Leukotrienes are a class of highly biologically active inflammatory mediators, which are eicosanoid unsaturated acids with a conjugated triene structure obtained from the lipoxygen metabolism of arachidonic acid. They are classified into six categories according to the nature of their substituents. Leukotrienes C4 (LTC4), leukotriene D4 (LTD4), and leukotriene E4 (LTE4) are also known as cysteinyl leukotrienes (CysLTs) because they contain cysteinyl groups on C-6.

Physiological functions of leukotrienes

Leukotrienes are a class of highly biologically active inflammatory mediators with high physiological activity despite their minimal levels in the body. Leukotriene B4 (LTB4) is an important leukocyte activator that stimulates leukocyte chemotaxis, aggregation, and the release of oxygen radicals and lysosomal enzymes, increases vascular wall permeability, and stimulates bronchial mucus secretion. LTC4 and LTD4 increase airway resistance and vascular permeability, but have little effect on nasal itching and sneezing, and are less capable of inducing nasal overflow than histamine. CysLTs improve the activity of neural pathways associated with the airway and significantly enhance smooth muscle contractile responses to blood vessels. LTD4 enhances histamine-induced bronchoconstriction and is also a potent kinin and neuropeptide inducer.

Receptors for leukotrienes

The leukotriene receptors are divided into two types according to the target cells: BLT receptors activated by LTB4 and CysLTR receptors activated by CysLTs. BLT receptors include two subtypes, BLT1 and BLT2. BLT1 receptors are high-affinity receptors expressed on leukocytes, especially neutrophils, macrophages and eosinophils, and their main function is to participate in the chemotaxis of leukocytes, especially neutrophils. BLT2 receptors are expressed at high levels in leukocytes, spleen, liver and small intestine, and are low affinity receptors. CysLTR receptors have important biological functions in asthma, cardiovascular regulation and neuroendocrine regulation.

Detection of leukotrienes

• Double antibody sandwich ELISA

Leukotrienes can be measured in blood, bronchoalveolar lavage fluid, and urine of people with metabolic reactions. LTB4 and LTC4 levels are usually measured in serum specimens, and LTE4 can be measured from urine.

The level of LTB4 or LTC4 in the specimen can be determined by double antibody sandwich enzyme immunoassay. Urinary LTE4 is measured using a competitive inhibition method. Urinary LTE4 measurement is a sensitive and non-invasive method that uses urinary LTE4 concentration as a predictor of susceptibility with leukotriene receptor antagonists for the observation of asthma efficacy and determination of prognostic potential.

• Liquid chromatography - mass spectrometry (LC-MS) and LC-MS-MS methods

Liquid chromatography with tandem mass spectrometry is a powerful analytical technique that combines the separation capabilities of liquid chromatography with the high sensitivity and selective mass analysis capabilities of triple quadrupole mass spectrometry. A sample solution containing the target analytes is pumped through a stationary phase (LC column) by a mobile phase flowing under high pressure. The method has the advantages of high sensitivity, low detection limit, low sample usage, high throughput, and fast detection speed.