Pharmacokinetics of Naja sumatrana (equatorial spitting cobra) venom and its major toxins in experimentally envenomed rabbits

Improving in vivo assays in snake venom and antivenom research: A community discussion

On the 26 th January 2023, a free to attend, 'improving in vivo snake venom research: a community discussion' meeting was held virtually. This webinar brought together researchers from around the world to discuss current neutralisation of venom lethality mouse assays that are used globally to assess the efficacy of therapies for snakebite envenoming. The assay's strengths and weaknesses were highlighted, and we discussed what improvements could be made to refine and reduce animal testing, whilst supporting preclinical antivenom and drug discovery for snakebite envenoming. This report summarises the issues highlighted, the discussions held, with additional commentary on key perspectives provided by the authors.

Global parameter optimisation and sensitivity analysis of antivenom pharmacokinetics and pharmacodynamics

In recent years it has become possible to design snakebite antivenoms with diverse pharmacokinetic properties. Owing to the pharmacokinetic variability of venoms, the choice of antivenom scaffold may influence a treatment's neutralisation coverage. Computation offers a useful medium through which to assess the pharmacokinetics and pharmacodynamics of envenomation-treatment systems, as antivenoms with identical neutralising capacities can be simulated. In this study, we simulate envenomation and treatment with a variety of antivenoms, to define the properties of effective antivenoms. Systemic envenomation and treatment were described using a two-compartment pharmacokinetic model. Treatment of Naja sumatrana and Cryptelytrops purpureomaculatus envenomation was simulated with a set of 200,000 theoretical antivenoms across 10 treatment time delays. These two venoms are well-characterised and have differing pharmacokinetic properties. The theoretical antivenom set varied across molecular weight, dose, kon, koff, and valency. The best and worst treatments were identified using an area under the curve metric, and a global sensitivity analysis was performed to quantify the influence of the input parameters on treatment outcome. The simulations show that scaffolds of diverse molecular formats can be effective. Molecular weight and valency have a negligible direct impact on treatment outcome, however low molecular weight scaffolds offer more flexibility across the other design parameters, particularly when treatment is delayed. The simulations show kon to primarily mediate treatment efficacy, with rates above 105 M-1s-1 required for the most effective treatments. koff has the greatest impact on the performance of less effective scaffolds. While the same scaffold preferences for improved treatment are seen for both model snakes, the parameter bounds for C. purpureomaculatus envenomation are more constrained. This paper establishes a computational framework for the optimisation of antivenom design.

Singapore's herpetofauna: updated and annotated checklist, history, conservation, and distribution

Given Singapore's location at the confluence of important maritime trading routes, and that it was established as a British East India Company trading post in 1819, it is unsurprising that Singapore has become one of the centres of natural history collecting and research in Southeast Asia. Despite its small size, Singapore is home to a diverse herpetofauna assemblage and boasts a rich herpetological history. The first systematic studies of Singapore's herpetofauna (within the Linnaean binomial framework) date back to Stamford Raffles and the naturalists hired by him who first came to the island in 1819. Specimens that were collected during and after this time were deposited in museums worldwide. Over time, 39 species from Singapore were described as new to science. Due to the entrepôt nature of Singapore with its associated purchasing and trading of specimens (both alive and dead), poor record-keeping, and human introductions, numerous extraneous species from outside of Singapore were reported to occur on the island. Such issues have left a complicated legacy of ambiguous records and taxonomic complications concerning the identity of Singapore's species-rich herpetofauna, many of which were only resolved in the past 30-40 years. By compiling a comprehensive collection of records and publications relating to the herpetofauna of Singapore, we construct an updated and more accurate listing of the herpetofauna of Singapore. Our investigation culminated in the evaluation of 309 species, in which we compiled a final species checklist recognising 166 species (149 native and 17 non-native established species). Among the 149 native species are two caecilians, 24 frogs, one crocodilian, 13 turtles (three visitors), 34 lizards, and 75 snakes. Of the 17 non-native species are five frogs, four turtles, six lizards, and two snakes. The remaining 143 species represent species to be excluded from Singapore's herpetofauna species checklist. For each of the 309 species examined, we provide species accounts and explanatory annotations. Furthermore, we discuss Singapore's herpetofauna from a historical and conservation perspective. Immediate deforestation and nationwide urbanisation following colonisation completely eliminated many species from throughout much of the country and restricted them to small, degraded forest patches. We hope this publication highlights the importance of publishing observations and serves as a valuable resource to future researchers, naturalists, biological consultants, and policy makers in initiating studies on species ecology, distribution, status, and promoting conservation efforts to safeguard Singapore's herpetofauna.

