EP EP and EP receptor expression
EP1, EP3 and EP4 receptor expression on HMVEC-L was shown recently by flow cytometry . However, only EP4 mRNA expression was previously described in these cells . Our data obtained with RT-PCR showed EP4 mRNA and very low levels of EP1 mRNA, but no EP2 and EP3 mRNA expression was detectable in HMVEC-L. Although EP1 receptor mRNA was detected, the effects of the purported EP1/EP3 receptor agonist 17-pt-PGE2 on human pulmonary microvascular endothelial cells were exclusively mediated via EP4 receptor activation. In contrast, 17-pt-PGE2 acted on human isolated platelets as an EP3 receptor agonist. The preferential activation of EP4 receptors rather than EP3 receptors can be explained by the lack of EP3 receptor expression and comparatively low amount of EP1 receptors on HMVEC-L.
Conclusion In conclusion, our results provide evidence that the purported EP1/EP3 receptor agonist 17-pt-PGE2 possesses anti-inflammatory properties, promotes microvascular endothelial barrier function in vitro and further abates neutrophil recruitment and plasma extravasation in a murine model of pulmonary inflammation. Our data suggest that these effects are mediated by EP4 receptor activation and that its mode of action might be tissue and cell specific. We show here for the first time that 17-pt-PGE2 exerts a beneficial effect on pulmonary inflammatory diseases.
Acknowledgements Grant support: this work was supported by the FWF (DK-MOLIN - W1241, and stand-alone grants P22521 to AH, P25531 to VK and P26185 to RS). AT is a recipient of a DOC Fellowship (24409) of the Austrian Academy of Science at the Institute of Experimental and Clinical Pharmacology.
Introduction Based on a series of investigations we suggested key signalling factors of the P-glycoprotein regulatory cascade as novel targets to restore pharmacosensitivity in drug-refractory epilepsies (Potschka, 2010). These targets include factors of the arachidonic hdac inhibitors signalling cascade including the prostaglandin E2 EP1 receptor and the inflammatory enzyme cyclooxygenase-2 (COX-2) (Zibell et al., 2009, Pekcec et al., 2009, van Vliet et al., 2010). Moreover, evidence exists that targeting EP1 receptors and COX-2 can protect from excitatory neuronal cell damage (Abe et al., 2009, McCullough et al., 2004, Kawaguchi et al., 2005, Kunz and Oliw, 2001, Takemiya et al., 2006, Kunz et al., 2005, Kawano et al., 2006). Further development of respective therapeutic approaches requires careful tolerability and safety considerations. In addition to peripheral side effects associated with the specific targets putative effects on seizure thresholds and seizure development need to be taken into account. Recently, we demonstrated that sub-chronic treatment with the EP1 receptor antagonist SC-51089 during a massive kindling paradigm did not affect seizure development with the supra-threshold stimulation condition used in the paradigm (Pekcec et al., 2009). However, these data do not rule out that SC-51089 might affect seizure thresholds or seizure development at threshold stimulation. Therefore, we aimed to further evaluate the impact of EP1 receptor antagonism in the amygdala kindling model in mice. The model was chosen based on its excellent predictive validity for temporal lobe epilepsy allowing detection of anticonvulsant and proconvulsant effects (Loscher, 2002, McIntyre and Gilby, 2009, Potschka et al., 2000). Whereas there is an obvious lack of studies evaluating the effects of EP1 receptor antagonists on seizure generation and spread, the situation is completely different for COX-2 inhibitors. Multiple studies determined the impact of COX-2 inhibitors with different selectivity in a variety of rodent models (Kulkarni and Dhir, 2009). Most of these studies focused on the effects of COX-2 inhibition in acute seizure and status epilepticus models, i.e. models in which seizures are elicited in naïve mice or rats. Whereas the majority of studies revealed beneficial effects of COX-2 inhibitors including inhibition of seizure development or indicated no impact of COX-2 inhibition, a small subset of studies described seizure aggravation and lowering of seizure thresholds in response to COX-2 inhibition (Baik et al., 1999, Kim et al., 2001, Kim et al., 2008, Akarsu et al., 2006). These latter studies leave some concern regarding further translational development of COX-2 inhibitor based approaches in epilepsy therapy. Therefore, we aimed to thoroughly evaluate the effects of COX-2 inhibition in a chronic model with a high predictive validity for temporal lobe epilepsy, i.e. the amygdala kindling model.