NITRIC-OXIDE INDUCES UP-REGULATION OF FAS AND APOPTOSIS IN VASCULAR SMOOTH-MUSCLE

Interleukin-1 induced a time-dependent release of high levels of nitri c oxide from rat vascular smooth muscle cells up to 96 hours. A time-d ependent release of lactate dehydrogenase was also induced by Interleu kin-1 from 72 to 96 hours after its stimulation. In situ nick end-labe ling assay revealed that incubation for 48 hours with interleukin-1 in duced a positive staining of fragmented nuclei. However, N-G-monomethy l-L-arginine, an inhibitor of nitric oxide synthase, inhibited both la ctate dehydrogenase release and DNA fragmentation induced by interleuk in-1. Furthermore, sodium nitroprusside, a nitric oxide donor, also in duced lactate dehydrogenase release and DNA fragmentation. Fluorescent staining of DNA revealed patches of irregularly dispersed, brightly s taining, and condensed chromatin in rat vascular smooth muscle cells t reated with sodium nitroprusside. Flow cytometric analysis with monocl onal antibody against human Fas revealed that expression of Fas was up regulated by sodium nitroprusside in human vascular smooth muscle cell s. Methylene blue, an inhibitor of soluble guanylate cyclase, did not affect sodium nitroprusside-induced upregulation of Fas. Furthermore, 8-bromoguanosine 3':5'-cyclic monophosphate, an analogue of cGNP, did not upregulate Fas expression. These findings indicate that nitric oxi de released from vascular smooth muscle cells may induce apoptosis in vascular smooth muscle cells themselves and also induces upregulation of Fas via a cGMP-independent mechanism. Thus, nitric oxide could trig ger the remodeling of atherosclerotic plaques.