Pharmacokinetics of habutobin in rabbits

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.

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.

Snake venoms are integrated systems, but abundant venom proteins evolve more rapidly

Background

While many studies have shown that extracellular proteins evolve rapidly, how selection acts on them remains poorly understood. We used snake venoms to understand the interaction between ecology, expression level, and evolutionary rate in secreted protein systems. Venomous snakes employ well-integrated systems of proteins and organic constituents to immobilize prey. Venoms are generally optimized to subdue preferred prey more effectively than non-prey, and many venom protein families manifest positive selection and rapid gene family diversification. Although previous studies have illuminated how individual venom protein families evolve, how selection acts on venoms as integrated systems, is unknown.

Results

Using next-generation transcriptome sequencing and mass spectrometry, we examined microevolution in two pitvipers, allopatrically separated for at least 1.6 million years, and their hybrids. Transcriptomes of parental species had generally similar compositions in regard to protein families, but for a given protein family, the homologs present and concentrations thereof sometimes differed dramatically. For instance, a phospholipase A₂ transcript comprising 73.4 % of the Protobothrops elegans transcriptome, was barely present in the P. flavoviridis transcriptome (<0.05 %). Hybrids produced most proteins found in both parental venoms. Protein evolutionary rates were positively correlated with transcriptomic and proteomic abundances, and the most abundant proteins showed positive selection. This pattern holds with the addition of four other published crotaline transcriptomes, from two more genera, and also for the recently published king cobra genome, suggesting that rapid evolution of abundant proteins may be generally true for snake venoms. Looking more broadly at Protobothrops, we show that rapid evolution of the most abundant components is due to positive selection, suggesting an interplay between abundance and adaptation.

Conclusions

Given log-scale differences in toxin abundance, which are likely correlated with biosynthetic costs, we hypothesize that as a result of natural selection, snakes optimize return on energetic investment by producing more of venom proteins that increase their fitness. Natural selection then acts on the additive genetic variance of these components, in proportion to their contributions to overall fitness. Adaptive evolution of venoms may occur most rapidly through changes in expression levels that alter fitness contributions, and thus the strength of selection acting on specific secretome components.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1832-6) contains supplementary material, which is available to authorized users.

Pharmacokinetics of Cryptelytrops purpureomaculatus (mangrove pit viper) venom following intravenous and intramuscular injections in rabbits

The pharmacokinetic profiles of Cryptelytrops purpureomaculatus (mangrove pit viper) venom following intravenous and intramuscular injections were investigated in rabbits. The serum levels of the venom were estimated using double-sandwich enzyme-linked immunosorbent assay (ELISA). After intravenous injection (0.2 mg/kg), the serum venom concentration–time course declined in a biexponential manner, consistent with a two-compartment model, with an α-phase half-life of 0.25 h and a β-phase half-life of 27.7 h. The volume of distribution by area was 2.19 L/kg and systemic clearance was 54.7 mL/h/kg. When the venom was injected intramuscularly (0.5 mg/kg), the serum level increased rapidly to reach a peak (500 ng/mL) at about 1 h, which then declined rapidly to a plateau (104–142 ng/mL) at 3–10 h before further gradual decline until the end of the 72-hour study. The terminal half-life (27.0 h), clearance (54.7 mL/h/kg) and volume of distribution (2.13 L/kg) of the venom for intramuscular route were not significantly different from the corresponding values for intravenous route, and the intramuscular bioavailability of the venom was estimated to be 41.6%.

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

BACKGROUND

The optimization of snakebite management and the use of antivenom depend greatly on the knowledge of the venom's composition as well as its pharmacokinetics. To date, however, pharmacokinetic reports on cobra venoms and their toxins are still relatively limited. In the present study, we investigated the pharmacokinetics of Naja sumatrana (Equatorial spitting cobra) venom and its major toxins (phospholipase A2, neurotoxin and cardiotoxin), following intravenous and intramuscular administration into rabbits.

