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Indoleamines are neurotransmitters that transfer signals across nerve endings. They are formed by linking indole groups with amino acids. Serotonin, melatonin, and tryptophan are examples of indoleamines with specific functions in the body. Serotonin is a neurotransmitter that affects mood and is targeted by antidepressants. Melatonin regulates the circadian rhythm and is used to treat sleep disorders. Tryptophan is metabolized by the enzyme 2,3-dioxygenase and has antimicrobial properties. Indoleamine 2,3-dioxygenase inhibitors are being investigated for their potential use in immunotherapy.
Indoleamines are a group of neurotransmitters in the body that are characterized by the linking of definite indole groups with an amino group. Indoles are nitrogen-containing molecules that form an important part of many biologically active molecules. In general, these and other neurotransmitters are chemical groups that enable and facilitate the transfer of signals across nerve endings. They are responsible for the whole range of sensations and emotions. The biochemistry behind how indoleamine compounds work and why can be difficult to understand without a lot of background knowledge, but using three examples can make the task a little easier. Serotonin, melatonin and tryptophan are all prevalent amino acids in the body and linked to certain specific brain signals. When these compounds are linked to indole chains and their structures are metabolized, highly specific indoleamines are synthesized as a result.
General composition
Indole, which bears the chemical formula C8H7N, is a common compound in both human biology and the natural world in general. Indole groups are commonly formed when these compounds join together in a chain. When one of the indoles in the chain is replaced by an amino acid, the entire compound is transformed into an indoleamine, usually with a unique set of neurochemical responsibilities and tasks depending on the amino group involved. There are 20 amino acids that serve as the building blocks of proteins, and any of these can be used to form this type of neurotransmitter grouping.
Serotonin as an example
Most, if not all groups of indoleamines have marked biological activity. The prototypical example is serotonin. This compound is a specific neurotransmitter and is one of the most studied indoleamines. It is found in animals, plants and fungi. It is consumed in the human diet in fruits and vegetables. In animals, most of the serotonin is found in the gastrointestinal tract. The rest is found in the central nervous system.
Double Role in Physiology and Pharmacology
Many studies have been conducted on serotonin for its effects on human physiology. It is thought to directly or indirectly impact most brain cells and have large effects on mood. One theory of depression posits that depression results from an imbalance in serotonin levels. To remedy this, selective serotonin reuptake inhibitors (SSRIs) have been developed. These compounds are widely used as antidepressants.
These drugs are thought to work because they prevent the reuptake of serotonin. The neurotransmitter remains active, so the increase in serotonin has a greater effect. If SSRIs are removed, serotonin levels drop. This leads to an increase in depression.
Serotonin is inactivated by the enzyme monoamine oxidase, also known as MAO. MAO inhibitors (MAOIs) are an older class of antidepressants. They can sometimes interact with compounds in the human diet. These inhibitors are used less frequently than SSRIs. There is some controversy surrounding the use of SSRIs in young adults and children, as there is a side effect of an increased risk of suicide.
Melatonin and tryptophan
Melatonin is another indoleamine and is synthesized from serotonin. This hormone is found throughout the body, especially in the skin, and helps regulate the circadian rhythm. This is the body’s way of keeping time on 24-hour cycles. Melatonin is sometimes taken as a supplement to help regulate sleep/wake cycles for people with jet lag or circadian rhythm disorders. Some countries do not allow melatonin to be sold as a human supplement.
The amino acid L-tryptophan is metabolized by the enzyme 2,3-dioxygenase. This enzyme is found in a number of tissues. Degrades L-tryptophan to kynurenine compounds. These compounds have antimicrobial properties.
Role in immune suppression
Indoleamine 2,3-dioxygenase degradation products are also involved in suppressing the immune response. If overexpressed, this can lead to impairment of the immune system. Researchers are investigating the use of indolamine 2,3-dioxygenase inhibitors to block this activity and provide a form of immunotherapy.
