Neurotoxicity of Micrurus lemniscatus lemniscatus (South American coralsnake) venom in vertebrate neuromuscular preparations in vitro and neutralization by antivenom

Red-on-Yellow Queen: Bio-Layer Interferometry Reveals Functional Diversity Within Micrurus Venoms and Toxin Resistance in Prey Species

Snakes in the family Elapidae largely produce venoms rich in three-finger toxins (3FTx) that bind to the α 1 subunit of nicotinic acetylcholine receptors (nAChRs), impeding ion channel activity. These neurotoxins immobilize the prey by disrupting muscle contraction. Coral snakes of the genus Micrurus are specialist predators who produce many 3FTx, making them an interesting system for examining the coevolution of these toxins and their targets in prey animals. We used a bio-layer interferometry technique to measure the binding interaction between 15 Micrurus venoms and 12 taxon-specific mimotopes designed to resemble the orthosteric binding region of the muscular nAChR subunit. We found that Micrurus venoms vary greatly in their potency on this assay and that this variation follows phylogenetic patterns rather than previously reported patterns of venom composition. The long-tailed Micrurus tend to have greater binding to nAChR orthosteric sites than their short-tailed relatives and we conclude this is the likely ancestral state. The repeated loss of this activity may be due to the evolution of 3FTx that bind to other regions of the nAChR. We also observed variations in the potency of the venoms depending on the taxon of the target mimotope. Rather than a pattern of prey-specificity, we found that mimotopes modeled after snake nAChRs are less susceptible to Micrurus venoms and that this resistance is partly due to a characteristic tryptophan → serine mutation within the orthosteric site in all snake mimotopes. This resistance may be part of a Red Queen arms race between coral snakes and their prey.

The Cloning and Characterization of a Three-Finger Toxin Homolog (NXH8) from the Coralsnake Micrurus corallinus That Interacts with Skeletal Muscle Nicotinic Acetylcholine Receptors

Coralsnakes (Micrurus spp.) are the only elapids found throughout the Americas. They are recognized for their highly neurotoxic venom, which is comprised of a wide variety of toxins, including the stable, low-mass toxins known as three-finger toxins (3FTx). Due to difficulties in venom extraction and availability, research on coralsnake venoms is still very limited when compared to that of other Elapidae snakes like cobras, kraits, and mambas. In this study, two previously described 3FTx from the venom of M. corallinus, NXH1 (3SOC1_MICCO), and NXH8 (3NO48_MICCO) were characterized. Using in silico, in vitro, and ex vivo experiments, the biological activities of these toxins were predicted and evaluated. The results showed that only NXH8 was capable of binding to skeletal muscle cells and modulating the activity of nAChRs in nerve-diaphragm preparations. These effects were antagonized by anti-rNXH8 or antielapidic sera. Sequence analysis revealed that the NXH1 toxin possesses eight cysteine residues and four disulfide bonds, while the NXH8 toxin has a primary structure similar to that of non-conventional 3FTx, with an additional disulfide bond on the first loop. These findings add more information related to the structural diversity present within the 3FTx class, while expanding our understanding of the mechanisms of the toxicity of this coralsnake venom and opening new perspectives for developing more effective therapeutic interventions.

Cardiac Effects of Micrurus corallinus and Micrurus dumerilii carinicauda (Elapidae) Venoms and Neutralization by Brazilian Coralsnake Antivenom and Varespladib

