Phosphocreatine Resynthesis Research Articles

The impact of exogenous ketone body suppletion on energy and pH balance in skeletal muscle during exercise in chronic heart failure patients: a prospective randomized double-blind cross-over study

Abstract Background Heart Failure (HF) is characterized by impediments in exercise capacity. Disruptions in the energy metabolism of skeletal muscle contribute to this condition. Pre-clinical and clinical evidence showed that reductions in carbohydrate and FA metabolism in HF may be partially overcome by a compensatory increase in ketone body oxidation and suggest that suppletion of ketone bodies (KB) may improve energy metabolism in HF. Purpose We tested the effect of exogenous KB suppletion on energy and pH balance during cycling exercise using 31P Magnetic Resonance (MR) Spectroscopy of the exercising quadriceps muscle in patients with HF. Methods In a randomized, double-blind, placebo-controlled cross-over study, 14 stable HF patients with reduced ejection fraction and diminished exercise capacity underwent maximal exercise testing in a MR scanner fitted with a cycling ergometer after KB or placebo treatment. Phosphocreatine (PCr) and inorganic phosphate (Pi) resonance amplitudes and frequencies were measured continuously in the quadriceps muscle during rest, exercise and recovery using in-vivo 31P MR spectroscopy (Figure 1). Results Patients had a median age of 66 [53 – 75] years, were 14% female, had a median LVEF of 37% [27 – 40] and circulating NT-pro BNP levels of 411 [182 – 946] pg/mL. Peak oxygen uptake (VO2) was 18.2 [15.2 – 20.3] ml/kg/min, which is 68% [62 – 78%] of predicted. After treatment, exercise performance in terms of cycling duration and workload were comparable between treatment arms (Figure 2). Quadriceps acidification during exercise was larger after KB suppletion compared to placebo (ΔpH: -0.2 [-0.3 - -0.1] vs -0.1 [-0.3 - -0.1] respectively; p=0.041) while quadriceps energy depletion during exercise was not altered by treatment (ΔPi/PCr 0.77 [0.55 – 2.51] vs 0.66 [0.46 – 0.81] respectively; p=0.087). Post-exercise mitochondrial oxidative function was similar between treatment arms (KB: PCr resynthesis rate 48 sec [25 – 59] versus placebo: 42 sec [36 – 63]; p=0.767). Conclusions Ketone body suppletion increased acidification and did not improve energy balance in skeletal muscle during exercise or mitochondrial function during recovery in patients with chronic HF. These results question the value of ketone bodies as treatment to boost muscular energy metabolism during exercise in HF.31P MRS Spectrum during exercise in HFExercise and energy parameters

DYNamic Assessment of Multi-Organ level dysfunction in patients recovering from COVID-19: DYNAMO COVID-19.

We evaluated the impacts of COVID-19 on multi-organ and metabolic function in patients following severe hospitalised infection compared to controls. Patients (n=21) without previous diabetes, cardiovascular or cerebrovascular disease were recruited 5-7months post-discharge alongside controls (n=10) with similar age, sex and body mass. Perceived fatigue was estimated (Fatigue Severity Scale) and the following were conducted: oral glucose tolerance (OGTT) alongside whole-body fuel oxidation, validated magnetic resonance imaging and spectroscopy during resting and supine controlled exercise, dual-energy X-ray absorptiometry, short physical performance battery (SPPB), intra-muscular electromyography, quadriceps strength and fatigability, and daily step-count. There was a greater insulin response (incremental area under the curve, median (inter-quartile range)) during the OGTT in patients [18,289 (12,497-27,448) mIU/min/L] versus controls [8655 (7948-11,040) mIU/min/L], P<0.001. Blood glucose response and fasting and post-prandial fuel oxidation rates were not different. This greater insulin resistance was not explained by differences in systemic inflammation or whole-body/regional adiposity, but step-count (P=0.07) and SPPB scores (P=0.004) were lower in patients. Liver volume was 28% greater in patients than controls, and fat fraction adjusted liver T1, a measure of inflammation, was raised in patients. Patients displayed greater perceived fatigue scores, though leg muscle volume, strength, force-loss, motor unit properties and post-exercise muscle phosphocreatine resynthesis were comparable. Further, cardiac and cerebral architecture and function (at rest and on exercise) were not different. In this cross-sectional study, individuals without known previous morbidity who survived severe COVID-19 exhibited greater insulin resistance, pointing to a need for physical function intervention in recovery.

