Isolation and characterization of a lethal myotoxic phospholipase A from the venom of the common sea snake Enhydrina schistosa causing myoglobinuria in mice

On characterizing the Red-headed Krait (Bungarus flaviceps) venom: Decomplexation proteomics, immunoreactivity and toxicity cross-neutralization by hetero-specific antivenoms

The Red-headed Krait (Bungarus flaviceps) is a medically important venomous snake species in Southeast Asia, while there is no specific antivenom available for its envenoming. This study investigated the venom composition through a decomplexation proteomic approach, and examined the immunoreactivity as well as cross-neutralization efficacy of two hetero-specific krait antivenoms, Bungarus candidus Monovalent Antivenom (BcMAV) and Bungarus fasciatus Monovalent Antivenom (BfMAV), against the venom of B. flaviceps from Peninsular Malaysia. A total of 43 non-redundant proteoforms belonging to 10 toxin families were identified in the venom proteome, which is dominated by phospholipases A₂ including beta-bungarotoxin lethal subunit (56.20 % of total venom proteins), Kunitz-type serine protease inhibitors (19.40 %), metalloproteinases (12.85 %) and three-finger toxins (7.73 %). The proteome varied in quantitative aspect from the earlier reported Indonesian (Sumatran) sample, suggesting geographical venom variation. BcMAV and BfMAV were immunoreactive toward the B. flaviceps venom, with BcMAV being more efficacious in immunological binding. Both antivenoms cross-neutralized the venom lethality with varying efficacy, where BcMAV was more potent than BfMAV by ~13 times (normalized potency: 38.04 mg/g vs. 2.73 mg/g, defined as the venom amount completely neutralized by one-gram antivenom protein), supporting the potential utility of BcMAV for para-specific neutralization against B. flaviceps venom.

Australian Sea Snake Envenoming Causes Myotoxicity and Non-Specific Systemic Symptoms - Australian Snakebite Project (ASP-24)

Background: Sea snakes are venomous snakes found in the warm parts of the Indo-Pacific, including around Australia. Most sea snake envenoming causes myotoxicity, but previous Australian case reports describe neurotoxicity. We aimed to describe the epidemiology and clinical presentation of Australian sea snake envenoming and the effectiveness of antivenom.

Methods: Patients were recruited to the Australian Snakebite Project (ASP), an Australia-wide prospective observational study recruiting all patients with suspected or confirmed snakebite >2 years. Information about demographics, bite circumstances, species involved, clinical and laboratory features of envenoming, and treatment is collected and entered into a purpose-built database.

Results: Between January 2002 and August 2020, 13 patients with suspected sea snake bite were recruited to ASP, 11 were male; median age was 30 years. Bites occurred in Queensland and Western Australia. All patients were in or around, coastal waters at the time of bite. The species involved was identified in two cases (both Hydrophis zweifeli). Local effects occurred in 9 patients: pain (5), swelling (5), bleeding (2), bruising (1). Envenoming occurred in eight patients and was characterised by non-specific systemic features (6) and myotoxicity (2). Myotoxicity was severe (peak CK 28200 and 48100 U/L) and rapid in onset (time to peak CK 13.5 and 15.1 h) in these two patients. Non-specific systemic features included nausea (6), headache (6), abdominal pain (3), and diaphoresis (2). Leukocytosis, neutrophilia, and lymphopenia occurred in both patients with myotoxicity and was evident on the first blood test. No patients developed neurotoxicity or coagulopathy. Early Seqirus antivenom therapy was associated with a lower peak creatine kinase.

Conclusion: While relatively rare, sea snake envenoming is associated with significant morbidity and risk of mortality. Early antivenom appears to have a role in preventing severe myotoxicity and should be a goal of therapy.

De Novo Venom-Gland Transcriptomics of Spine-Bellied Sea Snake (Hydrophis curtus) from Penang, Malaysia-Next-Generation Sequencing, Functional Annotation and Toxinological Correlation

Envenomation resulted from sea snake bite is a highly lethal health hazard in Southeast Asia. Although commonly caused by sea snakes of Hydrophiinae, each species is evolutionarily distinct and thus, unveiling the toxin gene diversity within individual species is important. Applying next-generation sequencing, this study investigated the venom-gland transcriptome of Hydrophis curtus (spine-bellied sea snake) from Penang, West Malaysia. The transcriptome was de novo assembled, followed by gene annotation and sequence analyses. Transcripts with toxin annotation were only 96 in number but highly expressed, constituting 48.18% of total FPKM in the overall transcriptome. Of the 21 toxin families, three-finger toxins (3FTX) were the most abundantly expressed and functionally diverse, followed by phospholipases A₂. Lh_FTX001 (short neurotoxin) and Lh_FTX013 (long neurotoxin) were the most dominant 3FTXs expressed, consistent with the pathophysiology of envenomation. Lh_FTX001 and Lh_FTX013 were variable in amino acid compositions and predicted epitopes, while Lh_FTX001 showed high sequence similarity with the short neurotoxin from Hydrophis schistosus, supporting cross-neutralization effect of Sea Snake Antivenom. Other toxins of low gene expression, for example, snake venom metalloproteinases and L-amino acid oxidases not commonly studied in sea snake venom were also identified, enriching the knowledgebase of sea snake toxins for future study.

Australian snakebite myotoxicity (ASP-23)

BACKGROUND

Myotoxicity is a recognised but poorly characterised effect of snake envenoming worldwide. We aimed to describe the clinical effects, complications and effectiveness of antivenom in myotoxicity from Australian snake envenoming.

METHODS

Patients were recruited to the Australian Snakebite Project (ASP), a prospective, observational study of patients with suspected or proven snakebite countrywide. After informed consent data is collected and stored in a dedicated database and blood samples are taken and stored. We included patients with envenoming and biochemical evidence of myotoxicity (peak creatine kinase [CK] > 1000 U/L). Snake species was determined by expert identification or venom specific enzyme immunoassay. Analysis included patient demographics, clinical findings, pathology results, treatment and outcomes (length of hospital stay, complications).

