A technical improvement for the thyroid peroxidase iodination assay

Thyroid peroxidase (TPO) iodination activity is generally evaluated in vitro by the iodination of poorly iodinated thyroglobulin or bovine serum albumin, followed by separation of protein-bound and inorganic iodide by paper chromatography,. Precipitation of protein-bound iodine by trichloroacetic acid (TCA) was evaluated as an alternative to the time-consuming paper chromatographic separation (PC) in normal rat TPO preparations. The protein-bound iodine estimates as well as the iodination activities determined by these two procedures were significantly correlated (r = 0.95 and 0.98, respectively, P<0.001), and the iodination activities regression line slope (b = 0.97 + or - 0.11) was not different from 1. The protein-bound iodine separation by TCA is simpler and faster, without loss of precision. Thus, it can be a useful alternative step in the thyroid peroxidase iodination assay

Thyroid peroxidase activity in human nodular goiters

1. Thyroid peroxidase (TPO, iodide-oxidation) activity was evaluated in nodular and paranodular tissue samples from 27 patients with nodular goiter (19 "cold" and 8 "hot" nodules), and compared to 11 diffuse toxic goiter and 9 normal thyroid tissue samples. 2. In terms of U/g digitonin solubilized protein, TPO activity was increased in hot nodules (p<0.05), although not as much as in diffuse toxic goiters (p<0.01> 3. The mean TPO activity of tissues paranodular to a cold nodule was not different from that of normal thyroids. 4. Both the highest and the lowest TPO activities were found in cold nodules, but their mean value did not differ from those of their paranodular tissues or normal thyroids. 5. Inter-tissue variability was significantly increased (p<0.01) in cold nodules and in tissues paranoudular to a hot nodule. 6. These data show that heterogeneity both within and among tissues contributes to the wide range of TPO activity detected in nodular goiters