Fatty acid profile of skeletal muscle phospholipid is altered in mdx mice and is predictive of disease markers

GDE5/Gpcpd1 activity determines phosphatidylcholine composition in skeletal muscle and regulates contractile force in mice

Glycerophosphocholine (GPC) is an important precursor for intracellular choline supply in phosphatidylcholine (PC) metabolism. GDE5/Gpcpd1 hydrolyzes GPC into choline and glycerol 3-phosphate; this study aimed to elucidate its physiological function in vivo. Heterozygous whole-body GDE5-deficient mice reveal a significant GPC accumulation across tissues, while homozygous whole-body knockout results in embryonic lethality. Skeletal muscle-specific GDE5 deletion (Gde5 skKO) exhibits reduced passive force and improved fatigue resistance in electrically stimulated gastrocnemius muscles in vivo. GDE5 deficiency also results in higher glycolytic metabolites and glycogen levels, and glycerophospholipids alteration, including reduced levels of phospholipids that bind polyunsaturated fatty acids (PUFAs), such as DHA. Interestingly, this PC fatty acid compositional change is similar to that observed in skeletal muscles of denervated and Duchenne muscular dystrophy mouse models. These are accompanied by decrease of GDE5 expression, suggesting a regulatory role of GDE5 activity for glycerophospholipid profiles. Furthermore, a DHA-rich diet enhances contractile force and lowers fatigue resistance, suggesting a functional relationship between PC fatty acid composition and muscle function. Finally, skinned fiber experiments show that GDE5 loss increases the probability of the ryanodine receptor opening and lowers the maximum Ca2+-activated force. Collectively, GDE5 activity plays roles in PC and glucose/glycogen metabolism in skeletal muscle.

Concentration of lipids, cholesterol, and fatty acid profile in chicken breast meat affected by wooden breast myopathy frozen for up to 12 mo

The aim of this study was to examine the effects of frozen storage for 12 mo on the concentrations of lipids and cholesterol and fatty acid profile of wooden chicken breast meat. A total of 120 samples of chicken breasts were selected, according to the degree of "wooden breast" myopathy ["severe," "moderate," and "normal" (absence of myopathy)], from male chickens slaughtered at 42 d of age, from Cobb 500 strain. Part of the samples (n = 20/grade of severity) were evaluated on the day of collection and the remainder were packaged, frozen and stored at -18°C for up to 12 mo. At the beginning (collection day) and at the end of the proposed freezing period (12 mo), analyses of lipid, cholesterol, and fatty acid profile were carried out. Percentage of saturated (SFA), monounsaturated (MUFA), and polyunsaturated (PUFA) fatty acids were evaluated. Meats affected by wooden breast myopathy had lower levels of PUFA that exert beneficial effects on health, such as DHA, EPA and ARA, and this profile is impaired by prolonged storage (12 mo), which results in important nutritional losses for the consumer.

Lipidomic Analyses Reveal Specific Alterations of Phosphatidylcholine in Dystrophic Mdx Muscle

In Duchenne muscular dystrophy (DMD), lack of dystrophin increases the permeability of myofiber plasma membranes to ions and larger macromolecules, disrupting calcium signaling and leading to progressive muscle wasting. Although the biological origin and meaning are unclear, alterations of phosphatidylcholine (PC) are reported in affected skeletal muscles of patients with DMD that may include higher levels of fatty acid (FA) 18:1 chains and lower levels of FA 18:2 chains, possibly reflected in relatively high levels of PC 34:1 (with 16:0_18:1 chain sets) and low levels of PC 34:2 (with 16:0_18:2 chain sets). Similar PC alterations have been reported to occur in the mdx mouse model of DMD. However, altered ratios of PC 34:1 to PC 34:2 have been variably reported, and we also observed that PC 34:2 levels were nearly equally elevated as PC 34:1 in the affected mdx muscles. We hypothesized that experimental factors that often varied between studies; including muscle types sampled, mouse ages, and mouse diets; may strongly impact the PC alterations detected in dystrophic muscle of mdx mice, especially the PC 34:1 to PC 34:2 ratios. In order to test our hypothesis, we performed comprehensive lipidomic analyses of PC and phosphatidylethanolamine (PE) in several muscles (extensor digitorum longus, gastrocnemius, and soleus) and determined the mdx-specific alterations. The alterations in PC 34:1 and PC 34:2 were closely monitored from the neonate period to the adult, and also in mice raised on several diets that varied in their fats. PC 34:1 was naturally high in neonate’s muscle and decreased until age ∼3-weeks (disease onset age), and thereafter remained low in WT muscles but was higher in regenerated mdx muscles. Among the muscle types, soleus showed a distinctive phospholipid pattern with early and diminished mdx alterations. Diet was a major factor to impact PC 34:1/PC 34:2 ratios because mdx-specific alterations of PC 34:2 but not PC 34:1 were strictly dependent on diet. Our study identifies high PC 34:1 as a consistent biochemical feature of regenerated mdx-muscle and indicates nutritional approaches are also effective to modify the phospholipid compositions.

