Reason of postprandial low-density lipoprotein cholesterol reduction measured by enzymatic assays: based on nuclear magnetic resonance method / 中华检验医学杂志

ABSTRACT

Objective:To explore the postprandial plasma low-density lipoprotein cholesterol (LDL-C) changes by various detection methods.Methods:A total of 85 subjects admitted to the Second Xiangya Hospital of Central South University from November 2017 to May 2019 were included. Serum samples were collected from fasting and the 2 nd hour and the 4 th hour after breakfast. Serum lipid levels were measured with enzymatic assays and nuclear magnetic resonance spectroscopy (NMRS), and proprotein invertase subtilisin/kexin type 9 (PCSK9) levels were measured with enzyme-linked immunosorbent assays. The differences of blood lipid components at different time points were compared by Friedman two-way rank analysis of variance and Wilcoxon signed rank test, and the correlation between PCSK9 level and lipoprotein particles was analyzed by Spearman correlation. Results:Measured by enzymatic assays, compared with the fasting state, LDL-C decreased at the 2 nd hour and the 4 th hour after the meal (2.58[2.09, 3.12], 2.47[1.92, 3.02], 2.37[1.82, 2.80] mmol/L, P<0.001). Measured by NMRS, the concentration of LDL particles (1 086[830, 1 239], 1 083[848, 1 213], 1 061[814, 1 213] nmol/L, P=0.417) did not change significantly, and cholesterol in LDL particles were 2.13 (1.56, 2.54), 2.16 (1.68, 2.50), 2.06 (1.58, 2.50) mmol/L, respectively ( P=0.047)，and postprandial cholesterol in LDL particles in the 2 nd hour and in the 4 th hour did not change significantly compared with fasting ( P>0.05). while the concentration of large LDL particles (185.2[150.6,221.6], 173.0[144.8,220.3], 178.1[144.0,233.6] nmol/L, P=0.001), and the cholesterol level in large LDL particles (0.49[0.39, 0.57], 0.47[0.38, 0.57], 0.46[0.37, 0.58]mmol/L, P<0.001) decreased after the meal. The PCSK9 level also decreased significantly after the meal (299[233, 397], 257[208, 342], 251[215, 340] ng/ml, P<0.001). There was an independent positive correlation between the decrease of PCSK9 levels and the increase of remnant cholesterol detected by MNRS after the meal ( r=0.232, P=0.035). Conclusions:The postprandial LDL-C level measured by NMRS and enzymatic assays is not consistent. The decrease of LDL-C measured by enzymatic assays is not caused by the clearance of LDL particles, but by the redistribution of cholesterol in each LDL subfraction.