Effects of Systemic Inflammation on Endothelium-Dependent Vasodilation

Abstract

The importance of inflammation in the pathogenesis of atherosclerosis is well established. The vascular endothelium contributes to and is affected by the inflammatory process. For example, a variety of cytokines have the ability to "activate" the endothelium and thereby promote expression of adhesion molecules and chemotactic factors that accelerate the inflammatory process and direct accumulation of leukocytes to specific sites in the arterial tree. In experimental systems, activation of endothelial cells is also associated with a loss of the biologic activity of endothelium-derived nitric oxide, an effect that accelerates the inflammatory process and also promotes local thrombosis and impairs local control of vasomotor tone. Consistent with these experimental studies, recent studies have provided evidence that inflammation is associated with an impairment of nitric oxide-dependent responses in human subjects. This article will review the experimental and clinical studies that support the relevance of inflammation to nitric oxide bioactivity in human atherosclerosis.It is now well recognized that atherosclerosis is an inflammatory disease (Ross 1999). Systemic risk factors induce a state of inflammation that contributes to all stages of atherosclerosis from the initiating events in lesion formation to the latest phase when plaques rupture, thrombose, and produce clinical syndromes such as myocardial infarction or stroke (Libby et al. 2002). The importance of inflammation in atherosclerosis is supported by recent studies showing that elevated levels of inflammatory markers identify individuals with increased risk for cardiovascular events (Pearson et al. 2003). In particular, the acute phase reactant C-reactive protein (CRP) shows promise as a clinically useful marker of cardiovascular risk (Ridker 2003).The vascular endothelium is both affected by and contributes to the inflammatory process that leads to atherosclerosis. For example, proinflammatory factors "activate" endothelial cells to promote an atherogenic phenotype. The activated endothelium, in turn, expresses adhesion molecules and chemotactic factors that accelerate and localize the inflammatory process. An important consequence of endothelial activation is loss of the biologic activity of endotheliumderived nitric oxide. Investigators have argued that a broad alteration of endothelial function, including loss of nitric oxide under proinflammatory conditions, might be a critical mechanism that links systemic states of inflammation to atherosclerosis (Vallance et al. 1997). This article will review the recent studies that support the relevance of systemic inflammation to nitric oxide bioactivity in human subjects. The Endothelium as a Regulator of Vascular HomeostasisThe endothelium regulates vasomotor tone, blood fluidity, growth of vascular smooth muscle cells, and local inflammation by elaborating a number of paracrine factors, including nitric oxide (Widlansky et al. 2003a). Endothelium-derived nitric oxide is a potent vasodilator and acts ...

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