Pharmacokinetics in rabbits and anti-sphingomyelinase D neutralizing power of Fab, F(ab')2, IgG and IgG(T) fragments from hyper immune equine plasma

A consensus recombinant elapid long-chain α-neurotoxin and how protein folding matters for antibody recognition and neutralization of elapid venoms

Antivenoms are essential in the treatment of the neurotoxicity caused by elapid snakebites. However, there are elapid neurotoxins, e.g., long-chain α-neurotoxins (also known as long-chain three-finger toxins) that are barely neutralized by commercial elapid antivenoms; so, recombinant elapid neurotoxins could be an alternative or complements for improving antibody production against the lethal long-chain α-neurotoxins from elapid venoms. This work communicates the expression of a recombinant long-chain α-neurotoxin, named HisrLcNTx or rLcNTx, which based on the most lethal long-chain α-neurotoxins reported, was constructed de novo. The gene of rLcNTx was synthesized and introduced into the expression vector pQE30, which contains a proteolytic cleavage region for exscinding the mature protein, and His residues in tandem for affinity purification. The cloned pQE30/rLcNTx was transfected into Escherichia coli Origami cells to express rLcNTx. After expression, it was found in inclusion bodies, and folded in multiple Cys-Cys structural isoforms. To observe the capability of those isoforms to generate antibodies against native long-chain α-neurotoxins, groups of rabbits were immunized with different cocktails of Cys-Cys rLcNTx isoforms. In vitro, and in vivo analyses revealed that rabbit antibodies raised against different rLcNTx Cys-Cys isoforms were able to recognize pure native long-chain α-neurotoxins and their elapid venoms, but they were unable to neutralize bungarotoxin, a classical long-chain α-neurotoxin, and other elapid venoms. The rLcNTx Cys-Cys isoform 2 was the immunogen that produced the best neutralizing antibodies in rabbits. Yet to neutralize the elapid venoms from the black mamba Dendroaspis polylepis, and the coral shield cobra Aspidelaps lubricus, it was required to use two types of antibodies, the ones produced using rLcNTx Cys-Cys isoform 2 and antibodies produced using short-chain α-neurotoxins. Expression of recombinant elapid neurotoxins as immunogens could be an alternative to improve elapid antivenoms; nevertheless, recombinant elapid neurotoxins must be well-folded to be used as immunogens for obtaining neutralizing antibodies.

Pharmacokinetic evaluation of a single chain antibody fragment against scorpion toxins in sheep

A key aspect during the development of antivenoms is the evaluation of the efficiency and security of the therapeutic molecules. In this work, we report the pharmacokinetic analysis of a neutralizing single chain antibody fragment named LR (scFv LR) where three sheep were used as a large animal model. The animals were injected through i.v. route with 2 mg of scFv LR. Blood samples were drawn every minute within the first 15 min, the sampling continues at 20, 25, 30, 45, 60, 90, 120 min, subsequently at 1-h intervals, 3, 4, 5, 6 h, two more samples at 9 and 12 h and, two more samples at 24 and 48 h and finally at one-day intervals during 4 days. scFv LR levels were measured from blood serum and urine samples by an ELISA. The pharmacokinetics of the experimental data was analyzed using the three-exponential kinetics. The value of the fast initial component (τ1=0.409±0.258min) indicated that the scFv is distributed rapidly into the tissues. The mean residence time, MRT, was 45 ± 0.51 min and the clearance (CL), 114.3 ± 14.3 mL/min. From urine samples it was possible to detect significant amounts of scFv LR, which is evidence of renal elimination.

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.

Fab Fragment of Immunoglobulin Y Modulates NF-κB and MAPK Signaling through TLR4 and αVβ3 Integrin and Inhibits the Inflammatory Effect on R264.7 Macrophages

High-purity Fab fragment and immunoglobulin Y (IgY) were prepared to evaluate their anti-inflammatory activity in the lipopolysaccharide (LPS)-induced Raw 264.7 macrophage system. Compared with IgY, the Fab fragment possessed a greater potency in inhibiting the inflammation by nitric oxide (NO)/inducible nitric oxide synthase (iNOS) and prostaglandin-E2 (PGE2)/cyclooxygenase-2 (COX-2) pathways. The Fab fragment attenuated the levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-10 (IL-10) to 38.07 ± 1.86-48.39 ± 11.33 pg/mL (63.1-71.0% inhibition), 31.59 ± 3.91-38.08 ± 4.44 pg/mL (72.4-77.1% inhibition), and 20.62 ± 0.46-21.91 ± 0.65 pg/mL (50-53% inhibition), respectively. Additionally, the Fab fragment significantly inhibited the translocation of nuclear transcription factor-κB (NF-κB) p65 and the phosphorylation of mitogen-activated protein kinase (MAPK) proteins, including ERK1/2 (41.5/33.2%), JNK1/2 (44.2/39.6%), and p38 (42.2%). The Fab fragment could be internalized into cells, and the pretreatment of RAW 264.7 macrophages with the Fab fragment reduced the mRNA expression of the Toll-like receptor (TLR4, 32.7-44.4% inhibition) and αVβ3 integrin (76.1% inhibition). In conclusion, Fab fragments regulated the TLR4 and αVβ3 integrin-mediated inflammatory processes by blocking the NF-κB and MAPKs pathways in the LPS-induced RAW 264.7 macrophage system.

