Arachidonic acid release by cPLA 2 may be causally related to NO‐induced apoptosis in vascular smooth muscle cells

Apoptosis has been shown to occur in vascular smooth muscle cells during the development of atherosclerosis. In order to investigate the possible role of arachidonic acid during apoptosis in vascular smooth muscle, we induced apoptosis in cultured rat aortal smooth muscle cells (SMCs) by treatment with either UV (ultraviolet) radiation, tumor necrosis factor‐α (TNF‐α) or NO donor drugs (sodium nitroprusside, or S‐nitroso‐ N ‐acetyl‐ D ‐penicillamine, SNAP). Apoptosis was detected by either DNA fragmentation analysis or by TUNEL analysis. UV radiation, TNF‐α and NO were observed to stimulate apoptosis in the cells as well as to stimulate arachidonate release from the cells. NO also increased levels of cPLA 2 in the cells, which is an enzyme that is frequently activated in cells that release arachidonate. These agents stimulated arachidonate release somewhat earlier than they stimulated apoptosis in the cells. The inhibition of cPLA 2 by arachidonyl trifluoromethyl ketone (AACOCF 3 ) also led to the inhibition of arachidonate release from the cells as well as the inhibition of nitroprusside stimulated apoptosis. Arachidonic acid itself could induce apoptosis in the cultured cells. These observations provide evidence that arachidonate may be involved in apoptosis in vascular smooth muscle. J. Cell. Physiol. 191: 191–197, 2002. © 2002 Wiley‐Liss, Inc.