From Vietnamese plants to a biflavonoid that relieves inflammation by triggering the lipid mediator class switch to resolution

Chronic inflammation results from excessive pro-inflammatory signaling and the failure to resolve the inflammatory reaction. Lipid mediators orchestrate both the initiation and resolution of inflammation. Switching from pro-inflammatory to pro-resolving lipid mediator biosynthesis is considered as efficient strategy to relieve chronic inflammation, though drug candidates exhibiting such features are unknown. Starting from a library of Vietnamese medical plant extracts, we identified isomers of the biflavanoid 8-methylsocotrin-4'-ol from Dracaena cambodiana, which limit inflammation by targeting 5-lipoxygenase and switching the lipid mediator profile from leukotrienes to specialized pro-resolving mediators (SPM). Elucidation of the absolute configurations of 8-methylsocotrin-4'-ol revealed the 2S,γS-isomer being most active, and molecular docking studies suggest that the compound binds to an allosteric site between the 5-lipoxygenase subdomains. We identified additional subordinate targets within lipid mediator biosynthesis, including microsomal prostaglandin E2 synthase-1. Leukotriene production is efficiently suppressed in activated human neutrophils, macrophages, and blood, while the induction of SPM biosynthesis is restricted to M2 macrophages. The shift from leukotrienes to SPM was also evident in mouse peritonitis in vivo and accompanied by a substantial decrease in immune cell infiltration. In summary, we disclose a promising drug candidate that combines potent 5-lipoxygenase inhibition with the favorable reprogramming of lipid mediator profiles.

Endogenous metabolites of vitamin E limit inflammation by targeting 5-lipoxygenase

Systemic vitamin E metabolites have been proposed as signaling molecules, but their physiological role is unknown. Here we show, by library screening of potential human vitamin E metabolites, that long-chain ω-carboxylates are potent allosteric inhibitors of 5-lipoxygenase, a key enzyme in the biosynthesis of chemoattractant and vasoactive leukotrienes. 13-((2R)-6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)-2,6,10-trimethyltridecanoic acid (α-T-13'-COOH) can be synthesized from α-tocopherol in a human liver-on-chip, and is detected in human and mouse plasma at concentrations (8-49 nM) that inhibit 5-lipoxygenase in human leukocytes. α-T-13'-COOH accumulates in immune cells and inflamed murine exudates, selectively inhibits the biosynthesis of 5-lipoxygenase-derived lipid mediators in vitro and in vivo, and efficiently suppresses inflammation and bronchial hyper-reactivity in mouse models of peritonitis and asthma. Together, our data suggest that the immune regulatory and anti-inflammatory functions of α-tocopherol depend on its endogenous metabolite α-T-13'-COOH, potentially through inhibiting 5-lipoxygenase in immune cells.

Pharmacological profile and efficiency in vivo of diflapolin, the first dual inhibitor of 5-lipoxygenase-activating protein and soluble epoxide hydrolase

Arachidonic acid (AA) is metabolized to diverse bioactive lipid mediators. Whereas the 5-lipoxygenase-activating protein (FLAP) facilitates AA conversion by 5-lipoxygenase (5-LOX) to pro-inflammatory leukotrienes (LTs), the soluble epoxide hydrolase (sEH) degrades anti-inflammatory epoxyeicosatrienoic acids (EETs). Accordingly, dual FLAP/sEH inhibition might be advantageous drugs for intervention of inflammation. We present the in vivo pharmacological profile and efficiency of N-[4-(benzothiazol-2-ylmethoxy)-2-methylphenyl]-N′-(3,4-dichlorophenyl)urea (diflapolin) that dually targets FLAP and sEH. Diflapolin inhibited 5-LOX product formation in intact human monocytes and neutrophils with IC₅₀ = 30 and 170 nM, respectively, and suppressed the activity of isolated sEH (IC₅₀ = 20 nM). Characteristic for FLAP inhibitors, diflapolin (I) failed to inhibit isolated 5-LOX, (II) blocked 5-LOX product formation in HEK cells only when 5-LOX/FLAP was co-expressed, (III) lost potency in intact cells when exogenous AA was supplied, and (IV) prevented 5-LOX/FLAP complex assembly in leukocytes. Diflapolin showed target specificity, as other enzymes related to AA metabolism (i.e., COX1/2, 12/15-LOX, LTA₄H, LTC₄S, mPGES₁, and cPLA₂) were not inhibited. In the zymosan-induced mouse peritonitis model, diflapolin impaired vascular permeability, inhibited cysteinyl-LTs and LTB₄ formation, and suppressed neutrophil infiltration. Diflapolin is a highly active dual FLAP/sEH inhibitor in vitro and in vivo with target specificity to treat inflammation-related diseases.

