Site-specific trapping of reactive species in low-density lipoprotein oxidation: biological implications.
Abundant data suggest that the oxidative modification of low-density lipoprotein is mediated by lipid-derived free radicals and aldehydes derived from them. In this report we have addressed the site-specific aspects of low-density lipoprotein modification. To this end, both water-soluble and lipid-soluble spin traps (i.e., diamagnetic organic molecules containing nitroso or nitrone functional groups) were used. Radical adducts were detected by electron spin resonance-spin trapping technique. Biochemical indices of low-density lipoprotein modification were thiobarbituric acid reactive substances formation, electrophoretic mobility and macrophage-mediated uptake of oxidized low-density lipoprotein. Results from this study have shown that the lipophilic spin trap, alpha-phenyl-tert-butyl-N-nitrone, traps a primary low-density lipoprotein lipid-derived radical, while also inhibiting the total oxidative modification in a dose-dependent manner. The more hydrophilic analog, i.e., alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone, appeared to trap the secondary alkyl radicals and did not exert any inhibitory effect on oxidative modification of low-density lipoprotein. The lipophilic nitroso spin trap, 2-methyl-2-nitroso propane, which traps a lipid-derived radical, inhibited the low-density lipoprotein modification as did the water-soluble nitroso analog, 2-hydroxymethyl-2-nitroso propane. However, the water-soluble nitroso analog did not trap the lipid radical. The inhibitory effect of 2-hydroxymethyl-2-nitroso propane was tentatively attributed to trapping of aldehydes. It is conceivable that spin traps can inhibit the oxidative modification of low-density lipoprotein by trapping of the lipid radicals as well as trapping aldehydes formed from lipid peroxidation.
Kalyanaraman
B
B
Biophysics Research Institute, Medical College of Wisconsin, Milwaukee 53226.
Joseph
J
J
Parthasarathy
S
S
D000818:Animals; D001055:Apolipoproteins B / Q000737:chemistry; D002460:Cell Line; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006801:Humans; D015227:Lipid Peroxidation; D008077:Lipoproteins, LDL / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008956:Models, Chemical; D009589:Nitrogen Oxides; D009603:Nitroso Compounds; D010084:Oxidation-Reduction; D011725:Pyridines; D011817:Rabbits; D013113:Spin Labels; D017392:Thiobarbituric Acid Reactive Substances / Q000032:analysis
D001055:Apolipoproteins B; D003497:Cyclic N-Oxides; D005609:Free Radicals; D008077:Lipoproteins, LDL; D009589:Nitrogen Oxides; D009603:Nitroso Compounds; D011725:Pyridines; D013113:Spin Labels; D017392:Thiobarbituric Acid Reactive Substances; C043438:alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone; C029217:phenyl-N-tert-butylnitrone; C034526:tert-nitrosobutane