In this work, we examined the action of two South American coralsnake (Micrurus corallinus and Micrurus dumerilii carinicauda) venoms on rat heart function in the absence and presence of treatment with Brazilian coralsnake antivenom (CAV) and varespladib (VPL), a potent phospholipase A₂ inhibitor. Anesthetized male Wistar rats were injected with saline (control) or a single dose of venom (1.5 mg/kg, i.m.) and monitored for alterations in echocardiographic parameters, serum CK-MB levels and cardiac histomorphology, the latter using a combination of fractal dimension and histopathological methods. Neither of the venoms caused cardiac functional alterations 2 h after venom injection; however, M. corallinus venom caused tachycardia 2 h after venom injection, with CAV (given i.p. at an antivenom:venom ratio of 1:1.5, v/w), VPL (0.5 mg/kg, i.p.) and CAV + VPL preventing this increase. Both venoms increased the cardiac lesional score and serum CK-MB levels compared to saline-treated rats, but only the combination of CAV + VPL prevented these alterations, although VPL alone was able to attenuate the increase in CK-MB caused by M. corallinus venom. Micrurus corallinus venom increased the heart fractal dimension measurement, but none of the treatments prevented this alteration. In conclusion, M. corallinus and M. d. carinicauda venoms caused no major cardiac functional alterations at the dose tested, although M. corallinus venom caused transient tachycardia. Both venoms caused some cardiac morphological damage, as indicated by histomorphological analyses and the increase in circulating CK-MB levels. These alterations were consistently attenuated by a combination of CAV and VPL.

Recovery from the Neuroparalysis Caused by the Micrurus nigrocinctus Venom Is Accelerated by an Agonist of the CXCR4 Receptor

Snake envenoming is a major but neglected human disease in tropical and subtropical regions. Among venomous snakes in the Americas, coral snakes of the genus Micrurus are particularly dangerous because they cause a peripheral neuroparalysis that can persist for many days or, in severe cases, progress to death. Ventilatory support and the use of snake species-specific antivenoms may prevent death from respiratory paralysis in most cases. However, there is a general consensus that additional and non-expensive treatments that can be delivered even long after the snake bite are needed. Neurotoxic degeneration of peripheral motor neurons activates pro-regenerative intercellular signaling programs, the greatest of which consist of the chemokine CXCL12α, produced by perisynaptic Schwann cells, which act on the CXCR4 receptor expressed on damaged neuronal axons. We recently found that the CXCR4 agonist NUCC-390 promotes axonal growth. Here, we show that the venom of the highly neurotoxic snake Micrurus nigrocinctus causes a complete degeneration of motor axon terminals of the soleus muscle, followed by functional regeneration whose time course is greatly accelerated by NUCC-390. These results suggest that NUCC-390 is a potential candidate for treating human patients envenomed by Micrurus nigrocinctus as well as other neurotoxic Micrurus spp. in order to improve the recovery of normal neuromuscular physiology, thus reducing the mortality and hospital costs of envenoming.

Partial efficacy of a Brazilian coralsnake antivenom and varespladib in neutralizing distinct toxic effects induced by sublethal Micrurus dumerilii carinicauda envenoming in rats

In this work, we report the efficacy of a combination of Brazilian therapeutic coralsnake antivenom (CAV) and varespladib (phospholipase A₂ inhibitor - VPL) in partially neutralizing selected toxic effects of Micrurus dumerilii carinicauda coralsnake venom in rats. Venom caused local myonecrosis and systemic neurotoxicity, nephrotoxicity, and hepatotoxicity within 2 h of injection. CAV and VPL administered separately failed to prevent most of these alterations. However, a combination of CAV plus VPL offered variable protection against venom-induced coagulation disturbances, leukocytosis, and renal and hepatic morphological alterations.

Comparison of biological activities of Tityus pachyurus venom from two Colombian regions

Background

In the present study, we have tested whether specimens of the medically relevant scorpion Tityus pachyurus, collected from two climatically and ecologically different regions, differ in the biological activities of the venom.

Methods

Scorpions were collected in Tolima and Huila, Colombia. Chemical profiles of the crude venom were obtained from 80 scorpions for each region, using SDS-PAGE and RP-HPLC. Assays for phospholipase A₂, direct and indirect hemolytic, proteolytic, neuromuscular, antibacterial, and insecticidal activities were carried out.