RESULTS

1638 patients were recruited January 2003-December 2016, 935 (57%) were envenomed, 148 developed myotoxicity (16%). Snake species most commonly associated with myotoxicity were Notechis spp. (30%), Pseudechis porphyriacus (20%) and Pseudechis australis (13%). Bite site effects occurred in 19 patients. Non-specific systemic symptoms occurred in 135 patients (91%), specific signs and symptoms in 83. In 120 patients with early serial CK results, the median peak CK was 3323 U/L (IQR;1050-785100U/L), the median time to first CK >500 U/L was 11.1 h and median time to peak CK of 34.3 h. White cell count was elevated in 136 patients (93%; median time to elevation, 4.9 h). 37 patients had elevated creatinine, six were dialysed. Two patients died from complications of severe myotoxicity. Antivenom given before the first abnormal CK (>500 U/L) was associated with less severe myotoxicity (2976 versus 7590 U/L). Non-envenomed patients with elevated CK had rapid rise to abnormal CK (median 3.5 h) and less had elevated WCC (32%).

CONCLUSION

Myotoxicity from Australian snakes is relatively common and has systemic effects, with significant associated morbidity and mortality. CK is not a good early biomarker of mytoxicity. Early antivenom may play a role in reducing severity.

Unlocking the secrets of banded coral snake (Calliophis intestinalis, Malaysia): A venom with proteome novelty, low toxicity and distinct antigenicity

The Asiatic coral snakes are basal in the phylogeny of coral snakes. Although envenoming by the Asiatic coral snakes is rarely fatal, little is known about their venom properties and variability from the American coral snakes. Integrating reverse-phase high performance liquid chromatography and nano-liquid chromatography-tandem mass spectrometry, we showed that the venom proteome of the Malaysian banded or striped coral snake (Calliophis intestinalis) was composed of mainly phospholipases A₂ (PLA₂, 43.4%) and three-finger toxins (3FTx, 20.1%). Within 3FTx, the cytotoxins or cardiotoxins (CTX) dominated while the neurotoxins' content was much lower. Its subproteomic details contrasted with the 3FTx profile of most Micrurus sp., illustrating a unique dichotomy of venom phenotype between the Old and the New World coral snakes. Calliophis intestinalis venom proteome was correlated with measured enzymatic activities, and in vivo it was myotoxic but non-lethal to mice, frogs and geckos at high doses (5-10 μg/g). The venom contains species-specific toxins with distinct sequences and antigenicity, and the antibodies raised against PLA₂ and CTX of other elapids showed poor binding toward its venom antigens. The unique venom proteome of C. intestinalis unveiled a repertoire of novel toxins, and the toxicity test supported the need for post-bite monitoring of myotoxic complication. SIGNIFICANCE: Malaysian banded or striped coral snake (Calliophis intestinalis) has a cytotoxin (CTX)-predominating venom proteome, a characteristic shared by its congener, the Malayan blue coral snake (Calliophis bivirgata). With little neurotoxins (NTX), it illustrates a CTX/NTX dichotomy of venom phenotype between the Old World and the New World coral snakes. The low toxicity of the venom imply that C. intestinalis bite envenoming can be managed via symptomatic relief of the mild to moderate pain with appropriate analgesia. Systemically, the serum creatine kinase level of patients should be monitored serially for potential complication of myotoxicity. The distinct antigenicity of the venom proteins implies that the empirical use of heterologous antivenom is mostly inappropriate and not recommended.

Lemnitoxin, the major component of Micrurus lemniscatus coral snake venom, is a myotoxic and pro-inflammatory phospholipase A2

The venom of Micrurus lemniscatus, a coral snake of wide geographical distribution in South America, was fractionated by reverse-phase HPLC and the fractions screened for phospholipase A2 (PLA2) activity. The major component of the venom, a PLA2, here referred to as 'Lemnitoxin', was isolated and characterized biochemically and toxicologically. It induces myotoxicity upon intramuscular or intravenous injection into mice. The amino acid residues Arg15, Ala100, Asn108, and a hydrophobic residue at position 109, which are characteristic of myotoxic class I phospholipases A2, are present in Lemnitoxin. This PLA2 is antigenically related to M. nigrocinctus nigroxin, Notechis scutatus notexin, Pseudechis australis mulgotoxin, and Pseudonaja textilis textilotoxin, as demonstrated with monoclonal and polyclonal antibodies. Lemnitoxin is highly selective in its targeting of cells, being cytotoxic for differentiated myotubes in vitro and muscle fibers in vivo, but not for undifferentiated myoblasts or endothelial cells. Lemnitoxin is not lethal after intravenous injection at doses up to 2μg/g in mice, evidencing its lack of significant neurotoxicity. Lemnitoxin displays anticoagulant effect on human plasma and proinflammatory activity also, as it induces paw edema and mast cell degranulation. Thus, the results of this work demonstrate that Lemnitoxin is a potent myotoxic and proinflammatory class I PLA2.

Danger in the reef: Proteome, toxicity, and neutralization of the venom of the olive sea snake, Aipysurus laevis

Four specimens of the olive sea snake, Aipysurus laevis, were collected off the coast of Western Australia, and the venom proteome was characterized and quantitatively estimated by RP-HPLC, SDS-PAGE, and MALDI-TOF-TOF analyses. A. laevis venom is remarkably simple and consists of phospholipases A2 (71.2%), three-finger toxins (3FTx; 25.3%), cysteine-rich secretory proteins (CRISP; 2.5%), and traces of a complement control module protein (CCM; 0.2%). Using a Toxicity Score, the most lethal components were determined to be short neurotoxins. Whole venom had an intravenous LD50 of 0.07 mg/kg in mice and showed a high phospholipase A2 activity, but no proteinase activity in vitro. Preclinical assessment of neutralization and ELISA immunoprofiling showed that BioCSL Sea Snake Antivenom was effective in cross-neutralizing A. laevis venom with an ED50 of 821 μg venom per mL antivenom, with a binding preference towards short neurotoxins, due to the high degree of conservation between short neurotoxins from A. laevis and Enhydrina schistosa venom. Our results point towards the possibility of developing recombinant antibodies or synthetic inhibitors against A. laevis venom due to its simplicity.

