Neuro-cognitive disabilities are a well-recognized complication of hypothermic circulatory arrest. We and others have reported that prolonged
cardiac arrest (CA) produces neuronal death and microglial proliferation and activation that are only partially mitigated by
hypothermia. Microglia, and possibly other cells, are suggested to elaborate
tumor necrosis factor alpha (TNF-α), which can trigger neuronal death cascades and exacerbate
edema after CNS insults.
Minocycline is neuroprotective in some
brain ischemia models in part by blunting the microglial response. We tested the hypothesis that
minocycline would attenuate
neuroinflammation as reflected by brain tissue levels of TNF-α after hypothermic CA in rats. Rats were subjected to rapid
exsanguination, followed by a 6 min normothermic CA.
Hypothermia (30 °C) was then induced by an aortic saline flush. After a total of 20 min CA,
resuscitation was achieved via
cardiopulmonary bypass (CPB). After 5 min reperfusion,
minocycline (90 mg kg−1; n = 6) or vehicle (PBS; n = 6) was given.
Hypothermia (34 °C) was maintained for 6 h. Rats were sacrificed at 6 or 24 h. TNF-α was quantified (ELISA) in four brain regions (cerebellum, CEREB; cortex, CTX; hippocampus, HIP; striatum, STRI). Naïve rats (n = 6) and rats subjected to the same
anesthesia and CPB but no CA served as controls (n = 6). Immunocytochemistry was used to localize TNF-α. Naïve rats and CPB controls had no detectable TNF-α in any brain region. CA markedly increased brain TNF-α. Regional differences were seen, with the highest TNF-α levels in striatum in CA groups (10-fold higher, P < 0.05 vs. all other brain regions). TNF-α was undetectable at 24 h.
Minocycline attenuated TNF-α levels in CTX, HIP and STRI (P < 0.05). TNF-α showed unique co-localization with neurons. In conclusion, we report region-dependent early increases in brain TNF-α levels after prolonged hypothermic CA, with maximal increases in striatum. Surprisingly, TNF-α co-localized in neurons and not microglia.
Minocycline attenuated TNF-α by approximately 50% but did not totally ablate its production. That
minocycline decreased brain TNF-α levels suggests that it may represent a therapeutic adjunct to
hypothermia in CA neuroprotection. University of Pittsburgh IACUC 0809278B-3.