How Does Botox Work?

Mechanism of Action

Botulinum A toxin is a freeze dried, vacuum stored, purified protein which temporarily relaxes the muscles which cause wrinkles/sweating by trimming off a receptor that usually helps pass the message from the nerve to the muscle.

The receptor regenerates in 3 to 6 months when the treatment “wears off”.

Current Scientific Understanding: The Botulinum A toxin protein is enzymatic agent which cleaves receptors in acetylecholine producing nerve synapses. One molecule can cleave many receptors, and this is why so little is required to get an effect. This is different to most medication that binds as a ligand to just one receptor. This is why pound for pound it is one of the most powerful drugs ever known, and is also described therefore as the most powerful neurotoxin ever discovered.

SEQUENCE

A) Binding: Once injected, the heavy chain portion of the active of toxin binds to the cell membrane of the motor nerve via an unidentified high‐affinity “acceptor” molecule. This high‐affinity binding action allows for efficient uptake of Botulinum A toxin by the motor nerve and facilitates selective, targeted treatment at the injection site. For practical purposes, complete binding and internalization is considered to occur within a centimeter of the location of injection.

B) Internalizing: After binding, the Botulinum A toxin protein molecule passes through the cell membrane of the motor nerve and into its cytoplasm via endocytosis. It is here that the enzymatic component (light chain) of the Botulinum A toxin® protein molecule is activated.

C) Blocking: Inside the motor nerve, the light chain of the Botulinum A toxin protein molecule cleaves apart a protein (called SNAP25) that enables vesicles which store the neurotransmitter acetylcholine to attach to the cell membrane. This prevents these vesicles from fusing with the membrane and stops the release of acetylcholine into the neuromuscular junction. Cleaving SNAP25 also blocks release of neuropeptides involved in the transmission of pain (including substance P, glutamate and calcitonin

This may be how Botulinum A toxin® reduces the neck pain associated with cervical dystonia and migraine, although the exact mechanism of action is unknown. The cleaved snap-25 is either regenerated or a new synapse is made after around 4 months, and muscle returns to fully operational state.