Investigation of human mitochondrial myopathies by phosphorus magnetic resonance spectroscopy

Evidence of brain target engagement in Parkinson's disease and multiple sclerosis by the investigational nanomedicine, CNM-Au8, in the REPAIR phase 2 clinical trials

BACKGROUND

Impaired brain energy metabolism has been observed in many neurodegenerative diseases, including Parkinson's disease (PD) and multiple sclerosis (MS). In both diseases, mitochondrial dysfunction and energetic impairment can lead to neuronal dysfunction and death. CNM-Au8® is a suspension of faceted, clean-surfaced gold nanocrystals that catalytically improves energetic metabolism in CNS cells, supporting neuroprotection and remyelination as demonstrated in multiple independent preclinical models. The objective of the Phase 2 REPAIR-MS and REPAIR-PD clinical trials was to investigate the effects of CNM-Au8, administered orally once daily for twelve or more weeks, on brain phosphorous-containing energy metabolite levels in participants with diagnoses of relapsing MS or idiopathic PD, respectively.

RESULTS

Brain metabolites were measured using 7-Tesla 31P-MRS in two disease cohorts, 11 participants with stable relapsing MS and 13 participants with PD (n = 24 evaluable post-baseline scans). Compared to pre-treatment baseline, the mean NAD+/NADH ratio in the brain, a measure of energetic capacity, was significantly increased by 10.4% after 12 + weeks of treatment with CNM-Au8 (0.584 units, SD: 1.3; p = 0.037, paired t-test) in prespecified analyses of the combined treatment cohorts. Each disease cohort concordantly demonstrated increases in the NAD+/NADH ratio but did not reach significance individually (p = 0.11 and p = 0.14, PD and MS cohorts, respectively). Significant treatment effects were also observed for secondary and exploratory imaging outcomes, including β-ATP and phosphorylation potential across both cohorts.

CONCLUSIONS

Our results demonstrate brain target engagement of CNM-Au8 as a direct modulator of brain energy metabolism, and support the further investigation of CNM-Au8 as a potential disease modifying drug for PD and MS.

Magnetic field therapy enhances muscle mitochondrial bioenergetics and attenuates systemic ceramide levels following ACL reconstruction: Southeast Asian randomized-controlled pilot trial

Background

Metabolic disruption commonly follows Anterior Cruciate Ligament Reconstruction (ACLR) surgery. Brief exposure to low amplitude and frequency pulsed electromagnetic fields (PEMFs) has been shown to promote in vitro and in vivo murine myogeneses via the activation of a calcium–mitochondrial axis conferring systemic metabolic adaptations. This randomized-controlled pilot trial sought to detect local changes in muscle structure and function using MRI, and systemic changes in metabolism using plasma biomarker analyses resulting from ACLR, with or without accompanying PEMF therapy.

Methods

20 patients requiring ACLR were randomized into two groups either undergoing PEMF or sham exposure for 16 weeks following surgery. The operated thighs of 10 patients were exposed weekly to PEMFs (1 ​mT for 10 ​min) for 4 months following surgery. Another 10 patients were subjected to sham exposure and served as controls to allow assessment of the metabolic repercussions of ACLR and PEMF therapy. Blood samples were collected prior to surgery and at 16 weeks for plasma analyses. Magnetic resonance data were acquired at 1 and 16 weeks post-surgery using a Siemens 3T Tim Trio system. Phosphorus (³¹P) Magnetic Resonance Spectroscopy (MRS) was utilized to monitor changes in high-energy phosphate metabolism (inorganic phosphate (P_i), adenosine triphosphate (ATP) and phosphocreatine (PCr)) as well as markers of membrane synthesis and breakdown (phosphomonoesters (PME) and phosphodiester (PDE)). Quantitative Magnetization Transfer (qMT) imaging was used to elucidate changes in the underlying tissue structure, with T1-weighted and 2-point Dixon imaging used to calculate muscle volumes and muscle fat content.

Results

Improvements in markers of high-energy phosphate metabolism including reductions in ΔP_i/ATP, P_i/PCr and (P_i ​+ ​PCr)/ATP, and membrane kinetics, including reductions in PDE/ATP were detected in the PEMF-treated cohort relative to the control cohort at study termination. These were associated with reductions in the plasma levels of certain ceramides and lysophosphatidylcholine species. The plasma levels of biomarkers predictive of muscle regeneration and degeneration, including osteopontin and TNNT1, respectively, were improved, whilst changes in follistatin failed to achieve statistical significance. Liquid chromatography with tandem mass spectrometry revealed reductions in small molecule biomarkers of metabolic disruption, including cysteine, homocysteine, and methionine in the PEMF-treated cohort relative to the control cohort at study termination. Differences in measurements of force, muscle and fat volumes did not achieve statistical significance between the cohorts after 16 weeks post-ACLR.

Conclusion

The detected changes suggest improvements in systemic metabolism in the post-surgical PEMF-treated cohort that accords with previous preclinical murine studies. PEMF-based therapies may potentially serve as a manner to ameliorate post-surgery metabolic disruptions and warrant future examination in more adequately powered clinical trials.

The Translational Potential of this Article

Some degree of physical immobilisation must inevitably follow orthopaedic surgical intervention. The clinical paradox of such a scenario is that the regenerative potential of the muscle mitochondrial pool is silenced. The unmet need was hence a manner to maintain mitochondrial activation when movement is restricted and without producing potentially damaging mechanical stress. PEMF-based therapies may satisfy the requirement of non-invasively activating the requisite mitochondrial respiration when mobility is restricted for improved metabolic and regenerative recovery.

Impaired aerobic capacity and premature fatigue preceding muscle weakness in the skeletal muscle Tfam-knockout mouse model

Mitochondrial diseases are genetic disorders that lead to impaired mitochondrial function, resulting in exercise intolerance and muscle weakness. In patients, muscle fatigue due to defects in mitochondrial oxidative capacities commonly precedes muscle weakness. In mice, deletion of the fast-twitch skeletal muscle-specific Tfam gene (Tfam KO) leads to a deficit in respiratory chain activity, severe muscle weakness and early death. Here, we performed a time-course study of mitochondrial and muscular dysfunctions in 11- and 14-week-old Tfam KO mice, i.e. before and when mice are about to enter the terminal stage, respectively. Although force in the unfatigued state was reduced in Tfam KO mice compared to control littermates (wild type) only at 14 weeks, during repeated submaximal contractions fatigue was faster at both ages. During fatiguing stimulation, total phosphocreatine breakdown was larger in Tfam KO muscle than in wild-type muscle at both ages, whereas phosphocreatine consumption was faster only at 14 weeks. In conclusion, the Tfam KO mouse model represents a reliable model of lethal mitochondrial myopathy in which impaired mitochondrial energy production and premature fatigue occur before muscle weakness and early death.

Summary: A time-course study of mitochondrial and muscular dysfunctions in a mouse model of mitochondrial myopathy reveals that decreased resistance to fatigue together with decreased oxidative capacities arise ahead of muscle weakness.

