Platelet activation triggered by Chlamydia pneumoniae is antagonized by 12-lipoxygenase inhibitors but not cyclooxygenase inhibitors

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

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

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

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

Multiple omics study identifies an interspecies conserved driver for nonalcoholic steatohepatitis

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Ginkgolide B Mediated Alleviation of Inflammatory Cascades and Altered Lipid Metabolism in HUVECs via Targeting PCSK-9 Expression and Functionality

The potential of oxidized-LDL (Ox-LDL) to elicit inflammatory responses in macrophages leading to the atherosclerosis (AS) progression is well known. Since proprotein convertase subtilisin/Kexin-9 (PCSK-9), the posttranslational regulator of LDL-receptor, is associated with elevated LDL in the circulation, the present report was aimed to uncover the ameliorative effects of Ginkgolide B, a terpenic lactone from Ginkgo biloba, against Ox-LDL-induced alterations in cholesterol metabolism in HUVECs. Consequently, our results demonstrated that incubation with Ox-LDL significantly upregulated the PCSK-9 expression in HUVECs, which was significantly downregulated, both at mRNA and protein level, after Ginkgolide B treatment via subsequent suppression of sterol element binding protein (SREBP-2) expression. Moreover, Ginkgolide B-mediated inhibition of PCSK-9 activity was also validated by in silico methods which revealed that it interferes the PSCK-9 interaction with LDL-receptor (LDL-R). Interestingly, Ox-LDL-induced LDL-R expression was further enhanced by Ginkgolide B treatment in HUVECs. Moreover, Ginkgolide B treatment lead to downregulation of lectin-like Ox-LDL receptor (LOX-1) and NADPH oxidase (NOX-4) expression which was upregulated in Ox-LDL-treated HUVECs, along with the attenuation of mitochondrial ROS generation. Furthermore, Ginkgolide B significantly inhibited the augmented expression of intercellular adhesion molecule-1 (ICAM-1) and vascular adhesion molecule-1 (VCAM-1) in Ox-LDL-activated HUVECs. Ginkgolide B also significantly ameliorated the inflammatory response in Ox-LDL-activated HUVECs by suppressing the expression of IL-1α, IL-1β, IL-6, CXCL-1, CXCL-2, and monocyte chemotactic protein (MCP-1), at mRNA and protein level. Our in vitro and in silico study established that Ginkgolide B alleviated the Ox-LDL-induced inflammatory cascades and altered lipid metabolism in HUVECs by suppressing the PCSK-9 and, thus, could be established as a treasured alternative therapeutic candidate in the atherosclerosis management.

Ginkgolide B ameliorates oxidized low-density lipoprotein-induced endothelial dysfunction via modulating Lectin-like ox-LDL-receptor-1 and NADPH oxidase 4 expression and inflammatory cascades

The current study was undertaken to delineate the protective effect of Ginkgolide B, a phyto-constituent from Ginkgo biloba, on oxidized (ox)-LDL-induced endothelial dysfunction via targeting Lectin-like ox-LDL-receptor-1 (LOX-1), NADPH oxidase 4 (NOX-4), and other inflammatory proteins. Our results have shown that Ginkgolide B downregulated the expression of LOX-1 in ox-LDL-treated human umbilical vein endothelial cells (HUVECs) and RAW246.7 murine macrophages which ultimately resulted in decreased cholesterol deposits in HUVECs and RAW264.7. Moreover, Ginkgolide B suppressed the enhanced NOX4 expression, which was associated with attenuation of ROS generation in ox-LDL-stimulated HUVECs and RAW264.7 cells. Ginkgolide B also ameliorated the endothelial dysfunction by inhibiting the augmented expression of monocyte chemotactic protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) in ox-LDL-activated HUVECs. Furthermore, the enhanced expression of many inflammatory cytokines in ox-LDL-induced RAW264.7 macrophages, both at transcription and protein level, was significantly down-regulated after Ginkgolide B treatment. Ginkgolide B also illustrated atheroprotective property via suppressing the augmented expression of matrix metalloproteinase-1 and cyclooxygenase-2 in ox-LDL-stimulated RAW264.7 macrophages. In summary, our study has established that Ginkgolide B ameliorates endothelial dysfunction via targeting LOX-1, NOX-4, MCP-1, ICAM-1, and VCAM-1 along with the markers associated with inflammatory cascades and thus could be promoted as a valuable therapeutic agent in prevention and management of atherosclerosis.

