Electrophilic fatty acid nitroalkenes are systemically transported and distributed upon esterification to complex lipids

Nitro-oleic acid enhances mitochondrial metabolism and ameliorates heart failure with preserved ejection fraction in mice

The prevalence of heart failure with preserved ejection fraction (HFpEF) is increasing, while treatment options are inadequate. Hypertension and obesity-related metabolic dysfunction contribute to HFpEF. Nitro-oleic acid (NO2-OA) impacts metabolic syndromes by improving glucose tolerance and adipocyte function. Here we show that treatment with NO2-OA ameliorates diastolic dysfunction and heart failure symptoms in a HFpEF mouse model induced by high-fat diet and inhibition of the endothelial nitric oxide synthase. Proteomic analysis of left ventricular tissue reveals that one-third of identified proteins, predominantly mitochondrial, are upregulated in hearts of NO2-OA-treated HFpEF mice compared to naïve and vehicle-treated HFpEF mice. Increased mitochondrial mass and numbers, and enhanced mitochondrial respiration are linked with this response, as assessed by transmission electron microscopy and high-resolution respirometry. Activation of the 5'-adenosine-monophosphate-activated-protein-kinase (AMPK) signaling pathway mediates the enhancement of mitochondrial dynamics in hearts of NO2-OA-treated HFpEF mice. These findings suggest that targeting mitochondrial function with NO2-OA may represent a promising therapeutic strategy for HFpEF.

Human glutathione transferases catalyze the reaction between glutathione and nitrooleic acid

Nitroalkene fatty acids (NO2-FAs) are formed endogenously. They regulate cell signaling pathways and are being developed clinically to treat inflammatory diseases. NO2-FAs are electrophilic and form thioether adducts with glutathione (GSH), which are exported from cells. Glutathione transferases (GSTs), a superfamily of enzymes, contribute to the cellular detoxification of hydrophobic electrophiles by catalyzing their conjugation to GSH. Herein, we evaluated the capacity of five human GSTs (M1-1, M2-2, M4-4, A4-4, and P1-1) to catalyze the reaction between nitrooleic acid (NO2-OA) and GSH. The reaction was monitored by HPLC-ESI-MS/MS, and catalytic activity was detected with hGSTs M1-1 and A4-4. Using stopped-flow spectrophotometry, a 1400- and 7500-fold increase in the apparent second-order rate constant was observed for hGST M1-1 and hGST A4-4, respectively, compared to the uncatalyzed reaction (pH 7.4, 25 °C). The acceleration was in part due to a higher availability of the thiolate. The crystal structure of hGST M1-1 in complex with the adduct was solved at 2.55 Å resolution, revealing that the ligand was bound within the active site, and establishing a foundation to build a model of hGST A4-4 in complex with the adduct. A larger number of interactions between the enzyme and the fatty acid were observed for hGST A4-4 compared to hGST M1-1, probably contributing to the increased catalysis. Altogether, these results show, for the first time, that hGSTs can catalyze the reaction between GSH and NO2-FAs, likely affecting the signaling actions of these metabolites and expanding the repertoire of GST substrates.

Chemoproteomic analysis reveals RECQL4 as a mediator of nitroalkene-dependent double-strand break repair inhibition in cancer

Nitroalkenes are endogenous products generated by the metabolism of unsaturated fatty acids. They are generated under oxidative stress conditions, mediating important anti-inflammatory signaling activities through covalent modification of protein cysteine thiols. Despite being cytoprotective in benign tissue, nitroalkenes display single-agent anti-proliferative activity in breast cancer cells and sensitize them to multiple DNA-damaging agents. Initial mechanistic evidence suggested that nitroalkene anti-cancer activities are partially mediated by inhibition of homologous recombination (HR) through the recombinase RAD51 at Cys319. However, nitroalkenes are multi-target agents, and thus, it is likely that other important DNA repair targets beyond RAD51 are modified by nitroalkenes, contributing to their anti-cancer effects. We, therefore, conducted a global proteomics analysis to address this question. This analysis led to the identification of the recQ helicase RECQL4 with a nitro-alkylation at Cys1052. This modification was further confirmed by click chemistry-based chemoproteomics and determined to be DNA damage-dependent. Functional analyses demonstrated that nitroalkene modification inhibits RECQL4 ATP-dependent helicase activity and disrupts DSB end resection and downstream homology-dependent repair. Furthermore, experiments with C1052S mutant RECQL4 revealed that RECQL4 is a major mediator of nitroalkene effects on end resection, DSB formation, and repair. The evidence presented here denotes RECQL4 as an important nitroalkene target conferring DSB repair inhibition and supports further evaluation of nitroalkenes as therapeutic agents in RECQL4-amplified cancers.