Phospholipids: Identification and Implication in Muscle Pathophysiology

Phospholipids (PLs) are amphiphilic molecules that were essential for life to become cellular. PLs have not only a key role in compartmentation as they are the main components of membrane, but they are also involved in cell signaling, cell metabolism, and even cell pathophysiology. Considered for a long time to simply be structural elements of membranes, phospholipids are increasingly being viewed as sensors of their environment and regulators of many metabolic processes. After presenting their main characteristics, we expose the increasing methods of PL detection and identification that help to understand their key role in life processes. Interest and importance of PL homeostasis is growing as pathogenic variants in genes involved in PL biosynthesis and/or remodeling are linked to human diseases. We here review diseases that involve deregulation of PL homeostasis and present a predominantly muscular phenotype.

Fasting increases 18:2-containing phosphatidylcholines to complement the decrease in 22:6-containing phosphatidylcholines in mouse skeletal muscle

Fasting stimulates catabolic reactions in skeletal muscle to survive nutrient deprivation. Cellular phospholipids have large structural diversity due to various polar-heads and acyl-chains that affect many cellular functions. Skeletal muscle phospholipid profiles have been suggested to be associated with muscle adaptations to nutritional and environmental status. However, the effect of fasting on skeletal muscle phospholipid profiles remains unknown. Here, we analyzed phospholipids using liquid chromatography mass spectrometry. We determined that fasting resulted in a decrease in 22:6-containing phosphatidylcholines (PCs) (22:6-PCs) and an increase in 18:2-containing PCs (18:2-PCs). The fasting-induced increase in 18:2-PCs was sufficient to complement 22:6-PCs loss, resulting in the maintenance of the total amount of polyunsaturated fatty acid (PUFA)-containing PCs. Similar phospholipid alterations occurred in insulin-deficient mice, which indicate that these observed phospholipid perturbations were characteristic of catabolic skeletal muscle. In lysophosphatidic acid acyltransferase 3-knockout muscles that mostly lack 22:6-PCs, other PUFA-containing PCs, mainly 18:2-PCs, accumulated. This suggests a compensatory mechanism for skeletal muscles to maintain PUFA-containing PCs.

Acute exercise in mice transiently remodels the hepatic lipidome in an intensity-dependent manner

Background

The content of triacylglycerol (TAG) in the liver is known to rapidly increase after a single bout of exercise followed by recovery to sedentary levels. The response of other hepatic lipids, and acyl chain composition of lipid classes, would provide a deeper understanding of the response of hepatic lipid metabolism to acute exercise.

Methods

Female mice performed a single bout of continuous exercise (CE), high-intensity interval exercise (HIIE), or no exercise (CON). The total content of various lipids in the liver, and fatty acids within lipid classes, were measured in tissues collected 3 h after exercise (Day 1) and the day following exercise (Day 2).

Results

The total concentration of TAG rose on Day 1 after exercise (P < 0.05), with a greater elevation in HIIE than CE (P < 0.05), followed by a decline toward CON levels on Day 2. The total concentration of other measured lipid classes was not significantly altered by exercise. However, n-6 polyunsaturated fatty acid relative abundance in diacylglycerol (DAG) was increased by HIIE (P < 0.05). In CON liver, TAG content was positively correlated with DAG and phosphatidylethanolamine (P < 0.05), while these statistical associations were disrupted in exercised mice on Day 1.

