15-Deoxy-Delta 12,14-prostaglandin J2 inhibition of NF-kappaB-DNA binding through covalent modification of the p50 subunit

4-Aza Cyclopentenone Prostaglandin Analogues: Synthesis and NF-κB Inhibitory Activities

Inspired by the cyclopentenone family of prostaglandins, a series of 4-aza, cross-conjugated cyclopentenones is described. Synthesised from N-protected (4R)-aza-cyclopentenone 5, the exocyclic alkene was installed using a modified Baylis-Hillman type aldol reaction, whereby carbon-carbon bond formation is accompanied by dehydration. In this manner octanal and octenal, for example, can be introduced to mimic the ω-group present in the natural prostaglandins. Similarly, a focused range of alternative substituents were introduced using different aldehydes and ketones. The presence of the tert-butyloxycarbonyl (Boc) group on the 4-amino-cyclopentenone substituent enabled subsequent derivatisation and various electrophiles were successfully incorporated. The ability of the family of 4-amino functionalised cross-conjugated cyclopentenones to block activation of nuclear factor-kappa B (NF-κB) was studied and compared with the natural prostanoid, Δ12,14-15-deoxy-PGJ2 (2). Thereafter, the synthesis of a series of thiol adducts from these compounds were prepared and similarly evaluated biologically. The adducts showed comparable and, on occasion, more potent inhibition of NF-κB than their cyclopentenone precursors and generally demonstrated diminished cytotoxicity. For example, cross-conjugated dieneone 12 inhibited the activation of NF-κB with an IC50 value of 6.2 μM, whereas its endocyclic N-Boc (27) and N-acetyl (28) cysteine adducts blocked NF-κB activity with values of 1.0 and 8.0 μM respectively.

15-keto-PGE2 alleviates nonalcoholic steatohepatitis through its covalent modification of NF-κB factors

15-keto-PGE2 is one of the eicosanoids with anti-inflammatory properties. In this study, we demonstrated that 15-keto-PGE2 post-translationally modified the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) subunits p105/p50 and p65 at Cys59 and Cys120 sites, respectively, hence inhibiting the activation of NF-κB signaling in macrophages. In mice fed a high-fat and high-sucrose diet (HFHSD), 15-keto-PGE2 treatment reduced pro-inflammatory cytokines and fasting glucose levels. In mice with non-alcoholic steatohepatitis (NASH) induced by a prolonged HFHSD, 15-keto-PGE2 treatment significantly decreased liver inflammation, lowered serum levels of alanine transaminase (ALT) and aspartate transferase (AST), and inhibited macrophage infiltration. It also reduced lipid droplet size and downregulated key regulators of lipogenesis. These findings highlight the potential of 15-keto-PGE2, through NF-κB modification, in preventing the development and progression of steatohepatitis, emphasizing the significance of endogenous lipid mediators in the inflammatory response.

Exploration of the Molecular Basis of Forsythia Fruit in the Prevention and Treatment of Cholestatic Liver Injury through Network Pharmacology and Molecular Docking

Forsythia fruit, edible fruit of Forsythia suspensa (Thunb.) Vahl, which has been found to be effective in treating cholestasis. However, its key component for alleviating cholestasis has not been determined. In this study, four representative active ingredients in forsythia fruit were selected. Through network pharmacology and molecular docking technology, we tried to find the key component for its treatment of cholestasis. Furthermore, the model of cholestasis in mice was established to verify the protective effect of the key component on cholestasis. Network pharmacology and molecular docking showed that forsythoside A (FTA) is the key component of forsythia fruit in the treatment of cholestasis. In vivo experiments revealed that FTA treatment could alleviate liver injury, dysfunction, and collagen deposition induced by cholestasis in mice. At the same time, FTA treatment inhibited inflammatory factor release and fibrosis-related factor expression. In addition, FTA treatment also reduced MMP-2, TLR4, MYD88, NF-κB p65, and p-NF-κB p65 protein expression. In conclusion, FTA, a key component of forsythia fruit, alleviated liver damage and fibrosis caused by cholestasis via inhibiting the TLR4/NF-κB pathway, extracellular matrix accumulation, and inflammatory cytokine expression. The research results could provide a scientific reference for the development of forsythia fruit as a drug or functional food to prevent and treat cholestasis.

Andrographolide-based potential anti-inflammatory transcription inhibitors against nuclear factor NF-kappa-B p50 subunit (NF-κB p50): an integrated molecular and quantum mechanical approach

The unregulated activation of nuclear factor-κB (NF-κB) is a critical event in the progression of various inflammatory diseases such as ulcerative colitis, asthma, rheumatoid arthritis, bacterial induced gastritis, etc. Hence, blocking the transcriptional activity of NF-κB is a promising strategy towards the development of an anti-inflammatory agent. In this study, an integrated molecular and quantum mechanical approach was carried out to find a new potent andrographolide (AGP)-based analog that can inhibit DNA binding to NF-κB p50 and manifest anti-inflammatory activity. Our approach includes multiple sequence alignment, virtual screening, molecular docking (protein-ligand and protein-DNA), in silico site-directed mutagenesis, ADMET prediction, DFT (HOMO, LUMO, HLG, and EPM energy) analysis, MD simulation, and MM/GBSA rescoring. The virtual screening analysis of 237 AGP analogs yielded the five lead compounds based on the binding affinity. Further, molecular interactive docking and ADMET prediction of hit analogs revealed that Ana2 ((3Z,4S)-3-[2-[(4aR,6aS,7R,10aS,10bR)-3,3,6a,10b-tetramethyl-8-methylidene-1,4a,5,6,7,9,10,10a-octahydronaphtho[2,1-d][1,3]dioxin-7-yl]ethylidene]-4-hydroxyoxolan-2-one) is the most potent moiety as it displays the strongest binding affinity and better molecular/pharmacokinetic features. Moreover, DFT, MD simulation, and MM/GBSA studies corroborated the docking results and demonstrated better chemical and dynamic stability with the least binding free energy (- 29.99 kcal/mol) for the Ana2. Site-directed mutagenesis investigation (Cys62Ala) establishes the importance of the Cys62 amino acid residue towards the binding interaction and stability of Ana2 with NF-κB p50. Overall, the identified NF-κB p50 inhibitor opens up a new research horizon towards the development of plant-based anti-inflammatory drugs to combat progressive inflammatory diseases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03431-9.

Inhibition of Lipopolysaccharide-Induced Inflammatory Signaling by Soft Coral-Derived Prostaglandin A2 in RAW264.7 Cells

Lipopolysaccharide (LPS) is a component of the outer membrane of Gram-negative bacteria and causes inflammatory diseases. We searched MeOH extracts of collected marine organisms for inhibitors of LPS-induced nitric oxide (NO) production in RAW264.7 cells and identified prostaglandin A₂ (PGA₂) as an active compound from the MeOH extract of the soft coral Lobophytum sp. PGA₂ inhibited the production of NO and reduced the expression of inducible NO synthase (iNOS) in LPS-stimulated RAW264.7 cells. Although short preincubation with PGA₂ did not inhibit LPS-induced degradation and resynthesis of IκBα, the suppressive effect of PGA₂ was observed only after a prolonged incubation period prior to LPS treatment. In addition, PGA₂-inhibited NO production was negated by the addition of the EP4 antagonist L161982. Thus, PGA₂ was identified as an inhibitor of LPS-induced inflammatory signaling in RAW264.7 cells.

