Iptakalim protects against hypoxic brain injury through multiple pathways associated with ATP-sensitive potassium channels

Cerebrovascular effects of glibenclamide investigated using high-resolution magnetic resonance imaging in healthy volunteers

Glibenclamide inhibits sulfonylurea receptor (SUR), which regulates several ion channels including SUR1-transient receptor potential melastatin 4 (SUR1-TRPM4) channel and ATP-sensitive potassium (K_ATP) channel. Stroke upregulates SURl-TRPM4 channel, which causes a rapid edema formation and brain swelling. Glibenclamide may antagonize the formation of cerebral edema during stroke. Preclinical studies showed that glibenclamide inhibits K_ATP channel-induced vasodilation without altering the basal vascular tone. The in vivo human cerebrovascular effects of glibenclamide have not previously been investigated.In a randomized, double-blind, placebo-controlled, three-way cross-over study, we used advanced 3 T MRI methods to investigate the effects of glibenclamide and K_ATP channel opener levcromakalim on mean global cerebral blood flow (CBF) and intra- and extracranial artery circumferences in 15 healthy volunteers. Glibenclamide administration did not alter the mean global CBF and the basal vascular tone. Following levcromakalim infusion, we observed a 14% increase of the mean global CBF and an 8% increase of middle cerebral artery (MCA) circumference, and glibenclamide did not attenuate levcromakalim-induced vascular changes. Collectively, the findings demonstrate the vital role of K_ATP channels in cerebrovascular hemodynamic and indicate that glibenclamide does not inhibit the protective effects of K_ATP channel activation during hypoxia and ischemia-induced brain injury.

Involvement of Epigenetic Mechanisms and Non-coding RNAs in Blood-Brain Barrier and Neurovascular Unit Injury and Recovery After Stroke

Cessation of blood flow leads to a complex cascade of pathophysiological events at the blood-vascular-parenchymal interface which evolves over time and space, and results in damage to neural cells and edema formation. Cerebral ischemic injury evokes a profound and deleterious upregulation in inflammation and triggers multiple cell death pathways, but it also induces a series of the events associated with regenerative responses, including vascular remodeling, angiogenesis, and neurogenesis. Emerging evidence suggests that epigenetic reprograming could play a pivotal role in ongoing post-stroke neurovascular unit (NVU) changes and recovery. This review summarizes current knowledge about post-stroke recovery processes at the NVU, as well as epigenetic mechanisms and modifiers (e.g., DNA methylation, histone modifying enzymes and microRNAs) associated with stroke injury, and NVU repair. It also discusses novel drug targets and therapeutic strategies for enhancing post-stroke recovery.

Anticerebral Ischemia-Reperfusion Injury Activity of Synthesized Puerarin Derivatives

When cerebral ischemia-reperfusion injury happened in patients, multiple pathological processes occur, such as leukocyte infiltration, platelet, and complement activation, which would result in cognitive dysfunction and inflammation. Puerarin has shown protective effect on injury of neural cell. In order to enhance this protective effect of puerarin, puerarin derivatives with different log⁡P values were designed and synthesized. The original phenolic hydroxyl in the puerarin molecules was substituted in order to change the blood-brain barrier permeability and thus enhance the efficacy for preventing cerebral ischemia/reperfusion injury. And the structure of the newly synthesized molecules was confirmed by 1H NMR spectroscopy and mass spectrometry. The mouse model of cerebral artery ischemia/reperfusion injury was established to test the anticerebral ischemia-reperfusion injury activity of the puerarin derivatives. The assays of the water maze, Y maze, brain cortex Ca²⁺-Mg²⁺-ATP enzyme, and iNOS enzyme activity were performed in this mouse model. The results showed that puerarin derivative P1-EA and P2-EA were resulting in an increased lipophilicity that enabled the derivatives to pass more efficiently through the blood-brain barrier, thus, improving the protective effects against cerebral ischemia/reperfusion injury. Therefore, derivatives of puerarin may serve as promising approach to improve neuron function in ischemia-reperfusion brain injury-related disorders.

