Sterol metabolism--XLVI. Synthesis of oxidized cholesterol fatty acyl esters

Modulation of retinoic acid receptor-related orphan receptor alpha and gamma activity by 7-oxygenated sterol ligands

The retinoic acid receptor-related orphan receptors alpha and gamma (RORalpha (NR1F1) and RORgamma (NR1F3)) are orphan nuclear receptors and perform critical roles in regulation of development, metabolism, and immune function. Cholesterol and cholesterol sulfate have been suggested to be RORalpha ligands, but the physiological significance is unclear. To date, no endogenous RORgamma ligands have been described. Here, we demonstrate that 7-oxygenated sterols function as high affinity ligands for both RORalpha and RORgamma by directly binding to their ligand-binding domains (K(i) approximately 20 nM), modulating coactivator binding, and suppressing the transcriptional activity of the receptors. One of the 7-oxygenated sterols, 7alpha-hydroxycholesterol (7alpha-OHC), serves as a key intermediate in bile acid metabolism, and we show that 7alpha-OHC modulates the expression of ROR target genes, including Glc-6-Pase and phosphoenolpyruvate carboxykinase, in an ROR-dependent manner. Furthermore, glucose output from hepatocytes is suppressed by 7alpha-OHC functioning as an RORalpha/gamma ligand. Thus, RORalpha and RORgamma are ligand-regulated members of the NR superfamily and may serve as sensors for 7-oxygenated sterols.

Esterification of oxysterols by human plasma lecithin-cholesterol acyltransferase

In the present study, lecithin-cholesterol acyltransferase (LCAT) catalyzed esterification of oxysterols was investigated by using discoidal bilayer particles (DBP) containing various oxysterols, phosphatidylcholines, and apolipoprotein A-I. The esterified oxysterols were analyzed by high pressure liquid chromatography, gas chromatography, and mass spectrometry. LCAT esterified all oxysterols tested that are known to be present in human plasma. The esterification yields in almost all cases were relatively high, often as high as the yield of cholesterol esterification. When DBP preparations containing 27-hydroxycholesterol and various phosphatidylcholines were used for the LCAT reaction, both monoesters and diesters were produced. The mass spectrometry analysis showed that the monoester was produced by the esterification of the 3 beta-hydroxyl group and not the 27-hydroxyl group. The diesters were apparently produced by the esterification of the 27-hydroxyl group only after the esterification of the 3 beta-hydroxyl group. Phosphatidylcholine containing a saturated acyl group at sn-1 position and an unsaturated acyl group at sn-2 position gave generally high esterification yield. The esterification of various oxysterols was compared by using DBP containing dioleoyl-phosphatidylcholine and individual oxysterols. All oxysterols produced 3 beta-oleoyl monoesters. Unlike 27-hydroxycholesterol, 25-hydroxycholesterol, 7 alpha-hydroxycholesterol, 7 beta-hydroxycholesterol, or cholestanetriol did not produce diesters. Various factors influencing the formation of the monoesters and diesters from 27-hydroxycholesterol were investigated. When dioleoyl-phosphatidylcholine was used as the acyl donor, prolonged dialysis of DBP preparations and increase in the ratio of the enzyme concentration to substrate particle concentration increased the diester formation. Significant amounts of diesters were also produced by using 1-palmitoyl-2-oleoyl-phosphatidylcholine and other phosphatidylcholines as the acyl donors. By analyzing the conditions of monoester and diester formation, a scheme for the LCAT reaction pathway was proposed.

Influence of 26-hydroxycholesterol on the composition and function of gel-filtered platelets

The influence of 26-hydroxycholesterol (26-OH-CHOL) on the structure and function of gel-filtered rat platelets, as a model membrane, was studied in vitro. Its influence on structure was determined by a fatty acid and a phospholipid analysis of the platelet lipids and on function by the cytoplasmic calcium concentration of the platelets exposed to increasing concentrations of 26-OH-CHOL for various periods of time. The intracellular free calcium (Ca2+)i of the gel-filtered rat platelets was monitored by a fluorescent probe (quin 2) after incubation in a 37 degrees C water bath with 1 mM Ca2+ and 20 microM quin 2/AM. The presence of 26-OH-CHOL in the incubation media changed both the phospholipid composition and the mixed fatty acid composition in the membrane and increased the intracellular free Ca2+ level of the platelets. As the incubation of platelets with cholesterol (CHOL) or esterified 26-OH-CHOL did not increase intracellular Ca2+ levels, these results indicate that the hydrophilic free 26-hydroxy group in 26-OH-CHOL may have influenced the enzymes catalyzing the synthesis of the phospholipid in the platelet membrane so as to allow it to become more and more "leaky" to Ca2+. Such a fundamental change in membrane structure and function may be responsible for the development of atherosclerosis in the intimal layer of the coronary arteries.

Cholesterol autoxidation 1981-1986

Literature published between 1980 and 1986 dealing broadly with the topic of cholesterol autoxidation is reviewed. The review builds on the detailed 1981 monographic treatment of the topic by the author and covers new items of chemistry, analysis, and metabolism.