Search for new plant constituents with potential antiphlogistic and antiallergic activity.

Structure-activity relationships obtained from in vitro screening results obviously indicate that the highest inhibition effects on cyclooxygenase and 5-lipoxygenase are found amongst the class of phenolic compounds (flavonoids, polyphenols, coumestans, phenol carboxylic acids) and arachidonic acid analogous (alkylamides, retinoids, arylheptanoids, thiosulfinates, sulfinyl disulfides). The antiinflammatory activities of some triterpenenic acids, sesquiterpene lactones, and polysaccharides may be due to their immunomodulating activities on the complement and/or T-lymphocyte populations, respectively. In the search for potential antiallergic and antiasthmatic compounds, the thiosulfinates of onion were found to be active principles of the drug. The mechanism of action of some other antiallergic plant drugs (i.e. Tylophora asthmatica, Adhatoda vasica, etc.) has not yet been clarified.