Hypertonic saline inhibits neutrophil (PMN) priming via attenuation of p38MAPK signaling

Priming of the neutrophil cytotoxic response is central to the pathogenesis of early postinjury multiple organ failure (MOF). Platelet-activating fact or (PAF) has been implicated as a key inflammatory mediator in postinjury n eutrophil priming and requires p38 MAPK signaling to produce its biologic e ffects. Hypertonic saline (HTS) resuscitation decreases the postinjury infl ammatory response following shock in animals and decreases receptor-mediate d neutrophil (PMN) cytotoxic functions in vitro. We hypothesized that HTS a ttenuates PAF priming of the PMN cytotoxic response by interfering with PAF -mediated p38 MAPK signal transduction. Isolated PMNs were preincubated in isotonic buffer or HTS (Na+ = 180 mM), then primed with PAF, Neutrophil CD1 1b/CD18 expression was measured by flow cytometry. Receptor-dependent (fMLP ), N-formyl-methionyl-leucyl-phenylalanine, fMLP) and receptor-independent (PMA) O2- production was measured by reduction of cytochrome c in resting a nd PAF primed PMNs. Total p38 MAPK protein PAF-mediated p38 MAPK activation was assessed by western blot of PMN lysates. Clinically relevant levels of HTS attenuated PAF-mediated beta (2)-integrin expression. While HIS attenu ated receptor-dependent (fMLP and PAF/fMLP) O2- production, receptor-indepe ndent (PMA) O2- production was unaffected. Conversely, HTS attenuated PAF p riming of PMA-mediated O2- production. PAF and HTS did not alter total cell ular p38 MAPK content. Clinically relevant levels of HTS alone did not acti vate p38 MARK but inhibited PAF mediated p38 MAPK activation. HTS attenuate s PAF priming of the PMN cytotoxic response by altering intracellular signa l transduction. Therefore, HTS resuscitation may attenuate postinjury PMN p riming and ultimately the risk of developing MOF.