Protein synthesis and degradation in isolated muscle. Effect of omega 3 and omega 6 fatty acids

Effects of fish oil during hemodialysis on nutritional status and quality of life: a randomized double-blinded trial

Background

Supplementation of fish oil has been shown to exert beneficial effects in patients undergoing hemodialysis. The aim of this study was to investigate the efficacy of fish oil in improving the quality of life of these patients through a randomized, double-blinded clinical trial.

Methods

Among the 103 patients enrolled in the study, a total of 74 patients were randomized to receive fish oil (intervention group) or placebo (n=37 per group). Patients received identical soft-gel capsules, with each capsule containing either 1000 mg fish oil or placebo for 4 months. Personnel responsible for data collection and analyses were blinded to the grouping.

Results

The reduction of protein-energy wasting (PEW) in the intervention group was significantly more prominent compared to the placebo group (P=0.023). The intervention group demonstrated significant increase in midarm circumference, arm muscle circumference, and triceps skinfold thickness after fish oil intake. The intervention group also exhibited significant differences from the placebo group in creatinine, uric acid, and serum calcium levels. Significant improvement was seen regarding the physical role and energy/figure in the intervention group.

Conclusions

Our study demonstrated that fish oil intake in patient undergoing hemodialysis can significantly reduce PEW, and improve physical and biochemical parameters and quality of life, which could provide guidance to clinical management of these patients.

Delta-6-desaturase (FADS2) inhibition and omega-3 fatty acids in skeletal muscle protein turnover

Polyunsaturated fatty acids (PUFAs) are essential dietary components. They are not only used for energy, but also act as signaling molecules. The delta-6 desaturase (D6D) enzyme, encoded by the FADS2 gene, is one of two rate limiting enzymes that convert the PUFA precursors – α-linolenic (n-3) and linoleic acid (n-6) to their respective metabolites. Alterations in the D6D enzyme activity alters fatty acid profiles and are associated with metabolic and inflammatory diseases including cardiovascular disease and type 2 diabetes. Omega-3 PUFAs, specifically its constituent fatty acids DHA and EPA, are known for their anti-inflammatory ability and are also beneficial in the prevention of skeletal muscle wasting, however the mechanism for muscle preservation is not well understood. Moreover, little is known of the effects of altering the n-6/n-3 ratio in the context of a high-fat diet, which is known to downregulate protein synthesis. Twenty C57BL6 male mice were fed a high-fat lard (HFL, 45% fat (mostly lard), 35% carbohydrate and 20% protein, n-6:n-3 PUFA, 13:1) diet for 6 weeks. Mice were then divided into 4 groups (n = 5 per group): HFL– , high-fat oil– (HFO, 45% fat (mostly Menhaden oil), 35% carbohydrate and 20% protein, n-6:n-3 PUFA, 1:3), HFL+ (HFL diet plus an orally administered FADS2 inhibitor, 100 mg/kg/day), and HFO+ (HFO diet plus an orally administered FADS2 inhibitor, 100 mg/kg/day). After 2 weeks on their respective diets and treatments, animals were sacrificed and gastrocnemius muscle harvested. Protein turnover signaling were analyzed via Western Blot. 4-EBP1 and ribosomal protein S6 expression were measured. A two-way ANOVA revealed no significant change in the phosphorylation of both 4EBP-1 and ribosomal protein S6 with diet or inhibitor. There was a significant reduction in STAT3 phosphorylation with the inhibition of FADS2 (p = 0.03). Additionally, we measured markers of protein degradation through levels of FOXO phosphorylation, ubiquitin, and LC3B expression; there was a trend towards increased phosphorylation of FOXO (p = 0.08) and ubiquitinated proteins (p = 0.05) with FADS2 inhibition. LC3B expression, a marker of autophagy, was significantly higher in the HFL plus FADS2 inhibition group from all other comparisons. Lastly, we analyzed activation of mitochondrial biogenesis which is closely linked with protein synthesis through PGC1-α and Cytochrome-C expression, however no significant differences were associated with either marker across all groups. Collectively, these data suggest that the protective effects of muscle mass by omega-3 fatty acids are from inhibition of protein degradation. Our aim was to determine the role of PUFA metabolites, DHA and EPA, in skeletal muscle protein turnover and assess the effects of n-3s independently. We observed that by inhibiting the FADS2 enzyme, the protective effect of n-3s on protein synthesis and proliferation was lost; concomitantly, protein degradation was increased with FADS2 inhibition regardless of diet.

