Mitochondrial Myopathy Patients Research Articles

Modeling in vivo recovery of intracellular pH in muscle to provide a novel index of proton handling: Application to the diagnosis of mitochondrial myopathy

Post-exercise recovery of intracellular pH (pHi) assessed using phosphorus magnetic resonance spectroscopy has not been previously evaluated in its entirety due to its complex time-course and missing data points resulting from a transient loss of inorganic phosphate signal. By considering the transition from exercise to recovery as a step function input, pHi recovery was modeled based on the creatine-kinase equilibrium, and the entire pHi recovery was characterized by calculating the time required for pHi recovery (tpHrec). Applying this methodology, normal subjects showed a strong linear correlation between phosphocreatine (PCr) half-time and tpHrec (r = 0.90, P < 0.001). In mitochondrial myopathy (MM) patients with weakness in the limb examined, 9/10 had faster pHi recovery relative to PCr recovery; wide normal ranges from a control group which included deconditioned subjects resulted in 7 of those 10 patients having otherwise normal recovery indices. Therefore, modeling pHi recovery allows characterization of the entire pHi recovery and detects altered proton handling in MM patients, including those with otherwise normal recovery indices. Magn Reson Med 46:870–878, 2001. © 2001 Wiley-Liss, Inc.

Modeling in vivo recovery of intracellular pH in muscle to provide a novel index of proton handling: application to the diagnosis of mitochondrial myopathy.

Post-exercise recovery of intracellular pH (pH(i)) assessed using phosphorus magnetic resonance spectroscopy has not been previously evaluated in its entirety due to its complex time-course and missing data points resulting from a transient loss of inorganic phosphate signal. By considering the transition from exercise to recovery as a step function input, pH(i) recovery was modeled based on the creatine-kinase equilibrium, and the entire pH(i) recovery was characterized by calculating the time required for pH(i) recovery (t(pHrec)). Applying this methodology, normal subjects showed a strong linear correlation between phosphocreatine (PCr) half-time and t(pHrec) (r = 0.90, P < 0.001). In mitochondrial myopathy (MM) patients with weakness in the limb examined, 9/10 had faster pH(i) recovery relative to PCr recovery; wide normal ranges from a control group which included deconditioned subjects resulted in 7 of those 10 patients having otherwise normal recovery indices. Therefore, modeling pH(i) recovery allows characterization of the entire pH(i) recovery and detects altered proton handling in MM patients, including those with otherwise normal recovery indices.

Exercise intolerance in mitochondrial myopathy is not related to lactic acidosis

In a double-blinded, placebo-controlled, crossover study in seven mitochondrial myopathy patients (MM), we investigated whether lowering of lactate with dichloroacetate (DCA) can improve exercise tolerance and oxidative capacity in MM. DCA lowered plasma lactate at rest and during exercise (from 10.5 +/- 2.0 to 5.0 +/- 1.6 mM; p = 0.005) but did not improve maximal work load or VO2 in cycle exercise or phosphorous magnetic resonance spectroscopy (31P-MRS)-assessed indices of muscle oxidative metabolism. This indicates that lactate acidosis is not the primary cause of exercise intolerance in MM.

Lack of IL-6 production during exercise in patients with mitochondrial myopathy.

In the present study we investigated the possibility that exercise-induced increases in plasma levels of interleukin (IL)-6 are associated with plasma lactate levels. Patients with mitochondrial myopathy (MM) are characterised by high levels of plasma lactate. In this study, seven patients with MM underwent an ergometer cycle test for 25 min without treatment. They were then treated with dichloroacetate (DCA) for 15 days. DCA inhibits pyruvate-dehydrogenase-kinase, thereby increasing the activity of the pyruvate-dehydrogenase complex. The same exercise test was repeated on the last day of treatment. DCA lowered the plasma lactate and increased plasma IL-6 concentrations at rest. IL-6 increased in response to exercise only during DCA treatment. Furthermore, plasma IL-6 was negatively correlated to plasma lactate at rest (r = -0.786, P = 0.05). Given that IL-6 is a cytokine with growth-promoting potential, the results of this study suggest that high lactate production contributes to the decreased muscle function observed in MM patients by inhibiting the production of IL-6.

Mitochondrial DNA in focal dystonia: a cybrid analysis.

