Mechanisms of leukotriene B4--triggered monocyte adhesion

Platelet activation: a promoter for psoriasis and its comorbidity, cardiovascular disease

Psoriasis is a chronic inflammatory skin disease with a prevalence of 0.14% to 1.99%. The underlying pathology is mainly driven by the abnormal immune responses including activation of Th1, Th17, Th22 cells and secretion of cytokines. Patients with psoriasis are more likely to develop cardiovascular disease (CVD) which has been well recognized as a comorbidity of psoriasis. As mediators of hemostasis and thromboinflammation, platelets play an important part in CVD. However, less is known about their pathophysiological contribution to psoriasis and psoriasis-associated CVD. A comprehensive understanding of the role of platelet activation in psoriasis might pave the path for more accurate prediction of cardiovascular (CV) risk and provide new strategies for psoriasis management, which alleviates the increased CV burden associated with psoriasis. Here we review the available evidence about the biomarkers and mechanisms of platelet activation in psoriasis and the role of platelet activation in intriguing the common comorbidity, CVD. We further discussed the implications and efficacy of antiplatelet therapies in the treatment of psoriasis and prevention of psoriasis-associated CVD.

Blockade of the BLT1-LTB4 axis does not affect mast cell migration towards advanced atherosclerotic lesions in LDLr-/- mice

Mast cells have been associated with the progression and destabilization of advanced atherosclerotic plaques. Reducing intraplaque mast cell accumulation upon atherosclerosis progression could be a potent therapeutic strategy to limit plaque destabilization. Leukotriene B₄ (LTB₄) has been reported to induce mast cell chemotaxis in vitro. Here, we examined whether antagonism of the LTB₄-receptor BLT1 could inhibit mast cell accumulation in advanced atherosclerosis. Expression of genes involved in LTB₄ biosynthesis was determined by single-cell RNA sequencing of human atherosclerotic plaques. Subsequently, Western-type diet fed LDLr^-/- mice with pre-existing atherosclerosis were treated with the BLT1-antagonist CP105,696 or vehicle control three times per week by oral gavage. In the spleen, a significant reduction in CD11b⁺ myeloid cells was observed, including Ly6C^lo and Ly6C^hi monocytes as well as dendritic cells. However, atherosclerotic plaque size, collagen and macrophage content in the aortic root remained unaltered upon treatment. Finally, BLT1 antagonism did not affect mast cell numbers in the aortic root. Here, we show that human intraplaque leukocytes may be a source of locally produced LTB₄. However, BLT1-antagonism during atherosclerosis progression does not affect either local mast cell accumulation or plaque size, suggesting that other mechanisms participate in mast cell accumulation during atherosclerosis progression.

Role of leukotriene B4 (LTB4)-LTB4 receptor 1 signaling in post-incisional nociceptive sensitization and local inflammation in mice

Leukotriene B4 (LTB4) is a potent lipid mediator involved in the recruitment and activation of neutrophils, which is an important feature of tissue injury and inflammation. The biological effects of LTB4 are primarily mediated through the high-affinity LTB4 receptor, BLT1. Postoperative incisional pain is characterized by persistent acute pain at the site of tissue injury and is associated with local inflammation. Here, we compared the role of LTB4-BLT1 signaling in postoperative incisional pain between BLT1-knockout (BLT1KO) and wild-type (BLT1WT) mice. A planter incision model was developed, and mechanical pain hypersensitivity was determined using the von Frey test before and after incision. Local infiltration of neutrophils and inflammatory monocytes was quantified by flow cytometry. Inflammatory cytokine levels in the incised tissue were also determined. Mechanical pain hypersensitivity was significantly reduced in BLT1KO mice compared to BLT1WT mice at 2, 3, and 4 days after incision. LTB4 levels in the tissue at the incision site peaked 3 hours after the incision. Infiltrated neutrophils peaked 1 day after the incision in both BLT1KO and BLT1WT mice. The accumulation of inflammatory monocytes increased 1-3 days after the incision and was significantly more reduced in BLT1KO mice than in BLT1WT mice. In BLT1KO mice, Interleukin-1β and Tumor Necrosis Factor-α levels 1 day after the incision were significantly lower than those of BLT1WT mice. Our data suggest that LTB4 is produced and activates its receptor BLT1 in the very early phase of tissue injury, and that LTB4-BLT1 signaling exacerbates pain responses by promoting local infiltration of inflammatory monocytes and cytokine production. Thus, LTB4-BLT1 signaling is a potential target for therapeutic intervention of acute and persistent pain induced by tissue injury.

Eicosanoids in inflammation in the blood and the vessel

Polyunsaturated fatty acids (PUFAs) are structural components of membrane phospholipids in cells. PUFAs regulate cellular function through the formation of derived lipid mediators termed eicosanoids. The oxygenation of 20-carbon PUFAs via the oxygenases cyclooxygenases, lipoxygenases, or cytochrome P450, generates a class of classical eicosanoids including prostaglandins, thromboxanes and leukotrienes, and also the more recently identified hydroxy-, hydroperoxy-, epoxy- and oxo-eicosanoids, and the specialized pro-resolving (lipid) mediators. These eicosanoids play a critical role in the regulation of inflammation in the blood and the vessel. While arachidonic acid-derived eicosanoids are extensively studied due to their pro-inflammatory effects and therefore involvement in the pathogenesis of inflammatory diseases such as atherosclerosis, diabetes mellitus, hypertension, and the coronavirus disease 2019; in recent years, several eicosanoids have been reported to attenuate exacerbated inflammatory responses and participate in the resolution of inflammation. This review focused on elucidating the biosynthesis and the mechanistic signaling of eicosanoids in inflammation, as well as the pro-inflammatory and anti-inflammatory effects of these eicosanoids in the blood and the vascular wall.

Recent advances in function and structure of two leukotriene B4 receptors: BLT1 and BLT2

Leukotriene B₄ (LTB₄) is generated by the enzymatic oxidation of arachidonic acid, which is then released from the cell membrane and acts as a potent activator of leukocytes and other inflammatory cells. Numerous studies have demonstrated the physiological and pathophysiological significance of this lipid in various diseases. LTB₄ exerts its activities by binding to its specific G protein-coupled receptors (GPCRs): BLT1 and BLT2. In mouse disease models, treatment with BLT1 antagonists or BLT1 gene ablation attenuated various diseases, including bronchial asthma, arthritis, and psoriasis, whereas BLT2 deficiency exacerbated several diseases in the skin, cornea, and small intestine. Therefore, BLT1 inhibitors and BLT2 activators could be beneficial for the treatment of several inflammatory and immune disorders. As a result, attractive compounds targeting LTB₄ receptors have been developed by several pharmaceutical companies. This review aims to understand the potential of BLT1 and BLT2 as therapeutic targets for the treatment of various inflammatory diseases. In addition, recent topics are discussed with major focuses on the structure and post-translational modifications of BLT1 and BLT2. Collectively, current evidence on modulating LTB₄ receptor functions provides new strategies for the treatment of various diseases.

