Ricin distribution

In oral administration of ricin in mice, the approximate LD50 dose is 20mg/kg with time to death up to 85 h (Fodstad et al, 1979). In a rat study, ricin was absorbed in the lymphatic blood vessels and largely distributed in the spleen and liver within 2 h of ingestion (Ishiguro et al, 1983). The study also demonstrated that up to 72 h after ingestion, approximately 20-45% of ricin is excreted in the feces (Ishiguro et al, 1992). 

Fodstad, O., Olsnes, S., Pihl, A. (1976). Toxicity, distribution and elimination of the cancerostatic lectins abrin and ricin after parenteral injection into mice. Br. J. Cancer 34 418-25. Fodstad, O., Johannessen, J.V., Schjerven, L., Pihl, A. (1979). Toxicity of abrin and ricin in mice and dogs. J. Toxicol. Environ. Health 5 1073-84. 

Glycoproteins are large molecules and are poorly absorbed from the gastrointestinal tract. Many cell surfaces contain receptors specific for ricin and the toxin is taken up by active transport. The primary site of distribution of ricin is the liver, spleen, and adrenal cortex in the mouse. A high concentration was also found in the bone marrow (Godal etal, 1984). In rats, abrin is distributed primarily to the liver (12%) and spleen (Lin et al, 1970, 1971). 

The glycoproteins (ricin) are poorly absorbed from the gastrointestinal tract however, once absorbed, they most likely follow a distribution pattern similar to that of albumin. Many cell surfaces contain receptors specific for the ricin molecules. This molecule consists of two subunits, A and B, bound by a disulfide link. When this link is broken, the B subunit binds to galactose-containing receptors in the cell wall and is transported intracellularly. The A subunit inhibits protein synthesis. The liver, spleen, adrenal cortex, and bone marrow are the primary sites of distribution. The biotransformation and elimination of toxalbumins are poorly understood. The elimination half-life in one patient was 2 days. The reported disappearance of ricin from the plasma is according to first-order kinetics when... 

Movement of the biological material ricin with soil-size fractions are shown in Figures 4.6 and 4.7. Studies on peanut (Arachis hypogaea) seed lectin show similar results (Zartman et al. 2005). These lectin data are similar in distribution to published values (Ravi et al. 2004). The inhalation of dust generated from ricin-contami-nated soils could pose a serious hazard to war fighters. Work of A. H. Corwin cited in Lamanna (1961) stated that ricin particles with a median diameter of 2 /(ui are 2.75 times as toxic as particles with a maximal particle size of 4.2 pm. 

Roy et al. (2003) compared the lethahty of different particle size distributions of ricin aerosols in laboratory mice aerosols composed of particles in a size distribution >3 p.m were significantly less... 

In the absence of an unambiguous history of ricin exposure, the preferred diagnostic method is specific immunoassay of ricin in serum, respiratory secretions, or other clinical samples associated with poisoning. Most of the methods described for ricin detection are experimental or are under development. The CDC and the Federal Laboratory Response Network have the capability to detect ricin in environmental specimens using validated polymerase chain reaction (PCR) tests and time-resolved immunofluorescence assays, with cell-based bioassays to confirm ricin activity. The U.S. Department of Defense has produced experimental field immunoassays, but commercial distribution of field test kits currently is limited. 

Fodstad, O., Olsnes, S. and Pihl, A. (1976) Toxicity, distribution and elimination of the cancerostatic lectins abrin and ricin after parenteral injection into mice. Br J Cancer, 34, 418 425. 

Ramsden CS, Drayson MT and Bell EB (1989). The toxicity, distribution and excretion of ricin holo-toxin in rats. Toxicology, 55, 161-171. 

The persistent chemical agents which could be used in a foodborne attack, aimed at poisoning human consumers, include the nerve agent VX, any of the mycotoxins—aflatoxin, T-2 toxin, nivalenol (see Appendix A for discussion of their toxicology)—and compounds such as ricin produced from the castor bean plant. Chapter 5 should be consulted for a full discussion on natural toxins. These chemicals, combined with the biotoxins listed above, could potentially be used in the food supply. This would not be an easy task since many of these agents are toxic to animals and thus might kill the host, preventing dissemination into the food distribution system. 

Ramsden C, Drayson M, Bell E. The toxicity, distribution, and excretion of ricin holotoxin in rats. Toxicology. 1989 55 161-171. 

T. from plants (phytotoxins) include both high- and low-molecular weight substances. Examples of the former are the lectins distributed in legumes (abrin, con-canavalin A, crotin, phasin, ricin). The low-molecular weight plant T. are more numerous and of greater diversity, including the cardiac glycosides, saponins. 

In summary, nutritional improvement may result from inactivation of trypsin inhibitors and introduction of new disulfide bonds via sulfhydryl-disulfide interchange and oxidation reaction among added thiols, inhibitors, and structural proteins. Such an approach should be useful for inactivating related disulfide-containing toxic compounds such as lectins (hemagglutinins) and ricin, widely distributed in legumes and castor beans, respectively. 

Lectins are widely distributed in both the plant and animal kingdoms, and are even present in some microorganisms. The maximum amounts are found in the seeds of plants. The most frequently occurring lectins, their content and important properties are shown in Table 10.21. Some lectins traditionally have trivial names, for example the lectin (albumin) of castor seeds is ricin, and the lectin of jack beans (Canavalia ensiformis, Fabaceae) is trivially called concavalin A. 

Foxwell, B.M., Blakey, D.C., Brown, A.N., et al., 1987. The preparation of deglyco-sylated ricin by recombination of glycosidase-treated A- and B-chains effects of deglycosylation on toxicity and in vivo distribution. Biochim. Biophys. Acta 923, 59-65. 

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