Inducible nitric oxide synthase (iNOS) gene deficiency increases the mortality of sepsis in mice

Background. Nitric oxide (NO) produced by the inducible isoform of NO synth ase (iNOS or NOS2) has been implicated in the hypotension, organ failure, a nd death that complicate sepsis. To avoid the confounding effects and limit ations of iNOS Inhibitors, we used iNOS gene "knockout" mice to examine the effect of inducible NO production In a model of polymicrobial abdominal se psis treated with antibiotics. We hypothesized that iNOS gene deficiency wo uld significantly alter outcome. Methods. C57BL6 wild-type (control) and congenic iNOS knockout mice were st udied concurrently. Under halothane anesthesia, the ceca were ligated with 4-0 silk suture and punctured twice with a 26-needle (cecal ligation and pu ncture, CLP). Survival was followed for 7 days, after which necropsies were performed in surviving animals. In an accompanying study examining the acu te effects of sepsis, organ injury at 18 hours after CLP as determined Dy h istology and the degree of cell death by apoptosis were examined with the u se of hematoxylin and cosin (H&E) and TUNEL staining and two- channel fluor escence-activated cell sorter (FACS) analysis. Results. Sham laparotomy produced no lethality in either knockout (n = 3) o r wild-type (n = 3) animals. Compared with survival in controls (n = 20), s urvival after CLP in iNOS knockout nice (n = 21) was significantly decrease d (P < .01 at 2 days, P = .080 at 7 days, Mantel-Haenszel log-rank test). C LP-induced nf,apoptotic cell death was significantly less in the thymus of iNOS knockout mice compared with wild-type mice. Conclusions. We conclude that iNOS gene function provides a survival benefi t in septic mice and is associated with increased sepsis-induced thymocyte apoptosis. To our knowledge, this is the first survival study examining the Effect of iNOS gene deficiency in a clinically relevant model of sepsis.