Multimodality assessment of heart failure with preserved ejection fraction skeletal muscle reveals differences in the machinery of energy fuel metabolism.

AIMS: Skeletal muscle (SkM) abnormalities may impact exercise capacity in patients with heart failure with preserved ejection fraction (HFpEF). We sought to quantify differences in SkM oxidative phosphorylation capacity (OxPhos), fibre composition, and the SkM proteome between HFpEF, hypertensive (HTN), and healthy participants. METHODS AND RESULTS: Fifty-nine subjects (20 healthy, 19 HTN, and 20 HFpEF) performed a maximal-effort cardiopulmonary exercise test to define peak oxygen consumption (VO2, peak ), ventilatory threshold (VT), and VO2 efficiency (ratio of total work performed to O2 consumed). SkM OxPhos was assessed using Creatine Chemical-Exchange Saturation Transfer (CrCEST, n = 51), which quantifies unphosphorylated Cr, before and after plantar flexion exercise. The half-time of Cr recovery (t1/2, Cr ) was taken as a metric of in vivo SkM OxPhos. In a subset of subjects (healthy = 13, HTN = 9, and HFpEF = 12), percutaneous biopsy of the vastus lateralis was performed for myofibre typing, mitochondrial morphology, and proteomic and phosphoproteomic analysis. HFpEF subjects demonstrated lower VO2,peak , VT, and VO2 efficiency than either control group (all P < 0.05). The t1/2, Cr was significantly longer in HFpEF (P = 0.005), indicative of impaired SkM OxPhos, and correlated with cycle ergometry exercise parameters. HFpEF SkM contained fewer Type I myofibres (P = 0.003). Proteomic analyses demonstrated (a) reduced levels of proteins related to OxPhos that correlated with exercise capacity and (b) reduced ERK signalling in HFpEF. CONCLUSIONS: Heart failure with preserved ejection fraction patients demonstrate impaired functional capacity and SkM OxPhos. Reductions in the proportions of Type I myofibres, proteins required for OxPhos, and altered phosphorylation signalling in the SkM may contribute to exercise intolerance in HFpEF.

Zone- and layer-specific differences in proteoglycan content in patellofemoral pain syndrome are detectable on T1ρ MRI.

OBJECTIVE: Determine if differences in T1ρ would be detected in specific regions or layers of patellofemoral cartilage between patients with symptomatic patellofemoral pain syndrome and asymptomatic control subjects. MATERIALS AND METHODS: Ten subjects diagnosed with patellofemoral pain syndrome were compared with ten age-, gender-, and BMI-matched control subjects with no knee pain or prior trauma. Conventional turbo (fast) spin echo sequences and T1ρ-weighted imaging were performed on the symptomatic knee in each of the ten subjects. At the patella and distal femur, cartilage regions of interest were divided into medial and lateral sub-regions, each then further sub-divided by layer (superficial, middle, or deep). Two-tailed t test and chi-squared tests were used to analyze demographic data. A mixed effect model was run for each sub-region of T1ρ imaging. Statistical significance was determined using the likelihood ratio test against reduced models without patellofemoral pain syndrome symptomatic status as a fixed effect. RESULTS: There was no difference in age, sex, or BMI between symptomatic and control patients. T1ρ values were significantly higher among patellofemoral pain syndrome patients when compared with controls in the superficial zone of the lateral patella (58.43 vs. 50.83, p = 0.03) and the middle zone of the lateral patella (52.67 vs. 43.60, p = 0.03). T1ρ was also higher in the superficial zone of the medial femur (50.94 vs. 46.70, p = 0.09) with a value approaching statistical significance. CONCLUSION: We report statistically significant differences in the T1ρ value in the superficial and middle zones of the lateral patella in patients with patellofemoral pain syndrome who had no abnormalities seen on conventional MRI sequences, suggesting an alteration the macromolecular structure of the cartilage in this population.

