No abstract

Abstract-Neointimal formation, the leading cause of restenosis, is caused by proliferation of vascular smooth muscle cells (VSMCs). Patients with diabetes mellitus have higher restenosis rates after coronary angioplasty than nondiabetic patients. Cilostazol, a selective type 3 phosphodiesterase inhibitor, is currently used to treat patients with diabetic vascular complications. Cilostazol is a potent antiplatelet agent that inhibits VSMC proliferation. In the present study, we examine whether the antiproliferative effect of cilostazol on VSMCs is mediated by inhibition of an important cell cycle transcription factor, E2F. Cilostazol inhibited the proliferation of human VSMCs in response to high glucose in vitro and virtually abolished neointimal formation in rats subjected to carotid artery injury in vivo. Moreover, the compound suppressed high-glucose-induced E2F-DNA binding activity, and the expression of E2F1, E2F2, cyclin A, and PCNA proteins. These data suggest that the beneficial effects of cilostazol on high-glucose-stimulated proliferation of VSMCs are mediated by the downregulation of E2F activity and expression of its downstream target genes, including E2F1, E2F2, cyclin A, and PCNA. The transcription factor, E2F, has been implicated in the periodic regulation of cellular genes required for transition through G1 and entry into the S phase, including dihydrofolate reductase, c-myc, DNA polymerase, cdc2, and proliferating cell nuclear antigen (PCNA). 5-7 E2F activity is regulated by interactions with RB family members. As cells progress toward S phase, RB family proteins are phosphorylated by G1 cyclin-complexes, resulting in the release of transcriptionally active E2F, which then leads to the activation of genes required for cell cycle progression. 8 -10 We recently showed that high glucose activates the DNA-binding activity of E2F, and decoy oligodeoxynucleotides against E2F inhibit the proliferation of VSMCs. 11 These data suggest that downregulation of E2F could constitute a therapeutic target to prevent restenosis after angioplasty in patients with diabetes.Cilostazol increases intracellular cAMP concentrations by selectively blocking phosphodiesterase type III. The clinical implications and pharmacokinetics with respect to the effects and safety of this drug have been well-established, especially in peripheral vascular disease. 12 Cilostazol is a potent antiplatelet agent currently used in clinical practice to treat patients with diabetic vascular complications. [13][14][15] Several lines of evidence indicate that cilostazol additionally inhibits the proliferation of VSMCs, reduces neointimal formation in balloon-injured rat carotid arteries, 16 -18 and inhibits restenosis after percutaneous transluminal coronary angioplasty. 19,20 One mechanism by which cilostazol may inhibit VSMC proliferation is via an increase in intracellular cAMP, because cAMP inhibits the proliferation of VSMCs by induction of p53-mediated and p21-mediated apoptosis. 21 However, Nadri et al demonstrated that increased cAMP...