Natural products triggering biological targets--a review of the anti-inflammatory phytochemicals targeting the arachidonic acid pathway in allergy asthma and rheumatoid arthritis.

Inflammation is a natural response of living organisms to the presence of internal and external substances which are recognized by the host as being "non-self" or "foreign invader". It is also a cascade leading to the healing of damaged tissue. Uncontrolled inflammation often results in chronic diseases such as arthritis, autoimmune disorder, cancer, dementia, diabetic, neurodegeneration and vascular disease. The list keeps growing due to the increasing numbers of identified molecular markers that are associated with inflammatory genes or transcription factors. Among various transcription factors, nuclear factor kappa B (NF-kB) is the master switch for proinflammatory genes and transactivates arachidonic acid pathway enzymes when activated. Through evolution, plants have developed vast classes of compounds to fight inflammation. Most of them belong to the chemical group of alkaloids, coumarins, flavonoids, polyphenols and terpenoids. This review article presents and discusses results obtained from literature search on recent findings in plant-derived compounds, which exhibit anti-inflammatory activity in rheumatoid arthritis, allergy and asthma via the suppression of the arachidonic acid pathway. IC(50)s of the compounds obtained from the literature are thus tabulated into six groups of inhibitors based on the enzyme target of phospholipase A2, cyclooxygenase 1 and 2, 5-, 12- and 15-lipoxygenase. Modulation of Th1/Th2 cytokines and histamine/mucus release by some of these enzyme inhibitors are also briefly discussed.