title: In vivo formation of 25-hydroxycholesterol from endogenous cholesterol after a single meal, dietary cholesterol challenge.
abstract: The role of oxysterols as regulatory molecules in the suppression of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity was investigated in the intact rat in response to an acute dietary cholesterol challenge. When rats were fed highly purified cholesterol as a single meal at a level of 5% of the diet, maximal inhibition of enzyme activity (66%) occurred 120 min after the completion of the meal. Furthermore, when nonsaponifiable liver extracts were chromatographically resolved and analyzed by high performance liquid chromatography (HPLC) and capillary gas chromatography-mass spectrometry (GC-MS), 25-hydroxycholesterol was identified in the livers of rats 120 min after the completion of the single cholesterol meal. Significantly, only barely detectable amounts of 25-hydroxycholesterol were observed in the livers from control rats fed a sterol-free diet. The biosynthetic origin of 25-hydroxycholesterol was investigated with the use of deuterated water. Rats were fed deuterium oxide (33%) ad libitum for 3 days and then killed 120 min after the completion of a single cholesterol meal. As before, 25-hydroxycholesterol was detected in the livers from cholesterol-fed rats, but not to a significant extent in livers from control-fed rats receiving a sterol-free diet. Isotope ratio mass spectrometry revealed that the fractional incorporation of deuterium into 25-hydroxycholesterol (21%) was less than that observed for cholesterol (24%) isolated from the same livers, indicating that 25-hydroxycholesterol was produced endogenously from exogenous cholesterol and not from autoxidation of cholesterol. In a separate experiment it was also shown that [3H]mevalonate was incorporated into 25-hydroxycholesterol after a single meal cholesterol challenge, but was barely detected in the livers of control rats. The evidence obtained in the present article supports the hypothesis that 25-hydroxycholesterol is endogenously produced from cholesterol at early time intervals after an acute dietary cholesterol challenge. In addition, rat liver HMG-CoA reductase was inhibited by the administration of a single intragastric dose (1 microgram/kg) of an aqueous solution of 25-hydroxycholesterol. Thus, the results provide strong support for the conclusion that 25-hydroxycholesterol plays a significant role in the in vivo regulation of rat liver cholesterol biosynthesis after an acute dietary cholesterol challenge.
authors.affiliation: Department of Biochemistry, University of New Mexico, Albuquerque 87131.
authors.forename: K A
authors.initials: KA
authors.lastname: Johnson
authors.forename: C J
authors.initials: CJ
authors.lastname: Morrow
authors.forename: G D
authors.initials: GD
authors.lastname: Knight
authors.forename: T J
authors.initials: TJ
authors.lastname: Scallen
mesh_terms: D000818:Animals; D002197:Capillary Action; D002784:Cholesterol / Q000378:metabolism*; D002791:Cholesterol, Dietary / Q000008:administration & dosage*; D002851:Chromatography, High Pressure Liquid; D003903:Deuterium; D008401:Gas Chromatography-Mass Spectrometry; D006888:Hydroxycholesterols / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D007700:Kinetics; D008099:Liver / Q000737:chemistry / Q000378:metabolism; D008297:Male; D008798:Mevalonic Acid / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D002791:Cholesterol, Dietary; D006888:Hydroxycholesterols; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; C007997:25-hydroxycholesterol; D002784:Cholesterol; D003903:Deuterium; D006903:Hydroxymethylglutaryl CoA Reductases; D008798:Mevalonic Acid