Abacavir causes leukocyte/platelet crosstalk by activating neutrophil P2X7 receptors thus releasing soluble lectin-like oxidized low-density lipoprotein receptor-1.

BACKGROUND AND PURPOSE: Abacavir, an antiretroviral drug used in HIV therapy associated with myocardial infarction, promotes thrombosis through P2X7 receptors. The role of platelets as pro-thrombotic cells is acknowledged whereas that of neutrophils-due to their secretory capacity-is gaining recognition. This study analyses the role of neutrophils-specifically the secretome of abacavir-treated neutrophils (SNABC )-in platelet activation that precedes thrombosis. EXPERIMENTAL APPROACH: Effects of abacavir or SNABC on platelet activation and platelet-leukocyte interactions and expression of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) were analysed by flow cytometry. The secretome was analysed by proteomics. The role of leukocytes in the actions of abacavir was evaluated in a mouse model of thrombosis. KEY RESULTS: Abacavir induced platelet-leukocyte interactions, not directly via effects of abacavir on platelets, but via activation of neutrophils, which triggered interactions between platelet P-selectin and neutrophil P-selectin glycoprotein ligand-1 (PSGL-1). SNABC stimulated platelet activation and platelet-leukocyte interactions through a process that was dependent on LOX-1, neutrophil P2X7 and platelet P2Y1, P2Y12 and P2X1 receptors. Abacavir induced the expression of LOX-1 on neutrophils and of the soluble form of LOX-1 (sLOX-1) in SNABC . Neutrophils, LOX-1, P2X7, P2Y1, P2Y12 and P2X1 receptors were required for the pro-thrombotic actions of abacavir in vivo. CONCLUSION AND IMPLICATIONS: Neutrophils are target cells in abacavir-induced thrombosis. Abacavir released sLOX-1 from neutrophils via activation of their P2X7 receptors, which in turn activated platelets. Hence, sLOX-1 could be the missing link in the cardiovascular risk associated with abacavir.

Abacavir Increases Purinergic P2X7 Receptor Activation by ATP: Does a Pro-inflammatory Synergism Underlie Its Cardiovascular Toxicity?

The cardiovascular toxicity of Abacavir is related to its purinergic structure. Purinergic P2X7-receptors (P2X7R), characterized by activation by high concentrations of ATP and with high plasticity, seem implicated. We appraise the nature of the interplay between Abacavir and P2X7R in generating vascular inflammation. The effects of Abacavir on leukocyte-endothelium interactions were compared with those of its metabolite carbovir triphosphate (CBV-TP) or ATP in the presence of apyrase (ATP-ase) or A804598 (P2X7R-antagonist). CBV-TP and ATP levels were evaluated by HPLC, while binding of Abacavir, CBV-TP and ATP to P2X7R was assessed by radioligand and docking studies. Hypersensitivity studies explored a potential allosteric action of Abacavir. Clinical concentrations of Abacavir (20 µmol/L) induced leukocyte-endothelial cell interactions by specifically activating P2X7R, but the drug did not show affinity for the P2X7R ATP-binding site (site 1). CBV-TP levels were undetectable in Abacavir-treated cells, while those of ATP were unaltered. The effects of Abacavir were Apyrase-dependent, implying dependence on endogenous ATP. Exogenous ATP induced a profile of proinflammatory actions similar to Abacavir, but was not entirely P2X7R-dependent. Docking calculations suggested ATP-binding to sites 1 and 2, and Abacavir-binding only to allosteric site 2. A combination of concentrations of Abacavir (1 µmol/L) and ATP (0.1 µmol/L) that had no effect when administered separately induced leukocyte-endothelium interactions mediated by P2X7R and involving Connexin43 channels. Therefore, Abacavir acts as a positive allosteric modulator of P2X7R, turning low concentrations of endogenous ATP themselves incapable of stimulating P2X7R into a functional proinflammatory agonist of the receptor.

Structural and Functional Basis for Understanding the Biological Significance of P2X7 Receptor.

The P2X7 receptor (P2X7R) possesses a unique structure associated to an as yet not fully understood mechanism of action that facilitates cell permeability to large ionic molecules through the receptor itself and/or nearby membrane proteins. High extracellular adenosine triphosphate (ATP) levels-inexistent in physiological conditions-are required for the receptor to be triggered and contribute to its role in cell damage signaling. The inconsistent data on its activation pathways and the few studies performed in natively expressed human P2X7R have led us to review the structure, activation pathways, and specific cellular location of P2X7R in order to analyze its biological relevance. The ATP-gated P2X7R is a homo-trimeric receptor channel that is occasionally hetero-trimeric and highly polymorphic, with at least nine human splice variants. It is localized predominantly in the cellular membrane and has a characteristic plasticity due to an extended C-termini, which confers it the capacity of interacting with membrane structural compounds and/or intracellular signaling messengers to mediate flexible transduction pathways. Diverse drugs and a few endogenous molecules have been highlighted as extracellular allosteric modulators of P2X7R. Therefore, studies in human cells that constitutively express P2X7R need to investigate the precise endogenous mediator located nearby the activation/modulation domains of the receptor. Such research could help us understand the possible physiological ATP-mediated P2X7R homeostasis signaling.

