Iptakalim, an ATP-sensitive potassium channel opener, confers neuroprotection against cerebral ischemia/reperfusion injury in rats by protecting neurovascular unit cells

ATP-sensitive potassium channel opener, Nicorandil, inhibits NF-κB/AIM2/GSDMD pathway activation to protect against neuroinflammation in ischemic stroke

The absent in melanoma 2 (AIM2) inflammasome contributes to ischemic brain injury by inducing cell pyroptosis and inflammatory responses. Our research group has previously demonstrated that ATP-sensitive potassium channels (KATP channels) openers can modulate neuronal synaptic plasticity post-ischemic stroke for neuroprotection. However, the specific mechanisms of KATP channels in the inflammatory response following ischemic stroke remain unclear. Here, we assessed cellular damage by observing changes in BV-2 morphology and viability. 2,3,5-Triphenyl tetrazolium chloride (TTC) staining, mNSS scoring, Nissl staining, and TdT-mediated dUTP nick end labeling (TUNEL) staining were used to evaluate behavioral deficits, brain injury severity, and neuronal damage in mice subjected to middle cerebral artery occlusion (MCAO). Quantitative real-time polymerase chain reaction (qRT-PCR), Western blotting, immunofluorescence, and enzyme-linked immunosorbent assay (ELISA) were used to measure cell pyroptosis and nuclear factor-kappaB (NF-κB) activation in vivo and in vitro. We observed that AIM2 protein expression was upregulated and localized within the cytoplasm of BV-2 cells. Notably, low-dose Nicorandil treatment reduced inflammatory cytokine secretion and pyroptosis-related protein expression, including AIM2, cleaved cysteinyl aspartate-specific protease-1 (cleaved caspase-1), and Gasdermin D N-terminal (GSDMD-NT). Further investigations revealed that the KATP channel inhibitor 5-HD upregulated p-NF-κB p65, NF-κB p65, and p-IκBα expression, reversing Nicorandil's neuroprotective effect in vivo. In summary, our results suggest that Nicorandil may serve as a potential therapeutic option for ischemic stroke. Targeting AIM2 and NF-κB represents effective strategies for inhibiting neuroinflammation.

No-reflow after recanalization in ischemic stroke: From pathomechanisms to therapeutic strategies

Endovascular reperfusion therapy is the primary strategy for acute ischemic stroke. No-reflow is a common phenomenon, which is defined as the failure of microcirculatory reperfusion despite clot removal by thrombolysis or mechanical embolization. It has been reported that up to 25% of ischemic strokes suffer from no-reflow, which strongly contributes to an increased risk of poor clinical outcomes. No-reflow is associated with functional and structural alterations of cerebrovascular microcirculation, and the injury to the microcirculation seriously hinders the neural functional recovery following macrovascular reperfusion. Accumulated evidence indicates that pathology of no-reflow is linked to adhesion, aggregation, and rolling of blood components along the endothelium, capillary stagnation with neutrophils, astrocytes end-feet, and endothelial cell edema, pericyte contraction, and vasoconstriction. Prevention or treatment strategies aim to alleviate or reverse these pathological changes, including targeted therapies such as cilostazol, adhesion molecule blocking antibodies, peroxisome proliferator-activated receptors (PPARs) activator, adenosine, pericyte regulators, as well as adjunctive therapies, such as extracorporeal counterpulsation, ischemic preconditioning, and alternative or complementary therapies. Herein, we provide an overview of pathomechanisms, predictive factors, diagnosis, and intervention strategies for no-reflow, and attempt to convey a new perspective on the clinical management of no-reflow post-ischemic stroke.

