Surfactant-based homogeneous assay for the measurement of triglyceride concentrations in VLDL and intermediate-density lipoprotein

BACKGROUND: Existing studies have demonstrated the clinical significance of triglyceride content in VLDL (VLDL-TG) and intermediate-density lipoprotein (IDL-TG). We developed a homogeneous assay protocol to directly measure VLDL-TG. METHODS: Possible reagents and conditions for measuring VLDL-TG were comprehensively tested, and the "best" combination was determined. Healthy persons were instructed to consume a fatty meal after 15-h overnight fasting. Serum VLDL-TG + IDL-TG concentrations were measured using the proposed method. Patients with serum LDL-cholesterol concentrations > or = 3.62 mmol/L (140 mg/dL) were administered simvastatin at a daily dose of 5 mg, and serum VLDL-TG concentrations were then measured. RESULTS: The combination of 2 nonionic surfactants played an important role in differentiating VLDL and IDL from other lipoproteins, probably via specific interactions with phospholipids and apolipoproteins. The regression line of the proposed method (y) and the ultracentrifugal assay (x) was: y = 0.98x + 0.31 mmol/L (r = 0.98; n = 73; P < 0.05). The difference between postprandial total TG and VLDL-TG concentrations was statistically significant (P < 0.05). After 8 weeks of therapy with simvastatin, total TG and LDL-cholesterol concentrations were 13.6% and 26.3% lower, respectively (P < 0.05), whereas VLDL-TG did not show any significant decrease. CONCLUSION: Our homogeneous method can measure TG content in VLDL and IDL.