Multiple mechanisms for inhibition of low density lipoprotein oxidation by novel cyclic nitrone spin traps
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+)-depend...
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Published in | The Journal of biological chemistry Vol. 269; no. 45; pp. 28055 - 28061 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
United States
American Society for Biochemistry and Molecular Biology
11.11.1994
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Subjects | |
Online Access | Get full text |
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Summary: | 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. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0021-9258 1083-351X |
DOI: | 10.1016/s0021-9258(18)46894-9 |