Environmental factors are associated with hospital admissions for sepsis-related pneumonia: A bidirectional case-crossover design.

OBJECTIVE: Pneumonia is a common cause of morbidity and sepsis worldwide, mainly in the elderly. We evaluated the impact of short-term exposure to environmental factors on hospital admissions for sepsis-related pneumonia in a nationwide study in Spain. METHODS: We conducted a bidirectional case-crossover study in patients who had sepsis-related pneumonia in 2013. Data were obtained from the Minimum Basic Data Set (MBDS) and the State Meteorological Agency (AEMET) of Spain. Conditional logistic regressions were used to evaluate the association between environmental factors (temperature, relative humidity, NO2, SO2, O3, PM10, and CO) and hospital admissions with sepsis-related pneumonia. RESULTS: A total of 3,262,758 hospital admissions were recorded in the MBDS, of which, 253,467 were patients with sepsis. Among those, 67,443 had sepsis-related pneumonia and zip code information. We found inverse associations [adjusted odds ratio (aOR) values < 1] between short-term exposure to temperature and hospital admissions for sepsis-related pneumonia. Moreover, short-term exposure to higher levels of relative humidity, NO2, SO2, O3, PM10, and CO were directly associated (aOR values > 1) with a higher risk of hospital admissions for sepsis-related pneumonia. Overall, the impact of environmental factors was more prominent with increasing age, mainly among the elderly aged 65 or over. CONCLUSION: Short-term exposure to environmental factors (temperature, relative humidity, NO2, SO2, O3, CO, and PM10) was associated with a higher risk of hospital admissions for sepsis-related pneumonia. Our findings support the role of environmental factors in monitoring the risk of hospital admissions for sepsis-related pneumonia and can help plan and prepare public health resources.

Epidemiological trends of sepsis in the twenty-first century (2000-2013): an analysis of incidence, mortality, and associated costs in Spain.

BACKGROUND: Sepsis has represented a substantial health care and economic burden worldwide during the previous several decades. Our aim was to analyze the epidemiological trends of hospital admissions, deaths, hospital resource expenditures, and associated costs related to sepsis during the twenty-first century in Spain. METHODS: We performed a retrospective study of all sepsis-related hospitalizations in Spanish public hospitals from 2000 to 2013. Data were obtained from records in the Minimum Basic Data Set. The outcome variables were sepsis, death, length of hospital stay (LOHS), and sepsis-associated costs. The study period was divided into three calendar periods (2000-2004, 2005-2009, and 2010-2013). RESULTS: Overall, 2,646,445 patients with sepsis were included, 485,685 of whom had died (18.4%). The incidence of sepsis (events per 1000 population) increased from 3.30 (2000-2004) to 4.28 (2005-2009) to 4.45 (2010-2013) (p < 0.001). The mortality rates from sepsis (deaths per 10,000 population) increased from 6.34 (2000-2004) to 7.88 (2005-2009) to 7.89 (2010-2013) (p < 0.001). The case fatality rate (CFR) or proportion of patients with sepsis who died decreased from 19.1% (2000-2004) to 18.4% (2005-2009) to 17.9% (2010-2013) (p < 0.001). The LOHS (days) decreased from 15.9 (2000-2004) to 15.7 (2005-2009) to 14.5 (2010-2013) (p < 0.001). Total and per patient hospital costs increased from 2000 to 2011, and then decreased by the impact of the economic crisis. CONCLUSIONS: Sepsis has caused an increasing burden in terms of hospital admission, deaths, and costs in the Spanish public health system during the twenty-first century, but the incidence and mortality seemed to stabilize in 2010-2013. Moreover, there was a significant decrease in LOHS in 2010-2013 and a decline in hospital costs after 2011.

Abacavir Induces Arterial Thrombosis in a Murine Model.

Background: The purinergic system is known to underlie prothrombotic and proinflammatory vascular programs, making the profile of experimental actions demonstrated by abacavir compatible with thrombogenesis. However, direct evidence of a prothrombotic effect by the drug has been lacking. Methods: The present study appraised the effects of abacavir in a well-validated animal model of arterial thrombosis. The role of ATP-P2X7 receptors in the actions of the drug was also assessed, and the actions of recognized vascular-damaging agents and other nucleoside reverse-transcriptase inhibitors (NRTIs) were evaluated and compared to those of abacavir. Results: Abacavir dose-dependently promoted thrombus formation. This effect was reversed by a P2X7-receptor antagonist and was nonexistent in P2X7 knockout mice. The effects of abacavir were similar to those of diclofenac and rofecoxib. Other NRTIs had no thrombosis-related effects. Conclusion: Abacavir promotes arterial thrombosis through interference with purinergic signaling, suggesting a possible biological mechanism for the clinical association of abacavir with cardiovascular diseases.