Lipoxin A4: a novel anti-inflammatory molecule?

Time-Dependent Protective and Pro-Resolving Effects of FPR2 Agonists on Lipopolysaccharide-Exposed Microglia Cells Involve Inhibition of NF-κB and MAPKs Pathways

Prolonged or excessive microglial activation may lead to disturbances in the resolution of inflammation (RoI). The importance of specialized pro-resolving lipid mediators (SPMs) in RoI has been highlighted. Among them, lipoxins (LXA4) and aspirin-triggered lipoxin A4 (AT-LXA4) mediate beneficial responses through the activation of N-formyl peptide receptor-2 (FPR2). We aimed to shed more light on the time-dependent protective and anti-inflammatory impact of the endogenous SPMs, LXA4, and AT-LXA4, and of a new synthetic FPR2 agonist MR-39, in lipopolysaccharide (LPS)-exposed rat microglial cells. Our results showed that LXA4, AT-LXA4, and MR-39 exhibit a protective and pro-resolving potential in LPS-stimulated microglia, even if marked differences were apparent regarding the time dependency and efficacy of inhibiting particular biomarkers. The LXA4 action was found mainly after 3 h of LPS stimulation, and the AT-LXA4 effect was varied in time, while MR-39′s effect was mainly observed after 24 h of stimulation by endotoxin. MR-39 was the only FPR2 ligand that attenuated LPS-evoked changes in the mitochondrial membrane potential and diminished the ROS and NO release. Moreover, the LPS-induced alterations in the microglial phenotype were modulated by LXA4, AT-LXA4, and MR-39. The anti-inflammatory effect of MR-39 on the IL-1β release was mediated through FPR2. All tested ligands inhibited TNF-α production, while AT-LXA4 and MR-39 also diminished IL-6 levels in LPS-stimulated microglia. The favorable action of LXA4 and MR-39 was mediated through the inhibition of ERK1/2 phosphorylation. AT-LXA4 and MR39 diminished the phosphorylation of the transcription factor NF-κB, while AT-LXA4 also affected p38 kinase phosphorylation. Our results suggest that new pro-resolving synthetic mediators can represent an attractive treatment option for the enhancement of RoI, and that FPR2 can provide a perspective as a target in immune-related brain disorders.

Lipoxin A4 Regulates Lipopolysaccharide-Induced BV2 Microglial Activation and Differentiation via the Notch Signaling Pathway

Inflammatory responses contribute to the pathogenesis of various neurological diseases, and microglia plays an important role in the process. Activated microglia can differentiate into the pro-inflammatory, tissue-damaging M1 phenotype or the anti-inflammatory, tissue-repairing M2 phenotype. Regulating microglia differentiation, hence limiting a harmful response, might help improve the prognosis of inflammation-related nervous system diseases. The present study aimed 1. to observe the anti-inflammatory effect of lipoxin A4 (LXA4) on the inflammatory response associated to lipopolysaccharide (LPS)-induced microglia activation, 2. to clarify that LXA4 modulates the activation and differentiation of microglia induced by LPS stimulation, 3. to determine whether LXA4 regulates the activation and differentiation of microglia through the Notch signaling pathway, 4. to provide a foundation for the use of LXA4 for the treatment of inflammatory related neurological diseases. To construct a model of cellular inflammation, immortalized murine BV2 microglia cells were provided 200 ng/ml LPS. To measure the mRNA and protein levels of inflammatory factors (interleukin [IL]-1β, IL-10, and tumor necrosis factor [TNF]-α) and M1 and M2 microglia markers (inducible nitric oxide synthase [iNOS], cluster of differentiation [CD]32, arginase [Arg]1, and CD206), we performed quantitative reverse transcription polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA), immunofluorescence, or flow cytometry. To determine the mRNA and protein levels of Notch signaling components (Notch1, Hes1, and Hes5), we performed qRT-PCR and western blot. LXA4 inhibits the expression of Notch1 and Hes1 associated with M1 type microglial differentiation and decreases the M1 type microglia marker iNOS and related inflammatory factors IL-1β and TNF-α. Moreover, LXA4 upregulates the expression of the M2-associated Hes5, as well as the expression of the M2 microglia marker Arg1 and the associated inflammatory factor IL-10. These effects are blocked by the administration of the γ-secretase inhibitor DAPT, a specific blocker of the Notch signaling pathway. LXA4 inhibits the microglia activation induced by LPS and the differentiation into M1 type with pro-inflammatory effect, while promoting the differentiation to M2 type with anti-inflammatory effect. LXA4 downregulates the inflammatory mediators IL-1β, TNF-α, and iNOS, while upregulating the anti-inflammatory mediator IL-10, which acts through the Notch signaling pathway.

