Purification of arachidonate 5-lipoxygenase from porcine leukocytes and its reactivity with hydroperoxyeicosatetraenoic acids

Identification of the arachidonic acid 5-lipoxygenase and its function in the immunity of Apostichopus japonicus

A number of studies have been demonstrated that arachidonate 5-lipoxygenase (ALOX-5) plays a role in regulating a range of physiological and pathological processes through the catalysis of leukotriene formation from arachidonic acid (ARA). The coding sequence of ALOX-5 from Apostichopus japonicus (Aj-ALOX-5) was successfully amplified, resulting in a 2028 bp ORF sequence that encodes 674 amino acids. A comparison of the amino acid sequence with those of other 5-lipoxygenases revealed that Aj-ALOX-5 has the N-terminal "PLAT domain" and C-terminal "lipoxygenase structural domain" characteristic of this enzyme family. The enzyme activity sites and Ca2⁺-binding sites exhibited high levels of conservation. The phylogenetic tree also indicated that Aj-ALOX-5 was closely related to starfish 5-lipoxygenase. The recombinant Aj-ALOX-5 (rAj-ALOX-5) was obtained through the exogenous expression of an engineered bacterium and purified using Ni2+-NTA. rAj-ALOX-5 was observed to catalyze ARA to produce 5-HPETE and LTA4, which indicated that the Aj-ALOX-5 protein belonged to the 5-lipoxygenase family. qRT-PCR demonstrated that Aj-ALOX-5 is widely distributed in tissues. Furthermore, the Aj-ALOX-5 mRNA and the production of 5-HETE were found to be significantly up-regulated in response to stress induced by Vibrio splendidus. Inhibition of Aj-ALOX-5 expression by the optimal caffeic acid resulted in a significant increase in mortality rates of sea cucumbers. Further investigation revealed that the production of 5-HPETE and NF-κB I was also significantly suppressed. It can be hypothesized that Aj-ALOX-5 plays an important role in the immune response of sea cucumbers by mediating the NF-κB I pathway.

Lipoxygenases at the Intersection of Infection and Carcinogenesis

The persisting presence of opportunistic pathogens like Pseudomonas aeruginosa poses a significant threat to many immunocompromised cancer patients with pulmonary infections. This review highlights the complexity of interactions in the host's defensive eicosanoid signaling network and its hijacking by pathogenic bacteria to their own advantage. Human lipoxygenases (ALOXs) and their mouse counterparts are integral elements of the innate immune system, mostly operating in the pro-inflammatory mode. Taking into account the indispensable role of inflammation in carcinogenesis, lipoxygenases have counteracting roles in this process. In addition to describing the structure-function of lipoxygenases in this review, we discuss their roles in such critical processes as cancer cell signaling, metastases, death of cancer and immune cells through ferroptosis, as well as the roles of ALOXs in carcinogenesis promoted by pathogenic infections. Finally, we discuss perspectives of novel oncotherapeutic approaches to harness lipoxygenase signaling in tumors.

Synthesis and Significance of Arachidonic Acid, a Substrate for Cyclooxygenases, Lipoxygenases, and Cytochrome P450 Pathways in the Tumorigenesis of Glioblastoma Multiforme, Including a Pan-Cancer Comparative Analysis

Glioblastoma multiforme (GBM) is one of the most aggressive gliomas. New and more effective therapeutic approaches are being sought based on studies of the various mechanisms of GBM tumorigenesis, including the synthesis and metabolism of arachidonic acid (ARA), an omega-6 polyunsaturated fatty acid (PUFA). PubMed, GEPIA, and the transcriptomics analysis carried out by Seifert et al. were used in writing this paper. In this paper, we discuss in detail the biosynthesis of this acid in GBM tumors, with a special focus on certain enzymes: fatty acid desaturase (FADS)1, FADS2, and elongation of long-chain fatty acids family member 5 (ELOVL5). We also discuss ARA metabolism, particularly its release from cell membrane phospholipids by phospholipase A₂ (cPLA₂, iPLA₂, and sPLA₂) and its processing by cyclooxygenases (COX-1 and COX-2), lipoxygenases (5-LOX, 12-LOX, 15-LOX-1, and 15-LOX-2), and cytochrome P450. Next, we discuss the significance of lipid mediators synthesized from ARA in GBM cancer processes, including prostaglandins (PGE₂, PGD₂, and 15-deoxy-Δ^12,14-PGJ₂ (15d-PGJ₂)), thromboxane A₂ (TxA₂), oxo-eicosatetraenoic acids, leukotrienes (LTB₄, LTC₄, LTD₄, and LTE₄), lipoxins, and many others. These lipid mediators can increase the proliferation of GBM cancer cells, cause angiogenesis, inhibit the anti-tumor response of the immune system, and be responsible for resistance to treatment.

15-Lipoxygenase-1 biosynthesis of 7S,14S-diHDHA implicates 15-lipoxygenase-2 in biosynthesis of resolvin D5

The two oxylipins 7S,14S-dihydroxydocosahexaenoic acid (diHDHA) and 7S,17S-diHDHA [resolvin D5 (RvD5)] have been found in macrophages and infectious inflammatory exudates and are believed to function as specialized pro-resolving mediators (SPMs). Their biosynthesis is thought to proceed through sequential oxidations of DHA by lipoxygenase (LOX) enzymes, specifically, by human 5-LOX (h5-LOX) first to 7(S)-hydroxy-4Z,8E,10Z,13Z,16Z,19Z-DHA (7S-HDHA), followed by human platelet 12-LOX (h12-LOX) to form 7(S),14(S)-dihydroxy-4Z,8E,10Z,12E,16Z,19Z-DHA (7S,14S-diHDHA) or human reticulocyte 15-LOX-1 (h15-LOX-1) to form RvD5. In this work, we determined that oxidation of 7(S)-hydroperoxy-4Z,8E,10Z,13Z,16Z,19Z-DHA to 7S,14S-diHDHA is performed with similar kinetics by either h12-LOX or h15-LOX-1. The oxidation at C14 of DHA by h12-LOX was expected, but the noncanonical reaction of h15-LOX-1 to make over 80% 7S,14S-diHDHA was larger than expected. Results of computer modeling suggested that the alcohol on C7 of 7S-HDHA hydrogen bonds with the backbone carbonyl of Ile399, forcing the hydrogen abstraction from C12 to oxygenate on C14 but not C17. This result raised questions regarding the synthesis of RvD5. Strikingly, we found that h15-LOX-2 oxygenates 7S-HDHA almost exclusively at C17, forming RvD5 with faster kinetics than does h15-LOX-1. The presence of h15-LOX-2 in neutrophils and macrophages suggests that it may have a greater role in biosynthesizing SPMs than previously thought. We also determined that the reactions of h5-LOX with 14(S)-hydroperoxy-4Z,7Z,10Z,12E,16Z,19Z-DHA and 17(S)-hydroperoxy-4Z,7Z,10Z,13Z,15E,19Z-DHA are kinetically slow compared with DHA, suggesting that these reactions may be minor biosynthetic routes in vivo. Additionally, we show that 7S,14S-diHDHA and RvD5 have anti-aggregation properties with platelets at low micromolar potencies, which could directly regulate clot resolution.

