Karsten Gronert

Resolvins A Family of Bioactive Products of Omega-3 Fatty Acid Transformation Circuits Initiated by Aspirin Treatment that Counter Proinflammation Signals

Aspirin (ASA) is unique among current therapies because it acetylates cyclooxygenase (COX)-2 enabling the biosynthesis of R-containing precursors of endogenous antiinflammatory mediators. Here, we report that lipidomic analysis of exudates obtained in the resolution phase from mice treated with ASA and docosahexaenoic acid (DHA) (C22:6) produce a novel family of bioactive 17R-hydroxy-containing di- and tri-hydroxy-docosanoids termed resolvins. Murine brain treated with aspirin produced endogenous 17R-hydroxydocosahexaenoic acid as did human microglial cells. Human COX-2 converted DHA to 13-hydroxy-DHA that switched with ASA to 17R-HDHA that also proved a major route in hypoxic endothelial cells. Human neutrophils transformed COX-2-ASA–derived 17R-hydroxy-DHA into two sets of novel di- and trihydroxy products; one initiated via oxygenation at carbon 7 and the other at carbon 4. These compounds inhibited (IC50 ∼50 pM) microglial cell cytokine expression and in vivo dermal inflammation and peritonitis at ng doses, reducing 40–80% leukocytic exudates. These results indicate that exudates, vascular, leukocytes and neural cells treated with aspirin convert DHA to novel 17R-hydroxy series of docosanoids that are potent regulators. These biosynthetic pathways utilize omega-3 DHA and EPA during multicellular events in resolution to produce a family of protective compounds, i.e., resolvins, that enhance proresolution status.

Lipid mediator class switching during acute inflammation: signals in resolution

Leukotrienes (LTs) and prostaglandins (PGs) amplify acute inflammation, whereas lipoxins (LXs) have unique anti-inflammatory actions. Temporal analyses of these eicosanoids in clinical and experimental exudates showed early coordinate appearance of LT and PG with polymorphonuclear neutrophil (PMN) recruitment. This was followed by LX biosynthesis, which was concurrent with spontaneous resolution. Human peripheral blood PMNs exposed to PGE2 (as in exudates) switched eicosanoid biosynthesis from predominantly LTB4 and 5-lipoxygenase (5-LO)–initiated pathways to LXA4, a 15-LO product that “stopped” PMN infiltration. These results indicate that first-phase eicosanoids promote a shift to anti-inflammatory lipids: functionally distinct lipid-mediator profiles switch during acute exudate formation to “reprogram” the exudate PMNs to promote resolution.

Novel docosanoids Inhibit brain ischemia-reperfusion-mediated leukocyte infiltration and pro-inflammatory gene expression

Ischemic stroke triggers lipid peroxidation and neuronal injury. Docosahexaenoic acid released from membrane phospholipids during brain ischemia is a major source of lipid peroxides. Leukocyte infiltration and pro-inflammatory gene expression also contribute to stroke damage. In this study using lipidomic analysis, we have identified stereospecific messengers from docosahexaenoate-oxygenation pathways in a mouse stroke model. Aspirin, widely used to prevent cerebrovascular disease, activates an additional pathway, which includes the 17R-resolvins. The newly discovered brain messenger 10,17S-docosatriene potently inhibited leukocyte infiltration, NFκB, and cyclooxygenase-2 induction in experimental stroke and elicited neuroprotection. In addition, in neural cells in culture, this lipid messenger also inhibited both interleukin 1-β-induced NFκB activation and cyclooxygenase-2 expression. Thus, the specific novel bioactive docosanoids generated in vivo counteract leukocyte-mediated injury as well as pro-inflammatory gene induction. These results challenge the view that docosahexaenoate only participates in brain damage and demonstrate that this fatty acid is also the endogenous precursor to a neuroprotective signaling response to ischemia-reperfusion.

