Mode of action of mangosteen extracts
Phenolic compounds are believed to induce lesions in cell
membranes that initiate a series of events that can lead to cell
death.27,42 The effects of mangosteen extracts on membrane
integrity were verified using two independent methods based on
the uptake of propidium iodide (PI) or leakage of ATP by cells with
compromised membranes. The phenolic vanillic acid, which has
no antimicrobial activity against Gram-positive bacteria at neutral
pH22 wasusedas anegative control,andcetyltrimethylammonium
served as a positive control for the measurements. Table 6 reveals
that uptake of PI by L. monocytogenes and S. aureus cells was
dramatically enhanced by exposure to pericarp and bark methanol
extracts. Relative PI uptake was higher than in control samples
treated with the powerful cell membrane disruptor CTAB.23 PI
uptake by cells exposed to aqueous extracts was comparatively
lower, although differences with controls indicate that some
membrane damage occurred. Leakage of ATP by cells treated with
the extracts is illustrated by measurements summarized in Table
7. Extracellular ATP concentrations were clearly higher in treated
samples and methanol extracts again induced increases in excess
of those obtained with the positive control. These observations
provided strong evidence that mangosteen extracts caused injury
to theGram-positive cellmembraneand that the extent ofdamage
was greatest in methanol extracts