What Are Indoleamines?

Indoleamines are a group of neurotransmitters in the body that are characterized by the linking of defined indole groups with an amine group. Indoles are nitrogen-containing molecules that make up 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’re responsible for all range of sensations and emotions. The biochemistry behind how indoleamine compounds work and why can be challenging to understand without a lot of background knowledge, but using three examples can make the undertaking a bit simpler. Serotonin, melatonin, and tryptophan are all amino acids prevalent in the body and linked to certain specific brain signals. When these compounds are linked to indole chains and their structures metabolized, highly specific indoleamines are synthesized as a result.

Indole, which carries the chemical formula C₈H₇N, is a commonly occurring compound both in human biology and in the natural world at large. Indole groups commonly form when these compounds join together in a chain. When one of the indoles in the chain is substituted for an amino acid, the whole compound changes into an indoleamine, usually with a unique set of responsibilities and neurochemical duties 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 sort of neurotransmitter grouping.

Most if not all indoleamine groupings have pronounced biological activity. The prototypical example is serotonin. This compound is a specific neurotransmitter and is one of the most closely 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 remainder is found in the central nervous system.

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 has great effects on mood. One theory of depression postulates that depression results from an imbalance in the levels of serotonin. 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 the serotonin. The neurotransmitter remains active, thus, the increased serotonin has a greater effect. If the SSRIs are removed, the serotonin levels decrease. This brings about 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 the SSRIs. There is some controversy about the use of SSRIs in young adults and children, since there is a side effect of an increased risk of suicide.

Melatonin is another indoleamine and is synthesized from serotonin. This hormone is widespread throughout the body, particularly in the skin, and helps to regulate the circadian rhythm. This is the body's way of keeping time over 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 the sale of melatonin as a supplement for humans.

The amino acid L-tryptophan is metabolized by the enzyme 2,3-dioxygenase. This enzyme is found in a number of tissues. It degrades L-tryptophan to the compounds kynurenines. These compounds have antimicrobial properties.

The breakdown products of indoleamine 2,3-dioxygenase are also involved in the suppression of the immune response. If over-expressed, this can result in the compromise 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.