Systematic administration of iptakalim, an ATP-sensitive potassium channel opener, prevents rotenone-induced motor and neurochemical alterations in rats

Decrease of KATP channel expression through D3 receptor-mediated GSK3β signaling alleviates levodopa-induced dyskinesia (LID) in Parkinson's disease mouse model

AIMS

The standard Parkinson's disease (PD) treatment is L-3,4-dihydroxyphenylalanine (L-DOPA); however, its long-term use may cause L-DOPA-induced dyskinesia (LID). Aberrant activation of medium spiny neurons (MSNs) contributes to LID, and MSN excitability is regulated by dopamine D3 receptor (D3R) and ATP-sensitive potassium (KATP) channel activity. Nevertheless, it remains unclear if D3R and KATP channels may be linked in the context of LID.

METHODS

Wild-type and tyrosine hydroxylase (TH)-specific Kir6.2 knockout mice were injected with 6-hydroxydopamine (6-OHDA) to generate a PD mouse model, then chronically treated with L-DOPA to induce LID. Analyses included immunohistochemical staining, biochemical endpoints, and behavior tests. The mechanisms by which D3R/KATP channels regulate LID in the PD/LID mouse model were probed by treatment with a D3R antagonist, KATP channel opener and glycogen synthase kinase 3β (GSK3β) inhibitor, followed by evaluation of abnormal involuntary movements (AIMs).

KEY FINDINGS

The D3R antagonist FAUC365 alleviated LID, reducing AIMs and protecting against degeneration of the nigrostriatal pathway, which occurred through a direct interaction between D3Rs and KATP channels. In line with this mechanism, activation of D3R/GSK3β signaling increased KATP channel expression in the striatum of PD/LID mice. Additionally, the KATP channel opener Diz slowed LID progression and preserved nigrostriatal projections. Consistently, mice with TH-specific knockout of Kir6.2 exhibited reduced PD-like symptoms and less severe LID.

SIGNIFICANCE

D3Rs act through GSK3β signaling to regulate expression of KATP channels, which may subsequently modulate LID. Inhibition of KATP channels in TH-positive cells is sufficient to reduce AIMs in a mouse model of PD/LID.

The impact of ATP-sensitive potassium channel modulation on mitochondria in a Parkinson's disease model using SH-SY5Y cells depends on their differentiation state

Inward rectifying potassium channels sensitive to ATP levels (KATP) have been the subject of investigation for several decades. Modulators of KATP channels are well-established treatments for metabolic as well as cardiovascular diseases. Experimental studies have also shown the potential of KATP modulation in neurodegenerative disorders. However, to date, data regarding the effects of KATP antagonists/agonists in experiments related to neurodegeneration remain inconsistent. The main source of confusion in evaluating available data seems to be the choice of experimental models. The present study aims to provide a comprehensive understanding of the effects of both opening and blocking KATP channels in two forms of SH-SY5Y cells. Our results offer valuable insights into the significance of metabolic differences between differentiated and non-differentiated SH-SY5Y cells, particularly in the context of glibenclamide and diazoxide effects under normal conditions and during the initiation of pathological events simulating Parkinson's disease in vitro. We emphasize the analysis of mitochondrial functions and changes in mitochondrial network morphology. The heightened protein expression of KATP channels identified in non-differentiated SH-SY5Y cells seems to be a platform for a more significant impact of KATP modulators in this cell type. The efficiency of rotenone treatment in inducing morphological changes in the mitochondrial network depends on the differentiation status of SH-SY5Y cells.

Sodium butyrate activates the KATP channels to regulate the mechanism of Parkinson's disease microglia model inflammation

BACKGROUND

Parkinson's disease (PD) is a common neurodegenerative disorder. Microglia-mediated neuroinflammation has emerged as an involving mechanism at the initiation and development of PD. Activation of adenosine triphosphate (ATP)-sensitive potassium (KATP ) channels can protect dopaminergic neurons from damage. Sodium butyrate (NaB) shows anti-inflammatory and neuroprotective effects in some animal models of brain injury and regulates the KATP channels in islet β cells. In this study, we aimed to verify the anti-inflammatory effect of NaB on PD and further explored potential molecular mechanisms.

METHODS

We established an in vitro PD model in BV2 cells using 1-methyl-4-phenylpyridinium (MPP+ ). The effects of MPP+ and NaB on BV2 cell viability were detected by cell counting kit-8 assays. The morphology of BV2 cells with or without MPP+ treatment was imaged via an optical microscope. The expression of Iba-1 was examined by the immunofluorescence staining. The intracellular ATP content was estimated through the colorimetric method, and Griess assay was conducted to measure the nitric oxide production. The expression levels of pro-inflammatory cytokines and KATP channel subunits were evaluated by reverse transcription-quantitative polymerase chain reaction and western blot analysis.

