Asymmetric Synthesis and Biological Screening of Quinoxaline-Containing Synthetic Lipoxin A4 Mimetics (QNX-sLXms).

Failure to resolve inflammation underlies many prevalent pathologies. Recent insights have identified lipid mediators, typified by lipoxins (LXs), as drivers of inflammation resolution, suggesting potential therapeutic benefit. We report the asymmetric preparation of novel quinoxaline-containing synthetic-LXA4-mimetics (QNX-sLXms). Eight novel compounds were screened for their impact on inflammatory responses. Structure-activity relationship (SAR) studies showed that (R)-6 (also referred to as AT-02-CT) was the most efficacious and potent anti-inflammatory compound of those tested. (R)-6 significantly attenuated lipopolysaccharide (LPS)- and tumor-necrosis-factor-α (TNF-α)-induced NF-κB activity in monocytes and vascular smooth muscle cells. The molecular target of (R)-6 was investigated. (R)-6 activated the endogenous LX receptor formyl peptide receptor 2 (ALX/FPR2). The anti-inflammatory properties of (R)-6 were further investigated in vivo in murine models of acute inflammation. Consistent with in vitro observations, (R)-6 attenuated inflammatory responses. These results support the therapeutic potential of the lead QNX-sLXm (R)-6 in the context of novel inflammatory regulators.

Potent Anti-Inflammatory and Pro-Resolving Effects of Anabasum in a Human Model of Self-Resolving Acute Inflammation.

Anabasum is a synthetic analog of Δ8 -tetrahydrocannabinol (THC)-11-oic acid that in preclinical models of experimental inflammation exerts potent anti-inflammatory actions with minimal central nervous system (CNS) cannabimimetic activity. Here we used a novel model of acute inflammation driven by i.d. UV-killed E. coli in healthy humans and found that anabasum (5 mg) exerted a potent anti-inflammatory effect equivalent to that of prednisolone in terms of inhibiting neutrophil infiltration, the hallmark of acute inflammation. These effects arose from the inhibition of the neutrophil chemoattractant LTB4 , while the inhibition of antiphagocytic prostanoids (PGE2 , TxB2 , and PGF2 α) resulted in enhanced clearance of inflammatory stimulus from the injected site. Anabasum at the higher dose of 20 mg possessed the additional properties of triggering the biosynthesis of specialized pro-resolving lipid mediators including LXA4 , LXB4 , RvD1, and RvD3. Collectively, we demonstrate for the first time a striking anti-inflammatory and pro-resolution effects of a synthetic analog of THC in healthy humans.

Prolonged immune alteration following resolution of acute inflammation in humans.

Acute inflammation is an immediate response to infection and injury characterised by the influx of granulocytes followed by phagocytosing mononuclear phagocytes. Provided the antigen is cleared and the immune system of the host is fully functional, the acute inflammatory response will resolve. Until now it is considered that resolution then leads back to homeostasis, the physiological state tissues experienced before inflammation occurred. Using a human model of acute inflammation driven by intradermal UV killed Escherichia coli, we found that bacteria and granulocyte clearance as well as pro-inflammatory cytokine catabolism occurred by 72h. However, following a lag phase of about 4 days there was an increase in numbers of memory T cells and CD163+ macrophage at the post-resolution site up to day 17 as well as increased biosynthesis of cyclooxygenase-derived prostanoids and DHA-derived D series resolvins. Inhibiting post-resolution prostanoids using naproxen showed that numbers of tissue memory CD4 cells were under the endogenous control of PGE2, which exerts its suppressive effects on T cell proliferation via the EP4 receptor. In addition, we re-challenged the post-resolution site with a second injection of E. coli, which when compared to saline controls resulted in primarily a macrophage-driven response with comparatively fewer PMNs; the macrophage-dominated response was reversed by cyclooxygenase inhibition. Re-challenge experiments were also carried out in mice where we obtained similar results as in humans. Therefore, we report that acute inflammatory responses in both humans and rodents do not revert back to homeostasis, but trigger a hitherto unappreciated sequence of immunological events that dictate subsequent immune response to infection.

