Nitrite-generated NO circumvents dysregulated arginine/NOS signaling to protect against intimal hyperplasia in Sprague-Dawley rats

Abstract

Vascular disease, a significant cause of morbidity and mortality in the developed world, results from vascular injury. Following vascular injury, damaged or dysfunctional endothelial cells and activated SMCs engage in vasoproliferative remodeling and the formation of flow-limiting intimal hyperplasia (IH). We hypothesized that vascular injury results in decreased bioavailability of NO secondary to dysregulated arginine-dependent NO generation. Furthermore, we postulated that nitrite-dependent NO generation is augmented as an adaptive response to limit vascular injury/proliferation and can be harnessed for its protective effects. Here we report that sodium nitrite (intraperitoneal, inhaled, or oral) limited the development of IH in a rat model of vascular injury. Additionally, nitrite led to the generation of NO in vessels and SMCs, as well as limited SMC proliferation via p21 Waf1/Cip1 signaling. These data demonstrate that IH is associated with increased arginase-1 levels, which leads to decreased NO production and bioavailability. Vascular injury also was associated with increased levels of xanthine oxidoreductase (XOR), a known nitrite reductase. Chronic inhibition of XOR and a diet deficient in nitrate/nitrite each exacerbated vascular injury. Moreover, established IH was reversed by dietary supplementation of nitrite. The vasoprotective effects of nitrite were counteracted by inhibition of XOR. These data illustrate the importance of nitrite-generated NO as an endogenous adaptive response and as a pathway that can be harnessed for therapeutic benefit. IntroductionVascular disease contributes significantly to morbidity and mortality in the developed world (1). Current treatments for this disease process, including surgical bypass and percutaneous interventions, are limited by the formation of intimal hyperplasia (IH) and restenosis (2). IH is an exaggerated healing process initiated by injury and characterized by platelet aggregation, leukocyte chemotaxis, extracellular matrix changes, endothelial cell apoptosis, and vascular SMC proliferation and migration (3). Investigations into vascular biology have led to the association of vascular pathology with decreased bioavailability of NO. NO is endogenously formed in the vascular endothelium by NOS using l-arginine as a substrate (4). The decreased bioavailability may occur secondary to increased consumption of NO by reactive oxygen species within the injured vessel wall or impaired synthesis of NO, possibly via decreased endothelial NO synthase, eNOS uncoupling, or dysregulation of l-arginine metabolism.l-Arginine is an important substrate for both NOS and arginase-1 enzymes, and increased arginase activity can deplete substrate availability for NO production. Interestingly, arginase-1 produces l-ornithine and activates the ornithine decarboxylase

Arginase inhibition prevents bleomycin-induced pulmonary hypertension, vascular remodeling, and collagen deposition in neonatal rat lungs

“…This is in accordance with the observations in our current experiments, in which the concentrations of NOx in lung were reduced in bleomycin-treated rats, despite the finding that NOS2 expression was increased significantly. A similar discrepancy between NOS2 expression and NO production can also be observed in arterial injury models, where NOS2 expression is induced (57,64), but the simultaneous increase in arginase I compromises NO synthesis at the site of injury (1).…”

Antiinflammatory actions of inorganic nitrate stabilize the atherosclerotic plaque

“…This effect on smooth muscle may seem counterintuitive. It has been long known that NO inhibits smooth muscle proliferation with evidence of this effect both in vitro (31) and in vivo (32), and that nitrite also exerts inhibitory effects on proliferation in a vascular injury model (33). We propose that the accumulation of smooth muscle within the plaque is likely an indirect effect of reduced macrophage content.…”

Mice Heterozygous for the Xanthine Oxidoreductase Gene Facilitate Lipid Accumulation in Adipocytes

“…1 It has been reported that XOR is a critical source of reactive oxygen species (ROS) and nitric oxide and also plays an important role in a variety of physiological 2 and pathophysiological conditions, such as ischemia-reperfusion injury, 3 endothelial dysfunction in diabetes mellitus, 4 and various cardiovascular diseases. [5][6][7][8][9] Furthermore, XOR is a structural component of membraneencapsulated milk fat globules, 10 and mice lacking XOR have defects in fat droplet secretion. 11 We also showed that XOR gene disruption induced the deletion of uric acid and the accumulation of triglyceride-rich substances and crystals in the renal tubules, with increased expression of adipogenesisrelated genes such as peroxisome proliferator-activated receptor (PPAR) γ and the CCAAT enhancer-binding proteins (C/ EBP) β and C/EBPα.…”