Ensemble-based molecular docking and spectrofluorometric analysis of interaction between cytotoxin and tumor necrosis factor receptor 1

Cytotoxin (CTX) is a three-finger toxin presents predominantly in cobra venom. The functional site of the toxin is located at its three hydrophobic loop tips. Its actual mechanism of cytotoxicity remains inconclusive as few conflicting hypotheses have been proposed in addition to direct cytolytic effects. The present work investigated the interaction between CTX and death receptor families via ensemble-based molecular docking and fluorescence titration analysis. Multiple sequence alignments of different CTX isoforms obtained a conserved CTX sequence. The three-dimensional structure of the conserved CTX was later determined using homology modelling, and its quality was validated. Ensemble-based molecular docking of CTX was performed with different death receptors, such as Fas-ligand and tumor necrosis factor receptor families. Our results showed that tumor necrosis factor receptor 1 (TNFR1) was the best receptor interacting with CTX attributed to the interaction of all three functional loops and evinced with low HADDOCK, Z-score and RMSD value. The interaction between CTX and TNFR1 was also supported by a concentration-dependent reduction of fluorescence intensity with increasing binding affinity. The possible intermolecular interactions between CTX and TNFR1 were Van der Waals forces and hydrogen bonding. Our findings suggest a possibility that CTX triggers apoptosis cell death through non-covalent interactions with TNFR1.Communicated by Ramaswamy H. Sarma.

Effect of Several Naja atra Antivenom Injection Methods on the Rabbit Model of Naja naja atra Bite Poisoning

Snakebite is a global public health concern, which often occurs in tropical and subtropical underdeveloped areas, but it is often neglected. In the southern China, Naja naja atra (Chinese cobra) is a common venomous snake that causes swelling and necrosis of local tissues, even amputation and death. Currently, the main therapy is the administration of Naja atra antivenom, which greatly reduces mortality. However, the antivenom is not particularly effective in the improvement of local tissue necrosis. Clinically, antivenom is mainly administered intravenously. We speculated that the method of injection influences the efficacy of antivenom. In this study, the rabbit model was used to explore the effects of different antivenom injection methods on systemic and local poisoning symptoms. If topical injection of antivenom contributes to ameliorate tissue necrosis, then we need to reconsider the use of Naja atra antivenom.

In Vitro neurotoxicity and myotoxicity of Malaysian Naja sumatrana and Naja kaouthia venoms: Neutralization by monovalent and Neuro Polyvalent Antivenoms from Thailand

Naja sumatrana and Naja kaouthia are medically important elapids species found in Southeast Asia. Snake bite envenoming caused by these species may lead to morbidity or mortality if not treated with the appropriate antivenom. In this study, the in vitro neurotoxic and myotoxic effects N. sumatrana and N. kaouthia venoms from Malaysian specimens were assessed and compared. In addition, the neutralizing capability of Cobra Antivenom (CAV), King Cobra Antivenom (KCAV) and Neuro Polyvalent Antivenom (NPAV) from Thailand were compared. Both venoms produced concentration-dependent neurotoxic and myotoxic effects in the chick biventer cervicis nerve-muscle preparation. Based on the time to cause 90% inhibition of twitches (i.e. t₉₀) N. kaouthia venom displayed more potent neurotoxic and myotoxic effects than N. sumatrana venom. All three of the antivenoms significantly attenuated venom-induced twitch reduction of indirectly stimulated tissues when added prior to venom. When added after N. sumatrana venom, at the t₉₀ time point, CAV and NPAV partially restored the twitch height but has no significant effect on the reduction in twitch height caused by N. kaouthia venom. The addition of KCAV, at the t₉₀ time point, did not reverse the attenuation of indirectly stimulated twitches caused by either venom. In addition, none of the antivenoms, when added prior to venom, prevented attenuation of directly stimulated twitches. Differences in the capability of antivenoms, especially NPAV and CAV, to reverse neurotoxicity and myotoxicity indicate that there is a need to isolate and characterize neurotoxins and myotoxins from Malaysian N. kaouthia and N. sumatrana venoms to improve neutralization capability of the antivenoms.

An immunodetection assay developed using cobra cytotoxin-specific antibodies: Potential diagnostics for cobra envenoming

Cobra (Naja spp.) envenoming is a life-threatening medical emergency, and a correct diagnosis is crucial to initiating timely and appropriate antivenom treatment. However, snakebite diagnostics remain unavailable in Southeast Asia. This study, therefore, developed an immunodetection assay with a potential diagnostic application for cobra envenoming. The cytotoxin of Naja kaouthia (Thai Monocled Cobra) (Nk-CTX) was purified from its venom to produce CTX-specific antibodies in rabbits and chickens. A double-antibody sandwich enzyme-linked immunosorbent assay was developed using the purified anti-Nk-CTX antibodies (immunoglobulin G and immunoglobulin Y), and its selectivity, specificity, and sensitivity for the venoms of five major cobra species in Southeast Asia (N. kaouthia, Naja sumatrana, Naja sputatrix, and Naja siamensis, Naja philippinensis) were studied. The results showed the immunoassay discriminates cobra venoms from other species commonly implicated in snakebites in Southeast Asia, i.e., the Malayan Krait, Many-banded Krait, King Cobra, Eastern Russell's Viper, Malayan Pit Viper and White-lipped Pit Viper. The immunoassay has a high sensitivity for the five cobra venoms, with detection limits (LoD) ranging from 0.6 to 2.6 ng/ml. Together, the findings suggest the potential diagnostic application of the cytotoxin immunoassay for cobra envenoming. The immunoassay was found to exhibit high immunoreactivity toward ten Asiatic cobra venoms (absorbance>1.5), in contrast to African cobra venoms with low immunoreactivity (absorbance<0.9). Considering the varying CTX antigenicity between Asiatic and African cobras, the immunoassay for African cobras should utilize antibodies produced specifically from the cytotoxins of African cobra venoms.