STAT3 as a Potential Target for Tumor Suppressive Effects of 15-Deoxy-Δ12,14-prostaglandin J2 in Triple Negative Breast Cancer

STAT3 plays a prominent role in proliferation and survival of tumor cells. Thus, STAT3 has been considered to be a prime target for development of anti-cancer therapeutics. The electrophilic cyclopentenone prostaglandin,15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) has been well recognized for its capability to modulate intracellular signaling pathways involved in cancer cell growth and progression. We previously reported that 15d-PGJ₂ had potent cytotoxicity against harvey-ras transformed human mammary epithelial cells through direct interaction with STAT3. In this study, we have attempted to verify the inhibitory effects of 15d-PGJ₂ on STAT3 signaling in human breast tumor cells. The triple negative breast cancer cell lines, MDA-MB-231 and MDA-MB-468 displaying constitutive phosphorylation of STAT3 on the tyrosine 705 (Tyr705) residue, underwent apoptosis upon inhibition of STAT3 by 15d-PGJ₂. In contrast, estrogen receptor positive MCF-7 breast cancer cells that do not exhibit elevated STAT3 phosphorylation were much less susceptible to 15d-PGJ₂-induced apoptosis as assessed by PARP cleavage. Furthermore, 15d-PGJ₂ inhibited interleukin-6-induced tyrosine phosphorylation of STAT3 in LNCaP cells. According to molecular docking studies, 15d-PGJ₂ may preferentially bind to the cysteine 259 residue (Cys259) present in the coiled-coil domain of STAT3. Site-directed mutagenesis of STAT3 identified Cys259 to be the critical amino acid for the 15d-PGJ₂-induced apoptosis as well as epithelial-to-mesenchymal transition. Taken together, these findings suggest STAT3 inactivation through direct chemical modification of its Cys259 as a potential therapeutic approach for treatment of triple negative breast cancer treatment.

Cyclopentenone Prostaglandins: Biologically Active Lipid Mediators Targeting Inflammation

Cyclopentenone prostaglandins (cyPGs) are biologically active lipid mediators, including PGA2, PGA1, PGJ2, and its metabolites. cyPGs are essential regulators of inflammation, cell proliferation, apoptosis, angiogenesis, cell migration, and stem cell activity. cyPGs biologically act on multiple cellular targets, including transcription factors and signal transduction pathways. cyPGs regulate the inflammatory response by interfering with NF-κB, AP-1, MAPK, and JAK/STAT signaling pathways via both a group of nuclear receptor peroxisome proliferator-activated receptor-gamma (PPAR-γ) dependent and PPAR-γ independent mechanisms. cyPGs promote the resolution of chronic inflammation associated with cancers and pathogen (bacterial, viral, and parasitic) infection. cyPGs exhibit potent effects on viral infections by repressing viral protein synthesis, altering viral protein glycosylation, inhibiting virus transmission, and reducing virus-induced inflammation. We summarize their anti-proliferative, pro-apoptotic, cytoprotective, antioxidant, anti-angiogenic, anti-inflammatory, pro-resolution, and anti-metastatic potential. These properties render them unique therapeutic value, especially in resolving inflammation and could be used in adjunct with other existing therapies. We also discuss other α, β -unsaturated carbonyl lipids and cyPGs like isoprostanes (IsoPs) compounds.

Nitric Oxide and Electrophilic Cyclopentenone Prostaglandins in Redox signaling, Regulation of Cytoskeleton Dynamics and Intercellular Communication

Nitric oxide (NO) and electrophilic cyclopentenone prostaglandins (CyPG) are local mediators that modulate cellular response to oxidative stress in different pathophysiological processes. In particular, there is increasing evidence about their functional role during inflammation and immune responses. Although the mechanistic details about their relationship and functional interactions are still far from resolved, NO and CyPG share the ability to promote redox-based post-translational modification (PTM) of proteins that play key roles in cellular homeostasis, signal transduction and transcription. NO-induced S-nitrosylation and S-glutathionylation as well as cyclopentenone-mediated adduct formation, are a few of the main PTMs by which intra- and inter-cellular signaling are regulated. There is a growing body of evidence indicating that actin and actin-binding proteins are susceptible to covalent PTM by these agents. It is well known that the actin cytoskeleton is key for the establishment of interactions among leukocytes, endothelial and muscle cells, enabling cellular activation and migration. In this review we analyze the current knowledge about the actions exerted by NO and CyPG electrophilic lipids on the regulation of actin dynamics and cytoskeleton organization, and discuss some open questions regarding their functional relevance in the regulation of intercellular communication.

15-Deoxy-Δ12,14-prostaglandin J2 Upregulates VEGF Expression via NRF2 and Heme Oxygenase-1 in Human Breast Cancer Cells

There is a plethora of evidence to support that inflammation is causally linked to carcinogenesis. Cyclooxygenase-2 (COX-2), a rate-limiting enzyme in the biosynthesis of prostaglandins, is inappropriately overexpressed in various cancers and hence recognized as one of the hallmarks of chronic inflammation-associated malignancies. However, the mechanistic role of COX-2 as a link between inflammation and cancer remains largely undefined. In this study, we found that 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), one of the final products of COX-2, induced upregulation of vascular endothelial growth factor (VEGF) and capillary formation and migration through nuclear factor erythroid 2-related factor 2 (NRF2)-dependent heme oxygenase-1 (HO-1) induction in MCF-7 cells. Analysis of the publicly available TCGA data set showed that high mRNA levels of both COX-2 and NRF2 correlated with the poor clinical outcomes in breast cancer patients. Moreover, human tissue analysis showed that the levels of 15d-PGJ₂ as well the expression of COX-2, NRF2, and HO-1 were found to be increased in human breast cancer tissues. In conclusion, the elevated levels of 15d-PGJ₂ during inflammatory response activate VEGF expression through NRF2-driven induction of HO-1 in human breast cancer cells, proposing a novel mechanism underlying the oncogenic function of 15d-PGJ₂.

