2.10. Cupric Ion-Induced Human Low-Density Lipoprotein (LDL) Peroxidation

The LDL oxidation inhibition activity of sea cucumbers was measured based on the method of Ambigaipalan and Shahidi [20], with slight modification. Briefly, human LDL (5 mg/mL) was dialyzed in 10 mM phosphate buffer (PBS, pH 7.4, 0.15 M NaCl) at 4 °C for 12 h. Then, 0.8 mL of diluted LDL cholesterol (0.04 mg LDL/mL) was mixed with 0.1 mL sea cucumber extract (0.1 mg/mL), followed by pre-incubation at 37 °C for 15 min. To initiate the oxidation reaction, a solution of cupric sulfate (0.1 mL, 100 μM) was added to the mixture, followed by incubation at 37 °C for 22 h. A diode array spectrophotometer was used to measure the formation of conjugated dienes (CD) produced from the oxidation of LDL cholesterol at 234 nm. Blanks were prepared by replacing LDL and CuSO₄ with PBS.