Proliferative capacity of vein graft smooth muscle cells and fibroblasts in vitro correlates with graft stenosis

Abstract

Objective: About a quarter of peripheral vein grafts fail due in part to intimal hyperplasia. The proliferative capacity and response to growth inhibitors of medial smooth muscle cells and adventitial fibroblasts in vitro were studied to test the hypothesis that intrinsic differences in cells of vein grafts are associated with graft failure.

Methods: Cells were grown from explants of the medial and adventitial layers of samples of vein grafts obtained at the time of implantation. Vein graft patency and function were monitored over the first 12 months using ankle pressures and Duplex ultrasound to determine vein graft status. Cells were obtained from veins from 11 patients whose grafts remained patent (non-stenotic) and from seven patients whose grafts developed stenosis. Smooth muscle cells (SMCs) derived from media and fibroblasts derived from adventitia were growth arrested in serum-free medium and then stimulated with 1 muM sphingosine-1-phosphate (S1P), 10 nM thrombin, 10 ng/ml epidermal growth factor (EGF), 10 ng/ml platelet-derived growth factor-BB (PDGF-BB), PDGF-BB plus S1P, or PDGF-BB plus thrombin for determination of incorporation of [(3)H]-thymidine into DNA. Cells receiving PDGF-BB or thrombin were also treated with or without 100 microg/ml heparin, which is a growth inhibitor. Cells receiving thrombin were also treated with or without 150 nM AG1478, an EGF receptor kinase inhibitor.

Results: SMCs and fibroblasts from veins of patients that developed stenosis responded more to the growth factors, such as PDGF-BB alone or in combination with thrombin or S1P, than cells from veins of patients that remained patent (P = .012). In addition, while PDGF-BB-mediated proliferation of fibroblasts from grafts that remained patent was inhibited by heparin (P < .03), PDGF-BB-mediated proliferation of fibroblasts from veins that developed stenosis was not (P > .5).

Conclusion: Inherent differences in the proliferative response of vein graft cells to PDGF-BB and heparin may explain, in part, the variability among patients regarding long term patency of vein grafts.

Figure 1

DNA synthesis in reponse to growth factors by saphenous vein smooth muscle cells (A) and fibroblasts (B) from veins that developed stenosis (open bars) compared to. veins that remained patent (closed bars). Values are the mean ± SEM of fold of control values of ³H-thymidine incorporation after treatment with the indicated growth factors. Values for N are indicated within the bars.

Figure 1

DNA synthesis in reponse to growth factors by saphenous vein smooth muscle cells (A) and fibroblasts (B) from veins that developed stenosis (open bars) compared to. veins that remained patent (closed bars). Values are the mean ± SEM of fold of control values of ³H-thymidine incorporation after treatment with the indicated growth factors. Values for N are indicated within the bars.

Figure 2

Effect of heparin (100 μg/ml) on PDGF-BB- mediated ³H-thymidine incorporation (A; *-P<.05 comparing PDGF-BB plus heparin vs. PDGF-BB alone) and on thrombin-mediated ³H-thymidine incorporation (B; *- P<.05 comparing thrombin plus heparin vs. thrombin alone). SMC: smooth muscle cells; Fibs: fibroblasts; values for N are indicated in the bars.