5 S,15 S-Dihydroperoxyeicosatetraenoic Acid (5,15-diHpETE) as a Lipoxin Intermediate: Reactivity and Kinetics with Human Leukocyte 5-Lipoxygenase, Platelet 12-Lipoxygenase, and Reticulocyte 15-Lipoxygenase-1

The reaction of 5 S,15 S-dihydroperoxyeicosatetraenoic acid (5,15-diHpETE) with human 5-lipoxygenase (LOX), human platelet 12-LOX, and human reticulocyte 15-LOX-1 was investigated to determine the reactivity and relative rates of producing lipoxins (LXs). 5-LOX does not react with 5,15-diHpETE, although it can produce LXA₄ when 15-HpETE is the substrate. In contrast, both 12-LOX and 15-LOX-1 react with 5,15-diHpETE, forming specifically LXB₄. For 12-LOX and 5,15-diHpETE, the kinetic parameters are k_cat = 0.17 s^-1 and k_cat/ K_M = 0.011 μM^-1 s^-1 [106- and 1600-fold lower than those for 12-LOX oxygenation of arachidonic acid (AA), respectively]. On the other hand, for 15-LOX-1 the equivalent parameters are k_cat = 4.6 s^-1 and k_cat/ K_M = 0.21 μM^-1 s^-1 (3-fold higher and similar to those for 12-HpETE formation by 15-LOX-1 from AA, respectively). This contrasts with the complete lack of reaction of 15-LOX-2 with 5,15-diHpETE [Green, A. R., et al. (2016) Biochemistry 55, 2832-2840]. Our data indicate that 12-LOX is markedly inferior to 15-LOX-1 in catalyzing the production of LXB₄ from 5,15-diHpETE. Platelet aggregation was inhibited by the addition of 5,15-diHpETE, with an IC₅₀ of 1.3 μM; however, LXB₄ did not significantly inhibit collagen-mediated platelet activation up to 10 μM. In summary, LXB₄ is the primary product of 12-LOX and 15-LOX-1 catalysis, if 5,15-diHpETE is the substrate, with 15-LOX-1 being 20-fold more efficient than 12-LOX. LXA₄ is the primary product with 5-LOX but only if 15-HpETE is the substrate. Approximately equal proportions of LXA₄ and LXB₄ are produced by 12-LOX but only if LTA₄ is the substrate, as described previously [Sheppard, K. A., et al. (1992) Biochim. Biophys. Acta 1133, 223-234].

Host Lipid Mediators in Leprosy: The Hypothesized Contributions to Pathogenesis

The spectrum of clinical forms observed in leprosy and its pathogenesis are dictated by the host's immune response against Mycobacterium leprae, the etiological agent of leprosy. Previous results, based on metabolomics studies, demonstrated a strong relationship between clinical manifestations of leprosy and alterations in the metabolism of ω3 and ω6 polyunsaturated fatty acids (PUFAs), and the diverse set of lipid mediators derived from PUFAs. PUFA-derived lipid mediators provide multiple functions during acute inflammation, and some lipid mediators are able to induce both pro- and anti-inflammatory responses as determined by the cell surface receptors being expressed, as well as the cell type expressing the receptors. However, little is known about how these compounds influence cellular immune activities during chronic granulomatous infectious diseases, such as leprosy. Current evidence suggests that specialized pro-resolving lipid mediators (SPMs) are involved in the down-modulation of the innate and adaptive immune response against M. leprae and that alteration in the homeostasis of pro-inflammatory lipid mediators versus SPMs is associated with dramatic shifts in the pathogenesis of leprosy. In this review, we discuss the possible consequences and present new hypotheses for the involvement of ω3 and ω6 PUFA metabolism in the pathogenesis of leprosy. A specific emphasis is placed on developing models of lipid mediator interactions with the innate and adaptive immune responses and the influence of these interactions on the outcome of leprosy.

Strict Regiospecificity of Human Epithelial 15-Lipoxygenase-2 Delineates Its Transcellular Synthesis Potential

Lipoxins are an important class of lipid mediators that induce the resolution of inflammation and arise from transcellular exchange of arachidonic acid (AA)-derived lipoxygenase products. Human epithelial 15-lipoxygenase-2 (h15-LOX-2), the major lipoxygenase in macrophages, has exhibited strict regiospecificity, catalyzing only the hydroperoxidation of carbon 15 of AA. To determine the catalytic potential of h15-LOX-2 in transcellular synthesis events, we reacted it with the three lipoxygenase-derived monohydroperoxy-eicosatetraenoic acids (HPETE) in humans: 5-HPETE, 12-HPETE, and 15-HPETE. Only 5-HPETE was a substrate for h15-LOX-2, and the steady-state catalytic efficiency (kcat/Km) of this reaction was 31% of the kcat/Km of AA. The only major product of h15-LOX-2's reaction with 5-HPETE was the proposed lipoxin intermediate, 5,15-dihydroperoxy-eicosatetraenoic acid (5,15-diHPETE). However, h15-LOX-2 did not react further with 5,15-diHPETE to produce lipoxins. This result is consistent with the specificity of h15-LOX-2 despite the increased reactivity of 5,15-diHPETE. Density functional theory calculations determined that the radical, after abstracting the C10 hydrogen atom from 5,15-diHPETE, had an energy 5.4 kJ/mol lower than that of the same radical generated from AA, demonstrating the facility of 5,15-diHPETE to form lipoxins. Interestingly, h15-LOX-2 does react with 5S,6R-diHETE, forming LipoxinA4, indicating the gemdiol does not prohibit h15-LOX-2 reactivity. Taken together, these results demonstrate the strict regiospecificity of h15-LOX-2 that circumscribes its role in transcellular synthesis.