Conclusions

The response of lipid metabolism to exercise involves the coordination of metabolism between various tissues, and the lipid metabolism response to acute exercise places a metabolic burden upon the liver. The present findings describe how the liver copes with this metabolic challenge. The flexibility of the TAG pool size in the liver, and other remodeling of the hepatic lipidome, may be fundamental components of the physiological response to intense exercise.

Glycerophospholipid profile alterations are associated with murine muscle-wasting phenotype

INTRODUCTION

Phospholipids are essential components of cellular membranes and are closely associated with cellular functions, but relationships involving skeletal muscle phospholipid profiles and their physiological phenotypes have remained unclear.

METHODS

We carried out comprehensive phospholipid analyses using liquid chromatography-tandem mass spectrometry to determine the phospholipid profiles of skeletal muscles derived from muscle-wasting mouse models, including denervated and Duchenne muscular dystrophy mouse models (mdx) as well as rescued mdx mice expressing truncated dystrophin.

RESULTS

Consistent phosphatidylcholine and phosphatidylethanolamine alterations in skeletal muscles isolated from denervated and mdx mice were observed. Notably, the levels of these phospholipids binding polyunsaturated fatty acids were reduced in denervated and mdx muscles. Moreover, rescuing the mdx pathology by expressing truncated dystrophin led to the restoration of phospholipid profiles.

DISCUSSION

Our findings support the hypothesis that phospholipid profiles of the skeletal muscle may be associated with skeletal muscle function.

Age-dependent changes in metabolite profile and lipid saturation in dystrophic mice

Duchenne Muscular Dystrophy (DMD) is a fatal X-linked genetic disorder. In DMD, the absence of the dystrophin protein causes decreased sarcolemmal integrity resulting in progressive replacement of muscle with fibrofatty tissue. The effects of lacking dystrophin on muscle and systemic metabolism are still unclear. Therefore, to determine the impact of the absence of dystrophin on metabolism, we investigated the metabolic and lipid profile at two different, well-defined stages of muscle damage and stabilization in mdx mice. We measured NMR-detectable metabolite and lipid profiles in the serum and muscles of mdx mice at 6 and 24 weeks of age. Metabolites were determined in muscle in vivo using ¹ H MRI/MRS, in isolated muscles using ¹ H-HR-MAS NMR, and in serum using high resolution ¹ H/¹³ C NMR. Dystrophic mice were found to have a unique lipid saturation profile compared with control mice, revealing an age-related metabolic change. In the 6-week-old mdx mice, serum lipids were increased and the degree of lipid saturation changed between 6 and 24 weeks. The serum taurine-creatine ratio increased over the life span of mdx, but not in control mice. Furthermore, the saturation index of lipids increased in the serum but decreased in the tissue over time. Finally, we demonstrated associations between MRI-T₂ , a strong indicator of inflammation/edema, with tissue and serum lipid profiles. These results indicate the complex temporal changes of metabolites in the tissue and serum during repetitive bouts of muscle damage and regeneration that occur in dystrophic muscle.

Comparison of quality traits among breast meat affected by current muscle abnormalities

Over the past several decades, as a result of the increasing growth rate and body size of modern hybrid birds, poultry industry has been facing up the occurrence of many breast meat abnormalities, such as White Striping (WS), Wooden Breast (WB) and Spaghetti Meat (SM), whose incidence has recently reached alarming levels. Thus, the present study aimed at simultaneously investigating the implications of WS, WB and SM abnormalities on meat colour, pH, proximate composition, fatty acid profile, collagen, thermal properties as well as texture and water mobility, assessed on both superficial and deep section of Pectoralis major muscle. Overall, the occurrence of breast abnormalities is associated with a higher ultimate pH and a significant increase in moisture and fat level, coupled with a decrease in protein and ash content with WB showing the most detrimental effect. However, fatty acid profile resulted to be mildly modified only by WS. Moreover, WB fillets showed significantly higher (P < .001) collagen content and stromal protein denaturation enthalpy associated with an altered water distribution and mobility within the muscle tissue. On the contrary, SM samples displayed a lower (P < .001) collagen cross-linking and a softer texture after the cooking. Overall, these findings reveal that the occurrence of WB abnormality exerts a more profound and prominent effect on meat quality traits rather than the presence not only of WS, but also of SM.

