Hypercholesterolemic patients have higher eryptosis and erythrocyte adhesion to human endothelium independently of statin therapy.

BACKGROUND: Phosphatidylserine (PS) externalization out of the membrane facilitates the eryptotic erythrocytes (EE) binding to endothelial cells (EC), potentially leading to atherosclerosis. Thus, the levels of eryptosis and interactions of EE-EC in hypercholesterolemic patients, either non-medicated or medicated, compared with healthy subjects were studied. METHODS: A total of 56 subjects clustered into three groups: (control (n = 20), hypercholesterolemic non-treated (HCNT) (n = 15), and statin-treated (HCT) (n = 21)) were enrolled in this cross-sectional study. Biochemical parameters were determined with validated and standard methods. PS exposure was estimated from annexin-V-binding, cell volume from forward scatter (FSC), and GSH from CMFDA fluorescence by flow cytometry. The erythrocyte-EC adhesion assay was performed by using the parallel-plate flow chamber technique. RESULTS: Higher PS externalization and adhesion of erythrocytes to EC (P < .05) was found in hypercholesterolemic subjects, regardless of statin treatment, compared with the control group. Although no correlation between FSC and PS externalization with other parameters was found, GSH was inversely correlated with erythrocyte adhesion, which was significantly correlated with total cholesterol, LDL-c, and apolipoprotein B. CONCLUSION: The link between hypercholesterolemia and eryptosis suggests a possible detrimental impact of this binomial on endothelial function with possible further development of atherosclerosis and microcirculation problems in hypercholesterolemic patients, independently of statin therapy.

The Neutrophil Secretome as a Crucial Link between Inflammation and Thrombosis.

Cardiovascular diseases are a leading cause of death. Blood-cell interactions and endothelial dysfunction are fundamental in thrombus formation, and so further knowledge of the pathways involved in such cellular crosstalk could lead to new therapeutical approaches. Neutrophils are secretory cells that release well-known soluble inflammatory signaling mediators and other complex cellular structures whose role is not fully understood. Studies have reported that neutrophil extracellular vesicles (EVs) and neutrophil extracellular traps (NETs) contribute to thrombosis. The objective of this review is to study the role of EVs and NETs as key factors in the transition from inflammation to thrombosis. The neutrophil secretome can promote thrombosis due to the presence of different factors in the EVs bilayer that can trigger blood clotting, and to the release of soluble mediators that induce platelet activation or aggregation. On the other hand, one of the main pathways by which NETs induce thrombosis is through the creation of a scaffold to which platelets and other blood cells adhere. In this context, platelet activation has been associated with the induction of NETs release. Hence, the structure and composition of EVs and NETs, as well as the feedback mechanism between the two processes that causes pathological thrombus formation, require exhaustive analysis to clarify their role in thrombosis.

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.

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.

Efavirenz induces interactions between leucocytes and endothelium through the activation of Mac-1 and gp150,95.

OBJECTIVES: The potential cardiovascular (CV) toxicity associated with combined antiretroviral therapy (cART) has been attributed mainly to the nucleoside reverse transcriptase inhibitors abacavir and didanosine. However, the other two components of cART--non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs)--may also be implicated, either directly or by influencing the action of the other drugs. This study evaluates the acute direct effects of the NNRTIs efavirenz and nevirapine and one of the most widely employed PIs, lopinavir, on leucocyte-endothelium interactions, a hallmark of CV disease. METHODS: Drugs were analysed in vitro in human cells (interactions of peripheral blood polymorphonuclear or mononuclear cells with human umbilical vein endothelial cells) using a flow chamber system, and in vivo in rat mesenteric vessels by means of intravital microscopy. The expression of adhesion molecules in leucocytes and endothelial cells was studied by flow cytometry, and the role of these molecules in white cell recruitment was evaluated by pre-treating human cells or rats with blocking antibodies. RESULTS: Efavirenz and nevirapine, but not lopinavir, increased the rolling flux and adhesion of leucocytes in vitro and in vivo while inducing emigration in rat venules. Efavirenz, but not nevirapine, augmented the levels of CD11b, CD11c and CD18 in neutrophils and monocytes. The actions of efavirenz, but not of nevirapine, were reversed by antibodies against Mac-1 (CD11b/CD18), gp150,95 (CD11c/CD18) or ICAM-1 (CD54). CONCLUSIONS: NNRTIs, but not PIs, interfere with leucocyte-endothelial interactions. However, differences between efavirenz and nevirapine suggest a specific CV profile for each compound.

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.

Role of Neutrophil Extracellular Traps in COVID-19 Progression: An Insight for Effective Treatment.

The coronavirus disease 2019 (COVID-19), caused by SARS-CoV-2, has resulted in a pandemic with over 270 million confirmed cases and 5.3 million deaths worldwide. In some cases, the infection leads to acute respiratory distress syndrome (ARDS), which is triggered by a cytokine storm and multiple organ failure. Clinical hematological, biochemical, coagulation, and inflammatory markers, such as interleukins, are associated with COVID-19 disease progression. In this regard, neutrophilia, neutrophil-to-lymphocyte ratio (NLR), and neutrophil-to-albumin ratio (NAR), have emerged as promising biomarkers of disease severity and progression. In the pathophysiology of ARDS, the inflammatory environment induces neutrophil influx and activation in the lungs, promoting the release of cytokines, proteases, reactive oxygen species (ROS), and, eventually, neutrophil extracellular traps (NETs). NETs components, such as DNA, histones, myeloperoxidase, and elastase, may exert cytotoxic activity and alveolar damage. Thus, NETs have also been described as potential biomarkers of COVID-19 prognosis. Several studies have demonstrated that NETs are induced in COVID-19 patients, and that the highest levels of NETs are found in critical ones, therefore highlighting a correlation between NETs and severity of the disease. Knowledge of NETs signaling pathways, and the targeting of points of NETs release, could help to develop an effective treatment for COVID-19, and specifically for severe cases, which would help to manage the pandemic.