Effect of endocannabinoids on soybean lipoxygenase-1 activity

Endocannabinoids appear to be involved in a variety of physiological processes. Lipoxygenase activity has been known to be affected by unsaturated fatty acids or phenolic compounds. In this study, we examined whether endocannabinoids containing both N-acyl group and phenolic group can affect the activity of soybean lipoxygenase (LOX)-1, similar to mammalian 15-lipoxygenase in physicochemical properties. First, N-arachidonoyl dopamine and N-oleoyl dopamine were found to inhibit soybean LOX-1-catalyzed oxygenation of linoleic acid in a non-competitive manner with a Ki value of 3.7 μM and 6.2 μM, respectively. Meanwhile, other endocannabinoids failed to show a remarkable inhibition of soybean LOX-1. Separately, N-arachidonoyl dopamine and N-arachidonoyl serotonin were observed to inactivate soybean LOX-1 with Kin value of 27 μM and 24 μM, respectively, and k3 value of 0.12 min(-1) and 0.35 min(-1), respectively. Furthermore, such an inactivation was enhanced by ascorbic acid, but suppressed by 13(S)-hydroperoxy-9,11-octadecadienoic acid. Taken together, it is proposed that endocannabinoids containing polyunsaturated acyl moiety and phenolic group may be efficient for the inhibition as well as inactivation of 15-lipoxygenase.

COX-2-dependent and -independent biosynthesis of dihydroxy-arachidonic acids in activated human leukocytes

Biosynthesis of 5,15-dihydroxyeicosatetraenoic acid (5,15-diHETE) in leukocytes involves consecutive oxygenation of arachidonic acid by 5-lipoxygenase (LOX) and 15-LOX in either order. Here, we analyzed the contribution of cyclooxygenase (COX)-2 to the biosynthesis of 5,15-diHETE and 5,11-diHETE in isolated human leukocytes activated with lipopolysaccharide and calcium ionophore A23187. Transformation of arachidonic acid was initiated by 5-LOX providing 5S-HETE as a substrate for COX-2 forming 5S,15S-diHETE, 5S,15R-diHETE, and 5S,11R-diHETE as shown by LC/MS and chiral phase HPLC analyses. The levels of 5,15-diHETE were 0.45 ± 0.2 ng/10⁶ cells (mean ± SEM, n = 6), reaching about half the level of LTB₄ (1.3 ± 0.5 ng/10⁶ cells, n = 6). The COX-2 specific inhibitor NS-398 reduced the levels of 5,15-diHETE to below 0.02 ng/10⁶ cells in four of six samples. Similar reduction was achieved by MK-886, an inhibitor of 5-LOX activating protein but the above differences were not statistically significant. Aspirin treatment of the activated cells allowed formation of 5,15-diHETE (0.1 ± 0.05 ng/10⁶ cells, n = 6) but, as expected, abolished formation of 5,11-diHETE. The mixture of activated cells also produced 5S,12S-diHETE with the unusual 6E,8Z,10E double bond configuration, implicating biosynthesis by 5-LOX and 12-LOX activity rather than by hydrolysis of the leukotriene A₄-epoxide. Exogenous octadeuterated 5S-HETE and 15S-HETE were converted to 5,15-diHETE, implicating that multiple oxygenation pathways of arachidonic acid occur in activated leukocytes. The contribution of COX-2 to the biosynthesis of dihydroxylated derivatives of arachidonic acid provides evidence for functional coupling with 5-LOX in activated human leukocytes.

Applications of stereospecifically-labeled Fatty acids in oxygenase and desaturase biochemistry

Oxygenation and desaturation reactions are inherently associated with the abstraction of a hydrogen from the fatty acid substrate. Since the first published application in 1965, stereospecific placement of a labeled hydrogen isotope (deuterium or tritium) at the reacting carbons has proven a highly effective strategy for investigating the chemical mechanisms catalyzed by lipoxygenases, hemoprotein fatty acid dioxygenases including cyclooxygenases, cytochromes P450, and also the desaturases and isomerases. This review presents a synopsis of all published studies through 2010 on the synthesis and use of stereospecifically labeled fatty acids (71 references), and highlights some of the mechanistic insights gained by application of stereospecifically labeled fatty acids.

Regulation of lipoxygenase activity by polyunsaturated lysophosphatidylcholines or their oxygenation derivatives

Lysophosphatidylcholines (lysoPCs) have been known to play a role as lipid mediators in various cellular responses. In this study, we examined whether lysoPC containing linoleoyl, arachidonoyl, or docosahexaenoyl groups or their peroxy derivatives affect lipoxygenase (LOX)-catalyzed oxygenation of native substrates. First, arachidonoyl lysoPC and docosahexaenoyl lysoPC were found to inhibit potato 5-LOX-catalyzed oxygenation of linoleic acid (LA) in a noncompetitive type with Ki values of 0.38 and 1.90 microM, respectively. Likewise, arachidonoyl lysoPC and docosahexaenoyl lysoPC also inhibited 5-LOX activity from rat basophilic leukemia cells-2H3 (RBL-2H3) with IC50 values (50% inhibitory concentration) of 18.5 +/- 3.06 and 30.6 +/- 1.06 microM, respectively. Additionally, arachidonoyl lysoPC and docosahexaenoyl lysoPC also inhibited 15-LOX activity from RBL-2H3 with IC50 values of 16.6 +/- 1.3 and 24.1 +/- 2.4 microM, respectively. In a separate experiment, where lysoPC peroxides were tested for the effect on soybean LOX-1, 15(S)-hydroperoxy-5,8,11,13-eicosatetraenoyl lysoPC and 17(S)-hydroperoxy-4,7,10,13,15,19-docosahexaenoyl lysoPC potently inhibited soybean LOX-1 activity with Ki values of 6.8 and of 1.54 microM, respectively. In contrast, 13(S)-hydroperoxy-9,11-octadecadienoyl lysoPC was observed to stimulate soybean LOX-1-catalyzed oxygenation of LA markedly with AC50 value (50% activatory concentration) of 1.5 microM. Taken together, it is proposed that lysoPCs containing polyunsaturated acyl groups or their peroxy derivatives may participate in the regulation of LOX activity in biological systems.

