Lipid Myopathies

Plasma Acylcarnitines as Metabolic Signatures of Declining Health-Related Quality of Life Measure in Community-Dwelling Older Adults: A Combined Cross-sectional and Longitudinal Pilot Study

BACKGROUND

Health-related quality of life (HRQoL) measures are predictors of adverse health outcomes in older adults. Studies have demonstrated cross-sectional associations between HRQoL measures and blood-based biochemical markers. Acylcarnitines (ACs) are a class of metabolites generated in the mitochondria and are predictive of multiple geriatric syndromes. Changes in ACs reflect alterations in central carbon metabolic pathways. However, the prospective relationship between plasma ACs and declining HRQoL has not been examined. This study aimed to investigate both cross-sectional and longitudinal associations of baseline ACs with baseline and declining EuroQol-5 Dimension/EuroQol Visual Analogue Scale (EQ-5D/EQ-VAS) in community-dwelling older adults.

METHODS

One hundred and twenty community-dwelling older adults with EQ-5D/EQ-VAS measurements at baseline and follow-up were included. We quantified ACs at baseline using targeted plasma metabolomics profiling. Multivariate regressions were performed to examine cross-sectional and longitudinal associations between the measures.

RESULTS

Cross-sectionally, ACs showed no significant associations with either EQ-5D index or EQ-VAS scores. Longitudinally, multiple baseline short-chain ACs were significantly and inversely associated with declining EQ-5D index score, explaining up to 8.5% of variance in the decline.

CONCLUSIONS

Within a cohort of community-dwelling older adults who had high HRQoL at baseline, we showed that higher levels of short-chain ACs are longitudinally associated with declining HRQoL. These findings reveal a novel association between central carbon metabolic pathways and declining HRQoL. Notably, dysregulation in mitochondrial central carbon metabolism could be detected prior to clinically important decline in HRQoL, providing the first evidence of objective biomarkers as novel predictors to monitor HRQoL in nonpharmacological interventions and epidemiology.

Haploinsufficiency of Lipin3 leads to hypertriglyceridemia and obesity by disrupting the expression and nucleocytoplasmic localization of Lipin1

Lipin proteins including Lipin 1-3 act as transcriptional co-activators and phosphatidic acid phosphohydrolase enzymes, which play crucial roles in lipid metabolism. However, little is known about the function of Lipin3 in triglyceride (TG) metabolism. Here, we identified a novel mutation (NM_001301860: p.1835A>T/p.D612V) of Lipin3 in a large family with hypertriglyceridemia (HTG) and obesity through whole-exome sequencing and Sanger sequencing. Functional studies revealed that the novel variant altered the half-life and stability of the Lipin3 protein. Hence, we generated Lipin3 heterozygous knockout (Lipin3-heKO) mice and cultured primary hepatocytes to explore the pathophysiological roles of Lipin3 in TG metabolism. We found that Lipin3-heKO mice exhibited obvious obesity, HTG, and non-alcoholic fatty liver disorder. Mechanistic study demonstrated that the haploinsufficiency of Lipin3 in primary hepatocytes may induce the overexpression and abnormal distribution of Lipin1 in cytosol and nucleoplasm. The increased expression of Lipin1 in cytosol may contribute to TG anabolism, and the decreased Lipin1 in nucleoplasm can reduce PGC1α, further leading to mitochondrial dysfunction and reduced TG catabolism. Our study suggested that Lipin3 was a novel disease-causing gene inducing obesity and HTG. We also established a relationship between Lipin3 and mitochondrial dysfunction.

Biomolecules of Muscle Fatigue in Metabolic Myopathies

Metabolic myopathies are a group of genetic disorders that affect the normal functioning of muscles due to abnormalities in metabolic pathways. These conditions result in impaired energy production and utilization within muscle cells, leading to limitations in muscle function with concomitant occurrence of related signs and symptoms, among which fatigue is one of the most frequently reported. Understanding the underlying molecular mechanisms of muscle fatigue in these conditions is challenging for the development of an effective diagnostic and prognostic approach to test targeted therapeutic interventions. This paper outlines the key biomolecules involved in muscle fatigue in metabolic myopathies, including energy substrates, enzymes, ion channels, and signaling molecules. Potential future research directions in this field are also discussed.

Causal relationship between lipid profile and muscle atrophy: A bi-directional Mendelian randomization study

BACKGROUND

The aim of this study was to analyze the bi-directional causal relationship between lipid profile and characteristics related to muscle atrophy by using a bi-directional Mendelian randomization (MR) analysis.