•

High fat omega-3 rich diets increase STAT3 signaling in a FADS2 dependent manner.

•

Inhibition of FADS2 attenuates the protective effects of omega-3 rich diet.

•

Inhibition of FADS2 increases protein degradation regardless of diet.

Effect of dietary arachidonic acid supplementation on acute muscle adaptive responses to resistance exercise in trained men: a randomized controlled trial

Arachidonic acid (ARA), a polyunsaturated ω-6 fatty acid, acts as precursor to a number of prostaglandins with potential roles in muscle anabolism. It was hypothesized that ARA supplementation might enhance the early anabolic response to resistance exercise (RE) by increasing muscle protein synthesis (MPS) via mammalian target of rapamycin (mTOR) pathway activation and/or the late anabolic response by modulating ribosome biogenesis and satellite cell expansion. Nineteen men with ≥1 yr of resistance-training experience were randomized to consume either 1.5 g daily ARA or a corn-soy-oil placebo in a double-blind manner for 4 wk. Participants then undertook fasted RE (8 sets each of leg press and extension at 80% 1-repetition maximum), with vastus lateralis biopsies obtained before exercise, immediately postexercise, and at 2, 4, and 48 h of recovery. MPS (measured via stable isotope infusion) was not different between groups ( P = 0.212) over the 4-h recovery period. mTOR pathway members p70 S6 kinase and S6 ribosomal protein were phosphorylated postexercise ( P < 0.05), with no difference between groups. 45S preribosomal RNA increased 48 h after exercise only in ARA ( P = 0.012). Neural cell adhesion molecule-positive satellite cells per fiber increased 48 h after exercise ( P = 0.013), with no difference between groups ( P = 0.331). Prior ARA supplementation did not alter the acute anabolic response to RE in previously resistance-trained men; however, at 48 h of recovery, ribosome biogenesis was stimulated only in the ARA group. The findings do not support a mechanistic link between ARA and short-term anabolism, but ARA supplementation in conjunction with resistance training may stimulate increases in translational capacity.

NEW & NOTEWORTHY Four weeks of daily arachidonic acid supplementation in trained men did not alter their acute muscle protein synthetic or anabolic signaling response to resistance exercise. However, 48 h after exercise, men supplemented with arachidonic acid showed greater ribosome biogenesis and a trend toward greater change in satellite cell content. Chronic arachidonic acid supplementation does not appear to regulate the acute anabolic response to resistance exercise but may augment muscle adaptation in the following days of recovery.

High Dose Omega-3 Fatty Acid Administration and Skeletal Muscle Protein Turnover in Maintenance Hemodialysis Patients

BACKGROUND AND OBJECTIVES

Protein energy wasting and systemic inflammation are prevalent in maintenance hemodialysis (MHD) patients. Omega-3 (ω-3) fatty acids have anti-inflammatory properties and have been shown to improve protein homeostasis. We hypothesized that administration of high-dose (2.9 g/d) ω-3 would be associated with decreased muscle protein breakdown in MHD patients with systemic inflammation.

DESIGN, SETTING, PARTICIPANTS & MEASUREMENTS

This is a substudy from a randomized, placebo-controlled study (NCT00655525). Patients were recruited between September 2008 and June 2011. Primary inclusion criteria included signs of chronic inflammation (average C-reactive protein of ≥5 mg/L over three consecutive measurements), lack of active infectious or inflammatory disease, no hospitalization within 1 month prior to the study, and not receiving steroids (>5 mg/d) and/or immunosuppressive agents. The primary outcomes were forearm muscle and whole body protein breakdown and synthesis before and after the intervention. The patients received ω-3 (n=11) versus placebo (n=9) for 12 weeks. Analysis of covariance was used to compare outcome variables at 12 weeks. Models were adjusted for a propensity score that was derived from age, sex, race, baseline high sensitivity C-reactive protein, diabetes mellitus, and fat mass because the groups were not balanced for several characteristics.

