Studies of ATP-sensitive potassium channels on 6-hydroxydopamine and haloperidol rat models of Parkinson's disease: implications for treating Parkinson's disease?

Unraveling the Ties: Type 2 Diabetes and Parkinson's Disease - A Nano-Based Targeted Drug Delivery Approach

The link between Type 2 Diabetes (T2DM) and Parkinson's Disease (PD) dates back to the early 1960s, and ongoing research is exploring this association. PD is linked to dysregulation of dopaminergic pathways, neuroinflammation, decreased PPAR-γ coactivator 1-α, increased phosphoprotein enriched in diabetes, and accelerated α-Syn amyloid fibril production caused by T2DM. This study aims to comprehensively evaluate the T2DM-PD association and risk factors for PD in T2DM individuals. The study reviews existing literature using reputable sources like Scopus, ScienceDirect, and PubMed, revealing a significant association between T2DM and worsened PD symptoms. Genetic profiles of T2DM-PD individuals show similarities, and potential risk factors include insulin-resistance and dysbiosis of the gut-brain microbiome. Anti-diabetic drugs exhibit neuroprotective effects in PD, and nanoscale delivery systems like exosomes, micelles, and liposomes show promise in enhancing drug efficacy by crossing the Blood-Brain Barrier (BBB). Brain targeting for PD uses exosomes, micelles, liposomes, dendrimers, solid lipid nanoparticles, nano-sized polymers, and niosomes to improve medication and gene therapy efficacy. Surface modification of nanocarriers with bioactive compounds (such as angiopep, lactoferrin, and OX26) enhances α-Syn conjugation and BBB permeability. Natural exosomes, though limited, hold potential for investigating DM-PD pathways in clinical research. The study delves into the underlying mechanisms of T2DM and PD and explores current therapeutic approaches in the field of nano-based targeted drug delivery. Emphasis is placed on resolved and ongoing issues in understanding and managing both conditions.

Ion Channels and Metal Ions in Parkinson's Disease: Historical Perspective to the Current Scenario

Parkinson's disease (PD) is a neurodegenerative condition linked to the deterioration of motor and cognitive performance. It produces degeneration of the dopaminergic neurons along the nigrostriatal pathway in the central nervous system (CNS), which leads to symptoms such as bradykinesias, tremors, rigidity, and postural instability. There are several medications currently approved for the therapy of PD, but a permanent cure for it remains elusive. With the aging population set to increase, a number of PD cases are expected to shoot up in the coming times. Hence, there is a need to look for new molecular targets that could be investigated both preclinically and clinically for PD treatment. Among these, several ion channels and metal ions are being studied for their effects on PD pathology and the functioning of dopaminergic neurons. Ion channels such as N-methyl-D-aspartate (NMDA), γ-aminobutyric acid A (GABAA), voltage-gated calcium channels, potassium channels, HCN channels, Hv1 proton channels, and voltage-gated sodium channels and metal ions such as mercury, zinc, copper, iron, manganese, calcium, and lead showed prominent involvement in PD. Pharmacological agents have been used to target these ion channels and metal ions to prevent or treat PD. Hence, in the present review, we summarize the pathophysiological events linked to PD with an emphasis on the role of ions and ion channels in PD pathology, and pharmacological agents targeting these ion channels have also been listed.

Calcium carbonate supplementation causes motor dysfunction

We previously showed that a diet containing calcium carbonate causes impairments in spatial and recognition memory in mice. In this study, we investigated the effects of calcium carbonate supplementation on motor function. Motor function was determined using different tests that have been used to analyze different aspects of Parkinsonism. A catalepsy test for akinesia; a muscular strength assessment, pole test, beam-walking test, and gait analysis for motor coordination and balance assessment; and an open-field test for locomotor activity assessment were performed. The mice were fed diets containing 0.6% or 1.0% calcium carbonate for eight weeks, after which they were evaluated for motor functions. The diets containing calcium carbonate caused significant motor dysfunction, as revealed by the different tests, although the spontaneous locomotor activity did not change. Calcium carbonate supplementation decreased the dopamine content in the basal ganglia, including the striatum and substantia nigra, and the number of tyrosine hydroxylase-positive neurons in the substantia nigra. In addition, administration of L-dopa led to at least a partial recovery of motor dysfunction, suggesting that calcium carbonate supplementation causes motor dysfunction by decreasing the dopamine content in the basal ganglia. These results suggest that mice with calcium carbonate-induced motor dysfunction may be useful as a new animal model for Parkinson’s disease and Huntington’s disease.

Neuroprotective effect of α-pinene self-emulsifying nanoformulation against 6-OHDA induced neurotoxicity on human SH-SY5Y cells and its in vivo validation for anti-Parkinson's effect

Oxidative stress (OS) is involved in the multifaceted pathogenic paradigm of neurodegenerative diseases like Parkinson's disease (PD). Monoterpenes like α-pinene (ALP) is considered to be a therapeutically potent antioxidant agent able to attenuate and scavenge various reactive oxygen species and reactive nitrogen species. The present study aimed to evaluate the in vitro and in vivo neuroprotective effect of α-pinene self-emulsifying nanoformulation (ALP-SENF) for PD. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay was done to evaluate the neurotoxic dose of the ALP-SENF; however, the neuroprotective effect was assessed by 6-hydroxydopamine (6-OHDA) induced neurotoxicity model on SH-SY5Y taking NAC (N-acetyl-l-cysteine) as standard. The in vivo anti-Parkinson's activity of the ALP-SENF was compared with that of the plain ALP suspension by using reserpine antagonism and haloperidol-induced Parkinsonism model in rats. Various behavioral tests and biochemical antioxidant enzymes were estimated. The in vitro results revealed that treatment with ALP-SENF at a concentration of 100 and 200 µM was found to show significant neuronal SH-SY5Y cell viability against 50 µM 6-OHDA. ALP-SENF treated animals have seen significant neurobehavioral improvement. Furthermore, the levels of antioxidative enzymes in biochemical test reveals a marked enhancement in the expression of antioxidant enzymes that significantly attenuated the OS induced neurodegeneration. Due to the mechanisms of their antioxidant action, it was probably due to the scavenging of free radicals and the expression of antioxidant enzymes. It also improved neurobehavioral changes induced by reserpine and haloperidol.

