Ibuprofen is as or more efficacious than acetaminophen for the treatment of pain and fever in adult and pediatric populations and is equally safe.

Regulation of platelet activation plays a central role in hemostasis and pathophysiological processes such as coronary artery disease. Thrombin is the most potent activator of platelets. Human platelets express two thrombin receptors, PAR1 and PAR4, both of which signal platelet activation. Evidence is lacking on the mechanism by which PAR1 and PAR4 may differentially signal platelet aggregation. Here we show that at the relatively high concentration of agonist most likely found at the site of a local thrombus, dual inhibition of the P2Y 12 receptor and calcium mobilization result in a complete inhibition of PAR4-induced aggregation, while having no effect on either thrombin or PAR1-mediated platelet aggregation. Both PAR1-and PAR4-mediated aggregation are independent of calcium mobilization. Furthermore, we show that P2Y 12 receptor activation is not required for protease-activated receptor-mediated aggregation at higher agonist concentrations and is only partially required for Rap1 as well as GPIIbIIIa activation. P2Y 12 receptor inhibitors clinically in use such as clopidogrel are postulated to decrease platelet aggregation through partial inhibition of PAR1 signaling. Our data, however, indicate that at high local concentrations of thrombin, it is the signaling through PAR4 rather than PAR1 that may be regulated through purinergic feedback. Thus, our data identify an intra-platelet mechanism that may function as a future site for therapeutic intervention.

Thrombin-mediated activation of platelets is critical for hemostasis, but the signaling pathways responsible for this process are not completely understood. In addition, signaling within this cascade can also lead to thrombosis. In this study, we have defined a new signaling pathway for the thrombin receptor protease activated receptor-1 (PAR1) in human platelets. We show that PAR1 couples to G i/o in human platelets and activates phosphoinositide-3 kinase (PI3K). PI3K activation regulates platelet integrin ␣IIb␤3 activation and platelet aggregation and potentiates the PAR1-mediated increase in intraplatelet calcium concentration. PI3K inhibitors eliminated these effects downstream of PAR1, but they had no effect on PAR4 signaling. This study has identified an important role for the direct activation of G i/o by PAR1 in human platelets. Given the efficacy of clopidogrel, which blocks the G i/o -coupled P2Y purinoceptor 12, as an antiplatelet/antithrombotic drug, our data suggest that specifically blocking only PAR1-mediated G i/o signaling could also be an effective therapeutic approach with the possibility of less unwanted bleeding.

Novel biocompatible macromolecular vectors were developed that not only enable transport of bioactive cargo across the cell membrane but also control the delivery into defined intracellular compartments. This work describes the synthesis and design of two non-peptidic fluorescently labeled Newkome-type dendrimers, differentiated over a varied alkyl spacer with guanidine end moieties. The internalization of the fluorescein-labeled molecular transporter into mammalian cells showed strong subcellular localizations, evident with both live cells and fixed cells costained with DAPI, a nuclear stain. We observed that the subcellular distribution of these vectors varied significantly, as one of the vectors concentrates in the nucleus (FD-1) while the other (FD-2) concentrates in the cytosol. All experiments performed with NIH-3T3 fibroblasts and human microvascular endothelial cells (HMEC) showed similar results. The differential localization patterns of the two molecular transporters can be controlled through the variation of alkyl spacer length at the terminal generation of the dendrimer. Intracellular delivery of bioactive entities into specific subcellular locations, utilizing this practical approach, might overcome limitations in drug delivery and pioneer future technologies in drug transport.

Pathological conditions such as coronary artery disease are clinically controlled via therapeutic regulation of platelet activity. Thrombin, through protease-activated receptor (PAR) 1 and PAR4, plays a central role in regulation of human platelet function in that it is known to be the most potent activator of human platelets. Currently, direct thrombin inhibitors used to block platelet activation result in unwanted side effects of excessive bleeding. An alternative therapeutic strategy would be to inhibit PAR-mediated intracellular platelet signaling pathways. To elucidate the best target, we are studying differences between the two platelet thrombin receptors, PAR1 and PAR4, in mediating thrombin's action. In this study, we show that platelet activation by PAR1-activating peptide (PAR1-AP) requires a phospholipase D (PLD)-mediated phosphatidic acid (PA) signaling pathway. We show that this PAR1-specific PA-mediated effect is not regulated through differential granule secretion after PARinduced platelet activation. Perturbation of this signaling pathway via inhibition of lipid phosphate phosphatase-1 (LPP-1) by propranolol or inhibition of the phosphatidylcholine-derived phosphatidic acid (PA) formation by PLD with a primary alcohol significantly attenuated platelet activation by PAR1-AP. Platelet activation by thrombin or PAR4-AP was insensitive to these inhibitors. Furthermore, these inhibitors significantly attenuated activation of Rap1 after stimulation by PAR1-AP but not thrombin or PAR4-AP. Because PA metabolites such as diacylglycerol play an important role in intracellular signaling, identifying crucial differences in PA regulation of PAR-induced platelet activation may lead to a greater understanding of the role of PAR1 versus PAR4 in progression of thrombosis.Platelets are regulated through numerous agonist-induced signaling pathways, the most potent of which is thrombin (Davey and Luscher, 1967;Jamieson, 1997). Human platelets express two functional thrombin receptors, protease activated receptor-1 and -4 (PAR1 and PAR4) (Kahn et al., 1998;Coughlin, 2005), whereas mouse platelets express PAR3 and PAR4. Previous work from our lab has indicated that PAR1 and PAR4 mediate platelet activation through distinct signaling pathways (Holinstat et al., 2006). How differential signaling through the thrombin receptors is regulated and the potential physiological consequences of selective activation of PAR1 and PAR4 remain unclear. Several intermediates within this signaling scheme, such as PKC␣ and the small GTPase Rap1 have been identified to be important to regulating platelet function (Franke et al., 2000;Chrzanowska-Wodnicka et al., 2005). Genetic studies in the mouse have confirmed the role of Rap1b in platelet aggregation and subsequent clot formation (Chrzanowska-Wodnicka et al., 2005). How Rap1 is involved in the initial and irreversible phases of platelet aggregation (Franke et al., 2000) and whether Rap1 is differentially regulated in human platelets by PAR1 and PAR4 remain elusive.In mouse pla...