METHODS

The appendicular lean mass (ALM), whole body fat-free mass (WBFFM) and trunk fat-free mass (TFFM) were used as genome-wide association study (GWAS) data for evaluating muscle mass; the usual walking pace (UWP) and low grip strength (LGS) were used as GWAS data for evaluating muscle strength; and the triglycerides (TG), total cholesterol (TC), high density lipoprotein cholesterol (HDL), low density lipoprotein cholesterol (LDL), apolipoprotein A-1 (Apo A-1), and apolipoprotein B (Apo B) were used as GWAS data for evaluating lipid profile. For specific investigations, we mainly employed inverse variance weighting for causal estimation and MR-Egger for pleiotropy analysis.

RESULTS

MR results showed that the lipid profile predicted by genetic variants was negatively correlated with muscle mass, positively correlated with UWP, and was not causally correlated with LGS. On the other hand, the muscle mass predicted by genetic variants was negatively correlated with lipid profile, the UWP predicted by genetic variants was mainly positively correlated with lipid profile, while the LGS predicted by genetic variants had no relevant causal relationship with lipid profile.

CONCLUSIONS

Findings of this MR analysis suggest that hyperlipidemia may affect muscle mass and lead to muscle atrophy, but has no significant effect on muscle strength. On the other hand, increased muscle mass may reduce the incidence of dyslipidemia.

The effects of pollutant mixture released from grafted adipose tissues on fatty acid and lipid metabolism in the skeletal muscles, kidney, heart, and lungs of male mice

Persistent organic pollutants (POPs) accumulated in the adipose tissue can affect the fatty acid and lipid metabolism in the body. Gas chromatography-mass spectrometry (GC-MS) metabolomics analysis was carried out to study the metabolic changes induced by internal exposure to the POPs in mouse skeletal muscle (soleus, plantaris, and gastrocnemius), kidney, heart, and lungs. Male donor mice were injected with a mixture of 10 POPs at concentrations of 0 × and 5 × lowest-observed-adverse-effect level (LOAEL). Their adipose tissue (AT) containing the POP was then grafted onto the host mice and the metabolic change of the host mice was monitored for 3 or 21 days. The metabolites related to fatty acid and lipid metabolism were studied. For the host mice engrafted with POP-containing fat pad, there was dysregulation of the fatty acids and glycerides observed in all the organs studied 3 days after the graft. However, there was no longer a significant change in the metabolites 21 days after the graft. The difference in significant values and metabolite regulation in each of the skeletal muscles showed that the POP mixture affects different types of skeletal muscle in a heterogeneous manner. Fold change analysis showed that certain metabolites in the kidney of host mice exposed to POPs for 3 days were greatly affected. Using multivariate analysis, apart from the plantaris, most treated groups exposed to POPs for 3 days are well distinguished from the control groups. However, for host mice exposed to POPs for 21 days, apart from the kidney and heart, groups are not well-distinguished from the control group. This study helps bring new insight into the effects of the pollutants mixture released from AT on fatty acid and lipid metabolism at different periods and how the dysregulation of metabolites might result in diseases associated with the organs.

A loss-of-function variant in canine GLRA1 associates with a neurological disorder resembling human hyperekplexia

Hereditary hyperekplexia is a rare neuronal disorder characterized by an exaggerated startle response to sudden tactile or acoustic stimuli. In this study, we present a Miniature Australian Shepherd family showing clinical signs, which have genetic and phenotypic similarities with human hereditary hyperekplexia: episodes of muscle stiffness that could occasionally be triggered by acoustic stimuli. Whole genome sequence data analysis of two affected dogs revealed a 36-bp deletion spanning the exon-intron boundary in the glycine receptor alpha 1 (GLRA1) gene. Further validation in pedigree samples and an additional cohort of 127 Miniature Australian Shepherds, 45 Miniature American Shepherds and 74 Australian Shepherds demonstrated complete segregation of the variant with the disease, according to an autosomal recessive inheritance pattern. The protein encoded by GLRA1 is a subunit of the glycine receptor, which mediates postsynaptic inhibition in the brain stem and spinal cord. The canine GLRA1 deletion is located in the signal peptide and is predicted to cause exon skipping and subsequent premature stop codon resulting in a significant defect in glycine signaling. Variants in GLRA1 are known to cause hereditary hyperekplexia in humans; however, this is the first study to associate a variant in canine GLRA1 with the disorder, establishing a spontaneous large animal disease model for the human condition.

