The Cytoprotective Effects of Dantrolene

Dantrolene paradoxically exacerbates short-term brain glucose hypometabolism, hippocampal damage and neuroinflammation induced by status epilepticus in the rat lithium-pilocarpine model

Status epilepticus (SE) is a neurologic emergency characterized by prolonged or rapidly recurring seizures. Increased intracellular calcium concentration ([Ca2+]i) occurring after SE is a key mediator of excitotoxicity that contributes to the brain damage associated with the development of epilepsy. Accumulated evidence indicates that dantrolene, a ryanodine receptor (RyR) blocker may have protective effects against the SE-induced damage. We evaluated whether dantrolene (10 mg/kg, i.p.) administered twice, 5 min and 24 h after the lithium-pilocarpine-induced SE in rats, had neuroprotective effects. Dantrolene by itself had no effects on control rats. However, it exacerbated the signs of damage in rats that underwent SE, increasing brain glucose hypometabolism as measured by PET neuroimaging 3 days after SE. Likewise, the neurohistochemical studies revealed that dantrolene aggravated signs of hippocampal neurodegeneration, neuronal death and microglia-induced neuroinflammation. Besides, the damaging effects were reflected by severe body weight loss. Overall, our results point towards a deleterious effect of dantrolene in the lithium-pilocarpine-induced SE model. Nonetheless, our results are in opposition to the reported neuroprotective effects of dantrolene. Whether the mechanisms underlying [Ca2+]i increase might significantly differ depending on the particularities of the model of epilepsy used and general experimental conditions need further studies. Besides, it is yet to be determined which isoform of RyRs significantly contributes to Ca2+-induced excitotoxicity in the lithium-pilocarpine SE rat model.

Intranasal dantrolene nanoparticles inhibit inflammatory pyroptosis in 5XFAD mice brains

Background

This study investigates the effects of intranasal dantrolene nanoparticles on inflammation and programmed cell death by pyroptosis in 5XFAD Alzheimer's Disease (AD) mice.

Methods

5XFAD and wild type (WT) B6SJLF1/J mice were treated with intranasal dantrolene nanoparticles (5 mg/kg), daily, Monday to Friday, for 12 weeks continuously, starting at 9 months of age. Blood and brain were harvested at 13 months of age, one month after completion of 12 weeks intranasal dantrolene nanoparticle treatment. Blood biomarkers function of liver (Alanine transaminase, ALT), kidney (Creatinine), and thyroid (TSH: Thyroid-stimulating hormone) were measured using ELISA. The changes of whole brain tissue proteins on Ca 2+ release channels on membrane of endoplasmic reticulum (type 2 ryanodine and type 1 InsP3 receptors, RyR-2 and InsP3R-1), lipid peroxidation byproduct malondialdehyde (MDA)-modified proteins, 4-HNE, pyroptosis regulatory proteins (NLR family pyrin domain containing 3 (NLRP3), cleaved caspase-1, full length or N-terminal of Gasdermin D (GSDMD), cytotoxic (IL-1, IL-18, IL-6, TNF-a) and cytoprotective (IL-10) cytokines, astrogliosis (GFAP), microgliosis (IBA-1) and synapse proteins (PSD-95, Synapsin-1) were determined using immunoblotting. Body weights were monitored regularly.

Results

Intranasal dantrolene nanoparticles significantly inhibited the increase of RyR-2 and InsP3R-1 proteins, MDA-modified proteins, 4-NHE, pyroptosis regulatory proteins (NLRP3, cleaved caspase-1, N-terminal GSDMD), cytotoxic cytokine (IL-1β, IL-18, IL-6, TNF-α), biomarkers for astrogliosis (GFAP) and microgliosis (IBA-1), and the decrease of cytoprotective cytokine (IL-10) and synaptic proteins (PSD-95, synpasin-1). Intranasal dantrolene nanoparticles for 12 weeks did not affect blood biomarkers for function of liver, kidney, and thyroid, not did it change body weight significantly.

Conclusion

Intranasal dantrolene nanoparticles significantly inhibit the increase of RyR-2 and InsP 3 R-1 Ca 2+ channel receptor proteins, ameliorate activation of the pyroptosis pathway and pathological inflammation, and the associated loss of synapse proteins. Intranasal dantrolene nanoparticles for three months did not affect liver, kidney and thyroid functions or cause other side effects.

Flupyradifurone activates DUM neuron nicotinic acetylcholine receptors and stimulates an increase in intracellular calcium through the ryanodine receptors

Insect neuronal nicotinic acetylcholine receptors (nAChRs) are transmembrane receptors that play a key role in the development and synaptic plasticity of both vertebrates and invertebrates, and are considered to be major targets of several insecticides. We used dorsal unpaired median (DUM) neurons, which are insect neurosecretory cells, to explore what type of nAChRs are involved in flupyradifurone's (FLU) mode of action, and to study the role of calcium release from intracellular stores in this process. Using whole-cell patch-clamp and fura-2-AM calcium imaging techniques, we found that inhibition of IP3Rs through application of 2-APB reduced FLU inward currents, but did not affect the intracellular calcium release induced by FLU. In contrast, inhibition of RyRs using ryanodine, led to reduction of intracellular calcium increase following FLU pulse application. These results suggested that FLU inward currents are likely due to a combination of the direct effects of FLU on DUM neuron nAChRs and the subsequent calcium release from RyRs.

Management of Suspected α-Pyrrolidinoisohexanophenone (α-PiHP)-Related Hyperthermia in a Young Adult: A Case Report

Synthetic cathinones, commonly known as "bath salts," have been increasingly implicated in severe health incidents. α-Pyrrolidinoisohexanophenone (α-PiHP) is one of the substances for which clinical data remain limited. In this article, we report a case of a 32-year-old male patient who ingested five grams of α-PiHP in a suicide attempt, resulting in hyperthermia and severe complications, including rhabdomyolysis and acute kidney injury. Despite the lack of confirmation for α-PiHP intoxication in toxicology screens, the patient's reported history was strongly suggestive. Considering a diagnostic uncertainty between serotonin syndrome and sympathomimetic toxidrome, and given the unavailability of cyproheptadine, dantrolene was administered to control the hyperthermia, resulting in a prompt and effective reduction in core body temperature. This case highlights the potential utility of dantrolene in treating hyperthermia induced by synthetic cathinones.