Study on the Regulation Effect of Optogenetic Technology on LFP of the Basal Ganglia Nucleus in Rotenone-Treated Rats

Background

Parkinson's disease (PD) is a common neurological degenerative disease that cannot be completely cured, although drugs can improve or alleviate its symptoms. Optogenetic technology, which stimulates or inhibits neurons with excellent spatial and temporal resolution, provides a new idea and approach for the precise treatment of Parkinson's disease. However, the neural mechanism of photogenetic regulation remains unclear.

Objective

In this paper, we want to study the nonlinear features of EEG signals in the striatum and globus pallidus through optogenetic stimulation of the substantia nigra compact part.

Methods

Rotenone was injected stereotactically into the substantia nigra compact area and ventral tegmental area of SD rats to construct rotenone-treated rats. Then, for the optogenetic manipulation, we injected adeno-associated virus expressing channelrhodopsin to stimulate the globus pallidus and the striatum with a 1 mW blue light and collected LFP signals before, during, and after light stimulation. Finally, the collected LFP signals were analyzed by using nonlinear dynamic algorithms.

Results

After observing the behavior and brain morphology, 16 models were finally determined to be successful. LFP results showed that approximate entropy and fractal dimension of rats in the control group were significantly greater than those in the experimental group after light treatment (p < 0.05). The LFP nonlinear features in the globus pallidus and striatum of rotenone-treated rats showed significant statistical differences before and after light stimulation (p < 0.05).

Conclusion

Optogenetic technology can regulate the characteristic value of LFP signals in rotenone-treated rats to a certain extent. Approximate entropy and fractal dimension algorithm can be used as an effective index to study LFP changes in rotenone-treated rats.

Hydrogen sulfide attenuates induction and prevents progress of the 6-hydroxydopamine-induced Parkinsonism in rat through activation of ATP-sensitive potassium channels and suppression of ER stress

PURPOSE

Studies argue in favor of hydrogen sulfide (H₂S) as the next potent therapeutic agent for neurodegenerative diseases. In present study, we investigated the effect of long term treatment with NaHS (as donor of H₂S) on induction and progress of the 6-hydroxydopamine (6-OHDA) -induced Parkinsonism in rat.

METHODS

The 6-OHDA was injected into medial forebrain bundle of right hemisphere by stereotaxic surgery. Behavioral tests and treatments were carried out to eight weeks after the toxin. Immunohistochemistry and western blotting were carried out to evaluate the survival of tyrosine hydroxylase (TH) -positive neurons in substantia nigra (SN) and also expression of glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP), the markers of endoplasmic reticulum (ER) stress, in striatum and SN.

RESULTS

Eight weeks assessment of the behavioral symptoms showed that NaHS especially at dose of 100 μmol/kg attenuates remarkably induction of the Parkinsonism and prevents its progress. NaHS also increased the survival of TH- positive neurons and suppressed 6-OHDA- induced overexpression of GRP78 and CHOP. Blockade of ATP-sensitive potassium (K-ATP) channels with glibenclamide (Glib) prevented markedly the effect of NaHS on both the induction phase and survival of TH- positive neurons. But Glib did not affect the preventing effect of NaHS on the progress phase and its suppressing effect on the overexpression of ER stress markers.

CONCLUSION

H₂S attenuates induction of the 6-OHDA- induced Parkinsonism and also increases the survival of dopaminergic neurons through activation of K-ATP channels. H₂S also prevents progress of the Parkinsonism probably through suppression of ER stress.

Haloperidol-induced catalepsy as an animal model for parkinsonism: A systematic review of experimental studies

Several useful animal models for parkinsonism have been developed so far. Haloperidol-induced catalepsy is often used as a rodent model for the study of motor impairments observed in Parkinson's disease and related disorders and for the screening of potential antiparkinsonian compounds. The objective of this systematic review is to identify publications that used the haloperidol-induced catalepsy model for parkinsonism and to explore the methodological characteristics and the main questions addressed in these studies. A careful systematic search of the literature was carried out by accessing articles in three different databases: Web of Science, PubMed and SCOPUS. The selection and inclusion of studies were performed based on the abstract and, subsequently, on full-text analysis. Data extraction included the objective of the study, study design and outcome of interest. Two hundred and fifty-five articles were included in the review. Publication years ranged from 1981 to 2020. Most studies used the model to explore the effects of potential treatments for parkinsonism. Although the methodological characteristics used are quite varied, most studies used Wistar rats as experimental subjects. The most frequent dose of haloperidol used was 1.0 mg/kg, and the horizontal bar test was the most used to assess catalepsy. The data presented here provide a framework for an evidence-based approach to the design of preclinical research on parkinsonism using the haloperidol-induced catalepsy model. This model has been used routinely and successfully and is likely to continue to play a critical role in the ongoing search for the next generation of therapeutic interventions for parkinsonism.

Therapeutic potential of ATP-sensitive potassium channels in Parkinson's disease

In the past decade, there was an increasing interest in the therapeutic potential targeting ATP-sensitive potassium (K_ATP) channels for an effective treatment of Parkinson's disease (PD). K_ATP channels are widely expressed in the central nervous system and were reported to mediate the degeneration and death of nigral dopamine neurons in the pathogenesis of PD. This review aims to address the pivotal roles of K_ATP channels played in the mechanisms underlying PD pathogenesis, and provide possible directions for further research from different perspectives, such as the vulnerability of dopamine neurons in the substantia nigra, neurotransmitter releasing, iron metabolism in the brain, α-synuclein secretion and mitochondrial dysfunction, which are off critical importance in the investigation of K_ATP channels-targeted precise therapeutic interventions for PD.

