Polymorphisms,de novo lipogenesis,and plasma triglyceride response following fish oil supplementation

Interindividual variability in the response of plasma triglyceride concentrations (TG) following fish oil consumption has been observed. Our objective was to examine the associations between single-nucleotide polymorphisms (SNPs) within genes encoding proteins involved in de novo lipogenesis and the relative change in plasma TG levels following a fish oil supplementation. Two hundred and eight participants were recruited in the greater Quebec City area. The participants completed a six-week fish oil supplementation (5 g fish oil/day: 1.9–2.2 g eicosapentaenoic acid and 1.1 g docosahexaenoic acid. SNPs within SREBF1, ACLY, and ACACA genes were genotyped using TAQMAN methodology. After correction for multiple comparison, only two SNPs, rs8071753 (ACLY) and rs1714987 (ACACA), were associated with the relative change in plasma TG concentrations (P = 0.004 and P = 0.005, respectively). These two SNPs explained 7.73% of the variance in plasma TG relative change following fish oil consumption. Genotype frequencies of rs8071753 according to the TG response groups (responders versus nonresponders) were different (P = 0.02). We conclude that the presence of certain SNPs within genes, such as ACLY and ACACA, encoding proteins involved in de novo lipogenesis seem to influence the plasma TG response following fish oil consumption.     

Role of CYP eicosanoids in the regulation of pharyngeal pumping and food uptake in Caenorhabditis elegans

Cytochrome P450 (CYP)-dependent eicosanoids comprise epoxy- and hydroxy-metabolites of long-chain PUFAs (LC-PUFAs). In mammals, CYP eicosanoids contribute to the regulation of cardiovascular and renal function. Caenorhabditis elegans produces a large set of CYP eicosanoids; however, their role in worm’s physiology is widely unknown. Mutant strains deficient in LC-PUFA/eicosanoid biosynthesis displayed reduced pharyngeal pumping frequencies. This impairment was rescued by long-term eicosapentaenoic and/or arachidonic acid supplementation, but not with a nonmetabolizable LC-PUFA analog. Short-term treatment with 17,18-epoxyeicosatetraenoic acid (17,18-EEQ), the most abundant CYP eicosanoid in C. elegans, was as effective as long-term LC-PUFA supplementation in the mutant strains. In contrast, 20-HETE caused decreased pumping frequencies. The opposite effects of 17,18-EEQ and 20-HETE were mirrored by the actions of neurohormones. 17,18-EEQ mimicked the stimulating effect of serotonin when added to starved worms, whereas 20-HETE shared the inhibitory effect of octopamine in the presence of abundant food. In wild-type worms, serotonin increased free 17,18-EEQ levels, whereas octopamine selectively induced the synthesis of hydroxy-metabolites. These results suggest that CYP eicosanoids may serve as second messengers in the regulation of pharyngeal pumping and food uptake in C. elegans.     

The fatty acid profile of muscle and adipose tissue of lambs fed camelina or linseed as oil or seeds

The objective of this study was to evaluate the impact of diets enriched with plant oils or seeds, high in polyunsaturated fatty acids (PUFA), on the fatty acid profile of sheep intramuscular and subcutaneous adipose tissue (SAT). Sixty-six lambs were blocked according to initial body weight and randomly assigned to six concentrate-based rations containing 60 g fat/kg dry matter from different sources: (1) Megalac (MG; ruminally protected saturated fat), (2) camelina oil (CO), (3) linseed oil (LO), (4) NaOH-treated camelina seed (CS), (5) NaOH-treated linseed (LS) or (6) CO protected from ruminal saturation by reaction with ethanolamine; camelina oil amides (CA). The animals were offered the experimental diets for 100 days, after which samples of m. longissimus dorsi and SAT were collected and the fatty acid profile determined by GLC. The data were analyzed using ANOVA with 'a priori' contrasts including camelina v. linseed, oil v. NaOH-treated seeds and CS v. CA. Average daily gain and total fatty acids in intramuscular adipose tissue were similar across treatments. The NaOH-treatment of seeds was more effective in enhancing cis-9, trans-11 conjugated linoleic acid (CLA) incorporation than the corresponding oil, but the latter resulted in a higher content of trans-11 18:1 in both muscle neutral and polar lipids (P < 0.01, P < 0.001, respectively). Inclusion of LS resulted in the highest PUFA:saturated fatty acid (SFA) ratio in total intramuscular fat (0.22). The NaOH-treatment of seeds resulted in a higher PUFA/SFA ratio (0.21 v. 0.18, P < 0.001) than oils and on average, linseed resulted in a higher PUFA/SFA ratio than camelina (P < 0.01). Lambs offered LS had the highest concentration of n-3 PUFA in the muscle, while those offered MG had the lowest (P < 0.001). This was reflected in the lowest (P < 0.001) n-6: n-3 PUFA ratio for LS-fed lambs (1.15) than any other treatment, which ranged from 2.14 to 1.72, and the control (5.28). The trends found in intramuscular fat were confirmed by the data for SAT. This study demonstrated the potential advantage from a human nutrition perspective of feeding NaOH-treated seeds rich in PUFA when compared to the corresponding oil. The use of camelina amides achieved a greater degree of protection of dietary PUFA, but decreased the incorporation of biohydrogenation intermediates such as cis-9, trans-11 CLA and trans-11 18:1 compared to NaOH-treated seeds.     

