Nitro-oleic acid protects the mouse kidney from ischemia and reperfusion injury

Adipocyte-specific Nrf2 deletion negates nitro-oleic acid benefits on glucose tolerance in diet-induced obesity

Obesity is commonly linked with white adipose tissue (WAT) dysfunction, setting off inflammation and oxidative stress, both key contributors to the cardiometabolic complications associated with obesity. To improve metabolic and cardiovascular health, countering these inflammatory and oxidative signaling processes is crucial. Offering potential in this context, the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) by nitro-fatty acids (NO2-FA) promote diverse anti-inflammatory signaling and counteract oxidative stress. Additionally, we previously highlighted that nitro-oleic acid (NO2-OA) preferentially accumulates in WAT and provides protection against already established high fat diet (HFD)-mediated impaired glucose tolerance. The precise mechanism accounting for these protective effects remained largely unexplored until now. Herein, we reveal that protective effects of improved glucose tolerance by NO2-OA is absent when Nrf2 is specifically ablated in adipocytes (ANKO mice). NO2-OA treatment did not alter body weight between ANKO and littermate controls (Nrf2fl/fl) mice on both the HFD and low-fat diet (LFD). As expected, at day 76 (before NO2-OA treatment) and notably at day 125 (daily treatment of 15 mg/kg NO2-OA for 48 days), both HFD-fed Nrf2fl/fl and ANKO mice exhibited increased fat mass and reduced lean mass compared to LFD controls. However, throughout the NO2-OA treatment, no distinction was observed between Nrf2fl/fl and ANKO in the HFD-fed mice as well as in the Nrf2fl/fl mice fed a LFD. Glucose tolerance tests revealed impaired glucose tolerance in HFD-fed Nrf2fl/fl and ANKO compared to LFD-fed Nrf2fl/fl mice. Notably, NO2-OA treatment improved glucose tolerance in HFD-fed Nrf2fl/fl but did not yield the same improvement in ANKO mice at days 15, 30, and 55 of treatment. Unraveling the pathways linked to NO2-OA's protective effects in obesity-mediated impairment in glucose tolerance is pivotal within the realm of precision medicine, crucially propelling future applications and refining novel drug-based strategies.

Nitro-oleic acid ameliorates erectile dysfunction in a streptozotocin-induced rat model of diabetes by inhibiting oxidative stress and apoptosis and activating the NO/cGMP pathway

The major vascular complications associated with diabetes make the management of diabetic mellitus erectile dysfunction (DMED) a challenging endeavor. Notable factors contributing to DMED include oxidative stress, nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway activation, and apoptosis, while nitro-oleic acid (NO 2 -OA) has been shown to be beneficial in treating these aspects of this condition. We, herein, investigated the effects and possible mechanisms of NO 2 -OA on erectile function as assessed in a streptozotocin-induced rat model of diabetes. Our results revealed that the erectile function of DMED rats was significantly impaired compared with that of the control group. However, in response to 4 weeks of NO 2 -OA treatment, there was an improvement in erectile function. The expression of oxidative stress-related indicators was significantly increased and the NO/cGMP pathway was impaired in the DMED group. The expression of proapoptotic factors was increased, while that of antiapoptotic factors was decreased in the DMED group. Moreover, the cell morphology in the cavernous tissue of the DMED group also changed adversely. NO 2 -OA treatment significantly reversed all these changes observed in the DMED group. In conclusion, NO 2 -OA treatment partially improved erectile function in DMED rats through mechanisms that included inhibition of oxidative stress, activation of the NO/cGMP pathway, and a reduction in apoptosis.

Fatty acid nitroalkenes - Multi-target agents for the treatment of sickle cell disease

Sickle cell disease (SCD) is a hereditary hematological disease with high morbidity and mortality rates worldwide. Despite being monogenic, SCD patients display a plethora of disease-associated complications including anemia, oxidative stress, sterile inflammation, vaso-occlusive crisis-related pain, and vasculopathy, all of which contribute to multiorgan dysfunction and failure. Over the past decade, numerous small molecule drugs, biologics, and gene-based interventions have been evaluated; however, only four disease-modifying drug therapies are presently FDA approved. Barriers regarding effectiveness, accessibility, affordability, tolerance, and compliance of the current polypharmacy-based disease-management approaches are challenging. As such, there is an unmet pharmacological need for safer, more efficacious, and logistically accessible treatment options for SCD patients. Herein, we evaluate the potential of small molecule nitroalkenes such as nitro-fatty acid (NO2-FA) as a therapy for SCD. These agents are electrophilic and exert anti-inflammatory and tissue repair effects through an ability to transiently post-translationally bind to and modify transcription factors, pro-inflammatory enzymes and cell signaling mediators. Preclinical and clinical studies affirm safety of the drug class and a murine model of SCD reveals protection against inflammation, fibrosis, and vascular dysfunction. Despite protective cardiac, renal, pulmonary, and central nervous system effects of nitroalkenes, they have not previously been considered as therapy for SCD. We highlight the pathways targeted by this drug class, which can potentially prevent the end-organ damage associated with SCD and contrast their prospective therapeutic benefits for SCD as opposed to current polypharmacy approaches.

Nitrated fatty acid, 10-nitrooleate protects against hyperoxia-induced acute lung injury in mice

The antioxidant and anti-inflammatory effects of electrophilic nitrated fatty acid (NFA); 10-nitrooleate, have been reported. The present study investigated whether 10-nitrooleate has a protective role against hyperoxic-induced acute lung injury (HALI). Using a C57BL/6 mice model of HALI, we investigated the protective effect of 10-nitrooleate. C57BL/6 mice were administered with NFA intratracheally, exposed to hyperoxia for 48 h to induce HALI, and kept at room air for 24 h. Bronchoalveolar lavage (BAL) fluid and lung samples were collected after 24 h of post hyperoxia to analyze markers associated with HALI. Intratracheal (IT) and intraperitoneal (IP) administration of NFA notably attenuated hyperoxia-induced infiltration of inflammatory cells, alveolar-capillary leakage, upregulation of proinflammatory cytokine levels (IL-6 and TNFα) into the BAL fluid, and resolution of inflammation in the lung. Western blot analyses showed that 10-nitrooleate reduced the expression of the inflammatory transcription factor NFκB p65 subunit and increased antioxidant proteins HO-1 and NQO1 expression in the lung tissues compared to vehicle-treated animals. Moreover, 10-nitrooleate reversed the hyperoxia-induced expression of mitophagy-associated markers (PINK1 and p62/SQSTM1), thereby protecting the HALI/ acute respiratory distress syndrome (ARDS). IT and IP delivery of 10-nitrooleate reduces hyperoxia-induced ALI/ARDS by regulating the antioxidant pathways and restoring the mitochondrial homeostasis by regulating mitophagy. It is suggested that NFAs can be further evaluated as supplementary therapy for critically ill patients like COVID-19/ARDS.

Nitro-oleic acid-mediated blood-brain barrier protection reduces ischemic brain injury

Nitro-oleic acid (OA-NO₂), a nitroalkene formed in nitric oxide-dependent oxidative reactions, has been found in human plasma and is thought to regulate pathophysiological functions. Recently, accumulating evidence suggests that OA-NO₂ may function as an anti-inflammatory mediator, and ameliorate the progression of diabetes and cardiovascular diseases. However, the role of OA-NO₂ in ischemic brain injury remains unexplored. In this study, C57BL/6 mice were subjected to 1 h transient middle cerebral artery occlusion (MCAO) and followed by 1- 7 days of reperfusion. These mice were treated with vehicle, OA, or OA-NO₂ (10 mg/kg) via tail vein injection at 2 h after the onset of MCAO. Our results show that intravenous administration of OA-NO₂ led to reduced BBB leakage in ischemic brains, reduced brain infarct, and improved sensorimotor functions in response to ischemic insults when compared to OA and vehicle controls. Also, OA-NO₂ significantly reduced BBB leakage-triggered infiltration of neutrophils and macrophages in the ischemic brains. Moreover, OA-NO₂ treatment reduced the M1-type microglia and increased M2-type microglia. Mechanistically, OA-NO₂ alleviated the decline of mRNA and protein level of major endothelial TJs including ZO-1 in stroke mice. Treatment of OA-NO₂ also significantly inhibited stroke-induced inflammatory mediators, iNOS, E-selectin, P-selectin, and ICAM1, in mouse brains. In conclusion, OA-NO₂ preserves BBB integrity and confers neurovascular protection in ischemic brain damage. OA-NO₂-mediated brain protection may help us to develop a novel therapeutic strategy for the treatment of ischemic stroke.

