An experimental model of mitochondrial myopathy: Germanium-induced myopathy and coenzyme Q10 administration

In skeletal muscles from rats treated with germanium for 23 weeks, there were numerous ragged-red fibers and cytochrome-c oxidase (COX)-deficient fibers. Biochemically, germanium reduced the enzyme activities in the mitochondrial respiratory chain. Rotenone-sensitive NADH–cytochrome-c reductase as well as COX activities were markedly reduced, while succinate–cytochrome-c reductase was less severely, but significantly, affected. The histopathological findings in these muslces were similar to those seen in patients with mitochondrial encephalomyopathy, suggesting that germanium-induced myopathy may be a useful experimental model. Coenzyme Q₁₀ administration appeared to be ineffective in preventing this experimental myopathy. © 1992 John Wiley & Sons, Inc.     

Cytochrome c oxidase reaction improves histopathological assessment of zidovudine myopathy

Zidovudine can induce a mitochondrial myopathy with ragged-red fibers and partial cytochrome c oxidase deficency. In an attempt to improve histological assessment of zidovudine myopathy, we evaluated cytochorme c oxidase histochemical reaction in the muscle of 10 patients with biopsy-proven zidovudine myopathy (Group 1), 10 myopathic immunodeficiency virus (HIV)-infected patients not treated by zidovudine who had an immunohistological profile of HIV-associated myopathy or other neuromuscular disorders (Group 3). Among zidovudine receivers, cytochrome c oxidase deficiency was found in 10 of 10 patients from Group 1 and 7 of 10 from Group 2. No cytochrome c oxidase deficiency was observed in patients not treated by zidovudine. When present, cytochrome c oxidase-negative fibers accounted for 2 to 28% of fibers, and there was no difference for the number of cytchrome c oxidase-negative fibers between Group 1 and Group 2. Most patients with cytochrome c oxidase deficiency that could be evaluated clinically after muscle biopsy improved after withdrawal of zidovudine (5 of 7 in Group 1,5 of 5 in Group 2). Patients who did not improve had an HIV-associated myopathy concurrently with zidovudine myopathy. We conclude that cytochrome c oxidase reaction may be used as a reliable marker of zidovudine mitochondrial toxicity in HIV-infected patients with muscular symptoms.     

Coenzyme Q10 is frequently reduced in muscle of patients with mitochondrial myopathy

Coenzyme Q₁₀ (CoQ₁₀) deficiency has been associated with an increasing number of clinical phenotypes. Whereas primary CoQ₁₀ defects are related to mutations in ubiquinone biosynthetic genes, which are now being unraveled, and respond well to CoQ₁₀ supplementation, the etiologies, and clinical phenotypes related to secondary deficiencies are largely unknown.The purpose of this multicenter study was to evaluate the frequency of muscle CoQ₁₀ deficiency in a cohort of 76 patients presenting with clinically heterogeneous mitochondrial phenotypes which included myopathy among their clinical features. A reliable diagnostic tool based on HPLC quantification was employed to measure muscle CoQ₁₀ levels. A significant proportion of these patients (28 over 76) displayed CoQ₁₀ deficiency that was clearly secondary in nine patients, who harbored a pathogenic mutation of mitochondrial DNA. This study provides a rationale for future therapeutic trials on the effect of CoQ₁₀ supplementation in patients with mitochondrial diseases presenting with myopathy among clinical features.     

Mitochondrial abnormalities in the myofibrillar myopathies

Myofibrillar myopathies are a genetically diverse group of skeletal muscle disorders, with distinctive muscle histopathology. Causative mutations have been identified in the genes MYOT, LDB3, DES, CRYAB, FLNC, BAG3, DNAJB6, FHL1, PLEC and TTN, which encode proteins which either reside in the Z‐disc or associate with the Z‐disc. Mitochondrial abnormalities have been described in muscle from patients with a myofibrillar myopathy. We reviewed the literature to determine the extent of mitochondrial dysfunction in each of the myofibrillar myopathy subtypes. Abnormal mitochondrial distribution is a frequent finding in each of the subtypes, but a high frequency of COX‐negative or ragged red fibres, a characteristic finding in some of the conventional mitochondrial myopathies, is a rare finding. Few in vitro studies of mitochondrial function have been performed in affected patients.     

