Loss of hypothermic and anti-pyretic action of paracetamol in cyclooxygenase-1 knockout mice is indicative of inhibition of cyclooxygenase-1 variant enzymes.

Paracetamol (acetaminophen), is a centrally-acting antipyretic analgesic drug, which can also lower body temperature. Despite a century of clinical use, its mechanism of pharmacological action has not been completely elucidated. Previously, we demonstrated significant attenuation in the paracetamol induced hypothermia in parallel with its inhibitory action on the synthesis of brain prostaglandin E2 (PGE2) in cyclooxygenase-1 (COX-1) knockout mice in comparison to wild-type mice. The above reported pharmacological actions by paracetamol were completely retained in COX-2 knockout mice. We thus concluded that the mechanism of hypothermic action of paracetamol is dependent on inhibition of a COX-1 gene-derived enzyme. In the current investigation, we provide further support for this notion by demonstrating that the paracetamol-induced hypothermia is not mediated through inhibition of COX-1 as neither the COX-1 selective inhibitor, SC560, nor the COX-1/COX-2 dual inhibitor, indomethacin, induced hypothermia at pharmacologically active doses in mice. In addition, using a COX-2-dependent and PGE2-mediated model of endotoxin-induced fever, paracetamol induced anti-pyretic and hypothermic actions in COX-1 wild-type mice. These effects were fully or partially attenuated in COX-1 knockout mice after prophylactic or therapeutic administration, respectively. Therapeutically-administered paracetamol also reduced hypothalamic PGE2 biosynthesis in febrile COX-1 wild-type mice, but not in febrile COX-1 knockout mice. In conclusion, we provide further evidence which suggests that the hypothermic and now anti-pyretic actions of paracetamol are mediated through inhibition of a COX-1 variant enzyme.

Oiling the wheels of discovery.

LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

The Anti-allergic Cromones: Past, Present, and Future.

The anti-allergic cromones were originally synthesized in the 1960s by Fisons Plc, and the first drug to emerge from this program, disodium cromoglycate was subsequently marketed for the treatment of asthma and other allergic conditions. Whilst early studies demonstrated that the ability of the cromones to prevent allergic reactions was due to their 'mast cell stabilizing' properties, the exact pharmacological mechanism by which this occurred, remained a mystery. Here, we briefly review the history of these drugs, recount some aspects of their pharmacology, and discuss two new explanations for their unique actions. We further suggest how these findings could be used to predict further uses for the cromones.

Mast cells mediate early neutrophil recruitment and exhibit anti-inflammatory properties via the formyl peptide receptor 2/lipoxin A4 receptor.

BACKGROUND AND PURPOSE: In recent years, studies have focused on the resolution of inflammation, which can be achieved by endogenous anti-inflammatory agonists such as Annexin A1 (AnxA1). Here, we investigated the effects of mast cells (MCs) on early LPS-induced neutrophil recruitment and the involvement of the AnxA1-formyl peptide receptor 2/ALX (FPR2/ALX or lipoxin A4 receptor) pathway. EXPERIMENTAL APPROACH: Intravital microscopy (IVM) was used to visualize and quantify the effects of LPS (10 µg per mouse i.p.) on murine mesenteric cellular interactions. Furthermore, the role that MCs play in these inflammatory responses was determined in vivo and in vitro, and effects of AnxA1 mimetic peptide Ac2-26 were assessed. KEY RESULTS: LPS increased both neutrophil endothelial cell interactions within the mesenteric microcirculation and MC activation (determined by IVM and ruthenium red dye uptake), which in turn lead to the early stages of neutrophil recruitment. MC recruitment of neutrophils could be blocked by preventing the pro-inflammatory activation (using cromolyn sodium) or enhancing an anti-inflammatory phenotype (using Ac2-26) in MCs. Furthermore, MCs induced neutrophil migration in vitro, and MC stabilization enhanced the release of AnxA1 from neutrophils. Pharmacological approaches (such as the administration of FPR pan-antagonist Boc2, or the FPR2/ALX antagonist WRW4) revealed neutrophil FPR2/ALX to be important in this process. CONCLUSIONS AND IMPLICATIONS: Data presented here provide evidence for a role of MCs, which are ideally positioned in close proximity to the vasculature, to act as sentinel cells in neutrophil extravasation and resolution of inflammation via the AnxA1-FPR2/ALX pathway.

