Prostaglandin H synthase and lipoxygenase mediated activation of xenobiotics in platelets

To investigate the involvement of prostaglandin H synthase (PHS) and lipoxygenase (LPO) in the activation of xenobiotics in platelets, platelet sonicates were preincubated with α-naphthol. Protein covalent binding of α-naphthol was measured following addition of arachidonic acid. Protein covalent binding was increased in a dose-dependent manner until it plateaued at 500 μM arachidonic acid. Pretreatment by two inhibitors of PHS, aspirin and indomethacin, resulted in a dose-dependent inhibition of α-naphthol-induced covalent binding, confirming PHS involvement. In addition, pretreatment by a LPO inhibitor, nordihydroguaiaretic acid (NDGA), also prevented covalent binding substantially, showing that LPO may be an alternative pathway for xenobiotic activation in platelets. Furthermore, combined treatment of aspirin and NDGA almost abolished the increase of (α-naphthol-induced covalent binding, suggesting that PHS and LPO are both major pathways for xenobiotic activation in platelets.