|
 botox
Botulin toxin is a neurotoxic protein produced by the bacterium clostridium
botulinum. It is the most poisonous naturally occuring substance in the world. A
single drop is capable of killing 50,000 people. Though it is highly toxic, it
is used in minute doses both to treat painful muscle spasms, and as a cosmetic
treatment in some parts of the world. It is sold commercially under the brand
names Botox® and Dysport® for this purpose. The terms Botox and Dysport are
trade names and are not used generically to describe the neurotoxins produced by
Clostridia species. botox
Chemical mechanism of toxicity
The heavy chain of the toxin is particularly important for targeting the
toxin to specific types of axon terminals. The toxin must get inside the axon
terminals in order to cause paralysis. Following the attachment of the toxin
heavy chain to proteins on the surface of axon terminals, the toxin can be taken
into neurons by endocytosis. The light chain is able to leave endocytotic
vesicles and reach the cytoplasm. The light chain of the toxin has protease
activity. The type A toxin proteolytically degrades the SNAP-25 protein, a type
of SNARE protein. The SNAP-25 protein is required for the release of
neurotransmitter substances from the axon endings [4]. Botulin toxin
specifically cleave these SNAREs, and so prevent neuro-secretory vesicles from
docking/fusing with the nerve synapse plasma membrane and releasing their
neurotransmitters.
Though it affects the nervous system, common nerve agent treatments (namely
the injection of atropine and 2-pam-chloride) will increase mortality by
enhancing botulin toxin's mechanism of toxicity. Attacks involving botulin toxin
are distinguishable from those involving nerve agent in that NBC detection
equipment (such as M-8 paper or the ICAM) will not indicate a "positive" when a
sample of the agent is tested. |
