Presence and characterization of prostaglandin D2-related molecules in nasal mucosa of patients with allergic rhinitis

Evaluation of Urtica dioica Phytochemicals against Therapeutic Targets of Allergic Rhinitis Using Computational Studies

Allergic rhinitis (AR) is a prevalent inflammatory condition affecting millions globally, with current treatments often associated with significant side effects. To seek safer and more effective alternatives, natural sources like Urtica dioica (UD) are being explored. However, UD's mechanism of action remains unknown. Therefore, to elucidate it, we conducted an in silico evaluation of UD phytochemicals' effects on known therapeutic targets of allergic rhinitis: histamine receptor 1 (HR1), neurokinin 1 receptor (NK1R), cysteinyl leukotriene receptor 1 (CLR1), chemoattractant receptor-homologous molecule expressed on type 2 helper T cells (CRTH2), and bradykinin receptor type 2 (BK2R). The docking analysis identified amentoflavone, alpha-tocotrienol, neoxanthin, and isorhamnetin 3-O-rutinoside as possessing a high affinity for all the receptors. Subsequently, molecular dynamics (MD) simulations were used to analyze the key interactions; the free energy of binding was calculated through Generalized Born and Surface Area Solvation (MMGBSA), and the conformational changes were evaluated. Alpha-tocotrienol exhibited a high affinity while also inducing positive conformational changes across all targets. Amentoflavone primarily affected CRTH2, neoxanthin targeted NK1R, CRTH2, and BK2R, and isorhamnetin-3-O-rutinoside acted on NK1R. These findings suggest UD's potential to treat AR symptoms by inhibiting these targets. Notably, alpha-tocotrienol emerges as a promising multi-target inhibitor. Further in vivo and in vitro studies are needed for validation.

Emerging Role of Phospholipase-Derived Cleavage Products in Regulating Eosinophil Activity: Focus on Lysophospholipids, Polyunsaturated Fatty Acids and Eicosanoids

Eosinophils are important effector cells involved in allergic inflammation. When stimulated, eosinophils release a variety of mediators initiating, propagating, and maintaining local inflammation. Both, the activity and concentration of secreted and cytosolic phospholipases (PLAs) are increased in allergic inflammation, promoting the cleavage of phospholipids and thus the production of reactive lipid mediators. Eosinophils express high levels of secreted phospholipase A2 compared to other leukocytes, indicating their direct involvement in the production of lipid mediators during allergic inflammation. On the other side, eosinophils have also been recognized as crucial mediators with regulatory and homeostatic roles in local immunity and repair. Thus, targeting the complex network of lipid mediators offer a unique opportunity to target the over-activation and 'pro-inflammatory' phenotype of eosinophils without compromising the survival and functions of tissue-resident and homeostatic eosinophils. Here we provide a comprehensive overview of the critical role of phospholipase-derived lipid mediators in modulating eosinophil activity in health and disease. We focus on lysophospholipids, polyunsaturated fatty acids, and eicosanoids with exciting new perspectives for future drug development.

Probiotic NVP-1703 Alleviates Allergic Rhinitis by Inducing IL-10 Expression: A Four-week Clinical Trial

Although several recent studies reported that probiotics might be beneficial for allergic rhinitis (AR), the effect of probiotics on AR is not consistent and have not been reproduced between studies. We aimed to determine the efficacy and safety of probiotic NVP-1703, a mixture of Bifidobacterium longum and Lactobacillus plantarum, in subjects with perennial AR. Adult subjects with perennial AR received either NVP-1703 (n = 47) or placebo (n = 48) for four weeks. Total nasal symptom scores (TNSS), rhinitis control assessment test (RCAT), blood eosinophil count, allergen-specific IgE, and immunological parameters in serum and urine were compared at baseline and after four weeks. TNSS changes from baseline at weeks 1, 3, and 4 were significant between the NVP-1703 and placebo groups (p = 0.033, 0.031, and 0.029, respectively). RCAT score showed significant differences between the NVP-1703 and placebo groups (p = 0.049) at week 4. Dermatophagoides farinae-specific IgE levels and serum IL-10 levels were significantly different between the NVP-1703 and placebo groups (p = 0.033 and p = 0.047, respectively). IL-10/IL-4 and IL-10/IL-13 ratios were different between the NVP-1703 and placebo groups at week 4 (p = 0.046 and 0.018, respectively). NVP-1703 treatment reduced urinary prostaglandin F_2α and leukotriene E₄ levels (p > 0.05). Therefore, NVP-1703 can be treatment option for perennial AR.

