Ricin: Chemistry, Sources, Exposures, Toxicology and Medical Aspects

The chapter covers the origins of ricin toxin, which is present in the seeds of the many cultivars of the castor oil plant. The structure and biogenesis of the dimeric (A and B chain toxin) ricin (RCA60) is described, compared with the related, but less toxic, Ricinus agglutinin (RCA120) and the toxic activity of ricin, the N-glycosidase activity of the A chain, is explained. The intoxication process is further described and developed through in vitro and in vivo studies, which then focus on several possible routes of exposure. These include inhalation, that route which has been the primary focus of military-oriented research through oral and parenteral routes of intoxication; histopathology and symptomatology are described, using evidence from human cases of ricin poisoning, wherever possible. Information is then presented on the development of medical countermeasures against ricin poisoning, including pretreatment approaches (vaccines) and postexposure approaches, which include antitoxins. More novel and currently research-based studies are considered, including inhibitors of N-glycosidase, substrate competitors or approaches to interfere with the binding of the ricin B chain to galactose moieties. Keywords: ricinus cultivars; structure; biogenesis; inhalation toxicology; oral toxicology; parenteral toxicology; medical countermeasures; vaccines; antitoxin; inhibitor studies