Germanium myopathy: clinical and experimental pathological studies

Summary Pathological examinations were carried out on the skeletal muscle of a patient with germanium intoxication. The prominent histochemical finding was vacuolar myopathy with lipid excess, increased acid phosphatase activity and decreased cytochrome c oxidase activity. Ultrastructural lesions revealed a mitochondrial abnormality, autophagic vacuoles and accumulation of high electron-dense materials in deformed mitochondria and at the periphery of lipid droplets. Furthermore, the toxic effect of germanium on skeletal muscle was confirmed by the experimentally induced germanium myopathy, which showed autophagic degeneration, decreased cytochrome c oxidase activity and a mitochondrial abnormality with high electron-dense materials.     

Mosaicism of mitochondria in mitochondrial myopathy: an electronmicroscopic analysis of cytochrome c oxidase

Summary Electron microscopic histochemistry was applied to the study of cytochrome c oxidase activity in each mitochondrion of biopsied muscles from four patients with mitochondrial myopathy [one case of fatal infantile mitochondrial myopathy, one case of myoclonus epilepsy associated with ragged-red fibers (MERRF), and two cases of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS)]. In the patient with fatal infantile mitochondrial myopathy, intercellular heterogeneity of mitochondria was recognized. In the three patients with either MERRF or MELAS, cytochrome c oxidase activity was segmentally changed from positive to negative within single muscle fibers. In the two patients with MELAS, small groups of positive-stained mitochondria were located among negative-stained mitochondria in the negative segment of a few muscle fibers. These findings revealed that there were heterogeneous populations of normal and abnormal mitochondria intracellularly or intercellularly within the muscles of these patients.Supported in part by Grant-in-Aid for Scientific Research 63570422 from the Ministry of Education, Science and Culture, and Grant 62A-5-08 from the National Center of Neurology and Psychiatry (NCNP) of the Ministry of Health and Welfare, Japan     

Gene locus for autosomal recessive distal myopathy with rimmed vacuoles maps to chromosome 9

Distal myopathy with rimmed vacuoles is an autosomal recessive muscular disorder, characterized clinically by weakness of the distal muscles in the lower limbs in early adulthood. Recently, the gene locus for familial vacuolar myopathy with autosomal recessive inheritance (hereditary inclusion body myopathy) was mapped to chromosome 9 by genome-wide linkage analysis of nine Persian-Jewish families. Since both disease conditions share similar clinical, genetic, and histopathological features, we analyzed seven families with distal myopathy with rimmed vacuoles using ten microsatellite markers within the region of the hereditary inclusion body myopathy locus. Significantly high cumulative pairwise lod scores were obtained with three markers: D9S248 (Z_max = 5.90 at Θ = 0), D9S43 (Z_max = 5.25 at Θ = 0), and D9S50 (Z_max = 4.23 at Θ = 0). Detection of obligate recombination events as well as multipoint linkage analysis revealed that the most likely location of the distal myopathy with rimmed vacuoles gene is in a 23.3-cM interval defined by D9S319 and D9S276 on chromosome 9. The results raise the possibility that distal myopathy with rimmed vacuoles and hereditary inclusio body myopathy in Persian Jews are allelic diseases.     

Co-localization of amyloid-associated proteins with amyloid β in rat soleus muscle in chloroquine-induced myopathy: a possible model for amyloid β formation in Alzheimer's disease

Chloroquine, a potent lysosomotropic agent, induces myopathy in experimental animals similar to rimmed vacuole (RV) myopathy in humans. The abnormal accumulation of amyloid β protein (A β), which is the invariable pathological alterations in the brains affected by Alzheimer's disease (AD), has been demonstrated in denervated soleus muscle fibers in chloroquine-induced myopathy in rats. In AD affected brains, a variety of additional proteins are associated with the extracellular deposition of A β, which leads to the intracellular accumulation of neurofibrillary tangles and finally to neuronal death. In this study, we demonstrate that amyloid-associated proteins,α₁-antichymotrypsin, apolipoprotein E, SP-40,40 and ubiquitin co-localize with A β in vacuolated muscle fibers in chloroquine-induced myopathy. There are striking similarities in immunopathology between experimental RV myopathy and AD. Chloroquine-induced myopathy in rats provides a suitable model not only to obtain insight into the basic mechanisms underlying RV formation in muscle, but also to understand amyloid precursor protein processing into A β, and the role of amyloid-associated proteins in terms of the pathogenesis of AD.     

