Mast cell-derived prostaglandin D2 limits the subcutaneous absorption of honey bee venom in mice.

Mast cells play pivotal roles in innate host defenses against venom. Activated mast cells release large amounts of prostaglandin D2 (PGD2). However, the role of PGD2 in such host defense remains unclear. We found that c-kit-dependent and c-kit-independent mast cell-specific hematopoietic prostaglandin D synthase (H-pgds) deficiency significantly exacerbated honey bee venom (BV)-induced hypothermia and increased mortality rates in mice. BV absorption via postcapillary venules in the skin was accelerated upon endothelial barrier disruption resulting in increased plasma venom concentrations. These results suggest that mast cell-derived PGD2 may enhance host defense against BV and save lives by inhibiting BV absorption into circulation.

Deficiency of interleukin-19 exacerbates acute lung injury induced by intratracheal treatment of hydrochloric acid.

Interleukin (IL-19) belongs to the IL-10 family of cytokines and plays diverse roles in inflammation, cell development, viral responses, and lipid metabolism. Acute lung injury (ALI) is a severe respiratory condition associated with various diseases, including severe pneumonia, sepsis, and trauma, lacking established treatments. However, the role of IL-19 in acute inflammation of the lungs is unknown. We reported the impact of IL-19 functional deficiency in mice crossed with an ALI model using HCl. Lungs damages, neutrophil infiltration, and pulmonary edema induced by HCl were significantly worse in IL-19 knockout (KO) mice than in wild-type (WT) mice. mRNA expression levels of C-X-C motif chemokine ligand 1 (CXCL1) and IL-6 in the lungs were significantly higher in IL-19 KO mice than in WT mice. Little apoptosis was detected in lung injury in WT mice, whereas apoptosis was observed in exacerbated area of lung injury in IL-19 KO mice. These results are the first to show that IL-19 is involved in acute inflammation of the lungs, suggesting a novel molecular mechanism in acute respiratory failures. If it can be shown that neutrophils have IL-19 receptors and that IL-19 acts directly on them, it would be a novel drug target.

Prostaglandin F2α receptor antagonist attenuates LPS-induced systemic inflammatory response in mice.

Although it is known that prostaglandin (PG) F2α level is elevated in the plasma of patients with sepsis, the roles of PGF2α is still unknown. We aimed to clarify the roles of PGF2α in the regulation of lipopolysaccharide (LPS)-induced systemic inflammation. At 24 hours after LPS administration, neutrophil infiltration in peritoneal cavity, the mRNA expression of pro-inflammatory cytokines such as tumor necrosis factor-α, interleukin (IL)-1ß, IL-6, and macrophage inflammatory protein-2, and tissue damages in lung, liver, and kidney were all increased. Inhibition of FP receptors significantly decreased LPS-induced neutrophil infiltration and lowered the mRNA expression of the pro-inflammatory cytokines. At 6 hour after LPS administration, the level of anti-inflammatory cytokine, IL-10 in peritoneal lavage fluid was higher than that in naïve mice. Inhibition of FP receptors in these mice increased IL-10 level further. Stimulation of isolated peritoneal neutrophils by LPS increased the gene expression of IL-10, which was further increased by AL8810 treatment. Administration of an anti-IL-10 antibody antagonized the AL8810-decreased mRNA expression of pro-inflammatory cytokines and tissue damages. These results indicate that inhibition of FP receptors by AL8810 attenuated LPS-induced systemic inflammation in mice via enhanced IL-10 production.

Inhibition of Prostaglandin F2α Receptors Exaggerates HCl-Induced Lung Inflammation in Mice.

