Prostaglandin D2 and leukotriene E4 synergize to stimulate diverse TH2 functions and TH2 cell/neutrophil crosstalk.

BACKGROUND: Prostaglandin D2 (PGD2) and cysteinyl leukotrienes (cysLTs) are lipid mediators derived from mast cells, which activate TH2 cells. The combination of PGD2 and cysLTs (notably cysteinyl leukotriene E4 [LTE4]) enhances TH2 cytokine production. However, the synergistic interaction of cysLTs with PGD2 in promoting TH2 cell activation is still poorly understood. The receptors for these mediators are drug targets in the treatment of allergic diseases, and hence understanding their interaction is likely to have clinical implications. OBJECTIVE: We aimed to comprehensively define the roles of PGD2, LTE4, and their combination in activating human TH2 cells and how such activation might allow the TH2 cells to engage downstream effectors, such as neutrophils, which contribute to the pathology of allergic responses. METHODS: The effects of PGD2, LTE4, and their combination on human TH2 cell gene expression were defined by using a microarray, and changes in specific inflammatory pathways were confirmed by means of PCR array, quantitative RT-PCR, ELISA, Luminex, flow cytometry, and functional assays, including analysis of downstream neutrophil activation. Blockade of PGD2 and LTE4 was tested by using TM30089, an antagonist of chemoattractant receptor-homologous molecule expressed on TH2 cells, and montelukast, an antagonist of cysteinyl leukotriene receptor 1. RESULTS: PGD2 and LTE4 altered the transcription of a wide range of genes and induced diverse functional responses in TH2 cells, including cell adhesion, migration, and survival and cytokine production. The combination of these lipids synergistically or additively enhanced TH2 responses and, strikingly, induced marked production of diverse nonclassical TH2 inflammatory mediators, including IL-22, IL-8, and GM-CSF, at concentrations sufficient to affect neutrophil activation. CONCLUSIONS: PGD2 and LTE4 activate TH2 cells through different pathways but act synergistically to promote multiple downstream effector functions, including neutrophil migration and survival. Combined inhibition of both PGD2 and LTE4 pathways might provide an effective therapeutic strategy for allergic responses, particularly those involving interaction between TH2 cells and neutrophils, such as in patients with severe asthma.

Inhibition of the asthmatic allergen challenge response by the CRTH2 antagonist OC000459.

CRTH2 (chemoattractant receptor expressed on T-helper (Th) type 2 cells) is a G-protein-coupled receptor expressed by Th2 lymphocytes and eosinophils that mediates prostaglandin (PG)D(2)-driven chemotaxis. We studied the efficacy of the oral CRTH2 antagonist OC000459 in steroid-naïve asthmatic patients. A randomised, double-blind, placebo-controlled, two-way crossover study of 16 days' treatment with OC000459 (200 mg twice daily) on the late (LAR) and early (EAR) asthmatic responses to bronchial allergen challenge was conducted, with 16 subjects completing the study. There was a 25.4% (95% CI 5.1-45.6%) reduction in the LAR area under the curve (AUC) for change in forced expiratory volume in 1 s with OC000459 compared with placebo (p=0.018) but no effect on the EAR. Sputum eosinophil counts at 1 day post-allergen challenge were lower after OC000459 treatment (p=0.002). PGD(2)-induced blood eosinophil shape change ex vivo was assessed at day 7 (n=7). The AUC of eosinophil shift for OC000459 was lower than placebo; the mean difference was -33.6% (95% CI -66.8- -0.4%; p=0.048). OC000459 treatment inhibited LAR and post-allergen increase in sputum eosinophils. This CRTH2 antagonist appears to inhibit allergic inflammation in asthma.

PGH1, the precursor for the anti-inflammatory prostaglandins of the 1-series, is a potent activator of the pro-inflammatory receptor CRTH2/DP2.