A partial deficiency of cytochrome c oxidase in chronic progressive external ophthalmoplegia

A partial deficiency of cytochrome oxidase has been found in 7 patients with chronic progressive external ophthalmoplegia and proximal myopathy or craniosomatic abnormalities. Muscle biopsies from all these patients showed morphological mitochondrial abnormalities (“ragged red” fibres) and cytochemical assay of cytochrome oxidase showed that these fibres contained no demonstrable enzyme activity. The incidence of cytochrome oxidase-negative fibres was greater than that of “ragged-red” fibres suggesting that the enzyme defect preceded the development of morphological mitochondrial changes. Biochemical analysis of skeletal muscle mitochondrial fractions from 3 patients revealed in 1 case a significantly lower concentration of cytochrome aa₃ and a decreased ratio of cytochrome oxidase/succinate-cytochrome c reductase. Fasting blood metabolites were elevated in 2 patients. We suggest that partial cytochrome oxidase deficiency is the underlying defect in mitochondrial myopathy associated with the oculocraniosomatic syndromes.     

Chronic corticosteroid administration causes mitochondrial dysfunction in skeletal muscle

Corticosteroid myopathy is a major clinical problem in patients undergoing chronic corticosteroid treatment and shows insidious and progressive muscle atrophy in proximal limbs. Although several mechanisms underlying the pathophysiology of muscle injury have been postulated, precise pathogenesis is still not clear. We evaluated the mitochondrial functions in patients receiving corticosteroids compared with those in healthy controls or patients not receiving corticosteroids. The serum levels and total production of lactate were investigated by an aerobic exercise test using a bicycle ergometer. Mitochondrial respiratory activities and oxidative damage in biopsied skeletal muscles were also studied. The results of aerobic exercise tests revealed a significant overproduction of lactate in patients treated with corticosteroids (p < 0.005), which was positively correlated with total corticosteroid doses administered (p < 0.0001). In these patients, mitochondrial enzyme activity in complex I was significantly decreased (p < 0.05) and oxidative damage of biopsied skeletal muscle was remarkable both in mitochondrial and nuclear DNAs (p < 0.001). The results suggest that chronic corticosteroid administration induces mitochondrial dysfunction and oxidative damage in skeletal muscles, which may be the pathogenesis, at least in part, of corticosteroid-induced myopathy. Received: 5 November 2001 Received in revised form: 4 February 2002 Accepted: 7 February 2002     

Hereditary myopathies with early respiratory insufficiency in adults

Introduction: Hereditary myopathies with early respiratory insufficiency as a predominant feature of the clinical phenotype are uncommon and underestimated in adults. Methods: We reviewed the clinical and laboratory data of patients with hereditary myopathies who demonstrated early respiratory insufficiency before the need for ambulatory assistance. Only patients with disease‐causing mutations or a specific histopathological diagnosis were included. Patients with cardiomyopathy were excluded. Results: We identified 22 patients; half had isolated respiratory symptoms at onset. The diagnosis of the myopathy was often delayed, resulting in delayed ventilatory support. The most common myopathies were adult‐onset Pompe disease, myofibrillar myopathy, multi‐minicore disease, and myotonic dystrophy type 1. Single cases of laminopathy, MELAS (mitochondrial encephalomyopathy with lactic acidosis and strokelike events), centronuclear myopathy, and cytoplasmic body myopathy were identified. Conclusion: We highlighted the most common hereditary myopathies associated with early respiratory insufficiency as the predominant clinical feature, and underscored the importance of a timely diagnosis for patient care. Muscle Nerve 56 : 881–886, 2017     