Protein Lipoxidation: Basic Concepts and Emerging Roles

Protein lipoxidation is a non-enzymatic post-translational modification that consists of the covalent addition of reactive lipid species to proteins. This occurs under basal conditions but increases in situations associated with oxidative stress. Protein targets for lipoxidation include metabolic and signalling enzymes, cytoskeletal proteins, and transcription factors, among others. There is strong evidence for the involvement of protein lipoxidation in disease, including atherosclerosis, neurodegeneration, and cancer. Nevertheless, the involvement of lipoxidation in cellular regulatory mechanisms is less understood. Here we review basic aspects of protein lipoxidation and discuss several features that could support its role in cell signalling, including its selectivity, reversibility, and possibilities for regulation at the levels of the generation and/or detoxification of reactive lipids. Moreover, given the great structural variety of electrophilic lipid species, protein lipoxidation can contribute to the generation of multiple structurally and functionally diverse protein species. Finally, the nature of the lipoxidised proteins and residues provides a frameshift for a complex interplay with other post-translational modifications, including redox and redox-regulated modifications, such as oxidative modifications and phosphorylation, thus strengthening the importance of detailed knowledge of this process.

15-Deoxy-Δ12,14 -prostaglandin J2 binds and inactivates STAT3 via covalent modification of cysteine 259 in H-Ras-transformed human breast epithelial cells

Signal transducer and activator of transcription 3 (STAT3) has been considered as a potential target for development of anticancer therapeutics. Here, we report a novel mechanism by which the cyclopentenone prostaglandin, 15-deoxy-Δ^12,14 -prostaglandin J₂ (15d-PGJ₂ ) functions as an allosteric inhibitor of STAT3. 15d-PGJ₂ inhibits phosphorylation, dimerization, nuclear translocation, and transcriptional activity of STAT3 in H-Ras-transformed human mammary epithelial cells (MCF10A-Ras) through the Michael addition reaction at cysteine 259 of STAT3. Comparative studies with 15d-PGJ₂ analogues reveal that both C12-C13 and C9-C10 double bonds conjugated to the carbonyl group in the cyclopentenone ring of 15d-PGJ₂ are essential for STAT3 binding. Antiproliferative and pro-apoptotic activities of 15d-PGJ₂ in MCF10A-Ras cells are attributable to covalent modification of STAT3 on Cys259, and mimic the effects induced by mutation of this amino acid.

A Comprehensive Review on Source, Types, Effects, Nanotechnology, Detection, and Therapeutic Management of Reactive Carbonyl Species Associated with Various Chronic Diseases

Continuous oxidation of carbohydrates, lipids, and amino acids generate extremely reactive carbonyl species (RCS). Human body comprises some important RCS namely hexanal, acrolein, 4-hydroxy-2-nonenal, methylglyoxal, malondialdehyde, isolevuglandins, and 4-oxo-2- nonenal etc. These RCS damage important cellular components including proteins, nucleic acids, and lipids, which manifests cytotoxicity, mutagenicity, multitude of adducts and crosslinks that are connected to ageing and various chronic diseases like inflammatory disease, atherosclerosis, cerebral ischemia, diabetes, cancer, neurodegenerative diseases and cardiovascular disease. The constant prevalence of RCS in living cells suggests their importance in signal transduction and gene expression. Extensive knowledge of RCS properties, metabolism and relation with metabolic diseases would assist in development of effective approach to prevent numerous chronic diseases. Treatment approaches for RCS associated diseases involve endogenous RCS metabolizers, carbonyl metabolizing enzyme inducers, and RCS scavengers. Limited bioavailability and bio efficacy of RCS sequesters suggest importance of nanoparticles and nanocarriers. Identification of RCS and screening of compounds ability to sequester RCS employ several bioassays and analytical techniques. Present review describes in-depth study of RCS sources, types, properties, identification techniques, therapeutic approaches, nanocarriers, and their role in various diseases. This study will give an idea for therapeutic development to combat the RCS associated chronic diseases.

TPP-based mitocans: a potent strategy for anticancer drug design

Cancer is one of the most important problems that endanger human health. The number of cancer patients is increasing rapidly worldwide. Compared with normal cells, cancer cells exhibit abnormal metabolism (abnormal glycolysis and oxidative phosphorylation, high levels of reactive oxygen species, anti-apoptosis, high mitochondrial membrane potential, and so on), and specific targeting of these metabolic abnormalities would be a promising drug design direction. These physiological characteristics are closely related to tumorigenesis and development, which are mainly regulated by mitochondria. Therefore, mitochondria have become important anticancer drug targets, attracting much attention in recent years. In this review, we systematically summarize various mitochondrial anticancer drugs developed, especially mitocans based on triphenylphosphonium (TPP), and discuss the advantages of TPP in endowing mitochondrial targeting function.

15-Deoxy-Δ12,14-prostaglandin J2 Induces Apoptosis in Ha-ras-transformed Human Breast Epithelial Cells by Targeting IκB kinase-NF-κB Signaling

15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), an endogenous ligand for PPARγ, has differential effects on cancer cell proliferation and survival depending on the dose and the type of cells. In the present study, we have investigated the effects of 15d-PGJ₂ on apoptosis of the Ha-ras transformed human breast epithelial (MCF10A-ras) cells. When MCF10A-ras cells were treated with 15d-PGJ₂ (10 μM) for 24 hours, they underwent apoptosis as evidenced by characteristic morphological features, an increased proportion of sub-G₀/G₁ cell population, a typical pattern of annexin V/propidium iodide staining, perturbation of mitochondrial transmembrane potential (Δψ_m), and cleavage of caspase-3 and its substrate PARP. A pan-caspase inhibitor, Z-Val-Ala-Asp (OCH₃)-fluoromethyl ketone attenuated cytotoxicity and proteolytic cleavage of caspase-3 induced by 15d-PGJ₂. The 15d-PGJ₂-induced apoptosis was accompanied by enhanced intracellular accumulation of reactive oxygen species (ROS), which was abolished by the antioxidant N-acetyl-L-cysteine (NAC). 15d-PGJ₂ inhibited the DNA binding activity of NF-κB which was associated with inhibition of expression and catalytic activity of IκB kinase β (IKKβ). 15d-PGJ₂-mediated inhibition of IKKβ and nuclear translocation of phospho-p65 was blocked by NAC treatment. 9,10-Dihydro-PGJ₂, a non-electrophilic analogue of 15d-PGJ₂, failed to produce ROS, to inhibit NF-κB DNA binding, and to induce apoptosis, suggesting that the electrophilic α,β-unsaturated carbonyl group of 15d-PGJ₂ is essential for its pro-apoptotic activity. 15d-PGJ₂-induced inactivation of IKKβ was also attributable to its covalent thiol modification at the cysteine 179 residue of IKKβ. Based on these findings, we propose that 15d-PGJ₂ inactivates IKKβ–ΝF-κB signaling through oxidative or covalent modification of IKKβ, thereby inducing apoptosis in Ha-ras transformed human breast epithelial cells.

