Isolation and characterization of a novel toxin from the venom of the spider Grammostola rosea that blocks sodium channels

Transcriptional profiling of neuronal ion channels in dorsal root ganglion-derived immortal cell line (F-11) under different culture conditions

Pathological pain is a prevalent condition that affects majority of adults with a variety of underlying disease conditions. Current available pharmacological pain treatments have several negative and potentially life-threatening side effects associated with their long-term use. Due to the heterogeneity of pain perception and the diversity of neuronal mechanisms that contribute to pain, high-throughput screening of small molecules that may have underlying analgesic properties is essential for identifying new analgesic treatments that are both effective and safe. The F-11 hybrid immortalized cell line is one of the currently available dorsal root ganglion (DRG) cell lines used for drug screening. While F-11 cells are commonly used as analogs to primary DRG sensory neurons, they differ significantly in physiological properties. The present study investigated the impact of differentiation protocols on the expression of mature neuron ion channels and receptors in F-11 cells. Using a customized gene array of more than eighty neuronal ion channels and receptors including voltage-gated ion channels, transient receptor potential channels, and cannabinoid receptors, we assessed the following groups: control F-11 cells; F-11 cells cultured under different culture conditions, and murine DRG tissue. The expression profiles of majority of the investigated ion channels and receptors in F-11 cells were found to be lower compared to primary mouse DRG neurons. F-11 cells cultured under low serum (LSM) conditions had increased expression of several investigated targets including voltage-gated ion channels and cannabinoid receptors when compared to control F-11 cells. The study showed that the culture conditions significantly modulated the transcriptional expression of studied ion channels and receptors, and that long-term culture (21 days) may adversely affect the expression of many of the studied targets.

Immortalized Dorsal Root Ganglion Neuron Cell Lines

Pain is one of the most significant causes of suffering and disability world-wide, and arguably the most burdensome global health challenge. The growing number of patients suffering from chronic pain conditions such as fibromyalgia, complex regional pain syndrome, migraine and irritable bowel syndrome, not only reflect the complexity and heterogeneity of pain types, but also our lack of understanding of the underlying mechanisms. Sensory neurons within the dorsal root ganglia (DRG) have emerged as viable targets for effective chronic pain therapy. However, DRG's contain different classes of primary sensory neurons including pain-associated nociceptive neurons, non-nociceptive temperature sensing, mechanosensory and chemoreceptive neurons, as well as multiple types of immune and endothelial cells. This cell-population heterogeneity makes investigations of individual subgroups of DRG neurons, such as nociceptors, difficult. In attempts to overcome some of these difficulties, a limited number of immortalized DRG-derived cell lines have been generated over the past few decades. In vitro experiments using DRG-derived cell lines have been useful in understanding sensory neuron function. In addition to retaining phenotypic similarities to primary cultured DRG neurons, these cells offer greater suitability for high throughput assays due to ease of culture, maintenance, growth efficiency and cost-effectiveness. For accurate interpretation and translation of results it is critical, however, that phenotypic similarities and differences of DRG-derived cells lines are methodically compared to native neurons. Published reports to date show notable variability in how these DRG-derived cells are maintained and differentiated. Understanding the cellular and molecular differences stemming from different culture methods, is essential to validate past and future experiments, and enable these cells to be used to their full potential. This review describes currently available DRG-derived cell lines, their known sensory and nociceptor specific molecular profiles, and summarize their morphological features related to differentiation and neurite outgrowth.

The Role of Toxins in the Pursuit for Novel Analgesics

Chronic pain is a major medical issue which reduces the quality of life of millions and inflicts a significant burden on health authorities worldwide. Currently, management of chronic pain includes first-line pharmacological therapies that are inadequately effective, as in just a portion of patients pain relief is obtained. Furthermore, most analgesics in use produce severe or intolerable adverse effects that impose dose restrictions and reduce compliance. As the majority of analgesic agents act on the central nervous system (CNS), it is possible that blocking pain at its source by targeting nociceptors would prove more efficient with minimal CNS-related side effects. The development of such analgesics requires the identification of appropriate molecular targets and thorough understanding of their structural and functional features. To this end, plant and animal toxins can be employed as they affect ion channels with high potency and selectivity. Moreover, elucidation of the toxin-bound ion channel structure could generate pharmacophores for rational drug design while favorable safety and analgesic profiles could highlight toxins as leads or even as valuable therapeutic compounds themselves. Here, we discuss the use of plant and animal toxins in the characterization of peripherally expressed ion channels which are implicated in pain.

