Role of Cardiorespiratory Fitness and Mitochondrial Oxidative Capacity in Reduced Walk Speed of Older Adults with Diabetes

Cardiorespiratory fitness and mitochondrial oxidative capacity are associated with reduced walking speed in older adults. The impact of cardiorespiratory fitness and mitochondrial oxidative capacity on walking speed in older adults with diabetes has not been clearly defined. We examined differences in cardiorespiratory fitness and skeletal muscle mitochondrial oxidative capacity between older adults with and without diabetes as well as determine their relative contribution to slower walking speed in older adults with diabetes. Participants with diabetes (n=159) had lower cardiorespiratory fitness and mitochondrial respiration in permeabilized fiber bundles when compared to those without diabetes (n=717), following adjustments for covariates including BMI, chronic comorbid health conditions, and physical activity. 4-m and 400-m walking speeds were slower in those with diabetes. Mitochondrial oxidative capacity alone or combined with cardiorespiratory fitness mediated ∼20-70% of the difference in walk speed between older adults with and without diabetes. Additional adjustments with BMI and co-morbidities further explained the group differences in walk speed. Cardiorespiratory fitness and skeletal muscle mitochondrial oxidative capacity contribute to slower walking speeds in older adults with diabetes.

Relationships between GABA, glutamate, and GABA/glutamate and social and olfactory processing in children with autism spectrum disorder

Theories of altered inhibitory/excitatory signaling in autism spectrum disorder (ASD) suggest that gamma amino butyric acid (GABA) and glutamate (Glu) abnormalities may underlie social and sensory challenges in ASD. Magnetic resonance spectroscopy was used to measure Glu and GABA+ levels in the amygdala-hippocampus region and cerebellum in autistic children (n = 30), a clinical control group with sensory abnormalities (SA) but not ASD (n = 30), and children with typical development (n = 37). All participants were clinically assessed using the Autism Diagnostic Interview-Revised, the Autism Diagnostic Observation Scale-2, and the Child Sensory Profile-2. The Social Responsiveness Scale-2, Sniffin Sticks Threshold Test, and the University of Pennsylvania Smell Identification Test were administered to assess social impairment and olfactory processing. Overall, autistic children showed increased cerebellar Glu levels compared to TYP children. Evidence for altered excitatory/inhibitory signaling in the cerebellum was more clear-cut when analyses were restricted to male participants. Further, lower cerebellar GABA+/Glu ratios were correlated to more severe social impairment in both autistic and SA males, suggesting that the cerebellum may play a transdiagnostic role in social impairment. Future studies of inhibitory/excitatory neural markers, powered to investigate the role of sex, may aid in parsing out disorder-specific neurochemical profiles.

Effect of Urolithin A Supplementation on Muscle Endurance and Mitochondrial Health in Older Adults: A Randomized Clinical Trial

IMPORTANCE

Aging is associated with a decline in mitochondrial function and reduced exercise capacity. Urolithin A is a natural gut microbiome-derived food metabolite that has been shown to stimulate mitophagy and improve muscle function in older animals and to induce mitochondrial gene expression in older humans.

OBJECTIVE

To investigate whether oral administration of urolithin A improved the 6-minute walk distance, muscle endurance in hand and leg muscles, and biomarkers associated with mitochondrial and cellular health.

DESIGN, SETTING, AND PARTICIPANTS

This double-blind, placebo-controlled randomized clinical trial in adults aged 65 to 90 years was conducted at a medical center and a cancer research center in Seattle, Washington, from March 1, 2018, to July 30, 2020. Muscle fatigue tests and plasma analysis of biomarkers were assessed at baseline, 2 months, and 4 months. Six-minute walk distance and maximal ATP production were assessed using magnetic resonance spectroscopy at baseline and at the end of study at 4 months. The analysis used an intention-to-treat approach.

INTERVENTIONS

Participants were randomized to receive daily oral supplementation with either 1000 mg urolithin A or placebo for 4 months.

