Skeletal muscle bioenergetics in myotonic dystrophy

What is known about the effects of exercise or training to reduce skeletal muscle impairments of patients with myotonic dystrophy type 1? A scoping review

BACKGROUND

Myotonic dystrophy type 1 (DM1) is a neuromuscular disease characterized by multisystemic involvements including a progressive loss of maximal muscle strength and muscle wasting. Poor lower-limb strength is an important factor explaining disrupted social participation of affected individuals. This review aims to map what is known about the effects of exercise and training programs undertaken to counteract skeletal muscle impairments in DM1 patients.

METHODS

Medline, CINAHL and EMBASE databases were searched. Regarding study eligibility, title and abstract of 704 studies followed by 45 full articles were reviewed according to the following eligibility criteria. Inclusion: (1) humans with DM1 and (2) experimental protocol relying on exercise or training. Exclusion: (1) studies that do not evaluate skeletal muscle responses or adaptations, (2) reviews covering articles already included and (3) pharmacological intervention at the same time of exercise or training program.

RESULTS

Twenty-one papers were selected for in-depth analysis. Different exercise or training protocols were found including: acute exercise, neuromuscular electric stimulation, strength training, aerobic training, balance training and multiple rehabilitation interventions. Seven studies reported clinical measurements only, five physiological parameters only and nine both types.

CONCLUSION

This scoping review offers a complete summary of the current scientific literature on the effect of exercise and training in DM1 and a framework for future studies based on the concomitant evaluation of the several outcomes in present literature. Although there were a good number of studies focusing on clinical measurements, heterogeneity between studies does not allow to identify what are the adequate training parameters to obtain exercise or training-induced positive impacts on muscle function. Scientific literature is even more scarce regarding physiological parameters, where much more research is needed to understand the underlying mechanisms of exercise response in DM1.

Elevated phosphodiester and T2 levels can be measured in the absence of fat infiltration in Duchenne muscular dystrophy patients

Quantitative MRI and MRS are increasingly important as non-invasive outcome measures in therapy development for Duchenne muscular dystrophy (DMD). Many studies have focussed on individual measures such as fat fraction and metabolite levels in relation to age and functionality, but much less attention has been given to how these indices relate to each other. Here, we assessed spatially resolved metabolic changes in leg muscles of DMD patients, and classified muscles according to the degree of fat replacement compared with healthy controls. Quantitative MRI (three-point Dixon and multi-spin echo without fat suppression and a tri-exponential fit) and 2D-CSI ³¹ P MRS scans were obtained from 18 DMD patients and 12 healthy controls using a 3 T and a 7 T MR scanner. Metabolite levels, T₂ values and fat fraction were individually assessed for five lower leg muscles. In muscles with extensive fat replacement, phosphodiester over adenosine triphosphate (PDE/ATP), inorganic phosphate over phosphocreatine, intracellular tissue pH and T₂ were significantly increased compared with healthy controls. In contrast, in muscles without extensive fat replacement, only PDE/ATP and T₂ values were significantly elevated. Overall, our results show that PDE levels and T₂ values increase prior to the occurrence of fat replacement and remain elevated in later stages of the disease. This suggests that these individual measures could not only function as early markers for muscle damage but also reflect potentially reversible pathology in the more advanced stages.

In vivo (31)P NMR spectroscopy assessment of skeletal muscle bioenergetics after spinal cord contusion in rats

PURPOSE

Muscle paralysis after spinal cord injury leads to muscle atrophy, enhanced muscle fatigue, and increased energy demands for functional activities. Phosphorus magnetic resonance spectroscopy ((31)P-MRS) offers a unique non-invasive alternative of measuring energy metabolism in skeletal muscle and is especially suitable for longitudinal investigations. We determined the impact of spinal cord contusion on in vivo muscle bioenergetics of the rat hind limb muscle using (31)P-MRS.

METHODS

A moderate spinal cord contusion injury (cSCI) was induced at the T8-T10 thoracic spinal segments. (31)P-MRS measurements were performed weekly in the rat hind limb muscles for 3 weeks. Spectra were acquired in a Bruker 11 T/470 MHz spectrometer using a 31P surface coil. The sciatic nerve was electrically stimulated by subcutaneous needle electrodes. Spectra were acquired at rest (5 min), during stimulation (6 min), and recovery (20 min). Phosphocreatine (PCr) depletion rates and the pseudo first-order rate constant for PCr recovery (k PCr) were determined. The maximal rate of PCr resynthesis, the in vivo maximum oxidative capacity (V max) and oxidative adenosine triphosphate (ATP) synthesis rate (Q max) were subsequently calculated.

RESULTS

One week after cSCI, there was a decline in the resting total creatine of the paralyzed muscle. There was a significant reduction (~24 %) in k PCr measures of the paralyzed muscle, maximum in vivo mitochondrial capacity (V max) and the maximum oxidative ATP synthesis rate (Q max) at 1 week post-cSCI. During exercise, the PCr depletion rates in the paralyzed muscle one week after injury were rapid and to a greater extent than in a healthy muscle.