Exploring the links of skeletal muscle mitochondrial oxidative capacity, physical functionality, and mental well-being of cancer survivors

Physical impairments following cancer treatment have been linked with the toxic effects of these treatments on muscle mass and strength, through their deleterious effects on skeletal muscle mitochondrial oxidative capacity. Accordingly, we designed the present study to explore relationships of skeletal muscle mitochondrial oxidative capacity with physical performance and perceived cancer-related psychosocial experiences of cancer survivors. We assessed skeletal muscle mitochondrial oxidative capacity using in vivo phosphorus-31 magnetic resonance spectroscopy (31P MRS), measuring the postexercise phosphocreatine resynthesis time constant, τPCr, in 11 post-chemotherapy participants aged 34–70 years. During the MRS procedure, participants performed rapid ballistic knee extension exercise to deplete phosphocreatine (PCr); hence, measuring the primary study outcome, which was the recovery rate of PCr (τPCr). Patient-reported outcomes of psychosocial symptoms and well-being were assessed using the Patient-Reported Outcomes Measurement Information System and the 36-Item Short Form health survey (SF-36). Rapid bioenergetic recovery, reflected through a smaller value of τPCr was associated with worse depression (rho ρ = − 0.69, p = 0.018, and Cohen’s d = − 1.104), anxiety (ρ = − 0.61, p = .046, d = − 0.677), and overall mental health (ρ = 0.74, p = 0.010, d = 2.198) scores, but better resilience (ρ = 0.65, p = 0.029), and coping-self efficacy (ρ = 0.63, p = 0.04) scores. This is the first study to link skeletal muscle mitochondrial oxidative capacity with subjective reports of cancer-related behavioral toxicities. Further investigations are warranted to confirm these findings probing into the role of disease status and personal attributes in these preliminary results.

Repeated-Sprint Training With Blood Flow Restriction: A Novel Approach to Improve Repeated-Sprint Ability?

ABSTRACT Team sport athletes commonly perform repeated short-duration sprints (≤10 seconds) separated by brief recovery periods (≤60 seconds). The ability to maintain performance over a series of sprints is termed repeated-sprint ability (RSA). The physiological limiters of RSA include decreased force production capacity, insufficient energy supply, and metabolite accumulation. These limiting factors can be improved through repeated-sprint training, with greater RSA gains when performing this training with systemic hypoxia (i.e., reduced fraction of inspired oxygen). Exercising with blood flow restriction (BFR) causes localized hypoxia and a substantial metabolite load, which may provide an adjunct training method to improve RSA. Training with BFR augments muscular strength and adenosine triphosphate supply, which may improve subsequent sprint performance. Improved aerobic fitness, phosphocreatine resynthesis, and metabolite removal from BFR training could also enhance between-sprint recovery to resist fatigue. Despite the possible physiological benefits of repeated-sprint BFR training to improve RSA, there are no published reviews to collate this information. Therefore, this review proposes a theoretical framework for how BFR training could combat fatiguing factors and improve RSA based on current knowledge of the physiological impact of repeated-sprint training and BFR. Finally, guidance will be provided regarding how practitioners may implement BFR training to improve RSA.

Synergistic marmalade for sports person to improve muscle performance and ergogenic activity

