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

Interleukin-16 is increased in obesity and alters adipogenesis and inflammation in vitro

Introduction

Obesity is a chronic condition associated with low-grade inflammation mainly due to immune cell infiltration of white adipose tissue (WAT). WAT is distributed into two main depots: subcutaneous WAT (sWAT) and visceral WAT (vWAT), each with different biochemical features and metabolic roles. Proinflammatory cytokines including interleukin (IL)-16 are secreted by both adipocytes and infiltrated immune cells to upregulate inflammation. IL-16 has been widely studied in the peripheral proinflammatory immune response; however, little is known about its role in adipocytes in the context of obesity.

Aim & Methods

We aimed to study the levels of IL-16 in WAT derived from sWAT and vWAT depots of humans with obesity and the role of this cytokine in palmitate-exposed 3T3-L1 adipocytes.

Results

The results demonstrated that IL-16 expression was higher in vWAT compared with sWAT in individuals with obesity. In addition, IL-16 serum levels were higher in patients with obesity compared with normal-weight individuals, increased at 6 months after bariatric surgery, and at 12 months after surgery decreased to levels similar to before the intervention. Our in vitro models showed that IL-16 could modulate markers of adipogenesis (Pref1), lipid metabolism (Plin1, Cd36, and Glut4), fibrosis (Hif1a, Col4a, Col6a, and Vegf), and inflammatory signaling (IL6) during adipogenesis and in mature adipocytes. In addition, lipid accumulation and glycerol release assays suggested lipolysis alteration.

Discussion

Our results suggest a potential role of IL-16 in adipogenesis, lipid and glucose homeostasis, fibrosis, and inflammation in an obesity context.

Eicosapentaenoic Acid Induces the Inhibition of Adipogenesis by Reducing the Effect of PPARγ Activator and Mediating PKA Activation and Increased COX-2 Expression in 3T3-L1 Cells at the Differentiation Stage

Obesity has received increasing attention in recent years because it is a factor in the development of non-communicable diseases. The current study aimed to analyze how representative fatty acids (FAs) such as palmitic acid, stearic acid, oleic acid, α-linolenic acid (ALA), and eicosapentaenoic acid (EPA) affected adipogenesis when/if introduced at the differentiation stage of 3T3-L1 cell culture. These FAs are assumed to be potentially relevant to the progression or prevention of obesity. EPA added during the differentiation stage reduced intracellular triacylglycerol (TAG) accumulation, as well as the expression of the established adipocyte-specific marker genes, during the maturation stage. However, no other FAs inhibited intracellular TAG accumulation. Coexistence of Δ12-prostaglandin J2, a peroxisome proliferator-activated receptor γ activator, with EPA during the differentiation stage partially attenuated the inhibitory effect of EPA on intracellular TAG accumulation. EPA increased cyclooxygenase-2 (COX-2) expression and protein kinase A (PKA) activity at the differentiation stage, which could explain the inhibitory actions of EPA. Taken together, exposure of preadipocytes to EPA only during the differentiation stage may be sufficient to finally reduce the mass of white adipose tissue through increasing COX-2 expression and PKA activity.

Delta-6 desaturase (Fads2) deficiency alters triacylglycerol/fatty acid cycling in murine white adipose tissue

The Δ-6 desaturase (D6D) enzyme is not only critical for the synthesis of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from α-linolenic acid (ALA), but recent evidence suggests that it also plays a role in adipocyte lipid metabolism and body weight; however, the mechanisms remain largely unexplored. The goal of this study was to investigate if a D6D deficiency would inhibit triacylglycerol storage and alter lipolytic and lipogenic pathways in mouse white adipose tissue (WAT) depots due to a disruption in EPA and DHA production. Male C57BL/6J D6D knockout (KO) and wild-type (WT) mice were fed either a 7% w/w lard or flax (ALA rich) diet for 21 weeks. Energy expenditure, physical activity, and substrate utilization were measured with metabolic caging. Inguinal and epididymal WAT depots were analyzed for changes in tissue weight, fatty acid composition, adipocyte size, and markers of lipogenesis, lipolysis, and insulin signaling. KO mice had lower body weight, higher serum nonesterified fatty acids, smaller WAT depots, and reduced adipocyte size compared to WT mice without altered food intake, energy expenditure, or physical activity, regardless of the diet. Markers of lipogenesis and lipolysis were more highly expressed in KO mice compared to WT mice in both depots, regardless of the diet. These changes were concomitant with lower basal insulin signaling in WAT. Collectively, a D6D deficiency alters triacylglycerol/fatty acid cycling in WAT by promoting lipolysis and reducing fatty acid re-esterification, which may be partially attributed to a reduction in WAT insulin signaling.

Effects of co-incubation of LPS-stimulated RAW 264.7 macrophages on leptin production by 3T3-L1 adipocytes: a method for co-incubating distinct adipose tissue cell lines

BACKGROUND

Adipose tissue is a major endocrine organ capable of releasing inflammatory adipokines that are linked to changes occurring in the overfed state, where tissue remodeling results in hypertrophic adipocytes that recruit monocytes to infiltrate the tissue and take on an inflammatory phenotype. Increases in macrophage-specific inflammatory mediator levels contribute to the inflamed state and worsen the inflammatory loop between the macrophages and adipocytes. Although most inflammatory adipokines are released by macrophages, adipocytes can also release immunomodulatory adipokines, such as leptin. The objective of this research was to determine if co-incubation of activated macrophages with mature adipocytes, using transwell inserts, affected adipocyte leptin release. We also examined if there were differences in levels of cell-secreted products quantified in cell-conditioned media collected from macrophage-containing (transwell insert) and adipocyte-containing (well) compartments.

METHODS

Mature adipocytes were co-incubated with control and lipopolysaccharide-stimulated (0.01 mg/ml) murine macrophages, and nitric oxide, interleukin-6, and leptin levels were quantified in the cell-conditioned media from both compartments.

RESULTS

Activation status of the macrophages did not affect leptin release by the adipocytes. We observed higher amounts of leptin in wells compared to transwells. Nitric oxide and interleukin-6 levels were similar between transwells and wells, suggesting that these adipokines travel through the transwell inserts and are reaching equilibrium between the two compartments.

CONCLUSION

Our results suggest that co-incubating activated macrophages and adipocytes using transwell inserts can result in distinct microenvironments in the different cellular compartments and that separate sampling of these compartments is required to detect the subtle signaling dynamics that exist between these cells.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s42269-022-00747-7.

Treatment of preadipocytes with fish oil, mixed oil, or soybean oil-based lipid emulsions have differential effects on the regulation of lipogenic and lipolytic genes in mature 3T3-L1 adipocytes

The key adipose tissue characteristics are established during early development, where lipids play an essential role. Lipid emulsions used in total parenteral nutrition have different omega-(n) 6 to n-3 fatty acid ratios. A lower n-6:n-3 fatty acid decreases lipid accumulation; however, the effects of lipid emulsions with different n-6 to n-3 fatty acid ratios on the programming of preadipocytes to affect lipid accumulation in mature adipocytes is not known. This study compared the effects of Fish oil (FO), Mixed oil (MO), and Soybean oil (SO) based lipid emulsion on genes involved in adipogenesis, lipogenesis, lipolysis, and β-oxidation in 3T3-L1 adipocytes. Preadipocytes were treated with specific lipid emulsions and then differentiated to mature adipocytes in the absence of lipid emulsions. In a separate experiment, mature 3T3-L1 adipocytes were treated with lipid emulsions to investigate the effects on genes involved in lipolysis. Fatty acid composition, triacylglycerol levels, and the mRNA expression of genes involved in adipogenesis, lipogenesis, lipolysis, and β-oxidation were measured. Preadipocytes and mature adipocytes treated with FO showed higher incorporation of n-3 polyunsaturated fatty acids, lower triacylglycerol levels, and decreased mRNA expression of adipogenic and lipogenic genes, followed by MO and SO. FO and MO increased the mRNA expression of carnitine palmitoyltransferase-1, while FO decreased the mRNA expression of lipolytic genes compared to untreated cells. Our findings suggest that FO programs preadipocytes to prevent adipose tissue dysfunction in mature adipocytes; the effects of FO-based lipid emulsion were followed by MO and SO.

