Inappropriate neutrophil activation contributes to the pathogenesis of acute lung injury (ALI). Apoptosis is essential for removal of neutrophils from inflamed tissues and timely resolution of inflammation. Resolvin E1 (RvE1) is an endogenous lipid mediator derived from the ω-3 polyunsaturated fatty acid eicosapentaenoic acid that displays proresolving actions. Because the balance of prosurvival and proapoptosis signals determines the fate of neutrophils, we investigated the impact of RvE1 on neutrophil apoptosis and the outcome of neutrophil-mediated pulmonary inflammation in mice. Culture of human neutrophils with RvE1 accelerated apoptosis evoked by phagocytosis of opsonized Escherichia coli or yeast. RvE1 through the leukotriene B ₄ receptor BLT1 enhanced NADPH oxidase-derived reactive oxygen species generation and subsequent activation of caspase-8 and caspase-3. RvE1 also attenuated ERK and Akt-mediated apoptosis-suppressing signals from myeloperoxidase, serum amyloid A, and bacterial DNA, shifting the balance of pro- and anti-survival signals toward apoptosis via induction of mitochondrial dysfunction. In mice, RvE1 treatment enhanced the resolution of established neutrophil-mediated pulmonary injury evoked by intratracheal instillation or i.p. administration of live E. coli or intratracheal instillation of carrageenan plus myeloperoxidase via facilitating neutrophil apoptosis and their removal by macrophages. The actions of RvE1 were prevented by the pan-caspase inhibitor zVAD-fmk. These results identify a mechanism, promotion of phagocytosis-induced neutrophil apoptosis and mitigation of potent anti-apoptosis signals, by which RvE1 could enhance resolution of acute lung inflammation.

The prototypic acute-phase reactant C-reactive protein (CRP) has long been recognized as a useful marker and gauge of inflammation. CRP also plays an important role in host defense against invading pathogens as well as in inflammation. CRP consists of five identical subunits arranged as a cyclic pentamer. CRP exists in at least two conformationally distinct forms, i.e. native pentameric CRP (pCRP) and modified/monomeric CRP (mCRP). These isoforms bind to distinct receptors and lipid rafts, and exhibit distinct functional properties. Dissociation of pCRP into its subunits occurs within the inflammatory microenvironment and newly formed mCRP may then contribute to localizing the inflammatory response. Accumulating evidence indicates that pCRP possesses both pro- and anti-inflammatory actions in a context-dependent manner, whereas mCRP exerts potent pro-inflammatory actions on endothelial cells, endothelial progenitor cells, leukocytes and platelets, and thus may amplify inflammation. Here, we review recent advances that may explain how conformational changes in CRP contribute to shaping the inflammatory response and discuss CRP isomers as potential therapeutic targets to dampen inflammation.

Lipoxin A₄(LXA₄) and aspirin-triggered 15-epi-LXA₄(ATL) are emerging as endogenous braking signals for neutrophil-mediated tissue injury. Recent studies indicate that peroxynitrite (ONOO⁻) may function as an intracellular signal for the production of IL-8, a potent proinflammatory cytokine in human leukocytes. In this study, we evaluated the impact of the metabolically stable analogues of LXA₄/ATL on lipopolysaccharide (LPS)-induced ONOO⁻formation and ONOO⁻-mediated IL-8 gene expression in human leukocytes. At nanomolar concentrations, LXA₄analogues markedly reduced LPS-stimulated superoxide formation, evoked increases in intracellular diamino-fluorescein fluorescence (an indicator of NO formation), and consequently reduced ONOO⁻formation in isolated neutrophils, as well as in neutrophils, monocytes, and lymphocytes, in whole blood. LXA₄/ATL analogues attenuated nuclear accumulation of activator protein-1 and nuclear factor-κB in both polymorphonuclear and mononuclear leukocytes and inhibited IL-8 mRNA expression and IL-8 release by 50–65% in response to LPS. The LXA₄inhibitory responses were concentration dependent and were not shared by 15-deoxy-LXA₄. None of the LXA₄analogues studied affected neutrophil survival, nor reversed the apoptosis delaying action of LPS in neutrophils. In addition, LXA₄analogues had no significant effect on exogenous ONOO⁻-induced IL-8 gene and protein expression. These findings suggest that by attenuating ONOO⁻formation, LXA₄and ATL can oppose ONOO⁻signaling in leukocytes and provide a rationale for using stable synthetic analogues as antiinflammatory compoundsin vivo.

