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Papers In Press, published online ahead of print December 1, 2004
J. Lipid Res., doi:10.1194/jlr.M400213-JLR200

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Journal of Lipid Research, Vol. 45, 2260-2268, December 2004
Copyright © 2004 by American Society for Biochemistry and Molecular Biology

Purified human serum PON1 does not protect LDL against oxidation in the in vitro assays initiated with copper or AAPH

John F. Teiber, Dragomir I. Draganov and Bert N. La Du¹

Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI

¹ To whom correspondence should be addressed. e-mail: bladu{at}umich.edu

Purified serum paraoxonase (PON1) had been shown to attenuate the oxidation of LDL in vitro. We critically reevaluated the antioxidant properties of serum PON1 in the in vitro assays initiated with copper or the free radical generator 2,2'-azobis-2-amidinopropane hydrochloride (AAPH). The antioxidant activity of different purified PON1 preparations did not correlate with their arylesterase (AE), lactonase, or phospholipase A₂ activities or with the amounts of detergent or protein. Dialysis of three of these preparations resulted in a 30–40% loss of their AE activities but in a complete loss of their antioxidant activities. We also followed the distribution of the antioxidant activity during human serum PON1 purification by two purification methods. The antioxidant activity of the anion-exchange chromatography fractions did not copurify with PON1 using either method and could largely be accounted for by the "antioxidant" activity of the detergent present.

In conclusion, using the copper or AAPH in vitro assays, no PON1-mediated antioxidant activity was detected, suggesting that the removal of PON1 from its natural environment may impair its antioxidative activity and that this assay with highly purified PON1 may be an inappropriate method with which to study the antioxidative properties of the enzyme.

Abbreviations: AAPH, 2,2'-azobis-2-amidinopropane hydrochloride; AE, arylesterase; DDM, n-dodecyl-ß-D-maltoside; DLPC, L--dilauroylphosphatidylcholine; PLA₂, phospholipase A₂; PON1, paraoxonase; TBARS, thiobarbituric acid-reactive substances

Supplementary key words paraoxonase 1 • oxidized low density lipoprotein • antioxidants • atherosclerosis • 2,2'-azobis-2-amidinopropane hydrochloride

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