and 41 %, respectively, and improved glucose tolerance by 16 %. Calanus oil supplementation reduced adipocyte size and increased the mRNA expression of adiponectin in adipose tissue. It also reduced macrophage infiltration by more than 70 %, accompanied by reduced mRNA expression of pro-inflammatory cytokines (TNF-α, IL-6 and monocyte chemotactic protein-1). The effects of Calanus oil were not only preventive, but also therapeutic, as the oil proved to be beneficial, regardless of whether the supplementation was started before or after the onset of obesity and glucose intolerance. Although the present study cannot pinpoint the active component(s) of the oil, there is reason to believe that the n-3 fatty acids EPA and DHA and/or antioxidants are responsible for its beneficial effects. It should be noted that the concentration of n-3 fatty acids in the Calanus oil diet was considerably lower than the concentrations used in similar studies reporting beneficial effects on obesity and obesity-related abnormalities.

The modifying effects of fish oil on fasting ghrelin mRNA expression in weaned rats

Ghrelin expression and secretion seem to be influenced by the fat content of the diet. However, data on the probable adverse effect of high fat diet (HFD) with different dietary fats and saturation level of fatty acids is inconclusive. This study aimed at investigating the effects of HFDs on fasting total and acyl-ghrelin plasma levels, gastric fundus and duodenum ghrelin mRNA expressions. Weaned Wistar rats (n=50) were randomly divided to five groups of HFDs with fish oil (HF-F), olive oil (HF-O), soy oil (HF-S), butter (HF-B) and the controls. After 8 weeks, blood samples were collected. While the animals were fasting for 24h, their blood and tissue samples were obtained. Plasma parameters of total and acyl ghrelin and ghrelin mRNA expression level in stomach and duodenum were measured. The HF-B fed group had lower fasting plasma acyl ghrelin level than the control, HF-F and HF-O groups (P<0.05); furthermore, the HF-F group had significantly higher acyl ghrelin level than the HF-S one (P<0.05). After feeding, all the groups, except for the HF-B one, had a significantly lower plasma acyl ghrelin levels (P<0.05), compared with the fasting state. Ghrelin mRNA expression levels in the gastric fundus and duodenum were significantly lower in the HF-B as compared to the control group. Furthermore, the HF-F group had significantly higher mRNA level in the duodenum, in comparison with the HF-B and HF-S groups. As HF-F and HF-O diets had the highest stimulatory effect on fasting ghrelin expression and plasma level, consumption of these dietary oils can play an important role in ghrelin regulation, which might affect feeding behavior and energy intake.

n-3 polyunsaturated fatty acids increase thermic effect of food in men with metabolic syndrome

PURPOSE

Effects on energy metabolism of a test meal and a two-week dietary intervention were observed in men with metabolic syndrome (MetS). Both the meal and the intervention included foods containing fish-derived n-3 polyunsaturated fats (PUFA).

METHODS

Six men with MetS (46.7 ± 12.1 years, 37.2 ± 5.6 kg/m(2), mean ± standard deviation) completed two test days, separated by a 14-day dietary intervention during which they consumed at least 2.0 g per day of n-3 PUFA from supplied foods. Pre- and post-intervention measurements included body composition, resting metabolic rate (RMR), and the thermic effect of food (TEF) measured for six hours after ingestion of a test meal consisting of 1.43 g of fish-derived n-3 PUFA.

RESULTS

Intakes of n-3 PUFA increased over the 14-day intervention, from 0.43 g per day ± 0.48 to 2.92 g per day ± 1.97 (p=0.013), while no changes were observed in total energy intakes, weight, body composition, or RMR (all p>0.05). The TEF increased by 51.3% (p=0.036), and the non-protein respiratory quotient decreased by 36.0% (p=0.700).

CONCLUSIONS

Subjects increased their intake of fish-derived n-3 PUFA in an isocaloric manner while maintaining body weight and composition, and increased the TEF. More studies with larger sample sizes and longer intervention periods are required to confirm the use of fish-derived n-3 PUFA as a therapeutic dietary strategy for people with MetS.

Fish oil -- how does it reduce plasma triglycerides?

Long chain omega-3 fatty acids (FAs) are effective for reducing plasma triglyceride (TG) levels. At the pharmaceutical dose, 3.4g/day, they reduce plasma TG by about 25-50% after one month of treatment, resulting primarily from the decline in hepatic very low density lipoprotein (VLDL-TG) production, and secondarily from the increase in VLDL clearance. Numerous mechanisms have been shown to contribute to the TG overproduction, but a key component is an increase in the availability of FAs in the liver. The liver derives FAs from three sources: diet (delivered via chylomicron remnants), de novo lipogenesis, and circulating non-esterified FAs (NEFAs). Of these, NEFAs contribute the largest fraction to VLDL-TG production in both normotriglyceridemic subjects and hypertriglyceridemic, insulin resistant patients. Thus reducing NEFA delivery to the liver would be a likely locus of action for fish oils (FO). The key regulator of plasma NEFA is intracellular adipocyte lipolysis via hormone sensitive lipase (HSL), which increases as insulin sensitivity worsens. FO counteracts intracellular lipolysis in adipocytes by suppressing adipose tissue inflammation. In addition, FO increases extracellular lipolysis by lipoprotein lipase (LpL) in adipose, heart and skeletal muscle and enhances hepatic and skeletal muscle β-oxidation which contributes to reduced FA delivery to the liver. FO could activate transcription factors which control metabolic pathways in a tissue specific manner regulating nutrient traffic and reducing plasma TG. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.

Different adipose depots: their role in the development of metabolic syndrome and mitochondrial response to hypolipidemic agents

Adipose tissue metabolism is closely linked to insulin resistance, and differential fat distributions are associated with disorders like hypertension, diabetes, and cardiovascular disease. Adipose tissues vary in their impact on metabolic risk due to diverse gene expression profiles, leading to differences in lipolysis and in the production and release of adipokines and cytokines, thereby affecting the function of other tissues. In this paper, the roles of the various adipose tissues in obesity are summarized, with particular focus on mitochondrial function. In addition, we discuss how a functionally mitochondrial-targeted compound, the modified fatty acid tetradecylthioacetic acid (TTA), can influence mitochondrial function and decrease the size of specific fat depots.