Basal omega-3 fatty acid status affects fatty acid and oxylipin responses to high-dose n3-HUFA in healthy volunteers

A subject's baseline FA composition may influence the ability of dietary highly unsaturated omega-3 FAs (n3-HUFA) to change circulating profiles of esterified FAs and their oxygenated metabolites. This study evaluates the influence of basal n3-HUFA and n3-oxylipin status on the magnitude of response to n3-HUFA consumption. Blood was collected from fasting subjects (n = 30) before and after treatment (4 weeks; 11 ± 2 mg/kg/day n3-HUFA ethyl esters). Esterified FAs were quantified in erythrocytes, platelets, and plasma by GC-MS. Esterified oxylipins were quantified in plasma by LC-MS/MS. Treatment with n3-HUFAs increased n3-HUFAs and decreased n6-HUFAs in all reservoirs and increased plasma n3-oxylipins without significantly changing n6-oxylipin concentrations. As subject basal n3-HUFAs increased, treatment-associated changes decreased, and this behavior was reflected in the percentage of 20:5n3 + 22:6n3 in red blood cell membrane FAs (i.e., the omega-3 index). To maintain an omega-3 index of 8% and thus reduce cardiovascular disease risk, our analyses suggest a maintenance dose of 7 mg/kg/day n3-HUFA ethyl esters for a 70-kg individual. These results suggest that the basal n3 index may have clinical utility to establish efficacious therapeutic experimental feeding regimens and to evaluate the USDA Dietary Guidelines recommendations for n3-HUFA consumption.     

Dietary omega-6 fatty acid lowering increases bioavailability of omega-3 polyunsaturated fatty acids in human plasma lipid pools

BackgroundDietary linoleic acid (LA, 18:2n-6) lowering in rats reduces n-6 polyunsaturated fatty acid (PUFA) plasma concentrations and increases n-3 PUFA (eicosapentaenoic (EPA) and docosahexaenoic acid (DHA)) concentrations.ObjectiveTo evaluate the extent to which 12 weeks of dietary n-6 PUFA lowering, with or without increased dietary n-3 PUFAs, alters unesterified and esterified plasma n-6 and n-3 PUFA concentrations in subjects with chronic headache.DesignSecondary analysis of a randomized trial. Subjects with chronic headache were randomized for 12 weeks to (1) average n-3, low n-6 (L6) diet; or (2) high n-3, low n-6 LA (H3–L6) diet. Esterified and unesterified plasma fatty acids were quantified at baseline (0 weeks) and after 12 weeks on a diet.ResultsCompared to baseline, the L6 diet reduced esterified plasma LA and increased esterified n-3 PUFA concentrations (nmol/ml), but did not significantly change plasma arachidonic acid (AA, 20:4n-6) concentration. In addition, unesterified EPA concentration was increased significantly among unesterified fatty acids. The H3–L6 diet decreased esterified LA and AA concentrations, and produced more marked increases in esterified and unesterified n-3 PUFA concentrations.ConclusionDietary n-6 PUFA lowering for 12 weeks significantly reduces LA and increases n-3 PUFA concentrations in plasma, without altering plasma AA concentration. A concurrent increase in dietary n-3 PUFAs for 12 weeks further increases n-3 PUFA plasma concentrations and reduces AA.     

Dosing profile profoundly influences nicotinic acid's ability to improve metabolic control in rats

Acute nicotinic acid (NiAc) administration results in rapid reduction of plasma FFA concentrations. However, sustained NiAc exposure is associated with tolerance development resulting in return of FFA to pretreatment levels. The aim of this study was to determine whether a 12 h rectangular exposure profile (intermittent dose group) could avoid tolerance development and thereby reverse insulin resistance induced by lipid overload. FFA lowering was assessed in male Sprague Dawley (lean) and obese Zucker rats (obese) in response to a 5 h NiAc infusion, in either NiAc-naïve animals or after 5 days of continuous (24 h/day) or intermittent (12 h/day) NiAc dosing (via implantable, programmable minipump). We found that intermittent dosing over 5 days preserved NiAc-induced FFA lowering, comparable to dosing in NiAc-naïve animals. By contrast, following 5 days continuous administration, NiAc-induced FFA lowering was lost. The effect of intermittent NiAc infusion on insulin sensitivity was assessed in obese Zucker rats using hyperinsulinemic-isoglycemic clamps. The acute effect of NiAc to elevate glucose infusion rate (vs. saline control) was indeed preserved with intermittent dosing, while being lost upon continuous infusion. In conclusion, an intermittent but not continuous NiAc dosing strategy succeeded in retaining NiAc’s ability to lower FFA and improve insulin sensitivity in obese Zucker rats.—Kroon, T., A. Kjellstedt, P. Thalén, J. Gabrielsson, and N. D. Oakes.     