RESULTS

NaB (5 mM) activated the KATP channels through elevating Kir6.1 and Kir6.1 expression in MPP+ -challenged BV2 cells. Both NaB and pinacidil (a KATP opener) suppressed the MPP+ -induced activation of BV2 cells and reduced the production of nitrite and pro-inflammatory cytokines in MPP+ -challenged BV2 cells.

CONCLUSION

NaB treatment alleviates the MPP+ -induced inflammatory responses in microglia via activation of KATP channels.

Involvement of adenosine triphosphate-sensitive potassium channels in the neuroprotective activity of hydrogen sulfide in the 6-hydroxydopamine-induced animal model of Parkinson's disease

Studies have shown that hydrogen sulfide (H2S) exerts a neuroprotective effect and may have a therapeutic value for treating neurodegenerative diseases including Parkinson's disease. However, little is known about the mechanisms underlying the neuroprotective activity of H2S in vivo. Here, we evaluated the effect of glibenclamide, an ATP-sensitive potassium channel blocker, on the neuroprotective activity of H2S in the 6-hydroxydopamine (6-OHDA) animal model of Parkinson's disease. 6-OHDA was administered by stereotaxic surgery into the medial forebrain bundle. Sodium hydrosulfate (NaHS, 3 and 5.6 mg/kg), as a donor of H2S, alone or in combination with glibenclamide (5 mg/kg), was daily injected for 7 days starting 1-2 h before the stereotaxic surgery. After an apomorphine-induced rotational test, the number of tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta was determined by immunofluorescence. The striatal dopamine level and oxidative stress markers were also measured in brain homogenates. Pretreatment with NaHS significantly attenuated 6-OHDA-induced motor asymmetry in the rotational test. Histological and biochemical evaluations demonstrated that NaHS, especially at high dose, increased the survival of tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta and reduced the decreasing effect of 6-OHDA on striatal dopamine levels. However, co-administration of glibenclamide reversed the antiparkinsonian and neuroprotective effects of NaHS. However, glibenclamide did not change the reducing effect of NaHS on 6-OHDA-induced overproduction of malondialdehyde. Our data show that ATP-sensitive potassium channels are involved in the antiparkinsonian and neuroprotective effects of H2S in the 6-OHDA animal model of Parkinson's disease.

Hallmarks of Brain Aging: Adaptive and Pathological Modification by Metabolic States

During aging, the cellular milieu of the brain exhibits tell-tale signs of compromised bioenergetics, impaired adaptive neuroplasticity and resilience, aberrant neuronal network activity, dysregulation of neuronal Ca2+ homeostasis, the accrual of oxidatively modified molecules and organelles, and inflammation. These alterations render the aging brain vulnerable to Alzheimer's and Parkinson's diseases and stroke. Emerging findings are revealing mechanisms by which sedentary overindulgent lifestyles accelerate brain aging, whereas lifestyles that include intermittent bioenergetic challenges (exercise, fasting, and intellectual challenges) foster healthy brain aging. Here we provide an overview of the cellular and molecular biology of brain aging, how those processes interface with disease-specific neurodegenerative pathways, and how metabolic states influence brain health.

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.

MicroRNA as biomarkers of mitochondrial toxicity

Mitochondrial toxicity can be difficult to detect as most cells can tolerate reduced activity as long as minimal capacity for function is maintained. However, once minimal capacity is lost, apoptosis or necrosis occurs quickly. Identification of more sensitive, early markers of mitochondrial toxicity was the objective of this work. Rotenone, a mitochondrial complex I inhibitor, and 3-nitropropionic acid (3-NP), a mitochondrial complex II inhibitor, were administered daily to male Sprague-Dawley rats at subcutaneous doses of 0.1 or 0.3mg/kg/day and intraperitoneal doses of 5 or 10mg/kg/day, respectively, for 1week. Samples of kidney, skeletal muscle (quadriceps femoris), and serum were collected for analysis of mitochondrial DNA (mtDNA) copy number and microRNA (miRNA) expression patterns. MtDNA was significantly decreased with administration of rotenone at 0.3mg/kg/day and 3-NP at 5 and 10mg/kg/day in the quadriceps femoris and with 3-NP at 10mg/kg/day in the kidney. Additionally, rotenone and 3-NP treatment produced changes to miRNA expression that were similar in direction (i.e. upregulation, downregulation) to those previously linked to mitochondrial functions, such as mitochondrial damage and biogenesis (miR-122, miR-202-3p); regulation of ATP synthesis, abolished oxidative phosphorylation, and loss of membrane potential due to increased reactive oxygen species (ROS) production (miR-338-5p, miR-546, miR-34c); and mitochondrial DNA damage and depletion (miR-546). These results suggest that miRNAs may be sensitive biomarkers for early detection of mitochondrial toxicity.