Antiobesity effect of eicosapentaenoic acid in high-fat/high-sucrose diet-induced obesity: importance of hepatic lipogenesis

OBJECTIVE

Given the pleiotropic effect of eicosapentaenoic acid (EPA), it is interesting to know whether EPA is capable of improving obesity. Here we examined the anti-obesity effect of EPA in mice with two distinct models of obesity.

RESEARCH DESIGN AND METHODS

Male C57BL/6J mice were fed a high-fat/high-sucrose diet (25.0% [w/w] fat, 32.5% [w/w] sucrose) (HF/HS group) or a high-fat diet (38.1% [w/w] fat, 8.5% [w/w] sucrose) (HF group) for 4-20 weeks. A total of 5% EPA was administered by partially substituting EPA for fat in the HF/HS + EPA and HF + EPA groups.

RESULTS

Both the HF/HS and HF groups similarly developed obesity. EPA treatment strongly suppresses body weight gain and obesity-related hyperglycemia and hyperinsulinemia in HF/HS-fed mice (HF/HS + EPA group), where hepatic triglyceride content and lipogenic enzymes are increased. There is no appreciable effect of EPA on body weight in HF-fed mice (HF + EPA group) without enhanced expression of hepatic lipogenic enzymes. Moreover, EPA is capable of reducing hepatic triglyceride secretion and changing VLDL fatty acid composition in the HF/HS group. By indirect calorimetry analysis, we also found that EPA is capable of increasing energy consumption in the HF/HS + EPA group.

CONCLUSIONS

This study is the first demonstration that the anti-obesity effect of EPA in HF/HS-induced obesity is associated with the suppression of hepatic lipogenesis and steatosis. Because the metabolic syndrome is often associated with hepatic lipogenesis and steatosis, the data suggest that EPA is suited for treatment of the metabolic syndrome.

Suppressive actions of eicosapentaenoic acid on lipid droplet formation in 3T3-L1 adipocytes

Background

Lipid droplet (LD) formation and size regulation reflects both lipid influx and efflux, and is central in the regulation of adipocyte metabolism, including adipokine secretion. The length and degree of dietary fatty acid (FA) unsaturation is implicated in LD formation and regulation in adipocytes. The aims of this study were to establish the impact of eicosapentaenoic acid (EPA; C20:5n-3) in comparison to SFA (STA; stearic acid, C18:0) and MUFA (OLA; oleic acid, C18:1n-9) on 3T3-L1 adipocyte LD formation, regulation of genes central to LD function and adipokine responsiveness. Cells were supplemented with 100 μM FA during 7-day differentiation.

Results

EPA markedly reduced LD size and total lipid accumulation, suppressing PPARγ, Cidea and D9D/SCD1 genes, distinct from other treatments. These changes were independent of alterations of lipolytic genes, as both EPA and STA similarly elevated LPL and HSL gene expressions. In response to acute lipopolysaccharide exposure, EPA-differentiated adipocytes had distinct improvement in inflammatory response shown by reduction in monocyte chemoattractant protein-1 and interleukin-6 and elevation in adiponectin and leptin gene expressions.

Conclusions

This study demonstrates that EPA differentially modulates adipogenesis and lipid accumulation to suppress LD formation and size. This may be due to suppressed gene expression of key proteins closely associated with LD function. Further analysis is required to determine if EPA exerts a similar influence on LD formation and regulation in-vivo.

Postnatal hepatic fatty acid oxidative capacity of preterm pigs receiving TPN does not differ from that of term pigs and is not affected by supplemental arachidonic and docosahexaenoic acids

To improve pediatric care of preterm infants, a better understanding of the metabolic processes associated with immaturity is needed. To this end, preterm and term pigs were delivered and administered either a control, a low-PUFA [0.3 and 0.6% of total lipids as docosahexaenoic acid (DHA) and arachidonic acid (AA), respectively], or a high-PUFA (5 and 11% of total lipids as DHA and AA, respectively) parenteral solution. Hepatic oxidative capacity and carnitine palmitoyltransferase (CPT) mRNA and activity in the presence or absence of malonyl-CoA were determined after 6 d. Oxidation of [1-(14)C]-palmitate or [1-(14)C]-glucose was similar in liver homogenates isolated from preterm and term pigs receiving the control solution. Oxidative capacity for either substrate did not differ with parenteral solution in preterm pigs, whereas in term pigs, glucose oxidation was 64% greater when the high-PUFA solution was administered relative to the control (P < 0.05). In preterm pigs, CPT I mRNA determined after 6 d of parenteral feeding were 1.5-fold greater (P < 0.05) than newborn estimates irrespective of solution administered, whereas CPT I mRNA were only greater for term pigs receiving the low- and high-PUFA solutions (66 and 115%, respectively; P < 0.05) relative to newborn estimates. Malonyl-CoA-sensitive CPT activity did not differ between preterm and term pigs or parenteral solution. Postnatal adaptations demonstrated by parenterally fed term neonates are present following preterm birth and are not improved by the provision of DHA and AA to parenteral solutions.

Dietary supplementation of tetradecylthioacetic acid increases feed intake but reduces body weight gain and adipose depot sizes in rats fed on high-fat diets

AIM

The pan-peroxisome proliferator-activated receptor (PPAR) ligand and fatty acid analogue tetradecylthioacetic acid (TTA) may reduce plasma lipids and enhance hepatic lipid metabolism, as well as reduce adipose tissue sizes in rats fed on high-fat diets. This study further explores the effects of TTA on weight gain, feed intake and adipose tissue functions in rats that are fed a high-fat diet for 7 weeks.

METHODS

The effects on feed intake and body weight during 7 weeks' dietary supplement with TTA ( approximately 200 mg/kg bw) were studied in male Wistar rats fed on a lard-based diet containing approximately 40% energy from fat. Adipose tissue mass, body composition and expression of relevant genes in fat depots and liver were measured at the end of the feeding.

