Induction of NF-κB, IκB-α, and iNOS in rat gastric mucosa during endotoxemia

Upregulation of inducible nitric oxide synthase (iNOS) contributes to the development of gastric injury during endotoxemia. The molecular mechanisms related to its induction are unknown. Because the transcription factor nuclear factor-kappa B (NF-κB) regulates inflammatory genes in response to endotoxemia, we hypothesized that its activity in gastric mucosa would increase while its inhibitor IκB-α would decrease commensurate with changes in iNOS expression. Rats were given intraperitoneal saline or lipopolysaccharide (LPS; 20 mg/kg) for 5, 15, or 30 min, or for 1, 3, or 5 h, and killed, and the gastric mucosa was prepared for determination of iNOS and IκB-α by Western immunoblotting, iNOS mRNA by quantitative real-time RT-PCR, and NF-κB by electrophoretic mobility-shift assay. LPS caused a significant increase in iNOS mRNA and protein immunoreactivity at 1, 3, and 5 h compared to controls. NF-κB-binding activity increased in the nuclear fraction of gastric mucosa at 1 h and steadily increased over time after LPS administration. The activated NF-κB consisted mainly of p50 with a lesser amount of p65 subunits as demonstrated by a supershift assay. IκB-α decreased in gastric cytosolic fractions over time, consistent with its degradation. These data suggest that during endotoxemia expression of the inflammatory mediator iNOS in the gastric mucosa may be upregulated by degradation of IκB-α and subsequent translocation of NF-κB into the nucleus and increased NF-κB activity.