Canine immunoglobulin F(ab')2 fragments protect cats against feline parvovirus virus infection

Feline parvovirus virus (FPV) causes severe diarrhea and leukopenia in felines, and threatening the health of wild and domestic felines. Currently, specific drugs to treat FPV have not yet been developed. In this study, IgG was extracted from inactivated FPV-immunized dog sera. Canine F(ab')₂ fragments were obtained from pepsin-digested IgG and then purified by protein-G column chromatography. The results showed that canine immunoglobulin F(ab')₂ fragments showed efficient neutralizing activity in vitro against FPV and had therapeutic and prophylactic effects in FPV infected cats. The anti-FPV-specific F(ab')₂ fragment can significantly alleviate the clinical symptoms of FPV infected cats and reduce the viral loads of the intestinal tract. These results indicated that the F(ab')₂ fragment prepared from inactivated FPV-immunized felines may be used as a prophylactic and therapeutic agent for diseases caused by FPV.

Equine immunoglobulin F(ab')2 fragments protect cats against feline calicivirus infection

Feline calicivirus (FCV) causes upper respiratory tract infections in felines and threatens the health of wild and domestic felines. Clinically, specific drugs to treat FCV have not yet been developed. Here, IgG was extracted from inactivated FCV-immunized horse sera. Equine F(ab')₂ fragments were obtained from pepsin-digested IgG and then purified by protein-G column chromatography. In our study, equine immunoglobulin F(ab')₂ fragments showed efficient neutralizing activity in vitro against FCV and had therapeutic and prophylactic effects in FCV-infected cats. The anti-FCV-specific F(ab')₂ fragment can significantly alleviate the clinical symptoms of FCV-infected cats and reduce the viral loads of the trachea, lung and spleen. These results indicate that the F(ab')₂ fragment prepared from inactivated FCV-immunized horses may be used as a prophylactic and therapeutic agent for diseases caused by FCV.

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High-purity anti-FCV F(ab')₂ fragments were prepared from equine IgG.

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F(ab')₂ fragments can bind to FCV both in vivo and in vitro.

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F(ab')₂ fragments can reduce the clinical symptoms in kittens infected with FCV.

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Passive transfer of equine immune antibodies significantly reduced virus titers in the lungs and trachea of kittens.

Antivenom effect on lymphatic absorption and pharmacokinetics of coral snake venom using a large animal model

Context: Historically, administration and dosing of antivenom (AV) have been guided primarily by physician judgment because of incomplete understanding of the envenomation process. As demonstrated previously, lymphatic absorption plays a major role in the availability and pharmacokinetics (PK) of coral snake venom injected subcutaneously, which suggests that absorption from subcutaneous tissue is the limiting step for venom bioavailability, supporting the notion that the bite site is an ongoing venom depot. This feature may underlie the recurrence phenomena reported in viperid envenomation that appear to result from a mismatch between venom and AV PK. The role of lymphatic absorption in neutralization of venom by AV administered intravenously remains unclear. Methods: The effect of AV on systemic bioavailability and neutralization of Micrurus fulvius venom was assessed using a central lymph-cannulated sheep model. Venom was administered by subcutaneous injection in eight sheep, four with and four without thoracic duct cannulation and drainage. Two hours after venom injection, AV was administered intravenously. Venom and AV concentrations in serum and lymph were determined by ELISA assay from samples collected over a 6-h period and in tissues harvested post-mortem. Results: After AV injection, venom levels in serum fell immediately to undetectable with a subsequent increase in concentration attributable to non-toxic venom proteins. In lymph, AV became detectable 6 min after treatment; venom levels dropped concurrently but remained detectable 4 h later. Post-mortem samples from the venom injection site confirmed the presence of venom near the point of injection. Neither venom nor AV was detected at significant concentrations in major organs or contralateral skin. Conclusions: Intravenous AV immediately neutralizes venom in the bloodstream and can extravasate to neutralize venom absorbed by lymph but this neutralization seems to be slow and incomplete. Residual venom in the inoculation site demonstrates that this site functions as a depot where it is not neutralized by AV, which allows the venom to remain active with slow delivery to the bloodstream for ongoing systemic distribution.