Venomics of the beaked sea snake, Hydrophis schistosus: A minimalist toxin arsenal and its cross-neutralization by heterologous antivenoms

The venom proteome of Hydrophis schistosus (syn: Enhydrina schistosa) captured in Malaysian waters was investigated using reverse-phase HPLC, SDS-PAGE and high-resolution liquid chromatography-tandem mass spectrometry. The findings revealed a minimalist profile with only 18 venom proteins. These proteins belong to 5 toxin families: three-finger toxin (3FTx), phospholipase A2 (PLA2), cysteine-rich secretory protein (CRISP), snake venom metalloprotease (SVMP) and L-amino acid oxidase (LAAO). The 3FTxs (3 short neurotoxins and 4 long neurotoxins) constitute 70.5% of total venom protein, 55.8% being short neurotoxins and 14.7% long neurotoxins. The PLA2 family consists of four basic (21.4%) and three acidic (6.1%) isoforms. The minor proteins include one CRISP (1.3%), two SVMPs (0.5%) and one LAAO (0.2%). This is the first report of the presence of long neurotoxins, CRISP and LAAO in H. schistosus venom. The neurotoxins and the basic PLA2 are highly lethal in mice with an intravenous median lethal dose of <0.2 μg/g. Cross-neutralization by heterologous elapid antivenoms (Naja kaouthia monovalent antivenom and Neuro polyvalent antivenom) was moderate against the long neurotoxin and basic PLA2, but weak against the short neurotoxin, indicating that the latter is the limiting factor to be overcome for improving the antivenom cross-neutralization efficacy.

Phospholipase A2-dependent effects of the venom from the new guinean small-eyed snakeMicropechis ikaheka

The New Guinean small-eyed snake (Micropechis ikaheka) is a cause of life-threatening envenoming. Previous studies on M. ikaheka venom have indicated the presence of neurotoxins as well as myotoxins. This study examined the in vitro myotoxic effects of M. ikaheka venom and the efficacy of a polyvalent antivenom in neutralizing these effects. Venom (50 microg/ml) produced a slowly developing contracture and inhibition of direct twitches of the chick biventer cervicis nerve-muscle preparation in the presence of tubocurarine (10 microM). Myotoxicity was confirmed by subsequent histological examination of tissues. This myotoxicity was prevented by the prior addition of polyvalent snake antivenom (30 U/ml). However, the addition of antivenom (30 U/ml) 1 h after venom administration failed to reverse or prevent the further inhibition of direct twitches. In addition, venom (1-10 microg/ml) produced concentration-dependent contractions of the guinea-pig isolated ileum. These effects were dependent on phospholipase A2 (PLA2) activity of the venom as evidenced by the ability of the PLA2 inhibitor 4-bromophenacyl bromide (4-BPB; 1.8 mM) to prevent this activity. This study indicates that M. ikaheka venom causes significant myotoxicity and that polyvalent snake antivenom may be a potential treatment for the myotoxic effects in patients envenomed by this species.

Most cited papers in Toxicon

Citation of a published work is one of the parameters considered in the analysis of relevance and importance of scientific contributions. In 2002, for the first time the Impact Factor of Toxicon has risen above 2.0, placing it at the 17th position among 76 journals in the 'toxicology' field. The aim of this article was to identify the most cited articles in Toxicon, that have contributed to the steady increase of its Impact Factor. The number of citations, complete reference and type of all documents appearing in Toxicon in the period 1963-2003 were retrieved from the ISI Web-of-Science homepage. The documents retrieved were sorted by the number of citations received. A 'citation index', defined as the number of citations divided by the number of years since publication, was calculated for each document. It was clearly seen that reviews in Toxicon received 4.4-fold more citations than articles. Unexpectedly, it was found that recent papers were proportionally more cited than old ones. A decrease in the proportion of papers dealing on 'snake*' through out the period and the broadened range of subjects of the most cited papers recently published in Toxicon reflects an increased 'visibility' in other fields of toxinology. Research on plant toxins gained its own space in Toxicon with newer publications showing high citation indexes. It can be postulated that these facts helped to increase Toxicon's Impact Factor from 1.248 in 1999 to 2.003 in 2002. With the increased number of issues in Toxicon as well as publications of subject-dedicated volumes containing mostly reviews, the Impact Factor of Toxicon is expected to keep rising in the near future.

Skeletal muscle degeneration induced by venom phospholipases A2: insights into the mechanisms of local and systemic myotoxicity

Local and systemic skeletal muscle degeneration is a common consequence of envenomations due to snakebites and mass bee attacks. Phospholipases A2 (PLA2) are important myotoxic components in these venoms, inducing a similar pattern of degenerative events in muscle cells. Myotoxic PLA2s bind to acceptors in the plasma membrane, which might be lipids or proteins and which may differ in their affinity for the PLA2s. Upon binding, myotoxic PLA2s disrupt the integrity of the plasma membrane by catalytically dependent or independent mechanisms, provoking a pronounced Ca2+ influx which, in turn, initiates a complex series of degenerative events associated with hypercontraction, activation of calpains and cytosolic Ca(2+)-dependent PLA2s, and mitochondrial Ca2+ overload. Cell culture models of cytotoxicity indicate that some myotoxic PLA2s affect differentiated myotubes in a rather selective fashion, whereas others display a broad cytolytic effect. A model is presented to explain the difference between PLA2s that induce predominantly local myonecrosis and those inducing both local and systemic myotoxicity. The former bind not only to muscle cells, but also to other cell types, thereby precluding a systemic distribution of these PLA2s and their action on distant muscles. In contrast, PLA2s that bind muscle cells in a more selective way are not sequestered by non-specific interactions with other cells and, consequently, are systemically distributed and reach muscle cells in other locations.