The Biology of Prostaglandins and Their Role as a Target for Allergic Airway Disease Therapy

Prostaglandins (PGs) are a family of lipid compounds that are derived from arachidonic acid via the cyclooxygenase pathway, and consist of PGD₂, PGI₂, PGE₂, PGF₂, and thromboxane B₂. PGs signal through G-protein coupled receptors, and individual PGs affect allergic inflammation through different mechanisms according to the receptors with which they are associated. In this review article, we have focused on the metabolism of the cyclooxygenase pathway, and the distinct biological effect of each PG type on various cell types involved in allergic airway diseases, including asthma, allergic rhinitis, nasal polyposis, and aspirin-exacerbated respiratory disease.

Potential synergistic effects of novel hematopoietic prostaglandin D synthase inhibitor TAS-205 and different types of anti-allergic medicine on nasal obstruction in a Guinea pig model of experimental allergic rhinitis

Nasal obstruction is one of the most bothersome symptoms of allergic rhinitis (AR) affecting sleep-related quality of life in AR patients. Although several treatments were tested to control nasal obstruction, some patients with moderate to severe AR do not respond to current treatments, including the combined administration of different types of anti-allergic medicine. Thus, new options for AR treatment are needed. This study aimed to evaluate the effects of combined treatment with a novel inhibitor of hematopoietic prostaglandin D synthase (HPGDS), TAS-205, and different types of anti-allergic medicine on nasal obstruction in AR. Firstly, we demonstrated that TAS-205 selectively inhibited prostaglandin D₂ (PGD₂) synthesis in an enzymatic assay in a cell-based assay and in vivo models of AR. Moreover, treatment with TAS-205 alone suppressed eosinophil infiltration into the nasal cavity and late phase nasal obstruction. The combined administration of TAS-205 with montelukast, a cysteinyl leukotriene receptor 1 antagonist, showed significant additive inhibitory effects on eosinophil infiltration and late phase nasal obstruction compared to treatment with each agent alone. In contrast, concomitant treatment with TAS-205 and fexofenadine, a histamine H₁ blocker, showed inhibitory effects on late phase and early phase nasal obstruction, although the magnitude of the inhibitory effects upon combined administration was comparable to that of each single treatment. These results suggest that combined treatment with an HPGDS inhibitor and different types of anti-allergic medicine may be a promising strategy to control nasal obstruction in AR patients.

Therapeutic Potential of Hematopoietic Prostaglandin D2 Synthase in Allergic Inflammation

Worldwide, there is a rise in the prevalence of allergic diseases, and novel efficient therapeutic approaches are still needed to alleviate disease burden. Prostaglandin D₂ (PGD₂) has emerged as a central inflammatory lipid mediator associated with increased migration, activation and survival of leukocytes in various allergy-associated disorders. In the periphery, the hematopoietic PGD synthase (hPGDS) acts downstream of the arachidonic acid/COX pathway catalysing the isomerisation of PGH₂ to PGD₂, which makes it an interesting target to treat allergic inflammation. Although much effort has been put into developing efficient hPGDS inhibitors, no compound has made it to the market yet, which indicates that more light needs to be shed on potential PGD₂ sources and targets to determine which particular condition and patient will benefit most and thereby improve therapeutic efficacy. In this review, we want to revisit current knowledge about hPGDS function, expression in allergy-associated cell types and their contribution to PGD₂ levels as well as beneficial effects of hPGDS inhibition in allergic asthma, rhinitis, atopic dermatitis, food allergy, gastrointestinal allergic disorders and anaphylaxis.

Neuroendocrine cells derived chemokine vasoactive intestinal polypeptide (VIP) in allergic diseases

