Structural and functional biology of arachidonic acid 15-lipoxygenase-1 (ALOX15)

Arachidonate 15-lipoxygenase type B: Regulation, function, and its role in pathophysiology

As a lipoxygenase (LOX), arachidonate 15-lipoxygenase type B (ALOX15B) peroxidizes polyenoic fatty acids (PUFAs) including arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and linoleic acid (LA) to their corresponding fatty acid hydroperoxides. Distinctive to ALOX15B, fatty acid oxygenation occurs with positional specificity, catalyzed by the non-heme iron containing active site, and in addition to free PUFAs, membrane-esterified fatty acids serve as substrates for ALOX15B. Like other LOX enzymes, ALOX15B is linked to the formation of specialized pro-resolving lipid mediators (SPMs), and altered expression is apparent in various inflammatory diseases such as asthma, psoriasis, and atherosclerosis. In primary human macrophages, ALOX15B expression is associated with cellular cholesterol homeostasis and is induced by hypoxia. Like in inflammation, the role of ALOX15B in cancer is inconclusive. In prostate and breast carcinomas, ALOX15B is attributed a tumor-suppressive role, whereas in colorectal cancer, ALOX15B expression is associated with a poorer prognosis. As the biological function of ALOX15B remains an open question, this review aims to provide a comprehensive overview of the current state of research related to ALOX15B.

Proteomic global proteins analysis in blast lung injury reveals the altered characteristics of crucial proteins in response to oxidative stress, oxidation-reduction process and lipid metabolic process

Background: Blast lung injury (BLI) is the most common fatal blast injury induced by overpressure wave in the events of terrorist attack, gas and underground explosion. Our previous work revealed the characteristics of inflammationrelated key proteins involved in BLI, including those regulating inflammatory response, leukocyte transendothelial migration, phagocytosis, and immune process. However, the molecular characteristics of oxidative-related proteins in BLI ar still lacking. Methods: In this study, protein expression profiling of the blast lungs obtained by tandem mass tag (TMT) spectrometry quantitative proteomics were re-analyzed to identify the characteristics of oxidative-related key proteins. Forty-eight male C57BL/6 mice were randomly divided into six groups: control, 12 h, 24 h, 48 h, 72 h and 1 w after blast exposure. The differential protein expression was identified by bioinformatics analysis and verified by western blotting. Results: The results demonstrated that thoracic blast exposure induced reactive oxygen species generation and lipid peroxidation in the lungs. Analysis of global proteins and oxidative-related proteomes showed that 62, 59, 73, 69, 27 proteins (accounted for 204 distinct proteins) were identified to be associated with oxidative stress at 12 h, 24 h, 48 h, 72 h, and 1 week after blast exposure, respectively. These 204 distinct proteins were mainly enriched in response to oxidative stress, oxidation-reduction process and lipid metabolic process. We also validated these results by western blotting. Conclusions: These findings provided new perspectives on blast-induced oxidative injury in lung, which may potentially benefit the development of future treatment of BLI.

Identification of Candidate Genes and Regulatory Competitive Endogenous RNA (ceRNA) Networks Underlying Intramuscular Fat Content in Yorkshire Pigs with Extreme Fat Deposition Phenotypes

Intramuscular fat (IMF) content is vital for pork quality, serving an important role in economic performance in pig industry. Non-coding RNAs, with mRNAs, are involved in IMF deposition; however, their functions and regulatory mechanisms in porcine IMF remain elusive. This study assessed the whole transcriptome expression profiles of the Longissimus dorsi muscle of pigs with high (H) and low (L) IMF content to identify genes implicated in porcine IMF adipogenesis and their regulatory functions. Hundreds of differentially expressed RNAs were found to be involved in fatty acid metabolic processes, lipid metabolism, and fat cell differentiation. Furthermore, combing co-differential expression analyses, we constructed competing endogenous RNAs (ceRNA) regulatory networks, showing crosstalk among 30 lncRNAs and 61 mRNAs through 20 miRNAs, five circRNAs and 11 mRNAs through four miRNAs, and potential IMF deposition-related ceRNA subnetworks. Functional lncRNAs and circRNAs (such as MSTRG.12440.1, ENSSSCT00000066779, novel_circ_011355, novel_circ_011355) were found to act as ceRNAs of important lipid metabolism-related mRNAs (LEP, IP6K1, FFAR4, CEBPA, etc.) by sponging functional miRNAs (such as ssc-miR-196a, ssc-miR-200b, ssc-miR10391, miR486-y). These findings provide potential regulators and molecular regulatory networks that can be utilized for research on IMF traits in pigs, which would aid in marker-assisted selection to improve pork quality.

Structural basis for altered positional specificity of 15-lipoxygenase-1 with 5S-HETE and 7S-HDHA and the implications for the biosynthesis of resolvin E4

Human 15-lipoxygenases (LOX) are critical enzymes in the inflammatory process, producing various pro-resolution molecules, such as lipoxins and resolvins, but the exact role each of the two 15-LOXs in these biosynthetic pathways remains elusive. Previously, it was observed that h15-LOX-1 reacted with 5S-HETE in a non-canonical manner, producing primarily the 5S,12S-diHETE product. To determine the active site constraints of h15-LOX-1 in achieving this reactivity, amino acids involved in the fatty acid binding were investigated. It was observed that R402L did not have a large effect on 5S-HETE catalysis, but F414 appeared to π-π stack with 5S-HETE, as seen with AA binding, indicating an aromatic interaction between a double bond of 5S-HETE and F414. Decreasing the size of F352 and I417 shifted oxygenation of 5S-HETE to C12, while increasing the size of these residues reversed the positional specificity of 5S-HETE to C15. Mutants at these locations demonstrated a similar effect with 7S-HDHA as the substrate, indicating that the depth of the active site regulates product specificity for both substrates. Together, these data indicate that of the three regions proposed to control positional specificity, π-π stacking and active site cavity depth are the primary determinants of positional specificity with 5S-HETE and h15-LOX-1. Finally, the altered reactivity of h15-LOX-1 was also observed with 5S-HEPE, producing 5S,12S-diHEPE instead of 5S,15S-diHEPE (aka resolvin E₄ (RvE₄). However, h15-LOX-2 efficiently produces 5S,15S-diHEPE from 5S-HEPE. This result is important with respect to the biosynthesis of the RvE₄ since it obscures which LOX isozyme is involved in its biosynthesis. Future work detailing the expression levels of the lipoxygenase isoforms in immune cells and selective inhibition during the inflammatory response will be required for a comprehensive understanding of RvE₄ biosynthesis.

Biology and pharmacology of platelet-type 12-lipoxygenase in platelets, cancer cells, and their crosstalk

Platelet-type lipoxygenase (pl12-LOX), encoded by ALOX12, catalyzes the production of the lipid mediator 12S-hydroperoxyeicosa-5,8,10,14-tetraenoic acid (12S-HpETE), which is quickly reduced by cellular peroxidases to form 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid (12S-HETE). Platelets express high levels of pl12-LOX and generate considerable amounts of 12S-HETE from arachidonic acid (AA; C20:4, n-6). The development of sensitive chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods has allowed the accurate quantification of 12S-HETE in biological samples. Moreover, advances in the knowledge of the mechanism of action of 12S-HETE have been achieved. The orphan G-protein-coupled receptor 31 (GPR31) has been identified as the high-affinity 12S-HETE receptor. Moreover, upon platelet activation, 12S-HETE is produced, and significant amounts are found esterified to membrane phospholipids (PLs), such as phosphatidylethanolamine (PE) and phosphatidylcholine (PC), promoting thrombin generation. Platelets play many roles in cancer metastasis. Among them, the platelets' ability to interact with cancer cells and transfer platelet molecules by the release of extracellular vesicles (EVs) is noteworthy. Recently, it was found that platelets induce epithelial-mesenchymal transition(EMT) in cancer cells, a phenomenon known to confer high-grade malignancy, through the transfer of pl12-LOX contained in platelet-derived EVs. These cancer cells now generate 12-HETE, considered a key modulator of cancer metastasis. Interestingly, 12-HETE was mainly found esterified in plasmalogen phospholipids of cancer cells. This review summarizes the current knowledge on the regulation and functions of pl12-LOX in platelets and cancer cells and their crosstalk.Novel approaches to preventing cancer and metastasis by the pharmacological inhibition of pl12-LOX and the internalization of mEVs are discussed.

