Abstract
Treatment with hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors has been accompanied by a reduced risk of cardiovascular events. Rapid onset of clinical benefit and weak correlations between plasma low density lipoprotein-cholesterol levels and coronary lumen change or cardiovascular events indicates that nonlipid mechanisms are involved in this beneficial effects with HMG-CoA reductase inhibitors. Furthermore, more rapid onset of clinical benefit with HMG-CoA reductase inhibitors in patients with acute coronary syndromes or acute myocardial infarction than in those with stable coronary heart disease suggest that HMG-CoA reductase inhibitors facilitate repair of ruptured or ulcerated atherosclerotic plaque, facilitate plaque stabilization and/or reduce thrombus formation on ruptured plaques. Treatment with HMG-CoA reductase inhibitors improved endothelial dysfunction in patients with hypercholesterolemia and this improvement in endothelial function was not correlated with reduction in total serum cholesterol levels. Similarly, reduction in endothelial pre-proendothelin mRNA expression and endothelin synthesis and blood pressure lowering with HMG-CoA reductase inhibitors occurred independent of lipid-lowering. Finally, HMG-CoA reductase inhibitors increased endothelial nitric oxide levels i.e. upregulated endothelial nitric oxide synthetase expression via post-transcriptional mechanisms and prevented its down-regulation by oxidized LDL-C. HMG-CoA reductase inhibitors have been shown to modulate the immune response by inhibiting activation of immune-competent cells such as macrophages, and antigen presentation to macrophages by T cells. Treatment with HMG-CoA reductase inhibitors can reduce expression, production and circulating levels of chemokines (monocyte chemoattractant protein-1) and proinflammatory cytokines [tumor necrosis factoralpha, interleukin (IL)-6 and IL-1beta]. HMG-CoA reductase inhibitors reduced inflammation in human atheroma: significantly fewer macrophages and T cells, less oxidized LDL-C and higher collagen content. In addition, treatment with HMG-CoA reductase inhibitor led to decreased cell death within the atheroma. Treatment with these agents also reduced expression of inducible cellular adhesion molecules, decreased secretion of metalloproteinases by macrophages, reduced vascular smooth muscle cell apoptosis. Lastly, HMG-CoA reductase inhibitors appear to have important effects on the thrombogenesis: reduced expression of tissue factor production and activity; increased production of tissue factor package inhibitor; decreased platelet thrombus formation and improved fibrinolysis as a result of lowered plasminogen activator inhibitor-1 levels. As the pluripotential cardioprotective mechanisms of HMG-CoA reductase inhibitors are further elucidated, it is envisaged that treatment with HMG-CoA reductase inhibitors will be initiated earlier and more frequently in patients with hypercholesterolemia.
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