Physiological constraints dictate toxin spatial heterogeneity in snake venom glands

Background

Venoms are ecological innovations that have evolved numerous times, on each occasion accompanied by the co-evolution of specialised morphological and behavioural characters for venom production and delivery. The close evolutionary interdependence between these characters is exemplified by animals that control the composition of their secreted venom. This ability depends in part on the production of different toxins in different locations of the venom gland, which was recently documented in venomous snakes. Here, we test the hypothesis that the distinct spatial distributions of toxins in snake venom glands are an adaptation that enables the secretion of venoms with distinct ecological functions.

Results

We show that the main defensive and predatory peptide toxins are produced in distinct regions of the venom glands of the black-necked spitting cobra (Naja nigricollis), but these distributions likely reflect developmental effects. Indeed, we detected no significant differences in venom collected via defensive ‘spitting’ or predatory ‘biting’ events from the same specimens representing multiple lineages of spitting cobra. We also found the same spatial distribution of toxins in a non-spitting cobra and show that heterogeneous toxin distribution is a feature shared with a viper with primarily predatory venom.

Conclusions

Our findings suggest that heterogeneous distributions of toxins are not an adaptation to controlling venom composition in snakes. Instead, it likely reflects physiological constraints on toxin production by the venom glands, opening avenues for future research on the mechanisms of functional differentiation of populations of protein-secreting cells within adaptive contexts.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01350-y.

Developing a computational pharmacokinetic model of systemic snakebite envenomation and antivenom treatment

Snakebite envenomation is responsible for over 100,000 deaths and 400,000 cases of disability annually, most of which are preventable through access to safe and effective antivenoms. Snake venom toxins span a wide molecular weight range, influencing their absorption, distribution, and elimination within the body. In recent years, a range of scaffolds have been applied to antivenom development. These scaffolds similarly span a wide molecular weight range and subsequently display diverse pharmacokinetic behaviours. Computational simulations represent a powerful tool to explore the interplay between these varied antivenom scaffolds and venoms, to assess whether a pharmacokinetically optimal antivenom exists. The purpose of this study was to establish a computational model of systemic snakebite envenomation and treatment, for the quantitative assessment and comparison of conventional and next-generation antivenoms. A two-compartment mathematical model of envenomation and treatment was defined and the system was parameterised using existing data from rabbits. Elimination and biodistribution parameters were regressed against molecular weight to predict the dynamics of IgG, F(ab')₂, Fab, scFv, and nanobody antivenoms, spanning a size range of 15-150 kDa. As a case study, intramuscular envenomation by Naja sumatrana (equatorial spitting cobra) and its treatment using Fab, F(ab')₂, and IgG antivenoms was simulated. Variable venom dose tests were applied to visualise effective antivenom dose levels. Comparisons to existing antivenoms and experimental rescue studies highlight the large dose reductions that could result from recombinant antivenom use. This study represents the first comparative in silico model of snakebite envenomation and treatment.

Isolation and Characterization of A2-EPTX-Nsm1a, a Secretory Phospholipase A2 from Malaysian Spitting Cobra (Naja sumatrana) Venom

Phospholipase A₂ (PLA₂) toxins are one of the main toxin families found in snake venom. PLA₂ toxins are associated with various detrimental effects, including neurotoxicity, myotoxicity, hemostatic disturbances, nephrotoxicity, edema, and inflammation. Although Naja sumatrana venom contains substantial quantities of PLA₂ components_, there is limited information on the function and activities of PLA₂ toxins from the venom. In this study, a secretory PLA₂ from the venom of Malaysian N. sumatrana, subsequently named A2-EPTX-Nsm1a, was isolated, purified, and characterized. A2-EPTX-Nsm1a was purified using a mass spectrometry-guided approach and multiple chromatography steps. Based on LC-MSMS, A2-EPTX-Nsm1a was found to show high sequence similarity with PLA₂ from venoms of other Naja species. The PLA₂ activity of A2-EPTX-Nsm1 was inhibited by 4-BPB and EDTA. A2-EPTX-Nsm1a was significantly less cytotoxic in a neuroblastoma cell line (SH-SY5Y) compared to crude venom and did not show a concentration-dependent cytotoxic activity. To our knowledge, this is the first study that characterizes and investigates the cytotoxicity of an Asp49 PLA₂ isolated from Malaysian N. sumatrana venom in a human neuroblastoma cell line.