Androgen-mediated sex bias impairs efficiency of leukotriene biosynthesis inhibitors in males

Proinflammatory leukotrienes (LTs) are produced by 5-lipoxygenase (5-LO) aided by 5-LO-activating protein (FLAP). LT biosynthesis inhibitors are currently under clinical investigation as treatments for respiratory and cardiovascular diseases. Here, we have revealed a sex bias in the efficiency of clinically relevant LT biosynthesis inhibitors, showing that their effects are superior in females. We found that androgens cause these sex differences by impeding the LT-biosynthetic 5-LO/FLAP complex assembly. Lower doses of the FLAP inhibitor MK886 were required to reduce LTB4 levels in exudates of female versus male mice and rats. Following platelet-activating factor-induced shock, MK886 increased survival exclusively in female mice, and this effect was abolished by testosterone administration. FLAP inhibitors and the novel-type 5-LO inhibitors licofelone and sulindac sulfide exhibited higher potencies in human blood from females, and bioactive 5-LO/FLAP complexes were formed in female, but not male, human and murine leukocytes. Supplementation of female blood or leukocytes with 5α-dihydrotestosterone abolished the observed sex differences. Our data suggest that females may benefit from anti-LT therapy to a greater extent than males, prompting consideration of sex issues in LT modifier development.

Modulation of actin dynamics as potential macrophage subtype-targeting anti-tumour strategy

Tumour-associated macrophages mainly comprise immunosuppressive M2 phenotypes that promote tumour progression besides anti-tumoural M1 subsets. Selective depletion or reprogramming of M2 may represent an innovative anti-cancer strategy. The actin cytoskeleton is central for cellular homeostasis and is targeted for anti-cancer chemotherapy. Here, we show that targeting G-actin nucleation using chondramide A (ChA) predominantly depletes human M2 while promoting the tumour-suppressive M1 phenotype. ChA reduced the viability of M2, with minor effects on M1, but increased tumour necrosis factor (TNF)α release from M1. Interestingly, ChA caused rapid disruption of dynamic F-actin filaments and polymerization of G-actin, followed by reduction of cell size, binucleation and cell division, without cellular collapse. In M1, but not in M2, ChA caused marked activation of SAPK/JNK and NFκB, with slight or no effects on Akt, STAT-1/-3, ERK-1/2, and p38 MAPK, seemingly accounting for the better survival of M1 and TNFα secretion. In a microfluidically-supported human tumour biochip model, circulating ChA-treated M1 markedly reduced tumour cell viability through enhanced release of TNFα. Together, ChA may cause an anti-tumoural microenvironment by depletion of M2 and activation of M1, suggesting induction of G-actin nucleation as potential strategy to target tumour-associated macrophages in addition to neoplastic cells.

BRP-187: A potent inhibitor of leukotriene biosynthesis that acts through impeding the dynamic 5-lipoxygenase/5-lipoxygenase-activating protein (FLAP) complex assembly

