Post-exposure targeting of specific epitopes on ricin toxin abrogates toxin-induced hypoglycemia, hepatic injury, and lethality in a mouse model

Abstract

Effects in the liver of fatal intoxication with the binary toxin ricin are unclear. We report a robust neutrophil influx into the liver of C57BL/6 mice after lethal parenteral ricin challenge, occurring in peri-portal and centro-lobular hepatic areas within 2 h, followed by the abrupt disappearance of hepatic macrophages/Kupffer cells. Chemokine profiles determined by microarray, ribonuclease protection assays, northern blotting, and enzyme-linked immunosorbent assays showed rapid (2 h) upregulation and persistence of those for neutrophils (CXCL1/KC, CXCL2/MIP-2) and monocytes (CCL2/MCP-1). Red blood cell pooling (8-12 h), loss of hepatocyte glycogen (8-48 h) associated with progressive hypoglycemia, fibrin deposition (24-48 h), and death (72-96 h) followed. Monoclonal antibody to ricin A chain, administered intravenously, blunted hypoglycemia, and abrogated death. This outcome was observed when anti-ricin antibody was given before toxin exposure as well as when administered approximately 10 h after toxin exposure. Targeting antibody to specific amino-acid sequences on the ricin A chain (HAEL and QXXWXXA) was critical to the therapeutic effect. Re-emergence of liver macrophages/Kupffer cells and replenishment of glycogen in previously depleted hepatocytes preceded full recovery of the host. These data identify critical events for liver injury and healing in ricin intoxication, as well as a new means and specific targets for post-exposure therapeutic intervention.

A Monoclonal Immunoglobulin G Antibody Directed against an Immunodominant Linear Epitope on the Ricin A Chain Confers Systemic and Mucosal Immunity to Ricin

“…These data suggest that the polyclonal response to RTA consists of a mixture of neutralizing and nonneutralizing antibodies and that the ratio of the two types of antibodies can differ from individual to individual. This interpretation is supported by work from Maddaloni and colleagues, who identified both potent neutralizing monoclonal antibodies (MAbs) (e.g., RAC18) and a number of MAbs that bound to RTA with high avidity but failed to neutralize ricin in vitro or in vivo (23,37). In fact, one MAb, designated RAC23, actually enhanced ricin toxicity in vivo.…”

Activation of the Cholinergic Antiinflammatory Pathway Reduces Ricin-Induced Mortality and Organ Failure in Mice

“…Results are mean ± SEM (n = 10), *P < 0.05, **P < 0.01 versus vehicle-treated mice, † P < 0.05, † † P < 0.01 versus ricin-treated mice. results in hypoglycemia and hepatic injury, effects linked to an increased neutrophil and monocyte infiltration with a subsequent increase in inflammatory cytokine levels (26). Ricin may increase the multiple organ damage induced by inflammatory cytokines by affecting cellular antioxidant enzyme levels; ricin exposure reduces the activities of superoxide dismutase and glutathione peroxidase while increasing xanthine oxidase activity in both kidney and liver, resulting in increased lipid peroxidation products (27)(28)(29)(30), an effect observed in this study.…”

“…Human airway cells exposed to ricin show a marked inflammatory response with activation of nuclear factor (NF)-κB and increased expression of cytokines such as TNF-α (31). The resulting organ failure, which has been observed in humans following exposure to ricin (32) eventually leads to death (26,33). The proinflammatory effects of ricin have been linked to increased stimulation of the secondary messenger systems ERK (extracellular signal-regulated protein kinase), JNK, and p38 MAPK, with resulting activation of transcription factor NF-κB, which leads to inflammatory gene expression (2,3,31,34).…”

“…The proinflammatory effects of ricin have been linked to increased stimulation of the secondary messenger systems ERK (extracellular signal-regulated protein kinase), JNK, and p38 MAPK, with resulting activation of transcription factor NF-κB, which leads to inflammatory gene expression (2,3,31,34). These pathways are activated by ricin not only in macrophages and inflammatory cells (3,35,36) but also other cell types such as hepatocytes and lung cells (6,23,26,31). The resulting increased expression of proinflammatory chemokines and cytokines can enhance immune cell infiltration and increase the damage to specific organs, including the lung, kidney, and liver (33).…”

“…Ricin exposure has previously been shown to cause significant organ damage, particularly in the kidney (5,6) and the liver (26). This ricin-mediated damage has been linked to its proinflammatory actions and cytokine release leading to a proinflammatory transcriptional response in the target organs, increased oxidative stress, and subsequent cellular dysfunction.…”