31P Magnetic Resonance Spectroscopy Research Articles

Lactate and hydrogen ions play a predominant role in evoking the exercise pressor reflex during ischaemic contractions but not during freely perfused contractions.

We investigated the role played by lactate and hydrogen in evoking the exercise pressor reflex (EPR) in decerebrated rats whose hindlimb muscles were either freely perfused or ischaemic. Production of lactate and hydrogen by the contracting hindlimb muscles was manipulated by knocking out the myophosphorylase gene (pygm). In knockout rats (pygm-/-; n=13) or wild-type rats (pygm+/+; n=13), the EPR was evoked by isometrically contracting the triceps surae muscles. Blood pressure, tension, blood flow, renal sympathetic nerve activity and blood lactate concentrations were measured. Intramuscular metabolites and pH changes induced by the contractions were quantified by 31P-magnetic resonance spectroscopy (n=5). In a subset of pygm-/- rats (n=5), contractions were evoked with prior infusion of lactate (pH 6.0) in an attempt to restore the effect of lactate and hydrogen ions. Contraction of freely perfused muscles increased blood lactate and decreased muscle pH in pygm+/+ rats only. Despite these differences, the reflex pressor and sympathetic responses to freely perfused contraction did not differ between groups (P=0.992). During ischaemia, contraction increased muscle lactate and hydrogen ion production in pygm+/+ rats (P<0.0134), whereas it had no effect in pygm-/- rats (P>0.783). Likewise, ischaemia exaggerated the reflex pressor, and sympathetic responses to contraction in pygm+/+ but not in pygm-/- rats. This exaggeration was restored when a solution of lactate (pH 6.0) was infused prior to the contraction in pygm-/- rats. We conclude that lactate and hydrogen accumulation in contracting myocytes play a key role in evoking the metabolic component of the EPR during ischaemic but not during freely perfused contractions. KEY POINTS: Conflicting results exist about the role played by lactate and hydrogen ions in evoking the exercise pressor reflex. Using CRISP-Cas9, we rendered the myophosphorylase gene non-functional to block the production of lactate and hydrogen ions. The exercise pressor reflex was evoked in decerebrated rats by statically contracting the triceps surae muscles with or without muscle ischaemia. Static contraction elevated the concentration of lactate and hydrogen ions in pygm+/+ but not in pygm-/- rats. Despite these differences, the exercise pressor reflex was not different between groups. Acute muscle ischaemia exaggerated the concentration of lactate and hydrogen ions in pygm+/+ but not in pygm-/- rats. Likewise, acute muscle ischaemia exaggerated the exercise pressor reflex in pygm+/+ but not in pygm-/- rats. We conclude that lactate and hydrogen play a key role in evoking the exercise pressor reflex during ischaemic but not during freely perfused contractions.

Plasma metabolomic markers underlying skeletal muscle mitochondrial function relationships with cognition and motor function.

Lower skeletal muscle mitochondrial function is associated with future cognitive impairment and mobility decline, but the biological underpinnings for these associations are unclear. We examined metabolomic markers underlying skeletal muscle mitochondrial function, cognition and motor function. We analysed data from 560 participants from the Baltimore Longitudinal Study of Aging (mean age: 68.4years, 56% women, 28% Black) who had data on skeletal muscle oxidative capacity (post-exercise recovery rate of phosphocreatine, kPCr) via 31P magnetic resonance spectroscopy and targeted plasma metabolomics using LASSO model. We then examined which kPCr-related markers were also associated with cognition and motor function in a larger sample (n = 918, mean age: 69.4, 55% women, 27% Black). The LASSO model revealed 24 metabolites significantly predicting kPCr, with the top 5 being asymmetric dimethylarginine, lactic acid, lysophosphatidylcholine a C18:1, indoleacetic acid and triacylglyceride (17:1_34:3), also significant in multivariable linear regression. The kPCr metabolite score was associated with cognitive or motor function, with 2.5-minute usual gait speed showing the strongest association (r = 0.182). Five lipids (lysophosphatidylcholine a C18:1, phosphatidylcholine ae C42:3, cholesteryl ester 18:1, sphingomyelin C26:0, octadecenoic acid) and 2 amino acids (leucine, cystine) were associated with both cognitive and motor function measures. Our findings add evidence to the hypothesis that mitochondrial function is implicated in the pathogenesis of cognitive and physical decline with aging and suggest that targeting specific metabolites may prevent cognitive and mobility decline through their effects on mitochondria. Future omics studies are warranted to confirm these findings and explore mechanisms underlying mitochondrial dysfunction in aging phenotypes.

