The cyclolignan picropodophyllin attenuates intimal hyperplasia after rat carotid balloon injury by blocking insulin-like growth factor-1 receptor signaling

ObjectiveSmooth 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.MethodsThe 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.ResultsPPP 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.ConclusionThese 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.Clinical RelevanceIntimal hyperplasia remains a major obstacle to vessel patency after vascular surgery. Although the role of various growth factors, including insulin-like growth factor-1 (IGF-1), has been studied in the development of intimal hyperplasia, no clinical therapy has emerged to date. IGF-1, either from the systemic circulation or locally produced by smooth muscle cells (SMCs) after vascular injury, binds to its receptor (IGF-1R) on SMCs and leads to activation of a number of signaling pathways known to be involved in SMC proliferation and survival. Drugs that specifically inhibit activation of IGF-1R without affecting the insulin receptor have previously not been available. In this study, we used picropodophyllin, a newly developed and highly specific IGF-1R inhibitor, to investigate the therapeutic potential of targeting the IGF-1 axis in the prevention of intimal hyperplasia after vascular injury