Probing inhibitory effects of Antrodia camphorata isolates using insect cell-based impedance spectroscopy: inhibition vs chemical structure.

A continuous online technique based on electric cell-substrate impedance sensing (ECIS) was used for probing inhibitory effects on Spodoptera frugiperda Sf9 insect cells exposed to structurally similar compounds isolated and purified from the fruiting bodies of the fungus Antrodia camphorata. Such chemicals consisted of three ergostane-related steroids and five lanosta-related triterpenes, which are known for their diverse properties and use in the formulation of nutraceuticals and functional foods. The half-inhibition concentration (ECIS(50)), the level at which 50% inhibition of the resistance response was obtained, was determined from the response function to establish inhibitory effects of the different isolates. A slight change in their chemical structures resulted in significant effects on inhibition as probed by impedance spectroscopy. The ergostane-related steroids were mostly inhibitory, but replacing their ketone groups with hydrogen or hydroxyl groups significantly reduced the inhibition. Similarly, the addition of methyl or carboxymethyl groups also lowered the inhibition. Removal of the double bond conjugation within the rings (sulfurenic acid) of the isolate drastically reduced the inhibition.