NF-κB signaling regulates the formation of proliferating Müller glia-derived progenitor cells in the avian retina

Retinal regeneration is robust in some cold-blooded vertebrates, but this process is ineffective in warm-blooded vertebrates. Understanding the mechanisms that suppress the reprogramming of Müller glia into neurogenic progenitors is key to harnessing the regenerative potential of the retina. Inflammation and reactive microglia are known to influence the formation of Müller glia-derived progenitor cells (MGPCs), but the mechanisms underlying this interaction are unknown. We used a chick in vivo model to investigate nuclear factor kappa B (NF-κB) signaling, a critical regulator of inflammation, during the reprogramming of Müller glia into proliferating progenitors. We find that components of the NF-κB pathway are dynamically regulated by Müller glia after neuronal damage or treatment with growth factors. Inhibition of NF-κB enhances, whereas activation suppresses, the formation of proliferating MGPCs. Following microglia ablation, the effects of NF-κB-agonists on MGPC-formation are reversed, suggesting that signals provided by reactive microglia influence how NF-κB impacts Müller glia reprogramming. We propose that NF-κB is an important signaling 'hub' that suppresses the reprogramming of Müller glia into proliferating MGPCs and this 'hub' coordinates signals provided by reactive microglia.

A unique mechanism for thiolation of serum albumins by disulphide molecules

Protein S-thiolation is a reversible oxidative modification that serves as an oxidative regulatory mechanism for certain enzymes and binding proteins with reactive cysteine residues. It is generally believed that the thiolation occurs at free sulphydryl group of cysteine residues. Meanwhile, despite the fact that disulphide linkages, serving structural and energetic roles in proteins, are stable and inert to oxidative modification, a recent study shows that the thiolation could also occur at protein disulphide linkages when human serum albumin (HSA) was treated with disulphide molecules, such as cystine and homocystine. A chain reaction mechanism has been proposed for the thiolation at disulphide linkages, in which free cysteine (Cys34) is involved in the reaction with disulphide molecules to form free thiols (cysteine or homocysteine) that further react with protein disulphide linkages to form the thiolated cysteine residues in the protein. This review focuses on the recent finding of this unique chain reaction mechanism of protein thiolation.

Electrophiles Against (Skin) Diseases: More Than Nrf2

The skin represents an indispensable barrier between the organism and the environment and is the first line of defense against exogenous insults. The transcription factor NRF2 is a central regulator of cytoprotection and stress resistance. NRF2 is activated in response to oxidative stress by reactive oxygen species (ROS) and electrophiles. These electrophiles oxidize specific cysteine residues of the NRF2 inhibitor KEAP1, leading to KEAP1 inactivation and, subsequently, NRF2 activation. As oxidative stress is associated with inflammation, the NRF2 pathway plays important roles in the pathogenesis of common inflammatory diseases and cancer in many tissues and organs, including the skin. The electrophile and NRF2 activator dimethyl fumarate (DMF) is an established and efficient drug for patients suffering from the common inflammatory skin disease psoriasis and the neuro-inflammatory disease multiple sclerosis (MS). In this review, we discuss possible molecular mechanisms underlying the therapeutic activity of DMF and other NRF2 activators. Recent evidence suggests that electrophiles not only activate NRF2, but also target other inflammation-associated pathways including the transcription factor NF-κB and the multi-protein complexes termed inflammasomes. Inflammasomes are central regulators of inflammation and are involved in many inflammatory conditions. Most importantly, the NRF2 and inflammasome pathways are connected at different levels, mainly antagonistically.

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.

Integrated approaches to unravel the impact of protein lipoxidation on macromolecular interactions

Protein modification by lipid derived reactive species, or lipoxidation, is increased during oxidative stress, a common feature observed in many pathological conditions. Biochemical and functional consequences of lipoxidation include changes in the conformation and assembly of the target proteins, altered recognition of ligands and/or cofactors, changes in the interactions with DNA or in protein-protein interactions, modifications in membrane partitioning and binding and/or subcellular localization. These changes may impact, directly or indirectly, signaling pathways involved in the activation of cell defense mechanisms, but when these are overwhelmed they may lead to pathological outcomes. Mass spectrometry provides state of the art approaches for the identification and characterization of lipoxidized proteins/residues and the modifying species. Nevertheless, understanding the complexity of the functional effects of protein lipoxidation requires the use of additional methodologies. Herein, biochemical and biophysical methods used to detect and measure functional effects of protein lipoxidation at different levels of complexity, from in vitro and reconstituted cell-like systems to cells, are reviewed, focusing especially on macromolecular interactions. Knowledge generated through innovative and complementary technologies will contribute to comprehend the role of lipoxidation in pathophysiology and, ultimately, its potential as target for therapeutic intervention.

Crth2 receptor signaling down-regulates lipopolysaccharide-induced NF-κB activation in murine macrophages via changes in intracellular calcium

Prostaglandin D₂ and its cyclopentenone metabolites [cyclopentenone prostaglandins (CyPGs)], Δ¹²prostaglandin J₂ and 15-deoxy-Δ^12,14-prostaglandin J₂, act through 2 GPCRs, d-type prostanoid 1 and the chemoattractant receptor homologous molecule expressed on type 2 T-helper cells (Crth2). In addition to its role in allergy and asthma, the role of Crth2 in the resolution of inflammation, to mediate the proresolving functions of endogenous CyPGs, is not well understood. We investigated the regulation of LPS or zymosan-induced inflammatory response by signals from the Crth2 receptor in macrophages that lack Crth2 expression [knockout (KO)]. Increased expression of proinflammatory genes, including Tnf-α, was observed in Crth2 KO cells. Targeting the endogenous biosynthetic pathway of CyPGs with indomethacin or HQL79, which inhibit cyclooxygenases or hematopoietic prostaglandin D synthase, respectively, or use of Crth2 antagonists recapitulated the proinflammatory phenotype as in Crth2 KO cells. Ligand-dependent activation of Crth2 by 13,14-dihydro-15-keto-prostaglandin D₂ increased Ca²⁺ influx through store-operated Ca²⁺ entry (SOCE) accompanied by the up-regulation of stromal interaction molecule 1 and calcium release-activated calcium modulator 1 expression, suggesting that the proresolution effects of CyPG-dependent activation of SOCE could be mediated by Crth2 during inflammation. Interestingly, Crth2 signaling down-regulated the Ca²⁺-regulated heat stable protein 1 that stabilizes Tnf-α mRNA via the increased expression of microRNA 155 to dampen inflammatory responses triggered through the TNF-α-NF-κB axis. In summary, these studies present a novel regulatory role for Crth2 during inflammatory response in macrophages.-Diwakar, B. T., Yoast, R., Nettleford, S., Qian, F., Lee, T.-J., Berry, S., Huffnagle, I., Rossi, R. M., Trebak, M., Paulson, R. F., Prabhu, K. S. Crth2 receptor signaling down-regulates lipopolysaccharide-induced NF-κB activation in murine macrophages via changes in intracellular calcium.

