Establishment of a Novel Oral Murine Model of Ricin Intoxication and Efficacy Assessment of Ovine Ricin Antitoxins

Ricin, produced from the castor beans of Ricinus communis, is a cytotoxin that exerts its action by inactivating ribosomes and causing cell death. Accidental (e.g., ingestion of castor beans) and/or intentional (e.g., suicide) exposure to ricin through the oral route is an area of concern from a public health perspective and no current licensed medical interventions exist to protect from the action of the toxin. Therefore, we examined the oral toxicity of ricin in Balb/C mice and developed a robust food deprivation model of ricin oral intoxication that has enabled the assessment of potential antitoxin treatments. A lethal oral dose was identified and mice were found to succumb to the toxin within 48 h of exposure. We then examined whether a despeciated ovine F(ab')₂ antibody fragment, that had previously been demonstrated to protect mice from exposure to aerosolised ricin, could also protect against oral intoxication. Mice were challenged orally with an LD₉₉ of ricin, and 89 and 44% of mice exposed to this otherwise lethal exposure survived after receiving either the parent anti-ricin IgG or F(ab')₂, respectively. Combined with our previous work, these results further highlight the benefit of ovine-derived polyclonal antibody antitoxin in providing post-exposure protection against ricin intoxication.