Inflammatory Mediators in Atherosclerotic Vascular Remodeling

Atherosclerotic vascular disease remains the most common cause of ischemia, myocardial infarction, and stroke. Vascular function is determined by structural and functional properties of the arterial vessel wall, which consists of three layers, namely the adventitia, media, and intima. Key cells in shaping the vascular wall architecture and warranting proper vessel function are vascular smooth muscle cells in the arterial media and endothelial cells lining the intima. Pathological alterations of this vessel wall architecture called vascular remodeling can lead to insufficient vascular function and subsequent ischemia and organ damage. One major pathomechanism driving this detrimental vascular remodeling is atherosclerosis, which is initiated by endothelial dysfunction allowing the accumulation of intimal lipids and leukocytes. Inflammatory mediators such as cytokines, chemokines, and modified lipids further drive vascular remodeling ultimately leading to thrombus formation and/or vessel occlusion which can cause major cardiovascular events. Although it is clear that vascular wall remodeling is an elementary mechanism of atherosclerotic vascular disease, the diverse underlying pathomechanisms and its consequences are still insufficiently understood.

Differentiation potential and functional properties of a CD34‑CD133+ subpopulation of endothelial progenitor cells

Endothelial progenitor cells (EPCs) promote angiogenesis and play an important role in myocardial and vascular repair after ischemia and infarction. EPCs consist of different subpopulations including CD34‑CD133+ EPCs, which are precursors of more mature CD34+CD133+ EPCs and functionally more active in terms of homing and endothelial regeneration. In the present study we analyzed the functional and differentiation abilities of CD34‑CD133+ EPCs. Isolation of EPC populations (CD34+CD133+, CD34‑CD133+) were performed by specific multi‑step magnetic depletion. After specific stimulation a significant higher adhesive and migrative capacity of CD34‑CD133+ cells could be detected compared to CD34+CD133+ cells (P<0.001, respectively). Next to this finding, not only significantly higher rates of proliferation (P<0.005) were detected among CD34‑CD133+ cells, but also a higher potential of cell‑differentiation capacity into other cell types. Next to a significant increase of CD34‑CD133+ EPCs differentiating into a fibroblast cell‑type (P<0.001), an enhancement into a hepatocytic cell‑type (P=0.033) and a neural cell‑type (P=0.016) could be measured in contrast to CD34+CD133+ cells. On the other hand, there was no significant difference in differentiation into a cardiomyocyte cell‑type between these EPC subpopulations (P=0.053). These results demonstrate that EPC subpopulations vary in their functional abilities and, to different degrees, have the capacity to transdifferentiate into unrelated cell‑types such as fibroblasts, hepatocytes, and neurocytes. This indicates that CD34‑CD133+ cells are more pluripotent compared to the CD34+CD133+ EPC subset, which may have important consequences for the therapy of vascular diseases.

CD18 Regulates Monocyte Hematopoiesis and Promotes Resistance to Experimental Schistosomiasis

Infection with Schistosoma mansoni causes a chronic parasitic disease that progress to severe liver and gastrointestinal damage, and eventually death. During its development into mammalian hosts, immature schistosomula transit through the lung vasculature before they reach the liver to mature into adult worms. A low grade inflammatory reaction is induced during this process. However, molecules that are required for efficient leukocyte accumulation in the lungs of S. mansoni-infected subjects are unknown. In addition, specific leukocyte subsets that mediate pulmonary response during S. mansoni migration through the lung remain to be elucidated. β₂ integrins are fundamental regulators of leukocyte trans-endothelial migration and function. Therefore, we investigated their role during experimental schistosomiasis. Mice that express low levels of CD18 (the common β₂ integrin subunit) and wild type C57BL/6 mice were subcutaneously infected with S. mansoni cercariae. Cellular profiles of lungs and livers were evaluated in different time points after infection by flow cytometry. Low levels of CD18 affected the accumulation of patrolling Ly6C^low, intermediate Ly6C^inter monocytes, monocyte-derived macrophages and monocyte-derived dendritic cells in the lungs 7 days after infection. This correlated with increased TNF-α levels. Strikingly, low CD18 expression resulted in monocytopenia both in the peripheral blood and bone marrow during acute infection. After 48 days, S. mansoni worm burdens were higher in the hepatic portal system of CD18^low mice, which also displayed reduced hepatic accumulation of patrolling Ly6C^low and intermediate Ly6C^inter, but not inflammatory Ly6C^high monocytes. Higher parasite burden resulted in increased granulomatous lesions in the liver, increased egg deposition and enhanced mortality. Overall, our data point for a fundamental role of CD18 for monocyte hematopoiesis during infection, which promotes an efficient host response against experimental schistosomiasis.

Leukotriene receptors as potential therapeutic targets

Leukotrienes, a class of arachidonic acid-derived bioactive molecules, are known as mediators of allergic and inflammatory reactions and considered to be important drug targets. Although an inhibitor of leukotriene biosynthesis and antagonists of the cysteinyl leukotriene receptor are clinically used for bronchial asthma and allergic rhinitis, these medications were developed before the molecular identification of leukotriene receptors. Numerous studies using cloned leukotriene receptors and genetically engineered mice have unveiled new pathophysiological roles for leukotrienes. This Review covers the recent findings on leukotriene receptors to revisit them as new drug targets.

Biochemical and immunological characterization of a novel monoclonal antibody against mouse leukotriene B4 receptor 1

Leukotriene B₄ (LTB₄) receptor 1 (BLT1) is a G protein-coupled receptor expressed in various leukocyte subsets; however, the precise expression of mouse BLT1 (mBLT1) has not been reported because a mBLT1 monoclonal antibody (mAb) has not been available. In this study, we present the successful establishment of a hybridoma cell line (clone 7A8) that produces a high-affinity mAb for mBLT1 by direct immunization of BLT1-deficient mice with mBLT1-overexpressing cells. The specificity of clone 7A8 was confirmed using mBLT1-overexpressing cells and mouse peripheral blood leukocytes that endogenously express BLT1. Clone 7A8 did not cross-react with human BLT1 or other G protein-coupled receptors, including human chemokine (C-X-C motif) receptor 4. The 7A8 mAb binds to the second extracellular loop of mBLT1 and did not affect LTB₄ binding or intracellular calcium mobilization by LTB₄. The 7A8 mAb positively stained Gr-1-positive granulocytes, CD11b-positive granulocytes/monocytes, F4/80-positive monocytes, CCR2-high and CCR2-low monocyte subsets in the peripheral blood and a CD4-positive T cell subset, Th1 cells differentiated in vitro from naïve CD4-positive T cells. This mAb was able to detect Gr-1-positive granulocytes and monocytes in the spleens of naïve mice by immunohistochemistry. Finally, intraperitoneal administration of 7A8 mAb depleted granulocytes and monocytes in the peripheral blood. We have therefore succeeded in generating a high-affinity anti-mBLT1 mAb that is useful for analyzing mBLT1 expression in vitro and in vivo.