CONCLUSIONS

Using in vivo MRS assessments, we reveal an acute oxidative metabolic defect in the paralyzed hind limb muscle. These altered muscle bioenergetics might contribute to the host of motor dysfunctions seen after cSCI.

Dynamic three-dimensional imaging of phosphocreatine recovery kinetics in the human lower leg muscles at 3T and 7T: a preliminary study

The rate of phosphocreatine (PCr) resynthesis after physical exercise has been extensively studied with phosphorus (³¹P)-MRS. Previous studies have used small surface coils that were limited to measuring one superficial muscle per experiment. This study focuses on the development and implementation of a spectrally selective three-dimensional turbo spin echo (3D-TSE) sequence at 3T and 7T with temporal resolution of 24 s, using two geometrically identical volume coils. We acquired imaging data of PCr recovery from four healthy volunteers and one diabetic patient, who performed plantar flexions using resistance bands. We segmented the anatomical regions of six different muscles from the lower leg, namely the gastrocnemius [lateral (GL) and medial (GM)], the tibialis [anterior (TA) and posterior (TP)], the soleus (S) and the peroneus (P) and measured the local PCr resynthesis rate constants. During the same examination, we also acquired unlocalized (³¹P-MRS data at a temporal resolution of 6 s. At 3T, the PCr resynthesis rate constants were measured at 25.4 ± 3.7 s [n = 4, mean ± standard deviation (SD)] using the MRS method and 25.6 ± 4.4 s using the MRI method. At 7T, the measured rates were 26.4 ± 3.2 s and 26.2 ± 4.7 s for MRS and MRI. Using our imaging method, we measured the local PCr resynthesis rate constants in six individual muscles of the lower leg (min/max 20.2/31.7 ). The recovery rate constants measured for the diabetic patient were 55.5 s (MRS) and 52.7 s (MRI). The successful implementation of our 3D-method suggests that imaging is possible at both fields with a relatively high spatial resolution (voxel size: 4.2 mL at 3T and 1.6 mL at 7T) using volume coils and that local PCr resynthesis rates can be obtained in a single measurement. The advantage of the imaging method is that it can highlight differences in PCr resynthesis rates between different muscles in a single measurement in order to study spatial gradients of metabolic properties of diseased states for which very little is currently known.

Muscle LIM protein interacts with cofilin 2 and regulates F-actin dynamics in cardiac and skeletal muscle

The muscle LIM protein (MLP) and cofilin 2 (CFL2) are important regulators of striated myocyte function. Mutations in the corresponding genes have been directly associated with severe human cardiac and skeletal myopathies, and aberrant expression patterns have often been observed in affected muscles. Herein, we have investigated whether MLP and CFL2 are involved in common molecular mechanisms, which would promote our understanding of disease pathogenesis. We have shown for the first time, using a range of biochemical and immunohistochemical methods, that MLP binds directly to CFL2 in human cardiac and skeletal muscles. The interaction involves the inter-LIM domain, amino acids 94 to 105, of MLP and the amino-terminal domain, amino acids 1 to 105, of CFL2, which includes part of the actin depolymerization domain. The MLP/CFL2 complex is stronger in moderately acidic (pH 6.8) environments and upon CFL2 phosphorylation, while it is independent of Ca(2+) levels. This interaction has direct implications in actin cytoskeleton dynamics in regulating CFL2-dependent F-actin depolymerization, with maximal depolymerization enhancement at an MLP/CFL2 molecular ratio of 2:1. Deregulation of this interaction by intracellular pH variations, CFL2 phosphorylation, MLP or CFL2 gene mutations, or expression changes, as observed in a range of cardiac and skeletal myopathies, could impair F-actin depolymerization, leading to sarcomere dysfunction and disease.

Gene expression analysis in myotonic dystrophy: indications for a common molecular pathogenic pathway in DM1 and DM2