Iptakalim improves cerebral microcirculation in mice after ischemic stroke by inhibiting pericyte contraction

Pericytes are present tight around the intervals of capillaries, play an essential role in stabilizing the blood-brain barrier, regulating blood flow and immunomodulation, and persistent contraction of pericytes eventually leads to impaired blood flow and poor clinical outcomes in ischemic stroke. We previously show that iptakalim, an ATP-sensitive potassium (K-ATP) channel opener, exerts protective effects in neurons, and glia against ischemia-induced injury. In this study we investigated the impacts of iptakalim on pericytes contraction in stroke. Mice were subjected to cerebral artery occlusion (MCAO), then administered iptakalim (10 mg/kg, ip). We showed that iptakalim administration significantly promoted recovery of cerebral blood flow after cerebral ischemia and reperfusion. Furthermore, we found that iptakalim significantly inhibited pericytes contraction, decreased the number of obstructed capillaries, and improved cerebral microcirculation. Using a collagen gel contraction assay, we demonstrated that cultured pericytes subjected to oxygen-glucose deprivation (OGD) consistently contracted from 3 h till 24 h during reoxygenation, whereas iptakalim treatment (10 μM) notably restrained pericyte contraction from 6 h during reoxygenation. We further showed that iptakalim treatment promoted K-ATP channel opening via suppressing SUR2/EPAC1 complex formation. Consequently, it reduced calcium influx and ET-1 release. Taken together, our results demonstrate that iptakalim, targeted K-ATP channels, can improve microvascular disturbance by inhibiting pericyte contraction after ischemic stroke. Our work reveals that iptakalim might be developed as a promising pericyte regulator for treatment of stroke.

Iptakalim alleviates synaptic damages via targeting mitochondrial ATP-sensitive potassium channel in depression

Synaptic plasticity damages play a crucial role in the onset and development of depression, especially in the hippocampus, which is more susceptible to stress and the most frequently studied brain region in depression. And, mitochondria have a major function in executing the complex processes of neurotransmission and plasticity. We have previously demonstrated that Iptakalim (Ipt), a new ATP-sensitive potassium (K-ATP) channel opener, could improve the depressive-like behavior in mice. But the underlying mechanisms are not well understood. The present study demonstrated that Ipt reversed depressive-like phenotype in vivo (chronic mild stress-induced mice model of depression) and in vitro (corticosterone-induced cellular model). Further study showed that Ipt could upregulate the synaptic-related proteins postsynaptic density 95 (PSD 95) and synaptophysin (SYN), and alleviated the synaptic structure damage. Moreover, Ipt could reverse the abnormal mitochondrial fission and fusion, as well as the reduced mitochondrial ATP production and collapse of mitochondrial membrane potential in depressive models. Knocking down the mitochondrial ATP-sensitive potassium (Mito-KATP) channel subunit MitoK partly blocked the above effects of Ipt. Therefore, our results reveal that Ipt can alleviate the abnormal mitochondrial dynamics and function depending on MitoK, contributing to improve synaptic plasticity and exert antidepressive effects. These findings provide a candidate compound and a novel target for antidepressive therapy.

Neuroprotective Effects of Nicorandil in Chronic Cerebral Hypoperfusion-Induced Vascular Dementia

BACKGROUND

Ischemia-induced chronic cerebral hypoperfusion (CCH) is associated with reduced cerebral blood flow and vascular dementia (VaD). Brain mitochondrial potassium (adenosine triphosphate-sensitive potassium [K_ATP]) channels have a beneficial role in various brain conditions. The utility of K_ATP channels in CCH-induced VaD is still unknown. The aim of this study is to investigate the role of nicorandil, a selective K_ATP channel opener, in CCH-induced VaD.

METHODS

The method of 2-vessel occlusion (2VO) was used to induce CCH in mice. Cognitive impairment was assessed using Morris water maze. Serum nitrosative stress (nitrite/nitrate), brain cholinergic dysfunction (acetylcholinesterase [AChE] activity), brain oxidative stress (thiobarbituric acid reactive substances, glutathione [GSH], catalase [CAT], and superoxide dismutase [SOD]), inflammation (myeloperoxidase [MPO]), and infarct size (2,3,5-triphenyltetrazolium chloride staining) were assessed.

RESULTS

2-vessels-occluded animals have shown significant cognitive impairment, serum nitrosative stress (reduced nitrite/nitrate), cholinergic dysfunction (increased brain AChE activity), and increased brain oxidative stress (reduction in GSH content and SOD and CAT activities with a significant increase in lipid peroxidation), along with a significant increase in MPO activity and infarct size. However, nicorandil treatment has significantly attenuated various CCH-induced behavioral and biochemical impairments.