Lonidamine Induced Selective Acidification and De-Energization of Prostate Cancer Xenografts: Enhanced Tumor Response to Radiation Therapy.

Prostate cancer is a multi-focal disease that can be treated using surgery, radiation, androgen deprivation, and chemotherapy, depending on its presentation. Standard dose-escalated radiation therapy (RT) in the range of 70-80 Gray (GY) is a standard treatment option for prostate cancer. It could be used at different phases of the disease (e.g., as the only primary treatment when the cancer is confined to the prostate gland, combined with other therapies, or as an adjuvant treatment after surgery). Unfortunately, RT for prostate cancer is associated with gastro-intestinal and genitourinary toxicity. We have previously reported that the metabolic modulator lonidamine (LND) produces cancer sensitization through tumor acidification and de-energization in diverse neoplasms. We hypothesized that LND could allow lower RT doses by producing the same effect in prostate cancer, thus reducing the detrimental side effects associated with RT. Using the Seahorse XFe96 and YSI 2300 Stat Plus analyzers, we corroborated the expected LND-induced intracellular acidification and de-energization of isolated human prostate cancer cells using the PC3 cell line. These results were substantiated by non-invasive 31P magnetic resonance spectroscopy (MRS), studying PC3 prostate cancer xenografts treated with LND (100 mg/kg, i.p.). In addition, we found that LND significantly increased tumor lactate levels in the xenografts using 1H MRS non-invasively. Subsequently, LND was combined with radiation therapy in a growth delay experiment, where we found that 150 µM LND followed by 4 GY RT produced a significant growth delay in PC3 prostate cancer xenografts, compared to either control, LND, or RT alone. We conclude that the metabolic modulator LND radio-sensitizes experimental prostate cancer models, allowing the use of lower radiation doses and diminishing the potential side effects of RT. These results suggest the possible clinical translation of LND as a radio-sensitizer in patients with prostate cancer.

Association between dietary phosphate intake and skeletal muscle energetics in adults without cardiovascular disease.

Highly bioavailable inorganic phosphate (Pi) is present in large quantities in the typical Western diet and represents a large fraction of total phosphate intake. Dietary Pi excess induces exercise intolerance and skeletal muscle mitochondrial dysfunction in normal mice. However, the relevance of this to humans remains unknown. The study was conducted on 13 individuals without a history of cardiopulmonary disease (46% female, 15% Black participants) enrolled in the pilot-phase of the Dallas Heart and Mind Study. Total dietary phosphate was estimated from 24-h dietary recall (ASA24). Muscle ATP synthesis was measured at rest, and phosphocreatinine (PCr) dynamics was measured during plantar flexion exercise using 7-T 31P magnetic resonance (MR) spectroscopy in the calf muscle. Correlation was assessed between dietary phosphate intake normalized to total caloric intake, resting ATP synthesis, and PCr depletion during exercise. Higher dietary phosphate intake was associated with lower resting ATP synthesis (r = -0.62, P = 0.03), and with higher levels of PCr depletion during plantar flexion exercise relative to the resting period (r = -0.72; P = 0.004). These associations remain significant after adjustment for age and estimated glomerular filtration rate (both P < 0.05). High dietary phosphate intake was also associated with lower serum Klotho levels, and Klotho levels are in turn associated with PCr depletion and higher ADP accumulation post exercise. Our study suggests that higher dietary phosphate is associated with reduced skeletal muscle mitochondrial function at rest and exercise in humans providing new insight into potential mechanisms linking the Western diet to impaired energy metabolism.NEW & NOTEWORTHY This is the first translational research study directly demonstrating the adverse effects of dietary phosphate on muscle energy metabolism in humans. Importantly, our data show that dietary phosphate is associated with impaired muscle ATP synthesis at rest and during exercise, independent of age and renal function. This is a new biologic paradigm with significant clinical dietary implications.

1H and 31P magnetic resonance spectroscopy reveals potential pathogenic and biomarker metabolite alterations in Lafora disease.

