Effect of DHA-rich fish oil on PPARγ target genes related to lipid metabolism in type 2 diabetes: A randomized, double-blind, placebo-controlled clinical trial

BACKGROUND

The beneficial effects of omega-3 polyunsaturated fatty acids on lipid levels are well documented. However, the related molecular mechanisms are widely unknown. Omega-3 polyunsaturated fatty acids are natural ligand for peroxisome proliferator-activated receptor γ (PPARγ).

OBJECTIVE

The aim of this study was to evaluate the effect of docosahexaenoic acid (DHA)-rich fish oil supplementation on modulation of some PPARγ-responsive genes related to lipid metabolism.

METHODS

Patients with type 2 diabetes were randomly assigned to consume either DHA-rich fish oil (containing 2400 mg/d fish oil; DHA: 1450 mg and eicosapentaenoic acid: 400 mg) or placebo for 8 weeks. Lipid profile and glycemic control parameters as well as the gene expression of PPARγ, liver x receptor-a, ATP-binding cassette A1, and CD36 in peripheral blood mononuclear cells were measured at baseline and after 8 weeks.

RESULTS

DHA-rich fish oil supplementation resulted in decreased triglycerides (TG) level compared with placebo group, independently of the baseline value of TG (all patients (P = .003), hypertriglyceridemic subjects (P = .01), and normotriglyceridemic subjects (P = .02)). Moreover, a higher reduction in TG level was observed in hypertriglyceridemic subjects, comparing to normotriglyceridemic subjects with DHA-rich fish oil supplementation (P = .01). Other lipid parameters as well as the expression of PPARγ, liver x receptor-a, ATP-binding cassette A1, and CD36 were not affected by DHA-rich fish oil supplementation. Only in hypertriglyceridemic subjects, DHA-rich fish oil supplementation upregulated CD36 expression, compared with the placebo group (P = .01).

CONCLUSIONS

DHA-rich fish oil supplementation for 8 weeks increased CD36 expression in hypertriglyceridemic subjects, which might result to higher reduction in TG level, comparing with normotriglyceridemic subjects. However, this finding should be investigated in further studies.

Omega-3 fatty acids and adipose tissue function in obesity and metabolic syndrome

The n-3 long-chain polyunsaturated fatty acids (n-3 PUFAs) such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) have been reported to improve obesity-associated metabolic disorders including chronic inflammation, insulin resistance and dyslipidaemia. Growing evidence exits about adipose tissue as a target in mediating the beneficial effects of these marine n-3 PUFAs in adverse metabolic syndrome manifestations. Therefore, in this manuscript we focus in reviewing the current knowledge about effects of marine n-3 PUFAs on adipose tissue metabolism and secretory functions. This scope includes n-3 PUFAs actions on adipogenesis, lipogenesis and lipolysis as well as on fatty acid oxidation and mitochondrial biogenesis. The effects of n-3 PUFAs on adipose tissue glucose uptake and insulin signaling are also summarized. Moreover, the roles of peroxisome proliferator-activated receptor γ (PPARγ) and AMPK activation in mediating n-3 PUFAs actions on adipose tissue functions are discussed. Finally, the mechanisms underlying the ability of n-3 PUFAs to prevent and/or ameliorate adipose tissue inflammation are also revised, focusing on the role of n-3 PUFAs-derived specialized proresolving lipid mediators such as resolvins, protectins and maresins.

Maternal omega-3 fatty acids and micronutrients modulate fetal lipid metabolism: A review

It is well established that alterations in the mother's diet or metabolism during pregnancy has long-term adverse effects on the lipid metabolism in the offspring. There is growing interest in the role of specific nutrients especially omega-3 fatty acids in the pathophysiology of lipid disorders. A series of studies carried out in humans and rodents in our department have consistently suggested a link between omega-3 fatty acids especially docosahexaenoic acid and micronutrients (vitamin B12 and folic acid) in the one carbon metabolic cycle and its effect on the fatty acid metabolism, hepatic transcription factors and DNA methylation patterns. However the association of maternal intake or metabolism of these nutrients with fetal lipid metabolism is relatively less explored. In this review, we provide insights into the role of maternal omega-3 fatty acids and vitamin B12 and their influence on fetal lipid metabolism through various mechanisms which influence phosphatidylethanolamine-N-methyltransferase activity, peroxisome proliferator activated receptor, adiponectin signaling pathway and epigenetic process like chromatin methylation. This will help understand the possible mechanisms involved in fetal lipid metabolism and may provide important clues for the prevention of lipid disorders in the offspring.

Transgenic ω-3 PUFA enrichment alters morphology and gene expression profile in adipose tissue of obese mice: Potential role for protectins

OBJECTIVE

Dietary administration of ω-3 polyunsaturated fatty acids (PUFA) is often associated with altered adipose tissue (AT) morphology and/or function in obese mice. Yet, it is unclear whether this is an indirect consequence of reduced weight gain or results from direct actions of ω-3 PUFA. Here we studied the AT of high fat (HF)-fed fat-1 transgenic mice that convert endogenous ω-6 to ω-3 PUFA while maintaining equivalent fat accretion as their wild-type (WT) counterparts.

MATERIALS AND METHODS

Adipocyte size profiling, Affymetrix microarray pathway analysis, qPCR and protectin identification and analysis were performed in epididymal AT from hemizygous fat-1(+/-) mice and their wild type littermates that had been fed a HF diet for 8weeks from 6weeks of age.

RESULTS

Despite equivalent fat pad mass, we found that epididymal AT from HF-fed transgenic animals possesses fewer large and very large but more mid-size adipocytes compared to WT mice. In order to better understand the underlying mechanisms contributing to the observed alteration in adipocyte size we performed an Affymetrix microarray. Pathway analysis of these data highlighted adipogenesis, cholesterol biosynthesis, insulin signaling, prostaglandin synthesis/regulation and small ligand GPCRs as points where differentially expressed genes were significantly overrepresented. Observed changes were confirmed for four candidate genes: Cnr1, Cnr2, Faah and Pparg by qPCR. Finally we demonstrated that protectin DX is present in AT and that protectin DX and protectin D1 promote comparable PPARγ transcriptional activity.

