Acids In Skeletal Muscle Research Articles

Efficacy of Aceneuramic Acid for Distal Myopathy with Rimmed Vacuoles

Distal myopathy with rimmed vacuoles (DMRV), also known as GNE myopathy, is a rare disease affecting the distal muscles, such as the tibialis anterior muscle. The GNE gene, which codes for a key enzyme in the sialic acid biosynthesis pathway, is mutated in a homozygous or compound heterozygous manner, and the lack of sialic acid in skeletal muscle is the critical underlying mechanism in DMRV pathogenesis. DMRV mouse models were established, and supplementation with sialic acid improved the phenotypes of the models. A phase 1 clinical trial using aceneuramic acid was conducted at Tohoku University Hospital, Japan, followed by trials using a slow-release product. A phase II/III study, subsequent extended trial, and confirmatory trial were also conducted. Regulatory approval is currently under review.

AMPK Mediates Early Activation of the Unfolded Protein Response through a Positive Feedback Loop in Palmitate-Treated Muscle Cells.

Activation of the unfolded protein response (UPR) is closely related to the pathogenesis of many metabolic disorders. Accumulating evidence also shows that UPR and metabolic signaling pathways are interdependent. The AMP-activated protein kinase (AMPK) signal pathway controls the energy balance of eukaryotes. The aim of this study was therefore to investigate the possible interaction between AMPK signaling and UPR in muscle cells exposed to saturated fatty acids, as well as the potential mechanism. The saturated fatty acid palmitate was used to induce UPR in C2C12 myotubes. Compound C or knockdown of AMPKα with short hairpin RNA (shRNA) were used to inhibit the AMPK signaling pathway in palmitate-treated muscle cells. AMPK signaling in myotubes was activated using 5-amino-1-β-D-ribofuranosylimidazole-4-carboxamide (AICAR) or ex229. C2C12 myotubes were pre-treated with taurourdodeoxycholic acid (TUDCA) to inhibit UPR before adding palmitate. Real-time PCR and Western blotting were performed to evaluate the expression of UPR markers and activation of AMPK. Palmitate treatment induced UPR in C2C12 myotubes while activating AMPK signaling. Inhibition of the AMPK pathway with compound C or AMPK shRNA reduced palmitate-induced activation of UPR, while inhibition of UPR with TUDCA reduced palmitate-induced AMPK activation. This indicates a positive feedback loop between UPR and AMPK. Furthermore, activation of the AMPK pathway with AICAR or ex229 caused a dose-dependent upregulation of UPR markers, including activating transcription factor 4 (ATF4), binding immunoglobulin protein (BIP), and growth arrest and DNA damage-inducible 34 (GADD34) protein. These results provide the first evidence that AMPK signaling is involved in the early activation of UPR caused by saturated fatty acids in skeletal muscle. Furthermore, they indicate that physiological or pharmacological activation of the AMPK pathway (e.g., by exercise or phenformin, respectively) can promote muscle health and function, thereby improving the quality of life in individuals with metabolic disorders due to a high-fat diet or obesity.

Thyroid Hormone Regulates the Lipid Content of Muscle Fibers, Thus Affecting Physical Exercise Performance.

Skeletal muscle (SkM) lipid composition plays an essential role in physiological muscle maintenance and exercise performance. Thyroid hormones (THs) regulate muscle formation and fuel energy utilization by modulating carbohydrates and lipid and protein metabolism. The best-known effects of THs in SkM include the promotion of mitochondrial biogenesis, the fiber-type switch from oxidative to glycolytic fibers, and enhanced angiogenesis. To assess the role of THs on the lipidic composition of SkM fibers, we performed lipidomic analyses of SkM cells and tissues, glucose tolerance experiments, and exercise performance tests. Our data demonstrated that TH treatment induces remodeling of the lipid profile and changes the proportion of fatty acids in SkM. In brief, THs significantly reduced the ratio of stearic/oleic acid in the muscle similar to what is induced by physical activity. The increased proportion of unsaturated fatty acids was linked to an improvement in insulin sensitivity and endurance exercise. These findings point to THs as critical endocrine factors affecting exercise performance and indicate that homeostatic maintenance of TH signals, by improving cell permeability and receptor stability at the cell membrane, is crucial for muscle physiology.