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are severe respiratory disorders that are caused by aspiration, sepsis, trauma, and pneumonia. A clinical feature of ALI/ARDS is the acute onset of severe hypoxemia, and the mortality rate, which is estimated at 38-50%, remains high. Although prostaglandins (PGs) are detected in the bronchoalveolar lavage fluid of patients with ALI/ARDS, the role of PGF2α in ALI remains unclear. We aimed to clarify the role of PGF2α/PGF2α receptor (FP) signaling in acid-induced ALI using an FP receptor antagonist, AL8810. Intratracheal injection of hydrochloric acid (HCl) increased neutrophil migration into the lungs, leading to respiratory dysfunction. Pre-administration of AL8810 further increased these features. Moreover, pre-treatment with AL8810 enhanced the HCl-induced expression of pro-inflammatory cytokines and neutrophil migratory factors in the lungs. Administration of HCl decreased the gene expression of lung surfactant proteins, which was further reduced by co-administration of AL8810. Administration of AL8810 also increased lung edema and reduced mRNA expression of epithelial sodium channel in the lungs, indicating that AL8810 reduced fluid clearance. Furthermore, AL8810 also increased lipopolysaccharide-induced expression of adhesion molecules such as intracellular adhesion molecule-1 and E-selectin in human umbilical vein endothelial cells. These results indicate that inhibition of FP receptors by AL8810 exacerbated HCl-induced ALI.

Epithelial cell-derived prostaglandin D2 inhibits chronic allergic lung inflammation in mice.

The precise role of prostaglandin D (PGD)2 in allergic lung inflammation remains controversial. Here, we aimed to clarify the role of PGD2 in chronic allergic lung inflammation using hematopoietic PGD synthase (H-PGDS)-deficient mice. Repeated intranasal administration of ovalbumin (OVA) resulted in eosinophilic infiltration and mucin production in the lungs of wild type (WT) mice, leading to respiratory dysfunction. H-PGDS deficiency exacerbated these effects, which were accompanied by increased mRNA expression of TNF-α and eosinophil chemoattractants. The bronchial epithelium expressed both H-PGDS and TNF-α in the inflamed WT lung, and H-PGDS deficiency increased TNF-α expression further. In cultured bronchial tissue of WT mice, treatment with LPS elevated mRNA expression of TNF-α and eosinophil chemoattractants. H-PGDS deficiency promoted the expression of these factors, which was inhibited by treatment with PGD2 receptor, D prostanoid (DP) receptor agonist, or PGD2 metabolite 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2). Treatment with TNF-α receptor antibody inhibited eosinophil chemoattractant expression. In vivo, administration of DP agonist or 15d-PGJ2 inhibited OVA-induced allergic lung inflammation. Bronchial epithelial cell-derived PGD2 attenuated lung eosinophilic infiltration with chronic allergic inflammation; these phenomena are at least partly attributed to the inhibition of TNF-α production via DP activation or 15-deoxy-Δ12,14-PGJ2 signaling.-Maehara, T., Nakamura, T., Maeda, S., Aritake, K., Nakamura, M., Murata, T. Epithelial cell-derived prostaglandin D2 inhibits chronic allergic lung inflammation in mice.

Hematopoietic prostaglandin D synthase-derived prostaglandin D2 ameliorates adjuvant-induced joint inflammation in mice.

Although prostaglandins (PGs) are known to be involved in the progression of arthritis, the role of PGD2 remains unclear. In this study, we evaluated the role of PGD2 in joint inflammation using genetically modified mice. Injection of complete Freund's adjuvant (CFA) increased the production of PGD2 and induced paw swelling and cartilage erosion in wild-type (WT) mice. These phenomena were accompanied with an increase in the mRNA levels of TNF-α, IL-6, IL-1ß, and matrix-degrading metalloproteinase-9. Knockdown of hematopoietic PGD synthase (H-PGDS) abolished the PGD2 production and exacerbated all of the arthritic manifestations in the inflamed paw. Immunostaining revealed that infiltrating macrophages strongly expressed H-PGDS in the CFA-injected paw. Morphologic studies revealed vascular hyperpermeability and angiogenesis in the inflamed WT paw. H-PGDS deficiency was accelerated, whereas daily administration of a PGD2 receptor D prostanoid (DP) agonist attenuated the CFA-induced hyperpermeability and angiogenesis. We further confirmed that DP deficiency exacerbated, whereas the administration of the DP agonist improved, the CFA-induced arthritic manifestations. The findings demonstrate that H-PGDS-derived PGD2 ameliorates joint inflammation by attenuating vascular permeability and subsequent angiogenesis and indicates the therapeutic potential of a DP agonist for arthritis.-Tsubosaka, Y., Maehara, T., Imai, D., Nakamura, T., Kobayashi, K., Nagata, N., Fujii, W., Murata, T. Hematopoietic prostaglandin D synthase-derived prostaglandin D2 ameliorates adjuvant-induced joint inflammation in mice.