Pomegranate juice exacerbates oxidative stress and nigrostriatal degeneration in Parkinson's disease

Numerous factors contribute to the death of substantia nigra (SN) dopamine (DA) neurons in Parkinson's disease (PD). Compelling evidence implicates mitochondrial deficiency, oxidative stress, and inflammation as important pathogenic factors in PD. Chronic exposure of rats to rotenone causes a PD-like syndrome, in part by causing oxidative damage and inflammation in substantia nigra. Pomegranate juice (PJ) has the greatest composite antioxidant potency index among beverages, and it has been demonstrated to have protective effects in a transgenic model of Alzheimer's disease. The present study was designed to examine the potential neuroprotective effects of PJ in the rotenone model of PD. Oral administration of PJ did not mitigate or prevent experimental PD but instead increased nigrostriatal terminal depletion, DA neuron loss, the inflammatory response, and caspase activation, thereby heightening neurodegeneration. The mechanisms underlying this effect are uncertain, but the finding that PJ per se enhanced nitrotyrosine, inducible nitric oxide synthase, and activated caspase-3 expression in nigral DA neurons is consistent with its potential pro-oxidant activity.

Effects of pioglitazone and retinoic acid in a rotenone model of Parkinson's disease

Parkinson's disease (PD) is a late-onset, progressive and neurodegenerative disorder of unknown etiology. Besides the other therapeutic approaches, new drug options in pharmacotherapy of PD are important. The aim of the present study was to investigate the effects of pioglitazone and retinoic acid, antioxidant and neuroprotective agents, on rotenone-induced model of PD in rats. Adult male Wistar rats (260-373 g) were subjects. Rotenone (2.5mg/kg, sc) was injected to rats for 70 days. At the end of rotenone administration, rats were treated with pioglitazone (10mg/kg, ip) and retinoic acid (1mg/kg, ip) or vehicles for 15 days. Then, rats were tested for evaluation of Parkinson signs by measurement of locomotor activity. In addition, dopamine levels were detected in striatum, hippocampus and hypothalamus in individual groups of control, rotenone and pioglitazone or retinoic acid-treated rats. Rotenone significantly reduced locomotor activity of the rats. It also significantly reduced dopamine levels in striatum and hippocampus, but not hypothalamus. Pioglitazone and retinoic acid reversed in reduction of locomotor activity significantly. Pioglitazone, but not retinoic acid, significantly reversed the reduced striatal dopamine level. Both drugs were ineffective on reduced levels of dopamine in hippocampus. Our results suggest that pioglitazone and retinoic acid have some beneficial effects on rotenone-induced model of PD in rats. Pioglitazone seems to be more effective than retinoic acid. These agents may be helpful for preventing or controlling of some signs of PD.

Reversal of rotenone-induced dysfunction of astrocytic connexin43 by opening mitochondrial ATP-sensitive potassium channels

Growing evidence suggests that the astrocytic gap junctions (GJs), mainly formed by connexin 43 (Cx43), play an important role in physiological maintenance and various central nervous system (CNS) pathological conditions. However, little is known about the role of Cx43 in Parkinson's disease (PD). In this article, we report that rotenone, a classic neurotoxin for PD, could inhibit expression of astrocytic Cx43 and gap junction permeability. ATP-sensitive potassium (K(ATP)) channel openers, iptakalim (IPT) and diazoxide (DZ), exerted protective effect on rotenone-induced dysfunction of Cx43 and astrocyte apoptosis, which was reversed by selective mitochondrial K(ATP) (mitoK(ATP)) channel blocker 5-hydroxydecanoate (5-HD). Taken together, our findings reveal that rotenone-induced dysfunction of astrocytic Cx43 may be involved in the pathology of PD. Moreover, opening mitoK(ATP) channels in astrocytes can reverse rotenone-induced dysfunction of astrocytic Cx43 and therefore protect against toxicity of rotenone on astrocytes.

The hydrolysis of striatal adenine- and guanine-based purines in a 6-hydroxydopamine rat model of Parkinson's disease

Parkinson's disease (PD) is characterized by a progressive neurodegeneration in the substantia nigra and a striatal dopamine decrease. Striatal extracellular adenosine and ATP modulate the dopaminergic neurotransmission whereas guanosine has a protective role in the brain. Therefore, the regulation of their levels by enzymatic activity may be relevant to the clinical feature of PD. Here it was evaluated the extracellular nucleotide hydrolysis from striatal slices 4 weeks after a unilateral infusion with 6-OHDA into the medial forebrain bundle. This infusion increased ADP, AMP, and GTP hydrolysis by 15, 25, and 41%, respectively, and decreased GDP hydrolysis by 60%. There was no change in NTPDases1, 2, 3, 5, 6, and 5'-nucleotidase transcription. Dopamine depletion changes nucleotide hydrolysis and, therefore, alters the regulation of striatal nucleotide levels. These changes observed in 6-OHDA-lesioned animals may contribute to the symptoms observed in the model and provide evidence to indicate that extracellular purine hydrolysis is a key factor in understanding PD, giving hints for new therapies.