The Application of Creatine Supplementation in Medical Rehabilitation

Numerous health conditions affecting the musculoskeletal, cardiopulmonary, and nervous systems can result in physical dysfunction, impaired performance, muscle weakness, and disuse-induced atrophy. Due to its well-documented anabolic potential, creatine monohydrate has been investigated as a supplemental agent to mitigate the loss of muscle mass and function in a variety of acute and chronic conditions. A review of the literature was conducted to assess the current state of knowledge regarding the effects of creatine supplementation on rehabilitation from immobilization and injury, neurodegenerative diseases, cardiopulmonary disease, and other muscular disorders. Several of the findings are encouraging, showcasing creatine's potential efficacy as a supplemental agent via preservation of muscle mass, strength, and physical function; however, the results are not consistent. For multiple diseases, only a few creatine studies with small sample sizes have been published, making it difficult to draw definitive conclusions. Rationale for discordant findings is further complicated by differences in disease pathologies, intervention protocols, creatine dosing and duration, and patient population. While creatine supplementation demonstrates promise as a therapeutic aid, more research is needed to fill gaps in knowledge within medical rehabilitation.

Exercise Testing, Physical Training and Fatigue in Patients with Mitochondrial Myopathy Related to mtDNA Mutations

Mutations in mitochondrial DNA (mtDNA) cause disruption of the oxidative phosphorylation chain and impair energy production in cells throughout the human body. Primary mitochondrial disorders due to mtDNA mutations can present with symptoms from adult-onset mono-organ affection to death in infancy due to multi-organ involvement. The heterogeneous phenotypes that patients with a mutation of mtDNA can present with are thought, at least to some extent, to be a result of differences in mtDNA mutation load among patients and even among tissues in the individual. The most common symptom in patients with mitochondrial myopathy (MM) is exercise intolerance. Since mitochondrial function can be assessed directly in skeletal muscle, exercise studies can be used to elucidate the physiological consequences of defective mitochondria due to mtDNA mutations. Moreover, exercise tests have been developed for diagnostic purposes for mitochondrial myopathy. In this review, we present the rationale for exercise testing of patients with MM due to mutations in mtDNA, evaluate the diagnostic yield of exercise tests for MM and touch upon how exercise tests can be used as tools for follow-up to assess disease course or effects of treatment interventions.

Post-exercise intramuscular O2 supply is tightly coupled with a higher proximal-to-distal ATP synthesis rate in human tibialis anterior

Key points

The post‐exercise recovery of phosphocreatine, a measure of the oxidative capacity of muscles, as assessed by ³¹P MR spectroscopy, shows a striking increase from distal to proximal along the human tibialis anterior muscle.

To investigate why this muscle exhibits a greater oxidative capacity proximally, we tested whether the spatial variation in phosphocreatine recovery rate is related to oxygen supply, muscle fibre type or type of exercise.

We revealed that oxygen supply also increases from distal to proximal along the tibialis anterior, and that it strongly correlated with phosphocreatine recovery. Carnosine level, a surrogate measure for muscle fibre type was not different between proximal and distal, and type of exercise did not affect the gradient in phosphocreatine recovery rate.

Taken together, the findings of this study suggest that the post‐exercise spatial gradients in oxygen supply and phosphocreatine recovery are driven by a higher intrinsic mitochondrial oxidative capacity proximally.

Abstract

Phosphorus magnetic resonance spectroscopy (³¹P MRS) of human tibialis anterior (TA) revealed a strong proximo‐distal gradient in the post‐exercise phosphocreatine (PCr) recovery rate constant (k_PCr), a measure of muscle oxidative capacity. The aim of this study was to investigate whether this k_PCr gradient is related to O₂ supply, resting phosphorylation potential, muscle fibre type, or type of exercise. Fifteen male volunteers performed continuous isometric ankle dorsiflexion at 30% maximum force until exhaustion. At multiple locations along the TA, we measured the oxidative PCr resynthesis rate (V_PCr = k_PCr × PCr depletion) by ³¹P MRS, the oxyhaemoglobin recovery rate constant (k_O2Hb) by near infrared spectroscopy, and muscle perfusion with MR intravoxel incoherent motion imaging. The k_O2Hb, k_PCr, V_PCr and muscle perfusion depended on measurement location (P < 0.001, P < 0.001, P = 0.032 and P = 0.003, respectively), all being greater proximally. The k_O2Hb and muscle perfusion correlated with k_PCr (r = 0.956 and r = 0.852, respectively) and V_PCr (r = 0.932 and r = 0.985, respectively), the latter reflecting metabolic O₂ consumption. Resting phosphorylation potential (PCr/inorganic phosphate) was also higher proximally (P < 0.001). The surrogate for fibre type, carnosine content measured by ¹H MRS, did not differ between distal and proximal TA (P = 0.884). Performing intermittent exercise to avoid exercise ischaemia, still led to larger k_PCr proximally than distally (P = 0.013). In conclusion, the spatial k_PCr gradient is strongly associated with the spatial variation in O₂ supply. It cannot be explained by exercise‐induced ischaemia nor by fibre type. Our findings suggest it is driven by a higher proximal intrinsic mitochondrial oxidative capacity, apparently to support contractile performance of the TA.

The post‐exercise recovery of phosphocreatine, a measure of the oxidative capacity of muscles, as assessed by ³¹P MR spectroscopy, shows a striking increase from distal to proximal along the human tibialis anterior muscle.

To investigate why this muscle exhibits a greater oxidative capacity proximally, we tested whether the spatial variation in phosphocreatine recovery rate is related to oxygen supply, muscle fibre type or type of exercise.

We revealed that oxygen supply also increases from distal to proximal along the tibialis anterior, and that it strongly correlated with phosphocreatine recovery. Carnosine level, a surrogate measure for muscle fibre type was not different between proximal and distal, and type of exercise did not affect the gradient in phosphocreatine recovery rate.

Taken together, the findings of this study suggest that the post‐exercise spatial gradients in oxygen supply and phosphocreatine recovery are driven by a higher intrinsic mitochondrial oxidative capacity proximally.

Unexplained exertional intolerance associated with impaired systemic oxygen extraction

PURPOSE

The clinical investigation of exertional intolerance generally focuses on cardiopulmonary diseases, while peripheral factors are often overlooked. We hypothesize that a subset of patients exists whose predominant exercise limitation is due to abnormal systemic oxygen extraction (SOE).

METHODS

We reviewed invasive cardiopulmonary exercise test (iCPET) results of 313 consecutive patients presenting with unexplained exertional intolerance. An exercise limit due to poor SOE was defined as peak exercise (Ca-vO₂)/[Hb] ≤ 0.8 and VO_2max < 80% predicted in the absence of a cardiac or pulmonary mechanical limit. Those with peak (Ca-vO₂)/[Hb] > 0.8, VO_2max ≥ 80%, and no cardiac or pulmonary limit were considered otherwise normal. The otherwise normal group was divided into hyperventilators (HV) and normals (NL). Hyperventilation was defined as peak PaCO₂ < [1.5 × HCO₃ + 6].

RESULTS

Prevalence of impaired SOE as the sole cause of exertional intolerance was 12.5% (32/257). At peak exercise, poor SOE and HV had less acidemic arterial blood compared to NL (pHa = 7.39 ± 0.05 vs. 7.38 ± 0.05 vs. 7.32 ± 0.02, p < 0.001), which was explained by relative hypocapnia (PaCO₂ = 29.9 ± 5.4 mmHg vs. 31.6 ± 5.4 vs. 37.5 ± 3.4, p < 0.001). For a subset of poor SOE, this relative alkalemia, also seen in mixed venous blood, was associated with a normal PvO₂ nadir (28 ± 2 mmHg vs. 26 ± 4, p = 0.627) but increased SvO₂ at peak exercise (44.1 ± 5.2% vs. 31.4 ± 7.0, p < 0.001).