Unbalanced Expression of Glutathione Peroxidase 4 and Arachidonate 15-Lipoxygenase Affects Acrosome Reaction and In Vitro Fertilization

Glutathione peroxidase 4 (Gpx4) and arachidonic acid 15 lipoxygenase (Alox15) are counterplayers in oxidative lipid metabolism and both enzymes have been implicated in spermatogenesis. However, the roles of the two proteins in acrosomal exocytosis have not been explored in detail. Here we characterized Gpx4 distribution in mouse sperm and detected the enzyme not only in the midpiece of the resting sperm but also at the anterior region of the head, where the acrosome is localized. During sperm capacitation, Gpx4 translocated to the post-acrosomal compartment. Sperm from Gpx4^+/Sec46Ala mice heterozygously expressing a catalytically silent enzyme displayed an increased expression of phosphotyrosyl proteins, impaired acrosomal exocytosis after in vitro capacitation and were not suitable for in vitro fertilization. Alox15-deficient sperm showed normal acrosome reactions but when crossed into a Gpx4-deficient background spontaneous acrosomal exocytosis was observed during capacitation and these cells were even less suitable for in vitro fertilization. Taken together, our data indicate that heterozygous expression of a catalytically silent Gpx4 variant impairs acrosomal exocytosis and in vitro fertilization. Alox15 deficiency hardly impacted the acrosome reaction but when crossed into the Gpx4-deficient background spontaneous acrosomal exocytosis was induced. The detailed molecular mechanisms for the observed effects may be related to the compromised redox homeostasis.

Genetic and Epigenetic Regulation of Lipoxygenase Pathways and Reverse Cholesterol Transport in Atherogenesis

Atherosclerosis is one of the most important medical and social problems of modern society. Atherosclerosis causes a large number of hospitalizations, disability, and mortality. A considerable amount of evidence suggests that inflammation is one of the key links in the pathogenesis of atherosclerosis. Inflammation in the vascular wall has extensive cross-linkages with lipid metabolism, and lipid mediators act as a central link in the regulation of inflammation in the vascular wall. Data on the role of genetics and epigenetic factors in the development of atherosclerosis are of great interest. A growing body of evidence is strengthening the understanding of the significance of gene polymorphism, as well as gene expression dysregulation involved in cross-links between lipid metabolism and the innate immune system. A better understanding of the genetic basis and molecular mechanisms of disease pathogenesis is an important step towards solving the problems of its early diagnosis and treatment.

Formation of eicosanoids and other oxylipins in human macrophages

In this review it is attempted to summarize current studies about formation of eicosanoids and other oxylipins in different human macrophages. There are several reports on M1 and M2 cells, also other phenotypes have been described. The eicosanoids formed in the largest amounts are the COX products TxB₂ and PGE₂. Thus shortlived bioactive TxA₂ is a dominating product both in M1- and in M2-lineages, one exception seems to be M_{GM-CSF, TGFβ} cells. 5-LOX products are produced in both M1 and M2 macrophages, as well as in not fully polarized cells of both lineages. M_M-CSF as well as M2 macrophages produced LTC₄ more readily compared to M1 lineage cells. In M_{GM-CSF, TGFβ} cells LTB₄ is a major eicosanoid, in line with high expression of LTA₄ hydrolase. Recent reports described increased formation of leukotrienes in macrophages subjected to trained immunity with inflammatory transcriptional reprogramming. Also in macrophages derived from monocytes collected from post-COVID-19 patients. 15-LOX-1 is strongly upregulated in CD206⁺ M2 cells (M2a), differentiated in presence of IL-4. These macrophages also express 15-LOX-2. In incubations with pathogenic E. coli as well as other stimuli 15(S)-HETE and 17(S)-HDHA were major oxylipins formed. Also, the SPM precursor 5,15-diHETE and the SPM RvD5 were produced in considerable amounts, while other SPMs were less abundant. In M2 macrophages incubated with E. coli or S. aureus the cytosolic 15-LOX-1 enzyme accumulated to punctuate structures in a Ca²⁺ dependent manner with a relatively slow time course, leading to formation of mediators from endogenous substrate. Chalcones, flavone-like anti-inflammatory natural products, induced translocation of 15-LOX-1 in M2 cells, with high formation of 15-LOX derived oxylipins.

Free docosahexaenoic acid promotes ferroptotic cell death via lipoxygenase dependent and independent pathways in cancer cells

PURPOSE

Ferroptosis is a form of regulated cell death that has the potential to be targeted as a cancer therapeutic strategy. But cancer cells have a wide range of sensitivities to ferroptosis, which limits its therapeutic potential. Accumulation of lipid peroxides determines the occurrence of ferroptosis. However, the type of lipid involved in peroxidation and the mechanism of lipid peroxide accumulation are less studied.

METHODS

The effects of fatty acids (10 μM) with different carbon chain length and unsaturation on ferroptosis were evaluated by MTT and LDH release assay in cell lines derived from prostate cancer (PC3, 22RV1, DU145 and LNCaP), colorectal cancer (HT-29), cervical cancer (HeLa) and liver cancer (HepG2). Inhibitors of apoptosis, necroptosis, autophagy and ferroptosis were used to determine the type of cell death. Then the regulation of reactive oxygen species (ROS) and lipid peroxidation by docosahexaenoic acid (DHA) was measured by HPLC-MS and flow cytometry. The avtive form of DHA was determined by siRNA mediated gene silencing. The role of lipoxygenases was checked by inhibitors and gene silencing. Finally, the effect of DHA on ferroptosis-mediated tumor killing was verified in xenografts.

RESULTS

The sensitivity of ferroptosis was positively correlated with the unsaturation of exogenously added fatty acid. DHA (22:6 n-3) sensitized cancer cells to ferroptosis-inducing reagents (FINs) at the highest level in vitro and in vivo. In this process, DHA increased ROS accumulation, lipid peroxidation and protein oxidation independent of its membrane receptor, GPR120. Inhibition of long chain fatty acid-CoA ligases and lysophosphatidylcholine acyltransferases didn't affect the role of DHA. DHA-involved ferroptosis can be induced in both arachidonate lipoxygenase 5 (ALOX5) negative and positive cells. Down regulation of ALOX5 inhibited ferroptosis, while overexpression of ALOX5 promoted ferroptosis.

CONCLUSION

DHA can effectively promote ferroptosis-mediated tumor killing by increasing intracellular lipid peroxidation. Both ALOX5 dependent and independent pathways are involved in DHA-FIN induced ferroptosis. And during this process, free DHA plays an important role.

Structural and functional evaluation mammalian and plant lipoxygenases upon association with nanodics as membrane mimetics

Lipoxygenases (LOX) are a family lipid oxygenating enzymes that can generate bioactive lipids of clinical relevance from polyunsaturated fatty acids. Most LOXs display a Ca²⁺-dependent association with membranes for their activity. Nanodiscs (ND) are stable self-assembled discoidal fragments of lipid bilayers that can mimic the plasma membrane. In this study, we evaluated the association of mammalian 15-LOXs (ALOX15 and ALOX15B) and soybean LOX-1 with NDs (LOX-ND), their enzymatic activities and inhibition. Mammalian LOXs associated with NDs showed better retention of enzymatic function compared to soybean LOX-1. Treatment of both LOX-NDs and free enzymes with the pan-LOX inhibitor nordihydroguaiaretic acid (NDGA) showed an approximately 5-fold more effective inhibition of the enzymes associated with NDs compared to the free form. NDs are easy to generate membrane mimics that can be used as an effective tool to determine enzymatic function and inhibition of membrane associated proteins.

4-Chlorophenyl-N-furfuryl-1,2,4-triazole Methylacetamides as Significant 15-Lipoxygenase Inhibitors: an Efficient Approach for Finding Lead Anti-inflammatory Compounds

Lipoxygenases (LOXs) are a class of enzymes that catalyze the production of pro-inflammatory mediators, such as leukotrienes and lipoxins, via an arachidonic acid cascade as soon as they are released from the membrane phospholipids after tissue injury. In continuation of our efforts in search for new LOX inhibitors, a series of chlorophenyl-furfuryl-based 1,2,4-triazole derivatives were prepared and evaluated for their 15-LOX inhibitory activities. A simple precursor, 4-chlorobenzoic acid (a), was consecutively transformed into benzoate (1), hydrazide (2), semicarbazide (3), and N-furfuryl 5-(4-chlorobenzyl)-4H-1,2,4-triazole (4), which when further merged with electrophiles (6a-o) resulted in end products (7a-o). The structural elucidations of the newly synthesized compounds (7a-o) were carried out by Fourier transform infrared, 1H-, 13C NMR spectroscopy, EI-MS, and HR-EI-MS spectrometry. The inhibitive capability of compounds (7a-o) on soybean 15-LOX was performed in vitro using the chemiluminescence method. The compounds 7k, 7o, 7m, 7b, and 7i demonstrated potent activities (IC50 17.43 ± 0.38, 19.35 ± 0.71, 23.59 ± 0.68, 26.35 ± 0.62, and 27.53 ± 0.82 μM, respectively). These compounds revealed 79.5 to 98.8% cellular viability as measured by the MTT assay at 0.25 mM concentration. The structure-activity relationship (SAR) studies showed that the positions and the nature of substituents bonded to the phenyl ring are important in the determination of 15-LOX inhibitory activities. ADME, in silico, and density functional theory studies supported the evidence as yet another class of triazoles with potential lead properties in search for anti-LOX compounds with a safe gastrointestinal safety profile for various inflammatory diseases. Further work is in progress on the synthesis of more derivatives in search for anti-inflammatory agents.

