Chemical, biochemical, and bioanalytical studies of sterols and isoprenoids: Smith-Lemli-Opitz syndrome, Langer-Giedion syndrome, activation of meiosis, nuclear orphan receptor LXRalpha and cytochrome P450s.

摘要

Sterols and isoprenoids are vital cellular constituents. In studies of their formation, metabolism, and biological effects, the separation and identification of individual isomers present formidable challenges. Approximately 30 unsaturated C27 sterols were prepared and purified as authentic standards to evaluate and develop chromatographic and spectral methods. Novel chromatographic conditions were devised for silver ion HPLC (Ag+-HPLC), a technique that provided unprecedented separations of these closely related sterols. Ag+-HPLC proved very powerful in addressing several important problems in medicine and biology relating to the biochemical effects of sterols and isoprenoids; described herein. Smith-Lemli-Opitz syndrome (SLOS) is a genetic disorder of development associated with the accumulation of unsaturated C27, sterols. My analysis of SLOS and normal blood samples unequivocally demonstrated that only the Delta5,7, Delta5,8, and Delta5,7,9(11) sterols accumulate significantly in SLOS patients. The 19-nor-Delta5,7,9 sterol, which has been reported to accumulate in SLOS blood by several research groups, was not detected in my analyses and was demonstrated to be a GC artifact arising from the thermal decomposition of cholesta-5,8-dien-3beta-ol. Alternative pathways in the late stages of cholesterol biosynthesis relating to the biological origin and metabolism of the beta5,8, beta6,8, and beta6,8(14) sterols were elucidated by incubation of tritium-labeled substrates in rat liver preparations. Also, a simple and rapid colorimetric method was developed for the clinical screening of SLOS. Ag +-HPLC played a critical role in studying a possible biochemical defect in another genetic disorder, Langer-Giedion syndrome, and in isolating isomers of (20R,22R)-dihydroxycholesterol), all-trans geranylgeranoic acid, other isoprenoids, and 4,4-dimethyl-sterols, compounds obtained from novel and efficient chemical syntheses. (20R,22R)-Dihydroxycholesterol proved to be a moderately potent activator of the nuclear orphan receptor LXRalpha, whereas all trans geranylgeranoic acid was found to be an inhibitor. The synthetic 4,4-dimethyl sterols caused a resumption of meiosis in mouse oocytes. Famesoic acid was demonstrated to be an extraordinarily potent substrate inducer of cytochrome P450BM-3.