The Octadecanoids: Synthesis and Bioactivity of 18-Carbon Oxygenated Fatty Acids in Mammals, Bacteria, and Fungi

The octadecanoids are a broad class of lipids consisting of the oxygenated products of 18-carbon fatty acids. Originally referring to production of the phytohormone jasmonic acid, the octadecanoid pathway has been expanded to include products of all 18-carbon fatty acids. Octadecanoids are formed biosynthetically in mammals via cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) activity, as well as nonenzymatically by photo- and autoxidation mechanisms. While octadecanoids are well-known mediators in plants, their role in the regulation of mammalian biological processes has been generally neglected. However, there have been significant advancements in recognizing the importance of these compounds in mammals and their involvement in the mediation of inflammation, nociception, and cell proliferation, as well as in immuno- and tissue modulation, coagulation processes, hormone regulation, and skin barrier formation. More recently, the gut microbiome has been shown to be a significant source of octadecanoid biosynthesis, providing additional biosynthetic routes including hydratase activity (e.g., CLA-HY, FA-HY1, FA-HY2). In this review, we summarize the current field of octadecanoids, propose standardized nomenclature, provide details of octadecanoid preparation and measurement, summarize the phase-I metabolic pathway of octadecanoid formation in mammals, bacteria, and fungi, and describe their biological activity in relation to mammalian pathophysiology as well as their potential use as biomarkers of health and disease.

Nitro-fatty acids: promising agents for the development of new cancer therapeutics

Nitro-fatty acids (NO2-FAs) are endogenous pleiotropic lipid mediators regarded as promising drug candidates for treating inflammatory and fibrotic diseases. Over the past two decades, the anti-inflammatory and cytoprotective actions of NO2-FAs and several molecular targets have been identified. More recently, preclinical studies have demonstrated their potential as prospective cancer therapeutics with favorable safety and tumor-selective profiles. In this review, we describe the mechanisms of action, with a focus on NO2-FA antineoplastic and chemosensitizing effects. We also address the potential therapeutic applications of endogenous and structurally modified NO2-FAs species in cancer treatment.

Development of nitroalkene-based inhibitors to target STING-dependent inflammation

Stimulator of Interferon Genes (STING) is essential for the inflammatory response to cytosolic DNA. Despite that aberrant activation of STING is linked to an increasing number of inflammatory diseases, the development of inhibitors has been challenging, with no compounds in the pipeline beyond the preclinical stage. We previously identified endogenous nitrated fatty acids as novel reversible STING inhibitors. With the aim of improving the specificity and efficacy of these compounds, we developed and tested a library of nitroalkene-based compounds for in vitro and in vivo STING inhibition. The structure-activity relationship study revealed a robustly improved electrophilicity and reduced degrees of freedom of nitroalkenes by conjugation with an aromatic moiety. The lead compounds CP-36 and CP-45, featuring a β-nitrostyrene moiety, potently inhibited STING activity in vitro and relieved STING-dependent inflammation in vivo. This validates the potential for nitroalkene compounds as drug candidates for STING modulation to treat STING-driven inflammatory diseases, providing new robust leads for preclinical development.

Digestive interaction between dietary nitrite and dairy products generates novel nitrated linolenic acid products

Nitrated fatty acids are important anti-inflammatory and protective lipids formed in the gastric compartment, with conjugated linoleic acid (rumenic acid, RA, 9Z,11E-18:2) being the primary substrate for lipid nitration. The recently reported identification of nitrated rumelenic acid (NO2-RLA) in human urine has led to hypothesize that rumelenic acid (RLA, 9Z,11E,15Z-18:3) from dairy fat is responsible for the formation of NO2-RLA. To evaluate the source and mechanism of NO2-RLA formation, 15N labeled standards of NO2-RLA were synthesized and characterized. Afterward, milk fat with different RA and RLA levels was administered to mice in the presence of nitrite, and the appearance of nitrated fatty acids in plasma and urine followed. We confirmed the formation of NO2-RLA and defined the main metabolites in plasma, urine, and tissues. In conclusion, RLA obtained from dairy products is the main substrate for forming this novel electrophilic lipid reported to be present in human urine.

Endogenous anti-tumorigenic nitro-fatty acids inhibit the ubiquitin-proteasome system by directly targeting the 26S proteasome

Nitro-fatty acids (NFAs) are endogenous lipid mediators causing a spectrum of anti-inflammatory effects by covalent modification of key proteins within inflammatory signaling pathways. Recent animal models of solid tumors have helped demonstrate their potential as anti-tumorigenic therapeutics. This study evaluated the anti-tumorigenic effects of NFAs in colon carcinoma cells and other solid and leukemic tumor cell lines. NFAs inhibited the ubiquitin-proteasome system (UPS) by directly targeting the 26S proteasome, leading to polyubiquitination and inhibition of the proteasome activities. UPS suppression induced the unfolded protein response, resulting in tumor cell death. The NFA-mediated effects were substantial, specific, and enduring, representing a unique mode of action for UPS suppression. This study provides mechanistic insights into the biological actions of NFAs as possible endogenous tumor-suppressive factors, indicating that NFAs might be key structures for designing a novel class of direct proteasome inhibitors.