Inflammatory Resolution Triggers a Prolonged Phase of Immune Suppression through COX-1/mPGES-1-Derived Prostaglandin E2.

Acute inflammation is characterized by granulocyte infiltration followed by efferocytosing mononuclear phagocytes, which pave the way for inflammatory resolution. Until now, it was believed that resolution then leads back to homeostasis, the physiological state tissues experience before inflammation occurred. However, we discovered that resolution triggered a prolonged phase of immune suppression mediated by prostanoids. Specifically, once inflammation was switched off, natural killer cells, secreting interferon γ (IFNγ), infiltrated the post-inflamed site. IFNγ upregulated microsomal prostaglandin E synthase-1 (mPGES-1) alongside cyclo-oxygenase (COX-1) within macrophage populations, resulting in sustained prostaglandin (PG)E2 biosynthesis. Whereas PGE2 suppressed local innate immunity to bacterial infection, it also inhibited lymphocyte function and generated myeloid-derived suppressor cells, the net effect of which was impaired uptake/presentation of exogenous antigens. Therefore, we have defined a sequence of post-resolution events that dampens the propensity to develop autoimmune responses to endogenous antigens at the cost of local tissue infection.

CYP450-derived oxylipins mediate inflammatory resolution.

Resolution of inflammation has emerged as an active process in immunobiology, with cells of the mononuclear phagocyte system being critical in mediating efferocytosis and wound debridement and bridging the gap between innate and adaptive immunity. Here we investigated the roles of cytochrome P450 (CYP)-derived epoxy-oxylipins in a well-characterized model of sterile resolving peritonitis in the mouse. Epoxy-oxylipins were produced in a biphasic manner during the peaks of acute (4 h) and resolution phases (24-48 h) of the response. The epoxygenase inhibitor SKF525A (epoxI) given at 24 h selectively inhibited arachidonic acid- and linoleic acid-derived CYP450-epoxy-oxlipins and resulted in a dramatic influx in monocytes. The epoxI-recruited monocytes were strongly GR1(+), Ly6c(hi), CCR2(hi), CCL2(hi), and CX3CR1(lo) In addition, expression of F4/80 and the recruitment of T cells, B cells, and dendritic cells were suppressed. sEH (Ephx2)(-/-) mice, which have elevated epoxy-oxylipins, demonstrated opposing effects to epoxI-treated mice: reduced Ly6c(hi) monocytes and elevated F4/80(hi) macrophages and B, T, and dendritic cells. Ly6c(hi) and Ly6c(lo) monocytes, resident macrophages, and recruited dendritic cells all showed a dramatic change in their resolution signature following in vivo epoxI treatment. Markers of macrophage differentiation CD11b, MerTK, and CD103 were reduced, and monocyte-derived macrophages and resident macrophages ex vivo showed greatly impaired phagocytosis of zymosan and efferocytosis of apoptotic thymocytes following epoxI treatment. These findings demonstrate that epoxy-oxylipins have a critical role in monocyte lineage recruitment and activity to promote inflammatory resolution and represent a previously unidentified internal regulatory system governing the establishment of adaptive immunity.

Bile duct-ligated mice exhibit multiple phenotypic similarities to acute decompensation patients despite histological differences.

