Effective and safe antiobesity drugs are still needed in face of the obesity pandemic worldwide. Recent interventions in rodents revealed 3,5-diiodo-L-thyronine (3,5-T2) as a metabolically active iodothyronine affecting energy and lipid metabolism without thyromimetic side effects typically associated with T3 administration. Accordingly, 3,5-T2 has been proposed as a potential hypolipidemic agent for treatment of obesity and hepatic steatosis. In contrast to other observations, our experiments revealed dose-dependent thyromimetic effects of 3,5-T2 akin to those of T3 in diet-induced obese male C57BL/6J mice. 3,5-T2 treatment exerted a negative feedback regulation on the hypothalamus-pituitary-thyroid axis, similar to T3. This is demonstrated by decreased expression of genes responsive to thyroid hormones (TH) in pituitary resulting in a suppressed thyroid function with lower T4 and T3 concentrations in serum and liver of 3,5-T2-treated mice. Analyses of hepatic TH target genes involved in lipid metabolism revealed T3-like changes in gene expression and increased type I-deiodinase activity after application of 3,5-T2 (2.5 μg/g body weight). Reduced hepatic triglyceride and serum cholesterol concentrations reflected enhanced lipid metabolism. Desired increased metabolic rate and reduction of different fat depots were, however, compromised by increased food intake preventing significant body weight loss. Moreover, enlarged heart weights indicate potential cardiac side effects of 3,5-T2 beyond hepatic thyromimetic actions. Altogether, the observed thyromimetic effects of 3,5-T2 in several mouse TH target tissues raise concern about indiscriminate administration of 3,5-T2 as powerful natural hormone for the treatment of hyperlipidemia and pandemic obesity.

The endogenous thyroid hormone (TH) metabolite 3,5-diiodo-l-thyronine (3,5-T 2 ) acts as a metabolically active substance affecting whole-body energy metabolism and hepatic lipid handling in a desirable manner. Considering possible adverse effects regarding thyromimetic action of 3,5-T 2 treatment in rodents, the current literature remains largely controversial. To obtain further insights into molecular mechanisms and to identify novel target genes of 3,5-T 2 in liver, we performed a microarray-based liver tissue transcriptome analysis of male lean and diet-induced obese euthyroid mice treated for 4 weeks with a dose of 2.5 µg/g bw 3,5-T 2 . Our results revealed that 3,5-T 2 modulates the expression of genes encoding Phase I and Phase II enzymes as well as Phase III transporters, which play central roles in metabolism and detoxification of xenobiotics. Additionally, 3,5-T 2 changes the expression of TH responsive genes, suggesting a thyromimetic action of 3,5-T 2 in mouse liver. Interestingly, 3,5-T 2 in obese but not in lean mice influences the expression of genes relevant for cholesterol and steroid biosynthesis, suggesting a novel role of 3,5-T 2 in steroid metabolism of obese mice. We concluded that treatment with 3,5-T 2 in lean and diet-induced obese male mice alters the expression of genes encoding hepatic xenobiotic-metabolizing enzymes that play a substantial role in catabolism and inactivation of xenobiotics and TH and are also involved in hepatic steroid and lipid metabolism. The administration of this high dose of 3,5-T 2 might exert adverse hepatic effects. Accordingly, the conceivable use of 3,5-T 2 as pharmacological hypolipidemic agent should be considered with caution.3,5-T 2 alters murine genes relevant for xenobiotic, steroid, and thyroid hormone metabolism

A liquid-liquid extraction and liquid chromatography-electrospray ionization tandem mass spectrometry (LC-MS/MS) method to determine iodothyronines and thyronamines (TAM) from cell culture media was developed. Thyroid hormones (TH) are metabolized by sequential deiodination to eventually yield thyronine (T₀), but can also be decarboxylated, resulting in TAM. The method presented here for extraction of DMEM/F12 cell culture media is a fundamental procedure for a precise determination of 9 TH and 6 TAM from a single LC run. Analytes and internal standards (IS) were extracted from DMEM/F12 (w/o phenol red) by liquid-liquid extraction using isopropanol-TBME (30:70 v/v). Measurement of TH and TAM was performed during a 10-min run time using ¹³C₆-T₄, ¹³C₆-T₃, ¹³C₆-rT₃, ¹³C₆-3,3′T₂ and ²H₄-T₁AM as IS. Calibration curves covered 11 calibrators measured as triplicates each for the analysis of the 9 TH and 6 TAM metabolites, and the 5 IS were linear and reproducible in the range of 0.12-120 nM (R² 0.991-0.999) for all calibrators. The lower limit of quantification was 0.078-0.234 nM. Method validation and robustness were demonstrated by the analysis of precision, accuracy, process efficiency, matrix effects and recoveries, as well as intra- and interassay stability. These parameters were investigated for high, middle and low concentrations of quality controls of all 9 TH and 6 TAM metabolites. This validated, sensitive and interaction-free LC-MS/MS method allows rapid analysis and accurate determination of TH and TAM from DMEM/F12 (w/o phenol red) conditioned media and seems to be easily transferable and applied to commonly used buffers and cell culture media.

Vitamin D deficiency in humans is widespread, and only a few food items are important natural sources of vitamin D. This study investigated the effect of UVB exposure of laying hens on the vitamin D content in egg yolk. In a two-factorial design, hens fed a vitamin D-deficient (-D) or -adequate (+D) diet were nonexposed or exposed to UVB light over a period of 4 weeks. UVB exposure of the -D group caused nearly normal egg production rate and egg shell quality; exposure of the +D group did not further improve these parameters. UVB exposure tended to improve the concentration of plasma 25-hydroxycholecalciferol (25(OH)D(3)), but had no effect on 1,25-dihydroxycholecalciferol in plasma or on cholecalciferol and 25(OH)D(3) in egg yolk. The present study shows that a short-term exposure of laying hens to UVB light is not an appropriate way to improve the vitamin D content of egg yolk.

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