CONCLUSIONS

We identified a cohort of patients whose exercise limitation is due only to systemic oxygen extraction, due to either an intrinsic abnormality of skeletal muscle mitochondrion, limb muscle microcirculatory dysregulation, or hyperventilation and left shift the oxyhemoglobin dissociation curve.

Muscle oxidative phosphorylation quantitation using creatine chemical exchange saturation transfer (CrCEST) MRI in mitochondrial disorders

Systemic mitochondrial energy deficiency is implicated in the pathophysiology of many age-related human diseases. Currently available tools to estimate mitochondrial oxidative phosphorylation (OXPHOS) capacity in skeletal muscle in vivo lack high anatomic resolution. Muscle groups vary with respect to their contractile and metabolic properties. Therefore, muscle group-specific estimates of OXPHOS would be advantageous. To address this need, a noninvasive creatine chemical exchange saturation transfer (CrCEST) MRI technique has recently been developed, which provides a measure of free creatine. After exercise, skeletal muscle can be imaged with CrCEST in order to make muscle group-specific measurements of OXPHOS capacity, reflected in the recovery rate (τCr) of free Cr. In this study, we found that individuals with genetic mitochondrial diseases had significantly (P = 0.026) prolonged postexercise τCr in the medial gastrocnemius muscle, suggestive of less OXPHOS capacity. Additionally, we observed that lower resting CrCEST was associated with prolonged τPCr, with a Pearson's correlation coefficient of -0.42 (P = 0.046), consistent with previous hypotheses predicting that resting creatine levels may correlate with ³¹P magnetic resonance spectroscopy-based estimates of OXPHOS capacity. We conclude that CrCEST can noninvasively detect changes in muscle creatine content and OXPHOS capacity, with high anatomic resolution, in individuals with mitochondrial disorders.

Mitochondrial Dysfunction and Migraine

The molecular basis of migraine is still not completely understood. An impairment of mitochondrial oxidative metabolism might play a role in the pathophysiology of this disease, by influencing neuronal information processing. Biochemical assays of platelets and muscle biopsies performed in migraine sufferers have shown a decreased activity of the respiratory chain enzymes. Studies with phosphorus magnetic resonance spectroscopy (31P-MRS) have demonstrated an impairment of the brain oxidative energy metabolism both during and between migraine attacks. However, molecular genetic studies have not detected specific mitochondrial DNA (mtDNA) mutations in patients with migraine, although other studies suggest that particular genetic markers (i.e. neutral polymorphisms or secondary mtDNA mutations) might be present in some migraine sufferers. Further studies are still needed to clarify if migraine is associated with unidentified mutations on the mtDNA or on nuclear genes that code mitochondrial proteins. In this paper, we review morphological, biochemical, imaging and genetic studies which bear on the hypothesis that migraine may be related to mitochondrial dysfunction at least in some individuals.

MRI assessment of regional differences in phosphorus-31 metabolism and morphological abnormalities of the foot muscles in diabetes

PURPOSE

To assess differences in the phosphorus-31 (³¹ P) metabolism and morphology in multiple muscle regions in the forefoot of diabetic patients and normal subjects.

MATERIALS AND METHODS

Fifteen diabetic patients and 15 normal subjects were assessed for muscle atrophy by ¹ H magnetic resonance imaging (MRI) at 3T to grade the flexor hallucis, adductor hallucis, interosseous regions, and entire foot cross-section. Each region and the entire foot were also quantitatively evaluated for metabolic function using ³¹ P imaging for spatial mapping of the inorganic phosphate (Pi) to phosphocreatine (PCr) ratio (Pi/PCr). The ratio of viable muscle area to the predefined region areas (³¹ P/¹ H) was calculated. The variability of each method was assessed by its coefficient of variation (CV).

RESULTS

Muscle atrophy was significantly more severe in diabetic compared to normal subjects in all regions (P < 0.01). The ³¹ P/¹ H area ratio was significantly larger in the adductor hallucis than in the other two regions (P < 0.05). The Pi/PCr ratio was significantly different between the two groups in the flexor hallucis and interosseous regions (P < 0.05) but not adductor hallucis region. The CV for Pi/PCr ranged from 10.13 to 55.84, while it ranged from 73.40 to 263.90 for qualitative grading.

CONCLUSION

Changes in atrophy and metabolism appear to occur unequally between different regions of the forefoot in diabetes. The adductor hallucis region appears more capable of maintaining structural and metabolic integrity than the flexor hallucis or interosseous regions. The CV analysis suggests that the quantitative ³¹ P methods have less variability than the qualitative grading. J. Magn. Reson. Imaging 2016;44:1132-1142.

Altered Energetics of Exercise Explain Risk of Rhabdomyolysis in Very Long-Chain Acyl-CoA Dehydrogenase Deficiency

Rhabdomyolysis is common in very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) and other metabolic myopathies, but its pathogenic basis is poorly understood. Here, we show that prolonged bicycling exercise against a standardized moderate workload in VLCADD patients is associated with threefold bigger changes in phosphocreatine (PCr) and inorganic phosphate (Pi) concentrations in quadriceps muscle and twofold lower changes in plasma acetyl-carnitine levels than in healthy subjects. This result is consistent with the hypothesis that muscle ATP homeostasis during exercise is compromised in VLCADD. However, the measured rates of PCr and Pi recovery post-exercise showed that the mitochondrial capacity for ATP synthesis in VLCADD muscle was normal. Mathematical modeling of oxidative ATP metabolism in muscle composed of three different fiber types indicated that the observed altered energy balance during submaximal exercise in VLCADD patients may be explained by a slow-to-fast shift in quadriceps fiber-type composition corresponding to 30% of the slow-twitch fiber-type pool in healthy quadriceps muscle. This study demonstrates for the first time that quadriceps energy balance during exercise in VLCADD patients is altered but not because of failing mitochondrial function. Our findings provide new clues to understanding the risk of rhabdomyolysis following exercise in human VLCADD.

Forearm P-31 Nuclear Magnetic Resonance Spectroscopy Studies in Oculopharyngeal Muscular Dystrophy

Five siblings with autosomal dominant oculopharyngeal muscular dystrophy (OPMD) underwent P-31 Nuclear Magnetic Resonance Spectroscopy studies of forearm flexor muscles. Mean values of PCr/(PCr + Pi) in the patients were reduced (p = 0.01) and pH elevated (p = 0.02) in resting muscle when compared to controls. During exercise PCr/(PCr + Pi) fell quickly to values less than controls (p < 0.0001) despite submaximal exercise output and developed exercise-induced acidosis which exceeded that of controls (p = 0.05). Acidosis recovered slowly despite relatively normal recovery of PCr/(PCr + Pi) following exercise. Within the patient group, however, one member had normal resting, exercise and recovery values. The studies suggest that OPMD is a more widespread disorder of striated muscle than clinically appreciated. The pattern of findings observed in OPMD differs from those identified in denervation, disuse and mitochondrial myopathy.