BACKGROUND & AIMS: Patients with decompensated cirrhosis are susceptible to infection. Innate immune dysfunction and development of organ failure are considered to underlie this. A rodent model of liver disease sharing these phenotypic features would assist in vivo study of underlying mechanisms and testing of therapeutics. We evaluated three models to identify which demonstrated the greatest clinical and immunological phenotypic similarity to patients with acutely decompensated (AD) cirrhosis. METHODS: We selected Bile Duct Ligation (BDL) rats at 4 weeks, BDL mice at 14 days and Carbon tetrachloride (CCl4 ) mice at 10 weeks (with studies performed 7 days after final CCl4 infection). We examined organ dysfunction, inflammatory response to carrageenan-in-paw, plasma eicosanoid concentrations, macrophage cytokine production and responses to peritoneal infection. RESULTS: Bile duct ligation caused sarcopenia, liver, cardiovascular and renal dysfunction whereas CCl4 mice demonstrated no clinical abnormalities. BDL rodents exhibited depressed response to carrageenan-in-paw unlike CCl4 mice. BDL rats have slightly elevated plasma eicosanoid levels and plasma showed partial PGE2 -mediated immune suppression whereas CCl4 mice did not. Plasma NOx was elevated in patients with acute or chronic liver failure (AoCLF) compared to healthy volunteers and BDL rodents but not CCl4 mice. Elevated nitric oxide (NO) via inducible nitric oxide synthase (iNOS) mediates defective leucocyte trafficking in BDL rodent models. CONCLUSIONS: We conclude that BDL mice and rats are not simply models of cholestatic liver injury but may be used to study mechanisms underlying poor outcome from infection in AD and have identified elevated NO as a potential mediator of depressed leucocyte trafficking.

Resolution of acute inflammation bridges the gap between innate and adaptive immunity.

Acute inflammation is traditionally characterized by polymorphonuclear leukocytes (PMN) influx followed by phagocytosing macrophage (Mφs) that clear injurious stimuli leading to resolution and tissue homeostasis. However, using the peritoneal cavity, we found that although innate immune-mediated responses to low-dose zymosan or bacteria resolve within days, these stimuli, but not hyperinflammatory stimuli, trigger a previously overlooked second wave of leukocyte influx into tissues that persists for weeks. These cells comprise distinct populations of tissue-resident Mφs (resMφs), Ly6c(hi) monocyte-derived Mφs (moMφs), monocyte-derived dendritic cells (moDCs), and myeloid-derived suppressor cells (MDSCs). Postresolution mononuclear phagocytes were observed alongside lymph node expansion and increased numbers of blood and peritoneal memory T and B lymphocytes. The resMφs and moMφs triggered FoxP3 expression within CD4 cells, whereas moDCs drive T-cell proliferation. The resMφs preferentially clear apoptotic PMNs and migrate to lymph nodes to bring about their contraction in an inducible nitric oxide synthase-dependent manner. Finally, moMφs remain in tissues for months postresolution, alongside altered numbers of T cells collectively dictating the magnitude of subsequent acute inflammatory reactions. These data challenge the prevailing idea that resolution leads back to homeostasis and asserts that resolution acts as a bridge between innate and adaptive immunity, as well as tissue reprogramming.

Immunosuppression in acutely decompensated cirrhosis is mediated by prostaglandin E2.

Liver disease is one of the leading causes of death worldwide. Patients with cirrhosis display an increased predisposition to and mortality from infection due to multimodal defects in the innate immune system; however, the causative mechanism has remained elusive. We present evidence that the cyclooxygenase (COX)-derived eicosanoid prostaglandin E2 (PGE2) drives cirrhosis-associated immunosuppression. We observed elevated circulating concentrations (more than seven times as high as in healthy volunteers) of PGE2 in patients with acute decompensation of cirrhosis. Plasma from these and patients with end-stage liver disease (ESLD) suppressed macrophage proinflammatory cytokine secretion and bacterial killing in vitro in a PGE2-dependent manner via the prostanoid type E receptor-2 (EP2), effects not seen with plasma from patients with stable cirrhosis (Child-Pugh score grade A). Albumin, which reduces PGE2 bioavailability, was decreased in the serum of patients with acute decompensation or ESLD (<30 mg/dl) and appears to have a role in modulating PGE2-mediated immune dysfunction. In vivo administration of human albumin solution to these patients significantly improved the plasma-induced impairment of macrophage proinflammatory cytokine production in vitro. Two mouse models of liver injury (bile duct ligation and carbon tetrachloride) also exhibited elevated PGE2, reduced circulating albumin concentrations and EP2-mediated immunosuppression. Treatment with COX inhibitors or albumin restored immune competence and survival following infection with group B Streptococcus. Taken together, human albumin solution infusions may be used to reduce circulating PGE2 levels, attenuating immune suppression and reducing the risk of infection in patients with acutely decompensated cirrhosis or ESLD.