CONCLUSIONS

These data provide unprecedented evidence that ω-3 PUFA coordinately regulate AT gene expression programs in a manner that is independent of restriction of weight gain or fat accrual and highlight an important influence of ω-3 PUFA on adipogenesis. Furthermore we provide primary evidence suggesting that protectins likely contribute to these effects via their influence on PPARγ.

Modulation of adipocyte differentiation by omega-3 polyunsaturated fatty acids involves the ubiquitin-proteasome system

We have evaluated the effects of three different omega-3 polyunsaturated fatty acids (ω-3 PUFAs) – docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA) on fat accumulation and expression of adipogenic and inflammatory markers using both 3T3-L1 pre-adipocytes and differentiated 3T3-L1 adipocytes. Our results indicate that ω-3 PUFAs induce the degradation of fatty acid synthase through the ubiquitin-proteasome system, which is likely to have beneficial metabolic effect on adipose cells. Omega-3 PUFAs also increase overall levels of polyubiquitinated proteins, at least in part through decreasing the expression of proteasome subunits. Moreover, adipocytes are resistant to proteasome inhibition, which induces adipophilin while decreasing perilipin expression. On the other hand, ω-3 PUFAs decrease expression of SREBP1 while inducing expression of adipophilin and GLUT4. Moreover, all three ω-3 PUFAs appear to induce tumour necrosis factor-α without affecting NFκB levels. All three ω-3 PUFAs appear to have overall similar effects. Further research is needed to elucidate their mechanism of action.

Pros and cons of fatty acids in bone biology

Despite the growing interest in deciphering the causes and consequences of obesity-related disorders, the mechanisms linking fat intake to bone behaviour remain unclear. Since bone fractures are widely associated with increased morbidity and mortality, most notably in elderly and obese people, bone health has become a major social and economic issue. Consistently, public health system guidelines have encouraged low-fat diets in order to reduce associated complications. However, from a bone point of view, mechanisms linking fat intake to bone alteration remain quite controversial. Thus, after more than a decade of dedicated studies, this timely review offers a comprehensive overview of the relationships between bone and fatty acids. Using clinical evidences as a starting-point to more complex molecular elucidation, this work highlights the complexity of the system and reveals that bone alteration that cannot be solved simply by taking ω-3 pills. Fatty acid effects on bone metabolism can be both direct and indirect and require integrated investigations. Furthermore, even at the level of a single cell, one fatty acid is able to trigger several different independent pathways (receptors, metabolites…) which may all have a say in the final cellular metabolic response.

Arachidonic acid has a dominant effect to regulate lipogenic genes in 3T3-L1 adipocytes compared to omega-3 fatty acids

BACKGROUND

The effects of long-chain n-3 and n-6 polyunsaturated fatty acids (PUFA) on the regulation of adipocytes metabolism are well known. These fatty acids are generally consumed together in our diets; however, the metabolic regulation of adipocytes in the presence of these fatty acids when given together is not known.

OBJECTIVE

To investigate the effects of n-3 PUFA and arachidonic acid (AA), an n-6 PUFA, on the regulation of adipogenic and lipogenic genes in mature 3T3-L1 adipocytes.

METHODS

3T3-L1 adipocytes were incubated in the presence or absence of 100 µM of eicosapentaenoic acid, EPA; docosahexaenoic acid, DHA; docosapentaenoic acid, DPA and AA, either alone or AA+n-3 PUFA; control cells received bovine serum albumin alone. The mRNA expression of adipogenic and lipogenic genes was measured. The fatty acid composition of adipocytes was analyzed using gas chromatography.

RESULTS

Individual n-3 PUFA or AA had no effect on the mRNA expression of peroxisome-proliferator-activated receptor-γ; however, AA+EPA and AA+DPA significantly increased (P<0.05) the expression compared to control cells (38 and 42%, respectively). AA and AA+EPA increased the mRNA expression of acetyl-CoA carboxylase 1 (P<0.05). AA treatment decreased the mRNA expression of stearoyl-CoA desaturase (SCD1) (P<0.01), while n-3 PUFA, except EPA, had no effect compared to control cells. AA+DHA and AA+DPA inhibited SCD1 gene expression (P<0.05) suggesting a dominant effect of AA. Fatty acids analysis of adipocytes revealed a higher accretion of AA compared to n-3 PUFA.

CONCLUSIONS

Our findings reveal that AA has a dominant effect on the regulation of lipogenic genes in adipocytes.

n-3 polyunsaturated fatty acids and insulin secretion

n-3 polyunsaturated fatty acids (PUFAs) are a subgroup of fatty acids with broad health benefits, such as lowering blood triglycerides and decreasing the risk of some types of cancer. A beneficial effect of n-3 PUFAs in diabetes is indicated by results from some studies. Defective insulin secretion is a fundamental pathophysiological change in both types 1 and 2 diabetes. Emerging studies have provided evidence of a connection between n-3 PUFAs and improved insulin secretion from pancreatic β-cells. This review summarizes the recent findings in this regard and discusses the potential mechanisms by which n-3 PUFAs influence insulin secretion from pancreatic β-cells.

Effects of α-lipoic acid and eicosapentaenoic acid in overweight and obese women during weight loss

OBJECTIVE

To evaluate the potential body weight-lowering effects of dietary supplementation with eicosapentaenoic acid (EPA) and α-lipoic acid separately or combined in healthy overweight/obese women following a hypocaloric diet.

METHODS

This is a short-term double-blind placebo-controlled study with parallel design that lasted 10 weeks. Of the randomized participants, 97 women received the allocated treatment [Control, EPA (1.3 g/d), α-lipoic acid (0.3 g/d), and EPA+α-lipoic acid (1.3 g/d+0.3 g/d)], and 77 volunteers completed the study. All groups followed an energy-restricted diet of 30% less than total energy expenditure. Body weight, anthropometric measurements, body composition, resting energy expenditure, blood pressure, serum glucose, and insulin and lipid profile, as well as leptin and ghrelin levels, were assessed at baseline and after nutritional intervention.

RESULTS

Body weight loss was significantly higher (P<0.05) in those groups supplemented with α-lipoic acid. EPA supplementation significantly attenuated (P<0.001) the decrease in leptin levels that occurs during weight loss. Body weight loss improved lipid and glucose metabolism parameters but without significant differences between groups.

CONCLUSIONS

The intervention suggests that α-lipoic acid supplementation alone or in combination with EPA may help to promote body weight loss in healthy overweight/obese women following energy-restricted diets.