RESULTS

Despite higher feed intake during the final 2 weeks of the study, rats fed on TTA gained less body weight than lard-fed rats and had markedly decreased subcutaneous, epididymal, perirenal and mesenteric adipose depots. The effects of TTA feeding with reduced body weight gain and energy efficiency (weight gain/feed intake) started between day 10 and 13. Body contents of fat, protein and water were reduced after feeding lard plus TTA, with a stronger decrease in fat relative to protein. Plasma lipids, including Non-Esterified Fatty Acids (NEFA), were significantly reduced, whereas fatty acid beta-oxidation in liver and heart was enhanced in lard plus TTA-fed rats. Hepatic UCP3 was expressed ectopically both at protein and mRNA level (>1900-fold), whereas Ucp1 mRNA was increased approximately 30-fold in epididymal and approximately 90-fold in mesenteric fat after lard plus TTA feeding.

CONCLUSION

Our data support the hypothesis that TTA feeding may increase hepatic fatty acid beta-oxidation, and thereby reduce the size of adipose tissues. The functional importance of ectopic hepatic UCP3 is unknown, but might be associated with enhanced energy expenditure and thus the reduced feed efficiency.

Metabolism and secretory function of white adipose tissue: effect of dietary fat

Approximately 40% of the total energy consumed by western populations is represented by lipids, most of them being ingested as triacylglycerols and phospholipids. The focus of this review is to analyze the effect of the type of dietary fat on white adipose tissue metabolism and secretory function, particularly on haptoglobin, TNF-α, plasminogen activator inhibitor-1 and adiponectin secretion. Previous studies have demonstrated that the duration of the exposure to the high-fat feeding, amount of fatty acid present in the diet and the type of fatty acid may or may not have a significant effect on adipose tissue metabolism. However, the long-term or short-term high fat diets, especially rich in saturated fatty acids, probably by activation of toll-like receptors, stimulated the expression of proinflammatory adipokines and inhibited adiponectin expression. Further studies are needed to investigate the cellular mechanisms by which dietary fatty acids affect white adipose tissue metabolism and secretory functions.

Estimation of the metabolizable energy content of meat and bone meal for swine

Experiments were conducted to determine apparent ME (AME) and apparent nitrogen-corrected ME (AME(n)) of 21 meat and bone meal (MBM) samples and to develop regression equations for predicting energy value of MBM. One hundred ninety-eight 32-kg of BW barrows were used for the study. The 22 treatments consisted of 1 corn-soybean meal reference diet and 21 test diets in which 21 MBM samples replaced 100 g/kg of corn and soybean meal such that the ratio of corn and soybean meal was the same in the reference and test diets. The DE, AME, and AME(n) of the MBM samples were determined by the difference method in a metabolism study consisting of 5-d adjustment and 5 d of total collection of feces and urine. On a DM basis, GE of MBM ranged from 3,895 to 5,193 kcal/kg, CP ranged from 491 to 641 g/kg, and ash ranged from 142 to 338 g/kg. The AME of the MBM samples ranged from 2,320 to 3,872 kcal/kg, whereas AME(n) ranged from 2,212 to 3,767 kcal/kg. None of the proximate compositions explained >50% of the variation in energy content of the MBM. Fat was positively correlated with GE, DE, AME, and AME(n) (r < or = 0.44), but CP, ash, Ca, and P were negatively correlated with DE, AME, and AME(n). The ratios of the proximate compositions to each other were correlated with the energy contents of the MBM. Crude protein:fat and GE:fat were negatively correlated with DE, AME, and AME(n) of the MBM (r ranged from -0.17 to -0.39), but fat:ash had the greatest positive correlation with AME and AME(n) compared with other ratios tested. When the data from 1 MBM sample that was an outlier were removed from the analysis, R(2) was 0.42 for AME and AME(n). The 4 variables that produced the best prediction equation for AME and AME(n) were GE, CP, P, and ash. The prediction equation for AME using these variables was AME = 13,587 - (1.25 x GE, kcal/kg) - (3.51 x CP, g/kg) + (30.4 x P, g/kg) - (16.4 x Ash, g/kg), and for AME(n), the equation was AME(n) = 13,547 - (1.25 x GE, kcal/kg) - (3.59 x CP, g/kg) + (31.0 x P, g/kg) - (16.5 x Ash, g/kg). It was concluded from this study that MBM is a good energy source for pigs and that, although other extrinsic factors may contribute to the variations in energy content of MBM, proximate compositions should be sufficient to predict the energy value of MBM for pigs.

Marine n-3 fatty acids promote size reduction of visceral adipose depots, without altering body weight and composition, in male Wistar rats fed a high-fat diet

We evaluated the effects of partly substituting lard with marine n-3 fatty acids (FA) on body composition and weight, adipose tissue distribution and gene expression in five adipose depots of male Wistar rats fed a high-fat diet. Rats were fed diets including lard (19·5 % lard) or n-3 FA (9·1 % lard and 10·4 % Triomar™) for 7 weeks. Feed consumption and weight gain were similar, whereas plasma lipid concentrations were lower in the n-3 FA group. Magnetic resonance imaging revealed smaller visceral (mesenteric, perirenal and epididymal) adipose depots in the n-3 FA-fed animals (35, 44 and 32 % reductions, respectively). n-3 FA feeding increased mRNA expression of cytokines as well as chemokines in several adipose depots. Expression of Adipoq and Pparg was enhanced in the mesenteric adipose depots of the n-3 FA-fed rats, and fasting plasma insulin levels were lowered. Expression of the lipogenic enzymes Acaca and Fasn was increased in the visceral adipose depots, whereas Dgat1 was reduced in the perirenal and epididymal depots. Cpt2 mRNA expression was almost doubled in the mesenteric depot and liver. Carcass analyses showed similar body fat (%) in the two feeding groups, indicating that n-3 FA feeding led to redistribution of fat away from the visceral compartment.