Characterisation of leukocytes in a human skin blister model of acute inflammation and resolution.

There is an increasing need to understand the leukocytes and soluble mediators that drive acute inflammation and bring about its resolution in humans. We therefore carried out an extensive characterisation of the cantharidin skin blister model in healthy male volunteers. A novel fluorescence staining protocol was designed and implemented, which facilitated the identification of cell populations by flow cytometry. We observed that at the onset phase, 24 h after blister formation, the predominant cells were CD16hi/CD66b+ PMNs followed by HLA-DR+/CD14+ monocytes/macrophages, CD11c+ and CD141+ dendritic cells as well as Siglec-8+ eosinophils. CD3+ T cells, CD19+ B cells and CD56+ NK cells were also present, but in comparatively fewer numbers. During resolution, 72 h following blister induction, numbers of PMNs declined whilst the numbers of monocyte/macrophages remain unchanged, though they upregulated expression of CD16 and CD163. In contrast, the overall numbers of dendritic cells and Siglec-8+ eosinophils increased. Post hoc analysis of these data revealed that of the inflammatory cytokines measured, TNF-α but not IL-1ß or IL-8 correlated with increased PMN numbers at the onset. Volunteers with the greatest PMN infiltration at onset displayed the fastest clearance rates for these cells at resolution. Collectively, these data provide insight into the cells that occupy acute resolving blister in humans, the soluble mediators that may control their influx as well as the phenotype of mononuclear phagocytes that predominate the resolution phase. Further use of this model will improve our understanding of the evolution and resolution of inflammation in humans, how defects in these over-lapping pathways may contribute to the variability in disease longevity/chronicity, and lends itself to the screen of putative anti-inflammatory or pro-resolution therapies.

Transcriptomic analyses of murine resolution-phase macrophages.

Macrophages are either classically (M1) or alternatively-activated (M2). Whereas this nomenclature was generated from monocyte-derived macrophages treated in vitro with defined cytokine stimuli, the phenotype of in vivo-derived macrophages is less understood. We completed Affymetrix-based transcriptomic analysis of macrophages from the resolution phase of a zymosan-induced peritonitis. Compared with macrophages from hyperinflamed mice possessing a pro-inflammatory nature as well as naive macrophages from the uninflamed peritoneum, resolution-phase macrophages (rM) are similar to monocyte-derived dendritic cells (DCs), being CD209a positive but lacking CD11c. They are enriched for antigen processing/presentation (MHC class II [H2-Eb1, H2-Ab1, H2-Ob, H2-Aa], CD74, CD86), secrete T- and B-lymphocyte chemokines (Xcl1, Ccl5, Cxcl13) as well as factors that enhance macrophage/DC development, and promote DC/T cell synapse formation (Clec2i, Tnfsf4, Clcf1). rM are also enriched for cell cycle/proliferation genes as well as Alox15, Timd4, and Tgfb2, key systems in the termination of leukocyte trafficking and clearance of inflammatory cells. Finally, comparison with in vitro-derived M1/M2 shows that rM are neither classically nor alternatively activated but possess aspects of both definitions consistent with an immune regulatory phenotype. We propose that macrophages in situ cannot be rigidly categorized as they can express many shades of the inflammatory spectrum determined by tissue, stimulus, and phase of inflammation.