Prostaglandin H(1) (PGH(1)) is the cyclo-oxygenase metabolite of dihomo-γ-linolenic acid (DGLA) and the precursor for the 1-series of prostaglandins which are often viewed as "anti-inflammatory". Herein we present evidence that PGH(1) is a potent activator of the pro-inflammatory PGD(2) receptor CRTH2, an attractive therapeutic target to treat allergic diseases such as asthma and atopic dermatitis. Non-invasive, real time dynamic mass redistribution analysis of living human CRTH2 transfectants and Ca(2+) flux studies reveal that PGH(1) activates CRTH2 as PGH(2), PGD(2) or PGD(1) do. The PGH(1) precursor DGLA and the other PGH(1) metabolites did not display such effect. PGH(1) specifically internalizes CRTH2 in stable CRTH2 transfectants as assessed by antibody feeding assays. Physiological relevance of CRTH2 ligation by PGH(1) is demonstrated in several primary human hematopoietic lineages, which endogenously express CRTH2: PGH(1) mediates migration of and Ca(2+) flux in Th2 lymphocytes, shape change of eosinophils, and their adhesion to human pulmonary microvascular endothelial cells under physiological flow conditions. All these effects are abrogated in the presence of the CRTH2 specific antagonist TM30089. Together, our results identify PGH(1) as an important lipid intermediate and novel CRTH2 agonist which may trigger CRTH2 activation in vivo in the absence of functional prostaglandin D synthase.

Leukotriene E4 activates human Th2 cells for exaggerated proinflammatory cytokine production in response to prostaglandin D2.

PGD(2) exerts a number of proinflammatory responses through a high-affinity interaction with chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) and has been detected at high concentrations at sites of allergic inflammation. Because cysteinyl leukotrienes (cysLTs) are also produced during the allergic response, we investigated the possibility that cysLTs may modulate the response of human Th2 cells to PGD(2). PGD(2) induced concentration-dependent Th2 cytokine production in the absence of TCR stimulation. Leukotrienes D(4) and E(4) (LTE(4)) also stimulated the cytokine production but were much less active than PGD(2). However, when combined with PGD(2), cysLTs caused a greater than additive enhancement of the response, with LTE(4) being most effective in activating Th2 cells. LTE(4) enhanced calcium mobilization in response to PGD(2) in Th2 cells without affecting endogenous PGD(2) production or CRTH2 receptor expression. The effect of LTE(4) was inhibited by montelukast but not by the P2Y(12) antagonist methylthioadenosine 5'-monophosphate. The enhancing effect was also evident with endogenous cysLTs produced from immunologically activated mast cells because inhibition of cysLT action by montelukast or cysLT synthesis by MK886, an inhibitor of 5-lipoxygenase-activating protein, reduced the response of Th2 cells to the levels produced by PGD(2) alone. These findings reveal that cysLTs, in particular LTE(4), have a significant proinflammatory impact on T cells and demonstrate their effects on Th2 cells are mediated by a montelukast-sensitive receptor.

Pharmacologic profile of OC000459, a potent, selective, and orally active D prostanoid receptor 2 antagonist that inhibits mast cell-dependent activation of T helper 2 lymphocytes and eosinophils.

D prostanoid receptor 2 (DP2) [also known as chemoattractant receptor-homologous molecule expressed on T helper 2 (Th2) cells (CRTH2)] is selectively expressed by Th2 lymphocytes, eosinophils, and basophils and mediates recruitment and activation of these cell types in response to prostaglandin D2 (PGD2). (5-Fluoro-2-methyl-3-quinolin-2-ylmethylindo-1-yl)-acetic acid (OC000459) is an indole-acetic acid derivative that potently displaces [³H]PGD2 from human recombinant DP2 (K(i) = 0.013 µM), rat recombinant DP2 (K(i) = 0.003 µM), and human native DP2 (Th2 cell membranes; K(i) = 0.004 µM) but does not interfere with the ligand binding properties or functional activities of other prostanoid receptors (prostaglandin E1₋4 receptors, D prostanoid receptor 1, thromboxane receptor, prostacyclin receptor, and prostaglandin F receptor). OC000459 inhibited chemotaxis (IC50 = 0.028 µM) of human Th2 lymphocytes and cytokine production (IC50 = 0.019 µM) by human Th2 lymphocytes. OC000459 competitively antagonized eosinophil shape change responses induced by PGD2 in both isolated human leukocytes (pK(B) = 7.9) and human whole blood (pK(B) = 7.5) but did not inhibit responses to eotaxin, 5-oxo-eicosatetraenoic acid, or complement component C5a. OC000459 also inhibited the activation of Th2 cells and eosinophils in response to supernatants from IgE/anti-IgE-activated human mast cells. OC000459 had no significant inhibitory activity on a battery of 69 receptors and 19 enzymes including cyclooxygenase 1 (COX1) and COX2. OC000459 was found to be orally bioavailable in rats and effective in inhibiting blood eosinophilia induced by 13,14-dihydro-15-keto-PGD2 (DK-PGD2) in this species (ED50 = 0.04 mg/kg p.o.) and airway eosinophilia in response to an aerosol of DK-PGD2 in guinea pigs (ED50 = 0.01 mg/kg p.o.). These data indicate that OC000459 is a potent, selective, and orally active DP2 antagonist that retains activity in human whole blood and inhibits mast cell-dependent activation of both human Th2 lymphocytes and eosinophils.