MAIN OUTCOMES AND MEASURES

The primary end point was change from baseline in the 6-minute walk distance and change from baseline to 4 months in maximal ATP production in the hand skeletal muscle. The secondary end points were change in muscle endurance of 2 skeletal muscles (tibialis anterior [TA] in the leg and first dorsal interosseus [FDI] in the hand). Cellular health biomarkers were investigated via plasma metabolomics. Adverse events were recorded and compared between the 2 groups during the intervention period.

RESULTS

A total of 66 participants were randomized to either the urolithin A (n = 33) or the placebo (n = 33) intervention group. These participants had a mean (SD) age of 71.7 (4.94) years, were predominantly women (50 [75.8%]), and were all White individuals. Urolithin A, compared with placebo, significantly improved muscle endurance (ie, increase in the number of muscle contractions until fatigue from baseline) in the FDI and TA at 2 months (urolithin A: FDI, 95.3 [115.5] and TA, 41.4 [65.5]; placebo: FDI, 11.6 [147.4] and TA, 5.7 [127.1]). Plasma levels of several acylcarnitines, ceramides, and C-reactive protein were decreased by urolithin A, compared with placebo, at 4 months (baseline vs 4 mo: urolithin A, 2.14 [2.15] vs 2.07 [1.46]; placebo, 2.17 [2.52] vs 2.65 [1.86]). The mean (SD) increase from baseline in the 6-minute walk distance was 60.8 (67.2) m in the urolithin A group and 42.5 (73.3) m in the placebo group. The mean (SD) change from baseline to 4 months in maximal ATP production in the FDI was 0.07 (0.23) mM/s in the urolithin A group and 0.06 (0.20) mM/s in the placebo group; for the TA, it was -0.03 (0.10) mM/s in the urolithin A group and 0.03 (0.10) mM/s in the placebo group. These results showed no significant improvement with urolithin A supplementation compared with placebo. No statistical differences in adverse events were observed between the 2 groups.

CONCLUSIONS AND RELEVANCE

This randomized clinical trial found that urolithin A supplementation was safe and well tolerated in the assessed population. Although the improvements in the 6-minute walk distance and maximal ATP production in the hand muscle were not significant in the urolithin A group vs the placebo group, long-term urolithin A supplementation was beneficial for muscle endurance and plasma biomarkers, suggesting that urolithin A may counteract age-associated muscle decline; however, future work is needed to confirm this finding.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03283462.

Impaired skeletal muscle mitochondrial bioenergetics and physical performance in chronic kidney disease

The maintenance of functional independence is the top priority of patients with chronic kidney disease (CKD). Defects in mitochondrial energetics may compromise physical performance and independence. We investigated associations of the presence and severity of kidney disease with in vivo muscle energetics and the association of muscle energetics with physical performance. We performed measures of in vivo leg and hand muscle mitochondrial capacity (ATPmax) and resting ATP turnover (ATPflux) using 31phosphorus magnetic resonance spectroscopy and oxygen uptake (O2 uptake) by optical spectroscopy in 77 people (53 participants with CKD and 24 controls). We measured physical performance using the 6-minute walk test. Participants with CKD had a median estimated glomerular filtration rate (eGFR) of 33 ml/min per 1.73 m2. Participants with CKD had a -0.19 mM/s lower leg ATPmax compared with controls but no difference in hand ATPmax. Resting O2 uptake was higher in CKD compared with controls, despite no difference in ATPflux. ATPmax correlated with eGFR and serum bicarbonate among participants with GFR <60. ATPmax of the hand and leg correlated with 6-minute walking distance. The presence and severity of CKD associate with muscle mitochondrial capacity. Dysfunction of muscle mitochondrial energetics may contribute to reduced physical performance in CKD.

In vivo absolute quantification for mouse muscle metabolites using an inductively coupled synthetic signal injection method and newly developed (1) H/(31) P dual tuned probe

PURPOSE

To obtain robust estimates of (31) P metabolite content in mouse skeletal muscles using our recently developed MR absolute quantification method and a custom-built (1) H/(31) P dual tuned radiofrequency (RF) coil optimized for mouse leg.