Worldwide increase incidences of allergic diseases have heightened the interest of clinicians and researchers to understand the role of neuroendocrine cells in the recruitment and activation of inflammatory cells. Several pieces of evidence revealed the association of neuropeptides in the pathogenesis of allergic diseases. Importantly, one such peptide that is secreted by neuronal cells and immune cells exerts a wide spectrum of immunological functions as cytokine/chemokine is termed as Vasoactive Intestinal Peptide (VIP). VIP mediates immunological function through interaction with specific receptors namely VPAC-1, VPAC-2, CRTH2 and PAC1 that are expressed on several immune cells such as eosinophils, mast cells, neutrophils, and lymphocytes; therefore, provide the basis for the action of VIP on the immune system. Additionally, VIP mediated action varies according to target organ depending upon the presence of specific VIP associated receptor, involved immune cells and the microenvironment of the organ. Herein, we present an integrative review of the current understanding on the role of VIP and associated receptors in allergic diseases, the presence of VIP receptors on various immune cells with particular emphasis on the role of VIP in the pathogenesis of allergic diseases such as asthma, allergic rhinitis, and atopic dermatitis. Being crucial signal molecule of the neuroendocrine-immune network, the development of stable VIP analogue and/or antagonist may provide the future therapeutic drug alternative for the better treatment of these allergic diseases. Taken together, our current review summarizes the current understandings of VIP biology and further explore the significance of neuroendocrine cells derived VIP in the recruitment of inflammatory cells in allergic diseases that may be helpful to the investigators for planning the experiments and accordingly predicting new therapeutic strategies for combating allergic diseases. Summarized graphical abstract will help the readers to understand the significance of VIP in allergic diseases.

Tyrosine kinase inhibition is an important factor for gene expression of CRTH2 in human eosinophils and lymphocytes: A novel mechanism for explaining eosinophils recruitment by the neuro-immune axis in allergic rhinitis

We recently shown a novel neuro-immune competition between vasoactive intestinal peptide (VIP) and PGD2 for CRTH2 receptor, and that genistein augmented VIP and PGD2-induced eosinophil chemotaxis. However, there are neither studies on the CRTH2 gene expression in allergic rhinitis (AR) nor in the effect of tyrosine kinase inhibitors in CRTH2 gene regulation. Our Objectives were to study the gene expression modulation of CRTH2 receptor in AR patients and the effect of tyrosine kinase inhibitors (TKIs) on CRTH2 gene modulation. Nasal provocation tests, ELISA, qRT-PCR, western blot, flow cytometry and chemotaxis assays in modified micro-Boyden chambers, were all used, to achieve our objectives. Herein we show that AR patients increased the amounts of VIP and PGD2 in their nasal secretions in the early phase reaction, however CRTH2 gene expression from leukocytes recovered in their nasal secretions was upregulated only during the late phase reaction. The TKIs; Genistein, Erbstatin and Herbimycin A, induced the gene expression of CRTH2 and increased the protein content of CRTH2 in both human lymphocytes and eosinophils. This was functional as PGD2/VIP-induced eosinophil chemotaxis was augmented by the TKIs and inhibited by pervanadate, the tyrosine phosphatase inhibitor. These results open channels for therapeutic modalities targeting CRTH2 molecules in AR.

Role of Prostaglandin D2 and DP1 Receptor on Japanese Cedar Pollen-Induced Allergic Rhinitis in Mice

Although we previously demonstrated the contribution of the DP1receptor in nasal obstruction using animals sensitized with ovalbumin in the presence of adjuvant, the contribution of the DP1receptor in sneezing is unclear. Here, we developed a mouse model of Japanese cedar (JC:Cryptomeria japonica) pollinosis to evaluate the symptoms of sneezing. To achieve this, we used JC pollen crude extract in the absence of adjuvant to sensitize mice to develop a model closer to the pathophysiology of human JC pollinosis. The immunologic and pharmacologic features of this model are highly similar to those observed in JC pollinosis in humans. Using this model, we found that DP1receptor antagonists suppressed JC pollen extract-induced sneezing and that a DP1receptor agonist induced sneezing. Moreover, JC pollen extract-induced sneezing was diminished in DP1receptor knockout mice. In conclusion, we developed a novel mouse model of allergic rhinitis that closely mimics human JC pollinosis. A strong contribution of DP1receptor signaling to sneezing was demonstrated using this model, suggesting that DP1receptor antagonists could suppress sneezing and nasal obstruction, and therefore these agents could be a new therapeutic option for allergic rhinitis.

Mast cells, their subtypes, and relation to asthma phenotypes

Mast cells (MCs) are among the first cell types associated with allergies and asthma. Studies in human asthma have identified their presence in the lung submucosa and smooth muscle and also in the airway epithelium. As our understanding of the distribution and location of these MCs in the human airway has increased, it is clear that much remains to be understood regarding the presence and subtype of these MCs in relationship to asthma phenotypes, defined both clinically and on the basis of immunologic pathways. Human MCs have traditionally been divided into two major subtypes based on the protease granule content, with tryptase representing total MCs. There is emerging evidence that in the epithelium, MCs of an altered subtype (with tryptase, chymase, and/or carboxypeptidase A3) may play a role in the pathophysiology of poorly controlled, severe, Th2-associated asthma.

