Neuroprotective effect on brain injury by neurotoxins from the spider Phoneutria nigriventer

Animal toxins: As an alternative therapeutic target following ischemic stroke condition

Globally, Ischemic stroke (IS) has become the second leading cause of mortality and chronic disability. The process of IS has triggered by the blockages of blood vessels to form clots in the brain which initiates multiple interactions with the key signaling pathways, counting excitotoxicity, acidosis, ionic imbalance, inflammation, oxidative stress, and neuronal dysfunction of cells, and ultimately cells going under apoptosis. Currently, FDA has approved only tissue plasminogen activator therapy, which is effective against IS with few limitations. However, the mechanism of excitotoxicity and acidosis has spurred the investigation of a potential candidate for IS therapy. Acid-sensing ion channels (ASICs) and Voltage-gated Ca²⁺ channels (VDCCs) get activated and disturb the brain's normal physiology. Animal toxins are novel inhibitors of ASICs and VDCCs channels and have provided neuroprotective insights into the pathophysiology of IS. This review will discuss the potential directions of translational ASICs and VDCCs inhibitors research for clinical therapies.

Antiseizure potential of peptides from the venom of social wasp Chartergellus communis against chemically-induced seizures

Epilepsy is one of the most common neurological diseases in the world. The objective of this research was to investigate a new peptide from the venom of the social wasp Chartergellus communis useful to the study or pharmacotherapy of epilepsy. The wasps were collected, and their venom was extracted. Afterward, the steps of fractionation, sequencing, and identification were carried out to obtain four peptides. These molecules were synthesized for behavioral evaluation tests and electroencephalographic assays to determine their antiseizure potential (induction of acute seizures using the chemical compounds, pentylenetetrazole - PTZ, and pilocarpine - PILO) and analysis of neuropharmacological profile (general spontaneous activity and alteration in motor coordination). Chartergellus-CP1 (i.c.v. - 3.0 μg/animal) caused beneficial alterations in some of the parameters evaluated in both models: PTZ (latency and duration of maximum seizures) and PILO (latency and duration of, and protection against, maximum seizures, and reduction of the median of the seizure scores. When evaluated in 3 doses in the seizure model induced by PILO, the dose of 3.0 μg/animal protected the animals against seizures, with an estimated ED₅₀ of 1.49 μg/animal. Electroencephalographic evaluation of Chartergellus-CP1 showed an improvement in latency, quantity, and percentage of protection against generalized electroencephalographic seizures in the PILO model. Further, Chartergellus-CP1 did not cause adverse effects on general spontaneous activity and motor coordination of animals. This study demonstrated how compounds isolated from wasps' venom may be important resources in the search for new drugs. Such compounds can be considered valuable therapeutic and biotechnological tools for the study and future treatment of epileptic disorders. In this context, a peptide that is potentially useful for epilepsy pharmacotherapy was identified in the venom of C. communis.

Animal Venom Peptides as a Treasure Trove for New Therapeutics Against Neurodegenerative Disorders

BACKGROUND

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and cerebral ischemic stroke, impose enormous socio-economic burdens on both patients and health-care systems. However, drugs targeting these diseases remain unsatisfactory, and hence there is an urgent need for the development of novel and potent drug candidates.

METHODS

Animal toxins exhibit rich diversity in both proteins and peptides, which play vital roles in biomedical drug development. As a molecular tool, animal toxin peptides have not only helped clarify many critical physiological processes but also led to the discovery of novel drugs and clinical therapeutics.

RESULTS

Recently, toxin peptides identified from venomous animals, e.g. exenatide, ziconotide, Hi1a, and PcTx1 from spider venom, have been shown to block specific ion channels, alleviate inflammation, decrease protein aggregates, regulate glutamate and neurotransmitter levels, and increase neuroprotective factors.

CONCLUSION

Thus, components of venom hold considerable capacity as drug candidates for the alleviation or reduction of neurodegeneration. This review highlights studies evaluating different animal toxins, especially peptides, as promising therapeutic tools for the treatment of different neurodegenerative diseases and disorders.