An Algal Metabolite-Based PPAR-γ Agonist Displayed Anti-Inflammatory Effect via Inhibition of the NF-κB Pathway

In our previous study, a synthetic compound, (+)-(R,E)-6a1, that incorporated the key structures of anti-inflammatory algal metabolites and the endogenous peroxisome proliferator-activated receptor γ (PPAR-γ) ligand 15-deoxy-∆^12,14-prostaglandin J₂ (15d-PGJ₂), exerted significant PPAR-γ transcriptional activity. Because PPAR-γ expressed in macrophages has been postulated as a negative regulator of inflammation, this study was designed to investigate the anti-inflammatory effect of the PPAR-γ agonist, (+)-(R,E)-6a1. Compound (+)-(R,E)-6a1 displayed in vitro anti-inflammatory activity in lipopolysaccharides (LPS)-stimulated murine RAW264.7 macrophages. Compound (+)-(R,E)-6a1 suppressed the expression of proinflammatory factors, such as nitric oxide (NO), inducible NO synthase (iNOS), cyclooxygenase-2 (COX-2), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α), possibly by the inhibition of the nuclear factor-κB (NF-κB) pathway. In macrophages, (+)-(R,E)-6a1 suppressed LPS-induced phosphorylation of NF-κB, inhibitor of NF-κB α (IκBα), and IκB kinase (IKK). These results indicated that PPAR-γ agonist, (+)-(R,E)-6a1, exerts anti-inflammatory activity via inhibition of the NF-κB pathway.

Lipoxidation and cancer immunity

Lipoxidation is a well-known reaction between electrophilic carbonyl species, formed during oxidation of lipids, and specific proteins that, in most cases, causes an alteration in proteins function. This can occur under physiological conditions but, in many cases, it has been associated to pathological process, including cancer. Lipoxidation may have an effect in cancer development through their effects in tumour cells, as well as through the alteration of immune components and the consequent modulation of the immune response. The formation of protein adducts affects different proteins in cancer, triggering different mechanism, such as proliferation, cell differentiation and apoptosis, among others, altering cancer progression. The divergent results obtained documented that the formation of lipoxidation adducts can have either anti-carcinogenic or pro-carcinogenic effects, depending on the cell type affected and the specific adduct formed. Moreover, lipoxidation adducts may alter the immune response, consequently causing either positive or negative alterations in cancer progression. Therefore, in this review, we summarize the effects of lipoxidation adducts in cancer cells and immune components and their consequences in the evolution of different types of cancer.

Nuclear factor-kappa β as a therapeutic target for Alzheimer's disease

Alzheimer's disease (AD) is a typical progressive, chronic neurodegenerative disorder with worldwide prevalence. Its clinical manifestation involves the presence of extracellular plaques and intracellular neurofibrillary tangles (NFTs). NFTs occur in brain tissues as a result of both Aβ agglomeration and Tau phosphorylation. Although there is no known cure for AD, research into possible cures and treatment options continues using cell-cultures and model animals/organisms. The nuclear factor-kappa β (NF-κβ) plays an active role in the progression of AD. Impairment to this signaling module triggers undesirable phenotypic changes such as neuroinflammation, activation of microglia, oxidative stress related complications, and apoptotic cell death. These imbalances further lead to homeostatic abnormalities in the brain or in initial stages of AD essentially pushing normal neurons toward the degeneration process. Interestingly, the role of NF-κβ signaling associated receptor-interacting protein kinase is currently observed in apoptotic and necrotic cell death, and has been reported in brains. Conversely, the NF-κβ signaling pathway has also been reported to be involved in normal brain functioning. This pathway plays a crucial role in maintaining synaptic plasticity and balancing between learning and memory. Since any impairment in the pathways associated with NF-κβ signaling causes altered neuronal dynamics, neurotherapeutics using compounds including, antioxidants, bioflavonoids, and non-steroidal anti-inflammatory drugs against such abnormalities offer possibilities to rectify aberrant excitatory neuronal activity in AD. In this review, we have provided an extensive overview of the crucial role of NF-κβ signaling in normal brain homeostasis. We have also thoroughly outlined several established pathomechanisms associated with NF-κβ pathways in AD, along with their respective therapeutic approaches.

Modulation of nuclear receptor function: Targeting the protein-DNA interface

Nuclear receptors (NRs) are a superfamily of ligand-dependent transcription factors that modulate several biological processes. Traditionally, modulation of NRs has been focused on the development of ligands that recognize and bind to the ligand binding domain (LBD), resulting in activation or repression of transcription through the recruitment of coregulators. However, for more severe diseases, such as breast and prostate cancer, the conventional treatment addressing LBD modulation is not always successful, due to tumor resistance. To overcome these challenges and aiming to modulate NR activity by inhibiting the NR-DNA interaction, new studies focus on the development of molecules targeting alternative sites and domains on NRs. Here, we discuss two different approaches for this alternative NR modulation: one targeting the NR DNA binding domain (DBD); and the other targeting the DNA sites recognized by NRs. Our aim is to present the challenges and perspectives for developing specific inhibitors for each purpose, alongside with already reported examples.

Lipid mediators in immune regulation and resolution

We are all too familiar with the events that follow a bee sting-heat, redness, swelling, and pain. These are Celsus' four cardinal signs of inflammation that are driven by very well-defined signals and hormones. In fact, targeting the factors that drive this onset phase is the basis upon which most current anti-inflammatory therapies were developed. We are also very well aware that within a few hours, these cardinal signs normally disappear. In other words, inflammation resolves. When it does not, inflammation persists, resulting in damaging chronic conditions. While inflammatory onset is actively driven, so also is its resolution-years of research have identified novel internal counter-regulatory signals that work together to switch off inflammation. Among these signals, lipids are potent signalling molecules that regulate an array of immune responses including vascular hyper reactivity and pain, as well as leukocyte trafficking and clearance, so-called resolution. Here, we collate bioactive lipid research to date and summarize the major pathways involved in their biosynthesis and their role in inflammation, as well as resolution. LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

Lipoxidation in cardiovascular diseases

Lipids can go through lipid peroxidation, an endogenous chain reaction that consists in the oxidative degradation of lipids leading to the generation of a wide variety of highly reactive carbonyl species (RCS), such as short-chain carbonyl derivatives and oxidized truncated phospholipids. RCS exert a wide range of biological effects due to their ability to interact and covalently bind to nucleophilic groups on other macromolecules, such as nucleic acids, phospholipids, and proteins, forming reversible and/or irreversible modifications and generating the so-called advanced lipoxidation end-products (ALEs). Lipoxidation plays a relevant role in the onset of cardiovascular diseases (CVD), mainly in the atherosclerosis-based diseases in which oxidized lipids and their adducts have been extensively characterized and associated with several processes responsible for the onset and development of atherosclerosis, such as endothelial dysfunction and inflammation. Herein we will review the current knowledge on the sources of lipids that undergo oxidation in the context of cardiovascular diseases, both from the bloodstream and tissues, and the methods for detection, characterization, and quantitation of their oxidative products and protein adducts. Moreover, lipoxidation and ALEs have been associated with many oxidative-based diseases, including CVD, not only as potential biomarkers but also as therapeutic targets. Indeed, several therapeutic strategies, acting at different levels of the ALEs cascade, have been proposed, essentially blocking ALEs formation, but also their catabolism or the resulting biological responses they induce. However, a deeper understanding of the mechanisms of formation and targets of ALEs could expand the available therapeutic strategies.

