Differential effects of some cell signalling inhibitors upon nitric oxide synthase expression and nuclear factor-kappaB activation induced by lipopolysaccharide in rat aortic smooth muscle cells

Reduction of Ether-Type Glycerophospholipids, Plasmalogens, by NF-κB Signal Leading to Microglial Activation

Neuroinflammation characterized by activation of glial cells is observed in various neurodegenerative diseases including Alzheimer's disease (AD). Although the reduction of ether-type glycerophospholipids, plasmalogens (Pls), in the brain is reported in AD patients, the mechanism of the reduction and its impact on neuroinflammation remained elusive. In the present study, we found for the first time that various inflammatory stimuli reduced Pls levels in murine glial cells via NF-κB activation, which then downregulated a Pls-synthesizing enzyme, glycerone phosphate O-acyltransferase (Gnpat) through increased c-Myc recruitment onto the Gnpat promoter. We also found that systemic injection of lipopolysaccharide, aging, and chronic restraint stress reduced brain Pls contents that were associated with glial NF-κB activation, an increase in c-Myc expression, and downregulation of Gnpat in the mouse cortex and hippocampus. More interestingly, the reduction of Pls contents in the murine cortex itself could increase the activated phenotype of microglial cells and the expression of proinflammatory cytokines, suggesting further acceleration of neuroinflammation by reduction of brain Pls. A similar mechanism of Gnpat reduction was also found in human cell lines, triple-transgenic AD mouse brain, and postmortem human AD brain tissues. These findings suggest a novel mechanism of neuroinflammation that may explain prolonged progression of AD and help us to explore preventive and therapeutic strategies to treat neurodegenerative diseases.SIGNIFICANCE STATEMENT Ether-type glycerophospholipids, plasmalogens (Pls), are reduced in the brain of Alzheimer disease (AD) patients. We found that inflammatory stimuli reduced Pls contents by downregulation of the Pls-synthesizing enzyme glycerone phosphate O-acyltransferase (Gnpat) through NF-κB-mediated recruitment of c-Myc onto the Gnpat promoter in both murine and human cell lines. Murine brains after systemic lipopolysaccharide, chronic stress, and aging, as well as triple-transgenic AD mice and postmortem human AD brain tissues all showed increased c-Myc and reduced Gnpat expression. Interestingly, knockdown of Gnpat itself activated NF-κB in glial cell lines and microglia in mouse cortex. Our findings provide a new insight into the mechanism of neuroinflammation and may help to develop a novel therapeutic approach for neurodegenerative diseases such as AD.

Limb ischemic preconditioning protects against contrast-induced nephropathy via renalase

Clinical trials shows that remote ischemic preconditioning (IPC) can protect against contrast induced nephropathy (CIN) in risky patients, however, the exact mechanism is unclear. In this study, we explored whether renalase, an amine oxidase that has been previously shown to mediate reno-protection by local IPC, would also mediate the same effect elicited by remote IPC in animal model. Limb IPC was performed for 24 h followed by induction of CIN. Our results indicated that limb IPC prevented renal function decline, attenuated tubular damage and reduced oxidative stress and inflammation in the kidney. All those beneficial effects were abolished by silencing of renalase with siRNA. This suggests that similar to local IPC, renalase is also critically involved in limb IPC-elicited reno-protection. Mechanistic studies showed that limb IPC increased TNFα levels in the muscle and blood, and up-regulated renalase and phosphorylated IκBα expression in the kidney. Pretreatment with TNFα antagonist or NF-κB inhibitor, largely blocked renalase expression. Besides, TNFα preconditioning increased expression of renal renalase in vivo and in vitro, and attenuated H₂O₂ induced apoptosis in renal tubular cells. Collectively, our results suggest that limb IPC-induced reno-protection in CIN is dependent on increased renalase expression via activation of the TNFα/NF-κB pathway.

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Limb ischemic preconditioning (IPC) leads to renalase upregulation in kidney tissue.

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Renalase is critically involved in limb IPC-elicited renal protection in contrast induced nephropathy.

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Limb IPC induces renalase upregulation via activation of the tumor necrosis factor α (TNFα)/ nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway.