Metabolic flexibility in the development of insulin resistance and type 2 diabetes: effects of lifestyle

Lipotoxicity in skeletal muscle plays a critical role in the aetiology of insulin resistance and type 2 diabetes mellitus by interference of lipid metabolites with insulin signalling and action. The dynamics of lipid oxidation and fine tuning with fatty acid uptake and intramyocellular triacylglycerol turnover may be very important to limit the accumulation of lipid intermediates. The use of metabolic inflexibility, defined as the impaired capacity to increase fat oxidation upon increased fatty acid availability and to switch between fat and glucose as the primary fuel source after a meal, does more justice to the complexity of changes in fuel oxidation during the day. Fatty acid availability, uptake and oxidation all play a role in metabolic flexibility and insulin resistance. During high fatty acid availability, fatty acid transporters may limit cellular and mitochondrial fatty acid uptake and thus limit fat oxidation. After a meal, when the demand for fatty acids as fuel is low, an increased fractional extraction of lipids from plasma may promote intramyocellular lipid accumulation and insulin resistance. Furthermore, defects in fuel switching cluster together with impaired mitochondrial content and/or function. Lifestyle changes in dietary fat intake, physical activity and weight loss may improve metabolic flexibility in skeletal muscle, and thereby contribute to the prevention of type 2 diabetes.

Fish oil reduces heart rate and oxygen consumption during exercise

Dietary omega-3 polyunsaturated fatty acids (PUFAs) are readily incorporated into heart and skeletal muscle membranes where, in the heart, animal studies show they reduce O2 consumption. To test the hypothesis that omega-3 PUFAs alter O2 efficiency in humans, the effects of fish oil (FO) supplementation on O2 consumption during exercise were evaluated. Sixteen well-trained men (cyclists), randomly assigned to receive 8 x 1 g capsules per day of olive oil (control) or FO for 8 weeks in a double-blind, parallel design, completed the study (control: n = 7, age 27.1 +/- 2.7 years; FO: n = 9, age 23.2 +/- 1.2 years). Subjects used an electronically braked cycle ergometer to complete peak O2 consumption tests (VO 2peak) and sustained submaximal exercise tests at 55% of peak workload (from the VO 2peak test) before and after supplementation. Whole-body O2 consumption and indirect measurements of myocardial O2 consumption [heart rate and rate pressure product (RPP)] were assessed. FO supplementation increased omega-3 PUFA content of erythrocyte cell membranes. There were no differences in VO 2peak (mL kg(-1) min(-1)) (control: pre 66.8 +/- 2.4, post 67.2 +/- 2.3; FO: pre 68.3 +/- 1.4, post 67.2 +/- 1.2) or peak workload after supplementation. The FO supplementation lowered heart rate (including peak heart rate) during incremental workloads to exhaustion (P < 0.05). In addition, the FO supplementation lowered steady-state submaximal exercise heart rate, whole-body O2 consumption, and RPP (P < 0.01). Time to voluntary fatigue was not altered by FO supplementation. This study indicates that FOs may act within the healthy heart and skeletal muscle to reduce both whole-body and myocardial O2 demand during exercise, without a decrement in performance.

Eicosapentaenoic acid actions on adiposity and insulin resistance in control and high-fat-fed rats: role of apoptosis, adiponectin and tumour necrosis factor-alpha

n-3 PUFA have shown potential anti-obesity and insulin-sensitising properties. However, the mechanisms involved are not clearly established. The aim of the present study was to assess the effects of EPA administration, one of the n-3 PUFA, on body-weight gain and adiposity in rats fed on a standard or a high-fat (cafeteria) diet. The actions on white adipose tissue lipolysis, apoptosis and on several genes related to obesity and insulin resistance were also studied. Control and cafeteria-induced overweight male Wistar rats were assigned into two subgroups, one of them daily received EPA ethyl ester (1 g/kg) for 5 weeks by oral administration. The high-fat diet induced a very significant increase in both body weight and fat mass. Rats fed with the cafeteria diet and orally treated with EPA showed a marginally lower body-weight gain (P = 0.09), a decrease in food intake (P < 0.01) and an increase in leptin production (P < 0.05). EPA administration reduced retroperitoneal adipose tissue weight (P < 0.05) which could be secondary to the inhibition of the adipogenic transcription factor PPARgamma gene expression (P < 0.001), and also to the increase in apoptosis (P < 0.05) found in rats fed with a control diet. TNFalpha gene expression was significantly increased (P < 0.05) by the cafeteria diet, while EPA treatment was able to prevent (P < 0.01) the rise in this inflammatory cytokine. Adiposity-corrected adiponectin plasma levels were increased by EPA. These actions on both TNFalpha and adiponectin could explain the beneficial effects of EPA on insulin resistance induced by the cafeteria diet.

Effect of DHA supplementation on digestible starch utilization by rainbow trout

Rainbow trout has a limited ability to utilize digestible carbohydrates efficiently. Trout feeds generally contain high levels of DHA, a fatty acid known to inhibit a number of glycolytic and lipogenic enzymes in animals. A study was conducted to determine whether carbohydrate utilization by rainbow trout might be affected by dietary DHA level. Two low-carbohydrate (<4% digestible carbohydrate) basal diets were formulated to contain 1 (adequate) or 4 (excess)g/100g DHA diet respectively. The two basal diets were diluted with increasing levels of digestible starch (0%, 10%, 20% and 30%, respectively) to produce eight diets. These diets were fed to fish for 12 weeks at 15°C according to a pair-fed protocol that consisted of feeding the same amount of basal diet but different amounts of starch. Live weight, N and lipid gains, hepatic glycogen and plasma glucose values significantly increased, whereas feed efficiency (gain:feed) significantly decreased, with increasing starch intake (P<0·05). The retention efficiency of N (N gain/digestible N intake) improved with starch supplementation but was not affected by DHA level (P>0·05). Starch increased the activity of glucokinase, pyruvate kinase, glucose 6-phosphate dehydrogenase and fatty acid synthase (P<0·05) but did not affect hexokinase and malic enzyme activity. DHA had no effect on growth but increased plasma glucose and reduced carcass lipid and liver glycogen contents (P<0·05). Glycolytic and lipogenic enzymes were not affected by DHA level, except for pyruvate kinase, which was reduced by increasing DHA level. These results suggest only a marginal effect of dietary DHA on the ability of fish to utilize carbohydrate.