Resolvin E2: identification and anti-inflammatory actions: pivotal role of human 5-lipoxygenase in resolvin E series biosynthesis

The family of resolvins consists of omega-3 fatty acid-derived mediators, including E series resolvins generated from eicosapentaenoic acid (EPA), and carry potent anti-inflammatory properties. Here, we report the isolation, identification, and bioactions of resolvin E2 (RvE2), which is 5S,18-dihydroxy-eicosapentaenoic acid. RvE2 stopped zymosan-induced polymorphonuclear (PMN) leukocyte infiltration and displayed potent anti-inflammatory properties in murine peritonitis. We also demonstrate that human recombinant 5-lipoxygenase generates RvE2 from a common precursor of E series resolvins, namely, 18-hydroxyeicosapentaenoate (18-HEPE). Furthermore, the initial 5-hydroperoxide intermediate was also converted to a 5(6)-epoxide intermediate in RvE1 formation. These results demonstrate that RvE2, together with RvE1, may contribute to the beneficial actions of omega-3 fatty acids in human diseases. Moreover, they indicate that the 5-lipoxygenase in human leukocytes is a pivotal enzyme that can produce both pro- and anti-inflammatory chemical mediators.

Binding investigation of human 5-lipoxygenase with its inhibitors by SPR technology correlating with molecular docking simulation

The binding features of a series of 5-lipoxygenase (5-LOX) inhibitors (caffeic acid, NDGA, AA-861, CDC, esculetin, gossypol and phenidone) to human 5-LOX have been studied by using surface plasmon resonance biosensor (SPR) technology based Biacore 3000 and molecular docking simulation analyses. The SPR results showed that the equilibrium dissociation constant (KD) values evaluated by Biacore 3000 for the inhibitors showed a good correlation with its reported IC50, suggesting that SPR technology might be applicable as a direct assay method in screening new 5-LOX inhibitors at an early stage. In addition, the 3D structural model of 5-LOX was generated according to the crystal structure of rabbit reticulocyte 15-lipoxygenase, and the molecular docking simulation analyses revealed that the predicted binding free energies for the inhibitors correlated well with the KD values measured by SPR assay, which implies the correctness of the constructed 3D structural model of 5-LOX. This current work has potential for application in structure-based 5-LOX inhibitor discovery.

Regulation of 5-lipoxygenase enzyme activity

In this article, regulation of human 5-lipoxygenase enzyme activity is reviewed. First, structural properties and enzyme activities are described. This is followed by the activating factors: Ca2+, membranes, ATP, and lipid hydroperoxide. Also, studies on phosphorylation of 5-lipoxygenase and nuclear localization sequences are reviewed.

Stress-induced nuclear export of 5-lipoxygenase

A key enzyme for leukotriene biosynthesis is 5-lipoxygenase (5-LO), which we found is exported from the nucleus when p38 MAPK is activated. CHO-K1 cells stably express green fluorescent protein-5-lipoxygenase fusion protein (GFP-5LO), which is located predominantly in the nucleus, and is exported by anisomycin, hydrogen peroxide, and sorbitol, with activation of p38 MAPK. SB203580, an inhibitor of p38 MAPK, and Leptomycin B, an inhibitor of the nuclear export, blocked the anisomycin-induced export of GFP-5LO. When HEK293 cells were transformed with plasmids for wild-type GFP-5LO, GFP-5LO-S271A or GFP-5LO-S271E mutants, most wild-type GFP-5LO and GFP-5LO-S271A localized in the nucleus, but GFP-5LO-S271E localized in the cytosol. Thus, phosphorylation at Ser-271 of 5-LO is important for its export. Endogenous 5-LO in RBL cells stimulated with anisomycin was also exported from the nucleus. These results suggest that the nuclear export of 5-LO depends on the stress-induced activation of the p38 MAPK pathway.

Close Functional Coupling between Ca2+ Release-activated Ca2+ Channels, Arachidonic Acid Release, and Leukotriene C4 Secretion

In non-excitable cells, one major route for Ca2+ influx is through store-operated Ca2+ channels in the plasma membrane. These channels are activated by the emptying of intracellular Ca2+ stores, and in some cell types, particularly of hemopoietic origin, store-operated influx occurs through Ca2+ release-activated Ca2+ (CRAC) channels. However, little is known about the downstream consequences of CRAC channel activation. Here, we report that Ca2+ entry through CRAC channels stimulates arachidonic acid production, whereas Ca2+ release from the stores is ineffective even though the latter evokes a robust intracellular Ca2+ signal. We find that arachidonic acid released by Ca2+ entering through CRAC channels is used to synthesize the potent paracrine proinflammatory signal leukotriene C4 (LTC4). Both pharmacological inhibitors of CRAC channels and mitochondrial depolarization, which impairs CRAC channel activity, suppress arachidonic acid release and LTC4 secretion. Thus, arachidonic acid release is preferentially stimulated by elevated subplasmalemmal Ca2+ levels due to open CRAC channels, suggesting that the enzyme is located close to the CRAC channels. Our results also identify a novel role for CRAC channels, namely the activation of a downstream signal transduction pathway resulting in the secretion of LTC4. Finally, mitochondria are key determinants of the generation of both intracellular (arachidonic acid) and paracrine (LTC4) signals through their effects on CRAC channel activity.

Arachidonate 5-lipoxygenase

In this article, it has been attempted to review data primarily on the activation of human 5-lipoxygenase, in vitro and in the cell. First, structural properties and enzyme activities are described. This is followed by the activating factors: Ca2+, membranes, ATP, and lipid hydroperoxide. Also, studies on phosphorylation of 5-lipoxygenase, interaction with other proteins, and the intracellullar mobility of 5-lipoxygenase, are reviewed.

Immunohistochemical localization of guinea-pig leukotriene B4 12-hydroxydehydrogenase/15-ketoprostaglandin 13-reductase

We have cloned cDNA for leukotriene B4 12-hydroxydehydrogenase (LTB4 12-HD)/15-ketoprostaglandin 13-reductase (PGR) from guinea-pig liver. LTB4 12-HD catalyzes the conversion of LTB4 into 12-keto-LTB4 in the presence of NADP+, and plays an important role in inactivating LTB4. The cDNA contained an ORF of 987 bp that encodes a protein of 329 amino-acid residues with a 78% identity with porcine LTB4 12-HD. The amino acids in the putative NAD+/NADP+ binding domain are well conserved among the pig, guinea-pig, human, rat, and rabbit enzymes. The guinea-pig LTB4 12-HD (gpLTB4 12-HD) was expressed as a glutathione S-transferase (GST) fusion protein in Escherichia coli, which exhibited similar enzyme activities to porcine LTB4 12-HD. We examined the 15-ketoprostaglandin 13-reductase (PGR) activity of recombinant gpLTB4 12-HD, and confirmed that the Kcat of the PGR activity is higher than that of LTB4 12-HD activity by 200-fold. Northern and Western blot analyses revealed that gpLTB4 12-HD/PGR is widely expressed in guinea-pig tissues such as liver, kidney, small intestine, spleen, and stomach. We carried out immunohistochemical analyses of this enzyme in various guinea-pig tissues. Epithelial cells of calyx and collecting tubules in kidney, epithelial cells of airway, alveoli, epithelial cells in small intestine and stomach, and hepatocytes were found to express the enzyme. These findings will lead to the identification of the unrevealed roles of PGs and LTs in these tissues.

