Rapid loss of perihematomal cell viability in the collagenase intracerebral hemorrhage model.

The effective time window of any therapeutic in an experimental stroke model is limited by the rate of injury progression. Intracerebral hemorrhage in rodents is commonly induced by striatal injection of either autologous blood or bacterial collagenase, which digests local blood vessels. During time window studies of the heme oxygenase-1 inducer hemin, which is protective when administered within 1-3 h in both models, the rate of perihematomal injury was directly compared after striatal blood or collagenase injection. Surprisingly, about 80% of the loss of perihematomal cell viability as measured by MTT reduction assay occurred within 6 h of collagenase injection. In contrast, significant viability loss was not observed at this time point after autologous blood injection, but rather it progressed over the subsequent four days to a level similar to that produced by collagenase. Consistent with these observations, systemic hemin therapy reduced blood-brain barrier disruption and perihematomal cell injury when initiated at 6 h after striatal injection of blood but not collagenase. These results indicate that the rate of early cell injury differs markedly in the collagenase and blood injection ICH models, which may contribute to inconsistent results in time window studies. The blood injection model may be more appropriate for prolonged time window studies of a neuroprotective agent.