Regulation of muscle plasticity and trophism by fatty acids: A short review

The skeletal muscle tissue has a remarkable ability to alter its plastic structural and functional properties after a harmful stimulus, regulating the expression of proteins in complex events such as muscle regeneration. In this context, considering that potential therapeutic agents have been widely studied, nutritional strategies have been investigated in order to improve the regenerative capacity of skeletal muscle. There is evidence of the modulatory action of fatty acids, such that oleic and linoleic acids, that are abundant in Western diets, on muscle function and trophism. Thus, fatty acids appear to be potential candidates to promote or impair the recovery of muscle mass and function during regeneration, since they modulate intracellular pathways that regulate myogenesis. This study is the first to describe and discuss the effect of fatty acids on muscle plasticity and trophism, with emphasis on skeletal muscle regeneration and in vitro differentiation of muscle cells.

Contractile function recovery in severely injured gastrocnemius muscle of rats treated with either oleic or linoleic acid

NEW FINDINGS

What is the central question of this study? Oleic and linoleic acids modulate fibroblast proliferation and myogenic differentiation in vitro. However, their in vivo effects on muscle regeneration have not yet been examined. We investigated the effects of either oleic or linoleic acid on a well-established model of muscle regeneration after severe laceration. What is the main finding and its importance? We found that linoleic acid increases fibrous tissue deposition and impairs muscle regeneration and recovery of contractile function, whereas oleic acid has the opposite effects in severely injured gastrocnemius muscle, suggesting that linoleic acid has a harmful effect and oleic acid a potential therapeutic effect on muscle regeneration. Oleic and linoleic acids control fibroblast proliferation and myogenic differentiation in vitro; however, there was no study in skeletal muscle in vivo. The aim of this study was to evaluate the effects of either oleic or linoleic acid on the fibrous tissue content (collagen deposition) of muscle and recovery of contractile function in rat gastrocnemius muscle after being severely injured by laceration. Rats were supplemented with either oleic or linoleic acid for 4 weeks after laceration [0.44 g (kg body weight)^-1 day^-1 ]. Muscle injury led to an increase in oleic-to-stearic acid and palmitoleic-to-palmitic acid ratios, suggesting an increase in Δ⁹ desaturase activity. Increased fibrous tissue deposition and reduced isotonic and tetanic specific forces and resistance to fatigue were observed in the injured muscle. Supplementation with linoleic acid increased the content of eicosadienoic (20:2, n-6) and arachidonic (20:4, n-6) acids, reduced muscle mass and fibre cross-sectional areas, increased fibrous tissue deposition and further reduced the isotonic and tetanic specific forces and resistance to fatigue induced by laceration. Supplementation with oleic acid increased the content of docosahexaenoic acid (22:6, n-3) and abolished the increase in fibrous tissue area and the decrease in isotonic and tetanic specific forces and resistance to fatigue induced by muscle injury. We concluded that supplementation with linoleic acid impairs muscle regeneration and increases fibrous tissue deposition, resulting in impaired recovery of contractile function. Oleic acid supplementation reduced fibrous tissue deposition and improved recovery of contractile function, attenuating the tissue damage caused by muscle injury.

Eicosapentaenoic and Docosahexaenoic Acid-Enriched High Fat Diet Delays Skeletal Muscle Degradation in Mice

Low-grade chronic inflammatory conditions such as ageing, obesity and related metabolic disorders are associated with deterioration of skeletal muscle (SkM). Human studies have shown that marine fatty acids influence SkM function, though the underlying mechanisms of action are unknown. As a model of diet-induced obesity, we fed C57BL/6J mice either a high fat diet (HFD) with purified marine fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (HFD-ED), a HFD with corn oil, or normal mouse chow for 8 weeks; and used transcriptomics to identify the molecular effects of EPA and DHA on SkM. Consumption of ED-enriched HFD modulated SkM metabolism through increased gene expression of mitochondrial β-oxidation and slow-fiber type genes compared with HFD-corn oil fed mice. Furthermore, HFD-ED intake increased nuclear localization of nuclear factor of activated T-cells (Nfatc4) protein, which controls fiber-type composition. This data suggests a role for EPA and DHA in mitigating some of the molecular responses due to a HFD in SkM. Overall, the results suggest that increased consumption of the marine fatty acids EPA and DHA may aid in the prevention of molecular processes that lead to muscle deterioration commonly associated with obesity-induced low-grade inflammation.

