Healthy plasma lipidomic signatures depend on sex, age, body mass index, and contraceptives but not perceived stress.

Perceived stress is thought to contribute to the pathogenesis of metabolic, vascular, mental, and immune diseases, with different susceptibilities in women and men. The present study investigated if and how perceived stress and/or demographic variables including sex, age, body mass index, regular prescription drugs, occasional analgesics, or dietary supplements manifested in plasma lipidomic profiles, obtained by targeted and untargeted mass spectrometry analyses. The study included 217 healthy women and 108 healthy men, aged 18-68 years, who were recruited in a 2:1 female:male ratio to account for women with/without contraceptives. As expected, dehydroepiandrosterone sulfate (DHEAS) and ceramides were higher in men than women, and DHEAS decreased with age, while ceramides increased. Contrary to expectations, neither DHEAS nor ceramides were associated with perceived stress (PSQ30 questionnaire), which was however, associated with BMI in men, but not in women. None of the lipid species or classes showed a similar "age X sex X BMI" interaction, but the endocannabinoid palmitoylethanolamide (PEA) correlated with BMI and hypertension. Independent of perceived stress, lysophosphatidylcholines (LPCs) were lower in women than men, whereas LPC metabolites, lysophosphatidic acids (LPAs), were higher in women. The LPA:LPC ratio was particularly high in women using oral contraceptives suggesting a strong hormone-induced extracellular conversion of LPCs to LPAs, which is catalyzed by the phospholipase D, autotaxin. The results reveal complex sex differences in perceived stress and lipidomic profiles, the latter being exacerbated by contraceptive use, but perceived stress and lipids were not directly correlated.

Macrophages acquire a TNF-dependent inflammatory memory in allergic asthma.

BACKGROUND: Infectious agents can reprogram or "train" macrophages and their progenitors to respond more readily to subsequent insults. However, whether such an inflammatory memory exists in type 2 inflammatory conditions such as allergic asthma was not known. OBJECTIVE: We sought to decipher macrophage-trained immunity in allergic asthma. METHODS: We used a combination of clinical sampling of house dust mite (HDM)-allergic patients, HDM-induced allergic airway inflammation in mice, and an in vitro training setup to analyze persistent changes in macrophage eicosanoid, cytokine, and chemokine production as well as the underlying metabolic and epigenetic mechanisms. Transcriptional and metabolic profiles of patient-derived and in vitro trained macrophages were assessed by RNA sequencing or metabolic flux analysis and liquid chromatography-tandem mass spectrometry analysis, respectively. RESULTS: We found that macrophages differentiated from bone marrow or blood monocyte progenitors of HDM-allergic mice or asthma patients show inflammatory transcriptional reprogramming and excessive mediator (TNF-α, CCL17, leukotriene, PGE2, IL-6) responses upon stimulation. Macrophages from HDM-allergic mice initially exhibited a type 2 imprint, which shifted toward a classical inflammatory training over time. HDM-induced allergic airway inflammation elicited a metabolically activated macrophage phenotype, producing high amounts of 2-hydroxyglutarate (2-HG). HDM-induced macrophage training in vitro was mediated by a formyl peptide receptor 2-TNF-2-HG-PGE2/PGE2 receptor 2 axis, resulting in an M2-like macrophage phenotype with high CCL17 production. TNF blockade by etanercept or genetic ablation of Tnf in myeloid cells prevented the inflammatory imprinting of bone marrow-derived macrophages from HDM-allergic mice. CONCLUSION: Allergen-triggered inflammation drives a TNF-dependent innate memory, which may perpetuate and exacerbate chronic type 2 airway inflammation and thus represents a target for asthma therapy.

Lysophospholipids Contribute to Oxaliplatin-Induced Acute Peripheral Pain.

