The Intracellular Localisation and Phosphorylation Profile of the Human 5-Lipoxygenase Δ13 Isoform Differs from That of Its Full Length Counterpart

Single and multiple inhibitors of the biosynthesis of 5-, 12-, 15-lipoxygenase products derived from cinnamyl-3,4-dihydroxy-α-cyanocinnamate: Synthesis and structure-activity relationship

The involvement of lipoxygenases in various pathologies, combined with the unavailability of safe and effective inhibitors of the biosynthesis of their products, is a source of inspiration for the development of new inhibitors. Based on a structural analysis of known inhibitors of lipoxygenase products biosynthesis, a comprehensive structure-activity study was carried out, which led to the discovery of several novel compounds (16a-c, 17a) demonstrating promising potency to inhibit the biosynthesis of products of 5-, 12- and 15-LO. Compounds 16b and 16c outperformed zileuton (1), the only FDA-approved 5-LO inhibitor, as well as known inhibitors such as caffeic acid phenethyl ester (CAPE (2)) and cinnamyl-3,4-dihydroxy-α-cyanocinnamate (CDC (4)). However, the introduction of a cyano group at the α-position of the carbonyl abolished the activity. Compounds 16a and 17a also inhibited the biosynthesis of 12- and 15-LO products. Compounds 16a, 17a far surpassed baicalein, a known 12-LO inhibitor, as inhibitors of 12-LO products biosynthesis. Compound 17a and CDC (4) showed equivalent inhibition of LO products, proposing that the double bond in the ester moiety is not necessary for the inhibitory activity. The introduction of the cyano group, as in compound 17a, at the α-position of the carbonyl in compound 16a significantly reduced the inhibitory activity against the biosynthesis of 15-LO products. In addition to the interactions with residues His372 and Phe421 also found with zileuton and CAPE, compounds 16a and 16c each interact with residue His367 as shown by molecular docking. This new interaction may explain their high affinity with the 5-LO active site.

Algerian Propolis from Distinct Geographical Locations: Chemical Profiles, Antioxidant Capacity, Cytotoxicity and Inhibition of 5-Lipoxygenase Product Biosynthesis

Propolis was collected from honeybee hives in three geographically distinct Algerian climates and extracts were characterized for composition and bioactivity. Bees were identified as native subspecies using an in-silico DraI mtDNA COI-COII test. Over 20 compounds were identified in extracts by LC-MS. Extracts from the Medea region were more enriched in phenolic content (302±28 mg GAE/g of dry extract) than those from Annaba and Ghardaia regions. Annaba extracts had the highest flavonoid content (1870±385 mg QCE/g of dry extract). Medea extracts presented the highest free-radical scavenging activity (IC50=13.5 μg/mL) using the DPPH radical assay while Ghardaia extracts from the desert region were weak (IC50>100 μg/mL). Antioxidant activities measured using AAPH oxidation of linoleic acid were similar in all extracts with IC50 values ranging from 2.9 to 4.9 μg/mL. All extracts were cytotoxic (MTT assay) and proapoptotic (Annexin-V) against human leukemia cell lines in the low μg/mL range, although the Annaba extract was less active against the Reh cell line. Extracts inhibited cellular 5-lipoxygenase product biosynthesis with IC50 values ranging from 0.6 to 3.2 μg/mL. Overall, examined propolis extracts exhibited significant biological activity that warrant further characterization in cellular and in vivo models.

Structure-Activity Relationship Studies of New Sinapic Acid Phenethyl Ester Analogues Targeting the Biosynthesis of 5-Lipoxygenase Products: The Role of Phenolic Moiety, Ester Function, and Bioisosterism