Exercised accelerated the production of muscle-derived kynurenic acid in skeletal muscle and alleviated the postmenopausal osteoporosis through the Gpr35/NFκB p65 pathway.

BackgroundReduced serum estrogen levels in postmenopausal patients not only aggravate bone loss but also impact myokine secretion. Emerging evidence has revealed the importance of myokines in bone metabolism, and exercise can interfere with the secretion of myokines. However, few studies have explored the impact of exercise on myokine secretion in the postmenopausal osteoporosis (PMOP) process.MethodsTen-weeks-old C57B/L6 female mice were used for constructing the postmenopausal osteoporosis model. The expression levels of kynurenine aminotransferases (Kats) were detected by RT-PCR and Western Blot. The concentration of serum kynurenic acid (Kyna) was detected by HPLC-MS. Micro-CT analysis was used for determine the changes of bone mineral density and the microstructure. The primary osteoblast and osteoclast were isolated from mice to determine the effect and mechanism of Kyna on the bone formation and resorption.ResultsIn our research, we found a lower serum level of muscle-derived kynurenic acid (Kyna) in PMOP model mice, accompanied by a decreased level of kynurenine aminotransferases (Kats) in the gastrocnemius muscle. Moreover, treadmill-running exercise upregulated the muscle levels of KATs and increased the serum concentration of Kyna, which was positively correlated with the alleviation of bone loss. Furthermore, we found that exogenous Kyna treatment alleviated bone mineral loss and microstructure destruction in PMOP mice by inhibiting osteoclast maturation and increasing osteoblast viability. Mechanistically, we observed that Kyna reduced the NFκB p65 phosphorylation level by activating the Gpr35 receptor, which inhibited NFATc1 expression in osteoclasts and upregulated Runx2 expression in osteoblasts.ConclusionOur results revealed that the muscle levels of Kats and serum level of Kyna were negatively correlated with the severity of PMOP. Exercise intervention and exogenous Kyna treatment alleviated the impairment of bone microstructure through the Gpr35 receptor, paving the way for a novel therapeutic intervention in PMOP.The Translational potential of this articleThis study provides evidences that Kyna could increase the osteoblastgenesis and inhibit the osteoclastgenesis, which could be a novel therapeutic approach for osteoporosis treatment.

Disruption of Hyaluronic Acid in Skeletal Muscle Induces Decreased Voluntary Activity via Chemosensitive Muscle Afferent Sensitization in Male Mice.

PEGPH20, a human recombinant hyaluronidase, has been proposed as a coadjutant to pancreatic cancer chemotherapy. In early trials, patients reported increased widespread muscle pain as the main adverse reaction to PEGPH20. To understand how PEGPH20 caused musculoskeletal pain, we systemically administered PEGPH20 to male mice and measured voluntary wheel activity and pain-related behaviors. These were paired with ex vivo electrophysiology of primary sensory neurons, whole DRG real-time PCR, and immunohistochemistry of hindpaw muscle. PEGPH20 induced significantly lower wheel running, compared with vehicle-treated animals, and decreased mechanical withdrawal thresholds 5 d after PEGPH20 injections. Chemo-sensory muscle afferents showed increased responses to noxious chemical stimulation of their receptive fields (RFs) in the PEGPH20-treated group. This was correlated with upregulation of the NGF receptor TrkA, the transient receptor potential vanilloid type 1 (TRPV1) channel and ATP-sensitive channel P2X3 in the DRG. Immunohistochemistry of hindpaw muscles revealed damage to the muscle architecture and extensive infiltration of the tissue by cells of the myelomonocytic lineage 3 d after PEGPH20 injection. Peripheral macrophage ablation in macrophage Fas-induced apoptosis (MaFIA) mice, however, did not prevent the decreased voluntary activity and instead caused even lower levels of running. These results suggest that disruption of hyaluronic acid (HA) within the muscle extracellular matrix (ECM) sensitizes chemo-nociceptive muscle afferents possibly leading to altered pain-like behaviors. Ablation experiments suggest macrophages are necessary for adequate recovery of voluntary activity after HA disruption. These data support a role for HA and macrophages in tissue integrity and muscle pain development in patients taking PEGPH20.

