Metabolism of apolipoprotein B-containing lipoproteins in familial hypercholesterolaemia: effects of plasma exchange.

The turnover of apolipoprotein B (apo B) in very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and low density lipoprotein (LDL) was investigated in 2 homozygous and 3 heterozygous patients with familial hypercholesterolaemia. The effects of a marked reduction in plasma LDL concentration, brought about by plasma exchange, upon apo B turnover were studied in 4 patients. Specific activity-time curves for the the plasma apo B after intravenous radioactive VLDL before plasma exchange indicated that in the heterozygotes all IDL-apo B was derived from VLDL and all LDL-apo B was derived from IDL, but the curves from the homozygotes showed that a significant fraction of the LDL in the plasma was not derived from IDL. Plasma exchange did not increase the rates of synthesis of LDL-apo B or VLDL-apo B and had no significant effect on the precursor--product relationship between IDL-apo B and LDL-apo B in heterozygous or homozygous patients. These findings provide no support for the hypothesis that apo B synthesis is controlled by the plasma LDL.