Annexin V is known to bind to the phosphatidylserine (PS) of damaged cell membranes. We recently demonstrated that annexin V binds to oxidized red blood cells (oxRBC). The aim of this study was to find whether annexin V binds to oxidized lipids or to the PS of oxRBC.

Red blood cells (RBC) were oxidized by the addition of CuSO₄, and the degree of oxidation evaluated using the semiquantitative measurement of thiobarbituric acid reactive substance (TBARS). The binding of annexin V to oxRBC was evaluated by flow cytometry.

Annexin V was found to bind to oxRBC, but not to native RBC. The percentage of RBC binding to annexin V was closely correlated with the degree of oxidation, as measured using TBARS (r=0.99, p=0.000) in relation to the concentration of CuSO₄. The binding of annexin V to oxRBC was attenuated in the presence of oxidized low density lipoprotein (oxLDL), with these phenomena also being dose-dependent. The binding was reduced by 71.0±3.0% in the presence of 100 µg/mL oxLDL. LDL had no influence on the binding of annexin V to oxRBC.

These findings suggest that annexin V may bind to the oxidized lipids of cell membranes. Further studies will be required to evaluate the relative importance between oxidized lipids and PS, and to find the characteristics of oxidized lipids in the binding of annexin V to damaged cell membranes.