RESULTS

Compared with placebo, ω-3 supplementation was significantly associated with decreased muscle protein breakdown at 12 weeks (-31, [interquartile range, -98--13] versus 26 [interquartile range, 13-87] µg/100 ml per min; P=0.01), which remained significant after multivariate adjustment (-46, [95% confidence interval, -102 to -1] µg/100 ml per min). ω-3 Supplementation resulted in decreased forearm muscle protein synthesis while the rate in the placebo group increased; however, there is no longer a statistically significant difference in skeletal muscle protein synthesis or in net protein balance after multivariate adjustment. There was no statistically significant effect of ω-3 supplementation on whole body protein synthesis or breakdown.

CONCLUSIONS

High-dose ω-3 supplementation over 12 weeks in MHD patients with systemic inflammation was associated with attenuation of forearm muscle protein breakdown but did not influence skeletal muscle protein synthesis, skeletal muscle net protein balance or any component of the whole-body protein balance. These results should be interpreted cautiously given the imbalance in the two groups and the short duration of the intervention.

The effects of omega-3 fatty acid supplementation on dexamethasone-induced muscle atrophy

Corticosteroids cause muscle atrophy by acting on proteasomal and lysosomal systems and by affecting pathways related to muscular trophysm, such as the IGF-1/PI-3k/Akt/mTOR. Omega-3 fatty acid (n-3) has been used beneficially to attenuate muscle atrophy linked to sepsis and cachexia; however, its effect on dexamethasone-induced muscle atrophy has not been evaluated. Objectives. We evaluated whether n-3 supplementation could mitigate the development of dexamethasone-induced muscle atrophy. Methods. Two groups of Wistar rats were orally supplemented with n-3 or vehicle solution for 40 days. In the last 10 days, dexamethasone, or saline solution, was administrated establishing four groups: control, dexamethasone, n-3, and dexamethasone + n-3. The cross-sectional areas of muscle fibers, gene expression (MyoD, Myogenin, MuRF-1, and Atrogin-1), and protein expression (Akt, GSK3β, FOXO3a, and mTOR) were assessed. Results. Dexamethasone induced a significant loss in body and muscle weight, atrophy in type 2B fibers, and decreased expression of P-Akt, P-GSK3β, and P-FOXO3a. N-3 supplementation did not attenuate the negative effects of dexamethasone on skeletal muscle; instead, it caused atrophy in type 1, 2A, reduced the expression of Myogenin, and increased the expression of Atrogin-1. Conclusion. Food supplements containing n-3 are usually healthful, but they may potentiate some of the side effects of glucocorticoids.

The effect of eicosapentaenoic and docosahexaenoic acid on protein synthesis and breakdown in murine C2C12 myotubes

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been found to stimulate protein synthesis with little information regarding their effects on protein breakdown. Furthermore whether there are distinct effects of EPA and DHA remains to be established. The aim of the current study was to determine the distinct effects of EPA and DHA on protein synthesis, protein breakdown and signalling pathways in C2C12 myotubes. Fully differentiated C2C12 cells were incubated for 24h with 0.1% ethanol (control), 50 μM EPA or 50 μM DHA prior to experimentation. After serum (4h) and amino acid (1h) starvation cells were stimulated with 2 mM L-leucine and protein synthesis measured using (3)H-labelled phenylalanine. Protein breakdown was measured using (3)H-labelled phenylalanine and signalling pathways (Akt, mTOR, p70S6k, 4EBP1, rps6 and FOXO3a) via Western blots. Data revealed that after incubation with EPA protein synthesis was 25% greater (P<0.05) compared to control cells, with no effect of DHA. Protein breakdown was 22% (P<0.05) lower, compared to control cells, after incubation with EPA, with no effect of DHA. Analysis of signalling pathways revealed that both EPA and DHA incubation increased (P<0.05) p70s6k phosphorylation, EPA increased (P<0.05) FOXO3a phosphorylation, with no alteration in other signalling proteins. The current study has demonstrated distinct effects of EPA and DHA on protein metabolism with EPA showing a greater ability to result in skeletal muscle protein accretion.