ABCC9/SUR2 in the brain: Implications for hippocampal sclerosis of aging and a potential therapeutic target

The ABCC9 gene and its polypeptide product, SUR2, are increasingly implicated in human neurologic disease, including prevalent diseases of the aged brain. SUR2 proteins are a component of the ATP-sensitive potassium ("KATP") channel, a metabolic sensor for stress and/or hypoxia that has been shown to change in aging. The KATP channel also helps regulate the neurovascular unit. Most brain cell types express SUR2, including neurons, astrocytes, oligodendrocytes, microglia, vascular smooth muscle, pericytes, and endothelial cells. Thus it is not surprising that ABCC9 gene variants are associated with risk for human brain diseases. For example, Cantu syndrome is a result of ABCC9 mutations; we discuss neurologic manifestations of this genetic syndrome. More common brain disorders linked to ABCC9 gene variants include hippocampal sclerosis of aging (HS-Aging), sleep disorders, and depression. HS-Aging is a prevalent neurological disease with pathologic features of both neurodegenerative (aberrant TDP-43) and cerebrovascular (arteriolosclerosis) disease. As to potential therapeutic intervention, the human pharmacopeia features both SUR2 agonists and antagonists, so ABCC9/SUR2 may provide a "druggable target", relevant perhaps to both HS-Aging and Alzheimer's disease. We conclude that more work is required to better understand the roles of ABCC9/SUR2 in the human brain during health and disease conditions.

The role of Levosimendan in cardiopulmonary resuscitation

Although initial resuscitation from cardiac arrest (CA) has increased over the past years, long term survival rates remain dismal. Epinephrine is the vasopressor of choice in the treatment of CA. However, its efficacy has been questioned, as it has no apparent benefits for long-term survival or favorable neurologic outcome. Levosimendan is an inodilator with cardioprotective and neuroprotective effects. Several studies suggest that it is associated with increased rates of return of spontaneous circulation as well as improved post-resuscitation myocardial function and neurological outcome. The purpose of this article is to review the properties of Levosimendan during cardiopulmonary resuscitation (CPR) and also to summarize existing evidence regarding the use of Levosimendan in the treatment of CA.

Pharmacologic preconditioning: translating the promise

A transient, ischemia-resistant phenotype known as "ischemic tolerance" can be established in brain in a rapid or delayed fashion by a preceding noninjurious "preconditioning" stimulus. Initial preclinical studies of this phenomenon relied primarily on brief periods of ischemia or hypoxia as preconditioning stimuli, but it was later realized that many other stressors, including pharmacologic ones, are also effective. This review highlights the surprisingly wide variety of drugs now known to promote ischemic tolerance, documented and to some extent mechanistically characterized in preclinical animal models of stroke. Although considerably more experimentation is needed to thoroughly validate the ability of any currently identified preconditioning agent to protect ischemic brain, the fact that some of these drugs are already clinically approved for other indications implies that the growing enthusiasm for translational success in the field of pharmacologic preconditioning may be well justified.

Modulation of crucial adenosinetriphosphatase activities due to U-74389G administration in a porcine model of intracerebral hemorrhage

Spontaneous intracerebral hemorrhage (ICH) represents a partially-understood cerebrovascular disease of high incidence, morbidity and mortality. We, herein, report the findings of our study concerning the role of two important adenosinetriphosphatases (ATPases) in a porcine model of spontaneous ICH that we have recently developed (by following recent references as well as previously-established models and techniques), with a focus on the first 4 and 24 h following the lesion's induction, in combination with a study of the effectiveness of the lazaroid antioxidant U-74389G administration. Our study demonstrates that the examined ICH model does not cause a decrease in Na(+),K(+)-ATPase activity (the levels of which are responsible for a very large part of neuronal energy expenditure) in the perihematomal basal ganglia territory, nor a change in the activity of Mg(2+)-ATPase. This is the first report focusing on these crucial ATPases in the experimental setting of ICH and differs from the majority of the findings concerning the behavior of these (crucial for central nervous system cell survival) enzymes under stroke-related ischemic conditions. The administration of U-74389G (an established antioxidant) in this ICH model revealed an injury specific type of behavior, that could be considered as neuroprotective provided that one considers that Na(+),K(+)- and Mg(2+)-ATPase inhibition might in this case diminish the local ATP consumption.

Levosimendan limits reperfusion injury in a rat middle cerebral artery occlusion (MCAO) model

Background

Neuroprotective strategies in ischemic stroke are an important challenge in clinical and experimental research as an adjunct to reperfusion therapy that may reduce neurologic injury and improve outcome. The neuroprotective properties of levosimendan in traumatic brain injury in vitro, transient global brain ischemia and focal spinal cord ischemia suggest the potential for similar effects in transient brain ischemia.

