Arachidonate 12-lipoxygenases with reference to their selective inhibitors

Improvement of Health-Promoting Functionality of Rye Bread by Fortification with Free and Microencapsulated Powders from Amelanchier alnifolia Nutt

This study established the appropriate amounts of a functional Saskatoon berry fruit powder in fortified rye bread acceptable to consumers and determined the potential relative bioaccesibility of bioactive compounds exhibiting antioxidant activity, and enzymatic in vitro inhibitory activity against lipoxygenase, cyclooxigenase-1, cyclooxigenase-2, acetylcholinesterase, pancreatic lipase α-glucosidase, and α-amylase, as well as the relative digestibility of nutrients. The content of polyphenolic compounds and antioxidant capability were strongly, positively correlated with the content of the functional additive. The highest phenolics content and antioxidant activity were determined in the products enriched with the powders microencapsulated with maltodextrin (an increase by 91% and 53%, respectively, compared with the control). The highest overall acceptability was shown for the products with 3% addition of the functional additive, regardless of its type. The simulated in vitro digestion released phenols (with the highest bioaccessibility shown for anthocyanins) and enhanced the antioxidant activity of rye bread. In turn, the microencapsulation contributed to the improvement in the relative bioaccesibility of antioxidant compounds. Bread fortification led to an increased inhibitory activity against α-amylase, α-glucosidase, and lipoxygenase. Furthermore, the additive microencapsulated with maltodextrin and inulin improved the capacity to inhibit the activities of pancreatic lipase and cyclooxigenase-2. The results presented allowed concluding that the powders from Saskatoon berry fruits, especially microencapsulated ones, may be a promising functional additive dedicated for the enrichment of rye bread.

Anti-Inflammatory Activity of a Polymeric Proanthocyanidin from Serjania schiedeana

The ethyl acetate extract (SsAcOEt) from Serjania schiedeana, select fractions (F-6, F-12, F-13, F-14), and one isolated compound, were evaluated in 12-O-tetradecanoylphorbol 13-acetate (TPA) ear edema and kaolin/carrageenan (KC)-induced monoarthritis assays. SsEtOAc induced edema inhibition of 90% (2.0 mg/ear), fractions showed activity within a range of 67–89%. Due to the fact F-14 showed the highest effect, it was separated, yielding a proanthocyanidin-type called epicatechin–(4β → 8)–epicatechin–(4β → 8, 2β → O → 7) epicatechin (ETP). This compound (2.0 mg/ear) provoked 72% of edema inhibition (ED50 = 0.25 mg/ear, Emax = 52.9%). After 9 days of treatment, joint inflammation was decreasing, and on the last day, SsEtOAc (400 mg/kg), F-14 and ETP (10 mg/kg), SsEtOAc (200 mg/kg), methotrexate (MTX) 1.0 mg/kg and meloxicam (MEL) 1.5 mg/kg, produced an inhibition articulate edema of 94, 62, 36, 21, 80, and 54%, respectively. In the joint, pro-inflammatory molecules were elevated in animals without treatment (vehicle group, VEH). Treatments from S. schiedeana induced a decrease in the concentration of interleukin (IL)-1β, IL-17, and IL-6, and SsEtOAc at a higher dose diminished tumor necrosis factor (TNF-α). IL-10 and IL-4 were fewer in the VEH group in comparison with healthy mice; the animals with treatments from S. schiedeana induced an increment in the levels of these cytokines in joint and spleen.

