Ricin Poisoning

Detection of ricin in complex samples by immunocapture and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Ricin, the toxin component of Ricinus communis is considered as a potential chemical weapon. Several complementary techniques are required to confirm its presence in environmental samples. Here, we report a method combining immunocapture and analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the accurate detection of different species of R. communis. Liquid environmental samples were applied to magnetic particles coated with a monoclonal antibody directed against the B-chain of the toxin. After acidic elution, tryptic peptides of the A- and B-chains were obtained by accelerated digestion with trypsin in the presence of acetonitrile. Of the 20 peptides observed by MALDI-TOF MS, three were chosen for detection ( m/ z 1013.6, m/ z 1310.6 and m/ z 1728.9, which correspond to peptides 161-LEQLAGNLR-169, 150-YTFAFGGNYDR-160, and 233-SAPDPSVITLENSWGR-248, respectively). Their selection was based on several parameters such as detection sensitivity, specificity toward ricin forms and absence of isotopic overlap with unrelated peptides. To increase assay reproducibility, stable isotope-labeled peptides were incorporated during the sample preparation phase. The final assay has a limit of detection estimated at approximately 50 ng/mL ( approximately 0.8 nM) of ricin in buffer. No interference was observed when the assay was applied to ricin-spiked milk samples. In addition, several varieties of R. communis or from different geographical origins were also shown to be detectable. The present assay provides a new tool with a total analytical time of approximately 5 h, which is particularly relevant in the context of a bioterrorist incident.

Evaluation of an in vitro bioassay for the detection of purified ricin and castor bean in beverages and liquid food matrices

The potential use of ricin as a biological weapon in food highlights the necessity for the development of food-specific detection methods. Current methods for the detection of ricin consist of various immunoassays, which detect only one subunit of the ricin toxin and therefore may not be indicative of a biologically active molecule. An in vivo assay, such as a mouse bioassay, can indicate the biological activity of the toxin; however, this method is not feasible for laboratories that do not have animal testing facilities. The purpose of this study was to develop an in vitro assay for the detection of biologically active ricin in beverages and liquid foods. Acidic and high-protein beverages were spiked with either purified ricin or ground castor beans and added to cultured human Jurkat cells. After an overnight incubation, the supernatant was tested for lactate dehydrogenase (LDH) activity with a colorimetric assay. LDH was released from the cytosol upon cell damage and was positively correlated with cell death. Ricin was detectable in all the matrices tested, with a sensitivity of 10 to 100 pg/ml. Biologically active ricin was detectable in all the matrices incubated with ground castor bean material. This method provides a confirmatory way to detect biologically active ricin that can be utilized by laboratories lacking animal facilities.

Acute demyelinating encephalitis after jequirity pea ingestion (Abrus precatorius)

INTRODUCTION

Castor and jequirity beans are uncommon causes of poisoning. The more common but less severe castor poisoning is well described, but jequirity bean (Abrus Precatorius) poisoning is rare. The toxicity is attributed to toxalbumins (ricin and abrin) that act by inhibiting protein synthesis. Their use as agents of biological warfare, mechanisms of action, and clinical features of poisoning are summarized.

CASE REPORT

A 30-year-old previously healthy female presented with bloody diarrhea and deep coma following ingestion of 3-4 seeds of a plant called 'ratti.' Investigations, including an MRI brain scan, showed evidence of acute demyelinating encephalitis. The patient died three days later due to progressive central nervous system depression.

DISCUSSION

This is a previously unreported manifestation of jequirity bean poisoning. Demyelination is immune-mediated, and Abrus is a well-known immuno-modulator and stimulator. A possible immunological pathogenic mechanism is hypothesized.

Evidence for widespread epithelial damage and coincident production of monocyte chemotactic protein 1 in a murine model of intestinal ricin intoxication

The development of small-animal models is necessary to understand host responses and immunity to emerging infectious diseases and potential bioterrorism agents. In this report we have characterized a murine model of intestinal ricin intoxication. Ricin administered intragastrically (i.g.) to BALB/c mice at doses ranging from 1 to 10 mg/kg of body weight induced dose-dependent morphological changes in the proximal small intestine (i.e., duodenum), including widespread villus atrophy and epithelial damage. Coincident with epithelial damage was a localized increase in monocyte chemotactic protein 1, a chemokine known to be associated with inflammation of the intestinal mucosa. Immunity to intestinal ricin intoxication was achieved by immunizing mice i.g. with ricin toxoid and correlated with elevated levels of antitoxin mucosal immunoglobulin A (IgA) and serum IgG antibodies. We expect that this model will serve as a valuable tool in identifying the inflammatory pathways and protective immune responses that are elicited in the intestinal mucosa following ricin exposure and will prove useful in the evaluation of antitoxin vaccines and therapeutics.

