Implementation of a point-of-care ultrasound skills practicum for hospitalists.

INTRODUCTION: Point-of-care ultrasound is recognized as a safe and valuable diagnostic tool for patient evaluation. Hospitalists are prime candidates for advancing the point-of-care ultrasound field given their crucial role in inpatient medicine. Despite this, there is a notable lack of evidence-based ultrasound training for hospitalists. Most research focuses on diagnostic accuracy rather than the training required to achieve it. This study aims to improve hospitalists' point-of-care ultrasound knowledge and skills through a hands-on skills practicum. METHODS: Four skill practicums were conducted with pre-course, post-course, and six-month evaluations and knowledge assessments. RESULTS: The mean pre- vs. post-course knowledge assessment scores significantly improved, 41.7% vs. 75.9% (SD 16.1% and 12.7%, respectively, p < 0.0001). The mean ultrasound skills confidence ratings on a 10-point Likert scale significantly increased post-course (2.60 ± 1.66 vs. 6.33 ± 1.63, p < 0.0001), but decreased at six months (6.33 ± 1.63 vs. 4.10 ± 2.22, p < 0.0001). The greatest limitations to usage pre-course and at six months were knowledge/skills and lack of machine access. While knowledge/skills decreased from pre-course (82.0%) as compared to six-months (64.3%), lack of machine access increased from pre-course (15.8%) to six-months (28.6%) (p = 0.28). CONCLUSION: Hospitalists agree that point-of-care ultrasound has utility in the diagnostic and therapeutic management of patients, though the lack of training is a significant limitation. Our study demonstrated that a brief skills practicum significantly improves hospitalists' confidence and knowledge regarding ultrasound image acquisition and interpretation in the short term. Long-term confidence and usage wanes, which appears to be due to the lack of machine access.

Thrombocytopenia and disseminated histoplasmosis in immunocompetent adults.

Disseminated histoplasmosis among immunocompetent patients is rare, but may be associated with clinically significant refractory thrombocytopenia. Platelet counts often return to normal levels following antifungal therapy. Therefore, the most important management of this refractory thrombocytopenia is the recognition and treatment of histoplasmosis infection.

Binding of autotaxin to integrins localizes lysophosphatidic acid production to platelets and mammalian cells.

Autotaxin (ATX) is a secreted lysophospholipase D that generates the bioactive lipid mediator lysophosphatidic acid (LPA). We and others have reported that ATX binds to integrins, but the function of ATX-integrin interactions is unknown. The recently reported crystal structure of ATX suggests a role for the solvent-exposed surface of the N-terminal tandem somatomedin B-like domains in binding to platelet integrin αIIbß(3). The opposite face of the somatomedin B-like domain interacts with the catalytic phosphodiesterase (PDE) domain to form a hydrophobic channel through which lysophospholipid substrates enter and leave the active site. Based on this structure, we hypothesize that integrin-bound ATX can access cell surface substrates and deliver LPA to cell surface receptors. To test this hypothesis, we investigated the integrin selectivity and signaling pathways that promote ATX binding to platelets. We report that both platelet ß1 and ß3 integrins interact in an activation-dependent manner with ATX via the SMB2 domain. ATX increases thrombin-stimulated LPA production by washed platelets ~10-fold. When incubated under conditions to promote integrin activation, ATX generates LPA from CHO cells primed with bee venom phospholipase A(2), and ATX-mediated LPA production is enhanced more than 2-fold by CHO cell overexpression of integrin ß(3). The effects of ATX on platelet and cell-associated LPA production, but not hydrolysis of small molecule or detergent-solubilized substrates, are attenuated by point mutations in the SMB2 that impair integrin binding. Integrin binding therefore localizes ATX activity to the cell surface, providing a mechanism to generate LPA in the vicinity of its receptors.

Structural basis of substrate discrimination and integrin binding by autotaxin.

Autotaxin (ATX, also known as ectonucleotide pyrophosphatase/phosphodiesterase-2, ENPP2) is a secreted lysophospholipase D that generates the lipid mediator lysophosphatidic acid (LPA), a mitogen and chemoattractant for many cell types. ATX-LPA signaling is involved in various pathologies including tumor progression and inflammation. However, the molecular basis of substrate recognition and catalysis by ATX and the mechanism by which it interacts with target cells are unclear. Here, we present the crystal structure of ATX, alone and in complex with a small-molecule inhibitor. We have identified a hydrophobic lipid-binding pocket and mapped key residues for catalysis and selection between nucleotide and phospholipid substrates. We have shown that ATX interacts with cell-surface integrins through its N-terminal somatomedin B-like domains, using an atypical mechanism. Our results define determinants of substrate discrimination by the ENPP family, suggest how ATX promotes localized LPA signaling and suggest new approaches for targeting ATX with small-molecule therapeutic agents.

Autotaxin/lysopholipase D and lysophosphatidic acid regulate murine hemostasis and thrombosis.

The lipid mediator lysophosphatidic acid (LPA) is a potent regulator of vascular cell function in vitro, but its physiologic role in the cardiovasculature is largely unexplored. To address the role of LPA in regulating platelet function and thrombosis, we investigated the effects of LPA on isolated murine platelets. Although LPA activates platelets from the majority of human donors, we found that treatment of isolated murine platelets with physiologic concentrations of LPA attenuated agonist-induced aggregation. Transgenic overexpression of autotaxin/lysophospholipase D (Enpp2), the enzyme necessary for production of the bulk of biologically active LPA in plasma, elevated circulating LPA levels and induced a bleeding diathesis and attenuation of thrombosis in mice. Intravascular administration of exogenous LPA recapitulated the prolonged bleeding time observed in Enpp2-Tg mice. Enpp2+/- mice, which have approximately 50% normal plasma LPA levels, were more prone to thrombosis. Plasma autotaxin associated with platelets during aggregation and concentrated in arterial thrombus, and activated but not resting platelets bound recombinant autotaxin/lysoPLD in an integrin-dependent manner. These results identify a novel pathway in which LPA production by autotaxin/lysoPLD regulates murine hemostasis and thrombosis and suggest that binding of autotaxin/lysoPLD to activated platelets may provide a mechanism to localize LPA production.