Perspectives on scaling production of adipose tissue for food applications

With rising global demand for food proteins and significant environmental impact associated with conventional animal agriculture, it is important to develop sustainable alternatives to supplement existing meat production. Since fat is an important contributor to meat flavor, recapitulating this component in meat alternatives such as plant based and cell cultured meats is important. Here, we discuss the topic of cell cultured or tissue engineered fat, growing adipocytes in vitro that could imbue meat alternatives with the complex flavor and aromas of animal meat. We outline potential paths for the large scale production of in vitro cultured fat, including adipogenic precursors during cell proliferation, methods to adipogenically differentiate cells at scale, as well as strategies for converting differentiated adipocytes into 3D cultured fat tissues. We showcase the maturation of knowledge and technology behind cell sourcing and scaled proliferation, while also highlighting that adipogenic differentiation and 3D adipose tissue formation at scale need further research. We also provide some potential solutions for achieving adipose cell differentiation and tissue formation at scale based on contemporary research and the state of the field.

Co-administration of oleic and docosahexaenoic acids enhances glucose uptake rather than lipolysis in mature 3T3-L1 adipocytes cell culture

This study investigated the effect of different types of long-chain fatty acids and their combination on the triglyceride accumulation, glucose utilisation, and lipolysis in already obese adipocytes. 3T3-L1 MBX cells were first differentiated into mature adipocytes using adipogenic inducers (3-isobutyl-1-methylxanthine, dexamethasone, indomethacin, insulin, and high glucose), then 100 µM 0.1% ethanol extracts of palmitic (PA), oleic (OA), or docosahexaenoic acid (DHA) were applied for nine days. Unsaturated fatty acids decreased the intracellular lipid accumulation while maintaining glucose utilisation levels. However, unlike OA, self-administration of DHA only intensified lipolysis by 25% vs induced untreated control (IC), which may have a direct detrimental impact on the whole body’s metabolic state. DHA applied in equal proportion with PA elevated triglyceride accumulation by 10% compared to IC, but applied with OA, enhanced glucose uptake without any significant changes in the lipogenic drive and the lipolytic rate, suggesting that this unsaturated fatty acids combination may offer a considerable advantage in amelioration of obesity-related disorders.

Adipose Tissue Dysfunctions in Response to an Obesogenic Diet Are Reduced in Mice after Transgenerational Supplementation with Omega 3 Fatty Acids

Obesity is characterized by profound alterations in adipose tissue (AT) biology, leading to whole body metabolic disturbances such as insulin resistance and cardiovascular diseases. These alterations are related to the development of a local inflammation, fibrosis, hypertrophy of adipocytes, and dysregulation in energy homeostasis, notably in visceral adipose tissue (VAT). Omega 3 (n-3) fatty acids (FA) have been described to possess beneficial effects against obesity-related disorders, including in the AT; however, the long-term effect across generations remains unknown. The current study was conducted to identify if supplementation with n-3 polyunsaturated FA (PUFA) for three generations could protect from the consequences of an obesogenic diet in VAT. Young mice from the third generation of a lineage receiving a daily supplementation (1% of the diet) with fish oil rich in eicosapentaenoic acid (EPA) or an isocaloric amount of sunflower oil, were fed a high-fat, high-sugar content diet for 4 months. We explore the transcriptomic adaptations in each lineage using DNA microarray in VAT and bioinformatic exploration of biological regulations using online databases. Transgenerational intake of EPA led to a reduced activation of inflammatory processes, perturbation in metabolic homeostasis, cholesterol metabolism, and mitochondrial functions in response to the obesogenic diet as compared to control mice from a control lineage. This suggests that the continuous intake of long chain n-3 PUFA could be preventive in situations of oversupply of energy-dense, nutrient-poor foods.

Fighting Fat With Fat: n-3 Polyunsaturated Fatty Acids and Adipose Deposition in Broiler Chickens

Modern broiler chickens are incredibly efficient, but they accumulate more adipose tissue than is physiologically necessary due to inadvertent consequences of selection for rapid growth. Accumulation of excess adipose tissue wastes feed in birds raised for market, and it compromises well-being in broiler-breeders. Studies driven by the obesity epidemic in humans demonstrate that the fatty acid profile of the diet influences adipose tissue growth and metabolism in ways that can be manipulated to reduce fat accretion. Omega-3 polyunsaturated fatty acids (n-3 PUFA) can inhibit adipocyte differentiation, induce fatty acid oxidation, and enhance energy expenditure, all of which can counteract the accretion of excess adipose tissue. This mini-review summarizes efforts to counteract the tendency for fat accretion in broilers by enriching the diet in n-3 PUFA.

Eicosapentaenoic acid supplemented to in vitro maturation medium results in lesser lipid content and intracellular reactive oxygen species in blastocysts of cattle

Sub-optimal cattle embryo development to the blastocyst stage still is a problem when conducting in vitro production (IVP) procedures. Supplementation of in vitro maturation (IVM) medium with omega 3-polyunsaturated eicosapentaenoic acid (EPA) is an approach that might have positive effects on lipid metabolism of cattle oocytes, potentially improving subsequent embryo development. The aim of this study was to evaluate effects of EPA addition to serum-free IVM medium on pronuclear formation after in vitro fertilization, cleavage, and blastocyst rates. Effects of EPA on lipid accumulation and intracellular reactive oxygen species (ROS) generation with IVP of cattle embryos was also investigated. In all experiments, cumulus-oocyte complexes were matured in IVM medium supplemented with 0 nM, 1 nM, or 1 μM EPA for 24 h. Pronuclear formation, cleavage, and blastocyst rates were similar for embryos when there was supplementation of EPA at all concentrations to those of the control group (P > 0.05). The inclusion of 1 nM EPA in medium resulted in a greater lipid content and less intracellular ROS in day 8-embryos compared with those of the Control group (P < 0.05). There were no differences, however, when there was inclusion of 1 μM EPA compared to embryos of the Control group at the day 8 developmental stage (P > 0.05). In conclusion, supplementation with IVM medium with the 1 nM EPA concentration resulted in a lesser blastocyst lipid and intracellular ROS concentration, without modifying embryo development, therefore, EPA could be a desirable supplement to improve embryo quality in cattle.

