First evidence for an LDL- and HDL-associated nitratase activity that denitrates albumin-bound nitrotyrosine-Physiological consequences (original) (raw)
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Journal of Biological Chemistry, 2001
Nitric oxide, a pivotal molecule in vascular homeostasis, is converted under aerobic conditions to nitrite. Recent studies have shown that myeloperoxidase (MPO), an abundant heme protein released by activated leukocytes, can oxidize nitrite (NO 2 ؊) to a radical species, most likely nitrogen dioxide. Furthermore, hypochlorous acid (HOCl), the major strong oxidant generated by MPO in the presence of physiological concentrations of chloride ions, can also react with nitrite, forming the reactive intermediate nitryl chloride. Since MPO and MPO-derived HOCl, as well as reactive nitrogen species, have been implicated in the pathogenesis of atherosclerosis through oxidative modification of low density lipoprotein (LDL), we investigated the effects of physiological concentrations of nitrite (12.5-200 M) on MPOmediated modification of LDL in the absence and presence of physiological chloride concentrations. Interestingly, nitrite concentrations as low as 12.5 and 25 M significantly decreased MPO/H 2 O 2 /Cl ؊-induced modification of apoB lysine residues, formation of N-chloramines, and increases in the relative electrophoretic mobility of LDL. In contrast, none of these markers of LDL atherogenic modification were affected by the MPO/ H 2 O 2 /NO 2 ؊ system. Furthermore, experiments using ascorbate (12.5-200 M) and the tyrosine analogue 4-hydroxyphenylacetic acid (12.5-200 M), which are both substrates of MPO, indicated that nitrite inhibits MPOmediated LDL modifications by trapping the enzyme in its inactive compound II form. These data offer a novel mechanism for a potential antiatherogenic effect of the nitric oxide congener nitrite.
Biochemical Journal, 2002
Protein nitration is a common characteristic of oxidative injury caused by the invasion of leucocytes into inflammatory lesions. Two distinct pathways of nitration of protein tyrosine residues, namely the peroxynitrite (ONOO − )-mediated pathway and another catalysed by the haem-containing peroxidases, have been reported under experimental conditions. However, the contribution of these two pathways in human leucocytes is still controversial. The present study demonstrates that the process of phenolic nitration of proteins in cultured human leucocytes is mainly ONOO − -mediated and that it differs between granulocytes and mononuclear cells, depending on the cell compartment and the stimuli. We have also shown that NO induces protein nitration via a ONOO − -dependent pathway, whereas NO # − , the
Nitric oxide and its role in lipid peroxidation
Diabetes-metabolism Research and Reviews, 1999
Nitric oxide (NO) is a free radical with an unpaired electron in the highest orbital. This is why it behaves as a potential antioxidant agent by virtue of its ability to reduce other molecules. In vitro experiments support this concept inasmuch as NO is able to inhibit lipid peroxidation. However, NO is rapidly inactivated by the superoxide anion (O X 2 ) to form peroxynitrite (ONOO x ), which is a potent oxidant. Therefore, in the presence of O X 2 , NO behaves as a potent pro-oxidant. This is the mechanism that accounts for the low density lipoprotein (LDL) oxidation that occurs when NO and O X 2 are simultaneously present in the medium. As NO and O X 2 are simultaneously released by cells such as endothelial cells, the balance between these two radicals is crucial in understanding the net effect of NO on lipid peroxidation. Thus an excess of NO will favour lipid peroxidation inhibition, while an excess of O X 2 or equimolar concentration of NO and O X 2 will induce lipid peroxidation. Modulation of this balance may have important clinical implications, particularly in the atherosclerotic process in which oxidant stress seems to play a pivotal role in the onset and progression of vascular lesions.
