Nitrated apolipoprotein A-I, a potential new cardiovascular marker, is markedly increased in low high-density lipoprotein cholesterol subjects.

Background: Oxidative stress plays an important role in the pathogenesis of coronary artery disease. Recent work showed that high-density lipoproteins isolated from atherosclerotic lesions and blood of patients with established coronary artery disease contain elevated levels of nitrated apolipoprotein A-I. Methods to quantify nitrated apolipoprotein A-I in the plasma may facilitate in the determination of a correlation between plasma levels of nitrated apolipoprotein A-I and risk of atherosclerosis.

Methods: In this report, the presence of plasma nitrated apolipoprotein A-I in subjects with cardiovascular disease was detected by Western blot analysis and quantified by a newly developed specific sandwich enzyme-linked immunosorbent assay.

Results: The precision of the assay was indicated by the good correlation obtained between enzyme-linked immunosorbent assay and Western blot (r(2)=0.96). Using these two methods, we were able to detect significant elevations (3-fold increase) of plasma nitrated apolipoprotein A-I in low high-density lipoprotein cholesterol subjects as compared to high-density lipoprotein cholesterol subjects. In addition, we found that both plasma and serum samples can be used by enzyme-linked immunosorbent assay to quantify nitrated apolipoprotein A-I concentrations. More importantly, the degree of nitrated apolipoprotein A-I-containing high-density lipoprotein particles was negatively correlated with levels of circulating apolipoprotein A-I.

Conclusions: Measurement of nitrated apolipoprotein A-I levels by this rapid and reproducible new method has the advantages of great sensitivity with no sample manipulations, thus we suggest that this novel method could be useful to monitor levels of circulating nitrated apolipoprotein A-I in order to investigate its value as a potential biological marker for inflammatory vascular disease.