Nutritional ingredients modulate adipokine secretion and inflammation in human primary adipocytes

Nutritional factors such as casein hydrolysates and long chain polyunsaturated fatty acids have been proposed to exert beneficial metabolic effects. We aimed to investigate how a casein hydrolysate (eCH) and long chain polyunsaturated fatty acids could affect human primary adipocyte function in vitro. Incubation conditions with the different nutritional factors were validated by assessing cell vitality with lactate dehydrogenase (LDH) release and neutral red incorporation. Intracellular triglyceride content was assessed with Oil Red O staining. The effect of eCH, a non-peptidic amino acid mixture (AA), and long-chain polyunsaturated fatty acids (LC-PUFAs) on adiponectin and leptin secretion was determined by enzyme-linked immunosorbent assay (ELISA). Intracellular adiponectin expression and nuclear factor-κB (NF-κB) activation were analyzed by Western blot, while monocyte chemoattractant protein-1 (MCP-1) release was explored by ELISA. The eCH concentration dependently increased adiponectin secretion in human primary adipocytes through its intrinsic peptide bioactivity, since the non-peptidic mixture, AA, could not mimic eCH’s effects on adiponectin secretion. Eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and DHA combined with arachidonic acid (ARA) upregulated adiponectin secretion. However, only DHA and DHA/ARA exerted a potentanti-inflammatory effect reflected by prevention of tumor necrosis factor-α (TNF-α) induced NF-κB activation and MCP-1 secretion in human adipocytes. eCH and DHA alone or in combination with ARA, may hold the key for nutritional programming through their anti-inflammatory action to prevent diseases with low-grade chronic inflammation such as obesity or diabetes.

Docosahexaenoic acid-enriched canola oil increases adiponectin concentrations: a randomized crossover controlled intervention trial

BACKGROUND AND AIMS

Little is known about the effect of various dietary fatty acids on pro- and anti-inflammatory processes. We investigated the effect of 5 oils containing various amounts of alpha-linolenic acid (ALA), linoleic acid (LA), oleic acid (OA) and docosahexaenoic acid (DHA) on plasma inflammatory biomarkers and expression levels of key inflammatory genes and transcription factors in whole blood cells.

METHODS AND RESULTS

In a randomized, crossover controlled nutrition intervention, 114 adult men and women with abdominal obesity and at least one other criterion for the metabolic syndrome consumed 5 experimental isoenergetic diets for 4 weeks each, separated by 4-week washout periods. Each diet provided 60 g/3000 kcal of different oils: 1) control corn/safflower oil blend (CornSaff; LA-rich), 2) flax/safflower oil blend (FlaxSaff; ALA-rich), 3) conventional canola oil (Canola; OA-rich), 4) high oleic canola oil (CanolaOleic; highest OA content), 5) DHA-enriched high oleic canola oil (CanolaDHA; OA- and DHA-rich). Gene expression in whole blood cells was assessed in a subset of 62 subjects. CanolaDHA increased plasma adiponectin concentrations compared with the control CornSaff oil treatment (+4.5%, P = 0.04) and FlaxSaff (+6.9%, P = 0.0008). CanolaDHA also reduced relative expression levels of interleukin (IL)1B compared with CornSaff and Canola (-11% and -13%, respectively, both P = 0.03). High-sensitivity C-reactive protein concentrations were lower after Canola than after FlaxSaff (-17.8%, P = 0.047).

CONCLUSION

DHA-enriched canola oil exerts anti-inflammatory effects compared with polyunsaturated fatty acids from plant sources.

Docosahexaenoic Acid-Rich Fish Oil Supplementation Improves Body Composition without Influence of the PPAR&#947; Pro12Ala Polymorphism in Patients with Type 2 Diabetes: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

<b><i>Background:</i></b> The aims of this research were to investigate (1) the impact of docosahexaenoic acid (DHA)-rich fish oil supplementation on body composition, plasma adiponectin level, and peroxisome proliferator-activated receptor &#947; (PPAR&#947;) gene expression, and (2) whether the effect of DHA-rich fish oil supplementation on the aforementioned variables is modulated by PPAR&#947; Pro12Ala polymorphism. <b><i>Methods:</i></b> We genotyped PPAR&#947; Pro12Ala polymorphism in subjects with type 2 diabetes mellitus (T2DM). Ala carriers and non-Ala carriers were randomly assigned to DHA-rich fish oil or placebo intake for 8 weeks. <b><i>Results:</i></b> Glycemic control was not affected by the intervention. The supplementation with DHA-rich fish oil decreased waist circumference (p < 0.001), body fat mass (p = 0.01), body fat percent (p = 0.04), and visceral fat rating (p = 0.02) as well as trunk fat mass (p = 0.04). Weight, body mass index, fat-free mass, adiponectin level, and PPAR&#947; gene expression changes showed no significant difference. No gene-diet interaction was found on body composition, adiponectin level, and PPAR&#947; gene expression. <b><i>Conclusions:</i></b> DHA-rich fish oil supplementation favorably modulated body composition in patients with T2DM and could be useful to reduce visceral obesity. However, the PPAR&#947; Pro12Ala polymorphism did not influence the changes in the desired variables.

n-3 polyunsaturated fatty acids and mechanisms to mitigate inflammatory paracrine signaling in obesity-associated breast cancer

Globally, the prevalence of obesity is increasing which subsequently increases the risk of the development of obesity-related chronic diseases. Low-grade chronic inflammation and dysregulated adipose tissue inflammatory mediator/adipokine secretion are well-established in obesity, and these factors increase the risk of developing inflammation-associated cancer. Breast cancer is of particular interest given that increased inflammation within the subcutaneous mammary adipose tissue depot can alter the local tissue inflammatory microenvironment such that it resembles that of obese visceral adipose tissue. Therefore, in obese women with breast cancer, increased inflammatory mediators both locally and systemically can perpetuate inflammation-associated pro-carcinogenic signaling pathways, thereby increasing disease severity. Herein, we discuss some of these inflammation-associated pro-carcinogenic mechanisms of the combined obese breast cancer phenotype and offer evidence that dietary long chain n-3 polyunsaturated fatty acids (PUFA) may have utility in mitigating the severity of obesity-associated inflammation and breast cancer.