The pro-inflammatory leukotrienes (LTs) are formed from arachidonic acid (AA) in activated leukocytes, where 5-lipoxygenase (5-LO) translocates to the nuclear envelope to assemble a functional complex with the integral nuclear membrane protein 5-LO-activating protein (FLAP). FLAP, a MAPEG family member, facilitates AA transfer to 5-LO for efficient conversion, and LT biosynthesis critically depends on FLAP. Here we show that the novel LT biosynthesis inhibitor BRP-187 prevents the 5-LO/FLAP interaction at the nuclear envelope of human leukocytes without blocking 5-LO nuclear redistribution. BRP-187 inhibited 5-LO product formation in human monocytes and polymorphonuclear leukocytes stimulated by lipopolysaccharide plus N-formyl-methionyl-leucyl-phenylalanine (IC₅₀=7-10nM), and upon activation by ionophore A23187 (IC₅₀=10-60nM). Excess of exogenous AA markedly impaired the potency of BRP-187. Direct 5-LO inhibition in cell-free assays was evident only at >35-fold higher concentrations, which was reversible and not improved under reducing conditions. BRP-187 prevented A23187-induced 5-LO/FLAP complex assembly in leukocytes but failed to block 5-LO nuclear translocation, features that were shared with the FLAP inhibitor MK886. Whereas AA release, cyclooxygenases and related LOs were unaffected, BRP-187 also potently inhibited microsomal prostaglandin E₂ synthase-1 (IC₅₀=0.2μM), another MAPEG member. In vivo, BRP-187 (10mg/kg) exhibited significant effectiveness in zymosan-induced murine peritonitis, suppressing LT levels in peritoneal exudates as well as vascular permeability and neutrophil infiltration. Together, BRP-187 potently inhibits LT biosynthesis in vitro and in vivo, which seemingly is caused by preventing the 5-LO/FLAP complex assembly and warrants further preclinical evaluation.

Development of smart cell-free and cell-based assay systems for investigation of leukotriene C4 synthase activity and evaluation of inhibitors

Cysteinyl leukotrienes (cys-LTs) cause bronchoconstriction in anaphylaxis and asthma. They are formed by 5-lipoxygenase (5-LOX) from arachidonic acid (AA) yielding the unstable leukotriene A₄ (LTA₄) that is subsequently conjugated with glutathione (GSH) by LTC₄ synthase (LTC₄S). Cys-LT receptor antagonists and LTC₄S inhibitors have been developed, but only the former have reached the market. High structural homology to related enzymes and lack of convenient test systems due to instability of added LTA₄ have hampered the development of LTC₄S inhibitors. We present smart cell-free and cell-based assay systems based on in situ-generated LTA₄ that allow studying LTC₄S activity and investigating LTC₄S inhibitors. Co-incubations of microsomes from HEK293 cells expressing LTC₄S with isolated 5-LOX efficiently converted exogenous AA to LTC₄ (~1.3μg/200μg protein). Stimulation of HEK293 cells co-expressing 5-LOX and LTC₄S with Ca²⁺-ionophore A23187 and 20μM AA resulted in strong LTC₄ formation (~250ng/10⁶ cells). MK-886, a well-known 5-LOX activating protein (FLAP) inhibitor that also acts on LTC₄S, consistently inhibited LTC₄ formation in all assay types (IC₅₀=3.1-3.5μM) and we successfully confirmed TK04a as potent LTC₄S inhibitor in these assay systems (IC₅₀=17 and 300nM, respectively). We demonstrated transcellular LTC₄ biosynthesis between neutrophils or 5-LOX-expressing HEK293 cells that produce LTA₄ from AA and HEK293 cells expressing LTC₄S that transform LTA₄ to LTC₄. In conclusion, our assay approaches are advantageous as the substrate LTA₄ is generated in situ and are suitable for studying enzymatic functionality of LTC₄S including site-directed mutations and evaluation of LTC₄S inhibitors.

Humudifucol and Bioactive Prenylated Polyphenols from Hops (Humulus lupulus cv. "Cascade")

Humulus lupulus (hop plant) has long been used in traditional medicine as a sedative and antimicrobial agent. More recently, attention has been devoted to the phytoestrogenic activity of the plant extracts as well as to the anti-inflammatory and chemopreventive properties of the prenylated chalcones present. In this study, an Italian sample of H. lupulus cv. "Cascade" has been investigated and three new compounds [4-hydroxycolupulone (6), humudifucol (7) and cascadone (8)] have been purified and identified by means of NMR spectroscopy along with four known metabolites. Notably, humudifucol (7) is the first prenylated dimeric phlorotannin discovered in nature. Because structurally related phloroglucinols from natural sources were found previously to inhibit microsomal prostaglandin E2 synthase (mPGES)-1 and 5-lipoxygenase (5-LO), the isolated compounds were evaluated for their bioactivity against these pro-inflammatory target proteins. The prenylated chalcone xanthohumol inhibited both enzymes at low μM concentrations.