Double target concept for smoking cessation

Tobacco use is estimated to be the largest single cause of premature death in the world. Nicotine is the major addictive substance in tobacco products. After cigarette smoking, nicotine quickly acts on its target, nicotinic acetylcholine receptors (nAChRs), which are widely distributed throughout the mammalian central nervous system and are expressed as diverse subtypes on cell bodies, dendrites and/or nerve terminals. Through the nAChRs in brain reward circuits, nicotine alters dopaminergic (DA) neuronal function in the ventral tegmental area (VTA) and increases dopamine release from VTA to nuclear accumbens (NA), which leads to nicotine reward, tolerance and dependence. After quitting smoking, smokers experience withdrawal symptoms, including depression, irritability, difficulty concentrating or sleeping, headache, and tiredness. Recently, evidence has been accumulated to reveal the molecular and cellular mechanisms of nicotine reward, tolerance and dependence. The outcomes of these investigations provide pharmacological basis for smoking cessation. Here, I briefly summarize recent advancements of our understanding of nicotine reward, tolerance and dependence. Based on these understandings, I propose a double target hypothesis, in which nAChRs and dopamine release process are two important targets for smoking cessation. Dysfunction of nAChRs (antagonism or desensitization) is crucial to abolish nicotine dependence and the maintenance of an appropriate level of extracellular dopamine eliminates nicotine withdrawal syndromes. Therefore, the medications simultaneously act on these two targets should have the desired effect for smoking cessation. I discuss how to use this double target concept to interpret recent therapies and to develop new candidate compounds for smoking cessation.

Iptakalim ameliorates MPP+-induced astrocyte mitochondrial dysfunction by increasing mitochondrial complex activity besides opening mitoK(ATP) channels

In addition to the established role of the mitochondrion in energy metabolism, regulation of cell death has been regarded as a major function of this organelle. Our previous studies have demonstrated that iptakalim (IPT), a novel ATP-sensitive potassium channel (K(ATP) channel) opener, protects against 1-methyl-4-phenyl-pyridinium ion (MPP+)-induced astrocyte apoptosis via mitochondria and mitogen-activated protein kinase signal pathways. The present study aimed to investigate whether IPT can protect astrocyte mitochondria against MPP+-induced mitochondrial dysfunction. We showed that treatment with IPT could ameliorate the inhibitory effect of MPP+ on mitochondrial respiration and ATP production by using mitochondrial complex I-supported substrates. IPT could also inhibit the increased production of mitochondrial reactive oxygen species (ROS) and the release of cytochrome c from mitochondria induced by MPP+. However, mitochondrial ATP-sensitive potassium (mitoK(ATP)) channel blocker 5-hydroxydecanoate (5-HD) could partly abolish all of the above effects of IPT. Because mitochondrial complex dysfunction impairs mitochondrial respiration and ATP production, a further experiment was undertaken to study the effects of IPT on the activity of mitochondrial complex (COX) I and COX IV. It was found that IPT inhibited the decrease in mitochondrial COX I and COX IV activity induced by MPP+, but 5-HD failed to abolish these effects. Taken together, these findings suggest that IPT may protect astrocyte mitochondrial function by regulating complex activity in addition to opening mitoK(ATP) channels.

Iptakalim protects against MPP+-induced degeneration of dopaminergic neurons in association with astrocyte activation

Astrocyte activation observed in the MPTP mouse model and Parkinson's disease patients participates in the cascade of deleterious events that ultimately leads to death of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The present study aimed to elucidate whether inhibiting astrocyte activation was involved in the protective effects of iptakalim (Ipt), a novel ATP-sensitive potassium channel opener, on MPP+-induced degeneration of dopaminergic neurons. The results showed that Ipt could decrease MPP+-induced TNF-alpha release and p38 MAPK activation in reactive astrocytes. The effects of Ipt were reversed by the mitochondrial KATP blocker, 5-hydroxydecanoate, indicating that mitochondrial KATP channels participate in the regulation of astrocyte activation. Moreover, systematic administration of Ipt could significantly alleviate MPP+-induced behavioural symptoms in motor coordination, the loss of dopaminergic neurons, and the activation of astrocyte and microglia in the SNpc. Together, these findings suggest that Ipt may protect against MPP+-induced degeneration of dopaminergic neurons by inhibiting astrocyte activation and subsequent release of pro-inflammatory factors.

Opening of microglial K(ATP) channels inhibits rotenone-induced neuroinflammation

As activated microglia (MG) is an early sign that often precedes and triggers neuronal death, inhibition of microglial activation and reduction of subsequent neurotoxicity may offer therapeutic benefit. The present study demonstrates that rat primary cultured MG expressed Kir6.1 and SUR2 subunits of K_ATP channel, which was identical to that expressed in BV-2 microglial cell line. The classic K_ATP channel opener pinacidil and selective mitochondrial K_ATP (mito-K_ATP) channel opener diazoxide prevented rotenone-induc microglial activation and production of pro-inflammatory factors (tumour necrosis factor[TNF]-α and prostaglandin E₂[PGE₂]). And the effects of pinacidil and diazoxide were reversed by mito-K_ATP blocker 5-hydroxydecanoate (5-HD), indicating that mito-K_ATP channels participate in the regulation of microglial activation. Moreover, the underlying mechanisms involved the stabilization of mitocho drial membrane potential and inhibition of p38/c-Jun-N-terminal kinase (JNK) activation in microglia. Furthermore, the in vivo study confirmed that diazoxide exhibited neuroprotective effects against rotenone along with the inhibition of microglial activation and neuroinflammation. Thus, microglial mito-K_ATP channel might be a novel prospective target for the treatment of neuroinflammation-related degenerative disorders such as Parkinson's disease.