Lafora disease is a fatal teenage-onset progressive myoclonus epilepsy and neurodegenerative disease associated with polyglucosan bodies. Polyglucosans are long-branched and as a result precipitation- and aggregation-prone glycogen. In mouse models, downregulation of glycogen synthase, the enzyme that elongates glycogen branches, prevents polyglucosan formation and rescues Lafora disease. Mouse work, however, has not yet revealed the mechanisms of polyglucosan generation, and few in vivo human studies have been performed. Here, non-invasive in vivo magnetic resonance spectroscopy (1H and 31P) was applied to test scan feasibility and assess neurotransmitter balance and energy metabolism in Lafora disease towards a better understanding of pathogenesis. Macromolecule-suppressed gamma-aminobutyric acid (GABA)-edited 1H magnetic resonance spectroscopy and 31P magnetic resonance spectroscopy at 3 and 7 tesla, respectively, were performed in 4 Lafora disease patients and a total of 21 healthy controls (12 for the 1H magnetic resonance spectroscopy and 9 for the 31PMRS). Spectra were processed using in-house software and fit to extract metabolite concentrations. From the 1H spectra, we found 33% lower GABA concentrations (P = 0.013), 34% higher glutamate + glutamine concentrations (P = 0.011) and 24% lower N-acetylaspartate concentrations (P = 0.0043) in Lafora disease patients compared with controls. From the 31P spectra, we found 34% higher phosphoethanolamine concentrations (P = 0.016), 23% lower nicotinamide adenine dinucleotide concentrations (P = 0.003), 50% higher uridine diphosphate glucose concentrations (P = 0.004) and 225% higher glucose 6-phosphate concentrations in Lafora disease patients versus controls (P = 0.004). Uridine diphosphate glucose is the substrate of glycogen synthase, and glucose 6-phosphate is its extremely potent allosteric activator. The observed elevated uridine diphosphate glucose and glucose 6-phosphate levels are expected to hyperactivate glycogen synthase and may underlie the generation of polyglucosans in Lafora disease. The increased glutamate + glutamine and reduced GABA indicate altered neurotransmission and energy metabolism, which may contribute to the disease's intractable epilepsy. These results suggest a possible basis of polyglucosan formation and potential contributions to the epilepsy of Lafora disease. If confirmed in larger human and animal model studies, measurements of the dysregulated metabolites by magnetic resonance spectroscopy could be developed into non-invasive biomarkers for clinical trials.

A study protocol to investigate if acipimox improves muscle function and sarcopenia: an open-label, uncontrolled, before-and-after experimental medicine feasibility study in community-dwelling older adults

IntroductionSarcopenia is the age-associated loss of muscle mass and strength. Nicotinamide adenine dinucleotide (NAD) plays a central role in both mitochondrial function and cellular ageing processes implicated in sarcopenia. NAD...

Reproducibility of absolute quantification of adenosine triphosphate and inorganic phosphate in the liver with localized 31 P-magnetic resonance spectroscopy at 3-T using different coils.

Concentrations of the key metabolites of hepatic energy metabolism, adenosine triphosphate (ATP) and inorganic phosphate (Pi ), can be altered in metabolic disorders such as diabetes mellitus. 31 Phosphorus (31 P)-magnetic resonance spectroscopy (MRS) is used to noninvasively measure hepatic metabolites, but measuring their absolute molar concentrations remains challenging. This study employed a 31 P-MRS method based on the phantom replacement technique for quantifying hepatic 31 P-metabolites on a 3-T clinical scanner. Two surface coils with different size and geometry were used to check for consistency in terms of repeatability and reproducibility and absolute concentrations of metabolites. Day-to-day (n = 8) and intra-day (n = 6) reproducibility was tested in healthy volunteers. In the day-to-day study, mean absolute concentrations of γ-ATP and Pi were 2.32 ± 0.24 and 1.73 ± 0.26 mM (coefficient of variation [CV]: 7.3% and 8.8%) for the single loop, and 2.32 ± 0.42 and 1.73 ± 0.27 mM (CVs 6.7% and 10.6%) for the quadrature coil, respectively. The intra-day study reproducibility using the quadrature coil yielded CVs of 4.7% and 6.8% for γ-ATP and Pi without repositioning, and 6.3% and 7.1% with full repositioning of the volunteer. The results of the day-to-day data did not differ between coils and visits. Both coils robustly yielded similar results for absolute concentrations of hepatic 31 P-metabolites. The current method, applied with two different surface coils, can be readily utilized in long-term and interventional studies. In comparison with the single loop coil, the quadrature coil also allows measurements at a greater distance between the coil and liver, which is relevant for studying people with obesity.