Electrophilic nitro-fatty acids suppress psoriasiform dermatitis: STAT3 inhibition as a contributory mechanism

Psoriasis is a chronic inflammatory skin disease with no cure. Although the origin of psoriasis and its underlying pathophysiology remain incompletely understood, inflammation is a central mediator of disease progression. In this regard, electrophilic nitro-fatty acids (NO₂–FAs) exert potent anti-inflammatory effects in several in vivo murine models of inflammatory diseases, such as chronic kidney disease and cardiovascular disease. To examine the therapeutic potential of NO₂–FAs on psoriasiform dermatitis, we employed multiple murine models of psoriasis. Our studies demonstrate that oral treatment with nitro oleic acid (OA-NO₂) has both preventative and therapeutic effects on psoriasiform inflammation. In line with this finding, oral OA-NO₂ downregulated the production of inflammatory cytokines in the skin. In vitro experiments demonstrate that OA-NO₂ decreased both basal IL-6 levels and IL-17A-induced expression of IL-6 in human dermal fibroblasts through the inhibition of NF-κB phosphorylation. Importantly, OA-NO₂ diminished STAT3 phosphorylation and nuclear translocation via nitroalkylation of STAT3, which inhibited keratinocyte proliferation. Overall, our results affirm the critical role of both NF-κB and STAT3 in the incitement of psoriasiform dermatitis and highlight the pharmacologic potential of small molecule nitroalkenes for the treatment of cutaneous inflammatory diseases, such as psoriasis.

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Oral OA-NO₂ has a therapeutic effect on inflammation in murine models of psoriasis.

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Cutaneous inflammatory cytokines are suppressed following oral OA-NO₂ treatment.

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OA-NO₂ decreases basal and IL-17A-induced IL-6 expression in vitro.

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OA-NO₂ diminishes STAT3 activation through nitroalkylation of STAT3.

Nitro-Oleic Acid in Seeds and Differently Developed Seedlings of Brassica napus L

Similar to animals, it has recently been proven that nitro-fatty acids such as nitro-linolenic acid and nitro-oleic acid (NO₂-OA) have relevant physiological roles as signalling molecules also in plants. Although NO₂-OA is of great therapeutic importance, its presence in plants as a free fatty acid has not been observed so far. Since Brassica napus (oilseed rape) is a crop with high oleic acid content, the abundance of NO₂-OA in its tissues can be assumed. Therefore, we quantified NO₂-OA in B. napus seeds and differently developed seedlings. In all samples, NO₂-OA was detectable at nanomolar concentrations. The seeds showed the highest NO₂-OA content, which decreased during germination. In contrast, nitric oxide (•NO) levels increased in the early stages of germination and seedling growth. Exogenous NO₂-OA treatment (100 µM, 24 h) of Brassica seeds resulted in significantly increased •NO level and induced germination capacity compared to untreated seeds. The results of in vitro approaches (4-Amino-5-methylamino-2′,7′-difluorofluorescein (DAF-FM) fluorescence, •NO-sensitive electrode) supported the •NO liberating capacity of NO₂-OA. We observed for the first time that Brassica seeds and seedlings contain free NO₂-OA which may be involved in germination as an •NO donor as suggested both by the results of exogenous NO₂-OA treatment of seeds and in vitro approaches. Due to their high NO₂-OA content, Brassica sprouts can be considered as a good source of dietary NO₂-OA intake.

Nitro-Fatty Acid Logistics: Formation, Biodistribution, Signaling, and Pharmacology

In addition to supporting cellular energetic demands and providing building blocks for lipid synthesis, fatty acids (FAs) are precursors of potent signaling molecules. In particular, the presence of conjugated double bonds on the fatty-acyl chain provides a preferential target for nitration generating nitro-FAs (NO₂-FAs). The formation of NO₂-FAs is a nonenzymatic process that requires reactive nitrogen species and occurs locally at the site of inflammation or during gastric acidification. NO₂-FAs are electrophilic and display pleiotropic signaling actions through reversible protein alkylation. This review focuses on the endogenously formed NO₂-FAs' mechanism of absorption, systemic distribution, signaling, and preclinical models. Understanding the dynamics of these processes will facilitate targeted dietary interventions and further the current pharmacological development aimed at low-grade inflammatory diseases.

Electrophilic nitro-oleic acid reverses obesity-induced hepatic steatosis

Non-alcoholic fatty liver disease (NAFLD) is linked to obesity and insulin resistance and is the most prevalent chronic liver disease. During the development of obesity and NAFLD, mitochondria adapt to the increased lipid load in hepatocytes by increasing the rate of fatty acid oxidation. In concert with this, reactive species (RS) generation is increased, damaging hepatocytes and inducing inflammation. Hepatic mitochondrial dysfunction is central to the pathogenesis of NAFLD via undefined mechanisms. There are no FDA approved treatments for NAFLD other than weight loss and management of glucose tolerance. Electrophilic nitro-oleic acid (NO₂-OA) displays anti-inflammatory and antioxidant signaling actions, thus mitochondrial dysfunction, RS production and inflammatory responses to NO₂-OA and the insulin sensitizer rosiglitazone were evaluated in a murine model of insulin resistance and NAFLD. Mice on HFD for 20 wk displayed increased adiposity, insulin resistance and hepatic lipid accumulation (steatosis) compared to mice on normal chow (NC). The HFD mice had mitochondrial dysfunction characterized by lower hepatic mitochondrial complex I, IV and V activity compared to mice on NC. Treatment with NO₂-OA or rosiglitazone for the last 42 days (out of 20 wk) abrogated HFD-mediated decreases in hepatic mitochondrial complex I, IV and V activity. Notably, NO₂-OA treatment normalized hepatic triglyceride levels and significantly reversed hepatic steatosis. Despite the improved glucose tolerance observed upon rosiglitazone treatment, liver weight and hepatic triglycerides were significantly increased over vehicle-treated HFD mice. These observations support that the pleiotropic signaling actions of electrophilic fatty acids limit the complex hepatic and systemic pathogenic responses instigated by obesity, without the adverse effects of thiazolidinedione drugs such as rosiglitazone.

Discovery of bioactive nitrated lipids and nitro-lipid-protein adducts using mass spectrometry-based approaches

Nitro-fatty acids (NO₂-FA) undergo reversible Michael adduction reactions with cysteine and histidine residues leading to the post-translational modification (PTM) of proteins. This electrophilic character of NO₂-FA is strictly related to their biological roles. The NO₂-FA-induced PTM of signaling proteins can lead to modifications in protein structure, function, and subcellular localization. The nitro lipid-protein adducts trigger a series of downstream signaling events that culminates with anti-inflammatory, anti-hypertensive, and cytoprotective effects mediated by NO₂-FA. These lipoxidation adducts have been detected and characterized both in model systems and in biological samples by using mass spectrometry (MS)-based approaches. These MS approaches allow to unequivocally identify the adduct together with the targeted residue of modification. The identification of the modified proteins allows inferring on the possible impact of the NO₂-FA-induced modification. This review will focus on MS-based approaches as valuable tools to identify NO₂-FA-protein adducts and to unveil the biological effect of this lipoxidation adducts.

Electrophiles modulate glutathione reductase activity via alkylation and upregulation of glutathione biosynthesis

Cells evolved robust homeostatic mechanisms to protect against oxidation or alkylation by electrophilic species. Glutathione (GSH) is the most abundant intracellular thiol, protects cellular components from oxidation and is maintained in a reduced state by glutathione reductase (GR). Nitro oleic acid (NO₂-OA) is an electrophilic fatty acid formed under digestive and inflammatory conditions that both reacts with GSH and induces its synthesis upon activation of Nrf2 signaling. The effects of NO₂-OA on intracellular GSH homeostasis were evaluated. In addition to upregulation of GSH biosynthesis, we observed that NO₂-OA increased intracellular GSSG in an oxidative stress-independent manner. NO₂-OA directly inhibited GR in vitro by covalent modification of the catalytic Cys61, with k_on of (3.45 ± 0.04) × 10³ M⁻¹ s⁻¹, k_off of (4.4 ± 0.4) × 10⁻⁴ s⁻¹, and K_eq of (1.3 ± 0.1) × 10⁻⁷ M. Akin to NO₂-OA, the electrophilic Nrf2 activators bardoxolone-imidazole (CDDO-Im), bardoxolone-methyl (CDDO-Me) and dimethyl fumarate (DMF) also upregulated GSH biosynthesis while promoting GSSG accumulation, but without directly inhibiting GR activity. In vitro assays in which GR was treated with increasing GSH concentrations and GSH depletion experiments in cells revealed that GR activity is finely regulated via product inhibition, an observation further supported by theoretical (kinetic modeling of cellular GSSG:GSH levels) approaches. Together, these results describe two independent mechanisms by which electrophiles modulate the GSH/GSSG couple, and provide a novel conceptual framework to interpret experimentally determined values of GSH and GSSG.