Cross-reactivity of some Micrurus venoms against experimental and therapeutic anti-Micrurus antivenoms

We developed experimental equine polyvalent and monovalent antivenoms against the venoms of Micrurus (M.) fulvius, M. nigrocinctus and M. surinamensis and studied their immunochemical reactivity on the venoms used as immunogens and on M. pyrrhocryptus, M altirostris and M. balyocoriphus venoms. Assessment of the neutralizing capacity of the polyvalent experimental antivenom was based on inhibition of lethality (preincubation and rescue assay experiments in mice) and indirect hemolytic and phospholipase activities. The immunochemical reactivity and neutralizing capacity were compared with those of two therapeutic antivenoms used for the treatment of coral snake envenomation in North America and in Argentina. In general, the experimental antivenom conferred a comparable level of neutralization against the venoms used as immunogens when compared to the therapeutic antivenoms and a certain level of cross-neutralization against the other venoms. The results suggest the need for additional venoms in the immunogenic mixture used, in order to obtain a broad spectrum anti-Micrurus antivenom with a good neutralizing potency. Paraspecific neutralization of South American coral snake venoms, although present at a higher level than the neutralization conferred by available nonspecific Micrurus therapeutic antivenoms, was rather low in relation to the specific neutralizing capacity.

Population pharmacokinetics of Pseudechis porphyriacus (red-bellied black snake) venom in snakebite patients

OBJECTIVES

Understanding the time course of venom exposure in snakebite patients is important for the optimisation of treatment including antivenom dose and timing. We aimed to investigate the pharmacokinetics of red-bellied black snake (RBBS; Pseudechis porphyriacus) venom in envenomed patients.

METHODS

Timed venom concentration data were obtained from patients with RBBS envenomation recruited to the Australian Snakebite Project (ASP), including demographics and antivenom treatment. Venom concentrations were measured using an enzyme immunoassay. Data were modelled using NONMEM version 7.3. Uncertainty in venom "dose" was accounted for by arbitrarily fixing the average amount to 1 mg and incorporating between-subject variability on relative bioavailability. A scale parameter for venom clearance was implemented to account for the rapid venom clearance following antivenom dosing. A sensitivity analysis was performed to determine the magnitude of venom clearance amplification.

RESULTS

There were 457 venom concentrations in 114 patients (median age 41, 2-90 y; 80 male). Antivenom was administered to 54 patients a median of 4.2 h post-bite (0.67 to 32 h). A one-compartment model with first-order absorption and elimination provided the best description of the data. The estimated clearance and volume of distribution were 5.21 L/h and 39.9 L, respectively. The calculated elimination half-life of P. porphyriacus venom from the final pharmacokinetic model was 5.35 ± 0.36 h. The variability in the relative dose of injected venom was 140%. Antivenom administration increased venom clearance by 40-fold. Ten patients showed evidence of a double peak in the absorption profile.

CONCLUSION

The information on the exposure time of venom in the body following envenomation will help improve treatment and the timing of antivenom.

Dynamic changes of serum protein in rats with acute intoxication of Chinese cobra snake venom by proteomic analysis

To elucidate the toxic mechanism of snake venom at the protein level, proteomics technology was applied to investigate the effect of venom on circulation in the mammalian body. Temporal proteomic analysis was performed to profile the dynamic changes in the sera of Sprague–Dawley rats administered with Chinese cobra venom or saline. Using 8-plex iTRAQ analysis, 392 and 636 serum proteins were identified to be linearly upregulated or downregulated over time in the low-dose group and high-dose group, respectively. These proteins were mainly associated with the acute phase response pathway, complement system, and liver X receptor (LXR)/retinoid X receptor (RXR) and farnesoid X receptor (FXR)/RXR activation pathways. Compared with the low-dose group, the immune response and integrin pathways were inhibited in the high-dose group, although no obvious effect was observed. With consistently higher or lower expression in the high-dose group compared to the low-dose group throughout the whole process of venom poisoning, two proteins, Kininogen-1 (KNG1) and orosomucoid 1 (ORM1), which are involved in metabolism and immune response, occupied a core position in the pathway network and are considered venom dose-dependent biomarker candidates.

