31P MR spectroscopy and in vitro markers of oxidative capacity in type 2 diabetes patients

Background: Skeletal muscle mitochondrial function in type 2 diabetes (T2D) is currently being studied intensively. In vivo P-31 magnetic resonance spectroscopy (P-31 MRS) is a noninvasive tool to measure mitochondrial respiratory function (MIFU) in skeletal muscle tissue. However, microvascular co-morbidity in long-standing T2D can interfere with the P-31 MRS methodology. Aim: To compare P-31 MRS-derived parameters describing in vivo MIFU with an in vitro assessment of muscle respiratory capacity and muscle fiber-type composition in T2D patients. Methods: P-31 MRS was applied in long-standing, insulin-treated T2D patients. P-31 MRS markers of MIFU were measured in the M. vastus lateralis. Muscle biopsy samples were collected from the same muscle and analyzed for succinate dehydrogenase activity (SDH) and fiber-type distribution. Results: Several P-31 MRS parameters of MIFU showed moderate to good correlations with the percentage of type I fibers and type I fiber-specific SDH activity (Pearson's R between 0.70 and 0.75). In vivo and in vitro parameters of local mitochondrial respiration also correlated well with whole-body fitness levels (VO2peak) in these patients (Pearson's R between 0.62 and 0.90). Conclusion: Good correlations exist between in vivo and in vitro measurements of MIFU in long-standing insulin-treated T2D subjects, which are qualitatively and quantitatively consistent with previous results measured in healthy subjects. This justifies the use of 31P MRS to measure MIFU in relation to T2D.