PGC-1α-mediated changes in phospholipid profiles of exercise-trained skeletal muscle

Exercise training influences phospholipid fatty acid composition in skeletal muscle and these changes are associated with physiological phenotypes; however, the molecular mechanism of this influence on compositional changes is poorly understood. Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a nuclear receptor coactivator, promotes mitochondrial biogenesis, the fiber-type switch to oxidative fibers, and angiogenesis in skeletal muscle. Because exercise training induces these adaptations, together with increased PGC-1α, PGC-1α may contribute to the exercise-mediated change in phospholipid fatty acid composition. To determine the role of PGC-1α, we performed lipidomic analyses of skeletal muscle from genetically modified mice that overexpress PGC-1α in skeletal muscle or that carry KO alleles of PGC-1α. We found that PGC-1α affected lipid profiles in skeletal muscle and increased several phospholipid species in glycolytic muscle, namely phosphatidylcholine (PC) (18:0/22:6) and phosphatidylethanolamine (PE) (18:0/22:6). We also found that exercise training increased PC (18:0/22:6) and PE (18:0/22:6) in glycolytic muscle and that PGC-1α was required for these alterations. Because phospholipid fatty acid composition influences cell permeability and receptor stability at the cell membrane, these phospholipids may contribute to exercise training-mediated functional changes in the skeletal muscle.

Lipogenesis mitigates dysregulated sarcoplasmic reticulum calcium uptake in muscular dystrophy

Muscular dystrophy is accompanied by a reduction in activity of sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) that contributes to abnormal Ca(2+) homeostasis in sarco/endoplasmic reticulum (SR/ER). Recent findings suggest that skeletal muscle fatty acid synthase (FAS) modulates SERCA activity and muscle function via its effects on SR membrane phospholipids. In this study, we examined muscle's lipid metabolism in mdx mice, a mouse model for Duchenne muscular dystrophy (DMD). De novo lipogenesis was ~50% reduced in mdx muscles compared to wildtype (WT) muscles. Gene expressions of lipogenic and other ER lipid-modifying enzymes were found to be differentially expressed between wildtype (WT) and mdx muscles. A comprehensive examination of muscles' SR phospholipidome revealed elevated phosphatidylcholine (PC) and PC/phosphatidylethanolamine (PE) ratio in mdx compared to WT mice. Studies in primary myocytes suggested that defects in key lipogenic enzymes including FAS, stearoyl-CoA desaturase-1 (SCD1), and Lipin1 are likely contributing to reduced SERCA activity in mdx mice. Triple transgenic expression of FAS, SCD1, and Lipin1 (3TG) in mdx myocytes partly rescued SERCA activity, which coincided with an increase in SR PE that normalized PC/PE ratio. These findings implicate a defect in lipogenesis to be a contributing factor for SERCA dysfunction in muscular dystrophy. Restoration of muscle's lipogenic pathway appears to mitigate SERCA function through its effects on SR membrane composition.

Compared with that of MUFA, a high dietary intake of n-3 PUFA does not reduce the degree of pathology in mdx mice

Duchenne muscular dystrophy (DMD) is a severe muscle disease that affects afflicted males from a young age, and the mdx mouse is an animal model of this disease. Although new drugs are in development, it is also essential to assess potential dietary therapies that could assist in the management of DMD. In the present study, we compared two diets, high-MUFA diet v. high-PUFA diet, in mdx mice. To generate the high-PUFA diet, a portion of dietary MUFA (oleic acid) was replaced with the dietary essential n-3 PUFA α-linolenic acid (ALA). We sought to determine whether ALA, compared with oleic acid, was beneficial in mdx mice. Consumption of the high-PUFA diet resulted in significantly higher n-3 PUFA content and reduced arachidonic acid content in skeletal muscle phospholipids (PL), while the high-MUFA diet led to higher oleate content in PL. Mdx mice on the high-MUFA diet exhibited 2-fold lower serum creatine kinase activity than those on the high-PUFA diet (P< 0·05) as well as a lower body fat percentage (P< 0·05), but no significant difference in skeletal muscle histopathology results. There was no significant difference between the dietary groups with regard to phosphorylated p65 (an inflammatory marker) in skeletal muscle. In conclusion, alteration of PL fatty acid (FA) composition by the high-PUFA diet made mdx muscle more susceptible to sarcolemmal leakiness, while the high-MUFA diet exhibited a more favourable impact. These results may be important for designing dietary treatments for DMD patients, and future work on dietary FA profiles, such as comparing other FA classes and dose effects, is needed.

