doi: 10.1111/j.1472-8206.2010.00898.x ORIGINAL ARTICLE Microparticles from apoptotic monocytes enhance nitrosative stress in human endothelial cells Maria Letizia Mastronardi   , Hadj Ahmed Mostefai   , Raffaella Soleti, Abdelali Agouni, Maria Carmen Martı ´nez, Ramaroson Andriantsitohaina* INSERM, U694, France; Universite ´ d’Angers, Angers, France INTRODUCTION Microparticles (MPs) are vesicles shed from blebbing plasma membrane of various cell types, such as platelets, T and B cells, monocytes, and endothelial cells during activation by agonists, shear stress or apoptosis. Cellular MPs constitute heterogeneous populations, depending the cell origin, number, size, antigenic composition and functional properties [1]. MPs bear cell surface proteins and the cytoplasmic component of the original cell accounting for their procoagulant character and proin- flammatory and adhesive properties, including alteration of vascular function [1,2]. MPs may transfer bioactive molecules to other cells, different from those from which they have been produced [3,4], and thereby stimulating cells to produce cytokines, cell-adhesion molecules, growth factors and tissue factor, and modulate endothe- lial functions [1,5]. However, the mechanisms involved in these effects are different depending on the cell origin of MPs and the stimuli used for their generation. Elevated levels of circulating MPs have been detected in pathological states associated with vascular dysfunc- tion, including attenuation of endothelium-dependent vasodilatation and/or alteration of responsiveness of vascular smooth muscle to vasoconstrictor stimuli in conductance and resistance arteries [6–9]. Circulating Keywords endothelial cells, microvesicles, nitric oxide, nitrosative stress Received 2 April 2010; revised 13 August 2010; accepted 11 October 2010 *Correspondence and reprints: ramaroson.andriantsitohaina@ univ-angers.fr   Both authors participate equally in this work. ABSTRACT Microparticles are membrane vesicles with procoagulant and proinflammatory properties released during cell activation or apoptosis. Microparticles from monocytes have been implicated in atherosclerosis and vascular inflammation, but their direct effects on endothelial cells are not completely elucidated. The present study was designed to dissect the signaling pathways of monocytic microparticles in endothelial cells with respect to both NO pathway and reactive oxygen species. Microparticles were produced by treatment of human monocytic cell line THP-1 with the apoptotic agent VP-16. Human endothelial cells were treated with monocytic microparticles and then, we studied their effects on nitrosative and oxidative stresses. Incubation of human endothelial cells with microparticles enhanced the production of NO without affecting superoxide anions ðO  2 Þ generation. Microparticles did not affect endothelial NO synthase expression and its phosphorylation. Interestingly, microparticles decreased caveolin-1 expression and increased its phosphorylation. Inhibition of PI-3-kinase or MEK1/2 reversed the effects of microparticles on caveolin-1 expression but not its phosphorylation. Moreover, microparticles increased nitration of several proteins, reflecting peroxynitrite production, which was prevented by blockade of PI-3-kinase pathway. In summary, monocyte microparticles active multiple path- ways related to nitrosative stress in endothelial cells including both PI-3-kinase and ERK1/2 in the regulation of caveolin-1 expression. These data underscore the pleiotropic effect of microparticles on endothelial cells and suggest that they probably play a critical role on vascular function. ª 2010 The Authors Fundamental and Clinical Pharmacology ª 2010 Socie ´ te ´ Franc ¸aise de Pharmacologie et de The ´ rapeutique Fundamental & Clinical Pharmacology 25 (2011) 653–660 653 Fundamental & Clinical Pharmacology