Charged phospholipid effects on AAPH oxidation assay as determined using liposomes

Area of Science:

• Lipid chemistry
• Biophysical chemistry
• Spectroscopic analysis

Background:

• Liposomes are common matrices for testing antioxidant capacity.
• Spectroscopic assays, particularly using 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH), are standard for this purpose.
• The influence of charged lipids on these assays is not fully understood.

Purpose of the Study:

• To investigate the effect of charged lipids on AAPH antioxidation assays.
• To determine if liposome size or zeta potential is more influential in the assay.
• To assess the impact of varying cationic or anionic lipid concentrations on assay results.

Main Methods:

• Liposomes containing the reporter molecule C11-BODIPY® 581/591 were prepared.
• Varying molar percentages (0-10%) of cationic or anionic lipids were incorporated.
• Liposome diameter, zeta potential, and spectroscopic fluorescence decay (rate and AUC) were measured.

Main Results:

• Increasing charged lipid content altered liposome diameter.
• Liposome size showed minimal effect on fluorescence decay rate and AUC.
• Changes in zeta potential (positive or negative) significantly affected fluorescence decay rates and AUC.

Conclusions:

• Zeta potential, rather than liposome size, is a critical factor in AAPH antioxidation assays.
• The presence and charge of lipids must be considered for accurate antioxidant capacity measurements.
• This study highlights the importance of characterizing liposome surface charge in assay development.