Infectious Agents in Atherosclerotic Cardiovascular Diseases through Oxidative Stress

Accumulating evidence demonstrates that vascular oxidative stress is a critical feature of atherosclerotic process, potentially triggered by several infectious agents that are considered as risk co-factors for the atherosclerotic cardiovascular diseases (CVDs). C. pneumoniae has been shown to upregulate multiple enzymatic systems capable of producing reactive oxygen species (ROS) such as NADPH oxidase (NOX) and cyclooxygenase in vascular endothelial cells, NOX and cytochrome c oxidase in macrophages as well as nitric oxide synthase and lipoxygenase in platelets contributing to both early and late stages of atherosclerosis. P. gingivalis seems to be markedly involved in the atherosclerotic process as compared to A. actinomycetemcomitans contributing to LDL oxidation and foam cell formation. Particularly interesting is the evidence describing the NLRP3 inflammasome activation as a new molecular mechanism underlying P. gingivalis-induced oxidative stress and inflammation. Amongst viral agents, immunodeficiency virus-1 and hepatitis C virus seem to have a major role in promoting ROS production, contributing, hence, to the early stages of atherosclerosis including endothelial dysfunction and LDL oxidation. In conclusion, oxidative mechanisms activated by several infectious agents during the atherosclerotic process underlying CVDs are very complex and not well-known, remaining, thus, an attractive target for future research.

Chlamydia pneumoniae-Mediated Inflammation in Atherosclerosis: A Meta-Analysis

Several studies have attempted to relate the C. pneumoniae-mediated inflammatory state with atherosclerotic cardiovascular diseases, providing inconsistent results. Therefore, we performed a meta-analysis to clarify whether C. pneumoniae may contribute to the pathogenesis of atherosclerosis by enhancing inflammation. 12 case-control, 6 cross-sectional, and 7 prospective studies with a total of 10,176 patients have been included in this meta-analysis. Odds Ratio (OR) with a 95% confidence interval was used to assess the seroprevalence of C. pneumoniae and differences between levels of inflammatory markers were assessed by standard mean differences. Publication bias was performed to ensure the statistical power. hsCRP, fibrinogen, interleukin- (IL-) 6, TNF-α, and IFN-γ showed a significant increase in patients with atherosclerosis compared to healthy controls (P < 0.05), along with a higher seroprevalence of C. pneumoniae (OR of 3.11, 95% CI: 2.88–3.36, P < 0.001). More interestingly, hsCRP, IL-6, and fibrinogen levels were significantly higher in C. pneumoniae IgA seropositive compared to seronegative atherosclerotic patients (P < 0.0001). In conclusion, the present meta-analysis suggests that C. pneumoniae infection may contribute to atherosclerotic cardiovascular diseases by enhancing the inflammatory state, and, in particular, seropositivity to C. pneumoniae IgA, together with hsCRP, fibrinogen, and IL-6, may be predictive of atherosclerotic cardiovascular risk.

The role of Porphyromonas gingivalis gingipains in platelet activation and innate immune modulation

Platelets are considered to have important functions in inflammatory processes and as actors in the innate immunity. Several studies have shown associations between cardiovascular disease and periodontitis, where the oral anaerobic pathogen Porphyromonas gingivalis has a prominent role in modulating the immune response. Porphyromonas gingivalis has been found in atherosclerotic plaques, indicating spreading of the pathogen via the circulation, with an ability to interact with and activate platelets via e.g. Toll-like receptors (TLR) and protease-activated receptors. We aimed to evaluate how the cysteine proteases, gingipains, of P. gingivalis affect platelets in terms of activation and chemokine secretion, and to further investigate the mechanisms of platelet-bacteria interaction. This study shows that primary features of platelet activation, i.e. changes in intracellular free calcium and aggregation, are affected by P. gingivalis and that arg-gingipains are of great importance for the ability of the bacterium to activate platelets. The P. gingivalis induced a release of the chemokine RANTES, however, to a much lower extent compared with the TLR2/1-agonist Pam3 CSK4 , which evoked a time-dependent release of the chemokine. Interestingly, the TLR2/1-evoked response was abolished by a following addition of viable P. gingivalis wild-types and gingipain mutants, showing that both Rgp and Kgp cleave the secreted chemokine. We also demonstrate that Pam3 CSK4 -stimulated platelets release migration inhibitory factor and plasminogen activator inhibitor-1, and that also these responses were antagonized by P. gingivalis. These results supports immune-modulatory activities of P. gingivalis and further clarify platelets as active players in innate immunity and in sensing bacterial infections, and as target cells in inflammatory reactions induced by P. gingivalis infection.

