Nitric oxide synthase activities in white blood cells of septic patients

Introduction

The bulk of data that links inducible nitric oxide synthase (iNOS) activity to the pathophysiology of sepsis originates in animal studies. However, the role of iNOS in human sepsis is controversial. Therefore, we measured in this pilot study iNOS activity in inflammatory cells from septic ICU patients compared to normal controls.

Methods

Blood samples from 5 ICU patients with clinically and bacteriologically documented sepsis, and from four healthy volunteers were centrifuged to separate the plasma/buffy coat. The buffy coat was layered onto Histopaque 1077 and centrifuged at 400 g to finally isolate white blood cells (WBCs). Constitutive (cNOS) and iNOS activities were analyzed in WBCs by the [³H] L-arginine-L-citrulline assay and measured in Units (pmol L-citrulline evolved/min/mg protein). The metabolic end-products of nitric oxide (nitrite/nitrate; NO_N ^-S) were also determined in plasma from these subjects by chemiluminescence.

Results

Plasma NO_N ^- levels were elevated in septic compared to control subjects (208 ± 107 vs 26 ± 7 μmol/l, respcctively). WBCs from septic patients exhibited low cNOS activities (0.1 ± 0.1 vs 1.0 ± 0.6 Units for controls). iNOS activity from the septic WBCs was elevated, compared to controls (3.1 ± 1.8 vs 0.5 ± 0.3 Units, respectively).

Conclusion

This pilot data suggests, that consistent with the plasma accumulation of nitric oxide metabolites, inflammatory cells of septic humans produce high levels of iNOS compared to healthy controls while cNOS production is suppressed. These findings support the theory that iNOS has an important role in the pathogenesis of human sepsis.