Iptakalim alleviates rotenone-induced degeneration of dopaminergic neurons through inhibiting microglia-mediated neuroinflammation

Inhibition of microglia-mediated neuroinflammation has been regarded as a prospective strategy for treating neurodegenerative disorders, such as Parkinson's disease (PD). In the present study, we demonstrated that systematic administration with iptakalim (IPT), an adenosine triphosphate (ATP)-sensitive potassium channel (K(ATP)) opener, could alleviate rotenone-induced degeneration of dopaminergic neurons in rat substantia nigra along with the downregulation of microglial activation and mRNA levels of tumor necrosis factor-alpha (TNF-alpha) and cyclooxygenase-2 (COX-2). In rat primary cultured microglia, pretreatment with IPT suppressed rotenone-induced microglial activation evidenced by inhibition of microglial amoeboid morphological alteration, declined expression of ED1 (a marker for activated microglia), and decreased production of TNF-alpha and prostaglandin E2 (PGE(2)). These inhibitory effects of IPT could be reversed by selective mitochondrial K(ATP) (mitoK(ATP)) channel blocker 5-hydroxydecanoate (5-HD). Furthermore, pretreatment with IPT prevented rotenone-induced mitochondrial membrane potential loss and p38/c-jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) activation in microglia, which might in turn regulate microglial activation and subsequent production of TNF-alpha and PGE(2). These data strongly suggest that the K(ATP) opener IPT may be a novel and promising neuroprotective drug via inhibiting microglia-mediated neuroinflammation.

ATP-sensitive potassium channel opener iptakalim protects against MPP+-induced astrocytic apoptosis via mitochondria and mitogen-activated protein kinase signal pathways

Inhibition of astrocytic apoptosis has been regarded as a novel prospective strategy for treating neurodegenerative disorders such as Parkinson's disease. In the present study, we demonstrated that iptakalim (IPT), an ATP-sensitive potassium channel (K(ATP) channel) opener, exerted protective effect on MPP(+)-induced astrocytic apoptosis, which was reversed by selective mitochondrial K(ATP) channel blocker 5-hydroxydecanoate. Further study revealed that IPT inhibited glutathione (GSH) depletion, mitochondrial membrane potential loss and subsequent release of pro-apoptotic factors (cytochrome c and apoptosis-inducing factor (AIF), and c-Jun NH(2)-terminal kinase/mitogen-activated protein kinases (MAPK) phosphorylation induced by MPP(+). Meanwhile, extracellular signal-regulated kinase (ERK) 1/2 inhibitor PD98059 inhibited the protective effect of IPT on MPP(+)-induced astrocytic apoptosis. Furthermore, IPT could also activate ERK/MAPK and maintain increased phospho-ERK1/2 level after MPP(+) exposure. Taken together, these findings reveal for the first time that IPT protects against MPP(+)-induced astrocytic apoptosis via inhibition of mitochondria apoptotic pathway and regulating the MAPK signal transduction pathways by opening mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels in astrocytes. And targeting K(ATP) channels expressed in astrocytes may provide a novel therapeutic strategy for neurodegenerative disorders.

Iptakalim modulates ATP-sensitive K(+) channels in dopamine neurons from rat substantia nigra pars compacta

Iptakalim, a novel cardiovascular ATP-sensitive K(+) (K(ATP)) channel opener, exerts neuroprotective effects on dopaminergic (DA) neurons against metabolic stress-induced neurotoxicity, but the mechanisms are largely unknown. Here, we examined the effects of iptakalim on functional K(ATP) channels in the plasma membrane (pm) and mitochondrial membrane using patch-clamp and fluorescence-imaging techniques. In identified DA neurons acutely dissociated from rat substantia nigra pars compacta (SNc), both the mitochondrial metabolic inhibitor rotenone and the sulfonylurea receptor subtype (SUR) 1-selective K(ATP) channel opener (KCO) diazoxide induced neuronal hyperpolarization and abolished action potential firing, but the SUR2B-selective KCO cromakalim exerted little effect, suggesting that functional K(ATP) channels in rat SNc DA neurons are mainly composed of SUR1. Immunocytochemical staining showed a SUR1-rather than a SUR2B-positive reaction in most dissociated DA neurons. At concentrations between 3 and 300 microM, iptakalim failed to hyperpolarize DA neurons; however, 300 microM iptakalim increased neuronal firing. In addition, iptakalim restored DA neuronal firing during rotenone-induced hyperpolarization and suppressed rotenone-induced outward current, suggesting that high concentrations of iptakalim close neuronal K(ATP) channels. Furthermore, in human embryonic kidney 293 cells, iptakalim (300-500 microM) closed diazoxide-induced Kir6.2/SUR1 K(ATP) channels, which were heterologously expressed. In rhodamine-123-preloaded DA neurons, iptakalim neither depolarized mitochondrial membrane nor prevented rotenone-induced mitochondrial depolarization. These data indicate that iptakalim is not a K(ATP) channel opener in rat SNc DA neurons; instead, iptakalim is a pm-K(ATP) channel closer at high concentrations. These effects of iptakalim stimulate further pharmacological investigation and the development of possible therapeutic applications.