Renalase, a kidney-secreted protein, serves as extracellular pro-survival signals and has been reported to participate in the local ischemic preconditioning (IPC) induced renal protection against ischemia-reperfusion injury. Whether renalase contributes to the beneficial effects of limb IPC on contrast induced nephropathy (CIN) remains unknown. This study revealed that limb IPC induced reno-protection in CIN was at least in part dependent on increased renalase expression, which is evidenced by our observations that knockdown of renalase abolished reno-protective effects conferred by limb IPC. The upregulation of renalase elicited by limb IPC may be mediated by activation of TNFα/NF-κB pathway.

Effects of aldosterone and related steroids on LPS-induced increased expression of inducible NOS in rat aortic smooth muscle cells

BACKGROUND AND PURPOSE

Expression of inducible NOS (iNOS) is important in certain inflammatory diseases. We determined if the hormone aldosterone, a mineralocorticoid receptor (MR) agonist, affects LPS activation of iNOS expression in rat aortic smooth muscle cells (RASMC).

EXPERIMENTAL APPROACH

Cultured RASMC were treated with LPS, with or without agonists/antagonists of steroid receptors. iNOS expression was determined by nitrite assays on culture medium removed from treated cells and by immunoblotting of cell protein extracts.

KEY RESULTS

LPS (1 µg·mL(-1) ) increased nitrite and iNOS protein above that in control (untreated) cells. These effects of LPS were reduced by aldosterone (0.1-10 µM). The MR antagonists, eplerenone (10 µM) and spironolactone (10 or 50 µM), did not inhibit these actions of 1 µM aldosterone, but the latter were prevented by 10 µM mifepristone, a glucocorticoid (GR) and progestogen receptor (PR) antagonist. Mifepristone also prevented the reduction of LPS-induced nitrite increase produced by 1 µM dexamethasone (GR agonist) and 10 µM progesterone (PR agonist). Spironolactone (10-50 µM) by itself decreased LPS-induced increases in nitrite and iNOS protein. Mifepristone (10 µM) partially reversed these effects of 10 µM spironolactone, but not those of 50 µM; the effects of 50 µM spironolactone were also unchanged when mifepristone was increased to 50 µM.

CONCLUSIONS AND IMPLICATIONS

This pharmacological profile suggests that aldosterone, and possibly 10 µM spironolactone, use mechanisms that are dependent on PR and/or GR, but not MR, to inhibit iNOS induction in RASMC. With 50 µM spironolactone, other inhibitory mechanisms requiring further investigation may become predominant.

Differential effects of apolipoprotein E3 and E4 on markers of oxidative status in macrophages

ApoE is secreted by macrophages at the lesion site of the atherosclerotic plaque, where it is thought to play a protective role against atherosclerosis independently of its effects on lipid metabolism. Of the three common isoforms for apoE, apoE4 is associated with higher risk of cardiovascular disease (CVD). In vitro studies have shown that recombinant apoE may act as an antioxidant in an isoform-dependent manner (E2 > E3 > E4). The oxidative status of the macrophages plays a key role in the process of atherosclerosis. In the present study the possible differential actions of apoE3 and apoE4 on several parameters of oxidative status were determined in stably transfected murine macrophages (RAW 264-7-apoE3 and - apoE4). No differences between genotypes were observed after peroxide challenge in either protection against cytotoxicity or in cell membrane oxidation, and modest differences were observed in the non-enzymatic antioxidants (glutathione and alpha-tocopherol) in apoE3 v. apoE4 macrophages. Importantly, cells secreting apoE4 showed increased membrane oxidation under basal conditions, and produced more NO and superoxide anion radicals than the apoE3 macrophages after stimulation. The present data suggest that apoE genotype influences the oxidative status of macrophages, and this could partly contribute to the higher CVD risk observed in apoE4 carriers.

Ethanol preconditioning protects against ischemia/reperfusion-induced brain damage: role of NADPH oxidase-derived ROS

