Investigation of human mitochondrial myopathies by phosphorus magnetic resonance spectroscopy

Abnormal mitochondria are an increasingly recognized cause of neuromuscular disease. We have used phosphorus magnetic resonance spectroscopy to monitor noninvasively the metabolism of high-energy phosphates and the intracellular pH of human skeletal muscle in vivo in 12 patients with mitochondrial myopathy. At rest, an abnormality could be demonstrated in 11 of 12 patients. Ten patients had evidence of a reduced muscle energy state with at least one of the following abnormalities: low phosphorylation potential, low phosphocreatine concentration, high adenosine diphosphate concentration, or high inorganic phosphate concentration. Two patients had abnormal resting muscle intracellular pH. In some patients phosphocreatine concentration decreased to low values during exercise despite limited work output. This was not accompanied by particularly severe intracellular acidosis. Evidence of impaired rephosphorylation of adenosine diphosphate to adenosine triphosphate during recovery from exercise was found in approximately half the patients. Phosphorus magnetic resonance spectroscopy is useful in the noninvasive diagnosis of mitochondrial myopathies and in defining the pathophysiological basis of these disorders.     

In vivo magnetic resonance spectroscopy of brain and muscle in a type of mitochondrial encephalomyopathy (MERRF)

Phosphorus magnetic resonance spectroscopy allows noninvasive measurement of the intracellular phosphate-containing metabolites and intracellular pH in localized volumes of human muscle and brain in vivo. This technique was used to study 8 patients with a mitochondrial cytopathy (myoclonus epilepsy with ragged red fibers). Phosphorus magnetic resonance spectroscopy of resting gastrocnemius muscle demonstrated significantly increased relative intracellular inorganic phosphate concentrations (p less than 0.0005) and decreased phosphocreatine to inorganic phosphate concentration ratios (p less than 0.01) in the patients, although only 3 had myopathic signs or symptoms. We propose, therefore, that phosphorus magnetic resonance spectroscopy of resting skeletal muscle is a useful clinical test in evaluation of progressive myoclonus epilepsy. In contrast to results from muscle, however, the relative phosphate metabolite concentrations and intracellular pH in central volumes of the brains of these patients were normal, despite evidence from our previous positron emission tomography studies suggesting that there is diffuse impairment of cerebral oxidative metabolism.     

Phosphorus magnetic resonance spectroscopy (31P MRS) in neuromuscular disorders.

Phosphorus magnetic resonance spectroscopy monitors muscle energy metabolism by recording the ratio of phosphocreatine to inorganic phosphate at rest, during exercise, and during recovery from exercise. In mitochondrial diseases, abnormalities may appear during some or all these phases. Low phosphocreatine-inorganic phosphate ratios at rest are not disease-specific, but can be increased by drug therapy in several myopathies. Phosphorus magnetic resonance spectroscopy can also record intracellular pH and thus identify disorders of glycogen metabolism in which the production of lactic acid is blocked during ischemic exercise. The measurements of accumulated sugar phosphate intermediates further delineate glycolytic muscle defects. Myophosphorylase deficiency responds to intravenous glucose administration with improved exercise bioenergetics, but no such response is seen in phosphofructokinase deficiency. The muscular dystrophies show no specific bioenergetic abnormality; however, elevation of phospholipids metabolites and phosphodiesters was detected in some cases. While phosphorus magnetic resonance spectroscopy remains primarily a research tool in metabolic myopathies, it will be clinically useful in identifying new therapies and monitoring their effects in a variety of neuromuscular disorders.     

Application of NMR spectroscopy to monitoring MELAS treatment: a case report

1H magnetic resonance spectroscopy (MRS) of the brain and (31)P MRS and saturation transfer of resting skeletal muscle were used to investigate intracellular metabolites and fluxes through the creatine kinase (CK) reaction in a patient with the syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS). Acute cortical lesions were characterized by severely elevated lactate levels and reduced concentrations of N-acetylaspartyl compounds, glutamate, and myo-inositol. Similar but less extreme alterations were also observed in gray matter regions that appeared normal on magnetic resonance images. Investigation of the gastrocnemius muscle at rest demonstrated a reduced phosphocreatine level, elevated concentrations of inorganic phosphate and free adenosine 5'-diphosphate, and an abnormally low phosphorylation potential. Besides a moderately increased muscular phosphocreatine concentration, none of the metabolic disturbances detected on MRS improved with oral creatine supplementation. Forward and reverse fluxes through the CK reaction did not significantly change upon creatine treatment. Follow-up MRS investigations may thus provide objective markers of treatment response in vivo without the hazards or inconvenience of biopsy.     