Profile of uterine flush lipid mediators in cows with subclinical endometritis: pilot study.

Subclinical endometritis affects reproductive outcomes and causes economic losses in dairy cows, thus, it is important to understand disease progression mechanisms and develop diagnostic procedures for better disease management. We measured the levels of 146 lipid mediators in uterine flush samples using lipid chromatography-mass spectrometry. We detected 25 lipid mediators in the uterine flush of both the control and subclinical endometritis cows; 15 of the 25 lipid mediators were AA-derived metabolites. Among the AA-derived metabolites, cyclooxygenase (COX)-generated mediators were the most abundant. Specifically, levels of 11ß-13,14-dihydro-15-keto prostaglandin (PG) F2α, PGE2, PGA2, 13-hydroxyoctadecadienoic acid, and PGD1 were elevated in all the cows with subclinical endometritis. This study may provide new insights for the management of subclinical bovine endometritis.

Leukotriene C4 synthase is a novel PPARγ target gene, and leukotriene C4 and D4 activate adipogenesis through cysteinyl LT1 receptors in adipocytes.

Leukotriene (LT) C4 synthase (LTC4S) catalyzes the conversion from LTA4 to LTC4, which is a proinflammatory lipid mediator in asthma and other inflammatory diseases. LTC4 is metabolized to LTD4 and LTE4, all of which are known as cysteinyl (Cys) LTs and exert physiological functions through CysLT receptors. LTC4S is expressed in adipocytes. However, the function of CysLTs and the regulatory mechanism in adipocytes remain unclear. In this study, we investigated the expression of LTC4S and production of CysLTs in murine adipocyte 3T3-L1 cells and their underlying regulatory mechanisms. Expression of LTC4S and production of LTC4 and CysLTs increased during adipogenesis, whereas siRNA-mediated suppression of LTC4S expression repressed adipogenesis by reducing adipogenic gene expression. The CysLT1 receptor, one of the two LTC4 receptors, was expressed in adipocytes. LTC4 and LTD4 increased the intracellular triglyceride levels and adipogenic gene expression, and their enhancement was suppressed by co-treatment with pranlukast, a CysLT1 receptor antagonist. Moreover, the expression profiles of LTC4S gene/protein during adipogenesis resembled those of peroxisome proliferator-activated receptor (PPAR) γ. LTC4S expression was further upregulated by treatment with troglitazone, a PPARγ agonist. Promoter-luciferase and chromatin immunoprecipitation assays showed that PPARγ directly bound to the PPAR response element of the LTC4S gene promoter in adipocytes. These results indicate that the LTC4S gene expression was enhanced by PPARγ, and LTC4 and LTD4 activated adipogenesis through CysLT1 receptors in 3T3-L1 cells. Thus, LTC4S and CysLT1 receptors are novel potential targets for the treatment of obesity.

Protection of 6-OHDA neurotoxicity by PGF2α through FP-ERK-Nrf2 signaling in SH-SY5Y cells.

6-Hydroxydopamine (6-OHDA) is a neurotoxin that destroy dopaminergic neurons and widely used to establish animal models of Parkinson's disease. Prostaglandins (PGs) are involved in various cellular processes, including the damage and repair of neuronal cells. However, the function of PGF2α in neuronal cells remains unclear. In this study, we investigated the effects of PGF2α against 6-OHDA-mediated toxicity in human neuroblastoma SH-SY5Y cells and elucidated its underlying molecular mechanism. When the cells were treated with 6-OHDA (50 µM) for 6 h, the expression levels of PGF2α synthetic enzymes; cyclooxygenase-2 and aldo-keto reductase 1C3 as PGF2α synthase were enhanced in an incubation-time-dependent manner. In addition, the production of PGF2α was increased in 6-OHDA-treated cells. Fluprostenol, a PGF2α receptor (FP) agonist (500 nM), suppressed 6-OHDA-induced cell death by decreasing the production of reactive oxygen species (ROS) and increasing the expression of the anti-oxidant genes. These fluprostenol-mediated effects were inhibited by co-treatment with AL8810, an FP receptor antagonist (1 µM) or transfection with FP siRNA (20 nM). Moreover, 6-OHDA-induced phosphorylation of extracellular signal-regulated kinase (ERK), a member of the mitogen-activated protein kinase family, was inhibited by co-incubation with AL8810. Furthermore, fluprostenol itself enhanced ERK phosphorylation and further elevated the 6-OHDA-induced phosphorylation of ERK. In addition, 6-OHDA induced nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2), activating anti-oxidant gene expression, was repressed by co-culturing with AL8810. These results indicate that PGF2α suppressed 6-OHDA-induced neuronal cell death by enhancing anti-oxidant gene expression via the FP receptor-ERK-Nrf2 signaling. Thus, FP receptor is a potential target for inhibition of ROS-mediated neuronal cell death.