The aim of this study is to provide natural ergogenic food products to the sports person. Marmalade is a food product made using fruit, peel and pulp. This acts as a convenient food for a sports person before a performance on the go. The ingredients Purple grapes, Watermelon and Beetroot juices were selected due to the following reasons. Purple grapes provide high run time (ergogenic effect) with the consumption of single dose. Watermelon juice relieves muscle soreness and fatigue. Beetroot juice increases the level of phosphocreatine resynthesis, increases muscle power in trained athletes and improves the release and reuptake of the calcium at the sarcoplasmic reticulum. The Synergistic marmalade was prepared in different variations and is compared with standard Grapes marmalade and the best one (Variation D) was selected using sensory analysis by 30 semi-trained panel members. The Nutrient analysis and Physiochemical analysis were carried out. The nutrients such as Potassium and Magnesium in Standard Grapes marmalade and Selected best sample were 210.3mg/100g and 10.16mg/100g and 213.6mg /100g and 12.32mg/100g respectively. Physiochemical analysis such as TSS was 65 % for standard as well as the selected variant, Titrable acidity was 0.67% for standard and 0.39% for selected variant and pH was 3.5 for standard and 3.27 for selected variant. All these parameters were tested to check the physical and chemical attributes of the Synergistic marmalade to be compared with the standard marmalade. The best variation was stored in two different packaging material – Glass jar and a Airtight plastic container in a refrigerator for a period of 21 days. During this period shelflife study was carried out using sensory evaluation and microbial analysis on 1st, 7th, 14th and 21st day. The results showed that the product is fit for consumption until 21 days and both the packaging were good for storage. The synergistic marmalade was popularized among adult sports persons by briefing on the significance, nutritional aspects, functional properties and other health benefits with the help of a pamphlet and questionnaire and analyzing the aftermath of the session.

Intracellular PO2 Does Not Limit Skeletal Muscle Bioenergetics During Fatiguing Contractions In Vivo

Perturbations to the intracellular milieu during muscular work can include the accumulation of fatigue‐inducing metabolites in skeletal muscle. It has been suggested that oxygen availability contributes to fatigue by limiting the bioenergetic pathways that support contractile activity. Our purpose was to examine the role of intracellular oxygen (PO2) in the disruption of muscle bioenergetics and consequent fatigue in vivo. We hypothesized that fatigue (decrease in peak power) would be associated with acidosis and inorganic phosphate (Pi), but not with PO2, which would remain above the critical threshold for limiting mitochondrial respiration. Seven untrained adults (35 ± 3 yr, mean ± SD; 5 F) performed 120 maximal, isotonic contractions (1 every 2 s) at 20% of peak torque on an MR‐compatible knee extension ergometer in a 3‐tesla magnetic resonance (MR) system. Phosphorus (2000‐ms repetition time) and proton (30‐ms repetition time) MR spectra were collected concurrently with a dual‐tuned (1H/31P) surface coil on the vastus lateralis muscle during 60 s of rest and 4 min of contractions; spectra were averaged to obtain 20‐s temporal resolution. Peaks corresponding to phosphocreatine (PCr), Pi, ATP and deoxymyoglobin (dMb) were fit using jMRUI. [PCr] and [Pi] were calculated assuming ATP = 8.2 mM at rest. Oxidative ATP synthesis (ATPOX, mM·s‐1) was calculated as Vmax·(1+K·([ADP][Pi][ATP]‐1))‐1 where Vmax was determined from PCr resynthesis kinetics, [ADP] was calculated using the creatine kinase equilibrium, and K = 1.1 mM. PO2 was calculated using the oxygen binding curve for myoglobin (Mb; P50 · [(1‐□)/□]), where □ is fractional Mb desaturation relative to maximal dMb during cuff occlusion, assuming a P50 for Mb of 2.39 Torr. Statistics: paired t‐tests and Pearson correlations on individual data. PO2 was fit using bilinear regression to obtain the time to PO2 plateau. Peak power declined to 63.1 ± 16.2% of initial (p &lt; 0.01), indicating significant fatigue. PCr declined from 31.6 ± 1.7 mM at rest to 5.6 ± 4.4 mM, Pi increased from 2.9 ± 0.4 mM to 22.0 ± 3.1 mM, and pH declined to 6.61 ± 0.17 (p &lt; 0.01, all). PO2was 36.5 ± 6.4 Torr at rest and decreased rapidly at the onset of contractions. By 27.4 ± 2.4 s, PO2 plateaued at 1.54 ± 0.6 Torr, well above the critical threshold of 0.35 Torr. ATPOX increased steadily from the start of contractions to 0.49 ± 0.16 mM·s‐1 at 100 s, which is well beyond the time when PO2 plateaued, further indicating that PO2 did not limit oxidative phosphorylation. Changes in pH and Pi were linearly associated with changes in peak power (r = 0.74 ± 0.2 and r = ‐0.66 ± 0.1, respectively), consistent with their role in myosin cross‐bridge impairment in fatigue. In contrast, there was no linear relationship between PO2 and fatigue, pH, or [Pi] during or at the end of the contraction protocol (p &gt; 0.22, all). Overall, the maintenance of PO2 above its critical threshold, as well as its dissociation from ATPOX, fatigue and the metabolites that cause it, indicate that an oxygen limitation does not impair bioenergetic pathways or power production during maximal knee extension contractions in vivo.