Eicosapentaenoic acid (20:5 n-3) increases fatty acid and glucose uptake in cultured human skeletal muscle cells

This study was conducted to evaluate the chronic effects of eicosapentaenoic acid (EPA) on fatty acid and glucose metabolism in human skeletal muscle cells. Uptake of [14C]oleate was increased >2-fold after preincubation of myotubes with 0.6 mM EPA for 24 h, and incorporation into various lipid classes showed that cellular triacylgycerol (TAG) and phospholipids were increased 2- to 3-fold compared with control cells. After exposure to oleic acid (OA), TAG was increased 2-fold. Insulin (100 nM) further increased the incorporation of [14C]oleate into all lipid classes for EPA-treated myotubes. Fatty acid beta-oxidation was unchanged, and complete oxidation (CO2) decreased in EPA-treated cells. Basal glucose transport and oxidation (CO2) were increased 2-fold after EPA, and insulin (100 nM) stimulated glucose transport and oxidation similarly in control and EPA-treated myotubes, whereas these responses to insulin were abolished after OA treatment. Lower concentrations of EPA (0.1 mM) also increased fatty acid and glucose uptake. CD36/FAT (fatty acid transporter) mRNA expression was increased after EPA and OA treatment compared with control cells. Moreover, GLUT1 expression was increased 2.5-fold by EPA, whereas GLUT4 expression was unchanged, and activities of the mitogen-activated protein kinase p38 and extracellular signal-regulated kinase were decreased after treatment with OA compared with EPA. Together, our data show that chronic exposure of myotubes to EPA promotes increased uptake and oxidation of glucose despite a markedly increased fatty acid uptake and synthesis of complex lipids.

Substituting dietary linoleic acid with alpha-linolenic acid improves insulin sensitivity in sucrose fed rats

This study describes the effect of substituting dietary linoleic acid (18:2 n-6) with alpha-linolenic acid (18:3 n-3) on sucrose-induced insulin resistance (IR). Wistar NIN male weanling rats were fed casein based diet containing 22 energy percent (en%) fat with approximately 6, 9 and 7 en% saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) respectively for 3 months. IR was induced by replacing starch (ST) with sucrose (SU). Blends of groundnut, palmolein, and linseed oil in different proportions furnished the following levels of 18:3 n-3 (g/100 g diet) and 18:2 n-6/18:3 n-3 ratios respectively: ST-220 (0.014, 220), SU-220 (0.014, 220), SU-50 (0.06, 50), SU-10 (0.27, 10) and SU-2 (1.1, 2). The results showed IR in the sucrose fed group (SU-220) as evidenced by increase in fasting plasma insulin and area under the curve (AUC) of insulin in response to oral glucose load. In SU-220, the increase in adipocyte plasma membrane cholesterol/phospholipid ratio was associated with a decrease in fluidity, insulin stimulated glucose transport, antilipolytic effect of insulin and increase in basal and norepinephrine stimulated lipolysis in adipocytes. In SU-50, sucrose induced alterations in adipocyte lipolysis and antilipolysis were normalized. However, in SU-2, partial corrections in plasma insulin, AUC of insulin and adipocyte insulin stimulated glucose transport were observed. Further, plasma triglycerides and cholesterol decreased in SU-2. In diaphragm phospholipids, the observed dose dependent increase in long chain (LC) n-3 PUFA was associated with a decrease in LC-n-6 PUFA but insulin stimulated glucose transport increased only in SU-2. Thus, this study shows that the substitution of one-third of dietary 18:2 n-6 with 18:3 n-3 (SU-2) results in lowered blood lipid levels and increases peripheral insulin sensitivity, possibly due to the resulting high LCn-3 PUFA levels in target tissues of insulin action. These findings suggest a role for 18:3 n-3 in the prevention of insulin resistant states. The current recommendation to increase 18:3 n-3 intake for reducing cardiovascular risk may also be beneficial for preventing IR in humans.

Regulation of adipocyte differentiation and function by polyunsaturated fatty acids

A diet enriched in PUFAs, in particular of the n-3 family, decreases adipose tissue mass and suppresses development of obesity in rodents. Although several nuclear hormone receptors are identified as PUFA targets, the precise molecular mechanisms underlying the effects of PUFAs still remain to be elucidated. Here we review research aimed at elucidating molecular mechanisms governing the effects of PUFAs on the differentiation and function of white fat cells. This review focuses on dietary PUFAs as signaling molecules, with special emphasis on agonistic and antagonistic effects on transcription factors currently implicated as key players in adipocyte differentiation and function, including peroxisome proliferator activated receptors (PPARs) (alpha, beta and gamma), sterol regulatory element binding proteins (SREBPs) and liver X receptors (LXRs). We review evidence that dietary n-3 PUFAs decrease adipose tissue mass and suppress the development of obesity in rodents by targeting a set of key regulatory transcription factors involved in both adipogensis and lipid homeostasis in mature adipocytes. The same set of factors are targeted by PUFAs of the n-6 family, but the cellular/physiological responses are dependent on the experimental setting as n-6 PUFAs may exert either an anti- or a proadipogenic effect. Feeding status and hormonal background may therefore be of particular importance in determining the physiological effects of PUFAs of the n-6 family.

The hypotriglyceridemic effect of dietary n-3 FA is associated with increased beta-oxidation and reduced leptin expression