Reproducibility of 2D GluCEST in healthy human volunteers at 7 T.

PURPOSE: To investigate the reproducibility of gray and white matter glutamate contrast of a brain slice among a small group of healthy volunteers by using the 2D single-slice glutamate CEST (GluCEST) imaging technique. METHODS: Six healthy volunteers were scanned multiple times for within-day and between-day reproducibility. One more volunteer was scanned for within-day reproducibility at 7T MRI. Glutamate CEST contrast measurements were calculated for within subjects and among the subjects and the coefficient of variations are reported. RESULTS: The GluCEST measurements were highly reproducible in the gray and white matter area of the brain slice, whether it was within-day or between-day with a coefficient of variation of less than 5%. CONCLUSION: This preliminary study in a small group of healthy volunteers shows a high degree of reproducibility of GluCEST MRI in brain and holds promise for implementation in studying age-dependent changes in the brain.

In vivo GluCEST MRI: Reproducibility, background contribution and source of glutamate changes in the MPTP model of Parkinson's disease.

Glutamate Chemical Exchange Saturation Transfer (GluCEST) MRI is a recently developed technique to image glutamate. In the present study, we evaluated the reproducibility and background contamination to the GluCEST and source of the GluCEST changes in a mouse model of Parkinson's disease. Repeated measurements in five mice demonstrated an intra-animal coefficient of variation (CV) of GluCEST signal to be 2.3 ± 1.3% and inter-animal CV of GluCEST to be 3.3 ± 0.3%. Mice were treated with MPTP to create a localized striatal elevation of glutamate. We found an elevation in the GluCEST contrast of the striatum following MPTP treatment (Control: 23.3 ± 0.8%, n = 16; MPTP: 26.2 ± 0.8%, n = 19; p ≤ 0.001). Additionally, the positive association between glutamate concentration measured via 1H MRS and GluCEST signal was used to estimate background contribution to the measured GluCEST. The contribution of signal from non-glutamate sources was found to be ~28% of the total GluCEST. Immunohistochemical analysis of the brain showed co-localization of glutamate with GFAP in the striatum. This suggests that the elevated glutamate present in the striatum in this mouse model reflects astroglial proliferation or reactivity due to the action of MPTP. The potential of GluCEST as a biomarker for imaging inflammation mediated gliosis is discussed.

Non-caloric sweetener provides magnetic resonance imaging contrast for cancer detection.

BACKGROUND: Image contrast enhanced by exogenous contrast agents plays a crucial role in the early detection, characterization, and determination of the precise location of cancers. Here, we investigate the feasibility of using a non-nutritive sweetener, sucralose (commercial name, Splenda), as magnetic resonance imaging (MRI) contrast agent for cancer studies. METHODS: High-resolution nuclear-magnetic-resonance spectroscopy and MR studies on sucralose solution phantom were performed to detect the chemical exchange saturation transfer (CEST) property of sucralose hydroxyl protons with bulk water (sucCEST). For the animal experiments, female Fisher rats (F344/NCR) were used to generate 9L-gliosarcoma model. MRI with CEST experiments were performed on anesthetized rats at 9.4 T MR scanner. Following the baseline CEST scans, sucralose solution was intravenously administered in control and tumor bearing rats. CEST acquisitions were continued during and following the administration of sucralose. Following the sucCEST, Gadolinium-diethylenetriamine pentaacetic acid was injected to perform Gd-enhanced imaging for visualizing the tumor. RESULTS: The sucCEST contrast in vitro was found to correlate positively with the sucralose concentration and negatively with the pH, indicating the potential of this technique in cancer imaging. In a control animal, the CEST contrast from the brain was found to be unaffected following the administration of sucralose, demonstrating its blood-brain barrier impermeability. In a 9L glioma model, enhanced localized sucCEST contrast in the tumor region was detected while the unaffected brain region showed unaltered CEST effect implying the specificity of sucralose toward the tumorous tissue. The CEST asymmetry plots acquired from the tumor region before and after the sucralose infusion showed elevation of asymmetry at 1 ppm, pointing towards the role of sucralose in increased contrast. CONCLUSIONS: We show the feasibility of using sucralose and sucCEST in study of preclinical models of cancer. This study paves the way for the potential development of sucralose and other sucrose derivatives as contrast agents for clinical MRI applications.

