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

Capybara Oil Improves Renal Pathophysiology and Inflammation in Obese Mice

Obesity is an inflammatory disease associated with secondary diseases such as kidney disease, which can cause lipotoxicity, inflammation and loss of organ function. Polyunsaturated fatty acids act in the production of lipid mediators and have anti-inflammatory characteristics. In this work, the objective was to evaluate renal histopathology in obese mice and the effects of treatment with capybara oil (CO) (5000 mg/kg/day for 4 weeks). Parameters such as body mass, lipid profile, systolic blood pressure, urinary creatinine and protein excretion, structure and ultrastructure of the renal cortex, fibrosis, tissue inflammation and oxidative stress were analyzed. CO treatment in obese mice showed improvement in the lipid profile and reduction in systolic blood pressure levels, in addition to beneficial remodeling of the renal cortex. Our data demonstrated that CO decreased inflammation, oxidative stress and renal fibrosis, as evidenced by quantifying the expression of TNF-α, IL-10, CAT, SOD, α-SMA and TGF-β. Although treatment with CO did not show improvement in renal function, ultrastructural analysis showed that the treatment was effective in restoring podocytes and pedicels, with restructuring of the glomerular filtration barrier. These results demonstrate, for the first time, that treatment with CO is effective in reducing kidney damage, being considered a promising treatment for obesity.

Remodeling of the soleus muscle of ovariectomized old female rats submitted to resistance training and different diet intake

Sarcopenia is a common condition that is associated mainly with hormonal factors, nutritional status, physical activity, leading to a lower quality of life. Thus, this study aimed to evaluate the effects of diets with vegetable or animal proteins (AP) associated with resistance training on the structure of the soleus muscle in aged Wistar rats. The histochemical technique was used for the typing of muscle fibers, the cross-sectional area of myocytes, and volume densities of myocytes and interstitium. Picrosirius stain was used to quantify the collagen density. Diet intake, mainly animal protein, associated with resistance training leaded to muscle remodeling, and increased deposit of collagen fibers. We observed hypertrophy in animal groups that consumed animal protein diet, even the sedentary group, although more evident in those trained.

The nutraceutical potential of Lepidium sativum L. seed flavonoid-rich extract in managing metabolic syndrome components

The present study aimed to investigate the phytochemical and pharmacological identities of a Lepidium sativum L. (LS) flavonoid-rich extract and its beneficial effects on metabolic, hormonal, and histological status. Chemical screening, as well as high-performance liquid chromatography with diode-array detection (HPLC-DAD) identified high concentrations of the main flavonoid compounds in LS crude extract such as flavonols (quercetin, kaempferol), flavones (luteolin, apigenin), and especially flavanones (naringin, naringenin). Examinations of the biochemical and histopathological aspects showed the curative effects carried by LS flavonoid-rich extracts on high-fat diet-fed Wistar rats. In this study, we propose that these molecules probably exerted the bioactivity observed in the treated group through improving insulin sensitivity, dyslipidemia, inflammation, and pancreas β cell integrity. PRACTICAL APPLICATIONS: The LS seed is widely used in traditional medicine to treat hyperglycemia and inflammation. During the traditional mixture preparation, the thermal procedures could impair the bioactions of the most interesting group of LS phytoconstituants, flavonoids. In the present study, we propose an appropriate procedure to preserve those phytochemicals and suggest them as a substitute for the management of metabolic diseases. The dried LS extract showed an incredible set of effective flavonoids, which revealed hypoglycemic, hypolipidemic, anti-inflammatory, cytoprotective, and antidiabetic activities. Thus, LS flavonoids constitute a remarkable product to consider in pharmaceutical industry targeting diabetes and heart diseases. Due to their enormous antioxidant potential, the LS flavonoids could be also used in food engineering and cosmetic preparations. Their practical applications is however often limited by low solubility and stability in lipophilic media. Therefore, a modification of the flavonoid structure is possibly required.

Plasma Cholesteryl Ester Fatty Acids do not Mediate the Association of Ethnicity with Type 2 Diabetes: Results From the HELIUS Study

SCOPE

Ethnic minority groups have a higher risk of type 2 diabetes (T2D) than the host population. Our aim is to identify whether plasma cholesteryl ester fatty acids (CEFA) mediate the ethnic differences in type 2 diabetes.