Purinergic agonists increase [Ca2+]i in rat conjunctival goblet cells through ryanodine receptor type 3

ATP and benzoylbenzoyl-ATP (BzATP) increase free cytosolic Ca2+ concentration ([Ca2+]i) in conjunctival goblet cells (CGCs) resulting in mucin secretion. The purpose of this study was to investigate the source of the Ca2+i mobilized by ATP and BzATP. First-passage cultured rat CGCs were incubated with Fura-2/AM, and [Ca2+]i was measured under several conditions with ATP and BzATP stimulation. The following conditions were used: 1) preincubation with the Ca2+ chelator EGTA, 2) preincubation with the SERCA inhibitor thapsigargin (10-6 M), which depletes ER Ca2+ stores, 3) preincubation with phospholipase C (PLC) or protein kinase A (PKA) inhibitor, or 4) preincubation with the voltage-gated calcium channel antagonist nifedipine (10-5 M) and the ryanodine receptor (RyR) antagonist dantrolene (10-5 M). Immunofluorescence microscopy (IF) and quantitative reverse transcription polymerase chain reaction (RT-qPCR) were used to investigate RyR presence in rat and human CGCs. ATP-stimulated peak [Ca2+]i was significantly lower after chelating Ca2+i with 2 mM EGTA in Ca2+-free buffer. The peak [Ca2+]i increase in CGCs preincubated with thapsigargin, the PKA inhibitor H89, nifedipine, and dantrolene, but not the PLC inhibitor, was reduced for ATP at 10-5 M and BzATP at 10-4 M. Incubating CGCs with dantrolene alone decreased [Ca2+]i and induced CGC cell death at a high concentration. RyR3 was detected in rat and human CGCs with IF and RT-qPCR. We conclude that ATP- and BzATP-induced Ca2+i increases originate from the ER and that RyR3 may be an essential regulator of CGC [Ca2+]i. This study contributes to the understanding of diseases arising from defective Ca2+ signaling in nonexcitable cells.NEW & NOTEWORTHY ATP and benzoylbenzoyl-ATP (BzATP) induce mucin secretion through an increase in free cytosolic calcium concentration ([Ca2+]i) in conjunctival goblet cells (CGCs). The mechanisms through which ATP and BzATP increase [Ca2+]i in CGCs are unclear. Ryanodine receptors (RyRs) are fundamental in [Ca2+]i regulation in excitable cells. Herein, we find that ATP and BzATP increase [Ca2+]i through the activation of protein kinase A, voltage-gated calcium channels, and RyRs, and that RyRs are crucial for nonexcitable CGCs' Ca2+i homeostasis.

Dantrolene corrects cellular disease features of Darier disease and may be a novel treatment

Darier disease (DD) is a rare severe acantholytic skin disease caused by mutations in the ATP2A2 gene that encodes for the sarco/endoplasmic reticulum calcium ATPase isoform 2 (SERCA2). SERCA2 maintains endoplasmic reticulum calcium homeostasis by pumping calcium into the ER, critical for regulating cellular calcium dynamics and cellular function. To date, there is no treatment that specifically targets the disease mechanisms in DD. Dantrolene sodium (Dl) is a ryanodine receptor antagonist that inhibits calcium release from ER to increase ER calcium levels and is currently used for non-dermatological indications. In this study, we first identified dysregulated genes and molecular pathways in DD patient skin, demonstrating downregulation of cell adhesion and calcium homeostasis pathways, as well as upregulation of ER stress and apoptosis. We then show in various in vitro models of DD and SERCA2 inhibition that Dl aided in the retention of ER calcium and promoted cell adhesion. In addition, Dl treatment reduced ER stress and suppressed apoptosis. Our findings suggest that Dl specifically targets pathogenic mechanisms of DD and may be a potential treatment.

Dantrolene alleviates mitochondrial dysfunction and neuroinflammation in traumatic brain injury by modulating the NF-ĸβ/Akt pathway

Traumatic brain injury (TBI) triggers a bevy of changes including mitochondrial dysfunction, apoptosis, oxidative stress, neurobehavioural impairment, and neuroinflammation, among others. Dantrolene (DNT), a muscle relaxant which inhibits intracellular Ca2+ signaling from the ER, has been repurposed as a potential neuroprotective agent in various neurological diseases. However, there have been limited studies on whether it can mitigate TBI-induced deficits and restore impaired mitochondrial dynamics. This study sought to evaluate whether Dantrolene can potentially provide neuroprotection in an in vivo model of TBI. Male wistar rats subjected to TBI were treated with DNT (10 mg/kg) 1 h and 12 h post surgery. Animals were assessed 24 h post-TBI to evaluate neurobehavioural deficits and cerebral edema. We evaluated the protein expressions of apoptotic, autophagic, and neuroinflammatory markers by immunoblotting, as well as Mitochondrial Membrane Potential (MMP) and Reactive Oxygen Species (ROS) via Flow Cytometry to ascertain the effects of DNT on TBI. We further analysed immunofluorescence staining with Glial Fibrillary Acidic Protein (GFAP) and immunohistochemistry with NF-κβ to investigate neuroinflammation. H&E staining was also performed post-TBI. Our findings revealed DNT administration inhibits mitochondria-mediated apoptotis and reduces heightened oxidative stress. DNT treatment was also found to reverse neurobehavioural impairments and offer neuroprotection by preserving neuronal architechture. We also demonstrated that DNT inhibits neuronal autophagy and alleviates neuroinflammation following TBI by modulating the NF-κβ/Akt signaling pathway. Thus, our results suggest a novel application of DNT in ameliorating the multitude of deficits induced by TBI, thereby conferring neuroprotection.

Dantrolene and coenzyme Q10 as a suggested combination therapy to statin-induced myopathy in high fat diet rats: A possible interference with ROS/ TGF-β / Smad4 signaling pathway

One of the major hitches for statins' utilization is the development of myotoxicity. Versatile studies reported that the underlining molecular mechanisms including coenzyme Q10 (CoQ10)/ubiquinone depletion, as well as the disturbance in the cytoplasmic Ca2+ homeostasis. Therefore, we investigated the consequences of supplementing CoQ10 and dantrolene, a cytoplasmic Ca2+ reducing agent, in combination with simvastatin. This adjuvant therapy normalized the simvastatin-mediated elevation in serum ALT, AST, CK-MM, as well as tissue Ca2+ content, in addition to suppressing the simvastatin-mediated oxidative stress in simvastatin-treated rats, while having no effect upon statin-induced antihyperlipidemic effect. Additionally, the combination inhibited the simvastatin-induced TGF-β/ Smad4 pathway activation. Collectively, the current study emphasizes on the potential utilization of dantrolene and CoQ10 as an adjuvant therapy to statins treatment for improving their side effect profile.

RyR2-dependent modulation of neuronal hyperactivity: A potential therapeutic target for treating Alzheimer's disease

Increasing evidence suggests that simply reducing β-amyloid (Aβ) plaques may not significantly affect the progression of Alzheimer's disease (AD). There is also increasing evidence indicating that AD progression is driven by a vicious cycle of soluble Aβ-induced neuronal hyperactivity. In support of this, it has recently been shown that genetically and pharmacologically limiting ryanodine receptor 2 (RyR2) open time prevents neuronal hyperactivity, memory impairment, dendritic spine loss and neuronal cell death in AD mouse models. By contrast, increased RyR2 open probability (Po) exacerbates the onset of familial AD-associated neuronal dysfunction and induces AD-like defects in the absence of AD-causing gene mutations. Thus, RyR2-dependent modulation of neuronal hyperactivity represents a promising new target for combating AD.