An activity-dependent assay for ricin and related RNA N-glycosidases based on electrochemiluminescence

Synthetic biotinylated RNA substrates were cleaved by the combined actions of ricin holotoxin and a chemical agent, N,N'-dimethylethylenediamine. The annealing of the product with a ruthenylated oligodeoxynucleotide resulted in the capture of ruthenium chelate onto magnetic beads, enabling the electrochemiluminescence (ECL)-based detection of RNA N-glycosidase activities of toxins. ECL immunoassays and the activity assay exhibited similar limits of detection just below signals with 0.1 ng/ml of ricin; the ECL response was linear as the ricin concentration increased by two orders of magnitude. Activities were detected with other adenine-specific RNA N-glycosidases, including Ricinus communis agglutinin (RCA), saporin, and abrin II. The substrate that provided the greatest sensitivity was composed of a four-residue loop, GdAGA, in a hairpin structure. When the 2'-deoxyadenosine (dA) was substituted with adenosine (A), 2'-deoxyinosine, or 2'-deoxyuridine, toxin-dependent signals were abolished. Placing the GdAGA motif in a six-residue loop or replacing it with GdAdGA or GdAAA resulted in measurable activities and signal patterns that were reproducible for a given toxin. Data indicated that saporin and abrin II shared one pattern, while ricin and RCA shared a distinct pattern. A monoclonal antibody that enhanced the activities of ricin, RCA, and abrin II to different extents, thus improving the diagnostic potential of the assay, was identified .

Characterization of a novel high-affinity monoclonal immunoglobulin G antibody against the ricin B subunit

There is an urgent need for the development of a passive immunotherapy against the category B select agent ricin, a lethal ribosome-inactivating toxin composed of an enzymatic A subunit (RTA) and a single binding B subunit (RTB). To date, only one monoclonal antibody (MAb), a mouse immunoglobulin G (IgG1) against RTA called R70, has been deemed sufficiently potent in animal models to warrant further testing in humans. In this study, we have identified and characterized MAb 24B11, a murine IgG1 directed against RTB. In a Vero cell cytotoxicity assay, 24B11 was approximately two times more effective at neutralizing ricin than was R70. The equilibrium dissociation constants of 24B11 (KD = 4.2 x 10(-9) M) and R70 (KD = 3.2 x 10(-9) M) were virtually identical, suggesting that the difference in neutralization activity between the two MAbs was not due to differing affinities for the toxin. 24B11 blocked ricin attachment to galactoside receptors on primary mouse splenocytes and on the apical surfaces of human mucosal epithelial cell monolayers. Surprisingly, R70 also effectively interfered with ricin attachment to receptors on cell surfaces. Using a phage-displayed peptide library, we determined that 24B11 binds an epitope on RTB adjacent to, but not within, one of the two galactose binding domains. Finally, we demonstrate that R70 and 24B11, when combined, function synergistically to neutralize ricin in vitro, raising the possibility that these two MAbs could serve as a novel immunotherapeutic in vivo.

Retrospective identification of ricin in animal tissues following administration by pulmonary and oral routes

A previously characterised amplified ELISA for ricin (sensitivity limit approximately 200 pgmL(-1)) has been employed to quantify ricin following a novel recovery method from selected tissues. Tissue samples from rats dosed by pulmonary instillation or orally with ricin were homogenised and treated with an elution buffer to extract ricin. This is the first time that ex vivo recovery of ricin post exposure following pulmonary or oral challenge has been achieved using clinically acceptable sampling methods, with promise in terms of diagnosis for the timely implementation of therapy. The toxin was detected and quantified using the ELISA in conjunction with pure ricin standards. Extracts from tissues sampled, including lung, blood, liver and spleen tested positive for ricin with maximum yield in lung associated fractions for pulmonary dosing and liver tissue for oral administration. This indicates the potential of lavage and blood sampling for timely diagnosis of ricin poisoning by pulmonary and oral routes, respectively. Time course analysis at 24 and 48 h also indicated the progression of ricin from surfaces of the lung into the lung tissue. Inter-subject variation was observed in the case of oral dosing, with data for ricin-treated and vehicle control tissues not statistically different in all samples. In addition the oral toxicity of the crude ricin administered was found to be higher than expected in the rat, based upon published information and an unpublished in house murine study.