Oxaliplatin, a platinum-based chemotherapeutic drug, which is used as first-line treatment for some types of colorectal carcinoma, causes peripheral neuropathic pain in patients. In addition, an acute peripheral pain syndrome develop in almost 90% of patients immediately after oxaliplatin treatment, which is poorly understood mechanistically but correlates with incidence and severity of the later-occurring neuropathy. Here we investigated the effects of acute oxaliplatin treatment in a murine model, showing that male and female mice develop mechanical hypersensitivity 24 h after oxaliplatin treatment. Interestingly, we found that the levels of several lipids were significantly altered in nervous tissue during oxaliplatin-induced acute pain. Specifically, the linoleic acid metabolite 9,10-EpOME (epoxide of linoleic acid) as well as the lysophospholipids lysophosphatidylcholine (LPC) 18:1 and LPC 16:0 were significantly increased 24 h after oxaliplatin treatment in sciatic nerve, DRGs, or spinal cord tissue as revealed by untargeted and targeted lipidomics. In contrast, inflammatory markers including cytokines and chemokines, ROS markers, and growth factors are unchanged in the respective nervous system tissues. Importantly, LPC 18:1 and LPC 16:0 can induce Ca2+ transients in primary sensory neurons, and we identify LPC 18:1 as a previously unknown endogenous activator of the ligand-gated calcium channels transient receptor potential V1 and M8 (transient receptor potential vanilloid 1 and transient receptor potential melastatin 8) in primary sensory neurons using both pharmacological inhibition and genetic knockout. Additionally, a peripheral LPC 18:1 injection was sufficient to induce mechanical hypersensitivity in naive mice. Hence, targeting signaling lipid pathways may ameliorate oxaliplatin-induced acute peripheral pain and the subsequent long-lasting neuropathy.SIGNIFICANCE STATEMENT The first-line cytostatic drug oxaliplatin can cause acute peripheral pain and chronic neuropathic pain. The former is causally connected with the chronic neuropathic pain, but its mechanisms are poorly understood. Here, we performed a broad unbiased analysis of cytokines, chemokines, growth factors, and ∼200 lipids in nervous system tissues 24 h after oxaliplatin treatment, which revealed a crucial role of lysophospholipids lysophosphatidylcholine (LPC) 18:1, LPC 16:0, and 9,10-EpOME in oxaliplatin-induced acute pain. We demonstrate for the first time that LPC 18:1 contributes to the activation of the ion channels transient receptor potential vanilloid 1 and transient receptor potential melastatin 8 in sensory neurons and causes mechanical hypersensitivity after peripheral injection in vivo These findings suggest that the LPC-mediated lipid signaling is involved in oxaliplatin-induced acute peripheral pain.

Sphingosine-1-phosphate (S1P) induces potent anti-inflammatory effects in vitro and in vivo by S1P receptor 4-mediated suppression of 5-lipoxygenase activity.

Sphingosine-1-phosphate (S1P) is involved in the regulation of important cellular processes, including immune-cell trafficking and proliferation. Altered S1P signaling is strongly associated with inflammation, cancer progression, and atherosclerosis; however, the mechanisms underlying its pathophysiologic effects are only partially understood. This study evaluated the effects of S1P in vitro and in vivo on the biosynthesis of leukotrienes (LTs), which form a class of lipid mediators involved in the pathogenesis of inflammatory diseases. Here, we report for the first time that S1P potently suppresses LT biosynthesis in Ca2+-ionophore-stimulated intact human neutrophils. S1P treatment resulted in intracellular Ca2+ mobilization, perinuclear translocation, and finally irreversible suicide inactivation of the LT biosynthesis key enzyme 5-lipoxygenase (5-LO). Agonist studies and S1P receptor mRNA expression analysis provided evidence for a S1P receptor 4-mediated effect, which was confirmed by a functional knockout of S1P4 in HL60 cells. Systemic administration of S1P in wild-type mice decreased both macrophage and neutrophil migration in the lungs in response to LPS and significantly attenuated 5-LO product formation, whereas these effects were abrogated in 5-LO or S1P4 knockout mice. In summary, targeting the 5-LO pathway is an important mechanism to explain S1P-mediated pathophysiologic effects. Furthermore, agonism at S1P4 represents a novel effective strategy in pharmacotherapy of inflammation.-Fettel, J., Kühn, B., Guillen, N. A., Sürün, D., Peters, M., Bauer, R., Angioni, C., Geisslinger, G., Schnütgen, F., Meyer zu Heringdorf, D., Werz, O., Meybohm, P., Zacharowski, K., Steinhilber, D., Roos, J., Maier, T. J. Sphingosine-1-phosphate (S1P) induces potent anti-inflammatory effects in vitro and in vivo by S1P receptor 4-mediated suppression of 5-lipoxygenase activity.