METHODS AND RESULTS

We included 202 Dutch, 206 South-Asian Surinamese, 205 African Surinamese, 215 Turkish, and 213 Moroccan origin participants of the HELIUS study (Amsterdam, the Netherlands). Logistic regression is used to determine the associations between plasma CEFA and T2D. Mediation analysis is used to identify whether CEFA contributed to the association between ethnicity and T2D. We adjusted for ethnicity, age, sex, smoking, physical activity, and BMI. Associations between plasma CEFA and T2D were similar across all ethnic groups. Although differences in plasma CEFA across ethnic groups were observed, CEFA did not mediate the differences in T2D prevalence between ethnic groups.

CONCLUSION

Although ethnic differences in plasma CEFA are found and CEFA are associated with T2D, CEFA does not contribute to the difference in T2D prevalence between ethnic groups. If confirmed, this implies that maintenance of the more beneficial CEFA profiles in the non-Dutch ethnic groups may be encouraged to prevent an even higher prevalence of T2D in these groups.

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.

Adipokines at the crossroad between obesity and cardiovascular disease

Obesity, and especially excessive visceral adipose tissue accumulation, is considered as a low-grade inflammatory state that is responsible for adipocyte dysfunction and associated metabolic disorders. Adipose tissue displays endocrine functions by releasing pro- or antiinflammatory bioactive molecules named adipokines. An altered expression of these molecules, provoked by obesity or adipocyte dysregulation, contributes to major metabolic diseases such as insulin resistance and type 2 diabetes mellitus that are important risk factors for cardiovascular disease. However, obesity is also characterised by the expansion of perivascular adipose tissue that acts locally via diffusion of adipokines into the vascular wall. Local inflammation within blood vessels induced by adipokines contributes to the onset of endothelial dysfunction, atherosclerosis and thrombosis, but also to vascular remodelling and hypertension. A fast expansion of obesity is expected in the near future, which will rapidly increase the incidence of these cardiovascular diseases. The focus of this review is to summarise the link between metabolic and cardiovascular disease and discuss current treatment approaches, limitations and future perspectives for more targeted therapies.

Revisiting the membrane-centric view of diabetes

Fundamental questions remain unresolved in diabetes: What is the actual mechanism of glucose toxicity? Why is there insulin resistance in type 2 diabetes? Why do diets rich in sugars or saturated fatty acids increase the risk of developing diabetes? Studying the C. elegans homologs of the anti-diabetic adiponectin receptors (AdipoR1 and AdipoR2) has led us to exciting new discoveries and to revisit what may be termed “The Membrane Theory of Diabetes”. We hypothesize that excess saturated fatty acids (obtained through a diet rich in saturated fats or through conversion of sugars into saturated fats via lipogenesis) leads to rigid cellular membranes that in turn impair insulin signalling, glucose uptake and blood circulation, thus creating a vicious cycle that contributes to the development of overt type 2 diabetes. This hypothesis is supported by our own studies in C. elegans and by a wealth of literature concerning membrane composition in diabetics. The purpose of this review is to survey this literature in the light of the new results, and to provide an admittedly membrane-centric view of diabetes.

Fish Oil-Derived Long-Chain n-3 Polyunsaturated Fatty Acids Reduce Expression of M1-Associated Macrophage Markers in an ex vivo Adipose Tissue Culture Model, in Part through Adiponectin

Adipose tissue (AT) macrophages (ATM) play a key role in obesity-associated pathologies, and their phenotype can be influenced by the local tissue microenvironment. Interestingly, long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFA) and the LC n-3 PUFA-upregulated adipokine, adiponectin (Ad), may mitigate excessive ATM inflammatory M1-polarization responses. However, to what extent LC n-3 PUFA and Ad work in concert to affect macrophage phenotype has not been examined. Thus, we used an established ex vivo AT organ culture model using visceral AT from mice fed a control (CON; 10% w/w safflower oil) n-6 PUFA-rich diet or an isocaloric fish oil (FO; 3% w/w menhaden oil + 7% w/w safflower oil)-derived LC n-3 PUFA-rich diet to generate AT conditioned media (ACM). We then evaluated if CON or FO ACM affected macrophage polarization markers in a model designed to mimic acute [18 h ACM plus lipopolysaccharide (LPS) for the last 6 h] or chronic (macrophages treated with LPS-challenged CON or FO ACM for 24 h) inflammation ± Ad-neutralizing antibody and the LPS-neutralizing agent, polymyxin B. In the acute inflammation model, macrophages treated with FO ACM had decreased lipid uptake and mRNA expression of M1 markers (Nos2, Nfκb, Il6, Il18, Ccl2, and Ccl5) compared with CON ACM (p ≤ 0.05); however, these effects were largely attenuated when Ad was neutralized (p > 0.05). Furthermore, in the chronic inflammation model, macrophages treated with FO ACM had decreased mRNA expression of M1 markers (Nos2, Tnfα, Ccl2, and Il1β) and IL-6 and CCL2 secretion (p ≤ 0.05); however, some of these effects were lost when Ad was neutralized, and were further exacerbated when both Ad and LPS were neutralized. Taken together, this work shows that LC n-3 PUFA and Ad work in concert to suppress certain M1 macrophage responses. Thus, future strategies to modulate the ATM phenotype should consider the role of both LC n-3 PUFA and Ad in mitigating obese AT inflammation.