Potassium channels and their emerging role in parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, which is associated with a selective loss of dopaminergic neurons in the substantia nigra (SN) and a reduction of dopamine in the striatum. Recently, ion channel dysfunction has been considered a reason for the pathogenesis of PD. Potassium (K⁺) channels are widespread in the central nervous system, and play key roles in modulating cellular excitability, synaptic transmission, and neurotransmitter release. Based on recent studies and data, we propose that K⁺ channels may be new therapeutic targets for PD that slow the progressive loss of dopaminergic neurons and attenuate motor and non-motor symptoms. In this review, we mainly focus on: delayed rectifier, inwardly rectifying, and double-pore K⁺ channels. We summarize the expression and function of these channels in PD-related brain regions. We also discuss the effects of pharmacological blockade or activation of K⁺ channels in the progression and treatment of PD.

Analysis of the Relationship between Type II Diabetes Mellitus and Parkinson's Disease: A Systematic Review

In the early sixties, a discussion started regarding the association between Parkinson's disease (PD) and type II diabetes mellitus (T2DM). Today, this potential relationship is still a matter of debate. This review aims to analyze both diseases concerning causal relationships and treatments. A total of 104 articles were found, and studies on animal and “in vitro” models showed that T2DM causes neurological alterations that may be associated with PD, such as deregulation of the dopaminergic system, a decrease in the expression of peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α), an increase in the expression of phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes 15 (PED/PEA-15), and neuroinflammation, as well as acceleration of the formation of alpha-synuclein amyloid fibrils. In addition, clinical studies described that Parkinson's symptoms were notably worse after the onset of T2DM, and seven deregulated genes were identified in the DNA of T2DM and PD patients. Regarding treatment, the action of antidiabetic drugs, especially incretin mimetic agents, seems to confer certain degree of neuroprotection to PD patients. In conclusion, the available evidence on the interaction between T2DM and PD justifies more robust clinical trials exploring this interaction especially the clinical management of patients with both conditions.

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.

Kir6.2 Deficiency Promotes Mesencephalic Neural Precursor Cell Differentiation via Regulating miR-133b/GDNF in a Parkinson's Disease Mouse Model

The loss of dopaminergic (DA) neurons in the substantia nigra (SN) is a major feature in the pathology of Parkinson's disease (PD). Using neural stem or progenitor cells (NSC/NPCs), the prospect of replacing the missing or damaged DA neurons is very attractive for PD therapy. However, little is known about the endogenous mechanisms and molecular pathways regulating the NSC/NPC proliferation and differentiation in the development of PD. Herein, using Kir6.2 knockout (Kir6.2-/-) mice, we observed that genetic deficiency of Kir6.2 exacerbated the loss of SN DA neurons relatively early in a chronic MPTP/probenecid (MPTP/p) injection course, but rescued the damage of neurons 7 days after the last MPTP/p injection. Meanwhile, we found that Kir6.2 knockout predominantly increased the differentiation of nuclear receptor-related 1 (Nurr1+) precursors to DA neurons, indicating that Kir6.2 deficiency could activate an endogenous self-repair process. Furthermore, we demonstrated in vivo and in vitro that lack of Kir6.2 promoted neuronal differentiation via inhibiting the downregulation of glia cell line-derived neurotrophic factor (GDNF), which negatively related to the level of microRNA-133b. Notably, we revealed that Gdnf is a target gene of miR-133b and transfection of miR-133b could attenuate the enhancement of neural precursor differentiation induced by Kir6.2 deficiency. Collectively, we clarify for the first time that Kir6.2/K-ATP channel functions as a novel endogenous negative regulator of NPC differentiation, and provide a promising neuroprotective target for PD therapeutics.

Interplay between adenosine receptor antagonist and cyclooxygenase inhibitor in haloperidol-induced extrapyramidal effects in mice

Antipsychotic drugs are the mainstay of psychotic disorders. The 'typical' antipsychotic agents are commonly employed for the positive symptoms of schizophrenia, though at an expense of extrapyramidal side effects (EPS). In the present study, we employed haloperidol (HP)-induced catalepsy model in mice to evaluate the role of adenosine receptor antagonist and cyclooxygenase (COX) enzyme inhibitor in the amelioration of EPS. HP produced a full blown catalepsy, akinesia and a significant impairment in locomotion and antioxidant status. Pre-treatment with COX inhibitor; naproxen (NPx) and adenosine receptor antagonist; caffeine (CAF), showed a significant impact on HP-induced cataleptic symptoms. Adenosine exerts pivotal control on dopaminergic receptors and is also involved in receptor internalization and recycling. On the other hand, prostaglandins (PGs) are implicated as neuro-inflammatory molecules released due to microglial activation in both Parkinson's disease (PD) and antipsychotics-induced EPS. The involvement of these neuroeffector molecules has led to the possibility of use of CAF and COX inhibitors as therapeutic approaches to reduce the EPS burden of antipsychotic drugs. Both these pathways seem to be interlinked to each other, where adenosine modulates the formation of PGs through transcriptional modulation of COXs. We observed an additive effect with combined treatment of NPx and CAF against HP-induced movement disorder. These effects lead us to propose that neuromodulatory pathways of dopaminergic circuitry need to be explored for further understanding and utilizing the full therapeutic potential of antipsychotic agents.

