Prostaglandin D2 as a mediator of allergic asthma

Cutting edge: chemoattractant receptor-homologous molecule expressed on Th2 cells plays a restricting role on IL-5 production and eosinophil recruitment

PGs play key regulatory roles in inflammation and immunity. PGD2, released from mast cells and Th2 cells during allergic responses, has recently been shown to target a novel receptor, chemoattractant receptor-homologous molecule expressed TH2 cells (CRTH2), in addition to the classic PGD (DP) receptor. CRTH2 is expressed on Th2 cells and eosinophils and mediates chemotaxis of these cells to PGD2. Thus, CRTH2 is thought to be a key receptor mediating eosinophil and Th2 cell recruitment during allergic responses. To examine the role of CRTH2 in this context in vivo, we generated CRTH2 knockout mice. Surprisingly, in an allergic inflammatory model of asthma, CRTH2 knockout mice showed enhanced eosinophil recruitment into the lung compared with wild-type littermate mice. This is consistent with our observation that CRTH2 knockout cells produce significantly higher amounts of IL-5 and IL-3 in vitro. These results suggest a nonredundant role of CRTH2 in restricting eosinophilia and allergic response in vivo.

What targets have knockouts revealed in asthma?

There have been numerous studies of mice rendered genetically deficient of various genes in the context of allergic inflammatory airway disease. These studies have provided invaluable information about basic immune processes, but have also been considered to be useful in predicting novel pharmacological targets. In this review, the effect of a wide range of individual knockouts (KO) on the development of asthma-like pathologies in mice is compiled and considered. How the results of these studies compare with effects of agents that interfere with the function of each gene product, where known, is also described. Finally, a personal view of the utility of these studies in drug development is presented.

Absence of leukotriene B4 receptor 1 confers resistance to airway hyperresponsiveness and Th2-type immune responses

Bronchial asthma is an increasingly common disorder that remains poorly understood and difficult to manage. The disease is characterized by airway hyperresponsiveness, chronic inflammation, and mucus overproduction. Based on the finding that leukotriene B4 receptor 1 (BLT1) is expressed highly in Th2 lymphocytes, we analyzed the roles of BLT1 using an OVA-induced bronchial asthma model. BLT1-null mice did not develop airway hyperresponsiveness, eosinophilic inflammation, and hyperplasia of goblet cells. Attenuated symptoms were accompanied by reduced IgE production, and accumulation of IL-5 and IL-13 in bronchoalveolar lavage fluid, suggesting attenuated Th2-type immune response in BLT1-null mice. Peribronchial lymph node cells of sensitized BLT1-null mice showed much attenuated proliferation and production of Th2 cytokines upon re-stimulation with Ag in vitro. Thus, LTB4-BLT1 axis is required for the development of Th2-type immune response, and blockade of LTB4 functions through BLT1 would be novel and useful in the effort to ameliorate bronchial asthma and related Th2-biased immune disorders.

Prostaglandin D2 Induces Chemotaxis in Eosinophils Via Its Receptor CRTH2 and Eosinophils May Cause Severe Ocular Inflammation in Patients With Allergic Conjunctivitis

PURPOSE

Eosinophils are known to have important roles in the pathogenesis of allergic conjunctivitis. Prostaglandin (PG) D2, which has been implicated as a factor in allergic diseases, is known to have chemotactic activity for eosinophils. Its receptor, chemoattractant receptor homologous molecule expressed on TH2 (CRTH2), serves as a receptor for PGD2 and has been reported to mediate PGD2-dependent migration of eosinophils. In the present study, both eosinophil toxic activity for corneal epithelial cells and chemotaxis induced by PGD2 in normal volunteers were investigated. Expression of CRTH2 in normal subjects was also measured.

METHODS

Primary cultured corneal epithelial cells and eosinophils in serum from normal volunteers were used and a human corneal epithelial cell line was established. Studies were performed with/without amniotic membrane. CRTH2 expression on eosinophils was assessed by flow cytometry. Chemotaxis experiments were performed using a modified Boyden chamber technique.

RESULTS

Corneal epithelial cells cultured with eosinophils showed higher floating epithelial cells and epithelial defect than those cultured in the absence of eosinophils. Flow cytometry analysis revealed that eosinophils expressed CRTH2. PGD2 induced chemotaxis of eosinophils.

CONCLUSIONS

Corneal epithelial damage might be caused by eosinophils, which are recruited by PGD2 secretion via CRTH2 expressed on eosinophils.

CRTH2-specific binding characteristics of [3H]ramatroban and its effects on PGD2-, 15-deoxy-Delta12, 14-PGJ2- and indomethacin-induced agonist responses

We previously showed that ramatroban (Baynastrade mark), a thromboxane A(2) (TxA(2)) antagonist, had inhibited prostaglandin D(2) (PGD(2))-stimulated human eosinophil migration mediated through activation of chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). However, detailed pharmacological characterization of its inhibitory activity has not been described. In the present study, we showed that [(3)H]ramatroban bound to a single receptor site on CRTH2 transfectants with a similar K(d) value (7.2 nM) to a TxA(2) receptor (8.7 nM). We also demonstrated that ramatroban inhibited PGD(2)-, 15-deoxy-Delta(12, 14)-PGJ(2) (15d-PGJ(2))- and indomethacin-induced calcium responses on CRTH2 transfectants in a competitive manner with similar pA(2) values (8.5, 8.5, and 8.6, respectively). This is the first report showing the evidence for direct binding of ramatroban to CRTH2, revealing its competitive inhibitory effects and another interesting finding that PGD(2), indomethacin and 15d-PGJ(2) share the same binding site with ramatroban on CRTH2.

Sertoli cell differentiation is induced both cell-autonomously and through prostaglandin signaling during mammalian sex determination

We have raised an antibody specifically recognizing endogenous mouse SRY protein and used it to investigate the molecular and cellular mode of action of SRY in testis determination. We find that expression of SRY protein closely mirrors the expression of Sry mRNA in mouse genital ridges and is detectable for 6 to 8 h after the mRNA ceases to be detectable. The subset of somatic cells that expresses SRY begins to express SOX9 almost immediately. Since these SOX9-positive cells go on to develop as Sertoli cells, it appears that SRY expression marks the pre-Sertoli cell lineage and leads to up-regulation of Sox9 expression cell-autonomously. However, a small proportion of SOX9-positive cells did not appear to express SRY, possibly reflecting the additional involvement of paracrine signaling in activating Sox9 transcription in these cells. We confirmed by ex vivo cell mixing experiments that SRY is able to engage receptor-mediated signaling to up-regulate Sox9 expression. Finally, we showed by employing specific inhibitors that the causative signaling molecule is prostaglandin D2 (PGD2) and that PGD2 can induce Sox9 transcription in cultured XX gonads. Our data indicate a mechanism whereby Sry uses both a cell-autonomous mechanism and a PGD2-mediated signaling mechanism to stimulate expression of Sox9 and induce the differentiation of Sertoli cells in vivo.