Proinflammatory effects of arachidonic acid in a lipopolysaccharide-induced inflammatory microenvironment in 3T3-L1 adipocytes in vitro

Long-chain n-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA), have known anti-inflammatory effects, including the modulation of adipose tissue-derived inflammatory mediators (i.e., adipokines) implicated in obesity-related pathologies, such as insulin resistance. Less is known about the effects of plant-derived n-3 PUFA, α-linolenic acid (ALA, 18:3n-3) and stearidonic acid (SDA 18:4n-3), or n-6 PUFA linoleic acid (LA, 18:2n-6) and arachidonic acid (AA, 20:4n-6), especially in combination with an inflammatory stimulus, such as lipopolysaccharide (LPS), at a dose intended to mimic obesity-associated low-grade inflammation. To study this, 3T3-L1 adipocytes were incubated with 100 μmol/L of various n-3 or n-6 PUFA with or without 10 ng/mL LPS for up to 24 h. AA in the presence of LPS synergistically increased (p < 0.05) pro-inflammatory monocyte chemoattractant protein-1 (MCP)-1 and interleukin (IL)-6 secretion and gene expression, as well as COX-2 and TLR2 gene expression at 6 and/or 24 h, suggesting their potential roles in the synergistic effects of AA and LPS. Plant-derived fatty acids ALA, SDA, and LA did not differentially affect adipokine gene expression or secretion, whereas LPS-induced pro-inflammatory IL-1β expression and MCP-1 secretion was decreased (p < 0.05) by EPA, DHA, and/or EPA+DHA (50 μmol/L each) compared with LPS alone. Only DHA increased (p < 0.05) gene expression of the n-3 PUFA receptor GPR120 and simultaneously decreased LPS-induced nuclear factor-κB activation compared with control. Our findings emphasize that specific fatty acids within the n-3 or n-6 PUFA class warrant consideration in the development of nutritional strategies to improve obesity-associated inflammation.

Unraveling biochemical pathways affected by mitochondrial dysfunctions using metabolomic approaches

Mitochondrial dysfunction(s) (MDs) can be defined as alterations in the mitochondria, including mitochondrial uncoupling, mitochondrial depolarization, inhibition of the mitochondrial respiratory chain, mitochondrial network fragmentation, mitochondrial or nuclear DNA mutations and the mitochondrial accumulation of protein aggregates. All these MDs are known to alter the capacity of ATP production and are observed in several pathological states/diseases, including cancer, obesity, muscle and neurological disorders. The induction of MDs can also alter the secretion of several metabolites, reactive oxygen species production and modify several cell-signalling pathways to resolve the mitochondrial dysfunction or ultimately trigger cell death. Many metabolites, such as fatty acids and derived compounds, could be secreted into the blood stream by cells suffering from mitochondrial alterations. In this review, we summarize how a mitochondrial uncoupling can modify metabolites, the signalling pathways and transcription factors involved in this process. We describe how to identify the causes or consequences of mitochondrial dysfunction using metabolomics (liquid and gas chromatography associated with mass spectrometry analysis, NMR spectroscopy) in the obesity and insulin resistance thematic.

Maternal micronutrients, omega-3 fatty acids, and placental PPARγ expression

An altered one-carbon cycle is known to influence placental and fetal development. We hypothesize that deficiency of maternal micronutrients such as folic acid and vitamin B12 will lead to increased oxidative stress, reduced long-chain polyunsaturated fatty acids, and altered expression of peroxisome proliferator activated receptor (PPARγ) in the placenta, and omega-3 fatty acid supplementation to these diets will increase the expression of PPARγ. Female rats were divided into 5 groups: control, folic acid deficient, vitamin B12 deficient, folic acid deficient + omega-3 fatty acid supplemented, and vitamin B12 deficient + omega-3 fatty acid supplemented. Dams were dissected on gestational day 20. Maternal micronutrient deficiency leads to lower (p < 0.05) levels of placental docosahexaenoic acid, arachidonic acid, PPARγ expression and higher (p < 0.05) levels of plasma malonidialdehyde, placental IL-6, and TNF-α. Omega-3 fatty acid supplementation to a vitamin B12 deficient diet normalized the expression of PPARγ and lowered the levels of placental TNF-α. In the case of supplementation to a folic acid deficient diet it lowered the levels of malonidialdehyde and placental IL-6 and TNF-α. This study has implications for fetal growth as oxidative stress, inflammation, and PPARγ are known to play a key role in the placental development.

Role of n-3 fatty acids in muscle loss and myosteatosis

Image-based methods such as computed tomography for assessing body composition enables quantification of muscle mass and muscle density and reveals that low muscle mass and myosteatosis (fat infiltration into muscle) are common in people with cancer. Myosteatosis and low muscle mass have emerged as independent risk factors for mortality in cancer; however, the characteristics and pathogenesis of these features have not been resolved. Muscle depletion is associated with low plasma eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) in cancer and supplementation with n-3 fatty acids has been shown to ameliorate muscle loss and myosteatosis in clinical studies, suggesting a relationship between n-3 fatty acids and muscle health. Since the mechanisms by which n-3 fatty acids alter body composition in cancer remain unknown, related literature from other conditions associated with myosteatosis, such as insulin resistance and obesity is considered. In these noncancer conditions, it has been reported that n-3 fatty acids act by increasing insulin sensitivity, reducing inflammatory mediators, and altering adipokine profiles and transcription factors; therefore, the plausibility of these mechanisms of action in the neoplastic state are considered. The aim of this review is to summarize what is known about the effects of n-3 fatty acids with regards to muscle condition and to discuss potential mechanisms for effects of n-3 fatty acids on muscle health.