Contribution of FP receptors in M1 macrophage polarization via IL-10-regulated nuclear translocation of NF-κB p65.

Macrophages are the effector immune cells with plasticity to differentiate as M1 (classically activated) and M2 (alternatively activated) phenotypes. Prostaglandins (PGs) have various important roles and are involved in the regulation of macrophage activation. However, the role of PGF2α in macrophage activation remains unclear. We investigated the role of PGF2α receptor (FP)-mediated signaling in the M1 macrophage polarization using murine macrophage RAW264.7 cells. Stimulation with lipopolysaccharide (LPS) + interferon (IFN)-γ increased the mRNA expression of the M1 macrophage markers such as inducible nitric oxide synthase, tumor necrosis factor-α, and CD11c. Pre-treatment with AL8810, an FP receptor antagonist, further enhanced the expression of these genes. In contrast, treatment with fluprostenol, an FP receptor agonist, decreased the LPS + IFN-γ-induced expression of M1 markers. LPS-induced M1 macrophage polarization was dependent on the activation of NF-κB p65. Treatment with IκB kinase ß inhibitor reduced AL8810-induced mRNA expression of the M1 markers. Stimulation with LPS + IFN-γ increased the expression of IL-10. Pre-treatment with AL8810 lowered LPS + IFN-γ-induced IL-10 expression, and further enhanced LPS + IFN-γ-stimulated nuclear translocation of NF-κB p65. In contrast, co-treatment with IL-10 reversed AL8810-induced nuclear translocation of NF-κB p65. These results indicate that the FP receptor signaling was involved in the control of M1 polarization of macrophages via IL-10-regulated nuclear translocation of NF-κB p65.

Bicarbonate enhances the inflammatory response by activating JAK/STAT signalling in LPS + IFN-γ-stimulated macrophages.

Macrophages, which develop by changing their functions according to various environmental conditions and stimuli, defend against the pathogens and play roles in homoeostasis and disease states. Bicarbonate (HCO3-) is important in the maintenance of intracellular and extracellular pH in the body. However, the effects of bicarbonate on macrophage function have not been examined. In this study, we investigated the effects of bicarbonate on macrophage activation in lipopolysaccharide (LPS) and interferon (IFN)-γ (LPS + IFN-γ)-stimulated murine macrophage-like RAW264.7 cells. The expression of the interleukin (IL)-6, inducible nitric oxide (NO) synthase and cyclooxygenase-2 genes was enhanced by sodium bicarbonate (NaHCO3) in a concentration-dependent manner in LPS + IFN-γ-stimulated RAW264.7 cells. The production of IL-6, NO2- and prostaglandin E2 was also increased by treatment with NaHCO3 in these cells. Moreover, NaHCO3-mediated elevation of inflammatory gene expression was abrogated by solute carrier (SLC) transporter inhibitors. Furthermore, its NaHCO3-mediated activation was negated by a JAK inhibitor , tofacitinib. NaHCO3-enhanced phosphorylation of STAT1, and its enhancement was abrogated by pre-treating with SLC transporter inhibitors in LPS + IFN-γ-stimulated RAW264.7 cells. In addition, similar results were obtained in murine bone marrow-derived macrophages. These results indicate that bicarbonate enhanced the inflammatory response through the JAK/STAT signalling in LPS + IFN-γ-stimulated macrophages.