Shrimp Oil Extracted from Shrimp Processing By-Product Is a Rich Source of Omega-3 Fatty Acids and Astaxanthin-Esters, and Reveals Potential Anti-Adipogenic Effects in 3T3-L1 Adipocytes

The province of Newfoundland and Labrador, Canada, generates tons of shrimp processing by-product every year. Shrimp contains omega (n)-3 polyunsaturated fatty acids (PUFA) and astaxanthin (Astx), a potent antioxidant that exists in either free or esterified form (Astx-E). In this study, shrimp oil (SO) was extracted from the shrimp processing by-product using the Soxhlet method (hexane:acetone 2:3). The extracted SO was rich in phospholipids, n-3 PUFA, and Astx-E. The 3T3-L1 preadipocytes were differentiated to mature adipocytes in the presence or absence of various treatments for 8 days. The effects of SO were then investigated on fat accumulation, and the mRNA expression of genes involved in adipogenesis and lipogenesis in 3T3-L1 cells. The effects of fish oil (FO), in combination with Astx-E, on fat accumulation, and the mRNA expression of genes involved in adipogenesis and lipogenesis were also investigated. The SO decreased fat accumulation, compared to untreated cells, which coincided with lower mRNA expression of adipogenic and lipogenic genes. However, FO and FO + Astx-E increased fat accumulation, along with increased mRNA expression of adipogenic and lipogenic genes, and glucose transporter type 4 (Glut-4), compared to untreated cells. These findings have demonstrated that the SO is a rich source of n-3 PUFA and Astx-E, and has the potential to elicit anti-adipogenic effects. Moreover, the SO and FO appear to regulate adipogenesis and lipogenesis via independent pathways in 3T3-L1 cells.

Maternal high-fat-diet exposure is associated with elevated blood pressure and sustained increased leptin levels through epigenetic memory in offspring

Maternal metabolism dysregulation during pregnancy predisposes offspring to major diseases, including hypertension, in later life, but the mechanism involved remains to be fully elucidated. A high-fat-diet (HFD) pregnant rat model was used to investigate whether excessive intrauterine lipid exposure was associated with elevated blood pressure in offspring and increased levels of leptin, an important biomarker and mediator of vascular dysfunction and hypertension. We found that gestational hyperlipidemia predisposed offspring to blood pressure elevation and sustained increases in leptin levels with no difference in body weight in the rat model. Increased leptin expression and leptin promoter hypomethylation were found in adipose tissues of HFD-exposed offspring. The treatment of mesenchymal stem cells with free fatty acids during adipogenic differentiation resulted in increased leptin expression, accompanied by leptin promoter hypomethylation. In addition, we also followed up 121 children to evaluate the association between maternal triglyceride levels and offspring blood pressure. Consistent with the animal study results, we observed elevated serum leptin levels and blood pressure in the offspring born to women with gestational hypertriglyceridemia. Our findings provide new insights that maternal hyperlipidemia is associated with elevated blood pressure in offspring and is associated with increases in leptin levels through epigenetic memory.

A review on differential effects of dietary fatty acids on weight, appetite and energy expenditure

The association between weight and chronic diseases is well defined. The quality and quantity of dietary fatty acids is an important external factor and appetite and energy expenditure, are important internal factors in determining body weight. On the other hand, dietary fatty acids composition can modulate appetite and energy metabolism, but not all fats are equal in producing metabolic responses.Given the accumulating evidence for differential effects of various dietary fatty acids, one important area of investigation is to scrutinize their roles in weight, appetite and energy expenditure modulation. There is substantial evidence to suggest that saturated fatty acids have a greater effect on appetite control, although in the long run may result in more weight gain than unsaturated fatty acids due to a weaker stimulation of energy expenditure. In contrast, mono-unsaturated fats do not have much effects on appetite control, but they can be beneficial in weight control over the long term due to stimulatory effects on energy expenditure. Interestingly, in case of poly unsaturated fats, including n-3 and n-6, their effect on increasing energy expenditure is aligned, but they act differently in controlling weight and appetite.

DHA Modulates Immune Response and Mitochondrial Function of Atlantic Salmon Adipocytes after LPS Treatment

Adipocytes play a central role in overall energy homeostasis and are important contributors to the immune system. Fatty acids (FAs) act as signaling molecules capable to modulate adipocyte metabolism and functions. To identify the effects of two commonly used FAs in Atlantic salmon diets, primary adipocytes were cultured in the presence of oleic (OA) or docosahexaenoic (DHA) acid. DHA decreased adipocyte lipid droplet number and area compared to OA. The increase in lipid load in OA treated adipocytes was paralleled by an increase in iNOS activity and mitochondrial SOD2-GFP activity, which was probably directed to counteract increase in oxidative stress. Under lipopolysaccharide (LPS)-induced inflammation, DHA had a greater anti-inflammatory effect than OA, as evidenced by the higher SOD2 activity and the transcriptional regulation of antioxidant enzymes and pro- and anti-inflammatory markers. In addition, DHA maintained a healthy mitochondrial structure under induced inflammation while OA led to elongated mitochondria with a thin thread like structures in adipocytes exposed to LPS. Overall, DHA possess anti-inflammatory properties and protects Atlantic salmon against oxidative stress and limits lipid deposition. Furthermore, DHA plays a key role in protecting mitochondria shape and function.

Determination of Fat Accumulation Reduction by Edible Fatty Acids and Natural Waxes In Vitro

Natural edible waxes mixed with plant oils, containing high levels of unsaturated fatty acids (FAs), are known as oleogels. Oleogels are used for replacing saturated FAs in animal-derived food with unsaturated FAs. However, the health effects of edible waxes are not yet clearly defined. The purpose of this study was to investigate the effect of FAs and natural waxes on the adipogenesis in 3T3-L1 cells. The 3T3-L1 cells were differentiated and treated with FAs and waxes. These FAs [Palmitic acid (PA), Stearic acid (SA), Oleic acid (OA), Linoleic acid (LA), and Alpha-linolenic acid (ALA)] and waxes [beeswax (BW) and carnauba wax (CW)] were prepared at varying concentrations, and cell toxicity, triglyceride accumulation, lipid droplets size, and distribution inside of cells were determined. Adipogenic gene expression including PPARγ, FASN, C/EBPα, SREBP-1, and CPT-1 was determined. Results showed that increasing the concentration of FAs and waxes led to a decrease in the adipocyte cells viability and metabolic performance. SA showed the highest level of triglyceride accumulation (p<0.05), whereas ALA showed the lowest (p<0.05). Both BW and CW at 3.0 ppm showed significantly higher lipid accumulation than in the control and other groups (p<0.05). ALA had significantly downregulated adipogenic gene expression levels, excluding those of CPT-1, compared to the other treatment groups (p<0.05). Moreover, BW demonstrated similar adipogenic gene expression levels as ALA compared to CW. Consequently, ALA and BW may have health benefits by reducing adipogenesis and can be used in processed meat.

Dietary DHA/EPA supplementation ameliorates diabetic nephropathy by protecting from distal tubular cell damage

The aim was to explore the influence of experimental diabetes mellitus type 1 (DM1) and potential protective/deleterious effects of different dietary n-6/n-3 PUFA ratios on renal phospholipid composition and pathological changes caused by DM1. Male Wistar rats were injected with 55 mg/kg streptozotocin or citrate buffer (control group). Control (C) and diabetic groups (STZ) were fed with n-6/n-3 ratio of ≈ 7, STZ + N6 with n-6/n-3 ratio ≈ 60 and STZ + DHA with n-6/n-3 ratio of ≈ 1 containing 16% EPA and 19% DHA. Tissues were harvested 30 days after DM1 induction. Blood and kidneys were collected and analysed for phospholipid fatty acid composition, pathohystological changes, ectopic lipid accumulation and expression of VEGF, NF-kB and special AT-rich sequence-binding protein-1 (SATB1). Pathological changes were studied also by using transmission electron microscopy, after immunostaining for VEGF. Substantial changes in renal phospholipid fatty acid composition resulted from DM1 and dietary PUFA manipulation. Extensive vacuolization of distal tubular cells (DTCs) was found in DM1, but it was attenuated in the STZ + DHA group, in which the highest renal NF-kB expression was observed. The ectopic lipid accumulation was observed in proximal tubular cells (PTCs) of all diabetic animals, but it was worsened in the STZ + N6 group. In DM1, we found disturbance of VEGF-transporting vesicular PTCs system, which was substantially worsened in STZ + DHA and STZ + N6. Results have shown that the early phase of DN is characterized with extent damage and vacuolization of DTCs, which could be attenuated by DHA/EPA supplementation. We concluded that dietary fatty acid composition can strongly influence the outcomes of DN.

