High levels of homocysteine inhibit lysyl oxidase (LOX) and downregulate LOX expression in vascular endothelial cells

Background: Hyperhomocysteinemia, an independent risk factor for cardiovascular disease and atherothrombosis, alters endothelial function through a mechanism not fully understood. Downregulation of lysyl oxidase (LOX), an enzyme involved in extracellular matrix maturation, impairs the endothelial barrier function and could be involved in homocysteine (HC)-induced endothelial dysfunction. Objective: The aim of this study was to analyze the effect of HC on LOX regulation in vascular endothelial cells. Results: HC at pathophysiological concentrations (35 muM) inhibited LOX activity in porcine aortic endothelial cells. Homocysteine thiolactone and related molecules containing sulfhydryl groups (cysteine), but not methionine or homocystine (non-containing thiol-group) inhibited LOX. In addition, the blockade of HC-sulfhydryl group by N-ethylmaleimide abrogated HC-induced LOX downregulation. This process was triggered by oxidative stress since superoxide dismutase and vitamin C reverted LOX inhibition caused by HC. On the contrary, the effect was not mediated through the induction of endoplasmic reticulum stress. Finally, higher doses of HC (200 muM), common in severe hyperhomocysteinemia, decreased LOX mRNA levels (approximate to 2-fold) and LOX promoter activity in transient transfection experiments. Conclusions: These findings suggest that LOX inhibition contributes to the endothelial dysfunction associated with hyperhomocysteinemia. This effect was dependent on a mechanism involving both an inhibition of LOX activity and a reduction of LOX expression. (C) 2004 Elsevier Ireland Ltd. All rights reserved.