Prostaglandin D₂ pathway upregulation: relation to asthma severity, control, and TH2 inflammation

BACKGROUND

Bronchoalveolar lavage (BAL) fluid prostaglandin D₂(PGD₂) levels are increased in patients with severe, poorly controlled asthma in association with epithelial mast cells (MCs). PGD₂, which is generated by hematopoietic prostaglandin D synthase (HPGDS), acts on 3 G protein-coupled receptors, including chemoattractant receptor-homologous molecule expressed on TH2 lymphocytes (CRTH2) and PGD₂ receptor 1 (DP1). However, much remains to be understood regarding the presence and activation of these pathway elements in asthmatic patients.

OBJECTIVE

We sought to compare the expression and activation of PGD₂ pathway elements in bronchoscopically obtained samples from healthy control subjects and asthmatic patients across a range of disease severity and control, as well as in relation to TH2 pathway elements.

METHODS

Epithelial cells and BAL fluid were evaluated for HPGDS (quantitative real-time PCR/immunohistochemistry [IHC]) and PGD₂ (ELISA/liquid chromatography mass spectrometry) in relation to levels of MC proteases. Expression of the 2 inflammatory cell receptors DP1 and CRTH2 was evaluated on luminal cells. These PGD₂ pathway markers were then compared with asthma severity, level of control, and markers of TH2 inflammation (blood eosinophils and fraction of exhaled nitric oxide).

RESULTS

Confirming previous results, BAL fluid PGD₂ levels were highest in patients with severe asthma (overall P = .0001). Epithelial cell compartment HPGDS mRNA and IHC values differed among groups (P = .008 and P < .0001, respectively) and correlated with MC protease mRNA. CRTH2 mRNA and IHC values were highest in patients with severe asthma (P = .001 and P = .0001, respectively). Asthma exacerbations, poor asthma control, and TH2 inflammatory markers were associated with higher PGD₂, HPGDS, and CRTH2 levels.

CONCLUSION

The current study identifies coordinated upregulation of the PGD₂ pathway in patients with severe, poorly controlled, TH2-high asthma despite corticosteroid use.

Novel association between vasoactive intestinal peptide and CRTH2 receptor in recruiting eosinophils: a possible biochemical mechanism for allergic eosinophilic inflammation of the airways

We explored the relation between vasoactive intestinal peptide (VIP), CRTH2, and eosinophil recruitment. It is shown that CRTH2 expression by eosinophils from allergic rhinitis (AR) patients and eosinophil cell line (Eol-1 cells) was up-regulated by VIP treatment. This was functional and resulted in exaggerated migratory response of cells against PGD2. Nasal challenge of AR patients resulted in a significant increase of VIP contents in nasal secretion (ELISA), and the immunohistochemical studies of allergic nasal tissues showed significant expression of VIP in association with intense eosinophil recruitment. Biochemical assays showed that VIP-induced eosinophil chemotaxis from AR patients and Eol-1 cells was mediated through the CRTH2 receptor. Cell migration against VIP was sensitive to protein kinase C (PKC) and protein kinase A (PKA) inhibition but not to tyrosine kinase or p38 MAPK inhibition or calcium chelation. Western blot demonstrated a novel CRTH2-mediated cytosol-to-membrane translocation of PKC-ε, PKC-δ, and PKA-α, -γ, and -IIαreg in Eol-1 cells upon stimulation with VIP. Confocal images and FACS demonstrated a strong association and co-localization between VIP peptide and CRTH2 molecules. Further, VIP induced PGD2 secretion from eosinophils. Our results demonstrate the first evidence of association between VIP and CRTH2 in recruiting eosinophils.

Eosinophils as a novel cell source of prostaglandin D2: autocrine role in allergic inflammation