Male Knock-in Mice Expressing an Arachidonic Acid Lipoxygenase 15B (Alox15B) with Humanized Reaction Specificity Are Prematurely Growth Arrested When Aging

Mammalian arachidonic acid lipoxygenases (ALOXs) have been implicated in cell differentiation and in the pathogenesis of inflammation. The mouse genome involves seven functional Alox genes and the encoded enzymes share a high degree of amino acid conservation with their human orthologs. There are, however, functional differences between mouse and human ALOX orthologs. Human ALOX15B oxygenates arachidonic acid exclusively to its 15-hydroperoxy derivative (15S-HpETE), whereas 8S-HpETE is dominantly formed by mouse Alox15b. The structural basis for this functional difference has been explored and in vitro mutagenesis humanized the reaction specificity of the mouse enzyme. To explore whether this mutagenesis strategy may also humanize the reaction specificity of mouse Alox15b in vivo, we created Alox15b knock-in mice expressing the arachidonic acid 15-lipoxygenating Tyr603Asp+His604Val double mutant instead of the 8-lipoxygenating wildtype enzyme. These mice are fertile, display slightly modified plasma oxylipidomes and develop normally up to an age of 24 weeks. At later developmental stages, male Alox15b-KI mice gain significantly less body weight than outbred wildtype controls, but this effect was not observed for female individuals. To explore the possible reasons for the observed gender-specific growth arrest, we determined the basic hematological parameters and found that aged male Alox15b-KI mice exhibited significantly attenuated red blood cell parameters (erythrocyte counts, hematocrit, hemoglobin). Here again, these differences were not observed in female individuals. These data suggest that humanization of the reaction specificity of mouse Alox15b impairs the functionality of the hematopoietic system in males, which is paralleled by a premature growth arrest.

Branched-Chain Fatty Acids Alter the Expression of Genes Responsible for Lipid Synthesis and Inflammation in Human Adipose Cells

Recently, we have demonstrated a decreased level of iso-branched-chain fatty acids (iso-BCFAs) in patients with excessive weight. However, it is still unclear whether BCFAs may influence lipid metabolism and inflammation in lipogenic tissues. To verify this, human visceral adipocytes were cultured with three different concentrations of selected iso-BCFA (14-methylpentadecanoic acid) and anteiso-BCFA (12-methyltetradecanoic acid), and then the expression of genes associated with lipid metabolism (FASN-fatty acid synthase; SREBP1-sterol regulatory element-binding protein 1; SCD1-stearoyl-CoA desaturase; ELOVL4-fatty acid elongase 4; ELOVL6-fatty acid elongase 6; FADS2-fatty acid desaturase 2; FADS1-fatty acid desaturase 1) and inflammation (COX-2-cyclooxygenase 2; ALOX-15-lipoxygenase 15; IL-6-interleukin 6) were determined. This study demonstrates for the first time that incubation with iso-BCFA decreases the expression of adipocyte genes that are associated with lipid metabolism (except FASN) and inflammation. These findings suggest that changes in the iso-BCFA profile in obese patients may contribute to adipose inflammation and dyslipidemia. Further studies should evaluate whether iso-BCFA supplementation in obese patients would be beneficial.

Multiomics Studies Investigating Recurrent Pregnancy Loss: An Effective Tool for Mechanism Exploration

Patients with recurrent pregnancy loss (RPL) account for approximately 1%-5% of women aiming to achieve childbirth. Although studies have shown that RPL is associated with failure of endometrial decidualization, placental dysfunction, and immune microenvironment disorder at the maternal-fetal interface, the exact pathogenesis remains unknown. With the development of high-throughput technology, more studies have focused on the genomics, transcriptomics, proteomics and metabolomics of RPL, and new gene mutations and new biomarkers of RPL have been discovered, providing an opportunity to explore the pathogenesis of RPL from different biological processes. Bioinformatics analyses of these differentially expressed genes, proteins and metabolites also reflect the biological pathways involved in RPL, laying a foundation for further research. In this review, we summarize the findings of omics studies investigating decidual tissue, villous tissue and blood from patients with RPL and identify some possible limitations of current studies.

Staphylococcus aureus controls eicosanoid and specialized pro-resolving mediator production via lipoteichoic acid

Staphylococcus aureus causes severe infections associated with inflammation, such as sepsis or osteomyelitis. Inflammatory processes are regulated by distinct lipid mediators (LMs) but how their biosynthetic pathways are orchestrated in S. aureus infections is elusive. We show that S. aureus strikingly not only modulates pro-inflammatory, but also inflammation-resolving LM pathways in murine osteomyelitis and osteoclasts as well as in human monocyte-derived macrophages (MDMs) with different phenotype. Targeted LM metabololipidomics using ultra-performance liquid chromatography-tandem mass spectrometry revealed massive generation of LM with distinct LM signature profiles in acute and chronic phases of S. aureus-induced murine osteomyelitis in vivo. In human MDM, S. aureus elevated cyclooxygenase-2 (COX-2) and microsomal prostaglandin E₂  synthase-1 (mPGES-1), but impaired the levels of 15-lipoxygenase-1 (15-LOX-1), with respective changes in LM signature profiles initiated by these enzymes, that is, elevated PGE₂ and impaired specialized pro-resolving mediators, along with reduced M2-like phenotypic macrophage markers. The cell wall component, lipoteichoic acid (LTA), mimicked the impact of S. aureus elevating COX-2/mPGES-1 expression via NF-κB and p38 MAPK signalling in MDM, while the impairment of 15-LOX-1 correlates with reduced expression of Lamtor1. In conclusion, S. aureus dictates LM pathways via LTA resulting in a shift from anti-inflammatory M2-like towards pro-inflammatory M1-like LM signature profiles.

Transcriptional Profiles Elucidate Differential Host Responses to Infection with Cryptococcus neoformans and Cryptococcus gattii

Many aspects of the host response to invasive cryptococcal infections remain poorly understood. In order to explore the pathobiology of infection with common clinical strains, we infected BALB/cJ mice with Cryptococcus neoformans, Cryptococcus gattii, or sham control, and assayed host transcriptomic responses in peripheral blood. Infection with C. neoformans resulted in markedly greater fungal burden in the CNS than C. gattii, as well as slightly higher fungal burden in the lungs. A total of 389 genes were significantly differentially expressed in response to C. neoformans infection, which mainly clustered into pathways driving immune function, including complement activation and TH2-skewed immune responses. C. neoformans infection demonstrated dramatic up-regulation of complement-driven genes and greater up-regulation of alternatively activated macrophage activity than seen with C gattii. A 27-gene classifier was built, capable of distinguishing cryptococcal infection from animals with bacterial infection due to Staphylococcus aureus with 94% sensitivity and 89% specificity. Top genes from the murine classifiers were also differentially expressed in human PBMCs following infection, suggesting cross-species relevance of these findings. The host response, as manifested in transcriptional profiles, informs our understanding of the pathophysiology of cryptococcal infection and demonstrates promise for contributing to development of novel diagnostic approaches.

The Reaction Specificity of Mammalian ALOX15 Orthologs is Changed During Late Primate Evolution and These Alterations Might Offer Evolutionary Advantages for Hominidae

Arachidonic acid lipoxygenases (ALOXs) have been implicated in the immune response of mammals. The reaction specificity of these enzymes is decisive for their biological functions and ALOX classification is based on this enzyme property. Comparing the amino acid sequences and the functional properties of selected mammalian ALOX15 orthologs we previously hypothesized that the reaction specificity of these enzymes can be predicted based on their amino acid sequences (Triad Concept) and that mammals, which are ranked in evolution below gibbons, express arachidonic acid 12-lipoxygenating ALOX15 orthologs. In contrast, Hominidae involving the great apes and humans possess 15-lipoxygenating enzymes (Evolutionary Hypothesis). These two hypotheses were based on sequence data of some 60 mammalian ALOX15 orthologs and about half of them were functionally characterized. Here, we compared the ALOX15 sequences of 152 mammals representing all major mammalian subclades expressed 44 novel ALOX15 orthologs and performed extensive mutagenesis studies of their triad determinants. We found that ALOX15 genes are absent in extant Prototheria but that corresponding enzymes frequently occur in Metatheria and Eutheria. More than 90% of them catalyze arachidonic acid 12-lipoxygenation and the Triad Concept is applicable to all of them. Mammals ranked in evolution above gibbons express arachidonic acid 15-lipoxygenating ALOX15 orthologs but enzymes with similar specificity are only present in less than 5% of mammals ranked below gibbons. This data suggests that ALOX15 orthologs have been introduced during Prototheria-Metatheria transition and put the Triad Concept and the Evolutionary Hypothesis on a much broader and more reliable experimental basis.