Neutrophil granulocytes form the first line of host defense against invading pathogens and tissue injury. They are rapidly recruited from the blood to the affected sites, where they deploy an impressive arsenal of effectors to eliminate invading microbes and damaged cells. This capacity is endowed in part by readily mobilizable proteins acquired during granulopoiesis and stored in multiple types of cytosolic granules with each granule type containing a unique cargo. Once released, granule proteins contribute to killing bacteria within the phagosome or the extracellular milieu, but are also capable of inflicting collateral tissue damage. Neutrophil‐driven inflammation underlies many common diseases. Research over the last decade has documented neutrophil heterogeneity and functional versatility far beyond their antimicrobial function. Emerging evidence indicates that neutrophils utilize granule proteins to interact with innate and adaptive immune cells and orchestrate the inflammatory response. Granule proteins have been identified as important modulators of neutrophil trafficking, reverse transendothelial migration, phagocytosis, neutrophil life span, neutrophil extracellular trap formation, efferocytosis, cytokine activity, and autoimmunity. Hence, defining their roles within the inflammatory locus is critical for minimizing damage to the neighboring tissue and return to homeostasis. Here, we provide an overview of recent advances in the regulation of degranulation, granule protein functions, and signaling in modulating neutrophil‐mediated immunity. We also discuss how targeting granule proteins and/or signaling could be harnessed for therapeutic benefits.

C-reactive protein (CRP) is well-recognized as a sensitive biomarker of inflammation. Association of elevations in plasma/serum CRP level with disease state has received considerable attention, even though CRP is not a specific indicator of a single disease state. Circulating CRP levels have been monitored with a varying degree of success to gauge disease severity or to predict disease progression and outcome. Elevations in CRP level have been implicated as a useful marker to identify patients at risk for cardiovascular disease and certain cancers, and to guide therapy in a context-dependent manner. Since even strong associations do not establish causality, the pathogenic role of CRP has often been over-interpreted. CRP functions as an important modulator of host defense against bacterial infection, tissue injury and autoimmunity. CRP exists in conformationally distinct forms, which exhibit distinct functional properties and help explaining the diverse, often contradictory effects attributed to CRP. In particular, dissociation of native pentameric CRP into its subunits, monomeric CRP, unmasks “hidden” pro-inflammatory activities in pentameric CRP. Here, we review recent advances in CRP targeting strategies, therapeutic lowering of circulating CRP level and development of CRP antagonists, and a conformation change inhibitor in particular. We will also discuss their therapeutic potential in mitigating the deleterious actions attributed to CRP under various pathologies, including cardiovascular, pulmonary and autoimmune diseases and cancer.

Rationale: Apoptosis is essential for removal of neutrophils from inflamed tissues and efficient resolution of inflammation. Myeloperoxidase (MPO), abundantly expressed in neutrophils, not only generates cytotoxic oxidants but also signals through the β2 integrin Mac-1 to rescue neutrophils from constitutive apoptosis, thereby prolonging inflammation. Objectives: Because aspirin-triggered 15-epi-lipoxin A4 (15-epi-LXA4) modulates Mac-1 expression, we investigated the impact of 15-epi-LXA4 on MPO suppression of neutrophil apoptosis and MPO-mediated neutrophil-dependent acute lung injury. Methods: Human neutrophils were cultured with MPO with or without 15-epi-LXA4 to investigate development of apoptosis. Acute lung injury was produced by intratracheal injection of carrageenan plus MPO or intraperitoneal injection of live Escherichia coli in mice, and the animals were treated with 15-epi-LXA4 at the peak of inflammation. Measurements and Main Results: 15-Epi-LXA4 through down-regulation of Mac-1 expression promoted apoptosis of human neutrophils by attenuating MPO-induced activation of extracellular signal–regulated kinase and Akt-mediated phosphorylation of Bad and by reducing expression of the antiapoptotic protein Mcl-1, thereby aggravating mitochondrial dysfunction. The proapoptotic effect of 15-epi-LXA4 was dominant over MPO-mediated effects even when it was added at 4 hours post MPO. In mice, treatment with 15-epi-LXA4 accelerated the resolution of established carrageenan plus MPO-evoked as well as E. coli–induced neutrophil-dependent pulmonary inflammation through redirecting neutrophils to caspase-mediated cell death and facilitating their removal by macrophages. Conclusions: These results demonstrate that aspirin-triggered 15-epi-LXA4 enhances resolution of inflammation by overriding the powerful antiapoptosis signal from MPO, thereby demonstrating a hitherto unrecognized mechanism by which aspirin promotes resolution of inflammation.