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Skeletal muscle necrosis is a common clinical manifestation of snakebite envenoming. The predominant myotoxic components in snake venoms are catalytically-active phospholipases A2 (PLA2) and PLA2 homologs devoid of enzymatic activity, which have been used as models to investigate various aspects of muscle degeneration. This review addresses the changes in the contractile apparatus of skeletal muscle induced by these toxins. Myotoxic components initially disrupt the integrity of sarcolemma, generating a calcium influx that causes various degenerative events, including hypercontraction of myofilaments. There is removal of specific sarcomeric proteins, owing to the hydrolytic action of muscle calpains and proteinases from invading inflammatory cells, causing an initial redistribution followed by widespread degradation of myofibrillar material. Experiments using skinned cardiomyocytes and skeletal muscle fibers show that these myotoxins do not directly affect the contractile apparatus, implying that hypercontraction is due to cytosolic calcium increase secondary to sarcolemmal damage. Such drastic hypercontraction may contribute to muscle damage by generating mechanical stress and further sarcolemmal damage. [ABSTRACT FROM AUTHOR]

Snakebite envenoming is an important public health issue responsible for mortality and severe morbidity. Where mortality is mainly caused by venom toxins that induce cardiovascular disturbances, neurotoxicity, and acute kidney injury, morbidity is caused by toxins that directly or indirectly destroy cells and degrade the extracellular matrix. These are referred to as 'tissue-damaging toxins' and have previously been classified in various ways, most of which are based on the tissues being affected (e.g., cardiotoxins, myotoxins). This categorisation, however, is primarily phenomenological and not mechanistic. In this review, we propose an alternative way of classifying cytotoxins based on their mechanistic effects rather than using a description that is organ- or tissue-based. The mechanisms of toxin-induced tissue damage and their clinical implications are discussed. This review contributes to our understanding of fundamental biological processes associated with snakebite envenoming, which may pave the way for a knowledge-based search for novel therapeutic options. The snake venom toxins responsible for tissue damage, their mechanisms of action and pathological effects are reviewed, together with the search of novel therapeutic alternatives to abrogate their effects [ABSTRACT FROM AUTHOR]

Morbidity from snakebite envenoming affects approximately 400,000 people annually. Tissue damage at the bite-site often leaves victims with catastrophic life-long injuries and is largely untreatable by current antivenoms. Repurposed small molecule drugs that inhibit specific snake venom toxins show considerable promise for tackling this neglected tropical disease. Using human skin cell assays as an initial model for snakebite-induced dermonecrosis, we show that the drugs 2,3-dimercapto-1-propanesulfonic acid (DMPS), marimastat, and varespladib, alone or in combination, inhibit the cytotoxicity of a broad range of medically important snake venoms. Thereafter, using preclinical mouse models of dermonecrosis, we demonstrate that the dual therapeutic combinations of DMPS or marimastat with varespladib significantly inhibit the dermonecrotic activity of geographically distinct and medically important snake venoms, even when the drug combinations are delivered one hour after envenoming. These findings strongly support the future translation of repurposed drug combinations as broad-spectrum therapeutics for preventing morbidity caused by snakebite. Three drugs initially developed for other conditions, 2,3-dimercapto-1-propanesulfonic acid (DMPS), marimastat and varespladib, have shown promise in preventing the lethality of snakebite envenoming. Here, Hall et al., show that a combination of these drugs can combat the local dermonecrotic effects caused by diverse cytotoxic venoms. [ABSTRACT FROM AUTHOR]