Effects of naturally occurring prenylated flavonoids on enzymes metabolizing arachidonic acid: cyclooxygenases and lipoxygenases

Prenylated flavonoids are chemical entities having an isoprenyl, a geranyl, a 1,1-dimethylallyl, and/or a lavandulyl moiety as part of their flavonoid backbone structure. In this study, the effects of 19 naturally occurring prenylated flavonoids, isolated from medicinal plants, on cyclooxygenase (COX)-1 and COX-2 and on 5-lipoxygenase (5-LOX) and 12-LOX were investigated using [14C]arachidonic acid as a substrate. The homogenates of bovine platelets and polymorphonuclear leukocytes were used as COX-1, 12-LOX, and 5-LOX enzyme sources; the homogenate of aspirin-pretreated lipopolysaccharide-induced RAW 264.7 cells was used for the COX-2 enzyme source. Among the 19 prenylated flavonoids, morusin, kuwanon C, sanggenon B, sanggenon D and kazinol B inhibited COX-2 activity (ic(50) = 73-100 microM), but the potencies were far less than that of NS-398 (ic(50) = 2.9 microM). In contrast, many prenylated flavonoids, such as kuraridin, kuwanon C and sophoraisoflavanone A, inhibited COX-1 activity. Of the COX-1 inhibiting prenylated flavonoids, kuraridin, kurarinone, and sophoraflavanone G, all having a C-8 lavandulyl moiety, showed potent activity (ic(50) = 0.1 to 1 microM) comparable to that of indomethacin (ic(50) = 0.7 microM). Most of the prenylated flavonoids tested inhibited 5-LOX activity with ic(50) values ranging from 0.09 to 100 microM. Of these, only kuwanon C, papyriflavonol A and sophoraflavanone G showed inhibitory activity against 12-LOX at low concentration ranges (ic(50) = 19-69 microM) comparable to that of NDGA (ic(50) = 2.6 microM). Our results suggest that the position and the nature of the prenyl substitution greatly influence in vitro biological activities of these molecules.

Anti-inflammatory activities of LDP-392, a dual PAF receptor antagonist and 5-lipoxygenase inhibitor

Leukotrienes (LTs) and platelet-activating factor (PAF) are important mediators of inflammation and allergy. LDP-392, a novel dual PAF receptor antagonist and 5-lipoxygenase (5-LO) inhibitor, has been identified. LDP-392 is 17.9-fold more potent than zileuton (5-LO inhibitor) in the RBL cytosolic 5-LO assay, and equally potent as MK 287 (PAF receptor antagonist) in the human platelet PAF receptor binding assay. The in vivo dual activities of LDP-392 were confirmed by measuring the inhibition of ex vivo LTB(4)production in rats and PAF-induced hemoconcentration in mice. Intravenous administration of LDP-392 demonstrated greater inhibition than zileuton, BN 50739 or MK 287 on arachidonic acid-induced ear edema and protected mice from LPS-induced lethality. Topical administration of LDP-392, in a dose-dependent manner, inhibited TPA-induced ear edema in mice and UVB-induced erythema in guinea-pigs. These data suggest that LDP-392, as a dual PAF receptor antagonist and 5-LO inhibitor, may be of greater clinical effectiveness.

The N-terminal "beta-barrel" domain of 5-lipoxygenase is essential for nuclear membrane translocation

5-Lipoxygenase is the key enzyme in the formation of leukotrienes, which are potent lipid mediators of asthma pathophysiology. This enzyme translocates to the nuclear envelope in a calcium-dependent manner for leukotriene biosynthesis. Eight green fluorescent protein (GFP)-lipoxygenase constructs, representing the major human and mouse enzymes within this family, were constructed and their cDNAs transfected into human embryonic kidney 293 cells. Of these eight lipoxygenases, only the 5-lipoxygenase was clearly nuclear localized and translocated to the nuclear envelope upon stimulation with the calcium ionophore. The N-terminal "beta -barrel" domain of 5-lipoxygenase, but not the catalytic domain, was necessary and sufficient for nuclear envelope translocation. The GFP-N-terminal 5-lipoxygenase domain translocated faster than GFP-5-lipoxygenase. beta-Barrel/catalytic domain chimeras with 12- and 15-lipoxygenase indicated that only the N-terminal domain of 5-lipoxygenase could carry out this translocation function. Mutations of iron atom binding ligands (His550 or deletion of C-terminal isoleucine) that disrupt nuclear localization do not alter translocation capacity indicating distinct determinants of nuclear localization and translocation. Moreover, data show that GFP-5-lipoxygenase beta-barrel containing constructs can translocate to the nuclear membrane whether cytoplasmic or nuclear localized. Thus, the predicted beta-barrel domain of 5-lipoxygenase may function like the C2 domain within protein kinase C and cytosolic phospholipase A(2) with unique determinants that direct its localization to the nuclear envelope.

Localization and regulation of cytosolic phospholipase A(2)

Liberation of arachidonic acid by cytosolic phospholipase A(2) (cPLA(2)) upon cell activation is often the initial and rate-limiting step in leukotriene and prostaglandin biosynthesis. This review discusses the essential features of cPLA(2) isoforms and addresses intriguing insights into the catalytic and regulatory mechanisms. Gene expression, posttranslational modification and subcellular localization can regulate these isoforms. Translocation of cPLA(2)alpha from the cytosol to the perinuclear region in response to calcium transients is critical for the immediate arachidonic acid release. Therefore, particular emphasis is placed on the mechanism of the translocation and the role of the proteins and lipids implicated in this process. The regional distribution and cellular localization of cPLA(2) may help to better understand its function as an arachidonic acid supplier to downstream enzymes and as a regulator of specific cellular processes.