Production of Hydroxy Fatty Acids, Precursors of γ-Hexalactone, Contributes to the Characteristic Sweet Aroma of Beef

Aroma is an essential factor for meat quality. The meat of Japanese Black cattle exhibits fine marbling and a rich and sweet aroma with a characteristic lactone composition. The mechanism of lactone formation associated with beef aroma has not been elucidated. In this study, we examined the precursors of γ-hexalactone, an indicator of the sweet aroma of beef and identified the mechanism underlying γ-hexalactone production. A low-temperature vacuum system was used to prepare beef tallow from Japanese Black cattle and Holstein cattle. The odor components were identified using headspace–gas chromatography. The analysis revealed that γ-hexalactone, γ-dodecalactone, δ-tetradecalactone, and δ-hexadecalactone were present as sweet aroma components of beef tallow prepared from marbling and muscle. Since we previously reported that γ-hexalactone formation correlates with linoleic acid content in beef, we analyzed ten oxidized fatty acids derived from linoleic acid by liquid chromatography–triple quadrupole mass spectrometry and detected two hydroxy-octadecadienoic acids (9S-HODE and 13S-HODE) in beef tallow. Significant differences in arachidonic acid 15-lipoxygenase and cyclooxygenase protein expression levels among subcutaneous fat, intramuscular fat, and muscle tissue were observed. Our results suggest that the combination of linoleic acid and the expression of lipid oxidase derived from beef muscle and intramuscular fat produce hydroxy fatty acids that result in a sweet aroma.

Cepharanthine Attenuates Early Brain Injury after Subarachnoid Hemorrhage in Mice via Inhibiting 15-Lipoxygenase-1-Mediated Microglia and Endothelial Cell Ferroptosis

Background

Ferroptosis is a newly identified form of programmed cell death caused by iron-dependent lipid peroxidation. Our study was designed to determine the expression patterns and role of 15-lipoxygenase-1 (ALOX15) in subarachnoid hemorrhage (SAH) and to investigate whether cepharanthine (CEP) can inhibit ferroptosis by inhibiting ALOX15 in specific cell types.

Methods

A mouse model of SAH was developed by the endovascular perforation method. bEend.3 endothelial cells and BV2 microglial cells as well as RSL3 and hemin were used to simulate SAH in vitro. Mice and cell lines were treated with CEP and a group of specific oxygenase inhibitors to explore the protection effect from ferroptosis. Lipid peroxidation staining with BODIPY 581/591 C11 and transmission electron microscopy were used to identify ferroptosis in vitro and in vivo.

Results

In the present study, the accumulation of lipid peroxide, a defect in the glutathione peroxidase 4 (GPx4)/glutathione (GSH) antioxidant system, highly expressed ALOX15 in microglia and endothelium, and ferroptotic changes in microglial mitochondria confirmed the occurrence of ferroptosis after SAH in vivo. Further, CEP was shown to inhibit ferroptosis and improve neurological function by downregulating the expression of ALOX15. During in vitro experiments, we investigated the important role ALOX15 in RSL3-induced endothelial ferroptosis. In addition, we found that M2-type microglia are more sensitive to RSL3-induced ferroptosis than M1-type microglia and that hemin probably induced ferroptosis in M2-type microglia by increasing ALOX15 levels and decreasing GPx4 levels. The effect of CEP treatment was also demonstrated in vitro.

Conclusions

In summary, to the best of our knowledge, this is the first study demonstrating that ferroptosis occurred in the microglia and endothelium after SAH, and this process was facilitated by increased ALOX15 levels. More importantly, treatment with CEP could inhibit ferroptosis through downregulating the expression of ALOX15.

Microbial (co)infections: Powerful immune influencers

It is well established that by modulating various immune functions, host infection may alter the course of concomitant inflammatory diseases, of both infectious and autoimmune etiologies. Beyond the major impact of commensal microbiota on the immune status, host exposure to viral, bacterial, and/or parasitic microorganisms also dramatically influences inflammatory diseases in the host, in a beneficial or harmful manner. Moreover, by modifying pathogen control and host tolerance to tissue damage, a coinfection can profoundly affect the development of a concomitant infectious disease. Here, we review the diverse mechanisms that underlie the impact of (co)infections on inflammatory disorders. We discuss epidemiological studies in the context of the hygiene hypothesis and shed light on the sometimes dual impact of germ exposure on human susceptibility to inflammatory disease. We then summarize the immunomodulatory mechanisms at play, which can involve pleiotropic effects of immune players and discuss the possibility to harness pathogen-derived compounds to the host benefit.

Shifting the Biosynthesis of Leukotrienes Toward Specialized Pro-Resolving Mediators by the 5-Lipoxygenase-Activating Protein (FLAP) Antagonist BRP-201

Background and Purpose

Lipid mediators (LM) play crucial roles in the complex inflammation process with respect to initiation, maintenance, and resolution. Proinflammatory leukotrienes (LTs), generated by 5-lipoxygenase (LOX) and the 5-LOX-activating protein (FLAP), initiate and maintain inflammation while specialized pro-resolving mediators (SPMs) formed by various LOXs as key enzymes promote inflammation resolution and the return to homeostasis. Since 5-LOX also contributes to SPM biosynthesis, smart pharmacological manipulation of the 5-LOX pathway and accompanied activation of 12-/15-LOXs may accomplish suppression of LT formation but maintain or even elevate SPM formation. Here, we demonstrated that the FLAP antagonist BRP-201 possesses such pharmacological profile and causes a switch from LT toward SPM formation.

Methods and Results

Comprehensive LM metabololipidomics with activated human monocyte-derived macrophages (MDM) of M1 or M2 phenotype showed that BRP-201 strongly inhibits LT formation induced by bacterial exotoxins. In parallel, SPM levels and 12/15-LOX-derived products were markedly elevated, in particular in M2-MDM. Intriguingly, in unstimulated MDM, BRP-201 induced formation of 12/15-LOX products including SPM and caused 15-LOX-1 subcellular redistribution without affecting 5-LOX. Experiments with HEK293 cells stably expressing either 5-LOX with or without FLAP, 15-LOX-1 or 15-LOX-2 confirmed suppression of 5-LOX product formation due to FLAP antagonism by BRP-201 but activated 15-LOX-1 in the absence of FLAP. Finally, in zymosan-induced murine peritonitis, BRP-201 (2 mg/kg, ip) lowered LT levels but elevated 12/15-LOX products including SPMs.

Conclusion

BRP-201 acts as FLAP antagonist but also as 12/15-LOX activator switching formation of pro-inflammatory LTs toward inflammation-resolving SPM, which reflects a beneficial pharmacological profile for intervention in inflammation.

Involvement of Fatty Acids and Their Metabolites in the Development of Inflammation in Atherosclerosis

Despite all the advances of modern medicine, atherosclerosis continues to be one of the most important medical and social problems. Atherosclerosis is the cause of several cardiovascular diseases, which are associated with high rates of disability and mortality. The development of atherosclerosis is associated with the accumulation of lipids in the arterial intima and the disruption of mechanisms that maintain the balance between the development and resolution of inflammation. Fatty acids are involved in many mechanisms of inflammation development and maintenance. Endothelial cells demonstrate multiple cross-linkages between lipid metabolism and innate immunity. In addition, these processes are linked to hemodynamics and the function of other cells in the vascular wall, highlighting the central role of the endothelium in vascular biology.

Human and Mouse Eosinophils Differ in Their Ability to Biosynthesize Eicosanoids, Docosanoids, the Endocannabinoid 2-Arachidonoyl-glycerol and Its Congeners

High eosinophil (EOS) counts are a key feature of eosinophilic asthma. EOS notably affect asthmatic response by generating several lipid mediators. Mice have been utilized in hopes of defining new pharmacological targets to treat asthma. However, many pinpointed targets in mice did not translate into clinics, underscoring that key differences exist between the two species. In this study, we compared the ability of human (h) and mouse (m) EOS to biosynthesize key bioactive lipids derived from arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). hEOS were isolated from the blood of healthy subjects and mild asthmatics, while mEOSs were differentiated from the bone marrow. EOSs were treated with fatty acids and lipid mediator biosynthesis assessed by LC-MS/MS. We found that hEOS biosynthesized leukotriene (LT) C₄ and LTB₄ in a 5:1 ratio while mEOS almost exclusively biosynthesized LTB₄. The biosynthesis of the 15-lipoxygenase (LO) metabolites 15-HETE and 12-HETE also differed, with a 15-HETE:12-HETE ratio of 6.3 for hEOS and 0.727 for mEOS. EOS biosynthesized some specialized pro-resolving mediators, and the levels from mEOS were 9-times higher than those of hEOS. In contrast, hEOS produced important amounts of the endocannabinoid 2-arachidonoyl-glycerol (2-AG) and its congeners from EPA and DHA, a biosynthetic pathway that was up to ~100-fold less prominent in mEOS. Our data show that hEOS and mEOS biosynthesize the same lipid mediators but in different amounts. Compared to asthmatics, mouse models likely have an amplified involvement of LTB₄ and specialized pro-resolving mediators and a diminished impact of the endocannabinoid 2-arachidonoyl-glycerol and its congeners.