Small molecule nitroalkenes inhibit RAD51-mediated homologous recombination and amplify triple-negative breast cancer cell killing by DNA-directed therapies

Nitro fatty acids (NO2-FAs) are endogenously generated lipid signaling mediators from metabolic and inflammatory reactions between conjugated diene fatty acids and nitric oxide or nitrite-derived reactive species. NO2-FAs undergo reversible Michael addition with hyperreactive protein cysteine thiolates to induce posttranslational protein modifications that can impact protein function. Herein, we report a novel mechanism of action of natural and non-natural nitroalkenes structurally similar to (E) 10-nitro-octadec-9-enoic acid (CP-6), recently de-risked by preclinical Investigational New Drug-enabling studies and Phase 1 and Phase 2 clinical trials and found to induce DNA damage in a TNBC xenograft by inhibiting homologous-recombination (HR)-mediated repair of DNA double-strand breaks (DSB). CP-6 specifically targets Cys319, essential in RAD51-controlled HR-mediated DNA DSB repair in cells. A nitroalkene library screen identified two structurally different nitroalkenes, a non-natural fatty acid [(E) 8-nitro-nonadec-7-enoic acid (CP-8)] and a dicarboxylate ester [dimethyl (E)nitro-oct-4-enedioate (CP-23)] superior to CP-6 in TNBC cells killing, synergism with three different inhibitors of the poly ADP-ribose polymerase (PARP) and γ-IR. CP-8 and CP-23 effectively inhibited γ-IR-induced RAD51 foci formation and HR in a GFP-reported assay but did not affect benign human epithelial cells or cell cycle phases. In vivo, CP-8 and CP-23's efficacies diverged as only CP-8 showed promising anticancer activities alone and combined with the PARP inhibitor talazoparib in an HR-proficient TNBC mouse model. As preliminary preclinical toxicology analysis also suggests CP-8 as safe, our data endorse CP-8 as a novel anticancer molecule for treating cancers sensitive to homologous recombination-mediated DNA repair inhibitors.

Small molecule nitroalkenes inhibit RAD51-mediated homologous recombination and amplify triple-negative breast cancer cell killing by DNA-directed therapies

Nitro fatty acids (NO 2 -FAs) are endogenously generated lipid signaling mediators from metabolic and inflammatory reactions between conjugated diene fatty acids and nitric oxide or nitrite-derived reactive species. NO 2 -FAs undergo reversible Michael addition with hyperreactive protein cysteine thiolates to induce posttranslational protein modifications that can impact protein function. Herein, we report a novel mechanism of action of natural and non-natural nitroalkenes structurally similar to ( E ) 10-nitro-octadec-9-enoic acid (CP-6), recently de-risked by preclinical Investigational New Drug-enabling studies and Phase 1 and Phase 2 clinical trials and found to induce DNA damage in a TNBC xenograft by inhibiting homologous-recombination (HR)-mediated repair of DNA double-strand breaks (DSB). CP-6 specifically targets Cys319, essential in RAD51-controlled HR-mediated DNA DSB repair in cells. A nitroalkene library screen identified two structurally different nitroalkenes, a non-natural fatty acid [( E ) 8-nitro- nonadec-7-enoic acid (CP-8)] and a dicarboxylate ester [dimethyl ( E )nitro-oct-4-enedioate (CP- 23)] superior to CP-6 in TNBC cells killing, synergism with three different inhibitors of the poly ADP-ribose polymerase (PARP) and γ-IR. CP-8 and CP-23 effectively inhibited γ-IR-induced RAD51 foci formation and HR in a GFP-reported assay but did not affect benign human epithelial cells or cell cycle phases. In vivo, CP-8 and CP-23's efficacies diverged as only CP-8 showed promising anticancer activities alone and combined with the PARP inhibitor talazoparib in an HR-proficient TNBC mouse model. As preliminary preclinical toxicology analysis also suggests CP-8 as safe, our data endorse CP-8 as a novel anticancer molecule for treating cancers sensitive to homologous recombination-mediated DNA repair inhibitors.

Neuroprotective actions of a fatty acid nitroalkene in Parkinson's disease

To date there are no therapeutic strategies that limit the progression of Parkinson's disease (PD). The mechanisms underlying PD-related nigrostriatal neurodegeneration remain incompletely understood, with multiple factors modulating the course of PD pathogenesis. This includes Nrf2-dependent gene expression, oxidative stress, α-synuclein pathology, mitochondrial dysfunction, and neuroinflammation. In vitro and sub-acute in vivo rotenone rat models of PD were used to evaluate the neuroprotective potential of a clinically-safe, multi-target metabolic and inflammatory modulator, the electrophilic fatty acid nitroalkene 10-nitro-oleic acid (10-NO2-OA). In N27-A dopaminergic cells and in the substantia nigra pars compacta of rats, 10-NO2-OA activated Nrf2-regulated gene expression and inhibited NOX2 and LRRK2 hyperactivation, oxidative stress, microglial activation, α-synuclein modification, and downstream mitochondrial import impairment. These data reveal broad neuroprotective actions of 10-NO2-OA in a sub-acute model of PD and motivate more chronic studies in rodents and primates.