What does beta-bungarotoxin do at the neuromuscular junction?

beta-Bungarotoxin from the Taiwan banded krait, Bungarus multicinctus is a basic protein (pI=9.5), with a molecular weight of 21,800 consisting of two different polypeptide subunits. A phospholipase A(2) subunit named the A-chain and a non-phospholipase A(2) subunit named the B-chain, which is homologous to Kunitz protease inhibitors. The A-chain and the B-chain are covalently linked by one disulphide bridge. On mouse hemi-diaphragm nerve-muscle preparations, partially paralysed by lowering the external Ca(2+) concentration, beta-bungarotoxin classically produces triphasic changes in the contraction responses to indirect nerve stimulation. The initial transient inhibition of twitches (phase 1) is followed by a prolonged facilitatory phase (phase 2) and finally a blocking phase (phase 3). These changes in twitch tension are mimicked, to some extent, by similar changes to end plate potential amplitude and miniature end plate potential frequency. The first and second phases are phospholipase-independent and are thought to be due to the B-chain (a dendrotoxin mimetic) binding to or near to voltage-dependent potassium channels. The last phase (phase 3) is phospholipase dependent and is probably due to phospholipase A(2)-mediated destruction of membrane phospholipids in motor nerve terminals.

Sea snake Hydrophis cyanocinctus venom. II. Histopathological changes, induced by a myotoxic phospholipase A2 (PLA2-H1)

A toxic phospholipase A2 (PLA2-H1), isolated from the venom of the sea snake Hydrophis cyanocinctus, was tested for its ability to induce myonecrosis and histopathological changes in albino rats and mice. Induction of myonecrosis was demonstrated by their ability to release creatine kinase (CK) from damaged muscle fibers and direct histopathological examination of the injected muscles (i.m.). PLA2-H1 exhibits intense myonecrosis characterized by the changes including, necrosis and edematous appearance with cellular infiltrate, vacuolation and degenerated muscle cells with delta lesions and heavy edema in between the cells. No myoglobinuria was noted in any group of animals. The purified PLA2-H1 was also administered intraperitoneally into the experimental animals and tissue samples were taken at several time intervals. Light microscopic examination of the kidney sections revealed severe damage, evident by focal tubular necrosis, complete disquamation of epithelial lining and epithelial degeneration of tubules in all test animals. Light micrographs of liver sections after 24 h of injection shows fatty infiltration in parenchyma and squashed hepatocytes, while after 48 h, fatty vacuolation of parenchyma in a generalized pattern was observed. Furthermore, sections of the lungs of the same group of animals (48 h) show dilated bronchia and marked infiltration of inflammatory cells within alveoli. Our results suggest that the purified PLA2-H1 induced moderate myotoxicity in muscles and mild histopathological changes in other vital organs without myoglobinuria.

Myoglobinuria

Myoglobinuria refers to an abnormal pathologic state in which an excessive amount of myoglobin is found in the urine, imparting a cola-like hue, usually in association with myonecrosis and a clinical picture of weakness, myalgias, and edema. Myoglobinuria is produced by multiple causes: any condition that accelerates the use or interferes with the availability of oxygen or energy substrates to muscle cells can result in myoglobinuria, as can events that produce direct muscle injury, either mechanical or chemical. Acute renal failure is the most serious complication, which can be prevented by prompt, aggressive treatment. In patients surviving acute attacks, recovery of muscle and renal function is usually complete.

Histopathological studies of the acute inflammation in synovial tissue of rat knee joint following intra-articular injection of PLA2 from Chinese Cobra (Naja naja atra) venom

A phospholipase A2 was purified from Chinese Cobra Naja naja atra by a two-step procedure: gel filtration on Superdex 75 and reverse-phase high-performance liquid chromatography (HPLC) on a NUCLEOSIL 5 C18 column. Purified phospholipase A2 was homogeneous, as indicated by capillary electrophoresis and electrospray mass spectrometry. It was a basic protein (pI = 8.2 +/- 0.03) with a molecular mass of 13,258 Da. Amino acid sequence analysis of the N-terminal demonstrated a high degree of homology with other related PLA2 from elapid venoms. The histopathological effects of the purified PLA2 on synovial tissue of knee joint were studied in Wistar rats. Rats were injected intra-articularly with 100 microl solution of PLA2 of different concentrations. Synovial tissue samples with patella were taken for light microscope study. Histopathological evaluation revealed a significant induction of acute inflammation in synovial tissue after injection, as indicated by synovial lining-cell hyperplasia, subsynovial cellular infiltration, and peri-articular soft-tissue cellular infiltration. Marked inflammatory and proliferative changes in synovial tissue were evident after repeated intra-articular injections of 100 microg PLA2. This study failed to show any significant histological changes in cartilage of patella as well as in the surrounding muscle tissue of the knee joints. These results suggest that PLA2 purified from Chinese Cobra venom induce time- and dose-dependent inflammatory changes in the synovial tissue of rat knee joint.

Hugh Alistair Reid OBE MD: investigation and treatment of snake bite

Alistair Reid was an outstanding clinician, epidemiologist and scientist. At the Penang General Hospital, Malaya, his careful observation of sea snake poisoning revealed that sea snake venoms were myotoxic in man leading to generalized rhabdomyolysis, and were not neurotoxic as observed in animals. In 1961, Reid founded and became the first Honorary Director of the Penang Institute of Snake and Venom Research. Effective treatment of sea snake poisoning required specific antivenom which was produced at the Commonwealth Serum Laboratories in Melbourne from Enhydrina schistosa venom supplied by the Institute. From the low frequency of envenoming following bites, Reid concluded that snakes on the defensive when biting man seldom injected much venom. He provided clinical guidelines to assess the degree of envenoming, and the correct dose of specific antivenom to be used in the treatment of snake bite in Malaya. Reid demonstrated that the non-clotting blood of patients bitten by the pit viper, Calloselasma rhodostoma [Ancistrodon rhodostoma] was due to venom-induced defibrination. From his clinical experience of these patients, Reid suggested that a defibrinating derivative of C. rhodostoma venom might have a useful role in the treatment of deep vein thrombosis. This led to Arvin (ancrod) being used clinically from 1968. After leaving Malaya in 1964, Alistair Reid joined the staff of the Liverpool School of Tropical Medicine, as Senior Lecturer. Enzyme-linked immunosorbent assay (ELISA) for detecting and quantifying snake venom and venom-antibody was developed at the Liverpool Venom Research Unit: this proved useful in the diagnosis of snake bite, in epidemiological studies of envenoming patterns, and in screening of antivenom potency. In 1977, Dr H. Alistair Reid became Head of the WHO Collaborative Centre for the Control of Antivenoms based at Liverpool.