Myonecrosis is a frequent clinical manifestation of envenomings by Viperidae snakes, mainly caused by the toxic actions of secreted phospholipase A2 (sPLA2) enzymes and sPLA2-like homologs on skeletal muscle fibers. A hallmark of the necrotic process induced by these myotoxins is the rapid appearance of hypercontracted muscle fibers, attributed to the massive influx of Ca2+ resulting from cell membrane damage. However, the possibility of myotoxins having, in addition, a direct effect on the contractile machinery of skeletal muscle fibers when internalized has not been investigated. This question is here addressed by using an ex vivo model of single-skinned muscle fibers, which lack membranes but retain an intact contractile apparatus. Rabbit psoas skinned fibers were exposed to two types of myotoxins of Bothrops asper venom: Mt-I, a catalytically active Asp49 sPLA2 enzyme, and Mt-II, a Lys49 sPLA2-like protein devoid of phospholipolytic activity. Neither of these myotoxins affected the main parameters of force development in striated muscle sarcomeres of the skinned fibers. Moreover, no microscopical alterations were evidenced after their exposure to Mt-I or Mt-II. In contrast to the lack of effects on skinned muscle fibers, both myotoxins induced a strong hypercontraction in myotubes differentiated from murine C2C12 myoblasts, with drastic morphological alterations that reproduce those described in myonecrotic tissue in vivo. As neither Mt-I nor Mt-II showed direct effects upon the contractile apparatus of skinned fibers, it is concluded that the mechanism of hypercontraction triggered by both myotoxins in patients involves indirect effects, i.e., the large cytosolic Ca2+ increase after sarcolemma permeabilization. [ABSTRACT FROM AUTHOR]

Snakebite envenomation is a neglected tropical disease of high mortality and morbidity largely due to insufficient supply of effective and affordable antivenoms. Snake antivenoms are mostly effective against the venoms used in their production. It is thus crucial that effective and affordable antivenom(s) with wide para-specificity, capable of neutralizing the venoms of a large number of snakes, be produced. Here we studied the pan-specific antiserum prepared previously by a novel immunization strategy involving the exposure of horses to a 'diverse toxin repertoire' consisting of 12 neurotoxic Asian snake toxin fractions/ venoms from six species. This antiserum was previously shown to exhibit wide para-specificity by neutralizing 11 homologous and 16 heterologous venoms from Asia and Africa. We now show that the antiserum can neutralize 9 out of 10 additional neurotoxic venoms. Altogether, 36 snake venoms belonging to 10 genera from 4 continents were neutralized by the antiserum. Toxin profiles previously generated using proteomic techniques of these 36 venoms identified α-neurotoxins, β-neurotoxins, and cytotoxins as predominant toxins presumably neutralized by the antiserum. The bases for the wide para-specificity of the antiserum are discussed. These findings indicate that it is feasible to generate antivenoms of wide para-specificity against elapid neurotoxic venoms from different regions in the world and raises the possibility of a universal neurotoxic antivenom. This should reduce the mortality resulting from neurotoxic snakebite envenomation. [ABSTRACT FROM AUTHOR]

Matrix metalloproteinases have been implicated in diabetic microvascular complications. However, little is known about the pathophysiological links between MMP-10 and the renin-angiotensin system (RAS) in diabetic kidney disease (DKD). We tested the hypothesis that MMP-10 may be up-regulated in early stage DKD, and could be down-regulated by angiotensin II receptor blockade (telmisartan). Serum MMP-10 and TIMP-1 levels were measured in 268 type 2 diabetic subjects and 111 controls. Furthermore, histological and molecular analyses were performed to evaluate the renal expression of Mmp10 and Timp1 in a murine model of early type 2 DKD (db/db) after telmisartan treatment. MMP-10 (473 ± 274 pg/ml vs. 332 ± 151; p = 0.02) and TIMP-1 (573 ± 296 ng/ml vs. 375 ± 317; p < 0.001) levels were significantly increased in diabetic patients as compared to controls. An early increase in MMP-10 and TIMP-1 was observed and a further progressive elevation was found as DKD progressed to end-stage renal disease. Diabetic mice had 4-fold greater glomerular Mmp10 expression and significant albuminuria compared to wild-type, which was prevented by telmisartan. MMP-10 and TIMP-1 are increased from the early stages of type 2 diabetes. Prevention of MMP-10 upregulation observed in diabetic mice could be another protective mechanism of RAS blockade in DKD. [ABSTRACT FROM AUTHOR]