Use of irradiated elapid and viperid venoms for antivenom production in small and large animals

This work evaluated the feasibility of using toxoids obtained by gamma radiation in the production of antivenoms in small and large animals. Mixtures of African snake venoms from viperids or elapids were used. The viperid mixture contained the crude venom of five species of the genera Echis and Bitis, while the elapid mixture contained the crude venom of six species of the genera Naja and Dendroaspis. The viperid mixture had an LD₅₀ of 1.25 mg/kg in mice, and the elapid mixture had an LD₅₀ of 0.46 mg/kg. Both viper and elapid aqueous mixtures were subjected to Cobalt-60 gamma irradiation in three physical states: lyophilized, frozen and liquid. Radiation doses ranged from 0.5 to 100 kGy. The LD₅₀s of the lyophilized and frozen mixtures of both viperid and elapid mixtures remained unaltered with radiation doses as high as 100 kGy; nevertheless, in the liquid state, doses of 3.5 and 5.5 kGy reduced the venom toxicity of both the viperid and elapid mixtures to 7.25 mg/kg and 1.74 mg/kg; less toxic by factors of 5.8 and 3.8, respectively. Groups of four rabbits and three horses were immunized with either irradiated or non-irradiated mixtures. In vitro and in vivo analysis of the rabbit and horse sera revealed that neutralizing antibodies were produced against both irradiated (toxoids) and native venom mixtures. None of the animals used in this study, either immunized with native venom or toxoids, developed severe local effects due to the application of venoms mixtures. Gamma-irradiated detoxified venoms mixtures, under well-controlled and studied conditions, could be a practical alternative for the production of polyvalent equine serum with high neutralization potency against snake venoms.

Short-chain consensus alpha-neurotoxin: a synthetic 60-mer peptide with generic traits and enhanced immunogenic properties

The three-fingered toxin family and more precisely short-chain α-neurotoxins (also known as Type I α-neurotoxins) are crucial in defining the elapid envenomation process, but paradoxically, they are barely neutralized by current elapid snake antivenoms. This work has been focused on the primary structural identity among Type I neurotoxins in order to create a consensus short-chain α-neurotoxin with conserved characteristics. A multiple sequence alignment considering the twelve most toxic short-chain α-neurotoxins reported from the venoms of the elapid genera Acanthophis, Oxyuranus, Walterinnesia, Naja, Dendroaspis and Micrurus led us to propose a short-chain consensus α-neurotoxin, here named ScNtx. The synthetic ScNtx gene was de novo constructed and cloned into the expression vector pQE30 containing a 6His-Tag and an FXa proteolytic cleavage region. Escherichia coli Origami cells transfected with the pQE30/ScNtx vector expressed the recombinant consensus neurotoxin in a soluble form with a yield of 1.5 mg/L of culture medium. The 60-amino acid residue ScNtx contains canonical structural motifs similar to α-neurotoxins from African elapids and its LD₅₀ of 3.8 µg/mice is similar to the most toxic short-chain α-neurotoxins reported from elapid venoms. Furthermore, ScNtx was also able to antagonize muscular, but not neuronal, nicotinic acetylcholine receptors (nAChR). Rabbits immunized with ScNtx were able to immune-recognize short-chain α-neurotoxins within whole elapid venoms. Type I neurotoxins are difficult to isolate and purify from natural sources; therefore, the heterologous expression of molecules such ScNtx, bearing crucial motifs and key amino acids, is a step forward to create common immunogens for developing cost-effective antivenoms with a wider spectrum of efficacy, quality and strong therapeutic value.

Safety, potential efficacy, and pharmacokinetics of specific polyclonal immunoglobulin F(ab')₂ fragments against avian influenza A (H5N1) in healthy volunteers: a single-centre, randomised, double-blind, placebo-controlled, phase 1 study

BACKGROUND

Human infection with the avian influenza A H5N1 virus results in disease with a high fatality rate, against which antiviral treatments have limited efficacy. We aimed to investigate the safety, pharmacokinetics, and therapeutic potential of specific polyclonal immunoglobulin equine F(ab')₂ fragments raised against influenza A/Vietnam/1194/2004 virus (H5N1 subtype) in healthy volunteers.