Limonoid 7-Deacetoxy-7-oxogedunin from Andiroba, Carapa guianensis, Meliaceae, Decreased Body Weight Gain, Improved Insulin Sensitivity, and Activated Brown Adipose Tissue in High-Fat-Diet-Fed Mice.

We examined the antiobesity effect of a limonoid 7-deacetoxy-7-oxogedunin, named CG-1, purified from the seeds of Carapa guianensis, Meliaceae, known as andiroba in high-fat-diet (HFD)-fed mice. C57BL/6 mice were fed a low-fat diet or an HFD and orally administered CG-1 (20 mg/kg) for 7 weeks. CG-1 lowered the body weight gain and improved the serum triglyceride level and insulin sensitivity in HFD-fed mice. The expression level of the adipogenesis-related genes was lowered by CG-1 in the visceral white adipose tissue (vWAT). The mRNA expression level of the macrophage-related genes decreased in vWAT following the administration of CG-1 to HFD-fed mice. It is noteworthy that CG-1 activated the brown adipose tissue (BAT) with enhanced expression of uncoupling protein 1 and increased the rectal temperature in HFD-fed mice. These results indicate that the limonoid CG-1 decreased body weight gain and ameliorated hypertriglyceridemia and insulin resistance with the activation of BAT in HFD-fed mice.

L-PGDS-produced PGD2 in premature, but not in mature, adipocytes increases obesity and insulin resistance.

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is responsible for the production of PGD2 in adipocytes and is selectively induced by a high-fat diet (HFD) in adipose tissue. In this study, we investigated the effects of HFD on obesity and insulin resistance in two distinct types of adipose-specific L-PGDS gene knockout (KO) mice: fatty acid binding protein 4 (fabp4, aP2)-Cre/L-PGDS flox/flox and adiponectin (AdipoQ)-Cre/L-PGDS flox/flox mice. The L-PGDS gene was deleted in adipocytes in the premature stage of the former strain and after maturation of the latter strain. The L-PGDS expression and PGD2 production levels decreased in white adipose tissue (WAT) under HFD conditions only in the aP2-Cre/L-PGDS flox/flox mice, but were unchanged in the AdipoQ-Cre/L-PGDS flox/flox mice. When fed an HFD, aP2-Cre/L-PGDS flox/flox mice significantly reduced body weight gain, adipocyte size, and serum cholesterol and triglyceride levels. In WAT of the HFD-fed aP2-Cre/L-PGDS flox/flox mice, the expression levels of the adipogenic, lipogenic, and M1 macrophage marker genes were decreased, whereas those of the lipolytic and M2 macrophage marker genes were enhanced or unchanged. Insulin sensitivity was improved in the HFD-fed aP2-Cre/L-PGDS flox/flox mice. These results indicate that PGD2 produced by L-PGDS in premature adipocytes is involved in the regulation of body weight gain and insulin resistance under nutrient-dense conditions.

Discovery of anti-inflammatory role of prostaglandin D2.

Nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin are one of the most frequently used classes of drug worldwide and inhibit prostaglandin (PG) production by inhibiting cyclooxygenase activity. Although NSAIDs are broadly used against inflammatory diseases, they have side effects including alimentary canal disorders, kidney damage, infection and cardiovascular disorders. Thus, it is necessary to elucidate the pathophysiological role of each PG in various diseases to develop better therapies with fewer and milder side effects. PGD2 is a PG that was identified in 1973 by Hamberg and is produced by the activities of cyclooxygenase and either hematopoietic or lipocalin-type PGD synthase. PGD2 exerts its physiological effects by stimulating two distinct G protein-coupled receptors, namely D prostanoid receptor (DP) and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). The physiological role of PGD2 remains controversial. Some studies have reported that PGD2 has bronchoconstrictory and pro-inflammatory effects inducing immune cell accumulation. In contrast, other groups have reported that PGD2 has anti-inflammatory effects by inhibiting the recruitment of dendritic cells and neutrophils. We have investigated the pathophysiological role of PGD2 using various disease models and reported on its anti-inflammatory actions. Here, we review the anti-inflammatory roles of PGD2 and the underlying mechanisms.

Prostaglandin D2 Attenuates Bleomycin-Induced Lung Inflammation and Pulmonary Fibrosis.