Priming innate immune responses to infection by cyclooxygenase inhibition kills antibiotic-susceptible and -resistant bacteria.

Inhibition of cyclooxygenase (COX)-derived prostaglandins (PGs) by nonsteroidal anti-inflammatory drugs (NSAIDs) mediates leukocyte killing of bacteria. However, the relative contribution of COX1 versus COX2 to this process, as well as the mechanisms controlling it in mouse and humans, are unknown. Indeed, the potential of NSAIDs to facilitate leukocyte killing of drug-resistant bacteria warrants investigation. Therefore, we carried out a series of experiments in mice and humans, finding that COX1 is the predominant isoform active in PG synthesis during infection and that its prophylactic or therapeutic inhibition primes leukocytes to kill bacteria by increasing phagocytic uptake and reactive oxygen intermediate-mediated killing in a cyclic adenosine monophosphate (cAMP)-dependent manner. Moreover, NSAIDs enhance bacterial killing in humans, exerting an additive effect when used in combination with antibiotics. Finally, NSAIDs, through the inhibition of COX prime the innate immune system to mediate bacterial clearance of penicillin-resistant Streptococcus pneumoniae serotype 19A, a well-recognized vaccine escape serotype of particular concern given its increasing prevalence and multi-antibiotic resistance. Therefore, these data underline the importance of lipid mediators in host responses to infection and the potential of inhibitors of PG signaling pathways as adjunctive therapies, particularly in the con-text of antibiotic resistance.

In vivo models to study cyclooxygenase products in health and disease: Introduction to Part III.

Inflammation is a primordial response that protects against injury and infection with the ultimate aim of restoring damaged tissue to its normal physiological functioning state. In fact, our well-being and survival depends upon its efficiency and carefully balanced control and to which we are alerted in the form of pain, swelling, and redness. Prostaglandins (PG), lipids derived from arachidonic acid metabolism by the enzyme cyclooxygenase, are historically one of the most well-studied mediators of the acute inflammatory response; so much so that their inhibition by so-called non-steroidal anti-inflammatory drugs (NSAIDs) has been the mainstay for the treatment of diseases where inflammation becomes a pathological driving force. However, while NSAIDs relieve the symptoms of dyregulated inflammatory responses, they do not cure the underlying disease and have associated gastrointestinal and renal toxicity. These side effects arose from inhibiting constitutively expressed, protective cyclooxygenase (COX-1). Finding another inducible COX (COX-2) expressed only at sites of injury provided a new era in inflammation research and a new era in treating inflammation-driven diseases. The hope was that high levels of COX-2 expression at sites of pain and tissue injury drove that disease process and that its inhibition would possess all the benefits of traditional NSAIDS without the side effects that arise from the inhibition of protective COX-1. However, by discussing data derived from experimental disease models of acute inflammation, in this chapter we suggest that delineating between the roles of COX-1 and COX-2 might not be as simple as once thought. We provide examples of data where a pathological role for COX-1 is evident and where COX-2 is clearly protective.

Dichotomy in duration and severity of acute inflammatory responses in humans arising from differentially expressed proresolution pathways.

Lipoxins (Lxs) and aspirin-triggered epi-Lxs (15-epi-LxA(4)) act through the ALX/FPRL1 receptor to block leukocyte trafficking, dampen cytokine/chemokine synthesis, and enhance phagocytic clearance of apoptotic leukocytes-key requisites for inflammatory resolution. Although studies using primarily inbred rodents have highlighted resolution as an active event, little is known about the role resolution pathways play in controlling the duration/profile of inflammatory responses in humans. To examine this, we found two types of responders to cantharidin-induced skin blisters in male healthy volunteers: those with immediate leukocyte accumulation and cytokine/chemokine synthesis followed by early resolution and a second group whose inflammation increased gradually over time followed by delayed resolution. In early resolvers, blister 15-epi-LxA(4) and leukocyte ALX were low, but increased as inflammation abated. In contrast, in delayed resolvers, 15-epi-LxA(4) and ALX were high early in the response but waned as inflammation progressed. Elevating 15-epi-LxA(4) in early resolvers using aspirin increased blister leukocyte ALX but reduced cytokines/chemokines as well as polymorphonuclear leukocyte and macrophage numbers. These findings show that two phenotypes exist in humans with respect to inflammation severity/longevity controlled by proresolution mediators, namely 15-epi-LxA(4). These data have implications for understanding the etiology of chronic inflammation and future directions in antiinflammatory therapy.

