Post-conditioning and reperfusion injury in the treatment of stroke

Commentary: Can astrocytic mitochondria therapy be used as antioxidant conditioning to protect neurons?

In the context of central nervous system (CNS) disease, oxidative stress may cause progression of cell death and neuroinflammation. Therefore, restoring mitochondrial antioxidant ability within cells is a major therapeutic strategy in many CNS disorders. A recent study uncovers a novel mechanism of astrocytic mitochondria being neuroprotective after intracerebral hemorrhage in mice. In their work, systemic administration of mitochondria obtained from astrocytes restores neuronal antioxidant defense, prevents neuronal death while promoting neurite outgrowth, indicating that extracellular mitochondria may play key roles in mediating beneficial non-cell autonomous effects. Given that mitochondria are also responsible for tolerance to stress and injury, is it possible that exogenous mitochondria signals may regulate cellular conditioning by boosting antioxidant ability? Further studies are warranted to build on these emerging findings in the pursuit of conditioning therapies mediated by mitochondrial transplantation in CNS injury and disease.

rt-PA with remote ischemic postconditioning for acute ischemic stroke

Objective

To investigate the feasibility and safety of remote ischemic postconditioning (RIPC) in acute ischemic stroke patients after intravenous recombinant tissue plasminogen activator (rt‐PA) thrombolysis (IVT).

Methods

We performed a pilot randomized trial involving acute ischemic stroke patients with IVT. The patients were randomized 1:1 to receive RIPC or standard medical therapy. In the RIPC group, the participants underwent instant RIPC within 2 h of IVT, followed by repeated RIPC therapy for 7 days. The feasibility end point was the completion of RIPC and time from the first RIPC to finishing IVT in the RIPC group. The safety end point included tissue and neurovascular injury resulting from RIPC, changes in vital signs, level of plasma myoglobin, any hemorrhagic transformation, and other adverse events.

Results

Thirty patients (15 RIPC and 15 Control) were recruited after IVT. The mean age was 65.7 ± 10.2 years, with a National Institutes of Health Stroke Scale (NIHSS) score of 6.5 (4.0–10.0). The completion rate for RIPC was 97.0%. The mean time from first RIPC to completing IVT was 66.0 (25.0–75.0) min in the RIPC group. One case of hemorrhagic transformation was observed in the RIPC group. No significant difference was found in the level of myoglobin between the two groups (P > 0.05).

Interpretation

RIPC is effective and safe for AIS patients after intravenous rt‐PA thrombolysis.

Remote ischemic conditioning for acute stroke patients treated with thrombectomy

Objective

Remote ischemic conditioning (RIC) has been demonstrated to be safe and feasible for patients with acute ischemic stroke (AIS), as well as for those receiving intravenous thrombolysis. We assessed the safety and feasibility of RIC for AIS patients undergoing endovascular treatment (ET).

Methods

We conducted a pilot study with patients with AIS who were suspected of having an emergent large‐vessel occlusion in the anterior circulation and who were scheduled for ET within 6 hours of ictus. Four cycles of RIC were performed before recanalization, immediately following recanalization, and once daily for the subsequent 7 days. The primary outcome was any serious RIC‐related adverse events.

Results

Twenty subjects, aged 66.1 ± 12.1 years, were recruited. No subject experienced serious RIC‐related adverse events. The intracranial pressure, cranial perfusion pressure, mean arterial pressure, heart rate, middle cerebral artery peak systolic flow velocity, and pulsatility index did not change significantly before, during, or after the limb ischemia (P > 0.1 for all). Of 80 cycles, 71 (89%) were completed before recanalization and 80 (100%) were completed immediately after recanalization; 444 of 560 cycles (78%) were completed within 7 days posttreatment. No patients had to stop RIC because it affected routine clinical managements. Six subjects (30%) experienced intracerebral hemorrhage, which was symptomatic in one case (5%). At the 3‐month follow‐up, 11 subjects (55%) had achieved functional independence, and two subjects (10%) died.

Interpretation

RIC appears to be safe and feasible for patients with AIS undergoing ET. Investigations are urgently needed to determine the efficacy of RIC in this patient population.

Pharmacologic Protection of Mitochondrial DNA Integrity May Afford a New Strategy for Suppressing Lung Ischemia-Reperfusion Injury