Sinapic acid is found in many edible plants and fruits, such as rapeseed, where it is the predominant phenolic compound. New sinapic acid phenethyl ester (SAPE) analogues were synthesized and screened as inhibitors of the biosynthesis of 5-lipoxygenase (5-LO) in stimulated HEK293 cells and polymorphonuclear leukocytes (PMNL). Inhibition of leukotriene biosynthesis catalyzed by 5-LO is a validated therapeutic strategy against certain inflammatory diseases and allergies. Unfortunately, the only inhibitor approved to date has limited clinical use because of its poor pharmacokinetic profile and liver toxicity. With the new analogues synthesized in this study, the role of the phenolic moiety, ester function, and bioisosterism was investigated. Several of the 34 compounds inhibited the biosynthesis of 5-LO products, and 20 compounds were 2-11 times more potent than zileuton in PMNL, which are important producers of 5-LO products. Compounds 5i (IC₅₀: 0.20 μM), 5l (IC₅₀: 0.20 μM), and 5o (IC₅₀: 0.21 μM) bearing 4-trifluoromethyl, methyl, or methoxy substituent at meta-position of the phenethyl moiety were 1.5 and 11.5 times more potent than SAPE (IC₅₀: 0.30 μM) and zileuton (IC₅₀: 2.31 μM), respectively. Additionally, compound 9 (IC₅₀: 0.27 μM), which was obtained after acetylation of the 4-hydroxyl of SAPE, was equivalent to SAPE and 8 times more active than zileuton. Furthermore, compound 20b (IC₅₀: 0.27 μM) obtained after the bioisosteric replacement of the ester function of SAPE by the 1,2,4-oxadiazole heterocycle was equivalent to SAPE and 8 times more active than zileuton. Thus, this study provides a basis for the rational design of new molecules that could be developed further as anti 5-LO therapeutics.

Untangling the web of 5-lipoxygenase-derived products from a molecular and structural perspective: The battle between pro- and anti-inflammatory lipid mediators

Arachidonic acid (AA) is the precursor to leukotrienes (LT), potent mediators of the inflammatory response. In the 35 + years since cysteinyl-LTs were reported to mediate antigen-induced constriction of bronchi in tissue from asthma patients, numerous cellular responses evoked by the LTs, such as chemoattraction and G protein-coupled receptor (GPCR) activation, have been elucidated and revealed a potential for 5-lipoxygenase (5-LOX) as a promising drug target that goes beyond asthma. We describe herein early work identifying 5-LOX as the key enzyme that initiates LT biosynthesis and the discovery of its membrane-embedded helper protein required to execute the two-step reaction that transforms AA to the progenitor leukotriene A4 (LTA4). 5-LOX must traffic to the nuclear membrane to interact with its partner and undergo a conformational change so that AA can enter the active site. Additionally, the enzyme must retain the hydroperoxy-reaction intermediate for its final transformation to LTA4. Each of these steps provide a unique target for inhibition. Next, we describe the recent structures of GPCRs that recognize metabolites of the 5-LOX pathway and thus provide target alternatives. We also highlight the role of 5-LOX in the biosynthesis of anti-inflammatory lipid mediators (LM), the so-called specialized pro-resolving mediators (SPM). The involvement of 5-LOX in the biosynthesis of LM with opposing functions undoubtedly complicates the continuing search for 5-LOX inhibitors as therapeutic leads. Finally, we address the recent discovery of how some allosteric 5-LOX inhibitors promote oxygenation at the 12/15 carbon on AA to generate mediators that resolve, rather than promote, inflammation.

New Zileuton-Hydroxycinnamic Acid Hybrids: Synthesis and Structure-Activity Relationship towards 5-Lipoxygenase Inhibition

A novel series of zileuton-hydroxycinnamic acid hybrids were synthesized and screened as 5-lipoxygenase (5-LO) inhibitors in stimulated HEK293 cells and polymorphonuclear leukocytes (PMNL). Zileuton’s (1) benzo[b]thiophene and hydroxyurea subunits combined with hydroxycinnamic acid esters’ ester linkage and phenolic acid moieties were investigated. Compound 28, bearing zileuton’s (1) benzo[b]thiophene and sinapic acid phenethyl ester’s (2) α,β-unsaturated phenolic acid moiety 28, was shown to be equipotent to zileuton (1), the only clinically approved 5-LO inhibitor, in stimulated HEK293 cells. Compound 28 was three times as active as zileuton (1) for the inhibition of 5-LO in PMNL. Compound 37, bearing the same sinapic acid (3,5-dimethoxy-4-hydroxy substitution) moiety as 28, combined with zileuton’s (1) hydroxyurea subunit was inactive. This result shows that the zileuton’s (1) benzo[b]thiophene moiety is essential for the inhibition of 5-LO product biosynthesis with our hydrids. Unlike zileuton (1), Compound 28 formed two π–π interactions with Phe177 and Phe421 as predicted when docked into 5-LO. Compound 28 was the only docked ligand that showed a π–π interaction with Phe177 which may play a part in product specificity as reported.