801-P: SGLT2 Inhibitor, Luseogliflozin, Prevent Sarcopenia by Improving Extracellular Lipidome

Aims: It has been reported that there is a close relationship between sarcopenia obesity and metabolic disorder such as lipid metabolism. Here we investigated the effect on lipid metabolism of the sodium glucose cotransporter-2 inhibitor (SGLT-2i) luseogliflozin in skeletal muscle. We preformed microarray analysis of mRNA in skeletal muscle and investigated the lipid profile in skeletal muscle and serum. Methods: Eight-week-old mice were fed a standard diet or a standard diet supplemented with luseogliflozin (0.01% w/w chow) for 8 weeks. Mice were divided into the following three genotype/diet groups: Db/m mice without (w/o) SGLT-2i, Db/Db w/o SGLT-2i, and Db/Db with SGLT-2i. After 8 weeks of diet, in each group, body weight, glucose tolerance, muscle weight and cross-sectional area, free fatty acid concentration, muscle and gene expression in serum were investigated. Results: The ratio of soleus muscle to body weight and the cross-sectional area of soleus muscle were significantly higher in Db/Db mice with SGLT-2i than in Db/Db mice w/o SGLT-2i. In addition, the concentration of saturated fatty acids in skeletal muscle and serum of Db/Db mice with SGLT-2i was significantly lower than that w/o SGLT2i, and the expression of Fasn, Elovl6, and Scd1, which are involved in fatty acid synthesis, in skeletal muscle was significantly increased in Db/Db w/o SGLT-2i compared to Db/m mice with SGLT-2i, and significantly decreased in Db/Db with SGLT-2i compared to mice w/o SGLT-2i. Furthermore, in cell experiments using C2C12 myotube cells, the administration of saturated fatty acid increased the expression of muscle atrophy-related genes. Conclusion: The administration of luseogliflozin suppressed skeletal muscle atrophy and reduced the concentration of saturated fatty acids in skeletal muscle. Based on these findings, we hypothesized that secondary effects, other than the hypoglycemic effects of SGLT2i, might lead to the alleviation of obesity-dependent sarcopenia. Disclosure R. Bamba: None. T. Okamura: None. Y. Hashimoto: None. T. Senmaru: None. M. Hamaguchi: Research Support; Spouse/Partner; AstraZeneca K. K. M. Fukui: None.

Enhanced small neutral but not branched chain amino acid transport after epigenetic sodium coupled neutral amino acid transporter-2 (SNAT2) cDNA expression in myoblasts.

BackgroundSkeletal muscle mass and function are partly maintained by the supply of amino acids, altered amino acid transport is an important cause of frailty that can lead to decreased independence with increasing age and slow trauma recovery. The system‐A sodium coupled neutral amino acid transporter (SNAT)‐2 coded by gene family SLC38A2 generates a 506 amino acid 56 kDa protein that is an important transporter of amino acids in skeletal muscle. Ageing is associated with a decrease in expression of SNAT2 transporters.MethodsIn this study, we used the C2C12 cell line, using myoblast cells and cells differentiated into myotubes. We investigated if the expression of SNAT2 DNA would enhance intracellular amino acid levels and increase their availability for protein synthesis.ResultsIn control myoblasts and myotubes, we found significantly decreased expression of SNAT2 (6.5× decrease, n = 4 per group, P < 0.05) in myotubes than found in myoblasts. After transfection with a SNAT2‐eGFP cDNA plasmid, C2C12 myoblasts significantly increased perinuclear punctate SNAT2‐eGFP expression that persisted and was more cytoplasmic after differentiation into myotubes. Interestingly, transfected cells were significantly more responsive to the hormone 5α‐dihydrotestosterone (DHT, 4.5 nM, by 1.6×, n = 3 per group, P < 0.04). Starvation significantly enhanced the amino acid C14‐MeAIB transport (1.7×, n = 3 per group, P < 0.05) indicating increased function of SNAT2. Inhibiting SNAT2 with high concentrations of MeAIB (3.3 or 5 mM) significantly reduced C14‐Isoleucine transport by L‐type amino acid transporter (LAT2, 52.8% and 77%, respectively, n = 3 per group, P < 0.05). However, there was no increase in the LAT2 transport of C14‐isoleucine detectable in SNAT2‐eGFP transfected cells after DHT (4.5 nM) exposure. This indicated that small amino acid availability was not rate limiting to LAT2 function in myoblasts.ConclusionsOverall, these data show that transfection of SNAT2‐eGFP expression enhanced its function following starvation and treatment with physiological levels of DHT. Enhanced SNAT2 expression in muscle cells offers a viable epigenetic target in pathological conditions associated with altered amino acid transport.