Ethanol preconditioning (EtOH-PC) refers to a phenomenon in which tissues are protected from the deleterious effects of ischemia/reperfusion (I/R) by prior ingestion of ethanol at low to moderate levels. In this study, we tested whether prior (24 h) administration of ethanol as a single bolus that produced a peak plasma concentration of 42-46 mg/dl in gerbils would offer protective effects against neuronal damage due to cerebral I/R. In addition, we also tested whether reactive oxygen species (ROS) derived from NADPH oxidase played a role as initiators of these putative protective effects. Groups of gerbils were administered either ethanol or the same volume of water by gavage 24 h before transient global cerebral ischemia induced by occlusion of both common carotid arteries for 5 min. In some experiments, apocynin, a specific inhibitor of NADPH oxidase, was administered (5 mg/kg body wt, i.p.) 10 min before ethanol administration. EtOH-PC ameliorated behavioral deficit induced by cerebral I/R and protected the brain against I/R-induced delayed neuronal death, neuronal and dendritic degeneration, oxidative DNA damage, and glial cell activation. These beneficial effects were attenuated by apocynin treatment coincident with ethanol administration. Ethanol ingestion was associated with translocation of the NADPH oxidase subunit p67(phox) from hippocampal cytosol fraction to membrane, increased NADPH oxidase activity in hippocampus within the first hour after gavage, and increased lipid peroxidation (4-hydroxy-2-nonenal) in plasma and hippocampus within the first 2 h after gavage. These effects were also inhibited by concomitant apocynin treatment. Our data are consistent with the hypothesis that antecedent ethanol ingestion at socially relevant levels induces neuroprotective effects in I/R by a mechanism that is triggered by ROS produced through NADPH oxidase. Our results further suggest the possibility that preconditioning with other pharmacological agents that induce a mild oxidative stress may have similar therapeutic value for suppressing stroke-mediated damage in brain.

''Iatrogenic Gilbert syndrome''--a strategy for reducing vascular and cancer risk by increasing plasma unconjugated bilirubin

The catabolism of heme, generating biliverdin, carbon monoxide, and free iron, is mediated by heme oxygenase (HO). One form of this of this enzyme, heme oxygenase-1, is inducible by numerous agents which promote oxidative stress, and is now known to provide important antioxidant protection, as demonstrated in many rodent models of free radical-mediated pathogenesis, and suggested by epidemiology observing favorable health outcomes in individuals carrying high-expression alleles of the HO-1 gene. The antioxidant impact of HO-1 appears to be mediated by bilirubin, generated rapidly from biliverdin by ubiquitously expressed biliverdin reductase. Bilirubin efficiently scavenges a wide range of physiological oxidants by electron donation. In the process, it is often reconverted to biliverdin, but biliverdin reductase quickly regenerates bilirubin, thereby greatly boosting its antioxidant potential. There is also suggestive evidence that bilirubin inhibits the activity or activation of NADPH oxidase. Increased serum bilirubin is associated with reduced risk for atherogenic disease in epidemiological studies, and more limited data show an inverse correlation between serum bilirubin and cancer risk. Gilbert syndrome, a genetic variant characterized by moderate hyperbilirubinemia attributable to reduced hepatic expression of the UDP-glucuronosyltransferase which conjugates bilirubin, has been associated with a greatly reduced risk for ischemic heart disease and hypertension in a recent study. Feasible strategies for boosting serum bilirubin levels may include administration of HO-1 inducers, supplementation with bilirubin or biliverdin, and administration of drugs which decrease the efficiency of hepatic bilirubin conjugation. The well-tolerated uricosuric drug probenecid achieves non-competitive inhibition of hepatic glucuronidation reactions by inhibiting the transport of UDP-glucuronic acid into endoplasmic reticulum; probenecid therapy is included in the differential diagnosis of hyperbilirubinemia, and presumably could be used to induce an ''iatrogenic Gilbert syndrome''. Other drugs, such as rifampin, can raise serum bilirubin through competitive inhibition of hepatocyte bilirubin uptake--although unfortunately rifampin is not as safe as probenecid. Measures which can safely achieve moderate serum elevations of bilirubin may prove to have value in the prevention and/or treatment of a wide range of disorders in which oxidants play a prominent pathogenic role, including many vascular diseases, cancer, and inflammatory syndromes. Phycobilins, algal biliverdin metabolites that are good substrates for biliverdin reductase, may prove to have clinical antioxidant potential comparable to that of bilirubin.

