Interleukin-18 does not influence infarct volume or functional outcome in the early stage after transient focal brain ischemia in mice

Targeting pyroptosis to treat ischemic stroke: From molecular pathways to treatment strategy

Ischemic stroke is the primary reason for human disability and death, but the available treatment options are limited. Hence, it is imperative to explore novel and efficient therapies. In recent years, pyroptosis (a pro-inflammatory cell death characterized by inflammation) has emerged as an important pathological mechanism in ischemic stroke that can cause cell death through plasma membrane rupture and release of inflammatory cytokines. Pyroptosis is closely associated with inflammation, which exacerbates the inflammatory response in ischemic stroke. The level of inflammasomes, GSDMD, Caspases, and inflammatory factors is increased after ischemic stroke, exacerbating brain injury by mediating pyroptosis. Hence, inhibition of pyroptosis can be a therapeutic strategy for ischemic stroke. In this review, we have summarized the relationship between pyroptosis and ischemic stroke, as well as a series of treatments to attenuate pyroptosis, intending to provide insights for new therapeutic targets on ischemic stroke.

Ameliorative effects of Portulaca oleracea L. (purslane) and its active constituents on nervous system disorders: A review

Nowadays, the global interest in the use of herbal medicines and their main components in developing novel effective medications with fewer adverse effects is rising. Precise medicinal plants have potential advantageous applications for several neurodegenerative disorders. Portulaca oleracea L. (purslane) belongs to the Portulacaceae Juss family. In folk medicine, it has been used as a febrifuge, antiseptic, vermifuge, and in treating arthritis, burns, cough, headache, intestine, stomach, liver disorders, as well as shortness of breath. Pharmacological investigations have also disclosed its antioxidant, anti-inflammatory, anti-apoptotic, immunomodulatory, antidepressant, anxiolytic, and neuroprotective properties. The current work prepared an updated and broad literature review on purslane highlighting its therapeutic effects on some nervous system disorders. It has been shown that P. oleracea and its active constituents have considerable neuroregenerative, neuroprotective, and antinociceptive properties. Accordingly, our team classified and discussed the outcomes of some nervous system disorders comprising Alzheimer's disease, Parkinson's disease, depression, epilepsy, anxiety, psychosis, drug dependence, hypoxia, and pain; although, additional preclinical and clinical assessments are necessary to reinforce the beneficial effects of purslane on nervous system disorders.

Inhibiting the PGE2 Receptor EP2 Mitigates Excitotoxicity and Ischemic Injury

Prostaglandin E2 (PGE2) is elevated in the brain by excitotoxic insults and, in turn, aggravates the neurotoxicity mainly through acting on its Gαs-coupled receptor EP2, inspiring a therapeutic strategy of targeting this key proinflammatory pathway. Herein, we investigated the effects of several highly potent and selective small-molecule antagonists of the EP2 receptor on neuronal excitotoxicity both in vitro and in vivo. EP2 inhibition by these novel compounds largely decreased the neuronal injury in rat primary hippocampal cultures containing both neurons and glia that were treated with N-methyl-d-aspartate and glycine. Using a bioavailable and brain-permeant analogue TG6-10-1 that we recently developed to target the central EP2 receptor, we found that the poststroke EP2 inhibition in mice decreased the neurological deficits and infarct volumes as well as downregulated the prototypic inflammatory cytokines in the brain after a transient ischemia. Our preclinical findings together reinforced the notion that targeting the EP2 receptor represents an emerging therapeutic strategy to prevent the neuronal injury and inflammation following ischemic stroke.