Identification of benzopyrone as a common structural feature in compounds with anti-inflammatory activity in a zebrafish phenotypic screen.

Neutrophils are essential for host defence and are recruited to sites of inflammation in response to tissue injury or infection. For inflammation to resolve, these cells must be cleared efficiently and in a controlled manner, either by apoptosis or reverse migration. If the inflammatory response is not well-regulated, persistent neutrophils can cause damage to host tissues and contribute to the pathogenesis of chronic inflammatory diseases, which respond poorly to current treatments. It is therefore important to develop drug discovery strategies that can identify new therapeutics specifically targeting neutrophils, either by promoting their clearance or by preventing their recruitment. Our recent in vivo chemical genetic screen for accelerators of inflammation resolution identified a subset of compounds sharing a common chemical signature, the bicyclic benzopyrone rings. Here, we further investigate the mechanisms of action of the most active of this chemical series, isopimpinellin, in our zebrafish model of neutrophilic inflammation. We found that this compound targets both the recruitment and resolution phases of the inflammatory response. Neutrophil migration towards a site of injury is reduced by isopimpinellin and this occurs as a result of PI3K inhibition. We also show that isopimpinellin induces neutrophil apoptosis to drive inflammation resolution in vivo using a new zebrafish reporter line detecting in vivo neutrophil caspase-3 activity and allowing quantification of flux through the apoptotic pathway in real time. Finally, our studies reveal that clinically available 'cromones' are structurally related to isopimpinellin and have previously undescribed pro-resolution activity in vivo These findings could have implications for the therapeutic use of benzopyrones in inflammatory disease.

Definition of a Novel Pathway Centered on Lysophosphatidic Acid To Recruit Monocytes during the Resolution Phase of Tissue Inflammation.

Blood-derived monocytes remove apoptotic cells and terminate inflammation in settings as diverse as atherosclerosis and Alzheimer's disease. They express high levels of the proresolving receptor ALX/FPR2, which is activated by the protein annexin A1 (ANXA1), found in high abundance in inflammatory exudates. Using primary human blood monocytes from healthy donors, we identified ANXA1 as a potent CD14(+)CD16(-) monocyte chemoattractant, acting via ALX/FPR2. Downstream signaling pathway analysis revealed the p38 MAPK-mediated activation of a calcium independent phospholipase A2 with resultant synthesis of lysophosphatidic acid (LPA) driving chemotaxis through LPA receptor 2 and actin cytoskeletal mobilization. In vivo experiments confirmed ANXA1 as an independent phospholipase A2-dependent monocyte recruiter; congruently, monocyte recruitment was significantly impaired during ongoing zymosan-induced inflammation in AnxA1(-/-) or alx/fpr2/3(-/-) mice. Using a dorsal air-pouch model, passive transfer of apoptotic neutrophils between AnxA1(-/-) and wild-type mice identified effete neutrophils as the primary source of soluble ANXA1 in inflammatory resolution. Together, these data elucidate a novel proresolving network centered on ANXA1 and LPA generation and identify previously unappreciated determinants of ANXA1 and ALX/FPR2 signaling in monocytes.

Annexin-A1 restricts Th17 cells and attenuates the severity of autoimmune disease.