Curcumin interacts directly with the Cysteine 259 residue of STAT3 and induces apoptosis in H-Ras transformed human mammary epithelial cells

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that is latent but constitutively activated in many types of cancers. It is well known that STAT3 plays a key role in inflammation-associated tumorigenesis. Curcumin is an anti-inflammatory natural compound isolated from the turmeric (Curcuma longa L., Zingiberaceae) that has been extensively used in a traditional medicine over the centuries. In the present study, we have found that curcumin inhibits STAT3 signaling that is persistently overactivated in H-Ras transformed breast epithelial cells (H-Ras MCF10A). Specific cysteine residues present in STAT3 appear to be critical for the activity as well as conformation of this transcription factor. We identified the cysteine residue 259 of STAT3 as a putative site for curcumin binding. Site-directed mutation of this cysteine residue abolished curcumin-induced inactivation of STAT3 and apoptosis in H-Ras MCF10A cells. The α,β-unsaturated carbonyl moiety of curcumin appears to be essential in its binding to STAT3 in H-Ras MCF10A cells. Tetrahydrocurcumin that lacks such electrophilic moiety failed to interact with STAT3 and to induce apoptosis in the same cell line. Taken together, our findings suggest that curcumin can abrogate aberrant activation of STAT3 through direct interaction, thereby inhibiting STAT3-mediated mammary carcinogenesis.

TGA2 signaling in response to reactive electrophile species is not dependent on cysteine modification of TGA2

Reactive electrophile species (RES), including prostaglandins, phytoprostanes and 12-oxo phytodienoic acid (OPDA), activate detoxification responses in plants and animals. However, the pathways leading to the activation of defense reactions related to abiotic or biotic stress as a function of RES formation, accumulation or treatment are poorly understood in plants. Here, the thiol-modification of proteins, including the RES-activated basic region/leucine zipper transcription factor TGA2, was studied. TGA2 contains a single cysteine residue (Cys186) that was covalently modified by reactive cyclopentenones but not required for induction of detoxification genes in response to OPDA or prostaglandin A1. Activation of the glutathione-S-transferase 6 (GST6) promoter was responsive to cyclopentenones but not to unreactive cyclopentanones, including jasmonic acid suggesting that thiol reactivity of RES is important to activate the TGA2-dependent signaling pathway resulting in GST6 activation We show that RES modify thiols in numerous proteins in vivo, however, thiol reactivity alone appears not to be sufficient for biological activity as demonstrated by the failure of several membrane permeable thiol reactive reagents to activate the GST6 promoter.

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.

The Crosstalk between Nrf2 and Inflammasomes

The Nrf2 (nuclear factor E2-related factor or nuclear factor (erythroid-derived 2)-like 2) transcription factor is a key player in cytoprotection and activated in stress conditions caused by reactive oxygen species (ROS) or electrophiles. Inflammasomes represent central regulators of inflammation. Upon detection of various stress factors, assembly of the inflamasome protein complex results in activation and secretion of proinflammatory cytokines. In addition, inflammasome activation causes pyroptosis, a lytic form of cell death, which supports inflammation. There is growing evidence of a crosstalk between the Nrf2 and inflammasome pathways at different levels. For example, Nrf2 activating compounds inhibit inflammasomes and consequently inflammation. This review summarizes what is known about the complex and predominantly antagonistic relationship of both stress-activated pathways.

Mitochondria-Targeted Triphenylphosphonium-Based Compounds: Syntheses, Mechanisms of Action, and Therapeutic and Diagnostic Applications

Mitochondria are recognized as one of the most important targets for new drug design in cancer, cardiovascular, and neurological diseases. Currently, the most effective way to deliver drugs specifically to mitochondria is by covalent linking a lipophilic cation such as an alkyltriphenylphosphonium moiety to a pharmacophore of interest. Other delocalized lipophilic cations, such as rhodamine, natural and synthetic mitochondria-targeting peptides, and nanoparticle vehicles, have also been used for mitochondrial delivery of small molecules. Depending on the approach used, and the cell and mitochondrial membrane potentials, more than 1000-fold higher mitochondrial concentration can be achieved. Mitochondrial targeting has been developed to study mitochondrial physiology and dysfunction and the interaction between mitochondria and other subcellular organelles and for treatment of a variety of diseases such as neurodegeneration and cancer. In this Review, we discuss efforts to target small-molecule compounds to mitochondria for probing mitochondria function, as diagnostic tools and potential therapeutics. We describe the physicochemical basis for mitochondrial accumulation of lipophilic cations, synthetic chemistry strategies to target compounds to mitochondria, mitochondrial probes, and sensors, and examples of mitochondrial targeting of bioactive compounds. Finally, we review published attempts to apply mitochondria-targeted agents for the treatment of cancer and neurodegenerative diseases.

Lipid Mediators in Inflammation

Lipids are potent signaling molecules that regulate a multitude of cellular responses, including cell growth and death and inflammation/infection, via receptor-mediated pathways. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. This diversity arises from their synthesis, which occurs via discrete enzymatic pathways and because they elicit responses via different receptors. This review will collate the bioactive lipid research to date and summarize the major pathways involved in their biosynthesis and role in inflammation. Specifically, lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins, and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins, and maresins) will be discussed herein.

Identification of a novel series of anti-inflammatory and anti-oxidative phospholipid oxidation products containing the cyclopentenone moiety in vitro and in vivo: Implication in atherosclerosis

Oxidative stress and inflammation are two major contributing factors to atherosclerosis, a leading cause of cardiovascular disease. Oxidation of phospholipids on the surface of low density lipoprotein (LDL) particles generated under oxidative stress has been associated with the progression of atherosclerosis, but the underlying molecular mechanisms remain poorly defined. We identified a novel series of oxidation products containing the cyclopentenone moiety, termed deoxy-A₂/J₂-isoprostanes-phosphocholine, from 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine in vivo using mass spectrometry and by comparison to a chemically synthesized standard. Transcriptomic analysis (RNA-seq) demonstrated that these compounds affected >200 genes in bone marrow-derived macrophages, and genes associated with inflammatory and anti-oxidative responses are among the top 5 differentially expressed. To further investigate the biological relevance of these novel oxidized phospholipids in atherosclerosis, we chemically synthesized a representative compound 1-palmitoyl-2-15-deoxy-δ-12,14-prostaglandin J₂-sn-glycero-3-phosphocholine (15d-PGJ₂-PC) and found that it induced anti-inflammatory and anti-oxidant responses in macrophages through modulation of NF-κB, peroxisome proliferator-activated receptor γ (PPARγ), and Nrf2 pathways; this compound also showed potent anti-inflammatory properties in a mice model of LPS-induced systematic inflammatory response syndrome. Additionally, 15d-PGJ₂-PC inhibited macrophage foam cell formation, suggesting a beneficial role against atherosclerosis. These properties were consistent with decreased levels of these compounds in the plasma of patients with coronary heart disease compared with control subjects. Our findings uncovered a novel molecular mechanism for the negative regulation of inflammation and positive enhancement of anti-oxidative responses in macrophages by these oxidized phospholipids in LDL in the context of atherosclerosis.