Effects of polyunsaturated fatty acids on the development of pig oocytes in vitro following parthenogenetic activation and on the lipid content of oocytes and embryos

As oocytes and embryos of pigs have greater lipid content in the cytoplasm than those of other species, supplementation of the medium for in vitro maturation (IVM) of oocytes with omega-3 polyunsaturated fatty acids (PUFA) may help to improve embryo development. This study was conducted to evaluate effects of the inclusion of the docosaexaenoic (DHA) and of the eicosapentaenoic acids (EPA) in the IVM medium on the development of pig oocytes and on the lipid content of oocytes and embryos. In all experiments, control media consisted of porcine follicular fluid and oocytes were activated through parthenogenesis. In Experiment 1, there were four treatments for each PUFA: one control; and three treatments including EPA or DHA in the IVM medium at 12.5 μM, 25.0 μM and 50.0 μM). In Experiment 2, inclusion of 50 μM DHA was compared against the control. Cleavage rates in the IVM medium including 12.5 μM EPA and blastocyst development rates in media at any EPA concentration were less than for the control in Experiment 1 (P <  0.05). Compared to the control, inclusion of 50 μM DHA in the IVM medium was related to greater cleavage rates and greater number of embryo cells, in Experiment 1, and lesser lipid content in oocytes after 22 and 44 h and in embryos after 7 days, in Experiment 2 (both P <  0.05). Addition of DHA in the IVM medium may benefit the development of pig oocytes, but EPA appears to be cytotoxic.

Omega-3 polyunsaturated fatty acids attenuate inflammatory activation and alter differentiation in human adipocytes

BACKGROUND

Omega-3 polyunsaturated fatty acids, specifically the fish-oil-derived eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been proposed as inflammation-resolving agents via their effects on adipose tissue.

OBJECTIVE

We proposed to determine the effects of EPA and DHA on human adipocyte differentiation and inflammatory activation in vitro.

METHODS

Primary human subcutaneous adipocytes from lean and obese subjects were treated with 100 μM EPA and/or DHA throughout differentiation (differentiation studies) or for 72 h postdifferentiation (inflammatory studies). THP-1 monocytes were added to adipocyte wells for co-culture experiments. Subcutaneous and visceral adipose explants from obese subjects were treated for 72 h with EPA and DHA. Oil Red O staining was performed on live cells. Cells were collected for mRNA analysis by quantitative polymerase chain reaction, and media were collected for protein quantification by enzyme-linked immunosorbent assay.

RESULTS

Incubation with EPA and/or DHA attenuated inflammatory response to lipopolysaccharide (LPS) and monocyte co-culture with reduction in post-LPS mRNA expression and protein levels of IL6, CCL2 and CX3CL1. Expression of inflammatory genes was also reduced in the endogenous inflammatory response in obese adipose. Both DHA and EPA reduced lipid droplet formation and lipogenic gene expression without alteration in expression of adipogenic genes or adiponectin secretion.

CONCLUSIONS

EPA and DHA attenuate inflammatory activation of in vitro human adipocytes and reduce lipogenesis.

EPA plays multiple roles in regulating lipid accumulation of grass carp Ctenopharyngodon idella adipose tissue in vitro and in vivo

This study was conducted to assess the effect of eicosapentaenoic acid (20:5n-3, EPA) on lipid accumulation in grass carp Ctenopharyngodon idella adipose tissue both in vitro and in vivo. EPA was observed to inhibit the adipocyte viability in a time and dose-dependent manner. EPA was also found to induce reactive oxygen species accumulation in vitro. The mRNA levels of caspase 3a and caspase 3b, as well as the activity of Caspase 3 increased significantly in vitro and in vivo, whereas the value of B cell leukemia 2-Bcl-2 associated X protein decreased significantly. Besides, the pro-apoptotic effect was relieved by α-tocopherol. Dietary 0.52% EPA had no apparent effect on intraperitoneal fat index. Moreover, EPA promoted the hydrolytic gene expressions in vitro and in vivo, including adipose triglyceride lipase and hormone sensitive lipase-a. Meanwhile, the lipogenic gene expressions of liver X receptor α, sterol regulatory element binding protein-1c and fatty-acid synthase were down-regulated by EPA in vitro and in vivo. However, EPA also acted to promote the marker gene expressions of adipogenesis, including peroxisome proliferator-activated receptor γ and lipoprotein lipase in vitro and in vivo. Contents of EPA increased significantly in the treatment groups in vitro and in vivo. These results support that EPA affects multiple aspects of lipid metabolism, including hydrolysis, lipogenesis, adipogenesis and apoptosis. However, it barely functioned in decreasing the lipid accumulation of Ctenopharyngodon idella under the current culture conditions.

The Impact of Lipid Types and Liposomal Formulations on Osteoblast Adiposity and Mineralization

Recent studies have demonstrated that fat accumulation in bone cells is detrimental to bone mass. Both adipocytes and osteoblasts are derived from common multipotent mesenchymal stem cells (MSCs) and hence the presence of fat may increase adipocyte proliferation, differentiation and fat accumulation while inhibiting osteoblast differentiation and bone formation. Lipids are common constituents in supramolecular vesicles (e.g., micelles or liposomes) that serve as drug delivery systems. Liposomal formulations such as Meriva^® were proven to decrease joint pain and improve joint function in osteoarthritis (OA) patients. In this study, we evaluated how lipid types and liposomal formulations affect osteoblast behavior including cell viability, differentiation, mineralization and inflammation. Various liposomal formulations were prepared using different types of lipids, including phosphatidylcholine (PC), 1,2-dioleoyl-sn-glycero-3-phospho-ethanolamine (DOPE), cholesterol (Chol), 3β-[N-(N′,N′-dimethylaminoethane)-carbamoyl] cholesterol hydrochloride (DC-cholesterol HCl), and 1,2-dioleoyl-3-trimethylammonium-propane chloride salt (DOTAP) to investigate the impact on osteoblast differentiation and inflammation. The results indicated that cationic lipids, DC-cholesterol and DOTAP, presented higher dose-dependent cytotoxicity and caused high level of inflammatory responses. Due to the natural properties of lipids, all the lipids can induce lipid droplet formation in osteoblasts but the level of lipid droplet accumulation was different. In comparison with cationic lipids, neutral lipids induced less adiposity, and maintained high osteoblast mineralization. Similar to previous researches, we also confirmed an inverse relationship between lipid droplet formation and osteoblast mineralization in 7F2 mouse osteoblasts. Importantly, PC containing liposomes (PC only and PC/DOTAP) suppressed IL-1β-induced gene expression of COX-2 and MMP-3 but not Chol/DOTAP liposomes or DC-Chol/DOPE liposomes. Taken together, we suggested that PC contained liposomes could provide the best liposomal formulation for the treatment of bone diseases.