Longitudinal imaging reveals subhippocampal dynamics in glutamate levels associated with histopathologic events in a mouse model of tauopathy and healthy mice.

Tauopathies are neurodegenerative disorders characterized by abnormal intracellular aggregates of tau protein, and include Alzheimer's disease, corticobasal degeneration, frontotemporal dementia, and traumatic brain injury. Glutamate metabolism is altered in neurodegenerative disorders manifesting in higher or lower concentrations of glutamate, its transporters or receptors. Previously, glutamate chemical exchange saturation transfer (GluCEST) magnetic resonance imaging (MRI) demonstrated that glutamate levels are reduced in regions of synapse loss in the hippocampus of a mouse model of late-stage tauopathy. We performed a longitudinal GluCEST imaging experiment paired with a cross-sectional study of histologic markers of tauopathy to determine whether (1) early GluCEST changes are associated with synapse loss before volume loss occurs in the hippocampus, and whether (2) subhippocampal dynamics in GluCEST are associated with histopathologic events related to glutamate alterations in tauopathy. Live imaging of the hippocampus in three serial slices was performed without exogenous contrast agents, and subregions were segmented based on a k-means cluster model. Subregions of the hippocampus were analyzed (cornu ammonis CA1, CA3, dentate gyrus DG, and ventricle) in order to associate local MRI-observable changes in glutamate with histological measures of glial cell proliferation (GFAP), synapse density (synaptophysin, VGlut1) and glutamate receptor (NMDA-NR1) levels. Early differences in GluCEST between healthy and tauopathy mice were measured in the CA1 and DG subregions (30% reduction, P ≤ 0.001). Synapse density was also significantly reduced in every subregion of the hippocampus in tauopathy mice by 6 months. Volume was not significantly reduced in any subregion until 13 months. Further, a gradient in glutamate levels was observed in vivo along hippocampal axes that became polarized as tauopathy progressed. Dynamics in hippocampal glutamate levels throughout lifetime were most closely correlated with combined changes in synaptophysin and GFAP, indicating that GluCEST imaging may be a surrogate marker of glutamate concentration in glial cells and at the synaptic level. © 2016 Wiley Periodicals, Inc.

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

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

Localized, gradient-reversed ultrafast z-spectroscopy in vivo at 7T.

PURPOSE: To collect ultrafast z-spectra in vivo in situations where voxel homogeneity cannot be assured. THEORY: Saturating in the presence of a gradient encodes the frequency offset spatially across a voxel. This encoding can be resolved by applying a similar gradient during readout. Acquiring additional scans with the gradient polarity reversed effectively mirrors the spatial locations of the frequency offsets so that the same physical location of a positive offset in the original scan will contribute a negative offset in the gradient-reversed scan. METHODS: Gradient-reversed ultrafast z-spectroscopy (GRUFZS) was implemented and tested in a modified, localized PRESS sequence at 7T. Lysine phantoms were scanned at various concentrations and compared with coventionally-acquired z-spectra. Scans were acquired in vivo in human brain from homogeneous and inhomogeneous voxels with the ultrafast direction cycled between read, phase, and slice. Results were compared to those from a similar conventional z-spectroscopy PRESS-based sequence. RESULTS: Asymmetry spectra from GRUFZS are more consistent and reliable than those without gradient reversal and are comparable to those from conventional z-spectroscopy. GRUFZS offers significant acceleration in data acquisition compared to traditional chemical exchange saturation transfer methods with high spectral resolution and showed higher relative SNR effficiency. CONCLUSION: GRUFZS offers a method of collecting ultrafast z-spectra in voxels with the inhomogeneity often found in vivo. Magn Reson Med 76:1039-1046, 2016. © 2016 Wiley Periodicals, Inc.