Profile of Arachidonic Acid-Derived Inflammatory Markers and Its Modulation by Nitro-Oleic Acid in an Inherited Model of Amyotrophic Lateral Sclerosis

The lack of current treatments for amyotrophic lateral sclerosis (ALS) highlights the need of a comprehensive understanding of the biological mechanisms of the disease. A consistent neuropathological feature of ALS is the extensive inflammation around motor neurons and axonal degeneration, evidenced by accumulation of reactive astrocytes and activated microglia. Final products of inflammatory processes may be detected as a screening tool to identify treatment response. Herein, we focus on (a) detection of arachidonic acid (AA) metabolization products by lipoxygenase (LOX) and prostaglandin endoperoxide H synthase in SOD1^G93A mice and (b) evaluate its response to the electrophilic nitro-oleic acid (NO₂-OA). Regarding LOX-derived products, a significant increase in 12-hydroxyeicosatetraenoic acid (12-HETE) levels was detected in SOD1^G93A mice both in plasma and brain whereas no changes were observed in age-matched non-Tg mice at the onset of motor symptoms (90 days-old). In addition, 15-hydroxyeicosatetraenoic acid (15-HETE) levels were greater in SOD1^G93A brains compared to non-Tg. Prostaglandin levels were also increased at day 90 in plasma from SOD1^G93A compared to non-Tg being similar in both types of animals at later stages of the disease. Administration of NO₂-OA 16 mg/kg, subcutaneously (s/c) three times a week to SOD1^G93A female mice, lowered the observed increase in brain 12-HETE levels compared to the non-nitrated fatty acid condition, and modified many others inflammatory markers. In addition, NO₂-OA significantly improved grip strength and rotarod performance compared to vehicle or OA treated animals. These beneficial effects were associated with increased hemeoxygenase 1 (HO-1) expression in the spinal cord of treated mice co-localized with reactive astrocytes. Furthermore, significant levels of NO₂-OA were detected in brain and spinal cord from NO₂-OA -treated mice indicating that nitro-fatty acids (NFA) cross brain–blood barrier and reach the central nervous system to induce neuroprotective actions. In summary, we demonstrate that LOX-derived oxidation products correlate with disease progression. Overall, we are proposing that key inflammatory mediators of AA-derived pathways may be useful as novel footprints of ALS onset and progression as well as NO₂-OA as a promising therapeutic compound.

Nitrolipids in kidney physiology and disease

The kidneys are vital organs responsible for maintaining body fluid homeostasis within proper physiologic ranges. Kidney disease is an epidemic clinical problem causing significant morbidity and mortality, and current treatments are limited to renin-angiotensin system blockade or renal replacement therapy for the majority of affected individuals. There is a critical, unmet need for novel pharmacological agents to improve the outcome of patients with kidney disease. Nitro-oleic acid (NO2-OA) is an endogenously generated electrophilic compound with the capacity to modify thiols in proteins, altering their function. The most important targets appear to be the Keap1/Nrf2 and NF-κB pathways, which have widespread effects on antioxidant, detoxifying, and inflammatory responses in cells and tissues. Through these and potentially additional protective actions, NO2-OA may be capable of preserving or enhancing kidney function in acute and chronic kidney diseases.

Inflammatory signaling and metabolic regulation by nitro-fatty acids

The addition of nitrogen dioxide (NO2) to the double bond of unsaturated fatty acids yields an array of electrophilic nitro-fatty acids (NO2-FA) with unique biochemical and signaling properties. During the last decade, NO2-FA have been shown to exert a protective role in various inflammatory and metabolic disorders. NO2-FA exert their biological effects primarily by regulating two central physiological adaptive responses: the canonical inflammatory signaling and metabolic pathways. In this mini-review, we summarize current knowledge on the regulatory role of NO2-FA in the inflammatory and metabolic response via regulation of nuclear factor kappa B (NF-κB) and peroxisome proliferator-activated receptor γ (PPARγ), master regulators of inflammation and metabolism. Moreover, the engagement of novel signaling and metabolic pathways influenced by NO2-FA, beyond NF-κB and PPAR signaling, is discussed herein.

Regulation of stress signaling pathways by nitro-fatty acids

Electrophilic nitrated-fatty acids (NO2-FA, nitroalkenes) are formed during reactions of NO-derived oxidized species (•NO, •NO2) with either free or esterified polyunsaturated fatty acids. Due to their electrophilic character, they react with nucleophiles such as cysteine thiols in signaling proteins, thereby triggering downstream signaling cascades. Herein, we review two stress-signaling pathways activated by nitroalkenes, the KEAP1-NRF2 signaling pathway and the heat shock response (HSR) pathway. In addition, their biological and pharmacological relevance are discussed. Given that perturbations in both proteostasis and redox balance are common in many disease processes, dual activation of both pathways by nitroalkenes is a promising pharmacological approach for their treatment.

Topical electrophilic nitro-fatty acids potentiate cutaneous inflammation

Endogenous electrophilic fatty acids mediate anti-inflammatory responses by modulating metabolic and inflammatory signal transduction and gene expression. Nitro-fatty acids and other electrophilic fatty acids may thus be useful for the prevention and treatment of immune-mediated diseases, including inflammatory skin disorders. In this regard, subcutaneous (SC) injections of nitro oleic acid (OA-NO₂), an exemplary nitro-fatty acid, inhibit skin inflammation in a model of allergic contact dermatitis (ACD). Given the nitration of unsaturated fatty acids during metabolic and inflammatory processes and the growing use of fatty acids in topical formulations, we sought to further study the effect of nitro-fatty acids on cutaneous inflammation. To accomplish this, the effect of topically applied OA-NO₂ on skin inflammation was evaluated using established murine models of contact hypersensitivity (CHS). In contrast to the effects of subcutaneously injected OA-NO₂, topical OA-NO₂ potentiated hapten-dependent inflammation inducing a sustained neutrophil-dependent inflammatory response characterized by psoriasiform histological features, increased angiogenesis, and an inflammatory infiltrate that included neutrophils, inflammatory monocytes, and γδ T cells. Consistent with these results, HPLC-MS/MS analysis of skin from psoriasis patients displayed a 56% increase in nitro-conjugated linoleic acid (CLA-NO₂) levels in lesional skin compared to non-lesional skin. These results suggest that nitro-fatty acids in the skin microenvironment are products of cutaneous inflammatory responses and, in high local concentrations, may exacerbate inflammatory skin diseases.

Targeting nitric oxide and NMDA receptor-associated pathways in treatment of high grade glial tumors. Hypotheses for nitro-memantine and nitrones

Glioblastoma multiforme (GBM) is a devastating brain cancer with no curative treatment. Targeting Nitric Oxide (NO) and glutamatergic pathways may help as adjunctive treatments in GBM. NO at low doses promotes tumorigenesis, while at higher levels (above 300 nM) triggers apoptosis. Gliomas actively secrete high amounts of glutamate which activates EGR signaling and mediates degradation of peritumoral tissues via excitotoxic injury. Memantine inhibits NMDA-subtype of glutamate receptors (NMDARs) and induces autophagic death of glioma cells in vitro and blocks glioma growth in vivo. Nitro-memantines may exert further benefits by limiting NMDAR signaling and by delivery of NO to the areas of excessive NMDAR activity leading NO-accumulation at tumoricidal levels within gliomas. Due to the duality of NO in tumorigenesis, agents which attenuate NO levels may also act beneficial in treatment of GBM. Nitrone compounds including N-tert-Butyl-α-phenylnitrone (PBN) and its disulfonyl-phenyl derivative, OKN-007 suppress free radical formation in experimental cerebral ischemia. OKN-007 failed to show clinical efficacy in stroke, but trials demonstrated its high biosafety in humans including elderly subjects. PBN inhibits the signaling pathways of NF-κB, inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX). In animal models of liver cancer and glioblastoma, OKN-007 seemed more efficient than PBN in suppression of cell proliferation, microvascular density and in induction of apoptosis. OKN-007 also inhibits SULF2 enzyme, which promotes tumor growth via versatile pathways. We assume that nitromemantines may be more beneficial concomitant with chemo-radiotherapy while nitrones alone may act useful in suppressing basal tumor growth and angiogenesis.