Quantification of skeletal muscle mitochondrial function by 31P magnetic resonance spectroscopy techniques: a quantitative review

Magnetic resonance spectroscopy (MRS) can give information about cellular metabolism in vivo which is difficult to obtain in other ways. In skeletal muscle, non-invasive (31) P MRS measurements of the post-exercise recovery kinetics of pH, [PCr], [Pi] and [ADP] contain valuable information about muscle mitochondrial function and cellular pH homeostasis in vivo, but quantitative interpretation depends on understanding the underlying physiology. Here, by giving examples of the analysis of (31) P MRS recovery data, by some simple computational simulation, and by extensively comparing data from published studies using both (31) P MRS and invasive direct measurements of muscle O2 consumption in a common analytical framework, we consider what can be learnt quantitatively about mitochondrial metabolism in skeletal muscle using MRS-based methodology. We explore some technical and conceptual limitations of current methods, and point out some aspects of the physiology which are still incompletely understood.

Mitochondrial dysfunctions in myalgic encephalomyelitis/chronic fatigue syndrome explained by activated immuno-inflammatory, oxidative and nitrosative stress pathways

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/cfs) is classified by the World Health Organization as a disorder of the central nervous system. ME/cfs is an neuro-immune disorder accompanied by chronic low-grade inflammation, increased levels of oxidative and nitrosative stress (O&NS), O&NS-mediated damage to fatty acids, DNA and proteins, autoimmune reactions directed against neoantigens and brain disorders. Mitochondrial dysfunctions have been found in ME/cfs, e.g. lowered ATP production, impaired oxidative phosphorylation and mitochondrial damage. This paper reviews the pathways that may explain mitochondrial dysfunctions in ME/cfs. Increased levels of pro-inflammatory cytokines, such as interleukin-1 and tumor necrosis factor-α, and elastase, and increased O&NS may inhibit mitochondrial respiration, decrease the activities of the electron transport chain and mitochondrial membrane potential, increase mitochondrial membrane permeability, interfere with ATP production and cause mitochondrial shutdown. The activated O&NS pathways may additionally lead to damage of mitochondrial DNA and membranes thus decreasing membrane fluidity. Lowered levels of antioxidants, zinc and coenzyme Q10, and ω3 polyunsaturated fatty acids in ME/cfs may further aggravate the activated immuno-inflammatory and O&NS pathways. Therefore, it may be concluded that immuno-inflammatory and O&NS pathways may play a role in the mitochondrial dysfunctions and consequently the bioenergetic abnormalities seen in patients with ME/cfs. Defects in ATP production and the electron transport complex, in turn, are associated with an elevated production of superoxide and hydrogen peroxide in mitochondria creating adaptive and synergistic damage. It is argued that mitochondrial dysfunctions, e.g. lowered ATP production, may play a role in the onset of ME/cfs symptoms, e.g. fatigue and post exertional malaise, and may explain in part the central metabolic abnormalities observed in ME/cfs, e.g. glucose hypometabolism and cerebral hypoperfusion.

MITOCHONDRIA: investigation of in vivo muscle mitochondrial function by 31P magnetic resonance spectroscopy

The most important function of mitochondria is the production of energy in the form of ATP. The socio-economic impact of human diseases that affect skeletal muscle mitochondrial function is growing, and improving their clinical management critically depends on the development of non-invasive assays to assess mitochondrial function and monitor the effects of interventions. 31P magnetic resonance spectroscopy provides two approaches that have been used to assess in vivo ATP synthesis in skeletal muscle: measuring Pi→ATP exchange flux using saturation transfer in resting muscle, and measuring phosphocreatine recovery kinetics after exercise. However, Pi→ATP exchange does not represent net mitochondrial ATP synthesis flux and has no simple relationship with mitochondrial function. Post-exercise phosphocreatine recovery kinetics, on the other hand, yield reliable measures of muscle mitochondrial capacity in vivo, whose ability to define the site of functional defects is enhanced by combination with other non-invasive techniques.

Bioenergetics of the calf muscle in Friedreich ataxia patients measured by 31P-MRS before and after treatment with recombinant human erythropoietin

Friedreich ataxia (FRDA) is caused by a GAA repeat expansion in the FXN gene leading to reduced expression of the mitochondrial protein frataxin. Recombinant human erythropoietin (rhuEPO) is suggested to increase frataxin levels, alter mitochondrial function and improve clinical scores in FRDA patients. Aim of the present pilot study was to investigate mitochondrial metabolism of skeletal muscle tissue in FRDA patients and examine effects of rhuEPO administration by phosphorus 31 magnetic resonance spectroscopy (31P MRS). Seven genetically confirmed FRDA patients underwent 31P MRS of the calf muscles using a rest-exercise-recovery protocol before and after receiving 3000 IU of rhuEPO for eight weeks. FRDA patients showed more rapid phosphocreatine (PCr) depletion and increased accumulation of inorganic phosphate (Pi) during incremental exercise as compared to controls. After maximal exhaustive exercise prolonged regeneration of PCR and slowed decline in Pi can be seen in FRDA. PCr regeneration as hallmark of mitochondrial ATP production revealed correlation to activity of complex II/III of the respiratory chain and to demographic values. PCr and Pi kinetics were not influenced by rhuEPO administration. Our results confirm mitochondrial dysfunction and exercise intolerance due to impaired oxidative phosphorylation in skeletal muscle tissue of FRDA patients. MRS did not show improved mitochondrial bioenergetics after eight weeks of rhuEPO exposition in skeletal muscle tissue of FRDA patients.

Trial Registration

EU Clinical Trials Register2008-000040-13

Decreased frontal lobe phosphocreatine levels in methamphetamine users

BACKGROUND

Mitochondria-related mechanisms have been suggested to mediate methamphetamine (METH) toxicity. However, changes in brain energetics associated with high-energy phosphate metabolism have not been investigated in METH users. Phosphorus-31 ((31)P) magnetic resonance spectroscopy (MRS) was used to evaluate changes in mitochondrial high energy phosphates, including phosphocreatine (PCr) and β-nucleoside triphosphate (β-NTP, primarily ATP in brain) levels. We hypothesized that METH users would have decreased high-energy PCr levels in the frontal gray matter.

METHODS

Study participants consisted of 51 METH (age=32.8±6.7) and 23 healthy comparison (age=31.1±7.5) subjects. High-energy phosphate metabolite levels were compared between the groups and potential gender differences were explored.

RESULTS

METH users had lower ratios of PCr to total pool of exchangeable phosphate (PCr/TPP) in the frontal lobe as compared to the healthy subjects (p=.001). The lower PCr levels in METH subjects were significantly associated with lifetime amount of METH use (p=.003). A sub-analysis for gender differences revealed that female METH users, who had lower daily amounts (1.1±1.0g) of METH use than males (1.4±1.7g), had significantly lower PCr/TPP ratios than male METH users, controlling for the amount of METH use (p=.02).

CONCLUSIONS

The present findings suggest that METH compromises frontal lobe high-energy phosphate metabolism in a dose-responsive manner. Our findings also suggest that the abnormality in frontal lobe high-energy phosphate metabolism might be more prominent in female than in male METH users. This is significant as decreased PCr levels have been associated with depressive symptoms, and poor responses to antidepressant treatment have been reported in those with decreased PCr levels.