An RNA gain-of-function of expanded transcripts is the most accredited molecular mechanism for myotonic dystrophy type 1 (DM1) and 2 (DM2). To disclose molecular parallels and divergences in pathogenesis of both disorders, we compared the expression profile of muscle biopsies from DM1 and DM2 patients to controls. DM muscle tissues showed a reduction in the major skeletal muscle chloride channel (CLCN1) and transcription factor Sp1 transcript levels and an abnormal processing of the CLCN1 and insulin receptor (IR) pre-mRNAs. No essential differences were observed in the muscle blind-like gene (MBNL1) and CUG binding protein 1 (CUGBP1) transcript levels as well as in the splicing pattern of the myotubularin-related 1 (MTMR1) gene. Macroarray analysis of 96 neuroscience-related genes revealed a considerable similar expression profile between the DM samples, reflective of a common muscle pathology origin. Using a twofold threshold, we found six misregulated genes important in calcium and potassium metabolism and in mitochondrial functions. Our results indicate that the DM1 and DM2 overlapping clinical phenotypes may derive from a common trans acting mechanism that traps and influences shared genes and proteins. An RNA gain-of-function of expanded transcripts is the most accredited molecular mechanism for myotonic dystrophy type 1 (DM1) and 2 (DM2). To disclose molecular parallels and divergences in pathogenesis of both disorders, we compared the expression profile of muscle biopsies from DM1 and DM2 patients to controls. DM muscle tissues showed a reduction in the major skeletal muscle chloride channel (CLCN1) and transcription factor Sp1 transcript levels and an abnormal processing of the CLCN1 and insulin receptor (IR) pre-mRNAs. No essential differences were observed in the muscle blind-like gene (MBNL1) and CUG binding protein 1 (CUGBP1) transcript levels as well as in the splicing pattern of the myotubularin-related 1 (MTMR1) gene. Macroarray analysis of 96 neuroscience-related genes revealed a considerable similar expression profile between the DM samples, reflective of a common muscle pathology origin. Using a twofold threshold, we found six misregulated genes important in calcium and potassium metabolism and in mitochondrial functions. Our results indicate that the DM1 and DM2 overlapping clinical phenotypes may derive from a common trans acting mechanism that traps and influences shared genes and proteins.

Fatigue and neuromuscular diseases

PURPOSE

To identify the role of fatigue, its evaluation and its causes in the pathophysiology context of acquired or hereditary neuromuscular diseases of the spinal anterior horn cell, peripheral nerve, neuromuscular junction and muscle.

MATERIAL AND METHODS

A literature review has been done on Medline with the following keywords: neuromuscular disease, peripheral neuropathy, myopathy, fatigue assessment, exercise intolerance, force assessment, fatigue scale and questionnaire, then with the terms: Fatigue Severity Scale, Chalder Fatigue Scale, Fatigue Questionnaire, Piper Fatigue Scale, electromyography and the combination of the word Fatigue with the following terms: Amyotrophic Lateral Sclerosis (ALS), Post-Polio Syndrome (PPS), Guillain-Barre Syndrome, Immune Neuropathy, Charcot-Marie-Tooth Disease, Myasthenia Gravis (MG), Metabolic Myopathy, Mitochondrial Myopathy, Muscular Dystrophy, Facioscapulohumeral Dystrophy, Myotonic Dystrophy.

RESULTS

Fatigue is a symptom very frequently reported by patients. Fatigue is mainly evaluated by strength loss after an exercise, by change in electromyographic activity during a given exercise and by questionnaires that takes into account the subjective (psychological) part of fatigue. Due to the large diversity of motor disorders, there are multiple clinical expressions of fatigue that differ in their presentation, consequences and therapeutic approach.

CONCLUSION

This review shows that fatigue has to be taken into account in patients with neuromuscular diseases. In this context, pathophysiology of fatigue often implies the motor component but the disease evolution and the physical obligates of daily life also induce an important psychological component.

Phenotypic variability in myotonia congenita

Myotonia congenita is a hereditary chloride channel disorder characterized by delayed relaxation of skeletal muscle (myotonia). It is caused by mutations in the skeletal muscle chloride channel gene CLCN1 on chromosome 7. The phenotypic spectrum of myotonia congenita ranges from mild myotonia disclosed only by clinical examination to severe and disabling myotonia with transient weakness and myopathy. The most severe phenotypes are seen in patients with two mutated alleles. Heterozygotes are often asymptomatic but for some mutations heterozygosity is sufficient to cause pronounced myotonia, although without weakness and myopathy. Thus, the phenotype depends on the mutation type to some extent, but this does not explain the fact that severity varies greatly between heterozygous family members and may even vary with time in the individual patient. In this review, existing knowledge about phenotypic variability is summarized, and the possible contributing factors are discussed.

Cardiac and skeletal muscle involvement in myotonic dystrophy type 2 (DM2): a quantitative 31P-MRS and MRI study

In myotonic dystrophy type 2 (DM2/PROMM), cardiac muscle involvement is usually more benign than in DM1, but clinically severe cardiomyopathy has been reported in some patients. Using a novel method of magnetic resonance spectroscopy (MRS), we examined the left ventricular myocardium and the left gastrocnemius muscle in 11 unselected DM2/PROMM patients without overt cardiac disease. Data on cardiac morphology and function were obtained by gradient echo two-dimensional cine magnetic resonance imaging (MRI); no significant differences were found between DM2 patients and healthy controls, but using a median split approach older patients showed mildly increased left ventricular (LV) volumes, i.e., 59% increase of end-systolic volume index (ESVI) and 35% increase of end-diastolic volume index (EDVI), and an increase of LV mass (26%). On cardiac MRS, DM2/PROMM patients showed a reduction of phosphocreatine (PCr) and adenosine triphosphate (ATP) by 25 and 20% compared to matched healthy controls. No significant differences were found between younger and older patients. In skeletal muscle of the DM2 patients, no significant decrease of PCr and ATP concentrations was found. However, in older patients, who commonly show overt hip flexor muscle weakness, we observed reduced values for PCr and ATP. Our MRS and MRI findings reveal evidence for subclinical cardiomyopathy in DM2/PROMM patients without overt heart disease. Future prospective studies are needed to clarify the risk of developing overt cardiac disease in DM2 and to define prognostic factors.

