['Cilostazol, a selective inhibitor of PDE3, has a protective effect on endothelium after ischemic vascular damage, through production of nitric oxide (NO). The purpose of the present study was to clarify the molecular mechanisms underlying the preventive effect of treatment with cilostazol on oxidative stress-induced premature senescence in human endothelial cells.', 'Prematurely senescent human umbilical vein endothelial cells (HUVECs) were induced by treatment with hydrogen peroxide (H(2)O(2)) as judged by senescence-associated beta-galactosidase assay (SA-betagal), cell morphological appearance, and plasminogen activator inhibitor-1 (PAI-1) expression. Treatment with H(2)O(2) caused 93% of the cells to be SA-betagal positive, whereas 46% of cilostazol (100 micromol/L)-treated cells were positive. HUVECs treated with other cAMP-elevating agents and DETA-NO showed a reduction of SA-betagal-positive cells as well. Cilostazol increased phosphorylation of Akt at Ser(473) and of endothelial nitric oxide synthase (eNOS) at Ser(1177), with a dose-dependent increase in Sirt1 expression. Moreover, the effect of cilostazol on premature senescence was abrogated through inhibition of Sirt1.'] Does cilostazol inhibit oxidative stress-induced premature senescence via upregulation of Sirt1 in human endothelial cells?