Species specific sensitivity towards the hemorrhagin of Ophiophagus hannah (Elapidae)

King Cobra and snakebite envenomation: on the natural history, human-snake relationship and medical importance of Ophiophagus hannah

King Cobra (Ophiophagus hannah) has a significant place in many cultures, and is a medically important venomous snake in the world. Envenomation by this snake is highly lethal, manifested mainly by neurotoxicity and local tissue damage. King Cobra may be part of a larger species complex, and is widely distributed across Southeast Asia, southern China, northern and eastern regions as well as the Western Ghats of India, indicating potential geographical variation in venom composition. There is, however, only one species-specific King Cobra antivenom available worldwide that is produced in Thailand, using venom from the snake of Thai origin. Issues relating to the management of King Cobra envenomation (e.g., variation in the composition and toxicity of the venom, limited availability and efficacy of antivenom), and challenges faced in the research of venom (in particular proteomics), are rarely addressed. This article reviews the natural history and sociocultural importance of King Cobra, cases of snakebite envenomation caused by this species, current practice of management (preclinical and clinical), and major toxinological studies of the venom with a focus on venom proteomics, toxicity and neutralization. Unfortunately, epidemiological data of King Cobra bite is scarce, and venom proteomes reported in various studies revealed marked discrepancies in details. Challenges, such as inconsistency in snake venom sampling, varying methodology of proteomic analysis, lack of mechanistic and antivenomic studies, and controversy surrounding antivenom use in treating King Cobra envenomation are herein discussed. Future directions are proposed, including the effort to establish a standard, comprehensive Pan-Asian proteomic database of King Cobra venom, from which the venom variation can be determined. Research should be undertaken to characterize the toxin antigenicity, and to develop an antivenom with improved efficacy and wider geographical utility. The endeavors are aligned with the WHO´s roadmap that aims to reduce the disease burden of snakebite by 50% before 2030.

Venom-gland transcriptome and venom proteome of the Malaysian king cobra (Ophiophagus hannah)

Background

The king cobra (Ophiophagus hannah) is widely distributed throughout many parts of Asia. This study aims to investigate the complexity of Malaysian Ophiophagus hannah (MOh) venom for a better understanding of king cobra venom variation and its envenoming pathophysiology. The venom gland transcriptome was investigated using the Illumina HiSeq™ platform, while the venom proteome was profiled by 1D-SDS-PAGE-nano-ESI-LCMS/MS.

Results

Transcriptomic results reveal high redundancy of toxin transcripts (3357.36 FPKM/transcript) despite small cluster numbers, implying gene duplication and diversification within restricted protein families. Among the 23 toxin families identified, three-finger toxins (3FTxs) and snake-venom metalloproteases (SVMPs) have the most diverse isoforms. These 2 toxin families are also the most abundantly transcribed, followed in descending order by phospholipases A₂ (PLA₂s), cysteine-rich secretory proteins (CRISPs), Kunitz-type inhibitors (KUNs), and L-amino acid oxidases (LAAOs). Seventeen toxin families exhibited low mRNA expression, including hyaluronidase, DPP-IV and 5’-nucleotidase that were not previously reported in the venom-gland transcriptome of a Balinese O. hannah. On the other hand, the MOh proteome includes 3FTxs, the most abundantly expressed proteins in the venom (43 % toxin sbundance). Within this toxin family, there are 6 long-chain, 5 short-chain and 2 non-conventional 3FTx. Neurotoxins comprise the major 3FTxs in the MOh venom, consistent with rapid neuromuscular paralysis reported in systemic envenoming. The presence of toxic enzymes such as LAAOs, SVMPs and PLA₂ would explain tissue inflammation and necrotising destruction in local envenoming. Dissimilarities in the subtypes and sequences between the neurotoxins of MOh and Naja kaouthia (monocled cobra) are in agreement with the poor cross-neutralization activity of N. kaouthia antivenom used against MOh venom. Besides, the presence of cobra venom factor, nerve growth factors, phosphodiesterase, 5’-nucleotidase, and DPP-IV in the venom proteome suggests its probable hypotensive action in subduing prey.