Chlamydia pneumoniae infection in atherosclerotic lesion development through oxidative stress: a brief overview

Chlamydia pneumoniae, an obligate intracellular pathogen, is known as a leading cause of respiratory tract infections and, in the last two decades, has been widely associated with atherosclerosis by seroepidemiological studies, and direct detection of the microorganism within atheroma. C. pneumoniae is presumed to play a role in atherosclerosis for its ability to disseminate via peripheral blood mononuclear cells, to replicate and persist within vascular cells, and for its pro-inflammatory and angiogenic effects. Once inside the vascular tissue, C. pneumoniae infection has been shown to induce the production of reactive oxygen species in all the cells involved in atherosclerotic process such as macrophages, platelets, endothelial cells, and vascular smooth muscle cells, leading to oxidative stress. The aim of this review is to summarize the data linking C. pneumoniae-induced oxidative stress to atherosclerotic lesion development.

Transient heparin-induced platelet activation linked to generation of platelet 12-lipoxygenase. Findings from a randomised controlled trial

Previously we demonstrated that heparin administration during carotid endarterectomy (CEA) caused a marked, but transient increase in platelet aggregation to arachidonic acid (AA) and adenosine diphosphate (ADP), despite effective platelet cyclo-oxygenase-1 (COX-1) inhibition with aspirin. Here we investigated the metabolism of AA via platelet 12-lipoxygenase (12-LOX) as a possible mediator of the observed transient aspirin resistance, and compared the effects of unfractionated (UFH) and low-molecular-weight (LMWH) heparin. A total of 43 aspirinated patients undergoing CEA were randomised in the trial to 5,000 IU UFH (n=22) or 2,500 IU LMWH (dalteparin, n=21). Platelet aggregation to AA (4x10⁻³) and ADP (3x10⁻⁶) was determined, and the products of the COX-1 and 12-LOX pathways; thromboxane B₂ (TXB₂) and 12-hydroxyeicosatretraenoic acid (12-HETE) were measured in plasma, and in material released from aggregating platelets.Aggregation to AA increased significantly (~10-fold) following heparinisation (p<0.0001), irrespective of heparin type (p=0.33). Significant, but smaller (~2-fold) increases in aggregation to ADP were also seen, which were significantly lower in the platelets of patients randomised to LMWH (p<0.0001). Plasma levels of TxB2 did not rise following heparinisation (p=0.93), but 12-HETE increased significantly in the patients' plasma, and released from platelets stimulated in vitro withADP, with both heparin types (p<0.0001). The magnitude of aggregation to ADP correlated with 12-HETE generation (p=0.03). Heparin administration during CEA generates AA that is metabolised to 12-HETE via the 12-LOX pathway, possibly explaining the phenomenon of transient heparin-induced platelet activation. LMWH has less effect on aggregation and 12-HETE generation than UFH when the platelets are stimulated with ADP.

Bidirectional crosstalk between platelets and monocytes initiated by Toll-like receptor: an important step in the early defense against fungal infections?

Monocytes are important in the defense against fungal infections due to their phagocytic and immunoregulatory functions. Platelets also contribute in such immune responses through their release of soluble mediators, including chemokines as well as several other soluble mediators. Both monocytes and platelets express several Toll-like receptors (TLRs) that can recognize fungal molecules and thus initiate intracellular signaling events. TLR ligation on monocytes and platelets may thereby be an early immunological event and function as an initiator of a local proinflammatory crosstalk between platelets and monocytes resulting in (i) monocyte-induced increase of platelet activation and (ii) platelet-associated enhancement of the monocyte activation/function. These effects may have clinical implications both for the efficiency of antifungal treatment and for the predisposition to fungal infections, for example, increased predisposition in patients with thrombocytopenia/monocytopenia due to chemotherapy- or disease-induced bone marrow failure.

Purinergic receptors are required for HIV-1 infection of primary human macrophages

Macrophages play a significant role in HIV infection, viral rebound, and the development of AIDS. However, the function of host proteins in viral replication is incompletely characterized in macrophages. Purinergic receptors P2X and P2Y are major components of the macrophage immune response to pathogens, inflammation, and cellular damage. We demonstrate that these receptors are necessary for HIV infection of primary human macrophages. Inhibition of purinergic receptors results in a significant reduction in HIV replication in macrophages. This inhibition is independent of viral strain and is dose dependent. We also identify that P2X(1), P2X(7), and P2Y(1) receptors are involved in viral replication. We show that P2X(1), but not P2X(7) or P2Y(1), is necessary for HIV entry into macrophages. We demonstrate that interaction of the HIV surface protein gp120 with macrophages stimulates an increase in ATP release. Thus, we propose that HIV's binding to macrophages triggers a local release of ATP that stimulates purinergic receptors and facilitates HIV entry and subsequent stages of viral replication. Our data implicate a novel role for a family of host proteins in HIV replication in macrophages and suggest new therapeutic targets to reduce the devastating consequences of HIV infection and AIDS.