Myoglobinuria, malignant hyperthermia, neuroleptic malignant syndrome and serotonin syndrome

This article presents an overview of the causes and manifestations of myoglobinuria and provides criteria for its diagnosis and management. The article also reviews neuroleptic malignant syndrome, malignant hyperthermia, and serotonin syndrome, all of which could cause rhabdomyolysis and myoglobinuria.

Pathological changes induced by an acidic phospholipase A2 from Ophiophagus hannah venom on heart and skeletal muscle of mice after systemic injection

An acidic phospholipase A2 (OHV A-PLA2) isolated from the venom of the king cobra (Ophiophagus hannah) was tested for its ability to cause pathological changes to myocardium, skeletal muscle and cardiac ganglia. White mice were injected intravenously with dose of 8 mg/kg or 4 mg/kg of OHV A-PLA2 and tissue samples were taken at 6 or 24 hr. Light microscopic examination failed to show significant changes in cardiac muscle and ganglia. Skeletal muscle showed myofibre degeneration and necrosis. Electron microscopic study revealed myodegeneration in cardiac and skeletal muscles, and reduction in synaptic vesicle population of preganglionic nerve terminals in cardiac ganglia. Ultrastructural changes in tissues were dose related. The lower dose (4 mg/kg) of OHV A-PLA2 produced mild myocardial changes, the myofilaments were intact but contracted, and the A band and I band were skewed. OHV A-PLA2 caused myocardial degeneration at a higher dose of 8 mg/kg. The changes included dissolution of actin and myosin filaments, dilatation and disorganization of sarcoplasmic reticulum and degeneration of mitochondria. The skeletal muscle lesions were more severe than the myocardial changes. Some of the myofibrils were severely disorganized and lack typical striated appearance, sarcomeres disrupted, most of mitochondria were vesiculated and destroyed.

An investigation into the antigenic cross-reactivity of Ophiophagus hannah (king cobra) venom neurotoxin, phospholipase A2, hemorrhagin and L-amino acid oxidase using enzyme-linked immunosorbent assay

The antigenic cross-reactivity of four Ophiophagus hannah (king cobra) venom components, the neurotoxin (OH-NTX), phospholipase A2 (OH-PLA2), hemorrhagin (OH-HMG) and L-amino acid oxidase (OH-LAAO) were examined by indirect and double sandwich ELISAs. The indirect ELISAs for OH-NTX, OH-PLA2 and OH-HMG were very specific when assayed against the various heterologous snake venoms and O. hannah venom components, at 25 ng/ml antigen level. At higher antigen concentrations (100-400 ng/ml), there were moderate to strong indirect ELISA cross-reactions between anti-O. hannah neurotoxin and venoms from various species of cobra as well as two short neurotoxins. However, anti-O. hannah hemorrhagin did not cross-react with any of the venoms tested, even at these high antigen concentrations, indicating that O. hannah hemorrhagin is antigenically very different from other venom hemorrhagins. Examination of the indirect ELISA cross-reactions between anti-O. hannah PLA2 and several elapid PLA2 enzymes suggests that the elapid PLA2 antigenic class has more than two subgroups. The antibodies to O. hannah L-amino acid oxidase, however, yielded indirect ELISA cross-reactions with many venoms as well as with OH-NTX, OH-PLA2 and OH-HMG, indicating that OH-LAAO shares common epitopes even with unrelated proteins. The double sandwich ELISAs for the four anti-O. hannah venom components, on the other hand, generally exhibited a higher degree of selectivity than the indirect ELISA procedure.

Notexin-induced muscle injury in the dog

Notexin, a myotoxic phospholipase, was used to induce focal necrosis in the sartorius muscles of normal mixed-breed adult dogs and in 12-week-old beagles. Notexin injury caused pathologic changes similar to those of Duchenne muscular dystrophy (DMD) and its canine homologue, golden retriever muscular dystrophy (GRMD). All three conditions are characterized by increased serum creatine kinase (CK) levels, sarcolemmal defects, delta lesions, hyaline degeneration of myofibers, calcium-positive myofibers, and minimal effects on neurovascular structures. Four and 24 h after exposure to notexin, serum CK levels were elevated, and many myofibers were necrotic. In addition, by 24 h the necrotic areas were heavily invaded by mononuclear cells, and calcium-positive myofibers were prominent. Capillaries appeared intact even in areas of marked myonecrosis. Massive cellular infiltrate and myotube formation was evident at 3 days post injury. By 7 days, most affected fascicles were occupied by small immature myofibers. Regeneration was largely complete at 21 days. Our results suggest that notexin-induced muscle injury in dogs will be useful in the evaluation of potential therapies for DMD such as myoblast transplantation.

Comparative characterization of two toxic phospholipases A2 from Indian cobra (Naja naja naja) venom

Indian cobra venom contains many phospholipase A2 (PLA2) toxins. In the present study two toxic PLA2s have been purified from the Indian cobra (Naja naja naja) venom by column chromatography. The NN-XIa-and NN-XIb-PLA2s have mol. wts between 10,700 and 15,000. The NN-XIa-PLA2 induces myotoxic effects, oedema and neurotoxicity in mice and has an i.p. LD50 of 8.5 mg/kg body weight. The NN-XIa-PLA2 is also cytotoxic to Ehrlich ascites tumour cells. The other PLA2, NN-XIb, in contrast has an i.p. LD50 of 0.22 mg/kg body weight, and it induces acute neurotoxicity. The NN-XIb-PLA2 is devoid of the other biological activities which are exhibited by NN-XIa-PLA2.

Pathologic changes induced by phospholipase A2 isolated from the venom of Collett's snake, Pseudechis colletti: a light and electron microscopic study

Pseudechis colletti is an Australian elapid snake with a range limited to central Queensland, Australia. The venom of this snake, as well as that of several other Australian elapids, has been shown to contain a phospholipase A2 (PLA2) which can cause a marked myoglobinuria in mice. Few studies have described the histopathologic and ultrastructural changes that result from myotoxic PLA2-induced damage. Our investigation demonstrated that the isolated PLA2 induced myodegeneration and necrosis in myocardium in a dose-related manner, with subsequent myoglobinuria and myoglobinuric nephropathy.