Obesity-induced insulin resistance and hepatic steatosis are alleviated by ω-3 fatty acids: a role for resolvins and protectins

Omega‐3‐polyunsaturated fatty acids (w‐3‐PUFAs) have well‐documented protective effects that are attributed not only to eicosanoid inhibition but also to the formation of novel biologically active lipid mediators (i.e., resolvins and protectins). In this study, we examined their effects on ob/ob mice, an obesity model of insulin resistance and fatty liver disease. Dietary intake ofw‐3‐PUFAs had insulin‐sensitizing actions in adipose tissue and liver and improved insulin tolerance in obese mice. Genes involved in insulin sensitivity (PPAR/γ), glucose transport (GLUT‐2/GLUT–4), and insulin receptor signaling (IRS‐1/IRS–2) were up‐regulated byw‐3‐PUFAs. Moreover,w‐3‐PUFAs increased adiponectin, an anti‐inflammatory and insulin‐sensitizing adipokine, and induced AMPK phosphorylation, a fuel‐sensing enzyme and a gatekeeper of the energy balance. Concomitantly, hepatic steatosis was alleviated byw‐3‐PUFAs. A lipidomic analysis with liquid chromatography/mass spectrome‐try/mass spectrometry revealed that w‐3‐PUFAs inhibited the formation of w‐6‐PUFA‐derived eicosanoids, while triggering the formation of w‐3‐PUFA‐derived resolvins and protectins. Moreover, representative members of these lipid mediators, namely resolvin E1 and protectin D1, mimicked the insulin‐sensitizing and antisteatotic effects of w‐3‐PUFAs and induced adiponectin expression to a similar extent that of rosigli‐tazone, a member of the thiazolidinedione family of antidiabetic drugs. Taken together, these findings uncover beneficial actions of w‐3‐PUFAs and their bioactive lipid autacoids in preventing obesity‐induced insulin resistance and hepatic steatosis.—Gonzalez‐Periz, A.,Horrillo, R., Ferre, N., Gronert, K., Dong, B., Moran‐Salvador, E.,Titos, E., Martinez‐Clemente, M.,Lopez‐Parra, M.,Arroyo, V., Claria, J. Obesity‐induced insulin resistance and hepatic steatosis are alleviated byw‐3 fatty acids: a role for resolvins and protectins. FASEB J. 23, 1946–1957 (2009)

Leukotriene B4 receptor transgenic mice reveal novel protective roles for lipoxins and aspirin-triggered lipoxins in reperfusion

Polymorphonuclear neutrophil (PMN) activation is pivotal in acute inflammation and injury from reperfusion. To elucidate components controlling PMNs in vivo, we prepared novel transgenic mice with the human leukotriene (LT) B4 receptor (BLTR) for functional characterization. Overexpression of BLTR in leukocytes dramatically increased PMN trafficking to skin microabscesses and lungs after ischemia-reperfusion, whereas mice deficient in 5-lipoxygenase (5-LO) showed diminished PMN accumulation in reperfused lungs. Hence, both BLTR expression and LT biosynthesis are critical for PMN infiltration in reperfusion-initiated second-organ injury. Also, in BLTR transgenic mice, 5-LO expression and product formation were selectively increased in exudates, demonstrating that receptor overexpression amplifies proinflammatory circuits. Endogenous lipoxin (LX) A4 was produced in ischemic lungs and elevated by reperfusion. Because LXA4 and aspirin-triggered 15-epimeric LXA4 (ATL) selectively regulate leukocyte responses, they were tested in BLTR transgenic mice. Despite excessive PMN recruitment in BLTR transgenic mice, intravenous injection of ATL sharply diminished reperfusion-initiated PMN trafficking to remote organs, and topical application of LX was protective in acute dermal inflammation. These results demonstrate a direct role for BLTR with positive feedback, involving BLTR and 5-LO signaling in controlling PMNs. Moreover, LXA4 and ATL counter BLTR-amplified networks, revealing a novel protective role for LX and ATL in stress responses that has applications in perioperative medicine.

Neutrophil-mediated changes in vascular permeability are inhibited by topical application of aspirin-triggered 15-epi-lipoxin A4 and novel lipoxin B4 stable analogues.