Results

The electrophoretic profiles of venom from the two regions showed similar bands of 6-14 kDa, 36-45 kDa, 65 kDa and 97 kDa. However, bands between 36 kDa and 65 kDa were observed with more intensity in venoms from Tolima, and a 95 kDa band occurred only in venoms from Huila. The chromatographic profile of the venoms showed differences in the intensity of some peaks, which could be associated with changes in the abundance of some components between both populations. Phospholipase A₂ and hemolytic activities were not observable, whereas both venoms showed proteolytic activity towards casein. Insecticidal activity of the venoms from both regions showed significant variation in potency, the bactericidal activity was variable and low for both venoms. Moreover, no differences were observed in the neuromuscular activity assay.

Conclusion

Our results reveal some variation in the activity of the venom between both populations, which could be explained by the ecological adaptations like differences in feeding, altitude and/or diverse predator exposure. However more in-depth studies are necessary to determine the drivers behind the differences in venom composition and activities.

In vivo treatment with varespladib, a phospholipase A2 inhibitor, prevents the peripheral neurotoxicity and systemic disorders induced by Micrurus corallinus (coral snake) venom in rats

In this study, we investigated the action of varespladib (VPL) alone or in combination with a coral snake antivenom (CAV) on the local and systemic effects induced by Micrurus corallinus venom in rats. Adult male Wistar rats were exposed to venom (1.5 mg/kg - i.m.) and immediately treated with CAV (antivenom:venom ratio 1:1.5 'v/w' - i.p.), VPL (0.5 mg/kg - i.p.), or both of these treatments. The animals were monitored for 120 min and then anesthetized to collect blood samples used for haematological and serum biochemical analysis; after euthanasia, skeletal muscle, renal and hepatic tissue samples were collected for histopathological analysis. M. corallinus venom caused local oedema without subcutaneous haemorrhage or apparent necrosis formation, although there was accentuated muscle morphological damage; none of the treatments prevented oedema formation but the combination of CAV and VPL reduced venom-induced myonecrosis. Venom caused neuromuscular paralysis and respiratory impairment in approximately 60 min following envenomation; CAV alone did not prevent the neurotoxic action, whereas VPL alone prevented neurotoxic symptoms developing as did the combination of CAV and VPL. Venom induced significant increase of serum CK and AST release, mostly due to local and systemic myotoxicity, which was partially prevented by the combination of CAV and VPL. The release of hepatotoxic serum biomarkers (LDH and ALP) induced by M. corallinus venom was not prevented by CAV and VPL when individually administered; their combination effectively prevented ALP release. The venom-induced nephrotoxicity (increase in serum creatinine concentration) was prevented by all the treatments. VPL alone or in combination with CAV significantly prevented the venom-induced lymphocytosis. In conclusion, VPL shows to be effective at preventing the neurotoxic, nephrotoxic, and inflammatory activities of M. corallinus venom. In addition, VPL acts synergistically with antivenom to prevent a number of systemic effects caused by M. corallinus venom.

Sweet as honey, bitter as bile: Mitochondriotoxic peptides and other therapeutic proteins isolated from animal tissues, for dealing with mitochondrial apoptosis

Mitochondria are subcellular organelles involved in cell metabolism and cell life-cycle. Their role in apoptosis regulation makes them an interesting target of new drugs for dealing with cancer or rare diseases. Several peptides and proteins isolated from animal and plant sources are known for their therapeutic properties and have been tested on cancer cell-lines and xenograft murine models, highlighting their ability in inducing cell-death by triggering mitochondrial apoptosis. Some of those molecules have been even approved as drugs. Conversely, many other bioactive compounds are still under investigation for their proapoptotic properties. In this review we report about a group of peptides, isolated from animal venoms, with potential therapeutic properties related to their ability in triggering mitochondrial apoptosis. This class of compounds is known with different names, such as mitochondriotoxins or mitocans.

