Mast cells link immune sensing to antigen-avoidance behaviour.

The physiological functions of mast cells remain largely an enigma. In the context of barrier damage, mast cells are integrated in type 2 immunity and, together with immunoglobulin E (IgE), promote allergic diseases. Allergic symptoms may, however, facilitate expulsion of allergens, toxins and parasites and trigger future antigen avoidance1-3. Here, we show that antigen-specific avoidance behaviour in inbred mice4,5 is critically dependent on mast cells; hence, we identify the immunological sensor cell linking antigen recognition to avoidance behaviour. Avoidance prevented antigen-driven adaptive, innate and mucosal immune activation and inflammation in the stomach and small intestine. Avoidance was IgE dependent, promoted by Th2 cytokines in the immunization phase and by IgE in the execution phase. Mucosal mast cells lining the stomach and small intestine rapidly sensed antigen ingestion. We interrogated potential signalling routes between mast cells and the brain using mutant mice, pharmacological inhibition, neural activity recordings and vagotomy. Inhibition of leukotriene synthesis impaired avoidance, but overall no single pathway interruption completely abrogated avoidance, indicating complex regulation. Collectively, the stage for antigen avoidance is set when adaptive immunity equips mast cells with IgE as a telltale of past immune responses. On subsequent antigen ingestion, mast cells signal termination of antigen intake. Prevention of immunopathology-causing, continuous and futile responses against per se innocuous antigens or of repeated ingestion of toxins through mast-cell-mediated antigen-avoidance behaviour may be an important arm of immunity.

Helical remodeling augments 5-lipoxygenase activity in the synthesis of proinflammatory mediators.

The synthesis of proinflammatory leukotrienes implicated in asthma, allergic rhinitis, and atherosclerosis is initiated by the enzyme 5-lipoxygenase (5-LOX). The crystal structure of human Stable-5-LOX revealed a conformation where the catalytic iron was inaccessible to bulk solvent as two aromatic residues on a conserved helix-α2 (Hα2) plugged the substrate access portal. Whether 5-LOX can also adopt a more open conformation has not been resolved. Here, we present a new conformation of 5-LOX where Hα2 adopts an elongated conformation equivalent to that described in other animal lipoxygenase structures. Our observation of the sigmoidal kinetic behavior of 5-LOX, which is indicative of positive cooperativity, is consistent with a substrate-induced conformational change that shifts the ensemble of enzyme populations to favor the catalytically competent state. Strategic point mutations along Hα2 designed to unlock the closed conformation and elongate Hα2 resulted in improved kinetic parameters, altered limited proteolysis data, and a drastic reduction in the length of the lag phase yielding the most active Stable-5-LOX to date. Structural predictions by AlphaFold2 of these variants statistically favor an elongated Hα2 and reinforce a model in which improved kinetic parameters correlate with a more readily adopted open conformation. Taken together, these data provide valuable insights into the synthesis of leukotrienes.

Ethoxy acetalated dextran-based nanocarriers accomplish efficient inhibition of leukotriene formation by a novel FLAP antagonist in human leukocytes and blood.

Leukotrienes are pro-inflammatory lipid mediators generated by 5-lipoxygenase aided by the 5-lipoxygenase-activating protein (FLAP). BRP-201, a novel benzimidazole-based FLAP antagonist, inhibits leukotriene biosynthesis in isolated leukocytes. However, like other FLAP antagonists, BRP-201 fails to effectively suppress leukotriene formation in blood, which limits its therapeutic value. Here, we describe the encapsulation of BRP-201 into poly(lactide-co-glycolide) (PLGA) and ethoxy acetalated dextran (Ace-DEX) nanoparticles (NPs), aiming to overcome these detrimental pharmacokinetic limitations and to enhance the bioactivity of BRP-201. NPs loaded with BRP-201 were produced via nanoprecipitation and the physicochemical properties of the NPs were analyzed in-depth using dynamic light scattering (size, dispersity, degradation), electrophoretic light scattering (effective charge), NP tracking analysis (size, dispersity), scanning electron microscopy (size and morphology), UV-VIS spectroscopy (drug loading), an analytical ultracentrifuge (drug release, degradation kinetics), and Raman spectroscopy (chemical attributes). Biological assays were performed to study cytotoxicity, cellular uptake, and efficiency of BRP-201-loaded NPs versus free BRP-201 to suppress leukotriene formation in primary human leukocytes and whole blood. Both PLGA- and Ace-DEX-based NPs were significantly more efficient to inhibit leukotriene formation in neutrophils versus free drug. Whole blood experiments revealed that encapsulation of BRP-201 into Ace-DEX NPs strongly increases its potency, especially upon pro-longed (≥ 5 h) incubations and upon lipopolysaccharide-challenge of blood. Finally, intravenous injection of BRP-201-loaded NPs significantly suppressed leukotriene levels in blood of mice in vivo. These results reveal the feasibility of our pharmacological approach using a novel FLAP antagonist encapsulated into Ace-DEX-based NPs with improved efficiency in blood to suppress leukotriene biosynthesis.