Bioenergetic heterogeneity of human mitochondrial myopathies: phosphorus magnetic resonance spectroscopy study

Twelve adults with mitochondrial myopathies were studied by phosphorus magnetic resonance spectroscopy of muscle. All 12 had abnormal 31P-NMR findings; recovery from exercise was abnormal in 11 patients. At rest, the ratio of phosphocreatine to inorganic phosphate was reduced in 10. Exercise transfer characteristics were abnormal in all five patients who could exercise. Exercise-induced intracellular acidosis was subnormal in nine patients. The range of abnormalities indicates biochemical heterogeneity, with two possible groups: primary defects of energy metabolism with marked 31P-NMR abnormalities, and secondary, less specific 31P-NMR abnormalities.     

Exploration of exercise intolerance by 31P NMR spectroscopy of calf muscles coupled with MRI and ergometry

One hundred patients presenting with exercise intolerance or rhabdomyolysis episodes have been examined successively by 31P Nuclear Magnetic Resonance Spectroscopy (MRS) of leg plantar flexor muscles with exercise test. In all cases a muscle biopsy was performed. At the end of investigations, diagnosis of a metabolic myopathy was made in 33 patients: glycogenolysis or glycolysis deficiency in 8 cases, mitochondrial myopathy in 24 cases and CPT II deficiency in one case. Muscular dystrophy or congenital myopathy were diagnosed in 6 cases. No precise etiology could be found in 30 patients with either high CK levels or muscle biopsy abnormalities. Seven patients had rhabdomyolysis related to excessive physical activities. Twenty-four patients had functional symptoms. The principal MRS parameters used for diagnosis were the values of intracellular pH at the end of exercise and the time constant of phosphocreatine resynthesis during recovery. Lack of acidosis after exercise was observed in all patients with blockade of glycogenolysis or glycolysis. A slowing in phosphocreatine resynthesis was found in 66 p.cent of patients with definite mitochondrial myopathy. The specificity of these parameters were respectively 92.4 p.cent and 85.5 p.cent for the two groups. In conclusion (31)P MRS allows the detection of muscular glycogenoses with a sensitivity close to 100 p.cent. However, its sensitivity was lower for the detection of mitochondrial myopathies, as is also known for the other in vivo metabolic investigations, reflecting the heterogeneity of expression of mitochondrial abnormalities in a given muscle. The integration of imaging in the examination protocol may help to orientate towards the diagnostic of a dystrophy in some patients.     

The brain is hypothermic in patients with mitochondrial diseases

We sought to study brain temperature in patients with mitochondrial diseases in different functional states compared with healthy participants. Brain temperature and mitochondrial function were monitored in the visual cortex and the centrum semiovale at rest and during and after visual stimulation in seven individuals with mitochondrial diseases (n=5 with mitochondrial DNA mutations and n=2 with nuclear DNA mutations) and in 14 age- and sex-matched healthy control participants using a combined approach of visual stimulation, proton magnetic resonance spectroscopy (MRS), and phosphorus MRS. Brain temperature in control participants exhibited small changes during visual stimulation and a consistent increase, together with an increase in high-energy phosphate content, after visual stimulation. Brain temperature was persistently lower in individuals with mitochondrial diseases than in healthy participants at rest, during activation, and during recovery, without significant changes from one state to another and with a decrease in the high-energy phosphate content. The lowest brain temperature was observed in the patient with the most deranged mitochondrial function. In patients with mitochondrial diseases, the brain is hypothermic because of malfunctioning oxidative phosphorylation. Neuronal activity is reduced at rest, during physiologic brain stimulation, and after stimulation.     