Arachidonic acid metabolic pathways regulating activity of renal Na(+)-K(+)-ATPase are age dependent

Locally formed arachidonic acid (AA) metabolites are important as modulators of many aspects of renal tubular function, including regulation of the activity of tubular Na(+)-K(+)-ATPase. Here we examined the ontogeny of the AA metabolic pathways regulating proximal convoluted tubular (PCT) Na(+)-K(+)-ATPase activity in infant and adult rats. Eicosatetraynoic acid, an inhibitor of all AA-metabolizing pathways, abolished this effect. AA inhibition of PCT Na(+)-K(+)-ATPase was blocked by the 12-lipoxygenase inhibitor baicalein in infant but not in adult rats and by the specific cytochrome P-450 fatty acid omega-hydroxylase inhibitor 17-octadecynoic acid in adult but not in infant rats. The lipoxygenase metabolite 12(S)-hydroxyeicosatetraenoic acid (HETE) and the cytochrome P-450 metabolite 20-HETE both inhibited PCT Na(+)-K(+)-ATPase in a protein kinase C-dependent manner, but the effect was significantly more pronounced in infant PCT. Lipoxygenase mRNA was only detected in infant cortex. Expression of renal isoforms of cytochrome P-450 mRNA was more prominent in adult cortex. In summary, the AA metabolic pathways that modulated the activity of rat renal proximal tubular Na(+)-K(+)-ATPase are age dependent.

An anti-platelet agent, OPC-29030, inhibits translocation of 12-lipoxygenase and 12-hydroxyeicosatetraenoic acid production in human platelets

1. In human platelets, arachidonic acid is mainly metabolized by the two enzyme systems; cyclo-oxygenase and 12-lipoxygenase. Cyclo-oxygenase produces prostaglandin H(2) which is further converted to thromboxane B(2). 12-Lipoxygenase synthesizes 12(S)-hydroperoxyeicosatetraenoic acid which is reduced to 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE). 2. An anti-platelet compound, OPC-29030, dose-dependently inhibited 12(S)-HETE production with an IC(50) of 0.06+/-0.01 microM, but not synthesis of thromboxane B(2) in human platelets. Although the compound suppressed 12(S)-HETE production in human platelets, cytosolic 12-lipoxygenase activity was not inhibited up to 10 microM. Essentially identical data were obtained with a 12-lipoxygenase of human erythroleukaemia cells which had megakaryocyte/platelet-like properties. 3. OPC-29030 also suppressed production of 5(S)-HETE, a 5-lipoxygenase product, in rat basophilic leukaemia cells without inhibiting enzyme activity. It has been shown that 5-lipoxygenase binds to membrane 5-lipoxygenase-activating protein (FLAP) to produce 5(S)-HETE, and thus FLAP inhibitor suppresses cellular 5(S)-HETE production. 4. A FLAP inhibitor, L-655,238, suppressed platelet 12(S)-HETE production, but had no effect on the 12-lipoxygenase activity. 5. Western blot analysis showed that platelet 12-lipoxygenase translocated from cytosol to membranes upon thrombin stimulation, and OPC-29030 suppressed this process in a dose-dependent manner. 6. These results suggest that the 12-lipoxygenase of human platelets binds to FLAP or a similar protein, and OPC-29030 suppresses 12(S)-HETE production by inhibiting a certain step of the 12-lipoxygenase translocation.

The biology of 5-lipoxygenase: function, structure, and regulatory mechanisms

5-Lipoxygenase (5-LO) catalyzes the two-step conversion of arachidonic acid to leukotriene A4 (LTA4). The first step consists of the oxidation of arachidonic acid to the unstable intermediate 5-hydroperoxyeicosatetraenoic acid (5-HPETE), and the second step is the dehydration of 5-HPETE to form LTA4. These events are the first committed reactions leading to the synthesis of all leukotrienes and play a critical role in controlling leukotriene production. 5-LO has evolved many complex structural features and regulatory mechanisms to allow it to fulfill this highly specialized role. The biology of 5-LO is reviewed here with an emphasis on enzymatic function, protein and gene structure, essential cofactors, and the many regulatory mechanisms controlling its expression.

Inhibitory effect of phospholipid hydroperoxide glutathione peroxidase on the activity of lipoxygenases and cyclooxygenases

The partially purified phospholipid hydroperoxide glutathione peroxidase (PHGPx) from A431 cells was used to systematically compare the inhibitory effect on the enzyme activity of various lipoxygenases and cyclooxygenases. Under the standard assay system, platelet 12-lipoxygenase, 15-lipoxygenase, and cyclooxygenase-2 were the most sensitive to the inhibition by PHGPx. 5-Lipoxygenase and cyclooxygenase-1 were less sensitive to the inhibition by PHGPx than platelet 12-lipoxygenase and cyclooxygenase-2, respectively, and the difference was approximately 10-fold. Reduction of 12(S)-hydroperoxyeicosatetraenoic acid to 12(S)-hydroxyeicosatetraenoic acid by PHGPx was observed in the presence of glutathione (GSH), and the inhibitory effect of PHGPx on 12-lipoxygenase-catalyzed arachidonate metabolism was reversed by the addition of exogenous lipid hydroperoxide. The results indicate that PHGPx directly reduced lipid hydroperoxides and then down-regulated the activity of arachidonate oxygenases. Moreover, a high-level expression of PHGPx mRNA and its 12-lipoxygenase-inhibitory activity was observed in cancer cells and endothelial cells, and these results suggest that PHGPx may play a significant role in the regulation of reactive oxygen species formation in these cells.

Novel polymorphism of the 5-lipoxygenase activating protein (FLAP) promoter gene associated with asthma

The human 5-lipoxygenase activating protein (FLAP) gene is one of the key genes involved in the production of the cysteinyl-leukotrienes. We studied novel polymorphism of the FLAP promoter gene and attempted to clarify the relationship between this polymorphism and asthma. We sequenced the FLAP promoter region, containing the -170 to +46-bp sequence from the translational start codon, and found two homozygotes of novel alleles in the polyadenyl region which showed 21 A repeats and 18 A repeats, respectively. The frequency of the 21 A repeats was 52/71 (73.2%) in asthmatics and 39/71 (54.9%) in control subjects. The difference between these frequencies was statistically significant (P = 0.035). This is the first report of FLAP promoter gene polymorphism associated with asthma. Our data suggest that FLAP promoter gene polymorphism might play a crucial role in the pathogenesis of asthma.