Boyer L, D. Possani L, López-Casillas F, Olvera A, Romero C, Zamudio F, Alagón A. Neotropical Rattlesnake (Crotalus simus) Venom Pharmacokinetics in Lymph and Blood Using an Ovine Model

The most abundant protein families in viper venoms are Snake Venom Metalloproteases (SVMPs), Snake Venom Serine Proteases (SVSPs) and Phospholipases (PLA₂s). These are primarily responsible for the pathophysiology caused by the bite of pit-vipers; however, there are few studies that analyze the pharmacokinetics (PK) of whole venom (WV) and its protein families. We studied the pathophysiology, PK profile and differential absorption of representative toxins from venom of Neotropical Rattlesnake (Crotalus simus) in a large animal model (ovine). Toxins studied included crotoxin (the main lethal component), which causes moderate to severe neurotoxicity; SVSPs, which deplete fibrinogen; and SVMPs, which cause local tissue damage and local and systemic hemorrhage. We found that Whole Venom (WV) was highly bioavailable (86%) 60 h following intramuscular (IM) injection, and extrapolation suggests that bioavailability may be as high as 92%. PK profiles of individual toxins were consistent with their physicochemical properties and expected clinical effects. Lymph cannulated animals absorbed 1.9% of WV through lymph during the first 12 h. Crotoxin was minimally detectable in serum after intravenous (IV) injection; however, following IM injection it was detected in lymph but not in blood. This suggests that crotoxin is quickly released from the blood toward its tissue targets.

The Influence of the Different Disposition Characteristics of Snake Toxins on the Pharmacokinetics of Snake Venom

Snake venom is comprised of a combination of different proteins and peptides with a wide range of molecular weights and different disposition processes inherent to each compound. This causes venom to have a complex exposure profile. Our study investigates 1) how each molecular weight fraction (toxin) of venom contributes to the overall time course of the snake venom, and 2) the ability to determine toxin profiles based on the profile of the overall venom only. We undertook an in silico simulation and modelling study. Sixteen variations of venom, comprising of two to nine toxins with different molecular weights were investigated. The pharmacokinetic parameters (i.e., clearance, CL, and volume of distribution, V) of each toxin were generated based on a log-linear relationship with molecular weight. The concentration–time data of each toxin were simulated for 100 virtual patients using MATLAB and the total concentration–time data of each toxin were modelled using NONMEM. We found that the data of sixteen mixtures were best described by either two- or three-compartment models, despite the venom being made up of more than three different toxins. This suggests that it is generally not possible to determine individual toxin profiles based on measurements of total venom concentrations only.

Pharmacokinetics of Snake Venom

Understanding snake venom pharmacokinetics is essential for developing risk assessment strategies and determining the optimal dose and timing of antivenom required to bind all venom in snakebite patients. This review aims to explore the current knowledge of snake venom pharmacokinetics in animals and humans. Literature searches were conducted using EMBASE (1974–present) and Medline (1946–present). For animals, 12 out of 520 initially identified studies met the inclusion criteria. In general, the disposition of snake venom was described by a two-compartment model consisting of a rapid distribution phase and a slow elimination phase, with half-lives of 5 to 48 min and 0.8 to 28 h, respectively, following rapid intravenous injection of the venoms or toxins. When the venoms or toxins were administered intramuscularly or subcutaneously, an initial absorption phase and slow elimination phase were observed. The bioavailability of venoms or toxins ranged from 4 to 81.5% following intramuscular administration and 60% following subcutaneous administration. The volume of distribution and the clearance varied between snake species. For humans, 24 out of 666 initially identified publications contained sufficient information and timed venom concentrations in the absence of antivenom therapy for data extraction. The data were extracted and modelled in NONMEM. A one-compartment model provided the best fit, with an elimination half-life of 9.71 ± 1.29 h. It is intended that the quantitative information provided in this review will provide a useful basis for future studies that address the pharmacokinetics of snakebite in humans.

Naja atra snakebite in Taiwan

BACKGROUND

Naja atra snakebite is uncommon in Taiwan and causes distinct effects on its victims. Although the Taiwan government produces its own specific antivenom, little information on the management of N. atra snakebite is available.

MATERIALS AND METHODS

We retrospectively evaluated 183 patients admitted to two medical centers. Of these, 45 were identified as definite cases of N. atra snakebite, 86 as suspected cases, and 52 as clinical cases. Demographic data, symptomatology, and management were compared between these case groups.

RESULTS

Symptomatology and management were similar in the three groups. Among the 183 patients, 10 (5.5%) were asymptomatic and nine (4.9%) had transient and partial ptosis or body weakness. The principal effects were local tissue swelling and pain in 173 patients (94.5%), followed by clinically suspected wound infection in 148 (80.9%), skin necrosis in 120 (65.6%), necrotizing soft tissue infection in 77 (42.1%), fever in 59 (32.2%), and gastrointestinal effects in 53 (29%). The median total dose of specific antivenom needed to treat N. atra envenoming was 10 vials. In the envenomed patients, debridement was required in 74 patients (42.8%), fasciotomy/fasciectomy in 46 (26.6%), and finger or toe amputation in seven (4%). The first operation was performed at a median of 3.5 days after the bite.

