Heme oxygenase-1 deficiency promotes severity of sepsis in a non-surgical preterm mouse model

Sepsis in preterm infants is associated with systemic inflammatory responses. The stress-response protein heme oxygenase-1 (HO-1) has protective anti-inflammatory properties. Recently, we reported a protective role of HO-1 using our non-surgical cecal slurry (CS) model in wild-type (WT) mouse pups. Here, we extend these findings to investigate the association of HO-1 deficiency with sepsis severity. Adapting the Wynn model, we induced sepsis in 4-day-old HO-1-deficient (HO-1+/−, Het) pups to determine if HO-1 deficiency affected survival rates at the LD40 (2.0 mg/g) of WT pups. To see if HO-1 induction affected sepsis severity, we gave 30-μmol heme/kg subcutaneously to 3-day-old mice 24 h prior to sepsis induction. Post-sepsis induction, Het pups had a mortality of 85.0% (n = 20) and increased expression of the pro-inflammatory gene in the livers and affected hematologic profiles. Heme treatment 24 h prior to sepsis induction significantly increased liver HO activity, reduced mortality to 24.5% (n = 17), attenuated inflammatory responses, reduced spleen bacterial counts, and significantly increased peripheral neutrophils. A partial deficiency in HO-1 increased the progression and mortality in sepsis. Furthermore, induction of HO-1 significantly reduced the mortality even in Het pups. Thus, we conclude that HO-1 plays an important role in the protection against preterm sepsis.