Animal Toxins as Therapeutic Tools to Treat Neurodegenerative Diseases

Neurodegenerative diseases affect millions of individuals worldwide. So far, no disease-modifying drug is available to treat patients, making the search for effective drugs an urgent need. Neurodegeneration is triggered by the activation of several cellular processes, including oxidative stress, mitochondrial impairment, neuroinflammation, aging, aggregate formation, glutamatergic excitotoxicity, and apoptosis. Therefore, many research groups aim to identify drugs that may inhibit one or more of these events leading to neuronal cell death. Venoms are fruitful natural sources of new molecules, which have been relentlessly enhanced by evolution through natural selection. Several studies indicate that venom components can exhibit selectivity and affinity for a wide variety of targets in mammalian systems. For instance, an expressive number of natural peptides identified in venoms from animals, such as snakes, scorpions, bees, and spiders, were shown to lessen inflammation, regulate glutamate release, modify neurotransmitter levels, block ion channel activation, decrease the number of protein aggregates, and increase the levels of neuroprotective factors. Thus, these venom components hold potential as therapeutic tools to slow or even halt neurodegeneration. However, there are many technological issues to overcome, as venom peptides are hard to obtain and characterize and the amount obtained from natural sources is insufficient to perform all the necessary experiments and tests. Fortunately, technological improvements regarding heterologous protein expression, as well as peptide chemical synthesis will help to provide enough quantities and allow chemical and pharmacological enhancements of these natural occurring compounds. Thus, the main focus of this review is to highlight the most promising studies evaluating animal toxins as therapeutic tools to treat a wide variety of neurodegenerative conditions, including Alzheimer’s disease, Parkinson’s disease, brain ischemia, glaucoma, amyotrophic lateral sclerosis, and multiple sclerosis.

Calcium Channels and Associated Receptors in Malignant Brain Tumor Therapy

Malignant brain tumors are highly lethal and aggressive. Despite recent advances in the current therapies, which include the combination of surgery and radio/chemotherapy, the average survival rate remains poor. Altered regulation of ion channels is part of the neoplastic transformation, which suggests that ion channels are involved in cancer. Distinct classes of calcium-permeable channels are abnormally expressed in cancer and are likely involved in the alterations underlying malignant growth. Specifically, cytosolic Ca(2+) activity plays an important role in the regulation of cell proliferation, and Ca(2+) signaling is altered in proliferating tumor cells. A series of previous studies emphasized the importance of the T-type low-voltage-gated calcium channels (VGCC) in different cancer types, including gliomas, and remarkably, pharmacologic inhibition of T-type VGCC caused antiproliferative effects and triggered apoptosis of human glioma cells. Other calcium permeable channels, such as transient receptor potential (TRP) channels, contribute to changes in Ca(2+) by modulating the driving force for Ca(2+) entry, and some TRP channels are required for proliferation and migration in gliomas. Furthermore, recent evidence shows that TRP channels contribute to the progression and survival of the glioblastoma patients. Likewise, the purinergic P2X7 receptor acts as a direct conduit for Ca(2+)-influx and an indirect activator of voltage-gated Ca(2+)-channel. Evidence also shows that P2X7 receptor activation is linked to elevated expression of inflammation promoting factors, tumor cell migration, an increase in intracellular mobilization of Ca(2+), and membrane depolarization in gliomas. Therefore, this review summarizes the recent findings on calcium channels and associated receptors as potential targets to treat malignant gliomas.

PhTx3-4, a Spider Toxin Calcium Channel Blocker, Reduces NMDA-Induced Injury of the Retina