Docosahexaenoic acid decreases pro-inflammatory mediators in an in vitro murine adipocyte macrophage co-culture model

Paracrine interactions between adipocytes and macrophages contribute to chronic inflammation in obese adipose tissue. Dietary strategies to mitigate such inflammation include long-chain polyunsaturated fatty acids, docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids, which act through PPARγ-dependent and independent pathways. We utilized an in vitro co-culture model designed to mimic the ratio of macrophages:adipocytes in obese adipose tissue, whereby murine 3T3-L1 adipocytes were cultured with RAW 264.7 macrophages in direct contact, or separated by a trans-well membrane (contact-independent mechanism), with 125 µM of albumin-complexed DHA, EPA, palmitic acid (PA), or albumin alone (control). Thus, we studied the effect of physical cell contact versus the presence of soluble factors, with or without a PPARγ antagonist (T0070907) in order to elucidate putative mechanisms. After 12 hr, DHA was the most anti-inflammatory, decreasing MCP1 and IL-6 secretion in the contact system (−57%, −63%, respectively, p≤0.05) with similar effects in the trans-well system. The trans-well system allowed for isolation of cell types for inflammatory mediator analysis. DHA decreased mRNA expression (p<0.05) of Mcp1 (−7.1 fold) and increased expression of the negative regulator, Mcp1-IP (+1.5 fold). In macrophages, DHA decreased mRNA expression of pro-inflammatory M1 polarization markers (p≤0.05), Nos2 (iNOS; −7 fold), Tnfα (−4.2 fold) and Nfκb (−2.3 fold), while increasing anti-inflammatory Tgfβ1 (+1.7 fold). Interestingly, the PPARγ antagonist co-administered with DHA or EPA in co-culture reduced (p≤0.05) adiponectin cellular protein, without modulating other cytokines (protein or mRNA). Overall, our findings suggest that DHA may lessen the degree of MCP1 and IL-6 secreted from adipocytes, and may reduce the degree of M1 polarization of macrophages recruited to adipose tissue, thereby decreasing the intensity of pro-inflammatory cross-talk between adipocytes and macrophages in obese adipose tissue.

N-3 long-chain PUFA supplementation prevents high fat diet induced mouse liver steatosis and inflammation in relation to PPAR-α upregulation and NF-κB DNA binding abrogation

SCOPE

Dietary n-3 long-chain PUFAs (n-3 LCPUFAs) supplementation was studied in an HFD-induced (HFD is high-fat diet) steatosis and inflammation in relation to peroxisome proliferator-activated receptor alpha (PPAR-α) and nuclear factor κB (NF-κB) signaling.

METHODS AND RESULTS

Male C57BL/6J mice received (i) control diet (10% fat, 20% protein, 70% carbohydrate), (ii) control diet plus n-3 LCPUFAs (daily doses of 108 mg/kg body weight of eicosapentaenoic acid plus 92 mg/kg body weight of docosahexaenoic acid), (iii) HFD (60% fat, 20% protein, 20% carbohydrate), or (iv) HFD plus n-3 LCPUFAs for 12 wk. PPAR-α, tumor necrosis factor alpha (TNF-α), and IL-1β mRNA expression, acyl-CoA oxidase 1 (ACOX1), and carnitine-acyl-CoA transferase 1 (CAT-I) protein contents, and NF-κB DNA binding activity were measured. HFD significantly decreased liver PPAR-α, ACOX1, and CAT-I levels with NF-κB activation, higher TNF-α and IL-1β expression, and steatosis development. These changes were either reduced or normalized to control values in animals subjected to HFD plus n-3 LCPUFAs, with establishment of an inverse association between NF-κB activation and PPAR-α mRNA expression (r = -0.66, p < 0.0001).

CONCLUSION

Data presented indicate that n-3 LCPUFAs supplementation prevents liver steatosis and inflammation induced by HFD, with underlying mechanisms involving enhanced PPAR-α signaling and diminished NF-κB activation.

In vitro and in vivo enhancement of adipogenesis by Italian ryegrass (Lolium multiflorum) in 3T3-L1 cells and mice

Adipogenesis is very much important in improving the quality of meat in animals. The aim of the present study was to investigate the in vitro and in vivo adipogenesis regulation properties of Lolium multiflorum on 3T3-L1 pre-adipocytes and mice. Chemical composition of petroleum ether extract of L. multiflorum (PET-LM) confirmed the presence of fatty acids, such as α-linolenic acid, docosahexaenoic acid, oleic acid, docosatetraenoic acid, and caprylic acid, as the major compounds. PET-LM treatment increased viability, lipid accumulation, lipolysis, cell cycle progression, and DNA synthesis in the cells. PET-LM treatment also augmented peroxysome proliferator activated receptor (PPAR)-γ2, CCAAT/enhancer binding protein-α, adiponectin, adipocyte binding protein, glucose transporter-4, fatty acid synthase, and sterol regulatory element binding protein-1 expression at mRNA and protein levels in differentiated adipocytes. In addition, mice administered with 200 mg/kg body weight PET-LM for 8 weeks showed greater body weight than control mice. These findings suggest that PET-LM facilitates adipogenesis by stimulating PPARγ-mediated signaling cascades in adipocytes which could be useful for quality meat development in animals.

The influence of EPA and DHA on markers of inflammation in 3T3-L1 cells at different stages of cellular maturation

BACKGROUND

EPA and DHA have been reported to have anti-obesity and anti-inflammatory properties. Recent studies revealed that these positive actions of n-3 PUFA at least partially are connected with their influence on metabolism and secretory functions of the adipose tissue. However, their impact on old adipocytes is still poorly understood. Therefore the aim of the present study was to evaluate the influence of EPA and DHA on markers of inflammation in 3T3-L1 cells at different stages of cellular maturation.

METHODS

Young, mature and old differentiated 3T3-L1 adipocytes were cultured for 48 h in the presence of 100 μM EPA, or 50 μM DHA complexed to albumin, whereas in control conditions only albumin was added to the medium. The Oil Red O staining was used to confirm adipocytes differentiation, and measure triglycerides content in cells. The concentration of adipokines (interleukin 6, adiponectin and leptin) in conditioned media was measured using mouse-specific ELISA kits.

RESULTS

The fat accumulation in 3T3-L1 adipocytes was positively correlated with their age; however, EPA and DHA did not affect lipid accumulation on any stage of maturation. EPA and DHA increased the concentration of secreted adiponectin when compared with control, but only in the case of young adipocytes (58% and 35%, respectively). Moreover, EPA supplementation increased interleukin 6 concentration in conditioned medium, while DHA exerted an opposite effect on all stages of cellular maturation. Furthermore, EPA treatment increased leptin release from young cells, while DHA did not affect the secretion of this adipokine. In mature 3T3-L1 adipocytes both experimental factors decreased synthesis of leptin; however, in old cells no impact of these PUFA was noted.

CONCLUSIONS

In summary, age is an important determinant of fat accumulation in adipocytes and affects adipokines secretion by these cells. Moreover, the impact of investigated fatty acids: EPA and DHA on fat cells varies depending on the stage of maturation, and seems to be stronger in young cells than in mature and old ones. Docosahexaenoic acid exerts an anti-inflammatory action; however, on the basis of the obtained data it was not possible to determine whether eicosapentaenoic acid shows anti- or pro-inflammatory properties.

