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

Electrophilic fatty acids impair RAD51 function and potentiate the effects of DNA-damaging agents on growth of triple-negative breast cells

Homologous recombination (HR)-directed DNA double-strand break (DSB) repair enables template-directed DNA repair to maintain genomic stability. RAD51 recombinase (RAD51) is a critical component of HR and facilitates DNA strand exchange in DSB repair. We report here that treating triple-negative breast cancer (TNBC) cells with the fatty acid nitroalkene 10-nitro-octadec-9-enoic acid (OA-NO₂) in combination with the antineoplastic DNA-damaging agents doxorubicin, cisplatin, olaparib, and γ-irradiation (IR) enhances the antiproliferative effects of these agents. OA-NO₂ inhibited IR-induced RAD51 foci formation and enhanced H2A histone family member X (H2AX) phosphorylation in TNBC cells. Analyses of fluorescent DSB reporter activity with both static-flow cytometry and kinetic live-cell studies enabling temporal resolution of recombination revealed that OA-NO₂ inhibits HR and not nonhomologous end joining (NHEJ). OA-NO₂ alkylated Cys-319 in RAD51, and this alkylation depended on the Michael acceptor properties of OA-NO₂ because nonnitrated and saturated nonelectrophilic analogs of OA-NO₂, octadecanoic acid and 10-nitro-octadecanoic acid, did not react with Cys-319. Of note, OA-NO₂ alkylation of RAD51 inhibited its binding to ssDNA. RAD51 Cys-319 resides within the SH3-binding site of ABL proto-oncogene 1, nonreceptor tyrosine kinase (ABL1), so we investigated the effect of OA-NO₂-mediated Cys-319 alkylation on ABL1 binding and found that OA-NO₂ inhibits RAD51-ABL1 complex formation both in vitro and in cell-based immunoprecipitation assays. The inhibition of the RAD51-ABL1 complex also suppressed downstream RAD51 Tyr-315 phosphorylation. In conclusion, RAD51 Cys-319 is a functionally significant site for adduction of soft electrophiles such as OA-NO₂ and suggests further investigation of lipid electrophile-based combinational therapies for TNBC.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Nitro-fatty acid formation and metabolism

Nitro-fatty acids (NO₂-FA) are pleiotropic modulators of redox signaling pathways. Their effects on inflammatory signaling have been studied in great detail in cell, animal and clinical models primarily using exogenously administered nitro-oleic acid. While we know a considerable amount regarding NO₂-FA signaling, endogenous formation and metabolism is relatively unexplored. This review will cover what is currently known regarding the proposed mechanisms of NO₂-FA formation, dietary modulation of endogenous NO₂-FA levels, pathways of NO₂-FA metabolism and the detection of NO₂-FA and corresponding metabolites.

The KEAP1-NRF2 System: a Thiol-Based Sensor-Effector Apparatus for Maintaining Redox Homeostasis

The Kelch-like ECH-associated protein 1-NF-E2-related factor 2 (KEAP1-NRF2) system forms the major node of cellular and organismal defense against oxidative and electrophilic stresses of both exogenous and endogenous origins. KEAP1 acts as a cysteine thiol-rich sensor of redox insults, whereas NRF2 is a transcription factor that robustly transduces chemical signals to regulate a battery of cytoprotective genes. KEAP1 represses NRF2 activity under quiescent conditions, whereas NRF2 is liberated from KEAP1-mediated repression on exposure to stresses. The rapid inducibility of a response based on a derepression mechanism is an important feature of the KEAP1-NRF2 system. Recent studies have unveiled the complexities of the functional contributions of the KEAP1-NRF2 system and defined its broader involvement in biological processes, including cell proliferation and differentiation, as well as cytoprotection. In this review, we describe historical milestones in the initial characterization of the KEAP1-NRF2 system and provide a comprehensive overview of the molecular mechanisms governing the functions of KEAP1 and NRF2, as well as their roles in physiology and pathology. We also refer to the clinical significance of the KEAP1-NRF2 system as an important prophylactic and therapeutic target for various diseases, particularly aging-related disorders. We believe that controlled harnessing of the KEAP1-NRF2 system is a key to healthy aging and well-being in humans.

Pharmacological activities of the organic extracts and fatty acid composition of the petroleum ether extract from Haplophyllum tuberculatum leaves

ETHNOPHARMACOLOGICAL RELEVANCE

Haplophyllum tuberculatum is used in traditional medicine to treat many disorders including inflammation and pain. The aim of this study is to investigate the organic extracts from H. tuberculatum leaves against inflammation, gastric ulcer and pain.

MATERIALS AND METHODS

Acute toxicity was studied in vivo to determine the toxic doses of the organic extracts. Anti-inflammatory activity was also evaluated in vivo using carrageenan-induced paw edema in Wistar rats. Gastroprotective activity was tested using the HCl/ethanol-induced gastric ulcer test in rats. Peripheral and central analgesic activities were assessed using the acetic acid-induced writhing test and the hot-plate method, respectively. The chemical composition of the fatty acids in the petroleum ether (PE) extract was determined with GC-MS.