A new strategy for the identification of novel molecules with targeted proresolution of inflammation properties.

As our understanding of inflammatory resolution increases, drugs that trigger proresolution pathways may become significant in treating chronic inflammatory diseases. However, anti-inflammatory drugs are traditionally tested during the first hours of onset (i.e., to dampen leukocyte and edema formation), and their ability to trigger proresolution processes has never been investigated. Moreover, there is no model available to screen for putative proresolving agents. In this study, we present a new strategy to identify therapeutics for their ability to switch inflammation off and restore homeostasis. Injecting 1.0 mg of zymosan i.p. causes transient inflammation characterized by polymorphonuclear neutrophil clearance and dominated by recently described resolution-phase macrophages along with an innate-type lymphocyte repopulation, the latter being a marker of tissue homeostasis. In contrast, 10 mg of zymosan elicits an aggressive response characterized by classically activated macrophages leading to systemic inflammation and impaired lymphocyte repopulation. Although this latter model eventually resolves, it nonetheless represents inflammation in the clinically relevant setting of polymorphonuclear neutrophil/classically activated macrophage dominance driving a cytokine storm. Treating such a reaction therapeutically with proresolution drugs provides quantifiable indices of resolution--polymorphonuclear neutrophil/macrophage clearance, macrophage phenotype switching (classically activated to resolution phase), and repopulation with resolution-phase lymphocytes--cardinal signs of inflammatory resolution and homeostasis in the peritoneum. As an illustration, mice bearing peritonitis induced by 10 mg of zymosan were given ibuprofen, resolvin E1, a prostaglandin D(2) receptor 1 agonist, dexamethasone, rolipram, or azithromycin, and their ability to trigger resolution and homeostasis in this new inflammatory setting was investigated. We present the first model for testing drugs with targeted proresolution properties using quantifiable parameters of inflammatory resolution and homeostasis.

Effects of low-dose aspirin on acute inflammatory responses in humans.

Aspirin is a unique nonsteroidal anti-inflammatory drug; at high doses (aspirin(high), 1g), it is anti-inflammatory stemming from the inhibition of cyclooxygenase and proinflammatory signaling pathways including NF-kappaB, but is cardioprotective at lower doses (aspirin(low), 75 mg). The latter arises from the inhibition of thromboxane (Tx) B(2), a prothrombotic eicosanoid also implicated in polymorphonuclear leukocyte trafficking. As a result, aspirin(low) is widely used as a primary and secondary preventative against vascular disease. Despite this and its ability to synthesize proresolution 15-epi-lipoxin A(4) it is not known whether aspirin(low) is anti-inflammatory in humans. To address this, we generated skin blisters by topically applying cantharidin on the forearm of healthy male volunteers, causing an acute inflammatory response including dermal edema formation and leukocyte trafficking. Although not affecting blister fluid volume, aspirin(low) (75 mg, oral, once daily/10 days) reduced polymorphonuclear leukocyte and macrophage accumulation independent of NF-kappaB-regulated gene expression and inhibition of conventional prostanoids. However, aspirin(low) triggered 15-epi-lipoxin A(4) synthesis and up-regulated its receptor (FPRL1, ALX). From complimentary in vitro experiments, we propose that 15-epi-lipoxin A(4) exerts its protective effects by triggering antiadhesive NO, thereby dampening leukocyte/endothelial cell interaction and subsequent extravascular leukocyte migration. Since similar findings were obtained from murine zymosan-induced peritonitis, we suggest that aspirin(low) possesses the ability to inhibit mammalian innate immune-mediated responses. This highlights 15-epi-lipoxin A(4) as a novel anti-inflammatory working through a defined receptor and suggests that mimicking its mode of action represents a new approach to treating inflammation-driven diseases.

