Potent Antiedematous and Protective Effects of Ciprofloxacin in Pulmonary Ricinosis

Abstract

The plant toxin ricin is considered a biological threat agent of concern and is most toxic when inhaled. Pulmonary exposure to a lethal dose of ricin can be redressed by treatment with antiricin antibodies; however, late antitoxin intervention is of limited efficacy. This limitation is associated with overt lung damage, clinically manifested as severe pulmonary inflammation, which develops over time. Increased evidence indicates that ciprofloxacin, a broad-spectrum antimicrobial agent, possesses immunomodulatory properties. Here we demonstrate that while antiricin antibody administration at late hours after intranasal exposure to ricin confers limited protection to mice, highly efficient protection can be achieved by adding ciprofloxacin to the antibody treatment. We further demonstrate that parameters associated with lung injury, in particular, pulmonary proinflammatory cytokine production, neutrophil migration, and edema, are sharply reduced in ricin-intoxicated mice that were treated with ciprofloxacin. The presented data highlight the potential clinical application of ciprofloxacin as a beneficial immunomodulatory agent in the course of ricin intoxication. Ricin, a type II ribosome-inactivating protein, is a plant toxin derived from the seeds of Ricinus communis (castor beans). The holotoxin consists of two polypeptide chains (A and B) linked by a disulfide bond. The B chain is a lectin, which binds to galactose residues on the cell surface. The A chain possesses RNA Nglycosidase activity that irreversibly inactivates the 28S rRNA of the mammalian 60S ribosome subunit, subsequently arresting cell protein synthesis (1). Due to its high availability and relative ease of production, ricin is considered a biological threat agent (2). The toxicity of ricin depends on the route of exposure, inhalatory exposure being considered the most severe (3). Pathological studies of pulmonary ricin intoxication have demonstrated that injury is confined mostly to the lungs (4) and characterized by a local cytokine storm, massive neutrophil recruitment, increased prooxidant enzyme activity, and development of proteinaceous pulmonary edema, subsequently resulting in respiratory failure and death (4, 5).Prophylactic antiricin vaccines are being developed (6), yet postexposure medical countermeasures are needed for treatment of unvaccinated victims after pulmonary exposure to lethal doses of the toxin. Previous studies have examined the possibility of protecting animals against pulmonary ricinosis by passive immunization with polyclonal antiricin antibodies; nevertheless, under this mode of protection, survival rates declined sharply in correlation with antitoxin administration timing following intoxication, so that antiricin antibodies administered 24 h after exposure gave rise to limited rates of survival (5, 7). At this late time point, the pathophysiological condition of some of the intoxicated mice may have deteriorated so that the loss of function of the lungs is irreversible. Conversely, we previously showed that higher sur...

Total Body Irradiation Mitigates Inflammation and Extends the Therapeutic Time Window for Anti-Ricin Antibody Treatment against Pulmonary Ricinosis in Mice

“…We would like to point out in this context that since this study was performed with outbred mice, employing an adoptive transfer approach to prove unequivocally the role of the neutrophils in promotion of toxicity is not possible. Understandably, TBI is not an applicable clinical countermeasure against ricin intoxication, however, the results obtained in this work strongly strengthen our findings from the past, indicating that attenuation of inflammation is critical for optimal treatment of pulmonary ricinosis, especially if antibody-based treatment begins at late time points following intoxication [ 11 , 14 ]. Furthermore, the present study strongly suggests that clinical approaches aimed to attenuate neutrophil-mediated damage could be implemented in the future in the development of an effective anti-ricin medical countermeasure.…”

“…Pulmonary ricin intoxication is characterized by a confined lung pathology associated with cytokine storm, massive neutrophil infiltration, and ultimately, severe edema formation, leading to respiratory failure and death. Neutrophils are considered a major hallmark of ricin- [ 11 , 14 , 16 ], as well as non-ricin- [ 19 , 20 , 22 , 23 ] mediated lung injuries, where aggressive or prolonged neutrophil responses result in deleterious inflammatory conditions and tissue destruction, while on the other hand, decreased pulmonary neutrophil infiltration is associated with attenuation of injury severity [ 18 , 21 , 26 ].…”

“…We have previously demonstrated that co-administration of the anti-inflammatory drugs doxycycline or ciprofloxacin with anti-ricin antibodies to mice intranasally exposed to lethal doses of ricin, significantly attenuated lung injury and improved treatment outcome in comparison to mice treated with anti-ricin antibodies alone. This improved protection was attributed to a significant quantitative reduction of various inflammatory related markers—cytokine response, neutrophil infiltration, and vascular hyperpermeability [ 11 , 14 ]. The anti-inflammatory effects of doxycycline or ciprofloxacin were significant, yet limited, and their application without co-administration of anti-ricin antibody did not confer protection.…”

Treatments for Pulmonary Ricin Intoxication: Current Aspects and Future Prospects

“…Consistent with this finding, the levels of the serum-resident enzyme cholinesterase, as well as total protein, are increased significantly in the BALF of intoxicated mice, indicating that the blood-lung barrier is severely impaired. Increased Evans Blue dye extravasation, as a marker for increased vascular permeability, has also been reported [ 12 , 39 ].…”

“…Recent data suggests that small-molecule compounds that either interfere with or inhibit the intracellular trafficking of ricin may also be beneficial against ricinosis [ 7 , 8 , 9 , 10 ]. Another approach has recently shown that the co-administration of antitoxin antibodies with immunomodulatory drugs enables toxin neutralization while decreasing lung injury severity, thus improving treatment outcomes [ 11 , 12 ].…”