ADP and other metabolites released from Acanthamoeba castellanii lead to human monocytic cell death through apoptosis and stimulate the secretion of proinflammatory cytokines

Monocytes/macrophages are thought to be involved in Acanthamoeba infections. The aim of this work was to
study whether soluble metabolites (ADP and other compounds) released by Acanthamoeba castellanii trophozoites
could induce morphological and biochemical changes in human monocytic cells in vitro. We demonstrate
here that ADP constitutively released in the medium by A. castellanii, interacting with specific P2y2 purinoceptors
expressed on the monocytic cell membrane, caused a biphasic rise in [Ca2]i, morphological changes
characteristics of cells undergoing apoptosis, caspase-3 activation, and secretion of tumor necrosis factor alpha
(TNF-). The same results were found in monocytes exposed to purified ADP. Cell damage and TNF- release
induced by amoebic ADP were blocked by the P2y2 inhibitor suramin. Other metabolites contained in amoebic
cell-free supernatants, with molecular masses of, respectively, >30 kDa and between 30 and 10 kDa, also
caused morphological modifications and activation of intracellular caspase-3, characteristics of programmed
cell death. Nevertheless, mechanisms by which these molecules trigger cell damage appeared to differ from that
of ADP. In addition, other amoebic thermolable metabolites with molecular masses of <10 kDa caused the
secretion of interleukin-1. These findings suggest that pathogenic free-living A. castellanii by release of ADP
and other metabolites lead to human monocytic cell death through apoptosis and stimulate the secretion of
proinflammatory cytokines