The effect of the novel phosphodiesterase-4 inhibitor MEM 1414 on the allergen induced responses in mild asthma.

BACKGROUND: Inhaled allergen challenge is a standard method to study airway responses to inflammatory provocation and evaluate the therapeutic potential of novel anti-inflammatory compounds in asthma. MEM 1414 is a novel oral PDE4 inhibitor with high affinity and selectivity creating the potential for an improved side effect profile vs non-selective PDE inhibitors. We evaluated the tolerability and effect of MEM 1414 on airway responses in mild asthmatics. METHODS: A randomised double blind placebo controlled cross over study in two centres, in which sixteen steroid naïve atopic asthmatics were challenged with inhaled allergen. Subjects were dosed with MEM 1414 (600 mg) or placebo, twice daily orally for 7 days. Allergen challenge was performed on day 6 (2 hours post-dose), and methacholine responsiveness was measured 24 hours post allergen (day 7). Biomarkers of drug effects using ex vivo LPS stimulation of whole blood production of interleukin (IL)-6 and leukotriene (LT)-B4 and fractional exhaled nitric oxide (FeNO) were measured on day 6 (0, 2 and 8 hours post-dose). Plasma pharmacokinetics were measured on days 1, 6 and 7. The primary endpoint was the effect on late asthmatic response to allergen. RESULTS: Treatment with MEM 1414 abrogated the late phase response with a mean difference in FEV1 (LAR 3-10 hours) of 104 ml (25%) vs placebo (p < 0.005), with no effect on the early response. Biomarker responses were also attenuated with MEM 1414 treatment with reductions in LPS-stimulated whole blood assays for TNFα at 8 hours (p < 0.03) and LTB4 at 24 hours (p = 0.0808) with no change in the IL-6 response. The MEM 1414 treatment phase was associated with higher incidence of nausea (6/16 MEM 1414 vs 2/16 placebo) and vomiting (3/16 vs 0/16 placebo). CONCLUSIONS: Oral MEM 1414, a novel PDE4 inhibitor, significantly reduces the late response following inhaled allergen challenge. MEM 1414 also inhibited whole blood assays of cytokine production from inflammatory cells. MEM 1414 was associated with a typical adverse event profile of PDE4 inhibitors, namely nausea and vomiting although these were mild side effects. TRIAL REGISTRATION NUMBER: Current controlled trials ISRCTN48047493.

PPARbeta/delta agonists modulate platelet function via a mechanism involving PPAR receptors and specific association/repression of PKCalpha--brief report.

OBJECTIVE: Peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) is a nuclear receptor found in platelets. PPARbeta/delta agonists acutely inhibit platelet function within a few minutes of addition. As platelets are anucleated, the effects of PPARbeta/delta agonists on platelets must be nongenomic. Currently, the particular role of PPARbeta/delta receptors and their intracellular signaling pathways in platelets are not known. METHODS AND RESULTS: We have used mice lacking PPARbeta/delta (PPARbeta/delta(-/-)) to show the effects of the PPARbeta/delta agonist GW501516 on platelet adhesion and cAMP levels are mediated specifically by PPARbeta/delta, however GW501516 had no PPARbeta/delta-specific effect on platelet aggregation. Studies in human platelets showed that PKCalpha, which can mediate platelet activation, was bound and repressed by PPARbeta/delta after platelets were treated with GW501516. CONCLUSIONS: These data provide evidence of a novel mechanism by which PPAR receptors influence platelet activity and thereby thrombotic risk.

Antiplatelet actions of statins and fibrates are mediated by PPARs.

OBJECTIVES: Statins and fibrates are hypolipidemic drugs which decrease cardiac events in individuals without raised levels of cholesterol. These drugs inhibit platelet function, but the mechanisms by which this pleiotropic effect is exerted are not known. METHODS AND RESULTS: We used a range of approaches to show statins inhibit human platelet activation in vitro while engaging PPARalpha and PPARgamma. The effects of simvastatin were prevented by the PPARgamma antagonist GW9662 or the PPARalpha antagonist GW6471. In a small-scale human study fluvastatin activated PPARalpha and PPARgamma in platelets and reduced aggregation in response to arachidonic acid ex vivo. The effects of fenofibrate were prevented by PPARalpha antagonism with GW6471. Fenofibrate increased bleeding time in wild-type, but not in PPARalpha-/- mice. The inhibitory effect of fenofibrate, but not simvastatin, on aggregation was prevented by deletion of PPARalpha in murine platelets. PKCalpha, which influences platelet activation, associated and immune-precipitated with PPARgamma in platelets stimulated with statins and with PPARalpha in platelets stimulated with fenofibrate. CONCLUSIONS: This study is the first to provide a unifying explanation of how fibrates and statins reduce thrombotic and cardiovascular risk. Our findings that PPARs associate with PKCalpha in platelets also provide a mechanism by which these effects are mediated.

Role of prostacyclin versus peroxisome proliferator-activated receptor beta receptors in prostacyclin sensing by lung fibroblasts.

Prostacyclin and its mimetics are used therapeutically for the treatment of pulmonary hypertension. These drugs act via cell surface prostacyclin receptors (IP receptors); however, some of them can also activate the nuclear receptor peroxisome proliferator-activated receptor beta (PPARbeta). We examined the possibility that PPARbeta is a therapeutic target for the treatment of pulmonary hypertension. Using the newly approved (for pulmonary hypertension) prostacyclin mimetic treprostinil sodium, reporter gene assays for PPARbeta activation and measurement of lung fibroblast proliferation were analyzed. Treprostinil sodium was found to activate PPARbeta in reporter gene assays and to inhibit proliferation of human lung fibroblasts at concentrations consistent with an effect on PPARs but not on IP receptors. The effects of treprostinil sodium on human lung cell proliferation are mimicked by those of the highly selective PPARbeta ligand GW0742. There are no receptor antagonists for PPARbeta or for IP receptors, but by using lung fibroblasts cultured from mice lacking PPARbeta (PPARbeta-/-) or IP (IP-/-), we demonstrate that the antiproliferative effects of treprostinil sodium are mediated by PPARbeta and not IP in lung fibroblasts. These observations suggest that some of the local, longer-term benefits of treprostinil sodium on reducing the remodeling associated with pulmonary hypertension may be mediated by PPARbeta. This study is the first to identify PPARbeta as a potential therapeutic target for the treatment of pulmonary hypertension, which is important because orally active PPARbeta ligands have been developed for the treatment of dyslipidemia.

Role of nuclear receptor signaling in platelets: antithrombotic effects of PPARbeta.

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that heterodimerize with the retinoid X receptor and then modulate at the transcriptional level the function of many target genes. Three PPARs are known: alpha, beta (sometimes called delta), and gamma. The better studied are PPARalpha and PPARgamma, which are activated by fibrates and thiazolidinediones/glitazones, respectively. It is now believed that activation of the PPARs could be associated with the prevention of heart attack and stroke in humans. Here we report, for the first time, that human platelets contain PPARbeta and that its selective activation inhibits platelet aggregation. PPARbeta is a putative receptor for prostacyclin. Prostacyclin is an important antithrombotic hormone that synergizes with nitric oxide to inhibit platelet aggregation. In the current study, we show that PPARbeta ligands similarly synergize with nitric oxide to inhibit platelet aggregation. These observations challenge our view of a nuclear receptor because PPARbeta is present and active in nonnucleated platelets. Furthermore, these data suggest that some of the antithrombotic actions of prostacyclin may be mediated via activation of PPARs. Thus, our results identify PPARbeta as a novel antiplatelet target that may mediate some of the effects of prostacyclin in blood.