Development of a prostaglandin D2 receptor antagonist: discovery of a new chemical lead

A series of N-(p-alkoxy)benzoyl-5-methoxy-2-methylindole-3-acetic acids and N-(p-butoxy)benzoyl-2-methylindole-4-acetic acid were discovered as new chemical leads for a prostaglandin D2 (PGD2) receptor antagonist. Most of them exhibited PGD2 receptor binding and blocked cyclic adenosine 3',5'-monophosphate (cAMP) formation in vitro. In particular, 2-methylindole-4-acetic acid analog 1 showed markedly increased receptor affinity and cAMP antagonist activity. Chemistry and structure activity relationship (SAR) data are also presented.

Identification of Determinants of Ligand Binding Affinity and Selectivity in the Prostaglandin D2 Receptor CRTH2

The chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) is a G protein-coupled receptor that mediates the pro-inflammatory effects of prostaglandin D(2) (PGD(2)) generated in allergic inflammation. The CRTH2 receptor shares greatest sequence similarity with chemoattractant receptors compared with prostanoid receptors. To investigate the structural determinants of CRTH2 ligand binding, we performed site-directed mutagenesis of putative mCRTH2 ligand-binding residues, and we evaluated mutant receptor ligand binding and functional properties. Substitution of alanine at each of three residues in the transmembrane (TM) helical domains (His-106, TM III; Lys-209, TM V; and Glu-268, TM VI) and one in extracellular loop II (Arg-178) decreased PGD(2) binding affinity, suggesting that these residues play a role in binding PGD(2). In contrast, the H106A and E268A mutants bound indomethacin, a nonsteroidal anti-inflammatory drug, with an affinity similar to the wild-type receptor. HEK293 cells expressing the H106A, K209A, and E268A mutants displayed reduced inhibition of intracellular cAMP and chemotaxis in response to PGD(2), whereas the H106A and E268A mutants had functional responses to indomethacin similar to the wild-type receptor. Binding of PGE(2) by the E268A mutant was enhanced compared with the wild-type receptor, suggesting that Glu-268 plays a role in determining prostanoid ligand selectivity. Replacement of Tyr-261 with phenylalanine did not affect PGD(2) binding but decreased the binding affinity for indomethacin. These results provided the first details of the ligand binding pocket of an eicosanoid-binding chemoattractant receptor.

Induction of cyclooxygenase-2 expression by allergens in lymphocytes from allergic patients

Cyclooxygenase (COX) is a key enzyme in prostaglandin (PG) synthesis. Up-regulation of COX-2 expression is responsible for increased PG release during inflammatory conditions and is thought to be also involved in allergic states. In this study, we demonstrate that in human T, B and natural killer lymphocytes from allergic patients, COX-2 expression became induced upon cell challenge with specific allergens and that this process is presumably IgE dependent and occurs after CD23 receptor ligation. This induction took place at both mRNA and protein levels and was accompanied by PGD2 release. IgE-dependent lymphocyte treatment elicited, in parallel, an activation of the MAPK p38 and extracellular signal-regulated kinase 1/2, an enhancement of calcineurin (CaN) activity, and an increase of the DNA-binding activity of the nuclear factor of activated T cells and of NF-kappaB, with a concomitant decrease in the levels of the cytosolic inhibitor of kappaB, IkappaB. In addition, specific chemical inhibitors of MAPK, such as PD098059 and SB203580, as well as MG-132, an inhibitor of proteasomal activity, abolished allergen-induced COX-2 up-regulation, suggesting that this process is mediated by MAPK and NF-kappaB. However, induction of COX-2 expression was not hampered by the CaN inhibitor cyclosporin A. We also examined the effect of a selective COX-2 inhibitor, NS-398, on cytokine production by human lymphocytes. Treatment with NS-398 severely diminished the IgE-dependently induced production of IL-8 and TNF-alpha. These results underscore the relevant role of lymphocyte COX-2 in allergy and suggest that COX-2 inhibitors may contribute to the improvement of allergic inflammation through the reduction of inflammatory mediator production by human lymphocytes.

Prostaglandin D2 mediates neuronal protection via the DP1 receptor

Cyclo-oxygenases (COXs) catalyze the first committed step in the synthesis of the prostaglandins PGE(2), PGD(2), PGF(2alpha), PGI(2) and thomboxane A(2). Expression and enzymatic activity of COX-2, the inducible isoform of COX, are observed in several neurological diseases and result in significant neuronal injury. The neurotoxic effect of COX-2 is believed to occur through downstream effects of its prostaglandin products. In this study, we examined the function of PGD(2) and its two receptors DP1 and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) (DP2) in neuronal survival. PGD(2) is the most abundant prostaglandin in brain and regulates sleep, temperature and nociception. It signals through two distinct G protein-coupled receptors, DP1 and DP2, that have opposing effects on cyclic AMP (cAMP) production. Physiological concentrations of PGD(2) potently and unexpectedly rescued neurons in paradigms of glutamate toxicity in cultured hippocampal neurons and organotypic slices. This effect was mimicked by the DP1-selective agonist BW245C but not by the PGD(2) metabolite 15d-PGJ(2), suggesting that neuroprotection was mediated by the DP1 receptor. Conversely, activation of the DP2 receptor promoted neuronal loss. The protein kinase A inhibitors H89 and KT5720 reversed the protective effect of PGD(2), indicating that PGD(2)-mediated neuroprotection was dependent on cAMP signaling. These studies indicate that activation of the PGD(2) DP1 receptor protects against excitotoxic injury in a cAMP-dependent manner, consistent with recent studies of PGE(2) receptors that also suggest a neuroprotective effect of prostaglandin receptors. Taken together, these data support an emerging and paradoxical neuroprotective role of prostaglandins in the CNS.

Response of the lung to pulmonary insulin dosing in the rat model and effects of changes in formulation

BACKGROUND

The hope that pulmonary insulin will provide increased patient compliance and quality of life has created great interest in patients with diabetes, the medical community, and the general public. A pulmonary insulin product is becoming a reality with clinical trials indicating comparable glycemic control with no change in pulmonary function. However, the longterm effects of pulmonary insulin dosing are not known, and as more pulmonary formulations for insulin and other proteins are rapidly being developed the need for further safety data continues to grow.

METHODS

Using gene microarrays, we compared differences in the levels of mRNAs in the lung tissue of rats that were administered a subcutaneous injection or a pulmonary instillation of insulin, as well as rats receiving an pulmonary instillation of insulin and a drug delivery agent.