Neutrophil (PMN) activation is critical in inflammation and reperfusion injury, suggesting that PMN-directed therapies may be of clinical use. Here, leukotriene B4 (LTB4)-induced PMN influx in ear skin was equivalent between 5-lipoxygenase knockout and wild-type mice. To explore actions of lipoxin (LX) in PMN-mediated tissue injury, we prepared several novel LX stable analogues, including analogues of LXA4 and aspirin-triggered 15-epi-LXA4 as well as LXB4, and examined their impact in PMN infiltration and vascular permeability. Each applied topically to mouse ears inhibited dramatically PMN-mediated increases in vascular permeability (IC50 range of 13-26 nmol) with a rank order of 15(R/S)-methyl-LXA4 > 16-para-fluoro-phenoxy-LXA4 approximately 5(S)-methyl-LXB4 >/= 16-phenoxy-LXA4 > 5(R)-methyl-LXB4. These LX mimetics were as potent as an LTB4 receptor antagonist, yet results from microphysiometry with mouse leukocytes indicated that they do not act as LTB4 receptor level antagonists. In addition, within 24 h of delivery, > 90% were cleared from ear biopsies. Neither IL-8, FMLP, C5a, LTD4, nor platelet-activating factor act topically to promote PMN influx. When applied with LTB4, PGE2 enhanced sharply both infiltration and vascular permeability, which were inhibited by a fluorinated stable analogue of aspirin-triggered LX. These results indicate that mimetics of LXs and aspirin-triggered 15-epi-LXA4 are topically active in this model and are potent inhibitors of both PMN infiltration and PMN-mediated vascular injury.

Rapid induction of inflammatory lipid mediators by the inflammasome in vivo.

Detection of microbial products by host inflammasomes is an important mechanism of innate immune surveillance. Inflammasomes activate the caspase-1 (CASP1) protease, which processes the cytokines interleukin (IL)-1β and IL-18, and initiates a lytic host cell death called pyroptosis. To identify novel CASP1 functions in vivo, we devised a strategy for cytosolic delivery of bacterial flagellin, a specific ligand for the NAIP5 (NLR family, apoptosis inhibitory protein 5)/NLRC4 (NLR family, CARD-domain-containing 4) inflammasome. Here we show that systemic inflammasome activation by flagellin leads to a loss of vascular fluid into the intestine and peritoneal cavity, resulting in rapid (less than 30 min) death in mice. This unexpected response depends on the inflammasome components NAIP5, NLRC4 and CASP1, but is independent of the production of IL-1β or IL-18. Instead, inflammasome activation results, within minutes, in an ‘eicosanoid storm’—a pathological release of signalling lipids, including prostaglandins and leukotrienes, that rapidly initiate inflammation and vascular fluid loss. Mice deficient in cyclooxygenase-1, a critical enzyme in prostaglandin biosynthesis, are resistant to these rapid pathological effects of systemic inflammasome activation by either flagellin or anthrax lethal toxin. Inflammasome-dependent biosynthesis of eicosanoids is mediated by the activation of cytosolic phospholipase A2 in resident peritoneal macrophages, which are specifically primed for the production of eicosanoids by high expression of eicosanoid biosynthetic enzymes. Our results therefore identify eicosanoids as a previously unrecognized cell-type-specific signalling output of the inflammasome with marked physiological consequences in vivo.

Selectivity of Recombinant Human Leukotriene D4, Leukotriene B4, and Lipoxin A4 Receptors with Aspirin-Triggered 15-epi-LXA4 and Regulation of Vascular and Inflammatory Responses

Aspirin-triggered lipoxin A(4) (ATL, 15-epi-LXA(4)) and leukotriene D(4) (LTD(4)) possess opposing vascular actions mediated via receptors distinct from the LXA(4) receptor (ALX) that is involved in leukocyte trafficking. Here, we identified these receptors by nucleotide sequencing and demonstrate that LTD(4) receptor (CysLT(1)) is induced in human vascular endothelia by interleukin-1beta. Recombinant CysLT(1) receptor gave stereospecific binding with both [(3)H]-LTD(4) and a novel labeled mimetic of ATL ([(3)H]-ATLa) that was displaced with LTD(4) and ATLa ( approximately IC(50) 0.2 to 0.9 nmol/L), but not with a bioinactive ATL isomer. The clinically used CysLT(1) receptor antagonist, Singulair, showed a lower rank order for competition with [(3)H]-ATLa (IC(50) approximately 8.3 nmol/L). In contrast, LTD(4) was an ineffective competitive ligand for recombinant ALX receptor with [(3)H]-ATLa, and ATLa did not compete for [(3)H]-LTB(4) binding with recombinant LTB(4) receptor. Endogenous murine CysLT(1) receptors also gave specific [(3)H]-ATLa binding that was displaced with essentially equal affinity by LTD(4) or ATLa. Systemic ATLa proved to be a potent inhibitor (>50%) of CysLT(1)-mediated vascular leakage in murine skin (200 microg/kg) in addition to its ability to block polymorphonuclear leukocyte recruitment to dorsal air pouch (4 microg/kg). These results indicate that ATL and LTD(4) bind and compete with equal affinity at CysLT(1), providing a molecular basis for aspirin-triggered LXs serving as a local damper of both vascular CysLT(1) signals as well as ALX receptor-regulated polymorphonuclear leukocyte traffic.

