Posted by: Chris Maloney | November 3, 2011

Ricin Bioterrorism: How Toxic Is the Castor Bean?

The ricin (2aai) structure

Image via Wikipedia

The LA Times reports a terrorist plot using ricin as a weapon.  Using ricin, a component of castor beans, as a weapon has been long considered a possibility.  It is relatively easy to obtain from the squeezings after the extraction of castor oil, but a study showing the methodology used by terrorists only produced a 1% extract of ricin.

Despite its low concentration, ricin is toxic in minute doses and may generate symptoms from respiration of the particles.  The most famous case of ricin used in an assassination was the death of Georgi Markov, a well-known Bulgarian writer.  In that case, a dose of ricin was administered by an umbrella gun into his thigh.

The results of that assassination have led to a variety of laboratory identification schemes for recognizing the ricin.  We might die from the inhalation, but they will definitely tell us where it came from.

More importantly, a vaccine against ricin poisoning is in the works, and is quite effective in mice.  The only cases of recent poisoning I was able to find was a successful suicide from ricin injection.

The mechanism that ricin uses to poison us is quite interesting and is being used in trials against cancers because it tends to attack the most actively growing cells first.

Castor oil, which is used in the home medicine community as both a topical and occasionally as a strong laxative, is ricin free (food grade).

For more information, here’s the CDC website and a number of abstracts below, including a chilling one on the impact of heat on ricin in orange or apple juice.

Toxicon. 2011 Oct 12. [Epub ahead of print]

A nanoparticle-based bio-barcode assay for ultrasensitive detection of
ricin toxin.

Yin HQ, Jia MX, Yang S, Wang SQ, Zhang JG.


Institute of Transfusion Medicine, The Academy of Military Medical
Sciences, Beijing 100850, China.


The ultrasensitive bio-barcode amplification assay (BCA) technique was
developed for the specific detection of the A chain of ricin toxin. The target
antigen A chain was first captured by gold nanoparticles (GNPs) coated with
polyclonal antibodies. Magnetic microparticles (MMPs) coated with A chain
monoclonal antibody were then added to form a sandwich immuno-complex. After
the immuno-complex was formed, signal DNA annealed to DNA strands covalently
bound to the GNPs were released by heating and characterized by PCR and
real-time fluorescence PCR. A detection limit of 1fg/ml was measured for A
chain, six orders of magnitude more sensitive than that of conventional
antigen-capture ELISA. The coefficient of variation (CV) of intra-assay and
inter-assay ranged from 3.39% to 6.84%. The BCA can detect the A chain in milk
and water mimic samples. In the following work it is demonstrated that this
assay is a highly sensitive method for the detection of ricin proteins that
could be adapted to measure other proteins.

Copyright © 2011. Published by Elsevier Ltd.

PMID: 22005297

Toxicol Sci. 2011 Oct 10. [Epub ahead of print]

Protective Effect of Two Recombinant Ricin Subunit Vaccines in the New
Zealand White Rabbit Subjected to a Lethal Aerosolized Ricin Challenge:
Survival, Immunological Response and Histopathological Findings.

McLain DE, Lewis BS, Chapman JL, Wannemacher RW, Lindsey CY, Smith LA.


Walker Downey & Associates, Inc., Verona, WI 53593;


Ricin isolated from the castor bean plant Ricinus communis is included
on the Centers for Disease Control and Prevention (CDC) Category B list of
bioterrorism agents, indicating that the toxin is moderately easy to
disseminate and could result in moderate morbidity rates. This study evaluated
two promising recombinant ricin subunit vaccines, one made using an Escherichia
coli codon-optimized gene and the other using a yeast codon-optimized gene in
E. coli-based fermentations. Rabbits were vaccinated four times over a period
of 6 months and challenged with ∼10-30 times
the median lethal dose of aerosolized ricin. All unvaccinated control rabbits
were either found dead or humanely euthanized within 30 h postchallenge while
the rabbits vaccinated with either vaccine survived the exposure without
adverse clinical signs. When the protective antibody responses were analyzed,
no significant difference was seen between the two vaccines. However, there was
a significant difference in the immune response over time for both vaccines
tested. Although clinical pathology was unremarkable, significant histological
lesions in the control animals included fibrinonecrotic pneumonia, acute
necrotizing lesions in the upper respiratory tract, and necrotizing
lymphadenitis in the lymph nodes draining the upper and lower respiratory
tract. Vaccine treated rabbits exhibited resolving lesions associated with
ricin exposure, namely chronic inflammation in the upper respiratory tract and
lungs, fibrosis, type II pneumocyte hyperplasia, and bronchiolitis obliterans.
This study confirmed the safety and efficacy of two recombinant ricin subunit
vaccines in rabbits, offering potential protection to warfighters and select

PMID: 21987460

Inhal Toxicol. 2011 Apr;23(5):247-56. Epub 2011 Apr 8.

