Cerebral ischemia followed by reperfusion activates numerous pathways that lead to cell death. One such pathway involves the release of large quantities of the
excitatory amino acid glutamate into the synapse and activation of
N-methyl-D-aspartate receptors. This causes an increase in mitochondrial
calcium levels ([Ca(2+)](m)) and a production of
reactive oxygen species (ROS), both of which may induce the mitochondrial permeability transition (MPT). As a consequence, there is eventual mitochondrial failure culminating in either apoptotic or necrotic cell death. Thus, agents that inhibit MPT might prove useful as therapeutic interventions in
cerebral ischemia. In this study, we have investigated the neuroprotective efficacy of the novel compound
NIM811. Similar in structure of its parent compound
cyclosporin A,
NIM811 is a potent inhibitor of the MPT. Unlike
cyclosporin A, however, it is essentially void of immunosuppressive actions, allowing the role of MPT to be clarified in
ischemia/reperfusion injury. The results of these studies demonstrate that
NIM811 provides almost 40% protection in a model of transient focal
cerebral ischemia. This was associated with a nearly 10% reduction in mitochondrial reactive species formation and 34% and 38% reduction of
cytochrome c release in core and penumbra, respectively. Treatment with
NIM811 also increased
calcium retention capacity by approximately 20%. Interestingly,
NIM811 failed to improve
ischemia-induced impairment of bioenergetics. The
neuroprotective effects of
NIM811 were not due to
drug-induced alterations in cerebral perfusion after
ischemia. Activation of MPT appears to be an important process in
ischemia/reperfusion injury and may be a therapeutic target.