T1ρ Magnetic Resonance Imaging to Assess Cartilage Damage After Primary Shoulder Dislocation.

BACKGROUND: Patients who suffer anterior shoulder dislocations are at higher risk of developing glenohumeral arthropathy, but little is known about the initial cartilage damage after a primary shoulder dislocation. T1ρ is a magnetic resonance imaging (MRI) technique that allows quantification of cartilage proteoglycan content and can detect physiologic changes in articular cartilage. PURPOSE: This study aimed to establish baseline T1ρ MRI values for glenoid and humeral head cartilage, determine whether T1ρ MRI can detect glenohumeral cartilage damage after traumatic primary shoulder dislocation, and assess for patterns in cartilage damage in anterior shoulder dislocation. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Nine male patients (mean age, 32.0 years; range, 20-59 years) who sustained first-time anterior shoulder dislocations underwent 3T T1ρ MRI. Five healthy controls (mean age, 27.4 years; range, 24-30 years) without prior dislocation or glenohumeral arthritis also underwent 3T T1ρ MRI. The T1ρ relaxation constant was determined for the entire glenoid and humeral head for patients with a dislocation and for healthy controls. The glenoid and humeral head were divided into 9 zones, and T1ρ values were determined for each zone in dislocated and control shoulders to identify patterns in cartilage damage in dislocated shoulders. RESULTS: Average overall T1ρ values for humeral head cartilage in dislocated shoulders were significantly greater than in controls (41.7 ± 3.9 ms vs 38.4 ± 0.6 ms, respectively; P = .03). However, average overall T1ρ values for glenoid cartilage were not significantly different in dislocated shoulders compared with controls (44.0 ± 3.3 ms vs 44.6 ± 2.4 ms, respectively; P = .40), suggesting worse damage to humeral head cartilage. T1ρ values in the posterior-middle humeral head were higher in patients with a dislocation compared with controls (41.5 ± 3.8 ms vs 38.2 ± 2.2 ms, respectively; P = .021) and trended toward significance in the posterior-superior and middle-superior zones (35.2 ± 4.9 ms vs 31.3 ± 1.0 ms and 33.7 ± 5.0 ms vs 30.5 ± 1.3 ms, respectively; P = .056). These 3 humeral head zones are where Hill-Sachs lesions predominate. T1ρ values in the anterior-inferior glenoid zone trended toward significance in patients with a dislocation compared with controls (47.4 ± 5.0 ms vs 43.5 ± 3.5 ms, respectively; P = .073). CONCLUSION: Humeral head cartilage sustained greater damage than glenoid cartilage in primary dislocation. T1ρ values were higher in glenohumeral zones associated with Bankart and Hill-Sachs lesions. Widespread initial cartilage damage may predispose patients to glenohumeral arthropathy.

Glutaminase catalyzes reaction of glutamate to GABA.

Here, for the first time, we report an NMR spectroscopy study of l-Glutamine (Gln) conversion by Glutaminase (Glnase), which shows that the reaction involves two distinct steps. In the first step, Glnase rapidly hydrolyzes Gln to Glutamate (Glu) (∼16.87 µmol of Gln/min/mg of Glnase) and in the second step, Glu generated in the first step is decarboxylated into gamma-amino butyric acid (GABA) with a much slower rate (∼0.185 µmol/min/mg). When Glnase was added to the sample containing l-Glu alone, it was also converted to GABA, at a similar rate as in the second step mentioned above. The rate of Glu decarboxylation into GABA by Glnase is about an order of magnitude lower than that by commonly known enzyme, Glutamate decarboxylase. Potential impact of these findings, on the mechanistic aspects of Gln-Glu shuttle in neuroscience and glutaminolysis in tumors, is discussed.