Chronic exposure to rapamycin induces endothelial dysfunction in vitro

Abstract

We investigate here the effects of the mTOR inhibitor rapamycin, widely employed in drug eluting stents to prevent restenosis, on endothelial viability and function in vitro. The cell model adopted consisted of human umbilical vein endothelial cells, treated for 24h or 48h with rapamycin under both basal and inflammatory conditions, mimicked by the presence of TNFα. As demonstrated with TUNEL assay and annexin V staining, rapamycin, either alone or, more markedly, in the presence of TNFα, increases the percentage of cells in apoptosis and inhibits endothelial mobility in wounding healing assays. Moreover, rapamycin enhances TNFα stimulation of the expression of proteins associated with endothelial activation, such as E-selectin and CAT2 arginine transporters. Consistently, it stimulates arginine uptake and raises the intracellular concentration of the cationic amino acid. However, under the same conditions, NOS3 expression is inhibited thus leading to a fall in NO output despite the increased availability of the NO precursor. These results point to an important role for mTOR activity in the preservation of endothelial function and viability and provide a rationale for the late complications observed in patients with rapamycin eluting stents. Aided by MIUR (PRIN “In vitro models of endothelial damage of ischemia-reperfusion: role of arginine and nitric oxide), Rome, Italy