Calcium and calmodulin in cellular intoxication with Clostridium difficile toxin B

Area of Science:

• Cell Biology
• Microbiology
• Toxicology

Background:

• Clostridium difficile toxin B (TcdB) is a potent cytotoxin causing significant cellular damage.
• Understanding the mechanisms of TcdB intoxication is crucial for developing effective countermeasures.

Purpose of the Study:

• To investigate the role of ionophores, calcium channels, and calmodulin in the cellular uptake and action of Clostridium difficile toxin B.
• To determine whether these factors are involved in toxin internalization or its subsequent cytosolic effects.

Main Methods:

• Cultured human lung fibroblasts were treated with Clostridium difficile toxin B.
• The effects of various agents, including the proton ionophore monensin, calcium channel blockers (verapamil, LaCl3), and calmodulin antagonists (trifluoperazine, amitriptyline, R 24571, dansylcadaverine), were assessed.
• Agents were added at different time points relative to toxin exposure to distinguish between effects on internalization and cytosolic action.

Main Results:

• Monensin inhibited the cytopathogenic effect of TcdB, while other ionophores did not.
• Verapamil, LaCl3, and several calmodulin antagonists protected fibroblasts against TcdB intoxication.
• These protective agents were ineffective when added after toxin internalization was complete.

Conclusions:

• Calmodulin and the uptake of extracellular calcium are essential for the internalization of Clostridium difficile toxin B into host cells.
• These cellular components are not required for the toxin's action once it has entered the cytosol.