Hydrogen peroxide-induced production of a 40 kDa immunoreactive thyroglobulin fragment in human thyroid cells: the onset of thyroid autoimmunity?

Abstract

We recently reported that, during in vitro thyroid-hormone synthesis, H2O2 stress cleaved thyroglobulin (Tg) into C-terminal peptides. These peptides were found to contain the immunodominant region of Tg recognized by Tg autoantibodies from patients with an autoimmune thyroid disease. To test the hypothesis that Tg fragmentation is an early upstream initiating event involved in Tg autoimmune response and the consequence of oxidative injuries, we studied the effect of H2O2 stress on human thyroid cells. In culture conditions allowing Tg synthesis and iodine organification by the cells, we found that bolus addition of increasing millimolar doses of H2O2 induced a dose–response appearance of floating cells in the culture medium. These cells apparently resulted from a necrotic process, and they bore iodinated Tg fragments. These fragments were found to be similar to those previously obtained in vitro from purified Tg. In both cases, Tg peptides were recognized by a well-defined monoclonal antibody directed to the immunodominant region of Tg. The smallest immunoreactive Tg peptide had a molecular mass of 40kDa and entered human thyrocytes more efficiently than the entire Tg. These data suggest that thyrocytes exposed to locally increased H2O2 doses accumulate fragmented Tg for further delivery into surrounding living thyrocytes in the course of an autoimmune response.

Soy extracts suppressed iodine uptake and stimulated the production of autoimmunogen in rat thyrocytes

“…Additionally, treatment of FRTL cells with genistein significantly increased the content of P40, an identified autoimmunogen that might be responsible for the onset of ATD. 3,5,11,12,33 The content of the intact Tg (P330) was increased in parallel with P40 by the same genistein and Novasoy treatments. Novasoy also increased, although to a lesser extent, the content of P330 and P40 Tg fragments that may be attributed to the action of the genistein contained.…”

“…Various studies showed that the amount of cleaved Tg peptides increased in proportion to the iodoamino acid content of Tg molecules. 3,33 Moreover, higher thyroid hormone synthesis and iodination were associated with generation of excessive reactive oxygen species, resulting in the oxidative cleavage of Tg to produce P40 and expose its cryptic epitopes. 11,12 Increased production of reactive oxygen species also induces cell necrosis which in turn causes an inflammatory response that triggers thyrocytes to internalize P40 and present them to T-cells.…”

The Influence of Oxidative Stress on Thyroid Diseases

“…Inflammatory lesions in the thyroid gland result in the destruction of follicular cells and fibrosis, leading to hypothyroidism [67]. NOX participation in the production of hydrogen peroxide for the purposes of thyroid hormone synthesis may be associated with the pathophysiology of autoimmune thyroid diseases, through interacting with thyroperoxidase and thyroglobulin (TG) and altering their activity, promoting immunogenicity [75,81]. Excessive iodine intake is regarded as an additional risk factor for the development of autoimmune thyroid disease due to enhancing ROS production and, at the same time, reducing internal antioxidant levels.…”

Dual oxidase, hydrogen peroxide and thyroid diseases

“…66 The high level of H 2 O 2 also produces the antigenic antigen from oxidation damaged iodinated Tg. 68 Antioxidants blocked the generation of ROS and ICAM-1 expression. In a non-susceptible mouse, 100 μmol/L iodide did not generate H 2 O 2 .…”