The expression of tuftelin 1 as a new theranostic marker in early diagnosis and as a therapeutic target in hepatocellular carcinoma

Currently, many challenges are associated with hepatocellular carcinoma (HCC) as the failure of early diagnosis, and the lack of effective therapy. This study aimed to investigate the possible role of tuftelin 1 (TUFT 1) in the early diagnosis of HCC and evaluate the potential contribution of the TUFT 1/Ca+2 /phosphinositol 3 kinase (PI3K) pathway in dantrolene sodium (Dan) therapeutic outcomes. The study was performed on two sets of rats, the staging (30 rats) and treatment sets (80 rats). HCC was induced by a single dose of diethylnitrosamine (DENA). The hepatic content of TUFT 1 protein was assayed via western blot and immunohistochemistry (IHC), while PI3K, vascular endothelial growth factor (VEGF), Cyclin D1, and matrix-metalloproteinase-9 (MMP-9) contents were assessed using enzyme-linked immunosorbent assay. Hepatic and serum calcium were measured colorimetrically. Furthermore, the nuclear proliferation marker, (Ki-67), (Kiel [Ki] where the antibody was produced in the University Department of Pathology and the original clone number is 67)-expression was assessed by IHC. TUFT 1/Ca+2 /PI3K signaling pathway was progressively activated in the 3 studied stages of HCC with subsequent upregulation of angiogenesis, cell cycle, and metastasis. More interestingly, Dan led to TUFT 1/Ca+2 /PI3K pathway disruption by diminution of the hepatic contents of TUFT 1, calcium, PI3K, VEGF, Cyclin D1, and MMP-9 in a dose-dependent pattern. TUFT 1 can serve as a theranostic biomarker in HCC. Moreover, Dan exerted an antineoplastic effect against HCC via the interruption of TUFT 1/Ca+2 /PI3K pathway.

Effects of chronic intranasal dantrolene on nasal mucosa morphology in mice

OBJECTIVE

We have previously shown that the intranasal administration of dantrolene ameliorated cognitive dysfunction in the 5XFAD mouse model of Alzheimer's disease. This study examines the morphology of the nasal mucosa after 10 months of intranasal dantrolene in 5XFAD mice.

MATERIALS AND METHODS

5XFAD mice were either treated with intranasal dantrolene (5 mg/kg, 3 times/wk) from 2 months to 12 months of age or given no treatment at all. The mice were euthanatized at 12 months of age and the snouts were processed for histological examination. The morphology of the nasal mucosa was assessed and compared between the two groups.

RESULTS

There were no significant differences in the thickness of the olfactory epithelium or the proportion of the thickness of the glandular layer to the wall of mucosa and submucosa in the nasal passages.

CONCLUSIONS

Long-term intranasal administration of dantrolene did not significantly change the nasal mucosa morphology in 5XFAD mice.

Intranasal Dantrolene as a Disease-Modifying Drug in Alzheimer 5XFAD Mice

Background/Objective:

This study compares the effectiveness and safety of intranasal versus subcutaneous administration of dantrolene in 5XFAD Alzheimer’s disease (AD) mice.

Methods:

5XFAD and wild type (WT) B6SJLF1/J mice were treated with intranasal or subcutaneous dantrolene (5 mg/kg, 3×/wk), or vehicle. The early (ETG) and late (LTG) treatment groups began treatment at 2 or 6 months of age, respectively, and both treatment groups finished at12 months of age. Behavior was assessed for olfaction (buried food test), motor function (rotarod), and cognition (fear conditioning, Morris water maze). Liver histology (H & E staining) and function, synaptic proteins, and brain amyloid immunohistochemistry were examined. Plasma and brain dantrolene concentrations were determined in a separate cohort after intranasal or subcutaneous administration.

Results:

Intranasal dantrolene achieved higher brain and lower plasma concentrations than subcutaneous administration. Dantrolene administration at both approaches significantly improved hippocampal-dependent and -independent memory in the ETG, whereas only intranasal dantrolene improved cognition in the LTG. Dantrolene treatment had no significant change in the amyloid burden or synaptic proteins and no significant side effects on mortality, olfaction, motor, or liver functions in 5XFAD mice. Intranasal dantrolene treatment significantly ameliorated memory loss when it was started either before or after the onset of AD symptoms in 5XFAD mice.

Conclusions:

The long-term intranasal administration of dantrolene had therapeutic effects on memory compared to the subcutaneous approach even started after onset of AD symptoms, suggesting use as a disease-modifying drug, without significant effects on amyloid plaques, side effects, or mortality.

Calcium ions trigger the exposure of phosphatidylserine on the surface of necrotic cells

Intracellular Ca²⁺ level is under strict regulation through calcium channels and storage pools including the endoplasmic reticulum (ER). Mutations in certain ion channel subunits, which cause mis-regulated Ca²⁺ influx, induce the excitotoxic necrosis of neurons. In the nematode Caenorhabditis elegans, dominant mutations in the DEG/ENaC sodium channel subunit MEC-4 induce six mechanosensory (touch) neurons to undergo excitotoxic necrosis. These necrotic neurons are subsequently engulfed and digested by neighboring hypodermal cells. We previously reported that necrotic touch neurons actively expose phosphatidylserine (PS), an “eat-me” signal, to attract engulfing cells. However, the upstream signal that triggers PS externalization remained elusive. Here we report that a robust and transient increase of cytoplasmic Ca²⁺ level occurs prior to the exposure of PS on necrotic touch neurons. Inhibiting the release of Ca²⁺ from the ER, either pharmacologically or genetically, specifically impairs PS exposure on necrotic but not apoptotic cells. On the contrary, inhibiting the reuptake of cytoplasmic Ca²⁺ into the ER induces ectopic necrosis and PS exposure. Remarkably, PS exposure occurs independently of other necrosis events. Furthermore, unlike in mutants of DEG/ENaC channels, in dominant mutants of deg-3 and trp-4, which encode Ca²⁺ channels, PS exposure on necrotic neurons does not rely on the ER Ca²⁺ pool. Our findings indicate that high levels of cytoplasmic Ca²⁺ are necessary and sufficient for PS exposure. They further reveal two Ca²⁺-dependent, necrosis-specific pathways that promote PS exposure, a “two-step” pathway initiated by a modest influx of Ca²⁺ and further boosted by the release of Ca²⁺ from the ER, and another, ER-independent, pathway. Moreover, we found that ANOH-1, the worm homolog of mammalian phospholipid scramblase TMEM16F, is necessary for efficient PS exposure in thapsgargin-treated worms and trp-4 mutants, like in mec-4 mutants. We propose that both the ER-mediated and ER-independent Ca²⁺ pathways promote PS externalization through activating ANOH-1.

Necrosis is a type of cell death that exhibits distinct morphological features such as cell and organelle swelling. Necrotic cells expose phosphatidylserine (PS)–a type of phospholipid—on their outer surfaces. Receptor molecules on phagocytes detect PS on necrotic cells and subsequently initiate the engulfment process. As necrosis is associated with stroke, cancer, neurodegenerative diseases, and heart diseases, studying necrotic cell clearance has important medical relevance. In the model organism the nematode C. elegans, we previously identified membrane proteins that promote the exposure of PS on necrotic cell surfaces by studying neurons that are induced to undergo necrosis by dominant mutations in ion channels. Here, in C. elegans, we have discovered that the necrotic insults trigger an increase of the cytoplasmic calcium ion (Ca²⁺), which in turn promotes PS externalization on necrotic cell surfaces. Furthermore, we have identified two different mechanisms that increase cytoplasmic Ca²⁺ levels, one dependent on the Ca²⁺ contribution from the endoplasmic reticulum (ER), the other independent of the ER. The Ca²⁺ signal targets ANOH-1, a worm homolog of mammalian proteins capable of externalizing PS, for promoting PS exposure on necrotic cells. Our findings reveal novel upstream regulatory mechanisms that promote necrotic cell clearance in animals.

