title: Spin trapping of lipid-derived radicals in liposomes.
abstract: Electron-spin resonance-spin trapping has been used to detect lipid-derived radicals in liposomes. Using the lipid-soluble spin trap 2-methyl-nitrosopropane (MNP), we have detected both the lipid and hydrogen-atom spin adducts in liposomes composed of a fully saturated phospholipid (dimyristoylphosphatidylcholine, DMPC) with various mol fractions of unsaturated phospholipid (1-palmitoyl-2-arachidonoylphosphatidylcholine, PAPC) or fatty acid (arachidonic acid, AA). The lipid-derived spin adduct formed during autoxidation of liposomes was separated by thin-layer chromatography and found to co-migrate with the product(s) formed by direct addition of MNP to the corresponding unsaturated lipid or fatty acid. Both the MNP-PAPC and MNP-AA spin adducts showed some restriction of rotational motion when in the liposome bilayer (rotational correlation times 0.72 and 0.69.10(-9) s, respectively), and nitrogen hyperfine coupling constants (14.94-14.96 G) consistent with a hydrophobic localization. Radical versus non-radical mechanisms of spin adduct formation during liposome autoxidation were separated using alpha-tocopherol as a radical scavenger. The utility of nitroso spin traps in trapping of radicals in liposomes is discussed.
authors.affiliation: Department of Radiology, Medical College of Wisconsin, Milwaukee 53226.
authors.forename: J B
authors.initials: JB
authors.lastname: Feix
authors.forename: B
authors.initials: B
authors.lastname: Kalyanaraman
mesh_terms: D002855:Chromatography, Thin Layer; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005609:Free Radicals; D050356:Lipid Metabolism; D008055:Lipids; D008081:Liposomes / Q000032:analysis; D009603:Nitroso Compounds; D010101:Oxygen Consumption / Q000187:drug effects; D010742:Phospholipid Ethers; D013113:Spin Labels; D013329:Structure-Activity Relationship; D014810:Vitamin E / Q000494:pharmacology
chemical_list: D005609:Free Radicals; D008055:Lipids; D008081:Liposomes; D009603:Nitroso Compounds; D010742:Phospholipid Ethers; D013113:Spin Labels; D014810:Vitamin E; C043051:1-O-hexadecyl-2-arachidonyl-sn-glycero-3-phosphocholine; C034526:tert-nitrosobutane