Metabolic Myopathies in the Era of Next-Generation Sequencing

Metabolic myopathies are rare inherited disorders that deserve more attention from neurologists and pediatricians. Pompe disease and McArdle disease represent some of the most common diseases in clinical practice; however, other less common diseases are now better-known. In general the pathophysiology of metabolic myopathies needs to be better understood. Thanks to the advent of next-generation sequencing (NGS), genetic testing has replaced more invasive investigations and sophisticated enzymatic assays to reach a final diagnosis in many cases. The current diagnostic algorithms for metabolic myopathies have integrated this paradigm shift and restrict invasive investigations for complicated cases. Moreover, NGS contributes to the discovery of novel genes and proteins, providing new insights into muscle metabolism and pathophysiology. More importantly, a growing number of these conditions are amenable to therapeutic approaches such as diets of different kinds, exercise training protocols, and enzyme replacement therapy or gene therapy. Prevention and management-notably of rhabdomyolysis-are key to avoiding serious and potentially life-threatening complications and improving patients' quality of life. Although not devoid of limitations, the newborn screening programs that are currently mushrooming across the globe show that early intervention in metabolic myopathies is a key factor for better therapeutic efficacy and long-term prognosis. As a whole NGS has largely increased the diagnostic yield of metabolic myopathies, but more invasive but classical investigations are still critical when the genetic diagnosis is unclear or when it comes to optimizing the follow-up and care of these muscular disorders.

Pathophysiology and Management of Fatigue in Neuromuscular Diseases

Fatigue is a major determinant of quality of life and motor function in patients affected by several neuromuscular diseases, each of them characterized by a peculiar physiopathology and the involvement of numerous interplaying factors. This narrative review aims to provide an overview on the pathophysiology of fatigue at a biochemical and molecular level with regard to muscular dystrophies, metabolic myopathies, and primary mitochondrial disorders with a focus on mitochondrial myopathies and spinal muscular atrophy, which, although fulfilling the definition of rare diseases, as a group represent a representative ensemble of neuromuscular disorders that the neurologist may encounter in clinical practice. The current use of clinical and instrumental tools for fatigue assessment, and their significance, is discussed. A summary of therapeutic approaches to address fatigue, encompassing pharmacological treatment and physical exercise, is also overviewed.

Quantitative proteomics reveals Polygonum perfoliatum L. ameliorates hepatic steatosis by promoting PPARs/CPT1A/CPT2-mediated fatty acid β-oxidation

Non-alcoholic fatty liver disease (NAFLD) is a predominant contributor to end-stage liver disease in the forthcoming decades. Polygonum perfoliatum L. (PPL) is an herbal medicine with anti-lipid peroxidation and anti-inflammatory properties. However, detailed hepatoprotective effects of PPL against NAFLD and its underlying mechanisms are not fully understood. Here, we found that PPL protects against high fat diet (HFD)-induced hepatic steatosis, lipid peroxidation, and glucose-lipid metabolism dysfunction in NAFLD mice. We therefore performed a label-free quantitative proteomic profiling analysis to determine the effect of PPL treatment on liver tissue proteomics and identified that activated PPARs/CPT1A/CPT2-mediated hepatic fatty acid β-oxidation (FAO) process was significantly altered. In vitro treatment of hepatocytes with PPL confirmed this altered process and FAO inhibitor etomoxir (ETO) attenuated the lipid-lowering activity of PPL in hepatocytes. Ultra-high-performance liquid chromatography/Q Exactive-HFX (UPLC/QE-HFX) was used to determine the material basis of anti-NAFLD activity of PPL. Our results have demonstrated the efficacy and potential mechanisms of PPL as an effective pharmacological therapy of NAFLD.

Statins Induce Locomotion and Muscular Phenotypes in Drosophila melanogaster That Are Reminiscent of Human Myopathy: Evidence for the Role of the Chloride Channel Inhibition in the Muscular Phenotypes

The underlying mechanisms for statin-induced myopathy (SIM) are still equivocal. In this study, we employ Drosophila melanogaster to dissect possible underlying mechanisms for SIM. We observe that chronic fluvastatin treatment causes reduced general locomotion activity and climbing ability. In addition, transmission microscopy of dissected skeletal muscles of fluvastatin-treated flies reveals strong myofibrillar damage, including increased sarcomere lengths and Z-line streaming, which are reminiscent of myopathy, along with fragmented mitochondria of larger sizes, most of which are round-like shapes. Furthermore, chronic fluvastatin treatment is associated with impaired lipid metabolism and insulin signalling. Mechanistically, knockdown of the statin-target Hmgcr in the skeletal muscles recapitulates fluvastatin-induced mitochondrial phenotypes and lowered general locomotion activity; however, it was not sufficient to alter sarcomere length or elicit myofibrillar damage compared to controls or fluvastatin treatment. Moreover, we found that fluvastatin treatment was associated with reduced expression of the skeletal muscle chloride channel, ClC-a (Drosophila homolog of CLCN1), while selective knockdown of skeletal muscle ClC-a also recapitulated fluvastatin-induced myofibril damage and increased sarcomere lengths. Surprisingly, exercising fluvastatin-treated flies restored ClC-a expression and normalized sarcomere lengths, suggesting that fluvastatin-induced myofibrillar phenotypes could be linked to lowered ClC-a expression. Taken together, these results may indicate the potential role of ClC-a inhibition in statin-associated muscular phenotypes. This study underlines the importance of Drosophila melanogaster as a powerful model system for elucidating the locomotion and muscular phenotypes, promoting a better understanding of the molecular mechanisms underlying SIM.