Nitrated Fatty-Acids Distribution in Storage Biomolecules during Arabidopsis thaliana Development

The non-enzymatic interaction of polyunsaturated fatty acids with nitric oxide (NO) and derived species results in the formation of nitrated fatty acids (NO₂-FAs). These signaling molecules can release NO, reversibly esterify with complex lipids, and modulate protein function through the post-translational modification called nitroalkylation. To date, NO₂-FAs act as signaling molecules during plant development in plant systems and are involved in defense responses against abiotic stress conditions. In this work, the previously unknown storage biomolecules of NO₂-FAs in Arabidopsis thaliana were identified. In addition, the distribution of NO₂-FAs in storage biomolecules during plant development was determined, with phytosterol esters (SE) and TAGs being reservoir biomolecules in seeds, which were replaced by phospholipids and proteins in the vegetative, generative, and senescence stages. The detected esterified NO₂-FAs were nitro-linolenic acid (NO₂-Ln), nitro-oleic acid (NO₂-OA), and nitro-linoleic acid (NO₂-LA). The last two were detected for the first time in Arabidopsis. The levels of the three NO₂-FAs that were esterified in both lipid and protein storage biomolecules showed a decreasing pattern throughout Arabidopsis development. Esterification of NO₂-FAs in phospholipids and proteins highlights their involvement in both biomembrane dynamics and signaling processes, respectively, during Arabidopsis plant development.

Synthesis of Amino-Acid-Based Nitroalkenes

Fatty-acid-based nitroalkenes have recently received great attention because of their bioactivities. On the contrary, peptide- or amino-acid-based nitroalkenes have been scarcely explored so far, although they may exhibit interesting biological properties, for example, as enzyme inhibitors. In this work, we study protocols for the efficient synthesis of nitroalkenes based on natural amino acids. A variety of N-protected amino alcohols and Weinreb amides, derived from α-amino acids, were converted to the corresponding N-protected amino aldehydes, and, through a Henry reaction with nitroalkanes, produced the corresponding nitro alcohols. The subsequent elimination reaction led to the (E)-isomer of amino-acid-based nitroalkenes in moderate to high yields.

Serum albumin as a primary non-covalent binding protein for nitro-oleic acid

This work explores the interaction of 9/10-nitro-oleic acid (NO₂-OA) with human serum albumin (HSA). The molecular mechanism of the biological action of NO₂-OA is to our knowledge based on a reversible covalent reaction-Michael addition of nucleophilic amino acid residues of proteins. Since HSA is an important fatty acid transporter, a key question is whether NO₂-OA can bind covalently or non-covalently to HSA, similarly to oleic acid (OA), which can interact with the FA1-FA7 binding sites of the HSA molecule. ¹H NMR studies and competition analysis with OA and the drugs ibuprofen and warfarin were used to investigate a potential non-covalent binding mode. NO₂-OA/HSA binding was confirmed to compete with warfarin for FA-7 with significantly higher affinity. NO₂-OA competes with ibuprofen for FA-3 and FA-6, however, in contrast to the situation with warfarin, the binding affinities are not significantly different. The described interactions are based exclusively on non-covalent binding. No covalent binding of NO₂-OA to HSA was detected by MS/MS. More detailed studies based on MALDI-TOF-MS and Ellman's assay indicated that HSA can be covalently modified in the presence of NO₂-OA to a very limited extent. It was also shown that NO₂-OA has a higher affinity to HSA than that of OA.

Chemoproteomic profiling reveals cellular targets of nitro-fatty acids

Nitro-fatty acids are a class of endogenous electrophilic lipid mediators with anti-inflammatory and cytoprotective effects in a wide range of inflammatory and fibrotic disease models. While these beneficial biological effects of nitro-fatty acids are mainly attributed to their ability to form covalent adducts with proteins, only a small number of proteins are known to be nitro-alkylated and the scope of protein nitro-alkylation remains undetermined. Here we describe the synthesis and application of a clickable nitro-fatty acid probe for the detection and first global identification of mammalian proteins that are susceptible to nitro-alkylation. 184 high confidence nitro-alkylated proteins were identified in THP1 macrophages, majority of which are novel targets of nitro-fatty acids, including extended synaptotagmin 2 (ESYT2), signal transducer and activator of transcription 3 (STAT3), toll-like receptor 2 (TLR2), retinoid X receptor alpha (RXRα) and glucocorticoid receptor (NR3C1). In particular, we showed that 9-nitro-oleate covalently modified and inhibited dexamethasone binding to NR3C1. Bioinformatic analyses revealed that nitro-alkylated proteins are highly enriched in endoplasmic reticulum and transmembrane proteins, and are overrepresented in lipid metabolism and transport pathways. This study significantly expands the scope of protein substrates targeted by nitro-fatty acids in living cells and provides a useful resource towards understanding the pleiotropic biological roles of nitro-fatty acids as signaling molecules or as multi-target therapeutic agents.