Pathogen-reduced Ebola virus convalescent plasma: first steps towards standardization of manufacturing and quality control including assessment of Ebola-specific neutralizing antibodies

BACKGROUND

Ebola virus disease is a public health emergency of international concern, and enormous efforts are being made in the development of vaccines and therapies. Ebola virus convalescent plasma is a promising anti-infective treatment of Ebola virus disease. Therefore, we developed and implemented a pathogen-reduced Ebola virus convalescent plasma concept in accordance with national, European and global regulatory framework.

MATERIALS AND METHODS

Ebola virus convalescent plasma manufacture and distribution was managed by a collection centre, two medical centres and an expert group from the European Blood Alliance. Ebola virus convalescent plasma was collected twice with an interval of 61 days from a donor recovering from Ebola virus disease in Germany. After pathogen reduction, the plasma was analysed for Ebola virus-specific immunoglobulin G (IgG) antibodies and its Ebola virus neutralizing activity.

RESULTS

Convalescent plasma could be collected without adverse events. Anti-Ebola virus IgG titres and Ebola-specific neutralizing antibodies in convalescent plasma were only slightly reduced after pathogen reduction treatment with S59 amotosalen/UVA. A patient in Italy with Ebola virus disease was treated with convalescent plasma without apparent adverse effects.

DISCUSSION

As proof of principle, we describe a concept and practical implementation of pathogen-reduced Ebola virus convalescent plasma manufacture, quality control and its clinical application to an Ebola virus disease patient.

A procedure for efficient non-viral siRNA transfection of primary human monocytes using nucleofection

Monocytes are an important constituent of the innate immune system. Therefore, manipulating gene expression of primary human monocytes is a crucial mean to study and characterize the functions of targeted proteins in monocytes. Gene silencing by transfection of cells with small interfering RNA (siRNA) leading to the degradation of the corresponding mRNA and thus to reduced target protein levels is an important tool to investigate gene and protein function of interest. However, non-viral transfection of primary monocytes is challenging because siRNA uptake by these suspended cells is tricky, and the individual cells vary among different donors and do not proliferate. Here, we describe a procedure for efficient non-viral transfection of primary human monocytes isolated from peripheral blood, which maintains cell viability and cell functions, such as responsiveness to stimuli like LPS and IL-10. Nucleofection was used as an electroporation technique that enables efficient introduction of siRNA and silencing of target genes. Using a modification of our previously published protocol for the fast-proliferating THP-1 monocytic cell line, we transfected primary human monocytes with siRNA targeting 5-lipoxygenase (5-LO). In fact, we successfully downregulated 5-LO mRNA resulting in reduced protein levels and enzymatic activity.

The novel benzimidazole derivative BRP-7 inhibits leukotriene biosynthesis in vitro and in vivo by targeting 5-lipoxygenase-activating protein (FLAP)

BACKGROUND AND PURPOSE

Leukotrienes (LTs) are inflammatory mediators produced via the 5-lipoxygenase (5-LOX) pathway and are linked to diverse disorders, including asthma, allergic rhinitis and cardiovascular diseases. We recently identified the benzimidazole derivative BRP-7 as chemotype for anti-LT agents by virtual screening targeting 5-LOX-activating protein (FLAP). Here, we aimed to reveal the in vitro and in vivo pharmacology of BRP-7 as an inhibitor of LT biosynthesis.

EXPERIMENTAL APPROACH

We analysed LT formation and performed mechanistic studies in human neutrophils and monocytes, in human whole blood (HWB) and in cell-free assays. The effectiveness of BRP-7 in vivo was evaluated in rat carrageenan-induced pleurisy and mouse zymosan-induced peritonitis.

KEY RESULTS

BRP-7 potently suppressed LT formation in neutrophils and monocytes and this was accompanied by impaired 5-LOX co-localization with FLAP. Neither the cellular viability nor the activity of 5-LOX in cell-free assays was affected by BRP-7, indicating that a functional FLAP is needed for BRP-7 to inhibit LTs, and FLAP bound to BRP-7 linked to a solid matrix. Compared with the FLAP inhibitor MK-886, BRP-7 did not significantly inhibit COX-1 or microsomal prostaglandin E2 synthase-1, implying the selectivity of BRP-7 for FLAP. Finally, BRP-7 was effective in HWB and impaired inflammation in vivo, in rat pleurisy and mouse peritonitis, along with reducing LT levels.

