L-type voltage-dependent calcium channel is involved in the snake venom group IA secretory phospholipase A2-induced neuronal apoptosis

What Are the Neurotoxins in Hemotoxic Snake Venoms?

Snake venoms as tools for hunting are primarily aimed at the most vital systems of the prey, especially the nervous and circulatory systems. In general, snakes of the Elapidae family produce neurotoxic venoms comprising of toxins targeting the nervous system, while snakes of the Viperidae family and most rear-fanged snakes produce hemotoxic venoms directed mainly on blood coagulation. However, it is not all so clear. Some bites by viperids results in neurotoxic signs and it is now known that hemotoxic venoms do contain neurotoxic components. For example, viperid phospholipases A₂ may manifest pre- or/and postsynaptic activity and be involved in pain and analgesia. There are other neurotoxins belonging to diverse families ranging from large multi-subunit proteins (e.g., C-type lectin-like proteins) to short peptide neurotoxins (e.g., waglerins and azemiopsin), which are found in hemotoxic venoms. Other neurotoxins from hemotoxic venoms include baptides, crotamine, cysteine-rich secretory proteins, Kunitz-type protease inhibitors, sarafotoxins and three-finger toxins. Some of these toxins exhibit postsynaptic activity, while others affect the functioning of voltage-dependent ion channels. This review represents the first attempt to systematize data on the neurotoxins from "non-neurotoxic" snake venom. The structural and functional characteristic of these neurotoxins affecting diverse targets in the nervous system are considered.

The role of Shunaoxin pills in the treatment of chronic cerebral hypoperfusion and its main pharmacodynamic components

Chronic cerebral hypoperfusion (CCH) is a frequent ischemic cerebrovascular disease that induces brain dysfunction. Shunaoxin pills (SNX) are traditional Chinese medicines (TCM), frequently used for the treatment of CCH. The purpose of this study was to develop an activity-based screening system to identify the active ingredients of SNX. We developed a model of CCH and revealed that SNX induces cerebrovascular dilatation and protects against CCH-induced nerve cell injury in rats. Using the transcriptome analysis, we found that Ca2+-related signaling pathways play a major role in the effect of SNX against CCH. We developed an activity-based screening system based on the ultra-high performance liquid chromatography with quadrupole time-of-flight mass spectrometry coupled with a dual-luciferase reporter calcium assay to identify the active components of SNX. As a result, SNX dilates cerebral blood vessels, increasing cerebral blood flow by modulating calcium-related signaling pathways and regulating calcium homeostasis. Two calcium antagonists, ligustilide and senkyunolide I, were identified as active ingredients in SNX. In conclusion, we developed a rapid screening method suitable for the discovery of active natural products in TCM by integrating genomics and target pathway-oriented spectroscopic analysis.

Secreted Phospholipases A2 - not just Enzymes: Revisited

Secreted phospholipases A₂ (sPLA₂s) participate in a very broad spectrum of biological processes through their enzymatic activity and as ligands for membrane and soluble receptors. The physiological roles of sPLA₂s as enzymes have been very well described, while their functions as ligands are still poorly known. Since the last overview of sPLA₂-binding proteins (sPLA₂-BPs) 10 years ago, several important discoveries have occurred in this area. New and more sensitive analytical tools have enabled the discovery of additional sPLA₂-BPs, which are presented and critically discussed here. The structural diversity of sPLA₂-BPs reveals sPLA₂s as very promiscuous proteins, and we offer some structural explanations for this nature that makes these proteins evolutionarily highly advantageous. Three areas of physiological engagement of sPLA₂-BPs have appeared most clearly: cellular transport and signalling, and regulation of the enzymatic activity of sPLA₂s. Due to the multifunctionality of sPLA₂s, they appear to be exceptional pharmacological targets. We reveal the potential to exploit interactions of sPLA₂s with other proteins in medical terms, for the development of original diagnostic and therapeutic procedures. We conclude this survey by suggesting the priority questions that need to be answered.