Modulatory Effect of Limosilactobacillus fermentum grx08 on the Anti-Oxidative Stress Capacity of Liver, Heart, and Kidney in High-Fat Diet Rats

To explore the modulating effect of Limosilactobacillus fermentum (L. fermentum) grx08 on anti-oxidative stress in the liver, heart, and kidney of high-fat diet in rats, a low-fat diet as a control and a high-fat diet was used to induce oxidative stress injury in rats. L. fermentum grx08 and its heat-inactivated bacteria were used to intervene. The results showed that the high-fat diet had caused oxidative stress injury in the liver, heart, and kidney of rats. L. fermentum grx08 significantly reduced the serum levels of liver, heart, and kidney injury markers (ALT, AST, LDH, CK-MB, UA, and Crea), while restoring the balance of lipid metabolism in the liver. It also enhanced the activity of antioxidant enzymes such as GSH-Px in the liver, heart, and kidney, scavenging NO radicals and reducing the content of MDA, a product of lipid peroxidation, which can regulate the anti-oxidative stress capacity of the liver, heart, and kidney to varying degrees. Among them, L. fermentum grx08 showed better modulating effect on kidney anti-oxidative stress, followed by liver, and the weakest modulating effect on heart. At the same time, L. fermentum grx08 heat-inactivated bacteria also had a partial modulatory effect as well as a similar effect profile to that of live bacteria.

Metabolite patterns associated with individual response to supervised exercise therapy in patients with intermittent claudication

Objective

Supervised exercise therapy (SET) is the first line treatment for intermittent claudication owing to peripheral arterial disease. Despite multiple randomized controlled trials proving the efficacy of SET, there are large differences in individual patient's responses. We used plasma metabolomics to identify potential metabolic influences on the individual response to SET.

Methods

Primary metabolites, complex lipids, and lipid mediators were measured on plasma samples taken at before and after Gardner graded treadmill walking tests that were administered before and after 12 weeks of SET. We used an ensemble modeling approach to identify metabolites or changes in metabolites at specific time points that associated with interindividual variability in the functional response to SET. Specific time points analyzed included baseline metabolite levels before SET, dynamic metabolomics changes before SET, the difference in pre- and post-SET baseline metabolomics, and the difference (pre- and post-SET) of the dynamic (pre- and post-treadmill).

Results

High levels of baseline anandamide levels pre- and post-SET were associated with a worse response to SET. Increased arachidonic acid (AA) and decreased levels of the AA precursor dihomo-γ-linolenic acid across SET were associated with a worse response to SET. Participants who were able to tolerate large increases in AA during acute exercise had longer, or better, walking times both before and after SET.

Conclusions

We identified two pathways of relevance to individual response to SET that warrant further study: anandamide synthesis may activate endocannabinoid receptors, resulting in worse treadmill test performance. SET may train patients to withstand higher levels of AA, and inflammatory signaling, resulting in longer walking times.

Clinical Relevance

This manuscript describes the use of metabolomic techniques to measure the interindividual effects of SET in patients with peripheral artery disease (PAD). We identified high levels of AEA are linked to CB1 signaling and activation of inflammatory pathways. This alters energy expenditure in myoblasts by decreasing glucose uptake and may induce an acquired skeletal muscle myopathy. SET may also help participants tolerate increased levels of AA and inflammation produced during exercise, resulting in longer walking times. This data will enhance understanding of the pathophysiology of PAD and the mechanism by which SET improves walking intolerance.

A Review of free fatty acid-induced cell signaling, angiopoietin-like protein 4, and skeletal muscle differentiation

Postnatal skeletal muscle differentiation from quiescent satellite cells is a highly regulated process, although our understanding of the contribution of nutritional factors in myogenesis is limited. Free fatty acids (FFAs) are known to cause detrimental effects to differentiated skeletal muscle cells by increasing oxidative stress which leads to muscle wasting and insulin resistance in skeletal muscle. In addition, FFAs are thought to act as inhibitors of skeletal muscle differentiation. However, the precise molecular mechanisms underlying the effects of FFAs on skeletal muscle differentiation remains to be elucidated. There is a clear relationship between dietary FFAs and their ability to suppress myogenesis and we propose the hypothesis that the FFA-mediated increase in angiopoietin-like protein 4 (ANGPTL4) may play a role in the inhibition of differentiation. This review discusses the role of FFAs in skeletal muscle differentiation to-date and proposes potential mechanisms of FFA-induced ANGPTL4 mediated inhibition of skeletal muscle differentiation.