15-Lipoxygenase worsens renal fibrosis, inflammation, and metabolism in a murine model of ureteral obstruction

15-Lipoxygenase (15-LO) is a nonheme iron-containing dioxygenase that has both pro- and anti-inflammatory roles in many tissues and disease states. 15-LO is thought to influence macrophage phenotype, and silencing 15-LO reduces fibrosis after acute inflammatory triggers. The goal of the present study was to determine whether altering 15-LO expression influences inflammation and fibrogenesis in a murine model of unilateral ureteral obstruction (UUO). C57BL/6J mice, 15-LO knockout (Alox15-/-) mice, and 15-LO transgenic overexpressing (15LOTG) mice were subjected UUO, and kidneys were analyzed at 3, 10, and 14 days postinjury. Histology for fibrosis, inflammation, cytokine quantification, flow cytometry, and metabolomics were performed on injured tissues and controls. PD146176, a specific 15-LO inhibitor, was used to complement experiments involving knockout animals. Compared with wild-type animals undergoing UUO, Alox15-/- mouse kidneys had less proinflammatory, profibrotic message along with less fibrosis and macrophage infiltration. PD146176 inhibited 15-LO and resulted in reduced fibrosis and macrophage infiltration similar to Alox15-/- mice. Flow cytometry revealed that Alox15-/- UUO-injured kidneys had a dynamic change in macrophage phenotype, with an early blunting of CD11bHiLy6CHi "M1" macrophages and an increase in anti-inflammatory CD11bHiLy6CInt "M2c" macrophages and reduced expression of the fractalkine receptor chemokine (C-X3-C motif) receptor 1. Many of these findings were reversed when UUO was performed on 15LOTG mice. Metabolomics analysis revealed that wild-type kidneys developed a glycolytic shift postinjury, while Alox15-/- kidneys exhibited increased oxidative phosphorylation. In conclusion, 15-LO manipulation by genetic or pharmacological means induces dynamic changes in the inflammatory microenvironment in the UUO model and appears to be critical in the progression of UUO-induced fibrosis.NEW & NOTEWORTHY 15-Lipoxygenase (15-LO) has both pro- and anti-inflammatory functions in leukocytes, and its role in kidney injury and repair is unexplored. Our study showed that 15-LO worsens inflammation and fibrosis in a rodent model of chronic kidney disease using genetic and pharmacological manipulation. Silencing 15-LO promotes an increase in M2c-like wound-healing macrophages in the kidney and alters kidney metabolism globally, protecting against anaerobic glycolysis after injury.

Natural chalcones elicit formation of specialized pro-resolving mediators and related 15-lipoxygenase products in human macrophages

Specialized pro-resolving mediators (SPMs) comprise lipid mediators (LMs) produced from polyunsaturated fatty acids (PUFAs) via stereoselective oxygenation particularly involving 12/15-lipoxygenases (LOXs). In contrast to pro-inflammatory LMs such as leukotrienes formed by 5-LOX and prostaglandins formed by cyclooxygenases, the SPMs have anti-inflammatory and inflammation-resolving properties. Although glucocorticoids and non-steroidal anti-inflammatory drugs (NSAIDs) that block prostaglandin production are still prime therapeutics for inflammation-related diseases despite severe side effects, novel concepts focus on SPMs as immunoresolvents for anti-inflammatory pharmacotherapy. Here, we studied the natural chalcone MF-14 and the corresponding dihydrochalcone MF-15 from Melodorum fruticosum, for modulating the biosynthesis of LM including leukotrienes, prostaglandins, SPM and their 12/15-LOX-derived precursors in human monocyte-derived macrophage (MDM) M1- and M2-like phenotypes. In MDM challenged with Staphylococcus aureus-derived exotoxins both compounds (10 µM) significantly suppressed 5-LOX product formation but increased the biosynthesis of 12/15-LOX products, especially in M2-MDM. Intriguingly, in resting M2-MDM, MF-14 and MF-15 strikingly evoked generation of 12/15-LOX products and of SPMs from liberated PUFAs, along with translocation of 15-LOX-1 to membranous compartments. Enhanced 12/15-LOX product formation by the chalcones was evident also when exogenous PUFAs were supplied, excluding increased substrate supply as sole underlying mechanism. Rather, MF-14 and MF-15 stimulate the activity of 15-LOX-1, supported by experiments with HEK293 cells transfected with either 5-LOX, 15-LOX-1 or 15-LOX-2. Together, the natural chalcone MF-14 and the dihydrochalcone MF-15 favorably modulate LM biosynthesis in human macrophages by suppressing pro-inflammatory leukotrienes but stimulating formation of SPMs by differential interference with 5-LOX and 15-LOX-1.

Polarized Macrophages in Periodontitis: Characteristics, Function, and Molecular Signaling

Periodontitis (PD) is a common chronic infectious disease. The local inflammatory response in the host may cause the destruction of supporting periodontal tissue. Macrophages play a variety of roles in PD, including regulatory and phagocytosis. Moreover, under the induction of different factors, macrophages polarize and form different functional phenotypes. Among them, M1-type macrophages with proinflammatory functions and M2-type macrophages with anti-inflammatory functions are the most representative, and both of them can regulate the tendency of the immune system to exert proinflammatory or anti-inflammatory functions. M1 and M2 macrophages are involved in the destructive and reparative stages of PD. Due to the complex microenvironment of PD, the dynamic development of PD, and various local mediators, increasing attention has been given to the study of macrophage polarization in PD. This review summarizes the role of macrophage polarization in the development of PD and its research progress.

Paralog- and ortholog-specificity of inhibitors of human and mouse lipoxygenase-isoforms

Lipoxygenases (ALOX-isoforms) are lipid peroxidizing enzymes, which have been implicated in cell differentiation and maturation but also in the biosynthesis of lipid mediators playing important roles in the pathogenesis of inflammatory, hyperproliferative and neurological diseases. In mammals these enzymes are widely distributed and the human genome involves six functional genes encoding for six distinct human ALOX paralogs. In mice, there is an orthologous enzyme for each human ALOX paralog but the catalytic properties of human and mouse ALOX orthologs show remarkable differences. ALOX inhibitors are frequently employed for deciphering the biological role of these enzymes in mouse models of human diseases but owing to the functional differences between mouse and human ALOX orthologs the uncritical use of such inhibitors is sometimes misleading. In this study we evaluated the paralog- and ortholog-specificity of 13 frequently employed ALOX-inhibitors against four recombinant human and mouse ALOX paralogs (ALOX15, ALOX15B, ALOX12, ALOX5) under different experimental conditions. Our results indicated that except for zileuton, which exhibits a remarkable paralog-specificity for mouse and human ALOX5, no other inhibitor was strictly paralog specific but some compounds exhibit an interesting ortholog-specificity. Because of the variable isoform specificities of the currently available ALOX inhibitors care must be taken when the biological effects of these compounds observed in complex in vitro and in vivo systems are interpreted.

Specialized pro-resolving mediators: biosynthesis and biological role in bacterial infections

Acute inflammation caused by bacterial infections is an essential biological defence mechanism of the host in order to neutralize and clear the invaders and to return to homeostasis. Despite its protective function, inflammation may become persistent and uncontrolled, resulting in chronic diseases and tissue destruction as consequence of the unresolved inflammatory process. Therefore, spatiotemporal induction of endogenous inflammation resolution programs that govern bacterial clearance as well as tissue repair and regeneration, are of major importance in order to enable tissues to restore functions. Lipid mediators that are de-novo biosynthesized from polyunsaturated fatty acids (PUFAs) mainly by lipoxygenases and cyclooxygenases, critically regulate the initiation, the maintenance but also the resolution of infectious inflammation and tissue regeneration. The discovery of specialized pro-resolving mediators (SPMs) generated from omega-3 PUFAs stimulated intensive research in inflammation resolution, especially in infectious inflammation elicited by bacteria. SPMs are immunoresolvents that actively terminate inflammation by limiting neutrophil influx, stimulating phagocytosis, bacterial killing and clearance as well as efferocytosis of apoptotic neutrophils and cellular debris by macrophages. Moreover, SPMs prevent collateral tissue damage, promote tissue repair and regeneration and lower antibiotic requirement. Here, we review the biosynthesis of SPMs in bacterial infections and cover specific mechanisms of SPMs that govern the resolution of bacteria-initiated inflammation.