15-Deoxy-Δ12,14-Prostaglandin J2 Modifies Components of the Proteasome and Inhibits Inflammatory Responses in Human Endothelial Cells

15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is an electrophilic lipid mediator derived from PGD₂ with potent anti-inflammatory effects. These are likely to be due to the covalent modification of cellular proteins, via a reactive α,β-unsaturated carbonyl group in its cyclopentenone ring. This study was carried out to identify novel cellular target(s) for covalent modification by 15d-PGJ₂ and to investigate the anti-inflammatory effects of the prostaglandin on endothelial cells (EC). The data presented here show that 15d-PGJ₂ modifies and inhibits components of the proteasome and consequently inhibits the activation of the NF-κB pathway in response to TNF-α. This, in turn, inhibits the adhesion and migration of monocytes toward activated EC, by reducing the expression of adhesion molecules and chemokines in the EC. The effects are consistent with the covalent modification of 13 proteins in the 19S particle of the proteasome identified by mass spectrometry and the suppression of proteasome function, and were similar to the effects seen with a known proteasome inhibitor (MG132). The ubiquitin-proteasome system has been implicated in the regulation of several inflammatory processes and the observation that 15d-PGJ₂ profoundly affects the proteasome functions in human EC suggests that 15d-PGJ₂ may regulate the progression of inflammatory disorders such as atherosclerosis.

PGA1-induced apoptosis involves specific activation of H-Ras and N-Ras in cellular endomembranes

The cyclopentenone prostaglandin A₁ (PGA₁) is an inducer of cell death in cancer cells. However, the mechanism that initiates this cytotoxic response remains elusive. Here we report that PGA₁ triggers apoptosis by a process that entails the specific activation of H- and N-Ras isoforms, leading to caspase activation. Cells without H- and N-Ras did not undergo apoptosis upon PGA₁ treatment; in these cells, the cellular demise was rescued by overexpression of either H-Ras or N-Ras. Consistently, the mutant H-Ras-C118S, defective for binding PGA₁, did not produce cell death. Molecular analysis revealed a key role for the RAF-MEK-ERK signaling pathway in the apoptotic process through the induction of calpain activity and caspase-12 cleavage. We propose that PGA₁ evokes a specific physiological cell death program, through H- and N-Ras, but not K-Ras, activation at endomembranes. Our results highlight a novel mechanism that may be of potential interest for tumor treatment.

Cyclopentenone-containing oxidized phospholipids and their isoprostanes as pro-resolving mediators of inflammation

Inflammation represents a powerful innate immune response that defends tissue homeostasis. However, the appropriate termination of inflammatory processes is essential to prevent the development of chronic inflammatory disorders. The resolution of inflammation is actively induced by specialized pro-resolving lipid mediators, which include eicosanoids, resolvins, protectins and maresins. The responsible pro-resolution pathways have emerged as promising targets for anti-inflammatory therapies since they mitigate excessive inflammation without compromising the anti-microbial defenses of the host. We have recently shown that the lipid peroxidation of membrane phospholipids, which is associated with inflammatory conditions, generates oxidized phospholipid (OxPL) species with potent pro-resolving activities. These pro-resolving OxPLs contain a cyclopentenone as their common determinant, and are structurally and functionally related to endogenous pro-resolving prostaglandins. Here, we review the regulation of inflammatory responses by OxPLs with particular focus on the bioactivities and structural characteristics of cyclopentenone-OxPLs, and discuss the impact of the responsible signaling pathways on inflammatory diseases. This article is part of a Special Issue entitled: Lipid modification and lipid peroxidation products in innate immunity and inflammation edited by Christoph J. Binder.

Synthesis and Characterization of Fatty Acid Conjugates of Niacin and Salicylic Acid

This report describes the synthesis and preliminary biological characterization of novel fatty acid niacin conjugates and fatty acid salicylate conjugates. These molecular entities were created by covalently linking two bioactive molecules, either niacin or salicylic acid, to an omega-3 fatty acid. This methodology allows the simultaneous intracellular delivery of two bioactives in order to elicit a pharmacological response that could not be replicated by administering the bioactives individually or in combination. The fatty acid niacin conjugate 5 has been shown to be an inhibitor of the sterol regulatory element binding protein (SREBP), a key regulator of cholesterol metabolism proteins such as PCSK9, HMG-CoA reductase, ATP citrate lyase, and NPC1L1. On the other hand, the fatty acid salicylate conjugate 11 has been shown to have a unique anti-inflammatory profile based on its ability to modulate the NF-κB pathway through the intracellular release of the two bioactives.

The Therapeutic Potential of Rosemary (Rosmarinus officinalis) Diterpenes for Alzheimer's Disease

Rosemary (Rosmarinus officinalis L.) is one of the most economically important species of the family Lamiaceae. Native to the Mediterranean region, the plant is now widely distributed all over the world mainly due to its culinary, medicinal, and commercial uses including in the fragrance and food industries. Among the most important group of compounds isolated from the plant are the abietane-type phenolic diterpenes that account for most of the antioxidant and many pharmacological activities of the plant. Rosemary diterpenes have also been shown in recent years to inhibit neuronal cell death induced by a variety of agents both in vitro and in vivo. The therapeutic potential of these compounds for Alzheimer's disease (AD) is reviewed in this communication by giving special attention to the chemistry of the compounds along with the various pharmacological targets of the disease. The multifunctional nature of the compounds from the general antioxidant-mediated neuronal protection to other specific mechanisms including brain inflammation and amyloid beta (Aβ) formation, polymerisation, and pathologies is discussed.

Molecular Interactions and Implications of Aldose Reductase Inhibition by PGA1 and Clinically Used Prostaglandins

Aldose reductase (AKR1B1) is a critical drug target because of its involvement in diabetic complications, inflammation, and tumorigenesis. However, to date, development of clinically useful inhibitors has been largely unsuccessful. Cyclopentenone prostaglandins (cyPGs) are reactive lipid mediators that bind covalently to proteins and exert anti-inflammatory and antiproliferative effects in numerous settings. By pursuing targets for modification by cyPGs we have found that the cyPG PGA1 binds to and inactivates AKR1B1. A PGA1-AKR1B1 adduct was observed, both by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and by SDS-PAGE using biotinylated PGA1 (PGA1-B). Insight into the molecular interactions between AKR1B1 and PGA1 was advanced by molecular modeling. This anticipated the addition of PGA1 to active site Cys298 and the potential reversibility of the adduct, which was supported experimentally. Indeed, loss of biotin label from the AKR1B1-PGA1-B adduct was favored by glutathione, indicating a retro-Michael reaction, which unveils new implications of cyPG-protein interaction. PGA1 elicited only marginal inhibition of aldehyde reductase (AKR1A1), considered responsible for the severe adverse effects of many AKR1B1 inhibitors. Interestingly, other prostaglandins (PGs) inhibited the enzyme, including non-electrophilic PGE1 and PGE2, currently used in clinical practice. Moreover, both PGA1 and PGE1 reduced the formation of sorbitol in an ex-vivo model of diabetic cataract to an extent comparable to that attained by the known AKR inhibitor epalrestat. Taken together, these results highlight the role of PGs as AKR1B1 inhibitors and the interest in PG-related molecules as leads for the development of novel pharmacological tools.