Bio-energetic impairment in human calf muscle in thyroid disorders: a 31P MRS study

Mitochondrial metabolism particularly oxidative phosphorylation is greatly influenced by thyroid hormones. Earlier studies have described neuromuscular symptoms as well as impaired muscle metabolism in hypothyroid and hyperthyroid patients. In this study, we intend to look in to the muscle bioenergetics including phosphocreatine recovery kinetics based oxidative metabolism in thyroid dysfunction using in vivo (31)P nuclear magnetic resonance spectroscopy (MRS). (31)P MRS was carried out at resting state on 32 hypothyroid, 10 hyperthyroid patients and 25 control subjects. Nine out of 32 hypothyroid patients and 17 out of 25 control subjects under went exercise protocol for oxidative metabolism study and performed plantar flexion exercise while lying supine in 1.5 T magnetic resonance scanner using custom built exercise device. MRS measurements of inorganic phosphate (Pi), phosphocreatine (PCr), phosphodiesters (PDE) and adenosine triphosphate (ATP) of the calf muscle were acquired during rest, exercise and recovery phase. PCr recovery rate constant (k(PCr)) and oxidative capacity were calculated by monoexponential fit of PCr versus time (t) at the beginning of recovery. During resting condition in hypothyroid patients, PCr/Pi ratio was reduced whereas PDE/ATP and Pi/ATP were increased. However, in case of hyperthyroidism, an increased PCr/Pi ratio and reduced PDE/ATP and Pi/ATP were observed. The results confirmed differential energy status of the muscle due to increased or decreased levels of thyroid hormone. Our results also demonstrate reduced oxidative metabolism in hypothyroid patients based on PCr recovery kinetics. PCr recovery kinetics study after exercise revealed decreased PCr recovery rate constant (k(PCr)) in hypothyroid patients compared to controls that resulted in decrease in oxidative capacity of muscle by 50% in hypothyroids. These findings are consistent with a defect of high energy phosphate mitochondrial metabolism in thyroid dysfunction.

A plasma signature of human mitochondrial disease revealed through metabolic profiling of spent media from cultured muscle cells

Mutations in either the mitochondrial or nuclear genomes can give rise to respiratory chain disease (RCD), a large class of devastating metabolic disorders. Their clinical management is challenging, in part because we lack facile and accurate biomarkers to aid in diagnosis and in the monitoring of disease progression. Here we introduce a sequential strategy that combines biochemical analysis of spent media from cell culture with analysis of patient plasma to identify disease biomarkers. First, we applied global metabolic profiling to spotlight 32 metabolites whose uptake or secretion kinetics were altered by chemical inhibition of the respiratory chain in cultured muscle . These metabolites span a wide range of pathways and include lactate and alanine, which are used clinically as biomarkers of RCD. We next measured the cell culture-defined metabolites in human plasma to discover that creatine is reproducibly elevated in two independent cohorts of RCD patients, exceeding lactate and alanine in magnitude of elevation and statistical significance. In cell culture extracellular creatine was inversely related to the intracellular phosphocreatine:creatine ratio suggesting that the elevation of plasma creatine in RCD patients signals a low energetic state of tissues using the phosphocreatine shuttle. Our study identifies plasma creatine as a potential biomarker of human mitochondrial dysfunction that could be clinically useful. More generally, we illustrate how spent media from cellular models of disease may provide a window into the biochemical derangements in human plasma, an approach that could, in principle, be extended to a range of complex diseases.

Multinuclear magnetic resonance spectroscopy for in vivo assessment of mitochondrial dysfunction in Parkinson's disease

Parkinson's disease (PD) is a common and often devastating neurodegenerative disease affecting up to one million individuals in the United States alone. Multiple lines of evidence support mitochondrial dysfunction as a primary or secondary event in PD pathogenesis; a better understanding, therefore, of how mitochondrial function is altered in vivo in brain tissue in PD is a critical step toward developing potential PD biomarkers. In vivo study of mitochondrial metabolism in human subjects has previously been technically challenging. However, proton and phosphorus magnetic resonance spectroscopy ((1)H and (31)P MRS) are powerful noninvasive techniques that allow evaluation in vivo of lactate, a marker of anaerobic glycolysis, and high energy phosphates, such as adenosine triphosphate and phosphocreatine, directly reflecting mitochondrial function. This article reviews previous (1)H and (31)P MRS studies in PD, which demonstrate metabolic abnormalities consistent with mitochondrial dysfunction, and then presents recent (1)H MRS data revealing abnormally elevated lactate levels in PD subjects.

Structural evidence for co-evolution of the regulation of contraction and energy production in skeletal muscle

Skeletal muscle phosphorylase kinase (PhK) is a Ca(2+)-dependent enzyme complex, (alpha beta gamma delta)(4), with the delta subunit being tightly bound endogenous calmodulin (CaM). The Ca(2+)-dependent activation of glycogen phosphorylase by PhK couples muscle contraction with glycogen breakdown in the "excitation-contraction-energy production triad." Although the Ca(2+)-dependent protein-protein interactions among the relevant contractile components of muscle are well characterized, such interactions have not been previously examined in the intact PhK complex. Here we show that zero-length cross-linking of the PhK complex produces a covalent dimer of its catalytic gamma and CaM subunits. Utilizing mass spectrometry, we determined the residues cross-linked to be in an EF hand of CaM and in a region of the gamma subunit sharing high sequence similarity with the Ca(2+)-sensitive molecular switch of troponin I that is known to bind actin and troponin C, a homolog of CaM. Our findings represent an unusual binding of CaM to a target protein and supply an explanation for the low Ca(2+) stoichiometry of PhK that has been reported. They also provide direct structural evidence supporting co-evolution of the coordinate regulation by Ca(2+) of contraction and energy production in muscle through the sharing of a common structural motif in troponin I and the catalytic subunit of PhK for their respective interactions with the homologous Ca(2+)-binding proteins troponin C and CaM.

Muscle metabolism in patients with polymyositis simultaneously evaluated by using 31P-magnetic resonance spectroscopy and near-infrared spectroscopy

Simultaneous measurements of muscle energy metabolism using (31)P-magnetic resonance spectroscopy ((31)P-MRS) and the kinetics of muscular oxygen metabolism using near-infrared spectroscopy (NIRS) were conducted in polymyositis (PM) patients. The subjects were 12 PM patients (age 45 +/- 12 years) and 12 normal controls (age 41 +/- 12 years). The muscle phosphocreatine (PCr) index and intracellular pH (pHi) were determined with (31)P-MRS and the changes in intramuscular oxygenated (oxy-Hb), deoxygenated (deoxy-Hb), and total haemoglobin (total Hb) were evaluated with NIRS . The pHi and PCr index before steroid therapy in PM patients were significantly lower during exercise than in normal controls, and their recovery was statistically significantly delayed compared with the controls. The pattern of changes in NIRS over time before steroid therapy in PM patients differed from that in normal controls. There were smaller changes in deoxy-Hb and oxy-Hb during exercise, and total Hb decreased during exercise. In contrast, the kinetics of muscular metabolism after steroid therapy showed changes similar to those seen in normal controls. Simultaneous (31)P-MRS and NIRS measurements to determine the kinetics of muscular metabolism are expected to be useful as a noninvasive approach for the evaluation of treatment effects in PM patients.