Changes of Free Amino Acids in Skeletal Muscle and Serum after Exercise Injury

Changes of Free Amino Acids in Skeletal Muscle and Serum after Exercise Injury

1137-P: Anti–Skeletal Muscle Atrophy Effect of Luseogliflozin via Lipidome Modification in db/db Mice

It has been controversial that the sodium glucose cotransporter-2 inhibitor (SGLT2i) have a protective effect for muscle atrophy. We previously reported that muscle atrophy in Db/Db mice were improved by luseogliflozin via upregulation of foxo1 expression. Here we show that systemic or local lipidome were altered in Db/Db mice, which were modified by luseogliflozin. Additionally, we investigated the underling molecular mechanisms between altered lipidome and gene expressions in the atrophic soleus muscle. Eight-week-old mice were fed a standard diet or the standard diet with added luseogliflozin (0.01% w/w in chow) for 8 weeks. The mice were divided into the following three genotype/dietary groups: Db/m mice without (w/o) SGLT2i, Db/Db w/o SGLT2i, and Db/Db with SGLT2i. Concentration of stearate acids in blood in Db/Db mice with SGLT2i decreased compared to that without. The expression of scd1 or foxo1 increased in Db/Db mice w/o SGLT2i and decreased in Db/Db mice with SGLT2i. Stearate acids in blood increased in Db/Db mice, which increased stearate acids in skeletal muscle. Increased stearate acid concentration in skeletal muscle stimulates the expression of scd1, on the other hand, the administration of luseogliflozin decreased stearate acids in blood and skeletal muscle, which decreased the expression of scd1 in skeletal muscle. Disclosure R. Bamba: Research Support; Spouse/Partner; Taisho Pharmaceutical Co., Ltd.

Role of Ascorbic Acid in Skeletal Muscle Regeneration

Total amount of L‐ascorbic acid (AsA) in human skeletal muscle is approximately 40%. As satellite cells, muscle specific stem cells, are responsible for providing new myoblast cells during the muscle regeneration process. Myoblast cells construct myofibers in the regenerative process including proliferation and differentiation. AsA is known to prevent scurvy helping dioxygenases for the prolines hydroxylation in collagen. It has been reported that AsA accelerated Ten‐Eleven Translocation (Tet) methylcytosine dioxygenase‐mediated generation of 5‐hydroxymethylcytosine (5hmc) from 5‐methylcytosine. We have previously reported that AsA deficiency causes skeletal muscle atrophy and deterioration in physical performance in senescence marker protein 30 knockout (SMP30‐KO) mice. In this study, we showed that AsA deficiency causes a delay of skeletal muscle regeneration in SMP30‐KO mouse which is unable to biosynthesis of AsA. Moreover, AsA administration after skeletal muscle injury recovered it regeneration. In vitro experiment, AsA treated C2C12 mouse myoblast cells showed higher cell proliferation rate, mRNA expression levels of myogenic differentiation markers such as myogenin and myomaker, and fusion index compared to untreated cells. Finally, we examine the 5hmc levels in AsA‐treated and untreated C2C12 cells. The 5hmc levels was higher in AsA‐treated cells than untreated cells. These results suggest that AsA induced skeletal muscle regeneration by enhancing the myoblast proliferation, differentiation, and DNA demethylation.Support or Funding InformationGrant‐in‐Aid for Early‐Career Scientists. Funding Agency: Japan Society for the Promotion of Science. Project number: 19K19822

