Abstract 3602: Inhibition of Soluble Epoxide Hydrolase Improves Neuronal Survival after Cardiac Arrest and Alters Microglial Activation towards a Neuroprotective Phenotype
Introduction: Ischemia/reperfusion during cardiac arrest and cardiopulmonary resuscitation (CA/CPR) causes significant neuronal death and leads to long-term functional deficits. While neuronal death in the hippocampus is one likely cause of memory loss after CA/CPR, the local inflammatory milieu present after CA/CPR also contributes to functional deficit. However, the signaling pathways involved in the inflammatory response are poorly understood. Microglia, the brain resident immune cells, are activated in response to different types of brain injury. We hypothesized that CA/CPR activates microglia, which then contribute to subsequent neuronal loss and functional deficit. We tested whether pharmacologic inhibition of the pro-inflammatory enzyme soluble epoxide hydrolase (sEH) alters microglial activation and neuronal death in a mouse model of CA/CPR.
Methods: Male adult C57Bl/6 mice underwent 8 minutes of CA followed by CPR. The sEH inhibitor 4-phenylchalcone oxide (4-PCO; 5 mg/kg ip) was administered at 5 minutes and 24 hours after CA/CPR. Microglial activation was assessed histologically by immunostaining for the activation marker Mac-2 at 24 and 72 hours after CA/CPR. Surviving CA1 hippocampal neurons were counted at 72 hours after CA/CPR. Hippocampal expression of inflammatory cytokines was measured by quantitative RT-PCR.
Results: Phenotypically activated microglia expressing Mac-2 appeared in the hippocampus as early as 24 hours after CA/CPR, before significant neuronal death was present. Concurrently, expression of the pro-inflammatory cytokines tumor necrosis factor (TNF)-α and interleukin (IL)-1β increased. In animals treated with 4-PCO, hippocampal expression of the anti-inflammatory cytokine IL-10 was significantly increased (2-fold vs. vehicle), while expression of pro-inflammatory TNF- α and IL-1 β was unchanged. Subsequent death of CA1 neurons at 72 hours after CA/CPR was significantly reduced in animals treated with 4-PCO (34+/-3.7% 4-PCO vs. 52+/-7.1% vehicle), whereas the number of Mac-2 positive microglia was unchanged.
Conclusions: Microglia are activated and produce pro-inflammatory cytokines early after CA/CPR. Inhibition of sEH induces hippocampal expression of anti-inflammatory and neuroprotective IL-10 and reduces subsequent neuronal death after CA/CPR, without altering the number of phenotypically activated Mac-2 positive microglia or expression of pro-inflammatory cytokines in the hippocampus. This suggests that sEH inhibition may alter gene expression in activated microglia after brain ischemia, thus protecting neurons and maintaining function. IL-10 induction by sEH inhibition is a promising therapeutic approach after ischemic brain injury from CA/CPR.
- © 2012 by American Heart Association, Inc.