Phospholipid and cholesteryl ester transfer are increased in lipoprotein lipase deficiency

Phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP) are key enzymes in lipoprotein metabolism by mediating the transfer and exchange of phospholipids (PL) and neutral lipids between lipoproteins. Lipoprotein lipase (LPL) deficiency is associated with low HDL-cholesterol (HDL-C) levels in both, the homozygous and heterozygous state. In the present study we set out to investigate the role of lipid transfer proteins, which are known to strongly determine HDL-C levels, in LPL deficiency.

Phospholipid acceptor and donor properties of lipoproteins, PLTP activity, CETP mass, activity and cholesteryl ester (CE) transfer were determined in two homozygous and six heterozygous LPL-deficient subjects and in 10 healthy, normolipidaemic controls, respectively.

The HDL isolated from LPL-deficient subjects showed strongly increased PL-acceptance when compared with controls (homozygotes versus heterozygotes versus control: 26.46 +/- 15.26 vs. 3.41 +/- 1.61 vs. 1.89 +/- 0.33 micromol mL-1 h-1/micromol mL-1 PL; all P < 0.05). Phospholipid transfer from apolipoprotein B containing lipoproteins was increased in heterozygotes when compared with controls (46.66 +/- 23.3 vs. 28.91 +/- 18.05 micromol mL-1 h-1/micromol mL-1 PL, P = 0.05). PLTP activity, however, was similar in LPL-deficient subjects and controls. CETP mass was highest in homozygotes, whilst enzyme activity was similar in LPL-deficient subjects and controls. CE transfer was highest in homozygotes (72.5 +/- 8.8%) and lowest in controls (28.7 +/- 5.2%, P < 0.01).

In conclusion, PL and CE transfer are increased in LPL deficiency and thus, partly explain low HDL-levels in LPL-deficient subjects. Enhanced transfer seems rather to be the result of altered lipoprotein composition and concentration than altered enzyme activity. Our findings on mechanisms leading to low HDL-C levels might show another aspect in atherogenesis in LPL deficiency.