Parenteral administration of horse- and sheep-derived antivenoms constitutes the cornerstone in the therapy of envenomations induced by animal bites and stings. Depending on the type of neutralising molecule, antivenoms are made of: (i) whole IgG molecules (150 kDa), (ii) F(ab′)[sub 2] immunoglobulin fragments (100 kDa) or (iii) Fab immunoglobulin fragments (50 kDa). Because of their variable molecular mass, these three types of antivenoms have different pharmacokinetic profiles. Fab fragments have the largest volume of distribution and readily reach extravascular compartments. They are catabolised mainly by the kidney, having a more rapid clearance than F(ab′)[sub 2] fragments and IgG. On the other hand, IgG molecules have a lower volume of distribution and a longer elimination half-life, showing the highest cycling through the interstitial spaces in the body. IgG elimination occurs mainly by extrarenal mechanisms. F(ab′)[sub 2] fragments display a pharmacokinetic profile intermediate between those of Fab fragments and IgG molecules. Such diverse pharmacokinetic properties have implications for the pharmacodynamics of these immunobiologicals, since a pronounced mismatch has been described between the pharmacokinetics of venoms and antivenoms. Some venoms, such as those of scorpions and elapid snakes, are rich in low-molecular-mass neurotoxins of high diffusibility and large volume of distribution that reach their tissue targets rapidly after injection. In contrast, venoms rich in high-molecular-mass toxins, such as those of viperid snakes, have a pharmacokinetic profile characterised by a rapid initial absorption followed by a slow absorption process from the site of venom injection. Such delayed absorption has been linked with recurrence of envenomation when antibody levels in blood decrease. This heterogeneity in pharmacokinetics and mechanism of action of venom components requires a detailed analysis of each venom-antivenom system in order to determine the most appropriate type of neutralising molecule for each particular venom. Besides having a high affinity for toxicologically relevant venom components, an ideal antivenom should possess a volume of distribution as similar as possible to that of the toxins being neutralised. Moreover, high levels of neutralising antibodies should remain in blood for a relatively prolonged time to assure neutralisation of toxins reaching the bloodstream later in the course of envenomation, and to promote redistribution of toxins from extravascular compartments to blood. Additional studies are required on different venoms and antivenoms in order to further understand the pharmacokinetic-pharmacodynamic relationships of antibodies and their fragments and to optimise the immunotherapy of envenomations. [ABSTRACT FROM AUTHOR]

The World Health Organization recently listed snakebite envenoming as a Neglected Tropical Disease, proposing strategies to significantly reduce the global burden of this complex pathology by 2030. In this context, effective adjuvant treatments to complement conventional antivenom therapy based on inhibitory molecules for specific venom toxins have gained renewed interest. Varespladib (LY315920) is a synthetic molecule clinically tested to block inflammatory cascades of several diseases associated with elevated levels of secreted phospholipase A2 (sPLA2). Most recently, Varespladib was tested against several whole snake venoms and isolated PLA2 toxins, demonstrating potent inhibitory activity. Herein, we describe the first structural and functional study of the complex between Varespladib and a PLA2-like snake venom toxin (MjTX-II). In vitro and in vivo experiments showed this compound's capacity to inhibit the cytotoxic and myotoxic effects of MjTX-II from the medically important South American snake, Bothrops moojeni. Crystallographic and bioinformatics analyses revealed interactions of Varespladib with two specific regions of the toxin, suggesting inhibition occurs by physical blockage of its allosteric activation, preventing the alignment of its functional sites and, consequently, impairing its ability to disrupt membranes. Furthermore, based on the analysis of several crystallographic structures, a distinction between toxin activators and inhibitors is proposed. [ABSTRACT FROM AUTHOR]