Haloperidol-induced parkinsonism is attenuated by varenicline in mice

Background Parkinson's disease (PD) is a neurodegenerative disorder of the central nervous system (CNS). However, there is no known drug to stop/slow down this neurodegeneration. Varenicline is an anti-smoking drug and has the potential to prevent neurodegeneration. Thus, the present study was designed to evaluate the effect of varenicline in animal models of PD. Methods Levodopa and haloperidol were administered in doses of 30 and 1 mg/kg, intraperitoneally (i.p.), respectively. Group 1 was administered haloperidol; groups 2, 3 and 4 were administered haloperidol along with varenicline in doses of 0.5, 1.5 and 2.5 mg/kg, i.p., respectively and group 5 was administered levodopa along with haloperidol. Varenicline was administered daily, 30 min prior to the administration of haloperidol. Varenicline was administered for the first 8 days, and then from the 9th day until the 15th day. Behavioral assessment (rotarod and catalepsy tests) was performed on days 9 and 15. Assessment of striatal dopamine levels and histopathology were also performed. Results In the haloperidol-treated groups, significant decrease in latency to fall off (on rotarod) and increase in catalepsy duration (in catalepsy test) were observed as compared to the control group. In the levodopa-treated group, significant increase in latency to fall off the rotarod and significant decrease in catalepsy duration were observed as compared to the haloperidol-treated groups. Further, on day 9, varenicline (2.5 mg/kg) significantly increased the latency to fall off the rotarod, while varenicline (0.5 and 1.5 mg/kg) did not cause any significant change in latency to fall off the rotarod as compared to the haloperidol-treated group. On day 15, significant increase in latency to fall off the rotarod was observed in varenicline (at all doses) as compared to the haloperidol-treated group. In the catalepsy test, the varenicline-treated (at all doses) groups showed significant decrease in duration of catalepsy on day 9 and day 15 as compared to the haloperidol-treated group. Significant decrease in striatal dopamine levels was observed among the haloperidol-treated groups as compared to the control group. Further, varenicline-treated (at all doses) and levodopa-treated groups showed significant increase in striatal dopamine levels when compared with the haloperidol-treated group. In histology, varenicline (0.5 mg/kg) showed moderate decrease in neurons, while varenicline (1.5 and 2.5 mg/kg) showed mild decrease in neurons. However, the levodopa-treated group did not show any significant decrease in neurons. Thus, varenicline has shown promising results and has provided novel strategy for the treatment of PD.

Attenuation of hyperalgesia responses via the modulation of 5-hydroxytryptamine signalings in the rostral ventromedial medulla and spinal cord in a 6-hydroxydopamine-induced rat model of Parkinson's disease

Background Although pain is one of the most distressing non-motor symptoms among patients with Parkinson's disease, the underlying mechanisms of pain in Parkinson's disease remain elusive. The aim of the present study was to investigate the role of serotonin (5-hydroxytryptamine) in the rostral ventromedial medulla (RVM) and spinal cord in pain sensory abnormalities in a 6-hydroxydopamine-treated rat model of Parkinson's disease. Methods The rotarod test was used to evaluate motor function. The radiant heat test and von Frey test were conducted to evaluate thermal and mechanical pain thresholds, respectively. Immunofluorescence was used to examine 5-hydroxytryptamine neurons and fibers in the rostral ventromedial medulla and spinal cord. High-performance liquid chromatography was used to determine 5-hydroxytryptamine and 5-hydroxyindoleacetic acid levels. Results The duration of running time on the rotarod test was significantly reduced in 6-hydroxydopamine-treated rats. Nociceptive thresholds of both mechanical and heat pain were reduced compared to sham-treated rats. In addition to the degeneration of cell bodies and fibers in the substantia nigra pars compacta, the number of rostral ventromedial medulla 5-hydroxytryptamine neurons and 5-hydroxytryptamine fibers in the spinal dorsal horn was dramatically decreased. 5-Hydroxytryptamine concentrations in both the rostral ventromedial medulla and spinal cord were reduced. Furthermore, the administration of citalopram significantly attenuated pain hypersensitivity. Interestingly, Intra-rostral ventromedial medulla (intra-RVM) microinjection of 5,7-dihydroxytryptamine partially reversed pain hypersensitivity of 6-hydroxydopamine-treated rats. Conclusions These results suggest that the decreased 5-hydroxytryptamine contents in the rostral ventromedial medulla and spinal dorsal horn may be involved in hyperalgesia in the 6-hydroxydopamine-induced rat model of Parkinson's disease.

The Anti-Parkinsonism Effects of KATP Channel Blockade in the 6-Hydroxydopamine-Induced Animal Model: The Role of Oxidative Stress

INTRODUCTION

Studies suggest that ATP-sensitive potassium (K_ATP) channels are a potential pharmacotherapeutic target for neuroprotection in neurodegenerative diseases. The current study aimed at evaluating the effect of pretreatment with glibenclamide (Glib) and B vitamins supplement on the severity of behavioral symptoms in 6-hydroxydopamine (OHDA)-induced Parkinsonism. Also malondialdehyde (MDA) concentration was measured in the blood and brain suspensions to find probable neuroprotective mechanism of Glib.

METHODS

The 6-OHDA was injected into striatum of rats by stereotaxic surgery. Treatment with Glib and B vitamins was started before the surgery and continued up to 3 weeks after that. Development and severity of Parkinsonism were evaluated by conventional behavioral tests. MDA values were measured spectrophotometrically using thiobarbituric acid and MDA standard curve.

RESULTS

Pretreatments with Glib, at both doses of 1 and 5 mg/kg or B vitamins significantly ameliorated severity of the behavioral symptoms. Pretreatment with a combination of Glib and B vitamins was more effective than pretreatment with Glib or B vitamins alone. Also, pretreatment with B vitamins, Glib, or a combination of them reduced MDA concentration in the brain suspensions. Decrease in MDA concentration in the group of rats that received a combination of B vitamins and Glib was more prominent than that of the Glib groups.

CONCLUSION

As severity of the behavioral symptoms in the 6-OHDA-induced Parkinsonism reflects the degree of the lesion in Substantia Nigra (SN) dopaminergic neurons, it is suggested that Glib pretreatment has neuroprotective effect against 6-OHDA-induced neurotoxicity. The current study data also showed that this effect may be mediated by antioxidant effect of Glib.

Changes in SK channel expression in the basal ganglia after partial nigrostriatal dopamine lesions in rats: Functional consequences

Parkinson's disease (PD) is a progressive neurodegenerative disease originating from the loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNC). The small-conductance calcium-activated potassium (SK) channels play an essential role in the regulation of midbrain DA neuron activity patterns, as well as excitability of other types of neurons of the basal ganglia. We therefore questioned whether the SK channel expression in the basal ganglia is modified in parkinsonian rats and how this could impact behavioral performance in a reaction time task. We used a rat model of early PD in which the progressive nigrostriatal DA degeneration was produced by bilateral infusions of 6-hydroxydopamine (6-OHDA) into the striatum. In situ hybridization of SK2 and SK3 mRNA and binding of iodinated apamin (SK2/SK3 blocker) were performed at 1, 8 or 21 days postsurgery in sham and 6-OHDA lesion groups. A significant decrease of SK3 channel expression was found in the SNC of lesioned animals at the three time points, with no change of SK2 channel expression. Interestingly, an upregulation of SK2 mRNA and apamin binding was found in the subthalamic nucleus (STN) at 21 days postlesion. These results were confirmed using quantitative real time polymerase chain reaction (qRT-PCR) approach. Functionally, the local infusion of apamin into the STN of parkinsonian rats enhanced the akinetic deficits produced by nigrostriatal DA lesions in a reaction time task while apamin infusion into the SNC had an opposite effect. These effects disappear when the positive modulator of SK channels (CyPPA) is co-administered with apamin. These findings suggest that an upregulation of SK2 channels in the STN may underlie the physiological adjustment to increased subthalamic excitability following partial DA denervation.

