Characterization of cellular density and determination of neointimal extracellular matrix constituents in human lower extremity vein graft stenoses

Arterial restenosis has been attributed to a hyperproliferative smooth musc le cell response. Paradoxically, studies of human coronary atherectomy and vein graft stenotic lesions have demonstrated a relatively low nuclear prol iferative rate with the majority of the neointimal mass consisting of extra cellular matrix. The purpose of the present study was to characterize the c ellular density and determine the relative composition of the extracellular matrix protein constituents in stenotic, human lower extremity vein-bypass graft lesions. Methods: Duplex surveillance of 148 consecutive infrainguin al bypass grafts identified 17 patients with 22 preocclusive autogenous vei n graft stenoses (mean graft age 7 months). Morphological analyses of these stenotic lesions were compared with excised samples of 20 greater saphenou s vein segments taken at the time of graft implantation from matched contro l patients. Intimal and medial areas were compared and cell density was det ermined with fluorescent nuclear (Bisbenzimide) staining. Differential ligh t microscopy with pentachrome staining was pet-formed to determine the rela tive percent composition of intimal matrix constituents by stereological mo rphometric (point-count) techniques. Results: The intimal areas for control and stenotic vein segments were 1.64 x 10(6) mu m(2) and 3.85 x 10(6) mu m (2), P < 0.0001, whereas the intimal nuclear densities (cells/unit volume) were 1.42 x 10(3) and 1.70 x 10(3) cells/mu m(2), P = 0,03, respectively. T he corresponding medial area and medial nuclear densities were 5.01 x 10(6) mu m(2), 3.31 x 10(6) mu m(2): P = 0.08, and 2.27 x 10(3), 3.29 x 10(3), P = 0.001, for control and stenotic specimens, respectively. The intima:medi a area ratios were much greater, whereas the intimal and medial cell densit ies were only slightly greater in the stenotic compared with control veins. The relative composition of intimal extracellular matrix proteins of steno tic vein graft segments consisted of 21% cellular (fibrous) material, 33% c ollagen, and 46% glycosaminoglycan ground substance. Conclusion: The intima l lesions responsible for lower extremity vein graft stenosis are more hype rtrophic than hyperplastic, Therapies aimed at preventing arterial and vein graft restenosis may thus need to inhibit matrix biosynthetic processes in addition to cellular proliferation. (C) 1999 The International Society for Cardiovascular Surgery. Published by Elsevier Science Ltd. All rights rese rved.