A comparative study of the biological properties of some sea snake venoms

1. The protease, phosphodiesterase, alkaline phosphomonoesterase, L-amino acid oxidase, acetylcholinesterase, phospholipase A, 5'-nucleotidase, hyaluronidase, arginine ester hydrolase, procoagulant, anticoagulant and hemorrhagic activities of ten samples of venoms from seven taxa of sea snakes were examined. 2. The results show that venoms of sea snakes of both subfamilies of Hydrophiinae and Laticaudinae are characterized by a very low level of enzymatic activities, except phospholipase A activity and, for some species, hyaluronidase activity. 3. Because of the low levels of enzymatic activities and the total lack of procoagulant and hemorrhagic activities, venom biological properties are not useful for the differentiation of species of sea snakes. Nevertheless, the unusually low levels of enzymatic activities of sea snake venoms may be used to distinguish sea snake venoms from other elapid or viperid venoms.

Myotoxic components of snake venoms: their biochemical and biological activities

Necrosis of skeletal muscle is produced by two types of snake venom components: single chain peptides consisting of 42-44 amino acid residues and phospholipases A2 representing either single chain proteins or existing as complexes of several enzyme subunits or combined with other nonenzymatic proteins. Vacuolation, lysis and necrosis of skeletal muscle cells are the major pathological effects of these myotoxins. Although the exact mode of action of these toxins is not clear, interactions with the plasma membrane leading to permeability changes for ions and to their complete destruction is evident. The high specificities of some venom phospholipases A2 for skeletal muscle cells suggest a specific binding to certain membrane receptors; however, an enzymatic action on membranes may also be involved.

Muscle necrosis caused by snake venoms and toxins

Snake bite is often associated with localised soft tissue necrosis. Less frequently victims may suffer extensive muscle damage leading to rhabdomyolysis and the loss of muscle-specific protein. This review describes the organisation and structure of mammalian skeletal muscle, and its response to myotoxic venoms and to isolated pure myotoxic venom fractions. The clinical reports of muscle damage in man following snake bite are discussed, and the various classes of myotoxic toxins are introduced. Muscle damage caused by the toxins is next described, particular emphasis being placed on the correlation between muscle pathology seen at the light level and the morphological changes seen at the level of the electron microscope. Where known, those subcellular components of the muscle fibre that are especially sensitive to assault, and those components that appear to be spared, are identified. The relevance of the selective sparing of some components to the regenerative capacity of the skeletal muscle is considered.

Binding of crotoxin, a presynaptic phospholipase A2 neurotoxin, to negatively charged phospholipid vesicles

Crotoxin, isolated from the venom of Crotalus durissus terrificus, is a potent neurotoxin consisting of a basic and weakly toxic phospholipase A2 subunit (component B) and an acidic nonenzymatic subunit (component A). The nontoxic component A enhances the toxicity of the phospholipase subunit by preventing its nonspecific adsorption. The binding of crotoxin and of its subunits to small unilamellar phospholipid vesicles was examined under experimental conditions that prevented any phospholipid hydrolysis. Isolated component B rapidly bound with a low affinity (Kapp in the millimolar range) to zwitterionic phospholipid vesicles and with a high affinity (Kapp of less than 1 microM) to negatively charged phospholipid vesicles. On the other hand, the crotoxin complex did not interact with zwitterionic phospholipid vesicles but dissociated in the presence of negatively charged phospholipid vesicles; the noncatalytic component A was released into solution, whereas component B remained tightly bound to lipid vesicles, with apparent affinity constants from 100 to less than 1 microM, according to the chemical composition of the phospholipids. On binding, crotoxin or its component B caused the leakage of a dye entrapped in vesicles of negatively charged but not of zwitterionic phospholipids. The selective binding of crotoxin suggests that negatively charged phospholipids may constitute a component of the acceptor site of crotoxin on the presynaptic plasma membrane.

Purification and characterization of a myotoxic phospholipase A2 from Indian cobra (Naja naja naja) venom

A major phospholipase A2 (NN-XIII-PLA2) which constitutes 20% of the whole Naja naja naja venom was purified to homogeneity on CM-Sephadex C-25 column chromatography. NN-XIII-PLA2 is a basic protein with a mol. wt of 11,200 by SDS-PAGE. This enzyme has low enzymatic activity but is more toxic to mice than the whole venom. The LD50 value (i.p.) of NN-XIII-PLA2 is 2.4 mg/kg body weight (whole venoms LD50 is 2.8 mg/kg body weight). It induces neurotoxic-like signs in experimental animals. It induces myotoxicity when injected i.m. into the thigh muscle of mice and edema when injected into the foot pads of mice. This enzyme has a fluorescence maxima between 310-316 nm which is typical of tyrosine residues.

Acidimetric assay for phospholipase A using egg yolk suspension as substrate

A convenient acidimetric assay for phospholipase A using egg yolk suspension as substrate has been developed. The substrate mixture consists of 1 part egg yolk, 1 part 8.1 mM sodium deoxycholate, and 1 part 18 mM calcium chloride. Phospholipase A activity is measured by following the initial rate of pH change, which is linear between pH 8.0 and 7.75 and is proportional to enzyme concentration over a wide range. The assay is highly reproducible, with a coefficient of variation of 3%, and as sensitive as most established assays for phospholipase A. The assay uses inexpensive and easily available substrate and is simple to perform. It is particularly useful for monitoring phospholipase A activity in chromatography fractions.

