Leukotriene antagonists

Leukotrienes are fatty signaling molecules,  - naturally produced lipid mediators  - and their production usually accompanies the production of histamine.  Leukotrienes produced within a cell convey signals that act either on the cell producing them (autocrine signalling) or on neighboring cells (paracrine signalling) to regulate the immune response.

The name leukotriene  comes from the words leukocyte and triene.  What would be later named leukotriene C, "slow reaction smooth muscle-stimulating substance" (SRS) was originally isolated from lung tissue after a prolonged period following exposure to snake venom and histamine.

Leukotrienes act principally on a subfamily of G protein-coupled receptors. They are involved in asthmatic and allergic reactions and act to sustain inflammatory reactions. This may seem a barmy action for a naturally occurring chemical but it is a protective mechanism against hostile substances entering the body.  By contracting the smooth muscles in the lungs and trachea for example, they serve to prevent any more of the noxious substance entering the body, in effect limiting the damage they are doing by restricting where they go and how far round the bloodstream they get – an attempt to keep them well away from the brain and other vital organs. 

Their production is a major cause of inflammation in asthma and allergic rhinitis.  In 'excess', the cysteinyl leukotrienes, for example,  can induce anaphylactic shock.

There are a lot of types of leukotriene.  Examples of leukotrienes are LTA₄, LTB₄, LTC₄, LTD₄, LTE₄, and LTF₄.  LTC4, LTD4 and LTE4 are often called cysteinylleukotrienes due to the presence of the amino acid cysteine in their structure. Leukotriene D₄ , for example, is used to trigger contractions in the smooth muscles lining the trachea.

All the drugs in this group of treatments are antagonists of the Leukotrienes.

Because Leukotrienes contribute to the pathophysiology of asthma and other inflammatory responses , antagonists serve to treat these diseases by inhibiting the production or activity of leukotrienes.  They are thus there to treat the following leukotriene mediated symptoms:

• airflow obstruction
• increased secretion of mucus
• mucosal accumulation
• bronchoconstriction
• infiltration of inflammatory cells in the airway wall

In June, 2009 the Food and Drug Administration concluded their review into the possibility of neuropsychiatric side effects with leukotriene modulator drugs.

Observations

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• Accolate
• Singulair and Montelukast