Conclusion

This study reports the diversity and abundance of toxins in the venom of the Malaysian king cobra (MOh). The results correlate with the pathophysiological actions of MOh venom, and dispute the use of Naja cobra antivenoms to treat MOh envenomation. The findings also provide a deeper insight into venom variations due to geography, which is crucial for the development of a useful pan-regional antivenom.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1828-2) contains supplementary material, which is available to authorized users.

Functional proteomic approach to discover geographic variations of king cobra venoms from Southeast Asia and China

This study deciphers the geographic variations of king cobra (Ophiophagus hannah) venom using functional proteomics. Pooled samples of king cobra venom (abbreviated as Ohv) were obtained from Indonesia, Malaysia, Thailand, and two provinces of China, namely Guangxi and Hainan. Using two animal models to test and compare the lethal effects, we found that the Chinese Ohvs were more fatal to mice, while the Southeast Asian Ohvs were more fatal to lizards (Eutropis multifasciata). Various phospholipases A2 (PLA2s), three-finger toxins (3FTxs) and Kunitz-type inhibitors were purified from these Ohvs and compared. Besides the two Chinese Ohv PLA2s with known sequences, eight novel PLA2s were identified from the five Ohv samples and their antiplatelet activities were compared. While two 3FTxs (namely oh-55 and oh-27) were common in all the Ohvs, different sets of 3FTx markers were present in the Chinese and Southeast Asian Ohvs. All the Ohvs contain the Kunitz inhibitor, OH-TCI, while only the Chinese Ohvs contain the inhibitor variant, Oh11-1. Relative to the Chinese Ohvs which contained more phospholipases, the Southeast Asian Ohvs had higher metalloproteinase, acetylcholine esterase, and alkaline phosphatase activities.

BIOLOGICAL SIGNIFICANCE

Remarkable variations in five king cobra geographic samples reveal fast evolution and dynamic translational regulation of the venom which probably adapted to different prey ecology as testified by the lethal tests on mice and lizards. Our results predict possible variations of the king cobra envenoming to human and the importance of using local antivenin for snakebite treatment.

Comparative proteomic analysis of the venom of the taipan snake, Oxyuranus scutellatus, from Papua New Guinea and Australia: role of neurotoxic and procoagulant effects in venom toxicity

The venom proteomes of populations of the highly venomous taipan snake, Oxyuranus scutellatus, from Australia and Papua New Guinea (PNG), were characterized by reverse-phase HPLC fractionation, followed by analysis of chromatographic fractions by SDS-PAGE, N-terminal sequencing, MALDI-TOF mass fingerprinting, and collision-induced dissociation tandem mass spectrometry of tryptic peptides. Proteins belonging to the following seven protein families were identified in the two venoms: phospholipase A(2) (PLA(2)), Kunitz-type inhibitor, metalloproteinase (SVMP), three-finger toxin (3FTx), serine proteinase, cysteine-rich secretory proteins (CRISP), and coagulation factor V-like protein. In addition, C-type lectin/lectin-like protein and venom natriuretic peptide were identified in the venom of specimens from PNG. PLA(2)s comprised more than 65% of the venoms of these two populations. Antivenoms generated against the venoms of these populations showed a pattern of cross-neutralization, corroborating the immunological kinship of these venoms. Toxicity experiments performed in mice suggest that, at low venom doses, neurotoxicity leading to respiratory paralysis represents the predominant mechanism of prey immobilization and death. However, at high doses, such as those injected in natural bites, intravascular thrombosis due to the action of the prothrombin activator may constitute a potent and very rapid mechanism for killing prey.

