Peroxynitrite enhances the ability of Salmonella dublin to invade T84 monolayers

In the intestine, epithelial cells continually produce and secrete low levels of nitric oxide (NO). Salmonella sp. invade epithelium by responding to environmental stimuli. The aims of this study were to determine the effect of reactive nitrogen intermediates (RNIs) on S. dublin and S. typhimurium growth and invasion of T84 epithelial monolayers. Intracellular NO formation was inhibited by 7-nitroindazole (7-NI) or N(G)-monomethyl-L-arginine, monoacetate (L-NMMA); extracellular NO and peroxynitrite were scavenged with ferro-hemoglobin or urate. The effect of authentic peroxynitrite (ONOO-); 3-morpholino-sydnonimine (SIN-1), which releases ONOO- via NO and superoxide; spermine NONOate, which releases only NO; or superoxide generated by xanthine oxidase and pterin on S. dublin and S. typhimurium growth and invasion were examined. Inhibition of NO synthesis and scavenging of extracellular NO or peroxynitrite reduced S. dublin invasion into T84 monolayers and enhanced bacterial growth. Pre-exposure of S. dublin to ONOO- and SIN-1 increased subsequent bacterial invasion into T84 monolayers. Conversely, exposure of bacteria to spermine NONOate or superoxide did not affect S. dublin invasion. In contrast, S. typhimurium invasion was not affected by pre-treatment with NO donors. In conclusion, exposure of S. dublin to ONOO- enhances the ability of the bacteria to invade epithelial cells. These results suggest that luminal ONOO- may have a novel role as an extracellular signal between invasive bacteria and epithelial cells.