5$\alpha$-Cholest-8(14)-en-3$\beta$-ol-15-one is a potent inhibitor of cholesterol biosynthesis which has been found to have significant hypocholesterolemic action upon oral administration to rodents and nonhuman primates. The metabolism of (2,4-$\sp3$H) 5$\alpha$-cholest-8(14)-3n-3$\beta$-ol-15-one was studied in Chinese hamster ovary (CHO-K1) cells. The incorporation of the labeled 15-ketosterol into the cells was linear with respect to sterol concentration in the medium over the range of concentrations studied and was higher than the uptake of cholesterol. The results of detailed analyses of the lipids recovered from the cells after 6 hours of incubation with the (2,4-$\sp3$H) -15-ketosterol indicated that most of the $\sp3$H was associated with the free 15-ketosterol. Considerably smaller amounts of $\sp3$H were associated with esters of the 15-ketosterol. No conversion of the 15-ketosterol to cholesterol or other C$\sb{27}$ monohydroxysterols was observed. The labeled material with the chromatographic behavior of esters of the 15-ketosterol gave, after mild saponification, the free 15-ketosterol which was characterized by cocrystallization and chromatographic studies.
The metabolism of the 15-ketosterol was also studied in male baboons (Papio cynocephalus) treated with the 15-ketosterol. After oral administration of a mixture of (2,4-$\sp3$H) 5$\alpha$-cholest-8(14)-en-3$\beta$-ol-15-one and (4-$\sp{14}$C) cholesterol, blood samples were obtained at various times. Marked differences in the time courses of the levels of $\sp3$H and $\sp{14}$C in plasma were observed. $\sp3$H showed maximum levels at 4 to 8 h, while maximum values for the levels of $\sp{14}$C were observed much later. Total lipid extraction of plasma showed that essentially all of the $\sp{14}$C of plasma was recovered in the lipid extract. In contrast, while most of the $\sp3$H was recovered in the lipid extract, a significant amount of $\sp3$H remained in the aqueous phase after lipid extraction. Most of the $\sp3$H in plasma was found as metabolites of the 15-ketosterol, i.e., esters of the 15-ketosterol, cholesterol and cholesteryl esters. The plasma levels of the 15-ketosterol and of each of these metabolites showed different changes with time. The labeled cholesterol (and the cholesterol of cholesteryl esters), formed from the 15-ketosterol, was thoroughly characterized by chromatography and by purification by way of it dibromide derivative.
Detailed studies were also made of the effects of the 15-ketosterol and of two other oxygenated sterols on the distribution of $\sp3$H in nonsaponifiable lipids after incubation of ($\sp3$H) acetate with the 10,000 x g supernatant fraction of rat liver homogenates. Whereas 14$\alpha$-ethyl-5$\alpha$-cholest-7-ene-3$\beta$,15$\alpha$-diol (1 $\mu$M) caused a marked accumulation of labeled lanosterol and 24,25-dihydrolanosterol (characterized by chromatographic and cocrystallization experiments), 5$\alpha$-cholest-8(14)-en-3$\beta$-ol-15-one (100 $\mu$M) and 25-hydroxycholesterol (6.25 $\mu$M and 12.5 $\mu$M) had no demonstrable effect on the distribution of $\sp3$H in the nonsaponifiable lipids.
| Identifer | oai:union.ndltd.org:RICE/oai:scholarship.rice.edu:1911/16276 |
| Date | January 1989 |
| Creators | Pajewski, Thomas Nikolaus |
| Source Sets | Rice University |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | application/pdf |
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