Fish-oil-derived n-3 PUFAs reduce inflammatory and chemotactic adipokine-mediated cross-talk between co-cultured murine splenic CD8+ T cells and adipocytes

BACKGROUND

Obese adipose tissue (AT) inflammation is characterized by dysregulated adipokine production and immune cell accumulation. Cluster of differentiation (CD) 8+ T cell AT infiltration represents a critical step that precedes macrophage infiltration. n-3 (ω-3) Polyunsaturated fatty acids (PUFAs) exert anti-inflammatory effects in obese AT, thereby disrupting AT inflammatory paracrine signaling.

OBJECTIVE

We assessed the effect of n-3 PUFAs on paracrine interactions between adipocytes and primary CD8+ T cells co-cultured at the cellular ratio observed in obese AT.

METHODS

C57BL/6 mice were fed either a 3% menhaden fish-oil + 7% safflower oil (FO) diet (wt:wt) or an isocaloric 10% safflower oil (wt:wt) control (CON) for 3 wk, and splenic CD8+ T cells were isolated by positive selection (via magnetic microbeads) and co-cultured with 3T3-L1 adipocytes. Co-cultures were unstimulated (cells alone), T cell receptor stimulated, or lipopolysaccharide (LPS) stimulated for 24 h.

RESULTS

In LPS-stimulated co-cultures, FO reduced secreted protein concentrations of interleukin (IL)-6 (-42.6%), tumor necrosis factor α (-67%), macrophage inflammatory protein (MIP) 1α (-52%), MIP-1β (-62%), monocyte chemotactic protein (MCP) 1 (-23%), and MCP-3 (-19%) vs. CON, which coincided with a 74% reduction in macrophage chemotaxis toward secreted chemotaxins in LPS-stimulated FO-enriched co-culture-conditioned media. FO increased mRNA expression of the inflammatory signaling negative regulators monocyte chemoattractant 1-induced protein (Mcpip; +9.3-fold) and suppressor of cytokine signaling 3 (Socs3; +1.7-fold), whereas FO reduced activation of inflammatory transcription factors nuclear transcription factor κB (NF-κB) p65 and signal transducer and activator of transcription 3 (STAT3) by 27% and 33%, respectively. Finally, mRNA expression of the inflammasome components Caspase1 (-36.4%), Nod-like receptor family pyrin domain containing 3 (Nlrp3; -99%), and Il1b (-68.8%) were decreased by FO compared with CON (P ≤ 0.05).

CONCLUSION

FO exerted an anti-inflammatory and antichemotactic effect on the cross-talk between CD8+ T cells and adipocytes and has implications in mitigating macrophage-centered AT-driven components of the obese phenotype.

Enriching the diet with menhaden oil improves peripheral neuropathy in streptozotocin-induced type 1 diabetic rats

The purpose of this study was to determine the effect of supplementing the diet of type 1 diabetic rats with menhaden oil on diabetic neuropathy. Menhaden oil is a natural source for n-3 fatty acids, which have been shown to have beneficial effects in cardiovascular disease and other morbidities. Streptozotocin-induced diabetic rats were used to examine the influence of supplementing their diet with 25% menhaden oil on diabetic neuropathy. Both prevention and intervention protocols were used. Endpoints included motor and sensory nerve conduction velocity, thermal and mechanical sensitivity, and innervation and sensitivity of the cornea and hindpaw. Diabetic neuropathy as evaluated by the stated endpoints was found to be progressive. Menhaden oil did not improve elevated HbA1C levels or serum lipid levels. Diabetic rats at 16-wk duration were thermal hypoalgesic and had reduced motor and sensory nerve conduction velocities, and innervation and sensitivity of the cornea and skin were impaired. These endpoints were significantly improved with menhaden oil treatment following the prevention or intervention protocol. We found that supplementing the diet of type 1 diabetic rats with menhaden oil improved a variety of endpoints associated with diabetic neuropathy. These results suggest that enriching the diet with n-3 fatty acids may be a good treatment strategy for diabetic neuropathy.