Apoptotic Cancer Cells Suppress 5-Lipoxygenase in Tumor-Associated Macrophages.

The enzyme 5-lipoxygenase (5-LO) is key in the synthesis of leukotrienes, which are potent proinflammatory lipid mediators involved in chronic inflammatory diseases including cancer. 5-LO is expressed in immune cells but also found in cancer cells. Although the role of 5-LO in tumor cells is beginning to emerge, with the notion that tumor-promoting functions are attributed to its products, the function of 5-LO in the tumor microenvironment remains unclear. To understand the role of 5-LO and its products in the tumor microenvironment, we analyzed its expression and function in tumor-associated macrophages (TAMs). TAMs were generated by coculturing primary human macrophages (MΦ) with human MCF-7 breast carcinoma cells, which caused cell death of cancer cells followed by phagocytosis of cell debris by MΦ. Expression and activity of 5-LO in TAMs were reduced upon coculture with cancer cells. Downregulation of 5-LO in TAMs required tumor cell death and the direct contact between MΦ and dying cancer cells via Mer tyrosine kinase. Subsequently, upregulation of proto-oncogene c-Myb in TAMs induced a stable transcriptional repression of 5-LO. Reduced 5-LO expression in TAMs was mechanistically coupled to an attenuated T cell recruitment. In primary TAMs from human and murine breast tumors, 5-LO expression was absent or low when compared with monocyte-derived MΦ. Our data reveal that 5-LO, which is required for leukotriene production and subsequent T cell recruitment, is downregulated in TAMs through Mer tyrosine kinase-dependent recognition of apoptotic cancer cells. Mechanistically, we noticed transcriptional repression of 5-LO by proto-oncogene c-Myb and conclude that loss of stromal 5-LO expression favors tumor progression.

Targeting CYP2J to reduce paclitaxel-induced peripheral neuropathic pain.

Chemotherapy-induced peripheral neuropathic pain (CIPNP) is a severe dose- and therapy-limiting side effect of widely used cytostatics that is particularly difficult to treat. Here, we report increased expression of the cytochrome-P450-epoxygenase CYP2J6 and increased concentrations of its linoleic acid metabolite 9,10-EpOME (9,10-epoxy-12Z-octadecenoic acid) in dorsal root ganglia (DRGs) of paclitaxel-treated mice as a model of CIPNP. The lipid sensitizes TRPV1 ion channels in primary sensory neurons and causes increased frequency of spontaneous excitatory postsynaptic currents in spinal cord nociceptive neurons, increased CGRP release from sciatic nerves and DRGs, and a reduction in mechanical and thermal pain hypersensitivity. In a drug repurposing screen targeting CYP2J2, the human ortholog of murine CYP2J6, we identified telmisartan, a widely used angiotensin II receptor antagonist, as a potent inhibitor. In a translational approach, administration of telmisartan reduces EpOME concentrations in DRGs and in plasma and reverses mechanical hypersensitivity in paclitaxel-treated mice. We therefore suggest inhibition of CYP2J isoforms with telmisartan as a treatment option for paclitaxel-induced neuropathic pain.

The leukotriene B4 receptors BLT1 and BLT2 form an antagonistic sensitizing system in peripheral sensory neurons.