Extracellular Signal-Regulated Kinase (ERK1/2) Contributes to Endotoxin-Induced Hyporeactivity via Nitric Oxide and Prostacyclin Production in Rat Aorta

This study was conducted to determine if mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK1/2) contribute to endotoxin-induced vascular hyporeactivity via nitric oxide (NO) and/or prostacyclin (PGI(2)) production in the rat isolated thoracic aorta. Incubation of endothelium-intact rings with endotoxin (100 microg/ml) for 4 h decreased the E(max) value and increased the EC(50) value of norepinephrine. The endotoxin-induced increase in the EC(50) value of norepinephrine was decreased by phenylene-1,3-bis[ethane-2-isothiourea] dihydrobromide (1,3-PBIT), a selective inducible NO synthase inhibitor, and U0126, a selective inhibitor of ERK1/2 phosphorylation by MAPK kinase. The endotoxin-induced decrease in the E(max) value of norepinephrine was reversed by 1,3-PBIT and further decreased by U0126. 1,3-PBIT and U0126 decreased the endotoxin-induced increase in the tissue nitrite and 6-keto-PGF(1)(alpha) levels. These data suggest that events related to the activation of ERK1/2 contribute to the endotoxin-induced hyporeactivity by increasing NO and PGI(2) production.

c-Jun N-terminal kinase inhibition and alpha-tocopherol protect midbrain dopaminergic neurons from interferon-gamma/lipopolysaccharide-induced injury without affecting nitric oxide production

Interferon-gamma (IFN-gamma)/lipopolysaccharide (LPS) induces delayed dopaminergic neuron loss in midbrain slice cultures, because of nitric oxide production resulting from p38 mitogen-activated protein kinase (p38 MAPK)-dependent induction of inducible nitric oxide synthase (iNOS). In this study, we show that inhibition of c-Jun N-terminal kinase (JNK), but not of extracellular signal-regulated kinase, protects dopaminergic neurons from IFN-gamma/LPS-induced degeneration. In contrast to a p38 MAPK inhibitor, SB203580, however, a JNK inhibitor, anthra[1,9-cd]pyrazol-6(2H)-one (SP600125), did not suppress IFN-gamma/LPS-induced iNOS expression and nitric oxide production. Involvement of NADPH oxidase-derived superoxide production in dopaminergic neurodegeneration was not obvious, in that superoxide dismutase/catalase or manganese 3-methoxy-N,N'-bis(salicylidene)ethylenediamine chloride (EUK-134), a superoxide dismutase/catalase mimetic, did not afford neuroprotection. Moreover, the NADPH oxidase inhibitors apocynin and diphenylene iodonium were protective against IFN-gamma/LPS cytotoxicity only at concentrations that suppressed nitric oxide production. Notably, alpha-tocopherol effectively prevented IFN-gamma/LPS-induced dopaminergic neuron degeneration, without affecting iNOS induction and nitric oxide production. These results underscore the neuroprotective potential of JNK inhibitor and alpha-tocopherol, in the sense that both agents could rescue dopaminergic neurons under inflammatory conditions associated with robust increases in nitric oxide production.

Bilirubin decreases nos2 expression via inhibition of NAD(P)H oxidase: implications for protection against endotoxic shock in rats

We investigated a possible beneficial role for bilirubin, one of the products of heme degradation by the cytoprotective enzyme heme oxygenase-1 in counteracting Escherichia coli endotoxin-mediated toxicity. Homozygous jaundice Gunn rats, which display high plasma bilirubin levels due to deficiency of glucuronyl transferase activity, and Sprague-Dawley rats subjected to sustained exogenous bilirubin administration were more resistant to endotoxin (LPS)-induced hypotension and death compared with nonhyperbilirubinemic rats. LPS-stimulated production of nitric oxide (NO) was significantly decreased in hyperbilirubinemic rats compared with normal animals; this effect was associated with reduction of inducible NO synthase (NOS2) expression in renal, myocardial, and aortic tissues. Furthermore, NOS2 protein expression and activity were reduced in murine macrophages stimulated with LPS and preincubated with bilirubin at concentrations similar to that found in the serum of hyperbilirubinemic animals. This effect was secondary to inhibition of NAD(P)H oxidase since 1) inhibition of NAD(P)H oxidase attenuated NOS2 induction by LPS, 2) bilirubin decreased NAD(P)H oxidase activity in vivo and in vitro, and 3) down-regulation of NOS2 by bilirubin was reversed by addition of NAD(P)H. These findings indicate that bilirubin can act as an effective agent to reduce mortality and counteract hypotension elicited by endotoxin through mechanisms involving a decreased NOS2 induction secondary to inhibition of NAD(P)H oxidase.