Changes in inorganic phosphate and force production in human skeletal muscle after cast immobilization

Cast immobilization is associated with decreases in muscle contractile area, specific force, and functional ability. The pathophysiological processes underlying the loss of specific force production as well as the role of metabolic alterations are not well understood. The aim of this study was to quantify changes in the resting energy-rich phosphate content and specific force production after immobilization. (31)P-magnetic resonance spectroscopy, three-dimensional magnetic resonance imaging, and isometric strength testing were performed in healthy subjects and patients with an ankle fracture after 7 wk of immobilization and during rehabilitation. Muscle biopsies were obtained in a subset of patients. After immobilization, there was a significant decrease in the specific plantar flexor torque and a significant increase in the inorganic phosphate (P(i)) concentration (P < 0.001) and the P(i)-to-phosphocreatine (PCr) ratio (P < 0.001). No significant change in the PCr content or basal pH was noted. During rehabilitation, both the P(i) content and the P(i)-to-PCr ratio decreased and specific torque increased, approaching control values after 10 wk of rehabilitation. Regression analysis showed an inverse relationship between the in vivo P(i) concentration and specific torque (r = 0.65, P < 0.01). In vitro force mechanics performed on skinned human muscle fibers demonstrated that varying the P(i) levels within the ranges observed across individuals in vivo (4-10 mM) changed force production by approximately 16%. In summary, our findings clearly depict a change in the resting energy-rich phosphate content of skeletal muscle with immobilization, which may negatively impact its force generation.

Skeletal muscle metabolism in Duchenne muscular dystrophy (DMD): an in-vitro proton NMR spectroscopy study

The metabolic differences in the skeletal muscle of patients with Duchenne muscular dystrophy (DMD) and normal subjects (controls) were investigated using in-vitro high-resolution proton NMR spectroscopy. In all, 56 metabolites were unambiguously identified in the perchloric acid extract of muscle tissue using one- and two-dimensional NMR. The concentrations of glycolytic substrate glucose (Glc; p < 0.05), gluconeogenic amino acids such as glutamine (Gln; p < 0.05) and alanine (Ala; p < 0.05) and the glycolytic product lactate (Lac; p < 0.05) were statistically significantly lower in DMD patients as compared to controls. A significant reduction in the concentrations of total creatine (TCr; p < 0.05), glycerophosphoryl choline + phosphoryl choline + carnitine (GPC/PC/Car; p < 0.05), choline (Cho; p < 0.05) and acetate (Ace; p < 0.05) was also observed in these patients. Decrease in the level of glucose may be attributed to the reduction in the concentrations of gluconeogenic substrates or membrane abnormalities in degenerated muscle of DMD patients. Lower levels of choline containing compounds indicate membrane abnormalities. Decrease in the concentration of lactate in the muscle of DMD patients may be due to the reduction in anaerobic glycolytic activity or lower substrate concentration. The decrease in the concentration of acetate may reflect reduced transport of fatty acids into mitochondria due to decreased concentration of carnitine in DMD patients. Kreb's cycle intermediate alpha-ketoglutarate was observed only in the diseased muscle, which is suggestive of predominant oxidative metabolism for energy generation.

Role of fatigue in limiting physical activities in humans with neuromuscular diseases

New methods of examining both central and peripheral fatigue are now available. A broader understanding of the mechanisms of fatigue in healthy human subjects has begun to emerge. The mechanisms of fatigue in patients with various neuromuscular diseases are even more complex than in healthy persons. Examples of both central and peripheral fatigue in various neuromuscular diseases and other disorders are presented, including metabolic myopathy, chronic fatigue syndrome, postpolio syndrome, and amyotrophic lateral sclerosis.