Redox-dependent dimerization of p38α mitogen-activated protein kinase with mitogen-activated protein kinase kinase 3

The kinase p38α MAPK (p38α) plays a pivotal role in many biological processes. p38α is activated by canonical upstream kinases that phosphorylate the activation region. The purpose of our study was to determine whether such activation may depend on redox-sensing cysteines within p38α. p38α was activated and formed a disulfide-bound heterodimer with MAP2K3 (MKK3) in rat cardiomyocytes and isolated hearts exposed to H₂O₂. This disulfide heterodimer was sensitive to reduction by mercaptoethanol and was enhanced by the thioredoxin-reductase inhibitor auranofin. We predicted that Cys-119 or Cys-162 of p38α, close to the known MKK3 docking domain, were relevant for these redox characteristics. The C119S mutation decreased whereas the C162S mutation increased the dimer formation, suggesting that these two Cys residues act as vicinal thiols, consistent with C119S/C162S being incapable of sensing H₂O₂. Similarly, disulfide heterodimer formation was abolished in H9C2 cells expressing both MKK3 and p38α C119S/C162S and subjected to simulated ischemia and reperfusion. However, the p38α C119S/C162S mutants did not exhibit appreciable alteration in activating dual phosphorylation. In contrast, the anti-inflammatory agent 10-nitro-oleic acid (NO₂-OA), a component of the Mediterranean diet, reduced p38α activation and covalently modified Cys-119/Cys-162, probably obstructing MKK3 access. Moreover, NO₂-OA reduced the dephosphorylation of p38α by hematopoietic tyrosine phosphatase (HePTP). Furthermore, steric obstruction of Cys-119/Cys-162 by NO₂-OA pretreatment in Langendorff-perfused murine hearts prevented the p38-MKK3 disulfide dimer formation and attenuated H₂O₂-induced contractile dysfunction. Our findings suggest that cysteine residues within p38α act as redox sensors that can dynamically regulate the association between p38 and MKK3.

Electrophilic nitro-fatty acids suppress allergic contact dermatitis in mice

BACKGROUND

Reactions between nitric oxide (NO), nitrite (NO2-), and unsaturated fatty acids give rise to electrophilic nitro-fatty acids (NO₂ -FAs), such as nitro oleic acid (OA-NO₂ ) and nitro linoleic acid (LNO₂ ). Endogenous electrophilic fatty acids (EFAs) mediate anti-inflammatory responses by modulating metabolic and inflammatory signal transduction reactions. Hence, there is considerable interest in employing NO₂ -FAs and other EFAs for the prevention and treatment of inflammatory disorders. Thus, we sought to determine whether OA-NO₂ , an exemplary nitro-fatty acid, has the capacity to inhibit cutaneous inflammation.

METHODS

We evaluated the effect of OA-NO₂ on allergic contact dermatitis (ACD) using an established model of contact hypersensitivity in C57Bl/6 mice utilizing 2,4-dinitrofluorobenzene as the hapten.

RESULTS

We found that subcutaneous (SC) OA-NO₂ injections administered 18 h prior to sensitization and elicitation suppresses ACD in both preventative and therapeutic models. In vivo SC OA-NO₂ significantly inhibits pathways that lead to inflammatory cell infiltration and the production of inflammatory cytokines in the skin. Moreover, OA-NO₂ is capable of enhancing regulatory T-cell activity. Thus, OA-NO₂ treatment results in anti-inflammatory effects capable of inhibiting ACD by inducing immunosuppressive responses.

CONCLUSION

Overall, these results support the development of OA-NO₂ as a promising therapeutic for ACD and provides new insights into the role of electrophilic fatty acids in the control of cutaneous immune responses potentially relevant to a broad range of allergic and inflammatory skin diseases.

Evaluation of 10-Nitro Oleic Acid Bio-Elimination in Rats and Humans

Nitrated fatty acids are endogenously present in human and animal tissues, as well as in plant-derived oils. In particular, 10-nitro oleic acid (10-NO₂-OA) potently induces Nrf2-dependent antioxidant gene expression and inhibits TLR4/NF-κB signaling, thus promoting an overall cyto-protective and anti-inflammatory response. 10-NO₂-OA has been extensively tested in animal models and is currently undergoing clinical evaluation in humans. Bio-elimination pathways for 10-NO₂-OA were evaluated in rats (30 mg/kg·day) and in humans (0.34 mg/kg) using samples obtained from a double-blind, dose-rising clinical trial. Quantitative radiochromatographic/MS analysis indicated that the renal and fecal pathways are the main routes for 10-NO₂-OA excretion in rats, and allowed the identification of 4-nitro-octanedioic acid (NO₂-8:0-diCOOH) as the most abundant metabolite in rat urine. In addition, high resolution LC-MS/MS analysis revealed the presence of a novel series of urinary metabolites including ω-carboxylation and β-oxidation products, as well as N-acetylcysteine, taurine and sulfo-conjugates in both rats and humans. Overall, the findings reported herein not only provide valuable tools for the experimental evaluation of 10-NO₂-OA levels in vivo, but importantly they also set the basis for monitoring its metabolism during potential clinical interventions in humans.

The Chemical Basis of Thiol Addition to Nitro-conjugated Linoleic Acid, a Protective Cell-signaling Lipid

Nitroalkene fatty acids are formed in vivo and exert protective and anti-inflammatory effects via reversible Michael addition to thiol-containing proteins in key signaling pathways. Nitro-conjugated linoleic acid (NO₂-CLA) is preferentially formed, constitutes the most abundant nitrated fatty acid in humans, and contains two carbons that could potentially react with thiols, modulating signaling actions and levels. In this work, we examined the reactions of NO₂-CLA with low molecular weight thiols (glutathione, cysteine, homocysteine, cysteinylglycine, and β-mercaptoethanol) and human serum albumin. Reactions followed reversible biphasic kinetics, consistent with the presence of two electrophilic centers in NO₂-CLA located on the β- and δ-carbons with respect to the nitro group. The differential reactivity was confirmed by computational modeling of the electronic structure. The rates (k_on and k_off) and equilibrium constants for both reactions were determined for different thiols. LC-UV-Visible and LC-MS analyses showed that the fast reaction corresponds to β-adduct formation (the kinetic product), while the slow reaction corresponds to the formation of the δ-adduct (the thermodynamic product). The pH dependence of the rate constants, the correlation between intrinsic reactivity and thiol pK_a, and the absence of deuterium solvent kinetic isotope effects suggested stepwise mechanisms with thiolate attack on NO₂-CLA as rate-controlling step. Computational modeling supported the mechanism and revealed additional features of the transition states, anionic intermediates, and final neutral products. Importantly, the detection of cysteine-δ-adducts in human urine provided evidence for the biological relevance of this reaction. Finally, human serum albumin was found to bind NO₂-CLA both non-covalently and to form covalent adducts at Cys-34, suggesting potential modes for systemic distribution. These results provide new insights into the chemical basis of NO₂-CLA signaling actions.

Nitro-fatty acid pharmacokinetics in the adipose tissue compartment

Electrophilic nitro-FAs (NO₂-FAs) promote adaptive and anti-inflammatory cell signaling responses as a result of an electrophilic character that supports posttranslational protein modifications. A unique pharmacokinetic profile is expected for NO₂-FAs because of an ability to undergo reversible reactions including Michael addition with cysteine-containing proteins and esterification into complex lipids. Herein, we report via quantitative whole-body autoradiography analysis of rats gavaged with radiolabeled 10-nitro-[¹⁴C]oleic acid, preferential accumulation in adipose tissue over 2 weeks. To better define the metabolism and incorporation of NO₂-FAs and their metabolites in adipose tissue lipids, adipocyte cultures were supplemented with 10-nitro-oleic acid (10-NO₂-OA), nitro-stearic acid, nitro-conjugated linoleic acid, and nitro-linolenic acid. Then, quantitative HPLC-MS/MS analysis was performed on adipocyte neutral and polar lipid fractions, both before and after acid hydrolysis of esterified FAs. NO₂-FAs preferentially incorporated in monoacyl- and diacylglycerides, while reduced metabolites were highly enriched in triacylglycerides. This differential distribution profile was confirmed in vivo in the adipose tissue of NO₂-OA-treated mice. This pattern of NO₂-FA deposition lends new insight into the unique pharmacokinetics and pharmacologic actions that could be expected for this chemically-reactive class of endogenous signaling mediators and synthetic drug candidates.