The in vivo neuroprotective effect of PhTx3-4, a spider toxin N-P/Q calcium channel blocker, was studied in a rat model of NMDA-induced injury of the retina. NMDA (N-Methyl-d-Aspartate)-induced retinal injury in rats reduced the b-wave amplitude by 62% ± 3.6%, indicating the severity of the insult. PhTx3-4 treatment increased the amplitude of the b-wave, which was almost equivalent to the control retinas that were not submitted to injury. The PhTx3-4 functional protection of the retinas recorded on the ERG also was observed in the neuroprotection of retinal cells. NMDA-induced injury reduced live cells in the retina layers and the highest reduction, 84%, was in the ganglion cell layer. Notably, PhTx3-4 treatment caused a remarkable reduction of dead cells in the retina layers, and the highest neuroprotective effect was in the ganglion cells layer. NMDA-induced cytotoxicity of the retina increased the release of glutamate, reactive oxygen species (ROS) production and oxidative stress. PhTx3-4 treatment reduced glutamate release, ROS production and oxidative stress measured by malondialdehyde. Thus, we presented for the first time evidence of in vivo neuroprotection from NMDA-induced retinal injury by PhTx3-4 (-ctenitoxin-Pn3a), a spider toxin that blocks N-P/Q calcium channels.

Neuroactive compounds obtained from arthropod venoms as new therapeutic platforms for the treatment of neurological disorders

The impact of neurological disorders in society is growing with alarming estimations for an incidence increase in the next decades. These disorders are generally chronic and can affect individuals early during productive life, imposing real limitations on the performance of their social roles. Patients can have their independence, autonomy, freedom, self-image, and self-confidence affected. In spite of their availability, drugs for the treatment of these disorders are commonly associated with side effects, which can vary in frequency and severity. Currently, no effective cure is known. Nowadays, the biopharmaceutical research community widely recognizes arthropod venoms as a rich source of bioactive compounds, providing a plethora of possibilities for the discovery of new neuroactive compounds, opening up novel and attractive opportunities in this field. Several identified molecules with a neuropharmacological profile can act in the central nervous system on different neuronal targets, rendering them useful tools for the study of neurological disorders. In this context, this review aims to describe the current main compounds extracted from arthropod venoms for the treatment of five major existing neurological disorders: stroke, Alzheimer’s disease, epilepsy, Parkinson’s disease, and pathological anxiety.

Vascular endothelial growth factor increases during blood-brain barrier-enhanced permeability caused by Phoneutria nigriventer spider venom

Phoneutria nigriventer spider accidental envenomation provokes neurotoxic manifestations, which when critical, results in epileptic-like episodes. In rats, P. nigriventer venom (PNV) causes blood-brain barrier breakdown (BBBb). The PNV-induced excitotoxicity results from disturbances on Na⁺, K⁺ and Ca²⁺ channels and glutamate handling. The vascular endothelial growth factor (VEGF), beyond its angiogenic effect, also, interferes on synaptic physiology by affecting the same ion channels and protects neurons from excitotoxicity. However, it is unknown whether VEGF expression is altered following PNV envenomation. We found that adult and neonates rats injected with PNV showed immediate neurotoxic manifestations which paralleled with endothelial occludin, β-catenin, and laminin downregulation indicative of BBBb. In neonate rats, VEGF, VEGF mRNA, and Flt-1 receptors, glutamate decarboxylase, and calbindin-D28k increased in Purkinje neurons, while, in adult rats, the BBBb paralleled with VEGF mRNA, Flk-1, and calbindin-D28k increases and Flt-1 decreases. Statistically, the variable age had a role in such differences, which might be due to age-related unequal maturation of blood-brain barrier (BBB) and thus differential cross-signaling among components of the glial neurovascular unit. The concurrent increases in the VEGF/Flt-1/Flk-1 system in the cerebellar neuron cells and the BBBb following PNV exposure might imply a cytokine modulation of neuronal excitability consequent to homeostatic perturbations induced by ion channels-acting PNV neuropeptides. Whether such modulation represents neuroprotection needs further investigation.