Unraveling the complex relationship triad between lipids, obesity, and inflammation

Obesity today stands at the intersection between inflammation and metabolic disorders causing an aberration of immune activity, and resulting in increased risk for diabetes, atherosclerosis, fatty liver, and pulmonary inflammation to name a few. Increases in mortality and morbidity in obesity related inflammation have initiated studies to explore different lipid mediated molecular pathways of attempting resolution that uncover newer therapeutic opportunities of anti-inflammatory components. Majorly the thromboxanes, prostaglandins, leukotrienes, lipoxins, and so forth form the group of lipid mediators influencing inflammation. Of special mention are the omega-6 and omega-3 fatty acids that regulate inflammatory mediators of interest in hepatocytes and adipocytes via the cyclooxygenase and lipoxygenase pathways. They also exhibit profound effects on eicosanoid production. The inflammatory cyclooxygenase pathway arising from arachidonic acid is a critical step in the progression of inflammatory responses. New oxygenated products of omega-3 metabolism, namely, resolvins and protectins, behave as endogenous mediators exhibiting powerful anti-inflammatory and immune-regulatory actions via the peroxisome proliferator-activated receptors (PPARs) and G protein coupled receptors (GPCRs). In this review we attempt to discuss the complex pathways and links between obesity and inflammation particularly in relation to different lipid mediators.

Chronic intake of proanthocyanidins and docosahexaenoic acid improves skeletal muscle oxidative capacity in diet-obese rats

Obesity has become a worldwide epidemic. The cafeteria diet (CD) induces obesity and oxidative-stress-associated insulin resistance. Polyunsaturated fatty acids and polyphenols are dietary compounds that are intensively studied as products that can reduce the health complications related to obesity. We evaluate the effects of 21 days of supplementation with grape seed proanthocyanidins extract (GSPE), docosahexaenoic-rich oil (DHA-OR) or both compounds (GSPE+DHA-OR) on skeletal muscle metabolism in diet-obese rats. The supplementation with different treatments did not reduce body weight, although all groups used more fat as fuel, particularly when both products were coadministered; muscle β-oxidation was activated, the mitochondrial functionality and oxidative capacity were higher, and fatty acid uptake gene expressions were up-regulated. In addition to these outcomes shared by all treatments, GSPE reduced insulin resistance and improved muscle status. Both treatments increased 5'-AMP-activated protein kinase (AMPK) phosphorylation, which was consistent with higher plasma adiponectin levels. Moreover, AMPK activation by DHA-OR was also correlated with an up-regulation of peroxisome proliferator-activated receptor alpha (Pparα). GSPE+DHA-OR, in addition to activating AMPK and enhancing fatty acid oxidation, increased the muscle gene expression of uncoupling protein 2 (Ucp2). In conclusion, GSPE+DHA-OR induced modifications that improved muscle status and could counterbalance the deleterious effects of obesity, and such modifications are mediated, at least in part, through the AMPK signaling pathway.