From leukocyte recruitment to resolution of inflammation: the cardinal role of integrins

Integrins constitute a large group of adhesion receptors that are formed as heterodimers of α and β subunits. Their presence and activation status on the surface of leukocytes modulate a broad spectrum of processes in inflammation and immunity. This mini review critically outlines research advances with regard to the function of leukocyte integrins in regulating and integrating the onset and resolution of acute inflammation. Specifically, we summarize and discuss relevant, current literature that supports the multifunctional role of integrins and their partners. The latter include molecules that physically associate with integrins or regulate their activity in the context of the following: 1) leukocyte recruitment to an inflamed tissue, 2) recognition and phagocytosis of apoptotic neutrophils (efferocytosis), and 3) egress of efferocytic macrophages from the inflamed site to lymphoid tissues. The understanding of the fine-tuning mechanisms of the aforementioned processes by integrins and their functional partners may enable the design of therapeutic tools to counteract destructive inflammation and promote more efficient resolution of inflammation.

ω-3 Fatty Acids and Cardiovascular Diseases: Effects, Mechanisms and Dietary Relevance

ω-3 fatty acids (n-3 FA) have, since the 1970s, been associated with beneficial health effects. They are, however, prone to lipid peroxidation due to their many double bonds. Lipid peroxidation is a process that may lead to increased oxidative stress, a condition associated with adverse health effects. Recently, conflicting evidence regarding the health benefits of intake of n-3 from seafood or n-3 supplements has emerged. The aim of this review was thus to examine recent literature regarding health aspects of n-3 FA intake from fish or n-3 supplements, and to discuss possible reasons for the conflicting findings. There is a broad consensus that fish and seafood are the optimal sources of n-3 FA and consumption of approximately 2-3 servings per week is recommended. The scientific evidence of benefits from n-3 supplementation has diminished over time, probably due to a general increase in seafood consumption and better pharmacological intervention and acute treatment of patients with cardiovascular diseases (CVD).

Leukotrienes orchestrating allergic skin inflammation

Leukotrienes constitute a group of lipid mediators, which may be subdivided into two groups, with leukotriene B4 on the one hand and cysteinyl leukotrienes on the other. Although leukotrienes are abundantly expressed in skin affected by diverse chronic inflammatory diseases, including atopic dermatitis, psoriasis, pemphigus vulgaris and bullous pemphigoid, their pathological roles in these diseases have remained elusive. Recent data now reveal that both leukotriene B4 and cysteinyl leukotrienes are indispensable in the pathogenesis of atopic dermatitis, with leukotriene B4 initiating the recruitment of inflammatory cells, particularly neutrophils and TH 2 cells into the skin, and cysteinyl leukotrienes later inducing characteristic structural alterations of chronically affected skin, specifically skin fibrosis and keratinocyte proliferation. Thus, these results reveal a sequential cooperation of LTB4 and cysteinyl leukotrienes to initiate and perpetuate allergic skin inflammation. These new insights highlight leukotrienes as promising therapeutic targets in allergic skin inflammation and should encourage more research into the role of leukotrienes in other inflammatory skin diseases.

Role of leukotriene A4 hydrolase aminopeptidase in the pathogenesis of emphysema

The leukotriene A4 hydrolase (LTA4H) is a bifunctional enzyme with epoxy hydrolase and aminopeptidase activities. We hypothesize that the LTA4H aminopeptidase activity alleviates neutrophilic inflammation, which contributes to cigarette smoke (CS)-induced emphysema by clearing proline-glycine-proline (PGP), a triamino acid chemokine known to induce chemotaxis of neutrophils. To investigate the biological contributions made by the LTA4H aminopeptidase activity in CS-induced emphysema, we exposed wild-type mice to CS over 5 mo while treating them with a vehicle or a pharmaceutical agent (4MDM) that selectively augments the LTA4H aminopeptidase without affecting the bioproduction of leukotriene B4. Emphysematous phenotypes were assessed by premortem lung physiology with a small animal ventilator and by postmortem histologic morphometry. CS exposure acidified the airspaces and induced localization of the LTA4H protein into the nuclei of the epithelial cells. This resulted in accumulation of PGP in the airspaces by suppressing the LTA4H aminopeptidase activity. When the LTA4H aminopeptidase activity was selectively augmented by 4MDM, the levels of PGP in the bronchoalveolar lavage fluid and infiltration of neutrophils into the lungs were significantly reduced without affecting the levels of leukotriene B4. This protected murine lungs from CS-induced emphysematous alveolar remodeling. In conclusion, CS exposure promotes the development of CS-induced emphysema by suppressing the enzymatic activities of the LTA4H aminopeptidase in lung tissues and accumulating PGP and neutrophils in the airspaces. However, restoring the leukotriene A4 aminopeptidase activity with a pharmaceutical agent protected murine lungs from developing CS-induced emphysema.

Leukotriene B4-driven neutrophil recruitment to the skin is essential for allergic skin inflammation

Scratching triggers skin flares in atopic dermatitis. We demonstrate that scratching of human skin and tape stripping of mouse skin cause neutrophil influx. In mice, this influx was largely dependent on the generation of leukotriene B4 (LTB4) by neutrophils and their expression of the LTB4 receptor BLT1. Allergic skin inflammation in response to epicutaneous (EC) application of ovalbumin to tape-stripped skin was severely impaired in Ltb4r1(-/-) mice and required expression of BLT1 on both T cells and non-T cells. Cotransfer of wild-type (WT) neutrophils, but not neutrophils deficient in BLT1 or the LTB4-synthesizing enzyme LTA4H, restored the ability of WT CD4(+) effector T cells to transfer allergic skin inflammation to Ltb4r1(-/-) recipients. Pharmacologic blockade of LTB4 synthesis inhibited allergic skin inflammation elicited by cutaneous antigen challenge in previously EC-sensitized mice. Our results demonstrate that a neutrophil-T cell axis reliant on LTB4-BLT1 interaction is required for allergic skin inflammation.

Leukotriene A4 Hydrolase: Biology, Inhibitors and Clinical Applications

Leukotriene A4 hydrolase is a zinc-containing cytosolic enzyme with both hydrolase and aminopeptidase activity. LTA4H stereospecifically catalyzes the transformation of the unstable epoxide LTA4 to the potent pro-inflammatory mediator LTB4. Variations in the lta4h gene have been linked to susceptibility to multiple diseases including myocardial infarction, stroke and asthma. Pre-clinical animal models and human biomarker data have implicated LTB4 in inflammatory diseases. Several groups have now identified selective inhibitors of LTA4H, many of which were influenced by the disclosure of a protein crystal structure a decade ago. Clinical validation of LTA4H remains elusive despite the progression of inhibitors into pre-clinical and clinical development.