CONCLUSIONS AND IMPLICATIONS

BRP-7 potently suppresses LT biosynthesis by interacting with FLAP and exhibits anti-inflammatory effectiveness in vivo, with promising potential for further development.

Elucidation of the molecular mechanism and the efficacy in vivo of a novel 1,4-benzoquinone that inhibits 5-lipoxygenase

BACKGROUND AND PURPOSE

1,4-Benzoquinones are well-known inhibitors of 5-lipoxygenase (5-LOX, the key enzyme in leukotriene biosynthesis), but the molecular mechanisms of 5-LOX inhibition are not completely understood. Here we investigated the molecular mode of action and the pharmacological profile of the novel 1,4-benzoquinone derivative 3-((decahydronaphthalen-6-yl)methyl)-2,5-dihydroxycyclohexa-2,5-diene-1,4-dione (RF-Id) in vitro and its effectiveness in vivo.

EXPERIMENTAL APPROACH

Mechanistic investigations in cell-free assays using 5-LOX and other enzymes associated with eicosanoid biosynthesis were conducted, along with cell-based studies in human leukocytes and whole blood. Molecular docking of RF-Id into the 5-LOX structure was performed to illustrate molecular interference with 5-LOX. The effectiveness of RF-Id in vivo was also evaluated in two murine models of inflammation.

KEY RESULTS

RF-Id consistently suppressed 5-LOX product synthesis in human leukocytes and human whole blood. RF-Id also blocked COX-2 activity but did not significantly inhibit COX-1, microsomal PGE2 synthase-1, cytosolic PLA2 or 12- and 15-LOX. Although RF-Id lacked radical scavenging activity, reducing conditions facilitated its inhibitory effect on 5-LOX whereas cell stress impaired its efficacy. The reduced hydroquinone form of RF-Id (RED-RF-Id) was a more potent inhibitor of 5-LOX as it had more bidirectional hydrogen bonds within the 5-LOX substrate binding site. Finally, RF-Id had marked anti-inflammatory effects in mice in vivo.

CONCLUSIONS AND IMPLICATIONS

RF-Id represents a novel anti-inflammatory 1,4-benzoquinone that potently suppresses LT biosynthesis by direct inhibition of 5-LOX with effectiveness in vivo. Mechanistically, RF-Id inhibits 5-LOX in a non-redox manner by forming discrete molecular interactions within the active site of 5-LOX.

Targeting V-ATPase in primary human monocytes by archazolid potently represses the classical secretion of cytokines due to accumulation at the endoplasmic reticulum

The macrolide archazolid inhibits vacuolar-type H(+)-ATPase (V-ATPase), a proton-translocating enzyme involved in protein transport and pH regulation of cell organelles, and potently suppresses cancer cell growth at low nanomolar concentrations. In view of the growing link between inflammation and cancer, we investigated whether inhibition of V-ATPase by archazolid may affect primary human monocytes that can promote cancer by sustaining inflammation through the release of tumor-promoting cytokines. Human primary monocytes express V-ATPase, and archazolid (10-100nM) increases the vesicular pH in these cells. Archazolid (10nM) markedly reduced the release of pro-inflammatory (TNF-α, interleukin-6 and -8) but also of anti-inflammatory (interleukin-10) cytokines in monocytes stimulated with LPS, without affecting cell viability up to 1000nM. Of interest, secretion of interleukin-1β was increased by archazolid. Comparable effects were obtained by the V-ATPase inhibitors bafilomycin and apicularen. The phosphorylation of p38 MAPK and ERK-1/2, Akt, SAPK/JNK or of the inhibitor of NFκB (IκBα) as well as mRNA expression of IL-8 were not altered by archazolid in LPS-stimulated monocytes. Instead, archazolid caused endoplasmic reticulum (ER) stress response visualized by increased BiP expression and accumulation of IL-8 (and TNF-α) at the ER, indicating a perturbation of protein secretion. In conclusion, by interference with V-ATPase, archazolid significantly affects the secretion of cytokines due to accumulation at the ER which might be of relevance when using these agents for cancer therapy.