Dantrolene Induces Mitigation of Myocardial Ischemia-Reperfusion Injury by Ryanodine Receptor Inhibition

The impairment of intracellular calcium homeostasis plays an essential role during ischemia-reperfusion injury. Calcium release from sarcoplasmic reticulum which is triggered by myocardial ischemia is mainly mediated by ryanodine receptors. Dantrolene sodium is a ryanodine receptor antagonist. The objective of the present study was to evaluate the in-vivo impact of dantrolene sodium on myocardial ischemia-reperfusion injury in swine models. An in vivo, experimental trial comparing 10 experimental animals which received dantrolene sodium with 9 control swine models was conducted. Their left anterior descending coronary artery was temporarily occluded for 75 minutes via a vessel tourniquet, which was then released. Myocardial reperfusion was allowed for 24 hours. Dantrolene was administered at the onset of the reperfusion period and levels of troponin, creatine phosphokinase and creatine kinase myocardial band between the two groups were compared. Additionally, various other hemodynamic parameters and left ventricular morphology and function were examined. There were significantly lower values of troponin, creatine phosphokinase and creatine kinase myocardial band in the dantrolene group indicating less ischemia-reperfusion injury. Moreover, the postischemic cardiac index was also greater in the dantrolene group, whereas viable myocardium was also better preserved. In conclusion, the in vivo cardioprotective role of dantrolene sodium against ischemia-reperfusion injury in swine models was indicated in this study. Therefore, dantrolene sodium administration could be a promising treatment against ischemia-reperfusion injury in humans. However, large randomized clinical studies should be firstly carried out to prove this hypothesis.

Could dantrolene be explored as a repurposed drug to treat COVID-19 patients by restoring intracellular calcium homeostasis?

Dantrolene, an FDA approved drug to treat malignant hyperthermia and muscle spasm, has been demonstrated to inhibit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mediated toxicity of host cells. Ryanodine receptor overactivation and associated disruption of intracellular Ca2+ homeostasis play important roles in SARS-CoV-2 infection and replication of host cells. Dantrolene, as an inhibitor of RyRs, is expected to ameliorate these detrimental effects of SARS-CoV-2 in host cells. Additionally, dantrolene has also been shown to inhibit multiple cell or organ damage induced by hypoxia/ischemia, mitochondria damage, oxidative stresses, inflammation, impairment of autophagy and apoptosis, etc., which are often the causes of severity and mortality of COVID-19 patients. We have repurposed that dantrolene has a high potential at treating COVID-19 patients and reducing its morbidity and mortality.

Ryanodine Receptors: A Potential Treatment Target in Various Neurodegenerative Disease

Progressive neuronal demise is a key contributor to the key pathogenic event implicated in many different neurodegenerative disorders (NDDs). There are several therapeutic strategies available; however, none of them are particularly effective. Targeted neuroprotective therapy is one such therapy, which seems a compelling option, yet remains challenging due to the internal heterogeneity of the mechanisms underlying various NDDs. An alternative method to treat NDDs is to exploit common modalities involving molecularly distinct subtypes and thus develop specialized drugs with broad-spectrum characteristics. There is mounting evidence which supports for the theory that dysfunctional ryanodine receptors (RyRs) disrupt intracellular Ca²⁺ homeostasis, contributing to NDDs significantly. This review aims to provide direct and indirect evidence on the intersection of NDDs and RyRs malfunction, and to shed light on novel strategies to treat RyRs-mediated disease, modifying pharmacological therapies such as the potential therapeutic role of dantrolene, a RyRs antagonist.

A "crush" course on rhabdomyolysis: risk stratification and clinical management update for the perioperative clinician

Rhabdomyolysis, the release of myoglobin and other cellular breakdown products from necrotic muscle tissue, is seen in patients with crush injuries, drug overdose, malignant hyperthermia, muscular dystrophy, and with increasing frequency in obese patients undergoing routine procedures. For the perioperative clinician, managing the resultant shock, hyperkalemia, acidosis, and myoglobinuric acute kidney injury can present a significant challenge. Prompt recognition, hydration, and correction of metabolic disturbances may reduce or eliminate the need for long-term renal replacement therapy. This article reviews the pathophysiology and discusses key issues in the perioperative diagnosis, risk stratification, and management of rhabdomyolysis.

Dantrolene Ameliorates Impaired Neurogenesis and Synaptogenesis in Induced Pluripotent Stem Cell Lines Derived from Patients with Alzheimer's Disease

BACKGROUND

Overactivation of ryanodine receptors and the resulting impaired calcium homeostasis contribute to Alzheimer's disease-related pathophysiology. This study hypothesized that exposing neuronal progenitors derived from induced pluripotent stems cells of patients with Alzheimer's disease to dantrolene will increase survival, proliferation, neurogenesis, and synaptogenesis.

METHODS

Induced pluripotent stem cells obtained from skin fibroblast of healthy subjects and patients with familial and sporadic Alzheimer's disease were used. Biochemical and immunohistochemical methods were applied to determine the effects of dantrolene on the viability, proliferation, differentiation, and calcium dynamics of these cells.

RESULTS

Dantrolene promoted cell viability and proliferation in these two cell lines. Compared with the control, differentiation into basal forebrain cholinergic neurons significantly decreased by 10.7% (32.9 ± 3.6% vs. 22.2 ± 2.6%, N = 5, P = 0.004) and 9.2% (32.9 ± 3.6% vs. 23.7 ± 3.1%, N = 5, P = 0.017) in cell lines from sporadic and familial Alzheimer's patients, respectively, which were abolished by dantrolene. Synapse density was significantly decreased in cortical neurons generated from stem cells of sporadic Alzheimer's disease by 58.2% (237.0 ± 28.4 vs. 99.0 ± 16.6 arbitrary units, N = 4, P = 0.001) or familial Alzheimer's disease by 52.3% (237.0 ± 28.4 vs.113.0 ± 34.9 vs. arbitrary units, N = 5, P = 0.001), which was inhibited by dantrolene in the familial cell line. Compared with the control, adenosine triphosphate (30 µM) significantly increased higher peak elevation of cytosolic calcium concentrations in the cell line from sporadic Alzheimer's patients (84.1 ± 27.0% vs. 140.4 ± 40.2%, N = 5, P = 0.049), which was abolished by the pretreatment of dantrolene. Dantrolene inhibited the decrease of lysosomal vacuolar-type H-ATPase and the impairment of autophagy activity in these two cell lines from Alzheimer's disease patients.

CONCLUSIONS

Dantrolene ameliorated the impairment of neurogenesis and synaptogenesis, in association with restoring intracellular Ca homeostasis and physiologic autophagy, cell survival, and proliferation in induced pluripotent stem cells and their derived neurons from sporadic and familial Alzheimer's disease patients.