Clinical and biochemical footprints of inherited metabolic disorders: X. Metabolic myopathies

Metabolic myopathies are characterized by the deficiency or dysfunction of essential metabolites or fuels to generate energy for muscle contraction; they most commonly manifest with neuromuscular symptoms due to impaired muscle development or functioning. We have summarized associations of signs and symptoms in 358 inherited metabolic diseases presenting with myopathies. This represents the tenth of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to system involvement.

Mutation spectrum of primary lipid storage myopathies

Background:

Lipid storage myopathies (LSM) constitute an important group of treatable myopathies. Genetic testing is essential for confirming the diagnosis and also helps in explaining phenotypic heterogeneity. The objective of this study was to describe the clinical features and genetic spectrum of LSM seen in a quaternary referral center in India.

Methods:

Eleven cases of suspected LSM underwent clinical, biochemical, histopathological and genetic evaluation. Tandem Mass Spectrometry and clinical exome sequencing with Sanger validation were performed.

Results:

All patients had exertion induced myalgia and either progressive or episodic limb girdle muscle weakness (LGMW). The age of onset ranged 10 to 31 years (mean- 21 ± 6.7y), age at presentation- 14 to 49 years (mean- 26.5 ± 9.5y). Mutations identified: ETFDH = 5, CPT2 = 3, FLAD1 = 1, ACADVL = 1, FLAD1 = 1. Dropped head syndrome was seen in two patients with ETFDH mutations. Bulbar symptoms and Beevor's sign were noted in a patient with FLAD1 variant. Novel variants were identified in seven patients.

Conclusions:

This is the first report on the genetic spectrum of LSM from India. LSM should be considered in patients with exertion induced myalgias, LGMW, cranial nerve involvement or dropped head syndrome. Genetic testing is essential for identification of these treatable disorders.

Guidelines for genetic testing of muscle and neuromuscular junction disorders

Despite recent advances in the understanding of inherited muscle and neuromuscular junction diseases, as well as the advent of a wide range of genetic tests, patients continue to face delays in diagnosis of sometimes treatable disorders. These guidelines outline an approach to genetic testing in such disorders. Initially, a patient's phenotype is evaluated to identify myopathies requiring directed testing, including myotonic dystrophies, facioscapulohumeral muscular dystrophy, oculopharyngeal muscular dystrophy, mitochondrial myopathies, dystrophinopathies, and oculopharyngodistal myopathy. Initial investigation in the remaining patients is generally a comprehensive gene panel by next-generation sequencing. Broad panels have a higher diagnostic yield and can be cost-effective. Due to extensive phenotypic overlap and treatment implications, genes responsible for congenital myasthenic syndromes should be included when evaluating myopathy patients. For patients whose initial genetic testing is negative or inconclusive, phenotypic re-evaluation is warranted, along with consideration of genes and variants not included initially, as well as their acquired mimickers.

Successful plasmapheresis and immunoglobulin treatment for severe lipid storage myopathy: Doing the right thing for the wrong reason

Three consecutive skeletal muscle biopsies during a several months time-frame, showing different degrees of neutral lipid storage. This is highlighted by Oil-red-O stains (D, E, F) and electron microscopy (G, H, I). Note the impact on mitochondrial morphology with so called 'parking lots (K, L). Zooming 'in and out' into the ultrastructure, using the nanotomy platform provides interesting detailled information (http://nanotomy.org). ​.

ETF dehydrogenase advances in molecular genetics and impact on treatment

Electron transfer flavoprotein dehydrogenase, also called ETF-ubiquinone oxidoreductase (ETF-QO), is a protein localized in the inner membrane of mitochondria, playing a central role in the electron-transfer system. Indeed, ETF-QO mediates electron transport from flavoprotein dehydrogenases to the ubiquinone pool. ETF-QO mutations are often associated with riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency (RR-MADD, OMIM#231680), a multisystem genetic disease characterized by various clinical manifestations with different degrees of severity. In this review, we outline the clinical features correlated with ETF-QO deficiency and the benefits obtained from different treatments, such as riboflavin, L-carnitine and/or coenzyme Q10 supplementation, and a diet poor in fat and protein. Moreover, we provide a detailed summary of molecular and bioinformatic investigations, describing the mutations identified in ETFDH gene and highlighting their predicted impact on enzymatic structure and activity. In addition, we report biochemical and functional analysis, performed in HEK293 cells and patient fibroblasts and muscle cells, to show the relationship between the nature of ETFDH mutations, the variable impairment of enzyme function, and the different degrees of RR-MADD severity. Finally, we describe in detail 5 RR-MADD patients carrying different ETFDH mutations and presenting variable degrees of clinical symptom severity.