Nitro-oleic acid ameliorates oxygen and glucose deprivation/re-oxygenation triggered oxidative stress in renal tubular cells via activation of Nrf2 and suppression of NADPH oxidase

Nitroalkene derivative of oleic acid (OA-NO₂), due to its ability to mediate revisable Michael addition, has been demonstrated to have various biological properties and become a therapeutic agent in various diseases. Though its antioxidant properties have been reported in different models of acute kidney injury (AKI), the mechanism by which OA-NO₂ attenuates intracellular oxidative stress is not well investigated. Here, we elucidated the anti-oxidative mechanism of OA-NO₂ in an in vitro model of renal ischemia/reperfusion (I/R) injury. Human tubular epithelial cells were subjected to oxygen and glucose deprivation/re-oxygenation (OGD/R) injury. Pretreatment with OA-NO₂ (1.25 μM, 45 min) attenuated OGD/R triggered reactive oxygen species (ROS) generation and subsequent mitochondrial membrane potential disruption. This action was mediated via up-regulating endogenous antioxidant defense components including superoxide dismutase (SOD1), heme oxygenase 1 (HO-1), and γ-glutamyl cysteine ligase modulatory subunits (GCLM). Moreover, subcellular fractionation analyses demonstrated that OA-NO₂ promoted nuclear translocation of nuclear factor-E2- related factor-2 (Nrf2) and Nrf2 siRNA partially abrogated these protective effects. In addition, OA-NO₂ inhibited NADPH oxidase activation and NADPH oxidase 4 (NOX4), NADPH oxidase 2 (NOX2) and p22^phox up-regulation after OGD/R injury, which was not relevant to Nrf2. These results contribute to clarify that the mechanism of OA-NO₂ reno-protection involves both inhibition of NADPH oxidase activity and induction of SOD1, Nrf2-dependent HO-1, and GCLM.

Nitrated Fatty Acids Reverse Cigarette Smoke-Induced Alveolar Macrophage Activation and Inhibit Protease Activity via Electrophilic S-Alkylation

Nitrated fatty acids (NFAs), endogenous products of nonenzymatic reactions of NO-derived reactive nitrogen species with unsaturated fatty acids, exhibit substantial anti-inflammatory activities. They are both reversible electrophiles and peroxisome proliferator-activated receptor γ (PPARγ) agonists, but the physiological implications of their electrophilic activity are poorly understood. We tested their effects on inflammatory and emphysema-related biomarkers in alveolar macrophages (AMs) of smoke-exposed mice. NFA (10-nitro-oleic acid or 12-nitrolinoleic acid) treatment downregulated expression and activity of the inflammatory transcription factor NF-κB while upregulating those of PPARγ. It also downregulated production of inflammatory cytokines and chemokines and of the protease cathepsin S (Cat S), a key mediator of emphysematous septal destruction. Cat S downregulation was accompanied by decreased AM elastolytic activity, a major mechanism of septal destruction. NFAs downregulated both Cat S expression and activity in AMs of wild-type mice, but only inhibited its activity in AMs of PPARγ knockout mice, pointing to a PPARγ-independent mechanism of enzyme inhibition. We hypothesized that this mechanism was electrophilic S-alkylation of target Cat S cysteines, and found that NFAs bind directly to Cat S following treatment of intact AMs and, as suggested by in silico modeling and calculation of relevant parameters, elicit S-alkylation of Cys25 when incubated with purified Cat S. These results demonstrate that NFAs' electrophilic activity, in addition to their role as PPARγ agonists, underlies their protective effects in chronic obstructive pulmonary disease (COPD) and support their therapeutic potential in this disease.

Nitro-oleic acid modulates classical and regulatory activation of macrophages and their involvement in pro-fibrotic responses

Inflammation is an immune response triggered by microbial invasion and/or tissue injury. While acute inflammation is directed toward invading pathogens and injured cells, thus enabling tissue regeneration, chronic inflammation can lead to severe pathologies and tissue dysfunction. These processes are linked with macrophage polarization into specific inflammatory "M1-like" or regulatory "M2-like" subsets. Nitro-fatty acids (NO2-FAs), produced endogenously as byproducts of metabolism and oxidative inflammatory conditions, may be useful for treating diseases associated with dysregulated immune homeostasis. The goal of this study was to characterize the role of nitro-oleic acid (OA-NO2) in regulating the functional specialization of macrophages induced by bacterial lipopolysaccharide or interleukin-4, and to reveal specific signaling mechanisms which can account for OA-NO2-dependent modulation of inflammation and fibrotic responses. Our results show that OA-NO2 inhibits lipopolysaccharide-stimulated production of both pro-inflammatory and immunoregulatory cytokines (including transforming growth factor-β) and inhibits nitric oxide and superoxide anion production. OA-NO2 also decreases interleukin-4-induced macrophage responses by inhibiting arginase-I expression and transforming growth factor-β production. These effects are mediated via downregulation of signal transducers and activators of transcription, mitogen-activated protein kinase and nuclear factor-кB signaling responses. Finally, OA-NO2 inhibits fibrotic processes in an in vivo model of angiotensin II-induced myocardial fibrosis by attenuating expression of α-smooth muscle actin, systemic transforming growth factor-β levels and infiltration of both "M1-" and "M2-like" macrophage subsets into afflicted tissue. Overall, the electrophilic fatty acid derivative OA-NO2 modulates a broad range of "M1-" and "M2-like" macrophage functions and represents a potential therapeutic approach to target diseases associated with dysregulated macrophage subsets.

Nitro-fatty acids in cardiovascular regulation and diseases: characteristics and molecular mechanisms

Electrophilic nitro-fatty acids (NO2-FAs) are endogenously formed by redox reactions of nitric oxide ((.)NO)- and nitrite ((.)NO2)- derived nitrogen dioxide with unsaturated fatty acids. Nitration preferentially occurs on polyunsaturated fatty acids with conjugated dienes under physiological or pathophysiological conditions such as during digestion, metabolism and as adaptive inflammatory processes. Nitro-fatty acids are present in free and esterified forms achieving broad biodistribution in humans and experimental models. Structural, functional and biological characterization of NO2-FAs has revealed clinically relevant protection from inflammatory injury in a number of cardiovascular, renal and metabolic experimental models. NO2-FAs are engaged in posttranslational modifications (PTMs) of a selective redox sensitive pool of proteins and regulate key adaptive signaling pathways involved in cellular homeostasis and inflammatory response. Here, we review and update the biosynthesis, metabolism and signaling actions of NO2-FAs, highlighting their diverse protective roles relevant to the cardiovascular system.

Protection of nitro-fatty acid against kidney diseases

Nitrated derivatives of unsaturated fatty acids are endogenously formed under oxidative and nitrative stress condition and are defined as electrophilic fatty acids containing a nitro group to a carbon-carbon double bond. Among the most studied nitro derivatives of unsaturated fatty acids are nitro-oleic acid (OA-NO₂) and nitro-linoleic acid (LNO₂). These products exhibit novel protective actions in a variety of rodent disease models. Diverse signaling events are responsible for effects of nitrated fatty acid, including activating peroxisome proliferator-activated receptor-dependent gene expression, suppressing NF-κB-induced inflammation, inhibiting oxidative stress, and increasing both endothelial nitric oxide synthase- and Nrf2-dependent gene regulation. Nitrated fatty acids have been emerging not only as a unique class of signaling molecules produced endogenously and but also as multipotent modulators of cell signaling pathways in cardiovascular and renal diseases. In this review, we discuss biochemical properties of nitrated fatty acid and its signaling pathways in the modulation of cellular events. A major focus is to review recent knowledge of nitrated fatty acid on the treatment of kidney diseases and its therapeutic potential for inflammation and metabolic disorders, with special emphasis on acute kidney injury and diabetic kidney disease.

Designing drugs that combat kidney damage

INTRODUCTION

Kidney disease remains one of the last worldwide frontiers in the field of non-communicable human disease. From 1990 to 2013, chronic kidney disease (CKD) was the top non-communicable cause of death with a greatest increase in global years of life lost while mortality of acute kidney injury (AKI) still hovers around 50%. This reflects the paucity (for CKD) or lack of (for AKI) therapeutic approaches beyond replacing renal function. Understanding what the barriers are and what potential pathways may facilitate the design of new drugs to combat kidney disease is a key public health priority.

AREAS COVERED

The authors discuss the hurdles and opportunities for future drug development for kidney disease in light of experience accumulated with drugs that made it to clinical trials.

EXPERT OPINION

Inflammation, cell death and fibrosis are key therapeutic targets to combat kidney damage. While the specific targeting of drugs to kidney cells would be desirable, the technology is only working at the preclinical stage and with mixed success. Nanomedicines hold promise in this respect. Most drugs undergoing clinical trials for kidney disease have been repurposed from other indications. Currently, the chemokine receptor inhibitor CCX140 holds promise for CKD and the p53 inhibitor QPI-1002 for AKI.

