English abstract
recognized to correlate with increased triglycerides (TGs), and low HDL-cholesterol (HDL-C). Indeed, it is known that the TG concentration is inversely associated with LDL size.Methods for measurement of sd LDL concentration are too laborious for clinical use. A new technique was recently established to quantify sd LDL concentration. It is a simple precipitation method consisting of two steps: first, to precipitate the lipoproteins (density (d) = 1.044 to 1.063 g/ml) using heparin-magnesium; and second, to measure LDL cholesterol in the supernatant using automated clinical chemistry analyzer.The aim of this study was to measure sd LDL concentration in Omani subjects with different lipid profiles, particularly subjects with high and normal TG levels. The accuracy of this method was verified by measuring LDL size using the conventional method; Polyacrylamide Gradient Gel Electrophoresis (PAGGE).132 serum samples were collected from normolipidemic and dyslipidemic Omani men and women. The subjects were categorized according to their serum triglyceride levels. LDL cholesterol, HDL cholesterol, apoprotein B, apopreotein A-1 and glucose were also measured.Using the precipitation method, we found that subjects with hypertriglyceridemia (TG > 1.7 mmole/L or TG/HDL > 0.9) had a significantly higher concentration of sd LDL than subjects with normal TG levels. Bivariate correlation analysis, in general, showed a significant positive correlation between TG levels and sd LDL concentration (r = 0.395, p<0.0001), which was higher than the correlation of TG levels with conventionally measured LDL-C.This was coherent with our findings using PAGGE where TG levels negatively correlated with size of LDL in our subjects (r = -0.432, p<0.0001) and in fact, stepwise multiple regression showed that TG levels, regardless of LDL-C concentration, were the only significant determinant of LDL size (- -1.46. p<0.0001). Furthermore, a significant negative correlation was found between LDL size and concentration of sd LDL determined using the precipitation method (r = . 0.207, p<0.05).These results underline the importance of increased TG levels in serum, as the increase in TG levels alone in serum even without an increase in LDL-C levels is associated with increased sd LDL concentration and decreased LDL size which are major CAD risk factors.This simple precipitation method may be useful and applicable to obtain a direct estimate of sd LDL concentration created due to increased TG levels in serum. Therefore, the results also suggest that TG levels should not be overlooked as a major risk factor for CAD and measuring TG levels may be a valuable inexpensive screening tool to identify patients at risk of CAD due to increased sd LDL-C.