DISCUSSION AND CONCLUSIONS

Based on these typical manifestations, clinical diagnosis of N. atra snakebites may be feasible and practical. In contrast to other snakes of Elapidae family, N. atra bite did not cause serious neurological effects. Early surgical consultation should be obtained because half of the patients underwent surgery due to infectious complications. Acute compartment syndrome was the surgical indication in rare cases; however, overestimation of the incidence may have occurred. This syndrome should be confirmed by serial intracompartmental pressure monitoring instead of only physical examination, and a sufficient dose of antivenom should be given prior to surgical decompression.

Comparative pharmacokinetics of eight major bioactive components in normal and bacterial diarrhea mini-pigs after oral administration of Gegen Qinlian Decoction

Healthy animals are most widely used in current pharmacokinetic(PK) studies. However, neglecting the effects of specific diseases on drug absorption results in the PK parameters of those experiments not accurately reflecting in vivo drug concentration changes during treatment. In this study, an E. coli infective diarrheal minipig model was applied to explore the pharmacokinetics of Gegen Qinlian decoction (GQD). A simple and rapid ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed to determine the concentrations of the eight GQD components in minipig plasma after intragastric administration of GQD. The PK parameters of the main GQD components in normal and model minipigs after oral administration of GQD were compared. There were statistically significant differences (p<0.05) in the pharmacokinetic parameters of Puerarin, Wogonin and Daidzein involving the AUC_0-t, Cmax, MRT_(0-t), t_1/2z between normal and model minipigs. Results showed that bacterial diarrhea had a great impact on the biological availability of the main ingredients in GQD. More importantly, the results obtained suggest that the bacterial diarrheal minipig model can be successfully applied in PK studies and may be used in other PK studies of drugs targeting intestinal disease.

Genus Calliophis of Asiatic coral snakes: A deficiency of venom cross-reactivity and neutralization against seven regional elapid antivenoms

Venoms of Calliophis bivirgata and Calliophis intestinalis exhibited moderate binding activities toward Neuro Bivalent Antivenom (Taiwan) but not the other six elapid monovalent or bivalent antivenoms available in the region. All antivenoms failed to neutralize C. bivirgata venom lethality in mice. The findings indicate the need to validate antivenom cross-reactivity with in vivo cross-neutralization, and imply that distinct antigens of Calliophis venoms should be incorporated in the production of a pan-regional poly-specific antivenom.

Geographical venom variations of the Southeast Asian monocled cobra (Naja kaouthia): venom-induced neuromuscular depression and antivenom neutralization

The Southeast Asian monocled cobras (Naja kaouthia) exhibit geographical variations in their venom proteomes, especially on the composition of neurotoxins. This study compared the neuromuscular depressant activity of the venoms of N. kaouthia from Malaysia (NK-M), Thailand (NK-T) and Vietnam (NK-V), and the neutralization of neurotoxicity by a monospecific antivenom. On chick biventer cervicis nerve-muscle preparation, all venoms abolished the indirect twitches, with NK-T venom being the most potent (shortest t90, time to 90% twitch inhibition), followed by NK-V and NK-M. Acetylcholine and carbachol failed to reverse the blockade, indicating irreversible/pseudo-irreversible post-synaptic neuromuscular blockade. KCl restored the twitches variably (NK-M preparation being the least responsive), consistent with different degree of muscle damage. The findings support that NK-T venom has the most abundant curarimimetic alpha-neurotoxins, while NK-M venom contains more tissue-damaging cytotoxins. Pre-incubation of tissue with N. kaouthia monovalent antivenom (NKMAV) prevented venom-induced twitch depression, with the NK-T preparation needing the largest antivenom dose. NKMAV added after the onset of neuromuscular depression could only halt the inhibitory progression but failed to restore full contraction. The findings highlight the urgency of early antivenom administration to sequester as much circulating neurotoxins as possible, thereby hastening toxin elimination from the circulation. In envenomed mice, NKMAV administered upon the first neurological sign neutralized the neurotoxic effect, with the slowest full recovery noticed in the NK-T group. This is consistent with the high abundance of neurotoxins in the NK-T venom, implying that a larger amount or repeated dosing of NKMAV may be required in NK-T envenomation.

A single-label fluorescent derivatization method for quantitative determination of neurotoxin in vivo by capillary electrophoresis coupled with laser-induced fluorescence detection

