ATP, phosphocreatine and lactate in exercising muscle in mitochondrial disease and McArdle's disease

We studied exercise-induced changes in the adenosine triphosphate (ATP), phosphocreatine (PCr), and lactate levels in the skeletal muscle of mitochondrial patients and patients with McArdle's disease. Needle muscle biopsy specimens for biochemical measurement were obtained before and immediately after maximal short-term bicycle exercise test from 12 patients suffering from autosomal dominant and recessive forms of progressive external ophthalmoplegia and multiple deletions of mitochondrial DNA (adPEO, arPEO, respectively), five patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) 3243 A-->G point mutation, and four patients with McArdle's disease. Muscle ATP and PCr levels at rest or after exercise did not differ significantly from those of the controls in any patient group. In patients with mitochondrial disease, muscle lactate tended to be lower at rest and increase more during exercise than in controls, the most remarkable rise being measured in patients with adPEO with generalized muscle symptoms and in patients with MELAS point mutation. In McArdle patients, the muscle lactate level decreased during exercise. No correlation was found between the muscle ATP and PCr levels and the respiratory chain enzyme activity.     

Residual muscle cytochrome c oxidase activity accounts for submaximal exercise lactate threshold in chronic progressive external ophthalmoplegia

The data from histological, biochemical, and mitochondrial DNA (mtDNA) studies of muscle biopsies from 10 patients affected with chronic progressive external ophthalmoplegia (CPEO) were related to dynamic and metabolic parameters of incremental submaximal exercise. Maximum power output was reduced in all patients as compared to controls. Analysis of the venous lactate curve during exercise revealed a lactate threshold at exercise levels ranging from 40 to 50% of the predicted maximal power output. An earlier significant increase in lactate could be detected by calculating the mean δ lactate. Lactate values were inversely correlated with the cytochrome c oxidase (COX) activity of isolated muscle mitochondria. No relationship was found between lactate values and the number of ragged red fibers, or cytochrome c oxidase-negative fibers or the proportion of deleted mtDNA measured in muscle biopsy specimens. The discussion underscores the value of lactate kinetics in assessing skeletal muscle function, as well as the use of muscle COX levels to predict the effectiveness of wild-type complementation of deleted skeletal muscle mtDNA in in vivo contractile performance of CPEO subjects. © 1996 John Wiley & Sons, Inc.     

Is Parkinson's disease a mitochondrial disorder?

Parkinson's disease (PD) is a common degenerative disease, but its etiology is still unknown. However, since the discovery of MPTP, many investigators have been interested in the mitochondrial function in PD. We investigated mitochondrial functions in PD patients using the methods which have successfully been applied to mitochondrial myopathies (MM), i.e. assay of lactate and pyruvate, measurement of muscle mitochondrial respiratory enzyme activities and Southern blot analysis of muscle mitochondrial DNA. Parkinson's disease patients did not differ from controls in the mean blood and CSF (cerebrospinal fluid) lactate and pyruvate levels at the basal resting state or during an aerobic exercise. But mitochondrial complex I activity of the skeletal muscle was significantly decreased in PD. In the Southern blot analysis, we could not find major deletions or insertions of mitochondrial DNA in PD. Our studies disclosed a differential mitochondrial impairment between PD and MM. We discuss the implication of our observation.     

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     

Low anaerobic threshold and increased skeletal muscle lactate production in subjects with Huntington's disease

Mitochondrial defects that affect cellular energy metabolism have long been implicated in the etiology of Huntington's disease (HD). Indeed, several studies have found defects in the mitochondrial functions of the central nervous system and peripheral tissues of HD patients. In this study, we investigated the in vivo oxidative metabolism of exercising muscle in HD patients. Ventilatory and cardiometabolic parameters and plasma lactate concentrations were monitored during incremental cardiopulmonary exercise in twenty‐five HD subjects and twenty‐five healthy subjects. The total exercise capacity was normal in HD subjects but notably the HD patients and presymptomatic mutation carriers had a lower anaerobic threshold than the control subjects. The low anaerobic threshold of HD patients was associated with an increase in the concentration of plasma lactate. We also analyzed in vitro muscular cell cultures and found that HD cells produce more lactate than the cells of healthy subjects. Finally, we analyzed skeletal muscle samples by electron microscopy and we observed striking mitochondrial structural abnormalities in two out of seven HD subjects. Our findings confirm mitochondrial abnormalities in HD patients' skeletal muscle and suggest that the mitochondrial dysfunction is reflected functionally in a low anaerobic threshold and an increased lactate synthesis during intense physical exercise. © 2010 Movement Disorder Society     

Effects of aerobic training on lactate and catecholaminergic exercise responses in mitochondrial myopathies