Leukotriene A synthase activity of purified mouse skin arachidonate 8-lipoxygenase expressed in Escherichia coli

Mouse skin 8-lipoxygenase was expressed in COS-7 cells by transient transfection of its cDNA in pEF-BOS carrying an elongation factor-1alpha promoter. When crude extract of the transfected COS-7 cells was incubated with arachidonic acid, 8-hydroxy-5,9,11, 14-eicosatetraenoic acid was produced as assessed by reverse- and straight-phase high performance liquid chromatographies. The recombinant enzyme also reacted on alpha-linolenic and docosahexaenoic acids at almost the same rate as that with arachidonic acid. Eicosapentaenoic and gamma-linolenic acids were also oxygenated at 43% and 56% reaction rates of arachidonic acid, respectively. In contrast, linoleic acid was a poor substrate for this enzyme. The 8-lipoxygenase reaction with these fatty acids proceeded almost linearly for 40 min. The 8-lipoxygenase was also expressed in an Escherichia coli system using pQE-32 carrying six histidine residues at N-terminal of the enzyme. The expressed enzyme was purified over 380-fold giving a specific activity of approximately 0.2 micromol/45 min per mg protein by nickel-nitrilotriacetate affinity chromatography. The enzymatic properties of the purified 8-lipoxygenase were essentially the same as those of the enzyme expressed in COS-7 cells. When the purified 8-lipoxygenase was incubated with 5-hydroperoxy-6,8,11, 14-eicosatetraenoic acid, two epimers of 6-trans-leukotriene B4, degradation products of unstable leukotriene A4, were observed upon high performance liquid chromatography. Thus, the 8-lipoxygenase catalyzed synthesis of leukotriene A4 from 5-hydroperoxy fatty acid. Reaction rate of the leukotriene A synthase was approximately 7% of arachidonate 8-lipoxygenation. In contrast to the linear time course of 8-lipoxygenase reaction with arachidonic acid, leukotriene A synthase activity leveled off within 10 min, indicating suicide inactivation.

Affinities of various mammalian arachidonate lipoxygenases and cyclooxygenases for molecular oxygen as substrate

In an attempt to study affinities for molecular oxygen of mammalian arachidonate oxygenases, which remain unclarified at present, we determined activities of platelet-type 12-lipoxygenase, leukocyte-type 12-lipoxygenase, 5-lipoxygenase, 15-lipoxygenase, cyclooxygenase-1 and cyclooxygenase-2 at various oxygen concentrations. Activities of all the tested enzymes were assessed by oxygenation of radioactive arachidonic acid under hypoxic conditions, and part of the enzymes were also assayed by monitoring oxygen consumption. Their Km values for oxygen ranged between 10 and 26 microM. These results should be considered in investigations of arachidonic acid metabolism in pathophysiological processes associated with hypoxia.

Determinants of 5-lipoxygenase nuclear localization using green fluorescent protein/5-lipoxygenase fusion proteins

5-Lipoxygenase catalyzes the first two steps in the biosynthesis of leukotrienes, potent extracellular mediators of inflammation and allergic disorders. The unanticipated observation of 5-lipoxygenase in the nucleus of some cell types including bone marrow-derived mast cells (Chen, X. S., Naumann, T. A., Kurre, U., Jenkins, N. A., Copeland, N. G., and Funk, C. D. (1995) J. Biol. Chem. 270, 17993-17999) has raised speculation about intranuclear actions of leukotrienes or the enzyme itself. To explore the entry of 5-lipoxygenase into the nucleus we have transfected various cell types with expression vectors encoding native 5-lipoxygenase and green fluorescent protein/5-lipoxygenase (GFP-5LO) fusion proteins. 5-Lipoxygenase and green fluorescent protein/5-lipoxygenase co-localized with the nuclear DNA stain Hoechst 33258 in each cell type. The three main basic regions of 5-lipoxygenase were incapable of acting as "classical" nuclear localization signal sequences. Mutations that abolished enzyme activity/non-heme iron resulted in proteins that would no longer enter the nucleus. An NH2-terminal 5-lipoxygenase fragment of 80 residues was sufficient for directing nuclear localization of green fluorescent protein but not cytosolic pyruvate kinase. The combined data suggest that 5-lipoxygenase enters the nucleus not by a classical nuclear localization signal but by a non-conventional signal located in the predicted beta-barrel domain that may be masked by structural alterations.

A selective inhibitor of arachidonate 5-lipoxygenase scavenging peroxide activator

A novel compound termed YT-18 (2,3-dihydro-2,4,6,7-tetramethyl-2-[(4-phenyl-1-piperazinyl) methyl]-5-benzofuranamine) selectively inhibited 5-lipoxygenases of porcine leukocytes (IC50 value, 7.5 microM), human leukocytes (1.5 microM), and rat basophilic leukemia cells (14 microM), which are responsible for bioactive leukotriene synthesis. In contrast, the compound up to 1 mM had almost no effect on 12-lipoxygenases of leukocytes and platelets, 15-lipoxygenase, and cyclooxygenases-1 and -2. YT-18 also inhibited the leukotriene synthesis in intact rat basophilic leukemia cells. In the 5-lipoxygenase reaction, YT-18 caused a lag phase, thereby delaying the start of the reaction. The lag was abolished by the addition of 13-hydroperoxy-linoleic acid in a dose-dependent manner, and most (but not all) of the reduced 5-lipoxygenase activity was recovered.

Physiochemical characterization of ATP binding to human 5-lipoxygenase

Human 5-lipoxygenase requires ATP as a stimulatory factor. At the two preferred concentrations of the free Ca2+, 0.02 microM with a resting cell and 20 microM with a stimulated cell, Scatchard analysis revealed that 5-lipoxygenase has one affinity ATP binding site with a Kd of 4.6 microM at the low Ca2+ concentration but has two affinity ATP binding sites with a higher Kd of 4.4 microM and a lower Kd of 14.5 microM at the high Ca2+ concentration. In contrast, in a Tween 20 reaction system, 5-lipoxygenase had similar activation coefficients for ATP at both Ca2+ concentrations; these were 12.7 microM at the low Ca2+ concentration and 12.0 microM at the high Ca2+ concentration. These results showed that 5-lipoxygenase has an ATP binding site and suggest that self-association of 5-lipoxygenase in 20 microM Ca2+ may affect ATP binding affinity as measured by Scatchard analysis.