Fatty acid profile of cardiac muscle phospholipid and triacylglycerol in MDX mice and C57BL/10ScSnJ controls

The mdx mouse is a model for Duchenne muscular dystrophy (DMD), a debilitating disease affecting striated muscle. It is established that the fatty acid (FA) composition of skeletal muscle phospholipid (PL) is altered in mdx mice, but it is not known if cardiac muscle is similarly affected by dystrophin-deficiency. We tested FA profiles in PL and triacylglycerol (TAG) in cardiac muscle of 12-week old mdx and control (con) mice. Of 22 different FA, similar to our previous finding for skeletal muscle, the most abundant FA in heart PL were palmitic, stearic, cis-vaccenic, linoleic, and docosahexaenoic acid, while for TAG the most abundant FA were palmitic, oleic, cis-vaccenic, and linoleic acid. In comparing mdx and con, no significant group differences were detected for any FA in PL or TAG. Thus, unlike skeletal muscle, FA composition in cardiac muscle PL is not different between mdx and con at the age studied. The results can be understood in the context of tissue-specific disease severity in mdx mice, as pathology is quite modest in cardiac compared with skeletal muscle.

Postprandial triglyceride and free fatty acid metabolism in obese women after either endurance or resistance exercise

We investigated the effects of two exercise modalities on postprandial triglyceride (TG) and free fatty acid (FFA) metabolism. Sedentary, obese women were studied on three occasions in randomized order: endurance exercise for 60 min at 60-65% aerobic capacity (E), ~60 min high-intensity resistance exercise (R), and a sedentary control trial (C). After exercise, a liquid-mixed meal containing [U-(13)C]palmitate was consumed, and subjects were studied over 7 h. Isotopic enrichment (IE) of plasma TG, plasma FFA, and breath carbon dioxide compared with meal IE indicated the contribution of dietary fat to each pool. Total and endogenously derived plasma TG content was reduced significantly in both E and R compared with C (P < 0.05), with no effect of exercise on circulating exogenous (meal-derived) TG content. Exogenous plasma FFA content was increased significantly following both E and R compared with C (P < 0.05), whereas total and endogenous FFA concentrations were elevated only in E (P < 0.05) compared with C. Fatty acid (FA) oxidation rates were increased significantly after E and R compared with C (P < 0.05), with no difference between exercise modalities. The present results indicate that E and R may be equally effective in reducing postprandial plasma TG concentration and enhancing lipid oxidation when the exercise sessions are matched for duration rather than for energy expenditure. Importantly, tracer results indicated that the reduction in postprandial lipemia after E and R exercise bouts is not achieved by enhanced clearance of dietary fat but rather, is achieved by reduced abundance of endogenous FA in plasma TG.

Gas chromatography-mass spectrometry-based profiling of serum fatty acids in acetaminophen-induced liver injured rats

In this study, we have developed and validated a simple, accurate and sensitive gas chromatography-mass spectrometry (GC-MS) method for simultaneous quantification of 18 fatty acids in rat serum, including both non-esterified (NEFA) and esterified (EFA) fatty acids, and subsequent analysis of fatty acid metabolic profiles. This novel method was used to evaluate the serum levels of fatty acids from vehicle- and acetaminophen (APAP)-treated rats. Serum levels of 7 NEFAs and 14 EFAs were significantly higher in APAP-treated rats 24 h after APAP administration at 1500 mg kg⁻¹ when compared with vehicle-treated controls. Control and APAP-treated rats could be differentiated based on their metabolic profiles using two different chemometric analysis methods: principle component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA). More importantly, we identified the following NEFAs as potential biomarkers of APAP-induced liver injury: oleic acid (C18:1n9), linoleic acid (C18:2n6), docosahexaenoic acid (C22:6n3) and arachidonic acid (C20:4n6). The serum concentrations of C18:1n9, C18:2n6 and C22:6n3 were all positively correlated (r > 0.8; Pearson's correlation analysis) with the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). These results suggest that a novel targeted metabolomics method based on the metabolic profiling of fatty acids analyzed by GC-MS provides exact serum concentrations of fatty acids as well as a prospective methodology to evaluate chemically induced hepatotoxicity.

