Cell permeable exogenous ceramide reduces infarct size in spontaneously hypertensive rats supporting in vitro studies that have implicated ceramide in induction of tolerance to ischemia

Previous work in primary cell culture has shown that TNF-alpha: and ceramid e are involved in the signaling that induces tolerance to brain ischemia (G inis et al., 1999; Liu et al., 2000). To validate the in vitro studies, the authors administered cell permeable analogs of ceramides intracisternally or intravenously to examine their effect on neuroprotection after focal cer ebral ischemia. Permanent middle cerebral artery occlusion (MCAO) was perfo rmed in spontaneously hypertensive rats. Infarct volumes were assessed at 2 4 hours after surgery. D-erythro-N-acetylsphingosine (C2-ceramide) or its v ehicle was infused intracisternally for 1 hour before MCAO. In a second set of studies, D-erythro-N-octanoylsphingosine (C8-ceramide) or its vehicle w as injected intravenously 48 or 24 hours before MCAO to mimic preconditioni ng (PC) and was also injected 5 minutes after MCAO. C2-ceramide infusion si gnificantly reduced infarct volumes by approximately 14% (P < 0.05). C2-cer amide injection reduced infarct volumes approximately 17% compared with con trols. This effect was constant and significant compared with controls over the time periods examined (P < 0.01). This work supports findings in prima ry brain cell cultures that implicate ceramide as a downstream signal that is proximate to development of tolerance to brain ischemia. Because the deg ree of protection represents approximately 50% of the maximal infarct reduc tion observed in this model, there are probably additional signaling pathwa ys that subserve tolerance.