RESULTS

At 25, 50 and 100mg/kg PE extract was the most active against inflammation. Percentages inhibition 5h after carrageenan-injection were 51.12; 86.71% and 96.92%, respectively. The same extract at 100mg/kg showed good analgesic activities using the acetic acid-induced writhing test and the hot-plate method. The chloroform, ethyl acetate (EtOAc) and butanolic (n-BuOH) extracts exhibited strong anti-inflammatory, gastroprotective and analgesic activities at 100mg/kg. The GC-FID analysis revealed that the PE extract was rich in γ-linolenic acid (45.50%) followed by palmitic acid (18.48%), linoleic acid (10.73%), erucic acid (4.72), stearic acid (3.96%) and oleic acid (2.57%).

CONCLUSION

The results of the present study support the traditional use of the leaves of H. tuberculatum and may possibly serve as prospective material for further development of safe new phytochemical anti-inflammatory, gastroprotective and/or analgesic agents.

Biological properties of nitro-fatty acids in plants

Nitro-fatty acids (NO2-FAs) are formed from the reaction between nitrogen dioxide (NO2) and mono and polyunsaturated fatty acids. Knowledge concerning NO2-FAs has significantly increased within a few years ago and the beneficial actions of these species uncovered in animal systems have led to consider them as molecules with therapeutic potential. Based on their nature and structure, NO2-FAs have the ability to release nitric oxide (NO) in aqueous environments and the capacity to mediate post-translational modifications (PTM) by nitroalkylation. Recently, based on the potential of these NO-derived molecules in the animal field, the endogenous occurrence of nitrated-derivatives of linolenic acid (NO2-Ln) was assessed in plant species. Moreover and through RNA-seq technology, it was shown that NO2-Ln can induce a large set of heat-shock proteins (HSPs) and different antioxidant systems suggesting this molecule may launch antioxidant and defence responses in plants. Furthermore, the capacity of this nitro-fatty acid to release NO has also been demonstrated. In view of this background, here we offer an overview on the biological properties described for NO2-FAs in plants and the potential of these molecules to be considered new key intermediaries of NO metabolism in the plant field.

The chemical foundations of nitroalkene fatty acid signaling through addition reactions with thiols

Nitroalkene fatty acids can be formed in vivo and administered exogenously. They exert pleiotropic signaling actions with cytoprotective and antiinflammatory effects. The presence of the potent electron withdrawing nitro group confers electrophilicity to the adjacent β-carbon. Thiols (precisely, thiolates) are strong nucleophiles and can react with nitroalkene fatty acids through reversible Michael addition reactions. In addition, nitroalkene fatty acids can undergo several other processes including metabolic oxidation, reduction, esterification, nitric oxide release and partition into hydrophobic compartments. The signaling actions of nitroalkenes are mainly mediated by reactions with critical thiols in regulatory proteins. Thus, the thio-Michael addition reaction provides a framework for understanding the molecular basis of the biological effects of nitroalkene fatty acids at the crossroads of thiol signaling and electrophilic lipid signaling. In this review, we describe the reactions of nitroalkene fatty acids in biological contexts. We focus on the Michael addition-elimination reaction with thiols and its mechanism, and extrapolate kinetic and thermodynamic considerations to in vivo settings.

The effect of the electrophilic fatty acid nitro-oleic acid on TRP channel function in sensory neurons

Nitro-oleic acid (NO2-OA) and related nitroalkenes are electrophilic fatty acid derivatives that are present in normal tissues at nanomolar concentrations and can increase significantly during inflammation. These substances can suppress multiple intracellular signaling pathways contributing to inflammation by reversible Michael addition reactions with nucleophilic residues such as cysteine and histidine leading to post-translational modification of proteins. NO2-OA also can influence inflammation and pain by acting on transient receptor potential (TRP) channels in primary sensory neurons. TRPV1, TRPA1 and TRPC can respond to electrophilic fatty acids because they have ankyrin-like repeats in their N terminus that are rich in cysteine residues that react with electrophiles and other thiol modifying species. NO2-OA acts on TRP channels to initially depolarize and induce firing in sensory neurons followed by desensitization and suppression of firing. In vivo experiments revealed that pretreatment with NO2-OA reduces nociceptive behavior evoked by local administration of a TRPA1 agonist (AITC) to the rat hind paw. These results raise the possibility that NO2-OA might be useful clinically to reduce neurogenic inflammation and certain types of painful sensations by desensitizing TRPA1 expressing nociceptive afferents.

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.