Iptakalim protects PC12 cell against H2O2-induced oxidative injury via opening mitochondrial ATP-sensitive potassium channel

The final common pathway in the demise of dopaminergic neurons in Parkinson's disease may involve oxidative stress and excitotoxicity. In this study, we examined the neuroprotective effects of a novel ATP-sensitive potassium channel (K(ATP)) opener, iptakalim (IPT), against H(2)O(2)-induced cytotoxicity in rat dopaminergic PC12 cells. Pretreatment with IPT could attenuate increased extracellular glutamate levels and inhibit calcium influxing induced by H(2)O(2). Moreover, IPT regulated the expressions of bcl-2 and bax which were responsible for inhibiting apoptosis in PC12 cells. These protective effects of IPT were abolished by selective mitoK(ATP) channel blocker 5-hydroxydecanoate. Therefore, IPT can protect PC12 cells against H(2)O(2)-induced oxidative injury via activating mitoK(ATP) channel.

Iptakalim inhibits nicotinic acetylcholine receptor-mediated currents in dopamine neurons acutely dissociated from rat substantia nigra pars compacta

Iptakalim hydrochloride, a novel cardiovascular ATP-sensitive K(+) (K(ATP)) channel opener, has shown remarkable antihypertensive and neuroprotective effects in a variety of studies using in vivo and in vitro preparations. We recently found that iptakalim blocked human alpha4-containing nicotinic acetylcholine receptors (nAChRs) heterologously expressed in the human SH-EP1 cell line. In the present study, we examined the effects of iptakalim on several neurotransmitter-induced current responses in single DA neurons freshly dissociated from rat substantia nigra pars compacta (SNc), using perforated patch-clamp recordings combined with a U-tube rapid drug application. In identified DA neurons under voltage-clamp configuration, glutamate-, NMDA-, and GABA-induced currents were insensitive to co-application with iptakalim (100 microM), while whole-cell currents induced by ACh (1 mM+1 microM atropine) or an alpha4beta2 nicotinic acetylcholine receptors relatively selective agonist, RJR-2403 (300 microM), were eliminated by iptakalim. Iptakalim inhibited RJR-2403-induced current in a concentration-dependent manner, and reduced maximal RJR-2403-induced currents at the highest agonist concentration, suggesting a non-competitive block. In current-clamp mode, iptakalim failed to affect resting membrane potential and spontaneous action potential firing, but abolished RJR-2403-induced neuronal firing acceleration. Together, these results indicate that in dissociated SNc DA neurons, alpha4-containing nAChRs, rather than ionotropic glutamate receptors, GABA(A) receptors or perhaps K-ATP channels are the sensitive targets to mediate iptakalim's pharmacological roles.

Protective effects of iptakalim, a novel ATP-sensitive potassium channel opener, on global cerebral ischemia-evoked insult in gerbils

AIM

To investigate the protective role of iptakalim, a novel ATP sensitive potassium channel opener, on global cerebral ischemia-evoked insult in gerbils and glutamate-induced PC12 cell injury.

METHODS

Global cerebral ischemia was induced by occluding the bilateral common carotid arteries in gerbils for 5 min. The open field maze and T-maze were employed to investigate the experimental therapeutic value of iptakalim on ischemic brain insult (n=8). The pyramidal cells in the hippocampal CA1 regions were counted to assess the protective effects of iptakalim. Glutamate released from the gerbil hippocampus and PC12 cells were determined by HPLC. Intracellular calcium was measured by Fluo-3 AM with A Bio-Rad Radiance 2100TM confocal system in conjunction with a Nikon TE300 microscope. Astrocyte glutamate uptake measurements were determined by liquid scintillation counting.

RESULTS

Iptakalim (0.5-4.0 mg/kg per day, ip) could reduce the high locomotor activity evoked by ischemia and improve global cerebral ischemia-induced working memory impairments. Histological studies revealed that iptakalim could increase the survival neuron in the hippocampus CA1 zone in a dose-dependent manner. Moreover, iptakalim could reverse ischemia-evoked increases of glutamate in the hippocampus of gerbils. In an in vitro study, iptakalim protected PC12 cells against glutamate-induced excitotoxicity, reduced the [Ca(2+)](i) increases, and enhanced the glutamate uptake activity of primary cultured astrocytes.

