In normal conditions, nitric oxide (NO) is oxidized to the anion nitrite, but in hypoxia, this nitrite may be reduced back to NO by the nitrite reductase action of deoxygenated hemoglobin, acidic disproportionation, or xanthine oxidoreductase (XOR). Herein, is investigated the effects of topical sodium nitrite administration in a rat model of renal ischemia/reperfusion (I/R) injury. Rats were subjected to 60 min of bilateral renal ischemia and 6 h of reperfusion in the absence or presence of sodium nitrite (30 nmol) administered topically 1 min before reperfusion. Serum creatinine, serum aspartate aminotransferase, creatinine clearance, fractional excretion of Na ؉ , and plasma nitrite/nitrate concentrations were measured. The nitrite-derived NO-generating capacity of renal tissue was determined under acidic and hypoxic conditions by ozone chemiluminescence in homogenates of kidneys that were subjected to sham, ischemia-only, and I/R conditions. Nitrite significantly attenuated renal dysfunction and injury, an effect that was abolished by previous treatment of rats with the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide (2.5 mol intravenously 5 min before ischemia and 50 nmol topically 6 min before reperfusion). Renal tissue homogenates produced significant amounts of NO from nitrite, an effect that was attenuated significantly by the xanthine oxidoreductase inhibitor allopurinol. Taken together, these findings demonstrate that topically administered sodium nitrite protects the rat kidney against I/R injury and dysfunction in vivo via the generation, in part, of xanthine oxidoreductase-catalyzed NO production. These observations suggest that nitrite therapy might prove beneficial in protecting kidney function and integrity during periods of I/R such as those encountered in renal transplantation. U ntil recently, the nitrite anion was regarded merely as an inactive metabolite of nitric oxide (NO) oxidation produced under normal physiologic conditions, accounting for approximately 70% of the endogenous nitrite pool (1). However, we (2) and others (3) recently demonstrated that, far from being inactive, nitrite has marked protective effects in ischemia/reperfusion (I/R) injury of both the heart and the liver. Moreover, these studies demonstrate that the beneficial effects of nitrite are related to its reduction to NO, under ischemic conditions. J Am Soc NephrolThe generation of NO is attributed conventionally to the enzyme NO synthase (NOS), of which there are three isoforms. Endothelial NOS (eNOS)-derived NO plays an important role in determining and maintaining aspects of normal renal function, for instance proximal tubule sodium reabsorption (4,5), but in elevated concentrations, NO also contributes to renal pathophysiology (6), such as in proximal tubule ischemic injury (4). This dual nature of NO perhaps is an oversimplification, because NO either ameliorates or exacerbates renal injury, depending on the site and the rate of NO production and the chemical fate of NO (7,8). Further...

Abstract-Reduction of nitrite (NO 2Ϫ ) provides a major source of nitric oxide (NO) in the circulation, especially in hypoxemic conditions. Our previous studies suggest that xanthine oxidoreductase (XOR) is an important nitrite reductase in the heart and kidney. Herein, we have demonstrated that conversion of nitrite to NO by blood vessels and RBCs was enhanced in the presence of the XOR substrate xanthine (10 mol/L) and attenuated by the XOR inhibitor allopurinol (100 mol/L) in acidic and hypoxic conditions only. Whereas endothelial nitric oxide synthase (eNOS) inhibition had no effect on vascular nitrite reductase activity, in RBCs L-NAME, L-NMMA, and L-arginine inhibited nitrite-derived NO production by Ͼ50% (PϽ0.01) at pH 7.4 and 6.8 under hypoxic conditions. Western blot and immunohistochemical analysis of RBC membranes confirmed the presence of eNOS and abundant XOR on whole RBCs. Thus, XOR and eNOS are ideally situated on the membranes of RBCs and blood vessels to generate intravascular vasodilator NO from nitrite during ischemic episodes. In addition to the proposed role of deoxyhemoglobin, our findings suggest that the nitrite reductase activity within the circulation, under hypoxic conditions (at physiological pH), is mediated by eNOS; however, as acidosis develops, a substantial role for XOR becomes evident. (Circ Res. 2008;103:957-964.)Key Words: blood vessels Ⅲ cardiovascular research Ⅲ hypoxia Ⅲ nitric oxide U ntil recently, nitrite (NO 2 Ϫ ) was considered to be merely an inactive metabolite of the pleiotropic molecule nitric oxide (NO). However, recent studies have demonstrated that this view is incorrect, and, indeed, nitrite is now believed to be an important functional vascular mediator. This functionality is thought to lie in its role as an important storage form of NO 1 that is released particularly in situations where conventional NO synthesis, via the L-arginine-NO synthase (NOS) pathway, 2 has been compromised. This reduction to NO has been implicated as underlying nitrite-induced protection against ischemia/reperfusion (I/R) and hypoxic injury in the myocardial, 3-5 hepatic, 4 renal, 6 pulmonary, 7 and cerebral vasculature. 8 More recently, the functional remit of nitrite has been extended further with the proposal that it is active in physiological conditions. Indeed, nitrite causes dosedependent vasodilatation in the brachial artery of normal volunteers, 9,10 and we have recently demonstrated that dietary nitrate, via its bioconversion to nitrite, causes a marked decrease in blood pressure, inhibition of platelet aggregation, and the prevention of endothelial dysfunction following an I/R insult in the human forearm. 11 Such findings support the thesis that nitrite may have an important role in maintaining vascular homeostasis, in addition to its protective effects against cardiovascular disease.A number of distinct endogenous pathways have been identified in facilitating reduction of nitrite to NO in the circulation, over and above that achieved by simple chemical acidification. In par...