RESULTS

While the insulin doses achieved comparable blood glucose depression and serum insulin concentrations, 30 mRNAs were differentially regulated in response to pulmonary dosing, including 10 mRNAs associated with an immune response and four associated with the lung's response to injury, as well as ion channels and transcription factors. When disodium 8-((N-salicyloyl-2-amino-4-chloro)phenoxy)octanoate, a drug delivery agent known to facilitate pulmonary absorption, was instilled in combination with the pulmonary insulin dose, an attenuation of this response was observed.

CONCLUSIONS

These findings suggest that undesirable effects of pulmonary dosing may be avoided by changes in formulation and that further evaluation of the effects of chronic pulmonary administration of insulin is warranted.

Consensual immunity: success-driven development of T-helper-1 and T-helper-2 responses

Non-germline-encoded T- and B-cell receptors allow humans to effectively deal with rapidly mutating pathogens. Here, we argue that, in addition to determining the antigenic specificity of immune responses, the same receptor systems can also regulate the T-helper-1/T-helper-2 profile of immunity. Such a mechanism--based on feedback from distinct effector cells to dendritic cells, rather than on instruction from pathogens--uses the effectiveness of particular effector cells at targeting and destroying a pathogen as a reliable, experience-based criterion to induce and maintain the appropriately polarized response.

Prostaglandin D2 induces nuclear import of the sex-determining factor SOX9 via its cAMP-PKA phosphorylation

During mammalian gonadal development, nuclear import/export of the transcription factor SOX9 is a critical step of the Sry-initiated testis-determining cascade. In this study, we identify a molecular mechanism contributing to the SOX9 nuclear translocation in NT2/D1 cells, which is mediated by the prostaglandin D2 (PGD2) signalling pathway via stimulation of its adenylcyclase-coupled DP1 receptor. We find that activation of cAMP-dependent protein kinase A (PKA) induces phosphorylation of SOX9 on its two S64 and S181 PKA sites, and its nuclear localization by enhancing SOX9 binding to the nucleocytoplasmic transport protein importin beta. Moreover, in embryonic gonads, we detect a male-specific prostaglandin D synthase expression and an active PGD2 signal at the time and place of SOX9 expression. We thus propose a new step in the sex-determining cascade where PGD2 acts as an autocrine factor inducing SOX9 nuclear translocation and subsequent Sertoli cell differentiation.

Protein Kinase C Activates Human Lipocalin-type Prostaglandin D Synthase Gene Expression through De-repression of Notch-HES Signaling and Enhancement of AP-2β Function in Brain-derived TE671 Cells

Here we investigated the regulatory mechanism of lipocalin-type prostaglandin D synthase (L-PGDS) gene expression in human TE671 (medulloblastoma of cerebellum) cells. Reporter analysis of the promoter region from -730 to +75 of the human L-PGDS gene demonstrated that deletion or mutation of the N-box at -337 increased the promoter activity 220-300%. The N-box was bound by Hes-1, a mammalian homologue of Drosophila Hairy and enhancer of split, as examined by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Functional expression of the Notch intracellular domain significantly increased Hes-1 expression and decreased L-PGDS expression level in TE671 cells. Moreover, knock-down of Hes-1 mRNA by RNA interference significantly enhanced the L-PGDS mRNA level, indicating that the L-PGDS gene expression is repressed by the Notch-Hes signaling. When the AP-2 element at -98 of the promoter region was deleted or mutated, the promoter activity was drastically decreased to approximately 10% of normal. The AP-2 element was bound by AP-2beta dominantly expressed in TE671 cells, according to the results of electrophoretic mobility shift assay and chromatin immunoprecipitation assay. L-PGDS expression was induced by 12-O-tetradecanoylphorbol-13-acetate in TE671 cells, and this induction was inhibited by a protein kinase C inhibitor. Stimulation of TE671 cells with 12-O-tetradecanoylphorbol-13-acetate or transfection with protein kinase Calpha expression vector induced phosphorylation of Hes-1, inhibition of DNA binding of Hes-1 to the N-box, and activation of the AP-2beta function to up-regulate L-PGDS gene expression. These results reveal a novel transcriptional regulatory mechanism responsible for the high level expression of the human L-PGDS gene in TE671 cells.

Activation of the prostaglandin D2 receptor DP2/CRTH2 increases allergic inflammation in mouse

Allergic pathologies are often associated with IgE production, mast cell activation, and eosinophilia. PGD2 is the major eicosanoid, among several inflammatory mediators, released by mast cells. PGD2 binds to two membrane receptors, D prostanoid receptor (DP)1 and DP2, endowed with antagonistic properties. In humans, DP2 is preferentially expressed on type 2 lymphocytes, eosinophils, and basophils and mediates chemotaxis in vitro. Although not yet supported by in vivo studies, DP2 is thought to be important in the promotion of Th2-related inflammation. Herein, we demonstrate that mouse eosinophils express both DP1 and DP2 and that PGD2 exerts in vitro chemotactic effects on eosinophils through DP2 activation. Furthermore, 13,14-dihydro-15-keto-PGD2, a specific DP2 agonist not only increases eosinophil recruitment at inflammatory sites but also the pathology in two in vivo models of allergic inflammation: atopic dermatitis and allergic asthma. By contrast, DP1 activation tends to ameliorate the pathology in asthma. Taken together, these results support the hypothesis that DP2 might play a critical role in allergic diseases and underline the interest of DP2 antagonists in human therapy.

Thromboxane A2 and prostaglandin F2alpha mediate inflammatory tachycardia

Systemic inflammation induces various adaptive responses including tachycardia. Although inflammation-associated tachycardia has been thought to result from increased sympathetic discharge caused by inflammatory signals of the immune system, definitive proof has been lacking. Prostanoids, including prostaglandin (PG) D(2), PGE(2), PGF(2alpha), PGI(2) and thromboxane (TX) A(2), exert their actions through specific receptors: DP, EP (EP(1), EP(2), EP(3), EP(4)), FP, IP and TP, respectively. Here we have examined the roles of prostanoids in inflammatory tachycardia using mice that lack each of these receptors individually. The TXA(2) analog I-BOP and PGF(2alpha) each increased the beating rate of the isolated atrium of wild-type mice in vitro through interaction with TP and FP receptors, respectively. The cytokine-induced increase in beating rate was markedly inhibited in atria from mice lacking either TP or FP receptors. The tachycardia induced in wild-type mice by injection of lipopolysaccharide (LPS) was greatly attenuated in TP-deficient or FP-deficient mice and was completely absent in mice lacking both TP and FP. The beta-blocker propranolol did not block the LPS-induced increase in heart rate in wild-type animals. Our results show that inflammatory tachycardia is caused by a direct action on the heart of TXA(2) and PGF(2alpha) formed under systemic inflammatory conditions.