Candida albicans-induced leukotriene biosynthesis in neutrophils is restricted to the hyphal morphology.

Neutrophils are the most abundant leukocytes in circulation playing a key role in acute inflammation during microbial infections. Phagocytosis, one of the crucial defence mechanisms of neutrophils against pathogens, is amplified by chemotactic leukotriene (LT)B4 , which is biosynthesized via 5-lipoxygenase (5-LOX). However, extensive liberation of LTB4 can be destructive by over-intensifying the inflammatory process. While enzymatic biosynthesis of LTB4 is well characterized, less is known about molecular mechanisms that activate 5-LOX and lead to LTB4 formation during host-pathogen interactions. Here, we investigated the ability of the common opportunistic fungal pathogen Candida albicans to induce LTB4 formation in neutrophils, and elucidated pathogen-mediated drivers and cellular processes that activate this pathway. We revealed that C. albicans-induced LTB4 biosynthesis requires both the morphological transition from yeast cells to hyphae and the expression of hyphae-associated genes, as exclusively viable hyphae or yeast-locked mutant cells expressing hyphae-associated genes stimulated 5-LOX by [Ca2+ ]i mobilization and p38 MAPK activation. LTB4 biosynthesis was orchestrated by synergistic activation of dectin-1 and Toll-like receptor 2, and corresponding signaling via SYK and MYD88, respectively. Conclusively, we report hyphae-specific induction of LTB4 biosynthesis in human neutrophils. This highlights an expanding role of neutrophils during inflammatory processes in the response to C. albicans infections.

Angioedema: differential diagnosis and acute management.

A clinical vignette illustrates a typical presentation of a patient seeking help for acute angioedema. Despite the risks of SARS-CoV-2 (COVID-19) exposure, it is critical to evaluate patients with acute angioedema in person, because there is always the potential for angioedema to progress to the head, neck, or lungs, which can rapidly compromise the airways and require immediate intervention to avoid potential asphyxiation. There are three mediators of angioedema, histamine, leukotriene, or bradykinin, each requiring different management. This article provides clinicians essential information for differentiating between these types of angioedema, including an overview of the underlying pathogenies of angioedema, and the subjective and objective findings that are useful in differentiating between angioedema types. The article ends with the appropriate management for each type of acute angioedema, including the medications approved by the FDA for on-demand treatment of an HAE attack.

Magic Peptide: Unique Properties of the LRR11 Peptide in the Activation of Leukotriene Synthesis in Human Neutrophils.

Neutrophil-mediated innate host defense mechanisms include pathogen elimination through bacterial phagocytosis, which activates the 5-lipoxygenase (5-LOX) product synthesis. Here, we studied the effect of synthetic oligodeoxyribonucleotides (ODNs), which mimic the receptor-recognized sites of bacterial (CpG-ODNs) and genomic (G-rich ODNs) DNAs released from the inflammatory area, on the neutrophil functions after cell stimulation with Salmonella typhimurium. A possible mechanism for ODN recognition by Toll-like receptor 9 (TLR9) and RAGE receptor has been proposed. We found for the first time that the combination of the magic peptide LRR11 from the leucine-rich repeat (LRR) of TLR9 with the CpG-ODNs modulates the uptake and signaling from ODNs, in particular, dramatically stimulates 5-LOX pathway. Using thickness shear mode acoustic method, we confirmed the specific binding of CpG-ODNs, but not G-rich ODN, to LRR11. The RAGE receptor has been shown to play an important role in promoting ODN uptake. Thus, FPS-ZM1, a high-affinity RAGE inhibitor, suppresses the synthesis of 5-LOX products and reduces the uptake of ODNs by neutrophils; the inhibitor effect being abolished by the addition of LRR11. The results obtained revealed that the studied peptide-ODN complexes possess high biological activity and can be promising for the development of effective vaccine adjuvants and antimicrobial therapeutics.