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.

Abacavir induces platelet-endothelium interactions by interfering with purinergic signalling: A step from inflammation to thrombosis.

The controversy connecting Abacavir (ABC) with cardiovascular disease has been fuelled by the lack of a credible mechanism of action. ABC shares structural similarities with endogenous purines, signalling molecules capable of triggering prothrombotic/proinflammatory programmes. Platelets are leading actors in the process of thrombosis. Our study addresses the effects of ABC on interactions between platelets and other vascular cells, while exploring the adhesion molecules implicated and the potential interference with the purinergic signalling pathway. The effects of ABC on platelet aggregation and platelet-endothelium interactions were evaluated, respectively, with an aggregometer and a flow chamber system that reproduced conditions in vivo. The role of adhesion molecules and purinergic receptors in endothelial and platelet populations was assessed by selective pre-incubation with specific antagonists and antibodies. ABC and carbovir triphosphate (CBT) levels were evaluated by HPLC. The results showed that ABC promoted the adherence of platelets to endothelial cells, a crucial step for the formation of thrombi. This was not a consequence of a direct effect of ABC on platelets, but resulted from activation of the endothelium via purinergic ATP-P2X7 receptors, which subsequently triggered an interplay between P-selectin and ICAM-1 on endothelial cells with constitutively expressed GPIIb/IIIa and GPIbα on platelets. ABC did not induce platelet activation (P-selectin expression or Ca2+ mobilization) or aggregation, even at high concentrations. CBT levels in endothelial cells were lower than those required to induce platelet-endothelium interactions. Thus, ABC interference with endothelial purinergic signalling leads to platelet recruitment. This highlights the endothelium as the main cell target of ABC in this interaction, which is in line with previous experimental evidence that ABC induces manifestations of vascular inflammation.

Differential effects of anti-TNF-α and anti-IL-12/23 agents on human leukocyte-endothelial cell interactions.

Enhanced leukocyte recruitment is an inflammatory process that occurs during early phases of the vascular dysfunction that characterises atherosclerosis. We evaluated the impact of anti-TNF-α (adalimumab, infliximab and etanercept) and anti-IL-12/23 (ustekinumab) on interactions between human leukocytes and endothelial cells in a flow chamber that reproduced in vivo conditions. Clinical concentrations of anti-TNF-α were evaluated on the leukocyte recruitment induced by a variety of endothelial (TNF-α, interleukin-1ß, lymphotoxin-α and angiotensin-II) and leukocyte (PAF, IL-12 and IL-23) stimuli related to inflammation and atherosclerosis. Treatment with anti-TNF-α, even before or after establishing the inflammatory situation induced by TNF-α, diminished leukocyte-endothelial cell interactions induced by this stimuli. Our results also implicated adhesion molecules (ICAM-1, VCAM-1 and E-selectin) in the actions of anti-TNF-α in terms of leukocyte adhesion to endothelium. However, anti-TNF-α drugs did not influence the actions of interleukin-1ß, but prevented those of lymphotoxin-α and angiotensin-II. However, once established, inflammatory response elicited by the latter three stimuli could not be reversed. Pre-treatment with anti-TNF-α, also prevented leukocyte actions induced by IL-23 on PBMC rolling flux and rolling velocity and by IL-12 on PMN adhesion. Ustekinumab exhibited a more discreet profile, having no effect on leukocyte recruitment induced by any of the endothelial stimuli, while blocking the effects of IL-23 on leukocyte activation and those of IL-12 on PMN adhesion and PAF on PBMC rolling velocity. These findings endorse the idea that biological anti-inflammatory drugs, in particular anti-TNF-α, have the capacity to influence cardiovascular risk accompanying psoriasis and rheumatoid arthritis by ameliorating vascular inflammation.

Distribution of nitric oxide synthase in normal and cirrhotic human liver.

Chronic liver disorders represent a serious health problem, considering that 300 million people worldwide are hepatitis B virus carriers, and 8,000-10,000 patients per year, in the U.S. alone, die as a result of liver failure caused by hepatitis C infection. Nitric oxide synthase (NOS) regulates hepatic vasculature; however, the patterns of expression and activity of NOS proteins in healthy and diseased human livers are unknown. Sections of diseased (n = 42) and control livers (n = 14) were collected during orthotopic liver transplants and partial hepatectomy. The diseased sections included alcoholic cirrhosis, viral hepatitis, cholestasis, acute necrosis, and uncommon pathologies including alpha(1)-anti-trypsin disorder. The endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS) were studied by using the citrulline assay, Western immunoblot, immunohistochemistry, and in situ hybridization. The systemic generation of plasma NO metabolites was measured by HPLC. In control livers, Ca(2+)-dependent and -independent NOS activities were identified by Western analysis as eNOS and iNOS, respectively. The eNOS was uniformly distributed in the hepatocytes and also detected in the endothelium of hepatic arteries, terminal hepatic venules, sinusoids, and in biliary epithelium. The iNOS was detected in hepatocytes and localized mainly in the periportal zone of the liver acinus. This pattern of distribution of eNOS and iNOS in normal liver was confirmed by in situ hybridization. In diseased livers, there was a significant increase in Ca(2+)-independent NOS with the corresponding strong appearance of iNOS in the cirrhotic areas. The eNOS was translocated to hepatocyte nuclei. Thus, eNOS and iNOS proteins are differentially expressed in healthy human liver, and this expression is significantly altered in cirrhotic liver disorders.