Serum diiodotyrosine - a biomarker to differentiate destructive thyroiditis from Graves' disease.

OBJECTIVE: Conventional diagnostic methods are limited in their ability to differentiate destructive thyroiditis from Graves' disease. We hypothesised that serum diiodotyrosine (DIT) and monoiodotyrosine (MIT) levels could be biomarkers for differentiating destructive thyroiditis from Graves' disease. DESIGN: Patients with destructive thyroiditis (n = 13) and Graves' disease (n = 22) were enrolled in this cross-sectional study. METHODS: We assayed the serum DIT and MIT levels using liquid chromatography-tandem mass spectrometry. A receiver operating characteristic (ROC) curve analysis was used to determine the sensitivity and specificity of the serum DIT and MIT levels as biomarkers for differentiating destructive thyroiditis from Graves' disease. RESULTS: The serum DIT and MIT levels were significantly higher in patients with destructive thyroiditis than in those with Graves' disease. The ROC curve analysis showed that the serum DIT levels (≥359.9 pg/mL) differentiated destructive thyroiditis from Graves' disease, significantly, with 100.0% sensitivity and 95.5% specificity (P < 0.001). The diagnostic accuracy of the serum MIT levels (≥119.4 pg/mL) was not as high as that of the serum DIT levels (sensitivity, 84.6%; specificity, 77.3%; P = 0.001). CONCLUSIONS: The serum DIT levels may serve as a novel diagnostic biomarker for differentiating destructive thyroiditis from Graves' disease.

Evaluating Iodide Recycling Inhibition as a Novel Molecular Initiating Event for Thyroid Axis Disruption in Amphibians.

The enzyme iodotyrosine deiodinase (dehalogenase, IYD) catalyzes iodide recycling and promotes iodide retention in thyroid follicular cells. Loss of function or chemical inhibition of IYD reduces available iodide for thyroid hormone synthesis, which leads to hormone insufficiency in tissues and subsequent negative developmental consequences. IYD activity is especially critical under conditions of lower dietary iodine and in low iodine environments. Our objective was to evaluate the toxicological relevance of IYD inhibition in a model amphibian (Xenopus laevis) used extensively for thyroid disruption research. First, we characterized IYD ontogeny through quantification of IYD mRNA expression. Under normal development, IYD was expressed in thyroid glands, kidneys, liver, and intestines, but minimally in the tail. Then, we evaluated how IYD inhibition affected developing larval X. laevis with an in vivo exposure to a known IYD inhibitor (3-nitro-l-tyrosine, MNT) under iodine-controlled conditions; MNT concentrations were 7.4-200 mg/L, with an additional 'rescue' treatment of 200 mg/L MNT supplemented with iodide. Chemical inhibition of IYD resulted in markedly delayed development, with larvae in the highest MNT concentrations arrested prior to metamorphic climax. This effect was linked to reduced glandular and circulating thyroid hormones, increased thyroidal sodium-iodide symporter gene expression, and follicular cell hypertrophy and hyperplasia. Iodide supplementation negated these effects, effectively rescuing exposed larvae. These results establish toxicological relevance of IYD inhibition in amphibians. Given the highly conserved nature of the IYD protein sequence and scarcity of environmental iodine, IYD should be further investigated as a target for thyroid axis disruption in freshwater organisms.

[The study of the metabolism of iodotyrosines included in the iodized milk protein in rats].