P062 31P MRS and MRI phenotyping of muscle metabolic quality in IBD fatigue

Abstract Background Fatigue perception and exercise intolerance are common in inflammatory bowel disease (IBD). The mechanisms are unknown, although physical deconditioning is greater in fatigued relative to non-fatigued patients, suggesting an aetiological role for deconditioning. To assess peripheral muscle quality in Crohn’s disease (CD), we quantified the time-course of muscle phosphocreatine (PCr) recovery, which is wholly mitochondrial dependent, following ischaemic high-intensity exercise in fatigued CD and HV. Methods Participant body mass and regional body composition was assessed by DEXA. All MR data was collected using a 3T Philips Achieva scanner and a 14cm 31P coil on the medial gastrocnemius muscle. 1H mDIXON scans were acquired to image the calf prior to ischaemic plantar flexion exercise at 50% maximum voluntary contraction (MVC) using an MR-compatible ergometer (Trispect, Ergospect) during non-localized pulse-acquire 31P-MRS. 31P spectra were analysed using jMRUI Beta 6.0 using the AMARES function with prior knowledge. Cytosolic pH was estimated using the chemical shift difference between Pi and PCr peaks. Post exercise PCr recovery was quantified after reinstating limb blood flow. PCr recovery was expressed relative to baseline (non-ischaemic) signal amplitude and fit to a mono-exponential function in GraphPad prism. (PCr(t) = PCrinitial+(PCrend – PCrinitial)(1-exp(-k.t)) where t is the time from the start of non-ischaemic recovery, PCrinitial and PCrend is the PCr signal at the initial and end of recovery phases. An FSL and Matlab pipeline was used to obtain calf muscle volume and fat fraction from 1H mDIXON images. Results 13 quiescent CD patients (7 female, HBI 1±2, CRP &amp;lt;5) and 9 HVs (4 female) were matched for age (P = 0.986) and BMI (P = 0.845). General fatigue score was greater in CD (13 ± 4) relative to HV (8 ± 3) (t19=3.08, P = 0.006) (Table 1.) End-exercise muscle PCr depletion (%) (85.25 ± 10.12 vs 83.28 ± 7.8%, P = 0.639) and estimated end-exercise muscle pH (6.6 ± 0.2 vs 6.5 ± 0.2, P = 0.320) was consistent between HV and CD. The mean rate constant of PCr resynthesis (kPCr min-1) in CD (0.76 ± 0.23) was significantly less (t20 = 2.6, P = 0.016) than HV (1.03 ± 0.23). PCr recovery curves were well described using a mono-exponential function in CD (R2=0.98 ± 0.01, R2value) and HV (R2=0.96 ± 0.03) (Table 3). Conclusion The PCr resynthesis rate following intensity matched ischemic exercise was less in fatigued CD patients relative to HV. This points to peripheral muscle deconditioning and associated loss of mitochondrial mass as a driver of exercise intolerance in IBD. This may be amenable to exercise training intervention.

Creatine Supplementation in Women's Health: A Lifespan Perspective.

Despite extensive research on creatine, evidence for use among females is understudied. Creatine characteristics vary between males and females, with females exhibiting 70–80% lower endogenous creatine stores compared to males. Understanding creatine metabolism pre- and post-menopause yields important implications for creatine supplementation for performance and health among females. Due to the hormone-related changes to creatine kinetics and phosphocreatine resynthesis, supplementation may be particularly important during menses, pregnancy, post-partum, during and post-menopause. Creatine supplementation among pre-menopausal females appears to be effective for improving strength and exercise performance. Post-menopausal females may also experience benefits in skeletal muscle size and function when consuming high doses of creatine (0.3 g·kg−1·d−1); and favorable effects on bone when combined with resistance training. Pre-clinical and clinical evidence indicates positive effects from creatine supplementation on mood and cognition, possibly by restoring brain energy levels and homeostasis. Creatine supplementation may be even more effective for females by supporting a pro-energetic environment in the brain. The purpose of this review was to highlight the use of creatine in females across the lifespan with particular emphasis on performance, body composition, mood, and dosing strategies.