Endogenous generation of nitro-fatty acid hybrids having dual nitrate ester (RONO2) and nitroalkene (RNO2) substituents

Organic nitrate esters, long-recognized therapies for cardiovascular disorders, have not been detected biologically. We characterize in rat stomach unsaturated fatty acid nitration reactions that proceed by generation of nitro-nitrate intermediates (NO2-ONO2-FA) via oxygen and nitrite dependent reactions. NO2-ONO2-lipids represent ∼70% of all nitrated lipids in the stomach and they decay in vitro at neutral or basic pH by the loss of the nitrate ester group (-ONO2) from the carbon backbone upon deprotonation of the α-carbon (pKa ∼7), yielding nitrate, nitrite, nitrosative species, and an electrophilic fatty acid nitroalkene product (NO2-FA). Of note, NO2-FA are anti-inflammatory and tissue-protective signaling mediators, which are undergoing Phase II trials for the treatment of kidney and pulmonary diseases. The decay of NO2-ONO2-FA occurs during intestinal transit and absorption, leading to the formation of NO2-FA that were subsequently detected in circulating plasma triglycerides. These observations provide new insight into unsaturated fatty acid nitration mechanisms, identify nitro-nitrate ester-containing lipids as intermediates in the formation of both secondary nitrogen oxides and electrophilic fatty acid nitroalkenes, and expand the scope of endogenous products stemming from metabolic reactions of nitrogen oxides.

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.

Role of electrophilic nitrated fatty acids during development and response to abiotic stress processes in plants

Nitro-fatty acids are generated from the interaction of unsaturated fatty acids and nitric oxide (NO)-derived molecules. The endogenous occurrence and modulation throughout plant development of nitro-linolenic acid (NO2-Ln) and nitro-oleic acid (NO2-OA) suggest a key role for these molecules in initial development stages. In addition, NO2-Ln content increases significantly in stress situations and induces the expression of genes mainly related to abiotic stress, such as genes encoding members of the heat shock response family and antioxidant enzymes. The promoter regions of NO2-Ln-induced genes are also involved mainly in stress responses. These findings confirm that NO2-Ln is involved in plant defense processes against abiotic stress conditions via induction of the chaperone network and antioxidant systems. NO2-Ln signaling capacity lies mainly in its electrophilic nature and allows it to mediate a reversible post-translational modification called nitroalkylation, which is capable of modulating protein function. NO2-Ln is a NO donor that may be involved in NO signaling events and is able to generate S-nitrosoglutathione, the major reservoir of NO in cells and a key player in NO-mediated abiotic stress responses. This review describes the current state of the art regarding the essential role of nitro-fatty acids as signaling mediators in development and abiotic stress processes.

Mass spectrometry-based study defines the human urine nitrolipidome

Nitrated fatty acids (NO2-FA) are an endogenous class of signaling mediators formed mainly during digestion and inflammation. The signaling actions of NO2-FA have been extensively studied, but their detection and characterization lagged. Several different nitrated fatty acid species have been reported in animals and humans, but their formation remains controversial, and a systemic approach to define the endogenous pool of NO2-FA is needed. Herein, we screened for endogenous NO2-FA in urine from healthy human volunteers as this is the main excretion route for NO2-FA and its metabolites, and it provides an excellent matrix for evaluation. Only isomers of two fatty acids, conjugated linoleic and linolenic acid were found to be nitrated. Several, previously unknown, nitrated species were identified and confirmed using high-resolution mass spectrometry, fragmentation analysis, and compared to synthetic nitrated standards, the main group corresponding to nitrated conjugated linolenic acid (NO2-CLnA). In contrast, we were unable to confirm the presence of previously reported nitrated omega-3's, oleic acid, arachidonic acid and α- and γ-linolenic acid, suggesting that their biological formation and presence in humans should be re-evaluated. Metabolite analysis of NO2-CLnA in human urine identified cysteine adducts and β-oxidation products, which were compared to the metabolic products of nitrated standards obtained using primary mouse hepatocytes. Importantly, NO2-CLnA isomers belong to two defined groups, are electrophilic, participate in Michael addition reactions and account for 39% of total urinary NO2-FA, highlighting their relative abundance and possible role in cell signaling.

Fatty acid nitroalkenes inhibit the inflammatory response to bleomycin-mediated lung injury

Fatty acid nitroalkenes are reversibly-reactive electrophiles, endogenously detectable at nM concentrations, displaying anti-inflammatory actions. Nitroalkenes like 9- or 10-nitro-octadec-9-enoic acid (e.g. nitro-oleic acid, OA-NO₂) pleiotropically suppress cardiovascular inflammatory responses, with pulmonary responses less well defined. C57BL/6 J male mice were intratracheally administered bleomycin (3 U/kg, ITB), to induce pulmonary inflammation and acute injury, or saline and were treated with 50 μL OA-NO₂ (50 μg) or vehicle in the same instillation and 72 h post-exposure to assess anti-inflammatory properties. Bronchoalveolar lavage (BAL) and lung tissue were collected 7d later. ITB mice lost body weight, with OA-NO₂ mitigating this loss (-2.3 ± 0.94 vs -0.4 ± 0.83 g). Histology revealed ITB induced cellular infiltration, proteinaceous debris deposition, and tissue injury, all significantly reduced by OA-NO₂. Flow cytometry analysis of BAL demonstrated loss of Siglec F⁺/F4/80⁺/CD45⁺ alveolar macrophages with ITB (89 ± 3.5 vs 30 ± 3.7%). Analysis of CD11b/CD11c expressing cells showed ITB-induced non-resident macrophage infiltration (4 ± 2.3 vs 43 ± 2.4%) was decreased by OA-NO₂ (24 ± 2.4%). Additionally, OA-NO₂ attenuated increases in mature, activated interstitial macrophages (23 ± 4.8 vs. 43 ± 5.4%) in lung tissue digests. Flow analysis of CD31^-/CD45^-/Sca-1⁺ mesenchymal cells revealed ITB increased CD44⁺ populations (1 ± 0.4 vs 4 ± 0.4MFI), significantly reduced by OA-NO₂ (3 ± 0.4MFI). Single cell analysis of mesenchymal cells by western blotting showed profibrotic ZEB1 protein expression induced by ITB. Lung digest CD45⁺ cells revealed ITB increased HMGB1⁺ cells, with OA-NO₂ suppressing this response. Inhibition of HMGB1 expression correlated with increased basal phospholipid production and SP-B expression in the lung lining. These findings indicate OA-NO₂ inhibits ITB-induced pro-inflammatory responses by modulating resident cell function.