The cause and pathophysiology of dystonia remain unknown. The recent identification of mitochondrial complex I deficiency in platelets from patients with sporadic focal dystonia suggests that a defect of energy metabolism may be relevant in a proportion of patients. We have addressed the possible contribution of mitochondrial DNA (mtDNA) to the complex I deficiency in dystonia by the use of genome transfer technology. Platelets from patients deficient for complex I were fused with A549 p0 (mtDNA-less) cells to form cybrids comprising the A549 nucleus and dystonia mtDNA. Mixed cybrid cell lines were analyzed for 9 controls and 9 dystonia patients, and clonal cybrid lines were generated for 2 control and 2 dystonia patients. Subsequent biochemical analysis showed that the dystonia complex I defect was complemented in both the mixed and the clonal cybrid lines. These results contrast with similar studies in mitochondrial myopathy and Parkinson's disease patients, in which the mitochondrial defect was maintained in at least a proportion of A549 cybrids, and suggest that the complex I defect in dystonia is not caused by an mtDNA mutation.

Cardiac involvement in patients with myotonic dystrophy, Becker's muscular dystrophy and mitochondrial myopathy.

The aim of this prospective study was to classify cardiac involvement in myopathies by means of a comprehensive cardiac investigation, to determine the rate of cardiac involvement in myopathies according to this classification and to compare the validity of previously reported electro-cardiographic myopathy indices (QT/PQs, P/PQs, R/S) with that of the comprehensive cardiac investigation. We included 14 patients with myotonic dystrophy, 6 patients with Becker's muscular dystrophy and 10 patients with mitochondrial myopathy. Cardiac involvement was classified as either "definite", "equivocal" or "absent" by assessing cardiovascular history, physical examination, electrocardiography, echocardiography and 24-hour ambulatory electrocardiography. "Definite"/"equivocal"/"absent" cardiac involvement was found in 12/2/0 myotonic dystrophy, 3/3/0 Becker's muscular dystrophy and 6/3/1 mitochondrial myopathy patients. Electrocardiographic myopathy indices were pathologic in 3 Becker's muscular dystrophy, 6 mitochondrial myopathy but in none of the myotonic dystrophy patients. The proposed comprehensive cardiac investigation is simple, inexpensive and effective in assessing cardiac involvement in patients with myotonic dystrophy. Becker's muscular dystrophy and mitochondrial myopathy. In case of cardiac involvement, cardiac therapy might be one of the few therapeutic options for these patients.

Sensitivity to Mivacurium in a Patient with Mitochondrial Myopathy

Sensitivity to Mivacurium in a Patient with Mitochondrial Myopathy

Morphology of the mitochondria in heat shock protein 60 deficient fibroblasts from mitochondrial myopathy patients. Effects of stress conditions.

We have described two mitochondrial (mt) myopathy patients with reduced activities of various mt enzymes associated with significantly decreased amounts of heat shock protein 60 (hsp60). Experimental evidence suggested that the lack of hsp60 was the primary defect. Since hsp60 is essential for the proper folding of enzyme subunits in the mt matrix a partial deficiency of this protein can explain the observed defects of the mitochondria. Here we report on morphological studies aimed at obtaining more insight into the relation between lack of hsp60 and pathological changes of the mitochondria. Under standard culture conditions mitochondria in the partially hsp60 deficient fibroblasts showed profound morphological aberrations. In contrast, the mitochondria in fibroblasts from a MELAS patient and a cytochrome c oxidase-deficient patient appeared normal. Under stress conditions the integrity of the hsp60 deficient mitochondria declined even further: heat shock induced a temporary collapse of the electrochemical potential across the inner mt membrane, but did not affect the ultrastructure of the mitochondria; prolonged growth in confluent cultures resulted in decrease in mt number. The altered mt morphology in the hsp60 deficient cells is probably indicative of the severely impaired mt metabolism whereas the decreased stress tolerance is likely to be a direct result of paucity of the heat shock protein. Both variables are potentially useful in the diagnosis and molecular characterization of mt disorders with systemic manifestation and multiple enzyme deficiency.

Extensive Tissue Oxygenation Associated with Mitochondrial DNA Mutations

Extensive tissue oxygenation in the mitochondrial myopathy patients caused by the mitochondrial DNA mutations was first demonstrated noninvasively by a tissue oxymeter measuring near infrared light. The extent of oxygenation of the tissue due to dysfunction of mitochondria correlated with the seriousness of mitochondrial DNA mutations resulting in defects in oxidative phosphorylation system, and causing suppressed oxygen utilization. Such oxygen stress furthers mitochondrial DNA mutations during the progressive course of the disease. This noninvasive diagnosis will find useful application in the diagnosis and management of patients of advanced age.