METHODS

We did a randomised, double-blind, placebo-controlled, single-centre phase 1 study. In stage 1 (one infusion) and stage 2 (five infusions) of the trial, we randomly assigned healthy male volunteers to receive once-daily intravenous infusions of 0·85 U/kg body weight of F(ab')₂ or once-daily saline placebo. Randomisation was done centrally, with one block of four patients and one block for substitutes (three actives, one placebo) in stage 1, and two blocks of six patients (five actives and one placebo) and the same block for substitutes in stage 2. The primary objective was assessment of the clinical and laboratory safety of F(ab')₂, which was monitored for 22 days in the group that received one dose (assessments on days 0-2, 4, 8, 15, and 22) and 33 days in the group that received five doses (days 0-6, 8, 10, 12, 19, 26, and 33). A final post-study safety assessment was done at 120 days. We also assessed pharmacokinetic outcomes, and assayed haemagglutination and seroneutralisation activity. Analysis was done according to intention-to-treat. This trial is registered with ClinicalTrials.gov, number NCT02295813.

FINDINGS

We enrolled 16 healthy Asian men between Sept 28 and Dec 28, 2012, and randomly assigned 13 to one or five doses of F(ab')₂ and three to placebo. F(ab')₂ was well tolerated, and no deaths or serious adverse events occurred. Three patients had mild adverse events (one each of blepharospasm, sinusitis, and pyrexia). The pyrexia (38°C) was regarded as probably related to the infusion, and resolved after 37 min. Our laboratory assessments of blood and urine samples and physical examinations of heart rate, electrocardiogram readings, and weight showed no clinically significant safety issues. Mean peak plasma concentrations were 19·3 μg/mL (SD 3·5) with the one dose schedule and 23·0 μg/mL (4·5) with the five-dose schedule. F(ab')₂ were still detectable in plasma on average up to 5 days after five doses. Haemagglutination inhibition was only increased after the third dose, but in-vitro seroneutralisation activity was transiently increased after each of the five doses to concentrations regarded as clinically beneficial in infected patients.

INTERPRETATION

F(ab')₂ showed good safety, tolerability, and therapeutic potential for managing of H5N1 exposed patients.

FUNDING

Fab'entech.

IgY pharmacokinetics in rabbits: implications for IgY use as antivenoms

This paper presents the first study of chicken IgY pharmacokinetics (PK) in rabbits. We measured IgY blood serum concentrations using a specific high sensitivity ELISA method. The fast initial component observed when studying horse Fab, F(ab')2 or IgG was absent from IgY PK. During the first 80 min of observation there was only a single slow exponential decay, which sped up afterward to the point that IgY became undetectable after 216 h of observation; due to this time course, PK parameters were determined with trapezoidal integration. The most significant IgY pharmacokinetic parameters determined were (all presented as medians and their 95% confidence interval): Area Under the Curve = 183.8 (135.2, 221.5) mg·h·L(-1); Distribution volume of the central compartment·[Body Weight (BW)](-1) = 46.0 (21.7, 70.3) mL·kg(-1); Distribution volume in steady state·BW(-1) = 56.8 (44.4, 68.5) mLkg(-1); Mean Residence Time = 40.1 (33.6, 48.5) h; Total plasma clearance·BW(-1) = 1.44 (1.15, 1.66) mL·h(-1)·kg(-1). Anti IgY IgG titers determined by ELISA increased steadily after 72 h, and reached 2560 (1920, 5760) dilution(-1) at 264 h; anti-chicken IgG concentrations rose up to 3.19 (2.31, 6.17) μg/mL in 264 h. Our results show that IgY PK lacks the fast initial decay observed in other PK studies using horse IgG, F(ab')2 or Fab, remains in the body 39.0 (28.7, 47.2) % much as IgG and is ≈3 times more immunogenic that horse IgG in rabbits.

Subacute coagulopathy in a randomized, comparative trial of Fab and F(ab')2 antivenoms

BACKGROUND

Envenomation by pit vipers is associated with coagulation disorders including hypofibrinogenemia and thrombocytopenia. These abnormalities correct following antivenom treatment during the acute phase of the disease. Delayed or recurrent coagulation abnormalities have been reported following use of Fab antivenom, resulting in risk of hemorrhage or death.

METHODS

We hypothesized that the longer plasma persistence of F(ab')2 antivenom, relative to Fab, in patients at risk of coagulopathy would result in decreased venonemia and coagulopathy one week after treatment. We conducted a Phase 2, randomized comparative clinical trial of rattlesnake bitten adults presenting for care in Tucson, Arizona, USA. Patients were randomly assigned to receive either Fab or F(ab')2 antivenom using a predefined treatment schedule. Endpoints included platelet counts, fibrinogen levels, and venom and antivenom ELISAs. Measurements were conducted at baseline and at various times over the following two weeks.