Opening of ATP-sensitive K(+) (KATP) channels enhance hydroxyl radical generation induced by MPP(+) in rat striatum

The present study examined whether opening of adenosine triphosphate (ATP) sensitive K(+) (KATP) channels can enhance 1-methyl-4-phenylpyridinium (MPP(+))-induced hydroxyl radical (OH) generation in rat striatum. Rats were anesthetized, and sodium salicylate in Ringer's solution (0.5nmol/ml per min) was infused through a microdialysis probe to detect the generation of OH as reflected by the non-enzymatic formation of 2.3-dihydroxybenzoic acid (DHBA) in the striatum. MPP(+) (5mM) enhanced generation of OH with concomitant increased efflux of dopamine (DA). Cromakalim (100μM), a KATP channel opener, through the microdialysis probe significantly increased both DA efflux and OH formation induced by MPP(+). Another KATP channel opener, nicorandil (1mM), also increased the level DA or DHBA, but these changes were not significant. However, in the presence of glibenclamide (10μM), a KATP channel antagonist, and the increase of MPP(+)-induced DA or DHBA were not observed. Cromakalim (10, 50 and 100μM) increased MPP(+)-induced DHBA formation in a concentration-dependent manner. However, the effects of cromakalim in the presence of glibenclamide were abolished. These results suggest that opening of KATP channels may cause OH generation by MPP(+).

Anti-Parkinson Activity of Petroleum Ether Extract of Ficus religiosa (L.) Leaves

In the present study, we evaluated anti-Parkinson's activity of petroleum ether extract of Ficus religiosa (PEFRE) leaves in haloperidol and 6 hydroxydopamine (6-OHDA) induced experimental animal models. In this study, effects of Ficus religiosa (100, 200, and 400 mg/kg, p.o.) were studied using in vivo behavioral parameters like catalepsy, muscle rigidity, and locomotor activity and its effects on neurochemical parameters (MDA, CAT, SOD, and GSH) in rats. The experiment was designed by giving haloperidol to induce catalepsy and 6-OHDA to induce Parkinson's disease-like symptoms. The increased cataleptic scores (induced by haloperidol) were significantly (p < 0.001) found to be reduced, with the PEFRE at a dose of 200 and 400 mg/kg (p.o.). 6-OHDA significantly induced motor dysfunction (muscle rigidity and hypolocomotion). 6-OHDA administration showed significant increase in lipid peroxidation level and depleted superoxide dismutase, catalase, and reduced glutathione level. Daily administration of PEFRE (400 mg/kg) significantly improved motor performance and also significantly attenuated oxidative damage. Thus, the study proved that Ficus religiosa treatment significantly attenuated the motor defects and also protected the brain from oxidative stress.

Sodium and Potassium Relating to Parkinson's Disease and Traumatic Brain Injury

Alkali metals, especially sodium and potassium, are plentiful and vital in biological systems. They take on important roles in health and disease. Such roles include the regulation of homeostasis, osmosis, blood pressure, electrolytic equilibria, and electric current. However, there is a limit to our present understanding; the ions have a great ability and capacity for action in health and disease, much greater than our current understanding. For the regulation of physiological homeostasis, there is a crucial regulator (renin-angiotensin system, RAS), found at both peripheral and central levels. Misregulation of the Na(+)-K(+) pump, and sodium channels in RAS are important for the understanding of disease progression, hypertension, diabetes, and neurodegenerative diseases, etc. In particular, RAS displays direct or indirect interaction important to Parkinson's disease (PD). In this chapter, the relationship between the regulation of sodium/potassium concentration and PD was sought. In addition, some recent biochemical and clinical findings are also discussed that help describe sodium and potassium in the context of traumatic brain injury (TBI). TBI is caused from the heavy striking of the head; this strongly affects ion flux in the affected tissue (brain) and damages cellular regulation systems. Thus, inappropriate concentrations of ions (hyper- and hyponatremia, and hyper- and hypokalemia) will perturb homeostasis giving rise to important and far reaching effects. These changes also impact osmotic pressure and the concentration of other metal ions, such as the calcium(II) ion.

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.

Complex Membrane Channel Blockade: A Unifying Hypothesis for the Prodromal and Acute Neuropsychiatric Sequelae Resulting from Exposure to the Antimalarial Drug Mefloquine

The alkaloid toxin quinine and its derivative compounds have been used for many centuries as effective medications for the prevention and treatment of malaria. More recently, synthetic derivatives, such as the quinoline derivative mefloquine (bis(trifluoromethyl)-(2-piperidyl)-4-quinolinemethanol), have been widely used to combat disease caused by chloroquine-resistant strains of the malaria parasite, Plasmodium falciparum. However, the parent compound quinine, as well as its more recent counterparts, suffers from an incidence of adverse neuropsychiatric side effects ranging from mild mood disturbances and anxiety to hallucinations, seizures, and psychosis. This review considers how the pharmacology, cellular neurobiology, and membrane channel kinetics of mefloquine could lead to the significant and sometimes life-threatening neurotoxicity associated with mefloquine exposure. A key role for mefloquine blockade of ATP-sensitive potassium channels and connexins in the substantia nigra is considered as a unifying hypothesis for the pathogenesis of severe neuropsychiatric events after mefloquine exposure in humans.

