Forhidrol, a bioactive fraction of Phaleria macrocarpa (Scheff.) Boerl., increases reverse cholesterol transport pathway by down-regulation of cholesteryl ester transfer protein activity

Abstract

Phaleria macrocarpa (Scheff.) Boerl. is one of the most popular medicinal plants in Indonesia. This plant has traditionally been used to lower cholesterol and control hypertension. This study was performed to examine the effect of Forhidrol, a bioactive fraction of P. macrocarpa (Scheff.) Boerl., to increase reverse cholesterol transport through the down-regulation of cholesteryl ester transfer protein (CETP) activity in hepatocellular carcinoma cell lines. Measurement of target genes including liver X receptor (LXR), sterol regulatory element-binding protein 1 (SREBP-1), scavenger receptor class B type 1, low-density lipoprotein (LDL) receptor, apolipoprotein B, CYP11B1, CYP11B2, peroxisome proliferatoractivated receptor α (PPARα), peroxisome proliferator-activated receptor δ (PPARδ) and peroxisome proliferator-activated receptor γ (PPARγ) were done using real-time polymerase chain reaction assay. Secreted CETP and apolipoprotein A-1 were analyzed using western blot. CETP activity in vitro was measured using CETP inhibitor drug screening kit and triglyceride synthesis was measured using enzyme-linked immunosorbent assay. Forhidrol was found to significantly down-regulate CETP mRNA expression, as well as total CETP and cholesteryl esters transfer activity (P<0.05). It specifically reduced transcriptional level of regulatory genes of CETP promoter including SREBP-1 and LXR. Forhidrol also significantly increased PPARδ and PPARα expression (P<0.05) and slightly repressed triglycerides synthesis. In vivo study showed elevated high-density lipoprotein (HDL) levels in rabbits after 4-week treatment of Forhidrol at a dose of 37.5 mg/1.5 kg body weight compared to placebo. Conversely, LDL, triglyceride and CETP activity were decreased. Forhidrol increased HDL levels by reducing CETPdependent transfer of cholesterol from HDL to LDL particles. Looking at possible side effects, Forhidrol apparently acted as a safe agent without negative effect towards blood pressure. These findings suggested that Forhidrol may be further developed as a potential antiatherogenic drug. IntroductionCholesteryl ester transfer protein (CETP) is a 74-kDa hydrophobic glycoprotein which is mainly synthesized in liver and secreted to plasma. [1][2][3][4] It is also produced in lymph, adipose tissue, heart, kidney and small intestine, although in a lower level. 2,5 CETP is a major determinant of plasma levels of high-density lipoprotein (HDL) cholesterol in human by mediating the exchange of cholesteryl esters (CE) in HDL particles for triglycerides in lowdensity lipoprotein (LDL) and very low-density lipoprotein (VLDL) particles through reverse cholesterol transport (RCT) pathway. 2,4,[6][7][8] In epidemiological studies, subjects with CETP gene deficiency possessed higher HDL cholesterol and lower LDL cholesterol levels. 3,9 Decreased HDL levels constitute a major risk factor for Contributions: GB as the first author contributed to the research study design, laboratory and experimental works, statistical data analysis and manuscript draft...

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