A functional polymorphism in the promoter region of the cyclooxygenase-2 gene is not associated with asthma and atopy in an Australian population

BACKGROUND

Cyclooxygenase (COX)-2 is a key inducible enzyme that regulates the production of anti-inflammatory prostaglandin E(2). A single-nucleotide polymorphism, -765G>C, located within a stimulatory protein-1 binding site in the COX-2 promoter region, has been shown to have significantly lower promoter activity in vitro compared with the wild-type and was associated with decreased plasma levels of C-reactive protein after coronary artery bypass surgery. We hypothesized that this polymorphism, which may result in decreased COX-2 transcription, could be associated with more severe asthma, and/or aspirin-intolerant asthma (AIA).

OBJECTIVE

To determine the association between the -765G>C COX-2 polymorphism and asthma, disease severity and AIA in a large, well-phenotyped Australian population.

METHODS

PCR and restriction fragment length polymorphism analysis was used to characterize the polymorphism in an Australian Caucasian population of patients with mild (n=322), moderate (n=254) or severe (n=88) asthma and in non-asthmatic control subjects (n=512), as well as in patients with AIA (n=58). Genotype and allele association analyses were performed using chi(2) tests.

RESULTS

The polymorphic -765C allele was present in approximately 30% of asthmatic patients and non-asthmatic controls. There was no association between the -765G>C polymorphism and asthma (P=0.920), disease severity (P=0.840), atopy (P=0.655) or AIA (P=0.841) in this population.

CONCLUSION

Although the -765G>C polymorphism may have lower promoter activity and result in decreased COX-2 expression, it is not associated with asthma, disease severity, AIA or atopy in this Australian population.

Chemokines and their receptors in the pathogenesis of allergic asthma: progress and perspective

PURPOSE OF REVIEW

The importance of chemokines and their receptors to development and maintenance of allergic asthma is reflected in the burgeoning amount of literature currently devoted to this topic. Based on a series of selected references published during the last year, this review now summarizes recent advances and discusses the likely implications of these findings.

RECENT FINDINGS

Of particular interest are reports describing novel interactions between chemokines and both eosinophils and mast cells, including a role for CXCL5 (epithelial cell-derived neutrophil-activating peptide-78) and intracellular CCR3. New insights into TH2-cell dominance are presented in reports dealing with a range of chemokines, including CCL3 (MIP-1alpha), CCL4 (MIP-1beta), CCL5 (RANTES), CXCL9 (Mig), and CXCL10 (IP-10). The increasing importance of structural cell participation is emphasized by reports focusing on the eotaxin family (CCL11, CCL24, and CCL26), as well as CCL17 (TARC), CCL22 (MDC), CXCL9 (Mig), and CX3CL1 (Fractalkine). A developing role for nonreceptor regulatory mechanisms is also emphasized by seminal work relating to metalloproteinases, as well as reports focusing on proteoglycans and beta-Arrestin-2. Finally, significant progress in the field of asthma heritability is featured in reports relating to both known and novel genes, including those encoding CCR5 and DPP-10.

SUMMARY

The critical influence of chemokine biology on the outcome of allergic asthma continues to be highlighted in recent reports describing novel mechanisms by which eosinophils are recruited into the lung and local TH2-cell dominance is maintained. Also of considerable interest is the increasing emphasis currently being realized for structural cell participation, nonreceptor regulatory mechanisms, and the influence of susceptibility genes.

Minor structural modifications convert the dual TP/CRTH2 antagonist ramatroban into a highly selective and potent CRTH2 antagonist

Ramatroban, a thromboxane A(2) receptor (TP) antagonist with clinical efficacy in asthma and allergic rhinitis, was recently shown to also antagonize the prostaglandin D(2) receptor CRTH2. Here we report that minor structural changes to ramatroban result in a compound (13) with complete lack of activity on TP but sub-nanomolar potency toward CRTH2. This is the first selective CRTH2 antagonist described to date, and should prove highly valuable in further elucidating the biological significance of CRTH2.

Suppression of allergic inflammation by the prostaglandin E receptor subtype EP3

Prostaglandins, including PGD(2) and PGE(2), are produced during allergic reactions. Although PGD(2) is an important mediator of allergic responses, aspirin-like drugs that inhibit prostaglandin synthesis are generally ineffective in allergic disorders, suggesting that another prostaglandin-mediated pathway prevents the development of allergic reactions. Here we show that such a pathway may be mediated by PGE(2) acting at the prostaglandin E receptor EP3. Mice lacking EP3 developed allergic inflammation that was much more pronounced than that in wild-type mice or mice deficient in other prostaglandin E receptor subtypes. Conversely, an EP3-selective agonist suppressed the inflammation. This suppression was effective when the agonist was administered 3 h after antigen challenge and was associated with inhibition of allergy-related gene expression. Thus, the PGE(2)-EP3 pathway is an important negative modulator of allergic reactions.

Effects of prostaglandin D2, 15-deoxy-Delta12,14-prostaglandin J2, and selective DP1 and DP2 receptor agonists on pulmonary infiltration of eosinophils in Brown Norway rats

Prostaglandin (PG) D2 is an arachidonic acid metabolite that is released by allergen-stimulated mast cells. It is a potent in vitro chemoattractant for human eosinophils, acting through the DP2 receptor/chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). Furthermore, there is in vivo evidence that PGD2 contributes to allergen-induced pulmonary eosinophilia via its classic DP1 receptor. The PGD2-derived product 15-deoxy-Delta12,14-PGJ2 is widely used as a peroxisome proliferator-activated receptor gamma agonist and has been shown to have anti-inflammatory properties. However, this substance can also activate eosinophils in vitro through the DP2 receptor. The objectives of the present study were to determine whether PGD2 and 15-deoxy-Delta12,14-PGJ2 can induce pulmonary eosinophilia, and, if so, to examine the abilities of selective DP1 and DP2 receptor agonists to induce this response. Brown Norway rats were treated by intratracheal instillation of PGs. Vehicle and 5-oxo-6,8,11,14-eicosatetraenoic acid were used as negative and positive controls, respectively. Lung eosinophils were identified by immunostaining of lung sections with an antibody to major basic protein. Both PGD2 and 15-deoxy-Delta12,14-PGJ2 induced robust eosinophilic responses that were apparent by 12 h and persisted for at least 48 h. Two selective DP2 receptor agonists, 15R-methyl-PGD2 and 13-14-dihydro-15-keto-PGD2, induced similar responses, the former being more potent than PGD2, whereas the latter was less potent. The selective DP1 receptor agonist BW245C [(4S)-(3-[(3R,S)-3-cyclohexyl-3-hydroxypropyl]-2,5-dioxo)-4-imidazolidineheptanoic acid] was completely inactive. We conclude that PGD2 and 15-deoxy-Delta12,14-PGJ2 induce eosinophil infiltration into the lungs through the DP2 receptor. The potent in vitro DP2 receptor agonist 15R-methyl-PGD2 is also very active in vivo and should be a useful tool in examining the role of this receptor.

