Faculty Collaboration Database

Multiple mechanisms for inhibition of low density lipoprotein oxidation by novel cyclic nitrone spin traps. J Biol Chem 1994 Nov 11;269(45):28055-61

Date

11/11/1994

Pubmed ID

7961741

Scopus ID

2-s2.0-0028104414 (requires institutional sign-in at Scopus site)   27 Citations

Abstract

Oxidation of low density lipoproteins (LDL) may be a critical atherogenic event owing to the diverse array of biologic effects attributed to modified LDL. Recently, we and others have demonstrated that the lipophilic nitrone spin trap alpha-phenyl-N-tert-butyl nitrone (PBN) can inhibit Cu(2+)-dependent LDL oxidation while the related, more hydrophilic analog alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone is ineffective. Because the inhibitory activity of PBN is relatively weak as compared to hydrophobic phenolic antioxidants, we have synthesized a number of cyclic analogues of PBN that encompass a wide range of hydrophobicity and examined their ability to inhibit LDL oxidation in vitro. Formation of a six-membered ring by a bond formed from one methyl of the tert-butyl group to the aromatic ring yielded MDL 101,002, which was 3- and 24-fold more active than PBN against Cu2+ and 2,2'-azobis-2-amidinopropane hydrochloride-dependent oxidation, respectively. The effect of aromatic substituents was examined and, in general, activity positively correlated with hydrophobicity, particularly with Cu2+. Electron spin resonance (ESR) spectroscopy demonstrated that the PBN adduct in oxidized LDL is composed of a mobile component (exposed to the LDL aqueous phase) and an immobilized component, localized in the lipid-protein interface or in the bulk lipid. The most active cyclic nitrones exhibited only highly immobilized adducts, suggesting they are buried within the particle. Studies with MDL 105,185 (which is a chloro-substituted nitrone containing a seven-membered ring rather than six-membered as for MDL 101,002) demonstrated radical trapping in both the lipid and apoprotein fractions. Compounds in which a spirocyclohexyl ring was substituted for the gem-dimethyl methylene (MDL 102,832 and 101,694) formed hydrophobic Cu2+ complexes that were observed in the lipid fraction by ESR. This result was confirmed by fractionation of LDL oxidation reaction mixtures and spectrophotometric quantitation of associated Cu2+. The ability to bind Cu2+ was dependent upon the presence of the spirocyclohexyl ring. These data demonstrate that cyclic nitrones can inhibit LDL oxidation at exceedingly low concentrations by multiple mechanisms: 1) trapping of lipid-derived radicals, 2) trapping of apoprotein B-derived radicals, and 3) binding of Cu2+ ions. It is suggested that this new class of highly potent spin traps may be used as effective radical traps in free radical biology and medicine.

Author List

Thomas CE, Ohlweiler DF, Kalyanaraman B

Author

Balaraman Kalyanaraman PhD Professor in the Biophysics department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Copper
Electron Spin Resonance Spectroscopy
Humans
Lipoproteins, LDL
Nitrogen Oxides
Oxidation-Reduction
Protein Binding
Spin Labels
Structure-Activity Relationship