To study the mechanisms responsible for the hypotriglyceridemic effect of marine oils, we monitored the effects of high dietary intake of n-3 PUFA on hepatic and muscular beta-oxidation, plasma leptin concentration, leptin receptor gene expression, and in vivo insulin action. Two groups of male Wistar rats were fed either a high-fat diet [28% (w/w) of saturated fat] or a high-fat diet containing 10% n-3 PUFA and 18% saturated fat for 3 wk. The hypotriglyceridemic effect of n-3 PUFA was accompanied by increased hepatic oxidation of palmitoyl-CoA (125%, P < 0.005) and palmitoyl-L-carnitine (480%, P < 0.005). These findings were corroborated by raised carnitine palmitoyltransferase-2 activity (154%, P < 0.001) and mRNA levels (91%, P < 0.01) as well as by simultaneous elevation of hepatic peroxisomal acyl-CoA oxidase activity (144%, P < 0.01) and mRNA content (82%, P < 0.05). In contrast, hepatic carnitine palmitoyltransferase-1 activity remained unchanged despite a twofold increased mRNA level after n-3 PUFA feeding. Skeletal muscle FA oxidation was less affected by dietary n-3 PUFA, and the stimulatory effect was found only in peroxisomes. Dietary intake of n-3 PUFA was followed by increased acyl-CoA oxidase activity (48%, P < 0.05) and mRNA level (83%, P < 0.05) in skeletal muscle. The increased FA oxidation after n-3 PUFA supplementation of the high-fat diet was accompanied by lower plasma leptin concentration (-38%, P < 0.05) and leptin mRNA expression (-66%, P < 0.05) in retroperitoneal adipose tissue, and elevated hepatic mRNA level for the leptin receptor Ob-Ra (140%, P < 0.05). Supplementation of the high-fat diet with n-3 PUFA enhanced in vivo insulin sensitivity, as shown by normalization of the glucose infusion rate during euglycemic hyperinsulinemic clamp. Our results indicate that the hypotriglyceridemic effect of dietary n-3 PUFA is associated with stimulation of FA oxidation in the liver and to a smaller extent in skeletal muscle. This may ameliorate dyslipidemia, tissue lipid accumulation, and insulin action, in spite of decreased plasma leptin level and leptin mRNA in adipose tissue.

Arachidonic acid-dependent inhibition of adipocyte differentiation requires PKA activity and is associated with sustained expression of cyclooxygenases

Arachidonic acid inhibits adipocyte differentiation of 3T3-L1 cells via a prostaglandin synthesis-dependent pathway. Here we show that this inhibition requires the presence of a cAMP-elevating agent during the first two days of treatment. Suppression of protein kinase A activity by H-89 restored differentiation in the presence of arachidonic acid. Arachidonic acid treatment led to a prolonged activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2), and suppression of ERK1/2 activity by the addition of U0126 rescued differentiation. Upon induction of differentiation, expression of cyclooxygenase-2 (COX-2) was transiently induced and then declined, whereas COX-1 expression declined gradually as differentiation progressed. Treatment with arachidonic acid led to sustained expression of COX-1 and COX-2. Omission of a cAMP-elevating agent or addition of H-89 or U0126 prevented sustained expression of COX-2. Unexpectedly, we observed that selective COX-1 or COX-2 inhibitors rescued adipocyte differentiation in the presence of arachidonic acid as effectively as did the nonselective COX-inhibitor indomethacin. De novo fatty acid synthesis, diacylglycerol acyltransferase (DGAT) activity, and triacylglycerol accumulation were repressed in cells treated with arachidonic acid. Indomethacin restored DGAT activity and triacylglycerol accumulation without restoring de novo fatty acid synthesis, resulting in an enhanced incorporation of arachidonic acid into cellular triacylglycerols.

Dietary effect of different high-fat diet on rat liver stereology

BACKGROUND/AIMS

Dietary habits are considered to be responsible for a fatty liver. The aims of this work are to study the effects of different lipid sources on rat hepatic structure.

METHODS

Twenty 21-day-old to 18-month-old male rats were fed one of the following diets: soybean oil, canola oil, lard and egg yolk (LE), or canola oil+lard and egg yolk (CA+LE). The blood serum triglyceride samples were analyzed. The following hepatic biometry and the stereology parameters were determined: densities of volume (V(v)) and surface (S(v)), absolute volume (V) and surface (S) of the hepatocytes (h), fat globules (g), and hepatic sinusoids (s), and numerical density of the hepatocytes (N(v)[h]).

RESULTS

The largest values of V(v)[h], S(v)[h], V[h], and S[h] were found in the LE group. However, the largest values of V(v)[g], S(v)[g], and S[g] were found in the CA+LE group, and the smallest values of those parameters were found in the LE group. On the other hand, V[g] was larger in the CA+LE group. V(v)[s] and V[s] were larger in the LE group and smaller in the CA+ LE group.

CONCLUSION

Long-term administration of canola oil or soybean oil resulted in similar effects on hepatocytes, hepatic sinusoids, and fat globules. Long-term administration of lard and egg yolk attenuates hepatic fat accumulation and increases hepatic sinusoids. The administration of the canola oil and lard and egg yolk mixture increases hepatic fat accumulation, reducing the hepatic sinusoids.

Dietary fish oil increases lipid mobilization but does not decrease lipid storage-related enzyme activities in adipose tissue of insulin-resistant, sucrose-fed rats

Fish oil feeding has been shown to limit visceral fat accumulation in insulin-resistant rats. Our goal was to determine whether this finding is due to increased fat mobilization or decreased lipid storage. Adipocytes were isolated from rats fed for 3 wk a diet containing 57.5 g/100 g sucrose and 14 g/100 g lipids as either fish oil (SF) or a mixture of standard oils (SC); there was also a reference group (R). Substituting fish oil for standard oils protected rats from visceral fat hypertrophy, hypertriglyceridemia and hyperglycemia. The stimulation of lipolysis was greater in adipocytes isolated from SF-fed rats than in those from SC-fed rats. Fatty acid synthase (FAS) activity was markedly lower in the liver but not in the adipose tissues of rats fed SF. Lipoprotein lipase (LPL) activity was 2.2-fold higher in the adipose tissues but not in the muscle in rats fed the SF diet than in those fed the SC diet. The decrease in visceral fat in rats fed fish oil could be attributed to decreased plasma triacylglycerol concentration and/or increased lipid mobilization rather than to reduced lipid storage.