An experimental cell-based model for studying the cell biology and molecular pharmacology of 5-lipoxygenase-activating protein in leukotriene biosynthesis

BACKGROUND

Subcellular distribution of 5-lipoxygenase (5-LO) to the perinuclear region and interaction with the 5-LO-activating protein (FLAP) are assumed as key steps in leukotriene biosynthesis and are prone to FLAP antagonists.

METHODS

FLAP and/or 5-LO were stably expressed in HEK293 cells, 5-LO products were analyzed by HPLC, and 5-LO and FLAP subcellular localization was visualized by immunofluorescence microscopy.

RESULTS

5-LO and FLAP were stably expressed in HEK293 cells, and upon Ca(2+)-ionophore A23187 stimulation exogenous AA was efficiently transformed into the 5-LO products 5-hydro(pero)xyeicosatetraenoic acid (5-H(p)ETE) and the trans-isomers of LTB4. A23187 stimulation caused 5-LO accumulation at the nuclear membrane only when FLAP was co-expressed. Unexpectedly, A23187 stimulation of HEK cells expressing 5-LO and FLAP without exogenous AA failed in 5-LO product synthesis. HEK cells liberated AA in response to A23187, and transfected HEK cells expressing 12-LO generated 12-HETE after A23187 challenge from endogenous AA. FLAP co-expression increased 5-LO product formation in A23187-stimulated cells at low AA concentrations. Only in cells expressing FLAP and 5-LO, the FLAP antagonist MK886 blocked FLAP-mediated increase in 5-LO product formation, and prevented 5-LO nuclear membrane translocation and co-localization with FLAP.

CONCLUSION

The cellular biosynthesis of 5-LO products from endogenously derived substrate requires not only functional 5-LO/FLAP co-localization but also additional prerequisites which are dispensable when exogenous AA is supplied; identification of these determinants is challenging.

GENERAL SIGNIFICANCE

We present a cell model to study the role of FLAP as 5-LO interacting protein in LT biosynthesis in intact cells and for characterization of putative FLAP antagonists.

Indirubin-3'-monoxime exerts a dual mode of inhibition towards leukotriene-mediated vascular smooth muscle cell migration

Aims

The small molecule indirubin-3′-monoxime (I3MO) has been shown to inhibit vascular smooth muscle cell (VSMC) proliferation and neointima formation in vivo. The influence of I3MO on VSMC migration and vascular inflammation, two additional key players during the onset of atherosclerosis and restenosis, should be investigated.

Methods and results

We examined the influence of I3MO on VSMC migration, with focus on monocyte-derived leukotrienes (LTs) and platelet-derived growth factors (PDGFs) as elicitors. Exogenous LTB4 and cysteinyl leukotrienes as well as LT-enriched conditioned medium of activated primary human monocytes induced VSMC migration, which was inhibited by I3MO. I3MO also blunted migration of VSMC stimulated with the PDGF, the strongest motogen tested in this study. Induction of haem oxygenase 1 accounted for this anti-migratory activity of I3MO in VSMC. Notably, I3MO not only interfered with the migratory response in VSMC, but also suppressed the production of pro-migratory LT in monocytes. Conditioned media from monocytes that were activated in the presence of I3MO failed to induce VSMC migration. In cell-based and cell-free assays, I3MO selectively inhibited 5-lipoxygenase (5-LO), the key enzyme in LT biosynthesis, with an IC₅₀ in the low micromolar range.

Conclusion

Our study reveals a novel dual inhibitory mode of I3MO on LT-mediated VSMC migration: (i) I3MO interferes with pro-migratory signalling in VSMC and (ii) I3MO suppresses LT biosynthesis in monocytes by direct inhibition of 5-LO. These inhibitory actions on both migratory stimulus and response complement the previously demonstrated anti-proliferative properties of I3MO and may further promote I3MO as promising vasoprotective compound.