Molecular mechanisms of dopaminergic subset specification: fundamental aspects and clinical perspectives

Dopaminergic (DA) neurons in the ventral mesodiencephalon control locomotion and emotion and are affected in psychiatric and neurodegenerative diseases, such as Parkinson's disease (PD). A clinical hallmark of PD is the specific degeneration of DA neurons located within the substantia nigra (SNc), whereas neurons in the ventral tegmental area remain unaffected. Recent advances have highlighted that the selective vulnerability of the SNc may originate in subset-specific molecular programming during DA neuron development, and significantly increased our understanding of the molecular code that drives specific SNc development. We here present an up-to-date overview of molecular mechanisms that direct DA subset specification, integrating our current knowledge about subset-specific roles of transcription factors, signaling pathways and morphogenes. We discuss strategies to further unravel subset-specific gene-regulatory networks, and the clinical promise of fundamental knowledge about subset specification of DA neurons, with regards to cell replacement therapy and cell-type-specific vulnerability in PD.

Subcellular expression and neuroprotective effects of SK channels in human dopaminergic neurons

Small-conductance Ca(2+)-activated K(+) channel activation is an emerging therapeutic approach for treatment of neurological diseases, including stroke, amyotrophic lateral sclerosis and schizophrenia. Our previous studies showed that activation of SK channels exerted neuroprotective effects through inhibition of NMDAR-mediated excitotoxicity. In this study, we tested the therapeutic potential of SK channel activation of NS309 (25 μM) in cultured human postmitotic dopaminergic neurons in vitro conditionally immortalized and differentiated from human fetal mesencephalic cells. Quantitative RT-PCR and western blotting analysis showed that differentiated dopaminergic neurons expressed low levels of SK2 channels and high levels of SK1 and SK3 channels. Further, protein analysis of subcellular fractions revealed expression of SK2 channel subtype in mitochondrial-enriched fraction. Mitochondrial complex I inhibitor rotenone (0.5 μM) disrupted the dendritic network of human dopaminergic neurons and induced neuronal death. SK channel activation reduced mitochondrial membrane potential, while it preserved the dendritic network, cell viability and ATP levels after rotenone challenge. Mitochondrial dysfunction and delayed dopaminergic cell death were prevented by increasing and/or stabilizing SK channel activity. Overall, our findings show that activation of SK channels provides protective effects in human dopaminergic neurons, likely via activation of both membrane and mitochondrial SK channels. Thus, SK channels are promising therapeutic targets for neurodegenerative disorders such as Parkinson's disease, where dopaminergic cell loss is associated with progression of the disease.

Potassium channel in the mitochondria of human keratinocytes

The activation of mitochondrial potassium channels induces cytoprotection in various cell types. Hence, the identification of ion channels present in the inner mitochondrial membrane of keratinocytes is important in distinguishing possible protective mechanisms in these cells. In this paper, inner membrane mitochondrial ion channels of the human keratinocyte HaCaT cell line were investigated using a patch-clamp technique. We observed potassium-selective channel activity with a conductance of 83 pS at positive voltages. The I-V curve indicates that the observed channel has rectifying properties. Moreover, the channel activity was inhibited by acidic pH and 1 mM lidocaine. Using reverse transcriptase-PCR, we found an mRNA transcript for the TASK-3 (tandem pore domain acid-sensitive K channels) channel. We observed co-localization of the TASK-3 protein and a mitochondrial marker in the mitochondria of HaCaT cells. Additionally, we showed that TASK-3 knockdown HaCaT cells markedly decreased viability after UVB radiation exposure compared with control cells. In summary, the single-channel activity and properties of a mitochondrial potassium channel in a keratinocyte HaCaT cell line have been described.

Dopaminergic mechanisms underlying catalepsy, fear and anxiety: do they interact?

Haloperidol is a dopamine D2 receptor antagonist that induces catalepsy when systemically administered to rodents. The haloperidol-induced catalepsy is a state of akinesia and rigidity very similar to that seen in Parkinson's disease. There exists great interest in knowing whether or not some degree of emotionality underlies catalepsy. If so, what kind of emotional distress would permeate such motor disturbance? This study is an attempt to shed some light on this issue through an analysis of ultrasound vocalizations (USVs) of 22 kHz, open-field test, and contextual conditioned fear in rats with some degree of catalepsy induced by haloperidol. Systemic administration of haloperidol caused catalepsy and decreased exploratory activity in the open-field. There was no difference in the emission of USVs between groups during the catalepsy or the exploratory behavior in the open-field test. In the contextual conditioned fear, when administered before training session, haloperidol did not change the emission of USVs or the freezing response. When administered before testing session, haloperidol enhanced the freezing response and decreased the emission of USVs on the test day. These findings suggest that the involvement of dopaminergic mechanisms in threatening situations depends on the nature of the aversive stimulus. Activation of D2 receptors occurs in the setting up of adaptive responses to conditioned fear stimuli so that these mechanisms seem to be important for the emission of 22 kHz USVs during the testing phase of the contextual conditioned fear, but not during the training session or the open-field test (unconditioned fear stimuli). Catalepsy, on the other hand, is the result of the blockage of D2 receptors in neural circuits associated to motor behavior that appears to be dissociated from those directly linked to dopamine-mediated neural mechanisms associated to fear.

