Adenovirus-mediated gene transfer to ischemic brain - Ischemic flow threshold for transgene expression

Background and Purpose-Gene therapy may be a promising approach for treatme nt of brain ischemia, although protein synthesis is generally inhibited in ischemic conditions. Our goal in this study was to examine effects of brain ischemia on transgene expression of adenovirus-mediated gene transfer to i schemic brain. Methods-Brain ischemia was produced by photochemical occlusion of the dista l middle cerebral artery of spontaneously hypertensive rats (n=15). Ninety minutes after ischemia, adenoviral vectors encoding bacterial beta -galacto sidase were injected into ipsilateral (nonischemic [I-n], peri-ischemic [I- p], and ischemic core [I-c] areas) and contralateral parietal (C) cortices. Cerebral blood flow before and during ischemia at each injected area was m easured by laser-Doppler flowmetry. Expression of transgene was detected by histochemistry for semiquantitative scoring or by biochemical assay for qu antitative analysis. Results-Blood flow to the cortex decreased to 72 +/- 10% (mean +/- SEM) at I-n, 41 +/-6% at I-p, and 23 +/-3% at I-c after 10 minutes of ischemia. Exp ression of the reporter gene was consistently detected at C and I-n at each survival period. The semiquantitative score for transgene expression decre ased according to severity of ischemia (C, 2.3; I-n, 2.6; I-p, 1.1; I-c, 0. 3; mean values). beta -Galactosidase activity detected by chemiluminescent assay revealed that the values (mean +/- SEM) in the ischemic area (I-p, 15 .9 +/-9.2 mU/mg protein; I-c, 1.3 +/-0.5) were significantly smaller than t hat of the nonischemic area (C, 45.4 +/-6.9). Analysis of cerebral blood fl ow at I-p revealed that cerebral blood flow threshold for transgene express ion was approximately 40% of the resting value. Conclusions-Adenovirus-mediated gene transfer into the ischemic brain provi ded effective expression of transgene at the nonischemic and peri-ischemic areas. Gene transfer to the ischemic brain may be a promising approach for treatment of ischemic penumbra.