Integrated Immunomodulatory Mechanisms through which Long-Chain n-3 Polyunsaturated Fatty Acids Attenuate Obese Adipose Tissue Dysfunction

Obesity is a global health concern with rising prevalence that increases the risk of developing other chronic diseases. A causal link connecting overnutrition, the development of obesity and obesity-associated co-morbidities is visceral adipose tissue (AT) dysfunction, characterized by changes in the cellularity of various immune cell populations, altered production of inflammatory adipokines that sustain a chronic state of low-grade inflammation and, ultimately, dysregulated AT metabolic function. Therefore, dietary intervention strategies aimed to halt the progression of obese AT dysfunction through any of the aforementioned processes represent an important active area of research. In this connection, fish oil-derived dietary long-chain n-3 polyunsaturated fatty acids (PUFA) in the form of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been demonstrated to attenuate obese AT dysfunction through multiple mechanisms, ultimately affecting AT immune cellularity and function, adipokine production, and metabolic signaling pathways, all of which will be discussed herein.

Maternal consumption of fish oil programs reduced adiposity in broiler chicks

Maternal intake of eicosapentaenoic acid (EPA; 20:5 n-3) and docosahexaenoic acid (22:6 n-3) has been associated with reduced adiposity in children, suggesting the possibility to program adipose development through dietary fatty acids before birth. This study determined if enriching the maternal diet in fish oil, the primary source of EPA and DHA, affected adipose development in offspring. Broiler chickens were used because they are obesity-prone, and because fatty acids provided to the embryo can be manipulated through the hen diet. Hens were fed diets supplemented (2.8% wt:wt) with corn oil (CO; n-6) or fish oil (FO; n-3) for 28 d. Chicks from both maternal diet groups were fed the same diet after hatch. Maternal FO consumption enriched chick adipose tissue in EPA and DHA and reduced adiposity by promoting more, but smaller, adipocytes. This adipocyte profile was paralleled by lower expression of the adipogenic regulator PPARG and its co-activator PPARGC1B, and elevated expression of LPL. Proteomics identified 95 differentially abundant proteins between FO and CO adipose tissue, including components of glucose metabolism, lipid droplet trafficking, and cytoskeletal organization. These results demonstrate that the maternal dietary fatty acid profile programs offspring adipose development.

DHA increases adiponectin expression more effectively than EPA at relative low concentrations by regulating PPARγ and its phosphorylation at Ser273 in 3T3-L1 adipocytes

BACKGROUND

Enhancing circulating adiponectin is considered as a potential approach for the prevention and treatment of non-communicable diseases (NCDs). Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were reported to increase adiponectin by previous studies using a mixture of them. However, their individual effects on adiponectin and the underlying mechanisms are still unclear. In the present study, we observed and compared the individual effect of DHA and EPA on adiponectin in 3T3-L1 adipocytes, and further tested whether DHA or EPA regulated adiponectin by peroxisome proliferator-activated receptor γ (PPARγ) and its phosphorylation at Ser273 to provide a plausible explanation for their distinct actions.

METHODS

Firstly, 3T3-L1 adipocytes were treated with different doses of DHA or EPA for 24 h. Secondly, 3T3-L1 adipocytes were treated with DHA or EPA in the presence or absence of GW9662. Thirdly, 3T3-L1 adipocytes were pretreated with DHA or EPA for 24 h, followed by being respectively co-incubated with tumor necrosis factor α (TNF-α) or roscovitine for another 2 h. Bovine serum albumin treatment served as the control. After treatments, cellular and secreted adiponectin, cellular PPARγ and its phosphorylation at Ser273 were determined.

RESULTS

Compared with the control, DHA increased cellular and secreted adiponectin at 50 and 100 μmol/L, while EPA increased them at 100 and 200 μmol/L. Adiponectin expressions in DHA treated groups were significantly higher than those in EPA treated groups at 50 and 100 μmol/L. Both DHA and EPA enhanced PPARγ expression, but DHA was more effective. GW9662 blocked DHA- and EPA-induced increases in PPARγ as well as adiponectin. Remarkably, an opposite regulation of PPARγ phosphorylation was detected after fatty acids treatment: DHA inhibited it but EPA stimulated it. TNF-α blocked DHA-induced decrease in PPARγ phosphorylation, which eventually led to a decrease in adiponectin. Roscovitine blocked EPA-induced increase in PPARγ phosphorylation, but the corresponding increase in adiponectin was non-significant.

CONCLUSION

DHA compared with EPA led to a greater increase in cellular and secreted adiponectin at relative low concentrations by increasing PPARγ expression and inhibiting its phosphorylation at Ser273. DHA may be more beneficial than EPA in reducing risks of NCDs.

Stimulation of glycerol kinase in grass carp preadipocytes by EPA

This study was conducted to assess the effect of eicosapentaenoic acid (EPA) on grass carp preadipocyte glycerol kinase (GyK) expression, as well as to explore the mechanism. Here, we cloned partial sequence of grass carp GyK gene and analyzed its tissue distribution. The result showed that GyK gene expressed most in the liver, followed by adipose tissue and the kidney. Besides, 400 μM oleic acid (18:1n-9, OA) was used to establish a hypertrophic preadipocyte model. GyK gene expression and enzyme activity were significantly enhanced after model cells were treated with 100 μM eicosapentaenoic acid (20:5n-3, EPA) for 6, 12, and 24 h. Meanwhile, peroxisome proliferative-activated receptor (PPAR)γ, adipose triglyceride lipase (ATGL), and the two isoforms of grass carp HSL gene were first identified by Sun et al (2016), and they defined the two isoforms as HSLa and HSLb. Therefore, maybe HSLa and HSLb are appropriate.. The content of triglyceride was dramatically increased by EPA treatment for 24 h. Further, a competitive ATGL antagonist, HY-15859, attenuated the increase in GyK induced by EPA at 12 h. Surprisingly, the enhanced lipolysis and PPARγ gene expression induced by serum deprivation were paralleled by an increase in GyK gene expression, whereas a stabilization in GyK enzyme activity. Other fatty acids, including docosahexaenoic acid, alpha-linolenic acid, linoleic acid, and OA also promoted GyK gene expression. Moreover, an irreversible PPARγ antagonist, GW9662, was used to investigate the role of PPARγ in GyK induction. Data showed that GW9662 abolished the induction of GyK by EPA at 12 h. Together, these data suggested that EPA elevated grass carp preadipocytes GyK expression. ATGL and PPARγ contributed to the induction of GyK. PPARγ may be a key regulator in response to GyK expression induced by EPA.

Effects of dietary supplementation with EPA and/or α-lipoic acid on adipose tissue transcriptomic profile of healthy overweight/obese women following a hypocaloric diet

In obesity, the increment of adiposity levels disrupts the whole body homeostasis, promoting an over production of oxidants and inflammatory mediators. The current study aimed to characterize the transcriptomic changes promoted by supplementation with eicosapentaenoic acid (EPA, 1.3 g/day), α-lipoic acid (0.3 g/day), or both (EPA + α-lipoic acid, 1.3 g/day + 0.3 g/day) in subcutaneous abdominal adipose tissue from overweight/obese healthy women, who followed a hypocaloric diet (30% of total energy expenditure) during ten weeks, by using a microarray approach. At the end of the intervention, a total of 33,297 genes were analyzed using Affymetrix GeneChip arrays. EPA promoted changes in extracellular matrix remodeling gene expression, besides a rise of genes associated with either chemotaxis or wound repair. α-Lipoic acid decreased expression of genes related with cell adhesion and inflammation. Furthermore, α-lipoic acid, especially in combination with EPA, upregulated the expression of genes associated with lipid catabolism while downregulated genes involved in lipids storage. Together, all these data suggest that some of the metabolic effects of EPA and α-lipoic acid could be related to their regulatory actions on adipose tissue metabolism. © 2016 BioFactors, 43(1):117-131, 2017.