Annexin-A1 (Anx-A1) is an endogenous anti-inflammatory molecule and while described as a repressor of innate immune responses, the role of Anx-A1 in adaptive immunity, and in particular in T helper (Th) cell responses, remains controversial. We have used a T-cell mediated mouse model of retinal autoimmune disease to unravel the role of Anx-A1 in the development of autoreactive Th cell responses and pathology. RBP1-20-immunized C57BL/6 Anx-A1(-/-) mice exhibit significantly enhanced retinal inflammation and pathology as a result of an uncontrolled proliferation and activation of Th17 cells. This is associated with a limited capacity to induce SOCS3, resulting in un-restricted phosphorylation of STAT3. RBP1-20-specific CD4(+) cells from immunized Anx-A1(-/-) animals generated high levels of Th17 cells-associated cytokines. Following disease induction, daily systemic administration of human recombinant Anx-A1 (hrAnx-A1), during the afferent phase of disease, restrained autoreactive CD4(+) cell proliferation, reduced expression of pro-inflammatory cytokines IL-17, IFN-γ and IL-6 and attenuated autoimmune retinal inflammatory disease. Furthermore, in man, Anx-A1 serum levels when measured in active uveitis patient sera were low and associated with the detection of IgM and IgG anti-Anx-A1 antibodies when compared to healthy individuals. This data supports Anx-A1 as an early and critical regulator of Th17 cell driven autoimmune diseases such as uveitis.

Nonredundant protective properties of FPR2/ALX in polymicrobial murine sepsis.

Sepsis is characterized by overlapping phases of excessive inflammation temporally aligned with an immunosuppressed state, defining a complex clinical scenario that explains the lack of successful therapeutic options. Here we tested whether the formyl-peptide receptor 2/3 (Fpr2/3)--ortholog to human FPR2/ALX (receptor for lipoxin A4)--exerted regulatory and organ-protective functions in experimental sepsis. Coecal ligature and puncture was performed to obtain nonlethal polymicrobial sepsis, with animals receiving antibiotics and analgesics. Clinical symptoms, temperature, and heart function were monitored up to 24 h. Peritoneal lavage and plasma samples were analyzed for proinflammatory and proresolving markers of inflammation and organ dysfunction. Compared with wild-type mice, Fpr2/3(-/-) animals exhibited exacerbation of disease severity, including hypothermia and cardiac dysfunction. This scenario was paralleled by higher levels of cytokines [CXCL1 (CXC receptor ligand 1), CCL2 (CC receptor ligand 2), and TNFα] as quantified in cell-free biological fluids. Reduced monocyte recruitment in peritoneal lavages of Fpr2/3(-/-) animals was reflected by a higher granulocyte/monocyte ratio. Monitoring Fpr2/3(-/-) gene promoter activity with a GFP proxy marker revealed an over threefold increase in granulocyte and monocyte signals at 24 h post-coecal ligature and puncture, a response mediated by TNFα. Treatment with a receptor peptido-agonist conferred protection against myocardial dysfunction in wild-type, but not Fpr2/3(-/-), animals. Therefore, coordinated physio-pharmacological analyses indicate nonredundant modulatory functions for Fpr2/3 in experimental sepsis, opening new opportunities to manipulate the host response for therapeutic development.

Identification of a novel recycling sequence in the C-tail of FPR2/ALX receptor: association with cell protection from apoptosis.

Formyl-peptide receptor type 2 (FPR2; also called ALX because it is the receptor for lipoxin A4) sustains a variety of biological responses relevant to the development and control of inflammation, yet the cellular regulation of this G-protein-coupled receptor remains unexplored. Here we report that, in response to peptide agonist activation, FPR2/ALX undergoes ß-arrestin-mediated endocytosis followed by rapid recycling to the plasma membrane. We identify a transplantable recycling sequence that is both necessary and sufficient for efficient receptor recycling. Furthermore, removal of this C-terminal recycling sequence alters the endocytic fate of FPR2/ALX and evokes pro-apoptotic effects in response to agonist activation. This study demonstrates the importance of endocytic recycling in the anti-apoptotic properties of FPR2/ALX and identifies the molecular determinant required for modulation of this process fundamental for the control of inflammation.

Annexin A1 mediates hydrogen sulfide properties in the control of inflammation.

