Okadaic acid, an inhibitor of type 1 and type 2A phosphatases, modulates the activation of phospholipase D in formyl peptide- and mastoparan-stimulated human neutrophils

Okadaic acid induces sustained activation of NFkappaB and degradation of the nuclear IkappaBalpha in human neutrophils

Human neutrophils differ from other cells by containing high amount of IkappaBalpha in the nucleus, and this increased nuclear IkappaBalpha accumulation is associated with the inhibition of NFkappaB activity and increased apoptosis. However, the mechanisms regulating NFkappaB activation and IkappaBalpha degradation in human neutrophils are little understood. The objective of this study was to provide a further insight into the mechanisms regulating NFkappaB activity and IkappaBalpha degradation in human neutrophils. We show that okadaic acid (OA), an inhibitor of protein phosphatases PP1 and PP2A, induces sustained activation of NFkappaB and degradation of the nuclear IkappaBalpha, and increases interleukin-8 expression in the neutrophils. Furthermore, inhibitors of protein kinase C-delta (PKCdelta) and IkappaB kinase (IKK) inhibit the OA-induced activation of NFkappaB. Collectively, our results indicate that in human neutrophils, the sustained activation of NFkappaB is regulated by a continuous phosphorylation and degradation of the nuclear IkappaBalpha.

Sodium stibogluconate (Pentostam) potentiates oxidant production in murine visceral leishmaniasis and in human blood

Sodium stibogluconate (Sbb), a leishmanicidal drug, was studied for its in vivo effect on the formation of reactive oxygen species (ROS), assessed by chemiluminescence (CL) in the whole blood of mice infected with Leishmania infantum. Stimulation of ROS formation induced ex vivo by zymosan particles or the protein kinase C activator phorbol myristate acetate (PMA) was reduced by approximately 25% (P < 0.05) after infection of mice. Treatment of infected mice with Sbb (50 to 400 mg/kg of body weight) enhanced the blood CL induced by zymosan and PMA (47 to 96%, P < 0.01). The drug potentiation effect also occurred in uninfected mice. In vitro treatment of normal human blood with Sbb (1, 10, or 100 microg/ml) for 1 h primed the CL response to PMA (29 to 54%). The priming effect of Sbb was also observed on the production of superoxide by isolated polymorphonuclear leukocytes stimulated either by PMA and zymosan or by the chemoattractants N-formyl-Met-Leu-Phe and platelet-activating factor. These data provide the first evidence of priming of the phagocyte respiratory burst by Sbb. This novel property of Sbb may contribute to the drug's leishmanicidal effect.