Objectives: To study the role of the LDL receptor in the clearance of chylomicron remnants in humans.
Design: Chylomicron remnant clearance was studied in five untreated subjects with heterozygous familial hypercholesterolaemia (FH) and nine normolipidaemic controls, by oral retinyl palmitate-fat loading tests. Fasting plasma triglycerides (TG), which are important determinators of chylomicron and remnant clearance, were not significantly different between FH (1.76+/-0.32 mmol L(-1), mean+/-SEM) and controls (1.26+/-0.18 mmol L(-1). Chylomicrons (Sf > 1000) and their remnants (Sf < 1000) were separated by flotation and their clearance was estimated by calculating the area under the 24 h-retinyl palmitate curve (AUC-RP). The factors determining chylomicron and remnant clearance were studied by univariate and multiple regression analysis.
Results: Triglyceride clearance in plasma, Sf > 1000 fractions and Sf < 1000 fractions was not significantly different between FH subjects and controls. In subjects with heterozygous FH, chylomicron remnant clearance was two-fold delayed (AUC-RP, 49.39+/-11.61 h.mg L(-1) compared to controls (27.45+/-3.95 h.mg L(-1); P = 0.048). Moreover, 28.4% higher fasting plasma TG in FH resulted in 44.4% higher areas under the remnant-curves compared to controls. The clearance of chylomicron RP was associated to plasma apo E (beta = 0.73, P = 0.011), plasma LDL cholesterol (beta = 0.62, P = 0.018) and plasma TG (beta = 0.58, P = 0.029). The clearance of remnant RP was associated to the diagnosis (FH vs. non-FH), but not to the well-known determinants of remnant clearance like plasma TG.
Conclusions: The clearance of chylomicrons and large remnants isolated in the Sf > fraction depends primarily on the apo B, E (LDL) receptor and to a lesser extent on plasma triglycerides. The clearance of smaller chylomicron remnants isolated in the Sf < 1000 depends to a large extent on the apo B, E (LDL) receptor.