Nitrooleic acid protects against cisplatin nephropathy: role of COX-2/mPGES-1/PGE2 cascade

Nitrooleic acid (OA-NO₂) is an endogenous lipid product which has novel signaling properties, particularly the activation of peroxisome proliferator-activated receptors. The current study aimed to evaluate the protective effects of OA-NO₂ against cisplatin-induced kidney injury in mice. Mice were pretreated with OA-NO₂ for 48 h before cisplatin administration, and the cisplatin-caused nephrotoxicity was evaluated. After the cisplatin treatment (72 h), the vehicle-treated mice displayed renal dysfunction, as evidenced by the elevated plasma urea and creatinine, which was consistent with the histological damage, such as tubular necrosis, dilation, protein cast, and desquamation of epithelial cells. In contrast, the severity of the renal dysfunction and histological change were reduced in the OA-NO₂ pretreated mice. The renal COX-2 and mPGES-1 mRNAs and their respective proteins expression, together with the renal PGE₂ amounts, were induced by the cisplatin treatment, but their initiation was reduced by OA-NO₂. Moreover, the circulating TNF-α, renal TNF-α, IL-1β, MCP-1, ICAM-1, and VACAM-1 mRNA levels were higher in the cisplatin-treated mice, compared with the controls, but they were attenuated in the OA-NO₂ pretreatment group. In summary, the pretreatment with OA-NO₂ remarkably ameliorated the cisplatin-induced kidney injury in mice, possibly via the inhibition of the inflammatory response, associated with the COX-2/mPGES-1/PGE₂ cascade.

Nitrooleic Acid Attenuates Lipid Metabolic Disorders and Liver Steatosis in DOCA-Salt Hypertensive Mice

Nitrooleic acid (OA-NO2) is endogenous ligands for peroxisome proliferator-activated receptors. The present study was aimed at investigating the beneficial effects of OA-NO2 on the lipid metabolism and liver steatosis in deoxycorticosterone acetate- (DOCA-) salt induced hypertensive mice model. Male C57BL/6 mice were divided to receive DOCA-salt plus OA-NO2 or DOCA-salt plus vehicle and another group received neither DOCA-salt nor OA-NO2 (control group). After 3-week treatment with DOCA-salt plus 1% sodium chloride in drinking fluid, the hypertension was noted; however, OA-NO2 had no effect on the hypertension. In DOCA-salt treated mice, the plasma triglyceride and total cholesterol levels were significantly increased compared to control mice, and pretreatment with OA-NO2 significantly reduced these parameters. Further, the histopathology of liver exhibited more lipid distribution together with more serious micro- and macrovesicular steatosis after DOCA-salt treatment and that was consistent with liver tissue triglyceride and nonesterified fatty acids (NEFA) content. The mice pretreated with OA-NO2 showed reduced liver damage accompanied with low liver lipid content. Moreover, the liver TBARS, together with the expressions of gp91phox and p47phox, were parallelly decreased. These findings indicated that OA-NO2 had the protective effect on liver injury against DOCA-salt administration and the beneficial effect could be attributed to its antihyperlipidemic activities.

TRPM2 mediates ischemic kidney injury and oxidant stress through RAC1

Ischemia is a leading cause of acute kidney injury. Kidney ischemia is associated with loss of cellular ion homeostasis; however, the pathways that underlie ion homeostasis dysfunction are poorly understood. Here, we evaluated the nonselective cation channel transient receptor potential melastatin 2 (TRPM2) in a murine model of kidney ischemia/reperfusion (I/R) injury. TRPM2-deficient mice were resistant to ischemic injury, as reflected by improved kidney function, reduced histologic damage, suppression of proapoptotic pathways, and reduced inflammation. Moreover, pharmacologic TRPM2 inhibition was also protective against I/R injury. TRPM2 was localized mainly in kidney proximal tubule epithelial cells, and studies in chimeric mice indicated that the effects of TRPM2 are due to expression in parenchymal cells rather than hematopoietic cells. TRPM2-deficient mice had less oxidative stress and lower levels of NADPH oxidase activity after ischemia. While RAC1 is a component of the NADPH oxidase complex, its relation to TRPM2 and kidney ischemic injury is unknown. Following kidney ischemia, TRPM2 promoted RAC1 activation, with active RAC1 physically interacting with TRPM2 and increasing TRPM2 expression at the cell membrane. Finally, inhibition of RAC1 reduced oxidant stress and ischemic injury in vivo. These results demonstrate that TRPM2-dependent RAC1 activation increases oxidant stress and suggest that therapeutic approaches targeting TRPM2 and/or RAC1 may be effective in reducing ischemic kidney injury.

New Insights into the PPAR γ Agonists for the Treatment of Diabetic Nephropathy

Diabetic nephropathy (DN) is a severe complication of diabetes and serves as the leading cause of chronic renal failure. In the past decades, angiotensin-converting enzyme inhibitors (ACEIs)/angiotensin II receptor blockers (ARBs) based first-line therapy can slow but cannot stop the progression of DN, which urgently requests the innovation of therapeutic strategies. Thiazolidinediones (TZDs), the synthetic exogenous ligands of nuclear receptor peroxisome proliferator-activated receptor- γ (PPAR γ ), had been thought to be a promising candidate for strengthening the therapy of DN. However, the severe adverse effects including fluid retention, cardiovascular complications, and bone loss greatly limited their use in clinic. Recently, numerous novel PPAR γ agonists involving the endogenous PPAR γ ligands and selective PPAR γ modulators (SPPARMs) are emerging as the promising candidates of the next generation of antidiabetic drugs instead of TZDs. Due to the higher selectivity of these novel PPAR γ agonists on the regulation of the antidiabetes-associated genes than that of the side effect-associated genes, they present fewer adverse effects than TZDs. The present review was undertaken to address the advancements and the therapeutic potential of these newly developed PPAR γ agonists in dealing with diabetic kidney disease. At the same time, the new insights into the therapeutic strategies of DN based on the PPAR γ agonists were fully addressed.

Redox-dependent anti-inflammatory signaling actions of unsaturated fatty acids

Unsaturated fatty acids are metabolized to reactive products that can act as pro- or anti-inflammatory signaling mediators. Electrophilic fatty acid species, including nitro- and oxo-containing fatty acids, display salutary anti-inflammatory and metabolic actions. Electrophilicity can be conferred by both enzymatic and oxidative reactions, via the homolytic addition of nitrogen dioxide to a double bond or via the formation of α,β-unsaturated carbonyl and epoxide substituents. The endogenous formation of electrophilic fatty acids is significant and influenced by diet, metabolic, and inflammatory reactions. Transcriptional regulatory proteins and enzymes can sense the redox status of the surrounding environment upon electrophilic fatty acid adduction of functionally significant, nucleophilic cysteines. Through this covalent and often reversible posttranslational modification, gene expression and metabolic responses are induced. At low concentrations, the pleiotropic signaling actions that are regulated by these protein targets suggest that some classes of electrophilic lipids may be useful for treating metabolic and inflammatory diseases.

Asymmetric dimethylarginine accumulates in the kidney during ischemia/reperfusion injury

Ischemia/reperfusion injury is the leading cause of acute tubular necrosis. Nitric oxide has a protective role against ischemia/reperfusion injury; however, the role of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, in ischemia/reperfusion injury remains unclear. ADMA is produced by protein arginine methyltransferase (PRMT) and is mainly degraded by dimethylarginine dimethylaminohydrolase (DDAH). Here we examined the kinetics of ADMA and PRMT and DDAH expression in the kidneys of ischemia/reperfusion-injured mice. After the injury, DDAH-1 levels were decreased and renal and plasma ADMA values were increased in association with renal dysfunction. Renal ADMA was correlated with 8-hydroxy-2'-deoxyguanosine, a marker of oxidative stress. An antioxidant, N-acetylcysteine, or a proteasomal inhibitor, MG-132, restored these alterations. Infusion of subpressor dose of ADMA exacerbated renal dysfunction, capillary loss, and tubular necrosis in the kidneys of ischemia/reperfusion-injured wild mice, while damage was attenuated in DDAH transgenic mice. Thus, ischemia/reperfusion injury-induced oxidative stress may reduce DDAH expression and cause ADMA accumulation, which may contribute to capillary loss and tubular necrosis in the kidney.

Combined losartan and nitro-oleic acid remarkably improves diabetic nephropathy in mice

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease (ESRD). The inhibitors of renin-angiotensin-aldosterone system (RAAS) can alleviate some of the symptoms of DN but fail to stop the progression to ESRD. Our previous studies demonstrate renoprotective action of nitro-oleic acid (OA-NO2) in several rodent models of renal disease. Here we examined the therapeutic potential and the underlying mechanism of combination of losartan and OA-NO2 in db/db mice. OA-NO2 was infused at 5 mg·kg(-1)·day(-1) via osmotic minipump, and losartan was incorporated into diet at 10 mg·kg(-1)·day(-1), each administered alone or in combination for 2 wk. Diabetic db/db mice developed progressive albuminuria and glomerulosclerosis, accompanied by podocytes loss, increased indexes of renal fibrosis, oxidative stress, and inflammation. Treatment of the diabetic mice with OA-NO2 or losartan alone moderately ameliorated kidney injury; however, the combined treatment remarkably reduced albuminuria, restored glomerular filtration barrier structure, and attenuated glomerulosclerosis, accompanied with significant suppression of renal oxidative stress and inflammation. These data demonstrate that combination of losartan and OA-NO2 effectively reverses renal injury in DN.