The kinin B1 receptor is an inducible receptor not normally expressed but induced by inflammatory stimuli and plays a major role in neutrophil recruitment, particularly in response to the cytokine interleukin-1β (IL-1β). However, the exact mechanism involved in this response is unclear. The aim of this study was to dissect the molecular mechanism involved, in particular to determine whether specific ELR-CXCL chemokines (specific neutrophil chemoattractants) played a role. Using intravital microscopy, we demonstrated that IL-1 β induced leukocyte rolling, adherence and emigration in mesenteric venules of wild type (WT) mice, associated with an increase of B1 receptor mRNA expression, was substantially attenuated (>80%) in B1 receptor knockout mice (B1KO). This effect in B1KO mice was correlated with a selective down regulation of IL-1β-induced CXCL5 mRNA and protein expression compared to WT mice. Furthermore a selective neutralizing CXCL5 antibody caused profound suppression of leukocyte emigration in IL-1β treated WT mice. Finally, treatment of human endothelial cells with IL-1β enhanced mRNA expression of B1 receptor and the human CXCL5 homologues (hCXCL5 and hCXCL6). This response was suppressed by ~50% when cells were pretreated with the B1 receptor antagonist des-Arg9[Leu]8BK whilst treatment with des-Arg9-BK, the B1 receptor agonist, caused a concentration-dependent increase in hCXCL5 and hCXCL6 mRNA expression. This study unveils a pro-inflammatory pathway centred on kinin B1 receptor activation of CXCL5 leading to leukocyte trafficking, and highlights the B1 receptor as a potential target in the therapeutics of inflammatory disease.

Objective-The proinflammatory phenotype induced by low laminar shear stress (LSS) is implicated in atherogenesis. The kinin B1 receptor (B1R), known to be induced by inflammatory stimuli, exerts many proinflammatory effects including vasodilatation and leukocyte recruitment. We investigated whether low LSS is a stimulus for endothelial B1R expression and function. Methods and Results-Human and mouse atherosclerotic plaques expressed high level of B1R mRNA and protein. In addition, B1R expression was upregulated in the aortic arch (low LSS region) of ApoE Ϫ/Ϫ mice fed a high-fat diet compared to vascular regions of high LSS and animals fed normal chow. Of interest, a greater expression of B1R was noticed in endothelial cells from regions of low LSS in aortic arch of ApoE Ϫ/Ϫ mice. B1R was also upregulated in human umbilical vein endothelial cells (HUVECs) exposed to low LSS (0 to 2 dyn/cm 2 ) compared to physiological LSS (6 to 10 dyn/cm 2 ): an effect similarly evident in murine vascular tissue perfused ex vivo. Functionally, B1R activation increased prostaglandin and CXCL5 expression in cells exposed to low, but not physiological, LSS. IL-1␤ and ox-LDL induced B1R expression and function in HUVECs, a response substantially enhanced under low LSS conditions and inhibited by blockade of NFB activation. Conclusion-Herein, we show that LSS is a major determinant of functional B1R expression in endothelium. Furthermore, whereas physiological high LSS is a powerful repressor of this inflammatory receptor, low LSS at sites of atheroma is associated with substantial upregulation, identifying this receptor as a potential therapeutic target. (Arterioscler Thromb