PCr/ATP ratios and mitochondrial function in the heart. A comparative study in humans.

Cardiac energy status, measured as phosphocreatine (PCr)/adenosine triphosphate (ATP) ratio with 31P-Magnetic Resonance Spectroscopy (31P-MRS) in vivo, is a prognostic factor in heart failure and is lowered in cardiometabolic disease. It has been suggested that, as oxidative phosphorylation is the major contributor to ATP synthesis, PCr/ATP ratio might be a reflection of cardiac mitochondrial function. The objective of the study was to investigate whether PCr/ATP ratios can be used as in vivo marker for cardiac mitochondrial function. We enrolled thirty-eight patients scheduled for open-heart surgery in this study. Cardiac 31P-MRS was performed before surgery. Tissue from the right atrial appendage was obtained during surgery for high-resolution respirometry for the assessment of mitochondrial function. There was no correlation between the PCr/ATP ratio and ADP-stimulated respiration rates (octanoylcarnitine R2 < 0.005, p = 0.74; pyruvate R2 < 0.025, p = 0.41) nor with maximally uncoupled respiration (octanoylcarnitine R2 = 0.005, p = 0.71; pyruvate R2 = 0.040, p = 0.26). PCr/ATP ratio did correlate with indexed LV end systolic mass. As no direct correlation between cardiac energy status (PCr/ATP) and mitochondrial function in the heart was found, the study suggests that mitochondrial function might not the only determinant of cardiac energy status. Interpretation should be done in the right context in cardiac metabolic studies.

Thigh muscles are more susceptible to age-related muscle loss when compared to lower leg and pelvic muscles.

BACKGROUND: A key hallmark of aging is the progressive loss of skeletal muscle mass. Due to limitations of the various methods typically applied to assess muscle mass, only limited information is available on age-related differences between various muscle groups. This study assessed differences in individual lower body muscle group volumes between healthy young and older males. METHODS: Lower body muscle mass assessments were performed in 10 young (age: 27 ± 4 y) and 10 older (age: 71 ± 6 y) healthy, male adults using Dual-energy X-ray Absorptiometry (DXA), single slice (thigh) Computed Tomography (CT), as well as Magnetic Resonance Imaging (MRI). Muscle volumes of all individual muscle groups in the lower body were assessed by MRI. RESULTS: Leg lean mass, as assessed with DXA, was not significantly different between older (9.2 ± 1.0 kg) and young (10.5 ± 2.0 kg) men (P = 0.075). Thigh muscle cross-sectional area, as assessed with CT, was significantly lower (by 13 %) in the older (137 ± 17 cm2) compared to young (157 ± 24 cm2) participants (P = 0.044). MRI-derived lower body muscle volume was also significantly lower (by 20 %) in older (6.7 ± 0.9 L) compared to young (8.3 ± 1.3 L) men (P = 0.005). This was primarily attributed to substantial differences in thigh (24 %), rather than lower leg (12 %) and pelvis (15 %) muscle volume in the older vs the young. Thigh muscle volume averaged 3.4 ± 0.5 L in older and 4.5 ± 0.7 L in young men (P = 0.001). Of all thigh muscle groups, the quadriceps femoris showed the most profound difference (30 %) between young (2.3 ± 0.4 L) and older (1.6 ± 0.2 L) men (P < 0.001). CONCLUSIONS: The most profound differences in lower body muscle volume between young and older men are observed in the thigh. Within the thigh muscle groups, the quadriceps femoris shows the largest difference in muscle volume between young and older men. Finally, DXA appears less sensitive when compared to CT and MRI to assess age-related differences in muscle mass.

Application of a BIlinear Rotation Decoupling (BIRD) filter in combination with J-difference editing for indirect 13 C measurements in the human liver.

PURPOSE: Recently, we introduced a quantum coherence based method (ge-HSQC) for indirect 13 C-MRS in the liver to track 13 C-labeled lipids into the hepatic lipid pool in vivo. This approach is more robust in case of respiratory motion, however, inherently leads to a signal loss of 50% when compared with a conventional J-difference editing technique (JDE). Here, we intend to improve the robustness of a regular JDE (STEAM-ACED) with the use of a BIlinear Rotation Decoupling (BIRD) filter to achieve 100% higher signal gain when compared with ge-HSQC. METHODS: To determine the efficiency of the BIRD filter 1 H-[13 C] lipid spectra were acquired on 3T from a peanut oil phantom, with three different MR sequences: ge-HSQC, STEAM-ACED, and the BIRD filter together with STEAM-ACED (BIRD-STEAM-ACED). Finally, our proposed method is tested in vivo in five healthy volunteers with varying liver fat content. In these subjects we quantified the 1 H-[13 C]-signal from the hepatic lipid pool and determined 13 C enrichment, which is expected to be 1.1% according to the natural abundance of 13 C. RESULTS: The application of the proposed BIRD filter reduces the subtraction artifact of 1 H-[12 C] lipid signal efficiently in JDE experiments, which leads to a signal gain of 100% of 1 H-[13 C]-lipid signals when compared with the ge-HSQC. Phase distortions in vivo were minimal with the use of BIRD compared with STEAM-ACED, which enabled us to robustly quantify the 13 C-enrichment in all five subjects. CONCLUSION: The BIRD-STEAM-ACED sequence is an efficient and promising tool for 13 C-tracking experiments in the human liver in vivo.