Gabrielle Fredman

Infection regulates pro-resolving mediators that lower antibiotic requirements.

Underlying mechanisms for how bacterial infections contribute to active resolution of acute inflammation are unknown. Here, we performed exudate leukocyte trafficking and mediator-metabololipidomics of murine peritoneal Escherichia coli infections with temporal identification of pro-inflammatory (prostaglandins and leukotrienes) and specialized pro-resolving mediators (SPMs). In self-resolving E. coli exudates (105 colony forming units, c.f.u.), the dominant SPMs identified were resolvin (Rv) D5 and protectin D1 (PD1), which at 12 h were at significantly greater levels than in exudates from higher titre E. coli (107 c.f.u.)-challenged mice. Germ-free mice had endogenous RvD1 and PD1 levels higher than in conventional mice. RvD1 and RvD5 (nanograms per mouse) each reduced bacterial titres in blood and exudates, E. coli-induced hypothermia and increased survival, demonstrating the first actions of RvD5. With human polymorphonuclear neutrophils and macrophages, RvD1, RvD5 and PD1 each directly enhanced phagocytosis of E. coli, and RvD5 counter-regulated a panel of pro-inflammatory genes, including NF-κB and TNF-α. RvD5 activated the RvD1 receptor, GPR32, to enhance phagocytosis. With self-limited E. coli infections, RvD1 and the antibiotic ciprofloxacin accelerated resolution, each shortening resolution intervals (Ri). Host-directed RvD1 actions enhanced ciprofloxacin’s therapeutic actions. In 107 c.f.u. E. coli infections, SPMs (RvD1, RvD5, PD1) together with ciprofloxacin also heightened host antimicrobial responses. In skin infections, SPMs enhanced vancomycin clearance of Staphylococcus aureus. These results demonstrate that specific SPMs are temporally and differentially regulated during infections and that they are anti-phlogistic, enhance containment and lower antibiotic requirements for bacterial clearance.

Resolvin D Series and Protectin D1 Mitigate Acute Kidney Injury

Omega-3 fatty acid docosahexaenoic acid is converted to potent resolvins (Rv) and protectin D1 (PD1), two newly identified families of natural mediators of resolution of inflammation. We report that, in response to bilateral ischemia/reperfusion injury, mouse kidneys produce D series resolvins (RvDs) and PD1. Administration of RvDs or PD1 to mice before the ischemia resulted in a reduction in functional and morphological kidney injury. Initiation of RvDs and RvD1 administration 10 min after reperfusion also resulted in protection of the kidney as measured by serum creatinine 24 and 48 h later. Interstitial fibrosis after ischemia/reperfusion was reduced in mice treated with RvDs. Both RvDs and PD1 reduced the number of infiltrating leukocytes and blocked TLR-mediated activation of macrophages. Thus, the renal production of Rv and protectins, a previously unrecognized endogenous anti-inflammatory response, may play an important role in protection against and resolution of acute kidney injury. These data may also have therapeutic implications for potentiation of recovery from acute kidney injury.

Inflammation and its Resolution as Determinants of Acute Coronary Syndromes

Inflammation contributes to many of the characteristics of plaques implicated in the pathogenesis of acute coronary syndromes. Moreover, inflammatory pathways not only regulate the properties of plaques that precipitate acute coronary syndromes but also modulate the clinical consequences of the thrombotic complications of atherosclerosis. This synthesis will provide an update on the fundamental mechanisms of inflammatory responses that govern acute coronary syndromes and also highlight the ongoing balance between proinflammatory mechanisms and endogenous pathways that can promote the resolution of inflammation. An appreciation of the countervailing mechanisms that modulate inflammation in relation to acute coronary syndromes enriches our fundamental understanding of the pathophysiology of this important manifestation of atherosclerosis. In addition, these insights provide glimpses into potential novel therapeutic interventions to forestall this ultimate complication of the disease.

