Regulation of Cytokine-Induced Nitric Oxide Synthesis by Asymmetric Dimethylarginine

Abstract

Abstract-In response to vascular insults, inflammatory cytokines stimulate vascular smooth muscle cells (SMCs) to express an inducible isoform of nitric oxide synthase (iNOS). Asymmetric dimethylarginine (ADMA), an endogenous NO synthase inhibitor, is metabolized by dimethylarginine dimethylaminohydrolase (DDAH). To determine whether the ADMA-DDAH system regulates cytokine-induced NO production, cultured rat SMCs were exposed to interleukin-1␤ (IL-1␤). IL-1␤ (1 to 100 U/mL) dose-dependently stimulated not only iNOS but also DDAH expression and enzyme activity, accompanied by an increase in NO metabolite and by a decrease in ADMA content in culture media. A DDAH inhibitor (4124W, 5 mmol/L) augmented ADMA production (PϽ0.01) and decreased NO synthesis (PϽ0.01) in IL-1␤-stimulated SMCs. On the other hand, an adenovirus-mediated overexpression of DDAH reduced ADMA and enhanced NO production. Exogenous administration of NO donors (SNAP and SIN-1) dose-dependently increased NO metabolite in the culture media but had no effect on ADMA. Our results indicate two mechanisms of IL-1␤-induced NO synthesis: the direct stimulation of the expression of iNOS and the indirect stimulation of iNOS activity by upregulating DDAH and reducing ADMA. The ADMA-DDAH system may be another regulatory mechanism of inflammation-mediated NO production for human vascular diseases. Key Words: nitric oxide Ⅲ nitric oxide synthase Ⅲ interleukins Ⅲ smooth muscle Ⅲ atherosclerosis N itric oxide (NO) plays an important role in the regulation of not only vascular tone but also architecture. There are two types of nitric oxide synthase in vessels, endotheliumderived NO synthase (eNOS) and inducible NO synthase (iNOS); the former is constitutively present in the endothelium, and the latter is induced by the inflammatory stimuli in the vascular wall. 1,2 N G ,N G Ϫ Dimethyl-L-arginine (ADMA) is an endogenous NOS inhibitor that inhibits activities of both eNOS and iNOS. We and others have demonstrated that increased plasma levels of ADMA are associated with hypertension, 3 hypercholesterolemia, 4 and the clustering of coronary risk factors in vivo in humans. 5 Furthermore, a close association has been found between plasma ADMA level and carotid intima-media thickness 5 or the severity of peripheral arterial occlusive diseases. 6 These lines of evidence suggest that ADMA is involved in the pathophysiology of human vascular diseases. ADMA is metabolized by a key limiting enzyme, N G ,N G Ϫ dimethylarginine dimethylaminohydrolase (DDAH). 7-9 DDAH is identified in human aortic tissues. 10 -13 It has been reported that oxidized low-density lipoprotein upregulates the synthesis of ADMA in cultured human endothelial cells in association with decreased activity of DDAH. 13 Collectively, the ADMA-DDAH system may be involved in the regulation of endogenous NO synthesis. 14 -17 Inflammatory response plays a crucial role in human vascular diseases. 18 Monocyte-derived macrophages, recognized at every stage of disease, promote continuous activation of the cytokine ...

Asymmetric Dimethylarginine and 3-Nitrotyrosine Levels of the Heart Tissue aſter Endotoxemia

“…In the other in vivo study, it has been reported that E. coli mediated endotoxemia decreases the plasma arginine level but ADMA did not change [19]. Ueda et al demonstrated exogenous administration of NO donors dose-dependently increased NO synthesis in the cultured media but had no effect on ADMA and L-arginine levels [20]. In conclusion we could not find a link between ADMA, L-arginine concentrations and ONOO-production in the heart after endotoxin administration.…”

Inflammation and reduced endothelial function in the course of severe acute heart failure

“…In vitro studies on endothelial cells, however, have demonstrated that oxidative stress, stimulation with TNFa, and nitrosative stress resulting from an induction of inducible NO synthase cause an accumulation of ADMA secondary to reduced DDAH activity. 48,49 However, increased DDAH activity secondary to stimulation with inflammatory cytokine have been reported in rat vascular smooth muscle cells, 50 and a mechanistic knowledge of the important metabolic responses and the regulation of the NOsystem and vasculature is still warranted.…”

C-Reactive Protein and Asymmetric Dimethylarginine: Markers or Mediators in Cardiovascular Disorders?

“…There is conflicting evidence about TNF-polymorphisms and the effects on plasma CRP concentrations [187,189]. Carriers of a genetic variant in the Toll-like Glucose protein / activity [149] Erythropoietin activity [147] IL-1 activity [154] Oestrogen activity [155] Retinoic acid DDAHII mRNA/protein/activity [156] Shear stress DDAHI expression [157] en Identified.…”