Digitonide precipitable sterols: A reevaluation with special attention to lanosterol

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Abstract
The ability of digitonin to precipitate lanosterol from prepared mixtures and biological sources was evaluated. Commercially available lanosterol was determined to be composed of about 60% lanosterol and 40% dihydrolanosterol. Both sterols were only partially precipitated by digitonin under all conditions examined. The presence of cholesterol increased the precipitation of lanosterol, but never to completion. About 40% of the lanosterols from saponified sheep's-wool fat was not precipitated by digitonin. Also14C-labeled lanosterol recovered from rat brain following intracerebral injection of 2-[14C] mevalonate was only 70% precipitated by digitonin. Steric hinderance by the methyl groups at carbon −4 is suggested to explain the poor precipitability of this sterol. In conclusion, lanosterol can not be considered to be a digitonide-precipitable sterol equivalent to cholesterol. Caution should be exercised in situations where digitonin-precipitable sterols are being prepared from sources containing significant concentrations of lanosterol (i.e., mass and/or radiolabel).