Iron-based compounds coordinated with phospho-polymers as biocompatible probes for dual 31P/1H magnetic resonance imaging and spectroscopy

In this work, we present the synthesis and evaluation of magnetic resonance (MR) properties of novel phosphorus/iron-containing probes for dual 31P and 1H MR imaging and spectroscopy (MRI and MRS). The presented probes are composed of biocompatible semitelechelic and multivalent phospho-polymers based on poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC) coordinated with small paramagnetic Fe3+ ions or superparamagnetic maghemite (γ-Fe2O3) nanoparticles via deferoxamine group linked to the end or along the polymer chains. All probes provided very short 1H T1 and T2 relaxation times even at low iron concentrations. The presence of iron had a significant impact on the shortening of 31P relaxation, with the effect being more pronounced for probes based on γ-Fe2O3 and multivalent polymer. While the water-soluble probe having one Fe3+ ion per polymer chain was satisfactorily visualized by both 31P-MRS and 31P-MRI, the probe with multiple Fe3+ ions could only be detected by 31P-MRS, and the probes consisting of γ-Fe2O3 nanoparticles could not be imaged by either technique due to their ultra-short 31P relaxations. In this proof-of-principle study performed on phantoms at a clinically relevant magnetic fields, we demonstrated how the different forms and concentrations of iron affect both the 1H MR signal of the surrounding water molecules and the 31P MR signal of the phospho-polymer probe. Thus, this double contrast can be exploited to simultaneously visualize body anatomy and monitor probe biodistribution.

Qualitative and quantitative analysis of Brønsted and Lewis acid sites in zeolites: A combined probe-assisted 1H MAS NMR and NH3-TPD investigation

Zeolite is one of the most important heterogeneous catalysts in acid catalytic reactions. Considering that the catalytic behaviors of zeolites are mostly related to their acidic characteristics, extensive attention has been attracted to the measurements of acid type, strength and concentration in zeolites. Numerous techniques including Fourier-transform infrared spectroscopy (FTIR), probe-assisted 1H, 13C and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) as well as temperature programmed desorption of ammonia (NH3-TPD) have been developed for determining the acid sites. Nevertheless, a single approach is defective to characterize the acid sites comprehensively. Herein, combining the probe-assisted (e.g., NH3 and CD3CN) 1H MAS NMR and NH3-TPD, the acid sites in different zeolites including the acid type, density and strength were determined. The commonly utilized NH3-TPD to determine the acid strength of zeolite samples with different topologies should be rigorously considered owing to zeolite confinement effect. Controlling the desorption temperature of NH3 probe molecules, the acid type (i.e., Brønsted acid sites (BAS) and Lewis acid sites (LAS)) and the corresponding density could be determined by NH3 probe-assisted 1H MAS NMR spectroscopy, while the acid strength could be investigated via CD3CN probe-assisted 1H MAS NMR spectroscopy.

Muscular stress is equal when resistance exercise with blood flow restriction is matched in total work volume: A cross-sectional, cross-over study.

We compared muscular metabolic stress during exercise performed at multiple intensities, from very low to moderate, with blood flow restriction (BFR) adjusted by the same work volume. Twenty-five healthy young adults performed unilateral plantar flexion at 1 repetition/2 s in a magnetic resonance system. The BFR exercise protocols were as follows: (A) exercise with 10% of one repetition maximum (1-RM) for 360 s, (B) 15% 1-RM for 240 s, (C) 20% 1-RM for 180 s, (D) 30% 1-RM for 120 s, and (E) 40% 1-RM for 90 s. All protocols had the same total work volume (load × repetitions = 1800). A high-intensity protocol at 65% 1-RM without BFR (60 s) was also performed for comparison. We used 31 P-magnetic resonance spectroscopy to evaluate the muscular metabolic stress in the subjects' calf muscle, defined as decreases in phosphocreatine and intramuscular pH. The phosphocreatine depletion (A: 15.6 ± 0.7, B: 14.8 ± 0.8, C: 15.2 ± 0.6, D: 14.3 ± 0.6, E: 10.9 ± 0.5 mM; no significant difference [ns]) and the intramuscular pH decrease (A: 6.82 ± 0.02, B: 6.84 ± 0.01, C: 6.83 ± 0.02, D: 6.83 ± 0.02, E: 6.77 ± 0.02; ns) at the end of each exercise were similar and greater than those produced by the 65% 1-RM without BFR. If the total work volumes are equal, the metabolic stress in exercising muscle may reach similar levels at the end of exercise with BFR and could provide similar successful training effects.

Frontal-temporal regional differences in brain energy metabolism and mitochondrial function using 31P MRS in older adults.