Merosin-positive congenital muscular dystrophy: neuroimaging findings

Congenital muscle dystrophy (CMD) is a heterogeneous group of autosomal recessive myopathies. It is known that CMD may affect the central nervous system (CNS). Some authors have shown that merosin-negative CMD patients may have encephalic metabolic disturbances. In order to study metabolic changes within the brain, the authors performed a magnetic resonance spectroscopy (MRS) study in a 1-year-old girl with merosin-positive CMD (MP-CMD). MRS of brain demonstrated that NAA/Cr ratio was decreased (1.52), while Cho/Cr ratio was increased (1.78). These findings suggest that metabolic changes in CNS can also be found in patients with MP-CMD.     

Muscle phosphorus magnetic resonance spectroscopy oxidative indices correlate with physical activity

The purpose of this study was to assess the effect of physical deconditioning on skeletal muscle's oxidative metabolism as evaluated by phosphorus-31 magnetic resonance spectroscopy ((31)P MRS). Twenty-seven subjects without muscle disease, representing a wide range of fitness levels, were evaluated with (31)P MRS. Spectra were obtained at rest and during recovery from in-magnet exercise. The data show a significant correlation between maximum resting metabolic equivalent (MET) score and the following (31)P MRS recovery indices: adenosine diphosphate and phosphocreatine recovery half-time; initial phosphocreatine resynthesis rate; calculated estimation of mitochondrial capacity; pH at end of exercise; and phosphocreatine depletion. In addition, significant differences between the deconditioned and conditioned group were found for all of the aforementioned recovery indices. At rest, only the inorganic phosphate concentration was significantly different between the two groups. These data indicate that physical activity level should be taken into account when assessing patients' oxidative metabolism with (31)P MRS.     

Treatment of mitochondrial myopathy due to complex III deficiency with vitamins K3 and C: A 31P-NMR follow-up study

A patient with mitochondrial myopathy due to complex III deficiency who was treated with vitamin K3 (menadiol sodium diphosphate, 40 mg daily) and vitamin C showed clinical improvement. A 1-year study with phosphorus 31 nuclear magnetic resonance (31P-NMR) monitoring has shown that clinical and metabolic improvement was maintained by this therapy; increasing the dose of vitamin K3 to 80 mg daily improved the bioenergetic state of the patient's muscles at rest; postexercise recovery was less responsive to the increased dose; and a higher dose of vitamin K3 (80 mg/day) did not produce side effects. The differential therapeutic effects of vitamin K3 at rest and during exercise recovery are probably due to the differential kinetics of each metabolic state. Monitoring muscle bioenergetics with 31P-NMR is valuable in documenting therapeutic improvements in mitochondrial myopathies.     

MELAS syndrome with mitochondrial tRNA(Leu)(UUR) mutation: correlation of clinical state, nerve conduction, and muscle 31P magnetic resonance spectroscopy during treatment with nicotinamide and riboflavin.

We report a patient with mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes treated with riboflavin and nicotinamide for 18 months, during which time previously frequent encephalopathic spells ceased. To confirm clinical benefit, we withdrew treatment and monitored response with muscle 31P magnetic resonance spectroscopy (MRS) and sural nerve conduction studies. Of three prospectively chosen MRS variables, two changed coincidentally with clinical end points; phosphocreatine (PCr)/adenosine triphosphate recovery rates fell in parallel with sural nerve sensory amplitudes, and a drop in muscle bioenergetic efficiency (relationship of inorganic phosphate/PCr to the accelerating force of contracting muscle) coincided with development of encephalopathy. Investigations revealed a deficiency of respiratory complex I and mutation of the mitochondrial tRNA(Leu)(UUR). We suggest that a defective cellular energy state in mitochondrial disease may be partially treatable and that changes seen in appropriate muscle spectroscopy studies may parallel improvement in brain and peripheral nerve function.     

Proton magnetic resonance spectroscopy for the diagnosis and management of cerebral disorders.

