Abstract
Defects in skeletal muscle energy metabolism are indicative of systemic disorders such as obesity or type 2 diabetes. Phosphorus magnetic resonance spectroscopy (31P-MRS), in particularly dynamic 31P-MRS, provides a powerful tool for the non-invasive investigation of muscular oxidative metabolism. The increase in spectral and temporal resolution of 31P-MRS at ultra high fields (i.e., 7T) uncovers new potential for previously implemented techniques, e.g., saturation transfer (ST) or highly resolved static spectra. In this study, we aimed to investigate the differences in muscle metabolism between overweight-to-obese sedentary (Ob/Sed) and lean active (L/Ac) individuals through dynamic, static, and ST 31P-MRS at 7T. In addition, as the dynamic 31P-MRS requires a complex setup and patient exercise, our aim was to identify an alternative technique that might provide a biomarker of oxidative metabolism. The Ob/Sed group exhibited lower mitochondrial capacity, and, in addition, static 31P-MRS also revealed differences in the Pi-to-ATP exchange flux, the alkaline Pi-pool, and glycero-phosphocholine concentrations between the groups. In addition to these differences, we have identified correlations between dynamically measured oxidative flux and static concentrations of the alkaline Pi-pool and glycero-phosphocholine, suggesting the possibility of using high spectral resolution 31P-MRS data, acquired at rest, as a marker of oxidative metabolism.
Highlights
Resulting in the progression of metabolic disease, such as type 2 diabetes, even in a young, overweight-to-obese, sedentary population[9,10,11]
The group of obese sedentary (Ob/Sed) subjects had significantly lower mitochondrial capacity (Qmax) and Pi-to-ATP exchange flux (FATP) values compared to the lean active (L/Ac) group
We compared parameters of skeletal muscle metabolism, measured by static and dynamic 31P-MRS methods, between a group of overweight-to-obese sedentary subjects, who are prone to diabetes, and a group of lean active individuals
Summary
Resulting in the progression of metabolic disease, such as type 2 diabetes, even in a young, overweight-to-obese, sedentary population[9,10,11]. Dynamic 31P-MRS, during exercise and recovery, in particular, allows direct estimation of the oxidative ATP synthesis rate in challenged muscle[12,13,14,15], which reflects maximal mitochondrial capacity[7]. The measurement of resting Pi-to-ATP flux (FATP) using 31P-MRS saturation transfer (ST), correlates with the findings of dynamic experiments[21,22]. The absolute values of FATP do not provide a direct measure of oxidative metabolism[23], it has been related to insulin resistance[24,25]. Our aim was to compare the skeletal muscle metabolism of overweight-to-obese sedentary (Ob/Sed) subjects, who are prone to type 2 diabetes, and lean active (L/Ac) individuals, using static and dynamic 31P-MRS measurements in the quadriceps femoris muscle at 7 T. The interrelations between the derived parameters were investigated to determine possible alternatives to exercise-recovery experiments
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