Ricin lethal dose

Eiklid, K., Olsnes, S., and Pihl, A. (1980) Entry of lethal doses of abrin, ricin, and modeccin into the cytosol of Hela cells. Exp. Cell Res. 126, 321-326. 

Balint (1974) and later Zhang et al. (1994) foimd that at the lethal dose in rabbits, ricin caused hemorrhage and necrosis. Christiansen et al. (1994) foimd that the release of norepinephrine from sympathetic nerves in the vasculature is not impaired by ricin. The CDC, under signs and symptoms of ricin poisoning that may be encountered, cite cardiovascular collapse (hypovolemic shock). 

Abrin is a plant source Type 2 RIP. It is found in Abrus precatorius (rosary pea, Indian licorice, jequirity bean). The toxicology of abrin is considered to be very similar to ricin. A similar Abrus toxin is pulchellin, produced by A. pul-chellus (Millard and LeClaire, 2008). The rosary pea has been reported to be more toxic than castor beans (Griffiths et al, 1994). Species sensitivity is variable and horses are considered to be the most sensitive. The mature goat is considered to be a more resistant species and 2 g of seed/kg body weight is reported as a lethal dose. The lethal dose for cattle is reported at 600 mg of seed/kg body weight. It is likely that abrin is denatured in the rumen (Burrows and Tyrl, 2001). 

Transdermal exposure to ricin is not serious, since it is not well absorbed through the skin. Oral exposure, for example by ingestion of castor beans, can cause severe gastroenteritis, gastrointestinal hemorrhage, and death due to circulatory collapse. Parenteral injection of ricin is rapidly fatal, as is aerosol exposure the lethal dose by these routes is 5-10 micrograms/kg (8). 

Animal Lethal Dose of Ingested Castor Seed (g/kg) Lethal Dose of Injected (i.m.) Ricin (p.g/kg) Lethal Dose of Injected (i.p. or i.v.) Ricin (pig/kg) Relative Resistance to Injected (s.c.) Ricin ... 

Lethal dose determined from a single study using a highly purified preparation of ricin the postexposure observation interval was 3 days for goat and unspecified for other animals (Field, 1910 Hunt et al., 1918). 

The acute parenteral LD50 of ricin in mice is approximately 0.8-10 pg/kg with a minimum lethal dose of 0.7—2 pg/kg (Fodstad et al., 1976, 1979 Stirpe and BatteUi, 1990). The LD50 value of 0.8 pg/kg was measured 7 days after exposure in 25-27 g BALB/c mice (Fulton et al., 1986). 

The lethal dose of ricin by injection for humans is unknown, but it has been estimated to be in the range of 1-10 pg/kg bodyweight based on analogy with NHP studies and from extrapolation of human clinical trials (see below). 

It is is the third most toxic substance known after plutonium and botulism it is a protein toxin that is extracted from the castor bean (Ricinus communis). The USA Centers for Disease Control (CDC) considers 500 pg to be the lethal dose of ricin in humans if exposure is from injection or inhalation. Ricin is poisonous if inhaled, injected, or ingested, acting by the inhibition of protein synthesis. While there is no known antidote, the US military has developed a vaccine. 

SEB and ricin can cause similar systemic symptoms, however, neither of them produce eye or skin symptoms. If the eyes are exposed, eye pain, tearing, redness, foreign-body sensation, and blurred vision may result. Irrespective of the route of exposure, when the toxin reaches the rest of the body s systems, it may cause weakness, prostration, dizziness, ataxia, and loss of coordination. When victims have been exposed to lethal doses, tachycardia, hypothermia, and hypotension follow. Death may occur in minutes, hours, or days. No antidotes are known for mycotoxins. Treatment is supportive and symptomatic. 

As is the case in toxicity and pathogenesis of intoxication, the route of exposure is important in relation to possible modes and their likelihood of success of prophylaxis and therapy. For oral intoxication, supportive therapy includes activated charcoal administration and intravenous fluid and electrolyte replacement. For inhalational intoxication, supportive therapy to counteract acute pulmonary edema and respiratory distress is indicated. Symptomatic care is the only intervention presently available to clinicians for the treatment of incapacitating or lethal doses of inhaled ricin. Positive end-expiratory ventilatory therapy, fluid and electrolyte replacement, antiinflammatory agents, and analgesics... 

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