Polycyclic aromatic hydrocarbons present in cigarette smoke cause endothelial cell apoptosis by a phospholipase A2dependent mechanism

Abstract

Smoking is a major risk factor for endothelial cell injury and subsequent coronary artery disease. Epidemiological studies implicate the phospholipase A2/arachidonic acid cascade in the mechanism by which smoking causes heart disease. However, specific components of cigarette smoke that activate this pathway have not been identified. The purpose of this study was to investigate the effects of polycyclic aromatic hydrocarbons contained in cigarette smoke on phospholipase A2 (PLA2) activity and apoptosis of human coronary artery endothelial cells. 1methylanthracene (1â MA), phenanthrene (PA), and benzo(a)pyrene (B(a)P) caused significant release of 3Hâ arachidonate from endothelial cells. 1â MA and PA, but not B(a)P, also caused significant release of 3Hâ linoleic acid. Release of fatty acids from membrane phospholipids preceded the onset of apoptosis. 3Hâ arachidonate release and apoptosis induced by 1â MA, B(a)P, and PA were inhibited by methylarachidonoylâ fluorophosphonate, an inhibitor of Groups IV and VI PLA2s. Bromoenol lactone, an inhibitor of Group VI enzymes, inhibited both 3Hâ arachidonate release and apoptosis induced by 1â MA and PA, but not B(a)P. MJ33, an inhibitor of the acidic calciumâ independent PLA2, attenuated 3Hâ arachidonate release and apoptosis by PA, but not 1MA or B(a)P. The presence of Groups IV and VI and the acidic iPLA2 in endothelial cells was demonstrated by reverse transcriptaseâ polymerase chain reaction and Western analysis. These data suggest that 1â MA, B(a)P and PA induce apoptosis of endothelial cells by a mechanism that involves activation of these three distinct isoforms of PLA2.