Effect Of Tacrolimus On Intimal Hyperplasia In Autogenous Vein Grafts Of Rats

Objective Coronary artery disease (CAD) is the pathological accumulation of atherosclerotic plaque in the epicardial coronary artery lumen, resulting in its narrowing and occlusion. The restoration of coronary artery blood flow as early as possible is vital to salvaging the myocardium.And the primary way to treat the disease is to make a surgical bypass of the blocked segment of the coronary artery using autologous vascular grafts which is called coronary artery bypass grafting (CABG). The saphenous vein (SV) is still used as a bypass conduit, since it is expendable in most patients, easy to work with, adequate in length for many anastomoses, easy to harvest and its large conduit。 The major setback is its low patency rate。There are many approaches to resist the graft failure such as "No-touch technique"and "endoscopic vein-graft harvesting"of SV,the use of antiplatelet agents, Gene therapy etc.However, there is no significantly change in the long-term patency rate. For now how to gain an available long term patency rate in vein graft after CABG become a hot spot of research. We try to find the effect of tacrolimus on intimal hyperplasia in autogenous vein grafts of rats by in vivo and vitro exprements, and provide a reference for medication of graft failure after CABG.Methods Twenty-eight male Sprague-Dawley rats which weigh 200-240g, were randomly divided into two groups. Animals in the treatment groups had daily intramuscular injections of tacrolimus at 0.2mg/kg (n=14).The control group had equal volume of normal saline。After 1 week, the right common carotid arteries were reconstructed using homolateral external jugular vein in rats. The vein grafts were harvested at the time point of two or four week after surgery. The sample was cut to pathological section prepared for microscopic examination,and the photographs were made. And the neointima thickness was measured by Computer image analysis software. Expression of cell-cycle regulatory protein 27 was determined after harvesting using antibodies against p27 with β-actin as a loading control. In vitro, human saphenous vein smooth muscle cells (HSVSMC) were cultured for several days. For proliferation experiment, a dose-response relationship was established by exposing HSVSMC to tacrolimus of 0.4nmol·L-1,4nmol·-L-1,40nmol·L-1,400nmol·L-1,4000nmol·L-1. MTT was performed to detect the cell counts. For migration experiment, HSVSMC were treated with different dose of tacrolimus plus PDGF-bb. And the migration was assessed by transwell after 24 hours.Results Tacrolimus significantly attenuated intimal thickening compared with the control group both at 2 week[(20.56±4.55)μm VS (28.35±5.86)μm,P <0.05]and 4 weeks[(36.22±6.33) μm VS (62.13±7.60) μm,P<0.01]. For western blot expression detection, the expression of p27 in treatment group was markedly higher than that in control group after 2 weeks. And the tendency was the same after 4 weeks. In the proliferation experiment, tacrolimus administration significantly reduced cell proliferation from both low and higher dose group compared with negative group, but failed with blank control (P< 0.05).For the migration experiment, the migrated cells are significantly lower than that in control group(P<0.01).Conclusion Tacrolimus can obviously inhibit hyperplasia of intimal thickness after venous transplantation, which may be related to the higher expression of p27 and inhibition of smooth muscle cell proliferation.