Antihemorrhagin in the blood serum of king cobra (Ophiophagus hannah): purification and characterization

King cobra (Ophiophagus hannah) serum was found to possess antihemorrhagic activity against king cobra hemorrhagin. The activity was stronger than that in commercial king cobra antivenom. An antihemorrhagin has been purified by ion exchange chromatography, affinity chromatography and gel filtration with a 22-fold purification and an overall yield of 12% of the total antihemorrhagic activity contained in crude serum. The purified antihemorrhagin was homogeneous in disc-PAGE and SDS-PAGE. Its apparent molecular weight determined by SDS-PAGE was 120 kDa. The antihemorrhagin was also active against other hemorrhagic snake venoms obtained in Thailand and Japan such as Calloselasma rhodostoma, Trimeresurus albolabris, Trimeresurus macrops and Trimeresurus flavoviridis (Japanese Habu). It inhibited the proteolytic activity of king cobra venom. It is an acid- and thermolabile protein and does not form precipitin lines against king cobra venom.

Toxins isolated from the venom of the Brazilian coral snake (Micrurus frontalis frontalis) include hemorrhagic type phospholipases A2 and postsynaptic neurotoxins

Toxins isolated from the venom of the Brazilian coral snake (Micrurus frontalis frontalis) include hemorrhagic type phospholipases A2 and postsynaptic neurotoxins. Toxicon 35, 1193-1203, 1997.-Two sets of proteins have been purified from the venom of the Brazilian coral snake, Micrurus frontalis frontalis. One set has mol. wts, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), in the 8000-13,000 range and includes some proteins which are toxic to mice and others which are not. These proteins appear to be isoforms of postsynaptic toxins. The other set shows phospholipase A2 (PLA2) activity and the toxic members of this set promote hemorrhage in mice in a manner closely resembling that produced by PLA2s isolated from the venom of the Australian tiger snake (Notechis scutatus scutatus). These PLA2s migrate on SDS-PAGE with apparent mol. wts in the 18,000-22,000 range which is characteristic of PLA2s that have an alpha-helix D similar to pancreatic PLA2s. Elapid venom PLA2s of the type which typically migrate on SDS-PAGE with mol. wts in the 13,000-16,000 range and do not have alpha-helix D have not been detected in M. f. frontalis venom.

Characterization and cytotoxicity of L-amino acid oxidase from the venom of king cobra (Ophiophagus hannah)

The aim of this project was to determine the cytotoxic components from the venom of king cobra, Ophiophagus hannah. Venom was purified by a combination of gel-filtration, ion-exchange and reversed-phase chromatographic steps. The biochemical properties of the cytotoxic component were consistent with those of L-amino acid oxidase. The molecular weight of the enzyme was estimated to be 150,000 by gel filtration and 70,000 under the denaturing conditions of SDS-PAGE, indicating a dimer. It has an isoelectric point of 4.5 and is a glycoprotein. The N-terminal sequence of L-amino acid oxidase from the king cobra venom was determined to be SVINLEESFQEPEYE. The cytotoxicity of L-amino acid oxidase was observed in stomach cancer, murine melanoma, fibrosarcoma, colorectal cancer and Chinese hamster ovary cell lines. Cytotoxicity resulted in the loss of ability in attachment and inhibition of cell proliferation. The cytotoxic protein decreased the level of cell proliferation by 74% according to [3H]thymidine uptake assay. The mechanism of enzyme action may be related to the inhibition of thymidine incorporation and an interaction with DNA.

Characterization of OhS1, an arginine/lysine amidase from the venom of king cobra (Ophiophagus hannah)

In this paper, we present the results of purification and characterization of an arginine/lysine amidase from the venom of Ophiophagus hannah (OhS1). It was purified by Sephadex G-75 gel filtration and ion-exchange chromatography on DEAE-Sepharose CL-6B. It is a protein of about 43,000, consisting of a single polypeptide chain. It is a minor component in the venom. The purified enzyme was capable of hydrolysing several tripeptidyl-p-nitroanilide substrates having either arginine or lysine as the C-terminal residue. We studied the kinetic parameters of OhS1 on six these chromogenic substrates. OhS1 did not clot fibrinogen. Electrophoresis of fibrinogen degraded with OhS1 revealed the disappearance of the alpha- and beta-chains and the appearance of lower mol. wt fragments. OhS1 had no hemorrhagic activity. It did not hydrolyse casein, nor did it act on blood coagulation factor X, prothrombin and plasminogen. The activity of OhS1 was completely inhibited by NPGB, PMSF, DFP, benzamidine and soybean trypsin inhibitor, suggesting it is a serine protease. Metal chelator (EDTA) had no effect on it.

