Apolipoprotein-lipid association in oxidatively modified HDL and LDL

Area of Science:

• Biochemistry
• Lipid Peroxidation
• Protein Chemistry

Background:

• High-density lipoprotein (HDL) and low-density lipoprotein (LDL) are crucial for lipid transport.
• Lipid peroxidation can alter protein structure and function within lipoproteins.
• Tryptophan (Trp) residues are sensitive indicators of protein conformational changes.

Purpose of the Study:

• To investigate the impact of Cu2+-catalyzed lipid peroxidation on tryptophan residues in HDL and LDL.
• To assess the effects of peroxidation on apolipoprotein-lipid association in HDL and LDL.
• To characterize structural changes in apolipoproteins A-I (apo HDL) and B (apo LDL) following oxidation.

Main Methods:

• Incubation of HDL and LDL with Cu2+ to induce peroxidation.
• Measurement of tryptophan fluorescence intensity and maximum emission wavelength (lambda max).
• Analysis of apolipoprotein status using guanidine hydrochloride (GuHCl) denaturation, SDS-PAGE, nondenaturing gradient gel electrophoresis, and ultracentrifugation.

Main Results:

• Cu2+ oxidation rapidly decreased Trp fluorescence in both HDL and LDL, increasing lambda max in HDL but not LDL.
• Oxidized HDL (4h-oxHDL) showed increased lambda max linked to protein crosslinking and larger particle formation, not dissociation.
• Oxidized LDL (4h-oxLDL) exhibited apo B fragmentation without dissociation or change in particle size, with fluorescence changes apparent only with GuHCl.
• Apolipoprotein-lipid association stability was higher in oxidized HDL compared to native HDL, and comparable between oxidized and native LDL.

Conclusions:

• Lipid peroxidation directly affects Trp residues in HDL and LDL apolipoproteins.
• HDL oxidation induces conformational changes, crosslinking, and particle enlargement, enhancing apolipoprotein-lipid stability.
• LDL oxidation results in apo B fragmentation without dissociation, with altered fluorescence properties under denaturing conditions.
• The stability of apolipoprotein-lipid association differs between oxidized HDL and LDL.