Effects of Botulinum Toxin
A Substance Responsible for Botulism and Useful as Botox
People may have heard of an injectable medication called Botox, known for being a cosmetic treatment for wrinkles. Others may be aware of a poisonous condition called botulism, associated with spoiled canned food. Interestingly, the same substance is actually involved in both contexts: botulinum toxin. The reason is explained by how the toxin works.
Origin and Mechanism of Botulinum Toxin
Botulinum toxin is produced by a gram-positive anaerobic bacterium called Clostridium botulinum. The toxin comes in different serotypes, designated A through G, that are similar in molecular structure but different in potency and duration of effect.
Generally, a nerve that terminates in a muscle releases a neurotransmitter called acetylcholine. This neurotransmitter acts on receptors in the neuromuscular junction to stimulate muscle contraction. Afterwards, acetylcholine is either broken down by an enzyme called acetylcholinesterase or transported back into the nerve terminal for reuse.
Botulinum toxin is taken up by the nerve terminal. Once inside the cell, the toxin interferes with proteins that help release acetylcholine. Because aceylcholine cannot be released to contract muscle, the muscle becomes paralyzed. This effect of botulinum toxin last for three to six months.
Botulinum Toxin in Disease
Clostridium botulinum is responsible for the condition known as botulism. This occurs when botulinum toxin is swallowed or, rarely, introduced into wounds. One example is home-canned food, which can harvest the bacterium and its toxin.
When the toxin is distributed by the bloodstream, the effects are systemic. Botulism is characterized by multiple symptoms, including but not limited to nausea, vomiting, abdominal pain, and blurry vision due to dysfunction in eye muscles. The most feared complication is respiratory failure because of paralysis of the diaphragm muscle necessary for voluntary breathing.
Botulinum Toxin as Therapy
In contrast, the paralytic properties of botulinum toxin can be used in therapeutic ways. Commonly referred to by the trade name Botox, botulinum toxin can treat conditions characterized by involuntary, spasmodic, or continuous muscle contraction (dystonia), such as cervical dystonia and involuntary forced eyelid closure (blepharospasm). It is also used to treat certain sweating disorders and cosmetically to treat facial wrinkles.
Because Botox is injected locally into muscle, it rarely enters the bloodstream to cause systemic effects, though it is not impossible. Most of the side effects of Botox are related to excessive muscle weakness, such as dry eyes after overtreatment of blepharospasm. The clinician must take several factors into account in order to administer Botox as safely as possible.
