Inhibition of in vitro macrophage-induced low density lipoprotein oxidation by thyroid compounds.

Oxidized low density lipoproteins (LDL) are highly suspected of initiating the atherosclerosis process. Thyroid hormones and structural analogues have been reported to protect LDL from lipid peroxidation induced by Cu2+ or the free radical generator 2,2'-azobis-'2-amidinopropane' dihydrochloride in vitro. We have examined the effects of thyroid compounds on macrophage-induced LDL oxidation. Human monocyte-derived macrophages (differentiated U937 cells) were incubated for 24 h with LDL and different concentrations (0-20 microM) of 3,5,3'-triiodo-l -thyronine (T3), 3,5,3',5'-tetraiodo-L-thyronine (T4), 3,3',5'-tri-iodo-l -thyronine (rT3), the T3 acetic derivative (3,5,3'-tri-iodothyroacetic acid; TA3) or L-thyronine (T0) (experiment 1). Cells were also preincubated for 24 h with 1 or 10 microM of the compounds, washed twice, then incubated again for 24 h with LDL (experiment 2). Oxidation was evaluated by measurement of thiobarbituric acid-reactive substances (TBARS) and cell viability by lactate deshydrogenase release. In experiment 1, T0 had no effect, whereas the other compounds decreased LDL TBARS production, but T3 and TA3 were less active than T4 and rT3 (IC50: 11.0 +/- 2.6 and 8.1 +/- 0.8 vs 1.4 +/- 0.5 and 0.9 +/- 0.3 microM respectively). In experiment 2, the compounds at 1 microM had no effect; at 10 microM, T3 and rT3 slightly reduced LDL TBARS production, whereas TA3 and T4 inhibited it by about 50% and 70% respectively. TBARS released by the cells were also highly decreased by T3, T4, rT3 and TA3 in experiment 1, but only by T3 (30%) and T4 (70%) in experiment 2. Cell viability was not affected by the compounds except slightly by TA3 at 10 microM. The data suggested that the physico-chemical antioxidant capacity of thyroid compounds was modulated by their action on the intracellular redox systems of macrophage. Overall cellular effects of T3 led to a reduction of its antioxidant capacity whereas those of T4 increased it. Thus T4 might protect LDL against cellular oxidation in vivo more than T3.

In vitro free radical scavenging capacity of thyroid hormones and structural analogues.

It was reported that thyroid hormones decreased Cu(2+)-induced low-density lipoprotein (LDL) oxidation in vitro. Here, we investigated free radical scavenging capacities of thyroid hormones (3,5,3'-tri-iodo-L-thyronine (T(3)), thyroxine (T(4)) and 3,3',5'-tri-iodo-L-thyronine (rT(3))) and structural analogues (L-thyronine (T(0)), 3,5,3'tri-iodothyroacetic acid (TA(3)) and 3,5,3',5'-tetra-iodothyroacetic acid (TA(4))), using three different models of free radical generation. T(0), T(3) and TA(3) slowed down production of conjugated diene and thiobarbituric acid-reactive substances during LDL oxidation by 2,2'-azobis-[2-amidinopropane] (water-soluble), whereas rT(3), T(4) and TA(4) had practically no effect. In this system, T(0) was the more active compound. Using a 1,1-diphenyl-2-picrylhydrazyl (lipid-soluble) test, all compounds also revealed free radical scavenging capacities, but rT(3), T(4) and TA(4) were more active than T(0), T(3) and TA(3). T(3) was able to scavenge superoxide anion and hydroxyl radicals generated in an aqueous phase by a xanthine-xanthine oxidase system, as measured by electron paramagnetic resonance spectroscopy. It may be concluded that: (1) thyroid hormones and analogues with a 4'-hydroxy diphenylether structure have free radical scavenging capacities, (2) this property is influenced by the number of iodines on the phenolic ring, and (3) thyroid hormone scavenging capacity should not be the only mechanism explaining their protective effect on Cu(2+)-induced LDL oxidation. The physiological significance of the findings is discussed.

In vitro assessment of thyroid and estrogenic endocrine disruptors in wastewater treatment plants, rivers and drinking water supplies in the greater Paris area (France).

The presence of estrogenomimetic compounds in the environment, and particularly in water resources, is well known. In contrast, little data is available about the disruption of the thyroid system, even though thyroid hormones are strongly involved in regulating metabolism, growth and development. The aim of this study was to carry out a parallel evaluation of the disruptions of thyroid and estrogenic hormone receptor transcriptional activities, induced by water samples from two wastewater treatment plants (WWTPs), in the river Seine, and from four drinking treatment plants located in the Paris area. Two in vitro bioassays were used for the evaluation of thyroid (PC-DR-LUC) and estrogenic (MELN) disruption. Our observations of thyroidal activity show that a disruption potential was only present in the WWTPs influents, whereas estrogenicity was systematically detected in both influents and effluents. The great majority of endocrine activity was removed during the biological process. In the river Seine, only estrogenicity was detected, and no activity was observed in drinking water supplies. Fractionation of the influents revealed that most of the thyroidal effect was associated with compounds with low polarity, and could be partly attributable to 4-nonylphenol.