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Concept: Lipoxin

168

BACKGROUND: The neuroinflammatory responses in the spinal cord following bone cancer development have been shown to play an important role in cancer-induced bone pain (CIBP). Lipoxins (LXs), endogenous lipoxygenase-derived eicosanoids, represent a unique class of lipid mediators that possess a wide spectrum of anti-inflammatory and pro-resolving actions. In this study, we investigated the effects of intrathecal injection with lipoxin and related analogues on CIBP in rats. METHODS: The CIBP model was induced by intra-tibia inoculation of Walker 256 mammary gland carcinoma cells. Mechanical thresholds were determined by measuring the paw withdrawal threshold to probing with a series of calibrated von Frey filaments. Lipoxins and analogues were administered by intrathecal (i.t.) or intravenous (i.v.) injection. The protein level of LXA4 receptor (ALX) was tested by western blot. The localization of lipoxin receptor in spinal cord was assessed by fluorescent immunohistochemistry. Real-time PCR was carried out for detecting the expression of pro-inflammatory cytokines. RESULTS: Our results demonstrated that: 1) i.t. injection with the same dose (0.3 nmol) of lipoxin A4 (LXA4), lipoxin B4 (LXB4) or aspirin-triggered-15-epi-lipoxin A4 (ATL) could alleviate the mechanical allodynia in CIBP on day 7 after surgery. ATL showed a longer effect than the others and the effect lasted for 6 hours. ATL administered through i.v. injection could also attenuate the allodynia in cancer rats. 2) The results from western blot indicate that there is no difference in the expression of ALX among the naive, sham or cancer groups. 3) Immunohistochemistry showed that the lipoxin receptor (ALX)-like immunoreactive substance was distributed in the spinal cord, mainly co-localized with astrocytes, rarely co-localized with neurons, and never co-localized with microglia. 4) Real-time PCR analysis revealed that, compared with vehicle, i.t. injection with ATL could significantly attenuate the expression of the mRNA of proinflammatory cytokines (IL-1beta and TNF-alpha) in the spinal cord in CIBP. CONCLUSIONS: Taken together, the results of our study suggest that LXs and analogues exert strong analgesic effects on CIBP. These analgesic effects in CIBP are associated with suppressing the expression of spinal proinflammatory cytokines.

Concepts: Inflammation, Polymerase chain reaction, Molecular biology, Pain, Eicosanoids, Lipoxin, Nonclassic eicosanoid, Epi-lipoxin

165

Cerebral malaria is caused by infection with Plasmodium falciparum and can lead to severe neurological manifestations and predominantly affects sub-Saharan African children. The pathogenesis of this disease involves unbalanced over-production of pro-inflammatory cytokines. It is clear that signaling though IL-12 receptor is a critical step for development of cerebral malaria, IL-12 genetic deficiency failed to show the same effect, suggesting that there is redundancy among the soluble mediators which leads to immunopathology and death. Consequently, counter-regulatory mediators might protect the host during cerebral malaria. We have previously showed that endogenously produced lipoxins, which are anti-inflammatory mediators generated by 5-lipoxygenase (5-LO)-dependent metabolism of arachidonic acid, limit host damage in a model of mouse toxoplasmosis. We postulated here that lipoxins might also play a counter-regulatory role during cerebral malaria. To test this hypothesis, we infected 5-LO-deficient hosts with P. berghei ANKA strain, which induces a mouse model of cerebral malaria (ECM). Our results show accelerated mortality concomitant with exuberant IL-12 and IFN-γ production in the absence of 5-lipoxygenase. Moreover, in vivo administration of lipoxin to 5-LO-deficient hosts prevented early mortality and reduced the accumulation of CD8(+)IFN-γ (+) cells in the brain. Surprisingly, WT animals treated with lipoxin either at the time of infection or 3 days post-inoculum also showed prolonged survival and diminished brain inflammation, indicating that although protective, endogenous lipoxin production is not sufficient to optimally protect the host from brain damage in cerebral malaria. These observations establish 5-LO/LXA4 as a host protective pathway and suggest a new therapeutic approach against human cerebral malaria (HCM). (255 words).

