Mild and deep hypothermia differentially affect cerebral neuroinflammatory and cold shock response following cardiopulmonary bypass in rat.

Introduction: Targeted temperature management (TTM) is considered to be a neuroprotective strategy during cardiopulmonary bypass (CPB) assisted procedures, possibly through the activation of cold shock proteins. We therefore investigated the effects of mild compared with deep hypothermia on the neuroinflammatory response and cold shock protein expression after CPB in rats.

Methods: Wistar rats were subjected to 1 hr of mild (33 °C) or deep (18 °C) hypothermia during CPB or sham procedure. PET scan analyses using TSPO ligand [C]PBR28 were performed on day 1 (short-term) or day 3 and 7 post-procedure (long-term) to assess neuroinflammation. Hippocampal and cortical samples were obtained at day 1 in the short-term group and at day 7 in the long-term group. mRNA expression of M1 and M2 microglia associated cytokines was analysed with RT-PCR. Cold shock protein RNA-binding motive 3 (RBM3) and tyrosine receptor kinase B (TrkB) receptor protein expression were determined with Western Blot and quantified.

Results: In both groups target temperature was reached within an hour. Standard uptake values (SUV) of [C]PBR28 in CPB rats at 1 day and 3 days were similar to that of sham animals. At 7 days after CPB the SUV was significantly higher in amygdala and hippocampal regions of the CPB 18 °C group as compared to the CPB 33 °C group. No differences were observed in the expression of M1 and M2 microglia-related cytokines between TTM 18 °C and 33 °C. RBM3 protein levels in cortex and hippocampus were significantly higher in CPB 33 °C compared to CPB 18 °C and sham 33 °C, at day 1 and day 7, respectively.

Conclusions: TTM at 18 °C increased the neuroinflammatory response in amygdala and hippocampus compared to TTM at 33 °C in rats undergoing a CPB procedure. Additionally, TTM at 33 °C induced increased expression of TrkB and RBM3 in cortex and hippocampus of rats on CPB compared to TTM at 18 °C. Together, these data indicate that neuroinflammation is alleviated by TTM at 33 °C, possibly by recruiting protective mechanisms through cold shock protein induction.