title: Microglial depletion using intrahippocampal injection of liposome-encapsulated clodronate in prolonged hypothermic cardiac arrest in rats.
abstract: Trauma patients who suffer cardiac arrest (CA) from exsanguination rarely survive. Emergency preservation and resuscitation using hypothermia was developed to buy time for resuscitative surgery and delayed resuscitation with cardiopulmonary bypass (CPB), but intact survival is limited by neuronal death associated with microglial proliferation and activation. Pharmacological modulation of microglia may improve outcome following CA. Systemic injection of liposome-encapsulated clodronate (LEC) depletes macrophages. To test the hypothesis that intrahippocampal injection of LEC would attenuate local microglial proliferation after CA in rats, we administered LEC or PBS into the right or left hippocampus, respectively. After rapid exsanguination and 6min no-flow, hypothermia was induced by ice-cold (IC) or room-temperature (RT) flush. Total duration of CA was 20min. Pre-treatment (IC, RTpre) and post-treatment (RTpost) groups were studied, along with shams (cannulation only) and CPB controls. On day 7, shams and CPB groups showed neither neuronal death nor microglial activation. In contrast, the number of microglia in hippocampus in each individual group (IC, RTpre, RTpost) was decreased with LEC vs. PBS by ∼34-46% (P<0.05). Microglial proliferation was attenuated in the IC vs. RT groups (P<0.05). Neuronal death did not differ between hemispheres or IC vs. RT groups. Thus, intrahippocampal injection of LEC attenuated microglial proliferation by ∼40%, but did not alter neuronal death. This suggests that microglia may not play a pivotal role in mediating neuronal death in prolonged hypothermic CA. This novel strategy provides us with a tool to study the specific effects of microglia in hypothermic CA.
authors.affiliation: Safar Center for Resuscitation Research, University of Pittsburgh, Pittsburgh, PA 15260, USA. drabekt@anes.upmc.edu
authors.forename: Tomas
authors.initials: T
authors.lastname: Drabek
authors.forename: Andreas
authors.initials: A
authors.lastname: Janata
authors.forename: Edwin K
authors.initials: EK
authors.lastname: Jackson
authors.forename: Brad
authors.initials: B
authors.lastname: End
authors.forename: Jason
authors.initials: J
authors.lastname: Stezoski
authors.forename: Vincent A
authors.initials: VA
authors.lastname: Vagni
authors.forename: Keri
authors.initials: K
authors.lastname: Janesko-Feldman
authors.forename: Caleb D
authors.initials: CD
authors.lastname: Wilson
authors.forename: Nico
authors.initials: N
authors.lastname: van Rooijen
authors.forename: Samuel A
authors.initials: SA
authors.lastname: Tisherman
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Kochanek
mesh_terms: D000818:Animals; D016887:Cardiopulmonary Resuscitation / Q000379:methods* / Q000401:mortality; D049109:Cell Proliferation / Q000187:drug effects; D004002:Clodronic Acid / Q000008:administration & dosage*; D004195:Disease Models, Animal; D006323:Heart Arrest / Q000401:mortality / Q000628:therapy*; D006624:Hippocampus / Q000187:drug effects / Q000473:pathology; D007036:Hypothermia, Induced / Q000379:methods*; D015552:Injections, Intralesional; D008081:Liposomes; D008297:Male; D017628:Microglia / Q000187:drug effects* / Q000473:pathology; D009410:Nerve Degeneration / Q000517:prevention & control*; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D018570:Risk Assessment; D015996:Survival Rate
chemical_list: D008081:Liposomes; D004002:Clodronic Acid