Protective features of peripheral monocytes/macrophages in stroke

Hematogenous recruitment of monocytes and macrophages has traditionally been viewed as a harmful process causing exacerbation of brain injury after stroke. However, emerging findings suggest equally important protective features. Inflammatory monocytes are rapidly recruited to ischemic brain via a CCR2-dependent pathway and undergo secondary differentiation in the target tissue towards non-inflammatory macrophages, mediating neuroprotection and repair of the ischemic neurovascular unit. In contrast, independent recruitment of non-inflammatory monocytes via CX3CR1 does not occur. Thus, protective features of hematogenous macrophages mainly depend on initial CCR2-dependent cell recruitment. Under therapeutic considerations, specific modulation of monocyte-derived macrophages will therefore be more appropriate than non-selectively blocking their hematogenous recruitment. This article is part of a Special Issue entitled: Neuro Inflammation edited by Helga E. de Vries and Markus Schwaninger.

Endogenous Generation and Signaling Actions of Omega-3 Fatty Acid Electrophilic Derivatives

Dietary omega-3 polyunsaturated fatty acids (PUFAs) are beneficial for a number of conditions ranging from cardiovascular disease to chronic airways disorders, neurodegeneration, and cancer. Growing evidence has shown that bioactive oxygenated derivatives are responsible for transducing these salutary effects. Electrophilic oxo-derivatives of omega-3 PUFAs represent a class of oxidized derivatives that can be generated via enzymatic and nonenzymatic pathways. Inflammation and oxidative stress favor the formation of these signaling species to promote the resolution of inflammation within a fine autoregulatory loop. Endogenous generation of electrophilic oxo-derivatives of omega-3 PUFAs has been observed in in vitro and ex vivo human models and dietary supplementation of omega-3 PUFAs has been reported to increase their formation. Due to the presence of an α,β-unsaturated ketone moiety, these compounds covalently and reversibly react with nucleophilic residues on target proteins triggering the activation of cytoprotective pathways, including the Nrf2 antioxidant response, the heat shock response, and the peroxisome proliferator activated receptor γ (PPARγ) and suppressing the NF-κB proinflammatory pathway. The endogenous nature of electrophilic oxo-derivatives of omega-3 PUFAs combined with their ability to simultaneously activate multiple cytoprotective pathways has made these compounds attractive for the development of new therapies for the treatment of chronic disorders and acute events characterized by inflammation and oxidative stress.

Synthesis and in vitro cytotoxicity of cross-conjugated prostaglandin A and J series and their hydroxy derivatives

The synthesis of two cross-conjugated prostaglandin analogues of known neurotrophic activity and their new hydroxy derivatives was accomplished starting from the diastereoisomeric (+)-camphor protected 3-[(dimethoxyphosphoryl)methyl]-4,5-dihydroxycyclopent-2-enones. The cytotoxicity of these compounds was determined against HeLa, K562, HL-60 human cancer cell lines and normal human cells (HUVEC). We found that NEPP11 and its C7-hydroxy derivative demonstrated high anticancer activity against the HeLa and HL-60 human cancer cell lines at concentrations ranging from 1 to 2 μM. Moreover, the C7-hydroxy derivative of NEPP11 displayed high cytotoxic selectivity between cancer cell lines and normal human cells. On the other hand, the J-type prostaglandin analogue of NEPP11 and its C13-hydroxy derivatives were much less toxic or nontoxic against the cancer and normal cells at concentrations up to 1 mM.

Protein lipoxidation: Detection strategies and challenges

Enzymatic and non-enzymatic lipid metabolism can give rise to reactive species that may covalently modify cellular or plasma proteins through a process known as lipoxidation. Under basal conditions, protein lipoxidation can contribute to normal cell homeostasis and participate in signaling or adaptive mechanisms, as exemplified by lipoxidation of Ras proteins or of the cytoskeletal protein vimentin, both of which behave as sensors of electrophilic species. Nevertheless, increased lipoxidation under pathological conditions may lead to deleterious effects on protein structure or aggregation. This can result in impaired degradation and accumulation of abnormally folded proteins contributing to pathophysiology, as may occur in neurodegenerative diseases. Identification of the protein targets of lipoxidation and its functional consequences under pathophysiological situations can unveil the modification patterns associated with the various outcomes, as well as preventive strategies or potential therapeutic targets. Given the wide structural variability of lipid moieties involved in lipoxidation, highly sensitive and specific methods for its detection are required. Derivatization of reactive carbonyl species is instrumental in the detection of adducts retaining carbonyl groups. In addition, use of tagged derivatives of electrophilic lipids enables enrichment of lipoxidized proteins or peptides. Ultimate confirmation of lipoxidation requires high resolution mass spectrometry approaches to unequivocally identify the adduct and the targeted residue. Moreover, rigorous validation of the targets identified and assessment of the functional consequences of these modifications are essential. Here we present an update on methods to approach the complex field of lipoxidation along with validation strategies and functional assays illustrated with well-studied lipoxidation targets.

MAP kinase phosphatase-1 expression is regulated by 15-deoxy-Δ12,14-prostaglandin J2 via a HuR-dependent post-transcriptional mechanism

In the present study, we demonstrate a mechanism through which 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2) induces MKP-1 expression in rat primary astrocytes, leading to the regulation of inflammatory responses. We show that 15d-PGJ2 enhances the efficiency of MKP-1 pre-mRNA processing (constitutive splicing and 3'-end processing) and increases the stability of the mature mRNA. We further report that this occurs via the RNA-binding protein, Hu antigen R (HuR). Our experiments show that HuR knockdown abrogates the 15d-PGJ2-induced increases in the pre-mRNA processing and mature mRNA stability of MKP-1, whereas HuR overexpression further enhances the 15d-PGJ2-induced increases in these parameters. Using cysteine (Cys)-mutated HuR proteins, we show that the Cys-245 residue of HuR (but not Cys-13 or Cys-284) is critical for the direct binding of HuR with 15d-PGJ2 and the effects downstream of this interaction. Collectively, our data show that HuR is a novel target of 15d-PGJ2 and reveal HuR-mediated pre-mRNA processing and mature mRNA stabilization as important regulatory steps in the 15d-PGJ2-induced expression of MKP-1. The potential to use a small molecule such as 15d-PGJ2 to regulate the induction of MKP-1 at multiple levels of gene expression could be exploited as a novel therapeutic strategy aimed at combating a diverse range of MKP-1-associated pathologies.