Isolation of plasma small-dense low-density lipoprotein using a simple air-driven ultracentrifuge and quantification using immunoassay of apolipoprotein B.
Small-dense low-density lipoprotein (SD-LDL) is associated with coronary heart disease risk. Current methods for its quantification are expensive, complex and time-consuming. Plasma was adjusted to a density (D) of 1.044 g/ml in a volume of 0.18 ml and centrifuged in a Beckman Airfuge at 160 000 x g for 3 h 7 min and apolipoprotein B (apoB) then determined in the infranatant. Results were compared with centrifugation of 5 ml of plasma at D = 1.044 g/ml at 144 000 x g for 18 h in a preparative ultracentrifuge (UC). We obtained blood samples from healthy subjects (n = 73) and from dyslipidaemic patients (n = 112). SD-LDL apoB levels as determined using the UC method ranged from 0.01-0.43 g/l and there was a good correlation with Airfuge results (r = 0.925; p < 0.0001; n = 185). There was a mean difference of 0.0125 g/l between methods. SD-LDL apoB levels as determined using the Airfuge showed a reasonable agreement with results obtained using density gradient ultracentrifugation (r = 0.773; p < 0.01; n = 12). Airfuge results correlated directly with triglyceride concentration, in both healthy men (r = 0.296; p < 0.05) and dyslipidaemic men (r = 0.520; p < 0.001) and also in dyslipidaemic women (r = 0.463; p < 0.005). Airfuge results correlated inversely with high-density lipoprotein-cholesterol (HDL-C) concentration, in both healthy men (r = -0.237; p < 0.05) and dyslipidaemic men (r = -0.293; p < 0.005). Using a micro-method, we obtained results which establish that the Airfuge provides a more rapid and less expensive method for quantification of SD-LDL.