Nitric oxide inhibits proliferation of human endothelial cells via a mechanism independent of cGMP

Endothelial cell-derived nitric oxide (NO) has been suggested to inhibit sm ooth muscle cell proliferation, resulting in the reduction of intimal hyper plasia during atherogenesis. The present study investigates the role of NO from exogenous and endogenous sources on the proliferation of human umbilic al vein endothelial cells (HUVEC) and human coronary artery endothelial cel ls (CAEC). Three different NO-generating compounds [sodium nitroprusside (S NP), S-nitroso-glutathione (GSNO) and S-nitroso-acetylpenicillamine (SNAP)] were found to inhibit endothelial cell proliferation measured with three i ndependent methods (cell counting, [H-3]thymidine incorporation, DNA histog rams) with significant inhibition occurring at concentrations greater than or equal to 100 mu M. Growth-inhibiting effects were observed after long-te rm treatment (18-96 h) as well as after short stimulation with NO donors (1 0 min with a subsequent NO donor-free culture period of 18 h) and were comp arable in culture medium (20% serum, growth factor supplementation) and ser um-deficient medium (1% serum). The NO donor effects were mediated by the r elease of NO as they were prevented by NO scavenging. Superoxide dismutase (SOD) was found not to interfere with these effects suggesting that peroxyn itrite formation was unlikely to be involved. 1H-[1,2,4]Oxadiazolo[4,3,-alp ha]quinoxalin-1-one (ODQ), a specific inhibitor of the soluble guanylate cy clase, was observed not to alter the antiproliferative effects of NO donors although it completely prevented NO-mediated increase of cyclic guanosine 3',5'-monophosphate (cGMP), suggesting that the NO-induced growth inhibitio n was not mediated by cGMP. Furthermore, inhibition of endogenous NO produc tion by N-nitro-L-arginine methylester (L-NAME) did not affect endothelial cell growth regardless of using serum plus growth factor supplement, growth factor supplement alone, or thrombin to stimulate proliferation. We sugges t that constitutively synthesized NO may not regulate endothelial cell prol iferation whereas the growth-inhibiting NO effects may occur when an induci ble NO synthase associated with a persistently high NO production is expres sed in the atherosclerotic vessel wall. (C) 1999 Elsevier Science Ireland L td. All rights reserved.