Recombinant human thrombomodulin inhibits arterial neointimal hyperplasia after balloon injury

Smooth muscle cell proliferation is a major pathophysiologic factor in injury-induced neointimal hyperplasia and recurrent stenosis. We have demonstrated that recombinant human thrombomodulin (rTM) inhibits thrombin-induced arterial smooth muscle cell proliferation in vitro. The purpose of this study was to investigate the effect of rTM on neointimal hyperplasia in vivo.

A rabbit femoral artery balloon injury model was used. Bilateral superficial femoral arteries were deendothelialized with a 2F arterial embolectomy catheter. rTM (145 microg/kg; 2.0 microg/mL in circulation) or Tris-hydrochloride vehicle control was administered intravenously during the procedure, then either discontinued (group A) or administered twice daily for an additional 48 hours (group B). Rabbits were euthanized at 4 days and at 1, 2, and 4 weeks, and femoral artery specimens were prepared with in situ perfusion fixation and paraffin embedding. Luminal, intima, media, and whole artery areas were quantitated with digital imaging computerized planimetry. Intima-media and lumen-whole artery ratios were calculated. The injury-induced inflammatory reaction was also evaluated with light microscopy, scanning and transmission electron microscopy, and immunohistochemical and immunohistofluorescence staining.

In the buffer control group, neointimal hyperplasia after femoral artery balloon injury was evident at 2 weeks, and was pronounced at 4 weeks (P <.0001). Infusion of rTM significantly inhibited intimal hyperplasia at both 2 and 4 weeks (P <.0001). In group A, rTM reduced the intima-media ratio by 27% and 39% at 2 and 4 weeks, respectively. Extended administration of rTM (group B) resulted in inhibition of hyperplasia by 57% and 30% at 2 and 4 weeks, respectively, but failed to reach significance compared with the shorter exposure. rTM infusion significantly inhibited thrombosis (8.1-fold) compared with the buffer control group (P =.012). rTM had no significant effect on lumen area or lumen-whole artery ratio, but treated arteries demonstrated significantly less compensatory dilatation (P =.045), as measured by whole artery area in response to less intimal hyperplasia. rTM administration inhibited platelet adhesion and inhibition of neutrophil infiltration to a degree that approached statistical significance (P =.0675).

Systemic intravenous administration of rTM significantly decreases neointimal hyperplasia and improves patency in the rabbit femoral artery after balloon injury. In addition to exhibiting antithrombotic and antiproliferative effects, rTM may also invoke an anti-inflammatory mechanism, and may alter vascular remodeling in a multidimensional role to inhibit recurrent stenosis after arterial injury.