Discovery of orally active prostaglandin D2 receptor antagonists

A series of N-(p-alkoxy)benzoyl-2-methylindole-4-acetic acids were synthesized and evaluated for prostaglandin D(2) (DP) receptor affinity and antagonist activity. Some of them exhibited strong receptor binding and were potent in the cAMP formation assays. These antagonists also suppressed allergic inflammatory responses such as the PGD(2)-induced increase of microvascular permeability. Structure-activity relationship (SAR) data are presented.

Inflammation Research Association: 12th international conference

The Inflammation Research Association held its 12th international meeting at the Sagamore at Bolton Landing in New York State (3 - 7 October 2004). These meetings were originally intended for scientists from the pharmaceutical industry to get together and discuss the latest developments in inflammation drug discovery, and it remains an industry-dominated affair. The conference covered some highly topical issues such as cyclooxygenase-2 inhibitors (rofecoxib/Vioxx [Merck & Co., Inc.] was withdrawn from the market only a few days before the conference), along with areas of ongoing interest to the pharmaceutical and biotechnology industry, including p38 MAPK inhibitors, nuclear hormone receptor modulators and prostaglandin receptor antagonists. This review will cover the main themes that emerged during the meeting.

Prostaglandin D2-induced eosinophilic airway inflammation is mediated by CRTH2 receptor

Mast cell-derived prostaglandin D(2) (PGD(2)) is one of the essential modulators of eosinophilic airway inflammation in asthma and allergic rhinitis. Two G protein-coupled receptors for PGD(2), prostaglandin D(2) receptor (DP) and chemoattractant receptor-homologous molecule expressed on Th(2) cells (CRTH2), are both expressed on the surface of eosinophils, and CRTH2 has been demonstrated to mediate PGD(2)-induced eosinophil mobilization in vitro. However, it has not yet been determined whether PGD(2) and its receptors mediate in vivo eosinophil trafficking into the airways or other organs. We demonstrated that intratracheal administration of PGD(2) in rats pretreated with systemic interleukin-5 (IL-5) injection induced marked airway eosinophilia, determined by the differential counts of cells in bronchoalveolar lavage (BAL) fluid and lung histology, within 2 h. Systemic IL-5 alone significantly increased the number of eosinophils in the peripheral blood but showed no effect on airway eosinophilia. Three CRTH2-specific agonists (13,14-dihydro-15-keto-PGD(2), 11-deoxy-11-methylene-15-keto-PGD(2), and indomethacin) demonstrated equivalent induction of BAL eosinophilia to that of PGD(2), but a DP agonist (BW 245C [5-(6-carboxyhexyl)-1-(3-cyclohexyl-3-hydroxypropyl)-hydantoin]) or a thromboxane A(2) receptor (TP) agonist ([1S-1alpha,2beta(5Z), 3alpha(1E,3R*),4alpha)]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo-[2.2.1]heptan-2-yl]-5-heptenoic acid) showed no effect. PGD(2) or CRTH2 agonist-induced BAL eosinophilia was almost completely inhibited by pretreatment with a CRTH2/TP antagonist, ramatroban [BAY-u3405; (+)-(3R)-3-(4-fluorobenzenesulfonamido)-1,2,3,4-tetra-hydrocarbazole-9-propionic acid], whereas a TP-specific antagonist, SQ29,548 (5-heptenoic, 7-[3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]-hept-2-yl]-[1S-[1alpha,2alpha(Z),3alpha,4alpha]]), or a DP-specific antagonist, BW A868C [3-benzyl-5-(6-carboxyhexyl)-1-(2-cyclohexy-2-hydroxyethylamino)-hydantoin], did not inhibit the effects of PGD(2). These results suggest that CRTH2 plays a significant role in the eosinophil trafficking from the bloodstream into the airways in PGD(2)-related airway inflammation.

Pharmacology and signaling of prostaglandin receptors: multiple roles in inflammation and immune modulation

Prostaglandins are lipid-derived autacoids that modulate many physiological systems including the CNS, cardiovascular, gastrointestinal, genitourinary, endocrine, respiratory, and immune systems. In addition, prostaglandins have been implicated in a broad array of diseases including cancer, inflammation, cardiovascular disease, and hypertension. Prostaglandins exert their effects by activating rhodopsin-like seven transmembrane spanning G protein-coupled receptors (GPCRs). The prostanoid receptor subfamily is comprised of eight members (DP, EP1-4, FP, IP, and TP), and recently, a ninth prostaglandin receptor was identified-the chemoattractant receptor homologous molecule expressed on Th2 cells (CRTH2). The precise roles prostaglandin receptors play in physiologic and pathologic settings are determined by multiple factors including cellular context, receptor expression profile, ligand affinity, and differential coupling to signal transduction pathways. This complexity is highlighted by the diverse and often opposing effects of prostaglandins within the immune system. In certain settings, prostaglandins function as pro-inflammatory mediators, but in others, they appear to have anti-inflammatory properties. In this review, we will discuss the pharmacology and signaling of the nine known prostaglandin GPCRs and highlight the specific roles that these receptors play in inflammation and immune modulation.

Asymmetric Synthesis of a Prostaglandin D2Receptor Antagonist

An asymmetric synthesis was developed for the production of a prostaglandin D(2) receptor antagonist for the treatment of allergic rhinitis. The stereogenic center was set using asymmetric allylic alkylation chemistry, and the core of the structure was constructed via Pd-catalyzed N-cyclization/Heck methodology. The synthesis relies on a late stage indoline oxidation which does not racemize the product.

Role of human mast cells and basophils in bronchial asthma

Mast cells and basophils are the only cells expressing the tetrameric (alphabetagamma2) structure of the high affinity receptor for IgE (FcepsilonRI) and synthesizing histamine in humans. Human FcepsilonRI+ cells are conventionally considered primary effector cells of bronchial asthma. There is now compelling evidence that these cells differ immunologically, biochemically, and pharmacologically, which suggests that they might play distinct roles in the appearance and fluctuation of the asthma phenotype. Recent data have revealed the complexity of the involvement of human mast cells and basophils in asthma and have shed light on the control of recruitment and activation of these cells in different lung compartments. Preliminary evidence suggests that these cells might not always be detrimental in asthma but, under some circumstances, they might exert a protective effect by modulating certain aspects of innate and acquired immunity and allergic inflammation.