The use of magnetism in medicine has a long and colorful history since its legendary discovery in the Western world by the shepherd Magnes. More recent use of magnetism has centered on nuclear magnetic resonance. Magnetic resonance spectroscopy (MRS) provides chemical information on tissue metabolites. Both hydrogen 1 (1H) and phosphorus 31 resonances have been used to study brain tissue, but the magnetic resonance sensitivity for protons is far greater than it is for phosphorus. One of the most important contributions of 1H-MRS to clinical neurology is its ability to quantify neuronal loss and to demonstrate reversible neuronal damage. 1H-magnetic resonance spectroscopy has been found to be a useful research tool in elucidating the pathophysiology underlying certain diseases. This review focuses on the use of proton MRS to study various neurologic diseases, including epilepsy, multiple sclerosis, brain tumors, human immunodeficiency virus 1-associated neurologic disorders, as well as cerebrovascular, neurodegenerative, and metabolic diseases. It highlights the contributions of 1H-MRS to the diagnosis and the monitoring of these neurologic diseases that make it a useful adjunct in patient management.     

Impairment of muscle mitochondrial oxidative metabolism in McArdle's disease

Impairment of muscle glycogenolysis in McArdle's disease (myophosphorylase deficiency) leads to exercise intolerance and exercise-induced myalgia. The pathophysiology of these symptoms is not entirely clear. We used phosphorus magnetic resonance spectroscopy to measure muscle phosphate metabolite concentrations and intracellular pH during brief ischemic exercise and in the period of aerobic metabolic recovery after exercise, with special attention to cytoplasmic adenosine 5′-diphosphate (ADP). In 5 patients with McArdle's disease, calculated muscle intracellular ADP concentrations at the beginning of recovery were higher than in normal control subjects (70–425 mmol/L, control mean: 73 ± 40 mmol/L, P < 0.05). The half-time for intracellular ADP recovery after exercise, an index of maximal mitochondrial oxidative phosphorylation, was 0.16 ± 0.07 in normal controls and was independent of metabolic state or intracellular pH. ADP recoveries were abnormally slow in all patients with McArdle's disease (range: 0.32–0.83 min, mean = 0.2 min, P < 0.0001). These results are indicative of a limitation in the rate of oxidative phosphorylation in muscle of patients with McArdle's disease, most likely due to impaired substrate delivery to mitochondria. This impairment of mitochondrial function may contribute to the exercise-related symptoms in McArdle's disease. © 1996 John Wiley & Sons, Inc.     

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.     

Magnetic resonance imaging and magnetic resonance spectroscopy for detection of early Alzheimer's disease

Alzheimer's disease is the most common form of neurodegenerative disorder and early detection is of great importance if new therapies are to be effectively administered. We have investigated whether the discrimination between early Alzheimer's disease (AD) and elderly healthy control subjects can be improved by adding magnetic resonance spectroscopy (MRS) measures to magnetic resonance imaging (MRI) measures. In this study 30 AD patients and 36 control subjects were included. High resolution T1-weighted axial magnetic resonance images were obtained from each subject. Automated regional volume segmentation and cortical thickness measures were determined for the images. 1H MRS was acquired from the hippocampus and LCModel was used for metabolic quantification. Altogether, this yielded 58 different volumetric, cortical thickness and metabolite ratio variables which were used for multivariate analysis to distinguish between subjects with AD and Healthy controls. Combining MRI and MRS measures resulted in a sensitivity of 97% and a specificity of 94% compared to using MRI or MRS measures alone (sensitivity: 87%, 76%, specificity: 86%, 83% respectively). Adding the MRS measures to the MRI measures more than doubled the positive likelihood ratio from 6 to 17. Adding MRS measures to a multivariate analysis of MRI measures resulted in significantly better classification than using MRI measures alone. The method shows strong potential for discriminating between Alzheimer's disease and controls.     

Evidence for mitochondrial dysfunction in patients with alternating hemiplegia of childhood

Phosphorus magnetic resonance spectra of resting muscle were obtained from 4 patients with alternating hemiplegia of childhood. All patients had abnormally high resonance intensities from inorganic phosphate and an abnormally law calculared cytosolic phosphorylation potential. Tow of the 4 patients had abnormally law resonance intensities from phosphocreatine and an abnormally high calculated cytosolic free adenosine diphosphare conecntration. These abnormalities are indicative of mitochondrial dysfunction. The combination of a central nervous system disorder and evidence of mitochondrial dysfunction in muscle suggests that alternating hemiplegia of childhood may represent a previously unrecognized phenotype of mitochondrial disease.     