Protective activities of distinct omega-3 enriched oils are linked to their ability to upregulate specialized pro-resolving mediators.

Clinical studies using a range of omega-3 supplements have yielded conflicting results on their efficacy to control inflammation. Omega-3 fatty acids are substrate for the formation of potent immune-protective mediators, termed as specialized pro-resolving mediators (SPM). Herein, we investigated whether observed differences in the potencies of distinct omega-3 supplements were linked with their ability to upregulate SPM formation. Using lipid mediator profiling we found that four commercially available supplements conferred a unique SPM signature profile to human macrophages, with the overall increases in SPM concentrations being different between the four supplements. These increases in SPM concentrations were linked with an upregulation of macrophage phagocytosis and a decreased uptake of oxidized low-density lipoproteins. Pharmacological inhibition of two key SPM biosynthetic enzymes 5-Lipoxygenase or 15-Lipoxygenase reversed the macrophage-directed actions of each of the omega-3 supplements. Furthermore, administration of the two supplements that most potently upregulated macrophage SPM formation and reprogrammed their responses in vitro, to APOE-/- mice fed a western diet, increased plasma SPM concentrations and reduced vascular inflammation. Together these findings support the utility of SPM as potential prognostic markers in determining the utility of a given supplement to regulate macrophage responses and inflammation.

Deciphering the Molecular Details of the Lipoxin Formation Mechanism in the 5(S),15(S)-DiHpETE Biosynthetic Pathway Catalyzed by Reticulocyte 15-Lipoxygenase-1.

Chronic inflammation is now widely recognized to play important roles in many commonly occurring diseases, including COVID-19. The resolution response to this chronic inflammation is an active process governed by specialized pro-resolving mediators (SPMs) like the lipid mediators known as lipoxins. The biosynthesis of lipoxins is catalyzed by several lipoxygenases (LOXs) from arachidonic acid. However, the molecular details of the mechanisms involved are not well known yet. In this paper, we have combined molecular dynamics (MD) simulations and quantum mechanics/molecular mechanics (QM/MM) calculations to analyze how reticulocyte 15-LOX-1 catalyzes the production of lipoxins from 5(S),15(S)-diHpETE. Our results indicate that the dehydration mechanism from 5(S),15(S)-diHpETE, via the formation of an epoxide, presents huge energy barriers even though it was one of the two a priori synthetic proposals. This result is compatible with the fact that no epoxide has been directly detected as an intermediate in the catalytic formation of lipoxins from 5(S),15(S)-diHpETE. Conversely, the oxygenation of 5(S),15(S)-diHpETE at C14 is feasible because there is an open channel connecting the protein surface with this carbon atom, and the energy barrier for oxygen addition through this channel is small. The analysis of the following steps of this mechanism, leading to the corresponding hydroperoxide at the 15-LOX-1 active site, indicates that the oxygenation mechanism will lead to the formation of lipoxinB4 after the final action of a reductase. In contrast, our calculations are in agreement with experiments that lipoxinA4 cannot derive from 5(S),15(S)-diHpETE by either of the two proposed mechanisms and that 5(S),15(S)-diHETE is not an intermediate of lipoxin biosynthesis catalyzed by 15-LOX-1.

Microglia depletion diminishes key elements of the leukotriene pathway in the brain of Alzheimer's Disease mice.