Two new monoterpene glycosides from Qing Shan Lu Shui tea with inhibitory effects on leukocyte-type 12-lipoxygenase activity

We evaluated the inhibitory effect of 12 Chinese teas on leukocyte-type 12-lipoxygenase (LOX) activity. Tea catechins such as epigallocatechin gallate have been known to exhibit leukocyte-type 12-LOX inhibition. Qing Shan Lu Shui, which contains lower catechin levels than the other tested teas, suppressed leukocyte-type 12-LOX activity. To characterize the bioactive components of Qing Shan Lu Shui, leukocyte-type 12-LOX inhibitory activity–guided fractionation of the aqueous ethanol extract of the tea was performed, resulting in the isolation of two new monoterpene glycosides: liguroside A (1) and B (2). The structures of compounds 1 and 2 were characterized as (2E,5E)-7-hydroperoxy-3,7-dimethyl-2,5-octadienyl-O-(α-l-rhamnopyranosyl)-(1″→3′)-(4′″-O-trans-p-coumaroyl)-β-d-glucopyranoside and (2E,5E)-7-hydroperoxy-3,7-dimethyl-2,5-octa-dienyl-O-(α-l-rhamnopyranosyl)-(1″→3′)-(4′″-O-cis-p-coumaroyl)-β-d-glucopyranoside, respectively, based on spectral and chemical evidence. Ligurosides A (1) and B (2) showed inhibitory effects on leukocyte-type 12-LOX activity, with IC₅₀ values of 1.7 and 0.7 μM, respectively.

12-lipoxygenase: a potential target for novel anti-platelet therapeutics

Platelets play an essential role in the regulation of hemostasis and thrombosis and controlling their level of activation is central to prevention of occlusive clot formation and stroke. Although a number of anti-platelet targets have been identified to address this issue including COX-1, the P2Y(12) receptor, the integrin αIIbβ3, and more recently the protease-activated receptor-1, these targets often result in a significant increased risk of bleeding which may lead to pathologies as serious as the thrombosis they were meant to treat including intracranial hemorrhage and gastrointestinal bleeding. Therefore, alternative approaches to treat uncontrolled platelet activation are warranted. Platelet-type 12-lipoxygenase is an enzyme which oxidizes the free fatty acid in the platelet resulting in the production of the stable metabolite 12-hydroxyeicosatetraenoic acid (12-HETE). The role of 12-HETE in the platelet has been controversial with reports associating its function as being both anti- and pro-thrombotic. In this review, the role of 12-lipoxygenase and its bioactive metabolites in regulation of platelet reactivity, clot formation, and hemostasis is described. Understanding the mechanisms by which 12-lipoxygenase and its metabolites modulate platelet function may lead to the development of a novel class of anti-platelet therapies targeting the enzyme in order to attenuate injury-induced clot formation, vessel occlusion and pathophysiological shifts in hemostasis.

Discovery of potent and selective inhibitors of human platelet-type 12- lipoxygenase

We report the discovery of novel small molecule inhibitors of platelet-type 12-human lipoxygenase, which display nanomolar activity against the purified enzyme, using a quantitative high-throughput screen (qHTS) on a library of 153607 compounds. These compounds also exhibit excellent specificity, >50-fold selectivity vs the paralogues, 5-human lipoxygenase, reticulocyte 15-human lipoxygenase type-1, and epithelial 15-human lipoxygenase type-2, and >100-fold selectivity vs ovine cyclooxygenase-1 and human cyclooxygenase-2. Kinetic experiments indicate this chemotype is a noncompetitive inhibitor that does not reduce the active site iron. Moreover, chiral HPLC separation of two of the racemic lead molecules revealed a strong preference for the (-)-enantiomers (IC(50) of 0.43 ± 0.04 and 0.38 ± 0.05 μM) compared to the (+)-enantiomers (IC(50) of >25 μM for both), indicating a fine degree of selectivity in the active site due to chiral geometry. In addition, these compounds demonstrate efficacy in cellular models, which underscores their relevance to disease modification.