Diagnostic and Pharmacological Potency of Creatine in Post-Viral Fatigue Syndrome.

Post-viral fatigue syndrome (PVFS) is a widespread chronic neurological disease with no definite etiological factor(s), no actual diagnostic test, and no approved pharmacological treatment, therapy, or cure. Among other features, PVFS could be accompanied by various irregularities in creatine metabolism, perturbing either tissue levels of creatine in the brain, the rates of phosphocreatine resynthesis in the skeletal muscle, or the concentrations of the enzyme creatine kinase in the blood. Furthermore, supplemental creatine and related guanidino compounds appear to impact both patient- and clinician-reported outcomes in syndromes and maladies with chronic fatigue. This paper critically overviews the most common disturbances in creatine metabolism in various PVFS populations, summarizes human trials on dietary creatine and creatine analogs in the syndrome, and discusses new frontiers and open questions for using creatine in a post-COVID-19 world.

Hypoxic Training Is Beneficial in Elite Athletes.

There is no doubt that many hypoxic conditions or prolonged exposures to altitude result in “biological costs of hypoxic adaptations that outweigh their benefits” (1), particularly in endurance athletes exposed to a) exercise-induced arterial hypoxemia leading to a larger decrease in VO2max and aerobic endurance; b) increased sympathetic activity and decreased baroreflex sensitivity; and c) increased pulmonary arterial pressure. There is also no doubt that sleeping in moderate altitude (2000-3000 m) as performed by the athletes using either live high-train high (LHTH) or live high-train low (LHTL) methods leads to periodic breathing, intermittent hypoxia (IH) and increase in desaturation periods; e.g. 3% oxygen desaturation index, but to a larger extent in hypobaric hypoxia (HH, real altitude) than in normobaric hypoxia (NH, simulated altitude), as shown at 2250 m (2). The three main questions debated in the present contrasting perspective are however different: 1. Are there any evidences showing if the “counteracting maladaptation” (reported above) outweigh the benefits of the different hypoxic methods at short- or long-term in elite athletes? ; 2. Are there any robust data supporting that hypoxic training is beneficial in elite athletes? ; 3. Contradictory, are there robust data showing that hypoxic training is not beneficial in elite athletes?

High-Resolution Dynamic 31P-MR Spectroscopic Imaging for Mapping Mitochondrial Function.

To enable non-invasive dynamic metabolic mapping in rodent model studies of mitochondrial function using 31P-MR spectroscopic imaging (MRSI). We developed a novel method for high-resolution dynamic 31P-MRSI. The method synergistically integrates physics-based models of spectral structures, biochemical modeling of molecular dynamics, and subspace learning to capture spatiospectral variations. Fast data acquisition was achieved using rapid spiral trajectories and sparse sampling of (k, t, T)-space; image reconstruction was accomplished using a low-rank tensor-based framework. The proposed method provided high-resolution dynamic metabolic mapping in rat hindlimb at spatial and temporal resolutions of 4[Formula: see text]2mm3 and 1.28s, respectively. This allowed for in vivo mapping of the time-constant of phosphocreatine resynthesis, a well established index of mitochondrial oxidative capacity. Multiple rounds of in vivo experiments were performed to demonstrate reproducibility, and in vitro experiments were used to validate the accuracy of the estimated metabolite maps. A new model-based method is proposed to achieve high-resolution dynamic 31P-MRSI. The proposed method's ability to delineate metabolic heterogeneity was demonstrated in rat hindlimb. Abnormal mitochondrial metabolism is a key cellular dysfunction in many prevalent diseases such as diabetes and heart disease; however, current understanding of mitochondrial function is mostly gained from studies on isolated mitochondria under nonphysiological conditions. The proposed method has the potential to open new avenues of research by allowing in vivo and longitudinal studies of mitochondrial dysfunction in disease development and progression.

