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DAO: diamine oxidase HNMT: histamine-N-methyltransferase ALDH: aldehyde dehydrogenase MAO: monoamine oxidase. HNMT catalyzes the methylation of the secondary amine group of the histamine imidazole aromatic heterocycle by a reaction requiring the S-adenosyl methionine cosubstrate as a methyl group donor.
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On the other hand, histamine can be metabolized to 1-methylhistamine by the enzyme HNMT (EC 2.1.1.8), a small monomeric protein encoded by a gene located on chromosome 2q22.1. This functional enzyme, a homodimer with two isoforms, catalyzes the oxidative deamination of the primary amine group of histamine.
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DAO (EC 1.4.3.22), also called histaminase or amiloride-binding protein, is a copper-dependent amino oxidase encoded by the AOC1 gene located on chromosome 7 (7q34-36).
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Two main histamine metabolic pathways are known in humans, involving the enzymes diamine oxidase (DAO) and histamine-N-methyltransferase (HNMT) ( Figure 2). These wide-ranging physiological effects occur by interaction with four G-protein-coupled receptors with seven transmembrane domains (H1, H2, H3 and H4), which activate signal transduction pathways upon perceiving their ligand, histamine. In addition, histamine functions as a neurotransmitter, being synthesized by neurons located in the posterior region of the hypothalamus whose axons extend through the brain. Functionally, this amine is involved in various immune and physiological mechanisms, stimulating gastric acid secretion, inflammation, smooth muscle cell contraction, vasodilation and cytokine production, among other processes. Specifically, histamine is synthesized and stored in high concentrations in secretory granules, mainly in basophils and mast cells, and also in gastric enterochromaffin cells, lymph nodes and the thymus. The physiological and pathophysiological effects of histamine on the body were first described in 1910 by Dale and Laidlaw, two pioneering researchers who studied the functions of this organic compound at the Wellcome Physiological Research Laboratories. Synthesis of histamine by decarboxylation of its precursor amino acid. This review aims to analyze the pathophysiological relevance of dietary histamine, giving special focus to the adverse effects derived from histamine intake and, in particular, to the state of the art concerning the etiology, diagnosis and treatment of histamine intolerance. The inability of certain individuals to metabolize histamine in the intestine, resulting in sensitivity to normal or even low histamine levels in food, may help to explain some of the uncertainties historically associated with histamine intoxication.ĭuring the last decade, histamine intolerance has gained social and scientific recognition, with a significant increase in the interest of researchers to investigate this disorder. In recent years, another disorder associated with histamine intake, arising from an enzymatic deficiency, has been described. First described more than 60 years ago, the deleterious effects of excessive histamine ingestion were initially referred to as scombroid fish poisoning or scombrotoxicosis, as they were associated with the consumption of fish in this family, but the condition is now known as histamine intoxication or histamine poisoning. Among them, histamine has the highest toxic potential, along with tyramine, and is therefore of great interest in terms of food safety. In 2011, the European Food Safety Authority (EFSA) issued a scientific report warning that the levels of biogenic amines found in foods marketed in European Union countries may still entail a consumer health risk.