In the course of evolution in animals and humans, a complex and effective system for providing the body with iodine in the form of various organic and inorganic compounds was developed. The metabolism of inorganic iodine has been studied quite well, in contrast to the mechanism of assimilation of its organic compounds. Among the latter, iodotyrosines, which are part of iodinated milk proteins, are of particular interest. To distinguish the peculiarities of the biotransformation of iodotyrosines in the animals' organism, their concentration and the concentration of tyrosine in blood plasma of rats after single administration of iodinated milk proteins were determined. For comparison, in parallel a group of animals received potassium iodide. The tested preparations were administered intragastrically with a probe in the form of aqueous solutions at a dose equivalent to 30 µg iodine per 1 kg of body weight. The level of mono- and diiodotyrosine in rat blood plasma was determined by HPLC with a mass spectrometer detector. The tyrosine content was determined on an automatic amino acid analyzer. The registration of the indices was carried out before the administration and 1, 4 and 24 hours after the administration of the substances. In the course of the conducted studies it was found that when iodinated milk proteins are once administered, a significant increase in the concentrations of monoiodotyrosine and diiodotyrosine is observed. The maximum level of iodinated amino acids, exceeding the control values by more than 6 fold, was recorded 4 hours after the ingestion of iodine-containing organic compounds into the body. At the same time interval, an increase in the concentration of tyrosine was observed in one of the experimental groups receiving iodinated milk protein. The simultaneous presence of tyrosine and its iodinated derivatives in blood plasma may indicate that monoiodotyrosine and diiodotyrosine are capable of being absorbed into the systemic bloodstream without metabolic transformations in the liver. Under introduction of potassium iodide, an increase in blood plasma concentration of monoiodotyrosine by 35% compared to the control was observed only after 24 hours, which may be a consequence of the activation of the thyroid gland due to the intake of an increased amount of iodine.

Towards the pre-clinical diagnosis of hypothyroidism caused by iodotyrosine deiodinase (DEHAL1) defects.

DEHAL1 (also named IYD) is the thyroidal enzyme that deiodinates mono- and diiodotyrosines (MIT, DIT) and recycles iodine, a scarce element in the environment, for the efficient synthesis of thyroid hormone. Failure of this enzyme leads to the iodotyrosine deiodinase deficiency (ITDD), characterized by hypothyroidism, compressive goiter and variable mental retardation, whose diagnostic hallmark is the elevation of iodotyrosines in serum and urine. However, the specific diagnosis of this type of hypothyroidism is not routinely performed, due to technical and practical difficulties in iodotyrosine determinations. A handful of mutations in the DEHAL1 gene have been identified as the molecular basis for the ITDD. Patients harboring DEHAL1 defects so far described all belong to consanguineous families, and psychomotor deficits were present in some affected individuals. This is probably due to the lack of biochemical expression of the disease at the beginning of life, which causes ITDD being undetected in screening programs for congenital hypothyroidism, as currently performed. This worrying feature calls for efforts to improve pre-clinical detection of iodotyrosine deiodinase deficiency during the neonatal time. Such a challenge poses questions of patho-physiological (natural history of the disease, environmental factors influencing its expression) epidemiological (prevalence of ITDD) and technical nature (development of optimal methodology for safe detection of pre-clinical ITDD), which will be addressed in this review.

Iodine speciation in human serum by reversed-phase liquid chromatography-ICP-mass spectrometry.

Reversed-phase liquid chromatography-inductively coupled plasma mass spectrometric hyphenation was used for iodine speciation in human serum. First investigations showed that iodine species nearly quantitatively were eluted in the void volume. The result indicated that protein-linked thyroid hormones were not interacting with the stationary phase, thus being not retained. Investigations were performed about T4-TBG (thyroxin-thyroxin-binding globulin) complex generation and its retention during chromatography. It was shown that T4-TBG was not retained on the column. Therefore, a protease treatment was introduced for serum sample preparation. The analysis of "normal" sera (after protease) gave reasonable results lying in the range published in literature: I-:11; di-iodothyrosine (DIT): 2.1; mono-iodothyrosine (MIT): 1.6; reversed tri-iodothyronine (rT3): 3.9; T3: 5.9; T4: 60; each micrograms iodine per liter. The method also proved to recognize abnormalities in a pathologic serum, having rT3 as the predominant species. In this case the method obviously was superior compared to standard immunoassay methods, as it is monitoring the iodine in the species (physiologically active iodine species), whereas immunoassay methods may sometimes detect deiodinated (inactive) compounds.

Extrathyroidal physiology of monoiodotyrosine in humans.

Normal serum monoiodotyrosine (MIT) levels (n = 152) were 0.69 +/- 0.20 nmol/l. There was wide variation of MIT levels in a 24-hour period without diurnal pattern, and there was no change throughout the menstrual cycle. MIT levels declined upon aging, but levels in hypo- and hyperthyroidism were not significantly different. MIT levels were detected in athyrotic patients (0.32 +/- 0.08 nmol/l). Desiccated thyroid raised the athyrotic MIT levels to the normal range, while levothyroxine did not. Diiodotyrosine (DIT) infusion caused an MIT rise which paralleled but lagged 1 h behind the DIT rise. These data suggest thyroidal as well as nonthyroidal sources of MIT, one of which is deiodination of DIT. Ingestion of 1 g MIT increased serum MIT to 10.6 +/- 1.7 mumol/l in women, and 7.1 +/- 2.3 mumol/l in men 30 min after ingestion; the serum half-life was 45 min.