Intranasal administration of dantrolene increased brain concentration and duration

Dantrolene has been demonstrated to be neuroprotective for multiple neurodegenerative diseases. However, dantrolene's limited penetration into the CNS hampers its effectiveness as a neuroprotective agent. Here, we studied whether the intranasal administration of dantrolene provided better penetration into the brain than the commonly used oral approach. C57BL/6 mice, aged 2-4 months, received a single dose of either intranasal or oral dantrolene (5mg/kg). Inhibition of dantrolene clearance from the brain was examined by co-administration with P-gp/BCRP inhibitors, nimodipine or elacridar. The concentration of dantrolene in the brain and plasma was measured at 10, 20, 30, 50, 70, 120, 150 and 180 minutes after administration. Separate cohorts of mice were given intranasal dantrolene (5mg/kg) or vehicle, 3 times/ week, for either 3 weeks or 4 months, to examine potential adverse side effects on olfaction and motor coordination, respectively. We found that Dantrolene concentrations were sustained in the brain after intranasal administration for 180 min, while concentrations fell to zero at 120 min for oral administration. Chronic use of intranasal dantrolene did not impair olfaction or motor function in these mice. Blood brain barrier pump inhibitors did not further increase dantrolene peak concentrations in the brain. Our results suggested that Intranasal administration of dantrolene is an effective route to increase its concentration and duration in the brain compared to the oral approach, without any obvious side effects on olfaction or motor function.

Dantrolene Attenuates Cardiotoxicity of Doxorubicin Without Reducing its Antitumor Efficacy in a Breast Cancer Model

Dysregulation of calcium homeostasis is a major mechanism of doxorubicin (DOX)-induced cardiotoxicity. Treatment with DOX causes activation of sarcoplasmic reticulum (SR) ryanodine receptor (RYR) and rapid release of Ca²⁺ in the cytoplasm resulting in depression of myocardial function. The aim of this study was to examine the effect of dantrolene (DNT) a RYR blocker on both the cardiotoxicity and antitumor activity of DOX in a rat model of breast cancer. Female F344 rats with implanted MAT B III breast cancer cells were randomized to receive intraperitoneal DOX twice per week (12 mg/kg total dose), 5 mg/kg/day oral DNT or a combination of DOX + DNT for 3 weeks. Echocardiography and blood troponin I levels were used to measure myocardial injury. Hearts and tumors were evaluated for histopathological alterations. Blood glutathione was assessed as a measure of oxidative stress. The results showed that DNT improved DOX-induced alterations in the echocardiographic parameters by 50%. Histopathologic analysis of hearts showed reduced DOX induced cardiotoxicity in the group treated with DOX + DNT as shown by reduced interstitial edema, cytoplasmic vacuolization, and myofibrillar disruption, compared with DOX-only–treated hearts. Rats treated with DNT lost less body weight, had higher blood GSH levels and lower troponin I levels than DOX-treated rats. These data indicate that DNT is able to provide protection against DOX cardiotoxicity without reducing its antitumor activity. Further studies are needed to determine the optimal dosing of DNT and DOX in a tumor-bearing host.

Exposure of Developing Brain to General Anesthesia: What Is the Animal Evidence?

Recently, the U.S. Food and Drug Administration issued an official warning to all practicing physicians regarding potentially detrimental behavioral and cognitive sequelae of an early exposure to general anesthesia during in utero and in early postnatal life. The U.S. Food and Drug Administration concern is focused on children younger than three years of age who are exposed to clinically used general anesthetics and sedatives for three hours or longer. Although human evidence is limited and controversial, a large body of scientific evidence gathered from several mammalian species demonstrates that there is a potential foundation for concern. Considering this new development in public awareness, this review focuses on nonhuman primates because their brain development is the closest to humans in terms of not only timing and duration, but in terms of complexity as well. The review compares those primate findings to previously published work done with rodents.

Ca2+ homeostasis dysregulation in Alzheimer's disease: a focus on plasma membrane and cell organelles

Emerging evidence indicates that Ca²⁺ is a vital factor in modulating the pathogenesis of Alzheimer's disease (AD). In healthy neurons, Ca²⁺ concentration is balanced to maintain a lower level in the cytosol than in the extracellular space or certain intracellular compartments such as endoplasmic reticulum (ER) and the lysosome, whereas this homeostasis is broken in AD. On the plasma membrane, the AD hallmarks amyloid-β (Aβ) and tau interact with ligand-gated or voltage-gated Ca²⁺-influx channels and inhibit the Ca²⁺-efflux ATPase or exchangers, leading to an elevated intracellular Ca²⁺ level and disrupted Ca²⁺ signal. In the ER, the disabled presenilin "Ca²⁺ leak" function and the direct implications of Aβ and presenilin mutants contribute to Ca²⁺-signal disorder. The enhanced ryanodine receptor (RyR)-mediated and inositol 1,4,5-trisphosphate receptor (IP₃R)-mediated Ca²⁺ release from the ER aggravates cytosolic Ca²⁺ disorder and triggers apoptosis; the down-regulated ER Ca²⁺ sensor, stromal interaction molecule (STIM), alleviates store-operated Ca²⁺ entry in plasma membrane, leading to spine loss. The increased transfer of Ca²⁺ from ER to mitochondria through mitochondria-associated ER membrane (MAM) causes Ca²⁺ overload in the mitochondrial matrix and consequently opens the cellular damage-related channel, mitochondrial permeability transition pore (mPTP). In this review, we discuss the effects of Aβ, tau and presenilin on neuronal Ca²⁺ signal, focusing on the receptors and regulators in plasma membrane and ER; we briefly introduce the involvement of MAM-mediated Ca²⁺ transfer and mPTP opening in AD pathogenesis.-Wang, X., Zheng, W. Ca²⁺ homeostasis dysregulation in Alzheimer's disease: a focus on plasma membrane and cell organelles.

Dantrolene : From Malignant Hyperthermia to Alzheimer's Disease

Dantrolene, a ryanodine receptor antagonist, is primarily known as the only clinically acceptable and effective treatment for Malignant Hyperthermia (MH). Inhibition of Ryanodine Receptor (RyR) by dantrolene decreases the abnormal calcium release from the Sarcoplasmic Reticulum (SR) or Endoplasmic Reticulum (ER), where RyR is located. Recently, emerging researches on dissociated cells, brains slices, live animal models and patients have demonstrated that altered RyR expression and function can also play a vital role in the pathogenesis of Alzheimer's Disease (AD). Therefore, dantrolene is now widely studied as a novel treatment for AD, targeting the blockade of RyR channels or another alternative pathway, such as the inhibitory effects of NMDA glutamate receptors and the effects of ER-mitochondria connection. However, the therapeutic effects are not consistent. In this review, we focus on the relationship between the altered RyR expression and function and the pathogenesis of AD, and the potential application of dantrolene as a novel treatment for the disease.

Ryanodine receptor antagonism alleviates skeletal muscle ischemia reperfusion injury by modulating TNF-α and IL-10

BACKGROUND

Intracellular calcium overload has been implicated in various pathological conditions including ischemia reperfusion injury. This study aims to explore the effect and probable mechanism of dantrolene, a ryanodine receptor and intracellular calcium antagonist, on the skeletal muscle ischemia reperfusion injury.