PGD(2) is a key mediator of allergic inflammatory diseases that is mainly synthesized by mast cells, which constitutively express high levels of the terminal enzyme involved in PGD(2) synthesis, the hematopoietic PGD synthase (H-PGDS). In this study, we investigated whether eosinophils are also able to synthesize, and therefore, supply biologically active PGD(2). PGD(2) synthesis was evaluated within human blood eosinophils, in vitro differentiated mouse eosinophils, and eosinophils infiltrating inflammatory site of mouse allergic reaction. Biological function of eosinophil-derived PGD(2) was studied by employing inhibitors of synthesis and activity. Constitutive expression of H-PGDS was found within nonstimulated human circulating eosinophils. Acute stimulation of human eosinophils with A23187 (0.1-5 μM) evoked PGD(2) synthesis, which was located at the nuclear envelope and was inhibited by pretreatment with HQL-79 (10 μM), a specific H-PGDS inhibitor. Prestimulation of human eosinophils with arachidonic acid (10 μM) or human eotaxin (6 nM) also enhanced HQL-79-sensitive PGD(2) synthesis, which, by acting on membrane-expressed specific receptors (D prostanoid receptors 1 and 2), displayed an autocrine/paracrine ability to trigger leukotriene C(4) synthesis and lipid body biogenesis, hallmark events of eosinophil activation. In vitro differentiated mouse eosinophils also synthesized paracrine/autocrine active PGD(2) in response to arachidonic acid stimulation. In vivo, at late time point of the allergic reaction, infiltrating eosinophils found at the inflammatory site appeared as an auxiliary PGD(2)-synthesizing cell population. Our findings reveal that eosinophils are indeed able to synthesize and secrete PGD(2), hence representing during allergic inflammation an extra cell source of PGD(2), which functions as an autocrine signal for eosinophil activation.

Prostaglandin D₂ induces contractions through activation of TP receptors in peripheral lung tissue from the guinea pig

Prostaglandin D(2) (PGD(2)), released through mast cell activation, is used as a non-invasive biomarker in patients with asthma. Since PGD(2) can elicit opposing effects on airway tone via activation of the PGD(2) receptors DP(1) and DP(2) as well as the thromboxane receptor TP, the aim of this study was to characterize the receptors that are activated by PGD(2) in the guinea pig lung parenchyma. PGD(2) and the thromboxane analog U46619 induced concentration-dependent contractions. U46619 was more potent and caused stronger effect than PGD(2). The specific TP receptor antagonist SQ-29548 and the combined TP and DP(2) receptor antagonist BAYu3405 concentration-dependently shifted the curves for both agonists to the right. The DP(1) receptor agonist BW245 induced a weak relaxation at high concentrations, whereas the DP(1) receptor antagonist BWA868C did not affect the PGD(2) induced contractions. The specific DP(2) receptor agonist 13,14-dihydro-15-keto-PGD(2) showed neither contractile nor relaxant effect in the parenchyma. Furthermore, studies in precision-cut lung slices specified that airways as well as pulmonary arteries and veins contracted to both PGD(2) and U46619. When the lung parenchyma from ovalbumin sensitized guinea pigs were exposed to ovalbumin, both thromboxane B(2) and PGD(2) were released. Ovalbumin also induced maximal contractions at similar level as PGD(2) in the parenchyma, which was partly reduced by SQ-29548. These data show that PGD(2) should be recognized as a TP receptor agonist in the peripheral lung inducing contraction on airways, arteries and veins. Therefore, a TP receptor antagonist can be useful in combination treatment of allergic responses in asthma.

Role of hematopoietic prostaglandin D synthase in biphasic nasal obstruction in guinea pig model of experimental allergic rhinitis

We investigated the role of hematopoietic prostaglandin D synthase (H-PGDS) in biphasic nasal obstruction in allergic rhinitis using a new specific inhibitor, (N-methoxy-N-methyl)-4-(5-benzoylbenzimidazole-2-yl)-3,5-dimethylpyrrole-2-carboxamide hydrochloride (TAS-204). First, we developed a novel guinea pig model of allergic rhinitis. Guinea pigs sensitized to ovalbumin without adjuvant were challenged with intranasal exposure to ovalbumin once a week. After the 3rd antigen challenge, they exhibited biphasic nasal obstruction. Additionally, analysis of nasal lavage fluid revealed an increase in the level of prostaglandin D(2) in both early and late phases. Treatment with oral TAS-204 for 15 days during the period of antigen challenges suppressed increases in nasal airway resistance in both phases. It is noteworthy that the late phase nasal obstruction was almost completely abrogated by inhibiting H-PGDS alone. Eosinophil infiltration in nasal lavage fluid and nasal hyperresponsiveness to histamine was also reduced by TAS-204 administration. These findings suggest that H-PGDS plays a critical role in the development of allergic rhinitis, especially in the induction of late phase nasal obstruction.