Cinnamyl-3,4-dihydroxy-α-cyanocinnamate is a potent inhibitor of 5-lipoxygenase

Lipoxygenases (LOs) are iron-containing enzymes that catalyze the conversion of arachidonic acid into hydroperoxyeicosatetraenoic acids (HPETEs) and other bioactive lipid mediators. In mammals, 5-LO, 15-LO, and 12-LO enzymes seem to have distinct roles in pathophysiological contexts, which have emphasized the need for selective inhibitors. Cinnamyl-3,4-dihydroxy-α-cyanocinnamate (CDC) has been proposed as potent and selective inhibitor of platelet-type 12-LO (p12-LO). Here, we re-evaluated the selectivity profile of CDC on LOs, and we show that CDC is a potent and direct inhibitor of 5-LO. CDC reduced 5-LO activity in cell-free assays (purified human recombinant enzyme or leukocyte homogenates), with IC(50) values in the low nanomolar range (9-25 nM) and a selectivity index of approximately 35 and 15 over p12-LO and 15-LO1, respectively. Likewise, CDC inhibited 5-LO product formation in intact human polymorphonuclear leukocytes and monocytes (IC(50) = 0.45-0.8 μM). A lower potency was observed for 15-LO1, whereas p12-LO activity in platelets was hardly affected. In human whole blood, CDC efficiently reduced the formation of 5-LO products, and similar effects were observed for 12(S)-H(P)ETE and 15(S)-H(P)ETE. Finally, CDC (3.5 and 7 mg/kg i.p.) was effective in vivo in the platelet-activating factor-induced shock in mice and reduced formation of the 5-LO product leukotriene B(4) in the rat carrageenan-induced pleurisy after a single oral dose of 10 mg/kg. Together, our data demonstrate that CDC is a potent inhibitor of 5-LO with efficacy in vivo and encourage further development of CDC as the lead compound.

Cytoprotective effects of vitamin E homologues against glutamate-induced cell death in immature primary cortical neuron cultures: Tocopherols and tocotrienols exert similar effects by antioxidant function

Glutamate plays a critical role in pathological cell death within the nervous system. Vitamin E is known to protect cells from glutamate cytotoxicity, either by direct antioxidant action or by indirect nonantioxidant action. Further, α-tocotrienol (α-T3) has been reported to be more effective against glutamate-induced cytotoxicity than α-tocopherol (α-T). To shed more light on the function of vitamin E against glutamate toxicity, the protective effects of eight vitamin E homologues and related compounds, 2,2,5,7,8-pentamethyl-6-chromanol (PMC) and 2-carboxy-2,5,7,8-pentamethyl-6-chromanol (Trolox), against glutamate-induced cytotoxicity on immature primary cortical neurons were examined using different protocols. Glutamate induced the depletion of glutathione and generation of reactive oxygen species and lipid hydroperoxides, leading to cell death. α-, β-, γ-, and δ-T and -T3; PMC; and Trolox all exerted cytoprotective effects against glutamate-induced cytotoxicity, and a longer preincubation time increased both the cellular content and the cytoprotective effects of T more significantly than those of T3, the effect of preincubation being relatively small for T3 and PMC. The protective effect of Trolox was less potent than that of PMC. The cytoprotective effects of α-T and α-T3 corresponded to their intracellular content. Further, lipid peroxidation products were measured after reduction with triphenylphosphine followed by saponification with potassium hydroxide. It was found that glutamate treatment increased the formation of hydroxyeicosatetraenoic acid, hydroxyoctadecadienoic acid, and 8-F(2)-isoprostane 2α, which was suppressed by α-T. This study shows that vitamin E protects cells from glutamate-induced toxicity primarily by direct antioxidant action and that the apparent higher capacity of T3 compared to T is ascribed to the faster uptake of T3 compared to T into the cells. It is suggested that, considering the bioavailability, α-T should be more effective than α-T3 against glutamate toxicity in vivo.