High capacity for leukotriene biosynthesis in peripheral blood during pregnancy

Pregnancy is accompanied by major immunological changes to maintain both tolerance for the fetus and immune competence. Leukotrienes are powerful 5-lipoxygenase-derived inflammatory mediators and the characteristics of leukotriene-related diseases (e.g., asthma, allergic rhinitis) change during pregnancy. Here, we show that pregnancy affects leukotriene synthesis in human blood and leukocytes. 5-Lipoxygenase product formation in stimulated blood of pregnant women was significantly higher than in non-pregnant females. Although a pregnancy-related increase in neutrophil and monocyte counts may explain these observations, granulocytes of pregnant donors have lower leukotriene-synthetic capacities. On the other hand, granulocytes from non-pregnant woman produced more leukotrienes when resuspended in plasma of pregnant women than of non-pregnant females. Together, we show that leukotriene biosynthesis in maternal blood is increased by the interrelations of higher leukocyte numbers, lower cellular capacity for leukotriene synthesis and stimulatory effects of plasma. This bias may affect leukotriene-related diseases during pregnancy and their pharmacological treatment.

Potent inhibition of human 5-lipoxygenase and microsomal prostaglandin E₂ synthase-1 by the anti-carcinogenic and anti-inflammatory agent embelin

Embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone) possesses anti-inflammatory and anti-carcinogenic properties in vivo, and these features have been related to interference with multiple targets including XIAPs, NFκB, STAT-3, Akt and mTOR. However, interference with these proteins requires relatively high concentrations of embelin (IC₅₀>4 μM) and cannot fully explain its bioactivity observed in several functional studies. Here we reveal human 5-lipoxygenase (5-LO) and microsomal prostaglandin E₂ synthase (mPGES)-1 as direct molecular targets of embelin. Thus, embelin potently suppressed the biosynthesis of eicosanoids by selective inhibition of 5-LO and mPGES-1 with IC₅₀=0.06 and 0.2 μM, respectively. In intact human polymorphonuclear leukocytes and monocytes, embelin consistently blocked the biosynthesis of various 5-LO products regardless of the stimulus (fMLP or A23187) with IC₅₀=0.8-2 μM. Neither the related human 12- and 15-LO nor the cyclooxygenases-1 and -2 or cytosolic phospholipase A₂ were significantly affected by 10 μM embelin. Inhibition of 5-LO and mPGES-1 by embelin was (I) essentially reversible after wash-out, (II) not impaired at higher substrate concentrations, (III) unaffected by inclusion of Triton X-100, and (IV) did not correlate to its proposed antioxidant properties. Docking simulations suggest concrete binding poses in the active sites of both 5-LO and mPGES-1. Because 5-LO- and mPGES-1-derived eicosanoids play roles in inflammation and cancer, the interference of embelin with these enzymes may contribute to its biological effects and suggests embelin as novel chemotype for development of dual 5-LO/mPGES-1 inhibitors.

Testosterone suppresses phospholipase D, causing sex differences in leukotriene biosynthesis in human monocytes

Sex disparities in inflammation have been reported, but the cellular and molecular basis for these discrepancies is unknown. Monocytes are central effector cells in immunity and possess high capacities to produce proinflammatory leukotrienes (LTs). Here, we investigated sex differences in the activation of 5-lipoxygenase (5-LO), the key enzyme in LT biosynthesis, in human peripheral monocytes. In cells from females, 5-LO product formation was 1.8-fold higher than in cells from males, as evaluated by HPLC. When female monocytes were resuspended in plasma from males, 5-LO products were significantly lower than in female plasma. Interestingly, 5α-dihydrotestosterone (5α-DHT, 10 nM) repressed LT synthesis in female cells down to the levels observed in males, while estradiol (100 nM) was without effect, and progesterone (100 nM) caused only a slight inhibition. 5α-DHT (10 nM) caused ERK phosphorylation and inhibition of phospholipase D (PLD), as evaluated by Western blot and measurement of PLD activity via radioenzymatic diacylglyceride (DAG) and nonradioactive choline assays. Accordingly, PLD activity and DAG formation were 1.4- to 1.8-fold lower in male vs. female monocytes connected to increased ERK phosphorylation. Our data indicate that ERK activation by androgens in monocytes represses PLD activity, resulting in impaired 5-LO product formation due to lack of activating DAGs.