Inhibition of hematopoietic prostaglandin D synthase improves allergic nasal blockage in guinea pigs

Although it has been suggested that prostaglandin (PG) D(2) is involved in the pathogenesis of allergic rhinitis, whether the inhibition of hematopoietic PGD(2) synthase (H-PGDS) shows beneficial effects on allergic rhinitis has been unclear. We evaluated the effects of a selective H-PGDS inhibitor, TFC-007, on nasal symptoms on Japanese cedar pollen-induced allergic rhinitis of guinea pigs. Sensitized animals were challenged with the pollen once a week. TFC-007 (30mg/kg, p.o.) given once before a challenge almost completely suppressed PGD(2) production in the nasal tissue early and late after the challenge. Although pre-treatment did not affect the incidences of sneezing and early phase nasal blockage, late phase nasal blockage was partially but significantly attenuated; however, nasal eosinophilia was not suppressed. In contrast, when TFC-007 was given once 1.5h after the challenge, the late phase response was not affected. Collectively, PGD(2) produced by H-PGDS early after an antigen challenge can participate in the induction of late phase nasal blockage, although the mechanism may be independent of eosinophil infilatration. The strategy for H-PGDS inhibition may be beneficial for allergic rhinitis therapy.

Chitin particles induce size-dependent but carbohydrate-independent innate eosinophilia

Murine Mϕ that phagocytose CMP develop into M1; this response depends on the size and the chemical composition of the particles. In contrast, recent studies concluded that chitin particles induce M2 and eosinophil migration, promoting acquired Th2 immune responses against chitin-containing microbes or allergens. This study examined whether these apparently inconsistent responses to chitin could be induced by variation in the size and chemical composition of the chitin particles. We compared the responses of Mϕ with CMP, LCB, and Sephadex G-100 beads (>40 μm). Beads were given i.p. to WT mice and to mice deficient in a CRTH2, a receptor for the eosinophil chemoattractant PGD(2). In contrast to the M1 activation induced by CMP, i.p. administration of LCB or Sephadex beads induced within 24 h a CRTH2-dependent peritoneal eosinophilia, as well as CRTH2-independent activation of peritoneal Mϕ that expressed Arg I, an M2 phenotype. LCB-induced Mϕ exhibited elevated Arg I and a surface MR, reduced surface TLR2 levels, and no change in the levels of CHI3L1 or IL-10 production. Our results indicate that the effects of chitin in vivo are highly dependent on particle size and that large, nonphagocytosable beads, independent of their chemical composition, induce innate eosinophilia and activate Mϕ expressing several M2, but not M1, phenotypes.

Pathophysiology of nasal congestion

Nasal congestion is a common symptom in rhinitis (both allergic and nonallergic), rhinosinusitis and nasal polyposis. Congestion can also be caused by physical obstruction of nasal passages and/or modulation of sensory perception. Mucosal inflammation underlies many of the specific and interrelated factors that contribute to nasal congestion, as well as other symptoms of both allergic rhinitis and rhinosinusitis. A wide range of biologically active agents (eg, histamine, tumor necrosis factor-α, interleukins, cell adhesion molecules) and cell types contribute to inflammation, which can manifest as venous engorgement, increased nasal secretions and tissue swelling/edema, ultimately leading to impaired airflow and the sensation of nasal congestion. Inflammation-induced changes in the properties of sensory afferents (eg, expression of peptides and receptors) that innervate the nose can also contribute to altered sensory perception, which may result in a subjective feeling of congestion. Increased understanding of the mechanisms underlying inflammation can facilitate improved treatment selection and the development of new therapies for congestion.

Clinical studies of the DP1 antagonist laropiprant in asthma and allergic rhinitis

BACKGROUND

Prostaglandin D(2) is a proinflammatory mediator believed to be important in asthma and allergic rhinitis (AR). Allelic variants in the prostaglandin D(2) receptor type 1 (DP1) gene (PTGDR) have been suggested to be associated with asthma susceptibility.

OBJECTIVES

We sought to investigate the efficacy of the DP1 antagonist laropiprant (alone or with montelukast) in asthma and seasonal AR and explore whether sequence variations in PTGDR are associated with asthma severity.

METHODS

For asthma, in a double-blind crossover study, 100 patients with persistent asthma were randomized to placebo or laropiprant, 300 mg/d for 3 weeks, followed by addition of montelukast, 10 mg/d for 2 weeks. PTGDR promoter haplotypes were categorized as high, medium, or low transcriptional efficiency. The primary efficacy end point was FEV(1). For AR, in a double-blind parallel-group study, 767 patients sensitized to a regionally prevalent fall allergen with symptomatic fall rhinitis were allocated to laropiprant, 25 mg/d or 100 mg/d; cetirizine, 10mg/d; or placebo for 2 weeks. The primary end point was the Daytime Nasal Symptoms Score.