Methods

Transient brain ischemia was induced for 60 min by intraluminal occlusion of the middle cerebral artery in 40 male Wistar rats under general anesthesia with s-ketamine and xylazine and with continuous monitoring of their blood pressure and cerebral perfusion. Five minutes before inducing reperfusion, a levosimendan bolus (24 μg kg ^-1) was administered over a 20 minute period. Infarct size, brain swelling, neurological function and the expression of inflammatory markers were quantified 24 hours after reperfusion.

Results

Although levosimendan limited the infarct size and brain swelling by 40% and 53%, respectively, no effect on neurological outcome or mortality could be demonstrated. Upregulation of tumor necrosis factor α and intercellular adhesion molecule 1 was significantly impeded. Cerebral blood flow during reperfusion was significantly reduced as a consequence of sustained autoregulation.

Conclusions

Levosimendan demonstrated significant neuroprotective properties in a rat model of transient brain ischemia by reducing reperfusion injury.

Establishment and evaluation of an experimental animal model of high altitude cerebral edema

The aim of our study was to develop a model of high altitude cerebral edema (HACE) using an acute, hypobaric hypoxia environment combined with exhaustive exercise. Forty healthy male Sprague-Dawley rats were randomly divided into a plains control group (PC group) and a plateau altitude hypoxia group (AH group). After 2 days of treadmill adaptation under normoxic conditions, the AH group was housed in hypobaric conditions (simulating 4000 m above sea level) for 2 days while performing exhaustive exercise. The simulated altitude was then increased to 8000 m for 3 days of simple hypobaric hypoxia exposure. Compared with the PC group, the AH group showed significantly greater (P<0.01) water content and Evans blue staining in their brain tissue. Furthermore, the hippocampal formation was seriously damaged, and the number of pyramidal cells decreased. In addition, the brain structure was altered into a loose state with notable edema, which was demonstrated by the leakage of lanthanum nitrate particles from brain microvessels into the surrounding tissue through widened tight junctions. Some neurons and glial cell organelles were swollen and some nerve fibers were demyelinated as well. We have shown that acute hypobaric hypoxia exposure with exhaustive exercise increases the permeability of the blood-brain barrier and leads to cerebral edema, making this a valid animal model of HACE.

Kir6.1 knockdown aggravates cerebral ischemia/reperfusion-induced neural injury in mice

BACKGROUND AND PURPOSE

ATP-sensitive potassium (K-ATP) channels couple energy metabolism with electric activity, which play important roles in brain diseases including stroke. However, the impacts of Kir6.1-containing K-ATP channels that mainly expressed on glia in stroke remain unclear.

METHODS AND RESULTS

In this study, we found that expression of Kir6.1 was significantly decreased in the ischemic brain area of C57BL/6J mice after 1-h middle cerebral artery occlusion (MCAO) and 24-h reperfusion. Then, we subjected Kir6.1 heterozygote knockout (Kir6.1(+/-) ) mice to cerebral ischemia/reperfusion (I/R) injury and found that Kir6.1(+/-) mice exhibited exacerbated neurological disorder and enlarged infarct size, companied by glial over-activation and blood-brain barrier (BBB) damages. Furthermore, we showed that Kir6.1 knockdown aggravated endoplasmic reticulum (ER) stress and thereby increased the levels of proinflammatory factors tumor necrosis factor-α and interleukin-1β (TNF-α and IL-1β) in mouse brain.

CONCLUSIONS

Our findings reveal that Kir6.1 knockdown exacerbates cerebral I/R-induced brain damages via increasing ER stress and inflammatory response, indicating that Kir6.1-containing K-ATP channels may be a potential therapeutic target for stroke.

The effects of levosimendan on brain metabolism during initial recovery from global transient ischaemia/hypoxia

BACKGROUND

Neuroprotective strategies after cardiopulmonary resuscitation are currently the focus of experimental and clinical research. Levosimendan has been proposed as a promising drug candidate because of its cardioprotective properties, improved haemodynamic effects in vivo and reduced traumatic brain injury in vitro. The effects of levosimendan on brain metabolism during and after ischaemia/hypoxia are unknown.

METHODS

Transient cerebral ischaemia/hypoxia was induced in 30 male Wistar rats by bilateral common carotid artery clamping for 15 min and concomitant ventilation with 6% O2 during general anaesthesia with urethane. After 10 min of global ischaemia/hypoxia, the rats were treated with an i.v. bolus of 24 μg kg-1 levosimendan followed by a continuous infusion of 0.2 μg kg-1 min-1. The changes in the energy-related metabolites lactate, the lactate/pyruvate ratio, glucose and glutamate were monitored by microdialysis. In addition, the effects on global haemodynamics, cerebral perfusion and autoregulation, oedema and expression of proinflammatory genes in the neocortex were assessed.