Suppression of long chain acyl-CoA synthetase blocks intracellular fatty acid flux and glucose uptake in skeletal myotubes

Alterations in fatty acid metabolism are associated with impaired glucose uptake in skeletal muscle. Long-chain acyl-CoA synthetase (Acsl) 6 is the one of the Acsl isoforms expressed in skeletal muscle although its role in muscle energy metabolism has not been studied. Thus, the aims of this study were to investigate the role of Acsl6 in fatty acid partitioning and glucose uptake in differentiated skeletal myotubes using a siRNA-mediated knockdown approach. Compared with cells transfected with control siRNA, cells transfected with Acsl6 siRNA exhibited reduced intracellular triacylglycerol (TAG) accumulation. The initial rate of [1‑14C]‑oleic acid uptake was not altered while the incorporation of [1‑14C]‑acetic acids into total cellular lipids decreased under Acsl6 knockdown (p < 0.05). In a metabolic labeling study, Acsl6 suppression decreased the incorporation of [1‑14C]‑oleic acids and [1‑14C]‑acetic acids into TAG and diacylglycerol (DAG) (p < 0.05). During the chase period of a pulse-chase experiment, Acsl6 suppression increased the intracellular free fatty acids and decreased the fatty acid channeling toward the reacylation of TAG (p < 0.05). The incorporation of the labeled fatty acids into acid-soluble metabolites, β-oxidation product, was not changed under Acsl6 knockdown. Acsl6 siRNA decreased the insulin-induced uptake of [1‑14C]‑2‑deoxyglucose (p < 0.05) but did not change the glucose uptake in the presence of acipimox, inhibitor of lipolysis. Suppression of Acsl6 deteriorated Akt phosphorylation and Glut4 mRNA expression in response to insulin. These results suggest that Acsl6 activates and channels fatty acids toward anabolic pathways and has a role in glucose and fatty acid cycling through the re-esterification of fatty acids in skeletal muscle.

Endurance Training Counteracts the High-Fat Diet-Induced Profiling Changes of ω-3 Polyunsaturated Fatty Acids in Skeletal Muscle of Middle-Aged Rats.

PurposeTo investigate the effects of endurance training on the content of ω-3 polyunsaturated fatty acids (PUFAs) and their distribution among lipid classes in skeletal muscle in middle aged, high-fat diet fed rats.MethodThirty 10-month old male Sprague Dawley (SD) rats were assigned to four groups. Two groups of rats remained sedentary and were fed chow diet (C group), or high-fat diet (H group), respectively. The other two groups of rats were subjected to endurance training while maintaining their chow diet (EC group), or high-fat diet (EH group). After 16 weeks endurance training and/or diet intervention, the content of ω-3 PUFAs and ω-3 PUFA-containing lipids in rat soleus muscle were analyzed by lipidomics.ResultsRats fed a high-fat diet exhibited decreased overall amount of ω-3 PUFAs in soleus muscle, while endurance training preserved the total amount of ω-3 PUFAs. Both the endurance training and high-fat diet alone changed the profiles of ω-3 PUFAs in different lipid classes. Specifically, the amount of triacylglycerol (TG), lysophosphatidylcholine (LPC), phosphatidylcholine (PC), and phosphatidylglycerol (PG) containing ω-3 PUFAs in soleus muscle was increased by endurance training, but the amount of lysophosphatidylenthanol (LPE), lysophosphatidylinositol (LPI), lysophosphatidylserine (LPS), cardiolipin (CL), phosphatidic acid (PA), and phosphatidylinositol (PI) was decreased. The high-fat diet induced a decrease of ω-3 PUFAs in TG, LPE, LPS, CL, platelet activating factor (PAF), PC, phosphatidylethanolamine (PE), and phosphatidylserine (PS), and an increase in LPC, LPI, PA, and PG. In addition, the effects of the endurance training on ω-3 PUFAs in skeletal muscle was also evident in high-fat diets fed rats, which counteracts the profiling changes caused by high-fat diet feeding.ConclusionThe beneficial effects of endurance training on skeletal muscle may be achieved to some extent through recovering the content of ω-3 PUFAs that has been decreased by high-fat diet feeding.

