Background: Lipoprotein(a) [Lp(a)] is known to be a cholesterol-rich lipoprotein, however, the contribution of Lp(a)-cholesterol [Lp(a)-C] to the serum cholesterol and LDL-C levels has not yet been fully evaluated.
Methods: We determined the serum Lp(a)-C in 55 subjects with serum Lp(a) concentrations ranging from 9 to 129 mg/dl. To measure the serum Lp(a)-C concentrations, we developed an immunoaffinity gel assay; serum was incubated with Sepharose 4B gel coupled with immunoglobulin G (IgG) prepared from a polyclonal anti-Lp(a) goat antiserum. After separating Lp(a) from other lipoproteins, we determined the serum Lp(a)-C concentrations. Validation of the assay showed satisfactory results in terms of the specificity and reproducibility.
Results: The mean cholesterol content of Lp(a), determined as Lp(a)-C/Lp(a), was 29.5±10.4%. The serum Lp(a)-C values were found to be highly correlated with the serum Lp(a) mass (r=0.923, p<0.001). At serum Lp(a) levels of over 50mg/dl, the contribution of Lp(a)-C to the serum total cholesterol was 10.2%. Further, the Friedewald formula overestimated the serum LDL-C by 20.4%.
Conclusions: Lp(a) contains approximately 30% cholesterol in each molecule. In subjects with markedly elevated serum Lp(a) concentrations, the Lp(a)-C values should be taken into account when evaluating the serum LDL-C.
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