Phosphorylation of 5-LOX: The Potential Set-point of Inflammation

Inflammation secondary to tissue injuries serves as a double-edged sword that determines the prognosis of tissue repair. As one of the most important enzymes controlling the inflammation process by producing leukotrienes, 5-lipoxygenase (5-LOX, also called 5-LO) has been one of the therapeutic targets in regulating inflammation for a long time. Although a large number of 5-LOX inhibitors have been explored, only a few of them can be applied clinically. Surprisingly, phosphorylation of 5-LOX reveals great significance in regulating the subcellular localization of 5-LOX, which has proven to be an important mechanism underlying the enzymatic activities of 5-LOX. There are at least three phosphorylation sites in 5-LOX jointly to determine the final inflammatory outcomes, and adjustment of phosphorylation of 5-LOX at different phosphorylation sites brings hope to provide an unrecognized means to regulate inflammation. The present review intends to shed more lights into the set-point-like mechanisms of phosphorylation of 5-LOX and its possible clinical application by summarizing the biological properties of 5-LOX, the relationship of 5-LOX with neurodegenerative diseases and brain injuries, the phosphorylation of 5-LOX at different sites, the regulatory effects and mechanisms of phosphorylated 5-LOX upon inflammation, as well as the potential anti-inflammatory application through balancing the phosphorylation-depended set-point.

Extraction, Antioxidant Capacity, 5-Lipoxygenase Inhibition, and Phytochemical Composition of Propolis from Eastern Canada

Soxhlet (SE), microwave-assisted (MAE) and ultrasound-assisted (UAE) extraction were compared using ten extraction solvents for their efficiency to extract phenolic and flavonoid antioxidants from Eastern Canada propolis. Extracts were compared for total phenolic (TPC) and total flavonoid (TFC) content, and radical scavenging activities. Anti-inflammatory activity through inhibition of 5-lipoxygenase (5-LO) products biosynthesis in HEK293 cells was also evaluated. The results showed that SE extracts using polar solvents had the highest TPC and TFC. Extracts obtained with ethanol, methanol and acetone were effective free radical scavengers, and showed 5-LO inhibition similar to zileuton. UAE was an effective extraction method since the extracts obtained were comparable to those using SE and the MAE while being done at room temperature. With UAE, extracts of less polar solvents showed similar free radical scavenging and 5-LO inhibition to extracts of much more polar solvents such as methanol or ethanol. Reversed-phase liquid chromatography tandem mass spectrometry confirmed the presence of 21 natural compounds in the propolis extracts based on the comparison of intact mass, chromatographic retention time and fragmentation patterns derived from commercial analytical standards. The current study is the first of its kind to concurrently investigate solvent polarity as well as extraction techniques of propolis.

Phenolic acid phenethylesters and their corresponding ketones: Inhibition of 5-lipoxygenase and stability in human blood and HepaRG cells

5-lipoxygenase (5-LO) catalyzes the biosynthesis of leukotrienes, potent lipid mediators involved in inflammatory diseases, and both 5-LO and the leukotrienes are validated therapeutic targets. Caffeic acid phenethyl ester (CAPE) is an effective inhibitor of 5-LO and leukotriene biosynthesis but is susceptible to hydrolysis by esterases. In this study a number of CAPE analogues were synthesized with modifications to the caffeoyl moiety and the replacement of the ester linkage with a ketone. Several new molecules showed better inhibition of leukotriene biosynthesis than CAPE in isolated human neutrophils and in whole blood with IC50 values in the nanomolar (290-520 nmol/L) and low micromolar (1.0-2.3 µmol/L) ranges, respectively. Sinapic acid and 2,5-dihydroxy derivatives were more stable than CAPE in whole blood, and ketone analogues were degraded more slowly in HepaRG hepatocyte cultures than esters. All compounds underwent modification consistent with glucuronidation in HepaRG cultures as determined using LC-MS/MS analysis, though the modified sinapoyl ketone (10) retained 50% of its inhibitory activity after up to one hour of incubation. This study has identified at least one CAPE analogue, compound 10, that shows favorable properties that warrant further in vivo investigation as an antiinflammatory compound.