Aging is a major risk for cognitive decline and transition to dementia. One well-known age-related change involves decreased brain efficiency and energy production, mediated in part by changes in mitochondrial function. Damaged or dysfunctional mitochondria have been implicated in the pathogenesis of age-related neurodegenerative conditions like Alzheimer's disease (AD). The aim of the current study was to investigate mitochondrial function over frontal and temporal regions in a sample of 70 cognitively normal older adults with subjective memory complaints and a first-degree family history of AD. We hypothesized cerebral mitochondrial function and energy metabolism would be greater in temporal as compared to frontal regions based on the high energy consumption in the temporal lobes (i.e., hippocampus). To test this hypothesis, we used phosphorous (31P) magnetic resonance spectroscopy (MRS) which is a non-invasive and powerful method for investigating in vivo mitochondrial function via high energy phosphates and phospholipid metabolism ratios. We used a single voxel method (left temporal and bilateral prefrontal) to achieve optimal sensitivity. Results of separate repeated measures analyses of variance showed 31P MRS ratios of static energy, energy reserve, energy consumption, energy demand, and phospholipid membrane metabolism were greater in the left temporal than bilateral prefrontal voxels. Our findings that all 31P MRS ratios were greater in temporal than bifrontal regions support our hypothesis. Future studies are needed to determine whether findings are related to cognition in older adults.

The Association of Skeletal Muscle Energetics With Recurrent Falls in Older Adults Within the Study of Muscle, Mobility and Aging.

Falls in the older population are a major public health concern. While many physiological and environmental factors have been associated with fall risk, muscle mitochondrial energetics has not yet been investigated. In this analysis, 835 Study of Muscle, Mobility and Aging (SOMMA) participants aged 70-94 were surveyed for number of falls (total), recurrent falls (2+), and fall-related injuries over the past 12 months at baseline and again after 1 year. Skeletal muscle energetics were assessed at baseline in vivo using 31P Magnetic Resonance Spectroscopy for the maximal rate of adenosine triphosphate recovery (ATPmax)after an acute bout of exercise, and ex vivo by High-Resolution Respirometry for the maximal rate of complex I and II supported oxygen consumption (MaxOXPHOS) in permeabilized muscle fibers from the vastus lateralis. At least 1 fall was reported in 28.7% of SOMMA participants in the first year of the study, with 12% of older adults reporting recurrent falls (2+). Individuals who experienced recurrent falls had a slower 400-m walk gait speed (1.0±0.2 vs 1.1±0.2, p < .001), reported fewer alcoholic drinks per week in the past year (2.4±4.3 vs 2.8±4.4, p = .054), and took a significantly greater number of medication in the 30 days before their baseline visit (5.6±4.4 vs 4.2±3.4, p < .05). A history of falls was reported in 63% of individuals who experienced recurrent falls in the first year of the study compared to 22.8% who experienced 1 or fewer falls. MaxOXPHOS was significantly lower in those who reported recurrent falls (p = .008) compared to those with 1 or fewer falls, but there was no significant difference in ATPmax (p = .369). Neither muscle energetics measure was significantly associated with total number of falls or injurious falls, but recurrent falls were significantly higher with lower MaxOXPHOS (risk ratio = 1.33, 95% confidence interval = 1.02-1.73, p = .033). However, covariates accounted for the increased risk. Mitochondrial energetics were largely unrelated to fall risk in older adults when accounting for variables, suggesting that the complex etiology of falls may not be related to a single "hallmark of aging" biological pathway.

Chemical kinetics of silver diammine fluoride in demineralization and remineralization solutions-an in vitro study.

Silver Diammine Fluoride (SDF) is a clinical minimal intervention to manage dentin caries. Its chemistry in demineralization conditions has been investigated widely, but far less in remineralization conditions. The aim was to investigate and compare the chemical reactions when SDF is added to remineralization and demineralization solutions. 0.01 ml SDF (Riva Star) was added to deionized water (DW); demineralization (DS = pH4) and remineralization (RS = pH7.0) solutions. The time sequence of concentrations of NH4+, F-, and Ag+ were measured using ion selective electrodes (ISEs) every 2 min. The pH was also measured. Precipitates were characterized using x-ray Diffraction (XRD) and, 31P and 19F nuclear magnetic resonance spectroscopy (NMR). The concentrations of NH4+ and Ag+ showed decreasing trends in DW (-0.12 and -0.08 mM/h respectively), and in DS (-1.06 and -0.5 mM/h respectively); with corresponding increase in F- concentration (0.04 and 0.7 mM/h respectively). However, in RS, NH4+ concentration showed little change (0.001 mM/h), and Ag+ and F- concentrations were negligible. XRD results showed that precipitates (in RS only) contained AgCl, and metallic Ag. NMR showed that fluorapatite/carbonated fluorapatite (FAP/CFAP) were formed. The pH increased after SDF addition in all three solutions. SDF dissolved to release NH4+, F- and Ag + . In DW and DS, NH4+ combined with Ag+ to form diamminesilver, causing an increase of F- and pH. In RS, F- reacted with Ca2+ and (PO)43- to form FAP/CFAP, and Ag+ reacted with Cl- to form AgCl/Ag. These suggests why SDF is effective in managing dentin caries.