Combinations of bio-active dietary constituents affect human white adipocyte function in-vitro

Background

Specific bio-active dietary compounds modulate numerous metabolic processes in adipose tissue (AT), including pre-adipocyte proliferation and differentiation. AT dysfunction, rather than an increased fat mass per se, is strongly associated with the development of insulin resistance and is characterized by impaired adipogenesis, hypertrophic adipocytes, inflammation, and impairments in substrate metabolism. A better understanding of mechanisms underlying AT dysfunction may provide new strategies for the treatment of obesity-associated metabolic diseases. Here we evaluated the role of (all-E)-lycopene (Lyc), eicosapentaenoic acid (EPA) or trans-resveratrol (Res) and combinations thereof on human white adipocyte function.

Methods

In-vitro differentiating human pre-adipocytes were treated with EPA, Lyc and Res or their combinations for 14 days. The effects on intracellular lipid droplet (LD) accumulation, secreted anti- and pro-inflammatory cyto-/adipokines (e.g. adiponectin, IL-6, IL-8/CXCL-8 and MCP-1/CCL2) and on gene expression of markers of adipocyte differentiation and substrate metabolism (e.g. PPAR-gamma, C/EBP-alpha, GLUT-4, FAS, ATGL, HSL, and PLIN-1) were measured by fluorescent microscopy (Cellomics™), multi-parametric LiquiChip® technology and quantitative RT-PCR, respectively.

Results

Treatment of differentiating adipocytes for 14 days with the combination of Lyc/Res and EPA/Res resulted in significantly inhibited LD formation (~ -25 and -20%, respectively) compared to the effects of the single compounds. These morphological changes were accompanied by increased mRNA levels of the adipogenic marker PPAR-gamma and the lipase ATGL and by decreased expression levels of lipogenic markers (LPL, FAS, GLUT-4) and the LD-covering protein PLIN-1. In addition, a blunted adipocyte secretion of pro-inflammatory cytokines (IL-6 and MCP-1) and adiponectin was observed following treatment with these compounds.

Conclusion

The combination of the dietary bio-actives Lyc and EPA with Res might influence adipocyte function by affecting the balance between adipogenic, lipogenic and lipolytic gene expression, resulting in a reduced LD storage and a less inflammatory secretion profile. Taken together, our results indicate that combinations of dietary compounds may be beneficial for the prevention and treatment of metabolic disorders via effects on human white adipocyte function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0143-5) contains supplementary material, which is available to authorized users.

A post-weaning fish oil dietary intervention reverses adverse metabolic outcomes and 11β-hydroxysteroid dehydrogenase type 1 expression in postnatal overfed rats

Early life is considered a critical period for determining long-term metabolic health. Postnatal over-nutrition may alter glucocorticoid (GC) metabolism and increase the risk of developing obesity and metabolic disorders in adulthood. Our aim was to assess the effects of the dose and timing of a fish oil diet on obesity and the expression of GC-activated enzyme 11β-hydroxysteroid dehydrogenase type 1 (HSD1) in postnatal overfed rats. Litter sizes were adjusted to three (small litter (SL)) or ten (normal litter) rats on postnatal day 3 to induce overfeeding or normal feeding. The SL rats were divided into three groups after weaning: high-dose fish oil (HFO), low-dose fish oil (LFO) and standard-diet groups. After 10 weeks, the HFO diet reduced body weight gain (16 %, P0·05). In conclusion, the post-weaning HFO diet could reverse adverse outcomes and decrease tissue GC activity in postnatal overfed rats.

Forskolin Inhibits Lipopolysaccharide-Induced Modulation of MCP-1 and GPR120 in 3T3-L1 Adipocytes through an Inhibition of NFκB

In an obese state, Toll-like receptor-4 (TLR-4) upregulates proinflammatory adipokines secretion including monocyte chemotactic protein-1 (MCP-1) in adipose tissue. In contrast, G-protein coupled receptor 120 (GPR120) mediates antiobesity effects. The aim of this study was to determine the signaling pathway by which Forskolin (FK), a cyclic adenosine monophosphate- (cAMP-) promoting agent causing positive changes in body composition in overweight and obese adult men, affects MCP-1 and GPR120 expression during an inflammatory response induced by lipopolysaccharide (LPS) in adipocytes, such as in an obese state. 3T3-L1 cells differentiated into adipocytes (DC) were stimulated with LPS in the absence or presence of FK and inhibitors of TLR-4 and inhibitor of kappa B (IκBα). In DC, LPS increased MCP-1, TLR-4, and nuclear factor-κB1 (NFκB1) mRNA levels, whereas it decreased GPR120 mRNA levels. In DC, FK inhibited the LPS-induced increase in MCP-1, TLR-4, and NFκB1 mRNA levels and the LPS-induced decrease in GPR120 mRNA. BAY11-7082 and CLI-095 abolished these LPS-induced effects. In conclusion, FK inhibits LPS-induced increase in MCP-1 mRNA levels and decrease in GPR120 mRNA levels in adipocytes and may be a potential treatment for inflammation in obesity. Furthermore, TLR-4-induced activation of NFκB may be involved in the LPS-induced regulation of these genes.

Role of n-3 Polyunsaturated Fatty Acids in Ameliorating the Obesity-Induced Metabolic Syndrome in Animal Models and Humans

The incidence of obesity and its comorbidities, such as insulin resistance and type II diabetes, are increasing dramatically, perhaps caused by the change in the fatty acid composition of common human diets. Adipose tissue plays a role as the major energy reservoir in the body. An excess of adipose mass accumulation caused by chronic positive energy balance results in obesity. The n-3 polyunsaturated fatty acids (n-3 PUFA), DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) exert numerous beneficial effects to maintain physiological homeostasis. In the current review, the physiology of n-3 PUFA effects in the body is delineated from studies conducted in both human and animal experiments. Although mechanistic studies in human are limited, numerous studies conducted in animals and models in vitro provide potential molecular mechanisms of the effects of these fatty acids. Three aspects of n-3 PUFA in adipocyte regulation are discussed: (1) lipid metabolism, including adipocyte differentiation, lipolysis and lipogenesis; (2) energy expenditure, such as mitochondrial and peroxisomal fatty acid β-oxidation; and (3) inflammation, including adipokines and specialized pro-resolving lipid mediators. Additionally, the mechanisms by which n-3 PUFA regulate gene expression are highlighted. The beneficial effects of n-3 PUFA may help to reduce the incidence of obesity and its comorbidities.

Eicosapentaenoic acid promotes mitochondrial biogenesis and beige-like features in subcutaneous adipocytes from overweight subjects

Eicosapentaenoic acid (EPA), a n-3 long-chain polyunsaturated fatty acid, has been reported to have beneficial effects in obesity-associated metabolic disorders. The objective of the present study was to determine the effects of EPA on the regulation of genes involved in lipid metabolism, and the ability of EPA to induce mitochondrial biogenesis and beiging in subcutaneous adipocytes from overweight subjects. Fully differentiated human subcutaneous adipocytes from overweight females (BMI: 28.1-29.8kg/m²) were treated with EPA (100-200 μM) for 24 h. Changes in mRNA expression levels of genes involved in lipogenesis, fatty acid oxidation and mitochondrial biogenesis were determined by qRT-PCR. Mitochondrial content was evaluated using MitoTracker® Green stain. The effects on peroxisome proliferator-activated receptor gamma, co-activator 1 alpha (PGC-1α) and AMP-activated protein kinase (AMPK) were also characterized. EPA down-regulated lipogenic genes expression while up-regulated genes involved in fatty acid oxidation. Moreover, EPA-treated adipocytes showed increased mitochondrial content, accompanied by an up-regulation of nuclear respiratory factor-1, mitochondrial transcription factor A and cytochrome c oxidase IV mRNA expression. EPA also promoted the activation of master regulators of mitochondrial biogenesis such as sirtuin 1, PGC1-α and AMPK. In parallel, EPA induced the expression of genes that typify beige adipocytes such as fat determination factor PR domain containing 16, uncoupling protein 1 and cell death-inducing DFFA-like effector A, T-Box protein 1 and CD137. Our results suggest that EPA induces a remodeling of adipocyte metabolism preventing fat storage and promoting fatty acid oxidation, mitochondrial biogenesis and beige-like markers in human subcutaneous adipocytes from overweight subjects.