Inflammation, Lipid (Per)oxidation, and Redox Regulation

Significance: Inflammation increases during the aging process. It is linked to mitochondrial dysfunction and increased reactive oxygen species (ROS) production. Mitochondrial macromolecules are critical targets of oxidative damage; they contribute to respiratory uncoupling with increased ROS production, redox stress, and a cycle of senescence, cytokine production, and impaired oxidative phosphorylation. Targeting the formation or accumulation of oxidized biomolecules, particularly oxidized lipids, in immune cells and mitochondria could be beneficial for age-related inflammation and comorbidities. Recent Advances: Inflammation is central to age-related decline in health and exhibits a complex relationship with mitochondrial redox state and metabolic function. Improvements in mass spectrometric methods have led to the identification of families of oxidized phospholipids (OxPLs), cholesterols, and fatty acids that increase during inflammation and which modulate nuclear factor erythroid 2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor gamma (PPARγ), activator protein 1 (AP1), and NF-κB redox-sensitive transcription factor activity. Critical Issues: The kinetic and spatial resolution of the modified lipidome has profound and sometimes opposing effects on inflammation, promoting initiation at high concentration and resolution at low concentration of OxPLs. Future Directions: There is an emerging opportunity to prevent or delay age-related inflammation and vascular comorbidity through a resolving (oxy)lipidome that is dependent on improving mitochondrial quality control and restoring redox homeostasis.

Nitrite elicits divergent NO-dependent signaling that associates with outcome in out of hospital cardiac arrest

Brain and heart injury cause most out-of-hospital cardiac arrest deaths but limited pharmacotherapy exists to protect these tissues. Nitrite is a nitric oxide precursor that is protective in pre-clinical models of ischemic injury and safe in Phase I testing. Protection may occur by cGMP generation via the sGC pathway or through S-nitrosothiol and nitrated conjugated linoleic acid (NO₂-CLA) formation. We hypothesized that nitrite provided during CPR signals through multiple pathways and that activation of signals is associated with OHCA outcome. To this end, we performed a secondary analysis of a phase 1 study of intravenous nitrite administration during resuscitation in adult out-of-hospital cardiac arrest. Associations between whole blood nitrite and derived plasma signals (cGMP and NO₂-CLA) with patient characteristics and outcomes were defined using Chi-square or t-tests and multiple logistic regression. Whole blood nitrite levels correlated inversely with plasma NO₂-CLA (p = 0.039) but not with cGMP. Patients with shockable rhythms had higher cGMP (p = 0.027), NO₂-CLA (p < 0.0001) and trended towards lower nitrite (p = 0.077). Importantly, plasma cGMP and NO₂-CLA levels were higher in survivors (p = 0.033 and 0.019) and in those with good neurological outcome (p = 0.046 and 0.021). Nitrite was lower in patients with good neurologic outcome (p = 0.029). cGMP (OR 4.02; 95% CI 1.04–15.54; p = 0.044) and NO₂-CLA (OR 3.74; 95% CI 1.11–12.65; p = 0.034) were associated with survival. Nitrite (OR 0.20; 95% CI 0.05–0.08; p = 0.026) and NO₂-CLA (OR 3.96; 95% CI 1.01–15.60; p = 0.049) were associated with favorable neurologic outcome. In summary, nitrite administration was associated with increased plasma cGMP and NO₂-CLA formation in selected OHCA patients. Furthermore, patients with the highest levels of cGMP and NO₂-CLA were more likely to survive and experience better neurological outcomes.

