placing external non-restrictive macro-porous stents around porcine vein grafts prevents
neointima formation and medial thickening in both the short and long term. Whether
the porosity of the stent material influences this effect, however, has not been determined.
Therefore, the effect on neointimal and medial thickening of external macro-porous
(polyester) and micro-porous (polytetrafluorethylene) stents of equal diameter were
compared. The effect on expression of platelet-derived growth factor (PDGF), a potent
mediator of vascular smooth muscle cell migration and proliferation and its receptors
was also investigated.
saphenous vein-carotid artery interposition grafting was performed in Landrace pigs
with external placement of 8 mm diameter macro- and micro-porous stents contralaterally.
One month after surgery, graft wall dimensions, PDGF and PDGF receptor expression
and cell proliferation using proliferating cell nuclear antigen (PCNA) were measured
on histological sections. Macro-porous stents significantly reduced neointimal and
medial thickening compared with micro-porous stents (0.1+/-0.02 vs. 0.25+/-0.03 mm,
P<0.002, and 0.10+/-0.02 vs. 0.17+/-0.02 mm, P<0.014, respectively). Macro-porous
stents significantly reduced the percentage of cells expressing PDGF and PCNA, compared
with micro-porous stents (36+/-9 vs. 80+/-7, P < 0.002, and 11+/-3 vs. 21+/-2, P <
0.02, respectively). The percentage of cells expressing PDGF receptors was similar
with both the stent types. Adventitial microvessel formation occurred across macro-porous
stents but was markedly suppressed by micro-porous stents.
porosity is crucial to the efficacy of external stents in reducing neointima formation
in porcine vein grafts. Decreases in PDGF expression and cell proliferation accompany
the reduction in neointima formation. In addition, macro-porous stents allow adventitial
microvessels to connect with the vasculature outside the stent, thereby potentially
improving oxygenation. Although external stenting is highly effective in reducing
neointima formation after vein grafting, the properties of the stent material necessary
for this effect have not been defined. This study establishes that macro-porosity
is one essential feature required to reduce PDGF expression cell proliferation and
neointima formation.