Differential effects of eicosapentaenoic acid and docosahexaenoic acid in promoting the differentiation of 3T3-L1 preadipocytes

The objective of this study was to determine the effects of enrichment with n-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on the differentiation of 3T3-L1 preadipocytes. Enrichment with DHA but not EPA significantly increased the differentiation markers compared to control differentiated cells. DHA compared to EPA treatment led to a greater increase in adiponectin secretion and, conditioned media collected from DHA treated cells inhibited monocyte migration. Moreover, DHA treatment resulted in inhibition of pro-inflammatory signaling pathways. DHA treated cells predominantly accumulated DHA in phospholipids whereas EPA treatment led to accumulation of both EPA and its elongation product docosapentaenoic acid (DPA), an n-3 fatty acid. Of note, adding DPA to DHA inhibited DHA-induced differentiation. The differential effects of EPA and DHA on preadipocyte differentiation may be due, in part, to differences in their intracellular modification which could impact the type of n-3 fatty acids incorporated into the cells.

Potential treatment of human nonalcoholic fatty liver disease with long-chain omega-3 polyunsaturated fatty acids

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder in the Western world. Its prevalence has increased with the growing obesity epidemic, yet no definitive treatment has been developed, and optimal management remains a clinical challenge. Long-chain omega-3 polyunsaturated fatty acids (PUFAs) have recently been proposed as a potential treatment for liver inflammation associated with fat accumulation. PubMed literature and the ClinicalTrials.gov database were reviewed for the effects of omega-3 PUFA treatment on NAFLD, from mechanisms to the results of preclinical studies, human studies, and unreported ongoing clinical trials, using terms such as NAFLD, nonalcoholic steatohepatitis, omega-3 fatty acids, and fish oil. Articles published over the last 3-4 years were emphasized, and relevancy was ensured by scanning their abstracts. Preliminary studies have confirmed an ameliorative effect, yet the translation of promising early data into therapeutic interventions will have to await the results of larger, properly conducted, ongoing clinical trials.

PPARγ-mediated and arachidonic acid-dependent signaling is involved in differentiation and lipid production of human sebocytes

The transcriptional basis of sebocyte differentiation and lipid production is mostly unclear. Peroxisome proliferator-activated receptor gamma (PPARγ), a lipid-activated transcription factor, has been implicated in differentiation and lipid metabolism of various cell types. Here, we show that PPARγ is differentially expressed in normal and pathological human sebocytes and appears to have roles in their differentiation and lipid production. We used laser-microdissected normal and pathological human sebaceous glands (SGs) and SZ95 cells (immortalized sebocyte cell line) analyzed by real-time quantitative PCR and immunohistochemistry. Lipids were analyzed by quantitative fluorimetry- and mass spectrometry-based approaches. We have observed that PPARγ and its target genes, ADRP (adipose differentiation-related protein) and PGAR (PPARγ angiopoietin-related protein), are expressed in sebocytes and show association with their level of differentiation. Also, PPARγ is present in normal and hyperplastic SG, whereas its expression levels are decreased in SG adenoma and SG carcinoma cells, reflecting a maturation-linked expression pattern. Furthermore, in SZ95 sebocytes, naturally occurring lipids, including arachidonic acid and arachidonic acid keto-metabolites (e.g., 5-KETE (5-oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid), 12-KETE (12-oxo-5Z,8Z,10E,14Z-eicosatetraenoic acid)), appear to regulate PPARγ signaling pathways, which in turn modulate phospholipid biosynthesis and induce neutral lipid synthesis. Collectively, our findings highlight the importance of endogenous ligand-activated PPARγ signaling in human sebocyte biology and suggest that PPARγ might be a promising candidate for the clinical management of SG disorders.

Nutritional lipidomics: molecular metabolism, analytics, and diagnostics

The field of lipidomics is providing nutritional science a more comprehensive view of lipid intermediates. Lipidomics research takes advantage of the increase in accuracy and sensitivity of mass detection of MS with new bioinformatics toolsets to characterize the structures and abundances of complex lipids. Yet, translating lipidomics to practice via nutritional interventions is still in its infancy. No single instrumentation platform is able to solve the varying analytical challenges of the different molecular lipid species. Biochemical pathways of lipid metabolism remain incomplete and the tools to map lipid compositional data to pathways are still being assembled. Biology itself is dauntingly complex and simply separating biological structures remains a key challenge to lipidomics. Nonetheless, the strategy of combining tandem analytical methods to perform the sensitive, high-throughput, quantitative, and comprehensive analysis of lipid metabolites of very large numbers of molecules is poised to drive the field forward rapidly. Among the next steps for nutrition to understand the changes in structures, compositions, and function of lipid biomolecules in response to diet is to describe their distribution within discrete functional compartments lipoproteins. Additionally, lipidomics must tackle the task of assigning the functions of lipids as signaling molecules, nutrient sensors, and intermediates of metabolic pathways.

The eicosapentaenoic acid metabolite 15-deoxy-δ(12,14)-prostaglandin J3 increases adiponectin secretion by adipocytes partly via a PPARγ-dependent mechanism

The intake of ω-3 polyunsaturated fatty acids (PUFAs), which are abundant in marine fish meat and oil, has been shown to exert many beneficial effects. The mechanisms behind those effects are numerous, including interference with the arachidonic acid cascade that produces pro-inflammatory eicosanoids, formation of novel bioactive lipid mediators, and change in the pattern of secreted adipocytokines. In our study, we show that eicosapentaenoic acid (EPA) increases secreted adiponectin from 3T3-L1 adipocytes and in plasma of mice as early as 4 days after initiation of an EPA-rich diet. Using 3T3-L1 adipocytes, we report for the first time that 15-deoxy-δ^12,14-PGJ₃ (15d-PGJ₃), a product of EPA, also increases the secretion of adiponectin. We demonstrate that the increased adiponectin secretion induced by 15d-PGJ₃ is partially peroxisome proliferator-activated receptor-gamma (PPAR-γ)-mediated. Finally, we show that 3T3-L1 adipocytes can synthesize 15d-PGJ₃ from EPA. 15d-PGJ₃ was also detected in adipose tissue from EPA-fed mice. Thus, these studies provide a novel mechanism(s) for the therapeutic benefits of ω-3 polyunsaturated fatty acids dietary supplementation.