Leukotrienes (LTs) contribute to the neuropathology of chronic neurodegenerative disorders including Alzheimer's Disease (AD), where they mediate neuroinflammation and neuronal cell-death. In consequence, blocking the action of Leukotrienes (LTs) ameliorates pathologies and improves cognitive function in animal models of neurodegeneration. Surprisingly, the source of Leukotrienes (LTs) in the brain is largely unknown. Here, we identified the Leukotriene (LT) synthesis rate-limiting enzyme 5-Lipoxygenase (5-Lox) primarily in neurons and to a lesser extent in a subpopulation of microglia in human Alzheimer´s Disease (AD) hippocampus brain sections and in brains of APP Swedish PS1 dE9 (APP-PS1) mice, a transgenic model for Alzheimer´s Disease (AD) pathology. The 5-Lipoxygenase (5-Lox) activating protein (FLAP), which anchors 5-Lipoxygenase (5-Lox) to the membrane and mediates the contact to the substrate arachidonic acid, was confined exclusively to microglia with the entire microglia population expressing 5-Lipoxygenase activating protein (FLAP). To define the contribution of microglia in the Leukotriene (LT) biosynthesis pathway, we ablated microglia using the colony stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 in wildtype (WT) and APP-PS1 mice. Microglia ablation not only diminished the expression of FLAP and of the Leukotriene (LT) receptor Cysteinylleukotriene receptor 1 (CysLTR1), as expected based on their microglia cell type-specific expression, but also drastically reduced 5-Lipoxygenase (5-Lox) mRNA expression in the brain and its protein expression in neurons, in particular in wildtype (WT) mice. In conclusion i) microglia are key in Leukotriene (LT) biosynthesis, and ii) they regulate neuronal 5-Lipoxygenase (5-Lox) expression implying a yet unknown signaling mechanism between neurons and microglia.

Cellular Source of Cysteinyl Leukotrienes Following Chlorine Exposure.

Exposure of mice to high concentrations of chlorine leads to the synthesis of cysteinyl leukotrienes (cysLTs). CysLTs contribute to chlorine-induced airway hyperresponsiveness. The aim of the current study was to determine the cellular source of the cysLTs. To achieve this aim, we exposed mice to 100 ppm of chlorine for 5 minutes. Intranasal instillation of clodronate in liposomes and of diphtheria toxin in CD11c-DTR mice was used to deplete macrophages. CCR2-/- mice were used to assess the contribution of recruited macrophages. Eosinophils and neutrophils were depleted with specific antibodies. Platelet-neutrophil aggregation was prevented with an antibody against P-selectin. The potential roles of phagocytosis of neutrophils by macrophages and of transcellular metabolism between epithelial cells and neutrophils were explored in coculture systems. We found that depletion of neutrophils was the only intervention that inhibited the synthesis of cysLTs at 24 hours after chlorine exposure. Although macrophages did synthesize cysLTs in response to phagocytosis of neutrophils, depletion of macrophages did not reduce the increment in cysLTs triggered by chlorine exposure. However, coculture of airway epithelial cells with neutrophils resulted in a significant increase in the synthesis of cysLTs, dependent on the expression of 5-lipoxygenase by neutrophils. We conclude that cysLT synthesis following chlorine exposure may be dependent on transcellular metabolism by neutrophil-epithelial interactions.

Mammalian-Like Inflammatory and Pro-Resolving Oxylipins in Marine Algae.

Oxylipins constitute a family of oxidized fatty acids, that are well known as tissue hormones in mammals. They contribute to inflammation and its resolution. The major classes of these lipid mediators are inflammatory prostaglandins (PGs) and leukotrienes (LTs) as well as pro-resolving resolvins (Rvs). Understanding their biosynthetic pathways and modes of action is important for anti-inflammatory interventions. Besides mammals, marine algae also biosynthesize mammalian-like oxylipins and thus offer new opportunities for oxylipin research. They provide prolific sources for these compounds and offer unique opportunities to study alternative biosynthetic pathways to the well-known lipid mediators. Herein, we discuss recent findings on the biosynthesis of oxylipins in mammals and algae including an alternative pathway to prostaglandin E2 , a novel pathway to a precursor of leukotriene B4 , and the production of resolvins in algae. We evaluate the pharmacological potential of the algal metabolites with implications in health and disease.

Differential role of vacuolar (H+)-ATPase in the expression and activity of cyclooxygenase-2 in human monocytes.

