Global profiling of the muscle metabolome: method optimization, validation and application to determine exercise-induced metabolic effects

Skeletal muscle represents a crucial metabolic organ in the body characterized by a tremendous metabolic plasticity and the ability to influence important metabolic events elsewhere in the body. In order to understand the metabolic implications of skeletal muscle, it is imperative to characterize the metabolites within the tissue itself. In this work we aimed at developing a suitable analytical pipeline to analyze the metabolome of muscle tissue. Methanol/chloroform/water at neutral pH was selected as the method of choice for metabolite extraction prior to analysis by chromatographic-mass spectrometry systems in five different platforms covering a relevant part of the muscle metabolome: organic acids, amines, nucleotides, coenzymes, acylcarnitines and oxylipins. This analytical pipeline was extensively validated and proved to be robust, precise, accurate and biologically sound. The capability of our analytical method to capture metabolic alterations upon challenges was finally tested using a small proof-of-concept study involving an exercise intervention. Mild but consistent metabolic patterns were observed, allowing the discrimination between non-exercised and exercised muscles. Despite the low numbers of subjects enrolled in this study (5), these results are indicative that our method is suitable to determine intervention effects in skeletal muscle tissue whenever applied to adequately powered and well characterized studies.