5-lipoxygenase-dependent biosynthesis of novel 20:4 n-3 metabolites with anti-inflammatory activity

5-lipoxygenase (5-LO) catalyzes the conversion of arachidonic acid (AA) into pro-inflammatory leukotrienes. N-3 PUFA like eicosapentaenoic acid are subject to a similar metabolism and are precursors of pro-resolving mediators. Stearidonic acid (18:4 n-3, SDA) is a plant source of n-3 PUFA that is elongated to 20:4 n-3, an analogue of AA. However, no 5-LO metabolites of 20:4 n-3 have been reported. In this study, control and 5-LO-expressing HEK293 cells were stimulated in the presence of 20:4 n-3. Metabolites were characterized by LC-MS/MS and their anti-inflammatory properties assessed using AA-induced autocrine neutrophil stimulation and leukotriene B₄-mediated chemotaxis. 8‑hydroxy‑9,11,14,17-eicosatetraenoic acid (Δ¹⁷-8-HETE) and 8,15-dihydroxy-9,11,13,17-eicosatetraenoic acid (Δ¹⁷-8,15-diHETE) were identified as novel metabolites. Δ¹⁷-8,15-diHETE production was inhibited by the leukotriene A₄ hydrolase inhibitor SC 57461A. Autocrine neutrophil leukotriene stimulation and neutrophil chemotaxis, both BLT1-dependent processes, were inhibited by Δ¹⁷-8,15-diHETE at low nM concentrations. These data support an anti-inflammatory role for Δ¹⁷-8,15-diHETE, a novel 5-LO product.

New Hydroxycinnamic Acid Esters as Novel 5-Lipoxygenase Inhibitors That Affect Leukotriene Biosynthesis

Leukotrienes are inflammatory mediators that actively participate in the inflammatory response and host defense against pathogens. However, leukotrienes also participate in chronic inflammatory diseases. 5-lipoxygenase is a key enzyme in the biosynthesis of leukotrienes and is thus a validated therapeutic target. As of today, zileuton remains the only clinically approved 5-lipoxygenase inhibitor; however, its use has been limited due to severe side effects in some patients. Hence, the search for a better 5-lipoxygenase inhibitor continues. In this study, we investigated structural analogues of caffeic acid phenethyl ester, a naturally-occurring 5-lipoxygenase inhibitor, in an attempt to enhance the inhibitory activity against 5-lipoxygenase and determine structure-activity relationships. These compounds were investigated for their ability to attenuate the biosynthesis of leukotrienes. Compounds 13 and 19, phenpropyl and diphenylethyl esters, exhibited significantly enhanced inhibitory activity when compared to the reference molecules caffeic acid phenethyl ester and zileuton.

Characterization and cellular localization of human 5-lipoxygenase and its protein isoforms 5-LOΔ13, 5-LOΔ4 and 5-LOp12

