Digitonin-precipitable sterols as a measure of cholesterol biosynthesis: contradictory results

In experiments with 4 different types of cells, we evaluated the cholesterogenic activity by incorporation of 14C-acetic acid into cholesterol and digitonin-precipitable sterols. In every case, the cholesterogenesis appeared considerably faster when expressed as digitonid than when expressed as real cholesterol production, and sometimes the data obtained by the 2 methods were contradictory. Detailed analysis of both digitonid components and nonprecipitable radioactive metabolites showed that a very variable fraction of methyl sterols (including bifunctional methyl sterols) co-precipitates with the C-27 sterols. In cholesterol regulation studies and particularly when the cells exhibit a low cholesterogenesis, the digitonin method is unsuitable and can lead to erroneous interpretations.