Introduction
We and others reported the neuroprotective effect of 3-aminobenzamide (3-AB), a poly(ADP-ribose) polymerase (PARP) inhibitor in cerebral ischemia1, 2. The aim of this study was to evaluate the effect of 3-AB in transient focal cerebral ischemia performed in mice under two distinct anaesthetics: chloral hydrate (CH) and ketamine/xylazine (KX).
Materials
Male Swiss mice (27–32 g) anaesthetized i. p with ketamine (50 mg/kg) + xylazine hydrochloride (6 mg/kg) or with chloral hydrate (400 mg/kg) were subjected to a 1 h-intraluminal occlusion of the left middle cerebral artery (MCAo) followed by reperfusion. Ischemia was controlled by measuring cerebral blood flow in the MCA territory (using MoorLab® laser doppler flowmeter). Treatments with 3-AB at 40 mg/kg or with its vehicle (saline) were administered i.p 15 min prior to reperfusion and again 3 h after its onset. The functional outcome (neurological score, grip test, loss of weight) were examined 24 h after MCAo and infarct volumes were measured after triphenyltetrazolium chloride staining. In a second experiment, PARP activation was evaluated by western blotting of poly(ADP-ribose) polymers 6 hours after ischemia in the ipsilateral brain parenchyma of sham-operated animals (undergoing all the surgery except the filament insertion) and of ischemic mice given 3-AB or its vehicle.
Results
The drop in cerebral blood flow (68–72%) did not statistically differ among the four groups. The infarct volume of mice anaesthetized with CH (n=6) was increased by 27% (P<0.05) as compared with mice anaesthetized with KX (n=6). In “CH” mice, 3-AB reduced by 26% the infarct volume (n=6, P<0.05). By contrast, 3-AB (n=8) was devoid of effect in “KX” animals. None of the functional outcome was improved by 3-AB whatever the anaesthetic. In “KX” mice, ischemia induced a 2-fold increase in the level of poly(ADP-ribose) polymers in comparison with sham-operated animals (122±13 arbitrary units (n=6) vs 61±4 arbitrary units (n=6), P<0.01). This PARP activation was inhibited by 90% by 3-AB (67±11 arbitrary units (n=6), P<0.01).
Conclusion
One hour MCAo led to larger infarct volumes in mice anaesthetized with chloral hydrate. In this model, 3-AB is neuroprotective suggesting a deleterious role of PARP in cerebral ischemia. By contrast, 3-AB failed to reduce the infarct volume in ketamine+xylazine anaesthetized mice although it completely blocked PARP activation. Thus anesthesia altered the role of PARP in cerebral ischemia.