Studying the differential efficacy of postsymptom antitoxin treatment in type A versus type B botulism using a rabbit spirometry model

Abstract

Botulinum neurotoxin (BoNT) serotypes A, B and E are responsible for most cases of human botulism. The only approved therapy for botulism is antitoxin treatment administered to patients after symptom onset. However, a recent meta-analysis of antitoxin efficacy in human botulism cases over the past century concluded that a statistically significant reduction in mortality is associated with the use of type E and type A antitoxin, but not with type B antitoxin. Animal models could be highly valuable in studying postsymptom antitoxin efficacy (PSAE). However, the few attempts to evaluate PSAE in animals relied on subjective observations and showed ∼50% protection. Recently, we developed a novel spirometry model for the quantitative evaluation of PSAE in rabbits and used it to demonstrate full protection against BoNT/E. In the current study, a comparative evaluation of PSAE in botulism types A and B was conducted using this quantitative respiratory model. A lethal dose of each toxin induced a comparable course of disease both in terms of time to symptoms (TTS, 41.9±1.3 and 40.6±1.1 h, respectively) and of time to death (TTD, 71.3±3.1 and 66.3±1.7 h, respectively). However, in accordance with the differential serotypic PSAE observed in humans, postsymptom antitoxin treatment was fully effective only in BoNT/A-intoxicated rabbits. This serotypic divergence was reflected by a positive and statistically significant correlation between TTS and TTD in BoNT/A-intoxicated rabbits (r=0.91, P=0.0006), but not in those intoxicated with BoNT/B (r=0.06, P=0.88). The rabbit spirometry system might be useful in the evaluation toolkit of botulism therapeutics, including those under development and intended to act when antitoxin is no longer effective.

A Rabbit Model for Prolonged Continuous Intravenous Infusion Via a Peripherally Inserted Central Catheter

“…The simplicity of using a PICC-based prolonged continuous infusion via the marginal ear vein, together with the power of daily spirometry in unrestrained rabbits, can serve as a valuable tool in various research fields, for example, when respiration monitoring is needed. Recently, we established a rabbit spirometry model to monitor respiration and control the treatment timing following exposure to botulinum toxins (BoNTs), the most poisonous substances known in nature ( Diamant et al, 2018 ; Torgeman et al, 2018 ). Spirometry was shown in these studies to serve as an accurate, quantitative, and objective means to detect early symptoms of botulism in rabbits, and deviation from the normal minute volume (Mv) following exposure to BoNT was found to be the earliest symptom to be measured among other spirometry-related parameters.…”

“…Spirometry was shown in these studies to serve as an accurate, quantitative, and objective means to detect early symptoms of botulism in rabbits, and deviation from the normal minute volume (Mv) following exposure to BoNT was found to be the earliest symptom to be measured among other spirometry-related parameters. Accurate quantification of the postintoxication Mv decline by a spirometer qualified the Mv symptom to become a reliable clinical symptom of botulism ( Diamant et al, 2018 ; Torgeman et al, 2018 ). Currently, we are involved in an effort to test a small molecule inhibitor (SMI) against BoNT by continuous infusion using our PICC-based rabbit model via the marginal ear vein.…”

“…Respiratory data were collected and analyzed as detailed previously ( Diamant et al, 2018 ; Torgeman et al, 2018 ). Briefly, Rabbits were acclimated to spirometry measurements for several days while carrying minipumps on their backs with disconnected syringes filled with 50 ml of water (imitating the conditions during the infusion period).…”

“…Respiration was individually monitored prior to and during the infusion period using a spirometer. This mode of respiration monitoring in unrestrained rabbits has recently been demonstrated to be an efficient quantitative tool to detect the manifestation of botulism symptoms ( Diamant et al, 2018 ; Torgeman et al, 2018 ).…”

Isolation and characterization of a highly specific monoclonal antibody targeting the botulinum neurotoxin type E exposed SNAP-25 neoepitope

“…Standard therapy for botulism in adults, including in cases of BoNT/E intoxications, involves treatment with antitoxin preparations [12, 13] derived from hyperimmune horses (A human antitoxin preparation is also available for infant botulism cases involving BoNT/A or BoNT/B [14]). The potencies of both the pharmaceutical antitoxin and the toxicity of BoNT/E preparations intended for horse immunization, are determined in vivo by the pharmacopeia mouse neutralization assay (PMNA) [15] and by the mouse bioassay (MBA) [16], respectively. However, these in vivo assays require a large number of laboratory animals, and hence development of alternative in vitro methods to measure activity of BoNT/E and concentration of neutralizing antibodies is imperative.…”