PRINCIPAL FINDINGS

The serum antigen concentration-time profile of the N. sumatrana venom and its major toxins injected intravenously fitted a two-compartment model of pharmacokinetics. The systemic clearance (91.3 ml/h), terminal phase half-life (13.6 h) and systemic bioavailability (41.9%) of N. sumatrana venom injected intramuscularly were similar to those of N. sputatrix venom determined in an earlier study. The venom neurotoxin and cardiotoxin reached their peak concentrations within 30 min following intramuscular injection, relatively faster than the phospholipase A2 and whole venom (Tmax=2 h and 1 h, respectively). Rapid absorption of the neurotoxin and cardiotoxin from the injection site into systemic circulation indicates fast onsets of action of these principal toxins that are responsible for the early systemic manifestation of envenoming. The more prominent role of the neurotoxin in N. sumatrana systemic envenoming is further supported by its significantly higher intramuscular bioavailability (Fi.m.=81.5%) compared to that of the phospholipase A2 (Fi.m.=68.6%) or cardiotoxin (Fi.m.=45.6%). The incomplete absorption of the phospholipase A2 and cardiotoxin may infer the toxins' affinities for tissues at the injection site and their pathological roles in local tissue damages through synergistic interactions.

CONCLUSION/SIGNIFICANCE

Our results suggest that the venom neurotoxin is absorbed very rapidly and has the highest bioavailability following intramuscular injection, supporting its role as the principal toxin in systemic envenoming.

Pharmacokinetics of the Sri Lankan hump-nosed pit viper (Hypnale hypnale) venom following intravenous and intramuscular injections of the venom into rabbits

The knowledge of venom pharmacokinetics is essential to improve the understanding of envenomation pathophysiology. Using a double-sandwich ELISA, this study investigated the pharmacokinetics of the venom of hump-nosed pit viper (Hypnale hypnale) following intravenous and intramuscular injections into rabbits. The pharmacokinetics of the venom injected intravenously fitted a three-compartment model. There is a rapid (t1/2π = 0.4 h) and a slow (t1/2α = 0.8 h) distribution phase, followed by a long elimination phase (t1/2β = 19.3 h) with a systemic clearance of 6.8 mL h(-1) kg(-1), consistent with the prolonged abnormal hemostasis reported in H. hypnale envenomation. On intramuscular route, multiple peak concentrations observed in the beginning implied a more complex venom absorption and/or distribution pattern. The terminal half-life, volume of distribution by area and systemic clearance of the venom injected intramuscularly were nevertheless not significantly different (p > 0.05) from that of the venom injected intravenously. The intramuscular bioavailability was exceptionally low (Fi.m. = 4%), accountable for the highly varied median lethal doses between intravenous and intramuscular envenomations in animals. The findings indicate that the intramuscular route of administration does not significantly alter the pharmacokinetics of H. hypnale venom although it significantly reduces the systemic bioavailability of the venom.

Toxicokinetics of Naja sputatrix (Javan spitting cobra) venom following intramuscular and intravenous administrations of the venom into rabbits

Existing protocols for antivenom treatment of snake envenomations are generally not well optimized due partly to inadequate knowledge of the toxicokinetics of venoms. The toxicokinetics of Naja sputatrix (Javan spitting cobra) venom was investigated following intravenous and intramuscular injections of the venom into rabbits using double-sandwich ELISA. The toxicokinetics of the venom injected intravenously fitted a two-compartment model. When the venom was injected intramuscularly, the serum concentration-time profile exhibited a more complex absorption and/or distribution pattern. Nevertheless, the terminal half-life, volume of distribution by area and systemic clearance of the venom injected intramuscularly were not significantly different (p > 0.05) from that of the venom injected intravenously. The systemic bioavailability of the venom antigens injected by intramuscular route was 41.7%. Our toxicokinetic finding is consistent with other reports, and may indicate that some cobra venom toxins have high affinity for the tissues at the site of injection. Our results suggest that the intramuscular route of administration doesn't significantly alter the toxicokinetics of N. sputatrix venom although it significantly reduces the systemic bioavailability of the venom.