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.

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.

The role of inflammation in regulating platelet production and function: Toll-like receptors in platelets and megakaryocytes

Platelets have been extensively studied as hemostatic regulators, stopping uncontrolled flow of blood from an injured vessel and allowing for repair. However, multiple studies have shown that platelets can interact with bacterial proteins, particularly seen during sepsis and inflammation. Immune cells recognize pathogens through Toll-like Receptors (TLRs). These same receptors allow platelets to recognize bacterial proteins and regulate platelet immunity and function. This review examines the TLRs expressed on platelets and megakaryocytes and how these receptors affect the function of these cells. Through TLRs, platelets go beyond hemostatic regulation and play a pivotal role in inflammation and infection.

Helicobacter pylori urease activates blood platelets through a lipoxygenase-mediated pathway

The bacterium Helicobacter pylori causes peptic ulcers and gastric cancer in human beings by mechanisms yet not fully understood. H. pylori produces urease which neutralizes the acidic medium permitting its survival in the stomach. We have previously shown that ureases from jackbean, soybean or Bacillus pasteurii induce blood platelet aggregation independently of their enzyme activity by a pathway requiring platelet secretion, activation of calcium channels and lipoxygenase-derived eicosanoids. We investigated whether H. pylori urease displays platelet-activating properties and defined biochemical pathways involved in this phenomenon. For that the effects of purified recombinant H. pylori urease (HPU) added to rabbit platelets were assessed turbidimetrically. ATP secretion and production of lipoxygenase metabolites by activated platelets were measured. Fluorescein-labelled HPU bound to platelets but not to erythrocytes. HPU induced aggregation of rabbit platelets (ED(50) 0.28 microM) accompanied by ATP secretion. No correlation was found between platelet activation and ureolytic activity of HPU. Platelet aggregation was blocked by esculetin (12-lipoxygenase inhibitor) and enhanced approximately 3-fold by indomethacin (cyclooxygenase inhibitor). A metabolite of 12-lipoxygenase was produced by platelets exposed to HPU. Platelet responses to HPU did not involve platelet-activating factor, but required activation of verapamil-inhibitable calcium channels. Our data show that purified H. pylori urease activates blood platelets at submicromolar concentrations. This property seems to be common to ureases regardless of their source (plant or bacteria) or quaternary structure (single, di- or tri-chain proteins). These properties of HPU could play an important role in pathogenesis of gastrointestinal and associated cardiovascular diseases caused by H. pylori.

Correlation between rises in Chlamydia pneumoniae-specific antibodies, platelet activation and lipid peroxidation after percutaneous coronary intervention

We recently showed that Chlamydia pneumoniae activates platelets in vitro, with an associated oxidation of low-density lipoproteins. The aim of this study was to investigate whether C. pneumoniae is released during percutaneous coronary intervention (PCI) and, thereby, causes platelet activation and lipid peroxidation. Seventy-three patients undergoing coronary angiography and following PCI or coronary artery bypass graft (CABG) and 57 controls were included in the study. C. pneumoniae antibodies, serotonin and lipid peroxidation were measured before and 24 h, 1 month and 6 months after angiography. The results show that serum C. pneumoniae IgA concentrations were significantly higher in patients than in the controls. Furthermore, in 38% of the C. pneumoniae IgG positive patients, the C. pneumoniae IgG concentration increased 1 month after PCI. The levels of C. pneumoniae IgG antibodies 1 month after PCI correlated with plasma-lipid peroxidation (r = 0.91, P < 0.0001) and platelet-derived serotonin (r = 0.62, P = 0.02). There was no elevation in the total serum IgG 1 month after PCI. In conclusion, the present results suggest that PCI treatment of coronary stenosis releases C. pneumoniae from the atherosclerotic lesions, which leads to platelet activation and lipid peroxidation.

Role of Chlamydia pneumoniae in atherosclerosis

Cardiovascular disease, resulting from atherosclerosis, is a leading cause of global morbidity and mortality. Genetic predisposition and classical environmental risk factors explain much of the attributable risk for cardiovascular events in populations, but other risk factors for the development and progression of atherosclerosis, which can be identified and modified, may be important therapeutic targets. Infectious agents, such as Chlamydia pneumoniae, have been proposed as contributory factors in the pathogenesis of atherosclerosis. In the present review, we consider the experimental evidence that has accumulated over the last 20 years evaluating the role of C. pneumoniae in atherosclerosis and suggest areas for future research in this field.