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.

Proteins isolated from the venom of the common tiger snake (Notechis scutatus scutatus) promote hypotension and hemorrhage

Notechis scutatus scutatus venom contains several toxic acidic proteins called HTa-i which promote hypotension and hemorrhage in mice. They have apparent mol. wts in the 18,000-21,000 range, i.v. LD50 values between 0.5 and 1.5 micrograms/g, and no detectable phospholipase, arginine esterase, proteolytic or hemolytic activities. A polyclonal antibody raised against HTg binds to other purified proteins, suggesting that they are isoforms of the same protein. Many other elapid crude venoms contain proteins which recognize the polyclonal antibody raised against HTg. Crotalid and viperid crude venoms do not recognize this antibody, although some of their component proteins are known to exhibit hypotensive and hemorrhagic activities. A combination of gel-filtration on Sephacryl S-200, cation-exchange and anion-exchange chromatography allows isolation of the N. s. scutatus proteins in high purity. They are the first hypotension-inducing proteins to be purified from an Australian elapid.

Preparation of antibodies to king cobra (Ophiophagus hannah) venom hemorrhagin and investigation of their cross-reactivity

Hannahtoxin, the major hemorrhagin purified from king cobra (Ophiophagus hannah) venom, elicits hemorrhages in rabbits but not in mice. Two antisera against hannahtoxin were prepared: one raised against purified hannahtoxin, while the other was raised against glutaraldehyde cross-linked and detoxified hannahtoxin. The antisera were refined by pepsin digestion and ammonium sulfate precipitation. They are of approximately equal potency in their ability to neutralize the hemorrhagic activity of king cobra venom in rabbits. The antisera did not form a precipitin line with venom of snakes of the Viperidae family nor neutralize hemorrhages elicited in mice by any of these venoms. However, when the hemorrhagic activity was assayed in rabbits, both antisera were able to abolish the hemorrhages elicited by all of the venoms tested. These results suggest that hannahtoxin displays few epitopes in common with hemorrhagins of viperid venoms, except those involved in the neutralization of hemorrhagic activity in rabbits. The epitopes of viperid venom hemorrhagins involved in the neutralization reaction in rabbits are different from those in mice.

Isolation and characterization of a hemorrhagin from the venom of Ophiophagus hannah (king cobra)

The major hemorrhagin (termed hannahtoxin) of the venom of Ophiophagus hannah (king cobra) was purified to electrophoretic homogeneity by DEAE-Sephacel ion exchange chromatography, Sephadex G-200 gel filtration followed by a second DEAE-Sephacel chromatography. Proteolytic activity was associated with the hemorrhagic activity throughout the purification procedures. Hannahtoxin constituted approximately 2% of the crude venom. It had an isoelectric point of 5.3, a carbohydrate content of 12%, a mol. wt of 66,000 as determined by SDS-polyacrylamide gel electrophoresis and 63,000 as determined by gel filtration. It contains 1 mole of Zn per mole of protein. The minimum hemorrhage doses for hannahtoxin are 0.7 microgram and 75 micrograms, respectively, in rabbits and in mice. Hannahtoxin was not lethal to mice at a dose of 2 mg/kg (i.v.) but killed rabbits at doses above 0.18 mg/kg (i.v.). It liberated protein from rabbit glomerular basement membrane but not rat glomerular basement membrane. Treatment of the hemorrhagin with EDTA and 1,10-phenanthroline eliminated both the proteolytic and hemorrhagic activities completely.