In situ generation, metabolism and immunomodulatory signaling actions of nitro-conjugated linoleic acid in a murine model of inflammation

Conjugated linoleic acid (CLA) is a prime substrate for intra-gastric nitration giving rise to the formation of nitro-conjugated linoleic acid (NO₂-CLA). Herein, NO₂-CLA generation is demonstrated within the context of acute inflammatory responses both in vitro and in vivo. Macrophage activation resulted in dose- and time-dependent CLA nitration and also in the production of secondary electrophilic and non-electrophilic derivatives. Both exogenous NO₂-CLA as well as that generated in situ, attenuated NF-κB-dependent gene expression, decreased pro-inflammatory cytokine production and up-regulated Nrf2-regulated proteins. Importantly, both CLA nitration and the corresponding downstream anti-inflammatory actions of NO₂-CLA were recapitulated in a mouse peritonitis model where NO₂-CLA administration decreased pro-inflammatory cytokines and inhibited leukocyte recruitment. Taken together, our results demonstrate that the formation of NO₂-CLA has the potential to function as an adaptive response capable of not only modulating inflammation amplitude but also protecting neighboring tissues via the expression of Nrf2-dependent genes.

Anti-inflammatory and antioxidative effects of Camellia oleifera Abel components

Camellia oleifera Abel is a member of Camellia, and its seeds are used to extract Camellia oil, which is generally used as cooking oil in the south of China. Camellia oil consists of unsaturated fatty acids, tea polyphenol, squalene, saponin, carrot element and vitamins, etc. The seed remains after oil extraction of C. oleifera Abel are by-products of oil production, named as Camellia oil cake. Its extracts contain bioactive compounds including sasanquasaponin, flavonoid and tannin. Major components from Camellia oil and its cake have been shown to have anti-inflammatory, antioxidative, antimicrobial and antitumor activities. In this review, we will summarize the latest advance in the studies on anti-inflammatory or antioxidative effects of C. oleifera products, thus providing valuable reference for the future research and development of C. oleifera Abel.

Privileged Electrophile Sensors: A Resource for Covalent Drug Development

This Perspective delineates how redox signaling affects the activity of specific enzyme isoforms and how this property may be harnessed for rational drug design. Covalent drugs have resurged in recent years and several reports have extolled the general virtues of developing irreversible inhibitors. Indeed, many modern pharmaceuticals contain electrophilic appendages. Several invoke a warhead that hijacks active-site nucleophiles whereas others take advantage of spectator nucleophilic side chains that do not participate in enzymatic chemistry, but are poised to bind/react with electrophiles. The latest data suggest that innate electrophile sensing-which enables rapid reaction with an endogenous signaling electrophile-is a quintessential resource for the development of covalent drugs. For instance, based on recent work documenting isoform-specific electrophile sensing, isozyme non-specific drugs may be converted to isozyme-specific analogs by hijacking privileged first-responder electrophile-sensing cysteines. Because this approach targets functionally relevant cysteines, we can simultaneously harness previously untapped moonlighting roles of enzymes linked to redox sensing.

Enterosalivary nitrate metabolism and the microbiome: Intersection of microbial metabolism, nitric oxide and diet in cardiac and pulmonary vascular health

Recent insights into the bioactivation and signaling actions of inorganic, dietary nitrate and nitrite now suggest a critical role for the microbiome in the development of cardiac and pulmonary vascular diseases. Once thought to be the inert, end-products of endothelial-derived nitric oxide (NO) heme-oxidation, nitrate and nitrite are now considered major sources of exogenous NO that exhibit enhanced vasoactive signaling activity under conditions of hypoxia and stress. The bioavailability of nitrate and nitrite depend on the enzymatic reduction of nitrate to nitrite by a unique set of bacterial nitrate reductase enzymes possessed by specific bacterial populations in the mammalian mouth and gut. The pathogenesis of pulmonary hypertension (PH), obesity, hypertension and CVD are linked to defects in NO signaling, suggesting a role for commensal oral bacteria to shape the development of PH through the formation of nitrite, NO and other bioactive nitrogen oxides. Oral supplementation with inorganic nitrate or nitrate-containing foods exert pleiotropic, beneficial vascular effects in the setting of inflammation, endothelial dysfunction, ischemia-reperfusion injury and in pre-clinical models of PH, while traditional high-nitrate dietary patterns are associated with beneficial outcomes in hypertension, obesity and CVD. These observations highlight the potential of the microbiome in the development of novel nitrate- and nitrite-based therapeutics for PH, CVD and their risk factors.

Nitro-fatty acids in plant signaling: New key mediators of nitric oxide metabolism

Recent studies in animal systems have shown that NO can interact with fatty acids to generate nitro-fatty acids (NO2-FAs). They are the product of the reaction between reactive nitrogen species and unsaturated fatty acids, and are considered novel mediators of cell signaling based mainly on a proven anti-inflammatory response. Although these signaling mediators have been described widely in animal systems, NO2-FAs have scarcely been studied in plants. Preliminary data have revealed the endogenous presence of free and protein-adducted NO2-FAs in extra-virgin olive oil (EVOO), which appear to be contributing to the cardiovascular benefits associated with the Mediterranean diet. Importantly, new findings have displayed the endogenous occurrence of nitro-linolenic acid (NO2-Ln) in the model plant Arabidopsis thaliana and the modulation of NO2-Ln levels throughout this plant's development. Furthermore, a transcriptomic analysis by RNA-seq technology established a clear signaling role for this molecule, demonstrating that NO2-Ln was involved in plant-defense response against different abiotic-stress conditions, mainly by inducing the chaperone network and supporting a conserved mechanism of action in both animal and plant defense processes. Thus, NO2-Ln levels significantly rose under several abiotic-stress conditions, highlighting the strong signaling role of these molecules in the plant-protection mechanism. Finally, the potential of NO2-Ln as a NO donor has recently been described both in vitro and in vivo. Jointly, this ability gives NO2-Ln the potential to act as a signaling molecule by the direct release of NO, due to its capacity to induce different changes mediated by NO or NO-related molecules such as nitration and S-nitrosylation, or by the electrophilic capacity of these molecules through a nitroalkylation mechanism. Here, we describe the current state of the art regarding the advances performed in the field of NO2-FAs in plants and their implication in plant physiology.