CONCLUSIONS

Iptakalim plays a key role in preventing global cerebral ischemia-evoked insults in gerbils and glutamate-induced PC12 cell injury by anti-excitotoxicity. Iptakalim might be a promising novel candidate for the prevention and/or treatment of stroke.

Effects of systemic administration of iptakalim on extracellular neurotransmitter levels in the striatum of unilateral 6-hydroxydopamine-lesioned rats

The function of ATP-sensitive potassium (KATP) channels in nigrostriatal pathway in Parkinson's disease (PD) was studied by employing a novel KATP channel opener iptakalim (Ipt). Apomorphine-induced rotation behavior test and microdialysis experiment were carried out in unilateral 6-hydroxydopamine (6-OHDA) lesioned rats. Behavior test showed that systemic administration of Ipt failed to significantly alleviate apomorphine-induced rotation in unilateral 6-OHDA-lesioned PD model rats. However, using in vivo microdialysis in this PD model rats, it was found that Ipt could increase extracellular dopamine levels in the lesioned side of the striatum and decrease dopamine levels in the intact side of the striatum. Meanwhile, Ipt had no influence on glutamate levels in the intact side, but it did decrease glutamate levels in the lesioned side of the striatum of PD rats. Additionally, in primary cultured rat astrocytes, 6-OHDA decreased overall glutamate uptake activity, but this decrease was recovered and glutamate uptake activity was restored by the opening of KATP channels induced by Ipt and pinacidil. The classical KATP channel blocker glibenclamide completely abolished the effects of Ipt and pinacidil. The present study suggests that (i) the function of KATP channels in the lesioned and intact nigrostriatal pathway is different in unilateral 6-OHDA-lesioned PD model rats. (ii) KATP channels regulate extracellular neurotransmitter levels in the striatum of unilateral 6-OHDA-lesioned rats and may play neuroprotective roles due to their effects on glutamate transporters.

Iptakalim inhibits nicotine-induced enhancement of extracellular dopamine and glutamate levels in the nucleus accumbens of rats

Iptakalim (Ipt) is a novel ATP-sensitive potassium channel opener. It has been reported that Ipt inhibited cocaine-induced dopamine and glutamate release, suggesting that Ipt may regulate drug addiction. Recently, we found that Ipt blocked nicotinic acetylcholine receptor (nAChR)-mediated currents in a heterologously expressed SH-EP1 cell line and in native midbrain dopamine neurons. In the present study, we examined whether Ipt prevents nicotine-induced neurotransmitter release in the nucleus accumbens (NAc) using in vivo microdialysis methods in awake, freely moving rats. Ipt was administered through a microdialysis probe, following systemic administration of nicotine (0.5 mg/kg, s.c.). The results show that acute nicotine treatment induced an increase of both dopamine and glutamate levels in the rat NAc, and that Ipt significantly attenuated nicotine's effects in a concentration-dependent manner. Therefore, Ipt may serve as a novel compound to block nicotine-induced dopamine and glutamate release in the brain reward center, in turn decreasing nicotine reinforcement and dependence.

Effects of iptakalim on extracellular glutamate and dopamine levels in the striatum of unilateral 6-hydroxydopamine-lesioned rats: A microdialysis study

In a previous study, we demonstrated that iptakalim (Ipt) significantly ameliorated hypolocomotion and catalepsy induced by haloperidol and rotenone in rats. In order to further understand the mechanism(s), using a rat model of Parkinson's disease (PD) established by unilateral 6-hydroxydopamine (6-OHDA) administration to the substantia nigra pars compacta (SNpc) and reverse microdialysis techniques with high performance liquid chromatography (HPLC), we investigated the effects of Ipt on extracellular levels of glutamate, dopamine (DA) and its metabolite dihydroxyphenylacetic acid (DOPAC) in the striatum of conscious and freely moving rats. The results indicated that unilateral 6-OHDA-lesioned rats have a significantly higher level of extracellular glutamate and a lower level of extracellular DOPAC in the lesioned-side of the striatum, and a lower level of extracellular DA in both sides of the striatum compared to the striatum of control rats. Ipt reduced extracellular glutamate levels in both sides of striatum of the lesioned and control rats in a concentration-dependent manner. Ipt, at lower concentrations (0.01, 0.1, 1 microM), enhanced extracellular DA levels in the lesioned-side striatum of the unilateral 6-OHDA-lesioned rats, while causing no significant changes in the intact side striatum, and even a significant decline in striatum of control rats at higher concentrations of Ipt (10, 100 microM). In addition, Ipt also caused a significant decline in the extracellular DOPAC levels in the lesioned-side striatum of unilateral 6-OHDA-lesioned rats. These data suggest that the major mechanism underlying the ameliorative effects of Ipt on the behavior in 6-OHDA-lesioned rats is the alteration of levels of extracellular neurotransmitters, such as glutamate and DA in the striatum of unilateral 6-OHDA-lesioned rats.