CONCLUSIONS

It may be said that 2VO provoked CCH leading to VaD, which was attenuated by the treatment of nicorandil. So, modulation of K_ATP channels may provide benefits in CCH-induced VaD.

Cytomembrane ATP-sensitive K+ channels in neurovascular unit targets of ischemic stroke in the recovery period

The present study was to analyze the mechanism of cytomembrane ATP-sensitive K⁺ channels (K_ATP) in the neurovascular unit treatment of ischemic stroke in the recovery period. A total of 24 healthy adult male Wistar rats of 5–8 weeks age, weighing 160–200 g were randomly divided into the control (sham-operation group), model, K_ATP blocker and K_ATP opener groups (n=6 rats per group). Nylon cerebral artery occlusion was conducted using nylon monofilament coated with Poly-L-lysine, which was used to produce a cerebral infarction model. After feeding normally for 3 days, 5-hydroxydecanoate (40 mg/Kg), and diazoxide (40 mg/Kg) were injected to the abdominal cavity in the blocker, and opener groups, respectively. The control received an equivalent normal saline that was injected into the sham-operation and model groups. The animals were mutilated and samples were collected after 3 days. RT-PCR was used to detect the expression levels of the three subunits of K_ATP, i.e., kir6.1, and sulfonylurea receptor (SUR) 1 and SUR2 mRNA, as well as to calculate infarct size in tetrazolium chloride staining. The expression level of mRNA in the opener group were significantly higher, followed by the model and blocker groups, with the control group being the lowest (P<0.05). Infarct size in the opener group was markedly smaller than the model and blocker groups, and infarct size in the blocker group was significantly larger (P<0.05). Thus, the target treatment on K_ATP may improve the prognosis of ischemic stroke during the recovery period.

Melatonin receptor and KATP channel modulation in experimental vascular dementia

Cerebrovascular and cardiovascular diseases are stated as important risk factors of vascular dementia (VaD) and other cognitive disorders. In the central nervous system, melatonin (MT1/MT2) as well as serotonin subtype 2C (5-HT2C) receptors is pharmacologically associated with various neurological disorders. Brain mitochondrial potassium channels have been reported for their role in neuroprotection. This study has been structured to investigate the role of agomelatine, a melatonergic MT1/MT2 agonist and nicorandil, a selective ATP sensitive potassium (KATP) channel opener in renal artery ligation (two-kidney-one-clip: 2K1C) hypertension induced endothelial dysfunction, brain damage and VaD. 2K1C-renovascular hypertension has increased mean arterial blood pressure (MABP), impaired memory (elevated plus maze and Morris water maze), endothelial function, reduced serum nitrite/nitrate and increased brain damage (TTC staining of brain sections). Furthermore, 2K1C animals have shown high levels of oxidative stress in serum (increased thiobarbituric acid reactive species-TBARS with decreased levels of glutathione-GSH, superoxide dismutase-SOD and catalase-CAT), in the aorta (increased aortic superoxide anion) and in the brain (increased TBARS with decreased GSH, SOD and CAT). 2K1C has also induced a significant increase in brain inflammation (myeloperoxidase-MPO levels), acetylcholinesterase activity (AChE) and calcium levels. Impairment in mitochondrial complexes like NADH dehydrogenase (complex-I), succinate dehydrogenase (complex-II) and cytochrome oxidase (complex-IV) was also noted in 2K1C animals. Administration of agomelatine, nicorandil and donepezil significantly attenuated 2K1C-hypertension induced impairments in memory, endothelial function, nitrosative stress, mitochondrial dysfunction, inflammation and brain damage. Therefore, modulators of MT1/MT2 receptors and KATP channels may be considered as potential agents for the management of renovascular hypertension induced VaD.

