Diazepam-binding inhibitor-derived peptides induce intracellular calcium changes and modulate human neutrophil function

We studied the effects of two diazepam-binding inhibitor (DBI)-derived peptides, triakontatetraneuropeptide (DBI 17-50, TTN) and eiksoneuropeptide (DBI 51-70, ENP), on cytosolic free Ca2+ concentrations ([Ca2+](i)), chemotaxis, superoxide anion (O-2(-)) generation, and phagocytosis in human neutrophils, Both TTN and ENP induced a rapid and transient rise of [Ca2+](i). The effect of TTN depended on the presence of extracellular Ca2+, whereas the effect of ENP also persisted after extracellular Ca2+ chelation, TTN induced neutrophil chemotaxis, stimulated O-2(-) generation, and enhanced phagocytosis. ENP did not affect cell migration and oxidative metabolism but enhanced phagocytosis, Both peptides modulated N-formyl-methionyl-leucyl-phenylalanine- and phorbol myristate acetate-induced O-2(-) generation. Because neutrophils express benzodiazepine receptors of the peripheral type (pBRs) and DBI-derived peptides may interact with such receptors, we investigated the possible role of pBRs in TTN- or ENP-induced effects. The synthetic pBR ligand RO 5-4864 increased [Ca2+](i) through extracellular Ca2+ influx and this effect was prevented by the pBR antagonist PK-11195, RO 5-4864, however, was ineffective on neutrophil migration and O-2(-) generation and only slightly affected phagocytosis. Moreover, PK-11195 delayed the [Ca2+](i) rise induced by TTN but did not significantly affect its extent, and had no effect on the [Ca2+](i) rise induced by ENP, We conclude that DBI-derived peptides induce [Ca2+](i) changes and modulate neutrophil function mainly through pBR-independent pathways. In view of the wide cell and tissue distribution of DBI in the brain and in peripheral organs, modulation of neutrophil function by DBI-derived peptides may be relevant for both the neuroimmune network and the development and regulation of the inflammatory processes.