Novel function of CRTH2 in preventing apoptosis of human Th2 cells through activation of the phosphatidylinositol 3-kinase pathway.

It is now well established that interaction of PGD(2) with chemoattractant receptor- homologous molecule expressed on Th2 cells (CRTH2) promotes chemotaxis and proinflammatory cytokine production by Th2 lymphocytes. In this study we show a novel function of CRTH2 in mediating an inhibitory effect of PGD(2) on the apoptosis of human Th2 cells induced by cytokine deprivation. This effect was mimicked by the selective CRTH2 agonist 13,14-dihydro-15-keto-PGD(2), inhibited by the CRTH2 antagonists ramatroban and TM30089, and not observed in CRTH2-negative T cells. D prostanoid receptor 1 (DP(1)) or the thromboxane-like prostanoid (TP) receptor did not play a role in mediating the effects of PGD(2) on the apoptosis of Th2 cells because neither the DP(1) antagonist BW868C nor the TP antagonist SQ29548 had any effect on the antiapoptotic effect of PGD(2). Apoptosis of Th2 cells induced by Fas ligation was not suppressed by treatment with PGD(2), illustrating that activation of CRTH2 only inhibits apoptosis induced by cytokine deprivation. Treatment with PGD(2) induced phosphorylation of Akt and BAD, prevented release of cytochrome c from mitochondria, and suppressed cleavage of caspase-3 and poly(ADP-ribose) polymerase in Th2 cells deprived of IL-2. The PI3K inhibitor LY294002 blocked the effect of PGD(2) both on the signaling events and on the apoptotic death of Th2 cells. These data suggest that in addition to promoting the recruitment and activation of Th2 cells, PGD(2) may also impede the resolution of allergic inflammation through inhibiting apoptosis of Th2 cells.

Antagonists of the prostaglandin D2 receptor CRTH2.

Prostaglandin D(2) (PGD(2)) is produced by mast cells, Th2 lymphocytes and dendritic cells and causes activation of Th2 lymphocytes, eosinophils and basophils through a high-affinity interaction with the G protein-coupled receptor chemoattractant homologous receptor expressed on Th2 cells (CRTH2, also known as DP(2)). Activation of CRTH2 induces chemotaxis of Th2 lymphocytes and eosinophils and has the unusual property of promoting cytokine production by Th2 lymphocytes in the absence of allergen or co-stimulation. The ability of supernatants from immunologically activated mast cells to activate Th2 cells and eosinophils is mediated by CRTH2. This receptor also plays an important role in amplifying allergic responses through paracrine activation of Th2 cells. Pharmacological blockade or genetic ablation of CRTH2 is associated with a reduction in airways inflammation and reduced levels of mucus, Th2 cytokines and immunoglobulin E. The central role played by CRTH2 in mediating these effects suggests that antagonism of this receptor is an attractive approach to the treatment of chronic allergic disease.

A paracrine role for chemoattractant receptor-homologous molecule expressed on T helper type 2 cells (CRTH2) in mediating chemotactic activation of CRTH2+ CD4+ T helper type 2 lymphocytes.