Intersubject differences in the effect of acidosis on phosphocreatine recovery kinetics in muscle after exercise are due to differences in proton efflux rates

(31)P magnetic resonance spectroscopy provides the possibility of obtaining bioenergetic data during skeletal muscle exercise and recovery. The time constant of phosphocreatine (PCr) recovery (tau(PCr)) has been used as a measure of mitochondrial function. However, cytosolic pH has a strong influence on the kinetics of PCr recovery, and it has been suggested that tau(PCr) should be normalized for end-exercise pH. A general correction can only be applied if there are no intersubject differences in the pH dependence of tau(PCr). We investigated the pH dependence of tau(PCr) on a subject-by-subject basis. Furthermore, we determined the kinetics of proton efflux at the start of recovery. Intracellular acidosis slowed PCr recovery, and the pH dependence of tau(PCr) differed among subjects, ranging from -33.0 to -75.3 s/pH unit. The slope of the relation between tau(PCr) and end-exercise pH was positively correlated with both the proton efflux rate and the apparent proton efflux rate constant, indicating that subjects with a smaller pH dependence of tau(PCr) have a higher proton efflux rate. Our study implies that simply correcting tau(PCr) for end-exercise pH is not adequate, in particular when comparing patients and control subjects, because certain disorders are characterized by altered proton efflux from muscle fibers.

31P-MRS of skeletal muscle is not a sensitive diagnostic test for mitochondrial myopathy

Clinical phenotypes of persons with mitochondrial DNA (mtDNA) mutations vary considerably. Therefore, diagnosing mitochondrial myopathy (MM) patients can be challenging and warrants diagnostic guidelines. (31)phosphorous magnetic resonance spectroscopy ((31)P-MRS) have been included as a minor diagnostic criterion for MM but the diagnostic strength of this test has not been compared with that of other commonly used diagnostic procedures for MM. To investigate this, we studied seven patients with single, large-scale deletions-, nine with point mutations of mtDNA and 14 healthy subjects, who were investigated for the following: 1) (31)P-MRS of lower arm and leg muscles before and after exercise, 2) resting and peak-exercise induced increases of plasma lactate, 3) muscle morphology and -mitochondrial enzyme activity, 4) maximal oxygen uptake (VO(2max)), 5) venous oxygen desaturation during handgrip exercise and 6) a neurological examination. All MM patients had clinical symptoms of MM, > 2% ragged red fibers in muscle, and impaired oxygen desaturation during handgrip. Fourteen of 16 patients had impaired VO(2max), 10/16 had elevated resting plasma lactate, and 10/11 that were investigated had impaired citrate synthase-corrected complex I activity. Resting PCr/P(i) ratio and leg P(i) recovery were lower in MM patients vs. healthy subjects. PCr and ATP production after exercise were similar in patients and healthy subjects. Although the specificity for MM of some (31)P-MRS variables was as high as 100%, the sensitivity was low (0-63%) and the diagnostic strength of (31)P-MRS was inferior to the other diagnostic tests for MM. Thus, (31)P-MRS should not be a routine test for MM, but may be an important research tool.

31P MR spectroscopy and in vitro markers of oxidative capacity in type 2 diabetes patients

BACKGROUND

Skeletal muscle mitochondrial function in type 2 diabetes (T2D) is currently being studied intensively. In vivo (31)P magnetic resonance spectroscopy ((31)P MRS) is a noninvasive tool used to measure mitochondrial respiratory function (MIFU) in skeletal muscle tissue. However, microvascular co-morbidity in long-standing T2D can interfere with the (31)P MRS methodology.

AIM

To compare (31)P MRS-derived parameters describing in vivo MIFU with an in vitro assessment of muscle respiratory capacity and muscle fiber-type composition in T2D patients.

METHODS

(31)P MRS was applied in long-standing, insulin-treated T2D patients. (31)P MRS markers of MIFU were measured in the M. vastus lateralis. Muscle biopsy samples were collected from the same muscle and analyzed for succinate dehydrogenase activity (SDH) and fiber-type distribution.

RESULTS

Several (31)P MRS parameters of MIFU showed moderate to good correlations with the percentage of type I fibers and type I fiber-specific SDH activity (Pearson's R between 0.70 and 0.75). In vivo and in vitro parameters of local mitochondrial respiration also correlated well with whole-body fitness levels (VO (2peak)) in these patients (Pearson's R between 0.62 and 0.90).

CONCLUSION

Good correlations exist between in vivo and in vitro measurements of MIFU in long-standing insulin-treated T2D subjects, which are qualitatively and quantitatively consistent with previous results measured in healthy subjects. This justifies the use of (31)P MRS to measure MIFU in relation to T2D.

Dynamic MRS and MRI of skeletal muscle function and biomechanics

MR is a powerful technique for studying the biomechanical and functional properties of skeletal muscle in vivo in health and disease. This review focuses on 31P, 1H and 13C MR spectroscopy for assessment of the dynamics of muscle metabolism and on dynamic 1H MRI methods for non-invasive measurement of the biomechanical and functional properties of skeletal muscle. The information thus obtained ranges from the microscopic level of the metabolism of the myocyte to the macroscopic level of the contractile function of muscle complexes. The MR technology presented plays a vital role in achieving a better understanding of many basic aspects of muscle function, including the regulation of mitochondrial activity and the intricate interplay between muscle fiber organization and contractile function. In addition, these tools are increasingly being employed to establish novel diagnostic procedures as well as to monitor the effects of therapeutic and lifestyle interventions for muscle disorders that have an increasing impact in modern society.

Friedreich's ataxia: from disease mechanisms to therapeutic interventions

Friedreich's ataxia (FRDA) is the most common inherited ataxia. FRDA is an autosomal recessive degenerative disorder caused by a GAA triplet expansion or point mutations in the FRDA gene on chromosome 9q13. The FRDA gene product, frataxin, is a widely expressed mitochondrial protein that is severely reduced in FRDApatients. The function of frataxin has not been established yet. Studies of the yeast and animal model of the disease as well as of tissues from FRDA patients have demonstrated that deficit of frataxin is associated with mitochondrial iron accumulation, increased sensitivity to oxidative stress, deficit of respiratory chain complex activities and in vivo impairment of tissue energy metabolism. Pilot studies have shown the potential effect of antioxidant therapy in this condition and provide a strong rationale for designing larger clinical randomized trials.

Aerobic exercise and muscle metabolism in patients with mitochondrial myopathy

Exercise therapy improves mitochondrial function in patients with mitochondrial myopathy (MM). We undertook this study to determine the metabolic abnormalities that are improved by exercise therapy. This study identified metabolic pathology using (31)P-magnetic resonance spectroscopy and magnetic resonance imaging (MRI) in a group of patients with MM compared to a control group matched for age, gender, and physical activity. We also observed the effect of exercise therapy for 12 weeks on muscle metabolism and physical function in the MM group. During muscle activity, there was impaired responsiveness of the mitochondria to changes in cytosolic adenosine diphosphate concentration, increased dependence on anaerobic energy pathways, and an adaptive increase in proton efflux in patients with MM. Following exercise therapy, mitochondrial function and muscle mass improved without any change in proton efflux rate. These metabolic findings were accompanied by improvements in functional ability. We conclude that there are significant metabolic differences between patients with MM and a control population, independent of age, gender, and physical activity. Exercise therapy can assist in improving mitochondrial function in MM patients.

The influence of tissue blood flow volume on energy metabolism in masseter muscles

This study investigated the energy metabolism of masseter muscles by 31P-Magnetic Resonance Spectroscopy (MRS) during increased blood flow induced by hot pack application to clarify the influence of changes in blood flow on muscle fatigue. Twelve healthy subjects with no history of muscle pain in the masticatory system participated in this study. The 31P-MRS measurements were performed before and after hot pack application and the ratio of phosphocreatine (PCr) acting as the energy source to reproduce ATP to beta-ATP, the PCr/beta-ATP ratio, was analyzed. Results showed that PCr/beta-ATP ratios increased significantly by an average of 22.4% after the hot pack application. The results suggest that changes in blood flow volume influence the energy metabolism in masseter muscles and that blood flow increases due to the hot pack cause higher energy levels in masseter muscles and offer an advantageous condition for preventing and relieving muscle fatigue.