Neurotoxin (NT), a short-chain α-neurotoxin, is the main neurotoxic protein identified from the venom of Naja naja atra. As an effective drug for the analgesis of advanced cancer patients, NT lasts longer than morphine and does not cause addiction. However, achieving a sensitive and high-resolution measurement of NT is difficult because of the extra-low content of NT in vivo. Therefore, developing a novel method to quantify NT is essential to study its pharmacokinetics in vivo. Although NT contains four primary amine groups that could react with the thiourea in fluorescein isothiocyanate (FITC), we developed a simple and reproducible single-label fluorescent derivatization method for NT which is related to the reaction of N-terminal α-amino of NT alone under optimized derivatization conditions. Furthermore, neurotoxin labelled with fluorescein isothiocyanate (NT-FITC) was prepared by high-performance liquid chromatography (HPLC) with a purity value higher than 99.29% and identified by MALDI-TOF/TOF-MS. Finally, NT-FITC could be detected at 0.8 nmol L(-1) in rat plasma using capillary electrophoresis coupled with laser induced fluorescence detection (CE-LIF). In this paper, the established method robustly and reliably quantified NT labelled with FITC via intravenous and intramuscular administrations in vivo. In addition, this work fully demonstrated the pharmacokinetic characteristics of NT in vivo, which could reduce the risk of drug accumulation, optimize therapies, and provide sufficient evidence for the rational use of NT in clinical and research laboratories.

Venom and Purified Toxins of the Spectacled Cobra (Naja naja) from Pakistan: Insights into Toxicity and Antivenom Neutralization

Geographical variations of snake venoms can result in suboptimal effectiveness of Indian antivenoms that are currently used in most South Asian countries. This study investigated the toxicity and neutralization profile of the venom and toxins from Pakistani spectacled cobra, Naja naja, using VINS polyvalent antivenom (VPAV, India), Naja kaouthia monovalent antivenom (NKMAV, Thailand), and neuro bivalent antivenom (NBAV, Taiwan). Cation-exchange and reverse-phase high-performance liquid chromatography fractionations followed by toxin identification through liquid chromatography-mass spectrometry (MS)/MS indicated that the venom comprised mainly of postsynaptic neurotoxins (NTXs) (long neurotoxins [LNTXs], 28.3%; short neurotoxins [SNTXs], 8%), cytotoxins (CTXs) (31.2%), and acidic phospholipases A2 (12.3%). NKMAV is the most effective in neutralizing the lethal effect of the venom (potency = 1.1 mg venom/mL) and its LNTX (potency = 0.5 mg toxin/mL), consistent with the high content of LNTX in N. kaouthia venom. VPAV was effective in neutralizing the CTX (potency = 0.4 mg toxin/mL), in agreement with the higher CTX abundance in Indian cobra venom. All the three antivenoms were weak in neutralizing the SNTX (potency = 0.03-0.04 mg toxin/mL), including NBAV that was raised from the SNTX-rich Taiwanese cobra venom. In a challenge-rescue experiment, envenomed mice were prevented from death by a maximal dose of VPAV (intravenous 200 μL) but the recovery from paralysis was slow, indicating the need for higher or repeated doses of VPAV. Our results suggest that optimal neutralization for Pakistani N. naja venom may be achieved by improving the formulation of antivenom production to enhance antivenom immunoreactivity against long and SNTXs.

Neutralization of the Principal Toxins from the Venoms of Thai Naja kaouthia and Malaysian Hydrophis schistosus: Insights into Toxin-Specific Neutralization by Two Different Antivenoms

Antivenom neutralization against cobra venoms is generally low in potency, presumably due to poor toxin-specific immunoreactivity. This study aimed to investigate the effectiveness of two elapid antivenoms to neutralize the principal toxins purified from the venoms of the Thai monocled cobra (Naja kaouthia, Nk-T) and the Malaysian beaked sea snake (Hydrophis schistosus, Hs-M). In mice, N. kaouthia Monovalent Antivenom (NKMAV) neutralization against Nk-T long neurotoxin (LNTX) and cytotoxin was moderate (potency of 2.89–6.44 mg toxin/g antivenom protein) but poor against the short neurotoxin (SNTX) (1.33 mg/g). Its cross-neutralization against Hs-M LNTX of Hs-M is compatible (0.18 mg/g) but much weaker against Hs-M SNTX (0.22 mg/g). Using CSL (Seqirus Limited) Sea Snake Antivenom (SSAV), we observed consistently weak neutralization of antivenom against SNTX of both species, suggesting that this is the limiting factor on the potency of antivenom neutralization against venoms containing SNTX. Nevertheless, SSAV outperformed NKMAV in neutralizing SNTXs of both species (0.61–2.49 mg/g). The superior efficacy of SSAV against SNTX is probably partly attributable to the high abundance of SNTX in sea snake venom used as immunogen in SSAV production. The findings indicate that improving the potency of cobra antivenom may be possible with a proper immunogen formulation that seeks to overcome the limitation on SNTX immunoreactivity.

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.

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.