Snake envenoming causes several potentially lethal pathologies. The specific pathology is dictated by the toxin composition of venom, which varies by species, geography and ontogeny. This variation severely restricts the paraspecific efficacy of antivenoms used to treat snakebite victims. With a view to devising pathology-specific snakebite treatments, we assessed the procoagulant activity of 57 snake venoms and investigated the efficacy of various antivenoms. We find that procoagulant venoms act differentially on key steps of the coagulation cascade, and that certain monospecific antivenoms work in a previously unrecognised paraspecific manner to neutralise this activity, despite conventional assumptions of congener-restricted efficacy. Moreover, we demonstrate that the metal chelator EDTA is also capable of neutralising venom-induced lethality in vivo. This study illustrates the exciting potential of developing new, broad-spectrum, toxin-targeting antivenoms capable of treating key snakebite pathologies, and advocates a thorough re-examination of enzyme inhibiting compounds as alternative therapies for treating snakebite victims. Stuart Ainsworth and colleagues characterized the coagulopathic activity of snake venom and demonstrated that certain monospecific antivenoms can neutralize procoagulant venoms from more than one species. This study suggests a possibility of developing broad-spectrum, toxin-targeting antivenoms to treat snakebite victims. [ABSTRACT FROM AUTHOR]

In the original version of this Article, the sixth sentence of the first paragraph of the Introduction incorrectly read ‘Particularly, elapid antivenoms often have an unbalanced antibody content with relatively low amounts of antibodies against small neurotoxic venom components that have low immunogenicity, which often leads to low immune cgqtns in production animals8-10’. The correct version states ‘responses’ instead of ‘cgqtns’. This has been corrected in both the PDF and HTML versions of the Article. [ABSTRACT FROM AUTHOR]

The black mamba (Dendroaspis polylepis) is one of the most feared snake species of the African savanna. It has a potent, fast-acting neurotoxic venom comprised of dendrotoxins and α-neurotoxins associated with high fatality in untreated victims. Current antivenoms are both scarce on the African continent and present a number of drawbacks as they are derived from the plasma of hyper-immunized large mammals. Here, we describe the development of an experimental recombinant antivenom by a combined toxicovenomics and phage display approach. The recombinant antivenom is based on a cocktail of fully human immunoglobulin G (IgG) monoclonal antibodies capable of neutralizing dendrotoxin-mediated neurotoxicity of black mamba whole venom in a rodent model. Our results show the potential use of fully human monoclonal IgGs against animal toxins and the first use of oligoclonal human IgG mixtures against experimental snakebite envenoming. Current anti-venoms against black mamba (Dendroaspis polylepis) bites are animal-derived and associated with several limitations. Here, Laustsen and colleagues develop an experimental recombinant anti-venom based on oligoclonal human IgG antibodies and establish its potential protective value in neutralizing dendrotoxin-mediated neurotoxicity using venom challenge in vivo models. [ABSTRACT FROM AUTHOR]

Snakebite envenoming is a serious condition requiring medical attention and administration of antivenom. Current antivenoms are antibody preparations obtained from the plasma of animals immunised with whole venom(s) and contain antibodies against snake venom toxins, but also against other antigens. In order to better understand the molecular interactions between antivenom antibodies and epitopes on snake venom toxins, a high-throughput immuno-profiling study on all manually curated toxins from Dendroaspis species and selected African Naja species was performed based on custom-made high-density peptide microarrays displaying linear toxin fragments. By detection of binding for three different antivenoms and performing an alanine scan, linear elements of epitopes and the positions important for binding were identified. A strong tendency of antivenom antibodies recognizing and binding to epitopes at the functional sites of toxins was observed. With these results, high-density peptide microarray technology is for the first time introduced in the field of toxinology and molecular details of the evolution of antibody-toxin interactions based on molecular recognition of distinctive toxic motifs are elucidated. [ABSTRACT FROM AUTHOR]

An abstract for the article "Backbone Flexibility Controls the Activity and Specificity of a Protein-Protein Interface- Specificity in Snake Venom Metalloproteases (SVMPs)," by Hannes G. Wallnoefer, Torsten Lingott, Klaus R. Liedl and colleagues is presented.