OXIDATIVE MODIFICATION OF HDL3 IN-VITRO AND ITS EFFECT ON PLTP-MEDIATED PHOSPHOLIPID TRANSFER

The oxidation of HDL, by Cu(II) and its effect on the ability of these particles to act as phospholipid accepters in human plasma phospholip id transfer protein (PLTP)-mediated lipid transfer were investigated. Oxidation of HDL3 was monitored by measuring the following parameters: (i) formation of conjugated dienes, (ii) production of thiobarbituric acid reactive substances (TBARS), (iii) decrease in reactive lysine a nd (iv) tryptophan residues, (v) change in particle charge and (vi) di ameter, and (vii) oligomerisation of apoA-I and apoA-II. Formation of conjugated dienes was the parameter responding to the oxidative treatm ent with the fastest kinetics. The appearance of TBARS and modificatio n of apolipoprotein tryptophan residues were detected simultaneously b ut required higher Cu(II) concentrations for maximal kinetics. Cross-l inking of the major protein constituents of HDL3, apoA-I and apoA-II, represented later steps of the oxidation process. Further, the oxidati ve modification was accompanied by a progressive change in HDL3 partic le charge and a minor increase in particle diameter. PLTP-mediated pho spholipid transfer to the oxidized particles was investigated using an assay measuring the transfer of fluorescent, pyrene-labeled PC. The t ransfer was significantly inhibited, but only after extensive modifica tion of the HDL proteins, suggesting that the HDL oxidative modificati ons occurring in vivo do not essentially impair its phospholipid accep tor function. A similar but less pronounced inhibition was observed wh en two other phospholipid transfer proteins, the nonspecific lipid tra nsfer protein (ns-LTP) and the phosphatidylcholine transfer protein (P C-TP), were studied in parallel. This indicates that the inhibition wa s partly due to unspecific effects of the modification on acceptor par ticle surface properties, but included an aspect specific for PLTP. (C ) 1998 Elsevier Science B.V.