5-(4-Hydroxy-2,3,5-trimethylbenzylidene) thiazolidine-2,4-dione attenuates atherosclerosis possibly by reducing monocyte recruitment to the lesion

A variety of benzylidenethiazole analogs have been demonstrated to inhibit 5-lipoxygenase (5-LOX). Here we report the anti-atherogenic potential of 5-(4-hydroxy- 2,3,5-trimethylbenzylidene) thiazolidin-2,4-dione (HMB-TZD), a benzylidenethiazole analog, and its potential mechanism of action in LDL receptor-deficient (Ldlr-/-) mice. HMB-TZD Treatment reduced leukotriene B4 (LTB4) production significantly in RAW264.7 macrophages and SVEC4-10 endothelial cells. Macrophages or endothelial cells pre-incubated with HMB-TZD for 2 h and then stimulated with lipopolysaccharide or tumor necrosis factor-alpha (TNF-α) displayed reduced cytokine production. Also, HMB-TZD reduced cell migration and adhesion in accordance with decreased proinflammatory molecule production in vitro and ex vivo. HMB-TZD treatment of 8-week-old male Ldlr-/- mice resulted in significantly reduced atherosclerotic lesions without a change to plasma lipid profiles. Moreover, aortic expression of pro-atherogenic molecules involved in the recruitment of monocytes to the aortic wall, including TNF-α , MCP-1, and VCAM-1, was downregulated. HMB-TZD also reduced macrophage infiltration into atherosclerotic lesions. In conclusion, HMB-TZD ameliorates atherosclerotic lesion formation possibly by reducing the expression of proinflammatory molecules and monocyte/macrophage recruitment to the lesion. These results suggest that HMB-TZD, and benzylidenethiazole analogs in general, may have therapeutic potential as treatments for atherosclerosis.

Lipid-cytokine-chemokine cascades orchestrate leukocyte recruitment in inflammation

Chemoattractants are pivotal mediators of host defense, orchestrating the recruitment of immune cells into sites of infection and inflammation. Chemoattractants display vast chemical diversity and include bioactive lipids, proteolytic fragments of serum proteins, and chemokines (chemotactic cytokines). All chemoattractants induce chemotaxis by activating seven-transmembrane-spanning GPCRs expressed on immune cells, establishing the concept that all chemoattractants are related in function. However, although chemoattractants have overlapping functions in vitro, recent in vivo data have revealed that they function, in many cases, nonredundantly in vivo. The chemically diverse nature of chemoattractants contributes to the fine control of leukocyte trafficking in vivo, with sequential chemoattractant use guiding immune cell recruitment into inflammatory sites. Lipid mediators frequently function as initiators of leukocyte recruitment, attracting the first immune cells into tissues. These initial responding immune cells produce cytokines locally, which in turn, induce the local release of chemokines. Local chemokine production then markedly amplifies subsequent waves of leukocyte recruitment. These new discoveries establish a paradigm for leukocyte recruitment in inflammation--described as lipid-cytokine-chemokine cascades--as a driving force in the effector phase of immune responses.

Cooperative and redundant signaling of leukotriene B4 and leukotriene D4 in human monocytes

BACKGROUND

Leukotriene B(4) (LTB(4)) and cysteinyl leukotrienes (cysLTs) are important immune mediators, often found concomitantly at sites of inflammation. Although some of the leukotriene-mediated actions are distinctive (e.g., bronchial constriction for cysLTs), many activities such as leukocyte recruitment to tissues and amplification of inflammatory responses are shared by both classes of leukotrienes.

OBJECTIVE

We used human monocytes to characterize leukotriene-specific signaling, gene expression signatures, and functions and to identify interactions between LTB(4)- and cysLTs-induced pathways.

METHODS

Responsiveness to leukotrienes was assessed using oligonucleotide microarrays, real-time PCR, calcium mobilization, kinase activation, and chemotaxis assays.

RESULTS

Human monocytes were found to express mRNA for high- and low-affinity LTB(4) receptors, BLT(1) and BLT(2), but signal predominantly through BLT(1) in response to LTB(4) stimulation as shown using selective agonists, inhibitors, and gene knock down experiments. LTB(4) acting through BLT(1) coupled to G-protein α inhibitory subunit activated calcium signaling, p44/42 mitogen-activated protein kinase, gene expression, and chemotaxis. Twenty-seven genes, including immediate early genes (IEG), transcription factors, cytokines, and membrane receptors were significantly up-regulated by LTB(4). LTB(4) and LTD(4) had similar effects on signaling, gene expression, and chemotaxis indicating redundant cell activation pathways but costimulation with both lipid mediators was additive for many monocyte functions.

CONCLUSION

Leukotriene B(4) and LTD(4) display both redundant and cooperative effects on intracellular signaling, gene expression, and chemotaxis in human monocytes. These findings suggest that therapies targeting either leukotriene alone may be less effective than approaches directed at both.

Leukotriene B4 receptor-1 mediates intermittent hypoxia-induced atherogenesis

RATIONALE

Obstructive sleep apnea, which is characterized by intermittent hypoxia (IH) during sleep, has emerged as an independent risk factor for cardiovascular disease, including atherosclerosis. Leukotriene B4 (LTB4) production is increased in patients with obstructive sleep apnea and negatively correlates to hypoxic levels during sleep, with continuous positive airway pressure therapy decreasing LTB4 production.

OBJECTIVES

Determine the potential role of LTB4 in IH-induced atherosclerosis in a monocyte cellular model and a murine model.

METHODS

THP-1 cells were exposed to IH for 3, 6, 24, and 48 hours. Macrophage transformation and foam cell formation were assessed after IH exposures. Apolipopotein E (ApoE)(-/-) or BLT1(-/-)/ApoE(-/-) mice were fed an atherogenic diet and exposed to IH (alternating 21% and 5.7% O(2) from 7 am to 7 PM each day) for 10 weeks. Atherosclerotic lesion formation in en face aorta was examined by oil red O staining.

MEASUREMENTS AND MAIN RESULTS

IH increased production of LTB4 and the expression of 5-lipoxygenase and leukotriene A4 hydrolase, the key enzymes for producing LTB4. IH was associated with transformation of monocytes to activated macrophages, as evidenced by increased expression of CD14 and CD68. In addition, IH exposures promoted increased cellular cholesterol accumulation and foam cell formation. The LTB4 receptor 1 (BLT1) antagonist U-75302 markedly attenuated IH-induced changes. Furthermore, IH promoted atherosclerotic lesion formation in ApoE(-/-) mice. IH-induced lesion formation was markedly attenuated in BLT1(-/-)/ApoE(-/-) mice.

