Ischemic stroke

Neuroprotective effects of methanolic extract from Chuanxiong Rhizoma in mice with middle cerebral artery occlusion-induced ischemic stroke: suppression of astrocyte- and microglia-related inflammatory response

BACKGROUND

In traditional Asian medicine, dried rhizomes of Ligusticum chuanxiong Hort. (Chuanxiong Rhizoma [CR]) have long been used to treat pain disorders that affect the head and face such as headaches. Furthermore, they have been used primarily for blood circulation improvement or as an analgesic and anti-inflammatory medicine. This study aimed to investigate the neuroprotective effects of a methanol extract of CR (CRex) on ischemic stroke in mice caused by middle cerebral artery occlusion (MCAO).

METHODS

C57BL/6 mice were given a 1.5-h transient MCAO (MCAO control and CRex groups); CRex was administered in the mice of the CRex group at 1,000-3,000 mg/kg either once (single dose) or twice (twice dose) before MCAO. The mechanism behind the neuroprotective effects of CRex was examined using the following techniques: brain infarction volume, edema, neurological deficit, novel object recognition test (NORT), forepaw grip strength, and immuno-fluorescence staining.

RESULTS

Pretreating the mice with CRex once at 1,000 or 3,000 mg/kg and twice at 1,000 mg/kg 1 h before MCAO, brought about a significantly decrease in the infarction volumes. Furthermore, pretreating mice with CRex once at 3,000 mg/kg 1 h before MCAO significantly suppressed the reduction of forepaw grip strength of MCAO-induced mice. In the MCAO-induced group, preadministration of CRex inhibited the reduction in the discrimination ratio brought on by MCAO in a similar manner. CRex exhibited these effects by suppressing the activation of astrocytes and microglia, which regulated the inflammatory response.

CONCLUSIONS

This study proposes a novel development for the treatment of ischemic stroke and provides evidence favoring the use of L. chuanxiong rhizomes against ischemic stroke.

Therapeutic Role of a Cysteine Precursor, OTC, in Ischemic Stroke Is Mediated by Improved Proteostasis in Mice

Oxidative stress aggravates brain injury following ischemia/reperfusion (I/R). We previously showed that ubiquilin-1 (Ubqln1), a ubiquitin-like protein, improves proteostasis and protects brains against oxidative stress and I/R-induced brain injury. Here, we demonstrate that a small molecule compound, L-2-oxothiazolidine-4-carboxylic acid (OTC) that functions as a precursor of cysteine, upregulated Ubqln1 and protected cells against oxygen-glucose deprivation-induced cell death in neuronal cultures. Further, the administration of OTC either at 1 h prior to ischemia or 3 h after the reperfusion significantly reduced brain infarct injury and improved behavioral outcomes in a stroke model. Administration of OTC also increased glutathione (GSH) level and decreased superoxide production, oxidized protein, and neuroinflammation levels in the penumbral cortex after I/R in the stroke mice. Furthermore, I/R reduced both Ubqln1 and the glutathione S-transferase protein levels, whereas OTC treatment restored both protein levels, which was associated with reduced ubiquitin-conjugated protein level. Interestingly, in the Ubqln1 knockout (KO) mice, OTC treatment showed reduced neuroprotection and increased ubiquitin-conjugated protein level when compared to the similarly treated non-KO mice following I/R, suggesting that OTC-medicated neuroprotection is, at least partially, Ubqln1-dependent. Thus, OTC is a potential therapeutic agent for stroke and possibly for other neurological disorders and its neuroprotection involves enhanced proteostasis.

Critical Role of Nrf2 in Experimental Ischemic Stroke

Ischemic stroke is one of the leading causes of death and long-term disability worldwide; however, effective clinical approaches are still limited. The transcriptional factor Nrf2 is a master regulator in cellular and organismal defense against endogenous and exogenous stressors by coordinating basal and stress-inducible activation of multiple cytoprotective genes. The Nrf2 network not only tightly controls redox homeostasis but also regulates multiple intermediary metabolic processes. Therefore, targeting Nrf2 has emerged as an attractive therapeutic strategy for the prevention and treatment of CNS diseases including stroke. Here, the current understanding of the Nrf2 regulatory network is critically examined to present evidence for the contribution of Nrf2 pathway in rodent ischemic stroke models. This review outlines the literature for Nrf2 studies in preclinical stroke and focuses on the in vivo evidence for the role of Nrf2 in primary and secondary brain injuries. The dynamic change and functional importance of Nrf2 signaling, as well as Nrf2 targeted intervention, are revealed in permanent, transient, and global cerebral ischemia models. In addition, key considerations, pitfalls, and future potentials for Nrf2 studies in preclinical stroke investigation are discussed.