The docosatriene protectin D1 is produced by TH2 skewing and promotes human T cell apoptosis via lipid raft clustering

Docosahexaenoic acid, a major ω-3 fatty acid in human brain, synapses, retina, and other neural tissues, displays beneficial actions in neuronal development, cancer, and inflammatory diseases by mechanisms that remain to be elucidated. In this study we found, using lipid mediator informatics employing liquid chromatography-tandem mass spectrometry, that (10,17S)-docosatriene/neuroprotectin D1, now termed protectin D1 (PD1), is generated from docosahexaenoic acid by T helper type 2-skewed peripheral blood mononuclear cells in a lipoxygenase-dependent manner. PD1 blocked T cell migration in vivo, inhibited tumor necrosis factor α and interferon-γ secretion, and promoted apoptosis mediated by raft clustering. These results demonstrated novel anti-inflammatory roles for PD1 in regulating events associated with inflammation and resolution.

MicroRNAs in resolution of acute inflammation: identification of novel resolvin D1-miRNA circuits

Mechanisms controlling resolution of acute inflammation are of wide interest. Here, we investigated microRNAs (miRNAs) in self‐limited acute inflammatory exudates and their regulation by resolvin D1 (RvD1). Using real‐time PCR analysis, we found in resolving exudates that miR‐21, miR‐146b, miR‐208a, miR‐203, miR‐142, miR‐302d, and miR‐219 were selectively regulated (P<0.05) in self‐limited murine peritonitis. RvD1 (300 ng/mouse or 15 µgkg‐1) reduced zymosan‐elicited neutrophil infiltration into the peritoneum 25–50% and shortened the resolution interval (ßi)by ~4 h. In peritonitis at 12 h, RvD1 up‐regulated miR‐21, miR‐146b, and miR‐219 and down‐regulated miR‐208a in vivo. In human macrophages overexpressing recombinant RvD1 receptors ALX/FPR2 or GPR32, these same miRNAs were significantly regulated (P<0.05) by RvD1 at concentrations as low as 10 nM, recapitulating the in vivo circuit. In addition, RvD1‐miRNAs identified herein target cytokines and proteins involved in the immune system, e.g., miR‐146b targeted NF‐κB signaling, and miR‐219 targeted 5‐lipoxygenase and reduced leukotriene production. RvD1 also reduced nuclear translocation of NF‐κB and SMAD and down‐regulated phospho‐IκB. Taken together, these results indicate that resolvin‐regulated specific miR‐NAs target genes involved in resolution and establish a novel resolution circuit involving RvD1 receptor‐dependent regulation of specific miRNAs.—Recchiuti, A., Krishnamoorthy, S., Fredman, G., Chiang, N., and Serhan, C. N. MicroRNAs in resolution of acute inflammation: identification of novel resolvin D1‐miRNA circuits. FASEB J. 25, 544–560 (2011). www.fasebj.org

Resolvin E1, an EPA-derived mediator in whole blood, selectively counterregulates leukocytes and platelets.

Resolvin E1 (RvE1) is an omega-3 eicosapentaenoic acid (EPA)-derived lipid mediator generated during resolution of inflammation and in human vasculature via leukocyte-endothelial cell interactions. RvE1 possesses anti-inflammatory and proresolving actions. Here, we report that RvE1 in human whole blood rapidly regulates leukocyte expression of adhesion molecules. RvE1 in the 10- to 100-nM range stimulated L-selectin shedding, while reducing CD18 expression in both neutrophils and monocytes. When added to whole blood, RvE1 did not stimulate reactive oxygen species by either neutrophils or monocytes, nor did it directly stimulate cytokine/chemokine production in heparinized blood. Intravital microscopy (IVM) demonstrated that RvE1 rapidly reduced leukocyte rolling (approximately 40%) in venules of mice. In human platelet-rich plasma (PRP), RvE1 selectively blocked both ADP-stimulated and thromboxane receptor agonist U46619-stimulated platelet aggregation in a concentration-dependent manner. In contrast, Delta 6,14-trans-RvE1 isomer was inactive. RvE1 did not block collagen-stimulated aggregation, and regulation of ADP-induced platelet aggregation was not further enhanced with aspirin treatment. These results indicate RvE1 is a potent modulator of leukocytes as well as selective platelet responses in blood and PRP, respectively. Moreover, the results demonstrate novel agonist-specific antiplatelet actions of RvE1 that are potent and may underlie some of the beneficial actions of EPA in humans.

