Cold thyroid nodules (CTNs) represent a frequent endocrine disorder accounting for up to 85% of thyroid nodules in a population living in an iodine-deficient area. Benign CTNs need to be distinguished from thyroid cancer, which is relatively rare. The molecular etiology of benign CTNs is unresolved. To obtain novel insights into their pathogenesis, protein expression profiling was performed in a series of 27 solitary CTNs (10 follicular adenoma and 20 adenomatous nodules) and surrounding normal thyroid tissues (STs) using 2D gel-electrophoresis combined with mass spectrometry analysis, Western blotting and immunohistochemistry.

The proteome analysis revealed a specific fingerprint of CTNs with upregulation of three functional systems: 1. thyroid cell proliferation, 2. turnover of thyroglobulin, and 3. H₂O₂-detoxification. Western blot analysis and immunohistochemisty confirmed the proteome data and showed that CTNs exhibit significant upregulation of proteins involved in thyroid hormone synthesis, yet are deficient in thyroxine containing thyroglobulin. This is consequential to intranodular iodide deficiency, mainly due to cytoplasmatic NIS localization, and portrays the CTN as an activated proliferating lesion with an intranodular hypothyroid milieu. Furthermore, we provide preliminary evidence that upregulation of H₂O₂-generation in CTNs could override the antioxidative system resulting in oxidative stress, which is suggested by the finding of raised 8-oxo-G DNA-adduct formation in CTNs.