Lipoxygenase inhibitory constituents from rhubarb

Phytochemical study on the ethanol extract of rhubarb led to the isolation of fifteen compounds, including five anthraquinones: chrysophanol (1), physcion (2), emodin (7), chrysophanol-8-O-beta-D: -glucopyranoside (9) and emodin-8-O-beta-D: -glucopyranoside (15), and ten stilbenes: desoxyrhaponticin (3), rhaponticin (4), resveratrol (5), desoxyrhapotigenin (6), rhapontigenin (8), piceatannol-3'-O-beta-D: -glucopyranoside (10), piceid (11), epsilon-viniferin (12), ampelopsin B (13) and isorhaponticin (14). Their structures were identified by comparing the physicochemical data with those of published papers. Among the isolated compounds, stilbene derivatives (3-6, 8 and 10-14) showed remarkable inhibitory effect on lipoxygenase with IC(50) values ranging from 6.7 to 74.1 microM. The inhibition kinetics analyzed by Lineweaver-Burk plots found that they were competitive inhibitors with the linoleic acid at the active site of lipoxygenase. In addition, stilbenes exhibited significantly free radical scavenging activity against ABTS(.+) with trolox equivalent activity capacity (TEAC) values ranging from 1.16 to 4.64. Whereas, anthraquinone derivatives (1-2, 7, 9 and 15) neither inhibited lipoxygenase nor scavenged free radical ABTS(.+). These results indicated that stilbene derivatives were considerate to be mainly lipoxygenase inhibitor and free radical scavenger constituents of rhubarb.

Human platelet 12-lipoxygenase, new findings about its activity, membrane binding and low-resolution structure

Human platelet 12-lipoxygenase (hp-12LOX, 662 residues+iron nonheme cofactor) and its major metabolite 12S-hydroxyeicosatetraenoic acid have been implicated in cardiovascular and renal diseases, many types of cancer and inflammatory responses. However, drug development is slow due to a lack of structural information. The major hurdle in obtaining a high-resolution X-ray structure is growing crystals, a process that requires the preparation of highly homogenous, reproducible and stable protein samples. To understand the properties of hp-12LOX, we have expressed and studied the behavior, function and low-resolution structure of the hp-12LOX His-tagged recombinant enzyme and its mutants in solution. We have found that it is a dimer easily converted into bigger aggregates, which are soluble/covalent-noncovalent/reversible. The heavier oligomers show a higher activity at pH 8, in contrast to dimers with lower activity showing two maxima at pH 7 and pH 8, indicating the existence of two different conformers. In the seven-point C-->S mutant, aggregation is diminished, activity has one broad peak at pH 8 and there is no change in specificity. Truncation of the N(t)-beta-barrel domain (PLAT, residues 1-116) reduces activity to approximately 20% of that shown by the whole enzyme, does not affect regio- or stereospecificity and lowers membrane binding by a factor of approximately 2. "NoPLAT" mutants show strong aggregation into oligomers containing six or more catalytic domains regardless of the status of the seven cysteine residues tested. Time-of-flight mass spectrometry suggests two arachidonic acid molecules bound to one molecule of enzyme. Small angle X-ray scattering studies (16 A resolution, chi approximately 1) suggest that two hp-12LOX monomers are joined by the catalytic domains, with the PLAT domains floating on the flexible linkers away from the main body of the dimer.

Discovery of platelet-type 12-human lipoxygenase selective inhibitors by high-throughput screening of structurally diverse libraries

Human lipoxygenases (hLO) have been implicated in a variety of diseases and cancers and each hLO isozyme appears to have distinct roles in cellular biology. This fact emphasizes the need for discovering selective hLO inhibitors for both understanding the role of specific lipoxygenases in the cell and developing pharmaceutical therapeutics. To this end, we have modified a known lipoxygenase assay for high-throughput (HTP) screening of both the National Cancer Institute (NCI) and the UC Santa Cruz marine extract library (UCSC-MEL) in search of platelet-type 12-hLO (12-hLO) selective inhibitors. The HTP screen led to the characterization of five novel 12-hLO inhibitors from the NCI repository. One is the potent but non-selective michellamine B, a natural product, anti-viral agent. The other four compounds were selective inhibitors against 12-hLO, with three being synthetic compounds and one being alpha-mangostin, a natural product, caspase-3 pathway inhibitor. In addition, a selective inhibitor was isolated from the UCSC-MEL (neodysidenin), which has a unique chemical scaffold for a hLO inhibitor. Due to the unique structure of neodysidenin, steady-state inhibition kinetics were performed and its mode of inhibition against 12-hLO was determined to be competitive (K(i)=17microM) and selective over reticulocyte 15-hLO-1 (K(i) 15-hLO-1/12-hLO>30).

