Inhibition of endothelial cell thromboresistance by homocysteine.

Homocysteine (HC) is a highly reactive thiol intermediate in amino acid metabolism, which can modify the function of endothelial cells in a myriad of ways. In vitro, homocysteine can inhibit the thromboresistance properties of the endothelial cell by induction of procoagulant factors, inactivation of natural anticoagulant systems, and suppression of vasodilatory and platelet-modulating factors. HC also inhibits the fibrinolytic system by impairing the ability of the endothelial cell to bind tissue plasminogen activator (t-PA), by interacting directly with the t-PA binding "tail" domain of its endothelial cell receptor, annexin II. Moreover, HC influences endothelial cell gene expression as exemplified by induction of the elongation factor-1 family of polypeptides, which promote polypeptide chain elongation during mRNA translation. Induction of EF-1 subunits alpha, beta, gamma and delta by homocysteine is associated with increased turnover of at least one free thiol-containing protein, suggesting that up-regulation of these subunits may represent a mechanism for replacement of damaged or modified proteins. A more complete understanding of the diverse effects of homocysteine on endothelial cell function may provide important clues to the precise role homocysteine may play in the initiation and progression of vascular disease.