Quantitative comparison on the refinement of horse antivenom by salt fractionation and ion-exchange chromatography

A Quest for a Universal Plasma-Derived Antivenom Against All Elapid Neurotoxic Snake Venoms

This review describes the research aimed at the development of universal antivenom against elapid neurotoxic snake venoms. The antivenoms produced in Thailand in the 1980s were of low potency, especially against the elapid venoms. This was thought to be due to the low immunogenicity of the α-neurotoxins, which are the most lethal toxins in these venoms. Comparisons of various α-neurotoxin conjugates and polymers, and also different immunological adjuvants, showed that the adjuvant used is the major determinant in the antibody response in horses. The potent Freund's adjuvant was not used due to its severe local side-effect in horses. Therefore, a novel immunization protocol termed 'low dose, low volume multi-site' was developed for use in horses. This immunization protocol has led to the production of highly potent monospecific antivenoms against several elapid and viperid venoms, and two potent polyspecific antivenoms, one against 4 neurotoxic and another against 3 hematotoxic venoms. The immunization protocol has also led to other improvements in antivenom production including: several fold increases in antiserum potency, a reduction in the time required to reach therapeutically useful antibody titers, a 90% reduction in the amount of venom used, and 100% of the horses responding to the immunization program. This development is partly responsible for significant decrease in the Thailand's annual snakebite death toll from a few dozens to mostly nil in recent years. Finally, a simple and novel immunization strategy, using a 'diverse toxin repertoire' composed of numerous elapid toxin fractions as immunogen, was proposed and tested. This immunization procedure has resulted in the successful production of a widely paraspecific antiserum against at least 36 neurotoxic venoms of 28 species encompassing 10 genera and from 20 countries on four continents, and possibly against all elapid venoms with α-neurotoxins as the lethal toxins. These results indicate that, with optimizations of the composition of the 'diverse toxin repertoire', the immunization scheme and antibody fractionation to increase the antivenom neutralizing potency, an effective universal antivenom against the neurotoxic elapid snakes of the world can be produced.

Quality-Related Properties of Equine Immunoglobulins Purified by Different Approaches

Whole IgG antivenoms are prepared from hyperimmune animal plasma by various refinement strategies. The ones most commonly used at industrial scale are precipitation by sodium or ammonium sulphate (ASP), and caprylic acid precipitation (CAP) of non-immunoglobulin proteins. The additional procedures, which have so far been used for experimental purposes only, are anion-exchange (AEX) and cation-exchange chromatography (CEX), as well as affinity chromatography (AC) using IgG’s Fc-binding ligands. These protocols extract the whole IgG fraction from plasma, which contains both venom-specific and therapeutically irrelevant antibodies. Such preparations represent a complex mixture of various IgG subclasses whose functional and/or structural properties, as well as relative distribution, might be affected differently, depending on employed purification procedure. The aim of this work was to compare the influence of aforementioned refinement strategies on the IgG subclass distribution, venom-specific protective efficacy, thermal stability, aggregate formation and retained impurity profile of the final products. A unique sample of Vipera ammodytes ammodytes specific hyperimmune horse plasma was used as a starting material, enabling direct comparison of five purification approaches. The highest purity was achieved by CAP and AC (above 90% in a single step), while the lowest aggregate content was present in samples from AEX processing. Albumin was the main contaminant in IgG preparations obtained by ASP and CEX, while transferrin dominantly contaminated IgG sample from AEX processing. Alpha-1B-glycoprotein was present in CAP IgG fraction, as well as in those from ASP- and AEX-based procedures. AC approach induced the highest loss of IgG(T) subclass. CEX and AEX showed the same tendency, while CAP and ASP had almost no impact on subclass distribution. The shift in IgG subclass composition influenced the specific protective efficacy of the respective final preparation as measured in vivo. AC and CEX remarkably affected drug’s venom-neutralization activity, in contrary to the CAP procedure, that preserved protective efficacy of the IgG fraction. Presented data might improve the process of designing and establishing novel downstream processing strategies and give guidance for optimization of the current ones by providing information on potency-protecting and purity-increasing properties of each purification principle.