Free amino acid concentration in serum and trapezius muscle from male and female silver foxes (Vulpes vulpes)

Serum and muscle concentrations of 29 amino acids were determined in Silver fox. Serum concentrations of proline, alanine, tyrosine and aromatic amino acids were significantly higher in males than in females (all P = 0.05). Taurine and glycine concentrations in skeletal muscles were significantly higher in males than in females (P &amp;lt; 0.01). Muscle concentrations of cysteic acid, taurine, aspartate, threonine, serine, glycine, alanine, citruline, valine, leucine, gamma-amino-butyrate, ethanoloamine, lysine and histidine were significantly higher than in serum in both sexes (P &amp;lt; 0.05). In females, the concentrations of glutamate, glutamine, cystathionine, isoleucine, tyrosine, phenylalanine, arginine and amino-adipic acid were significantly higher in muscles than in serum (P &amp;lt; 0.05). Tryptophan concentration was significantly higher in serum from males than in muscles (P = 0.01). The concentration of branched-chain amino acids in skeletal muscles was approximately two times higher than in serum in both groups of foxes (P ≤ 0.01). Similar differences were obtained for aromatic amino acids in females (P = 0.04). The elaborated experimental model may serve for further studies focused on amino acid metabolism regulation in Canide and other monogastric mammals, especially with the use of environmental, dietary, pharmacological and toxicological factors. The elaborated experimental model may be an attractive alternative to replace some experiments on dogs.

PO-146 Effects of aerobic exercise training on GTT and ITT in apelin Knockout mice

Objective Aerobic exercise training is important to prevent and cure chronic diseases such as diabetes, cardiovascular diseases and so on. Apelin has been identified as a novel myokine in recent years, and the exogenous supplementation of apelin can promote the glucose absorption, the biosynthesis of mitochondria and the oxidation of fatty acids in skeletal muscle. Intraperitoneal glucose (GTT) and insulin tolerance tests (ITT) are useful in vivo assays that provide approximations of glucose metabolism and homeostasis. The bigger area under the curve (AUC) confirmed the decreased glucose clearance, which is evaluated by GTT. However, the mechanism of apelin mediating glucose metabolism during aerobic exercise training is not clear. Our study was to investigate the differences of GTT and ITT after four weeks training between wild-type (WT) mice (C57BL/6J) and apelin Knockout (KO) mice.&#x0D; Methods Two-month-old WT and KO were divided into trained and control groups (n=8-10/group) respectively. There are four groups: WT control (WC), apelin KO control (KC), WT trained (WT), and apelin KO trained (KT). The trained groups were trained on treadmills for four weeks (six days per week and one hour per day). In order to maintain the exercise intensity, the speed is at 70%-75% VO2max with an incline of 5 degrees. The control groups were kept at a sedentary condition. after four weeks of interventions, glucose was measured at 0, 15, 30, 45, 60, 90, 120min following GTT. Glucose was also measured at 0, 30, 60, 90, 120min following ITT.&#x0D; Results (1) blood glucose levels and AUC of the KC were significantly bigger than those of WC. ITT showed that KC also had slower insulin-stimulated glucose clearance compared with the WC. (2) Following 4-week training, KT had lower blood glucose levels and AUC of the KT was significantly smaller than those of KC. KT had faster insulin-stimulated glucose clearance compared with KC.&#x0D; Conclusions Without apelin, glucose tolerance and insulin tolerance in mice will decrease. And aerobic exercise training improves them in apelin deficiency mice.