Concepts: Immune system, Inflammation, Malaria, Plasmodium falciparum, Sub-Saharan Africa, Plasmodium, Plasmodium vivax, Lipoxin

28

Background  Lipoxins are potential anti-inflammatory mediators and serve as an endogenous ‘braking signal’ in the inflammatory process. Accumulating evidence has indicated the efficacy of lipoxin A(4) (LXA(4) ) and its analogs in the treatment of many animal models of inflammatory diseases. Objectives  This study investigates the efficacy and safety of 15(R/S)-methyl-lipoxin A(4) in the topical treatment of infantile eczema. Patients and methods  In this two-centre, double-blind, placebo-controlled, randomized, parallel-groups comparative study, 60 patients were randomly assigned to receive either the 15(R/S)-methyl-lipoxin A(4) cream, mometasone furoate (Eloson, Schering-Plough, Shanghai, China) or placebo for 10 days. The efficacy was determined using the Severity Scale Score (SSS), Eczema Area and Severity Index (EASI) and the Infants' Dermatitis Quality of Life Index (IDQOL). Safety was monitored by physical examination, laboratory investigation and documentation of clinical adverse events. Results  The treatment of eczema with 15(R/S)-methyl-LXA(4) cream significantly relieved the severity, induced a recovery, and improved the quality of life of the patients, as demonstrated by significantly reduced SSS, EASI and IDQOL, respectively, in a way similar to the efficacy of Eloson. All safety parameters remained within normal limits. No clinical adverse event was found in the three patient groups. Conclusions  15(R/S)-methyl-LXA(4) was well tolerated, and significantly reduced the severity of eczema. The results of this small exploratory study suggest that 15(R/S)-methyl-LXA(4) warrants further investigation in the treatment of eczema.

Concepts: Inflammation, Clinical trial, Asthma, Anti-inflammatory, Clinical research, Eczema, Dermatitis, Lipoxin

27

Nonresolving inflammation is a hallmark of many types of tumors and the molecular mechanisms maintaining this inflammation are still largely unknown. In a two stage carcinogenesis model, we observed here that the lack of IFNγ receptor or neutralization of IFNγ accelerated spontaneous papilloma regression in mice. The impaired maintenance of local inflammation was associated with reduced IFNγ and enhanced biosynthesis of pro-resolution lipid mediator lipoxin A4 (LXA4). Interestingly, blocking LXA4 eliminated the effect of anti-IFNγ, while treatment of mice with a therapeutic dose of LXA4 accelerated papilloma regression in an IFNγ independent manner. These results link for the first time a cytokine-dependent maintenance of inflammation with a down-regulated production of pro-resolution lipid mediators. Strategies promoting spontaneous resolution of chronic inflammation by blocking IFNγ and/or increasing LXA4 may be useful for the treatment of inflammation-associated tumors.

Concepts: Immune system, Inflammation, Therapeutic effect, Metabolism, Adenosine triphosphate, Stage, Mediation, Lipoxin

20

Astrocytes perform critical non-cell autonomous roles following CNS injury that involve either neurotoxic or neuroprotective effects. Yet the nature of potential prosurvival cues has remained unclear. In the current study, we utilized the close interaction between astrocytes and retinal ganglion cells (RGCs) in the eye to characterize a secreted neuroprotective signal present in retinal astrocyte conditioned medium (ACM). Rather than a conventional peptide neurotrophic factor, we identified a prominent lipid component of the neuroprotective signal through metabolomics screening. The lipoxins LXA4 and LXB4 are small lipid mediators that act locally to dampen inflammation, but they have not been linked directly to neuronal actions. Here, we determined that LXA4 and LXB4 are synthesized in the inner retina, but their levels are reduced following injury. Injection of either lipoxin was sufficient for neuroprotection following acute injury, while inhibition of key lipoxin pathway components exacerbated injury-induced damage. Although LXA4 signaling has been extensively investigated, LXB4, the less studied lipoxin, emerged to be more potent in protection. Moreover, LXB4 neuroprotection was different from that of established LXA4 signaling, and therapeutic LXB4 treatment was efficacious in a chronic model of the common neurodegenerative disease glaucoma. Together, these results identify a potential paracrine mechanism that coordinates neuronal homeostasis and inflammation in the CNS.