Role of Phospholipases A2 in Vascular Relaxation and Sympatholytic Effects of Five Australian Brown Snake, Pseudonaja spp., Venoms in Rat Isolated Tissues

Human envenoming by Australian brown snakes (Pseudonaja spp.) may result in potentially life-threatening hypotension and subsequent cardiovascular collapse. There have been relatively few studies of the cardiovascular and sympathetic effects of Pseudonaja spp. venoms. In this study, we have examined the effects of venom from five brown snake species-P. affinis, aspidorhyncha, inframacula, nuchalis, and textilis-on cardiac inotropic and chronotropic responses, vascular tone, and sympathetic nerve-induced vascular contractions in rat isolated tissues. The role of phospholipases A₂ (PLA₂s) in venom-induced effects was assessed with the sPLA₂ inhibitor varespladib. In rat isolated left and right atria, there were no physiologically relevant effects of Pseudonaja venoms (0.1-30 µg/ml) on left atrial force of contraction (inotropy) or right atrial rate (chronotropy). In contrast, in isolated small mesenteric arteries precontracted with a thromboxane mimetic, each of the five brown snake venoms (at 30 µg/ml) caused marked vasorelaxation (-60 to -90% of contractile tone). Pretreatment with varespladib (1 µM) significantly inhibited the vasorelaxation caused by P. aspidorhyncha, P. nuchalis, and P. textilis venoms. Electrically induced sympathetic nerve-mediated contractions of mesenteric arteries were significantly attenuated by only P. textilis, and P. affinis venoms (30 µg/ml) and these sympatholytic effects were inhibited by varespladib (1 µM). Based on their inhibition with the sPLA₂ inhibitor varespladib, we conclude that PLA₂ toxins in P. aspidorhyncha, P. nuchalis, and P. textilis venoms are involved in brown snake venom-induced vasorelaxation and the sympatholytic effects of P. affinis, and P. textilis venoms. Our study supports the promising potential role of varespladib as an initial (pre-referral) and/or adjunct (in combination with antivenom) therapeutic agent for brown snake envenoming.

A plausible involvement of plasmalemmal voltage-dependent anion channel 1 in the neurotoxicity of 15-deoxy-Δ12,14 -prostaglandin J2

INTRODUCTION

15-deoxy-Δ^12,14 -prostaglandin J₂ (15d-PGJ₂ ) causes neuronal apoptosis independently of its nuclear receptor, peroxysome-proliferator activated receptor γ. Its membrane receptor, chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), did not also mediate the neurotoxicity of 15d-PGJ₂ . In the present study, we ascertained whether membrane targets beside CRTH2 were involved in the neurotoxicity of 15d-PGJ₂ .

METHODS

Neuronal membrane targets for 15d-PGJ₂ were separated by two-dimensional electrophoresis, identified by proteomic approach. Their localizations were detected by microscopic immunofluorescence study. Cell viability and apoptosis was evaluated by MTT-reducing activity and caspase-3 activity, respectively.

RESULTS

Voltage-dependent anion channel 1 (VDAC1) was identified as one of membrane targets for 15d-PGJ₂ . Modification of VDAC1 with 15d-PGJ₂ was detected by pull-down assay. VDAC1 was detected in the plasma membrane and localized on the neuronal cell surface. VDAC1 was partially colocalized with membrane targets for 15d-PGJ₂ . The anti-VDAC antibody significantly attenuated the neurotoxicity of 15d-PGJ₂ , accompanied by the suppression of the 15d-PGJ₂ -stimulated caspase-3.

CONCLUSION

These findings suggested that the plasmalemmal VDAC might be involved in the neurotoxicity of 15d-PGJ₂ .

