Few in vitro screening assays for biological activities of plant extracts consider the effect of the gastrointestinal system. This is an important factor for the bioavailability of plant extracts intended to be administered via the oral route. In this study, crude water and methanol extracts of selected plants (i.e. green tea, ‘buchu', thyme, sage and wild camphor) were prepared and exposed to simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) during dissolution studies. The crude extracts and resulting SGF and SIF products were screened for antimicrobial activity. After exposure to SGF, the antimicrobial activity was reduced for most of the plant extracts investigated. After exposure to SIF, no antimicrobial activity was detected for four of the five selected plant extracts, which suggests chemical alteration or degradation of the ‘active' compounds. An exception was found for ‘buchu', where the crude water extract and SGF product exhibited no antimicrobial activity, while the SIF product exhibited antimicrobial activity. This suggests activation of constituents during exposure to SIF. Liquid chromatography coupled to an ultraviolet detector and a mass spectrometer (LC-UV-MS) was used to qualitatively assess the effect of exposure of the crude extracts to simulated gastrointestinal conditions on their chemical composition. In many cases, the peak area of compounds decreased after exposure to SGF and SIF, while the peak area of other compounds increased. The same technique was applied to determine the percentage transport of the samples across an in vitro intestinal epithelium model (i.e. Caco-2 cell monolayers), which serves as an indicator of intestinal absorption. It is evident from the results that some compounds are not transported across the epithelial cell layer or they are metabolised or degraded during passage through the Caco-2 monolayer while the transport of other compounds was high, suggesting good bioavailability. Thus, it can be deduced from the results that the chemical composition and antimicrobial activity was altered after exposure to intestinal conditions during dissolution studies and absorption processes.
Principal supervisor: Prof AM Viljoen
Co-supervisor: Prof AM Viljoen