Dietary (n-3) fat and cholesterol alter tissue antioxidant enzymes and susceptibility to oxidation in SHR and WKY rats

Previously, 8% fish oil blend diets, compared to butter and soybean oil blend diets, reduced specific antioxidant enzyme activities and tissue susceptibility to in vitro oxidative stress in spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats. Moreover, high cholesterol (5.0 g/kg diet) diets protected against in vitro tissue lipid oxidation. In this study, we hypothesized that 160 g fat/kg diet as blends of (n-6) or (n-3) oils and cholesterol would alter antioxidant enzyme activities and thus increase tissue susceptibility to oxidation. The effects of diet blends of saturated (butter, B), (n-6) (soybean oil, SBO) or (n-3) (menhaden oil, MO) oils with cholesterol (0.5 or 5.0 g/kg) on systolic blood pressure (SBP), plasma lipids, antioxidant enzymes and susceptibility to oxidation were examined in SHR and WKY rats. SBP at 13 wk of age was greater (P < 0.001) in SHR than in WKY rats, but was not affected by diets. Plasma cholesterol and triacylglycerols were decreased (P < 0.001) by MO diets. Hepatic glutathione reductase activities were reduced (P < 0.001) in SBO-fed SHR and enhanced in SBO- and MO-fed WKY rats. Glutathione levels were reduced (P < 0.001) in RBC and enhanced (P < 0.001) in livers of MO-fed rats. Lipid oxidation was enhanced (P < 0.001) in red blood cells (RBC) from SBO groups, and hearts and livers of MO groups. High cholesterol diets reduced (P < or = 0.001) susceptibility to lipid peroxidation in RBC and liver of SHR and WKY rats. Greater amounts of dietary (n-3) fat enhance tissue susceptibility to oxidation, which can be modulated by increased dietary cholesterol in SHR and WKY rats.

Role of dietary fat type in the development of adiposity from dietary obesity-susceptible Sprague-Dawley rats

The present study was designed to define how dietary fat type regulates body adiposity in dietary obesity-susceptible (DOS) Sprague-Dawley (SD) rats. Eighty-three SD rats received a purified diet containing 50 g maize oil (MO)/kg for 3 weeks and then thirty-nine of the rats, designated as the DOS rats, were allotted to diets containing 160 g MO (DOS-MO), beef tallow (DOS-BT) or fish oil (DOS-FO)/kg for 9 weeks. As a result of the experiment, the DOS-FO rats had significantly (P<0.05) reduced weight gain and abdominal and epididymal fat-pad mass than the DOS-MO and DOS-BT rats. Serum leptin level was also significantly (P<0.05) lower in the DOS-FO rats; however, hypothalamic leptin receptor (a and b) mRNA and neuropeptide Y expressions were not altered by dietary fat sources. A lower acetyl-CoA carboxylase mRNA expression in the liver was observed in the DOS-FO group, whereas hepatic peroxisome proliferator-activated receptor-gamma mRNA and protein expressions were markedly elevated in the DOS-FO group compared with those in the other groups. We did not observe differences in acetyl-CoA carboxylase and peroxisome proliferator-activated receptor-gamma expressions in epididymal fat of the DOS rats consuming MO, BT or FO. It is concluded from our present observations that dietary fat type, especially that rich in FO, plays a potential role in down-regulation of adiposity by altering hepatic lipogenic genes, rather than feeding behaviour, in the DOS-SD rats.

Diets rich in polyunsaturated fatty acids: effect on hepatic metabolism in rats

OBJECTIVE

We investigated the effect of diets rich in omega-6 and omega-3 fatty acids on hepatic metabolism.

METHODS

Male Wistar rats, just weaned, were fed ad libitum for 8 wk with one of the following diets: rat chow (C), rat chow containing 15% (w/w) soybean oil (S), rat chow containing 15% (w/w) fish oil (F), and rat chow containing 15% soy bean and fish oil (SF; 5:1, w/w). Casein was added to the fatty diets to achieve the same content of protein (20%) as the control chow. The rats were killed by decapitation, and the hepatic tissue was removed and weighed. Tissue lipid, glycogen, and protein content, in vivo lipogenesis rate, and adenosine triphosphate citrate lyase and malic enzyme activities were evaluated. Plasma total lipids, triacylglycerol, and cholesterol concentrations were assessed.

RESULTS

Body weight gain was higher in F and SF than in C and S rats. Liver weight, lipid content, and lipogenesis rate increased in F and SF rats, although adenosine triphosphate citrate lyase activity decreased. Glycogen concentration decreased in S, F, and SF rats compared with C rats. Plasma total lipids and triacylglycerol concentrations were lower in F and SF than in C rats. Total and high-density lipoprotein cholesterol (HDL-C) plasma levels decreased in F rats, with maintenance of the total:HDL-C ratio. In SF rats, an increase in HDL-C led to a lower total:HDL-C ratio.

CONCLUSIONS

These results indicated that an enrichment of the diet with omega-3 polyunsaturated fatty acids produces hypolipidemia but may cause changes in liver metabolism that favor lipid deposition. They also suggested that the addition of a small amount of eicosapentaenoic and docosahexaenoic polyunsaturated fatty acids to an omega-6-rich diet further improve the circulating lipid profile, in comparison with an omega-3-rich diet, but it does not prevent excess liver lipid accumulation.

Effects of dietary fatty acids and exercise on body-weight regulation and metabolism in rats

OBJECTIVE

To assess the interaction of high-fat diets (HF) made with different dietary fatty acids and exercise on body-weight regulation, adiposity, and metabolism.

RESEARCH METHODS AND PROCEDURES

Male Wistar rats born to dams fed HF diets (40% w/w) made with either fish oil (FO), soybean oil (SO), or palm oil (PO) were fed diets similar to their dams and divided randomly into exercise (EX, swimming) or sedentary control (SD) groups when they were 9 weeks old. EX lasted for 6 weeks. Twenty-four hours after the last EX bout, fasted rats were killed by decapitation. Chemical analyses and body composition analysis were conducted.

RESULTS

The results demonstrated that different fatty acids had different effects on body weight, composition, and metabolism. SO-fed rats gained the most weight and fat. EX reduced body weight of FO- and PO-fed rats, but SO-fed rats were still heavier and fatter than other rats. Data from SO- and PO-fed rats suggested that they are insulin resistant and that EX normalized this abnormality. Of the three HF diets used, FO produced the least adverse effects compared with PO and SO.

DISCUSSION

Not only the quantity of dietary fat, but also the type of fat used, will produce different effects on body weight and metabolism. EX ameliorates the suggested insulin resistance induced in rats fed either highly saturated or n-6 polyunsaturated fatty acids. Long-chain n-3 polyunsaturated fatty acids, as found in fish oil, are more beneficial than n-6 polyunsaturated fatty acids when fed in high amounts to rats.