Interleukin-18 from neurons and microglia mediates depressive behaviors in mice with post-stroke depression

Post-stroke depression (PSD) is a common and serious complication that is affecting one thirds of stroke patients which leaves them with a poor quality of life, high mortality rate, high recurrent rate, and slow recovery. Recent studies showed that serum interleukin-18 (IL-18) level is a biomarker for patients with PSD. However, the role of IL-18 in the pathology of PSD is still unclear. In this study, we demonstrated that the IL-18 level in the ischemic brain significantly increased in mice with depression-like behaviors that were caused by the combined use of chronic spatial restraint stress and middle cerebral artery occlusion. Interestingly, IL-18 expression was mainly found in neurons at early phase and in microglia at a later phase. Injection of the exogenous IL-18 into the amygdala, but not the hippocampus or the striatum caused severe depression-like behaviors. On the contrary, the blockage of endogenous IL-18 by IL-18 binding protein, a specific antagonist of IL-18, repressed depressive phenotypes in SIR mice. IL-18 KO mice exhibited the resistance to spatial restraint stress and cerebral ischemia injury. Finally, we found that IL-18 mediated depressive behaviors by the interaction of IL-18 receptor and NKCC1, a sodium-potassium chloride co-transporter that is related to GABAergic inhibition. Administration of NKCC1 antagonist bumetanide exerted a therapeutic effect on the in IL-18-induced depressive mice. In conclusion, we demonstrated that increased IL-18 in the brain causes depression-like behaviors by promoting the IL-18 receptor/NKCC1 signaling pathway. Targeting IL-18 and its downstream pathway is a promising strategy for the prevention and treatment of PSD.

Uric Acid Treatment After Stroke Prevents Long-Term Middle Cerebral Artery Remodelling and Attenuates Brain Damage in Spontaneously Hypertensive Rats

Hypertension is the most important modifiable risk factor for stroke and is associated with poorer post-stroke outcomes. The antioxidant uric acid is protective in experimental normotensive ischaemic stroke. However, it is unknown whether this treatment exerts long-term protection in hypertension. We aimed to evaluate the impact of transient intraluminal middle cerebral artery (MCA) occlusion (90 min)/reperfusion (1-15 days) on brain and vascular damage progression in adult male Wistar-Kyoto (WKY; n = 36) and spontaneously hypertensive (SHR; n = 37) rats treated (i.v./120 min post-occlusion) with uric acid (16 mg kg^-1) or vehicle (Locke's buffer). Ischaemic brain damage was assessed longitudinally with magnetic resonance imaging and properties of MCA from both hemispheres were studied 15 days after stroke. Brain lesions in WKY rats were associated with a transitory increase in circulating IL-18 and cerebrovascular oxidative stress that did not culminate in long-term MCA alterations. In SHR rats, more severe brain damage and poorer neurofunctional outcomes were coupled to higher cortical cerebral blood flow at the onset of reperfusion, a transient increase in oxidative stress and long-lasting stroke-induced MCA hypertrophic remodelling. Thus, stroke promotes larger brain and vascular damage in hypertensive rats that persists for long-time. Uric acid administered during early reperfusion attenuated short- and long-term brain injuries in both normotensive and hypertensive rats, an effect that was associated with abolishment of the acute oxidative stress response and prevention of stroke-induced long-lasting MCA remodelling in hypertension. These results suggest that uric acid might be an effective strategy to improve stroke outcomes in hypertensive subjects.

A possible molecular mechanism of hearing loss during cerebral ischemia in mice

Ischemic brain stroke is a leading cause of disability and includes hearing loss. Clinical reports have also suggested that there is hearing loss in stroke patients but the mechanism was not determined. Therefore, we hypothesized that hearing loss after cerebral ischemia may be associated with changes to the synapse, gap junction, and sodium channel (NaC) proteins. Ischemia-reperfusion injury was induced in wild-type mice (I/R group). The lesion volume was determined by 2,3,5-triphenyltetrazolium chloride (TTC) staining of the brain sections. BBB disruption was confirmed by Evans blue staining and leakage of bovine serum albumin labeled with fluorescein isothiocyanate (BSA-FITC). We found that brain edema, infarct size, and permeability were increased in ischemic mice as compared with the sham-operated group. Caspase-3, caspase-9, and TUNEL-positive cells were increased in I/R mice, indicating neuronal apoptosis. Moreover, there were increased expressions of matrix metalloprotease's (MMP-2, -3, -9, and -13), interleukin (IL)-6, and decreased expressions of tight junction proteins (TJP) in the I/R group, as compared with the sham group, which signifies inflammation and BBB disruption. We also observed decreased levels of post-synaptic density protein-95 (PSD-95), synapse-associated protein 97 (SAP-97), connexin-43, NaC-α, and NaC-β, and increased expression of connexin-45, whereas no substantial change was observed in connexin-26 expression in the I/R group. Interestingly, auditory response was reduced in the I/R mice, indicating hearing loss. These data suggest that hearing loss in ischemic mice was primarily due to alterations in connexin, synapses, and NaC channels.

