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Induction of the phospholipid transfer protein gene accounts for the high density lipoprotein enlargement in mice treated with fenofibrate.
Fibrate treatment in mice is known to modulate high density lipoprotein (HDL) metabolism by regulating apolipoprotein (apo)AI and apoAII gene expression. In addition to alterations in plasma HDL levels, fibrates induce the emergence of large, cholesteryl ester-rich HDL in treated transgenic mice expressing human apoAI (HuAITg). The mechanisms of these changes may not be restricted to the modulation of apolipoprotein gene expression, and the aim of the present study was to determine whether the expression of factors known to affect HDL metabolism (i.e. phospholipid transfer protein (PLTP), lecithin:cholesterol acyltransferase, and hepatic lipase) are modified in fenofibrate-treated mice. Significant rises in plasma PLTP activity were observed after 2 weeks of fenofibrate treatment in both wild-type and HuAITg mice. Simultaneously, hepatic PLTP mRNA levels increased in a dose-dependent fashion. In contrast to PLTP, lecithin:cholesterol acyltransferase mRNA levels in HuAITg mice were not significantly modified by fenofibrate despite a significant decrease in plasma cholesterol esterification activity. Fenofibrate did not induce any change in hepatic lipase activity. Fenofibrate significantly increased HDL size, an effect that was more pronounced in HuAITg mice than in wild-type mice. This effect in wild-type mice was completely abolished in PLTP-deficient mice. Finally, fenofibrate treatment did not influence PLTP activity or hepatic mRNA in peroxisome proliferator-activated receptor-alpha-deficient mice. It is concluded that 1) fenofibrate treatment increases plasma phospholipid transfer activity as the result of up-regulation of PLTP gene expression through a peroxisome proliferator-activated receptor-alpha-dependent mechanism, and 2) increased plasma PLTP levels account for the marked enlargement of HDL in fenofibrate-treated mice.
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