Pulmonary fibrosis is a progressive and fatal lung disease with limited therapeutic options. Although it is well known that lipid mediator prostaglandins are involved in the development of pulmonary fibrosis, the role of prostaglandin D2 (PGD2) remains unknown. Here, we investigated whether genetic disruption of hematopoietic PGD synthase (H-PGDS) affects the bleomycin-induced lung inflammation and pulmonary fibrosis in mouse. Compared with H-PGDS naïve (WT) mice, H-PGDS-deficient mice (H-PGDS-/-) represented increased collagen deposition in lungs 14 days after the bleomycin injection. The enhanced fibrotic response was accompanied by an increased mRNA expression of inflammatory mediators, including tumor necrosis factor-α, monocyte chemoattractant protein-1, and cyclooxygenase-2 on day 3. H-PGDS deficiency also increased vascular permeability on day 3 and infiltration of neutrophils and macrophages in lungs on day 3 and 7. Immunostaining showed that the neutrophils and macrophages expressed H-PGDS, and its mRNA expression was increased on day 3and 7 in WT lungs. These observations suggest that H-PGDS-derived PGD2 plays a protective role in bleomycin-induced lung inflammation and pulmonary fibrosis.

Therapeutic action of 5-HT3 receptor antagonists targeting peritoneal macrophages in post-operative ileus.

BACKGROUND AND PURPOSE: Post-operative ileus (POI) is induced by intestinal inflammation. Here, we aimed to clarify the effects of 5-HT3 receptor antagonists against POI. EXPERIMENTAL APPROACH: We administered three 5-HT3 receptor antagonists, ondansetron, tropisetron and palonosetron, to a mouse model of POI induced by surgical intestinal manipulation (IM). Immunohistochemistry, intestinal transit, inflammatory mediator mRNA expression and 5-HT content were measured. In some experiments, 5-HT3 A receptor null mice were used. KEY RESULTS: Three 5-HT3 receptor antagonists reduced IM-induced infiltration of inflammatory CD68-positive macrophages and myeloperoxidase-stained neutrophils. Ondansetron exhibited no anti-inflammatory actions in 5-HT3 A receptor null mice. Ondansetron inhibited expression of the chemokine CCL2, IL-1ß, IL-6, TNF-α and iNOS mRNAs up-regulated by IM, and also ameliorated the delayed gastrointestinal transit. Peritoneal macrophages, but not most infiltrating monocyte-derived macrophages, expressed 5-HT3 receptors. IM stimulation increased the 5-HT content of peritoneal lavage fluid, which up-regulated mRNA expression of proinflammatory cytokines in peritoneal macrophages. Immunohistochemical localization of 5-HT3 receptors suggests that ondansetron suppressed expression of these mRNAs in activated peritoneal macrophages, adhering to the serosal region of the inflamed intestinal wall. CONCLUSION AND IMPLICATIONS: 5-HT3 receptor antagonists were anti-inflammatory, mainly targeting peritoneal macrophages expressing these receptors. They also restored the delayed gastrointestinal transit by IM. 5-HT3 receptor antagonists should be therapeutically useful agents against POI.

PGD2 deficiency exacerbates food antigen-induced mast cell hyperplasia.

Prostaglandin D2 (PGD2) is a major prostanoid secreted mainly by mast cells. Although PGD2 has been identified as a modulator of allergic inflammation, its precise role remains unclear. Here we investigate the role of PGD2 in food allergy. Oral administration of ovalbumin induces allergic responses in sensitized wild-type (WT) mice. Systemic gene deficiency of haematopoietic PGD synthase (H-PGDS(-/-)) exacerbates all of the manifestations accompanying severe mast cell hyperplasia in the intestine. Morphological studies show that c-kit/FcɛRI-positive WT mast cells strongly express H-PGDS. Transplantation of H-PGDS(-/-) mast cells also aggravates ovalbumin-induced mast cell hyperplasia and allergic symptoms in mast cell null mice. H-PGDS deficiency accelerates the production of SDF-1α and the activity of MMP-9 in the antigen-stimulated intestine. SDF-1α receptor blockade or MMP-9 inhibition relieves the exacerbated mast cell hyperplasia and manifestations observed in H-PGDS(-/-). Thus, PGD2 deficiency results in food antigen-induced mast cell hyperplasia.