The aim of this study was to evaluate the effects of an aerobic training program on the metabolic and sympathetic responses to exercise in 12 patients with mitochondrial myopathies. A 10-week course of aerobic training, consisting of supervised exercise every other day on an electrically braked pedal-rate bicycle ergometer was prescribed to each patient and four healthy controls. Venous lactate, epinephrine (EP) and norepinephrine (NEP) levels were assessed at baseline and after the aerobic training by means of constant-workload exercise performed at near lactate threshold (LT). In patients, a decrease in exercise peak values, significant for lactate (-38.6%, P < 0.01) but not for catecholamines (EP: -26.0%, NEP: -22.1%) was observed after training, findings confirmed by the lactate/EP and lactate/NEP area ratios. The results show that lactate accumulation during exercise is decreased after aerobic training in mitochondrial myopathies and that the effect is partially dissociated from the catecholaminergic response. This in turn suggests that the lactate decrease can be explained, at least in part, by the improved muscle oxidative metabolism consequent to the proposed training program.     

Lactate metabolism during exercise in patients with mitochondrial myopathy

Patients with mitochondrial DNA mutations often have elevated plasma lactate at rest and during exercise, but it is unknown whether the high lactate levels are caused by a high production, an impaired oxidation or a combination. We studied lactate kinetics in 10 patients with mtDNA mutations and 10 matched healthy control subjects at rest and during cycle exercise with a combination of femoral arterio-venous differences of lactate, and lactate tracer dilution methodology. During exercise, lactate concentration and production rates were several-fold higher in patients, but despite mitochondrial dysfunction, lactate was oxidized in muscle to the same extent as in healthy control subjects. This surprisingly high ability to burn lactate in working muscle with defective mitochondria, probably relates to the variability of oxidative capacity among muscle fibers. The data suggests that lactate is not solely an indicator of impaired oxidative capacity, but an important fuel for oxidative metabolism, even in muscle with severely impaired mitochondrial function.     

A patient with mitochondrial encephalomyopathy presenting gynecomastia with elevation of serum estriol level]

We report a 23-year-old man with mitochondrial encephalomyopathy. At 21 years of age, he noted speech distubance. Since his dysarthria did not improve thereafter, he was admitted to our hospital. On admission, he showed mild gynecomastia. Neurological examination revealed mild decrease in performance IQ in WAIS-R, mild scanning speech, mild left hearing disturbance, mild to moderate muscle weakness in proximal four extremities, mild bilateral limb ataxia, and mild to moderate truncal ataxia. While, no brisk deep tendon reflex, pathological reflex, aberrant muscle tonus, sensory disturbance, retinopathy, myoclonus or autonomic disorder was found. Serum levels of lactate (23.2 mg/dl, normal<18.7) and pyruvate (1.23 mg/dl, normal<0.94) were elevated, and serum lactate levels were markedly elevated (118.1 mg/dl) after 15-minute exercise (15 Watts/minute). CSF levels of lactate (31.2 mg/dl, normal<12.5) and pyruvate (1.48 mg/dl, normal<0.75) were also elevated. Head MRI showed mild cerebral and cerebellar atrophy, but 1H-MRS showed no lactate peak. Moreover, muscle biopsy from left biceps muscle showed lots of ragged-red fibers, and he was thus diagnosed as having mitochondrial encephalomyopathy. However, nt3243 mutation of mitochondria DNA was not present. Next, we confirmed gynecomastia by mammography, and checked serum levels of estrogens. Mildly decreased estradiol (19.9 pg/ml, normal, 20-59), normal estrone (24.0 pg/ml, normal<30.0) and mildly increased estriol (6.03 pg/ml, normal<5.0) were found. While, the serum levels of cortisol, dehydroepiandrosterone-sulfate (DHEA-S), androstenedione, testosterone, luteinizing hormone (LH) and follicle stimulating hormone (FSH) were all within normal limits. Since the steroid hormone synthesis system and hypothalamus-pituitary system seem to be normal, 16alpha-hydroxylase that converts estradiol to estriol may be upregulated. While, aromatase (P-450arom) is well known to convert androgens to estrogens. In addition, 16alpha-hydroxylase and P-450arom convert DHEA-S to estriol. Since it is recently reported that P-450arom is considerably expressed in muscle tissues as well as fat tissues and that muscle tissue may be a major organ to produce estrogens in men and postmenopausal women, estriol production may be increased in the present patient's muscle. Although hypogonadism due to hypothalamus-pituitary disorders was sometimes reported, there have been no reports that suggest an increased estrogen production in skeletal muscles in mitochondrial encephalomyopathies. Recently, estrogen has been known to protect muscle fibers from oxidative damages due to exercise. Thus, it is of potential that estrogens increased locally in muscle tissues of the patients with mitochondrial encephalomyopathies protect muscle fibers from oxidative damage due to mitochondrial dysfunction.     