Nonresolving inflammation in gp91phox-/- mice, a model of human chronic granulomatous disease, has lower adenosine and cyclic adenosine 5'-monophosphate.

In chronic granulomatous disease (CGD), there is failure to generate reactive oxygen metabolites, resulting in recurrent infections and persistent inflammatory events. Because responses to sterile stimuli in murine models of CGD also result in nonresolving inflammation, we investigated whether defects in endogenous counterregulatory mechanisms and/or proresolution pathways contribute to the etiology of CGD. To this end, we conducted a series of experiments finding, in the first instance that adenosine and cAMP, which dampen innate immune-mediated responses, show a biphasic profile in resolving peritonitis; peaking at onset, waning as inflammation progresses, and rising again at resolution. We also found elevations in adenosine and cAMP in resolving human peritonitis. In gp91(phox-/-) mice, an experimental model of CGD, levels of adenosine and cAMP were significantly lower at onset and again at resolution. Corroborating the finding of others, we show that adenosine, signaling through its A(2A) receptor and therefore elevating cAMP, is not only anti-inflammatory, but, importantly, it does not impair proresolution pathways, properties typical of nonsteroidal anti-inflammatory drugs. Conversely, antagonizing the A(2A) receptor worsens acute inflammation and prolongs resolution. Taking this further, activating the A(2A) receptor in gp91(phox-/-) mice was dramatically anti-inflammatory regardless of the phase the inflammatory response A(2A) agonists were administered, i.e., onset or resolution, demonstrating wide and robust pharmacological flexibility that is unlikely to subvert proresolution pathways. Therefore, we describe the biphasic profile of adenosine and cAMP throughout the time course of acute inflammation that is dysregulated in CGD.

Resolution-phase macrophages possess a unique inflammatory phenotype that is controlled by cAMP.

Neutralizing injurious stimuli, proinflammatory mediator catabolism, and polymorphonuclear leukocyte (PMN) clearance are determinants of inflammatory resolution. To this, we recently added innate-type lymphocyte repopulation as being central for restoring postinflammation tissue homeostasis with a role in controlling innate immune-mediated responses to secondary infection. However, although macrophages dominate resolution, their phenotype and role in restoring tissue physiology once inflammation abates are unknown. Therefore, we isolated macrophages from the resolving phase of acute inflammation and found that compared with classically activated proinflammatory M1 cells, resolution-phase macrophages (rMs) possess weaker bactericidal properties and express an alternatively activated phenotype but with elevated markers of M1 cells including inducible cyclooxygenase (COX 2) and nitric oxide synthase (iNOS). This phenotype is controlled by cAMP, which, when inhibited, transforms rM to M1 cells. Conversely, elevating cAMP in M1 cells transforms them to rMs, with implications for cAMP in the resolution of systemic inflammation. It transpires that although rMs are dispensable for clearing PMNs during self-limiting inflammation, they are essential for signaling postresolution lymphocyte repopulation via COX 2 lipids. Thus, rM macrophages are neither classically nor alternatively activated but a hybrid of both, with a role in mediating postresolution innate-lymphocyte repopulation and restoring tissue homeostasis.

Targeting lipoxygenases with care.

Though fish oils possess cardio-protective, anti-inflammatory, and anti-cancer properties, their molecular and biochemical mechanism of action is lacking. In this issue of Chemistry & Biology, Tjonahen and colleagues identify a new metabolite of eicosapentanoic acid, resolvin E2, produced by 5-lipoxygenase.