Activation of human CRTH2(+) CD4(+) T helper type 2 (Th2) cells with anti-CD3/anti-CD28 led to time-dependent production of prostaglandin D(2) (PGD(2)) which peaked at 8 hr. The production of PGD(2) was completely inhibited by cotreatment with the cyclo-oxygenase inhibitor diclofenac (10 microm) but was not affected by cotreatment with ramatroban, a dual antagonist of both the thromboxane-like prostanoid (TP) receptor and the chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). Supernatants from activated CRTH2(+) CD4(+) Th2 cells caused a concentration-dependent increase in the migration of naive CRTH2(+) CD4(+) Th2 cells compared to supernatants from unstimulated CRTH2(+) CD4(+) Th2 cells. The level of chemotactic activity peaked at 8 hr after activation, corresponding to the peak levels of PGD(2), but production of chemotactic activity was only partially inhibited by the cyclo-oxygenase inhibitor diclofenac. In contrast, ramatroban completely inhibited the chemotactic responses of naive Th2 cells to supernatants from activated CRTH2(+) CD4(+) Th2 cells collected up to 8 hr after activation, although supernatants collected 24 hr after activation were less sensitive to inhibition by ramatroban. The selective TP antagonist SQ29548 did not inhibit migration of Th2 cells, implicating CRTH2 in this response. These data suggest that CRTH2 plays an important paracrine role in mediating chemotactic activation of Th2 cells. Interestingly, although PGD(2) is produced from Th2 cells and contributes to this paracrine activation, it appears that additional CRTH2 agonist factors are also produced by activated Th2 cells and the production of these factors occurs independently of the cyclo-oxygenase pathway of the arachidonic acid metabolism.

Antagonism of the prostaglandin D2 receptors DP1 and CRTH2 as an approach to treat allergic diseases.

Immunological activation of mast cells is an important trigger in the cascade of inflammatory events leading to the manifestation of allergic diseases. Pharmacological studies using the recently discovered DP(1) and CRTH2 antagonists combined with genetic analysis support the view that these receptors have a pivotal role in mediating aspects of allergic diseases that are resistant to current therapy. This Review focuses on the emerging roles that DP(1) and CRTH2 (also known as DP(2)) have in acute and chronic aspects of allergic diseases and proposes that, rather than having opposing actions, these receptors have complementary roles in the initiation and maintenance of the allergy state. We also discuss recent progress in the discovery and development of selective antagonists of these receptors.

Inhibition of PI3K and calcineurin suppresses chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2)-dependent responses of Th2 lymphocytes to prostaglandin D(2).

Interaction of prostaglandin D2 (PGD2) with chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) triggers chemotaxis and pro-inflammatory cytokine production by Th2 lymphocytes. We have investigated the role of inhibitors of various cell-signalling pathways on the responses of human CRTH2+ CD4+ Th2 cells to PGD2. Phosphatidylinositol 3-kinase (PI3K) and Ca2+/calcineurin/nuclear factor of activated T cells (NFAT) pathways were activated by PGD2 in Th2 cells in a CRTH2-dependent manner. Inhibition of the PI3K pathway with LY294002 significantly reduced both PGD2-induced cell migration and cytokine (interleukin-4, interleukin-5 and interleukin-13) production. The inhibitory effect of LY294002 on cell migration is likely to be related to cytoskeleton reorganization as it showed a similar potency on PGD2-induced actin polymerization. The calcineurin inhibitors, tacrolimus (FK506) and cyclosporin A, had no effect on cell migration but completely blocked both cytokine production and the nuclear translocation of NFATc1 suggesting that Ca2+/calcineurin/NFAT is involved in CRTH2-dependent cytokine production but not chemotaxis. The promotion of NFAT nuclear location by PI3K activation may be mediated by negative regulation of glycogen synthase kinase-3beta (GSK3beta), since the PGD2-stimulated increase in phospho-GSK3beta was down-regulated by LY294002, and inhibition of GSK3beta by SB216763 enhanced PGD2-induced Th2 cytokine production and reversed the inhibitory effect of LY294002. These data suggest that PI3K and Ca2+/calcineurin/NFAT signalling pathways are critically involved in pro-inflammatory responses of Th2 cells to PGD2.

Salbutamol inhibits trypsin-mediated production of CXCL8 by keratinocytes.