Effect of plasma triglyceride metabolism on lipid storage in adipose tissue: Studies using genetically engineered mouse models

The obesity epidemic is associated with an increased incidence of type 2 diabetes, cardiovascular morbidity and various types of cancer. A better insight into the molecular mechanisms that underlie adipogenesis and obesity may result in novel therapeutic handles to fight obesity and these associated diseases. Adipogenesis is determined by the balance between uptake of fatty acids (FA) from plasma into adipocytes, intracellular FA oxidation versus esterification of FA into triglycerides (TG), lipolysis of TG by intracellular lipases, and secretion of FA from adipocytes. Here, we review the mechanisms that are specifically involved in the entry of FA into adipose tissue. In plasma, these originating FA are either present as TG within apoB-containing lipoproteins (i.e. chylomicrons and VLDL) or as free FA bound to albumin. Kinetic studies, however, have revealed that TG are the major source of FA entering adipose tissue, both in the fed and fasted condition. In fact, studies with genetically engineered mice have revealed that the activity of lipoprotein lipase (LPL) is a major determinant for the development of obesity. As a general rule, high fat diet-induced adipogenesis is aggravated by stimulated LPL activity (e.g. by adipose tissue-specific overexpression of LPL or deficiency for apoCIII), and attenuated by inhibited LPL activity (e.g. by adipose-specific deficiency for LPL, overexpression of apoCI or angptl4, or by deficiency for apoE or the VLDL receptor). In addition, we describe that the trans-membrane transport of FA and cytoplasmic binding of FA in adipocytes can also dramatically affect adipogenesis. The relevance of these findings for human pathophysiology is discussed.     

Dietary n‐3 long‐chain polyunsaturated fatty acids modify phosphoenolpyruvate carboxykinase activity and lipid synthesis from glucose in adipose tissue of rats fed a high‐sucrose diet

Long‐chain polyunsaturated n‐3 fatty acids (n‐3 LCPUFAs) have hypolipidemic effects and modulate intermediary metabolism to prevent or reverse insulin resistance in a way that is not completely elucidated. Here, effects of these fatty acids on the lipid profile, phosphoenolpyruvate carboxykinase (PEPCK) activity, lipid synthesis from glucose in epididymal adipose tissue (Ep‐AT) and liver were investigated. Male rats were fed a high‐sucrose diet (SU diet), containing either sunflower oil or a mixture of sunflower and fish oil (SU–FO diet), and the control group was fed a standard diet. After 13 weeks, liver, adipose tissue and blood were harvested and analysed. The dietary n‐3 LCPUFAs prevented sucrose‐induced increase in adiposity and serum free fat acids, serum and hepatic triacylglycerol and insulin levels. Furthermore, these n‐3 LCPUFAs decreased lipid synthesis from glucose and increased PEPCK activity in the Ep‐AT of rats fed the SU–FO diet compared to those fed the SU diet, besides reducing lipid synthesis from glucose in hepatic tissue. Thus, the inclusion of n‐3 LCPUFAs in the diet may be beneficial for the prevention or attenuation of dyslipidemia and insulin resistance, and for reducing the risk of related chronic diseases. Copyright © 2013 John Wiley & Sons, Ltd.     

ELOVL4 protein preferentially elongates 20:5n3 to very long chain PUFAs over 20:4n6 and 22:6n3

We hypothesized that reduction/loss of very long chain PUFAs (VLC-PUFAs) due to mutations in the ELOngase of very long chain fatty acid-4 (ELOVL4) protein contributes to retinal degeneration in autosomal dominant Stargardt-like macular dystrophy (STGD3) and age-related macular degeneration; hence, increasing VLC-PUFA in the retina of these patients could provide some therapeutic benefits. Thus, we tested the efficiency of elongation of C20-C22 PUFA by the ELOVL4 protein to determine which substrates are the best precursors for biosynthesis of VLC-PUFA. The ELOVL4 protein was expressed in pheochromocytoma cells, while green fluorescent protein-expressing and nontransduced cells served as controls. The cells were treated with 20:5n3, 22:6n3, and 20:4n6, either individually or in equal combinations. Both transduced and control cells internalized and elongated the supplemented FAs to C22-C26 precursors. Only ELOVL4-expressing cells synthesized C28-C38 VLC-PUFA from these precursors. In general, 20:5n3 was more efficiently elongated to VLC-PUFA in the ELOVL4-expressing cells, regardless of whether it was in combination with 22:6n3 or with 20:4n6. In each FA treatment group, C34 and C36 VLC-PUFAs were the predominant VLC-PUFAs in the ELOVL4-expressing cells. In summary, 20:5n3, followed by 20:4n6, seems to be the best precursor for boosting the synthesis of VLC-PUFA by ELOVL4 protein.