Exploration of lipid metabolism in relation with plasma membrane properties of Duchenne muscular dystrophy cells: influence of L-carnitine

Duchenne muscular dystrophy (DMD) arises as a consequence of mutations in the dystrophin gene. Dystrophin is a membrane-spanning protein that connects the cytoskeleton and the basal lamina. The most distinctive features of DMD are a progressive muscular dystrophy, a myofiber degeneration with fibrosis and metabolic alterations such as fatty infiltration, however, little is known on lipid metabolism changes arising in Duchenne patient cells. Our goal was to identify metabolic changes occurring in Duchenne patient cells especially in terms of L-carnitine homeostasis, fatty acid metabolism both at the mitochondrial and peroxisomal level and the consequences on the membrane structure and function. In this paper, we compared the structural and functional characteristics of DMD patient and control cells. Using radiolabeled L-carnitine, we found, in patient muscle cells, a marked decrease in the uptake and the intracellular level of L-carnitine. Associated with this change, a decrease in the mitochondrial metabolism can be seen from the analysis of mRNA encoding for mitochondrial proteins. Probably, associated with these changes in fatty acid metabolism, alterations in the lipid composition of the cells were identified: with an increase in poly unsaturated fatty acids and a decrease in medium chain fatty acids, mono unsaturated fatty acids and in cholesterol contents. Functionally, the membrane of cells lacking dystrophin appeared to be less fluid, as determined at 37°C by fluorescence anisotropy. These changes may, at least in part, be responsible for changes in the phospholipids and cholesterol profile in cell membranes and ultimately may reduce the fluidity of the membrane. A supplementation with L-carnitine partly restored the fatty acid profile by increasing saturated fatty acid content and decreasing the amounts of MUFA, PUFA, VLCFA. L-carnitine supplementation also restored muscle membrane fluidity. This suggests that regulating lipid metabolism in DMD cells may improve the function of cells lacking dystrophin.

Perturbed voltage-gated channel activity in perturbed bilayers: implications for ectopic arrhythmias arising from damaged membrane

The ceaseless opening and closing of the voltage-gated channels (VGCs) underlying cardiac rhythmicity is controlled, in each VGC, by four mobile voltage sensors embedded in bilayer. Every action potential necessitates extensive packing/repacking of voltage sensor domains with adjacent interacting lipid molecules. This renders VGC activity mechanosensitive (MS), i.e., energetically sensitive to the bilayer's mechanical state. Irreversible perturbations of sarcolemmal bilayer such as those associated with ischemia, reperfusion, inflammation, cortical-cytoskeleton abnormalities, bilayer-disrupting toxins, diet aberrations, etc, should therefore perturb VGC activity. Disordered/fluidized bilayer states that facilitate voltage sensor repacking, and thus make VGC opening too easy could, therefore, explain VGC-leakiness in these conditions. To study this in membrane patches we impose mechanical blebbing injury during pipette aspiration-induced membrane stretch, a process that modulates VGC activity irreversibly (plastic regime) and then, eventually, reversibly (elastic regime). Because of differences in sensor-to-gate coupling among different VGCs, their responses to stretch fall into two major categories, MS-Speed, MS-Number, exemplified by Nav and Cav channels. For particular VGCs in perturbed bilayers, leak mechanisms depend on whether or not the rate-limiting voltage-dependent step is MS. Mode-switch transitions might also be mechanosensitive and thus play a role. Incorporated mathematically in axon models, plastic-regime Nav responses elicit ectopic firing behaviors typical of peripheral neuropathies. In cardiomyocytes with mild bleb damage, Nav and/or Cav leaks from irreversible MS modulation (MS-Speed, MS-Number, respectively) could, similarly, foster ectopic arrhythmias. Where pathologically leaky VGCs reside in damaged bilayer, peri-channel bilayer disorder/fluidity conditions could be an important "target feature" for anti-arrhythmic VGC drugs.