Determination of 3-iodothyronamine (3-TAM) in mouse liver using liquid chromatography-tandem mass spectrometry.

3-iodothyronamine (3-TAM) has been suggested as a novel chemical messenger and potent trace amine-associated receptor 1 ligand in the CNS that occurs naturally as endogenous metabolite of the thyroid hormones. Discrepancies and variations in 3-TAM plasma and tissue concentrations have nonetheless caused controversy regarding the existence and biological role of 3-TAM. These discussions are at least partially based on potential analytical artefacts caused by differential decay kinetics of 3-TAM and the widely used deuterated quantification standard D-TAM. Here, we report a novel LC-MS/MS method for the quantification of 3-TAM in biological specimens using stable isotope dilution with C-TAM, a new internal standard that showed pharmacodynamic properties comparable to endogenous 3-TAM. The method detection limit (MDL) and method quantification limit (MQL) of 3-TAM were 0.04 and 0.09 ng/g, respectively. The spike-recoveries of 3-TAM were between 85.4% and 94.3%, with a coefficient of variation of 3.7-5.8%. The intra-day and inter-day variations of 3-TAM were 8.45-11.2% and 3.58-5.73%, respectively. Endogenous 3-TAM liver values in C57BL/6J mice were 2.20 ± 0.49 pmol/g with a detection frequency of 50%. Higher liver 3-TAM values were found when C57BL/6J mice were treated with N-acetyl-3-iodothyronamine or O-acetyl-3-iodothyronamine. Overall, our new stable isotope dilution LC-MS/MS method improves both the sensitivity and selectivity compared with existing methods. The concomitant possibility to quantify additional thyroid hormones such as thyroxine, 3,5,3'-triiodo--thyronine, 3,3',5'-triiodo--thyronine, 3,3'-diiodo--thyronine, and 3,5-diiodo--thyronine further adds to the value of our novel method in exploring the natural occurrence and fate of 3-TAM in biological tissues and fluids.