The metabolic profile of growing lambs fed diets rich in unsaturated fatty acids

The effect of two diets enriched with unsaturated fatty acids--one containing the addition of dried distillers grains with solubles (DGS) and the other the addition of false flax--Camelina sativa cake (CS)--on some metabolic parameters and hormone concentration in growing lambs was determined in this experiment. A total of 21 ram lambs of the Polish Whiteheaded mutton sheep were divided into three groups (the control, receiving DGS and CS). The diets were administered to animals for 6 weeks. During the experiment, peripheral blood was collected. Glucose (GL), total cholesterol (CH), triglycerides (TG), free fatty acids (FFA), insulin (IN), leptin (LE), triiodothyronine (T3) and thyroxine (T4) were assayed in serum. The age-dependent reduction in CH and TG limited by both experimental diets were observed. A significant increase in FFA concentration was observed in samples collected in the last, that is, third, time period. This was most probably caused by a 12-h pre-slaughter fasting period. A significantly lower dynamic of FFA increase in that experimental period was found in animals receiving the experimental feed. Insulin concentration in DGS-receiving lambs was increased, in contrast to the CS-receiving lambs, in which it was lower when compared to the control. LE concentration was decreased by both experimental diets, more markedly in the DGS-receiving animals. No differences between the experimental groups and the control were observed in T3 and T4 concentrations. The effect of 12-h pre-slaughter fasting was statistically highly significant for the levels of examined blood markers and hormones, except for TG and IN in the group of lambs receiving the experimental diet with CS.

Adiponectin action in skeletal muscle

The beneficial metabolic effects of adiponectin which confer insulin-sensitizing and anti-diabetic effects are well established. Skeletal muscle is an important target tissue for adiponectin where it regulates glucose and fatty acid metabolism directly and via insulin sensitizing effects. Cell surface receptors and the intracellular signaling events via which adiponectin orchestrates metabolism are now becoming well characterized. The initially accepted dogma of adiponectin action was that the physiological effects were mediated via endocrine effects of adipose-derived adiponectin. However, in recent years it has been established that skeletal muscle can also produce and secrete adiponectin that can elicit important functional effects. There is evidence that skeletal muscle adiponectin resistance may develop in obesity and play a role in the pathogenesis of diabetes. In summary, adiponectin acting in an autocrine and endocrine manner has important metabolic and insulin sensitizing effects on skeletal muscle which contribute to the overall anti-diabetic outcome of adiponectin action.

Fish oil increases muscle protein mass and modulates Akt/FOXO, TLR4, and NOD signaling in weanling piglets after lipopolysaccharide challenge

Proinflammatory cytokines play a key role in the pathophysiology of muscle atrophy. In addition, n3 polyunsaturated fatty acids (PUFAs) exert an inhibitory effect on proinflammatory cytokines affecting many inflammatory diseases. We hypothesized that dietary supplementation of fish oil could attenuate lipopolysaccharide (LPS)-induced muscle atrophy. Weanling pigs were used in a 2 × 2 factorial design and the main factors included diet (5% corn oil or 5% fish oil) and immunological challenge (LPS or saline). After 21 d of treatment with either fish oil or corn oil, pigs received an i.p. injection of either saline or LPS. At 4 h postinjection, blood and muscle samples were obtained. Fish oil led to enrichment of eicosapentaenoic acid, docosahexaenoic acid, and total n3 PUFAs in muscles. Fish oil increased muscle protein mass, indicated by a higher protein:DNA ratio in gastrocnemius and longissimus dorsi (LD) muscles. In addition, fish oil increased Akt1 mRNA abundance and decreased Forkhead Box O (FOXO) 1 and FOXO4 mRNA abundance. Fish oil also increased phosphorylation of Akt and FOXO1 in gastrocnemius and LD muscles. Fish oil decreased the mRNA abundance of muscle atrophy F-box (MAFbx) and muscle RING finger 1 in gastrocnemius and LD muscles. Moreover, fish oil reduced the plasma tumor necrosis factor (TNF) α, muscle TNFα, and prostaglandin E2 concentrations, and muscle TNFα and cyclooxygenase 2 (COX2) mRNA abundance. Finally, fish oil downregulated the mRNA abundance of muscle toll-like receptor (TLR4) and its downstream signaling molecules [myeloid differentiation factor 88 (MyD88), TNFα receptor-associated factor 6 (TRAF6), and NF-κB p65], and nucleotide-binding oligomerization domain protein (NOD1), NOD2, and their adaptor molecule [receptor-interacting serine/threonine-protein kinase 2 (RIPK2)]. These results indicate fish oil may suppress muscle proinflammatory cytokine production via regulation of TLR and NOD signaling pathways and therefore improve muscle protein mass, possibly through maintenance of Akt/FOXO signaling.

