Apolipoprotein A-I(Milano) and apolipoprotein A-I(Paris) exhibit an antioxidant activity distinct from that of wild-type apolipoprotein A-I.
Apolipoprotein A-I(Milano) (apoA-I(Milano)) and apoA-I(Paris) are rare cysteine variants of apoA-I that produce a HDL deficiency in the absence of cardiovascular disease in humans. This paradox provides the basis for the hypothesis that the cysteine variants possess a beneficial activity not associated with wild-type apoA-I (apoA-I(WT)). In this study, a unique antioxidant activity of apoA-I(Milano) and apoA-I(Paris) is described. ApoA-I(Milano) was twice as effective as apoA-I(Paris) in preventing lipoxygenase-mediated oxidation of phospholipids, whereas apoA-I(WT) was poorly active. Antioxidant activity was observed using the monomeric form of the variants and was equally effective before and after initiation of oxidative events. ApoA-I(Milano) protected phospholipid from reactive oxygen species (ROS) generated via xanthine/xanthine oxidase (X/Xo) but failed to inhibit X/Xo-induced reduction of cytochrome c. These results indicate that apoA-I(Milano) was unable to directly quench ROS in the aqueous phase. There were no differences between lipid-free apoA-I(Milano,) apoA-I(Paris), and apoA-I(WT) in mediating the efflux of cholesterol from macrophages, indicating that the cysteine variants interacted normally with the ABCA1 efflux pathway. The results indicate that incorporation of a free thiol within an amphipathic alpha helix of apoA-I confers an antioxidant activity distinct from that of apoA-I(WT). These studies are the first to relate gain of function to rare cysteine mutations in the apoA-I primary sequence.
Bielicki
John K
JK
Genome Sciences Department, Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. jkbielicki@lbl.gov
Oda
Michael N
MN
D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D016632:Apolipoprotein A-I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001161:Arteriosclerosis / Q000517:prevention & control; D002460:Cell Line; D003545:Cysteine / Q000235:genetics; D019281:Dimerization; D014644:Genetic Variation; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D015227:Lipid Peroxidation; D008075:Lipoproteins, HDL / Q000378:metabolism; D051379:Mice; D009154:Mutation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D000975:Antioxidants; D016632:Apolipoprotein A-I; D008075:Lipoproteins, HDL; D011994:Recombinant Proteins; C080631:apolipoprotein A-I Milano; D003545:Cysteine