Mitochondrial respiratory-chain defects presenting as nonspecific features in children

Patients with mitochondrial respiratory-chain defects frequently exhibit lactic acidosis, ragged red fibers in skeletal muscle samples, and abnormal enzyme assays for the respiratory-chain complex. However, ragged red fibers and lactic acidosis are not always seen in all patients with mitochondrial respiratory-chain defects. We have encountered six children with biochemically proven respiratory chain defects, but typical ragged red fibers were not found in all six patients, and only five patients had increased serum lactate levels. Initially, they present with nonspecific features. However, persistent or progressive clinical features or multiple organ involvement eventually led to the diagnosis of respiratory-chain defects in these patients. Mitochondrial respiratory-chain defects should be considered in the differential diagnosis when persistent, progressive features and especially multiple organ involvement occur.     

Skeletal muscle bioenergetics in the chronic fatigue syndrome.

Skeletal muscle bioenergetics and control of intracellular pH have been investigated in 46 patients with chronic fatigue syndrome by phosphorus magnetic resonance spectroscopy. The results have been compared with those from healthy controls and from a group of patients with mitochondrial cytopathies affecting skeletal muscle. No consistent abnormalities of glycolysis, mitochondrial metabolism or pH regulation were identified in the group when taken as a whole, although in 12 of the 46 patients the relationship between pH and phosphocreatine utilisation during exercise fell outside the normal range. Of these, 6 patients showed increased acidification relative to phosphocreatine depletion while 6 showed reduced acidification. These findings do not support the hypothesis that any specific metabolic abnormality underlies fatigue in this syndrome although abnormalities may be present in a minority of patients.     

The effects of partial chronic denervation on forearm metabolism.

Effects of chronic denervation upon in vivo forearm metabolism were studied in six patients and six controls. The diagnosis was amyotrophic lateral sclerosis in four patients, the neuronal form of Charcot-Marie Tooth disease in one patient, and an unclassified chronic disease of the lower motor neurons in one patient. In all cases the forearm muscles showed clinical weakness and electrical evidence of denervation, while muscle biopsy from a proximal muscle of the upper limb showed typical denervation atrophy. At rest there was increased oxygen utilization and lactate output as well as a tendency for increased uptake of glucose and long chain fatty acids from arterial blood per 100 ml of forearm tissue. During exercise the abnormally high lactate output increased further. An increased arterial lactate concentration was present during rest and exercise. Oxidation of fatty acids was not impaired. It is suggested that these abnormalities are consistent with an augmented utilization of blood borne fuels at rest by denervated muscles. A concurrent regional ischemia of muscles during rest and exercise, possibly due to defective autoregulation of skeletal muscle blood flow, may explain the abnormally high lactate generation.     

Chronic fatigue and myalgia syndrome: mitochondrial and glycolytic studies in skeletal muscle.

Clinical and biochemical findings in skeletal muscle in 11 patients with chronic fatigue myalgia syndromes of unknown aetiology are reported. All patients had severe asthenia for from one to 10 years with greatly limited exercise capacity and protracted exhaustion after minor exercise. Diffuse myalgia was prominent and was exacerbated for hours to days after exercise. Assay of skeletal muscle carnitine, phosphorylase, all glycolytic enzymes and the mitochondrial marker enzymes monoamine oxidase, isocitrate dehydrogenase and cytochrome oxidase were normal. These findings lend no support to the presence of a major defect in muscle intermediary energy pathways in this syndrome.     

Improvement of abnormal pyruvate metabolism and cardiac conduction defect with coenzyme Q10 in Kearns-Sayre syndrome

In a patient with Kearns-Sayre syndrome, concentration of coenzyme Q10, a component of the mitochondrial electron transport system, was decreased in serum and in the mitochondrial fraction of skeletal muscle. Serum concentrations of lactate and pyruvate were abnormally high, especially after exercise or oral glucose loading. Levels of folic acid in plasma and CSF were decreased. ECG showed a first-degree atrioventricular block. After administration of coenzyme Q10 60 to 120 mg daily for 3 months, serum levels of lactate and pyruvate became normal, with improvement of atrioventricular block and ocular movements.     