Prostanoids in the cutaneous immune response

Prostanoids, consisting of the prostaglandins and the thromboxanes, are the cyclooxygenase metabolites of arachidonic acid. They exert a range of actions mediated by their respective receptors expressed in the target cells. In the skin, it is well known that prostanoids are abundantly produced and that the prostanoid receptors are highly expressed. However, the physiological role of prostanoids in the skin has not been clarified. Recent developments in the molecular biology of the prostanoid receptors have enabled the investigation of the physiological roles of each receptor by disruption of the respective genes in combination with prostanoid receptor selective compounds. Here, we review novel findings relating to the roles of prostanoids in the cutaneous immune responses. These may prove useful in the development of new therapeutic agents that can selectively manipulate the actions mediated by each receptor.

Regulation of Candida albicans morphogenesis by fatty acid metabolites

Candida albicans is an opportunistic dimorphic fungus that inhabits various host mucosal sites. Conversion from the yeast to the hyphal form has been associated with increased virulence and mucosal invasiveness. C. albicans morphogenesis is regulated by multiple signals and signaling pathways. However, signals that control morphogenesis in vivo are unknown. We investigated the effects of host long chain fatty acids, eicosanoids, and bacterial short chain fatty acids on control of germination. None of the C18 or C20 fatty acids tested had an effect on enhancing germ tube formation (arachidonic acid, oleic acid, linolenic acid, or gamma-linolenic acid). Among the different eicosanoids, both prostaglandin E2 and thromboxane B2 significantly enhanced serum-induced germination by C. albicans. Addition of antiprostaglandin or antithromboxane antibodies to serum alone inhibited germ tube formation by almost 30%, while control antibody had no effect, indicating that these eicosanoids are major morphogenic factors in the serum. Since these molecules also bind to albumin, this may also explain the hyphal transforming activity in serum that associates with albumin. Interestingly, short chain fatty acids (butyric acid), the product of lactic acid bacteria (LAB), inhibited germination. In addition, LAB culture supernatants as well as live LAB also inhibited C. albicans morphogenesis. Overall, these results indicate that fatty acid metabolites and fatty acid pathways can up-regulate and down-regulate germination in C. albicans.

Mutant G-protein-coupled receptors as a cause of human diseases

G-protein-coupled receptors (GPCR) are involved in directly and indirectly controlling an extraordinary variety of physiological functions. Their key roles in cellular communication have made them the target for more than 60% of all currently prescribed drugs. Mutations in GPCR can cause acquired and inherited diseases such as retinitis pigmentosa (RP), hypo- and hyperthyroidism, nephrogenic diabetes insipidus, several fertility disorders, and even carcinomas. To date, over 600 inactivating and almost 100 activating mutations in GPCR have been identified which are responsible for more than 30 different human diseases. The number of human disorders is expected to increase given the fact that over 160 GPCR have been targeted in mice. Herein, we summarize the current knowledge relevant to understanding the molecular basis of GPCR function, with primary emphasis on the mechanisms underlying GPCR malfunction responsible for different human diseases.

Prostanoids and prostanoid receptors in signal transduction

Prostanoids are arachidonic acid metabolites and are generally accepted to play pivotal functions in amongst others inflammation, platelet aggregation, and vasoconstriction/relaxation. Inhibition of their production with, for instance, aspirin has been used for over a century to combat a large variety of pathophysiological processes, with great clinical success. Hence, the cellular changes induced by prostanoids have been subject to an intensive research effort and especially prostanoid-dependent signal transduction has been extensively studied. In this review, we discuss the impact of the five basic prostanoids, TxA(2), PGF(2alpha), PGE(2), PGI(2), and PGD(2), via their receptors on cellular physiology. These inflammatory lipids may stimulate serpentine plasma membrane-localized receptors, which in turn affect major signaling pathways, such as the MAP kinase pathway and the protein kinase A pathway, finally resulting in altered cellular physiology. In addition, prostanoids may activate the PPARgamma members of the steroid/thyroid family of nuclear hormone receptors, which act as transcription factors and may thus directly influence gene transcription. Finally, evidence exists that prostanoids act as second messengers downstream of mitogen receptor activation, mediating events, such as cytoskeletal changes, maybe via direct interaction with GTPase activating proteins. The final cellular reaction to prostaglandin stimulation will most likely depend on combined effects of the above-mentioned levels of interaction between prostaglandins and their cellular receptors.

New drugs for asthma

Asthma is a major and increasing global health problem and, despite major advances in therapy, many patients' symptoms are not adequately controlled. Treatment with combination inhalers, which contain a corticosteroid and long-acting beta(2) adrenoceptor agonist, is the most effective current therapy. There is therefore a search for new therapies, particularly safe and effective oral treatments and those that are more efficacious in severe asthma. New therapies in development include mediator antagonists and inhibitors of cytokines, although these therapies might be too specific to be very effective. New anti-inflammatory therapies include corticosteroids and inhibitors of phosphodiesterase-4, p38 mitogen-activated protein kinase and nuclear factor-kappaB. The prospects for a curative treatment are on the horizon.

Inhibition of cell cycle progression and migration of vascular smooth muscle cells by prostaglandin D2 synthase: resistance in diabetic Goto-Kakizaki rats

The regulation of vascular smooth muscle cell (VSMC) proliferation, migration, and apoptosis plays a clear role in the atherosclerotic process. Recently, we reported on the inhibition of the exaggerated growth phenotype of VSMCs isolated from hypertensive rats by lipocalin-type prostaglandin D2 synthase (L-PGDS). In the present study, we report the differential effects of L-PGDS on VSMC cell cycle progression, migration, and apoptosis in wild-type VSMCs vs. those from a type 2 diabetic model. In wild-type VSMCs, exogenously added L-PGDS delayed serum-induced cell cycle progression from the G1 to S phase, as determined by gene array analysis and the decreased protein expressions of cyclin-dependent kinase-2, p21Cip1, and cyclin D1. Cyclin D3 protein expression was unaffected by L-PGDS, although its gene expression was stimulated by L-PGDS in wild-type cells. In addition, platelet-derived growth factor-induced VSMC migration was inhibited by L-PGDS in wild-type cells. Type 2 diabetic VSMCs, however, were resistant to the L-PGDS effects on cell cycle progression and migration. L-PGDS did suppress the hyperproliferation of diabetic cells, albeit through a different mechanism, presumably involving the 2.5-fold increase in apoptosis and the concomitant 10-fold increase of L-PGDS uptake we observed in these cells. We propose that in wild-type VSMCs, L-PGDS retards cell cycle progression and migration, precluding hyperplasia of the tunica media, and that diabetic cells appear resistant to the inhibitory effects of L-PGDS, which consequently may help explain the increased atherosclerosis observed in diabetes.