Neuroprotective effects of rutaecarpine on cerebral ischemia reperfusion injury

Rutaecarpine, an active component of the traditional Chinese medicine Tetradium ruticarpum, has been shown to improve myocardial ischemia reperfusion injury. Because both cardiovascular and cerebrovascular diseases are forms of ischemic vascular disease, they are closely related. We hypothesized that rutaecarpine also has neuroprotective effects on cerebral ischemia reperfusion injury. A cerebral ischemia reperfusion model was established after 84, 252 and 504 μg/kg carpine were given to mice via intraperitoneal injection, daily for 7 days. Results of the step through test, 2,3,5-triphenyl tetrazolium chloride dyeing and oxidative stress indicators showed that rutaecarpine could improve learning and memory ability, neurological symptoms and reduce infarction volume and cerebral water content in mice with cerebral ischemia reperfusion injury. Rutaecarpine could significantly decrease the malondialdehyde content and increase the activities of superoxide dismutase and glutathione peroxidase in mouse brain. Therefore, rutaecarpine could improve neurological function following injury induced by cerebral ischemia reperfusion, and the mechanism of this improvement may be associated with oxidative stress. These results verify that rutaecarpine has neuroprotective effects on cerebral ischemia reperfusion in mice.

Effects of nateglinide and repaglinide administered intracerebroventricularly on the CA3 hippocampal neuronal cell death and hyperglycemia induced by kainic acid in mice

Meglitinides (nateglinide and repaglinide) are widely used oral drugs for the treatment of type II diabetes mellitus. In the present study, the effects of meglinitides administered supraspinally on kainic acid (KA)-induced hippocampal neuronal cell death and hyperglycemia were studied in ICR mice. Mice were pretreated intracerebroventricularly (i.c.v.) with 30 μg of nateglinide and repaglinide for 10 min and then, mice were administered i.c.v. with KA (0.1 μg). The neuronal cell death in the CA3 region in the hippocampus was assessed 24h after KA administration and the blood glucose level was measured 30, 60, and 120 min after KA administration. We found that i.c.v. pretreatment with repaglinide attenuated the KA-induced neuronal cell death in CA3 region of the hippocampus and hyperglycemia. However, nateglinide pretreated i.c.v. did not affect the KA-induced neuronal cell death and hyperglycemia. In addition, KA administered i.c.v. caused an elevation of plasma corticosterone level and a reduction of the plasma insulin level. Furthermore, i.c.v. pretreatment with repaglinide attenuated KA-induced up-regulation of plasma corticosterone level. Furthermore, i.c.v. administration of repaglinide alone increased plasma insulin level and repaglinide pretreated i.c.v. caused a reversal of KA-induced hypoinsulinemic effect. Our results suggest that supraspinally administered repaglinide, but not nateglinide, exerts a protective effect against the KA-induced neuronal cells death in CA3 region of the hippocampus. The neuroprotective effect of repaglinide appears to be mediated by lowering the blood glucose level induced by KA.

Functional Recovery after Scutellarin Treatment in Transient Cerebral Ischemic Rats: A Pilot Study with (18) F-Fluorodeoxyglucose MicroPET

Objective. To investigate neuroprotective effects of scutellarin (Scu) in a rat model of cerebral ischemia with use of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) micro positron emission tomography (microPET). Method. Middle cerebral artery occlusion was used to establish cerebral ischemia. Rats were divided into 5 groups: sham operation, cerebral ischemia-reperfusion untreated (CIRU) group, Scu-25 group (Scu 25 mg/kg/d), Scu-50 group (Scu 50 mg/kg/d), and nimodipine (10 mg/Kg/d). The treatment groups were given for 2 weeks. The therapeutic effects in terms of cerebral infarct volume, neurological deficit scores, and cerebral glucose metabolism were evaluated. Levels of vascular density factor (vWF), glial marker (GFAP), and mature neuronal marker (NeuN) were assessed by immunohistochemistry. Results. The neurological deficit scores were significantly decreased in the Scu-50 group compared to the CIRU group (P < 0.001). ¹⁸F-FDG accumulation in the ipsilateral cerebral infarction increased steadily over time in Scu-50 group compared with CIRU group (P < 0.01) and Scu-25 group (P < 0.01). Immunohistochemical analysis demonstrated Scu-50 enhanced neuronal maturation. Conclusion. ¹⁸F-FDG microPET imaging demonstrated metabolic recovery after Scu-50 treatment in the rat model of cerebral ischemia. The neuroprotective effects of Scu on cerebral ischemic injury might be associated with increased regional glucose activity and neuronal maturation.