Sensitization of the heat-activated ion channel transient receptor potential vanilloid 1 (TRPV1) through lipids is a fundamental mechanism during inflammation-induced peripheral sensitization. Leukotriene B4 is a proinflammatory lipid mediator whose role in peripheral nociceptive sensitization is not well understood to date. Two major G-protein-coupled receptors for leukotriene B4 have been identified: the high-affinity receptor BLT1 and the low-affinity receptor BLT2. Transcriptional screening for the expression G-protein-coupled receptors in murine dorsal root ganglia showed that both receptors were among the highest expressed in dorsal root ganglia. Calcium imaging revealed a sensitization of TRPV1-mediated calcium increases in a relative narrow concentration range for leukotriene B4 (100-200 nm). Selective antagonists and neurons from knock-out mice demonstrated a BLT1-dependent sensitization of TRPV1-mediated calcium increases. Accordingly, leukotriene B4-induced thermal hyperalgesia was mediated through BLT1 and TRPV1 as shown using the respective knock-out mice. Importantly, higher leukotriene B4 concentrations (>0.5 µm) and BLT2 agonists abolished sensitization of the TRPV1-mediated calcium increases. Also, BLT2 activation inhibited protein kinase C- and protein kinase A-mediated sensitization processes through the phosphatase calcineurin. Consequently, a selective BLT2-receptor agonist increased thermal and mechanical withdrawal thresholds during zymosan-induced inflammation. In accordance with these data, immunohistochemical analysis showed that both leukotriene B4 receptors were expressed in peripheral sensory neurons. Thus, the data show that the two leukotriene B4 receptors have opposing roles in the sensitization of peripheral sensory neurons forming a self-restricting system.

The oxidized linoleic acid metabolite 12,13-DiHOME mediates thermal hyperalgesia during inflammatory pain.

Eicosanoids play a crucial role in inflammatory pain. However, there is very little knowledge about the contribution of oxidized linoleic acid metabolites in inflammatory pain and peripheral sensitization. Here, we identify 12,13-dihydroxy-9Z-octadecenoic acid (12,13-DiHOME), a cytochrome P450-derived linoleic acid metabolite, as crucial mediator of thermal hyperalgesia during inflammatory pain. We found 12,13-DiHOME in increased concentrations in peripheral nervous tissue during acute zymosan- and complete Freund's Adjuvant-induced inflammatory pain. 12,13-DiHOME causes calcium transients in sensory neurons and sensitizes the transient receptor potential vanilloid 1 (TRPV1)-mediated intracellular calcium increases via protein kinase C, subsequently leading to enhanced TRPV1-dependent CGRP-release from sensory neurons. Peripheral injection of 12,13-DiHOME in vivo causes TRPV1-dependent thermal pain hypersensitivity. Finally, application of the soluble epoxide hydrolase (sEH)-inhibitor TPPU reduces 12,13-DiHOME concentrations in nervous tissue and reduces zymosan- and CFA-induced thermal hyperalgesia in vivo. In conclusion, we identify a novel role for the lipid mediator 12,13-DiHOME in mediating thermal hyperalgesia during inflammatory pain and propose a novel mechanism that may explain the antihyperalgesic effects of sEH inhibitors in vivo.

Mutual inversion of flurbiprofen enantiomers in various rat and mouse strains.

Flurbiprofen (F) is a nonsteroidal anti-inflammatory drug (NSAID) used therapeutically as the racemate of (R)-enantiomer and (S)-enantiomer. The inversion of RF to SF and vice versa was investigated in C57Bl/6 and SJL mice and Dark Agouti and Lewis rats. The enzyme α-methylacyl-CoA racemase (AMACR) is involved in the chiral inversion pathway that converts members of the 2-arylpropionic acid NSAIDs from the R-enantiomer to the S-enantiomer. We studied C57Bl/6 mice deficient in AMACR postulating that they should show reduced inversion of RF to SF. In line with the data of others in mice, (R)-inversion to (S)-inversion was relatively high in both the C57Bl/6 and SJL mice (fraction inverted, FI  = 37.7% and 24.7%, respectively). In contrast, in AMACR deficient mice, there was no measurable peak for SF after administration of RF. The results in both rat strains (Dark Agouti and Lewis rats, FI  = 1.4% and 4.1%, respectively) confirm the low chiral inversion of the enantiomers of flurbiprofen in the rat, as observed by other authors in the Sprague-Dawley strain (<5%). From the present results, we conclude that for the study of flurbiprofen enantiomers, the rat is more suitable than the mouse as a model for the human in which (R)-inversion to (S)-inversion is negligible.

Epigenetic control of microsomal prostaglandin E synthase-1 by HDAC-mediated recruitment of p300.