Modulation of visceral fat adipokine secretion by dietary fatty acids and ensuing changes in skeletal muscle inflammation

Given the link between obesity and insulin resistance, the role of adipose-derived factors in communicating with skeletal muscle to affect its function is important. We sought to determine if high fat diets modulate visceral adipose tissue (VAT) adipokines with subsequent effects on skeletal muscle inflammation and insulin sensitivity. Rats were fed (i) low fat (LF), (ii) high saturated fatty acid (SFA), or (iii) high SFA with n-3 polyunsaturated fatty acid (SFA/n-3 PUFA) diets for 4 weeks. VAT-derived adipokines were measured in adipose conditioned medium (ACM) after 72 h. Next, skeletal muscles from LF-fed rats were incubated for 8 h in (i) control buffer (CON), (ii) CON with 2 mmol·L(-1) palmitate (PALM, positive control), (iii) ACM from LF, (iv) ACM from SFA, or (v) ACM from SFA/n-3 PUFA. ACM from rats fed SFA and SFA/n-3 PUFA had increased (P ≤ 0.05) interleukin-6 (IL-6) (+31%) and monocyte chemoattractant protein-1 (MCP-1) (+30%). Adiponectin was decreased (-29%, P ≤ 0.05) in ACM from SFA, and this was prevented in SFA/n-3 PUFA ACM. Toll-like receptor 4 (TLR4) gene expression was increased (P ≤ 0.05) in PALM soleus muscle (+356%) and all ACM groups (+175%-191%). MCP-1 gene expression was elevated (P ≤ 0.05) in PALM soleus muscle (+163%) and soleus muscle incubated in ACM from animals fed SFA (+159%) and SFA/n-3 PUFA (+151%). Glucose transport was impaired (P ≤ 0.05) in PALM muscles but preserved in ACM groups. Acute exposure of muscle to fatty acid modulated adipokines affects skeletal muscle inflammatory gene expression but not insulin sensitivity.

Ethnic- and sex-specific associations between plasma fatty acids and markers of insulin resistance in healthy young adults

BACKGROUND

Although evidence indicates that fatty acids (FA) can affect insulin resistance (IR), not all FA contribute equally to the process. Indeed, monounsaturated FA (MUFA) and polyunsaturated FA (PUFA) are reported to reduce IR, whereas saturated FA (SFA) and trans FA appear to increase IR. However, it is not yet clear how individual FA are associated with markers of IR, and whether these relationships are influenced by ethnicity and/or sex. Therefore, the goal of this study was to examine the ethnic- and sex-specific relationships between plasma FA and markers of IR in a cohort of healthy young Caucasian, East Asian, and South Asian adults.

METHODS

Gas chromatography was used to quantify fasting plasma FA from young Canadian adults (22.6 ± 0.1 yrs) of Caucasian (n = 461), East Asian (n = 362), or South Asian (n = 104) descent. Linear regression models were used to investigate associations between plasma FA and markers of IR (i.e. fasting insulin, glucose, and HOMA-IR) according to ethnicity and sex.

RESULTS

Numerous significant associations (P < 0.05, adjusted for multiple testing) were identified between individual FA and markers of IR, with the majority identified in Caucasians. For SFA, positive associations were found between 14:0 and fasting insulin and HOMA-IR in Caucasian and East Asian populations, and 18:0 and fasting glucose in Caucasians only. Several positive associations were also found for specific MUFA (18:1t11 and 18:1t6-8 with HOMA-IR, and 18:1c9 with fasting glucose) and PUFA (18:2n6 with fasting glucose and 18:2c9t11 with HOMA-IR) in Caucasian adults only. Most of the aforementioned associations were stronger in males compared to females. Interestingly, no significant associations were found between FA and markers of IR in South Asian adults.

CONCLUSIONS

We report numerous associations between plasma FA and markers of IR in Caucasian and East Asian populations, but not in South Asian individuals. Furthermore, these associations appeared to be more robust in men. This demonstrates the importance of investigating associations between FA and markers of IR in an ethnic- and sex-specific manner in order to better understand the contribution of plasma FA to the development of IR and type-2 diabetes.

Long chain omega-3 fatty acids: micronutrients in disguise

Considerable information has accumulated to show that DHA and EPA have unique roles that differ from other n-3 fatty acids and the n-6 fatty acids, with increasing understanding of the mechanisms through which these fatty acids reduce risk of disease. DHA and EPA regulate hepatic lipid and glucose metabolism, but are present in foods of animal origin, which are generally high in protein with variable triglycerides and low carbohydrate. Biological activity at intakes too low to provide significant amounts of energy is consistent with the definition of a vitamin for which needs are modified by life-stage, diet and genetic variables, and disease. Recent studies reveal that DHA may play a central role in co-coordinating complex networks that integrate hepatic glucose, fatty acid and amino acid metabolism for the purpose of efficient utilization of dietary protein, particularly during early development when the milk diet provides large amounts of energy from fat.