A FABP4-PPARγ signaling axis regulates human monocyte responses to electrophilic fatty acid nitroalkenes

Nitro-fatty acids (NO2-FA) are electrophilic lipid mediators derived from unsaturated fatty acid nitration. These species are produced endogenously by metabolic and inflammatory reactions and mediate anti-oxidative and anti-inflammatory responses. NO2-FA have been postulated as partial agonists of the Peroxisome Proliferator-Activated Receptor gamma (PPARγ), which is predominantly expressed in adipocytes and myeloid cells. Herein, we explored molecular and cellular events associated with PPARγ activation by NO2-FA in monocytes and macrophages. NO2-FA induced the expression of two PPARγ reporter genes, Fatty Acid Binding Protein 4 (FABP4) and the scavenger receptor CD36, at early stages of monocyte differentiation into macrophages. These responses were inhibited by the specific PPARγ inhibitor GW9662. Attenuated NO2-FA effects on PPARγ signaling were observed once cells were differentiated into macrophages, with a significant but lower FABP4 upregulation, and no induction of CD36. Using in vitro and in silico approaches, we demonstrated that NO2-FA bind to FABP4. Furthermore, the inhibition of monocyte FA binding by FABP4 diminished NO2-FA-induced upregulation of reporter genes that are transcriptionally regulated by PPARγ, Keap1/Nrf2 and HSF1, indicating that FABP4 inhibition mitigates NO2-FA signaling actions. Overall, our results affirm that NO2-FA activate PPARγ in monocytes and upregulate FABP4 expression, thus promoting a positive amplification loop for the downstream signaling actions of this mediator.

Endogenous Biosynthesis of S-Nitrosoglutathione From Nitro-Fatty Acids in Plants

Nitro-fatty acids (NO₂-FAs) are novel molecules resulting from the interaction of unsaturated fatty acids and nitric oxide (NO) or NO-related molecules. In plants, it has recently been described that NO₂-FAs trigger an antioxidant and a defence response against stressful situations. Among the properties of NO₂-FAs highlight the ability to release NO therefore modulating specific protein targets through post-translational modifications (NO-PTMs). Thus, based on the capacity of NO₂-FAs to act as physiological NO donors and using high-accuracy mass-spectrometric approaches, herein, we show that endogenous nitro-linolenic acid (NO₂-Ln) can modulate S-nitrosoglutathione (GSNO) biosynthesis in Arabidopsis. The incubation of NO₂-Ln with GSH was analyzed by LC-MS/MS and the in vitro synthesis of GSNO was noted. The in vivo confirmation of this behavior was carried out by incubating Arabidopsis plants with ¹⁵N-labeled NO₂-Ln throughout the roots, and ¹⁵N-labeled GSNO (GS¹⁵NO) was detected in the leaves. With the aim to go in depth in the relation of NO₂-FA and GSNO in plants, Arabidopsis alkenal reductase mutants (aer mutants) which modulate NO₂-FAs levels were used. Our results constitute the first evidence of the modulation of a key NO biological reservoir in plants (GSNO) by these novel NO₂-FAs, increasing knowledge about S-nitrosothiols and GSNO-signaling pathways in plants.

iNOS as a metabolic enzyme under stress conditions

Nitric oxide (NO) is a free radical acting as a cellular signaling molecule in many different biochemical processes. NO is synthesized from l-arginine through the action of the nitric oxide synthase (NOS) family of enzymes, which includes three isoforms: endothelial NOS (eNOS), neuronal NOS (nNOS) and inducible NOS (iNOS). iNOS-derived NO has been associated with the pathogenesis and progression of several diseases, including liver diseases, insulin resistance, obesity and diseases of the cardiovascular system. However, transient NO production can modulate metabolism to survive and cope with stress conditions. Accumulating evidence strongly imply that iNOS-derived NO plays a central role in the regulation of several biochemical pathways and energy metabolism including glucose and lipid metabolism during inflammatory conditions. This review summarizes current evidence for the regulation of glucose and lipid metabolism by iNOS during inflammation, and argues for the role of iNOS as a metabolic enzyme in immune and non-immune cells.

Insight into the cellular effects of nitrated phospholipids: Evidence for pleiotropic mechanisms of action

Nitrated phospholipids have been recently identified in biological systems and showed to display anti-oxidant and anti-inflammatory potential in models of inflammation in vitro. Here, we have explored the effects of nitrated 1-palmitoyl-2-oleyl-phosphatidyl choline (NO2-POPC) in cellular models. We have observed that NO2-POPC, but not POPC, induces cellular changes consisting in cytoskeletal rearrangement and cell shrinking, and ultimately, loss of cell adhesion or impaired cell attachment. NO2-POPC releases NO in vitro and induces accumulation of NO in cells. Nevertheless, the effects of NO2-POPC are not superimposable with those of NO donors, which points to distinctive mechanisms of action. Notably, they show a stronger parallelism, although not complete overlap, with the effects of nitrated fatty acids. Interestingly, redistribution of vimentin by NO2-POPC is attenuated in a C328S mutant, thus indicating that this residue may be a target for direct or indirect modification in NO2-POPC-treated cells. Additionally, NO2-POPC interacts with several typical lipoxidation targets in vitro, including vimentin and PPARγ constructs, likely through cysteine residues. Therefore, nitrated phospholipids emerge as potential novel electrophilic lipid mediators with selective actions.