Enzymatic and toxic properties of Ophiophagus hannah (king cobra) venom and venom fractions

Some enzymatic activities and toxic properties of four samples of Ophiophagus hannah (king cobra) venom were investigated. There is little intraspecific variation in enzyme contents, protein composition and toxic properties of the venom. The venom does not exhibit hemolytic or edema-inducing activity but is characterized by an exceptionally high alkaline phosphomonoesterase activity. DEAE-Sephacel ion exchange chromatography and Sephadex G-75 gel filtration chromatography of the venom indicate that the major lethal toxins are the low mol.wt, non-enzymatic basic proteins. Venom fractions exhibiting high enzymatic activities apparently do not play an important role in the lethality in mice of Ophiophagus hannah venom.

Proteolytic, hemorrhagic and hemolytic activities of snake venoms

Proteolytic, hemorrhagic and hemolytic activities were tested on 47 different venoms from the Crotalidae, Viperidae, Elapidae, and Hydrophiidae families. Antihemorrhagic activity of crude opossum (Didelphis virginiana) and woodrat (Neotoma micropus) serum was tested against the venoms that presented hemorrhagic activity. All venoms showed proteolytic activity when non-specific substrates such as hide powder and collagen were used. Members of the Crotalidae family had the highest hide powder, chymotrypsin-like and hemorrhagic activity. However, members of the Elapidae family had the highest collagen activity. Hemolytic activity was present in 85% of the snake venoms tested. The crude opossum and woodrat serum neutralized the hemorrhagic activity of all the hemorrhagic venoms. Of particular interest is the poor correlation between the venom activities measured here and the phylogenetic position of the snake that possess them. This is particularly true at the genus and species level. Differences in activities were found among individuals of the same genus. The significance of these differences among venoms of closely related snakes is unknown. They do not seem to be adaptive, however little is known of the physiology and habits of most venomous snakes.

A protease in the venom of king cobra (Ophiophagus hannah): purification, characterization and substrate specificity on oxidized insulin B-chain

A protease in the venom of Ophiophagus hannah (king cobra) has been purified to a homogeneous state by successive chromatographies on Sephadex G-100 superfine, DEAE-cellulose, hydroxyapatite and CM-polyvinylalcohol copolymer columns. The mol.wt as determined by SDS-PAGE and gel filtration was approximately 70,000. The purified enzyme possessed a specific activity approximately 1/25 that of crystalline trypsin, whereas it had no hemorrhagic activity. The substrate specificity was determined using oxidized insulin B-chain as a substrate; the enzyme cleaved the Asn3-Gln4, Gln4-His5, His10-Leu11, Ala14-Leu15 and Tyr16-Leu17 positions. The sites cleaved by the protease were compared to proteases from other snake venoms.

Isolation and characterization of a hemorrhagic factor from the venom of the snake Atractaspis engaddensis (Atractaspididae)

The venom of Atractaspis is unique in its composition and contains both high and low molecular weight fractions. The first peak obtained by gel filtration on Sephadex G-50 (S1) induces hemorrhage in the skin of mice. The hemorrhagic activity is stable over a pH range of 6-9; at pH 5 or 9.5 the activity decreases to half of the original and it is destroyed when incubated at 56 degrees C for 15 min. The hemorrhagic fraction was further purified by ion exchange chromatography on DEAE-Sepharose followed by ammonium sulphate precipitation. The purified factor had a molecular weight of about 50,000 and, in acrylamide disc electrophoresis, showed an acidic band which strongly stained with Coomassie Brilliant Blue and Periodic Acid Schiff. The specific activity of the isolated hemorrhagin was about 12 times higher than that of the crude venom. It has no measurable protease activity on azocoll, casein or gelatin, but the hemorrhagic activity was inactivated by EDTA and was not restored by prolonged incubation with Ca2+ or Zn2+. This activity was also neutralized by sera of venomous and non-venomous snakes. Moreover, antibodies prepared against the venom of Vipera palaestinae neutralized the activity of Atractaspis hemorrhagin and formed one precipitation line in the immunodiffusion test. It is thus evident that Atractaspis, now considered to belong to a separate family, has a hemorrhagic factor which is similar to that of the venoms of the Viperidae.