An anticholinesterase is a chemical that inhibits the breakdown of an enzyme involved in the transmission of signals between nerve cells and muscles. It is found naturally in some snake venoms. Such a compound has uses ranging from the treatment of diseases to use as pesticides or as weapons of mass destruction.
Many of the body’s neurons rely on acetylcholine to transmit signals between the neuron and a muscle. After the muscle has been signaled to contract, it needs to relax. Cholinesterase enzyme breaks down the acetylcholine, enabling this relaxation to occur.
If an anticholinesterase is present, the muscle is unable to relax. It will keep contracting, which can lead to paralysis and eventually death by asphyxiation. There are different types of anticholinesterase inhibitors, also known as acetylcholinesterase inhibitors. Ones used medically to treat diseases are reversible. Those used to kill insects or poison people, such as nerve gas or some snake venoms, bind irreversibly. This makes them much more dangerous to humans.
Intentional or accidental pesticide poisoning is a worldwide problem. The classes of pesticides that are anticholintesterases are organophosphates and carbamates. It is recommended that people who will be working with one of these classes of pesticides be tested for their blood baseline levels of cholinesterase. This provides a benchmark in case the person is exposed to high levels of pesticide, so that medical personnel can determine whether the person has been exposed to a toxic level. One problem to this monitoring is that levels below those that affect blood cholinesterase levels have been found to cause toxicity to neurons.
Organophosphate compounds can also be potent nerve gases. Sarin is the most well known of these compounds. This compound was vaporized on the Tokyo subway in 1995, killing 12 people. Sarin is much more toxic even than cyanide. There are international treaties prohibiting its manufacture.
Medical conditions treated with an anticholinesterase include myasthenia gravis and several types of dementia. For myasthenia gravis treatment, acetylcholinesterase inhibitors are the first treatment used. This disease has symptoms of muscle weakness and prevents acetylcholine from stimulating the muscles. Thus, treatment with an anticholinesterase, such as pyridostigmine, helps restore muscle function. This compound is usually introduced at a low dose and gradually increased.
Both Alzheimer’s disease and Lewy Body Dementia (LBD) have been treated with acetylcholinesterase inhibitors. Alzheimer’s disease was formerly thought to be due to an inadequate supply of acetylcholine. The treatment of this disease with these inhibitors has not been found to be very effective, however. Current research focuses more on a different pathology of the disease.
LBD is a widespread form of dementia, second in prevalence only to Alzheimer’s. Patients exhibit a mixture of symptoms of both Alzheimer’s and Parkinson’s diseases. Acetylcholinesterase inhibitors are used to treat the cognitive decline associated with the dementia caused by this disease.