Role of prostanoid DP receptor variants in susceptibility to asthma

BACKGROUND

Previous genetic studies have associated the region of the human genome (14q22.1) containing the gene for the prostanoid DP receptor (PTGDR) with asthma. A study of a mouse model suggests that the receptor is required for the expression of the asthma phenotype. Our associations of asthma with functional genetic variants of PTGDR link these observations.

METHODS

We identified and evaluated combinations of genetic variants that influence PTGDR transcription for disease association in case-control studies of 518 white patients with asthma and 175 white controls and 80 black patients with asthma and 45 black controls.

RESULTS

We identified four novel and two previously reported single-nucleotide polymorphisms (SNPs) in PTGDR and its vicinity. These define four common three-SNP haplotypes, which vary in their ability to support transcription of PTGDR and have distinct DNA-binding-protein affinity profiles. Individual PTGDR SNPs were significantly associated with asthma in both populations. Specific PTGDR haplotypes were significantly associated with a diagnosis of asthma in a large case-control study of whites (P=0.002); we confirmed these findings in a second population of blacks (P=0.01). Multivariate analysis of the haplotype combinations (diplotypes) demonstrated that both whites (odds ratio, 0.55; 95 percent confidence interval, 0.38 to 0.80; P=0.002) and blacks (odds ratio, 0.32; 95 percent confidence interval, 0.12 to 0.89; P=0.03) who had at least one copy of the haplotype with a low transcriptional efficiency had a lower risk of asthma than subjects with no copies of the haplotype.

CONCLUSIONS

Our functional and genetic findings identify PTGDR as an asthma-susceptibility gene.

T-cell trafficking in asthma: lipid mediators grease the way

Recruitment of T cells to the airways is crucial in the pathogenesis of asthma, and it is thought to be mediated mainly by peptide chemokines. By contrast, lipid mediators such as leukotrienes and prostaglandins have classically been thought to contribute to asthma pathogenesis by other mechanisms. However, as we discuss here, the recent molecular identification of leukotriene and prostaglandin receptors, as well as the generation of mice that are genetically deficient in them, has revealed that two of these lipids - leukotriene B(4) and prostaglandin D(2) - also direct T-cell migration and seem to cooperate with chemokines in a non-redundant, sequential manner to recruit T cells to the airways in asthma.

Discovery of a new class of potent, selective, and orally active prostaglandin D2 receptor antagonists

The process of discovering a series of N-(p-alkoxy)benzoyl-2-methylindole-4-acetic acid analogs is presented since these compounds represent a new class of potent, selective, and orally active prostaglandin D2 (PGD2) receptor antagonists. Most of these compounds exhibit strong PGD2 receptor binding and PGD2 receptor antagonism in cAMP formation assays. When given orally, these new antagonists dramatically suppress allergic inflammatory responses, such as the PGD2-induced or OVA-induced increase of vascular permeability. Structure-activity relationship (SAR) data are also discussed.

MITF is necessary for generation of prostaglandin D2 in mouse mast cells

Mast cells generate eicosanoids that are linked to asthma and other inflammatory diseases. A basic-helix-loop-helix leucine zipper transcription factor termed MITF is essential for the development of mast cells. Although other substances also linked to inflammatory reactions (such as various proteases and serotonin) require MITF for their expression, the role of MITF in eicosanoid generation has not been studied. We examined eicosanoid generation in bone marrow-derived mast cells (BMMCs) of tg/tg mice that lack MITF. Most eicosanoids generated by BMMCs are either prostaglandin (PG) D2 or leukotriene C4. The former is synthesized via the cyclooxygenase pathway, whereas the latter is synthesized via the 5-lipoxygenase pathway. In response to stimulation with IgE and antigens, BMMCs of tg/tg mice synthesized leukotriene C4 normally. However, neither immediate nor delayed PGD2 production was detected in these BMMCs. This indicates that MITF is a transcription factor that specifically activates the cyclooxygenase pathway, but not the 5-lipoxygenase pathway. Significant decreases in expression of hematopoietic PGD2 synthase (hPGDS, a terminal synthase for PGD2) were observed at both mRNA and protein levels in tg/tg BMMCs. MITF transactivated the hPGDS gene via a CACCTG motif located in the promoter region. MITF appeared to be essential for generation of PGD2 by enhancing expression of the hPGDS gene in BMMCs.

Uteroglobin represses allergen-induced inflammatory response by blocking PGD2 receptor-mediated functions

Uteroglobin (UG) is an antiinflammatory protein secreted by the epithelial lining of all organs communicating with the external environment. We reported previously that UG-knockout mice manifest exaggerated inflammatory response to allergen, characterized by increased eotaxin and Th2 cytokine gene expression, and eosinophil infiltration in the lungs. In this study, we uncovered that the airway epithelia of these mice also express high levels of cyclooxygenase (COX)-2, a key enzyme for the production of proinflammatory lipid mediators, and the bronchoalveolar lavage fluid (BALF) contain elevated levels of prostaglandin D₂. These effects are abrogated by recombinant UG treatment. Although it has been reported that prostaglandin D₂ mediates allergic inflammation via its receptor, DP, neither the molecular mechanism(s) of DP signaling nor the mechanism by which UG suppresses DP-mediated inflammatory response are clearly understood. Here we report that DP signaling is mediated via p38 mitogen–activated protein kinase, p44/42 mitogen–activated protein kinase, and protein kinase C pathways in a cell type–specific manner leading to nuclear factor–κB activation stimulating COX-2 gene expression. Further, we found that recombinant UG blocks DP-mediated nuclear factor–κB activation and suppresses COX-2 gene expression. We propose that UG is an essential component of a novel innate homeostatic mechanism in the mammalian airways to repress allergen-induced inflammatory responses.

Discovery of new chemical leads for prostaglandin D2 receptor antagonists

A series of Indomethacin analogs were synthesized and biologically evaluated. Among the compounds tested, N-(p-butoxy)benzoyl-2-methylindole-4-acetic acid 2 was discovered as a new chemical lead for a prostaglandin D2 (PGD2) receptor antagonist. Structure-activity relationship data are also presented.

