Lymphocytic microparticles confer endothelial protection through activation of antioxidant defenses

Oxidative stress plays an important role in the initial occurrence of cardiovascular diseases. Previous studies demonstrated that microparticles (MPs) released from activated and apoptotic lymphocytes improve endothelial function due to their ability to decrease reactive oxygen species (ROS). Here, we evaluated the capacity of these MPs to modulate ROS production during actinomicyn D (ActD)-induced apoptosis in human umbilical vein endothelial cells (HUVECs). MPs were generated from T lymphocytes undergoing activation with phytohemagglutinin and then, by stimulation with phorbol-12 myristate-13 acetate and ActD. HUVECs were grown for 24h in absence or presence of ActD (1g/ml), and/or 10Pg protein/ml of MPs. Once evaluated that MPs are able to prevent ActD-evoked apoptosis, we investigated the time course of modifcations in ROS production (i.e. 1, 2, 4, 6, 8, 10 and 24h) by electron paramagnetic resonance. ActD enhances ROS production after 2h and 10h of treatment that was prevented by MPs after 2h but not at 10h, indicating that they act during the early phase of apoptosis. Interestingly at 24h, superoxide dismutase (SOD) mimetic, manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin (MnTMPyP) decreases cell death and inhibition of apoptosis induced by MPs, suggesting that MPs may behave as an SOD mimetic. Although these MPs carry functionally active extracellular SOD and catalase, as demonstrated by western blot analysis, treatment of HUVECs with these MPs does not modify expression of these enzymes. Under the same experimental conditions, MPs increase the expressions of other antioxidant enzymes such as Cu/Zn SOD and Mn SOD in HUVECs that may explain the protective effects induced by MPs. Thus, the present study illustrates new mechanisms by which MPs from activated/apoptotic lymphocytes may confer endothelial protection under pathological conditions in which oxidative stress is enhanced by a subtle modulation of antioxidant defense mechanism