Coral snake venoms: mode of action and pathophysiology of experimental envenomation (1)

Coral snakes, the New World Elapidae, are included in the genera Micniroides and Micrurus. The genus Mlcrurus comprises nearly all coral snake species and those which are responsible for human snake-bite accidents. The following generalizations concerning the effects induced by their venoms, and their venom-properties can be made. Coral snake venoms are neurotoxic, producing loss of muscle strenght and death by respiratory paralysis. Local edema and necrosis are not induced nor blood coagulation or hemorrhages. Proteolysis activity is absent or of very low grade. They display phospholipase A2 activity. Nephrotoxic effects are not evoked. The main toxins from elapid venoms are postsynaptic and presynaptic neurotoxins and cardiotoxins. Phospholipases A2 endowed with myonecrotic or cardiotoxin-like properties are important toxic components from some elapid venoms. The mode of action of Micrurus frontalis, M. lemniscatus, M. corallinus and M. fulvius venoms has been investigated in isolated muscle preparations and is here discussed. It is shown that while M. frontalis and M. lemniscatus venoms must contain only neurotoxins that act at the cholinergic end-plate receptor (postsynaptic neurotoxins), M. corallinus venom also inhibits evoked acetylcholine release by the motor nerve endings (presynaptic neurotoxin-like effect) and M. fulvius induces muscle fiber membrane depolarization (cardiotoxin-like effect). The effects produced by M. corallinus and M. fulvius venoms in vivo in dogs and M. frontalis venom in dogs and monkeys are also reported.

Isolation and characterization of a phospholipase B from venom of Collett's snake, Pseudechis colletti

Phospholipase B in the venom of the Australian elapid snake, Pseudechis colletti, was purified to near homogeneity. By means of gel filtration it had an Mr of about 35,000, and by SDS-polyacrylamide gel electrophoresis an Mr of about 16,500. These presumably are dimeric and monomeric forms of the enzyme. It was isoelectric at pH 6.2 as compared to 7.8 for phospholipase A2 from which it was readily separated. It was relatively thermostable. As determined by release of water-soluble phosphorous, it degraded phosphatidylcholine and phosphatidylethanolamine, but did not degrade other phospholipids tested. The purified enzyme was strongly hemolytic in vitro for rabbit and human erythrocytes, but not for bovine or ovine erythrocytes. Hemolysis of rabbit erythrocytes gave rise to membranes showing ultrastructural changes that may be unique for this enzyme. The protein was highly active in producing turbidity in dilute solutions of egg yolk. It was cytotoxic for cultured rhabdomyosarcoma cells and was lethal for mice in which death was preceded by massive myoglobinuria.

Structure-function relationships of phospholipases. II: Charge density distribution and the myotoxicity of presynaptically neurotoxic phospholipases

The charge density distribution of 24 phospholipases A2 has been examined to identify the involvement of charged amino acid residues in the determination of the pharmacological properties of these proteins. There is no characteristic difference between the presynaptically neurotoxic and non-neurotoxic phospholipases, however, presynaptically neurotoxic phospholipases which are also myotoxic have a distinct charge distribution pattern. There is a characteristic cationic site around residues 79-87. This site has a relatively fixed position with respect to the hydrophobic 'neurotoxic' region, on the NH2 terminal side. This cationic region is located on the outer surface in the three-dimensional structure of phospholipase, just before hydrophobic helix E, and is available for interaction with membranes. Such a characteristic region is absent in non-myotoxic phospholipases which are either presynaptically active or inactive. On the other hand, myotoxins, a group of non-enzymatic proteins inducing myotoxicity, also possess such characteristic regions of cationic and hydrophobic sites.

Pharmacological activities of a toxic phospholipase A isolated from the venom of the snake Bothrops asper

A toxic phospholipase A was isolated from the venom of Bothrops asper. It induced skeletal muscle damage, anticoagulant effects and edema in the foot pad. The toxin had an intravenous LD50 of 95 micrograms/16-18 g mouse body wt and an intraventricular LD50 of 0.42 micrograms/16-18 g mouse body wt. Upon intramuscular and intravenous injections, the toxin induced a prominent increase in serum creatine kinase (CK) levels; only the CK-MM isozyme increased markedly. The toxin induced CK and creatine release from skeletal muscle incubated in vitro. The rate of efflux of creatine was higher than that of CK, although both markers were partially released as early as 15 min after incubation. The toxin also induced elevation of serum levels of lactic dehydrogenase isozymes. However, histological examination of skeletal muscle, kidneys, heart and lungs revealed cell damage only in skeletal muscle. The toxin was not cytotoxic to erythrocytes, lymphocytes or macrophages. In addition, it did not induce a mitogenic response on lymphocytes. In the absence of albumin in the medium, there was no significant difference between myotoxic activities in Ca2+-free and Ca2+-containing bathing solutions. However, when albumin was added, there was a significantly higher myotoxic effect in the presence of Ca2+. Thus, although phospholipolytic activity of the toxin plays a role in muscle damage when albumin is present, the toxin induces muscle damage even when phospholipase A activity is inhibited.

Acetylcholine receptors of human skeletal muscle: a species difference detected by snake neurotoxins

The binding abilities of the nicotinic acetylcholine receptors (AChRs) of the skeletal muscles of man and other vertebrates to two typical curaremimetic toxins, erabutoxin b (Eb) and alpha-bungarotoxin (alpha-BT), were investigated. Fluorescent microscopy using rhodamine-labeled erabutoxin b (TMR-Eb) and FITC-labeled alpha-bungarotoxin (FITC-alpha-BT) revealed that AChRs of human and chimpanzee muscles were stained with FITC-alpha-BT, but not with TMR-Eb. In contrast, the AChRs of mouse muscle were stained with both fluorescent toxins. The stainings of human and chimpanzee AChRs with FITC-alpha-BT were inhibited by preincubation with unmodified alpha-BT, but not with either unmodified Eb or other short-chain neurotoxins. Binding experiments using 125I-labeled Eb ([125I]Eb) and 125I-labeled alpha-BT ([125I]alpha-BT) showed that the affinity of human AChRs for [125I]Eb was unusually low. Electrophysiological experiments showed that both acetylcholine potential and end-plate potential of human muscle were blocked by addition of alpha-BT, but not by Eb. On the contrary, acetylcholine potential of rat muscle was blocked by addition of Eb. All these results indicate that AChRs of human and chimpanzee muscles are different from those of other animals in having an exceptionally low affinity for Eb and other short-chain neurotoxins. The results suggest a heterogeneity among vertebrate AChRs concerning their reactivities to curaremimetic toxins.

