Role of Inflammation and Endothelial Nitric Oxide Synthase in Coronary Vasospasm

Autor: Ming Jui Hung, 洪明銳
Rok vydání: 2010
Druh dokumentu: 學位論文 ; thesis
Popis: 98
Background Coronary vasospasm (CVsp) plays an important role in a wide variety of ischemic heart disease, not only in variant angina but also in other forms of angina pectoris, myocardial infarction, and sudden death. The mechanism remains elusive. Previous studies involving histological evaluation in patients with variant angina have reported evidence of intimal injury indicating an early inflammatory coronary artery condition. Plasma interleukin-6 (IL-6) levels are increased in cardiovascular disease, including atherosclerosis, diabetes mellitus, hypertension as well as coronary vasospasm. The exposure of endothelial cells to proinflammatory cytokines leads to the expression of cell surface adhesion molecules and impairs endothelium-dependent vascular relaxation. Endothelial nitric oxide synthase (eNOS) has been reported to be quantitatively associated with caveolin-1 in endothelial cells. In basal condition, eNOS becomes hyperactivated in the absence of caveolin-1. In the present study, we hypothesize that: 1) inflammatory markers may be elevated in patients with coronary vasospastic angina (CVsA); 2) IL-6 might affect the eNOS–caveolin-1 interaction and result in decreased nitric oxide bioavailability in the setting of low-grade inflammation; 3) IL-6 signal pathway may play a role in the expression and activation of eNOS and caveolin-1. Methods In this study, we first measured the circulating level of monocyte count, high-sensitivity C-reactive protein (hs-CRP), IL-6, monocyte-chemoattractant protein-1 (MCP-1), soluble intercellular adhesion molecule-1 (sICAM-1) and soluble vascular adhesion molecule-1 (sVCAM-1) in patients with CVsA and no significant obstructive coronary artery disease (CAD), and investigate their relations to CVsA and determine the most independent association marker. Secondly, we tested the hypothesis that IL-6 affects the eNOS–caveolin-1 interaction and results in decreased nitric oxide bioavailability in the setting of low-grade inflammation in human umbilical vein endothelial cells (HUVECs). Finally, the potential role of IL-6 signal pathway on eNOS and caveolin-1 in HUVECs was investigated in vitro. Results We demonstrated that the peripheral blood monocyte count and serum hs-CRP were increased in patients with CVsA and no significant obstructive CAD. There was an independent association between increased peripheral monocyte count, elevated serum hs-CRP level and diagnosis of CVsA. Subsequently, the level of serum inflammatory markers were demonstrated to be highest in the acute coronary syndrome group and lowest in the control group, with intermediate values observed in the stable angina pectoris and CVsp group, with the exception of sICAM, the level of which was highest in the CVsp group. Multivariate analysis showed that log (IL-6) was independently associated with a diagnosis of CVsA in patients without significant obstructive CAD. In the laboratory study, we demonstrated that IL-6 inhibited the phosphorylation of eNOS at Ser1177 and the bradykinin-stimulated nitric oxide production; however, eNOS protein expression and mRNA level were not changed. In addition, IL-6 inhibited bradykinin-stimulated Akt phosphorylation at Ser473 and Thr 308 without affecting the Akt protein expression. IL-6 did not alter the mRNA level of caveolin-1; however, the caveolin-1 protein level was significantly increased dose-dependently. The binding of eNOS and caveolin-1 in endothelial cells, as demonstrated by co-immunoprecipitation assay, was increased by IL-6 treatment. IL-6 treatment was found to stabilize caveolin-1 protein and its half-life was estimated to prolong from 7.5 hr to longer than 12 hr. Furthermore, treatment with PD98059 and short interference RNA of extracellular signal-regulated kinase gene reversed the effects of IL-6 on eNOS and caveolin-1. Conclusions Our results indicated that inflammation can exist in CVsp without significant obstructive CAD with the most independent association marker of IL-6. In addition to decreasing Akt phosphorylation, the results of this study further demonstrate, for the first time, the molecular mechanism underlying the effect of IL-6 to decrease the nitric oxide bioavailability by increasing the half-life and therefore the protein levels of caveolin-1. The increased caveolin-1 proteins bind more eNOS and consequently decrease eNOS activation by reducing the Ser1177 phosphorylation.
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