Lipoprotein(a) enhances the expression of intercellular adhesion molecule-1 in cultured human umbilical vein endothelial cells.

Abstract

We reported an increase in serum lipoprotein(a) [Lp(a)] levels in patients with thromboangiitis obliterans, suggesting that Lp(a) could also contribute to the pathogenesis of cardiovascular diseases by a mechanism different from atherosclerosis. Adhesion molecules were shown to contribute to the development of not only atherosclerotic but also inflammatory vascular diseases. We evaluated the effect of Lp(a) on the expression of intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and E-selectin in human umbilical vein endothelial cells by a cell ELISA. Lp(a) dramatically enhanced the levels of ICAM-1 in a dose-dependent manner. A discernible increase in ICAM-1 expression was observed at a physiological concentration of 0.26 mmol cholesterol/L Lp(a) after 48-hour incubation. A 1.8-fold increase in ICAM-1 expression was observed 48 hours after the addition of Lp(a) (1.04 mmol cholesterol/L). Northern blot analysis demonstrated that the amount of ICAM-1 mRNA was increased after treatment with Lp(a). In contrast to ICAM-1, the expression of VCAM-1 and E-selectin was not significantly affected by Lp(a). Lp(a-) [apolipoprotein(a)- removed Lp(a) by reduction with dithiothreitol] and LDL had no significant effect on the expression of ICAM-1. In contrast, recombinant apolipoprotein(a) protein alone significantly enhanced ICAM-1 expression. Lp(a) decreased the level of active transforming growth factor (TGF)-beta in the conditioned medium. Furthermore, recombinant TGF-beta significantly decreased the Lp(a)-induced ICAM-1 expression. These findings suggested that Lp(a) may enhance the ICAM-1 expression by decreasing active TGF-beta level. Lp(a) could contribute to the development of cardiovascular diseases by enhancing the expression of ICAM-1 in endothelial cells.