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.

Nitro-oleic acid regulates growth factor-induced differentiation of bone marrow-derived macrophages

Many diseases accompanied by chronic inflammation are connected with dysregulated activation of macrophage subpopulations. Recently, we reported that nitro-fatty acids (NO₂-FAs), products of metabolic and inflammatory reactions of nitric oxide and nitrite, modulate macrophage and other immune cell functions. Bone marrow cell suspensions were isolated from mice and supplemented with macrophage colony-stimulating factor (M-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF) in combination with NO₂-OA for different times. RAW 264.7 macrophages were used for short-term (1-5min) experiments. We discovered that NO₂-OA reduces cell numbers, cell colony formation, and proliferation of macrophages differentiated with colony-stimulating factors (CSFs), all in the absence of toxicity. In a case of GM-CSF-induced bone marrow-derived macrophages (BMMs), NO₂-OA acts via downregulation of signal transducer and activator of transcription 5 and extracellular signal-regulated kinase (ERK) activation. In the case of M-CSF-induced BMMs, NO₂-OA decreases activation of M-CSFR and activation of related PI3K and ERK. Additionally, NO₂-OA also attenuates activation of BMMs. In aggregate, we demonstrate that NO₂-OA regulates the process of macrophage differentiation and that NO₂-FAs represent a promising therapeutic tool in the treatment of inflammatory pathologies linked with increased accumulation of macrophages in inflamed tissues.

Histone Ketoamide Adduction by 4-Oxo-2-nonenal Is a Reversible Posttranslational Modification Regulated by Sirt2

Lipid-derived electrophiles (LDEs) directly modify proteins to modulate cellular signaling pathways in response to oxidative stress. One such LDE, 4-oxo-2-nonenal (4-ONE), has recently been found to target histones and interfere with histone assembly into nucleosomes. Unlike other LDEs that preferentially modify cysteine via nucleophilic Michael addition, 4-ONE reacts with histone lysine residues to form a new histone modification, gamma-oxononanoylation (Kgon). However, it remains unclear whether Kgon can cause irreversible damage or be regulated by enzymes "erasing" this nonenzymatic modification. Here, we report that human Sirt2 catalyzes the removal of histone Kgon. Among the tested human sirtuins, Sirt2 showed robust deacylase activity toward the Kgon-carrying histone peptides in vitro. We use alkynyl-4-ONE as a chemical reporter for Kgon to demonstrate that Sirt2 is responsible for removing histone Kgon in cells. Furthermore, we develop a ketone-reactive chemical probe to detect histones modified by endogenous 4-ONE in macrophages in response to inflammatory stimulation. Using this probe, we show Sirt2 as a deacylase able to control histone Kgon in stimulated macrophages. This study unravels a new mechanism for the regulation of LDE-derived protein posttranslational modifications, as well as a novel role played by Sirt2 as a histone Kgon deacylase in cytoprotective signaling responses.

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.

In vitro nitro-fatty acid release from Cys-NO2-fatty acid adducts under nitro-oxidative conditions

Stress situations are characterized by a rise in reactive oxygen (ROS) and nitrogen (RNS) species levels. Nitro-fatty acids (NO₂-FAs), or nitroalkenes, are produced by the interaction of RNS and unsaturated fatty acids, stored in cells, mostly as part of protein-adducted NO₂-FAs, and are esterified in complex lipids. These molecules, which have been shown to play a pivotal role as anti-inflammatory and pro-survival players, have been widely characterized in animal systems. Recently, it has been reported that NO₂-FAs play an important role in plant defense against several stress conditions. Furthermore, a significant increase in NO₂-FA levels has been observed under various inflammatory and stressful conditions in both animal and plant systems. In this study, we describe the in vitro release of NO₂-FAs from protein-adducts under nitro-oxidative stress conditions. The findings of this study highlight the ability of hydrogen peroxide and peroxynitrite, as representative ROS and RNS molecules induced under stress conditions, to oxidize cysteine-adducted NO₂-FAs, which is followed by the release of free nitroalkenes. This release may be partly responsible for the increase in NO₂-FA content observed under different stressful conditions in both animal and plant systems as well as the activation of antioxidant and anti-inflammatory properties attributed to these molecules.

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.