Resolution of inflammation pathways in preeclampsia-a narrative review

Preeclampsia (PE) is one of the leading causes of maternal morbidity and mortality worldwide. This disease is believed to occur in two stages with placental dysfunction in early pregnancy leading to maternal clinical findings after 20 weeks of gestation, as consequence of systemic inflammation, oxidative stress, and endothelial dysfunction. Much evidence suggests that PE women display an overshooting inflammatory response throughout pregnancy due to an unbalanced regulation of innate and adaptive immune responses. Recently, it has been suggested that dysregulation of endogenous protective pathways might be associated with PE etiopathogenesis. Resolution of inflammation is an active process coordinated by mediators from diverse nature that regulate key cellular events to restore tissue homeostasis. Inadequate or insufficient resolution of inflammation is believed to play an important role in the development of chronic inflammatory diseases, like PE. In this narrative review, we discuss possible pro-resolution pathways that might be compromised in PE women, which could be targets to novel therapeutic strategies in this disease.

Gene profiling analysis reveals the contribution of CD24 and P2Y6R to the susceptibility of young rats to Plasmodium berghei infection

Our previous studies have shown that Plasmodium berghei infection induces distinct clinical, parasitological and immunological states in young susceptible rats versus adult resistant rats. This susceptibility was mainly found to be related to inadequate cellular responses. In this study we first identified the altered genes in young susceptible rats. Unexpectedly, transcriptome analysis did not reveal any alteration of effector cytokines or their receptors. At day 13 p.i., six transcripts corresponding to faim3, mesothelin, gas3 (PMP22), gas7, CD24 and P2Y6R were significantly decreased in young infected rats when compared with adult infected rats. Because CD24 and P2Y6R participate in cellular immune responses, we next evaluated their role in the course of infection. Adoptive transfer experiments showed a transient but robust participation of CD24+ cells in the control of parasitaemia. The role of P2Y6R was investigated via its specific ability to be activated by Uridine di-Phosphate (UDP). Young rats treated with UDP partially restored the expression of P2Y6R, controlled parasitaemia and survived thereafter. In conclusion, this study contributes to the discovery of novel biomarkers in young susceptible rats and suggests that the decrease in their expression could be among the reasons for the development of severe pathology in malaria.

Serum amyloid a is a biomarker of acute exacerbations of chronic obstructive pulmonary disease

RATIONALE

Much of the total disease burden and cost of chronic obstructive pulmonary disease (COPD) is associated with acute exacerbations of COPD (AECOPD). Serum amyloid A (SAA) is a novel candidate exacerbation biomarker identified by proteomic screening.

OBJECTIVES

To assess SAA as a biomarker of AECOPD.

METHODS

Biomarkers were assessed (1) cross-sectionally (stable vs. AECOPD; 62 individuals) and (2) longitudinally with repeated measures (baseline vs. AECOPD vs. convalescence; 78 episodes in 37 individuals). Event severity was graded (I, ambulatory; II, hospitalized; III, respiratory failure) based on consensus guidelines.

MEASUREMENTS AND MAIN RESULTS

Presumptively newly acquired pathogens were associated with onset of symptomatic AECOPD. In the cross-sectional study, both SAA and C-reactive protein (CRP) were elevated at AECOPD onset compared with stable disease (SAA median, 7.7 vs. 57.6 mg/L; P < 0.01; CRP median, 4.6 vs. 12.5 mg/L; P < 0.01). Receiver operator characteristics analysis was used to generate area-under-curve values for event severity. SAA discriminated level II/III events (SAA, 0.88; 95% confidence interval, 0.80-0.94 vs. CRP, 0.80; 95% confidence interval, 0.70-0.87; P = 0.05). Combining SAA or CRP with major symptoms (Anthonisen criteria, dyspnea) did not further improve the prediction model for severe episodes. IL-6 and procalcitonin were not informative.

CONCLUSIONS

SAA is a novel blood biomarker of AECOPD that is more sensitive than CRP alone or in combination with dyspnea. SAA may offer new insights into the pathogenesis of AECOPD.

Interactions between lipoxin A4, the stable analogue 16-phenoxy-lipoxin A4 and leukotriene B4 in cytokine generation by human monocytes

Lipoxins display both stimulatory and inhibitory actions with leucocytes that are cell-type dependent. We tested whether lipoxin A4 (LXA4) and its stable synthetic analogue 16-phenoxy-17-18,19,20-tetranor-lipoxin-A4 (16-phe-LXA4) modulated the ability of human blood monocytes (MO) to express mRNA and proteins for interleukin-1beta (IL-1beta), IL-6 and IL-1 receptor antagonist (IL-1Ra) in vitro and compared their actions with lipopolysaccharide (LPS) and leukotriene B4 (LTB4). 16-phe-LXA4, LPS and LTB4, but not LXA4, induced gene expression of IL-1beta in MO. IL-1beta protein synthesis increased by LPS (1500-fold), LTB4 (280-fold) and 16-phe-LXA4 (30-fold). Although the IL-1Ra gene was constitutively activated, mRNA concentration not affected by any of the stimulants, IL-Ra protein synthesis was increased by LPS (with 74%), 16-phe-LXA4 (35%) and LTB4 (20%), but not by LXA4. Each of these stimuli upregulated the IL-6 gene. Increases of IL-6 protein were 3000-fold for LPS, threefold for 16-phe-LXA4, eightfold for LXA(4 and) twofold for LTB4. Prior exposure of MO to 16-phe-LXA4, but not LXA4, reduced LTB4 induced synthesis of IL-1beta with 66%, IL-6 with 20% and IL-1Ra with 29%. Thus, a stable LXA analogue, that resists rapid inactivation by monocytes, displays novel actions in cytokine generation, intimately involved in the regulation of inflammation.