Sirtuin 6 protects the brain from cerebral ischemia/reperfusion injury through NRF2 activation

Sirtuin 6 (SIRT6), a member of the sirtuin family of NAD(+)-dependent deacetylases, has been shown to produce beneficial effects in myocardial ischemia/reperfusion (I/R). However, the role of SIRT6 in cerebral I/R is largely unclear. In this study, we investigated the effects of SIRT6 overexpression in regulating I/R injury in a mouse cerebral I/R model in vivo and in oxygen-glucose-deprivation/reoxygenation (OGD/R)-stimulated neuro-2a neuroblastoma cells in vitro. We found that cerebral I/R (1 h/24 h) resulted in decreased SIRT6 expression in the cerebral cortex (P < 0.01). SIRT6 overexpression in the brain by in vivo gene transfer enhanced the antioxidant NRF2 signaling (P < 0.05), reduced oxidative stress (P < 0.05), and attenuated cerebral I/R-induced brain tissue damage and neurological deficits (P < 0.05). These neuroprotective effects of SIRT6 overexpression were abolished in NRF2 knockout mice. In neuro-2A neuroblastoma cells, SIRT6 overexpression increased total and nuclear NRF2 levels (P < 0.05), reduced oxidative stress (P < 0.05), and attenuated OGD/R-induced cell death (P < 0.05); these protective effects were blocked by NRF2 knockdown (P < 0.05). Moreover, in OGD/R-stimulated neuro-2A cells, SIRT6 overexpression produced similar protective effects to those induced by the antioxidant NAC, but no added benefits were detected when SIRT6 overexpression was used in combination with NAC (P > 0.05). These findings provide evidence that SIRT6 can protect the brain from cerebral I/R injury by suppressing oxidative stress via NRF2 activation. Thus, SIRT6 may serve as a potential therapeutic target for ischemic stroke.

Application of cavitation promoting surfaces in management of acute ischemic stroke

High frequency, low intensity ultrasound has the potential to accelerate the clearance of thrombotic occlusion in the absence of cavitation. At high frequency ultrasound, high acoustic pressures, >5.2MPa, are required to generate cavitation in thrombus. The focus of this study was to reduce the cavitation threshold by applying materials with appropriate nucleation sites at the transducer-thrombus boundary to further augment sonothrombolysis. Heterogeneous and homogenous nucleation sites were generated on the outer surface of a polyimide tube (PI) using microfringed (MPI) and laser induced (LPI) microcavities. The cavitation threshold of these materials was determined using a passive cavitation detection system. Furthermore, the biological impact of both materials was investigated in vitro. The results revealed that both MPI and LPI have the potential to induce cavitation at acoustic pressure levels as low as 2.3MPa. In the presence of cavitation, thrombolysis rate could be enhanced by up to two times without any evidence of hemolysis that is generally associated with cavitation activities in blood. A prototype ultrasonic catheter operating at 1.7MHz frequency and acoustic pressure of 2.3MPa with either of MPI or LPI could be considered as a viable option for treatment of acute ischemic stroke.

Neuroprotective effect of green tea extract in experimental ischemia-reperfusion brain injury

Eicosanoids accumulation and formation of oxygen free radicals have been implicated in the pathogenesis of ischemia/reperfusion brain injury. In the present study, we examined whether green tea extract protects against ischemia/reperfusion-induced brain injury by minimizing eicosanoid accumulation and oxygen radical-induced oxidative damage in the brain. Green tea extract (0.5%) was orally administered to Wistar rats for 3 weeks before induction of ischemia. Ischemia was induced by the occlusion of middle cerebral arteries for 60 min and reperfusion was achieved for 24 h. Infarction volume in the ipsilateral hemisphere of ischemia/reperfusion animals was 114 +/- 16 mm(3) in the 0.5% green tea pretreated animals compared to 180 +/- 54 mm(3) in left hemisphere of nontreated animals. Green tea extract (0.5%) also reduced ischemia/reperfusion-induced eicosanoid concentration: Leukotriene C(4) (from 245 +/- 51 to186 +/- 22), prostoglandin E(2) (from 306 +/- 71 to 212 +/- 43) and thromboxane A(2) (327 +/- 69 to 251 +/- 87 ng/mg protein). Ischemia/reperfusion-induced increases of hydrogen peroxide level (from 688 +/- 76 to 501 +/- 99 nmole/mg protein), lipid peroxidation products (from 1010 +/- 110 to 820 +/- 70 nmole/mg protein) and 8-oxodG formation (from 1.3 +/- 0.3 to 0.8 +/- 0.2 ng/microg DNA, x10(-2)) were also reduced. Moreover, 0.5% green tea extract also reduced the apoptotic cell number (from 44 +/- 11 to 29 +/- 1 in the striatum, and from 72 +/- 11 to 42 +/- 5 apoptotic cells/high power field in the cortex region). Green tea extract pretreatment also promoted recovery from the ischemia/reperfusion-induced inhibition of active avoidance. The present study shows that the minimizing effect of green tea extract on the eicosanoid accumulation and oxidative damage in addition to the reduction of neuronal cell death could eventually result in protective effect on the ischemia/reperfusion-induced brain injury and behavior deficit.

Acute ischemic stroke management

The use of thrombolytic therapy represents one of many recent developments in the management of acute ischemic stroke. The development of stroke teams and protocols has been driven by these new demands for an urgent response to ischemic stroke. The short time window of 3 hours for therapy with intravenous recombinant tissue plasminogen activator requires efficient evaluation and treatment of stroke patients and also necessitates a rigorous approach to blood pressure management, electrolytes, fluids, and temperature. Anticoagulation has not been proven to safely prevent progression or early recurrence of stroke, but antiplatelet therapy is worthwhile.

Acute ischemic stroke therapy

Acute ischemic stroke is a medical emergency that requires rapid evaluation and treatment. Prehospital and emergency department care can be streamlined to meet those goals. Intravenous rt-PA therapy improves outcome in selected patients with ischemic stroke if given within 3 hours of stroke onset, but offers no benefit beyond that time window. Intra-arterial thrombolytic therapy and intravenous defibrogenating agents may also be beneficial in selected patients. Newer thrombolytic agents such as aspirin and heparin in acute ischemic stroke treatment have been clarified by recent trials.