Targeted Therapies for Metabolic Myopathies Related to Glycogen Storage and Lipid Metabolism: a Systematic Review and Steps Towards a 'Treatabolome'

BACKGROUND

Metabolic myopathies are a heterogenous group of muscle diseases typically characterized by exercise intolerance, myalgia and progressive muscle weakness. Effective treatments for some of these diseases are available, but while our understanding of the pathogenesis of metabolic myopathies related to glycogen storage, lipid metabolism and β-oxidation is well established, evidence linking treatments with the precise causative genetic defect is lacking.

OBJECTIVE

The objective of this study was to collate all published evidence on pharmacological therapies for the aforementioned metabolic myopathies and link this to the genetic mutation in a format amenable to databasing for further computational use in line with the principles of the "treatabolome" project.

METHODS

A systematic literature review was conducted to retrieve all levels of evidence examining the therapeutic efficacy of pharmacological treatments on metabolic myopathies related to glycogen storage and lipid metabolism. A key inclusion criterion was the availability of the genetic variant of the treated patients in order to link treatment outcome with the genetic defect.

RESULTS

Of the 1,085 articles initially identified, 268 full-text articles were assessed for eligibility, of which 87 were carried over into the final data extraction. The most studied metabolic myopathies were Pompe disease (45 articles), multiple acyl-CoA dehydrogenase deficiency related to mutations in the ETFDH gene (15 articles) and systemic primary carnitine deficiency (8 articles). The most studied therapeutic management strategies for these diseases were enzyme replacement therapy, riboflavin, and carnitine supplementation, respectively.

CONCLUSIONS

This systematic review provides evidence for treatments of metabolic myopathies linked with the genetic defect in a computationally accessible format suitable for databasing in the treatabolome system, which will enable clinicians to acquire evidence on appropriate therapeutic options for their patient at the time of diagnosis.

Diagnostic challenges in metabolic myopathies

INTRODUCTION

Metabolic myopathies comprise a clinically etiological diverse group of disorders caused by defects in cellular energy metabolism including the breakdown of carbohydrates and fatty acids, which include glycogen storage diseases and fatty acid oxidation disorders. Their wide clinical spectrum ranges from infantile severe multisystemic disorders to adult-onset myopathies. To suspect in adults these disorders, clinical features such as exercise intolerance and recurrent myoglobinuria need investigation while another group presents fixed weakness and cardiomyopathy as a clinical pattern.

AREAS COVERED

In metabolic myopathies, clinical manifestations are important to guide diagnostic tests used in order to lead to the correct diagnosis. The authors searched in literature the most recent techniques developed. The authors present an overview of the most common phenotypes of Pompe disease and what is currently known about the mechanism of ERT treatment. The most common disorders of lipid metabolism are overviewed, with their possible dietary or supplementary treatments.

EXPERT COMMENTARY

The clinical suspicion is the clue to conduct in-depth investigations in suspected cases of metabolic myopathies that lead to the final diagnosis with biochemical molecular studies and often nowadays by the use of Next Generation Sequencing (NGS) to determine gene mutations.

Investigation of adult-onset multiple acyl-CoA dehydrogenase deficiency associated with peripheral neuropathy

Multiple Acyl-CoA dehydrogenase deficiency (MADD), one of the most common lipid storage myopathies (LSMs), is a heterogeneous inherited muscular disorder that is pathologically characterized by numerous lipid droplets in muscle fibers due to lipid metabolism disturbance. MADD exhibits a wide range of clinical features, including skeletal muscle weakness and multisystem dysfunctions. However, MADD, as well as other types of LSM, associated with peripheral neuropathy has rarely been reported during the past four decades. Here, we present four Chinese patients affected by MADD with peripheral neuropathy in our neuromuscular center. Clinically, these four patients showed skeletal muscle weakness and prominent paresthesia. Muscle biopsy detected characteristic myopathological patterns of LSM, such as obvious lipid droplets in muscle fibers. Sural nerve biopsy revealed a severe reduction in number of myelinated nerve fibers, which is a typical neuropathological pattern of peripheral neuropathy. Causative ETFDH mutations were found in all four cases. The skeletal muscle weakness was rapidly improved after some treatments while paresthesia showed unsatisfactory improvement. The features of previously reported patients of this specific type are also summarized in this paper. We propose that MADD with peripheral neuropathy may be a new phenotypic subtype because the pathology and reaction to riboflavin treatment are different from those of traditional MADD, although further research on the precise pathogenesis and mechanisms is needed.