Temporal relationship between aquaporin-4 and glial fibrillary acidic protein in cerebellum of neonate and adult rats administered a BBB disrupting spider venom

Two astrocyte markers, the glial water channel aquaporin-4 (AQP4) and the glial fibrillary acidic protein (GFAP), have been implicated in several physiological and pathological conditions in the central nervous system (CNS) as well as in blood-brain barrier breakdown (BBBb). By color segmentation the immunoreactivity of both proteins, we demonstrate that the expression of AQP4 and GFAP was increased in the cerebellum of neonate (14-day-old, P14) and adult (8-week-old) rats administered Phoneutria nigriventer spider venom (PNV) known to cause perivascular edema, BBBb and convulsion. In the cerebellum's gray matter, PNV produced a major response, especially in the granular layer. Parallel increases in AQP4 and GFAP expression occurred 24 h after envenomation in the white matter of P14 and in the molecular layer of adults, as well as in the granular layer 2 h after envenomation. In the Purkinje layer there was a tendency of increased AQP4, for both, neonates (5 h), and adults (2 and 24 h). Moreover, PNV also provoked nonparallel upregulation of both markers with prevalence of upregulation of AQP 4 for P14 rats, and GFAP for adults. The major expression of both proteins was in the gray matter. The data indicates a venom effect in water/electrolyte balance in the cerebellum and the participation of AQP4 in these effects. Age-related and time-related regional differences probably reflect specificity in AQP4 distribution in different astrocytic membrane domains as well as its participation in K(+) buffering and neural activity. This study is the first to associate astrocytic AQP4 expression and reactive gliosis in a model of BBB permeability promoted by P. nigriventer venom. Our data provide compelling evidence that AQP4 expression was increased in the cerebellum of rats administered PNV.

Peptide neurotoxins that affect voltage-gated calcium channels: a close-up on ω-agatoxins

Peptide neurotoxins found in animal venoms have gained great interest in the field of neurotransmission. As they are high affinity ligands for calcium, potassium and sodium channels, they have become useful tools for studying channel structure and activity. Peptide neurotoxins represent the clinical potential of ion-channel modulators across several therapeutic fields, especially in developing new strategies for treatment of ion channel-related diseases. The aim of this review is to overview the latest updates in the domain of peptide neurotoxins that affect voltage-gated calcium channels, with a special focus on ω-agatoxins.

Control of intracellular calcium signaling as a neuroprotective strategy

Both acute and chronic degenerative diseases of the nervous system reduce the viability and function of neurons through changes in intracellular calcium signaling. In particular, pathological increases in the intracellular calcium concentration promote such pathogenesis. Disease involvement of numerous regulators of intracellular calcium signaling located on the plasma membrane and intracellular organelles has been documented. Diverse groups of chemical compounds targeting ion channels, G-protein coupled receptors, pumps and enzymes have been identified as potential neuroprotectants. The present review summarizes the discovery, mechanisms and biological activity of neuroprotective molecules targeting proteins that control intracellular calcium signaling to preserve or restore structure and function of the nervous system. Disease relevance, clinical applications and new technologies for the identification of such molecules are being discussed.

Erection induced by Tx2-6 toxin of Phoneutria nigriventer spider: expression profile of genes in the nitric oxide pathway of penile tissue of mice

The peptides Tx2-5 and Tx2-6, isolated from the whole venom of "armed-spider"Phoneutria nigriventer venom, are directly linked with the induction of persistent and painful erection in the penis of mammals. The erection induced by Tx2-6 has been associated with the activation of nitric oxide synthases. There is a scarcity of studies focusing on the outcome of Tx2-6 at the molecular level, by this reason we evaluated the gene profile activity of this toxin at the nitric oxide (NO) pathway. After microarray analyses on cavernous tissue of mice inoculated with Tx2-6 we found that only 10.4% (10/96) of these genes were differentially expressed, showing a limited effect of the toxin on the NO pathway. We found the genes sparc, ednrb, junb, cdkn1a, bcl2, ccl5, abcc1 over-expressed and the genes sod1, s100a10 and fth1 under-expressed after inoculation of Tx2-6. The differential expressions of sparc and ednrb genes were further confirmed using real-time PCR. Interestingly, ednrb activates the L-arginine/NO/cGMP pathway that is involved in the relaxation of the cavernous body. Therefore the priapism induced by Tx2-6 is a consequence of a highly specific interference of this neurotoxin with the NO pathway.

Corneal, limbal, and conjunctival epithelium of bovine eyes imaged in vitro by using a confocal laser scanning microscope

PURPOSE

To provide a description of the distribution and cell morphology, by using fluorescent markers and confocal laser scanning microscopy, of the corneal, limbal, and conjunctival epithelium of bovine eyes in vitro.

