RESUMEN
The synthetic hormone sodium levothyroxine (LTX) is one of the most prescribed drugs in the world and the most effective in hypothyroidism treatment. The presence of LTX in the environment has become a matter of major concern due to the widespread use of this hormone and by the fact that it is only partially removed in conventional water and sewage treatment plants. However, information regarding the photochemical fate of this hormone in environmental or engineered systems is scarce in the literature. In this work, the sunlight-driven direct and indirect LTX degradation was investigated by determining the photolysis quantum yield, ΦLTX = 3.80 (± 0.02) × 10-5, as well as the second-order kinetic constants of the reactions with hydroxyl radicals, kLTX,â¢OH = 1.50 (± 0.01) × 1010 L mol-1 s-1 and singlet oxygen, kLTX,1O2 = 1.47 (± 0.66) × 108 L mol-1 s-1. Mathematical simulations indicate that LTX photodegradation is favored in shallow, nitrite-rich, and dissolved organic matter (DOM)-poor environments, with LTX half-life times varying from less than 10 days to about 80 days. LTX removals of 85 and 95% were achieved by UVC photolysis and UVC/H2O2 after 120 min, respectively. Three transformation products, triiodothyronine, diiodothyronine, and diiodotyrosine, were identified during LTX degradation by the UVC-based processes studied. The results herein regarding photo-induced kinetics coupled with environmental fate simulations may help evaluate LTX persistence and also the design of water and wastewater treatment processes.
Asunto(s)
Procesos Fotoquímicos , Tiroxina/química , Contaminantes Químicos del Agua/química , Biodegradación Ambiental , Diyodotironinas/química , Diyodotirosina/química , Peróxido de Hidrógeno/química , Radical Hidroxilo/química , Cinética , Modelos Teóricos , Fotólisis , Oxígeno Singlete/química , Luz Solar , Triyodotironina/química , Aguas Residuales/químicaRESUMEN
125I-labeled human growth hormone (125I-labeled.hGH) was prepared by using two variants of the chloramine T labelling procedure and purified by polyacrylamide gel electrophoresis (PAGE) of the reaction mixture. Variant A produced a tracer with high specific activity (100 +/- 10 microCi/microgram), high maximal binding capacity to antibodies (93%) and long-term stability (at least 150 days at -20 degrees C). No diiodinated tyrosil residues could be detected in this tracer. Variant B was devised to obtain higher yields of labeled hormone. The electrophoresis of the iodination mixture revealed two radioactive components with Rm values of 0.49 and 0.55 which result from the iodination of hGH variants preexisting in the starting material. Both tracers had similar specific activities (70 +/- 10 microCi/microgram), high maximal binding capacity to antibodies or receptors (80-100%, after 80 days of their obtention) and high stability (at least 100 days at -20 degrees C). It is concluded that the iododerivatives of hGH obtained by either method are adequate to perform radioimmunoassay and receptor studies and have long-term stability.
Asunto(s)
Hormona del Crecimiento/aislamiento & purificación , Compuestos de Tosilo , Cloraminas , Diyodotirosina/análisis , Estabilidad de Medicamentos , Electroforesis en Gel de Poliacrilamida , Hormona del Crecimiento/metabolismo , Humanos , Técnicas In Vitro , Radioisótopos de Yodo , Monoyodotirosina/análisis , Radioinmunoensayo , Ensayo de Unión RadioliganteRESUMEN
A specific, sensitive, and reproducible in vitro assay for antithyroid compounds and environmental goitrogens has been used to investigate antithyroid activity (AA) in small samples of water supplying 15 localities in endemic and nonendemic goiter areas of western Colombia. A significant positive correlation was observed between goiter prevalence and AA in water collected from the pipelines of these localities. Samples at the water source showed only borderline significance. No significant correlation was observed in waters between AA and total hardness (ppm) or concentrations of Ca, Mg, sulfates, chlorides, silicates, nitrates, and iodine. AA was also demonstrated by this in vitro assay in well water previously shown experimentally to be goitrogenic and that supplied the endemic goiter district of Candelaria town in western Colombia. In contrast, water from the well supplying the area of lower endemicity was found to possess little AA. These results provide experimental support for epidemiological observations that demonstrate a relationship between the sources of drinking water and goiter prevalence rates, and are consistent with previous findings indicating that organic antithyroid compounds contaminate water supplies in areas where goiter persists despite adequate iodine supplementation.