MATERIALS AND METHODS

SD rats were randomly divided into three groups: sham group which underwent anaesthesia and exposure of femoral vein, reperfusion group that received 2 h ischemia and the amount of diluent via femoral vein before 4 h reperfusion, dantrolene group that underwent 2 h ischemia and was given 2 mg/kg dantrolene via femoral vein before 4 h reperfusion. The parameters measured at the end of reperfusion included serum maleic dialdehyde (MDA), tissue myeloperoxidase (MPO) and muscle histology, as well as serum TNF-α and IL-10.

RESULTS

Levels of MDA, MPO and TNF-α increased in the reperfusion group, whereas the relevant expressions in the dantrolene group decreased significantly. Histological examination demonstrated significant improvements between the same both groups. IL-10 reflected the protection observed above with a significant up-regulation of expression after dantrolene administration.

CONCLUSION

Ryanodine receptor antagonist dantrolene exerted a significant protective effect against the inflammatory injury of skeletal muscle ischemia reperfusion. The underlying molecular mechanism is probably related to the suppression of TNF-α levels and the increment of IL-10 expression.

Calcium dysregulation and Cdk5-ATM pathway involved in a mouse model of fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurological disorder that affects premutation carriers with 55-200 CGG-expansion repeats (preCGG) in FMR1, presenting with early alterations in neuronal network formation and function that precede neurodegeneration. Whether intranuclear inclusions containing DNA damage response (DDR) proteins are causally linked to abnormal synaptic function, neuronal growth and survival are unknown. In a mouse that harbors a premutation CGG expansion (preCGG), cortical and hippocampal FMRP expression is moderately reduced from birth through adulthood, with greater FMRP reductions in the soma than in the neurite, despite several-fold elevation of Fmr1 mRNA levels. Resting cytoplasmic calcium concentration ([Ca2+]i) in cultured preCGG hippocampal neurons is chronically elevated, 3-fold compared to Wt; elevated ROS and abnormal glutamatergic responses are detected at 14 DIV. Elevated µ-calpain activity and a higher p25/p35 ratio in the cortex of preCGG young adult mice indicate abnormal Cdk5 regulation. In support, the Cdk5 substrate, ATM, is upregulated by 1.5- to 2-fold at P0 and 6 months in preCGG brain, as is p-Ser1981-ATM. Bax:Bcl-2 is 30% higher in preCGG brain, indicating a greater vulnerability to apoptotic activation. Elevated [Ca2+]i, ROS, and DDR signals are normalized with dantrolene. Chronic [Ca2+]i dysregulation amplifies Cdk5-ATM signaling, possibly linking impaired glutamatergic signaling and DDR to neurodegeneration in preCGG brain.

Anesthetic neurotoxicity: Apoptosis and autophagic cell death mediated by calcium dysregulation

A number of findings suggested that general anesthetics induced neural cell death by apoptosis in various animal models. Although clinical evidence regarding the correlation between anesthetic exposures at young age and subsequent cognitive impairments remains unclear, repeated or consistent exposures to general anesthetics may be a potential harmful risk in developing human brains. The mechanisms underlying the anesthetic neurotoxicity have received extensive attention recently. We will attempt a brief review to summarize current understanding on the role of both apoptosis and autophagic cell death mediated by calcium dysregulation in anesthetic neurotoxicity.

Long-term dantrolene treatment reduced intraneuronal amyloid in aged Alzheimer triple transgenic mice

In this study, we investigated the long-term treatment of dantrolene on amyloid and tau neuropathology, brain volume, and cognitive function in aged triple transgenic Alzheimer (3xTg-AD) mice. Fifteen-month old 3xTg-AD mice and wild-type controls were treated with oral dantrolene (5 mg/kg) or vehicle control twice a week for 6 months. Learning and memory were examined using the Morris Water Maze at 21 and 22 months of age. After the behavioral testing, hippocampal and cortical brain volumes were calculated with magnetic resonance imaging and motor function was evaluated using the rotorod. The amyloid burden and tau neurofibrillary tangles in the hippocampus were determined using immunohistochemistry. We found that dantrolene significantly decreased the intraneuronal amyloid accumulation by as much as 76% compared with its corresponding vehicle control, together with a trend to reduce phosphorylated tau in the hippocampus. No significant differences could be detected in hippocampal or cortical brain volume, motor function or cognition among all experimental groups, indicating that the mice were still presymptomatic for Alzheimer disease. Thus, presymptomatic and long-term dantrolene treatment significantly decreased the intraneuronal amyloid burden in aged 3xTg-AD mice before significant changes in brain volume, or cognition.

Effect of ruthenium red, a ryanodine receptor antagonist in experimental diabetes induced vascular endothelial dysfunction and associated dementia in rats

Diabetes mellitus is considered as a main risk factor for vascular dementia. In the past, we have reported the induction of vascular dementia by experimental diabetes. This study investigates the efficacy of a ruthenium red, a ryanodine receptor antagonist and pioglitazone in the pharmacological interdiction of pancreatectomy diabetes (PaD) induced vascular endothelial dysfunction and subsequent vascular dementia in rats. Attentional set shifting and Morris water-maze test were used for assessment of learning and memory. Vascular endothelial function, blood brain barrier permeability, serum glucose, serum nitrite/nitrate, oxidative stress (viz. aortic superoxide anion, brain thiobarbituric acid reactive species and brain glutathione), brain calcium and inflammation (myeloperoxidase) were also estimated. PaD rats have shown impairment of endothelial function, blood brain barrier permeability, learning and memory along with an increase in brain inflammation, oxidative stress and calcium. Administration of ruthenium red and pioglitazone has significantly attenuated PaD induced impairment of learning, memory, blood brain barrier permeability, endothelial function and biochemical parameters. It may be concluded that ruthenium red, a ryanodine receptor antagonist and pioglitazone, a PPAR-γ agonist may be considered as potent pharmacological agent for the management of PaD induced endothelial dysfunction and subsequent vascular dementia. Ryanodine receptor may be explored further for their possible benefits in vascular dementia.

Rescue of an in vitro neuron phenotype identified in Niemann-Pick disease, type C1 induced pluripotent stem cell-derived neurons by modulating the WNT pathway and calcium signaling

Niemann-Pick disease, type C1 (NPC1) is a familial disorder that has devastating consequences on postnatal development with multisystem effects, including neurodegeneration. There is no Food and Drug Administration-approved treatment option for NPC1; however, several potentially therapeutic compounds have been identified in assays using yeast, rodent models, and NPC1 human fibroblasts. Although these discoveries were made in fibroblasts from NPC1 subjects and were in some instances validated in animal models of the disease, testing these drugs on a cell type more relevant for NPC1 neurological disease would greatly facilitate both study of the disease and identification of more relevant therapeutic compounds. Toward this goal, we have generated an induced pluripotent stem cell line from a subject homozygous for the most frequent NPC1 mutation (p.I1061T) and subsequently created a stable line of neural stem cells (NSCs). These NSCs were then used to create neurons as an appropriate disease model. NPC1 neurons display a premature cell death phenotype, and gene expression analysis of these cells suggests dysfunction of important signaling pathways, including calcium and WNT. The clear readout from these cells makes them ideal candidates for high-throughput screening and will be a valuable tool to better understand the development of NPC1 in neural cells, as well as to develop better therapeutic options for NPC1.

