Spin trapping agent, phenyl N-tert-butyl nitrone, inhibits induction of nitric oxide synthase in endotoxin-induced shock in mice.

Spin trapping agent, phenyl N-tert-butyl nitrone (PBN) significantly reduces mortality due to lipopolysaccharide (LPS)-induced shock in Balb/c mice as had previously been shown in rats. We hypothesized that PBN decreases mortality by directly or indirectly inhibiting nitric oxide (NO) generation. Therefore, we determined the effect of PBN administration on LPS-induced NO generation in mice. NO generation was monitored in the mouse liver after administration of LPS by an in vivo NO-spin trapping, followed by ex vivo EPR measurement. When the mice was treated with PBN 0.5hr before LPS administration, NO generation in the liver was reduced by 80%. However, when PBN was given 3hrs after LPS, NO generation did not change. Both pre- or post-administration of NO synthase (NOS) inhibitor, NG-monomethyl-L-arginine inhibited the NO generation. Western blotting of inducible NOS (iNOS) in mouse liver cytosol obtained from PBN-pretreated animals demonstrated a decreased expression of iNOS, indicating the reduction in NO generation was caused by the decrease in the amount of enzyme present but not by the inhibition of iNOS enzyme activity per se.