Department of Experimental Medicine, Sapienza University of Rome, Rome, Italy.
Thyroid. 2013 Feb;23(2):231-8. doi: 10.1089/thy.2011.0524.
Thyroid hormone (TH) plays an important role in the modulation of cardiac function, including contractility and systemic vascular resistance (SVR). 3,5,3'-triiodothyronine (T(3)), the active form of TH, induces the activation of endothelial nitric oxide synthase via PI3K/AKT non-genomic signaling. Hypothyroidism is associated with an increase in SVR and serum low-density lipoproteins (LDL) levels, and accumulation of oxidized LDL (oxLDL) may impair endothelial-dependent vascular relaxation. The aim of this study was to investigate the effects of both native LDL (nLDL) and oxLDL on T(3)-mediated AKT phosphorylation, nitric oxide (NO), and cyclic guanosine monophosphate (cGMP) production in human endothelial cells.
Human umbilical vein endothelial cells were exposed to either nLDL or oxLDL for 3 hours and then stimulated with T(3) (10(-7) M) or pretreated with an antioxidant mixture of vitamins E and C for 12 hours before treatment with LDL. An analysis of AKT phosphorylation was performed by Western blot, and NO production was evaluated by using 4,5-diaminofluorescein diacetate. Intracellular production of cGMP was measured by enzymatic immunoassay. LDL oxidation was carried out by incubating LDL with CuSO(4), and α-tocopherol content of LDL was evaluated by high-performance liquid chromatography.
OxLDL impaired T(3)-mediated AKT phosphorylation at serine 473 and significantly decreased the production of both NO (oxLDL+T(3) vs. T(3), 9.79±0.5 AU vs. 80.75±2.8 AU, mean±standard deviation, p<0.0001) and cGMP. Furthermore, pretreatment with the antioxidant mixture obviated the inhibitory effect of LDL on T(3) action.
The results of this study demonstrate that oxLDL may contribute to a blunting of the non-genomic action of T(3) and impair the effect of T(3) on NO and cGMP production in endothelial cells. These data suggest that oxLDL, apart from inducing the atherosclerotic process, may also promote a mechanism of peripheral resistance to T(3,) further amplifying the impact of hypothyroidism on endothelial function by increasing SVR.
甲状腺激素（TH）在调节心脏功能方面发挥着重要作用，包括心肌收缩力和全身血管阻力（SVR）。三碘甲状腺原氨酸（T3）是 TH 的活性形式，通过 PI3K/AKT 非基因组信号诱导内皮型一氧化氮合酶的激活。甲状腺功能减退与 SVR 和血清低密度脂蛋白（LDL）水平升高有关，氧化型 LDL（oxLDL）的积累可能损害内皮依赖性血管舒张。本研究旨在探讨天然 LDL（nLDL）和 oxLDL 对 T3 介导的 AKT 磷酸化、一氧化氮（NO）和环鸟苷单磷酸（cGMP）产生的影响。
将人脐静脉内皮细胞暴露于 nLDL 或 oxLDL 中 3 小时，然后用 T3（10⁻⁷ M）刺激或用维生素 E 和 C 的抗氧化混合物预处理 12 小时，再用 LDL 处理。通过 Western blot 分析 AKT 磷酸化，用 4,5-二氨基荧光素二乙酸酯评估 NO 产生，用酶免疫测定法测量细胞内 cGMP 的产生。通过将 LDL 与 CuSO4 孵育进行 LDL 氧化，并用高效液相色谱法评估 LDL 的 α-生育酚含量。
oxLDL 损害了 T3 介导的丝氨酸 473 上的 AKT 磷酸化，显著降低了 NO（oxLDL+T3 与 T3 相比，9.79±0.5 AU 与 80.75±2.8 AU，平均值±标准偏差，p<0.0001）和 cGMP 的产生。此外，抗氧化混合物预处理可消除 LDL 对 T3 作用的抑制作用。
本研究结果表明，oxLDL 可能导致 T3 非基因组作用减弱，并损害 T3 对内皮细胞中 NO 和 cGMP 产生的作用。这些数据表明，oxLDL 除了诱导动脉粥样硬化过程外，还可能促进外周对 T3 的抵抗机制，通过增加 SVR 进一步放大甲状腺功能减退对内皮功能的影响。