First presentation of LPIN1 acute rhabdomyolysis in adolescence and adulthood

LPIN1 mutations are a known common cause of autosomal recessive, recurrent and life-threatening acute rhabdomyolysis of childhood-onset. The first episode of rhabdomyolysis usually happens in nearly all cases before the age of 5 and death is observed in 1/3 of patients. Here we present two cases of acute rhabdomyolysis with a milder phenotype caused by LPIN1 mutation presenting in adolescence (11 years old) and adulthood (40 years old) after Parvovirus infection and metabolic stress, respectively. In our opinion, the mutation types, epigenetic factors, the environment exposition to triggers or the existence of proteins with a similar structure of LPIN1, may have a role in modulating the onset of rhabdomyolysis. LPIN1 should be included on a panel of genes analysed in the investigation of adult individuals with rhabdomyolysis. Metabolic and viral stressors should be included in the list of possible rhabdomyolysis precipitant.

The Association Between Acylcarnitine Metabolites and Cardiovascular Disease in Chinese Patients With Type 2 Diabetes Mellitus

Objective: The association between acylcarnitine metabolites and cardiovascular disease (CVD) in type 2 diabetes mellitus (T2DM) remains uncertain. This study aimed to investigate associations between acylcarnitines and CVD in Chinese patients with T2DM. Methods: A cross-sectional study was conducted from May 2015 to August 2016. Medical records of 741 patients with T2DM were retrieved from the main electronic database of Liaoning Medical University First Affiliated Hospital. CVD was defined as having either coronary artery disease (CAD) or heart failure (HF) or stroke. Mass Spectrometry was utilized to measure levels of 25 acylcarnitine metabolites in fasting plasma. Factor analysis was used to reduce the dimensions and extracted factors of the 25 acylcarnitine metabolites. Multivariable binary logistic regression was used to obtain odds ratios (OR) of the factors extracted from the 25 acylcarnitine metabolites and their 95% confidence intervals (CI) for CVD. Results: Of the 741 patients with T2DM, 288 had CVD. Five factors were extracted from the 25 acylcarnitines and they accounted for 65.9% of the total variance. Factor 1 consisted of acetylcarnitine, butyrylcarnitine, hydroxylbutyrylcarnitine, glutarylcarnitine, hexanoylcarnitine, octanoylcarnitine, and tetradecanoyldiacylcarnitine. Factor 2 consisted of decanoylcarnitine, lauroylcarnitine, myristoylcarnitine, 3-hydroxyl-tetradecanoylcarnitine, tetradecenoylcarnitine, and 3-hydroxypalmitoylcarnitine. After adjusting for potential confounders, increased factor 1 and 2 were associated with increased risks of CVD in T2DM (OR of factor 1: 1.45, 95% CI: 1.03-2.03; OR of factor 2: 1.23, 95% CI: 1.02-1.50). Conclusions: Elevated plasma levels of some acylcarnitine metabolites, i.e., those extracted into factor 1 and 2, were associated with CVD risk in T2DM.

Mitochondrial and Metabolic Myopathies

PURPOSE OF REVIEW

This article provides an overview of mitochondrial and metabolic biology, the genetic mechanisms causing mitochondrial diseases, the clinical features of mitochondrial diseases, lipid myopathies, and glycogen storage diseases, all with a focus on those syndromes and diseases associated with myopathy. Over the past decade, advances in genetic testing have revolutionized patient evaluation. The main goal of this review is to give the clinician the basic understanding to recognize patients at risk of these diseases using the standard history and physical examination.

RECENT FINDINGS

Primary mitochondrial disease is the current designation for the illnesses resulting from genetic mutations in genes whose protein products are necessary for mitochondrial structure or function. In most circumstances, more than one organ system is involved in mitochondrial disease, and the value of the classic clinical features as originally described early in the history of mitochondrial diseases has reemerged as being important to identifying patients who may have a primary mitochondrial disease. The use of the genetic laboratory has become the most powerful tool for confirming a diagnosis, and nuances of using genetic results will be discussed in this article. Treatment for mitochondrial disease is symptomatic, with less emphasis on vitamin and supplement therapy than in the past. Clinical trials using pharmacologic agents are in progress, with the field attempting to define proper goals of treatment. Several standard accepted therapies exist for many of the metabolic myopathies.

SUMMARY

Mitochondrial, lipid, and glycogen diseases are not uncommon causes of multisystem organ dysfunction, with the neurologic features, especially myopathy, occurring as a predominant feature. Early recognition requires basic knowledge of the varied clinical phenotypes before moving forward with a screening evaluation and possibly a genetic evaluation. Aside from a few specific diseases for which there are recommended interventions, treatment for the majority of these disorders remains symptomatic, with clinical trials currently in progress that will hopefully result in standard treatments.