Concepts: Inflammation, Nervous system, Neurology, Retina, Retinal ganglion cell, Neuroprotection, Lipoxin, Nonclassic eicosanoid

2

When 5-lipoxygenase (5-LO) is inhibited, roughly half of the CNS effect of the prototypic endocannabinoid anandamide (AEA) is lost. Therefore, we decided to investigate whether inhibiting this enzyme would influence physiological functions classically described as being under control of the endocannabinoid system. Although 5-LO inhibition by MK-886 reduced lipoxin A4 levels in the brain, no effect was found in the elevated plus maze (EPM), even at the highest possible doses, via i.p. (10 mg/kg,) or i.c.v. (500 pmol/2 µl) routes. Accordingly, no alterations in anxiety-like behavior in the EPM test were observed in 5-LO KO mice. Interestingly, aged mice, which show reduced circulating lipoxin A4 levels, were sensitive to MK-886, displaying an anxiogenic-like state in response to treatment. Moreover, exogenous lipoxin A4 induced an anxiolytic-like profile in the EPM test. Our findings are in line with other reports showing no difference between FLAP KO or 5-LO KO and their control strains in adult mice, but increased anxiety-like behavior in aged mice. We also show for the first time that lipoxin A4 affects mouse behavior. In conclusion, we propose an age-dependent relevancy of endogenous 5-LO derivatives in the modulation of anxiety-like behavior, in addition to a potential for exogenous lipoxin A4 in producing an anxiolytic-like state.

Concepts: Inflammation, Brain, Inhibitor, Mouse, Eicosanoids, Lipoxin, Relevance, Arachidonate 5-lipoxygenase

0

Dysfunction in the resolution of inflammation may play a key role in Alzheimer’s disease (AD). In this study, we found that the levels of specialized pro-resolving lipid mediators (SPMs) in the hippocampus of 5xFAD mice are significantly lower than in non-transgenic littermates. We, therefore, tested the hypothesis that treatment with resolvin E1 (RvE1) and lipoxin A4 (LXA4) alone or in combination will reverse the neuroinflammatory process and decrease Aβ pathology. 5xFAD mice were treated intraperitoneally starting at 1month of age with RvE1 or LXA4 alone or in combination at a dose of 1.5 μg/kg, 3 times a week until 3months of age. We found that treatment with RvE1 or LXA4 alone or in combination increased the concentration of RvE1, LXA4, and RvD2 in the hippocampus as measured by ELISA. Combination treatment of RvE1 and LXA4 had a more potent effect on the activation of microglia and astrocytes than either treatment alone, measured by immunohistochemistry with Iba1 and GFAP antibodies, respectively. The concentrations of Aβ40 and Aβ42 were measured by ELISA and the percentage of Aβ plaques were analyzed by immunohistochemistry. All treatments single and in combination, decreased the measures of Aβ pathology and restored the homeostasis reversing the inflammatory process for inflammatory cytokines and chemokines (GM-CSF, IFN-γ, IL-1β, IL-6, IL-10, TNF-α, MCP-1, MIP-1α, MIP-1β, and RANTES) as measured by multiplex immunoassay. Overall, the study showed that the levels of SPMs in the hippocampus of 5xFAD mice were significantly lower than in wild-type mice; that treatment with RvE1 and LXA4 restored the level of these compounds, reversed the inflammatory process, and decreased the neuroinflammation associated with Aβ pathology in 5xFAD mice.

Concepts: Inflammation, Antibody, Pneumonia, Anti-inflammatory, Chemokine, Reverse, Lipoxin, Nonclassic eicosanoid

0

The involvement of microRNA (miR) in cystic fibrosis (CF) pathobiology is rapidly emerging. We previously documented that miR-181b controls the expression of the ALX/FPR2 receptor, which is recognized by the endogenous proresolution ligand, lipoxin (LX)A4. Here, we examined whether the miR-181b-ALX/FPR2 circuit was altered in CF. We examined human airways epithelial cells, normal (16HBE14o-), carrying the ΔF508 mutation (CFBE41o-) or corrected for this mutation (CFBE41o-/CEP-CFTR wt 6.2 kb), as well as monocyte-derived macrophages (MΦs) from CF patients. CFBE41o- cells exhibited higher miR-181b and reduced ALX/FPR2 levels compared to 16HBE14o- and CFBE41o-/CEP-CFTR wt 6.2 kb cells. An anti-mir-181b significantly enhanced ALX/FPR2 expression (+ 60%) as well as LXA4-induced increase in transepithelial electric resistance (+ 25%) in CFBE41o- cells. MΦs from CF patients also displayed increased miR-181b (+ 100%) and lower ALX/FPR2 levels (- 20%) compared to healthy cells. An anti-mir-181b enhanced ALX/FPR2 expression (+ 40%) and normalized receptor-dependent LXA4-induced phagocytosis of fluorescent-labeled zymosan particles as well as of Pseudomonas aeruginosa by CF-MΦs. These results provide the first evidence that miR-181b is overexpressed in CF cells, impairing some mechanisms of the ALX/FPR2-dependent pathway of inflammation resolution. Thus, targeting miR-181b may represent a strategy to enhance anti-inflammatory and anti-microbial defense mechanisms in CF.