Vascular effects of dietary nitrate (as found in green leafy vegetables and beetroot) via the nitrate-nitrite-nitric oxide pathway

The discovery that dietary (inorganic) nitrate has important vascular effects came from the relatively recent realization of the 'nitrate-nitrite-nitric oxide (NO) pathway'. Dietary nitrate has been demonstrated to have a range of beneficial vascular effects, including reducing blood pressure, inhibiting platelet aggregation, preserving or improving endothelial dysfunction, enhancing exercise performance in healthy individuals and patients with peripheral arterial disease. Pre-clinical studies with nitrate or nitrite also show the potential to protect against ischaemia-reperfusion injury and reduce arterial stiffness, inflammation and intimal thickness. However, there is a need for good evidence for hard endpoints beyond epidemiological studies. Whilst these suggest reduction in cardiovascular risk with diets high in nitrate-rich vegetables (such as a Mediterranean diet), others have suggested possible small positive and negative associations with dietary nitrate and cancer, but these remain unproven. Interactions with other nutrients, such as vitamin C, polyphenols and fatty acids may enhance or inhibit these effects. In order to provide simple guidance on nitrate intake from different vegetables, we have developed the Nitrate 'Veg-Table' with 'Nitrate Units' [each unit being 1 mmol of nitrate (62 mg)] to achieve a nitrate intake that is likely to be sufficient to derive benefit, but also to minimize the risk of potential side effects from excessive ingestion, given the current available evidence. The lack of data concerning the long term effects of dietary nitrate is a limitation, and this will need to be addressed in future trials.

The nitrated fatty acid 10-nitro-oleate attenuates allergic airway disease

Asthma is a serious, growing problem worldwide. Inhaled steroids, the current standard therapy, are not always effective in this chronic inflammatory disease and can cause adverse effects. We tested the hypothesis that nitrated fatty acids (NFAs) may provide an effective alternative treatment. NFAs are endogenously produced by nonenzymatic reaction of NO with unsaturated fatty acids and exert anti-inflammatory actions both by activating the nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR)γ and via PPAR-independent mechanisms, but whether they might ameliorate allergic airway disease was previously untested. We found that pulmonary delivery of the NFA 10-nitro-oleic acid (OA-NO2) reduced the severity of murine allergic airway disease, as assessed by various pathological and molecular markers. Fluticasone, an inhaled steroid commonly used to treat asthma, produced similar effects on most end points, but only OA-NO2 induced robust apoptosis of neutrophils and their phagocytosis by alveolar macrophages. This suggests that OA-NO2 may be particularly effective in neutrophil-rich, steroid-resistant severe asthma. In primary human bronchial epithelial cells, OA-NO2 blocked phosphorylation and degradation of IκB and enhanced inhibitory binding of PPARγ to NF-κB. Our results indicate that the NFA OA-NO2 is efficacious in preclinical models of allergic airway disease and may have potential for treating asthma patients.

Modulation of nitro-fatty acid signaling: prostaglandin reductase-1 is a nitroalkene reductase

Inflammation, characterized by the activation of both resident and infiltrated immune cells, is accompanied by increased production of oxidizing and nitrating species. Nitrogen dioxide, the proximal nitrating species formed under these conditions, reacts with unsaturated fatty acids to yield nitroalkene derivatives. These electrophilic products modulate protein function via post-translational modification of susceptible nucleophilic amino acids. Nitroalkenes react with Keap1 to instigate Nrf2 signaling, activate heat shock response gene expression, and inhibit NF-κB-mediated signaling, inducing net anti-inflammatory and tissue-protective metabolic responses. We report the purification and characterization of a NADPH-dependent liver enzyme that reduces the nitroalkene moiety of nitro-oleic acid, yielding the inactive product nitro-stearic acid. Prostaglandin reductase-1 (PtGR-1) was identified as a nitroalkene reductase by protein purification and proteomic studies. Kinetic measurements, inhibition studies, immunological and molecular biology approaches as well as clinical analyses confirmed this identification. Overexpression of PtGR-1 in HEK293T cells promoted nitroalkene metabolism to inactive nitroalkanes, an effect that abrogated the Nrf2-dependent induction of heme oxygenase-1 expression by nitro-oleic acid. These results situate PtGR-1 as a critical modulator of both the steady state levels and signaling activities of fatty acid nitroalkenes in vivo.

Characterization and quantification of endogenous fatty acid nitroalkene metabolites in human urine

The oxidation and nitration of unsaturated fatty acids transforms cell membrane and lipoprotein constituents into mediators that regulate signal transduction. The formation of 9-NO2-octadeca-9,11-dienoic acid and 12-NO2-octadeca-9,11-dienoic acid stems from peroxynitrite- and myeloperoxidase-derived nitrogen dioxide reactions as well as secondary to nitrite disproportionation under the acidic conditions of digestion. Broad anti-inflammatory and tissue-protective responses are mediated by nitro-fatty acids. It is now shown that electrophilic fatty acid nitroalkenes are present in the urine of healthy human volunteers (9.9 ± 4.0 pmol/mg creatinine); along with electrophilic 16- and 14-carbon nitroalkenyl β-oxidation metabolites. High resolution mass determinations and coelution with isotopically-labeled metabolites support renal excretion of cysteine-nitroalkene conjugates. These products of Michael addition are in equilibrium with the free nitroalkene pool in urine and are displaced by thiol reaction with mercury chloride. This reaction increases the level of free nitroalkene fraction >10-fold and displays a K(D) of 7.5 × 10(-6) M. In aggregate, the data indicates that formation of Michael adducts by electrophilic fatty acids is favored under biological conditions and that reversal of these addition reactions is critical for detecting both parent nitroalkenes and their metabolites. The measurement of this class of mediators can constitute a sensitive noninvasive index of metabolic and inflammatory status.

Nitro-oleic acid protects against adriamycin-induced nephropathy in mice

Adriamycin (ADR) administration in susceptible rodents such as the BALB/c mouse strain produces injury to the glomerulus mimicking human focal glomerular sclerosis. The goal of the present study was to use this model to investigate antiproteinuric action of nitro-oleic acid (OA-NO2), a nitric oxide-derived endogenous lipid product, which has exhibited multiple attractive signaling properties particularly in the kidney. BALB/c mice were pretreated for 2 days with OA-NO2 at 5 mg·kg(-1)·day(-1) via an osmotic minipump, followed by a single injection of vehicle or adriamycin (10 mg/kg) via the tail vein. Albuminuria and renal function were analyzed at 1 wk post-ADR treatment. ADR mice developed prominent albuminuria, hypoalbuminemia, hyperlipidemia, and severe ascites. In contrast, the symptoms of nephrotic syndrome were greatly improved by OA-NO2 treatment. In parallel, plasma creatinine and plasma urea nitrogen were elevated in the ADR group, and the severity was less in the ADR+OA-NO2 group. OA-NO2 attenuates ADR-induced glomerulosclerosis, podocyte loss, and tubulointerstitial fibrosis. Indices of oxidative stress, including plasma and urinary thiobarbituric acid-reactive substances and renal expression of NAD(P)H oxidase p47(phox) and gp91(phox), and inflammation, including renal expression of TNF-α, IL-1β, and MCP-1 in response to ADR, were all similarly suppressed. Together, these findings suggest that OA-NO2 exerts renoprotective action against ADR nephropathy likely via its anti-inflammatory and antioxidant properties.