Group I mGluRs evoke K-ATP current by intracellular Ca2+ mobilization in rat subthalamus neurons

We reported previously that Ca(2+) influx through N-methly-d-aspartate-gated channels evokes ATP-sensitive K(+) (K-ATP) currents in rat subthalamic nucleus (STN) neurons. By using whole-cell patch clamp recordings in brain slices, we investigated the ability of (RS)-3,5-dihydroxyphenylglycine (DHPG), a group I metabotropic glutamate receptor (mGluR) agonist, to evoke K-ATP currents. DHPG (20 µM) evoked outward current at -70 mV and was associated with a positive slope conductance of 2.7 nS. The sulfonylurea agent tolbutamide (100 µM) converted the positive slope to negative slope conductance, indicating mediation by K-ATP channels (ATP-sensitive K+ channels). Currents evoked by DHPG were significantly reduced by a combination of mGluR1 and mGluR5 negative allosteric modulators. DHPG-evoked outward current was blocked by cyclopiazonic acid and thapsigargin and mimicked by caffeine, suggesting mediation by release of intracellular Ca(2+). DHPG outward current was also blocked by ryanodine and 2-aminoethoxydiphenylborane, suggesting mediation by ryanodine- and inositol 1,4,5-triphosphate-sensitive Ca(2+) release. The nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester and inhibitors of protein kinase G activity also suppressed DHPG-induced outward current. Voltage recordings showed that tolbutamide prolonged depolarizing plateau potentials and increased the spontaneous firing rate of STN neurons recorded in the presence of DHPG. These results show that group I mGluR stimulation generates K-ATP current by a nitric oxide- and protein kinase G-dependent process that is mediated by release of Ca(2+) from intracellular stores. Because burst firing is linked to symptoms of Parkinson's disease, we suggest that K-ATP channels might provide a physiologically important inhibitory influence on STN neuronal activity.

Chronic dopamine depletion augments the functional expression of K-ATP channels in the rat subthalamic nucleus

Symptoms of Parkinson's disease caused by dopamine depletion are associated with burst firing in the subthalamic nucleus (STN). Moreover, regularization or suppression of STN neuronal activity is thought to improve symptoms of Parkinson's disease. We reported recently that N-methyl-D-aspartate (NMDA) receptor stimulation of rat STN neurons evokes ATP-sensitive K(+) (K-ATP) current via a Ca(2+)- and nitric oxide-dependent mechanism. The present studies were done to determine whether or not K-ATP channel function in STN neurons is altered in a model of chronic dopamine depletion. Brain slices were prepared from rats with unilateral dopamine depletion caused by intracerebral 6-hydroxydopamine (6-OHDA) injections. Whole-cell patch-clamp recordings showed that NMDA evoked more outward current at -70 mV and greater positive slope conductance in STN neurons located ipsilateral to 6-OHDA treatment compared to neurons located contralateral. Moreover, extracellular, loose-patch recordings showed that NMDA increased spontaneous firing rate in STN neurons in slices from normal rats, whereas NMDA produced a tolbutamide-sensitive inhibition of firing rate in STN neurons located ipsilateral to 6-OHDA treatment. These results show that K-ATP channel function in STN neurons is up-regulated by chronic dopamine deficiency. We suggest that K-ATP channel activation in the STN might benefit symptoms of Parkinson's disease.

Iptakalim enhances adult mouse hippocampal neurogenesis via opening Kir6.1-composed K-ATP channels expressed in neural stem cells

BACKGROUND AND PURPOSE

Emerging evidence indicates that stimulating adult neurogenesis provides novel strategies for central nervous system diseases. Iptakalim (Ipt), a novel ATP-sensitive potassium (K-ATP) channel opener, has been demonstrated to play multipotential neuroprotective effects in vivo and in vitro. However, it remains unknown whether Ipt could regulate the adult neurogenesis.

METHODS AND RESULTS

Based on the finding that adult neural stem cells (ANSCs) in hippocampus expressed Kir6.1/SUR1-composed K-ATP channel, Kir6.1 heterozygotic (Kir6.1(+/-) ) mice were used to investigate whether and how Ipt regulates adult hippocampal neurogenesis. We showed that administration of Ipt (10 mg/kg) or fluoxetine (Flx, 10 mg/kg) for 4 weeks significantly increased newborn ANSCs in subgranular zone (SGZ) of Kir6.1(+/+) mice but failed to affect those of Kir6.1(+/-) mice. Meanwhile, ANSCs in Kir6.1(+/-) mice exhibited decreased survival rate and impaired ability of differentiation into astrocytes. We further found that Kir6.1(+/-) mice showed lower level of brain-derived neurotrophic factor (BDNF) in hippocampus compared with Kir6.1(+/+) mice. Furthermore, Ipt increased the levels of BDNF and basic fibroblast growth factor (FGF-2) throughout the hippocampus in Kir6.1(+/+) mice but not in Kir6.1(+/-) mice. Moreover, Ipt and Flx enhanced the phosphorylation of Akt and CREB in the hippocampus of Kir6.1(+/+) mice. Notably, these effects were completely abolished in Kir6.1(+/-) mice.

CONCLUSIONS

Our findings demonstrate that Ipt stimulates the adult hippocampal neurogenesis via activation of Akt and CREB signal following the opening of Kir6.1-composed K-ATP channels, which gives us an insight into the therapeutic implication of Ipt in the diseases with adult neurogenesis deficiency, such as major depression.

Verification of expressions of Kir2 as potential peripheral biomarkers in lymphocytes from patients with Parkinson's disease

Prior studies have reported gene expression alterations in peripheral blood lymphocytes (PBLs) obtained from patients with Parkinson's disease (PD) as compared to healthy controls. These alterations can not only be regarded as potential biomarkers, but also enhance understanding of the pathogenic mechanism of PD. In the present study, the gene expression levels of dopamine receptor (D2, D3), inward rectified potassium channels subunits Kir2 (Kir2.1, Kir2.2, Kir2.3, Kir2.4) and ATP-sensitive potassium channel subunit Kir6.2 in PBLs were analyzed using quantitative real-time PCR among 20 PD patients with medication, 10 PD patients without medication and 16 healthy controls, respectively. The results showed that there was a significantly decrease of the D2, D3 mRNA expression in PBLs of PD patients compared with that in healthy controls. The four inward rectified potassium channels Kir2.1, Kir2.2, Kir2.3, and Kir2.4 mRNA expression in PBLs from PD patients were also significantly down-regulated than that from age-matched healthy controls. However, there was no apparent difference in expression of another potassium channel Kir6.2 mRNA between PD patients and healthy controls. We proposed that the Kir2 potassium channels mRNA on blood lymphocytes may be regarded as a potential biomarker for PD screening.

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.

