LECTIN-LIKE OXIDIZED LOW-DENSITY LIPOPROTEIN RECEPTOR (LOX-1), THYROID HORMONE (T3) AND REACTIVE OXYGEN SPECIES (ROS): POSSIBLE CROSS-TALK IN ANGIOGENESIS

摘要

Angiogenesis is a physiological process required for embryonic vascular development and involved in the pathophysiological progress of diseases such as atherosclerosis. In fact, hypoxia, ischemia and oxidative stress are common events in atherosclerotic plaque that stimulate angiogenesis, leading to the formation of a neovascularization in the intima of atherosclerotic lesions. The presence of these capillaries favours the progression of the plaque instability. Several studies indicate oxidised low-density lipoprotein (ox-LDL) and its endothelial receptor lectin-like oxidised low-densi-ty lipoprotein (LOX-1) as the major responsible for the occurrence and progression of atherosclerosis through apoptosis. At the same time, some authors showed that moderate concentrations of ox-LDL stimulate angiogenesis via LOX-1 activation of NADPH oxidase, MAPKs-NF-KB pathways and the generation of low levels of reactive oxygen species (ROS). Thyroid hormones have well documented effects on angiogenesis through genomic and non-genomic action and increased levels of ROS have been reported in hyperthyroidism. Moreover, by in vitro studies triiodothyronine (T3) and L-thyroxine (T4) significantly increased the intracellular ROS production based on the oxidation of 2',7'-dichloro dihydrofluorescein to a fluorescent 2', 1 '-dichlorofluo-resein. Previous findings showed that ROS directly increase LOX-1 production in microvas-cular endothelial cells. New in vitro studies demonstrated the capability of T3 at supra-phys-iological doses to upregulate the LOX-1 expression in human microvascular endothelial cells. Thus, we can speculate the existence of a crosstalk between LOX-1-ROS and high levels of T3, suggesting that high levels of T3, as in hyperthyroidism, could cause a worsening of plaque vulnerability inducing.