RESULTS

Levosimendan reduced blood pressure during initial reperfusion (72 ± 14 vs. 109 ± 2 mmHg, p = 0.03) and delayed flow maximum by 5 minutes (p = 0.002). Whereas no effects on time course of lactate, glucose, pyruvate and glutamate concentrations in the dialysate could be observed, the lactate/pyruvate ratio during initial reperfusion (144 ± 31 vs. 77 ± 8, p = 0.017) and the glutamate release during 90 minutes of reperfusion (75 ± 19 vs. 24 ± 28 μmol·L-1) were higher in the levosimendan group. The increased expression of IL-6, IL-1ß TNFα and ICAM-1, extend of cerebral edema and cerebral autoregulation was not influenced by levosimendan.

CONCLUSION

Although levosimendan has neuroprotective actions in vitro and on the spinal cord in vivo and has been shown to cross the blood-brain barrier, the present results showed that levosimendan did not reduce the initial neuronal injury after transient ischaemia/hypoxia.

Similar cation channels mediate protection from cerebellar exitotoxicity by exercise and inheritance

Exercise and inherited factors both affect recovery from stroke and head injury, but the underlying mechanisms and interconnections between them are yet unknown. Here, we report that similar cation channels mediate the protective effect of exercise and specific genetic background in a kainate injection model of cerebellar stroke. Microinjection to the cerebellum of the glutamatergic agonist, kainate, creates glutamatergic excito-toxicity characteristic of focal stroke, head injury or alcoholism. Inherited protection and prior exercise were both accompanied by higher cerebellar expression levels of the Kir6.1 ATP-dependent potassium channel in adjacent Bergmann glia, and voltage-gated KVbeta2 and cyclic nucleotide-gated cation HCN1 channels in basket cells. Sedentary FVB/N and exercised C57BL/6 mice both expressed higher levels of these cation channels compared to sedentary C57BL/6 mice, and were both found to be less sensitive to glutamate toxicity. Moreover, blocking ATP-dependent potassium channels with Glibenclamide enhanced kainate-induced cell death in cerebellar slices from the resilient sedentary FVB/N mice. Furthermore, exercise increased the number of acetylcholinesterase-positive fibres in the molecular layer, reduced cerebellar cytokine levels and suppressed serum acetylcholinesterase activity, suggesting anti-inflammatory protection by enhanced cholinergic signalling. Our findings demonstrate for the first time that routine exercise and specific genetic backgrounds confer protection from cerebellar glutamatergic damages by similar molecular mechanisms, including elevated expression of cation channels. In addition, our findings highlight the involvement of the cholinergic anti-inflammatory pathway in insult-inducible cerebellar processes. These mechanisms are likely to play similar roles in other brain regions and injuries as well, opening new venues for targeted research efforts.

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

OBJECTIVE

To investigate the role of iptakalim, an ATP-sensitive potassium channel opener, in transient cerebral ischemia/reperfusion (I/R) injury and its involved mechanisms.

METHODS

Intraluminal occlusion of middle cerebral artery (MCAO) in a rat model was used to investigate the effect of iptakalim at different time points. Infarct volume was measured by staining with 2,3,5-triphenyltetrazolium chloride, and immunohistochemistry was used to evaluate the expressions of Bcl-2 and Bax. In vitro, neurovascular unit (NVU) cells, including rat primary cortical neurons, astrocytes, and cerebral microvascular endothelial cells, were cultured and underwent oxygen-glucose deprivation (OGD). The protective effect of iptakalim on NVU cells was investigated by cell viability and injury assessments, which were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and release of lactate dehydrogenase. Caspase-3, Bcl-2 and Bax mRNA expressions were evaluated by real-time polymerase chain reaction (PCR).

RESULTS

Administration of iptakalim 0 or 1 h after reperfusion significantly reduced infarct volumes, improved neurological scores, and attenuated brain edema after cerebral I/R injury. Iptakalim treatment (0 h after reperfusion) also reduced caspase-3 expression and increased the ratio of Bcl-2 to Bax by immunohistochemistry. Iptakalim inhibited OGD-induced cell death in cultured neurons and astrocytes, and lactate dehydrogenase release from cerebral microvascular endothelial cells. Iptakalim reduced mRNA expression of caspase-3 and increased the ratio of Bcl-2 to Bax in NVU cells.