Impaired performance of skeletal muscle in alpha-glucosidase knockout mice

Glycogen storage disease type II (GSD II) is an inherited progressive muscle disease in which lack of functional acid alpha-glucosidase (AGLU) results in lysosomal accumulation of glycogen. We report on the impact of a null mutation of the acid alpha-glucosidase gene (AGLU(-/-)) in mice on the force production capabilities, contractile mass, oxidative capacity, energy status, morphology, and desmin content of skeletal muscle. Muscle function was assessed in halothane-anesthetized animals, using a recently designed murine isometric dynamometer. Maximal torque production during single tetanic contraction was 50% lower in the knockout mice than in wild type. Loss of developed torque was found to be disproportionate to the 20% loss in muscle mass. During a series of supramaximal contraction, fatigue, expressed as percentile decline of developed torque, did not differ between AGLU(-/-) mice and age-matched controls. Muscle oxidative capacity, energy status, and protein content (normalized to either dry or wet weight) were not changed in knockout mice compared to control. Alterations in muscle cell morphology were clearly visible. Desmin content was increased, whereas alpha-actinin was not. As the decline in muscle mass is insufficient to explain the degree in decline of mechanical performance, we hypothesize that the large clusters of noncontractile material present in the cytoplasm hamper longitudinal force transmission, and hence muscle contractile function. The increase in muscular desmin content is most likely reflecting adaptations to altered intracellular force transmission.

New parameters reducing the interindividual variability of metabolic changes during muscle contraction in humans. A (31)P MRS study with physiological and clinical implications

Interindividual variations in skeletal muscle metabolism make comparative analyses difficult. In this study, we have addressed the issue of capturing the variability of metabolic performance observed during muscle exercise in humans by using an original method of normalization.Metabolic changes induced by various kinds of exercise were investigated using 31P magnetic resonance spectroscopy (MRS) at 4.7 T in 65 normal subjects (23 women and 42 men) and 12 patients with biopsy-proven muscular disorders. Large variations in the extent of PCr breakdown and intracellular acidosis were recorded among subjects and exercise protocols. For all the data pooled, the amplitude of mechanical performance accounts for 50% of these variations. When scaled to the work output, variations of PCr consumption account for 65% of pH changes through a linear relationship. This linear relationship was substantially improved (90%) when both variables were scaled to the square of work output performed (P1 and P2). By capturing most of the initial interindividual variability (90%), P1 vs. P2 relationship represents an ideal standardization procedure, independent of any anthropometric measurements. This relationship also discloses a significant link between the extent of PCr breakdown and intracellular acidosis regardless of exercise protocol. Moreover, changes in the slope of the P1 vs. P2 regression curve, as measured in old subjects and in selected patients, directly reflect alterations of energy production in muscle.

Quantitative assessment of motor fatigue in amyotrophic lateral sclerosis

Motor fatigue is a common complaint in patients with amyotrophic lateral sclerosis (ALS), but is often excluded, unlike weakness, from the clinical assessment of these patients. This could be due to the complexity and often painful assessment techniques of this motor deficit. This study examines the feasibility of quantitative assessment of motor fatigue by modifying presently available force measurements. The relationship between weakness and fatigue in ALS patients was also examined. Fifty-four ALS patients and 39 normal control subjects performed 30 s of sustained maximal voluntary isometric contraction (MVIC) of elbow flexors (EF), knee extensors (NE), and ankle dorsiflexors (DF), using a computerized force measurement system and standardized testing procedures. Fatigue index (FI) was digitally calculated, from the force-time curve, as the percentage of MVIC unable to be sustained over the 30-s period. Fatigue was greater in ALS patients than in normal control (mean=23% vs. 15%) in all muscles including muscles that were not clearly weak. Weakness and fatigue were poorly correlated in ALS patients and may be independent measures of the pathogeneses of ALS.

Functional and metabolic early changes in calf muscle occurring during nutritional repletion in malnourished elderly patients

BACKGROUND

Metabolic alterations in skeletal muscle associated with malnutrition and the potential reversibility of such alterations during refeeding are not fully understood.

OBJECTIVE

We characterized early changes in muscle during refeeding in malnourished, hospitalized elderly subjects.

DESIGN

Muscle function, metabolism, and mass were evaluated in 24 clinically stable patients (11 were malnourished) by using isokinetic plantar flexor torque measurements and nuclear magnetic resonance (NMR) imaging for medial gastrocnemius mass assessment and 31P and 13C NMR spectroscopy for inorganic phosphate (Pi), phosphocreatine, and glycogen quantitation.

RESULTS

Malnourished subjects had lower muscle mass (P < 0.02) and tended to have lower strength than did control subjects. In malnourished subjects, muscle strength increased after refeeding (P < 0.01) whereas muscle mass was unchanged. The ratio of Pi to ATP was lower in malnourished than in control subjects (P < 0.001) and increased during refeeding (P < 0.01). The mean ratio of phosphocreatine to ATP was lower in malnourished than in control subjects (P < 0.01) and increased to control values after refeeding. Muscle glycogen showed a scattered distribution for malnourished subjects; the mean value did not differ significantly from that of control subjects, either at baseline or after refeeding.

CONCLUSIONS

The lower ratio of phosphocreatine to ATP in malnourished subjects could have resulted from either lower total muscle creatine or reduced oxidative capacities. High or normal glycogen associated with a low Pi-to-ATP ratio in malnourished subjects suggested preferential use of lipid over carbohydrate for energy supply, which is known to reduce muscle performance. The data suggest that normalization of muscle metabolite content after refeeding improves muscle strength in malnourished subjects.