CONCLUSIONS

BLT1-dependent pathways underlie IH-induced atherogenesis, and may become a potential novel therapeutic target for obstructive sleep apnea-associated cardiovascular disease.

Leukotriene pathway in sickle cell disease: a potential target for directed therapy

Sickle cell disease (SCD) is characterized by recurrent episodes of vaso-occlusion, resulting in tissue ischemia and end-organ damage. Inflammation is critical to the pathogenesis of vaso-occlusion and has been associated with SCD-related morbidity and mortality. Despite the impact of inflammation, no directed anti-inflammatory therapies for the treatment or prevention of vaso-occlusive events currently exist. Among individuals with SCD, asthma is a comorbid inflammatory condition that increases the risk of pain episodes, acute chest syndrome and death. Inflammation associated with asthma could augment the proinflammatory state of SCD, increasing episodes of vaso-occlusion. Leukotrienes are inflammatory mediators that play a prominent role in the pathogenesis of asthma and have been associated with SCD-related morbidity. Targeting inflammatory mediators, such as leukotrienes, is a promising approach for the development of novel therapies for the treatment of SCD. This review will examine the relationship between inflammation and vaso-occlusion, with particular focus on the leukotriene pathway.

Differential chemokine receptor expression regulates functional specialization of endothelial progenitor cell subpopulations

Postnatal vasculogenesis is mediated by endothelial progenitor cells (EPCs) which consist of subpopulations with different functional capacities. Our goal was to profile chemokine receptor expression on relevant subsets of EPCs and to characterize their role for effector functions. CD34(+)/CD133(+)/VEGFR2(+) EPCs were characterized by high expression of chemokine receptors CXCR4, CX3CR1, BLT1, and low level expression of CXCR2 and CCR2, while primordial CD34(-)/CD133(+)/VEGFR2(+) EPCs express these chemokine receptors at comparably low levels. Migration assays revealed that SDF-1, fractalkine, and LTB4 significantly increase migration of CD34(-)/CD133(+)/VEGFR2(+) EPCs, while SDF-1 was the only potent agonist of migration of CD34(+)/CD133(+)/VEGFR2(+) EPCs. SDF-1, fractalkine, and LTB4 trigger significant increase adhesion of CD34(+)/CD133(+)/VEGFR2(+) EPCs, while in CD34(-)/CD133(+)/VEGFR2(+) EPCs SDF-1 and fractalkine are equipotent agonists and LTB4 triggers a smaller though still significant increase in adhesion. Differential expression of specific chemokine receptors is an important regulator in terms of migration and adhesion of biologically relevant EPC-subpopulations, which may have implications for cell therapeutic strategies for treatment of ischemic vascular disease.

Role of LTB₄ in the pathogenesis of elastase-induced murine pulmonary emphysema

Exaggerated levels of the leukotriene B₄ (LTB₄) frequently coexist at sites of inflammation and tissue remodeling. Therefore, we hypothesize that the LTB₄ pathway plays an important role in the pathogenesis of neutrophilic inflammation that contributes to pulmonary emphysema. In this study, significant levels of LTB₄ were detected in human lung tissues with emphysema compared with lungs without emphysema (9,497 ± 2,839 vs. 4,142 ± 1,173 pg/ml, n = 9 vs. 10, P = 0.04). To further determine the biological role of LTB₄ in the pathogenesis of emphysema, we compared the lungs of wild-type (WT) and LTA₄ hydrolase-/- mice (LTB₄ deficient, LTA₄H-/-) exposed to intranasal elastase or vehicle control. We found that intranasal elastase induced accumulation of LTB₄ in the lungs and caused progressively worsening emphysema between 14 and 28 days after elastase exposure in WT mice but not in LTA₄H-/- mice. Premortem physiology documented increased lung compliance in elastase-exposed WT mice compared with elastase-exposed LTA₄H-/- mice as measured by Flexivent (0.058 ± 0.005 vs. 0.041 ± 0.002 ml/cmH₂O pressure). Postmortem morphometry documented increased total lung volume and alveolar sizes in elastase-exposed WT mice compared with elastase-exposed LTA₄H-/- mice as measured by volume displacement and alveolar chord length assessment. Furthermore, elastase-exposed LTA₄H-/- mice were found to have significantly delayed influx of the CD45(high)CD11b(high)Ly6G(high) leukocytes compatible with neutrophils compared with elastase-exposed WT mice. Mechanistic insights to these phenotypes were provided by demonstrating protection from elastase-induced murine emphysema with neutrophil depletion in the elastase-exposed WT mice and by demonstrating time-dependent modulation of cysteinyl leukotriene biosynthesis in the elastase-exposed LTA₄H-/- mice compared with elastase-exposed WT mice. Together, these findings demonstrated that LTB₄ played an important role in promoting the pathogenesis of pulmonary emphysema associated with neutrophilic pulmonary inflammation.

Nutrigenomic analysis of the protective effects of bilberry anthocyanin-rich extract in apo E-deficient mice

Intake of anthocyanin-rich foods has been associated with a reduced risk of cardiovascular diseases. Supplementation with anthocyanin-rich extracts from black rice or purple sweet potato was reported to attenuate atherosclerotic lesion development in apolipoprotein E-deficient (apo E(-/-)) mice. However, the mechanism(s) of their preventive action are not completely understood. Previous studies revealed that anthocyanins altered mRNA levels of genes related to atherosclerosis in cultured macrophages and endothelial cells, but in vivo studies remain scarce. The aim of the study was to investigate the impact of bilberry anthocyanin-rich extract (BE) supplementation on gene expression in the liver of apo E(-/-) mice, the widely used model of atherosclerosis. The liver was chosen because it is the main site of lipid metabolism. Apo E(-/-) mice received for 2 weeks a standard diet supplemented with a nutritional dose of BE (0.02%). This study focused on the early stage of atherosclerosis development for better assessment of anthocyanin action on initiation mechanisms of this pathology. The results showed that a 2-week supplementation significantly reduced plasmatic total cholesterol and hepatic triglyceride levels, whereas the plasmatic antioxidant status remained unchanged. Transcriptional analysis, using microarrays, revealed that the expression of 2,289 genes was significantly altered. BE over-expressed genes involved in bile acid synthesis and cholesterol uptake into the liver and down-regulated the expression of pro-inflammatory genes. These results suggest an anti-atherogenic effect of BE through the regulation of cholesterol metabolism and liver inflammation and provide a global integrated view of the mechanisms involved in the preventive action of this extract.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12263-010-0171-0) contains supplementary material, which is available to authorized users.