Staphylococcus aureus-Derived α-Hemolysin Evokes Generation of Specialized Pro-resolving Mediators Promoting Inflammation Resolution

Underlying mechanisms of how infectious inflammation is resolved by the host are incompletely understood. One hallmark of inflammation resolution is the activation of specialized pro-resolving mediators (SPMs) that enhance bacterial clearance and promote tissue repair. Here, we reveal α-hemolysin (Hla) from Staphylococcus aureus as a potent elicitor of SPM biosynthesis in human M2-like macrophages and in the mouse peritoneum through selective activation of host 15-lipoxygenase-1 (15-LOX-1). S. aureus-induced SPM formation in M2 is abolished upon Hla depletion or 15-LOX-1 knockdown. Isolated Hla elicits SPM formation in M2 that is reverted by inhibition of the Hla receptor ADAM10. Lipid mediators derived from Hla-treated M2 accelerate planarian tissue regeneration. Hla but not zymosan provokes substantial SPM formation in the mouse peritoneum, devoid of leukocyte infiltration and pro-inflammatory cytokine secretion. Besides harming the host, Hla may also exert beneficial functions by stimulating SPM production to promote the resolution of infectious inflammation.

Jordan et al. reveal that α-hemolysin from Staphylococcus aureus stimulates specialized pro-resolving mediator (SPM) formation through activation of 15-lipoxygenase-1 in human macrophages involving ADAM10. The host may exploit α-hemolysin as an SPM inducer to better cope with S. aureus infections and to promote inflammation resolution and tissue regeneration.

Arachidonic Acid 15-Lipoxygenase: Effects of Its Expression, Metabolites, and Genetic and Epigenetic Variations on Airway Inflammation

Arachidonic acid 15-lipoxygenase (ALOX15) is an enzyme that can oxidize polyunsaturated fatty acids. ALOX15 is strongly expressed in airway epithelial cells, where it catalyzes the conversion of arachidonic acid to 15-hydroxyeicosatetraenoic acid (15-HETE) involved in various airway inflammatory diseases. Interleukin (IL)-4 and IL-13 induce ALOX15 expression by activating Jak2 and Tyk2 kinases as well as signal transducers and activators of transcription (STATs) 1/3/5/6. ALOX15 up-regulation and subsequent association with phosphatidylethanolamine-binding protein 1 (PEBP1) activate the mitogen-activated extracellular signal-regulated kinase (MEK)-extracellular signal-regulated kinase (ERK) pathway, thus inducing eosinophil-mediated airway inflammation. In addition, ALOX15 plays a significant role in promoting the migration of immune cells, such as immature dendritic cells, activated T cells, and mast cells, and airway remodeling, including goblet cell differentiation. Genome-wide association studies have revealed multiple ALOX15 variants and their significant correlation with the risk of developing airway diseases. The epigenetic modifications of the ALOX15 gene, such as DNA methylation and histone modifications, have been shown to closely relate with airway inflammation. This review summarizes the role of ALOX15 in different phenotypes of asthma, chronic obstructive pulmonary disease, chronic rhinosinusitis, aspirin-exacerbated respiratory disease, and nasal polyps, suggesting new treatment strategies for these airway inflammatory diseases with complex etiology and poor treatment response.

Inflammatory response and matrix metalloproteinases in chronic kidney failure: Modulation by adropin and spexin

Chronic kidney disease is a major global public health problem. The peptide hormones adropin and spexin modulate many physiological functions such as energy balance and glucose, lipid and protein metabolism. However, it is unclear whether these peptides may exert effects on renal damage, tissue remodeling, and inflammatory conditions. In view of the limited information, we aimed to investigate the effect of adropin and spexin on matrix metalloproteinase and inflammatory response genes a rat model of adenine-induced chronic kidney failure. Chronic kidney failure was induced in rats by administering adenine hemisulfate. Renal function was determined in an autoanalyzer. Histopathological modifications were assessed by H&E staining. mRNA expression levels of ALOX 15, COX 1, COX 2, IL-1β, IL-10, IL-17A, IL-18 IL-21, IL-33, KIM-1, MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, MMP-13, NGAL, TGFβ1, TIMP-1, and TNFα in kidney tissue were measured by qPCR. Our results showed an increase of 24-h urine volume, serum creatinine, BUN, and urine protein levels in group with adenine-induced CKF. Adropin and spexin treatments decreased urine protein and 24-h urine volume. Renal damage, TIMP-1, IL-33, and MMP-2 increased after CKF induction, while COX 1, MMP-9, and MMP-13 levels were significantly reduced. Furthermore, KIM-1, TIMP-1, IL-33, and MMP-2 were downregulated by spexin treatment. Renal damage, NGAL, TIMP-1 IL-17A, IL-33, MMP-2, and MMP-3 decreased after adropin treatment, while MMP-13 levels were upregulated. Treatment with adropin+spexin decreased KIM-1, NGAL, TIMP-1, IL-1β, IL-17A, IL-18, IL-33, ALOX 15, COX 1, COX 2, TGFβ1, TNFα, MMP-2, MMP-3, and MMP-7, but increased MMP-13 levels. Our findings revealed that inflammatory response and MMP genes were modulated by adropin and spexin. These peptides may have protective effects on inflammation and chronic kidney damage progression.

Combining Structural with Functional Model Properties in Iron Synthetic Analogue Complexes for the Active Site in Rabbit Lipoxygenase

Iron complexes that model the structural and functional properties of the active iron site in rabbit lipoxygenase are described. The ligand sphere of the mononuclear pseudo-octahedral cis-(carboxylato)(hydroxo)iron(III) complex, which is completed by a tetraazamacrocyclic ligand, reproduces the first coordination shell of the active site in the enzyme. In addition, two corresponding iron(II) complexes are presented that differ in the coordination of a water molecule. In their structural and electronic properties, both the (hydroxo)iron(III) and the (aqua)iron(II) complex reflect well the only two essential states found in the enzymatic mechanism of peroxidation of polyunsaturated fatty acids. Furthermore, the ferric complex is shown to undergo hydrogen atom abstraction reactions with O-H and C-H bonds of suitable substrates, and the bond dissociation free energy of the coordinated water ligand of the ferrous complex is determined to be 72.4 kcal·mol^-1. Theoretical investigations of the reactivity support a concerted proton-coupled electron transfer mechanism in close analogy to the initial step in the enzymatic mechanism. The propensity of the (hydroxo)iron(III) complex to undergo H atom abstraction reactions is the basis for its catalytic function in the aerobic peroxidation of 2,4,6-tri(tert-butyl)phenol and its role as a radical initiator in the reaction of dihydroanthracene with oxygen.

Experimental Babesia rossi infection induces hemolytic, metabolic, and viral response pathways in the canine host

Background

Babesia rossi is a leading cause of morbidity and mortality among the canine population of sub-Saharan Africa, but pathogenesis remains poorly understood. Previous studies of B. rossi infection were derived from clinical cases, in which neither the onset of infection nor the infectious inoculum was known. Here, we performed controlled B. rossi inoculations in canines and evaluated disease progression through clinical tests and whole blood transcriptomic profiling.

Results

Two subjects were administered a low inoculum (10⁴ parasites) while three received a high (10⁸ parasites). Subjects were monitored for 8 consecutive days; anti-parasite treatment with diminazene aceturate was administered on day 4. Blood was drawn prior to inoculation as well as every experimental day for assessment of clinical parameters and transcriptomic profiles. The model recapitulated natural disease manifestations including anemia, acidosis, inflammation and behavioral changes. Rate of disease onset and clinical severity were proportional to the inoculum. To analyze the temporal dynamics of the transcriptomic host response, we sequenced mRNA extracted from whole blood drawn on days 0, 1, 3, 4, 6, and 8. Differential gene expression, hierarchical clustering, and pathway enrichment analyses identified genes and pathways involved in response to hemolysis, metabolic changes, and several arms of the immune response including innate immunity, adaptive immunity, and response to viral infection.

Conclusions

This work comprehensively characterizes the clinical and transcriptomic progression of B. rossi infection in canines, thus establishing a large mammalian model of severe hemoprotozoal disease to facilitate the study of host-parasite biology and in which to test novel anti-disease therapeutics. The knowledge gained from the study of B. rossi in canines will not only improve our understanding of this emerging infectious disease threat in domestic dogs, but also provide insight into the pathobiology of human diseases caused by Babesia and Plasmodium species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07889-4.

Functionalized Homologues and Positional Isomers of Rabbit 15-Lipoxygenase RS75091 Inhibitor

BACKGROUND

RS75091 is a cinnamic acid derivative that has been used for the crystallization of the rabbit ALOX15-inhibitor complex. The atomic coordinates of the resolved ALOX15-inhibitor complex were later used to define the binding sites of other mammalian lipoxygenase orthologs, for which no direct structural data with ligand has been reported so far.

INTRODUCTION

The putative binding pocket of the human ALOX5 was reconstructed on the basis of its structural alignment with rabbit ALOX15-RS75091 inhibitor. However, considering the possible conformational changes the enzyme may undergo in solution, it remains unclear whether the existing models adequately mirror the architecture of the ALOX5 active site.

METHODS

In this study, we prepared a series of RS75091 derivatives using a Sonogashira coupling reaction of regioisomeric bromocinnamates with protected acetylenic alcohols and tested their inhibitory properties on rabbit ALOX15.

