[Decreased apoptosis as a pathogenic factor in intimal hyperplasia of human arteriosclerosis lesions]

Abstract

Restenosis remains a persistent problem following intravascular reconstruction. Smooth muscle cell proliferation, extracellular matrix production and remodeling are accepted mechanisms of restenotic lesion formation. Decreased programmed cell death (apoptosis) may also contribute to restenosis by prolonging the life span of intimal cells, with their subsequent accumulation and development of hyperplastic lesions. The objectives of the present study were as follows: i) to identify cell death, ii) to distinguish and quantify apoptosis from necrosis, and iii) to compare restenotic with primary lesions. To this end, human atherectomy specimens from 25 primary and 14 restenotic coronary and peripheral lesions were studied by TUNEL test (TdT-mediated dUTP Nick End Labeling; detection of cell death by the presence of fragmented DNA), transmission electron microscopy and morphometric analysis. Intimal hyperplasia was more consistent with restenosis than with primary lesion origin, and was mainly attributed to increased smooth muscle cell density (649 vs. 219 cells/mm2; p < 0.001). The main finding of the present study is that hypercellular restenotic tissue contains fewer TUNEL+ cells than hypocellular plaques (14% vs. 27%; p < 0.05). Most importantly, ultrastructural evaluation revealed a markedly reduced portion of intimal plaque cells, especially smooth muscle cells exhibiting distinct morphologic signs of apoptosis (3% vs. 13%; p < 0.001). In contrast, incidence of necroses did not differ between both lesion types (0.13 vs. 0.12 necroses/ cell; p = 0.49). Thus, our data indicate apoptosis and not necrosis to be the crucial cell death form to account for the apparent discrepancy found in both lesion types with reduced apoptosis in cell-rich restenoses. The findings of the present study suggest that decreased apoptosis is an important regulatory mechanism ultimately leading to intimal hyperplasia as commonly found in human restenosis post angioplasty.