Evidence of cardiovascular protection by moderate alcohol: role of nitric oxide

Epidemiological evidence indicates that moderate alcohol consumption reduces the incidence of heart disease. Endothelial nitric oxide synthase (eNOS) is a key regulator of vascular homeostasis and myocardial functions through the controlled production of nitric oxide (*NO). These studies were conducted to determine if the apparent alcohol-associated cardioprotection is mediated, in part, through modulation of the eNOS protein and activity in the cardiovascular system. Rats were fed alcohol and eNOS protein and *NO production were evaluated at the end of 8 weeks. Myocardial and vascular function was assessed ex vivo in a subset of animals. Moderate alcohol improved postischemic myocardial systolic and diastolic function and attenuated the postischemic reduction in coronary vascular resistance. Moderate alcohol also enhanced maximum vascular relaxation by 26 +/- 0.2% and increased plasma *NO production concomitant with a greater than 2.5-fold increase in eNOS protein. Higher levels of alcohol impaired maximum vascular relaxation by 22 +/- 0.1%. These results suggest that moderate alcohol improves postischemic myocardial functions and increases *NO production by vascular endothelium. An increase in *NO may explain, at least in part, the cardioprotective benefits of moderate alcohol consumption.

Late preconditioning by ethanol is initiated via an oxidant-dependent signaling pathway

Ingestion of alcoholic beverages at low to moderate levels 24 h prior to ischemia and reperfusion (I/R) prevents postischemic leukocyte/endothelial cell adhesive interactions, a phenomenon referred to as late ethanol preconditioning (EtOH-PC). The aim of this study was to determine whether oxidants act as initiators of late EtOH-PC. Ethanol was instilled into the stomachs of C57BL/6 mice as a bolus by gavage at a dose that produced a peak plasma concentration of 45 mg/dl 30 min after administration and returned to control levels 60 min after ingestion. Twenty four hours later, the superior mesenteric artery was occluded for 45 min followed by 70 min of reperfusion. The numbers of rolling and firmly adherent leukocytes were quantified in postcapillary venules of the small intestine in sham animals (no EtOH-PC, no I/R), in mice subjected to I/R alone or EtOH-PC + I/R, and in animals treated with Mn-TBAP (a cell-permeant superoxide dismutase mimetic), oxypurinol (a XO inhibitor), the NAD(P)H oxidase inhibitors PR-39 or apocynin, or oxypurinol plus PR39 during the period of EtOH-PC on Day 1 followed by I/R on Day 2. In separate groups of mice, oxypurinol or apocynin were also administered 1 h after ethanol ingestion on Day 1, with induction of I/R 24 h later. I/R induced marked increases in leukocyte rolling and adherence, effects that were completely prevented by EtOH-PC. Coincident treatment with Mn-TBAP, oxypurinol, PR-39, apocynin, or oxypurinol plus PR-39 with ethanol attenuated these anti-inflammatory actions of EtOH-PC. However, administration of oxypurinol or apocynin 1 h after ethanol ingestion failed to prevent these protective effects of EtOH-PC. Our results indicate that reactive oxygen species formed during the period of ethanol exposure on Day 1 trigger the development of an anti-inflammatory phenotype that renders the small bowel resistant to the proadhesive effects of I/R 24 h later.

Ascorbate inhibits iNOS expression in endotoxin- and IFN gamma-stimulated rat skeletal muscle endothelial cells

Lipopolysaccharide endotoxin and interferon-gamma induced inducible nitric oxide synthase (iNOS) protein expression and nitrite/nitrate formation in microvascular endothelial cell cultures (ECs) derived from rat skeletal muscle. Pretreatment of ECs with ascorbate accumulated a large amount of ascorbate inside the cells and consequently decreased both intracellular oxidant level and iNOS induction. These effects of ascorbate were abolished in the presence of exogenous superoxide generated by xanthine oxidase/xanthine plus catalase but were not altered when N-nitro-L-arginine methyl ester was applied to inhibit nitric oxide synthesis. Ascorbate also attenuated the activation of transcription factor IRF-1 but not NF kappa B. These results indicate that ascorbate inhibits iNOS expression in ECs by an antioxidant mechanism independent of both NF kappa B activation and the reported negative feedback effect of nitric oxide.