CONCLUSIONS

Iptakalim confers neuroprotection against cerebral I/R injury by protecting NVU cells via inhibiting of apoptosis.

Salvinorin A produces cerebrovasodilation through activation of nitric oxide synthase, κ receptor, and adenosine triphosphate-sensitive potassium channel

BACKGROUND

Salvinorin A is a nonopioid, selective κ opioid-receptor agonist. Despite its high potential for clinical application, its pharmacologic profile is not well known. In the current study, we hypothesized that salvinorin A dilates pial arteries via activation of nitric oxide synthase, adenosine triphosphate-sensitive potassium channels, and opioid receptors.

METHODS

Cerebral artery diameters and cyclic guanosine monophosphate in cortical periarachnoid cerebrospinal fluid were monitored in piglets equipped with closed cranial windows. Observation took place before and after salvinorin A administration in the presence or absence of an opioid antagonist (naloxone), a κ opioid receptor-selective antagonist (norbinaltorphimine), nitric oxide synthase inhibitors (N(G)-nitro-L-arginine and 7-nitroindazole), a dopamine receptor D2 antagonist (sulpiride), and adenosine triphosphate-sensitive potassium and Ca-activated K channel antagonists (glibenclamide and iberiotoxin). The effects of salvinorin A on the constricted cerebral artery induced by hypocarbia and endothelin were investigated. Data were analyzed by repeated measures ANOVA (n = 5) with statistical significance set at a P value of less than 0.05.

RESULTS

Salvinorin A induced immediate but brief vasodilatation that was sustained for 30 min via continual administration every 2 min. Vasodilatation and the associated cyclic guanosine monophosphate elevation in cerebrospinal fluid were abolished by preadministration N(G)-nitro-L-arginine, but not 7-nitroindazole. Although naloxone, norbinaltorphimine, and glibenclamide abolished salvinorin A-induced cerebrovasodilation, this response was unchanged by iberiotoxin and sulpiride. Hypocarbia and endothelin-constricted pial arteries responded similarly to salvinorin A, to the extent observed under resting tone.

CONCLUSIONS

Salvinorin A dilates cerebral arteries via activation of nitric oxide synthase, adenosine triphosphate-sensitive potassium channel, and the κ opioid receptor.

Patents related to therapeutic activation of K(ATP) and K(2P) potassium channels for neuroprotection: ischemic/hypoxic/anoxic injury and general anesthetics

BACKGROUND

Mechanisms of neuroprotection encompass energy deficits in brain arising from insufficient oxygen and glucose levels following respiratory failure; ischemia or stroke, which produce metabolic stresses that lead to unconsciousness and seizures; and the effects of general anesthetics. Foremost among those K(+) channels viewed as important for neuroprotection are ATP-sensitive (K(ATP)) channels, which belong to the family of inwardly rectifying K(+) channels (K(ir)) and contain a sulfonylurea subunit (SUR1 or SUR2) combined with either K(ir)6.1 (KCNJ8) or K(ir)6.2 (KCNJ11) channel pore-forming alpha-subunits, and various members of the tandem two-pore or background (K(2P)) K(+) channel family, including K(2P)1.1 (KCNK1 or TWIK1), K(2P)2.1 (KCNK2 or TREK/TREK1), K(2P)3.1 (KCNK3 or TASK), K(2P)4.1 (KCNK4 or TRAAK), and K(2P)10.1 (KCNK10 or TREK2).

OBJECTIVES

This review covers patents and patent applications related to inventions of therapeutics, compound screening methods and diagnostics, including K(ATP) channel openers and blockers, as well as K(ATP) and K(2P) nucleic/amino acid sequences and proteins, vectors, transformed cells and transgenic animals. Although the focus of this patent review is on brain and neuroprotection, patents covering inventions of K(ATP) channel openers for cardioprotection, diabetes mellitus and obesity, where relevant, are addressed.

RESULTS/CONCLUSIONS

Overall, an important emerging therapeutic mechanism underlying neuroprotection is activation/opening of K(ATP) and K(2P) channels. To this end substantial progress has been made in identifying and patenting agents that target K(ATP) channels. However, current K(2P) channels patents encompass compound screening and diagnostics methodologies, reflecting an earlier 'discovery' stage (target identification/validation) than K(ATP) in the drug development pipeline; this reveals a wide-open field for the discovery and development of K(2P)-targeting compounds.