Cyclooxygenase isozymes: the biology of prostaglandin synthesis and inhibition

Nonsteroidal anti-inflammatory drugs (NSAIDs) represent one of the most highly utilized classes of pharmaceutical agents in medicine. All NSAIDs act through inhibiting prostaglandin synthesis, a catalytic activity possessed by two distinct cyclooxygenase (COX) isozymes encoded by separate genes. The discovery of COX-2 launched a new era in NSAID pharmacology, resulting in the synthesis, marketing, and widespread use of COX-2 selective drugs. These pharmaceutical agents have quickly become established as important therapeutic medications with potentially fewer side effects than traditional NSAIDs. Additionally, characterization of the two COX isozymes is allowing the discrimination of the roles each play in physiological processes such as homeostatic maintenance of the gastrointestinal tract, renal function, blood clotting, embryonic implantation, parturition, pain, and fever. Of particular importance has been the investigation of COX-1 and -2 isozymic functions in cancer, dysregulation of inflammation, and Alzheimer's disease. More recently, additional heterogeneity in COX-related proteins has been described, with the finding of variants of COX-1 and COX-2 enzymes. These variants may function in tissue-specific physiological and pathophysiological processes and may represent important new targets for drug therapy.

Role of antibiotics and fungal microbiota in driving pulmonary allergic responses

Over the past four decades, there has been a significant increase in allergy and asthma in westernized countries, which correlates with alterations in fecal microbiota (microflora) and widespread use of antibiotics (the "hygiene hypothesis"). Antibiotics also lead to overgrowth of the yeast Candida albicans, which can secrete potent prostaglandin-like immune response modulators. We have developed a mouse model of antibiotic-induced microbiota disruption that includes stable increases in gastrointestinal (GI) enteric bacteria and GI Candida levels with no introduction of microbes into the lungs. Mice are treated for 5 days with cefoperazone in the drinking water, followed by a single oral gavage of C. albicans. This results in alterations of GI bacterial populations and increased yeast numbers in the GI microbiota for at least 2 to 3 weeks and can drive the development of a CD4 T-cell-mediated allergic airway response to subsequent mold spore (Aspergillus fumigatus) exposure in immunocompetent mice without previous systemic antigen priming. The allergic response in the lungs is characterized by increased levels of eosinophils, mast cells, interleukin-5 (IL-5), IL-13, gamma interferon, immunoglobulin E, and mucus-secreting cells. In the absence of antibiotics, mice exposed to Aspergillus spores do not develop an allergic response in the airways. This study provides the first experimental evidence to support a role for antibiotics and fungal microbiota in promoting the development of allergic airway disease. In addition, these studies also highlight the concept that events in distal mucosal sites such as the GI tract can play an important role in regulating immune responses in the lungs.

Differential modulation of human basophil functions through prostaglandin D2 receptors DP and chemoattractant receptor-homologous molecule expressed on Th2 cells/DP2

BACKGROUND

Both prostaglandin (PG) D receptor (DP) and CRTH2 (chemoattractant receptor-homologous molecule expressed on Th2 cells)/DP2 are high-affinity receptors for PGD2. Previous studies have demonstrated that PGD2 enhances releasability and induces CRTH2/DP2-mediated migration in human basophils, but the precise effects of PGD2 on basophils as well as receptor usage have not been fully clarified.

OBJECTIVE

We comprehensively explored the roles of DP and CRTH2/DP2 in basophil functions by using selective agonists and antagonists for each receptor.

METHODS

DP and CRTH2/DP2 transcripts were quantified by real-time PCR. We studied the effects of selective agonists (DP: BW245C; CRTH2/DP2: 13,14-dihydro-15-keto (DK)-PGD2) and/or antagonists (DP: BWA868C; CRTH2/DP2: ramatroban) on Ca2+ mobilization, migration, degranulation, CD11b expression and survival of human basophils.

RESULTS

Basophils expressed transcripts of both DP and CRTH2/DP2, but the levels of CRTH2/DP2 transcripts were ca. 100-fold higher compared with DP transcripts. Ca2+ influx was induced in basophils by either PGD2 or DK-PGD2/CRTH2 agonist but not by BW245C/DP agonist. Basophils treated with PGD2 were completely desensitized to subsequent stimulation with DK-PGD2, but not vice versa. DK-PGD2 as well as PGD2 up-regulated CD11b expression, induced migration and enhanced degranulation, and those effects were completely antagonized by ramatroban/CRTH2 antagonist. In contrast, BW245C/DP agonist exhibited an inhibitory effect on basophil migration and IgE-mediated degranulation, and the migration inhibitory effect was effectively antagonized by BWA868C/DP antagonist. On the other hand, while PGD2 significantly shortened the basophil life-span, neither DK-PGD2/CRTH2 agonist nor BW245C/DP agonist did.

CONCLUSION

CRTH2/DP2 is primarily responsible for the pro-inflammatory effects of PGD2 on human basophils, while DP introduces negative signals capable of antagonizing the effects of CRTH2/DP2 in these cells. The effects of PGD2 on longevity imply a mechanism(s) other than via DP or CRTH2/DP2. CRTH2/DP2 on basophils may afford opportunities for therapeutic targeting in allergic inflammation.

Effect of inhalation aspirin challenge on exhaled nitric oxide in patients with aspirin-inducible asthma

BACKGROUND

A complex relationship between arachidonic acid metabolites and nitric oxide (NO) synthesis has been reported in asthma. The effects of inhaled aspirin on fractional exhaled NO (FENO) in patients with aspirin-tolerant (ATA) and aspirin-inducible (AIA) asthma compared with normal controls have been investigated.

METHODS

The FENO was measured baseline, after saline and lysine-aspirin (L-ASA) bronchial challenge in 10 patients with ATA and in 10 patients with AIA [mean (PD(20)FEV(1) L-ASA): 14.7 +/- 12.7 mg], who had comparable age and baseline FEV(1). Ten healthy subjects served as controls. Sputum eosinophils were counted after saline and after L-ASA challenge in the two groups of asthmatics.

RESULTS

Asthmatic patients had baseline FENO significantly higher than controls (29.7 +/- 6.8 vs 9.8 +/- 2.05 p.p.b. respectively, P < 0.0001). No difference was observed in methacholine PD(20)FEV(1) and baseline FENO between ATA and AIA patients. After L-ASA inhalation, FENO increased significantly only in patients with AIA, reaching the peak value 4 h after bronchoconstriction (from 31.1 +/- 6 to 43 +/- 4.8 p.p.b., P < 0.001), while no change was observed in patients with ATA and in controls. Sputum eosinophils increased significantly after L-ASA inhalation only in patients with AIA (from 8.1 +/- 2.7 to 11.1 +/- 2.8%, P < 0.005) and there was a significant relationship between the increase in sputum eosinophils and the increase in FENO after ASA challenge.

CONCLUSION

Exhaled NO may indicate eosinophilic airway inflammation during ASA exposure in patients with ASA inducible asthma.