Serial Changes of Smooth Muscle Cell Phenotype in Rabbit Aorta After Balloon Injury : Effect of Antisense Nonmuscle Myosin Heavy Chain Oligonucleotides on Smooth Muscle Cell Proliferation and Phenotypic Modulation

The process of vascular smooth muscle cell (SMC) growth plays a major role in restenosis after coronary angioplasty. We evaluated the serial changes of SMC phenotype after balloon injury in vivo and the inhibitory effects of antisense nonmuscle myosin heavy chain-A oligonucleotides (AS) on the migration, proliferation and phenotypic modulation of SMC in vitro. Balloon inflation of the lower abdominal aorta was performed in Japanese white rabbits. Phenotypes of SMC in the intima were classified into three cell types electron-microscopically: synthetic, intermediate and contractile. Proliferating response was examined immunohistochemically using proliferating cell nuclear antigen (PCNA). Cultured SMC were obtained by both explant and enzymatic dispersion methods. To evaluate the inhibitory effect of AS, cell counting and video image analysis were performed and compared with sense oligonucleotides. Enzymatically dispersed cells were investigated electron microscopically 3 days after the addition of AS. The number of PCNA-positive cells correlated with the ratio of synthetic cells in the intima, but this correlation was not observed in the intima on the internal elastic lammina (IEL) side on Day 28. Late stage (21～28 days) SMC proliferation was observed in the intima on the IEL side, and this proliferation probably involved mainly the intermediate phenotype of SMC in this experimental model. After the addition of AS to the medium, SMC proliferation was suppressed in a concentration-dependent manner. However AS did not inhibit SMC migration significantly as assessed by continuous video image analysis, nor did it inhibit the "phenotypic modulation" of SMC as evaluated electron-microscopically. These results suggested that the late stage intermediate phenotype SMC proliferation (delayed proliferation) might be implicated in restenosis after balloon injury. AS suppressed SMC proliferation, and may be useful as a therapy to prevent restenosis