Diamine oxidase

Diamine oxidase (DAO), also known "amine oxidase, copper-containing, 1" (AOC1), formerly called histaminase, is an enzyme () involved in the metabolism, oxidation, and inactivation of histamine and other polyamines such as putrescine or spermidine. The enzyme belongs to the amine oxidase (copper-containing) (AOC) family of amine oxidase enzymes.

The enzyme is expressed in bilateria, a biological group of animals. The enzyme is encoded by the AOC1 gene. This gene is highly conserved across the bilateria group which includes mammals, birds, reptiles, fish and insects, to name a few.

Chemical activity 
DAO catalyzes the oxidative deamination of polyamines, such as histamine and putrescine, to produce aminoaldehydes, hydrogen peroxide, and ammonia.

Biological role 
DAO is involved in the physiology of digestion and other physiological processes, such as inflammation, immune response, and wound healing. Dysfunction of DAO has been associated with various diseases, including allergies, autoimmune disorders, and cancer. DAO also plays a role in healthy pregnancy in placental mammals.

In case of a shortage or low enzymatic activity of diamine oxidase in the human body, it may appear as an allergy or histamine intolerance.

Expression 
In placental mammals, including humans, the highest levels of DAO expression are observed in the digestive tract (intestinal mucosa) and the placenta. DAO expression is also observed in kidney of various species.

DAO is also expressed in eosinophils.

The role in human pregnancy 
In humans, a certain subtype of cells of the placenta, namely the extravillous trophoblasts, express the enzyme and secrete it into the blood stream of a pregnant woman.

During pregnancy, DAO plays a crucial role in maintaining fetal growth and development by regulating histamine levels. DAO levels in the blood circulation increases vastly in pregnant women suggesting a protective mechanism against adverse histamine. Histamine is a potent vasodilator and can cause uterine contractions, which can lead to premature labor. DAO in the placenta breaks down histamine to prevent its accumulation and maintain a healthy pregnancy. Low levels of DAO in the placenta may contribute to preeclampsia, a pregnancy-related disorder characterized by mother's high blood pressure and damage to mother's organs such as the liver and kidneys; the baby may also be affected if the condition is severe or left untreated, but it is not the primary target of the disorder.

Lowered diamine oxidase values in maternal blood in early pregnancy might be an indication for trophoblast-related pregnancy disorders like early-onset preeclampsia.

Research 
Exogenous DAO (supplements) are being studied as complimentary treatment for the relief of histamine intolerance symptoms, and other conditions, such as migraine or fibromyalgia. However, the results are inconclusive because studies to date have involved small study populations and short intervention periods.

Although DAO supplements may have some benefits, research is limited. DAO supplements are available over the counter but are not FDA-approved.

References

External links 
 

EC 1.4.3
Histamine
Copper enzymes