The regulation of rotenone-induced inflammatory factor production by ATP-sensitive potassium channel expressed in BV-2 cells

Our previous studies have demonstrated that activating ATP-sensitive potassium channel (K(ATP) channel), not only improved Parkinsonian behavior and neurochemical symptoms, but also reduced iNOS activity and mRNA levels in striatum and nigra of rotenone rat model of Parkinson's disease (PD). In this study, it was first shown that the subunits of K(ATP) channels are expressed in BV-2 cells, and then it was investigated whether K(ATP) channel was involved in regulating inflammatory factor production from BV-2 cells activated by rotenone. It was found that K(ATP) channel was expressed in BV-2 cell and formed by the combination of Kir 6.1 and SUR 2A/2B. K(ATP) channel openers (KCOs) including pinacidil, diazoxide and iptakalim (Ipt) exerted beneficial effects on rotenone-induced morphological alterations of BV-2 cells, decreased tumor necrosis factor alpha (TNF-alpha) production and the expression and activity of inducible isoform of nitric oxide synthase (iNOS). Either glibenclamide or 5-hydroxydecanoate acid (a selective mitochondrial K(ATP) channel blocker) could abolish the effects of KCOs, suggesting that K(ATP) channels, especially mitochondrial ATP-sensitive potassium channels (mitoK(ATP) channels), played a crucial role in preventing the activation of BV-2 cells, and subsequently the production of a variety of proinflammatory factors. Therefore, activation of K(ATP) channel might be a new therapeutic strategy for treating neuroinflammatory and neurodegenerative disorders.

Iptakalim as a human nicotinic acetylcholine receptor antagonist

Nicotinic acetylcholine receptors (nAChRs) play many critical roles in nervous system function and have been implicated in a variety of diseases. Drugs acting at nAChRs, perhaps in nAChR subtype-selective manners, can be used to dissect receptor function and perhaps as medications. In the present study, we used patch-clamp whole-cell recording and pharmacological manipulations to evaluate effects of iptakalim hydrochloride (Ipt), which is a drug reported to act as an ATP-sensitive potassium (K(ATP)) channel opener, on selected human nAChRs heterologously expressed in the native nAChR-null SH-EP1 human epithelial cell line. Ipt reduced both peak and steady-state whole-cell current amplitudes mediated by human alpha4beta2-nAChRs in response to nicotinic agonists. It also accelerated current decay, caused a decline in apparent efficacy of agonists, and acted in voltage- and use-dependent manners at alpha4beta2-nAChRs. These findings and the inability of Ipt to block radiolabeled epibatidine binding to alpha4beta2-nAChRs suggest a noncompetitive mechanism of antagonism. Other studies discount effects of Ipt on nAChR internalization or involvement of K(ATP) channels in Ipt-induced inhibition of alpha4beta2-nAChR function. By comparison, alpha7-nAChRs were less sensitive than alpha4beta2-nAChRs to Ipt acting as an antagonist. Thus, alpha4beta2-nAChRs are among the molecular targets of Ipt, which has utility as a tool in functional characterization and pharmacological profiling of nAChRs.

ATP-sensitive potassium channel opener iptakalim protected against the cytotoxicity of MPP+ on SH-SY5Y cells by decreasing extracellular glutamate level

Mounting evidence reveals that ATP-sensitive potassium (K(ATP)) channel openers (KCOs) exert significant neuroprotection in vivo and in vitro in several models of Parkinson's disease (PD). However, the mechanisms are not well understood. In this study, we demonstrated that SH-SY5Y cells expressed mRNA and proteins for Kir6.1, Kir6.2, SUR1 and SUR2 subunits of K(ATP) channels. Moreover, our results showed that 1-methyl-4-phenyl-pyridinium ion (MPP+) induced up-regulation of mRNA for the Kir6.2 subunit and down-regulation of SUR1. It was further found that pretreatment with iptakalim, a novel K(ATP) channel opener, could attenuate increased extracellular glutamate level and decreased cell survival in SH-SY5Y cell culture after exposure to MPP+. Trans-pyrrolidine-2, 4-dicarboxylic acid (t-PDC), a glutamate transporter inhibitor, partially blocked the effect of iptakalim decreasing extracellular glutamate level. Additionally, iptakalim prevented MPP+-induced inhibition of glutamate uptake in primary cultured astrocytes. The beneficial effects of iptakalim on glutamate uptake of astrocytes were abolished by selective mitochondrial K(ATP) (mitoK(ATP)) channel blocker 5-HD. These results suggest (i) K(ATP) channel dysfunction may be involved in the mechanisms of MPP+-induced cytotoxicity and (ii) iptakalim may modulate glutamate transporters and subsequently alleviate the increase of extracellular glutamate levels induced by MPP+ through opening mitoK(ATP) channels, thereby protecting SH-SY5Y cells against MPP+-induced cytotoxicity.