Oxidative risk for atherothrombotic cardiovascular disease

In the vasculature, reactive oxidant species, including reactive oxygen, nitrogen, or halogenating species, and thiyl, tyrosyl, or protein radicals may oxidatively modify lipids and proteins with deleterious consequences for vascular function. These biologically active free radical and nonradical species may be produced by increased activation of oxidant-generating sources and/or decreased cellular antioxidant capacity. Once formed, these species may engage in reactions to yield more potent oxidants that promote transition of the homeostatic vascular phenotype to a pathobiological state that is permissive for atherothrombogenesis. This dysfunctional vasculature is characterized by lipid peroxidation and aberrant lipid deposition, inflammation, immune cell activation, platelet activation, thrombus formation, and disturbed hemodynamic flow. Each of these pathobiological states is associated with an increase in the vascular burden of free radical species-derived oxidation products and, thereby, implicates increased oxidant stress in the pathogenesis of atherothrombotic vascular disease.

Malnutrition promotes prostaglandin over leukotriene production and dysregulates eicosanoid-cytokine crosstalk in activated resident macrophages

We previously described a murine model of malnutrition that mimicked features of moderate human malnutrition, and led to increased dissemination of Leishmania donovani. In this study, we investigated the effect of malnutrition on macrophage production of cytokines, prostaglandins (PGs), and leukotrienes (LTs). Using either LPS or calcium ionophore A23187 as a stimulus, macrophages from the malnourished mice produced a 3-fold higher PG/LT ((PGE(2)+6-keto-PGF(1alpha))/(LTB(4)+cysteinyl leukotrienes)) ratio than macrophages from well-nourished mice. LPS-stimulated macrophages from the malnourished mice produced decreased levels of TNF-alpha, GM-CSF, and IL-10, but similar levels of IL-6 and NO compared to well-nourished mice. A complex crosstalk between the eicosanoids and cytokines in the LPS-stimulated macrophages from the malnourished mice was evident by the following: (1) high levels of PG secretion despite low levels of TNF-alpha; (2) supplemental IL-10 modulated the excessive PG production; (3) GM-CSF rectified the PG/LT ratio, but did not correct the abnormal cytokine profile; and (4) inhibitors of cyclooxygenase decreased the PG/LT ratio, but did not affect TNF-alpha. Thus, in this model of malnutrition, there is a relative increase in anti-inflammatory PGs compared to pro-inflammatory LTs, which may contribute to immunodeficiency.

The CysLT1 ligand leukotriene D4 supports alpha4beta1- and alpha5beta1-mediated adhesion and proliferation of CD34+ hematopoietic progenitor cells

Cytokines and chemokines control hematopoietic stem and progenitor cell (HPC) proliferation and trafficking. However, the role of nonpeptide mediators in the bone marrow microenvironment has remained elusive. Particularly CysLT(1), a G protein-coupled receptor recognizing inflammatory mediators of the cysteinyl leukotriene family, is highly expressed in HPCs. We therefore analyzed the effects of its ligands on human CD34(+) HPCs. The most potent CysLT(1) ligand, LTD(4), rapidly and significantly up-regulated alpha(4)beta(1) and alpha(5)beta(1) integrin-dependent adhesion of both primitive and committed HPC. LTD(4)-triggered adhesion was inhibited by specific CysLT(1) antagonists. The effects of other CysLT(1) ligands were weak (LTC(4)) or absent (LTE(4)). In serum-free liquid cultures supplemented with various hematopoietic cytokines including IL-3, only LTD(4) significantly augmented the expansion of HPCs in a dose-dependent manner comparable to that of peptide growth factors. LTC(4) and LTE(4) were less effective. In CD34(+) cell lines and primary HPCs, LTD(4) induced phosphorylation of p44/42 ERK/MAPK and focal adhesion kinase-related tyrosine kinase Pyk2, which is linked to integrin activation. Bone marrow stromal cells produced biologically significant amounts of cysteinyl leukotrienes only when hematopoietic cells were absent, suggesting a regulatory feedback mechanism in the hematopoietic microenvironment. In contrast to antagonists of the homing-related G protein-coupled receptor CXCR4, administration of a CysLT(1) antagonist failed to induce human CD34(+) HPC mobilization in vivo. Our results suggest that cysteinyl leukotriene may contribute to HPC retention and proliferation only when cysteinyl leukotriene levels are increased either systemically during inflammation or locally during marrow aplasia.

Identification of a potent, selective, and orally active leukotriene a4 hydrolase inhibitor with anti-inflammatory activity

LTA 4H is a ubiquitously distributed 69 kDa zinc-containing cytosolic enzyme with both hydrolase and aminopeptidase activity. As a hydrolase, LTA 4H stereospecifically catalyzes the transformation of the unstable epoxide LTA 4 to the diol LTB 4, a potent chemoattractant and activator of neutrophils and a chemoattractant of eosinophils, macrophages, mast cells, and T cells. Inhibiting the formation of LTB 4 is expected to be beneficial in the treatment of inflammatory diseases such as inflammatory bowel disease (IBD), asthma, and atherosclerosis. We developed a pharmacophore model using a known inhibitor manually docked into the active site of LTA 4H to identify a subset of compounds for screening. From this work we identified a series of benzoxazole, benzthiazole, and benzimidazole inhibitors. SAR studies resulted in the identification of several potent inhibitors with an appropriate cross-reactivity profile and excellent PK/PD properties. Our efforts focused on further profiling JNJ 27265732, which showed encouraging efficacy in a disease model relevant to IBD.

Synthesis of glutamic acid analogs as potent inhibitors of leukotriene A4 hydrolase

Leukotriene B(4) (LTB(4)) is a potent pro-inflammatory mediator that has been implicated in the pathogenesis of multiple diseases, including psoriasis, inflammatory bowel disease, multiple sclerosis and asthma. As a method to decrease the level of LTB(4) and possibly identify novel treatments, inhibitors of the LTB(4) biosynthetic enzyme, leukotriene A(4) hydrolase (LTA(4)-h), have been explored. Here we describe the discovery of a potent inhibitor of LTA(4)-h, arylamide of glutamic acid 4f, starting from the corresponding glycinamide 2. Analogs of 4f are then described, focusing on compounds that are both active and stable in whole blood. This effort culminated in the identification of amino alcohol 12a and amino ester 6b which meet these criteria.

Endothelium-dependent vascular responses induced by leukotriene B4

Leukotriene B(4) (LTB(4)) is an inflammatory mediator derived from the 5-lipoxygenase pathway of arachidonic acid metabolism and has recently implicated in the pathogenesis of atherosclerosis. There are two membrane bound receptors for LTB(4): BLT(1) and BLT(2), which represent the high and low affinity receptors, respectively. BLT receptors are expressed on leukocytes, and LTB(4) is a potent chemoattractant for neutrophils, eosinophils, and T lymphocytes. Recent studies have in addition shown that LTB(4) is an indirectly acting vasoconstrictor of isolated vascular preparations. In the guinea pig aorta, the LTB(4)-induced contractions were inhibited by endothelium-denudation. In addition, pre-treatment with the NO synthase inhibitor, L-NOARG, significantly enhanced the contractions induced by LTB(4). The contractile response induced by LTB(4) in the guinea pig aorta was abolished by the selective BLT(1) receptor antagonist U75302 and the expression of BLT(1) receptor mRNA in the guinea pig aorta was established by RT-PCR. Taken together, these results suggest that LTB(4) activates BLT(1) receptors on the endothelium of the guinea pig aorta, associated with the release of both contractile factors and NO.

