Minocycline attenuates brain tissue levels of TNF-α produced by neurons after prolonged hypothermic cardiac arrest in rats

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-alpha), 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-alpha after hypothermic CA in rats. Rats were subjected to rapid exsanguination, followed by a 6 min normothermic CA. Hypothermia (30 degrees 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 degrees C) was maintained for 6 h. Rats were sacrificed at 6 or 24 h. TNF-alpha was quantified (ELISA) in four brain regions (cerebellum, CEREB; cortex, CTX; hippocampus, HIP; striatum, STRI). Naive 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-alpha. Na ve rats and CPB controls had no detectable TNF-alpha in any brain region. CA markedly increased brain TNF-alpha. Regional differences were seen, with the highest TNF-alpha levels in striatum in CA groups (10-fold higher, P < 0.05 vs. all other brain regions). TNF-alpha was undetectable at 24 h. Minocycline attenuated TNF-alpha levels in CTX, HIP and STRI (P < 0.05). TNF-alpha showed unique co-localization with neurons. In conclusion, we report region-dependent early increases in brain TNF-alpha levels after prolonged hypothermic CA, with maximal increases in striatum. Surprisingly, TNF-alpha co-localized in neurons and not microglia. Minocycline attenuated TNF-alpha by approximately 50% but did not totally ablate its production. That minocycline decreased brain TNF-alpha levels suggests that it may represent a therapeutic adjunct to hypothermia in CA neuroprotection. University of Pittsburgh IACUC 0809278B-3. (C) 2013 Elsevier Ireland Ltd. All rights reserved.