Plasma apolipoprotein E concentration is an important determinant of phospholipid transfer protein activity in type 2 diabetes mellitus.
BACKGROUND
Phospholipid transfer protein (PLTP) transfers phospholipids between lipoproteins and plays an important role in HDL metabolism. PLTP exists as a high-activity and a low-activity form in the circulation. In vitro studies have shown that apolipoprotein (apo) E is involved in maintaining PLTP in the active form, while the low-activity form is associated with apo AI. We have therefore investigated whether plasma apo AI, B and E concentrations are important determinants of plasma PLTP activity in type 2 diabetes, a condition associated with increased plasma PLTP activity.


METHODS
Plasma PLTP activity was assayed by measuring the transfer of radiolabelled phosphatidylcholine from liposomes to HDL; apo AI and B by rate nephelometry and apo E by a 2-point turbidimetric assay.


RESULTS
Type 2 diabetic patients (n = 230) had higher PLTP activity than controls (n = 97) (2374 +/- 628 nmol/mL/h versus 1862 +/- 585 respectively, p < 0.01). They also had increased fasting triglyceride and low HDL. Plasma apo B (p < 0.01) and apo E (p < 0.05) were increased, whereas apo AI was reduced (p < 0.01). Univariate analysis showed that plasma PLTP activity correlated mainly with apolipoproteins AI and E. Stepwise regression analysis showed that apo E was the main determinant of plasma PLTP activity, accounting for 23% of its variability in the diabetic subjects and 8% in the controls respectively.


CONCLUSIONS
The associations between plasma apo AI and E concentrations and PLTP activity suggest that these apolipoproteins are important regulators of PLTP activity in vivo. The increase in PLTP activity in type 2 diabetes is partly related to the changes in these apolipoproteins.
Tan
K C B
KC
Department of Medicine, University of Hong Kong, Queen Mary Hospital, Pokfulam Road, Hong Kong. kcbtan@hkucc.hku.hk
Shiu
S W M
SW
Wong
Y
Y
Wong
W K
WK
Tam
S
S
D000328:Adult; D001057:Apolipoproteins E / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D049294:Phospholipid Transfer Proteins / Q000097:blood*; D012016:Reference Values; D012044:Regression Analysis
D001057:Apolipoproteins E; C493430:PLTP protein, human; D049294:Phospholipid Transfer Proteins