Muscle high-energy phosphates in central nervous system disorders. The phosphorus MRS experience

Phosphorus magnetic resonance spectroscopy (MRS) was used to study muscle phosphates metabolism in several brain disorders. Those with primary mitochondrial encephalomyopathies showed the typical pattern of impaired oxidative metabolism at rest and during recovery after exercise. In migraine, Parkinson's disease and alternating hemiplegia muscle MRS observations lend support to a possible mitochondrial dysfunction. Similar observations in multiple sclerosis are probably the result of secondary deconditioning. In post polio syndrome and in some of the hereditary ataxias, elevated intracellular inorganic phosphates may be the result of another, yet unknown, metabolic impairment. Thus, muscle phosphate metabolism may be altered in various central nervous system (CNS) disorders by different metabolic impairments. All these possibilities should be taken into account when evaluating MRS results in brain diseases.

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Sommario La risonanza magnetica spettroscopica del fosforo è usata per studiare il metabolismo dei fosfati del muscolo in molti disordini cerebrali. Le encefalomiopatie mitocondriali primitive evidenziano un pattern tipico di alterato metabolismo muscolare a riposo e durante il recupero dall'esercizio. Nelle cefalee, nella malattia di Parkinson e nell'emiplegia alternante le osservazioni di risonanza magnetica spettroscopica del muscolo supportano l'ipotesi di una possibile disfunzione mitocondriale in tali patologie. Simili risultati ottenuti in pazienti con sclerosi multipla sono probabilmente da mettere in relazione a un secondario decondizionamento muscolare. In pazienti con sindrome post poliomielitica e con alcune forme di atassia ereditaria, l'aumento del fosfato inorganico muscolare potrebbe essere dovuto ad un difetto metabolico ancora sconosciuto. In conclusione, in varie patologie del sistema nervoso centrale il metabolismo dei fosfati del muscolo scheletrico può essere alterato e tale alterazione può essere dovuta a differenti meccanismi patogenetici. Tutte le differenti possibilità dovrebbero essere prese in considerazione nel valutare i risultati della risonanza magnetica spettroscopica nelle malattie del sistema nervoso centrale.

     

Investigation of the cerebral energy status in patients with glutaric aciduria type I by 31P magnetic resonance spectroscopy

In vivo phosphorus magnetic resonance spectroscopy (MRS) was used to investigate markers of the cerebral energy status in two patients with glutaric aciduria type I (GA-I). Besides an increased concentration of phosphomonoesters in one patient, no other significant alterations from controls were found. This might indicate increased resynthesis of dendritic processes secondary to preceding metabolic crises. In contrast to previous cell-culture studies, no cerebral depletion of phosphocreatine (PCr) was observed. In conclusion, a severe global and permanent depletion of cerebral energy supplies must be ruled out. The benefit of a permanent creatine substitution to stabilize mitochondrial energy metabolism seems thus questionable. However, as MRS was performed during stable clinical conditions, the possibility of a PCr decrease during acute metabolic crises cannot be assessed.     

Short-term aerobic training response in chronic myopathies.

We have previously demonstrated that patients with mitochondrial myopathies can benefit from short-term aerobic exercise training. In this study, we compared the responses to short-term aerobic training of patients with mitochondrial myopathies, patients with nonmetabolic myopathies, and sedentary normal subjects. Training consisted of 8 weeks of treadmill exercise at 70% to 85% of estimated maximum heart rate reserve. All groups showed significant improvements in estimated aerobic capacity as well as heart rate and blood lactate at submaximal exercise intensities. The increase in estimated aerobic capacity was greater in the mitochondrial myopathy patients than in the other two groups. Phosphorus magnetic resonance spectroscopy demonstrated increased oxidative capacity of muscle in patients with mitochondrial myopathies in response to this training but not in patients with other, nonmetabolic myopathies or sedentary control subjects. A self-assessed measurement of functional status (SF-36) suggested improved quality of life associated with the training. This study demonstrates that short-term aerobic training at low intensity can benefit patients with nonmetabolic myopathies but to a lesser extent than patients with mitochondrial myopathies.