The Anti-Neuron-Specific Enolase Antibody Induced Neuronal Cell Death in a Novel Fashion

Suppression of ubiquitin proteasome pathway (UPP) and stimulation of caspase-3 are involved in neurodegeneration. Can UPP activators and caspase-3 inhibitors ameliorate neurodegeneration? Here, we found a novel neuronal cell death accompanied with UPP activation and caspase-3 inhibition. Recently, plasmalemmal neuron-specific enolase (NSE) has been identified as one of membrane targets of 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂). 15d-PGJ₂ induces neuronal apoptosis via activating caspase-3 and inactivating UPP, whereas the anti-NSE antibody inactivated caspase-3, activated UPP, and caused neuronal cell death. The anti-NSE antibody activated caspase-1 (pyroptosis marker), but not condense chromatin (apoptosis marker). The anti-NSE antibody declined intracellular level of ATP, which is not altered in pyroptosis. The intracellular level of calcium is elevated in necrosis and pyroptosis, but its chelator did not ameliorate the neurotoxicity of anti-NSE. Thiol antioxidants such as N-acetyl cysteine and glutathione reduced the neurotoxicity of 15d-PGJ₂ but enhanced that of the anti-NSE antibody. The anti-NSE antibody incorporated propidium iodide into neurons through the disrupted plasma membrane, which are not observed in ferroptosis and autophagic cell death. Thus, the anti-NSE antibody induced neuronal cell death in a novel fashion distinguished from necrosis, necroptosis, apoptosis, pyroptosis, ferroptosis, and autophagic cell death.

4,4-Diisothiocyanatostilbene Disulfonic Acid Enhanced 15-Deoxy-Δ12,14-prostaglandin J2-Induced Neuronal Apoptosis

4,4-Diisothiocyanatostilbene disulfonic acid (DIDS), an antagonist of anion channel including voltage-dependent anion channel (VDAC), acts as both neurotoxicant and neuroprotectant, resulting in the controversy. VDAC contributes to neuronal apoptosis and is a candidate target protein of 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂). Caspase-3 is activated during neuronal apoptosis caused by 15d-PGJ₂. In the present study, we ascertained whether DIDS was neuroprotective or neurotoxic in the primary culture of rat cortical neurons. Neuronal cell viabilities were primarily evaluated by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide (MTT) reduction assay. Plasma membrane integrity and apoptosis were detected by the staining of propidium iodide (PI) and Hoechst33342, respectively. Alternatively, apoptosis was also measured by caspase-3 assay kit. DIDS did not prevent neurons from undergoing the 15d-PGJ₂-induced apoptosis. In contrast, DIDS caused neuronal cell death in a concentration-dependent manner by itself, confirming its neurotoxicity. The sublethal application of DIDS did not decrease MTT-reducing activity, increase caspase-3 activity, condense chromatin, allow PI to enter neuron and degenerate neuronal morphology significantly. Interestingly, DIDS enhanced the 15d-PGJ₂-induced neuronal apoptosis markedly under the sublethal condition. To our knowledge, this is the first report of synergistic effects of DIDS on the neurotoxicity of 15d-PGJ₂.

15-Deoxy-Δ12,14-prostaglandin J2 induced neurotoxicity via suppressing phosphoinositide 3-kinase

15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) induces neuronal cell death via apoptosis independently of its receptors. 15d-PGJ₂ inhibits growth factor-induced cell proliferation of primary astrocytes via down-regulating phosphoinositide 3-kinase (PI3K)-Akt pathway. Although 15d-PGJ₂-reduced cell viability is accompanied with attenuation of the PI3K signaling in neuroblastoma, it has not been sufficiently clarified how 15d-PGJ₂ induces cell death in primary neurons. Here, we found that 15d-PGJ₂ exhibited neurotoxicity via inhibiting the PI3K signaling in the primary culture of rat cortical neurons. A PI3K inhibitor induced neuronal cell death regardless serum throughout maturation, confirming that PI3K is required for neuronal cell survival. The inhibitor disrupted neuronal cell bodies, shortened neurites thinly, damaged plasma membranes and activated caspase-3 similarly to 15d-PGJ₂. Little additive or synergistic neurotoxicity was detected between 15d-PGJ₂ and the PI3K inhibitor. A PI3K activator prevented neurons from undergoing the 15d-PGJ₂-induced cell death in vitro. In vivo, the PI3K signaling is required for contextual memory retrieval, which was impaired by bilateral injection of 15d-PGJ₂ into hippocampus. The activator suppressed the 15d-PGJ₂-impaired memory retrieval significantly. In neurons as well as primary astrocytes and neuroblastomas, 15d-PGJ₂ exhibited cytotoxicity via suppressing the PI3K-Akt pathway in vivo and in vitro.