Resolvin D1 receptor stereoselectivity and regulation of inflammation and proresolving microRNAs.

Resolution of acute inflammation is an active process that involves the biosynthesis of specialized proresolving lipid mediators. Among them, resolvin D1 (RvD1) actions are mediated by two G protein-coupled receptors (GPCRs), ALX/FPR2 and GPR32, that also regulate specific microRNAs (miRNAs) and their target genes in novel resolution circuits. We report the ligand selectivity of RvD1 activation of ALX/FPR2 and GPR32. In addition to RvD1, its aspirin-triggered epimer and RvD1 analogs each dose dependently and effectively activated ALX/FPR2 and GPR32 in GPCR-overexpressing β-arrestin systems using luminescence and electric cell-substrate impedance sensing. To corroborate these findings in vivo, neutrophil infiltration in self-limited peritonitis was reduced in human ALX/FPR2-overexpressing transgenic mice that was further limited to 50% by RvD1 treatment with as little as 10 ng of RvD1 per mouse. Analysis of miRNA expression revealed that RvD1 administration significantly up-regulated miR-208a and miR-219 in exudates isolated from ALX/FPR2 transgenic mice compared with littermates. Overexpression of miR-208a in human macrophages up-regulated IL-10. In comparison, in ALX/FPR2 knockout mice, RvD1 neither significantly reduced leukocyte infiltration in zymosan-induced peritonitis nor regulated miR-208a and IL-10 in these mice. Together, these results demonstrate the selectivity of RvD1 interactions with receptors ALX/FPR2 and GPR32. Moreover, they establish a new molecular circuit that is operative in the resolution of acute inflammation activated by the proresolving mediator RvD1 involving specific GPCRs and miRNAs.

Targeted nanoparticles containing the proresolving peptide Ac2-26 protect against advanced atherosclerosis in hypercholesterolemic mice.

Targeted nanoparticles containing Ac2-26 protect against the progression of advanced atherosclerosis in mice by promoting resolution of inflammation through activating FPR2/ALX on myeloid cells. Inflammation resolution: A solution for advanced atherosclerosis In atherosclerosis, fatty plaques build up in the arteries. It is therefore common that people with cardiovascular disease at risk for atherosclerosis will take statins, or lipid-lowering drugs. However, a complementary approach may be to resolve the ongoing, chronic inflammation in atherosclerosis. Such a proresolving tactic was adopted by Fredman et al. The authors encapsulated a small fragment of annexin A1—a protein that promotes the resolution of inflammation—in a polymeric nanoparticle, and decorated the nanoparticle with a collagen IV–binding peptide, to target the therapeutic package to advanced atherosclerotic plaques. The Ac2-26 nanoparticles accumulated at vessel lesions in a mouse model of advanced atherosclerosis. Once in place, the particles slowly released Ac2-26, which bound to immune cells, reducing oxidative stress, promoting collagen buildup, and increasing the anti-inflammatory cytokine interleukin-10—in sum, working to resolve inflammation and stabilize the plaque. This new proresolving nanomedicine approach will need to be tested in larger vessels and in animal models more similar to human atherosclerosis. But this targeted therapy is a first of its kind, paving the way for a new type of therapy to prevent heart disease. Chronic, nonresolving inflammation is a critical factor in the clinical progression of advanced atherosclerotic lesions. In the normal inflammatory response, resolution is mediated by several agonists, among which is the glucocorticoid-regulated protein called annexin A1. The proresolving actions of annexin A1, which are mediated through its receptor N-formyl peptide receptor 2 (FPR2/ALX), can be mimicked by an amino-terminal peptide encompassing amino acids 2–26 (Ac2-26). Collagen IV (Col IV)–targeted nanoparticles (NPs) containing Ac2-26 were evaluated for their therapeutic effect on chronic, advanced atherosclerosis in fat-fed Ldlr−/− mice. When administered to mice with preexisting lesions, Col IV–Ac2-26 NPs were targeted to lesions and led to a marked improvement in key advanced plaque properties, including an increase in the protective collagen layer overlying lesions (which was associated with a decrease in lesional collagenase activity), suppression of oxidative stress, and a decrease in plaque necrosis. In mice lacking FPR2/ALX in myeloid cells, these improvements were not seen. Thus, administration of a resolution-mediating peptide in a targeted NP activates its receptor on myeloid cells to stabilize advanced atherosclerotic lesions. These findings support the concept that defective inflammation resolution plays a role in advanced atherosclerosis, and suggest a new form of therapy.

