Abstract Body: Introduction
While increased awareness and advanced technologies have improved survival rates and CPR outcomes after cardiac arrest, survivors often experience lasting neurological injury. In addition to neuronal injury sustained through prolonged global ischemia, secondary brain damage occurs in the days and weeks following cardiac arrest through several related mechanisms. Recently, emphasis has been placed on post-arrest neuroinflammation, which is comprised of resident glial cell activation and infiltration of peripheral immune cells from the bloodstream. Among these, helper T cells (CD4⁺) and monocyte-derived macrophages (CD11b⁺CD45^Hi) have been identified as key therapeutic targets.
Hypothesis
The relationship between the duration of cardiac arrest and the degree of peripheral immune cell infiltration into the brain parenchyma is currently unknown. We hypothesized that rats exposed to longer cardiac arrest duration would have increased infiltration of helper T cells and monocyte-derived macrophages.
Methods
21 adult Sprague-Dawley rats (450g-550g) were randomized to receive 6, 8, or 10 minutes of asphyxial cardiac arrest and resuscitation or no cardiac arrest. 24 hours post-arrest, rats were sacrificed and brains were bisected into lateral hemispheres. One hemisphere was used for immunofluorescence microscopy evaluation of neuronal apoptosis (TUNEL and anti-Neun) and T-cell infiltration (anti-CD3 and anti-CD4), while the other hemisphere was dissected to isolate hippocampal and cortical tissue. Isolated tissues were dissociated and analyzed by flow cytometry after fluorescent antibody staining.
Results
We did not observe any significant differences in peripheral immune cell infiltration into hippocampal tissue between groups. In cortical tissue, flow cytometry analysis revealed significant differences in peripheral monocyte frequency between groups (one-way ANOVA; p=0.045). Among these, the 10-minute cardiac arrest group had the highest level of infiltration (4.0±0.6% of live cells). Immunofluorescent TUNEL staining confirmed worsening neuronal damage with increasing cardiac arrest duration.
Conclusion(s)
Our analyses found that greater cardiac arrest duration is associated with greater infiltration of peripheral monocytes in cortical tissue, but not in hippocampal tissue. While a causative association has not been established, monocyte infiltration may be a promising target for neuro-protective therapies after cardiac arrest.