Inorganic phosphate, protons and diprotonated phosphate may contribute to the exacerbated muscle fatigue in older adults

Inorganic phosphate, protons and diprotonated phosphate may contribute to the exacerbated muscle fatigue in older adults

Repeated sprint training in hypoxia – an innovative method

The year 2018 marked the 50th anniversary of the Mexico Olympic games, which represents the starting point of scientific research on hypoxic training. Since the original “Live High – Train High”, many altitude/hypoxic training methods have been developed. The aim of the present review is to present the most recent method called “Repeated Sprint training in Hypoxia” (RSH). RSH is of unprecedented interest in the altitude training area with 25 studies published in the 5-year period following the pioneer article in 2013, and with only two studies that did not report any beneficial effects. Potential mechanisms include transcriptional factors involved in oxygen-signaling and oxygen-carrying capacity and mitochondrial metabolism enzymes, improved behavior of fasttwitch fibers notably via compensatory vasodilatation, improved vascular relaxation and greater microvascular oxygen delivery as well as faster rate of phosphocreatine resynthesis. In general, RSH leads to superior repeated-sprint ability (i.e., faster mean sprint times or higher power outputs associated with a better resistance to fatigue during a repeated-sprint test) in normoxic conditions. RSH where hypoxia is induced by voluntary hypoventilation at low lung volume (named VHL) may also improve repeated-sprint performance more than in normoxia. Practically, RSH benefits have been demonstrated for a large range of team- (rugby, football, LaCrosse, Australian Football, field hockey), endurance (cycling, track and field, cross-country ski), racket (tennis) or combat (Jiu-Jitsu) sports.

Ischaemia-induced muscle metabolic abnormalities are poorly alleviated by endurance training in a mouse model of sickle cell disease.

What is the central question of this study? The aim of this study was to evaluate the potential beneficial effects of endurance training during an ischaemia-reperfusion protocol in a mouse model of sickle cell disease (SCD). What is the main finding and its importance? Endurance training did not reverse the metabolic defects induced by a simulated vaso-occlusive crisis in SCD mice, with regard to intramuscular acidosis, mitochondrial dysfunction or anatomical properties. Our results suggest that endurance training would reduce the number of vaso-occlusive crises rather than the complications related to vaso-occlusive crises. The aim of this study was to investigate whether endurance training could limit the abnormalities described in a mouse model of sickle cell disease (SCD) in response to an ischaemia-reperfusion (I/R) protocol. Ten sedentary (HbSS-SED) and nine endurance-trained (HbSS-END) SCD mice were submitted to a standardized protocol of I/R of the leg, during which ATP, phosphocreatine and inorganic phosphate concentrations and intramuscular pH were measured using magnetic resonance spectroscopy. Forty-eight hours later, skeletal muscles were harvested. Oxidative stress markers were then measured. Although the time course of protons accumulation was slightly different between trained and sedentary mice (P<0.05), the extent of acidosis was similar at the end of the ischaemic period. The initial rate of phosphocreatine resynthesis measured at blood flow restoration, illustrating mitochondrial function, was not altered in trained mice compared with sedentary mice. Although several oxidative stress markers were not different between groups (P>0.05), the I/R-related increase of uric acid concentration observed in sedentary SCD mice (P<0.05) was not present in the trained group. The spleen weight, generally used as a marker of the severity of the disease, was not different between groups (P>0.05). In conclusion, endurance training did not limit the metabolic consequences of an I/R protocol in skeletal muscle of SCD mice, suggesting that the reduction in the severity of the disease previously demonstrated in the basal state would be attributable to a reduction of the occurrence of vaso-occlusive crises rather than a decrease of the deleterious effects of vaso-occlusive crises.

Effects of altered pyruvate dehydrogenase activity on contracting skeletal muscle bioenergetics.