Isometric skeletal muscle force measurement in primary myopathies

Introduction: In myopathy patients, it is useful to measure skeletal muscle forces. Conventional methods require voluntary muscle activation, which can be unreliable. We evaluated a device for nonvoluntary force assessment. Methods: We tested 8 patients (unknown myopathy n = 2, inflammatory myopathy, facioscapulohumeral muscular dystrophy, mitochondrial myopathy, dysferlinopathy, multi‐minicore disease, Becker‐Kiener muscular dystrophy, n = 1 each). Isometric twitch torques of ankle dorsiflexors were measured after fibular nerve stimulation. Results: Six patients had decreased torques vs. 8 controls (men: median Newton‐meter 1.6 vs. 5.7, women: 0.2 vs. 3.9, both P < 0.0001). Values correlated with Manual Muscle Test results (r = 0.73; r² = 0.53; P < 0.0001). In weak dorsiflexors, torque could be measured despite lower signal‐to‐noise ratios. In 2 patients with hypertrophy, we measured increased torques. Conclusions: Nonvoluntary muscle force assessment can be used in patients with myopathies, and values correlate with voluntary forces determined by traditional methods. Muscle Nerve 53 : 913–917, 2016     

Plasma carnitine insufficiency and effectiveness of L-carnitine therapy in patients with mitochondril myopathy

Plasma carnitine “insufficiency,” (plasma esterified carnitine to free carnitine ratio above 0.25) was found in 21 48 (43.8%) patients with mitochondrial myopathy, of whom 4 also showed both total and free carnitine deficiencies in plasma. In addition, plasma levels of SCAC and LCAC were higher in patients with mitochondrial myopathy than in controls (P < 0.001 and P <0.01, respectively). Patients diagnosed as having plasma carnitine insufficiency or deficiency were treated with L-carnitine (50–200 mg/kg per day in four daily doses). Muscle weakness improved in 19 of 20 patients, failure to thrive in 4 of 8, encephalopathy in 1 of 9, and cardiomyopathy in 8 of 8 patients. Plasma carnitine “insufficiency” provides an additional clue to the diagnosis of mitochondrial myopathy and an indication for L-carnitine therapy. © 1993 John Wiley & Sons, Inc.     

Muscle carnitine deficiency and lipid storage myopathy in patients with mitochondrial myopathy

Abnormal carnitine distribution in muscle was found in 22 of 77 patients (29%), with mitochondrial myopathy. Furthermore, total (TC) and free (FC) carnitine levels in muscle were lower in patients than in controls (P < 0.01). Muscle long-chain acylcarnitines (LCAC) were significantly increased in these patients (P < 0.01). Muscle carnitine deficiency was found in 31.5% of patients with lipid storage myopathy (LSM) and in 25.6% of patients with ragged-red fibers (RRF). Therefore, carnitine deficiency can be found in patients with mitochondrial myopathy even in the absence of LSM. Muscle levels of TC and FC were lower in patients with respiratory chain defects than in those with normal respiratory chain (P < 0.01). In contrast, LCAC levels were significantly increased (P < 0.05). Carnitine levels did not differ significantly, among patients with different respiratory-chain defects. Consequently, these patients, owing to their biochemical block, reduce progressively the muscle carnitine pool and subsequent LCAC rise, due to long-chain fatty acid (LCFA) accumulation.     