Endogenous anti-inflammatory mediators from arachidonate in human neutrophils

Eicosanoids have been historically involved in the pathogenesis of various inflammatory diseases. Lipoxins (LXs) and epi-LXs show physiological effects relevant to inflammation regulation. In this study, we focused on LX precursors based on the hypothesis that their entrance and metabolism into the cell may facilitate their targeting at the inflammation site. Because compound chirality is of considerable importance in the efficacy of therapeutic agents, our aim was to study the anti-inflammatory effects of various epimers of LXA(4) precursors compared to LXA(4). Blood polymorphonuclear cells (PMNs) were incubated with 15(S)- or 15(R)-hydroxyeicosatetraenoic acid (HETE), 14(R)-,15(S)-, or 14(S),15(S)-diHETE, and LXA(4) and then stimulated with the calcium ionophore A23187. We found that 15(R)-HETE rather than 15(S)-HETE was preferentially metabolized and that 15-epi-LXs were produced in larger amounts than LXs. In contrast, when PMNs were incubated with the diastereoisomers of 14,15(S)-diHETE, 14-epi-LXB(4) was produced in lower amounts than LXB(4). Enantiomers of 15-HETE and diastereoisomers of 14,15-diHETE and LXA(4) were able to significantly decrease LTB(4) release by PMNs. These results suggest a potential resolution of the inflammatory process through endogenous anti-inflammatory mediators released by the way of trans-cellular metabolism.

Generation of eicosanoids from 15(S)-hydroxyeicosatetraenoic acid in blood monocytes from steroid-dependent asthmatic patients

The aim of this study was to investigate eicosanoid metabolism by human peripheral blood monocytes (PBM) from steroid-dependent asthmatic patients as compared to control subjects and untreated asthmatic patients. Eicosanoid biosynthesis by PBM isolated from venous blood using Percoll gradient centrifugation was evaluated following stimulation of 5 x 10(6) cells with calcium ionophore A23187, with or without exogenous 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE), and analyzed by reverse phase high performance liquid chromatography (RP-HPLC). Without 15(S)-HETE, PBM synthesized leukotriene B4 (LTB4) only (40 +/- 12 ng and 59 +/- 11 ng for untreated and steroid-dependent asthmatics, respectively). In the presence of 15(S)-HETE, PBM produced six-fold smaller amounts of leukotriene B4 (P < 0.0001). They also released 5(S),15(S)-dihydroxyeicosatetraenoic acid (5(S),15(S)-diHETE) in similar amounts for all the populations, whereas low amounts of lipoxins (LXs) were produced by PBM from asthmatics only (2.7 +/- 0.7 ng and 4.6 +/- 2.8 ng for untreated and steroid-dependent asthmatics, respectively). Moreover, PBM were also able to release an unknown compound containing conjugated triene chromophore. Cells from steroid-dependent asthmatic patients synthesized this unknown metabolite in higher amounts than controls and untreated asthmatics (133 +/- 18 ng vs 52 +/- 19 ng and 68 +/- 15 ng, respectively, P < 0.02). This work shows for the first time that human PBM are able to metabolize 15(S)-HETE and lead to lipoxins and to an unknown metabolite, with the amounts of the latter being enhanced by long-term corticosteroid treatment.

Lipoxins and novel aspirin-triggered 15-epi-lipoxins (ATL): a jungle of cell-cell interactions or a therapeutic opportunity?

Lipid-derived mediators play critical roles in inflammation and other multicellular vascular processes, including atherosclerosis and thrombosis. The lipoxins (LXs) were first isolated in 1984, and have continued to show intriguing and potentially important biological roles. These compounds carry a trihydroxytetraene structure and are both structurally and functionally unique among arachidonic acid-derived bioactive products. The availability of synthetic materials for evaluation of bioactions as well as appropriate methods of detection to determine when and where LX are generated has, in recent studies, catapulted our understanding of the formation and actions of the lipoxins. This mini-review addresses new concepts in the formation and biological roles of these lipid-derived mediators and considers whether the lipoxins and the newly discovered aspirin-triggered lipoxins (ATL) represent novel approaches for therapeutic opportunities. Recent findings indicate that select cytokines and aspirin initiate and regulate LX biosynthetic events. These circuits involve cell-cell interfacing that facilitates transcellular events to form LX that display anti-inflammatory actions in both in vitro and in vivo models. These recent results suggest that LX biosynthetic circuits assemble to evoke anti-inflammatory actions and generate LX that can serve as "stop signals" in appropriate microenvironments.