Albumin-bound quercetin repairs vitamin E oxidized by apolipoprotein radicals in native HDL3 and LDL.
In the minor fraction of HDL3 containing alpha-tocopherol (alphaTocOH), selective one-electron oxidation of Trp and Tyr residues of apolipoproteins A-I and A-II by *Br2- radical-anions produces the corresponding semioxidized species, TyrO* and *Trp. Repair of TyrO* by endogenous alphaTocOH generates the alpha-tocopheroxyl radical (alphaTocO*). Fast spectroscopic studies show that two populations representing 80% of alphaTocO* initially formed are repaired over several seconds with rate constants of 3.0 x 10(6) and 1.5 x 10(5) M-1 s-1 by quercetin bound to human serum albumin (HSA) at physiologically relevant concentration. Formation of HSA-bound quercetin radicals (*Qb) is observed. In the major fraction of HDL3 particles lacking alphaTocOH, TyrO* and *Trp are repaired by free and HSA-bound quercetin. In LDL particles which all contain alphaTocOH, alphaTocO* radicals are formed in the millisecond time scale by repair of TyrO* radicals produced in apolipoprotein B. Then, 75% of initial alphaTocO* are repaired over seconds by HSA-bound quercetin (rate constant: 2.0 x 10(6) M-1 s-1). HSA-bound quercetin can also repair *Trp radicals. In O2-saturated solutions, the fraction of alphaTocO* radicals (more than 50%) not repaired by superoxide radical-anions can be repaired by HSA-bound quercetin with formation of *Qb but to a much lesser extent in LDL than in HDL.
Filipe
Paulo
P
Faculdade de Medicina de Lisboa, Hospital Santa Maria, Clinica UniversitAria de Dermatologia, 1600 Lisbon, Portugal.
Patterson
Larry K
LK
Bartels
David M
DM
Hug
Gordon L
GL
Freitas
João P
JP
Mazière
Jean-Claude
JC
Santus
René
R
Morlière
Patrice
P
D016632:Apolipoprotein A-I / Q000494:pharmacology*; D016633:Apolipoprotein A-II / Q000494:pharmacology*; D005609:Free Radicals / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D053440:Lipoproteins, HDL3 / Q000494:pharmacology*; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D010084:Oxidation-Reduction; D011485:Protein Binding; D011794:Quercetin / Q000494:pharmacology*; D012709:Serum Albumin / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry; D014810:Vitamin E / Q000378:metabolism*
D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D005609:Free Radicals; D053440:Lipoproteins, HDL3; D008077:Lipoproteins, LDL; D012709:Serum Albumin; D014810:Vitamin E; D014443:Tyrosine; D014364:Tryptophan; D011794:Quercetin