Prenatal lipopolysaccharide reduces motor activity after an immune challenge in adult male offspring

Prenatal lipopolysaccharide (LPS) exposure causes reproductive, behavioral and neurochemical injuries in both the mother and pups. Previous investigations by our group showed that prenatal LPS administration (100 microg/kg, i.p.) on gestational day 9.5 impaired the male offspring's social behavior in infancy and adulthood. In the present study, we investigated whether these social behavioral changes were associated with motor activity impairment. Male rat pups treated prenatally with LPS or not were tested for reflexological development and open field general activity during infancy. In adulthood, animals were tested for open field general activity, haloperidol-induced catalepsy and apomorphine-induced stereotypy; striatal dopamine levels and turnover were also measured. Moreover, LPS-treated or untreated control pups were challenged with LPS in adulthood and observed for general activity in the open field. In relation to the control group, the motor behavior of prenatally treated male pups was unaffected at basal levels, both in infancy and in adulthood, but decreased general activity was observed in adulthood after an immune challenge. Also, striatal dopamine and metabolite levels were decreased in adulthood. In conclusion, prenatal LPS exposure disrupted the dopaminergic system involved with motor function, but this neurochemical effect was not accompanied by behavioral impairment, probably due to adaptive plasticity processes. Notwithstanding, behavioral impairment was revealed when animals were challenged with LPS, resulting in enhanced sickness behavior.

Ca2+ influx through NMDA-gated channels activates ATP-sensitive K+ currents through a nitric oxide-cGMP pathway in subthalamic neurons

Excessive burst firing of action potentials in subthalamic nucleus (STN) neurons has been correlated with the bradykinesia and rigidity seen in Parkinson's disease. Consequently, there is much interest in characterizing mechanisms that promote burst firing, such as the regulation of NMDA receptor function. Using whole-cell recording techniques in rat brain slices, we report that inward currents evoked by NMDA are greatly potentiated by ATP-sensitive K(+) (K-ATP) channel blocking agents in STN neurons but not in dopamine neurons in the substantia nigra. Moreover, we found that the ability of NMDA to evoke K-ATP current was blocked by inhibitors of nitric oxide synthase, guanylyl cyclase, and calcium/calmodulin. By altering firing patterns of STN neurons, this NMDA/K-ATP interaction may exert an important influence on basal ganglia output and thereby affect the clinical expression of Parkinson's disease.

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.

Hypersensitivity of aquaporin 4-deficient mice to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine and astrocytic modulation

Aquaporin 4 (AQP4) is a predominant water channel protein in mammalian brains, which is localized in the astrocyte plasma membrane. AQP4 has gained much attraction due to its involvement in the physiopathology of cerebral disorders including stroke, tumor, infection, hydrocephalus, epilepsy, and traumatic brain injury. But there is almost no evidence whether abnormal AQP4 levels are associated with degenerative diseases, such as Parkinson's disease (PD). In our studies, we established PD animal models by administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine to test the hypothesis that abnormal AQP4 expression is involved in the pathophysiology of this disease. We show that mutant mice lacking AQP4 were significantly more prone to MPTP-induced neurotoxicity than their wild-type littermates. Furthermore, after administration of MPTP, astroglial proliferation and GDNF protein synthesis were inhibited by AQP4 deficiency. This study demonstrates that AQP4 is important in the MPTP neurotoxic process and indicates that the therapeutic strategy targeted to astrocytic modulation with AQP4 may offer a great potential for the development of new treatment for PD.

Neuroprotective effects of PACAP27 in mice model of Parkinson's disease involved in the modulation of K(ATP) subunits and D2 receptors in the striatum

Pituitary adenylate cyclase activating polypeptide (PACAP) exhibits a protective effect against neural injury in vitro and in vivo. However, it has not been reported whether peripheral intravenous administration of PACAP could confer benefits in animal models of Parkinson's disease (PD). Furthermore, the underlying molecular mechanisms responsible for these effects are poorly understood. In the present experiments, we determined the effects and mechanism of action of intravenously administered PACAP27 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice. Our results indicate that intravenous injection of PACAP27 offers neuroprotective effects in the MPTP-induced PD mouse model which may not be directly associated with the expression levels of the monoamine transporters. However, this effect may be correlated with its ability to selectively regulate not only K(ATP) subunits, but D2 receptors in the striatum. Our findings suggest that the benefit of PACAP may accompany with changes not only in dopaminergic neurotransmission, but also in cholinergic neurotransmission that are relatively associated with the K(ATP) subunits and D2 receptors in the striatum.

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: a novel target for protection against UV-induced human skin cell damage

Ultraviolet radiation (UV) induces cell damages leading to skin photoaging and skin cancer. ATP-sensitive potassium (K(ATP)) channel openers (KCOs) have been shown to exert significant myocardial preservation and neuroprotection in vitro and in vivo, and yet the potential role of those KCOs in protection against UV-induced skin cell damage is unknown. We investigated the effects of pinacidil and diazoxide, two classical KCOs, on UV-induced cell death using cultured human keratinocytes (HaCat cells). Here, we demonstrated for the first time that Kir 6.1, Kir 6.2 and SUR2 subunits of K(ATP) channels are functionally expressed in HaCaT cells and both non-selective K(ATP) channel opener pinacidil and mitoK(ATP) (mitochondrial K(ATP)) channel opener diazoxide attenuated UV-induced keratinocytes cell death. The protective effects were abolished by both non-selective K(ATP) channel blocker glibenclamide and selective mitoK(ATP) channel blocker 5-hydroxydecanoate (5-HD). Also, activation of K(ATP) channel with pinacidil or diazoxide resulted in suppressive effects on UV-induced MAPK activation and reactive oxygen species (ROS) production. Unexpectedly, we found that the level of intracellular ROS was slightly elevated in HaCaT cells when treated with pinacidil or diazoxide alone. Furthermore, UV-induced mitochondrial membrane potential loss, cytochrome c release and ultimately apoptotic cell death were also inhibited by preconditioning with pinacidil and diazoxide, and their effects were reversed by glibenclamide and 5-HD. Taken together, we contend that mitoK(ATP) is likely to contribute the protection against UV-induced keratinocytes cell damage. Our findings suggest that K(ATP) openers such as pinacidil and diazoxide may be utilized to prevent from UV-induced skin aging.

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.