Wavelength dependence of photoinduced peroxidation and cytotoxicity of human low density lipoproteins.

The relative abilities of UV-A, B and C radiations to initiate lipid peroxidation and apolipoprotein (apo) B modification of human purified low density lipoproteins have been compared. Ultraviolet-B and C (at 310 and 254 nm, respectively) exhibited similar efficacy as shown by the increase in lipid peroxidation markers (conjugated dienes, thiobarbituric acid reactive substances and fluorescent lipid soluble products) and in oxysterols, as well as by the decrease of the contents of natural antioxidants (tocopherols and carotenes) and in polyunsaturated fatty acids. In contrast, UV-A (at 360 nm) was found poorly effective and only at very high radiation intensities.

Serum level of 7 alpha-hydroxycholesterol in hypercholesterolemic patients treated with cholestyramine.

Serum levels of 7 alpha-hydroxycholesterol (7 alpha (OH)C) were found to increase considerably in hypercholesterolemic patients treated with cholestyramine. After 3-5 days, the normal level, which is in the range of 0.04 mg/l, rose to 1 mg/l.

Intestinal absorption and fecal excretion of 5,6 alpha-epoxy-5 alpha-cholesta-3 beta-ol by the male Wistar rat.

The intestinal absorption of 5,6 alpha-epoxy-5 alpha-cholesta-3 beta-ol, an oxysterol formed by cholesterol autoxidation, has been evaluated in the male Wistar rat. Measurement of the 14C/3H ratio in the serum (by the method of Zilversmit and Hugues) and in the feces showed that a large proportion of the epoxide was absorbed. Epoxide clearance from the blood was very rapid, but its excretion in the stool continued for several days, corresponding to the fraction of the epoxide stored in the animal.

Autoxidation of cholesterol in tallows heated under deep frying conditions: evaluation of oxysterols by GLC and TLC-FID.

The products of cholesterol autoxidation (oxysterols) in heated animal food fat were determined qualitatively and quantitatively to evaluate their toxicity and those of the foods in which they occur. Samples of beef tallow were taken from deep-fat fryers while they were in use. The oxysterols were identified and assayed by gas liquid chromatography and thin layer chromatography on Chromarods with flame ionization detection (TLC-FID).

Preparation of autoxidized cholesterol mixtures from [4-14C] cholesterol and cholesteryl fatty acid esters.

Autoxidation of non-esterified cholesterol, in the solid state, at 100 degrees C, is known to be a relatively slow reaction. The presence of carefully chosen cholesteryl esters considerably increases the ratio of autoxidation. Using this method, mixtures of autoxidized free cholesterol (oxycholesterol) labelled on carbon 4 can be obtained almost quantitatively, in the presence of benzoyl peroxide.