Ribonucleotide reductase inhibitors reduce atherosclerosis in a double-injury rabbit model

Abstract

Atheroproliferative disorders such as atherosclerosis are an important health problem and one of the leading causes of morbidity and mortality in the United States. Minimally invasive therapeutic procedures, including angioplasty with stent deployment, are used frequently for obstructive coronary artery disease. However, restenosis, a proliferative vascular response, is a common sequela to this procedure. The current study investigated the effect of inhibiting ribonucleotide reductase (RR), an enzyme necessary for cellular proliferation, in an attempt to ameliorate the proliferative response. Two RR inhibitors, didox and hydroxyurea, were chosen for their potent antiproliferative properties. Studies were carried out by using a double-injury rabbit model, in which endothelial denudation was followed by the administration of a high-fat diet. At 4 wk after initial endothelial denudation, the developing atherosclerotic lesion was subjected to transluminal balloon dilation to simulate clinical intervention with percutaneous transluminal angioplasty. The degree of restenosis and atheroproliferation was assessed at 8 wk. Histologic evaluation of the lesion demonstrated that treatment with didox and hydroxyurea significantly decreased lesion area and lumen loss. These results suggest that RR inhibition may be an effective new tool for the treatment of atheroproliferative disorders.

Figure 1.

Fluoroscopy image depicting a 3-mm wire-guided balloon in the left common carotid artery (CCA) of a New Zealand White rabbit under general anesthesia. Balloons were inserted through the left or right femoral artery and inflated to 12 atm. The inflated balloons were moved in a forward and retrograde direction to produce endothelial injury.

Figure 2.

Effect of RR inhibitors on atherosclerosis. The groups comprised noninjured (control), untreated injured (injured), injured and didox-treated (200 mg/kg; Didox), and injured and hydroxyurea-treated (400 mg/kg; HU) animals. (A) Trichrome-stained sections from control, injured, and treated rabbits. (B) Atheroma area. (C) Lumen area. Data are presented as mean ± SE (n = 5 or) 6; *, value significantly (P < 0.05) from that of the control group; #, value significantly (P < 0.05) different from that for injured group.

Figure 3.

Effects of RR inhibitors on vascular reactivity. Endothelium-dependent relaxation was measured in untreated (circles), didox-treated (200 mg/kg; triangles), and hydroxyurea-treated (400 mg/kg; squares) animals. Rings were constricted with phenylephrine (0.5 µM), and the relaxation response to acetylcholine (Ach; 10 nM to 5 µM) was measured on a wire myograph. (A) Vascular relaxation response to acetylcholine from ipsilateral injured vessels. (B) Vascular relaxation response to acetylcholine from contralateral noninjured vessels. Data are presented as percentage relaxation compared to control (mean ± SE; n = 6). *, Value significantly (P < 0.05) different from that for control animals.