Urinary Iodine Metabolomics as a Novel Tool for Understanding Environmentally Induced Thyroid Hormone Metabolic Alteration

In this study, we developed a novel iodine metabolomic method and identified 42 iodine-containing compounds in urine. Using in vitro experiments, we confirmed that these compounds were degradation metabolites of thyroid hormones (THs) and may be used to understand the peripheral metabolism of THs. These metabolites were then measured in urine samples collected in a natural experiment in 26 healthy adults experiencing substantial environmental changes after traveling from Los Angeles to Beijing. Despite the absence of significant alterations in iodine intakes or circulating TH levels, the level of urinary TH metabolites significantly decreased by ≤52.4% in Beijing, in association with exposure to polycyclic aromatic hydrocarbons and metals and the subsequent oxidative–antioxidative responses. All of these changes were reversed after the participants had returned to Los Angeles. These results support the promising use of iodine metabolomics to detect early TH metabolic alteration and shed light on novel mechanisms for environmental impacts on TH homeostasis.