Leukotrienes (from ancient Greek λευκός leukós “white” and ancient Greek τρεῖς, τρία treis , tría “three”) belong to the eicosanoids , are chemically derived from arachidonic acid , a four-fold unsaturated fatty acid , and have three conjugated double bonds . Their role in metabolism is related to allergic or inflammatory reactions in the body (e.g. bronchial asthma). They were found in leukocytes (white blood cells).
The enzyme arachidonate-5-lipoxygenase catalyzes the reaction of arachidonic acid via 5-hydroperoxyeicosatetraenoic acid (5-HPETE) to leukotriene A4 (LTA4). The very unstable epoxide LTA4 is the direct starting compound for the biosynthesis of various leukotrienes. The group of substances is divided into the peptido (cysteinyl) leukotrienes LTC4, LTD4 and LTE4 and the cysteinyl- free LTB4, which are obtained with the help of the enzymes LTA4 hydrolase , LTC4 synthase , γ-glutamyl transferase and dipeptidase 2 . The last two reactions, starting from LTC4, require the export of LTC4 from the cell with the help of the multidrug resistance-related protein 1 (MRP1).
The 5-lipoxygenase-activating protein (FLAP) plays a regulating or inducing (triggering) role in the leukotriene synthesis pathway .
Medicinal substances: montelukast , pranlukast and zafirlukast are leukotriene receptor antagonists. Zileuton is a leukotriene synthesis inhibitor. Such leukotriene inhibitors are effective against bronchial asthma .