Activation of Fas Receptors, Caspase-8 and Caspase-3 by Fluoride Ions in Rat Erythrocytes in vitro

The goal of the study was to demonstrate the ability of fluoride ions (F−) to activate key components of the receptor-dependent apoptotic pathway, membrane Fas receptors, caspase-8 and caspase-3, in rat erythrocytes in vitro. Cells were incubated in the presence of increasing NaF concentrations (0.1–10 mM) for 1, 5 and 24 h. Caspase-8 and caspase-3 activities were assayed by flow cytometry, expression of Fas receptors by immunoblotting. It was found that the kinetics of stimulation of Fas receptors, caspases-8 and caspases-3 in rat erythrocytes by fluoride ions differs depending both on the fluoride concentration and exposure time. For instance, activation of caspases was observed as early as 1 h after incubation with fluoride, while treatment of erythrocytes with 5 mM NaF for 24 h increased the cell population with active caspases-8 and caspases-3 up to ca 15-16%. At the same time, expression of Fas receptors increased in a concentration-dependent manner only after 24 h of incubation with NaF. Thus, one of the mechanisms underlying premature death of rat erythrocytes induced by fluoride in vitro is the ability of the latter to stimulate messengers of the receptor-dependent apoptotic pathway. However, it is possible that caspase-8 and caspase-3 activation is, at least in part, independent of the membrane-associated mechanism of activation of Fas receptors.