The acute toxicity, tissue distribution, and histopathology of inhaled
ricin in Sprague Dawley rats and BALB/c mice.

Benson JM, Gomez AP, Wolf ML, Tibbetts BM, March TH


Lovelace Respiratory Research Institute, Albuquerque, NM 87108, USA.


Ricin is a highly toxic ribosome-inactivating protein derived from the
castor bean (Ricinus communis). Due to the relative ease of producing ricin, it
is characterized as a category B priority pathogen by the Center for Disease
Control and Prevention. The purpose of this study was to compare the acute
toxicity, associated histopathology, as well as the regional respiratory tract
deposition and clearance kinetics of inhaled ricin in rats and mice using a
single pure preparation. Acute toxicity was evaluated in five groups of six
animals per species exposed nose-only to ricin aerosols and followed up to 7
days post-exposure. Tissues were collected for histopathology. The calculated
median lethal doses (LD₅₀s) were 0.24 µg/kg (rats) and 0.58 µg/kg (mice).
Histological changes were noted in nose, larynges, trachea, lung, thymus, and
spleen of both species. Pulmonary deposition in rats inhaling 94-99 ng/L ricin
for 20 min (low dose) or 40 min (high dose) were 45.9 and 96 ng/g lung, respectively. Clearance was best described by a
single-component negative exponential function. Estimated lung doses were 0.38
and 1.43 µg/g·h among the low and high dose rats, respectively. In mice
inhaling 94 ng/L ricin for 20 min, pulmonary deposition was 91.1 ng/g lung
and the estimated tissue dose was 1.72 µg/g·h. No ricin was detected in
extra-respiratory tract tissue or in excreta. Results of this study demonstrate
differences exist in pulmonary deposition, clearance rates, and tissue dose and
histopathological changes between rats and mice inhaling ricin.

PMID: 21473711

J Food Sci. 2010 May;75(4):T65-71.

Thermal stability of ricin in orange and apple juices.

Jackson LS, Zhang Z, Tolleson WH.


Food and Drug Administration, Natl. Center for Toxicological Research,
Div. of Biochemical Toxicology, Jefferson, AR 72079, USA.


Ricin is a potent protein toxin that could be exploited for
bioterrorism. Although ricin may be detoxified using heat, inactivation
conditions in foods are not well characterized. Two brands of pulp-free orange
juice and 2 brands of single-strength apple juice (one clarified and the other
unclarified) containing 100 microg/mL added ricin were heated at 60 to 90 degrees
C for up to 2 h. With increasing heating times and temperatures the
heat-treated juices exhibited decreasing detectability of ricin by
enzyme-linked immunosorbent assay (ELISA) and cytotoxicity to cultured cells.
Z-values for ricin inactivation in orange juices were 14.4 +/- 0.8 degrees C
and 17 +/- 4 degrees C using cytotoxicity assays, compared to 13.4 +/- 1.5
degrees C and 14 +/- 2 degrees C determined by ELISA. Although insignificant
differences were apparent for z-values measured for the 2 orange juice brands,
significant differences were found in the z-values for the 2 brands of apple
juice. The z-values for ricin inactivation in the clarified and unclarified
apple juices were 21 +/- 4 degrees C and 9.5 +/- 1.1 degrees C, determined by
cytotoxicity assays, and 20 +/- 2 degrees C and 11.6 +/- 0.7 degrees C,
respectively, using ELISA. Overall, there were no significant differences
between results measured with ELISA and cytotoxicity assays. Ricin stability in
orange juice and buffer was evaluated at 25 degrees C. Half-lives of 10 +/- 3 d
and 4.9 +/- 0.4 d, respectively, indicated that active ricin in juice could
reach consumers. These results indicate that ricin in apple and orange juices
can remain toxic under some processing and product storage conditions.
PRACTICAL APPLICATION: Ricin is a potent toxin that is abundant in castor beans
and is present in the castor bean mash by-product after cold-press extraction
of castor oil. U.S. Health and Human Services recognizes that ricin could be
used for bioterrorism. This study reports the stability of ricin in apple and
orange fruit juices at temperatures ranging from 60 to 90 degrees C (140 to 194
degrees F).

PMID: 20546429

Drug Test Anal. 2009 Apr;1(4):184-91.

Ricin poisoning and forensic toxicology.

Musshoff F, Madea B.