Anti-diabetic activities of Gegen Qinlian Decoction in high-fat diet combined with streptozotocin-induced diabetic rats and in 3T3-L1 adipocytes

Gegen Qinlian Decoction (GGQLD) is one of the well-known traditional Chinese medicines. Recently, it was reported that GGQLD had good clinical effects on type 2 diabetes mellitus. However, few studies have confirmed in detail the anti-diabetic activities of GGQLD in vivo and in vitro. In the present study, we investigated the anti-diabetic effects of GGQLD in high-fat diet combined with streptozotocin-induced diabetic rats and in 3T3-L1 adipocytes. The present results suggested GGQLD (4.95, 11.55 and 18.15 g/kg) decreased significantly fasting blood glucose, glycosylated serum protein, and glycosylated hemoglobin of diabetic rats (p<0.05), and GGQLD (4.95 and 18.15 g/kg) decreased significantly fasting serum insulin levels of diabetic rats (p<0.05); in 3T3-L1 adipocytes, Gegen Qinlian Decoction-containing serum (GGQLD-CS) (4%, 8% and 16%) enhanced glucose consumption, triglyceride (TG) content, adiponectin protein concentration and the mRNA expression of adiponectin. Adiponectin contributes to the regulation of lipid and glucose metabolism, and can play a critical role in the development of diabetes mellitus; the mechanisms of action of GGQLD might be related to augmentation of adiponectin protein concentration and up-regulation of the mRNA expression of adiponectin. However, the multi-target mechanisms of action of GGQLD need to be clarified further. The present study further validated the beneficial effects of GGQLD as an anti-diabetic agent. These findings provide a new insight into the anti-diabetic application for GGQLD in clinic and display the potential of GGQLD as a new drug candidate for the treatment of diabetes mellitus.

Gas chromatography-mass spectrometry-based profiling of serum fatty acids in acetaminophen-induced liver injured rats

In this study, we have developed and validated a simple, accurate and sensitive gas chromatography-mass spectrometry (GC-MS) method for simultaneous quantification of 18 fatty acids in rat serum, including both non-esterified (NEFA) and esterified (EFA) fatty acids, and subsequent analysis of fatty acid metabolic profiles. This novel method was used to evaluate the serum levels of fatty acids from vehicle- and acetaminophen (APAP)-treated rats. Serum levels of 7 NEFAs and 14 EFAs were significantly higher in APAP-treated rats 24 h after APAP administration at 1500 mg kg⁻¹ when compared with vehicle-treated controls. Control and APAP-treated rats could be differentiated based on their metabolic profiles using two different chemometric analysis methods: principle component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA). More importantly, we identified the following NEFAs as potential biomarkers of APAP-induced liver injury: oleic acid (C18:1n9), linoleic acid (C18:2n6), docosahexaenoic acid (C22:6n3) and arachidonic acid (C20:4n6). The serum concentrations of C18:1n9, C18:2n6 and C22:6n3 were all positively correlated (r > 0.8; Pearson's correlation analysis) with the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). These results suggest that a novel targeted metabolomics method based on the metabolic profiling of fatty acids analyzed by GC-MS provides exact serum concentrations of fatty acids as well as a prospective methodology to evaluate chemically induced hepatotoxicity.

Distinguishing health benefits of eicosapentaenoic and docosahexaenoic acids

Long chain omega-3 polyunsaturated fatty acids (LC n-3 PUFAs) are recommended for management of patients with wide-ranging chronic diseases, including coronary heart disease, rheumatoid arthritis, dementia, and depression. Increased consumption of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is recommended by many health authorities to prevent (up to 0.5 g/day) or treat chronic disease (1.0 g/day for coronary heart disease; 1.2–4 g/day for elevated triglyceride levels). Recommendations for dietary intake of LC n-3 PUFAs are often provided for α-linolenic acid, and for the combination of EPA and DHA. However, many studies have also reported differential effects of EPA, DHA and their metabolites in the clinic and at the laboratory bench. The aim of this article is to review studies that have identified divergent responses to EPA and DHA, and to explore reasons for these differences. In particular, we review potential contributing factors such as differential membrane incorporation, modulation of gene expression, activation of signaling pathways and metabolite formation. We suggest that there may be future opportunity to refine recommendations for intake of individual LC n-3 PUFAs.

The role of dietary fatty acids in the pathology of metabolic syndrome

Dysfunctional lipid metabolism is a key component in the development of metabolic syndrome, a very frequent condition characterized by dyslipidemia, insulin resistance, abdominal obesity and hypertension, which are related to an elevated risk for type 2 diabetes mellitus. The prevalence of metabolic syndrome is strongly associated with the severity of obesity; its physiopathology is related to both genetics and food intake habits, especially the consumption of a high-caloric, high-fat and high-carbohydrate diet. With the progress of scientific knowledge in the field of nutrigenomics, it was possible to elucidate how the majority of dietary fatty acids influence plasma lipid metabolism and also the genes expression involved in lipolysis and lipogenesis within hepatocytes and adipocytes. The aim of this review is to examine the relevant mechanistic aspects of dietary fatty acids related to blood lipids, adipose tissue metabolism, hepatic fat storage and inflammatory process, all of them closely related to the genesis of metabolic syndrome.

Dietary fat and heart failure: moving from lipotoxicity to lipoprotection

There is growing evidence suggesting that dietary fat intake affects the development and progression of heart failure. Studies in rodents show that in the absence of obesity, replacing refined carbohydrate with fat can attenuate or prevent ventricular expansion and contractile dysfunction in response to hypertension, infarction, or genetic cardiomyopathy. Relatively low intake of n-3 polyunsaturated fatty acids from marine sources alters cardiac membrane phospholipid fatty acid composition, decreases the onset of new heart failure, and slows the progression of established heart failure. This effect is associated with decreased inflammation and improved resistance to mitochondrial permeability transition. High intake of saturated, monounsaturated, or n-6 polyunsaturated fatty acids has also shown beneficial effects in rodent studies. The underlying mechanisms are complex, and a more thorough understanding is needed of the effects on cardiac phospholipids, lipid metabolites, and metabolic flux in the normal and failing heart. In summary, manipulation of dietary fat intake shows promise in the prevention and treatment of heart failure. Clinical studies generally support high intake of n-3 polyunsaturated fatty acids from marine sources to prevent and treat heart failure. Additional clinical and animals studies are needed to determine the optimal diet in terms of saturated, monounsaturated, and n-6 polyunsaturated fatty acids intake for this vulnerable patient population.