Melatonin attenuated adipogenesis through reduction of the CCAAT/enhancer binding protein beta by regulating the glycogen synthase 3 beta in human mesenchymal stem cells

Adipogenic differentiation is characterized by an increase in two major transcription factors: peroxisome proliferator-activated receptor gamma (PPARγ) and the CCAAT/enhancer binding protein alpha (C/EBPα). These two signals are influenced by C/EBPβ and C/EBPδ and cross-regulate each other's expression during the initial stages of adipogenesis. Melatonin has been known to act as not only a direct scavenger of free radicals but also an inhibitor of glycogen synthase kinase 3β (GSK-3β). Here, we report that melatonin inhibits the adipogenic differentiation of human mesenchymal stem cells (hMSCs) which is due to the regulations of C/EBPβ in the early stage of adipogenic differentiation. Melatonin reduced the lipid accumulation, adiponectin, and lipoprotein lipase (LPL) during the adipogenic differentiation of hMSCs. Since C/EBPβ has been associated with the activation of PPARγ and the consensus site of ERK/GSK-3β, PPARγ and β-catenin were detected by immunofluorescence staining after pretreatment of melatonin. Melatonin blocked the activation of PPARγ which induced the degradation of β-catenin. Melatonin also decreased the levels of cyclic adenosine-3,5-monophosphate (cAMP) and reactive oxygen species (ROS). The cAMP triggered the activity of C/EBPβ which is a critical inducer of PPARγ and C/EBPα activation in the early stage of adipogenic differentiation, and this is further affected by ROS production. The adipogenic marker proteins such as PPARγ, C/EBPα, C/EBPβ, and pERK were also decreased by melatonin. In summary, melatonin inhibited the cAMP synthesis through ROS reduction and the phosphorylation of the ERK/GSK-3β site which is known to be responsible for C/EBPβ activation for adipogenic differentiation in hMSCs.

Reduction of circulating FABP4 level by treatment with omega-3 fatty acid ethyl esters

Background

Fatty acid-binding protein 4 (FABP4/A-FABP/aP2) mainly expressed in adipocytes is secreted and acts as an adipokine. Increased circulating FABP4 level is associated with obesity, insulin resistance and atherosclerosis. However, little is known about the modulation of serum FABP4 level by drugs including anti-dyslipidemic agents.

Methods

Patients with dyslipidemia were treated with omega-3 fatty acid ethyl esters (4 g/day; n = 14) containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for 4 weeks. Serum FABP4 level was measured before and after treatment. Expression and secretion of FABP4 were also examined in mouse 3T3-L1 adipocytes treated with EPA or DHA.

Results

Treatment with omega-3 fatty acid ethyl esters significantly decreased triglycerides and serum FABP4 level (13.5 ± 1.5 vs. 11.5 ± 1.1 ng/ml, P = 0.017). Change in FABP4 level by omega-3 fatty acids was negatively correlated with change in levels of EPA + DHA (r = −0.643, P = 0.013), EPA (r = −0.540, P = 0.046) and DHA (r = −0.650, P = 0.011) but not change in the level of triglycerides or other fatty acid composition. Treatment of 3T3-L1 adipocytes with EPA or DHA had no effect on short-term (2 h) secretion of FABP4. However, gene expression and long-term (24 h) secretion of FABP4 were significantly reduced by treatment with EPA or DHA.

Conclusions

Omega-3 fatty acids decrease circulating FABP4 level, possibly by reducing expression and consecutive secretion of FABP4 in adipocytes. Reducing FABP4 level might be involved in suppression of cardiovascular events by omega-3 fatty acids.

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.

Fungal Morphology, Iron Homeostasis, and Lipid Metabolism Regulated by a GATA Transcription Factor in Blastomyces dermatitidis

In response to temperature, Blastomyces dermatitidis converts between yeast and mold forms. Knowledge of the mechanism(s) underlying this response to temperature remains limited. In B. dermatitidis, we identified a GATA transcription factor, SREB, important for the transition to mold. Null mutants (SREBΔ) fail to fully complete the conversion to mold and cannot properly regulate siderophore biosynthesis. To capture the transcriptional response regulated by SREB early in the phase transition (0–48 hours), gene expression microarrays were used to compare SREB∆ to an isogenic wild type isolate. Analysis of the time course microarray data demonstrated SREB functioned as a transcriptional regulator at 37°C and 22°C. Bioinformatic and biochemical analyses indicated SREB was involved in diverse biological processes including iron homeostasis, biosynthesis of triacylglycerol and ergosterol, and lipid droplet formation. Integration of microarray data, bioinformatics, and chromatin immunoprecipitation identified a subset of genes directly bound and regulated by SREB in vivo in yeast (37°C) and during the phase transition to mold (22°C). This included genes involved with siderophore biosynthesis and uptake, iron homeostasis, and genes unrelated to iron assimilation. Functional analysis suggested that lipid droplets were actively metabolized during the phase transition and lipid metabolism may contribute to filamentous growth at 22°C. Chromatin immunoprecipitation, RNA interference, and overexpression analyses suggested that SREB was in a negative regulatory circuit with the bZIP transcription factor encoded by HAPX. Both SREB and HAPX affected morphogenesis at 22°C; however, large changes in transcript abundance by gene deletion for SREB or strong overexpression for HAPX were required to alter the phase transition.

Blastomyces dermatitidis belongs to a group of human pathogenic fungi that convert between two forms, mold and yeast, in response to temperature. Growth as yeast (37°C) in tissue facilitates immune evasion, whereas growth as mold (22°C) promotes environmental survival, sexual reproduction, and generation of transmissible spores. Despite the importance of dimorphism, how fungi regulate temperature adaptation is poorly understood. We identified SREB, a transcription factor that regulates disparate processes including dimorphism. SREB null mutants, which lack SREB, fail to fully complete the conversion to mold at 22°C. The goal of our research was to characterize how SREB regulates transcription during the switch to mold. Gene expression microarray along with chromatin binding and biochemical analyses indicated that SREB affected several processes including iron homeostasis, lipid biosynthesis, and lipid droplet formation. In vivo, SREB directly bound and regulated genes involved with iron uptake, lipid biosynthesis, and transcription. Functional analysis suggested that lipid metabolism may influence filamentous growth at 22°C. In addition, SREB interacted with another transcription factor, HAPX.

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.