Induction of muscle protein degradation by a tumour factor

An antigen of apparent molecular weight of 24,000, reactive with a murine monoclonal antibody, has been isolated from a cachexia-inducing tumour (MAC 16) and has been shown to initiate muscle protein degradation in vitro using isolated soleus muscle. Administration of this material to female NMRI mice (20 g) produced a pronounced depression in body weight (2.72 +/- 0.14 g; P<0.005 from control) over a 24 h period. This weight loss was attenuated in mice pretreated with the monoclonal antibody (0.06 +/- 0.26 g over 24 h) and occurred without a reduction in food and water intake. There was no change in body water composition, and the major contribution to the decrease in body weight was a decrease in the non-fat carcass dry weight (mainly lean body mass). The plasma levels of glucose and most amino acids were also significantly depressed. The decrease in lean body mass was accounted for by an increase (by 50%) in protein degradation and a decrease (by 50%) in protein synthesis in gastrocnemius muscle. Protein degradation was significantly decreased and protein synthesis increased to control values in mice pretreated with the monoclonal antibody. Protein degradation initiated in vitro with the proteolysis-inducing factor was abolished in mice pretreated with eicosapentaenoic acid (EPA), which had been shown to prevent muscle wastage in mice bearing the MAC16 tumour. Protein degradation was associated with a significant elevation of prostaglandin E2 production by isolated soleus muscle, which was inhibited by both the monoclonal antibody and EPA. These results suggest that this material may be the humoral factor mediating changes in skeletal muscle protein homeostasis during the process of cancer cachexia in animals bearing the MAC16 tumour, and could potentially be involved in other cases of cachexia.

Oxidative stress and muscular dystrophy

Oxidative stress may be the fundamental basis of many of the structural, functional and biochemical changes characteristic of the inherited muscular dystrophies in animals and humans. The presence of by-products of oxidative damage, and the compensatory increases in cellular antioxidants, both indicate oxidative stress may be occurring in dystrophic muscle. Changes in the proportions and metabolism of cellular lipids, abnormal functions of cellular membranes, altered activity of membrane-bound enzymes such as the SR Ca2+-ATPase, disturbances in cellular protein turnover and energy production and a variety of other changes all indicate that these inherited muscular dystrophies appear more like the results of oxidative stress to muscle than any other type of underlying muscle disturbance. Particular details of these altered characteristics of dystrophic muscle, in combination with current knowledge on the processes of oxidative damage to cells, may provide some insight into the underlying biochemical defect responsible for the disease, as well as direct research towards the ultimate goal of an effective treatment.

Effects of dietary-fish-oil feeding on muscle growth and damage in the rat

1. Giving diets containing 100 g fully-refined, non-hydrogenated fish oil/kg to rats caused substantial modification of skeletal-muscle-membrane fatty acid composition compared with control animals fed on an equivalent diet containing 100 g maize oil/kg. 2. Total muscle arachidonic acid (20:4 omega 6) was reduced from 138 (SD 25) mg/g total fatty acids to 15 (SD 2) mg/g and phospholipid arachidonic acid content showed equivalent changes. 3. Reduction in muscle arachidonic acid content had no influence on the growth of individual muscles. 4. Variation in muscle fatty acid composition exacerbated the response of muscle to calcium-induced damage assessed by efflux of intracellular creatine kinase (EC 2.7.3.2). 5. It is concluded that metabolites of arachidonic acid are unlikely to be primary controlling factors of muscle growth or specific mediators of muscle sarcolemmal damage leading to enzyme efflux.