Lung ischemia-reperfusion (IR) injury contributes to post-transplant complications, including primary graft dysfunction. Decades of reports show that reactive oxygen species generated during lung IR contribute to pulmonary vascular endothelial barrier disruption and edema formation, but the specific target molecule(s) that "sense" injury-inducing oxidant stress to activate signaling pathways culminating in pathophysiologic changes have not been established. This review discusses evidence that mitochondrial DNA (mtDNA) may serve as a molecular sentinel wherein oxidative mtDNA damage functions as an upstream trigger for lung IR injury. First, the mitochondrial genome is considerably more sensitive than nuclear DNA to oxidant stress. Multiple studies suggest that oxidative mtDNA damage could be transduced to physiologic dysfunction by pathways that are either a direct consequence of mtDNA damage per se or involve formation of proinflammatory mtDNA damage-associated molecular patterns. Second, transgenic animals or cells overexpressing components of the base excision DNA repair pathway in mitochondria are resistant to oxidant stress-mediated pathophysiologic effects. Finally, published and preliminary studies show that pharmacologic enhancement of mtDNA repair or mtDNA damage-associated molecular pattern degradation suppresses reactive oxygen species-induced or IR injury in multiple organs, including preclinical models of lung procurement for transplant. Collectively, these findings point to the interesting prospect that pharmacologic enhancement of DNA repair during procurement or ex vivo lung perfusion may increase the availability of lungs for transplant and reduce the IR injury contributing to primary graft dysfunction.

DNA damage related crosstalk between the nucleus and mitochondria

The electron transport chain is the primary pathway by which a cell generates energy in the form of ATP. Byproducts of this process produce reactive oxygen species that can cause damage to mitochondrial DNA. If not properly repaired, the accumulation of DNA damage can lead to mitochondrial dysfunction linked to several human disorders including neurodegenerative diseases and cancer. Mitochondria are able to combat oxidative DNA damage via repair mechanisms that are analogous to those found in the nucleus. Of the repair pathways currently reported in the mitochondria, the base excision repair pathway is the most comprehensively described. Proteins that are involved with the maintenance of mtDNA are encoded by nuclear genes and translocate to the mitochondria making signaling between the nucleus and mitochondria imperative. In this review, we discuss the current understanding of mitochondrial DNA repair mechanisms and also highlight the sensors and signaling pathways that mediate crosstalk between the nucleus and mitochondria in the event of mitochondrial stress.

Ischemia-reperfusion Injury in the Brain: Mechanisms and Potential Therapeutic Strategies

Ischemia-reperfusion injury is a common feature of ischemic stroke, which occurs when blood supply is restored after a period of ischemia. Reperfusion can be achieved either by thrombolysis using thrombolytic reagents such as tissue plasminogen activator (tPA), or through mechanical removal of thrombi. Spontaneous reperfusion also occurs after ischemic stroke. However, despite the beneficial effect of restored oxygen supply by reperfusion, it also causes deleterious effect compared with permanent ischemia. With the recent advancement in endovascular therapy including thrombectomy and thrombus disruption, reperfusion-injury has become an increasingly critical challenge in stroke treatment. It is therefore of extreme importance to understand the mechanisms of ischemia-reperfusion injury in the brain in order to develop effective therapeutics. Accumulating experimental evidence have suggested that the mechanisms of ischemia-reperfusion injury include oxidative stress, leukocyte infiltration, platelet adhesion and aggregation, complement activation, mitochondrial mediated mechanisms, and blood-brain-barrier (BBB) disruption, which altogether ultimately lead to edema or hemorrhagic transformation (HT) in the brain. Potential therapeutic strategies against ischemia-reperfusion injury may be developed targeting these mechanisms. In this review, we briefly discuss the pathophysiology and cellular and molecular mechanisms of cerebral ischemia-reperfusion injury, and potential therapeutic strategies.

Ischemic preconditioning protects the brain against injury via inhibiting CaMKII-nNOS signaling pathway

Although studies have shown that cerebral ischemic preconditioning (IPC) can ameliorate ischemia/reperfusion (I/R) induced brain damage, but its precise mechanisms remain unknown. Therefore, the aim of this study was to investigate the neuroprotective mechanisms of IPC against ischemic brain damage induced by cerebral I/R and to explore whether the Calcium/calmodulin-dependent protein kinase II (CaMKII)-mediated up-regulation of nNOS ser847-phosphorylation signaling pathway contributed to the protection provided by IPC. Transient global brain ischemia was induced by 4-vessel occlusion in adult male Sprague-Dawley rats. The rats were pretreated with 3 min of IPC alone or KN62 (selective antagonist of CaMKII) treatment before IPC, after reperfusion for 3 days, 6 min ischemia was induced. Cresyl violet staining was used to examine the survival of hippocampal CA1 pyramidal neurons. Immunoblotting was performed to measure the phosphorylation of CaMKII, nNOS, c-Jun and the expression of FasL. Immunoprecipitation was used to examine the binding between PSD95 and nNOS. The results showed that IPC could significantly protect neurons against cerebral I/R injury, furthermore, the combination of PSD95 and nNOS was increased, coinstantaneously the phosphorylation of CaMKII and nNOS (ser847) were up-regulated, however the activation of c-Jun and FasL were reduced. Conversely, KN62 treatment before IPC reversed all these effects of IPC. Taken together, the results suggest that IPC could diminish ischemic brain injury through CaMKII-mediated up-regulation of nNOS ser847-phosphorylation signaling pathway.