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

Increased Adhesiveness of Blood Cells Induced by Mercury Chloride: Protective Effect of Hydroxytyrosol

Mercury (Hg) is a highly toxic environmental contaminant that can harm human health, ultimately leading to endothelial dysfunction. Hg toxicity is partially mediated by the exposure of the cell membrane's surface of erythrocytes (RBCs) to phosphatidylserine (PS). In the context of these challenges, hydroxytyrosol, a phenolic compound of olive oil, has the ability to mitigate the toxic effects of Hg. This study aims to analyze the effect of Hg on the adhesion of RBCs and polymorphonuclear cells (PMNs) to the vascular endothelium and the potential protective effect of hydroxytyrosol, as these interactions are crucial in the development of cardiovascular diseases (CVDs). RBCs, PMNs, and human vein endothelial cells (HUVECs) were treated with increasing concentrations of HgCl2 and, in some cases, with hydroxytyrosol, and their adhesion to HUVECs and the expression of adhesion molecules were subsequently analyzed. Our results demonstrate that HgCl2 significantly increases the adhesion of both RBCs (2.72 ± 0.48 S.E.M., p-value < 0.02) and PMNs (11.19 ± 1.96 S.E.M., p-value < 0.05) to HUVECs and that their adhesiveness is significantly reduced following treatment with hydroxytyrosol (RBCs, 1.2 ± 1.18 S.E.M., p-value < 0.02 and PMNs, 4.04 ± 1.35 S.E.M., p-value < 0.06). Interestingly, HgCl2 does not alter the expression of adhesion molecules on either HUVECs or RBCs, suggesting that reduced exposure to PS is a key factor in hydroxytyrosol protection against HgCl2-induced RBC adhesion to the endothelium. On the other hand, HgCl2 induces increased expression of several PMN adhesion molecules (CD11b 215.4 ± 30.83 S.E.M. p-value < 0.01), while hydroxytyrosol inhibits their expression (e.g., CD11b 149 ± 14.35 S.E.M., p-value < 0.03), which would seem to be the mechanism by which hydroxytyrosol restricts PMN-endothelium interactions. These results provide new insights into the molecular mechanisms through which hydroxytyrosol mitigates the harmful effects of Hg on cardiovascular health, highlighting its potential as a therapeutic agent that can reduce the cardiovascular risk related to heavy metal exposure.

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 (SN_ABC )-in platelet activation that precedes thrombosis.

EXPERIMENTAL APPROACH

Effects of abacavir or SN_ABC 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). SN_ABC 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 SN_ABC . 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.

Agonists, Antagonists, and Modulators of P2X7 Receptors

The P2X7 receptor has been proposed as a novel drug target for different types of diseases associated with inflammation, including brain diseases, peripheral inflammation, and cancers. Structurally diverse P2X7 receptor antagonists, mainly negative allosteric modulators (NAMs), have been developed in recent years, and several P2X7 receptor antagonists are currently evaluated in clinical trials. The P2X7 receptor requires high micro- to even millimolar ATP concentrations to be activated. Selective agonists for the P2X7 receptor are not available. Positive allosteric modulators (PAMs) have been described, but PAMs with high potency and selectivity are still lacking. This chapter discusses medicinal chemistry approaches toward the development of P2X7 receptor modulators and presents a selection of recommended tool compounds for studying P2X7 receptors in humans and rodents.