METHODS

Fresh enucleated bovine eyes were dissected within 2 hours postmortem. Central cornea, limbus, and bulbar conjunctiva were imaged with confocal microscopy after staining with acridine orange (AO) or calcein-acetoxymethyl and ethidium homodimer-1. Epithelial thickness, cell density, cell lamination, and cell morphology were evaluated at these 3 locations.

RESULTS

Corneal epithelium was the thickest, and the conjunctival epithelium was the thinnest. The cell morphology was similar to that found in previous histologic studies, and the cell density gradually decreased from the basal to superficial layers. Nuclear AO staining particles increased from basal to superficial cells. Limbal superficial epithelial cells showed less AO staining than corneal and conjunctival superficial cells.

CONCLUSIONS

Confocal results of the corneal central, limbal, and conjunctival morphology are similar to those found in traditional microscopic observations. Bovine central corneal epithelium is thicker than limbal epithelium. However, the nuclear AO staining pattern of unfixed ocular surface epithelium of bovine eyes in vitro might represent the cell differentiation status. With the aid of the fluorescence dye, confocal laser scanning microscopy can provide unique morphometric information about corneal, limbal, and conjunctival epithelial cells.

Effective delivery of Pep-1-cargo protein into ischemic neurons and long-term neuroprotection of Pep-1-SOD1 against ischemic injury in the gerbil hippocampus

We examined the intracellular delivery of Pep-1-cargo protein against transient ischemic damage in the hippocampal CA1 region in gerbils. For this study, we introduced green fluorescent protein (GFP) and constructed Pep-1-GFP protein. At 12h after Pep-1-GFP treatment, GFP fluorescence was shown in almost CA1 pyramidal neurons in ischemic animals; in the sham-operated group, GFP fluorescence was shown in a few pyramidal neurons. Next, we confirmed the long-term effects of Pep-1-Cu,Zn-superoxide dismutase 1 (SOD1) against ischemic damage. In behavioral test, locomotor activity was significantly increased in Pep-1- and Pep-1-SOD1-treated groups 1 day after ischemia/reperfusion; the locomotor activity in the Pep-1-treated group was higher than that of the Pep-1-SOD1-treated group. Thereafter, the locomotor activity in both groups was decreased with time. Four days after ischemia/reperfusion, the locomotor activity in the Pep-1-SOD1-treated group was similar to that of the sham group; in the Pep-1-treated group, the activity was lower than that of the sham group. In the histochemical study, the cresyl violet positive neurons in the Pep-1-SOD1-treated group were abundantly detected in the hippocampal CA1 region 5 days after ischemia/reperfusion. In biochemical study, SOD1 protein level and activity in all Pep-1-treated ischemic groups were significantly lower than that of the Pep-1-SOD1-treated group. Our results indicate that Pep-1-cargo fusion proteins can be efficiently delivered into neurons in the ischemic hippocampus, and that Pep-1-SOD1 treatment in ischemic animals show a neuroprotection in the ischemic hippocampus for a long time.

Superoxide (·O2−) Production in CA1 Neurons of Rat Hippocampal Slices Exposed to Graded Levels of Oxygen

