Development of an improved murine model of necrotizing enterocolitis shows the importance of neutrophils in NEC pathogenesis.

Various research models to induce necrotizing enterocolitis (NEC) in animals exist, yet significant differences in NEC severity between murine animal models and human patients persist. One possible explanation for the difference in severity may be the variance in neutrophil concentration among newborn humans (50-70%) in comparison to neonatal mice (10-25%). However, neutrophil activity has yet to be evaluated in NEC pathogenesis. Thus, the aim of the study was to evaluate the effects of altered neutrophil concentrations in neonatal mice while simultaneously undergoing a NEC induction. A total of 44 neonatal mice were included in this study and 40 were subjected to an established NEC induction paradigm and 4 were assigned a sham group. Of the 40 mice, 30 received granulocyte-colony stimulating factor (G-CSF) on a daily basis, while 10 were used as controls (receiving inactivated G-CSF). Mice undergoing G-CSF treatment were further divided into two subgroups: (1) wildtype and (2) ELANE-knockout (KO). ELANE - KO mice are incapable of producing neutrophil elastase (NE) and were used to evaluate the role of neutrophils in NEC. For each of the groups, the following metrics were evaluated: survival, NEC severity, tissue damage, neutrophil count and activation, and NETs formation. An improved murine model of NEC was developed using (1) Lipopolysaccharides and Neocate gavage feeding, (2) hypoxia, and (3) G-CSF administration. The results suggest that the addition of G-CSF resulted in significantly elevated NEC manifestation rates with consequent tissue damage and intestinal inflammation, without affecting overall mortality. Animals without functioning NE (ELANE-KO) appeared to have been protected from NEC development. This study supports the importance of neutrophils in NEC pathogenesis. The optimized NEC induction paradigm, using G-CSF administration, resulted in elevated neutrophil counts, resembling those of neonatal humans. Elevation of neutrophil levels significantly improved NEC disease manifestation by modeling human physiology more accurately than current NEC models. Thus, in the future, murine NEC experiments should include the elevation of neutrophil levels to improve the transition of research findings from mice to humans.