retinol-palmitate and cholesteryl-oleate

The adrenal cortexes of humans and rodents accumulate lipofuscin with age, but the chemical nature of the substance that produces lipofuscin fluorescence in the gland is not known. Analysis of rat adrenal nonpolar lipids revealed a fluorescence profile with increased intensity in the lipids extracted from older animals (23-24 months > 6 months > 6 weeks). The peak occurred at a wavelength of 470 +/- 5 nm(n = 26) when excited at 340 nm. After sucrose density gradient centrifugation, the fluorescent substance was primarily concentrated in subcellular lipid droplets rather than supernatant or particulate. Prolonged stimulation of rats with ACTH for 7 consecutive days caused 14-51% decreases in the fluorescence levels, with a tendency of return to control levels poststimulation regardless of age. In contrast, the nonpolar lipids of mouse adrenal tumor (Y1) cells, which contain no lipofuscin, did not display this fluorescence in the presence or absence of ACTH. The chromatographic characteristics of the substance in a silica gel-60 column resembled those of authentic retinyl palmitate and cholesteryl oleate. Analysis of the substance by HPLC demonstrated at least three prominent peaks, designated XI-3 in order. X1 and X2 were minor peaks; X3 was the major peak. Whereas none of the peaks comigrated with cholesteryl esters, X1 comigrated with authentic retinyl palmitate. Determination of the fatty acid component of the major fluorescent substance X3 by gas-liquid chromatography disclosed stearic acid. Retinyl stearate was, therefore, synthesized. The fluorescent profiles, HPLC retention time and mass spectrometric fragmentation of purified X3 substance were all identical to those of the synthetic compound. In contrast, the rat liver principally accumulated retinyl palmitate with age. Thus, we conclude that 1) the major nonpolar fluorescent substance accumulated in the rat adrenal with age is retinyl stearate, which may be a fluorophore of adrenal lipofuscin; 2) ACTH action may be related to this accumulation; and 3) the type of retinyl ester accumulated in aged animals is organ specific.

Topics: Adrenal Cortex; Adrenocorticotropic Hormone; Aging; Animals; Centrifugation, Density Gradient; Cholesterol Esters; Chromatography, Gel; Chromatography, High Pressure Liquid; Diterpenes; Lipofuscin; Male; Mass Spectrometry; Rats; Rats, Inbred F344; Retinyl Esters; Spectrometry, Fluorescence; Stearic Acids; Vitamin A

There are inverse relationships between HDL cholesterol and plasma triacylglycerol concentrations in normal and in hypertriglyceridemic individuals. To investigate the interactions between triacylglycerol-rich lipid particles and HDL, a lipid emulsion model of the triacylglycerol-rich lipoproteins was prepared. When emulsion particles were incubated with rat high-density lipoproteins (HDL) in the presence of lipid transfer activity (d greater than 1.21 g/ml fractions) from rabbit or human plasma there was a rapid bi-directional exchange of cholesteryl oleate (CO) and phospholipid (PL) labels between lighter and heavier fractions of HDL and emulsion particles. The transfers of CO and PL labels between both light and heavy fractions of HDL and the emulsion particles were increased with increasing amounts of emulsion added to the incubations. Incubation with the d greater than 1.21 g/ml fraction from rat plasma resulted in only a small exchange of CO whereas PL exchange was similar to rabbit and human plasma. Retinyl palmitate label was not transferred from emulsion particles to the HDL fractions even in the presence of lipid transfer activity from rabbit or human plasma. The present study shows that the transfer protein-mediated exchanges of surface and core lipids between HDL and the triacylglycerol-rich lipoproteins are affected by the quantity of triacylglycerol-rich particles in the system. This mechanism may contribute to the inverse relationships between plasma triacylglycerol concentrations and HDL concentrations in normal and hypertriglyceridemic individuals.

Topics: Animals; Cholesterol Esters; Diterpenes; Electrophoresis, Polyacrylamide Gel; Humans; Lipoproteins, HDL; Male; Phospholipids; Rabbits; Rats; Retinyl Esters; Triglycerides; Vitamin A

In previous studies, retinyl palmitate hydrolase activity in rat liver was partly characterized and was found to correlate and to partially copurify with hydrolytic activities against cholesteryl oleate and triolein. The present studies were designed to further explore relationships between these three lipid ester hydrolase activities, by use of non-hydrolyzable ether analogs of cholesteryl esters and acylglycerides. Cholesteryl ether analogs were potent inhibitors of all three hydrolase activities with relative potencies for the series of ethers of: linoleyl greater than oleyl = palmitoyl greater than n-butyl = n-propyl greater than ethyl = methyl. Retinyl palmitate hydrolase activity was most strongly inactivated by this series of analogs, with 48-86% of the activity inhibited at cholesteryl ether levels of 1 microM. The acylglyceride ether analogs were much weaker inhibitors of the three hydrolase activities, with the triolein, diolein and dipalmitin analogs showing similar inhibitory potencies, greater than that of the monolein and monopalmitin analogs. The data demonstrate the potential usefulness of ether analogs of cholesteryl esters and acylglycerides for exploring some of the characteristics of lipid ester hydrolase activities.

Topics: Animals; Carboxylic Ester Hydrolases; Cholesterol; Cholesterol Esters; Diterpenes; Ethers; Glycerol; Lipase; Liver; Rats; Rats, Inbred Strains; Retinyl Esters; Sterol Esterase; Triolein; Vitamin A