General anesthetic isoflurane modulates inositol 1,4,5-trisphosphate receptor calcium channel opening

BACKGROUND

Pharmacological evidence suggests that inhalational general anesthetics induce neurodegeneration in vitro and in vivo through overactivation of inositol trisphosphate receptor (InsP3R) Ca-release channels, but it is not clear whether these effects are due to direct modulation of channel activity by the anesthetics.

METHODS

Using single-channel patch clamp electrophysiology, the authors examined the gating of rat recombinant type 3 InsP3R (InsP3R-3) Ca-release channels in isolated nuclei (N = 3 to 15) from chicken lymphocytes modulated by isoflurane at clinically relevant concentrations in the absence and presence of physiological levels of the agonist inositol 1,4,5-trisphosphate (InsP3). The authors also examined the effects of isoflurane on InsP3R-mediated Ca release from the endoplasmic reticulum and changes in intracellular Ca concentration ([Ca]i).

RESULTS

Clinically relevant concentrations (approximately 1 minimal alveolar concentration) of the commonly used general anesthetic, isoflurane, activated InsP3R-3 channels with open probability similar to channels activated by 1 µM InsP3 (Po ≈ 0.2). This isoflurane modulation of InsP3R-3 Po depended biphasically on [Ca]i. Combination of isoflurane with subsaturating levels of InsP3 in patch pipettes resulted in at least two-fold augmentations of InsP3R-3 channel Po compared with InsP3 alone. These effects were not noted in the presence of saturating [InsP3]. Application of isoflurane to DT40 cells resulted in a 30% amplification of InsP3R-mediated [Ca]i oscillations, whereas InsP3-induced increase in [Ca]i and cleaved caspase-3 activity were enhanced by approximately 2.5-fold.

CONCLUSION

These results suggest that the InsP3R may be a direct molecular target of isoflurane and plays a role in the mechanisms of anesthetic-mediated pharmacological or neurotoxic effects.

Isoflurane-induced neuronal apoptosis in developing hippocampal neurons

We hypothesized that the P2X7 receptor may be the target of isoflurane, so we investigated the roles of the P2X7 receptor and inositol triphosphate receptor in calcium overload and neuronal apoptosis induced by isoflurane in cultured embryonic rat hippocampal neurons. Results showed that isoflurane induced widespread neuronal apoptosis and significantly increased cytoplasmic Ca²⁺. Blockade of P2X7 receptors or removal of extracellular Ca²⁺ combined with blockade of inositol triphosphate receptors completely inhibited apoptosis or increase in cytoplasmic Ca²⁺. Removal of extracellular Ca²⁺ or blockade of inositol triphosphate receptor alone could partly inhibit these effects of isoflurane. Isoflurane could directly activate P2X7-gated channels and induce inward currents, but did not affect the expression of P2X7 receptor protein in neurons. These findings indicate that the mechanism by which isoflurane induced neuronal apoptosis in rat developing brain was mediated by intracellular calcium overload, which was caused by P2X7 receptor mediated calcium influx and inositol triphosphate receptor mediated calcium release.

Molecular and functional identification of a mitochondrial ryanodine receptor in neurons

Mitochondrial Ca(2+) controls numerous cell functions, such as energy metabolism, reactive oxygen species generation, spatiotemporal dynamics of Ca(2+) signaling, cell growth and death in various cell types including neurons. Mitochondrial Ca(2+) accumulation is mainly mediated by the mitochondrial Ca(2+) uniporter (MCU), but recent reports also indicate that mitochondrial Ca(2+)-influx mechanisms are regulated not only by MCU, but also by multiple channels/transporters. We previously reported that ryanodine receptor (RyR), which is a one of the main Ca(2+)-release channels at endoplasmic/sarcoplasmic reticulum (SR/ER) in excitable cells, is expressed at the mitochondrial inner membrane (IMM) and serves as a part of the Ca(2+) uptake mechanism in cardiomyocytes. Although RyR is also expressed in neuronal cells and works as a Ca(2+)-release channel at ER, it has not been well investigated whether neuronal mitochondria possess RyR and, if so, whether this mitochondrial RyR has physiological functions in neuronal cells. Here we show that neuronal mitochondria express RyR at IMM and accumulate Ca(2+) through this channel in response to cytosolic Ca(2+) elevation, which is similar to what we observed in another excitable cell-type, cardiomyocytes. In addition, the RyR blockers dantrolene or ryanodine significantly inhibits mitochondrial Ca(2+) uptake in permeabilized striatal neurons. Taken together, we identify RyR as an additional mitochondrial Ca(2+) uptake mechanism in response to the elevation of [Ca(2+)]c in neurons, suggesting that this channel may play a critical role in mitochondrial Ca(2+)-mediated functions such as energy metabolism.

Dual effects of neuroprotection and neurotoxicity by general anesthetics: role of intracellular calcium homeostasis

Although general anesthetics have long been considered neuroprotective, there are growing concerns about neurotoxicity. Preclinical studies clearly demonstrated that commonly used general anesthetics are both neuroprotective and neurotoxic, with unclear mechanisms. Recent studies suggest that differential activation of inositol 1,4,5-trisphosphate receptors, a calcium release channel located on the membrane of endoplasmic reticulum (ER), play important role on determining the fate of neuroprotection or neurotoxicity by general anesthetics. General anesthetics at low concentrations for short duration are sublethal stress factors which induce endogenous neuroprotective mechanisms and provide neuroprotection via adequate activation of InsP3R and moderate calcium release from ER. On the other hand, general anesthetics at high concentrations for prolonged duration are lethal stress factors which induce neuronal damage by over activation of InsP3R and excessive and abnormal Ca(2+) release from ER. This review emphasizes the dual effects of both neuroprotection and neurotoxicity via differential regulation of intracellular Ca(2+) homeostasis by commonly used general anesthetics and recommends strategy to maximize neuroprotective but minimize neurotoxic effects of general anesthetics.

Pharmacokinetic evaluation of oral dantrolene in the dog

The pharmacokinetics of dantrolene and its active metabolite, 5-hydroxydantrolene, after a single oral dose of either 5 or 10 mg/kg of dantrolene was determined. The effects of exposure to dantrolene and 5-hydroxydantrolene on activated whole-blood gene expression of the cytokines interleukin-2 (IL-2) and interferon-γ (IFN-γ) were also investigated. When dantrolene was administered at a 5 mg/kg dose, peak plasma concentration (Cmax ) was 0.43 μg/mL, terminal half-life (t1/2 ) was 1.26 h, and area under the time-concentration curve (AUC) was 3.87 μg·h/mL. For the 10 mg/kg dose, Cmax was 0.65 μg/mL, t1/2 was 1.21 h, and AUC was 5.94 μg·h/mL. For all calculated parameters, however, there were large standard deviations and wide ranges noted between and within individual dogs: t1/2 , for example, ranged from 0.43 to 6.93 h, Cmax ratios ranged from 1.05 to 3.39, and relative bioavailability (rF) values ranged from 0.02 to 1.56. While activated whole-blood expression of IL-2 and IFN-γ as measured by qRT-PCR was markedly suppressed following exposure to very high concentrations (30 and 50 μg/mL, respectively) of both dantrolene and 5-hydroxydantrolene, biologically and therapeutically relevant suppression of cytokine expression did not occur at the much lower drug concentrations achieved with oral dantrolene dosing.

