Fibrates Reduce Triacylglycerol Content by Upregulating Adipose Triglyceride Lipase in the Liver of Rats

Abstract

Abstract. Hepatic triacylglycerol (TAG) homeostasis is maintained by carefully regulated balance between its synthesis and disposal. Impairment in this balance causes steatosis. The aims of this study were i) to uncover whether fibrates control TAG concentration through the action of adipose triglyceride lipase (ATGL) and ii) to compare the potency of the effects on ATGL expression and TAG concentration among fenofibrate, bezafibrate, and clofibric acid in the liver of rats. Treatments of rats with the three fibrates induced ATGL and concomitantly decreased hepatic TAG concentration. The upregulation of ATGL was likely mediated through the activation of peroxisome proliferator-activated receptor a. Fibrates also expanded capacity of fatty acid b-oxidation. Importantly, three fibric acids (fenofibric, bezafibric, and clofibric acids) that are active metabolites formed in the liver exhibited almost the same potency to elevate ATGL expression in vivo, despite the fact that there were considerable differences in this regard among fenofibrate, bezafibrate, and clofibric acid when compared on the basis of their dosage. These results suggest that ATGL represents a potential therapeutic target for ameliorating hepatic steatosis and that fibric acids are promising agents to ameliorate and/or protect against hepatic steatosis.

Fatty Acid β-Oxidation Plays a Key Role in Regulating <i>cis</i>-Palmitoleic Acid Levels in the Liver

“…31) In brief, one portion of the liver was homogenized in lysis buffer (25 mM Tris-HCl [pH 7.6], 150 mM NaCl, 1% NP40, 1% sodium deoxycholate, and 0.1% sodium dodecyl sulfate (SDS) supplemented with protein inhibitors [aprotinin at 2 µg/mL, bestatin at 13.8 µg/ mL, leupeptin at 10 µg/mL, pepstatin at 5 µg/mL, and 4-(2-aminoethyl)-benzenesulfonyl fluoride hydrochloride at 250 µg/mL]) using a Polytrone homogenizer (Kinematica, Luzern, Switzerland) at 4°C, incubated on ice for 30 min, and centrifuged at 10000×g for 10 min. The supernatants were recentrifuged at 10000×g for 10 min, and the resulting supernatants were collected in order to measure protein concentrations using the BCA protein assay reagent (Thermo Fisher Scientific, Waltham, MA, U.S.A.).…”

“…A Western blot analysis of FAS, ACC, ATGL, and CPT1a was performed using the tissue lysate as described previously. 31,32) Proteins (15 µg each) were separated by SDS-polyacrylamide gel electrophoresis on 10% (ATGL and CPT1a) or 7.5% (ACC and FAS) gels. Proteins were transferred to polyvinylidene difluoride membranes, incubated with the primary Ab at room temperature for 1 h (FAS (1 : 1000), ACC (1 : 2000), CPT1a (1 : 1000), and β-actin (1 : 5000)) or 2 h (ATGL (1 : 600)) after the incubation at 4°C overnight with blocking buffer (Tris-buffered saline containing 0.1% Tween 20, 5% skim milk, and 1% BSA), and this was followed by an incubation with the secondary Ab at room temperature for 1 h (FAS, ACC, CPT1a, and β-actin) or 2 h (ATGL).…”

“…29) SCD activities were measured spectrophotometrically as reported previously 29) and activity was presented as the rate constant (k Assay for ATGL TAG hydrolase activity was measured as previously described 35) with some modifications. 31) A cytoplasmic fraction was prepared from the liver as reported previously. 31) Triolein [carboxy- 14 C] (PerkinElmer, Inc., Waltham, MA, U.S.A.) was purified before use by TLC on silica gel G plates, which were developed with n-hexane-diethyl ether-acetic acid (80 : 30 : 1, v/v/v).…”

“…31) A cytoplasmic fraction was prepared from the liver as reported previously. 31) Triolein [carboxy- 14 C] (PerkinElmer, Inc., Waltham, MA, U.S.A.) was purified before use by TLC on silica gel G plates, which were developed with n-hexane-diethyl ether-acetic acid (80 : 30 : 1, v/v/v). A substrate, [ 14 C] triolein (33.3 GBq/mol) mixed with phosphatidylcholine-phosphatidylinositol (3 : 1), was prepared as described previously.…”

“…A substrate, [ 14 C] triolein (33.3 GBq/mol) mixed with phosphatidylcholine-phosphatidylinositol (3 : 1), was prepared as described previously. 31) Substrate solution with the cytoplasmic fraction and buffer (20 mM potassium phosphate [pH 7.0], 1 mM EDTA, 1 mM dithioerythritol, and 0.02% (w/v) defatted BSA) were incubated at 37°C for 60 min. The control value, which was obtained from the incubation without the cytoplasmic fraction, was subtracted to give net TAG hydrolyzed by the cytoplasmic fraction.…”