Hydrogen sulfide (H2S) is a gaseous mediator synthesized in mammalian tissues by three main enzymes-cystathionine-ß-synthase (CBS), cystathionine-γ-lyase (CSE), and 3-mercaptopyruvate-sulfurtransferase-and its levels increase under inflammatory conditions or sepsis. Since H2S and H2S-releasing molecules afford inhibitory properties in leukocyte trafficking, we tested whether endogenous annexin A1 (AnxA1), a glucocorticoid-regulated inhibitor of inflammation acting through formylated-peptide receptor 2 (ALX), could display intermediary functions in the anti-inflammatory profile of H2S. We first investigated whether endogenous AnxA1 could modulate H2S biosynthesis. To this end, a marked increase in CBS and/or CSE gene products was quantified by quantitative real-time polymerase chain reaction in aortas, kidneys, and spleens collected from AnxA1(-/-) mice, as compared with wild-type animals. When lipopolysaccharide-stimulated bone marrow-derived macrophages were studied, H2S-donor sodium hydrosulfide (NaHS) counteracted the increased expression of inducible nitric oxide synthase and cyclooxygenase 2 mRNA evoked by the endotoxin, yet it was inactive in macrophages harvested from AnxA1(-/-) mice. Next we studied the effect of in vivo administration of NaHS in a model of interleukin-1ß (IL-1ß)-induced mesenteric inflammation. AnxA1(+/+) mice treated with NaHS (100 µmol/kg) displayed inhibition of IL-1ß-induced leukocyte adhesion/emigration in the inflamed microcirculation, not observed in AnxA1(-/-) animals. These results were translated by testing human neutrophils, where NaHS (10-100 µM) prompted an intense mobilization (>50%) of AnxA1 from cytosol to cell surface, an event associated with inhibition of cell/endothelium interaction under flow. Taken together, these data strongly indicate the existence of a positive interlink between AnxA1 and H2S pathway, with nonredundant functions in the control of experimental inflammation.

Ligand-specific conformational change of the G-protein-coupled receptor ALX/FPR2 determines proresolving functional responses.

Formyl-peptide receptor type 2 (FPR2), also called ALX (the lipoxin A4 receptor), conveys the proresolving properties of lipoxin A4 and annexin A1 (AnxA1) and the proinflammatory signals elicited by serum amyloid protein A and cathelicidins, among others. We tested here the hypothesis that ALX might exist as homo- or heterodimer with FPR1 or FPR3 (the two other family members) and operate in a ligand-biased fashion. Coimmunoprecipitation and bioluminescence resonance energy transfer assays with transfected HEK293 cells revealed constitutive dimerization of the receptors; significantly, AnxA1, but not serum amyloid protein A, could activate ALX homodimers. A p38/MAPK-activated protein kinase/heat shock protein 27 signaling signature was unveiled after AnxA1 application, leading to generation of IL-10, as measured in vitro (in primary monocytes) and in vivo (after i.p. injection in the mouse). The latter response was absent in mice lacking the ALX ortholog. Using a similar approach, ALX/FPR1 heterodimerization evoked using the panagonist peptide Ac2-26, identified a JNK-mediated proapoptotic path that was confirmed in primary neutrophils. These findings provide a molecular mechanism that accounts for the dual nature of ALX and indicate that agonist binding and dimerization state contribute to the conformational landscape of FPRs.

A vasculo-protective circuit centered on lipoxin A4 and aspirin-triggered 15-epi-lipoxin A4 operative in murine microcirculation.