Treatment of primary keratinocytes (HEKAp) with trypsin led to the production and release of CXCL8. Production of CXCL8 was exquisitely sensitive to inhibition by co-treatment with the beta(2) agonist sabutamol (IC(50)=1.1 nM). The inhibitory effect of salbutamol was beta receptor-mediated since the effect was prevented by the beta antagonist sotalol. Salbutamol also elevated intracellular levels of cAMP (EC(50)=82 nM) but the relationship to the inhibition of CXCL8 secretion was not clear-cut since much higher concentrations of salbutamol were required to elevate total cellular cAMP than inhibit CXCL8 production. However, the effect of salbutamol is likely to be mediated by elevation of cAMP since forskolin, an adenylyl cyclase activator, mimicked the effects of salbutamol while the adenylyl cyclase inhibitor 2',5'-dideoxyadenosine inhibited the effects of salbutamol. Potentiation of cAMP production by co-treatment with the phosphodiesterase type 4 inhibitor rolipram only marginally enhanced the inhibitory effect of salbutamol on CXCL8 production. Taken together, these data suggest that elevation of cAMP production is required for the inhibitory effect of salbutamol on CXCL8 production by keratinocytes and that low threshold levels of cAMP are sufficient to mediate this effect.

A dominant role for chemoattractant receptor-homologous molecule expressed on T helper type 2 (Th2) cells (CRTH2) in mediating chemotaxis of CRTH2+ CD4+ Th2 lymphocytes in response to mast cell supernatants.

Human cultured mast cells, immunologically activated with immunoglobuin E (IgE)/anti-IgE, released a factor(s) that promoted chemotaxis of human CRTH2+ CD4+ T helper type 2 (Th2) lymphocytes. Mast cell supernatants collected at 20 min, 1 hr, 2 hr and 4 hr after activation caused a concentration-dependent increase in the migration of Th2 cells. The effect of submaximal dilutions of mast-cell-conditioned media was inhibited in a dose-dependent manner by ramatroban (IC50 = 96 nm), a dual antagonist of both the thromboxane-like prostanoid (TP) receptor and the chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), but not by the selective TP antagonist SQ29548, implicating CRTH2 in mediating the chemotactic response of these Th2 cells. The effect of mast-cell-conditioned media was mimicked by prostaglandin D2 (PGD2) and this eicosanoid was detected in the conditioned media from activated mast cells in concentrations sufficient to account for the activity of the mast cell supernatants. Treatment of the mast cells with the cyclo-oxygenase inhibitor diclofenac (10 microm) inhibited both the production of PGD2 and the CRTH2+ CD4+ Th2-stimulatory activity, while addition of exogenous PGD2 to conditioned media from diclofenac-treated mast cells restored the ability of the supernatants to promote chemotaxis of these Th2 cells. The degree of inhibition caused by diclofenac treatment of the mast cells was concordant with the degree of inhibition of chemotactic responses afforded by CRTH2 blockade. These data suggest that PGD2, or closely related metabolites of arachidonic acid, produced from mast cells may play a central role in the activation of CRTH2+ CD4+ Th2 lymphocytes through a CRTH2-dependent mechanism.

Prostaglandin D2 causes preferential induction of proinflammatory Th2 cytokine production through an action on chemoattractant receptor-like molecule expressed on Th2 cells.

PGD2, produced by mast cells, has been detected in high concentrations at sites of allergic inflammation. It can stimulate vascular and other inflammatory responses by interaction with D prostanoid receptor (DP) and chemoattractant receptor-like molecule expressed on Th2 cells (CRTH2) receptors. A significant role for PGD2 in mediating allergic responses has been suggested based on the observation that enhanced eosinophilic lung inflammation and cytokine production is apparent in the allergen-challenged airways of transgenic mice overexpressing human PGD2 synthase, and PGD2 can enhance Th2 cytokine production in vitro from CD3/CD28-costimulated Th2 cells. In the present study, we investigated whether PGD2 has the ability to stimulate Th2 cytokine production in the absence of costimulation. At concentrations found at sites of allergic inflammation, PGD2 preferentially elicited the production of IL-4, IL-5, and IL-13 by human Th2 cells in a dose-dependent manner without affecting the level of the anti-inflammatory cytokine IL-10. Gene transcription peaked within 2 h, and protein release peaked approximately 8 h after stimulation. The effect of PGD2 was mimicked by the selective CRTH2 agonist 13,14-dihydro-15-keto-PGD2 but not by the selective DP agonist BW245C, suggesting that the stimulation is mediated by CRTH2 and not DP. Ramatroban, a dual CRTH2/thromboxane-like prostanoid receptor antagonist, markedly inhibited Th2 cytokine production induced by PGD2, while the selective thromboxane-like prostanoid receptor antagonist SQ29548 was without effect. These data suggest that PGD2 preferentially up-regulates proinflammatory cytokine production in human Th2 cells through a CRTH2-dependent mechanism in the absence of any other costimulation and highlight the potential utility of CRTH2 antagonists in the treatment of allergic diseases.