Concepts: Immune system, Inflammation, DNA, Bacteria, Pseudomonas aeruginosa, Cystic fibrosis, Endothelium, Lipoxin

0

Critical conditions such as sepsis following infection or traumatic injury disturb the complex state of homeostasis that may lead to uncontrolled inflammation resulting in organ failure, shock and death. They are associated with endogenous mediators that control the onset of acute inflammatory response, but the central problem remains the complete resolution of inflammation. Omega-3 enriched lipid emulsions (Ω-3(+) LEs) were used in experimental studies and clinical trials to establish homeostasis, yet with little understanding about their role on the resolution of inflammation and tissue regeneration. Here, we demonstrate that Ω-3 lipid emulsions (LEs) orchestrate inflammation-resolution/regeneration mechanism during sterile peritonitis and murine polymicrobial sepsis. Ω-3(+) LEs recessed neutrophil infiltration, reduced pro-inflammatory mediators, reduced the classical monocyte and enhanced the non-classical monocytes/macrophages recruitment and finally increased the efferocytosis in sepsis. The actions of Ω-3(+) LE were 5-lipoxygenase (5-LOX) and 12/15-lipoxygenase (12/15-LOX) dependent. Ω-3(+) LEs shortened the resolution interval by 56%, stimulated the endogenous biosynthesis of resolution mediators lipoxin A4, protectin DX and maresin 1 and contributed to tissue regeneration. Ω-3(+) LEs protected against hypothermia and weight loss and enhanced survival in murine polymicrobial sepsis. We highlighted a role of Ω-3(+) LEs in regulating key mechanisms within the resolution terrain during murine sepsis. This might form the basis for a rational design of sepsis specific clinical nutrition.Cell Death and Differentiation advance online publication, 20 October 2017; doi:10.1038/cdd.2017.177.

Concepts: Inflammation, Nutrition, Fatty acid, Cellular differentiation, Triglyceride, Omega-3 fatty acid, Prostaglandin, Lipoxin

0

Psoriasis is a chronic inflammatory skin disease that affects 2-3% of the global population, and there is still no known possibility of a cure. Lipoxin A4 (LXA4), an endogenous lipoxygenase-derived eicosanoid mediator, has potent dual pro-resolving and anti-inflammatory properties. BML-111 (5(S)-6®-7-trihydroxyheptanoic acid methyl ester), a lipoxin receptor agonist, has been previously confirmed to be equivalent to LXA4 in the anti-inflammatory processes. High mobility group box 1 (HMGB1) serves as an inflammatory cytokine when secreted extracellularly in psoriatic lesions and is involved in the development of psoriasis. Therefore, we investigated the effects of LXA4 and BML-111 on the HMGB1 signaling cascade and inflammation in lipopolysaccharide (LPS)-induced keratinocytes and imiquimod (IMQ)-induced psoriasiform dermatitis in mice. In the present study, we found that treatment with BML-111 attenuated the development of IMQ-induced psoriasiform dermatitis. Furthermore, treatment with BML-111 and LXA4 inhibited HMGB1 translocation from the nucleus to cytoplasm and downregulated the expression of toll-like receptor 4 (TLR4), receptor for advanced glycation end products (RAGE), p-ERK1/2, nuclear NF-κB p65, and proinflammatory cytokines in vivo and in vitro. Our findings indicate that LXA4 and its analog may be potential therapeutic candidates for psoriasis because of their ability to modulate the translocation and expression of HMGB1.

Concepts: Immune system, Inflammation, Cytokine, Hormone, Toll-like receptor, Anti-inflammatory, TLR 4, Lipoxin