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Protonophore antagonism of botulinum toxin in mouse muscle
1Neurotoxicology Branch, U.S. Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, MD 21010, USA.
Abstract:
Botulinum neurotoxins (BoNT) are thought to enter cells through endocytotic vesicles where acidification is required for release of these toxins into the cytoplasm. Two ionophores, nigericin and monensin, that increase membrane permeability to H+ and K+ or H+, Na+ and K+, respectively, block vesicle acidification by acting as H+ shunts to neutralize pH gradients. Nanomolar concentrations of nigericin or monensin delayed development of blockade in BoNT-A or BoNT-B treated muscles two-to threefold over onset times in unprotected muscles. However, higher concentrations of the ionophores directly blocked synapses. Thus, nigericin and monensin could delay onset of BoNT paralysis only over a narrow range of concentrations.
Insights
Botulinum neurotoxins (BoNT) enter cells via acidified vesicles. Ionophores like nigericin and monensin can delay BoNT paralysis by blocking this acidification, but only at specific concentrations.
Area of Science:
- Cell Biology
- Neuroscience
- Toxicology
Background:
- Botulinum neurotoxins (BoNT) are internalized into cells through endocytosis.
- Acidification of endocytotic vesicles is crucial for the release of BoNT into the cytoplasm.
Purpose of the Study:
- To investigate the role of vesicle acidification in BoNT intoxication.
- To determine if blocking acidification with ionophores can prevent or delay BoNT-induced paralysis.
Main Methods:
- Utilized ionophores nigericin and monensin, which disrupt pH gradients by shunting ions across membranes.
- Administered BoNT-A and BoNT-B to muscle preparations.
- Assessed the onset of paralysis in the presence and absence of ionophores at various concentrations.
Main Results:
- Nanomolar concentrations of nigericin and monensin significantly delayed the onset of paralysis caused by BoNT-A and BoNT-B.
- Higher concentrations of these ionophores directly inhibited synaptic function, counteracting the protective effect.
- The delay in BoNT paralysis was observed only within a narrow therapeutic window for the ionophores.
Conclusions:
- Vesicle acidification is a critical step in BoNT intoxication.
- Ionophores can interfere with BoNT cellular entry, offering a potential, albeit narrow, window for therapeutic intervention.
- Further research is needed to optimize strategies for blocking BoNT entry and mitigating its effects.