Objective: Despite the success of antiproliferative therapies, restenosis remains a common problem after percutaneous transluminal coronary angioplasty (PTCA). Longer-term clinical results of brachytherapy (intracoronary radiation), the lack of long-term clinical results after implantation of drug eluting stents, and the occurrence of late thrombosis after both procedures leave room for skepticism. Neointimal proliferation is not substantially inhibited at late time points after brachytherapy, and late lumen loss with a "catch-up" proliferation can occur. We hypothesized that the transcription factors nuclear factor-{kappa}B (NF-kappaB) and activator protein-1 (AP-1) are involved in these processes. We addressed the role of these mediators in a porcine model of coronary restenosis.
Methods: Thirty-nine pigs underwent PTCA in two major coronary arteries. One of the two balloon-injured arteries was randomly assigned to receive immediate 20 Gy beta-irradiation (Brachy group) using a noncentered source train ((90)Sr/Y Beta-Cath, Novoste). Animals were sacrificed after 1 day, 14 days, or 28 days. Proliferating cells were labeled prior to euthanasia.
Results: At late time points, lumen area was significantly smaller and the inflammatory response was more pronounced in the Brachy group than in the PTCA group. These findings coincided with sustained activation of MMP-9 and transcription factors like NF-kappaB and AP-1. Initially, cell proliferation was reduced in the Brachy group; however, at late time points, differences between the two treatment groups were no longer significant.
Conclusions: Brachytherapy initially inhibits cell proliferation; however, cellular and molecular inflammatory processes (e.g. activation of NF-kappaB) are enhanced within the arterial wall. This proinflammatory side effect may be responsible for the observed delayed proliferation and the resulting lumen loss.