Detection of 3-iodothyronamine in human patients: A preliminary study

Context and Objective: The primary purpose of this study was to detect and quantify 3-iodothyronamine (T ₁AM), an endogenous biogenic amine related to thyroid hormone, in human blood. Design: T ₁AM, total T ₃, and total T ₄ were assayed in serum by a novel HPLC tandem mass spectrometry assay, which has already been validated in animal investigations, and the results were related to standard clinical and laboratory variables. Setting and Patients: The series included one healthy volunteer, 24 patients admitted to a cardiological ward, and 17 ambulatory patients suspected of thyroid disease, who underwent blood sampling at admission for routine diagnostic purposes. Seven patients were affected by type 2 diabetes, and six patients showed echocardiographic evidence of impaired left ventricular function. Interventions: No intervention or any patient selection was performed. Main Outcome Measures: serum T ₁AM, total and free T ₃ and T ₄, routine chemistry, routine hematology, and echocardiographic parameters were measured. Results: T ₁AM was detected in all samples, and its concentration averaged 0.219 ± 0.012 pmol/ml. The T ₁AM concentration was significantly correlated to total T ₄ (r = 0.654, P < 0.001), total T ₃ (r = 0.705, P < 0.001), glycated hemoglobin (r = 0.508, P = 0.013), brain natriuretic peptide (r = 0.543, P = 0.016), and γ-glutamyl transpeptidase (r = 0.675, P < 0.001). In diabetic vs. nondiabetic patients T ₁AM concentration was significantly increased (0.232 ± 0.014 vs. 0.203 ± 0.006 pmol/ml, P = 0.044), whereas no significant difference was observed in patients with cardiac dysfunction. Conclusions: T ₁AM is an endogenous messenger that can be assayed in human blood. Our results are consistent with the hypothesis that circulating T ₁AM is produced from thyroid hormones and encourage further investigations on the potential role of T ₁AM in insulin resistance and heart failure.