Nonsteroidal anti-inflammatory drugs are the most widely used medicine to treat pain and inflammation, and to inhibit platelet function. Understanding the expression regulation of enzymes of the prostanoid pathway is of great medical relevance. Histone acetylation crucially controls gene expression. We set out to identify the impact of histone deacetylases (HDACs) on the generation of prostanoids and examine the consequences on vascular function. HDAC inhibition (HDACi) with the pan-HDAC inhibitor, vorinostat, attenuated prostaglandin (PG)E2 generation in the murine vasculature and in human vascular smooth muscle cells. In line with this, the expression of the key enzyme for PGE2 synthesis, microsomal PGE synthase-1 (PTGES1), was reduced by HDACi. Accordingly, the relaxation to arachidonic acid was decreased after ex vivo incubation of murine vessels with HDACi. To identify the underlying mechanism, chromatin immunoprecipitation (ChIP) and ChIP-sequencing analysis were performed. These results suggest that HDACs are involved in the recruitment of the transcriptional activator p300 to the PTGES1 gene and that HDACi prevented this effect. In line with the acetyltransferase activity of p300, H3K27 acetylation was reduced after HDACi and resulted in the formation of heterochromatin in the PTGES1 gene. In conclusion, HDAC activity maintains PTGES1 expression by recruiting p300 to its gene.

CD200 selectively upregulates prostaglandin E2 and D2 synthesis in LPS-treated bone marrow-derived macrophages.

The CD200/CD200R signalling pathway downregulates the synthesis of proinflammatory mediators and induces the synthesis of antiinflammatory mediators in macrophages and microglia. However, very little is known about the effect of this immunosuppressive pathway on the synthesis of lipid mediators. Therefore, we determined the synthesis of 35 lipids spanning 5 different lipid families in bone marrow-derived macrophages, which were treated with interleukin (IL) 4, IL10, lipopolysaccharide (LPS), or interferon γ (IFNγ) in absence and presence of CD200. Out of these conditions the only significant effect of CD200 was an increased synthesis of prostaglandin (PG) E2 and D2 in the presence of LPS. Accordingly, mRNA levels of cyclooxygenase-2, microsomal PGE2 synthase-1 and hematopoietic PGD synthase were upregulated by CD200 in presence of LPS. During Complete Freund's Adjuvant (CFA-) induced inflammation mPGES-1 was expressed in monocyte-derived macrophages and its expression was stronger in CD200R-positive than in CD200R-negative macrophages.

AMP-activated protein kinase suppresses arachidonate 15-lipoxygenase expression in interleukin 4-polarized human macrophages.

Macrophages respond to the Th2 cytokine IL-4 with elevated expression of arachidonate 15-lipoxygenase (ALOX15). Although IL-4 signaling elicits anti-inflammatory responses, 15-lipoxygenase may either support or inhibit inflammatory processes in a context-dependent manner. AMP-activated protein kinase (AMPK) is a metabolic sensor/regulator that supports an anti-inflammatory macrophage phenotype. How AMPK activation is linked to IL-4-elicited gene signatures remains unexplored. Using primary human macrophages stimulated with IL-4, we observed elevated ALOX15 mRNA and protein expression, which was attenuated by AMPK activation. AMPK activators, e.g. phenformin and aminoimidazole-4-carboxamide 1-ß-d-ribofuranoside inhibited IL-4-evoked activation of STAT3 while leaving activation of STAT6 and induction of typical IL-4-responsive genes intact. In addition, phenformin prevented IL-4-induced association of STAT6 and Lys-9 acetylation of histone H3 at the ALOX15 promoter. Activating AMPK abolished cellular production of 15-lipoxygenase arachidonic acid metabolites in IL-4-stimulated macrophages, which was mimicked by ALOX15 knockdown. Finally, pretreatment of macrophages with IL-4 for 48 h increased the mRNA expression of the proinflammatory cytokines IL-6, IL-12, CXCL9, and CXCL10 induced by subsequent stimulation with lipopolysaccharide. This response was attenuated by inhibition of ALOX15 or activation of AMPK during incubation with IL-4. In conclusion, limiting ALOX15 expression by AMPK may promote an anti-inflammatory phenotype of IL-4-stimulated human macrophages.

