In vivo P-31 MRS detection of an alkaline inorganic phosphate pool with short T1 in human resting skeletal muscle

Non-invasive determination of mitochondrial content is an important objective in clinical and sports medicine. P-31 MRS approaches to obtain information on this parameter at low field strength typically require in-magnet exercise. Direct observation of the intra-mitochondrial inorganic phosphate (Pi) pool in resting muscle would constitute an alternative, simpler method. In this study, we exploited the higher spectral resolution and signalto-noise at 7T to investigate the MR visibility of this metabolite pool. P-31 in vivo MR spectra of the resting soleus (SOL) muscle were obtained with H-1 MR image-guided surface coil localization (six volunteers) and of the SOL and tibialis anterior (TA) muscle using 2D CSI (five volunteers). A resonance at a frequency 0.38 ppm downfield from the cytosolic Pi resonance (Pi(1); pH 7.0 +/- 0.04) was reproducibly detected in the SOL muscle in all subjects and conditionally attributed to the intra-mitochondrial Pi pool (Pi(2); pH 7.3 +/- 0.07). In the SOL muscle, the Pi(2)/Pi(1) ratio was 1.6 times higher compared to the TA muscle in the same individual. Localized 3D CSI results showed that the Pi(2) peak was present in voxels well away from blood vessels. Determination of the T1 of the two Pi pools in a single individual using adiabatic excitation of the spectral region around 5 ppm yielded estimates of 4.3 +/- 0.4 s vs 1.4 +/- 0.5 s for Pi, and Pi(2), respectively. Together, these results suggest that the intra-mitochondrial Pi pool in resting human skeletal muscle may be visible with P-31 MRS at high field. Copyright (c) 2010 John Wiley & Sons, Ltd.Imaging- and therapeutic targets in neoplastic and musculoskeletal inflammatory diseas

Fiber-type-specific sensitivities and phenotypic adaptations to dietary fat overload differentially impact fast- versus slow-twitch muscle contractile function in C57BL/6J mice

High-fat diets (HFDs) have been shown to interfere with skeletal muscle energy metabolism and cause peripheral insulin resistance. However, understanding of HFD impact on skeletal muscle primary function, i.e., contractile performance, is limited. Male C57BL/6J mice were fed HFD containing lard (HFL) or palm oil (HFP), or low-fat diet (LFD) for 5 weeks. Fast-twitch (FT) extensor digitorum longus (EDL) and slow-twitch (ST) soleus muscles were characterized with respect to contractile function and selected biochemical features. In FT EDL muscle, a 30%–50% increase in fatty acid (FA) content and doubling of long-chain acylcarnitine (C14–C18) content in response to HFL and HFP feeding were accompanied by increase in protein levels of peroxisome proliferator-activated receptor-γ coactivator-1α, mitochondrial oxidative phosphorylation complexes and acyl-CoA dehydrogenases involved in mitochondrial FA β-oxidation. Peak force of FT EDL twitch and tetanic contractions was unaltered, but the relaxation time (RT) of twitch contractions was 30% slower compared to LFD controls. The latter was caused by accumulation of lipid intermediates rather than changes in the expression levels of proteins involved in calcium handling. In ST soleus muscle, no evidence for lipid overload was found in any HFD group. However, particularly in HFP group, the peak force of twitch and tetanic contractions was reduced, but RT was faster than LFD controls. The latter was associated with a fast-to-slow shift in troponin T isoform expression. Taken together, these data highlight fiber-type-specific sensitivities and phenotypic adaptations to dietary lipid overload that differentially impact fast- versus slow-twitch skeletal muscle contractile function

Body fat distribution in pubertal girls quantified by magnetic resonance imaging

We examined body fat distribution in relation to anthropometrically derived variables in 24 girls in early and late stages of puberty. The amounts of subcutaneous and intra-abdominal body fat were derived from transverse slices at the levels of the waist, hip and trochanter using magnetic resonance imaging (MRI), and were compared to the related circumferences, the circumference ratios and the trunk-to-extremity skinfold ratios. Waist, hip and trochanter circumferences were highly correlated to the respective related MRI total fat surface area both in early and late pubertal girls (r = 0.79-0.97), while waist circumference, and waist-hip, waist-thigh or skinfold ratios were not significantly correlated to intra-abdominal fat areas. Late pubertal girls (n = 11) were significantly taller, heavier and fatter compared to early pubertal girls (n = 13), yet their anthropometric waist-to-hip or waist-to-trochanter circumference ratios were significantly lower. The intra-abdominal fat area measured in a transverse MRI section at the level of the waist was 24.1 +/- 4.1 cm2 in early pubertal girls and 25.7 +/- 4.1 cm2 in late pubertal girls (mean +/- s.e.m.). As compared to early pubertal girls, the MRI derived amount of subcutaneous fat in late pubertal girls was significantly higher at the trochanter level (142.1 +/- 12.7 vs. 201.3 +/- 26.3 cm2; P less than 0.05). We conclude that circumferences at the trunk are good measures for the related amounts of fat in pubertal girls. In contrast conventional anthropometric measurements, such as trunk-to-extremity skinfold ratio or waist-to-hip circumference ratio, cannot be used to predict the amount of intra-abdominal fat in pubertal girls.(ABSTRACT TRUNCATED AT 250 WORDS