Insights into muscle diseases gained by phosphorus magnetic resonance spectroscopy

Phosphorus magnetic resonance spectroscopy (P-MRS) has now been used in the investigation of muscle energy metabolism in health and disease for over 15 years. The present review describes the basics of the metabolic observations made by P-MRS including the assumptions and problems associated with the use of this technique. Extramuscular factors, which may affect the P-MRS results, are detailed. The important P-MRS observations in patients with mitochondrial myopathies, including the monitoring of experimental therapies, are emphasized. The findings in other metabolic myopathies (those associated with glycolytic defects or endocrine disturbances) and in the destructive myopathies (the dystrophies and the inflammatory myopathies) are also described. Observations made in normal and abnormal fatigue, fibromyalgia, and malignant hyperthermia are considered. Finally, a summary of the possible diagnostic use of P-MRS in exercise intolerance is provided.

Dynamic phosphorus-31 magnetic resonance spectroscopy of the quadriceps muscle: effects of age and sex on spectroscopic results

RATIONALE AND OBJECTIVES

Phosphorus-31 (31p) magnetic resonance spectroscopy (MRS) is used to assess the influence of sex and age on quadriceps muscle metabolism before and after exercise.

METHODS

Fifty-four healthy volunteers and 56 patients with an arterial occlusive disease were examined by dynamic 31p MRS. In the magnet, the quadriceps muscle was stressed by an isometric and an isotonic form of exercise until exhaustion.

RESULTS

Older subjects showed a significantly larger ratio of inorganic phosphate (P(i)) to phosphocreatine (PCr) than younger subjects (r = 0.52, P = 8 x 10(-9)). With subjects' increasing age, the ratio of adenosine triphosphate (beta-ATP) to total phosphate decreased (r = -0.36, P = 5 x 10(-5)). The ratio of phosphomonoester to beta-ATP and phosphodiester (PDE) to beta-ATP showed a strong age dependence (r = 0.71 and 0.69, P = 3 x 10(-17) and 4 x 10(-15), respectively). The pH was the only one of the evaluated spectroscopic parameters that showed a sex dependence. Female subjects had a significantly lower pH (7.03+/-0.02) than male subjects (7.05+/-0.03) (P = 6 x 10(-4)). With increasing age, the maxima of P(i) to PCr were less extreme during both of the exercises (r = -0.51, P = 3 x 10(-16)). Likewise, the exercise-induced acidosis was less severe with increasing age (r = -0.51, P = 7 x 10(-16)). After the exercises ended, the times of half recovery of P(i) to PCr and the pH neither correlated with the subjects' age nor with sex or the cross-sectional area of the quadriceps muscle.

CONCLUSIONS

The sex and age of volunteers or patients may affect spectroscopic results in a significant way. This influence has to be considered in the interpretation of spectroscopic studies. According to the recovery rates of P(i) to PCr and the pH, an age-related deterioration of muscular metabolism seems to be avoidable by appropriate physical activity.

Correlative MR imaging and 31P-MR spectroscopy study in sarcoglycan deficient limb girdle muscular dystrophy

We combined magnetic resonance (MR) imaging and phosphorus magnetic resonance spectroscopy (31P-MRS) to study skeletal muscle in seven patients with limb girdle muscular dystrophy (LGMD) with a variable deficiency of the alpha-, beta-, and gamma-sarcoglycan but normal dystrophin expression on muscle biopsy. T1- and T2-weighted spin-echo axial leg images showed the highest degree of fat replacement in soleus, tibialis anterior and peroneal muscles while gastrocnemius and tibialis posterior were less affected. In LGMD patients as a group, calf muscle phosphorylated compound content did not differ from controls, but the cytosolic pH was increased (P = 0.02). The degree of calf muscle fat replacement correlated inversely with cytosolic pH (r = 0.74) and directly with PCr/ATP (r = 0.74). Muscle oxidative metabolism was normal in LGMD patients. Our findings show that primary deficits of sarcoglycan complex lead to specific morphological and metabolic patterns of skeletal muscle involvement.

In vivo skeletal muscle mitochondrial function in Leber's hereditary optic neuropathy assessed by 31P magnetic resonance spectroscopy

We used 31P magnetic resonance spectroscopy (31P-MRS) to assess in vivo skeletal muscle mitochondrial function in 10 Leber's hereditary optic neuropathy patients/carriers with a mitochondrial DNA (mtDNA) mutation at one of three nucleotide positions, 11,778, 14,484, and 3,460. We studied one affected patient for each mutation and two unaffected carriers with the 11,778 or 3,460 mutation and three carriers with 14,484. All subjects were homoplasmic except the two 3,460 carriers, who showed 80% and 15% of mutated mtDNA. 31P-MRS at rest disclosed some abnormalities in all subjects. In particular, the phosphorylation potential was below the normal range in all cases. During recovery from exercise, the maximum rate of mitochondrial ATP production (Vmax) was reduced to 27% of normal in the 11,778 mutation and to 53% in the 14,484 mutation patient/carrier groups. Mitochondrial Vmax was within the normal range in all subjects with the 3,460 mutation but correlated inversely with the percentage of mutated mtDNA. This in vivo study shows that the 11,778 mutation causes a mitochondrial impairment more severe than the 14,484 and that the 3,460 mutation results in only a mild depression of muscle mitochondrial function.