Lipoxin and resolvin biosynthesis is dependent on 5-lipoxygenase activating protein.

Resolution of acute inflammation is an active process coordinated by proresolving lipid mediators (SPMs) such as lipoxins (LXs) and resolvins (Rvs), which are formed by the concerted action of 2 lipoxygenases (LOs). Because the exact molecular mechanisms of SPM biosynthesis are not completely understood, we aimed to investigate LX and D-type Rv formation in human leukocytes and HEK293T cells overexpressing leukotriene (LT) pathway enzymes. Activity assays in precursor (15-hydroxyeicosatetraenoic acids, 17-HDoHE)-treated granulocytes [polymorphonuclear leukocytes (PMNLs)] showed a strict dependence of LXA4/RvD1 biosynthesis on cell integrity, and incubation with recombinant human 5-LO did not lead to LX or Rv formation. Pharmacologic inhibition of 5-LO activating protein (FLAP) by MK-886 inhibited LXA4/RvD1 biosynthesis in precursor-treated PMNLs (drug concentration causing 50% inhibition ∼ 0.3/0.2 µM), as did knockdown of the enzyme in MM6 cells, and precursor-treated HEK293T overexpressing 5-LO produced high amounts of LXA4 only in the presence of FLAP. In addition, inhibition of cytosolic phospholipase A2α (cPLA2α) interfered with LXA4/RvD1 formation from exogenous precursors in PMNLs. Furthermore, inhibition of the LT synthases LTA4 hydrolase and LTC4 synthase in PMNL/platelet coincubations augmented LXA4 levels. These findings show that several enzymes known to be involved in the biosynthesis of proinflammatory LTs, such as FLAP and cPLA2α, also contribute to LX and Rv formation.

R-Flurbiprofen Traps Prostaglandins within Cells by Inhibition of Multidrug Resistance-Associated Protein-4.

R-flurbiprofen is the non-COX-inhibiting enantiomer of flurbiprofen and is not converted to S-flurbiprofen in human cells. Nevertheless, it reduces extracellular prostaglandin E2 (PGE2) in cancer or immune cell cultures and human extracellular fluid. Here, we show that R-flurbiprofen acts through a dual mechanism: (i) it inhibits the translocation of cPLA2α to the plasma membrane and thereby curtails the availability of arachidonic acid and (ii) R-flurbiprofen traps PGE2 inside of the cells by inhibiting multidrug resistance-associated protein 4 (MRP4, ABCC4), which acts as an outward transporter for prostaglandins. Consequently, the effects of R-flurbiprofen were mimicked by RNAi-mediated knockdown of MRP4. Our data show a novel mechanism by which R-flurbiprofen reduces extracellular PGs at physiological concentrations, particularly in cancers with high levels of MRP4, but the mechanism may also contribute to its anti-inflammatory and immune-modulating properties and suggests that it reduces PGs in a site- and context-dependent manner.

Design, Synthesis and Cellular Characterization of a Dual Inhibitor of 5-Lipoxygenase and Soluble Epoxide Hydrolase.

The arachidonic acid cascade is a key player in inflammation, and numerous well-established drugs interfere with this pathway. Previous studies have suggested that simultaneous inhibition of 5-lipoxygenase (5-LO) and soluble epoxide hydrolase (sEH) results in synergistic anti-inflammatory effects. In this study, a novel prototype of a dual 5-LO/sEH inhibitor KM55 was rationally designed and synthesized. KM55 was evaluated in enzyme activity assays with recombinant enzymes. Furthermore, activity of KM55 in human whole blood and endothelial cells was investigated. KM55 potently inhibited both enzymes in vitro and attenuated the formation of leukotrienes in human whole blood. KM55 was also tested in a cell function-based assay. The compound significantly inhibited the LPS-induced adhesion of leukocytes to endothelial cells by blocking leukocyte activation.

Subcellular distribution of FTY720 and FTY720-phosphate in immune cells - another aspect of Fingolimod action relevant for therapeutic application.