Endogenous protective pathways mitigate the overshooting of inflammation after sterile or infectious injury. Here we report that formyl peptide receptor 2 (Fpr2/3) null mice display a major phenotype with exacerbated vascular inflammation observed postischemia reperfusion (IR) injury of the mesenteric artery, characterized by marked neutrophil adhesion and extravasation as visualized by intravital microscopy. Analysis of endogenous agonists for Fpr2/3 revealed that lipoxin A4 (LXA4) was generated by platelet/neutrophil aggregates during ischemia: this cellular response was attenuated in Fpr2/3(-/-) mice; hence, LXA4 levels were lower after 30 minutes' ischemia, and associated with augmented vascular inflammation in the reperfusion (45-180 minutes) phase. Exogenous delivery of LXA4 attenuated IR-mediated inflammation in Fpr2/3(+/+) but not Fpr2/3(-/-) mice; conversely, an Fpr2/3 antagonist skewed the vascular phenotype of Fpr2/3(+/+) mice to that of Fpr2/3(-/-) animals. Such LXA4-based circuit could be activated by aspirin (30-100 mg/kg), which triggered formation of 15-epi-LXA4 in wild-type mice, yet it was effective in Fpr2/3(-/-) mice. In summary, we propose that during ischemia, neutrophil Fpr2/3 controls platelet/neutrophil aggregates with the rapid generation of circulating LXA4, which in turn modulates downstream vascular inflammatory responses evident during the reperfusion phase.

Attenuation of plasma annexin A1 in human obesity.

Obesity-related metabolic disorders are characterized by mild chronic inflammation, leukocyte infiltration, and tissue fibrosis as a result of adipocytokine production from the expanding white adipose tissue. Annexin A1 (AnxA1) is an endogenous glucocorticoid regulated protein, which modulates systemic anti-inflammatory processes and, therefore, may be altered with increasing adiposity in humans. Paradoxically, we found that plasma AnxA1 concentrations inversely correlated with BMI, total percentage body fat, and waist-to-hip ratio in human subjects. Plasma AnxA1 was also inversely correlated with plasma concentrations of the acute-phase protein, C-reactive protein (CRP), and the adipocytokine leptin, suggesting that as systemic inflammation increases, anti-inflammatory AnxA1 is reduced. In addition, AnxA1 gene expression and protein were significantly up-regulated during adipogenesis in a human adipocyte cell line compared to vehicle alone, demonstrating for the first time that AnxA1 is expressed and excreted from human adipocytes. These data demonstrate a failure in the endogenous anti-inflammatory system to respond to increasing systemic inflammation resulting from expanding adipose tissue, a condition strongly linked to the development of type 2 diabetes and cardiovascular disease. These data raise the possibility that a reduction in plasma AnxA1 may contribute to the chronic inflammatory phenotype observed in human obesity.

Annexin A1 interaction with the FPR2/ALX receptor: identification of distinct domains and downstream associated signaling.

Understanding how proresolving agonists selectively activate FPR2/ALX is a crucial step in the clarification of proresolution molecular networks that can be harnessed for the design of novel therapeutics for inflammatory disease. FPR2/ALX, a G protein-coupled receptor belonging to the formyl peptide receptor (FPR) family, conveys the biological functions of a variety of ligands, including the proresolution mediators annexin A1 (AnxA1) and lipoxin A(4), as well as the activating and proinflammatory protein serum amyloid A. FPR2/ALX is the focus of intense screening for novel anti-inflammatory therapeutics, and the small molecule compound 43 was identified as a receptor ligand. Here, we used chimeric FPR1 and FPR2/ALX clones (stably transfected in HEK293 cells) to identify the N-terminal region and extracellular loop II as the FPR2/ALX domain required for AnxA1-mediated signaling. Genomic responses were also assessed with domain-specific effects emerging, so the N-terminal region is required for AnxA1 induction of JAG1 and JAM3, whereas it is dispensable for modulation of SGPP2. By comparison, serum amyloid A non-genomic responses were reliant on extracellular loops I and II, whereas the small molecule compound 43 activated extracellular loop I with downstream signaling dependent on transmembrane region II. In desensitization experiments, the N-terminal region was dispensable for AnxA1-induced FPR2/ALX down-regulation in both the homologous and heterologous desensitization modes.

Resolvin D1 limits polymorphonuclear leukocyte recruitment to inflammatory loci: receptor-dependent actions.

