Evaluation of deuterated cholesterol and deuterated sitostanol for measurement of cholesterol absorption in humans.

The continuous isotope feeding method of Crouse and Grundy (1978. J. Lipid Res. 19: 967-971) for measurement of dietary cholesterol absorption has been modified by using markers labeled with stable isotopes ([2,2,4,4,6-2H5]cholesterol or [25,26,26,26,27,27,27-2H4]cholesterol or [26,26,26,27,27,27-2H6] cholesterol and [5,6,22,23-2H4]sitostanol) quantified by gas-liquid chromatography-selected ion monitoring. Tracing of the isotope distribution of the authentic markers and after their intestinal passage, including the microbiological products (coprostanol and coprostanone) revealed stability of the labels. The new method was evaluated in six monkeys on two occasions by comparison with the original method using radioactively labeled cholesterol and sitosterol. The results obtained by the two different methods were in excellent agreement, and absorption ranged from 49% to 73% (mean 60%) for the stable isotope method and from 51% to 69% (mean 62%) for the radioactive method. The coefficient of variation of cholesterol absorption in animals ranged from 3.9% to 15.1% (mean 7.1%) for stable isotopes and 1.9% to 13.6% (mean 5.7%) for radioactive isotopes. In twelve subjects cholesterol absorption was measured by the new method from total fecal samples frozen immediately and compared to results obtained from small fecal aliquots (approximately 1 g) sent by ordinary mail to the laboratory. A significant correlation of cholesterol absorption between the two different sample handlings was obtained (r = 0.981, P < 0.001). In addition, measurement of cholesterol absorption twice in seven volunteers 2 weeks apart revealed identical results. Thus, the new method is extremely safe and reproducible without radioactive exposure to the subjects and labortory staff and can be used on women of child-bearing age.