Identification and quantification of 3-iodothyronamine metabolites in mouse serum using liquid chromatography-tandem mass spectrometry.

3-Iodothyronamine (T(1)AM) is an endogenous derivative of thyroxine. Recently there have been numerous reports of analytical methods to quantify endogenous T(1)AM levels, but substantial discrepancies in concentration depending on the method of analysis (LC-MS/MS or immunoassay) suggest endogenous T(1)AM may be covalently modified in vivo. Using information dependent acquisition methods to perform unbiased scans for T(1)AM metabolites following a single IP injection in mice, we have identified O-sulfonate-T(1)AM, N-acetyl-T(1)AM and T(1)AM-glucuronide as conjugates occurring in vivo, as well as the oxidatively deaminated 3-iodothyroacetic acid and non-iodinated thyroacetic acid. 3-iodothyroacetic acid, O-sulfonate-T(1)AM and T(1)AM-glucuronide are present in serum at greater concentrations that unmodified T(1)AM and all metabolites are extensively distributed to tissues. These results suggest covalent modifications of T(1)AM may play a critical role in regulating distribution and biological activity of T(1)AM, and analytical methods to quantify endogenous T(1)AM should be able to account for these metabolites as well.