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Differences in the Results and Interpretation of Oxidized LDL Cholesterol by Two ELISA Assays – An Evaluation with Samples from the PIOstat Study by Andreas Pfützner, Karagiannis Efstrathios, Mirjam Löbig, Franz Paul Armbruster, Markolf Hanefeld, Thomas Forst

Background: The oxidized LDL-particles (oxLDL) are considered to be an important driving factor in the pathophysiology of arteriosclerosis. Few methods exist today to directly determine oxLDL in human plasma. We evaluated the plausibility of results derived from a new ELISA (Immundiagnostik, Bensheim, Germany) in comparison to a different ELISA test (Mercodia, Uppsala, Sweden).
Methods: Samples from a previous prospective, randomized study comparing the effects of pioglitazone with simvastatin on chronic systemic inflammation were measured at baseline and endpoint with both tests. Both drugs are known to have a decreasing effect on circulating small dense oxLDL levels.
Results: In total, 84 patients without diabetes mellitus were included into this analysis (45 female, 39 male, age(mean±SD): 58±8 years). With the Mercodia ELISA, a decrease in oxLDL was seen with simvastatin only (Mean±SD: 54.2±12.5 U/L at baseline vs. 42.9±12.9 U/L at endpoint; p<0.001, pioglitzone: 53.8±13.2 U/L vs. 54.3±15.254 U/L, n.s.). In contrast, a decrease of oxLDL was observed with the new ELISA for both drugs (simva- statin 65.1±21.8 ng/mL vs. 52.7±19.8 ng/mL; pioglitazone: 72.8±26.1 ng/ml vs. 57.9±22.1 ng/ml, p < 0.01 vs. baseline in both cases).
Conclusion: Determination of oxLDL with the Mercodia method lead to lower results and detected only the changes with simvastatin. While statins decrease the overall number of oxLDL particles, pioglitazone predominantly changes the size and LDL composition leading to larger particles with lower oxidation. In our study, the Immundiagnostik ELISA but not the competitive method confirmed the expected efficacy of PPARγ-activation in decreasing the oxidation of LDL particles.

DOI: Clin. Lab. 2009;55:275-281