Acute cellular damage in medial smooth muscle cells following experimental coronary angioplasty in dog. Damage of cytoskeleton and apoptosis.

The purpose of the present study was to investigate the responses of the cytoskeleton and the presence of apoptosis following acute damage of medial smooth muscle cells after percutaneous transluminal coronary angioplasty (PTCA). We killed 20 dogs, 4h and 4 days after PTCA (n=10 in each group). Ten dogs without PTCA were used as controls. PTCA was achieved by inflating balloon catheters two times, for 60s each time, to 150 PSI, followed by a 60-s deflation. The coronary artery obtained from each dog was fixed in 10% formalin neutral buffer solution. The response of the cytoskeleton was studied immunohistochemically. using monoclonal antibodies against alpha-smooth muscle actin, vimentin, and beta-tubulin. Proliferation was determined by proliferating cell nuclear antigen (PCNA), and DNA fragmentation indicating apoptosis was determined by in situ nick end labeling. Four h after PTCA, endothelial denudation, microscopic mural thrombi, rupture of the internal elastic membrane, medial tear, and stretched smooth muscle cells with nuclei were found at the PTCA site. An immunohistochemical study revealed diffuse reduction or defective immunoreactivity in each cytoskeleton of medial smooth muscle cells, 4h after PTCA. The extent of positive immunoreactivity in the media decreased to 45+/-11% in alpha-smooth muscle actin (control value, 80+/-10%), 9+/-8% in vimentin (control value, 83+/-9%), and 10+/-7% in beta-tubulin (control value, 75+/-8%). The decrease was more significant in vimentin and beta-tubulin than in alpha-smooth muscle actin. Four days after PTCA, the features were diffuse cell death and the focal proliferation of medial cells, as well as macroscopic intramural thrombi. The extent of positive immunoreactivity in the media was 15+/-9% in alpha-smooth muscle actin, 13+/-7% in vimentin, and 14+/-11% in beta-tubulin. There were no smooth muscle cells with positive PCNA (0%) in the control and 4-h groups, but 4 days after PTCA the percentage was 19+/-4%. In situ nick end labeling showed DNA fragmentation in the nuclei of medial smooth muscle cells at a rate of 15+/-5% 4h after PTCA and at 8+/-6% 4 days after PTCA, compared with 0% in the control. We concluded that severe damage of the cytoskeleton and medial smooth muscle cell death were induced immediately after PTCA, followed by proliferation of smooth muscle cells. Apoptosis may be partially involved in the death of smooth muscle cells, in addition to necrosis. Damage to the cytoskeleton and apoptosis may play an important role in the pathogenesis of acute lesions and the proliferation of smooth muscle cells after PTCA.