RESULTS

Twelve patients were studied, with 6 randomly assigned to each treatment group. Early response of platelet counts, fibrinogen, and venom levels to acute treatment was similar in the two groups. One week following treatment, platelet counts and fibrinogen levels were lower in the Fab group than in the F(ab')2 group, following a characteristic pattern that reached its lowest point approximately one week after initial treatment. Venom levels dropped below detection limits in all patients following initial treatment but subsequently rebounded into the measurable range in 4 of 6 Fab cases. F(ab')2 antivenom levels demonstrated a longer plasma persistence than Fab levels, with a less rapid drop during the two days following treatment. Two patients in the Fab group had significant adverse events involving coagulation abnormalities, for which additional antivenom was administered following the initial treatment period.

CONCLUSIONS

Following the acute phase of presentation and treatment for pit viper envenomation, there appears to be a roughly 2-week subacute phase of the disease during which ongoing presence of venom may result in serious delayed or recurrent coagulation defects. Late hypofibrinogenemia and thrombocytopenia are associated with recurrent venonemia and drop in antivenom levels. This pattern was apparent in patients treated with Fab antivenom but was not seen among F(ab')2 recipients in this Phase 2 study, consistent with pharmacokinetic differences between the two products. Improved understanding of Fab pharmacokinetics is important for the management of coagulopathy-prone pit viper envenomation. Use of F(ab')2 antivenom may prevent recurrent venom effects, but larger studies are necessary for statistical confirmation of this observation.

Role of the animal model on the pharmacokinetics of equine-derived antivenoms

Antivenom pharmacokinetics has been studied in heterologous models in which the animal species used as immunoglobulin source is different from that used as recipient. In these models, after intravenous administration of antivenom, the plasma concentration of immunoglobulins shows a rapid initial declining-phase followed by a slower terminal-phase, which has been associated with antivenom distribution and elimination, respectively. We have compared pharmacokinetic parameters for equine-derived antivenom in homologous (horse) and heterologous (cow) models. It was found that the maximum concentration is lower in cows than in horses. Additionally, the steady-state distribution volume is higher in cows as compared to horses. On the other hand, models were not different in the time required to reach the maximum concentration, the area under the concentration/time curve, the half-life of decay during the slowest phase, the systemic clearance and the mean residence time. Similar results were obtained in a rabbit model, in which the pharmacokinetics was also affected by passive immunization of rabbits with anti-equine IgG. We conclude that, in addition to other physiological differences (e.g. cardiac frequency, plasmatic volume, glomerular filtration rate, etc.) between animal models, the ability to remove foreign immunoglobulins might influence the way in which the plasma concentration of antivenom decreases over time, thereby distorting the pharmacokinetic predictions based on non-compartmental models.

Pharmacokinetics of a F(ab')2 scorpion antivenom administered intramuscularly in healthy human volunteers

This paper presents the first study of F(ab')(2) scorpion antivenom pharmacokinetics in humans after intramuscular (im) administration. The specific anti-Centruroides scorpion antivenom was used in 6 human healthy volunteers. The fabotherapeutic was administered as a 47.5mg im bolus. Blood samples were drawn at 0, 5, 15, 30, 45, 60 , 90, 120, and 180 min, 6h and at 1, 2, 3, 4, 10 and 21 days after antivenom administration. We measured antivenom concentrations in serum using a specific high sensitivity ELISA method for F(ab')(2). Antivenom concentration in serum was fit to a 3 compartment model (inoculation site, plasma and extra vascular extracellular space), it was assumed that the venom may also be irreversibly removed from plasma. Calculated time course of antivenom content shows that at any time no more that 16.6 (5.3, 31.9)% (median and 95% confidence interval) of the antivenom bolus is present in plasma. The time to peak plasma [F(ab')(2)] was 45 (33, 74) h. The most significant antivenom pharmacokinetic parameters determined were: AUC(im,∞)=803 (605, 1463) mg·h·L(-1); V(c)=8.8 (2.8, 23.6) L; V(ss,im)=55 (47, 64) L; MRT(im)=776(326, 1335) h; CL(t)=3.7 (0.6, 1.9) mL·min(-1); f(im,)V(ss)=0.300 (0.153, 0.466). Comparing these parameters with the ones obtained intravenously by Vázquez et al., the parameters were more disperse between subjects, determined with more uncertainty in each individual subject, and the peak F(ab')(2) in plasma occurred with considerable delay; all indicating that the IM route should not be used to administer the antivenom, with the possible exception of cases occurring very far from hospitals, as an extreme means to provide some protection before the IV route becomes available.