PATHOGEN-INDUCED CHEMOKINE SECRETION FROM MODEL INTESTINAL EPITHELIUM IS INHIBITED BY LIPOXIN A4 ANALOGS

Enteric pathogens induce intestinal epithelium to secrete chemokines that direct movement of polymorphonuclear leukocytes. Mechanisms that might downregulate secretion of these proinflammatory chemokines and thus contain intestinal inflammation have not yet been elucidated. The antiinflammatory activities exhibited by the arachidonate metabolite lipoxin A4 (LXA4) suggests that this eicosanoid, which is biosynthesized in vivo at sites of inflammation, might play such a role. We investigated whether chemokine secretion could be regulated by stable analogs of LXA4. Monolayers of T84 intestinal epithelial cells were infected with Salmonella typhimurium, which elicits secretion of distinct apical (pathogen-elicited epithelial chemoattractant) and basolateral (IL-8) chemokines. Stable analogs of LXA4 inhibited S. typhimurium-induced (but not phorbol ester-induced) secretion of both IL-8 and pathogen-elicited epithelial chemoattractant. LXA4 stable analogs did not alter bacterial adherence to nor internalization by epithelia, indicating that LXA4 stable analogs did not block all signals that Salmonella typhimurium activates in intestinal epithelia, but likely led to attenuation of signals that mediate chemokine secretion. Inhibition of S. typhimurium-induced IL-8 secretion by LXA4 analogs was concentration- (IC50 approximately 1 nM) and time-dependent (maximal inhibition approximately 1 h). As a result of these effects, LXA4 stable analogs inhibited the ability of bacteria-infected epithelia to direct polymorphonuclear leukocyte movement. These data suggest that LXA4 and its stable analogs may be useful in downregulating active inflammation at mucosal surfaces.

Human ALX receptor regulates neutrophil recruitment in transgenic mice: roles in inflammation and host defense

Signaling pathways instrumental in the temporal and spatial progression of acute inflammation toward resolution are of wide interest. Here a transgenic mouse with myeloid‐selective expression of human lipoxin A4 receptor (hALX) was prepared and used to evaluate in vivo the effect of hALX expression. hALX‐transfected HEK293 cells transmitted LXA4 signals that inhibit TNFα‐induced NFκB activation. Transgenic FvB mice were generated by DNA injections of a 3.8 kb transgene consisting of the full‐length hALX cDNA driven by a fragment of the hCD11b promoter. When topically challenged via dermal ear skin, hALX transgenic mice gave attenuated neutrophil infiltration (∼80% reduction) in response to leukotriene B4 (LTB4) plus prostaglandin E2 (PGE2) as well as ∼50% reduction in PMN infiltrates (P<0.02) to receptor‐bypass inflammation evoked by phorbol ester. The hALX transgenic mice gave markedly decreased PMN infiltrates to the peritoneum with zymosan and altered the dynamics of this response. Transgenic hALX mice displayed increased sensitivity with >50% reduction in PMN infiltrates to suboptimal doses (10 ng/mouse) of the ligand lipoxin A4 stable analog compared with < 10% reduction of PMN in nontransgenic littermates. Soluble mediators generated within the local inflammatory milieu of hALX mice showed diminished ability to activate the proinflammatory transcription factor NFκB. Analyses of the lipid‐derived mediators from exudates using LC‐MS tandem mass spectroscopy indicated an altered profile in hALX transgenic mice that included lower levels of LTB4 and increased amounts of lipoxin A4 compared with nontransgenic littermates. Together these results demonstrate a gain‐of‐function with hALX transgenic mouse and indicate that ALX is a key receptor and sensor in formation of acute exudates and their resolution.