Oxidized ATP (oATP) attenuates proinflammatory signaling via P2 receptor‐independent mechanisms

Periodate‐oxidized ATP (oATP), which covalently modifies nucleotide‐binding proteins, can significantly attenuate proinflammatory signaling. Although the P2X 7 nucleotide receptor (P2X 7 R) is irreversibly antagonized by oATP, it is unclear whether anti‐inflammatory actions of oATP are predominantly mediated via its actions on P2X 7 R. Here, we describe inhibitory effects of oATP on proinflammatory responses in three human cell types that lack expression of P2X 7 R: human umbilical vein endothelial cells (HUVEC), HEK293 cells, and 1321N1 astrocytes. oATP decreased by 40–70% the secretion of interleukin (IL)‐8 stimulated by tumor necrosis factor‐ α (TNF‐ α ) in all three cell types, by IL‐1 β in HUVEC and 1321N1 cells, and by endotoxin in HUVEC. Attenuation of TNF‐ α ‐stimulated IL‐8 secretion by oATP was similar in wild‐type HEK cells or HEK cells stably expressing recombinant P2X 7 R. oATP also attenuated cytokine‐stimulated expression of nuclear factor‐ κ B‐luciferase reporter genes expressed in HEK or 1321N1 cells, but did not affect the rapid downregulation of I κ B. oATP had no effect on uridine triphosphate‐induced activation of native P2Y 2 receptors in HEK cells, but reduced the potency and efficacy of ADP as an agonist of native P2Y 1 receptors. However, inhibition of P2Y 1 receptors with the specific antagonist MRS2216 did not mimic the effects of oATP on TNF‐ α ‐stimulated IL‐8 secretion. Although 1321N1 astrocytes lack expression of any known P2 receptor subtypes, oATP markedly inhibited ecto‐ATPase activity in these cells, resulting in a significant accumulation of extracellular ATP. In summary, oATP can attenuate proinflammatory signaling by mechanisms independent of the expression or activation of known P2 receptor subtypes.British Journal of Pharmacology (2003) 140 , 507–519. doi: 10.1038/sj.bjp.0705470