Hypertonic saline activates lipid-primed human neutrophils for enhanced elastase release

Ongoing clinical trials have revived interest in hypertonic saline (HTS) for postinjury resuscitation; these studies have documented serum Na+ concentrations > or = 170 mmol/L. Recent animal studies have shown that HTS enhances T-cell and monocyte function, but effects on the polymorphonuclear neutrophil (PMN) remain unclear. The postinjury lipid mediators platelet-activating factor (PAF) and leukotriene B4 (LTB4) have been implicated in PMN priming for cytotoxicity, which is believed to be important in the pathogenesis of multiple organ failure. We hypothesized that HTS would stimulate PMN superoxide (O2-) and elastase release from PAF- and LTB4-primed PMNs.

Isolated PMNs from five donors were primed for 5 minutes with 200 nmol/L PAF or 1 micromol/L LTB4 in Kreb's-Ringer's phosphate with dextrose at a Na+ concentration of 140 mmol/L (normal serum Na+ concentration), pelleted, and resuspended in Kreb's-Ringer's phosphate with dextrose for 10 minutes at a Na+ concentration of 130 to 170 mmol/L. O2- generation was measured by superoxide dismutase-inhibitable reduction of cytochrome c and elastase release by cleavage of N-methoxysuccinyl-Ala-Ala-Pro-Val p-nitroanilide.

HTS with Na+ concentration up to 170 mmol/L had no significant effect on O2- production or elastase release from quiescent cells. Na+ concentration of 160 and 170 mmol/L, however, activated PAF- and LTB4-primed PMNs for enhanced elastase release with no effect on O2- production.

In clinically relevant concentrations, elevated Na+ activates lipid-primed neutrophils for enhanced elastase degranulation. Consequently, the administration of HTS in the early postinjury resuscitation period, when PMNs are maximally primed, may activate PMN elastase release and thereby promote the development of multiple organ failure.