Human 5-lipoxygenase (5-LO-WT) initiates the leukotriene (LT) biosynthesis. LTs play an important role in diseases like asthma, atherosclerosis and in many types of cancer. In this study, we investigated the 5-LO isoforms 5-LO∆13, 5-LO∆4 and 5-LOp12, lacking the exons 13, 4 or a part of exon 12, respectively. We were able to detect the mRNA of the isoforms 5-LO∆13 and 5-LOp12 in B and T cell lines as well as in primary B and T cells and monocytes. Furthermore, we found that expression of 5-LO and particularly of the 5-LO∆13 and 5-LOp12 isoforms is increased in monocytes from patients with rheumatoid arthritis and sepsis. Confocal microscopy of HEK293T cells stably transfected with tagged 5-LO-WT and/or the isoforms revealed that 5-LO-WT is localized in the nucleus whereas all isoforms are located in the cytosol. Additionally, all isoforms are catalytically inactive and do not seem to influence the specific activity of 5-LO-WT. S271A mutation in 5-LO-WT and treatment of the cells with sorbitol or KN-93/SB203580 changes the localization of the WT enzyme to the cytosol. Despite colocalization with the S271A mutant, the isoforms did not affect LT biosynthesis. Analysis of the phosphorylation pattern of 5-LO-WT and all the isoforms revealed that 5-LOp12 and 5-LO∆13 are highly phosphorylated at Ser271 and 5-LOp12 at Ser523. Furthermore, coexpression of the isoforms inhibited or stimulated 5-LO-WT expression in transiently and stably transfected HEK293T cells suggesting that the isoforms have other functions than canonical LT biosynthesis.

Identification and Characterization of a New Protein Isoform of Human 5-Lipoxygenase

Leukotrienes (LTs) are inflammatory mediators that play a pivotal role in many diseases like asthma bronchiale, atherosclerosis and in various types of cancer. The key enzyme for generation of LTs is the 5-lipoxygenase (5-LO). Here, we present a novel putative protein isoform of human 5-LO that lacks exon 4, termed 5-LOΔ4, identified in cells of lymphoid origin, namely the Burkitt lymphoma cell lines Raji and BL41 as well as primary B and T cells. Deletion of exon 4 does not shift the reading frame and therefore the mRNA is not subjected to non-mediated mRNA decay (NMD). By eliminating exon 4, the amino acids Trp144 until Ala184 are omitted in the corresponding protein. Transfection of HEK293T cells with a 5-LOΔ4 expression plasmid led to expression of the corresponding protein which suggests that the 5-LOΔ4 isoform is a stable protein in eukaryotic cells. We were also able to obtain soluble protein after expression in E. coli and purification. The isoform itself lacks canonical enzymatic activity as it misses the non-heme iron but it still retains ATP-binding affinity. Differential scanning fluorimetric analysis shows two transitions, corresponding to the two domains of 5-LO. Whilst the catalytic domain of 5-LO WT is destabilized by calcium, addition of calcium has no influence on the catalytic domain of 5-LOΔ4. Furthermore, we investigated the influence of 5-LOΔ4 on the activity of 5-LO WT and proved that it stimulates 5-LO product formation at low protein concentrations. Therefore regulation of 5-LO by its isoform 5-LOΔ4 might represent a novel mechanism of controlling the biosynthesis of lipid mediators.

On the cellular metabolism of the click chemistry probe 19-alkyne arachidonic acid

Alkyne and azide analogs of natural compounds that can be coupled to sensitive tags by click chemistry are powerful tools to study biological processes. Arachidonic acid (AA) is a FA precursor to biologically active compounds. 19-Alkyne-AA (AA-alk) is a sensitive clickable AA analog; however, its use as a surrogate to study AA metabolism requires further evaluation. In this study, AA-alk metabolism was compared with that of AA in human cells. Jurkat cell uptake of AA was 2-fold greater than that of AA-alk, but significantly more AA-Alk was elongated to 22:4. AA and AA-alk incorporation into and remodeling between phospholipid (PL) classes was identical indicating equivalent CoA-independent AA-PL remodeling. Platelets stimulated in the pre-sence of AA-alk synthesized significantly less 12-lipoxygenase (12-LOX) and cyclooxygenase products than in the presence of AA. Ionophore-stimulated neutrophils produced significantly more 5-LOX products in the presence of AA-alk than AA. Neutrophils stimulated with only exogenous AA-alk produced significantly less 5-LOX products compared with AA, and leukotriene B₄ (LTB₄₎-alk was 12-fold less potent at stimulating neutrophil migration than LTB₄, collectively indicative of weaker leukotriene B₄ receptor 1 agonist activity of LTB₄-alk. Overall, these results suggest that the use of AA-alk as a surrogate for the study of AA metabolism should be carried out with caution.