Carvedilol, a novel vasodilating beta-blocker with the potential for cardiovascular organ protection

Abstract

Carvedilol is a vasodilating beta-blocker currently marketed for the treatment of mild to moderate hypertension and application is being filed to the FDA for treatment of congestive heart failure. Carvedilol reduces peripheral vascular resistance by blocking arterial alpha 1-adrenoceptors, thereby producing vasodilation, while preventing reflex tachycardia by blocking cardiac beta 1- and beta 2-adrenoceptors. In addition to the safety and efficacy of carvedilol as an antihypertensive agent, experimental studies indicate that carvedilol also provides significant cardioprotection in animal models of acute myocardial infarction as well as protection against the vascular remodelling that occurs following injury of the vasculature. Recent pharmacological studies have uncovered several novel properties of carvedilol which may function to protect the heart and vasculature from chronic pathological processes, such as ischaemia, atherosclerosis and the remodelling that occurs in the heart and blood vessels as a consequence of pressure overload, injury or shear stress. Specifically, carvedilol, likely as a result of the carbazol moiety, is a potent anti-oxidant. In physicochemical, biochemical and cellular assays carvedilol and several of its metabolites inhibit lipid peroxidation, scavenge oxygen free radicals, inhibit the formation of reactive oxygen radicals and prevent the depletion of endogenous antioxidants, such as vitamin E and glutathione. Moreover, carvedilol blocks the oxidation of low-density lipoproteins (LDL), and thereby prevents the formation of oxidized-LDL which is believed to stimulate foam cell formation and augment the development of atherosclerotic plaque. The ability of carvedilol to prevent the formation of oxidized LDL, in addition to the general anti-oxidant properties of the compound, results in the protection of the endothelium from oxygen free radical injury, and thereby prevents the subsequent events triggered by endothelial damage. Recently, carvedilol has also been shown to inhibit vascular smooth muscle cell proliferation and migration. Because carvedilol can inhibit vascular smooth muscle cell proliferation induced by a wide variety of mitogens (e.g. growth factors, angiotensin II, endothelin, thrombin), it is likely that the site of inhibition occurs at some point beyond the specific mitogen receptors, possibly at a distal common pathway that affects the smooth muscle cell cycle. These unique activities of carvedilol have also been confirmed in vivo in a rat model of neointimal formation following vascular injury by balloon angioplasty, where vascular smooth muscle cell migration and proliferation are the key processes involved in the formation of neointima leading to vascular stenosis. In this model, carvedilol suppressed neointimal growth to a remarkable extent ( > 85% inhibition of neointimal formation) at a dose that is similar to the antihypertensive dose used clinically in hypertensive patients. Taken together, these unique multiple actions of carvedilol provide not only for adequate control of elevated blood pressure, but may also provide for protection of the heart and vasculature from secondary damage due to hypertension itself, as well as from other causes, such as ischaemia, pressure overload, shear stress, vascular injury and atherosclerosis.