The two faces of the 15-lipoxygenase in atherosclerosis

Chronic inflammation plays a major role in atherogenesis and understanding the role of inflammation and its resolution will offer novel approaches to interfere with atherogenesis. The 15(S)-lipoxygenase (15-LOX) plays a janus-role in inflammation with pro-inflammatory and anti-inflammatory effects in cell cultures and primary cells and even opposite effects on atherosclerosis in two different animal species. There is evidence for a pro-atherosclerotic effect of 15-LOX including the direct contribution to LDL oxidation and to the recruitment of monocytes to the vessel wall, its role in angiotensin II mediated mechanisms and in vascular smooth muscle cell proliferation. In contrast to the pro-atherosclerotic effects of 15-LOX, there is also a broad line of evidence that 15-LOX metabolites of arachidonic and linoleic acid have anti-inflammatory effects. The 15-LOX arachidonic acid metabolite 15-HETE inhibits superoxide production and polymorphonuclear neutrophil (PMN) migration across cytokine-activated endothelium and can be further metabolized to the anti-inflammatory lipoxins. These promote vasorelaxation in the aorta and counteract the action of most other pro-inflammatory factors like leukotrienes and prostanoids. Anti-atherogenic properties are also reported for the linoleic acid oxidation product 13-HODE through inhibition of adhesion of several blood cells to the endothelium. Furthermore, there is evidence that 15-LOX is involved in the metabolism of the long-chain omega-3 fatty acid docosahexaenoic acid (DHA) leading to a family of anti-inflammatory resolvins and protectins. From these cell culture and animal studies the role of the 15-LOX in human atherosclerosis cannot be predicted. However, recent genetic studies characterized the 15-LOX haplotypes in Caucasians and discovered a functional polymorphism in the human 15-LOX promoter. This will now allow large studies to investigate an association of 15-LOX with coronary artery disease and to answer the question whether 15-LOX is pro- or anti-atherogenic in humans.

Baicalein induction of hydroxyl radical formation via 12-lipoxygenase in human platelets: an ESR study

The pro-oxidant activities of baicalein, morin, myricetin, quercetin, and rutin were examined in various cell-containing systems including human platelets, rat vascular smooth muscle cells, human umbilical vein endothelial cells (HUVECs), human THP-1 cells, and fibroblast cells. Electron spin resonance (ESR) results showed that only baicalein generated hydroxyl radicals in a resting human platelet suspension, whereas the other flavonoids showed no effects on any of the resting cell systems. A low concentration of arachidonic acid (AA) increased the intensity of hydroxyl radicals, but a high concentration inhibited it. Collagen and thrombin, platelet aggregatory agents that can cause the release of AA by platelets, enhanced baicalein-induced hydroxyl radical formation, whereas ADP and U44619 showed no significant effects. Quinacrine and 5,8,11,14-eicosatetraenoic trifluoromethyl ketone, both PLA2 inhibitors, significantly attenuated baicalein-induced hydroxyl radical formation. These results suggest that baicalein-induced hydroxyl radical formation is associated with AA metabolite enzymes in human platelets. The formation of hydroxyl radicals was significantly inhibited by lipoxygenase inhibitors including nordihydroguaiaretic acid, (-)-epicatechin, (-)-epicatechin gallate, and hinokitiol, but was not affected by desferroxamine or the heme protein inhibitors KCN and NaN3. On the other hand, semiquinone free radicals were generated when baicalein was incubated with horseradish peroxidase/H2O2 or platelets/AA. The semiquinone radicals formed in the platelets/AA system could be extensively inhibited by desferroxamine, diethylenetriaminepentaacetic acid, KCN, and NaN3, indicating that prostaglandin H synthase (PGHS)-peroxidase may be involved. The results of this study led to the proposal that baicalein induces hydroxyl radical formation via 12-lipoxygenase and induces semiquinone radical formation via PGHS-peroxidase in human platelets.