AMP-dependent hypothermia affords protection from ischemic brain injury

Abstract

In light of the relevance of therapeutic hypothermia to stroke treatment, we investigated whether 5'-adenosine monophosphate (AMP)-dependent cooling affords protection from ischemic brain injury. We show that hypothermia by AMP is because of adenosine A1 receptor (A1R) activation and is not invariantly associated with hypotension. Inhibition of ecto-5'-nucleotidase-dependent constitutive degradation of brain extracellular AMP by methylene-ADP (AMPCP) also suffices to prompt A1R-dependent hypothermia without hypotension. Both intraischemic and postischemic hypothermia by AMP or AMPCP reduce infarct volumes and mortality of mice subjected to transient middle cerebral artery occlusion. Data disclose that AMP-dependent hypothermia is of therapeutic relevance to treatment of brain ischemia.

Figure 1

5′-Adenosine monophosphate (AMP) induces hypothermia in mice by activating hypothalamic adenosine A1 receptor (A1R). (A) Effects of different doses of AMP on body temperature (Tb). The effect of DPCPX (0.1 mg/kg intraperitoneally, 5 minutes pretreatment) on hypothermia by 50 mg/kg AMP is also shown. (B) Effects of AMP on blood pressure in mice. (C) Effects of the 5′-nucleotidase inhibitor AMPCP injected intracerebroventricularly on Tb of mice. The hypothermic effect or AMP (50 mg/kg intraperitoneally) is shown for comparison. (C, inset) Effect of DPCPX (0.1 mg/kg intraperitoneally) on hypothermia by AMPCP (50 μg intracerebroventricularly) 40 minutes after drug injection. (D) Effects of AMPCP on blood pressure in mice. Drugs were injected at T=0 (A, C) or T=5 minutes (B, D arrow). For all graphs, each point/column represents the mean±s.e.m., at least eight animals per group were used. *P<0.05, ***P<0.001 versus vehicle.

Figure 2

Effect of 5′-adenosine monophosphate (AMP) and AMPCP on ischemic brain injury and survival in mice. Effect of intraischemic injection of AMP (50 mg/kg intraperitoneally) on brain infarct areas and volumes (A) of mice subjected to 1 hour middle cerebral artery occlusion (MCAo)/23 hours reperfusion. Ischemic neuroprotection is lost in mice receiving AMP and artificially kept at 37°C. Effect of intraischemic injection of AMPCP (50 μg intracerebroventricularly) on brain infarct areas and volumes (B) of mice subjected to 1 hour MCAo/23 hours reperfusion. Ischemic neuroprotection is lost in mice receiving AMPCP and artificially kept at 37°C. Body temperature (Tb) of mice subjected to 1 hour MCAo and posttreatment protocols of 10 hours hypothermia/24 hours reperfusion (C) or 24 hours hypothermia/72 hours reperfusion (D) obtained with AMP injections (arrows) of 50 mg/kg intraperitoneally every 90 minutes. The effect of posttreatment protocols of 10 hours hypothermia/24 hours reperfusion or 24 hours hypothermia/72 hours reperfusion on ischemic areas and volumes is shown in (E) and (F), respectively. Effects of protocols of intraischemic (G) or postischemic (24 hours) (H) hypothermia by AMP on survival of mice subjected to 1 hour MCAo. (A, B) Each point/column represents the mean±s.e.m., of at least eight animals per group. **P<0.01, ***P<0.001 versus control (CRL). (E, F) Each point/column represents the mean±s.e.m., of at least eight animals per group. (G, H) Each line represents survival of groups of 10 ischemic mice. *P<0.05, **P<0.01 versus control (CRL).