Effect of eicosapentaenoic acid ethyl ester v. oleic acid-rich safflower oil on insulin resistance in type 2 diabetic model rats with hypertriacylglycerolaemia

The purpose of the present study was to test whether hyperlipidaemia and insulin resistance in type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats can be improved by dietary supplementation with purified eicosapentaenoic acid (EPA) or oleic acid (OA). Male OLETF rats were fed powdered chow (510 g fat/kg) alone (n 8) or chow supplemented with 10 g EPA- (n 8) or OA- (n 8) rich oil/kg per d from 5 weeks until 30 weeks of age. An oral glucose tolerance test and hyperinsulinaemic euglycaemic clamp was performed at 25 and 30 weeks of age. EPA supplementation resulted in significantly (P<0.05) reduced plasma lipids, hepatic triacylglycerols, and abdominal fat deposits, and more efficient in vivo glucose disposal compared with OA supplementation and no supplementation. OA supplementation was associated with significantly increased insulin response to oral glucose compared with EPA supplementation and no supplementation. Inverse correlation was noted between glucose uptake and plasma triacylglycerol levels (r -086, P<0.001) and abdominal fat volume (r -0.80, P<0.001). The result of oral glucose tolerance test study showed that the rats fed EPA tended to improve glucose intolerance, although this was not statistically significant. Levels of plasma insulin at 60 min after glucose was significantly increased in rats fed OA compared with the other two groups. The results indicate that long-term feeding of EPA might be effective in preventing insulin resistance in diabetes-prone rats, at least in part, due to improving hypertriacylglycerolaemia.

Polyunsaturated fatty acid-rich diets: effect on adipose tissue metabolism in rats

The aim of the present study was to evaluate the effect of diets rich in n-6 and n-3 fatty acids on adipose tissue metabolism. Starting at weaning, male Wistar rats were fed ad libitum, for 8 weeks with one of the following diets: C, rat chow; S, rat chow containing 15 % (w/w) soyabean oil; F, rat chow containing 15 % (w/w) fish oil; SF, rat chow containing 15 % (w/w) soyabean and fish oil (5:1, w/w). Casein was added to the fat diets to achieve the same 20 % (w/w) protein content as in the control chow. Food intake and body weight were measured weekly. The rats were killed by decapitation and the retroperitoneal (RET) and epididymal (EPI) white adipose tissues were removed and weighed. Tissue lipid and protein content, in vivo lipogenesis rate, uptake of diet-derived lipids, in vitro lipolytic rate, adipocyte area, lipoprotein lipase, ATP citrate lyase, and malic enzyme activities were evaluated. Carcass lipid and protein contents were also measured. Energy intake was reduced while carcass lipid content was increased in the three fat-fed groups. However, carcass protein and body weight gains were elevated only with diets F and SF. Lipolysis rate was diminished by diets F and SF, while the uptake of diet-derived lipids was elevated by the diet S in both RET and EPI tissues. These metabolic alterations may have contributed to the increase in in vivo lipogenesis rate in the presence of decreased ATP citrate lyase and malic enzyme activities induced by the three lipid diets. These results indicate that enrichment of the diet with polyunsaturated fatty acids causes changes in adipose tissue metabolism that favour fat deposition. Different metabolic pathways were preferentially affected by each type of fatty acid used.

Selectivity of fatty acids on lipid metabolism and gene expression

Triacylglycerols represent the main form of storage for a wide spectrum of fatty acids. Their utilization first involves mobilization from adipose tissue through lipolysis. The release of individual fatty acids from adipose tissue is selective in vitro and in vivo in animal studies and also in human subjects. Generally, fatty acids are more readily mobilized from fat cells when they are short-chain and unsaturated. This selectivity could affect the storage of individual fatty acids in adipose tissue, and their subsequent supply to tissues. The nature of the dietary fats could affect lipid homeostasis and body fat deposition. Dietary fish oil influences adipose tissue development in a site-specific manner as a function of diet and feeding period. A diet high in n-3 polyunsaturated fatty acids (PUFA) results in a preferential partitioning of ingested energy towards oxidation at the expense of storage. Fatty acids are important mediators of gene expression in the liver. Indeed, genes encoding both glycolytic and lipogenic enzymes and key metabolic enzymes involved in fatty acid oxidation are regulated by dietary PUFA. White adipose tissue could also be a target for PUFA control of gene expression. The treatment of pre-adipose cells by fatty acids induces the expression of numerous genes that encode proteins involved in fatty acid metabolism. The mechanisms of PUFA-mediated repression of gene expression in adipocytes seem to be different, at least partly, from those described in liver. Tissue-specific and site-specific factors are possibly involved in the specific effect of PUFA on gene expression, although other mechanisms cannot be excluded.

Dietary proteins modulate the effects of fish oil on triglyceridemia in the rat

Sprague-Dawley rats were fed purified diets varying in both protein (20%) and lipid (11%) content for 28 d to verify the independent and interactive effects of dietary proteins and lipids on serum and hepatic lipids, and on tissue lipoprotein lipase (LPL) activity in both fasted and postprandial states. These diets consisted of either casein-menhaden oil, casein-coconut oil, soy protein-menhaden oil (SPMO), soy protein-coconut oil, cod protein-menhaden oil, or cod protein-coconut oil. A randomized 3 x 2 factorial design was used. A significant protein-lipid interaction was seen on serum triglyceride levels: menhaden oil, compared with coconut oil, induced a decrease in serum triglyceride levels when combined with soy protein but not when combined with cod protein and casein. The lower serum triglyceride concentrations observed in the SPMO-fed rats could be the result of decreased hepatic triglycerides when soy protein was compared with casein and when menhaden oil was compared with coconut oil. Total LPL activity in the heart was higher in menhaden oil-fed rats than in coconut oil-fed rats in the postprandial state. The higher LPL activity in the heart could, however, explain only 10% of the reduction of serum triglycerides, contributing slightly to the lowering effects of SPMO diet on serum triglycerides. Therefore, the present results indicate that dietary proteins can modulate the effects of fish oil on triglyceridemia in the rat, and that could be mainly related to specific alterations in hepatic lipid concentrations.