Objective: Smooth muscle cell proliferation (SMC) is a pivotal factor in the development of intimal hyperplasia after vascular injury. A number of growth factors, including insulin-like growth factor-1 (IGF-1), have been shown to be involved in SMC proliferation. We evaluated the effect of picropodophyllin (PPP), a new IGF-1 receptor inhibitor, in the prevention of SMC proliferation and development of intimal hyperplasia after vascular injury.
Methods: The effects of systemic administration of PPP on intimal hyperplasia were studied in a balloon rat carotid injury model. Lesions were quantified by morphometry and SMC proliferation and apoptosis was studied by immunohistochemical staining for proliferating cell nuclear antigen (PCNA) and activated caspase 3, respectively. The effect of PPP on rat aortic SMC proliferation and apoptosis was studied in vitro by using cell counting, 3[H]-thymidine incorporation, and a flow cytometry assay for annexin V. Phosphorylation of the IGF-1 receptor, protein kinase B (Akt), and extracellular signal-regulated kinase 1/2 (ERK1/2) in vitro and in vivo were analyzed by using Western blotting.
Results: PPP inhibited IGF-1-mediated SMC proliferation in vitro but no significant increase in apoptosis was detected. In rats treated with PPP, a more than a twofold reduction in carotid intima area was observed 2 weeks after balloon injury, a significant decrease in PCNA staining was demonstrated in early lesions, but activated caspase 3 was not detected. In addition, PPP attenuated phosphorylation of the IGF-1 receptor, Akt, and ERK1/2 in IGF-1-stimulated SMCs in vitro, and a reduced phosphorylation of the IGF-1 receptor and Akt was found in balloon-injured carotid arteries in rats treated with PPP.
Conclusion: These results show that PPP potently blocks IGF-1-mediated phosphorylation of the IGF-1 receptor in SMCs, decreases downstream Akt and ERK1/2 activation, inhibits SMC replication, and subsequently attenuates intimal hyperplasia after balloon injury of rat carotid arteries.