Nitrite Reduces Acute Lung Injury and Improves Survival in a Rat Lung Transplantation Model

Abstract

Ischemia/reperfusion injury (IRI) is the most common cause of early mortality following lung transplantation (LTx). We hypothesized that nitrite, an endogenous source of nitric oxide (NO), may protect lung grafts from IRI. Rat lung grafts were stored in preservation solution at 4• C for 6 hours. Both grafts and recipients were treated with nitrite. Nitrite treatment was associated with significantly higher levels of tissue oxygenation, lower levels of cytokines and neutrophil/macrophage infiltration, lower myeloperoxidase activity, reduced oxidative injury and increased cGMP levels in grafts than in the controls. Treatment with either a nitric oxide scavenger or a soluble guanylyl cyclase (sGC) inhibitor diminished the beneficial effects of nitrite and decreased cGMP concentrations. These results suggest that nitric oxide, generated from nitrite, is the molecule responsible for the effects of nitrite via the nitric oxide/sGC/cGMP pathway. Allopurinol, a xanthine oxidoreductase (XOR) inhibitor, abrogated the protective effects of nitrite, suggesting that XOR is a key enzyme in the conversion of nitrite to nitric oxide. In vitro experiments demonstrated that nitrite prevented apoptosis in pulmonary endothelial cells. Nitrite also exhibits longer survival rate in recipients than control. In conclusion, nitrite inhibits lung IRI following cold preservation and had higher survival rate in LTx model.

Dispelling dogma and misconceptions regarding the most pharmacologically targetable source of reactive species in inflammatory disease, xanthine oxidoreductase

“…Nitrite reductase activity has thus far been assigned to AO, sulfite oxidase and XOR with the majority of reports focused on the later (Li et al 2009;Millar et al 1998;Millar 2004;Wang et al 2014;Li et al 2001Li et al , 2005Li et al , 2008. Evidence for XO-catalyzed • NO formation has originated from basic biochemical studies with purified enzyme preparations as well as in vivo models of ischemia/reperfusion where salutary outcomes attributable to NO 2 − administration were abrogated by concomitant XOR inhibition (Alef et al 2011;Samal et al 2012;Pickerodt et al 2012;Sugimoto et al 2012;Zuckerbraun et al 2010;Baker et al 2007;Tripatara et al 2007;Webb et al 2004;Lu et al 2005). In the aggregate, these studies reveal a novel function for XOR as a source of salutary • NO; yet, they identify a significant dilemma as they were conducted using models similar to or the same as those that have previously revealed XOR inhibition, in the absence of NO 2 − treatment, to be of benefit.…”

Nitrite Confers Preconditioning and Cytoprotection After Ischemia/Reperfusion Injury Through the Modulation of Mitochondrial Function

“…function in a rat model of lung transplant (158,206). In these lung I/R models, nitrite decreased the inflammatory response as evidenced by attenuated neutrophil infiltration and decreased cytokine and myeloperoxidase levels.…”

“…Unlike NO, which has dichotomous effects in the setting of ischemia/reperfusion (I/R) (97,205), one of the most reproducible biological effects of nitrite is its ability to mediate protection when exogenously administered to an organ during or prior to a prolonged ischemic episode (49,50,60,86,98,170,195,206,226). It was not entirely surprising that nitrite confers cytoprotection when administered during ischemia due to its ability to be reduced to NO during hypoxic and acidic conditions, which are prevalent during ischemia (86,110).…”

Working with nitric oxide and hydrogen sulfide in biological systems

“…Putative mechanisms of nitrite action involve activation of pulmonary vascular smooth muscle soluble guanylate cyclase (sGC) and the canonical NO signaling cascade (10). Moreover, nitrite therapy also protects against pulmonary and vascular smooth muscle remodeling after injury and improves lung function after transplantation (4,88,111,139). Additionally, nitrite therapy protects against ALI induced by mechanical ventilation and inhaled chemical toxicants, in the latter of which the risk of developing reactive airways is also reduced (40,96,101,132).…”