Oxidative damage in mitochondrial fatty acids oxidation disorders patients and the in vitro effect of l-carnitine on DNA damage induced by the accumulated metabolites

BACKGROUND

The mitochondrial fatty acids oxidation disorders (FAOD) are inherited metabolic disorders (IMD) characterized by the accumulation of fatty acids of different sizes of chain according to the affected enzyme.

METHODS

This study evaluated the lipid peroxidation by the measurement of 8-isoprostanes, nitrosative stress parameters by the measurement of nitrite and nitrate content and DNA and RNA oxidative damage by the measurement of oxidized guanine species in urine samples from long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD), medium-chain acyl-CoA dehydrogenase deficiency (MCADD) and multiple acyl-CoA dehydrogenase deficiency (MADD) patients. Also, we analyzed the in vitro DNA damage by comet assay induced by adipic acid, suberic acid, hexanoylglycine and suberylglycine, separated and in combination, as well as the effect of l-carnitine in human leukocytes.

RESULTS

An increase on 8-isoprostanes levels in all groups of patients was observed. The nitrite and nitrate levels were increased in LCHADD patients. DNA and RNA damage evaluation revealed increase on oxidized guanine species levels in LCHADD and MADD patients. The in vitro evaluation revealed an increase on the DNA damage induced by all metabolites, besides a potencialyzed effect. l-carnitine decreased the DNA damage induced by the metabolites.

CONCLUSION

These results demonstrate that toxic metabolites accumulated could be related to the increased oxidative and nitrosative stress of FAOD patients and that the metabolites, separated and in combination, cause DNA damage, which was reduced by l-carnitine, demonstrating antioxidant protection.

GENERAL SIGNIFICANCE

This work demonstrated oxidative stress in FAOD patients and the genotoxic potential of MCADD metabolites and the protective effect of l-carnitine.

Expression and significance of ETFDH in hepatocellular carcinoma

The ETFDH (electron transfer flavoprotein dehydrogenase) gene mutations are reported to be a major cause of riboflavin-responsive multiple acyl-coenzyme A dehydrogenation deficiency (MADD). However, the role of ETFDH in the prognosis of hepatocellular carcinoma (HCC) remains unclear. The aim of this study was to investigate the expression of ETFDH in HCC. Immunohistochemical staining of the 207 HCC tissue microarray showed that expression of ETFDH was significantly decreased in HCC compared with the matching noncancerous hepatic tissues (P < 0.001). Moreover, ETFDH expression levels were found to be correlated with AFP levels (P = 0.011). Intriguingly, ETFDH expression levels were significantly lower in poorly differentiated or undifferentiated HCCs as compared to the well or moderately differentiated cases (P =  0.001). Kaplan-Meier analysis revealed that low tumor expression of ETFDH was associated with a poorer overall survival in patients with HCC (P =  0.024). Furthermore, multivariate analysis showed that ETFDH (P =  0.047) was an independent predictor of overall survival. Our findings may shed new light on the identification of new prognostic marker for HCC.

ETF-QO Mutants Uncoupled Fatty Acid β-Oxidation and Mitochondrial Bioenergetics Leading to Lipid Pathology

The electron-transfer flavoprotein dehydrogenase gene (ETFDH) that encodes the ETF-ubiquinone oxidoreductase (ETF-QO) has been reported to be the major cause of multiple acyl-CoA dehydrogenase deficiency (MADD). ETF-QO is an electron carrier that mainly functions in mitochondrial fatty acid β-oxidation and the delivery of electrons to the ubiquinone pool in the mitochondrial respiratory chain. A high frequency of c.250G>A has been found in Taiwanese patients with late-onset MADD. We postulated that the ETFDH c.250G>A mutation may concomitantly impair fatty acid β-oxidation and mitochondrial function. Using MADD patient-derived lymphoblastoid cells and specifically overexpressed ETFDH c.92C>T, c.250G>A, or coexisted c.92C>T and c.250G>A (c.92C>T + c.250G>A) mutated lymphoblastoid cells, we addressed the genotype-phenotype relationship of ETFDH variation in the pathogenesis of MADD. The decreased adenosine triphosphate synthesis, dissipated mitochondrial membrane potentials, reduced mitochondrial bioenergetics, and increased neutral lipid droplets and lipid peroxides were found in the MADD patient-derived lymphoblastoid cells. Riboflavin and/or coenzyme Q10 supplementation rescued cells from lipid droplet accumulation. All three mutant types, c.92C>T, c.250G>A, or c.92C>T + c.250G>A, had increased lipid droplet accumulation after treatment with palmitic acid. These results help to clarify the molecular pathogenesis of MADD as a result of the high frequency of the ETFDH c.250G>A and c.92C>T mutations.