Investigating the interaction of Grammostola rosea venom peptides and model lipid bilayers with solid-state NMR and electron microscopy techniques

Spider venom contains a number of small peptides that can control the gating properties of a wide range of ion channels with high affinity and specificity. These ion channels are responsible for coordination and control of many bodily functions such as transducing signals into sensory functions, smooth muscle contractions as well as serving as sensors in volume regulation. Hence, these peptides have been the topic of many research efforts in hopes that they can be used as biomedical therapeutics. Several peptides are known to control the gating properties of ion channels by involving the lipid membrane. GsMTx4, originally isolated from the Chilean Rose tarantula (Grammostola rosea), is known to selectively inhibit mechanosensitive ion channels by partitioning into the lipid bilayer. To further understand this indirect gating mechanism, we investigated the interactions between native GsAF2, VsTx1 and a synthetic form of GsMTx4 with model DMPC lipid bilayers using ³¹P solid-state NMR, ¹³C CP-MAS NMR, NS-TEM and cryo-TEM. The results reveal that these inhibitor cystine knot peptides perforate the DMPC lipid vesicles similarly with some subtle differences and ultimately create small spherical vesicles and anisotropic cylindrical and discoidal vesicles at concentrations near 1.0-1.5 mol% peptide. The anisotropic components align with their long axes along the NMR static B₀ magnetic field, a property that should be useful in future NMR structural investigations of these systems. These findings move us forward in our understanding of how these peptides bind and interact with the lipid bilayer.

Sodium Channels and Venom Peptide Pharmacology

Venomous animals including cone snails, spiders, scorpions, anemones, and snakes have evolved a myriad of components in their venoms that target the opening and/or closing of voltage-gated sodium channels to cause devastating effects on the neuromuscular systems of predators and prey. These venom peptides, through design and serendipity, have not only contributed significantly to our understanding of sodium channel pharmacology and structure, but they also represent some of the most phyla- and isoform-selective molecules that are useful as valuable tool compounds and drug leads. Here, we review our understanding of the basic function of mammalian voltage-gated sodium channel isoforms as well as the pharmacology of venom peptides that act at these key transmembrane proteins.

Extraction and partial characterization of venom from the Colombian spider Pamphobeteus aff. nigricolor (Aranae:Theraphosidae)

We report the first studies of characterization and extraction of the Pamphobeteus aff. nigricolor (Pocock, 1901) (Aranae:Theraphosidae) venom done in Colombia using the electro-stimulation technique previous anesthesia with isofluorane. After each extraction process, a low viscosity, colorless venom was obtained. This venom showed a 1.01 mg/μl density and a pH of 5. The humidity percentage did not show a significance difference between males and females (P > 0.05) with a general media of 77.49 ± 1.74%. In all cases the venom yielded was variable between males and females, with a media of 22.45 ± 5.17 mg (wet weight) and 4.58 ± 0.94 mg (dry weigh), obtaining larger amounts in females, 28.34 ± 7.49 mg and 5.69 ± 1.36 (wet and dry weight respectively). Venom showed a hemolytic activity dependent of enzymatic active phospholipase and neither coagulant nor proteolytic activities were observed. Electrophoretic profile showed a main protein content with a molecular mass below 14 kDa. RP-HPLC venom profile revealed a difference among male and female venom's content where 17 and 21 main fractions were obtained respectively. Three peptides, Theraphotoxin-Pn1a, Theraphotoxin-Pn1b and Theraphotoxin-Pn2a, were identified using HPLC-nESI-MS/MS. These peptides showed a high identity with other peptides found on Theraphosides which are proved to affect voltage-gated calcium channels.

Voltage-gated K+ channels in adipogenic differentiation of bone marrow-derived human mesenchymal stem cells

AIM

To determine the presence of voltage-gated K(+) (Kv) channels in bone marrow-derived human mesenchymal stem cells (hMSCs) and their impact on differentiation of hMSCs into adipocytes.

METHODS

For adipogenic differentiation, hMSCs were cultured in adipogenic medium for 22 d. The degrees of adipogenic differentiation were examined using Western blot, Oil Red O staining and Alamar assay. The expression levels of Kv channel subunits Kv1.1, Kv1.2, Kv1.3, Kv1.4, Kv2.1, Kv3.1, Kv3.3, Kv4.2, Kv4.3, and Kv9.3 in the cells were detected using RT-PCR and Western blot analysis.

RESULTS

The expression levels of Kv2.1 and Kv3.3 subunits were markedly increased on d 16 and 22. In contrast, the expression levels of other Kv channel subunits, including Kv1.1, Kv1.2, Kv1.3, Kv1.4, Kv4.2, Kv4.3, and Kv9.3, were decreased as undifferentiated hMSCs differentiated into adipocytes. Addition of the Kv channel blocker tetraethylammonium (TEA, 10 mmol/L) into the adipogenic medium for 6 or 12 d caused a significant decrease, although not complete, in lipid droplet formation and adipocyte fatty acid-binding protein 2 (aP(2)) expressions. Addition of the selective Kv2.1 channel blocker guangxitoxin (GxTX-1, 40 nmol/L) into the adipogenic medium for 21 d also suppressed adipogenic differentiation of the cells.

CONCLUSION

The results demonstrate that subsets of Kv channels including Kv2.1 and Kv3.3 may play an important role in the differentiation of hMSCs into adipocytes.