Protein-linked iodotyrosines in serum after topical application of povidone-iodine (Betadine).

Markedly elevated serum PBI levels occur after therapy with povidone-iodine (Betadine), an iodine-polyvinylpyrrolidone iodophor. In this study, we investigated the serum iodine compounds from a severely burned patient with normal initial thyroid function tests who was swabbed with Betadine ointment and received daily therapeutic baths in Betadine. Three and 9 days after therapy, his serum contained 93 and 168 micrograms PGI/dl, respectively (normal range, 4-8), while the serum T4 and free T4 index were normal; the serum T3 level, however, was abnormally depressed. Most of the PBI was in albumin, and hydrolysis of the serum proteins with proteases released 35% of the PBI as monoiodotyrosine, 3.2% as diiodotyrosine, 0.01% as T3, and 2.5% as T4, as determined by competitive radioassays, anion exchange, and reversed phase high pressure liquid chromatography. The same concentrations of T4 and T3 were detected before and after hydrolysis. Failure of the proteases to completely hydrolyze iodoalbumin partially explains why all of the PBI was not recovered as iodotyrosines in the serum protein hydrolysates. Povidone-iodine rapidly iodinated tyrosine residues in human serum albumin at pH 7.4 and 37 C in vitro, and the ratio of diiodotyrosine to monoiodotyrosine increased as the molar ratio of povidone-iodine to albumin was increased. It is concluded that the abnormal increase in serum PBI resulted from absorption of the iodophor into the blood where it primarily iodinated albumin and, to a lesser extent, the globulins.

Gas-liquid chromatographic determination of mono- and diiodotyrosines in serum.

A sensitivie, reliable gas-chromatographic assay for monoiodotyrosine and diiodotyrosine in human serum is reported. The oxazolidinone-heptafluorobutyric anhydride derivatives allow the quantitation of both compounds in the linear range of 0.2 to 7.6 mg/L of serum. Analytical recovery averaged 88%, and mean accuracy and within-run precision were 98 and 2%, respectively. Concentrations of monoiodotyrosine in serum as low as 20 microgram/L and of diiodotyrosine as low as 100 microgram/L can be detected. Normal serum contains no detectable concentration of either compound, but the method is applicable as a diagnostic tool in the early prediction of thyroid disease. Both compounds were detected in the serum of a hypothyroid subject whose normal thyroid hormone concentrations were being maintained by therapy with desiccated thyroid extract.

[Quantitative aspects of iodine metabolism in one case of congenital iodotyrosine deiodinase defect (author's transl)]. / Aspects quantitatifs de la cinétique de l'iode dans un défaut d'iodotyrosine desiodase.

In a 27 years old patient an iodotyrosine deiodinase defect was responsible for a profound hypothyroidism (T4-RIA: indetectable -- TSH: 190 microU/ml) associated with a large goiter (about 300 g). MIT and DIT secretions were measured from the urinary cumulative specific activities, and the molar MIT/DIT ratio was 2.2. The thyroidal iodine exchangeable pool was as low as 177 micrograms. In two comparable patients rendered euthyroid by Lipodol injection, total thyroidal 127I pool was around 40 mg and the MIT/DIT ratio was degraded to 7 suggesting a mild biosynthetic defect by iodine excess.

Separation of labelled iodide, iodoprotein, iodotyrosines, and iodothronines in serum from patients treated with iodine-131, using an improved chromatographic method.

A method is described for complete separation of iodoprotein, 3-iodotyrosine (MIT), 3,5-diiodotyrosine (DIT), 3,5,3-triiodo-L-thyronine (T3), and L-throxine (T4) on a single column run on Sephadex G-25 superfine in alkaline solution. Sera from patients treated with 131I- have been analysed by this method after removal of I- by resin dialysis.