5-Lipoxygenase-activating protein: a potential link between innate and adaptive immunity in atherosclerosis and adipose tissue inflammation

Transforming growth factor-beta (TGF-beta) is a major antiinflammatory mediator in atherosclerosis. Transgenic ApoE(-/-) mice with a dominant-negative TGFbeta type II receptor (dnTGFbetaRII) on CD4(+) and CD8(+) T cells display aggravated atherosclerosis. The aim of the present study was to elucidate the mechanisms involved in this enhanced inflammatory response. Gene array analyses identified the 5-lipoxygenase-activating protein (FLAP) among the most upregulated genes in both the aorta and adipose tissue of dnTGFbetaRII transgenic ApoE(-/-) mice compared with their ApoE(-/-) littermates, a finding that was confirmed by real-time quantitative RT-PCR. Aortas from the former mice in addition produced increased amounts of the lipoxygenase product leukotriene B(4) after ex vivo stimulation. FLAP protein expression in both the aorta and adipose tissue was detected in macrophages, but not in T cells. Four weeks of treatment with the FLAP inhibitor MK-886 (10 mg/kg in 1% tylose delivered by osmotic pumps) significantly reduced atherosclerotic lesion size and T-cell content. Finally, FLAP mRNA levels were upregulated approximately 8-fold in adipose tissue derived from obese ob/ob mice. In conclusion, the results of the present study suggest a key role for mediators of the 5-lipoxygenase pathway in inflammatory reactions of atherosclerosis and metabolic disease.

Anti-inflammatory activity of a potent, selective leukotriene A4 hydrolase inhibitor in comparison with the 5-lipoxygenase inhibitor zileuton

Leukotriene A(4) hydrolase (LTA(4)H) catalyzes production of the proinflammatory lipid mediator, leukotriene (LT) B(4), which is implicated in a number of inflammatory diseases. We have identified a potent and selective inhibitor of both the epoxide hydrolase and aminopeptidase activities of recombinant human LTA(4)H (IC(50), approximately 10 nM). In a murine model of arachidonic acid-induced ear inflammation, the LTA(4)H inhibitor, JNJ-26993135 (1-[4-(benzothiazol-2-yloxy)-benzyl]-piperidine-4-carboxylic acid), dose-dependently inhibited ex vivo LTB(4) production in blood, in parallel with dose-dependent inhibition of neutrophil influx (ED(50), 1-3 mg/kg) and ear edema. In murine whole blood and in zymosan-induced peritonitis, JNJ-26993135 selectively inhibited LTB(4) production, without affecting cysteinyl leukotriene production, while maintaining or increasing production of the anti-inflammatory mediator, lipoxin (LX) A(4). The 5-lipoxygenase (5-LO) inhibitor zileuton showed inhibition of LTB(4), LTC(4), and LXA(4) production. Although zileuton inhibited LTB(4) production in the peritonitis model more effectively than the LTA(4)H inhibitor, the influx of neutrophils into the peritoneum after 1 and 2 h was significantly higher in zileuton- versus JNJ-26993135-treated animals. This difference may have been mediated by the increased LXA(4) levels in the presence of the LTA(4)H inhibitor. The selective inhibition of LTB(4) production by JNJ-26993135, while increasing levels of the anti-inflammatory mediator, LXA(4), may translate to superior therapeutic efficacy versus 5-LO or 5-LO-activating protein inhibitors in LTB(4)-mediated inflammatory diseases.

Licofelone, a balanced inhibitor of cyclooxygenase and 5-lipoxygenase, reduces inflammation in a rabbit model of atherosclerosis

Licofelone, a dual anti-inflammatory drug that inhibits 5-lipoxygenase (LOX) and cyclooxygenase (COX) enzymes, may have a better cardiovascular profile that cycloxygenase-2 inhibitors due to cycloxygenase-1 blockade-mediated antithrombotic effect and a better gastrointestinal tolerability. We examined the anti-inflammatory effect of licofelone on atherosclerotic lesions as well as in isolated neutrophils from whole blood of rabbits compared with a selective inhibitor of COX-2, rofecoxib. We also assessed the antithrombotic effect of licofelone in rabbit platelet-rich plasma. For this purpose, 30 rabbits underwent injury of femoral arteries, and they were randomized to receive 10 mg/kg/day licofelone or 5 mg/kg/day rofecoxib or no treatment during 4 weeks with atherogenic diet in all cases. Ten healthy rabbits were used as controls. Neutrophils and platelets were isolated from peripheral blood of rabbits for ex vivo studies. Licofelone reduced intima/media ratio in injured arteries, the macrophages infiltration in the neointimal area, monocyte chemoattractant protein-1 (MCP-1) gene expression, and the activation of nuclear factor-kappaB in rabbit atheroma. Moreover, licofelone inhibited COX-2 and 5-LOX protein expression in vascular lesions. Rofecoxib only diminished COX-2 protein expression and MCP-1 gene expression in vascular atheroma. Prostaglandin E(2) in rabbit plasma was attenuated by both drugs. Licofelone almost abolished 5-LOX activity by inhibiting leukotriene B4 generation in rabbit neutrophils and prevented platelet thromboxane B2 production from whole blood. Licofelone reduces neointimal formation and inflammation in an atherosclerotic rabbit model more markedly than rofecoxib. This effect, together with the antiplatelet activity of licofelone, suggests that this drug may have a favorable cardiovascular profile.

Leukotriene receptors in atherosclerosis

Leukotriene-forming enzymes are expressed within atherosclerotic lesions and locally produced leukotrienes exert pro-inflammatory actions within the vascular wall by means of cell surface receptors of the BLT and CysLT receptor subtypes. The migration and accumulation of inflammatory cells that follow leukotriene receptor activation have been implicated in atherosclerosis initiation and progression. Leukotriene receptors are in addition expressed on endothelial and vascular smooth muscle cells, associated with intimal hyperplasia in early atherosclerosis and restenotic lesions after angioplasty. Taken together, recent evidence suggests that leukotriene receptors may be a potential target in the treatment of atherosclerosis and in the prevention of restenosis after coronary interventions.