Institute of Forensic Medicine, University Bonn, Stiftsplatz 12, 53111
Bonn, Germany.

Erratum in

Drug Test Anal. 2009 Jul;1(7):363-4.


Ricin is one of the most fascinating poisons due to its high toxicity:
as little as 500 microg can kill an adult. It gained fame by its use in the
so-called ‘umbrella murder’ to kill the Bulgarian dissident Georgi Markov in
1978. Ricin also became known as a potential bio-terror agent to which people
could be exposed through the air, food, or water. The origin, biochemistry,
toxicity, and analytical procedures for the determination of ricin are
summarized. The homicide of Markov is described as well as recent cases of
criminal ricin use.

Copyright 2009 John Wiley & Sons, Ltd.

PMID: 20355196

Forensic Sci Int. 2009 Aug 10;189(1-3):e13-20. Epub 2009 May 23

Suicidal death after injection of a castor bean extract (Ricinus
communis L.).

Coopman V, De Leeuw M, Cordonnier J, Jacobs W.


Department of Analytical Toxicology, Chemiphar N.V., Lieven
Bauwensstraat 4, B-8200 Brugge, Belgium.


The castor bean plant (Ricinus communis L.) or wonder tree is
cultivated in many countries as an ornamental annual plant in gardens. The
highest concentration of the lectin ricin is present in the seeds and pods.
Ricin is considered as one of the most toxic natural poisons. Ricinine is a
piperidine alkaloidal toxin present in castor bean and is described as a biomarker
for the exposure to ricin. A case report is presented of a 49-year-old man who
committed suicide by intravenous and subcutaneous injection of a castor bean
extract. He was brought to the emergency department 24 h after injecting
himself. On admission, the patient was conscious and he presented with a
history of nausea, vomiting, diarrhoea, dyspnoea, vertigo and muscular pain.
Despite symptomatic and supportive intensive care, the man died 9 h after
admission due to multiorgan failure. A body external examination was performed.
Blood, urine, vitreous humour and the castor bean extract were submitted to the
laboratory for toxicological analysis. The identification of ricinine in the
extract was performed by solid phase extraction in combination with full-scan
gas chromatography/mass spectrometry, high-performance liquid chromatography
with photodiode array detection and liquid chromatography/mass spectrometry
operated in the full-scan mode, respectively. An extraction procedure with
Oasis HLB solid phase extraction cartridges was applied. Chromatography was
achieved using a Symmetry C18 column using a gradient mode with 0.15% formic
acid and 0.15% formic acid in acetonitrile as mobile phase. Exposure to the
castor bean extract was confirmed by identification of the biomarker ricinine
in blood, urine and vitreous humour using solid phase extraction and liquid
chromatography tandem mass spectrometry with electro spray source in positive
ionization mode. Multiple reaction monitoring was used for specific detection.
To the authors’ knowledge, it is the first time that ricinine has been
identified in vitreous humour in a case of castor bean poisoning. Based on the
clinical symptoms and the results of the toxicological analysis, we concluded
that death was caused by intoxication with plant toxins originated from R.
communis L.

PMID: 19477090

J Forensic Sci. 2001 Sep;46(5):1033-42.

Forensic determination of ricin and the alkaloid marker ricinine from
castor bean extracts.

Darby SM, Miller ML, Allen RO.


University of Virginia, Department of Chemistry, Charlottesville, VA,


Liquid chromatography/mass spectrometry (LC/ MS) and matrix assisted
laser desorption/ionization time-of-flight (MALDI-TOF) MS methods were
developed for the presumptive identification of ricin toxin and the alkaloid
marker ricinine from crude plant materials. Ricin is an extremely potent
poison, which is of forensic interest due to its appearance in terrorism
literature and its potential for use as a homicide agent. Difficulties arise in
attempting to analyze ricin because it is a large heterogeneous protein with
glycosylation. The general protein identification scheme developed uses LC/MS
or MALDI-TOF for size classification followed by the use of the same instrumentation
for the analysis of the tryptic digest. Fragments of the digest can be searched
in an online database for tentative identification of the unknown protein and
then followed by comparison to authentic reference materials. LC fractionation
or molecular weight cutoff filtration was used for preparation of the intact
toxin before analysis. Extracts from two types of castor beans were prepared
using a terrorist handbook procedure and determined to contain 1% ricin.
Additionally, a forensic sample suspected to contain ricin was analyzed using
the presented identification scheme (data not shown). The identification of the
alkaloid ricinine by GC/MS and LC/MS was shown to be a complementary technique
for the determination of castor bean extracts.

PMID: 11569541







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