Oxidation of LDL by hemoglobin.

(A) Standard reaction demonstrating the time-dependent increase in TBARS formation when LDL is incubated with hemoglobin (10 μM) in the presence of no haptoglobin, haptoglobin 1-1 (5 μM), or haptoglobin 2-2 (5 μM) as described in “Materials and methods.” Data shown are the mean ± SEM for 4 independent experiments. (B) Comparison of the ability to inhibit the hemoglobin-induced oxidation of LDL by haptoglobin 1-1 or 2-2. Hemoglobin was used at a concentration of 10 μM, and haptoglobin was used at the concentrations shown. Data are expressed as a percentage of inhibition of the amount of TBARS obtained in the absence of any haptoglobin over the entire incubation period by integrating the area under the TBARS versus the time curve using MATLAB, as described in “Materials and methods.” Data shown are the mean ± SEM of 4 independent experiments for each haptoglobin concentration. *Difference in the mean percentage inhibition between haptoglobin 1-1 and haptoglobin 2-2 was statistically significant (P < .004).