Atheroma Stabilizing Effects of Simvastatin Due to Depression of Macrophages or Lipid Accumulation in the Atheromatous Plaques of Coronary Plaque-prone WHHL Rabbits

Clinical studies showed that both hydrophilic and lipophilic statins reduce coronary events although in vitro studies demonstrated that lipophilic statins inhibited proliferation of arterial smooth muscle cells. Therefore, we examined whether lipophilic simvastatin reduces smooth muscle cells in atheromatous plaque and how simvastatin affects stability of atheroma in vivo. Coronary atherosclerosis-prone WHHLCA rabbits aged 10 months were given simvastatin (15 mg/kg) orally for 52 weeks and examined the serum lipid levels, plasma drug concentration, and aortic and coronary atherosclerosis. Compared to the placebo group, the plasma cholesterol levels decreased by about 20%. In the simvastatin group, the lipid component (macrophages+extracellular lipids) was decreased in the coronary and aortic atheroma, despite no decrease in the fibromuscular components. Consequently, the frequency of vulnerable plaque decreased. In the coronary plaque of the simvastatin group, PCNA-positive cells (which appeared to be macrophages) of the plaques decreased but the TUNEL-positive cells did not show significant change. Finally, fully differentiated smooth muscle cells increased in the aortic lesions of the simvastatin group. In conclusion, our results suggest that simvastatin did not depress the fibromuscular components in atheromatous plaques and the plaque-stabilizing effects were due to the reduction of macrophages/lipid deposits.