Reactivity of direct assays for low-density lipoprotein (LDL) cholesterol toward charge-modified LDL in hypercholesterolemia.

BACKGROUND: The aim of the present study was to compare 2 direct measurements for low-density lipoprotein cholesterol (LDL-C) with the Friedewald calculation (LDL-C [F]) in serum and their relationship with size-and charge-based LDL subfractions in serum ultracentrifugation fractions in patients with hypercholesterolemia (HC). METHODS AND RESULTS: Serum samples from 283 HC patients who participated in a statin trial (the PATROL trial) were analyzed. Homogeneous assays for LDL-C were performed using reagents from Sekisui Medical (LDL-C [Se]) and Kyowa Medex (LDL-C [Ky]). Charge-based LDL subfractions were analyzed by capillary isotachophoresis (cITP). In whole serum in HC patients at baseline, LDL-C (Se) and LDL-C (Ky) negatively and positively deviated, respectively, from LDL-C (F). The negative deviation of LDL-C (Se) from LDL-C (F) increased with increasing LDL-C, while the positive deviation of LDL-C (Ky) from LDL-C (F) was positively correlated with charge-modified LDL (cmLDL) as analyzed by cITP. In serum d>1.006 g/ml and >1.040 g/ml fractions (LDL and small, dense LDL fractions, respectively), the deviation of LDL-C (Ky) from LDL-C (Se) was positively correlated with LDL-apoB (the number of LDL particles) and cmLDL. CONCLUSIONS: The 2 homogenous assays for LDL-C differed with regard to reactivity toward LDL particles and cmLDL in patients with HC. Direct measurement of LDL-C that reflects modified LDL, could be a better marker for the risk of coronary heart disease.