Cytotoxicity of lidocaine to human corneal endothelial cells in vitro

Lidocaine has been reported to induce apoptosis on rabbit corneal endothelial cells. However, the apoptotic effect and exact mechanism involved in cytotoxicity of lidocaine are not well-established in human corneal endothelial (HCE) cells. In this study, we investigated the apoptosis-inducing effect of lidocaine on HCE cells in vitro. After HCE cells were treated with lidocaine at concentrations of 0.15625-10.0 g/l, the morphology and ultrastructure of the cells were observed by inverted light microscope and transmission electron microscope (TEM). Cell viability was measured by MTT assay, and the apoptotic ratio was evaluated with flow cytometry and fluorescent microscopic counting after FITC-Annexin V/PI and AO/EB staining. DNA fragmentation was detected by electrophoresis, and the activation of caspases was evaluated by ELISA. In addition, changes in mitochondrial membrane potential were determined by JC-1 staining. Results suggest that lidocaine above 1.25 g/l reduced cellular viability and triggered apoptosis in HCE cells in a time- and dose-dependent manner. Diminishment of ΔΨm and the activation of caspases indicate that lidocaine-induced apoptosis was caspase dependent and may be related to mitochondrial pathway.

The role of secretory phospholipase A₂ in the central nervous system and neurological diseases

Secretory phospholipase A2 (sPLA2s) are small secreted proteins (14-18 kDa) and require submillimolar levels of Ca(2+) for liberating arachidonic acid from cell membrane lipids. In addition to the enzymatic function, sPLA2 can exert various biological responses by binding to specific receptors. Physiologically, sPLA2s play important roles on the neurotransmission in the central nervous system and the neuritogenesis in the peripheral nervous system. Pathologically, sPLA2s are involved in the neurodegenerative diseases (e.g., Alzheimer's disease) and cerebrovascular diseases (e.g., stoke). The common pathology (e.g., neuronal apoptosis) of Alzheimer's disease and stroke coexists in the mixed dementia, suggesting common pathogenic mechanisms of the two neurological diseases. Among mammalian sPLA2s, sPLA2-IB and sPLA2-IIA induce neuronal apoptosis in rat cortical neurons. The excess influx of calcium into neurons via L-type voltage-dependent Ca(2+) channels mediates the two sPLA2-induced apoptosis. The elevated concentration of intracellular calcium activates PKC, MAPK and cytosolic PLA2. Moreover, it is linked with the production of reactive oxygen species and apoptosis through activation of the superoxide producing enzyme NADPH oxidase. NADPH oxidase is involved in the neurotoxicity of amyloid β peptide, which impairs synaptic plasticity long before its deposition in the form of amyloid plaques of Alzheimer's disease. In turn, reactive oxygen species from NADPH oxidase can stimulate ERK1/2 phosphorylation and activation of cPLA2 and result in a release of arachidonic acid. sPLA2 is up-regulated in both Alzheimer's disease and cerebrovascular disease, suggesting the involvement of sPLA2 in the common pathogenic mechanisms of the two diseases. Thus, our review presents evidences for pathophysiological roles of sPLA2 in the central nervous system and neurological diseases.