RESULTS

For asthma, no significant differences in FEV(1) or asthma symptoms were noted for laropiprant versus placebo or laropiprant plus montelukast vs montelukast (differences between montelukast and placebo: P <or= .001). No clear association was seen between haplotype pair (ie, diplotype) and asthma severity. For AR, although cetirizine (vs placebo) demonstrated an improvement in the Daytime Nasal Symptoms Score (P < .001), laropiprant did not.

CONCLUSION

Laropiprant did not demonstrate efficacy in asthmatic patients or patients with AR. Variations in PTGDR did not appear related to baseline asthma severity or treatment response (NCT00533208; NCT00783601).

Accumulation of CRTH2-positive leukocytes in human allergic nasal mucosa

BACKGROUND

Prostaglandin D2 (PGD2) has been thought to be a potent mediator involved in allergic rhinitis because PGD2 has been recovered from the nasal lavage fluid of patients with allergic rhinitis after allergen provocation and because PGD2 receptor antagonists relieved nasal allergic symptoms in an animal model of allergic rhinitis. The inflammatory effects of PGD2 are exerted through high-affinity interactions with 2 G protein-coupled receptors: D-prostanoid receptor 1 and chemoattractant-homologous receptor expressed on TH2 cells (CRTH2). CRTH2 may mediate the recruitment of leukocytes during a nasal allergic response.

OBJECTIVE

To evaluate the number of CRTH2-expressing cells in allergic and nonallergic human nasal mucosa by means of immunohistochemical analysis.

METHODS

Human turbinates were obtained after turbinectomy from 14 patients with nasal obstruction refractory to medical therapy. To identify cells expressing the CRTH2 protein, double immunostaining was performed using anti-CRTH2 antibody and monoclonal anti-leukocyte antibodies.

RESULTS

The immunohistochemical study revealed that anti-CRTH2 antibody labeled eosinophils, macrophages, mast cells, T lymphocytes, epithelial cells, and submucosal glands in the nasal mucosa. CRTH2 expressions of these leukocytes in allergic nasal mucosa are significantly up-regulated compared with those in nonallergic nasal mucosa.

CONCLUSION

These results suggest that CRTH2 may play an important role in the recruitment of leukocytes into allergic nasal mucosa.

Prostaglandin as a target molecule for pharmacotherapy of allergic inflammatory diseases

The purpose of this review is to summarize the role of prostaglandins (PGs) in allergic inflammation and to know the value of PGs, as a target molecule for an anti-allergic drug. PGD(2) is the major PG produced by the cyclooxygenase pathway in mast cells. Our and others findings indicate that PGD(2) is one of the potent allergic inflammatory mediators and must be a target molecule of anti-allergic agent. From our data, one of PGD(2) receptor antagonists show clear inhibition of airway hypersensitivity caused by allergic reaction. Concerning the role of PGE(2) in allergic inflammation, conflicting results have been reported. Many experimental data suggest an individual role of each PGE(2) receptor, EP(1), EP(2), EP(3) and EP(4) in allergic reaction. Our results indicate the protective action of PGE(2) on allergic reaction via EP(3). In addition, one of EP(3) agonists clearly inhibits the allergic airway inflammation. These findings indicate the value of EP(3) agonists as an anti-allergic agent. In addition, some investigators including us reported that PGI(2) plays an important role for the protection of the onset of allergic reaction. However, the efficacy of PGI(2) analogue as an anti-allergic agent is not yet fully investigated. Finally, the role of thromboxane A(2) (TxA(2)) in allergic reaction is discussed. Our experimental results suggest a different participation of TxA(2) in allergic reaction of airway and skin. In this review, the role of PGs in allergic inflammation is summarized and the value of PGs as a target molecule for developing a new anti-allergic agent will be discussed.

