noun, plural: leukotrienes
Eicosanoid is the generic term to refer to the compounds derived from arachidonic acid or other polyunsaturated fatty acids of 20-carbon length. Some of the prominent eicosanoids include (1) eoxins, (2) leukotrienes, (3) lipoxins, (4) prostacyclin, (5) prostaglandins, (6) resolvins, and (7) thromboxanes.
Coined by the Swedish biochemist Bengt I. Samuelsson, the term leukotriene is derived from leukocyte where it was initially observed. The leukotrienes belong to a family of biologically active compounds biosynthesized through the 5-lipoxygenase pathway. They are derived from arachidonic acid (or from an eicosapentaenoic acid, EPA). Initially, the arachidonic acid is oxidized to produce a metabolite [i.e. 15-HpETE] that will be converted serially and enzymatically to leukotrienes. The different types of leukotrienes are: leukotriene A4 (LTA4), leukotriene B4 (LTB4), leukotriene B5 (LTB5), leukotriene C4 (LTC4), leukotriene D4 (LTD4), leukotriene E4 (LTE4), leukotriene F4 (LTBF), etc.
A basic schematic biochemical pathway of leukotriene biosynthesis is as follows: Arachidonic acid + O2 → 15-HpETE → 15-HETE → LTA4→ LTC4 → LTD4 → LTE4
Cysteinyl leukotrienes are leukotrienes that have cysteine in their chemical structure. They include LTC4, LTD4, LTE4, and LTF4.
The leukotrienes act as signaling molecules that impacts cell of origin (by autocrine signaling) and neighboring cells (by paracrine signaling).
The leukotrienes participate in host defense reactions and pathophysiological conditions such as immediate hypersensitivity and inflammation. They have potent actions on many essential organs and systems, including cardiovascular, pulmonary, and central nervous system as well as the gastrointestinal tract and the immune system. Leukotriene D4, in particular, is responsible for the contractions of the smooth muscles that line the bronchioles. Thus, excess of such leukotrienes causes inflammation in allergic rhinitis and asthma.
Word origin: leuko- (derived from leukocyte) + triene (from its conjugated triene unit)