Development and in vivo efficacy of targeted polymeric inflammation-resolving nanoparticles

Excessive inflammation and failed resolution of the inflammatory response are underlying components of numerous conditions such as arthritis, cardiovascular disease, and cancer. Hence, therapeutics that dampen inflammation and enhance resolution are of considerable interest. In this study, we demonstrate the proresolving activity of sub–100-nm nanoparticles (NPs) containing the anti-inflammatory peptide Ac2-26, an annexin A1/lipocortin 1-mimetic peptide. These NPs were engineered using biodegradable diblock poly(lactic-co-glycolic acid)-b-polyethyleneglycol and poly(lactic-co-glycolic acid)-b-polyethyleneglycol collagen IV–targeted polymers. Using a self-limited zymosan-induced peritonitis model, we show that the Ac2-26 NPs (100 ng per mouse) were significantly more potent than Ac2-26 native peptide at limiting recruitment of polymononuclear neutrophils (56% vs. 30%) and at decreasing the resolution interval up to 4 h. Moreover, systemic administration of collagen IV targeted Ac2-26 NPs (in as low as 1 µg peptide per mouse) was shown to significantly block tissue damage in hind-limb ischemia-reperfusion injury by up to 30% in comparison with controls. Together, these findings demonstrate that Ac2-26 NPs are proresolving in vivo and raise the prospect of their use in chronic inflammatory diseases such as atherosclerosis.

Specialized proresolving mediator targets for RvE1 and RvD1 in peripheral blood and mechanisms of resolution

Inflammation when unchecked is associated with many prevalent disorders such as the classic inflammatory diseases arthritis and periodontal disease, as well as the more recent additions that include diabetes and cardiovascular maladies. Hence mechanisms to curtail the inflammatory response and promote catabasis are of immense interest. In recent years, evidence has prompted a paradigm shift whereby the resolution of acute inflammation is a biochemically active process regulated in part by endogenous PUFA (polyunsaturated fatty acid)-derived autacoids. Among these are a novel genus of SPMs (specialized proresolving mediators) that comprise novel families of mediators including lipoxins, resolvins, protectins and maresins. SPMs have distinct structures and act via specific G-protein seven transmembrane receptors that signal intracellular events on selective cellular targets activating proresolving programmes while countering pro-inflammatory signals. An appreciation of these endogenous pathways and mediators that control timely resolution opened a new terrain for therapeutic approaches targeted at stimulating resolution of local inflammation. In the present review, we provide an overview of the biosynthesis and actions of resolvin E1, underscoring its protective role in vascular systems and regulating platelet responses. We also give an overview of newly described resolution circuitry whereby resolvins govern miRNAs (microRNAs), and transcription factors that counter-regulate pro-inflammatory chemokines, cytokines and lipid mediators.