Pathogenesis of skeletal muscle necrosis induced by tarantula venom

The pathogenesis of myonecrosis induced by venoms of the Arkansas tarantula (Dugesiella hentzi, Girard) and the Honduran tarantula (Aphonopelma spp.) was studied using light and electron microscopy, scanning electron microscopy and x-ray microprobe analysis, and histochemistry. White mice were injected intraperitoneally with a sublethal dose of tarantula venom. Gross examination 24 hr after injection revealed white areas of apparent calcification in the diaphragm muscle. Light microscopic examination at 15 min revealed hypercontracted muscle cells, and necrotic masses containing areas of condensed myofibrils and clumps of mitochondria. By 12 hr numerous phagocytic cells were present around degenerated muscle cells. Electron microscopic examination revealed a myonecrosis of rapid onset with plasma membrane rupture and contraction bands 15 min after injection. At 3 hr only small patches of plasma membrane remained and mitochondrial changes such as swelling, dense intracristal spaces, partitioning, and flocculent densities were prominent. By 12 and 24 hr very dark spicular densities were present in mitochondria and numerous phagocytic cells were located within the intact basal lamina of necrotic cells. X-ray analysis and histochemistry of 24 hr samples showed that necrotic cells contained very high levels of calcium and phosphate. These two tarantula venoms caused a rapid onset myonecrosis in which the primary injury was rupture of the plasma membrane followed by inability of mitochondria and sarcoplasmic reticulum to maintain normal levels of calcium in the cytoplasm leading to cell death.

Acidic phospholipases A2 from the venom of common sea snake Enhydrina schistosa

Two acidic phospholipases A have been purified from the venom of common sea snake (Enhydrina schistosa) by chromatography on Sephadex G-75 gel media, Bio-Rex 70 ion-exchanger followed by repeated Chromatography on DEAE-Sephadex A-25 ion-exchanger. The two preparations were shown to be homogeneous by polyacrylamide gel electrophoresis and ion-exchange chromatography. The enzymes were shown to be specific for the 'two' position of egg yolk lecithin. The molecular weight of both enzymes determined by gel filtration chromatography and SDS-polyacrylamide gel electrophoresis was approx. 14 000. Both enzymes were non-lethal. Amino acid composition data indicated high contents of aspartic acid, glycine and alanine in both enzymes.

Presynaptic toxicity of the histidine-modified, phospholipase A2-inactive, beta-bungarotoxin, crotoxin and notexin

Beta-Bungarotoxin, crotoxin and notexin were treated extensively with p-bromophenacyl bromide in order to modify the histidine group of the active site and to greatly decrease the phospholipase A2(PLA) catalytic activity. They were studied for their residual presynaptic effects on the mouse isolated phrenic nerve-diaphragm and chick biventer cervicis muscle preparations. The modified toxins still had 1.7-5.2% PLA activity, which was inhibited by Sr2+, as is the enzyme activity of the native toxins. The neuromuscular blocking activity of these modified toxins, which was reduced 30-60 fold in the mouse diaphragm, was due to a presynaptic effect, as judged from the unchanged amplitude of m.e.p.p.s in the blocked preparations. In contrast to the native toxins, however, the presynaptic effect of modified beta-bungarotoxin and notexin was neither antagonized by Sr2+ nor accelerated by increasing the rate of nerve stimulation, indicating that the presynaptic effects of the modified beta-bungarotoxin and notexin are not likely to be due to their PLA enzyme activity. The modified toxins retained a much greater fraction of their early presynaptic effects in comparison to their enzymatic and neuromuscular blocking activities, although the time-course of the early effects was delayed. The results indicate that the modified neurotoxins per se have their own presynaptic effects, which are unrelated to the PLA enzyme activities.

Isolation and amino acid sequence of caudoxin, a presynaptic acting toxic phospholipase A2 from the venom of the horned puff adder (Bitis caudalis)

A presynaptic acting toxic phospholipase A2, designated caudoxin, was purified from the venom of Bitis caudalis by a combination of gel filtration and ion-exchange chromatography. The specificity of the enzyme was shown to be of the A2 type. The enzyme contains 121 amino acid residues in a single chain and is cross-linked by seven disulfide bridges. Application of cyanogen bromide cleavage and digestion with trypsin and chymotrypsin yielded peptides providing the necessary overlaps to complete derivation of the sequence. Structural features of caudoxin in relation to other toxic and non-toxic phospholipases A2 are discussed.

A study of the major Australian snake venoms in the monkey (Macaca fascicularis). II. Myolytic and haematological effects of venoms

Rhesus monkeys were kept in a restraining apparatus and while conscious injected with the venoms of a range of Australian snakes. Although the action of restraining itself caused an elevation of the animals' plasma creatine kinase (C.K.), the rise was up to 5 times greater in envenomed monkeys. The venoms of the Tiger snake, Mulga, Beaked Sea snake, Rough-Scaled, Copperhead and Red-Bellied snakes were all powerfully myolytic, and those of the Taipan and Small-Eyed snake less so. No myolytic activity was found in the venoms of the Common Brown snake and Death Adder, and the results with Dugite, Gwardar and Small-Scaled snake venom were equivocal. Significant coagulation disturbances were produced by all venoms studied except those of the Small-Eyed and Rough-Scaled snakes. When first aid measures were used, the coagulation disturbances which developed after the release of the injected venom were significantly less than when no first aid was used. This finding, which was observed with all snake venoms studied, suggests that the procoagulant factor may be subject to some inactivation whilst immobilized at the injection site.

Inhibition by neurotoxic phospholipases A2 of synaptosomal uptake of gamma-aminobutyric acid

A comparison has been made of the abilities of several neurotoxic and nontoxic phospholipases A2 from snake venoms to inhibit the intake of gamma-aminobutyric acid into synaptosomes from rat cerebral cortex. The neurotoxic phospholipase A2 inhibited GABA uptake more than the nontoxic enzymes did. However, there was a poor correlation between the measured specific enzyme activity of a phospholipase A2 and its ability to inhibit the uptake of GABA.