Monocytes are professional immune cells that produce abundant levels of pro-inflammatory eicosanoids including prostaglandins and leukotrienes during inflammation. Vacuolar (H+)-ATPase (V-ATPase) is critically involved in a variety of inflammatory processes including cytokine trafficking and lipid mediator biosynthesis. However, its role in eicosanoid biosynthetic pathways in monocytes remains elusive. Here, we present a differential role of V-ATPase in the expression and in the activity of cyclooxygenase (COX)-2 in human monocytes. Pharmacological targeting of V-ATPase increased the expression of COX-2 protein in lipopolysaccharide-stimulated primary monocytes, which was paralleled by enhanced phosphorylation of p38 MAPK and ERK-1/2, without impacting the NF-κB and SAPK/JNK pathways. Targeting of both p38 MAPK and ERK-1/2 pathways showed that the kinase pathways are crucial for COX-2 expression in human monocytes. Despite increased COX-2 protein levels, however, suppression of V-ATPase activity impaired the biosynthesis of COX- and also of 5-lipoxygenase (LOX)-derived lipid mediators in monocytes without affecting 12-/15-LOX products, assessed by a metabololipidomics approach using UPLC-MS-MS analysis. Our results indicate that changes in the intracellular pH may contribute to suppression of COX-2 and 5-LOX activities. We suggest that V-ATPase on one hand limits COX-2 protein levels via restricting p38 MAPK and ERK-1/2 activation, while on the other hand it governs the cellular activity of COX-2 through appropriate adjustment of the intracellular pH.

A combination of LCPUFA ameliorates airway inflammation in asthmatic mice by promoting pro-resolving effects and reducing adverse effects of EPA.

Lipid mediators derived from omega (n)-3 and n-6 long-chain polyunsaturated fatty acids (LCPUFA) play key roles in bronchoconstriction, airway inflammation, and resolution processes in asthma. This study compared the effects of dietary supplementation with either a combination of LCPUFAs or eicosapentaenoic acid (EPA) alone to investigate whether the combination has superior beneficial effects on the outcome of asthmatic mice. Mice were sensitized with house dust mite (HDM) extract, and subsequently supplemented with either a combination of LCPUFAs or EPA alone in a recall asthma model. After the final HDM and LCPUFA administration, airway hyperresponsiveness (AHR), bronchoalveolar lavages, and lung histochemistry were examined. Lipid mediator profiles were determined by liquid chromatography coupled with tandem mass spectrometry (LC-MS-MS). The LCPUFA combination reduced AHR, eosinophilic inflammation, and inflammatory cytokines (IL-5, IFN-γ, and IL-6) in asthmatic mice, whereas EPA enhanced inflammation. The combination of LCPUFAs was more potent in downregulating EPA-derived LTB5 and LTC5 and in supporting DHA-derived RvD1 and RvD4 (2.22-fold and 2.58-fold higher levels) than EPA alone. Ex vivo experiments showed that LTB5 contributes to granulocytes' migration and M1-polarization in monocytes. Consequently, the LCPUFA combination ameliorated airway inflammation by inhibiting adverse effects of EPA and promoting pro-resolving effects supporting the lipid mediator-dependent resolution program.

Exotoxins from Staphylococcus aureus activate 5-lipoxygenase and induce leukotriene biosynthesis.

Massive neutrophil infiltration is an early key event in infectious inflammation, accompanied by chemotactic leukotriene (LT)B4 generation. LTB4 biosynthesis is mediated by 5-lipoxygenase (5-LOX), but which pathogenic factors cause 5-LOX activation during bacterial infections is elusive. Here, we reveal staphylococcal exotoxins as 5-LOX activators. Conditioned medium of wild-type Staphylococcus aureus but not of exotoxin-deficient strains induced 5-LOX activation in transfected HEK293 cells. Two different staphylococcal exotoxins mimicked the effects of S. aureus-conditioned medium: (1) the pore-forming toxin α-hemolysin and (2) amphipathic α-helical phenol-soluble modulin (PSM) peptides. Interestingly, in human neutrophils, 5-LOX activation was exclusively evoked by PSMs, which was prevented by the selective FPR2/ALX receptor antagonist WRW4. 5-LOX activation by PSMs was confirmed in vivo as LT formation in infected paws of mice was impaired in response to PSM-deficient S. aureus. Conclusively, exotoxins from S. aureus are potent pathogenic factors that activate 5-LOX and induce LT formation in neutrophils.

