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APPLICATION OF ORGANIC IODINE SPECIES ANALYTICS: DETERMINING THYROID HORMONE STATUS IN ADULT DANIO RERIO AND DEVELOPING XENOPUS LAEVIS USING LC/ICP-MS
Simon, R., J E. Tietge, AND B. Michalke. APPLICATION OF ORGANIC IODINE SPECIES ANALYTICS: DETERMINING THYROID HORMONE STATUS IN ADULT DANIO RERIO AND DEVELOPING XENOPUS LAEVIS USING LC/ICP-MS. Presented at International Conference on Trace Element Speciation in Biomedical, Nutritional and Environmental Sciences, Munich, Germany, May 7-10, 2001.
Disruption of normal thyroid function by xenobiotic chemicals is an important ecological issue. Theoretically, normal thyroid hormone (TH) homeostasis and action can be disrupted at several sites in the synthetic and elimination pathways. Indeed, xenobiotic chemicals, which are known to interfere with normal thyroid hormone homeostasis and action, have been shown to act primarily by (1) up-regulation of catabolism of TH, (2) inhibition of iodide uptake, (3) inhibition of TH synthesis, or (4) inhibition and/or up-regulation of deiodinases. However, the most commonly used measurements of thyroid status are limited to circulating concentrations of thyroid stimulating hormone (TSH) and the two thyroid hormones. These measurements along are insufficient to determine the mechanism by which thyroid disruption occurs.
Recently a new approach for the analysis of iodinated organic species in human serum has been developed using liquid chromatography/inductively coupled plasma-mass spectrometry (LC/ICP-MS). This method is able to quantify iodide, T4 and T3, as well as inactivated TH, reverse T3 (rT3), and the synthetic precursors of TH, monoiodo-tyrosine (MIT) and diodo-tyrosine (DIT) in a single injection. In this work, the LC/ICP-MS approach was used to analyze whole body homogenates of adult male and female zebrafish (Danio rerio) and tadpoles of the African clawed frog (Xenopus laevis) at two different development stages (58 and 61). The data demonstrate that the LC/ICP-MS method was successful at measuring I-, MIT, DIT, T4, T3 and rT in these two species. Furthermore, the method also detected 5 additional iodinated compounds, which are currently unidentified.
The data show for female D. rerio higher T4, T3, rT3, and total iodine levels than for male ones.
The X. laevis data demonstrate higher TH synthetic activity at stage 61 than stage 58, as determined by significant increases in MIT, DIT, and T4 concentrations accompanied by reduced I- concentrations. Degradation of T4 to rT3 appears to be higher in the stage 58 than stage 61. Both observations are consistent with the fact that stage 61 organisms are in metamorphic climax.
Future work will focus on identifying the unidentified iodinated compounds observed in this preliminary study, defining the concentrations of the iodinated compounds through normal development and metamorphosis in X. laevis, and, ultimately determining the effects of known thyroid antagonists on the concentrations of the iodinated compounds in X. laevis and D. rerio.