Brain and skeletal muscle bioenergetic failure in familial hypobetalipoproteinaemia

OBJECTIVE

To determine whether a multisystemic bioenergetic deficit is an underlying feature of familial hypobetalipoproteinaemia.

METHODS

Brain and skeletal muscle bioenergetics were studied by in vivo phosphorus MR spectroscopy (31P-MRS) in two neurologically affected members (mother and son) and in one asymptomatic member (daughter) of a kindred with familial hypobetalipoproteinaemia. Plasma concentrations of vitamin E and coenzyme Q10 (CoQ10) were also assessed.

RESULTS

Brain 31P-MRS disclosed in all patients a reduced phosphocreatine (PCr) concentration whereas the calculated ADP concentration was increased. Brain phosphorylation potential was reduced in the members by about 40%. Skeletal muscle was studied at rest in the three members and during aerobic exercise and recovery in the son and daughter. Only the mother showed an impaired mitochondrial function at rest. Both son and daughter showed an increased end exercise ADP concentration whereas the rates of postexercise recovery of PCr and ADP were slow in the daughter. The rate of inorganic phosphate recovery was reduced in both cases. Plasma concentration of vitamin E and CoQ10 was below the normal range in all members.

CONCLUSIONS

Structural changes in mitochondrial membranes and deficit of vitamin E together with reduced availability of CoQ10 can be responsible for the multisystemic bioenergetic deficit. Present findings suggest that CoQ10 supplementation may be important in familial hypobetalipoproteinaemia.

Quantitative analysis of skeletal muscle bioenergetics and proton efflux in migraine and cluster headache

Phosphorus MR spectroscopy (31P-MRS) was used to quantify skeletal muscle bioenergetics and proton efflux in 63 patients with migraine (23 with migraine without aura, MwoA, 22 with migraine with aura, MwA, and 18 with prolonged aura or stroke, CM) and in 14 patients with cluster headache (CH), all in an attack-free period. At rest mitochondrial function was abnormal only in CM, as shown by a low phosphocreatine (PCr) concentration. At the end of a mixed glycolytic/aerobic exercise all three migraine groups showed a significantly smaller decrease of cytosolic pH compared to controls with a similar end-exercise PCr breakdown, while end-exercise pH was normal in cluster headache patients. The normal rate of proton efflux in all headache groups suggests that the reduced end-exercise acidification was due to a reduction of glycolytic flux in migraine patients. The maximum rate of mitochondrial ATP production (Qmax), calculated from the rate of post-exercise PCr recovery and the end-exercise [ADP], was low in cluster headache patients as well as in migraine patients except MwoA. In migraine the degree of the mitochondrial impairment, that apparently is associated with a reduced glycolytic flux, is related to the severity of the clinical phenotype.

Development and applications of in vivo clinical magnetic resonance spectroscopy

4.1 CURRENT STATUS. While an extensive clinical literature of MRS of muscle, brain, heart and liver has been achieved, the MRS technique is not considered essential for routine diagnosis because it is inherently insensitive and metabolic changes tend to be small. However, MRS techniques have proven to be of considerable value for prognosis in some circumstances, notably for predicting outcome following hypoxic-ischaemic injury in the newborn and also in predicting graft viability following organ transplantation. The chemical specificity of MRS has been illustrated, and exploiting the non-invasive nature of the technique, metabolic fingerprinting of pathophysiological processes throughout the natural history of a wide variety of diseases is now being accomplished. Particularly exciting are the applications of 13C MRS for measuring hepatic and muscle glycogen levels, for example in diabetics, and the use of hepatic 31P MRS for assessing liver function in cirrhosis. Other areas of excitement are the applications of 1H MRS in assessing neuronal function in epilepsy and stroke, and for measuring the evolution of lactate in stroke and hypoxic-ischaemic encephalopathy. Emphasis on technique development continues, and applications still tend to be technology-led. The availability of routine clinical MRI systems with spectroscopy capabilities has given MRS studies wider applicability. The recent improvements in spatial resolution have been impressive and the technique is slowly becoming more quantitative. 4.2. FUTURE PERSPECTIVES. Given the flexibility of clinical magnetic resonance techniques, particularly magnetic resonance imaging, it is likely that MRI will be the diagnostic tool of choice in a wider range of diseases, such as multiple sclerosis, stroke, neurodegenerative conditions, sports injuries and in staging malignancies. Since proton magnetic resonance spectroscopy packages have become a routine addition to many MRI systems, it is feasible to select the MRI sequences of most value in highlighting anatomical and pathological abnormalities and to incorporate specifically selected MRS sequences to emphasize biochemical differences. Improvements in technical methodologies are central to further developments. For example, use of internal coils, such as implantable or endoscopic coils, will enable small regions of tissue to be studied in considerable detail, which may otherwise be inaccessible to measurement. Chemical MRS studies have benefited from the use of higher magnetic fields, and the same may be expected for clinical MRS studies. Whole-body magnets up to 4 T have been used in a few centres, and certainly 3 T systems are becoming more widely available with the recent tremendous interest in functional imaging. Certainly, better control of artefacts can be expected; for example, improved definition of spectral changes due to voluntary or involuntary movements. Wider use of proton decoupling methods will improve the specificity of the spectra, by allowing definitive assignments of overlapping resonances, as well as the sensitivity. Comparing PET and MRS studies, it is becoming increasingly obvious that both will be required in parallel to explore parameters of brain metabolism and function. The ability to measure 13C MR signals in the brain has been demonstrated, which allows measurements of glutamate and glucose turnover. MRS measurements have the advantage of not requiring a radioactive isotope, as well as being insensitive to activity-related changes in regional cerebral blood flow. Also the study of cerebral glucose metabolism by MRS is very promising, allowing a resolution and sensitivity comparable to PET. A combination of MRS and PET studies will allow the pathogenesis of neuropsychiatric disorders to be better understood. (ABSTRACT TRUNCATED)

