PAF-acetylhydrolase, predominantly present in LDL in healthy subjects, is associated with HDL in a patient with LDL deficiency.
The degradation of platelet-activating factor (PAF) in plasma is catalyzed by PAF-acetylhydrolase resulting in lyso-PAF which is biologically inactive. Normally, most of the PAF-degrading activity is associated with low-density lipoproteins (LDL). The enzyme activity was measured in the plasma of a patient with abetalipoproteinemia, a disorder characterized by the absence of apolipoprotein-B-containing lipoproteins (chylomicrons, VLDL and LDL). Here we report that the plasma of the patient has a normal activity of PAF-acetylhydrolase. The enzyme activity is bound to high-density lipoproteins (HDL) and shows the kinetic properties of the LDL-associated enzyme of healthy subjects. Following administration of artificial triglyceride-rich particles (ATRP), part of the enzyme activity is found associated with ATRP, indicating that PAF-acetylhydrolase can transfer from HDL to triglyceride-containing lipid complexes in vivo.