The Effect of a Polyvalent Antivenom on the Serum Venom Antigen Levels of Naja sputatrix (Javan Spitting Cobra) Venom in Experimentally Envenomed Rabbits

The treatment protocol of antivenom in snake envenomation remains largely empirical, partly due to the insufficient knowledge of the pharmacokinetics of snake venoms and the effects of antivenoms on the blood venom levels in victims. In this study, we investigated the effect of a polyvalent antivenom on the serum venom antigen levels of Naja sputatrix (Javan spitting cobra) venom in experimentally envenomed rabbits. Intravenous infusion of 4 ml of Neuro Polyvalent Snake Antivenom [NPAV, F(ab')2 ] at 1 hr after envenomation caused a sharp decline of the serum venom antigen levels, followed by transient resurgence an hour later. The venom antigen resurgence was unlikely to be due to the mismatch of pharmacokinetics between the F(ab')2 and venom antigens, as the terminal half-life and volume of distribution of the F(ab')2 in serum were comparable to that of venom antigens (p > 0.05). Infusion of an additional 2 ml of NPAV was able to prevent resurgence of the serum venom antigen level, resulting in a substantial decrease (67.1%) of the total amount of circulating venom antigens over time course of envenomation. Our results showed that the neutralization potency of NPAV determined by neutralization assay in mice may not be an adequate indicator of its capability to modulate venom kinetics in relation to its in vivo efficacy to neutralize venom toxicity. The findings also support the recommendation of giving high initial dose of NPAV in cobra envenomation, with repeated doses as clinically indicated in the presence of rebound antigenemia and symptom recurrence.

Venomics, lethality and neutralization of Naja kaouthia (monocled cobra) venoms from three different geographical regions of Southeast Asia

Previous studies showed that venoms of the monocled cobra, Naja kaouthia from Thailand and Malaysia are substantially different in their median lethal doses. The intraspecific venom variations of N. kaouthia, however, have not been fully elucidated. Here we investigated the venom proteomes of N. kaouthia from Malaysia (NK-M), Thailand (NK-T) and Vietnam (NK-V) through reverse-phase HPLC, SDS-PAGE and tandem mass spectrometry. The venom proteins comprise 13 toxin families, with three-finger toxins being the most abundant (63-77%) and the most varied (11-18 isoforms) among the three populations. NK-T has the highest content of neurotoxins (50%, predominantly long neurotoxins), followed by NK-V (29%, predominantly weak neurotoxins and some short neurotoxins), while NK-M has the least (18%, some weak neurotoxins but less short and long neurotoxins). On the other hand, cytotoxins constitute the main bulk of toxins in NK-M and NK-V venoms (up to 45% each), but less in NK-T venom (27%). The three venoms show different lethal potencies that generally reflect the proteomic findings. Despite the proteomic variations, the use of Thai monovalent and Neuro polyvalent antivenoms for N. kaouthia envenomation in the three regions is appropriate as the different venoms were neutralized by the antivenoms albeit at different degrees of effectiveness.

BIOLOGICAL SIGNIFICANCE

Biogeographical variations were observed in the venom proteome of monocled cobra (Naja kaouthia) from Malaysia, Thailand and Vietnam. The Thai N. kaouthia venom is particularly rich in long neurotoxins, while the Malaysian and Vietnamese specimens were predominated with cytotoxins. The differentially expressed toxin profile accounts for the discrepancy in the lethal dose of the venom from different populations. Commercially available Thai antivenoms (monovalent and polyvalent) were able to neutralize the three venoms at different effective doses, hence supporting their uses in the three regions. While dose adjustment according to geographical region seems possible, changes to standard recommended dosage should only be made if further study validates that the monocled cobras within a population do not exhibit remarkable inter-individual venom variation.

Antivenom cross-neutralization of the venoms of Hydrophis schistosus and Hydrophis curtus, two common sea snakes in Malaysian waters

Sea snake envenomation is a serious occupational hazard in tropical waters. In Malaysia, the beaked sea snake (Hydrophis schistosus, formerly known as Enhydrina schistosa) and the spine-bellied sea snake (Hydrophis curtus, formerly known as Lapemis curtus or Lapemis hardwickii) are two commonly encountered species. Australian CSL sea snake antivenom is the definitive treatment for sea snake envenomation; it is unfortunately extremely costly locally and is not widely available or adequately stocked in local hospitals. This study investigated the cross-neutralizing potential of three regionally produced anti-cobra antivenoms against the venoms of Malaysian H. schistosus and H. curtus. All three antivenoms conferred paraspecific protection from sea snake venom lethality in mice, with potency increasing in the following order: Taiwan bivalent antivenom < Thai monocled cobra monovalent antivenom < Thai neuro polyvalent antivenom (NPAV). NPAV demonstrated cross-neutralizing potencies of 0.4 mg/vial for H. schistosus venom and 0.8 mg/vial for H. curtus, which translates to a dose of less than 20 vials of NPAV to neutralize an average amount of sea snake venom per bite (inferred from venom milking). The cross-neutralization activity was supported by ELISA cross-reactivity between NPAV and the venoms of H. schistosus (58.4%) and H. curtus (70.4%). These findings revealed the potential of NPAV as a second-line treatment for sea snake envenomation in the region. Further profiling of the cross-neutralization activity should address the antivenomic basis using purified toxin-based assays.