SKELETAL MUSCLE ENERGETICS ARE ASSOCIATED WITH PERFORMANCE FATIGABILITY

Abstract Performance fatigability manifests as insufficient energy to complete daily physical tasks and worsens with aging, exacerbating vulnerability to disability. Skeletal muscle energetics also declines with aging. Thus, we hypothesized muscle energetics may be an important contributor to performance fatigability. In the Study of Muscle, Mobility and Aging (SOMMA), participants completed a usual-paced 400m walk while wearing a wrist-worn ActiGraph, from which raw data were used to derive the Pittsburgh Performance Fatigability Index (PPFI, higher=more severe fatigability) that quantifies percent decline in the entire individual cadence-versus-time trajectory. Maximal oxidative phosphorylation (maxOXPHOS) in skeletal muscle mitochondria was quantified in vitro using high-resolution respirometry in permeabilized fiber bundles from vastus lateralis muscle biopsies. Maximal adenosine triphosphate production (ATPmax) was assessed in vivo by 31P magnetic resonance spectroscopy. We conducted separate tobit regressions to examine associations of maxOXPHOS and ATPmax with PPFI, adjusting for technician/site, age, sex, race, height, weight, and mins/day moderate-to-vigorous physical activity measured by ActiGraph in free-living, in N=795 participants with complete PPFI scores and &amp;gt;1 energetics measure (70-94 yrs, 58% women). Median PPFI scores were 1.4% [IQR: 0-2.9%]. After adjustment, each SD (18.4 pmol/(s*mg)) lower maxOXPHOS was associated with 0.55% (95% CI: 0.26, 0.85) higher PPFI scores, while each SD (0.2 mM/sec) lower ATPmax was associated with 0.54% (95% CI: 0.27, 0.81) higher PPFI scores. Our results indicate that lower skeletal muscle energetics were associated with more severe performance fatigability. This suggests that therapeutics targeting muscle energetics may thereby potentially mitigate fatigability and lessen susceptibility to disability among older adults.

ASSOCIATION OF DIABETES WITH BODY COMPOSITION, CARDIORESPIRATORY FITNESS, AND MITOCHONDRIAL ENERGETICS

Abstract We investigated the association of diabetes with cardiorespiratory fitness and skeletal muscle mitochondrial energetics in older adults (N=876, mean age ± SD: 76.3 ± 5.0 yrs.; 59% females) from the Study of Muscle, Mobility and Aging (SOMMA). Participants were grouped by self-reported diabetes status (N=131, with diabetes). Cardiorespiratory fitness (modified Balke protocol), mitochondrial energetics (31P magnetic resonance spectroscopy [31P-MRS] and high resolution respirometry from skeletal muscle biopsy), physical activity (wearable accelerometer) and body composition (magnetic resonance imaging) were measured. Generalized linear regression models were used to calculate means adjusted by age, race, gender, BMI, and co-morbidities. Thigh fat-free muscle volume (p=0.12) and abdominal subcutaneous adipose tissue depot (p=0.15) were similar between those with and without diabetes. However, visceral (18.84%, p&amp;gt;0.01) and intramuscular adipose tissue (6.57%, p=0.02) were higher in older adults with diabetes. VO2peak (-4.79%, p&amp;gt;0.01), and mitochondria energetics measured by ATPmax (-5.10%, p=0.04), maximum complex I+II carbohydrate (maxOXPHOSCHO) (-6.67%, p=0.02) and fatty acid (maxOXPHOSFAO) (-8.70%, p=0.01) stimulated respiration were lower in those with diabetes compared to those without. Following further adjustments for both physical activity and visceral adiposity, revealed that only VO2peak (-4.65%, p&amp;gt;0.01) and maxOXPHOSFAO (-7.38%, p=0.02) remained significantly lower in older adults with diabetes. Overall, our data suggests that cardiorespiratory fitness and skeletal muscle mitochondria energetics are reduced in older adults with diabetes, independent of visceral adiposity and physical activity.