Antitumor activity of Annona squamosa seed oil

CONTEXT

Custard apple (Annona squamosa Linn.) is an edible tropical fruit, and its seeds have been used to treat "malignant sore" (cancer) and other usage as insecticide. A comparison of extraction processes, chemical composition analysis and antitumor activity of A. squamosa seed oil (ASO) were investigated.

MATERIALS AND METHODS

The optimal extraction parameters of ASO were established by comparing percolation, soxhlet, ultrasonic and SFE-CO₂ extraction methods. The chemical composition of fatty acid and content of total annonaceous acetogenins (ACGs) of ASO was investigated by GC-MS and colorimetric assay, and anti-tumor activity of ASO was tested using H₂₂ xenografts bearing mice.

RESULTS

The optimal extraction parameters of ASO were obtained as follows: using soxhlet extraction method with extraction solvent of petroleum ether, temperature of 80°C, and extraction time of 90min. Under these conditions, the yield of ASO was 22.65%. GC-MS analysis results showed that the main chemical compositions of fatty acid of ASO were palmitic acid (9.92%), linoleic acid (20.49%), oleic acid (56.50%) and stearic acid (9.14%). The total ACGs content in ASO was 41.00mg/g. ASO inhibited the growth of H₂₂ tumor cells in mice with a maximum inhibitory rate of 53.54% by oral administration. Furthermore, it was found that ASO exerted an antitumor effect via decreasing interleukin-6 (IL-6), janus kinase (Jak) and phosphorylated signal transducers and activators of transcription (p-Stat3) expression.

DISCUSSION AND CONCLUSION

The results demonstrated that ASO suppressed the H₂₂ solid tumor development may due to its main chemical constituents unsaturated fatty acid and ACGs via IL-6/Jak/Stat3 pathway. ASO may be a potential candidate for the treatment of cancer.

T-REX on-demand redox targeting in live cells

This protocol describes targetable reactive electrophiles and oxidants (T-REX)-a live-cell-based tool designed to (i) interrogate the consequences of specific and time-resolved redox events, and (ii) screen for bona fide redox-sensor targets. A small-molecule toolset comprising photocaged precursors to specific reactive redox signals is constructed such that these inert precursors specifically and irreversibly tag any HaloTag-fused protein of interest (POI) in mammalian and Escherichia coli cells. Syntheses of the alkyne-functionalized endogenous reactive signal 4-hydroxynonenal (HNE(alkyne)) and the HaloTag-targetable photocaged precursor to HNE(alkyne) (also known as Ht-PreHNE or HtPHA) are described. Low-energy light prompts photo-uncaging (t1/2 <1-2 min) and target-specific modification. The targeted modification of the POI enables precisely timed and spatially controlled redox events with no off-target modification. Two independent pathways are described, along with a simple setup to functionally validate known targets or discover novel sensors. T-REX sidesteps mixed responses caused by uncontrolled whole-cell swamping with reactive signals. Modification and downstream response can be analyzed by in-gel fluorescence, proteomics, qRT-PCR, immunofluorescence, fluorescence resonance energy transfer (FRET)-based and dual-luciferase reporters, or flow cytometry assays. T-REX targeting takes 4 h from initial probe treatment. Analysis of targeted redox responses takes an additional 4-24 h, depending on the nature of the pathway and the type of readouts used.

Bioorthogonal Chemical Reporters for Monitoring Unsaturated Fatty-Acylated Proteins

Dietary unsaturated fatty acids, such as oleic acid, have been shown to be covalently incorporated into a small subset of proteins, but the generality and diversity of this protein modification has not been studied. We synthesized unsaturated fatty-acid chemical reporters and determined their protein targets in mammalian cells. The reporters can induce the formation of lipid droplets and be incorporated site-specifically onto known fatty-acylated proteins and label many proteins in mammalian cells. Quantitative proteomics analysis revealed that unsaturated fatty acids modify similar protein targets to saturated fatty acids, including several immunity-associated proteins. This demonstrates that unsaturated fatty acids can directly modify many proteins to exert their unique and often beneficial physiological effects in vivo.

