Active and low-active forms of serum phospholipid transfer protein in a normal Finnish population sample.

Human serum phospholipid transfer protein (PLTP) exists as a catalytically active (HA-PLTP) and a low-active (LA-PLTP) form. In this study, the association of PLTP activity and the concentrations of both forms with lipid and carbohydrate parameters were investigated. In a random Finnish population sample, serum PLTP concentration (n = 250) was 6.56 ′ 1.45 mg/l, the mean lipoprotein-independent (PLTP e x o ) phospholipid transfer activity was 6.59 ′ 1.66 μmol/ml/h, and the mean lipoprotein-dependent (PLTP e n d o ) activity was 1.37 ′ 0.29 μmol/ml/h. Of the serum PLTP concentration, ∼46% was in a catalytically active form. HA-PLTP concentration correlated positively with serum PLTP e x o activity (r = 0.380, P < 0.001), HDL cholesterol (r = 0.291, P < 0.001), and apolipoprotein A-I (r = 0.187, P < 0.01). Of the potential regulatory factors for PLTP, apolipoprotein E showed a weak positive correlation with serum PLTP e x o (r = 0.154, P < 0.05) and PLTP e n d o (r = 0.192, P < 0.01) activity but not with PLTP concentration. Weak associations were also observed between PLTP parameters and determinants of glucose homeostasis (glucose, insulin, and homeostasis model assessment for insulin resistance). The present data on PLTP activity and concentration reveal novel connections of the two PLTP forms to lipid and carbohydrate metabolism.