Rapid loss of adiponectin-stimulated fatty acid oxidation in skeletal muscle of rats fed a high fat diet is not due to altered muscle redox state

A high fat (HF) diet rapidly impairs the ability of adiponectin (Ad) to stimulate fatty acid (FA) oxidation in oxidative soleus muscle, but the underlying mechanism remains elusive. Mere days of HF feeding also increase the muscle’s production and accumulation of reactive oxygen species (ROS) and shift cellular redox to a more oxidized state. It seems plausible that this shift towards a more oxidized state might act as negative feedback to suppress the ability of Ad to stimulate FA oxidation and generate more ROS. Therefore, we sought to determine whether i) a shift towards a more oxidized redox state (reduction in GSH/2GSSG) coincided with impaired Ad-stimulated palmitate oxidation in oxidative and glycolytic rodent muscle after 5 days of HF feeding (60% kCal), and ii) if supplementation with the antioxidant, N-acetylcysteine (NAC) could prevent the HF-diet induced impairment in Ad-response. Globular Ad (gAd) increased palmitate oxidation in isolated soleus and EDL muscles by 42% and 34%, respectively (p<0.05) but this was attenuated with HF feeding in both muscles. HF feeding decreased total GSH (−26%, p<0.05) and GSH/2GSSG (−49%, p<0.05) in soleus, but not EDL. Supplementation with NAC prevented the HF diet-induced reductions in GSH and GSH/2GSSG in soleus, but did not prevent the loss of Ad response in either muscle. Furthermore, direct incubations with H₂O₂ did not impair Ad-stimulated FA oxidation in either muscle. In conclusion, our data indicates that skeletal muscle Ad resistance is rapidly induced in both oxidative and glycolytic muscle, independently of altered cellular redox state.

Fish oil supplementation for two generations increases insulin sensitivity in rats

We investigated the effect of fish oil supplementation for two consecutive generations on insulin sensitivity in rats. After the nursing period (21 days), female rats from the same prole were divided into two groups: (a) control group and (b) fish oil group. Female rats were supplemented with water (control) or fish oil at 1 g/kg body weight as a single bolus for 3 months. After this period, female rats were mated with male Wistar rats fed on a balanced chow diet (not supplemented). Female rats continued to receive supplementation throughout gestation and lactation periods. The same treatment was performed for the next two generations (G1 and G2). At 75 days of age, male offspring from G1 and G2 generations from both groups were used in the experiments. G1 rats did not present any difference with control rats. However, G2 rats presented reduction in glycemia and lipidemia and improvement in in vivo insulin sensitivity (model assessment of insulin resistance, insulin tolerance test) as well as in vitro insulin sensitivity in soleus muscle (glucose uptake and metabolism). This effect was associated with increased insulin-stimulated p38 MAP kinase phosphorylation and lower n-6/n-3 fatty acid ratio, but not with activation of proteins from insulin signaling (IR, IRS-1 and Akt). Global DNA methylation was decreased in liver but not in soleus muscle. These results suggest that long-term fish oil supplementation improves insulin sensitivity in association with increased insulin-stimulated p38 activation and decreased n-6:n-3 ratio in skeletal muscle and decreased global DNA methylation in liver.

Exercise restores insulin, but not adiponectin, response in skeletal muscle of high-fat fed rodents