High-energy phosphate metabolism in the calf muscle during moderate isotonic exercise under different degrees of cuff compression: A phosphorus 31 magnetic resonance spectroscopy study

BACKGROUND

The purpose of this study was to investigate phosphocreatine (PCr) and inorganic phosphate levels as well as pH changes in exercising muscle at a workload of 4.5 W under progressive cuff stenoses, whereby the flow reduction due to cuff compression was quantified by flow-sensitive magnetic resonance imaging.

METHODS

By using a whole-body 1.5-T magnetic resonance scanner and an exercise bench, serial phosphorus 31 (31P) magnetic resonance spectroscopy with a time resolution of 30 seconds was performed in 10 healthy men. Percentage changes in PCr, inorganic phosphate (Pi), and pH were statistically evaluated in comparison with baseline. The exercise protocol was characterized by a constant workload level of 4.5 W. Ischemic conditions were achieved by a cuff that was placed at the upper leg. Consecutively, increments of 0, 60, 90, 120, and 150 mm Hg were applied. Each increment lasted for 3 minutes. The following rest period was 10 minutes.

RESULTS

Blood flow increased significantly immediately after the onset of muscle exercise. No significant changes in blood flow were detected as long as the air pressure of the pneumatic cuff was 60 to 90 mm Hg. Significant reductions in blood flow were observed immediately after inflation of the cuff to 120 and 150 mm Hg. PCr passed into a steady state during the first increment with 0 mm Hg and showed no substantial changes during the increment with 60, 90, and 120 mm Hg. PCr hydrolysis seemed progressive during the 150-mm Hg increment. Pi passed into a plateau level at the onset of exercise and increased significantly at the increment of 150 mm Hg. The pH turned into a steady state with no significant changes during the increments up to 120 mm Hg. At 150 mm Hg, pH decreased progressively. PCr levels at the end of the 150-mm Hg increment correlated significantly and moderately with the reduction in blood flow.

CONCLUSIONS

Our study shows that the ischemic condition during constant muscle exercise is clearly characterized by PCr and Pi kinetics, as well as by pH changes. The correlation between the degree of blood flow reduction and PCr levels in the exercising muscle groups, which are supplied by the stenosed arteries, is the first essential of using 31P magnetic resonance spectroscopy in the assessment of the effect of arterial stenoses on muscle function in claudicants.

Creatine has no beneficial effect on skeletal muscle energy metabolism in patients with single mitochondrial DNA deletions: a placebo-controlled, double-blind 31P-MRS crossover study

The purpose of our randomized, double-blind, placebo-controlled crossover study in 15 patients with chronic progressive external ophthalmoplegia (CPEO) or Kearns-Sayre syndrome (KSS) because of single large-scale mitochondrial (mt) DNA deletions was to determine whether oral creatine (Cr) monohydrate can improve skeletal muscle energy metabolism in vivo. Each treatment phase with Cr in a dosage of 150 mg/kg body weight/day or placebo lasted 6 weeks. The effect of Cr was estimated by phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS), clinical and laboratory tests. (31)P-MRS analysis prior to treatment showed clear evidence of severe mitochondrial dysfunction. However, there were no relevant changes in (31)P-MRS parameters under Cr. In particular, phosphocreatine (PCr)/ATP at rest did not increase, and there was no facilitation of post-exercise PCr recovery. Clinical scores and laboratory tests did not alter significantly under Cr, which was tolerated without major side-effects in all patients. Cr supplementation did not improve skeletal muscle oxidative phosphorylation in our series of patients. However, one explanation for our negative findings may be the short study duration or the limited number of patients included.

Magnetic resonance spectroscopy in patients with MELAS

Localized magnetic resonance spectroscopy (MRS) yields sensitive metabolic markers to provide insight into the pathophysiology of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) in vivo. Findings in full MELAS syndrome at 1H MRS of the brain typically include severely elevated lactate and reduced N-acetylaspartate, glutamate, myo-inositol, and total creatine concentrations in stroke-like lesions. Similar but less extreme alterations are also common in gray matter (GM) regions that appear normal at magnetic resonance imaging. Phosphorus spectroscopy of peripheral muscle permits investigation of the bioenergetic status. A decline of the phosphorylation potential indicates a low energy reserve at rest. Phosphocreatine resynthesis during post-exercise recovery is delayed pointing to reduced mitochondrial capacity. As MRS is inherently non-invasive, follow-up studies can be performed to assess treatment response quantitatively.

The mono-exponential pattern of phosphocreatine recovery after muscle exercise is a particular case of a more complex behaviour

A mathematical model is proposed showing that the mono-exponential recovery of phosphocreatine (PCr) after exercise is an approximation of a more complex pattern, which is identified by a second-order differential equation. The model predicts the possibility of three different patterns of PCr recovery: bi-exponential, oscillatory damped, and critically damped; the mono-exponential pattern being a particular case of the functions which are solutions of the differential equation. The model was tested on a sample of recovery data from 50 volunteers, checking whether the recovery patterns predicted by the model lead to a significant improvement of fit (IF) compared with the mono-exponential pattern. Results show that the IF is linked to pH. Bi-exponential solutions showed an IF in the pH range 6.65-6.85, and the oscillatory solutions at pH>6.9. Critically damped solutions displayed a poor IF. Oscillation frequencies found in the oscillatory recoveries increase at increasing pH. These results show that pH has a pivotal role on the pattern of PCr recovery and implications on the regulation of oxidative phosphorylation are discussed.

Abnormal blood lactate accumulation after exercise in patients with multiple mitochondrial DNA deletions and minor muscular symptoms

STUDY OBJECTIVES

Muscle is one of the most commonly affected organs in mitochondrial disorders, and the symptoms are often exercise related. The cardiopulmonary exercise test with the determination of lactic acid formation could give supplementary information about the exercise-induced metabolic stress and compensatory mechanisms used in these disorders. The aim of this study was to evaluate the exercise capacity and lactate kinetics related to exercise in subjects with two genetically characterized mitochondrial disorders (multiple mitochondrial DNA deletions with PEO, MELAS) compared with lactate kinetics in subjects with metabolic myopathy (McArdle's disease) and in the healthy controls.

DESIGN

The subjects were consecutive, co-operative patients of Department of Neurology of Helsinki University Hospital. Molecular genetic analyses were used for group classification of the mitochondrial myopathy.

STUDY SUBJECTS

The study groups consisted of 11 patients with multiple deletions (PEO) and five patients with a point mutation in the mitochondrial DNA (MELAS), four patients with a muscle phosphorylase enzyme deficiency (McArdle's disease) and 13 healthy controls. The clinical disease of the patients was relatively mild.

MEASUREMENTS AND RESULTS

A graded exercise test with ventilatory gas analyses and venous blood lactic acid analyses was performed. The main finding was the prolonged accumulation of blood lactate after the exercise in the PEO and MELAS groups compared with the controls. An overcompensation in ventilation was found in the MELAS and PEO group.

