Abstract
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.
Highlights
Abacavir (ABC), a guanosine analogue belonging to the Nucleoside Reverse transcriptase Inhibitor (NRTI) family, has been widely prescribed to treat human immunodeficiency virus (HIV)
Clinical concentrations of ABC (20 μmol/L), to BzATP, exhibited a profile of pro-inflammatory actions that were in accordance with those demonstrated previously (De Pablo et al, 2010; De Pablo et al, 2012; Esplugues et al, 2016); in other words, they induced a significant decrease in human leukocyte rolling velocity (Figure 2A) while increasing leukocyte rolling flux (Figure 2C) and adhesion (Figure 2E) to endothelial cells
Both adenosine triphosphate (ATP) and carbovir triphosphate (CBVTP) mimicked the effects of ABC, though these actions depended on the dose (Figures 2A,C,E, 3A,C); while CBVTP induced human peripheral blood polymorphonuclear (PMN)-endothelium interactions or overexpression of the two subunits of the β2-integrins in a range of concentrations similar to those of ABC (10–20 μmol/L), doses of ATP 10–20 times lower (1 μmol/L) were capable of producing the same effects
Summary
Abacavir (ABC), a guanosine analogue belonging to the Nucleoside Reverse transcriptase Inhibitor (NRTI) family, has been widely prescribed to treat human immunodeficiency virus (HIV). It has been associated with a higher risk of myocardial infarction (Alvarez et al, 2017; Sabin et al, 2018), and so major clinical guidelines do not recommend the drug, in patients with cardiovascular risk (Gunthard et al, 2016; Saag et al, 2018). Like all P2X receptors, it is an ATP-gated ion channel receptor with a trimeric structure (Rassendren et al, 1997; Moura et al, 2015); in contrast to other members of its family, P2X7R displays a high degree of plasticity with an allosteric binding pocket (Coddou et al, 2011; Moura et al, 2015; Rissiek et al, 2015; Di Virgilio et al, 2018), and requires unusually high extracellular concentrations of ATP (≥100 μmol/L) to become activated (Yan et al, 2010)
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