Nitric Oxide Circulates in Mammalian Plasma Primarily as an S-Nitroso Adduct of Serum Albumin
Proceedings of The National Academy of Sciences, 1992
We have recently shown that nitric oxide or authentic endothelium-derived relaxing factor generated in a biologic system reacts in the presence of specific protein thiols to form S-nitrosoprotein derivatives that have endotheliumderived relaxing factor-like properties. The single free cysteine of serum albumin, Cys-34, is particularly reactive toward nitrogen oxides (most likely nitrosonium ion) under physiologic conditions, primarily because of its anomalously low pK; given its abundance in plasma, where it accounts for -0.5 mM thiol, we hypothesized that this plasma protein serves as a reservoir for nitric oxide produced by the endothelial cell. To test this hypothesis, we developed a methodology, which involves UV photolytic cleavage of the S-NO bond before reaction with ozone for chemiluminescence detection, with which to measure free nitric oxide, S-nitrosodiols, and S-nitrosoproteins in biologic systems. We found that human plasma contains =7 pIM S-nitrosothiols, of which 96% are S-nitrosoproteins, 82% of which is accounted for by S-nitrosoerum albumin. By contrast, plasma levels of free nitric oxide are only in the 3-nM range. In rabbits, plasma S-nitrosothiols are present at -1 #M; 60 min after administration of NG-monomethyl-Larginine at 50 mg/ml, a selective and potent inhibitor of nitric oxide synthetases, S-nitrosothiols decreased by "40% (>95% of which were accounted for by S-nitrosoproteins, and ""80% of which was S-nitroso-serum albumin); this decrease was accompanied by a concomitant increase in mean arterial blood pressure of 22%. These data suggest that naturally produced nitric oxide circulates in plasma primarily complexed in S-nitrosothiol species, principal among which is S-nitroso-serum albumin. This abundant, relatively long-lived adduct likely serves as a reservoir with which plasma levels of highly reactive, short-lived free nitric oxide can be regulated for the maintenance of vascular tone.
Seminars in Perinatology, 1997
Since the discovery that at least one form of endothefium derived relaxing factor is nitric oxide (NO), numerous studies have uncovered diverse roles for this free radical in a variety of physiological and pathophysiological processes. NO production, a process mediated by a family of enzymes termed NO synthases, has been detected in most cell types. Many of the effects of NO are thought to be mediated through its direct interaction with specific and defined cell signaling pathways. The nature of such interactions are highly dependent on the concentration of NO and cell type. Furthermore, specific NO derived reaction products, such as peroxynitrite, also have the potential to effect cell signal transduction events. As with NO, this can occur through diverse mechanisms and depends on concentration and cell type. It is perhaps not surprising that the reported effects of NO in different disease states are often conflicting. In this brief overview, a framework for placing these apparently disparate properties of NO will be described and Hill focus on the effects of NO and peroxynitrite on signaling pathways.
Circulation Research, 2002
Nitration of unsaturated fatty acids such as linoleate by NO-derived reactive species forms novel derivatives (including nitrolinoleate [LNO 2 ]) that can stimulate smooth muscle relaxation and block platelet activation by either NO/cGMP or cAMP-dependent mechanisms. Here, LNO 2 was observed to inhibit human neutrophil function. LNO 2 , but not linoleic acid or the nitrated amino acid 3-nitrotyrosine, dose-dependently (0.2 to 1 mol/L) inhibited superoxide (O 2 ·Ϫ ) generation, Ca 2ϩ influx, elastase release, and CD11b expression in response to either phorbol 12-myristate 13-acetate or N-formyl-Met-Leu-Phe. LNO 2 did not elevate cGMP, and inhibition of guanylate cyclase by 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one did not restore neutrophil responses, ruling out a role for NO. In contrast, LNO 2 caused elevations in intracellular cAMP in the presence and absence of phosphodiesterase inhibition, suggesting activation of adenylate cyclase. Compared with phorbol 12-myristate 13-acetate-activated neutrophils, N-formyl-Met-Leu-Phe-activated neutrophils were more susceptible to the inhibitory effects of LNO 2 , indicating that LNO 2 may inhibit signaling both upstream and downstream of protein kinase C. These data suggest novel signaling actions for LNO 2 in mediating its potent inhibitory actions. Thus, nitration of lipids by NO-derived reactive species yields products with antiinflammatory properties, revealing a novel mechanism by which NO-derived nitrated biomolecules can influence the progression of vascular disease. (Circ Res. 2002;91:375-381.)