A diet defined by its content of bovine milk exosomes and their RNA cargos has moderate effects on gene expression, amino acid profiles and grip strength in skeletal muscle in C57BL/6 mice

Exosomes are nanoparticles that transfer cargos from donor cells to recipient cells where they elicit changes in gene expression and metabolism. Evidence suggests that exosomes and their cargos are also absorbed from dietary sources such as bovine milk, and bovine exosomes promote the growth of myofibers in murine C2C12 myotube cell cultures. The aim of the current study was to determine whether the dietary intake of bovine milk exosomes alters strength, gene expression and amino acid profiles in murine skeletal muscles. Male and female C57BL/6 mice, age three weeks, were fed an AIN93G-based, exosome and RNA-depleted (ERD) diet for six weeks; controls were fed an exosome and RNA-sufficient (ERS) diet. Variables of feeding behavior, metabolism, grip strength, liver and kidney function, amino acid profiles, and gene expression patterns were analyzed by using metabolic cages, grip strength analyzers, clinical chemistry analyzers, targeted LC/MS–MS, and RNA sequencing analysis. The diets had no effect on food and water intake, respiratory exchange rate, physical activity, grip strength, markers of liver and kidney dysfunction, and amino acid profiles in muscle. Only twelve and nine mRNAs were differentially expressed in skeletal muscle from female and male mice, respectively, fed ERD and ERS diets. The modest effect of the ERD diet on gene expression and levels of free amino acids in skeletal muscle is consistent with observations that bovine milk exosomes and their cargos accumulate in tissues other than skeletal muscle.

Phenolic Elderberry Extracts, Anthocyanins, Procyanidins, and Metabolites Influence Glucose and Fatty Acid Uptake in Human Skeletal Muscle Cells.

Uptake of glucose and fatty acids in skeletal muscle is of interest for type 2 diabetes treatment. The aim was to study glucose and fatty acid uptake in skeletal muscle cells, antioxidant effects, and inhibition of carbohydrate-hydrolyzing enzymes by elderberries. Enhanced glucose and oleic acid uptake in human skeletal muscle cells were observed after treatment with phenolic elderberry extracts, anthocyanins, procyanidins, and their metabolites. The 96% EtOH and the acidified MeOH extracts were highly active. Of the isolated substances, cyanidin-3-glucoside and cyanidin-3-sambubioside showed highest stimulation of uptake. Phloroglucinol aldehyde was most active among the metabolites. Isolated anthocyanins and procyanidins are strong radical scavengers and are good inhibitors of 15-lipoxygenase and moderate inhibitors of xanthine oxidase. As α-amylase and α-glucosidase inhibitors, they are considerably better than the positive control acarbose. The antidiabetic property of elderberry phenolics increases the nutritional value of this plant and indicates potential as functional food against diabetes.

Therapeutic development for GNE myopathy.

GNE myopathy is rare muscle disease which affect distal muscles. GNE gene, which encodes for a key enzyme in the sialic acid biosynthesis pathway, is mutated in the homozygote or compound heterozygote in the disease. The lack of sialic acid in skeletal muscle is the critical pathological process in GNE myopathy. GNE myopathy model mouse was established and supplementation of sialic acid improves the phenotype of model mouse. Phase Ⅰ clinical trial was conducted at Tohoku University Hospital using aceneuramic acid, followed by the trials using slow release product of sialic acid. Phase Ⅱ/Ⅲ study is ongoing.

Differential effects of docoosahexaenoic and arachidonic acid on fatty acid composition and myosin heavy chain-related genes of slow- and fast-twitch skeletal muscle tissues.