Nickel requires hypoxia-inducible factor-1 alpha, not redox signaling, to induce plasminogen activator inhibitor-1

Human epidemiological and animal studies have associated inhalation of nickel dusts with an increased incidence of pulmonary fibrosis. At the cellular level, particulate nickel subsulfide inhibits fibrinolysis by transcriptionally inducing expression of plasminogen activator inhibitor (PAI)-1, an inhibitor of the urokinase-type plasminogen activator. Because nickel is known to mimic hypoxia, the present study examined whether nickel transcriptionally activates PAI-1 through the hypoxia-inducible factor (HIF)-1 alpha signaling pathway. The involvement of the NADPH oxidase complex, reactive oxygen species, and kinases in mediating nickel-induced HIF-1 alpha signaling was also investigated. Addition of nickel to BEAS-2B human airway epithelial cells increased HIF-1 alpha protein levels and elevated PAI-1 mRNA levels. Pretreatment of cells with the extracellular signal-regulated kinase inhibitor U-0126 partially blocked HIF-1 alpha protein and PAI-1 mRNA levels induced by nickel, whereas antioxidants and NADPH oxidase inhibitors had no effect. Pretreating cells with antisense, but not sense, oligonucleotides to HIF-1 alpha mRNA abolished nickel-stimulated increases in PAI-1 mRNA. These data indicate that signaling through extracellular signal-regulated kinase and HIF-1 alpha is required for nickel-induced transcriptional activation of PAI-1.

Effects of aminoguanidine on nitric oxide production induced by inflammatory cytokines and endotoxin in cultured rat hepatocytes

AIM: To study the effects of aminoguanidine (AG) and two L-arginine analogues N^ω-nitro-L-arginine methyl ester (L-NAME) and N^ω-nitro-L-arginine (L-NNA) on nitric oxide (NO) production induced by cytokines (TNF-α, IL-1β, and IFN-γ) and bacterial lipopolysaccharide (LPS) mixture (CM) in the cultured rat hepatocytes, and examine their mechanisms action.

METHODS: Rat hepatocytes were incubated with AG, L-NAME, L-NNA, Actinomycin D (ActD) and dexamethasone in a medium containing CM (LPS plus TNF-α, IL-1β, and IFN-γ) for 24 h. NO production in the cultured supernatant was measured with the Griess reaction. Intracellular cGMP level was detected with radioimmunoassy.

RESULTS: NO production was markedly blocked by AG and L-NAME in a dose-dependent manner under inflammatory stimuli condition triggered by CM in vitro. The rate of the maximum inhibitory effects of L-NAME (38.9%) was less potent than that obtained with AG (53.7%, P < 0.05). There was no significant difference between the inhibitory effects of AG and two L-arginine analogues on intracellular cGMP accumulation in rat cultured hepatocytes. Non-specific NOS expression inhibitor dexamethasone(DEX) and iNOS mRNA transcriptional inhibitor ActD also significantly inhibited CM-induced NO production. AG (0.1 mmol·L^-1) and ActD (0.2 ng·L^-1) were equipotent in decreasing NO production induced by inflammatory stimuli in vitro, and both effects were more potent than that induced by non-selectivity NOS activity inhibitor L-NAME (0.1 mmol·L^-1) under similar stimuli conditions (P < 0.01).

CONCLUSION: AG is a potent selective inhibitor of inducible isoform of NOS, and the mechanism of action may be not only competitive inhibition in the substrate level, but also the gene expression level in rat hepatocytes.

Interactions between nitric oxide and lipid oxidation pathways: implications for vascular disease

Nitric oxide ((.)NO) signaling pathways and lipid oxidation reactions are of central importance in both the maintenance of vascular homeostasis and the progression of vascular disease. Because both of these pathways involve free radical species that can also react together at extremely fast rates, convergent interactions between these pathways are expected. Biochemical and cell biology studies have defined multiple interactions of (.)NO with oxidizing lipids that could lead to either vascular protection or potentiation of inflammatory vascular injury. For example, low levels of (.)NO generated by endothelial nitric oxide synthase can terminate propagating lipid radicals and inhibit lipoxygenases, reactions that would be protective. Alternatively, if generated at elevated levels, for example, after inducible nitric oxide synthase expression in inflammation, (.)NO can be converted to prooxidant species, such as peroxynitrite (ONOO(-)) and nitrogen dioxide ((.)NO(2)), that can potentiate inflammatory injury to vascular cells. Finally, both enzymatic and nonenzymatic lipid oxidation reactions can influence (.)NO bioactivity by directly scavenging (.)NO or altering the induction and catalytic activity of nitric oxide synthase enzymes. In this review, we summarize the biochemical interactions between (.)NO and lipid oxidation reactions and discuss the recognized and potential roles of these reactions in the vasculature.