RESULTS

A bulky pentafluorophenyl moiety linked to either ortho- or metha-ethynylcinnamates via aliphatic spacer does not significantly impair the inhibitory properties of RS75091.

CONCLUSION

Hydroxylated 2- and 3-alkynylcinnamates may be suitable candidates for incorporation of an aromatic linker group like tetrafluorophenylazides for photoaffinity labeling assays.

Identification of NSAIDs as lipoxygenase inhibitors through highly sensitive chemiluminescence method, expression analysis in mononuclear cells and computational studies

Here we report the inhibitory effects of nine non-steroidal anti-inflammatory drugs (NSAIDs) on soybean 15-lipoxygenase (15-LOX) enzyme (EC 1.13.11.12) by three different methods; UV-absorbance, colorimetric and chemiluminescence methods. Only two drugs, Ibuprofen and Ketoprofen, exhibited enzyme inhibition by UV-absorbance method but none of the drug showed inhibition through colorimetric method. Chemiluminescence method was found highly sensitive for the identification of 15-LOX inhibitors and it was more sensitive and several fold faster than the other methods. All tested drugs showed 15-LOX-inhibition with IC₅₀ values ranging from 3.52 ± 0.08 to 62.6 ± 2.15 µM by chemiluminescence method. Naproxen was the most active inhibitor (IC₅₀ 3.52 ± 0.08 µM) followed by Aspirin (IC₅₀ 4.62 ± 0.11 µM) and Acetaminophen (IC₅₀ 6.52 ± 0.14 µM). Ketoprofen, Diclofenac and Mefenamic acid showed moderate inhibitory profiles (IC₅₀ 24.8 ± 0.24 to 39.62 ± 0.27 µM). Piroxicam and Tenoxicam were the least active inhibitors with IC₅₀ values of 62.6 ± 2.15 µM and 49.5 ± 1.13 µM, respectively. These findings are supported by expression analysis, molecular docking studies and density functional theory calculations. The expression analysis and flow cytometry apoptosis analysis were carried out using mononuclear cells (MNCs) which express both human 15-LOX and 5-LOX. Selected NSAIDs did not affect the cytotoxic activity of MNCs at IC₅₀ concentrations and the cell death showed dose dependent effect. However, MNCs apoptosis increased only at the higher concentrations, demonstrating that these drugs may not induce loss of immunity in septic and other inflammatory conditions at the acceptable inhibitory concentrations. The data collectively suggests that NSAIDs not only inhibit COX enzymes as reported in the literature but soybean 15-LOX and MNCs LOXs are also inhibited at differential values. A comparison of the metabolomics studies of arachidonic acid pathway after inhibition of either COX or LOX enzymes may reconfirm these findings.

Understanding the complex pharmacology of cannabidiol: Mounting evidence suggests a common binding site with cholesterol

Cannabidiol is claimed to bind to a large number of protein targets based on in vitro assays. This suggests opportunities for a wide range of therapeutic applications. On the other hand, the existence of phytochemical 'nuisance compounds' suggests some measure of caution - these compounds are capable of altering membrane biophysical properties and changing protein function without directly contacting a binding site. Like cannabidiol, cholesterol alters membrane properties, but it also binds directly to membrane proteins through abundant cholesterol recognition sites. We present the evidence that cannabidiol and cholesterol may bind to the same site on some proteins. As a starting point for further research, we also used blind docking to show that cannabidiol binds to a cholesterol binding site on the CB1 receptor. Elucidation of the mechanism(s) of action of cannabidiol will assist the prioritisation of in vitro hits across targets, improve the success rate of medicinal chemistry campaigns, and ultimately benefit patient populations by focusing resources on programs with the most translational potential.

Characterization of Mice Ubiquitously Overexpressing Human 15-Lipoxygenase-1: Effect of Diabetes on Peripheral Neuropathy and Treatment with Menhaden Oil

To rigorously explore the role of omega-3 polyunsaturated fatty acids (PUFA) in the treatment of diabetic peripheral neuropathy (DPN), we have created a transgenic mouse utilizing a Cre-lox promoter to control overexpression of human 15-lipoxygenase-1 (15-LOX-1). In this study, we sought to determine the effect of treating type 2 diabetic wild-type mice and transgenic mice ubiquitously overexpressing 15-LOX-1 with menhaden oil on endpoints related to DPN. Wild-type and transgenic mice on a C57Bl/6J background were divided into three groups. Two of each of these groups were used to create a high-fat diet/streptozotocin model for type 2 diabetes. The remaining mice were control groups. Four weeks later, one set of diabetic mice from each group was treated with menhaden oil for twelve weeks and then evaluated using DPN-related endpoints. Studies were also performed using dorsal root ganglion neurons isolated from wild-type and transgenic mice. Wild-type and transgenic diabetic mice developed DPN as determined by slowing of nerve conduction velocity, decreased sensory nerve fibers in the skin and cornea, and impairment of thermal and mechanical sensitivity of the hindpaw compared to their respective control mice. Although not significant, there was a trend for the severity of these DPN-related deficits to be less in the diabetic transgenic mice compared to the diabetic wild-type mice. Treating diabetic wild-type and transgenic mice with menhaden oil improved the DPN-related endpoints with a trend for greater improvement or protection by menhaden oil observed in the diabetic transgenic mice. Treating dorsal root ganglion neurons with docosahexanoic acid but not eicosapentaenoic acid significantly increased neurite outgrowth with greater efficacy observed with neurons isolated from transgenic mice. Targeting pathways that will increase the production of the anti-inflammatory metabolites of omega-3 PUFA may be an efficacious approach to developing an effective treatment for DPN.

Mechanistic Insight into the Regulation of Lipoxygenase-Driven Lipid Peroxidation Events in Human Spermatozoa and Their Impact on Male Fertility

A prevalent cause of sperm dysfunction in male infertility patients is the overproduction of reactive oxygen species, an attendant increase in lipid peroxidation and the production of cytotoxic reactive carbonyl species such as 4-hydroxynonenal. Our previous studies have implicated arachidonate 15-lipoxygenase (ALOX15) in the production of 4-hydroxynonenal in developing germ cells. Here, we have aimed to develop a further mechanistic understanding of the lipoxygenase-lipid peroxidation pathway in human spermatozoa. Through pharmacological inhibition studies, we identified a protective role for phospholipase enzymes in the liberation of peroxidised polyunsaturated fatty acids from the human sperm membrane. Our results also revealed that arachidonic acid, linoleic acid and docosahexanoic acid are key polyunsaturated fatty acid substrates for ALOX15. Upon examination of ALOX15 in the spermatozoa of infertile patients compared to their normozoospermic counterparts, we observed significantly elevated levels of ALOX15 protein abundance in the infertile population and an increase in 4-hydroxynonenal adducts. Collectively, these data confirm the involvement of ALOX15 in the oxidative stress cascade of human spermatozoa and support the notion that increased ALOX15 abundance in sperm cells may accentuate membrane lipid peroxidation and cellular dysfunction, ultimately contributing to male infertility.

Efferocytosis potentiates the expression of arachidonate 15-lipoxygenase (ALOX15) in alternatively activated human macrophages through LXR activation

Macrophages acquire anti-inflammatory and proresolving functions to facilitate resolution of inflammation and promote tissue repair. While alternatively activated macrophages (AAMs), also referred to as M2 macrophages, polarized by type 2 (Th2) cytokines IL-4 or IL-13 contribute to the suppression of inflammatory responses and play a pivotal role in wound healing, contemporaneous exposure to apoptotic cells (ACs) potentiates the expression of anti-inflammatory and tissue repair genes. Given that liver X receptors (LXRs), which coordinate sterol metabolism and immune cell function, play an essential role in the clearance of ACs, we investigated whether LXR activation following engulfment of ACs selectively potentiates the expression of Th2 cytokine-dependent genes in primary human AAMs. We show that AC uptake simultaneously upregulates LXR-dependent, but suppresses SREBP-2-dependent gene expression in macrophages, which are both prevented by inhibiting Niemann–Pick C1 (NPC1)-mediated sterol transport from lysosomes. Concurrently, macrophages accumulate sterol biosynthetic intermediates desmosterol, lathosterol, lanosterol, and dihydrolanosterol but not cholesterol-derived oxysterols. Using global transcriptome analysis, we identify anti-inflammatory and proresolving genes including interleukin-1 receptor antagonist (IL1RN) and arachidonate 15-lipoxygenase (ALOX15) whose expression are selectively potentiated in macrophages upon concomitant exposure to ACs or LXR agonist T0901317 (T09) and Th2 cytokines. We show priming macrophages via LXR activation enhances the cellular capacity to synthesize inflammation-suppressing specialized proresolving mediator (SPM) precursors 15-HETE and 17-HDHA as well as resolvin D5. Silencing LXRα and LXRβ in macrophages attenuates the potentiation of ALOX15 expression by concomitant stimulation of ACs or T09 and IL-13. Collectively, we identify a previously unrecognized mechanism of regulation whereby LXR integrates AC uptake to selectively shape Th2-dependent gene expression in AAMs.

