H1-Antihistamines for Allergic Diseases: Old Aged but Not Old-Fashioned Drugs

Abstract

Histamine is a chemical messenger synthesized from the amino acid histidine by L-histidine decarboxylase. It plays an important role in the system of immunoregulation and in acute and chronic allergic inflammation binding to four subtypes of receptors H1, H2, H3 and H4, described as heptahelical transmembrane molecules that activate specific G-proteins. These receptors placed on the membranes of different cellular jambs (mast cells, endothelial cells, sensory nerve fibres, bronchial smooth muscle) cause different biological actions: Vasodilatation, increased vascular permeability, itching, smooth muscle contraction, coronary spasm, sleep-wake rhythm regulation. Histamine interaction with H1-receptors potentially leads to increasing antigen-presenting cell capacity, release of histamine and other mediators from mast cells and basophils inducing cellular adhesion molecule expression and chemotaxis of eosinophils and neutrophils.