Positive allosteric modulation by ivermectin of human but not murine P2X7 receptors

Abstract

BACKGROUND AND PURPOSEIn mammalian cells, the anti-parasitic drug ivermectin is known as a positive allosteric modulator of the ATP-activated ion channel P2X4 and is used to discriminate between P2X4-and P2X7-mediated cellular responses. In this paper we provide evidence that the reported isoform selectivity of ivermectin is a species-specific phenomenon. EXPERIMENTAL APPROACHComplementary electrophysiological and fluorometric methods were applied to evaluate the effect of ivermectin on recombinantly expressed and on native P2X7 receptors. A biophysical characterization of ionic currents and of the pore dilation properties is provided. KEY RESULTSUnexpectedly, ivermectin potentiated currents in human monocyte-derived macrophages that endogenously express hP2X7 receptors. Likewise, currents and [Ca 2+ ]i influx through recombinant human (hP2X7) receptors were potently enhanced by ivermectin at submaximal or saturating ATP concentrations. Since intracellular ivermectin did not mimic or prevent its activity when applied to the bath solution, the binding site of ivermectin on hP2X7 receptors appears to be accessible from the extracellular side. In contrast to currents through P2X4 receptors, ivermectin did not cause a delay in hP2X7 current decay upon ATP removal. Interestingly, NMDG + permeability and Yo-Pro-1 uptake were not affected by ivermectin. On rat or mouse P2X7 receptors, ivermectin was only poorly effective, suggesting a species-specific mode of action. CONCLUSIONS AND IMPLICATIONSThe data indicate a previously unrecognized species-specific modulation of human P2X7 receptors by ivermectin that should be considered when using this cell-biological tool in human cells and tissues. AZ 10606120, N-[2-[[2-[(2-hydroxyethyl)

Natural compounds with P2X7 receptor-modulating properties

“…Because high concentrations of these compounds may also modulate other receptor systems or ion channels like it is known for IVM [20], their selectivity must be verified in more detail. The potential for further structural modifications make the three natural products investigated attractive starting points for further optimization.…”

“…Figure 3a illustrates the modulatory effects of the three investigated natural compounds as well as those of some reference substances: the competitive tetrazole P2X7 antagonist A-438079 [18], the highly potent non-competitive P2X7 antagonist AZ 10606120 [19] and the antiparasitic drug IVM, recently described as a positive allosteric modulator of human P2X7 in the same cell line [20]. (Fig.…”

Quantifying Ca2+ Current and Permeability in ATP-gated P2X7 Receptors

“…Isolation of Human Macrophages-Monocyte-derived macrophages were obtained as described by Norenberg et al (58). Blood obtained from healthy volunteers was centrifuged at 500 ϫ g for 10 min to isolate plasma, buffy coat layer, and erythrocytes.…”

Tryptophan 46 is a site for ethanol and ivermectin action in P2X4 receptors

“…Ivermectin (IVM), an antiparasitic drug used in humans and animals, is a selective positive modulator of P2X4Rs [20,21]. We have shown that IVM antagonizes ethanolmediated inhibition of P2X4Rs in vitro [12].…”