Current Treatment of Dyslipidemia: Evolving Roles of Non-Statin and Newer Drugs

Since their introduction, statin (HMG-CoA reductase inhibitor) drugs have advanced the practice of cardiology to unparalleled levels. Even so, coronary heart disease (CHD) still remains the leading cause of death in developed countries, and is predicted to soon dominate the causes of global mortality and disability as well. The currently available non-statin drugs have had limited success in reversing the burden of heart disease, but new information suggests they have roles in sizeable subpopulations of those affected. In this review, the status of approved non-statin drugs and the significant potential of newer drugs are discussed. Several different ways to raise plasma high-density lipoprotein (HDL) cholesterol (HDL-C) levels have been proposed, but disappointments are now in large part attributed to a preoccupation with HDL quantity, rather than quality, which is more important in cardiovascular (CV) protection. Niacin, an old drug with many antiatherogenic properties, was re-evaluated in two imperfect randomized controlled trials (RCTs), and failed to demonstrate clear effectiveness or safety. Fibrates, also with an attractive antiatherosclerotic profile and classically used for hypertriglyceridemia, lacks evidence-based proof of efficacy, save for a subgroup of diabetic patients with atherogenic dyslipidemia. Omega-3 fatty acids fall into this category as well, even with an impressive epidemiological evidence base. Omega-3 research has been plagued with methodological difficulties yielding tepid, uncertain, and conflicting results; well-designed studies over longer periods of time are needed. Addition of ezetimibe to statin therapy has now been shown to decrease levels of low-density lipoprotein (LDL) cholesterol (LDL-C), accompanied by a modest decrease in the number of CV events, though without any improvement in CV mortality. Importantly, the latest data provide crucial evidence that LDL lowering is central to the management of CV disease. Of drugs that inhibit cholesteryl ester transfer protein (CETP) tested thus far, two have failed and two remain under investigation and may yet prove to be valuable therapeutic agents. Monoclonal antibodies to proprotein convertase subtilisin/kexin type 9, now in phase III trials, lower LDL-C by over 50 % and are most promising. These drugs offer new ability to lower LDL-C in patients in whom statin drug use is, for one reason or another, limited or insufficient. Mipomersen and lomitapide have been approved for use in patients with familial hypercholesterolemia, a more common disease than appreciated. Anti-inflammatory drugs are finally receiving due attention in trials to elucidate potential clinical usefulness. All told, even though statins remain the standard of care, non-statin drugs are poised to assume a new, vital role in managing dyslipidemia.

On-Demand Targeting: Investigating Biology with Proximity-Directed Chemistry

Proximity enhancement is a central chemical tenet underpinning an exciting suite of small-molecule toolsets that have allowed us to unravel many biological complexities. The leitmotif of this opus is "tethering"-a strategy in which a multifunctional small molecule serves as a template to bring proteins/biomolecules together. Scaffolding approaches have been powerfully applied to control diverse biological outcomes such as protein-protein association, protein stability, activity, and improve imaging capabilities. A new twist on this strategy has recently appeared, in which the small-molecule probe is engineered to unleash controlled amounts of reactive chemical signals within the microenvironment of a target protein. Modification of a specific target elicits a precisely timed and spatially controlled gain-of-function (or dominant loss-of-function) signaling response. Presented herein is a unique personal outlook conceptualizing the powerful proximity-enhanced chemical biology toolsets into two paradigms: "multifunctional scaffolding" versus "on-demand targeting". By addressing the latest advances and challenges in the established yet constantly evolving multifunctional scaffolding strategies as well as in the emerging on-demand precision targeting (and related) systems, this Perspective is aimed at choosing when it is best to employ each of the two strategies, with an emphasis toward further promoting novel applications and discoveries stemming from these innovative chemical biology platforms.

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.

Omega-3 and -6 fatty acids allocate somatic and germline lipids to ensure fitness during nutrient and oxidative stress in Caenorhabditis elegans

Animals in nature are continually challenged by periods of feast and famine as resources inevitably fluctuate, and must allocate somatic reserves for reproduction to abate evolutionary pressures. We identify an age-dependent lipid homeostasis pathway in Caenorhabditis elegans that regulates the mobilization of lipids from the soma to the germline, which supports fecundity but at the cost of survival in nutrient-poor and oxidative stress environments. This trade-off is responsive to the levels of dietary carbohydrates and organismal oleic acid and is coupled to activation of the cytoprotective transcription factor SKN-1 in both laboratory-derived and natural isolates of C. elegans. The homeostatic balance of lipid stores between the somatic and germ cells is mediated by arachidonic acid (omega-6) and eicosapentaenoic acid (omega-3) precursors of eicosanoid signaling molecules. Our results describe a mechanism for resource reallocation within intact animals that influences reproductive fitness at the cost of somatic resilience.

Chemoproteomic profiling of protein modifications by lipid-derived electrophiles

Lipid-derived electrophiles (LDEs) are a group of endogenous reactive metabolites generated as products of lipid peroxidation when cells are under oxidative stress. LDEs are able to covalently modify nucleophilic residues in proteins to alter their structures and activities, either resulting in irreversible functional damage or triggering aberrant signaling pathways. Traditional biochemical methods have revealed individual protein targets modified by LDEs, however, deciphering the toxicity and/or signaling roles of LDEs requires systematic studies of these modifications in a high-throughput fashion. Here we survey recent progress in developing chemical proteomic strategies to globally profile protein-LDE interactions directly from complex proteomes. These powerful chemoproteomic methods have yielded a rich inventory of proteins and residue sites that are sensitive to LDE modification, serving as valuable resources to investigate mechanisms of their cellular toxicity at the molecular level.