MATERIALS AND METHODS

We designed and fabricated a probe consisting of two dual tuned (1) H/(31) P solenoid coils: one leg was inserted to each solenoid. The mouse leg volume coil was incorporated with injector coils for MR absolute quantification. The absolute quantification method uses a synthetic reference signal injection approach and solves several challenges in MR absolute quantification including changes of coil loading and receiver gains.

RESULTS

The (1) H/(31) P dual tuned probe was composed of two separate solenoid coils, one for each leg, to increase coil filling factors and signal-to-noise ratio. Each solenoid was equipped with a second coil to allow injection of reference signals. (31) P metabolite concentrations determined for normal mice were well within the expected range reported in the literature.

CONCLUSION

We developed an RF probe and an absolute quantification approach adapted for mouse skeletal muscle.

Skeletal muscle mitochondrial energetics are associated with maximal aerobic capacity and walking speed in older adults

BACKGROUND

Lower ambulatory performance with aging may be related to a reduced oxidative capacity within skeletal muscle. This study examined the associations between skeletal muscle mitochondrial capacity and efficiency with walking performance in a group of older adults.

METHODS

Thirty-seven older adults (mean age 78 years; 21 men and 16 women) completed an aerobic capacity (VO2 peak) test and measurement of preferred walking speed over 400 m. Maximal coupled (State 3; St3) mitochondrial respiration was determined by high-resolution respirometry in saponin-permeabilized myofibers obtained from percutanous biopsies of vastus lateralis (n = 22). Maximal phosphorylation capacity (ATPmax) of vastus lateralis was determined in vivo by (31)P magnetic resonance spectroscopy (n = 30). Quadriceps contractile volume was determined by magnetic resonance imaging. Mitochondrial efficiency (max ATP production/max O2 consumption) was characterized using ATPmax per St3 respiration (ATPmax/St3).

RESULTS

In vitro St3 respiration was significantly correlated with in vivo ATPmax (r (2) = .47, p = .004). Total oxidative capacity of the quadriceps (St3*quadriceps contractile volume) was a determinant of VO2 peak (r (2) = .33, p = .006). ATPmax (r (2) = .158, p = .03) and VO2 peak (r (2) = .475, p < .0001) were correlated with preferred walking speed. Inclusion of both ATPmax/St3 and VO2 peak in a multiple linear regression model improved the prediction of preferred walking speed (r (2) = .647, p < .0001), suggesting that mitochondrial efficiency is an important determinant for preferred walking speed.

CONCLUSIONS

Lower mitochondrial capacity and efficiency were both associated with slower walking speed within a group of older participants with a wide range of function. In addition to aerobic capacity, lower mitochondrial capacity and efficiency likely play roles in slowing gait speed with age.

Quantitative 19F imaging using inductively coupled reference signal injection

This report describes recent efforts on our continuous development of a synthetic signal injection method for quantification of metabolite content in MR spectroscopy and MRI. Previous work showed that conversion of spectral peaks to quantitative units of metabolite content could be achieved with a calibrated synthetic free induction decay generated by an inductively coupled injection coil. This work demonstrates that calibrated synthetic voxels, injected in the same manner, can be used to quantify metabolite content in real (19)F image voxels. Images of vials containing different concentrations of sodium fluoride (NaF) were converted to units of moles by reference to precalibrated synthetically injected voxels. Additional images of vials containing variable sodium chloride (NaCl) demonstrate that the quantification process is robust and immune to changes in coil loading conditions.

Common phenotype of resting mouse extensor digitorum longus and soleus muscles: equal ATPase and glycolytic flux during transient anoxia