Neuronal signaling, plasticity, and pathologies in CA1 hippocampal neurons are all intimately related to the redox environment and, thus tissue oxygenation. This study tests the hypothesis that hyperoxic superfusate (95% O2) causes a time-dependent increase in superoxide anion (·O2−) production in CA1 neurons in slices, which will decrease as oxygen concentration is decreased. Hippocampal slices (400 μm) from weaned rats were incubated with the fluorescent probe dihydroethidium (DHE), which detects intracellular ·O2− production. Slices were loaded for 30 min using 10 μM DHE and maintained using one-sided superfusion or continuously loaded using 2.5 μM DHE and maintained using two-sided superfusion (36°C). Continuous loading of DHE and two-sided superfusion gave the highest temporal resolution measurements of ·O2− production, which was estimated by the increase in fluorescence intensity units (FIUs) per minute (FIU/min ± SE) over 4 h. Superoxide production (2.5 μM DHE, 2-sided superfusion) was greatest in 95% O2 (6.6 ± 0.4 FIU/min) and decreased significantly during co-exposure with antioxidants (100 μM melatonin, 25 μM MnTMPyP) and lower levels of O2 (60, 40, and 20% O2 at 5.3 ± 0.3, 3.3 ± 0.1, and 1.6 ± 0.2 FIU/min, respectively). CA1 cell death after 4 h (ethidium homodimer-1 staining) was greatest in 95% O2 and lowest in 40 and 20% O2. CA1 neurons generated evoked action potentials in 20% O2 for >4 h, indicating viability at lower levels of oxygenation. We conclude that ·O2− production and cell death in CA1 neurons increases in response to increasing oxygen concentration product (= PO2 × time). Additionally, lower levels of oxygen (20–40%) and antioxidants should be considered to minimize superoxide-induced oxidative stress in brain slices.

Neurotoxins from invertebrates as anticonvulsants: From basic research to therapeutic application

Invertebrate venoms have attracted considerable interest as a potential source of bioactive substances, especially neurotoxins. These molecules have proved to be extremely useful tools for the understanding of synaptic transmission events, and they have contributed to the design of novel drugs for the treatment of neurological disorders and pain. In this context, as epilepsy involves neuronal substrates, which are sites of action of many neurotoxins; venoms may be particularly useful for antiepileptic drug (AED) research. Epilepsy is a chronic disease whose treatment consists of controlling seizures with antiepileptics that very often induce strong undesirable side effects that may limit treatment. Here, we review the vast, but yet unexplored, world of neurotoxins from invertebrates used as probes in pharmacological screening for novel and less toxic antiepileptics. We briefly review (1) the molecular basis of epilepsy, as well as the sites of action of commonly used anticonvulsants (we bring a comprehensive review of the elements from invertebrate venoms which are mostly studied in neuroscience research and may be useful for drug development); (2) peptides from conus snails; (3) peptides and polyamine toxins from spiders and wasps; and (4) peptides from scorpions.

Spider venoms: a rich source of acylpolyamines and peptides as new leads for CNS drugs

Advances in NMR and mass spectrometry as well as in peptide biochemistry coupled to modern methods in electrophysiology have permitted the isolation and identification of numerous products from spider venoms, previously explored due to technical limitations. The chemical composition of spider venoms is diverse, ranging from low molecular weight organic compounds such as acylpolyamines to complex peptides. First, acylpolyamines (< 1000 Da) have an aromatic moiety linked to a hydrophilic lateral chain. They were characterized for the first time in spider venoms and are ligand-gated ion channel antagonists, which block mainly postsynaptic glutamate receptors in invertebrate and vertebrate nervous systems. Acylpolyamines represent the vast majority of organic components from the spider venom. Acylpolyamine analogues have proven to suppress hippocampal epileptic discharges. Moreover, acylpolyamines could suppress excitatory postsynaptic currents inducing Ca+ accumulation in neurons leading to protection against a brain ischemic insult. Second, short spider peptides (< 6000 Da) modulate ionic currents in Ca2+, Na+, or K+ voltage-gated ion channels. Such peptides may contain from three to four disulfide bridges. Some spider peptides act specifically to discriminate among Ca2+, Na+, or K+ ion channel subtypes. Their selective affinities for ion channel subfamilies are functional for mapping excitable cells. Furthermore, several of these peptides have proven to hyperpolarize peripheral neurons, which are associated with supplying sensation to the skin and skeletal muscles. Some spider N-type calcium ion channel blockers may be important for the treatment of chronic pain. A special group of spider peptides are the amphipathic and positively charged peptides. Their secondary structure is alpha-helical and they insert into the lipid cell membrane of eukaryotic or prokaryotic cells leading to the formation of pores and subsequently depolarizing the cell membrane. Acylpolyamines and peptides from spider venoms represent an interesting source of molecules for the design of novel pharmaceutical drugs.