Essential role for hematopoietic prostaglandin D2 synthase in the control of delayed type hypersensitivity.

Hematopoietic prostaglandin D(2) synthase (hPGD(2)S) metabolizes cyclooxygenase-derived prostaglandin (PG) H(2) to PGD(2), which is dehydrated to cyclopentenone PGs, including 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)). PGD(2) acts through two receptors (DP1 and DP2/CRTH2), whereas 15d-PGJ(2) can activate peroxisome proliferator-activated receptors or inhibit a range of proinflammatory signaling pathways, including NF-kappaB. Despite eliciting asthmatic and allergic reactions through the generation of PGD(2), it is not known what role hPGD(2)S plays in T helper (Th)1-driven adaptive immunity. To investigate this question, the severity and duration of a delayed type hypersensitivity reaction was examined in hPGD(2)S knockout and transgenic mice. Compared with their respective controls, knockouts displayed a more severe inflammatory response that failed to resolve, characterized histologically as persistent acute inflammation, whereas transgenic mice had little detectable inflammation. Lymphocytes isolated from inguinal lymph nodes of hPGD(2)S(-/-) animals showed hyperproliferation and increased IL-2 synthesis effects that were rescued by 15d-PGJ(2), but not PGD(2), working through either of its receptors. Crucially, 15d-PGJ(2) exerted its suppressive effects through the inhibition of NF-kappaB activation and not through peroxisome proliferator-activated receptor signaling. In contrast, lymph node cultures from transgenics proliferated more slowly and synthesized significantly less IL-2 than controls. Therefore, contrary to its role in driving Th2-like responses, this report shows that hPGD(2)S may act as an internal braking signal essential for bringing about the resolution of Th1-driven delayed type hypersensitivity reactions. Consequently, hPGD(2)S-derived cyclopentenone PGs may protect against inflammatory diseases, where T lymphocytes play a pathogenic role, as in rheumatoid arthritis, atopic eczema, and chronic rejection.

Reduced infiltration and increased apoptosis of leukocytes at sites of inflammation by systemic administration of a membrane-permeable IkappaBalpha repressor.

OBJECTIVE: NF-kappaB activation is associated with several inflammatory disorders, including rheumatoid arthritis (RA), making this family of transcription factors a good target for the development of antiinflammatory treatments. Although inhibitors of the NF-kappaB pathway are currently available, their specificity has not been adequately determined. IkappaBalpha is a physiologic inhibitor of NF-kappaB and a potent repressor experimentally when expressed in a nondegradable form. We describe here a novel means for specifically regulating NF-kappaB activity in vivo by administering a chimeric molecule comprising the super-repressor IkappaBalpha (srIkappaBalpha) fused to the membrane-transducing domain of the human immunodeficiency virus Tat protein (Tat-srIkappaBalpha). METHODS: The Wistar rat carrageenan-induced pleurisy model was used to assess the effects of in vivo administration of Tat-srIkappaBalpha on leukocyte infiltration and on cytokine and chemokine production. RESULTS: Systemic administration of Tat-srIkappaBalpha diminished infiltration of leukocytes into the site of inflammation. Analysis of the recruited inflammatory cells confirmed uptake of the inhibitor and reduction of the NF-kappaB activity. These cells exhibited elevated caspase activity, suggesting that NF-kappaB is required for the survival of leukocytes at sites of inflammation. Analysis of exudates, while showing decreases in the production of the proinflammatory cytokines tumor necrosis factor alpha and interleukin-1beta, also revealed a significant increase in the production of the neutrophil chemoattractants cytokine-induced neutrophil chemoattractant 1 (CINC-1) and CINC-3 compared with controls. This result could reveal a previously unknown feedback mechanism in which infiltrating leukocytes may down-regulate local production of these chemokines. CONCLUSION: These results provide new insights into the etiology of inflammation and establish a strategy for developing novel therapeutics by regulating the signaling activity of pathways known to function in RA.