OBJECTIVE: Resolvin D1 (RvD1) limits neutrophil recruitment during acute inflammation and is derived from omega-3 docosahexaenoic acid to promote catabasis. The contribution of its specific receptors, the lipoxin A(4)/Annexin-A1 receptor formyl-peptide receptor 2 (FPR2/ALX) and the orphan receptor G-protein-coupled receptor 32 (GPR32) are of considerable interest. METHODS AND RESULTS: RvD1 reduced human polymorphonuclear leukocytes recruitment to endothelial cells under shear conditions as quantified using a flow chamber system. Receptor-specific antibodies blocked these anti-inflammatory actions of RvD1, with low (1 nmol/L) concentrations sensitive to GPR32 blockade, while the higher (10 nmol/L) concentration appeared FPR2/ALX-specific. Interestingly, polymorphonuclear leukocytes surface expression of FPR2/ALX but not GPR32 increased following activation with pro-inflammatory stimuli, corresponding with secretory vesicle mobilization. Lipid mediator metabololipidomics carried out with 24-hour exudates revealed that RvD1 in vivo gave a significant reduction in the levels of a number of pro-inflammatory mediators including prostaglandins and leukotriene B(4). These actions of RvD1 were abolished in fpr2 null mice. CONCLUSIONS: Pro-resolving lipid mediators and their receptors, such as RvD1 and the 2 G-protein-coupled receptors, studied here regulate resolution and may provide new therapeutic strategies for diseases with a vascular inflammatory component.

Endogenous annexin A1 counter-regulates bleomycin-induced lung fibrosis.

BACKGROUND: The balancing functions of pro/anti-inflammatory mediators of the complex innate responses have been investigated in a variety of experimental inflammatory settings. Annexin-A1 (AnxA1) is one mediator of endogenous anti-inflammation, affording regulation of leukocyte trafficking and activation in many contexts, yet its role in lung pathologies has been scarcely investigated, despite being highly expressed in lung cells. Here we have applied the bleomycin lung fibrosis model to AnxA1 null mice over a 21-day time-course, to monitor potential impact of this mediator on the control of the inflammatory and fibrotic phases. RESULTS: Analyses in wild-type mice revealed strict spatial and temporal regulation of the Anxa1 gene, e.g. up-regulation in epithelial cells and infiltrated granulocytes at day 7, followed by augmented protein levels in alveolar macrophages by day 21. Absence of AnxA1 caused increases in: i) the degree of inflammation at day 7; and ii) indexes of fibrosis (assessed by deposition of hydroxyproline in the lung) at day 7 and 21. These alterations in AnxA1 null mice were paralleled by augmented TGF-ß1, IFN-γ and TNF-α generation compared to wild-type mice. Finally, treatment of wild type animals with an AnxA1 peptido-mimetic, given prophylactically (from day 0 to 21) or therapeutically (from day 14 onward), ameliorated both signs of inflammation and fibrosis. CONCLUSION: Collectively these data reveal a pathophysiological relevance for endogenous AnxA1 in lung inflammation and, more importantly, fibrosis, and may open new insights for the pharmacological treatment of lung fibrosis.

Paracetamol-induced hypothermia is independent of cannabinoids and transient receptor potential vanilloid-1 and is not mediated by AM404.

