David N. Ku

Early Effects of Arterial Hemodynamic Conditions on Human Saphenous Veins Perfused Ex Vivo

Exposure to the arterial hemodynamic environment is thought to be a potential trigger for the pathological remodeling of saphenous vein grafts. Using matched pairs of freshly isolated human saphenous vein, we analyzed the early effects of ex vivo hemodynamic conditions mimicking the venous (native) compared with arterial (graft) environment on the key components of vascular remodeling, ie, matrix metalloproteinase (MMP)-9 and MMP-2 and cell proliferation. Interestingly, we found that arterial conditions halved latent MMP-9 (50+/-11%, P=0.01) and MMP-2 (44+/-6%, P=0.005) levels relative to matched vein pairs maintained ex vivo under venous perfusion for up to 3 days. Immunostaining supported decreased MMP levels in the innermost area of arterially perfused veins. Either decreased synthesis or increased posttranslational processing may decrease MMP zymogen levels. Biosynthetic radiolabeling showed that arterial perfusion actually increased MMP-9 and MMP-2 production. When we then examined potential pathways for MMP zymogen processing, we found that arterial conditions did not affect the expression of MT-MMP-1, a cell-associated MMP activator, but that they significantly increased the levels of superoxide, another MMP activator, suggesting redox-dependent MMP processing. Additional experiments indicated that increased superoxide under arterial conditions was due to diminished scavenging by decreased extracellular superoxide dismutase. Arterial perfusion also stimulated cell proliferation (by 220% to 750%) in the majority of vein segments investigated. Our observations support the hypothesis that arterial hemodynamic conditions stimulate early vein graft remodeling. Furthermore, physiological arterial flow may work to prevent pathological remodeling, particularly the formation of intimal hyperplasia, through rapid inactivation of secreted MMPs and, possibly, through preferential stimulation of cell proliferation in the outer layers of the vein wall.

Recombinant Mitotoxin Basic Fibroblast Growth Factor–Saporin Reduces Venous Anastomotic Intimal Hyperplasia in the Arteriovenous Graft

BACKGROUND The plant cytotoxin saporin (SAP) is a potent ribosome-inactivating protein. When conjugated to basic fibroblast growth factor (FGF2), it selectively kills proliferating cells that have upregulated FGF receptors. In this study, we evaluated the effect of the recombinant chimeric mitotoxin rFGF2-SAP on venous anastomotic intimal hyperplasia, a major cause of failure of arteriovenous (AV) grafts. METHODS AND RESULTS Recently designed expanded polytet-rafluoroethylene-based local infusion devices were implanted bilaterally as femoral AV conduits in six dogs. The venous anastomoses were the sites of continuous delivery of rFGF2-SAP (2.7 micrograms.kg-1.d-1) to one side and vehicle (4.6 microL.kg-1.d-1) as control to the contralateral side for 14 days. All animals survived, and all grafts were patent. Liver enzyme levels and histological analyses of liver, kidneys, and brain were normal, indicating the absence of systemic toxicity. Morphometric measurements and measurements of cell proliferation by bromodeoxyuridine index analysis were performed at both arterial and venous anastomoses. There were no significant differences between the treated grafts and the control grafts in intimal hyperplasia and intimal cell proliferation at the arterial anastomoses. In contrast, rFGF2-SAP reduced intimal thickness by 32%, intimal area by 40%, and cell proliferation index by 33% at the treated venous anastomoses compared with the control venous anastomoses (P < .05). CONCLUSIONS These data demonstrate that local infusion of rFGF2-SAP significantly reduces venous anastomotic intimal hyperplasia and cell proliferation without systemic toxicity. This study suggests a new strategy for reducing intimal hyperplasia by the selective killing of proliferating smooth muscle cells with a potent chimeric mitotoxin through a novel local infusion device.

A Study of Predicted and Experimental Wall Collapse in Models of Highly Stenotic Arteries

This study was designed to investigate the effect of stenosis on wall motion and collapse in a latex tube model. Much work has been reported on the collapse of veins and other thin-walled tubes within Starling resistor chambers [1,2]. These papers identify critical controlling factors such as the transmural pressure, upstream and downstream pressure and longitudinal tension. Additionally, they report choking, the waterfall phenomenon, and dynamic behavior such as flutter. None of these articles specifically address the problem of wall excursion and collapse distal to a high grade stenosis. However, Elad et al [3] report on the increased likelihood of transition to supercritical flow with a local area constriction in a model of the pulmonary system which suggests that stenoses may cause collapse. In this article, we report theoretical and experimental physiologic conditions under which arterial wall collapse may occur distal to an atherosclerotic stenosis.

Cell Electrophoresis in Percoll Density Gradients

Abstract The existence of surface charges on living cells was recognized very early by Jurgensen in 1860 when he reported a migration of erythrocytes toward the anode(1). Since then, numerous attempts at qualitatively or quantitatively describing these charges have been made, which are now generally accepted as arising from the carboxyls of sialic acid residues(2). But because of serious theoretical and practical limitations of previous designs, these surface charges are not often measured.