A new avidin-biotin optical immunoassay for the detection of beta-bungarotoxin and application in diagnosis of experimental snake envenomation

A highly sensitive avidin-biotin optical immunoassay (AB-OIA) has been developed for the detection of beta-bungarotoxin (beta-BuTx), a neurotoxin from the venom of Bungarus multicinctus, in whole blood, plasma, and urine. Affinity purified rabbit IgG anti-beta-BuTx antibody was immobilized on an optically active silicon surface (SILIAS wafer). The test sample was incubated and the antigen-antibody reaction was monitored by the addition of a biotinylated monoclonal antibody (mAb 15) specific to the toxin, avidin-horseradish peroxidase (HRP) and tetramethylbenzidine substrate. The silicon assay surface technology enables us to directly visualize a physical change in the optical thickness of the antibody thin film. The change in thickness is due to the specific capture of the toxin on the surface and when the substrate is added, the binding event is amplified, which then alters the reflected light path and a change in colour is visualized. The assay could detect beta-BuTx levels as low as 16 pg/ml in sample buffer and 100 pg/ml in whole blood or plasma. The AB-OIA is simple, requires only 40 microl of biological fluid and can be performed without specialized equipment. The efficacy of the test for detection of beta-BuTx in blood or plasma obtained from mice during experimental envenomation with B. multicinctus venom was demonstrated. The AB-OIA was also used to quantitate the postmortem level of beta-BuTx in various organs such as brain, liver, and kidney, as well as the tissue at the site of injection. Development of a simple, rapid snake toxin detection kit based on AB-OIA technique potentially applicable in the clinics as well as in the field is discussed.

Tests for detection of snake venoms, toxins and venom antibodies: review on recent trends (1987-1997)

Various methods developed for the detection of snake venoms, toxins and venom antibodies, during the last decade is reviewed. Radioimmunoassay, agglutination assay, enzyme-linked immunosorbent assay (ELISA), fluorescence immunoassay etc. have been used for detection of venoms and toxins. Important contributions have been made to improve the specificity, sensitivity, rapidity and simplicity of the ELISA method. Monoclonal antibodies and affinity-purified venom-specific antibodies were used to achieve species specificity of ELISA and the latter seems to be the ideal for venom detection. Incorporation of avidin-biotin system as well as the fluorogenic substrate in the enzyme immunoassay sufficiently increased the sensitivity of the assay to detect venom concentrations to picogram levels. The ability to use undiluted blood and other whole biological fluids reduce the assay time considerably. Although there have been several reports were on venom detection, so far only a few field kits have been developed. This implies that the experiments and design were only at the laboratory levels and still more work has to be carried out before it could be used in the field. Concerning the venom antibody detection, ELISA has been used extensively and the humoral response of patients envenomed by snake has been investigated in detail. Non-specific reactivity along with cross-reactivity still limits the use of ELISA for species identification in epidemiological studies. Overall, ELISA remains the suitable method for the detection of snake venoms, toxins and venom antibodies in body fluids. The possible use of a biosensor approach to solve some of the problems associated with the ELISA method are also discussed.

Effect of Habu (Trimeresurus flavoviridis) antivenom on changes of hemostatic parameters following administration of crude venom from T. flavoviridis in rabbits

We carried out experiments to examine the efficacy of Habu antivenom in relation to variations of hemostatic parameters induced by the administration of crude venom to rabbits. For neutralization of the crude venom by Habu antivenom, the correlation between the concentrations of Habu antivenom (Y) and crude venom (X) was expressed by the equation: Y = -0.473 + 0.539X. We examined the variations in hemostatic parameters in the state which crude venom was neutralized by Habu antivenom following the administration of crude venom (1 mg/kg) from Trimeresurus flavoviridis. Although the hemostatic parameters [level of fibrinogen, antithrombin III (AT-III) activity and alpha 2-plasmin inhibitor (alpha 2-PI) activity] underwent decreases after the administration of crude venom, they revealed fluctuations within the normal range after the Habu antivenom administration. The AT-III activity, however, decreased gradually until 90 min after the antivenom administration. These results suggested that Habu antivenom was effective in improving the abnormal coagulant activity induced by crude venom. However, the neutralization effect towards the coagulant activity of crude venom by the Habu antivenom did not continue for a long time and did not lead to recovery of the AT-III activity. Since excessive doses of antivenom can induce serious medical problems, we expect that simultaneous use of antivenom and AT-III preparation, instead of excessive and single use of Habu antivenom could provide a useful therapy for snake bites from the present study.