A new approach to the quantitative measurement of dense LDL subfractions.
OBJECTIVE
Small dense low-density lipoproteins (LDLs) should be considered a major risk factor for cardiovascular disease, but there is still no recommended method for measuring them or expressing clinical values. We measured the dense LDL portion relatively simply by isolating it using density ultracentrifugation and then giving it a relative, quantitative value.


METHODS
Dense LDLs (d=1.048-1.063 g/mL) were isolated from human plasma at the same time as total LDL (d=1.021-1.063 g/mL) by means of sequential ultracentrifugation, and the former was assessed as a percentage of the latter. A receiver operator characteristic (ROC) curve was used to compare the different LDL components as markers of dense LDLs. The proposed method was compared with non-denaturing gradient gel electrophoresis (NDGGE). In order to obtain clinical data, the dense LDL portion was measured in diabetic and postmenopausal subjects and healthy controls.


RESULTS
The ROC curve showed that cholesterol level was a more accurate marker of dense LDLs. The within-run precision (CV) was 2.28%, and the between-run CV was 5.1%. Analytical recovery was 80.2+/-1.6%. The correlation between the proposed method and NDGGE was r=0.90, p<0.001. The dense LDL percentage significantly correlated with serum triglyceride (r=0.57, p<0.001) and high-density lipoprotein cholesterol levels (r=-0.33, p<0.01), but not with the LDL-cholesterol/apolipoprotein B ratio. The diabetic patients and postmenopausal women had higher dense LDL values than the healthy controls.


CONCLUSIONS
The results obtained using this procedure are in line with those obtained using NDGGE, which is the conventional assay system for measuring LDL size. Determining the small dense LDL portion by means of its cholesterol content may be a better approach to characterising the risk of cardiovascular disease, even in the presence of relatively normal LDL-cholesterol levels.
Berg
G
G
Laboratory of Lipids and Lipoproteins, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Argentina.
Muzzio
M L
ML
Wikinski
R
R
Schreier
L
L
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001055:Apolipoproteins B / Q000097:blood*; D002318:Cardiovascular Diseases / Q000097:blood; D002499:Centrifugation, Density Gradient / Q000379:methods*; D002784:Cholesterol / Q000097:blood; D008076:Cholesterol, HDL / Q000097:blood; D008078:Cholesterol, LDL / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D008875:Middle Aged; D017698:Postmenopause / Q000097:blood; D012372:ROC Curve; D012307:Risk Factors; D012680:Sensitivity and Specificity; D014280:Triglycerides / Q000097:blood
D001055:Apolipoproteins B; D008076:Cholesterol, HDL; D008078:Cholesterol, LDL; D014280:Triglycerides; D002784:Cholesterol