MITOCHONDRIAL ENERGETICS AND PERCEIVED PHYSICAL FATIGABILITY SEVERITY IN OLDER ADULTS

Abstract It has been hypothesized that lower skeletal muscle energetics may contribute to onset of age-related perceived fatigability. Consistent with this idea, previous research found that maximal ATP production (ATPmax) was associated with higher perceived exertion (i.e., fatigability) measured in older adults with the Borg Scale at the end of a slow walking task. We extend this work to SOMMA examining skeletal muscle energetics (ATPmax and maximal complex I&amp;II supported oxidative phosphorylation [maxOXPHOS]) with perceived physical fatigability using the Pittsburgh Fatigability Scale (PFS, range 0-50, higher=greater). PFS captures fatigue perception anchored to activities of varying intensity and duration. We assessed ATPmax in vivo by 31P magnetic resonance spectroscopy following an acute knee extensor exercise bout. maxOXPHOS was quantified ex vivo in permeabilized fiber bundles by high-resolution spectroscopy. Participants (N=721 with PFS and ≥1 energetics measure) were aged 76.4±5.0 years, 56.7% women, 86.7% White. Lower ATPmax (r=-0.21) and maxOXPHOS (r=-0.29) correlated with higher PFS scores (both p&amp;lt;0.001). Linear regressions adjusted for age, sex, technician, and total daily accelerometry-derived physical activity revealed that each one SD lower ATPmax (0.15 mM/sec) was associated with 1.15 (95% CI: 0.50, 1.79) higher PFS scores; each one SD lower maxOXPHOS (18.5 pmol/(sec*mg)) was associated with 1.79 (95% CI: 1.14, 2.45) higher PFS scores. Impaired skeletal muscle energetics may be implicated in the etiologic pathway of age-related fatigability. Next steps will examine the longitudinal association between changes in skeletal muscle energetics and age-related fatigability.

CARDIORESPIRATORY FITNESS AND MITOCHONDRIAL ENERGETICS IN THE OLDEST OLD: THE STUDY OF MUSCLE, MOBILITY AND AGING

Abstract Cardiorespiratory fitness (CRF) and mitochondrial energetics are known to decrease with aging, albeit with a great degree of heterogeneity. Studies reporting these declines typically include individuals younger than 85 years of age. We investigated CRF and mitochondrial energetics in a cohort of old (O: 70-84yrs.; n=698) and oldest old (OO: 85+yrs.; n=70) adults enrolled in SOMMA. Cardiorespiratory fitness (VO2peak) was measured by modified Balke treadmill protocol, and mitochondrial energetics was assessed by 31P Magnetic Resonance Spectroscopy (ATPmax) and high-resolution respirometry of myofibers (oxidative phosphorylation, OXPHOS). Bivariate associations and group differences were assessed using unadjusted and adjusted regression models with clinical site/technician, gender, race, body mass index and physical activity (steps per day) as covariates. Old and oldest old groups showed an association between VO2peak and OXPHOS (R2=0.282, p&amp;lt;0.001; R2=0279, p=0.0083; respectively, adjusted for site/technician), but only the old group showed associations between VO2peak and ATPmax (R2=0.201, p&amp;lt;0.001; R2=0.017, p=0.609; respectively, adjusted for site/technician). Group comparison adjusted for clinical site, gender, and race, showed lower VO2peak (p &amp;lt; 0.001), OXPHOS (p=0.026), and ATPmax (p=0.0014) in the OO compared to O group. However, no group differences in OXPHOS (p=0.08) and ATPmax (p=0.09) are observed when adjusting for body composition and physical activity, factors known to affect mitochondria. In conclusion, CRF associates with different measures of mitochondrial energetics in older adults, but only with mitochondrial respiration in oldest old. Additionally, we suggest that decreases in mitochondrial energetics observed in the oldest old are related to age, changes in body composition and physical activity.

DECONSTRUCTING MULTIMORBIDITY AND MUSCLE MITOCHONDRIAL RESPIRATION AND ENERGETICS IN OLDER ADULTS

Abstract Lower cardiorespiratory fitness among older adults is associated with greater multimorbidity burden, including cardiovascular disease, cancer, and dementia. Those with poorer muscle mitochondrial energetics also have lower cardiorespiratory fitness. We have previously shown lower mitochondrial respiration and energetics (OXPHOS and ATPmax) have higher morbidity burden using a summary measure, but the associations among specific conditions have not been examined. We leverage data from the SOMMA cohort (N=856, 76.4yrs, 59% women, 85.5% white); participants self-reported physician diagnosis of 11 age-related conditions (i.e., cancer, cardiac arrhythmia, chronic kidney disease (CKD), chronic obstructive pulmonary disease, coronary heart disease (CHD), depression, diabetes). Mitochondrial respiration was assessed by high-resolution respirometry of vastus lateralis using permeabilized fiber bundles. 31P magnetic resonance spectroscopy of the quadriceps measured ATPmax. In adjusted logistic models with beta-coefficients reported per SD decrement in each mitochondrial measure, fatty-acid-supported Leak respiration was associated with CKD (OR: 2.3(95%CI=1.2,4.3)), fatty acid and complex I&amp;II supported oxidative phosphorylation (OXPHOS) with depression (OR: 1.8(95%CI=1.1,2.7)). Many respirometry measures and ATPmax associated with diabetes, with maximal electron transport system (ETS) capacity having the highest odds (OR: 1.5(95%CI=1.1,2.0)). No other associations were statistically significant for conditions listed above. These results indicate that mitochondrial respiration and energetics are more impaired in depression, kidney disease, and diabetes. This raises new questions about the role of mitochondrial respiration and energetics as cause or consequences of these conditions. Overall, our analyses suggest compromised mitochondrial function may have implications for specific aging-related conditions, and global measures of morbidity burden may not reflect these distinctions.