In recent years, there has been increasing interest in hypothermia induced by paracetamol for therapeutic purposes, which, in some instances, has been reported as a side effect. Understanding the mechanism by which paracetamol induces hypothermia is therefore an important question. In this study, we investigated whether the novel metabolite of paracetamol, N-(4-hydroxyphenyl)arachidonylamide (AM404), which activates the cannabinoid (CB) and transient receptor potential vanilloid-1 (TRPV1) systems, mediates the paracetamol-induced hypothermia. The hypothermic response to 300 mg/kg paracetamol in CB(1) receptor (CB(1)R) and TRPV1 knockout mice was compared to wild-type mice. Hypothermia induced by paracetamol was also investigated in animals pretreated with the CB(1)R or TRPV1 antagonist 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperdinyl-1H-pyrazole-3-carboxamide trifluoroacetate salt (AM251) or 4'-chloro-3-methoxycinnamanilide (SB366791), respectively. In CB(1)R or TRPV1 knockout mice, paracetamol induced hypothermia to the same extent as in wild-type mice. In addition, in C57BL/6 mice pretreated with AM251 or SB366791, paracetamol induced hypothermia to the same extent as in control mice. AM404 failed to induce hypothermia at pharmacological doses. Inhibition of fatty acid amide hydrolase (FAAH), which is involved in the metabolism of paracetamol to AM404, did not prevent the development of hypothermia with paracetamol. Paracetamol also induced hypothermia in FAAH knockout mice to the same extent as wild-type mice. We conclude that paracetamol induces hypothermia independent of cannabinoids and TRPV1 and that AM404 does not mediate this response. In addition, potential therapeutic value of combinational drug-induced hypothermia is supported by experimental evidence.

Cutting edge: Humanized nano-proresolving medicines mimic inflammation-resolution and enhance wound healing.

Endogenous microparticles (MPs) were systematically profiled during the time course of self-limited inflammation. Precursors for specialized proresolving lipid mediators were identified in MPs from inflammatory exudates using liquid chromatography tandem mass spectrometry-based metabolomics. Hence, we postulated that formation of anti-inflammatory and proresolving lipid mediators could underlie beneficial effects attributed to MPs and that this process could serve as a basis for biomimicry. Using human neutrophil-derived MPs, we constructed novel nanoparticles (NPs) containing aspirin-triggered resolvin D1 or a lipoxin A(4) analog. Enriched NPs dramatically reduced polymorphonuclear cell influx in murine peritonitis, shortened resolution intervals, and exhibited proresolving actions accelerating keratinocyte healing. The enriched NPs protected against inflammation in the temporomandibular joint. These findings indicate that humanized NPs, termed nano-proresolving medicines, are mimetics of endogenous resolving mechanisms, possess potent beneficial bioactions, can reduce nanotoxicity, and offer new therapeutic approaches.

Evidence for an anti-inflammatory loop centered on polymorphonuclear leukocyte formyl peptide receptor 2/lipoxin A4 receptor and operative in the inflamed microvasculature.

The importance of proresolving mediators in the overall context of the resolution of acute inflammation is well recognized, although little is known about whether these anti-inflammatory and proresolving molecules act in concert. In this article, we focused on lipoxin A(4) (LXA(4)) and annexin A1 (AnxA1) because these two very different mediators converge on a single receptor, formyl peptide receptor type 2 (FPR2/ALX). Addition of LXA(4) to human polymorphonuclear leukocytes (PMNs) provoked a concentration- and time-dependent mobilization of AnxA1 onto the plasma membrane, as determined by Western blotting and flow cytometry analyses. This property was shared by another FPR2/ALX agonist, antiflammin-2, and partly by fMLF or peptide Ac2-26 (an AnxA1 derivative that can activate all three members of the human FPR family). An FPR2/ALX antagonist blocked AnxA1 mobilization activated by LXA(4) and antiflammin-2. Analysis of PMN degranulation patterns and phospho-AnxA1 status suggested a model in which the two FPR2/ALX agonists mobilize the cytosolic (and not the granular) pool of AnxA1 through an intermediate phosphorylation step. Intravital microscopy investigations of the inflamed mesenteric microvasculature of wild-type and AnxA1(-/-) mice revealed that LXA(4) provoked leukocyte detachment from the postcapillary venule endothelium in the former (>50% within 10 min; p < 0.05), but not the latter genotype (∼15%; NS). Furthermore, recruitment of Gr1(+) cells into dorsal air-pouches, inflamed with IL-1ß, was significantly attenuated by LXA(4) in wild-type, but not AnxA1(-/-), mice. Collectively, these data prompt us to propose the existence of an endogenous network in anti-inflammation centered on PMN AnxA1 and activated by selective FPR2/ALX agonists.