Structural considerations on lipoxygenase function, inhibition and crosstalk with nitric oxide pathways

Lipoxygenases (LOX) are non-heme iron-containing enzymes that catalyze regio- and stereo-selective dioxygenation of polyunsaturated fatty acids (PUFA). Mammalian LOXs participate in the eicosanoid cascade during the inflammatory response, using preferentially arachidonic acid (AA) as substrate, for the synthesis of leukotrienes (LT) and other oxidized-lipid intermediaries. This review focus on lipoxygenases (LOX) structural and kinetic implications on both catalysis selectivity, as well as the basic and clinical implications of inhibition and interactions with nitric oxide (^•NO) and nitroalkenes pathways. During inflammation ^•NO levels are increasingly favoring the formation of reactive nitrogen species (RNS). ^•NO may act itself as an inhibitor of LOX-mediated lipid oxidation by reacting with lipid peroxyl radicals. Besides, ^•NO may act as an O₂ competitor in the LOX active site, thus displaying a protective role on lipid-peroxidation. Moreover, RNS such as nitrogen dioxide (^•NO₂) may react with lipid-derived species formed during LOX reaction, yielding nitroalkenes (NO₂FA). NO₂FA represents electrophilic compounds that could exert anti-inflammatory actions through the interaction with critical LOX nucleophilic amino acids. We will discuss how nitro-oxidative conditions may limit the availability of common LOX substrates, favoring alternative routes of PUFA metabolization to anti-inflammatory or pro-resolutive pathways.

The Perspective of Diagnostic and Prognostic Values of Lipoxygenases mRNA Expression in Colon Adenocarcinoma

Background

This study was mainly to explore and study the potential application of lipoxygenases (ALOX) family genes in the diagnostic and prognostic values of colon adenocarcinoma (COAD).

Methods

Data sets related to the ALOX genes of COAD were obtained from The Cancer Genome Atlas and the University of California, Santa Cruz Xena browser. Then, the relevant biological information was downloaded from the public data platform. Finally, the bioinformatics technologies and clinical verification were employed to comprehensively analyze the potential values of ALOX genes.

Results

The Pearson correlation analysis indicated that there were correlations among ALOXE3, ALOX5, ALOX12, and ALOX12B. The diagnostic receiver operating characteristic (ROC) curves suggested that ALOXE3 and ALOX12 had significant diagnosis in COAD: ALOXE3; P<0.001, area under curve (AUC) 95%CI:=0.818 (0.773–0.862) and ALOX12; P<0.001, AUC 95%CI=0.774 (0.682–0.807). Besides, the verification study indicated that ALOX12 had a diagnostic value in COAD. Finally, our multivariate survival analysis and comprehensive prognosis of ALOX genes in COAD suggested that the ALOXE3 and ALOX12 were associated with COAD overall survival: ALOXE3; P=0.025, HR 95%CI=1.765 (1.074–2.901), ALOX12; P=0.046, HR 95%CI=1.680 (1.009–2.796), and the low expression of ALOXE3 and ALOX12 had a favorable prognosis of COAD (all P<0.05); on the contrary, the high regulation of them increased the risk of death.

Conclusion

In our study, we observed that the mRNA expressions of ALOX genes were associated with the diagnosis and prognosis of COAD. The results of the diagnostic analysis suggested that ALOX12 might have a diagnosis value in COAD. Besides, our comprehensive prognosis analysis indicated that ALOXE3 combined ALOX12 might serve as potential prognosis biomarkers for COAD.

Multi-omics profiling highlights lipid metabolism alterations in pigs fed low-dose antibiotics

Background

In order to study the relations of hepatocellular functions, weight gain and metabolic imbalance caused by low-dose antibiotics (LDA) via epigenetic regulation of gene transcription, 32 weaned piglets were employed as animal models and randomly allocated into two groups with diets supplemented with 0 or LDA (chlorotetracycline and virginiamycin).

Results

During the 4 weeks of the experiment, LDA showed a clear growth-promoting effect, which was exemplified by the significantly elevated body weight and average daily gain. Promoter methylome profiling using liquid hybridization capture-based bisulfite sequencing (LHC-BS) indicated that most of the 745 differential methylation regions (DMRs) were hypermethylated in the LDA group. Several DMRs were significantly enriched in genes related with fatty acids metabolic pathways, such as FABP1 and PCK1. In addition, 71 differentially expressed genes (DEGs) were obtained by strand-specific transcriptome analysis of liver tissues, including ALOX15, CXCL10 and NNMT, which are three key DEGs that function in lipid metabolism and immunity and which had highly elevated expression in the LDA group. In accordance with these molecular changes, the lipidome analyses of serum by LC-MS identified 38 significantly differential lipids, most of which were downregulated in the LDA group.

Conclusions

Our results indicate that LDA could induce epigenetic and transcriptional changes of key genes and lead to enhanced efficiency of lipid metabolism in the liver.

Systemic deficiency of mouse arachidonate 15-lipoxygenase induces defective erythropoiesis and transgenic expression of the human enzyme rescues this phenotype

Arachidonic acid 15-lipoxygenases (ALOX15) are lipid peroxidizing enzymes, which has previously been implicated in the maturational breakdown of intracellular organelles and plasma membrane remodeling during reticulocyte-erythrocyte transition. Conventional Alox15^-/- mice are viable, develop normally but do not exhibit a major defective erythropoietic phenotype. To characterize the putative in vivo relevance of Alox15 for red blood cell development, we explored the impact of systemic inactivation of the Alox15 gene on mouse erythropoiesis. We found that Alox15^-/- mice exhibited reduced erythrocyte counts, elevated reticulocyte counts and red cell hyperchromia. The structure of the plasma membrane of Alox15^-/- erythrocytes is altered and a significant share of the red cells was present as echinocytes and/or acanthocytes. An increased share of the Alox15^-/- erythrocytes cells were annexin V positive, which indicates a loss of plasma membrane asymmetry. Erythrocytes of Alox15^-/- mice were more susceptible to osmotic hemolysis and exhibited a reduced ex vivo life span. When we transgenically expressed human ALOX15 in Alox15^-/- mice under the control of the aP2 promoter the defective erythropoietic system was rescued and the impaired osmotic resistance was normalized. Together these data suggest the involvement Alox15 in the maturational remodeling of the plasma membrane during red cell development.

Human lipoxygenase isoforms form complex patterns of double and triple oxygenated compounds from eicosapentaenoic acid

Lipoxygenases (ALOX) are lipid peroxidizing enzymes that catalyze the biosynthesis of pro- and anti-inflammatory lipid mediators and have been implicated in (patho-)physiological processes. In humans, six functional ALOX isoforms exist and their arachidonic acid oxygenation products have been characterized. Products include leukotrienes and lipoxins which are involved in the regulation of inflammation and resolution. Oxygenation of n3-polyunsaturated fatty acids gives rise to specialized pro-resolving mediators, e.g. resolvins. However, the catalytic activity of different ALOX isoforms can lead to a multitude of potentially bioactive products. Here, we characterized the patterns of oxygenation products formed by human recombinant ALOX5, ALOX15, ALOX15B and ALOX12 from eicosapentaenoic acid (EPA) and its 18-hydroxy derivative 18-HEPE with particular emphasis on double and triple oxygenation products. ALOX15 and ALOX5 formed a complex mixture of various double oxygenation products from EPA, which include 5,15-diHEPE and various 8,15-diHEPE isomers. Their biosynthetic mechanisms were explored using heavy oxygen isotopes (H₂¹⁸O, ¹⁸O₂ gas) and three catalytic activities contributed to product formation: i) fatty acid oxygenase activity, ii) leukotriene synthase activity, iii) lipohydroperoxidase activity. For ALOX15B and ALOX12 more specific product patterns were identified, which was also the case when these enzymes reacted in concert with ALOX5. Several double oxygenated compounds were formed from 18-HEPE by ALOX5, ALOX15B and ALOX12 including previously identified resolvins (RvE2, RvE3), while formation of triple oxygenation products, e.g. 5,17,18-triHEPE, required ALOX5. Taken together our data show that EPA can be converted by human ALOX isoforms to a large number of secondary oxygenation products, which might exhibit bioactivity.

The enzymology of human eicosanoid pathways: the lipoxygenase branches

Eicosanoids are short-lived derivatives of polyunsaturated fatty acids that serve as autocrine and paracrine signaling molecules. They are involved numerous biological processes of both the well state and disease states. A thorough understanding of the progression the disease state and homeostasis of the well state requires a complete evaluation of the systems involved. This review examines the enzymology for the enzymes involved in the production of eicosanoids along the lipoxygenase branches of the eicosanoid pathways with particular emphasis on those derived from arachidonic acid. The enzymatic parameters, protocols to measure them, and proposed catalytic mechanisms are presented in detail.