Myosin heavy chain (MHC) mediates the metabolic and contractile responses of skeletal muscles. MHC displays different isoforms, each of which has different characteristics. To better understand the effect of polyunsaturated fatty acids in skeletal muscles, rats were fed with control-, docosahexaenoic acid (DHA)-, and arachidonic acid (ARA)-oil, and the effects on plasma and muscular fatty acid profile, oxidative stress, mRNA levels of myosin heavy chain isoforms MHC1 of slow-twitch muscle (SO) and MHC2A, MHC2X, and MHCB isoforms of extensor digitorum longus (EDL) of fast-twitch muscle were evaluated. Concomitantly, mRNA levels of anti-oxidative enzymes, such as, catalase, glutathione peroxidase (GPx) and superoxide dismutase (SOD were determined. The expressions of MHC1, MHC2A, MHC2X, and MHC2B were lower in the SO of the DHA-fed rats. In the EDL muscles of DHA-fed rats, the expressions of MHC1 and MHC2A increased; however, the expressions of MHC2X increased and that of the MHC2 were not altered. Oxidative stress, as indicated by the levels of LPO, was significantly higher in the plasma of the ARA-fed rats, when compared with that of the DHA-fed rats. The LPO levels were higher both in the SO and EDL muscles of ARA-fed rats. Compared with ARA oil intake, DHA oil showed higher mRNA levels of GPx and SOD. Catalase expression was higher only in the EDL but not in the SO-type muscles. Our studies finally indicate that DHA and ARA differentially affect the regulation of contractile and metabolic properties of slow- and fast-twitch skeletal muscles.

The mechanistic and ergogenic effects of phosphatidic acid in skeletal muscle.

Skeletal muscle mass plays a vital role in locomotion, whole-body metabolic health, and is a positive predictor of longevity. It is well established the mammalian target of rapamycin (mTOR) is a central regulator of skeletal muscle protein turnover. The pursuit to find novel nutrient compounds or functional food sources that possess the ability to activate mTOR and promote skeletal muscle protein accretion has been on going. Over the last decade, a key role has been proposed for the phospholipid phosphatidic acid (PA) in mTOR activation. Mechanical load-induced (i.e., resistance exercise) intramuscular PA can directly bind to and activate mTOR. In addition, PA provided exogenously in cell culture heightens mTOR activity, albeit indirectly. Thus, endogenously generated PA and exogenous provision of PA appear to act through distinct mechanisms that converge on mTOR and, potentially, may amplify muscle protein synthesis. In support of this notion, limited evidence from humans suggests that resistance exercise training combined with oral supplemental PA enhances strength gains and muscle hypertrophy. However, the precise mechanisms underpinning the augmented muscle remodelling response with supplemental PA remain elusive. In this review, we will critically examine available evidence from cell cultures and animal and human experimental models to provide an overview of the mechanisms through which endogenous and exogenous PA may act to promote muscle anabolism, and discuss the potential for PA as a therapeutic tool to maintain or restore skeletal muscle mass in the context of ageing and disease.

Increased Accumulation of Long‐chain Fatty Acids in Skeletal Muscle May Contribute Insulin Resistance in Znt7 Knockout Mice

The Slc30a7 (Znt7) gene encodes a ubiquitously expressed zinc transporter involved in transporting cytoplasmic zinc into the Golgi apparatus and vesicles. The Znt7 knockout (KO) mouse is mildly zinc deficient. Our previous studies have demonstrated that insulin resistance may underlie severe glucose intolerance in Znt7 KO mice fed a high fat diet (45% Kcal). In humans, insulin resistance in peripheral tissues is a precursor to Type 2 diabetes (T2D). Abnormal lipid metabolism in peripheral tissues is implicated in the development of insulin resistance in humans and in mouse models of T2D. To understand the mechanisms underlying insulin resistance in Znt7 KO mice, we used a metabolomics approach to detect changes in major metabolites related to fatty acid metabolism in peripheral tissues including skeletal muscle, liver and fat between Znt7 KO and age-matched control mice. We found that Znt7 KO mice had elevated triglycerides in skeletal muscle. Fatty acid levels including palmitic acid, stearic acid, oleic acid, linoleic acid, and arachidonic acid in skeletal muscle and subcutaneous fat tissues of Znt7 KO mice were 2-fold higher than the control. As a result, metabolic products from these free fatty acids, such as 13-hydroxyoctadecadienoic acid (13-HODE) and 12,13-dihydroxyo (12,13-DiHOME) were also elevated in the skeletal muscle and subcutaneous fat of Znt7 KO mice. These data suggest that abnormal free fatty acid metabolism may contribute to muscle and fat insulin resistance in Znt7 KO mice.