Exercise fuel mobilization in mitochondrial myopathy: A metabolic dilemma

In mitochondrial myopathy, severely impaired muscle oxidative capacity poses a dilemma for metabolic regulation in exercise. We inquired whether fuel mobilization during exercise in mitochondrial myopathy is adjusted to the reduced capacity to oxidize substrate, or if fuel is mobilized in excess of oxidative capacity. Hormonal and metabolic responses to 20 minutes of cycle exercise were studied in 4 patients with mitochondrial myopathy working at near maximal effort and in 4 healthy matched controls. On 2 separate days, controls were studied at the same absolute (A) workload (9 ± 3 W) and the same relative (R) workload (77 ± 9 W) as performed by the patients. During exercise, average glucose production was higher in patients (28 ± 5 μmol min^?1 kg^?1) than in controls at both workloads (A, 12 ± 1; R, 18 ± 2 μmol min^?1 kg^?1). Exercise-induced increases in plasma glucose, growth hormone, epinephrine, norepinephrine, corticotropin, and lactate, and decreases in plasma insulin and pH were also larger in patients compared with findings in controls at both workloads. In conclusion, mitochondrial myopathies are associated with excessive neuroendocrine responses and mobilization of glucose during exercise. These responses augment ATP synthesis but result in proressive accumulation of nonoxidized substrates. Apparently, substrate mobilization and neuroendocrine responses in exercise are linked to oxidative demand rather than to oxidative capacity in working muscle.     

Progressive myofiber loss with extensive fibro-fatty replacement in a child with mitochondrial DNA depletion syndrome and novel thymidine kinase 2 gene mutations

The mitochondrial DNA depletion syndromes (MDS) are autosomal recessive disorders with a decreased mitochondrial DNA copy number. Mutations in thymidine kinase 2 (TK2) have been responsible for the myopathic form of MDS. We describe a child with congenital muscle weakness who had a progressive mitochondrial myopathy associated with extensive fibro-fatty replacement of myofibers resembling muscular dystrophy. MDS was suspected based upon findings in the initial muscle biopsy. Sequence analysis of the TK2 gene revealed two novel heterozygous mutations: the frame shift mutation, c.255_c.258delAGAA, and the heterozygous missense mutation, c.515G>A, (p.R172Q). This report extends the phenotype and genotype of TK2 defects.     

Mitochondrial dysfunction with myoclonus epilepsy and ragged-red fibers point mutation in nerve,muscle, and adipose tissue of a patient with multiple isymmetric lipomatosis

We report a 64-year-old man presenting with multiple symmetric lipomatosis (MSL) and mitochondrial encephalomyoneuropathy. The diagnosis of a mitochondrial cytopathy was based on the typical clinical symptoms and signs, including chronic progressive external ophthalmoplegia, hearing impairment, cerebellar ataxia, proximal myopathy, and polyneuropathy, and on molecular genetic and histological examinations. As a unique finding, the A → G⁽⁸³⁴⁴⁾ myoclonus epilepsy and ragged-red fibers point mutation was found in peripheral nerve, muscle, and adipose tissue. Muscle biopsy revealed multiple ragged-red fibers and other morphological signs of a mitochondrial myopathy. Sural nerve biopsy demonstrated a mixed axonal and demyelinating neuropathy with extensive loss of myelinated fibers and conspicuous onion bulb formations, as well as structural mitochondrial abnormalities on electron microscopy. These findings clearly demonstrate mitochondrial dysfunction in muscle, adipose tissue, and for the first time also in nervous tissue of an MSL patient, and strongly support the concept of mitochondrial cytopathy as one of the possible causes of multiple symmetric lipomatosis. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 833–839, 1997     

Mitochondrial myopathy with progressive decrease in mitochondrial tRNALeu(UUR) mutant genomes

A female patient with mitochondrial myopathy had a mitochondrial DNA mutation at nucleotide pair 3243, commonly seen in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS), but unlike MELAS patients, she had no central nervous system symptoms. Muscle weakness, which was most severe when she was 7 years old, improved gradually with age. Comparison of two muscle biopsies obtained at an interval of 12.5 years (7 and 20 years of age, respectively), revealed that the number of ragged-red fibers was markedly decreased and histochemical cytochrome c oxidase activity increased in parallel with the decrease in population of mutant genomes.     

Hyperthyroidism associated with papilloedema and pyramidal tract involvement

Summary In a patient with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes [MELAS] who had normal mitochondrial enzyme activity, high doses of coenzyme Q₁₀ (CoQ) were administered. Clinical improvement with decreased serum lactate and pyruvate levels was observed. Though the mechanism of action of CoQ is not known, a trial is worthwhile in patients with MELAS.