Effect of Burosumab on Muscle Function and Strength, and Rates of ATP Synthesis in Skeletal Muscle in Adults With XLH.

In clinical trials, burosumab ameliorates symptoms of pain, fatigue, and stiffness and improves performance on certain muscle function studies in patients with X-linked hypophosphatemia (XLH). This work aimed to determine if burosumab increases adenosine triphosphate (ATP) synthesis in skeletal muscle of treatment-naive adults with XLH, and if so, whether that correlates with improved muscle function. Ten untreated, symptomatic adults with XLH had ATP synthesis rates measured in the right calf using the 31P magnetic resonance spectroscopy saturation transfer technique. Baseline muscle function tests and symptoms of pain, fatigue, stiffness, and lower-extremity joint pain were quantified. All participants were treated with burosumab, 1 mg/kg every 4 weeks for 12 weeks. ATP synthesis rates and muscle function tests were repeated 2 weeks ("peak") and 4 weeks ("trough") after the third dose of burosumab. All symptoms improved with treatment. Performance on the 6-Minute Walk Test (6MWT) and Sit to Stand (STS) tests also improved. Muscle strength and ATP synthesis rates did not change over the 3 months of the study. When individuals whose performances on the 6MWT and STS test were at or better than the median outcome for those tests were compared to those whose outcomes were below the median, no difference was observed in the rate of change in ATP synthesis. Intracellular muscle concentrations of phosphate were normal. The improvement in the 6MWT and STS test without changes in muscle strength or ATP synthesis rates suggests that reductions in pain, fatigue, and stiffness may partly explain the improved performance. Intracellular phosphate in skeletal muscle is insulated from hypophosphatemia in XLH.

The effect of contact/collision sport participation without concussion on neurometabolites: A systematic review and meta-analysis of magnetic resonance spectroscopy studies.

The aim of this study was to systematically review prior research investigating the effects of contact/collision sport participation on neurometabolite levels in the absence of concussion. Four online databases were searched to identify studies that measured neurometabolite levels in contact/collision sport athletes (without concussion) using proton (1 H) or phosphorus (31 P) magnetic resonance spectroscopy (MRS). All study designs were acceptable for inclusion. Meta-analytic procedures were used to quantify the effect of contact/collision sport participation on neurometabolite levels and explore the impact of specific moderating factors (where sufficient data were available). Narrative synthesis was used to describe outcomes that could not be meta-analysed. Nine observational studies involving 300 contact/collision sport athletes were identified. Six studies (providing 112 effect estimates) employed longitudinal (cohort) designs and three (that could not be meta-analysed) employed case-control designs. N-acetylaspartate (NAA; g = -0.331, p = 0.013) and total creatine (tCr; creatine + phosphocreatine; g = -0.524, p = 0.029), but not glutamate-glutamine (Glx), myo-inositol (mI) or total choline (tCho; choline-containing compounds; p's > 0.05), decreased between the pre-season and mid-/post-season period. Several moderators were statistically significant, including: sex (Glx: 6 female/23 male, g = -0.549, p = 0.013), sport played (Glx: 22 American football/4 association football [soccer], g = 0.724, p = 0.031), brain region (mI: 2 corpus callosum/9 motor cortex, g = -0.804, p = 0.015), and the MRS quantification approach (mI: 18 absolute/3 tCr-referenced, g = 0.619, p = 0.003; andtCho: 18 absolute/3 tCr-referenced, g = 0.554, p = 0.005). In case-control studies, contact/collision sport athletes had higher levels of mI, but not NAA or tCr compared to non-contact sport athletes and non-athlete controls. Overall, this review suggests that contact/collision sport participation has the potential to alter neurometabolites measured via 1 H MRS in the absence of concussion. However, further research employing more rigorous and consistent methodologies (e.g. interventional studies with consistent 1 H MRS pulse sequences and quantifications) is required to confirm and better understand the clinical relevance of observed effects.