Post-conditioning and reperfusion injury in the treatment of stroke

Abstract

Endogenous mechanisms of protection against ischemia can be demonstrated in brain and other organs. The induction of such protection is via a response to sub lethal stress which induces "preconditioning". The preconditioned organ is then "tolerant" to injury from subsequent severe stress of the same or different etiology. Protection is substantial (70% reduction) but delayed in onset and is transient. Gene expression is unique between brains preconditioned, injured (stroke) or made tolerant. Thus, preconditioning reprograms the response to lethal ischemic stress (stroke), reprogrammed from an injury induction response to a neuroprotective processes. Postconditioning refers to attenuation of injurious processes occurring during reperfusion of ischemic brain. Transient mechanical interruption of reperfusion induces post-conditioning which can attenuate reperfusion injury. Post-conditioning protects ischemic brain by decreasing reperfusion induced oxygen free radical formation. The free radicals produce injury via mitochondrial damage which can be repaired experimentally. Post-conditioning produces neuroprotection as potent as experimental preconditioning. The recognition of broad based gene silencing (suppression of thousands of genes) as the phenotype of the preconditioned, ischemic tolerant brain, may explain failure of all single target drugs for stroke. As risks of reperfusion injury accompany treatment for acute stroke, endogenous neuroprotective and repair mechanisms offer translational stroke therapy.

Keywords: Preconditioning; ischemia; post-conditioning; stroke.

FIGURE 1.

Schematic diagram showing the various permutations of ischemic challenges. For control ischemia, animals receive 100 mins of MCAO. Infarct volume is determined 24 h after the final ischemic challenge by TTC staining. Preconditioning was carried out as described previously, whereby a 30-min MCAO challenge is paired with 100 mins of MCAO after 72 h of reperfusion. Postconditioning was performed by combining 100 mins of MCAO followed by various brief ischemic durations and reperfusion periods. (From Pignataro et al. 2008)

FIGURE 2.

Nonadditive nature of pre- and postconditioning neuroprotection in the brain. (A) Schematic diagram of combined pre- and postconditioning. Animals were subject to 30 mins of MCAO, followed by 72 h reperfusion. Animals were then subject to 100 mins of MCAO, 10 mins of reperfusion, and a subsequent 10 mins of MCAO challenge. Infarct volume was determined 24 h later by TTC staining. (B) Quantification of pre-, postconditioning, and addition of pre- plus postconditioning ischemia. Note the lack of significant further protection by adding pre- and postconditioning. Data shown are mean7s.d. n=5. Data were analyzed by ANOVA with post hoc Bonferroni’s test, *P<0.01 versus 100 mins of MCAO. (From Pignataro et al. 2008)

FIGURE 3.

(A) Postconditioning is blocked by LY294002. Animals were administered LY294002, U0126, or SB203580 before ischemia and postconditioning. Infarct volume was determined 24 h later by TTC staining. Data shown are mean7s.d. n=5. Data were analyzed by ANOVA with post hoc Bonferroni’s test, *P<0.05 versus control 100 mins of MCAO, **P<0.05 versus vehicle. (B) Effect of SB203580, U0126, and LY294002 on preconditioning-induced neuroprotection. After preconditioning, vehicle or drug was administered. Animals were then subject to 100 mins of MCAO 72 h later and infarct volume determined by TTC staining. Data shown are mean7s.d., n=5. Data were analyzed by ANOVA followed by post hoc Bonferoni’s test, *P<0.05 versus 100 mins MCAO and **P<0.05 versus vehicle. (From Pignataro et al. 2008)

FIGURE 4.

Detection of mitochondrial DNA (mtDNA) damage induced by cerebral ischemia assessed by quantitative polymerase chain reaction (QPCR) amplification after 30-minute and 100-minute middle cerebral artery occlusion (MCAO) or sham (S). Repair of mtDNA damage occurs after 30-minute (but not 100-minute) MCAO. (From Chen et al. 2003)