During aerobic exercise (>65% of maximum oxygen consumption), the primary source of acetyl-CoA to fuel oxidative ATP synthesis in muscle is the pyruvate dehydrogenase (PDH) reaction. This study investigated how regulation of PDH activity affects muscle energetics by determining whether activation of PDH with dichloroacetate (DCA) alters the dynamics of the phosphate potential of rat gastrocnemius muscle during contraction. Twitch contractions were induced in vivo over a broad range of intensities to sample submaximal and maximal aerobic workloads. Muscle phosphorus metabolites were measured in vivo before and after DCA treatment by phosphorus nuclear magnetic resonance spectroscopy. At rest, DCA increased PDH activation compared with control (90 ± 12% vs. 23 ± 3%, P < 0.05), with parallel decreases in inorganic phosphate (Pi) of 17% (1.4 ± 0.2 vs. 1.7 ± 0.1 mM, P < 0.05) and an increase in the free energy of ATP hydrolysis (ΔGATP) (-66.2 ± 0.3 vs. -65.6 ± 0.2 kJ/mol, P < 0.05). During stimulation DCA increased steady-state phosphocreatine (PCr) and the magnitude of ΔGATP, with concomitant reduction in Pi and ADP concentrations. These effects were not due to kinetic alterations in PCr hydrolysis, resynthesis, or glycolytic ATP production and altered the flow-force relationship between mitochondrial ATP synthesis rate and ΔGATP. DCA had no significant effect at 1.0- to 2.0-Hz stimulation because physiological mechanisms at these high stimulation levels cause maximal activation of PDH. These data support a role of PDH activation in the regulation of the energetic steady state by altering the phosphate potential (ΔGATP) at rest and during contraction.

Exacerbated metabolic changes in skeletal muscle of sickle cell mice submitted to an acute ischemia-reperfusion paradigm.

Sickle cell disease (SCD) is characterized by painful vaso-occlusive crisis. While there are several metabolic abnormalities potentially associated with muscular ischemia-reperfusion cycles that could be harmful in the context of SCD, the metabolic consequences of such events are still unknown. Ten controls (HbAA), thirteen heterozygous (HbAS), and ten homozygous (HbSS) SCD mice were submitted to a standardized protocol of rest-ischemia-reperfusion of the left leg during which adenosine triphosphate, phosphocreatine, and inorganic phosphate concentrations as well as intramuscular pH were measured using phosphorous magnetic resonance spectroscopy (MRS). Forty-eight hours later, skeletal muscles were harvested. Oxidative stress markers were then measured on the tibialis anterior. At the end of the ischemic period, HbSS mice had a lower pH value as compared with the HbAA and HbAS groups (P<0.01). During the reperfusion period, the initial rate of phosphocreatine resynthesis was lower in HbSS mice as compared with HbAA (P<0.05) and HbAS (P<0.01) animals. No significant difference among groups was observed regarding oxidative stress markers. HbSS mice displayed a higher intramuscular acidosis during the ischemic period while their mitochondrial function was impaired as compared with their HbAA and HbAS counterparts. These metabolic abnormalities could worsen the complications related to the pathology of SCD.

Differences in Muscle Metabolism Between Triathletes and Normally Active Volunteers Investigated Using Multinuclear Magnetic Resonance Spectroscopy at 7T.

Purpose: The influence of endurance training on skeletal muscle metabolism can currently be studied only by invasive sampling or through a few related parameters that are investigated by either proton (1H) or phosphorus (31P) magnetic resonance spectroscopy (MRS). The aim of this study was to compare the metabolic differences between endurance-trained triathletes and healthy volunteers using multi-parametric data acquired by both, 31P- and 1H-MRS, at ultra-high field (7T) in a single experimental protocol. This study also aimed to determine the interrelations between these MRS-derived metabolic parameters.Methods: Thirteen male triathletes and ten active male volunteers participated in the study. Proton MRS data from the vastus lateralis yielded concentrations of acetylcarnitine, carnosine, and intramyocellular lipids (IMCL). For the measurement of phosphodiesters (PDEs), inorganic phosphate (Pi), phosphocreatine (PCr), and maximal oxidative capacity (Qmax) phosphorus MRS data were acquired at rest, during 6 min of submaximal exercise and following immediate recovery.Results: The triathletes exhibited significantly higher IMCL levels, higher initial rate of PCr resynthesis (VPCr) during the recovery period, a shorter PCr recovery time constant (τPCr), and higher Qmax. Multivariate stepwise regression analysis identified PDE as the strongest independent predictor of whole-body maximal oxygen uptake (VO2max).Conclusion: In conclusion, we cannot suggest a single MRS-based parameter as an exclusive biomarker of muscular fitness and training status. There is, rather, a combination of different parameters, assessable during a single multi-nuclear MRS session that could be useful for further cross-sectional and/or focused interventional studies on skeletal muscle fitness and training effects.

