C. STEUER¹, L. BERNASCONI¹, P. SCHÜTZ², A. R. HUBER<sup>1

1</sup>Institute of Laboratory Medicine, Kantonsspital Aarau, Aarau, Switzerland, ²Medical University Department, Division of General Internal and Emergency Medicine, Kantonsspital Aarau, Aarau, Switzerland

Phosphaditylcholine (PC)-derived metabolites like choline and its oxidized form betaine as well as other closely related quaternary ammonium compounds like L-carnitine and O-acetyl-L-carnitine, play a crucial role in the synthesis of membrane phospholipids, energy metabolism of adults and children and as methyl group donators in a number of biosynthetic reactions. Choline, betaine and L-carnitine are the main ingredients found in red meat, fish and sea-food. Especially L-carnitine can be found in many life-style and sports nutrition products as energy boost for high performance activities. Numerous in vitro and animal studies have substantiated the protective effect of L-carnitine, choline and betaine on cardiac metabolism and performance. However, these findings could not consistently be reproduced. Recent publications described the intestinal degradation of choline, betaine and L-carnitine to trimethylamine by gut flora microorganism. Trimethylamine is well absorbed in the intestine and subsequently oxidized in the liver to trimethylamine-N-oxid (TMAO) by flavin monooxygenases (FMO). Different research groups investigated the importance of plasma concentrations of TMAO and its chemical precursors in predicting cardiovascular events, long term mortality for chronic kidney disease (CKD)-patients and the influence in diabetes mellitus type 2 (T2DM). Thus, the rapid, sensitive and accurate simultaneous quantification of these five quaternary ammonium containing compounds is according to experts in the field of tremendous clinical interest. The LC-MS/MS-based assay described herein may increase the significance of future clinical studies investigating TMAO and related PC-derived metabolites as new metabolic markers for cardiovascular risk and all-cause mortality in different patient populations. Finally, the developed method was successfully applied to numerous samples of healthy volunteers.