Rates of ATPase and glycolysis are several times faster in actively contracting mouse extensor digitorum longus muscle (EDL) than soleus (SOL), but we find these rates are not distinguishable at rest. We used a transient anoxic perturbation of steady state energy balance to decrease phosphocreatine (PCr) reversibly and to measure the rates of ATPase and of lactate production without muscle activation or contraction. The rate of glycolytic ATP synthesis is less than the ATPase rate, accounting for the continual PCr decrease during anoxia in both muscles. We fitted a mathematical model validated with properties of enzymes and solutes measured in vitro and appropriate for the transient perturbation of these muscles to experimental data to test whether the model accounts for the results. Simulations showed equal rates of ATPase and lactate production in both muscles. ATPase controls glycolytic flux by feedback from its products. Adenylate kinase function is critical because a rise in [AMP] is necessary to activate glycogen phosphorylase. ATPase is the primary source of H+ production. The sum of contributions of the 13 reactions of the glycogenolytic and glycolytic network to total proton load is negligible. The stoichiometry of lactate and H+ production is near unity. These results identify a default state of energy metabolism for resting muscle in which there is no difference in the metabolic phenotype of EDL and SOL. Therefore, additional control mechanisms, involving higher ATPase flux and [Ca2+], must exist to explain the well-known difference in glycolytic rates in fast-twitch and slow-twitch muscles in actively contracting muscle.

Correlation of proton transverse relaxation rates (R2) with iron concentrations in postmortem brain tissue from alzheimer's disease patients

Iron accumulates in the Alzheimer's disease (AD) brain and is directly associated with beta-amyloid pathology. The proton transverse relaxation rate (R(2)) has a strong linear relationship with iron concentrations in healthy brain tissue; however, an independent test of this relationship has not been extended to AD brain tissue. In this study in vitro single spin-echo (SE) measurements were made on tissue samples from four human AD brains using a 4.7T MRI research scanner. R(2) values were calculated for 14 cortical and subcortical gray matter (GM) and white matter (WM) regions. Atomic absorption spectroscopy was used to measure iron concentrations in the corresponding excised brain regions. Significant positive linear correlations were observed between R(2) values and iron concentrations in GM regions assessed across individual tissue samples and data averaged by brain region. With the use of a predictive model for R(2), a threshold iron concentration of 55 microg Fe/g wet tissue was determined above which R(2) appears to be dominated by the affects of iron in AD brain tissue. High-field MRI may therefore be a useful research tool for assessing brain iron changes associated with AD.

Effects of pH and molecular charge on dipolar coupling interactions of solutes in skeletal muscle observed by DQF, 1H NMR spectroscopy

In this study we tested the effect of molecular charge and chirality as well as tissue pH on dipolar coupling interaction in skeletal muscle. These results were demonstrated by double quantum filtered, DQF, 1H NMR spectra acquired on permeable skeletal muscle samples dialyzed against buffered solutions containing three classes of solutes-electrolytes (lactate and Tris), zwitterions (alanine and glycine), and non-electrolytes (dioxane and ethanol)-as a function of pH ranging from 5.0 to 8.5. The results show that charge density on the protein filaments strongly influences dipolar coupling of solutes in muscle whereas charge on the solutes themselves has only a small effect. The frequency splitting of the dipolar coupled peaks for all the molecules tested was strongly affected by muscle pH. Higher pH increased negative charge density on the filaments and resulted in weaker dipolar coupling for anions and zwitterions but stronger coupling for the cation TRIS. Molecular charge per se or chirality did not affect the frequency splitting of the dipolar coupled peaks. The molecules, lactate, ethanol, and alanine, have scalar coupled spins and consequently a double quantum signal in solution. However, spectra acquired from these molecules in muscle showed an additional frequency splitting due to additional dipolar coupling interactions. Due to lack of scalar coupling, spectra from Tris, glycine, and dioxane showed no double quantum signal in solution but did when in muscle. All these observations can be explained by the fact that the net charge on protein filaments dominates the mechanism of dipolar coupling interactions in the highly anisotropic structures in muscle.

Double quantum filtered (1)H NMR spectroscopy enables quantification of lactate in muscle

In this study we address the question of quantification of muscle lactate using double quantum filtered (DQF) (1)H NMR spectroscopy where dipolar and scalar coupled spectra are acquired. For this, lactate content in muscle samples was independently determined using a conventional enzymatic assay and DQF, (1)H NMR spectroscopy. NMR quantification of lactate relied on comparison of muscle spectra with similarly acquired spectra of standard lactate solutions. Transverse relaxation, T(2), and dipolar coupling effects were investigated at two different orientations of muscle fibers relative to B(o) and at various lactate concentrations. In all cases, we found a biexponential T(2) decay of the lactate methyl signal with a long T(2) of 142 ms (+/-8 ms, n=24) and a short T(2) of 37 ms (+/-6 ms, n=24). Lactate content of muscle determined by NMR spectroscopy agreed with the results obtained from enzymatic assays of the same samples provided that T(2) effects as well as the presence of both scalar and dipolar coupling interactions of lactate in muscle were taken into account.