FTY720 (Fingolimod; Gilenya®) is an immune-modulatory prodrug which, after intracellular phosphorylation by sphingosine kinase 2 (SphK2) and export, mimics effects of the endogenous lipid mediator sphingosine-1-phosphate. Fingolimod has been introduced to treat relapsing-remitting multiple sclerosis. However, little has been published about the immune cell membrane penetration and subcellular distribution of FTY720 and FTY720-P. Thus, we applied a newly established LC-MS/MS method to analyze the subcellular distribution of FTY720 and FTY720-P in subcellular compartments of spleen cells of wild type, SphK1- and SphK2-deficient mice. These studies demonstrated that, when normalized to the original cell volume and calculated on molar basis, FTY720 and FTY720-P dramatically accumulated several hundredfold within immune cells reaching micromolar concentrations. The amount and distribution of FTY720 was differentially affected by SphK1- and SphK2-deficiency. On the background of recently described relevant intracellular FTY720 effects in the nanomolar range and the prolonged application in multiple sclerosis, this data showing a substantial intracellular accumulation of FTY720, has to be considered for benefit/risk ratio estimates.

Prostacyclin regulates spinal nociceptive processing through cyclic adenosine monophosphate-induced translocation of glutamate receptors.

BACKGROUND: Prostacyclin (PGI2) is known to be an important mediator of peripheral pain sensation (nociception) whereas little is known about its role in central sensitization. METHODS: The levels of the stable PGI2-metabolite 6-keto-prostaglandin F1α (6-keto-PGF1α) and of prostaglandin E2 (PGE2) were measured in the dorsal horn with the use of mass spectrometry after peripheral inflammation. Expression of the prostanoid receptors was determined by immunohistology. Effects of prostacyclin receptor (IP) activation on spinal neurons were investigated with biochemical assays (cyclic adenosine monophosphate-, glutamate release-measurement, Western blot analysis) in embryonic cultures and adult spinal cord. The specific IP antagonist Cay10441 was applied intrathecally after zymosan-induced mechanical hyperalgesia in vivo. RESULTS: Peripheral inflammation caused a significant increase of the stable PGI2 metabolite 6-keto-PGF1α in the dorsal horn of wild-type mice (n = 5). IP was located on spinal neurons and did not colocalize with the prostaglandin E2 receptors EP2 or EP4. The selective IP-agonist cicaprost increased cyclic adenosine monophosphate synthesis in spinal cultures from wild-type but not from IP-deficient mice (n = 5-10). The combination of fluorescence-resonance-energy transfer-based cyclic adenosine monophosphate imaging and calcium imaging showed a cicaprost-induced cyclic adenosine monophosphate synthesis in spinal cord neurons (n = 5-6). Fittingly, IP activation increased glutamate release from acute spinal cord sections of adult mice (n = 13-58). Cicaprost, but not agonists for EP2 and EP4, induced protein kinase A-dependent phosphorylation of the GluR1 subunit and its translocation to the membrane. Accordingly, intrathecal administration of the IP receptor antagonist Cay10441 had an antinociceptive effect (n = 8-11). CONCLUSION: Spinal prostacyclin synthesis during early inflammation causes the recruitment of GluR1 receptors to membrane fractions, thereby augmenting the onset of central sensitization.

Similar maximum systemic but not local cyclooxygenase-2 inhibition by 50 mg lumiracoxib and 90 mg etoricoxib: a randomized controlled trial in healthy subjects.

PURPOSE: Once daily doses of 100-400 mg lumiracoxib have been proposed to inhibit local prostaglandin synthesis longer than systemic prostaglandin synthesis due to local accumulation in inflamed, acidic tissue. Lower, less toxic doses, however, might still achieve the clinical goal and merit further contemplation. METHODS: In a randomized, double-blind, placebo-controlled, three-way cross-over study, 18 healthy men received, with an interval of 24 h, two oral doses of 50 mg lumiracoxib or for comparison, 90 mg etoricoxib, for which local tissue accumulation has not been claimed as therapeutic component. Systemic and local drug concentrations, assessed by means of subcutaneous in-vivo microdialysis, were related to COX-2 inhibiting effects, quantified as inhibition of prostaglandin ex-vivo production in whole blood as well as local tissue prostaglandin (PG) concentrations. RESULTS: Twenty-four hours after the first dose, only etoricoxib was detectable in plasma and inhibited PGE2 production. In contrast, after the second dose, systemic PGE2 concentrations were significantly reduced by both coxibs, indicating similar maximum systemic effects of the selected doses. The local COX-2 inhibition by etoricoxib was most pronounced for PGD2. To the contrary, no indication was given of local inhibition of PG production by lumiracoxib at the dose tested. CONCLUSIONS: Doses of 50 mg lumiracoxib and 90 mg etoricoxib produced similar maximum inhibition of systemic COX-2 function whereas 50 mg lumiracoxib was ineffective in producing local COX-2 inhibition. At a 50 mg dosage, lumiracoxib does not provide peripheral effects that outlast its systemic actions in therapies of rheumatic diseases such as osteoarthritis.