Indole-3-acetic acid antagonists of the prostaglandin D2 receptor CRTH2.

Prostaglandin D2 (PGD2) acting at the CRTH2 receptor (chemoattractant receptor-homologous molecule expressed on Th2 cells) has been linked with a variety of allergic and other inflammatory diseases. We describe a family of indole-1-sulfonyl-3-acetic acids that are potent and selective CRTH2 antagonists that possess good oral bioavailability. The compounds may serve as novel starting points for the development of treatments of inflammatory disease such as asthma, allergic rhinitis, and atopic dermatitis.

Identification of G-protein-coupled receptors involved in inflammatory disease by genetic association studies.

G-protein-coupled receptors are not only highly tractable drug targets but also attractive candidates for genetic association studies because they are more polymorphic than most other classes of gene and these polymorphisms frequently lead to functional changes in the levels of expression or biological activity that can predispose to common diseases. A large-scale study to identify functional variants in G-protein-coupled receptors associated with inflammatory diseases has highlighted a spectrum of novel biological insights that range from identifying the involvement of orphan receptors in certain diseases through to highlighting new therapeutic indications for existing drugs.

Delta12-prostaglandin D2 is a potent and selective CRTH2 receptor agonist and causes activation of human eosinophils and Th2 lymphocytes.

Prostaglandin D2 (PGD2) is a lipid mediator produced by mast cells, macrophages and Th2 lymphocytes and has been detected in high concentrations in the airways of asthmatic patients. There are two receptors for PGD2, namely the D prostanoid (DP) receptor and the chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). The proinflammatory effects of PGD2 leading to recruitment of eosinophils and Th2 lymphocytes into inflamed tissues is thought to be predominantly due to action on CRTH2. Several PGD2 metabolites have been described as potent and selective agonists for CRTH2. In this study we have characterized the activity of delta12-PGD2, a product of PGD2 isomerization by albumin. Delta12-PGD2 induced calcium mobilization in CHO cells expressing human CRTH2 receptor, with efficacy and potency similar to those of PGD2. These effects were blocked by the TP/CRTH2 antagonist ramatroban. delta12-PGD2 bound to CRTH2 receptor with a pKi of 7.63, and a 55-fold selectivity for CRTH2 compared to DP. In Th2 lymphocytes, delta12-PGD2 induced calcium mobilization with high potency and an efficacy similar to that of PGD2. delta12-PGD2 also caused activation of eosinophils as measured by shape change. Taken together, these results show that delta12-PGD2 is a potent and selective agonist for CRTH2 receptor and can cause activation of eosinophils and Th2 lymphocytes. These data also confirm the selective effect of other PGD2 metabolites on CRTH2 and illustrate how the metabolism of PGD2 may influence the pattern of leukocyte infiltration at sites of allergic inflammation.

The application of genetics to the discovery of better medicines.

The availability of the human genome sequence and the increasing knowledge of functional polymorphisms will highlight new therapeutic approaches to treat diseases with unmet medical need and will allow the targeting of new and existing therapies to those patients who will derive the most benefit without the risk of serious side effects. This review describes how genetic information can be used to improve the drug discovery and development process. It should be emphasized, however, that although it is anticipated that high-throughput genetic studies will provide novel biological insights into disease, it is not a replacement for careful hypothesis-driven experiments. Rather, it is essential to combine genetic studies with carefully conducted preclinical and clinical experiments to extract the true value of high-throughput genetics-based research.