Lipid droplets hypertrophy: a crucial determining factor in insulin regulation by adipocytes

Lipid droplets (LDs) hypertrophy in adipocytes is the main cause of energy metabolic system dysfunction, obesity and its afflictions such as T2D. However, the role of adipocytes in linking energy metabolic disorders with insulin regulation is unknown in humans. Human adipocytes constitutively synthesize and secrete insulin, which is biologically functional. Insulin concentrations and release are fat mass- and LDs-dependent respectively. Fat reduction mediated by bariatric surgery repairs obesity-associated T2D. The expression of genes, like PCSK1 (proinsulin conversion enzyme), GCG (Glucagon), GPLD1, CD38 and NNAT, involved in insulin regulation/release were differentially expressed in pancreas and adipose tissue (AT). INS (insulin) and GCG expression reduced in human AT-T2D as compared to AT-control, but remained unchanged in pancreas in either state. Insulin levels (mRNA/protein) were higher in AT derived from prediabetes BB rats with destructed pancreatic β-cells and controls than pancreas derived from the same rats respectively. Insulin expression in 10 human primary cell types including adipocytes and macrophages is an evidence for extrapancreatic insulin-producing cells. The data suggest a crosstalk between AT and pancreas to fine-tune energy metabolic system or may minimize the metabolic damage during diabetes. This study opens new avenues towards T2D therapy with a great impact on public health.

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.

Regulation of adipocytes lipolysis by n-3 HUFA in grass carp (Ctenopharyngodon idellus) in vitro and in vivo

N-3 highly unsaturated fatty acids (n-3 HUFA) have been shown to inhibit body fat accumulation in animals. To clarify the mechanism of this fat-lowering effect of n-3 HUFA in grass carp (Ctenopharyngodon idellus), two experiments were conducted. In experiment 1, isolated grass carp mature adipocytes were incubated with docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) at different concentrations for 6 h. The release of glycerol to the medium was detected, and the expression of the lipolysis-related genes was analyzed. In experiment 2, a 95-day feeding trial was conducted with two diets formulated with either lard oil (as control) or fish oil (supplying n-3 HUFA as treatment) as the main lipid source. The glycerol and free fatty acid (FFA) released from the isolated adipocytes of both groups were detected after the feeding period. The expression of select lipolysis-related genes in adipose tissue was also analyzed. The results from experiment 1 showed that the release of glycerol was significantly increased by DHA and EPA (P < 0.05). Moreover, the expression of lipolysis-related genes, such as adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), tumor necrosis factor α (TNFα) and leptin, was also significantly elevated in the treatment group (P < 0.05). Experiment 2 demonstrated that glycerol and FFA release from the isolated adipocytes were significantly higher in the treatment group compared to the control group (P < 0.05). The expression level of ATGL, HSL, TNFα and leptin in the treatment group was significantly higher than in the control group (P < 0.05). The present results provide novel evidence that n-3 HUFAs could regulate grass carp adipocyte lipolysis in vitro or in vivo, and the effect might be in part associated with their influence on the expression of lipolysis-related genes and lipolysis-related adipokines genes.

The inverse association between relative abundances of oleic acid and arachidonic acid is related to alpha -linolenic acid

Background

Many health effects of oils rich in oleic acid (OA, 18:1 n9) seem to be opposite those of arachidonic acid (AA, 20:4 n6), i.e. concerning cardiovascular risk. In recent studies in humans and in the rat we observed that percentages of OA and AA were inversely related, raising the question of whether the inverse association is a general one, and how it might be explained. In the present work we examine whether percentages of OA and AA are inversely associated in breast muscle lipids of chickens, and whether alpha-linolenic acid (ALA) may be related to the OA/AA ratio.

Methods

The study group consisted of 163 chickens. Breast muscle was collected, and the concentration of fatty acids in muscle lipids was determined using gas chromatography. We studied association between fatty acids using bivariate correlations (Pearson) and linear regression. Synthesis of OA from stearic acid (Stear) was estimated using the OA/Stear ratio, and formation of AA from linoleic acid (LA) was estimated by the AA/LA ratio.

Results

We found a strong inverse relationship (r = -0.942, p < 0.001; n = 163) between % OA and % AA in breast muscle lipids of the chickens. There was an inverse association (r = -0.887, p < 0.001) between the OA/Stearic acid ratio, estimating Delta9 desaturase, and the AA/LA ratio, estimating desaturases/elongase activities. Furthermore, there was a strong negative association between % AA and the OA/Stearic acid ratio (r = -0.925, p < 0.001), and % OA correlated negatively (r = -0.914, p < 0.001) with the AA/LA ratio. ALA was positively associated (r = 0.956, p < 0.001) with the OA/AA ratio, and this association prevailed when controlling for the other fatty acids. ALA was positively associated (r = 0.857, p < 0.001) with the OA/Stear ratio, but was negatively related (r = -0.827, p < 0.001) to the AA/LA ratio.

Conclusions

The relative abundances of OA and AA that are inversely related in muscle lipids of chickens may be explained by a feedback regulation between the synthesis of OA and AA, and related to ALA, which seems to stimulate formation of OA, and inhibit synthesis of AA, but further studies are required to clarify whether this hypothesis is valid.

The consumption of n-3 polyunsaturated fatty acids differentially modulates gene expression of peroxisome proliferator-activated receptor alpha and gamma and hypoxia-inducible factor 1 alpha in subcutaneous adipose tissue of obese adolescents

The aim of this study was to evaluate the effect of long-chain omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation on metabolic state and gene expression in subcutaneous adipose tissues of obese adolescents. Obese adolescents (n = 26, 10 girls and 16 boys) aged 12.4 ± 2.1 years were assigned to a 12-week regimen of n-3 PUFA intake. Five times per day, subjects received a food supplement consisting of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (3 g per day, 944 mg EPA, and 2,088 mg DHA). Blood parameters were measured, and subcutaneous adipose tissue biopsies were analyzed to determine gene expression at baseline and after 12 weeks. Student's t test and the Wilcoxon signed-rank test were used to estimate differences in arithmetic means of pre- and post-dietary supplementation for various anthropometric, biochemical, clinical, and gene expression parameters. After 12 weeks, n-3 PUFA consumption was associated with decreased body mass index (29.7 ± 4.6 vs. 27.8 ± 4.4 kg/m(2); P < 0.001), waist circumference (93.2 ± 9.9 vs. 90.5 ± 10.0 cm; P < 0.003), hip circumference (102.9 ± 10.9 vs. 101.1 ± 10.9 cm; P < 0.014), and blood triglyceride levels (220.8 ± 27.4 vs. 99.7 ± 32.7 mg/dL; P < 0.001). Fatty acid supplementation/n3 PUFA supplementation was associated with a downregulated expression of the genes encoding PPARγ and PGC-1α (P < 0.001), and an upregulated expression of the genes encoding PPARα (P < 0.007) and SREBP1 (P < 0.021). The expressions of SOD2 (P < 0.04), CAT (P < 0.001), GPX3 (P < 0.032) and HIF-1α protein also decreased. Our study demonstrated that n-3 PUFA consumption and dietary restriction improved the anthropometric parameters and decreased the triglycerides levels of the adolescents, suggesting a reduction in hypoxia in subcutaneous adipose tissue.

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.

Digital image analysis approach for lipid droplet size quantitation of Oil Red O-stained cultured cells

A simple approach was developed for the quantification of lipid droplet size and frequency distribution in images acquired by standard light microscopy. Oil Red O-stained cell images were thresholded for the lipid droplet signal using the freely available imaging software ImageJ. Watershed algorithms allowed analyzing the area of each individual lipid droplet. The method was validated by the decrease in lipid droplet size of 3T3-L1 adipocytes on lowered glucose availability associated with reduced glycerol-3-phosphate dehydrogenase activity and reduced transcription of lipid droplet size markers. This approach can be easily applied using standard laboratory equipment without requiring expensive and complex instrumentation.

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.