CRTH2 plays an essential role in the pathophysiology of Cry j 1-induced pollinosis in mice

PGD(2) is the major prostanoid produced during the acute phase of allergic reactions. Two PGD(2) receptors have been isolated, DP and CRTH2 (chemoattractant receptor-homologous molecule expressed on Th2 cells), but whether they participate in the pathophysiology of allergic diseases remains unclear. We investigated the role of CRTH2 in the initiation of allergic rhinitis in mice. First, we developed a novel murine model of pollinosis, a type of seasonal allergic rhinitis. Additionally, pathophysiological differences in the pollinosis were compared between wild-type and CRTH2 gene-deficient mice. An effect of treatment with ramatroban, a CRTH2/T-prostanoid receptor dual antagonist, was also determined. Repeated intranasal sensitization with Cry j 1, the major allergen of Cryptomeria japonica pollen, in the absence of adjuvants significantly exacerbated nasal hyperresponsive symptoms, Cry j 1-specific IgE and IgG1 production, nasal eosinophilia, and Cry j 1-induced in vitro production of IL-4 and IL-5 by submandibular lymph node cells. Additionally, CRTH2 mRNA in nasal mucosa was significantly elevated in Cry j 1-sensitized mice. Following repeated intranasal sensitization with Cry j 1, CRTH2 gene-deficient mice had significantly weaker Cry j 1-specific IgE/IgG1 production, nasal eosinophilia, and IL-4 production by submandibular lymph node cells than did wild-type mice. Similar results were found in mice treated with ramatroban. These results suggest that the PGD(2)-CRTH2 interaction is elevated following sensitization and plays a proinflammatory role in the pathophysiology of allergic rhinitis, especially pollinosis in mice.

Cyclooxygenase-2/prostaglandin D2/CRTH2 pathway mediates double-stranded RNA-induced enhancement of allergic airway inflammation

Respiratory RNA viruses responsible for the common cold often worsen airway inflammation and bronchial responsiveness, two characteristic features of human asthma. We studied the effects of dsRNA, a nucleotide synthesized during viral replication, on airway inflammation and bronchial hyperresponsiveness in murine models of asthma. Intratracheal instillation of poly I:C, a synthetic dsRNA, increased the airway eosinophilia and enhanced bronchial hyperresponsiveness to methacholine in OVA-sensitized, exposed rats. These changes were associated with induction of cyclooxygenase-2 (COX-2) expression and COX-2-dependent PGD2 synthesis in the lungs, particularly in alveolar macrophages. The direct intratracheal instillation of PGD2 enhanced the eosinophilic inflammation in OVA-exposed animals, whereas pretreatment with a dual antagonist against the PGD2 receptor-(CRTH2) and the thromboxane A2 receptor, but not with a thromboxane A2 receptor-specific antagonist, nearly completely eliminated the dsRNA-induced worsening of airway inflammation and bronchial hyperresponsiveness. CRTH2-deficient mice had the same degree of allergen-induced airway eosinophilia as wild-type mice, but they did not exhibit a dsRNA-induced increase in eosinophil accumulation. Our data demonstrate that COX-2-dependent production of PGD2 followed by eosinophil recruitment into the airways via a CRTH2 receptor are the major pathogenetic factors responsible for the dsRNA-induced enhancement of airway inflammation and responsiveness.

Contribution of prostaglandin D2 via prostanoid DP receptor to nasal hyperresponsiveness in guinea pigs repeatedly exposed to antigen

We examined the role of prostanoid DP receptor in nasal blockage in an experimental allergic rhinitis model in guinea pigs. Local inhalation of prostaglandin D(2) (PGD(2)) to the nasal cavity resulted in an increase in intranasal pressure in guinea pigs actively sensitized by repeated antigen exposure but not in non-sensitized guinea pigs. Nasal hyperresponsiveness was observed when the guinea pigs were exposed to histamine and U-46619 (11alpha, 9alpha-epoxymethano-PGH(2); a thromboxane (TX) A(2) mimetic) after repeated antigen exposure. S-5751 ((Z)-7-[(1R,2R,3S,5S)-2-(5-hydroxybenzo[b]thiophen-3-ylcarbonylamino)-10-norpinan-3-yl]hept-5-enoic acid), a prostanoid DP receptor antagonist, inhibited not only PGD(2)-induced nasal blockage but also nasal hyperresponsiveness to histamine and U-46619 in sensitized guinea pigs. Combined exposure of the nasal cavity of guinea pigs to an aerosol of PGD(2) with histamine or U-46619 at sub-threshold concentrations synergistically caused a marked increase in intranasal pressure. These responses were significantly suppressed by S-5751. These results suggest that PGD(2) plays a critical role in the increase in intranasal pressure via prostanoid DP receptor, probably through synergistically enhancing the nasal response with other chemical mediators released from mast cells and other inflammatory cells activated by allergens.