Suicide inactivation of porcine leukocyte 12-lipoxygenase associated with its incorporation of 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid derivative

Two isozymes of arachidonate 12-lipoxygenase, platelet-type and leukocyte-type, which were distinguished by their substrate specificities and primary structures, were investigated with reference to 'suicide' inactivation. Upon reaction with arachidonic acid the leukocyte-type enzyme was inactivated rapidly during the catalysis, whereas the platelet-type enzyme did not show such a rapid inactivation. The two 12-lipoxygenase isozymes were incubated with various hydroperoxy and hydroxy products from arachidonic acid. (15S)-Hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) was found to be a unique substrate of the leukocyte-type 12-lipoxygenase as follows. (1) 15-HPETE was an active substrate for porcine leukocyte 12-lipoxygenase, and converted anaerobically to a 14,15-epoxy compound (14,15-leukotriene A4). (2) A rapid inactivation of the enzyme was observed within 2 min upon aerobic and anaerobic incubations with 15-HPETE. (3) 15-HPETE was rapidly incorporated into the enzyme in a nearly equimolar amount under both aerobic and anaerobic conditions. (4) Several findings suggested a covalent binding of 15-HPETE or its derivative to the enzyme. (5) Such a rapid and stoichiometric incorporation of 15-HPETE was not observed with the platelet-type 12-lipoxygenase. On the basis of these findings we presumed that 15-HPETE was transformed to 14,15-leukotriene A4, which was covalently bound to the leukocyte-type 12-lipoxygenase leading to the suicide inactivation of the enzyme.

cDNA cloning, expression, and mutagenesis study of leukotriene B4 12-hydroxydehydrogenase

Leukotriene B4 12-hydroxydehydrogenase catalyzes the conversion of leukotriene B4 into its biologically less active metabolite, 12-oxo-leukotriene B4. This is an initial and key step of metabolic inactivation of leukotriene B4 in various tissues other than leukocytes. Here we report the cDNA cloning for porcine and human enzymes from kidney cDNA libraries. A full-length cDNA of the porcine enzyme contains an open reading frame consisting of 987 base pairs, corresponding to 329 amino acids. The human enzyme showed a 97.1% homology with the porcine enzyme. Northern blotting of human tissues revealed its high expression in the kidney, liver, and intestine but not in leukocytes. The porcine enzyme was expressed as a glutathione S-transferase fusion protein in Escherichia coli, which exhibited similar characteristics with the native enzyme. Because the enzymes have a homology, in part, with NAD(P)(+)-dependent alcohol dehydrogenases, a site-directed mutagenesis study was carried out. We found that three glycines at 152, 155, and 166 have crucial roles in the enzyme activity, possibly by producing an NADP+ binding pocket.

Oxidative inactivation of human 5-lipoxygenase in phosphatidylcholine vesicles

Human 5-lipoxygenase is a non-heme iron protein which possesses 5-oxygenase, leukotriene A4 synthase and pseudoperoxidase activities and which undergoes a rapid irreversible inactivation during these reactions. The inactivation of the enzyme was dependent on the structural characteristics of the substrate for the reaction, on O2 concentration and on exposure to phospholipids and calcium. The apparent first-order rate constant for enzyme inactivation (k(in)) was 0.6 min(-1) during the oxygenation of arachidonic acid in air-saturated buffer containing phosphatidylcholine vesicles and Ca2+. The rate of enzyme inactivation was dependent on the substrate for the reaction and was about threefold slower during the oxygenation of 5,8-icosadienoic acid and 12(S)-hydroxyicosatetraenoic acid compared with arachidonic acid. Lowering the 02 concentration to 60 microM during the oxygenation of arachidonic acid also caused a 2.5-fold decrease in k(in) without affecting the initial rate of the reaction resulting in an increase in both 5-hydroperoxyicosatetraenoic acid (5-HPETE) and leukotriene A4 accumulation. The concentration of 02 for half-maximal activity (initial rate and product accumulation) was approximately 10 microM. In contrast, the activity and the rate of inactivation during the leukotriene A4 synthase reaction with exogenous 5-HPETE (k(in)=2.0 min(-1) were independent of 02 concentration. A rapid inactivation of the enzyme was also observed during aerobic incubation with phosphatidylcholine vesicles and Ca2+ in the absence of substrate, with a sequential loss of the oxygenase (t1/2 = 0.5 min) and pseudoperoxidase (t1/2 = 7 min) activities. Protection against this turnover-independent inactivation was observed in the presence of the selective reversible 5-lipoxygenase inhibitor L-739,010 ([1S, 5R] 3-cyano-1-(3-furyl)-6-(6-[3-(3 alpha-hydroxy-6,8-dioxyabicyclo [3.2.11 octanyl)] pyridin-2-ylmethoxy) naphthalene) and by prior treatment of vesicles with sodium borohydride and, to a lesser extent, by glutathione peroxidase. The results show that the inactivation of 5-lipoxygenase in phospholipid vesicles is dependent on the structure of the unsaturated fatty acid substrate for the reaction, on the concentration of oxygen and on a turnover-independent oxidation at the active-site leading to the sequential loss of the oxygenase and pseudoperoxidase activities of the enzyme.

Lipoxygenase-catalyzed oxygenation of arachidonylethanolamide, a cannabinoid receptor agonist

Various purified lipoxygenases were incubated with [14C]arachidonylethanolamide which is an endogenous ligand for cannabinoid receptors. When radioactive products were analyzed by thin-layer chromatography, porcine leukocyte 12-lipoxygenase and rabbit reticulocyte and soybean 15-lipoxygenases produced polar compounds at about the same reaction rates as that of oxygenation of free arachidonic acid. In contrast, the reaction of human platelet 12-lipoxygenase proceeded at a much lower rate, and porcine leukocyte 5-lipoxygenase was totally inactive. The result indicated that the lipoxygenases, which had been shown previously to be capable of oxygenating esterified polyunsaturated fatty acids, were also active with the arachidonylethanolamide. High-performance liquid chromatography, ultraviolet and mass spectrometry and nuclear magnetic resonance spectroscopy identified the major product by leukocyte 12-lipoxygenase as 12-hydroperoxy-5,8,10,14-eicosatetraenoylethanolamide and that by 15-lipoxygenases as 15-hydroperoxy-5,8,11,13-eicosatetraenoylethanolamide. The 15-hydroxy derivative inhibited electrically-evoked contraction of mouse vas deferens with an IC50 of 0.63 microM as well as arachidonylethanolamide (0.17 microM), but the 12-hydroxy derivative was much less effective.

Panaxynol, a polyacetylene compound isolated from oriental medicines, inhibits mammalian lipoxygenases

Panaxynol is a polyacetylene compound isolated from commonly used oriental medicines, and its effects on various cyclooxygenases and lipoxygenases were investigated. The compound had only a marginal effect on cyclooxygenase activities (IC50 values >> 100 microM), but inhibited lipoxygenases; 5-lipoxygenase (IC50, 2 microM), two isoforms of 12-lipoxygenase (leukocyte-type, 1 microM; platelet-type, 67 microM) and 15-lipoxygenase (4 microM). Thus, panaxynol inhibited leukocyte-type 12-lipoxygenase much more effectively than platelet-type 12-lipoxygenase. Falcarindiol, an analogue of panaxynol, inhibited these lipoxygenases with higher IC50 values than panaxynol. These compounds could provide a clue to develop a selective inhibitor of one isoform of 12-lipoxygenase.