Fish oil prevents high-saturated fat diet-induced impairments in adiponectin and insulin response in rodent soleus muscle

High saturated fatty acid (SFA) diets contribute to the development of insulin resistance, whereas fish oil-derived n-3 polyunsaturated fatty acids (PUFA) increase the secretion of adiponectin (Ad), an adipocyte-derived protein that stimulates fatty acid oxidation (FAO) and improves skeletal muscle insulin response. We sought to determine whether fish oil could prevent and/or restore high SFA diet-induced impairments in Ad and insulin response in soleus muscle. Sprague-Dawley rats were fed 1) a low-fat control diet (CON group), 2) high-SFA diet (SFA group), or 3) high SFA with n-3 PUFA diet (SFA/n-3 PUFA group). At 4 wk, CON and SFA/n-3 PUFA animals were terminated, and SFA animals were either terminated or fed SFA or SFA/n-3 PUFA for an additional 2 or 4 wk. The effect of diet on Ad-stimulated FAO, insulin-stimulated glucose transport, and expression of Ad, insulin and inflammatory signaling proteins was determined in the soleus muscle. Ad stimulated FAO in CON and 4 wk SFA/n-3 PUFA (+36%, +39%, respectively P ≤ 0.05) only. Insulin increased glucose transport in CON, 4 wk SFA/n-3 PUFA, and 4 wk SFA + 4 wk SFA/n-3 PUFA (+82%, +33%, +25%, respectively P ≤ 0.05); this effect was lost in all other groups. TLR4 expression was increased with 4 wk of SFA feeding (+24%, P ≤ 0.05), and this was prevented in 4 wk SFA/n-3 PUFA. Suppressor of cytokine signaling-3 expression was increased in SFA and SFA/n-3 PUFA (+33 and +18%, respectively, P ≤ 0.05). Our results demonstrate that fish oil can prevent high SFA diet-induced impairments in both Ad and insulin response in soleus muscle.

Lifestyle factors increasing adiponectin synthesis and secretion

Adiponectin is an anti-inflammatory adipokine released from adipose tissue that is known to exert insulin-sensitizing effects in skeletal muscle and liver. Given that the secretion of adiponectin is impaired in obesity and related pathologies, strategies to enhance its synthesis and secretion are of interest. There is evidence that several lifestyle factors, including consumption of dietary long-chain n-3 PUFA, TZD administration, and weight loss can increase adiponectin synthesis and secretion. The effect of chronic exercise, independent of weight loss, is variable and less convincing. Potential mechanisms by which such lifestyle factors exert their favorable effects on adiponectin include activation of PPARγ and AMPK, regulation of posttranslational modifications, and changes in adipose tissue morphology and macrophage infiltration. As a clear role for adiponectin in mitigating obesity-related impairments in lipid metabolism and insulin sensitivity is evident, further research investigating factors that enhance adiponectin synthesis and secretion is distinctly warranted.

Health benefits of n-3 polyunsaturated fatty acids: eicosapentaenoic acid and docosahexaenoic acid

Marine-based fish and fish oil are the most popular and well-known sources of n-3 polyunsaturated fatty acids (PUFAs), namely, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These n-3 PUFAs are known to have variety of health benefits against cardiovascular diseases (CVDs) including well-established hypotriglyceridemic and anti-inflammatory effects. Also, various studies indicate promising antihypertensive, anticancer, antioxidant, antidepression, antiaging, and antiarthritis effects. Moreover, recent studies also indicate anti-inflammatory and insulin-sensitizing effects of these fatty acids in metabolic disorders. Classically, n-3 PUFAs mediate some of these effects by antagonizing n-6 PUFA (arachidonic acid)-induced proinflammatory prostaglandin E₂ (PGE₂) formation. Another well-known mechanism by which n-3 PUFAs impart their anti-inflammatory effects is via reduction of nuclear factor-κB activation. This transcription factor is a potent inducer of proinflammatory cytokine production, including interleukin 6 and tumor necrosis factor-α, both of which are decreased by EPA and DHA. Other evidence also demonstrates that n-3 PUFAs repress lipogenesis and increase resolvins and protectin generation, ultimately leading to reduced inflammation. Finally, beneficial effects of EPA and DHA in insulin resistance include their ability to increase secretion of adiponectin, an anti-inflammatory adipokine. In summary, n-3 PUFAs have multiple health benefits mediated at least in part by their anti-inflammatory actions; thus their consumption, especially from dietary sources, should be encouraged.

Site dependency of fatty acid composition in adipose triacylglycerol in rats and its absence as a result of high-fat feeding

It is currently believed that metabolic syndrome, in general, and type 2 diabetes mellitus, in particular, depend more on visceral than on subcutaneous adipose tissue. However, the relationship between insulin resistance and fatty acid composition in visceral and subcutaneous adipose tissues remains to be clarified. In the present study, we extracted the triacylglycerol from visceral (epididymis and mesentery) and subcutaneous adipose tissues in normal and insulin-resistant, high-fat-fed (HFF) rats and determined the composition of each fatty acid. The concentrations of palmitoleic, docosapentaenoic, docosahexaenoic, dihomo-γ-linolenic, arachidonic, and docosatetraenoic acids were higher in epididymal adipose tissue than in mesenteric and subcutaneous adipose tissues; but no significant differences were detected between mesenteric and subcutaneous tissues in the normal group or among all the sites in the HFF rats. In the HFF group, stearic and oleic acid concentrations were higher, whereas n-3 and n-6 polyunsaturated ones were lower, than those in the normal group. Palmitoleic acid and some n-3 and n-6 polyunsaturated fatty acid compositions in adipose tissue triacylglycerol depend on anatomical location, which may affect the properties and/or function of adipose tissues. These results at least in part suggest that the properties of adipose tissue are difficult to distinguish based only on their "visceral" or "subcutaneous" sites. In addition, the absence of site dependence and/or difference in balance among saturated, monounsaturated, and polyunsaturated fatty acids may play an important role in the development of insulin resistance in the HFF rats.

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.