Validation of whole-body magnetic resonance spectroscopy as a tool to assess murine body composition

OBJECTIVE

To evaluate proton magnetic resonance spectroscopy (MRS) as a tool for the non-invasive assessment of murine body composition.

DESIGN

Twenty C57/BL6 male mice with a wide range of body adiposities underwent both pre- and post-mortem whole-body MRS to assess body composition. MRS measures were compared to the results obtained by chemical carcass analysis, the current 'gold standard' for determination of body composition.

MEASUREMENTS

Areas under the curve (AUC) for lipid and water peaks of whole body MRS spectra (AUClipid and AUCH2O, respectively) were used to determine percentages of body fat (%FATMRS) and fat free mass by MRS (%FFMMRS). Total body fat, total body water, fat free mass, and total lean mass were determined by chloroform/methanol extraction of lipid from dessicated whole carcass and compared to MRS measures (%FATMRS, %FFMMRS, AUClipid, and AUCH2O). The variability of the MRS technique was assessed by determining the coefficients of variation (COV) associated with %FATMRS, AUClipid, and AUCH2O for mice of three different adiposities.

RESULTS

%FATMRS in live mice was highly correlated with body fat percentage (r=0.994, P<0.001) and total body fat (r=0.980, P<0.001) derived from chemical carcass analysis over a broad range of adiposities (7-48% body fat content by carcass analysis). There was no difference in %FATMRS measured pre- vs post-mortem (r=1.00, P<0.001). AUClipid was highly correlated with chemically derived total fat mass (r=0.996, P<0.001) and body fat percentage (r=0.981, P<0.001), while %FFMMRS was strongly correlated to chemical determinations of percentage body water (r=0.994, P<0. 001), percentage fat free mass (r=0.993, P<0.001), and percentage lean mass (r=0.792, P<0.001). AUCH2O was strongly associated with carcass analysis determinations of total body water (r=0.964, P<0. 001), total fat free mass (r=0.953, P<0.001), and total lean mass (r=0.89, P<0.001). In mice of 6%, 12%, and 43% body fat, COVs determined for %FATMRS and AUClipid were less than 10%. The COVs for AUCH2O were less than 2%.

CONCLUSIONS

MRS provides precise, accurate, rapid, and non-invasive measures of body fat, body water, fat free mass, and lean mass in living mice with a broad range of adiposities.

Anisotropic orientation of lactate in skeletal muscle observed by dipolar coupling in (1)H NMR spectroscopy

Double quantum (DQ), J-resolved (1)H NMR spectra from rat and bovine skeletal muscle showed a splitting frequency ( approximately 24 Hz) for the lactate methyl protons that varied with the orientation of the muscle fibers relative to the magnetic field. In contrast, spectra of lactate in solution consist of a J-coupled methyl doublet and a J-coupled methine quartet (J(HH) = 7 Hz) with no sensitivity to sample orientation. Spectra acquired in magnetic fields of 4.7, 7, and 11 T showed that the splitting was not due to inhomogeneities in magnetic susceptibility within the muscle, because the magnitude of the splitting did not scale with the strength of B(0) fields. Triple quantum coherence (TQC) spectra revealed two distinct transition frequencies on the methyl resonance. These frequencies resulted from intra-methyl and methine-methyl couplings in this four spin system (A(3)X). Decoupling experiments on the triple quantum coherence showed that the observed frequency splitting was due mainly to the dipolar interactions between the methine and methyl protons of the lactate molecule. Thus, all the proton resonances of the lactate molecules in muscle behave anisotropically in the magnetic field. Adequate design and interpretation of spectroscopic experiments to measure lactate in muscle, and possibly in any cell and organ which contain asymmetric structures, require that both the dipolar coupling described here and the well-known scalar coupling be taken into account.