Simple Protocol for immunoglobulin G Purification from Camel “Camelus dromedarius” Serum

The present study aimed to describe and standardize a simple and efficient protocol for purification of camel IgG from serum, which can be applied for Camilidae antibody production in research laboratories, the preindustrial stage. Camel serum IgG was separated with caprylic acid and ammonium sulfate, then the effect of four variables studied: caprylic acid concentration, pH, stirring time, and stirring intensity. Camel IgG prepared by standardized caprylic acid fractionation method for camel serum was compared with commercial anti-sera products. Camel IgG purification from undiluted sera using caprylic acid at concentration of 8% v/v gave the best results. Purification at different pH values using caprylic acid at 8% v/v revealed that pH 5.5 was optimal. Investigating purification at different stirring time intervals using 8% v/v caprylic acid at pH 5.5 demonstrated that stirring for 90 min gave the optimum results. Finally, studying purification at different stirring intensities using 8% v/v caprylic acid at pH 5.5 for 90 min, the best stirring intensity was at 450 rpm. Overall, the results suggest that caprylic acid purification of camel serum IgG is more effective and safe than ammonium sulfate method in simplicity, purity, and lower non-IgG proteins in the final preparation with lower protein aggregates.

New method to produce equine antirabies immunoglobulin F(ab')₂ fragments from crude plasma in high quality and yield

Rabies is still a major cause of human deaths in several developing countries. According to the World Health Organization, administration of antirabies serum or antirabies immunoglobulin is recommended for patients who have experienced a category-III exposure to rabies. Improvement of antirabies immunoglobulin production is required to enhance safety and efficacy of the products. In this paper, a new method to produce equine antirabies immunoglobulin F(ab')(2) fragments from crude plasma is proposed. First, protein G affinity chromatography was used to purify IgG from equine plasma. Moreover, purification of IgG was shown to facilitate its digestion by pepsin. Compared to the direct digestion of crude plasma, a lower amount of pepsin and a shorter digestion time were required to completely digest the purified IgG to F(ab')(2). Complete digestion of purified IgG to F(ab')(2) was achieved at a pepsin/IgG (w/w) ratio of 5:45 with preservation of structure and potency. Finally, purification of F(ab')(2) was accomplished by a combination of protein A affinity chromatography and ultrafiltration with a 50-kDa nominal molecular weight cut-off membrane. The new process resulted in 68.9±0.6 (%) total recovery of F(ab')(2) and a F(ab')(2) product of high potency.

Assessment of the viral safety of antivenoms fractionated from equine plasma

Antivenoms are preparations of intact or fragmented (F(ab′)₂ or Fab) immunoglobulin G (IgG) used in human medicine to treat the severe envenomings resulting from the bites and stings of various animals, such as snakes, spiders, scorpions, or marine animals, or from the contact with poisonous plants. They are obtained by fractionating plasma collected from immunized horses or, less frequently, sheep. Manufacturing processes usually include pepsin digestion at acid pH, papain digestion, ammonium sulphate precipitation, caprylic acid precipitation, heat coagulation and/or chromatography. Most production processes do not have deliberately introduced viral inactivation or removal treatments, but antivenoms have never been found to transmit viruses to humans. Nevertheless, the recent examples of zoonotic diseases highlight the need to perform a careful assessment of the viral safety of antivenoms.

This paper reviews the characteristics of equine viruses of antivenoms and discusses the potential of some manufacturing steps to avoid risks of viral contamination. Analysis of production parameters indicate that acid pH treatments and caprylic acid precipitations, which have been validated for the manufacture of some human IgG products, appear to provide the best potential for viral inactivation of antivenoms. As many manufacturers of antivenoms located in developing countries lack the resources to conduct formal viral validation studies, it is hoped that this review will help in the scientific understanding of the viral safety factors of antivenoms, in the controlled implementation of the manufacturing steps with expected impact on viral safety, and in the overall reinforcement of good manufacturing practices of these essential therapeutic products.

Immunochemical and biochemical comparisons of equine monovalent and polyvalent snake antivenoms

