What is Botulinum toxin aka Botox?
Botulinum toxin, better known as Botox, is a neurotoxin produced by the bacterium Clostridium botulinum. It is one of the most potent known toxins and can potentially be lethal even in small doses. Due to its muscle-relaxing properties, it has been successfully used in medicine and aesthetic medicine since the 1980s.
Molecular biological mechanism of action of Botox
Botox works by inhibiting the transmission of signals between nerves and muscles, thereby paralyzing the muscle. This happens because Botox blocks the release of acetylcholine, a neurotransmitter, at the so-called motor endplates. Molecularly, botulinum toxin is a two-chain polypeptide, consisting of a light chain (L-chain) and a heavy chain (H-chain) connected by a disulfide bridge. The H-chain facilitates the entry of the toxin into the nerve cell, where the L-chain can unfold its proteolytic activity, meaning it can cleave other proteins. In this case, it cleaves proteins necessary for the release of acetylcholine, and the absence of acetylcholine in the synaptic cleft leads to the absence of muscle contraction. The L-chain remains active in the cytosol of the cell for weeks.
The steps of the molecular action:
- Binding: Botox binds specifically to receptors of the presynaptic nerve cells.
- Endocytosis: After binding, Botox is taken up into the nerve cell.
- Translocation: Part of the botulinum toxin is released and transported through a pore into the nerve cell.
- Proteolysis: The other part cleaves proteins necessary for the release of acetylcholine.
- Inhibition of neurotransmitter release: The release of acetylcholine is prevented, leading to the absence of muscle contraction.
End of the duration of action
The effect of Botox is always temporary. This has the advantage that unwanted effects eventually subside, and the disadvantage that to achieve the desired effects again, a new injection is necessary.
The end of the effect is due to the fact that the cells form new connections and the L-chain of Botox, which prevents the release of acetylcholine, is eventually broken down, allowing signal transmission to normalize again.
Medical and cosmetic applications of Botulinum toxin
In medicine, botulinum toxin is used to treat various conditions, including chronic migraines, muscle spasms, and bladder dysfunctions. In cosmetics, Botox is mainly used to reduce wrinkles.
Conclusion
Botulinum toxin is an impressive example of how a potentially deadly poison can become a valuable therapeutic tool through scientific research and medical innovation. Its discovery and development reflect the progress of medicine in managing risks and maximizing benefits.
Sources:
Brin, M. F. (1997). Botulinum toxin: Chemistry, pharmacology, toxicity, and immunology. Muscle & Nerve, 20(S6), 146–168. https://doi.org/10.1002/(SICI)1097-4598(1997)6+<146::AID-MUS10>3.0.CO;2-4
Dressler, D., & Adib Saberi, F. (2005). Botulinum Toxin: Mechanisms of Action. European Neurology, 53(1), 3–9. https://doi.org/10.1159/000083259
Huang, W., Foster, J. A., & Rogachefsky, A. S. (2000). Pharmacology of botulinum toxin. Journal of the American Academy of Dermatology, 43(2), 249–259. https://doi.org/10.1067/mjd.2000.105567
