Background
Cilostazol, a specific phosphodiesterase-3 inhibitor, has been used for atherosclerotic stroke. Another anti-platelet agent, aspirin, is strongly recommended for treating acute ischemic stroke, but the effect of cilostazol has not been approved for use in the acute stage. In the current study, we sought to examine the potential effects of cilostazol on the cerebral infarction and on the functional outcome by using a newly developed mouse model of cerebral infarction which appeared neurogenesis after stroke 1 . The model is highly reproducible and survives for more than twelve weeks, and allows us to estimate the effect of cilostazol given immediately after the onset on the chronic phase of stroke.
Methods
Adult male severe combined immune deficiency (SCID) mice were used in this study. One hour after permanent left middle cerebral artery (MCA) occlusion, cilostazol (60 mg/kg, n=8) and aspirin (60 mg/kg, n=9) suspended with Arabian gum was administrated orally five times within 48 hours. Arabian gum only (n=9) were given as controls. All mice were reared under the free eating baits mixed with each drug (1% of concentration) during the whole post-stroke period. Brain damage was assessed continuously with brain MRI. Brain function was assessed behaviorally at 35 days after MCA occlusion. To examine the neuronal regeneration, mice were perfused with fixative at day 42, and brain was removed. Immunohistochemistry for MAP2, NeuN and PSA-NCAM was performed using vibratome sections.
Results
The brain damage of all mice examined was restricted to cerebral cortex, when judged by ADC and T2-weighted MRI image. The infract volume was almost same among three groups until day 3 of post-stroke (day 0: 40 mm3, day 1: 50 mm3, day 3: 30 mm3). The residual volume of ipsilateral cortex also was same among the groups on day 14 and 28, but on day 28 the volume of ipsilateral striatum of mice treated with cilostazol was significantly increased compared with those of other two groups (6.5 vs. 5.7 mm3) (P<0.05). Mice treated with cilostazol showed significantly lower locomotor activity than other two groups. Water maze test revealed impared working memory in all groups of mice at 35 days post-stroke, but mice treated with cirostazol showed significantly better memory than mice treated with aspirin. Immunohistochemistry revealed the expression of small NeuN-positive neuronal progenitor cells located in the corpus callosum of post-stroke brain on day 14 and 28. The number of these cells was higher in cilostazol groups, suggesting that treatment with cilostazol after stroke enhanced neurogenesis.
Conclusion
These data suggest that administration of cilostazol in acute phase of ischemic stroke is potentially useful as a therapeutic maneuver through the improvement of local cerebral blood flow and acceleration of neurogenesis. Our previous data have shown that neovascularization by transfusion of endothelial stem cells (CD34+) enhances neurogenesis in the same model of infarction 1 . Although the precise mechanism is unclear, it is suggested that an increase in cAMP level in endothelial cells contributes to this effects.