Although the merit of polyvalent antivenoms is well-recognized, there is still doubt in some medical circles as to the relative efficacy and the propensity to cause adverse reactions of polyvalent (pAV) as compared to monovalent (mAV) antivenoms. Immunochemical and biochemical comparisons of equine polyvalent and monovalent antivenoms prepared under the same immunization protocols were therefore made. These antivenoms were prepared against Naja kaouthia (NK), Ophiophagus hannah (OH) and Bungarus fasciatus (BF) venoms. SDS-PAGE analysis of both types of antivenoms showed similar serum protein profiles. The total amount of immunoglobulin (IgG(T)+IgG) in pAVs was slightly but significantly higher than that of mAVs, while the total serum protein content in mAVs was slightly but significantly higher than that of pAVs. The amounts of total hyperimmune IgG(T), determined by ELISA, were similar in mAVs and pAVs. pAVs contained specific antibodies against the principal NK postsynaptic toxin (NK 3) to the same extent as that observed with the anti-N. kaouthia mAV. The antibodies against OH and BF principal postsynaptic toxins (OH II and BF IX) in pAVs were significantly higher than those of the corresponding anti-O. hannah and anti-B. fasciatus mAVs. These results were in concordance with the comparable in vivo neutralization activities of mAVs and pAV previously reported. The apparent dissociation constant (Kd) of anti-OH II antibody in pAVs was comparable to that of the anti-O. hannah mAVs. The apparent K(d)s of anti-NK 3 and anti-BF IX antibodies in the corresponding mAVs were slightly lower than those in pAVs. The Kd values were all in nM range and were considered to be high affinity binding. It is concluded that pAVs could be prepared with potency and protein contents and thus the propensity to cause adverse reaction that were comparable to those of mAVs.

Anticomplementary activity of equine whole IgG antivenoms: comparison of three fractionation protocols

Early adverse reactions occur in a number of patients treated with heterologous antivenoms and have been associated with anticomplementary activity (ACA). In order to reduce the ACA of equine whole IgG antivenoms produced by caprylic acid fractionation, three different fractionation protocols were compared: (a) routine caprylic acid fractionation; (b) caprylic acid fractionation followed by beta-propiolactone treatment; and (c) caprylic acid fractionation followed by ion-exchange chromatography using a quaternary ammonium membrane. The three protocols yielded products with similar physicochemical characteristics and anti-Bothrops asper venom antibody titers, except that ion-exchange purified antivenom had a lower protein concentration. Antivenoms fractionated by using beta-propiolactone or filtration through quaternary ammonium membrane had a significantly reduced in vitro ACA. A preparation of caprylic acid-fractionated antivenom was heated in order to induce the formation of protein aggregates; however, its ACA was similar to non-heated antivenom. None of the antivenoms affected the hemolytic activity of serum complement in rabbits after a bolus intravenous administration. It is concluded that (a) beta-propiolactone and quaternary ammonium membranes significantly reduce in vitro ACA of caprylic acid-fractionated equine antivenom, and (b) the validity of in vitro ACA as a predictor of EAR needs to be reexamined in clinical and experimental studies, since it may not adequately predict in vivo complement activation by antivenoms.

Pharmacokinetic-pharmacodynamic relationships of immunoglobulin therapy for envenomation

Parenteral administration of horse- and sheep-derived antivenoms constitutes the cornerstone in the therapy of envenomations induced by animal bites and stings. Depending on the type of neutralising molecule, antivenoms are made of: (i) whole IgG molecules (150 kDa), (ii) F(ab')(2) immunoglobulin fragments (100 kDa) or (iii) Fab immunoglobulin fragments (50 kDa). Because of their variable molecular mass, these three types of antivenoms have different pharmacokinetic profiles. Fab fragments have the largest volume of distribution and readily reach extravascular compartments. They are catabolised mainly by the kidney, having a more rapid clearance than F(ab')(2) fragments and IgG. On the other hand, IgG molecules have a lower volume of distribution and a longer elimination half-life, showing the highest cycling through the interstitial spaces in the body. IgG elimination occurs mainly by extrarenal mechanisms. F(ab')(2) fragments display a pharmacokinetic profile intermediate between those of Fab fragments and IgG molecules. Such diverse pharmacokinetic properties have implications for the pharmacodynamics of these immunobiologicals, since a pronounced mismatch has been described between the pharmacokinetics of venoms and antivenoms. Some venoms, such as those of scorpions and elapid snakes, are rich in low-molecular-mass neurotoxins of high diffusibility and large volume of distribution that reach their tissue targets rapidly after injection. In contrast, venoms rich in high-molecular-mass toxins, such as those of viperid snakes, have a pharmacokinetic profile characterised by a rapid initial absorption followed by a slow absorption process from the site of venom injection. Such delayed absorption has been linked with recurrence of envenomation when antibody levels in blood decrease. This heterogeneity in pharmacokinetics and mechanism of action of venom components requires a detailed analysis of each venom-antivenom system in order to determine the most appropriate type of neutralising molecule for each particular venom. Besides having a high affinity for toxicologically relevant venom components, an ideal antivenom should possess a volume of distribution as similar as possible to that of the toxins being neutralised. Moreover, high levels of neutralising antibodies should remain in blood for a relatively prolonged time to assure neutralisation of toxins reaching the bloodstream later in the course of envenomation, and to promote redistribution of toxins from extravascular compartments to blood. Additional studies are required on different venoms and antivenoms in order to further understand the pharmacokinetic-pharmacodynamic relationships of antibodies and their fragments and to optimise the immunotherapy of envenomations.