A 31P magnetic resonance spectroscopy study of mitochondrial function in skeletal muscle of patients with Parkinson's disease

The activity of complex I of the respiratory chain is decreased in the substantia nigra of patients with Parkinson's disease (PD) but the presence of this defect in skeletal muscle is controversial. Therefore, the mitochondrial function of skeletal muscle in patients with PD was investigated in vivo using 31P magnetic resonance spectroscopy. Results from 7 PD patients, 11 age matched controls and 9 mitochondrial myopathy patients with proven complex I deficiency were obtained from finger flexor muscle at rest, during exercise and in recovery from exercise. In resting muscle, the patients with mitochondrial myopathy showed a low PCr ATP ratio, a low phosphorylation potential, a high P i PCr ratio and a high calculated free [ADP]. During exercise, stores of high energy phosphate were depleted more rapidly than normal, while in recovery, the concentration of phosphocreatine and free ADP returned to pre-exercise values more slowly than normal. In contrast, the patients with PD were not significantly different from normal for any of these variables, and no abnormality of muscle energetics was detected. Three of the PD patients also had mitochondrial function assessed biochemically in muscle biopsies. No respiratory chain defect was identified in any of these patients by polarography or enzyme analysis when compared with age-matched controls. These results suggest that skeletal muscle is not a suitable tissue for the investigation and identification of the biochemical basis of the nigral complex I deficiency in PD.

Skeletal muscle bioenergetics in myotonic dystrophy

Skeletal muscle function of 15 patients with myotonic dystrophy (dystrophia myotonica, DM) was investigated using 31P magnetic resonance spectroscopy to evaluate bioenergetics and intracellular pH at rest and during exercise and recovery. Results from DM patients, normal controls and mitochondrial myopathy patients were compared in order to assess the possible contribution of abnormal mitochondrial metabolism to muscle dysfunction in DM. In resting DM muscle, intracellular pH (pH i) was normal, but there were significant elevations in the concentration ratios of P i ATP , phosphomonoesters/ATP and phosphodiesters/ATP. In patients with the most severe exercise intolerance the phosphocreatine ATP ratio was also reduced. Resting muscle of 11 mitochondrial myopathy patients showed similar changes to those of the most exercise-intolerant DM patients. In exercising DM muscle, energy stores were rapidly depleted as in mitochondrial myopathy. Muscle acidified in all subjects, but in DM the decrease in pH i was less than in normal muscle. Recovery half-times for phosphocreatine, P i and ADP were normal in DM but slow in mitochondrial myopathy. The initial rate of phosphocreatine repletion after exercise was rapid in DM, consistent with high [ADP], but slow in mitochondrial myopathy in spite of elevated [ADP]. Because recovery is an oxidative process, we conclude that there was no decrease in the oxidative capacity of the muscles in this group of DM patients. In the subjects in whom it could be measured, the rate of recovery of intracellular pH was greater in the 3 DM patients (0.14, 0.15 and 0.16 U/min) than in the 7 normal controls (0.08–0.12 U/min, mean 0.10). The results do not rule out a minor abnormality in glycogenolysis, but they suggest that the failure to acidify normally during exercise is probably due to rapid proton efflux.

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) and diabetes mellitus: molecular genetic analysis and family study

Two MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) patients with diabetes mellitus (DM), and their family members are described clinically and genetically. The probands have the following features in common; normal early development, short stature, deterioration of intellectual ability, convulsions, cardiac conduction defect, sensorineural hearing loss, cortical blindness, and hemiparesis. Biochemical tests showed high levels of lactate and pyruvate in the blood and cerebrospinal fluid. Muscle biopsy showed ragged-red fibers. Molecular genetic analysis of both patients revealed that they had an A-to-G substitution at nucleotide position 3243 of the mitochondrial DNA in a heteroplasmic fashion. From these clinical and molecular genetic data they were diagnosed as having MELAS. In addition, fasting blood glucose levels were also high and they were diagnosed as having insulin-dependent DM. Some of the maternal family members in both cases also had insulin-dependent DM and several clinical symptoms of MELAS. DM and clinical features of MELAS were transmitted exclusively in the maternal line. In these cases, DM and MELAS might be a clinical manifestation of the same metabolic defect.