A quantitative and highly sensitive luciferase-based assay for bacterial toxins that inhibit protein synthesis

Inhibition of protein synthesis is a common mechanism by which bacterial and plant toxins injure human cells. Examples of toxins that inhibit protein synthesis include shiga toxins of Escherichia coli, diphtheria toxin, Pseudomonas exotoxin A and the plant toxin ricin. In order to facilitate studies on toxin pathogenesis and to enable screening for inhibitors of toxin action, a quantitative and highly sensitive assay for the action of these toxins on mammalian cells was developed. The cDNA encoding destabilized luciferase was cloned into an adenoviral expression plasmid and a high-titre viral stock was prepared. Following transduction of Vero cells, luciferase expression was found to be linear with respect to viral multiplicity of infection. Luciferase expression by as few as 10 cells was readily detected. Treatment of transduced cells with either cycloheximide or shiga toxin resulted in a decrease in luciferase activity, with a half-life ranging from 1 to 2 h. Inhibition of luciferase expression was evident at toxin concentrations as low as 1 pg ml(-1). The assay was adapted for use in 24-, 96- and 384-well plates, enabling rapid processing of large numbers of samples. Using this approach, susceptibility of Vero, Hep2, Chang, A549, COS-1 and HeLa cells to three different toxins was determined. These results demonstrate that the luciferase-based assay is applicable to the study of numerous cell types, is quantitative, highly sensitive and reproducible. These features will facilitate studies on pathophysiology of toxin-mediated diseases and allow high-throughput screening for inhibitors of cytotoxicity.

Ricin

Ricin is a potent toxin found within the beans of the castor plant. Ricin's widespread availability makes it a viable biological weapon. Ricin intoxication mimics a variety of disease states, thus a low threshold of suspicion must be maintained to recognize a potential epidemic. Treatment is largely supportive.

Vaccines against the category B toxins: Staphylococcal enterotoxin B, epsilon toxin and ricin

The threat of bioterrorism worldwide has accelerated the demand for the development of therapies and vaccines against the Category B toxins: staphylococcal enterotoxin B (SEB), epsilon toxin (ETX) produced by Clostridium perfringens types B and D, and ricin, a natural product of the castor bean. The diverse and unique nature of these toxins poses a challenge to vaccinologists. While formalin-inactivated toxins can successfully induce antibody-mediated protection in animals, their usefulness in humans is limited because of potential safety concerns. For this reason, research is now aimed at developing recombinant, attenuated vaccines based on a detailed understanding of the molecular mechanisms by which these toxins function. Vaccine development is further complicated by the fact that as bioterrorism agents, SEB, ETX and ricin would most likely be disseminated as aerosols or in food/water supplies. Our understanding of the mechanisms by which these toxins cross mucosal surfaces, and importance of mucosal immunity in preventing toxin uptake is only rudimentary.

Threat of infection: microbes of high pathogenic potential--strategies for detection, control and eradication

Infectious diseases due to microbes of high pathogenic potential remain a constant and variable threat for human and animal health. The emergence of new diseases or the re-emergence of diseases that were previously under control complicates the situation to date. Infectious disease research, which has undergone a dramatic progress in understanding disease mechanisms such as host-pathogen interactions, is now focusing increasingly on new strategies for prevention and therapy. Significant progress has been achieved in the development of delivery systems for protective heterologous protein antigens and in veterinary vaccinology. A landmark of infectious diseases research is the chemical synthesis of genomes, a major new field of research referred to as "synthetic biology", that to date has resulted in the chemical synthesis of the poliovirus and of phage phiX174 genomes and their expression as infectious viruses. On the molecular level the evolution of pathogens and mechanisms of genome flexibility, which account for several pathogenic properties of infectious agents, have received increased attention. Bacterial toxins are an additional threat to human health and their interference with host cells and cellular functions is receiving more attention.

Antitoxins: novel strategies to target agents of bioterrorism

Never before has there been such a strong possibility that biological agents might be used indiscriminately on civilian populations. This review focuses on the use of antitoxins - antibodies, receptor decoys, dominant-negative inhibitors of translocation, small-molecule inhibitors and substrate analogues - to counteract those biological weapons for which toxins are an important mechanism of disease pathogenesis.