Alpha-tocopherol ameliorates oxidative renal insult associated with spinal cord reperfusion injury

Ischemic-reperfusion procedures targeting a specific organ often results in remote multiple organ injuries mediated possibly by heightened oxidative stress levels. As the kidney is one of the most vulnerable organs for ischemic oxidative stress, the aim of the present study was to confirm the occurrence of renal complication secondary to spinal cord ischemic-reperfusion injury (SC-IRI) induced by aortic clamping. The study also investigated the possible prophylactic effect of long-term administration of α-tocopherol (α-TOL) against high level of renal oxidative stress and inflammatory processes induced by SC-IRI. In this study, a total of 60 male Sprague-Dawley rats were randomly divided into five equal groups: C group underwent no surgery; CE group received α-TOL 600 mg/kg intramuscular twice weekly for 6 weeks; S group were subjected to laparotomy without clamping of the aorta; SE group were handled as S group and treated with α-TOL as group CE; SC-IRI group were subjected to laparotomy with clamping of the aorta just above the bifurcation of the aorta for 45 min, then the clamp was released for 48 h for reperfusion. SC-IRIE group was subjected to IRI as in group SC-IRI and was injected with α-TOL in the same dose and route as α-TOL-treated control group. SC-IRI resulted in increases in serum creatinine, blood urea nitrogen, plasma nitrite/nitrate level, serum tumor necrosis factor alpha, renal tissue homogenate level for malondialdehyde, superoxide dismutase and prostaglandin E2. Long-term prophylactic treatment with α-TOL resulted in amelioration of the renal functional disturbances and all measured parameters of oxidative stress and inflammation. Ischemic reperfusion injury of the spinal cord induced some remote renal functional disturbances although some of the observed changes may have resulted from decreased renal blood flow due to the hypotension induced during the procedure. Prophylactic long-term α-TOL administration guards against the renal function disturbances an effect that can be attributed, at least partially, to improvement of the renal pro-oxidant/antioxidant balance and inhibition of the inflammatory processes.

Conjugated linoleic acid is a preferential substrate for fatty acid nitration

The oxidation and nitration of unsaturated fatty acids by oxides of nitrogen yield electrophilic derivatives that can modulate protein function via post-translational protein modifications. The biological mechanisms accounting for fatty acid nitration and the specific structural characteristics of products remain to be defined. Herein, conjugated linoleic acid (CLA) is identified as the primary endogenous substrate for fatty acid nitration in vitro and in vivo, yielding up to 10(5) greater extent of nitration products as compared with bis-allylic linoleic acid. Multiple enzymatic and cellular mechanisms account for CLA nitration, including reactions catalyzed by mitochondria, activated macrophages, and gastric acidification. Nitroalkene derivatives of CLA and their metabolites are detected in the plasma of healthy humans and are increased in tissues undergoing episodes of ischemia reperfusion. Dietary CLA and nitrite supplementation in rodents elevates NO(2)-CLA levels in plasma, urine, and tissues, which in turn induces heme oxygenase-1 (HO-1) expression in the colonic epithelium. These results affirm that metabolic and inflammatory reactions yield electrophilic products that can modulate adaptive cell signaling mechanisms.

Nitro-fatty acids as novel electrophilic ligands for peroxisome proliferator-activated receptors

Lipid nitration has been observed during oxidative/nitrative stress conditions generating a variety of biomolecules capable of modulating cellular responses. This concept has grown as a result of studies with nitro-derivatives of long-chain unsaturated fatty acids containing a nitroalkene group (nitro-fatty acids). This review focuses on the interactions of nitro-fatty acids with members of the peroxisome proliferator-activated receptors (PPARs) family. These nuclear receptors belong to a superfamily of ligand-activated transcription factors, which serve as sensors of lipophilic molecules and regulate the expression of a set of genes involved in glucose and lipid metabolism. Here we discuss how nitro-fatty acids bind and activate PPARs, including the current knowledge of the molecular interactions and cell signaling events involved as well as their therapeutic potential associated with chronic inflammation and metabolic disorders.

The Nitrated Fatty Acid 10-Nitro-oleate Diminishes Severity of LPS-Induced Acute Lung Injury in Mice

Acute lung injury (ALI) is an inflammatory condition culminating in respiratory failure. There is currently no effective pharmacological treatment. Nitrated fatty acids (NFAs) have been shown to exert anti-inflammatory effects. We therefore hypothesized that delivery of NFAs directly to the site of inflammation would reduce the severity of ALI. Pulmonary delivery of 10-nitro-oleate following endotoxin-induced ALI in mice reduced markers of lung inflammation and injury, including capillary leakage, lung edema, infiltration of neutrophils into the lung, and oxidant stress, as well as plasma levels of proinflammatory cytokines. Nitro-oleate delivery likewise downregulated expression of proinflammatory genes by alveolar macrophages, key cells in regulation of lung inflammation. These effects may be accounted for by the observed increases in the activity of PPAR-γ and the PPAR-γ-induced antioxidant transcription factor Nrf2, together with the decreased activity of NF-κB. Our results demonstrate that pulmonary delivery of NFAs reduces severity of acute lung injury and suggest potential utility of these molecules in other inflammatory lung diseases.

Carbon monoxide inhibits apoptosis during cold storage and protects kidney grafts donated after cardiac death

Ischemia/reperfusion (I/R) injury remains as a serious deleterious factor in kidney transplantation (KTx). We hypothesized that carbon monoxide (CO), an endogenous potent cytoprotective molecule, inhibits hypothermia-induced apoptosis of kidney grafts. Using the rat KTx model mimicking the conditions of donation after cardiac death (DCD) as well as nontransplantable human kidney grafts, this study examined effects of CO in preservation solution in improving the quality of marginal kidney grafts. After cardiac cessation, rat kidneys underwent 40 min warm ischemia (WI) and 24 h cold storage (CS) in control UW or UW containing CO (CO-UW). At the end of CS, kidney grafts in control UW markedly increased mitochondrial porin release into the cytosol and resulted in increased cleaved caspase-3 and PARP expression. In contrast, grafts in CO-UW had significantly reduced mitochondrial breakdown and caspase pathway activation. After KTx, recipient survival significantly improved with CO-UW with less TUNEL(+) cells and reduced mRNA upregulation for proinflammatory mediators (IL-6, TNF-α, iNOS). Furthermore, when nontransplantable human kidney grafts were stored in CO-UW for 24 h, graft PARP expression, TUNEL(+) cells, and proinflammatory mediators were less than those in control UW. CO in UW inhibited hypothermia-induced apoptosis and significantly improved kidney graft function and outcomes of KTx.

Nitro-oleic acid targets transient receptor potential (TRP) channels in capsaicin sensitive afferent nerves of rat urinary bladder

Nitro-oleic acid (9- and 10-nitro-octadeca-9-enoic acid, OA-NO(2)) is an electrophilic fatty acid nitroalkene derivative that modulates gene transcription and protein function via post-translational protein modification. Nitro-fatty acids are generated from unsaturated fatty acids by oxidative inflammatory reactions and acidic conditions in the presence of nitric oxide or nitrite. Nitroalkenes react with nucleophiles such as cysteine and histidine in a variety of susceptible proteins including transient receptor potential (TRP) channels in sensory neurons of the dorsal root and nodose ganglia. The present study revealed that OA-NO(2) activates TRP channels on afferent nerve terminals in the urinary bladder and thereby increases bladder activity. The TRPV1 agonist capsaicin (CAPS, 1 μM) and the TRPA1 agonist allyl isothiocyanate (AITC, 30 μM), elicited excitatory effects in bladder strips, increasing basal tone and amplitude of phasic bladder contractions (PBC). OA-NO(2) mimicked these effects in a concentration-dependent manner (1 μM-33 μM). The TRPA1 antagonist HC3-030031 (HC3, 30 μM) and the TRPV1 antagonist diaryl piperazine analog (DPA, 1 μM), reduced the effect of OA-NO(2) on phasic contraction amplitude and baseline tone. However, the non-selective TRP channel blocker, ruthenium red (30 μM) was a more effective inhibitor, reducing the effects of OA-NO(2) on basal tone by 75% and the effects on phasic amplitude by 85%. In bladder strips from CAPS-treated rats, the effect of OA-NO(2) on phasic contraction amplitude was reduced by 65% and the effect on basal tone was reduced by 60%. Pretreatment of bladder strips with a combination of neurokinin receptor antagonists (NK1 selective antagonist, CP 96345; NK2 selective antagonist, MEN 10,376; NK3 selective antagonist, SB 234,375, 1 μM each) reduced the effect of OA-NO(2) on basal tone, but not phasic contraction amplitude. These results indicate that nitroalkene fatty acid derivatives can activate TRP channels on CAPS-sensitive afferent nerve terminals, leading to increased bladder contractile activity. Nitrated fatty acids produced endogenously by the combination of fatty acids and oxides of nitrogen released from the urothelium and/or afferent nerves may play a role in modulating bladder activity.

Nitroalkylation--a redox sensitive signaling pathway

Redox-sensitive posttranslational modification emerged as important signaling mechanisms. Besides other posttranslational modifications nitroalkylation by nitrated fatty acids mediate favorable anti-inflammatory effects. This review gives an overview of the generation and the reactivity of nitrated fatty acids. Additionally, it provides insights into the so far described pathways regulated by nitrated fatty acids. This article is part of a Special Issue entitled Regulation of Cellular Processes by S-nitrosylation.