Erythrocyte fatty acid profiles and plasma homocysteine, folate and vitamin B6 and B12 in recurrent depression: Implications for co-morbidity with cardiovascular disease

Oxidative stress induced interactions between fatty acid (FA) and one-carbon metabolism may be involved in co-occurrence of major depressive disorder (MDD) and cardiovascular disease (CVD), which have been scarcely studied together. In 137 recurrent MDD-patients vs. 73 age- and sex-matched healthy controls, we simultaneously measured key components of one-carbon metabolism in plasma (homocysteine, folate, vitamins B6 and B12), and of FA-metabolism in red blood cell membranes [main polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (AA) and structural FA-indices (chain length, unsaturation, peroxidation)]. Results show significant positive associations of folate with EPA, DHA, and the peroxidation index, which were similar in patients and controls. After correction for confounders, these associations were lost except for EPA. Associations between B-vitamins and FA-parameters were non-significant, but also similar in patients and controls. Homocysteine and DHA were significantly less negatively associated in patients than in controls. In conclusion, these data indicate similarities but also differences in associations between parameters of one-carbon and FA-metabolism in recurrent MDD patients vs. controls, which may reflect differences in handling of oxidative stress. Further research should test the consequences of these differences, particularly the premature development of CVD in MDD.

Strategies to increase nitric oxide signalling in cardiovascular disease

Nitric oxide (NO) is a key signalling molecule in the cardiovascular, immune and central nervous systems, and crucial steps in the regulation of NO bioavailability in health and disease are well characterized. Although early approaches to therapeutically modulate NO bioavailability failed in clinical trials, an enhanced understanding of fundamental subcellular signalling has enabled a range of novel therapeutic approaches to be identified. These include the identification of: new pathways for enhancing NO synthase activity; ways to amplify the nitrate-nitrite-NO pathway; novel classes of NO-donating drugs; drugs that limit NO metabolism through effects on reactive oxygen species; and ways to modulate downstream phosphodiesterases and soluble guanylyl cyclases. In this Review, we discuss these latest developments, with a focus on cardiovascular disease.

Saturated fatty acids enhance TLR4 immune pathways in human trophoblasts

STUDY QUESTION

What are the effects of fatty acids on placental inflammatory cytokine with respect to toll-like receptor-4/nuclear factor-kappa B (TLR4/NF-kB)?

SUMMARY ANSWER

Exogenous fatty acids induce a pro-inflammatory cytokine response in human placental cells in vitro via activation of TLR4 signaling pathways.

WHAT IS KNOWN ALREADY

The placenta is exposed to changes in circulating maternal fatty acid concentrations throughout pregnancy. Fatty acids are master regulators of innate immune pathways through recruitment of toll-like receptors and activation of cytokine synthesis.

STUDY DESIGN, SIZE, DURATION

Trophoblast cells isolated from 14 normal term human placentas were incubated with long chain fatty acids (FA) of different carbon length and degree of saturation. The expression and secretion of interleukin-6 (IL-6), IL-8 and tumor necrosis factor-alpha (TNF-α) were measured by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. Antibodies against TLR4 ligand binding domain, downstream signaling and anti-p65 NFkB-inhibitor were used to characterize the pathways of FA action.

PARTICIPANTS/MATERIALS, SETTING, METHODS

General approach used primary human term trophoblast cell culture. Methods and end-points used real-time quantitative PCR, cytokine measurements, immunohistochemistry, western blots.

MAIN RESULTS AND THE ROLE OF CHANCE

The long chain saturated fatty acids, stearic and palmitic (PA), stimulated the synthesis as well as the release of TNF-α, IL-6 and IL-8 by trophoblast cells (2- to 6-fold, P < 0.001). In contrast, the unsaturated (palmitoleic, oleic, linoleic) acids did not modify cytokine expression significantly. Palmitate-induced inflammatory effects were mediated via TLR4 activation, NF-kB phosphorylation and nuclear translocation.

LIMITATIONS, REASONS FOR CAUTION

TNF-α protein level was close to the limit of detection in the culture medium even when cells were cultured with PA.

WIDER IMPLICATIONS OF THE FINDINGS

These mechanisms open the way to a better understanding of how changes in maternal lipid homeostasis may regulate placental inflammatory status.

STUDY FUNDING/COMPETING INTERESTS

X.Y. was recipient of fellowship award from West China Second University Hospital, Sichuan University (NIH HD 22965-19). The authors have nothing else to disclose.

TRIAL REGISTRATION NUMBER

None.

Convergence of biological nitration and nitrosation via symmetrical nitrous anhydride

Current perspective holds that the generation of secondary signaling mediators from nitrite (NO₂⁻) requires acidification to nitrous acid (HNO₂) or metal catalysis. Herein, the use of stable isotope-labeled NO₂⁻ and LC-MS/MS analysis of products revealed that NO₂⁻ also participates in fatty acid nitration and thiol S-nitrosation at neutral pH. These reactions occur in the absence of metal centers and are stimulated by nitric oxide (^•NO) autoxidation via symmetrical dinitrogen trioxide (nitrous anhydride, symN₂O₃) formation. While theoretical models have predicted physiological symN₂O₃ formation, its generation is now demonstrated in aqueous reaction systems, cell models and in viv, with the concerted reactions of ^•NO and NO₂⁻ shown to be critical for symN₂O₃ formation. These results reveal new mechanisms underlying the NO₂⁻ propagation of ^•NO signaling and the regulation of both biomolecule function and signaling network activity via NO₂⁻-dependent nitrosation and nitration reactions.

