Extracts of the aerial parts of the yellow star thistle (Centaurea solstitialis L.) were prepared using
petroleum ether,
chloroform and
methanol and toxicity assessed in primary cell cultures of striatum, frontal cortex and mesencephalon, containing the substantia nigra or raphe nucleus from the brain of the foetal rat.
Chloroform extracts significantly reduced the percentage of live cells whereas the
petroleum ether extract was inactive. The ability of the
methanol extract to reduce the percentage of live cells could not be distinguished from the effects of the vehicle controls for
methanol. Subsequently, the plant material was extracted with
dichloromethane and 10 fractions were obtained by column chromatography. Fractions 5, 6, 7 and 8 caused concentration-dependent cell death in the culture of substantia nigra, the other fractions were not toxic at the concentrations used. In further studies,
solstitialin A was isolated from fraction 9,
solstitialin A 13-acetate from fraction 6 and
solstitialin A-3
acetate and
cynaropicrin from fraction 7.
Solstitialin A 13-acetate and
cynaropicrin were toxic to cultures of substantia nigra cells. It is concluded that, of the compounds identified,
solstitialin A 13-acetate and
cynaropicrin have toxic potential in cell cultures, containing cells from the substantia nigra of the rat, the specificity of action to cells of the substantia nigra remains to be shown, and that a
toxic action in the midbrain may contribute to the nigro-pallidal
encephalomalacia, caused by the ingestion of the yellow star thistle by horses.