Omeprazole induces apoptosis in normal human polymorphonuclear leucocytes

We investigated in vitro apoptosis in human polymorphonuclear neutrophils (PMN) induced by omeprazole. This drug, both in the native (OM) and acidified (OM-HCl) form, is a potent inducer of PMN apoptosis. The effect is time- and dose-dependent. OM-HCl is more efficient than OM in inducing PMN apoptosis. In fact, after 24 h incubation in vitro at 1 x 10(-4) M OM-HCl induces apoptosis in 70% of the cell population compared to 37% induced by OM. Apoptosis induced by both forms of the drug is caspase dependent being significantly reduced by pretreating cells with the caspase 3 inhibitor (DEVDH-CHO). However, some differences in the apoptosis mechanisms between the two forms of the drug seem to exist because PMN treatment with the specific caspase 8 inhibitor (Z-IETD-FMK) only blocks OM-HCl mediated apoptosis. We observed cleavage of caspase 8 only in the cells incubated with OM-HCl while the executioner caspase 3 was activated with both forms of the drug. Furthermore, pretreatment with GM-CSF, a known activator of intracellular survival pathways in PMN, partially protected cells from OM-HCl induced apoptosis but did not contrast the apoptotic effect of OM. Cysteine cathepsin proteases also seem involved in the apoptotic mechanism of both drug forms since the specific inhibitor E64d gave a significant protection. To verify if OM-HCl induced apoptosis was dependent on the sulfenamide bound with the cell sulfhydryl groups we used molecules with thiol groups such as beta-mercaptoethanol (beta-ME) and reduced glutathione (GSH). Reactions of OM-HCl with cellular sulfhydryl groups are strongly involved in both the triggering and evolving phase of the apoptotic mechanism since significant protection from apoptosis was obtained when PMN were pretreated for 1 h with beta-ME (lipid-permeable) or GSH (lipid-impermeable). These results show that OM and OM-HCl induce apoptosis in human PMN and suggest that the second binds the sulfhydryl groups, present on the cell membrane, to then penetrate the cell thus causing a further significant increase in apoptosis. OM-induced PMN apoptosis during the treatment of gastric inflammatory disease could be an advantage for the resolution of the phlogosis state. However, this aspect should be further elucidated to assess the optimal therapeutical regimen for gastric diseases which are related to infective agents.