Pharmacokinetic and Pharmacodynamic Effects of Oral CXA-10, a Nitro Fatty Acid, After Single and Multiple Ascending Doses in Healthy and Obese Subjects

10‐nitro‐9(E)‐octadec‐9‐enoic acid (CXA‐10), a novel nitro fatty acid compound, demonstrates potential as a therapeutic agent in multiple disease indications in which oxidative stress, inflammation, fibrosis, and/or direct tissue toxicity play significant roles. Phase I studies were conducted in healthy and obese subjects to evaluate the pharmacokinetics (PK), pharmacodynamics (PD), safety, and tolerability of oral CXA‐10 after single and multiple doses in the fed and fasted states that would confirm the mechanisms of action of CXA‐10. After single and multiple ascending doses, CXA‐10 demonstrated dose‐proportional increases in plasma exposure. CXA‐10 decreased levels of biomarkers associated with altered inflammation and metabolic stress observed from nonclinical studies. In CXA‐10‐202, a consistent decrease from baseline was observed with CXA‐10 150 mg dose, but not 25 or 450 mg doses, for biomarkers of altered inflammation and metabolic dysfunction, including leptin, triglycerides, cholesterol, MCP‐1, and IL‐6. In CXA‐10‐203, after coadministration with CXA‐10, geometric mean peak plasma concentration (C_max) and area under the plasma concentration‐time curve from time point 0 to the end of the dosing interval (AUC_0−t) decreased 20% and 25% for pravastatin, increased 10% and 25% for simvastatin, and decreased 20% and 5% for ezetimibe. These findings are consistent with the pharmacological effects of CXA‐10. Adverse events (AEs) were dose‐related, and the most frequently reported AEs (>10% of subjects) were diarrhea, abdominal pain, and nausea. CXA‐10 was safe and well‐tolerated with no clinically significant abnormalities reported on physical examination, vital signs, clinical laboratory evaluations, or electrocardiographic evaluation. Phase II studies are underway in patients with focal segmental glomerulosclerosis and pulmonary arterial hypertension to investigate the efficacy and tolerability of CXA‐10 75–300 mg once daily.

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.

Novel gene regulatory networks identified in response to nitro-conjugated linoleic acid in human endothelial cells

Endothelial cell (EC) dysfunction is a crucial initiation event in the development of atherosclerosis and is associated with diabetes mellitus, hypertension, and heart failure. Both digestive and oxidative inflammatory conditions lead to the endogenous formation of nitrated derivatives of unsaturated fatty acids (FAs) upon generation of the proximal nitrating species nitrogen dioxide (·NO2) by nitric oxide (·NO) and nitrite-dependent reactions. Nitro-FAs (NO2-FAs) such as nitro-oleic acid (NO2-OA) and nitro-linoleic acid (NO2-LA) potently inhibit inflammation and oxidative stress, regulate cellular functions, and maintain cardiovascular homeostasis. Recently, conjugated linoleic acid (CLA) was identified as the preferential FA substrate of nitration in vivo. However, the functions of nitro-CLA (NO2-CLA) in ECs remain to be explored. In the present study, a distinct transcriptome regulated by NO2-CLA was revealed in primary human coronary artery endothelial cells (HCAECs) through RNA sequencing. Differential gene expression and pathway enrichment analysis identified numerous regulatory networks including those related to the modulation of inflammation, oxidative stress, cell cycle, and hypoxic responses by NO2-CLA, suggesting a diverse impact of NO2-CLA and other electrophilic nitrated FAs on cellular processes. These findings extend the understanding of the protective actions of NO2-CLA in cardiovascular diseases and provide new insight into the underlying mechanisms that mediate the pleiotropic cellular responses to NO2-CLA.

Redox properties and human serum albumin binding of nitro-oleic acid

Nitro-fatty acids modulate inflammatory and metabolic stress responses, thus displaying potential as new drug candidates. Herein, we evaluate the redox behavior of nitro-oleic acid (NO₂-OA) and its ability to bind to the fatty acid transporter human serum albumin (HSA). The nitro group of NO₂-OA underwent electrochemical reduction at -0.75 V at pH 7.4 in an aqueous milieu. Based on observations of the R-NO₂ reduction process, the stability and reactivity of NO₂-OA was measured in comparison to oleic acid (OA) as the negative control. These electrochemically-based results were reinforced by computational quantum mechanical modeling. DFT calculations indicated that both the C9-NO₂ and C10-NO₂ positional isomers of NO₂-OA occurred in two conformers with different internal angles (69° and 110°) between the methyl- and carboxylate termini. Both NO₂-OA positional isomers have LUMO energies of around -0.7 eV, affirming the electrophilic properties of fatty acid nitroalkenes. In addition, the binding of NO₂-OA and OA with HSA revealed a molar ratio of ~7:1 [NO₂-OA]:[HSA]. These binding experiments were performed using both an electrocatalytic approach and electron paramagnetic resonance (EPR) spectroscopy using 16-doxyl stearic acid. Using a Fe(DTCS)₂ spin-trap, EPR studies also showed that the release of the nitro moiety of NO₂-OA resulted in the formation of nitric oxide radical. Finally, the interaction of NO₂-OA with HSA was monitored via Tyr and Trp residue electro-oxidation. The results indicate that not only non-covalent binding but also NO₂-OA-HSA adduction mechanisms should be taken into consideration. This study of the redox properties of NO₂-OA is applicable to the characterization of other electrophilic mediators of biological and pharmacological relevance.