Leukotriene Synthesis Is Critical for Medulloblastoma Progression.

PURPOSE: Here, we examined the role of leukotrienes, well-known inflammatory mediators, in the tumorigenesis of hedgehog pathway-associated medulloblastoma, and tested the efficacies of antagonists of leukotriene biosynthesis in medulloblastoma treatment.Experimental Design: We examined the leukotriene levels in medulloblastoma cells by ELISA. We next tested whether leukotriene synthesis in medulloblastoma cells relied on activation of hedgehog pathway, or the presence of hedgehog ligand secreted by astrocytes. We then investigated whether leukotriene mediated hedgehog-induced Nestin expression in tumor cells. The functions of leukotriene in tumor cell proliferation and tumor growth in medulloblastoma were determined through knocking down 5-lipoxygenase (a critical enzyme for leukotriene synthesis) by shRNAs, or using 5-lipoxygenase-deficient mice. Finally, the efficacies of antagonists of leukotriene synthesis in medulloblastoma treatment were tested in vivo and in vitro. RESULTS: Leukotriene was significantly upregulated in medulloblastoma cells. Increased leukotriene synthesis relied on hedgehog ligand secreted by astrocytes, a major component of medulloblastoma microenvironment. Leukotriene stimulated tumor cells to express Nestin, a cytoskeletal protein essential for medulloblastoma growth. Genetic blockage of leukotriene synthesis dramatically suppressed medulloblastoma cell proliferation and tumor growth in vivo. Pharmaceutical inhibition of leukotriene synthesis markedly repressed medulloblastoma cell proliferation, but had no effect on proliferation of normal neuronal progenitors. Moreover, antagonists of leukotriene synthesis exhibited promising tumor inhibitory efficacies on drug-resistant medulloblastoma. CONCLUSIONS: Our findings reveal a novel signaling pathway that is critical for medulloblastoma cell proliferation and tumor progression, and that leukotriene biosynthesis represents a promising therapeutic target for medulloblastoma treatment.

The Role of Leukotrienes as Potential Therapeutic Targets in Allergic Disorders.

Leukotrienes (LTs) are lipid mediators that play pivotal roles in acute and chronic inflammation and allergic diseases. They exert their biological effects by binding to specific G-protein-coupled receptors. Each LT receptor subtype exhibits unique functions and expression patterns. LTs play roles in various allergic diseases, including asthma (neutrophilic asthma and aspirin-sensitive asthma), allergic rhinitis, atopic dermatitis, allergic conjunctivitis, and anaphylaxis. This review summarizes the biology of LTs and their receptors, recent developments in the area of anti-LT strategies (in settings such as ongoing clinical studies), and prospects for future therapeutic applications.

Roles of cysteinyl leukotrienes and their receptors in immune cell-related functions.

The cysteinyl leukotrienes (cys-LTs), leukotriene C4, (LTC4), LTD4, and LTE4, are lipid mediators of inflammation. LTC4 is the only intracellularly synthesized cys-LT through the 5-lipoxygenase and LTC4 synthase pathway and after transport is metabolized to LTD4 and LTE4 by specific extracellular peptidases. Each cys-LT has a preferred functional receptor in vivo; LTD4 to the type 1 cys-LT receptor (CysLT1R), LTC4 to CysLT2R, and LTE4 to CysLT3R (OXGR1 or GPR99). Recent studies in mouse models revealed that there are multiple regulatory mechanisms for these receptor functions and each receptor plays a distinct role as observed in different mouse models of inflammation and immune responses. This review focuses on the integrated host responses to the cys-LT/CysLTR pathway composed of sequential ligands with preferred receptors as seen from mouse models. It also discusses potential therapeutic targets for LTC4 synthase, CysLT2R, and CysLT3R.

Effects of anti-inflammatory and adaptogenic herbal extracts on gene expression of eicosanoids signaling pathways in isolated brain cells.