Mitochondrial dysfunction in myotonic dystrophy type 1

The pathophysiological mechanism linking the nucleotide expansion in the DMPK gene to the clinical manifestations of myotonic dystrophy type 1 (DM1) is still unclear. In vitro studies demonstrate DMPK involvement in the redox homeostasis of cells and the mitochondrial dysfunction in DM1, but in vivo investigations of oxidative metabolism in skeletal muscle have provided ambiguous results and have never been performed in the brain. Twenty-five DM1 patients (14M, 39 ± 11years) underwent brain proton MR spectroscopy (1H-MRS), and sixteen cases (9M, 40 ± 13 years old) also calf muscle phosphorus MRS (31P-MRS). Findings were compared to those of sex- and age-matched controls. Eight DM1 patients showed pathological increase of brain lactate and, compared to those without, had larger lateral ventricles (p < 0.01), smaller gray matter volumes (p < 0.05) and higher white matter lesion load (p < 0.05). A reduction of phosphocreatine/inorganic phosphate (p < 0.001) at rest and, at first minute of exercise, a lower [phosphocreatine] (p = 0.003) and greater [ADP] (p = 0.004) were found in DM1 patients compared to controls. The post-exercise indices of muscle oxidative metabolism were all impaired in DM1, including the increase of time constant of phosphocreatine resynthesis (TC PCr, p = 0.038) and the reduction of the maximum rate of mitochondrial ATP synthesis (p = 0.033). TC PCr values correlated with the myotonic area score (ρ = 0.74, p = 0.01) indicating higher impairment of muscle oxidative metabolism in clinically more affected patients. Our findings provide clear in vivo evidence of multisystem impairment of oxidative metabolism in DM1 patients, providing a rationale for targeted treatment enhancing energy metabolism.

Dynamic phosphocreatine imaging with unlocalized pH assessment of the human lower leg muscle following exercise at 3T

To develop a high temporal resolution imaging method that measures muscle-specific phosphocreatine (PCr) resynthesis time constant (τPCr ) and pH changes in muscles of the lower leg following exercise on a clinical 3T MRI scanner. We developed a frequency-selective 3D non-Cartesian FLORET sequence to measure PCr with 17-mm nominal isotropic resolution (28 mm actual resolution) and 6-s temporal resolution to capture dynamic metabolic muscle activity. The sequence was designed to additionally collect inorganic phosphate spectra for pH quantification, which were localized using sensitivity profiles of individual coil elements. Nineteen healthy volunteers were scanned while performing a plantar flexion exercise on an in-house developed ergometer. Data were acquired with a dual-tuned multichannel coil array that enabled phosphorus imaging and proton localization for muscle segmentation. After a 90-s plantar flexion exercise at 0.66 Hz with resistance set to 40% of the maximum voluntary contraction, τPCr was estimated at 22.9 ± 8.8 s (mean ± standard deviation) with statistical coefficient of determination r2 = 0.89 ± 0.05. The corresponding pH values after exercise were in the range of 6.9-7.1 in the gastrocnemius muscle. The developed technique allows measurement of muscle-specific PCr resynthesis kinetics and pH changes following exercise, with a temporal resolution and accuracy comparable to that of single voxel 31 P-MRS sequences. Magn Reson Med 79:974-980, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Exacerbated in vivo metabolic changes suggestive of a spontaneous muscular vaso-occlusive crisis in exercising muscle of a sickle cell mouse

While sickle cell disease (SCD) is characterized by frequent vaso-occlusive crisis (VOC), no direct observation of such an event in skeletal muscle has been performed in vivo. The present study reported exacerbated in vivo metabolic changes suggestive of a spontaneous muscular VOC in exercising muscle of a sickle cell mouse. Using magnetic resonance spectroscopy of phosphorus 31, phosphocreatine and inorganic phosphate concentrations and intramuscular pH were measured throughout two standardized protocols of rest – exercise – recovery at two different intensities in ten SCD mice. Among these mice, one single mouse presented divergent responses. A statistical analysis (based on confidence intervals) revealed that this single mouse presented slower phosphocreatine resynthesis and inorganic phosphate disappearance during the post-stimulation recovery of one of the protocols, what could suggest an ischemia. This study described, for the first time in a sickle cell mouse in vivo, exacerbated metabolic changes triggered by an exercise session that would be suggestive of a live observation of a muscular VOC. However, no evidence of a direct cause-effect relationship between exercise and VOC has been put forth.