Leukotriene B4 signaling through NF-kappaB-dependent BLT1 receptors on vascular smooth muscle cells in atherosclerosis and intimal hyperplasia

Leukotriene B(4) (LTB(4)), a potent leukocyte chemoattractant derived from the 5-lipoxygenase metabolism of arachidonic acid, exerts its action by means of specific cell surface receptors, denoted BLT(1) and BLT(2). In this study, BLT(1) receptor proteins were detected in human carotid artery atherosclerotic plaques, colocalizing with markers for macrophages, endothelial cells, and vascular smooth muscle cells (SMC). Challenge of human coronary artery SMC with either LTB(4) or U75302, a partial agonist that is selective for the BLT(1) receptor, induced an approximately 4-fold increase of whole-cell currents by using the patch-clamp technique, indicating that these cells express functional BLT(1) receptors. LTB(4) induced migration and proliferation of SMC in vitro, and treatment with the BLT receptor antagonist BIIL 284 (10 mg/kg, once daily) for 14 days after carotid artery balloon injury in vivo inhibited intimal hyperplasia in rats. In the latter model, SMC derived from the intima exhibited increased levels of BLT(1) receptor mRNA compared with medial SMC. BLT receptor up-regulation in the intima in vivo, as well as that induced by IL-1beta in vitro, were prevented by transfection with a dominant-negative form of Ikappa kinase beta carried by adenovirus, indicating that BLT(1) receptor expression depends on NF-kappaBeta. These results show that LTB(4) activates functional BLT(1) receptors on vascular SMC, inducing chemotaxis and proliferation, and that BLT(1) receptors were up-regulated through an Ikappa kinase beta/NF-kappaB-dependent pathway. Inhibition of LTB(4)/BLT(1) signaling during the response to vascular injury reduced intimal hyperplasia, suggesting this pathway as a possible target for therapy.

Pro- and anti-inflammatory substances modulate expression of the leukotriene B4receptor, BLT1, in human monocytes

The high-affinity leukotriene B(4) (LTB(4)) receptor, BLT1, is a chemotactic receptor involved in inflammatory responses. In this study, we have explored the regulation of BLT1 expression in human monocytes by pro- and anti-inflammatory cytokines, lipopolysaccharide (LPS), and dexamethasone. We found that proinflammatory mediators, such as interferon-gamma (IFN-gamma), tumor necrosis factor-alpha, and LPS, down-regulated expression, whereas the anti-inflammatory cytokine, interleukin-10, and dexamethasone up-regulated BLT1 mRNA expression. The effect of IFN-gamma on BLT1 mRNA expression was rapidly detectable (<4 h) and concentration-dependent (1-50 ng/ml) and seems to be exerted through a block in transcriptional activity. Alterations in mRNA expression were accompanied by changes in BLT1 surface expression, and receptor down-modulation following IFN-gamma stimulation resulted in a diminished chemotactic response to LTB(4). The regulation of BLT1 mRNA and receptor protein expression was similar to the regulation of the monocyte chemoattractant protein-1 chemokine receptor, CC chemokine recptor 2 (CCR2). Flow cytometric analysis of fresh peripheral blood cells revealed that classical (CD14(++)CD16(-)) monocytes express high levels of BLT1 and CCR2 and that both receptors are down-regulated on CD14(+)CD16(+) monocytes. Apart from providing insight into the regulation of BLT1 in human monocytes, our results reveal a parallel expression and regulation of BLT1 and CCR2, which may help to understand monocyte trafficking during pathophysiological conditions.

Serum ferritin elevation and acute lung injury in rats subjected to hemorrhage: reduction by mepacrine treatment

Ferritin regulates iron levels and, for unknown reasons, serum ferritin concentrations are increased in patients at risk for and with acute lung injury (ALI) and multiple organ failure. Uncomplexed iron could exacerbate the toxicity of the increased oxidative stress that occurs in patients with ALI and multiple organ failure and thereby contribute to disease. In the present investigation, the authors found that serum and lung lavage ferritin concentrations increased in hemorrhaged rats that develop ALI as manifested by increased lung inflammation (increased lung lavage leukocyte counts and lung myeloperoxidase activities) and increased lung leak (increased lung lavage protein concentrations). Treatment with mepacrine, a phospholipase A2 inhibitor, attenuated the increases in serum and lung lavage ferritin concentrations, lung inflammation, and lung leak that occur in rats subjected to hemorrhage. The findings show that serum and lung ferritin levels increase and may play a role in the development of acute lung injury caused by hemorrhage.

Leukotrienes and atherosclerosis: new roles for old mediators

Lipid mediators generated from arachidonic acid through the action of 5-lipoxygenase have been known for over two decades and are implicated in a wide variety of inflammatory disorders. G-protein-coupled receptors mediate the effects of different leukotrienes in distinct cell types. Novel cellular and molecular targets were recently discovered for these mediators, with important consequences for the function of both adaptive and innate immune systems. These studies have outlined crucial new roles for leukotrienes in the recruitment of T lymphocytes and in the development of atherosclerotic lesions, suggesting novel mechanisms for their actions. Through the development of appropriate animal models, leukotrienes are becoming renewed targets for treatment of many inflammatory diseases including atherosclerosis.

Leukotriene B 4 Strongly Increases Monocyte Chemoattractant Protein-1 in Human Monocytes

OBJECTIVE

Leukotriene B4 (LTB4), a product of the 5-lipoxygenase (5-LO) pathway of arachidonic acid metabolism, has been implicated in atherosclerosis. However, the molecular mechanisms for the atherogenic effect of LTB4 are not well understood. This study is to determine candidate mechanisms.

METHOD AND RESULTS

Primary human monocytes were treated with LTB4 and the supernatant was analyzed for cytokine/chemokine production by an immuno-protein array. This analysis revealed a strong increase of the monocyte chemoattractant protein-1 (MCP-1), a proinflammatory cytokine. Follow-up analyses with MCP-1 enzyme-linked immunosorbent assay (for quantitation of MCP-1 protein) and real-time polymerase chain reaction (PCR) (for MCP-1 mRNA) demonstrated that LTB4 strongly induced expression of MCP-1 protein and mRNA in a time-dependent and dose-dependent fashion. This induction was effectively abolished by CP-105,696, an antagonist for the LTB4 receptor BLT1. Selective inhibitors of ERK1/2 or JNK MAPK effectively blocked the LTB4-induced MCP-1 production. Furthermore, LTB4 increased NF-[kappa]B DNA binding activity, which was blocked by CP-105,696.

CONCLUSIONS

LTB4 strongly induces MCP-1 production in primary human monocytes. This induction is mediated through the BLT1 pathway increasing MCP-1 transcription. Activation of ERK1/2 or JNK MAPK is essential for this induction. The NF-[kappa]B activation may be involved in LTB4-increased MCP-1 expression. The LTB4-induced MCP-1 in human monocytes may play a critical role in the atherogenicity of LTB4.