Biologic aspects of thrombopoietin and the development of novel thrombopoietic agents for clinical use

Thrombocytopenia is a frequent finding in several clinical settings, including bone marrow failure associated with various disorders, immune-mediated thrombocytopenia, and chronic liver diseases. Currently, there is an unmet need for thrombopoietic agents to treat this condition. Thrombopoietin (TPO) is the key cytokine involved in thrombopoiesis, and is the endogenous ligand for the thrombopoietin receptor that is expressed on the surface of megakaryocytes and megakaryocytic precursors. Although clinical trials with first generation thrombopoietic agents were abruptly discontinued after the development of TPO autoantibodies had been observed, non-antigenic second generation thrombopoietic growth factors with unique pharmacological properties have been developed. These include TPO peptide mimetics (AMG 531 and Fab59), TPO nonpeptide mimetics (eltrombopag, NIP-004, and AKR-501) and TPO agonist antibodies. All of these bind to and activate the TPO receptor in different ways but all via JAK2/STAT signalling pathways, producing a dose-dependent rise in platelet counts. In view of their use as therapeutic agents, nonpeptide agonists seem to have an advantage over peptide agonists, in that they could be orally bioavailable. The aim of the present review is to illustrate the biology of TPO and its receptor, and to describe the structure and function of the new thrombopoietic agents. © 2007 Bentham Science Publishers Ltd

Novel thrombopoietic agents: A review of their use in idiopathic thrombocytopenic purpura

The underlying problem in idiopathic thrombocytopenic purpura (ITP) has traditionally been-recognized as accelerated platelet destruction. However, recent studies have provided evidence that the pathophysiology of ITP is more complex, and impaired platelet production has emerged as one of the mechanisms contributing to the thrombocytopenia. On these grounds, second-generation thrombopoietic agents have been used in clinical trials to stimulate platelet production in ITP patients who are not responsive to standard treatments. These new molecules bear no structural resemblance to thrombopoietin (TPO) but still bind and activate the TPO receptor. Studies have been completed for two TPO receptor agonists: romiplostim (formerly AMG 531) and eltrombopag (formerly SB497115). Romiplostim is a recombinant protein defined as a peptibody. Results of phase I-II trials published recently demonstrated that romiplostim given as a weekly subcutaneous injection for 1-6 weeks results in doubling of platelet counts and an increase to > 50 x 10(9)/L in most treated patients with minimal adverse effects. Eltrombopag is an orally available, small organic compound. In a randomized, double-blind, placebo-controlled phase III trial, ITP patients were given daily oral treatment with placebo or eltrombopag 50 mg. Platelet responses were observed in 59% of eltrombopag-treated patients and in 16% of patients in the placebo arm. No significant adverse events were seen. Other thrombopoietic agents in development, such as AKR-501 (formerly YM 477), appear promising in healthy volunteers. Ongoing phase III clinical trials will reveal the potential of these agents in the management of ITP prior to splenectomy and for long-term maintenance therapy, as well as their relative benefit compared with standard of care treatment

Leiomioma gastrico (Osservazione clinica).

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Perforazione di diverticolo di Meckel da corpo estraneo (Osservazione clinica).

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Intracardiac echocardiogram-guided use of a dormia basket to prevent major vegetation embolism during transvenous lead extraction

We discuss a case of transvenous lead extraction (TLE) in a patient with a large vegetation. To prevent embolization, a Dormia basket was placed in the pulmonary artery trunk. After uncomplicated TLE, the basket was withdrawn, and vegetation material was retrieved from it. Our experience confirms that TLE is feasible even with large vegetations, and the pulmonary circulation may be protected with a simple intravascular device