chondroitin-sulfates and 2-2--azobis(2-amidinopropane)

The mechanism of metal ion-catalyzed oxidative modification of apolipoprotein E (apoE) in human very-low-density lipoprotein (VLDL) and its inhibition by glycosaminoglycan (GAG) was investigated in vitro. The VLDL oxidation catalyzed by Cu2+ led to the lipid peroxidation, the formation of aggregates, and covalent modification of apoE. The modified apoE lost heparin-binding activity. These results suggest that the lipid peroxidation of VLDL and modification of apoE cause impairment of lipid uptake by cells and deposit the oxidized lipids in the tissues. The lipid peroxidation and oxidative modification of apoE in VLDL mediated by Cu2+ and an aqueous radical generator were suppressed by GAG, heparan sulfate, heparin, and chondroitin sulfate A, even though GAGs demonstrated no ability to scavenge alpha,alpha-diphenyl-beta-picrylhydrazyl radical. There were no relationships between inhibitory activity of GAGs in the VLDL oxidation and their number of sulfate groups which possess chelating activity of metal ion. Therefore, it can be considered that the inhibition of VLDL oxidation by GAGs is possibly due to the interaction between GAG and VLDL which bring about the steric hindrance, interference with the reaction between VLDL particle and the reactive oxygen species. These studies suggest that GAGs preserve the biological functions of apoE from oxidative stress.

Topics: Adult; Aldehydes; Alzheimer Disease; Amidines; Apolipoproteins E; Bepridil; Biphenyl Compounds; Chelating Agents; Cholesterol Esters; Chondroitin Sulfates; Copper Sulfate; Dextrans; Free Radical Scavengers; Glutathione; Glycosaminoglycans; Heparin; Hippocampus; Humans; Hydrogen-Ion Concentration; Lipid Peroxidation; Lipoproteins, VLDL; Male; Picrates; Reactive Oxygen Species; Thiobarbituric Acid Reactive Substances

The effect of various glycosaminoglycans on Cu(2+)- and AAPH-induced oxidation of human low-density lipoprotein (LDL) was studied by monitoring conjugated diene formation. Heparin (Hep) increased the lag phase (t(lag)) of LDL oxidation, and fast moving and slow moving Hep species modified the kinetics of LDL oxidation to the same extent. Beef spleen heparan sulfate (HS) sample produced a significant increase of the t(lag) and a decrease of the conjugated diene formation of LDL whilst beef kidney HS species modified LDL oxidation kinetics to a lower extent. Dermatan sulfate (DS) from different sources caused a significant increase of the t(lag) and a decrease of the conjugated diene formation of LDL. Hyaluronic acid had no effect. Chondroitin sulfate (CS) from beef trachea produced a very strong protective antioxidant effect evaluated by increasing of the t(lag) and decreasing of the conjugated diene formation. Hep was completely ineffective in protecting LDL from 2, 2'-azobis(2-amidinopropane) hydrochloride (AAPH)-mediated oxidation, whilst DS was moderately effective. Beef trachea CS showed a very strong ability to protect LDL oxidation induced by 1 mM AAPH. The different protective effect on Cu(2+)- and AAPH-induced LDL oxidation by glycosaminoglycans is discussed considering their various structures and properties, and their capacity to interact to different extents with hydrophobic regions of LDL protein is confirmed by measuring the LDL-tryptophan fluorescence kinetics.

Topics: Amidines; Animals; Cattle; Chondroitin Sulfates; Copper; Dermatan Sulfate; Glycosaminoglycans; Heparin; Heparitin Sulfate; Humans; In Vitro Techniques; Kinetics; Lipoproteins, LDL; Oxidation-Reduction; Spectrometry, Fluorescence; Structure-Activity Relationship; Swine