Quantitative analysis by 31P magnetic resonance spectroscopy of abnormal mitochondrial oxidation in skeletal muscle during recovery from exercise

We use the hyperbolic relationship between cytosolic [ADP] and the rate of phosphocreatine (PCr) resynthesis after exercise to estimate the apparent maximum rate of oxidative ATP synthesis (QMAX). We examine data from some human diseases in which mitochondrial oxidation may be impaired (due to reduced mitochondrial numbers, intrinsic mitochondrial defect or impaired vascular supply). Muscle responds to impaired oxidation by stimulating anaerobic ATP synthesis and/or by increasing [ADP], the stimulus to the mitochondrion. However, these responses interact: [ADP] depends on pH and [PCr], and lactic acid production tends to lower [ADP] (by lowering pH), while proton efflux has the opposite effect. We identify four patterns of results: (A) in mitochondrial myopathy, apparent QMAX is reduced and [ADP] is appropriately increased, because increased proton efflux reduces the pH change in exercise despite increased lactic acid production; (B) in some conditions (e.g., cyanotic congenital heart disease) apparent QMAX is reduced but there is no compensatory rise in [ADP], probably because anaerobic ATP synthesis during exercise is increased without increase in proton efflux; (C) in other conditions (e.g., myotonic dystrophy) [ADP] is increased during exercise but apparent QMAX is normal, suggesting either an increase in proton efflux and/or decrease in anaerobic ATP synthesis during exercise; (D) there are also conditions (e.g., respiratory failure) where, despite impaired oxygen supply, both apparent QMAX and end-exercise [ADP] are normal. We also discuss the metabolic conditions under which end-exercise [ADP] is increased by a mitochondrial defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular energetics of dystrophic muscle

Cytosolic pH and phosphorus metabolite ratios in skeletal muscle were measured by 31P magnetic resonance spectroscopy in patients with Duchenne muscular dystrophy (DMD) and Becker's muscular dystrophy (BMD) and in Duchenne/Becker carriers. In resting dystrophin-deficient muscle, there was a decrease in phosphocreatine (PCr) and increase in orthophosphate (Pi) relative to ATP, and an increase in calculated free [ADP]. Phosphomonester and phosphodiester were also increased relative to ATP. These changes were largest in DMD, smaller in BMD and small or absent in carriers. Cytosolic pH was increased substantially in DMD, moderately in BMD and slightly but significantly in gastrocnemius of carriers. Raised intracellular pH thus appears to be the most characteristic abnormality in dystrophin-deficient muscle. Responses to erobic exercise were studied in the forearm muscle flexor digitorum superficialis of carriers. PCr depletion during exercise was greater than normal but the fall in pH was disproportionately small, resulting in increased [ADP]. This is likely to result either from reduced anaerobic glycogenolysis to lactic acid or from increased proton efflux (as is seen in mitochondrial myopathy). Detailed analysis suggests: (1) at the start of exercise, calculated lactic acid production was increased, as was the rate of PCr depletion, suggesting that there was no absolute defect of glycogenolysis. (2) At the start of recovery, calculated proton efflux was not increased, although as the pH at the end of exercise was higher than in controls and proton efflux is normally pH-dependent, an up-regulation of proton efflux cannot be excluded. (3) Recovery of PCr, Pi and ADP after exercise were not impaired, suggesting that mitochondrial function is normal.