Fractionation of equine antivenom using caprylic acid precipitation in combination with cationic ion-exchange chromatography

A combined process of caprylic acid (CA) precipitation and ion-exchange chromatography on SP-Sepharose was studied as a means to fractionate pepsin-digested horse antivenom F(ab')(2) antibody. In the CA precipitation, the optimal concentration for fractionation of F(ab')(2) from pepsin-digested horse plasma was 2%, in which 89.61% of F(ab')(2) antibody activity was recovered in the supernatant with 1.5-fold purification. A significant amount of pepsin was not precipitated and remained active under these conditions. An analytical cation exchanger Protein-Pak SP 8HR HPLC column was tested to establish optimal conditions for the effective separation of IgG, albumin, pepsin and CA from the F(ab')(2) product. From these results, the supernatant from CA precipitation of pepsin-digested plasma was subjected to a SP-Sepharose column chromatography using a linear salt gradient. With stepwise elution, a peak containing F(ab')(2) antibody could be obtained by elution with 0.25 M NaCl. The total recovery of antibody was 65.56% with 2.91-fold purification, which was higher than that achieved by ammonium sulfate precipitation. This process simultaneously and effectively removed residual pepsin, high molecular weight aggregates and CA in the final F(ab')(2) product, and should be suitable for large-scale fractionation of therapeutic equine antivenoms.

A protocol for 'enhanced pepsin digestion': a step by step method for obtaining pure antibody fragments in high yield from serum

The digestion of ovine antiserum under acidic conditions (pH 3.5) by pepsin is highly effective at reducing all unwanted serum components to low molecular weight (< or =13 kDa) fragments while leaving the approximately 100-kDa F(ab')(2) intact. The pH is then raised to 6 to stop further digestion and the reaction mixture centrifuged or filtered to remove any insoluble contaminants. Next, unwanted low molecular weight fragments are removed by diafiltration with a 30-kDa nominal molecular weight cut-off membrane leaving an F(ab')(2) solution contaminated only with some pepsin and a small amount of the aggregated low molecular weight fragments. Material of this purity is suitable for many applications but, since all the contaminants are highly acidic, they can be easily removed by passage down an anion-exchange column to yield F(ab')(2) that is essentially free from pepsin and aggregates with a typical purity of over 96% and yields of 16-19 g/l serum. When an antivenom was processed, approximately 78% of the original serum's toxin neutralising capacity was recovered. This simple, high yield protocol for processing serum to highly purified F(ab')(2) avoids the need for an initial or any subsequent salt precipitation step and can be utilised for either bench or large scale production. If required, a mild reducing agent may be used finally to create Fab fragments.

Enhanced pepsin digestion: a novel process for purifying antibody F(ab')(2) fragments in high yield from serum

Enzyme-cleaved antibodies are used widely for the treatment of envenoming. Such products should comprise only 'highly pure' immunoglobulin fragments since Fc or other contaminating protein fragments or their aggregates may lead to side effects. The digestion of ovine antiserum and its purified IgG were investigated using pepsin and trypsin. Trypsin was effective at digesting purified IgG but unsuitable for the direct digestion of serum. In contrast, pepsin was highly effective at digesting all unwanted serum components to low molecular weight (< or =13 kDa) fragments while leaving the approximately 100-kDa F(ab')(2) intact. The optimum pH for pepsin digestion was between 3.25 and 3.50. The effects of salt concentration and pH on the digestion products were investigated by size exclusion chromatography under various conditions, which revealed a pH-dependent aggregation of some of the low molecular weight Fc and non-IgG fragments. These high molecular weight aggregates were not shown by SDS-PAGE. Unwanted low molecular weight fragments could be removed simply by diafiltration with a 30-kDa nominal molecular weight cutoff membrane and piperazine buffer (containing 150 mM NaCl, pH 6), leaving an F(ab')(2) solution contaminated only with some pepsin and a small amount of the aggregated low molecular weight fragments. These highly acidic contaminants were then removed easily using an anion exchange column and the F(ab')(2) produced following a subsequent concentration step was essentially free from pepsin and aggregates with a purity of over 96% and a yield of 19.3 g F(ab')(2)/l serum. This novel, high yield method for processing serum to highly pure F(ab')(2) avoids salt precipitation and centrifugation and should be suitable for large-scale production.