CONCLUSIONS

The blood lactate accumulation after exercise occurs in patients with multiple mitochondrial DNA deletions or MELAS even in patients with only mild exercise intolerance. Cardiopulmonary exercise can be used in the diagnostic process of patients with mitochondrial myopathies.

High-energy phosphate metabolism during incremental calf exercise in humans measured by 31 phosphorus magnetic resonance spectroscopy (31P MRS)

Several previous 31 phosphorus magnetic resonance spectroscopy ((31)P MRS) studies performing incremental or progressive muscle exercises have observed that a decrease in pH is accompanied with an acceleration in phosphocreatine (PCr) hydrolysis. The purpose of this study was to investigate the relationship between PCr breakdown and pH during isotonic, exhaustive, incremental plantar flexion exercises. We included eight healthy, male volunteers into this study. Using a 1.5 Tesla MR scanner and a self-built exercise bench, we performed serial free induction decay (FID) (31)P MRS measurements with a time resolution of 1 min at rest, isotonic calf muscle exercise, and recovery. The exercise protocol consisted of 5-min intervals with 4.5, 6, 7.5, and 9 W workload followed by 9-min recovery. Changes in PCr and inorganic phosphate (Pi) were determined as percent changes in comparison to the baseline. In addition, pH values were calculated. This study obtained significant decreases in PCr corresponding to the gradual increases in workload. In each workload level that was succeeded by all volunteers, PCr hydrolysis passed into a steady state. After an early biphasic response, we detected a significant decrease in pH from the first to the second minute of the 6-W workload level followed by a further continuous decrease in pH up to the second minute of the recovery phase. The decrease in pH was not accompanied by acceleration in PCr hydrolysis. In conclusion, this study shows that PCr hydrolysis during incremental plantar flexion exercises passes into a steady state at different workload levels. The observed decrease in pH does not result in acceleration of PCr hydrolysis.

Attenuation of free radical production and paracrystalline inclusions by creatine supplementation in a patient with a novel cytochrome b mutation

Mitochondrial cytopathies are associated with increased free radical generation and paracrystalline inclusions. Paracrystalline inclusions were serendipitously found in a young male athlete with a very high respiratory exchange ratio during steady-state exercise; he also had an unusually low aerobic capacity. Direct sequencing of the mitochondrial DNA (mtDNA) coding regions revealed a novel missense mutation (G15497A) resulting in a glycine-->serine conversion at a highly conserved site in the cytochrome b gene in the subject, his mother, and sister. Cybrids, prepared by fusion of the subject's platelets with either U87MG rho degrees or SH-SY5Y rho degrees cells, generated higher basal levels of reactive oxygen species (ROS), had a lower adenosine triphosphate (ATP) content, and were more sensitive to oxygen and glucose deprivation and peroxynitrite generation compared to control cybrids with wild-type mtDNA. Cell survival was significantly enhanced with 50 mmol/L creatine monohydrate (CM) administration. The subject was also treated with CM (10 g/d) for a period of 5 weeks and a repeat muscle biopsy showed no paracrystalline inclusions. The results suggest that the development of exercise-induced paracrystalline inclusions may be influenced by the G15497A mtDNA mutation, and that CM mitigates against the pathological consequences of this mutation.

Overexpressions of myoglobin and antioxidant enzymes in ragged-red fibers of skeletal muscle from patients with mitochondrial encephalomyopathy

To determine the relationship between myoglobin (Mb) and the defense system against reactive oxygen species in various myopathies, we performed immunohistochemical analyses of Mb and various antioxidant enzymes, including manganese superoxide dismutase (Mn-SOD), copper zinc SOD (CuZn-SOD), catalase (CAT), and glutathione peroxidase (GSH-Px). Biopsied muscle specimens were obtained from patients with chronic progressive external ophthalmoplegia (CPEO), Kearns-Sayre syndrome (KSS), Duchenne muscular dystrophy (DMD), and polymyositis (PM). In patients with CPEO/KSS, stainings of Mb, SOD, CAT, and GSH-Px in nonatrophic ragged-red fibers (RRFs) were more intense than those in non-RRFs. These pronounced stainings corresponded to ragged-red lesions. The staining intensities of these antioxidant enzymes were significantly correlated with that of Mb (P < 0.001). Atrophic RRFs in specimens from patients with CPEO/KSS showed intense stainings of these antioxidant enzymes but not intense staining of Mb. In specimens from patients with DMD/PM, the antioxidant enzymes but not Mb were overexpressed in degenerative fibers. These results suggest that oxidative stress is associated with Mb expression specifically in mitochondrial diseases. The antioxidant enzymes seem to be upregulated to protect against muscle damage in nonatrophic RRFs. However, the Mb-mediated oxidative damage may become more extensive and result in further mitochondrial dysfunction and progressive atrophy of RRF with impaired upregulation of Mb.

Influence of creatine monohydrate ingestion on muscle metabolites and intense exercise capacity in individuals with multiple sclerosis

OBJECTIVE

To evaluate the effectiveness of ingesting creatine monohydrate in elevating intramuscular creatine stores and improving exercise capacity in individuals with multiple sclerosis (MS).

DESIGN

Randomized, double-blind, placebo-controlled, pre-posttrial.

SETTING

A university-based exercise physiology laboratory.

PARTICIPANTS

Sixteen individuals with relapsing-remitting MS (median Expanded Disability Status Scale score, 4.75; range, 1.5-6.0).

INTERVENTION

Eight individuals with MS were randomized to the creatine group (20g/d of creatine monohydrate for 5d), and 8 others were randomized to the placebo group. Needle biopsies were performed on the vastus lateralis at rest before and after treatment. Subjects performed 3 bouts of 30 maximal knee extensions and flexions at 180 degrees /s with 1 minute of recovery between bouts before and after treatment.

MAIN OUTCOME MEASURES

Intramuscular total creatine, phosphocreatine, free creatine, and total work output.

RESULTS

Creatine ingestion did not significantly elevate intramuscular total creatine, phosphocreatine, or free creatine or improve total work production.

CONCLUSION

Creatine ingestion had no significant effect on muscle creatine stores or high-intensity exercise capacity in individuals with MS.

Biochemical characterization of muscle tissue of limb girdle muscular dystrophy: an 1H and 13C NMR study

The metabolic differences between the muscle biopsies of patients with limb girdle muscular dystrophy (LGMD) and normal controls were characterized using high-resolution 1H and 13C NMR spectroscopy. In all, 44 metabolites were unambiguously assigned in the perchloric acid extracts of skeletal muscle tissue, using 2D double quantum filtered (DQF COSY), total correlation (TOCSY), and 1H/13C heteronuclear multiple quantum coherence (HMQC) spectroscopy. The concentrations of glycolytic substrate, glucose (p=0.03), gluconeogenic amino acids, glutamine (p=0.02) and alanine (p=0.009) together with glycolytic product, lactate (p=0.04), were found to be significantly lowered in LGMD patients as compared with controls. The reduction in the concentration of glucose may be attributed to the decrease in the concentration of gluconeogenic amino acids in the degenerated muscle. Reduction in the rate of anaerobic glycolysis and lowered substrate concentration appear to be the possible reasons for the decrease in the concentration of lactate. A significant reduction in the concentration of choline in LGMD patients was also observed compared with controls. Lower concentration of choline may be the result of decreased rate of membrane turnover in LGMD patients. The data presented here provide an insight into the potentials of in-vitro NMR spectroscopy in the study of muscle metabolism.