Delayed brain ischemia tolerance induced by electroacupuncture pretreatment is mediated via MCP-induced protein 1

BACKGROUND

Emerging studies have demonstrated that pretreatment with electroacupuncture (EA) induces significant tolerance to focal cerebral ischemia. The present study seeks to determine the involvement of monocyte chemotactic protein-induced protein 1 (MCPIP1), a recently identified novel modulator of inflammatory reactions, in the cerebral neuroprotection conferred by EA pretreatment in the animal model of focal cerebral ischemia and to elucidate the mechanisms of EA pretreatment-induced ischemic brain tolerance.

METHODS

Twenty-four hours after the end of the last EA pretreatment, focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) for 90 minutes in male C57BL/6 mice and MCPIP1 knockout mice. Transcription and expression of MCPIP1 gene was monitored by qRT-PCR, Western blot and immunohistochemistry. The neurobehavioral scores, infarction volumes, proinflammatory cytokines and leukocyte infiltration in brain and NF-κB signaling were evaluated after ischemia/reperfusion.

RESULTS

MCPIP1 protein and mRNA levels significantly increased specifically in mouse brain undergoing EA pretreatment. EA pretreatment significantly attenuated the infarct volume, neurological deficits, upregulation of proinflammatory cytokines and leukocyte infiltration in the brain of wild-type mice after MCAO compared with that of the non-EA group. MCPIP1-deficient mice failed to evoke EA pretreatment-induced tolerance compared with that of the control MCPIP1 knockout group without EA treatment. Furthermore, the activation of NF-κB signaling was significantly reduced in EA-pretreated wild-type mice after MCAO compared to that of the non-EA control group and MCPIP1-deficient mice failed to confer the EA pretreatment-induced inhibition of NF-κB signaling after MCAO.

CONCLUSIONS

Our data demonstrated that MCPIP1 deficiency caused significant lack of EA pretreatment-induced cerebral protective effects after MCAO compared with the control group and that MCPIP1 is involved in EA pretreatment-induced delayed brain ischemia tolerance.

α(2)-adrenoceptors do not mediate neuroprotection in acute ischemic stroke in mice

We assessed the neuroprotective potential of α(2)-adrenoceptors in ischemic stroke using mice with targeted deletions of individual α(2)-adrenoceptor subtypes (α(2A)(-/-), α(2B)(-/-), α(2C)(-/-), α(2A/C)(-/-)). The effects of the α(2)-adrenoceptor agonist clonidine were studied in parallel. Focal cerebral ischemia was induced with or without clonidine pretreatment by transient middle cerebral artery occlusion. Neurologic outcome and infarct volumes were evaluated on day 1. Cerebral blood flow (CBF) and mean arterial pressure were determined. α(2)-Adrenoceptor null mice did not display larger infarct volumes compared with wild-type (WT) mice under basal conditions (P>0.05). In line with this finding, pretreatment with clonidine did not protect from ischemic brain damage in WT mice or α(2A)(-/-), α(2B)(-/-), and α(2C)(-/-) mice. Clonidine induced smaller infarct volumes only in α(2A/C)(-/-) mice (P<0.05), but this did not translate into improved neurologic function (P>0.05). Importantly, while clonidine caused a significant decrease in arterial blood pressure in all groups, it had no blood pressure lowering effect in α(2A/C)(-/-) mice, and this correlated with higher CBF and smaller infarct volumes in this group. In summary, we could not demonstrate a neuroprotective function of α(2)-adrenoceptors in focal cerebral ischemia. Careful controlling of physiological parameters relevant for stroke outcome is recommended in experimental stroke studies.