INTRODUCTION: The adaptogens modulate expression of genes playing key roles in development of aging-related disorders, which are considered as low-grade systemic inflammatory conditions characterized by an imbalance between pro-and anti-inflammatory eicosanoids. AIM OF THE STUDY: We compared the effects of anti-inflammatory and adaptogenic plant extracts on the expression of genes involved in biosynthesis of eicosanoids with the purpose to find those plants, which selectively upregulated the expression of anti-inflammatory lipoxins signaling pathways and inhibited pro-inflammatory signaling pathways associated with biosynthesis of leukotrienes, prostaglandins and thromboxanes. MATERIALS AND METHODS: We conducted transcriptome-wide RNA sequencing to profile gene expression alterations in T98G neuroglia cells upon treatment of plant extract and analyzed the relevance of deregulated genes to eicosanoids signaling pathways using in silico models. RESULTS: For the first time, we demonstrated that Rhodiola rosea, Withania somnifera and Eleutherococcus senticosus downregulate the expression of key genes (ALOX5AP, DPEP2, LTC4S) involved biosynthesis of leukotrienes A, B, C, D and E, resulting in inhibition of leukotriene signaling pathway suggesting their potential benefits in Alzheimer disease. The common feature for all tested anti-inflammatory plants extracts was related to downregulation of ALOX12, which was also associated with neuroprotective action of these medicinal plants as well as their potential benefits in neurodegenerative diseases. None of tested anti-inflammatory and adaptogenic plants selectively activated the ALOX15-mediated signaling pathway, which is associated with generation anti-inflammatory lipoxins. Almost all tested plants upregulated the expression of the prostaglandin E receptor 3 gene (PTGER3) suggesting their potential benefits in the treatment of cancer. CONCLUSION: Every single plant tested in this study revealed a specific "signature" on eicosanoid signaling-related gene expression, regardless of their common features as anti-inflammatory or adaptogenic activity. Further studies of the combination of Rhodiola with Withania (Adaptra) for the treatment of Alzheimer disease are required.

Beyond leukotriene formation-The noncanonical functions of 5-lipoxygenase.

5-lipoxygenase (5-LO) is the key enzyme in the biosynthesis of leukotrienes and specialized proresolving lipid mediators (SPM). It is mainly expressed in leukocytes and is part of the innate immune system. 5-LO can shuttle between the cytosol and the nucleus. Upon cell activation the protein translocates from soluble cellular compartments to the nuclear membrane. Besides FLAP which is required for cellular leukotriene and SPM formation, 5-LO interacts with other proteins like coactosin-like protein (CLP), Dicer, ß-catenin and p53. In this review, the factors involved in the regulation of 5-LO expression, the role of 5-LO in the regulation of stem cell proliferation and differentiation and its biological functions apart from leukotriene and SPM formation are summarized.

Novel benzoxanthene lignans that favorably modulate lipid mediator biosynthesis: A promising pharmacological strategy for anti-inflammatory therapy.

Lipid mediators (LM) encompass pro-inflammatory prostaglandins (PG) and leukotrienes (LT) but also specialized pro-resolving mediators (SPM) which display pivotal bioactivities in health and disease. Pharmacological intervention with inflammatory disorders such as osteoarthritis and rheumatoid arthritis commonly employs anti-inflammatory drugs that can suppress PG and LT formation, which however, possess limited effectiveness and side effects. Here, we report on the discovery and characterization of the two novel benzoxanthene lignans 1 and 2 that modulate select LM biosynthetic enzymes enabling the switch from pro-inflammatory LT to SPM biosynthesis as potential pharmacological strategy to intervene with inflammation. In cell-free assays, compound 1 and 2 inhibit microsomal prostaglandin E2 synthase-1 and leukotriene C4 synthase (IC50 ∼ 0.6-3.4 µM) and potently interfere with 5-lipoxygenase (5-LOX), the key enzyme in LT biosynthesis (IC50 = 0.04 and 0.09 µM). In human neutrophils, monocytes and M1 and M2 macrophages, compound 1 and 2 efficiently suppress LT biosynthesis (IC50 < 1 µM), accompanied by elevation of 15-LOX-derived LM including SPM. In zymosan-induced murine peritonitis, compound 1 and 2 ameliorated self-limited inflammation along with suppression of early LT formation and elevation of subsequent SPM biosynthesis in vivo. Together, these novel benzoxanthene lignans promote the LM class switch from pro-inflammatory towards pro-resolving LM to terminate inflammation, suggesting their suitability as novel leads for pharmacotherapy of arthritis and related inflammatory disorders.