The science of fatty acids and inflammation

Inflammation is believed to play a central role in many of the chronic diseases that characterize modern society. In the past decade, our understanding of how dietary fats affect our immune system and subsequently our inflammatory status has grown considerably. There are compelling data showing that high-fat meals promote endotoxin [e.g., lipopolysaccharide (LPS)] translocation into the bloodstream, stimulating innate immune cells and leading to a transient postprandial inflammatory response. The nature of this effect is influenced by the amount and type of fat consumed. The role of various dietary constituents, including fats, on gut microflora and subsequent health outcomes in the host is another exciting and novel area of inquiry. The impact of specific fatty acids on inflammation may be central to how dietary fats affect health. Three key fatty acid-inflammation interactions are briefly described. First, the evidence suggests that saturated fatty acids induce inflammation in part by mimicking the actions of LPS. Second, the often-repeated claim that dietary linoleic acid promotes inflammation was not supported in a recent systematic review of the evidence. Third, an explanation is offered for why omega-3 (n-3) polyunsaturated fatty acids are so much less anti-inflammatory in humans than in mice. The article closes with a cautionary tale from the genomic literature that illustrates why extrapolating the results from inflammation studies in mice to humans is problematic.

15-Oxoeicosatetraenoic acid is a 15-hydroxyprostaglandin dehydrogenase-derived electrophilic mediator of inflammatory signaling pathways

Bioactive lipids govern cellular homeostasis and pathogenic inflammatory processes. Current dogma holds that bioactive lipids, such as prostaglandins and lipoxins, are inactivated by 15-hydroxyprostaglandin dehydrogenase (15PGDH). In contrast, the present results reveal that catabolic "inactivation" of hydroxylated polyunsaturated fatty acids (PUFAs) yields electrophilic α,β-unsaturated ketone derivatives. These endogenously produced species are chemically reactive signaling mediators that induce tissue protective events. Electrophilic fatty acids diversify the proteome through post-translational alkylation of nucleophilic cysteines in key transcriptional regulatory proteins and enzymes that govern cellular metabolic and inflammatory homeostasis. 15PGDH regulates these processes as it is responsible for the formation of numerous electrophilic fatty acids including the arachidonic acid metabolite, 15-oxoeicosatetraenoic acid (15-oxoETE). Herein, the role of 15-oxoETE in regulating signaling responses is reported. In cell cultures, 15-oxoETE activates Nrf2-regulated antioxidant responses (AR) and inhibits NF-κB-mediated pro-inflammatory responses via IKKβ inhibition. Inhibition of glutathione S-transferases using ethacrynic acid incrementally increased the signaling capacity of 15-oxoETE by decreasing 15-oxoETE-GSH adduct formation. This work demonstrates that 15PGDH plays a role in the regulation of cell and tissue homeostasis via the production of electrophilic fatty acid signaling mediators.

Activation of TRPC channels contributes to OA-NO2-induced responses in guinea-pig dorsal root ganglion neurons

Effects of nitro-oleic acid (OA-NO2) on TRP channels were examined in guinea-pig dissociated dorsal root ganglia (DRG) neurons using calcium imaging and patch clamp techniques. OA-NO2 increased intracellular Ca(2+) in 60-80% DRG neurons. 1-Oleoyl-2acetyl-sn-glycerol (OAG), a TRPC agonist, elicited responses in 36% of OA-NO2-sensitive neurons while capsaicin (TRPV1 agonist) or allyl-isothiocyanate (AITC, TRPA1 agonist) elicited responses in only 16% and 10%, respectively, of these neurons. A TRPV1 antagonist (diarylpiperazine, 5 μm) in combination with a TRPA1 antagonist (HC-030031, 30 μm) did not change the amplitude of the Ca(2+) transients or percentage of neurons responding to OA-NO2; however, a reducing agent DTT (50 mm) or La(3+) (50 μm) completely abolished OA-NO2 responses. OA-NO2 also induced a transient inward current associated with a membrane depolarization followed by a prolonged outward current and hyperpolarization in 80% of neurons. The reversal potentials of inward and outward currents were approximately -20 mV and -60 mV, respectively. Inward current was reduced when extracellular Na(+) was absent, but unchanged by niflumic acid (100 μm), a Cl(-) channel blocker. Outward current was abolished in the absence of extracellular Ca(2+) or a combination of two Ca(2+)-activated K(+) channel blockers (iberiotoxin, 100 nm and apamin, 1 μm). BTP2 (1 or 10 μm), a broad spectrum TRPC antagonist, or La(3+) (50 μm) completely abolished OA-NO2 currents. RT-PCR performed on mRNA extracted from DRGs revealed the expression of all seven subtypes of TRPC channels. These results support the hypothesis that OA-NO2 activates TRPC channels other than the TRPV1 and TRPA1 channels already known to be targets in rat and mouse sensory neurons and challenge the prevailing view that electrophilic compounds act specifically on TRPA1 or TRPV1 channels. The modulation of sensory neuron excitability via actions on multiple TRP channels can contribute to the anti-inflammatory effect of OA-NO2.