Forty Years of the Description of Brown Spider Venom Phospholipases-D

Spiders of the genus Loxosceles, popularly known as Brown spiders, are considered a serious public health issue, especially in regions of hot or temperate climates, such as parts of North and South America. Although the venoms of these arachnids are complex in molecular composition, often containing proteins with distinct biochemical characteristics, the literature has primarily described a family of toxins, the Phospholipases-D (PLDs), which are highly conserved in all Loxosceles species. PLDs trigger most of the major clinical symptoms of loxoscelism i.e., dermonecrosis, thrombocytopenia, hemolysis, and acute renal failure. The key role played by PLDs in the symptomatology of loxoscelism was first described 40 years ago, when researches purified a hemolytic toxin that cleaved sphingomyelin and generated choline, and was referred to as a Sphingomyelinase-D, which was subsequently changed to Phospholipase-D when it was demonstrated that the enzyme also cleaved other cellular phospholipids. In this review, we present the information gleaned over the last 40 years about PLDs from Loxosceles venoms especially with regard to the production and characterization of recombinant isoforms. The history of obtaining these toxins is discussed, as well as their molecular organization and mechanisms of interaction with their substrates. We will address cellular biology aspects of these toxins and how they can be used in the development of drugs to address inflammatory processes and loxoscelism. Present and future aspects of loxoscelism diagnosis will be discussed, as well as their biotechnological applications and actions expected for the future in this field.

Effects of Mlx-8, a phospholipase A2 from Brazilian coralsnake Micrurus lemniscatus venom, on muscarinic acetylcholine receptors in rat hippocampus

Background:

Here, we described the presence of a neurotoxin with phospholipase A₂ activity isolated from Micrurus lemniscatus venom (Mlx-8) with affinity for muscarinic acetylcholine receptors (mAChRs).

Methods:

The purification, molecular mass determination, partial amino acid sequencing, phospholipase A₂ activity determination, inhibition of the binding of the selective muscarinic ligand [³H]QNB and inhibition of the total [³H]inositol phosphate accumulation in rat hippocampus of the Mlx-8 were determined.

Results:

Thirty-one fractions were collected from HPLC chromatography, and the Mlx-8 toxin was used in this work. The molecular mass of Mlx-8 is 13.628 Da. Edman degradation yielded the following sequence: NLYQFKNMIQCTNTRSWL-DFADYG-CYCGRGGSGT. The Mlx-8 had phospholipase A₂ enzymatic activity. The pK_i values were determined for Mlx-8 toxin and the M₁ selective muscarinic antagonist pirenzepine in hippocampus membranes via [³H]QNB competition binding assays. The pK_i values obtained from the analysis of Mlx-8 and pirenzepine displacement curves were 7.32 ± 0.15, n = 4 and 5.84 ± 0.18, n = 4, respectively. These results indicate that Mlx-8 has affinity for mAChRs. There was no effect on the inhibition ability of the [³H]QNB binding in hippocampus membranes when 1 µM Mlx-8 was incubated with 200 µM DEDA, an inhibitor of phospholipase A₂. This suggests that the inhibition of the phospholipase A₂ activity of the venom did not alter its ability to bind to displace [³H]QNB binding. In addition, the Mlx-8 toxin caused a blockade of 43.31 ± 8.86%, n = 3 and 97.42 ± 2.02%, n = 3 for 0.1 and 1 µM Mlx-8, respectively, on the total [³H]inositol phosphate content induced by 10 µM carbachol. This suggests that Mlx-8 inhibits the intracellular signaling pathway linked to activation of mAChRs in hippocampus.

Conclusion:

The results of the present work show, for the first time, that muscarinic receptors are also affected by the Mlx-8 toxin, a muscarinic ligand with phospholipase A₂ characteristics, obtained from the venom of the Elapidae snake Micrurus lemniscatus, since this toxin was able to compete with muscarinic ligand [³H]QNB in hippocampus of rats. In addition, Mlx-8 also blocked the accumulation of total [³H]inositol phosphate induced by muscarinic agonist carbachol. Thus, Mlx-8 may be a new pharmacological tool for examining muscarinic cholinergic function.