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

Nitrite, a dietary constituent and endogenous signaling molecule, mediates a number of physiological responses including modulation of ischemia/reperfusion injury, glucose tolerance and vascular remodeling. While the exact molecular mechanisms underlying nitrite’s actions are unknown, current paradigm suggests that these effects depend on the hypoxic reduction of nitrite to nitric oxide (NO). Mitochondrial biogenesis is a fundamental mechanism of cellular adaptation and repair. However, the effect of nitrite on mitochondrial number has not been explored. Herein, we report that nitrite stimulates mitochondrial biogenesis through a mechanism distinct from NO. We demonstrate that nitrite significantly increases cellular mitochondrial number by augmenting the activity of adenylate kinase, resulting in AMP kinase phosphorylation, downstream activation of sirtuin-1, and de-acetylation of PGC1, the master regulator of mitochondrial biogenesis. Unlike NO, nitrite-mediated biogenesis does not require the activation of soluble guanylate cyclase and results in the synthesis of more functionally efficient mitochondria. Further, we provide evidence that nitrite mediates biogenesis in vivo. In a rat model of carotid injury, two weeks of continuous oral nitrite treatment post-injury prevents the hyperproliferative response of smooth muscle cells. This protection is accompanied by a nitrite-dependent upregulation of PGC1 and increased mitochondrial number in the injured artery. These data are the first to demonstrate that nitrite mediates differential signaling than NO. They show that nitrite is a versatile regulator of mitochondrial function and number both in vivo and in vitro, and suggest that nitrite-mediated biogenesis may play a protective role in the setting of vascular injury.

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Background Prior studies comparing endografts with suprarenal and infrarenal fixation for endovascular abdominal aortic aneurysm repair (EVAR) have found conflicting results and did not account for differences in patient selection. This study aims to evaluate the differences in outcomes among surgeons who routinely use either suprarenal or infrarenal fixation, as well as all surgeons in the Vascular Study Group of New England (VSGNE). Methods All patients undergoing EVAR in the VSGNE from 2003–2014 were identified. All ruptured aneurysms, repairs with concomitant procedures, and infrequently used stent grafts (<50) were excluded. Suprarenal endografts included Talent, Zenith, and Endurant; infrarenal endografts included AneuRx and Excluder. Grafts were compared among surgeons who used only one type of endograft (suprarenal or infrarenal) for >80% of cases, as well as all surgeons. Multivariable regression and Cox hazard models were utilized to account for patient demographics, comorbidities, operative differences, and procedure year. Results This study identified 2,574 patients (Suprarenal: 1,264, Infrarenal: 1,310), with 888 endografts placed by routine users (Suprarenal: 409, Infrarenal: 479). There were no differences in baseline comorbidities, including estimated glomerular filtration rate, between suprarenal and infrarenal fixation, or between patients with endografts placed by routine and nonroutine users. Patients treated with suprarenal endografts received more contrast amongst all users (102mL vs. 100mL, P = .01) and routine users (110mL vs. 88mL, P < .01), but other vascular and operative details were similar. Amongst all users, patients treated with suprarenal grafts had higher rates of creatinine increase >0.5mg/dl (3.7% vs. 2.0%, P = .01), length of stay >2d (27% vs. 19%, P < .01), and discharge to skilled nursing facility (9.2% vs. 6.7%, P = .02). There were no differences in 30-day or one-year mortality. Following adjustment, suprarenal stent grafts remained associated with an increased risk of renal deterioration (OR: 2.0, 95% CI: 1.2–3.4) and prolonged length of stay (1.8, 1.4–2.2). Amongst routine users, suprarenal fixation was also associated with higher rates of renal dysfunction (3.7% vs. 1.3%, P = .02; OR 2.9, 95% CI: 1.1–7.8). Conclusion Despite potential differences in patient selection, endografts with suprarenal fixation among all users and routine users were associated with higher rates of renal deterioration and longer hospital length of stay. Longer-term data are needed to determine the duration and severity of renal function decline and to identify potential benefits of decreased migration or endoleak.