Remodeling of the coronary artery after vascular injury

Vascular injury, such as angioplasty, induces a complex healing process that is analogous to generalized wound healing. Following initial injury, platelet thrombi and an acute inflammatory response occur, followed by cellular inhibition by monocytes/macrophages, proliferation of vascular smooth muscle cells, and extracellular matrix deposition. The injury repair concludes with organization of the matrix and reendothelialization. Recent studies suggest that restenosis or renarrowing after vascular injury is due to two components: a cellular proliferative process leading to intimal hyperplasia and remodeling of the vessel with a change in vessel geometry. Animal and clinical studies have shown that at least 60% of restenosis can be explained by unfavorable remodeling with vessel constriction rather than intimal hyperplasia. Although a number of factors appear to be associated with remodeling, alterations in extracellular matrix metabolism may be most important.

Troglitazone inhibits vascular smooth muscle cell growth and intimal hyperplasia

Vascular smooth muscle cell (VSMC) proliferation and migration are responses to arterial injury that are highly important to the processes of restenosis and atherosclerosis. In the arterial balloon injury model in the rat, platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) are induced in the vessel wall and regulate these VSMC activities. Novel insulin sensitizing agents, thiazolidinediones, have been demonstrated to inhibit insulin and epidermal growth factor-induced growth of VSMCs. We hypothesized that these agents might also inhibit the effect of PDGF and bFGF on cultured VSMCs and intimal hyperplasia in vivo. Troglitazone (1 microM), a member of the thiazolidinedione class, produced a near complete inhibition of both bFGF-induced DNA synthesis as measured by bromodeoxyuridine incorporation (6.5+/-3.9 vs. 17.6+/-4.3% cells labeled, P < 0.05) and c-fos induction. This effect was associated with an inhibition (by 73+/-4%, P < 0.01) by troglitazone of the transactivation of the serum response element, which regulates c-fos expression. Inhibition of c-fos induction by troglitazone appeared to occur via a blockade of the MAP kinase pathway at a point downstream of MAP kinase activation by MAP kinase kinase. At this dose, troglitazone also inhibited PDGF-BB-directed migration of VSMC (by 70+/-6%, P < 0.01). These in vitro effects were operative in vivo. Quantitative image analysis revealed that troglitazone-treated rats had 62% (P < 0.001) less neointima/media area ratio 14 d after balloon injury of the aorta compared with injured rats that received no troglitazone. These results suggest troglitazone is a potent inhibitor of VSMC proliferation and migration and, thus, may be a useful agent to prevent restenosis and possibly atherosclerosis.