Purification and cDNA cloning of a novel neurotoxic peptide (Acra3) from the scorpion Androctonus crassicauda

Androctonus crassicauda is one of the Southeastern Anatolian scorpions of Turkey with ethno-medical and toxicological importance. Two toxic peptides (Acra1 and Acra2) were isolated and characterized from the venom of this scorpion. In this communication, the isolation of an additional toxin (Acra3) by chromatographic separations (HPLC and TSK-gel sulfopropyl) and its chemical and functional characterization is reported. Acra3 is a 7620Da molecular weight peptide, with 66 amino acid residues crosslinked by four disulfide bridges. The gene coding for this peptide was cloned and sequenced. Acra3 is anticipated to undergo post-translational modifications at the C-terminal region, having an amidated serine as last residue. Injection of Acra3 induces severe neurotoxic events in mice, such as: excitability and convulsions, leading to the death of the animals within a few minutes after injection. Electrophysiological assays conducted with pure Acra3, using cells that specifically expressed sodium channels (Nav1.1-Nav1.6) showed no clear effect. The exact molecular target of Acra3 remained undiscovered, similar to three other scorpion peptides that clustered very closely in the phylogenetic tree included here. The exact target of these four peptides is not very clear.

Toxin modulators and blockers of hERG K(+) channels

The K(+) channel encoded by the Ether-á-go-go-Related Gene (ERG) is expressed in different tissues of different animal species. There are at least three subtypes of this channel, being the sub-type 1 (ERG1) crucial in the repolarization phase of the cardiac action potential. Mutations in this gene can affect the properties of the channel producing the type II long QT syndrome (LQTS2) and many drugs are also known to affect this channel with a similar side effect. Various scorpion, spider and sea anemone toxins affect the ERG currents by blocking the ion-conducting pore from the external side or by modulating channel gating through binding to the voltage-sensor domain. By doing so, these toxins become very useful tools for better understanding the structural and functional characteristics of these ion channels. This review discusses the interaction between the ERG channels and the peptides isolated from venoms of these animals. Special emphasis is placed on scorpion toxins, although the effects of several spider venom toxins and anemone toxins will be also revised.

Molecular Cloning and Sequence Analysis of the cDNAs Encoding Toxin-Like Peptides from the Venom Glands of Tarantula Grammostola rosea

Tarantula venom glands produce a large variety of bioactive peptides. Here we present the identification of venom components obtained by sequencing clones isolated from a cDNA library prepared from the venom glands of the Chilean common tarantula, Grammostola rosea. The cDNA sequences of about 1500 clones out of 4000 clones were analyzed after selection using several criteria. Forty-eight novel toxin-like peptides (GTx1 to GTx7, and GTx-TCTP and GTx-CRISP) were predicted from the nucleotide sequences. Among these peptides, twenty-four toxins are ICK motif peptides, eleven peptides are MIT1-like peptides, and seven are ESTX-like peptides. Peptides similar to JZTX-64, aptotoxin, CRISP, or TCTP are also obtained. GTx3 series possess a cysteine framework that is conserved among vertebrate MIT1, Bv8, prokineticins, and invertebrate astakines. GTx-CRISP is the first CRISP-like protein identified from the arthropod venom. Real-time PCR revealed that the transcripts for TCTP-like peptide are expressed in both the pereopodal muscle and the venom gland. Furthermore, a unique peptide GTx7-1, whose signal and prepro sequences are essentially identical to those of HaTx1, was obtained.

Target promiscuity and heterogeneous effects of tarantula venom peptides affecting Na+ and K+ ion channels

Venom-derived peptide modulators of ion channel gating are regarded as essential tools for understanding the molecular motions that occur during the opening and closing of ion channels. In this study, we present the characterization of five spider toxins on 12 human voltage-gated ion channels, following observations about the target promiscuity of some spider toxins and the ongoing revision of their "canonical" gating-modifying mode of action. The peptides were purified de novo from the venom of Grammostola rosea tarantulas, and their sequences were confirmed by Edman degradation and mass spectrometry analysis. Their effects on seven tetrodotoxin-sensitive Na(+) channels, the three human ether-à-go-go (hERG)-related K(+) channels, and two human Shaker-related K(+) channels were extensively characterized by electrophysiological techniques. All the peptides inhibited ion conduction through all the Na(+) channels tested, although with distinctive patterns. The peptides also affected the three pharmaceutically relevant hERG isoforms differently. At higher concentrations, all peptides also modified the gating of the Na(+) channels by shifting the activation to more positive potentials, whereas more complex effects were recorded on hERG channels. No effects were evident on the two Shaker-related K(+) channels at concentrations well above the IC(50) value for the affected channels. Given the sequence diversity of the tested peptides, we propose that tarantula toxins should be considered both as multimode and target-promiscuous ion channel modulators; both features should not be ignored when extracting mechanistic interpretations about ion channel gating. Our observations could also aid in future structure-function studies and might help the development of novel ion channel-specific drugs.