Oleic acid released by sensory neurons inhibits TRPV1-mediated thermal hypersensitivity via GPR40.

Noxious stimuli activate nociceptive sensory neurons, causing action potential firing and the release of diverse signaling molecules. Several peptides have already been identified to be released by sensory neurons and shown to modulate inflammatory responses and inflammatory pain. However, it is still unclear whether lipid mediators can be released upon sensory neuron activation to modulate intercellular communication. Here, we analyzed the lipid secretome of capsaicin-stimulated nociceptive neurons with LC-HRMS, revealing that oleic acid is strongly released from sensory neurons by capsaicin. We further demonstrated that oleic acid inhibits capsaicin-induced calcium transients in sensory neurons and reverses bradykinin-induced TRPV1 sensitization by a calcineurin (CaN) and GPR40 (FFAR1) dependent pathway. Additionally, oleic acid alleviated zymosan-mediated thermal hypersensitivity via the GPR40, suggesting that the capsaicin-mediated oleic acid release from sensory neurons acts as a protective and feedback mechanism, preventing sensory neurons from nociceptive overstimulation via the GPR40/CaN/TRPV1-axis.

Machine learning and biological validation identify sphingolipids as potential mediators of paclitaxel-induced neuropathy in cancer patients.

Background: Chemotherapy-induced peripheral neuropathy (CIPN) is a serious therapy-limiting side effect of commonly used anticancer drugs. Previous studies suggest that lipids may play a role in CIPN. Therefore, the present study aimed to identify the particular types of lipids that are regulated as a consequence of paclitaxel administration and may be associated with the occurrence of post-therapeutic neuropathy. Methods: High-resolution mass spectrometry lipidomics was applied to quantify d=255 different lipid mediators in the blood of n=31 patients drawn before and after paclitaxel therapy for breast cancer treatment. A variety of supervised statistical and machine-learning methods was applied to identify lipids that were regulated during paclitaxel therapy or differed among patients with and without post-therapeutic neuropathy. Results: Twenty-seven lipids were identified that carried relevant information to train machine learning algorithms to identify, in new cases, whether a blood sample was drawn before or after paclitaxel therapy with a median balanced accuracy of up to 90%. One of the top hits, sphinganine-1-phosphate (SA1P), was found to induce calcium transients in sensory neurons via the transient receptor potential vanilloid 1 (TRPV1) channel and sphingosine-1-phosphate receptors.SA1P also showed different blood concentrations between patients with and without neuropathy. Conclusions: Present findings suggest a role for sphinganine-1-phosphate in paclitaxel-induced biological changes associated with neuropathic side effects. The identified SA1P, through its receptors, may provide a potential drug target for co-therapy with paclitaxel to reduce one of its major and therapy-limiting side effects. Funding: This work was supported by the Deutsche Forschungsgemeinschaft (German Research Foundation, DFG, Grants SFB1039 A09 and Z01) and by the Fraunhofer Foundation Project: Neuropathic Pain as well as the Fraunhofer Cluster of Excellence for Immune-Mediated Diseases (CIMD). This work was also supported by the Leistungszentrum Innovative Therapeutics (TheraNova) funded by the Fraunhofer Society and the Hessian Ministry of Science and Arts. Jörn Lötsch was supported by the Deutsche Forschungsgemeinschaft (DFG LO 612/16-1).