Extraction and quantitation of total cholesterol, dolichol and dolichyl phosphate from mammalian liver

A procedure is described for the determination of total cholesterol, dolichol and dolichyl phosphate (Dol-P) in mammalian liver. It is based on extraction of these compounds into diethyl ether after alkaline saponification of the tissue. Extractability is affected by the length of saponification and concentration of potassium hydroxide (KOH) in the saponification mixture. After extraction, total cholesterol and dolichol are quantitated directly by reverse-phase high pressure liquid chromatography (HPLC) on C18. Dol-P requires further purification before quantitation by HPLC, this is accomplished by chromatography on silicic acid. These methods gave recoveries of over 90% for cholesterol and dolichol and about 60% for Dol-P, using [4-14C]cholesterol, a polyprenol containing 15 isoprene units, and [1-14C]Dol-P as recovery standards. Concentrations of total cholesterol, dolichol and Dol-P in livers from one month-old-CBA mice were found to be 5.7 +/- 0.7 mg/g, 66.3 +/- 1.2 micrograms/g and 3.7 +/- 0.3 micrograms/g, respectively.