Role of endoplasmic reticulum Ca2+ signaling in the pathogenesis of Alzheimer disease

Alzheimer disease (AD) is a major threat of twenty-first century that is responsible for the majority of dementia in the elderly. Development of effective AD-preventing therapies are the top priority tasks for neuroscience research. Amyloid hypothesis of AD is a dominant idea in the field, but so far all amyloid-targeting therapies have failed in clinical trials. In addition to amyloid accumulation, there are consistent reports of abnormal calcium signaling in AD neurons. AD neurons exhibit enhanced intracellular calcium (Ca²⁺) liberation from the endoplasmic reticulum (ER) and reduced store-operated Ca²⁺ entry (SOC). These changes occur primarily as a result of ER Ca²⁺ overload. We argue that normalization of intracellular Ca²⁺ homeostasis could be a strategy for development of effective disease-modifying therapies. The current review summarizes recent data about changes in ER Ca²⁺ signaling in AD. Ca²⁺ channels that are discussed in the current review include: inositol trisphosphate receptors, ryanodine receptors, presenilins as ER Ca²⁺ leak channels, and neuronal SOC channels. We discuss how function of these channels is altered in AD and how important are resulting Ca²⁺ signaling changes for AD pathogenesis.

Rapid human melanoma cell death induced by sanguinarine through oxidative stress

Sanguinarine is a natural isoquinoline alkaloid derived from the root of Sanguinaria canadensis and from other poppy fumaria species, and is known to have a broad spectrum of pharmacological properties. Here we have found that sanguinarine, at low micromolar concentrations, showed a remarkably rapid killing activity against human melanoma cells. Time-lapse videomicroscopy showed rapid morphological changes compatible with an apoptotic cell death, which was further supported by biochemical markers, including caspase activation, poly(ADP-ribose) polymerase (PARP) cleavage and DNA breakdown. Pan-caspase inhibition blocked sanguinarine-induced cell death. Sanguinarine treatment also induced an increase in intracellular calcium concentration, which was inhibited by dantrolene, and promoted cleavage of BAP-31, thus suggesting a putative role for Ca(2+) release from endoplasmic reticulum and a cross-talk between endoplasmic reticulum and mitochondria in the anti-melanoma action of sanguinarine. Sanguinarine disrupted the mitochondrial transmembrane potential (ΔΨm), released cytochrome c and Smac/DIABLO from mitochondria to cytosol, and induced oxidative stress. Overexpression of Bcl-XL by gene transfer did not prevent sanguinarine-mediated cell death, oxidative stress or release of mitochondrial apoptogenic proteins. However, preincubation with N-acetyl-l-cysteine (NAC) prevented sanguinarine-induced oxidative stress, PARP cleavage, release of apoptogenic mitochondrial proteins, and cell death. Pretreatment with glutathione (GSH) also inhibited the anti-melanoma activity of sanguinarine. Thus, pretreatment with the thiol antioxidants NAC and GSH abrogated the killing activity of sanguinarine. Taking together, our data indicate that sanguinarine is a very rapid inducer of human melanoma caspase-dependent cell death that is mediated by oxidative stress.

Loss of endoplasmic reticulum Ca2+ homeostasis: contribution to neuronal cell death during cerebral ischemia

The loss of Ca(2+) homeostasis during cerebral ischemia is a hallmark of impending neuronal demise. Accordingly, considerable cellular resources are expended in maintaining low resting cytosolic levels of Ca(2+). These include contributions by a host of proteins involved in the sequestration and transport of Ca(2+), many of which are expressed within intracellular organelles, including lysosomes, mitochondria as well as the endoplasmic reticulum (ER). Ca(2+) sequestration by the ER contributes to cytosolic Ca(2+) dynamics and homeostasis. Furthermore, within the ER Ca(2+) plays a central role in regulating a host of physiological processes. Conversely, impaired ER Ca(2+) homeostasis is an important trigger of pathological processes. Here we review a growing body of evidence suggesting that ER dysfunction is an important factor contributing to neuronal injury and loss post-ischemia. Specifically, the contribution of the ER to cytosolic Ca(2+) elevations during ischemia will be considered, as will the signalling cascades recruited as a consequence of disrupting ER homeostasis and function.

Malignant hyperthermia

Malignant hyperthermia (MH) is an uncommon, life-threatening pharmacogenetic disorder of the skeletal muscle. It presents as a hypermetabolic response in susceptible individuals to potent volatile anesthetics with/without depolarizing muscle relaxants; in rare cases, to stress from exertion or heat stress. Susceptibility to malignant hyperthermia (MHS) is inherited as an autosomally dominant trait with variable expression and incomplete penetrance. It is known that the pathophysiology of MH is related to an uncontrolled rise of myoplasmic calcium, which activates biochemical processes resulting in hypermetabolism of the skeletal muscle. In most cases, defects in the ryanodine receptor are responsible for the functional changes of calcium regulation in MH, and more than 300 mutations have been identified in the RYR1 gene, located on chromosome 19q13.1. The classic signs of MH include increase of end-tidal carbon dioxide, tachycardia, skeletal muscle rigidity, tachycardia, hyperthermia and acidosis. Up to now, muscle contracture test is regarded as the gold standard for the diagnosis of MHS though molecular genetic test is used, on a limited basis so far to diagnose MHS. The mortality of MH is dramatically decreased from 70-80% to less than 5%, due to an introduction of dantrolene sodium for treatment of MH, early detection of MH episode using capnography, and the introduction of diagnostic testing for MHS. This review summarizes the clinically essential and important knowledge of MH, and presents new developments in the field.

Anesthesia-induced developmental neurodegeneration: the role of neuronal organelles

Exposure to general anesthetics (GAs) and antiepileptics during critical stages of brain development causes significant neurotoxicity to immature neurons. Many animal, and emerging human studies have shown long-term functional sequelae manifested as behavioral deficits and cognitive impairments. Since GAs and antiepileptic drugs are a necessity, current research is focused on deciphering the mechanisms responsible for anesthesia-induced developmental neurotoxicity so that protective strategies can be devised. These agents promote massive and wide-spread neuroapoptosis that is caused by the impairment of integrity and function of neuronal organelles. Mitochondria and endoplasmic reticulum are particularly vulnerable. By promoting significant release of intracellular calcium from the endoplasmic reticulum, anesthetics cause an increase in mitochondrial calcium load resulting in the loss of their integrity, release of pro-apoptotic factors, functional impairment of ATP synthesis, and enhanced accumulation of reactive oxygen species. The possibility that GAs may have direct damaging effects on mitochondria, resulting in the impairment of their morphogenesis, also has been proposed. This review will present evidence that neuronal organelles are critical and early targets of anesthesia-induced developmental neurotoxicity.