High-fat (HF) diets impair skeletal muscle response to the insulin-sensitizing adipokine adiponectin (Ad) in rodents, preceding the development of insulin resistance. Skeletal muscle insulin response in HF-fed rats can be restored with chronic exercise; whether recovery of skeletal muscle Ad response is necessary for the exercise-induced recovery of insulin-stimulated glucose transport is not known. In the current study, insulin and Ad resistance were induced in rodents with 4 wk of HF feeding (HF4; low-fat fed animals used as control). Rats were then treadmill-exercised (HF5EX1, HF6EX2) or supplemented orally with the pharmacological agent β-guadinoproprionic acid (GPA; HF5GPA1, HF6GPA2) for 1 or 2 wk with continued HF feeding. Insulin and Ad responses (glucose transport and palmitate oxidation, respectively) were assessed 48 h after the last exercise bout ex vivo in isolated solei. Insulin response was impaired following 4 wk of HF feeding and improved with 1 and 2 wk of exercise and β-GPA supplementation (HF5EX1, HF6EX2, HF5GPA1, and HF6GPA2). The recovery of insulin response generally coincided with improved Akt Thr308 phosphorylation in HF5GPA1, HF6EX2, and HF6GPA2, although not in HF5EX1. Ad-stimulated palmitate oxidation was not restored with either treatment. Total protein contents of AdipoR1, AdipoR2, APPL1, and APPL2, as well as total and phosphorylated AMPK and ACC were unaltered by diet, exercise, and β-GPA at the assessed time points. We conclude that the exercise and pharmacologically (β-GPA)-induced recovery of skeletal muscle insulin response after HF feeding is not dependent on the restoration of Ad response, as assessed ex vivo.

Partial replacement with menhaden oil improves peripheral neuropathy in high-fat-fed low-dose streptozotocin type 2 diabetic rat

Aims. To determine the effect of partial replacement of a high-fat diet with menhaden oil on diabetic neuropathy in an animal model of type 2 diabetes. Materials and Methods. High-fat/low-dose streptozotocin diabetic rats were used to examine the influence of replacing 50% of the source of the high-fat diet (lard) with menhaden oil, a natural source of n-3 fatty acids, on diabetic neuropathy. Endpoints included analyses of glucose tolerance, fatty liver disease, serum and liver fatty acid composition, serum lipid and adiponectin levels, motor and sensory nerve conduction velocity, thermal sensitivity and innervation of the hindpaw. Results. Diabetic rats were insulin resistant and menhaden oil did not improve whole animal glucose utilization. Menhaden oil did not improve elevated HbA₁C levels or serum lipid levels but serum levels of adiponectin were significantly increased and hepatic steatosis was significantly improved. Diabetic rats were thermal hypoalgesic, had reduced motor and sensory nerve conduction velocities and intraepidermal nerve fiber profiles were decreased in the hindpaw and these endpoints were significantly improved with menhaden oil. Conclusions. We found that enrichment of a high-fat diet with menhaden oil improved a number of endpoints associated with diabetic neuropathy.

Fish oil positively regulates anabolic signalling alongside an increase in whole-body gluconeogenesis in ageing skeletal muscle

PURPOSE

Fish oil, containing mainly long-chain n-3 polyunsaturated fatty acids (LCn-3PUFA), has been found to acutely stimulate protein synthesis and insulin-mediated glucose metabolism. However, the underlying mechanism and more prolonged effect of fish oil during ageing remain to be determined.

METHODS

Fish oil (EPAX6000; 49.6 % eicosapentaenoic acid, 50.4 % docosahexaenoic acid) or control oil (60 % olive, 40 % soy) supplementation was delivered, via chocolate-derived sweets, to rats for 8 weeks. Throughout the study, food intake and body weight were recorded and body composition was investigated using EchoMRI. During the last 40 min of a 6 h infusion, with labelled dextrose ([U-(13)C]glucose) and amino acids ([1-(13)C]phenylalanine), blood samples were collected to assess glucose and phenylalanine kinetics. Soleus and longissimus dorsi muscles were extracted for protein and mRNA analyses.

RESULTS

Fish oil had no effect on food intake or body composition. An increased whole-body glucose turnover, mainly accounted for via an increase in endogenous glucose production, was observed with fish oil feeding. No effects on whole-body phenylalanine turnover were observed. In longissimus dorsi, fish oil augmented the phosphorylation of phosphoinositide 3-kinase (PI3K)([Tyr458]) (P = 0.04) and 70 kDa ribosomal protein S6 kinase (p70s6k)([Thr389]) (P = 0.04). There were no differences in protein kinase B (Akt)([Ser473]), mammalian target of rapamycin (mTOR)([Ser2448]), protein phosphatase 2A (PP2A) 56 kDa regulatory B subunit γ (PP2A-B56-γ), forkhead box containing proteins O-subclass 3a (FOX03a)([Ser253]) or inflammatory markers (Interleukin-6, Interleukin-1 β, tumour necrosis factor-α, and cyclooxygenase-2).

CONCLUSIONS

Our data suggest that the fish oil may stimulate endogenous glucose production and increase anabolic signalling in ageing rats.