Partial deficiency of complexes I and IV of the mitochondrial respiratory chain in skeletal muscle of two patients with mitochondrial myopathy

Summary Respiratory chain enzymes were studied in isolated mitochondria of two patients with mitochrondrial myopathy. Both patients had been suffering from chronic progressive external ophthalmoplegia and abnormal muscular fatigability since late childhood. One of the patients exhibited the complete triad of symptoms characteristic of Kearns-Sayre syndrome. Venous lactate levels at rest and during minimal exercise were increased in both patients. Histochemical examination of muscle revealed ragged red fibres and intermingled fibres negative for cytochrome c oxidase. Biochemical studies showed decreased activities of complex I and complex IV of the respiratory chain in both patients. Reduced minus oxidized spectra of mitochondrial cytochromes revealed a decreased content of cytochrome aa₃ in only one patient, but a normal content in the other. A combined deficiency of complexes I and IV in muscle might either be due to a deficiency of a single subunit common to both complexes or to a coincidental deficiency of both complexes expressed either in the same or in different fibres.     

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.     

Clinical and biochemical correlations in mitochondrial myopathies treated with coenzyme Q10

We tested the efficacy of coenzyme Q10 (ubidecarenone, CoQ10) therapy in patients with Kearns-Sayre syndrome and other mitochondrial myopathies with chronic progressive external ophthalmoplegia (CPEO). We treated seven patients for 1 year with daily oral administration of 120 mg of CoQ10. Throughout the treatment most of our patients showed a progressive reduction of serum lactate and pyruvate levels following standard muscle exercise and generally improved neurologic functions. The ECG and echocardiogram showed no significant changes in our patients. None of our patients showed any improvement in ptosis and CPEO.     

Die Spiroergometrie in der Diagnostik mitochondrialer Erkrankungen

Cardiopulmonary exercise testing (CPX) is a non-invasive method of recording quantitative data from gas exchange and ventilation for the evaluation of oxidative metabolism at rest and during exercise. Determination of oxygen uptake (VO2) and carbon dioxide output (VCO2) describes the activity of anaerobic vs aerobic metabolism. An incremental exercise test measuring gas exchange, ventilation and lactate release was performed in healthy volunteers and in patients suffering from mitochondrial disorders. At rest as well as during exercise patients with mitochondrial disorders differ from healthy subjects with regard to gas exchange and ventilation parameters. During exercise, the decreased oxygen utilization of skeletal muscle and early activation of anaerobic metabolism in these patients are mirrored by a reduced anaerobic threshold, reduced maximal oxygen uptake and reduced oxygen pulse. Our study shows that CPX is a sensitive and practical clinical screening method of investigating mitochondrial disorders.     

Increased metabolic muscle fatigue is caused by some but not all mitochondrial mutations

CONTEXT: Excessive muscle fatigue occurs in patients with a mitochondrial encephalomyopathy (MEM), but it is also a frequent problem in patients with other neuromuscular disorders (ONMD). OBJECTIVE: To determine whether, and to what extent, metabolic muscle fatigue specifically occurs in patients with an MEM. DESIGN: Metabolic muscle fatigue was assessed in a series of 21 patients with an MEM, including 13 patients with chronic progressive external ophthalmoplegia and 8 patients with various mitochondrial point mutations; 27 patients with ONMD; and 25 healthy controls. Isometric twitch force of the ankle dorsiflexors was measured after supramaximal stimulation of peroneal nerves. Six trains of stimuli (of 1 minute's duration with rates from 0.2 to 5 stimuli per second) were given to each subject. RESULTS: An abnormal decrement of the twitch amplitude that occurred during a stimulation train was found in patients with MEM and in those with ONMD. The decrement of the twitch amplitude of controls and of patients with ONMD was strongly influenced by their muscle force (P<.001). After subtraction of the influence of the muscle force, specific fatigue was notably higher in patients with chronic progressive external ophthalmoplegia than in patients with ONMD and in controls, and it correlated well with elevations of serum lactate. Specific fatigue was also abnormal in a patient with a mitochondrial G7497A mutation, but normal in patients with an A3243G or a G11778A mutation. The heteroplasmy of mitochondrial DNA in muscle correlated neither with the force measures nor with the serum lactate levels. CONCLUSIONS: Generally, metabolic muscle fatigue accompanies muscular weakness. Specifically, some but not all mitochondrial mutations cause excessive metabolic muscle fatigue.     

Leber's hereditary optic neuropathy: genetic, biochemical, and phosphorus magnetic resonance spectroscopy study in an Italian family

Three siblings of a family affected with Leber's hereditary optic neuropathy (LHON) showed a mitochondrial DNA mutation at position 11778. The lactate response to a standardized effort was increased in only one case. Muscle biopsies and biochemistry of muscle and platelet mitochondrial enzymes were normal. All patients showed an altered energy metabolism during exercise and during recovery after exercise on phosphorus 31-magnetic resonance spectroscopy (31P-MRS) of muscle. Brain 31P-MRS showed a decreased energy reserve (decreased PCr/Pi ratio) in all patients. 31P-MRS noninvasively demonstrated an altered mitochondrial energy metabolism in muscle and, for the first time, in the brains of LHON patients.